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Constraints on the dark matter annihilation from Fermi-LAT observation
of M31: Gamma-ray is a good probe of dark matter (DM) particles in the Universe. We
search for the DM annihilation signals in the direction of the Andromeda galaxy
(M31) using 7.5 year Fermi-LAT pass 8 data. Similar to Pshirkov et al. (2016),
we find that there is residual excess emission from the direction of M31 if
only the galactic disk as traced by the far infrared emission is considered.
Adding a point-like source will improve the fitting effectively, although
additional slight improvements can be found if an extended component such as a
uniform disk or two bubbles is added instead. Taking the far infrared disk plus
a point source as the background model, we search for the DM annihilation
signals in the data. We find that there is strong degeneracy between the
emission from the galaxy and that from 10s GeV mass DM annihilation in the main
halo with quark final state. However, the required DM annihilation cross
section is about $10^{-25}-10^{-24}$ cm$^3$s$^{-1}$, orders of magnitude larger
than the constraints from observations of dwarf spheroidal galaxies, indicating
a non-DM origin of the emission. If DM subhalos are taken into account, the
degeneracy is broken. When considering the enhancement from DM subhalos, the
constraints on DM model parameters are comparable to (or slightly weaker than)
those from the population of dwarf spheroidal galaxies. We also discuss the
inverse Compton scattering component from DM annihilation induced
electrons/positrons. For the first time we include an energy dependent template
of the inverse Compton emission (i.e., a template cube) in the data analysis to
take into account the effect of diffusion of charged particles. We find a
significant improvement of the constraints in the high mass range of DM
particles after considering the inverse Compton emission. | The four cosmic tidal web elements from the $β$-skeleton: Precise cosmic web classification of observed galaxies in massive
spectroscopic surveys can be either highly uncertain or computationally
expensive. As an alternative, we explore a fast Machine Learning-based approach
to infer the underlying dark matter tidal cosmic web environment of a galaxy
distribution from its $\beta$-skeleton graph. We develop and test our
methodology using the cosmological magnetohydrodynamic simulation Illustris-TNG
at $z=0$. We explore three different tree-based machine-learning algorithms to
find that a random forest classifier can best use graph-based features to
classify a galaxy as belonging to a peak, filament or sheet as defined by the
T-Web classification algorithm. The best match between the galaxies and the
dark matter T-Web corresponds to a density field smoothed over scales of $2$
Mpc, a threshold over the eigenvalues of the dimensionless tidal tensor of
$\lambda_{\rm{th}}=0.0$ and galaxy number densities around $8\times 10^{-3}$
Mpc$^{-3}$. This methodology results on a weighted F1 score of 0.728 and a
global accuracy of 74\%. More extensive tests that take into account lightcone
effects and redshift space distortions (RSD) are left for future work. We make
one of our highest ranking random forest models available on a public
repository for future reference and reuse. |
The imprint of dissipation on the shapes of merger remnant LOSVDs: The properties of elliptical galaxies are broadly consistent with simulated
remnants of gas-rich mergers between spirals, motivating more detailed studies
of the imprint of this formation mechanism on the remnant distribution
function. Gas has a strong impact on the non-Gaussian shapes of the
line-of-sight velocity distributions (LOSVDs) of the merger remnant, owing to
the embedded disk that forms out of the gas that retains its angular momentum
during the merger, and the strong central mass concentration from the gas that
falls to the center. The deviations from Gaussianity are parametrized by the
Gauss-Hermite moments h_3 and h_4, which are related to the skewness and
kurtosis of the LOSVDs. We quantify the dependence of the (h_3,h_4)-v/sigma
relations on the initial gas fraction of the progenitor disks in 1:1 mergers,
using Gadget-2 simulations including star formation, radiative cooling, and
feedback from supernovae and AGN. For gas fractions f_gas < ~15% the overall
correlation between h_3 and v/sigma is weak, consisting of a flat negatively
correlated component arising from edge-on viewing angles plus a steep
positively correlated part from face-on projections. The spread in v/sigma
values decreases toward high positive h_4, and there is a trend toward lower
h_4 as the gas fraction increases from 0 to 15%. For f_gas > ~20% the (h_3,4)-
v/sigma distributions look quite different - there is a tight negative h_3-
v/sigma correlation, and a wide spread in v/sigma values at all h_4, in better
agreement with observations. Re-mergers of the high-f_gas remnants (dry
mergers) produce slowly rotating systems with nearly Gaussian LOSVDs. We
explain all of these trends in terms of the underlying orbit structure of the
remnants, as molded by their dissipative formation histories. | Search for CII Emission on Cosmological Scales at Redshift Z~2.6: We present a search for CII emission over cosmological scales at
high-redshifts. The CII line is a prime candidate to be a tracer of star
formation over large-scale structure since it is one of the brightest emission
lines from galaxies. Redshifted CII emission appears in the submillimeter
regime, meaning it could potentially be present in the higher frequency
intensity data from the Planck satellite used to measure the cosmic infrared
background (CIB). We search for CII emission over redshifts z=2-3.2 in the
Planck 545 GHz intensity map by cross-correlating the 3 highest frequency
Planck maps with spectroscopic quasars and CMASS galaxies from the Sloan
Digital Sky Survey III (SDSS-III), which we then use to jointly fit for CII
intensity, CIB parameters, and thermal Sunyaev-Zeldovich (SZ) emission. We
report a measurement of an anomalous emission
$\mathrm{I_\nu}=6.6^{+5.0}_{-4.8}\times10^4$ Jy/sr at 95% confidence, which
could be explained by CII emission, favoring collisional excitation models of
CII emission that tend to be more optimistic than models based on CII
luminosity scaling relations from local measurements; however, a comparison of
Bayesian information criteria reveal that this model and the CIB & SZ only
model are equally plausible. Thus, more sensitive measurements will be needed
to confirm the existence of large-scale CII emission at high redshifts.
Finally, we forecast that intensity maps from Planck cross-correlated with
quasars from the Dark Energy Spectroscopic Instrument (DESI) would increase our
sensitivity to CII emission by a factor of 5, while the proposed Primordial
Inflation Explorer (PIXIE) could increase the sensitivity further. |
The globular cluster system of NGC 1316. II - The extraordinary object
SH2: SH2 has been described as an isolated HII-region, located about 6.5 arcmin
south of the nucleus of NGC 1316 (Fornax A), a merger remnant in the the
outskirts of the Fornax cluster of galaxies. We give a first, preliminary
description of the stellar content and environment of this remarkable object.
We used photometric data in the Washington system and HST photometry from the
Hubble Legacy Archive for a morphological description and preliminary aperture
photometry. Low-resolution spectroscopy provides radial velocities of the
brightest star cluster in SH2 and a nearby intermediate-age cluster. SH2 is not
a normal HII-region, ionized by very young stars. It contains a multitude of
star clusters with ages of approximately 0.1 Gyr. A ring-like morphology is
striking. SH2 seems to be connected to an intermediate-age massive globular
cluster with a similar radial velocity, which itself is the main object of a
group of fainter clusters. Metallicity estimates from emission lines remain
ambiguous. The present data do not yet allow firm conclusions about the nature
or origin of SH2. It might be a dwarf galaxy that has experienced a burst of
extremely clustered star formation. We may witness how globular clusters are
donated to a parent galaxy. | On the relationship between Type Ia supernova luminosity and host-galaxy
properties: A string of recent studies has debated the exact form and physical origin of
an evolutionary trend between the peak luminosity of Type Ia supernovae (SNe
Ia) and the properties of the galaxies that host them. We shed new light on the
discussion by presenting an analysis of ~200 low-redshift SNe Ia in which we
measure the separation of Hubble residuals (HR; as probes of luminosity)
between two host-galaxy morphological types. We show that this separation can
test the predictions made by recently proposed models, using an independently
and empirically determined distribution of each morphological type in
host-property space. Our results are partially consistent with the new HR--age
slope, but we find significant scatter in the predictions from different galaxy
catalogues. The inconsistency in age illuminates an issue in the current debate
that was not obvious in the long-discussed mass models: HR--host-property
models are strongly dependent on the methods employed to determine galaxy
properties. While our results demonstrate the difficulty in constructing a
universal model for age as a proxy for host environment, our results indeed
identify evolutionary trends between mass, age, morphology, and HR values,
encouraging (or requiring, if such trends are to be accounted for in
cosmological studies) further investigation. |
Rastall gravity extension of the standard $Λ$CDM model:
theoretical features and observational constraints: We present a detailed investigation of the Rastall gravity extension of the
standard $\Lambda$CDM model. We review the model for two simultaneous
modifications of different nature in the Friedmann equation due to the Rastall
gravity: the new contributions of the material (actual) sources (considered as
effective source) and the altered evolution of the material sources. We discuss
the role/behavior of these modifications with regard to some low redshift
tensions, including the so-called $H_0$ tension, prevailing within the standard
$\Lambda$CDM. We constrain the model at the level of linear perturbations, and
obtain the first constraints through a robust and accurate analysis using the
latest full Planck CMB data, with and without including BAO data. We find that
the Rastall parameter $\epsilon$ (null for general relativity) is consistent
with zero at 68\% CL (with a tendency towards positive values, $-0.0001 <
\epsilon < 0.0007$ (CMB+BAO) at 68\% CL), which in turn implies no significant
statistical evidence for deviation from general relativity, and also a
precision of $\mathcal{O}(10^{-4})$ for the coefficient $-1/2$ of the term
$g_{\mu\nu}R$ in the Einstein field equations of general relativity
(guaranteeing the local energy-momentum conservation). We explore the
consequences led by the Rastall gravity on the cosmological parameters in the
light of the observational analyses. It turns out that the effective source
dynamically screens the usual vacuum energy at high redshifts, but this
mechanism barely works due to the opposition by the altered evolution of CDM.
Consequently, two simultaneous modifications of different nature in the
Friedmann equation act against each other, and do not help to considerably
relax the so-called low redshift tensions. Our results may offer a guide for
the research community that studies the Rastall gravity in various aspects of
gravitation and cosmology. | Constraints on fNL from Wilkinson Microwave Anisotropy Probe 7-year data
using a neural network classifier: We present a multi-class neural network (NN) classifier as a method to
measure nonGaussianity, characterised by the local non-linear coupling
parameter fNL, in maps of the cosmic microwave background (CMB) radiation. The
classifier is trained on simulated non-Gaussian CMB maps with a range of known
fNL values by providing it with wavelet coefficients of the maps; we consider
both the HealPix (HW) wavelet and the spherical Mexican hat wavelet (SMHW).
When applied to simulated test maps, the NN classfier produces results in very
good agreement with those obtained using standard chi2 minimization. The
standard deviations of the fNL estimates for WMAPlike simulations were {\sigma}
= 22 and {\sigma} = 33 for the SMHW and the HW, respectively, which are
extremely close to those obtained using classical statistical methods in Curto
et al. and Casaponsa et al. Moreover, the NN classifier does not require the
inversion of a large covariance matrix, thus avoiding any need to regularise
the matrix when it is not directly invertible, and is considerably faster. |
The Universe SPHEREx Will See: Empirically Based Galaxy Simulations and
Redshift Predictions: We simulate galaxy properties and redshift estimation for SPHEREx, the next
NASA Medium Class Explorer. To make robust models of the galaxy population and
test spectro-photometric redshift performance for SPHEREx, we develop a set of
synthetic spectral energy distributions based on detailed fits to COSMOS2020
photometry spanning 0.1-8 micron. Given that SPHEREx obtains low-resolution
spectra, emission lines will be important for some fraction of galaxies. Here
we expand on previous work, using better photometry and photometric redshifts
from COSMOS2020, and tight empirical relations to predict robust emission line
strengths and ratios. A second galaxy catalog derived from the GAMA survey is
generated to ensure the bright ($m_{AB}<18$ in the i-band) sample is
representative over larger areas. Using template fitting to estimate
photometric continuum redshifts, we forecast redshift recovery of 19 million
galaxies over 30000 sq. deg. with $\sigma_z<0.003(1+z)$, 445 million with
$\sigma_z<0.1(1+z)$ and 810 million with $\sigma_z<0.2(1+z)$. We also find
through idealized tests that emission line information from spectrally dithered
flux measurements can yield redshifts with accuracy beyond that implied by the
naive SPHEREx channel resolution, motivating the development of a hybrid
continuum-line redshift estimation approach. | Dark matter fluid constraints from galaxy rotation curves: Galaxy rotation curves are considered to be convincing evidence for dark
matter or some dynamically equivalent alternative mechanism. Starting only from
the rotation curve data, we present a model independent approach of testing a
general hypothesis that dark matter has the properties of a barotropic fluid.
It is shown how the speed of sound squared can be expressed in terms of
rotation curve data and their radial derivatives and how model independent
constraints can be obtained from the requirements that it is confined between 0
and $c^2$. Using the Milky Way rotation curve data available in the literature,
we obtain the constraints on the barotropic fluid speed of sound and illustrate
the potential of this approach. Technical challenges, limitations and possible
future extensions and improvements of the proposed approach are discussed. |
On the origin of M81 group extended dust emission: Galactic cirrus emission at far-infrared wavelengths affects many
extragalactic observations. Separating this emission from that associated with
extragalactic objects is both important and difficult. In this paper we discuss
a particular case, the M81 group, and the identification of diffuse structures
prominent in the infrared, but also detected at optical wavelengths. The origin
of these structures has previously been controversial, ranging from them being
the result of a past interaction between M81 and M82 or due to more local
Galactic emission. We show that over of order a few arcminute scales the
far-infrared (Herschel 250 &\mu&m) emission correlates spatially very well with
a particular narrow velocity (2-3 km/s) component of the Galactic HI. We find
no evidence that any of the far-infrared emission associated with these
features actually originates in the M81 group. Thus we infer that the
associated diffuse optical emission must be due to galactic light back
scattered off dust in our galaxy. Ultra-violet observations pick out young
stellar associations around M81, but no detectable far-infrared emission. We
consider in detail one of the Galactic cirrus features, finding that the
far-infrared HI relation breaks down below arc minute scales and that at
smaller scales there can be quite large dust temperature variations. | Magnetising the Cosmic Web during Reionisation: Evidence repeatedly suggests that cosmological sheets, filaments and voids
may be substantially magnetised today. The origin of magnetic fields in the
intergalactic medium is however currently uncertain. We discuss a
magnetogenesis mechanism based on the exchange of momentum between hard photons
and electrons in an inhomogeneous intergalactic medium. Operating near ionising
sources during the epoch of reionisation, it is capable of generating magnetic
seeds of relevant strengths over scales comparable to the distance between
ionising sources. Furthermore, when the contributions of all ionising sources
and the distribution of gas inhomogeneities are taken into account, it leads,
by the end of reionisation, to a level of magnetisation that may account for
the current magnetic fields strengths in the cosmic web. |
The effect of baryons on redshift space distortions and cosmic density
and velocity fields in the EAGLE simulation: We use the EAGLE galaxy formation simulation to study the effects of baryons
on the power spectrum of the total matter and dark matter distributions and on
the velocity fields of dark matter and galaxies. On scales
$k{\stackrel{>}{{}_\sim}} 4{h\,{\rm Mpc}^{-1}}$ the effect of baryons on the
amplitude of the total matter power spectrum is greater than $1\%$. The
back-reaction of baryons affects the density field of the dark matter at the
level of $\sim3\%$ on scales of $1\leq k/({h\,{\rm Mpc}^{-1}})\leq 5$. The dark
matter velocity divergence power spectrum at
$k{\stackrel{<}{{}_\sim}}0.5{h\,{\rm Mpc}^{-1}}$ is changed by less than $1\%$.
The 2D redshift-space power spectrum is affected at the level of $\sim6\%$ at
$|\vec{k}|{\stackrel{>}{{}_\sim}} 1{h\,{\rm Mpc}^{-1}}$ (for $\mu>0.5$), but
for $|\vec{k}|\leq 0.4{h\,{\rm Mpc}^{-1}}$ it differs by less than $1\%$. We
report vanishingly small baryonic velocity bias for haloes: the peculiar
velocities of haloes with $M_{200}>3\times10^{11}{{\rm M}_{\odot}}$ (hosting
galaxies with $M_{*}>10^9{{\rm M}_{\odot}}$) are affected at the level of at
most $1~$km/s, which is negligible for $1\%$-precision cosmology. We caution
that since EAGLE overestimates cluster gas fractions it may also underestimate
the impact of baryons, particularly for the total matter power spectrum.
Nevertheless, our findings suggest that for theoretical modelling of redshift
space distortions and galaxy velocity-based statistics, baryons and their
back-reaction can be safely ignored at the current level of observational
accuracy. However, we confirm that the modelling of the total matter power
spectrum in weak lensing studies needs to include realistic galaxy formation
physics in order to achieve the accuracy required in the precision cosmology
era. | Discovery of "Warm Dust" Galaxies in Clusters at z~0.3: Evidence for
Stripping of Cool Dust in the Dense Environment?: Using far-infrared imaging from the "Herschel Lensing Survey", we derive dust
properties of spectroscopically-confirmed cluster member galaxies within two
massive systems at z~0.3: the merging Bullet Cluster and the more relaxed
MS2137.3-2353. Most star-forming cluster sources (~90%) have characteristic
dust temperatures similar to local field galaxies of comparable infrared (IR)
luminosity (T_dust ~ 30K). Several sub-LIRG (L_IR < 10^11 L_sun) Bullet Cluster
members are much warmer (T_dust > 37K) with far-infrared spectral energy
distribution (SED) shapes resembling LIRG-type local templates. X-ray and
mid-infrared data suggest that obscured active galactic nuclei do not
contribute significantly to the infrared flux of these "warm dust" galaxies.
Sources of comparable IR-luminosity and dust temperature are not observed in
the relaxed cluster MS2137, although the significance is too low to speculate
on an origin involving recent cluster merging. "Warm dust" galaxies are,
however, statistically rarer in field samples (> 3sigma), indicating that the
responsible mechanism may relate to the dense environment. The spatial
distribution of these sources is similar to the whole far-infrared bright
population, i.e. preferentially located in the cluster periphery, although the
galaxy hosts tend towards lower stellar masses (M_* < 10^10 M_sun). We propose
dust stripping and heating processes which could be responsible for the
unusually warm characteristic dust temperatures. A normal star-forming galaxy
would need 30-50% of its dust removed (preferentially stripped from the outer
reaches, where dust is typically cooler) to recover a SED similar to a "warm
dust" galaxy. These progenitors would not require a higher IR-luminosity or
dust mass than the currently observed normal star-forming population. |
Are passive red spirals truly passive? - The current star formation
activity of optically-red disc galaxies: We use GALEX ultraviolet and WISE 22 micron observations to investigate the
current star formation activity of the optically-red spirals recently
identified as part of the Galaxy Zoo project. These galaxies were accurately
selected from the Sloan Digital Sky Survey in order to be pure discs with low
or no current star formation activity, representing one of the best
optically-selected samples of candidate passive spirals. However, we show that
these galaxies are not only still forming stars at a significant rate >= 1
M_sun/yr but, more importantly, their star formation activity is not different
from that of normal star-forming discs of the same stellar mass (M* >= 10^10.2
M_sun). Indeed, these systems lie on the UV-optical blue sequence, even without
any corrections for internal dust attenuation, and they follow the same
specific star formation rate vs. stellar mass relation of star-forming
galaxies. Our findings clearly show that, at high stellar masses, optical
colours do not allow to discriminate between actively star-forming and truly
quiescent systems. | Supermassive Population III Supernovae and the Birth of the First
Quasars: The existence of supermassive black holes as early as z ~ 7 is one of the
great unsolved problems in cosmological structure formation. One leading theory
argues that they are born during catastrophic baryon collapse in z ~ 15
protogalaxies in strong Lyman-Werner UV backgrounds. Atomic line cooling in
such galaxies fragments baryons into massive clumps that are thought to
directly collapse to 10^4 - 10^5 solar-mass black holes. We have now discovered
that some of these fragments can instead become supermassive stars that
eventually explode as pair-instability supernovae with energies of ~ 10^55 erg,
the most energetic explosions in the universe. We have calculated light curves
and spectra for supermassive Pop III PI SNe with the Los Alamos RAGE and
SPECTRUM codes. We find that they will be visible in NIR all-sky surveys by
Euclid out to z ~ 10 - 15 and by WFIRST and WISH out to z ~ 15 - 20, perhaps
revealing the birthplaces of the first quasars. |
The Mira-Titan Universe IV. High Precision Power Spectrum Emulation: Modern cosmological surveys are delivering datasets characterized by
unprecedented quality and statistical completeness; this trend is expected to
continue into the future as new ground- and space-based surveys come online. In
order to maximally extract cosmological information from these observations,
matching theoretical predictions are needed. At low redshifts, the surveys
probe the nonlinear regime of structure formation where cosmological
simulations are the primary means of obtaining the required information. The
computational cost of sufficiently resolved large-volume simulations makes it
prohibitive to run very large ensembles. Nevertheless, precision emulators
built on a tractable number of high-quality simulations can be used to build
very fast prediction schemes to enable a variety of cosmological inference
studies. We have recently introduced the Mira-Titan Universe simulation suite
designed to construct emulators for a range of cosmological probes. The suite
covers the standard six cosmological parameters $\{\omega_m,\omega_b, \sigma_8,
h, n_s, w_0\}$ and, in addition, includes massive neutrinos and a dynamical
dark energy equation of state, $\{\omega_{\nu}, w_a\}$. In this paper we
present the final emulator for the matter power spectrum based on 111
cosmological simulations, each covering a (2.1Gpc)$^3$ volume and evolving
3200$^3$ particles. An additional set of 1776 lower-resolution simulations and
TimeRG perturbation theory results for the power spectrum are used to cover
scales straddling the linear to mildly nonlinear regimes. The emulator provides
predictions at the two to three percent level of accuracy over a wide range of
cosmological parameters and is publicly released as part of this paper. | Phenomenological Dark Energy model with hybrid dynamic Cosmological
Constant: We investigate Dark Energy by associating it with vacuum energy or
Cosmological constant ${\Lambda}$ which is taken to be dynamic in nature. Our
approach is phenomenological and falls within the domain of variable-$\Lambda$
Cosmology. However, motivated by quantum theory of metastable vacuum decay, we
proposed a new phenomenological decay law of $\Lambda$(t) where $\Lambda$(t) is
a superposition of constant and variable components viz. $\Lambda$(t) =
$\Lambda_{C}$ + $\Lambda_{v}$ which is indicated by the word $"$hybrid
dynamic$"$ in the title. By taking a simplified two-fluid scenario with the
Universe consisting of Dark Energy and another major component, we found the
solutions for three particular phenomenological expressions and made a
parametrization of the model in terms of dilution parameter (the dilution
parameter has been defined in the text as the exponent of scale factor in the
expression of density of the other major component, representing the dilution
of the component with the expansion of Universe in the presence of dynamic Dark
Energy). For pressureless Dust and dynamic Dark Energy Universe, we found the
present-day matter density ($\Omega_{m0}$) and dilution parameter (u) to be
$\Omega_{m0}$ = 0.29 $\pm$ 0.03, u = 2.90 $\pm$ 0.54 at 1 $\sigma$ by analysing
580 supernova from Union 2.1 catalogue. The physical features of the model in
regard to scale factor evolution, deceleration parameter, cosmic age has also
been studied and parallels have been drawn with $\Lambda$CDM model. The status
of Cosmological problems in the model has also been checked which showed that
the model solves the Cosmological Constant Problem but the Coincidence problem
still exists in the model. |
On the Habitability of Universes without Stable Deuterium: In both stars and in the early universe, the production of deuterium is the
first step on the way to producing heavier nuclei. If the strong force were
slightly weaker, deuterium would not be stable, and many authors have noted
that nuclesynthesis would be compromised so that helium production could not
proceed through standard reaction chains. Motivated by the possibility that
other regions of space-time could have different values for the fundamental
constants, this paper considers stellar evolution in universes without stable
deuterium and argues that such universes can remain habitable. Even in
universes with no stellar nucleosynthesis, stars can form and will generate
energy through gravitational contraction. We show that such stars can be
sufficiently luminous and long-lived to support life. Stars with initial masses
that exceed the Chandrasekhar mass cannot be supported by degeneracy pressure
and explode at the end of their contraction phase. The resulting explosive
nucleosynthesis can provide the universe with some heavy elements. We also
explore the possibility that helium can be produced in stellar cores through a
triple-nucleon reaction (roughly analogous to the triple-alpha reaction). Next
we show that with even trace amounts of heavy elements --- produced through the
triple-nucleon process or by explosive nucleosynthesis --- the CNO cycle can
operate and allow stars to function. Finally, we consider Big Bang
Nucleosynthesis without stable deuterium and find that only trace amounts of
helium are produced, with even smaller abundances of other nuclei. With stars
evolving through gravitational contraction, explosive nucleosynthesis, the
triple-nucleon reaction, and the CNO cycle, universes with no stable deuterium
are thus potentially habitable, contrary to many previous claims. | What Can Gamma-rays from Space tell us About the Madala Hypothesis?: The recent Madala hypothesis, a conjecture that seeks to explain anomalies
within Large Hadron Collider (LHC) data (particularly in the transverse
momentum of the Higgs boson), is interesting for more than just a statistical
hint at unknown and unpredicted physics. This is because the model itself
contains additional new particles that may serve as Dark Matter (DM)
candidates. These particles interact with the Standard Model via a scalar
mediator boson $S$. More interesting still, the conjectured mass range for the
DM candidate ($65$ - $100$ GeV) lies within the region of models viable to try
explain the recent Galactic Centre (GC) gamma-ray excess seen by Fermi Large
Area Telescope (Fermi-LAT) and the High Energy Stereoscopic System (HESS).
Therefore, assuming $S$ decays promptly, it should be possible to check what
constraints are imposed upon the effective DM annihilation cross-section in the
Madala scenario by hunting signatures of $S$ decay that follows DM annihilation
within dense astrophysical structures. In order to make use of existing data,
we use the Reticulum II dwarf galaxy and the galactic centre gamma-ray excess
data sets from Fermi-LAT, and compare these to the consequences of various
decay paths for $S$ in the aforementioned environments. We find that, based on
this existing data, we can limit $\tau$ lepton, quark, direct gamma-ray, and
weak boson channels to levels below the canonical relic cross-section. This
allows us to set new limits on the branching ratios of $S$ decay, which can
rule out a Higgs-like decay branching for $S$, in the case where the Madala DM
candidate is assumed to comprise all DM. |
Sterile neutrino dark matter bounds from galaxies of the Local Group: We show that the canonical oscillation-based (non-resonant) production of
sterile neutrino dark matter is inconsistent at $>99$% confidence with
observations of galaxies in the Local Group. We set lower limits on the
non-resonant sterile neutrino mass of $2.5$ keV (equivalent to $0.7$ keV
thermal mass) using phase-space densities derived for dwarf satellite galaxies
of the Milky Way, as well as limits of $8.8$ keV (equivalent to $1.8$ keV
thermal mass) based on subhalo counts of $N$-body simulations of M 31
analogues. Combined with improved upper mass limits derived from significantly
deeper X-ray data of M 31 with full consideration for background variations, we
show that there remains little room for non-resonant production if sterile
neutrinos are to explain $100$% of the dark matter abundance. Resonant and
non-oscillation sterile neutrino production remain viable mechanisms for
generating sufficient dark matter sterile neutrinos. | Characterising the intra-cluster light in The Three Hundred simulations: We characterise the intra-cluster light (ICL) in ensembles of full-physics
cluster simulations from The Three Hundred project, a suite of 324
hydrodynamical resimulations of cluster-sized halos. We identify the ICL as
those stellar particles bound to the potential of the cluster itself, but not
to any of its substructures, and separate the brightest cluster galaxy (BCG) by
means of a fixed 50 kpc aperture. We find the total BCG+ICL mass to be in
agreement with state-of-the-art observations of galaxy clusters. The ICL mass
fraction of our clusters is between 30 and 50 per cent of the total stellar
mass within $R_{500}$, while the BCG represents around 10 percent. We further
find no trend of the ICL fraction with cluster halo mass, at least not in the
range $[0.2,3]\cdot10^{15}h^{-1}M_\odot$ considered here. For the dynamical
state, characterised both by theoretical estimators and by the recent merging
history of the cluster, there is a clear correlation, such that more relaxed
clusters and those that have undergone fewer recent mergers have a higher ICL
fraction. Finally, we investigate the possibility of using the ICL to explore
the dark matter (DM) component of galaxy clusters. We compute the volumetric
density profile for the DM and ICL components and show that, up to $R_{500}$,
the ratio between the two can be described by a power law. Working with the
velocity dispersion profiles instead, we show that the ratio can be fit by a
straight line. Providing the parameters of these fits, we show how the ICL can
be used to infer DM properties. |
On Possible Variation in the Cosmological Baryon Fraction: The fraction of matter that is in the form of baryons or dark matter could
have spatial fluctuations in the form of baryon-dark matter isocurvature
fluctuations. We use big bang nucleosynthesis calculations compared with
observed light element abundances as well as galaxy cluster gas fractions to
constrain cosmological variations in the baryon fraction. Light element
abundances constrain spatial variations to be less than 26-27%, while a sample
of "relaxed" galaxy clusters shows spatial variations in gas fractions less
than 8%. Larger spatial variations could cause differential screening of the
primary cosmic microwave background anisotropies, leading to asymmetries in the
fluctuations and ease some tension with the halo-star 7Li abundance.
