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Measuring chiral gravitational waves in Chern-Simons gravity with CMB
bispectra: Chern-Simons gravity coupled to the scalar sector through a generic coupling
function $f(\phi)$ can be tested at the very high energies of the inflationary
period. In 1706.04627, we computed the theoretical parity breaking signatures
of the $\langle \gamma \gamma \zeta \rangle$ primordial bispectrum which mixes
two gravitons and one scalar curvature perturbation. We defined a parameter
$\Pi$ which measures the level of parity breaking of the corresponding
bispectrum. In this work we forecast the expected $1 \sigma$ error on $\Pi$
using the cosmic microwave background (CMB) angular bispectra. We find that,
given the angular resolution of an experiment like $Planck$, $\Pi \sim 10^6$ is
detectable via the measurement of $BBT$ or $BBE$ angular bispectra if the
tensor-to-scalar ratio $r = 0.01$. We also show that, from the theoretical
point of view, $\Pi$ can be greater than $10^6$. Thus, our conclusion is that
$BBT$ or $BBE$ CMB angular bispectra can become an essential observable for
testing Chern-Simons gravity in the primordial universe. | Cosmic rays and the magnetic field in the nearby starburst galaxy NGC253
III. Helical magnetic fields in the nuclear outflow: Magnetic fields are a good tracer for gas compression by shock waves, which
can be caused by interaction of star-formation driven outflows from individual
star formation sites as described in the chimney model. We study the magnetic
field structure in the central part of the nuclear starburst galaxy NGC 253
with spatial resolutions between 40 and 150 pc to detect any filamentary
emission associated with the nuclear outflow. New VLA observations at 3 cm with
7.5" resolution were combined with archive data at 20 and 6 cm. We find
filamentary radio continuum emission in a geometrical distribution that we
interpret as the boundary of the northwestern nuclear outflow cone. The
scaleheight of the continuum emission is 150+/-20 pc, regardless of the
observing frequency. The equipartition magnetic field strength is 46+/-10
microG for the total field and 21+/-5 microG for the regular field in the
filaments. The ordered magnetic field is aligned along the filaments, in
agreement with amplification due to compression. The perpendicular diffusion
coefficient across the filaments is kappa_perp = 1.5 x 10^28 cm^2 s^-1
E(GeV)^(0.5+/-0.7). In the SE part of the nuclear outflow cone the magnetic
field is pointing away from the disc in form of a helix, with an azimuthal
component increasing up to at least 1200 pc height, where it is about equal to
the total component. The ordered magnetic field in the disc is anisotropic
within a radius of 2.2 kpc. At larger radii, the large-scale field is regular
and of even parity. The magnetic field is able to collimate the outflow, which
can explain the observed small opening angle of ~26 degree. Due to angular
momentum conservation, the field lines are frozen into the plasma and are wound
up into a helix. Strong adiabatic losses of the cosmic-ray electrons can partly
explain why the radio luminosity of the nucleus lies below the radio-FIR
correlation. |
The Effect of Interplanetary Scintillation on Epoch of Reionisation
Power Spectra: Interplanetary Scintillation (IPS) induces intensity fluctuations in small
angular size astronomical radio sources via the distortive effects of spatially
and temporally varying electron density associated with outflows from the Sun.
These radio sources are a potential foreground contaminant signal for
redshifted HI emission from the Epoch of Reionisation (EoR) because they yield
time-dependent flux density variations in bright extragalactic point sources.
Contamination from foreground continuum sources complicates efforts to
discriminate the cosmological signal from other sources in the sky. In IPS, at
large angles from the Sun applicable to EoR observations, weak scattering
induces spatially and temporally correlated fluctuations in the measured flux
density of sources in the field, potentially affecting the detectability of the
EoR signal by inducing non-static variations in the signal strength. In this
work, we explore the impact of interplanetary weak scintillation on EoR power
spectrum measurements, accounting for the instrumental spatial and temporal
sampling. We use published power spectra of electron density fluctuations and
parameters of EoR experiments to derive the IPS power spectrum in the
wavenumber phase space of EoR power spectrum measurements. The contrast of IPS
power to expected cosmological power is used as a metric to assess the impact
of IPS. We show that IPS has a different spectral structure to power from
foregrounds alone, but the additional leakage into the EoR observation
parameter space is negligible under typical IPS conditions, unless data are
used from deep within the foreground contamination region. | HerMES: Herschel-SPIRE observations of Lyman Break Galaxies: We present first results of a study of the submillimetre (rest frame
far-infrared) properties of z~3 Lyman Break Galaxies (LBGs) and their
lower-redshift counterparts BX/BM galaxies, based on Herschel-SPIRE
observations of the Northern field of the Great Observatories Origins Deep
Survey (GOODS-N). We use stacking analysis to determine the properties of LBGs
well below the current limit of the survey. Although LBGs are not detected
individually, stacking the infrared luminous LBGs (those detected with Spitzer
at 24 microns yields a statistically significant submm detection with mean flux
<S_{250}>= 5.9+/-1.4 mJy confirming the power of SPIRE in detecting UV-selected
high-redshift galaxies at submillimetre wavelengths. In comparison, the Spitzer
24 microns detected BX/BM galaxies appear fainter with a stacked value of
<S_{250}> = 2.7 +/-0.8 mJy. By fitting the Spectral Energy Distributions (SEDs)
we derive median infrared luminosities, L_{IR}, of 2.8x10^{12} Lsun and
1.5x10^{11} Lsun for z~3 LBGs and BX/BMs, respectively. We find that $L_{IR}
estimates derived from present measurements are in good agreement with those
based on UV data for z~2 BX/BM galaxies, unlike the case for z~3 infrared
luminous LBGs where the UV underestimates the true $L_{IR}. Although sample
selection effects may influence this result we suggest that differences in
physical properties (such as morphologies, dust distribution and extent of
star-forming regions) between z ~3 LBGs and z~2 BX/BMs may also play a
significant role. |
Toward Accurate Modeling of Galaxy Clustering on Small Scales: Halo
Model Extensions and Lingering Tension: This paper represents an effort to provide robust constraints on the
galaxy-halo connection and simultaneously test the Planck LCDM cosmology using
a fully numerical model of small-scale galaxy clustering. We explore two
extensions to the standard Halo Occupation Distribution model: assembly bias,
whereby halo occupation depends on both halo mass and the larger environment,
and velocity bias, whereby galaxy velocities do not perfectly trace the
velocity of the dark matter within the halo. Moreover, we incorporate halo mass
corrections to account for the impact of baryonic physics on the halo
population. We identify an optimal set of clustering measurements to constrain
this "decorated" HOD model for both low- and high-luminosity galaxies in SDSS
DR7. We find that, for low-luminosity galaxies, a model with both assembly bias
and velocity bias provides the best fit to the clustering measurements, with no
tension remaining in the fit. In this model we find evidence for both central
and satellite galaxy assembly bias at the 99% and 95% confidence levels,
respectively. In addition, we find evidence for satellite galaxy velocity bias
at the 99.9% confidence level. For high luminosity galaxies, we find no
evidence for either assembly bias or velocity bias, but our model exhibits
significant tension with SDSS measurements. We find that all of these
conclusions still stand when we include the effects of baryonic physics on the
halo mass function, suggesting that the tension we find for high luminosity
galaxies may be due to a problem with our assumed cosmological model. | The Fundamental Plane of Galaxy Group Mergers: We present a series of hundreds of collisionless simulations of galaxy group
mergers. These simulations are designed to test whether the properties of
elliptical galaxies - including the key fundamental plane scaling relation,
morphology and kinematics - can be simultaneously reproduced by dry multiple
mergers in galaxy groups. Preliminary results indicate that galaxy group
mergers can produce elliptical remnants lying on a tilted fundamental plane,
even without a central dissipational component from a starburst. This suggests
that multiple mergers in groups are an alternate avenue for the formation of
elliptical galaxies which could well dominate for luminous ellipticals. |
Gravitational lensing in a universe with matter and a cosmological
constant: We extend the results obtained in \cite{Piattella_2016, mcvittie_2015} and
\cite{Park_2008} for gravitational lensing in the McVittie metric by including
the effect of the transition from the matter-dominated epoch of the Universe to
the $\Lambda$-dominated era. We derive a formula that agrees with the previous
results for the McVittie metric at lowest order, and compare the lensing angle
predictions obtained from the Schwarzschild approximation, the McVittie model
and higher order corrections to the McVittie model. In doing this, we test if,
beyond the correction from the accelerated expansion of the Universe, there is
a need for including the matter content of the Universe in modeling lens
systems at the redshifts observed in lens systems. We investigate if there is a
need for a modification of the lens equation from these corrections, and if so,
to which order and whether it is measurable. We find that while the effect is
of the same order as the one calculated previously, there is no significant
contribution to the bending angle, as the 1st order effect is already of order
$\mathcal{O}(\theta_O^4)$ in the observed angle. | A Revised Parallel-Sequence Morphological Classification of Galaxies:
Structure and Formation of S0 and Spheroidal Galaxies: We update van den Bergh's parallel sequence galaxy classification in which S0
galaxies form a sequence S0a-S0b-S0c that parallels the sequence Sa-Sb-Sc of
spiral galaxies. The ratio B/T of bulge to total light defines the position of
a galaxy in each sequence. Our classification makes one improvement. We extend
the S0a-S0b-S0c sequence to spheroidal ("Sph'") galaxies that are positioned in
parallel to irregular galaxies in a similarly extended Sa-Sb-Sc-Im sequence.
This provides a natural "home" for spheroidals, which previously were omitted
from galaxy classifications. To motivate our juxtaposition of Sph and irregular
galaxies, we present photometry and bulge-disk decompositions of Virgo S0s,
including late-type S0s that bridge the gap between S0b and Sph galaxies. NGC
4762 is a SB0bc with B/T = 0.13. NGC 4452 is a SB0c galaxy with an even tinier
pseudobulge. VCC 2048 and NGC 4638 have properties of both S0cs and Sphs. We
update the structural parameter correlations Sphs, irregulars, bulges, and
disks. We show that spheroidals of increasing luminosity form a continuous
sequence with the disks (but not bulges) of S0c-S0b-S0a galaxies. Remarkably,
the Sph--S0-disk sequence is almost identical to that of irregular galaxies and
spiral galaxy disks. We review published observations for galaxy transformation
processes, particularly ram-pressure stripping of cold gas. We suggest that Sph
galaxies are transformed, "red and dead" Scd--Im galaxies in the same way that
many S0 galaxies are transformed, red and dead Sa-Sc spiral galaxies |
Tensor bispectrum mediated by an excited scalar field during inflation: We calculate the tensor bispectrum mediated by an excited scalar field during
inflation and find that the bispectrum peaks in the squeezed configuration,
which is different from that of gravitational waves induced by enhanced
curvature perturbations re-entering the horizon in the radiation-dominated era.
Measuring the bispectrum provides a promising way to distinguish the stochastic
gravitational-wave background generated during inflation from that generated
after inflation. | Simulations of Baryon Acoustic Oscillations II: Covariance matrix of the
matter power spectrum: We use 5000 cosmological N-body simulations of 1(Gpc/h)^3 box for the
concordance LCDM model in order to study the sampling variances of nonlinear
matter power spectrum. We show that the non-Gaussian errors can be important
even on large length scales relevant for baryon acoustic oscillations (BAO).
Our findings are (1) the non-Gaussian errors degrade the cumulative
signal-to-noise ratios (S/N) for the power spectrum amplitude by up to a factor
of 2 and 4 for redshifts z=1 and 0, respectively. (2) There is little
information on the power spectrum amplitudes in the quasi-nonlinear regime,
confirming the previous results. (3) The distribution of power spectrum
estimators at BAO scales, among the realizations, is well approximated by a
Gaussian distribution with variance that is given by the diagonal covariance
component. (4) For the redshift-space power spectrum, the degradation in S/N by
non-Gaussian errors is mitigated due to nonlinear redshift distortions. (5) For
an actual galaxy survey, the additional shot noise contamination compromises
the cosmological information inherent in the galaxy power spectrum, but also
mitigates the impact of non-Gaussian errors. The S/N is degraded by up to 30%
for a WFMOS-type survey. (6) The finite survey volume causes additional
non-Gaussian errors via the correlations of long-wavelength fluctuations with
the fluctuations we want to measure, further degrading the S/N values by about
30% even at high redshift z=3. |
The inflationary origin of the Cold Spot anomaly: Single-field inflation, arguably the simplest and most compelling paradigm
for the origin of our Universe, is strongly supported by the recent results of
the Planck satellite and the BICEP2 experiment. The results from Planck,
however, also confirm the presence of a number of anomalies in the Cosmic
Microwave Background (CMB), whose origin becomes problematic in single-field
inflation. Among the most prominent and well-tested of these anomalies is the
Cold Spot, which constitutes the only significant deviation from gaussianity in
the CMB. Planck's non-detection of primordial non-gaussianity on smaller scales
thus suggests the existence of a physical mechanism whereby significant
non-gaussianity is generated on large angular scales only. In this letter, we
address this question by developing a localized version of the inhomogeneous
reheating scenario, which postulates the existence of a scalar field able to
modify the decay of the inflaton on localized spatial regions only. We
demonstrate that if the Cold Spot is due to an overdensity in the last
scattering surface, the localization mechanism offers a feasible explanation
for it, thus providing a physical mechanism for the generation of localized
non-gaussianity in the CMB. If, on the contrary, the Cold Spot is caused by a
newly discovered supervoid (as recently claimed), we argue that the
localization mechanism, while managing to enhance underdensities, may well shed
light on the rarity of the discovered supervoid. | Baryonic impact on the dark matter distribution in Milky Way-size
galaxies and their satellites: We study the impact of baryons on the distribution of dark matter in a Milky
Way-size halo by comparing a high-resolution, moving-mesh cosmological
simulation with its dark matter-only counterpart. We identify three main
processes related to baryons -- adiabatic contraction, tidal disruption and
reionization -- which jointly shape the dark matter distribution in both the
main halo and its subhalos. The relative effect of each baryonic process
depends strongly on the subhalo mass. For massive subhalos with maximum
circular velocity $v_{\rm max} > 35 km/s$, adiabatic contraction increases the
dark matter concentration, making these halos less susceptible to tidal
disruption. For low-mass subhalos with $v_{\rm max} < 20 km/s$, reionization
effectively reduces their mass on average by $\approx$ 30% and $v_{\rm max}$ by
$\approx$ 20%. For intermediate subhalos with $20 km/s < v_{\rm max} < 35
km/s$, which share a similar mass range as the classical dwarf spheroidals,
strong tidal truncation induced by the main galaxy reduces their $v_{\rm max}$.
Moreover, the stellar disk of the main galaxy effectively depletes subhalos
near the central region. As a combined result of reionization and increased
tidal disruption, the total number of low-mass subhalos in the hydrodynamic
simulation is nearly halved compared to that of the $\textit{N-}$body
simulation. We do not find dark matter cores in dwarf galaxies, unlike previous
studies that employed bursty feedback-driven outflows. The substantial impact
of baryons on the abundance and internal structure of subhalos suggests that
galaxy formation and evolution models based on $\textit{N}$-body simulations
should include these physical processes as major components. |
21 cm Line Astronomy and Constraining New Physics: The 21 cm signal appears to be a treasure trove to provide an insight into
the period when the first generation of luminous objects formed in the
Universe. Hydrogen is the predominating fraction of the total baryonic matter
during cosmic dawn (CD). Therefore, it is convenient and advantageous to study
physics during CD using the 21 cm signal. The presence of any exotic source of
energy can inject energy into the intergalactic medium (IGM) and heat the gas.
Subsequently, it can modify the absorption amplitude in the global 21 cm
signal. This feature can provide a robust bound on such sources of energy
injection into the IGM gas. | A search for ultra-light axions using precision cosmological data: Ultra-light axions (ULAs) with masses in the range 10^{-33} eV <m <10^{-20}
eV are motivated by string theory and might contribute to either the
dark-matter or dark-energy density of the Universe. ULAs could suppress the
growth of structure on small scales, or lead to an enhanced integrated
Sachs-Wolfe effect on large-scale cosmic microwave-background (CMB)
anisotropies. In this work, cosmological observables over the full ULA mass
range are computed, and then used to search for evidence of ULAs using CMB data
from the Wilkinson Microwave Anisotropy Probe (WMAP), Planck satellite, Atacama
Cosmology Telescope, and South Pole Telescope, as well as galaxy clustering
data from the WiggleZ galaxy-redshift survey. In the mass range 10^{-32} eV < m
<10^{-25.5} eV, the axion relic-density \Omega_{a} (relative to the total
dark-matter relic density \Omega_{d}) must obey the constraints
\Omega_{a}/\Omega_{d} < 0.05 and \Omega_{a}h^{2} < 0.006 at 95%-confidence. For
m> 10^{-24} eV, ULAs are indistinguishable from standard cold dark matter on
the length scales probed, and are thus allowed by these data. For m < 10^{-32}
eV, ULAs are allowed to compose a significant fraction of the dark energy. |
Near-infrared Spectroscopy of GRB Host Galaxies at z >~ 1.5: Insights
into Host Galaxy Dynamics and Interpretations of Afterglow Absorption Spectra: This paper presents near-infrared echellette spectra of faint galaxies in the
fields around GRB 050820A at redshift z=2.613 and GRB 060418 at z=1.490. The
spectroscopic data show that both GRBs originate in a dynamic environment of
interacting galaxies separated by < 15 h^{-1} kpc in projected distance and
|dv| <~ 60 km/s in line-of-sight velocity. The optical afterglows revealed in
early-epoch Hubble Space Telescope images are at least 2.5 h^{-1} kpc (or 0.4")
away from the high surface brightness regions of the interacting members,
indicating that the GRB events occurred either in the outskirts of a compact
star-forming galaxy or in a low surface brightness satellite. Comparisons of
the systemic redshifts of the host galaxies and the velocity distribution of
absorbing clouds revealed in early-time afterglow spectra further show that the
majority of the absorbing clouds are redshifted from these compact star-forming
galaxies. These include the gas producing fine-structure absorption lines at
physical distances d ~ a few x 100 pc from the GRB afterglow. The lack of
blueshifted absorbing clouds and the spatial offset of the GRB event from the
star-forming regions make it difficult to attribute the observed large velocity
spread (~ 200-400 km/s) of absorbing gas in the GRB host to galactic-scale
outflows. We consider a scenario in which the GRB event occurred in a dwarf
satellite of the interacting group and interpret the broad absorption
signatures in the afterglow spectra as a collective effect of the turbulent
halo gas and the host star-forming ISM. We briefly discuss the implications for
the absorption properties observed in the afterglow spectra. | Hierarchy in the Phase Space and Dark Matter Astronomy: We develop a theoretical framework for describing the hierarchical structure
of the phase space of cold dark matter haloes, due to gravitationally bound
substructures. Because it includes the full hierarchy of the cold dark matter
initial conditions and is hence complementary to the halo model, the stable
clustering hypothesis is applied for the first time here to the small-scale
phase space structure. As an application, we show that the particle dark matter
annihilation signal could be up to two orders of magnitude larger than that of
the smooth halo within the Galactic virial radius. The local boost is inversely
proportional to the smooth halo density, and thus is O(1) within the solar
radius, which could translate into interesting signatures for dark matter
direct detection experiments: The temporal correlation of dark matter detection
can change by a factor of 2 in the span of 10 years, while there will be
significant correlations in the velocity space of dark matter particles. This
can introduce O(1) uncertainty in the direction of local dark matter wind,
which was believed to be a benchmark of directional dark matter searches or the
annual modulation signal. |
Transition To Order After Hilltop Inflation: We investigate the rich nonlinear dynamics during the end of hilltop
inflation by numerically solving the coupled Klein-Gordon-Friedmann equations
in a expanding universe. In particular, we search for coherent, nonperturbative
configurations that may emerge due to the combination of nontrivial couplings
between the fields and resonant effects from the cosmological expansion. We
couple a massless field to the inflaton to investigate its effect on the
existence and stability of coherent configurations and the effective equation
of state at reheating. For parameters consistent with data from the Planck and
WMAP satellites, and for a wide range of couplings between the inflaton and the
massless field, we identify a transition from disorder to order characterized
by emergent oscillon-like configurations. We verify that these configurations
can contribute a maximum of roughly 30% of the energy density in the universe.
At late times their contribution to the energy density drops to about 3%, but
they remain long-lived on cosmological time-scales, being stable throughout our
simulations. Cosmological oscillon emergence is described using a new measure
of order in field theory known as relative configurational entropy. | Spectrum oscillations from features in the potential of single-field
inflation: We study single-field inflationary models with steep step-like features in
the potential that lead to the temporary violation of the slow-roll conditions
during the evolution of the inflaton. These features enhance the power spectrum
of the curvature perturbations by several orders of magnitude at certain scales
and also produce prominent oscillatory patterns. We study analytically and
numerically the inflationary dynamics. We describe quantitatively the size of
the enhancement, as well as the profile of the oscillations, which are shaped
by the number and position of the features in the potential. The induced tensor
power spectrum inherits the distinctive oscillatory profile of the curvature
spectrum and is potentially detectable by near-future space interferometers.
