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X-ray fluorescent lines from the Compton-thick AGN in M51 | The cold disk/torus gas surrounding active galactic nuclei (AGN) emits
fluorescent lines when irradiated by hard X-ray photons. The fluorescent lines
of elements other than Fe and Ni are rarely detected due to their relative
faintness. We report the detection of K$\alpha$ lines of neutral Si, S, Ar, Ca,
Cr, and Mn, along with the prominent Fe K$\alpha$, Fe K$\beta$, and Ni
K$\alpha$ lines, from the deep Chandra observation of the low-luminosity
Compton-thick AGN in M51. The Si K$\alpha$ line at 1.74 keV is detected at
$\sim3\sigma$, the other fluorescent lines have a significance between 2 and
2.5 $\sigma$, while the Cr line has a significance of $\sim1.5\sigma$. These
faint fluorescent lines are made observable due to the heavy obscuration of the
intrinsic spectrum of M51, which is revealed by Nustar observation above 10
keV. The hard X-ray continuum of M51 from Chandra and Nustar can be fitted with
a power-law spectrum with an index of 1.8, reprocessed by a torus with an
equatorial column density of $N_{\rm H}\sim7\times10^{24}$ cm$^{-2}$ and an
inclination angle of $74$ degrees. This confirms the Compton-thick nature of
the nucleus of M51. The relative element abundances inferred from the fluxes of
the fluorescent lines are similar to their solar values, except for Mn, which
is about 10 times overabundant. It indicates that Mn is likely enhanced by the
nuclear spallation of Fe.
|
A mean density of $112\, M_{\odot}\,\rm pc^{-3}$ for Central Molecular
Zone clumps -- Evidences for shear-enabled pressure equilibrium in the
Galactic Center | We carry out a systematic study of the density structure of gas in the
Central Molecular Zone (CMZ) in the Galactic center by extracting clumps from
the APEX Telescope Large Area Survey of the Galaxy survey at 870 $\mu$m. We
find that the clumps follow a scaling of $m = \rho_0 r^3$ which corresponds to
a characteristic density of $n_{\rm H_2} = 1.6 \times 10^3\,\rm cm^{-3}$
($\rho_0 =112\;M_{\odot}\;\rm pc^{-3}$) with a variation of $\approx 0.5\,\rm
dex$, where we assumed a gas-to-dust mass ratio of 100. This characteristic
density can be interpreted as the result of thermal pressure equilibrium
between the molecular gas and the warm ambient interstellar medium. Such an
equilibrium can plausibly be established since shear has approximately the same
strength as self-gravity. Our findings may explain the fact that star formation
in the CMZ is highly inefficient compared to the rest of the Milky Way disk. We
also identify a population of clumps whose densities are two orders of
magnitudes higher in the vicinity of the Sgr B2 region, which we propose are
produced by collisions between the clumps of lower densities. For these
collisions to occur, processes such as compressive tides probably have created
the appropriate condition by assembling the clumps together.
|
H$_2$ mass-velocity relationship from 3D numerical simulations of
jet-driven molecular outflows | Previous numerical studies have shown that in protostellar outflows, the
mass-velocity distribution $m(v)$ can be well described by a broken power law
$\propto v^{- \gamma}$. On the other hand, recent observations of a sample of
outflows show that the CO intensity-velocity distribution, closely related to
$m(v)$, follows an exponential law $\propto \exp(-v/v_0)$. In the present work,
we revisit the physical origin of the mass-velocity relationship $m(v)$ in
jet-driven protostellar outflows. We investigate the respective contributions
of the different regions of the outflow, from the swept-up ambient gas to the
jet. We performed 3D numerical simulations of a protostellar jet propagating
into a molecular cloud using the hydrodynamical code Yguazu-a. The code takes
into account atomic and ionic species and was modified to include the H$_2$
gas. We find that by excluding the jet contribution, $m(v)$ is satisfyingly
fitted with a single exponential law, with $v_0$ well in the range of
observational values. The jet contribution results in additional components in
the mass-velocity relationship. This empirical mass-velocity relationship is
found to be valid locally in the outflow. The exponent $v_0$ is almost constant
in time and for a given level of mixing between the ambient medium and the jet
material. In general, $v_0$ displays only a weak spatial dependence. A simple
modeling of the L1157 outflow successfully reproduces the various components of
the observed CO intensity-velocity relationship. Our simulations indicate that
these components trace the outflow cavity of swept-up gas and the material
entrained along the jet, respectively. The CO intensity-velocity exponential
law is naturally explained by the jet-driven outflow model. The entrained
material plays an important role in shaping the mass-velocity profile.
|
An internally consistent distance framework in the Local Group | Accurate and precise astronomical distance determinations are crucial for
derivations of, among others, the masses and luminosities of a large variety of
distant objects. Astronomical distance determination has traditionally relied
on the concept of a `distance ladder.' Here we review our recent attempts to
establish a highly robust set of internally consistent distance determinations
to Local Group galaxies, which we recommend as the statistical basis of an
improved extragalactic distance ladder.
|
Electroweak Vacuum (In)Stability in an Inflationary Universe | Recent analysis shows that if the 125-126 GeV LHC resonance turns out to be
the Standard Model Higgs boson, the electroweak vacuum would be a metastable
state at 98% C.L. In this paper we argue that, during inflation, the
electroweak vacuum can actually be very short-lived, contrary to the conclusion
that follows from the flat spacetime analysis. Namely, in the case of a pure
Higgs potential the electroweak vacuum decays via the Hawking-Moss transition,
which has no flat spacetime analogue. As a result, the Higgs vacuum is
unstable, unless the rate of inflation is low enough: $H_{\rm inf}\lesssim
10^9-10^{12}$ GeV. Models of inflation with such a low rate typically predict
negligible tensor perturbations in the cosmic microwave background radiation
(CMBR). This is also true for models in which the perturbations are produced by
a curvaton field. We also find that if the effective curvature of the Higgs
potential at a local maximum (which may be induced by inflaton-Higgs
interactions) is large enough, then the decay of the electroweak vacuum is
dominated by the Coleman-de Luccia transition. The electroweak vacuum is also
short-lived in this case, due to a negative effective self-interaction
coupling. Based on our analysis of Higgs vacuum stability during inflation, we
conclude that the observation of tensor perturbations by the Planck satellite
would provide strong indirect evidence for new physics beyond the Standard
Model responsible for stabilisation of the electroweak vacuum.
|
CO Abundance Variations in the Orion Molecular Cloud | Infrared stellar photometry from 2MASS and spectral line imaging observations
of 12CO and 13CO J = 1-0 line emission from the FCRAO 14m telescope are
analysed to assess the variation of the CO abundance with physical conditions
throughout the Orion A and Orion B molecular clouds. Three distinct Av regimes
are identified in which the ratio between the 13CO column density and visual
extinction changes corresponding to the photon dominated envelope, the strongly
self-shielded interior, and the cold, dense volumes of the clouds. Within the
strongly self-shielded interior of the Orion A cloud, the 13CO abundance varies
by 100% with a peak value located near regions of enhanced star formation
activity. The effect of CO depletion onto the ice mantles of dust grains is
limited to regions with AV > 10 mag and gas temperatures less than 20 K as
predicted by chemical models that consider thermal-evaporation to desorb
molecules from grain surfaces.
Values of the molecular mass of each cloud are independently derived from the
distributions of Av and 13CO column densities with a constant 13CO-to-H2
abundance over various extinction ranges. Within the strongly self-shielded
interior of the cloud (Av > 3 mag), 13CO provides a reliable tracer of H2 mass
with the exception of the cold, dense volumes where depletion is important.
However, owing to its reduced abundance, 13CO does not trace the H2 mass that
resides in the extended cloud envelope, which comprises 40-50% of the molecular
mass of each cloud. The implied CO luminosity to mass ratios, M/L_{CO}, are 3.2
and 2.9 for Orion A and Orion B respectively, which are comparable to the value
(2.9), derived from gamma-ray observations of the Orion region. Our results
emphasize the need to consider local conditions when applying CO observations
to derive H2 column densities.
|
A minimal empirical model for the cosmic far-infrared background
anisotropies | Cosmic far-infrared background (CFIRB) probes unresolved dusty star-forming
galaxies across cosmic time and is complementary to ultraviolet and optical
observations of galaxy evolution. In this work, we interpret the observed CFIRB
anisotropies using an empirical model based on resolved galaxies in ultraviolet
and optical surveys. Our model includes stellar mass functions, star-forming
main sequence, and dust attenuation. We find that the commonly used linear
Kennicutt relation between infrared luminosity and star formation rate
overproduces the observed CFIRB amplitudes. The observed CFIRB requires that
low-mass galaxies have lower infrared luminosities than expected from the
Kennicutt relation, implying that low-mass galaxies have lower dust content and
weaker dust attenuation. Our results demonstrate that CFIRB not only provides a
stringent consistency check for galaxy evolution models but also constrains the
dust content of low-mass galaxies.
|
Dipolar Dark Matter with Massive Bigravity | Massive gravity theories have been developed as viable IR modifications of
gravity motivated by dark energy and the problem of the cosmological constant.
On the other hand, modified gravity and modified dark matter theories were
developed with the aim of solving the problems of standard cold dark matter at
galactic scales. Here we propose to adapt the framework of ghost-free massive
bigravity theories to reformulate the problem of dark matter at galactic
scales. We investigate a promising alternative to dark matter called dipolar
dark matter (DDM) in which two different species of dark matter are separately
coupled to the two metrics of bigravity and are linked together by an internal
vector field. We show that this model successfully reproduces the phenomenology
of dark matter at galactic scales (MOND) as a result of a mechanism of
gravitational polarisation. The model is safe in the gravitational sector, but
because of the particular couplings of the matter fields and vector field to
the metrics, a ghost in the decoupling limit is present in the dark matter
sector. However, it might be possible to push the mass of the ghost beyond the
strong coupling scale by an appropriate choice of the parameters of the model.
Crucial questions to address in future work are the exact mass of the ghost,
and the cosmological implications of the model.
|
Catalog-free modeling of galaxy types in deep images: Massive
dimensional reduction with neural networks | Current models of galaxy evolution are constrained by the analysis of
catalogs containing the flux and size of galaxies extracted from multiband deep
fields carrying inevitable observational and extraction-related biases which
can be highly correlated. In practice, taking all of these effects
simultaneously into account is difficult, and derived models are inevitably
biased. To address this issue, we use robust likelihood-free methods for the
inference of luminosity function parameters, made possible via massive
compression of multiband images using artificial neural networks. This
technique makes the use of catalogs unnecessary when comparing observed and
simulated multiband deep fields and constraining model parameters. A forward
modeling approach generates galaxies of multiple types depending on luminosity
function parameters and paints them on photometric multiband deep fields
including both the instrumental and observational characteristics. The
simulated and the observed images present the same selection effects and can
therefore be properly compared. We train a fully-convolutional neural network
to extract the most model-parameter-sensitive summary statistics out of these
realistic simulations, shrinking down the dimensionality of the summary space.
Finally, using the trained network to compress both observed and simulated deep
fields, the model parameter values are constrained through Population Monte
Carlo likelihood-free inference. Using synthetic photometric multiband deep
fields similar to the CFHTLS and D1/D2 deep fields and massively compressing
them through the convolutional neural network, we demonstrate the robustness,
accuracy and consistency of this new catalog-free inference method. We are able
to constrain the parameters of luminosity functions of different types of
galaxies and our results are fully compatible with the classic catalog
extraction approaches.
|
Preheating and Reheating after Standard Inflation | We study the two-phase scenario following inflation, where the initial step
is preheating, accompanied by a step of perturbative reheating at which
inflaton field decays transferring all of its energy to create relativistic
particles, the interaction of these particles will evolve towards a state of
thermal equilibrium with a temperature Tre called the reheating temperature. It
is observed that the scenario of reheating normally predicts the maximum
reheating temperature that corresponds to an almost instantaneous transition
from inflation to the radiation domination era. This will naturally lead to a
nonperturbative preheating. In this framework, we propose constraints on the
reheating duration parameters expressed in terms of the cosmic microwave
background (CMB) inflationary scalar spectral index. In this work, we study the
compatibility of polynomial and Higgs models of inflation with the
observational data obtained from Planck 2018.
|
Stellar Winds and Coronae of Low-mass Pop. II/III Stars | We investigated stellar winds from zero/low-metallicity low-mass stars by
magnetohydrodynamical simulations for stellar winds driven by \Alfven waves
from stars with mass $M_{\star}=(0.6-0.8)M_{\odot}$ and metallicity
$Z=(0-1)Z_{\odot}$, where $M_{\odot}$ and $Z_{\odot}$ are the solar mass and
metallicity, respectively. \Alfvenic waves, which are excited by the surface
convection, travel upward from the photosphere and heat up the corona by their
dissipation. For lower $Z$, denser gas can be heated up to the coronal
temperature because of the inefficient radiation cooling. The coronal density
of Pop.II/III stars with $Z\le 0.01Z_{\odot}$ is 1-2 orders of magnitude larger
than that of the solar-metallicity star with the same mass, and as a result,
the mass loss rate, $\dot{M}$, is $(4.5-20)$ times larger. This indicates that
metal accretion on low-mass Pop.III stars is negligible. The soft X-ray flux of
the Pop.II/III stars is also expected to be $\approx (1-30)$ times larger than
that of the solar-metallicity counterpart owing to the larger coronal density,
even though the radiation cooling efficiency is smaller. A larger fraction of
the input \Alfvenic wave energy is transmitted to the corona in low $Z$ stars
because they avoid severe reflection owing to the smaller density difference
between the photosphere and the corona. Therefore, a larger fraction is
converted to the thermal energy of the corona and the kinetic energy of the
stellar wind. From this energetics argument, we finally derived a scaling of
$\dot{M}$ as $\dot{M}\propto L R_{\star}^{11/9}M_{\star}^{-10/9}T_{\rm
eff}^{11/2}\left[\max (Z/Z_{\odot},0.01)\right]^{-1/5}$, where $L$,
$R_{\star}$, and $T_{\rm eff}$ are stellar luminosity, radius, and effective
temperature, respectively.
|
Fitting string inflation to real cosmological data: the Fibre Inflation
case | In this paper we show how the string landscape can be constrained using
observational data. We illustrate this idea by focusing on Fibre Inflation
which is a promising class of string inflationary models in type IIB flux
compactifications. We determine the values of the microscopic flux-dependent
parameters which yield the best fit to the most recent cosmological datasets.
