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Chemical abundance scaling relations for multiple elements in z~2-3
star-forming galaxies | The chemical abundance patterns of gas and stars in galaxies are powerful
probes of galaxies' star formation histories and the astrophysics of galaxy
assembly but are challenging to measure with confidence in distant galaxies. In
this paper, we report the first measurements of the correlation between stellar
mass and multiple tracers of chemical enrichment (including O, N, and Fe) in
individual z~2-3 galaxies, using a sample of 195 star-forming galaxies from the
Keck Baryonic Structure Survey (KBSS). The galaxies' chemical abundances are
inferred using photoionization models capable of reconciling high-redshift
galaxies' observed extreme rest-UV and rest-optical spectroscopic properties.
We find that the stellar mass-O/H relation for our sample is relatively
shallow, with moderately large scatter, and is offset ~0.35 dex higher than the
corresponding stellar mass-Fe/H relation. The two relations have very similar
slopes, indicating a high level of alpha-enhancement -- with O/Fe approximately
2.2 times higher than solar O/Fe -- across two decades in stellar mass. The
stellar mass-N/H relation has the steepest slope and largest intrinsic scatter,
which likely results from the fact that many z~2 galaxies are observed near or
past the transition from "primary" to "secondary" N production and may reflect
uncertainties in the astrophysical origin of N. Together, these results suggest
that z~2 galaxies are old enough to have seen substantial enrichment from
intermediate mass stars, but are still young enough that Type Ia supernovae
have not had time to contribute significantly to their enrichment.
|
Signatures of Light Massive Relics on nonlinear structure formation | Cosmologies with Light Massive Relics (LiMRs) as a subdominant component of
the dark sector are well-motivated from a particle physics perspective, and can
also have implications for the $\sigma_8$ tension between early and late time
probes of matter clustering. The effects of LiMRs on the Cosmic Microwave
Background (CMB) and structure formation on large (linear) scales have been
investigated extensively. In this paper, we initiate a systematic study of the
effects of LiMRs on smaller, nonlinear scales using cosmological $N$-body
simulations; focusing on quantities relevant for photometric galaxy surveys.
For most of our study, we use a particular model of nonthermal LiMRs but the
methods developed easily generalize to a large class of models of LiMRs -- we
explicitly demonstrate this by considering the Dodelson-Widrow form of the
velocity distribution. We find that, in general, the effects of LiMR on small
scales are distinct from those of a $\Lambda$CDM universe, even when the value
of $\sigma_8$ is matched between the models. We show that weak lensing
measurements around massive clusters, between $\sim 0.1 h^{-1}$Mpc and $\sim 10
h^{-1}$Mpc, should have sufficient signal-to-noise in future surveys to
distinguish between $\Lambda$CDM and LiMR models that are tuned to fit both CMB
data and large (linear) scale structure data at late times. Furthermore, we
find that different LiMR cosmologies which are indistinguishable by
conventional linear probes can be distinguished by these probes if their
velocity distributions are sufficiently different. LiMR models can, therefore,
be best tested and constrained by jointly analyzing data from CMB and late-time
structure formation on both large \textit{and} small scales.
|
Probing High Scale Dirac Leptogenesis via Gravitational Waves from
Domain Walls | We propose a novel way of probing high scale Dirac leptogenesis, a viable
alternative to canonical leptogenesis scenario where the total lepton number is
conserved, keeping light standard model (SM) neutrinos purely Dirac. The
simplest possible seesaw mechanism for generating light Dirac neutrinos involve
heavy singlet Dirac fermions and a singlet scalar. In addition to unbroken
global lepton number, a discrete $Z_2$ symmetry is imposed to forbid direct
coupling between right and left chiral parts of light Dirac neutrino.
Generating light Dirac neutrino mass requires the singlet scalar to acquire a
vacuum expectation value (VEV) that also breaks the $Z_2$ symmetry, leading to
formation of domain walls in the early universe. These walls, if made unstable
by introducing a soft $Z_2$ breaking term, generate gravitational waves (GW)
with a spectrum characterized by the wall tension or the singlet VEV, and the
soft symmetry breaking scale. The scale of leptogenesis depends upon the
$Z_2$-breaking singlet VEV which is also responsible for the tension of the
domain wall, affecting the amplitude of GW produced from the collapsing walls.
We find that most of the near future GW observatories will be able to probe
Dirac leptogenesis scale all the way upto $10^{11}$ GeV.
|
A Multi-Wavelength Photometric Census of AGN and Star Formation Activity
in the Brightest Cluster Galaxies of X-ray Selected Clusters | Despite their reputation as being "red and dead", the unique environment
inhabited by Brightest Cluster Galaxies (BCGs) can often lead to a
self-regulated feedback cycle between radiatively cooling intracluster gas and
star formation and AGN activity in the BCG. However the prevalence of "active"
BCGs, and details of the feedback involved, are still uncertain. We have
performed an optical, UV and Mid-IR photometric analysis of the BCGs in 981
clusters at 0.03 < z < 0.5, selected from the ROSAT All Sky Survey. Using
Pan-STARRS PS1 3pi, GALEX and WISE survey data we look for BCGs with
photometric colours which deviate from that of the bulk population of passive
BCGs - indicative of AGN and/or star formation activity within the BCG. We find
that whilst the majority of BCGs are consistent with being passive, at least
14% of our BCGs show a significant colour offset from passivity in at least one
colour index. And, where available, supplementary spectroscopy reveals the
majority of these particular BCGs show strong optical emission lines. On
comparing BCG "activity" with the X-ray luminosity of the host cluster, we find
that BCGs showing a colour offset are preferentially found in the more X-ray
luminous clusters, indicative of the connection between BCG "activity" and the
intracluster medium.
|
Non-universal BBN bounds on electromagnetically decaying particles | In Poulin and Serpico [Phys. Rev. Lett. 114, 091101 (2015)] we have recently
argued that when the energy of a photon injected in the primordial plasma falls
below the pair-production threshold, the universality of the non-thermal photon
spectrum from the standard theory of electromagnetic cascades onto a photon
background breaks down. We showed that this could reopen or widen the parameter
space for an exotic solution to the 'lithium problem'. Here we discuss another
application, namely the impact that this has on non-thermal big bang
nucleosynthesis constraints from 4He, 3He and 2H, using the parametric example
of monochromatic photon injection of different energies. Typically, we find
tighter bounds than those existing in the literature, up to more than one order
of magnitude. As a consequence of the non-universality of the spectrum, the
energy-dependence of the photodissociation cross-sections is important. We also
compare the constraints obtained with current level and future reach of cosmic
microwave background spectral distortion bounds.
|
Higgs Inflation, Reheating and Gravitino Production in No-Scale
Supersymmetric GUTs | We extend our previous study of supersymmetric Higgs inflation in the context
of no-scale supergravity and grand unification, to include models based on the
flipped SU(5) and the Pati-Salam group. Like the previous SU(5) GUT model,
these yield a class of inflation models whose inflation predictions interpolate
between those of the quadratic chaotic inflation and Starobinsky-like
inflation, while avoiding tension with proton decay limits. We further analyse
the reheating process in these models, and derive the number of e-folds, which
is independent of the reheating temperature. We derive the corresponding
predictions for the scalar tilt and the tensor-to-scalar ratio in cosmic
microwave background perturbations, as well as discussing the gravitino
production following inflation.
|
Quenching of supermassive black hole growth around the apparent maximum
mass | Recent quasar surveys have revealed that supermassive black holes (SMBHs)
rarely exceed a mass of $M_{\rm BH} \sim {\rm a~few}\times10^{10}~M_{\odot}$
during the entire cosmic history. It has been argued that quenching of the BH
growth is caused by a transition of a nuclear accretion disk into an advection
dominated accretion flow, with which strong outflows and/or jets are likely to
be associated. We investigate a relation between the maximum mass of SMBHs and
the radio-loudness of quasars with a well-defined sample of $\sim 10^5$ quasars
at a redshift range of $0<z<2$, obtained from the Sloan Digital Sky Surveys DR7
catalog. We find that the number fraction of the radio-loud (RL) quasars
increases above a threshold of $M_{\rm BH} \simeq 10^{9.5}~M_{\odot}$,
independent of their redshifts. Moreover, the number fraction of RL quasars
with lower Eddington ratios (out of the whole RL quasars), indicating lower
accretion rates, increases above the critical BH mass. These observational
trends can be natural consequences of the proposed scenario of suppressing BH
growth around the apparent maximum mass of $\sim 10^{10}~M_{\odot}$. The
ongoing VLA Sky Survey in radio will allow us to estimate of the exact number
fraction of RL quasars more precisely, which gives further insights to
understand quenching processes for BH growth.
|
Nonlinear superhorizon perturbations in Horava-Lifshitz gravity | We perform a fully nonlinear analysis of superhorizon perturbation in
Ho\v{r}ava-Lifshitz gravity, based on the gradient expansion method. We present
a concrete expression for the solution of gravity equations up to the second
order in the gradient expansion, and prove that the solution can be extended to
any order. The result provides yet another example for analogue of the
Vainshtein effect: the nonlinear solution is regular in the limit $\lambda\to
1$ and recovers general relativity coupled to dark matter at low energy.
Finally, we propose a definition of nonlinear curvature perturbation ${\cal R}$
in Ho\v{r}ava-Lifshitz gravity and show that it is conserved up to the first
order in the gradient expansion.
|
Confirmation of G6.31+0.54 as a part of a Galactic supernova remnant | A combination of archival multi-frequency radio observations with narrow-band
HAlpha optical imagery and new confirmatory optical spectroscopy have shown
that candidate supernova remnant G6.31+0.54 can now be confirmed as part of a
Galactic supernova remnant (SNR). It has non-thermal emission, an optical
emission line spectrum displaying shock excitation and standard SNR line
ratios, fine filamentary structures in HAlpha typical of optical remnants and
closely overlapping radio and optical footprints. An X-ray ROSAT source 1RXS
J175752.1-231105 was also found that matches the radio and optical emission
though a definite association is not proven. Nevertheless, taken together, all
these observed properties point to a clear SNR identification for this source.
We provide a rough estimate for the kinematic distance to G6.31+0.54 of
~4.5kpc. The detected optical filaments are some ~10arcminutes in extent (or
about 13 pc at the assumed distance). However, as only a partial arcuate
structure of the SNR can be seen (and not a full shell) the full angular extent
of the SNR is unclear. Hence the physical extent of the observed partial shell
is also difficult to estimate. If we assume an approximately circular shell
then a conservative fit to the optical arc shaped filaments gives an angular
diameter of ~20 arcminutes corresponding to a physical diameter of ~26 pc that
shows this to be an evolved remnant.
|
Inspecting the Cepheid parallax of pulsation using Gaia EDR3 parallaxes.
Projection factor and period-luminosity and period-radius relations | As primary anchors of the distance scale, Cepheid stars play a crucial role
in our understanding of the distance scale of the Universe because of their
period-luminosity relation. Determining precise and consistent parameters
(radius, temperature, color excess, and projection factor) of Cepheid pulsating
stars is therefore very important. With the high-precision parallaxes delivered
by the early third Gaia data release, we aim to derive various parameters of
Cepheid stars in order to calibrate the period-luminosity and period-radius
relations and to investigate the relation of period to p-factor. We applied an
implementation of the parallax-of-pulsation method through the algorithm called
Spectro-Photo-Interferometry of Pulsating Stars, which combines all types of
available data for a variable star in a global modeling of its pulsation. We
present the SPIPS modeling of a sample of 63 Galactic Cepheids. Adopting Gaia
EDR3 parallaxes as an input associated with the best available dataset, we
derive consistent values of parameters for these stars such as the radius,
multiband apparent magnitudes, effective temperatures, color excesses, period
changes, Fourier parameters, and the projection factor. We then derive new
calibrations of the period-luminosity and period-radius relations. After
investigating the dependences of the p-factor on the parameters of the stars,
we find a high dispersion of its values and no evidence of its correlation with
the period or with any other parameters. Statistically, the p-factor has an
average value of p=1.26$\pm$0.07, but with an unsatisfactory agreement. In
absence of any clear correlation between the p-factor and other quantities, the
best agreement is obtained under the assumption that the p-factor can take any
value in a band with a width of 0.15. This result highlights the need for a
further examination of the physics behind the p-factor.
|
Mid-infrared properties of nearby low-luminosity AGN at high angular
resolution | High spatial resolution mid-infrared (MIR) 12 \mum continuum imaging of
low-luminosity active galactic nuclei (LLAGN) obtained by VLT/VISIR is
presented. The goal of this investigation is to determine if the nuclear MIR
emission of LLAGN is consistent with the existence of a dusty obscuring torus.
A sample of 17 nearby LLAGN was selected and combined with archival VISIR data
of 9 additional LLAGN with available X-ray measurements. Of the 17 observed
LLAGN, 7 are detected, while upper limits are derived for the 10
non-detections. All detections except NGC 3125 appear point-like on a spatial
scale of \sim 0.35". The detections do not significantly deviate from the known
MIR-X-ray correlation but extend it by a factor of \sim 10 down to luminosities
< 10^41 erg/s with a narrow scatter. The latter is dominated by the
uncertainties in the X-ray luminosity. Interestingly, a similar correlation
with comparable slope but with a normalization differing by \sim 2.6 orders of
magnitude has been found for local starburst galaxies. In addition, the VISIR
data are compared with lower spatial resolution data from Spitzer/IRS and IRAS.
By using a scaled starburst template SED and the PAH 11.3 \mum emission line
the maximum nuclear star formation contamination to the VISIR photometry is
restricted to < 30% for 75% of the LLAGN. Exceptions are NGC 1097 and NGC 1566,
which may possess unresolved strong PAH emission. Furthermore, within the
uncertainties the MIR-X-ray luminosity ratio is unchanged over more than 4
orders of magnitude in accretion rate. These results are consistent with the
existence of the dusty torus in all observed LLAGN, although the jet or
accretion disk as origin of the MIR emission cannot be excluded. Finally, the
fact that the MIR-X-ray correlation holds for all LLAGN and Seyferts makes it a
very useful empirical tool for converting between the MIR and X-ray powers of
these nuclei.
|
SDSS J0025-10 at z=0.30: a (U)LIRG to optical QSO transition candidate | We have characterized the amount, spatial distribution and kinematics of the
molecular gas in the merging, double nucleus type 2 quasar SDSS J0025-10 at
z=0.30 using the CO(1-0) transition, based on data obtained with ATCA. This is
one of the scarce examples of quasar host galaxies where the CO emission has
been resolved spatially at any redshift. We infer a molecular gas mass M(H2) =
(6 +/- 1) x 1e9 Msun, which is distributed in two main reservoirs separated by
~9 kpc. ~60% of the gas is in the central region, associated with the QSO
nucleus and/or the intermediate region between the two nuclei. The other 40% is
associated with the northern tidal tail and is therefore unsettled.
With its high infrared luminosity L(IR) = (1.1 +/- 0.3) x 1e12 Lsun, SDSS
J0025-10 is an analogue of local luminous LIRGs and ULIRGs. On the other hand,
the clear evidence for an ongoing major merger of two gas rich progenitors, the
high L(IR) dominated by a starburst, the massive reservoir of molecular gas
with a large fraction still unsettled, and the quasar activity are all
properties consistent with a transition phase in the (U)LIRG-optical QSO
evolutionary scenario. We propose that we are observing the system during a
particular transient phase, prior to more advanced mergers where the nuclei
have already coalesced.
