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A method to estimate stellar ages from kinematical data | We present a method to build a probability density function (pdf) for the age
of a star based on its peculiar velocities $U$, $V$ and $W$ and its orbital
eccentricity. The sample used in this work comes from the Geneva-Copenhagen
Survey (GCS) which contains both the spatial velocities, orbital eccentricities
and isochronal ages for about $14\,000$ stars. Using the GCS stars, we fitted
the parameters that describe the relations between the distributions of
kinematical properties and age. This parametrization allows us to obtain an age
probability from the kinematical data. From this age pdf, we estimate an
individual average age for the star using the most likely age and the expected
age. We have obtained the stellar age pdf for the age of $9\,102$ stars from
the GCS and have shown that the distribution of individual ages derived from
our method is in good agreement with the distribution of isochronal ages. We
also observe a decline in the mean metallicity with our ages for stars younger
than 7 Gyr, similar to the one observed for isochronal ages. This method can be
useful for the estimation of rough stellar ages for those stars that fall in
areas of the HR diagram where isochrones are tightly crowded. As an example of
this method, we estimate the age of Trappist-1, which is a M8V star, obtaining
the age of $t(UVW) = 12.50(+0.29-6.23)$ Gyr.
|
Prediction of the Cosmic Evolution of the CO-Luminosity Functions | We predict the emission line luminosity functions (LFs) of the first 10
rotational transitions of CO in galaxies at redshift z=0 to z=10. This
prediction relies on a recently presented simulation of the molecular cold gas
content in ~3e7 evolving galaxies based on the Millennium Simulation. We
combine this simulation with a model for the conversion between molecular mass
and CO-line intensities, which incorporates the following mechanisms: (i)
molecular gas is heated by the CMB, starbursts (SBs), and active galactic
nuclei (AGNs); (ii) molecular clouds in dense or inclined galaxies can overlap;
(iii) compact gas can attain a smooth distribution in the densest part of
disks; (iv) CO-luminosities scale with metallicity changes between galaxies;
(v) CO-luminosities are always detected against the CMB. We analyze the
relative importance of these effects and predict the cosmic evolution of the
CO-LFs. The most notable conclusion is that the detection of regular galaxies
(i.e. no AGN, no massive SB) at high z>7 in CO-emission will be dramatically
hindered by the weak contrast against the CMB, in contradiction to earlier
claims that CMB-heating will ease the detection of high-redshift CO. The full
simulation of extragalactic CO-lines and the predicted CO-LFs at any redshift
can be accessed online, prior registration required} and they should be useful
for the modeling of CO-line surveys with future telescopes, such as ALMA, the
LMT, or the SKA.
|
Models for Small-Scale Structure on Cosmic Strings: II. Scaling and its
stability | We make use of the formalism described in a previous paper [Martins {\it et
al.} Phys. Rev. D90 (2014) 043518] to address general features of wiggly cosmic
string evolution. In particular, we highlight the important role played by
poorly understood energy loss mechanisms and propose a simple ansatz which
tackles this problem in the context of an extended velocity-dependent one-scale
model. We find a general procedure to determine all the scaling solutions
admitted by a specific string model and study their stability, enabling a
detailed comparison with future numerical simulations. A simpler comparison
with previous Goto-Nambu simulations supports earlier evidence that scaling is
easier to achieve in the matter era than in the radiation era. In addition, we
also find that the requirement that a scaling regime be stable seems to notably
constrain the allowed range of energy loss parameters.
|
Standardizing Type Ia Supernova Absolute Magnitudes Using Gaussian
Process Data Regression | We present a novel class of models for Type Ia supernova time-evolving
spectral energy distributions (SED) and absolute magnitudes: they are each
modeled as stochastic functions described by Gaussian processes. The values of
the SED and absolute magnitudes are defined through well-defined regression
prescriptions, so that data directly inform the models. As a proof of concept,
we implement a model for synthetic photometry built from the spectrophotometric
time series from the Nearby Supernova Factory. Absolute magnitudes at peak $B$
brightness are calibrated to 0.13 mag in the $g$-band and to as low as 0.09 mag
in the $z=0.25$ blueshifted $i$-band, where the dispersion includes
contributions from measurement uncertainties and peculiar velocities. The
methodology can be applied to spectrophotometric time series of supernovae that
span a range of redshifts to simultaneously standardize supernovae together
with fitting cosmological parameters.
|
Generalizations of teleparallel gravity and local Lorentz symmetry | We analyze the relation between teleparallelism and local Lorentz invariance.
We show that generic modifications of the teleparallel equivalent to general
relativity will not respect local Lorentz symmetry. We clarify the reasons for
this and explain why the situation is different in general relativity. We give
a prescription for constructing teleparallel equivalents for known theories. We
also explicitly consider a recently proposed class of generalized teleparallel
theories, called f(T) theories of gravity, and show why restoring local Lorentz
symmetry in such theories cannot lead to sensible dynamics, even if one gives
up teleparallelism.
|
New method to constrain the relativistic free-streaming gas in the
Universe | We discuss a method to constrain the fraction density $f$ of the relativistic
gas in the radiation dominant stage, by their impacts on a relic gravitational
waves and the cosmic microwave background (CMB) $B$ polarization power
spectrum. We find that the uncertainty of $f$ strongly depends on the noise
power spectra of the CMB experiments and the amplitude of the gravitational
waves. Taking into account of the CMBPol instrumental noises, an uncertainty
$\Delta f=0.046$ is obtained for the model with tensor-to scalar ratio $r=0.1$.
For an ideal experiment with only the reduced cosmic lensing as the
contamination of $B$-polarization, $\Delta f=0.008$ is obtained for the model
with $r=0.1$. So the precise observation of the CMB $B$-polarization provides a
great opportunity to study the relativistic components in the early Universe.
|
On the UV compactness and morphologies of typical Lyman-a emitters from
z~2 to z~6 | We investigate the rest-frame UV morphologies of a large sample of Lyman-a
emitters (LAEs) from z~2 to z~6, selected in a uniform way with 16 different
narrow- and medium-bands over the full COSMOS field. We use 3045 LAEs with HST
coverage in a stacking analysis and find that they have M_UV~-20, below M*_UV
at these redshifts. We also focus our analysis on a subsample of 780 individual
galaxies with i_AB<25 for which GALFIT converges for 429 of them. The
individual median size (re~1 kpc), ellipticities (slightly elongated with
(b/a)~0.45), S\'ersic index (disk-like with n<2) and light concentration
(comparable to that of disk or irregular galaxies, with C~2.7) of LAEs show
mild evolution from z~2 to z~6. LAEs with the highest rest-frame equivalent
widths (EW) are the smallest/most compact (re~0.8 kpc, compared to re~1.5 kpc
for the lower EW LAEs). When stacking our samples in bins of fixed Lya
luminosity and Lya EW we find evidence for redshift evolution in n and C, but
not in galaxy sizes. The evolution seems to be stronger for LAEs with 25<EW<100
{\AA}. When compared to other SFGs, LAEs are found to be smaller at all
redshifts. The difference between the two populations changes with redshift,
from a factor of ~1 at z>5 to SFGs being a factor of ~2-4 larger than LAEs for
z<2. This means that at the highest redshifts, where typical sizes approach
those of LAEs, the fraction of galaxies showing Lya in emission (and with a
high Lya escape fraction) should be much higher, consistent with observations.
|
Low-frequency integrated radio spectra of diffuse, steep-spectrum
sources in galaxy clusters: palaeontology with the MWA and ASKAP | Galaxy clusters have been found to host a range of diffuse, non-thermal
emission components, generally with steep, power law spectra. In this work we
report on the detection and follow-up of radio halos, relics, remnant radio
galaxies, and other fossil radio plasmas in Southern Sky galaxy clusters using
the Murchison Widefield Array and the Australian Square Kilometre Array
Pathfinder. We make use of the frequency coverage between the two radio
interferometers - from 88 to $\sim 900$ MHz - to characterise the integrated
spectra of these sources within this frequency range. Highlights from the
sample include the detection of a double relic system in Abell 3186, a
mini-halo in RXC J0137.2-0912, a candidate halo and relic in Abell 3399, and a
complex multi-episodic head-tail radio galaxy in Abell 3164. We compare this
selection of sources and candidates to the literature sample, finding sources
consistent with established radio power-cluster mass scaling relations.
Finally, we use the low-frequency integrated spectral index, $\alpha$ ($S_\nu
\propto \nu^\alpha$), of the detected sample of cluster remnants and fossil
sources to compare with samples of known halos, relics, remnants and fossils to
investigate a possible link between their electron populations. We find the
distributions of $\alpha$ to be consistent with relic and halo emission
generated by seed electrons that originated in fossil or remnant sources.
However, the present sample sizes are insufficient to rule out other scenarios.
|
The Radio-FIR correlation in the Milky Way | We investigate the scale on which the correlation arises between the 843 MHz
radio and the 60 micron far-infrared (FIR) emission from star forming regions
in the Milky way. The correlation, which exists on the smallest scales
investigated (down to ~4 pc), becomes noticeably tight on fields of size 30',
corresponding to physical scales of ~20-50 pc. The FIR to radio flux ratio on
this scale is consistent with the radio emission being dominated by thermal
emission. We also investigate the location dependence of q_mean, a parameter
measuring the mean FIR to radio flux ratio, of a sample of star forming
regions. We show that q_mean displays a modest dependence on galactic latitude.
If this is interpreted as a dependence on the intensity of star formation
activity, the result is consistent with studies of the Large Magellanic Cloud
(LMC) and other nearby galaxies that show elevated values for q in regions of
enhanced star formation.
|
First identification and absolute magnitudes of the red clump stars in
the Solar neighbourhood for WISE | We present the first determination of absolute magnitudes for the red clump
(RC) stars with the Wide-field Infrared Survey Explorer (WISE). We used
recently reduced parallaxes taken from the Hipparcos catalogue and identified
3889 RC stars with the WISE photometry in the Solar neighbourhood. Mode values
estimated from the distributions of absolute magnitudes and a colour of the RC
stars in WISE photometry are M_{W1}=-1.635(0.026), M_{W3}=-1.606(0.024) and
(W1-W3)_0=-0.028(0.001) mag. These values are consistent with those obtained
from the transformation formulae using 2MASS data. Distances of the RC stars
estimated by using their M_{W1} and M_{W3} absolute magnitudes are in agreement
with the ones calculated by the spectrophotometric method, as well. These WISE
absolute magnitudes can be used in astrophysical researches where distance
plays an important role.
|
The outer regions of the giant Virgo galaxy M87. Kinematic separation of
stellar halo and intracluster light | We present a spectroscopic study of 287 Planetary Nebulas (PNs) in a total
area of ~0.4 deg^2 around the BCG M87 in Virgo A. With these data we can
distinguish the stellar halo from the co-spatial intracluster light (ICL). PNs
were identified from their narrow and symmetric redshifted lambda 5007\4959
Angstrom [OIII] emission lines, and the absence of significant continuum. We
implement a robust technique to measure the halo velocity dispersion from the
projected phase-space to identify PNs associated with the M87 halo and ICL. The
velocity distribution of the spectroscopically confirmed PNs is bimodal,
containing a narrow component centred on the systemic velocity of the BCG and
an off-centred broader component, that we identify as halo and ICL,
respectively. Halo and ICPN have different spatial distributions: the halo PNs
follow the galaxy's light, whereas the ICPNs are characterised by a shallower
power-law profile. The composite PN number density profile shows the
superposition of different PN populations associated with the M87 halo and the
ICL, characterised by different PN alpha-parameters, the ICL contributing ~3
times more PNs per unit light. Down to m_5007=28.8, the M87 halo PN luminosity
function (PNLF) has a steeper slope towards faint magnitudes than the IC PNLF,
and both are steeper than the standard PNLF for the M31 bulge. Moreover, the IC
PNLF has a dip at ~1-1.5 mag fainter than the bright cutoff, reminiscent of the
PNLFs of systems with extended star formation history. The M87 halo and the
Virgo ICL are dynamically distinct components with different density profiles
and velocity distribution. The different alpha values and PNLF shapes of the
halo and ICL indicate distinct parent stellar populations, consistent with the
existence of a gradient towards bluer colours at large radii. These results
reflect the hierarchical build-up of the Virgo cluster.
|
Refined approximations for the distortion visibility function and
mu-type spectral distortions | The physical processes affecting the thermalization of cosmic microwave
background spectral distortions are very simple and well understood. This
allows us to make precise predictions for the distortions signals caused by
various energy release scenarios, where the theoretical uncertainty is largely
dominated by the physical ingredients that are used for the calculation. Here,
we revisit various approximations for the distortion visibility function --
defined using the fraction of the released energy that does not thermalize --
and early $\mu$-type distortions. Our approach is based on a perturbative
expansion, which allows us to identify and clarify the origin of different
improvements over earlier approximations. It provides a better than ~0.1%-1%
description of our numerical results over a wide range of parameters. In
particular, we are able to capture the high-frequency part of the
mu-distortion, which directly depends on the time derivative of the electron
temperature. We also include lowest order double Compton and Compton scattering
relativistic corrections, finding that because of cancelation they increase the
thermalization efficiency in the tail of the distortion visibility function by
only ~10% (at $z\lesssim 6\times10^6$), although individually their effect can
reach ~20%-40%.
|
Ultra-high energy cosmic rays from shocks in the lobes of powerful radio
galaxies | The origin of ultra-high energy cosmic rays (UHECRs) has been an open
question for decades. Here, we use a combination of hydrodynamic simulations
and general physical arguments to demonstrate that UHECRs can in principle be
produced by diffusive shock acceleration (DSA) in shocks in the backflowing
material of radio galaxy lobes. These shocks occur after the jet material has
passed through the relativistic termination shock. Recently, several authors
have demonstrated that highly relativistic shocks are not effective in
accelerating UHECRs. The shocks in our proposed model have a range of
non-relativistic or mildly relativistic shock velocities more conducive to
UHECR acceleration, with shock sizes in the range 1-10kpc. Approximately 10% of
the jet's energy flux is focused through a shock in the backflow of $M>3$.
Although the shock velocities can be low enough that acceleration to high
energy via DSA is still efficient, they are also high enough for the Hillas
energy to approach $10^{19-20}$eV, particularly for heavier CR composition and
in cases where fluid elements pass through multiple shocks. We discuss some of
the more general considerations for acceleration of particles to ultra-high
energy with reference to giant-lobed radio galaxies such as Centaurus A and
Fornax A, a class of sources which may be responsible for the observed
anisotropies from UHECR observatories.
|
On the Formation of Galactic Thick Disks | Recent spectroscopic observations in the Milky Way suggest that the
chemically defined thick disk (stars with high [alpha/Fe] ratios and thus old)
has a significantly smaller scale-length than the thin disk. This is in
apparent contradiction with observations of external edge-on galaxies, where
the thin and thick components have comparable scale-lengths. Moreover, while
observed disks do not flare (scale-height does not increase with radius),
numerical simulations suggest that disk flaring is unavoidable, resulting from
both environmental effects and secular evolution. Here we address these
problems by studying two different suites of simulated galactic disks formed in
the cosmological context. We show that the scale-heights of coeval populations
always increase with radius. However, the total population can be decomposed
morphologically into thin and thick disks, which do not flare. We relate this
to the disk inside-out formation, where younger populations have increasingly
larger scale-lengths and flare at progressively larger radii. In this new
picture, thick disks are composed of the imbedded flares of mono-age stellar
populations. Assuming that disks form inside out, we predict that
morphologically defined thick disks must show a decrease in age (or [alpha/Fe]
ratios) with radius and that coeval populations should always flare. This also
explains the observed inversion in the metallicity and [alpha/Fe] gradients for
stars away from the disk midplane in the Milky Way. The results of this work
are directly linked to, and can be seen as evidence of, inside-out disk growth.
|
Extended soft X-ray emission in 3CR radio galaxies at z < 0.3: High
Excitation and Broad Line Galaxies | We analyze Chandra observations of diffuse soft X-ray emission associated
with a complete sample of 3CR radio galaxies at z < 0.3. In this paper we focus
on the properties of the spectroscopic sub-classes of high excitation galaxies
(HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or
possibly extended) emission in about 40% of the sources; the fraction is even
higher (8/10) restricting the analysis to the objects with exposure times
larger than 10 ks. In the 18 BLOs, extended emission is seen only in 2 objects;
this lower detection rate can be ascribed to the presence of their bright X-ray
nuclei that easily outshine any genuine diffuse emission.