|
Radio-loud Narrow Line Seyfert 1 under a different perspective: a
revised black hole mass estimate from optical spectropolarimetry | Several studies indicate that radio-loud (RL) Active Galactic Nuclei (AGN)
are produced only by the most massive black holes (BH), $M_{\rm BH} \sim
10^8$-$10^{10} M_\odot$. This idea has been challenged by the discovery of RL
Narrow Line Seyfert 1 (RL NLSy1), having estimated masses of $M_{\rm
BH}$$\sim$$10^6$-$10^7$ M$_\odot$. However, these low $M_{\rm BH}$ estimates
might be due to projection effects. Spectropolarimetry allows us to test this
possibility by looking at RL NLSy1s under a different perspective, i.e., from
the viewing angle of the scattering material. We here report the results of a
pilot study of VLT spectropolarimetric observations of the RL NLSy1 PKS
2004-447. Its polarization properties are remarkably well reproduced by models
in which the scattering occurs in an equatorial structure surrounding its broad
line region, seen close to face-on. In particular, we detect a polarized
H$\alpha$ line with a width of $\sim$ 9,000 km s$^{-1}$, $\sim 6$ times broader
than the width seen in direct light. This corresponds to a revised estimate of
$M_{\rm BH}$$\sim$$6\times10^8$ M$_\odot$, well within the typical range of RL
AGN. The double-peaked polarized broad H$\alpha$ profile of the target suggests
that the rare combination of the orientation effects and a broad line region
dominated by the rotation might account for this class of objects, casting
doubts on the virial estimates of BH mass for type-I AGN.
|
Enhancement of the tidal disruption event rate in galaxies with a
nuclear star cluster: from dwarfs to ellipticals | We compute the tidal disruption event (TDE) rate around local massive black
holes (MBHs) with masses as low as $2.5\times10^4 {\rm M}_\odot$, thus probing
the dwarf regime for the first time. We select a sample of 37 galaxies for
which we have the surface stellar density profile, a dynamical estimate of the
mass of the MBH, and 6 of which, including our Milky Way, have a resolved
nuclear star cluster (NSC). For the Milky Way, we find a total TDE rate of
$\sim 10^{-4}{\rm yr}^{-1}$ when taking the NSC in account, and $\sim 10^{-7}
{\rm yr}^{-1}$ otherwise. TDEs are mainly sourced from the NSC for light
($<3\times 10^{10}{\rm M}_\odot$) galaxies, with a rate of few $10^{-5}{\rm
yr}^{-1}$, and an enhancement of up to 2 orders of magnitude compared to
non-nucleated galaxies. We create a mock population of galaxies using different
sets of scaling relations to explore trends with galaxy mass, taking into
account the nucleated fraction of galaxies. Overall, we find a rate of few
$10^{-5}{\rm yr}^{-1}$ which drops when galaxies are more massive than
$10^{11}{\rm M}_\odot$ and contain MBHs swallowing stars whole and resulting in
no observable TDE.
|
Was the Universe Actually Radiation Dominated Prior to Nucleosynthesis? | Maybe not. String theory approaches to both beyond the Standard Model and
Inflationary model building generically predict the existence of scalars
(moduli) that are light compared to the scale of quantum gravity. These moduli
become displaced from their low energy minima in the early universe and lead to
a prolonged matter-dominated epoch prior to BBN. In this paper, we examine
whether non-perturbative effects such as parametric resonance or tachyonic
instabilities can shorten, or even eliminate, the moduli condensate and
matter-dominated epoch. Such effects depend crucially on the strength of the
couplings, and we find that unless the moduli become strongly coupled the
matter-dominated epoch is unavoidable. In particular, we find that in string
and M-theory compactifications where the lightest moduli are near the TeV-scale
that a matter-dominated epoch will persist until the time of Big Bang
Nucleosynthesis.
|
CHAOS V: Recombination Line Carbon Abundances in M101 | The CHAOS project is building a large database of LBT H II region spectra in
nearby spiral galaxies to use direct abundances to better determine the
dispersion in metallicity as a function of galactic radius. Here, we present
CHAOS LBT observations of C II $\lambda$4267 emission detected in 10 H II
regions in M 101, and, using a new photoionization model based ionization
correction factor, we convert these measurements into total carbon abundances.
A comparison with M101 C II recombination line observations from the literature
shows excellent agreement, and we measure a relatively steep gradient in
log(C/H) of -0.37 +/- 0.06 dex/R_e. The C/N observations are consistent with a
constant value of log(C/N) = 0.84 with a dispersion of only 0.09 dex, which,
given the different nucleosynthetic sources of C and N, is challenging to
understand. We also note that when plotting N/O versus O/H, all of the H II
regions with detections of CII $\lambda$4267 present N/O abundances at the
minimum of the scatter in N/O at a given value of O/H. If the high surface
brightness necessary for the detection of the faint recombination lines is
interpreted as an indicator of H II region youth, then this may point to a lack
of nitrogen pollution in the youngest H II regions. In the future, we
anticipate that the CHAOS project will significantly increase the total number
of C II $\lambda$4267 measurements in extragalactic H II regions.
|
Implications of stochastic effects for primordial black hole production
in ultra-slow-roll inflation | We study the impact of stochastic noise on the generation of primordial black
hole (PBH) seeds in ultra-slow-roll (USR) inflation with numerical simulations.
We consider the non-linearity of the system by consistently taking into account
the noise dependence on the inflaton perturbations, while evolving the
perturbations on the coarse-grained background affected by the noise. We
capture in this way the non-Markovian nature of the dynamics, and demonstrate
that non-Markovian effects are subleading. Using the $\Delta N$ formalism, we
find the probability distribution $P(\mathcal{R})$ of the comoving curvature
perturbation $\mathcal{R}$. We consider inflationary potentials that fit the
CMB and lead to PBH dark matter with $i)$ asteroid, $ii)$ solar, or $iii)$
Planck mass, as well as $iv)$ PBHs that form the seeds of supermassive black
holes. We find that stochastic effects enhance the PBH abundance by a factor of
$\mathcal{O}(10)-\mathcal{O}(10^8)$, depending on the PBH mass. We also show
that the usual approximation, where stochastic kicks depend only on the Hubble
rate, either underestimates or overestimates the abundance by orders of
magnitude, depending on the potential. We evaluate the gauge dependence of the
results, discuss the quantum-to-classical transition, and highlight open issues
of the application of the stochastic formalism to USR inflation.
|
A Search for Spectral Galaxy Pairs of Overlapping Galaxies based on
Fuzzy Recognition | The Spectral Galaxy Pairs (SGPs) are defined as the composite galaxy spectra
which contain two independent redshift systems. These spectra are useful for
studying dust properties of the foreground galaxies. In this paper, a total of
165 spectra of SGPs are mined out from Sloan Digital Sky Survey (SDSS) Data
Release 9 (DR9) using the concept of membership degree from the fuzzy set
theory particularly defined to be suitable for fuzzily identifying emission
lines. The spectra and images of this sample are classified according to the
membership degree and their image features, respectively. Many of these 2nd
redshift systems are too small or too dim to select from the SDSS images alone,
making the sample a potentially unique source of information on dust effects in
low-luminosity or low-surface-brightness galaxies that are underrepresented in
morphological pair samples. The dust extinction of the objects with high
membership degree is also estimated by Balmer decrement. Additionally, analyses
for a series of spectroscopic observations of one SGP from 165 systems indicate
that a newly star-forming region of our Milky Way might occur.
|
The LOFAR Two Metre Sky Survey: Deep Fields. II. The ELAIS-N1 LOFAR deep
field | The LOFAR Two-metre Sky Survey (LoTSS) will cover the full northern sky and,
additionally, aims to observe the LoTSS deep fields to a noise level of ~10
microJy/bm over several tens of square degrees in areas that have the most
extensive ancillary data. This paper presents the ELAIS-N1 deep field, the
deepest of the LoTSS deep fields to date. With an effective observing time of
163.7 hours, it reaches a root mean square (RMS) noise level below 20
microJy/bm in the central region (and below 30 microJy/bm over 10 square
degrees). The resolution is 6 arcsecs and 84862 radio sources were detected in
the full area (68 sq. deg.) with 74127 sources in the highest quality area at
less than 3 degrees from the pointing centre. The observation reaches a sky
density of more than 5000 sources per sq. deg. in the central ~5 sq. deg.
region. We present the calibration procedure, which addresses the special
configuration of some observations and the extended bandwidth covered (115 to
177 MHz; central frequency 146.2 MHz) compared to standard LoTSS. We also
describe the methods used to calibrate the flux density scale using
cross-matching with sources detected by other radio surveys in the literature.
We find the flux density uncertainty related to the flux density scale to be
~6.5%. By studying the variations of the flux density measurements between
different epochs, we show that relative flux density calibration is reliable
out to about a 3 degree radius, but that additional flux density uncertainty is
present for all sources at about the 3 per cent level; this is likely to be
associated with residual calibration errors, and is shown to be more
significant in datasets with poorer ionosphere conditions. We also provide
intra-band spectral indices, which can be useful to detect sources with unusual
spectral properties. The final uncertainty in the flux densities is estimated
to be ~10% for ELAIS-N1.
|
Measuring Parity Violation in the Stochastic Gravitational Wave
Background with the LISA-Taiji network | Parity violation is a powerful observable to distinguish a cosmological
background of Gravitational Waves (GWs) from an astrophysical one. Planar
single GW interferometers, both on ground and in space, are unable to measure
the net circular polarization of an isotropic Stochastic Gravitational Wave
Background (SGWB). In this paper, we explore the possibility of detecting
circular polarization of an isotropic SGWB by cross-correlating two space-based
detectors planned to be launched around 2034: LISA and Taiji. We compute the
response of such a network to chirality and we perform a Fisher forecast
analysis on the $I$ and $V$ Stokes parameters for the SGWB. We find that a
clear measurement of chirality can be claimed for a maximally chiral signal
with $h^2 \, \Omega_{\rm GW} \simeq 10^{-12}$.
|
An Investigation of the Interstellar Environment of Supernova Remnant
CTB 87 | We present a new millimeter CO-line observation towards supernova remnant
(SNR) CTB 87, which was regarded purely as a pulsar wind nebula (PWN), and an
optical investigation of a coincident surrounding superbubble. The CO
observation shows that the SNR delineated by the radio emission is projectively
covered by a molecular cloud (MC) complex at V$_{\rm {LSR}}$ = $-60$ to $-54$
km s$^{-1}$. Both the symmetric axis of the radio emission and the trailing
X-ray PWN appear projectively to be along a gap between two molecular gas
patches at $-58$ to $-57$ km s$^{-1}$. Asymmetric broad profiles of $^{12}$CO
lines peaked at $-58$ km s$^{-1}$ are found at the eastern and southwestern
edges of the radio emission. This represents a kinematic signature consistent
with an SNR-MC interaction. We also find that a superbubble, $\sim 37'$ in
radius, appears to surround the SNR from HI 21cm (V$_{\rm {LSR}} \sim -61$ to
$-68$ km s$^{-1}$), WISE mid-IR, and optical extinction data. We build a
multi-band photometric stellar sample of stars within the superbubble region
and find 82 OB star candidates. The likely peak distance in the stars'
distribution seems consistent with the distance previously suggested for CTB
87. We suggest the arc-like radio emission is mainly the relic of the part of
blastwave that propagates into the MC complex and is now in a radiative stage
while the other part of blastwave has been expanding into the low-density
region in the superbubble. This scenario naturally explains the lack of the
X-ray emission related to the ejecta and blastwave. The SNR-MC interaction also
favours a hadronic contribution to the {\gamma}-ray emission from the CTB 87
region.
|
The Arecibo Galaxy Environment Survey IX: The Isolated Galaxy Sample | We have used the Arecibo L-band Feed Array to map three regions, each of 5
square degrees, around the isolated galaxies NGC 1156, UGC 2082, and NGC 5523.
In the vicinity of these galaxies we have detected two dwarf companions: one
near UGC 2082, previously discovered by ALFALFA, and one near NGC 1156,
discovered by this project and reported in an earlier paper. This is
significantly fewer than the 15.4 $^{+1.7}_{-1.5}$ that would be expected from
the field HI mass function from ALFALFA or the 8.9 $\pm$ 1.2 expected if the HI
mass function from the Local Group applied in these regions. The number of
dwarf companions detected is, however, consistent with a flat or declining HI
mass function as seen by a previous, shallower, HI search for companions to
isolated galaxies.We attribute this difference in Hi mass functions to the
different environments in which they are measured. This agrees with the general
observation that lower ratios of dwarf to giant galaxies are found in lower
density environments.
|
Helium Reionization Simulations. I. Modeling Quasars as Radiation
Sources | We introduce a new project to understand helium reionization using fully
coupled $N$-body, hydrodynamics, and radiative transfer simulations. This
project aims to capture correctly the thermal history of the intergalactic
medium (IGM) as a result of reionization and make predictions about the
Lyman-$\alpha$ forest and baryon temperature-density relation. The dominant
sources of radiation for this transition are quasars, so modeling the source
population accurately is very important for making reliable predictions. In
this first paper, we present a new method for populating dark matter halos with
quasars. Our set of quasar models include two different light curves, a
lightbulb (simple on/off) and symmetric exponential model, and
luminosity-dependent quasar lifetimes. Our method self-consistently reproduces
an input quasar luminosity function (QLF) given a halo catalog from an $N$-body
simulation, and propagates quasars through the merger history of halo hosts.
After calibrating quasar clustering using measurements from BOSS, we find that
the characteristic mass of quasar hosts is $M_h \sim 2.5 \times 10^{12}
M_\odot$ $h^{-1}$ for the lightbulb model, and $M_h \sim 2.3 \times 10^{12}
M_\odot$ $h^{-1}$ for the exponential model. In the exponential model, the peak
quasar luminosity for a given halo mass is larger than that in the lightbulb
model, typically by a factor of 1.5-2. The effective lifetime for quasars in
the lightbulb model is 59 Myr, and in the exponential case, the effective time
constant is about 15 Myr. We include semi-analytic calculations of helium
reionization, and discuss how to include these quasars as sources of ionizing
radiation for full hydrodynamics with radiative transfer simulations in order
to study helium reionization.
|
AGN STORM 2: I. First results: A Change in the Weather of Mrk 817 | We present the first results from the ongoing, intensive, multi-wavelength
monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this AGN
was, in part, selected for its historically unobscured nature, we discovered
that the X-ray spectrum is highly absorbed, and there are new blueshifted,
broad and narrow UV absorption lines, which suggest that a dust-free, ionized
obscurer located at the inner broad line region partially covers the central
source. Despite the obscuration, we measure UV and optical continuum
reverberation lags consistent with a centrally illuminated Shakura-Sunyaev thin
accretion disk, and measure reverberation lags associated with the optical
broad line region, as expected. However, in the first 55 days of the campaign,
when the obscuration was becoming most extreme, we observe a de-coupling of the
UV continuum and the UV broad emission line variability. The correlation
recovers in the next 42 days of the campaign, as Mrk 817 enters a less obscured
state. The short CIV and Ly alpha lags suggest that the accretion disk extends
beyond the UV broad line region.
|
Massive and Refined. II. The statistical properties of turbulent motions
in massive galaxy clusters with high spatial resolution | We study the properties of chaotic motions in the intra cluster medium using
a set of 20 galaxy clusters simulated with large dynamical range, using the
Adaptive Mesh Refinement code ENZO (e.g. Norman et al.2007). The adopted setup
allows us to study the spectral and spatial properties of turbulent motions in
galaxy clusters with unprecedented detail, achieving an maximum available
Reynolds number of the order of R=500-1000 for the largest eddies. The
correlations between the energy of these motions in the Intra Cluster Medium
and the dynamical state of the host systems are studied, and the statistical
properties of turbulent motions and their evolution with time support that
major merger events are responsible for the injection of the bulk of turbulent
kinetic energy inside cluster. Turbulence is found to account for a 20-30 per
cent of the thermal energy in merging clusters, while it accounts for a 5 per
cent in relaxed clusters. A comparison of the energies of turbulence and
motions in our simulated clusters with present upper-limits in real nearby
clusters, recently derived with XMM-Newton (Sanders et al.2010), is provided.