The enhancement of the power specrtum by step-like features, though
significant, may be insufficient to trigger the production of a sizeable number
of primordial black holes if radiation dominates the energy density of the
early universe. However, it can result in sufficient black hole production if
the universe is dominated by non-relativistic matter. For the latter scenario,
we find that deviations from the standard monochromatic profile of the mass
spectrum of primordial black holes are possible because of the multiple-peak
structure of the curvature power spectrum. |
Spectral Energy Distributions of low-luminosity radio galaxies at z~1-3:
a high-z view of the host/AGN connection: We study the Spectral Energy Distributions, SEDs, (from FUV to MIR bands) of
the first sizeable sample of 34 low-luminosity radio galaxies at high
redshifts, selected in the COSMOS field. To model the SEDs we use two different
template-fitting techniques: i) the Hyperz code that only considers single
stellar templates and ii) our own developed technique 2SPD that also includes
the contribution from a young stellar population and dust emission. The
resulting photometric redshifts range from z ~0.7 to 3 and are in substantial
agreement with measurements from earlier work, but significantly more accurate.
The SED of most objects is consistent with a dominant contribution from an old
stellar population with an age ~1 - 3 10^{9} years. The inferred total stellar
mass range is ~10^{10} - 10^{12} M(sun). Dust emission is needed to account for
the 24micron emission in 15 objects. Estimates of the dust luminosity yield
values in the range L_{dust} ~10^{43.5} -10^{45.5} erg s^{-1}. The global dust
temperature, crudely estimated for the sources with a MIR excess, is ~ 300-850
K. A UV excess is often observed with a luminosity in the range ~
10^{42}-10^{44} erg s^{-1} at 2000 A rest frame.
Our results show that the hosts of these high-z low-luminosity radio sources
are old massive galaxies, similarly to the local FRIs. However, the UV and MIR
excesses indicate the possible significant contribution from star formation
and/or nuclear activity in such bands, not seen in low-z FRIs. Our sources
display a wide variety of properties: from possible quasars at the highest
luminosities, to low-luminosity old galaxies. | Size dependence of the radio luminosity - mechanical power correlation
in radio galaxies: We examine the relationship between source radio luminosity and kinetic power
in Active Galactic Nucleus (AGN) jets. We show that neglecting various loss
processes can introduce a systematic bias in the jet powers inferred from radio
luminosities for a sample of radio galaxies. This bias can be corrected for by
considering source size as well as radio luminosity; effectively the source
size acts as a proxy for source age. Based on a sample of FR-II radio sources
with jet powers derived from the measured hotspot parameters, we empirically
determine a new expression for jet power that accounts for the source size,
Q_jet / 10^{36} W = 1.5 (L_151 / 10^{27} W/Hz)^{0.8} (1+z)^{1.0} (D /
kpc)^{0.58 \pm 0.17}, where D is source size and L_151 the 151 MHz radio
luminosity. By comparing a flux-limited and volume-limited sample, we show that
any derived radio luminosity - jet power relation depends sensitively on sample
properties, in particular the source size distribution and the size-luminosity
correlation inherent in the sample. Such bias will affect the accuracy of the
kinetic luminosity function derived from lobe radio luminosities and should be
treated with caution. |
AGN feedback in galaxy groups: a joint GMRT/X-ray study: We present an ongoing study of 18 nearby galaxy groups, chosen for the
availability of Chandra and/or XMM-Newton data and evidence for AGN/hot
intragroup gas interaction. We have obtained 235 and 610 MHz observations at
the GMRT for all the groups, and 327 and 150 MHz for a few. We discuss two
interesting cases - NGC 5044 and AWM 4 - which exhibit different kinds of
AGN/hot gas interaction. With the help of these examples we show how joining
low-frequency radio data (to track the history of AGN outbursts through
emission from aged electron populations) with X-ray data (to determine the
state of hot gas, its disturbances, heating and cooling) can provide a unique
insight into the nature of the feedback mechanism in galaxy groups. | Far-Ultraviolet Observations of Outflows from IR-Luminous Galaxies: We obtained medium-resolution ultraviolet (UV) spectra between 1150 and 1450
Angstroms of the four UV-bright, infrared (IR)-luminous starburst galaxies IRAS
F08339+6517, NGC 3256, NGC 6090, and NGC 7552 using the Cosmic Origins
Spectrograph onboard the Hubble Space Telescope. The selected sightlines
towards the starburst nuclei probe the properties of the recently formed
massive stars and the physical conditions in the starburst-driven galactic
superwinds. Despite being metal-rich and dusty, all four galaxies are strong
Lyman-alpha emitters with equivalent widths ranging between 2 and 13 Angstroms.
The UV spectra show strong P Cygni-type high-ionization features indicative of
stellar winds and blueshifted low-ionization lines formed in the interstellar
and circumgalactic medium. We detect outflowing gas with bulk velocities of
about 400 km/s and maximum velocities of almost 900 km/s. These are among the
highest values found in the local universe and comparable to outflow velocities
found in luminous Lyman-break galaxies at intermediate and high redshift. The
outflow velocities are unlikely to be high enough to cause escape of material
from the galactic gravitational potential. However, the winds are significant
for the evolution of the galaxies by transporting heavy elements from the
starburst nuclei and enriching the galaxy halos. The derived mass outflow rates
of ~100 Msol/yr are comparable to, or even higher than the star-formation
rates. The outflows can quench star formation and ultimately regulate the
starburst as has been suggested for high-redshift galaxies. |
Variability and stability in blazar jets on time scales of years:
Optical polarization monitoring of OJ287 in 2005-2009: (Abridged) OJ287 is a BL Lac object that has shown double-peaked bursts at
regular intervals of ~12 yr during the last ~40 yr. We analyse optical
photopolarimetric monitoring data from 2005-2009, during which the latest
double-peaked outburst occurred. The aim of this study is twofold: firstly, we
aim to analyse variability patterns and statistical properties of the optical
polarization light-curve. We find a strong preferred position angle in optical
polarization. The preferred position angle can be explained by separating the
jet emission into two components: an optical polarization core and chaotic jet
emission. The optical polarization core is stable on time scales of years and
can be explained as emission from an underlying quiescent jet component. The
chaotic jet emission sometimes exhibits a circular movement in the Stokes
plane. We interpret these events as a shock front moving forwards and backwards
in the jet, swiping through a helical magnetic field. Secondly, we use our data
to assess different binary black hole models proposed to explain the regularly
appearing double-peaked bursts in OJ287. We compose a list of requirements a
model has to fulfil. The list includes not only characteristics of the
light-curve but also other properties of OJ287, such as the black hole mass and
restrictions on accretion flow properties. We rate all existing models using
this list and conclude that none of the models is able to explain all
observations. We discuss possible new explanations and propose a new approach
to understanding OJ287. We suggest that both the double-peaked bursts and the
evolution of the optical polarization position angle could be explained as a
sign of resonant accretion of magnetic field lines, a 'magnetic breathing' of
the disc. | Cause and Effect of Feedback: Multiphase Gas in Cluster Cores Heated by
AGN Jets: Multiwavelength data indicate that the X-ray emitting plasma in the cores of
galaxy clusters is not cooling catastrophically. To large extent, cooling is
offset by heating due to active galactic nuclei (AGN) via jets. The cool-core
clusters, with cooler/denser plasmas, show multiphase gas and signs of some
cooling in their cores. These observations suggest that the cool core is
locally thermally unstable while maintaining global thermal equilibrium. Using
high-resolution, three-dimensional simulations we study the formation of
multiphase gas in cluster cores heated by highly-collimated bipolar AGN jets.
Our key conclusion is that spatially extended multiphase filaments form only
when the instantaneous ratio of the thermal instability and free-fall
timescales (t_TI/t_ff) falls below a critical threshold of \approx 10. When
this happens, dense cold gas decouples from the hot ICM phase and generates
inhomogeneous and spatially extended Halpha filaments. These cold gas clumps
and filaments `rain' down onto the central regions of the core, forming a cold
rotating torus and in part feeding the supermassive black hole. Consequently,
the self-regulated feedback enhances AGN heating and the core returns to a
higher entropy level with t_TI/t_ff > 10. Eventually the core reaches
quasi-stable global thermal equilibrium, and cold filaments condense out of the
hot ICM whenever t_TI/t_ff \lesssim 10. This occurs despite the fact that the
energy from AGN jets is supplied to the core in a highly anisotropic fashion.
The effective spatial redistribution of heat is enabled in part by the
turbulent motions in the wake of freely-falling cold filaments. Increased AGN
activity can locally reverse the cold gas flow, launching cold filamentary gas
away from the cluster center. Our criterion for the condensation of spatially
extended cold gas is in agreement with observations and previous idealized
simulations. |
Distance measurements to early-type galaxies by improving the
fundamental plane: Using SDSS DR15 to its full extent, we derived fundamental plane distances to
over 317 000 early-type galaxies up to a redshift of 0.4. In addition to
providing the largest sample of fundamental plane distances ever calculated, as
well as a well calibrated group catalogue covering the entire SDSS
spectroscopic footprint as far a redshift of 0.5, we present several
improvements reaching beyond the traditional definition of the fundamental
plane. In one approach, we adjusted the distances by removing systematic biases
and selection effects in redshift-magnitude space, thereby greatly improving
the quality of measurements. Alternatively, by expanding the traditional
fundamental plane by additional terms, we managed to remove systematic biases
caused by the selection of our SDSS spectroscopic galaxy sample as well as
notably reducing its scatter. We discuss the advantages and caveats of these
various methods and calibrations in detail. We found that improving the
fundamental plane distance estimates beyond the established methods requires a
delicate balancing act between various systematic biases and gains, but managed
to reduce the uncertainty of our distance measurements by about a factor of two
compared to the traditional fundamental plane. | Light cone effect on the reionization 21-cm signal II: Evolution,
anisotropies and observational implications: Measurements of the HI 21-cm power spectra from the reionization epoch will
be influenced by the evolution of the signal along the line-of-sight direction
of any observed volume. We use numerical as well as semi-numerical simulations
of reionization in a cubic volume of 607 Mpc across to study this so-called
light cone effect on the HI 21-cm power spectrum. We find that the light cone
effect has the largest impact at two different stages of reionization: one when
reionization is $\sim 20\%$ and other when it is $\sim 80\%$ completed. We find
a factor of $\sim 4$ amplification of the power spectrum at the largest scale
available in our simulations. We do not find any significant anisotropy in the
21-cm power spectrum due to the light cone effect. We argue that for the power
spectrum to become anisotropic, the light cone effect would have to make the
ionized bubbles significantly elongated or compressed along the line-of-sight,
which would require extreme reionization scenarios. We also calculate the
two-point correlation functions parallel and perpendicular to the line-of-sight
and find them to differ. Finally, we calculate an optimum frequency bandwidth
below which the light cone effect can be neglected when extracting power
spectra from observations. We find that if one is willing to accept a $10 \%$
error due to the light cone effect, the optimum frequency bandwidth for $k=
0.056 \, \rm{Mpc}^{-1}$ is $\sim 7.5$ MHz. For $k = 0.15$ and $0.41 \,
\rm{Mpc}^{-1}$ the optimum bandwidth is $\sim 11$ and $\sim 16$ MHz
respectively. |
Constraints on the velocity dispersion of Dark Matter from Cosmology and
new bounds on scattering from the Cosmic Dawn: The observational value of the velocity dispersion, $\Delta\upsilon$, is
missing in the Dark Matter (DM) puzzle. Non-zero or non-thermal DM velocities
can drastically influence Large Scale Structure and the 21-cm temperature at
the epoch of the Cosmic Dawn, as well as the estimation of DM physical
parameters, such as the mass and the interaction couplings. To study the
phenomenology of $\Delta\upsilon$ we model the evolution of DM in terms of a
simplistic and generic Boltzmann-like momentum distribution. Using cosmological
data from the Cosmic Microwave Background, Baryonic Acoustic Oscillations, and
Red Luminous Galaxies, we constrain the DM velocity dispersion for a broad
range of masses $10^{-3} eV < m_\chi < 10^9 eV$, finding $\Delta\upsilon_0
\lesssim$ 0.33 km/s (99% CL). Including the EDGES $T_{21}$-measurements, we
extend our study to constrain the baryon-DM interaction in the range of DM
velocities allowed by our analysis. As a consequence, we present new bounds on
two electromagnetic models of DM, namely minicharged particles (MCPs) and
electric dipole moment (EDM). For MCPs, the parameter region that is consistent
with EDGES and independent bounds on cosmological and stellar physics is very
small, pointing to the sub-eV mass regime of DM. A window in the MeV-GeV may
still be compatible with these bounds for MCP models without a hidden photon.
But the EDM parameter region consistent with EDGES is excluded by Big-Bang
Nucleosynthesis and Collider Physics. | The LBA Calibrator Survey of southern compact extragalactic radio
sources - LCS1: We present a catalogue of positions and correlated flux densities of 410
flat-spectrum, compact extragalactic radio sources, previously detected in the
AT20G survey. The catalogue spans the declination range -90deg, -40deg and was
constructed from four 24 hour VLBI observing sessions with the Australian Long
Baseline Array made at 8.3 GHz. The detection rate in these experiments is 97%.
The median uncertainty of source positions is 2.6 mas, the median correlated
flux density at baseline projections lengths longer than 1000 km is 0.14 Jy.
The goal of this work is 1) to provide a pool of sources with positions known
at the milliarcsecond level of accuracy that are needed for phase referencing
observations, for geodetic VLBI, and for space navigation; 2) to extend the
complete flux-limited sample of compact extragalactic sources to the southern
hemisphere; and 3) to investigate parsec-scale properties of high-frequency
selected sources from the AT20G survey. As a result of the campaign, the number
of compact radio sources with declinations < -40deg detectable with VLBI with
measured correlated flux densities and positions known with the milliarcsec
level of accuracies increased by a factor of 3.5. The catalogue and supporting
material is available at http://astrogeo.org/lcs1 . |
On the Anisotropy of the Gravitational Wave Background from Massless
Preheating: When a light scalar field is present during inflation, its value will vary on
superhorizon scales, modulating the preheating process at the end of inflation.
Consequently, the amplitude of the gravitational wave (GW) background produced
during preheating will also be modulated. The observed energy density of this
background will therefore appear anisotropic at different angles in the sky. We
provide a master formula for the angular power spectrum C_l of the anisotropies
in the GW background from preheating, valid for any scenario where the
anisotropies are due to the superhorizon modulation of a light degree of
freedom. Using lattice field theory simulations of massless preheating with
g^2/\lambda = 2, we find a flat angular spectrum l(l+1)C_l \approx 3x10^{-4},
which represents a strong anisotropy of order 1% variations on large angular
scales. For our choice of couplings, long wavelengths are amplified most
strongly during parametric resonance, which is crucial for the development of
the anisotropies. If future direct detection GW observatories are capable of
detecting backgrounds of cosmological origin, they should be able to detect
this effect. This could eventually become a powerful tool to discriminate among
inflationary and preheating scenarios. | Population Parameters of Intermediate-Age Star Clusters in the Large
Magellanic Cloud. I. NGC 1846 and its Wide Main Sequence Turnoff: The Advanced Camera for Surveys on board the Hubble Space Telescope has been
used to obtain deep, high-resolution images of the intermediate-age star
cluster NGC 1846 in the Large Magellanic Cloud. We present new color-magnitude
diagrams (CMDs) based on F435W, F555W, and F814W imaging. We test the
previously observed broad main sequence turnoff region for "contamination" by
field stars and (evolved) binary star systems. We find that while these impact
the number of objects in this region, none can fully account for the large
color spread. Our results therefore solidify the recent finding that stars in
the main sequence turnoff region of this cluster have a large spread in color
which is unrelated to measurement errors or contamination by field stars, and
likely due to a ~300 Myr range in the ages of cluster stars. An unbiased
estimate of the stellar density distribution across the main sequence turnoff
region shows that the spread is fairly continuous rather than strongly bimodal
as suggested previously. We fit the CMDs with several different sets of
theoretical isochrones, and determine systematic uncertainties for population
parameters when derived using any one set of isochrones. We note a degeneracy
between age and [alpha/Fe], which can be lifted by matching the shape
(curvature) of the full red giant branch in the CMD. We find that stars in the
upper part of the main sequence turnoff region are more centrally concentrated
than those in any other region of the CMD, including more massive red giant
branch and asymptotic giant branch stars. We consider several possible
formation scenarios which account for the unusual features observed in the CMD
of NGC 1846. |
Alleviating Cosmological Tensions with a Coupled Scalar Fields Model: In this paper, we investigate the interaction between early dark energy (EDE)
and scalar field dark matter, proposing a coupled scalar fields model to
address the Hubble tension and $S_8$ tension. While the EDE model successfully
alleviates the Hubble tension, it exacerbates the $S_8$ tension. To mitigate
the negative impact of EDE, we introduce the interaction between EDE and dark
matter. Specifically, we replace cold dark matter with scalar field dark
matter, given its capability to suppress structure growth on small scales. We
constrained the new model using cosmological observations including the
temperature and polarization anisotropy power spectra data of cosmic microwave
background radiation (CMB) from \textit{Planck} 2018 results, baryon acoustic
oscillations (BAO) measurements extracted from 6dFGS, SDSS and BOSS, the
Pantheon sample of type Ia supernovae (SNIa), the local distance-ladder data
(SH0ES), and the Dark Energy Survey Year-3 data. Employing Markov Chain Monte
Carlo method, we find that this novel model yields best-fit values of $H_0$ and
$S_8$ equal to $71.13$ km/s/Mpc and $0.8256$, respectively. Compared to the
$\Lambda$CDM model, the new model alleviates the Hubble tension but still fails
to resolve the $S_8$ tension. However, we obtain a smaller value of $S_8$
compared to the result of $0.8316$ obtained for EDE model, which mitigates to
some extent the shortcoming of the EDE model. | Anisotropic thermal Sunyaev-Zel'dovich effect and the possibility of an
independent measurement of the CMB dipole, quadrupole and octupole: We consider the effect of the cosmic microwave background (CMB) frequency
spectral distortions arising due to the Compton scattering of the anisotropic
radiation on Sunyaev-Zel'dovich (SZ) clusters. We derive the correction to the
thermal SZ effect due to the presence of multipoles with $\ell=1,2,3$ in the
anisotropy of the CMB radiation. We show that this effect gives us an
opportunity for an independent evaluation of the CMB dipole, quadrupole and
octupole angular anisotropy in our location using distorted signal from the
nearby galaxy clusters and to distinguish between the Sachs-Wolfe (SW) and the
Integrated Sachs-Wolfe (ISW) effects by combining such signals from distant and
nearby clusters. The future space mission 'Millimetron' will have unprecedented
sensitivity, which will make it possible to observe the spectral distortion we
are considering. |
An Independent Measurement of the Incidence of MgII Absorbers along
Gamma-Ray Burst Sightlines: the End of the Mystery?: In 2006, Prochter et al. reported a statistically significant enhancement of
very strong Mg II absorption systems intervening the sightlines to gamma-ray
bursts (GRBs) relative to the in- cidence of such absorption along quasar
sightlines. This counterintuitive result, has inspired a diverse set of
astrophysical explanations (e.g. dust, gravitational lensing) but none of these
has obviously resolved the puzzle. Using the largest set of GRB afterglow
spectra available, we reexamine the purported enhancement. In an independent
sample of GRB spectra with a survey path 3 times larger than Prochter et al.,
we measure the incidence per unit redshift of $\geq 1$\AA rest-frame equivalent
width Mg II absorbers at $z \approx 1$ to be l(z)= 0.18 $\pm$ 0.06. This is
fully consistent with current estimates for the incidence of such absorbers
along quasar sightlines. Therefore, we do not confirm the original enhancement
and suggest those results suffered from a statistical fluke. Signatures of the
original result do remain in our full sample (l(z) shows an $\approx 1.5$
enhancement over l(z)QSO), but the statistical significance now lies at
$\approx 90%$ c.l. Restricting our analysis to the subset of high-resolution
spectra of GRB afterglows (which overlaps substantially with Prochter et al.),
we still reproduce a statistically significant enhancement of Mg II absorption.