We argue that a fraction of the molecular gas reservoir is associated with a
tidal dwarf galaxy identified in the optical HST image at the tip of the
northern tidal tail. The formation of such structures is predicted by
simulations of colliding galaxies.
|
Thermal decoupling and the smallest subhalo mass in dark matter models
with Sommerfeld-enhanced annihilation rates | We consider dark matter consisting of weakly interacting massive particles
(WIMPs) and revisit in detail its thermal evolution in the early universe, with
a particular focus on models where the annihilation rate is enhanced by the
Sommerfeld effect. After chemical decoupling, or freeze-out, dark matter no
longer annihilates but is still kept in local thermal equilibrium due to
scattering events with the much more abundant standard model particles. During
kinetic decoupling, even these processes stop to be effective, which eventually
sets the scale for a small-scale cutoff in the matter density fluctuations.
Afterwards, the WIMP temperature decreases more quickly than the heat bath
temperature, which causes dark matter to reenter an era of annihilation if the
cross-section is enhanced by the Sommerfeld effect. Here, we give a detailed
and self-consistent description of these effects. As an application, we
consider the phenomenology of simple leptophilic models that have been
discussed in the literature and find that the relic abundance can be affected
by as much two orders of magnitude or more. We also compute the mass of the
smallest dark matter subhalos in these models and find it to be in the range of
about 10^{-10} to 10 solar masses; even much larger cutoff values are possible
if the WIMPs couple to force carriers lighter than about 100 MeV. We point out
that a precise determination of the cutoff mass allows to infer new limits on
the model parameters, in particular from gamma-ray observations of galaxy
clusters, that are highly complementary to existing constraints from g-2 or
beam dump experiments.
|
Axion Dark Matter | Axions are well-motivated dark matter candidates with simple cosmological
production mechanisms. They were originally introduced to solve the strong CP
problem, but also arise in a wide range of extensions to the Standard Model.
This Snowmass white paper summarizes axion phenomenology and outlines
next-generation laboratory experiments proposed to detect axion dark matter.
There are vibrant synergies with astrophysical searches and advances in
instrumentation including quantum-enabled readout, high-Q resonators and
cavities and large high-field magnets. This white paper outlines a clear
roadmap to discovery, and shows that the US is well-positioned to be at the
forefront of the search for axion dark matter in the coming decade.
|
Herschel Observations of Far-Infrared Cooling Lines in intermediate
Redshift (Ultra)-luminous Infrared Galaxies | We report the first results from a spectroscopic survey of the [CII] 158um
line from a sample of intermediate redshift (0.2<z<0.8) (ultra)-luminous
infrared galaxies, (U)LIRGs (LIR>10^11.5 Lsun), using the SPIRE-Fourier
Transform Spectrometer (FTS) on board the Herschel Space Observatory. This is
the first survey of [CII] emission, an important tracer of star-formation, at a
redshift range where the star-formation rate density of the Universe increases
rapidly. We detect strong [CII] 158um line emission from over 80% of the
sample. We find that the [CII] line is luminous, in the range (0.8-4)x10^(-3)
of the far-infrared continuum luminosity of our sources, and appears to arise
from photodissociation regions on the surface of molecular clouds. The
L[CII]/LIR ratio in our intermediate redshift (U)LIRGs is on average ~10 times
larger than that of local ULIRGs. Furthermore, we find that the L[CII]/LIR and
L[CII]/LCO(1-0) ratios in our sample are similar to those of local normal
galaxies and high-z star-forming galaxies. ULIRGs at z~0.5 show many
similarities to the properties of local normal and high-z star forming
galaxies. Our findings strongly suggest that rapid evolution in the properties
of the star forming regions of luminous infrared galaxies is likely to have
occurred in the last 5 billion years.
|
Primordial features due to a step in the inflaton potential | Certain oscillatory features in the primordial scalar power spectrum are
known to provide a better fit to the outliers in the cosmic microwave
background data near the multipole moments of $\ell=22$ and 40. These features
are usually generated by introducing a step in the popular, quadratic potential
describing the canonical scalar field. Such a model will be ruled out, if the
tensors remain undetected at a level corresponding to a tensor-to-scalar ratio
of, say, $r\simeq 0.1$. In this work, in addition to the popular quadratic
potential, we investigate the effects of the step in a small field model and a
tachyon model. With possible applications to future datasets (such as PLANCK)
in mind, we evaluate the tensor power spectrum exactly, and include its
contribution in our analysis. We compare the models with the WMAP (five as well
as seven-year), the QUaD and the ACBAR data. As expected, a step at a
particular location and of a suitable magnitude and width is found to improve
the fit to the outliers (near $\ell=22$ and 40) in all these cases. We point
out that, if the tensors prove to be small (say, $r\lesssim 0.01$), the
quadratic potential and the tachyon model will cease to be viable, and more
attention will need to be paid to examples such as the small field models.
|
The mmax-Mecl relation, the IMF and IGIMF: probabilistically sampled
functions? | We introduce a new method to measure the dispersion of mmax values of star
clusters and show that the observed sample of mmax is inconsistent with random
sampling from an universal stellar initial mass function (IMF) at a 99.9%
confidence level. The scatter seen in the mmax-Mecl data can be mainly (76%)
understood as being the result of observational uncertainties only. The scatter
of mmax values at a given Mecl are consistent with mostly measurement
uncertainties such that the true (physical) scatter may be very small.
Additionally, new data on the local star-formation regions Taurus-Auriga and
L1641 in Orion make stochastically formed stellar populations rather unlikely.
The data are however consistent with the local IGIMF (integrated galactic
stellar initial mass function) theory according to which a stellar population
is a sum of individual star-forming events each of which is described by well
defined physical laws. Randomly sampled IMFs and henceforth scale-free star
formation seems to be in contradiction to observed reality.
|
Radial stellar populations of AGN-host dwarf galaxies in SDSS-IV MaNGA
survey | Based on MaNGA integral field unit (IFU) spectroscopy we search 60 AGN
candidates, which have stellar masses
$M_{\star}\leqslant5\times10^{9}$$M_{\odot}$ and show AGN ionization signatures
in the BPT diagram. For these AGN candidates, we derive the spatially resolved
stellar population with the stellar population synthesis code STARLIGHT and
measure the gradients of the mean stellar age and metallicity. We find that the
gradients of mean stellar age (metallicity) of individual AGN-host dwarfs are
diverse in 0-0.5 Re, 0.5-1 Re and 0-1 Re. However, the overall behavior of the
mean stellar age (metallicity) profiles tend to be flat, as the median values
of the gradients are close to zero. We further study the overall behavior of
the mean stellar age (metallicity) by plotting the co-added radial profiles for
the AGN sample and compare with a control sample with similar stellar mass. We
find that the median values of light-weighted mean stellar ages of AGN sample
are as old as 2-3 ~Gyr within 2 Re,which are about 4-7 times older than those
of the control sample. Meanwhile, most of the AGN candidates are low-level
AGNs, as only eight sources have L[OIII]>$10^{39.5}$~erg~s$^{-1}$. Hence, the
AGNs in dwarf galaxies might accelerate the evolution of galaxies by
accelerating the consumption of the gas, resulting in an overall quenching of
the dwarf galaxies, and the AGNs also become weak due to the lack of gas. The
median values of mass-weighted mean stellar age of both samples within 2 $Re$
are similar and as old as about 10~Gyr, indicating that the stellar mass is
mainly contributed by old stellar populations.The gradients of co-added mean
stellar metallicity for both samples tend to be negative but close to zero, and
the similar mean stellar metallicity profiles for both samples indicate that
the chemical evolution of the host galaxy is not strongly influenced by the
AGN.
|
Spatially Resolved Outflows in a Seyfert Galaxy at z = 2.39 | We present the first spatially resolved analysis of rest-frame optical and UV
imaging and spectroscopy for a lensed galaxy at z = 2.39 hosting a Seyfert
active galactic nucleus (AGN). Proximity to a natural guide star has enabled
high signal-to-noise VLT SINFONI + adaptive optics observations of rest-frame
optical diagnostic emission lines, which exhibit an underlying broad component
with FWHM ~ 700 km/s in both the Balmer and forbidden lines. Measured line
ratios place the outflow robustly in the region of the ionization diagnostic
diagrams associated with AGN. This unique opportunity - combining gravitational
lensing, AO guiding, redshift, and AGN activity - allows for a magnified view
of two main tracers of the physical conditions and structure of the
interstellar medium in a star-forming galaxy hosting a weak AGN at cosmic noon.
By analyzing the spatial extent and morphology of the Ly-alpha and
dust-corrected H-alpha emission, disentangling the effects of star formation
and AGN ionization on each tracer, and comparing the AGN induced mass outflow
rate to the host star formation rate, we find that the AGN does not
significantly impact the star formation within its host galaxy.
|
A 31 GHz Survey of Low-Frequency Selected Radio Sources | The 100-m Robert C. Byrd Green Bank Telescope (GBT) and the Owens Valley
Radio Observatory (OVRO) 40-m radio telescope have been used to conduct a
survey of 3165 known extragalactic radio sources over 143 square degrees of the
sky. Target sources were selected from the NRAO VLA Sky Survey in fields
observed by the Cosmic Background Imager (CBI); most are extragalactic active
galactic nuclei (AGN) with 1.4 GHz flux densities of 3 to 10 mJy. The resulting
31 GHz catalogs are presented in full online. Using a Maximum-Likelihood
analysis to obtain an unbiased estimate of the distribution of the 1.4 to 31
GHz spectral indices of these sources, we find a mean 31 to 1.4 GHz flux ratio
of 0.110 +/- 0.003 corresponding to a spectral index of alpha=-0.71 +/- 0.01 (S
~ nu^alpha); 9.0 +/- 0.8 % of sources have alpha > -0.5 and 1.2 +/- 0.2 % have
alpha > 0. By combining this spectral index distribution with 1.4 GHz source
counts we predict 31 GHz source counts in the range 1 mJy < S_31 < 4 mJy,
N(>S_31) = (16.7 +/- 1.7) deg^2 (S_31/1 mJy)^(-0.80 +/- 0.07). We also assess
the contribution of mJy-level (S_1.4 < 3.4 mJy) radio sources to the 31 GHz CMB
power spectrum, finding a mean power of ell (ell+1) C^src_ell/(2 pi) = 44 +/-
14 micro-Kelvin^2 and a 95% upper limit of 80 micro-Kelvin^2 at ell = 2500.
Including an estimated contribution of 12 micro-Kelvin^2 from the population of
sources responsible for the turn-up in counts below S_1.4 = 1 mJy this amounts
to 21 +/- 7 % of what is needed to explain the CBI high-ell excess signal, 275
+/- 63 micro-Kelvin^2. These results are consistent with other measurements of
the 31 GHz point source foreground.
|
After LUX: The LZ Program | The LZ program consists of two stages of direct dark matter searches using
liquid Xe detectors. The first stage will be a 1.5-3 tonne detector, while the
last stage will be a 20 tonne detector. Both devices will benefit tremendously
from research and development performed for the LUX experiment, a 350 kg liquid
Xe dark matter detector currently operating at the Sanford Underground
Laboratory. In particular, the technology used for cryogenics and electrical
feedthroughs, circulation and purification, low-background materials and
shielding techniques, electronics, calibrations, and automated control and
recovery systems are all directly scalable from LUX to the LZ detectors.
Extensive searches for potential background sources have been performed, with
an emphasis on previously undiscovered background sources that may have a
significant impact on tonne-scale detectors. The LZ detectors will probe
spin-independent interaction cross sections as low as 5E-49 cm2 for 100 GeV
WIMPs, which represents the ultimate limit for dark matter detection with
liquid xenon technology.
|
Seeds of Life in Space SOLIS. IX. Chemical segregation of $\rm SO_2$ and
SO toward the low-mass protostellar shocked region of L1157 | We present observations of SO and $\rm SO_2$ lines toward the shocked regions
along the L1157 chemically rich outflow, taken in the context of the Seeds Of
Life In Space IRAM-NOrthern Extended Millimeter Array Large Program, and
supported by data from Submillimeter Array and IRAM-30 m telescope at 1.1--3.6
mm wavelengths. We simultaneously analyze, for the first time, all of the
brightest shocks in the blueshifted lobe, namely, B0, B1, and B2. We found the
following. (1) SO and $\rm SO_2$ may trace different gas, given that the
large(-scale) velocity gradient analysis indicates for $\rm SO_2$ a volume
density ($\rm 10^5\text{--}10^6\,cm^{-3}$) denser than that of the gas emitting
in SO by a factor up to an order of magnitude. (2) Investigating the 0.1 pc
scale field of view, we note a tentative gradient along the path of the
precessing jet. More specifically, $\rm \chi({SO/SO_2})$ decreases from the
B0-B1 shocks to the older B2. (3) At a linear resolution of 500--1400 au, a
tentative spatial displacement between the two emitting molecules is detected,
with the SO peak closer (with respect to $\rm SO_2$) to the position where the
recent jet is impinging on the B1 cavity wall. Our astrochemical modeling shows
that the SO and $\rm SO_2$ abundances evolve on timescales less than about 1000
years. Furthermore, the modeling requires high abundances ($2\times10^{-6}$) of
both $\rm H_2S/H$ and S/H injected in the gas phase due to the shock
occurrence, so pre-frozen OCS only is not enough to reproduce our new
observations.
|
Optical selection bias and projection effects in stacked galaxy cluster
weak lensing | Cosmological constraints from current and upcoming galaxy cluster surveys are
limited by the accuracy of cluster mass calibration. In particular, optically
identified galaxy clusters are prone to selection effects that can bias the
weak lensing mass calibration. We investigate the selection bias of the stacked
cluster lensing signal associated with optically selected clusters, using as
case study clusters identified by the redMaPPer algorithm in the Buzzard
simulations. We find that at a given cluster halo mass, the residuals of
redMaPPer richness and weak lensing signal are positively correlated. As a
result, for a given richness selection, the stacked lensing signal is biased
high compared with what we would expect from the underlying halo mass
probability distribution. The cluster lensing selection bias can thus lead to
overestimated mean cluster mass and biased cosmology results. We show that this
selection bias largely originates from spurious member galaxies within +/-20 to
60 Mpc/h along the line of sight, highlighting the importance of quantifying
projection effects associated with the broad redshift distribution of member
galaxies in photometric cluster surveys. While our results qualitatively agree
with those in the literature, precise quantitative modelling of selection bias
is needed to achieve the goals of cluster lensing cosmology. An accurate
calibration of the cluster lensing selection bias will require synthetic
catalogues covering a wide range of galaxy-halo connection models.