A very close correspondence between the soft X-ray and optical line
morphology emerges. We also find that the ratio between [O III] and extended
soft X-ray luminosity is confined within a factor of 2 around a median value of
5. Both results are similar to what is seen in Seyfert galaxies.
We discuss different processes that could explain the soft X-ray emission and
conclude that the photoionization of extended gas, coincident with the narrow
line region, is the favored mechanism.
|
Multi-frequency study of Local Group Supernova Remnants The curious case
of the Large Magellanic Cloud SNR J0528-6714 | Aims. Recent ATCA, XMM-Newton and MCELS observations of the Magellanic Clouds
(MCs) cover a number of new and known SNRs which are poorly studied, such as
SNR J0528-6714 . This particular SNR exhibits luminous radio-continuum
emission, but is one of the unusual and rare cases without detectable optical
and very faint X-ray emission (initially detected by ROSAT and listed as object
[HP99] 498). We used new multi-frequency radio-continuum surveys and new
optical observations at H{\alpha}, [S ii] and [O iii] wavelengths, in
combination with XMM-Newton X-ray data, to investigate the SNR properties and
to search for a physical explanation for the unusual appearance of this SNR.
Methods. We analysed the X-ray and Radio-Continuum spectra and present
multi-wavelength morphological studies of this SNR.
Results. We present the results of new moderate resolution ATCA observations
of SNR J0528-6714. We found that this object is a typical older SNR with a
radio spectral index of {\alpha}=-0.36 \pm 0.09 and a diameter of D=52.4 \pm
1.0 pc. Regions of moderate and somewhat irregular polarisation were detected
which are also indicative of an older SNR. Using a non-equilibrium ionisation
collisional plasma model to describe the X-ray spectrum, we find temperatures
kT of 0.26 keV for the remnant. The low temperature, low surface brightness,
and large extent of the remnant all indicate a relatively advanced age. The
near circular morphology indicates a Type Ia event.
Conclusions. Our study revealed one of the most unusual cases of SNRs in the
Local Group of galaxies - a luminous radio SNR without optical counterpart and,
at the same time, very faint X-ray emission. While it is not unusual to not
detect an SNR in the optical, the combination of faint X-ray and no optical
detection makes this SNR very unique.
|
Mid-infrared vibrational study of deuterium-containing PAH variants | Polycyclic Aromatic Hydrocarbon (PAH) molecules have been long proposed to be
a major carrier of 'Unidentified Infrared' (UIR) emission bands that have been
observed ubiquitously in various astrophysical environments. These molecules
can potentially be an efficient reservoir of deuterium. Once the infrared
properties of the deuterium- containing PAHs are well understood both
experimentally and theoretically, the interstellar UIR bands can be used as a
valuable tool to infer the cause of the deuterium depletion in the ISM.
Density Functional Theory (DFT) calculations have been carried out on
deuterium-containing ovalene variants to study the infrared properties of these
molecules. These include deuterated ovalene, cationic deuterated ovalene,
deuteronated ovalene and deuterated-deuteronated ovalene. We present a D/H
ratio calculated from our theoretical study to compare with the observationally
proposed D/H ratio.
|
The Impact of Baryonic Physics on the Structure of Dark Matter Halos:
the View from the FIRE Cosmological Simulations | We study the distribution of cold dark matter (CDM) in cosmological
simulations from the FIRE (Feedback In Realistic Environments) project, for
$M_{\ast}\sim10^{4-11}\,M_{\odot}$ galaxies in $M_{\rm
h}\sim10^{9-12}\,M_{\odot}$ halos. FIRE incorporates explicit stellar feedback
in the multi-phase ISM, with energetics from stellar population models. We find
that stellar feedback, without "fine-tuned" parameters, greatly alleviates
small-scale problems in CDM. Feedback causes bursts of star formation and
outflows, altering the DM distribution. As a result, the inner slope of the DM
halo profile ($\alpha$) shows a strong mass dependence: profiles are shallow at
$M_{\rm h}\sim10^{10}-10^{11}\,M_{\odot}$ and steepen at higher/lower masses.
The resulting core sizes and slopes are consistent with observations. This is
broadly consistent with previous work using simpler feedback schemes, but we
find steeper mass dependence of $\alpha$, and relatively late growth of cores.
Because the star formation efficiency $M_{\ast}/M_{\rm h}$ is strongly halo
mass dependent, a rapid change in $\alpha$ occurs around $M_{\rm h}\sim
10^{10}\,M_{\odot}$ ($M_{\ast}\sim10^{6}-10^{7}\,M_{\odot}$), as sufficient
feedback energy becomes available to perturb the DM. Large cores are not
established during the period of rapid growth of halos because of ongoing DM
mass accumulation. Instead, cores require several bursts of star formation
after the rapid buildup has completed. Stellar feedback dramatically reduces
circular velocities in the inner kpc of massive dwarfs; this could be
sufficient to explain the "Too Big To Fail" problem without invoking
non-standard DM. Finally, feedback and baryonic contraction in Milky Way-mass
halos produce DM profiles slightly shallower than the Navarro-Frenk-White
profile, consistent with the normalization of the observed Tully-Fisher
relation.
|
Highly ionized disc and transient outflows in the Seyfert galaxy IRAS
18325-5926 | We report on strong X-ray variability and the Fe K band spectrum of the
Seyfert galaxy IRAS 18325-5926 obtained from the 2001 XMM-Newton EPIC pn
observation of a 120 ks duration. While the X-ray source is highly variable,
the 8-10 keV band shows larger variability than that of the lower energies.
Amplified 8-10 keV flux variations are associated with two prominent flares of
the X-ray source during the observation. The Fe K emission is peaked at 6.6 keV
with moderate broadening. It is likely to originate from a highly ionized disc
with the ionization parameter of log xi ~3. The Fe K line flux responds to the
major flare, supporting its disc origin. There is a short burst of the Fe line
flux with no relation to the continuum brightness for which we have no clear
explanation. We also find transient, blueshifted Fe K absorption features,
which can be identified with high-velocity (~0.2 c) outflows of highly ionized
gas, as found in other active galaxies. The deepest absorption feature appears
only briefly (~1 hr) at the onset of the major flare and disappears when the
flare is declining. The rapid evolution of the absorption spectrum makes this
source peculiar among the active galaxies with high velocity outflows. Another
detection of the absorption feature also precedes the other flare. The
variability of the absorption feature partly accounts for the excess
variability in the 8-10 keV band where the absorption feature appears. Although
no reverberation measurement is available, the black hole mass of 2e6 Msun is
inferred from the X-ray variability. When this mass is assumed, the black hole
is accreting at around the Eddington limit, which may fit the highly ionized
disc and strong outflows observed in this galaxy.
|
Delayed star formation in high-redshift stream-fed galaxies | We propose that star formation is delayed relative to the inflow rate in
rapidly-accreting galaxies at very high redshift (z > 2) because of the energy
conveyed by the accreting gas. Accreting gas streams provide fuel for star
formation, but they stir the disk and increase turbulence above the usual
levels compatible with gravitational instability, reducing the star formation
efficiency in the available gas. After the specific inflow rate has
sufficiently decreased - typically at z < 3 - galaxies settle in a
self-regulated regime with efficient star formation. An analytic model shows
that this interaction between infalling gas and young galaxies can
significantly delay star formation and maintain high gas fractions (>40%) down
to z = 2, in contrast to other galaxy formation models. Idealized hydrodynamic
simulations of infalling gas streams onto primordial galaxies confirm the
efficient energetic coupling at z > 2, and suggest that this effect is largely
under-resolved in existing cosmological simulations.
|
The extended Baryon Oscillation Spectroscopic Survey (eBOSS): testing a
new approach to measure the evolution of the structure growth | The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is one of the
first of a new generation of galaxy redshift surveys that will cover a large
range in redshift with sufficient resolution to measure the baryon acoustic
oscillations (BAO) signal. For surveys covering a large redshift range we can
no longer ignore cosmological evolution, meaning that either the redshift
shells analysed have to be significantly narrower than the survey, or we have
to allow for the averaging over evolving quantities. Both of these have the
potential to remove signal: analysing small volumes increases the size of the
Fourier window function, reducing the large-scale information, while averaging
over evolving quantities can, if not performed carefully, remove differential
information. It will be important to measure cosmological evolution from these
surveys to explore and discriminate between models. We apply a method to
optimally extract this differential information to mock catalogues designed to
mimic the eBOSS quasar sample. By applying a set of weights to extract redshift
space distortion measurements as a function of redshift, we demonstrate an
analysis that does not invoke the problems discussed above. We show that our
estimator gives unbiased constraints.
|
Chemical evolution models for the Galactic disk based on H II region
abundances derived from a direct method and a temperature independent method | We present two chemical evolution models of our galaxy, both models are built
to fit the O/H ratios derived from H II regions, using two different methods.
One model is based on abundances obtained from the [O III] 4363/5007
temperatures (direct method, DM) and the other on abundances obtained from the
recombination line ratios of [O II/H I] (temperature independent method, TIM).
The differences between the O/H values obtained from these two methods are
about 0.25 dex. We find that the model based on the TIM values produces an
excellent fit to the observational stellar constraints (B-stars, Cepheids, and
the Sun), while the model based on the DM fails to reproduce each of them.
Moreover, the TIM model can explain the flattening of the O/H gradient observed
in the inner disk due to the assumption of an inside-out star formation
quenching, in the 3 - 6 kpc galactocentric range, starting ~ 9 Gyr ago.
|
Project MOMO: Multiwavelength Observations and Modelling of OJ 287 | Our project MOMO (Multiwavelength observations and modelling of OJ 287)
consists of dedicated, dense, long-term flux and spectroscopic monitoring and
deep follow-up observations of the blazar OJ 287 at >13 frequencies from the
radio to the X-ray band since late 2015. In particular, we are using Swift to
obtain optical-UV-X-ray spectral energy distributions (SEDs) and the Effelsberg
telescope to obtain radio measurements between 2 and 40 GHz. MOMO is the
densest long-term monitoring of OJ 287 involving X-rays and broad-band SEDs.
The theoretical part of the project aims at understanding jet and accretion
physics of the blazar central engine in general and the supermassive binary
black hole scenario in particular. Results are presented in a sequence of
publications and so far included: detection and detailed analysis of the bright
2016/17 and 2020 outbursts and the long-term light curve; Swift, XMM and NuSTAR
spectroscopy of the 2020 outburst around maximum; and interpretation of
selected events in the context of the binary black hole scenario of OJ 287
(papers I-IV). Here, we provide a description of the project MOMO, a summary of
previous results, the latest results, and we discuss future prospects.
|
High-resolution VLA Imaging of Obscured Quasars: Young Radio Jets Caught
in a Dense ISM | We present new sub-arcsecond-resolution Karl G. Jansky Very Large Array (VLA)
imaging at 10 GHz of 155 ultra-luminous ($L_{\rm bol}\sim10^{11.7-14.2}
L_\odot$) and heavily obscured quasars with redshifts $z \sim0.4-3$. The sample
was selected to have extremely red mid-infrared (MIR)-optical color ratios
based on data from Wide-Field Infrared Survey Explorer (WISE) along with a
detection of bright, unresolved radio emission from the NRAO VLA Sky Survey
(NVSS) or Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) Survey.
Our high-resolution VLA observations have revealed that the majority of the
sources in our sample (93 out of 155) are compact on angular scales
$<0.2^{\prime \prime}$ ($\leq 1.7$ kpc at $z \sim2$). The radio luminosities,
linear extents, and lobe pressures of our sources are similar to young radio
active galactic nuclei (AGN; e.g., Gigahertz Peaked Spectrum, GPS, and Compact
Steep Spectrum, CSS, sources), but their space density is considerably lower.
Application of a simple adiabatic lobe expansion model suggests relatively
young dynamical ages ($\sim10^{4-7}$ years), relatively high ambient ISM
densities ($\sim1-10^4$ cm$^{-3}$), and modest lobe expansion speeds
($\sim30-10,000$ km s$^{-1}$). Thus, we find our sources to be consistent with
a population of newly triggered, young jets caught in a unique evolutionary
stage in which they still reside within the dense gas reservoirs of their
hosts. Based on their radio luminosity function and dynamical ages, we estimate
only $\sim20\%$ of classical large scale FRI/II radio galaxies could have
evolved directly from these objects. We speculate that the WISE-NVSS sources
might first become GPS or CSS sources, of which some might ultimately evolve
into larger radio galaxies.
|
Instability of Evaporation Fronts in the Interstellar Medium | The neutral component of the interstellar medium is segregated into the cold
neutral medium (CNM) and warm neutral medium (WNM) as a result of thermal
instability. It was found that a plane-parallel CNM-WNM evaporation interface,
across which the CNM undergoes thermal expansion, is linearly unstable to
corrugational disturbances, in complete analogy with the Darrieus-Landau
instability (DLI) of terrestrial flames. We perform a full linear stability
analysis as well as nonlinear hydrodynamic simulations of the DLI of such
evaporation fronts in the presence of thermal conduction. We find that the DLI
is suppressed at short length scales by conduction. The length and time scales
of the fastest growing mode are inversely proportional to the evaporation flow
speed of the CNM and its square, respectively. In the nonlinear stage, the DLI
saturates to a steady state where the front deforms to a finger-like shape
protruding toward the WNM, without generating turbulence. The evaporation rate
at nonlinear saturation is larger than the initial plane-parallel value by a
factor of 2.4 when the equilibrium thermal pressure is 1800 k_B cm^-3 K. The
degrees of front deformation and evaporation-rate enhancement at nonlinear
saturation are determined primarily by the density ratio between the CNM and
WNM. We demonstrate that the Field length in the thermally unstable medium
should be resolved by at least four grid points to obtain reliable numerical
outcomes involving thermal instability.
|
Spin-Up/Spin-Down models for Type Ia Supernovae | In the single degenerate scenario for Type Ia supernova (SNeIa), a white
dwarf (WD) must gain a significant amount of matter from a companion star.
Because the accreted mass carries angular momentum, the WD is likely to achieve
fast spin periods, which can increase the critical mass, $M_{crit}$, needed for
explosion. When $M_{crit}$ is higher than the maximum mass achieved by the WD,
the WD must spin down before it can explode. This introduces a delay between
the time at which the WD has completed its epoch of mass gain and the time of
the explosion. Matter ejected from the binary during mass transfer therefore
has a chance to become diffuse, and the explosion occurs in a medium with a
density similar to that of typical regions of the interstellar medium. Also,
either by the end of the WD's mass increase or else by the time of explosion,
the donor may exhaust its stellar envelope and become a WD. This alters,
generally diminishing, explosion signatures related to the donor star.