Fluctuations within our allowed bounds can lead to "B-mode" CMB polarization
anisotropies at a non-negligible level. | The Properties of Cosmic Velocity Fields: Understanding the velocity field is very important for modern cosmology: it
gives insights to structure formation in general, and also its properties are
crucial ingredients in modelling redshift-space distortions and in interpreting
measurements of the kinetic Sunyaev-Zeldovich effect. Unfortunately,
characterising the velocity field in cosmological N-body simulations is
inherently complicated by two facts: i) The velocity field becomes manifestly
multi-valued after shell-crossing and has discontinuities at caustics. This is
due to the collisionless nature of dark matter. ii) N-body simulations sample
the velocity field only at a set of discrete locations, with poor resolution in
low-density regions. In this paper, we discuss how the associated problems can
be circumvented by using a phase-space interpolation technique. This method
provides extremely accurate estimates of the cosmic velocity fields and its
derivatives, which can be properly defined without the need of the arbitrary
"coarse-graining" procedure commonly used. We explore in detail the
configuration-space properties of the cosmic velocity field on very large
scales and in the highly nonlinear regime. In particular, we characterise the
divergence and curl of the velocity field, present their one-point statistics,
analyse the Fourier-space properties and provide fitting formulae for the
velocity divergence bias relative to the non-linear matter power spectrum. We
furthermore contrast some of the interesting differences in the velocity fields
of warm and cold dark matter models. We anticipate that the high-precision
measurements carried out here will help to understand in detail the dynamics of
dark matter and the structures it forms. |
Optimal constraints on primordial gravitational waves from the lensed
CMB: We demonstrate how to obtain optimal constraints on a primordial
gravitational wave component in lensed Cosmic Microwave Background (CMB) data
under ideal conditions. We first derive an estimator of the tensor-to-scalar
ratio, $r$, by using an error-controlled close approximation to the exact
posterior, under the assumption of Gaussian primordial CMB and lensing
deflection potential. This combines fast internal iterative lensing
reconstruction with optimal recovery of the unlensed CMB. We evaluate its
performance on simulated low-noise polarization data targeted at the
recombination peak. We carefully demonstrate our $r$-posterior estimate is
optimal and shows no significant bias, making it the most powerful estimator of
primordial gravitational waves from the CMB. We compare these constraints to
those obtained from $B$-mode band-power likelihood analyses on the same
simulated data, before and after map-level quadratic estimator delensing, and
iterative delensing. Internally, iteratively delensed band powers are only
slightly less powerful on average (by less than 10\%), promising
close-to-optimal constraints from a stage IV CMB experiment. | The extreme synchronicity of stellar ages of red galaxies in the JKCS041
cluster at z=2.2: Above redshift z ~ 1.4, we known little or nothing about the stellar ages of
red galaxies in clusters, yet at these high redshifts important changes are
predicted by current renditions of galaxy formation models embedded in the
standard hierarchical paradigm of structure formation. Red-sequence galaxies in
the cluster JKCS041 at z=2.2 show a tight distribution in colour that indicates
a star formation history that is highly synchronized across galaxies.
Specifically, we measure a spread in stellar age of 160+/-30 Myr, in marked
disagreement with the current understanding of how massive red galaxies form in
clusters, i.e. if they are produced somewhat stochastically in merging episodes
that sometimes involve gas, hence star formation. The existence of a tight
distribution in colour when the universe was at one quarter of its current age
implies that mechanisms that have not yet been implemented in current galaxy
formation scenarios long ago began to shape the star formation history of red
cluster galaxies. |
The stellar evolution of Luminous Red Galaxies, and its dependence on
colour, redshift, luminosity and modelling: We present a series of colour evolution models for Luminous Red Galaxies
(LRGs) in the 7th spectroscopic data release of the Sloan Digital Sky Survey
(SDSS), computed using the full-spectrum fitting code VESPA on high
signal-to-noise stacked spectra. The colour-evolution models are computed as a
function of colour, luminosity and redshift, and we do not a-priori assume that
LRGs constitute a uniform population of galaxies in terms of stellar evolution.
By computing star-formation histories from the fossil record, the measured
stellar evolution of the galaxies is decoupled from the survey's selection
function, which also evolves with redshift. We present these evolutionary
models computed using three different sets of Stellar Population Synthesis
(SPS) codes. We show that the traditional fiducial model of purely passive
stellar evolution of LRGs is broadly correct, but it is not sufficient to
explain the full spectral signature. We also find that higher-order corrections
to this model are dependent on the SPS used, particularly when calculating the
amount of recent star formation. The amount of young stars can be
non-negligible in some cases, and has important implications for the
interpretation of the number density of LRGs within the selection box as a
function of redshift. Dust extinction, however, is more robust to the SPS
modelling: extinction increases with decreasing luminosity, increasing
redshift, and increasing r-i colour. We are making the colour evolution tracks
publicly available at http://www.icg.port.ac.uk/~tojeiror/lrg_evolution/. | The Mass Function of Primordial Rogue Planet MACHOs in quasar
nanolensing: The recent Sumi et al (2010, 2011) detection of free roaming planet mass
MACHOs in cosmologically significant numbers recalls their original detection
in quasar microlening studies (Schild 1996, Colley and Schild 2003). We
consider the microlensing signature of such a population, and find that the
nano-lensing (microlensing) would be well characterized by a statistical
microlensing theory published previously by Refsdal and Stabel (1991).
Comparison of the observed First Lens microlensing amplitudes with the
theoretical prediction gives close agreement and a methodology for determining
the slope of the mass function describing the population. Our provisional
estimate of the power law exponent in an exponential approximation to this
distribution is $2.98^{+1.0}_{-0.5}.$ where a Salpeter slope is 2.35. |
Constraining DHOST theories with linear growth of matter density
fluctuations: We investigate the potential of cosmological observations, such as galaxy
surveys, for constraining degenerate higher-order scalar-tensor (DHOST)
theories, focusing in particular on the linear growth of the matter density
fluctuations. We develop a formalism to describe the evolution of the matter
density fluctuations during the matter dominated era and in the early stage of
the dark energy dominated era in DHOST theories, and give an approximate
expression for the gravitational growth index in terms of several parameters
characterizing the theory and the background solution under consideration. By
employing the current observational constraints on the growth index, we obtain
a new constraint on a parameter space of DHOST theories. Combining our result
with other constraints obtained from the Newtonian stellar structure, we show
that the degeneracy between the effective parameters of DHOST theories can be
broken without using the Hulse-Taylor pulsar constraint. | Diffuse Sources, Clustering and the Excess Anisotropy of the Radio
Synchrotron Background: We present the largest low frequency (120~MHz) arcminute resolution image of
the radio synchrotron background (RSB) to date, and its corresponding angular
power spectrum of anisotropies (APS) with angular scales ranging from $3^\circ$
to $0.3^\prime$. We show that the RSB around the North Celestial Pole has a
significant excess anisotropy power at all scales over a model of unclustered
point sources based on source counts of known source classes. This anisotropy
excess, which does not seem attributable to the diffuse Galactic emission,
could be linked to the surface brightness excess of the RSB. To better
understand the information contained within the measured APS, we model the RSB
varying the brightness distribution, size, and angular clustering of potential
sources. We show that the observed APS could be produced by a population of
faint clustered point sources only if the clustering is extreme and the size of
the Gaussian clusters is $\lesssim 1'$. We also show that the observed APS
could be produced by a population of faint diffuse sources with sizes $\lesssim
1'$, and this is supported by features present in our image. Both of these
cases would also cause an associated surface brightness excess. These classes
of sources are in a parameter space not well probed by even the deepest radio
surveys to date. |
Snowmass2021 Cosmic Frontier White Paper: Rubin Observatory after LSST: The Vera C. Rubin Observatory will begin the Legacy Survey of Space and Time
(LSST) in 2024, spanning an area of 18,000 square degrees in six bands, with
more than 800 observations of each field over ten years. The unprecedented data
set will enable great advances in the study of the formation and evolution of
structure and exploration of physics of the dark universe. The observations
will hold clues about the cause for the accelerated expansion of the universe
and possibly the nature of dark matter. During the next decade, LSST will be
able to confirm or dispute if tensions seen today in cosmological data are due
to new physics. New and unexpected phenomena could confirm or disrupt our
current understanding of the universe. Findings from LSST will guide the path
forward post-LSST. The Rubin Observatory will still be a uniquely powerful
facility even then, capable of revealing further insights into the physics of
the dark universe. These could be obtained via innovative observing strategies,
e.g., targeting new probes at shorter timescales than with LSST, or via modest
instrumental changes, e.g., new filters, or through an entirely new instrument
for the focal plane. This White Paper highlights some of the opportunities in
each scenario from Rubin observations after LSST. | Comparing approximate methods for mock catalogues and covariance
matrices II: Power spectrum multipoles: We study the accuracy of several approximate methods for gravitational
dynamics in terms of halo power spectrum multipoles and their estimated
covariance matrix. We propagate the differences in covariances into parameter
constrains related to growth rate of structure, Alcock-Paczynski distortions
and biasing. We consider seven methods in three broad categories: algorithms
that solve for halo density evolution deterministically using Lagrangian
trajectories (ICE-COLA, Pinocchio and PeakPatch), methods that rely on halo
assignment schemes onto dark-matter overdensities calibrated with a target
N-body run (Halogen, Patchy) and two standard assumptions about the full
density PDF (Gaussian and Lognormal). We benchmark their performance against a
set of three hundred N-body simulations, running similar sets of approximate
simulations with matched initial conditions, for each method. We find that most
methods reproduce the monopole to within $5\%$, while residuals for the
quadrupole are sometimes larger and scale dependent. The variance of the
multipoles is typically reproduced within $10\%$. Overall, we find that
covariances built from approximate simulations yield errors on model parameters
within $10\%$ of those from the N-body based covariance. |
Statistics of the structure components in S0s: implications for bar
induced secular evolution: The fractions and dimension of bars, rings and lenses are studied in the
Near-IR S0 galaxy Survey (NIRS0S). We find evidence that multiple lenses in
some barred S0s are related to bar resonances in a similar manner as the inner
and outer rings, for which the outer/inner length ratio 2. Inner lenses in the
non-barred galaxies normalized to galaxy diameter are clearly smaller than
those in the barred systems. Interestingly, these small lenses in the
non-barred galaxies have similar sizes as barlenses (lens-like structures
embedded in a bar), and therefore might actually be barlenses in former barred
galaxies, in which the outer, more elongated bar component, has been destroyed.
We also find that fully developed inner lenses are on average a factor 1.3
larger than bars, whereas inner rings have similar sizes as bars. The fraction
of inner lenses is found to be constant in all family classes (A, AB, B).
Nuclear bars appear most frequently among the weakly barred (AB) galaxies,
which is consistent with the theoretical models by Maciejewski & Athanassoula
(2008). Similar sized bars as the nuclear bars were detected in seven
'non-barred' S0s. Galaxy luminosity does not uniquely define the sizes of bars
or bar-related structures, neither is there any upper limit in galaxy
luminosity for bar formation. Although all the family classes cover the same
range of galaxy luminosity, the non-barred (A) galaxies are on average 0.6 mag
brighter than the strongly barred (B) systems. Overall, our results are
consistent with the idea that bars play an important role in the formation of
the structure components of galaxies. The fact that multiple lenses are common
in S0s, and that at least the inner lenses can have very old stellar
populations, implies that the last destructive merger, or major gas accretion
event, must have taken place at a fairly high redshift. | Intensity mapping: a new window into the cosmos: The technique of intensity mapping (IM) has emerged as a powerful tool to
explore the universe at $z < 6$. IM measures the integrated emission from
sources over a broad range of frequencies, unlocking significantly more
information than traditional galaxy surveys. Astrophysical uncertainties,
however, constitute an important systematic in our attempts to constrain
cosmology with IM. I describe an innovative approach which allows us to fully
utilize our current knowledge of astrophysics in order to develop cosmological
forecasts from IM. This framework can be used to exploit synergies with other
complementary surveys, thereby opening up the fascinating possibility of
constraining physics beyond $\Lambda$CDM from future IM observations. |
A case study of early galaxy cluster with the Athena X-IFU: Context: Observations of the hot gas in distant clusters of galaxies, though
challenging, are key to understand the role of intense galaxy activity,
super-massive black hole feedback and chemical enrichment in the process of
massive halos assembly. Aims: We assess the feasibility to retrieve, using
X-ray hyperspectral data only, the thermodymamical hot gas properties and
chemical abundances of a $z=2$ galaxy cluster of mass M500=7 x $10^{13}
M_{\odot}$, extracted from the Hydrangea hydrodynamical simulation. Methods: We
create mock X-ray observations of the future X-ray Integral Field Unit (X-IFU)
onboard the Athena mission. By forward-modeling the measured 0.4-1 keV surface
brightness, the projected gas temperature and abundance profiles, we
reconstruct the three-dimensional distribution for the gas density, pressure,
temperature and entropy. Results: Thanks to its large field-of-view, high
throughput and exquisite spectral resolution, one X-IFU exposure lasting 100ks
enables reconstructing density and pressure profiles with 20% precision out to
a characteristic radius of R500, accounting for each quantity's intrinsic
dispersion in the Hydrangea simulations. Reconstruction of abundance profiles
requires both higher signal-to-noise ratios and specific binning schemes. We
assess the enhancement brought by longer exposures and by observing the same
object at later evolutionary stages ($z=1-1.5$). Conclusions: Our analysis
highlights the importance of scatter in the radially binned gas properties,
which induces significant effects on the observed projected quantities. The
fidelity of the reconstruction of gas profiles is sensitive to the degree of
gas components mixing along the line-of-sight. Future analyses should aim at
involving dedicated hyper-spectral models and fitting methods that are able to
grasp the complexity of such three-dimensional, multi-phase, diffuse gas
structures. | Full forward model of galaxy clustering statistics with AbacusSummit
lightcones: Novel summary statistics beyond the standard 2-point correlation function
(2PCF) are necessary to capture the full astrophysical and cosmological
information from the small-scale (r < 30Mpc/h) galaxy clustering. However, the
analysis of beyond-2PCF statistics on small scales is challenging because we
lack the appropriate treatment of observational systematics for arbitrary
summary statistics of the galaxy field. In this paper, we develop a full
forward modeling pipeline for a wide range of summary statistics using the
large high-fidelity AbacusSummit lightcones that accounts for many systematic
effects but also remains flexible and computationally efficient to enable
posterior sampling. We apply our forward model approach to a fully realistic
mock galaxy catalog and demonstrate that we can recover unbiased constraints on
the underlying galaxy-halo connection model using two separate summary
statistics: the standard 2PCF and the novel k-th nearest neighbor (kNN)
statistics, which are sensitive to correlation functions of all orders. We will
extend this method to a full cosmology emulator in a follow up paper. We expect
this to become a powerful approach when applying to upcoming surveys such as
DESI where we can leverage a multitude of summary statistics across a wide
redshift range to maximally extract information from the non-linear scales. |
Shape of the inflaton potential and the efficiency of the universe
heating: It is shown that the efficiency of the universe heating by an inflaton field
depends not only on the possible presence of parametric resonance in the
production of scalar particles but also strongly depends on the character of
the inflaton approach to its mechanical equilibrium point. In particular, when
the inflaton oscillations deviate from pure harmonic ones toward a succession
of step functions, the production probability rises by several orders of
magnitude. This in turn leads to a much higher temperature of the universe
after the inflaton decay, in comparison to the harmonic case. An example of the
inflaton potential is presented which creates a proper modification of the
evolution of the inflaton toward equilibrium and does not destroy the nice
features of inflation. | Gas and stellar metallicities in HII galaxies: We examine the gas and stellar metallicities in a sample of HII galaxies from
the Sloan Digital Sky Survey, which possibly contains the largest homogeneous
sample of HII galaxy spectra to date. We eliminated all spectra with an
insufficient signal-to-noise ratio, without strong emission lines, and without
the [OII] lambda3727 {\AA} line, which is necessary for the determination of
the gas metallicity. This excludes galaxies with redshift <~ 0.033. Our final
sample contains ~700 spectra of HII galaxies. Through emission line strength
calibrations and a detailed stellar population analysis employing evolutionary
stellar synthesis methods, which we already used in previous works, we
determined the metallicities of both the gas and the stellar content of these
galaxies. We find that in HII galaxies up to stellar masses of 5\cdot10^9
M_sol, enrichment mechanisms do not vary with galactic mass, being the same for
low- and high-mass galaxies on average. They do seem to present a greater
variety at the high-mass end, though, indicating a more complex assembly
history for high-mass galaxies. In around 23 per cent of our HII galaxies we
find a metallicity decrease over the last few Gyr. Our results favour galaxy
evolution models featuring constantly infalling low-metallicity clouds that
retain part of the galactic winds. Above 5\cdot10^9 M_sol stellar mass, the
retention of high metallicity gas by the galaxies' gravitational potential
dominates. |
Formation and Evolution of Early-Type Galaxies. III Star formation
history as a function of mass and over-density: We investigate the influence of the initial proto-galaxies over-densities and
masses on their evolution, to understand whether the internal properties of the
proto-galactic haloes are sufficient to account for the varied properties of
the galactic populations. By means of fully hydrodynamical N-body simulations
performed with the code EvoL we produce twelve self-similar models of
early-type galaxies of different initial masses and over-densities, following
their evolution from z \geq 20 down to z \leq 1. The simulations include
radiative cooling, star formation, stellar energy feedback, a reionizing
photoheating background, and chemical enrichment of the ISM. We find a strong
correlation between the initial properties of the proto-haloes and their star
formation histories. Massive (10^13M\odot) haloes experience a single, intense
burst of star formation (with rates \geq 10^3M\odot/yr) at early epochs,
consistently with observations, with a less pronounced dependence on the
initial over-density; intermediate mass (10^11M\odot) haloes histories strongly
depend on their initial over-density, whereas small (10^9M\odot) haloes always
have fragmented histories, resulting in multiple stellar populations, due to
the "galactic breathing" phenomenon. The galaxy models have morphological,
structural and photometric properties comparable to real galaxies, often
closely matching the observed data; even though some disagreement is still
there, likely a consequence of some numerical choices. We conclude that
internal properties are essentially sufficient to explain many of the observed
features of early type galaxies, particularly the complicated and different
star formation histories shown by haloes of very different mass. In this
picture, nature seems to play the dominant role, whereas nurture has a
secondary importance. | Comment on "Cosmic radio dipole from NVSS and WENSS": We show that a recent purported correction to the effects of Doppler boosting
of flux density in an erstwhile published formula for calculating the
observer's motion from the cosmic radio dipole in sky brightness is erroneous.
The thereby computed downward correction in the estimated magnitude for the
observer's motion needs to be scrapped and the results derived therefore need
to be reverted back to their erstwhile values. |
Cosmology with the largest galaxy cluster surveys: Going beyond Fisher
matrix forecasts: We make the first detailed MCMC likelihood study of cosmological constraints
that are expected from some of the largest, ongoing and proposed, cluster
surveys in different wave-bands and compare the estimates to the prevalent
Fisher matrix forecasts. Mock catalogs of cluster counts expected from the
surveys -- eROSITA, WFXT, RCS2, DES and Planck, along with a mock dataset of
follow-up mass calibrations are analyzed for this purpose. A fair agreement
between MCMC and Fisher results is found only in the case of minimal models.
However, for many cases, the marginalized constraints obtained from Fisher and
MCMC methods can differ by factors of 30-100%. The discrepancy can be
alarmingly large for a time dependent dark energy equation of state, w(a); the
Fisher methods are seen to under-estimate the constraints by as much as a
factor of 4--5. Typically, Fisher estimates become more and more inappropriate
as we move away from LCDM, to a constant-w dark energy to varying-w dark energy
cosmologies. Fisher analysis, also, predicts incorrect parameter degeneracies.
From the point of mass-calibration uncertainties, a high value of unknown
scatter about the mean mass-observable relation, and its redshift dependence,
is seen to have large degeneracies with the cosmological parameters sigma_8 and
w(a) and can degrade the cosmological constraints considerably. We find that
the addition of mass-calibrated cluster datasets can improve dark energy and
sigma_8 constraints by factors of 2--3 from what can be obtained compared to
CMB+SNe+BAO only. Since, details of future cluster surveys are still being
planned, we emphasize that optimal survey design must be done using MCMC
analysis rather than Fisher forecasting. [abridged] | Halo Profile Evolution and Velocity Bias: We propose a simple model that elucidates the generation of halo velocity
bias. The fluid equation approximation is often adopted in modelling the
evolution of the halo density field. In this approach, halos are often taken to
be point particles even though in reality they are finite-sized objects. In
this paper, we generalize the fluid equation approximation to halos to include
the finite extent of halos by taking into account the halo profile. We compute
the perturbation of the halo density and velocity field to second order and
find that the profile correction gives rise to $k^2$ correction terms in
Fourier space. These corrections are more important for velocity than for
density. In particular, the profile correction generates $k^2$ correction term
in the velocity bias and the correction terms do not decay away in the long
term limit, but it is not constant. We model the halo profile evolution using
the spherical collapse model. We also measure the evolution of proto-halo
profile at various redshifts numerically. We find that the spherical collapse
model gives a reasonable description of the numerical profile evolution. Static
halo profile is often adopted in modelling halos in theories such as the
excursion set theory. Our work highlights the importance of including the
profile evolution in the calculations. |
Revealing the cosmic reionisation history with fast radio bursts in the
era of Square Kilometre Array: Revealing the cosmic reionisation history is at the frontier of extragalactic
astronomy. The power spectrum of the cosmic microwave background (CMB)
polarisation can be used to constrain the reionisation history. Here we propose
a CMB-independent method using fast radio bursts (FRBs) to directly measure the
ionisation fraction of the intergalactic medium (IGM) as a function of
redshift. FRBs are new astronomical transients with millisecond timescales.
Their dispersion measure (DM$_{\rm IGM}$) is an indicator of the amount of
ionised material in the IGM. Since the differential of DM$_{\rm IGM}$ against
redshift is proportional to the ionisation fraction, our method allows us to
directly measure the reionisation history without any assumption on its
functional shape. As a proof of concept, we constructed mock non-repeating FRB
sources to be detected with the Square Kilometre Array, assuming three
different reionisation histories with the same optical depth of Thomson
scattering. We considered three cases of redshift measurements: (A)
spectroscopic redshift for all mock data, (B) spectroscopic redshift for 10% of
mock data, and (C) redshift estimated from an empirical relation of FRBs
between their time-integrated luminosity and rest-frame intrinsic duration. In
all cases, the reionisation histories are consistently reconstructed from the
mock FRB data using our method. Our results demonstrate the capability of
future FRBs in constraining the reionisation history. | Inflationary model in minimally modified gravity theories: We have investigated inflationary model constructed from minimally modified
gravity (MMG) theories. The MMG theory in the form of $f({\bf H}) \propto {\bf
H}^{1+p}$ gravity where, ${\bf H}$ is the Hamiltonian constraint in the
Einstein gravity and $p$ is constant, has been studied. An inflation is
difficult to be achieved in this theory of gravity unless an additional scalar
field playing a role of inflaton is introduced in the model. We have found that
the inflaton with exponential potential can drive inflation with graceful exist
different from the case of Einstein gravity. The slow-roll parameter for both
the exponential and the power-law potentials is inversely proportional to
number of e-folding similar to the case of the Einstein gravity. We also have
found for the scalar perturbation that the curvature perturbation in the
comoving gauge on super Hubble radius scales grows rapidly during inflation
unless $p =0$. For the tensor modes, the amplitude of the perturbations is
constant on large scales, and sound speed of the perturbations can diviate from
unity and can vary with time depending on the form of $f({\bf H})$. |
Thermal Friction as a Solution to the Hubble Tension: A new component added to the standard model of cosmology that behaves like a
cosmological constant at early times and then dilutes away as radiation or
faster can resolve the Hubble tension. We show that a rolling axion coupled to
a non-Abelian gauge group exhibits the behavior of such an extra component at
the background level and can present a natural particle-physics model solution
to the Hubble tension. We compare the contribution of this bottom-up model to
the phenomenological fluid approximation and determine that CMB observables
sensitive only to the background evolution of the Universe are expected to be
similar in both cases, strengthening the case for this model to provide a
viable solution to the Hubble tension. | Probing $\sim L_{*}$ Lyman-break Galaxies at $z\approx 7$ in GOODS-South
with WFC3 on HST: We analyse recently acquired near-infrared Hubble Space Telescope imaging of
the GOODS-South field to search for star forming galaxies at z~7.0. By
comparing WFC 3 0.98 micron Y-band images with ACS z-band (0.85 micron) images,
we identify objects with colours consistent with Lyman break galaxies at
z~6.4-7.4. This new data covers an area five times larger than that previously
reported in the WFC3 imaging of the Hubble Ultra Deep Field, and affords a
valuable constraint on the bright end of the luminosity function. Using
additional imaging of the region in the ACS B, V and i-bands from GOODS v2.0
and the WFC3 J-band we attempt to remove any low-redshift interlopers. Our
selection criteria yields 6 candidates brighter than Y_AB = 27.0, of which all
except one are detected in the ACS z-band imaging and are thus unlikely to be
transients. Assuming all 6 candidates are at z~7 this implies a surface density
of objects brighter than Y_AB = 27.0 of 0.30\pm0.12 arcmin-2, a value
significantly smaller than the prediction from the z ~ 6 luminosity function.
