anchor
stringlengths 50
3.92k
| positive
stringlengths 55
6.16k
|
|---|---|
Ages and abundances in large-scale stellar disks of nearby S0 galaxies: By undertaking deep long-slit spectroscopy with the focal reducer SCORPIO of
the Russian 6m telescope, we studied stellar population properties and their
variation with radius in 15 nearby S0 galaxies sampling a wide range of
luminosities and environments. For the large-scale stellar disks of S0s, we
have measured SSP-equivalent metallicities ranging from the solar one down to
[Z/H]=-0.4 - -0.7, rather high magnesium-to-iron ratios, [Mg/Fe] > +0.2, and
mostly old SSP-equivalent ages. Nine of 15 (60%) galaxies have large-scale
stellar disks older than 10 Gyr, and among those we find all the galaxies which
reside in denser environments. The isolated galaxies may have intermediate-age
stellar disks which are 7-9 Gyr old. Only two galaxies of our sample, NGC 4111
and NGC 7332, reveal SSP-equivalent ages of their disks of 2-3 Gyrs. Just these
two young disks appear to be thin, while the other, older disks have scale
heights typical for thick stellar disks. The stellar populations in the bulges
at radii of 0.5r_eff are on the contrary more metal-rich than the solar
metallicity, with the ages homogeneously distributed between 2 and 15 Gyr,
being almost always younger than the disks. We conclude that S0 galaxies could
not form in groups at z=0.4 as is thought now; a new scenario of the general
evolution of disk galaxies is proposed instead. | How did the Virgo cluster form?: While the Virgo cluster is the nearest galaxy cluster and therefore the best
observed one, little is known about its formation history. In this paper, a set
of cosmological simulations that resemble the Local Universe is used to shed
the first light on this mystery. The initial conditions for these simulations
are constrained with galaxy peculiar velocities of the second catalog of the
Cosmicflows project using algorithms developed within the Constrained Local
UniversE Simulation project. Boxes of 500 Mpc/h on a side are set to run a
series of dark matter only constrained simulations. In each simulation, a
unique dark matter halo can be reliably identified as Virgo's counterpart. The
properties of these Virgo halos are in agreement at a 10-20% level with the
global properties of the observed Virgo cluster. Their zero-velocity masses
agree at one-sigma with the observational mass estimate. In all the
simulations, the matter falls onto the Virgo objects along a preferential
direction that corresponds to the observational filament and the slowest
direction of collapse. A study of the mass accretion history of the Virgo
candidates reveals the most likely formation history of the Virgo cluster,
namely a quiet accretion over the last 7 Gigayears. |
Cosmology constrains gravitational four-fermion interaction: If torsion exists, it generates gravitational four-fermion interaction
(GFFI). This interaction gets dominating on the Planck scale. If one confines
to the regular, axial-axial part of this interaction, the results do not comply
with the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmology for the spatial
flat or closed Universe. In principle, the anomalous, vector-vector interaction
could restore the agreement. | Cosmology with the shear-peak statistics: Weak-lensing searches for galaxy clusters are plagued by low completeness and
purity, severely limiting their usefulness for constraining cosmological
parameters with the cluster mass function. A significant fraction of `false
positives' are due to projection of large-scale structure and as such carry
information about the matter distribution. We demonstrate that by constructing
a "peak function", in analogy to the cluster mass function, cosmological
parameters can be constrained. To this end we carried out a large number of
cosmological N-body simulations in the \Omega_m-\sigma_8 plane to study the
variation of this peak function. We demonstrate that the peak statistics is
able to provide constraints competitive with those obtained from cosmic-shear
tomography from the same data set. By taking the full cross-covariance between
the peak statistics and cosmic shear into account, we show that the combination
of both methods leads to tighter constraints than either method alone can
provide. |
Constraining cosmology with the cosmic microwave and infrared
backgrounds correlation: We explore the use of the cosmic infrared background as a tracer of the LSS
for cross-correlating with the CMB and exploit the ISW. We use the improved
linear CIB model of Maniyar et al (2018) and derive the theoretical CIBxISW
cross-correlation for Planck HFI frequencies 217, 353, 545 and 857 GHz and IRAS
3000 GHz. We predict a positive cross-correlation between the CIB and CMB whose
amplitude decreases rapidly at small scales. We perform a signal-to-noise ratio
(SNR) analysis on this cross-correlation. In the ideal case of the
cross-correlation obtained over 70% (40%) of the sky with no residual
contaminants (e.g. galactic dust) in maps, the SNR ranges from 4.2-5.6
(3.2-4.3) with the highest for 857 GHz. A Fisher matrix analysis shows that an
ISW signal detected with such high SNR on the 40% sky can improve the
constraints on the cosmological parameters considerably; constraints on the
equation of state of the dark energy are improved by 80%. We then perform a
more realistic analysis with the effect of residual galactic dust contamination
in CIB maps. We calculate the dust power spectra for several frequencies and
sky fractions which dominate over CIB at lower multipoles we are interested in.
Considering conservative 10% residual level of galactic dust in the CIB power
spectra, we find that the SNR drops drastically making ISW detection difficult.
To check the capability of current maps to detect ISW via this method, we
measure the cross-correlation of the CIB and the CMB Planck maps on so called
GASS field covering an area of 11% in the southern hemisphere. We find that
with such a small sky fraction and dust residuals present in CIB maps, we do
not detect ISW signal and the measured signal is consistent with zero. In order
not to degrade the SNR for the ISW measurement by more than 10% on the 40% sky,
we find that the dust needs to be cleaned up to 0.01% level on the power
spectrum. | High-Redshift Star Formation in a Time-Dependent Lyman-Werner Background: The first generation of stars produces a background of Lyman-Werner (LW)
radiation which can photo-dissociate molecular hydrogen, increasing the mass of
dark matter halos required to host star formation. Previous studies have
determined the critical mass required for efficient molecular cooling with a
constant LW background. However, the true background is expected to increase
rapidly at early times. Neglecting this evolution could underestimate star
formation in small halos that may have started to cool in the past when the LW
intensity was much lower. Background evolution is a large source of uncertainty
in pre-reionization predictions of the cosmological 21cm signal, which can be
observed with future radio telescopes. To address this, we perform
zero-dimentional one-zone calculations that follow the density, chemical
abundances, and temperature of gas in the central regions of dark matter halos,
including hierarchical growth and an evolving LW background. We begin by
studying the physics of halos subjected to a background that increases
exponentially with redshift. We find that when the intensity increases more
slowly than $J_{\rm LW}(z) \propto 10^{-z/5}$, cooling in the past is a
relatively small effect. We then self-consistently compute the cosmological LW
background over $z=15-50$ and find that cooling in the past due to an evolving
background has a modest impact. Finally, we compare these results to
three-dimensional hydrodynamical cosmological simulations with varying LW
histories. While only a small number of halos were simulated, the results are
consistent with our one-zone calculations. |
On the "The Kolmogorov-Smirnov test for the CMB" by M.Frommert, R.Durrer
and J.Michaud: In arxiv:1108.5354 the Kolmogorov-Smirnov (K-S) test and Kolmogorov
stochasticity parameter (KSP) is applied to CMB data. Their interpretation of
the KSP method, however, lacks essential elements. In addition, their main
result on the Gaussianity of CMB was not a matter of debate in previous KSP-CMB
studies which also included predictions on cold spots, point sources. | Simulation studies of dark energy clustering induced by the formation of
dark matter halos: In this paper, we present a simulation method within the two-component
spherical collapse model to investigate dark energy perturbations associated
with the formation of dark matter halos. The realistic mass accretion history
of a dark matter halo taking into account its fast and slow growth is
considered by imposing suitable initial conditions and isotropized
virializations for the spherical collapse process. The dark energy component is
treated as a perfect fluid described by two important parameters, the equation
of state parameter $w$ and the sound speed $c_s$. Quintessence models with
$w>-1$ are analyzed. We adopt the Newtonian gauge to describe the spacetime
which is perturbed mainly by the formation of a dark matter halo. It is found
that the dark energy density perturbation $\delta_{DE}$ depends on $w$ and
$c_s$, and its behavior follows closely the gravitational potential $\Phi$ of
the dark matter halo with $\delta_{DE}\approx -(1+w)\Phi/c_s^2$. For $w>-1$,
the dark energy perturbation presents a clustering behavior with
$\delta_{DE}>0$ during the entire formation of the dark matter halo, from
linear to nonlinear and virialized stages. The value of $\delta_{DE}$ increases
with the increase of the halo mass. For a cluster of mass $M\sim 10^{15}
M_{\odot}$, $\delta_{DE}\sim 10^{-5}$ within the virialized region for $c_s^2
\in [0.5, 1]$, and it can reach $\delta_{DE}=O(1)$ with $c_s^2=0.00001$. For a
scalar-field dark energy model, we find that with suitably modeled $w$ and
$c_s$, its perturbation behavior associated with the nonlinear formation of
dark matter halos can well be analyzed using the fluid approach, demonstrating
the validity of the fluid description for dark energy even considering its
perturbation in the stage of nonlinear dark matter structure formation. |
Large Adiabatic Scalar Perturbations in a Regular Bouncing Universe: It has been shown that a contracting universe with a dust-like ($w \approx
0$) fluid may provide an almost scale invariant spectrum for the gravitational
scalar perturbations. As the universe contracts, the amplitude of such
perturbations are amplified. The gauge invariant variable $\Phi$ develops a
growing mode which becomes much larger than the constant one around the bounce
phase. The constant mode has its amplitude fixed by Cosmic Background Explorer
(COBE) normalization, thus the amplitude of the growing mode can become much
larger than 1. In this paper, we first show that this is a general feature of
bouncing models, since we expect that general relativity should be valid in all
scales away from the bounce. However, in the Newtonian gauge, the variable
$\Phi$ gives the value of the metric perturbation $\phi$, raising doubts on the
validity of the linear perturbative regime at the bounce. In order to address
this issue, we obtain a set of necessary conditions for the perturbative series
to be valid along the whole history of the model, and we show that there is a
gauge in which all these conditions are satisfied, for a set of models, if the
constant mode is fixed by COBE normalization. As a by-product of this analysis,
we point out that there are sets of solutions for the perturbation variables
where some gauge-fixing conditions are not well defined, turning these gauges
prohibited for those solutions. | Gravitational-Wave Constraints on the Abundance of Primordial Black
Holes: We investigate features of Gravitational Waves (GWs) induced by primordial
density fluctuations with a large amplitude peak associated with formation of
Primordial Black Holes (PBHs). It is shown that the spectrum of induced GW is
insensitive to the width of the peak in wavenumber space provided it is below a
certain value, but the amplitude of the spectrum reduces at the peak frequency
and decreases faster at low frequencies for a larger width. A correspondence
between the GW amplitude and PBH abundance is also investigated incorporating
the peak width. We find that PBHs with masses 10^{20-26}g can be probed by
space-based laser interferometers and atomic interferometers irrespective of
whether the peak width is small or not. Further we obtain constraints on the
abundance of the supermassive PBHs by comparing a low frequency tail of the GW
spectrum with CMB observations. |
Evolution of Massive Galaxy Structural Properties and Sizes via Star
Formation: We investigate the resolved star formation properties of a sample of 45
massive galaxies (M_*>10^11M_solar) within a redshift range of 1.5 < z < 3
detected in the GOODS NICMOS Survey (Conselice et al. 2011), a HST H-band
imaging program. We derive the star formation rate as a function of radius
using rest frame UV data from deep z_{850} ACS imaging. The star formation
present at high redshift is then extrapolated to z=0, and we examine the
stellar mass produced in individual regions within each galaxy. We also
construct new stellar mass profiles of the in-situ stellar mass at high
redshift from Sersic fits to rest-frame optical, H_{160}-band, data. We combine
the two stellar mass profiles to produce a modelled evolved stellar mass
profile. We then fit a new Sersic profile to the evolved profile, from which we
examine what effect the resulting stellar mass distribution added via star
formation has on the structure and size of each individual galaxy. We conclude
that due to the lack of sufficient size growth and Sersic evolution by star
formation other mechanisms such as merging must contribute a large proportion
to account for the observed structural evolution from z>1 to the present day. | Relating bars with the environment in the nearby Universe: We study the correlation between the fraction of barred spiral galaxies and
environmental parameters of galaxies to understand in which environments the
bars are more commonly found. For this purpose we apply the Blanton et al.
technique to a sample of spiral galaxies drawn from the Nair & Abraham
catalogue. Our results agree with previous findings in which the fraction of
barred galaxies is almost insensitive to environment. |
ARCRAIDER II: Arc search in a sample of non-Abell clusters: We present a search for gravitational arcs in a sample of X-ray luminous,
medium redshift clusters of galaxies. The sample of clusters is called
ARCRAIDER, is based on the ROSAT Bright Survey (RBS) and fulfills the following
criteria: (a) X-ray luminosity Lx>=0.5x10^45erg/s (0.5-2keV band), (b) redshift
range 0.1<=z<=0.52, (c) classified as clusters in the RBS, (d) not a member of
the Abell catalogue and, finally, (e) visible from the ESO sites La
Silla/Paranal (declination \delta<=20deg). In total we found more than 35
(giant) arc/arclet candidates, including a possible radial arc, one
galaxy-galaxy lensing event and a possible quasar triple image in 14 of the 21
clusters of galaxies. Hence 66% of the sample members are possible lenses. | Correlated primordial spectra in effective theory of inflation: We derive a direct correlation between the power spectrum and bispectrum of
the primordial curvature perturbation in terms of the Goldstone mode based on
the effective field theory approach to inflation. We show examples of
correlated bispectra for the parametrized feature models presented by the
Planck collaboration. We also discuss the consistency relation and the validity
of our explicit correlation between the power spectrum and bispectrum. |
Constraining a halo model for cosmological neutral hydrogen: We describe a combined halo model to constrain the distribution of neutral
hydrogen (HI) in the post-reionization universe. We combine constraints from
the various probes of HI at different redshifts: the low-redshift 21-cm
emission line surveys, intensity mapping experiments at intermediate redshifts,
and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a
Markov Chain Monte Carlo (MCMC) approach to combine the observations and place
constraints on the free parameters in the model. Our best-fit model involves a
relation between neutral hydrogen mass $M_{\rm HI}$ and halo mass $M$ with a
non-unit slope, and an upper and a lower cutoff. We find that the model fits
all the observables but leads to an underprediction of the bias parameter of
DLAs at $z \sim 2.3$. We also find indications of a possible tension between
the HI column density distribution and the mass function of HI-selected
galaxies at $z\sim 0$. We provide the central values of the parameters of the
best-fit model so derived. We also provide a fitting form for the derived
evolution of the concentration parameter of HI in dark matter haloes, and
discuss the implications for the redshift evolution of the HI-halo mass
relation. | Probing The Longest Dark Matter Lifetimes with the Line Emission Mapper: In the next decade, the proposed Line Emission Mapper (LEM) telescope concept
is poised to revolutionize Galactic and extragalactic X-ray sensitivity. The
instruments aboard LEM feature unprecedented eV scale energy resolution and an
effective area of 1600 cm$^2$ at 0.5 keV. Such features are ideally suited to
explore decaying dark matter candidates that predict X-ray signals, including
axion-like particles and sterile neutrinos. We present the first forecast of
LEM sensitivity to dark matter decays and find sensitivity to lifetimes beyond
$\sim 10^{32}$ s in the keV range, surpassing current limits by several orders
of magnitude. Notably, our results show that LEM will be the first ever
instrument to probe such long dark matter lifetimes in any mass range for any
decay channel. |
Planck intermediate results. XLVII. Planck constraints on reionization
history: We investigate constraints on cosmic reionization extracted from the Planck
cosmic microwave background (CMB) data. We combine the Planck CMB anisotropy
data in temperature with the low-multipole polarization data to fit LCDM models
with various parameterizations of the reionization history. We obtain a Thomson
optical depth tau=0.058 +/- 0.012 for the commonly adopted instantaneous
reionization model. This confirms, with only data from CMB anisotropies, the
low value suggested by combining Planck 2015 results with other data sets and
also reduces the uncertainties. We reconstruct the history of the ionization
fraction using either a symmetric or an asymmetric model for the transition
between the neutral and ionized phases. To determine better constraints on the
duration of the reionization process, we also make use of measurements of the
amplitude of the kinetic Sunyaev-Zeldovich (kSZ) effect using additional
information from the high resolution Atacama Cosmology Telescope and South Pole
Telescope experiments. The average redshift at which reionization occurs is
found to lie between z=7.8 and 8.8, depending on the model of reionization
adopted. Using kSZ constraints and a redshift-symmetric reionization model, we
find an upper limit to the width of the reionization period of Dz < 2.8. In all
cases, we find that the Universe is ionized at less than the 10% level at
redshifts above z~10. This suggests that an early onset of reionization is
strongly disfavoured by the Planck data. We show that this result also reduces
the tension between CMB-based analyses and constraints from other astrophysical
sources. | Vertical broad-line region structure in nearby active galactic nuclei: Broad emission lines are emitted in the surroundings of supermassive black
holes in the centers of active galactic nuclei (AGN). This region is spatially
not resolved. We intend to get information on the structure and geometry of
this broad emitting line region (BLR) based on line profile observations. We
model the rotational and turbulent velocities in the line-emitting regions
based on observed full-width at half maximum line values (FWHM) and
{\sigma}_{line} of the variable broad emission lines in four nearby AGN: NGC
3783, NGC 7469, NGC 5548, and 3C 390.3. On the basis of these velocities, we
estimate the height of the line-emitting regions above the midplane in context
with their distances from the center. The H{\beta} lines are emitted in a more
flattened configuration above the midplane in comparison to the highly ionized
lines. The H{\beta} lines originate at heights of 0.7 to 1.6 light-days and at
distances of 1.4 to 24 light-days with height/distance (H/R) ratios of only
0.07 to 0.5. The highly ionized lines originate at smaller radii than the
H{\beta} lines and/or at greater distances above the midplane with H/R values
of 0.2 to 1.7. In total, the emission lines do not originate in a thin
atmosphere of an accretion disk but rather at very extended regions above an
accretion disk. The observed geometries of the line-emitting regions resemble
the geometries of accretion disk wind models. Furthermore, the angle of the
central opening cone (generated by the emitting regions of the highly ionized
lines) is small for those galaxies with slow rotational velocities and
increases with the rotation velocity of the central region. The derived
geometries of the line-emitting regions of all four AGN are consistent with the
geometries that are predicted in outflowing disk wind models. |
Supernovae without host galaxies? The low surface brightness host of SN
2009Z: A remarkable fraction of supernovae (SNe) have no obvious host galaxy. Two
possible explanations are that (i) the host galaxy is simply not detected
within the sensitivity of the available data or that (ii) the progenitor is a
hypervelocity star that has escaped its parent galaxy. We use the Type IIb SN
2009Z as a prototype of case (i), an example of how a very faint (here Low
Surface Brightness; LSB) galaxy can be discovered via the observation of a
seemingly host-less SN. By identifying and studying LSB galaxies that host SNe
related to the death of massive stars, we can place constraints on the stellar
population and environment of LSB galaxies, which at present are poorly
understood. From an HI spectrum, a redshift of z = 0.02513+-0.00001 and an HI
mass of (2.96+-0.12) 10^9 M_sun are computed. This redshift is consistent with
that obtained from optical emission lines of SN 2009Z. Furthermore, a gas mass
fraction of f_g = 0.87+-0.04 is obtained, one of the highest fractions ever
measured. The host galaxy shows signs of recently enhanced star formation
activity with a far-UV derived extinction-corrected Star Formation Rate (SFR)
of 0.44+-0.34 M_sun/yr. Based on the B-band luminosity we estimate an
extinction-corrected metallicity following the calibration by Pilyugin (2001)
of 12 + log(O/H) = 8.24+-0.70. The presence of a Type IIb SN in an LSB galaxy
suggests, contrary to popular belief, that massive stars can be formed in this
type of galaxies. Furthermore, our results imply that LSB galaxies undergo
phases of small, local burst activity intermittent with longer phases of
inactivity. | The evolution of radio sources in the UKIDSS-DXS XMM-LSS field: We investigate the cosmic evolution of low luminosity
($L_{\rm{1.4GHz}}<10^{25}\rm{W~Hz^{-1}sr^{-1}}$) radio sources in the XMM Large
Scale Structure survey field (XMM-LSS). We match low frequency selected
(610~MHz) radio sources in the XMM-LSS field with near infrared $K$-band
observations over the same field from the UKIRT Infrared Deep Sky Survey. We
use both the mean $V/V_{\rm{max}}$ statistic and the radio luminosity function
of these matched sources to quantify the evolution of the co-moving space
density of the low luminosity radio sources in our sample. Our results indicate
that the low luminosity sources evolve differently to their high luminosity
counterparts out to a redshift of z$\sim$0.8. The derived luminosity function
is consistent with an increase in the co-moving space density of low luminosity
sources by a factor of $\sim$1.5 at z=0.8. We show that the use of the $K-z$
diagram for the radio source population, although coarser than a full
photometric redshift analysis, produces consistent results with previous
studies using $\sim >10$ band photometry. This offers a promising method for
conducting similar analyses over the whole sky with future near- and
mid-infrared surveys. |
Times, environments and channels of bulge formation in a LambdaCDM
cosmology: We analyze predictions from two independently developed galaxy formation
models to study the mechanisms, environments, and characteristic times of bulge
formation in a LambdaCDM cosmogony. For each model, we test different
prescriptions for bulge formation in order to quantify the relative importance
of different channels. Our results show that the strong correlation between
galaxy and halo mass for central galaxies, and the richer merger history of
more massive systems naturally give rise to a strong correlation between galaxy
mass and morphology, and between halo mass and morphological type of central
galaxies. Large fractions of the bulge mass are acquired through major and
minor mergers, but disc instability plays an important role, particularly for
intermediate mass galaxies. We find that the modelling of disc instability
events, as well as of the galaxy merger times, can affect significantly the
timing of bulge formation, and the relative importance of different channels.
Bulge dominated galaxies acquire their morphology through major mergers, but
this can be modified by cooling of gas from the surrounding hot halo. We find
that disc regrowth is a non negligible component of the evolution of bulge
dominated galaxies, particularly for low to intermediate masses, and at high
redshifts. | Do globular clusters possess Dark Matter halos? A case study in NGC 2419: We use recently published measurements of the kinematics, surface brightness
and stellar mass-to-light ratio of the globular cluster NGC 2419 to examine the
possibility that this Galactic halo satellite is embedded in a low-mass dark
matter halo. NGC 2419 is a promising target for such a study, since its extreme
Galactocentric distance and large mass would have greatly facilitated the
retention of dark matter. A Markov-Chain Monte Carlo approach is used to
investigate composite dynamical models containing a stellar and a dark matter
component. We find that it is unlikely that a significant amount of dark matter
(less than approx. 6% of the luminous mass inside the tidal limit of the
cluster) can be present if the stars follow an anisotropic Michie model and the
dark matter a double power law model. However, we find that more general
models, derived using a new technique we have developed to compute
non-parametric solutions to the spherical Jeans equation, suggest the presence
of a significant dark matter fraction (approximately twice the stellar mass).
Thus the presence of a dark matter halo around NGC 2419 cannot be fully ruled
out at present, yet any dark matter within the 10 arcmin visible extent of the
cluster must be highly concentrated and cannot exceed 1.1x10^6 Solar masses
(99% confidence), in stark contrast to expectations for a plausible progenitor
halo of this structure. |
Helium reionization and the thermal proximity effect: We examine the temperature structure of the intergalactic medium IGM)
surounding a hard radiation source, such as a Quasi-Stellar Object (QSO), as it
responds to the onset of helium reionization by the source. We model the
reionization using a radiative transfer (RT) code coupled to a particle-mesh
(PM) N-body code. Neutral hydrogen and helium are initially ionized by a
starburst spectrum, which is allowed to gradually evolve into a power law
spectrum (fnu ~ nu^(-0.5)). Multiple simulations were performed with different
times for the onset and dominance of the hard spectrum, with onset redshifts
ranging from z = 3.5 to 5.5. The source is placed in a high-density region to
mimic the expected local environment of a QSO. Simulations with the source
placed in a low-density environment were also performed as control cases to
explore the role of the environment on the properties of the surrounding IGM.
We find in both cases that the IGM temperature within the HeIII region produced
exceeds the IGM temperature before full helium reionization, resulting in a
"thermal proximity effect", but that the temperature in the HeIII region
increases systematically with distance from the source. With time the
temperature relaxes with a reduced spread as a function of impact parameter
along neighbouring lines of sight, although the trend continues to persist
until z = 2. Such a trend could be detected using the widths of intervening
metal absorption systems using high resolution, high signal-to-noise ratio
spectra. | Modelling the dusty universe II: The clustering of
submillimetre-selected galaxies: We combine the GALFORM semi-analytical model of galaxy formation, which
predicts the star formation and merger histories of galaxies, the GRASIL
spectro-photometric code, which calculates the spectral energy distributions
(SEDs) of galaxies self-consistently including reprocessing of radiation by
dust, and artificial neural networks (ANN), to investigate the clustering
properties of galaxies selected by their emission at submillimetre wavelengths
(SMGs). We use the Millennium Simulation to predict the spatial and angular
distribution of SMGs. At redshift z = 2, we find that these galaxies are
strongly clustered, with a comoving correlation length of r0 = 5.6 \pm 0.9
Mpc/h for galaxies with 850{\mu}m flux densities brighter than 5 mJy, in
agreement with observations. We predict that at higher redshifts these galaxies
trace denser and increasingly rarer regions of the universe. We present the
predicted dependence of the clustering on luminosity, submillimetre colour,
halo and total stellar masses. Interestingly, we predict tight relations
between correlation length and halo and stellar masses, independent of sub-mm
luminosity. |
The SPTpol Extended Cluster Survey: We describe the observations and resultant galaxy cluster catalog from the
2770 deg$^2$ SPTpol Extended Cluster Survey (SPT-ECS). Clusters are identified
via the Sunyaev-Zel'dovich (SZ) effect, and confirmed with a combination of
archival and targeted follow-up data, making particular use of data from the
Dark Energy Survey (DES). With incomplete followup we have confirmed as
clusters 244 of 266 candidates at a detection significance $\xi \ge 5$ and an
additional 204 systems at $4<\xi<5$. The confirmed sample has a median mass of
$M_{500c} \sim {4.4 \times 10^{14} M_\odot h_{70}^{-1}}$, a median redshift of
$z=0.49$, and we have identified 44 strong gravitational lenses in the sample
thus far. Radio data are used to characterize contamination to the SZ signal;
the median contamination for confirmed clusters is predicted to be $\sim$1% of
the SZ signal at the $\xi>4$ threshold, and $<4\%$ of clusters have a predicted
contamination $>10\% $ of their measured SZ flux. We associate SZ-selected
clusters, from both SPT-ECS and the SPT-SZ survey, with clusters from the DES
redMaPPer sample, and find an offset distribution between the SZ center and
central galaxy in general agreement with previous work, though with a larger
fraction of clusters with significant offsets. Adopting a fixed Planck-like
cosmology, we measure the optical richness-to-SZ-mass ($\lambda-M$) relation
and find it to be 28% shallower than that from a weak-lensing analysis of the
DES data---a difference significant at the 4 $\sigma$ level---with the
relations intersecting at $\lambda=60$ . The SPT-ECS cluster sample will be
particularly useful for studying the evolution of massive clusters and, in
combination with DES lensing observations and the SPT-SZ cluster sample, will
be an important component of future cosmological analyses. | Dilution of baryon asymmetry in the early universe due to primordial
blackhole decay: Primordial black holes which are created at the very early universe can get
decayed in the matter dominated era and thus produce photons, hence resulting
in dilution of the baryon asymmetry and evolution of the cosmological scale
factor. This process is tested and calculated by considering instant decay
approximation, the realistic model of universe expansion and also considering
the LogNormal spectrum of the primordial blackholes. |
A Caveat on Building Nonlocal Models of Cosmology: Nonlocal models of cosmology might derive from graviton loop corrections to
the effective field equations from the epoch of primordial inflation. Although
the Schwinger-Keldysh formalism would automatically produce causal and
conserved effective field equations, the models so far proposed have been
purely phenomenological. Two techniques have been employed to generate causal
and conserved field equations: either varying an invariant nonlocal effective
action and then enforcing causality by the ad hoc replacement of any advanced
Green's function with its retarded counterpart, or else introducing causal
nonlocality into a general ansatz for the field equations and then enforcing
conservation. We point out here that the two techniques access very different
classes of models, and that neither one of them may represent what would
actually arise from fundamental theory. | Ram pressure and dusty red galaxies - key factors in the evolution of
the multiple cluster system Abell 901/902: We present spectroscopic observations of 182 disk galaxies (96 in the cluster
and 86 in the field environment) in the region of the Abell 901/902 multiple
cluster system, which is located at a redshift of $z\sim 0.165$. The presence
of substructures and non-Gaussian redshift distributions indicate that the
cluster system is dynamically young and not in a virialized state. We find
evidence for two important galaxy populations. \textit{Morphologically
distorted galaxies} are probably subject to increased tidal interactions. They
show pronounced rotation curve asymmetries at intermediate cluster-centric
radii and low rest-frame peculiar velocities. \textit{Morphologically
undistorted galaxies} show the strongest rotation curve asymmetries at high
rest-frame velocities and low cluster-centric radii. Supposedly, this group is
strongly affected by ram-pressure stripping due to interaction with the
intra-cluster medium. Among the morphologically undistorted galaxies, dusty red
galaxies have particularly strong rotation curve asymmetries, suggesting ram
pressure is an important factor in these galaxies. Furthermore, dusty red
galaxies on average have a bulge-to-total ratio higher by a factor of two than
cluster blue cloud and field galaxies. The fraction of kinematically distorted
galaxies is 75% higher in the cluster than in the field environment. This
difference mainly stems from morphological undistorted galaxies, indicating a
cluster-specific interaction process that only affects the gas kinematics but
not the stellar morphology. Also the ratio between gas and stellar scale length
is reduced for cluster galaxies compared to the field sample. Both findings
could be best explained by ram-pressure effects. |
The relation between mid-plane pressure and molecular hydrogen in
galaxies: Environmental dependence: Molecular hydrogen (H2) is the primary component of the reservoirs of cold,
dense gas that fuel star formation in our galaxy. While the H2 abundance is
ultimately regulated by physical processes operating on small scales in the
interstellar medium (ISM), observations have revealed a tight correlation
between the ratio of molecular to atomic hydrogen in nearby spiral galaxies and
the pressure in the mid-plane of their disks. This empirical relation has been
used to predict H2 abundances in galaxies with potentially very different ISM
conditions, such as metal-deficient galaxies at high redshifts. Here, we test
the validity of this approach by studying the dependence of the pressure -- H2
relation on environmental parameters of the ISM. To this end, we follow the
formation and destruction of H2 explicitly in a suite of hydrodynamical
simulations of galaxies with different ISM parameters. We find that a pressure
-- H2 relation arises naturally in our simulations for a variety of dust-to-gas
ratios or strengths of the interstellar radiation field in the ISM. Fixing the
dust-to-gas ratio and the UV radiation field to values measured in the solar
neighborhood results in fair agreement with the relation observed in nearby
galaxies with roughly solar metallicity. However, the parameters (slope and
normalization) of the pressure -- H2 relation vary in a systematical way with
ISM properties. A particularly strong trend is the decrease of the
normalization of the relation with a lowering of the dust-to-gas ratio of the
ISM. We show that this trend and other properties of the pressure -- H2
relation are natural consequences of the transition from atomic to molecular
hydrogen with gas surface density. | Probing the Excitation of Extreme Starbursts: High Resolution Mid-IR
Spectroscopy of Blue Compact Dwarfs: We present an analysis of the mid-infrared emission lines for a sample of 12
low metallicity Blue Compact Dwarf (BCD) galaxies based on high resolution
observations obtained with Infrared Spectrograph on board the {\rm Spitzer}
Space Telescope. We compare our sample with a local sample of typical starburst
galaxies and active galactic nuclei (AGNs), to study the ionization field of
starbursts over a broad range of physical parameters and examine its difference
from the one produced by AGN. The high-ionization line [OIV]25.89$\mu$m is
detected in most of the BCDs, starbursts, and AGNs in our sample. We propose a
diagnostic diagram of the line ratios [OIV]25.89$\mu$m/[SIII]33.48$\mu$m as a
function of [NeIII]15.56$\mu$m/[NeII]12.81$\mu$m which can be useful in
identifying the principal excitation mechanism in a galaxy. Galaxies in this
diagram split naturally into two branches. Classic AGNs as well as starburst
galaxies with an AGN component populate the upper branch, with stronger AGNs
displaying higher [NeIII]/[NeII] ratios. BCDs and pure starbursts are located
in the lower branch. We find that overall the placement of galaxies on this
diagram correlates well with their corresponding locations in the
log([NII]/H$\alpha$) vs. log([OIII]/H$\beta$) diagnostic diagram, which has
been widely used in the optical. The two diagrams provide consistent
classifications of the excitation mechanism in a galaxy. On the other hand, the
diagram of [NeIII]15.56$\mu$m/[NeII]12.81$\mu$m vs.