The reason for this excess, if real, is still unclear since there is no
connection between the rapid afterglow follow-up process with echelle (or
echellette) spectrographs and the detectability of strong Mg II doublets. Only
a larger sample of such high-resolution data will shed some light on this
matter. | Evidence for Cosmic Acceleration is Robust to Observed Correlations
Between Type Ia Supernova Luminosity and Stellar Age: Type Ia Supernovae (SNe Ia) are powerful standardizable candles for
constraining cosmological models and provided the first evidence of the
accelerated expansion of the universe. Their precision derives from empirical
correlations, now measured from $>1000$ SNe Ia, between their luminosities,
light-curve shapes, colors and most recently with the stellar mass of their
host galaxy. As mass correlates with other galaxy properties, alternative
parameters have been investigated to improve SN Ia standardization though none
have been shown to significantly alter the determination of cosmological
parameters. We re-examine a recent claim, based on 34 SN Ia in nearby passive
host galaxies, of a 0.05 mag/Gyr dependence of standardized SN Ia luminosity on
host age which if extrapolated to higher redshifts, would be a bias up to 0.25
mag, challenging the inference of dark energy. We reanalyze this sample of
hosts using both the original method and a Bayesian hierarchical model and find
after a fuller accounting of the uncertainties the significance of a dependence
on age to be $\leq2\sigma$ and $\sim1\sigma$ after the removal of a single
poorly-sampled SN Ia. To test the claim that a trend seen in old stellar
populations can be applied to younger ages, we extend our analysis to a larger
sample which includes young hosts. We find the residual dependence of host age
(after all standardization typically employed for cosmological measurements) to
be consistent with zero for 254 SNe Ia from the Pantheon sample, ruling out the
large but low significance trend seen in passive hosts. |
Thermal Relic Abundances of Particles with Velocity-Dependent
Interactions: We reexamine the evolution of thermal relic particle abundances for the case
where the interaction rate depends on the particle velocities. For the case of
Sommerfeld enhancement, we show that the standard analytic approximation,
modified in a straightforward way, provides an estimate of the relic particle
abundance that is accurate to within 10% (in comparison to less than 1% error
for the non-Sommerfeld-enhanced case). We examine the effect of kinetic
decoupling on relic particle abundances when the interaction rate depends on
the velocity. For the case of pure p-wave annihilation, the effect of kinetic
decoupling is an increase in the relic abundance, but the effect is negligible
when the kinetic decoupling temperature is much less than the chemical
decoupling temperature. For the case of Sommerfeld-enhanced s-wave
annihilations, after kinetic decoupling occurs, annihilations continue to
change the particle abundance down to arbitrarily low temperatures, until
either matter domination begins or the Sommerfeld effect cuts off. We derive
analytic approximations to give the final relic particle abundances for both of
these cases. | How CMB and large-scale structure constrain chameleon interacting dark
energy: We explore a chameleon type of interacting dark matter-dark energy scenario
in which a scalar field adiabatically traces the minimum of an effective
potential sourced by the dark matter density. We discuss extensively the effect
of this coupling on cosmological observables, especially the parameter
degeneracies expected to arise between the model parameters and other
cosmological parameters, and then test the model against observations of the
cosmic microwave background (CMB) anisotropies and other cosmological probes.
We find that the chameleon parameters $\alpha$ and $\beta$, which determine
respectively the slope of the scalar field potential and the dark matter-dark
energy coupling strength, can be constrained to $\alpha < 0.17$ and $\beta <
0.19$ using CMB data alone. The latter parameter in particular is constrained
only by the late Integrated Sachs-Wolfe effect. Adding measurements of the
local Hubble expansion rate $H_0$ tightens the bound on $\alpha$ by a factor of
two, although this apparent improvement is arguably an artefact of the tension
between the local measurement and the $H_0$ value inferred from Planck data in
the minimal $\Lambda$CDM model. The same argument also precludes chameleon
models from mimicking a dark radiation component, despite a passing similarity
between the two scenarios in that they both delay the epoch of matter-radiation
equality. Based on the derived parameter constraints, we discuss possible
signatures of the model for ongoing and future large-scale structure surveys. |
δN versus covariant perturbative approach to non-Gaussianity
outside the horizon in multifield inflation: We compute the super-Hubble evolution of non-Gaussianity of primordial
curvature perturbations in two-field inflation models by employing two
formalisms: delta N and covariant formalisms. Although two formalisms treat the
evolution of fluctuations radically different, we show that the formulas of
f_{NL} parameter agree quantitatively with each other within 1 % accuracy. We
analytically find that the amplitude of f_{NL} decays no faster than a^{-3} as
the inflationary trajectory reaches to the adiabatic limit for generic
potentials. | Beyond $Λ$CDM with HI intensity mapping: robustness of
cosmological constraints in the presence of astrophysics: Mapping the unresolved intensity of the 21-cm emission of neutral hydrogen
(HI) is now regarded as one the most promising tools for cosmological
investigation in the coming decades. Here, we investigate, for the first time,
extensions of the standard cosmological model, such as modified gravity and
primordial non-Gaussianity, taking self-consistently into account the present
constraints on the astrophysics of HI clustering in the treatment of the
brightness temperature fluctuations. To understand the boundaries within which
results thus obtained can be considered reliable, we examine the robustness of
cosmological parameter estimation performed via studies of 21-cm intensity
mapping, against our knowledge of the astrophysical processes leading to HI
clustering. Modelling of astrophysical effects affects cosmological observables
through the relation linking the overall HI mass in a bound object, to the mass
of the underlying dark matter halo that hosts it. We quantify the biases in
estimates of standard cosmological parameters and those describing modified
gravity and primordial non-Gaussianity, that are obtained if one misconceives
the slope of the relation between HI mass and halo mass, or the lower virial
velocity cut-off for a dark matter halo to be able to host HI. Remarkably, we
find that astrophysical uncertainties will not affect searches for primordial
non-Gaussianity - one of the strongest science cases for HI intensity mapping -
despite the signal being deeply linked to the HI bias. |
Probing cosmic isotropy in the Local Universe: This is a model-independent analysis that investigates the statistical
isotropy in the Local Universe using the ALFALFA survey data ($0 < z < 0.06$).
We investigate the angular distribution of HI extra-galactic sources from the
ALFALFA catalogue and study whether they are compatible with the statistical
isotropy hypothesis using the two-point angular correlation function (2PACF).
Aware that the Local Universe is plenty of clustered structures and large
voids, we compute the 2PACF with the Landy-Szalay estimator performing
directional analyses to inspect 10 sky regions. We investigate these 2PACF
using power-law best-fit analyses, and determine the statistical significance
of the best-fit parameters for the 10 ALFALFA regions by comparison with the
ones obtained through the same procedure applied to a set of mock catalogues
produced under the homogeneity and isotropy hypotheses. Our conclusion is that
the Local Universe, as mapped by the HI sources of the ALFALFA survey, is in
agreement with the hypothesis of statistical isotropy within $2\,\sigma$
confidence level, for small and large angle analyses, with the only exception
of one region -- located near the Dipole Repeller -- which appears slightly
outlier ($2.4\,\sigma$). Interestingly, regarding the large angular
distribution of the HI sources, we found 3 regions where the presence of cosmic
voids reported in the literature left their signature in our 2PACF, suggesting
projected large underdensities there, with number-density contrast $\delta
\simeq -0.7$. According to the current literature these regions correspond,
partially, to the sky position of the void structures known as Local Cosmic
Void and Dipole Repeller. | Renormalized Primordial Black Holes: The formation of primordial black holes in the early universe may happen
through the collapse of large curvature perturbations generated during a
non-attractor phase of inflation or through a curvaton-like dynamics after
inflation. The fact that such small-scale curvature perturbation is typically
non-Gaussian leads to the renormalization of composite operators built up from
the smoothed density contrast and entering in the calculation of the primordial
black abundance. Such renormalization causes the phenomenon of operator mixing
and the appearance of an infinite tower of local, non-local and
higher-derivative operators as well as to a sizable shift in the threshold for
primordial black hole formation. This hints that the calculation of the
primordial black hole abundance is more involved than what generally assumed. |
The Swift X-ray Telescope Cluster Survey: data reduction and cluster
catalog for the GRB fields: (abridged) We present a new sample of X-ray selected galaxy groups and
clusters serendipitously observed with Swift and the X-ray Telescope (XRT). We
searched the XRT archive for extended sources among 336 GRB fields with
galactic latitude |b|>20{\deg}. Our selection algorithm yields a flux-limited
sample of 72 X-ray groups and clusters with a well defined selection function
and negligible contamination. The sky coverage of the survey goes from the
total 40 deg^2 to 1 deg^2 at a flux limit of 10^-14 erg/s/cm^-2 (0.5-2 keV).
Here we describe the XRT data processing, the statistical calibration of the
survey, and the catalog of detected cluster candidates. All the X-ray sources
are detected in the Swift-XRT soft (0.5-2 keV) band. A size parameter defined
as the half power radius (HPR) measured inside a box of 45x45 arcsec, is
assigned to each source. We select extended sources by applying a threshold on
the Half Power Radius and we calibrate its dependence on the measured net
counts and on the image background with extensive simulations in order to
identify all the sources with ~99% probability of being extended. We compute
the logN-logS of our sample, finding very good agreement with previous deep
cluster surveys. A cross correlation with published X-ray catalogs shows that
only 9 sources were already detected, none of them as extended. Therefore, ~90%
of our sources are new X-ray detections. We also cross correlated our sources
with optical catalogs, finding 20 previously identified clusters. Overall,
about ~65% of our sources are new detections. The XRT follow-up observation of
GRBs is providing an excellent serendipitous survey for groups and clusters of
galaxies, mainly thanks to the low background of XRT and its constant angular
resolution across the field of view. About 33% of the sample has spectroscopic
or photometric redshifts from public optical surveys. | Cross correlations of the CMB Doppler mode and the 21 cm brightness
temperature in the presence of a primordial magnetic field: The cross correlation between the CMB Doppler mode and the 21 cm line
brightness temperature is calculated in the presence of a stochastic primordial
magnetic field. Potential detectability is estimated for Planck 2018 bestfit
parameters in combination with configuration and survey design parameters of 21
cm line radio telescopes such as LOFAR and the future SKAO. Homogeneous as well
as inhomogeneous reionization has been considered. In particular the latter in
combination with SKA1-mid shows promising signal-over-noise ratios. |
Foreground and sensitivity analysis for broad band (2D) 21cm--Ly-alpha
and 21cm--H-alpha correlation experiments probing the Epoch of Reionization: A detection of the predicted anticorrelation between 21cm and either Ly-alpha
or H-alpha from the Epoch of Reionization (EOR) would be a powerful probe of
the first galaxies. While 3D intensity maps isolate foregrounds in low
k_\parallel modes, infrared surveys cannot yet match the field of view and
redshift resolution of radio intensity mapping experiments. In contrast, 2D
(i.e., broad band) infrared intensity maps can be measured with current
experiments and are limited by foregrounds instead of photon or thermal noise.
We show 2D experiments can measure most of the 3D fluctuation power at k<0.2
Mpc^-1 while preserving its correlation properties. However, we show
foregrounds pose two challenges: (1) simple geometric effects produce
percent-level correlations between radio and infrared fluxes, even if their
luminosities are uncorrelated; and (2) radio and infrared foreground residuals
contribute sample variance noise to the cross spectrum. The first challenge
demands better foreground masking and subtraction, while the second demands
large fields of view to average away uncorrelated radio and infrared power.
Using radio observations from the Murchison Widefield Array and near-infrared
observations from the Asteroid Terrestrial-impact Last Alert System, we set an
upper limit on residual foregrounds of the 21cm--Ly-alpha cross power spectrum
at z\sim7 of \Delta^2<181 kJy/sr * mK (95\%) at \ell\sim800. We predict levels
of foreground correlation and sample variance noise in future experiments,
showing that higher resolution surveys such as LOFAR, SKA-LOW, and the Dark
Energy Survey can start to probe models of the 21cm--Ly\alpha EOR cross
spectrum. | The complex interplay of dust and star light in spiral galaxy discs: Interstellar dust grains efficiently absorb and scatter UV and optical
radiation in galaxies, and therefore can significantly affect the apparent
structure of spiral galaxies. We discuss the effect of dust attenuation on the
observed structural properties of bulges and discs. We also present some first
results on modelling the dust content of edge-on spiral galaxies using both
optical and Herschel far-infrared data. Both of these results demonstrate the
complex interplay of dust and star light in spiral galaxies. |
Cosmic Microwave Background constraints on non-minimal couplings in
inflationary models with power law potentials: Inflationary models with power-law potentials are starting to be severely
constrained by the recent measurements of Cosmic Microwave Background
anisotropies provided by the Planck Satellite and by the BICEP2 telescope. In
particular, models with power-law potentials $V(\varphi)\propto \varphi^n$ with
$n \ge 2$ are strongly disfavored by present data since they predict a sizable
contribution of gravitational waves with a tensor/scalar ratio of $r\sim0.15$
that is at odds with current limits. A non-minimal coupling to gravity has been
proposed as a physical mechanism to lower the predictions for $r$. In this
paper we further investigate the issue, presenting constraints on non-minimal
couplings from current CMB data under the assumption of power-law potentials.
We found that models with $n>2$ show a statistically significant indication
(above $95 \%$ C.L.) for a non minimal coupling. Non minimal coupling is also
preferred by models with $n<2$ albeit just at about $68 \%$ C.L..
Interestingly, all the models considered show a non-zero running of the
spectral index, $ n_{\rm run}$, consistent with the 2018 Planck release value
of $-0.007 \pm 0.0068$. We point out how future accurate measurement of $
n_{\rm run}$ would be necessary to significantly constraint these models and
eventually rule out some or all of them. The combination of Planck data with
the Bicep/Keck dataset strengthen these considerations. | Accretion disks around black holes in modified strong gravity: Stellar-mass black holes offer what is perhaps the best scenario to test
theories of gravity in the strong-field regime. In particular, f(R) theories,
which have been widely discuss in a cosmological context, can be constrained
through realistic astrophysical models of phenomena around black holes. We aim
at building radiative models of thin accretion disks for both Schwarzschild and
Kerr black holes in f(R) gravity. We study particle motion in
f(R)-Schwarzschild and Kerr space-times. We present the spectral energy
distribution of the accretion disk around constant Ricci scalar f(R) black
holes, and constrain specific f(R) prescriptions using features of these
systems. A precise determination of both the spin and accretion rate onto black
holes along with X-ray observations of their thermal spectrum might allow to
identify deviations of gravity from General Relativity. We use recent data on
the high-mass X-ray binary Cygnus X-1 to restrict the values of the parameters
of a class of f(R) models. |
Massive star formation in Wolf-Rayet galaxies. V: Star formation rates,
masses and the importance of galaxy interactions: (Abridged) We have performed a comprehensive analysis of a sample of 20
starburst galaxies, most of them classified as Wolf-Rayet galaxies. In this
paper, the last of the series, we analyze the global properties of our galaxy
sample using multiwavelength data (X-ray, FUV, optical, NIR, FIR, and radio).
The agreement between our Ha-based SFR and those provided by indicators at
other wavelengths is remarkable, but we consider that the new Ha-based
calibration provided by Calzetti et al. (2007) should be preferred over older
calibrations. The FUV-based SFR provides a powerful tool to analyze the
star-formation activity in both global and local scales independently to the Ha
emission. We provide empirical relationships between the ionized gas mass,
neutral gas mass, dust mass, stellar mass, and dynamical mass with the
B-luminosity. Although all mass estimations increase with increasing
luminosity, we find important deviations to the general trend in some objects,
that seem to be consequence of their particular evolutionary histories. We
investigate the mass-metallicity relations and conclude that both the nature
and the star-formation history are needed to understand the relationships
between both properties. The majority of the galaxies follow a
Schmidt-Kennicutt scaling law of star-formation that agrees with that reported
in individual star-forming regions within M~51 but not with that found in
normal spiral galaxies. We found a relation between the reddening coefficient
and the warm dust mass indicating that the extinction is mainly internal to the
galaxies. Considering all data, we found that 17 up to 20 galaxies are clearly
interacting or merging with low-luminosity dwarf objects or HI clouds. We
conclude that interactions do play a fundamental role in the triggering
mechanism of the strong star-formation activity observed in dwarf starburst
galaxies. | The Canadian Cluster Comparison Project: weak lensing masses and SZ
scaling relations: The Canadian Cluster Comparison Project is a comprehensive multi-wavelength
survey targeting 50 massive X-ray selected clusters of galaxies to examine
baryonic tracers of cluster mass and to probe the cluster-to-cluster variation
in the thermal properties of the hot intracluster medium. In this paper we
present the weak lensing masses, based on the analysis of deep wide-field
imaging data obtained using the Canada-France-Hawaii-Telescope. The final
sample includes two additional clusters that were located in the field-of-view.
We take these masses as our reference for the comparison of cluster properties
at other wavelengths. In this paper we limit the comparison to published
measurements of the Sunyaev-Zel'dovich effect. We find that this signal
correlates well with the projected lensing mass, with an intrinsic scatter of
12\pm5% at ~r_2500, demonstrating it is an excellent proxy for cluster mass. |
Impact of SZ cluster residuals in CMB maps and CMB-LSS
cross-correlations: Residual foreground contamination in cosmic microwave background (CMB) maps,
such as the residual contamination from thermal Sunyaev-Zeldovich (SZ) effect
in the direction of galaxy clusters, can bias the cross-correlation
measurements between CMB and large-scale structure optical surveys. It is thus
essential to quantify those residuals and, if possible, to null out SZ cluster
residuals in CMB maps. We quantify for the first time the amount of SZ cluster
contamination in the released Planck 2015 CMB maps through (i) the stacking of
CMB maps in the direction of the clusters, and (ii) the computation of
cross-correlation power spectra between CMB maps and the SDSS-IV large-scale
structure data. Our cross-power spectrum analysis yields a $30\sigma$ detection
at the cluster scale ($\ell=1500-2500$) and a $39\sigma$ detection on larger
scales ($\ell=500-1500$) due to clustering of SZ clusters, giving an overall
$54\sigma$ detection of SZ cluster residuals in the Planck CMB maps. The Planck
2015 NILC CMB map is shown to have $44\pm4\%$ of thermal SZ foreground emission
left in it. Using the 'Constrained ILC' component separation technique, we
construct an alternative Planck CMB map, the 2D-ILC map, which is shown to have
negligible SZ contamination, at the cost of being slightly more contaminated by
Galactic foregrounds and noise. We also discuss the impact of the SZ residuals
in CMB maps on the measurement of the ISW effect, which is shown to be
negligible based on our analysis. | SIMPLE: Simple Intensity Map Producer for Line Emission: We present the Simple Intensity Map Producer for Line Emission (SIMPLE), a
public code for quickly simulating mock line-intensity maps, and an analytical
framework for modeling intensity maps including observational effects. SIMPLE
can be applied to any spectral line sourced by galaxies. The SIMPLE code is
based on lognormal mock catalogs of galaxies including positions and velocities
and assigns luminosities following the luminosity function. After applying a
selection function to distinguish between detected and undetected galaxies, the
code generates an intensity map, which can be modified with anisotropic
smoothing, noise, a mask, and sky subtraction, and calculates the power
spectrum multipoles. We show that the intensity autopower spectrum and the
galaxy-intensity cross-power spectrum agree well with the analytical estimates
in real space. We derive and show that the sky subtraction suppresses the
intensity autopower spectrum and the cross-power spectrum on scales larger than
the size of an individual observation. As an example application, we make
forecasts for the sensitivity of an intensity mapping experiment similar to the
Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) to the cross-power
spectrum of Ly$\alpha$-emitting galaxies and the Ly$\alpha$ intensity. We
predict that HETDEX will measure the galaxy-intensity cross-power spectrum with
a high signal-to-noise ratio on scales of $0.04\, h\,\mathrm{Mpc}^{-1} < k <
1\, h\,\mathrm{Mpc}^{-1}$. |
Detection of Baryon Acoustic Oscillation Features in the Large-Scale
3-Point Correlation Function of SDSS BOSS DR12 CMASS Galaxies: We present the large-scale 3-point correlation function (3PCF) of the SDSS
DR12 CMASS sample of $777,202$ Luminous Red Galaxies, the largest-ever sample
used for a 3PCF or bispectrum measurement. We make the first high-significance
($4.5\sigma$) detection of Baryon Acoustic Oscillations (BAO) in the 3PCF.