When the same spatial scales of turbulent motions are compared, the data from
simulations result well within the range presently allowed by observations.
Finally, we comment on the possibility that turbulence may accelerate
relativistic particles leading to the formation of giant radio halos in
turbulent (merging) clusters. Based on our simulations we confirm previous
semi-analytical studies that suggest that the fraction of turbulent clusters is
consistent with that of clusters hosting radio halos.
|
Dynamical Evolution of Multiple-Population Globular Clusters | We have carried out a set of Monte Carlo simulations to study a number of
fundamental aspects of the dynamical evolution of multiple stellar populations
in globular clusters with different initial masses, fractions of second
generation (2G) stars, and structural properties. Our simulations explore and
elucidate: 1) the role of early and long-term dynamical processes and stellar
escape in the evolution of the fraction of 2G stars and the link between the
evolution of the fraction of 2G stars and various dynamical parameters; 2) the
link between the fraction of 2G stars inside the cluster and in the population
of escaping stars during a cluster's dynamical evolution; 3) the dynamics of
the spatial mixing of the first-generation (1G) and 2G stars and the details of
the structural properties of the two populations as they evolve toward mixing;
4) the implications of the initial differences between the spatial distribution
of 1G and 2G stars for the evolution of the anisotropy in the velocity
distribution and the expected radial profile of the 1G and 2G anisotropy for
clusters at different stages of their dynamical history; 5) the variation of
the degree of energy equipartition of the 1G and the 2G populations as a
function of the distance from the cluster's centre and the cluster's
evolutionary phase.
|
Two c's in a pod: Cosmology independent measurement of the Type Ia
supernova colour-luminosity relation with a sibling pair | Using Zwicky Transient Facility (ZTF) observations, we identify a pair of
"sibling" Type Ia supernovae (SNe Ia), i.e., hosted by the same galaxy at z =
0.0541. They exploded within 200 days from each other at a separation of
$0.6^{"} $ corresponding to a projected distance of only 0.6 kpc. Performing
SALT2 light curve fits to the gri ZTF photometry, we show that for these
equally distant "standardizable candles", there is a difference of 2 magnitudes
in their rest frame B-band peaks, and the fainter SN has a significantly red
SALT2 colour $c = 0.57 \pm$ 0.04, while the stretch values $x_1$ of the two SNe
are similar, suggesting that the fainter SN is attenuated by dust in the
interstellar medium of the host galaxy. We use these measurements to infer the
SALT2 colour standardization parameter, $\beta$ = 3.5 $\pm$ 0.3, independent of
the underlying cosmology and Malmquist bias. Assuming the colour excess is
entirely due to dust, the result differs by $2\sigma$ from the average
Milky-Way total-to-selective extinction ratio, but is in good agreement with
the colour-brightness corrections empirically derived from the most recent SN
Ia Hubble-Lemaitre diagram fits. Thus we suggest that SN "siblings", which will
increasingly be discovered in the coming years, can be used to probe the
validity of the colour and lightcurve shape corrections using in SN Ia
cosmology while avoiding important systematic effects in their inference from
global multi-parameter fits to inhomogeneous data-sets, and also help constrain
the role of interstellar dust in SN Ia cosmology.
|
Dynamical evolution of a bulge in an N-body model of the Milky Way | The detailed dynamical structure of the bulge in the Milky Way is currently
under debate. Although kinematics of the bulge stars can be well reproduced by
a boxy-bulge, the possible existence of a small embedded classical bulge can
not be ruled out. We study the dynamical evolution of a small classical bulge
in a model of the Milky Way using a self-consistent high resolution N-body
simulation. Detailed kinematics and dynamical properties of such a bulge are
presented.
|
First Multi-wavelength Campaign on the Gamma-ray-loud Active Galaxy IC
310 | The extragalactic VHE gamma-ray sky is rich in blazars. These are jetted
active galactic nuclei viewed at a small angle to the line-of-sight. Only a
handful of objects viewed at a larger angle are known so far to emit above 100
GeV. Multi-wavelength studies of such objects up to the highest energies
provide new insights into the particle and radiation processes of active
galactic nuclei. We report the results from the first multi-wavelength campaign
observing the TeV detected nucleus of the active galaxy IC 310, whose jet is
observed at a moderate viewing angle of 10 deg - 20 deg. The multi-instrument
campaign was conducted between 2012 Nov. and 2013 Jan., and involved
observations with MAGIC, Fermi, INTEGRAL, Swift, OVRO, MOJAVE and EVN. These
observations were complemented with archival data from the AllWISE and 2MASS
catalogs. A one-zone synchrotron self-Compton model was applied to describe the
broad-band spectral energy distribution. IC 310 showed an extraordinary TeV
flare at the beginning of the campaign, followed by a low, but still detectable
TeV flux. Compared to previous measurements, the spectral shape was found to be
steeper during the low emission state. Simultaneous observations in the soft
X-ray band showed an enhanced energy flux state and a harder-when-brighter
spectral shape behaviour. No strong correlated flux variability was found in
other frequency regimes. The broad-band spectral energy distribution obtained
from these observations supports the hypothesis of a double-hump structure. The
harder-when-brighter trend in the X-ray and VHE emission is consistent with the
behaviour expected from a synchrotron self-Compton scenario. The
contemporaneous broad-band spectral energy distribution is well described with
a one-zone synchrotron self-Compton model using parameters that are comparable
to those found for other gamma-ray-emitting misaligned blazars.
|
The clustering of galaxies with pseudo bulge and classical bulge in the
local Universe | We investigate the clustering properties and close neighbour counts for
galaxies with different types of bulges and stellar masses. We select samples
of "classical" and "pseudo" bulges, as well as "bulge-less" disk galaxies,
based on the bulge/disk decomposition catalog of SDSS galaxies provided by
Simard et al. (2011). For a given galaxy sample we estimate: the projected
two-point cross-correlation function with respect to a spectroscopic reference
sample, w_p(r_p), and the average background-subtracted neighbour count within
a projected separation using a photometric reference sample, N_neighbour(<r_p).
We compare the results with the measurements of control samples matched in
color, concentration and redshift. We find that, when limited to a certain
stellar mass range and matched in color and concentration, all the samples
present similar clustering amplitudes and neighbour counts on scales above
~0.1h^{-1}Mpc. This indicates that neither the presence of a central bulge, nor
the bulge type is related to intermediate-to-large scale environments. On
smaller scales, in contrast, pseudo-bulge and pure-disk galaxies similarly show
strong excess in close neighbour count when compared to control galaxies, at
all masses probed. For classical bulges, small-scale excess is also observed
but only for M_stars < 10^{10} M_sun; at higher masses, their neighbour counts
are similar to that of control galaxies at all scales. These results imply
strong connections between galactic bulges and galaxy-galaxy interactions in
the local Universe, although it is unclear how they are physically linked in
the current theory of galaxy formation.
|
Inefficient jet-induced star formation in Centaurus A: High resolution
ALMA observations of the northern filaments | NGC 5128 is one of the best targets to study AGN-feedback in the local
Universe. At 13.5 kpc from the galaxy, optical filaments with recent star
formation lie along the radio-jet direction. It is a testbed region for
positive feedback (jet-induced star formation). APEX revealed strong CO
emission in star-forming regions but also in regions with no detected tracers
of star formation. When observed, star formation appears to be inefficient
compared to the Kennicutt-Schmidt relation.
We used ALMA to map the 12CO(1-0) emission all along the filaments at 1.3"~
23.8 pc resolution. The CO emission is clumpy and distributed in two main
structures: (i) the Horseshoe complex, outside the HI cloud, where gas is
mostly excited by shocks and no star formation is observed; (ii) the Vertical
filament, at the edge of the HI shell, which is a region of moderate star
formation.
We identified 140 molecular clouds. A statistical study reveals that they
have very similar physical properties that in the inner Milky Way. However, the
range of radius available with the present observations does not enable to
investigate whether the clouds follow the Larson relation or not. The large
virial parameter of the clouds suggests that gravity is not dominant.
Finally, the total energy injection in the filaments is of the same order as
in the inner part of the Milky Way. The strong CO emission detected in the
filaments is an indication that the energy injected by the jet acts positively
in the formation of dense molecular gas. The relatively high virial parameter
of the molecular clouds suggests that the injected kinetic energy is too strong
for star formation to be efficient. This is particularly the case in the
Horseshoe complex where the virial parameter is the largest and where strong CO
is detected with no associated star formation. This is the first evidence of
inefficient AGN positive feedback.
|
How well can we Measure the Intrinsic Velocity Dispersion of Distant
Disk Galaxies? | The kinematics of distant galaxies, from z=0.1 to z>2, play a key role in our
understanding of galaxy evolution from early times to the present. One of the
important parameters is the intrinsic, or local, velocity dispersion of a
galaxy, which allows one to quantify the degree of non-circular motions such as
pressure support. However, this is difficult to measure because the observed
dispersion includes the effects of (often severe) beam smearing on the velocity
gradient. Here we investigate four methods of measuring the dispersion that
have been used in the literature, to assess their effectiveness at recovering
the intrinsic dispersion. We discuss the biasses inherent in each method, and
apply them to model disk galaxies in order to determine which methods yield
meaningful quantities, and under what conditions. All the mean weighted
dispersion estimators are affected by (residual) beam smearing. In contrast,
the dispersion recovered by fitting a spatially and spectrally convolved disk
model to the data is unbiassed by the beam smearing it is trying to compensate.
Because of this, and because the bias it does exhibit depends only on the
signal-to-noise, it can be considered reliable. However, at very low
signal-to-noise, all methods should be used with caution.
|
Galaxy-scale ionised winds driven by ultra-fast outflows in two nearby
quasars | We use MUSE adaptive optics (AO) data in Narrow Field Mode to study the
properties of the ionised gas in MR 2251-178 and PG 1126-041, two nearby
(z~0.06) bright quasars hosting sub-pc scale Ultra Fast Outflows (UFOs)
detected in the X-ray band. We decompose the optical emission from diffuse gas
into a low- and a high-velocity components. The former is characterised by a
clean, regular velocity field and a low (~80 km/s) velocity dispersion. It
traces regularly rotating gas in PG 1126-041, while in MR 2251-178 it is
possibly associated to tidal debris from a recent merger or flyby. The other
component is found to be extended up to a few kpc from the nuclei, and shows a
high (~800 km/s) velocity dispersion and a blue-shifted mean velocity, as
expected from AGN-driven outflows. We estimate mass outflow rates up to a few
Mo/yr and kinetic efficiencies between 0.1-0.4 per cent, in line with those of
galaxies hosting AGNs of similar luminosity. The momentum rates of these
ionised outflows are comparable to those measured for the UFOs at sub-pc
scales, consistent with a momentum-driven wind propagation. Pure energy-driven
winds are excluded unless about 100x additional momentum is locked in massive
molecular winds. By comparing the outflow properties of our sources with those
of a small sample of well-studied QSOs hosting UFOs from the literature, we
find that winds seem to systematically lie either in a momentum-driven or in an
energy-driven regime, indicating that these two theoretical models bracket very
well the physics of AGN-driven winds.
|
The role of the accretion disk, dust, and jets in the IR emission of
low-luminosity AGN | We use recent high-resolution infrared (IR; 1 - 20 micron) photometry to
examine the origin of the IR emission in low-luminosity active galactic nuclei
(LLAGN). The data are compared with published model fits that describe the
spectral energy distribution of LLAGN in terms of an advection-dominated
accretion flow (ADAF), truncated thin accretion disk, and jet. The truncated
disk in these models is usually not luminous enough to explain the observed IR
emission, and in all cases its spectral shape is much narrower than the broad
IR peaks in the data. Synchrotron radiation from the jet appears to be
important in very radio-loud nuclei, but the detection of strong silicate
emission features in many objects indicates that dust must also contribute. We
investigate this point by fitting the IR SED of NGC 3998 using dusty torus and
optically thin (tau_MIR ~ 1) dust shell models. While more detailed modeling is
necessary, these initial results suggest that dust may account for the nuclear
mid-IR emission of many LLAGN.
|
Joint inverse cascade of magnetic energy and magnetic helicity in MHD
turbulence | We show that oppositely directed fluxes of energy and magnetic helicity
coexist in the inertial range in fully developed magnetohydrodynamic (MHD)
turbulence with small-scale sources of magnetic helicity. Using a helical shell
model of MHD turbulence, we study the high Reynolds number magnetohydrodynamic
turbulence for helicity injection at a scale that is much smaller than the
scale of energy injection. In a short range of scales larger than the forcing
scale of magnetic helicity, a bottleneck-like effect appears, which results in
a local reduction of the spectral slope. The slope changes in a domain with a
high level of relative magnetic helicity, which determines that part of the
magnetic energy related to the helical modes at a given scale. If the relative
helicity approaches unity, the spectral slope tends to $-3/2$. We show that
this energy pileup is caused by an inverse cascade of magnetic energy
associated with the magnetic helicity. This negative energy flux is the
contribution of the pure magnetic-to-magnetic energy transfer, which vanishes
in the non-helical limit. In the context of astrophysical dynamos, our results
indicate that a large-scale dynamo can be affected by the magnetic helicity
generated at small scales. The kinetic helicity, in particular, is not involved
in the process at all. An interesting finding is that an inverse cascade of
magnetic energy can be provided by a small-scale source of magnetic helicity
fluctuations without a mean injection of magnetic helicity.
|
Back-Reaction in Relativistic Cosmology | We introduce the concept of back-reaction in relativistic cosmological
modeling. Roughly speaking, this can be thought of as the difference between
the large-scale behaviour of an inhomogeneous cosmological solution of
Einstein's equations, and a homogeneous and isotropic solution that is a
best-fit to either the average of observables or dynamics in the inhomogeneous
solution. This is sometimes paraphrased as `the effect that structure has of
the large-scale evolution of the universe'. Various different approaches have
been taken in the literature in order to try and understand back-reaction in
cosmology. We provide a brief and critical summary of some of them,
highlighting recent progress that has been made in each case.
|
Higher order non-linear parameters with PLANCK | We investigate how higher order non-linear parameters affect lower order ones
through loop effects. We calculate the loop corrections up to two-loops and
explicitly show that the tree contribution is stable against loop terms in most
cases. We argue that, nevertheless, observational constraints on non-linear
parameters such as fNL and tauNL can also give a limit even for higher order
ones due to the loop contribution. We discuss these issues both for
single-source and multi-source cases.
|
Understanding Mass-Loss and the late Evolution of Intermediate Mass
Stars: Jets, Disks, Binarity, Dust and Magnetic Fields | Almost all stars in the 1-8 Msun range evolve through the Asymptotic Giant
Branch (AGB), preplanetary nebula (PPN) and planetary nebula (PN) evolutionary
phases. Most stars that leave the main sequence in a Hubble time will end their
lives in this way. The heavy mass loss which occurs during the AGB phase is
important across astrophysics, and the particulate matter crucial for the birth
of new solar systems is made and ejected by AGB stars. Yet stellar evolution
from the beginning of the AGB phase to the PN phase remains poorly understood.