[SIV]10.51$\mu$m/[SIII]18.71$\mu$m is not as efficient in separating AGNs from
BCDs and pure starbursts. (abridged) |
Far-infrared spectroscopy of a lensed starburst: a blind redshift from
Herschel: We report the redshift of HATLAS J132427.0+284452 (hereafter HATLAS J132427),
a gravitationally lensed starburst galaxy, the first determined 'blind' by the
Herschel Space Observatory. This is achieved via the detection of [C II]
consistent with z = 1.68 in a far-infrared spectrum taken with the SPIRE
Fourier Transform Spectrometer. We demonstrate that the [C II] redshift is
secure via detections of CO J = 2 - 1 and 3 - 2 using the Combined Array for
Research in Millimeter-wave Astronomy and the Institut de Radioastronomie
Millimetrique's Plateau de Bure Interferometer. The intrinsic properties appear
typical of high-redshift starbursts despite the high lensing-amplified fluxes,
proving the ability of the FTS to probe this population with the aid of
lensing. The blind detection of [C II] demonstrates the potential of the SAFARI
imaging spectrometer, proposed for the much more sensitive SPICA mission, to
determine redshifts of multiple dusty galaxies simultaneously without the
benefit of lensing. | Inverse Compton X-rays from Giant Radio Galaxies at z~1: We report XMM-Newton observations of three FR II radio galaxies at redshifts
between 0.85 and 1.34, which show extended diffuse X-ray emission within the
radio lobes, likely due to inverse-Compton up-scattering of the cosmic
microwave background. Under this assumption, through spectrum-fitting together
with archival VLA radio observations, we derive an independent estimate of the
magnetic field in the radio lobes of 3C 469.1 and compare it with the
equipartition value. We find concordance between these two estimates as long as
the turnover in the energy distribution of the particles occurs at a Lorentz
factor in excess of ~ 250. We determine the total energy in relativistic
particles in the radio emitting lobes of all three sources to range between
3e59 and 8e59 erg. The nuclei of these X-ray sources are heavily-absorbed
powerful AGN. |
A Spectroscopic Road Map for Cosmic Frontier: DESI, DESI-II, Stage-5: In this white paper, we present an experimental road map for spectroscopic
experiments beyond DESI. DESI will be a transformative cosmological survey in
the 2020s, mapping 40 million galaxies and quasars and capturing a significant
fraction of the available linear modes up to z=1.2. DESI-II will pilot
observations of galaxies both at much higher densities and extending to higher
redshifts. A Stage-5 experiment would build out those high-density and
high-redshift observations, mapping hundreds of millions of stars and galaxies
in three dimensions, to address the problems of inflation, dark energy, light
relativistic species, and dark matter. These spectroscopic data will also
complement the next generation of weak lensing, line intensity mapping and CMB
experiments and allow them to reach their full potential. | Planck ISW-lensing likelihood and the CMB temperature: We present a new Planck CMB lensing-CMB temperature cross-correlation
likelihood that can be used to constrain cosmology via the Integrated
Sachs-Wolfe (ISW) effect. CMB lensing is an excellent tracer of ISW, and we use
the latest PR4 Planck data maps and lensing reconstruction to produce the first
public Planck likelihood to constrain this signal. We demonstrate the
likelihood by constraining the CMB background temperature from Planck data
alone, where the ISW-lensing cross-correlation is a powerful way to break the
geometric degeneracy, substantially improving constraints from the CMB and
lensing power spectra alone. |
General relativistic bubble growth in cosmological phase transitions: We use a full general relativistic framework to study the self-similar
expansion of bubbles of the stable phase into a flat
Friedmann-Lema\^itre-Robertson-Walker Universe in a first order phase
transition in the early Universe. With a simple linear barotropic equation of
state in both phases, and in the limit of a phase boundary of negligible width,
we find that self-similar solutions exist, which are qualitatively similar to
the analogous solutions in Minkowski space, but with distinguishing features.
Rarefaction waves extend to the centre of the bubble, while spatial sections
near the centre of the bubble have negative curvature. Gravitational effects
redistribute the kinetic energy of the fluid around the bubble, and can change
the kinetic energy fraction significantly. The kinetic energy fraction of the
gravitating solution can be enhanced over the analogous Minkowski solution by
as much as $\mathcal{O}(1)$, and suppressed by a factor as larger as
$\mathcal{O}(10)$ in case of fast detonations. The amount of negative spatial
curvature at the centre of the bubble is of the same order of magnitude of the
naive expectation based on considerations of the energy density perturbation in
Minkowski solutions, with gravitating deflagrations less negatively curved, and
detonations more. We infer that general relativistic effects might have a
significant impact on accurate calculations of the gravitational wave power
spectrum when the bubble size becomes comparable to the cosmological Hubble
radius, affecting the primary generation from the fluid shear stress, and
inducing secondary generation by scalar perturbations. | Big Bounce Genesis and Possible Experimental Tests -- A Brief Review: We review the recent status of big bounce genesis as a new possibility of
using dark matter particle's mass and interaction cross section to test the
existence of a bounce universe at the early stage of evolution in our currently
observed universe. To study the dark matter production and evolution inside the
bounce universe, called big bounce genesis for short, we propose a model
independent approach. We shall present the motivation for proposing big bounce
as well the model independent predictions which can be tested by dark matter
direct searches. A positive finding shall have profound impact on our
understanding of the early universe physics. |
HETDEX pilot survey for emission-line galaxies - I. Survey design,
performance, and catalog: We present a catalog of emission-line galaxies selected solely by their
emission-line fluxes using a wide-field integral field spectrograph. This work
is partially motivated as a pilot survey for the upcoming Hobby-Eberly
Telescope Dark Energy Experiment (HETDEX). We describe the observations,
reductions, detections, redshift classifications, line fluxes, and counterpart
information for 397 emission-line galaxies detected over 169 sq.arcmin with a
3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral
resolution. The survey's best sensitivity for unresolved objects under
photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the
wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable.
This survey method complements narrowband and color-selection techniques in the
search for high redshift galaxies with its different selection properties and
large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS,
and XMM-LSS areas are rich with existing, complementary data. We find 104
galaxies via their high redshift Ly-alpha emission at 1.9<z<3.8, and the
majority of the remainder objects are low redshift [OII]3727 emitters at
z<0.56. The classification between low and high redshift objects depends on
rest frame equivalent width, as well as other indicators, where available.
Based on matches to X-ray catalogs, the active galactic nuclei (AGN) fraction
amongst the Ly-alpha emitters (LAEs) is 6%. We also analyze the survey's
completeness and contamination properties through simulations. We find five
high-z, highly-significant, resolved objects with full-width-half-maximum sizes
>44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three
high-z objects with rest frame Ly-alpha equivalent widths above the level
believed to be achievable with normal star formation, EW(rest)>240 Ang. | On backreaction effects in geometrical destabilisation of inflation: We study the geometrical instability arising in multi-field models of
inflation with negatively-curved field space. We analyse how the homogeneous
background evolves in presence of geometrical destabilisation, and show that,
in simple models, a kinematical backreaction effect takes place that shuts off
the instability. We also follow the evolution of the unstable scalar
fluctuations. We show that they assist the kinematical backreaction while
remaining in the perturbative regime. We conclude that, in the simplest models
of geometrical destabilisation, inflation does not end prematurely, but rather
proceeds along a modified, sidetracked, field-space trajectory. |
The statistics of primordial black holes in a radiation dominated
Universe -- recent and new results: We review the non-linear statistics of Primordial Black Holes that form from
the collapse of over-densities in a radiation dominated Universe. We focus on
the scenario in which large over-densities are generated by rare and Gaussian
curvature perturbations during inflation. As new results, we show that the mass
spectrum follows a power law determined by the critical exponent of the
self-similar collapse up to a power spectrum dependent cut-off, and that the
abundance related to very narrow power spectra is exponentially suppressed.
Related to this, we discuss and explicitly show that the Press-Schechter
approximation, as well as the statistics of mean profiles, lead to wrong
conclusions for the abundance and mass spectrum. Finally, we clarify that the
transfer function in the statistics of initial conditions for primordial black
holes formation (the abundance) does not play a significant role. | Constraints on the relative sizes of intervening Mg II-absorbing clouds
and quasar emitting regions: Context: A significantly higher incidence of strong (rest equivalent width
W_r > 1 {\AA}) intervening Mg II absorption is observed along gamma-ray burst
(GRB) sight-lines relative to those of quasar sight-lines. A geometrical
explanation for this discrepancy has been suggested: the ratio of the beam size
of the source to the characteristic size of a Mg II absorption system can
influence the observed Mg II equivalent width, if these two sizes are
comparable. Aims: We investigate whether the differing beam sizes of the
continuum source and broad-line region of Sloan Digital Sky Survey (SDSS)
quasars produce a discrepancy between the incidence of strong Mg II absorbers
illuminated by the quasar continuum region and those of absorbers illuminated
by both continuum and broad-line region light. Methods: We perform a
semi-automated search for strong Mg II absorbers in the SDSS Data Release 7
quasar sample. The resulting strong Mg II absorber catalog is available online.
We measure the sight-line number density of strong Mg II absorbers superimposed
on and off the quasar C IV 1550 {\AA} and C III] 1909 {\AA} emission lines.
Results: We see no difference in the sight-line number density of strong Mg II
absorbers superimposed on quasar broad emission lines compared to those
superimposed on continuum-dominated spectral regions. This suggests that the Mg
II-absorbing clouds typically observed as intervening absorbers in quasar
spectra are larger than the beam sizes of both the continuum-emitting regions
and broad line-emitting regions in the centers of quasars, corresponding to a
lower limit of the order of 10^17} cm for the characteristic size of a Mg II
absorbing cloud. |
The QCD nature of Dark Energy: The origin of the observed dark energy could be explained entirely within the
standard model, with no new fields required. We show how the low-energy sector
of the chiral QCD Lagrangian, once embedded in a non-trivial spacetime, gives
rise to a cosmological vacuum energy density which can be can be presented
entirely in terms of QCD parameters and the Hubble constant $H$ as
$\rho_\Lambda \simeq H \cdot m_q\la\bar{q}q\ra /m_{\eta'} \sim (4.3\cdot
10^{-3} \text{eV})^4$. In this work we focus on the dynamics of the ghost
fields that are essential ingredients of the aforementioned Lagrangian. In
particular, we argue that the Veneziano ghost, being unphysical in the usual
Minkowski QFT, becomes a physical degree of freedom if the universe is
expanding. As an immediate consequence, all relevant effects are naturally very
small as they are proportional to the rate of expansion $H/ \Lqcd \sim
10^{-41}$. The co-existence of these two drastically different scales ($\Lqcd
\sim 100 $ MeV and $H \sim 10^{-33}$ eV) is a direct consequence of the
auxiliary conditions on the physical Hilbert space that are necessary to keep
the theory unitary. The exact cancellation taking place in Minkowski space due
to this auxiliary condition is slightly violated when the system is upgraded to
an expanding background. Nevertheless, this "tiny" effect is in fact the
driving force accelerating the universe today. We also derive the time
dependent equation of state $w(t)$ for the dark energy component which tracks
the dynamics of the Veneziano ghost in a FLRW universe. Finally, we comment on
how the same physical phenomena can be recovered in Witten's approach to the
U(1) problem when the ghost degree of freedom is not even present in the
system. | Cosmological Redshift in FRW Metrics with Constant Spacetime Curvature: Cosmological redshift z grows as the Universe expands and is conventionally
viewed as a third form of redshift, beyond the more traditional Doppler and
gravitational effects seen in other applications of general relativity. In this
paper, we examine the origin of redshift in the Friedmann-Robertson-Walker
metrics with constant spacetime curvature, and show that---at least for the
static spacetimes---the interpretation of z as due to the "stretching" of space
is coordinate dependent. Namely, we prove that redshift may also be calculated
solely from the effects of kinematics and gravitational acceleration. This
suggests that its dependence on the expansion factor is simply a manifestation
of the high degree of symmetry in FRW, and ought not be viewed as evidence in
support of the idea that space itself is expanding. |
The Emergent Universe scheme and Tunneling: We present an alternative scheme for an Emergent Universe scenario, developed
previously in $Phys.\ Rev.\ D {\bf 86}, 083524 (2012)$, where the universe is
initially in a static state supported by a scalar field located in a false
vacuum. The universe begins to evolve when, by quantum tunneling, the scalar
field decays into a state of true vacuum. The Emergent Universe models are
interesting since they provide specific examples of non-singular inflationary
universes. | Vlasov versus N-body: the Hénon sphere: We perform a detailed comparison of the phase-space density traced by the
particle distribution in Gadget simulations to the result obtained with a
spherical Vlasov solver using the splitting algorithm. The systems considered
are apodized H\'enon spheres with two values of the virial ratio, R ~ 0.1 and
0.5. After checking that spherical symmetry is well preserved by the N-body
simulations, visual and quantitative comparisons are performed. In particular
we introduce new statistics, correlators and entropic estimators, based on the
likelihood of whether N-body simulations actually trace randomly the Vlasov
phase-space density. When taking into account the limits of both the N-body and
the Vlasov codes, namely collective effects due to the particle shot noise in
the first case and diffusion and possible nonlinear instabilities due to finite
resolution of the phase-space grid in the second case, we find a spectacular
agreement between both methods, even in regions of phase-space where nontrivial
physical instabilities develop. However, in the colder case, R=0.1, it was not
possible to prove actual numerical convergence of the N-body results after a
number of dynamical times, even with N=10$^8$ particles. |
The VIMOS VLT Deep Survey. The different assembly history of passive and
star-forming L_B >= L*_B galaxies in the group environment at z < 1: We use the VIMOS VLT Deep Survey to study the close environment of galaxies
in groups at 0.2 <= z < 0.95. Close neighbours of L_B >= L*_B galaxies (Me_B =
M_B + 1.1z <= -20) are identified with Me_B <= -18.25 and within a relative
distance 5h^-1 kpc <= rp <= 100h^-1 kpc and relative velocity Delta v <= 500
km/s . The richness N of a group is defined as the number of Me_B <= -18.25
galaxies belonging to that group. We split our principal sample into red,
passive galaxies with NUV - r >= 4.25 and blue, star-forming galaxies with NUV
- r < 4.25. We find that blue galaxies with a close companion are primarily
located in poor groups, while the red ones are in rich groups. The number of
close neighbours per red galaxy increases with N, with n_red being proportional
to 0.11N, while that of blue galaxies does not depend on N and is roughly
constant. In addition, these trends are found to be independent of redshift,
and only the average n_blue evolves, decreasing with cosmic time. Our results
support the following assembly history of L_B >= L*_B galaxies in the group
environment: red, massive galaxies were formed in or accreted by the dark
matter halo of the group at early times (z >= 1), therefore their number of
neighbours provides a fossil record of the stellar mass assembly of groups,
traced by their richness N. On the other hand, blue, less massive galaxies have
recently been accreted by the group potential and are still in their parent
dark matter halo, having the same number of neighbours irrespective of N. As
time goes by, these blue galaxies settle in the group potential and turn red
and/or fainter, thus becoming satellite galaxies in the group. With a toy
quenching model, we estimate an infall rate of field galaxies into the group
environment of R_infall = 0.9 - 1.5 x 10^-4 Mpc^-3 Gyr^-1 at z ~ 0.7. | Einstein's signature in cosmological large-scale structure: We show how the non-linearity of general relativity generates a
characteristic non-Gaussian signal in cosmological large-scale structure that
we calculate at all perturbative orders in a large scale limit. Newtonian
gravity and general relativity provide complementary theoretical frameworks for
modelling large-scale structure in $\Lambda$CDM cosmology; a relativistic
approach is essential to determine initial conditions which can then be used in
Newtonian simulations studying the non-linear evolution of the matter density.
Most inflationary models in the very early universe predict an almost Gaussian
distribution for the primordial metric perturbation, $\zeta$. However, we argue
that it is the Ricci curvature of comoving-orthogonal spatial hypersurfaces,
$R$, that drives structure formation at large scales. We show how the
non-linear relation between the spatial curvature, $R$, and the metric
perturbation, $\zeta$, translates into a specific non-Gaussian contribution to
the initial comoving matter density that we calculate for the simple case of an
initially Gaussian $\zeta$. Our analysis shows the non-linear signature of
Einstein's gravity in large-scale structure. |
Pop. III stars from turbulent fragmentation at redshift ~ 11: We report results from a cosmological simulation with non-equilibrium
chemistry of 21 species, including H2, HD, and LiH molecular cooling. Starting
from cosmological initial conditions, we focus on the evolution of the central
1.8 Kpc region of a 3 x 10^7 Msun halo. The crossing of a few 10^6 Msun halos
and the gas accretion through larger scale filaments generate a turbulent
environment within this region. Due to the short cooling time caused by the
non-equilibrium formation of H2, the supersonic turbulence results in a very
fragmented mass distribution, where dense, gravitationally unstable clumps
emerge from a complex network of dense filaments. At z=10.87, we find
approximately 25 well defined, gravitationally unstable clumps, with masses of
4 x 10^3-9 x 10^5 Msun, temperatures of approximately 300K, and cooling times
much shorter than the free-fall time. Only the initial phase of the collapse of
individual clumps is spatially resolved in the simulation. Depending on the
density reached in the collapse, the estimated average Bonnor-Ebert masses are
in the range 200-800 Msun. We speculate that each clump may further fragment
into a cluster of stars with a characteristic mass in the neighborhood of 50
Msun. This process at z ~ 11 may represent the dominant mode of Pop. III star
formation, causing a rapid chemical enrichment of the protogalactic
environment. | Why are some galaxy disks extremely thin?: Some low surface brightness galaxies are known to have extremely thin stellar
disks with the vertical to planar axes ratio 0.1 or less, often referred to as
superthin disks. Although their existence is known for over three decades, the
physical origin for the thin distribution is not understood. We model the
stellar thickness for a two-component (gravitationally coupled stars and gas)
disk embedded in a dark matter halo, for a superthin galaxy UGC 7321 which has
a dense, compact halo, and compare with a typical dwarf galaxy HoII which has a
non-compact halo. We show that while the presence of gas does constrain the
disk thickness, it is the compact dark matter halo which plays the decisive
role in determining the superthin disk distribution in low-mass disks. Thus the
compact dark matter halo significantly affects the disk structure and this
could be important for the early evolution of galaxies. |
Faint polarised sources in the Lockman Hole field at 1.4 GHz: We aim to study the nature of the faint, polarised radio source population
whose source composition and redshift dependence contain information about the
strength, morphology, and evolution of magnetic fields over cosmic timescales.
We use a 15 pointing radio continuum L-band mosaic of the Lockman Hole,
observed in full polarisation, generated from archival data of the WSRT. The
data were analysed using the RM-Synthesis technique. We achieved a noise of 7
{\mu}Jy/beam in polarised intensity, with a resolution of 15''. Using infrared
and optical images and source catalogues, we were able to cross-identify and
determine redshifts for one third of our detected polarised sources. We
detected 150 polarised sources, most of which are weakly polarised with a mean
fractional polarisation of 5.4 %. With a total area of 6.5 deg^2 and a
detection threshold of 6.25 {\sigma} we find 23 polarised sources per deg^2.
Based on our multi wavelength analysis, we find that our sample consists of AGN
only. We find a discrepancy between archival number counts and those present in
our data, which we attribute to sample variance. Considering the absolute radio
luminosty, to distinguish weak and strong sources, we find a general trend of
increased probability to detect weak sources at low redshift and strong sources
at high redshift. Further, we find an anti-correlation between fractional
polarisation and redshift for our strong sources sample at z{\geq}0.6. A
decrease in the fractional polarisation of strong sources with increasing
redshift cannot be explained by a constant magnetic field and electron density
over cosmic scales, however the changing properties of cluster environments
over the cosmic timemay play an important role. Disentangling these two effects
requires deeper and wider polarisation observations, and better models of the
morphology and strength of cosmic magnetic fields. | Photon-photon interactions as a source of CMB circular polarization: Photon-photon interactions mediated by the neutral hydrogen background can
transform plane polarization into circular polarization, through completely
forward processes, [gamma+gamma+atom-> gamma+ gamma+atom], in which only the
photon polarizations are changed. The ratio of circular to plane polarization
intensities is predicted to be at the level of several times 10^{-5} for some
regions of angular size less than 1/300 and with large plane polarizations. |
A Multiwavelength Study of Binary Quasars and Their Environments: We present Chandra X-ray imaging and spectroscopy for 14 quasars in spatially
resolved pairs, part of a complete sample of binary quasars with small
transverse separations drawn from Sloan Digital Sky Survey (DR6) photometry. We
find no significant difference in X-ray properties when compared with large
control samples of isolated quasars. We present infrared photometry from our
observations with SWIRC at the MMT, and from the WISE Preliminary Data Release,
and fit simple spectral energy distributions to all 14 QSOs. We find
preliminary evidence that substantial contributions from star formation are
required, but possibly no more so than for isolated X-ray-detected QSOs.
Sensitive searches of the X-ray images for extended emission, and the optical
images for optical galaxy excess show that these binary QSOs are not
preferentially found in rich cluster environments. While larger binary QSO
samples with richer far-IR and sub-millimeter multiwavelength data might better
reveal signatures of merging and triggering, optical color-selection of QSO
pairs may be biased against such signatures. X-ray and/or variability selection
of QSO pairs, while challenging, should be attempted. We present in our
Appendix a primer on X-ray flux and luminosity calculations. | Celestial dynamics and astrometry in expanding universe: The mathematical concept of the Newtonian limit of Einstein's field equations
in the expanding Friedmann universe is formulated. The geodesic equations of
motion of planets and light are derived and compared. |
Cosmic distance duality and cosmic transparency: We compare distance measurements obtained from two distance indicators,
Super- novae observations (standard candles) and Baryon acoustic oscillation
data (standard rulers). The Union2 sample of supernovae with BAO data from
SDSS, 6dFGS and the latest BOSS and WiggleZ surveys is used in search for
deviations from the distance duality relation. We find that the supernovae are
brighter than expected from BAO measurements. The luminosity distances tend to
be smaller then expected from angular diameter distance estimates as also found
in earlier works on distance duality, but the trend is not statistically
significant. This further constrains the cosmic transparency. | A redshift survey towards the CMB Cold Spot: We have carried out a redshift survey using the VIMOS spectrograph on the VLT
towards the Cosmic Microwave Background cold spot. A possible cause of the cold
spot is the Integrated Sachs-Wolfe effect imprinted by an extremely large void
(hundreds of Mpc in linear dimension) at intermediate or low redshifts. The
redshift distribution of over seven hundred z<1 emission-line galaxies drawn
from an I-band flux limited sample of galaxies in the direction of the cold
spot shows no evidence of a gap on scales of Delta-z> 0.05 as would be expected
if such a void existed at 0.35<z<1. There are troughs in the redshift
distribution on smaller scales (Delta-z ~0.01) indicating that smaller scale
voids may connect regions separated by several degrees towards the cold spot. A
comparison of this distribution with that generated from similarly-sized
subsamples drawn from widely-spaced pointings of the VVDS survey does not
indicate that the redshift distribution towards the cold spot is anomalous or
that these small gaps can be uniquely attributed to real voids. |
Nonlinear preheating with nonminimally coupled scalar fields in the
Starobinsky model: We study the preheating after inflation in the Starobinsky model with a
nonminimally coupled scalar field $\chi$. Using the lattice simulation, we
analyze the rescattering between the $\chi$ particles and the inflaton
condensate, and the backreaction effect of the scalar metric perturbations. We
find that the rescattering is an efficient mechanism promoting the growth of
the $\chi$ field variance. Meanwhile, copious inflaton particles can be knocked
out of the inflaton condensate by rescattering. As a result, the inflaton field
can become a nonnegligible gravitational wave source, even comparable with the
$\chi$ field in some parameter regions. For the scalar metric perturbations,
which are on the sub-Hubble scale in our analysis, our results show that they
have negligible effects on the evolution of scalar fields and the production of
gravitational waves in the model considered in present paper. | The contribution of starbursts and normal galaxies to infrared
luminosity functions at z < 2: We present a parameter-less approach to predict the shape of the infrared
(IR) luminosity function (LF) at redshifts z < 2. It requires no tuning and
relies on only three observables: (1) the redshift evolution of the stellar
mass function for star-forming galaxies, (2) the evolution of the specific star
formation rate (sSFR) of main-sequence galaxies, and (3) the double-Gaussian
decomposition of the sSFR-distribution at fixed stellar mass into a
contribution (assumed redshift- and mass-invariant) from main-sequence and
starburst activity. This self-consistent and simple framework provides a
powerful tool for predicting cosmological observables: observed IR LFs are
successfully matched at all z < 2, suggesting a constant or only weakly
redshift-dependent contribution (8-14%) of starbursts to the star formation
rate density. We separate the contributions of main-sequence and starburst
activity to the global IR LF at all redshifts. The luminosity threshold above
which the starburst component dominates the IR LF rises from log(LIR/Lsun) =
11.4 to 12.8 over 0 < z < 2, reflecting our assumed (1+z)^2.8-evolution of sSFR
in main-sequence galaxies. |
Cosmological constraints from harmonic space analysis of DES Y3 3x2
clustering: The large-scale distribution of matter, as mapped by photometric surveys like
the Dark Energy Survey (DES), serves as a powerful probe into cosmology. It is
especially sensitive to both the amplitude of matter clustering ($\sigma_8$)
and the total matter density ($\Omega_m$). The fiducial analysis of the
two-point clustering statistics of these surveys is invariably done in
configuration space where complex masking scheme is easier to handle. However,
such an analysis inherently mixes different scales together, requiring special
care in modeling. In this study, we present an analysis of DES Y3 3x2
clustering data in harmonic space where small and large scales are better
separated and can be neatly modeled using perturbative techniques. Using
conservative scale cuts together with Limber approximation and a Gaussian
covariance assumption in a first study, we model the clustering data under a
linear bias model for galaxies, incorporating comprehensive treatment for
astrophysical effects. We subsequently extend this fiducial analysis to explore
a third-order biasing prescription. For our fiducial analysis, we get
$S_8=0.789\pm0.020$, consistent with the configuration space analysis presented
by the DES collaboration, although under our different modeling choices, we
find a preference for a lower $\Omega_m$ and a higher $\sigma_8$. The analysis
sets the stage for a future search for signatures of primordial non-Gaussianity
and blue-tilted isocurvature perturbations from photometric surveys. | Sunyaev-Zel'dovich detection of the galaxy cluster Cl J1449+0856 at z =
1.99: the pressure profile in uv space: We present Atacama Large Millimetre Array and Atacama Compact Array
observations of the Sunyaev-Zel'dovich effect in the z = 2 galaxy cluster Cl
J1449+0856, an X-ray-detected progenitor of typical massive clusters in the
present day Universe. While in a cleaned but otherwise untouched 92 GHz map of
this cluster, little to no negative signal is visible, careful subtraction of
known sub-millimetre emitters in the uv plane reveals a decrement at 5$\sigma$
significance. The total signal is -190$\pm$36 $\mu$Jy, with a peak offset by
5"-9" ($\sim$50 kpc) from both the X-ray centroid and the still-forming
brightest cluster galaxy. A comparison of the recovered uv-amplitude profile of
the decrement with different pressure models allows us to derive total mass
constraints consistent with the $\sim$6$\times$10$^{13}$ M$_{\odot}$ estimated
from X-ray data. Moreover, we find no strong evidence for a deviation of the
pressure profile with respect to local galaxy clusters, although a slight
tension at small-to-intermediate spatial scales suggests a flattened central
profile, opposite to what seen in a cool core and possibly an AGN-related
effect. This analysis of the lowest mass single SZ detection so far illustrates
the importance of interferometers when observing the SZ effect in high-redshift
clusters, the cores of which cannot be considered quiescent, such that careful
subtraction of galaxy emission is necessary. |
Quintessential inflation and nonlinear effects of the tachyonic trap
mechanism: With the help of the tachyonic trapping mechanism one can potentially solve a
number of problems affecting quintessential inflation models. In this mechanism
we introduce a trapping field with a spontaneous symmetry breaking potential.