Nevertheless, the spin-up/spin-down model is highly predictive. Prior to
explosion, progenitors can be super-$M_{Ch}$ WDs in either wide binaries with
WD companions, or else in cataclysmic variables. These systems can be
discovered and studied through wide-field surveys. Post explosion, the
spin-up/spin-down model predicts a population of fast-moving WDs, low-mass
stars, and even brown dwarfs. In addition, the spin-up/spin-down model provides
a paradigm which may be able to explain both the similarities and the diversity
observed among SNeIa.
|
Impacts on Cosmological Constraints from Degeneracies | In this paper, we study the degeneracies among several cosmological
parameters in detail and discuss their impacts on the determinations of these
parameters from the current and future observations. By combining the latest
data sets, including type-Ia supernovae "Union2.1" compilation, WMAP seven-year
data and the baryon acoustic oscillations from the SDSS Data Release Seven, we
perform a global analysis to determine the cosmological parameters, such as the
equation of state of dark energy w, the curvature of the universe \Omega_k, the
total neutrino mass \sum{m_\nu}, and the parameters associated with the power
spectrum of primordial fluctuations (n_s, \alpha_s and r). We pay particular
attention on the degeneracies among these parameters and the influences on
their constraints, by with or without including these degeneracies,
respectively. We find that $w$ and \Omega_k or \sum{m_\nu} are strongly
correlated. Including the degeneracies will significantly weaken the
constraints. Furthermore, we study the capabilities of future observations and
find these degeneracies can be broken very well. Consequently, the constraints
of cosmological parameters can be improved dramatically.
|
Interferometric observations of warm deuterated methanol in the inner
regions of low-mass protostars | Methanol is a key species in astrochemistry since it is the most abundant
organic molecule in the ISM and is thought to be the mother molecule of many
complex organic species. Estimating the deuteration of methanol around young
protostars is of crucial importance because it highly depends on its formation
mechanisms and the physical conditions during its moment of formation. We
analyse dozens of transitions from deuterated methanol isotopologues coming
from various existing observational datasets from the IRAM-PdBI and ALMA sub-mm
interferometers to estimate the methanol deuteration surrounding three low-mass
protostars on Solar System scales. A population diagram analysis allows us to
derive a [CH$_2$DOH]/[CH$_3$OH] abundance ratio of 3-6 % and a
[CH$_3$OD]/[CH$_3$OH] ratio of 0.4-1.6 % in the warm inner protostellar
regions. These values are ten times lower than those derived with previous
single-dish observations towards these sources but they are 10-100 times higher
than the methanol deuteration measured in massive hot cores. Dust temperature
maps obtained from Herschel and Planck observations show that massive hot cores
are located in warmer molecular clouds than low-mass sources, with temperature
differences of $\sim$10 K. Comparison with the predictions of the gas-grain
astrochemical model GRAINOBLE shows that such a temperature difference is
sufficient to explain the different deuteration observed in low- to high-mass
sources, suggesting that the physical conditions of the molecular cloud at the
origin of the protostars mostly govern the present observed deuteration of
methanol. The methanol deuteration measured in this work is higher by a factor
of 5 than the upper limit in methanol deuteration estimated in comet Hale-Bopp,
implying that an important reprocessing of the organic material would have
occurred in the solar nebula during the formation of the Solar System.
|
Spatial and luminosity distributions of galactic satellites | We investigate the luminosity functions (LFs) and projected number density
profiles of galactic satellites around isolated primaries of different
luminosities. We measure these quantities for model satellites placed into the
Millennium and Millennium II dark matter simulations by the GALFORM
semi-analytic galaxy formation model for different bins of primary galaxy
magnitude and we investigate their dependence on satellite luminosity. We
compare our model predictions to the data of Guo et al. from the Sloan Digital
Sky Survey Data Release 8 (SDSS DR8). First, we use a mock light-cone catalogue
to verify that the method we used to count satellites in the SDSS DR8 is
unbiased. We find that the radial distributions of model satellites are similar
to those around comparable primary galaxies in the SDSS DR8, with only slight
differences at low luminosities and small projected radii. However, when
splitting the satellites by colour, the model and SDSS satellite systems no
longer resemble one another, with many red model satellites, in contrast to the
dominant blue fraction at similar luminosity in SDSS. The few model blue
satellites are also significantly less centrally concentrated in the halo of
their stacked primary than their SDSS counterparts. The implications of this
result for the GALFORM model are discussed.
|
Discovery of an Outstanding Disk in the cD Galaxy of the Hydra A Cluster | The central cD galaxy of the Hydra A cluster has one of the most powerful
active galactic nuclei (AGNs) in the nearby Universe (z <0.2). We report on the
discovery of a dust lane in the cD galaxy using Subaru telescope. The i'-band
image shows the existence of a dark band of the size of 3.6"x 0.7" (4 kpc x 0.8
kpc), which appears to be quite similar to the dust lane observed in Centaurus
A. The morphology indicates that the cold disk that seen as the dust lane is
almost edge-on and rotates around the AGN. Since the minor axis of the dust
lane is nearly parallel to the radio jets emerging from the AGN, the disk is
probably feeding its gas into the central black hole. From the absorption, we
estimate the hydrogen column density of the lane is N_H=2.0 x 10^21 cm^-2, and
the mass of the disk is ~8 x 10^7 M_sun. The column density is consistent with
constraints obtained from Chandra X-ray observations. The age of the disk is >~
4 x 10^7 yr. The position angle of the disk and the galaxy's photometric axis
are misaligned, which may imply that the cold gas in the disk is brought via
galaxy mergers. Our observations may indicate that the supply of cold gas by
galaxy mergers is required for the most intensive feedback from AGNs.
|
Calibrating the Davis-Chandrasekhar-Fermi method with numerical
simulations: uncertainties in estimating the magnetic field strength from
statistics of field orientations | The Davis-Chandrasekhar-Fermi (DCF) method is widely used to indirectly
estimate the magnetic field strength from the plane-of-sky field orientation.
In this work, we present a set of 3D MHD simulations and synthetic polarization
images using radiative transfer of clustered massive star-forming regions. We
apply the DCF method on the synthetic polarization maps to investigate its
reliability in high-density molecular clumps and dense cores where self-gravity
is significant. We investigate the validity of the assumptions of the DCF
method step by step and compare the model and estimated field strength to
derive the correction factors for the estimated uniform and total (rms)
magnetic field strength at clump and core scales. The correction factors in
different situations are catalogued. We find the DCF method works well in
strong field cases. However, the magnetic field strength in weak field cases
could be significantly overestimated by the DCF method when the turbulent
magnetic energy is smaller than the turbulent kinetic energy. We investigate
the accuracy of the angular dispersion function (ADF, a modified DCF method)
method on the effects that may affect the measured angular dispersion and find
that the ADF method correctly accounts for the ordered field structure, the
beam-smoothing, and the interferometric filtering, but may not be applicable to
account for the signal integration along the line of sight in most cases. Our
results suggest that the DCF methods should be avoided to be applied below
$\sim$0.1 pc scales if the effect of line-of-sight signal integration is not
properly addressed.
|
The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a
shallow and wide submillimeter imaging survey with SPIRE | A large sub-mm survey with Herschel will enable many exciting science
opportunities, especially in an era of wide-field optical and radio surveys and
high resolution cosmic microwave background experiments. The Herschel-SPIRE
Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250,
350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3
million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion
noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere
(3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which
have extensive multi-wavelength coverage and are easily accessible from ALMA.
Two thirds of the of the sources are expected to be at z > 1, one third at z >
2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary
anisotropy studies with Planck and ground-based CMB data. (c) Find at least
1200 strongly lensed bright sub-mm sources leading to a 2% test of general
relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an
unbiased study of the environmental dependence of star formation. (e) Perform
an unbiased survey for star formation and dust at high Galactic latitude and
make a census of debris disks and dust around AGB stars and white dwarfs.
|
The impact of galactic properties and environment on the quenching of
central and satellite galaxies: A comparison between SDSS, Illustris and
L-Galaxies | We quantify the impact that a variety of galactic and environmental
properties have on the quenching of star formation. We collate a sample of
$\sim$ 400,000 central and $\sim$ 100,000 satellite galaxies from the Sloan
Digital Sky Survey Data Release 7 (SDSS DR7). Specifically, we consider central
velocity dispersion ($\sigma_{c}$), stellar, halo, bulge and disk mass, local
density, bulge-to-total ratio, group-centric distance and galaxy-halo mass
ratio. We develop and apply a new statistical technique to quantify the impact
on the quenched fraction ($f_{\rm Quench}$) of varying one parameter, while
keeping the remaining parameters fixed. For centrals, we find that the $f_{\rm
Quench} - \sigma_{c}$ relationship is tighter and steeper than for any other
variable considered. We compare to the Illustris hydrodynamical simulation and
the Munich semi-analytic model (L-Galaxies), finding that our results for
centrals are qualitatively consistent with their predictions for quenching via
radio-mode AGN feedback, hinting at the viability of this process in explaining
our observational trends. However, we also find evidence that quenching in
L-Galaxies is too efficient and quenching in Illustris is not efficient enough,
compared to observations. For satellites, we find strong evidence that
environment affects their quenched fraction at fixed central velocity
dispersion, particularly at lower masses. At higher masses, satellites behave
identically to centrals in their quenching. Of the environmental parameters
considered, local density affects the quenched fraction of satellites the most
at fixed central velocity dispersion.
|
The ALMA Early Science View of FUor/EXor objects. II. The Very Wide
Outflow Driven by HBC 494 | We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle-2
observations of the HBC 494 molecular outflow and envelope. HBC 494 is an FU
Ori-like object embedded in the Orion A cloud and is associated with the
reflection nebulae Re50 and Re50N. We use $^{12}$CO, $^{13}$CO and C$^{18}$O
spectral line data to independently describe the outflow and envelope
structures associated with HBC 494. The moment-1 map of the $^{12}$CO emission
shows the widest outflow cavities in a Class I object known to date (opening
angle $\sim$ 150$^{^{\circ}}$). The morphology of the wide outflow is likely to
be due to the interaction between winds originating in the inner disc and the
surrounding envelope. The low-velocity blue- and red-shifted $^{13}$CO and
C$^{18}$O emission trace the rotation and infall motion of the circumstellar
envelope. Using molecular line data and adopting standard methods for
correcting optical depth effects, we estimate its kinematic properties,
including an outflow mass on the order of 10$^{-1}$ M$_{\odot}$. Considering
the large estimated outflow mass for HBC 494, our results support recent
theoretical work suggesting that wind-driven processes might dominate the
evolution of protoplanetary discs via energetic outflows.
|
Convergence of Galaxy Properties with Merger Tree Temporal Resolution | Dark matter halo merger trees are now routinely extracted from cosmological
simulations of structure formation. These trees are frequently used as inputs
to semi-analytic models of galaxy formation to provide the backbone within
which galaxy formation takes place. By necessity, these merger trees are
constructed from a finite set of discrete "snapshots" of the N-body simulation
and so have a limited temporal resolution. To date, there has been little
consideration of how this temporal resolution affects the properties of
galaxies formed within these trees. In particular, the question of how many
snapshots are needed to achieve convergence in galaxy properties has not be
answered. Therefore, we study the convergence in the stellar and total baryonic
masses of galaxies, distribution of merger times, stellar mass functions and
star formation rates in the Galacticus model of galaxy formation as a function
of the number of "snapshot" times used to represent dark matter halo merger
trees. When utilizing snapshots between z=20 and z=0, we find that at least 128
snapshots are required to achieve convergence to within 5% for galaxy masses.
This convergence is obtained for mean quantities averaged over large samples of
galaxies - significant variance for individual galaxies remains even when using
very large numbers of snapshots. We find only weak dependence of the rate of
convergence on the distribution of snapshots in time - snapshots spaced
uniformly in the expansion factor, uniformly in the logarithm of expansion
factor or uniformly in the logarithm of critical overdensity for collapse work
equally well in almost all cases. We provide input parameters to Galacticus
which allow this type of convergence study to be tuned to other simulations and
to be carried out for other galaxy properties.
|
Planck intermediate results. XXVI. Optical identification and redshifts
of Planck clusters with the RTT150 telescope | We present the results of approximately three years of observations of Planck
Sunyaev-Zeldovich (SZ) sources with the Russian-Turkish 1.5-m telescope
(RTT150), as a part of the optical follow-up programme undertaken by the Planck
collaboration. During this time period approximately 20% of all dark and grey
clear time available at the telescope was devoted to observations of Planck
objects. Some observations of distant clusters were also done at the 6-m
Bolshoy Telescope Azimutal'ny (BTA) of the Special Astrophysical Observatory of
the Russian Academy of Sciences. In total, deep, direct images of more than one
hundred fields were obtained in multiple filters. We identified 47 previously
unknown galaxy clusters, 41 of which are included in the Planck catalogue of SZ
sources. The redshifts of 65 Planck clusters were measured spectroscopically
and 14 more were measured photometrically. We discuss the details of cluster
optical identifications and redshift measurements. We also present new
spectroscopic redhifts for 39 Planck clusters that were not included in the
Planck SZ source catalogue and are published here for the first time.
|
Numerical simulation of time delay interferometry for eLISA/NGO | eLISA/NGO is a new gravitational wave detection proposal with arm length of
10^6 km and one interferometer down-scaled from LISA. Just like LISA and
ASTROD-GW, in order to attain the requisite sensitivity for eLISA/NGO, laser
frequency noise must be suppressed to below the secondary noises such as the
optical path noise, acceleration noise etc. In previous papers, we have
performed the numerical simulation of the time delay interferometry (TDI) for
LISA and ASTROD-GW with one arm dysfunctional by using the CGC 2.7 ephemeris.
The results are well below their respective limits which the laser frequency
noise is required to be suppressed. In this paper, we follow the same procedure
to simulate the time delay interferometry numerically. To do this, we work out
a set of 1000-day optimized mission orbits of the eLISA/NGO spacecraft starting
at January 1st, 2021 using the CGC 2.7 ephemeris framework. We then use the
numerical method to calculate the residual optical path differences in the
second-generation TDI solutions as in our previous papers. The maximum path
length difference, for all configurations calculated, is below 13 mm (43 ps).
It is well below the limit which the laser frequency noise is required to be
suppressed for eLISA/NGO. We compare and discuss the resulting differences due
to the different arm lengths for various mission proposals -- eLISA/NGO, an
NGO-LISA-type mission with a nominal arm length of 2 x 10^6 km, LISA and
ASTROD-GW.
|
Formation of Globular Cluster Systems II: Impact of the Cutoff of the
Cluster Initial Mass Function | Observations of young star clusters reveal that the high-mass end of the
cluster initial mass function (CIMF) deviates from a pure power-law and instead
truncates exponentially. We investigate the effects of this truncation on the
formation of globular cluster (GC) systems by updating our analytic model for
cluster formation and evolution, which is based on dark matter halo merger
trees coupled to empirical galactic scaling relations, and has been shown in
previous work to match a wide array of observational data. The cutoff masses of
$M_c=10^{6.5} M_{\odot}$ or $10^{7}M_{\odot}$ match many scaling relations:
between the GC system mass and host halo mass, between the average metallicity
of the GC system and host halo mass, and the distribution of cluster masses.
This range of $M_c$ agrees with indirect measurements from extragalactic GC
systems. Models with $M_c<10^{6.5}M_{\odot}$ cannot reproduce the observed GC
metallicity and mass distributions in massive galaxies. The slope of the
mass-metallicity relation for metal-poor clusters (blue tilt) for all $M_c$
models is consistent with observations within their errors, when measured using
the same method. We introduce an alternative, more robust fitting method, which
reveals a trend of increasing tilt slope for lower $M_c$. In our model the blue
tilt arises because the metal-poor clusters form in relatively low-mass
galaxies which lack sufficient cold gas to sample the CIMF at highest masses.