This suggests continued evolution of the bright end of the luminosity function
between z = 6 to 7, with number densities lower at higher redshift. |
How large is the contribution of cosmic web to $Ω_Λ$ ? A
preliminary study on a novel inhomogenous model: The distribution of matter in the universe shows a complex pattern, formed by
cluster of galaxies, voids and filaments denoted as cosmic web. Different
approaches have been proposed to model such structure in the framework of the
general relativity. Recently, one of us has proposed a generalization
($\Lambda$FB model) of the Fractal Bubble model, proposed by Wiltshire, which
accounts for such large scale structure. The $\Lambda$FB model is an evolution
of FB model and includes in a consistent way a description of inhomogeneous
matter distribution and a $\Lambda$ term. Here we analyze the $\Lambda$FB model
focusing on the relation between cosmological parameters. The main result is
the consistency of $\Lambda$CDM model values for $\Omega_{\Lambda0}$ ($\approx
0.7$) and $\Omega_{k0}$ ($|\Omega_{k0}|<\approx 0.01$) with a large fraction of
voids. This allows to quantify to which extent the inhomogeneous structure
could account for $\Lambda$ constant consistently with standard values of the
other cosmological parameters. | The evidence for a spatially flat Universe: We revisit the observational constraints on spatial curvature following
recent claims that the Planck data favour a closed Universe. We use a new and
statistically powerful Planck likelihood to show that the Planck temperature
and polarization spectra are consistent with a spatially flat Universe, though
because of a geometrical degeneracy cosmic microwave background spectra on
their own do not lead to tight constraints on the curvature density parameter
Omega_K. When combined with other astrophysical data, particularly geometrical
measurements of baryon acoustic oscillations, the Universe is constrained to be
spatially flat to extremely high precision, with Omega_ K = 0.0004 +/-0.0018 in
agreement with the 2018 results of the Planck team. In the context of
inflationary cosmology, the observations offer strong support for models of
inflation with a large number of e-foldings and disfavour models of incomplete
inflation. |
FMOS near-IR spectroscopy of Herschel selected galaxies: star formation
rates, metallicity and dust attenuation at z~1: We investigate the properties (e.g. star formation rate, dust attentuation,
stellar mass and metallicity) of a sample of infrared luminous galaxies at z
\sim 1 via near-IR spectroscopy with Subaru-FMOS. Our sample consists of
Herschel SPIRE and Spitzer MIPS selected sources in the COSMOS field with
photometric redshifts in the range 0.7 < z-phot < 1.8, which have been targeted
in 2 pointings (0.5 sq. deg.) with FMOS. We find a modest success rate for
emission line detections, with candidate H{\alpha} emission lines detected for
57 of 168 SPIRE sources (34 per cent). By stacking the near-IR spectra we
directly measure the mean Balmer decrement for the H{\alpha} and H{\beta}
lines, finding a value of <E(B-V)> = 0.51\pm0.27 for <LIR> = 10^12 Lsol sources
at <z> = 1.36. By comparing star formation rates estimated from the IR and from
the dust uncorrected H{\alpha} line we find a strong relationship between dust
attenuation and star formation rate. This relation is broadly consistent with
that previously seen in star-forming galaxies at z ~ 0.1. Finally, we
investigate the metallicity via the N2 ratio, finding that z ~ 1 IR-selected
sources are indistinguishable from the local mass-metallicity relation. We also
find a strong correlation between dust attentuation and metallicity, with the
most metal-rich IR-sources experiencing the largest levels of dust attenuation. | Cosmological Model Parameter Dependence of the Matter Power Spectrum
Covariance from the DEUS-PUR $Cosmo$ Simulations: Future galaxy surveys will provide accurate measurements of the matter power
spectrum across an unprecedented range of scales and redshifts. The analysis of
these data will require one to accurately model the imprint of non-linearities
of the matter density field. In particular, these induce a non-Gaussian
contribution to the data covariance that needs to be properly taken into
account to realise unbiased cosmological parameter inference analyses. Here, we
study the cosmological dependence of the matter power spectrum covariance using
a dedicated suite of N-body simulations, the Dark Energy Universe Simulation -
Parallel Universe Runs (DEUS-PUR) {\it Cosmo}. These consist of 512
realizations for 10 different cosmologies where we vary the matter density
$\Omega_m$, the amplitude of density fluctuations $\sigma_8$, the reduced
Hubble parameter $h$ and a constant dark energy equation of state $w$ by
approximately $10\%$. We use these data to evaluate the first and second
derivatives of the power spectrum covariance with respect to a fiducial
$\Lambda$CDM cosmology. We find that the variations can be as large as $150\%$
depending on the scale, redshift and model parameter considered. By performing
a Fisher matrix analysis we explore the impact of different choices in
modelling the cosmological dependence of the covariance. Our results suggest
that fixing the covariance to a fiducial cosmology can significantly affect the
recovered parameter errors and that modelling the cosmological dependence of
the variance while keeping the correlation coefficient fixed can alleviate the
impact of this effect. |
The Aemulus Project V: Cosmological constraint from small-scale
clustering of BOSS galaxies: We analyze clustering measurements of BOSS galaxies using a simulation-based
emulator of two-point statistics. We focus on the monopole and quadrupole of
the redshift-space correlation function, and the projected correlation
function, at scales of $0.1\sim60~h^{-1}$Mpc. Although our simulations are
based on $w$CDM with general relativity (GR), we include a scaling parameter of
the halo velocity field, $\gamma_f$, defined as the amplitude of the halo
velocity field relative to the GR prediction. We divide the BOSS data into
three redshift bins. After marginalizing over other cosmological parameters,
galaxy bias parameters, and the velocity scaling parameter, we find
$f\sigma_{8}(z=0.25) = 0.413\pm0.031$, $f\sigma_{8}(z=0.4) = 0.470\pm0.026$ and
$f\sigma_{8}(z=0.55) = 0.396\pm0.022$. Compared with Planck observations using
a flat $\Lambda$CDM model, our results are lower by $1.9\sigma$, $0.3\sigma$
and $3.4\sigma$ respectively. These results are consistent with other recent
simulation-based results at non-linear scales, including weak lensing
measurements of BOSS LOWZ galaxies, two-point clustering of eBOSS LRGs, and an
independent clustering analysis of BOSS LOWZ. All these results are generally
consistent with a combination of $\gamma_f^{1/2}\sigma_8\approx 0.75$. We note,
however, that the BOSS data is well fit assuming GR, i.e. $\gamma_f=1$. We
cannot rule out an unknown systematic error in the galaxy bias model at
non-linear scales, but near-future data and modeling will enhance our
understanding of the galaxy--halo connection, and provide a strong test of new
physics beyond the standard model. | Fast numerical method to generate halo catalogs in modified gravity
(part I): second-order Lagrangian Perturbation Theory: We present and test a new numerical method to determine second-order
Lagrangian displacement fields in the context of modified gravity (MG)
theories. We start from the extension of Lagrangian Perturbation Theory to a
class of MG models that can be described by a parametrized Poisson equation,
with the introduction of a scale-dependent function. We exploit fast Fourier
transforms to compute the full source term of the differential equation for the
second-order Lagrangian displacement field. We compare its mean to the source
term computed for specific configurations for which a k-dependent solution can
be found numerically. We choose the configuration that best matches the full
source term, thus obtaining an approximate factorization of the second-order
displacement field as the space term valid for standard gravity times a
k-dependent, second-order growth factor $D_2(k,t)$. This approximation is used
to compute second order displacements for particles. The method is tested
against N-body simulations run with standard and $f(R)$ gravity: we rely on the
results of a friends-of-friends code run on the N-body snapshots to assign
particles to halos, then compute the halo power spectrum. We find very
consistent results for the two gravity theories: second-order LPT (2LPT) allows
to recover the halo power spectrum of N-body simulations within $\sim 10\%$
precision to $k\sim 0.2-0.4\ h\ {\rm Mpc}^{-1}$, as well as halo positions,
with an error that is a fraction of the inter-particle distance. We show that,
when considering the same level of non-linearity in the density field, the
performance of 2LPT with MG is the same (within $1\%$) as the one obtained for
the standard $\Lambda$CDM model with General Relativity. When implemented in a
computer code, this formulation of 2LPT can quickly generate dark matter
distributions with $f(R)$ gravity, and can easily be extended to other MG
theories. |
Clusters in the Disperse cosmic web: Galaxy cluster mass halos ("clusters") in a dark matter simulation are
matched to nodes in several different cosmic webs found using the Disperse
cosmic web finder. The webs have different simulation smoothings and Disperse
parameter choices; for each, 4 methods are considered for matching Disperse
nodes to clusters. For most of the webs, Disperse nodes outnumber clusters, but
not every cluster has a Disperse node match (and sometimes $>1$ cluster matches
to the same Disperse node). The clusters frequently lacking a matching Disperse
node have a different distribution of local shear trends and perhaps merger
histories. It might be interesting to see in what other ways, e.g.,
observational properties, these clusters differ. For the webs with smoothing
$\leq$ 2.5 $Mpc/h$, and all but the most restrictive matching criterion,
$\sim$3/4 of the clusters always have a Disperse node counterpart. The nearest
cluster to a given Disperse node and vice versa, within twice the smoothing
length, obey a cluster mass-Disperse node density relation. Cluster pairs where
both clusters match Disperse nodes can also be assigned the filaments between
those nodes, but as the web and matching methods are varied, most such
filaments do not remain. There is an enhancement of subhalo counts and halo
mass between cluster pairs, averaging over cluster pairs assigned Disperse
filaments increases the enhancement. The approach here also lends itself to
comparing nodes across many cosmic web constructions, using the fixed
underlying cluster distribution to make a correspondence. | Distance determination to 12 Type II-P Supernovae using the Expanding
Photosphere Method: We use early-time photometry and spectroscopy of 12 Type II plateau
supernovae (SNe IIP) to derive their distances using the expanding photosphere
method (EPM). We perform this study using two sets of Type II supernova (SN II)
atmosphere models, three filter subsets ($\{BV\}$, $\{BVI\}$, $\{VI\}$), and
two methods for the host-galaxy extinction, which leads to 12 Hubble diagrams.
We find that systematic differences in the atmosphere models lead to $\sim $50%
differences in the EPM distances and to a value of ${\rm H_0}$ between 52 and
101 ${\rm km s^{-1} Mpc^{-1}}$. Using the $\{VI\}$ filter subset we obtain the
lowest dispersion in the Hubble diagram, {${\rm \sigma_{\mu} = 0.32}$ mag}. We
also apply the EPM analysis to the well-observed SN IIP 1999em. With the
$\{VI\}$ filter subset we derive a distance ranging from 9.3 $\pm$ 0.5 Mpc to
13.9 $\pm$ 1.4 Mpc depending on the atmosphere model employed. |
The inner structure of haloes in Cold+Warm dark matter models: We analyze the properties of dark matter halos in the cold-plus-warm dark
matter cosmologies (CWDM). We study their dependence on the fraction and
velocity dispersion of the warm particle, keeping the free-streaming scale
fixed. To this end we consider three models with the same free-streaming: (1) a
mixture of 90% of CDM and 10% of WDM with the mass 1 keV; (2) a mixture of 50%
of CDM and 50% of WDM with the mass 5 keV; and (3) pure WDM with the mass 10
keV. "Warm" particles have rescaled Fermi-Dirac spectrum of primordial
velocities (as non-resonantly produced sterile neutrinos would have). We
compare the properties of halos among these models and with a LCDM with the
same cosmological parameters. We demonstrate, that although these models have
the same free-streaming length and the suppression of matter spectra are
similar at scales probed by the Lyman-alpha forest comoving wave-numbers k<3-5
h/Mpc), the resulting properties of halos with masses below 1e11 Msun are
different due to the different behaviour of matter power spectra at smaller
scales. In particular, we find that while the number of galaxies remains the
same as in LCDM case, their density profiles become much less concentrated, and
hence in better agreement with current observational constraints. Our results
imply that a single parameter (e.g. free streaming length) description of these
models is not enough to fully capture their effects on the structure formation
process. | First Measurement of the Cross-Correlation of CMB Lensing and Galaxy
Lensing: We measure the cross-correlation of cosmic microwave background lensing
convergence maps derived from Atacama Cosmology Telescope data with galaxy
lensing convergence maps as measured by the Canada-France-Hawaii Telescope
Stripe 82 Survey. The CMB-galaxy lensing cross power spectrum is measured for
the first time with a significance of 4.2{\sigma}, which corresponds to a 12%
constraint on the amplitude of density fluctuations at redshifts ~ 0.9. With
upcoming improved lensing data, this novel type of measurement will become a
powerful cosmological probe, providing a precise measurement of the mass
distribution at intermediate redshifts and serving as a calibrator for
systematic biases in weak lensing measurements. |
Full covariance of CMB and lensing reconstruction power spectra: CMB and lensing reconstruction power spectra are powerful probes of
cosmology. However they are correlated, since the CMB power spectra are lensed
and the lensing reconstruction is constructed using CMB multipoles. We perform
a full analysis of the auto- and cross-covariances, including polarization
power spectra and minimum variance lensing estimators, and compare with
simulations of idealized future CMB-S4 observations. Covariances sourced by
fluctuations in the unlensed CMB and instrumental noise can largely be removed
by using a realization-dependent subtraction of lensing reconstruction noise,
leaving a relatively simple covariance model that is dominated by
lensing-induced terms and well described by a small number of principal
components. The correlations between the CMB and lensing power spectra will be
detectable at the level of $\sim 5\sigma$ for a CMB-S4 mission, and neglecting
those could underestimate some parameter error bars by several tens of percent.
However we found that the inclusion of external priors or data sets to estimate
parameter error bars can make the impact of the correlations almost negligible. | The MIP Ensemble Simulation: Local Ensemble Statistics in the Cosmic Web: We present a new technique that allows us to compute ensemble statistics on a
local basis, directly relating halo properties to their local environment. This
is achieved by the use of a correlated ensemble in which the Large Scale
Structure is common to all realizations while having each an independent halo
population. The correlated ensemble can be stacked, effectively increasing the
halo number density by an arbitrary factor, thus breaking the fundamental limit
in the halo number density given by the haloe mass function. This technique
allows us to compute \textit{local ensemble statistics} of the matter/haloe
distribution at any position in the simulation box, while removing the
intrinsic stochasticity in the halo formation process and directly relating
halo properties to their environment.
We introduce the \textit{Multum In Parvo} (MIP) correlated ensemble
simulation consisting of 220 realizations on a 32 h$^{-1}$ Mpc box with $256^3$
particles each. This is equivalent in terms of effective volume and number of
particles to a box of $\sim 193$ h$^{-1}$ Mpc of side with $\sim 1540^3$
particles containing $\sim 5\times 10^6$ haloes with a minimum mass of $3.25
\times 10^9$ h$^{-1}$ M$_{\odot}$.
The potential of the technique presented here is illustrated by computing the
local ensemble statistics of the halo ellipticity and halo shape-LSS alignment.
We show that, while there are general trends in the ellipticity and alignment
of haloes with their LSS, there are also significant spatial variations which
has important implications for observational studies of galaxy shape and
alignment. |
On the baryon acoustic oscillation amplitude as a probe of radiation
density: The baryon acoustic oscillation (BAO) feature in the distribution of galaxies
has been widely studied as an excellent standard ruler for probing cosmic
distances and expansion history, and hence dark energy. In contrast, the
amplitude of the BAO feature has received relatively little study, mainly due
to limited signal-to-noise, and complications due to galaxy biasing, effects of
non-linear clustering and dependence on several cosmological parameters. As
expected, the amplitude of the BAO feature is sensitive to the cosmic baryon
fraction: for standard radiation content, the cosmic microwave background (CMB)
acoustic peaks constrain this precisely and the BAO amplitude is largely a
redundant cross-check. However, the CMB mainly constrains the redshift of
matter-radiation equality, z_eq, and the baryon/photon ratio: if a non-standard
radiation density N_eff is allowed, increasing N_eff while matching the CMB
peaks leads to a reduced baryon fraction and a lower relative BAO amplitude. We
construct an observable for the relative area of the BAO feature from the
galaxy correlation function (Eq.~8); from linear-theory models, we find that
this is mainly sensitive to N_eff and quite insensitive to other cosmological
parameters. More detailed work from N-body simulations will be needed to
constrain the effects of non-linearity and scale-dependent galaxy bias on this
observable. | Artificial Wormhole: It is shown that recently reported result by the OPERA Collaboration
(arXive:1109.4897) of an early arrival time of muon neutrinos with respect to
the speed of light in vacuum does not violate standard physical laws. We show
that vacuum polarization effects in intensive external fields may form a
wormhole-like object. The simplest theory of such an effect is presented and
basic principles of formation of an artificial wormhole are also considered. |
The clustering of Lyman alpha emitters at z=7: implications for
reionization and host halo masses: The Ly$\alpha$ line of high-redshift galaxies has emerged as a powerful probe
of both early galaxy evolution and the epoch of reionization (EoR). Motivated
by the upcoming wide-field survey with the Subaru Hyper Suprime-Cam (HSC), we
study the angular correlation function (ACF) of narrow-band selected,
$z\approx7$ Ly$\alpha$ emitting galaxies (LAEs). The clustering of LAEs is
determined by both: (i) their typical host halo masses, $\bar{M}_{\rm h}$; and
(ii) the absorption due to a patchy EoR, characterized by an average neutral
fraction of the intergalactic medium, $\bar{x}_{\rm HI}$. We bracket the
allowed LAE ACFs by exploring extreme scenarios for both the intrinsic
Ly$\alpha$ emission and the large-scale pattern (i.e. morphology) of cosmic
ionized patches in physical EoR models. Independent of the EoR morphology,
current $z\approx 7$ ACF measurements constrain $\bar{x}_{\rm HI}\lesssim 0.5$
(1-$\sigma$). We also find that the low values of the currently-observed ACF
imply that LAEs are hosted by relatively small dark matter halos: $\bar{M}_{\rm
h} \lesssim 10^{10} M_{\odot}$, with corresponding duty cycles of $\lesssim$
few per cent. These values are over an order of magnitude lower than the
analogous ones for color-selected, Lyman break galaxies, suggesting that
$z\approx 7$ narrow-band LAEs searches are preferentially selecting young,
star-burst galaxies, residing in less massive halos. The upcoming Ultra Deep
campaign with the HSC will significantly improve constraints on both the EoR
and LAE host halos. | Nuclear Star Clusters and Black Holes: We summarize the recent results of our survey of the nearest nuclear star
clusters. The purpose of the survey is to understand nuclear star cluster
formation mechanisms and constrain the presence of black holes using adaptive
optics assisted integral field spectroscopy, optical spectroscopy, and HST
imaging in 13 galaxies within 5 Mpc. We discuss the formation history of the
nuclear star cluster and possible detection of an intermediate mass BH in NGC
404, the nearest S0 galaxy. |
A Comparative Analysis of the Supernova Legacy Survey Sample with
ΛCDM and the $R_{\rm h}=ct$ Universe: The use of Type~Ia SNe has thus far produced the most reliable measurement of
the expansion history of the Universe, suggesting that $\Lambda$CDM offers the
best explanation for the redshift--luminosity distribution observed in these
events. But the analysis of other kinds of source, such as cosmic chronometers,
gamma ray bursts, and high-$z$ quasars, conflicts with this conclusion,
indicating instead that the constant expansion rate implied by the $R_{\rm
h}=ct$ Universe is a better fit to the data. The central difficulty with the
use of Type~Ia SNe as standard candles is that one must optimize three or four
nuisance parameters characterizing supernova luminosities simultaneously with
the parameters of an expansion model. Hence in comparing competing models, one
must reduce the data independently for each. We carry~out such a comparison of
$\Lambda$CDM and the $R_{\rm h}=ct$ Universe, using the Supernova Legacy Survey
(SNLS) sample of 252 SN~events, and show that each model fits its individually
reduced data very well. But since $R_{\rm h}=ct$ has only one free parameter
(the Hubble constant), it follows from a standard model selection technique
that it is to be preferred over $\Lambda$CDM, the minimalist version of which
has three (the Hubble constant, the scaled matter density and either the
spatial curvature constant or the dark-energy equation-of-state parameter). We
estimate by the Bayes Information Criterion that in a pairwise comparison, the
likelihood of $R_{\rm h}=ct$ is $\sim 90\%$, compared with only $\sim 10\%$ for
a minimalist form of $\Lambda$CDM, in which dark energy is simply a
cosmological constant. Compared to $R_{\rm h}=ct$, versions of the standard
model with more elaborate parametrizations of dark energy are judged to be even
less likely. | HInet: Generating neutral hydrogen from dark matter with neural networks: Upcoming 21cm surveys will map the spatial distribution of cosmic neutral
hydrogen (HI) over very large cosmological volumes. In order to maximize the
scientific return of these surveys, accurate theoretical predictions are
needed. Hydrodynamic simulations currently are the most accurate tool to
provide those predictions in the mildly to non-linear regime. Unfortunately,
their computational cost is very high: tens of millions of CPU hours. We use
convolutional neural networks to find the mapping between the spatial
distribution of matter from N-body simulations and HI from the state-of-the-art
hydrodynamic simulation IllustrisTNG. Our model performs better than the widely
used theoretical model: Halo Occupation Distribution (HOD) for all statistical
properties up to the non-linear scales $k\lesssim1$ h/Mpc. Our method allows
the generation of 21cm mocks over very big cosmological volumes with similar
properties as hydrodynamic simulations. |
The Lyman-$α$ forest as a diagnostic of the nature of the dark
matter: The observed Lyman-$\alpha$ flux power spectrum (FPS) is suppressed on scales
below $\sim~ 30~{\rm km~s}^{-1}$. This cutoff could be due to the high
temperature, $T_0$, and pressure, $p_0$, of the absorbing gas or,
alternatively, it could reflect the free streaming of dark matter particles in
the early universe. We perform a set of very high resolution cosmological
hydrodynamic simulations in which we vary $T_0$, $p_0$ and the amplitude of the
dark matter free streaming, and compare the FPS of mock spectra to the data. We
show that the location of the dark matter free-streaming cutoff scales
differently with redshift than the cutoff produced by thermal effects and is
more pronounced at higher redshift. We, therefore, focus on a comparison to the
observed FPS at $z>5$. We demonstrate that the FPS cutoff can be fit assuming
cold dark matter, but it can be equally well fit assuming that the dark matter
consists of $\sim 7$ keV sterile neutrinos in which case the cutoff is due
primarily to the dark matter free streaming. | Comments on "Modeling Galaxy Halos Using Dark Matter with Pressure": We comment on the calculational mistake in the paper "Modeling galaxy halos
using dark matter with pressure" by Somnath Bharadwaj and Sayan Kar. The
authors made a mistake while calculating the metric, which led to an
overestimate of the deflection angle of light passing through the halos for
-1<w_r<-0.5 and an underestimate of the deflection angle for -0.5<w_r<0. In
addition, solution for w_r>0 should not exist. Although the Bharadwaj-Kar
solution should be corrected, it appears that the characteristics of the
deflection angle under the supposed non-conventional non-ideal fluid equation
of state for the dark matter halo remain sensitive to the impact parameter and
may be verifiable through observations. |
Symmetry and anti-symmetry of the CMB anisotropy pattern: Given an arbitrary function, we may construct symmetric and antisymmetric
functions under a certain operation. Since statistical isotropy and homogeneity
of our Universe has been a fundamental assumption of modern cosmology, we do
not expect any particular symmetry or antisymmetry in our Universe. Besides
fundamental properties of our Universe, we may also figure our contamination
and improve the quality of the CMB data products, by matching the unusual
symmetries and antisymmetries of the CMB data with known contaminantions.
Noting this, we have investigated the symmetry and antisymmetry of CMB
anisotropy pattern, which provides the deepest survey. If we let the operation
to be a coordinate inversion, the symmetric and antisymmetric functions have
even and odd-parity respectively. The investigation on the parity of the recent
CMB data shows a large-scale odd-parity preference, which is very unlikely in
the statistical isotropic and homogeneous Universe. We have investigated the
association of the WMAP systematics with the anomaly, but not found a definite
non-cosmological cause. Additionally, we have investigated the phase of even
and odd multipole data respectively, and found the behavior distinct from each
other. Noting the odd-parity preference anomaly, we have fitted a cosmological
model respectively to even and odd multipole data, and found significant
parametric tension. Besides anomalies explicitly associated with parity, there
are anomalous lack of large-scale correlation in CMB data. Noting the
equivalence between the power spectrum and the correlation, we have
investigated the association between the lack of large-angle correlation and
the odd-parity preference of the angular power spectrum. From our analysis, we
find that the odd-parity preference at low multipoles is, in fact,
phenomenologically identical with the lack of large-angle correlation. | Primordial Black Holes in Matter-Dominated Eras: the Role of Accretion: We consider the role of secondary infall and accretion onto an initially
overdense perturbation in matter-dominated eras, like the one which is likely
to follow the end of inflation. We show that primordial black holes may form
through post-collapse accretion, namely the accretion onto an initial
overdensity whose collapse has not given rise to a primordial black hole.
Accretion may be also responsible for the growth of the primordial black hole
masses by orders of magnitude till the end of the matter-dominated era. |
Constraints on feedback processes during the formation of early-type
galaxies: Galaxies are found to obey scaling relations between a number of observables.
These relations follow different trends at the low- and the high-mass ends. The
processes driving the curvature of scaling relations remain uncertain. In this
letter, we focus on the specific family of early-type galaxies, deriving the
star formation histories of a complete sample of visually classified galaxies
from SDSS-DR7 over the redshift range 0.01<z<0.025, covering a stellar mass
interval from 10^9 to 3 x 10^11 Msun. Our sample features the characteristic
"knee" in the surface brightness vs. mass distribution at Mstar~3 x 10^10 Msun.
We find a clear difference between the age and metallicity distributions of the
stellar populations above and beyond this knee, which suggests a sudden
transition from a constant, highly efficient mode of star formation in
high-mass galaxies, gradually decreasing towards the low-mass end of the
sample. At fixed mass, our early-type sample is more efficient in building up
the stellar content at early times in comparison to the general population of
galaxies, with half of the stars already in place by redshift z~2 for all
masses. The metallicity-age trend in low-mass galaxies is not compatible with
infall of metal-poor gas, suggesting instead an outflow-driven relation. | Partial coverage of the Broad Line Region of Q1232+082 by an intervening
H2-bearing cloud: We present a detailed analysis of the partial coverage of the Q1232+082 (z_em
=2.57) broad line region by an intervening H_2-bearing cloud at z_abs=2.3377.