When the quintessential inflaton passes the critical point, a sudden burst of
particle production is able to reheat the Universe and trap the inflaton away
from theminimum of its potential. However, self-interactions of the trapping
field suppress particle production and reduce the efficiency of this process.
We develop a method to compute the magnitude of the suppression and explore the
parameter space in which the mechanism can be applied effectively. | Dark Matter that can form Dark Stars: The first stars to form in the Universe may be powered by the annihilation of
weakly interacting dark matter particles. These so-called dark stars, if
observed, may give us a clue about the nature of dark matter. Here we examine
which models for particle dark matter satisfy the conditions for the formation
of dark stars. We find that in general models with thermal dark matter lead to
the formation of dark stars, with few notable exceptions: heavy neutralinos in
the presence of coannihilations, annihilations that are resonant at dark matter
freeze-out but not in dark stars, some models of neutrinophilic dark matter
annihilating into neutrinos only and lighter than about 50 GeV. In particular,
we find that a thermal DM candidate in standard Cosmology always forms a dark
star as long as its mass is heavier than about 50 GeV and the thermal average
of its annihilation cross section is the same at the decoupling temperature and
during the dark star formation, as for instance in the case of an annihilation
cross section with a non-vanishing s-wave contribution. |
A MIKE + UVES survey of Sub-Damped Lyman-Alpha Systems at z<1.5: We have combined the results from our recent observations of Damped and
sub-Damped Lyman-alpha systems with the MIKE and UVES spectrographs on the
Magellan Clay and VLT Kueyen telescopes with ones from the literature to
determine the N(HI)-weighted mean metallicity of these systems based both on
Fe, a depleted element in QSO absorbers and the local ISM, and Zn a relatively
undepleted element. In each case, the N(HI)-weighted mean metallicity is higher
and shows faster evolution in sub-DLAs than the classical DLA systems. Large
grids of photoionisation models over the sub-DLA \nhI range with CLOUDY show
that the ionisation corrections to the abundances are in general small, however
the fraction of ionized H can be up to ~90 per cent. The individual spectra
have been shifted to the rest frame of the absorber and averaged together to
determine the average properties of these systems at z<1.5. We find that the
average abundance pattern of the Sub-DLA systems is similar to the gas in the
halo of the Milky Way, with an offset of ~0.3 dex in the overall metallicity.
Both DLAs and Sub-DLAs show similar characteristics in their relative
abundances patterns, although the DLAs have smaller <[Mn/Zn]> as well as higher
<[Ti/Zn]> and <[Cr/Zn]>. We calculate the contribution of sub-DLAs to the metal
budget of the Universe, and find that the sub-DLA systems at z<1.5 contain a
comoving density of metals Omega_met (3.5-15.8)x10^{5} M_sun Mpc^{-3}, at least
twice the comoving density of metals in the DLA systems. The sub-DLAs do
however track global chemical evolution models much more closely than do the
DLAs, perhaps indicating that they are a less dust biased metallicity indicator
of galaxies at high redshifts than the DLA systems. | A Deep Chandra ACIS Study of NGC 4151. I. the X-ray Morphology of the 3
kpc-diameter Circum-nuclear Region and Relation to the Cold Interstellar
Medium: We report on the imaging analysis of 200 ks sub-arcsecond resolution Chandra
ACIS-S observations of the nearby Seyfert 1 galaxy NGC 4151. Bright, structured
soft X-ray emission is observed to extend from 30 pc to 1.3 kpc in the
south-west from the nucleus, much farther than seen in earlier X-ray studies.
The terminus of the north-eastern X-ray emission is spatially coincident with a
CO gas lane, where the outflow likely encounters dense gas in the host galactic
disk. X-ray emission is also detected outside the boundaries of the ionization
cone, which indicates that the gas there is not completely shielded from the
nuclear continuum, as would be the case for a molecular torus collimating the
bicone. In the central r<200 pc region, the subpixel processing of the ACIS
data recovers the morphological details on scales of <30~pc (<0.5") first
discovered in Chandra HRC images. The X-ray emission is more absorbed towards
the boundaries of the ionization cone, as well as perpendicular to the bicone
along the direction of a putative torus in NGC 4151. The innermost region where
X-ray emission shows the highest hardness ratio, is spatially coincident with
the near-infrared resolved H_2 emission and dusty spirals we find in an HST V-H
color image. The agreement between the observed H_2 line flux and the value
predicted from X-ray-irradiated molecular cloud models supports
photo-excitation by X-rays from the active nucleus as the origin of the H_2
line, although contribution from UV fluorescence or collisional excitation
cannot be fully ruled out with current data. The discrepancy between the mass
of cold molecular gas inferred from recent CO and near-infrared H_2
observations may be explained by the anomalous CO abundance in this X-ray
dominated region. The total H_2 mass derived from the X-ray observation agrees
with measurement in Storchi-Bergmann et al. |
Observational signatures of Higgs inflation: We investigate the dependency of Higgs inflation on the non-renormalisable
matching between the low energy Standard Model limit and the inflationary
regime at high energies. We show that for the top mass range $m_t \gtrsim
171.8$ GeV the scenario robustly predicts the spectral index $n_s \simeq 0.97$
and the tensor-to-scalar ratio $r\simeq 0.003$. The matching is however
non-trivial, even the best-fit values $m_h=125.09$ GeV and $m_t=173.21$ GeV
require a jump $\delta \lambda \sim 0.01$ in the Higgs coupling below the
inflationary scale. For $m_t\lesssim 171.8$ GeV, the matching may generate a
feature in the inflationary potential. In this case the predicted values of
$n_s$ and $r$ vary but the model is still falsifiable. For example, a detection
of negative running of spectral index at level $\alpha_s \lesssim -0.01$ would
rule out Higgs inflation. | Effect of the non-thermal Sunyaev-Zel'dovich Effect on the temperature
determination of galaxy clusters: A recent stacking analysis of Planck HFI data of galaxy clusters (Hurier
2016) allowed to derive the cluster temperatures by using the relativistic
corrections to the Sunyaev-Zel'dovich effect (SZE). However, the temperatures
of high-temperature clusters, as derived from this analysis, resulted to be
basically higher than the temperatures derived from X-ray measurements, at a
moderate statistical significance of $1.5\sigma$. This discrepancy has been
attributed by Hurier (2016) to calibration issues. In this paper we discuss an
alternative explanation for this discrepancy in terms of a non-thermal SZE
astrophysical component. We find that this explanation can work if non-thermal
electrons in galaxy clusters have a low value of their minimum momentum
($p_1\sim0.5-1$), and if their pressure is of the order of $20-30\%$ of the
thermal gas pressure. Both these conditions are hard to obtain if the
non-thermal electrons are mixed with the hot gas in the intra cluster medium,
but can be possibly obtained if the non-thermal electrons are mainly confined
in bubbles with high content of non-thermal plasma and low content of thermal
plasma, or in giant radio lobes/relics located in the outskirts of clusters. In
order to derive more precise results on the properties of non-thermal electrons
in clusters, and in view of more solid detections of a discrepancy between
X-rays and SZE derived clusters temperatures that cannot be explained in other
ways, it would be necessary to reproduce the full analysis done by Hurier
(2016) by adding systematically the non-thermal component of the SZE. |
Star formation in high redshift galaxies including Supernova feedback:
effect on stellar mass and luminosity functions: We present a semi-analytical model of high redshift galaxy formation. In our
model the star formation inside a galaxy is regulated by the feedback from
supernova (SNe) driven outflows. We derive a closed analytical form for star
formation rate in a single galaxy taking account of the SNe feedback in a
self-consistent manner. We show that our model can explain the observed
correlation between the stellar mass and the circular velocity of galaxies from
dwarf galaxies to massive galaxies of $10^{12} M_\odot$. For small mass dwarf
galaxies additional feedback other than supernova feedback is needed to explain
the spread in the observational data. Our models reproduce the observed 3-D
fundamental correlation between the stellar mass, gas phase metallicity and
star formation rate in galaxies establishing that the SNe feedback plays a
major role in building this relation. Further, the observed UV luminosity
functions of Lyman-Break galaxies (LBGs) are well explained by our feedback
induced star formation model for a vast redshift range of $1.5 \le z \le 8$. In
particular, the flattening of the luminosity functions at the low luminosity
end naturally arises due to our explicit SNe feedback treatment. | Testing Gaussianity in the WMAP data of OT foreground reduced map: A considerable effort has recently gone into the study of Gaussianity of
cosmic microwave background (CMB) data. Among such attempts, there is one with
two non-Gaussianity indicators, proposed by the authors, and used in a search
for significant deviation from Gaussianity in the WMAP internal linear
combination (ILC) and in the single frequency WMAP maps with the KQ75 mask.
Here we extend and complement these results by performing a similar analysis
for the de Oliveira-Costa and Tegmark (OT) WMAP three-year $KQ75$ masked map,
in which the foreground is reduced through a different statistical cleaning
procedure. |
Free Form Lensing Implications for the Collision of Dark Matter and Gas
in the Frontier Fields Cluster MACSJ0416.1-2403: We present a free form mass reconstruction of the massive lensing cluster
MACSJ0416.1-2403 using the latest Hubble Frontier Fields data. Our model
independent method finds that the extended lensing pattern is generated by two
elongated, closely projected clusters of similar mass. Our lens model
identifies new lensed images with which we improve the accuracy of the dark
matter distribution. We find that the bimodal mass distribution is nearly
coincident with the bimodal X-ray emission, but with the two dark matter peaks
lying closer together than the centroids of the X-ray emisison. We show this
can be achieved if the collision has occurred close to the plane and such that
the cores are deflected around each other. The projected mass profiles of both
clusters are well constrained because of the many interior lensed images,
leading to surprisingly flat mass profiles of both components in the region
15-100 kpc. We discuss the extent to which this may be generated by tidal
forces in our dynamical model which are large during an encounter of this type
as the cores "graze" each other. The relative velocity between the two cores is
estimated to be about 1200 km/s and mostly along the line of sight so that our
model is consistent with the relative redshift difference between the two cD
galaxies (dz = 0.04). | A hybrid model for the evolution of galaxies and Active Galactic Nuclei
in the infrared: [Abridged] We present a comprehensive investigation of the cosmological
evolution of the luminosity function (LF) of galaxies and active galactic
nuclei (AGN) in the infrared (IR). Based on the observed dichotomy in the ages
of stellar populations of early-type galaxies on one side and late-type
galaxies on the other, the model interprets the epoch-dependent LFs at z \geq
1.5 using a physical model for the evolution of proto-spheroidal galaxies and
of the associated AGNs, while IR galaxies at z<1.5 are interpreted as being
mostly late-type 'cold' (normal) and 'warm' (starburst) galaxies. As for
proto-spheroids, in addition to the epoch-dependent LFs of stellar and AGN
components separately, we have worked out the evolving LFs of these objects as
a whole (stellar plus AGN component). The model provides a physical explanation
for the observed positive evolution of both galaxies and AGNs up to z \simeq
2.5 and for the negative evolution at higher redshifts, for the sharp
transition from Euclidean to extremely steep counts at (sub-)mm wavelengths, as
well as the (sub-)mm counts of strongly lensed galaxies, that are hard to
account for by alternative, physical or phenomenological, approaches. The
evolution of late-type galaxies and of z<1.5 AGNs is described using a
parametric phenomenological approach. The modeled AGN contributions to the
counts and to the cosmic infrared background (CIB) are always subdominant with
maximal at mid-IR wavelengths. The model provides a good fit to the
multi-wavelength (from the mid-IR to millimeter waves) data on LFs at different
redshifts and on number counts (both global and per redshift slices). A
prediction of the present model is a systematic variation with wavelength of
the populations dominating the counts and the contributions to the CIB
intensity. The implied specific trend for cross-wavelength CIB power spectra is
found to be in good agreement with the data. |
Clumpy accretion onto black holes. I. Clumpy-ADAF structure and
radiation: In this paper, we investigate the dynamics of clumps embedded in and confined
by the advection-dominated accretion flows (ADAF), in which collisions among
the clumps are neglected. We start from the collisionless Boltzmann equation
and assume that interaction between the clumps and the ADAF is responsible for
transporting angular momentum of clumps outward. The inner edge of the
clumpy-ADAF is set to be the tidal radius of the clumps. We consider strong and
weak coupling cases, in which the averaged properties of clumps follow the ADAF
dynamics and mainly determined by the black hole potential, respectively. We
get the analytical solution of the dynamics of clumps for the two cases. The
velocity dispersion of clumps is one magnitude higher than the ADAF for the
strong coupling case. For the weak coupling case, we find that the mean radial
velocity of clumps is linearly proportional to the coefficient of the drag
force. We show that the tidally disrupted clumps would lead to accumulation of
the debris to form a debris disk in the Shakura-Sunyaev regime. The entire hot
ADAF will be efficiently cooled down by photons from the debris disk, giving
rise to collapse of the ADAF and quench the clumpy accretion. Subsequently,
evaporation of the collapsed ADAF drives resuscitate of a new clumpy-ADAF,
resulting in an oscillation of the global clumpy-ADAF. Applications of the
present model are briefly discussed to X-ray binaries, ionization nuclear
emission regions (LINERs) and BL Lac objects. | Primordial Black Holes as Dark Matter: Constraints From Compact
Ultra-Faint Dwarfs: The ground-breaking detections of gravitational waves from black hole mergers
by LIGO have rekindled interest in primordial black holes (PBHs) and the
possibility of dark matter being composed of PBHs. It has been suggested that
PBHs of tens of solar masses could serve as dark matter candidates. Recent
analytical studies demonstrated that compact ultra-faint dwarf galaxies can
serve as a sensitive test for the PBH dark matter hypothesis, since stars in
such a halo-dominated system would be heated by the more massive PBHs, their
present-day distribution can provide strong constraints on PBH mass. In this
study, we further explore this scenario with more detailed calculations, using
a combination of dynamical simulations and Bayesian inference methods. The
joint evolution of stars and PBH dark matter is followed with a Fokker-Planck
code PhaseFlow. We run a large suite of such simulations for different dark
matter parameters, then use a Markov Chain Monte Carlo approach to constrain
the PBH properties with observations of ultra-faint galaxies. We find that
two-body relaxation between the stars and PBH drives up the stellar core size,
and increases the central stellar velocity dispersion. Using the observed
half-light radius and velocity dispersion of stars in the compact ultra-faint
dwarf galaxies as joint constraints, we infer that these dwarfs may have a
cored dark matter halo with the central density in the range of 1-2
$\rm{M_{\odot}/pc^3}$, and that the PBHs may have a mass range of 2-14
$\rm{M_{\odot}}$ if they constitute all or a substantial fraction of the dark
matter. |
Testing the coupling of dark radiations in light of the Hubble tension: Self-interacting dark radiations (SIdr) can have significant implications in
the evolution of the universe, affecting the cosmic microwave background (CMB)
and the clustering of large-scale structures. In this work, we analyze the
implications of SIdr on the CMB power spectrum and explore its potential in
resolving the Hubble tension. SIdr exhibits two distinct behaviors based on the
interacting strength: strongly self-coupled and medium self-coupled. These
behaviors are evident in the analysis of CMB data. According to Planck data,
the dark radiation component consists of both free-streaming neutrinos and
possible SIdr. The total contribution from these components yields relativistic
species with $N_{\rm eff}=3.046$. In the framework of universal coupling
between dark radiations, a consistent value of $N_{\rm
eff}=3.27_{-0.31}^{+0.23}$ is obtained. Additionally, this coupling results in
an increase in the Hubble constant ($H_0$) to $70.1_{-1.6}^{+1.3},
\text{km/s/Mpc}$. However, when considering the number of free-streaming
neutrinos as a parameter, the existence of SIdr is not supported. This makes
its fraction in radiation to be $R_x=0.047^{+0.025}_{-0.053}$. Although the
Hubble constant is still enhanced, it comes at the expense of a higher $N_{\rm
eff}=3.52\pm0.25$. Our findings reveal that the ACT and SPT data provide
support for the presence of SIdr, particularly when considering a variable
number of free-streaming species. In this case, SIdr accounts for approximately
12.7\% of the total radiation content. However, it is important to note that
relying solely on SIdr is insufficient to completely resolve the Hubble
tension. Finally, we investigate the constraints on SIdr imposed by future
experiments, which improve the limits on scaled interacting strength
$\log_{10}\tilde G_{\rm eff}$ by a factor of 4.5 compared to the current
constraints. | Chern-Simons anomaly as polarization effect: The parity violating Chern-Simons term in the epoch before the electroweak
phase transition can be interpreted as a polarization effect associated to
massless right-handed electrons (positrons) in the presence of a large-scale
seed hypermagnetic field. We reconfirm the viability of a unified seed field
scenario relating the cosmological baryon asymmetry and the origin of the
protogalactic large-scale magnetic fields observed in astronomy. |
Density profile, velocity anisotropy and line-of-sight external
convergence of SLACS gravitational lenses: Data from 58 strong-lensing events surveyed by the Sloan Lens ACS Survey are
used to estimate the projected galaxy mass inside their Einstein radii by two
independent methods: stellar dynamics and strong gravitational lensing. We
perform a joint analysis of these two estimates inside models with up to three
degrees of freedom with respect to the lens density profile, stellar velocity
anisotropy, and line-of-sight (LOS) external convergence, which incorporates
the effect of the large-scale structure on strong lensing. A Bayesian analysis
is employed to estimate the model parameters, evaluate their significance and
compare models. We find that the data favor Jaffe's light profile over
Hernquist's, but that any particular choice between these two does not change
the qualitative conclusions with respect to the features of the system that we
investigate. The density profile is compatible with an isothermal, being
sightly steeper and having an uncertainty in the logarithmic slope of the order
of 5% in models that take into account a prior ignorance on anisotropy and
external convergence. We identify a considerable degeneracy between the density
profile slope and the anisotropy parameter, which largely increases the
uncertainties in the estimates of these parameters, but we encounter no
evidence in favor of an anisotropic velocity distribution on average for the
whole sample. An LOS external convergence following a prior probability
distribution given by cosmology has a small effect on the estimation of the
lens density profile, but can increase the dispersion of its value by nearly
40%. | The red halos of SDSS low surface brightness disk galaxies: The faint stellar halos of galaxies contain key information about the oldest
stars and the process of galaxy formation. A previous study of stacked SDSS
images of disk galaxies has revealed a halo with an abnormally red r-i colour,
seemingly inconsistent with our current understanding of stellar halos. Here,
we investigate the statistical properties of the faint envelopes of low surface
brightness disk galaxies to look for further support for a red excess. 1510
edge-on low surface brightness galaxies were selected from the SDSS Data
Release 5, rescaled to the same apparent size, aligned and stacked. This
procedure allows us to reach a surface brightness of mu_g ~ 31 mag arcsec^-2.
After a careful assessment of instrumental light scattering effects, we derive
median and average radial surface brightness and colour profiles in g,r and i.
The sample is then divided into 3 subsamples according to g-r colour. All three
samples exhibit a red colour excess in r-i in the thick disk/halo region. The
halo colours of the full sample, g-r = 0.60+-0.15 and r-i = 0.80+-0.15, are
found to be incompatible with the colours of any normal type of stellar
population. The fact that no similar colour anomaly is seen at comparable
surface brightness levels along the disk rules out a sky subtraction residual
as the source of the extreme colours. A number of possible explanations for
these abnormally red halos are discussed. We find that two different scenarios
-- dust extinction of extragalactic background light and a stellar population
with a very bottom-heavy initial mass function -- appear to be broadly
consistent with our observations and with similar red excesses reported in the
halos of other types of galaxies. |
The Dark Energy Survey Supernova Program: Cosmological Biases from Host
Galaxy Mismatch of Type Ia Supernovae: Redshift measurements, primarily obtained from host galaxies, are essential
for inferring cosmological parameters from type Ia supernovae (SNe Ia).
Matching SNe to host galaxies using images is non-trivial, resulting in a
subset of SNe with mismatched hosts and thus incorrect redshifts. We evaluate
the host galaxy mismatch rate and resulting biases on cosmological parameters
from simulations modeled after the Dark Energy Survey 5-Year (DES-SN5YR)
photometric sample. For both DES-SN5YR data and simulations, we employ the
directional light radius method for host galaxy matching. In our SN Ia
simulations, we find that 1.7% of SNe are matched to the wrong host galaxy,
with redshift difference between the true and matched host of up to 0.6. Using
our analysis pipeline, we determine the shift in the dark energy equation of
state parameter (Dw) due to including SNe with incorrect host galaxy matches.
For SN Ia-only simulations, we find Dw = 0.0013 +/- 0.0026 with constraints
from the cosmic microwave background (CMB). Including core-collapse SNe and
peculiar SNe Ia in the simulation, we find that Dw ranges from 0.0009 to 0.0032
depending on the photometric classifier used. This bias is an order of
magnitude smaller than the expected total uncertainty on w from the DES-SN5YR
sample of around 0.03. We conclude that the bias on w from host galaxy mismatch
is much smaller than the uncertainties expected from the DES-SN5YR sample, but
we encourage further studies to reduce this bias through better host-matching
algorithms or selection cuts. | Planck CMB Anomalies: Astrophysical and Cosmological Secondary Effects
and the Curse of Masking: Large-scale anomalies have been reported in CMB data with both WMAP and
Planck data. These could be due to foreground residuals and or systematic
effects, though their confirmation with Planck data suggests they are not due
to a problem in the WMAP or Planck pipelines. If these anomalies are in fact
primordial, then understanding their origin is fundamental to either validate
the standard model of cosmology or to explore new physics. We investigate three
other possible issues: 1) the trade-off between minimising systematics due to
foreground contamination (with a conservative mask) and minimising systematics
due to masking, 2) astrophysical secondary effects (the kinetic Doppler
quadrupole and kinetic Sunyaev-Zel'dovich effect), and 3) secondary
cosmological signals (the integrated Sachs-Wolfe effect). We address the
masking issue by considering new procedures that use both WMAP and Planck to
produce higher quality full-sky maps using the sparsity methodology (LGMCA
maps). We show the impact of masking is dominant over that of residual
foregrounds, and the LGMCA full-sky maps can be used without further processing
to study anomalies. We consider four official Planck PR1 and two LGMCA CMB
maps. Analysis of the observed CMB maps shows that only the low quadrupole and
quadrupole-octopole alignment seem significant, but that the planar octopole,
Axis of Evil, mirror parity and cold spot are not significant in nearly all
maps considered. After subtraction of astrophysical and cosmological secondary
effects, only the low quadrupole may still be considered anomalous, meaning the
significance of only one anomaly is affected by secondary effect subtraction
out of six anomalies considered. In the spirit of reproducible research all
reconstructed maps and codes will be made available for download here
http://www.cosmostat.org/anomaliesCMB.html. |
Stars quenching stars: how photoionization by local sources regulates
gas cooling and galaxy formation: Current models of galaxy formation lack an efficient and physically
constrained mechanism to regulate star formation (SF) in low and intermediate
mass galaxies. We argue that the missing ingredient could be the effect of
photoionization by local sources on the gas cooling. We show that the soft
X-ray and EUV flux generated by SF is able to efficiently remove the main
coolants (e.g., HeII, OV and FeIX) from the halo gas via direct
photoionization. As a consequence, the cooling and accretion time of the gas
surrounding star-forming galaxies may increase by one or two orders of
magnitude. For a given halo mass and redshift, the effect is directly related
to the value of the star formation rate (SFR). Our results suggest the
existence of a critical SFR above which "cold" mode accretion is stopped, even
for haloes with virial masses well below the critical shock-heating mass
suggested by previous studies.The evolution of the critical SFR with redshift,
for a given halo mass, resembles the respective steep evolution of the observed
SFR for z<1. This suggests that photoionization by local sources would be able
to regulate gas accretion and star formation, without the need for additional,
strong feedback processes. | Imprint of DES super-structures on the Cosmic Microwave Background: Small temperature anisotropies in the Cosmic Microwave Background can be
sourced by density perturbations via the late-time integrated Sachs-Wolfe
effect. Large voids and superclusters are excellent environments to make a
localized measurement of this tiny imprint. In some cases excess signals have
been reported. We probed these claims with an independent data set, using the
first year data of the Dark Energy Survey in a different footprint, and using a
different super-structure finding strategy. We identified 52 large voids and
102 superclusters at redshifts $0.2 < z < 0.65$. We used the Jubilee simulation
to a priori evaluate the optimal ISW measurement configuration for our
compensated top-hat filtering technique, and then performed a stacking
measurement of the CMB temperature field based on the DES data. For optimal
configurations, we detected a cumulative cold imprint of voids with $\Delta
T_{f} \approx -5.0\pm3.7~\mu K$ and a hot imprint of superclusters $\Delta
T_{f} \approx 5.1\pm3.2~\mu K$ ; this is $\sim1.2\sigma$ higher than the
expected $|\Delta T_{f}| \approx 0.6~\mu K$ imprint of such super-structures in
$\Lambda$CDM. If we instead use an a posteriori selected filter size
($R/R_{v}=0.6$), we can find a temperature decrement as large as $\Delta T_{f}
\approx -9.8\pm4.7~\mu K$ for voids, which is $\sim2\sigma$ above $\Lambda$CDM
expectations and is comparable to previous measurements made using SDSS
super-structure data. |
The ATLAS$^{\rm{3D}}$ project - XXV: Two-dimensional kinematic analysis
of simulated galaxies and the cosmological origin of fast and slow rotators: We present a detailed two-dimensional stellar dynamical analysis of a sample
of 44 cosmological hydrodynamical simulations of individual central galaxies
and their satellites. Kinematic maps of the stellar line-of-sight velocity,
velocity dispersion, and higher-order Gauss-Hermite moments $h_3$ and $h_4$ are
constructed for each central galaxy and for the most massive satellites. The
amount of rotation is quantified using the $\lambda_{\mathrm{R}}$-parameter.