Using these acoustic features in the 3PCF as a standard ruler, we measure the
distance to $z=0.57$ to $1.7\%$ precision (statistical plus systematic). We
find $D_{\rm V}= 2024\pm29\;{\rm Mpc\;(stat)}\pm20\;{\rm Mpc\;(sys)}$ for our
fiducial cosmology (consistent with Planck 2015) and bias model. This
measurement extends the use of the BAO technique from the 2-point correlation
function (2PCF) and power spectrum to the 3PCF and opens an avenue for deriving
additional cosmological distance information from future large-scale structure
redshift surveys such as DESI. Our measured distance scale from the 3PCF is
fairly independent from that derived from the pre-reconstruction 2PCF and is
equivalent to increasing the length of BOSS by roughly 10\%; reconstruction
appears to lower the independence of the distance measurements. Fitting a model
including tidal tensor bias yields a moderate significance ($2.6\sigma)$
detection of this bias with a value in agreement with the prediction from local
Lagrangian biasing. | The bispectra of galactic CMB foregrounds and their impact on primordial
non-Gaussianity estimation: We use the binned bispectrum estimator to determine the bispectra of the
dust, free-free, synchrotron, and AME galactic foregrounds using maps produced
by the Commander component separation method from Planck 2015 data. We find
that all of these peak in the squeezed configuration, allowing for potential
confusion with in particular the local primordial shape. Applying an additional
functionality implemented in the binned bispectrum estimator code, we then use
these galactic bispectra as templates in an $f_\mathrm{NL}$ analysis of other
maps. After testing and validating the method and code with simulations, we
show that we detect the dust in the raw 143 GHz map with the expected amplitude
(the other galactic foregrounds are too weak at 143 GHz to be detected) and
that no galactic residuals are detected in the cleaned CMB map. We also
investigate the effect of the mask on the templates and the effect of the
choice of binning on a joint dust-primordial $f_\mathrm{NL}$ analysis. |
N-body Simulations of $γ$ Gravity: We have investigated structure formation in the $\gamma$ gravity $f(R)$ model
with {\it N}-body simulations. The $\gamma$ gravity model is a proposal which,
unlike other viable $f(R)$ models, not only changes the gravitational dynamics,
but can in principle also have signatures at the background level that are
different from those obtained in $\Lambda$CDM (Cosmological constant, Cold Dark
Matter). The aim of this paper is to study the nonlinear regime of the model in
the case where, at late times, the background differs from $\Lambda$CDM. We
quantify the signatures produced on the power spectrum, the halo mass function,
and the density and velocity profiles. To appreciate the features of the model,
we have compared it to $\Lambda$CDM and the Hu-Sawicki $f(R)$ models. For the
considered set of parameters we find that the screening mechanism is
ineffective, which gives rise to deviations in the halo mass function that
disagree with observations. This does not rule out the model per se, but
requires choices of parameters such that $|f_{R0}|$ is much smaller, which
would imply that its cosmic expansion history cannot be distinguished from
$\Lambda$CDM at the background level. | Cosmic-Enu: An emulator for the non-linear neutrino power spectrum: Cosmology is poised to measure the neutrino mass sum $M_\nu$ and has
identified several smaller-scale observables sensitive to neutrinos,
necessitating accurate predictions of neutrino clustering over a wide range of
length scales. The FlowsForTheMasses non-linear perturbation theory for the
massive neutrino power spectrum, $\Delta^2_\nu(k)$, agrees with its companion
N-body simulation at the $10\%-15\%$ level for $k \leq 1~h/$Mpc. Building upon
the Mira-Titan IV emulator for the cold matter, we use FlowsForTheMasses to
construct an emulator for $\Delta^2_\nu(k)$ covering a large range of
cosmological parameters and neutrino fractions $\Omega_{\nu,0} h^2 \leq 0.01$,
which corresponds to $M_\nu \leq 0.93$~eV. Consistent with FlowsForTheMasses at
the $3.5\%$ level, it returns a power spectrum in milliseconds. Ranking the
neutrinos by initial momenta, we also emulate the power spectra of momentum
deciles, providing information about their perturbed distribution function.
Comparing a $M_\nu=0.15$~eV model to a wide range of N-body simulation methods,
we find agreement to $3\%$ for $k \leq 3 k_\mathrm{FS} = 0.17~h/$Mpc and to
$19\%$ for $k \leq 0.4~h/$Mpc. We find that the enhancement factor, the ratio
of $\Delta^2_\nu(k)$ to its linear-response equivalent, is most strongly
correlated with $\Omega_{\nu,0} h^2$, and also with the clustering amplitude
$\sigma_8$. Furthermore, non-linearities enhance the free-streaming-limit
scaling $\partial \log(\Delta^2_\nu / \Delta^2_{\rm m}) / \partial \log(M_\nu)$
beyond its linear value of 4, increasing the $M_\nu$-sensitivity of the
small-scale neutrino density. |
Testing models for molecular gas formation in galaxies: hydrostatic
pressure or gas and dust shielding?: Stars in galaxies form in giant molecular clouds that coalesce when the
atomic hydrogen is converted into molecules. There are currently two dominant
models for what property of the galactic disk determines its molecular
fraction: either hydrostatic pressure driven by the gravity of gas and stars,
or a combination of gas column density and metallicity. To assess the validity
of these models, we compare theoretical predictions to the observed atomic gas
content of low-metallicity dwarf galaxies with high stellar densities. The
extreme conditions found in these systems are optimal to distinguish the two
models, otherwise degenerate in nearby spirals. Locally, on scales <100 pc, we
find that the state of the interstellar medium is mostly sensitive to the gas
column density and metallicity rather than hydrostatic pressure. On larger
scales where the average stellar density is considerably lower, both pressure
and shielding models reproduce the observations, even at low metallicity. We
conclude that models based on gas and dust shielding more closely describe the
process of molecular formation, especially at the high resolution that can be
achieved in modern galaxy simulations or with future radio/millimeter arrays. | Constraining gravity with a new precision $E_G$ estimator using Planck +
SDSS BOSS: The $E_G$ statistic is a discriminating probe of gravity developed to test
the prediction of general relativity (GR) for the relation between
gravitational potential and clustering on the largest scales in the observable
universe. We present a novel high-precision estimator for the $E_G$ statistic
using CMB lensing and galaxy clustering correlations that carefully matches the
effective redshifts across the different measurement components to minimize
corrections. A suite of detailed tests is performed to characterize the
estimator's accuracy, its sensitivity to assumptions and analysis choices and
the non-Gaussianity of the estimator's uncertainty is characterized. After
finalization of the estimator, it is applied to $\textit{Planck}$ CMB lensing
and SDSS CMASS and LOWZ galaxy data. We report the first harmonic space
measurement of $E_G$ using the LOWZ sample and CMB lensing and also updated
constraints using the final CMASS sample and the latest $\textit{Planck}$ CMB
lensing map. We find $E_G^{Planck+CMASS} = 0.36^{+0.06}_{-0.05}$ (68.27%) and
$E_G^{\rm \textit{Planck}+LOWZ} = 0.40^{+0.11}_{-0.09} $ (68.27%), with
additional subdominant systematic error budget estimates of 2% and 3%
respectively. Using $\Omega_{\rm m,0}$ constraints from $\textit{Planck}$ and
SDSS BAO observations, $\Lambda$CDM-GR predicts $E_G^{\rm GR} (z = 0.555) =
0.401 \pm 0.005$ and $E_G^{\rm GR} (z = 0.316) = 0.452 \pm 0.005$ at the
effective redshifts of the CMASS and LOWZ based measurements. We report the
measurement to be in good statistical agreement with the $\Lambda$CDM-GR
prediction, and report that the measurement is also consistent with the more
general GR prediction of scale-independence for $E_G$. This work provides a
carefully constructed and calibrated statistic with which $E_G$ measurements
can be confidently and accurately obtained with upcoming survey data. |
The splashback radius of halos from particle dynamics: III. Halo
catalogs, merger trees, and host-subhalo relations: Virtually any investigation involving dark matter halos relies on a
definition of their radius, mass, and of whether they are a subhalo. The halo
boundary is most commonly defined to include a spherical overdensity contrast
(such as R200c, Rvir, and R200m), but different thresholds lead to significant
differences in radius and mass. The splashback radius has recently been
suggested as a more physically motivated (and generally larger) halo boundary,
adding to the range of definitions. It is often difficult to assess the impact
of a particular choice because most halo catalogs contain only one or a few
definitions and generally only one set of host-subhalo relations. To alleviate
this issue, we present halo catalogs and merger trees for 14 N-body simulations
of LambdaCDM and self-similar universes. Based on ROCKSTAR catalogs, we compute
additional halo properties using the SPARTA code and recombine them with the
original catalogs. The new catalogs contain numerous variants of spherical
overdensity and splashback radii and masses and, most critically, host-subhalo
relations for each definition. We also present a new merger tree format where
the data is stored as a compressed, two-dimensional matrix. We perform basic
tests of the relation between different definitions and present an updated
model for the splashback-spherical overdensity connection. The SPARTA code, as
well as our catalogs and merger trees, are publicly available. | Clues on the rejuvenation of the S0 galaxy NGC 404 from the chemical
abundance of its outer disk: The oxygen abundance of the outer disk of the nearby S0 galaxy NGC 404, a
prototypical early-type galaxy with extended star formation, has been derived
from the analysis of HII region spectra. The high mean value found,
12+log(O/H)=8.6 \pm 0.1, equivalent to approximately 80% of the solar value,
argues against both the previously proposed cold accretion and recent merger
scenarios as viable mechanisms for the assembly of the star-forming gas. The
combination of the present-day gas metallicity with the published star
formation history of this galaxy favors a model in which the recent star
forming activity represents the declining tail of the original one. |
Gaussianizing the non-Gaussian lensing convergence field I: the
performance of the Gaussianization: Motivated by recent works of Neyrinck et al. 2009 and Scherrer et al. 2010,
we proposed a Gaussianization transform to Gaussianize the non-Gaussian lensing
convergence field $\kappa$. It performs a local monotonic transformation
$\kappa\rightarrow y$ pixel by pixel to make the unsmoothed one-point
probability distribution function of the new variable $y$ Gaussian. We tested
whether the whole $y$ field is Gaussian against N-body simulations. (1) We
found that the proposed Gaussianization suppresses the non-Gaussianity by
orders of magnitude, in measures of the skewness, the kurtosis, the 5th- and
6th-order cumulants of the $y$ field smoothed over various angular scales
relative to that of the corresponding smoothed $\kappa$ field. The residual
non-Gaussianities are often consistent with zero within the statistical errors.
(2) The Gaussianization significantly suppresses the bispectrum. Furthermore,
the residual scatters around zero, depending on the configuration in the
Fourier space. (3) The Gaussianization works with even better performance for
the 2D fields of the matter density projected over $\sim 300 \mpch$ distance
interval centered at $z\in(0,2)$, which can be reconstructed from the weak
lensing tomography. (4) We identified imperfectness and complexities of the
proposed Gaussianization. We noticed weak residual non-Gaussianity in the $y$
field. We verified the widely used logarithmic transformation as a good
approximation to the Gaussianization transformation. However, we also found
noticeable deviations. | Higher-order extension of Starobinsky inflation: initial conditions,
slow-roll regime, and reheating phase: The most current observational data corroborate the Starobinsky model as one
of the strongest candidates in the description of an inflationary regime.
Motivated by such success, extensions of the Starobinsky model have been
increasingly recurrent in the literature. The theoretical justification for
this is well grounded: higher-order gravities arise in high-energy physics in
the search for the ultraviolet completeness of general relativity. In this
paper, we propose to investigate the inflation due to the extension of the
Starobinsky model characterized by the inclusion of the $R^{3}$ term. We make a
complete analysis of the potential and phase space of the model, where we
observe the existence of three regions with distinct dynamics for the scalar
field. We can establish restrictive limits for the number of $e$-folds through
a study of the reheating and by considering the usual couplings of the standard
matter fields and gravity. Thereby, we duly confront our model with the
observational data from Planck, BICEP3/Keck, and BAO. Finally, we discuss how
the inclusion of the cubic term restricts the initial conditions necessary for
the occurrence of a physical inflation. |
Optical Cluster Cosmology with SDSS redMaPPer clusters and HSC-Y3
lensing measurements: We present cosmology results obtained from a blind joint analysis of the
abundance, projected clustering, and weak lensing of galaxy clusters measured
from the Sloan Digital Sky Survey (SDSS) redMaPPer cluster catalog and the
Hyper-Suprime Cam (HSC) Year3 shape catalog. We present a full-forward model
for the cluster observables, which includes empirical modeling for the
anisotropic boosts on the lensing and clustering signals of optical clusters.
We validate our analysis via mock cluster catalogs which include observational
systematics, such as the projection effect and the effect of baryonic feedback,
and find that our analysis can robustly constrain cosmological parameters in an
unbiased manner without any informative priors on our model parameters. The
joint analysis of our observables in the context of the flat $\Lambda$CDM model
results in cosmological constraints for $S_8\equiv \sigma_8 \sqrt{\Omega_{\rm
m} / 0.3}=0.816^{+0.041}_{-0.039}$. Our result is consistent with the $S_8$
inference from other cosmic microwave background- and large scale
structure-based cosmology analyses, including the result from the \emph{Planck}
2018 primary CMB analysis. | Testing general scalar-tensor gravity and massive gravity with cluster
lensing: We explore the possibility of testing modified gravity exhibiting the
Vainshtein mechanism against observations of cluster lensing. We work in the
most general scalar-tensor theory with second-order field equations
(Horndeski's theory), and derive static and spherically symmetric solutions,
for which the scalar field is screened below a certain radius. It is found that
the essential structure of the problem in the most general case can be captured
by the program of classifying Vainshtein solutions out of different solutions
to a quintic equation, as has been performed in the context of massive gravity.
The key effect on gravitational lensing is that the second derivative of the
scalar field can substantially be large at the transition from screened to
unscreened regions, leaving a dip in the convergence. This allows us to put
observational constraints on parameters characterizing the general
scalar-tensor modification of gravity. We demonstrate how this occurs in
massive gravity as an example, and discuss its observational signatures in
cluster lensing. |
CMB hemispherical asymmetry from non-linear isocurvature perturbations: We investigate whether non-adiabatic perturbations from inflation could
produce an asymmetric distribution of temperature anisotropies on large angular
scales in the cosmic microwave background (CMB). We use a generalised
non-linear $\delta N$ formalism to calculate the non-Gaussianity of the
primordial density and isocurvature perturbations due to the presence of
non-adiabatic, but approximately scale-invariant field fluctuations during
multi-field inflation. This local-type non-Gaussianity leads to a correlation
between very long wavelength inhomogeneities, larger than our observable
horizon, and smaller scale fluctuations in the radiation and matter density.
Matter isocurvature perturbations contribute primarily to low CMB multipoles
and hence can lead to a hemispherical asymmetry on large angular scales, with
negligible asymmetry on smaller scales. In curvaton models, where the matter
isocurvature perturbation is partly correlated with the primordial density
perturbation, we are unable to obtain a significant asymmetry on large angular
scales while respecting current observational constraints on the observed
quadrupole. However in the axion model, where the matter isocurvature and
primordial density perturbations are uncorrelated, we find it may be possible
to obtain a significant asymmetry due to isocurvature modes on large angular
scales. Such an isocurvature origin for the hemispherical asymmetry would
naturally give rise to a distinctive asymmetry in the CMB polarisation on large
scales. | On the offset of the DM cusp and the interpretation of the 130 GeV line
as a DM signal: We show that the cusp in the dark matter (DM) distribution required to
explain the recently found excess in the gamma-ray spectrum at energies ~130
GeV in terms of the DM annihilations cannot survive the tidal forces if it is
offset by ~1.5^\circ from the Galactic centre as suggested by observations. |
Consistency conditions and primordial black holes in single field
inflation: We discuss new consistency relations for single field models of inflation
capable of generating primordial black holes (PBH), and their observational
implications for CMB $\mu$-space distortions. These inflationary models include
a short period of non-attractor evolution: the scale-dependent profile of
curvature perturbation is characterized by a pronounced dip, followed by a
rapid growth leading to a peak responsible for PBH formation. We investigate
the squeezed and the collapsed limits of three and four point functions of
curvature perturbation around the dip, showing that they satisfy consistency
relations connecting their values to the total amplification of the curvature
spectrum, and to the duration of the non-attractor era. Moreover, the
corresponding non-Gaussian parameters are scale-dependent in proximity of the
dip, with features that again depend on the amplification of the spectrum. For
typical PBH scenarios requiring an order ${\cal O}(10^7)$ enhancement of the
spectrum from large towards small scales, we generally find values $f_{\rm
NL}^{\rm sq}\,=\,{\cal O}(10)$ and $\tau_{\rm NL}^{\rm col}\,=\,{\cal O}(10^3)$
in a range of scales that can be probed by CMB $\mu$-space distortions. Using
these consistency relations, we carefully analyze how the scale-dependence of
non-Gaussian parameters leads to characteristic features in $\langle \mu T
\rangle$ and $\langle \mu \mu \rangle$ correlators, providing distinctive
probes of inflationary PBH scenarios that can be tested using well-understood
CMB physics. | A census of ultra-compact dwarf galaxies in nearby galaxy clusters: Ultra-compact dwarf galaxies (UCDs) are predominatly found in the cores of
nearby galaxy clusters. Besides the Fornax and Virgo cluster, UCDs have also
been confirmed in the twice as distant Hydra I and Centaurus clusters. Having
(nearly) complete samples of UCDs in some of these clusters allows the study of
the bulk properties with respect to the environment they are living in.