Massive blue clusters form in progressively more massive galaxies and inherit
their higher metallicity. The metal-rich clusters do not exhibit such a tilt
because they form in significantly more massive galaxies, which have enough
cold gas to fully sample the CIMF.
|
Formation of massive black holes via collisions and accretion | To explain the observed population of supermassive black holes at z~7, very
massive seed black holes or, alternatively, super-Eddington scenarios are
needed to reach final masses of the order of 10^9 solar masses. A popular
explanation for massive seeds has been the direct collapse model, which
predicts the formation of a single massive object due to the direct collapse of
a massive gas cloud. Simulations over the last years have however shown that
such a scenario is very difficult to achieve. A realistic model of black hole
formation should therefore take fragmentation into account, and consider the
interaction between stellar-dynamical and gas-dynamical processes. We present
here numerical simulations pursued with the AMUSE code, employing an
approximate treatment of the gas. Based on these simulations, we show that very
massive black holes of 10^4-10^5 solar masses may form depending on the gas
supply and the accretion onto the protostars.
|
A 3D Phase Space Analysis of Scalar Field Potentials | In this study, we present the phase-space analysis of Quintessence models
specified by the choice of two potentials, namely the Recliner potential and
what we call the broken exponential-law potential, which is a new proposal.
Using a dynamical system analysis we provide a systematic study of the
cosmological evolution of the two models and their properties. We find new
scaling solutions characterised by a constant ratio between the energy density
of the scalar field and that of the matter component. These solutions are of
high interest in light of the possibility to alleviate the coincidence problem.
Additionally, the models also show attractor solutions. We finally construct
concrete models built using a double potential according to which one potential
realises the early-time scaling regime and the second one allows to exit this
regime and to enter in the epoch of cosmic acceleration driven by a
scalar-field dominated attractor point.
|
The power spectrum and bispectrum of SDSS DR11 BOSS galaxies I: bias and
gravity | We analyse the anisotropic clustering of the Baryon Oscillation Spectroscopic
Survey (BOSS) CMASS Data Release 11 sample, which consists of $690 827$
galaxies in the redshift range $0.43 < z < 0.70$ and has a sky coverage of $8
498$ deg$^2$ corresponding to an effective volume of $\sim6\,\rm{Gpc}^3$. We
fit the Fourier space statistics, the power spectrum and bispectrum monopoles
to measure the linear and quadratic bias parameters, $b_1$ and $b_2$, for a
non-linear non-local bias model, the growth of structure parameter $f$ and the
amplitude of dark matter density fluctuations parametrised by $\sigma_8$. We
obtain $b_1(z_{\rm eff})^{1.40}\sigma_8(z_{\rm eff})=1.672\pm 0.060$ and
$b_2^{0.30}(z_{\rm eff})\sigma_8(z_{\rm eff})=0.579\pm0.082$ at the effective
redshift of the survey, $z_{\rm eff}=0.57$. The main cosmological result is the
constraint on the combination $f^{0.43}(z_{\rm eff})\sigma_8(z_{\rm
eff})=0.582\pm0.084$, which is complementary to $f\sigma_8$ constraints
obtained from 2-point redshift space distortion analyses. A less conservative
analysis yields $f^{0.43}(z_{\rm eff})\sigma_8(z_{\rm eff})=0.584\pm0.051$. We
ensure that our result is robust by performing detailed systematic tests using
a large suite of survey galaxy mock catalogs and N-body simulations. The
constraints on $f^{0.43}\sigma_8$ are useful for setting additional constrains
on neutrino mass, gravity, curvature as well as the number of neutrino species
from galaxy surveys analyses (as presented in a companion paper).
|
Can we overcome the neutrino floor at high masses? | The neutrino floor is a barrier in the parameter space of weakly interacting
massive particles (WIMPs) below which discovery is impeded due to an almost
irreducible background of neutrinos. Directional gas time projection chambers
could discriminate against solar neutrinos, relevant for WIMP masses
$\lesssim$10 GeV. At higher masses $\gtrsim$100 GeV the floor is set by the
background of atmospheric neutrinos. Probing below this part of the floor would
require very large target exposures. Since gas-based detectors would be
prohibitively large at this scale, we instead reevaluate the prospects for
liquid noble experiments to probe below the neutrino floor. We combine all
potential methods of subtracting the neutrino background to determine how much
of this difficult to reach, but well-motivated, parameter space it is feasible
to reach. Most notably, we quantify whether a proposed directional signal in
xenon and argon experiments called "columnar recombination" can help in this
task. We find that even if the strength of this effect is amplified beyond
current experimental results, the quantity of directional information contained
in the recombination signal is too low to realistically discriminate against
the atmospheric neutrino background. Instead, benefiting from the refined
measurements of neutrino fluxes by experiments such as DUNE and JUNO will be
the most practical means to push direct WIMP searches below the neutrino floor.
For an ultimate global coordination of xenon and argon experiments, we show
that the neutrino floor is a surmountable barrier. The direct detection of 100
GeV-scale supersymmetric WIMPs may, eventually, be within reach.
|
Binaries of massive black holes in rotating clusters: Dynamics,
gravitational waves, detection and the role of eccentricity | The dynamical evolution of binaries of intermediate-massive black holes
(IMBHs, massive black holes with a mass ranging between $10^2$ and $10^4
M_{\odot}$) in stellar clusters has recently received an increasing amount of
attention. This is at least partially due to the fact that if the binary is
hard enough to evolve to the phase at which it will start emitting
gravitational waves (GWs) efficiently, there is a good probability that it will
be detectable by future space-borne detectors like LISA. We study this
evolution in the presence of rotation in the cluster. The eccentricity is
strongly connected to the initial IMBHs velocities, and values of $\sim 0.7$ up
to 0.9 are reached for low initial velocities, while almost circular orbits
result if the initial velocities are increased. A Monte Carlo study indicates
that these sources will be detectable by a detector such as LISA with median
signal to noise ratios of between 10 and 20 over a three year period, although
some events had signal to noise ratios of 300 or greater. Furthermore, one
should also be able to estimate the chirp-mass with median fractional errors of
$10^{-4}$, reduced mass on the order of $10^{-3}$ and luminosity distance on
the order of $10^{-1}$. Finally, these sources will have a median angular
resolution in the LISA detector of about 3 square degrees, putting events
firmly in the field of view of future electromagnetic detectors such as LSST.
|
The long-lasting activity of 3C 454.3. GASP-WEBT and satellite
observations in 2008-2010 | We present multiwavelength observations of 3C 454.3 from April 2008 to March
2010. The radio to optical data are mostly from the GASP-WEBT, UV and X-ray
data from Swift, and gamma-ray data from the AGILE and Fermi satellites. We
improved the calibration of optical-UV data from the UVOT and OM instruments
and estimated the Lyalpha flux to disentangle the contributions from different
components in this spectral region. The observations reveal prominent
variability above 8 GHz. In the optical-UV band, the variability amplitude
decreases with increasing frequency due to a steadier radiation from both a
broad line region and an accretion disc. The optical flux reaches nearly the
same levels in the 2008-2009 and 2009-2010 observing seasons; the mm one shows
similar behaviour, whereas the gamma and X-ray flux levels rise in the second
period. Two prominent gamma-ray flares in mid 2008 and late 2009 show a
double-peaked structure, with a variable gamma/optical flux ratio. The X-ray
flux variations seem to follow the gamma-ray and optical ones by about 0.5 and
1 d, respectively. We interpret the multifrequency behaviour in terms of an
inhomogeneous curved jet, where synchrotron radiation of increasing wavelength
is produced in progressively outer and wider jet regions, which can change
their orientation in time. In particular, we assume that the long-term
variability is due to this geometrical effect. By combining the optical and mm
light curves to fit the gamma and X-ray ones, we find that the gamma (X-ray)
emission may be explained by inverse-Comptonisation of synchrotron optical (IR)
photons by their parent relativistic electrons (SSC process). A slight,
variable misalignment between the synchrotron and Comptonisation zones would
explain the increased gamma and X-ray flux levels in 2009-2010, as well as the
change in the gamma/optical flux ratio during the outbursts peaks.
|
Radial Velocity Measurements of an Orbiting Star Around Sgr A* | During the next closest approach of the orbiting star S2/S0-2 to the Galactic
supermassive black hole (SMBH), it is estimated that RV uncertainties of ~ 10
km/s allow us to detect post-Newtonian effects throughout 2018. To evaluate an
achievable uncertainty in RV and its stability, we have carried out
near-infrared, high resolution (R ~ 20,000) spectroscopic monitoring
observations of S2 using the Subaru telescope and the near-infrared
spectrograph IRCS from 2014 to 2016. The Br-gamma absorption lines are used to
determine the RVs of S2. The RVs we obtained are 497 km/s, 877 km/s, and 1108
km/s in 2014, 2015, and 2016, respectively. The statistical uncertainties are
derived using the jackknife analysis. The wavelength calibrations in our
three-year monitoring are stable: short-term (hours to days) uncertainties in
RVs are < 0.5 km/s, and a long-term (three years) uncertainty is 1.2 km/s. The
uncertainties from different smoothing parameter, and from the partial
exclusion of the spectra, are found to be a few km/s. The final results using
the Br-gamma line are 497 +- 17 (stat.) +- 3 (sys.) km/s in 2014, 877 +- 15
(stat.) +- 4 (sys.) km/s in 2015, and 1108 +- 12 (stat.) +- 4 (sys.) km/s in
2016. When we use two He I lines at 2.113\mum in addition to Br-gamma, the mean
RVs are 513 km/s and 1114 km/s for 2014 and 2016, respectively. The standard
errors of the mean are 16.2 km/s (2014) and 5.4 km/s (2016), confirming the
reliability of our measurements. The difference between the RVs estimated by
Newtonian mechanics and general relativity will reach about 200 km/s near the
next pericenter passage in 2018. Therefore our RV uncertainties of 13 - 17 km/s
with Subaru enable us to detect the general relativistic effects in the RV
measurements with more than 10 sigma in 2018.
|
Limits on Dark Matter Annihilation Signals from the Fermi LAT 4-year
Measurement of the Isotropic Gamma-Ray Background | We search for evidence of dark matter (DM) annihilation in the isotropic
gamma-ray background (IGRB) measured with 50 months of Fermi Large Area
Telescope (LAT) observations. An improved theoretical description of the
cosmological DM annihilation signal, based on two complementary techniques and
assuming generic weakly interacting massive particle (WIMP) properties, renders
more precise predictions compared to previous work. More specifically, we
estimate the cosmologically-induced gamma-ray intensity to have an uncertainty
of a factor ~20 in canonical setups. We consistently include both the Galactic
and extragalactic signals under the same theoretical framework, and study the
impact of the former on the IGRB spectrum derivation. We find no evidence for a
DM signal and we set limits on the DM-induced isotropic gamma-ray signal. Our
limits are competitive for DM particle masses up to tens of TeV and, indeed,
are the strongest limits derived from Fermi LAT data at TeV energies. This is
possible thanks to the new Fermi LAT IGRB measurement, which now extends up to
an energy of 820 GeV. We quantify uncertainties in detail and show the
potential this type of search offers for testing the WIMP paradigm with a
complementary and truly cosmological probe of DM particle signals.
|
Light-cone observations and cosmological models: implications for
inhomogeneous models mimicking dark energy | Cosmological observables are used to construct cosmological models. Since
cosmological observations are limited to the light cone, a fixed number of
observables (even measured to arbitrary accuracy) may not uniquely determine a
cosmological model without additional assumptions or considerations. A
prescription for constructing a spherically symmetric, inhomogeneous
cosmological model that exactly reproduces the luminosity-distance as a
function of redshift and the light-cone mass density as a function of redshift
of a $\Lambda$CDM model is employed to gain insight into how an inhomogeneous
cosmological model might mimic dark energy models.
|
On topological bias of discrete sources in the gas of wormholes | The model of space in the form of a static gas of wormholes is considered. It
is shown that the scattering on such a gas gives rise to the formation of a
specific diffuse halo around every discrete source. Properties of the halo are
determined by the distribution of wormholes in space and the halo has to be
correlated with the distribution of dark matter. This allows to explain the
absence of dark matter in intergalactic gas clouds. Numerical estimates for
parameters of the gas of wormholes are also obtained.
|
The Size and Shape of the Milky Way Disk and Halo from M-type Brown
Dwarfs in the BoRG Survey | We have identified 274 M-type Brown Dwarfs in the Hubble Space Telescope's
Wide Field Camera 3 (WFC3) pure parallel fields from the Brightest of
Reionizing Galaxies (BoRG) survey for high redshift galaxies. These are
near-infrared observations with multiple lines-of-sight out of our Milky Way.
Using these observed M-type Brown Dwarfs we fitted a Galactic disk and halo
model with a Markov chain Monte Carlo (MCMC) analysis. This model worked best
with the scale length of the disk fixed at $h$ = 2.6 kpc. For the scale height
of the disk, we found $z_0 = 0.29^{+0.02}_{-0.019}$ kpc and for the central
number density $\rho_0 = 0.29^{+0.20}_{-0.13}$ \#/pc$^3$. For the halo we
derived a flattening parameter $\kappa$ = 0.45$\pm{0.04}$ and a power-law index
$p$ = 2.4$\pm{0.07}$. We found the fraction of M-type brown dwarfs in the local
density that belong to the halo to be $f_{h}$ = 0.0075$^{+0.0025}_{-0.0019}$.
We found no correlation between subtype of M-dwarf and any model parameters.
The total number of M-type Brown Dwarfs in the disk and halo was determined
to be $58.2^{+9.81}_{-6.70} \times10^{9}$. We found an upper limit for the
fraction of M-type Brown Dwarfs in the halo of 7$^{+5}_{-4}$\%. The upper limit
for the total Galactic Disk mass in M-dwarfs is
$4.34^{+0.73}_{-0.5}\times10^{9}$ $M_{\odot}$, assuming all M-type Brown Dwarfs
have a mass of $80 M_J$.
|
Slowly Rotating Black Holes in Dynamical Chern-Simons Gravity:
Deformation Quadratic in the Spin | We derive a stationary and axisymmetric black hole solution to quadratic
order in the spin angular momentum. The previously found, linear-in-spin terms
modify the odd-parity sector of the metric, while the new corrections appear in
the even-parity sector. These corrections modify the quadrupole moment, as well
as the (coordinate-dependent) location of the event horizon and the ergoregion.
Although the linear-in-spin metric is of Petrov type D, the quadratic order
terms render it of type I. The metric does not possess a second-order Killing
tensor or a Carter-like constant. The new metric does not possess closed
timelike curves or spacetime regions that violate causality outside of the
event horizon. The new, even-parity modifications to the Kerr metric decay less
rapidly at spatial infinity than the leading-order in spin, odd-parity ones,
and thus, the former are more important when considering black holes that are
rotating moderately fast. We calculate the modifications to the Hamiltonian,
binding energy and Kepler's third law. These modifications are crucial for the
construction of gravitational wave templates for black hole binaries, which
will enter at second post-Newtonian order, just like dissipative modifications
found previously.
|
Star Formation Relations in the Milky Way | The relations between star formation and properties of molecular clouds are
studied based on a sample of star forming regions in the Galactic Plane.
Sources were selected by having radio recombination lines to provide
identification of associated molecular clouds and dense clumps. Radio continuum
and mid-infrared emission were used to determine star formation rates, while
13CO and submillimeter dust continuum emission were used to obtain masses of
molecular and dense gas, respectively. We test whether total molecular gas or
dense gas provides the best predictor of star formation rate. We also test two
specific theoretical models, one relying on the molecular mass divided by the
free-fall time, the other using the free-fall time divided by the crossing
time. Neither is supported by the data. The data are also compared to those
from nearby star forming regions and extragalactic data. The star formation
"efficiency," defined as star formation rate divided by mass, spreads over a
large range when the mass refers to molecular gas; the standard deviation of
the log of the efficiency decreases by a factor of three when the mass of
relatively dense molecular gas is used rather than the mass of all the
molecular gas.
|
Generation of Arbitrarily Non-Gaussian Fields with a Set Correlation
Structure | Non-Gaussianity in the cosmic microwave background and the large-scale
structure of galaxies provides an increasingly powerful probe of the universe.