|
Pair-matching of radio-loud and radio-quiet AGNs | Active galactic nuclei (AGNs) are known to cover an extremely broad range of
radio luminosities and the spread of their radio-loudness is very large at any
value of the Eddington ratio. This implies very diverse jet production
efficiencies which can result from the spread of the black hole spins and
magnetic fluxes. Magnetic fluxes can be developed stochastically in the
innermost zones of accretion discs, or can be advected to the central regions
prior to the AGN phase. In the latter case there could be systematic
differences between the properties of galaxies hosting radio-loud (RL) and
radio-quiet (RQ) AGNs. In the former case the differences should be negligible
for objects having the same Eddington ratio. To study the problem we decided to
conduct a comparison study of host galaxy properties of RL and RQ AGNs. In this
study we selected type II AGNs from SDSS spectroscopic catalogues. Our RL AGN
sample consists of the AGNs appearing in the Best & Heckman (2012) catalogue of
radio galaxies. To compare RL and RQ galaxies that have the same AGN parameters
we matched the galaxies in black hole mass, Eddington ratio and redshift. We
compared several properties of the host galaxies in these two groups of objects
like galaxy mass, colour, concentration index, line widths, morphological type
and interaction signatures. We found that in the studied group RL AGNs are
preferentially hosted by elliptical galaxies while RQ ones are hosted by
galaxies of later type. We also found that the fraction of interacting galaxies
is the same in both groups of AGNs. These results suggest that the magnetic
flux in RL AGNs is advected to the nucleus prior to the AGN phase.
|
Modeling X-ray binary evolution in normal galaxies: Insights from SINGS | We present the largest-scale comparison to date between observed
extragalactic X-ray binary (XRB) populations and theoretical models of their
production. We construct observational X-ray luminosity functions (oXLFs) using
Chandra observations of 12 late-type galaxies from the Spitzer Infrared Nearby
Galaxy Survey (SINGS). For each galaxy, we obtain theoretical XLFs (tXLFs) by
combining XRB synthetic models, constructed with the population synthesis code
StarTrack, with observational star formation histories (SFHs). We identify
highest-likelihood models both for individual galaxies and globally, averaged
over the full galaxy sample. Individual tXLFs successfully reproduce about half
of oXLFs, but for some galaxies we are unable to find underlying source
populations, indicating that galaxy SFHs and metallicities are not well matched
and/or XRB modeling requires calibration on larger observational samples. Given
these limitations, we find that best models are consistent with a product of
common envelope ejection efficiency and central donor concentration ~=0.1, and
a 50% uniform -- 50% "twins" initial mass-ratio distribution. We present and
discuss constituent subpopulations of tXLFs according to donor, accretor and
stellar population characteristics. The galaxy-wide X-ray luminosity due to
low-mass and high-mass XRBs, estimated via our best global model tXLF, follows
the general trend expected from the L_x - star formation rate and L_x - stellar
mass relations of Lehmer et al 2010. Our best models are also in agreement with
modeling of the evolution both of XRBs over cosmic time and of the galaxy X-ray
luminosity with redshift.
|
The Parker instability in axisymmetric filaments: Final equilibria with
longitudinal magnetic field | We study the final equilibrium states of the Parker instability arising from
an initially unstable cylindrical equilibrium configuration of gas in the
presence of a radial gravitational field and a longitudinal magnetic field. The
aim of this work is to compare the properties of the nonlinear final equilibria
with those found in a system with Cartesian geometry. Maps of the density and
magnetic field lines, when the strength of the gravitational field is constant,
are given in both geometries. In the axisymmetric model, the magnetic field
tends to expand in radius, forming magnetic arcades, while knots of gas are
formed because the plasma drains radially and strangulates the magnetic field
lines, leading to the formation of magnetic bottlenecks. We find that the
magnetic buoyancy and the drainage of gas along field lines are less efficient
under axial symmetry than in a Cartesian atmosphere. As a consequence, the
column density enhancement arising in gas condensations in the
axially-symmetric model is smaller than in Cartesian geometry. The
magnetic-to-gas pressure ratio in the final state takes more extreme values in
the Cartesian model. Models with non-uniform radial gravity are also discussed.
|
Atomic beings and the discovery of gravity | We aim to bring a new perspective about some aspects of the current research
in Cosmology. We start with a brief introduction about the main developments of
the field in the last century; then we introduce an analogy that shall
elucidate the main difficulties that observational sciences involve, which
might be part of the issue related to some of the contemporary cosmological
problems. The analogy investigates how microscopic beings could ever discover
and understand gravitational phenomena.
|
Extensions to the halo occupation distribution model for more accurate
clustering predictions | We test different implementations of the halo occupation distribution (HOD)
model to reconstruct the spatial distribution of galaxies as predicted by a
publicly available semi-analytical model (SAM). We compare the measured
two-point correlation functions of the HOD mock catalogues and the SAM samples
to quantify the fidelity of the reconstruction. We use fixed number density
galaxy samples selected according to stellar mass or star formation rate (SFR).
We develop three different schemes to populate haloes with galaxies with
increasing complexity, considering the scatter of the satellite HOD as an
additional parameter in the modelling. We first modify the SAM output, removing
assembly bias and using a standard Navarro-Frenk-White density profile for the
satellite galaxies as the target to reproduce with our HOD mocks. We find that
all models give similar reproductions of the two-halo contribution to the
clustering signal, but there are differences in the one-halo term. In
particular, the HOD mock reproductions work equally well using either the HOD
of central and satellites separately or using a model that also accounts for
whether or not the haloes contain a central galaxy. We find that the HOD
scatter does not have an important impact on the clustering predictions for
stellar mass selected samples. For SFR selections, we obtain the most accurate
results assuming a negative binomial distribution for the number of satellites
in a halo. The scatter in the satellites HOD is a key consideration for HOD
mock catalogues that mimic ELG or SFR selected samples in future galaxy
surveys.
|
Fab Four: When John and George play gravitation and cosmology | Scalar-tensor theories of gravitation have recently regained a great interest
after the discovery of the Chameleon mechanism and of the Galileon models. The
former allows, in principle, to reconcile the presence of cosmological scalar
fields with the constraints from experiments at the Solar System scale. The
latter open up the possibility of building inflationary models that, among
other things, do not need ad hoc potentials. Further generalizations have
finally led to the most general tensor-scalar theory, recently dubbed the "Fab
Four", with only first and second order derivatives of the fields in the
equations of motion and that self-tune to a vanishing cosmological constant.
This model has a very rich phenomenology that needs to be explored and
confronted with experimental data in order to constrain a very large parameter
space. In this paper, we present some results regarding a subset of the theory
named "John", which corresponds to a non-minimal derivative coupling between
the scalar field and the Einstein tensor in the action. We show that this
coupling gives rise to an inflationary model with very unnatural initial
conditions. Thus, we include a non-minimal, but non-derivative, coupling
between scalar field and Ricci scalar, a term named "George" in the Fab Four
terminology. In this way, we find a more sensible inflationary model, and, by
performing a post-newtonian expansion of spherically symmetric solutions, we
derive the set of equations that constrain the parameter space with data from
experiments in the solar system.
|
Megamaser detection and nuclear obscuration in Seyfert galaxies | We revisit the relation between H2O maser detection rate and nuclear
obscuration for a sample of 114 Seyfert galaxies, drawn from the CfA, 12um and
IRAS F25/F60 catalogs. These sources have mid-infrared spectra from the Spitzer
Space Telescope and they are searched for X-ray and [O III], 5007Angstrom
fluxes from the literature. We use the strength of the [O IV], 25.9um emission
line as tracer for the intrinsic AGN strength. After normalization by [O IV]
the observed X-ray flux provides information about X-ray absorption. The
distribution of X-ray / [O IV] flux ratios is significantly different for
masers and non-masers: The maser detected Seyfert-2s (Sy 1.8-2.0) populate a
distinct X-ray / [O IV] range which is, on average, about a factor four lower
than the range of Seyfert-2 non-masers and about a factor of ten lower than the
range of Seyfert-1s (Sy 1.0-1.5). Non-masers are almost equally distributed
over the entire X-ray / [O IV] range. This provides evidence that high nuclear
obscuration plays a crucial role for the probability of maser detection.
Furthermore, after normalization with [O IV], we find a similar but weaker
trend for the distribution of the maser detection rate with the absorption of
the 7um dust continuum. This suggests that the obscuration of the 7 um
continuum occurs on larger spatial scales than that of the X-rays. Hence, in
the AGN unified model, at moderate deviation from edge-on, the 7um dust
absorption may occur without proportionate X-ray absorption. The absorption of
[O III] appears unrelated to maser detections. The failure to detect masers in
obscured AGN is most likely due to insufficient observational sensitivity.
|
Prospects for measuring dark matter microphysics with observations of
dwarf spheroidal galaxies | Dark matter annihilation in dwarf spheroidal (dSph) galaxies near the Milky
Way has the potential to produce a detectable signature in gamma-rays. The
amplitude of this signal depends on the dark matter density in a dSph, the dark
matter particle mass, the number of photons produced in an annihilation, and
the possibly velocity-dependent dark matter annihilation cross section. We
argue that if the amplitude of the annihilation signal from multiple dSphs can
be measured, it is possible to determine the velocity-dependence of the
annihilation cross section. However, we show that doing so will require
improved constraints on the dSph density profiles, including control of
possible sources of systematic uncertainty. Making reasonable assumptions about
future improvements, we make forecasts for the ability of current and future
experiments -- including Fermi, CTA and AMEGO -- to constrain the dark matter
annihilation velocity dependence.
|
zCOSMOS 10k-bright spectroscopic sample: exploring mass and environment
dependence in early-type galaxies | We present the analysis of the U-V rest-frame color distribution and some
spectral features as a function of mass and environment for two sample of
early-type galaxies up to z=1 extracted from the zCOSMOS spectroscopic survey.
The first sample ("red galaxies") is defined with a photometric classification,
while the second ("ETGs") by combining morphological, photometric, and
spectroscopic properties to obtain a more reliable sample. We find that the
color distribution of red galaxies is not strongly dependent on environment for
all mass bins, with galaxies in overdense regions redder than galaxies in
underdense regions with a difference of 0.027\pm0.008 mag. The dependence on
mass is far more significant, with average colors of massive galaxies redder by
0.093\pm0.007 mag than low-mass galaxies throughout the entire redshift range.
We study the color-mass relation, finding a mean slope 0.12\pm0.005, while the
color-environment relation is flatter, with a slope always smaller than 0.04.
The spectral analysis that we perform on our ETGs sample is in good agreement
with our photometric results: we find for D4000 a dependence on mass between
high and low-mass galaxies, and a much weaker dependence on environment
(respectively a difference of of 0.11\pm0.02 and of 0.05\pm0.02); for the
equivalent width of H{\delta}we measure a difference of 0.28\pm0.08 {\AA}across
the same mass range and no significant dependence on environment.By analyzing
the lookback time of early-type galaxies, we support the possibility of a
downsizing scenario, in which massive galaxies with a stronger D4000 and an
almost constant equivalent width of $H\delta$ formed their mass at higher
redshift than lower mass ones. We also conclude that the main driver of galaxy
evolution is the galaxy mass, the environment playing a subdominant role.
|
The SDSS Coadd: Cosmic Shear Measurement | Stripe 82 in the Sloan Digital Sky Survey was observed multiple times,
allowing deeper images to be constructed by coadding the data. Here we analyze
the ellipticities of background galaxies in this 275 square degree region,
searching for evidence of distortions due to cosmic shear. The E-mode is
detected in both real and Fourier space with $>5$-$\sigma$ significance on
degree scales, while the B-mode is consistent with zero as expected. The
amplitude of the signal constrains the combination of the matter density
$\Omega_m$ and fluctuation amplitude $\sigma_8$ to be $\Omega_m^{0.7}\sigma_8 =
0.252^{+0.032}_{-0.052}$.
|
Artificial Neural Networks for cosmic gamma-ray propagation in the
Universe | We explore the potential of an artificial neural network (ANN) based method
intelligence to probe the propagation of cosmic $\gamma$-ray photons in the
extragalactic Universe. The journey of $\gamma$-rays emitted from a distant
source like blazar to the observer at the Earth is impeded by the absorption
through the interaction with the extragalactic background light (EBL), leading
to an electron-positron pair production. This process dominates for gamma ray
photons with energy above 10 GeV propagating over the cosmological distances.
The effect of $\gamma$-ray attenuation is characterized by a physical quantity
called \emph{optical depth}, which strongly depends on the $\gamma$-ray photon
energy, redshift of the source, and density of the EBL photons. We estimate the
optical depth values for $\gamma$-ray energies above 10 GeV emitted from the
sources at redshifts in the range 0.01 to 1 using three different and most
promising EBL models. These optical depth estimates are randomly divided into
two data sets for training and testing of the ANN using energy, redshift as
inputs and optical depth as output. The optimization of ANN-performance for
each EBL model employs standard back-propagation (BP) and radial-basis function
(RBF) algorithms. The performance of the ANN model using the RBF is found to be
superior to the BP method. In particular, the RBF-ANN with 40 neurons in the
hidden layer corresponding to the EBL model proposed by Finke et al. (2010)
shows the best performance for the propagation of $\gamma$-rays in the
Universe.
|
Photometric redshifts for the next generation of deep radio continuum
surveys - I: Template fitting | We present a study of photometric redshift performance for galaxies and
active galactic nuclei detected in deep radio continuum surveys. Using two
multi-wavelength datasets, over the NOAO Deep Wide Field Survey Bo\"otes and
COSMOS fields, we assess photometric redshift (photo-z) performance for a
sample of $\sim 4,500$ radio continuum sources with spectroscopic redshifts
relative to those of $\sim 63,000$ non radio-detected sources in the same
fields. We investigate the performance of three photometric redshift template
sets as a function of redshift, radio luminosity and infrared/X-ray properties.
We find that no single template library is able to provide the best performance
across all subsets of the radio detected population, with variation in the
optimum template set both between subsets and between fields. Through a
hierarchical Bayesian combination of the photo-z estimates from all three
template sets, we are able to produce a consensus photo-z estimate which equals
or improves upon the performance of any individual template set.
|
Measuring oxygen abundances from stellar spectra without oxygen lines | Oxygen is the most abundant "metal" element in stars and in the cosmos. But
determining oxygen abundances in stars has proven challenging, because of the
shortage of detectable atomic oxygen lines in their optical spectra as well as
observational and theoretical complications with these lines (e.g., blends, 3D,
non-LTE). Nonetheless, Ting et al. (2017) were recently able to demonstrate
that oxygen abundances can be determined from low-resolution (R$\simeq$2000)
optical spectra. Here we investigate the physical processes that enable such a
measurement for cool stars, such as K-giants. We show that the strongest
spectral diagnostics of oxygen come from the CNO atomic-molecular network, but
are manifested in spectral features that do not involve oxygen. In the outer
atmosphere layers most of the carbon is locked up in CO, and changes to the
oxygen abundance directly affect the abundances of all other carbon-bearing
molecules, thereby changing the strength of CH, CN, and C$_2$ features across
the optical spectrum. In deeper atmosphere layers most of the carbon is in
atomic form, and any change in the oxygen abundance has little effect on the
other carbon-bearing molecules. The key physical effect enabling such oxygen
abundance measurements is that spectral features in the optical arise from both
the CO-dominant and the atomic carbon-dominant regions, providing
non-degenerate constraints on both C and O. Beyond the case at hand, the
results show that physically sound abundances measurements need not be limited
to those elements that have observable lines themselves.
|
Ultraluminous X-ray bursts in two ultracompact companions to nearby
elliptical galaxies | An X-ray flaring source was found near the galaxy NGC 4697. Two flares were
seen, separated by four years. The flux increased by a factor of 90 on a
timescale of about one minute. Both flares were very brief. There is no optical
counterpart at the position of the flares, but if the source was at the
distance of NGC 4697, the luminosities were 10^39 erg/s. Here we report the
results of a search of archival X-ray data for 70 nearby galaxies looking for
similar such flares. We found two flaring sources in globular clusters or
ultra-compact dwarf companions of parent elliptical galaxies. One source flared
once to a peak luminosity of 9 x 10^40 erg/s, while the other flared five times
to 10^40 erg/s. All of the flare rise times were <1 minute, and they then
decayed over about an hour. When not flaring, the sources appear to be normal
accreting neutron star or black hole X-ray binaries, but they are located in
old stellar populations, unlike the magnetars, anomalous X-ray pulsars or soft
gamma repeaters that have repetitive flares of similar luminosities.
|
On the nature of dust clouds in the region towards M81 and NGC3077 | There is some controversy on the nature of dust clouds found in direction of
the interacting galaxy triplett M81, M82, and NGC3077. Are they associated with
the tidal arms seen in HI around those galaxies or are they simply Galactic
foreground clouds? Data from the SPIRE instrument onboard HERSCHEL and MIPS
onboard of SPITZER are used to derive physical parameters for the dust clouds.