Moreover, the relation of UCDs to other stellar systems in galaxy clusters,
like globular clusters and dwarf ellipticals, can be investigated in detail
with the present data sets. The general finding is that UCDs seem to be a
heterogenous class of objects. Their spatial distribution within the clusters
is in between those of globular clusters and dwarf ellipticals. In the
colour-magnitude diagram, blue/metal-poor UCDs coincide with the sequence of
nuclear star clusters, whereas red/metal-rich UCDs reach to higher masses and
might have originated from the amalgamation of massive star cluster complexes
in merger or starburst galaxies. |
The formation of CDM haloes II: collapse time and tides: We use two cosmological simulations of structure formation in the LambdaCDM
scenario to study the evolutionary histories of dark-matter haloes and to
characterize the Lagrangian regions from which they form. We focus on haloes
identified at redshift z_id=0 and show that the classic ellipsoidal collapse
model systematically overestimates their collapse times. If one imposes that
halo collapse takes place at z_id, this model requires starting from a
significantly lower linear density contrast than what is measured in the
simulations at the locations of halo formation. We attempt to explain this
discrepancy by testing two key assumptions of the model. First, we show that
the tides felt by collapsing haloes due to the surrounding large-scale
structure evolve non-linearly. Although this effect becomes increasingly
important for low-mass haloes, accounting for it in the ellipsoidal collapse
model only marginally improves the agreement with N-body simulations. Second,
we track the time evolution of the physical volume occupied by forming haloes
and show that, after turnaround, it generally stabilizes at a well-defined
redshift, z_c>z_id, contrary to the basic assumption of extended
Press-Schechter theory based on excursion sets. We discuss the implications of
this result for understanding the origin of the mass-dependence and scatter in
the linear threshold for halo formation. Finally, we show that, when tuned for
collapse at z_c, a modified version of the ellipsoidal collapse model that also
accounts for the triaxial nature of protohaloes predicts their linear density
contrast in an unbiased way. | Exploring the squeezed three-point galaxy correlation function with
generalized halo occupation distribution models: We present the GeneRalized ANd Differentiable Halo Occupation Distribution
(GRAND-HOD) routine that generalizes the standard 5 parameter halo occupation
distribution model (HOD) with various halo-scale physics and assembly bias. We
describe the methodology of 4 different generalizations: satellite distribution
generalization, velocity bias, closest approach distance generalization, and
assembly bias. We showcase the signatures of these generalizations in the
2-point correlation function (2PCF) and the squeezed 3-point correlation
function (squeezed 3PCF). We identify generalized HOD prescriptions that are
nearly degenerate in the projected 2PCF and demonstrate that these degeneracies
are broken in the redshift-space anisotropic 2PCF and the squeezed 3PCF. We
also discuss the possibility of identifying degeneracies in the anisotropic
2PCF and further demonstrate the extra constraining power of the squeezed 3PCF
on galaxy-halo connection models. We find that within our current HOD
framework, the anisotropic 2PCF can predict the squeezed 3PCF better than its
statistical error. This implies that a discordant squeezed 3PCF measurement
could falsify the particular HOD model space. Alternatively, it is possible
that further generalizations of the HOD model would open opportunities for the
squeezed 3PCF to provide novel parameter measurements. The GRAND-HOD Python
package is publicly available at https://github.com/SandyYuan/GRAND-HOD . |
Late universe decaying dark matter can relieve the H_0 tension: We study the cosmological effects of two-body dark matter decays where the
products of the decay include a massless and a massive particle. We show that
if the massive daughter particle is slightly warm it is possible to relieve the
tension between distance ladder measurements of the present day Hubble
parameter with measurements from the cosmic microwave background. | Unveiling the new generation of stars in NGC 604 with Gemini-NIRI: We present a near infrared study focused on the detection and
characterization of the youngest stellar component of the NGC 604 giant
star-forming region, in the Triangulum galaxy (M 33). By means of color-color
diagrams derived from the photometry of JHKs images taken with Gemini-NIRI, we
have found 68 candidate massive young stellar objects. The spatial distribution
of these sources matches the areas where previous studies suggested that star
formation might be taking place, and the high spatial resolution of our deep
NIRI imaging allows to pinpoint the star-forming knots. An analysis of the
fraction of objects that show infrared excess suggests that the star formation
is still active, supporting the presence of a second generation of stars being
born, although the evidence for or against sequential star formation does not
seem to be conclusive. |
CMB Lensing Constraints on Neutrinos and Dark Energy: Signatures of lensing of the cosmic microwave background radiation by
gravitational potentials along the line of sight carry with them information on
the matter distribution, neutrino masses, and dark energy properties. We
examine the constraints that Planck, PolarBear, and CMBpol future data,
including from the B-mode polarization or the lensing potential, will be able
to place on these quantities. We simultaneously fit for neutrino mass and dark
energy equation of state including time variation and early dark energy
density, and compare the use of polarization power spectra with an optimal
quadratic estimator of the lensing. Results are given as a function of
systematics level from residual foreground contamination. A realistic CMBpol
experiment can effectively constrain the sum of neutrino masses to within 0.05
eV and the fraction of early dark energy to 0.002. We also present a
surprisingly simple prescription for calculating dark energy equation of state
constraints in combination with supernova distances from JDEM. | The Star Formation & Chemical Evolution History of the Sculptor Dwarf
Spheroidal Galaxy: We have combined deep photometry in the B,V and I bands from CTIO/MOSAIC of
the Sculptor dwarf spheroidal galaxy, going down to the oldest Main Sequence
Turn-Offs, with spectroscopic metallicity distributions of Red Giant Branch
stars. This allows us to obtain the most detailed and complete Star Formation
History to date, as well as an accurate timescale for chemical enrichment. The
Star Formation History shows that Sculptor is dominated by old ($>$10 Gyr),
metal-poor stars, but that younger, more metal-rich populations are also
present. Using Star Formation Histories determined at different radii from the
centre we show that Sculptor formed stars with an increasing central
concentration with time. The old, metal-poor populations are present at all
radii, while more metal-rich, younger stars are more centrally concentrated. We
find that within an elliptical radius of 1 degree, or 1.5 kpc from the centre,
a total mass in stars of 7.8$\times10^{6}$ M$_{\odot}$ was formed, between 14
and 7 Gyr ago, with a peak at 13$-$14 Gyr ago. We use the detailed Star
Formation History to determine age estimates for individual Red Giant Branch
stars with high resolution spectroscopic abundances. Thus, for the first time,
we can directly determine detailed timescales for the evolution of individual
chemical elements. We find that the trends in alpha-elements match what is
expected from an extended, relatively uninterrupted period of star formation
continuing for 6$-$7 Gyr. The knee in the alpha-element distribution occurs at
an age of 10.9$\pm$1Gyr, suggesting that SNe Ia enrichment began
$\approx2\pm$1Gyr after the start of star formation in Sculptor. |
Relaxing cosmological tensions with a sign switching cosmological
constant: Inspired by the recent conjecture originated from graduated dark energy that
the Universe has recently transitioned from anti-de Sitter vacua to de Sitter
vacua, we extend the $\Lambda$CDM model by a cosmological constant
($\Lambda_{\rm s}$) that switches sign at a certain redshift $z_\dagger$, and
we call this model $\Lambda_{\rm s}$CDM. We discuss the construction and
theoretical features of this model and find out that, when the consistency of
$\Lambda_{\rm s}$CDM with the CMB data is ensured, (i) $z_\dagger\gtrsim1.1$ is
implied by the condition that the Universe monotonically expands, (ii) $H_0$
and $M_B$ (type Ia supernovae absolute magnitude) values are inversely
correlated with $z_\dagger$ and reach $H_0\approx74.5~{\rm km\, s^{-1}\,
Mpc^{-1}}$ and $M_B\approx-19.2\,{\rm mag}$ for $z_\dagger=1.5$, in agreement
with the SH0ES measurements, and (iii) $H(z)$ presents an excellent fit to the
Ly-$\alpha$ measurements provided that $z_\dagger\lesssim 2.34$. We further
investigate the model constraints by using the full Planck CMB data set, with
and without BAO data. We find that the CMB data alone does not constrain
$z_\dagger$, but the CMB+BAO data set favors the sign switch of $\Lambda_{\rm
s}$ providing the constraint: $z_\dagger=2.44\pm0.29$ (68% C.L.). Our analysis
reveals that the lower and upper limits of $z_\dagger$ are controlled by the
Galaxy and Ly-$\alpha$ BAO measurements, respectively, and the larger
$z_{\dagger}$ values imposed by the Galaxy BAO data prevent the model from
achieving the highest local $H_0$ measurements. In general, $\Lambda_{\rm
s}$CDM (i) relaxes the $H_0$ tension while being fully consistent with the TRGB
measurements, (ii) relaxes the $M_B$ tension, (iii) removes the discrepancy
with the Ly-$\alpha$ measurements, (iv) relaxes the $S_8$ tension, and (v)
finds a better agreement with the BBN constraints on the physical baryon
density. [Abridged] | Spectral ageing in the lobes of FR-II radio galaxies: New methods of
analysis for broadband radio data: The broad-bandwidth capabilities of next generation telescopes such as the
JVLA mean that the spectrum of any given source varies significantly within the
bandwidth of any given observation. Detailed spectral analysis taking this
variation into account is set to become standard practice when dealing with any
new broadband radio observations; it is therefore vital that methods are
developed to handle this new type of data. In this paper, we present the
Broadband Radio Astronomy ToolS (BRATS) software package and, use it to carry
out detailed analysis of JVLA observations of three powerful radio galaxies. We
compare two of the most widely used models of spectral ageing, the
Kardashev-Pacholczyk and Jaffe-Perola models and also results of the more
complex, but potentially more realistic, Tribble model. We find that the
Tribble model provides both a good fit to observations as well as providing a
physically realistic description of the source. We present the first
high-resolution spectral maps of our sources and find that the best-fitting
injection indices across all models take higher values than has previously been
assumed. We present characteristic hot spot advance speeds and make comparison
to those derived from dynamical ages, confirming the previously known
discrepancy in speed remains present when determined at high spectral
resolutions. We show that some previously common assumptions made in
determining spectral ages with narrow-band radio telescopes may not always hold
and strongly suggest these are accounted for in future investigations. |
Removal of two large scale Cosmic Microwave Background anomalies after
subtraction of the Integrated Sachs Wolfe effect: Though debated, the existence of claimed large-scale anomalies in the CMB is
not totally dismissed. In parallel to the debate over their statistical
significance, recent work focussed on masks and secondary anisotropies as
potential sources of these anomalies. In this work we investigate
simultaneously the impact of the method used to account for masked regions and
the impact of the ISW effect, which is the large-scale secondary anisotropy
most likely to affect the CMB anomalies. In this sense, our work is an update
of both Francis & Peacock 2010 and Kim et al. 2012. Our aim is to identify
trends in CMB data with different mask treatments. We reconstruct the ISW
signal due to 2MASS and NVSS galaxies. We account for missing data using the
sparse inpainting technique of Abrial et al. 2008 and sparse inpainting of the
CMB, LSS and ISW and find that it constitutes a bias-free reconstruction method
suitable to study large-scale statistical isotropy and the ISW effect. We focus
on three large-scale CMB anomalies: the low quadrupole, the quad/oct alignment,
and the octopole planarity. After sparse inpainting, the low quadrupole becomes
more anomalous, whilst the quad/oct alignment becomes less anomalous. The
significance of the low quadrupole is unchanged after subtraction of the ISW
effect, while the trend is that the quad/oct alignment has reduced
significance, yet other hypotheses remain possible as well (e.g. exotic
physics). Our results also suggest that both of these anomalies may be due to
the quadrupole alone. The octopole planarity significance is also reduced after
inpainting and after ISW subtraction, however, we do not find that it was very
anomalous to start with. In the spirit of reproducible research, we make all
codes and resulting products which constitute main results of this paper public
here: http://www.cosmostat.org/anomaliesCMB.html. | Nuclear Activity is more prevalent in Star-Forming Galaxies: We explore the question of whether low and moderate luminosity Active
Galactic Nuclei (AGNs) are preferentially found in galaxies that are undergoing
a transition from active star formation to quiescence. This notion has been
suggested by studies of the UV-to-optical colors of AGN hosts, which find them
to be common among galaxies in the so-called "Green Valley", a region of galaxy
color space believed to be composed mostly of galaxies undergoing
star-formation quenching. Combining the deepest current X-ray and Herschel.
PACS far-infrared (FIR) observations of the two Chandra Deep Fields (CDFs) with
redshifts, stellar masses and rest-frame photometry derived from the extensive
and uniform multi-wavelength data in these fields, we compare the rest-frame
U-V color distributions and SFR distributions of AGNs and carefully constructed
samples of inactive control galaxies. The UV-to-optical colors of AGNs are
consistent with equally massive inactive galaxies at redshifts out to z~2, but
we show that such colors are poor tracers of star formation. While the FIR
distributions of both star-forming AGNs and star-forming inactive galaxies are
statistically similar, we show that AGNs are preferentially found in
star-forming host galaxies, or, in other words, AGNs are less likely to be
found in weakly star-forming or quenched galaxies. We postulate that, among
X-ray selected AGNs of low and moderate accretion luminosities, the supply of
cold gas primarily determines the accretion rate distribution of the nuclear
black holes. |
Metallicities and dust content of proximate damped Lyman alpha systems
in the Sloan Digital Sky Survey: Composite spectra of 85 proximate absorbers (log N(HI)>20 and velocity
difference between the absorption and emission redshift, dv<10,000 km/s) in the
SDSS are used to investigate the trends of metal line strengths with velocity
separation from the QSO. We construct composites in 3 velocity bins: dv<3000
km/s, 3000<dv<6000 km/s and dv>6000 km/s, with further sub-samples to
investigate the metal line dependence on N(HI) and QSO luminosity. Low (e.g.
SiII and FeII) and high ionization (e.g. SiIV and CIV) species alike have
equivalent widths (EWs) that are larger by factors of 1.5 -- 3 in the dv<3000
km/s composite, compared to the dv>6000 km/s spectrum. The EWs show an even
stronger dependence on dv if only the highest neutral hydrogen column density
(log N(HI)>20.7) absorbers are considered. We conclude that PDLAs generally
have higher metallicities than intervening absorbers, with the enhancement
being a function of both dv and N(HI). It is also found that absorbers near
QSOs with lower rest-frame UV luminosities have significantly stronger metal
lines. We speculate that absorbers near to high luminosity QSOs may have had
their star formation prematurely quenched. Finally, we search for the signature
of dust reddening by the PDLAs, based on an analysis of the QSO continuum
slopes relative to a control sample and determine a limit of E(B-V)<0.014 for
an SMC extinction curve. This work provides an empirical motivation for
distinguishing between proximate and intervening DLAs, and establishes a
connection between the QSO environment and galaxy properties at high redshifts. | Optical Flares from the Tidal Disruption of Stars by Massive Black Holes: A star that wanders too close to a massive black hole (BH) is shredded by the
BH's tidal gravity. Stellar gas falls back to the BH, releasing a flare of
energy. In anticipation of upcoming transient surveys, we predict the light
curves and spectra of tidal flares as a function of time, highlighting the
unique signatures of tidal flares in the optical and near-IR. Some of the gas
initially bound to the BH is likely blown away when the fallback rate is
super-Eddington at early times. This outflow produces an optical luminosity
comparable to that of a supernova; such events have durations of ~10 days and
may have been missed in supernova searches that exclude the nuclear regions of
galaxies. When the fallback rate subsides below Eddington, the gas accretes
onto the BH via a thin disk whose emission peaks in the UV to soft X-rays. Some
of this emission is reprocessed by the unbound stellar debris, producing a
spectrum of very broad emission lines (with no corresponding narrow forbidden
lines). These lines are strongest for BHs with MBH ~ 10^5 - 10^6 Msun and thus
optical surveys are particularly sensitive to the lowest mass BHs in galactic
nuclei. Calibrating our models to ROSAT and GALEX observations, we predict
detection rates for Pan-STARRS, PTF, and LSST and highlight observational
challenges in the optical. Pan-STARRS should detect at least several events per
year--many more if current theoretical models of super-Eddington outflows are
correct. These surveys will significantly improve our knowledge of stellar
dynamics in galactic nuclei, the physics of super-Eddington accretion, the
demography of intermediate mass BHs, and the role of tidal disruption in the
growth of massive BHs. |
Big-Bang Nucleosynthesis in comparison with observed helium and
deuterium abundances - possibility of a non-standard model: Comparing the latest observed abundances of 4He and D, we make a ?2 analysis
to see whether it is possible to reconcile primordial nucleosynthesis using
up-to-date nuclear data of NACRE II and the mean-life of neutrons. If we adopt
the observational data of ${}^4_{}$He by Izotov et al., we find that it is
impossible to get reasonable concordance against the standard Big-Bang
nucleosynthesis. However, including degenerate neutrinos, we have succeeded in
obtaining consistent constraints between the neutrino degeneracy and the
baryon-to-photon ratio from detailed comparison of calculated abundances with
the observational data of ${}^4_{}$He and D: the baryon-to-photon ratio in
units of $10^{-10}$ is found to be in the range 6.02 < $\eta^{}_{10}$ < 6:54
for the specified parameters of neutrino degeneracy. | HERACLES: The HERA CO-Line Extragalactic Survey: We present the HERA CO-Line Extragalactic Survey (HERACLES), an atlas of CO
emission from 18 nearby galaxies that are also part of The HI Nearby Galaxy
Survey (THINGS) and the Spitzer Infrared Nearby Galaxies Survey (SINGS). We
used the HERA multi-pixel receiver on the IRAM 30-m telescope to map the CO
J=2-1 line over the full optical disk (defined by the isophotal radius r_25) of
each target, at 13" angular resolution and 2.6 km/s velocity resolution. Here
we describe the observations and reduction of the data and show channel maps,
azimuthally averaged profiles, integrated intensity maps, and peak intensity
maps. The implied H2 masses range from 7 \times 10^6 to 6 \times 10^9 M_sun,
with four low metallicity dwarf irregular galaxies yielding only upper limits.
In the cases where CO is detected, the integrated H2-to-HI ratios range from
0.02 - 1.13 and H2-to-stellar mass ratios from 0.01 to 0.25. Exponential scale
lengths of the CO emission for our targets are in the range 0.8 - 3.2 kpc, or
0.2 \pm 0.05 r_25. The intensity-weighted mean velocity of CO matches that of
HI very well, with a 1\sigma scatter of only 6 km/s. The CO J=2-1 / J=1-0 line
ratio varies over a range similar to that found in the Milky Way and other
nearby galaxies, \sim 0.6 - 1.0, with higher values found in the centers of
galaxies. The typical line ratio, \sim 0.8, could be produced by optically
thick gas with an excitation temperature of \sim 10 K. |
An Early & Comprehensive Millimeter and Centimeter Wave and X-ray Study
of Supernova 2011dh: A Non-Equipartition Blastwave Expanding into A Massive
Stellar Wind: Only a handful of supernovae (SNe) have been studied in multi-wavelength from
radio to X-rays, starting a few days after explosion. The early detection and
classification of the nearby type IIb SN2011dh/PTF11eon in M51 provides a
unique opportunity to conduct such observations. We present detailed data
obtained at the youngest phase ever of a core-collapse supernova (days 3 to 12
after explosion) in the radio, millimeter and X-rays; when combined with
optical data, this allows us to explore the early evolution of the SN blast
wave and its surroundings. Our analysis shows that the expanding supernova
shockwave does not exhibit equipartition (e_e/e_B ~ 1000), and is expanding
into circumstellar material that is consistent with a density profile falling
like R^-2. Within modeling uncertainties we find an average velocity of the
fast parts of the ejecta of 15,000 +/- 1800 km/s, contrary to previous
analysis. This velocity places SN 2011dh in an intermediate blast-wave regime
between the previously defined compact and extended SN IIb subtypes. Our
results highlight the importance of early (~ 1 day) high-frequency observations
of future events. Moreover, we show the importance of combined radio/X-ray
observations for determining the microphysics ratio e_e/e_B. | A numerical study of observational systematic errors in lensing analysis
of CMB polarization: Impacts of observational systematic errors on the lensing analysis of the
cosmic microwave background (CMB) polarization are investigated by numerical
simulations. We model errors of gain, angle, and pointing in observation of the
CMB polarization and simulate polarization fields modulated by the errors. We
discuss the response of systematics-induced $B$-modes to amplitude and spatial
scale of the imposed errors and show that the results of the lensing
reconstruction and delensing analysis behave according to it. It is observed
that error levels expected in the near future lead to no significant
degradation in delensing efficiency. |
Cosmic Near-infrared Background Tomography with SPHEREx Using Galaxy
Cross-correlations: The extragalactic background light (EBL) consists of integrated light from
all sources of emission throughout the history of the universe. At
near-infrared wavelengths, the EBL is dominated by stellar emission across
cosmic time; however, the spectral and redshift information of the emitting
sources is entangled and cannot be directly measured by absolute photometry or
fluctuation measurements. Cross-correlating near-infrared maps with tracers of
known redshift enables EBL redshift tomography, as EBL emission will only
correlate with external tracers from the same redshift. Here, we forecast the
sensitivity of probing the EBL spectral energy distribution as a function of
redshift by cross-correlating the upcoming near-infrared spectro-imaging
survey, SPHEREx, with several current and future galaxy redshift surveys. Using
a model galaxy luminosity function, we estimate the cross power spectrum
clustering amplitude on large scales, and forecast that the near-infrared EBL
spectrum can be detected tomographically out to $z\sim 6$. We also predict a
high-significance measurement ($\sim 10^2$-$10^4\sigma$) of the small-scale
cross-power spectrum out to $z\sim 10$. The amplitudes of the large-scale cross
power spectra can constrain the cosmic evolution of the stellar synthesis
process through both continuum and the line emission, while on the nonlinear
and Poisson noise scales, the high-sensitivity measurements can probe the mean
spectra associated with the tracer population across redshift. | The vast thin plane of M31 co-rotating dwarfs: an additional fossil
signature of the M31 merger and of its considerable impact in the whole Local
Group: The recent discovery by Ibata et al. (2013) of a vast thin disk of satellites
(VTDS) around M31 offers a new challenge for the understanding of the Local
Group properties. This comes in addition to the unexpected proximity of the
Magellanic Clouds (MCs) to the Milky Way (MW), and to another vast polar
structure (VPOS), which is almost perpendicular to our Galaxy disk. We find
that the VTDS plane is coinciding with several stellar, tidally-induced streams
in the outskirts of M31, and, that its velocity distribution is consistent with
that of the Giant Stream (GS). This is suggestive of a common physical
mechanism, likely linked to merger tidal interactions, knowing that a similar
argument may apply to the VPOS at the MW location. Furthermore, the VTDS is
pointing towards the MW, being almost perpendicular to the MW disk, as the VPOS
is.
We compare these properties to the modelling of M31 as an ancient, gas-rich
major merger, which has been successfully used to predict the M31 substructures
and the GS origin. We find that without fine tuning, the induced tidal tails
are lying in the VTDS plane, providing a single and common origin for many
stellar streams and for the vast stellar structures surrounding both the MW and
M31. The model also reproduces quite accurately positions and velocities of the
VTDS dSphs. Our conjecture leads to a novel interpretation of the Local Group
past history, as a gigantic tidal tail due to the M31 ancient merger is
expected to send material towards the MW, including the MCs. Such a link
between M31 and the MW is expected to be quite exceptional, though it may be in
qualitative agreement with the reported rareness of MW-MCs systems in nearby
galaxies. |
Sensitivity of the CUORE detector to $14.4$ keV solar axions emitted by
the M1 nuclear transition of$~^{57}$Fe: In this paper we present a calculation of the sensitivity of the CUORE
detector to the monoenergetic $14.4$ keV solar axions emitted by the M1 nuclear
transition of$~^{57}$Fe in the Sun and detected by inverse coherent
Bragg-Primakoff conversion in single-crystal $TeO_2$ bolometers. The expected
counting rate is calculated using density functional theory for the electron
charge density of $TeO_2$ and realistic background and energy resolution of
CUORE. Monte Carlo simulations for $5$ y $\times$ $741$ kg=$3705-$kg$\cdot$y of
exposure are analyzed using time correlation of individual events with the
theoretical time-dependent counting rate. We find an expected model-independent
limit on the product of the axion-photon coupling and the axion-nucleon
coupling $g_{a\gamma\gamma}g_{aN}^{\text{eff}}<1.105\times 10^{-16}$ /GeV for
axion masses less than 500 eV with $95\%$ confidence level. | Concordance Cosmology?: We propose a new intuitive metric for evaluating the tension between two
experiments, and apply it to several data sets. While our metric is
non-optimal, if evidence of tension is detected, this evidence is robust and
easy to interpret. Assuming a flat $\Lambda$CDM cosmological model, we find
that there is a modest $2.2\sigma$ tension between the DES Year 1 results and
the ${\it Planck}$ measurements of the Cosmic Microwave Background (CMB). This
tension is driven by the difference between the amount of structure observed in
the late-time Universe and that predicted from fitting the ${\it Planck}$ data,
and appears to be unrelated to the tension between ${\it Planck}$ and local
esitmates of the Hubble rate. In particular, combining DES, Baryon Acoustic
Oscillations (BAO), Big-Bang Nucleosynthesis (BBN), and supernovae (SNe)
measurements recovers a Hubble constant and sound horizon consistent with ${\it
Planck}$, and in tension with local distance-ladder measurements. If the
tension between these various data sets persists, it is likely that reconciling
${\it all}$ current data will require breaking the flat $\Lambda$CDM model in
at least two different ways: one involving new physics in the early Universe,
and one involving new late-time Universe physics. |
Measuring Linear and Non-linear Galaxy Bias Using Counts-in-Cells in the
Dark Energy Survey Science Verification Data: Non-linear bias measurements require a great level of control of potential
systematic effects in galaxy redshift surveys. Our goal is to demonstrate the
viability of using Counts-in-Cells (CiC), a statistical measure of the galaxy
distribution, as a competitive method to determine linear and higher-order
galaxy bias and assess clustering systematics. We measure the galaxy bias by
comparing the first four moments of the galaxy density distribution with those
of the dark matter distribution. We use data from the MICE simulation to
evaluate the performance of this method, and subsequently perform measurements
on the public Science Verification (SV) data from the Dark Energy Survey (DES).