Using curve of growth analysis and line profile fitting, we demonstrate that
the H_2-bearing component of the cloud covers the QSO intrinsic continuum
source completely but only part of the Broad Line Region (BLR). We find that
only 48\pm6 % of the C IV BLR emission is covered by the C I absorbing gas. We
observe residual light (~6 %) as well in the bottom of the O I {\lambda}1302
absorption from the cloud, redshifted on top of the QSO Lyman-{\alpha} emission
line. Therefore the extent of the neutral phase of the absorbing cloud is not
large enough to cover all of the background source. The most likely explanation
for this partial coverage is the small size of the intervening cloud, which is
comparable to the BLR size. We estimate the number densities in the cloud:
n_H2~110 cm^{-3} for the H_2-bearing core and n_H ~30 cm^{-3} for the neutral
envelope. Given the column densities, N(H2)=(3.71\pm0.97)\times10^19 cm^{-2}
and N(H I)=(7.94\pm1.6)\times10^20 cm^{-2}, we derive the linear size of the
H_2-bearing core and the neutral envelope along the line of sight to be
l_H2~0.15^{+0.05}_{-0.05} pc and l_HI~8.2^{+6.5}_{-4.1} pc, respectively. We
estimate the size of the C IV BLR by two ways (i) extrapolating size-luminosity
relations derived from reverberation observations and (ii) assuming that the
H_2-bearing core and the BLR are spherical in shape and the results are ~0.26
and ~0.18 pc, respectively. The large size we derive for the extent of the
neutral phase of the absorbing cloud together with a covering factor of ~0.94
of the Lyman-{\alpha} emission means that the Lyman-{\alpha} BLR is probably
fully covered but that the Lyman-{\alpha} emission extends well beyond the
limits of the BLR. |
Feedback-regulated star formation in molecular clouds and galactic discs: We present a two-zone theory for feedback-regulated star formation in
galactic discs, consistently connecting the galaxy-averaged star formation law
with star formation proceeding in giant molecular clouds (GMCs). Our focus is
on galaxies with gas surface density Sigma_g>~100 Msun pc^-2. In our theory,
the galactic disc consists of Toomre-mass GMCs embedded in a volume-filling
ISM. Radiation pressure on dust disperses GMCs and most supernovae explode in
the volume-filling medium. A galaxy-averaged star formation law is derived by
balancing the momentum input from supernova feedback with the gravitational
weight of the disc gas. This star formation law is in good agreement with
observations for a CO conversion factor depending continuously on Sigma_g. We
argue that the galaxy-averaged star formation efficiency per free fall time,
epsilon_ff^gal, is only a weak function of the efficiency with which GMCs
convert their gas into stars. This is possible because the rate limiting step
for star formation is the rate at which GMCs form: for large efficiency of star
formation in GMCs, the Toomre Q parameter obtains a value slightly above unity
so that the GMC formation rate is consistent with the galaxy-averaged star
formation law. We contrast our results with other theories of
turbulence-regulated star formation and discuss predictions of our model. Using
a compilation of data from the literature, we show that the galaxy-averaged
star formation efficiency per free fall time is non-universal and increases
with increasing gas fraction, as predicted by our model. We also predict that
the fraction of the disc gas mass in bound GMCs decreases for increasing values
of the GMC star formation efficiency. This is qualitatively consistent with the
smooth molecular gas distribution inferred in local ultra-luminous infrared
galaxies and the small mass fraction in giant clumps in high-redshift galaxies. | Time delays in PG1115+080: new estimates: We report new estimates of the time delays in the quadruple gravitationally
lensed quasar PG1115+080, obtained from the monitoring data in filter R with
the 1.5-m telescope at the Maidanak Mountain (Uzbekistan, Central Asia) in
2004-2006. The time delays are 16.4 days between images C and B, and 12 days
between C and A1+A2, with image C being leading for both pairs. The only known
estimates of the time delays in PG1115 are those based on observations by
Schechter et al. (1997) -- 23.7 and 9.4 days between images C and B, C and
A1+A2, respectively, as calculated by Schechter et al., and 25 and 13.3 days as
revised by Barkana (1997) for the same image components with the use of another
method. The new values of time delays in PG 1115+080 may be expected to provide
larger estimates of the Hubble constant thus decreasing a diversity between the
H_0 estimates taken from gravitationally lensed quasars and with other methods. |
Blazar Optical Variability in the Palomar-QUEST Survey: We study the ensemble optical variability of 276 FSRQs and 86 BL Lacs in the
Palomar-QUEST Survey with the goal of searching for common fluctuation
properties, examining the range of behavior across the sample, and
characterizing the appearance of blazars in such a survey so that future work
can more easily identify such objects. The survey, which covers 15,000 square
degrees multiple times over 3.5 years, allows for the first ensemble blazar
study of this scale. Variability amplitude distributions are shown for the FSRQ
and BL Lac samples for numerous time lags, and also studied through structure
function analyses. Individual blazars show a wide range of variability
amplitudes, timescales, and duty cycles. Of the best sampled objects, 35% are
seen to vary by more than 0.4 magnitudes; for these, the fraction of
measurements contributing to the high amplitude variability ranges constantly
from about 5% to 80%. Blazar variability has some similarities to that of type
I quasars but includes larger amplitude fluctuations on all timescales. FSRQ
variability amplitudes are particularly similar to those of QSOs on timescales
of several months, suggesting significant contributions from the accretion disk
to the variable flux at these timescales. Optical variability amplitudes are
correlated with the maximum apparent velocities of the radio jet for the subset
of FSRQs with MOJAVE VLBA measurements, implying that the optically variable
flux's strength is typically related to that of the radio emission. We also
study CRATES radio-selected FSRQ candidates, which show similar variability
characteristics to known FSRQs; this suggests a high purity for the CRATES
sample. | Direct measurement of evolving dark energy density and
super-accelerating expansion of the universe: A higher value of Hubble constant has been obtained from measurements with
nearby Type Ia supernovae, than that obtained at much higher redshift. With the
peculiar motions of their hosts, we find that the matter content at such low
redshift is only about 10% of that at much higher redshifts; such a low matter
density cannot be produced from density perturbations in the background of the
\Lambda CDM expansion. Recently the Planck team has reported a lower Hubble
constant and a higher matter content. We find that the dark energy density
increases with cosmic time, so that its equation-of-state parameter decreases
with cosmic time and is less than -1 at low redshift. Such dark energy
evolution is responsible for driving the super-accelerating expansion of the
universe. In this extended \Lambda CDM model, the cosmological redshift
represents time rather than radial coordinate, so that the universe complies to
the Copernican Principle. |
Triaxiality, principal axis orientation and non-thermal pressure in
Abell 383: While clusters of galaxies are regarded as one of the most important
cosmological probes, the conventional spherical modeling of the intracluster
medium (ICM) and the dark matter (DM), and the assumption of strict hydrostatic
equilibrium (i.e., the equilibrium gas pressure is provided entirely by thermal
pressure) are very approximate at best. Extending our previous works, we
developed further a method to reconstruct for the first time the full
three-dimensional structure (triaxial shape and principal axis orientation) of
both DM and intracluster (IC) gas, and the level of non-thermal pressure of the
IC gas. We outline an application of our method to the galaxy cluster Abell
383, taken as part of the CLASH multi-cycle treasury program, presenting
results of a joint analysis of X-ray and strong lensing measurements. We find
that the intermediate-major and minor-major axis ratios of the DM are
0.71+/-0.10 and 0.55+/-0.06, respectively, and the major axis of the DM halo is
inclined with respect to the line of sight of 21.1+/-10.1 deg. The level of
non-thermal pressure has been evaluated to be about 10% of the total energy
budget. We discuss the implications of our method for the viability of the CDM
scenario, focusing on the concentration parameter C and the inner slope of the
DM gamma, since the cuspiness of dark-matter density profiles in the central
regions is one of the critical tests of the cold dark matter (CDM) paradigm for
structure formation: we measure gamma=1.02+/-0.06 on scales down to 25 Kpc, and
C=4.76+/-0.51, values which are close to the predictions of the standard model,
and providing further evidences that support the CDM scenario. Our method
allows us to recover the three-dimensional physical properties of clusters in a
bias-free way, overcoming the limitations of the standard spherical modelling
and enhancing the use of clusters as more precise cosmological probes. | LINNA: Likelihood Inference Neural Network Accelerator: Bayesian posterior inference of modern multi-probe cosmological analyses
incurs massive computational costs. For instance, depending on the combinations
of probes, a single posterior inference for the Dark Energy Survey (DES) data
had a wall-clock time that ranged from 1 to 21 days using a state-of-the-art
computing cluster with 100 cores. These computational costs have severe
environmental impacts and the long wall-clock time slows scientific
productivity. To address these difficulties, we introduce LINNA: the Likelihood
Inference Neural Network Accelerator. Relative to the baseline DES analyses,
LINNA reduces the computational cost associated with posterior inference by a
factor of 8--50. If applied to the first-year cosmological analysis of Rubin
Observatory's Legacy Survey of Space and Time (LSST Y1), we conservatively
estimate that LINNA will save more than US $\$300,000$ on energy costs, while
simultaneously reducing $\rm{CO}_2$ emission by $2,400$ tons. To accomplish
these reductions, LINNA automatically builds training data sets, creates neural
network surrogate models, and produces a Markov chain that samples the
posterior. We explicitly verify that LINNA accurately reproduces the first-year
DES (DES Y1) cosmological constraints derived from a variety of different data
vectors with our default code settings, without needing to retune the algorithm
every time. Further, we find that LINNA is sufficient for enabling accurate and
efficient sampling for LSST Y10 multi-probe analyses. We make LINNA publicly
available at https://github.com/chto/linna, to enable others to perform fast
and accurate posterior inference in contemporary cosmological analyses. |
General framework for cosmological dark matter bounds using $N$-body
simulations: We present a general framework for obtaining robust bounds on the nature of
dark matter using cosmological $N$-body simulations and Lyman-alpha forest
data. We construct an emulator of hydrodynamical simulations, which is a
flexible, accurate and computationally-efficient model for predicting the
response of the Lyman-alpha forest flux power spectrum to different dark matter
models, the state of the intergalactic medium (IGM) and the primordial power
spectrum. The emulator combines a flexible parameterization for the small-scale
suppression in the matter power spectrum arising in "non-cold" dark matter
models, with an improved IGM model. We then demonstrate how to optimize the
emulator for the case of ultra-light axion dark matter, presenting tests of
convergence. We also carry out cross-validation tests of the accuracy of flux
power spectrum prediction. This framework can be optimized for the analysis of
many other dark matter candidates, e.g., warm or interacting dark matter. Our
work demonstrates that a combination of an optimized emulator and cosmological
"effective theories," where many models are described by a single set of
equations, is a powerful approach for robust and computationally-efficient
inference from the cosmic large-scale structure. | The Atacama Cosmology Telescope: Cross-Correlation of CMB Lensing and
Quasars: We measure the cross-correlation of Atacama Cosmology Telescope CMB lensing
convergence maps with quasar maps made from the Sloan Digital Sky Survey DR8
SDSS-XDQSO photometric catalog. The CMB lensing-quasar cross-power spectrum is
detected for the first time at a significance of 3.8 sigma, which directly
confirms that the quasar distribution traces the mass distribution at high
redshifts z>1. Our detection passes a number of null tests and systematic
checks. Using this cross-power spectrum, we measure the amplitude of the linear
quasar bias assuming a template for its redshift dependence, and find the
amplitude to be consistent with an earlier measurement from clustering; at
redshift z ~ 1.4, the peak of the distribution of quasars in our maps, our
measurement corresponds to a bias of b = 2.5 +/- 0.6. With the signal-to-noise
ratio on CMB lensing measurements likely to improve by an order of magnitude
over the next few years, our results demonstrate the potential of CMB lensing
cross-correlations to probe astrophysics at high redshifts. |
Mass Accretion Rates and Histories of Dark Matter Haloes: We use the extensive catalog of dark matter haloes from the Millennium
simulation to investigate the statistics of the mass accretion histories (MAHs)
and accretion rates of ~500,000 haloes from redshift z=0 to 6. We find only
about 25% of the haloes to have MAHs that are well described by a 1-parameter
exponential form. For the rest of the haloes, between 20% (Milky-Way mass) to
50% (cluster mass) experience late-time growth that is steeper than an
exponential, whereas the remaining haloes show plateau-ed late-time growth that
is shallower than an exponential. The haloes with slower late-time growth tend
to reside in denser environments, suggesting that either tidal stripping or the
"hotter" dynamics are suppressing the accretion rate of dark matter onto these
haloes. These deviations from exponential growth are well fit by introducing a
second parameter: M(z) \propto (1+z)^beta exp(-gamma z). The full distribution
of beta and gamma as a function of halo mass is provided. From the analytic
form of M(z), we obtain a simple formula for the mean accretion rate of dark
matter, dM/dt, as a function of redshift and mass. At z=0, this rate is 42
Msun/yr for 1e12 Msun haloes, which corresponds to a mean baryon accretion rate
of dMbaryon/dt=7 Msun/yr. This mean rate increases approximately as (1+z)^1.5
at low z and (1+z)^2.5 at high z, reaching dMbaryon/dt = 27, 69, and 140
Msun/yr at z=1, 2, and 3. The specific rate depends on halo mass weakly:
dlogM/dt \propto M^0.127. Results for the broad distributions about the mean
rates are also discussed. | Standard Siren Speeds: Improving velocities in gravitational-wave
measurements of $H_{0}$: We re-analyze data from the gravitational-wave event GW170817 and its host
galaxy NGC4993 to demonstrate the importance of accurate total and peculiar
velocities when measuring the Hubble constant using this nearby Standard Siren.
We show that a number of reasonable choices can be made to estimate the
velocities for this event, but that systematic differences remain between these
measurements depending on the data used. This leads to significant changes in
the Hubble constant inferred from GW170817. We present Bayesian Model Averaging
as one way to account for these differences, and obtain
$H_{0}=66.8^{+13.4}_{-9.2}\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$. Adding additional
information on the viewing angle from high resolution imaging of the radio
counterpart refines this to
$H_{0}=64.8^{+7.3}_{-7.2}\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$. During this analysis
we also present an alternative Bayesian model for the posterior on $H_{0}$ from
Standard Sirens that works more closely with observed quantities from redshift
and peculiar velocity surveys. Our results more accurately capture the true
uncertainty on the total and peculiar velocities of NGC4993 and show that
exploring how well different datasets characterize galaxy groups and the
velocity field in the local Universe could improve this measurement further.
These considerations impact any low-redshift distance measurement, and the
improvements we suggest here can also be applied to standard candles like type
Ia supernovae. GW170817 is particularly sensitive to peculiar velocity
uncertainties because it is so close. For future standard siren measurements
the importance of this error will decrease as (a) we will measure more distant
standard sirens, and (b) the random direction of peculiar velocities will
average out with more detections. |
Numerically Investigating the Emergent Cyclic Inflation Scenario: We provide a comprehensive numerical study of the Emergent Cyclic Inflation
scenario. This is a scenario where instead of traditional monotonic slow roll
inflation, the universe expands over numerous short asymmetric cycles due to
the production of entropy via interactions among different species. This is one
of the very few scenarios of inflation which provides a nonsingular
geodesically complete space-time and does not require any "reheating"
mechanism. | A z~3 radio galaxy and its protocluster: evidence for a superstructure?: We present spectroscopic follow-up observations of Lyman Break Galaxies
(LBGs) selected in the field surrounding the radio galaxy MRC0316-257 at z~3.13
(0316). Robust spectroscopic redshifts are determined for 20 out of 24 objects.
Three of the spectroscopically confirmed galaxies have 3.12<z<3.13 indicating
that these objects reside in a protocluster structure previously found around
the radio galaxy. An additional 5 objects are found 1600 km/s blue-shifted with
respect to the main protocluster structure. This is in addition to three [OIII]
emitters found at this redshift in a previous study. This is further evidence
that a structure exists directly in front of the 0316 protocluster. We estimate
that the foreground structure is responsible for half of the surface
overdensity of LBGs found in the field as a whole. The foreground structure is
associated with a strong surface density peak 1.4 Mpc to the North-West of the
radio galaxy and a 2D Kolmogorov-Smirnov test indicates that the spatial
distributions of the 0316 and foreground galaxies differ at the 3 sigma level.
In addition, we compare the properties of protocluster, foreground structure
and field galaxies, but we find no significant differences. In terms of the
nature of the two structures, a merger scenario is a possible option. Simple
merger dynamics indicates that the observed relative velocity of 1600 km/s can
be reproduced if the two structures have masses of ~5x10^14 Msun and have
starting separations of around 2.5 to 3 Mpc. It is also possible that the
foreground structure is unrelated to the 0316 protocluster in which case the
two structures will not interact before z=0. |
Super-Sample Signal: When extracting cosmological information from power spectrum measurements, we
must consider the impact of super-sample density fluctuations whose wavelengths
are larger than the survey scale. These modes contribute to the mean density
fluctuation $\delta_b$ in the survey and change the power spectrum in the same
way as a change in the cosmological background. They can be simply included in
cosmological parameter estimation and forecasts by treating $\delta_b$ as an
additional cosmological parameter enabling efficient exploration of its impact.
To test this approach, we consider here an idealized measurement of the matter
power spectrum itself in the $\Lambda$CDM cosmology though our techniques can
readily be extended to more observationally relevant statistics or other
parameter spaces. Using sub-volumes of large-volume $N$-body simulations for
power spectra measured with respect to either the global or local mean density,
we verify that the minimum variance estimator of $\delta_b$ is both unbiased
and has the predicted variance. Parameter degeneracies arise since the response
of the matter power spectrum to $\delta_b$ and cosmological parameters share
similar properties in changing the growth of structure and dilating the scale
of features especially in the local case. For matter power spectrum
measurements, these degeneracies can lead in certain cases to substantial error
degradation and motivates future studies of specific cosmological observables
such as galaxy clustering and weak lensing statistics with these techniques. | An analytic distribution function for a massless cored stellar system in
a cuspy dark matter halo: We demonstrate the existence of distribution functions that can be used to
represent spherical massless cored stellar systems embedded in cuspy dark
matter halos with constant mildly tangential velocity anisotropy. In
particular, we derive analytically the functional form of the distribution
function for a Plummer stellar sphere in a Hernquist dark halo, for \beta_0 =
-0.5 and for different degrees of embedding. This particular example satisfies
the condition that the central logarithmic slope of the light profile \gamma_0
> 2 \beta_0. Our models have velocity dispersion profiles similar to those
observed in nearby dwarf spheroidal galaxies. Hence they can be used to
generate initial conditions for a variety of problems, including N-body
simulations that may represent dwarf galaxies in the Local Group. |
Redshifted 21-cm bispectrum: Impact of the source models on the signal
and the IGM physics from the Cosmic Dawn: The radiations from the first luminous sources drive the fluctuations in the
21-cm signal at Cosmic Dawn (CD) via two dominant astrophysical processes i.e.
the Ly$\alpha$ coupling and X-ray heating, making this signal highly
non-Gaussian. The impact of these processes on the 21-cm signal and its
non-Gaussianity vary depending on the properties of these first sources of
light. In this work, we consider different CD scenarios by varying two major
source parameters i.e. the minimum halo mass $M_{\rm h,\, min}$ and X-ray
photon production efficiency $f_{\rm X}$ in a 1D radiative transfer code
GRIZZLY. We study the impact of variation in these source parameters on the
large scale ($k_1 = 0.16 {\, \rm Mpc}^{-1}$) 21-cm bispectrum for all possible
unique triangles in the Fourier domain. Our detailed and comparative analysis
of the power spectrum and bispectrum shows that the shape, sign and magnitude
of the bispectrum combinedly provide the best measure of the signal
fluctuations and its non-Gaussianity compared to the power spectrum. We also
conclude that it is important to study the sequence of sign changes along with
the variations in the shape and magnitude of the bispectrum throughout the CD
history to arrive at a robust conclusion about the dominant IGM processes at
different cosmic times. We further observe that among all the possible unique
$k$-triangles, the large-scale non-Gaussianity in signal is best probed by the
small $k$-triangles in the squeezed limit and by triangles of similar shapes.
This opens up the possibility of constraining the source parameters during the
CD using the 21-cm bispectrum. | Joining bits and pieces of reionization history: Cosmic Microwave Background temperature and polarization anisotropies from
Planck have estimated a lower value of the optical depth to reionization
($\tau$) compared to WMAP. A significant period in the reionization history
would then fall within $6<z< 10$, where detection of galaxies with Hubble
Frontier Fields program and independent estimation of neutral hydrogen in the
inter galactic medium by Lyman-$\alpha$ observations are also available. This
overlap allows an analysis of cosmic reionization which utilizes a direct
combination of CMB and these astrophysical measurements and potentially breaks
degeneracies in parameters describing the physics of reionization. For the
first time we reconstruct reionization histories by assuming photo-ionization
and recombination rates to be free-form and by allowing underlying cosmological
parameters to vary with CMB (temperature and polarization anisotropies and
lensing) data from Planck 2018 release and a compilation of astrophysical data.
We find an excellent agreement between the low-$\ell$ Planck 2018 HFI
polarization likelihood and astrophysical data in determining the integrated
optical depth. By combining both data, we report for a minimal reconstruction
$\tau=0.051^{+0.001+0.002}_{-0.0012-0.002}$ at 68\% and 95\% CL, which, for the
errors in the current astrophysical measurements quoted in the literature, is
nearly twice better than the projected cosmic variance limited CMB
measurements. For the duration of reionization, redshift interval between 10\%
and complete ionization, we get $2.9^{+0.12+0.29}_{-0.16-0.26}$ at 68\% and
95\% CL, which improves significantly on the corresponding result obtained by
using Planck 2015 data. By a Bayesian analysis of the combined results we do
not find evidence beyond monotonic reionization histories, therefore
multi-phase reionization scenario is disfavored compared to minimal
alternatives. |
Gas-phase metallicity of 27 galaxies at intermediate redshift: The purpose of this work is to make available new gas-phase oxygen abundance
measurements for a serendipitous sample of 27 galaxies with redshift
0.35<z<0.52. We measured the equivalent widths of the [O II]{\lambda}3727,
H{\beta}, and [O III]{\lambda}{\lambda}4959, 5007 emission lines observed in
the galaxy spectra obtained with the Visible Multi-Object Spectrograph mounted
at the Very Large Telescope. For each galaxy, we derived the
metallicity-sensitive emission lines ratio R23, ionization-sensitive emission
lines ratio O32, and gas-phase oxygen abundance 12+log(O/H). The values of
gas-phase oxygen abundance 12+log(O/H) we obtained for the sample galaxies are
consistent with previous findings for galaxies at intermediate redshift. | Deformation of the gravitational wave spectrum by density perturbations: We study the effect of primordial scalar curvature perturbations on the
propagation of gravitational waves over cosmic distances. We point out that
such curvature perturbations deform the isotropic spectrum of any stochastic
background of gravitational waves of primordial origin through the (integrated)
Sachs-Wolfe effect. Computing the changes in the amplitude and frequency of the
propagating gravitational wave induced at linear order by scalar curvature
perturbations, we show that the resulting deformation of each frequency bin of
the gravitational wave spectrum is described by a linearly biased Gaussian with
the variance $\sigma^2 \simeq \int d\ln k \Delta_{\mathcal R}^2$, where
$\Delta_{\mathcal R}^2(k)$ denotes the amplitude of the primordial curvature
perturbations. The linear bias encodes the correlations between the changes
induced in the frequency and amplitude of the gravitational waves. Taking into
account the latest bounds on $\Delta_{\mathcal R}^2$ from primordial black hole
and gravitational wave searches, we demonstrate that the resulting ${\mathcal
O}(\sigma)$ deformation can be significant for extremely peaked gravitational
wave spectra. We further provide an order of magnitude estimate for broad
spectra, for which the net distortion is ${\mathcal O}(\sigma^2)$. |
Fossil Galaxy Groups -- Ideal Laboratories for Studying the Effects of
AGN Heating: We present the first of a sample of fossil galaxy groups with pre-existing
Chandra and/or XMM-Newton X-ray observations and new or forthcoming low
frequency GMRT data -- RXJ1416.4+2315 (z=0.137). Fossil galaxy groups are ideal
laboratories for studying feedback mechanisms and how energy injection affects
the IGM, since due to the lack of recent merging activity, we expect the IGM to
be relatively pristine and affected only by any AGN activity that has occurred
in the group. Our Chandra X-ray observations reveal features resembling
AGN-inflated bubbles, whilst our GMRT radio data show evidence of extended
emission from the central AGN that may be filling the bubble. This has enabled
us to estimate the work done by the central AGN, place limits on the rates of
energy injection and discuss the nature of the plasma filling the bubble. | Proper Motion of the Sub-Parsec Scale Jet in the Radio Galaxy 3C 66B: We present proper motion of the sub-parsec scale jet in a nearby elliptical
galaxy 3C 66B. Observations were made using the VLBA and partly Effelsburg
100-m telescope at 2.3 GHz and 8.4 GHz at 10 epochs over 4 years. The 8.4 GHz
images showed that a proper motion increases from 0.21 to 0.70 mas/year,
corresponding to an apparent speed of 0.30 c to 0.96 c, with a distance from
the core on a sub-parsec scale. Our investigation suggests that the apparent
increase of the proper motion can be explained by changes in the viewing angle,
according to a relativistic beaming model. However, we still cannot eliminate
the possibility that acceleration of the jet outflow speed or of changes of
emissivity profile in the two-zone jet might be found in 3C 66B. |
The Integrated Sachs-Wolfe effect in $f(R)$ gravity: We study the late-time Integrated Sachs-Wolfe (ISW) effect in $f(R)$ gravity
using N-body simulations. In the $f(R)$ model under study, the linear growth
rate is larger than that in general relativity (GR). This slows down the decay
of the cosmic potential and induces a smaller ISW effect on large scales.
Therefore, the $\dot\Phi$ (time derivative of the potential) power spectrum at
$k<0.1h$/Mpc is suppressed relative to that in GR. In the non-linear regime,
relatively rapid structure formation in $f(R)$ gravity boosts the non-linear
ISW effect relative to GR, and the $\dot\Phi$ power spectrum at $k>0.1h$/Mpc is
increased (100$\%$ greater on small scales at $z=0$). We explore the
detectability of the ISW signal via stacking supercluster and supervoids. The
differences in the corresponding ISW cold or hot spots are $\sim 20\%$ for
structures of $\sim 100$Mpc/$h$. Such differences are greater for smaller
structures, but the amplitude of the signal is lower. The high amplitude of ISW
signal detected by Granett et al. can not explained in the $f(R)$ model. We
find relatively big differences between $f(R)$ and GR in the transverse bulk
motion of matter, and discuss its detectability via the relative frequency
shifts of photons from multiple lensed images. | Observable cosmological vector mode in the dark ages: The second-order vector mode is inevitably induced from the coupling of
first-order scalar modes in cosmological perturbation theory and might hinder a
possible detection of primordial gravitational waves from inflation through
21cm lensing observations. Here, we investigate the weak lensing signal in 21cm
photons emitted by neutral hydrogen atoms in the dark ages induced by the
second-order vector mode by decomposing the deflection angle of the 21cm
lensing signal into the gradient and curl modes. The curl mode is a good tracer
of the cosmological vector and tensor modes since the scalar mode does not
induce the curl one. By comparing angular power spectra of the 21cm lensing
curl mode induced by the second-order vector mode and primordial gravitational
waves whose amplitude is parametrized by the tensor-to-scalar ratio $r$, we
find that the 21cm curl mode from the second-order vector mode dominates over
that from primordial gravitational waves on almost all scales if $r \lesssim
10^{-5}$. If we use the multipoles of the power spectrum up to $\ell_{\rm max}
= 10^{5}$ and $10^{6}$ in reconstructing the curl mode from 21cm temperature
maps, the signal-to-noise ratios of the 21cm curl mode from the second-order
vector mode achieve ${\rm S/N} \approx 0.46$ and $73$, respectively.
Observation of 21cm radiation is, in principle, a powerful tool to explore not
only the tensor mode but also the cosmological vector mode. |
Can we really measure fnl from the galaxy power spectrum?: The scale-dependent galaxy bias generated by primordial non-Gaussianity (PNG)
can be used to detect and constrain deviations from standard single-field
inflation. The strongest signal is expected in the local model for PNG, where
the amplitude of non-Gaussianity can be expressed by a set of parameters (fnl,
gnl, ...). Current observational constraints from galaxy clustering on fnl and
gnl assume that the others PNG parameters are vanishing. Using two sets of
cosmological N-body simulations where both fnl and gnl are non-zero, we show
that this strong assumption generally leads to biased estimates and spurious
redshift dependencies of the parameters. Additionally, if the signs of fnl and
gnl are opposite, the amplitude of the scale-dependent bias is reduced,
possibly leading to a false null detection. Finally we show that model
selection techniques like the Bayesian evidence can (and should) be used to
determine if more than one PNG parameter is required by the data. | Low-ionization galaxies and evolution in a pilot survey up to z = 1: We present galaxy spectroscopic data on a pencil beam of $10.75' \times7.5'$
centered on the X-ray cluster RXJ0054.0-2823 at $z = 0.29$. We study the
spectral evolution of galaxies from $z=1$ down to the cluster redshift in a
magnitude-limited sample at $\rm R\leq23$, for which the statistical properties
of the sample are well understood. We divide emission-line galaxies in
star-forming galaxies, LINERs, and Seyferts by using emission-line ratios of
[OII], $\rm H\beta$, and [OIII], and derive stellar fractions from population
synthesis models. We focus our analysis on absorption and low-ionization
galaxies. For absorption-line galaxies we recover the well known result that
these galaxies have had no detectable evolution since $z\sim0.6-0.7$, but we
also find that in the range $z=0.65-1$ at least 50% of the stars in bright
absorption systems are younger than 2.5Gyr. Faint absorption-line galaxies in
the cluster at $z = 0.29$ also had significant star formation during the
previous 2-3Gyr, while their brighter counterparts seem to be composed only of
old stars. At $z\sim0.8$, our dynamically young cluster had a truncated
red-sequence. This result seems to be consistent with a scenario where the
final assembly of E/S0 took place at $z<1$. In the volume-limited range
$0.35\leq z\leq0.65$ we find that 23% of the early-type galaxies have
LINER-like spectra with $\rm H\beta$ in absorption and a significant component
of A stars. The vast majority of LINERs in our sample have significant
populations of young and intermediate-aged stars and are thus not related to
AGN, but to the population of `retired galaxies' recently identified by
Cid-Fernandes et al. (2010) in the SDSS. Early-type LINERs with various
fractions of A stars, and E+A galaxies appear to play an important role in the
formation of the red sequence. |
Phase statistics of the WMAP 7 year data: We performed a comprehensive statistical analysis using complex phases of the
a_lm coefficients computed from the most recent data of the Wilkinson Microwave
Anisotropy Probe (WMAP). Our aim was to confirm or constrain the presence of
non-Gaussianities in the data. We found phase correlations - that suggest
non-Gaussianity - at high-l in a_lm coefficients by applying various
statistical tests. Most of all, we detected a non-Gaussian signal reaching a
significance of 4.7 sigma using random walk statistics and simulations.
However, our conclusion is that the non-Gaussian behavior is due to
contamination from galactic foregrounds that show up in small scales only. When
masked out the contaminated regions, we found no significant non-Gaussianity.