These observions are compared to CO clouds previously mapped with the IRAM and
the FCRAO radio telescopes.SPIRE and MIPS maps show several dust clouds north
of M81 and south of NGC3077. Modelling of the dust emission provides total
hydrogen column densities between 1.5 and 5.0 * 10^20 cm^-2. Dust temperatures
are between 13 to 17K. No significant difference in the dust emission can be
found between individual clouds. It is shown that CO line emission provides the
best clues on the origin of those clouds. Most of the clouds seen towards M81
are associated with small-area molecular structures (SAMS), i.e. tiny CO clouds
of Galactic origin. The clouds seen towards NGC3077 are partly associated with
the tidal arms and are partly in the Galactic foreground associated with SAMS.
|
Propagation of Highly Efficient Star Formation in NGC 7000 | We surveyed the (1,1), (2,2), and (3,3) lines of NH3 and the H2O maser toward
the molecular cloud L935 in the extended HII region NGC 7000 with an angular
resolution of 1.6' using the Kashima 34-m telescope. We found five clumps in
the NH3 emission with a size of 0.2--1 pc and mass of 9--452 M_sun. The
molecular gas in these clumps has a similar gas kinetic temperature of 11--15 K
and a line width of 1--2 km/s. However, they have different star formation
activities such as the concentration of T-Tauri type stars and the association
of H2O maser sources. We found that these star formation activities are related
to the geometry of the HII region. The clump associated with the T-Tauri type
star cluster has a high star formation efficiency of 36--62%. This clump is
located near the boundary of the HII region and molecular cloud. Therefore, we
suggest that the star formation efficiency increases because of the triggered
star formation.
|
Fast likelihood-free cosmology with neural density estimators and active
learning | Likelihood-free inference provides a framework for performing rigorous
Bayesian inference using only forward simulations, properly accounting for all
physical and observational effects that can be successfully included in the
simulations. The key challenge for likelihood-free applications in cosmology,
where simulation is typically expensive, is developing methods that can achieve
high-fidelity posterior inference with as few simulations as possible.
Density-estimation likelihood-free inference (DELFI) methods turn inference
into a density estimation task on a set of simulated data-parameter pairs, and
give orders of magnitude improvements over traditional Approximate Bayesian
Computation approaches to likelihood-free inference. In this paper we use
neural density estimators (NDEs) to learn the likelihood function from a set of
simulated datasets, with active learning to adaptively acquire simulations in
the most relevant regions of parameter space on-the-fly. We demonstrate the
approach on a number of cosmological case studies, showing that for typical
problems high-fidelity posterior inference can be achieved with just
$\mathcal{O}(10^3)$ simulations or fewer. In addition to enabling efficient
simulation-based inference, for simple problems where the form of the
likelihood is known, DELFI offers a fast alternative to MCMC sampling, giving
orders of magnitude speed-up in some cases. Finally, we introduce
\textsc{pydelfi} -- a flexible public implementation of DELFI with NDEs and
active learning -- available at \url{https://github.com/justinalsing/pydelfi}.
|
Science with a lunar low-frequency array: from the dark ages of the
Universe to nearby exoplanets | Low-frequency radio astronomy is limited by severe ionospheric distortions
below 50 MHz and complete reflection of radio waves below 10-30 MHz. Shielding
of man-made interference from long-range radio broadcasts, strong natural radio
emission from the Earth's aurora, and the need for setting up a large
distributed antenna array make the lunar far side a supreme location for a
low-frequency radio array. A number of new scientific drivers for such an
array, such as the study of the dark ages and epoch of reionization,
exoplanets, and ultra-high energy cosmic rays, have emerged and need to be
studied in greater detail. Here we review the scientific potential and
requirements of these and other new scientific drivers and discuss the
constraints for various lunar surface arrays. In particular we describe
observability constraints imposed by the interstellar and interplanetary
medium, calculate the achievable resolution, sensitivity, and confusion limit
of a dipole array using general scaling laws, and apply them to various
scientific questions. Whichever science is deemed most important, pathfinder
arrays are needed to test the feasibility of these experiments in the not too
distant future. Lunar low-frequency arrays are thus a timely option to
consider, offering the potential for significant new insights into a wide range
of today's crucial scientific topics. This would open up one of the last
unexplored frequency domains in the electromagnetic spectrum.
|
Hybrid Inflation Revisited in Light of WMAP5 | We study the effects of including one-loop radiative corrections in a
non-supersymmetric hybrid inflationary model. These corrections can arise from
Yukawa couplings between the inflaton and right-handed neutrinos, and induce a
maximum in the potential which admits hilltop-type solutions in addition to the
standard hybrid solutions. We obtain a red-tilted spectral index $n_s$,
consistent with WMAP5 data, for sub-Planckian values of the field. This is in
contrast to the tree level hybrid analysis, in which a red-tilted spectrum is
achieved only for trans-Planckian values of the field. Successful reheating is
obtained at the end of the inflationary phase via conversion of the inflaton
and waterfall fields into right-handed neutrinos, whose subsequent decay can
explain the observed baryon asymmetry via leptogenesis.
|
The SONYC survey: Towards a complete census of brown dwarfs in star
forming regions | SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey
program to provide a census of the substellar population in nearby star forming
regions. We have conducted deep optical and near-infrared photometry in five
young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3),
combined with proper motions, and followed by extensive spectroscopic campaigns
with Subaru and VLT, in which we have obtained more than 700 spectra of
candidate low-mass objects. We have identified and characterized more than 60
new substellar objects, among them a handful of objects with masses close to,
or below the Deuterium burning limit. Through SONYC and surveys by other
groups, the substellar IMF is now well characterized down to ~ 5 - 10 MJup, and
we find that the ratio of the number of stars with respect to brown dwarfs lies
between 2 and 6. A comprehensive survey of NGC 1333 reveals that, down to
~5MJup, free-floating objects with planetary masses are 20-50 times less
numerous than stars, i.e. their total contribution to the mass budget of the
clusters can be neglected.
|
Constraint on a varying proton-to-electron mass ratio from H2 and HD
absorption at z = 2.34 | Molecular hydrogen absorption in the damped Lyman-alpha system at z = 2.34
towards quasar Q1232+082 is analyzed in order to derive a constraint on a
possible temporal variation of the proton-to-electron mass ratio, mu, over
cosmological timescales. Some 106 H2 and HD transitions, covering the range
3290-3726 \AA, are analyzed with a comprehensive fitting technique, allowing
for the inclusion of overlapping lines associated with hydrogen molecules, the
atomic hydrogen lines in the Lyman-alpha forest as well as metal lines. The
absorption model, based on the most recent and accurate rest wavelength for H2
and HD transitions, delivers a value of dmu/mu = (19 +/- 9 +/- 5)x 10^(-6). An
attempt to correct the spectrum for possible long-range wavelength distortions
is made and the uncertainty on the distortion correction is included in the
total systematic uncertainty. The present result is an order of magnitude more
stringent than a previous measurement from the analysis of this absorption
system, based on a line-by-line comparison of only 12 prominent and isolated H2
absorption lines. This is consistent with other measurements of dmu/mu from 11
other absorption systems in showing a null variation of the proton-to-electron
mass ratio over a look-back time of 11 Gyrs.
|
Dark Halos of M31 and the Milky Way | Grand rotation curves (GRC) within ~400 kpc of M31 and the Milky Way were
constructed by combining disk rotation velocities and radial velocities of
satellite galaxies and globular clusters. The GRC for the Milky Way was revised
using the most recent Solar rotation velocity. The derived GRCs were
deconvolved into a de Vaucouleurs bulge, exponential disk, and a dark halo with
the Navarro-Frenk-White (NFW) density profile by the least chi-squares fitting.
Comparison of the best-fit parameters revealed similarity of the disks and
bulges of the two galaxies, whereas the dark halo mass of M31 was found to be
twice the Galaxy's. We show that the NFW model may be a realistic approximation
to the observed dark halos in these two giant spirals.
|
Investigating the effect of precession on searches for
neutron-star-black-hole binaries with Advanced LIGO | The first direct detection of neutron-star-black-hole binaries will likely be
made with gravitational-wave observatories. Advanced LIGO and Advanced Virgo
will be able to observe neutron-star-black-hole mergers at a maximum distance
of 900Mpc. To acheive this sensitivity, gravitational-wave searches will rely
on using a bank of filter waveforms that accurately model the expected
gravitational-wave signal. The angular momentum of the black hole is expected
to be comparable to the orbital angular momentum. This angular momentum will
affect the dynamics of the inspiralling system and alter the phase evolution of
the emitted gravitational-wave signal. In addition, if the black hole's angular
momentum is not aligned with the orbital angular momentum it will cause the
orbital plane of the system to precess. In this work we demonstrate that if the
effect of the black hole's angular momentum is neglected in the waveform models
used in gravitational-wave searches, the detection rate of $(10+1.4)M_{\odot}$
neutron-star--black-hole systems would be reduced by $33 - 37%$. The error in
this measurement is due to uncertainty in the Post-Newtonian approximations
that are used to model the gravitational-wave signal of neutron-star-black-hole
inspiralling binaries. We describe a new method for creating a bank of filter
waveforms where the black hole has non-zero angular momentum, but is aligned
with the orbital angular momentum. With this bank we find that the detection
rate of $(10+1.4)M_{\odot}$ neutron-star-black-hole systems would be reduced by
$26-33%$. Systems that will not be detected are ones where the precession of
the orbital plane causes the gravitational-wave signal to match poorly with
non-precessing filter waveforms. We identify the regions of parameter space
where such systems occur and suggest methods for searching for highly
precessing neutron-star-black-hole binaries.
|
The evolution of the scatter of the cosmic average color-magnitude
relation: Demonstrating consistency with the ongoing formation of elliptical
galaxies | We present first measurements of the evolution of the scatter of the cosmic
average early-type galaxy color-magnitude relation (CMR) from z=1 to the
present day, finding that it is consistent with models in which galaxies are
constantly being added to the red sequence through truncation of star formation
in blue cloud galaxies. We used a sample of over 700 red sequence,
structurally-selected early-type galaxies (defined to have Sersic index >2.5)
with redshifts 0<z<1 taken from the Extended Chandra Deep Field South (173
galaxies) and the Sloan Digital Sky Survey (550 galaxies), constructing
rest-frame U-V colors accurate to <0.04mag. We find that the scatter of the CMR
of cosmic average early-type galaxies is ~0.1mag in rest-frame U-V color at
0.05<z<0.75, and somewhat higher at z=1. We compared these observations with a
model in which new red sequence galaxies are being constantly added at the rate
required to match the observed number density evolution, and found that this
model predicts the correct CMR scatter and its evolution. Furthermore, this
model predicts approximately the correct number density of `blue spheroids' -
structurally early-type galaxies with blue colors - albeit with considerable
model dependence. Thus, we conclude that both the evolution of the number
density and colors of the early-type galaxy population paint a consistent
picture in which the early-type galaxy population grows significantly between
z=1 and the present day through the quenching of star formation in blue cloud
galaxies.
|
Galactic Winds with MUSE: A Direct Detection of FeII* Emission from a z
= 1.29 Galaxy | Emission signatures from galactic winds provide an opportunity to directly
map the outflowing gas, but this is traditionally challenging because of the
low surface brightness. Using deep observations (27 hours) of the Hubble Deep
Field South from the Multi Unit Spectroscopic Explorer (MUSE) instrument, we
identify signatures of an outflow in both emission and absorption from a
spatially resolved galaxy at z = 1.29 with a stellar mass M* = 8 x 10^9 Msun,
star formation rate SFR = 77 Msun/yr, and star formation rate surface
brightness 1.6 Msun/kpc^2 within the [OII] half-light radius R_1/2,[OII] = 2.76
+- 0.17 kpc. From a component of the strong resonant MgII and FeII absorptions
at -350 km/s, we infer a mass outflow rate that is comparable to the star
formation rate. We detect non-resonant FeII* emission, at lambda 2626, 2612,
2396, and 2365, at 1.2-2.4-1.5-2.7 x 10^-18 egs s-1 cm-2 respectively. These
flux ratios are consistent with the expectations for optically thick gas. By
combining the four non-resonant FeII* emission lines, we spatially map the
FeII* emission from an individual galaxy for the first time. The FeII* emission
has an elliptical morphology that is roughly aligned with the galaxy minor
kinematic axis, and its integrated half-light radius R_1/2,FeII* = 4.1 +- 0.4
kpc is 50% larger than the stellar continuum (R_1/2,* = 2.34 +- 0.17 kpc) or
the [OII] nebular line. Moreover, the FeII* emission shows a blue wing
extending up to -400 km/s, which is more pronounced along the galaxy minor
kinematic axis and reveals a C-shaped pattern in a p-v diagram along that axis.
These features are consistent with a bi-conical outflow.
|
Feedback from Central Black Holes in Elliptical Galaxies:
Two-dimensional Models Compared to One-dimensional Models | We extend the black hole (BH) feedback models of Ciotti, Ostriker, and Proga
to two dimensions. In this paper, we focus on identifying the differences
between the one-dimensional and two-dimensional hydrodynamical simulations. We
examine a normal, isolated $L_*$ galaxy subject to the cooling flow instability
of gas in the inner regions. Allowance is made for subsequent star formation,
Type Ia and Type II supernovae, radiation pressure, and inflow to the central
BH from mildly rotating galactic gas which is being replenished as a normal
consequence of stellar evolution. The central BH accretes some of the infalling
gas and expels a conical wind with mass, momentum, and energy flux derived from
both observational and theoretical studies. The galaxy is assumed to have low
specific angular momentum in analogy with the existing one-dimensional case in
order to isolate the effect of dimensionality. The code then tracks the
interaction of the outflowing radiation and winds with the galactic gas and
their effects on regulating the accretion. After matching physical modeling to
the extent possible between the one-dimensional and two-dimensional treatments,
we find essentially similar results in terms of BH growth and duty cycle
(fraction of the time above a given fraction of the Eddington luminosity). In
the two-dimensional calculations, the cool shells forming at 0.1--1 kpc from
the center are Rayleigh--Taylor unstable to fragmentation, leading to a
somewhat higher accretion rate, less effective feedback, and a more irregular
pattern of bursting compared to the one-dimensional case.
|
Multimessenger Astronomy and Astrophysics Synergies | A budget neutral strategy is proposed for NSF to lead the implementation of
multimessenger astronomy and astrophysics, as outlined in the Astro2010 Decadal
Survey. The emerging capabilities for simultaneous measurements of physical and
astronomical data through the different windows of electromagnetic, hadronic
and gravitational radiation processes call for a vigorous pursuit of new
synergies. The proposed approach is aimed at the formation of new
collaborations and multimessenger data-analysis, to transcend the scientific
inquiries made within a single window of observations. In view of budgetary
constraints, we propose to include the multimessenger dimension in the ranking
of proposals submitted under existing NSF programs.
|
Setting firmer constraints on the evolution of the most massive, central
galaxies from their local abundances and ages | There is still much debate surrounding how the most massive, central galaxies
in the local universe have assembled their stellar mass, especially the
relative roles of in-situ growth versus later accretion via mergers. In this
paper, we set firmer constraints on the evolutionary pathways of the most
massive central galaxies by making use of empirical estimates on their
abundances and stellar ages. The most recent abundance matching and direct
measurements strongly favour that a substantial fraction of massive galaxies
with Mstar>3x10^11 Msun reside at the centre of clusters with mass
Mhalo>3x10^13 Msun. Spectral analysis supports ages >10 Gyrs, corresponding to
a formation redshift z_form >2. We combine these two pieces of
observationally-based evidence with the mass accretion history of their host
dark matter haloes. We find that in these massive haloes, the stellar mass
locked up in the central galaxy is comparable to, if not greater than, the
total baryonic mass at z_form. These findings indicate that either only a
relatively minor fraction of their present-day stellar mass was formed in-situ
at z_form, or that these massive, central galaxies form in the extreme scenario
where almost all of the baryons in the progenitor halo are converted into
stars. Interestingly, the latter scenario would not allow for any substantial
size growth since the galaxy's formation epoch either via mergers or expansion.