We find that the linear bias obtained with CiC is consistent with measurements
of the bias performed using galaxy-galaxy clustering, galaxy-galaxy lensing,
CMB lensing, and shear+clustering measurements. Furthermore, we compute the
projected (2D) non-linear bias using the expansion $\delta_{g} = \sum_{k=0}^{3}
(b_{k}/k!) \delta^{k}$, finding a non-zero value for $b_2$ at the $3\sigma$
level. We also check a non-local bias model and show that the linear bias
measurements are robust to the addition of new parameters. We compare our 2D
results to the 3D prediction and find compatibility in the large scale regime
($>30$ Mpc $h^{-1}$) | Resummed Kinetic Field Theory: Using Mesoscopic Particle Hydrodynamics
to Describe Baryonic Matter in a Cosmological Framework: Recently, Bartelmann et al. presented a 'Kinetic Field Theory' (KFT)
formalism to tackle the difficulties of large scale structure formation. In
this approach, the dynamics of a non-equilibrium ensemble of classical
particles are examined based on methods of statistical field theory. So far,
only contributions coming from dark matter were considered, which is assumed to
pose an accurate description of our universe on very large scales.
Nevertheless, going to smaller scales, also baryonic contributions have to be
taken into account. Building on the ideas of Viermann et al. we present an
effective particle model of hydrodynamics to describe baryonic matter in a
cosmological framework. Using this model, the baryonic density contrast power
spectrum is computed to lowest perturbative order within the resummed KFT
framework of Lilow et al. We discuss the qualitative differences to the dark
matter case and perform a quantitative comparison to the baryonic spectrum
obtained from Eulerian perturbation theory. A subsequent paper will resolve the
problem of coupling both theories describing dark and baryonic matter,
respectively, to gain a full model of cosmic matter. Even though our focus is
on cosmological systems only, we want to emphasize that all methods presented
here are of a quite general fashion, making it applicable also to other fields. |
Stellar Populations of Highly Magnified Lensed Galaxies: Young
Starbursts at z~2: We present a comprehensive analysis of the rest-frame UV to near-IR spectral
energy distributions and rest-frame optical spectra of four of the brightest
gravitationally lensed galaxies in the literature: RCSGA 032727-132609 at
z=1.70, MS1512-cB58 at z=2.73, SGAS J152745.1+065219 at z=2.76 and SGAS
J122651.3+215220 at z=2.92. This includes new Spitzer imaging for RCSGA0327 as
well as new spectra, near-IR imaging and Spitzer imaging for SGAS1527 and
SGAS1226. Lensing magnifications of 3-4 magnitudes allow a detailed study of
the stellar populations and physical conditions. We compare star formation
rates as measured from the SED fit, the H-alpha and [OII] emission lines, and
the UV+IR bolometric luminosity where 24 micron photometry is available. The
SFR estimate from the SED fit is consistently higher than the other indicators,
which suggests that the Calzetti dust extinction law used in the SED fitting is
too flat for young star-forming galaxies at z~2. Our analysis finds similar
stellar population parameters for all four lensed galaxies: stellar masses
3-7*10^9 M_sun, young ages ~ 100 Myr, little dust content E(B-V)=0.10-0.25, and
star formation rates around 20-100 M_sun/yr. Compared to typical values for the
galaxy population at z~2, this suggests we are looking at newly formed,
starbursting systems that have only recently started the build-up of stellar
mass. These results constitute the first detailed, uniform analysis of a sample
of the growing number of strongly lensed galaxies known at z~2. | A test of linearity of the ratio of dark matter to baryonic matter in
galaxy clusters: We search for a linearity in the ratio of dark matter to baryonic matter as a
function of radius for galaxy clusters, motivated by a recent result by Lovas
(arXiv:2206.11431), who has discovered such a linearity for a diverse suite of
galaxies in the SPARC sample. For our analysis, we used a sample of 54 non-cool
core clusters from the HIFLUGCS sample. We do not find any evidence for a
linear trend in the aforementioned ratio as a function of radius for individual
clusters. We then repeat this analysis for the stacked sample, which also does
not show this linearity. Therefore, the linear scaling found by Lovas is not a
universal property of dark matter haloes at all scales. |
Measuring Light from the Epoch of Reionization with CIBER, the Cosmic
Infrared Background Experiment: Ultraviolet emission from the first generation of stars in the Universe
ionized the intergalactic medium in a process which was completed by z~6; the
wavelength of these photons has been redshifted by (1+z) into the near infrared
today and can be measured using instruments situated above the Earth's
atmosphere. First flying in February 2009, the Cosmic Infrared Background
Experiment (CIBER) comprises four instruments housed in a single reusable
sounding rocket borne payload. CIBER will measure spatial anisotropies in the
extragalactic IR background caused by cosmological structure from the epoch of
reionization using two broadband imaging instruments, make a detailed
characterization of the spectral shape of the IR background using a low
resolution spectrometer, and measure the absolute brightness of the Zodical
light foreground with a high resolution spectrometer in each of our six science
fields. This paper presents the scientific motivation for CIBER and details of
its first two flights, including a review of the published scientific results
from the first flight and an outlook for future reionization science with CIBER
data. | The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy
Clusters at 148 GHz from Three Seasons of Data: [Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new
discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the
Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial
equator. A subsample of 48 clusters within the 270 square degree region
overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14
Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters,
the sample is studied further through a "Profile Based Amplitude Analysis"
using a single filter at a fixed \theta_500 = 5.9' angular scale. This new
approach takes advantage of the "Universal Pressure Profile" (UPP) to fix the
relationship between the cluster characteristic size (R_500) and the integrated
Compton parameter (Y_500). The UPP scalings are found to be nearly identical to
an adiabatic model, while a model incorporating non-thermal pressure better
matches dynamical mass measurements and masses from the South Pole Telescope. A
high signal to noise ratio subsample of 15 ACT clusters is used to obtain
cosmological constraints. We first confirm that constraints from SZ data are
limited by uncertainty in the scaling relation parameters rather than sample
size or measurement uncertainty. We next add in seven clusters from the ACT
Southern survey, including their dynamical mass measurements based on galaxy
velocity dispersions. In combination with WMAP7 these data simultaneously
constrain the scaling relation and cosmological parameters, yielding \sigma_8 =
0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results include
marginalization over a 15% bias in dynamical mass relative to the true halo
mass. In an extension to LCDM that incorporates non-zero neutrino mass density,
we combine our data with WMAP7+BAO+Hubble constant measurements to constrain
\Sigma m_\nu < 0.29 eV (95% C. L.). |
Through a Mini Halo, Darkly: In this Letter we explore the effects of the scattering of photons incident
on a dark matter halo through their interaction with either electrons or
photons produced by dark matter annihilation. Particularly, we examine the
effects of this scattering upon the observed spectrum of a distant AGN or of
the Cosmic Microwave Background. Our results indicate that ultra-compact mini
halos and other dense dark matter clumps can induce an observable
Comptonisation of AGN spectra as well as a Sunyaev-Zel'dovich effect (SZE) with
an optical depth similar to that attained by thermal electrons in the Coma
cluster. The rate of encounters between a distant AGN and these dense
mini-halos is also estimated using micro-lensing limits existing on the
population of dark compact bodies. | The Mid-infrared Emission of Narrow-Line Active Galactic Nuclei:
Star-Formation, Nuclear Activity and two populations revealed by WISE: We explore the nature of the long-wavelength mid-infrared (MIR) emission of a
sample of 13000 local Type II (narrow-line) Active Galactic Nuclei (AGNs) from
the Sloan Digital Sky Survey (SDSS) using 12 and 22 micron photometry from the
WISE all-sky survey. In combination with FIRST 1.4 GHz measurements, we show
that AGNs divide into two relatively distinct populations or "branches" in the
plane of MIR and radio luminosity. Seyfert galaxies lie almost exclusively on a
MIR-bright branch (Branch A), while low-ionization nuclear emission line
galaxies (LINERs) are split evenly into Branch A and the MIR-faint Branch B. We
devise various tests to constrain the processes that define the branches,
including a comparison to the properties of pure star-forming (SF) inactive
galaxies on the MIR-Radio plane. We demonstrate that the total MIR emission of
objects on Branch A, including most Seyfert galaxies, is governed primarily by
host star-formation, with about 15% of the 22 micron luminosity coming from
AGN-heated dust. This implies that on-going dusty star-formation is a general
property of Seyfert host galaxies. We show that the 12 micron broad-band
luminosity of AGNs on Branch A is suppressed with respect to star-forming
galaxies, possibly due to the destruction of PAHs or deeper 10 microns Si
absorption in AGNs. We uncover a correlation between the MIR luminosity and [O
III] luminosity in AGNs. This suggests a relationship between the SFR and
nuclear luminosity in the AGN population, but we caution on the importance of
selection effects inherent to such AGN-dominated emission-line galaxies in
driving such a correlation. We highlight the MIR-radio plane as a useful tool
in comparative studies of SF and nuclear activity in AGN. |
Quasi-extremal primordial black holes are a viable dark matter candidate: Black hole evaporation is generally considered inevitable for low-mass black
holes, yet there is no confirmation of this remarkable hypothesis. Here, we
propose a phenomenological model that appeals to the possible survival of light
quasi-extremal primordial black holes as a significant dark matter component
and show that the related cosmological and astrophysical constraints disappear
for reasonable degrees of quasi-extremality. The results obtained are general,
conservative and should be taken as a proof of principle for future,
model-specific analyses. | Remarks on the properties of elliptical galaxies in modified Newtonian
dynamics: Two incorrect arguments against MOND in elliptical galaxies could be that the
equivalent circular velocity curves tend to become flat at much larger
accelerations than in spiral galaxies, and that the Newtonian dark matter halos
are more concentrated than in spirals. Here, we compare published scaling
relations for the dark halos of elliptical galaxies to the scaling relations
expected for MONDian phantom halos. We represent the baryonic content of
galaxies by spherical profiles, and their corresponding MONDian phantom halos
by logarithmic halos. We then derive the surface densities, central densities,
and phase space densities and compare them with published scaling relations. We
conclude that it is possible to get flat circular velocity curves at high
acceleration in MOND, and that this happens for baryonic distributions
described by Jaffe profiles in the region where the circular velocity curve is
flat. Moreover, the scaling relations of dark halos of ellipticals are
remarkably similar to the scaling relations of phantom halos of MOND. |
Probing cosmic star formation up to z = 9.4 with GRBs: We propose a novel approach, based on Principal Components Analysis, to the
use of Gamma-Ray Bursts (GRBs) as probes of cosmic star formation history (SFH)
up to very high redshifts. The main advantage of such approach is to avoid the
necessity of assuming an \textit{ad hoc} parameterization of the SFH. We first
validate the method by reconstructing a known SFH from Monte Carlo-generated
mock data. We then apply the method to the most recent \textit{Swift} data of
GRBs with known redshift and compare it against the SFH obtained by independent
methods. The main conclusion is that the level of star formation activity at $z
\approx 9.4$ could have been already as high as the present-day one ($\approx
0.01 M_\odot$ yr$^{-1}$ Mpc$^{-3}$). This is a factor 3-5 times higher than
deduced from high-$z$ galaxy searches through drop-out techniques. If true,
this might alleviate the long-standing problem of a photon-starving
reionization; it might also indicate that galaxies accounting for most of the
star formation activity at high redshift go undetected by even the most deep
searches. | The CMB temperature bispectrum induced by cosmic strings: The Cosmic Microwave Background (CMB) bispectrum of the temperature
anisotropies induced by a network of cosmic strings is derived for small
angular scales, under the assumption that the principal cause of temperature
fluctuations is the Gott-Kaiser-Stebbins (GKS) effect. We provide analytical
expressions for all isosceles triangle configurations in Fourier space. Their
overall amplitude is amplified as the inverse cube of the angle and diverges
for flat triangles. The isosceles configurations generically lead to a negative
bispectrum with a power law decay l^(-6) for large multipole l. However,
collapsed triangles are found to be associated with a positive bispectrum
whereas the squeezed triangles still exhibit negative values. We then compare
our analytical estimates to a direct computation of the bispectrum from a set
of 300 statistically independent temperature maps obtained from Nambu-Goto
cosmic string simulations in a Friedmann-Lemaitre-Robertson-Walker (FLRW)
universe. We find good agreement for the overall amplitude, the power law
behaviour and angle dependency of the various triangle configurations. At l~500
the cosmic string GKS effect contributes approximately the same equilateral CMB
bispectrum amplitude as an inflationary model with |fNL|~10^3, if the strings
contribute about 10% of the temperature power spectrum at l=10. Current bounds
on fNL are not derived using cosmic string bispectrum templates, and so our fNL
estimate cannot be used to derive bounds on strings. However it does suggest
that string bispectrum templates should be included in the search of CMB
non-Gaussianities. |
A Comprehensive Analysis of Uncertainties Affecting the Stellar Mass -
Halo Mass Relation for 0<z<4: We conduct a comprehensive analysis of the relationship between central
galaxies and their host dark matter halos, as characterized by the stellar
mass-halo mass (SM-HM) relation, with rigorous consideration of uncertainties.
Our analysis focuses on results from the abundance matching technique, which
assumes that every dark matter halo or subhalo above a specific mass threshold
hosts one galaxy. We discuss the quantitative effects of uncertainties in
observed galaxy stellar mass functions (GSMFs) (including stellar mass
estimates and counting uncertainties), halo mass functions (including cosmology
and uncertainties from substructure), and the abundance matching technique used
to link galaxies to halos (including scatter in this connection). Our analysis
results in a robust estimate of the SM-HM relation and its evolution from z=0
to z=4. The shape and evolution are well constrained for z < 1. The largest
uncertainties at these redshifts are due to stellar mass estimates; however,
failure to account for scatter in stellar masses at fixed halo mass can lead to
errors of similar magnitude in the SM-HM relation for central galaxies in
massive halos. We also investigate the SM-HM relation to z=4, although the
shape of the relation at higher redshifts remains fairly unconstrained when
uncertainties are taken into account. These results will provide a powerful
tool to inform galaxy evolution models. [Abridged] | Imprints of Dark Energy on Cosmic Structure Formation: III. Sparsity of
Dark Matter Halo Profiles: We study the imprint of Dark Energy on the density profile of Dark Matter
halos using a set of high-resolution large volume cosmological N-body
simulations from the Dark Energy Universe Simulation Series (DEUSS). We first
focus on the analysis of the goodness-of-fit of the Navarro-Frenk-White (NFW)
profile which we find to vary with halo mass and redshift. We also find that
the fraction of halos ill-fitted by NFW varies with cosmology, thus indicating
that the mass assembly of halos with perturbed density profiles carries a
characteristic signature of Dark Energy. To access this information
independently of any parametric profile, we introduce a new observable
quantity: the halo sparsity $s_\Delta$. This is defined as the mass ratio
$M_{200}/M_\Delta$, i.e. the ratio of mass inside a sphere of radius $r_{200}$
to that contained within a radius $r_\Delta$, enclosing 200 and $\Delta$ times
the mean matter density respectively. We find the average sparsity to be nearly
independent of the total halo mass, while its value can be inferred to better
than a few percent from the ratio of the integrated halo mass functions at
overdensities $\Delta$ and 200 respectively. This provides a consistency
relation that can validate observational measurements of the halo sparsity.
Most importantly, the sparsity significantly varies with the underlying Dark
Energy model, thus providing an alternative cosmological probe. |
How will our knowledge of short gamma-ray bursts affect the distance
measurement of binary neutron stars?: GWs from BNS associated with SGRBs have drawn considerable attention due to
their prospect in cosmology. For such events, the sky locations of sources can
be pinpointed with techniques such as identifying the host galaxies. However,
the cosmological applications of these events still suffer from the problem of
degeneracy between luminosity distance and inclination angle. To address this
issue, a technique was proposed in previous study, i.e., using the property of
SGRBs. Based on the observations, we assume that the cosine of inclination
follows a Gaussian distribution, which may act as a prior in the Bayes analysis
to break the degeneracy. This paper investigates the effects of different
Gaussian priors and detector configurations on distance measurement and
cosmological research. We first derive a simplified Fisher information matrix
for demonstration, and then conduct quantitative analyses via simulation. By
varying the number of third-generation detectors and the scale of prior, we
generate four catalogs of 1000 events. It is shown that, in the same detecting
period, a network of detectors can recognize more and farther events than a
single detector. Besides, adopting tighter prior and employing multiple
detectors both decrease the error of luminosity distance. Also considered is
the performance of a widely adopted formula in the error budget, which turns
out to be a conservative choice in each case. As for cosmological applications,
for LCDM model, 500, 200, 600, and 300 events are required for the four
configurations to achieve 1% H_0 accuracy. With all 1000 events in each
catalog, H_0 and Omega_m can be constrained to 0.66%, 0.37%, 0.76%, 0.49%, and
0.010, 0.006, 0.013, 0.010, respectively. The results of the Gaussian process
also show that the GW standard siren can serve as a probe of high-redshift
universe. | Imprint of f(R) gravity in the cosmic magnification: f(R) gravity is one of the simplest viable modifications to General
Relativity: it passes local astrophysical tests, predicts both the early-time
cosmic inflation and the late-time cosmic acceleration, and also describes dark
matter. In this paper, we probe cosmic magnification on large scales in f(R)
gravity, using the well-known Hu-Sawicki model as an example. Our results
indicate that at redshifts z < 3, values of the model exponent n > 1 lead to
inconsistent behaviour in the evolution of scalar perturbations. Moreover, when
relativistic effects are taken into account in the large scale analysis, our
results show that as z increases, large-scale changes in the cosmic
magnification angular power spectrum owing to integral values of n tend to
share a similar pattern, while those of decimal values tend to share another.
This feature could be searched for in the experimental data, as a potential
"smoking gun" for the given class of gravity models. Furthermore, we found that
at z = 1 and lower, relativistic effects lead to a suppression of the cosmic
magnification on large scales in f(R) gravity, relative to the concordance
model; whereas, at z > 1, relativistic effects lead to a relative boost of the
cosmic magnification. In general, relativistic effects enhance the potential of
the cosmic magnification as a cosmological probe. |
Measuring Line-of-sight Distances to Haloes with Astrometric Lensing
B-mode: Relative astrometric shifts between multiply lensed images provide a valuable
tool to investigate haloes in the intergalactic space. In strong lens systems
in which a single lens plays the primary role in producing multiple images, the
gravitational force exerted by line-of-sight (LOS) haloes can slightly change
the relative positions of multiply lensed images produced by the dominant lens.