The velocity, velocity dispersion, $h_3$, and $h_4$ fields of the simulated
galaxies show a diversity similar to observed kinematic maps of early-type
galaxies in the ATLAS$^{\rm{3D}}$ survey. This includes fast (regular), slow,
and misaligned rotation, hot spheroids with embedded cold disk components as
well as galaxies with counter-rotating cores or central depressions in the
velocity dispersion. We link the present day kinematic properties to the
individual cosmological formation histories of the galaxies. In general, major
galaxy mergers have a significant influence on the rotation properties
resulting in both a spin-down as well as a spin-up of the merger remnant. Lower
mass galaxies with significant in-situ formation of stars, or with additional
gas-rich major mergers - resulting in a spin-up - in their formation history,
form elongated fast rotators with a clear anti-correlation of $h_3$ and
$v/\sigma$. An additional formation path for fast rotators includes gas poor
major mergers leading to a spin-up of the remnants. This formation path does
not result in anti-correlated $h_3$ and $v/\sigma$. The galaxies most
consistent with the rare class of non-rotating round early-type galaxies grow
by gas-poor minor mergers alone. In general, more massive galaxies have less
in-situ star formation since $z \sim 2$, rotate slower and have older stellar
populations. (shortened) | Statistical modelling of the cosmological dispersion measure: We have investigated the basic statistics of the cosmological dispersion
measure (DM) -- such as its mean, variance, probability distribution, angular
power spectrum and correlation function -- using the state-of-the-art
hydrodynamic simulations, IllustrisTNG300, for the fast radio burst (FRB)
cosmology. To model the DM statistics, we first measured the free-electron
abundance and the power spectrum of its spatial fluctuations. The free-electron
power spectrum turns out to be consistent with the dark matter power spectrum
at large scales, but it is strongly damped at small scales ($\lesssim 1$Mpc)
owing to the stellar and active galactic nucleus feedback. The free-electron
power spectrum is well modelled using a scale-dependent bias factor (the ratio
of its fluctuation amplitude to that of the dark matter). We provide analytical
fitting functions for the free-electron abundance and its bias factor. We next
constructed mock sky maps of the DM by performing standard ray-tracing
simulations with the TNG300 data. The DM statistics are calculated analytically
from the fitting functions of the free-electron distribution, which agree well
with the simulation results measured from the mock maps. We have also obtained
the probability distribution of source redshift for a given DM, which helps in
identifying the host galaxies of FRBs from the measured DMs. The angular
two-point correlation function of the DM is described by a simple power law,
$\xi(\theta) \approx 2400 (\theta/{\rm deg})^{-1} \, {\rm pc}^2 \, {\rm
cm}^{-6}$, which we anticipate will be confirmed by future observations when
thousands of FRBs are available. |
Can 21-cm observations discriminate between high-mass and low-mass
galaxies as reionization sources?: The prospect of detecting the first galaxies by observing their impact on the
intergalactic medium as they reionized it during the first billion years leads
us to ask whether such indirect observations are capable of diagnosing which
types of galaxies were most responsible for reionization. We attempt to answer
this by considering a set of large-scale radiative transfer simulations of
reionization in sufficiently large volumes to make statistically meaningful
predictions of observable signatures, while also directly resolving all
atomically-cooling halos down to 10^8 M_solar. We focus here on predictions of
the 21-cm background, to see if upcoming observations are capable of
distinguishing a universe ionized primarily by high-mass halos from one in
which both high-mass and low-mass halos are responsible, and to see how these
results depend upon the uncertain source efficiencies. We find that 21-cm
fluctuation power spectra observed by the first generation EoR/21-cm radio
interferometer arrays should be able to distinguish the case of reionization by
high-mass halos alone from that by both high- and low-mass halos, together.
Some reionization scenarios yield very similar power spectra and rms evolution
and thus can only be discriminated by their different mean reionization history
and 21-cm PDF distributions. We find that the skewness of the 21-cm PDF
distribution smoothed over LOFAR-like window shows a clear feature correlated
with the rise of the rms due to patchiness. Measurements of the mean
photoionization rates are sensitive to the average density of the regions being
studied and therefore could be strongly skewed in certain cases. (abridged) | Condensation of Galactic Cold Dark Matter: We consider the steady-state regime describing the density profile of a dark
matter halo, if dark matter is treated as a Bose-Einstein condensate. We first
solve the fluid equation for "canonical" cold dark matter, obtaining a class of
density profiles which includes the Navarro-Frenk-White profile, and which
diverge at the halo core. We then solve numerically the equation obtained when
an additional "quantum pressure" term is included in the computation of the
density profile. The solution to this latter case is finite at the halo core,
possibly avoiding the "cuspy halo problem" present in some cold dark matter
theories. Within the model proposed, we predict the mass of the cold dark
matter particle to be of the order of M_chi c2 = 10^-24 eV, which is of the
same order of magnitude as that predicted in ultra-light scalar cold dark
matter models. Finally, we derive the differential equation describing
perturbations in the density and the pressure of the dark matter fluid. |
Weak Lensing Observables in the Halo Model: The halo model (HM) describes the inhomogeneous universe as a collection of
halos. The full nonlinear power spectrum of the universe is well approximated
by the HM, whose prediction can be easily computed without lengthy numerical
simulations. This makes the HM a useful tool in cosmology. Here we explore the
lensing properties of the HM by use of the stochastic gravitational lensing
(sGL) method. We obtain for the case of point sources exact and simple integral
expressions for the expected value and variance of the lensing convergence,
which encode detailed information about the internal halo properties. In
particular a wide array of observational biases can be easily incorporated and
the dependence of lensing on cosmology is properly taken into account. This
simple setup should be useful for a quick calculation of the power spectrum and
the related lensing observables, which can play an important role in the
extraction of cosmological parameters from, e.g., SNe observations. Finally, we
discuss the probability distribution function of the HM which encodes more
information than the first two moments and can more strongly constrain the
large-scale structures of the universe. To check the accuracy of our modelling
we compare our predictions to the results from the Millennium Simulation. | Planck 2015 results. XVIII. Background geometry & topology: Full-sky CMB maps from the 2015 Planck release allow us to detect departures
from global isotropy on the largest scales. We present the first searches using
CMB polarization for correlations induced by a non-trivial topology with a
fundamental domain intersecting, or nearly intersecting, the last scattering
surface (at comoving distance $\chi_{rec}$). We specialize to flat spaces with
toroidal and slab topologies, finding that explicit searches for the latter are
sensitive to other topologies with antipodal symmetry. These searches yield no
detection of a compact topology at a scale below the diameter of the last
scattering surface. The limits on the radius $R_i$ of the largest sphere
inscribed in the topological domain (at log-likelihood-ratio $\Delta\ln{L}>-5$
relative to a simply-connected flat Planck best-fit model) are
$R_i>0.97\chi_{rec}$ for the cubic torus and $R_i>0.56\chi_{rec}$ for the slab.
The limit for the cubic torus from the matched-circles search is numerically
equivalent, $R_i>0.97\chi_{rec}$ (99% CL) from polarisation data alone. We also
perform a Bayesian search for a Bianchi VII$_h$ geometry. In the non-physical
setting where the Bianchi cosmology is decoupled from the standard cosmology,
Planck temperature data favour the inclusion of a Bianchi component. However,
the cosmological parameters generating this pattern are in strong disagreement
with those found from CMB anisotropy data alone. Fitting the induced
polarization pattern for this model to Planck data requires an amplitude of
$-0.1\pm0.04$ compared to +1 if the model were to be correct. In the physical
setting where the Bianchi parameters are fit simultaneously with the standard
cosmological parameters, we find no evidence for a Bianchi VII$_h$ cosmology
and constrain the vorticity of such models to $(\omega/H)_0<7.6\times10^{-10}$
(95% CL). [Abridged] |
A theoretical view on the T-web statistical description of the cosmic
web: The classification of the cosmic web into different environments is both a
tool to study in more detail the formation of halos and galaxies via the link
between their properties and the large-scale environment and as a class of
objects whose statistics contain cosmological information. In this paper, we
present an analytical framework to compute the probability of the different
environments in the cosmic web based on the T-web formalism that classifies
structures in four different classes (voids, walls, filaments, knots) by
studying the eigenvalues of the tidal tensor (Hessian of the gravitational
potential). This method relies on studying the eigenvalues of the tidal tensor
with respect to a given threshold and thus requires the knowledge of the JPDF
of those eigenvalues. We perform a change of variables in terms of minimally
correlated rotational invariants and we study their distribution in the linear
regime of structure formation, and in the quasi-linear regime with the help of
a Gram-Charlier expansion and tree-order Eulerian perturbation theory. This
expansion allows us to predict the probability of the different environments in
the density field at a given smoothing scale as a function of the chosen
threshold and redshift. We check the validity of our predictions by comparing
those predictions to measurements made in the N-body Quijote simulations. We
notably find that scaling the threshold value with the non-linear amplitude of
fluctuations allows us to capture almost entirely the redshift evolution of the
probability of the environments, even if we assume that the density field is
Gaussian (corresponding to the linear regime of structure formation). We also
show that adding mild non-Gaussian corrections in the form of third-order
cumulants of the field provides even more precise predictions for cosmic web
abundances up to scales as small as ~5 Mpc/h and redshifts down to z~0. | Constraints on Self-Interacting dark matter from relaxed galaxy groups: Self-interacting dark matter (SIDM) has been proposed as an alternative to
the standard collisionless cold dark matter to explain the diversity of
galactic rotation curves and core-cusp problems seen at small scales. Here, we
estimate the constraints on SIDM for a sample of 11 relaxed galaxy groups with
X-ray observations from Chandra and XMM-Newton. We fit the dark matter density
distribution to the Einasto profile and use the estimated Einasto $\alpha$
parameter to constrain the SIDM cross-section, based on the empirical relation
between the two, which was obtained in Eckert et al (2022). We obtain a
non-zero central estimate for the cross-section per unit mass ($\sigma/m$) for
seven groups, with the most precise estimate obtained for NGC 5044, given by
$\sigma/m=0.165 \pm 0.025~\rm{cm^2/g}$, for dark matter velocity dispersion of
about 300 km/sec. For the remaining four groups, we obtain 95% c.l. upper
limits on $\sigma/m < 0.16-6.61~\rm{cm^2/g}$ with dark matter velocity
dispersions between 200-500 km/sec, with the most stringent limit for our
sample obtained for the group MKW 4, given by $\sigma/m< 0.16~\rm{cm^2/g}$ for
dark matter velocity dispersion of about 350 km/sec. |
Testing anthropic reasoning for the cosmological constant with a
realistic galaxy formation model: The anthropic principle is one of the possible explanations for the
cosmological constant ($\Lambda$) problem. In previous studies, a dark halo
mass threshold comparable with our Galaxy must be assumed in galaxy formation
to get a reasonably large probability of finding the observed small value,
$P(<$$\Lambda_{\rm obs})$, though stars are found in much smaller galaxies as
well. Here we examine the anthropic argument by using a semi-analytic model of
cosmological galaxy formation, which can reproduce many observations such as
galaxy luminosity functions. We calculate the probability distribution of
$\Lambda$ by running the model code for a wide range of $\Lambda$, while other
cosmological parameters and model parameters for baryonic processes of galaxy
formation are kept constant. Assuming that the prior probability distribution
is flat per unit $\Lambda$, and that the number of observers is proportional to
stellar mass, we find $P(<$$\Lambda_{\rm obs}) = 6.7 \%$ without introducing
any galaxy mass threshold. We also investigate the effect of metallicity; we
find $P(<$$\Lambda_{\rm obs}) = 9.0 \%$ if observers exist only in galaxies
whose metallicity is higher than the solar abundance. If the number of
observers is proportional to metallicity, we find $P(<$$\Lambda_{\rm obs}) =
9.7 \%$. Since these probabilities are not extremely small, we conclude that
the anthropic argument is a viable explanation, if the value of $\Lambda$
observed in our universe is determined by a probability distribution. | Evolution of star clusters in a cosmological tidal field: We present a method to couple N-body star cluster simulations to a
cosmological tidal field, using the Astrophysical Multipurpose Software
Environment. We apply this method to star clusters embedded in the CosmoGrid
dark matter-only LambdaCDM simulation. Our star clusters are born at z = 10
(corresponding to an age of the Universe of about 500 Myr) by selecting a dark
matter particle and initializing a star cluster with 32,000 stars on its
location. We then follow the dynamical evolution of the star cluster within the
cosmological environment.
We compare the evolution of star clusters in two Milky-Way size haloes with a
different accretion history. The mass loss of the star clusters is continuous
irrespective of the tidal history of the host halo, but major merger events
tend to increase the rate of mass loss. From the selected two dark matter
haloes, the halo that experienced the larger number of mergers tends to drive a
smaller mass loss rate from the embedded star clusters, even though the final
masses of both haloes are similar. We identify two families of star clusters:
native clusters, which become part of the main halo before its final major
merger event, and the immigrant clusters, which are accreted upon or after this
event; native clusters tend to evaporate more quickly than immigrant clusters.
Accounting for the evolution of the dark matter halo causes immigrant star
clusters to retain more mass than when the z=0 tidal field is taken as a static
potential. The reason for this is the weaker tidal field experienced by
immigrant star clusters before merging with the larger dark matter halo. |
The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave
Background Power Spectra at 98 and 150 GHz: We present the temperature and polarization angular power spectra of the CMB
measured by the Atacama Cosmology Telescope (ACT) from 5400 deg$^2$ of the
2013-2016 survey, which covers $>$15000 deg$^2$ at 98 and 150 GHz. For this
analysis we adopt a blinding strategy to help avoid confirmation bias and,
related to this, show numerous checks for systematic error done before
unblinding. Using the likelihood for the cosmological analysis we constrain
secondary sources of anisotropy and foreground emission, and derive a
"CMB-only" spectrum that extends to $\ell=4000$. At large angular scales,
foreground emission at 150 GHz is $\sim$1% of TT and EE within our selected
regions and consistent with that found by Planck. Using the same likelihood, we
obtain the cosmological parameters for $\Lambda$CDM for the ACT data alone with
a prior on the optical depth of $\tau=0.065\pm0.015$. $\Lambda$CDM is a good
fit. The best-fit model has a reduced $\chi^2$ of 1.07 (PTE=0.07) with
$H_0=67.9\pm1.5$ km/s/Mpc. We show that the lensing BB signal is consistent
with $\Lambda$CDM and limit the celestial EB polarization angle to $\psi_P
=-0.07^{\circ}\pm0.09^{\circ}$. We directly cross correlate ACT with Planck and
observe generally good agreement but with some discrepancies in TE. All data on
which this analysis is based will be publicly released. | Probing $Λ$CDM cosmology with the Evolutionary Map of the Universe
survey: The Evolutionary Map of the Universe (EMU) is an all-sky survey in
radio-continuum which uses the Australian SKA Pathfinder (ASKAP). Using galaxy
angular power spectrum and the integrated Sachs-Wolfe effect, we study the
potential of EMU to constrain models beyond $\Lambda$CDM (i.e., local
primordial non-Gaussianity, dynamical dark energy, spatial curvature and
deviations from general relativity), for different design sensitivities. We
also include a multi-tracer analysis, distinguishing between star-forming
galaxies and galaxies with an active galactic nucleus, to further improve EMU's
potential. We find that EMU could measure the dark energy equation of state
parameters around 35\% more precisely than existing constraints, and that the
constraints on $f_{\rm NL}$ and modified gravity parameters will improve up to
a factor $\sim2$ with respect to Planck and redshift space distortions
measurements. With this work we demonstrate the promising potential of EMU to
contribute to our understanding of the Universe. |
I-ball formation with logarithmic potential: A coherently oscillating real scalar field with potential shallower than
quadratic one fragments into spherical objects called I-balls. We study the
I-ball formation for logarithmic potential which appears in many cosmological
models. We perform lattice simulations and find that the I-balls are formed
when the potential becomes dominated by the quadratic term. Furthermore, we
estimate the I-ball profile assuming that the adiabatic invariant is conserved
during formation and obtain the result that agrees to the numerical
simulations. | Galaxy cluster photons alter the ionisation state of the nearby warm-hot
intergalactic medium: The physical properties of the faint and extremely tenuous plasma in the far
outskirts of galaxy clusters, the circumgalactic media of normal galaxies, and
filaments of the cosmic web, remain one of the biggest unknowns in our story of
large-scale structure evolution. Modelling the spectral features due to
emission and absorption from this very diffuse plasma poses a challenge, as
both collisional and photo-ionisation processes must be accounted for. In this
paper, we study the ionisation by photons emitted by the intra-cluster medium
in addition to the photo-ionisation by the cosmic UV/X-ray background on gas in
the vicinity of galaxy clusters. For near massive clusters such as A2029, the
ionisation parameter can no longer describe the ionisation balance uniquely.
The ionisation fractions (in particular of C IV, C V, C VI, N VII, O VI, O VII,
O VIII, Ne VIII, Ne IX, and Fe XVII) obtained by taking into account the
photoionisation by the cosmic background are either an upper or lower limit to
the ionisation fraction calculated as a function of distance from the emission
from the cluster. Using a toy model of a cosmic web filament, we predict how
the cluster illumination changes the column densities for two different
orientations of the line of sight. For lines of sight passing close to the
cluster outskirts, O VI can be suppressed by a factor of up to $4.5$, O VII by
a factor of $2.2$, C V by a factor of $3$, and Ne VIII can be boosted by a
factor of $2$, for low density gas. |
Parity-Violating Trispectrum from Chern-Simons Gravity: We show that dynamical Chern-Simons (dCS) gravity imprints a parity-violating
signal in primordial scalar perturbations. Specifically, we find that, after
dCS amplifies one graviton helicity due to a tachyonic instability, the
graviton-mediated correlation between two pairs of scalars develops a
parity-odd component. This correlation, the primordial scalar trispectrum, is
then transferred to the corresponding curvature correlator and thus is
imprinted in both LSS and the CMB. We find that the parity-odd piece has
roughly the same amplitude as its parity-even counterpart, scaled linearly by
the degree of gravitational circular polarization $\Pi_{\rm circ} \sim
\sqrt{\varepsilon}[H^2/(M_{\rm Pl} f)] \leq 1$, with $\varepsilon$ the
slow-roll parameter, $H$ the inflationary Hubble scale, $f$ the dCS decay
constant, and the upper bound saturated for purely circularly-polarized
gravitons. We also find that, in the collapsed limit, the ratio of the two
trispectra contains direct information about the graviton's spin. In models
beyond standard inflationary dCS, e.g. those with multiple scalar fields or
superluminal scalar sound speed, there can be a large enhancement factor $F
\gtrsim 10^6$ to the trispectrum. We find that an LSS survey that contains
$N_{\rm modes}$ linear modes would place an $n\sigma$ constraint on $\Pi_{\rm
circ}r$ of $\sim 0.04\ (n/3)(10^6/F)(10^6/N_{\rm modes})^{1/2}$ from the
parity-odd galaxy trispectrum, for tensor-to-scalar ratio $r$. We also forecast
for several spectroscopic and 21-cm surveys. This constraint implies that, for
high-scale single-field inflation parameters, LSS can probe very large dCS
decay constants $f \lesssim 4\times 10^9\ {\rm GeV}(3/n)(F/10^6)\left(N_{\rm
modes}/10^6\right)^{1/2}$. Our result is the first example of a massless
particle yielding a parity-odd scalar trispectrum through spin-exchange. | A Redshift Dependent Color-Luminosity Relation in Type 1a Supernovae: Type 1a supernova magnitudes are used to fit cosmological parameters under
the assumption the model will fit the observed redshift dependence. We test
this assumption with the Union 2.1 compilation of 580 sources. Several
independent tests find the existing model fails to account for a significant
correlation of supernova color and redshift. The correlation of magnitude
residuals relative to the $\Lambda CDM$ model and $color \times redshift$ has a
significance equivalent to 13 standard deviations, as evaluated by randomly
shuffling the data. Extending the existing $B-V$ color correction to a relation
linear in redshift improves the goodness of fit $\chi^{2}$ by more than 50
units, an equivalent 7-$\sigma$ significance, while adding only one parameter.
The $color-redshift$ correlation is quite robust, cannot be attributed to
outliers, and passes several tests of consistency. We review previous hints of
redshift dependence in color parameters found in bin-by-bin fits interpreted as
parameter bias. We show that neither the bias nor the change $\Delta \chi^{2}$
of our study can be explained by those effects. The previously known relation
that bluer supernovae have larger absolute luminosity tends to empirically
flatten out with increasing redshift. The best-fit cosmological dark energy
density parameter is revised from $ \Omega_{\Lambda} =0.71 \pm 0.02$ to $
\Omega_{\Lambda} = 0.74 \pm 0.02$ assuming a flat universe. One possible
physical interpretation is that supernovae or their environments evolve
significantly with increasing redshift. |
Statistics of Thawing K-essence Dark Energy Models: K-essence is a minimally-coupled scalar field whose Lagrangian density
$\mathcal{L}$ is a function of the field value $\phi$ and the kinetic energy
$X=\frac{1}{2}\partial_\mu\phi\partial^\mu\phi$. In the thawing scenario, the
scalar field is frozen by the large Hubble friction in the early universe, and
therefore initial conditions are specified. We construct thawing k-essence
models by generating Taylor expansion coefficients of $\mathcal{L}(\phi, X)$
from random matrices. From the ensemble of randomly generated thawing k-essence
models, we select dark energy candidates by assuming negative pressure and
non-growth of sub-horizon inhomogeneities. For each candidate model the dark
energy equation of state function is fit to the Chevallier-Polarski-Linder
parameterization $w(a) \approx w_0+w_a(1-a)$, where $a$ is the scale factor.
The thawing k-essence dark models distribute very non-uniformly in the $(w_0,
w_a)$ space. About 90\% models cluster in a narrow band in the proximity of a
slow-roll line $w_a\approx -1.42
\left(\frac{\Omega_m}{0.3}\right)^{0.64}(1+w_0)$, where $\Omega_m$ is the
present matter density fraction. This work is a proof of concept that for a
certain class of models very non-uniform theoretical prior on $(w_0, w_a)$ can
be obtained to improve the statistics of model selection. | Galaxy Dynamics: Secular Evolution and Accretion: Recent results are reviewed on galaxy dynamics, bar evolution, destruction
and re-formation, cold gas accretion, gas radial flows and AGN fueling, minor
mergers. Some problems of galaxy evolution are discussed in particular,
exchange of angular momentum, radial migration through resonant scattering, and
consequences on abundance gradients, the frequency of bulgeless galaxies, and
the relative role of secular evolution and hierarchical formation. |
Weak-lensing $B$-modes as a probe of the isotropy of the universe: We compute the angular power spectrum of the $B$-modes of the weak-lensing
shear in a spatially anisotropic spacetime. We find that there must also exist
off-diagonal correlations between the $E$-modes, $B$-modes, and convergence
that allow one to reconstruct the eigendirections of expansion. Focusing on
future surveys such as Euclid and SKA, we show that observations can constrain
the geometrical shear in units of the Hubble rate at the percent level, or even
better, offering a new and powerful method to probe our cosmological model. | The SDSS-IV Extended Baryon Oscillation Spectroscopic Survey: final
Emission Line Galaxy Target Selection: We describe the algorithm used to select the Emission Line Galaxy (ELG)
sample at $z \sim 0.85$ for the extended Baryon Oscillation Spectroscopic
Survey of the Sloan Digital Sky Survey IV, using photometric data from the
DECam Legacy Survey. Our selection is based on a selection box in the $g-r$ vs.
$r-z$ colour-colour space and a cut on the $g$-band magnitude, to favour
galaxies in the desired redshift range with strong [OII] emission. It provides
a target density of 200 deg$^{-2}$ on the North Galactic Cap (NGC) and of 240
deg$^{-2}$ on the South Galactic Cap (SGC), where we use a larger selection box
because of deeper imaging. We demonstrate that this selection passes the eBOSS
requirements in terms of homogeneity. About 50,000 ELGs have been observed
since the observations have started in 2016, September. These roughly match the
expected redshift distribution, though the measured efficiency is slightly
lower than expected. The efficiency can be increased by enlarging the redshift
range and with incoming pipeline improvement. The cosmological forecast based
on these first data predict $\sigma_{D_V}/D_V = 0.023$, in agreement with
previous forecasts. Lastly, we present the stellar population properties of the
ELG SGC sample. Once observations are completed, this sample will be suited to
provide a cosmological analysis at $z \sim 0.85$, and will pave the way for the
next decade of massive spectroscopic cosmological surveys, which heavily rely
on ELGs. The target catalogue over the SGC will be released along with DR14. |
Observational Aspect of Black Hole Dark Matter: Advances in high angular resolution astronomy make it conceivable that black
hole dark matter could be detected via angular deviation effects. Assuming the
dark matter in the galaxy is made of solar mass black holes, there is a
non-trivial probability that a line-of-sight through the galaxy, leads to
micro-arcseconds deviations, a value that has been discussed for various
astronomical projects. In cosmology the effects are magnified by an increased
density at early times and an opening of angles due to redshift. If the dark
matter is made of primordial black holes, present at the CMB, random
deflections of the CMB photons lead to a limit on the angular resolution,
approximately ${3}\times 10^{-7} \sqrt{M/M_\odot}\, rad$, with $M$ the mass of
the black holes. Using the resolutions of $\sim 10^{-3} rad$ demonstrated in
observations of the "acoustic peaks" then implies the limit
$(M/M_\odot)\lesssim 10^{7}$. While this large value seems uninteresting,
improved resolutions would lead to significant limits or conceivably the
discovery of primordial black holes. | The paucity of globular clusters around the field elliptical NGC 7507: Context: There is strong evidence that globular cluster systems (GCSs) of
massive galaxies are largely assembled by infall/accretion processes.
Therefore, we expect the GCSs of isolated elliptical galaxies to be poor.
Alhough not completely isolated, NGC 7507 is a massive field elliptical galaxy
with an apparently very low dark matter content. Aims: We determine the
richness, the colour distribution, and the structural properties of the GCS of
NGC 7507. Methods: We perform wide-field Washington photometry with data
obtained with the MOSAIC II camera at the 4m-Blanco telescope, CTIO. Results:
The GCS is very poor with S_N ~ 0.6. We identify three subpopulations with
peaks at (C-T1) colours of 1.21, 1.42, and 1.72. The bluest population may
represent the old, metal-poor component. This interpretation is supported by
its shallow density profile. The red population is more concentrated,
resembling the galaxy light. The intermediate-colour population is strongly
peaked in colour and we interpret this population as the signature of a
starburst, whose age depends on the metallicity, but should be quite old, since
no signatures of a merger are identifiable. In addition, we find a main
sequence in the stellar foreground population, which we attribute to the
Sagittarius dwarf tidal stream. Conclusions: The extraordinarily poor GCS of
NGC 7507, a massive elliptical galaxy, is an illustration of how important the
environmental conditions are for producing rich GCSs. |
Does the Fe L-shell blend bias abundance measurements in
intermediate-temperature clusters?: In intermediate-temperature (T = 2.5 - 4.5 keV) galaxy clusters, abundance
measurements are almost-equally driven by Fe K and L transitions, at $\sim$ 6.7
keV and 0.9 - 1.3 keV, respectively. While K-shell-derived measurements are
considered reliable, the resolution of the currently available instrumentation,
as well as our current knowledge of the atomic processes, makes the modelling
of the L-line complex challenging, resulting in potential biases for abundance
measurements. In this work, we study systematics related to the modelling of
the Fe L-line complex that may influence iron-abundance measurements in the
intermediate-temperature range. To this aim, we select a sample of three bright
galaxy clusters, with long XMM-Newton observations available and temperature in
the 2.5 - 4.5 keV range. We fit spectra extracted from concentric rings with
APEC and APEC+APEC models, by alternatively excluding the L and K bands, and
derive the fractional difference of the metal abundances, $\Delta Z/Z$, as
indication of the consistency between K- and L-shell-derived measurements. The
$\Delta Z/Z$ distribution is then studied as a function of the cluster radius,
ring temperature and X-ray flux. The L-induced systematics, measured through an
individual fit of each MOS and pn spectrum, remain constant at a 5 - 6% value
in the whole 2.5 - 4.5 keV temperature range. Conversely, a joint fit of MOS
and pn spectra leads to a slight excess of 1 - 2% in the above estimate. No
significant dependence on the ring X-ray flux is highlighted. The measured 5 -
8% value indicates a modest contribution of the systematics to the derived iron
abundances, giving confidence for future measurements. To date, these findings
represent the best-achievable estimate of the systematics in analysis, while
future microcalorimeters will significantly improve our understanding of the
atomic processes underlying the Fe L emissions. | Absorption features in the quasar HS 1603+3820 II. Distance to the
absorber from photoionisation modelling: We present photoionisation modelling of the intrinsic absorber in the bright
quasar HS 1603+3820. We construct spectral energy distribution using
optical/UV/X-ray observations as an input to photoionisation calculations.