I implement an algorithm to generate realisations of fields that possess an
arbitrary probability distribution function and an arbitrary power spectrum and
demonstrate the code with a number of examples, including the uniform
distribution, the Laplace distribution, the $\chi$ and $\chi^2$ distributions,
Rayleigh and Maxwell-Boltzmann distributions. The code is available at
http://sourceforge.net/projects/nongaussian.
|
Dark Energy Survey Year 3 results: cosmology from combined galaxy
clustering and lensing -- validation on cosmological simulations | We present a validation of the Dark Energy Survey Year 3 (DES Y3)
$3\times2$-point analysis choices by testing them on Buzzard v2.0, a new suite
of cosmological simulations that is tailored for the testing and validation of
combined galaxy clustering and weak lensing analyses. We show that the Buzzard
v2.0 simulations accurately reproduce many important aspects of the DES Y3
data, including photometric redshift and magnitude distributions, and the
relevant set of two-point clustering and weak lensing statistics. We then show
that our model for the $3\times2$-point data vector is accurate enough to
recover the true cosmology in simulated surveys assuming the true redshift
distributions for our source and lens samples, demonstrating robustness to
uncertainties in the modeling of the non-linear matter power spectrum,
non-linear galaxy bias and higher-order lensing corrections. Additionally, we
demonstrate for the first time that our photometric redshift calibration
methodology, including information from photometry, spectroscopy, clustering
cross-correlations, and galaxy-galaxy lensing ratios, is accurate enough to
recover the true cosmology in simulated surveys in the presence of realistic
photometric redshift uncertainties.
|
The Effect of Environment on Massive Star Formation | In this contribution we review our recent numerical work discussing the
essential role of the local cluster environment in assembling massive stars.
First we show that massive stars are formed from low mass pre-stellar cores and
become massive due to accretion. Proto-stars that benefit from this accretion
are those situated at the centre of a cluster's potential well, which is the
focal point of the contraction of the cluster gas. Given that most of the mass
which makes up a massive star in this model comes from the cluster environment
rather than the core, it is important to model the molecular cloud environment
accurately. Preliminary results of a simulation which accurately treats the
chemistry and time-dependent thermodynamics of a molecular cloud show
quantitatively similar star formation to previous models, but allow a true
comparison to be made between simulation and observations. This method can also
be applied to cases with varying metallicities allowing star formation in
primordial gas to be studied. In general, these numerical studies of clustered
star formation yield IMFs which are compatible with the Salpeter mass function.
The only possible exception to this is in low density unbound regions of
molecular clouds which lack very low and high mass stars.
|
The impact of galaxy formation on satellite kinematics and
redshift-space distortions | Galaxy surveys aim to map the large-scale structure of the Universe and use
redshift space distortions to constrain deviations from general relativity and
probe the existence of massive neutrinos. However, the amount of information
that can be extracted is limited by the accuracy of theoretical models used to
analyze the data. Here, by using the L-Galaxies semi-analytical model run over
the MXXL N-body simulation, we assess the impact of galaxy formation on
satellite kinematics and the theoretical modelling of redshift-space
distortions. We show that different galaxy selection criteria lead to
noticeable differences in the radial distributions and velocity structure of
satellite galaxies. Specifically, whereas samples of stellar mass selected
galaxies feature satellites that roughly follow the dark matter, emission line
satellite galaxies are located preferentially in the outskirts of halos and
display net infall velocities. We demonstrate that capturing these differences
is crucial for modelling the multipoles of the correlation function in redshift
space, even on large scales. In particular, we show how modelling small scale
velocities with a single Gaussian distribution leads to a poor description of
the measure clustering. In contrast, we propose a parametrization that is
flexible enough to model the satellite kinematics, and that leads to and
accurate description of the correlation function down to sub-Mpc scales. We
anticipate that our model will be a necessary ingredient in improved
theoretical descriptions of redshift space distortions, which together could
result in significantly tighter cosmological constraints and a more optimal
exploitation of future large datasets.
|
Gravitational Waves from Mirror World | In this paper we consider the properties of the 10 confirmed by the LIGO
Collaboration gravitational wave signals from the black hole mergers. We want
to explain non-observation of electromagnetic counterpart and higher then
expected merging rates of these events, assuming the existence of their sources
in the hidden mirror universe. Mirror matter, which interacts with our world
only through gravity, is a candidate of dark matter and its density can exceed
ordinary matter density five times. Since mirror world is considered to be
colder, star formation there started earlier and mirror black holes had more
time to pick up the mass and to create more binary systems within the LIGO
reachable zone. In total, we estimate factor of 15 amplification of black holes
merging rate in mirror world with respect to our world, which is consistent
with the LIGO observations.
|
Improving the absolute accuracy of the gravitational wave detectors by
combining the photon pressure and gravity field calibrators | The absolute accuracy of the estimated parameters of gravitational wave
sources will be fundamentally limited by the calibration uncertainties of the
detectors in upcoming observation runs with the increased number of source
statistics. Photon calibrators have so far been the primary tools for absolute
calibration of test-mass displacement, relying on measurement of the photon
pressure. The current technological limit of the absolute calibration
uncertainty for gravitational-wave amplitudes is limited to a few percent, due
to the uncertainty in the laser power-standard maintained by the metrology
institutes. To reduce this uncertainty, this article proposes a novel
calibration method that combines a photon calibrator and a gravity field
calibrator. The gravity field calibrator achieves modulation of the
displacement of the test mass by generating a gravity gradient. In previous
studies, uncertainty in the distance between the test mass and the gravity
field calibrator has proven a serious source of systematic error. To suppress
this uncertainty, we propose a novel method that uses a combination of
quadrupole and hexapole mass distributions in the gravity field calibrator. We
estimate the absolute uncertainty associated with method to be as low as
0.17~%, which is ten times less than that of previous methods.
|
Hide-and-Seek with the Fundamental Metallicity Relation | We use $\sim$83,000 star-forming galaxies at $0.04<z<0.3$ from the Sloan
Digital Sky Survey to study the so-called fundamental metallicity relation
(FMR) and report on the disappearance of its anti-correlation between
metallicity and star formation rate (SFR) when using the new metallicity
indicator recently proposed by Dopita et al. In this calibration, metallicity
is primarily sensitive to the emission line ratio [NII]$\lambda$6584 /
[SII]$\lambda\lambda$6717, 6731 that is insensitive to dilution by pristine
infalling gas that may drive the FMR anti-correlation with SFR. Therefore, we
conclude that the apparent disappearance of the FMR (using this new metallicity
indicator) does not rule out its existence.
|
Density profile of multi-state fuzzy dark matter | Equations of motion for excited states of weakly self-interacting bosons
forming fuzzy dark matter are solved using the WKB approximation. The
contribution of self-interactions are neglected in the equations of motion.
Wave functions of excited states are expressed in terms of a yet undetermined
gravitational potential. At equilibrium, the contributions of states to the
density distribution are summed using Bose-Einstein statistics. Combined with
the Poisson equation, a differential equation is obtained for the gravitational
potential, which has physically acceptable solutions only if the energy
spectrum of excited states has a finite gap, corresponding to a finite virial
radius. Such a gap could be created by decay processes, in first order
perturbation of the self-interaction potential. The obtained density profile is
found to be similar to the Burkert profile.
|
A Giant Metrewave Radio Telescope search for associated H{\sc i} 21\,cm
absorption in GHz-peaked-spectrum sources | We report the first detections of associated H{\sc i} 21\,cm absorption in
Gigahertz-peaked-spectrum (GPS) sources at high redshifts, $z > 1$, using the
Giant Metrewave Radio Telescope (GMRT). Our GMRT search for associated H{\sc i}
21\,cm absorption in a sample of 12 GPS sources yielded two new detections of
absorption, towards TXS~1200+045 at $z = 1.226$ and TXS~1245$-$197 at $z =
1.275$, and five non-detections. These are only the sixth and seventh
detections of associated H{\sc i} 21\,cm absorption in active galactic nuclei
(AGNs) at $z > 1$. Both H{\sc i} 21\,cm absorption profiles are wide, with
velocity spans between nulls of $\approx 600$~km~s$^{-1}$ (TXS~1200+045) and
$\approx 1100$~km~s$^{-1}$ (TXS~1245$-$197). In both absorbers, the large
velocity spread of the absorption and its blueshift from the AGN, suggests that
it arises in outflowing neutral gas, perhaps driven by the radio jets to high
velocities. We derive mass outflow rates of ${\dot M} \approx 32 \; {\rm
M}_\odot$~yr$^{-1}$ (TXS~1200+045) and ${\dot M} \approx 18 \; {\rm
M}_\odot$~yr$^{-1}$ (TXS~1245$-$197), comparable to the mass outflow rates seen
earlier in low-redshift active galactic nuclei.
|
Dark-Matter Harmonics Beyond Annual Modulation | The count rate at dark-matter direct-detection experiments should modulate
annually due to the motion of the Earth around the Sun. We show that
higher-frequency modulations, including daily modulation, are also present and
in some cases are nearly as strong as the annual modulation. These higher-order
modes are particularly relevant if (i) the dark matter is light, O(10) GeV,
(ii) the scattering is inelastic, or (iii) velocity substructure is present;
for these cases, the higher-frequency modes are potentially observable at
current and ton-scale detectors. We derive simple expressions for the harmonic
modes as functions of the astrophysical and geophysical parameters describing
the Earth's orbit, using an updated expression for the Earth's velocity that
corrects a common error in the literature. For an isotropic halo velocity
distribution, certain ratios of the modes are approximately constant as a
function of nuclear recoil energy. Anisotropic distributions can also leave
observable features in the harmonic spectrum. Consequently, the higher-order
harmonic modes are a powerful tool for identifying a potential signal from
interactions with the Galactic dark-matter halo.
|
BeyondPlanck II. CMB map-making through Gibbs sampling | We present a Gibbs sampling solution to the map-making problem for CMB
measurements, building on existing destriping methodology. Gibbs sampling
breaks the computationally heavy destriping problem into two separate steps;
noise filtering and map binning. Considered as two separate steps, both are
computationally much cheaper than solving the combined problem. This provides a
huge performance benefit as compared to traditional methods, and allows us for
the first time to bring the destriping baseline length to a single sample. We
apply the Gibbs procedure to simulated Planck 30 GHz data. We find that gaps in
the time-ordered data are handled efficiently by filling them with simulated
noise as part of the Gibbs process. The Gibbs procedure yields a chain of map
samples, from which we may compute the posterior mean as a best-estimate map.
The variation in the chain provides information on the correlated residual
noise, without need to construct a full noise covariance matrix. However, if
only a single maximum-likelihood frequency map estimate is required, we find
that traditional conjugate gradient solvers converge much faster than a Gibbs
sampler in terms of total number of iterations. The conceptual advantages of
the Gibbs sampling approach lies in statistically well-defined error
propagation and systematic error correction, and this methodology forms the
conceptual basis for the map-making algorithm employed in the BeyondPlanck
framework, which implements the first end-to-end Bayesian analysis pipeline for
CMB observations.
|
An ALMA survey of submillimetre galaxies in the Extended Chandra Deep
Field South: High resolution 870um source counts | We report the first counts of faint submillimetre galaxies (SMG) in the
870-um band derived from arcsecond resolution observations with the Atacama
Large Millimeter Array (ALMA). We have used ALMA to map a sample of 122
870-um-selected submillimetre sources drawn from the (0.5x0.5)deg^2 LABOCA
Extended Chandra Deep Field South Submillimetre Survey (LESS). These ALMA maps
have an average depth of sigma(870um)~0.4mJy, some ~3x deeper than the original
LABOCA survey and critically the angular resolution is more than an order of
magnitude higher, FWHM of ~1.5" compared to ~19" for the LABOCA discovery map.
This combination of sensitivity and resolution allows us to precisely pin-point
the SMGs contributing to the submillimetre sources from the LABOCA map, free
from the effects of confusion. We show that our ALMA-derived SMG counts broadly
agree with the submillimetre source counts from previous, lower-resolution
single-dish surveys, demonstrating that the bulk of the submillimetre sources
are not caused by blending of unresolved SMGs. The difficulty which
well-constrained theoretical models have in reproducing the high-surface
densities of SMGs, thus remains. However, our observations do show that all of
the very brightest sources in the LESS sample, S(870um)>12mJy, comprise
emission from multiple, fainter SMGs, each with 870-um fluxes of <9mJy. This
implies a natural limit to the star-formation rate in SMGs of <10^3 M_Sun/yr,
which in turn suggests that the space densities of z>1 galaxies with gas masses
in excess of ~5x10^10 M_Sun is <10^-5 Mpc^-3. We also discuss the influence of
this blending on the identification and characterisation of the SMG
counterparts to these bright submillimetre sources and suggest that it may be
responsible for previous claims that they lie at higher redshifts than fainter
SMGs.
|
Amplification of Primordial Gravitational Waves by a Geometrically
Driven non-canonical Reheating Era | In order to describe inflation in general relativity, scalar fields must
inevitably be used, with all the setbacks of that description. On the other
hand, $f(R)$ gravity and other modified gravity theories seem to provide a
unified description of early and late-time dynamics without resorting to scalar
or phantom theories. The question is, can modified gravity affect directly the
mysterious radiation domination era? Addressing this question is the focus in
this work, and we shall consider the case for which in the early stages of the
radiation domination era, namely during the reheating era, the background
equation of state parameter is different from $w=1/3$. As we show, in the
context of $f(R)$ gravity, an abnormal reheating era can affect the primordial
gravitational wave energy spectrum today. Since future interferometers will
exactly probe this era, which consists of subhorizon modes that reentered the
horizon during the early stages of the radiation domination era, the focus in
this work is how a short abnormal reheating era that deviates from the standard
perfect fluid pattern with $w\neq 1/3$, and generated by higher order curvature
terms, can affect the primordial gravitational wave energy spectrum. Using a
WKB approach, we calculate the effect of an $f(R)$ gravity generated abnormal
reheating era, and as we show the primordial gravitational wave spectrum is
significantly amplified, a result which is in contrast to the general
relativistic case, where the effect is minor.
|
The TW Hya Rosetta Stone Project II: Spatially resolved emission of
formaldehyde hints at low-temperature gas-phase formation | Formaldehyde (H$_2$CO) is an important precursor to organics like methanol
(CH$_3$OH). It is important to understand the conditions that produce H$_2$CO
and prebiotic molecules during star and planet formation. H$_2$CO possesses
both gas-phase and solid-state formation pathways, involving either UV-produced
radical precursors or CO ice and cold ($\lesssim 20$ K) dust grains. To
understand which pathway dominates, gaseous H$_2$CO's ortho-to-para ratio (OPR)
has been used as a probe, with a value of 3 indicating "warm" conditions and
$<3$ linked to cold formation in the solid-state. We present spatially resolved
ALMA observations of multiple ortho- and para-H$_2$CO transitions in the TW Hya
protoplanetary disk to test H$_2$CO formation theories during planet formation.
We find disk-averaged rotational temperatures and column densities of $33\pm2$
K, ($1.1\pm0.1)\times10^{12}$ cm$^{-2}$ and $25\pm2$ K,
$(4.4\pm0.3)\times10^{11}$ cm$^{-2}$ for ortho- and para-H$_2$CO, respectively,
and an OPR of $2.49\pm0.23$. A radially resolved analysis shows that the
observed H$_2$CO emits mostly at rotational temperatures of 30-40 K,
corresponding to a layer with $z/R\ge0.25$. The OPR is consistent with 3 within
60 au, the extent of the pebble disk, and decreases beyond 60 au to
$2.0\pm0.5$. The latter corresponds to a spin temperature of 12 K, well below
the rotational temperature. The combination of relatively uniform emitting
conditions, a radial gradient in the OPR, and recent laboratory experiments and
theory on OPR ratios after sublimation, lead us to speculate that gas-phase
formation is responsible for the observed H$_2$CO across the TW Hya disk.
|
Designing an Inflation Galaxy Survey: how to measure $\sigma(f_{\rm NL})
\sim 1$ using scale-dependent galaxy bias | The most promising method for measuring primordial non-Gaussianity in the
post-Planck era is to detect large-scale, scale-dependent galaxy bias.