In such cases, a LOS halo positioned sufficiently far from the dominant lens
along the LOS can create a pattern in the reduced deflection angle that
corresponds to the B-mode (magnetic or divergence-free mode). By measuring both
the B-mode and E-mode (electric or rotation-free mode), we can determine the
LOS distance ratios, as well as the 'bare' convergence and shear perturbations
in the absence of the dominant lens. However, scale variations in the distance
ratio lead to mass-sheet transformations in the background lens plane,
introducing some uncertainty in the distance ratio estimation. This uncertainty
can be significantly reduced by measuring the time delays between the lensed
images. Additionally, if we obtain the redshift values of both the dominant and
perturbing haloes, along with the time delays between the multiply lensed
images that are affected by the haloes, the B-mode can break the degeneracy
related to mass-sheet transformations in both the foreground and background
lens planes. Therefore, measuring the astrometric lensing B-mode has the
potential to substantially decrease the uncertainty in determining the Hubble
constant. | Enhanced Gravitational Waves from Inflaton Oscillons: In broad classes of inflationary models the period of accelerated expansion
is followed by fragmentation of the inflaton scalar field into localized,
long-lived and massive oscillon excitations. We demonstrate that
matter-dominance of oscillons, followed by their rapid decay, significantly
enhances the primordial gravitational wave (GW) spectrum. These
oscillon-induced GWs, sourced by second-order perturbations, are distinct and
could be orders of magnitude lower in frequency than the previously considered
GWs associated with oscillon formation. We show that detectable
oscillon-induced GW signatures establish direct tests independent from cosmic
microwave background radiation (CMB) for regions of parameter space of
monodromy, logarithmic and pure natural (plateau) potential classes of
inflationary models, among others. We demonstrate that oscillon-induced GWs in
a model based on pure natural inflation could be directly observable with the
Einstein Telescope, Cosmic Explorer and DECIGO. These signatures offer a new
route for probing the underlying inflationary physics. |
Primordial non-Gaussianity with Angular correlation function: Integral
constraint and validation for DES: Local primordial non-Gaussianity (PNG) is a promising observable of the
underlying physics of inflation, characterised by $f_{\rm NL}^{\rm loc}$. We
present the methodology to measure $f_{\rm NL}^{\rm loc}$ from the Dark Energy
Survey (DES) data using the 2-point angular correlation function (ACF) with
scale-dependent bias. One of the focuses of the work is the integral
constraint. This condition appears when estimating the mean number density of
galaxies from the data and is key in obtaining unbiased $f_{\rm NL}^{\rm loc}$
constraints. The methods are analysed for two types of simulations: $\sim 246$
GOLIAT-PNG N-body small area simulations with $f_{\rm NL}$ equal to -100 and
100, and 1952 Gaussian ICE-COLA mocks with $f_{\rm NL}=0$ that follow the DES
angular and redshift distribution. We use the ensemble of GOLIAT-PNG mocks to
show the importance of the integral constraint when measuring PNG, where we
recover the fiducial values of $f_{\rm NL}$ within the $1\sigma$ when including
the integral constraint. In contrast, we found a bias of $\Delta f_{\rm NL}\sim
100$ when not including it. For a DES-like scenario, we forecast a bias of
$\Delta f_{\rm NL} \sim 23$, equivalent to $1.8\sigma$, when not using the IC
for a fiducial value of $f_{\rm NL}=100$. We use the ICE-COLA mocks to validate
our analysis in a realistic DES-like setup finding it robust to different
analysis choices: best-fit estimator, the effect of IC, BAO damping,
covariance, and scale choices. We forecast a measurement of $f_{\rm NL}$ within
$\sigma(f_{\rm NL})=31$ when using the DES-Y3 BAO sample, with the ACF in the
$1\ {\rm deg}<\theta<20\ {\rm deg}$ range. | Probability Friends-of-Friends (PFOF) Group Finder: Performance Study
and Observational Data Applications on Photometric Surveys: (Abridged) In tandem with observational datasets, we utilize realistic mock
catalogs, based on a semi-analytic galaxy formation model, constructed
specifically for Pan-STARRS1 Medium Deep Surveys in order to assess the
performance of the Probability Friends-of-Friends (PFOF, Liu et al.) group
finder, and aim to develop a grouping optimization method applicable to surveys
like Pan-STARRS1. Producing mock PFOF group catalogs under a variety of
photometric redshift accuracies ({\sigma}{\Delta}z/(1+zs)), we find that
catalog purities and completenesses from ``good' {\sigma}{\Delta}z/(1+zs)) ~
0.01) to ``poor' {\sigma}{\Delta}z/(1+zs)) ~ 0.07) photo-zs gradually degrade
respectively from 77% and 70% to 52% and 47%. To avoid model dependency of the
mock for use on observational data we apply a ``subset optimization' approach,
using spectroscopic-redshift group data from the target field to train the
group finder for application to that field, as an alternative method for the
grouping optimization. We demonstrate this approach using these
spectroscopically identified groups as the training set, i.e. zCOSMOS groups
for PFOF searches within PS1 Medium Deep Field04 (PS1MD04) and DEEP2 EGS groups
for searches in PS1MD07. We ultimately apply PFOF to four datasets spanning the
photo-z uncertainty range from 0.01 to 0.06 in order to quantify the dependence
of group recovery performance on photo-z accuracy. We find purities and
completenesses calculated from observational datasets broadly agree with their
mock analogues. Further tests of the PFOF algorithm are performed via matches
to X-ray clusters identified within the PS1MD04 and COSMOS footprints. Across
over a decade in group mass, we find PFOF groups match ~85% of X-ray clusters
in COSMOS and PS1MD04, but at a lower statistical significance in the latter. |
Galaxy cluster number count data constraints on cosmological parameters: [Abridged] We use data on massive galaxy clusters ($M_{\rm cluster} > 8
\times 10^{14} h^{-1} M_\odot$ within a comoving radius of $R_{\rm cluster} =
1.5 h^{-1}\Mpc$) in the redshift range $0.05 \lesssim z \lesssim 0.83$ to place
constraints, simultaneously, on the nonrelativistic matter density parameter
$\Omega_m$, on the amplitude of mass fluctuations $\sigma_8$, on the index $n$
of the power-law spectrum of the density perturbations, and on the Hubble
constant $H_0$, as well as on the equation-of-state parameters $(w_0,w_a)$ of a
smooth dark energy component.
For the first time, we properly take into account the dependence on redshift
and cosmology of the quantities related to cluster physics: the critical
density contrast, the growth factor, the mass conversion factor, the virial
overdensity, the virial radius and, most importantly, the cluster number count
derived from the observational temperature data.
We show that, contrary to previous analyses, cluster data alone prefer low
values of the amplitude of mass fluctuations, $\sigma_8 \leq 0.69 (1\sigma
C.L.)$, and large amounts of nonrelativistic matter, $\Omega_m \geq 0.38
(1\sigma C.L.)$, in slight tension with the $\Lambda$CDM concordance
cosmological model, though the results are compatible with $\Lambda$CDM at
$2\sigma$. In addition, we derive a $\sigma_8$ normalization relation,
$\sigma_8 \Omega_m^{1/3} = 0.49 \pm 0.06 (2\sigma C.L.)$. | What's Inside the Cone? Numerically reconstructing the metric from
observations: We investigate the possibility of using Gaussian process regression to smooth
data on the current past null-cone for use as the input to a relativistic
integration scheme. The algorithm we present is designed to reconstruct the
metric of spacetime within the class of spherically symmetric dust universes,
with or without a cosmological constant. Assuming that gravity is well
described by General Relativity, we demonstrate how the algorithm can be
employed to test the Copernican principle based on currently available
observations. It is shown that currently available data is not sufficient for a
conclusive result. The intrinsic noise present in realistic data presents a
challenge for our smoothing algorithm and we discuss some of its limitations as
well as possible extensions to it. We conclude by demonstrating how a direct
determination of the cosmological constant is possible using redshift drift
data. |
Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer
imaging data: We demonstrate the usability of mm-wavelength imaging data obtained from the
APEX-SZ bolometer array to derive the radial temperature profile of the hot
intra-cluster gas out to radius r_500 and beyond. The goal is to study the
physical properties of the intra-cluster gas by using a non-parametric
de-projection method that is, aside from the assumption of spherical symmetry,
free from modeling bias. We use publicly available X-ray imaging data from the
XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data
from the APEX-SZ experiment at 150 GHz to de-project the density and
temperature profiles for the relaxed cluster Abell 2204. We derive the gas
density, temperature and entropy profiles assuming spherical symmetry, and
obtain the total mass profile under the assumption of hydrostatic equilibrium.
For comparison with X-ray spectroscopic temperature models, a re-analysis of
the recent Chandra observation is done with the latest calibration updates.
Using the non-parametric modeling we demonstrate a decrease of gas temperature
in the cluster outskirts, and also measure the gas entropy profile. These
results are obtained for the first time independently of X-ray spectroscopy,
using SZE and X-ray imaging data. The contribution of the SZE systematic
uncertainties in measuring T_e at large radii is shown to be small compared to
the Chandra systematic spectroscopic errors. The upper limit on M_200 derived
from the non-parametric method is consistent with the NFW model prediction from
weak lensing analysis. | Morphology of galaxies: The study of the morphology of galaxies is important in order to understand
the formation and evolution of galaxies and their sub-components as a function
of luminosity, environment, and star-formation and galaxy assembly over cosmic
time. Disentangling the many variables that affect galaxy evolution and
morphology, requires large galaxy samples and automated ways to measure
morphology. The advent of large digital sky surveys, with unprecedented depth
and resolution, coupled with sophisticated quantitative methods for morphology
measurement are providing new insights in this fast evolving field of
astronomical research. |
Analyzing the Flux Anomalies of the Large-Separation Lensed Quasar SDSS
J1029+2623: Using a high resolution radio image, we successfully resolve the two fold
image components B and C of the quasar lens system SDSS J1029+2623. The flux
anomalies associated with these two components in the optical regime persist,
albeit less strongly, in our radio observations, suggesting that the cluster
must be modeled by something more than a single central potential. We argue
that placing substructure close to one of the components can account for a flux
anomaly with negligible changes in the component positions. Our best fit model
has a substructure mass of ~10^8 solar masses up to the mass-sheet degeneracy,
located roughly 0.1 arcsecs West and 0.1 arcsecs North of component B. We
demonstrate that a positional offset between the centers of the source
components can explain the differences between the optical and radio flux
ratios. | An effective theory of accelerated expansion: We work out an effective theory of accelerated expansion to describe general
phenomena of inflation and acceleration (dark energy) in the Universe. Our aim
is to determine from theoretical grounds, in a physically-motivated and model
independent way, which and how many (free) parameters are needed to broadly
capture the physics of a theory describing cosmic acceleration. Our goal is to
make as much as possible transparent the physical interpretation of the
parameters describing the expansion. We show that, at leading order, there are
five independent parameters, of which one can be constrained via general
relativity tests. The other four parameters need to be determined by observing
and measuring the cosmic expansion rate only, H(z). Therefore we suggest that
future cosmology surveys focus on obtaining an accurate as possible measurement
of $H(z)$ to constrain the nature of accelerated expansion (dark energy and/or
inflation). |
CLASH-VLT: Insights on the mass substructures in the Frontier Fields
Cluster MACS J0416.1-2403 through accurate strong lens modeling: We present a detailed mass reconstruction and a novel study on the
substructure properties in the core of the CLASH and Frontier Fields galaxy
cluster MACS J0416.1-2403. We show and employ our extensive spectroscopic data
set taken with the VIMOS instrument as part of our CLASH-VLT program, to
confirm spectroscopically 10 strong lensing systems and to select a sample of
175 plausible cluster members to a limiting stellar mass of log(M_*/M_Sun) ~
8.6. We reproduce the measured positions of 30 multiple images with a
remarkable median offset of only 0.3" by means of a comprehensive strong
lensing model comprised of 2 cluster dark-matter halos, represented by cored
elliptical pseudo-isothermal mass distributions, and the cluster member
components. The latter have total mass-to-light ratios increasing with the
galaxy HST/WFC3 near-IR (F160W) luminosities. The measurement of the total
enclosed mass within the Einstein radius is accurate to ~5%, including
systematic uncertainties. We emphasize that the use of multiple-image systems
with spectroscopic redshifts and knowledge of cluster membership based on
extensive spectroscopic information is key to constructing robust
high-resolution mass maps. We also produce magnification maps over the central
area that is covered with HST observations. We investigate the galaxy
contribution, both in terms of total and stellar mass, to the total mass budget
of the cluster. When compared with the outcomes of cosmological $N$-body
simulations, our results point to a lack of massive subhalos in the inner
regions of simulated clusters with total masses similar to that of MACS
J0416.1-2403. Our findings of the location and shape of the cluster dark-matter
halo density profiles and on the cluster substructures provide intriguing tests
of the assumed collisionless, cold nature of dark matter and of the role played
by baryons in the process of structure formation. | The 3-Dimensional Distribution of Dust in NGC 891: We produce three-dimensional Monte-Carlo radiative transfer models of the
edge-on spiral galaxy NGC 891, a fast-rotating galaxy thought to be an analogue
to the Milky Way. The models contain realistic spiral arms and a fractal
distribution of clumpy dust. We fit our models to Hubble Space Telescope images
corresponding to the B and I bands, using shapelet analysis and a genetic
algorithm to generate 30 statistically best-fitting models. These models have a
strong preference for spirality and clumpiness, with average face-on
attenuation decreasing from 0.24(0.16) to 0.03(0.03) mag in the B(I) band
between 0.5 and 2 radial scale-lengths. Most of the attenuation comes from
small high-density clumps with low (<10%) filling factors. The fraction of dust
in clumps is broadly consistent with results from fitting NGC 891's spectral
energy distribution. Because of scattering effects and the intermixed nature of
the dust and starlight, attenuation is smaller and less wavelength-dependent
than the integrated dust column-density. Our clumpy models typically have
higher attenuation at low inclinations than previous radiative transfer models
using smooth distributions of stars and dust, but similar attenuation at
inclinations above 70 degrees. At all inclinations most clumpy models have less
attenuation than expected from previous estimates based on minimizing scatter
in the Tully-Fisher relation. Mass-to-light ratios are higher and the intrinsic
scatter in the Tully-Fisher relation is larger than previously expected for
galaxies similar to NGC 891. The attenuation curve changes as a function of
inclination, with R_(B,B-I)=A_(B)/E(B-I) increasing by ~0.75 from face-on to
near-edge-on orientations. |
The Narrow-Line Region of Narrow-Line Seyfert 1 Galaxies: We have studied the physical properties of a sample of narrow-line Seyfert 1
(NLS1) galaxies, and present a summary of our previous results, and new
results. In particular, we have previously shown that (1) the locus of NLS1
galaxies on the M_BH-sigma_[OIII] plane does follow the relation of non-active
galaxies after removing objects obviously dominated by outflows as evidenced by
their [OIII] core blueshifts. We have (2) identified a number of so-called
'blue outliers' with large outflow velocities revealed by their emission-line
kinematic shifts. We also (3) present new correlations and trends which link
black hole mass, Eddington ratio and physical parameters of the emission-line
regions. | The HI intensity mapping bispectrum including observational effects: The bispectrum is a 3-point statistic with the potential to provide
additional information beyond power spectra analyses of survey datasets. Radio
telescopes which broadly survey the 21cm emission from neutral hydrogen (HI)
are a promising way to probe LSS and in this work we present an investigation
into the HI intensity mapping (IM) bispectrum using simulations. We present a
model of the redshift space HI IM bispectrum including observational effects
from the radio telescope beam and 21cm foreground contamination. We validate
our modelling prescriptions with measurements from robust IM simulations,
inclusive of these observational effects. Our foreground simulations include
polarisation leakage, on which we use a Principal Component Analysis cleaning
method. We also investigate the effects from a non-Gaussian beam including
side-lobes. For a MeerKAT-like single-dish IM survey at $z=0.39$, we find that
foreground removal causes a 8% reduction in the equilateral bispectrum's
signal-to-noise ratio $S/N$, whereas the beam reduces it by 62%. We find our
models perform well, generally providing $\chi^2_\text{dof}\sim 1$, indicating
a good fit to the data. Whilst our focus is on post-reionisation, single-dish
IM, our modelling of observational effects, especially foreground removal, can
also be relevant to interferometers and reionisation studies. |
Fuzzy Dark Matter at Cosmic Dawn: New 21-cm Constraints: Potential small-scale discrepancies in the picture of galaxy formation
painted by the $\Lambda$CDM paradigm have led to considerations of modified
dark matter models. One such dark matter model that has recently attracted much
attention is fuzzy dark matter (FDM). In FDM models, the dark matter is
envisaged to be an ultra-light scalar field with a particle mass $m_{\rm FDM}
\sim 10^{-22} $ eV. This yields astronomically large de Broglie wavelengths
which can suppress small-scale structure formation and give rise to the
observed kpc-sized density cores in dwarf galaxies. We investigate the
evolution of the 21-cm signal during Cosmic Dawn and the Epoch of Reionization
(EoR) in $\Lambda$FDM cosmologies using analytical models. The delay in source
formation and the absence of small halos in $\Lambda$FDM significantly postpone
the Ly$\alpha$ coupling, heating, as well as the reionization of the neutral
hydrogen of the intergalactic medium. As a result, the absorption feature in
the evolution of the global 21-cm signal has a significantly smaller full width
at half maximum ($\Delta z \lesssim 3$), than $\Lambda$CDM ($\Delta z \simeq
6$). This alone rules out $m_{\rm FDM} < 6 \times 10^{-22}$ eV as a result of
the $2\sigma$ lower limit $\Delta z \gtrsim 4$ from EDGES High-Band. As a
result, $\Lambda$FDM is not a viable solution to the potential small-scale
problems facing $\Lambda$CDM. Finally, we show that any detection of the 21-cm
signal at redshifts $z > 14$ by interferometers such as the SKA can also
exclude $\Lambda$FDM models. | The evolution of obscured accretion: Our current understanding of the evolution of obscured accretion onto
supermassive black holes is reviewed. We consider the literature results on the
relation between the fraction of moderately obscured, Compton-thin AGN and
redshift, and discuss the biases which possibly affect the various
measurements. Then, we discuss a number of methods - from ultradeep X-ray
observations to the detection of high-ionization optical emission lines - to
select the population of the most heavily obscured, Compton-thick AGN, whose
cosmological evolution is basically unknown. The space density of heavily
obscured AGN measured through different techniques is discussed and compared
with the predictions by current synthesis models of the X-ray background.
Preliminary results from the first half of the 3 Ms XMM observation of the
Chandra Deep Field South (CDFS) are also presented. The prospects for
population studies of heavily obscured AGN with future planned or proposed
X-ray missions are finally discussed. |
The Galaxy-Dark Matter Connection: A Cosmological Perspective: We present a method that uses observations of galaxies to simultaneously
constrain cosmological parameters and the galaxy-dark matter connection (aka
halo occupation statistics). The latter describes how galaxies are distributed
over dark matter haloes, and is an imprint of the poorly understood physics of
galaxy formation. A generic problem of using galaxies to constrain cosmology is
that galaxies are a biased tracer of the mass distribution, and this bias is
generally unknown. The great advantage of simultaneously constraining cosmology
and halo occupation statistics is that this effectively allows cosmological
constraints marginalized over the uncertainties regarding galaxy bias. Not only
that, it also yields constraints on the galaxy-dark matter connection, this
time properly marginalized over cosmology, which is of great value to inform
theoretical models of galaxy formation. We use a combination of the analytical
halo model and the conditional luminosity function to describe the galaxy-dark
matter connection, which we use to model the abundance, clustering and
galaxy-galaxy lensing properties of the galaxy population. We use a Fisher
matrix analysis to gauge the complementarity of these different observables,
and present some preliminary results from an analysis based on data from the
Sloan Digital Sky Survey. Our results are complementary to and perfectly
consistent with the results from the 7 year data release of the WMAP mission,
strengthening the case for a true 'concordance' cosmology. | Detailed optical and near-infrared polarimetry, spectroscopy and
broadband photometry of the afterglow of GRB 091018: Polarisation evolution: [Abridged] A number of phenomena have been observed in GRB afterglows that
defy explanation by simple versions of the standard fireball model, leading to
a variety of new models. Polarimetry can be a major independent diagnostic of
afterglow physics, probing the magnetic field properties and internal structure
of the GRB jets. In this paper we present the first high quality multi-night
polarimetric light curve of a Swift GRB afterglow, aimed at providing a well
calibrated dataset of a typical afterglow to serve as a benchmark system for
modelling afterglow polarisation behaviour. In particular, our dataset of the
afterglow of GRB 091018 (at redshift z=0.971) comprises optical linear
polarimetry (R band, 0.13 - 2.3 days after burst); circular polarimetry (R
band) and near-infrared linear polarimetry (Ks band). We add to that high
quality optical and near-infrared broadband light curves and spectral energy
distributions as well as afterglow spectroscopy. The linear polarisation varies
between 0 and 3%, with both long and short time scale variability visible. We
find an achromatic break in the afterglow light curve, which corresponds to
features in the polarimetric curve. We find that the data can be reproduced by
jet break models only if an additional polarised component of unknown nature is
present in the polarimetric curve. We probe the ordered magnetic field
component in the afterglow through our deep circular polarimetry, finding
P_circ < 0.15% (2 sigma), the deepest limit yet for a GRB afterglow, suggesting
ordered fields are weak, if at all present. Our simultaneous R and Ks band
polarimetry shows that dust induced polarisation in the host galaxy is likely
negligible. |
Dark energy domination in the local flow of giant galaxies: A dozen most luminous galaxies at distances up to 10 Mpc from the Local Group
are moving away from the group forming the local expansion flow of giants. We
use recent Hubble Space Telescope data on the local giants and their numerous
fainter companions to study the dynamical structure and evolutionary trends of
the flow. It is demonstrated that the dynamics of the flow is dominated by
local dark energy.