Furthermore, we constrained the f_NL parameter using CMB simulations that mimic
primordial non-Gaussianity. Our estimate is f_NL=40 +/- 200, in agreement with
previous measurements and inflationary expectations. | Pressure profiles and mass estimates using high-resolution
Sunyaev-Zel'dovich effect observations of Zwicky 3146 with MUSTANG-2: The galaxy cluster Zwicky 3146 is a sloshing cool core cluster at $z=0.291$
that in X-ray imaging does not appear to exhibit significant pressure
substructure in the intracluster medium (ICM). The published $M_{500}$ values
range between $3.88^{+0.62}_{-0.58}$ to $22.50 \pm 7.58 \times 10^{14}$
M$_{\odot}$, where ICM-based estimates with reported errors $<20$\% suggest
that we should expect to find a mass between $6.53^{+0.44}_{-0.44} \times
10^{14}$ M$_{\odot}$ (from Planck, with an $8.4\sigma$ detection) and
$8.52^{+1.77}_{-1.47} \times 10^{14}$ M$_{\odot}$ (from ACT, with a $14\sigma$
detection). This broad range of masses is suggestive that there is ample room
for improvement for all methods. Here, we investigate the ability to estimate
the mass of Zwicky 3146 via the Sunyaev-Zel'dovich (SZ) effect with data taken
at 90 GHz by MUSTANG-2 to a noise level better than $15\ \mu$K at the center,
and a cluster detection of $104\sigma$. We derive a pressure profile from our
SZ data which is in excellent agreement with that derived from X-ray data. From
our SZ-derived pressure profiles, we infer $M_{500}$ and $M_{2500}$ via three
methods -- $Y$-$M$ scaling relations, the virial theorem, and hydrostatic
equilibrium -- where we employ X-ray constraints from \emph{XMM-Newton} on the
electron density profile when assuming hydrostatic equilibrium. Depending on
the model and estimation method, our $M_{500}$ estimates range from $6.23 \pm
0.59$ to $10.6 \pm 0.95 \times 10^{14}$ M$_{\odot}$, where our estimate from
hydrostatic equilibrium, is $8.29^{+1.93}_{-1.24}$ ($\pm 19.1$\% stat)
${}^{+0.74}_{-0.68}$ ($\pm 8.6$\% sys, calibration) $\times 10^{14}$
M$_{\odot}$. Our fiducial mass, derived from a $Y$-$M$ relation is
$8.16^{+0.44}_{-0.54}$ ($\pm 5.5$\% stat) ${}^{+0.46}_{-0.43}$ ($\pm 5.5$\%
sys, $Y$-$M$) ${}^{+0.59}_{-0.55}$ ($\pm 7.0$\% sys, cal.) $\times 10^{14}$
M$_{\odot}$. |
Impact of H_2-based star formation model on the z>=6 luminosity function
and the ionizing photon budget for reionization: We present the results of a numerical study examining the effect of H_2-based
star formation (SF) model on the rest-frame UV luminosity function and star
formation rate function (SFRF) of z>=6 galaxies, and the implications for
reionization. Using cosmological hydrodynamical simulations outfitted with an
H_2-SF model, we find good agreement with our previous results (non-H_2 SF
model) and observations at Muv<=-18. However at Muv>-18, we find that the LF
deviates from both our previous work and current observational extrapolations,
producing significantly fewer low-luminosity galaxies and exhibiting additional
turnover at the faint end. We constrain the redshift evolution of this turnover
point using a modified Schechter function that includes additional terms to
quantify the turnover magnitude (Muv^t) and subsequent slope (Beta). We find
that Muv^t evolves from Muv^t=-17.33 (at z=8) to -15.38 (z=6), while Beta
becomes shallower by \Delta Beta=0.22 during the same epoch. This occurs in an
Muv range which will be observable by JWST. By integrating the SFRF, we
determine that even though H_2-SF model significantly reduces the number
density of low luminosity galaxies at Muv>-18, it does not suppress the total
SFR density enough to affect the capability of SF to maintain reionization. | Model-independent constraints on Lorentz invariance violation:
implication from updated Gamma-ray burst observations: Astrophysical observations provide a unique opportunity to test possible
signatures of Lorentz Invariance Violation (LIV), due to the high energies and
long distances involved. In quantum theory of gravity, one may expect the
modification of the dispersion relation between energy and momentum for
photons, which can be probed with the time-lag (the arrival time delay between
light curves in different energy bands) of Gamma-ray bursts (GRBs). In this
paper, by using the detailed time-delay measurements of GRB 160625B at
different energy bands, as well as 23 time-delay GRBs covering the redshifts
range of $z=0.168-2.5$ (which were measured at different energy channels from
the light curves), we propose an improved model-independent method (based on
the newly-compiled sample of $H(z)$ measurements) to probe the energy-dependent
velocity due to the modified dispersion relation for photons. In the framework
of a more complex and reasonable theoretical expression to describe the time
delays, our results imply that the intrinsic time lags can be better described
with more GRBs time delay data. More importantly, through direct fitting of the
time-delay measurements of a sample of GRBs, our limit on the LIV energy scale
is comparable to that with unknown constant for the intrinsic time lag, much
lower than the Planck energy scale in both linear LIV and quadratic LIV cases. |
The MUSIC of Galaxy Clusters II: X-ray global properties and scaling
relations: We present the X-ray properties and scaling relations of a large sample of
clusters extracted from the Marenostrum MUltidark SImulations of galaxy
Clusters (MUSIC) dataset. We focus on a sub-sample of 179 clusters at redshift
z~0.11, with 3.2e14M_sun/h<M_vir<2e15Msun/h, complete in mass. We employed the
X-ray photon simulator PHOX to obtain synthetic Chandra Observations and derive
observable-like global properties of the intracluster medium (ICM), as X-ray
temperature (T_X) and luminosity (L_X). T_X is found to slightly under-estimate
the true mass-weighted temperature, although tracing fairly well the cluster
total mass. We also study the effects of T_X on scaling relations with cluster
intrinsic properties: total (M_500) and gas (M_g500) mass; integrated Compton
parameter (Y_SZ) of the Sunyaev-Zel'dovich (SZ) thermal effect; Y_X=M_g500 T_X.
We confirm that Y_X is a very good mass proxy, with a scatter on M_500-Y_X and
Y_SZ-Y_X lower than 5%. The study of scaling relations among X-ray, intrinsic
and SZ properties indicates that MUSIC clusters reasonably resemble the
self-similar prediction, especially for correlations involving T_X. The
observational approach also allows for a more direct comparison with real
clusters, from which we find deviations mainly due to the physical description
of the ICM, affecting T_X and, particularly, L_X. | Boosting the annihilation boost: Tidal effects on dark matter subhalos
and consistent luminosity modeling: In the cold dark matter paradigm, structures form hierarchically, implying
that large structures contain smaller substructures. These subhalos will
enhance signatures of dark matter annihilation such as gamma rays. In the
literature, typical estimates of this boost factor assume a concentration-mass
relation for field halos, to calculate the luminosity of subhalos. However,
since subhalos accreted in the gravitational potential of their host loose mass
through tidal stripping and dynamical friction, they have a quite
characteristic density profile, different from that of the field halos of the
same mass. In this work, we quantify the effect of tidal stripping on the boost
factor, by developing a semi-analytic model that combines mass-accretion
history of both the host and subhalos as well as subhalo accretion rates. We
find that when subhalo luminosities are treated consistently, the boost factor
increases by a factor 2-5, compared to the typical calculation assuming a
field-halo concentration. This holds for host halos ranging from sub-galaxy to
cluster masses and is independent of the subhalo mass function or specific
concentration-mass relation. The results are particularly relevant for indirect
dark matter searches in the extragalactic gamma-ray sky. |
Different star formation laws for disks versus starbursts at low and
high redshifts: We present evidence that 'bona fide' disks and starburst systems occupy
distinct regions in the gas mass versus star formation (SF) rate plane, both
for the integrated quantities and for the respective surface densities. This
result is based on CO observations of galaxy populations at low and high
redshifts, and on the current consensus for the CO luminosity to gas mass
conversion factors. The data suggest the existence of two different star
formation regimes: a long-lasting mode for disks and a more rapid mode for
starbursts, the latter probably occurring during major mergers or in dense
nuclear SF regions. Both modes are observable over a large range of SF rates.
The detection of CO emission from distant near-IR selected galaxies reveals
such bimodal behavior for the first time, as they allow us to probe gas in disk
galaxies with much higher SF rates than are seen locally. The different regimes
can potentially be interpreted as the effect of a top-heavy IMF in starbursts.
However, we favor a different physical origin related to the fraction of
molecular gas in dense clouds. The IR luminosity to gas mass ratio (i.e., the
SF efficiency) appears to be inversely proportional to the dynamical (rotation)
timescale. Only when accounting for the dynamical timescale, a universal SF law
is obtained, suggesting a direct link between global galaxy properties and the
local SF rate. | The parameter space of Cubic Galileon models for cosmic acceleration: We use recent measurements of the expansion history of the universe to place
constraints on the parameter space of cubic Galileon models, in particular we
concentrate on those models which contain the simplest Galileon term plus a
linear potential. This gives strong constraints on the Lagrangian of these
models. Most dynamical terms in the Galileon Lagrangian are constraint to be
small and the acceleration is effectively provided by a constant term in the
scalar potential, thus reducing, effectively, to a LCDM model for current
acceleration. The effective equation of state is indistinguishable from that of
a cosmological constant w = -1 and the data constraint it to have no temporal
variations of more than at the few % level. The energy density of the Galileon
can contribute only to about 10% of the acceleration energy density, being the
other 90% a cosmological constant term. This demonstrates how useful direct
measurements of the expansion history of the universe are at constraining the
dynamical nature of dark energy. |
Femto-lensing due to a Cosmic String: We consider the femto-lensing due to a cosmic string. If a cosmic string with
the deficit angle $\Delta\sim 100$ [femto-arcsec] $\sim10^{-18}$ [rad] exists
around the line of sight to a gamma-ray burst, we may observe characteristic
interference patterns caused by gravitational lensing in the energy spectrum of
the gamma-ray burst. This "femto-lensing" event was first proposed as a tool to
probe small mass primordial black holes. In this paper, we propose use of the
femto-lensing to probe cosmic strings with extremely small tension.
Observability conditions and the event rate are discussed. Differences between
the cases of a point mass and a cosmic string are presented. | Type 1 AGN at low z: We present the emission properties of a sample of 3,579 type 1 AGN, selected
based on the detection of broad H-alpha emission. The sample covers the range
of black hole mass 10^6<M_BH/M_Sun<10^9.5 and luminosity in Eddington units
10^-3 < L/L_Edd < 1. Our main results are: 1. The distribution of the H-alpha
FWHM values is independent of luminosity. 2. The observed mean optical-UV SED
is well matched by a fixed shape SED of luminous quasars, which scales linearly
with broad H-alpha luminosity, and a host galaxy contribution. 3. The host
galaxy r-band (fibre) luminosity function follows well the luminosity function
of inactive non-emission line galaxies (NEG), consistent with a fixed fraction
of ~3% of NEG hosting an AGN, regardless of the host luminosity. 4. The
optical-UV SED of the more luminous AGN shows a small dispersion, consistent
with dust reddening of a blue SED, as expected for thermal thin accretion disc
emission. 5. There is a rather tight relation of nuL_nu(2 keV) and broad
H-alpha luminosity, which provides a useful probe for unobscured (true) type 2
AGN. |
Swiss-cheese models and the Dyer-Roeder approximation: In view of interpreting the cosmological observations precisely, especially
when they involve narrow light beams, it is crucial to understand how light
propagates in our statistically homogeneous, clumpy, Universe. Among the
various approaches to tackle this issue, Swiss-cheese models propose an
inhomogeneous spacetime geometry which is an exact solution of Einstein's
equation, while the Dyer-Roeder approximation deals with inhomogeneity in an
effective way. In this article, we demonstrate that the distance-redshift
relation of a certain class of Swiss-cheese models is the same as the one
predicted by the Dyer-Roeder approach, at a well-controlled level of
approximation. Both methods are therefore equivalent when applied to the
interpretation of, e.g., supernova observations. The proof relies on completely
analytical arguments, and is illustrated by numerical results. | Is cosmic birefringence due to dark energy or dark matter? A tomographic
approach: A pseudoscalar "axionlike" field, $\phi$, may explain the $3\sigma$ hint of
cosmic birefringence observed in the $EB$ power spectrum of the cosmic
microwave background (CMB) polarization data. Is $\phi$ dark energy or dark
matter? A tomographic approach can answer this question. The effective mass of
dark energy field responsible for the accelerated expansion of the Universe
today must be smaller than $m_\phi\simeq 10^{-33}$ eV. If $m_\phi \gtrsim
10^{-32}$ eV, $\phi$ starts evolving before the epoch of reionization and we
should observe different amounts of birefringence from the $EB$ power spectrum
at low ($l\lesssim 10$) and high multipoles. Such an observation, which
requires a full-sky satellite mission, would rule out $\phi$ being dark energy.
If $m_\phi \gtrsim 10^{-28}$ eV, $\phi$ starts oscillating during the epoch of
recombination, leaving a distinct signature in the $EB$ power spectrum at high
multipoles, which can be measured precisely by ground-based CMB observations.
Our tomographic approach relies on the shape of the $EB$ power spectrum and is
less sensitive to miscalibration of polarization angles. |
Nonlinear clustering in models with primordial non-Gaussianity: the halo
model approach: We develop the halo model of large-scale structure as an accurate tool for
probing primordial non-Gaussianity. In this study we focus on understanding the
matter clustering at several redshifts. The primordial non-Gaussianity is
modeled as a quadratic correction to the local Gaussian potential, and is
characterized by the parameter f_NL. In our formulation of the halo model we
pay special attention to the effect of halo exclusion, and show that this can
potentially solve the long standing problem of excess power on large scales in
this model. The model depends on the mass function, clustering and density
profiles of halos. We test these ingredients using a large ensemble of
high-resolution Gaussian and non-Gaussian numerical simulations. In particular,
we provide a first exploration of how density profiles change in the presence
of primordial non-Gaussianities. We find that for f_NL positive/negative high
mass halos have an increased/decreased core density, so being more/less
concentrated than in the Gaussian case. We also examine the halo bias and show
that, if the halo model is correct, then there is a small asymmetry in the
scale-dependence of the bias on very large scales, which arises because the
Gaussian bias must be renormalized. We show that the matter power spectrum is
modified by ~2.5% and ~3.5% on scales k~1.0 h/Mpc at z=0 and z=1, respectively.
Our halo model calculation reproduces the absolute amplitude to within 10% and
the ratio of non-Gaussian to Gaussian spectra to within 1%. We also measure the
matter correlation functions and find similarly good agreement between the
model and the data. We anticipate that this modeling will be useful for
constraining f_NL from measurements of the shear correlation function in future
weak lensing surveys such as Euclid. | Radio Halos From Simulations And Hadronic Models I: The Coma cluster: We use the results from a constrained, cosmological MHD simulation of the
Local Universe to predict the radio halo and the gamma-ray flux from the Coma
cluster and compare it to current observations. The simulated magnetic field
within the Coma cluster is the result of turbulent amplification of the
magnetic field during build-up of the cluster. The magnetic seed field
originates from star-burst driven, galactic outflows. The synchrotron emission
is calculated assuming a hadronic model. We follow four approaches with
different distributions for the cosmic-ray proton (CRp) population within
galaxy clusters. The radial profile the radio halo can only be reproduced with
a radially increasing energy fraction within the cosmic ray proton population,
reaching $>$100% of the thermal energy content at $\approx$ 1Mpc, e.g. the edge
of the radio emitting region. Additionally the spectral steepening of the
observed radio halo in Coma cannot be reproduced, even when accounting for the
negative flux from the thermal SZ effect at high frequencies. Therefore the
hadronic models are disfavored from present analysis. The emission of
$\gamma$-rays expected from our simulated coma is still below the current
observational limits (by a factor of $\sim$6) but would be detectable in the
near future. |
A kinematic study of the Andromeda dwarf spheroidal system: We present a homogeneous kinematic analysis of red giant branch stars within
18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies, obtained using the
Keck I LRIS and Keck II DEIMOS spectrographs. Based on their g-i colors (taken
with the CFHT MegaCam imager), physical positions on the sky, and radial
velocities, we assign probabilities of dSph membership to each observed star.
Using this information, the velocity dispersions, central masses and central
densities of the dark matter halos are calculated for these objects, and
compared with the properties of the Milky Way dSph population. We also measure
the average metallicity ([Fe/H]) from the co-added spectra of member stars for
each M31 dSph and find that they are consistent with the trend of decreasing
[Fe/H] with luminosity observed in the Milky Way population. We find that three
of our studied M31 dSphs appear as significant outliers in terms of their
central velocity dispersion, And XIX, XXI and XXV, all of which have large
half-light radii (>700 pc) and low velocity dispersions (sigma_v<5 km/s). In
addition, And XXV has a mass-to-light ratio within its half-light radius of
just [M/L]_{half}=10.3^{+7.0}_{-6.7}, making it consistent with a simple
stellar system with no appreciable dark matter component within its 1 sigma
uncertainties. We suggest that the structure of the dark matter halos of these
outliers have been significantly altered by tides. | X-Ray Absorption By WHIM in the Sculptor Wall: We present XMM RGS and Chandra LETG observations of the blazar, H 2356-309,
located behind the Sculptor Wall, a large-scale galaxy structure expected to
harbor high-density Warm-Hot Intergalactic Medium (WHIM). Our simultaneous
analysis of the RGS and LETG spectra yields a 3-sigma detection of the crucial
redshifted O vii K-alpha line with a column density (>~ 10^{16} cm^{-2})
consistent with similar large-scale structures produced in cosmological
simulations. This represents the first detection of non-local WHIM from X-ray
absorption studies where XMM and Chandra data are analyzed simultaneously and
the absorber redshift is already known, thus providing robust evidence for the
expected repository of the "missing baryons". |
Inflation with General Initial Conditions for Scalar Perturbations: We explore the possibility of a single field quasi-de Sitter inflationary
model with general initial state for primordial fluctuations. In this paper,
first we compute the power spectrum and the bispectrum of scalar perturbations
with coherent state as the initial state. We find that a large class of
coherent states are indistinguishable from the Bunch-Davies vacuum state and
hence consistent with the current observations. In case of a more general
initial state built over Bunch-Davies vacuum state, we show that the
constraints on the initial state from observed power spectrum and local
bispectrum are relatively weak and for quasi-de Sitter inflation a large number
of initial states are consistent with the current observations. However,
renormalizability of the energy-momentum tensor of the fluctuations constraints
the initial state further. | Secondary isocurvature perturbations from acoustic reheating: The superhorizon (iso)curvature perturbations are conserved if the following
conditions are satisfied: (i) (each) non adiabatic pressure perturbation is
zero, (ii) the gradient terms are ignored, that is, at the leading order of the
gradient expansion (iii) (each) total energy momentum tensor is conserved. We
consider the case with the violation of the last two requirements and discuss
the generation of secondary isocurvature perturbations during the late time
universe. Second order gradient terms are not necessarily ignored even if we
are interested in the long wavelength modes because of the convolutions which
may pick products of short wavelength perturbations up. We then introduce
second order conserved quantities on superhorizon scales under the conditions
(i) and (iii) even in the presence of the gradient terms by employing the full
second order cosmological perturbation theory. We also discuss the violation of
the condition (iii), that is, the energy momentum tensor is conserved for the
total system but not for each component fluid. As an example, we explicitly
evaluate second order heat conduction between baryons and photons due to the
weak Compton scattering, which dominates the period just before recombination.
We show that such secondary effects can be recast into the isocurvature
perturbations on superhorizon scales if the local type primordial non
Gaussianity exists a priori. |
Signatures of Primordial Gravitational Waves on the Large-Scale
Structure of the Universe: We study the generation and evolution of second-order energy-density
perturbations arising from primordial gravitational waves. Such "tensor-induced
scalar modes" approximately evolve as standard linear matter perturbations and
may leave observable signatures in the Large-Scale Structure of the Universe.
We study the imprint on the matter power-spectrum of some primordial models
which predict a large gravitational-wave signal at high frequencies. This novel
mechanism in principle allows us to constrain or detect primordial
gravitational waves by looking at specific features in the matter or galaxy
power-spectrum, thereby allowing to probe them on a range of scales unexplored
so far. | Non-minimally coupled Natural Inflation: Palatini and Metric formalism
with the recent BICEP/Keck: In this work, we show the effect of the non-minimal coupling $\xi \phi^2 R$
on the inflationary parameters by considering the single-field inflation and
present the inflationary predictions of the appealing potential for the
particle physics viewpoint: Natural Inflation, an axion-like inflaton which has
a cosine-type periodic potential and the inflaton naturally emerges as a
pseudo-Nambu-Goldstone boson with a spontaneously broken global symmetry. We
present the inflationary predictions for this potential, $n_s$, $r$, and
$\alpha=\mathrm{d}n_s/\mathrm{d}\ln k$. In addition, we assume standard thermal
history after inflation, and using this, for considered potential, we show
compatible regions for the $n_s$, $r$ within the recent BICEP/Keck results. |
Impact of string and monopole-type junctions on domain wall dynamics:
implications for dark energy: We investigate the potential role of string and monopole-type junctions in
the frustration of domain wall networks using a velocity-dependent one-scale
model for the characteristic velocity, $v$, and the characteristic length, $L$,
of the network. We show that, except for very special network configurations,
$v^2 \lsim (HL)^2 \lsim (\rho_\sigma + \rho_\mu)/\rho_m$ where $H$ is the
Hubble parameter and $\rho_\sigma$, $\rho_\mu$ and $\rho_m$ are the average
density of domain walls, strings and monopole-type junctions. We further show
that if domain walls are to provide a significant contribution to the dark
energy without generating exceedingly large CMB temperature fluctuations then,
at the present time, the network must have a characteristic length $ L_0 \lsim
10 \Omega_{\sigma 0}^{-2/3} {\rm kpc}$ and a characteristic velocity $v_0 \lsim
10^{-5} \Omega_{\sigma 0}^{-2/3}$ where $\Omega_{\sigma 0}=\rho_{\sigma
0}/\rho_{c 0}$ and $\rho_c$ is the critical density. In order to satisfy these
constraints with $\Omega_{\sigma 0} \sim 1$, $\rho_{m 0}$ would have to be at
least 10 orders of magnitude larger than $\rho_{\sigma 0}$, which would be in
complete disagreement with observations. This result provides very strong
additional support for the conjecture that no natural frustration mechanism,
which could lead to a significant contribution of domain walls to the dark
energy budget, exists. | The effect of baryons on the variance and the skewness of the mass
distribution in the universe at small scales: We study the dissipative effects of baryon physics on cosmic statistics at
small scales using a cosmological simulation of a (50 Mpc/h)^3 volume of the
universe. The MareNostrum simulation was performed using the AMR code RAMSES,
and includes most of the physical ingredients which are part of the current
theory of galaxy formation, such as metal-dependent cooling and UV heating,
subgrid modelling of the ISM, star formation and supernova feedback. We re-ran
the same initial conditions for a dark matter only universe, as a reference
point for baryon-free cosmic statistics. In this paper, we present the measured
small-scale amplification of sigma^2 and S_3 due to baryonic physics and their
interpretation in the framework of the halo model. As shown in recent studies,
the effect of baryons on the matter power spectrum can be accounted for at
scales k <~ 10 h/Mpc by modifying the halo concentration parameter. We propose
to extend this result by using a halo profile which is a linear combination of
a NFW profile for the dark matter and an exponential disk profile mimicking the
baryonic component at the heart of the halo. This halo profile form is
physically motivated, and depends on two parameters, the mass fraction f_d of
baryons in the disk, and the ratio lambda_d of the disk's characteristic scale
to the halo's virial radius. We find this composite profile to reproduce both
the small-scale variance and skewness boosts measured in the simulation up to k
~ 10^2 h/Mpc for physically meaningful values of the parameters f_d and
lambda_d. Although simulations like the one presented here usually suffer from
various problems when compared to observations, our modified halo model could
be used as a fitting model to improve the determination of cosmological
parameters from weak lensing convergence spectra and skewness measurements. |
Sussing Merger Trees: Stability and Convergence: Merger trees are routinely used to follow the growth and merging history of
dark matter haloes and subhaloes in simulations of cosmic structure formation.
Srisawat et al. (2013) compared a wide range of merger-tree-building codes.
Here we test the influence of output strategies and mass resolution on
tree-building. We find that, somewhat surprisingly, building the tree from more
snapshots does not generally produce more complete trees; instead, it tends to
short- en them. Significant improvements are seen for patching schemes which
attempt to bridge over occasional dropouts in the underlying halo catalogues or
schemes which combine the halo-finding and tree-building steps seamlessly. The
adopted output strategy does not affec- t the average number of branches
(bushiness) of the resultant merger trees. However, mass resolution has an
influence on both main branch length and the bushiness. As the resolution
increases, a halo with the same mass can be traced back further in time and
will encounter more small progenitors during its evolutionary history. Given
these results, we recommend that, for simulations intended as precursors for
galaxy formation models where of order 100 or more snapshots are analysed, the
tree-building routine should be integrated with the halo finder, or at the very
least be able to patch over multiple adjacent snapshots. | Negative cosmological constant in the dark sector?: We consider the possibility that the dark sector of our Universe contains a
negative cosmological constant dubbed $\lambda$. For such models to be viable,
the dark sector should contain an additional component responsible for the
late-time accelerated expansion rate ($X$). We explore the departure of the
expansion history of these models from the concordance $\Lambda$ Cold Dark
Matter model. For a large class of our models the accelerated expansion is
transient with a nontrivial dependence on the model parameters. All models with
$w_X>-1$ will eventually contract and we derive an analytical expression for
the scale factor $a(t)$ in the neighborhood of its maximal value. We find also
the scale factor for models ending in a Big Rip in the regime where dustlike
matter density is negligible compared to $\lambda$. We address further the
viability of such models, in particular when a high $H_0$ is taken into
account. While we find no decisive evidence for a nonzero $\lambda$, the best
models are obtained with a phantom behavior on redshifts $z\gtrsim 1$ with a
higher evidence for nonzero $\lambda$. An observed value for $h$ substantially
higher than $0.70$ would be a decisive test of their viability. |
The Stellar Halos of Massive Elliptical Galaxies II: Detailed Abundance
Ratios at Large Radius: We study the radial dependence in stellar populations of 33 nearby early-type
galaxies with central stellar velocity dispersions sigma* > 150 km/s. We
measure stellar population properties in composite spectra, and use ratios of
these composites to highlight the largest spectral changes as a function of
radius. Based on stellar population modeling, the typical star at 2 R_e is old
(~10 Gyr), relatively metal poor ([Fe/H] -0.5), and alpha-enhanced
([Mg/Fe]~0.3). The stars were made rapidly at z~1.5-2 in shallow potential
wells. Declining radial gradients in [C/Fe], which follow [Fe/H], also arise
from rapid star formation timescales due to declining carbon yields from
low-metallicity massive stars. In contrast, [N/Fe] remains high at large
radius. Stars at large radius have different abundance ratio patterns from
stars in the center of any present-day galaxy, but are similar to Milky Way
thick disk stars. Our observations are thus consistent with a picture in which
the stellar outskirts are built up through minor mergers with disky galaxies
whose star formation is truncated early (z~1.5-2). | Testing Local Anisotropy Using the Method of Smoothed Residuals I -
Methodology: We discuss some details regarding the method of smoothed residuals, which has
recently been used to search for anisotropic signals in low-redshift distance
measurements (Supernovae). In this short note we focus on some details
regarding the implementation of the method, particularly the issue of
effectively detecting signals in data that are inhomogeneously distributed on
the sky. Using simulated data, we argue that the original method proposed in
Colin et al. [1] will not detect spurious signals due to incomplete sky
coverage, and that introducing additional Gaussian weighting to the statistic
as in [2] can hinder its ability to detect a signal. Issues related to the
width of the Gaussian smoothing are also discussed. |
Fossil group origins - VI. Global X-ray scaling relations of fossil
galaxy clusters: We present the first pointed X-ray observations of 10 candidate fossil galaxy
groups and clusters. With these Suzaku observations, we determine global
temperatures and bolometric X-ray luminosities of the intracluster medium (ICM)
out to $r_{500}$ for six systems in our sample. The remaining four systems show
signs of significant contamination from non-ICM sources. For the six objects
with successfully determined $r_{500}$ properties, we measure global
temperatures in the range $2.8 \leq T_{\mathrm{X}} \leq 5.3 \ \mathrm{keV}$,
bolometric X-ray luminosities of $0.8 \times 10^{44} \ \leq L_{\mathrm{X,bol}}
\leq 7.7\times 10^{44} \ \mathrm{erg} \ \mathrm{s}^{-1}$, and estimate masses,
as derived from $T_{\mathrm{X}}$, of $M_{500} > 10^{14} \ \mathrm{M}_{\odot}$.
Fossil cluster scaling relations are constructed for a sample that combines our
Suzaku observed fossils with fossils in the literature. Using measurements of
global X-ray luminosity, temperature, optical luminosity, and velocity
dispersion, scaling relations for the fossil sample are then compared with a
control sample of non-fossil systems. We find the fits of our fossil cluster
scaling relations are consistent with the relations for normal groups and
clusters, indicating fossil clusters have global ICM X-ray properties similar
to those of comparable mass non-fossil systems. | The star cluster - field star connection in nearby spiral galaxies I.