Considering the information in the galaxy power spectrum, we here derive the
properties of a galaxy clustering survey that would optimize constraints on
primordial non-Gaussianity using this technique. Specifically, we ask the
question what survey design is needed to reach a precision $\sigma(f_{\rm
NL}^{\rm loc}) \approx 1$. To answer this question, we calculate the
sensitivity to $f_{\rm NL}^{\rm loc}$ as a function of galaxy number density,
redshift accuracy and sky coverage. We include the multitracer technique, which
helps minimize cosmic variance noise, by considering the possibility of
dividing the galaxy sample into stellar mass bins. We show that the ideal
survey for $f_{\rm NL}^{\rm loc}$ looks very different than most galaxy
redshift surveys scheduled for the near future. Since those are more or less
optimized for measuring the BAO scale, they typically require spectroscopic
redshifts. On the contrary, to optimize the $f_{\rm NL}^{\rm loc}$ measurement,
a deep, wide, multi-band imaging survey is preferred. An uncertainty
$\sigma(f_{\rm NL}^{\rm loc}) = 1$ can be reached with a full-sky survey that
is complete to an $i$-band AB magnitude $i \approx 23$ and has a number density
$\sim 8$ arcmin$^{-2}$. Requirements on the multi-band photometry are set by a
modest photo-$z$ accuracy $\sigma(z)/(1+z) < 0.1$ and the ability to measure
stellar mass with a precision $\sim 0.2$ dex or better (or another proxy for
halo mass with equivalent scatter). While here we focus on the information in
the power spectrum, even stronger constraints can potentially be obtained with
the galaxy bispectrum.
|
Hydrodynamical simulations of a compact source scenario for the Galactic
Center cloud G2 | The origin of the dense gas cloud G2 discovered in the Galactic Center
(Gillessen et al. 2012) is still a debated puzzle. G2 might be a diffuse cloud
or the result of an outflow from an invisible star embedded in it. We present
hydrodynamical simulations of the evolution of different spherically symmetric
winds of a stellar object embedded in G2. We find that the interaction with the
ambient medium and with the extreme gravitational field of the supermassive
black hole in the Galactic Center must be taken into account for such a source
scenario. The thermal pressure of the hot and dense atmosphere confines the
wind, while its ram pressure shapes it via stripping along the orbit, with the
details depending on the wind parameters. Tidal forces squeeze the wind near
pericenter, reducing it to a thin and elongated filament. We also find that in
this scenario most of the Br\gamma\ luminosity is expected to come from the
densest part of the wind, which has a highly filamentary structure with low
filling factor. The observations can be best matched by a mass outflow rate of
Mdot,w=8.8 x 10^{-8} Msun/yr and a wind velocity of vw = 50 km/s. These values
are compatible with those of a young T Tauri star wind, as already suggested by
(Scoville & Burkert 2013).
|
Two-component jet simulations: II. Combining analytical disk and stellar
MHD outflow solutions | Theoretical arguments along with observational data of YSO jets suggest the
presence of two steady components: a disk wind type outflow needed to explain
the observed high mass loss rates and a stellar wind type outflow probably
accounting for the observed stellar spin down.
Each component's contribution depends on the intrinsic physical properties of
the YSO-disk system and its evolutionary stage. The main goal of this paper is
to understand some of the basic features of the evolution, interaction and
co-existence of the two jet components over a parameter space and when time
variability is enforced. Having studied separately the numerical evolution of
each type of the complementary disk and stellar analytical wind solutions in
Paper I of this series, we proceed here to mix together the two models inside
the computational box. The evolution in time is performed with the PLUTO code,
investigating the dynamics of the two-component jets, the modifications each
solution undergoes and the potential steady state reached.
|
Millimeter-wave polarization of protoplanetary disks due to dust
scattering | We present a new method to constrain the grain size in protoplanetary disks
with polarization observations at millimeter wavelengths. If dust grains are
grown to the size comparable to the wavelengths, the dust grains are expected
to have a large scattering opacity and thus the continuum emission is expected
to be polarized due to self-scattering. We perform 3D radiative transfer
calculations to estimate the polarization degree for the protoplanetary disks
having radial Gaussian-like dust surface density distributions, which have been
recently discovered. The maximum grain size is set to be $100 {\rm~\mu m}$ and
the observing wavelength to be 870 ${\rm \mu m}$. We find that the polarization
degree is as high as 2.5 % with a subarcsec spatial resolution, which is likely
to be detected with near-future ALMA observations. The emission is polarized
due to scattering of anisotropic continuum emission. The map of the
polarization degree shows a double peaked distribution and the polarization
vectors are in the radial direction in the inner ring and in the azimuthal
direction in the outer ring. We also find the wavelength dependence of the
polarization degree: the polarization degree is the highest if dust grains have
a maximum size of $a_{\rm max}\sim\lambda/2\pi$, where $\lambda$ is the
observing wavelength. Hence, multi-wave and spatially resolved polarization
observations toward protoplanetary disks enable us to put a constraint on the
grain size. The constraint on the grain size from polarization observations is
independent of or may be even stronger than that from the opacity index.
|
The Intense Starburst HDF850.1 in a Galaxy Overdensity at z=5.2 in the
Hubble Deep Field | The Hubble Deep Field (HDF) is a region in the sky that provides one of the
deepest multi-wavelength views of the distant universe and has led to the
detection of thousands of galaxies seen throughout cosmic time. An early map of
the HDF at a wavelength of 850 microns that is sensitive to dust emission
powered by star formation revealed the brightest source in the field, dubbed
HDF850.1. For more than a decade, this source remained elusive and, despite
significant efforts, no counterpart at shorter wavelengths, and thus no
redshift, size or mass, could be identified. Here we report, using a millimeter
wave molecular line scan, an unambiguous redshift determination for HDF850.1 of
z=5.183. This places HDF850.1 in a galaxy overdensity at z~5.2 in the HDF,
corresponding to a cosmic age of only 1.1 Gyr after the Big Bang. This redshift
is significantly higher than earlier estimates and higher than most of the >100
sub-millimeter bright galaxies identified to date. The source has a star
formation rate of 850 M_sun/yr and is spatially resolved on scales of 5 kpc,
with an implied dynamical mass of ~1.3x10^11 M_sun, a significant fraction of
which is present in the form of molecular gas. Despite our accurate redshift
and position, a counterpart arising from starlight remains elusive.
|
On Sizes, Kinematics, M/L Gradients, and Light Profiles of Massive
Compact Galaxies at z~2 | We present a detailed analysis of the structure and resolved stellar
populations of simulated merger remnants, and compare them to observations of
compact quiescent galaxies at z ~ 2. We find that major merging is a viable
mechanism to produce systems of ~ 10^11 Msun and ~ 1 kpc size, provided the gas
fraction at the time of final coalescence is high (~ 40%), and provided that
the progenitors are compact star-forming galaxies, as expected at high
redshift. Their integrated spectral energy distributions and velocity
dispersions are in good agreement with the observations, and their position in
the (v_{maj}/sigma, ellipticity) diagram traces the upper envelope of the
distribution of lower redshift early-type galaxies. The simulated merger
remnants show time- and sightline-dependent M/L ratio gradients that result
from a superposition of radially dependent stellar age, stellar metallicity,
and extinction. The median ratio of effective radius in rest-frame V-band light
to that in mass surface density is ~ 2 during the quiescent remnant phase. This
is typically expressed by a negative color gradient (i.e., red core), which we
expect to correlate with the integrated color of the system. Finally, the
simulations differ from the observations in their surface brightness profile
shape. The simulated remnants are typically best fit by high (n >> 4) Sersic
indices, whereas observed quiescent galaxies at z ~ 2 tend to be less cuspy
(median n ~ 2.3). Limiting early star formation in the progenitors may be
required to prevent the simulated merger remnants from having extended wings.
|
XMM-Newton view of Swift J1834.9-0846 and its Magnetar Wind Nebula | We report on the analysis of two XMM-Newton observations of the recently
discovered soft gamma repeater Swift J1834.9-0846, taken in September 2005 and
one month after the source went into outburst on 2011 August 7. We performed
timing and spectral analyses on the point source as well as on the extended
emission. We find that the source period is consistent with an extrapolation of
the Chandra ephemeris reported earlier and the spectral properties remained
constant. The source luminosity decreased to a level of 1.6x10^34 erg s^-1
following a decay trend of $\propto t^{-0.5}$. Our spatial analysis of the
source environment revealed the presence of two extended emission regions
around the source. The first (Region A) is a symmetric ring around the point
source, starting at 25arcsec and extending to ~50arcsec. We argue that Region A
is a dust scattering halo. The second (Region B) has an asymmetrical shape
extending between 50arcsec and 150arcsec, and is detected both in the pre- and
post-outburst data. We argue that this region is a possible magnetar wind
nebula (MWN). The X-ray efficiency of the MWN with respect to the rotation
energy loss is substantially higher than those of rotation powered pulsars:
$\eta_{\rm X}\equiv L_{\rm MWN,0.5-8 keV}/\dot{E}_{\rm rot}\approx0.7$. The
higher efficiency points to a different energy source for the MWN of Swift
J1834.9-0846, most likely bursting activity of the magnetar, powered by its
high magnetic field, B=1.4x10^14 G.
|
Constraints on millicharged particles from Planck | We revisit cosmic microwave background (CMB) constraints on the abundance of
millicharged particles based on the Planck data. The stringent limit
Omega_{mcp}h^2 < 0.001 (95% CL) may be set using the CMB data alone if
millicharged particles participate in the acoustic oscillations of
baryon-photon plasma at the recombination epoch. The latter condition is valid
for a wide region of charges and masses of the particles. Adding the
millicharged component to LCDM shifts prefered scalar spectral index of
primordial perturbations to somewhat larger values as compared to minimal
model, even approaching Harrison-Zeldovich spectrum under some assumptions.
|
Reconstruction of f(R, T) gravity describing matter dominated and
accelerated phases | We investigate the cosmological reconstruction in modified f(R,T) gravity,
where R is the Ricci scalar and T the trace of the stress-energy tensor.
Special attention is attached to the case in which the function f is given by f
(R, T) = f1 (R) + f2 (T). The use of auxiliary scalar field is considered with
two known examples for the scale factor corresponding to an expanding universe.
In the first example, where ordinary matter is usually neglected for obtaining
the unification of matter dominated and accelerated phases with f(R)gravity, it
is shown in this paper that this unification can be obtained without neglect
ordinary matter. In the second example, as in f(R)gravity, model of f(R, T)
gravity with transition of matter dominated phase to the acceleration phase is
obtained. In both cases, linear function of the trace is assumed for f2(T) and
it is obtained that f1(R) is proportional to a power of R with exponents
depending on the input parameters.
|
Unravelling the enigmatic ISM conditions in Minkowski's Object | Local examples of jet-induced star formation lend valuable insight into its
significance in galaxy evolution and can provide important observational
constraints for theoretical models of positive feedback. Using optical integral
field spectroscopy, we present an analysis of the ISM conditions in Minkowski's
Object ($z = 0.0189$), a peculiar star-forming dwarf galaxy located in the path
of a radio jet from the galaxy NGC 541. Full spectral fitting with PPXF
indicates that Minkowski's Object primarily consists of a young stellar
population $\sim 10$ Myr old, confirming that the bulk of the object's stellar
mass formed during a recent jet interaction. Minkowski's Object exhibits line
ratios largely consistent with star formation, although there is evidence for a
low level ($\lesssim 15$ per cent) of contamination from a non-stellar ionising
source. Strong-line diagnostics reveal a significant variation in the gas-phase
metallicity within the object, with $\log\left( \rm O / H \right) + 12$ varying
by $\sim 0.5$ dex, which cannot be explained by in-situ star formation, an
enriched outflow from the jet, or enrichment of gas in the stellar bridge
between NGC 541 and NGC 545/547. We hypothesise that Minkowski's Object either
(a) was formed as a result of jet-induced star formation in pre-existing gas
clumps in the stellar bridge, or (b) is a gas-rich dwarf galaxy that is
experiencing an elevation in its star formation rate due to a jet interaction,
and will eventually redden and fade, becoming an ultra-diffuse galaxy as it is
processed by the cluster.
|
Demonstration of magnetic field tomography with starlight polarization
towards a diffuse sightline of the ISM | The availability of large datasets with stellar distance and polarization
information will enable a tomographic reconstruction of the
(plane-of-the-sky-projected) interstellar magnetic field in the near future. We
demonstrate the feasibility of such a decomposition within a small region of
the diffuse ISM. We combine measurements of starlight (R-band) linear
polarization obtained using the RoboPol polarimeter with stellar distances from
the second Gaia data release. The stellar sample is brighter than 17 mag in the
R band and reaches out to several kpc from the Sun. HI emission spectra reveal
the existence of two distinct clouds along the line of sight. We decompose the
line-of-sight-integrated stellar polarizations to obtain the mean polarization
properties of the two clouds. The two clouds exhibit significant differences in
terms of column density and polarization properties. Their mean
plane-of-the-sky magnetic field orientation differs by 60 degrees. We show how
our tomographic decomposition can be used to constrain our estimates of the
polarizing efficiency of the clouds as well as the frequency dependence of the
polarization angle of polarized dust emission. We also demonstrate a new method
to constrain cloud distances based on this decomposition. Our results represent
a preview of the wealth of information that can be obtained from a tomographic
map of the ISM magnetic field.
|
Jet-driving protostars identified from infrared observations of the
Carina Nebula complex | Aims: Jets are excellent signposts for very young embedded protostars, so we
want to identify jet-driving protostars as a tracer of the currently forming
generation of stars in the Carina Nebula, which is one of the most massive
galactic star-forming regions and which is characterised by particularly high
levels of massive-star feedback on the surrounding clouds.
Methods: We used archive data to construct large (> 2 deg x 2 deg) Spitzer
IRAC mosaics of the Carina Nebula and performed a spatially complete search for
objects with excesses in the 4.5 micron band, typical of shock-excited
molecular hydrogen emission. We also identified the mid-infrared point sources
that are the likely drivers of previously discovered Herbig-Haro jets and
molecular hydrogen emission line objects. We combined the Spitzer photometry
with our recent Herschel far-infrared data to construct the spectral energy
distributions, and used the Robitaille radiative-transfer modelling tool to
infer the properties of the objects.
Results: The radiative-transfer modelling suggests that the jet sources are
protostars with masses between ~1 M_sol and ~10 M_sol that are surrounded by
circumstellar disks and embedded in circumstellar envelopes.
Conclusions: The estimated protostar masses < 10 M_sol suggest that the
current star-formation activity in the Carina Nebula is restricted to low- and
intermediate-mass stars. More optical than infrared jets can be observed,
indicating that star formation predominantly takes place close to the surfaces
of clouds.
|
Post-Newtonian effects in N-body dynamics: Relativistic precession and
conserved quantities in hierarchical triple systems | Conventional approaches to incorporating general relativistic effects into
the dynamics of N-body systems containing central black holes, or of
hierarchical triple systems with a relativistic inner binary, may not be
adequate when the goal is to study the evolution of the system over a timescale
related to relativistic secular effects, such as the precession of the
pericenter. For such problems, it may necessary to include post-Newtonian
"cross terms" in the equations of motion in order to capture relativistic
effects consistently over the long timescales. Cross terms are post-Newtonian
(PN) terms that explicitly couple the two-body relativistic perturbations with
the Newtonian perturbations due to other bodies in the system. In this paper,
we show that the total energy and the normal component of total angular
momentum of a hierarchical triple system is manifestly conserved to Newtonian
order over the relativistic pericenter precession timescale of the inner binary
if and only if PN cross-term effects in the equations of motion are taken
carefully into account.
|
The VIMOS Public Extragalactic Redshift Survey (VIPERS): On the correct
recovery of the count-in-cell probability distribution function | We compare three methods to measure the count-in-cell probability density
function of galaxies in a spectroscopic redshift survey. From this comparison
we found that when the sampling is low (the average number of object per cell
is around unity) it is necessary to use a parametric method to model the galaxy
distribution. We used a set of mock catalogues of VIPERS, in order to verify if
we were able to reconstruct the cell-count probability distribution once the
observational strategy is applied. We find that in the simulated catalogues,
the probability distribution of galaxies is better represented by a Gamma
expansion than a Skewed Log-Normal. Finally, we correct the cell-count
probability distribution function from the angular selection effect of the
VIMOS instrument and study the redshift and absolute magnitude dependency of
the underlying galaxy density function in VIPERS from redshift $0.5$ to $1.1$.