We show our results hold irrespective of systematic uncertainties in stellar
mass, abundances, galaxy merger rates, stellar initial mass function, star
formation rate and dark matter accretion histories.
|
Measurement of Hubble constant with stellar-mass binary black holes | The direct detections of gravitational waves (GW) from merging binary black
holes (BBH) by aLIGO have brought us a new opportunity to utilize BBH for a
measurement of the Hubble constant. In this paper, we point out that there
exists a small number of BBH that gives significantly small sky localization
volume so that a host galaxy is uniquely identified. Then a redshift of a BBH
is obtained from a spectroscopic follow-up observation of the host galaxy.
Using these redshift-identified BBH, we show that the Hubble constant is
measured at a level of precision better than 1% with advanced detectors like
aLIGO at design sensitivity. Since a GW observation is completely independent
of other astrophysical means, this qualitatively new probe will help resolve a
well-known value discrepancy problem on the Hubble constant from cosmological
measurements and local measurements.
|
Constraints on neutrino mass in the scenario of vacuum energy
interacting with cold dark matter after Planck 2018 | In this work, we investigate the constraints on the total neutrino mass in
the scenario of vacuum energy interacting with cold dark matter (abbreviated as
I$\Lambda$CDM) by using the latest cosmological observations. We consider four
typical interaction forms, i.e., $Q=\beta H \rho_{\rm de}$, $Q=\beta H
\rho_{\rm c}$, $Q=\beta H_{0} \rho_{\rm de}$, and $Q=\beta H_{0} \rho_{\rm c}$,
in the I$\Lambda$CDM scenario. To avoid the large-scale instability problem in
interacting dark energy models, we employ the extended parameterized
post-Friedmann method for interacting dark energy to calculate the perturbation
evolution of dark energy in these models. The observational data used in this
work include the cosmic microwave background (CMB) measurements from the Planck
2018 data release, the baryon acoustic oscillation (BAO) data, the type Ia
supernovae (SN) observation (Pantheon compilation), and the 2019 local distance
ladder measurement of the Hubble constant $H_{0}$ from the Hubble Space
Telescope. We find that, compared with those in the $\Lambda$CDM+$\sum m_{\nu}$
model, the constrains on $\sum m_{\nu}$ are looser in the four
I$\Lambda$CDM+$\sum m_{\nu}$ models. When considering the three mass
hierarchies of neutrinos, the constraints on $\sum m_{\nu}$ are tightest in the
degenerate hierarchy case and loosest in the inverted hierarchy case. In
addition, in the four I$\Lambda$CDM+$\sum m_{\nu}$ models, the values of
coupling parameter $\beta$ are larger using the CMB+BAO+SN+$H_{0}$ data
combination than that using the CMB+BAO+SN data combination, and $\beta>0$ is
favored at more than 1$\sigma$ level when using CMB+BAO+SN+$H_{0}$ data
combination. The issue of the $H_{0}$ tension is also discussed in this paper.
We find that, compared with the $\Lambda$CDM+$\sum m_{\nu}$ model, the $H_{0}$
tension can be alleviated in the I$\Lambda$CDM+$\sum m_{\nu}$ model to some
extent.
|
Dark matter halos in the multicomponent model. I. Substructure | Multicomponent dark matter with self-interactions, which allows for
inter-conversions of species into one another, is a promising paradigm that is
known to successfully and simultaneously resolve major problems of the
conventional $\Lambda$CDM cosmology at galactic and sub-galactic scales. In
this paper, we present $N$-body simulations of the simplest two-component
(2cDM) model aimed at studying the distribution of dark matter halos with
masses $M\lesssim10^{12}M_\odot$. In particular, we investigate how the maximum
circular velocity function of the halos is affected by the velocity dependence
of the self-interaction cross-sections, $\sigma(v)\propto v^a$, and compare
them with available observational data. The results demonstrate that the 2cDM
paradigm with the range of self-interaction cross-section per particle mass
(evaluated at $v=100$ km s$^{-1}$) of $0.01\lesssim \sigma_0/m\lesssim 1 $
cm$^2$g$^{-1}$ and the mass degeneracy $\Delta m/m\sim 10^{-7}-10^{-8}$ is
robustly resolving the substructure and too-big-to-fail problems by suppressing
the substructure having small maximum circular velocities, $V_{\rm
max}\lesssim100$ km s$^{-1}$. We also discuss the disagreement between the
radial distribution of dwarfs in a host halo observed in the Local Group and
simulated with CDM. This can be considered as one more small-scale problem of
CDM. We demonstrate that such a disagreement is alleviated in 2cDM. Finally,
the computed matter power-spectra of the 2cDM structure indicate the model's
consistency with the existing Ly-$\alpha$ forest constraints.
|
The Swampland, Quintessence and the Vacuum Energy | It has recently been conjectured that string theory does not admit de Sitter
vacua, and that quintessence explains the current epoch of accelerated cosmic
expansion. A proposed, key prediction of this scenario is time-varying
couplings in the dark sector, induced by the evolving quintessence field. We
note that cosmological models with varying couplings suffer from severe
problems with quantum corrections, beyond those shared by all quintessence
models. The vacuum energy depends on all masses and couplings of the theory,
and even small variations of parameters can lead to overwhelmingly large
corrections to the effective potential. We find that quintessence models with
varying parameters can be realised in consistent quantum theories by either: 1)
enforcing exceptional levels of fine-tuning; 2) realising some unknown
mechanism that cancels all undesirable contributions to the effective potential
with unprecedented accuracy; or 3) ensuring that the quintessence field couples
exclusively to very light states, and does not backreact on heavy fields.
|
Role of the companion lensing galaxy in the CLASS gravitational lens
B1152+199 | We reinvestigate the Cosmic Lens All-Sky Survey (CLASS) gravitational lens
B1152+199 using archived Hubble Space Telescope (HST) data and Very Long
Baseline Interferometry (VLBI) data. A consistent luminosity ratio within
effective radius between the host galaxy and the X-galaxy is measured from HST
tri-band images, which leads to a mass ratio between the two galaxies as
$r_b\sim 2$. To determine the role of the X-galaxy in the lens system, we
modelled the dual-lens system with constraints from the VLBI-resolved jet
components and the HST images. The 8.4-GHz global-VLBI data currently provide
the most stringent constraints to the mass model, especially to the radial
power-law slope. The optimized models for this two-image three-component radio
lens favour a steeper-than-isothermal inner slope. The jet bending in image B
was also investigated and it turned out to be rather a misalignment than a
curvature. The goodness of fit indicates that the role of the X-galaxy is
crucial in the lens system if three pairs of resolved jet components are to be
fitted. When we imported the optimal model from radio constraints to optical
modelling with the HST tri-band data, the optimization kept the consistency of
the optimal model and successfully reproduced the features observed in the HST
images. This implies that the diffuse emission discovered in the HST images is
actually a detection of the secondary lensing effects from the companion lens.
|
Dust temperature and mid-to-total infrared color distributions for
star-forming galaxies at 0<z<4 | We present a new, publicly available library of dust spectral energy
distributions (SEDs). These SEDs are characterized by only three parameters:
the dust mass (Mdust), the dust temperature (Tdust), and the mid-to-total
infrared color (IR8=LIR/L8). The latter measures the relative contribution of
PAH molecules to the LIR. We used this library to model star-forming galaxies
at 0.5<z<4 in the CANDELS fields, using both individual detections and stacks
of Herschel and ALMA imaging, and extending this sample to z=0 using the
Herschel Reference Survey. At first order, the dust SED of a galaxy was found
independent of stellar mass, but evolving with redshift. We found trends of
increasing Tdust and IR8 with redshift and distance from the SFR--Mstar main
sequence (MS), and quantified for the first time their intrinsic scatter. Half
of the observed variation of these parameters was captured by these empirical
relations, with residual scatters of 12% and 0.18 dex, respectively. Second
order variations with stellar mass are discussed. Building on these results, we
constructed high-fidelity mock galaxy catalogs to predict the accuracy of LIR
and Mdust determined from a single flux measurement. Using a single JWST MIRI
band, we found that LIR is typically uncertain by 0.15 dex, with a maximum of
0.25 dex when probing the rest-frame 8 um, and this is not significantly
impacted by typical redshift uncertainties. On the other hand, we found that
ALMA bands 8-to-7 and 6-to-3 measure Mdust at better than 0.2 and 0.15 dex,
respectively, and independently of redshift, while bands 9-to-6 only measure
LIR at better than 0.2 dex at z>1, 3.2, 3.8, and 5.7, respectively. Starburst
galaxies above the MS have LIR significantly underestimated and Mdust
overestimated. These results can be used immediately to interpret more
accurately the large amount of archival data from Spitzer, Herschel and ALMA.
[abridged]
|
Effect of cosmic backreaction on the future evolution of an accelerating
universe | We investigate the effect of backreaction due to inhomogeneities on the
evolution of the present universe by considering a two-scale model within the
Buchert framework. Taking the observed present acceleration of the universe as
an essential input, we study the effect of inhomogeneities in the future
evolution. We find that the backreaction from inhomogeneities causes the
acceleration to slow down in the future for a range of initial configurations
and model parameters. The present acceleration ensures formation of the cosmic
event horizon, and our analysis brings out how the effect of the event horizon
could further curtail the global acceleration, and even lead in certain cases
to the emergence of a future decelerating epoch.
|
Impact of a Warm Dark Matter late-time velocity dispersion on
large-scale structures | We investigate whether the late-time (at $z\leq 100$) velocity dispersion
expected in Warm Dark Matter scenarios could have some effect on the cosmic web
(i.e., outside of virialized halos). We consider effective hydrodynamical
equations, with a pressurelike term that agrees at the linear level with the
analysis of the Vlasov equation. Then, using analytical methods, based on
perturbative expansions and the spherical dynamics, we investigate the impact
of this term for a 1 keV dark matter particle. We find that the late-time
velocity dispersion has a negligible effect on the power spectrum on
perturbative scales and on the halo mass function. However, it has a
significant impact on the probability distribution function of the density
contrast at $z \sim 3$ on scales smaller than $0.1 h^{-1}$Mpc, which correspond
to Lyman-$\alpha$ clouds. Finally, we note that numerical simulations should
start at $z_i\geq 100$ rather than $z_i \leq 50$ to avoid underestimating
gravitational clustering at low redshifts.
|
Direct dark matter detection: the next decade | Direct dark matter searches are promising techniques to identify the nature
of dark matter particles. I describe the future of this field of research,
focussing on the question of what can be achieved in the next decade. I will
present the main techniques and R&D projects that will allow to build so-called
ultimate WIMP detectors, capable of probing spin-independent interactions down
to the unimaginably low cross section of 1e-48 cm2, before the irreducible
neutrino background takes over. If a discovery is within the reach of a
near-future dark matter experiment, these detectors will be able to constrain
WIMP properties such as its mass, scattering cross section and possibly spin.
With input from the LHC and from indirect searches, direct detection
experiments will hopefully allow to determine the local density and to
constrain the local phase-space structure of our dark matter halo.
|
Calibration of the Mid-Infrared Tully-Fisher Relation | Distance measures on a coherent scale around the sky are required to address
the outstanding cosmological problems of the Hubble Constant and of departures
from the mean cosmic flow. The correlation between galaxy luminosities and
rotation rates can be used to determine distances to many thousands of galaxies
in a wide range of environments potentially out to 200 Mpc. Mid-infrared (3.6
microns) photometry with the Spitzer Space Telescope is particularly valuable
as the source of the luminosities because it provides products of uniform
quality across the sky. From a perch above the atmosphere, essentially the
total magnitude of targets can be registered in exposures of a few minutes.
Extinction is minimal and the flux is dominated by the light from old stars
which is expected to correlate with the mass of the targets.