Data analysis techniques and application to NGC 4395: It is generally assumed that a large fraction of stars are initially born in
clusters. However, a large fraction of these disrupt on short timescales and
the stars end up belonging to the field. Understanding this process is of
paramount importance if we wish to constrain the star formation histories of
external galaxies using star clusters. We attempt to understand the relation
between field stars and star clusters by simultaneously studying both in a
number of nearby galaxies. As a pilot study, we present results for the
late-type spiral NGC 4395 using HST/ACS and HST/WFPC2 images. Different
detection criteria were used to distinguish point sources (star candidates) and
extended objects (star cluster candidates). Using a synthetic CMD method, we
estimated the star formation history. Using simple stellar population model
fitting, we calculated the mass and age of the cluster candidates. The field
star formation rate appears to have been roughly constant, or to have possibly
increased by up to about a factor of two, for ages younger than $\sim$300 Myr
within the fields covered by our data. Our data do not allow us to constrain
the star formation histories at older ages. We identify a small number of
clusters in both fields. Neither massive ($>10^5$ M$_\odot$) clusters nor
clusters with ages $\geq1$ Gyr were found in the galaxy and we found few
clusters older than 100 Myr. Based on our direct comparison of field stars and
clusters in NGC 4395, we estimate the ratio of star formation rate in clusters
that survive for $10^7$ to $10^8$ years to the total star formation to be
$\Gamma\sim0.03$. We suggest that this relatively low $\Gamma$ value is caused
by the low star formation rate of NGC 4395. |
Cosmic magnetic fields with MASCLET: an application to galaxy clusters: We describe and test a new version of the adaptive mesh refinement (AMR)
cosmological code MASCLET. The new version of the code includes all the
ingredients of its previous version plus a description of the evolution of the
magnetic field under the approximation of the ideal magneto-hydrodynamics
(MHD). To preserve the divergence-free condition of MHD, the original
divergence cleaning algorithm of Dedner et al. (2002) is implemented. We
present a set of well-known 1D and 2D tests, such as several shock-tube
problems, the fast rotor and the Orszag-Tang vortex. The performance of the
code in all the tests is excellent with estimated median relative errors of
$\nabla \cdot {\bf B}$ in the 2D tests smaller than $5 \times 10^{-5}$ for the
fast rotor test, and $5 \times 10^{-3}$ for the Orszag-Tang vortex. As an
astrophysical application of the code, we present a simulation of a
cosmological box of 40 comoving Mpc side length in which a primordial uniform
comoving magnetic field of strength 0.1 nG is seeded. The simulation shows how
the magnetic field is channelled along the filaments of gas and is concentrated
and amplified within galaxy clusters. Comparison with the values expected from
pure compression reveals an additional amplification of the magnetic field
caused by turbulence in the central region of the cluster. Values of the order
of $\sim 1 \mu$G are obtained in clusters at $z\sim 0$ with median relative
errors of $\nabla \cdot {\bf B}$ below 0.4\%. The implications of a proper
description of the dynamics of the magnetic field and their possible
observational counterparts in future facilities are discussed. | Constraining primordial and gravitational mode coupling with the
position-dependent bispectrum of the large-scale structure: We develop and study the position-dependent bispectrum. It is a
generalization of the recently proposed position-dependent power spectrum
method of measuring the squeezed-limit bispectrum. The position-dependent
bispectrum can similarly be used to measure the squeezed-limit trispectrum in
which one of the wavelengths is much longer than the other three. In this work,
we will mainly consider the case in which the three smaller wavelengths are
nearly the same (the equilateral configuration). We use the Fisher information
matrix to forecast constraints on bias parameters and the amplitude of
primordial trispectra from the position-dependent bispectrum method. We find
that the method can constrain the local-type $g_{\rm NL}$ at a level of
$\sigma(g_{\rm NL}^{\rm local}) \approx 3 \times 10^5$ for a large volume
SPHEREx-like survey; improvements can be expected by including all the
triangular configurations of the bispectra rather than just the equilateral
configuration. However, the same measurement would also constrain a much larger
family of trispectra than local $g_{\rm NL}$ model. We discuss the implications
of the forecasted reach of future surveys in terms of super cosmic variance
uncertainties from primordial non-Gaussianities. |
Composition of Low Redshift Halo Gas: Halo gas in low-z (z<0.5) >0.1L* galaxies in high-resolution, large-scale
cosmological hydrodynamic simulations is examined with respect to three
components: (cold, warm, hot) with temperatures equal to (<10^5, 10^{5-6},
>10^6)K, respectively. The warm component is compared, utilizing O VI
\lambda\lambda 1032, 1038 absorption lines, to observations and agreement is
found with respect to the galaxy-O VI line correlation, the ratio of O VI line
incidence rate in blue to red galaxies and the amount of O VI mass in
star-forming galaxies. A detailed account of the sources of warm halo gas
(stellar feedback heating, gravitational shock heating and accretion from the
intergalactic medium), inflowing and outflowing warm halo gas metallicity
disparities and their dependencies on galaxy types and environment is also
presented. Having the warm component securely anchored, our simulations make
the following additional predictions. First, cold gas is the primary component
in inner regions, with its mass comprising 50% of all gas within
galacto-centric radius r=(30,150)kpc in (red, blue) galaxies. Second, at
r>(30,200)kpc in (red, blue) galaxies the hot component becomes the majority.
Third, the warm component is a perpetual minority, with its contribution
peaking at ~30% at r=100-300kpc in blue galaxies and never exceeding 5% in red
galaxies. The significant amount of cold gas in low-z early-type galaxies found
in simulations, in agreement with recent observations (Thom et al.), is
intriguing, so is the dominance of hot gas at large radii in blue galaxies. | Detection of relic gravitational waves in the CMB: Prospects for CMBPol
mission: Detection of relic gravitational waves, through their imprint in the cosmic
microwave background radiation, is one of the most important tasks for the
planned CMBPol mission. In the simplest viable theoretical models the
gravitational wave background is characterized by two parameters, the
tensor-to-scalar ratio $r$ and the tensor spectral index $n_t$. In this paper,
we analyze the potential joint constraints on these two parameters, $r$ and
$n_t$, using the potential observations of the CMBPol mission, which is
expected to detect the relic gravitational waves if $r\gtrsim0.001$. The
influence of the contaminations, including cosmic weak lensing, various
foreground emissions, and systematical errors, is discussed. |
Inflation with a constant rate of roll: We consider an inflationary scenario where the rate of inflaton roll defined
by $\ddot\phi/H\dot \phi$ remains constant. The rate of roll is small for
slow-roll inflation, while a generic rate of roll leads to the interesting case
of `constant-roll' inflation. We find a general exact solution for the inflaton
potential required for such inflaton behaviour. In this model, due to non-slow
evolution of background, the would-be decaying mode of linear scalar
(curvature) perturbations may not be neglected. It can even grow for some
values of the model parameter, while the other mode always remains constant.
However, this always occurs for unstable solutions which are not attractors for
the given potential. The most interesting particular cases of constant-roll
inflation remaining viable with the most recent observational data are
quadratic hilltop inflation (with cutoff) and natural inflation (with an
additional negative cosmological constant). In these cases even-order slow-roll
parameters approach non-negligible constants while the odd ones are
asymptotically vanishing in the quasi-de Sitter regime. | On the spectral resolution of the MILES stellar library: Empirical stellar libraries are extensively used to extract stellar
kinematics in galaxies and to build stellar population models. An accurate
knowledge of the spectral resolution of these libraries is critical to avoid
propagation errors and uncertain estimates of the intrinsic stellar velocity
dispersion of galaxies. In this research note we re-assess the spectral
resolution of the MILES stellar library and of the stellar population models
based on it. This exercise was performed, because of a recent controversy over
the exact MILES resolution. We perform our test through the comparison of MILES
stellar spectra with three different sets of higher-resolution templates, one
fully theoretical - the MARCS library - and two empirical ones, namely the
Indo-U.S. and ELODIE v3.1 libraries. The theoretical template has a
well-defined very high (R=20000) resolution. Hence errors on this theoretical
value do not affect our conclusions. Our approach based on the MARCS library
was crucial to constrain the values of the resolution also for the other two
empirical templates. We find that the MILES resolution has previously been
slightly overestimated. We derive a new spectral resolution of 2.54 A FWHM,
instead of the nominal 2.3 A. The reason for this difference is due to an
overestimation of the resolution for the Indo-U.S. library that was previously
used for estimates of the MILES resolution. For the Indo-U.S. we obtain a new
value of 1.35 A FWHM. Most importantly, the results derived from the MARCS and
ELODIE libraries are in very good agreement. These results are important for
users of the MILES spectra library and for further development of stellar
population models aimed to obtain accurate stellar kinematics in galaxies. |
Efficiently estimating mean, uncertainty and unconstrained large scale
fraction of local Universe simulations with paired fixed fields: Provided a random realization of the cosmological model, observations of our
cosmic neighborhood now allow us to build simulations of the latter down to the
non-linear threshold. The resulting local Universe models are thus accurate up
to a given residual cosmic variance. Namely some regions and scales are
apparently not constrained by the data and seem purely random. Drawing
conclusions together with their uncertainties involves then statistics implying
a considerable amount of computing time. By applying the constraining algorithm
to paired fixed fields, this paper diverts the original techniques from their
first use to efficiently disentangle and estimate uncertainties on local
Universe simulations obtained with random fields. Paired fixed fields differ
from random realizations in the sense that their Fourier mode amplitudes are
fixed and they are exactly out of phase. Constrained paired fixed fields show
that only 20% of the power spectrum on large scales (> tens of megaparsecs) is
purely random. Namely 80% of it is partly constrained by the large scale /
small scale data correlations. Additionally, two realizations of our local
environment obtained with paired fixed fields of the same pair constitute an
excellent non-biased average or quasi-linear realization of the latter, namely
the equivalent of hundreds of constrained simulations. The variance between
these two realizations gives the uncertainty on the achievable local Universe
simulations. These two simulations will permit enhancing faster our local
cosmic web understanding thanks to a drastically reduced required computational
time to appreciate its modeling limits and uncertainties. | Precise Mass Determination of SPT-CL J2106-5844, the Most Massive
Cluster at z>1: We present a detailed high-resolution weak-lensing (WL) study of SPT-CL
J2106-5844 at z=1.132, claimed to be the most massive system discovered at z >
1 in the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. Based on the
deep imaging data from the Advanced Camera for Surveys and Wide Field Camera 3
on-board the Hubble Space Telescope, we find that the cluster mass distribution
is asymmetric, composed of a main clump and a subclump ~640 kpc west thereof.
The central clump is further resolved into two smaller northwestern and
southeastern substructures separated by ~150 kpc. We show that this rather
complex mass distribution is more consistent with the cluster galaxy
distribution than a unimodal distribution as previously presented. The
northwestern substructure coincides with the BCG and X-ray peak while the
southeastern one agrees with the location of the number density peak. These
morphological features and the comparison with the X-ray emission suggest that
the cluster might be a merging system. We estimate the virial mass of the
cluster to be $M_{200c} = (10.4^{+3.3}_{-3.0}\pm1.0)~\times~10^{14}~M_{\odot}$,
where the second error bar is the systematic uncertainty. Our result confirms
that the cluster SPT-CL J2106-5844 is indeed the most massive cluster at z>1
known to date. We demonstrate the robustness of this mass estimate by
performing a number of tests with different assumptions on the centroids,
mass-concentration relations, and sample variance. |
Optimising cosmic shear surveys to measure modifications to gravity on
cosmic scales: We consider how upcoming photometric large scale structure surveys can be
optimized to measure the properties of dark energy and possible cosmic scale
modifications to General Relativity in light of realistic astrophysical and
instrumental systematic uncertainities. In particular we include flexible
descriptions of intrinsic alignments, galaxy bias and photometric redshift
uncertainties in a Fisher Matrix analysis of shear, position and position-shear
correlations, including complementary cosmological constraints from the CMB. We
study the impact of survey tradeoffs in depth versus breadth, and redshift
quality. We parameterise the results in terms of the Dark Energy Task Force
figure of merit, and deviations from General Relativity through an analagous
Modified Gravity figure of merit. We find that intrinsic alignments weaken the
dependence of figure of merit on area and that, for a fixed observing time, a
fiducial Stage IV survey plateaus above roughly 10,000deg2 for DE and peaks at
about 5,000deg2 as the relative importance of IAs at low redshift penalises
wide, shallow surveys. While reducing photometric redshift scatter improves
constraining power, the dependence is shallow. The variation in constraining
power is stronger once IAs are included and is slightly more pronounced for MG
constraints than for DE. The inclusion of intrinsic alignments and galaxy
position information reduces the required prior on photometric redshift
accuracy by an order of magnitude for both the fiducial Stage III and IV
surveys, equivalent to a factor of 100 reduction in the number of spectroscopic
galaxies required to calibrate the photometric sample. | Eddington-inspired Born-Infeld gravity: nuclear physics constraints and
the validity of the continuous fluid approximation: In this paper we investigate the classical non-relativistic limit of the
Eddington-inspired Born-Infeld theory of gravity. We show that strong bounds on
the value of the only additional parameter of the theory \kappa, with respect
to general relativity, may be obtained by requiring that gravity plays a
subdominant role compared to electromagnetic interactions inside atomic nuclei.
We also discuss the validity of the continuous fluid approximation used in this
and other astrophysical and cosmological studies. We argue that although the
continuous fluid approximation is expected to be valid in the case of
sufficiently smooth density distributions, its use should eventually be
validated at a quantum level. |
Probability distribution and statistical properties of spherically
compensated cosmic regions in $Λ$CDM cosmology: The statistical properties of cosmic structures are well known to be strong
probes for cosmology. In particular, several studies tried to use the cosmic
void counting number to obtain tight constrains on Dark Energy. In this paper
we address this question by using the CoSphere model as introduced in de
Fromont & Alimi (2017a). We derive their exact statistics in both primordial
and non linearly evolved Universe for the standard $\Lambda$CDM model. We first
compute the full joint Gaussian probability distribution for the various
parameters describing these profiles in the Gaussian Random Field. We recover
the results of Bardeen et al. (1986) only in the limit where the compensation
radius becomes very large, i.e. when the central extremum decouples from its
cosmic environment. We derive the probability distribution of the compensation
size in this primordial field. We show that this distribution is redshift
independent and can be used to model cosmic void size distribution.
Interestingly, it can be used for central maximum such as DM haloes. We compute
analytically the statistical distribution of the compensation density in both
primordial and evolved Universe. We also derive the statistical distribution of
the peak parameters already introduced by Bardeen et al. (1986) and discuss
their correlation with the cosmic environment. We thus show that small central
extrema with low density are associated with narrow compensation regions with a
small $R_1$ and a deep compensation density $\delta_1$ while higher central
extrema are located in larger but smoother over/under massive regions. | The Magellanic Quasars Survey. II. Confirmation of 144 New Active
Galactic Nuclei Behind the Southern Edge of the Large Magellanic Cloud: We quadruple the number of quasars known behind the Large Magellanic Cloud
(LMC) from 55 (42 in the LMC fields of the third phase of the Optical
Gravitational Lensing Experiment (OGLE)) to 200 by spectroscopically confirming
169 (144 new) quasars from a sample of 845 observed candidates in four ~3 deg^2
Anglo-Australian Telescope/AAOmega fields south of the LMC center. The
candidates were selected based on their Spitzer mid-infrared colors, X-ray
emission, and/or optical variability properties in the database of the OGLE
microlensing survey. The contaminating sources can be divided into 115 young
stellar objects (YSOs), 17 planetary nebulae (PNe), 39 Be and 24 blue stars, 68
red stars, and 12 objects classed as either YSO/PN or blue star/YSO. There are
also 402 targets with either featureless spectra or too low signal-to-noise
ratio for source classification. Our quasar sample is 50% (30%) complete at I =
18.6 mag (19.3 mag). The newly discovered active galactic nuclei (AGNs) provide
many additional reference points for proper motion studies of the LMC, and the
sample includes 10 bright AGNs (I < 18 mag) potentially suitable for absorption
line studies. Their primary use, however, is for detailed studies of quasar
variability, as they all have long-term, high cadence, continuously growing
light curves from the microlensing surveys of the LMC. Completing the existing
Magellanic Quasars Survey fields in the LMC and Small Magellanic Cloud should
yield a sample of ~700 well-monitored AGNs, and expanding it to the larger
regions covered by the OGLE-IV survey should yield a sample of ~3600 AGNs. |
New Model of Inflation that Predicts Natural Fermion Re-heating and a
Dark-Energy energy-fraction of 75%: We study a model cosmological solution of the coupled Einstein,
electromagnetic (with source) and second-gravity \cite{Nash2010} equations that
employs a flat universe Friedmann-\text{Lema{\^ \i}tre}-Robertson-Walker (FLRW)
line element with scale factor $a = a(t)$ [comoving coordinates] for the
Einstein sector. The solution of the coupled field equations yields a scale
factor $a(t)$ that initially varies exponentially $a(t) = a(0) {e}^{H t}$.
Exponential growth continues until the comoving time approaches the end of
inflation, then $a(t)$ rapidly transitions to a power law dependence on $t$.
Concomitant with the transition from inflation in this model is a natural
re-heating and excitation of Standard Model degrees of freedom, and in
particular of electrically charged quarks and leptons. No scalar inflaton
field, or slow-roll potential is introduced to achieve these effects.
This model is noteworthy in two respects. A plausible connection between the
second-gravity \emph{unit} field $\mathbf{u}$ and Dark Energy, through the
generalization of the photon wave function, is demonstrated, and a scenario is
outlined that allocates a 75% fraction of the total energy of the Universe to
Dark Energy. Secondly, we conjecture that an experimentally detectable
substructure of the of the photon can be observed if the (quantized) unit field
can be excited out of its ground state. | INTEGRAL constraints on primordial black holes and particle dark matter: The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has
yielded unprecedented measurements of the soft gamma-ray spectrum of our
Galaxy. Here we use those measurements to set constraints on dark matter (DM)
that decays or annihilates into photons with energies $E\approx 0.02-2$ MeV.
First, we revisit the constraints on particle DM that decays or annihilates to
photon pairs. In particular, for decaying DM, we find that previous limits were
overstated by roughly an order of magnitude. Our new, conservative analysis
finds that the DM lifetime must satisfy $\tau\gtrsim 5\times 10^{26}\,{\rm
s}\times (m_{\chi}/\rm MeV)^{-1}$ for DM masses $m_{\chi}=0.054-3.6$ MeV. For
MeV-scale DM that annihilates into photons INTEGRAL sets the strongest
constraints to date. Second, we target ultralight primordial black holes (PBHs)
through their Hawking radiation. This makes them appear as decaying DM with a
photon spectrum peaking at $E\approx 5.77/(8\pi G M_{\rm PBH})$, for a PBH of
mass $M_{\rm PBH}$. We use the INTEGRAL data to demonstrate that, at 95\% C.L.,
PBHs with masses less than $1.2\times 10^{17}$ g cannot comprise all of the DM,
setting the tightest bound to date on ultralight PBHs. |
Measuring Type Ia Supernova Populations of Stretch and Color and
Predicting Distance Biases: Simulations of Type Ia Supernovae (SNIa) surveys are a critical tool for
correcting biases in the analysis of SNIa to infer cosmological parameters.
Large scale Monte Carlo simulations include a thorough treatment of observation
history, measurement noise, intrinsic scatter models and selection effects. In
this paper, we improve simulations with a robust technique to evaluate the
underlying populations of SNIa color and stretch that correlate with
luminosity. In typical analyses, the standardized SNIa brightness is determined
from linear `Tripp' relations between the light curve color and luminosity and
between stretch and luminosity. However, this solution produces Hubble residual
biases because intrinsic scatter and measurement noise result in measured color
and stretch values that do not follow the Tripp relation. We find a $10\sigma$
bias (up to 0.3 mag) in Hubble residuals versus color and $5\sigma$ bias (up to
0.2 mag) in Hubble residuals versus stretch in a joint sample of 920
spectroscopically confirmed SNIa from PS1, SNLS, SDSS and several low-z
surveys. After we determine the underlying color and stretch distributions, we
use simulations to predict and correct the biases in the data. We show that
removing these biases has a small impact on the low-z sample, but reduces the
intrinsic scatter $\sigma_{\textrm{int}}$ from $0.101$ to $0.083$ in the
combined PS1, SNLS and SDSS sample. Past estimates of the underlying
populations were too broad, leading to a small bias in the equation-of-state of
dark energy $w$ of $\Delta w=0.005$. | Complete history of the observable 21-cm signal from the first stars
during the pre-reionization era: We present the first complete calculation of the history of the inhomogeneous
21-cm signal from neutral hydrogen during the era of the first stars. We use
hybrid computational methods to capture the large-scale distribution of the
first stars, whose radiation couples to the neutral hydrogen emission, and to
evaluate the 21-cm signal from z ~ 15-35. In our realistic picture large-scale
fluctuations in the 21-cm signal are sourced by the inhomogeneous density field
and by the Ly-alpha and X-ray radiative backgrounds. The star formation is
suppressed by two spatially varying effects: negative feedback provided by the
Lyman-Werner radiative background, and supersonic relative velocities between
the gas and dark matter. Our conclusions are quite promising: we find that the
fluctuations imprinted by the inhomogeneous Ly-alpha background in the 21-cm
signal at z ~ 25 should be detectable with the Square Kilometer Array. |
CALCLENS: Weak Lensing Simulations for Large-area Sky Surveys and
Second-order Effects in Cosmic Shear Power Spectra: I present a new algorithm, CALCLENS, for efficiently computing weak
gravitational lensing shear signals from large N-body light cone simulations
over a curved sky. This new algorithm properly accounts for the sky curvature
and boundary conditions, is able to produce redshift-dependent shear signals
including corrections to the Born approximation by using multiple-plane ray
tracing, and properly computes the lensed images of source galaxies in the
light cone. The key feature of this algorithm is a new, computationally
efficient Poisson solver for the sphere that combines spherical harmonic
transform and multgrid methods. As a result, large areas of sky (~10, 000
square degrees) can be ray traced efficiently at high-resolution using only a
few hundred cores on widely available machines. Using this new algorithm and
curved-sky calculations that only use a slower but more accurate spherical
harmonic transform Poisson solver, I study the shear B-mode and rotation mode
power spectra. Employing full-sky E/B-mode decompositions, I confirm that the
shear B-mode and rotation mode power spectra are equal at high accuracy (~1%),
as expected from perturbation theory up to second order. Coupled with realistic
galaxy populations placed in large N-body light cone simulations, this new
algorithm is ideally suited for the construction of synthetic weak lensing
shear catalogs to be used to test for systematic effects in data analysis
procedures for upcoming large-area sky surveys. The implementation presented in
this work, written in C and employing widely available software libraries to
maintain portability, is publicly available at
http://code.google.com/p/calclens. | TheHaloMod: An online calculator for the halo model: The halo model is a successful framework for describing the distribution of
matter in the Universe -- from weak lensing observables to galaxy 2-point
correlation functions. We review the basic formulation of the halo model and
several of its components in the context of galaxy two-point statistics,
developing a coherent framework for its application. We use this framework to
motivate the presentation of a new Python tool for simple and efficient
calculation of halo model quantities, and their extension to galaxy statistics
via a \textit{halo occupation distribution}, called \halomod. This tool is
efficient, simple to use, comprehensive and importantly provides a great deal
of flexibility in terms of custom extensions. This Python tool is complemented
by a new web-application at https://thehalomod.app that supports the generation
of many halo model quantities directly from the browser -- useful for
educators, students, theorists and observers. |
Unbiased likelihood-free inference of the Hubble constant from light
standard sirens: Multi-messenger observations of binary neutron star mergers offer a promising
path towards resolution of the Hubble constant ($H_0$) tension, provided their
constraints are shown to be free from systematics such as the Malmquist bias.
In the traditional Bayesian framework, accounting for selection effects in the
likelihood requires calculation of the expected number (or fraction) of
detections as a function of the parameters describing the population and
cosmology; a potentially costly and/or inaccurate process. This calculation
can, however, be bypassed completely by performing the inference in a framework
in which the likelihood is never explicitly calculated, but instead fit using
forward simulations of the data, which naturally include the selection. This is
Likelihood-Free Inference (LFI). Here, we use density-estimation LFI, coupled
to neural-network-based data compression, to infer $H_0$ from mock catalogues
of binary neutron star mergers, given noisy redshift, distance and peculiar
velocity estimates for each object. We demonstrate that LFI yields
statistically unbiased estimates of $H_0$ in the presence of selection effects,
with precision matching that of sampling the full Bayesian hierarchical model.
Marginalizing over the bias increases the $H_0$ uncertainty by only $6\%$ for
training sets consisting of $O(10^4)$ populations. The resulting LFI framework
is applicable to population-level inference problems with selection effects
across astrophysics. | Cosmological Interpretation for the Stochastic Signal in Pulsar Timing
Arrays: The pulsar timing array (PTA) collaborations have recently reported
compelling evidence for the presence of a stochastic signal consistent with a
gravitational-wave background. In this letter, we combine the latest data sets
from NANOGrav, PPTA and EPTA collaborations to explore the cosmological
interpretations for the detected signal from first-order phase transitions,
domain walls and cosmic strings, separately. We find that the first-order phase
transitions and cosmic strings can give comparable interpretations compared to
supermassive black hole binaries (SMBHBs) characterized by a power-law
spectrum, but the domain wall model is strongly disfavored with the Bayes
factor compared to the SMBHB model being 0.009. Furthermore, the constraints on
the parameter spaces indicate that: 1) a strong phase transition at
temperatures below the electroweak scale is favored and the bubble collisions
make the dominant contribution to the energy density spectrum; 2) the cosmic
string tension is $G \mu \in [1.46, 15.3]\times 10^{-12}$ at $90\%$ confidence
interval and a small reconnection probability $p<6.68\times 10^{-2}$ is
preferred at $95\%$ confidence level, implying that the strings in
(super)string theory are strongly favored over the classical field strings. |
Comment on "21-cm Radiation: A New Probe of Variation in the
Fine-Structure Constant": Khatri and Wandelt reported that change in the value of alpha by 1% changes
the mean brightness temperature $T_b$ decrement of the CMB due to 21 cm
absorption by 5% over the redshift range z $<$ 50. A drawback of their approach
is that the dimensionful parameters are used. Changing of units leads to the
change of the magnitude and even sign of the effect. Similar problems may be
identified in a large number of other publications which consider limits on the
variation of alpha using dimentionful parameters. We propose a method to obtain
consistent results and provide an estimate of the effect. | A thorough investigation of the prospects of eLISA in addressing the
Hubble tension: Fisher Forecast, MCMC and Machine Learning: We carry out an in-depth analysis of the capability of the upcoming
space-based gravitational wave mission eLISA in addressing the Hubble tension,
with a primary focus on observations at intermediate redshifts ($3<z<8$). We
consider six different parametrizations representing different classes of
cosmological models, which we constrain using the latest datasets of cosmic
microwave background (CMB), baryon acoustic oscillations (BAO), and type Ia
supernovae (SNIa) observations, in order to find out the up-to-date tensions
with direct measurement data. Subsequently, these constraints are used as
fiducials to construct mock catalogs for eLISA. We then employ Fisher analysis
to forecast the future performance of each model in the context of eLISA. We
further implement traditional Markov Chain Monte Carlo (MCMC) to estimate the
parameters from the simulated catalogs. Finally, we utilize Gaussian Processes
(GP), a machine learning algorithm, for reconstructing the Hubble parameter
directly from simulated data. Based on our analysis, we present a thorough
comparison of the three methods as forecasting tools. Our Fisher analysis
confirms that eLISA would constrain the Hubble constant ($H_0$) at the
sub-percent level. MCMC/GP results predict reduced tensions for
models/fiducials which are currently harder to reconcile with direct
measurements of $H_0$, whereas no significant change occurs for
models/fiducials at lesser tensions with the latter. This feature warrants
further investigation in this direction. |
Intermediate and Power-Law Inflation in the Tachyon Model with Constant
Sound Speed: By adopting the intermediate and power-law scale factors, we study the
tachyon inflation with constant sound speed. We perform some numerical analysis
on the perturbation and non-gaussianity parameters in this model and compare
the results with observational data. By using the constraints on the scalar
spectral index and tensor-to-scalar-ratio, obtained from Planck2018 TT, TE,
EE+lowE+lensing+BAO+BK14 data, the constraint on the running of the scalar
spectral index obtained from Planck2018 TT, TE, EE+lowEB+lensing data, and
constraint on tensor spectral index obtained from Planck2018 TT, TE, EE
+lowE+lensing+BK14+BAO+LIGO and Virgo2016 data, we find the observationally
viable ranges of the model's parameters at both $68\%$ CL and $95\%$ CL. We
also analyze the non-gaussian features of the model in the equilateral and
orthogonal configurations. Based on Planck2018 TTT, EEE, TTE and EET data, we
find the constraints on the sound speed as $0.276\leq c_{s}\leq 1$ at $68\%$
CL, $0.213\leq c_{s}\leq 1$ at $95\%$ CL, and $0.186\leq c_{s}\leq 1$ at $97\%$
CL. | Probing violation of the Copernican principle via the integrated
Sachs-Wolfe effect: Recent observational data of supernovae indicate that we may live in an
underdense region, which challenges the Copernican principle. We show that the
integrated Sachs-Wolfe (ISW) effect is an excellent discriminator between
anti-Copernican inhomogeneous models and the standard Copernican models. As a
reference model, we consider an anti-Copernican inhomogeneous model that
consists of two inner negatively curved underdense regions and an outer flat
Einstein-de Sitter region. We assume that these regions are connected by two
thin-walls at redshifts z = 0.067 and z=0.45. In the inner two regions, the
first-order ISW effect is dominant and comparable to that in the concordant
flat-Lambda models. In the outer Einstein-de Sitter region, the first-order ISW
effect vanishes but the second-order ISW effect plays a dominant role, while
the first-order ISW effect is dominant in the flat-Lambda models at moderate
redshifts. This difference can discrimate the anti-Copernican models from the
concordant flat-Lambda model. At high redshits, the second-order ISW effect is
dominant both in our inhomogeneous model and the concordant model. In the outer
region, moreover, the ISW effect due to large-scale density perturbations with
a present matter density contrast much less than 0.37 is negligible, while the
effect due to small-scale density perturbations (such as clusters of galaxies,
superclusters and voids) with matter density contrast much larger than 0.37
would generate anisotropies which are larger than those generated by the ISW
effect in the concordant model. |
Predicting Cosmological Observables with PyCosmo: Current and upcoming cosmological experiments open a new era of precision
cosmology, thus demanding accurate theoretical predictions for cosmological
observables. Because of the complexity of the codes delivering such
predictions, reaching a high level of numerical accuracy is challenging. Among
the codes already fulfilling this task, $\textsf{PyCosmo}$ is a Python based
framework providing solutions to the Einstein-Boltzmann equations and accurate
predictions for cosmological observables. In this work, we first describe how
the observables are implemented. Then, we check the accuracy of the theoretical
predictions for background quantities, power spectra and Limber and
beyond-Limber angular power spectra by comparison with other codes: the Core
Cosmology Library ($\texttt{CCL}$), $\texttt{CLASS}$, $\texttt{HMCode}$ and
$\texttt{iCosmo}$. In our analysis we quantify the agreement of
$\textsf{PyCosmo}$ with the other codes, for a range of cosmological models,
monitored through a series of $\textit{unit tests}$. $\textsf{PyCosmo}$,
conceived as a multi purpose cosmology calculation tool in $\texttt{Python}$,
is designed to be interactive and user friendly. A current version of the code
(without the Boltzmann Solver) is publicly available and can be used
interactively on the platform $\textsf{PyCosmo Hub}$, all accessible from this
link: https://cosmology.ethz.ch/research/software-lab/PyCosmo.html . On the hub
the users can perform their own computations using $\texttt{Jupyter Notebooks}$
without the need of installing any software, access to the results presented in
this work and benefit from tutorial notebooks illustrating the usage of the
code. The link above also redirects to the code release and documentation. | PRIMUS: The dependence of AGN accretion on host stellar mass and color: We present evidence that the incidence of active galactic nuclei (AGNs) and
the distribution of their accretion rates do not depend on the stellar masses
of their host galaxies, contrary to previous studies. We use hard (2-10 keV)
X-ray data from three extragalactic fields (XMM-LSS, COSMOS and ELAIS-S1) with
redshifts from the Prism Multi-object Survey to identify 242 AGNs with L_{2-10
keV}=10^{42-44} erg /s within a parent sample of ~25,000 galaxies at 0.2<z<1.0
over ~3.4 deg^2 and to i~23. We find that although the fraction of galaxies
hosting an AGN at fixed X-ray luminosity rises strongly with stellar mass, the
distribution of X-ray luminosities is independent of mass. Furthermore, we show
that the probability that a galaxy will host an AGN can be defined by a
universal Eddington ratio distribution that is independent of the host galaxy
stellar mass and has a power-law shape with slope -0.65. These results
demonstrate that AGNs are prevalent at all stellar masses in the range 9.5<log
M_*/M_sun<12 and that the same physical processes regulate AGN activity in all
galaxies in this stellar mass range. While a higher AGN fraction may be
observed in massive galaxies, this is a selection effect related to the
underlying Eddington ratio distribution. We also find that the AGN fraction
drops rapidly between z~1 and the present day and is moderately enhanced
(factor~2) in galaxies with blue or green optical colors. Consequently, while
AGN activity and star formation appear to be globally correlated, we do not
find evidence that the presence of an AGN is related to the quenching of star
formation or the color transformation of galaxies. |
Confirmation of a Dominating Hot-Dust Component in z~2 Star Forming
ULIRGs: This submission has been withdrawn. | The PRIsm MUlti-object Survey (PRIMUS). II. Data Reduction and Redshift
Fitting: The PRIsm MUti-object Survey (PRIMUS) is a spectroscopic galaxy redshift
survey to z~1 completed with a low-dispersion prism and slitmasks allowing for
simultaneous observations of ~2,500 objects over 0.18 square degrees. The final
PRIMUS catalog includes ~130,000 robust redshifts over 9.1 sq. deg. In this
paper, we summarize the PRIMUS observational strategy and present the data
reduction details used to measure redshifts, redshift precision, and survey
completeness. The survey motivation, observational techniques, fields, target
selection, slitmask design, and observations are presented in Coil et al 2010.