Spectra from Keck telescope show extremely high ratio of CIV to HI, for the
first absorber in system A, named A1. This value, together with high column
density of CIV ion, puts strong constraints on photoionisation model. We use
photoionisation modeling to derive hydrogen number density at the cloud
illuminated surface. Estimating bolometric luminosity of HS 1603+3820, from
typical formula for quasars, we calculate the distance to A1. The derived
location is as close as 0.1 pc, and situates an absorber even closer to the
nucleus than the possible location of the Broad Line Region in this object |
Dark Energy as a Critical Period in Binary Motion: Bounds from
Multi-scale Binaries: The two-body problem under the influence of both dark energy and
post-Newtonian modifications is studied. In this unified framework, we
demonstrate that dark energy plays the role of a critical period with
$T_{\Lambda} = 2\pi/c \sqrt{\Lambda} \approx 60~\text{Gyr}$. We also show that
the ratio between orbital and critical period naturally emerges from the
Kretschmann scalar, which is a quadratic curvature invariant characterizing all
binary systems effectively represented by a de Sitter-Schwarzschild spacetime.
The suitability of a binary system to constrain dark energy is determined by
the ratio between its Keplerian orbital period $T_\text{K}$ and the critical
period $T_\Lambda$. Systems with $T_\text{K} \approx T_\Lambda$ are optimal for
constraining the cosmological constant $\Lambda$, such as the Local Group and
the Virgo Cluster. Systems with $T_{\text{K}} \ll T_\Lambda$ are dominated by
attractive gravity (which are best suited for studying modified gravity
corrections). Systems with $T_{\text{K}} \gg T_\Lambda$ are dominated by
repulsive dark energy and can thus be used to constrain $\Lambda$ from below.
We use our unified framework of post-Newtonian and dark-energy modifications to
calculate the precession of bounded and unbounded astrophysical systems and
infer constraints on $\Lambda$ from them. Pulsars, the solar system, S stars
around Sgr A*, the Local Group, and the Virgo Cluster, having orbital periods
of days to gigayears, are analyzed. The results reveal that the upper bound on
the cosmological constant decreases when the orbital period of the system
increases, emphasizing that $\Lambda$ is a critical period in binary motion. | Improved measurements of the temperature and polarization of the CMB
from QUaD: We present an improved analysis of the final dataset from the QUaD
experiment. Using an improved technique to remove ground contamination, we
double the effective sky area and hence increase the precision of our CMB power
spectrum measurements by ~30% versus that previously reported. In addition, we
have improved our modeling of the instrument beams and have reduced our
absolute calibration uncertainty from 5% to 3.5% in temperature. The robustness
of our results is confirmed through extensive jackknife tests and by way of the
agreement we find between our two fully independent analysis pipelines. For the
standard 6-parameter LCDM model, the addition of QUaD data marginally improves
the constraints on a number of cosmological parameters over those obtained from
the WMAP experiment alone. The impact of QUaD data is significantly greater for
a model extended to include either a running in the scalar spectral index, or a
possible tensor component, or both. Adding both the QUaD data and the results
from the ACBAR experiment, the uncertainty in the spectral index running is
reduced by ~25% compared to WMAP alone, while the upper limit on the
tensor-to-scalar ratio is reduced from r < 0.48 to r < 0.33 (95% c.l). This is
the strongest limit on tensors to date from the CMB alone. We also use our
polarization measurements to place constraints on parity violating interactions
to the surface of last scattering, constraining the energy scale of Lorentz
violating interactions to < 1.5 x 10^{-43} GeV (68% c.l.). Finally, we place a
robust upper limit on the strength of the lensing B-mode signal. Assuming a
single flat band power between l = 200 and l = 2000, we constrain the amplitude
of B-modes to be < 0.57 micro-K^2 (95% c.l.). |
Intensity mapping of post-reionization 21-cm signal and its
cross-correlations as a probe of $f(R)$ gravity: We propose the intensity mapping of the redshifted HI 21-cm signal from the
post-reionization epoch as a cosmological probe of $f(R)$ gravity. We consider
the Hu-Sawicki class of $f(R)$ gravity models characterized by a single
parameter $f_{,R0}$. The $f(R)$ modification to gravity affects the
post-reionization $21$-cm power spectrum through the change in the growth rate
of density fluctuations. We find that a radio interferometric observation with
a SKA1-Mid like radio telescope in both auto-correlation and cross-correlation
with galaxy weak-lensing and Ly-$\alpha$ forest may distinguish $f(R)$ models
from $LCDM$ cosmology at a precision which is competitive with other probes of
$f(R)$ gravity. | A model-independent reconstruction of dark sector interactions: Relaxing the conventional assumption of a minimal coupling between the dark
matter (DM) and dark energy (DE) fields introduces significant changes in the
predicted evolution of the Universe. Therefore, testing such a possibility
constitutes an essential task not only for cosmology but also for fundamental
physics. In a previous communication [Phys. Rev. D99, 043521, 2019], we
proposed a new null test for the $\Lambda$CDM model based on the time
dependence of the ratio between the DM and DE energy densities which is also
able to detect potential signatures of interaction between the dark components.
In this work, we extend that analysis avoiding the $ \Lambda$CDM assumption and
reconstruct the interaction in the dark sector in a fully model-independent way
using data from type Ia supernovae, cosmic chronometers and baryonic acoustic
oscillations. According to our analysis, the $\Lambda$CDM model is consistent
with our model-independent approach at least at $3\sigma$ CL over the entire
range of redshift studied. On the other hand, our analysis shows that the
current background data do not allow us to rule out the existence of an
interaction in the dark sector. Finally, we present a forecast for
next-generation LSS surveys. In particular, we show that Euclid and SKA will be
able to distinguish interacting models with about 4\% of precision at $z\approx
1$. |
The Rise of Active Galactic Nuclei in the GAlaxy Evolution and Assembly
semi-analytic model: We present a new implementation of the GAlaxy Evolution and Assembly (GAEA)
semi-analytic model, that features an improved modelling of the process of cold
gas accretion onto supermassive black hole (SMBHs), derived from both analytic
arguments and high-resolution simulations. We consider different scenarios for
the loss of angular momentum required for the available cold gas to be accreted
onto the central SMBHs, and we compare different combinations of triggering
mechanisms, including galaxy mergers and disc instabilities in star forming
discs. We compare our predictions with the luminosity function (LF) observed
for Active Galactic Nuclei (AGN) and we confirm that a non-instantaneous
accretion timescale (either in the form of a low-angular momentum reservoir or
as an assumed light curve evolution) is needed in order to reproduce the
measured evolution of the AGN-LF and the so-called AGN-downsizing trend.
Moreover, we also study the impact of AGN feedback, in the form of AGN-driven
outflows, on the SF properties of model galaxies, using prescriptions derived
both from empirical studies or from numerical experiments. We show that
AGN-driven outflows are effective in suppressing the residual star formation
rate in massive galaxies ($> 10^{11} M_\odot$) without changing their overall
assembly history. These winds also affect the SFR of lower mass galaxies,
resulting in a too large fraction of passive galaxies at $< 10^{10} M_\odot$.
Finally, we study the Eddington ratio distribution as a function of SMBH mass,
showing that only objects more massive than $10^8 M_\odot$ are already in a
self-regulated state as inferred from observations. | A Region of Violent Star Formation in the Irr Galaxy IC 10: Structure
and Kinematics of Ionized and Neutral Gas: We have used observations of the galaxy IC 10 at the 6-m telescope of the
Special Astrophysical Observatory with the SCORPIO focal reducer in the
Fabry-Perot interferometer mode and with the MPFS spectrograph to study the
structure and kinematics of ionized gas in the central region of current
intense star formation. Archive VLA 21-cm observations are used to analyze the
structure and kinematics of neutral gas in this region. High-velocity wings of
the H-alpha and [SII] emission lines were revealed in the inner cavity of the
nebula HL 111 and in other parts of the complex of violent star formation. We
have discovered local expanding neutral-gas shells around the nebulae HL 111
and HL 106. |
Statistics of 21-cm Fluctuations in Cosmic Reionization Simulations:
PDFs and Difference PDFs: In the coming decade, low-frequency radio arrays will begin to probe the
epoch of reionization via the redshifted 21-cm hydrogen line. Successful
interpretation of these observations will require effective statistical
techniques for analyzing the data. Due to the difficulty of these measurements,
it is important to develop techniques beyond the standard power spectrum
analysis in order to offer independent confirmation of the reionization
history, probe different aspects of the topology of reionization, and have
different systematic errors. In order to assess the promise of probability
distribution functions (PDFs) as statistical analysis tools in 21-cm cosmology,
we first measure the 21-cm brightness temperature (one-point) PDFs in six
different reionization simulations. We then parametrize their most distinct
features by fitting them to a simple model. Using the same simulations, we also
present the first measurements of difference PDFs in simulations of
reionization. We find that while these statistics probe the properties of the
ionizing sources, they are relatively independent of small-scale, sub-grid
astrophysics. We discuss the additional information that the difference PDF can
provide on top of the power spectrum and the one-point PDF. | QSO Absorption Systems Detected in Ne VIII: High-Metallicity Clouds with
a Large Effective Cross Section: Using high resolution, high signal-to-noise ultraviolet spectra of the z =
0.9754 quasar PG1148+549 obtained with the Cosmic Origins Spectrograph (COS) on
the Hubble Space Telescope, we study the physical conditions and abundances of
NeVIII+OVI absorption line systems at z(abs) =0.68381, 0.70152, 0.72478. In
addition to NeVIII and OVI, absorption lines from multiple ionization stages of
oxygen (OII, OIII, OIV) are detected and are well-aligned with the more highly
ionized species. We show that these absorbers are multiphase systems including
hot gas (T ~ 10^{5.7} K) that produces NeVIII and OVI, and the gas metallicity
of the cool phase ranges from Z = 0.3 Z_{solar} to supersolar. The cool
(~10^{4} K) phases have densities n_{H} ~ 10^{-4} cm^{-3} and small sizes (<
4kpc); these cool clouds are likely to expand and dissipate, and the NeVIII may
be within a transition layer between the cool gas and a surrounding, much
hotter medium. The NeVIII redshift density, dN/dz = 7^{+7}_{-3}, requires a
large number of these clouds for every L > 0.1L* galaxy and a large effective
absorption cross section (>~ 100 kpc), and indeed, we find a star forming ~L*
galaxy at the redshift of the z(abs)=0.72478 system, at an impact parameter of
217 kpc. Multiphase absorbers like these NeVIII systems are likely to be an
important reservoir of baryons and metals in the circumgalactic media of
galaxies. |
A Detection of Weak Lensing Magnification using Galaxy Sizes and
Magnitudes: Weak lensing is commonly measured using shear through galaxy ellipticities,
or using the effect of magnification bias on galaxy number densities. Here, we
report on the first detection of weak lensing magnification with a new,
independent technique using the distribution of galaxy sizes and magnitudes.
These data come for free in galaxy surveys designed for measuring shear. We
present the magnification estimator and apply it to an X-ray selected sample of
galaxy groups in the COSMOS HST survey. The measurement of the projected
surface density \Sigma(r) is consistent with the shear measurements within the
uncertainties, and has roughly 40% of the signal-to-noise of the latter. We
discuss systematic issues and challenges to realizing the potential of this new
probe of weak lensing. | Influence of synchrotron self-absorption on the 21cm experiments: Presence of spectral curvature due to synchrotron self-absorption (SSA) of
extragalactic radio sources may break down the spectral smoothness feature-the
premise that bright radio foreground can be successfully removed in the 21cm
experiments of searching for the epoch of reionization (EOR).We present a
quantitative estimate of the effect on the measurement of the angular power
spectrum of the low-frequency sky,incorporating a phenomenological
model,characterized by the fraction of radio sources with turnover frequencies
in 100-1000MHz range and a broken power law for the spectral transition around
turnover frequencies nu_m,into the simulated radio sources over a small sky
area of 10x10 deg^2.We compare statistically the changes in their residual maps
with/without inclusion of the SSA after the bright sources of S_150MHz>=100mJy
are excised and the best-fitted polynomials in frequency domain on each pixel
are further subtracted.It has been shown that the effect of SSA on the
detection of EOR depends sensitively on the spectral profiles of radio sources
around the turnover frequencies: A hard transition model described by the
broken power law with the turnover of spectral index at nu_m would leave
pronounced imprints on the residual background and cause serious confusion with
the EOR signal.However,the spectral signatures on the angular power spectrum of
extragalactic foreground generated by a soft transition model,in which the rise
and fall power laws of spectral distribution around nu_m are connected through
a smooth transition spanning >=200 MHz in characteristic width,can be fitted
and consequently subtracted by employment of polynomials to an acceptable
degree(delta T<1mK).As this latter scenario seems to be favored by both
theoretical expectation and radio spectral observations,we conclude that the
influence of SSA on the 21cm experiments is probably very minor. |
Running vacuum versus Holographic dark energy: a cosmographic comparison: We perform a comparative study of different types of dynamical dark energy
models (DDES) using the cosmographic method. Among the models being examined
herein we have the Running Vacuum models (RVMs), which have demonstrated
considerable ability to fit the overall cosmological data at a level comparable
to the standard cosmological model, $\Lambda$CDM, and capable of alleviating
the $\sigma_8$ and $H_0$ tensions. At the same time we address a variety of
Holographic dark energy models (HDEs) with different options for the time
(redshift)-varying model parameter $c=c(z)$. We deal with the HDEs under the
double assumption of fixed and evolving holographic length scale and assess
which one is better. Both types of DDEs (RVMs and HDEs) are confronted with the
most robust cosmographic data available, namely the Pantheon sample of
supernovae (SnIa), the baryonic acoustic oscillation data (BAOs) extracted from
measurement of the power spectrum and bispectrum of the BOSS data release, and
the cosmic chronometer measurements of the Hubble rate (CCHs) at different
redshifts obtained from spectroscopic observations of passively evolving
galaxies. Using these data samples we assess the viability of the mentioned
DDEs and compare them with the concordance $\Lambda$CDM model. From
cosmographic analysis we conclude that the RVMs fare comparably well to the
$\Lambda$CDM, a fact which adds up more credit to their sound phenomenological
status. In contrast, while some of the HDEs are favored using the current
Hubble horizon as fixed holographic length, they become highly unfavoured in
the more realistic case when the holographic length is dynamical and evolves as
the Hubble horizon. | Early-type galaxies at large galactocentric radii - I. Stellar
kinematics and photometric properties: We present the results of a combined analysis of the kinematic and
photometric properties at large galactocentric radii of a sample of 14
low-luminosity early-type galaxies in the Fornax and Virgo clusters. From
Gemini South GMOS long-slit spectroscopic data we measure radial profiles of
the kinematic parameters v_{rot}, sigma, h_{3}, and h_{4} out to ~ 1 - 3
effective radii. Multi-band imaging data from the HST/ACS are employed to
evaluate surface brightness profiles and isophotal shape parameters of
ellipticity, position angle and discyness/boxiness. The galaxies are found to
host a cold and old stellar component which extend to the largest observed
radii and that is the dominant source of their dynamical support. The
prevalence of discy-shaped isophotes and the radial variation of their
ellipticity are signatures of a gradual gas dissipation. An early star-forming
collapse appears to be the main mechanism acting in the formation of these
objects. Major mergers are unlikely to have occurred in these galaxies. We can
not rule out a minor merging origin for these galaxies, but a comparison of our
results with model predictions of different merger categories places some
constraints on the possible merger progenitors. These merger events are
required to happen at high-redshift (i.e., z > 1), between progenitors of
different mass ratio (at least 3:1) and containing a significant amount of gas
(i.e., > 10 percent). A further scenario is that the low-luminosity galaxies
were originally late-type galaxies, whose star formation has been truncated by
removal of gas and subsequently the disc has been dynamically heated by high
speed encounters in the cluster environment. |
Mass bias evolution in tSZ cluster cosmology: Galaxy clusters observed through the thermal Sunyaev-Zeldovich (tSZ) effect
are a recent cosmological probe. The precision on the cosmological constraints
is affected mainly by the current knowledge of cluster physics, which enters
the analysis through the scaling relations. Here we aim to study one of the
most important sources of systematic uncertainties, the mass bias, $b$. We have
analysed the effects of a mass-redshift dependence, adopting a power-law
parametrisation. We applied this parametrisation to the combination of tSZ
number counts and power spectrum, finding a hint of redshift dependence that
leads to a decreasing value of the mass bias for higher redshift. We tested the
robustness of our results for different mass bias calibrations and a discrete
redshift dependence. We find our results to be dependent on the clusters sample
that we are considering, in particular obtaining an inverse (decreasing)
redshift dependence when neglecting $z<0.2$ clusters. We analysed the effects
of this parametrisation on the combination of cosmic microwave background (CMB)
primary anisotropies and tSZ galaxy clusters. We find a preferred constant
value of mass bias, having $(1-b) =0.62 \pm 0.05$. The corresponding value of
$b$ is too high with respect to weak lensing and numerical simulations
estimations. Therefore we conclude that this mass-redshift parametrisation does
not help in solving the remaining discrepancy between CMB and tSZ clusters
observations. | Breaking down the link between luminous and dark matter in massive
galaxies: We present a study on the clustering of a stellar mass selected sample of
galaxies with stellar masses M*>10^10Msol at redshifts 0.4<z<2.0, taken from
the Palomar Observatory Wide-field Infrared Survey. We examine the clustering
properties of these stellar mass selected samples as a function of redshift and
stellar mass, and find that galaxies with high stellar masses have a
progressively higher clustering strength than galaxies with lower stellar
masses. We also find that galaxies within a fixed stellar mass range have a
higher clustering strength at higher redshifts. We further estimate the average
total masses of the dark matter haloes hosting these stellar-mass selected
galaxies. For all galaxies in our sample the stellar-mass-to-total-mass ratio
is always lower than the universal baryonic mass fraction and the
stellar-mass-to-total-mass ratio is strongly correlated with the halo masses
for central galaxies, such that more massive haloes contain a lower fraction of
their mass in the form of stars. The remaining baryonic mass is included
partially in stars within satellite galaxies in these haloes, and as diffuse
hot and warm gas. We also find that, at a fixed stellar mass, the
stellar-to-total-mass ratio increases at lower redshifts. This suggests that
galaxies at a fixed stellar mass form later in lower mass dark matter haloes,
and earlier in massive haloes. We interpret this as a `halo downsizing' effect. |
Dark Matter as a Non-Relativistic Bose-Einstein Condensate with Massive
Gravitons: We confront a non-relativistic Bose--Einstein Condensate (BEC) model of light
bosons interacting gravitationally either through a Newtonian or a Yukawa
potential with the observed rotational curves of $12$ dwarf galaxies. The
baryonic component is modelled as an axisymmetric exponential disk and its
characteristics are derived from the surface luminosity profile of the
galaxies. The purely baryonic fit is unsatisfactory, hence a dark matter
component is clearly needed. The rotational curves of five galaxies could be
explained with high confidence level by the BEC model. For these galaxies, we
derive: (i) upper limits for the allowed graviton mass; and (ii) constraints on
a velocity-type and a density-type quantity characterizing the BEC, both being
expressed in terms of the BEC particle mass, scattering length and chemical
potential. The upper limit for the graviton mass is of the order of $10^{-26}$
$\text{eV/c}^2$, three orders of magnitude stronger than the limit derived from
recent gravitational wave detections. | The CFHT Legacy Survey: stacked images and catalogs: This paper describes the image stacks and catalogs of the CFHT Legacy Survey
produced using using the MegaPipe data pipeline at the Canadian Astronomy Data
Centre. The Legacy Survey is divided into to two parts: The Deep Survey
consists of 4 fields each of 1 square degree, with magnitude limits of u=27.5,
g=27.9, r=27.7, i=27.4, and z=26.2, and contains 1.6 million sources. The Wide
Survey consists of 171 square degree pointings split over 4 fields, with
magnitude limits of u=26.0, g=26.5, r=25.9, i=25.7, and z=24.6, and contains 30
million sources. This paper describes the calibration, image stacking and
catalog generation process. The images and catalogs are available on the web
through several interfaces: normal image and text file catalog downloads, a
Google Sky interface, an image cutout service, and a catalog database query
service. |
On Some Properties of the Neutrino in The Early Universe: The properties of the neutrino in the early universe have been investigated
incorporating a small inhomogeneity in the mass density of the early universe.
Dependence on this factor is found in studying mean free path and mass bound of
neutrinos. The oscillations of neutrinos flavours have been studied by assuming
a free wave packet to represent the time progression of the neutrino yielding
interesting results. | The Extreme High-Velocity Outflow in Quasar PG0935+417: We report the detection of OVI 1031,1037 and NV 1238,1242 absorption in a
system of "mini-broad" absorption lines (mini-BALs) previously reported to have
variable CIV 1548,1550 in the quasar PG0935+417. The formation of these lines
in an extreme high-velocity quasar outflow (with v ~ -50000 km/s) is confirmed
by the line variability, broad smooth absorption profiles, and partial covering
of the background light source. HI and lower ionization metals are not clearly
present. The resolved OVI doublet indicates that these lines are moderately
saturated, with the absorber covering ~80% of the quasar continuum source
(C_f~0.8). We derive ionic column densities of order 1015 cm^(-2) in CIV and
several times larger in OVI, indicating an ionization parameter of log U >~
-0.5. Assuming solar abundances, we estimate a total column density of N(H) ~5
x 10^(19) cm^(-2). This outflow emerged sometime between 1982 and 1993. Our
examination of the CIV data from 1993 to 2007 shows that there is variable
complex absorption across a range of velocities from -45000 to -54000 km/s.
There is no clear evidence for acceleration or deceleration of the outflow gas.
Outflows are common in Active Galactic Nuclei (AGN), but extreme speeds such as
those reported here are extremely rare. It is not clear what properties of
PG0935+417 might produce this unusual outflow. In fact, PG0935+417 has
significantly less X-ray absorption than typical BAL quasars even though its
outflow has a degree of ionization typical of BALs at speeds that are 2-3 times
larger than most BALs. These results might present a challenge to theoretical
models that invoke strong radiative shielding in the X-rays/far-UV to moderate
the outflow ionization and thus enable its radiative acceleration to high
speeds. |
Primordial gravitational waves from NANOGrav: a broken power-law
approach: We revisit the possibility that the stochastic common-spectrum process
recently detected by the NANOGrav pulsar timing array experiment could be due
to primordial gravitational waves (GWs). A na\"{i}ve extrapolation down to
interferometer scales of the blue GW spectrum required to explain NANOGrav
consistently with Cosmic Microwave Background (CMB) observations would strongly
violate upper limits on the stochastic GW background (SGWB) amplitude from
LIGO/Virgo. In combination with the fact that there are over 19 decades in
frequency between CMB and interferometer scales, this motivates us to move
beyond the commonly adopted approximation of a pure power-law GW spectrum. We
consider a broken power-law parametrization for the SGWB spectrum, which turns
from blue to red above the break frequency: while phenomenological, this choice
maps to various well-motivated early-Universe models, including scenarios
featuring non-instantaneous reheating or a non-standard background expansion
following reheating. After a detailed discussion of the contribution of the
resulting SGWB to the early-Universe radiation energy density, we constrain the
broken power-law model against a wide variety of multi-frequency cosmological
and GW observations. We find that this phenomenological model is able to
explain the NANOGrav signal while remaining in agreement with upper limits on
the tensor-to-scalar ratio on CMB scales, Big Bang Nucleosynthesis constraints
on the early-Universe radiation energy density, and upper limits on the SGWB
amplitude on interferometer scales. We briefly discuss the very bright
prospects for testing this model with next-generation probes across the GW
frequency landscape, which motivate further exploring connections to specific
well-motivated early-Universe models. | Symmetries, Invariants and Generating Functions: Higher-order Statistics
of Biased Tracers: Gravitationally collapsed objects are known to be biased tracers of an
underlying density contrast. Using symmetry arguments, generalised biasing
schemes have recently been developed to relate the halo density contrast
$\delta_h$ with the underlying density contrast $\delta$, divergence of
velocity $\theta$ and their higher-order derivatives. This is done by
constructing invariants such as $s, t, \psi,\eta$. We show how the generating
function formalism in Eulerian standard perturbation theory (SPT) can be used
to show that many of the additional terms based on extended Galilean and
Lifshitz symmetry actually do not make any contribution to the higher-order
statistics of biased tracers. Other terms can also be drastically simplified
allowing us to write the vertices associated with $\delta_h$ in terms of the
vertices of $\delta$ and $\theta$, the higher-order derivatives and the bias
coefficients. We also compute the cumulant correlators (CCs) for two different
tracer populations. These perturbative results are valid for tree-level
contributions but at an arbitrary order. We also take into account the
stochastic nature bias in our analysis. Extending previous results of a local
polynomial model of bias, we express the one-point cumulants ${\cal S}_N$ and
their two-point counterparts, the CCs i.e. ${\cal C}_{pq}$, of biased tracers
in terms of that of their underlying density contrast counterparts. As a
by-product of our calculation we also discuss the results using approximations
based on Lagrangian perturbation theory (LPT). |
Reconstruct the Distance Duality Relation by Gaussian Process: In this letter, the distance-duality (DD) relation is reconstructed by
Gaussian process (GP) which is cosmological model-independent. Generally, the
GP plays two important roles. One is to shape the $\eta$ tendency which denotes
the deviation from the DD relation, the other one is to produce the
luminosity-distance (LD, $D_{L}$) and the angular-diameter-distance (ADD,
$D_{A}$) data at the same redshift. The shapes of $\eta$ are given out based on
SNe Ia (Type Ia supernovae) data with different light-curve fitters (including
MLCS2K2 and SALT2) and ADD data with different galaxy cluster morphologies
(including the elliptical $\beta$ and spherical $\beta$ models). The data
related to MLCS2K2 light-curve fitter have higher values of $\eta$ compared to
that related to the SALT2 light-curve fitter. As for the morphology of galaxy
cluster, the DD relation is favored by the elliptical one. | LISA for Cosmologists: Calculating the Signal-to-Noise Ratio for
Stochastic and Deterministic Sources: We present the steps to forecast the sensitivity of the Laser Interferometer
Space Antenna (LISA) to both a stochastic gravitational wave background and
deterministic wave sources. We show how to use these expressions to estimate
the precision with which LISA can determine parameters associated with these
sources. Tools are included to enable easy calculation of the signal-to-noise
ratio and draw sensitivity curves. Benchmark values are given for easy
comparison and checking of methods in the case of two worked examples. The
first benchmark is the threshold stochastic gravitational wave background
$\Omega_{GW} h^2$ that LISA can observe. The second is the signal-to-noise
ratio that LISA would observe for a binary black hole system identical to
GW150914, radiating 4 years before merger. |
Galaxy clusters discovered via the Sunyaev-Zel'dovich effect in the
first 720 square degrees of the South Pole Telescope survey: We present a catalog of 224 galaxy cluster candidates, selected through their
Sunyaev-Zel'dovich (SZ) effect signature in the first 720 deg2 of the South
Pole Telescope (SPT) survey. This area was mapped with the SPT in the 2008 and
2009 austral winters to a depth of 18 uK-arcmin at 150 GHz; 550 deg2 of it was
also mapped to 44 uK-arcmin at 95 GHz. Based on optical imaging of all
candidates and near-infrared imaging of the majority of candidates, we have
found optical and/or infrared counterparts for 158 clusters. Of these, 135 were
first identified as clusters in SPT data, including 117 new discoveries
reported in this work. This catalog triples the number of confirmed galaxy
clusters discovered through the SZ effect. We report photometrically derived
(and in some cases spectroscopic) redshifts for confirmed clusters and redshift
lower limits for the remaining candidates. The catalog extends to high redshift
with a median redshift of z = 0.55 and maximum redshift of z = 1.37. Based on
simulations, we expect the catalog to be nearly 100% complete above M500 ~ 5e14
Msun h_{70}^-1 at z > 0.6. There are 121 candidates detected at signal-to-noise
greater than five, at which the catalog purity is measured to be 95%. From this
high-purity subsample, we exclude the z < 0.3 clusters and use the remaining
100 candidates to improve cosmological constraints following the method
presented by Benson et al., 2011. Adding the cluster data to CMB+BAO+H0 data
leads to a preference for non-zero neutrino masses while only slightly reducing
the upper limit on the sum of neutrino masses to sum mnu < 0.38 eV (95% CL).