In spite of the superior photometry, the correlation between mid-infrared
luminosities and rotation rates extracted from neutral hydrogen profiles is
slightly degraded from the correlation found with I band luminosities. A color
correction recovers a correlation that provides comparable accuracy to that
available at I band (~20% 1sigma in an individual distance) while retaining the
advantages identified above. Without the color correction the relation between
linewidth and [3.6] magnitudes is M^{b,i,k,a}_{[3.6]} = -20.34 - 9.74 (log
W_{mx}^{i} -2.5). This description is found with a sample of 213 galaxies in 13
clusters that define the slope and 26 galaxies with Cepheid or tip of the red
giant branch distances that define the zero point. A color corrected parameter
M_{C_{[3.6]}} is constructed that has reduced scatter: M_{C_{[3.6]}} = -20.34 -
9.13 (log W_{mx}^{i} -2.5). Consideration of the 7 calibration clusters beyond
50 Mpc, outside the domain of obvious peculiar velocities, provides a
preliminary Hubble Constant estimate of H_0=74+/-5 km/s/Mpc.
|
Formation and spatial distribution of hypervelocity stars in AGN
outflows | We study star formation within outflows driven by active galactic nuclei
(AGN) as a new source of hypervelocity stars (HVSs). Recent observations
revealed active star formation inside a galactic outflow at a rate of $\sim
15\,M_{\odot}\,\rm yr^{-1}$. We verify that the shells swept up by an AGN
outflow are capable of cooling and fragmentation into cold clumps embedded in a
hot tenuous gas via thermal instabilities. We show that cold clumps of $\sim
10^3\,M_{\odot}$ are formed within $\sim 10^5$ yrs. As a result, stars are
produced along outflow's path, endowed with the outflow speed at their
formation site. These HVSs travel through the galactic halo and eventually
escape into the intergalactic medium. The expected instantaneous rate of star
formation inside the outflow is $\sim 4-5$ orders of magnitude greater than the
average rate associated with previously proposed mechanisms for producing HVSs,
such as the Hills mechanism and three-body interaction between a star and a
black hole binary. We predict the spatial distribution of HVSs formed in AGN
outflows for future observational probe.
|
Some implications of signature-change in cosmological models of loop
quantum gravity | Signature change at high density has been obtained as a possible consequence
of deformed space-time structures in models of loop quantum gravity. This
article provides a conceptual discussion of implications for cosmological
scenarios, based on an application of mathematical results for mixed-type
partial differential equations (the Tricomi problem). While the effective
equations from which signature change has been derived are shown to be locally
regular and therefore reliable, the underlying theory of loop quantum gravity
may face several global problems in its semiclassical solutions.
|
A third cluster of red supergiants in the vicinity of the massive
cluster RSGC3 | Recent studies have shown that the area around the massive, obscured cluster
RSGC3 may harbour several clusters of red supergiants. In this paper, we
analyse a clump of photometrically selected red supergiant candidates 20' south
of RSGC3 in order to confirm the existence of another of these clusters. Using
medium-resolution infrared spectroscopy around 2.27 microns, we derived
spectral types and velocities along the line of sight for the selected
candidates, confirming their nature and possible association. We find a compact
clump of eight red supergiants and four other candidates at some distance, all
of them spectroscopically confirmed red supergiants. The majority of these
objects must form an open cluster, which we name Alicante 10. Because of the
high reddening and strong field contamination, the cluster sequence is not
clearly seen in 2MASS or GPS-UKIDSS. From the observed sources, we derive
E(J-Ks)=2.6 and d~6 kpc. Although the cluster is smaller than RSGC3, it has an
initial mass in excess of 10000 solar masses, and it seems to be part of the
RSGC3 complex. With the new members this association already has 35
spectroscopically confirmed red supergiants, confirming its place as one of the
most active sites of recent stellar formation in the Galaxy.
|
Atacama Cosmology Telescope: Dusty star-forming galaxies and active
galactic nuclei in the equatorial survey | We present a catalog of 510 radio-loud active galactic nuclei (AGN, primarily
blazars) and 287 dusty star-forming galaxies (DSFGs) detected by the Atacama
Cosmology Telescope at $>5\sigma$ significance in bands centered on 148 GHz (2
mm), 218 GHz (1.4 mm) and 277 GHz (1.1 mm), from a 480 square degrees strip on
the celestial equator with additional (360 square degrees) shallower fields.
Combining the deepest available 218 GHz wide-field imaging, 277 GHz data, and
multi-band filtering yields the most sensitive wide-field millimeter-wave DSFG
selection to date with rms noise referenced to 218 GHz reaching $<2$ mJy. We
developed techniques to remove Galactic contamination from the extragalactic
catalog, yielding 321 additional Galactic sources. We employ a new flux
debiasing method that handles the heterogeneous sample selection due to
Galactic cuts. We present spectral properties and source counts of the AGN and
DSFGs. The DSFG spectra depart from an optically thin modified blackbody
between 218 GHz and 277 GHz, consistent with optically thick emission or an
additional cold dust component. For bright AGN, the inter-year RMS fractional
deviation in flux density from source variability is $\sim40\%$. We report
8$-$2870 mJy source counts for AGN and 8$-$90 mJy source counts for DSFGs, the
latter probing both the brighter, lensed population and the fainter, unlensed
population. At 277 GHz we report the first source counts measurements at these
flux densities, finding an excess above most model count predictions. Finally,
we select thirty of the brightest DSFGs for multi-frequency study as candidate
high-$z$ lensed systems.
|
Magnetic Fields from Filaments to Cores | How important is the magnetic (B-) field when compared to gravity and
turbulence in the star-formation process? Does its importance depend on scale
and location? We summarize submm dust polarization observations towards the
large filamentary infrared dark cloud G34 and towards a dense core in the
high-mass star-forming region W51. We detect B-field orientations that are
either perpendicular or parallel to the G34 filament axis. These B-field
orientations further correlate with local velocity gradients. Towards three
cores in G34 we find a varying importance between B-field, gravity, and
turbulence that seems to dictate varying types of fragmentation. At highest
resolution towards the gravity-dominated collapsing core W51 e2 we resolve new
B-field features, such as converging B-field lines and possibly magnetic
channels.
|
Hierarchical Star Formation: Stars and Stellar Clusters in the Gould
Belt | We perform a study of the spatial and kinematical distribution of young open
clusters in the solar neighborhood, discerning between bound clusters and
transient stellar condensations within our sample. Then, we discriminate
between Gould Belt (GB) and local Galactic disk (LGD) members, using a previous
estimate of the structural parameters of both systems obtained from a sample of
O-B6 Hipparcos stars. Using this classified sample we analyze the spatial
structure and the kinematic behavior of the cluster system in the GB. The two
star formation regions that dominate and give the GB its characteristic
inclined shape show a striking difference in their content of star clusters:
while Ori OB1 is richly populated by open clusters, not a single one can be
found within the boundaries of Sco OB2. This is mirrored in the velocity space,
translating again into an abundance of clusters in the region of the kinematic
space populated by the members of Ori OB1, and a marginal number of them
associated to Sco OB2. In the light of these results we study the nature of the
GB with respect to the optical segment of the Orion Arm, and we propose that
the different content of star clusters, the different heights over the Galactic
plane and the different residual velocities of Ori OB1 and Sco OB2 can be
explained in terms of their relative position to the density maximum of the
Local Arm in the solar neighborhood. Although morphologically intriguing, the
GB appears to be the result of our local and biased view of a larger star
cluster complex in the Local Arm, that could be explained by the internal
dynamics of the Galactic disk.
|
Multicolor Photometry of the Galaxy Cluster A98: Substructures and Star
Formation Properties | An optical photometric observation with the
Beijing-Arizona-Taiwan-Connecticut (BATC) multicolor system is carried out for
A98 (z=0.104), a galaxy cluster with two large enhancements in X-ray surface
brightness. The spectral energy distributions (SEDs) covering 15 intermediate
bands are obtained for all sources detected down to V ~ 20 mag in a field of
$58' \times 58'$. After the star-galaxy separation by the color-color diagrams,
a photometric redshift technique is applied to the galaxy sample for further
membership determination. The color-magnitude relation is taken as a further
restriction of the early-type cluster galaxies. As a result, a list of 198
faint member galaxies is achieved. Based on newly generated sample of member
galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated
in detail. A separate galaxy group, A98X, is also found to the south of main
concentration of A98, which is gravitationally unbound to A98. For 74
spectroscopically confirmed member galaxies, the environmental effect on the
star formation histories is found. The bright galaxies in the core region are
found to have shorter time scales of star formation, longer mean stellar ages,
and higher metallicities of interstellar medium, which can be interpreted in
the context of hierarchical cosmological scenario.
|
The Flattening of Dust Attenuation Curve to z=2.5 | We examine the evolution of dust attenuation curve using a sample of 9504
disk star-forming galaxies (SFGs) selected from the CANDELS and 3D-HST surveys
and a new technique relying on the fact that disk SFGs of similar stellar
masses at the same cosmic epoch are statistically identical in stellar
populations. We attribute the discrepancy in median magnitude between face-on
(b/a>0.7) and edge-on (b/a<=0.4) subsamples solely to dust attenuation, and
obtain the average attenuation in the rest-frame UV and optical as functions of
stellar mass and redshift out to z=2.5. Our results show that the attenuation
curve becomes remarkably flatter at increasing redshift for both massive and
low-mass disk SFGs, and remains likely unchanged with galaxy stellar mass at a
fixed epoch within uncertainties. Compared with the Calzetti law, our dust
attenuation curves appear to be slightly steeper at 0.5<z<1.4 and remarkably
flatter at 1.4<z<2.5. Our findings are consistent with a picture in which the
evolution of dust grain size distribution is mainly responsible for the
evolution of the dust attenuation curve in SFGs; dust shattering becomes a
dominant process at z<~1.4, resulting in an enrichment of small dust grains and
consequently a steeper attenuation curve. We stress that extinction correction
for high-z galaxies should be done using mass- and redshift-dependent
attenuation curves.
|
A Comparison between Semi-Analytic Model Predictions for the CANDELS
Survey | We compare the predictions of three independently developed semi-analytic
galaxy formation models that are being used to aid in the interpretation of
results from the CANDELS survey. These models are each applied to the same set
of halo merger trees extracted from the "Bolshoi" simulation and are carefully
tuned to match the local galaxy stellar mass function using the powerful method
of Bayesian Inference coupled with MCMC or by hand. The comparisons reveal that
in spite of the significantly different parameterizations for star formation
and feedback processes, the three models yield qualitatively similar
predictions for the assembly histories of galaxy stellar mass and star
formation over cosmic time. We show that the SAMs generally require strong
outflows to suppress star formation in low-mass halos to match the present day
stellar mass function. However, all of the models considered produce
predictions for the star formation rates and metallicities of low-mass galaxies
that are inconsistent with existing data and diverge between the models. We
suggest that large differences in the metallicity relations and small
differences in the stellar mass assembly histories of model galaxies stem from
different assumptions for the outflow mass-loading factor. Importantly, while
more accurate observational measurements for stellar mass, SFR and metallicity
of galaxies at 1<z<5 will discriminate between models, the discrepancies
between the models and existing data of these observables have already revealed
challenging problems in understanding star formation and its feedback in galaxy
formation. The three sets of models are being used to construct catalogs of
mock galaxies on light cones that have the same geometry as the CANDELS survey,
which should be particularly useful for quantifying the biases and
uncertainties on measurements and inferences from the real observations.
-ABRIDGED
|
Surveying the Giant HII Regions of the Milky Way with SOFIA: III. W49A | We present our third set of results from our mid-infrared imaging survey of
Milky Way Giant HII (GHII) regions with our detailed analysis of W49A, one of
the most distant, yet most luminous, GHII regions in the Galaxy. We used the
FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy
(SOFIA) to obtain 20 and 37$\mu$m images of the entire ~5.0' x 3.5'
infrared-emitting area of W49A at a spatial resolution of ~3". Utilizing these
SOFIA data in conjunction with previous multi-wavelength observations from the
near-infrared to radio, including Spitzer-IRAC and Herschel-PACS archival data,
we investigate the physical nature of individual infrared sources and
sub-components within W49A. For individual compact sources we used the
multi-wavelength photometry data to construct spectral energy distributions
(SEDs) and fit them with massive young stellar object (MYSO) SED models, and
find 22 sources that are likely to be MYSOs. Ten new sources are identified for
the first time in this work. Even at 37$\mu$m we are unable to detect infrared
emission from the sources on the western side of the extremely extinguished
ring of compact radio emission sources known as the Welch Ring. Utilizing
multi-wavelength data, we derived luminosity-to-mass ratio and virial
parameters of the extended radio sub-regions of W49A to estimate their relative
ages and find that overall the sub-components of W49A have a very small spread
in evolutionary state compared to our previously studied GHII regions.
|
Measuring the Mass of the Large Magellanic Cloud with Stellar Streams
Observed by ${S}^5$ | Stellar streams are excellent probes of the underlying gravitational
potential in which they evolve. In this work, we fit dynamical models to five
streams in the Southern Galactic hemisphere, combining observations from the
Southern Stellar Stream Spectroscopic Survey (${S}^5$), Gaia EDR3, and the Dark
Energy Survey (DES), to measure the mass of the Large Magellanic Cloud (LMC).
With an ensemble of streams, we find a mass of the LMC ranging from 14 to $19
\times 10^{10}\ \mathrm{M}_{\odot}$, probed over a range of closest approach
times and distances. With the most constraining stream (Orphan-Chenab), we
measure an LMC mass of $18.8^{+ 3.5}_{- 4.0} \times 10^{10}\
\mathrm{M}_{\odot}$, probed at a closest approach time of 310 Myr and a closest
approach distance of 25.4 kpc. This mass is compatible with previous
measurements, showing that a consistent picture is emerging of the LMC's
influence on structures in the Milky Way. Using this sample of streams, we find
that the LMC's effect depends on the relative orientation of the stream and LMC
at their point of closest approach. To better understand this, we present a
simple model based on the impulse approximation and we show that the LMC's
effect depends both on the magnitude of the velocity kick imparted to the
stream and the direction of this kick.
|
Ion chemistry in the early universe: revisiting the role of HeH+ with
new quantum calculations | The role of HeH+ has been newly assessed with the aid of newly calculated
rates which use entirely ab initio methods, thereby allowing us to compute more
accurately the relevant abundances within the global chemical network of the
early universe. A comparison with the similar role of the ionic molecule LiH+
is also presented. Quantum calculations have been carried out for the gas-phase
reaction of HeH+ with H atoms with our new in-house code, based on the negative
imaginary potential method. Integral cross sections and reactive rate
coefficients obtained under the general conditions of early universe chemistry
are presented and discussed. With the new reaction rate, the abundance of HeH+
in the early universe is more than one order of magnitude larger than in
previous studies. Our more accurate findings further buttress the possibility
to detect cosmological signatures of HeH+.
|
A new model for the full shape of the large-scale power spectrum | We present a new model for the full shape of large-scale the power spectrum
based on renormalized perturbation theory. To test the validity of this
prescription, we compare this model against power spectra measured in a suite
of 50 large volume, moderate resolution N-body simulations. Our results
indicate that this simple model provides an accurate description of the full
shape of the power spectrum taking into account the effects of non-linear
evolution, redshift-space distortions and halo bias for scales k < 0.15 h/Mpc,
making it a valuable tool for the analysis of forthcoming galaxy surveys. Even
though its application is restricted to large scales, this prescription can
provide tighter constraints on the dark energy equation of state parameter
w_{DE} than those obtained by modelling the baryonic acoustic oscillations
signal only, where the information of the broad-band shape of the power
spectrum is discarded. Our model is able to provide constraints comparable to
those obtained by applying a similar model to the full shape of the correlation
function, which is affected by different systematics. Hence, with accurate
modelling of the power spectrum, the same cosmological information can be
extracted from both statistics.
|
Slow-roll approximation in loop quantum cosmology | The slow-roll approximation is an analytical approach to study dynamical
properties of the inflationary universe. In this article, systematic
construction of the slow-roll expansion for effective loop quantum cosmology is
presented. The analysis is performed up to the fourth order in both slow-roll
parameters and the parameter controlling the strength of deviation from the
classical case. The expansion is performed for three types of the slow-roll
parameters: Hubble slow-roll parameters, Hubble flow parameters and potential
slow-roll parameters. An accuracy of the approximation is verified by
comparison with the numerical phase space trajectories for the case with a
massive potential term. The results obtained in this article may be helpful in
the search for the subtle quantum gravitational effects with use of the
cosmological data.
|
The Ellipsoidal Universe and the Hubble tension | The Hubble tension resides in a statistically significant discrepancy between
early time and late time determinations of the Hubble constant. We discuss the
Hubble tension within the Ellipsoidal Universe cosmological model. We suggest
that allowing small anisotropies in the large-scale spatial geometry could
alleviate the tension. We, also, show that the discrepancy in the measurements
of the Hubble constant is reduced to a statistically acceptable level if we
assume sizeable cosmological anisotropies during the Dark Age. In addition, we
argue that the Ellipsoidal Universe cosmological model should resolve the $S_8$
tension.
|
Comment on N. Rijal et al. "Measurement of d + 7Be Cross Sections for
Big-Bang Nucleosynthesis" | Rijal, et al. in their recent publication [Phys. Rev. Lett {\bf 122}, 182701
(2019), arXiv:1808.07893], on "Measurement of d + $^7$Be Cross Sections for
Big-Bang Nucleosynthesis (BBN)", misrepresent their result, they misrepresent
previous work of Parker (72) and of Caughlan and Fowler (88), and quite
possibly, contradicts the very BBN theory that has been established over the
last few decades. This comment is intended to correct these misrepresentations
and critically review their claims on BBN.