We found very weak evolution of the probability density distribution function
and that it is well approximated, independently from the chosen tracers, by a
Gamma distribution.
|
Mass Extinction And The Structure Of The Milky Way | We use the most up to date Milky Way model and solar orbit data in order to
test the hypothesis that the Sun's galactic spiral arm crossings cause mass
extinction events on Earth. To do this, we created a new model of the Milky
Way's spiral arms by combining a large quantity of data from several surveys.
We then combined this model with a recently derived solution for the solar
orbit to determine the timing of the Sun's historical passages through the
Galaxy's spiral arms. Our new model was designed with a symmetrical appearance,
with the major alteration being the addition of a spur at the far side of the
Galaxy. A correlation was found between the times at which the Sun crosses the
spiral arms and six known mass extinction events. Furthermore, we identify five
additional historical mass extinction events that might be explained by the
motion of the Sun around our Galaxy. These five additional significant drops in
marine genera that we find include significant reductions in diversity at 415,
322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent
~60% of its time passing through our Galaxy's various spiral arms. Also, we
briefly discuss and combine previous work on the Galactic Habitable Zone with
the new Milky Way model.
|
Weak Lensing with Sizes, Magnitudes and Shapes | Weak lensing can be observed through a number of effects on the images of
distant galaxies; their shapes are sheared, their sizes and fluxes (magnitudes)
are magnified and their positions on the sky are modified by the lensing field.
Galaxy shapes probe the shear field whilst size, magnitude and number density
probe the convergence field. Both contain cosmological information. In this
paper we are concerned with the magnification of the size and magnitude of
individual galaxies as a probe of cosmic convergence. We develop a Bayesian
approach for inferring the convergence field from a measured size, magnitude
and redshift and demonstrate that the inference on convergence requires
detailed knowledge of the joint distribution of intrinsic sizes and magnitudes.
We build a simple parameterised model for the size-magnitude distribution and
estimate this distribution for CFHTLenS galaxies. In light of the measured
distribution, we show that the typical dispersion on convergence estimation is
~0.8, compared to ~0.38 for shear. We discuss the possibility of physical
systematics for magnification (similar to intrinsic alignments for shear) and
compute the expected gains in the Dark Energy Figure-of-Merit (FoM) from
combining magnification with shear for different scenarios regarding
systematics: when accounting for intrinsic alignments but no systematics on the
magnification signal, including magnification could improve the FoM by upto a
factor of ~2.5, whilst when accounting for physical systematics in both shear
and magnification we anticipate a gain between ~25% and ~65%. In addition to
the statistical gains, the fact that cosmic shear and magnification are subject
to different systematics makes magnification an attractive complement to any
cosmic shear analysis.
|
QSO 0347-383 and the invariance of m_p/m_e in the course of cosmic time | The variation of the dimensionless fundamental physical constant mu = m_p/m_e
(the proton to electron mass ratio) can be constrained via observation of Lyman
and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha
systems (DLAs) in the line of sight to distant QSOs. Drawing on VLT-UVES high
resolution data sets of QSO 0347-383 and its DLA obtained in 2009 our analysis
yields dmu/mu = (4.3 +/- 7.2) * 10^-6 at z_abs =3.025. We apply corrections for
the observed offsets between discrete spectra and for the first time we find
indications for inter-order distortions. Current analyses tend to underestimate
the impact of systematic errors. Based on the scatter of the measured redshifts
and the corresponding low significance of the redshift-sensitivity correlation
we estimate the limit of accuracy of line position measurements to about 220
m/s, consisting of roughly 150 m/s due to the uncertainty of the absorption
line fit and about 150 m/s allocated to systematics related to instrumentation
and calibration.
|
Strong Constraints on Fuzzy Dark Matter from Ultrafaint Dwarf Galaxy
Eridanus II | The fuzzy dark matter (FDM) model treats DM as a bosonic field with
astrophysically large de Broglie wavelength. A striking feature of this model
is $\mathcal{O}(1)$ fluctuations in the dark matter density on time scales
which are shorter than the gravitational timescale. Including for the first
time the effect of core oscillations, we demonstrate how such fluctuations lead
to heating of star clusters, and thus an increase in their size over time. From
the survival of the old star cluster in Eridanus II we infer $m_a\gtrsim
0.6\rightarrow 1\times 10^{-19}\text{ eV}$ within modelling uncertainty if FDM
is to compose all of the DM, and derive constraints on the FDM fraction at
lower masses. The subhalo mass function in the Milky Way implies $m_a\gtrsim
0.8\times 10^{-21}\text{ eV}$ to successfully form Eridanus II. The window
between $10^{-21}\text{ eV}\lesssim m_a\lesssim 10^{-20}\text{ eV}$ is affected
by narrow band resonances, and the limited applicability of the diffusion
approximation. Some of this window may be consistent with observations of
Eridanus II and more detailed investigations are required.
|
Suppressing the thermal SZ-induced variance in CMB-cluster lensing
estimators | Accurate galaxy cluster mass measurements from the gravitational lensing of
the cosmic microwave background temperature maps depend on mitigating potential
biases from the cluster's own thermal Sunyaev-Zel'dovich (SZ) effect signal.
Quadratic lensing estimators use a pair of maps to extract the lensing signal:
a large scale gradient map and a small scale lensing map. The SZ bias can be
eliminated by using an SZ-free map in the pair, with the gradient map being
favored for signal-to-noise reasons. However, while this approach eliminates
the bias, the SZ power in small scale lensing map adds extra variance that can
become significant for high mass clusters and low noise surveys. In this work,
we propose projecting out an SZ template to reduce the SZ variance. Any
residual SZ signal after template fitting is uncorrelated with the SZ-free
gradient map, and thus does not bias the mass measurements. For massive
clusters above $4\times 10^{14}$ $M_{\odot}$ observed by the upcoming CMB-S4 or
Simons Observatory experiments, we find that the template fitting approach
would increase the cluster lensing signal-to-noise by a factor of 1.4.
|
A study of the C$_3$H$_2$ isomers and isotopologues: first interstellar
detection of HDCCC | The partially deuterated linear isomer HDCCC of the ubiquitous cyclic carbene
($c$-C$_3$H$_2$) was observed in the starless cores TMC-1C and L1544 at 96.9
GHz, and a confirming line was observed in TMC-1 at 19.38 GHz. To aid the
identification in these narrow line sources, four centimetre-wave rotational
transitions (two in the previously reported $K_a =0$ ladder, and two new ones
in the $K_a =1$ ladder), and 23 transitions in the millimetre band between 96
and 272 GHz were measured in high-resolution laboratory spectra. Nine
spectroscopic constants in a standard asymmetric top Hamiltonian allow the
principal transitions of astronomical interest in the $K_a \le 3$ rotational
ladders to be calculated to within 0.1 km s$^{-1}$ in radial velocity up to 400
GHz. Conclusive evidence for the identification of the two astronomical lines
of HDCCC was provided by the $V_{\rm{LSR}}$ which is the same as that of the
normal isotopic species (H$_2$CCC) in the three narrow line sources. In these
sources, deuterium fractionation in singly substituted H$_2$CCC (HDCCC/H$_2$CCC
$\sim4\%\text{-}19\%$) is comparable to that in $c$-C$_3$H$_2$
($c$-C$_3$H$_2$/$c$-C$_3$HD $\sim5\%\text{-}17\%$), and similarly in doubly
deuterated $c$-C$_3$H$_2$ ($c$-C$_3$D$_2$/$c$-C$_3$HD $\sim3\%\text{-}17\%$),
implying that the efficiency of the deuteration processes in the H$_2$CCC and
$c$-C$_3$H$_2$ isomers are comparable in dark clouds.
|
X-ray selected galaxy clusters in the Pan-STARRS Medium-Deep Survey | [abridged]
We present the results of a pilot study for the extended MACS survey (eMACS),
a comprehensive search for distant, X-ray luminous galaxy clusters at z>0.5.
Our pilot study applies the eMACS concept to the 71 deg^2 area extended by the
ten fields of the Pan-STARRS1 (PS1) Medium Deep Survey (MDS). Candidate
clusters are identified by visual inspection of PS1 images in the g,r, i, and z
bands in a 5x5 arcmin^2 region around X-ray sources detected in the ROSAT
All-Sky Survey (RASS). To test and optimize the eMACS X-ray selection criteria,
our pilot study uses the largest possible RASS database, i.e., all RASS sources
listed in the Bright and Faint Source Catalogs (BSC and FSC) that fall within
the MDS footprint. Scrutiny of PS1/MDS images for 41 BSC and 200 FSC sources
combined with dedicated spectroscopic follow-up observations results in a
sample of 11 clusters with estimated or spectroscopic redshifts of z>0.3. X-ray
follow-up observations will be crucial in order to establish robust cluster
luminosities for eMACS clusters.
Although the small number of distant X-ray luminous clusters in the MDS does
not allow us to make firm predictions for the over 20,000 deg^2 of
extragalactic sky covered by eMACS, the identification of two extremely
promising eMACS cluster candidates at z>0.6 (both yet to be observed with
Chandra) in such a small solid angle is encouraging. Representing a tremendous
gain over the presently known two dozen such systems from X-ray, optical, and
SZ cluster surveys combined, the sample of over 100 extremely massive clusters
at z>0.5 expected from eMACS would be invaluable for the identification of the
most powerful gravitational lenses in the Universe, as well as for in-depth and
statistical studies of the physical properties of the most massive galaxy
clusters out to z~1.
|
Small vs large dust grains in transitional disks: do different cavity
sizes indicate a planet? | Transitional disks represent a short stage of the evolution of circumstellar
material. Studies of dust grains in these objects can provide pivotal
information on the mechanisms of planet formation. Dissimilarities in the
spatial distribution of small (micron-size) and large (millimeter-size) dust
grains have recently been pointed out. Constraints on the small dust grains can
be obtained by imaging the distribution of scattered light at near-infrared
wavelengths. We aim at resolving structures in the surface layer of
transitional disks (with particular emphasis on the inner 10 - 50 AU), thus
increasing the scarce sample of high resolution images of these objects. We
obtained VLT/NACO near-IR high-resolution polarimetric differential imaging
observations of SAO 206462 (HD135344B). This technique allows one to image the
polarized scattered light from the disk without any occulting mask and to reach
an inner working angle of 0.1''. A face-on disk is detected in H and Ks bands
between 0.1'' and 0.9''. No significant differences are seen between the H and
Ks images. In addition to the spiral arms, these new data allow us to resolve
for the first time an inner cavity for small dust grains. The cavity size
(about 28 AU) is much smaller than what is inferred for large dust grains from
(sub)mm observations (39 to 50 AU). The interaction between the disk and
potential orbiting companion(s) can explain both the spiral arm structure and
the discrepant cavity sizes for small and large dust grains. One planet may be
carving out the gas (and, thus, the small grains) at 28 AU, and generating a
pressure bump at larger radii (39 AU), which holds back the large grains. We
analytically estimate that, in this scenario, a single giant planet (with a
mass between 5 and 15 Jupiter masses) at 17 to 20 AU from the star is
consistent with the observed cavity sizes.
|
The Weak Lensing Masses of Filaments between Luminous Red Galaxies | In the standard model of non-linear structure formation, a cosmic web of
dark-matter dominated filaments connects dark matter halos. In this paper, we
stack the weak lensing signal of an ensemble of filaments between groups and
clusters of galaxies. Specifically, we detect the weak lensing signal, using
CFHTLenS galaxy ellipticities, from stacked filaments between SDSS-III/BOSS
luminous red galaxies (LRGs). As a control, we compare the physical LRG pairs
with projected LRG pairs that are more widely separated in redshift space. We
detect the excess filament mass density in the projected pairs at the $5\sigma$
level, finding a mass of $(1.6 \pm 0.3) \times 10^{13} M_{\odot}$ for a stacked
filament region 7.1 $h^{-1}$ Mpc long and 2.5 $h^{-1}$ Mpc wide. This filament
signal is compared with a model based on the three-point
galaxy-galaxy-convergence correlation function, as developed in Clampitt, Jain
& Takada (2014), yielding reasonable agreement.
|
The metallicity - redshift relations for emission-line SDSS galaxies:
examination of the dependence on the star formation rate | We analyse the oxygen abundance and specific star formation rates (sSFR)
variations with redshift in star-forming SDSS galaxies of different masses. We
find that the maximum value of the sSFR, sSFRmax, decreases when the stellar
mass, Ms, of a galaxy increases, and decreases with decreasing of redshift. The
sSFRmax can exceed the time-averaged sSFR by about an order of magnitude for
massive galaxies. The metallicity - redshift relations for subsamples of
galaxies with sSFR = sSFRmax and with sSFR = 0.1sSFRmax coincide for massive
(log(Ms/Mo) > 10.5, with stellar mass Ms in solar units) galaxies and differ
for low-mass galaxies. This suggests that there is no correlation between
oxygen abundance and sSFR in massive galaxies and that the oxygen abundance
correlates with the sSFR in low-mass galaxies. We find evidence in favour of
that the irregular galaxies show, on average, higher sSFR and lower oxygen
abundances than the spiral galaxies of similar masses and that the mass -
metallicity relation for spiral galaxies differs slightly from that for
irregular galaxies. The fact that our sample of low-mass galaxies is the
mixture of spiral and irregular galaxies can be responsible for the dependence
of the metallicity - redshift relation on the sSFR observed for the low-mass
SDSS galaxies. The mass - metallicity and luminosity - metallicity relations
obtained for irregular SDSS galaxies agree with corresponding relations for
nearby irregular galaxies with direct abundance determinations. We find that
the aperture effect does not make a significant contribution to the redshift
variation of oxygen abundances in SDSS galaxies.
|
The MURALES survey. V. Jet-induced star formation in 3C 277.3 (Coma A) | We present observations obtained with the VLT/MUSE optical integral field
spectrograph of the radio source 3C277.3, located at a redshift of 0.085 and
associated with the galaxy Coma A. An emission line region fully enshrouds the
double-lobed radio source, which is ~60 kpc x 90 kpc in size. Based on the
emission line ratios, we identified five compact knots in which the gas
ionization is powered by young stars located as far as ~60 kpc from the host.