For a spatially flat wCDM cosmological model, the addition of this catalog to
the CMB+BAO+H0+SNe results yields sigma8=0.807+-0.027 and w = -1.010+-0.058,
improving the constraints on these parameters by a factor of 1.4 and 1.3,
respectively. [abbrev] | The Star Formation Rate in the Reionization Era as Indicated by
Gamma-ray Bursts: High-redshift gamma-ray bursts (GRBs) offer an extraordinary opportunity to
study aspects of the early Universe, including the cosmic star formation rate
(SFR). Motivated by the two recent highest-z GRBs, GRB 080913 at z = 6.7 and
GRB 090423 at z = 8.1, and more than four years of Swift observations, we first
confirm that the GRB rate does not trace the SFR in an unbiased way. Correcting
for this, we find that the implied SFR to beyond z = 8 is consistent with
LBG-based measurements after accounting for unseen galaxies at the faint end of
the UV luminosity function. We show that this provides support for the
integrated star formation in the range 6 < z < 8 to have been alone sufficient
to reionize the Universe. |
On the Effects of Coupled Scalar Fields on Structure Formation: A coupling between a scalar field (representing the dark energy) and dark
matter could produce rich phenomena in cosmology. It affects cosmic structure
formation mainly through the fifth force, a velocity-dependent force that acts
parallel to particle's direction of motion and proportional to its speed, an
effective rescaling of the particle masses, and a modified background expansion
rate. In many cases these effects entangle and it is difficult to see which is
the dominant one. Here we perform N-body simulations to study their qualitative
behaviour and relative importance in affecting the key structure formation
observables, for a model with exponential scalar field coupling. We find that
the fifth force, a prominent example of the scalar-coupling effects, is far
less important than the rescaling of particle mass or the modified expansion
rate. In particular, the rescaling of particle masses is shown to be the key
factor leading to less concentration of particles in halos than in LCDM, a
pattern which is also observed in previous independent coupled scalar field
simulations. | $N$-body simulations for parametrised modified gravity: We present $\texttt{MG-evolution}$, an $N$-body code simulating the
cosmological structure formation for parametrised modifications of gravity. It
is built from the combination of parametrised linear theory with a
parametrisation of the deeply nonlinear cosmological regime extrapolated from
modified spherical collapse computations that cover the range of known
screening mechanisms. We test $\texttt {MG-evolution}$, which runs at the speed
of conventional $\Lambda$CDM simulations, against a suit of existing exact
model-specific codes, encompassing linearised and chameleon $f(R)$ gravity as
well as the normal branch of the Dvali-Gabadadz-Porrati braneworld model, hence
covering both large-field value and large-derivative screening effects. We
compare the nonlinear power spectra produced by the parametrised and
model-specific approaches over the full range of scales set by the box size and
resolution of our simulations, $k=(0.05-2.5)$~h/Mpc, and for two redshift
slices, $z=0$ and $z=1$. We find sub-percent to one-percent level recovery of
all the power spectra generated with the model-specific codes for the full
range of scales. $\texttt {MG-evolution}$ can be used for generalised and
accurate tests of gravity and dark energy with the increasing wealth of
high-precision cosmological survey data becoming available over the next
decade. |
The phenomenology of trapped inflation: Trapped inflation is a mechanism in which particle production from the moving
inflaton is the main source of friction in the inflaton equation of motion. The
produced fields source inflaton perturbations, which dominate over the vacuum
ones. We employ the set of equations for the inflaton zero mode and its
perturbations which was developed in the original work on trapped inflation,
and which we extend to second order in the perturbations. We build on this
study by updating the experimental constraints, and by replacing the existing
approximate solutions with more accurate ones. We obtain a different numerical
value for the amplitude of the scalar power spectrum, and a parametrically
different result for the bispectrum. This has implications for the allowed
region of parameter space in models of trapped inflation, and for some of the
phenomenological results obtained in this region. The main results in the
allowed region are the following: monomial inflaton potentials, such as $V
\propto \varphi ,\, \varphi^2$ can be compatible with the data, and (in a
portion of the allowed region) the inflaton can be sub-Planckian over all the
"observable" stage of inflation; gravitational waves from this mechanism are
too small to be observed in the foreseeable future; a non-gaussianity parameter
$-60 < f_{\rm NL} < -20 $ is obtained in the allowed region for exactly
equilateral configurations, with a mild dependence on the parameters of the
model and of the inflaton potential. | The Discovery and Nature of Optical Transient CSS100217:102913+404220: We report on the discovery and observations of the extremely luminous optical
transient CSS100217:102913+404220 (CSS100217 hereafter). Spectroscopic
observations show this transient was coincident with a galaxy at redshift
z=0.147, and reached an apparent magnitude of V ~ 16.3. After correcting for
foreground Galactic extinction we determine the absolute magnitude to be M_V
=-22.7 approximately 45 days after maximum light. Based on our unfiltered
optical photometry the peak optical emission was L = 1.3 x 10^45 erg s^-1, and
over a period of 287 rest-frame days had an integrated bolometric luminosity of
1.2 x 10^52 erg. Analysis of the pre-outburst SDSS spectrum of the source shows
features consistent with a Narrow-line Seyfert1 (NLS1) galaxy. High-resolution
HST and Keck followup observations show the event occurred within 150pc of
nucleus of the galaxy, suggesting a possible link to the active nuclear region.
However, the rapid outburst along with photometric and spectroscopic evolution
are much more consistent with a luminous supernova. Line diagnostics suggest
that the host galaxy is undergoing significant star formation. We use extensive
follow-up of the event along with archival CSS and SDSS data to investigate the
three most likely sources of such an event; 1) an extremely luminous supernova;
2) the tidal disruption of a star by the massive nuclear black hole; 3)
variability of the central AGN. We find that CSS100217 was likely an extremely
luminous type IIn supernova that occurred within range of the narrow-line
region of an AGN. We discuss how similar events may have been missed in past
supernova surveys because of confusion with AGN activity. |
Cosmography via Gaussian Process with Gamma Ray Bursts: In this paper, we firstly calibrate the Amati relation (the $E_{\rm p}-E_{\rm
iso}$ correlation) of gamma ray bursts (GRBs) at low redshifts ($z<0.8$) via
Gaussian process by using the type Ia supernovae samples from Pantheon+ under
the philosophy that objects at the same redshift should have the same
luminosity distance in any cosmology. As a result, this calibration derives the
distance moduli of GRBs at high redshifts ($z>0.8$). For an application of
these derived distance modulus of GRBs to cosmology, via Gaussian process
again, a series of cosmography parameters, which describe kinematics of our
Universe, up to the fifth oder and the redshift $z\sim 5$, i.e. the Hubble
parameter $H(z)$, the deceleration parameter $q(z)$, the jerk parameter $j(z)$,
the snap parameter $s(z)$ and the lerk parameter $l(z)$, are reconstructed from
the cosmic observations. The reconstructed cosmography parameters show a
transition singularity at $z\sim 6$, it may resort to two possible
explanations: one is that the GRBs data points at high redshift $z>5$ are still
reliable, it means that new physics beyond the $\Lambda$CDM model happens;
another one is that the quality and quantity of GRBs data points at high
redshift $z>5$ are not good enough to give any viable prediction of the
kinematics of our Universe. To pin down this problem, more high redshifts $z>5$
cosmic observational are still needed. | A Ratio-Preserving Approach to Cosmological Concordance: Cosmological observables are particularly sensitive to key ratios of energy
densities and rates, both today and at earlier epochs of the Universe.
Well-known examples include the photon-to-baryon and the matter-to-radiation
ratios. Equally important, though less publicized, are the ratios of
pressure-supported to pressureless matter and the Thomson scattering rate to
the Hubble rate around recombination, both of which observations tightly
constrain. Preserving these key ratios in theories beyond the $\Lambda$
Cold-Dark-Matter ($\Lambda$CDM) model ensures broad concordance with a large
swath of datasets when addressing cosmological tensions. We demonstrate that a
mirror dark sector, reflecting a partial $\mathbb{Z}_2$ symmetry with the
Standard Model, in conjunction with percent level changes to the visible
fine-structure constant and electron mass which represent a
\textit{phenomenological} change to the Thomson scattering rate, maintains
essential cosmological ratios. Incorporating this ratio preserving approach
into a cosmological framework significantly improves agreement to observational
data ($\Delta\chi^2=-35.72$) and completely eliminates the Hubble tension with
a cosmologically inferred $H_0 = 73.80 \pm 1.02$ km/s/Mpc when including the
S$H_0$ES calibration in our analysis. While our approach is certainly
nonminimal, it emphasizes the importance of keeping key ratios constant when
exploring models beyond $\Lambda$CDM. |
In search of the dark matter dark energy interaction: a kinematic
approach: The present work deals with a kinematic approach to the modelling the late
time dynamics of the universe. This approach is based upon the assumption of
constant value of cosmological jerk parameter, which is the dimensionless
representation of the 3rd order time derivative of the scale factor. For the
$\Lambda$CDM model, the value of jerk parameter is -1 throughout the evolution
history. Now any model dependent estimation of the value of the jerk parameter
would indicate the deviation of the model from the cosmological constant. In
the present work, it has also been shown that for a constant jerk parameter
model, any deviation of its value from -1 would not allow the dark matter to
have an independent conservation, thus indicating towards an interaction
between dark matter and dark energy. Statistical analysis with different
observational data sets (namely the observational Hubble parameter data (OHD),
the type Ia supernova data (SNe), and the baryon acoustic oscillation data
(BAO)) lead to a well constrained values of the jerk parameter and the model
remains at a very close proximity of the $\Lambda$CDM. The possibility of
interaction is found to be more likely at high redshift rather than at present
epoch. | Finding quadruply imaged quasars with machine learning. I. Methods: Strongly lensed quadruply imaged quasars (quads) are extraordinary objects.
They are very rare in the sky -- only a few tens are known to date -- and yet
they provide unique information about a wide range of topics, including the
expansion history and the composition of the Universe, the distribution of
stars and dark matter in galaxies, the host galaxies of quasars, and the
stellar initial mass function. Finding them in astronomical images is a classic
"needle in a haystack" problem, as they are outnumbered by other (contaminant)
sources by many orders of magnitude. To solve this problem, we develop
state-of-the-art deep learning methods and train them on realistic simulated
quads based on real images of galaxies taken from the Dark Energy Survey, with
realistic source and deflector models, including the chromatic effects of
microlensing. The performance of the best methods on a mixture of simulated and
real objects is excellent, yielding area under the receiver operating curve in
the range 0.86 to 0.89. Recall is close to 100% down to total magnitude i~21
indicating high completeness, while precision declines from 85% to 70% in the
range i~17-21. The methods are extremely fast: training on 2 million samples
takes 20 hours on a GPU machine, and 10^8 multi-band cutouts can be evaluated
per GPU-hour. The speed and performance of the method pave the way to apply it
to large samples of astronomical sources, bypassing the need for photometric
pre-selection that is likely to be a major cause of incompleteness in current
samples of known quads. |
Enhanced Star Formation in Narrow Line Seyfert 1 AGN revealed by Spitzer: We present new low resolution Spitzer mid-infrared spectroscopy of a sample
of 20 ROSAT selected local Narrow Line Seyfert 1 galaxies (NLS1s). We detect
strong AGN continuum in all and clear PAH emission in 70% of the sources. The
6.2 micron PAH luminosity spans three orders of magnitudes, from ~10^(39) erg/s
to ~10^(42) erg/s providing strong evidence for intense ongoing star formation
in the circumnuclear regions of these sources. Using the IRS/Spitzer archive we
gather a large number of additional NLS1s and their broad line counterparts
(BLS1s) and constructed NLS1 and BLS1 sub-samples to compare them in various
ways. The comparison shows a clear separation according to FWHM(H_beta) such
that objects with narrower broad H_beta lines are the strongest PAH emitters.
We test this division in various ways trying to remove biases due to luminosity
and aperture size. Specifically, we find that star formation activity around
NLS1 AGN is larger than around BLS1 of the same AGN luminosity. The above
result seems to hold over the entire range of distance and luminosity. Moreover
the star formation rate is higher in low black hole mass and high L/L_Edd
systems indicating that black hole growth and star formation are occurring
simultaneously. | Baryon Acoustic Oscillation Theory and Modelling Systematics for the
DESI 2024 results: This paper provides a comprehensive overview of how fitting of Baryon
Acoustic Oscillations (BAO) is carried out within the upcoming Dark Energy
Spectroscopic Instrument's (DESI) 2024 results using its DR1 dataset, and the
associated systematic error budget from theory and modelling of the BAO. We
derive new results showing how non-linearities in the clustering of galaxies
can cause potential biases in measurements of the isotropic
($\alpha_{\mathrm{iso}}$) and anisotropic ($\alpha_{\mathrm{ap}}$) BAO distance
scales, and how these can be effectively removed with an appropriate choice of
reconstruction algorithm. We then demonstrate how theory leads to a clear
choice for how to model the BAO and develop, implement and validate a new model
for the remaining smooth-broadband (i.e., without BAO) component of the galaxy
clustering. Finally, we explore the impact of all remaining modelling choices
on the BAO constraints from DESI using a suite of high-precision simulations,
arriving at a set of best-practices for DESI BAO fits, and an associated theory
and modelling systematic error. Overall, our results demonstrate the remarkable
robustness of the BAO to all our modelling choices and motivate a combined
theory and modelling systematic error contribution to the post-reconstruction
DESI BAO measurements of no more than $0.1\%$ ($0.2\%$) for its isotropic
(anisotropic) distance measurements. We expect the theory and best-practices
laid out to here to be applicable to other BAO experiments in the era of DESI
and beyond. |
Model-independent discovery prospects for primordial black holes at LIGO: Primordial black holes may encode the conditions of the early universe, and
may even constitute a significant fraction of cosmological dark matter. Their
existence has yet to be established. However, black holes with masses below
$\sim1~\mathrm{M}_\odot$ cannot form as an endpoint of stellar evolution, so
the detection of even one such object would be a smoking gun for new physics,
and would constitute evidence that at least a fraction of the dark matter
consists of primordial black holes. Gravitational wave detectors are capable of
making a definitive discovery of this kind by detecting mergers of light black
holes. But since the merger rate depends strongly on the shape of the black
hole mass function, it is difficult to determine the potential for discovery or
constraint as a function of the overall abundance of black holes. Here, we
directly maximize and minimize the merger rate to connect observational results
to the actual abundance of observable objects. We show that LIGO can discover
mergers of light primordial black holes within the next decade even if such
black holes constitute only a very small fraction of dark matter. A single
merger event involving such an object would (i) provide conclusive evidence of
new physics, (ii) establish the nature of some fraction of dark matter, and
(iii) probe cosmological history at scales far beyond those observable today. | Constraining dark energy with the integrated Sachs-Wolfe effect: We use the integrated Sachs-Wolfe (ISW) effect, by now detectable at $\sim
5\sigma$ within the context of $\Lambda{}$CDM cosmologies, to place strong
constraints on dynamical dark energy theories. Working within an effective
field theory framework for dark energy we find that including ISW constraints
from galaxy-CMB cross-correlations significantly strengthens existing
large-scale structure constraints, yielding bounds consistent with
$\Lambda{}$CDM and approximately reducing the viable parameter space by $\sim
70\%$. This is a direct consequence of ${\cal O}(1)$ changes induced in these
cross-correlations by otherwise viable dark energy models, which we discuss in
detail. We compute constraints by adapting the $\Lambda{}$CDM ISW likelihood
from [1] for dynamical dark energy models using galaxy data from 2MASS, WISE
$\times$ SuperCOSMOS, SDSS-DR12, QSOs and NVSS, CMB data from Planck 18, and
BAO and RSD large scale structure measurements from BOSS and 6dF. We show
constraints both in terms of EFT-inspired $\alpha_i$ and phenomenological
$\mu/\Sigma$ parametrisations. Furthermore we discuss the approximations
involved and related aspects of bias modelling in detail and highlight what
these constraints imply for the underlying dark energy theories. |
Sufficient observables for large scale structure in galaxy surveys: Beyond the linear regime, the power spectrum and higher order moments of the
matter field no longer capture all cosmological information encoded in density
fluctuations. While non-linear transforms have been proposed to extract this
information lost to traditional methods, up to now, the way to generalize these
techniques to discrete processes was unclear; ad hoc extensions had some
success. We pointed out in Carron and Szapudi (2013) that the logarithmic
transform approximates extremely well the optimal "sufficient statistics",
observables that extract all information from the (continuous) matter field.
Building on these results, we generalize optimal transforms to discrete galaxy
fields. We focus our calculations on the Poisson sampling of an underlying
lognormal density field. We solve and test the one-point case in detail, and
sketch out the sufficient observables for the multi-point case. Moreover, we
present an accurate approximation to the sufficient observables in terms of the
mean and spectrum of a non-linearly transformed field. We find that the
corresponding optimal non-linear transformation is directly related to the
maximum a posteriori Bayesian reconstruction of the underlying continuous field
with a lognormal prior as put forward in Kitaura et al (2010). Thus simple
recipes for realizing the sufficient observables can be built on previously
proposed algorithms that have been successfully implemented and tested in
simulations. | Linearized Kompaneetz equation as a relativistic diffusion: We show that Kompaneetz equation describing photon diffusion in an
environment of an electron gas, when linearized around its equilibrium
distribution, coincides with the relativistic diffusion discussed in recent
publications. The model of the relativistic diffusion is related to soluble
models of imaginary time quantum mechanics. We suggest some non-linear
generalizations of the relativistic diffusion equation and their astrophysical
applications (in particular to the Sunyaev-Zeldovich effect). |
Probing reionization with LOFAR using 21-cm redshift space distortions: One of the most promising ways to study the epoch of reionization (EoR) is
through radio observations of the redshifted 21-cm line emission from neutral
hydrogen. These observations are complicated by the fact that the mapping of
redshifts to line-of-sight positions is distorted by the peculiar velocities of
the gas. Such distortions can be a source of error if they are not properly
understood, but they also encode information about cosmology and astrophysics.
We study the effects of redshift space distortions on the power spectrum of
21-cm radiation from the EoR using large scale $N$-body and radiative transfer
simulations. We quantify the anisotropy introduced in the 21-cm power spectrum
by redshift space distortions and show how it evolves as reionization
progresses and how it relates to the underlying physics. We go on to study the
effects of redshift space distortions on LOFAR observations, taking instrument
noise and foreground subtraction into account. We find that LOFAR should be
able to directly observe the power spectrum anisotropy due to redshift space
distortions at spatial scales around $k \sim 0.1$ Mpc$^{-1}$ after $\gtrsim$
1000 hours of integration time. At larger scales, sample errors become a
limiting factor, while at smaller scales detector noise and foregrounds make
the extraction of the signal problematic. Finally, we show how the
astrophysical information contained in the evolution of the anisotropy of the
21-cm power spectrum can be extracted from LOFAR observations, and how it can
be used to distinguish between different reionization scenarios. | Transport equations for the inflationary spectral index: We present a simple and efficient method to compute the superhorizon
evolution of the spectral index in multi-field inflationary models, using
transport equation techniques. We illustrate the evolution of n_s with time for
various interesting potentials. |
Variations in the Fundamental constants in the QSO Host J1148+5251 at z
= 6.4 and the BR1202-0725 System at z = 4.7: We use sensitive observations of three high redshift sources; [CII] fine
structure and CO(2-1) rotational transitions for the z=6.4 Quasar host galaxy
(QSO) J1148+5251, and [CII] and CO(5-4) transitions from the QSO BR1202-0725
and its sub-millimeter companion (SMG) galaxy at z=4.7. We use these
observations to place constraints on the quantity Dz = z(CO) - z(CII) for each
source where z(CO) and z(CII) are the observed redshifts of the CO rotational
transition and [CII] fine structure transition respectively, using a
combination of approaches; 1) By modelling the emission line profiles using
`shapelets' to compare both the emission redshifts and the line profiles
themselves, in order to make inferences about the intrinsic velocity
differences between the molecular and atomic gas, and 2) By performing a
marginalisation over all model parameters in order to calculate a
non-parametric estimate of Dz. We derive 99% confidence intervals for the
marginalised posterior of Dz of (-1.9 pm 1.3) x10^-3, (-3 pm 8) x10^-4 and (-2
pm 4) x10^-3 for J1148+5251, and the BR1202-0725 QSO and SMG respectively. We
show the [CII] and CO(2-1) line profiles for J1148+5251 are consistent with
each other within the limits of the data, whilst the [CII] and CO(5-4) line
profiles from the BR1202-0725 QSO and SMG respectively have 65 and >99.9%
probabilities of being inconsistent, with the CO(5-4) lines ~ 30% wider than
the [CII] lines. Therefore whilst the observed values of Dz can correspond to
variations in the quantity Delta F/F with cosmic time, where F=alpha^2/mu, with
alpha the fine structure constant, and mu the proton-to-electron mass ratio, of
both (-3.3 pm 2.3) x10^-4 for a look back time of 12.9 Gyr and of (-5 pm 15)
x10^-5 for a look back time of 12.4 Gyr we propose that they are the result of
the two species of gas being spatially separated as indicated by the
inconsistencies in their line profiles. | Environmental dependence of different colors in the CMASS sample of the
SDSS DR9: In this study, I investigate the environmental dependence of galaxy colors in
the CMASS sample of the Sloan Digital Sky Survey Data Release 9 (SDSS DR9). To
decrease the radial selection effect, I divide the CMASS sample into subsamples
with a redshift binning size of 0.01 and analyze the environmental dependence
of the u-r, u-g, g-r, r-i and i-z colors for these subsamples in each redshift
bin. Statistical analysis shows that all the five colors weakly correlate with
the local environment, which may mean that the environmental processes
responsible for a galaxy's properties proceed slowly over cosmic time. |
Understanding X-ray and optical selection of galaxy clusters: A
comparison of the XXL and CAMIRA cluster catalogues obtained in the common
XXL-HSC SSP area: Large samples of galaxy clusters provide knowledge of both astrophysics in
the most massive virialised environments and the properties of the cosmological
model that defines our Universe. However, an important issue that affects the
interpretation of galaxy cluster samples is the role played by the selection
waveband and the potential for this to introduce a bias in the physical
properties of clusters thus selected. We aim to investigate waveband-dependent
selection effects in the identification of galaxy clusters by comparing the
X-ray Multi-Mirror (XMM) Ultimate Extra-galactic Survey (XXL) and Subaru Hyper
Suprime-Cam (HSC) CAMIRA cluster samples identified from a common 22.6 deg2 sky
area. We compare 150 XXL and 270 CAMIRA clusters in a common parameter space
defined by X-ray aperture brightness and optical richness. We find that 71/150
XXL clusters are matched to the location of a CAMIRA cluster, the majority of
which (67/71) display richness values N>15 that exceed the CAMIRA catalogue
richness threshold. We find that 67/270 CAMIRA clusters are matched to the
location of an XXL cluster (defined within XXL as an extended X-ray source). Of
the unmatched CAMIRA clusters, the majority display low X-ray fluxes consistent
with the lack of an XXL counterpart. However, a significant fraction (64/107)
CAMIRA clusters that display high X-ray fluxes are not asociated with an
extended source in the XXL catalogue. We demonstrate that this disparity arises
from a variety of effects including the morphological criteria employed to
identify X-ray clusters and the properties of the XMM PSF. | Asymmetric galaxy correlation functions: We study the two-point cross-correlation function between two populations of
galaxies: for instance a bright population and a faint population. We show that
this cross-correlation is asymmetric under the exchange of the line-of-sight
coordinate of the galaxies, i.e. that the correlation is different if the
bright galaxy is in front of, or behind, the faint galaxy. We give an
intuitive, quasi-Newtonian derivation of all the effects that contribute to
such an asymmetry in large-scale structure: gravitational redshift, Doppler
shift, lensing, light-cone, evolution and Alcock-Paczynski effects -
interestingly, the gravitational redshift term is exactly canceled by some of
the others, assuming geodesic motion. Most of these effects are captured by
previous calculations of general relativistic corrections to the observed
galaxy density fluctuation; the asymmetry arises from terms that are suppressed
by the ratio H/k - H is the Hubble constant and k is the wavenumber - which are
more readily observable than the terms suppressed by (H/k)^2. Some of the
contributions to the asymmetry, however, arise from terms that are generally
considered 'Newtonian' - the lensing and evolution - and thus represent a
contaminant in the search for general relativistic corrections. We propose
methods to disentangle these different contributions. A simple method reduces
the contamination to a level of < 10% for redshifts z<1. We also clarify the
relation to recent work on measuring gravitational redshifts by stacking
clusters. |
The 21 cm signal and the interplay between dark matter annihilations and
astrophysical processes: Future dedicated radio interferometers, including HERA and SKA, are very
promising tools that aim to study the epoch of reionization and beyond via
measurements of the 21 cm signal from neutral hydrogen. Dark matter (DM)
annihilations into charged particles change the thermal history of the Universe
and, as a consequence, affect the 21 cm signal. Accurately predicting the
effect of DM strongly relies on the modeling of annihilations inside halos. In
this work, we use up-to-date computations of the energy deposition rates by the
products from DM annihilations, a proper treatment of the contribution from DM
annihilations in halos, as well as values of the annihilation cross section
allowed by the most recent cosmological measurements from the Planck satellite.