Comparisons to existing higher-resolution spectroscopic measurements show a
typical precision of sigma_z/(1+z)=0.005. PRIMUS, both in area and number of
redshifts, is the largest faint galaxy redshift survey completed to date and is
allowing for precise measurements of the relationship between AGNs and their
hosts, the effects of environment on galaxy evolution, and the build up of
galactic systems over the latter half of cosmic history. |
Coupled Quintessence scalar field model in light of observational
datasets: We do a detailed analysis of a well-theoretically motivated interacting dark
energy scalar field model with a time-varying interaction term. Using current
cosmological datasets from CMB, BAO, Type Ia Supernova, $H(z)$ measurements
from cosmic chronometers, angular diameter measurements from Megamasers, growth
measurements, and local SH0ES measurements, we found that dark energy component
may act differently than a cosmological constant at early times. The
observational data also does not disfavor a small interaction between dark
energy and dark matter at late times. When using all these datasets in
combination, our value of $H_0$ agrees well with SH0ES results but in
3.5$\sigma$ tension with Planck results. We also did AIC and BIC analysis, and
we found that the cosmological data prefer coupled quintessence model over
$\Lambda$CDM, although the chi-square per number of degrees of freedom test
prefers the latter. | Tests for the existence of horizon through gravitational waves from a
small binary in the vicinity of a massive object: In this letter we calculate the gravitational waves (GWs) emitted from a
small binary (SB) by solving the Teukolsky equation in the background of a
massive exotic compact object (ECO) which is phenomenologically described by a
Schwarzschild geometry with a reflective boundary condition at its "would-be"
horizon. The "continuous echo" waves propagating to infinity due to
reflectivity of ECO at its "would-be" horizon provide an exquisite probe to the
nature of the ECO's horizon. |
A Second Set of RATAN-600 Observations of Giant Radio Galaxies: Results of RATAN-600 centimeter-wavelength flux-density measurements of the
extended components in five giant radio galaxies are reported. The spectra of
the components of these radio galaxies have been constructed using the data of
the WENSS, NVSS, and GB6 surveys together with new RATAN-600 data. Spectral
indices in the studied frequency range have been calculated. | Non-Gaussian bias: insights from discrete density peaks: Corrections induced by primordial non-Gaussianity to the linear halo bias can
be computed from a peak-background split or the widespread local bias model.
However, numerical simulations clearly support the prediction of the former, in
which the non-Gaussian amplitude is proportional to the linear halo bias. To
understand better the reasons behind the failure of standard Lagrangian local
bias, in which the halo overdensity is a function of the local mass overdensity
only, we explore the effect of a primordial bispectrum on the 2-point
correlation of discrete density peaks. We show that the effective local bias
expansion to peak clustering vastly simplifies the calculation. We generalize
this approach to excursion set peaks and demonstrate that the resulting
non-Gaussian amplitude, which is a weighted sum of quadratic bias factors,
precisely agrees with the peak-background split expectation, which is a
logarithmic derivative of the halo mass function with respect to the
normalisation amplitude. We point out that statistics of thresholded regions
can be computed using the same formalism. Our results suggest that halo
clustering statistics can be modelled consistently (in the sense that the
Gaussian and non-Gaussian bias factors agree with peak-background split
expectations) from a Lagrangian bias relation only if the latter is specified
as a set of constraints imposed on the linear density field. This is clearly
not the case of standard Lagrangian local bias. Therefore, one is led to
consider additional variables beyond the local mass overdensity. |
Why are central radio relics so rare?: In this paper we address the question why cluster radio relics that are
connected to shock acceleration, so-called radio gischt, have preferentially
been found in the outskirts of galaxy clusters. By identifying merger shock
waves in cosmological grid simulations, we explore several prescriptions for
relating the energy dissipated in shocks to the energy emitted in the radio
band. None of the investigated models produce detectable radio relics within
100-200 kpc from the cluster centre. All models cause > 50 per cent of the
detectable relic emission at projected distances > 800 kpc. Central radio
relics caused by shocks that propagate along the line-of-sight are rare events
for simple geometrical reasons, and they have a low surface brightness making
them elusive for current instruments. Our simulations show that the radial
distribution of observed relics can be explained by the radial trend of
dissipated kinetic energy in shocks, that increases with distance from the
cluster centre up until half of the virial radius. | Constraints on Neutrino Mass and Light Degrees of Freedom in Extended
Cosmological Parameter Spaces: From a combination of probes including the cosmic microwave background
(WMAP7+SPT), Hubble constant (HST), baryon acoustic oscillations (SDSS+2dFGRS),
and supernova distances (Union2), we have explored the extent to which the
constraints on the effective number of neutrinos and sum of neutrino masses are
affected by our ignorance of other cosmological parameters, including the
curvature of the universe, running of the spectral index, primordial helium
abundance, evolving late-time dark energy, and early dark energy. In a combined
analysis of the effective number of neutrinos and sum of neutrino masses, we
find mild (2.2 sigma) preference for additional light degrees of freedom.
However, the effective number of neutrinos is consistent with the canonical
expectation of 3 massive neutrinos and no extra relativistic species to within
1 sigma when allowing for evolving dark energy and relaxing the strong
inflation prior on the curvature and running. The agreement improves with the
possibility of an early dark energy component, itself constrained to be less
than 5% of the critical density (95% CL) in our expanded parameter space. In
extensions of the standard cosmological model, the derived amplitude of linear
matter fluctuations sigma_8 is found to closely agree with low-redshift cluster
abundance measurements. The sum of neutrino masses is robust to assumptions of
the effective number of neutrinos, late-time dark energy, curvature, and
running at the level of 1.2 eV (95% CL). The upper bound degrades to 2.0 eV
(95% CL) when further including the early dark energy density and primordial
helium abundance as additional free parameters. Even in extended cosmological
parameter spaces, Planck alone could determine the possible existence of extra
relativistic species at 4 sigma confidence and constrain the sum of neutrino
masses to 0.2 eV (68% CL). |
What we can learn from the spectral index of the tensor mode: If the beginning of inflation is defined at the moment when the vacuum energy
of the inflaton starts to dominate, the energy density of the other fields at
that moment is (by definition) comparable to the inflaton. Although the
fraction will be small at the horizon exit due to the inflationary expansion,
they can alter the scale dependence of the spectrum. At the same time, velocity
of the inflaton field may not coincide with the slow-roll (attractor) velocity.
Those dynamics could be ubiquitous but can easily alter the scale dependence of
the spectrum. Since the scale dependence is currently used to constrain or even
exclude inflation models, it is very important to measure its shift, which is
due to the dynamics that does not appear in the original inflation model.
Considering typical examples, we show that the spectral index of the tensor
mode is a useful measure of such effect. Precise measurement of the higher
runnings of the scalar mode will be helpful in discriminating the source. | Shear and Magnification: Cosmic Complementarity: The potential of cosmic shear to probe cosmology is well recognized and
future optical wide field surveys are currently being designed to optimize the
return of cosmic shear science. High precision cosmic shear analysis requires
high precision photometric redshift. With accurate photometric redshifts, it
becomes possible to measure the cosmic magnification on galaxies by galaxies
and use it as a probe of cosmology. This type of weak lensing measurement will
not use galaxy shapes, instead it will strongly rely on precise photometry and
detailed color information. In this work it is shown that such a measurement
would lead to competitive constraints of the cosmological parameters, with a
remarkable complementarity with cosmic shear. Future cosmic shear surveys could
gain tremendously from magnification measurements as an independent probe of
the dark matter distribution leading to a better control of observational and
theoretical systematics when combined with shear. |
Ultraviolet Emission-Line Correlations in Hubble/COS Spectra of Active
Galactic Nuclei: Single-Epoch Black Hole Masses: Effective methods of measuring supermassive black hole masses in active
galactic nuclei (AGN) are of critical importance to studies of galaxy
evolution. While there has been much success obtaining masses through
reverberation mapping, the extensive observing time required by this method has
limited the practicality of applying it to large samples at a variety of
redshifts. This limitation highlights the need to estimate these masses using
single-epoch spectroscopy of ultraviolet emission lines. We use ultraviolet
spectra of 44 AGN from HST/COS, IUE, and FUSE of the CIV 1549, OVI 1035, OIII]
1664, HeII 1640, CII 1335, and MgII 2800 emission lines and explore their
potential as tracers of the broad-line region and supermassive black hole mass.
The higher S/N and better spectral resolution of the Cosmic Origins
Spectrograph on Hubble Space Telescope resolves AGN intrinsic absorption and
produces more accurate line widths. From these, we test the viability of
mass-scaling relationships based on line widths and luminosities and carry out
a principal component analysis based on line luminosities, widths, skewness,
and kurtosis. At L_{1450} < 10^{45} erg/s, the UV line luminosities correlate
well with Hbeta, as does the 1450 Angstrom continuum luminosity. We find that
CIV, OVI, and MgII can be used as reasonably accurate estimators of AGN black
hole masses, while HeII and CII are uncorrelated. | BAL phosphorus abundance and evidence for immense ionic column densities
in quasar outflows: VLT X-Shooter observations of quasar SDSS J1512+1119: We present spectroscopic analysis of the broad absorption line outflow in
quasar SDSS J1512+1119. In particular, we focus our attention on a kinematic
component in which we identify PV and SIV/SIV* absorption troughs. The shape of
the unblended phosphorus doublet troughs and the three SIV/SIV* troughs allow
us to obtain reliable column density measurements for these two ions.
Photoionization modelling using these column densities and those of HeI*
constrain the abundance of phosphorus to the range of 0.5-4 times the solar
value. The total column density, ionization parameter and metalicity inferred
from the PV and SIV column densities leads to large optical depth values for
the common transition observed in BAL outflows. We show that the true CIV
optical depth, is about 1000 times greater in the core of the absorption
profile than the value deduced from its apparent optical depth. |
Illuminating a Dark Lens : A Type Ia Supernova Magnified by the Frontier
Fields Galaxy Cluster Abell 2744: SN HFF14Tom is a Type Ia Supernova (SN) discovered at z = 1.3457 +- 0.0001
behind the galaxy cluster Abell 2744 (z = 0.308). In a cosmology-independent
analysis, we find that HFF14Tom is 0.77 +- 0.15 magnitudes brighter than
unlensed Type Ia SNe at similar redshift, implying a lensing magnification of
mu_obs = 2.03 +- 0.29. This observed magnification provides a rare opportunity
for a direct empirical test of galaxy cluster lens models. Here we test 17 lens
models, 13 of which were generated before the SN magnification was known,
qualifying as pure "blind tests". The models are collectively fairly accurate:
8 of the models deliver median magnifications that are consistent with the
measured mu to within 1-sigma. However, there is a subtle systematic bias: the
significant disagreements all involve models overpredicting the magnification.
We evaluate possible causes for this mild bias, and find no single physical or
methodological explanation to account for it. We do find that model accuracy
can be improved to some extent with stringent quality cuts on multiply-imaged
systems, such as requiring that a large fraction have spectroscopic redshifts.
In addition to testing model accuracies as we have done here, Type Ia SN
magnifications could also be used as inputs for future lens models of Abell
2744 and other clusters, providing valuable constraints in regions where
traditional strong- and weak-lensing information is unavailable. | Hawaii Two-0: High-redshift galaxy clustering and bias: We perform an analysis of two-point galaxy clustering and galaxy bias using
Subaru Hyper-Suprime Cam (HSC) data taken jointly by the Subaru Strategic
Program and the University of Hawaii in the COSMOS field. The depth of the data
is similar to the ongoing Hawaii Two-0 (H20) optical galaxy survey, thus the
results are indicative of future constraints from tenfold area.
We measure the angular auto-power spectra of the galaxy overdensity in three
redshift bins, defined by dropouts from the g-, r- and i-bands, and compare
them to the theoretical expectation from concordance cosmology with linear
galaxy bias. We determine the redshift distribution of each bin using a
standard template-based photometric redshift method, coupled with a
self-organizing map (SOM) to quantify colour space coverage. We also
investigate sources of systematic errors to inform the methodology and
requirements for Hawaii Two-0.
The linear galaxy bias fit results are $b_{\mathrm{gal,g}} = 3.90 \pm 0.33
(\mathrm{stat}) \substack{ +0.64 \\ -0.24 } (\mathrm{sys})$ at redshift $z
\simeq 3.7$, $b_{\mathrm{gal,r}} = 8.44 \pm 0.63 (\mathrm{stat}) \substack{
+1.42 \\ -0.72 } (\mathrm{sys})$ at $z \simeq 4.7$, and $b_{\mathrm{gal,i}} =
11.94 \pm 2.24 (\mathrm{stat}) \substack{ +1.82 \\ -1.27 } (\mathrm{sys})$ at
$z \simeq 5.9$. |
Inflation vs. Ekpyrosis -- comparing stability in general non-minimal
theory: The scalar field is considered to have dominated the early Universe. One
subtle yet crucial requirement of this assumption is that the solution must be
highly stable, i.e., indifferent to any initial conditions because there are no
favored ones. Inflation, which is now the most successful early Universe
paradigm, answers most of the early Universe's problems, including the fact
that it is mostly stable. In this article, in addition to the inflationary
solution, we systematically investigate every possible early Universe solution
in the presence of a barotropic fluid in the general non-minimal
(scalar-tensor) theory. In doing so, we rely upon the classical perturbative
techniques. We find, to our surprise, that inflation does not always ensure
stability in the Einstein frame, although ekpyrosis can. We also discover that,
contrary to the inflationary paradigm, ekpyrosis always assures stability in
the presence of any fluid with any equation of state in general non-minimal
models. We utilize the conformal transformation to map the inflationary theory
in the minimal frame to the ekpyrotic theory in the non-minimal frame, and show
that the latter is always much more stable than the former, resulting in a much
more preferred model that can even be studied in different contexts such as
late time cosmology. | Inverse Construction of the $Λ$LTB Model from a Distance-redshift
Relation: Spherically symmetric dust universe models with a positive cosmological
constant $\Lambda$, known as $\Lambda$-Lema\^itre-Tolman-Bondi($\Lambda$LTB)
models, are considered. We report a method to construct the $\Lambda$LTB model
from a given distance-redshift relation observed at the symmetry center. The
spherical inhomogeneity is assumed to be composed of growing modes. We derive a
set of ordinary differential equations for three functions of the redshift,
which specify the spherical inhomogeneity. Once a distance-redshift relation is
given, with careful treatment of possible singular points, we can uniquely
determine the model by solving the differential equations for each value of
$\Lambda$. As a demonstration, we fix the distance-redshift relation as that of
the flat $\Lambda$CDM model with $(\Omega^{\rm dis}_{\rm m0}, \Omega^{\rm
dis}_{\rm \Lambda 0})=(0.3,0.7)$, where $\Omega^{\rm dis}_{\rm m0}$ and
$\Omega^{\rm dis}_{\rm \Lambda 0}$ are the normalized matter density and the
cosmological constant, respectively. Then, we construct the $\Lambda$LTB model
for several values of $\Omega_{\rm \Lambda 0}:=\Lambda/(3H_0^2)$, where $H_0$
is the present Hubble parameter observed at the symmetry center. We obtain void
structure around the symmetry center for $\Omega_{\Lambda 0}<\Omega^{\rm
dis}_{\Lambda 0}$. We show the relation between the ratio
$\Omega_{\Lambda0}/\Omega^{\rm dis}_{\Lambda 0}$ and the amplitude of the
inhomogeneity. |
Predictions of just-enough inflation: We find the best-fit cosmological parameters for a scenario of inflation with
only the sufficient amount of accelerated expansion for the $\lambda\phi^4$
potential. While for the simplest scenario of chaotic inflation all observable
primordial fluctuations cross the Hubble horizon during the slow-roll epoch,
for the scenario of just-enough inflation the slow-roll conditions are violated
at the largest length scales. Performing a numerical mode-by-mode integration
for the perturbations on the largest scales and comparing the predicted
anisotropies of the cosmic microwave background to results from the WMAP 7-yr
data analysis, we find the initial conditions in agreement with current
cosmological data. In contrast to the simplest chaotic model for the quartic
potential, the just-enough inflation scenario is not ruled out. Although this
scenario naturally gives rise to a modification of the first multipoles, for a
quartic potential it cannot explain the lack of power at the largest angular
scales. | Radial distribution of stars, gas and dust in SINGS galaxies. II.
Derived dust properties: We present a detailed analysis of the radial distribution of dust properties
in the SINGS sample, performed on a set of UV, IR and HI surface brightness
profiles, combined with published molecular gas profiles and metallicity
gradients. The internal extinction, derived from the TIR-to-FUV luminosity
ratio, decreases with radius, and is larger in Sb-Sbc galaxies. The TIR-to-FUV
ratio correlates with the UV spectral slope beta, following a sequence shifted
to redder UV colors with respect to that of starbursts. The star formation
history (SFH) is identified as the main driver of this departure. We have also
derived radial profiles of the total dust mass surface density, the fraction of
the dust mass contributed by PAHs, the fraction of the dust mass heated by very
intense starlight and the intensity of the radiation field heating the grains.
The dust profiles are exponential, their radial scale-length being constant
from Sb to Sd galaxies (only ~10% larger than the stellar scale-length). Many
S0/a-Sab galaxies have central depressions in their dust radial distributions.
The PAH abundance increases with metallicity for 12+\log(O/H)<9, and at larger
metallicities the trend flattens and even reverses, with the SFH being a
plausible underlying driver for this behavior. The dust-to-gas ratio is also
well correlated with metallicity and therefore decreases with galactocentric
radius. |
Improving the accuracy of estimators for the two-point correlation
function: We show how to increase the accuracy of estimates of the two-point
correlation function without sacrificing efficiency. We quantify the error of
the pair-counts and of the Landy-Szalay estimator by comparing them with exact
reference values. The standard method, using random point sets, is compared to
geometrically motivated estimators and estimators using quasi-Monte~Carlo
integration. In the standard method, the error scales proportionally to
$1/\sqrt{N_r}$, with $N_r$ being the number of random points. In our improved
methods, the error scales almost proportionally to $1/N_q$, where $N_q$ is the
number of points from a low-discrepancy sequence. We study the run times of the
new estimator in comparison to those of the standard estimator, keeping the
same level of accuracy. For the considered case, we always see a speedup
ranging from 50% up to a factor of several thousand. We also discuss how to
apply these improved estimators to incompletely sampled galaxy catalogues. | The Transverse Peculiar Velocity of the Q2237+0305 Lens Galaxy and the
Mean Mass of Its Stars: Using 11-years of OGLE V-band photometry of Q2237+0305, we measure the
transverse velocity of the lens galaxy and the mean mass of its stars. We can
do so because, for the first time, we fully include the random motions of the
stars in the lens galaxy in the analysis of the light curves. In doing so, we
are also able to correctly account for the Earth's parallax motion and the
rotation of the lens galaxy, further reducing systematic errors. We measure a
lower limit on the transverse speed of the lens galaxy, v_t > 338 km/s (68%
confidence) and find a preferred direction to the East. The mean stellar mass
estimate including a well-defined velocity prior is 0.12 <= <M/Msun> <= 1.94 at
68% confidence, with a median of 0.52 Msun. We also show for the first time
that analyzing subsets of a microlensing light curve, in this case the first
and second halves of the OGLE V-band light curve, give mutually consistent
physical results. |
Evidence for 1000 km/s Molecular Outflows in the Local ULIRG Population: The feedback from galactic outflows is thought to play an important role in
shaping the gas content, star formation history, and ultimately the stellar
mass function of galaxies. Here we present evidence for massive molecular
outflows associated with ultra-luminous infrared galaxies (ULIRGs) in the
coadded Redshift Search Receiver 12CO(1-0) spectrum. Our stacked spectrum of 27
ULIRGs at z = 0.043-0.11 (freq_rest = 110-120 GHz) shows broad wings around the
CO line with delta_V(FWZI)~2000 km/s. Its integrated line flux accounts for up
to 25+/-5% of the total CO line luminosity. When interpreted as a massive
molecular outflow wind, the associated mechanical energy can be explained by a
concentrated starburst with SFR \geq 100 M_sun/yr, which agrees well with their
SFR derived from the FIR luminosity. Using the high signal-to-noise stacked
composite spectrum, we also probe 13CO and 12CN emission in the sample and
discuss how the chemical abundance of molecular gas may vary depending on the
physical conditions of the nuclear region. | Weighing Neutrinos in $f(R)$ gravity: We constrain the neutrino properties in $f(R)$ gravity using the latest
observations from cosmic microwave background(CMB) and baryon acoustic
oscillation(BAO) measurements. We first constrain separately the total mass of
neutrinos $\sum m_\nu$ and the effective number of neutrino species $N_{\rm
eff}$. Then we constrain $N_{\rm eff}$ and $\sum m_\nu$ simultaneously. We find
$\sum m_\nu<0.462 {\rm eV}$ at a $95\%$ confidence level for the combination of
Planck CMB data, WMAP CMB polarization data, BAO data and high-$l$ data from
the Atacama Cosmology Telescope and the South Pole Telescope. We also find
$N_{\rm eff}=3.32^{+0.54}_{-0.51}$ at a $95\%$ confidence level for the same
data set. When constraining $N_{\rm eff}$ and $\sum m_\nu$ simultaneously, we
find $N_{\rm eff}=3.58^{+0.72}_{-0.69}$ and $\sum m_\nu<0.860{\rm eV}$ at a
$95\%$ confidence level, respectively. |
Local stochastic non-Gaussianity and N-body simulations: Large-scale clustering of highly biased tracers of large-scale structure has
emerged as one of the best observational probes of primordial non-Gaussianity
of the local type (i.e. f_{NL}^{local}). This type of non-Gaussianity can be
generated in multifield models of inflation such as the curvaton model.
Recently, Tseliakhovich, Hirata, and Slosar showed that the clustering
statistics depend qualitatively on the ratio of inflaton to curvaton power \xi
after reheating, a free parameter of the model. If \xi is significantly
different from zero, so that the inflaton makes a non-negligible contribution
to the primordial adiabatic curvature, then the peak-background split ansatz
predicts that the halo bias will be stochastic on large scales. In this paper,
we test this prediction in N-body simulations. We find that large-scale
stochasticity is generated, in qualitative agreement with the prediction, but
that the level of stochasticity is overpredicted by ~30%. Other predictions,
such as \xi independence of the halo bias, are confirmed by the simulations.
Surprisingly, even in the Gaussian case we do not find that halo model
predictions for stochasticity agree consistently with simulations, suggesting
that semi-analytic modeling of stochasticity is generally more difficult than
modeling halo bias. | $H_0$ as a Universal FLRW Diagnostic: We reverse the logic behind the apparent existence of $H_0$-tension, to
design diagnostics for cosmological models. The basic idea is that the
non-constancy of $H_0$ inferred from observations at different redshifts is a
null hypothesis test for models within the FLRW paradigm -- if $H_0$ runs, the
model is wrong. Depending on the kind of observational data, the most suitable
form of the diagnostic can vary. As examples, we present two $H_0$ diagnostics
that are adapted to two different BAO observables. We use these and the
corresponding BAO data to Gaussian reconstruct the running of $H_0$ in flat
$\Lambda$CDM with Planck values for the model parameters. For flat $\Lambda$CDM
when the radiation contribution can be neglected, with comoving distance data,
the diagnostic is a simple hypergeometric function. Possible late time
deviations from the FLRW paradigm can also be accommodated, by simply keeping
track of the (potentially anisotropic) sky variation of the diagnostic. |
Herschel photometric observations of the nearby low metallicity
irregular galaxy NGC 6822: We present the first Herschel PACS and SPIRE images of the low-metallicity
galaxy NGC6822 observed from 70 to 500 mu and clearly resolve the HII regions
with PACS and SPIRE. We find that the ratio 250/500 is dependent on the 24 mu
surface brightness in NGC6822, which would locally link the heating processes
of the coldest phases of dust in the ISM to the star formation activity. We
model the SEDs of some regions HII regions and less active regions across the
galaxy and find that the SEDs of HII regions show warmer ranges of dust
temperatures. We derive very high dust masses when graphite is used in our
model to describe carbon dust. Using amorphous carbon, instead, requires less
dust mass to account for submm emission due to its lower emissivity properties.