We do not understand how the mass-loss (rate, geometry, temporal history)
depends on fundamental stellar parameters or the presence of a binary
companion. While the study of evolved non-massive stars has maintained a
relatively modest profile in recent decades, we are nonetheless in the midst of
a quiet but exciting revolution in this area, driven by new observational
results, such as the discovery of jets and disks in stellar environments where
these were never expected, and by the recognition of new symmetries such as
multipolarity and point-symmetry occuring frequently in the nebulae resulting
from the outflows. In this paper we summarise the major unsolved problems in
this field, and specify the areas where allocation of effort and resources is
most likely to help make significant progress.
|
Structural properties of faint low surface brightness galaxies | We study the structural properties of Low Surface Brightness galaxies (LSB)
using a sample of 263 galaxies observed by the Green Bank Telescope (Schneider
et al 1992). We perform 2D decompositions of these galaxies in the SDSS $g$,
$r$ and $i$ bands using the GALFIT software. Our decomposition reveals that
about $60\%$ of these galaxies are bulgeless i.e., their light distributions
are well modelled by pure exponential disks. The rest of the galaxies were
fitted with two components: a Sersic bulge and an exponential disk. Most of
these galaxies have bulge-to-total (B/T) ratio less than 0.1. However, of these
104 galaxies, $20\%$ have $B/T > 0.1$ i.e., hosting significant bulge component
and they are more prominent amongst the fainter LSBs. According to $g - r$
colour criteria, most of the LSB galaxies in our sample are blue, with only 7
classified as red LSBs. About $15\%$ of the LSB galaxies (including both blue
and red) in our sample host stellar bars. The incidence of bars is more
prominent in relatively massive blue LSB galaxies with very high gas fraction.
These findings may provide important clues to the formation and evolution of
LSB galaxies - in particular on the bar/bulge formation in faint LSB disks.
|
The observed cosmic star formation rate density has an evolution which
resembles a {\Gamma}(a, bt) distribution and can be described successfully by
only 2 parameters | A debate is emerging regarding the recent inconsistent results of different
studies for the Cosmic Star Formation Rate Density (CSFRD) at high-z. We employ
UV and IR datasets to investigate the star formation rate function (SFRF) at
${\rm z \sim 0-9}$. We find that the SFRFs derived from the dust corrected
${\rm UV}$ (${\rm UV_{corr}}$) data contradict those from IR on some key issues
since they are described by different distributions (Schechter vs double-power
law), imply different physics for galaxy formation (${\rm UV_{corr}}$ data
suggest a SFR limit/strong mechanism that diminish the number density of high
star forming systems with respect IR) and compare differently with the stellar
mass density evolution obtained from SED fitting (${\rm UV_{corr}}$ is in
agreement, while IR in tension up to 0.5 dex). However, both tracers agree on a
constant CSFRD evolution at ${\rm z \sim 1-4}$ and point to a plateau instead
of a peak. In addition, using both indicators we demonstrate that the evolution
of the {\it observed} CSFRD can be described by only {\bf 2} parameters and a
function that has the form of a Gamma distribution (${\bf \Gamma(a,bt)}$). In
contrast to previous parameterizations used in the literature our framework
connects the parameters to physical properties like the star formation rate
depletion time and cosmic baryonic gas density. The build up of stellar mass
occurs in $\Gamma(a,bt)$ distributed steps and is the result of gas consumption
up to the limit that there is no eligible gas for SF at t = ${\rm \infty}$,
resulting to a final cosmic stellar mass density of $\sim 0.5 \times 10^9 \,
{\rm \frac{M_{\odot}}{Mpc^3}}$.
|
The XXL Survey XLV. Linking the ages of optically selected groups to
their X-ray emission | We investigate the properties of 232 optical spectroscopically selected
groups from the Galaxy And Mass Assembly (GAMA) survey that overlap the XXL
X-ray cluster survey. X-ray aperture flux measurements combined with GAMA group
data provides the largest available sample of optical groups with detailed
galaxy membership information and consistently measured X-ray fluxes and upper
limits. 142 of these groups are divided into three subsets based on the
relative strength of X-ray and optical emission, and we see a trend in galaxy
properties between these subsets: X-ray overluminous groups contain a lower
fraction of both blue and star forming galaxies compared with X-ray
underluminous systems. X-ray overluminous groups also have a more dominant
central galaxy, with a magnitude gap between first and second ranked galaxies
on average 0.22 mag larger than in underluminous groups. The central galaxy in
overluminous groups also lies closer to the centre of the group. We examine a
number of other structural properties of our groups, such as axis ratio,
velocity dispersion, and group crossing time and find trends with X-ray
emission in some of these properties despite the high stochastic noise from the
limited number of group galaxies. We attribute the trends we see to the
evolutionary state of groups, with X-ray overluminous systems being more
dynamically evolved than underluminous groups. The X-ray overluminous groups
have had more time to develop a luminous intragroup medium, quench member
galaxies, and build the mass of the central galaxy through mergers compared to
underluminous groups. However, a minority of X-ray underluminous groups have
properties that suggest them to be dynamically mature. The lack of hot gas in
these systems cannot be accounted for by high star formation efficiency,
suggesting that high gas entropy resulting from feedback is the likely cause of
their weak X-ray emission.
|
Deceleration versus Acceleration Universe in Different Frames of $F(R)$
Gravity | In this paper we study the occurrence of accelerating universe versus
decelerating universe between the F(R) gravity frame (Jordan frame) and
non-minimally coupled scalar field theory frame, and the minimally coupled
scalar field theory frame (Einstein frame) for various models. As we show, if
acceleration is imposed in one frame, it will not necessarily correspond to an
accelerating metric when transformed in another frame. As we will demonstrate,
this issue is model and frame-dependent but it seems there is no general scheme
which permits to classify such cases.
|
Gas flows in galaxy mergers: supersonic turbulence in bridges, accretion
from the circumgalactic medium, and metallicity dilution | In major galaxy mergers, the orbits of stars are violently perturbed, and gas
is torqued to the centre, diluting the gas metallicity and igniting a
starburst. In this paper, we study the gas dynamics in and around merging
galaxies using a series of cosmological magneto-hydrodynamical (MHD) zoom-in
simulations. We find that the gas bridge connecting the merging galaxies
pre-coalescence is dominated by turbulent pressure, with turbulent Mach numbers
peaking at values of 1.6-3.3. This implies that bridges are dominated by
supersonic turbulence, and are thus ideal candidates for studying the impact of
extreme environments on star formation. We also find that gas accreted from the
circumgalactic medium (CGM) during the merger significantly contributes (27-51
per cent) to the star formation rate (SFR) at the time of coalescence and
drives the subsequent reignition of star formation in the merger remnant.
Indeed, 19-53 per cent of the SFR at z=0 originates from gas belonging to the
CGM prior the merger. Finally, we investigate the origin of the
metallicity-diluted gas at the centre of merging galaxies. We show that this
gas is rapidly accreted onto the galactic centre with a time-scale much shorter
than that of normal star-forming galaxies. This explains why coalescing
galaxies are not well-captured by the fundamental metallicity relation.
|
Magnetic Flux of Progenitor Stars Sets Gamma-ray Burst Luminosity and
Variability | Long-duration gamma-ray bursts (GRBs) are thought to come from the
core-collapse of Wolf-Rayet stars. Whereas their stellar masses $M_*$ have a
rather narrow distribution, the population of GRBs is very diverse, with
gamma-ray luminosities $L_\gamma$ spanning several orders of magnitude. This
suggests the existence of a "hidden" stellar variable whose burst-to-burst
variation leads to a spread in $L_\gamma$. Whatever this hidden variable is,
its variation should not noticeably affect the shape of GRB lightcurves, which
display a constant luminosity (in a time-average sense) followed by a sharp
drop at the end of the burst seen with Swift/XRT. We argue that such a hidden
variable is progenitor star's large-scale magnetic flux. Shortly after the core
collapse, most of stellar magnetic flux accumulates near the black hole (BH)
and remains there. The flux extracts BH rotational energy and powers jets of
roughly a constant luminosity, $L_j$. However, once BH mass accretion rate
$\dot M$ falls below $\sim L_j/c^2$, the flux becomes dynamically important and
diffuses outwards, with the jet luminosity set by the rapidly declining mass
accretion rate, $L_j\sim \dot M c^2$. This provides a potential explanation for
the sharp end of GRBs and the universal shape of their lightcurves. During the
GRB, gas infall translates spatial variation of stellar magnetic flux into
temporal variation of $L_j$. We make use of the deviations from constancy in
$L_j$ to perform stellar magnetic flux "tomography". Using this method, we
infer the presence of magnetised tori in the outer layers of progenitor stars
for GRB 920513 and GRB 940210.
|
Variation of the fine-structure constant: an update of statistical
analyses with recent data | We analyze the consistency of different astronomical data of the variation in
the fine-structure constant obtained with KECK and VLT. We tested the
consistency using the Student test and confidence intervals. We splited the
data sets in to smaller intervals and grouped them acording to redshift and
angular position. Another statistical analysis is proposed that considers
phenomenological models for the variation in \alpha. Results show consistency
for the reduced intervals for each pair of data sets and suggests that the
variation in \alpha is significant at higher redshifts. Even though the dipole
model seems to be the most accurate phenomenological model, the statistical
analyses indicate that the variation in \alpha might be depending on both
redshift and angular position.
|
OCCASO III. Iron peak and $\alpha$ elements of 18 open clusters.
Comparison with chemical evolution models and field stars | The study of open-cluster chemical abundances provides insights on stellar
nucleosynthesis processes and on Galactic chemo-dynamical evolution. In this
paper we present an extended abundance analysis of 10 species (Fe, Ni, Cr, V,
Sc, Si, Ca, Ti, Mg, O) for red giant stars in 18 OCCASO clusters. This
represents a homogeneous sample regarding the instrument features, method, line
list and solar abundances from confirmed member stars. We perform an extensive
comparison with previous results in the literature, and in particular with the
Gaia FGK Benchmark stars Arcturus and $\mu$Leo. We investigate the dependence
of [X/Fe] with metallicity, Galactocentric radius ($6.5<R_{\rm GC}<11$ kpc),
age ($0.3<Age<10$ Gyr), and height above the plane ($|z|<1000$ pc). We discuss
the observational results in the chemo-dynamical framework, and the radial
migration impact when comparing with chemical evolution models. We also use
APOGEE DR14 data to investigate the differences between the abundance trends in
$R_{\rm GC}$ and $|z|$ obtained for clusters and for field stars.
|
Numerical simulation of time delay interferometry for a LISA-like
mission with the simplification of having only one interferometer | In order to attain the requisite sensitivity for LISA, laser frequency noise
must be suppressed below the secondary noises such as the optical path noise,
acceleration noise etc. In a previous paper (Dhurandhar et al., Class. Quantum
Grav., 27, 135013, 2010), we have found a large family of second-generation
analytic solutions of time delay interferometry with one arm dysfunctional, and
we also estimated the laser noise due to residual time-delay semi-analytically
from orbit perturbations due to Earth. Since other planets and solar-system
bodies also perturb the orbits of LISA spacecraft and affect the time delay
interferometry (TDI), we simulate the time delay numerically in this paper for
all solutions with the generation number n \leq 3. We have worked out a set of
3-year optimized mission orbits of LISA spacecraft starting at January 1, 2021
using the CGC2.7 ephemeris framework. We then use this numerical solution to
calculate the residual optical path differences in the second-generation
solutions of our previous paper, and compare with the semi-analytic error
estimate. The accuracy of this calculation is better than 1 cm (or 30 ps). The
maximum path length difference, for all configuration calculated, is below 1 m
(3 ns). This is well below the limit under which the laser frequency noise is
required to be suppressed. The numerical simulation in this paper can be
applied to other space-borne interferometers for gravitational wave detection
with the simplification of having only one interferometer.
|
Graviton Mass Bounds | Recently, aLIGO has announced the first direct detections of gravitational
waves, a direct manifestation of the propagating degrees of freedom of gravity.
The detected signals GW150914 and GW151226 have been used to examine the basic
properties of these gravitational degrees of freedom, particularly setting an
upper bound on their mass. It is timely to review what the mass of these
gravitational degrees of freedom means from the theoretical point of view,
particularly taking into account the recent developments in constructing
consistent massive gravity theories. Apart from the GW150914 mass bound, a few
other observational bounds have been established from the effects of the Yukawa
potential, modified dispersion relation and fifth force that are all induced
when the fundamental gravitational degrees of freedom are massive. We review
these different mass bounds and examine how they stand in the wake of recent
theoretical developments and how they compare to the bound from GW150914.
|
Assessing Compatibility of Direct Detection Data: Halo-Independent
Global Likelihood Analyses | We present two different halo-independent methods to assess the compatibility
of several direct dark matter detection data sets for a given dark matter model
using a global likelihood consisting of at least one extended likelihood and an
arbitrary number of Gaussian or Poisson likelihoods. In the first method we
find the global best fit halo function (we prove that it is a unique piecewise
constant function with a number of down steps smaller than or equal to a
maximum number that we compute) and construct a two-sided pointwise confidence
band at any desired confidence level, which can then be compared with those
derived from the extended likelihood alone to assess the joint compatibility of
the data. In the second method we define a "constrained parameter
goodness-of-fit" test statistic, whose $p$-value we then use to define a
"plausibility region" (e.g. where $p \geq 10\%$). For any halo function not
entirely contained within the plausibility region, the level of compatibility
of the data is very low (e.g. $p < 10 \%$). We illustrate these methods by
applying them to CDMS-II-Si and SuperCDMS data, assuming dark matter particles
with elastic spin-independent isospin-conserving interactions or exothermic
spin-independent isospin-violating interactions.
|
Astrometry - Challenging our Understanding of Stellar Structure and
Evolution | Stellar mass plays a central role in our understanding of star formation and
aging. Stellar astronomy is largely based on two maps, both dependent on mass,
either indirectly or directly: the Hertzprung-Russell Diagram (HRD) and the
Mass-Luminosity Relation (MLR). The extremes of both maps, while not terra
incognita, are characterized by large uncertainties. A precise HRD requires
precise distance obtained by direct measurement of parallax. A precise MLR
requires precise measurement of binary orbital parameters, with the ultimate
goal the critical test of theoretical stellar models. Such tests require mass
accuracies of ~1%. Substantial improvement in both maps requires astrometry
with microsecond of arc measurement precision. Why? First, the 'tops' of both
stellar maps contain relatively rare objects, for which large populations are
not found until the observing horizon reaches hundreds or thousands of parsecs.