Given current uncertainties on the description of the astrophysical processes
driving the epochs of reionization, X-ray heating and Lyman-$\alpha$ pumping,
we find that disentangling DM signatures from purely astrophysical effects,
related to early-time star formation processes or late-time galaxy X-ray
emissions, will be a challenging task. We conclude that only annihilations of
DM particles with masses of $\sim100$ MeV, could leave an unambiguous imprint
on the 21 cm signal and, in particular, on the 21 cm power spectrum. This is in
contrast to previous, more optimistic results in the literature, which have
claimed that strong signatures might also be present even for much higher DM
masses. Additional measurements of the 21 cm signal at different cosmic epochs
will be crucial in order to break the strong parameter degeneracies between DM
annihilations and astrophysical effects and undoubtedly single out a DM imprint
for masses different from $\sim100$ MeV. | Reheating temperature from the CMB: In the recent paper by Mielczarek \emph{et al.} (JCAP {\bf 1007} (2010) 004)
an idea of the method which can be used to put some constraint for the
reheating phase was proposed. Another method of constraining the reheating
temperature has been recently studied by Martin and Ringeval (Phys.\ Rev.\ D
{\bf 82} (2010) 023511). Both methods are based on observations of the cosmic
microwave background (CMB) radiation. In this paper, we develop the idea
introduced in this first article to put constraint on the reheating after the
slow-roll inflation. We restrict our considerations to the case of a massive
inflaton field. The method can be, however, easily extended to the different
inflationary scenarios. As a main result, we derive an expression on the
reheating temperature $T_{\text{RH}}$. Surprisingly, the obtained equation is
independent on the unknown number of relativistic degrees of freedom $g_*$
produced during the reheating. Based on this equation and the WMAP 7
observations, we find $T_{\text{RH}}=3.5\cdot 10^6$ GeV, which is consistent
with the current constraints. The relative uncertainty of the result is,
however, very high and equal to $\sigma(T_{\text{RH}})/T_{\text{RH}} \approx
53$. As we show, this uncertainty will be significantly reduced with future CMB
experiments. |
Subdominant Dark Matter sterile neutrino resonant production in the
light of Planck: Few independent detections of a weak X-ray line at an energy of $\sim$3.5 keV
seen toward a number of astrophysical sites have been reported. If this signal
will be confirmed to be the signature of decaying DM sterile neutrino with a
mass of ~7.1 keV, then the cosmological observables should be consistent with
its properties. In this paper we make a coupled treatment of the weak
decoupling, primordial nucleosynthesis and photon decoupling epochs in the
sterile neutrino resonant production scenario, including the extra radiation
energy density via N_eff. We compute the radiation and matter perturbations
including the full resonance sweep solution for active-sterile flavor
conversion in the expanding Universe. We show that the cosmological
measurements are in agreement with sub-dominant DM sterile neutrino resonant
production with following parameters (errors at 95 CL): sterile neutrino mass
6.08 \pm 3.22 keV, mixing angle \sin^2 2 \theta < 5.61 x 10^{-10}, lepton
number per flavor L_4 = 1.23 \pm 0.04 and sterile neutrino mass fraction f_\nu
< 0.078. Our results are in good agreement with the sterile neutrino resonant
production parameters inferred in Ref. [62] from the linear large scale
structure constraints to produce full Dark Matter density. | Mapping gas around massive galaxies: cross-correlation of DES Y3
galaxies and Compton-$y$-maps from SPT and Planck: We cross-correlate positions of galaxies measured in data from the first
three years of the Dark Energy Survey with Compton-$y$-maps generated using
data from the South Pole Telescope (SPT) and the {\it Planck} mission. We model
this cross-correlation measurement together with the galaxy auto-correlation to
constrain the distribution of gas in the Universe. We measure the hydrostatic
mass bias or, equivalently, the mean halo bias-weighted electron pressure
$\langle b_{h}P_{e}\rangle$, using large-scale information. We find $\langle
b_{h}P_{e}\rangle$ to be
$[0.16^{+0.03}_{-0.04},0.28^{+0.04}_{-0.05},0.45^{+0.06}_{-0.10},0.54^{+0.08}_{-0.07},0.61^{+0.08}_{-0.06},0.63^{+0.07}_{-0.08}]$
meV cm$^{-3}$ at redshifts $z \sim [0.30, 0.46, 0.62,0.77, 0.89, 0.97]$. These
values are consistent with previous work where measurements exist in the
redshift range. We also constrain the mean gas profile using small-scale
information, enabled by the high-resolution of the SPT data. We compare our
measurements to different parametrized profiles based on the cosmo-OWLS
hydrodynamical simulations. We find that our data are consistent with the
simulation that assumes an AGN heating temperature of $10^{8.5}$K but are
incompatible with the model that assumes an AGN heating temperature of
$10^{8.0}$K. These comparisons indicate that the data prefer a higher value of
electron pressure than the simulations within $r_{500c}$ of the galaxies'
halos. |
AMI SZ observation of galaxy-cluster merger CIZA J2242+5301:
perpendicular flows of gas and dark matter: AMI observations towards CIZA J2242+5301, in comparison with observations of
weak gravitational lensing and X-ray emission from the literature, are used to
investigate the behaviour of non-baryonic dark matter (NBDM) and gas during the
merger. Analysis of the Sunyaev-Zel'dovich (SZ) signal indicates the presence
of high pressure gas elongated perpendicularly to the X-ray and weak-lensing
morphologies which, given the merger-axis constraints in the literature,
implies that high pressure gas is pushed out into a linear structure during
core passing. Simulations in the literature closely matching the inferred
merger scenario show the formation of gas density and temperature structures
perpendicular to the merger axis. These SZ observations are challenging for
modified gravity theories in which NBDM is not the dominant contributor to
galaxy-cluster gravity. | The Faintest X-ray Sources from z=0-8: We use the new 4 Ms exposure of the CDF-S field obtained with the Chandra
X-ray satellite to investigate the properties of the faintest X-ray sources
over a wide range of redshifts. We use an optimized averaging procedure to
investigate the weighted mean X-ray fluxes of optically selected sources in the
CDF-S over the redshift range z=0-8 and down to 0.5-2 keV fluxes as low as
5e-19 erg/cm^2/s. None of the samples of sources at high redshifts (z>5) show
any significant flux, and at z=6.5 we place an upper limit on the X-ray
luminosity of 4e41 erg/s in the rest-frame 3.75-15 keV band for the sample of
Bouwens et al. (2006). This is consistent with any X-ray production in the
galaxies being solely due to star formation. At lower redshifts we find
significant weighted mean X-ray fluxes in many samples of sources over the
redshift range z=0-4. We use these to argue that (1) the relation between star
formation and X-ray production remains invariant over this redshift range, (2)
X-ray sources below the direct detection threshold in the CDF-S are primarily
star-forming, and (3) there is full consistency between UV and X-ray
estimations of the star formation history. |
Galaxy clusters in high definition: a dark matter search: Recent radio-frequency probes, with the ATCA and ASKAP telescopes, have
proven themselves to be at the forefront of placing indirect limits on the
properties of dark matter. The latter being able to substantially exceed the
constraining power of Fermi-LAT data. However, these observations were based
only on dwarf galaxies, where magnetic field uncertainties are large. Here we
re-examine the case for galaxy clusters, often ignored due to substantial
diffuse radio backgrounds, by considering the extrapolation of known cluster
surface brightness profiles down to scales observable with MeerKAT. Despite
large baryonic backgrounds, we find that clusters can be competitive with dwarf
galaxies. Extrapolated Coma data being able to rule out WIMPs of mass $< 700$
GeV annihilating via $b$-quarks. This is while having lesser uncertainties
surrounding the magnetic field and diffusive environment. Such compelling
results are possible due to a clash between the inner shape of the dark matter
halo and the flat inner profile of radio halos which is most pronounced for
NFW-like Einasto profiles, the presence of which having some supporting
evidence in the literature. | On vacuum density, the initial singularity and dark energy: Standard cosmology poses a number of important questions. Apart from its
singular origin, it possesses early and late accelerating phases required to
account for observations. The vacuum energy has been considered as a possible
way to resolve some of these questions. The vacuum energy density induced by
free fields in an early de Sitter phase has earlier been estimated to be
proportional to $H^4$, while more recently it has been suggested that the QCD
condensate induces a term proportional to H at late times. These results have
been employed in models which are non-singular and inflationary at early times
and accelerating at late times. Here we cast these models in terms of scalar
fields and study the corresponding spectrum of primordial perturbations. At
early times the spectrum is found to be not scale-invariant, thus implying that
slow-roll inflation is still required after the phase transition induced by the
vacuum. At late times the corresponding scalar-field potential is harmonic,
with a mass of the order of the Hubble scale, a result that may be understood
in the light of the holographic conjecture. |
Gravitational potential wells and the cosmic bulk flow: The bulk flow is a volume average of the peculiar velocities and a useful
probe of the mass distribution on large scales. The gravitational instability
model views the bulk flow as a potential flow that obeys a Maxwellian
Distribution. We use two N-body simulations, the LasDamas Carmen and the
Horizon Run, to calculate the bulk flows of various sized volumes in the
simulation boxes. Once we have the bulk flow velocities as a function of scale,
we investigate the mass and gravitational potential distribution around the
volume. We found that matter densities can be asymmetrical and difficult to
detect in real surveys, however, the gravitational potential and its gradient
may provide better tools to investigate the underlying matter distribution.
This study shows that bulk flows are indeed potential flows and thus provides
information on the flow sources. We also show that bulk flow magnitudes follow
a Maxwellian distribution on scales $>10\ h^{-1}$Mpc. | 21 cm radiation: A new probe of fundamental physics: New low frequency radio telescopes currently being built open up the
possibility of observing the 21-cm radiation before the Epoch of Reionization
in the future, in particular at redshifts 200 > z > 30, also known as the dark
ages. At these high redshifts, Cosmic Microwave Background (CMB) radiation is
absorbed by neutral hydrogen at its 21-cm hyperfine transition. This redshifted
21-cm signal thus carries information about the state of the early Universe and
can be used to test fundamental physics. We study the constraints these
observations can put on the variation of fundamental constants. We show that
the 21-cm radiation is very sensitive to the variations in the fine structure
constant and can in principle place constraints comparable to or better than
the other astrophysical experiments (fractional change < 10^ {-5}). Making such
observations will require radio telescopes of collecting area 10 - 10^6 sq. km
compared to 1 sq. km of current telescopes. These observations will thus
provide independent constraints on the fine structure constant at high
redshifts, observations of quasars being the only alternative. More importantly
the 21-cm absorption of CMB is the only way to probe the redshift range between
recombination and reionization. |
The Cosmological Impact of Luminous TeV Blazars I: Implications of
Plasma Instabilities for the Intergalactic Magnetic Field and Extragalactic
Gamma-Ray Background: Inverse-Compton cascades initiated by energetic gamma rays (E>100 GeV)
enhance the GeV emission from bright, extragalactic TeV sources. The absence of
this emission from bright TeV blazars has been used to constrain the
intergalactic magnetic field (IGMF), and the stringent limits placed upon the
unresolved extragalactic gamma-ray background (EGRB) by Fermi has been used to
argue against a large number of such objects at high redshifts. However, these
are predicated upon the assumption that inverse-Compton scattering is the
primary energy-loss mechanism for the ultra-relativistic pairs produced by the
annihilation of the energetic gamma rays on extragalactic background light
photons. Here we show that for sufficiently bright TeV sources
(isotropic-equivalent luminosities >10^{42} erg/s) plasma beam instabilities,
specifically the "oblique" instability, present a plausible mechanism by which
the energy of these pairs can be dissipated locally, heating the intergalactic
medium. Since these instabilities typically grow on timescales short in
comparison to the inverse-Compton cooling rate, they necessarily suppress the
inverse-Compton cascades. As a consequence, this places a severe constraint
upon efforts to limit the IGMF from the lack of a discernible GeV bump in TeV
sources. Similarly, it considerably weakens the Fermi limits upon the evolution
of blazar populations. Specifically, we construct a TeV-blazar luminosity
function from those objects presently observed and find that it is very well
described by the quasar luminosity function at z~0.1, shifted to lower
luminosities and number densities, suggesting that both classes of sources are
regulated by similar processes. Extending this relationship to higher
redshifts, we show that the magnitude and shape of the EGRB above ~10 GeV is
naturally reproduced with this particular example of a rapidly evolving
TeV-blazar luminosity function. | Evolution of violent gravitational disc instability in galaxies: Late
stabilization by transition from gas to stellar dominance: We address the cosmological evolution of violent gravitational instability in
high-redshift, massive, star-forming galactic discs. To this aim, we integrate
in time the equations of mass and energy conservation under self-regulated
instability of a two-component disc of gas and stars. The disc is assumed to be
continuously fed by cold gas at the average cosmological rate. The gas forms
stars and is partly driven away by stellar feedback. The gas and stars flow
inward through the disc to a central bulge due to torques that drive angular
momentum outwards. The gravitational energy released by the mass inflow down
the gravitational potential gradient drives the disc turbulence that maintains
the disc unstable with a Toomre instability parameter Q~1, compensating for the
dissipative losses of the gas turbulence and raising the stellar velocity
dispersion. We follow the velocity dispersion of stars and gas as they heat and
cool respectively and search for disc `stabilization', to be marked by a low
gas velocity dispersion comparable to the speed of sound ~10 km/s. We vary the
model parameters that characterize the accreted gas fraction, turbulence
dissipation rate, star-formation rate, and stellar feedback. We find that as
long as the gas input roughly follows the average cosmological rate, the disc
instability is a robust phenomenon at high redshift till z~1, driven by the
high surface density and high gas fraction due to the intense cosmological
accretion. For a broad range of model parameter values, the discs tend to
`stabilize' at z~0-0.5 as they become dominated by hot stars. When the model
parameters are pushed to extreme values, the discs may stabilize as early as
z~2, with the gas loss by strong outflows serving as the dominant stabilizing
factor. |
First Cosmological Results using Type Ia Supernovae from the Dark Energy
Survey: Measurement of the Hubble Constant: We present an improved measurement of the Hubble constant (H_0) using the
'inverse distance ladder' method, which adds the information from 207 Type Ia
supernovae (SNe Ia) from the Dark Energy Survey (DES) at redshift 0.018 < z <
0.85 to existing distance measurements of 122 low redshift (z < 0.07) SNe Ia
(Low-z) and measurements of Baryon Acoustic Oscillations (BAOs). Whereas
traditional measurements of H_0 with SNe Ia use a distance ladder of parallax
and Cepheid variable stars, the inverse distance ladder relies on absolute
distance measurements from the BAOs to calibrate the intrinsic magnitude of the
SNe Ia. We find H_0 = 67.8 +/- 1.3 km s-1 Mpc-1 (statistical and systematic
uncertainties, 68% confidence). Our measurement makes minimal assumptions about
the underlying cosmological model, and our analysis was blinded to reduce
confirmation bias. We examine possible systematic uncertainties and all are
below the statistical uncertainties. Our H_0 value is consistent with estimates
derived from the Cosmic Microwave Background assuming a LCDM universe (Planck
Collaboration et al. 2018). | Gravitational waves from cosmological phase transitions: First order phase transitions in the early universe can give rise to a
stochastic background of gravitational waves. A hypothetical first order
electroweak phase transition is particularly interesting in this respect, since
the signal is in the good frequency range to be detectable by the space
interferometer LISA. Three main processes lead to the production of the
gravitational wave signal: the collision of the broken phase bubbles, the
magnetohydrodynamical turbulence in the plasma stirred by the bubble
collisions, and the magnetic fields amplified by the magnetohydrodynamical
turbulence. The main features of the gravitational wave spectrum, such as the
peak frequency, the amplitude, and the slopes both at low and high wave-number
can be predicted by general arguments based on the characteristics of the
source: in particular, the structure of its space and time correlation. We find
that the gravitational wave signal from a first order phase transition
occurring at electroweak symmetry breaking falls into the LISA sensitivity
range if the phase transition lasts for about one hundredth of the Hubble time
and the energy density of the turbulent motions is about twenty percent of the
total energy density in the universe at the phase transition time. |
The stochastic background from cosmic (super)strings: popcorn and
(Gaussian) continuous regimes: In the era of the next generation of gravitational wave experiments a
stochastic background from cusps of cosmic (super)strings is expected to be
probed and, if not detected, to be significantly constrained. A popcorn-like
background can be, for part of the parameter space, as pronounced as the
(Gaussian) continuous contribution from unresolved sources that overlap in
frequency and time. We study both contributions from unresolved cosmic string
cusps over a range of frequencies relevant to ground based interferometers,
such as LIGO/Virgo second generation (AdLV) and Einstein Telescope (ET) third
generation detectors, the space antenna LISA and Pulsar Timing Arrays (PTA). We
compute the sensitivity (at $2 \sigma$ level) in the parameter space for AdLV,
ET, LISA and PTA. We conclude that the popcorn regime is complementary to the
continuous background. Its detection could therefore enhance confidence in a
stochastic background detection and possibly help determine fundamental string
parameters such as the string tension and the reconnection probability. | Cosmicflows-3: The Cosmicflows database of galaxy distances that in the 2nd edition
contained 8,188 entries is now expanded to 17,669 entries. The major additions
are 2,257 distances that we have derived from the correlation between galaxy
rotation and luminosity with photometry at 3.6 microns obtained with Spitzer
Space Telescope and 8,885 distances based on the Fundamental Plane methodology
from the 6dFGS collaboration. There are minor augmentations to the Tip of the
Red Giant Branch and Type Ia supernova compilations. A zero point calibration
of the supernova luminosities give a value for the Hubble Constant of 76.2
+-3.4(r) +-2.7(s) km/s/Mpc. Alternatively, a restriction on the peculiar
velocity monopole term representing global infall/outflow implies H_0 = 75 +-2
km/s/Mpc. |
Interacting radiation after Planck and its implications for the Hubble
Tension: Standard cosmology predicts that prior to matter-radiation equality about 41%
of the energy density was in free-streaming neutrinos. In many beyond Standard
Model scenarios, however, the amount and free-streaming nature of this
component is modified. For example, this occurs in models with new neutrino
self-interactions or an additional dark sector with interacting light
particles. We consider several extensions of the standard cosmology that
include a non-free-streaming radiation component as motivated by such particle
physics models and use the final Planck data release to constrain them. This
release contains significant improvements in the polarization likelihood which
plays an important role in distinguishing free-streaming from interacting
radiation species. Fixing the total amount of energy in radiation to match the
expectation from standard neutrino decoupling we find that the fraction of
free-streaming radiation must be $f_\mathrm{fs} > 0.8$ at 95% CL (combining
temperature, polarization and baryon acoustic oscillation data). Allowing for
arbitrary contributions of free-streaming and interacting radiation, the
effective number of new non-free-streaming degrees of freedom is constrained to
be $N_\mathrm{fld} < 0.6$ at 95% CL. Cosmologies with additional radiation are
also known to ease the discrepancy between the local measurement and CMB
inference of the current expansion rate $H_0$. We show that including a
non-free-streaming radiation component allows for a larger amount of total
energy density in radiation, leading to a mild improvement of the fit to
cosmological data compared to previously discussed models with only a
free-streaming component. | The complete census of optically selected AGNs in the Coma Supercluster:
the dependence of AGN activity on the local environment: To investigate the dependence of the occurrence of active galactic nuclei
(AGNs) on local galaxy density, we study the nuclear properties of ~5000
galaxies in the Coma Supercluster whose density spans 2 orders of magnitude
from the sparse filaments to the cores of the rich clusters. We obtained
optical spectra of the nuclei of 177 galaxies using the 1.5m Cassini telescope,
which are added to the 4785 spectra available from SDSS (DR7) to fill-in the
incomplete coverage by SDSS of luminous galaxies. We perform a spectral
classification of the nuclei of galaxies (with a completeness of 98% at
r<17.77), classifying the nuclear spectra in six classes: three of them (SEY,
sAGN, LIN) refer to AGNs and the remaining three (HII, RET, PAS) refer to
different stages of starburst activity. To perform such classification, we use
the WHAN diagnostic, after correcting Halpha by 1.3 A for underlying
absorption. We find that 482 (10%) of 5027 galaxies host an AGN: their
frequency strongly increases with increasing luminosity of the parent galaxies,
such that 32% of galaxies with Log(i-Lum)<10.2 (Solar) harbor an AGN at their
interior. In addition to their presence in luminous galaxies, AGNs are also
found in red galaxies with <g-i> < 1.15 \pm 0.15 mag. The majority of SEY and
sAGN (strong AGNs) are associated with luminous late-type (or S0a) galaxies,
while LIN (weak AGNs) and RET ("retired"), are mostly found among E/S0as. The
number density of AGNs, HII region-like, and retired galaxies is found to
anti-correlate with the local density of galaxies, such that their frequency
drops by a factor of two near the cluster cores, while the frequency of
galaxies containing passive nuclei increases by the same amount towards the
center of rich clusters. The dependence of AGN number density on the local
galaxy density is greater than the one implied by morphology segregation alone. |
Hubble constant and nuclear equation of state from kilonova
spectro-photometric light curves: The merger of two compact objects of which at least one is a neutron star is
signalled by transient electromagnetic emission in a kilonova (KN). This event
is accompanied by gravitational waves and possibly other radiation messengers
such as neutrinos or cosmic rays. The electromagnetic emission arises from the
radioactive decay of heavy $r-$process elements synthesized in the material
ejected during and after the merger. In this paper we show that the analysis of
KNe light curves can provide cosmological distance measurements and constrain
the properties of the ejecta. In this respect, MAAT, the new Integral Field
Unit in the OSIRIS spectrograph on the $10.4$ m Gran Telescopio CANARIAS (GTC),
is well suited for the study of KNe by performing absolute spectro-photometry
over the entire 3600-10000 Angstron spectral range. Here, we study the most
representative cases regarding the scientific interest of KNe from binary
neutron stars, and we evaluate the observational prospects and performance of
MAAT on the GTC to do the following: a) study the impact of the equation of
state on the KN light curve, and determine to what extent bounds on neutron
star (NS) radii or compactness deriving from KN peak magnitudes can be
identified and b) measure the Hubble constant, $H_0$, with precision improved
by up to 40$\%$, when both gravitational wave data and photometric-light curves
are used. In this context we discuss how the equation of state, the viewing
angle, and the distance affect the precision and estimated value of $H_0$. | Search of sub-parsec massive binary black holes through line diagnosis: We investigate on the spectral properties of an active black hole, member of
a massive (10^7 - 10^9 Msun) sub-parsec black hole binary. We work under the
hypothesis that the binary, surrounded by a circum-binary disc, has cleared a
gap, and that accretion occurs onto the secondary black hole fed by material
closer to the inner edge of the disc. Broad line emission clouds orbit around
the active black hole and suffer erosion due to tidal truncation at the Roche
Lobe surface, following gap opening and orbital decay. We consider three of the
most prominent broad emission lines observed in the spectra of AGNs, i.e. CIV,
MgII and H{\beta}, and compute the flux ratios between the lines of MgII and
CIV (FMgII/FCIV) and those of MgII and H{\beta} (FMgII/FH{\beta}). We find that
close black hole binaries have FMgII/FCIV up to one order of magnitude smaller
than single black holes. By contrast FMgII/FH{\beta} may be significantly
reduced only at the shortest separations. Peculiarly low values of line flux
ratios together with large velocity offsets between the broad and narrow
emission lines and/or periodic variability in the continuum (on timescales >=
years) would identify genuine sub-pc binary candidates. |
Extreme Axions Unveiled: a Novel Fluid Approach for Cosmological
Modeling: Axion-like particles (ALPs) are a well-motivated dark matter candidate that
solve some of the problems in the clustering of large scale structure in
cosmology. ALPs are often described by a simplified quadratic potential to
specify the dynamics of the axion field, and are included in cosmological
analysis codes using a modified fluid prescription. In this paper we consider
the extreme axion: a version of the axion with a high initial field angle that
produces an enhancement (rather than a suppression) of structure on small
scales around the Jeans length, which can be probed by measurements of
clustering such as the eBOSS DR14 Ly-$\alpha$ forest. We present a novel method
of modeling the extreme axion as a cosmological fluid, combining the
Generalized Dark Matter model with the effective fluid approach presented in
the \texttt{axionCAMB} software, as well as implementing a series of
computational innovations to efficiently simulate the extreme axions. We find
that for axion masses between $10^{-23} \text{ eV} \lesssim m_a \lesssim
10^{-22.5} \text{ eV}$, constraints on the axion fraction imposed by the eBOSS
DR14 Ly-$\alpha$ forest can be significantly weakened by allowing them to be in
the form of extreme axions with a starting angle between $\pi - 10^{-1}
\lesssim \theta_0 \lesssim \pi - 10^{-2}$. This work motivates and enables a
more robust hydrodynamical analysis of extreme axions in order to compare them
to high-resolution Ly-$\alpha$ forest data in the future. | Testing the isotropy of cosmic acceleration with Pantheon+SH0ES: A
cosmographic analysis: We use a recent Pantheon+SH0ES compilation of Type Ia Supernova distance
measurements at low-redshift, i.e., $0.01 \leq z \leq 0.10$, in order to
investigate the directional dependency of the deceleration parameter ($q_0$) in
different patches ($60^{\circ}$ size) across the sky, as a probe of the
statistical isotropy of the Universe. We adopt a cosmographic approach to
compute the cosmological distances, fixing $H_0$ and $M_B$ to reference values
provided by the collaboration. By looking at 500 different patches randomly
taken across the sky, we find a maximum $\sim 3\sigma$ CL anisotropy level for
$q_0$, whose direction points orthogonally to the CMB dipole axis, i.e.,
$(RA^{\rm SN},DEC^{\rm SN}) = (267^{\circ},6^{\circ})$ vs $(RA^{\rm
CMB},DEC^{\rm CMB}) = (167^{\circ},-7^{\circ})$. We assessed the statistical
significance of those results, finding that such a signal is expected due to
the limitations of the observational sample. These results support that there
is no significant evidence for a departure from the cosmic isotropy assumption,
one of the pillars of the standard cosmological model. |
Direct millicharged dark matter cannot explain EDGES: Heat transfer between baryons and millicharged dark matter has been invoked
as a possible explanation for the anomalous 21-cm absorption signal seen by
EDGES. Prior work has shown that the solution requires that millicharged
particles make up only a fraction $(m_\chi/{\rm MeV})\ 0.0115\% \lesssim f
\lesssim 0.4\%$ of the dark matter and that their mass $m_\chi$ and charge
$q_\chi$ have values $0.1 \lesssim (m_\chi/{\rm MeV})\lesssim 10$ and $10^{-6}
\lesssim (q_\chi/e)\lesssim 10^{-4}$. Here we show that such particles come
into chemical equilibrium before recombination, and so are subject to a
constraint on the effective number $N_{\rm eff}$ of relativistic degrees of
freedom, which we update using Planck 2018 data. We moreover determine the
precise relic abundance $f$ that results for a given mass $m_\chi$ and charge
$q_\chi$ and incorporate this abundance into the constraints on the
millicharged-dark-matter solution to EDGES. With these two results, the
solution is ruled out if the relic abundance is set by freeze-out. | Model-independent constraints on modified gravity from current data and
from the Euclid and SKA future surveys: The aim of this paper is to constrain modified gravity with redshift space
distortion observations and supernovae measurements. Compared with a standard
LCDM analysis, we include three additional free parameters, namely the initial
conditions of the matter perturbations,the overall perturbation normalization,
and a scale-dependent Y parameter modifying the Poisson equation, in an attempt
to perform a more model-independent analysis. First, we constrain the Poisson
parameter Y (also called Geff ) by using currently available fsigma_8 data and
the recent SN catalog JLA. We find that the inclusion of the additional free
parameters makes the constraints significantly weaker than when fixing them to
the standard cosmological value. Second, we constrain Y by using forecast
growth-rate data for Euclid and SKA missions. Here again we point out the
weakening of the constraints when the additional parameters are included.
Finally, we adopt as modified gravity Poisson parameter the specific Horndeski
form, and use scale-dependent forecasts to build an exclusion plot for the
Yukawa potential akin to the ones realized in laboratory experiments, both for
the Euclid and the SKA surveys. |
The WiggleZ Dark Energy Survey: Joint measurements of the expansion and
growth history at z < 1: We perform a joint determination of the distance-redshift relation and cosmic
expansion rate at redshifts z = 0.44, 0.6 and 0.73 by combining measurements of
the baryon acoustic peak and Alcock-Paczynski distortion from galaxy clustering
in the WiggleZ Dark Energy Survey, using a large ensemble of mock catalogues to
calculate the covariance between the measurements. We find that D_A(z) = (1205
+/- 114, 1380 +/- 95, 1534 +/- 107) Mpc and H(z) = (82.6 +/- 7.8, 87.9 +/- 6.1,
97.3 +/- 7.0) km/s/Mpc at these three redshifts. Further combining our results
with other baryon acoustic oscillation and distant supernovae datasets, we use
a Monte Carlo Markov Chain technique to determine the evolution of the Hubble
parameter H(z) as a stepwise function in 9 redshift bins of width dz = 0.1,
also marginalizing over the spatial curvature. Our measurements of H(z), which
have precision better than 7% in most redshift bins, are consistent with the
expansion history predicted by a cosmological-constant dark-energy model, in
which the expansion rate accelerates at redshift z < 0.7. | Comparing approximate methods for mock catalogues and covariance
matrices I: correlation function: This paper is the first in a set that analyses the covariance matrices of
clustering statistics obtained from several approximate methods for
gravitational structure formation. We focus here on the covariance matrices of
anisotropic two-point correlation function measurements. Our comparison
includes seven approximate methods, which can be divided into three categories:
predictive methods that follow the evolution of the linear density field
deterministically (ICE-COLA, Peak Patch, and Pinocchio), methods that require a
calibration with N-body simulations (Patchy and Halogen), and simpler recipes
based on assumptions regarding the shape of the probability distribution
function (PDF) of density fluctuations (log-normal and Gaussian density
fields). We analyse the impact of using covariance estimates obtained from
these approximate methods on cosmological analyses of galaxy clustering
measurements, using as a reference the covariances inferred from a set of full
N-body simulations. We find that all approximate methods can accurately recover
the mean parameter values inferred using the N-body covariances. The obtained
parameter uncertainties typically agree with the corresponding N-body results
within 5% for our lower mass threshold, and 10% for our higher mass threshold.
Furthermore, we find that the constraints for some methods can differ by up to
20% depending on whether the halo samples used to define the covariance
matrices are defined by matching the mass, number density, or clustering
amplitude of the parent N-body samples. The results of our configuration-space
analysis indicate that most approximate methods provide similar results, with
no single method clearly outperforming the others. |
Multiwavelength study of X-ray Luminous Clusters in the Hyper
Suprime-Cam Subaru Strategic Program S16A field: We present a joint X-ray, optical and weak-lensing analysis for X-ray
luminous galaxy clusters selected from the MCXC (Meta-Catalog of X-Ray Detected
Clusters of Galaxies) cluster catalog in the Hyper Suprime-Cam Subaru Strategic
Program (HSC-SSP) survey field with S16A data, As a pilot study of our planned
series papers, we measure hydrostatic equilibrium (H.E.) masses using
XMM-Newton data for four clusters in the current coverage area out of a sample
of 22 MCXC clusters. We additionally analyze a non-MCXC cluster associated with
one MCXC cluster. We show that H.E. masses for the MCXC clusters are correlated
with cluster richness from the CAMIRA catalog (Oguri et al. 2017), while that
for the non-MCXC cluster deviates from the scaling relation. The mass
normalization of the relationship between the cluster richness and H.E. mass is
compatible with one inferred by matching CAMIRA cluster abundance with a
theoretical halo mass function. The mean gas mass fraction based on H.E. masses
for the MCXC clusters is $\langle f_{\rm gas} \rangle = 0.125\pm0.012$ at
spherical overdensity $\Delta=500$, which is $\sim80-90$ percent of the cosmic
mean baryon fraction, $\Omega_b/\Omega_m$, measured by cosmic microwave
background experiments. We find that the mean baryon fraction estimated from
X-ray and HSC-SSP optical data is comparable to $\Omega_b/\Omega_m$. A
weak-lensing shear catalog of background galaxies, combined with photometric
redshifts, is currently available only for three clusters in our sample.