|
Diffuse gas properties and stellar metallicities in cosmological
simulations of disc galaxy formation | We analyse the properties of the circum-galactic medium and the metal content
of the stars comprising the central galaxy in eight hydrodynamical `zoom-in'
simulations of disc galaxy formation. We use these properties as a benchmark
for our model of galaxy formation physics implemented in the moving-mesh code
AREPO, which succeeds in forming quite realistic late-type spirals in the set
of `Aquarius' initial conditions of Milky Way-sized haloes. Galactic winds
significantly influence the morphology of the circum-galactic medium and induce
bipolar features in the distribution of heavy elements. They also affect the
thermodynamic properties of the circum-galactic gas by supplying an energy
input that sustains its radiative losses. Although a significant fraction of
the heavy elements are transferred from the central galaxy to the halo, and
even beyond the virial radius, enough metals are retained by stars to yield a
peak in their metallicity distributions at about $Z_{\odot}$. All our default
runs overestimate the stellar [O/Fe] ratio, an effect that we demonstrate can
be rectified by an increase of the adopted SN type Ia rate. Nevertheless, the
models have difficulty in producing stellar metallicity gradients of the same
strength as observed in the Milky Way.
|
Testing the Weak Equivalence Principle with Cosmological Gamma Ray
Bursts | Gamma Ray Bursts (GRBs) with rapid variations at cosmological distances are
used to place new limits on violations of the gravitational weak equivalence
principle (WEP). These limits track intrinsic timing deviations between GRB
photons of different energies as they cross the universe, in particular in the
KeV to GeV energy range. Previous limits in this energy range have involved
only the gravitational potential of local sources and utilized temporal
variability on the order of 0.1 seconds. Here WEP violation limits are derived
from sources with greater distance, faster variability, and larger intervening
mass. Specifically, GRB sources with redshifts as high as 6.5 are considered,
with variability as fast 0.2 milliseconds, and passing the gravitational
potentials of inferred clusters of galaxies distributed randomly around the
line of sight. WEP violation limits are derived from data from GRB 910711, GRB
920229, GRB 021206, GRB 051221, GRB 090429, and GRB 090510. The strongest
constraint in the very early universe comes from GRB 090429 which limits
$\gamma(500$ keV$) - \gamma(250$ keV$) < 1.2\times10^{-13}$. The strongest
overall constraint comes from GRB 090510 which yields a WEP violation limit of
$\gamma(30$ GeV$) - \gamma (1$ GeV$) < 6.6\times10^{-16}$. This strongest
constraint is not only a new record for WEP violation limit for gamma-ray
photons and in the early universe, but the strongest upper bound for $\Delta
\gamma$ that has ever been recorded between any two energy bands.
|
Active Galactic Nuclei Feedback in an Elliptical Galaxy with the Most
Updated AGN Physics (II): High-Angular Momentum Case | This is the second paper of our series of works of studying the effects of
active galactic nuclei (AGN) feedback on the cosmological evolution of an
isolated elliptical galaxy by performing two-dimensional high-resolution
hydrodynamical numerical simulations. In these simulations, the inner boundary
is chosen so that the Bondi radius is resolved. Physical processes like star
formation, SNe Ia and II are taken into account. Compared to previous works,
the main improvements is that we adopt the most updated AGN physics, which is
described in detail in the first paper of this series (Yuan et al. 2018, Paper
I). These improvements include the discrimination of the two accretion modes of
the central AGN and the most updated descriptions of the wind and radiation in
the two modes. In Paper I, we consider the case that the specific angular
momentum of the gas in the galaxy is very low. In this paper, we consider the
case that the specific angular momentum of the gas is high. In the galactic
scale, we adopt the gravitational torques raised due to non-axisymmetric
structure in the galaxy as the mechanism of the transfer of angular momentum of
gas, as proposed in some recent works. Since our simulations are axisymmetric,
we make use of a parameterized prescription to mimic this mechanism. Same as
Paper I, we investigate the AGN light curve, typical AGN lifetime, growth of
the black hole mass, AGN duty-cycle, star formation, and the X-ray surface
brightness of the galaxy. Special attention is paid to the effects of specific
angular momentum of the galaxy on these properties. We find that some results
are qualitatively similar to those shown in Paper I, while some results such as
star formation and black hole growth do show a significant difference due to
the mass concentration in the galactic disk as a consequence of galactic
rotation.
|
A modified WKB formulation for linear eigenmodes of a collisionless
self-gravitating disc in the epicyclic approximation | The short--wave asymptotics (WKB) of spiral density waves in self-gravitating
stellar discs is well suited for the study of the dynamics of tightly--wound
wavepackets. But the textbook WKB theory is not well adapted to the study of
the linear eigenmodes in a collisionless self-gravitating disc because of the
transcendental nature of the dispersion relation. We present a modified WKB of
spiral density waves, for collisionless discs in the epicyclic limit, in which
the perturbed gravitational potential is related to the perturbed surface
density by the Poisson integral in Kalnaj's logarithmic spiral form. An
integral equation is obtained for the surface density perturbation, which is
seen to also reduce to the standard WKB dispersion relation. We specialize to a
low mass (or Keplerian) self-gravitating disc around a massive black hole, and
derive an integral equation governing the eigenspectra and eigenfunctions of
slow precessional modes. For a prograde disc, the integral kernel turns out be
real and symmetric, implying that all slow modes are stable. We apply the slow
mode integral equation to two unperturbed disc profiles, the Jalali--Tremaine
annular discs, and the Kuzmin disc. We determine eigenvalues and eigenfunctions
for both $m = 1$ and $m = 2$ slow modes for these profiles and discuss their
properties. Our results compare well with those of Jalali--Tremaine.
|
Studies of Diffuse Interstellar Bands. V. Pairwise Correlations of Eight
Strong DIBs and Neutral Hydrogen, Molecular Hydrogen, and Color Excess | We establish correlations between equivalent widths of eight diffuse
interstellar bands (DIBs), and examine their correlations with atomic hydrogen,
molecular hydrogen, and EB-V . The DIBs are centered at \lambda\lambda 5780.5,
6204.5, 6283.8, 6196.0, 6613.6, 5705.1, 5797.1, and 5487.7, in decreasing order
of Pearson\^as correlation coefficient with N(H) (here defined as the column
density of neutral hydrogen), ranging from 0.96 to 0.82. We find the equivalent
width of \lambda 5780.5 is better correlated with column densities of H than
with E(B-V) or H2, confirming earlier results based on smaller datasets. We
show the same is true for six of the seven other DIBs presented here. Despite
this similarity, the eight strong DIBs chosen are not well enough correlated
with each other to suggest they come from the same carrier. We further conclude
that these eight DIBs are more likely to be associated with H than with H2, and
hence are not preferentially located in the densest, most UV shielded parts of
interstellar clouds. We suggest they arise from different molecules found in
diffuse H regions with very little H (molecular fraction f<0.01). Of the 133
stars with available data in our study, there are three with significantly
weaker \lambda 5780.5 than our mean H-5780.5 relationship, all of which are in
regions of high radiation fields, as previously noted by Herbig. The
correlations will be useful in deriving interstellar parameters when direct
methods are not available. For instance, with care, the value of N(H) can be
derived from W{\lambda}(5780.5).
|
Galaxy evolution in protoclusters | We investigate galaxy evolution in protoclusters using a semi-analytic model
applied to the Millennium Simulation, scaled to a Planck cosmology. We show
that the model reproduces the observed behaviour of the star formation history
(SFH) both in protoclusters and the field. The rate of star formation peaks
$\sim0.7\,{\rm Gyr}$ earlier in protoclusters than in the field and declines
more rapidly afterwards. This results in protocluster galaxies forming
significantly earlier: 80% of their stellar mass is already formed by $z=1.4$,
but only 45% of the field stellar mass has formed by this time. The model
predicts that field and protocluster galaxies have similar average specific
star-formation rates (sSFR) at $z>3$, and we find evidence of an enhancement of
star formation in the dense protoclusters at early times. At $z<3$,
protoclusters have lower sSFRs, resulting in the disparity between the SFHs. We
show that the stellar mass functions of protoclusters are top-heavy compared
with the field due to the early formation of massive galaxies, and the
disruption and merging of low-mass satellite galaxies in the main haloes. The
fundamental cause of the different SFHs and mass functions is that dark matter
haloes are biased tracers of the dark matter density field: the high density of
haloes and the top-heavy halo mass function in protoclusters result in the
early formation then rapid merging and quenching of galaxies. We compare our
results with observations from the literature, and highlight which observables
provide the most informative tests of galaxy formation.
|
Estimating Black Hole Masses in Active Galactic Nuclei Using the MgII
2800 Emission Line | We investigate the relationship between the linewidths of broad Mg II
\lambda2800 and Hbeta in active galactic nuclei (AGNs) to refine them as tools
to estimate black hole (BH) masses. We perform a detailed spectral analysis of
a large sample of AGNs at intermediate redshifts selected from the Sloan
Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra
for nearby sources monitored with reverberation mapping. Careful attention is
devoted to accurate spectral decomposition, especially in the treatment of
narrow-line blending and Fe II contamination. We show that, contrary to popular
belief, the velocity width of Mg II tends to be smaller than that of Hbeta,
suggesting that the two species are not cospatial in the broad-line region.
Using these findings and recently updated BH mass measurements from
reverberation mapping, we present a new calibration of the empirical
prescriptions for estimating virial BH masses for AGNs using the broad Mg II
and Hbeta lines. We show that the BH masses derived from our new formalisms
show subtle but important differences compared to some of the mass estimators
currently used in the literature.
|
A Lack of Evidence for Global Ram-pressure Induced Star Formation in the
Merging Cluster Abell 3266 | We have selected Abell 3266 to search for ram-pressure induced star formation
as a global property of a merging cluster. Abell 3266 (z = 0.0594) is a high
mass cluster that features a high velocity dispersion, an infalling subcluster
near to the line of sight, and a strong shock front. These phenomena should all
contribute to making Abell 3266 an optimum cluster to see the global effects of
RPS induced star formation. Using archival X-ray observations and published
optical data, we cross-correlate optical spectral properties ([OII, H$\beta$]),
indicative of starburst and post starburst, respectively with ram-pressure,
$\rho$v$^{2}$, calculated from the X-ray and optical data. We find that
post-starburst galaxies, classified as E+A, occur at a higher frequency in this
merging cluster than in the Coma cluster and at a comparable rate to
intermediate redshift clusters. This is consistent with increased star
formation due to the merger. However, both starburst and post-starburst
galaxies are equally likely to be in a low or high ram pressure environment.
From this result we infer that the duration of the starburst phase must be very
brief so that: (1) at any time only a small fraction of the galaxies in a high
ram pressure environment show this effect, and (2) most post-starburst galaxies
are in an environment of low ram pressure due too their continued orbital
motion in the cluster.
|
Signatures of Cool Gas Fueling a Star-Forming Galaxy at Redshift 2.3 | Galaxies are thought to be fed by the continuous accretion of intergalactic
gas, but direct observational evidence has been elusive. The accreted gas is
expected to orbit about the galaxy's halo, delivering not just fuel for
star-formation but also angular momentum to the galaxy, leading to distinct
kinematic signatures. Here we report observations showing these distinct
signatures near a typical distant star-forming galaxy where the gas is detected
using a background quasar passing 26 kpc from the host. Our observations
indicate that gas accretion plays a major role in galaxy growth since the
estimated accretion rate is comparable to the star-formation rate.
|
BOSS Great Wall: morphology, luminosity, and mass | We study the morphology, luminosity and mass of the superclusters from the
BOSS Great Wall (BGW), a recently discovered very rich supercluster complex at
the redshift $z = 0.47$. We have employed the Minkowski functionals to quantify
supercluster morphology. We calculate supercluster luminosities and masses
using two methods. Firstly, we used data about the luminosities and stellar
masses of high stellar mass galaxies with $\log(M_*/h^{-1}M_\odot) \geq 11.3$.
Secondly, we applied a scaling relation that combines morphological and
physical parameters of superclusters to obtain supercluster luminosities, and
obtained supercluster masses using the mass-to-light ratios found for local
rich superclusters. We find that the BGW superclusters are very elongated
systems, with shape parameter values of less than $0.2$. This value is lower
than that found for the most elongated local superclusters. The values of the
fourth Minkowski functional $V_3$ for the richer BGW superclusters ($V_3 = 7$
and $10$) show that they have a complicated and rich inner structure. We
identify two Planck SZ clusters in the BGW superclusters, one in the richest
BGW supercluster, and another in one of the poor BGW superclusters. The
luminosities of the BGW superclusters are in the range of $1 -
8\times~10^{13}h^{-2}L_\odot$, and masses in the range of $0.4 -
2.1\times~10^{16}h^{-1}M_\odot$. Supercluster luminosities and masses obtained
with two methods agree well. We conclude that the BGW is a complex of massive,
luminous and large superclusters with very elongated shape. The search and
detailed study, including the morphology analysis of the richest superclusters
and their complexes from observations and simulations can help us to understand
formation and evolution of the cosmic web.
|
Conformally related metrics and Lagrangians and their physical
interpretation in cosmology | Conformally related metrics and Lagrangians are considered in the context of
scalar-tensor gravity cosmology. After the discussion of the problem, we pose a
lemma in which we show that the field equations of two conformally related
Lagrangians are also conformally related if and only if the corresponding
Hamiltonian vanishes. Then we prove that to every non-minimally coupled scalar
field, we may associate a unique minimally coupled scalar field in a
conformally related space with an appropriate potential. The latter result
implies that the field equations of a non-minimally coupled scalar field are
the same at the conformal level with the field equations of the minimally
coupled scalar field. This fact is relevant in order to select physical
variables among conformally equivalent systems. Finally, we find that the above
propositions can be extended to a general Riemannian space of n-dimensions.
|
The Extended IRTF Spectral Library: Expanded coverage in metallicity,
temperature, and surface gravity | We present a $0.7-2.5\mu m$ spectral library of 284 stars observed with the
medium-resolution infrared spectrograph, SpeX, at the 3.0 meter NASA Infrared
Telescope Facility (IRTF) on Maunakea, Hawaii. This library extends the
metallicity range of the IRTF Cool Star library beyond solar metallicity to
$-1.7 <$ [Fe/H] $< 0.6$. All of the observed stars are also in the MILES
optical stellar library, providing continuous spectral coverage for each star
from $0.35-2.5\mu m$. The spectra are absolute flux calibrated using Two Micron
All Sky Survey photometry and the continuum shape of the spectra is preserved
during the data reduction process. Synthesized $JHK_S$ colors agree with
observed colors at the $1-2\%$ level, on average. We also present a spectral
interpolator that uses the library to create a data-driven model of spectra as
a function of $teff$, $logg$, and [Fe/H]. We use the library and interpolator
to compare empirical trends with theoretical predictions of spectral feature
behavior as a function of stellar parameters. These comparisons extend to the
previously difficult to access low-metallicity and cool dwarf regimes, as well
as the previously poorly sampled super-solar metallicity regime. The library
and interpolator are publicly available.