Second, the 'bottoms' and 'sides' of both maps contain stars, either
intrinsically faint, or whose rarity guarantees great distance, hence apparent
faintness. With an extensive collection of high accuracy masses that can only
be provided by astrometry with microsecond of arc measurement precision,
astronomers will be able to stress test theoretical models of stars at any mass
and at every stage in their aging processes.
|
Galaxy Structure, Stellar Populations, and Star Formation Quenching at
0.6 $\lesssim$ $z$ $\lesssim$ 1.2 | We use both photometric and spectroscopic data from the {\it Hubble Space
Telescope} to explore the relationships among 4000 \AA\ break (D4000) strength,
colors, stellar masses, and morphology, in a sample of 352 galaxies with
log$(M_{*}/M_{\odot}) > 9.44$ at 0.6 $\lesssim z \lesssim$ 1.2. We have
identified authentically quiescent galaxies in the $UVJ$ diagram based on their
D4000 strengths. This spectroscopic identification is in good agreement with
their photometrically-derived specific star formation rates (sSFR).
Morphologically, most (that is, 66 out of 68 galaxies, $\sim$ 97 \%) of these
newly identified quiescent galaxies have a prominent bulge component. However,
not all of the bulge-dominated galaxies are quenched. We found that
bulge-dominated galaxies show positive correlations among the D4000 strength,
stellar mass, and the S\'ersic index, while late-type disks do not show such
strong positive correlations. Also, bulge-dominated galaxies are clearly
separated into two main groups in the parameter space of sSFR vs. stellar mass
and stellar surface density within the effective radius, $\Sigma_{\rm e}$,
while late-type disks and irregulars only show high sSFR. This split is
directly linked to the `blue cloud' and the `red sequence' populations, and
correlates with the associated central compactness indicated by $\Sigma_{\rm
e}$. While star-forming massive late-type disks and irregulars (with D4000 $<$
1.5 and log$(M_{*}/M_{\odot}) \gtrsim 10.5$) span a stellar mass range
comparable to bulge-dominated galaxies, most have systematically lower
$\Sigma_{\rm e}$ $\lesssim$ $10^{9}M_{\odot}\rm{kpc^{-2}}$. This suggests that
the presence of a bulge is a necessary but not sufficient requirement for
quenching at intermediate redshifts.
|
Galactic HI supershells: Kinetic energies and possible origin | The Milky Way, when viewed in the neutral hydrogen line emission, presents
large structures called Galactic supershells (GSs). The origin of these
structures is still a subject of debate. The most common scenario invoked is
the combined action of strong winds from massive stars and their subsequent
explosion as supernova. The aim of this work is to determine the origin of 490
GSs that belong to the Catalog of HI supershell candidates in the outer part of
the Galaxy. To know the physical processes that took place to create these
expanding structures, it is necessary to determine their kinetic energies. To
obtain all the GS masses, we developed and used an automatic algorithm, which
was tested on 95 GSs whose masses were also estimated by hand. The estimated
kinetic energies of the GSs vary from $1\times10^{47}$ to $3.4\times10^{51}$
erg. Considering an efficiency of 20% for the conversion of mechanical stellar
wind energy into the kinetic energy of the GSs, the estimated values of the GS
energies could be reached by stellar OB associations. For the GSs located at
high Galactic latitudes, the possible mechanism for their creation could be
attributed to collision with high velocity clouds (HVC). We have also analysed
the distribution of GSs in the Galaxy, showing that at low Galactic latitudes,
$|b|<2^\circ$, most of the structures in the third Galactic quadrant seem to be
projected onto the Perseus Arm. The detection of GSs at very high distances
from the Galactic centre may be attributed to diffuse gas associated with the
circumgalactic medium of M31 and to intra-group gas in the Local Group
filament.
|
Electromagnetic Emission from Supermassive Binary Black Holes
Approaching Merger | We present the first fully relativistic prediction of the electromagnetic
emission from the surrounding gas of a supermassive binary black hole system
approaching merger. Using a ray-tracing code to post-process data from a
general relativistic 3-d MHD simulation, we generate images and spectra, and
analyze the viewing angle dependence of the light emitted. When the accretion
rate is relatively high, the circumbinary disk, accretion streams, and
mini-disks combine to emit light in the UV/EUV bands. We posit a thermal
Compton hard X-ray spectrum for coronal emission; at high accretion rates, it
is almost entirely produced in the mini-disks, but at lower accretion rates it
is the primary radiation mechanism in the mini-disks and accretion streams as
well. Due to relativistic beaming and gravitational lensing, the angular
distribution of the power radiated is strongly anisotropic, especially near the
equatorial plane.
|
Clustering analysis of high-redshift Luminous Red Galaxies in Stripe 82 | We present a clustering analysis of Luminous Red Galaxies in SDSS Stripe 82.
We study the angular 2-point correlation function, of 130,000 LRG candidates
via colour-cut selections in izK with the K band coverage coming from UKIDSS
LAS. We have used the cross-correlation technique of Newman (2008) to establish
the LRG redshift distribution. Cross-correlating with SDSS QSOs, MegaZ-LRGs and
DEEP2 galaxies implies an average LRG redshift of z~1 with space density,
n_g~3.2 +/-0.16 x10^-4 h^3 Mpc^-3. For theta<10', w(theta) significantly
deviates from a single power-law. A double power-law with a break at r_b~2.4
h^-1 Mpc fits the data better, with best-fit scale length, r_0,1=7.63+/-0.27
h^-1Mpc and slope gamma_1=2.01 +/-0.02 at small scales and r_0,2=9.92 +/-0.40
h^-1 Mpc and gamma_2=1.64 +/-0.04 at large scales. Due to the flat slope at
large scales, we find that a standard LambdaCDM linear model is accepted only
at 2-3sigma, with the best-fit bias factor, b=2.74+/-0.07. We also fitted HOD
models and estimate an effective halo mass of M_eff=3.3 +/-0.6x10^13 h^-1
M_sun. But at large scales, the current HOD models did not help explain the
power excess in the clustering signal. We then compare the w(theta) results to
those of Sawangwit et al. (2011) from 3 samples of LRGs at lower redshifts to
measure clustering evolution. We find that a long-lived model may be a poorer
fit than at lower redshifts, although this assumes that the Stripe 82 LRGs are
luminosity-matched to the AAOmega LRGs. We find stronger evidence for evolution
in the form of the z~1 LRG correlation function, with the above flat 2-halo
slope maintaining to r>50 h^-1 Mpc. Applying the cross-correlation test of Ross
et al. (2011), we find little evidence that the result is due to systematics.
Otherwise it may provide evidence for primordial non-Gaussianity in the matter
distribution, with f^local_NL=90+/-30.[Abridged]
|
XXL Survey XXI. The environment and clustering of X-ray AGN in the
XXL-South field | This work is part of a series of studies focusing on the environment and the
properties of the X-ray selected active galactic nuclei (AGN) population from
the XXL survey. The present survey, given its large area, continuity, extensive
multiwavelength coverage, and large-scale structure information, is ideal for
this kind of study. Here, we focus on the XXL-South (XXL-S) field. Our main aim
is to study the environment of the various types of X-ray selected AGN and
investigate its possible role in AGN triggering and evolution. We studied the
large-scale (>1 Mpc) environment up to redshift z=1 using the nearest neighbour
distance method to compare various pairs of AGN types. We also investigated the
small-scale environment (<0.4 Mpc) by calculating the local overdensities of
optical galaxies. In addition, we built a catalogue of AGN concentrations with
two or more members using the hierarchical clustering method and we correlated
them with the X-ray galaxy clusters detected in the XXL survey. It is found
that radio detected X-ray sources are more obscured than non-radio ones, though
not all radio sources are obscured AGN. We did not find any significant
differences in the large-scale clustering between luminous and faint X-ray AGN,
or between obscured and unobscured ones, or between radio and non-radio
sources. At local scales (<0.4 Mpc), AGN typically reside in overdense regions,
compared to non-AGN; however, no differences were found between the various
types of AGN. A majority of AGN concentrations with two or more members are
found in the neighbourhood of X-ray galaxy clusters within <25-45 Mpc. Our
results suggest that X-ray AGN are typically located in supercluster filaments,
but they are also found in over- and underdense regions.
|
On the origin of matter in the Universe | The understanding of the physical processes that lead to the origin of matter
in the early Universe, creating both an excess of matter over anti-matter that
survived until the present and a dark matter component, is one of the most
fascinating challenges in modern science. The problem cannot be addressed
within our current description of fundamental physics and, therefore, it
currently provides a very strong evidence of new physics. Solutions can either
reside in a modification of the standard model of elementary particle physics
or in a modification of the way we describe gravity, based on general
relativity, or at the interface of both. We will mainly discuss the first class
of solutions. Traditionally, models that separately explain either the
matter-antimatter asymmetry of the Universe or dark matter have been proposed.
However, in the last years there has also been an accreted interest and intense
activity on scenarios able to provide a unified picture of the origin of matter
in the early universe. In this review we discuss some of the main ideas
emphasising primarily those models that have more chances to be experimentally
tested during next years. Moreover, after a general discussion, we will focus
on extensions of the standard model that can also address neutrino masses and
mixing, since this is currently the only evidence of physics beyond the
standard model coming directly from particle physics and it is, therefore,
reasonable they might also provide a solution to the problem of the origin of
matter in the universe.
|
Ice coverage of dust grains in cold astrophysical environments | Surface processes on cosmic solids in cold astrophysical environments lead to
gas phase depletion and molecular complexity. Most astrophysical models assume
that the molecular ice forms a thick multilayer substrate, not interacting with
the dust surface. In contrast, we present experimental results demonstrating
the importance of the surface for porous grains. We show that cosmic dust
grains may be covered by a few monolayers of ice only. This implies that the
role of dust surface structure, composition, and reactivity in models
describing surface processes in cold interstellar, protostellar, and
protoplanetary environments has to be reevaluated.
|
Cosmological perturbations and structure formation in nonlocal infrared
modifications of general relativity | We study the cosmological consequences of a recently proposed nonlocal
modification of general relativity, obtained by adding a term
$m^2R\,\Box^{-2}R$ to the Einstein-Hilbert action. The model has the same
number of parameters as $\Lambda$CDM, with $m$ replacing $\Omega_{\Lambda}$,
and is very predictive. At the background level, after fixing $m$ so as to
reproduce the observed value of $\Omega_M$, we get a pure prediction for the
equation of state of dark energy as a function of redshift, $w_{\rm DE}(z)$,
with $w_{\rm DE}(0)$ in the range $[-1.165,-1.135]$ as $\Omega_M$ varies over
the broad range $\Omega_M\in [0.20,0.36]$. We find that the cosmological
perturbations are well-behaved, and the model fully fixes the dark energy
perturbations as a function of redshift $z$ and wavenumber $k$. The nonlocal
model provides a good fit to supernova data and predicts deviations from
General Relativity in structure formation and in weak lensing at the level of
3-4%, therefore consistent with existing data but readily detectable by future
surveys. For the logarithmic growth factor we obtain $\gamma\simeq 0.53$, to be
compared with $\gamma\simeq 0.55$ in $\Lambda$CDM. For the Newtonian potential
on subhorizon scales our results are well fitted by $\Psi(a;k)=[1+\mu_s
a^s]\Psi_{\rm GR}(a;k)$ with a scale-independent $\mu_s\simeq 0.09$ and
$s\simeq 2$, while the anisotropic stress is negligibly small.
|
Spherical galaxy models as equilibrium configurations in nonextensive
statistics | Considering galaxies as self - gravitating systems of many collisionless
particles allows to use methods of statistical mechanics inferring the
distribution function of these stellar systems. Actually, the long range nature
of the gravitational force contrasts with the underlying assumptions of
Boltzmann statistics where the interactions among particles are assumed to be
short ranged. A particular generalization of the classical Boltzmann formalism
is available within the nonextensive context of Tsallis q -statistics, subject
to non -additivity of the entropies of sub - systems. Assuming stationarity and
isotropy in the velocity space, it is possible solving the generalized
collsionless Boltzmann equation to derive the galaxy distribution function and
density profile. We present a particular set of nonextensive models and
investigate their dynamical and observable properties. As a test of the
viability of this generalized context, we fit the rotation curve of M33 showing
that the proposed approach leads to dark matter haloes in excellent agreement
with the observed data.
|
Preliminary Application of Reinsch Splines to Cosmology: Transition
Redshift Determination with Simulated OHD | Many schemes have been proposed to perform a model-independent constraint on
cosmological dynamics, such as nonparametric dark energy equation of state
(EoS) \omega(z) or the deceleration parameter q(z). These methods usually
contain derivative processes with respect to observational data with noise.
However, it still remains remarkably uncertain when one estimates the numerical
differentiation, especially the corresponding truncation errors. In this work,
we introduce a global numerical differentiation method, first formulated by
Reinsch(1967), which is smoothed by cubic spline functions. The optimal
solution is obtained by minimizing the functional \Phi(f). To investigate the
potential of the algorithm further, we apply it to the estimation of the
transition redshift z_{t} with simulated expansion rate E(z) based on
observational Hubble parameter data(OHD). An effective method to determine the
free parameter S appearing in Reinsch Splines is provided.
|
The Black Hole Mass Function from Gravitational Wave Measurements | We examine how future gravitational-wave measurements from merging black
holes (BHs) can be used to infer the shape of the black-hole mass function,
with important implications for the study of star formation and evolution and
the properties of binary BHs. We model the mass function as a power law,
inherited from the stellar initial mass function, and introduce lower and upper
mass cutoff parameterizations in order to probe the minimum and maximum BH
masses allowed by stellar evolution, respectively. We initially focus on the
heavier BH in each binary, to minimize model dependence. Taking into account
the experimental noise, the mass measurement errors and the uncertainty in the
redshift-dependence of the merger rate, we show that the mass function
parameters, as well as the total rate of merger events, can be measured to <10%
accuracy within a few years of advanced LIGO observations at its design
sensitivity. This can be used to address important open questions such as the
upper limit on the stellar mass which allows for BH formation and to confirm or
refute the currently observed mass gap between neutron stars and BHs. In order
to glean information on the progenitors of the merging BH binaries, we then
advocate the study of the two-dimensional mass distribution to constrain
parameters that describe the two-body system, such as the mass ratio between
the two BHs, in addition to the merger rate and mass function parameters. We
argue that several years of data collection can efficiently probe models of
binary formation, and show, as an example, that the hypothesis that some
gravitational-wave events may involve primordial black holes can be tested.