This indicates that SED models including Herschel constraints may require
different dust properties than commonly used. | Which is a better cosmological probe: Number counts or cosmic
magnification?: The next generation of cosmological surveys will have unprecedented
measurement precision, hence they hold the power to put theoretical ideas to
the most stringent tests yet. However, in order to realise the full potential
of these measurements, we need to ensure that we apply the most effective
analytical tools. We need to identify which cosmological observables are the
best cosmological probes. Two commonly used cosmological observables are galaxy
redshift number counts and cosmic magnification. Both of these observables have
been investigated extensively in cosmological analyses, but only separately. In
the light of interacting dark energy (IDE) emerging as a plausible means of
alleviating current cosmological tensions, we investigate both observables on
large scales in a universe with IDE, using the angular power spectrum: taking
into account all known terms, including relativistic corrections, in the
observed overdensity. Our results suggest that (given multi-tracer analysis)
measuring relativistic effects with cosmic magnification will be relatively
better than with galaxy redshift number counts, at all redshifts z. Conversely,
without relativistic effects, galaxy redshift number counts will be relatively
better in probing the imprint of IDE, at all z. At low z (up to around z =
0.1), relativistic effects enable cosmic magnification to be a relatively
better probe of the IDE imprint; while at higher z (up to z < 3), galaxy
redshift number counts become the better probe of IDE imprint. However, at z =
3 and higher, our results suggest that either of the observables will suffice. |
C-GOALS: Chandra observations of a complete sample of luminous infrared
galaxies from the IRAS Revised Bright Galaxy Survey: We present X-ray data for a complete sample of 44 luminous infrared galaxies
(LIRGs), obtained with the Chandra X-ray Observatory. These are the X-ray
observations of the high luminosity portion of the Great Observatory All-sky
LIRG Survey (GOALS), which includes the most luminous infrared selected
galaxies, log (Lir/Lsun) > 11.73, in the local universe, z < 0.088. X-rays were
detected from 43 out of 44 objects, and their arcsec-resolution images,
spectra, and radial brightness distributions are presented. With a selection by
hard X-ray colour and the 6.4 keV iron line, AGN are found in 37% of the
objects, with higher luminosity sources more likely to contain an AGN. These
AGN also tend to be found in late-stage mergers. The AGN fraction would
increase to 48% if objects with mid-IR [Ne V] detection are included. Double
AGN are clearly detected only in NGC 6240 among 24 double/triple systems. Other
AGN are found either in single nucleus objects or in one of the double nuclei
at similar rates. Objects without conventional X-ray signatures of AGN appear
to be hard X-ray quiet, relative to the X-ray to far-IR correlation for
starburst galaxies, as discussed elsewhere. Most objects also show extended
soft X-ray emission, which is likely related to an outflow from the nuclear
region, with a metal abundance pattern suggesting enrichment by core collapse
supernovae, as expected for a starburst. | Constraints on Cosmological Parameters from the 500 deg$^2$ SPTpol
Lensing Power Spectrum: We present cosmological constraints based on the cosmic microwave background
(CMB) lensing potential power spectrum measurement from the recent 500 deg$^2$
SPTpol survey, the most precise CMB lensing measurement from the ground to
date. We fit a flat $\Lambda$CDM model to the reconstructed lensing power
spectrum alone and in addition with other data sets: baryon acoustic
oscillations (BAO) as well as primary CMB spectra from Planck and SPTpol. The
cosmological constraints based on SPTpol and Planck lensing band powers are in
good agreement when analysed alone and in combination with Planck full-sky
primary CMB data. With weak priors on the baryon density and other parameters,
the CMB lensing data alone provide a 4\% constraint on $\sigma_8\Omega_m^{0.25}
= 0.0593 \pm 0.025$.. Jointly fitting with BAO data, we find $\sigma_8=0.779
\pm 0.023$, $\Omega_m = 0.368^{+0.032}_{-0.037}$, and $H_0 =
72.0^{+2.1}_{-2.5}\,\text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1} $, up to
$2\,\sigma$ away from the central values preferred by Planck lensing + BAO.
However, we recover good agreement between SPTpol and Planck when restricting
the analysis to similar scales. We also consider single-parameter extensions to
the flat $\Lambda$CDM model. The SPTpol lensing spectrum constrains the spatial
curvature to be $\Omega_K = -0.0007 \pm 0.0025$ and the sum of the neutrino
masses to be $\sum m_{\nu} < 0.23$ eV at 95\% C.L. (with Planck primary CMB and
BAO data), in good agreement with the Planck lensing results. With the
differences in the $S/N$ of the lensing modes and the angular scales covered in
the lensing spectra, this analysis represents an important independent check on
the full-sky Planck lensing measurement. |
The Dawn of Chemistry: Within the precise cosmological framework provided by the Lambda-Cold Dark
Matter model and standard Big Bang nucleosynthesis, the chemical evolution of
the pregalactic gas can now be followed with accuracy limited only by the
uncertainties on the reaction rates. Starting during the recombination era, the
formation of the first molecules and molecular ions containing hydrogen,
deuterium, helium, and lithium was severely hindered by the low density of the
expanding universe, the intensity of the cosmic radiation field, and the
absence of solid catalyzers. Molecular hydrogen and deuterated hydrogen, the
most abundant species formed in the gas phase prior to structure formation,
played a fundamental role in the cooling of the gas clouds that gave birth to
the first stellar generation, contributing to determine the scale of
fragmentation. Primordial molecules also interacted with the photons of the
cosmic background via resonant scattering, absorption and emission. In this
review we examine the current status of the chemistry of the early universe and
discuss the most relevant reactions for which uncertainties still exist from
theory or laboratory experiments. The prospects for detecting spectral
distortions or spatial anisotropies due to the first atoms and molecules are
also addressed. | AEGIS: The Morphologies of Green Galaxies at 0.4<z<1.2: We present quantitative morphologies of ~300 galaxies in the
optically-defined green valley at 0.4<z<1.2, in order to constrain the
mechanism(s) responsible for quenching star formation in the bulk of this
population. The sample is selected from galaxies in the All-Wavelength Extended
Groth Strip International Survey (AEGIS). While the green valley is defined
using optical U-B colors, we find that using a green valley sample defined
using NUV-R colors does not change the results. Using HST/ACS imaging, we study
several quantitative morphological parameters including CAS, B/T from GIM2D,
and Gini/M_20. We find that the green galaxy population is intermediate between
the red and blue galaxy populations in terms of concentration, asymmetry, and
morphological type and merger fraction estimated using Gini/M_20. We find that
most green galaxies are not classified as mergers; in fact, the merger fraction
in the green valley is lower than in the blue cloud. We show that at a given
stellar mass, green galaxies have higher concentration values than blue
galaxies and lower concentration values than red galaxies. Additionally, we
find that 12% of green galaxies have B/T = 0 and 21% with B/T \leq 0.05. Our
results show that green galaxies are generally massive (M\ast ~ 10^10.5 M_sun)
disk galaxies with high concentrations. We conclude that major mergers are
likely not the sole mechanism responsible for quenching star formation in this
population and that either other external processes or internal secular
processes play an important role both in driving gas towards the center of
these galaxies and in quenching star formation. |
Ram pressure effects in the galactic plane and galactic dynamos in the
no-z approximation: The magnetic field of galaxies is believed to be produced by internal dynamo
action, but can be affected by motion of the galaxy through the surrounding
medium. Observations of polarized radio emission of galaxies located in galaxy
clusters have revealed noticeable features of large-scale magnetic
configurations, including displacements of the magnetic structures from the
optical images and tails, which are possible imprints of ram pressure effects
arising from motion of the galaxies through the intracluster medium. We present
a quantitative dynamo model which attempts to describe the above effects. In
contrast to the traditional problem of a wind affecting a body with a
prescribed magnetic field, we investigate how a non-magnetized wind flow
affects a magnetic field that is being self-excited by galactic dynamo action.
In order to isolate the leading physical effects we exploit a simple dynamo
model that can describe relevant effects. In particular, we use what is known
as the 'no-z' approximation for the mean-field dynamo equations. In a suitable
parametric range we obtain displacements of the large-scale magnetic field, as
well as magnetic tails. However, the specific details of their locations are
quite counterintuitive. The direction of displacement is perpendicular to,
rather than parallel to, the wind direction. The point at which the tail
emerges from the galaxy depends on details of the model. The tail is eventually
directed downstream. In the simplest case the magnetic tail begins in the
region where the wind decreases the total gas velocity. Any wind that
penetrates the galaxy modifies the intrinsic dynamo action. These features are
different from those found in ram-pressure models. Any determination of
galactic motion through the cluster medium from observational data needs to
take the effects of dynamo action into account. | Cosmic Growth and Expansion Conjoined: Cosmological measurements of both the expansion history and growth history
have matured, and the two together provide an important test of general
relativity. We consider their joint evolutionary track, showing that this has
advantages in distinguishing cosmologies relative to considering them
individually or at isolated redshifts. In particular, the joint comparison
relaxes the shape degeneracy that makes $f\sigma_8(z)$ curves difficult to
separate from the overall growth amplitude. The conjoined method further helps
visualization of which combinations of redshift ranges provide the clearest
discrimination. We examine standard dark energy cosmologies, modified gravity,
and "stuttering" growth, each showing distinct signatures. |
Massive Black Holes from Dissipative Dark Matter: We show that a subdominant component of dissipative dark matter resembling
the Standard Model can form many intermediate-mass black hole seeds during the
first structure formation epoch. We also observe that, in the presence of this
matter sector, the black holes will grow at a much faster rate with respect to
the ordinary case. These facts can explain the observed abundance of
supermassive black holes feeding high-redshift quasars. The scenario will have
interesting observational consequences for dark substructures and gravitational
wave production. | Large Tensor-to-Scalar Ratio in Small-Field Inflation: We show that density perturbations seeded by the inflaton can be suppressed
when having additional light degrees of freedom contributing to the production
of perturbations. The inflaton fluctuations affect the light field dynamics by
modulating the length of the inflationary period, hence produce additional
density perturbations in the post-inflationary era. Such perturbations can
cancel those generated during inflation as both originate from the same
inflaton fluctuations. This allows production of large gravitational waves from
small-field inflation, which is normally forbidden by the Lyth bound on the
inflaton field excursion. We also find that the field bound is taken over by
the light scalar when the inflaton-induced perturbations are suppressed, thus
present a generalized form of the Lyth bound that applies to the total field
space. |
Field-level inference of cosmic shear with intrinsic alignments and
baryons: We construct a field-based Bayesian Hierarchical Model for cosmic shear that
includes, for the first time, the important astrophysical systematics of
intrinsic alignments and baryon feedback, in addition to a gravity model. We
add to the BORG-WL framework the tidal alignment and tidal torquing model
(TATT) for intrinsic alignments and compare them with the non-linear alignment
(NLA) model. With synthetic data, we have shown that adding intrinsic
alignments and sampling the TATT parameters does not reduce the constraining
power of the method and the field-based approach lifts the weak lensing
degeneracy. We add baryon effects at the field level using the enthalpy
gradient descent (EGD) model. This model displaces the dark matter particles
without knowing whether they belong to a halo and allows for self-calibration
of the model parameters, which are inferred from the data. We have also
illustrated the effects of model misspecification for the baryons. The
resulting model now contains the most important physical effects and is
suitable for application to data. | A joint 2- and 3-point clustering analysis of the VIPERS PDR2 catalogue
at z~1: breaking the degeneracy of cosmological parameters: We measure the galaxy 2- and 3-point correlation functions at $z=[0.5,0.7]$
and $z=[0.7, 0.9]$, from the final data release of the VIPERS survey (PDR2). We
model the two statistics including a nonlinear 1-loop model for the 2-point
function and a tree-level model for the 3-point function, and perform a joint
likelihood analysis. The entire process and nonlinear corrections are tested
and validated through the use of the 153 highly realistic VIPERS mock
catalogues, showing that they are robust down to scales as small as 10 $h^{-1}
\, \mathrm{Mpc}$. The mocks are also adopted to compute the covariance matrix
that we use for the joint 2- and 3-point analysis. Despite the limited
statistics of the two (volume-limited) sub-samples analysed, we demonstrate
that such a combination successfully breaks the degeneracy existing at 2-point
level between clustering amplitude $\sigma_8$, linear bias $b_1$ and the linear
growth rate of fluctuations $f$. For the latter, in particular, we measure
$f(z=0.61)=0.64^{+0.55}_{-0.37}$ and $f(z=0.8)=1.0\pm1.0$, while the amplitude
of clustering is found to be $\sigma_8(z=0.61)=0.50\pm 0.12$ and
$\sigma_8(z=0.8)=0.39^{+0.11}_{-0.13}$. These values are in excellent agreement
with the extrapolation of a Planck cosmology. |
The relation between mass and concentration in X-ray galaxy clusters at
high redshift: Galaxy clusters are the most recent, gravitationally-bound products of the
hierarchical mass accretion over cosmological scales. How the mass is
concentrated is predicted to correlate with the total mass in the cluster's
halo, with systems at higher mass being less concentrated at given redshift and
for any given mass, systems with lower concentration are found at higher
redshifts. Through a spatial and spectral X-ray analysis, we reconstruct the
total mass profile of 47 galaxy clusters observed with Chandra in the redshift
range $0.4<z<1.2$, selected to have no major mergers, to investigate the
relation between the mass and the dark matter concentration, and the evolution
of this relation with redshift. The sample in exam is the largest one
investigated so far at $z>0.4$, and is well suited to provide the first
constraint on the concentration--mass relation at $z>0.7$ from X-ray analysis.
Under the assumptions that the distribution of the X-ray emitting gas is
spherically symmetric and in hydrostatic equilibrium, we combine the
deprojected gas density and spectral temperature profiles through the
hydrostatic equilibrium equation to recover the parameters that describe a NFW
total mass distribution. The comparison with results from weak lensing analysis
reveals a very good agreement both for masses and concentrations. Uncertainties
are however too large to make any robust conclusion on the hydrostatic bias of
these systems. The relation is well described by the form $c \propto M^B
(1+z)^C$, with $B=-0.50 \pm 0.20$, $C=0.12 \pm 0.61$ (at 68.3\% confidence), it
is slightly steeper than the one predicted by numerical simulations
($B\sim-0.1$) and does not show any evident redshift evolution. We obtain the
first constraints on the properties of the concentration--mass relation at $z >
0.7$ from X-ray data, showing a reasonable good agreement with recent numerical
predictions. | Reaffirming the Cosmic Acceleration without Supernova and CMB: Recent discussions about supernova magnitude evolution have raised doubts
about the robustness of the late-universe acceleration. In a previous letter,
Huang did a null test of the cosmic acceleration by using a Parameterization
based on the cosmic Age (PAge), which covers a broad class of cosmological
models including the standard $\Lambda$ cold dark matter model and its many
extensions. In this work, we continue to explore the cosmic expansion history
with the PAge approximation. Using baryon acoustic oscillations ({\it without}
a CMB prior on the acoustic scale), gravitational strong lens time delay, and
passively evolving early galaxies as cosmic chronometers, we obtain $\gtrsim
4\sigma$ detections of cosmic acceleration for both flat and nonflat PAge
universes. In the nonflat case, we find a $\gtrsim 3\sigma$ tension between the
spatial curvatures derived from baryon acoustic oscillations and strong lens
time delay. Implications and possible systematics are discussed. |
Fingerprinting Dark Energy III: distinctive marks of viscosity: The characterisation of dark energy is one of the primary goals in cosmology
especially now that many new experiments are being planned with the aim of
reaching a high sensitivity on cosmological parameters. It is known that if we
move away from the simple cosmological constant model then we need to consider
perturbations in the dark energy fluid. This means that dark energy has two
extra degrees of freedom: the sound speed $\cs$ and the anisotropic stress
$\sigma$. If dark energy is inhomogenous at the scales of interest then the
gravitational potentials are modified and the evolution of the dark matter
perturbations is also directly affected. In this paper we add an anisotropic
component to the dark energy perturbations. Following the idea introduced in
\cite{Sapone:2009mb}, we solve analytically the equations of perturbations in
the dark sector, finding simple and accurate approximated solutions. We also
find that the evolution of the density perturbations is governed by an
effective sound speed which depends on both the sound speed and the anisotropic
stress parameter. We then use these solutions to look at the impact of the dark
energy perturbations on the matter power spectrum and on the Integrated
Sachs-Wolfe effect in the Cosmic Microwave Background. | Hubble expansion and structure formation in the "running FLRW model" of
the cosmic evolution: A new class of FLRW cosmological models with time-evolving fundamental
parameters should emerge naturally from a description of the expansion of the
universe based on the first principles of quantum field theory and string
theory. Within this general paradigm, one expects that both the gravitational
Newton's coupling, G, and the cosmological term, Lambda, should not be strictly
constant but appear rather as smooth functions of the Hubble rate. This
scenario ("running FLRW model") predicts, in a natural way, the existence of
dynamical dark energy without invoking the participation of extraneous scalar
fields. In this paper, we perform a detailed study of these models in the light
of the latest cosmological data, which serves to illustrate the
phenomenological viability of the new dark energy paradigm as a serious
alternative to the traditional scalar field approaches. By performing a joint
likelihood analysis of the recent SNIa data, the CMB shift parameter, and the
BAOs traced by the Sloan Digital Sky Survey, we put tight constraints on the
main cosmological parameters. Furthermore, we derive the theoretically
predicted dark-matter halo mass function and the corresponding redshift
distribution of cluster-size halos for the "running" models studied. Despite
the fact that these models closely reproduce the standard LCDM Hubble
expansion, their normalization of the perturbation's power-spectrum varies,
imposing, in many cases, a significantly different cluster-size halo redshift
distribution. This fact indicates that it should be relatively easy to
distinguish between the "running" models and the LCDM cosmology using realistic
future X-ray and Sunyaev-Zeldovich cluster surveys. |
Populations of filaments from the distribution of galaxies in numerical
simulations: We present a statistical study of the filamentary structures of the cosmic
web in the large hydro-dynamical simulations Illustris-TNG, Illustris, and
Magneticum at redshift z=0. We focus on the radial distribution of the galaxy
density around filaments detected using the Discrete Persistent Structure
Extractor (DisPerSE). We show that the average profile of filaments presents an
excess of galaxy density (> 5 sigma) up to radial distances of 27 Mpc from the
core. The relation between galaxy density and the length of filaments is
further investigated showing that short (L_f < 9 Mpc) and long (L_f > 20 Mpc)
filaments are two statistically different populations. Short filaments are
puffier, denser, and more connected to massive objects, whereas long filaments
are thinner, less dense, and more connected to less massive structures. These
two populations trace different environments and may correspond to bridges of
matter between over-dense structures (short filaments), and to cosmic filaments
shaping the skeleton of the cosmic web (long filaments). Through Markov Chain
Monte Carlo (MCMC) explorations, we find that the density profiles of both
short and long filaments can be described by the same empirical models
(generalised Navarro, Frenk and White, beta-model, a single and a double power
law) with different and distinct sets of parameters. | The Importance of Priors on LIGO-Virgo Parameter Estimation: the Case of
Primordial Black Holes: The black holes detected by current and future interferometers can have
diverse origins. Their expected mass and spin distributions depend on the
specifics of the formation mechanisms. When a physically motivated prior
distribution is used in a Bayesian inference, the parameters estimated from the
gravitational-wave data can change significantly, potentially affecting the
physical interpretation of certain gravitational-wave events and their
implications on theoretical models. As a case study we analyze primordial black
holes, which might be formed in the early universe and could comprise at least
a fraction of the dark matter. If accretion is not efficient during their
cosmic history, primordial black holes are expected to be almost non-spinning.
If accretion is efficient, massive binaries tend to be symmetrical and highly
spinning. We show that incorporating these priors can significantly change the
inferred mass ratio and effective spin of some binary black hole events,
especially those identified as high-mass, asymmetrical, or spinning by a
standard analysis using agnostic priors. For several events, the Bayes factors
are only mildly affected by the new priors, implying that it is hard to
distinguish whether merger events detected so far are of primordial or
astrophysical origin. In particular, if binaries identified by LIGO/Virgo as
strongly asymmetrical (including GW190412) are of primordial origin, their mass
ratio inferred from the data can be closer to unity. For GW190412, the latter
property is strongly affected by the inclusion of higher harmonics in the
waveform model. |
Transient Low-Mass X-Ray Binary Populations in Elliptical Galaxies NGC
3379 and NGC 4278: We propose a physically motivated and self-consistent prescription for the
modeling of transient neutron star (NS) low-mass X-ray binary (LMXB)
properties, such as duty cycle (DC), outburst duration and recurrence time. We
apply this prescription to the population synthesis (PS) models of field LMXBs
presented by Fragos et al. (2008), and compare the transient LMXB population to
the Chandra X-ray survey of the two elliptical galaxies NGC 3379 and NGC 4278,
which revealed several transient sources (Brassington et al., 2008, 2009). We
are able to exclude models with a constant DC for all transient systems, while
models with a variable DC based on the properties of each system are consistent
with the observed transient populations. We predict that the majority of the
observed transient sources in these two galaxies are LMXBs with red giant
donors. Our comparison suggests that LMXBs formed through evolution of
primordial field binaries are dominant in globular cluster (GC) poor elliptical
galaxies, while they still have a significant contribution in GC rich ones. | SPT-CLJ2040-4451: An SZ-Selected Galaxy Cluster at z = 1.478 With
Significant Ongoing Star Formation: SPT-CLJ2040-4451 -- spectroscopically confirmed at z = 1.478 -- is the
highest redshift galaxy cluster yet discovered via the Sunyaev-Zel'dovich
effect. SPT-CLJ2040-4451 was a candidate galaxy cluster identified in the first
720 deg^2 of the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, and
confirmed in follow-up imaging and spectroscopy. From multi-object spectroscopy
with Magellan-I/Baade+IMACS we measure spectroscopic redshifts for 15 cluster
member galaxies, all of which have strong [O II] 3727 emission.
SPT-CLJ2040-4451 has an SZ-measured mass of M_500,SZ = 3.2 +/- 0.8 X 10^14
M_Sun/h_70, corresponding to M_200,SZ = 5.8 +/- 1.4 X 10^14 M_Sun/h_70. The
velocity dispersion measured entirely from blue star forming members is sigma_v
= 1500 +/- 520 km/s. The prevalence of star forming cluster members (galaxies
with > 1.5 M_Sun/yr) implies that this massive, high-redshift cluster is
experiencing a phase of active star formation, and supports recent results
showing a marked increase in star formation occurring in galaxy clusters at z
>1.4. We also compute the probability of finding a cluster as rare as this in
the SPT-SZ survey to be >99%, indicating that its discovery is not in tension
with the concordance Lambda-CDM cosmological model. |
The cosmological evolution condition of the Planck constant in the
varying speed of light models through adiabatic expansion: There have been various varying speed of light (VSL) models with one free
parameter, $b$, to characterize the time variation of the speed of light as a
function of a scale factor, $c = c_0a^{b/4}$, based on the expanding universe.
One needs to induce cosmological evolutions of other physical constants and
quantities having different powers of scale factor as a function of $b$ to
satisfy all known local physics laws, including special relativity,
thermodynamics, and electromagnetic force. These models should be based on the
Friedmann-Lema\^{i}tre-Robertson-Walker metric satisfying the isotropic and
homogeneous three-space known as the cosmological principle. Adiabaticity is a
necessary condition to keep homogeneity and isotropy because a net energy flux
would falsify the isotropy if there is a preferential energy flow direction. It
also might forge homogeneity if the outward (inward) flow is isotropic. Thus,
any VSL model based on the expanding universe should preserve an adiabatic
expansion condition to be a viable model. We show that this condition specifies
the cosmological evolution of the Planck constant as $\hbar = \hbar_0
a^{-b/4}$. | The innocuousness of adiabatic instabilities in coupled scalar
field-dark matter models: Non-minimally coupled scalar field models suffer of unstable growing modes at
the linear perturbation level. The nature of these instabilities depends on the
dynamical state of the scalar field. In particular in systems which admit
adiabatic solutions, large scale instabilities are suppressed by the slow-roll
dynamics of the field. Here we review these results and present a preliminary
likelihood data analysis suggesting that along adiabatic solutions coupled
models with coupling of order of gravitational strength can provide viable
cosmological scenarios satisfying constraints from SN Ia, CMB and large scale
structure data. |
The implications of an extended dark energy cosmology with massive
neutrinos for cosmological tensions: We perform a comprehensive analysis of the most common early- and
late-Universe solutions to the $H_0$, Ly-$\alpha$, and $S_8$ discrepancies.
When considered on their own, massive neutrinos provide a natural solution to
the $S_8$ discrepancy at the expense of increasing the $H_0$ tension. If all
extensions are considered simultaneously, the best-fit solution has a neutrino
mass sum of $\sim 0.4$ eV, a dark energy equation of state close to that of a
cosmological constant, and no additional relativistic degrees of freedom.
However, the $H_0$ tension, while weakened, remains unresolved. Motivated by
this result, we perform a non-parametric reconstruction of the evolution of the
dark energy fluid density (allowing for negative energy densities), together
with massive neutrinos. When all datasets are included, there exists a residual
$\sim1.9\sigma$ tension with $H_0$. If this residual tension remains in the
future, it will indicate that it is not possible to solve the $H_0$ tension
solely with a modification of the late-Universe dynamics within standard
general relativity. However, we do find that it is possible to resolve the
tension if either galaxy BAO or JLA supernovae data are omitted. We find that
\textit{negative} dark energy densities are favored near redshift $z\sim2.35$
when including the Ly-$\alpha$ BAO measurement (at $\sim 2\sigma$). This
behavior may point to a negative curvature, but it is most likely indicative of
systematics or at least an underestimated covariance matrix. Quite remarkably,
we find that in the extended cosmologies considered in this work, the neutrino
mass sum is always close to $0.4$ eV regardless of the choice of external
datasets, as long as the $H_0$ tension is solved or significantly decreased. | Advances on GRB as cosmological tools: Several interesting correlations among Gamma Ray Bursts (GRB) prompt and
afterglow properties have been found in the recent years. Some of these
correlations have been proposed also to standardize GRB energetics to use them
as standard candles in constraining the expansion history of the universe up to
z>6. However, given the still unexplained nature of most of these correlations,
only the less scattered correlations can be used for constraining the
cosmological parameters. The updated E_peak-E_gamma correlation is presented.
Caveats of alternative methods of standardizing GRB energetics are discussed. |
Perturbation theory challenge for cosmological parameters estimation:
Matter power spectrum in real space: We study the accuracy with which cosmological parameters can be determined
from real space power spectrum of matter density contrast at weakly nonlinear
scales using analytical approaches. From power spectra measured in $N$-body
simulations and using Markov chain Monte-Carlo technique, the best-fitting
cosmological input parameters are determined with several analytical methods as
a theoretical template, such as the standard perturbation theory, the
regularized perturbation theory, and the effective field theory. We show that
at redshift 1, all two-loop level calculations can fit the measured power
spectrum down to scales $k \sim 0.2 \, h \, \mathrm{Mpc}^{-1}$ and cosmological
parameters are successfully estimated in an unbiased way. Introducing the
Figure of bias (FoB) and Figure of merit (FoM) parameter, we determine the
validity range of those models and then evaluate their relative performances.
With one free parameter, namely the damping scale, the regularized perturbation
theory is found to be able to provide the largest FoM parameter while keeping
the FoB in the acceptance range. | Tidal Formation of dark matter deficit diffuse galaxy NGC1052-DF2 by
SIDM: Observations have revealed a significant dark matter deficit in the
ultra-diffuse galaxy NGC1052-DF2 (DF2). It is widely accepted that the
formation of this unique galaxy can be attributed to the tidal stripping of its
host galaxy, NGC1052. In this study, we simulate the evolution of a satellite
system containing globular clusters (GCs) within an accreting host halo in the
framework of self-interacting dark matter (SIDM). Our simulation results
suggest that the heightened tidal stripping resulting from self-interaction can
give rise to the transformation of a conventional dwarf galaxy into a galaxy
resembling DF2 in all its observed properties. By comparing the simulation
results with identical initial conditions in both the standard cold dark matter
(CDM) and SIDM models, we find that the latter is more likely to replicate the
properties of DF2. Furthermore, we demonstrate that a DF2 analog can also be
produced on an orbit with a greater pericenter distance by increasing the
strength of self-interaction. This suggests that the issue of extreme orbital
parameters can be mitigated by implementing the SIDM model. The distributions
of the GC population derived in our SIDM simulation are consistent with the
observed characteristics of DF2. For comparison, we also explored the potential
for achieving GC distributions in the context of CDM. |
Detecting the anisotropic astrophysical gravitational wave background in
the presence of shot noise through cross-correlations: The spatial and temporal discreteness of gravitational wave sources leads to
shot noise that may, in some regimes, swamp any attempts at measuring the
anisotropy of the gravitational wave background. Cross-correlating a
gravitational wave background map with a sufficiently dense galaxy survey can
alleviate this issue, and potentially recover some of the underlying properties
of the gravitational wave background. We quantify the shot noise level and we
explicitly show that cross-correlating the gravitational wave background and a
galaxy catalog improves the chances of a first detection of the background
anisotropy with a gravitational wave observatory operating in the frequency
range (10Hz,100Hz), given sufficient sensitivity. | Testing quantum gravity effects with latest CMB observations: Inspired by quantum gravitational physics, the approach of non-commutative
(NC) phase space leads to a modified dispersion relation of gravitational
waves. This feature, if applied to the very early universe, gives rise to a
modified power spectrum of primordial tensor perturbations with a suppression
of power on large scales. We confront this phenomenon with the BICEP2 and
Planck experiments, and show that inflation with the modified dispersion
relation can simultaneously fit the observations better than the standard
inflationary paradigm. In particular, the numerical result implies that with
the latest cosmological microwave background (CMB) observations, a quantum
gravity modified power spectrum of primordial tensor modes is preferred at a
statistical significance of more than $3\sigma$ compared with the minimal
model. Our study indicates that the potential tension between the BICEP2 and
Planck data may be resolved by quantum gravity effects. |
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