|
Label Transfer from APOGEE to LAMOST: Precise Stellar Parameters for
450,000 LAMOST Giants | In this era of large-scale stellar spectroscopic surveys, measurements of
stellar attributes ("labels," i.e. parameters and abundances) must be made
precise and consistent across surveys. Here, we demonstrate that this can be
achieved by a data-driven approach to spectral modeling. With The Cannon, we
transfer information from the APOGEE survey to determine precise Teff, log g,
[Fe/H], and [$\alpha$/M] from the spectra of 450,000 LAMOST giants. The Cannon
fits a predictive model for LAMOST spectra using 9952 stars observed in common
between the two surveys, taking five labels from APOGEE DR12 as ground truth:
Teff, log g, [Fe/H], [\alpha/M], and K-band extinction $A_k$. The model is then
used to infer Teff, log g, [Fe/H], and [$\alpha$/M] for 454,180 giants, 20% of
the LAMOST DR2 stellar sample. These are the first [$\alpha$/M] values for the
full set of LAMOST giants, and the largest catalog of [$\alpha$/M] for giant
stars to date. Furthermore, these labels are by construction on the APOGEE
label scale; for spectra with S/N > 50, cross-validation of the model yields
typical uncertainties of 70K in Teff, 0.1 in log g, 0.1 in [Fe/H], and 0.04 in
[$\alpha$/M], values comparable to the broadly stated, conservative APOGEE DR12
uncertainties. Thus, by using "label transfer" to tie low-resolution (LAMOST R
$\sim$ 1800) spectra to the label scale of a much higher-resolution (APOGEE R
$\sim$ 22,500) survey, we substantially reduce the inconsistencies between
labels measured by the individual survey pipelines. This demonstrates that
label transfer with The Cannon can successfully bring different surveys onto
the same physical scale.
|
Decaying turbulence and magnetic fields in galaxy clusters | We explore the decay of turbulence and magnetic fields generated by
fluctuation dynamo action in the context of galaxy clusters where such a
decaying phase can occur in the aftermath of a major merger event. Using
idealized numerical simulations that start from a kinetically dominated regime
we focus on the decay of the steady state rms velocity and the magnetic field
for a wide range of conditions that include varying the compressibility of the
flow, the forcing wave number, and the magnetic Prandtl number. Irrespective of
the compressibility of the flow, both the rms velocity and the rms magnetic
field decay as a power-law in time. In the subsonic case we find that the
exponent of the power-law is consistent with the $-3/5$ scaling reported in
previous studies. However, in the transonic regime both the rms velocity and
the magnetic field initially undergo rapid decay with an $\approx t^{-1.1}$
scaling with time. This is followed by a phase of slow decay where the decay of
the rms velocity exhibits an $\approx -3/5$ scaling in time, while the rms
magnetic field scales as $\approx -5/7$. Furthermore, analysis of the Faraday
rotation measure reveals that the Faraday RM decays also decays as a power law
in time $\approx t^{-5/7}$; steeper than the $\sim t^{-2/5}$ scaling obtained
in previous simulations of magnetic field decay in subsonic turbulence. Apart
from galaxy clusters, our work can have potential implications in the study of
magnetic fields in elliptical galaxies.
|
The measurements of matter density perturbations amplitude from
cosmological data | We compare various physically different measurements of linear matter density
perturbation amplitude, $sigma_8$, which are obtained from the observations of
CMB anisotropy, galaxy cluster mass function, weak gravitation lensing, matter
power spectrum and redshift space distortions. We show that $\sigma_8$
measurement from CMB gravitational lensing signal based on Planck CMB
temperature anisotropy data at high multipoles, $\ell>1000$, contradict to all
other measurements obtained both from remaining Planck CMB anisotropy data and
from other cosmological data, at about $3.7\sigma$ significance level.
Therefore, these data currently should not be combined with other data to
constrain cosmological parameters.
With the exception of Planck CMB temperature anisotropy data at high
multipoles, all other measurements are in good agreement between each other and
give the following measurements of linear density perturbation amplitude:
$\sigma_8=0.792\pm0.006$, mean density of the Universe:
$\Omega_m=0.287\pm0.007$, and Hubble constant: $H_0 = 69.4\pm
0.6$~km~s$^{-1}$~Mpc$^{-1}$. Taking in account the data on baryon acoustic
oscillations and (or) direct measurements of the Hubble constant, one can
obtain different constraints on sum of neutrino mass and number of relativistic
species.
|
Chemical Abundances of Planetary Nebulae in the Substructures of M31 | We present deep spectroscopy of planetary nebulae (PNe) that are associated
with the substructures of the Andromeda Galaxy (M31). The spectra were obtained
with the OSIRIS spectrograph on the 10.4 m GTC. Seven targets were selected for
the observations, three in the Northern Spur and four associated with the Giant
Stream. The most distant target in our sample, with a rectified galactocentric
distance >100 kpc, was the first PN discovered in the outer streams of M31. The
[O III] 4363 auroral line was well detected in the spectra of all targets,
enabling electron temperature determination. Ionic abundances are derived based
on the [O III] temperatures, and elemental abundances of helium, nitrogen,
oxygen, neon, sulfur, and argon are estimated. The relatively low N/O and He/H
ratios as well as abundance ratios of alpha-elements indicate that our target
PNe might belong to populations as old as ~2 Gyr. Our PN sample, including the
current seven and the previous three observed by Fang et al., have rather
homogeneous oxygen abundances. The study of abundances and the spatial and
kinematical properties of our sample leads to the tempting conclusion that
their progenitors might belong to the same stellar population, which hints at a
possibility that the Northern Spur and the Giant Stream have the same origin.
This may be explained by the stellar orbit proposed by Merrett et al. Judging
from the position and kinematics, we emphasize that M32 might be responsible
for the two substructures. Deep spectroscopy of PNe in M32 will help to assess
this hypothesis.
|
The Cluster HEritage project with XMM-Newton: Mass Assembly and
Thermodynamics at the Endpoint of structure formation. I. Programme overview | The Cluster HEritage project with XMM-Newton - Mass Assembly and
Thermodynamics at the Endpoint of structure formation (CHEX-MATE) is a three
mega-second Multi-Year Heritage Programme to obtain X-ray observations of a
minimally-biased, signal-to-noise limited sample of 118 galaxy clusters
detected by Planck through the Sunyaev-Zeldovich effect. The programme,
described in detail in this paper, aims to study the ultimate products of
structure formation in time and mass. It is composed of a census of the most
recent objects to have formed (Tier-1: 0.05 < z < 0.2; 2 x 10e14 M_sun < M_500
< 9 x 10e14 M_sun), together with a sample of the highest-mass objects in the
Universe (Tier-2: z < 0.6; M_500 > 7.25 x 10e14 M_sun). The programme will
yield an accurate vision of the statistical properties of the underlying
population, measure how the gas properties are shaped by collapse into the dark
matter halo, uncover the provenance of non-gravitational heating, and resolve
the major uncertainties in mass determination that limit the use of clusters
for cosmological parameter estimation. We will acquire X-ray exposures of
uniform depth, designed to obtain individual mass measurements accurate to
15-20% under the hydrostatic assumption. We present the project motivations,
describe the programme definition, and detail the ongoing multi-wavelength
observational (lensing, SZ, radio) and theoretical effort that is being
deployed in support of the project.
|
Properties of Resonantly Produced Sterile Neutrino Dark Matter Subhalos | The anomalous 3.55 keV X-ray line recently detected towards a number of
massive dark matter objects may be interpreted as the radiative decays of 7.1
keV mass sterile neutrino dark matter. Depending on its parameters, the sterile
neutrino can range from cold to warm dark matter with small-scale suppression
that differs in form from commonly-adopted thermal warm dark matter. Here, we
numerically investigate the subhalo properties for 7.1 keV sterile neutrino
dark matter produced via the resonant Shi-Fuller mechanism. Using accurate
matter power spectra, we run cosmological zoom-in simulations of a Milky
Way-sized halo and explore the abundance of massive subhalos, their radial
distributions, and their internal structure. We also simulate the halo with
thermal 2.0 keV warm dark matter for comparison and discuss quantitative
differences. We find that the resonantly produced sterile neutrino model for
the 3.55 keV line provides a good description of structures in the Local Group,
including the number of satellite dwarf galaxies and their radial distribution,
and largely mitigates the too-big-to-fail problem. Future searches for
satellite galaxies by deep surveys, such as the Dark Energy Survey, Large
Synoptic Survey Telescope, and Wide Field Infrared Survey Telescope, will be a
strong direct test of warm dark matter scenarios.
|
The X-SHOOTER/ALMA sample of Quasars in the Epoch of Reionization. I.
NIR spectral modeling, iron enrichment and broad emission line properties | We present X-SHOOTER near-infrared spectroscopy of a large sample of 38
luminous ($M_{1450}=-29.0$ to $-24.4$) quasars at $5.78<z<7.54$, which have
complementary CII observations from ALMA. This X-SHOOTER/ALMA sample provides
us with the most comprehensive view of reionization-era quasars to date,
allowing us to connect the quasar properties with those of its host galaxy. In
this work we introduce the sample, discuss data reduction and spectral fitting,
and present an analysis of the broad emission line properties. The measured
FeII/MgII flux ratio suggests that the broad line regions of all quasars in the
sample are already enriched in iron. We also find the MgII line to be on
average blueshifted with respect to the CII redshift with a median of
$-391\,\rm{km}\,\rm{s}^{-1}$. A significant correlation between the MgII-CII
and CIV-CII velocity shifts indicates a common physical origin. Furthermore, we
frequently detect large CIV-MgII emission line velocity blueshifts in our
sample with a median value of $-1848\,\rm{km}\,\rm{s}^{-1}$. While we find all
other broad emission line properties not to be evolving with redshift, the
median CIV-MgII blueshift is much larger than found in low-redshift,
luminosity-matched quasars ($-800\,\rm{km}\,\rm{s}^{-1}$). Dividing our sample
into two redshift bins, we confirm an increase of the average CIV-MgII
blueshift with increasing redshift. Future observations of the rest-frame
optical spectrum with the James Webb Space Telescope will be instrumental in
further constraining the possible evolution of quasar properties in the epoch
of reionization.
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Radio broadband visualization of global three-dimensional
magneto-hydrodynamical simulations of spiral galaxies II. Faraday
Depolarization from 100MHz to 10GHz | Observational study of galactic magnetic fields is limited by projected
observables. Comparison with numerical simulations is helpful to understand the
real structures, and observational visualization of numerical data is an
important task. Machida et al. (2018) have reported Faraday depth maps obtained
from numerical simulations. They showed that the relation between azimuthal
angle and Faraday depth depends on the inclination angle. In this paper, we
investigate 100MHz to 10GHz radio synchrotron emission from spiral galaxies,
using the data of global three-dimensional magneto-hydrodynamic simulations. We
model internal and external Faraday depolarization at small scales and assume a
frequency independent depolarization. It is found that the internal and
external Faraday depolarization becomes comparable inside the disk and the
dispersion of Faraday depth becomes about 4rad/m^{2} for face-on view and
40rad/m2 for edge-on view, respectively. The internal depolarization becomes
ineffective in the halo. Because of the magnetic turbulence inside the disk,
frequency independent depolarization works well and the polarization degree
becomes 0.3 at high frequency. When the observed frequency is in the 100 MHz
band, polarized intensity vanishes in the disk, while that from the halo can be
observed. Because the remaining component of polarized intensity is weak in the
halo and the polarization degree is about a few %, it may be difficult to
observe that component. These results indicate that the structures of global
magnetic fields in spiral galaxies could be elucidated, if broadband
polarimetry such as that with the Square Kilometre Array is achieved.
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Large-scale peculiar motions and cosmic acceleration | Recent surveys seem to support bulk peculiar velocities well in excess of
those anticipated by the standard cosmological model. In view of these results,
we consider here some of the theoretical implications of large-scale drift
motions. We find that observers with small, but finite, peculiar velocities
have generally different expansion rates than the smooth Hubble flow. In
particular, it is possible for observers with larger than the average volume
expansion at their location, to experience apparently accelerated expansion
when the universe is actually decelerating. Analogous results have been
reported in studies of inhomogeneous (nonlinear) cosmologies and within the
context of the Lemaitre-Tolman-Bondi models. Here, they are obtained within the
linear regime of a perturbed, dust-dominated Friedmann-Robertson-Walker
cosmology.
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Three-dimensional Analytical Description of Magnetised Winds from
Oblique Pulsars | Rotating neutron stars, or pulsars, are plausibly the source of power behind
many astrophysical systems, such as gamma-ray bursts, supernovae, pulsar wind
nebulae and supernova remnants. In the past several years, 3D numerical
simulations made it possible to compute pulsar spindown luminosity from first
principles and revealed that oblique pulsar winds are more powerful than
aligned ones. However, what causes this enhanced power output of oblique
pulsars is not understood. In this work, using time-dependent 3D
magnetohydrodynamic (MHD) and force-free simulations, we show that, contrary to
the standard paradigm, the open magnetic flux, which carries the energy away
from the pulsar, is laterally non-uniform. We argue that this non-uniformity is
the primary reason for the increased luminosity of oblique pulsars. To
demonstrate this, we construct simple analytic descriptions of aligned and
orthogonal pulsar winds and combine them to obtain an accurate 3D description
of the pulsar wind for any obliquity. Our approach describes both the warped
magnetospheric current sheet and the smooth variation of pulsar wind properties
outside of it. We find that generically the magnetospheric current sheet
separates plasmas that move at mildly relativistic velocities relative to each
other. This suggests that the magnetospheric reconnection is a type of driven,
rather than free, reconnection. The jump in magnetic field components across
the current sheet decreases with increasing obliquity, which could be a
mechanism that reduces dissipation in near-orthogonal pulsars. Our analytical
description of the pulsar wind can be used for constructing models of pulsar
gamma-ray emission, pulsar wind nebulae, and magnetar-powered core-collapse
gamma-ray bursts and supernovae.
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Intrinsic Alignment in redMaPPer clusters -- II. Radial alignment of
satellites toward cluster centers | We study the orientations of satellite galaxies in redMaPPer clusters
constructed from the Sloan Digital Sky Survey at $0.1<z<0.35$ to determine
whether there is any preferential tendency for satellites to point radially
toward cluster centers. We analyze the satellite alignment (SA) signal based on
three shape measurement methods (re-Gaussianization, de Vaucouleurs, and
isophotal shapes), which trace galaxy light profiles at different radii. The
measured SA signal depends on these shape measurement methods. We detect the
strongest SA signal in isophotal shapes, followed by de Vaucouleurs shapes.
While no net SA signal is detected using re-Gaussianization shapes across the
entire sample, the observed SA signal reaches a statistically significant level
when limiting to a subsample of higher luminosity satellites. We further
investigate the impact of noise, systematics, and real physical isophotal
twisting effects in the comparison between the SA signal detected via different
shape measurement methods. Unlike previous studies, which only consider the
dependence of SA on a few parameters, here we explore a total of 17 galaxy and
cluster properties, using a statistical model averaging technique to naturally
account for parameter correlations and identify significant SA predictors. We
find that the measured SA signal is strongest for satellites with the following
characteristics: higher luminosity, smaller distance to the cluster center,
rounder in shape, higher bulge fraction, and distributed preferentially along
the major axis directions of their centrals. Finally, we provide physical
explanations for the identified dependences, and discuss the connection to
theories of SA.
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