Hydrostatic equilibrium masses roughly agree with weak-lensing masses, albeit
with large uncertainty. This study demonstrates that further multiwavelength
study for a large sample of clusters using X-ray, HSC-SSP optical and weak
lensing data will enable us to understand cluster physics and utilize
cluster-based cosmology. | The bispectrum covariance beyond Gaussianity: A log-normal approach: To investigate and specify the statistical properties of cosmological fields
with particular attention to possible non-Gaussian features, accurate formulae
for the bispectrum and the bispectrum covariance are required. The bispectrum
is the lowest-order statistic providing an estimate for non-Gaussianities of a
distribution, and the bispectrum covariance depicts the errors of the
bispectrum measurement and their correlation on different scales. Currently,
there do exist fitting formulae for the bispectrum and an analytical expression
for the bispectrum covariance, but the former is not very accurate and the
latter contains several intricate terms and only one of them can be readily
evaluated from the power spectrum of the studied field. Neglecting all
higher-order terms results in the Gaussian approximation of the bispectrum
covariance. We study the range of validity of this Gaussian approximation for
two-dimensional non-Gaussian random fields. For this purpose, we simulate
Gaussian and non-Gaussian random fields, the latter represented by log-normal
fields and obtained directly from the former by a simple transformation. From
the simulated fields, we calculate the power spectra, the bispectra, and the
covariance from the sample variance of the bispectra, for different degrees of
non-Gaussianity \alpha, which is equivalent to the skewness on a given angular
scale \theta g. We find that the Gaussian approximation provides a good
approximation for \alpha<0.6 and a reasonably accurate approximation for
\alpha< 1, both on scales >8\theta g. Using results from cosmic shear
simulations, we estimate that the cosmic shear convergence fields are described
by \alpha<0.7 at \theta g~4". We therefore conclude that the Gaussian
approximation for the bispectrum covariance is likely to be applicable in
ongoing and future cosmic shear studies. |
Detection of the 158 micron [CII] Transition at z=1.3: Evidence for a
Galaxy-Wide Starburst: We report the detection of 158 micron [CII] fine-structure line emission from
MIPS J142824.0+352619, a hyperluminous (L_IR ~ 10^13 L_sun) starburst galaxy at
z=1.3. The line is bright, and corresponds to a fraction L_[CII]/L_FIR = 2 x
10^-3 of the far-IR (FIR) continuum. The [CII], CO, and FIR continuum emission
may be modeled as arising from photodissociation regions (PDRs) that have a
characteristic gas density of n ~ 10^4.2 cm^-3, and that are illuminated by a
far-UV radiation field ~10^3.2 times more intense than the local interstellar
radiation field. The mass in these PDRs accounts for approximately half of the
molecular gas mass in this galaxy. The L_[CII]/L_FIR ratio is higher than
observed in local ULIRGs or in the few high-redshift QSOs detected in [CII],
but the L_[CII]/L_FIR and L_CO/L_FIR ratios are similar to the values seen in
nearby starburst galaxies. This suggests that MIPS J142824.0+352619 is a
scaled-up version of a starburst nucleus, with the burst extended over several
kiloparsecs. | AGN proximity zone fossils and the delayed recombination of metal lines: We model the time-dependent evolution of metal-enriched intergalactic and
circumgalactic gas exposed to the fluctuating radiation field from an active
galactic nucleus (AGN). We consider diffuse gas densities (n_H=10^-5-10^-3
cm^-3) exposed to the extra-galactic background (EGB) and initially in thermal
equilibrium (T \sim 10^4-10^4.5 K). Once the proximate AGN field turns on,
additional photo-ionisation rapidly ionises the HI and metals. The enhanced AGN
radiation field turns off after a typical AGN lifetime (tau_AGN=1-20 Myr) and
the field returns to the EGB intensity, but the metals remain out of ionisation
equilibrium for timescales that can significantly exceed tau_AGN. We define
this phase as the AGN proximity zone "fossil" phase and show that high
ionisation stages (e.g. OVI, NeVIII, MgX) are in general enhanced, while the
abundances of low ions are reduced. In contrast, HI re-equilibrates rapidly
(<<tau_AGN) owing to its low neutral fraction at diffuse densities. We
demonstrate that metal column densities of intervening gas observed in
absorption in quasar sight lines are significantly affected by delayed
recombination for a wide range of densities, metallicities, and AGN strengths,
lifetimes, and duty cycles. We model the exceptionally strong z=0.9 NeVIII
absorbers observed by Tripp et al. (2011) as arising in a possible fossil zone
or near a recently turned-on AGN and we demonstrate that at low redshift even
moderate strength AGN could significantly enhance the high-ion metal columns in
the circumgalactic media of galaxies observed without active AGN. Fossil
proximity zones may be very important during the quasar era, z \sim 2-5. AGN
proximity zone fossils allow a whole new class of non-equilibrium solutions
that may be applicable to a large fraction of observed metal absorbers and
which could potentially change the inferred physical conditions and masses of
diffuse gases. |
Probing the evolution of the EBL photon density out to $z~\sim 1$ via
$γ$-ray propagation measurements with Fermi: The redshift ($z$) evolution of the Extragalactic Background Light (EBL)
photon density is very important to understand the history of cosmological
structure formation of galaxies and stars since the epoch of recombination. The
EBL photons with the characteristic spectral energy distribution ranging from
ultraviolet/optical to far-infrared provide a major source of opacity of the
Universe to the GeV-TeV $\gamma$-rays travelling over cosmological distances.
The effect of the EBL is very significant through $\gamma \gamma \rightarrow
e^- e^+$ absorption process on the propagation of the $\gamma$-ray photons with
energy $E >$ 50 GeV emitted from the sources at $z \sim 1$. This effect is
characterized by the optical depth ($\tau$) which strongly depends on $E$, $z$
and density of the EBL photons. The proper density of the EBL photons increases
with $z$ due to expansion of the Universe whereas evolution of radiation
sources contributing to the EBL leads to a decrease in the density with
increasing $z$. Therefore, the resultant volumetric evolution of the EBL photon
density is approximated by a modified redshift dependence. In this work, we
probe evolution of the EBL photon density predicted by two prominent models
using cosmic gamma-ray horizon ($\tau (E,z)=$ 1) determined by the measurements
from the \emph{Fermi}-Large Area Telescope (LAT) observations. The modified
redshift dependence of the EBL photon density is optimized for a given EBL
model by estimating the same gamma-ray horizon as predicted by the
\emph{Fermi}-LAT observations. We further compare the optical depth estimates
in the energy range $E =$ 4 GeV-1 TeV and redshift range $z =0.01-1$ from the
\emph{Fermi}-LAT observations with the values derived from the two EBL models
to further constrain the evolution of the EBL photon density in the $z~\sim 1$
Universe. | Power spectrum for the Bose-Einstein condensate dark matter: We assume that dark matter is composed of scalar particles that form a
Bose-Einstein condensate (BEC) at some point during the cosmic evolution.
Afterwards, cold dark matter is in the form of a condensate and behaves
slightly different from the standard dark matter component. We study the large
scale perturbative dynamics of the BEC dark matter in a model where this
component coexists with baryonic matter and cosmological constant. The
perturbative dynamics is studied using neo- Newtonian cosmology (where the
pressure is dynamically relevant for the homogeneous and isotropic background)
which is assumed to be correct for small values of the sound speed. We show
that BEC dark matter effects can be seen in the matter power spectrum if the
mass of the condensate particle lies in the range 15meV < m < 700meV leading to
a small, but perceptible, excess of power at large scales. |
An Empirical Characterization of Extended Cool Gas Around Galaxies Using
MgII Absorption Features: We report results from a survey of MgII absorbers in the spectra of
background QSOs that are within close angular distances to a foreground galaxy
at z<0.5, using the Magellan Echellette Spectrograph. We have established a
spectroscopic sample of 94 galaxies at a median redshift of <z> = 0.24 in
fields around 70 distant background QSOs (z_QSO>0.6), 71 of which are in an
'isolated' environment with no known companions and located at rho <~ 120 h^-1
kpc from the line of sight of a background QSO. The rest-frame absolute B-band
magnitudes span a range from M_B-5log h=-16.4 to M_B-5log h=-21.4 and
rest-frame B_AB-R_AB colors range from B_AB-R_AB~0 to B_AB-R_AB~1.5. Of these
'isolated' galaxies, we find that 47 have corresponding MgII absorbers in the
spectra of background QSOs and rest-frame absorption equivalent width
W_r(2796)=0.1-2.34 A, and 24 do not give rise to MgII absorption to sensitive
upper limits. Our analysis shows that (1) Wr(2796) declines with increasing
distance from 'isolated' galaxies but shows no clear trend in 'group'
environments; (2) more luminous galaxies possess more extended MgII absorbing
halos with the gaseous radius scaled by B-band luminosity according to
R_gas=75x(L_B/L_B*)^(0.35+/-0.03) h^{-1} kpc; (3) there is little dependence
between the observed absorber strength and galaxy intrinsic colors; and (4)
within R_gas, we find a mean covering fraction of <kappa_0.3>~70% for absorbers
of Wr(2796)>=0.3 A and <kappa_0.1>~80% for absorbers of Wr(2796)>=0.1 A. The
lack of correlation between Wr(2796) and galaxy colors suggests a lack of
physical connection between the origin of extended MgII halos and recent star
formation history of the galaxies. Finally, we discuss the total gas mass in
galactic halos as traced by MgII absorbers. We also compare our results with
previous studies. | A Research Note on the Implementation of Star Formation and Stellar
Feedback in Semi-Analytic Models: We study the impact of star formation and stellar feedback prescriptions on
galaxy properties predicted by means of "stripped-down" versions of
independently developed semi-analytic models (SAMs). These include cooling,
star formation, feedback from supernovae (SNe) and simplified prescriptions for
galaxy merging, but no chemical evolution, disc instabilities or AGN feedback.
We run these versions on identical samples of dark matter (DM) haloes extracted
from high-resolution N-body simulations in order to perform both statistical
analysis and object-by-object comparisons. We compare our results with previous
work based on stripped-down versions of the same SAMs including only gas
cooling, and show that all feedback models provide coherent modifications in
the distribution of baryons between the various gas phases. In particular, we
find that the predicted hot gas fractions are considerably increased by up to a
factor of three, while the corresponding cold gas fractions are correspondingly
decreased, and a significant amount of mass is ejected from the DM halo.
Nonetheless, we also find relevant differences in the predicted properties of
model galaxies among the three SAMs: these deviations are more relevant at mass
scales comparable to that of our own Galaxy, and are reduced at larger masses,
confirming the varying impact of stellar feedback at different mass scales. We
also check the effect of enhanced star formation events (i.e. starbursts
modes), defined in connection with galaxy mergers. We find that, in general,
these episodes have a limited impact in the overall star formation histories of
model galaxies, even in massive DM halos where merger-driven star formation has
often been considered very important. |
Dark matter in dwarf galaxies of the Local Group: We review basic properties of the population of dwarf galaxies in the Local
Group focusing on dwarf spheroidal galaxies found in the immediate vicinity of
the Milky Way. The evidence for dark matter in these objects is critically
assessed. We describe the methods of dynamical modelling of such objects, using
a few examples of the best-studied dwarfs and discuss the sources of
uncertainties in mass estimates. We conclude with perspectives for dwarf
galaxies as targets for dark matter detection experiments. | COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses XI.
Techniques for time delay measurement in presence of microlensing: Measuring time delays between the multiple images of gravitationally lensed
quasars is now recognized as a competitive way to constrain the cosmological
parameters, and it is complementary with other cosmological probes. This
requires long and well sampled optical light curves of numerous lensed quasars,
such as those obtained by the COSMOGRAIL collaboration. High-quality data from
our monitoring campaign call for novel numerical techniques to robustly measure
the delays, as well as the associated random and systematic uncertainties, even
in the presence of microlensing variations. We propose three different point
estimators to measure time delays, which are explicitly designed to handle
light curves with extrinsic variability. These methods share a common
formalism, which enables them to process data from n-image lenses. Since the
estimators rely on significantly contrasting ideas, we expect them to be
sensitive to different bias sources. For each method and data set, we
empirically estimate both the precision and accuracy (bias) of the time delay
measurement using simulated light curves with known time delays that closely
mimic the observations. Finally, we test the self-consistency of our approach,
and we demonstrate that our bias estimation is serviceable. These new methods,
including the empirical uncertainty estimator, will represent the standard
benchmark for analyzing the COSMOGRAIL light curves. |
Non-Minimally Coupled Inflation with Initial Conditions from a
Pre-Inflation Anamorphic Contracting Era: Inflation due to a non-minimally coupled scalar field with a large
non-minimal coupling, as first proposed by Salopek, Bardeen and Bond (SBB), is
in good agreement with the observed value of the spectral index and constraints
on the tensor-to-scalar ratio. Here we explore the possibility that SBB
inflation represents the late stage of a Universe which emerges from an early
contracting era. We present a model in which the Universe smoothly transitions
from an anamorphic contracting era to late-time SBB inflation without
encountering a singular bounce. This corresponds to a continuous expansion in
the Einstein frame throughout. We show that the anamorphic contracting era is
able to provide the smooth superhorizon initial conditions necessary for
subsequent SBB inflation to occur. The model predicts corrections to the
non-minimal coupling, kinetic term and potential of SBB inflation which can
observably increase the observed spectral index relative to its SBB prediction. | Multi-Wavelength Studies of Spectacular Ram Pressure Stripping of a
Galaxy. II. Star Formation in the Tail: With multiband photometric data in public archives, we detected four
intracluster star-forming regions in the Virgo cluster. Two of them were at a
projected distance of 35 kpc away from NGC4388, and the other two were 66 kpc
away. Our new spectroscopic observation revealed that their recession
velocities were comparable to the ram-pressure-stripped tail of NGC4388 and
confirmed their association. The stellar mass of the star-forming regions
ranged from 10^4 - 10^4.5 M_sun except for that of the faintest one which would
be <10^3 M_sun. The metallicity was comparable to the solar abundance, and the
age of the stars was ~ 10^6.8 years. Their young stellar age meant that the
star formation should have started after the gas was stripped from NGC4388.
This implied in situ condensation of the stripped gas. We also found that two
star-forming regions lay near the leading edge of a filamentary dark cloud. The
extinction of the filament was smaller than that derived from the Balmer
decrement of the star-forming regions. It implied that the dust in the filament
would be locally dense around the star-forming regions. |
Cosmic microwave background lensing with optimal convergence and shear
estimators: We present the optimal convergence and shear estimators for lensing
reconstruction from the cosmic microwave background temperature field. This
generalizes the deflection estimator, is sensitive to non-lensing modes,
provides internal consistency checks, and is always at least as optimal.
Previously, these estimators were only known in the squeezed limit. This paper
decomposes convergence and shear fields into cosine and sine waves and the
lensed correlation function is then Taylor expanded in the wave amplitudes.
Maximizing the likelihood function gives the optimal estimators for the
convergence and shear fields.
This method has the potential to improve the lensing reconstruction of the
cosmic microwave background polarization field: the shear and convergence can
be optimally combined to form a deflection estimator, or used separately to
separate non-lensing modes, or utilize lensing of non-Gaussian secondary
foregrounds. | z~1 Lya Emitters I. The Luminosity Function: We construct a flux-limited sample of 135 candidate z~1 Lya emitters (LAEs)
from Galaxy Evolution Explorer (GALEX) grism data using a new data cube search
method. These LAEs have luminosities comparable to those at high redshifts and
lie within a 7 Gyr gap present in existing LAE samples. We use archival and
newly obtained optical spectra to verify the UV redshifts of these LAEs. We use
the combination of the GALEX UV spectra, optical spectra, and X-ray imaging
data to estimate the active galactic nucleus (AGN) fraction and its dependence
on Lya luminosity. We remove the AGNs and compute the luminosity function (LF)
from 60 z~1 LAE galaxies. We find that the best fit LF implies a luminosity
density increase by a factor of ~1.5 from z~0.3 to z~1 and ~20 from z~1 to z~2.
We find a z~1 volumetric Lya escape fraction of 0.7+/-0.4%. |
Improving parametric mass modelling of lensing clusters through a
perturbative approach: We present a new method to model the mass distribution of galaxy clusters
that combines a parametric and a free-form approach to reconstruct cluster
cores with strong lensing constraints. It aims at combining the advantages of
both approaches, by keeping the robustness of the parametric component with an
increased flexibility thanks to a free-form surface of B-spline functions. We
demonstrate the capabilities of this new approach on the simulated cluster
Hera, which has been used to evaluate lensing codes for the analysis of the
Frontier Fields clusters. The method leads to better reproduction of the
constraints, with an improvement by a factor $\sim3-4$ on the root-mean-square
error on multiple-image positions, when compared to parametric-only approaches.
The resulting models show a better accuracy in the reconstruction of the
amplitude of the convergence field while conserving a high fidelity on other
lensing observables already well reproduced. We make this method publicly
available through its implementation in the Lenstool software. | Machine learning cosmic backreaction and its effects on observations: Symbolic expressions for cosmic backreaction and mean redshift drift in a
range of 2-region models in terms of average quantities are presented. The
demonstration that these expressions can be obtained constitutes the opening of
a new avenue towards understanding the effects of cosmic backreaction in our
universe: With a symbolic expression for the redshift drift at hand, the
redshift drift can be used to constrain cosmological parameters including the
large-scale expansion rate and backreaction. In addition, by introducing
symbolic expressions for cosmic backreaction, this quantity can be constrained
with observations such as redshift-distance measures. |
Hydrodynamic Simulation of Non-thermal Pressure Profiles of Galaxy
Clusters: Cosmological constraints from X-ray and microwave observations of galaxy
clusters are subjected to systematic uncertainties. Non-thermal pressure
support due to internal gas motions in galaxy clusters is one of the major
sources of astrophysical uncertainties. Using a mass-limited sample of galaxy
clusters from a high-resolution hydrodynamical cosmological simulation, we
characterize the non-thermal pressure fraction profile and study its dependence
on redshift, mass, and mass accretion rate. We find that the non-thermal
pressure fraction profile is universal across redshift when galaxy cluster
radii are defined with respect to the mean matter density of the universe
instead of the commonly used critical density. We also find that the
non-thermal pressure is predominantly radial, and the gas velocity anisotropy
profile exhibits strong universality when galaxy cluster radii are defined with
respect to the mean matter density of the universe. However, we find that the
non-thermal pressure fraction is strongly dependent on the mass accretion rate
of the galaxy cluster. We provide fitting formulae for the universal
non-thermal pressure fraction and velocity anisotropy profiles of gas in galaxy
clusters, which should be useful in modeling astrophysical uncertainties
pertinent to using galaxy clusters as cosmological probes. | Mass function and bias of dark matter halos for non-Gaussian initial
conditions: We revisit the derivation of the mass function and the bias of dark matter
halos for non-Gaussian initial conditions. We use a steepest-descent approach
to point out that exact results can be obtained for the high-mass tail of the
halo mass function and the two-point correlation of massive halos. Focusing on
primordial non-Gaussianity of the local type, we check that these results agree
with numerical simulations. The high-mass cutoff of the halo mass function
takes the same form as the one obtained from the Press-Schechter formalism, but
with a linear threshold $\delta_L$ that depends on the definition of the halo.
We show that a simple formula, which obeys this high-mass asymptotic and uses
the fit obtained for Gaussian initial conditions, matches numerical simulations
while keeping the mass function normalized to unity. Next, by deriving the
real-space halo two-point correlation in the spirit of Kaiser (1984) and taking
a Fourier transform, we obtain good agreement with simulations for the
correction to the halo bias due to primordial non-Gaussianity. Therefore,
neither the halo mass function nor the bias require an ad-hoc parameter $q$
provided one uses the correct linear threshold $\delta_L$ and pays attention to
halo displacements. The nonlinear real-space expression can be useful for
checking that the "linearized" bias is a valid approximation. Moreover, it
clearly shows how the baryon acoustic oscillation at $\sim 100 h^{-1}$Mpc is
amplified by the bias of massive halos and modified by primordial
non-Gaussianity. On smaller scales, the correction to the real-space bias
roughly scales as $\fNL \, b_M(\fNL=0) \, x^2$. The low-$k$ behavior of the
halo bias does not imply a divergent real-space correlation, so that one does
not need to introduce counterterms that depend on the survey size. |
A combined analysis of the $H_0$ late time direct measurements and the
impact on the Dark Energy sector: We combine 23 Hubble constant measurements based on Cepheids-SN Ia, TRGB-SN
Ia, Miras-SN Ia, Masers, Tully Fisher, Surface Brightness Fluctuations, SN II,
Time-delay Lensing, Standard Sirens and $\gamma$-ray Attenuation, obtaining our
best {\it optimistic} $H_0$ estimate, that is $H_0=72.94\pm0.75$ km/s/Mpc at
68\% CL. This is in $5.9\sigma$ tension with the $\Lambda$CDM model, therefore
we evaluate its impact on the extended Dark Energy cosmological models that can
alleviate the tension. We find more than $4.9\sigma$ evidence for a phantom
Dark Energy equation of state in the $w$CDM scenario, the cosmological constant
ruled out at more than $3\sigma$ in a $w_0w_a$CDM model and more than
$5.7\sigma$ evidence for a coupling between Dark Matter and Dark Energy in the
IDE scenario. Finally, we check the robustness of our results, and we quote two
additional combinations of the Hubble constant. The {\it ultra-conservative}
estimate, $H_0=72.7\pm 1.1$ km/s/Mpc at 68\% CL, is obtained removing the
Cepheids-SN Ia and the Time-Delay Lensing based measurements, and confirms the
evidence for new physics. | Microlensing of Quasar Broad Emission Lines: Constraints on Broad Line
Region Size: We measure the differential microlensing of the broad emission lines between
18 quasar image pairs in 16 gravitational lenses. We find that high ionization
lines such as CIV are more strongly microlensed than low ionization lines,
indicating that the high ionization line emission regions are more compact. If
we statistically model the distribution of microlensing magnifications, we
obtain estimates for the broad line region radius of 24 (-15/+22) and 55
(-35/+150) light-days (90% confidence) for the high and low ionization lines,
respectively. When the sample is divided attending to quasar luminosity, we
find that the line emission regions of more luminous quasars are larger, with a
slope consistent with the expected scaling from photoionization models. Our
estimates also agree well with the results from local reveberation mapping
studies. |
Low red-shift formula for the luminosity distance in a LTB model with
cosmological constant: We calculate the low red-shift Taylor expansion for the luminosity distance
for an observer at the center of a spherically symmetric matter inhomogeneity
with a non vanishing cosmological constant. We then test the accuracy of the
formulas comparing them to the numerical calculation for different cases for
both the luminosity distance and the radial coordinate. The formulas can be
used as a starting point to understand the general non linear effects of a
local inhomogeneity in presence of a cosmological constant, without making any
special assumption about the inhomogeneity profile. | An MCMC approach to extracting the global 21-cm signal during the cosmic
dawn from sky-averaged radio observations: Efforts are being made to observe the 21-cm signal from the 'cosmic dawn'
using sky-averaged observations with individual radio dipoles. In this paper,
we develop a model of the observations accounting for the 21-cm signal,
foregrounds, and several major instrumental effects. Given this model, we apply
Markov Chain Monte Carlo techniques to demonstrate the ability of these
instruments to separate the 21-cm signal from foregrounds and quantify their
ability to constrain properties of the first galaxies. For concreteness, we
investigate observations between 40 and 120 MHz with the proposed DARE mission
in lunar orbit, showing its potential for science return. |
Constraints on inflation with LSS surveys: features in the primordial
power spectrum: We analyse the efficiency of future large scale structure surveys to unveil
the presence of scale dependent features in the primordial spectrum --resulting
from cosmic inflation-- imprinted in the distribution of galaxies. Features may
appear as a consequence of non-trivial dynamics during cosmic inflation, in
which one or more background quantities experienced small but rapid deviations
from their characteristic slow-roll evolution. We consider two families of
features: localized features and oscillatory extended features. To characterise
them we employ various possible templates parametrising their scale dependence
and provide forecasts on the constraints on these parametrisations for LSST
like surveys. We perform a Fisher matrix analysis for three observables: cosmic
microwave background (CMB), galaxy clustering and weak lensing. We find that
the combined data set of these observables will be able to limit the presence
of features down to levels that are more restrictive than current constraints
coming from CMB observations only. In particular, we address the possibility of
gaining information on currently known deviations from scale invariance
inferred from CMB data, such as the feature appearing at the $\ell \sim 20$
multipole (which is the main contribution to the low-$\ell$ deficit) and a
potential feature appearing at $\ell \sim 800$. | CMB Lens Sample Covariance and Consistency Relations: Gravitational lensing information from the two and higher point statistics of
the CMB temperature and polarization fields are intrinsically correlated
because they are lensed by the same realization of structure between last
scattering and observation. Using an analytic model for lens sample covariance,
we show that there is one mode, separately measurable in the lensed CMB power
spectra and lensing reconstruction, that carries most of this correlation. Once
these measurements become lens sample variance dominated, this mode should
provide a useful consistency check between the observables that is largely free
of sampling and cosmological parameter errors. Violations of consistency could
indicate systematic errors in the data and lens reconstruction or new physics
at last scattering, any of which could bias cosmological inferences and
delensing for gravitational waves. A second mode provides a weaker consistency
check for a spatially flat universe. Our analysis isolates the additional
information supplied by lensing in a model independent manner but is also
useful for understanding and forecasting CMB cosmological parameter errors in
the extended $\Lambda$CDM parameter space of dark energy, curvature and massive
neutrinos. We introduce and test a simple but accurate forecasting technique
for this purpose that neither double counts lensing information nor neglects
lensing in the observables. |
Structures and components in galaxy clusters: observations and models: Clusters of galaxies are the largest gravitationally bounded structures in
the Universe dominated by dark matter. We review the observational appearance
and physical models of plasma structures in clusters of galaxies. Bubbles of
relativistic plasma which are inflated by supermassive black holes of AGNs,
cooling and heating of the gas, large scale plasma shocks, cold fronts,
non-thermal halos and relics are observed in clusters. These constituents are
reflecting both the formation history and the dynamical properties of clusters
of galaxies. We discuss X-ray spectroscopy as a tool to study the metal
enrichment in clusters and fine spectroscopy of Fe X-ray lines as a powerful
diagnostics of both the turbulent plasma motions and the energetics of the
non-thermal electron populations. The knowledge of the complex dynamical and
feedback processes is necessary to understand the energy and matter balance as
well as to constrain the role of the non-thermal components of clusters. | Probing the imprint of interacting dark energy on very large scales: The observed galaxy power spectrum acquires relativistic corrections from
lightcone effects, and these corrections grow on very large scales. Future
galaxy surveys in optical, infrared and radio bands will probe increasingly
large wavelength modes and reach higher redshifts. In order to exploit the new
data on large scales, an accurate analysis requires inclusion of the
relativistic effects. This is especially the case for primordial
non-Gaussianity and for extending tests of dark energy models to horizon
scales. Here we investigate the latter, focusing on models where the dark
energy interacts non-gravitationally with dark matter. Interaction in the dark
sector can also lead to large-scale deviations in the power spectrum. If the
relativistic effects are ignored, the imprint of interacting dark energy will
be incorrectly identified and thus lead to a bias in constraints on interacting
dark energy on very large scales. |
Cosmic string loop distribution on all length scales and at any redshift: We analytically derive the expected number density distribution of Nambu-Goto
cosmic string loops at any redshift soon after the time of string formation to
today. Our approach is based on the Polchinski-Rocha model of loop formation
from long strings which we adjust to fit numerical simulations and complement
by a phenomenological modelling of gravitational backreaction. Cosmological
evolution drives the loop distribution towards scaling on all length scales in
both the radiation and matter era. Memory of any reasonable initial loop
distribution in the radiation era is shown to be erased well before Big Bang
Nucleosynthesis. In the matter era, the loop distribution reaches full scaling,
up to some residual loops from the radiation era which may be present for
extremely low string tension. Finally, the number density of loops below the
gravitational cutoff is shown to be scale independent, proportional to a
negative power of the string tension and insensitive to the details of the
backreaction modelling. As an application, we show that the energy density
parameter of loops today cannot exceed 10^(-5) for currently allowed string
tension values, while the loop number density cannot be less than 10^(-6) per
Mpc^3. Our result should provide a more robust basis for studying the
cosmological consequences of cosmic string loops. | Evidence for particle re-acceleration in the radio relic in the galaxy
cluster PLCKG287.0 +32.9: Radio relics are diffuse radio sources observed in galaxy clusters, probably
produced by shock acceleration during cluster-cluster mergers. Their large
size, of the order of 1 Mpc, indicates that the emitting electrons need to be
(re)accelerated locally. The usually invoked Diffusive Shock Acceleration
models have been challenged by recent observations and theory. We report the
discovery of complex radio emission in the Galaxy cluster PLCKG287.0 +32.9,
which hosts two relics, a radio halo, and several radio filamentary emission.
Optical observations suggest that the cluster is elongated, likely along an
intergalactic filament, and displays a significant amount of substructure. The
peculiar features of this radio relic are that (i) it appears to be connected
to the lobes of a radio galaxy and (ii) the radio spectrum steepens on either
side of the radio relic. We discuss the origins of these features in the
context of particle re-acceleration. |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.