Finally, we point out that in order to maximize the constraining power of the
data, it may be worthwhile to lower the signal-to-noise threshold imposed on
each candidate event and amass a larger statistical ensemble of BH mergers.
|
Evolution of the Cool Gas in the Circumgalactic Medium (CGM) of Massive
Halos -- A Keck Cosmic Web Imager (KCWI) Survey of Ly$\alpha$ Emission around
QSOs at $z\approx2$ | Motivated by the recent discovery of the near-ubiquity of Ly$\alpha$ emission
around $z \gtrsim 3$ QSOs, we performed a systematic study of QSO
circumgalactic Ly$\alpha$ emission at $z\approx2$, utilizing the unique
capability of the Keck Cosmic Web Imager (KCWI) -- a new wide-field, blue
sensitive integral-field spectrograph (IFU). In this paper, we present KCWI
observations on a sample of 16 ultraluminous Type-I QSOs at $z=2.1-2.3$ with
ionizing luminosities of $L_{\rm{\nu_{\rm{LL}}}}=10^{31.1-32.3}$ erg s$^{-1}$
Hz$^{-1}$. We found that 14 out of 16 QSOs are associated with Ly$\alpha$
nebulae with projected linear-sizes larger than 50 physical kpc (pkpc). Among
them, four nebulae have enormous Ly$\alpha$ emission with the Ly$\alpha$
surface brightness $SB_{\rm{Ly\alpha}} >10^{-17}$ erg s$^{-1}$ cm$^{-2}$
arcsec$^{-2}$ on the $>100$ kpc scale, extending beyond the field of view of
KCWI. Our KCWI observations reveal that most $z\approx2$ QSO nebulae have a
more irregular morphology compared to those at $z\gtrsim3$. In turn, we measure
that the circularly-averaged surface brightness (SB) at $z\approx2$ is 0.4 dex
fainter than the redshift-corrected, median SB at $z\gtrsim 3$. The Ly$\alpha$
SB profile (SB$_{\rm{Ly\alpha}}$) of QSOs at $z\approx 2$ can be described by a
power law of SB$_{\rm{Ly\alpha},z\approx2.3}=
3.7\times10^{-17}\times(r/40)^{-1.8}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$,
with the slope similar to that at $z\gtrsim3$. The observed lower
redshift-corrected, circularly-averaged SB may be mainly due to the lower
covering factor of cool gas clouds in massive halos at $z\approx2$.
|
Direct evidence of multiple reservoirs of volatile nitrogen in a
protosolar nebula analogue | Isotopic ratios are keys to understanding the origin and early evolution of
the solar system in the context of Galactic nucleosynthesis. The large range of
measured $^{14}$N/$^{15}$N isotopic ratios in the solar system reflects
distinct reservoirs of nitrogen whose origins remain to be determined. We have
directly measured a C$^{14}$N/C$^{15}$N abundance ratio of 323$\pm$30 in the
disk orbiting the nearby young star TW Hya. This value, which is in good
agreement with nitrogen isotopic ratios measured for prestellar cores, likely
reflects the primary present-day reservoir of nitrogen in the solar
neighbourhood. These results support models invoking novae as primary $^{15}$N
sources as well as outward migration of the Sun over its lifetime, and suggest
that comets sampled a secondary, $^{15}$N-rich reservoir during solar system
formation.
|
Study of galaxies in the Eridanus void. Sample and oxygen abundances | We present a sample of 66 galaxies belonging to the equatorial part (Dec.=
-7$^o$, +7$^o$) of the large so called Eridanus void (after Fairall 1998). The
void galaxies are selected as to be separated from the luminous galaxies
($M_{\rm B} < M_{\rm B}^{*} +1$), delineating the void, by more than 2 Mpc. Our
main goal is to study systematically the evolutionary parameters of the void
sample (metallicity and gas content) and to compare the void galaxy properties
with their counterparts residing in denser environments. Besides the general
galaxy parameters, compiled mainly from the literature, we present the results
of dedicated observations to measure the oxygen abundance O/H in HII-regions of
23 void galaxies obtained with the 11-m SALT telescope (SAAO) and the 6-m BTA
telescope (SAO), as well as the O/H estimates derived from the analysis of the
SDSS DR12 spectra for 3 objects. We compiled all available data on O/H in 36
these void galaxies, including those for 11 galaxies available in the
literature (for one object both SDSS and SALT spectra were used), and analyze
this data in relation to galaxy luminosity ($\log$(O/H) versus $M_{\rm B}$).
Comparing them with the control sample of similar type galaxies from the Local
Volume, we find clear evidence for a substantially lower average metallicity of
the Eridanus void galaxies. This result matches well the conclusions of our
recent similar study for galaxies in the Lynx-Cancer void.
|
The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: Effect of smoothing of density field on reconstruction
and anisotropic BAO analysis | The reconstruction algorithm introduced by \cite{Eis07}, which is widely used
in clustering analysis, is based on the inference of the first order Lagrangian
displacement field from the Gaussian smoothed galaxy density field in redshift
space. The \modif2{smoothing scale} applied to the density field affects the
inferred displacement field that is used to move {the galaxies}, and partially
\modif2{erases} the nonlinear evolution {of the density field}.
In this article, we explore this crucial step \modif2{in} the reconstruction
algorithm. We study the performance of the reconstruction technique using two
metrics: first, we study the performance using the anisotropic clustering,
extending previous studies focused on isotropic clustering; second, we study
its effect on the displacement field. We find that smoothing has a strong
effect in the quadrupole of the correlation function and affects the accuracy
and precision \modif2{with} which we can measure $D_A (z)$ and $H(z)$. We find
that the optimal smoothing scale to use in the reconstruction algorithm applied
to BOSS-CMASS is between 5-10 $h^{-1}$Mpc. Varying from the "usual"
15$h^{-1}$Mpc to $5 h^{-1}$Mpc \modif2{shows} $\sim$ 0.3\% variations in
$D_A(z)$ and $\sim$ 0.4\% $H(z)$ and uncertainties are also reduced by 40\% and
30\% respectively. We also find that the accuracy of velocity field
reconstruction depends strongly on the smoothing scale used for the density
field. We measure the bias and uncertainties associated with different choices
of smoothing length.
|
The Owl and other strigiform nebulae: multipolar cavities within a
filled shell | We present the results of long-slit echelle spectroscopy and deep narrow-band
imaging of the Owl Nebula (NGC 3587), obtained at the \textit{Observatorio
Astron\'omico Nacional, San Pedro M\'artir}. These data allow us to construct
an iso-velocity data cube and develop a 3-D morpho-kinematic model. We find
that, instead of the previously assumed bipolar dumbbell shape, the inner
cavity consists of multi-polar fingers within an overall tripolar structure. We
identify three additional planetary nebulae that show very similar morphologies
and kinematics to the Owl, and propose that these constitute a new class of
\textit{strigiform} (owl-like) nebulae. Common characteristics of the
strigiform nebulae include a double-shell (thin outside thick) structure,
low-luminosity and high-gravity central stars, the absence of a present-day
stellar wind, and asymmetric inner cavities, visible in both optical and
mid-infrared emission lines, that show no evidence for surrounding bright rims.
The origin of the cavities is unclear, but they may constitute relics of an
earlier stage of evolution when the stellar wind was active.
|
$\Lambda$CDM model with a scalar perturbation vs. preferred direction of
the universe | We present a scalar perturbation for the $\Lambda$CDM model, which breaks the
isotropic symmetry of the universe. Based on the Union2 data, the
least-$\chi^2$ fit of the scalar perturbed $\Lambda$CDM model shows that the
universe has a preferred direction
$(l,b)=(287^\circ\pm25^\circ,11^\circ\pm22^\circ)$. The magnitude of scalar
perturbation is about $-2.3\times10^{-5}$. The scalar perturbation for the
$\Lambda$CDM model implies a peculiar velocity, which is perpendicular to the
radial direction. We show that the maximum peculiar velocities at redshift
$z=0.15$ and $z=0.015$ equal to $73\pm28 \rm km\cdot s^{-1}$ and $1099\pm427
\rm km\cdot s^{-1}$, respectively. They are compatible with the constraints on
peculiar velocity given by Planck Collaboration.
|
BBN constraints on universally-coupled ultralight scalar dark matter | Ultralight scalar dark matter can interact with all massive Standard Model
particles through a universal coupling. Such a coupling modifies the Standard
Model particle masses and affects the dynamics of Big Bang Nucleosynthesis. We
model the cosmological evolution of the dark matter, taking into account the
modifications of the scalar mass by the environment as well as the full
dynamics of Big Bang Nucleosynthesis. We find that precision measurements of
the helium-4 abundance set stringent constraints on the available parameter
space, and that these constraints are strongly affected by both the dark matter
environmental mass and the dynamics of the neutron freeze-out. Furthermore, we
perform the analysis in both the Einstein and Jordan frames, the latter of
which allows us to implement the model into numerical Big Bang Nucleosynthesis
codes and analyze additional light elements. The numerical analysis shows that
the constraint from helium-4 dominates over deuterium, and that the effect on
lithium is insufficient to solve the lithium problem. Comparing to several
other probes, we find that Big Bang Nucleosynthesis sets the strongest
constraints for the majority of the parameter space.
|
Realistic systematic biases induced by residual intrinsic alignments in
cosmic shear surveys | We study the parameter estimation bias induced by intrinsic alignments on a
Euclid-like weak lensing survey. For the intrinsic alignment signal we assume a
composite alignment model for elliptical and spiral galaxies using tidal
shearing and tidal torquing as the alignment generating mechanism,
respectively. The parameter estimation bias is carried out analytically with a
Gaussian bias model and through running Monte-Carlo-Markov-chains on synthetic
data including the alignment signal with a likelihood only including the cosmic
shear signal. In particular, we study the impact of $II$ and $GI$ alignment
terms individually as well as the more realistic situation where both types of
alignment are present, and investigate the scaling of the estimation biases
with varying strength of the alignment signal. Our results show that intrinsic
alignments can cause substantial biases in cosmological parameters even if the
coupling of galaxies to the ambient large is small. Especially
$GI$-contributions strongly bias key cosmological parameters such as the dark
energy equation of state. We also correct the analytic expression for the
Gaussian bias model and find that the biases induced by intrinsic alignments
are not accurately recovered by the simple analytic model.
|
Molecular Emission in Dense Massive Clumps from the Star-Forming Regions
S231-S235 | The article deals with observations of star-forming regions S231-S235 in
'quasi-thermal' lines of ammonia (NH$_3$), cyanoacetylene (HC$_3$N) and maser
lines of methanol (CH$_3$OH) and water vapor (H$_2$O). S231-S235 regions is
situated in the giant molecular cloud G174+2.5. We selected all massive
molecular clumps in G174+2.5 using archive CO data. For the each clump we
determined mass, size and CO column density. After that we performed
observations of these clumps. We report about first detections of NH$_3$ and
HC$_3$N lines toward the molecular clumps WB89 673 and WB89 668. This means
that high-density gas is present there. Physical parameters of molecular gas in
the clumps were estimated using the data on ammonia emission. We found that the
gas temperature and the hydrogen number density are in the ranges 16-30 K and
2.8-7.2$\times10^3$ cm$^{-3}$, respectively. The shock-tracing line of CH$_3$OH
molecule at 36.2 GHz is newly detected toward WB89 673.
|
A new mass-loss rate prescription for red supergiants | Evolutionary models have shown the substantial effect that strong mass-loss
rates ($\dot{M}$) can have on the fate of massive stars. Red supergiant (RSG)
mass-loss is poorly understood theoretically, and so stellar models rely on
purely empirical \mdot-luminosity relations to calculate evolution. Empirical
prescriptions usually scale with luminosity and effective temperature, but
$\dot{M}$ should also depend on the current mass and hence the surface gravity
of the star, yielding more than one possible $\dot{M}$ for the same position on
the Hertzsprung-Russell diagram. One can solve this degeneracy by measuring
$\dot{M}$ for RSGs that reside in clusters, where age and initial mass ($M_{\rm
init}$) are known. In this paper we derive $\dot{M}$ values and luminosities
for RSGs in two clusters, NGC 2004 and RSGC1. Using newly derived $M_{\rm
init}$ measurements, we combine the results with those of clusters with a range
of ages and derive an $M_{\rm init}$-dependent $\dot{M}$-prescription. When
comparing this new prescription to the treatment of mass-loss currently
implemented in evolutionary models, we find models drastically over-predict the
total mass-loss, by up to a factor of 20. Importantly, the most massive RSGs
experience the largest downward revision in their mass-loss rates, drastically
changing the impact of wind mass-loss on their evolution. Our results suggest
that for most initial masses of RSG progenitors, quiescent mass-loss during the
RSG phase is not effective at removing a significant fraction of the H-envelope
prior to core-collapse, and we discuss the implications of this for stellar
evolution and observations of SNe and SN progenitors.
|
The Earliest Near-infrared Time-series Spectroscopy of a Type Ia
Supernova | We present ten medium-resolution, high signal-to-noise ratio near-infrared
(NIR) spectra of SN 2011fe from SpeX on the NASA Infrared Telescope Facility
(IRTF) and Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North, obtained
as part of the Carnegie Supernova Project. This data set constitutes the
earliest time-series NIR spectroscopy of a Type Ia supernova (SN Ia), with the
first spectrum obtained at 2.58 days past the explosion and covering -14.6 to
+17.3 days relative to B-band maximum. C I {\lambda}1.0693 {\mu}m is detected
in SN 2011fe with increasing strength up to maximum light. The delay in the
onset of the NIR C I line demonstrates its potential to be an effective tracer
of unprocessed material. For the first time in a SN Ia, the early rapid decline
of the Mg II {\lambda}1.0927 {\mu}m velocity was observed, and the subsequent
velocity is remarkably constant. The Mg II velocity during this constant phase
locates the inner edge of carbon burning and probes the conditions under which
the transition from deflagration to detonation occurs. We show that the Mg II
velocity does not correlate with the optical light-curve decline rate
{\Delta}m15. The prominent break at ~1.5 {\mu}m is the main source of concern
for NIR k-correction calculations. We demonstrate here that the feature has a
uniform time evolution among SNe Ia, with the flux ratio across the break
strongly correlated with {\Delta}m15. The predictability of the strength and
the onset of this feature suggests that the associated k-correction
uncertainties can be minimized with improved spectral templates.
|
Void Formation: Does the Void-in-Cloud Process Matter? | We investigate the basic properties of voids from high resolution,
cosmological N-body simulations of {\Lambda}-dominated cold dark matter
({\Lambda}CDM) models, in order to compare with the analytical model of Sheth
and van de Weygaert (SvdW) for void statistics. For the subsample of five dark
matter simulations in the {\Lambda}CDM cosmology with box sizes ranging from
1000 Mpc/h to 8 Mpc/h, we find that the standard void-in-cloud effect is too
simplified to explain several properties of identified small voids in
simulations. (i) The number density of voids is found to be larger than the
prediction of the analytical model up to 2 orders of magnitude below 1 Mpc/h
scales. The Press-Schechter model with the linear critical threshold of void
{\delta}_v = -2.71, or a naive power law, is found to provide an excellent
agreement with the void size function, suggesting that the void-in-cloud effect
does not suppress as much voids as predicted by the SvdW model. (ii) We then
measured the density and velocity profiles of small voids, and find that they
are mostly partially collapsing underdensities, instead of being completely
crushed in the standard void-in-cloud scenario. (iii) Finally, we measure the
void distributions in four different tidal environments, and find that the
void-in-void effect alone can explain the correlation between distribution and
environments, whereas the void-in-cloud effect is only weakly influencing the
abundance of voids, even in filaments and clusters.
|
Inflation near a metastable de Sitter vacuum from moduli stabilisation | We study the cosmological properties of a metastable de Sitter vacuum
obtained recently in the framework of type IIB flux compactifications in the
presence of three D7-brane stacks, based on perturbative quantum corrections at
both world-sheet and string loop level that are dominant at large volume and
weak coupling. In the simplest case, the model has one effective parameter
controlling the shape of the potential of the inflaton which is identified with
the volume modulus. The model provides a phenomenological successful
small-field inflation for a value of the parameter that makes the minimum very
shallow and near the maximum. The horizon exit is close to the inflection point
while most of the required e-folds of the Universe expansion are generated near
the minimum, with a prediction for the ratio of tensor-to-scalar primordial
fluctuations $r \sim 4 \times 10^{-4}$. Despite its shallowness, the minimum
turns out to be practically stable. We show that it can decay only through the
Hawking-Moss instanton leading to an extremely long decay rate. Obviously, in
order to end inflation and obtain a realistic model, new low-energy physics is
needed around the minimum, at intermediate energy scales of order $10^{12}$
GeV. An attractive possibility is by introducing a "waterfall"' field within
the framework of hybrid inflation.
|
First Principles Phenomenology of $H_0$ | In this letter we discuss infinite statistics and motivate its role in
quantum gravity. Then, we connect infinite statistics to a dynamical form of
dark energy, and we obtain an expression for the evolution of the Hubble
parameter that we compare to observation. The equation of state parameter
$w_{eff} < -1$ in this framework.
|
Can star cluster environment affect dust input from massive AGB stars? | We examine the fraction of massive asymptotic giant branch (AGB) stars
remaining bound in their parent star clusters and the effect of irradiation of
these stars by intracluster ultraviolet (UV) field. We employ a set of N-body
models of dynamical evolution of star clusters rotating in a galactic potential
at the solar galactocentric radius. The cluster models are combined with
stellar evolution formulae, a library of stellar spectra, and simple models for
SiO photodissociation in circumstellar environment (CSE). The initial stellar
masses of clusters are varied from $50\rm M_\odot$ to $10^{5}\rm M_\odot$.