The emission line filaments surrounding the radio emission are compatible with
ionization from fast shocks (with a velocity of 350-500 km/s), but a
contribution from star formation occurring at the edges of the radio source is
likely. Coma A might be a unique example in the local Universe in which the
expanding outflow triggers star formation throughout the whole radio source.
|
Primordial Bispectrum and Trispectrum Contributions to the Non-Gaussian
Excursion Set Halo Mass Function with Diffusive Drifting Barrier | The high-mass end of the halo mass function is a sensitive probe of
primordial non-Gaussianity (NG). In a recent study [9] we have computed the NG
halo mass function in the context of the Excursion Set theory and shown that
the primordial NG imprint is coupled to that induced by the non-linear collapse
of dark matter halos. We also found an excellent agreement with N-body
simulation results. Here, we perform a more accurate computation which accounts
for the interval validity of the bispectrum expansion to next-to-leading order
and extend the calculation to the case of a non-vanishing primordial
trispectrum.
|
BLAST: the far-infrared/radio correlation in distant galaxies | We investigate the correlation between far-infrared (FIR) and radio
luminosities in distant galaxies, a lynchpin of modern astronomy. We use data
from the Balloon-borne Large Aperture Submillimetre Telescope (BLAST), Spitzer,
the Large Apex BOlometer CamerA (LABOCA), the Very Large Array (VLA) and the
Giant Metre-wave Radio Telescope (GMRT) in the Extended Chandra Deep Field
South (ECDFS). For a catalogue of BLAST 250-micron-selected galaxies, we
re-measure the 70--870-micron flux densities at the positions of their most
likely 24-micron counterparts, which have a median [interquartile] redshift of
0.74 [0.25, 1.57]. From these, we determine the monochromatic flux density
ratio, q_250 = log_10 (S_250micron / S_1400MHz), and the bolometric equivalent,
q_IR. At z ~= 0.6, where our 250-micron filter probes rest-frame 160-micron
emission, we find no evolution relative to q_160 for local galaxies. We also
stack the FIR and submm images at the positions of 24-micron- and
radio-selected galaxies. The difference between q_IR seen for 250-micron- and
radio-selected galaxies suggests star formation provides most of the IR
luminosity in ~< 100-uJy radio galaxies, but rather less for those in the mJy
regime. For the 24-micron sample, the radio spectral index is constant across 0
< z < 3, but q_IR exhibits tentative evidence of a steady decline such that
q_IR is proportional to (1+z)^(-0.15 +/- 0.03) - significant evolution,
spanning the epoch of galaxy formation, with major implications for techniques
that rely on the FIR/radio correlation. We compare with model predictions and
speculate that we may be seeing the increase in radio activity that gives rise
to the radio background.
|
[CII] $158\,\mu\mathrm{m}$ line emission from Orion A. I. A template for
extragalactic studies? | The [CII] $158\,\mu\mathrm{m}$ fine-structure line is one of the dominant
coolants of the neutral interstellar medium. It is hence one of the brightest
far-infrared emission lines and can be observed not only in star-forming
regions throughout the Galaxy, but also in the diffuse interstellar medium and
in distant galaxies. [CII] line emission has been suggested to be a powerful
tracer of star-formation. We aim to understand the origin of [CII] emission and
its relation to other tracers of interstellar gas and dust. This includes a
study of the heating efficiency of interstellar gas as traced by the [CII] line
to test models of gas heating. We make use of a one-square-degree map of
velocity-resolved [CII] line emission towards the Orion Nebula complex,
including M43 and NGC 1977. The [CII] intensity is tightly correlated with PAH
emission in the IRAC $8\,\mu\mathrm{m}$ band and far-infrared emission from
warm dust. The correlation between [CII] and CO(2-1) is affected by the
detailed geometry of the region. We find particularly low [CII]-over-FIR
intensity ratios towards large columns of (warm and cold) dust, which suggest
the interpretation of the "[CII] deficit" in terms of a "FIR excess". A slight
decrease in the FIR line-over-continuum intensity ratio can be attributed to a
decreased heating efficiency of the gas. We find that, at the mapped spatial
scales, predictions of the star-formation rate from [CII] emission
underestimate the star-formation rate calculated from YSO counts in the Orion
Nebula complex by an order of magnitude. [CII] emission from the Orion Nebula
complex arises dominantly in the cloud surfaces, many viewed in edge-on
geometry. [CII] emission from extended faint cloud surfaces may contribute
significantly to the total [CII] emission on galactic scales.
|
Alternatives to Schwarzschild in the weak field limit of General
Relativity | The metric outside an isolated object made up of ordinary matter is bound to
be the classical Schwarzschild vacuum solution of General Relativity.
Nevertheless, some solutions are known (e.g. Morris-Thorne wormholes) that do
not match Schwarzschild asymptotically. On a phenomenological point of view,
gravitational lensing in metrics falling as $1/r^q$ has recently attracted
great interest. In this work, we explore the conditions on the source matter
for constructing static spherically symmetric metrics exhibiting an arbitrary
power-law as Newtonian limit. For such space-times we also derive the
expressions of gravitational redshift and force on probe masses, which,
together with light deflection, can be used in astrophysical searches of
non-Schwarzschild objects made up of exotic matter. Interestingly, we prove
that even a minimally coupled scalar field with a power-law potential can
support non-Schwarzschild metrics with arbitrary asymptotic behaviour.
|
Formation and Evolution of the Dust in Galaxies. III. The Disk of the
Milky Way | Models of chemical evolution of galaxies including the dust are nowadays
required to decipher the high-z universe. In a series of three papers we have
tackled the problem and set a modern chemical evolution model. In the first
paper (Piovan et al., 2011a) we revised the condensation coefficients for the
elements that typically are present in the dust. In the second paper (Piovan et
al., 2011b) we have implemented the dust into the Padova chemical model and
tested it against the observational data for the Solar Neighbourhood. In this
paper we extend it to the whole Disk of the Milky Way (MW). The Disk is used as
a laboratory to analyze the spatial and temporal behaviour of (i) several dust
grain families with the aid of which we can describe the ISM, (ii) the
abundances in the gas, dust, and total ISM of the elements present in the dust
and (iii) the depletion of the same elements. The temporal evolution of the
dust and gas across the Disk is calculated under the effect of radial flows and
a central Bar. The gradients of the abundances of C, N, O, Mg, Si, S, Ca and Fe
in gas and dust across the Disk are derived as a function of time. The
theoretical gradients nicely reproduce those derived from Cepheids, OB stars,
Red Giants and HII regions. This provides the backbone for the companion
processes of dust formation and evolution across the Disk. We examine in detail
the contributions to dust by AGB stars, SNae and grain accretion in the ISM at
different galacto-centric distances. Furthermore, we examine the variation of
the ratio silicates/carbonaceous grains with time and position in the Disk.
Finally, some hints about the depletion of the elements in regions of high and
low SFR (inner and outer Disk) are presented. The results obtained make it
possible to extend the model to other astrophysical situations or different
theoretical models like the chemo-dynamical N-Body simulations.
|
Mapping discrete galaxies at cosmic dawn with 21-centimeter observations | At cosmic dawn, the 21-centimeter signal from intergalactic hydrogen was
driven by Lyman-$\alpha$ photons from some of the earliest stars, producing a
spatial pattern that reflected the distribution of galaxies at that time. Due
to the large foreground, it is thought that around redshift 20 it is only
observationally feasible to detect 21-cm fluctuations statistically, yielding a
limited, indirect probe of early galaxies. Here we show that 21-cm images at
cosmic dawn should actually be dominated by large (tens of comoving
megaparsecs), high contrast bubbles surrounding individual galaxies. We
demonstrate this using a substantially upgraded semi-numerical simulation code
that realistically captures the formation and 21-cm effects of the small
galaxies expected during this era. Small number statistics associated with the
rarity of early galaxies, combined with the multiple scattering of photons in
the blue wing of the Lyman-$\alpha$ line, create the large bubbles and also
enhance the 21-cm power spectrum by a factor of 2--7 and add to it a feature
that measures the typical brightness of galaxies. These various signatures of
discrete early galaxies are potentially detectable with planned experiments
such as the Square Kilometer Array or the Hydrogen Epoch of Reionization Array,
even if the early stars formed in dark matter halos with masses as low as
$10^8\, M_\odot$, ten thousand times smaller than the Milky Way halo.
|
The observation of the Crab Nebula with LHAASO-KM2A for the performance
study | As a sub-array of the Large High Altitude Air Shower Observatory (LHAASO),
KM2A is mainly designed to cover a large fraction of the northern sky to hunt
for gamma-ray sources at energies above 10 TeV. Even though the detector
construction is still underway, a half of the KM2A array has been operating
stably since the end of 2019. In this paper, we present the pipeline of KM2A
data analysis and the first observation on the Crab Nebula, a standard candle
in very high energy gamma-ray astronomy. We detect gamma-ray signals from the
Crab Nebula in both energy ranges of 10$-$100 TeV and $>$100 TeV with high
significance, by analyzing the KM2A data of 136 live days between December 2019
and May 2020. With the observations, we test the detector performance including
angular resolution, pointing accuracy and cosmic ray background rejection
power.
The energy spectrum of the Crab Nebula in the energy range 10-250 TeV fits
well with a single power-law function dN/dE
=(1.13$\pm$0.05$_{stat}$$\pm$0.08$_{sys}$)$\times$10$^{-14}$$\cdot$(E/20TeV)$^{-3.09\pm0.06_{stat}\pm0.02_{sys}}$
cm$^{-2}$ s$^{-1}$ TeV$^{-1}$. It is consistent with previous measurements by
other experiments. This opens a new window of gamma-ray astronomy above 0.1 PeV
through which ultrahigh-energy gamma-ray new phenomena, such as cosmic
PeVatrons, might be discovered.
|
Constraining the structure and formation of the Galactic bulge from a
field in its outskirts. FLAMES-GIRAFFE spectra of about 400 red giants around
(l,b)=(0{\deg},-10{\deg}) | The presence of two stellar populations in the Milky Way bulge has been
reported recently. We aim at studying the abundances and kinematics of stars in
the outer bulge, thereby providing additional constraints on models of its
formation. Spectra of 401 red giant stars in a field at
(l,b)=(0{\deg},-10{\deg}) were obtained with FLAMES at the VLT. Stars of
luminosities down to below the two bulge red clumps (RCs) are included. From
these spectra we measure general metallicities, abundances of Fe and the
alpha-elements, and radial velocities (RV) of the stars. These measurements as
well as photometric data are compared to simulations with the Besancon and
TRILEGAL models of the Galaxy. We confirm the presence of two populations among
our sample stars: i) a metal-rich one at [M/H] ~+0.3, comprising about 30% of
the sample, with low RV dispersion and low alpha-abundance, and ii) a
metal-poor population at [M/H] ~-0.6 with high RV dispersion and high
alpha-abundance. The metal-rich population could be connected to the Galactic
bar. We identify this population as the carrier of the double RC feature. We do
not find a significant difference in metallicity or RV between the two RCs, a
small difference in metallicity being probably due to a selection effect. The
RV dispersion agrees well with predictions of the Besancon Galaxy model, but
the metallicity of the "thick bulge" model component should be shifted to lower
metallicity by 0.2 to 0.3dex to well reproduce the observations. We present
evidence that the metallicity distribution function depends on the evolutionary
state of the sample stars, suggesting that enhanced mass loss preferentially
removes metal-rich stars. We also confirm the decrease of \alpha-element
over-abundance with increasing metallicity.
|
Axions as Hot and Cold Dark Matter | The presence of a hot dark matter component has been hinted at 3 sigma by a
combination of the results from different cosmological observations. We examine
a possibility that pseudo Nambu-Goldstone bosons account for both hot and cold
dark matter components. We show that the QCD axions can do the job for the
axion decay constant f_a < O(10^10) GeV, if they are produced by the saxion
decay and the domain wall annihilation. We also investigate the cases of
thermal QCD axions, pseudo Nambu-Goldstone bosons coupled to the standard model
sector through the Higgs portal, and axions produced by modulus decay.
|
Probing cluster formation under extreme conditions: massive star
clusters in blue compact galaxies | The numerous and massive young star clusters in blue compact galaxies (BCGs)
are used to investigate the properties of their hosts. We test whether BCGs
follow claimed relations between cluster populations and their hosts, such as
the the fraction of the total luminosity contributed by the clusters as
function of the mean star formation rate density; the $V$ band luminosity of
the brightest youngest cluster as related to the mean host star formation rate;
and the cluster formation efficiency (i.e., the fraction of star formation
happening in star clusters) versus the density of the SFR. We find that BCGs
follow the trends, supporting a scenario where cluster formation and
environmental properties of the host are correlated. They occupy, in all the
diagrams, the regions of higher SFRs, as expected by the extreme nature of the
starbursts operating in these systems. We find that the star clusters
contribute almost to the 20 % of the UV luminosity of the hosts. We suggest
that the BCG starburst environment has most likely favoured the compression and
collapse of the giant molecular clouds, enhancing the local star formation
efficiency, so that massive clusters have been formed. The estimated cluster
formation efficiency supports this scenario. BCGs have a cluster formation
efficiency comparable to luminous IR galaxies and spiral starburst nuclei (the
averaged value is about 35 %) which is much higher than the 8 - 10 % reported
for quiescent spirals and dwarf star-forming galaxies.
|
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Dataset Card for arxiv_astro_co_ga
Dataset Summary
This is a dataset consisting of titles and abstracts for all Cosmology and Galaxy Astrophysics arXiv articles to date (99,659 papers).
Supported Tasks and Leaderboards
[More Information Needed]
Languages
English
Dataset Structure
Data Instances
{'title': 'Probing cluster formation under extreme conditions: massive star clusters in blue compact galaxies',
'abstract': ' The numerous and massive young star clusters in blue compact galaxies (BCGs) are used to investigate the properties of their hosts. We test whether BCGs follow claimed relations between cluster populations and their hosts, such as the the fraction of the total luminosity contributed by the clusters as function of the mean star formation rate density; the $V$ band luminosity of the brightest youngest cluster as related to the mean host star formation rate; and the cluster formation efficiency (i.e., the fraction of star formation happening in star clusters) versus the density of the SFR. We find that BCGs follow the trends, supporting a scenario where cluster formation and environmental properties of the host are correlated. They occupy, in all the diagrams, the regions of higher SFRs, as expected by the extreme nature of the starbursts operating in these systems. We find that the star clusters contribute almost to the 20 % of the UV luminosity of the hosts. We suggest that the BCG starburst environment has most likely favoured the compression and collapse of the giant molecular clouds, enhancing the local star formation efficiency, so that massive clusters have been formed. The estimated cluster formation efficiency supports this scenario. BCGs have a cluster formation efficiency comparable to luminous IR galaxies and spiral starburst nuclei (the averaged value is about 35 %) which is much higher than the 8 - 10 % reported for quiescent spirals and dwarf star-forming galaxies. '
}
Data Fields
title: Title of the paperabstract: The abstract of the paper
Data Splits
This dataset has 3 splits: train, validation, and test. Below are the statistics for these splits.
| Dataset Split | Number of Instances in Split |
|---|---|
| Train | 79,727 |
| Validation | 9966 |
| Test | 9966 |
Dataset Creation
Curation Rationale
[More Information Needed]
Source Data
The original dataset from which this subset was constructed can be found here: Kaggle arXiv Dataset Homepage.
Initial Data Collection and Normalization
[More Information Needed]
Who are the source language producers?
Various authors.
Annotations
This dataset contains no annotations.
Annotation process
[N/A]
Who are the annotators?
[N/A]
Personal and Sensitive Information
No author information included in this dataset.
Considerations for Using the Data
Social Impact of Dataset
[More Information Needed]
Discussion of Biases
[More Information Needed]
Other Known Limitations
[More Information Needed]
Additional Information
Dataset Curators
The original data is maintained by ArXiv, huge thanks to the team for building and maintaining that dataset.
Licensing Information
The arxiv_astro_co_ga dataset version 1.0.0 is released under the MIT License.
Citation Information
@misc{clement2019arxiv,
title={On the Use of ArXiv as a Dataset},
author={Colin B. Clement and Matthew Bierbaum and Kevin P. O'Keeffe and Alexander A. Alemi},
year={2019},
eprint={1905.00075},
archivePrefix={arXiv},
primaryClass={cs.IR}
}
Contributions
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Size of downloaded dataset files:
141 MB
Size of the auto-converted Parquet files:
81.6 MB
Number of rows:
99,659