Results derived for individual clusters are combined using a mass distribution
function for young star clusters. We find that about 30% of massive AGB stars
initially born in clusters become members of the field population, while the
rest evolves in star clusters. They are irradiated by strong intracluster UV
radiation resulting in the decrease of the photodissociation radius of SiO
molecules, in many stars down to the dust formation zone. In absence of dust
shielding, the UV photons penetrate in the CSE deeper than $10R_*$ in 64% and
deeper than $2 R_*$ in 42% of all massive AGB stars. If this suppresses
following dust formation, the current injection rate of silicate dust from AGB
stars in the local Galaxy decreases from $2.2 \times 10^{-4}\rm
M_\odot\,kpc^{-2}\,Gyr^{-1}$ to $1.8 \times 10^{-4}\rm
M_\odot\,kpc^{-2}\,Gyr^{-1}$ at most. A lower revised value of 40% for the
expected fraction of presolar silicate grains from massive AGB stars is still
high to explain the non-detection of these grains in meteorites.
|
Optimization of Neutrino Oscillation Parameters using Differential
Evolution | We combine Differential Evolution, a new technique, with the traditional grid
based method for optimization of solar neutrino oscillation parameters $\Delta
m^2$ and $\tan^{2}\theta$ for the case of two neutrinos. The Differential
Evolution is a population based stochastic algorithm for optimization of real
valued non-linear non-differentiable objective functions that has become very
popular during the last decade. We calculate well known chi-square ($\chi^2$)
function for neutrino oscillations for a grid of the parameters using total
event rates of chlorine (Homestake), Gallax+GNO, SAGE, Superkamiokande and SNO
detectors and theoretically calculated event rates. We find minimum $\chi^2$
values in different regions of the parameter space. We explore regions around
these minima using Differential Evolution for the fine tuning of the parameters
allowing even those values of the parameters which do not lie on any grid. We
note as much as 4 times decrease in $\chi^2$ value in the SMA region and even
better goodness-of-fit as compared to our grid-based results. All this
indicates a way out of the impasse faced due to CPU limitations of the larger
grid method.
|
Microscopic Origin of Volume Modulus Inflation | High-scale string inflationary models are in well-known tension with
low-energy supersymmetry. A promising solution involves models where the
inflaton is the volume of the extra dimensions so that the gravitino mass
relaxes from large values during inflation to smaller values today. We describe
a possible microscopic origin of the scalar potential of volume modulus
inflation by exploiting non-perturbative effects, string loop and higher
derivative perturbative corrections to the supergravity effective action
together with contributions from anti-branes and charged hidden matter fields.
We also analyse the relation between the size of the flux superpotential and
the position of the late-time minimum and the inflection point around which
inflation takes place. We perform a detailed study of the inflationary dynamics
for a single modulus and a two moduli case where we also analyse the
sensitivity of the cosmological observables on the choice of initial
conditions.
|
The critical geometry of a thermal big bang | We explore the space of scalar-tensor theories containing two
non-conformalmetrics, and find a discontinuity pointing to a "critical"
cosmological solution. Due to the different maximal speeds of propagation for
matter and gravity,the cosmological fluctuations start off inside the horizon
even without inflation, and will more naturally have a thermal origin (since
there is never vacuum domination). The critical model makes an unambiguous,
non-tuned prediction for the spectral index of the scalar fluctuations: $n_S=
0.96478(64)$. Considering also that no gravitational waves are produced, we
have unveiled the most predictive model on offer. The model has a simple
geometrical interpretation as a probe 3-brane embedded in an $EAdS_2\times E_3$
geometry.
|
Improved Modeling of the Mass Distribution of Disk Galaxies by the
Einasto Halo Model | (Abridged) The analysis of the rotation curves (RCs) of spiral galaxies
provides an efficient diagnostic for studying the properties of dark matter
halos and their relations with the baryonic material. We have modeled the RCs
of galaxies from The HI Nearby Galaxy Survey (THINGS) with the Einasto halo
model, which has emerged as the best-fitting model of the halos arising in
dissipationless cosmological N-body simulations. We find that the RCs are
significantly better fit with the Einasto halo than with either a
pseudo-isothermal sphere (Iso) or Navarro-Frenk-White (NFW) halo models. In our
best-fit models, the radius of density slope -2 and the density at this radius
are highly correlated. The Einasto index, which controls the overall shape of
the density profile, is near unity on average for intermediate and low mass
halos. This is not in agreement with the predictions from LCDM simulations. The
indices of the most massive halos are in rough agreement with those of
cosmological simulations and appear correlated with the halo virial mass. We
find that a typical Einasto density profile declines more strongly in its
outermost parts than any of the Iso or NFW models whereas it is relatively
shallow in its innermost regions. The core nature of those regions of halos
thus extends the cusp-core controversy found for the NFW model with low surface
density galaxies to the Einasto halo with more massive galaxies like those of
THINGS. We thus find that the Einasto halo model provides, so far, the best
match to the observed RCs, and can therefore be considered as a new standard
model for dark matter halos.
|
Evidence for the Late Arrival of Hot Jupiters in Systems with High
Host-star Obliquities | It has been shown that hot Jupiters systems with massive, hot stellar
primaries exhibit a wide range of stellar obliquities. On the other hand, hot
Jupiter systems with low-mass, cool primaries often have stellar obliquities
close to zero. Efficient tidal interactions between hot Jupiters and the
convective envelopes present in lower-mass main sequence stars have been a
popular explanation for these observations. If this explanation is accurate,
then aligned systems should be older than misaligned systems. Likewise, the
convective envelope mass of a hot Jupiter's host star should be an effective
predictor of its obliquity. We derive homogeneous stellar parameters --
including convective envelope masses -- for hot Jupiter host stars with
high-quality sky-projected obliquity inferences. Using a thin disk stellar
population's Galactic velocity dispersion as a relative age proxy, we find that
hot Jupiter host stars with larger-than-median obliquities are older than hot
Jupiter host stars with smaller-than-median obliquities. The relative age
difference between the two populations is larger for hot Jupiter host stars
with smaller-than-median fractional convective envelope masses and is
significant at the 3.6-$\sigma$ level. We identify stellar mass, not convective
envelope mass, as the best predictor of stellar obliquity in hot Jupiter
systems. The best explanation for these observations is that many hot Jupiters
in misaligned systems arrived in the close proximity of their host stars long
after their parent protoplanetary disks dissipated. The dependence of observed
age offset on convective envelope mass suggests that tidal realignment
contributes to the population of aligned hot Jupiters orbiting stars with
convective envelopes.
|
The Swift/UVOT Stars Survey. II. RR Lyrae Stars in M 3 and M 15 | We present the first results of an near-ultraviolet (NUV) survey of RR Lyrae
stars from the Ultraviolet Optical Telescope (UVOT) aboard the Swift Gamma-Ray
Burst Mission. It is well-established that RR Lyrae have large amplitudes in
the far- and near-ultraviolet. We have used UVOT's unique wide-field NUV
imaging capability to perform the first systematic NUV survey of variable stars
in the Galactic globular clusters M 3 and M 15. We identify 280 variable stars,
comprising 275 RR Lyrae, two anomalous Cepheids, one classical Cepheid, one SX
Phoenicis star and one possible long-period or irregular variable. Only two of
these are new discoveries. We compare our results to previous investigations
and find excellent agreement in the periods with significantly larger
amplitudes in the NUV. We map out, for the first time, an NUV Bailey diagram
from globular clusters, showing the usual loci for fundamental mode RRab and
first overtone RRc pulsators. We show the unique sensitivity of NUV photometry
to both the temperatures and the surface gravities of RR Lyrae stars. Finally,
we show evidence of an NUV period-metallicity-luminosity relationship. Future
investigations will further examine the dependence of NUV pulsation parameters
on metallicity and Oosterhoff classification.
|
Refining the Census of the Upper Scorpius Association with Gaia | We have refined the census of stars and brown dwarfs in the Upper Sco
association (~10 Myr, ~145 pc) by 1) updating the selection of candidate
members from our previous survey to include the high-precision astrometry from
the second data release of Gaia, 2) obtaining spectra of a few hundred
candidate members to measure their spectral types and verify their youth, and
3) assessing the membership (largely with Gaia astrometry) of 2020 stars toward
Upper Sco that show evidence of youth in this work and previous studies. We
arrive at a catalog of 1761 objects that are adopted as members of Upper Sco.
The distribution of spectral types among the adopted members is similar to
those in other nearby star-forming regions, indicating a similar initial mass
function. In previous studies, we have compiled mid-infrared photometry from
WISE and the Spitzer Space Telescope for members of Upper Sco and used those
data to identify the stars that show evidence of circumstellar disks; we
present the same analysis for our new catalog of members. As in earlier work,
we find that the fraction of members with disks increases with lower stellar
masses, ranging from <=10% for >1 Msun to ~22% for 0.01-0.3 Msun. Finally, we
have estimated the relative ages of Upper Sco and other young associations
using their sequences of low-mass stars in M(G_RP) versus G_BP-G_RP. This
comparison indicates that Upper Sco is a factor of two younger than the beta
Pic association (21-24 Myr) according to both non-magnetic and magnetic
evolutionary models.
|
Mg II line properties in lobe-dominated quasars | We investigate the relationships between Mg ii {\lambda}2798 emission line
properties, as well as between these properties and inclination angle and Fe ii
strength, in a lobe-dominated quasar sample. We find no correlation between Mg
ii line width and inclination, unlike previous studies of the general quasar
population. This suggests that the Mg ii emission region in these objects is
not of a thin disk geometry, however the average equivalent width of the line
negates a spherical alternative. A positive correlation between Mg ii
equivalent width and inclination cannot be ruled out, meaning there is no
strong evidence that Mg ii emission is anisotropic. Since thin disk emission
would be highly directional, the geometric implications of these two findings
are compatible. The lack of line width correlation with inclination may also
indicate that Mg ii is useful for estimating black hole masses in
lobe-dominated quasar samples, since it is unbiased by orientation. Some
quasars in our sample have almost edge-on viewing angles and therefore cannot
have a smooth toroidal obscurer co-planar with the accretion disk. Alternatives
may be a distorted dusty disk or a clumpy obscurer. This could result from the
sample selection bias towards high inclination objects, rather than intrinsic
differences between lobe-dominated and typical quasars. Five objects have
visible [O iii] allowing equivalent width calculation, revealing it to be
higher than in typical quasars. Since these objects are of high inclination,
this finding supports the positive correlation between [O iii] equivalent width
and inclination found in a previous study.
|
Warm Dark Matter and Cosmic Reionization | In models with dark matter made of particles with keV masses, such as a
sterile neutrino, small-scale density perturbations are suppressed, delaying
the period at which the lowest mass galaxies are formed and therefore shifting
the reionization processes to later epochs. In this study, focusing on Warm
Dark Matter (WDM) with masses close to its present lower bound, i.e. around the
$3$ keV region, we derive constraints from galaxy luminosy functions, the
ionization history and the Gunn-Peterson effect. We show that even if star
formation efficiency in the simulations is adjusted to match the observed UV
galaxy luminosity functions in both CDM and WDM models, the full distribution
of Gunn-Peterson optical depth retains the strong signature of delayed
reionization in the WDM model. However, until the star formation and stellar
feedback model used in modern galaxy formation simulations is constrained
better, any conclusions on the nature of dark matter derived from reionization
observables remain model-dependent.
|
The 5 - 10 keV AGN luminosity function at 0.01<z<4.0 | The active galactic nuclei X-ray luminosity function traces actively
accreting supermassive black holes and is essential for the study of the
properties of the active galactic nuclei (AGN) population, black hole
evolution, and galaxy-black hole coevolution. Up to now, the AGN luminosity
function has been estimated several times in soft (0.5-2 keV) and hard X-rays
(2-10 keV). AGN selection in these energy ranges often suffers from
identification and redshift incompleteness and, at the same time, photoelectric
absorption can obscure a significant amount of the X-ray radiation. We estimate
the evolution of the luminosity function in the 5-10 keV band, where we
effectively avoid the absorbed part of the spectrum, rendering absorption
corrections unnecessary up to NH=10^23 cm^-2. Our dataset is a compilation of
six wide, and deep fields: MAXI, HBSS, XMM-COSMOS, Lockman Hole, XMM-CDFS,
AEGIS-XD, Chandra-COSMOS, and Chandra-CDFS. This extensive sample of ~1110 AGN
(0.01<z<4.0, 41<log L_x<46) is 98% redshift complete with 68% spectroscopic
redshifts. We use Bayesian analysis to select the best parametric model from
simple pure luminosity and pure density evolution to more complicated
luminosity and density evolution and luminosity-dependent density evolution. We
estimate the model parameters that describe best our dataset separately for
each survey and for the combined sample. We show that, according to Bayesian
model selection, the preferred model for our dataset is the
luminosity-dependent density evolution (LDDE). Our estimation of the AGN
luminosity function does not require any assumption on the AGN absorption and
is in good agreement with previous works in the 2-10 keV energy band based on
X-ray hardness ratios to model the absorption in AGN up to redshift three. Our
sample does not show evidence of a rapid decline of the AGN luminosity function
up to redshift four. [abridged]
|
Cavity evolution in relativistic self-gravitating fluids | We consider the evolution of cavities within spherically symmetric
relativistic fluids, under the assumption that proper radial distance between
neighboring fluid elements remains constant during their evolution (purely
areal evolution condition). The general formalism is deployed and solutions are
presented. Some of them satisfy Darmois conditions whereas others present
shells and must satisfy Israel conditions, on either one or both boundary
surfaces. Prospective applications of these results to some astrophysical
scenarios is suggested.
|
A Deeper Look at Leo IV: Star Formation History and Extended Structure | We present MMT/Megacam imaging of the Leo~IV dwarf galaxy in order to
investigate its structure and star formation history, and to search for signs
of association with the recently discovered Leo~V satellite. Based on
parameterized fits, we find that Leo~IV is round, with $\epsilon < 0.23$ (at
the 68\% confidence limit) and a half-light radius of $r_{h} \simeq 130$ pc.
Additionally, we perform a thorough search for extended structures in the plane
of the sky and along the line of sight. We derive our surface brightness
detection limit by implanting fake structures into our catalog with stellar
populations identical to that of Leo~IV. We show that we are sensitive to
stream-like structures with surface brightness $\mu_{r}\lesssim29.6$ mag
arcsec$^{-2}$, and at this limit, we find no stellar bridge between Leo IV (out
to a radius of $\sim$0.5 kpc) and the recently discovered, nearby satellite Leo
V. Using the color magnitude fitting package StarFISH, we determine that Leo~IV
is consistent with a single age ($\sim$14 Gyr), single metallicity
($[Fe/H]\sim-2.3$) stellar population, although we can not rule out a
significant spread in these value. We derive a luminosity of
$M_{V}=-5.5\pm0.3$. Studying both the spatial distribution and frequency of
Leo~IV's 'blue plume' stars reveals evidence for a young ($\sim$2 Gyr) stellar
population which makes up $\sim$2\% of its stellar mass. This sprinkling of
star formation, only detectable in this deep study, highlights the need for
further imaging of the new Milky Way satellites along with theoretical work on
the expected, detailed properties of these possible 'reionization fossils'.
|
BICEP2, the curvature perturbation and supersymmetry | The tensor fraction $r\simeq 0.16$ found by BICEP2 corresponds to a Hubble
parameter $H\simeq 1.0\times 10^{14}\GeV$ during inflation.
This has two implications for the (single-field) slow-roll inflation
hypothesis. First, the inflaton perturbation must account for much more than
$10\%$ of the curvature perturbation $\zeta$, which barring fine-tuning means
that it accounts for practically all of it. It follows that a curvaton-like
mechanism for generating $\zeta$ requires an alternative to slow roll such as
k-inflation. Second, accepting slow-roll inflation, the excursion of the
inflaton field is at least of order Planck scale. As a result, the flatness of
the inflaton presumably requires a shift symmetry.
I point out that if such is the case, the resulting potential is likely to
have at least approximately the quadratic form suggested in 1983 by Linde,
which is known to be compatible with the observed $r$ as well as the observed
spectral index $\ns$. The shift symmetry does not require supersymmetry. Also,
the big $H$ may rule out a GUT by restoring the symmetry and producing fatal
cosmic strings. The absence of a GUT would correspond to the absence of
superpartners for the Standard Model particles, which indeed have yet to be
found at the LHC.
It therefore seems quite possible that the quantum field theory chosen by
Nature is not supersymmetric.
|
Morphology of CMB fields -- effect of weak gravitational lensing | We study the morphology of the cosmic microwave background temperature and
polarization fields using the shape and alignment parameters, $\beta$ and
$\alpha$, that are constructed from the contour Minkowski tensor. The primary
goal of our paper is to understand the effect of weak gravitational lensing on
the morphology of the CMB fields. In order to isolate different physical
effects that can be potentially confused with the effect of lensing, we first
study the effect of varying the cosmology on $\alpha$ and $\beta$, and show
that they are relatively insensitive to variation of cosmological parameters.
Next we analyze the signatures of hemispherical anisotropy, and show that
information of such anisotropy in $\alpha$ gets washed out at small angular
scales and become pronounced only at large angular scales. For $\beta$ we find
characteristic distortions which vary with the field threshold. We then study
the effect of weak gravitational lensing using simulations of lensed
temperature and $E$ and $B$ modes. We quantify the distortion induced in the
fields across different angular scales. We find that lensing makes structures
of all fields increasingly more anisotropic as we probe down to smaller scales.
We find distinct behaviour of morphological distortions as a function of
threshold for the different fields. The effect is small for temperature and $E$
mode, while it is significantly large for $B$ mode. Further, we find that
lensing does not induce statistical anisotropy, as expected from the isotropic
distribution of large scale structure of matter. We expect that the results
obtained in this work will provide insights on the reconstruction of the
lensing potential.
|
The 9.7 and 18 um silicate absorption profiles towards diffuse and
molecular cloud lines-of-sight | Studying the composition of dust in the interstellar medium (ISM) is crucial
in understanding the cycle of dust in our galaxy. The mid-infrared spectral
signature of amorphous silicates, the most abundant dust species in the ISM, is
studied in different lines-of-sight through the Galactic plane, thus probing
different conditions in the ISM. We have analysed 10 spectra from the Spitzer
archive, of which 6 lines-of-sight probe diffuse interstellar medium material
and 4 probe molecular cloud material. The 9.7 um silicate absorption features
in 7 of these spectra were studied in terms of their shape and strength. In
addition, the shape of the 18 um silicate absorption features in 4 of the
diffuse sightline spectra were analysed. The 9.7 um silicate absorption bands
in the diffuse sightlines show a strikingly similar band shape. This is also
the case for all but one of the 18 um silicate absorption bands observed in
diffuse lines-of-sight. The 9.7 um bands in the 4 molecular sightlines show
small variations in shape. These modest variations in the band shape are
inconsistent with the interpretation of the large variations in
{\tau}_9.7/E(J-K) between diffuse and molecular sightlines in terms of silicate
grain growth. Instead, we suggest that the large changes in {\tau}_9.7 / E(J-K)
must be due to changes in E(J-K).
|
Asteroids for microhertz gravitational-wave detection | A major challenge for gravitational-wave (GW) detection in the $\mu$Hz band
is engineering a test mass (TM) with sufficiently low acceleration noise. We
propose a GW detection concept using asteroids located in the inner Solar
System as TMs. Our main purpose is to evaluate the acceleration noise of
asteroids in the $\mu$Hz band. We show that a wide variety of environmental
perturbations are small enough to enable an appropriate class of $\sim 10$
km-diameter asteroids to be employed as TMs. This would allow a sensitive GW
detector in the band $\text{(few)} \times 10^{-7} \text{Hz} \lesssim
f_{\text{GW}} \lesssim \text{(few)} \times 10^{-5} \text{Hz}$, reaching strain
$h_c \sim 10^{-19}$ around $f_{\text{GW}} \sim 10 \mu$Hz, sufficient to detect
a wide variety of sources. To exploit these asteroid TMs, human-engineered base
stations could be deployed on multiple asteroids, each equipped with an
electromagnetic (EM) transmitter/receiver to permit measurement of variations
in the distance between them. We discuss a potential conceptual design with two
base stations, each with a space-qualified optical atomic clock measuring the
round-trip EM pulse travel time via laser ranging. Tradespace exists to
optimize multiple aspects of this mission: for example, using a radio-ranging
or interferometric link system instead of laser ranging. This motivates future
dedicated technical design study. This mission concept holds exceptional
promise for accessing this GW frequency band.
|
Observational Limits on Type 1 AGN Accretion Rate in COSMOS | We present black hole masses and accretion rates for 182 Type 1 AGN in
COSMOS. We estimate masses using the scaling relations for the broad Hb, MgII,
and CIV emission lines in the redshift ranges 0.16<z<0.88, 1<z<2.4, and
2.7<z<4.9. We estimate the accretion rate using an Eddington ratio L_I/L_Edd
estimated from optical and X-ray data. We find that very few Type 1 AGN accrete
below L_I/L_Edd ~ 0.01, despite simulations of synthetic spectra which show
that the survey is sensitive to such Type 1 AGN. At lower accretion rates the
BLR may become obscured, diluted or nonexistent. We find evidence that Type 1
AGN at higher accretion rates have higher optical luminosities, as more of
their emission comes from the cool (optical) accretion disk with respect to
shorter wavelengths. We measure a larger range in accretion rate than previous
works, suggesting that COSMOS is more efficient at finding low accretion rate
Type 1 AGN. However the measured range in accretion rate is still comparable to
the intrinsic scatter from the scaling relations, suggesting that Type 1 AGN
accrete at a narrow range of Eddington ratio, with L_I/L_Edd ~ 0.1.
|
Cosmic Ray transport in turbulent magnetic field | Cosmic ray (CR) transport and acceleration is determined by the properties of
magnetic turbulence. Recent advances in MHD turbulence call for revisions in
the paradigm of cosmic ray transport. We use the models of magnetohydrodynamic
turbulence that were tested in numerical simulation, in which turbulence is
injected at large scale and cascades to to small scales. We shall address the
issue of the transport of CRs, both parallel and perpendicular to the magnetic
field. We shall demonstrate compressible fast modes are dominant cosmic ray
scatterer from both quasilinear and nonlinear theories. We shall also show that
the self-generated wave growth by CRs are constrained by preexisting turbulence
and discuss the process in detail in the context of shock acceleration at
supernova remnants and their implications. In addition, we shall dwell on the
nonlinear growth of kinetic gyroresonance instability of cosmic rays induced by
large scale compressible turbulence. This gyroresonance of cosmic rays on
turbulence is demonstrated an important scattering mechanism in addition to
direct interaction with the compressible turbulence. The feedback of the
instability on large scale turbulence should be included in future simulations.
|
Numerical integration of a relativistic two-body problem via a multiple
scales method | We offer an analytical study on the dynamics of a two-body problem perturbed
by small post-Newtonian relativistic term. We prove that, while the angular
momentum is not conserved, the motion is planar. We also show that the energy
is subject to small changes due to the relativistic effect. We also offer a
periodic solution to this problem, obtained by a method based of separation of
timescales. We demonstrate that our solution is more general than the method
developed in the book by Brumberg (1991). The practical applicability of this
model may be studies of the long-term evolution of relativistic binaries
(neutron stars or black holes).
|
The contribution of HI-bearing ultra-diffuse galaxies to the cosmic
number density of galaxies | We estimate the cosmic number density of the recently identified class of
HI-bearing ultra-diffuse sources (HUDs) based on the completeness limits of the
ALFALFA survey. These objects fall in the range $8.5 < \log
M_{\rm{HI}}/\rm{M_{\odot}} < 9.5$, have average $r$-band surface brightnesses
fainter than 24 mag arsec$^{-2}$, half-light radii greater than 1.5 kpc, and
are separated from neighbours by at least 350 kpc. We find that HUDs contribute
at most 6% of the population of HI-bearing dwarfs, have a total cosmic number
density of $(1.5 \pm 0.6) \times 10^{-3}$ $\rm{Mpc^{-3}}$, and an HI mass
density of $(6.0 \pm 0.8) \times 10^{5}$ $\rm{M_{\odot}\,Mpc^{-3}}$. We
estimate that this is similar to the total cosmic number density of UDGs in
groups and clusters, and conclude that the relation between the number of UDGs
hosted in a halo and the halo mass, must have a break below $M_{200} \sim
10^{12}$ $\rm{M_{\odot}}$ in order to account for the abundance of HUDs. The
distribution of the velocity widths of HUDs rises steeply towards low values,
indicating a preference for slow rotation rates. These objects have been absent
from measurements of the galaxy stellar mass function owing to their low
surface brightness. However, we estimate that due to their low number density,
their inclusion would constitute a correction of less than 1%. Comparison with
the Santa Cruz SAM shows that it produces HI-rich central UDGs that have
similar colours to HUDs, but these are currently produced in much great a
number. While previous results from this sample have favoured formation
scenarios where HUDs form in high spin parameter halos, comparisons with the
results of Rong et al. 2017, which invokes that formation mechanism, reveal
that this model produces an order of magnitude more field UDGs than we observe
in the HUD population.(Abridged)
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Direct Detection of Leptophilic Dark Matter in a Model with Radiative
Neutrino Masses | We consider an electro-weak scale model for Dark Matter (DM) and radiative
neutrino mass generation. Despite the leptophilic nature of DM with no direct
couplings to quarks and gluons, scattering with nuclei is induced at the 1-loop
level through photon exchange. Effectively, there are charge-charge,
dipole-charge and dipole-dipole interactions. We investigate the parameter
space consistent with constraints from neutrino masses and mixing, charged
lepton-flavour violation, perturbativity, and the thermal production of the
correct DM abundance, and calculate the expected event rate in DM direct
detection experiments. We show that current data from XENON100 start to
constrain certain regions of the allowed parameter space, whereas future data
from XENON1T has the potential to significantly probe the model.
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Spectral analysis of stellar orbits in a tidally induced bar | Using numerical analysis of fundamental frequencies we study the orbital
structure of a tidally induced bar formed in a simulated dwarf galaxy orbiting
a Milky Way-like host. We find that only about 10% of stars have frequencies
compatible with x1 orbits, the classical periodic orbits in a barred potential.
The rest of the stars follows box orbits parallel to the bar, with varying
degree of elongation.
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General relativistic non-ideal fluid equations for dark matter from a
truncated cumulant expansion | A new truncation scheme based on the cumulant expansion of the one-particle
phase-space distribution function for dark matter particles is developed.
Extending the method of moments in relativistic kinetic theory, we derive
evolution equations which supplement the covariant conservation of the
energy-momentum tensor and particle number current. Truncating the cumulant
expansion we obtain a closed, covariant and hyperbolic system of equations
which can be used to model the evolution of a general relativistic non-ideal
fluid. As a working example we consider a Friedmann-Lema\^itre-Robertson-Walker
cosmology with dynamic pressure and solve for the time evolution of the
effective equation of state parameter.
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Fossil Groups in the Millennium Simulation: Their environment and its
evolution | Fossil systems are defined to be X-ray bright galaxy groups with a
2-magnitude difference between their two brightest galaxies within half the
projected virial radius,and represent an interesting extreme of the population
of galaxy agglomerations.However,the physical conditions and processes leading
to their formation are still poorly constrained.We compare the outskirts of
fossil systems with that of normal groups to understand whether environmental
conditions play a significant role in their formation.We study galaxy groups in
both,numerical simulations and observations.We use a variety of statistical
tools including the spatial cross-correlation function and the local density
parameter \Delta_5 to probe differences in the density and structure of the
environments of normal and fossil systems in the Millennium simulation.We find
that the number density of galaxies surrounding fossil systems evolves from
greater than that observed around normal systems at z=0.69, to lower than the
normal systems by z=0.Both fossil and normal systems exhibit an increment in
their otherwise radially declining local density measure (\Delta_5) at
distances of order 2.5r_{vir} from the system centre.We show that this
increment is more noticeable for fossil systems than normal systems and
demonstrate that this difference is linked to the earlier formation epoch of
fossil groups.Despite the importance of the assembly time, we show that the
environment is different for fossil and non-fossil systems with similar masses
and formation times along their evolution.We also confirm that the physical
characteristics identified in the Millennium simulation can also be detected in
SDSS observations.Our results confirm the commonly held belief that fossil
systems assembled earlier than normal systems but also show that the
surroundings of fossil groups could be responsible for the formation of their
large magnitude gap.
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