Keywords: Galaxies, groups and clusters of galaxies; local flows of galaxies;
dark energy. | Testing strong lensing subhalo detection with a cosmological simulation: Strong gravitational lensing offers a compelling test of the cold dark matter
paradigm, as it allows for subhaloes with masses of $\sim10^{9}$ M$_\odot$ and
below to be detected. We test commonly-used techniques for detecting subhaloes
superposed in images of strongly lensed galaxies. For the lens we take a
simulated galaxy in a $\sim10^{13}$ M$_\odot$ halo grown in a high-resolution
cosmological hydrodynamical simulation, which we view from two different
directions. Though the resolution is high, we note the simulated galaxy still
has an artificial core which adds additional complexity to the baryon dominated
region. To remove particle noise, we represent the projected galaxy mass
distribution by a series of Gaussian profiles which precisely capture the
features of the projected galaxy. We first model the lens mass as a (broken)
power-law density profile and then search for small haloes. Of the two
projections, one has a regular elliptical shape, while the other has distinct
deviations from an elliptical shape. For the former, the broken power-law model
gives no false positives and correctly recovers the mass of the superposed
small halo, but for the latter we find false positives and the inferred halo
mass is overestimated by $\sim4-5$ times. We then use a more complex model in
which the lens mass is decomposed into stellar and dark matter components. In
this case, we show that we can capture the simulated galaxy's complex projected
structures and correctly infer the input small halo. |
Exploring the mass and redshift dependence of the cluster pressure
profile with stacks on thermal SZ maps: We provide novel constraints on the parameters defining the universal
pressure profile (UPP) within clusters of galaxies, and explore their
dependence on the cluster mass and redshift, from measurements of
Sunyaev-Zel'dovich Compton-$y$ profiles. We employ both the $\textit{Planck}$
2015 MILCA and the ACT-DR4 $y$ maps over the common $\sim 2,100\,\text{deg}^2$
footprint. We combine existing cluster catalogs based on KiDS, SDSS and DESI
observations, for a total of 23,820 clusters spanning the mass range
$10^{14.0}\,\text{M}_{\odot}<M_{500}<10^{15.1}\,\text{M}_{\odot}$ and the
redshift range $0.02<z<0.98$. We split the clusters into three independent bins
in mass and redshift; for each combination we detect the stacked SZ cluster
signal and extract the mean $y$ angular profile. The latter is predicted
theoretically adopting a halo model framework, and MCMCs are employed to
estimate the UPP parameters, the hydrostatic mass bias $b_{\rm h}$ and possible
cluster miscentering effects. We constrain $[P_0,c_{500},\alpha,\beta]$ to
$[5.9,2.0,1.8,4.9]$ with $\textit{Planck}$ and to $[3.8,1.3,1.0,4.4]$ with ACT
using the full cluster sample, in agreement with previous findings. We do not
find any compelling evidence for a residual mass or redshift dependence, thus
expanding the validity of the cluster pressure profile over much larger
$M_{500}$ and $z$ ranges; this is the first time the model has been tested on
such a large (complete and representative) cluster sample. Finally, we obtain
loose constraints on the hydrostatic mass bias in the range 0.2-0.3, again in
broad agreement with previous works. | RCSLenS: The Red Cluster Sequence Lensing Survey: We present the Red-sequence Cluster Lensing Survey (RCSLenS), an application
of the methods developed for the Canada France Hawaii Telescope Lensing Survey
(CFHTLenS) to the ~785deg$^2$, multi-band imaging data of the Red-sequence
Cluster Survey 2 (RCS2). This project represents the largest public,
sub-arcsecond seeing, multi-band survey to date that is suited for weak
gravitational lensing measurements. With a careful assessment of systematic
errors in shape measurements and photometric redshifts we extend the use of
this data set to allow cross-correlation analyses between weak lensing
observables and other data sets. We describe the imaging data, the data
reduction, masking, multi-colour photometry, photometric redshifts, shape
measurements, tests for systematic errors, and a blinding scheme to allow for
more objective measurements. In total we analyse 761 pointings with r-band
coverage, which constitutes our lensing sample. Residual large-scale B-mode
systematics prevent the use of this shear catalogue for cosmic shear science.
The effective number density of lensing sources over an unmasked area of
571.7deg$^2$ and down to a magnitude limit of r~24.5 is 8.1 galaxies per
arcmin$^2$ (weighted: 5.5 arcmin$^{-2}$) distributed over 14 patches on the
sky. Photometric redshifts based on 4-band griz data are available for 513
pointings covering an unmasked area of 383.5 deg$^2$ We present weak lensing
mass reconstructions of some example clusters as well as the full survey
representing the largest areas that have been mapped in this way. All our data
products are publicly available through CADC at
http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/community/rcslens/query.html
in a format very similar to the CFHTLenS data release. |
A fake Interacting Dark Energy detection?: Models involving an interaction between the Dark Matter and the Dark Energy
sectors have been proposed to alleviate the long standing Hubble constant
tension. In this paper we analyze whether the constraints and potential hints
obtained for these interacting models remain unchanged when using simulated
Planck data. Interestingly, our simulations indicate that a dangerous fake
detection for a non-zero interaction among the Dark Matter and the Dark Energy
fluids could arise when dealing with current CMB Planck measurements alone. The
very same hypothesis is tested against future CMB observations, finding that
only cosmic variance limited polarization experiments, such as PICO or PRISM,
could be able to break the existing parameter degeneracies and provide reliable
cosmological constraints. This paper underlines the extreme importance of
confronting the results arising from data analyses with those obtained with
simulations when extracting cosmological limits within exotic cosmological
scenarios. | Non-gaussianity at tree and one-loop levels from vector field
perturbations: We study the spectrum P_\zeta and bispectrum B_\zeta of the primordial
curvature perturbation \zeta when the latter is generated by scalar and vector
field perturbations. The tree-level and one-loop contributions from vector
field perturbations are worked out considering the possibility that the
one-loop contributions may be dominant over the tree level terms (both (either)
in P_\zeta and (or) in B_\zeta) and viceversa. The level of non-gaussianity in
the bispectrum, f_{NL}, is calculated and related to the level of statistical
anisotropy in the power spectrum, g_\zeta. For very small amounts of
statistical anisotropy in the power spectrum, the level of non-gaussianity may
be very high, in some cases exceeding the current observational limit. |
On the Habitability of Our Universe: Is life most likely to emerge at the present cosmic time near a star like the
Sun? We consider the habitability of the Universe throughout cosmic history,
and conservatively restrict our attention to the context of "life as we know
it" and the standard cosmological model, LCDM. The habitable cosmic epoch
started shortly after the first stars formed, about 30 Myr after the Big Bang,
and will end about 10 Tyr from now, when all stars will die. We review the
formation history of habitable planets and find that unless habitability around
low mass stars is suppressed, life is most likely to exist near 0.1 solar mass
stars ten trillion years from now. Spectroscopic searches for biosignatures in
the atmospheres of transiting Earth-mass planets around low mass stars will
determine whether present-day life is indeed premature or typical from a cosmic
perspective. | Detection/estimation of the modulus of a vector. Application to point
source detection in polarization data: Given a set of images, whose pixel values can be considered as the components
of a vector, it is interesting to estimate the modulus of such a vector in some
localised areas corresponding to a compact signal. For instance, the
detection/estimation of a polarized signal in compact sources immersed in a
background is relevant in some fields like astrophysics. We develop two
different techniques, one based on the Neyman-Pearson lemma, the Neyman-Pearson
filter (NPF), and another based on prefiltering-before-fusion, the filtered
fusion (FF), to deal with the problem of detection of the source and estimation
of the polarization given two or three images corresponding to the different
components of polarization (two for linear polarization, three including
circular polarization). For the case of linear polarization, we have performed
numerical simulations on two-dimensional patches to test these filters
following two different approaches (a blind and a non-blind detection),
considering extragalactic point sources immersed in cosmic microwave background
(CMB) and non-stationary noise with the conditions of the 70 GHz \emph{Planck}
channel. The FF outperforms the NPF, especially for low fluxes. We can detect
with the FF extragalactic sources in a high noise zone with fluxes >=
(0.42,0.36) Jy for (blind/non-blind) detection and in a low noise zone with
fluxes >= (0.22,0.18) Jy for (blind/non-blind) detection with low errors in the
estimated flux and position. |
Gravitational Waves from Cosmological Phase Transitions: In the present thesis, the author reviews the physics of cosmological
first-order phase transitions that may have occured shortly after the Big Bang.
Such transitions proceed via the nucleation and expansion of true vacuum
bubbles and give rise to a rich phenomenology, for instance the emission of a
stochastic gravitational-wave background caused by bubble collisions. The
author discusses, in depth, the formalism of the effective scalar potential and
its different contributions in the loop expansion, points out the necessary
ingredients for a first-order transition, and assesses the detectability of the
associated gravitational-wave spectrum via future space-based observatories and
pulsar timing arrays. He then applies the the developed phenomenological
toolbox to investigate the detection prospect for phase transitions in the
context of specific theories such as the Vev Flip-Flop (a dark matter
mechanism) and the Dark Photon Model. | Quantum Entanglement in Multi-field Inflation: We study the emergence of quantum entanglement in multi-field inflation. In
this scenario, the perturbations of one field contribute to the observable
curvature perturbation, while multi-field dynamics with the other fields affect
the curvature perturbation through particle production and entanglement. We
develop a general formalism which defines the quantum entanglement between the
perturbations of the multiple fields both in the Heisenberg and Schr\"odinger
pictures, and show that entanglement between different fields can arise
dynamically in the context of multi-field inflationary scenarios. We also
present a simple model in which a sudden change in the kinetic matrix of the
scalar fields generates entanglement and an oscillatory feature appears in the
power spectrum of the inflaton perturbation. |
Big Bang nucleosynthesis with a stiff fluid: Models that lead to a cosmological stiff fluid component, with a density
$\rho_S$ that scales as $a^{-6}$, where $a$ is the scale factor, have been
proposed recently in a variety of contexts. We calculate numerically the effect
of such a stiff fluid on the primordial element abundances. Because the stiff
fluid energy density decreases with the scale factor more rapidly than
radiation, it produces a relatively larger change in the primordial helium-4
abundance than in the other element abundances, relative to the changes
produced by an additional radiation component. We show that the helium-4
abundance varies linearly with the density of the stiff fluid at a fixed
fiducial temperature. Taking $\rho_{S10}$ and $\rho_{R10}$ to be the stiff
fluid energy density and the standard density in relativistic particles,
respectively, at $T = 10$ MeV, we find that the change in the primordial helium
abundance is well-fit by $\Delta Y_p = 0.00024(\rho_{S10}/\rho_{R10})$. The
changes in the helium-4 abundance produced by additional radiation or by a
stiff fluid are identical when these two components have equal density at a
"pivot temperature", $T_*$, where we find $T_* = 0.55$ MeV. Current estimates
of the primordial $^4$He abundance give the constraint on a stiff fluid energy
density of $\rho_{S10}/\rho_{R10} < 30$. | The Dark Matter Haloes and Host Galaxies of MgII Absorbers at z~1: Strong foreground absorption features from singly-ionized Magnesium (Mg II)
are commonly observed in the spectra of quasars and are presumed to probe a
wide range of galactic environments. To date, measurements of the average dark
matter halo masses of intervening Mg II absorbers by way of large-scale
cross-correlations with luminous galaxies have been limited to z<0.7. In this
work we cross-correlate 21 strong (W{\lambda}2796>0.6 {\deg}A) Mg II absorption
systems detected in quasar spectra from the Sloan Digital Sky Survey Data
Release 7 with ~32,000 spectroscopically confirmed galaxies at 0.7<z<1.45 from
the DEEP2 galaxy redshift survey. We measure dark matter (DM) halo biases of
b_G=1.44\pm0.02 and b_A=1.49\pm0.45 for the DEEP2 galaxies and Mg II absorbers,
respectively, indicating that their clustering amplitudes are roughly
consistent. Haloes with the bias we measure for the Mg II absorbers have a
corresponding mass of 1.8(+4.2/-1.6) \times 10^12h-1M_sun, although the actual
mean absorber halo mass will depend on the precise distribution of absorbers
within DM haloes. This mass estimate is consistent with observations at z=0.6,
suggesting that the halo masses of typical Mg II absorbers do not significantly
evolve from z~1. We additionally measure the average W{\lambda}2796>0.6 \AA gas
covering fraction to be f =0.5 within 60 h-1kpc around the DEEP2 galaxies, and
we find an absence of coincident strong Mg II absorption beyond a projected
separation of ~40 h-1kpc. Although the star-forming z>1 DEEP2 galaxies are
known to exhibit ubiquitous blueshifted Mg II absorption, we find no direct
evidence in our small sample linking W{\lambda}2796>0.6 \AA absorbers to
galaxies with ongoing star formation. |
Determining Model-independent $H_0$ and Consistency Tests: We determine the Hubble constant $H_0$ precisely ($2.3\%$ uncertainty) in a
manner independent of cosmological model through Gaussian process regression,
using strong lensing and supernova data. Strong gravitational lensing of a
variable source can provide a time-delay distance $D_{\Delta t}$ and angular
diameter distance to the lens $D_{\rm{d}}$. These absolute distances can anchor
Type Ia supernovae, which give an excellent constraint on the shape of the
distance-redshift relation. Updating our previous results to use the H0LiCOW
program's milestone dataset consisting of six lenses, four of which have both
$D_{\Delta t}$ and $D_{\rm{d}}$ measurements, we obtain
$H_0=72.8_{-1.7}^{+1.6}\rm{\ km/s/Mpc}$ for a flat universe and
$H_0=77.3_{-3.0}^{+2.2}\rm{\ km/s/Mpc}$ for a non-flat universe. We carry out
several consistency checks on the data and find no statistically significant
tensions, though a noticeable redshift dependence persists in a particular
systematic manner that we investigate. Speculating on the possibility that this
trend of derived Hubble constant with lens distance is physical, we show how
this can arise through modified gravity light propagation, which would also
impact the weak lensing $\sigma_8$ tension. | Multi-color detection of gravitational arcs: Strong gravitational lensing provides fundamental insights into the
understanding of the dark matter distribution in massive galaxies, galaxy
clusters and the background cosmology. Despite their importance, the number of
gravitational arcs discovered so far is small. The urge for more complete,
large samples and unbiased methods of selecting candidates is rising. A number
of methods for the automatic detection of arcs have been proposed in the
literature, but large amounts of spurious detections retrieved by these methods
forces observers to visually inspect thousands of candidates per square degree
in order to clean the samples. This approach is largely subjective and requires
a huge amount of eye-ball checking, especially considering the actual and
upcoming wide field surveys, which will cover thousands of square degrees. In
this paper we study the statistical properties of colours of gravitational arcs
detected in the 37 deg^2 of the CARS survey. We have found that most of them
lie in a relatively small region of the (g'-r',r'-i') colour-colour diagram. To
explain this property, we provide a model which includes the lensing optical
depth expected in a LCDM cosmology that, in combination with the sources'
redshift distribution of a given survey, in our case CARS, peaks for sources at
redshift z~1. By further modelling the colours derived from the SED of the
galaxies dominating the population at that redshift, the model well reproduces
the observed colours. By taking advantage of the colour selection suggested by
both data and model, we show that this multi-band filtering returns a sample
83% complete and a contamination reduced by a factor of ~6.5 with respect to
the single-band arcfinder sample. New arc candidates are also proposed. |
Distinguishing freezing and thawing dark energy models through
measurements of the fine-structure constant: Mapping the behaviour of dark energy is a pressing task for observational
cosmology. Phenomenological classification divides dynamical dark energy models
into freezing and thawing, depending on whether the dark energy equation of
state is approaching or moving away from $w=p/\rho=-1$. Moreover, in realistic
dynamical dark energy models the dynamical degree of freedom is expected to
couple to the electromagnetic sector, leading to variations of the
fine-structure constant $\alpha$. We discuss the feasibility of distinguishing
between the freezing and thawing classes of models with current and forthcoming
observational facilities and using a parametrisation of the dark energy
equation of state, which can have either behaviour, introduced by Mukhanov as
fiducial paradigm. We illustrate how freezing and thawing models lead to
different redshift dependencies of $\alpha$, and use a combination of current
astrophysical observations and local experiments to constrain this class of
models, improving the constraints on the key coupling parameter by more than a
factor of two, despite considering a more extended parameter space than the one
used in previous studies. We also briefly discuss the improvements expected
from future facilities and comment on the practical limitations of this class
of parametrisations. In particular, we show that sufficiently sensitive data
can distinguish between freezing and thawing models, at least if one assumes
that the relevant parameter space does not include phantom dark energy models. | Supernovae as seen by off-center observers in a local void: Inhomogeneous universe models have been proposed as an alternative
explanation for the apparent acceleration of the cosmic expansion that does not
require dark energy. In the simplest class of inhomogeneous models, we live
within a large, spherically symmetric void. Several studies have shown that
such a model can be made consistent with many observations, in particular the
redshift--luminosity distance relation for type Ia supernovae, provided that
the void is of Gpc size and that we live close to the center. Such a scenario
challenges the Copernican principle that we do not occupy a special place in
the universe. We use the first-year Sloan Digital Sky Survey-II supernova
search data set as well as the Constitution supernova data set to put
constraints on the observer position in void models, using the fact that
off-center observers will observe an anisotropic universe. We first show that a
spherically symmetric void can give good fits to the supernova data for an
on-center observer, but that the two data sets prefer very different voids. We
then continue to show that the observer can be displaced at least fifteen
percent of the void scale radius from the center and still give an acceptable
fit to the supernova data. When combined with the observed dipole anisotropy of
the cosmic microwave background however, we find that the data compells the
observer to be located within about one percent of the void scale radius. Based
on these results, we conclude that considerable fine-tuning of our position
within the void is needed to fit the supernova data, strongly disfavouring the
model from a Copernican principle point of view. |
Amalgame: Cosmological Constraints from the First Combined Photometric
Supernova Sample: Future constraints of cosmological parameters from Type Ia supernovae (SNe
Ia) will depend on the use of photometric samples, those samples without
spectroscopic measurements of the SNe Ia. There is a growing number of analyses
that show that photometric samples can be utilised for precision cosmological
studies with minimal systematic uncertainties. To investigate this claim, we
perform the first analysis that combines two separate photometric samples, SDSS
and Pan-STARRS, without including a low-redshift anchor. We evaluate the
consistency of the cosmological parameters from these two samples and find they
are consistent with each other to under $1\sigma$. From the combined sample,
named Amalgame, we measure $\Omega_M = 0.328 \pm 0.024$ with SN alone in a flat
$\Lambda$CDM model, and $\Omega_M = 0.330 \pm 0.018$ and $w =
-1.016^{+0.055}_{-0.058}$ when combining with a Planck data prior and a flat
$w$CDM model. These results are consistent with constraints from the Pantheon+
analysis of only spectroscopically confirmed SNe Ia, and show that there are no
significant impediments to analyses of purely photometric samples of SNe Ia. | A Scaling Relation of the Evolving Tidal Fields in a LCDM Cosmology: We report the finding of a scaling relation among the cosmic-web anisotropy
parameter $A$, the linear density rms fluctuation sigma(r) and the linear
growth factor D(z). Using the tidal field derived from the Millennium
Simulation on 512^{3} grids at z=0, 2, 5 and 127, we calculate the largest
eigenvalues $\lambda$ of the local tidal tensor at each grid resolution and
measure its distance-averaged two-point correlation function, xi_{lambda}, as a
function of the cosines of polar angles cos(theta) in the local principal axis
frame. We show that xi_{lambda} is quite anisotropic, increasing toward the
directions of minimal matter compression, and that the anisotropy of
xi_{lambda} increases as the redshift, z, decreases and as the upper distance
cutoff r_{c} decreases. Fitting the numerical results to an analytic fitting
model \xi_{\lambda}(\cos\theta)\propto (1+A\cos^{n}\theta)^{-1}, it is found
that the best fit value of A, dubbed the cosmic-web anisotropy parameter,
varies systematically with sigma(r_{c}) and D(z), allowing us to determine the
simple empiral scaling relation A(r_{c},z)=0.8, D^{0.76}(z), sigma (r_{c})$. |
Planck Early Results: Origin of the submm excess dust emission in the
Magellanic Clouds: The integrated Spectral Energy Distributions of the Large and Small
Magellanic Cloud appear significantly flatter than expected from dust models
based on their FIR and radio emission. The origin of this millimetre excess is
still unexplained, and is here investigated using the Planck data. The
background CMB contribution is subtracted using an ILC method performed locally
around the galaxies. The foreground emission from the Milky Way is subtracted.
After subtraction, the emission of both galaxies correlates closely with the
gas emission of the LMC and SMC. The millimetre excess in the LMC can be
explained by CMB fluctuations, but a significant excess is still present in the
SMC SED. The Planck and IRIS data at 100 micron are combined to produce thermal
dust temperature and optical depth maps of the two galaxies. The LMC
temperature map shows the presence of a warm inner arm already found with the
Spitzer data, but also shows the existence of a previously unidentified cold
outer arm. Several cold regions are found along this arm, some of which are
associated with known molecular clouds. The average emissivity spectral index
is found to be consistent with beta=1.5 and beta=1.2 below 500 microns for the
LMC and SMC respectively, significantly flatter than the values observed in the
Milky Way. Furthermore, there is evidence in the SMC for a further flattening
of the SED in the sub-mm. The spatial distribution of the millimetre dust
excess in the SMC follows the gas and thermal dust distribution. Different
models are explored in order to fit the dust emission in the SMC. It is
concluded that the millimetre excess is unlikely to be caused by very cold dust
emission and that it could be due to a combination of spinning dust. emission
and thermal dust emission by more amorphous dust grains than those present in
our Galaxy. | Direct Parameter Inference from Global EoR Signal with Bayesian
Statistics: In the observation of sky-averaged HI signal from Epoch of Reionization,
model parameter inference can be a computation-intensive work, which makes it
hard to perform a direct one-stage model parameter inference by using MCMC
sampling method in Bayesian framework. Instead, a two-stage inference is
usually used, i.e., the parameters of some characteristic points on the EoR
spectrum model are first estimated, which are then used as the input to
estimate physical model parameters further. However, some previous works had
noticed that this kind of method could bias results, and it could be meaningful
to answer the question of whether it is feasible to perform direct one-stage
MCMC sampling and obtain unbiased physical model parameter estimations. In this
work, we studied this problem and confirmed the feasibility. We find that
unbiased estimations to physical model parameters can be obtained with a
one-stage direct MCMC sampling method. We also study the influence of some
factors that should be considered in practical observations to model parameter
inference. We find that a very tiny amplifier gain calibration error ($10^{-5}$
relative error) with complex spectral structures can significantly bias the
parameter estimation; the frequency-dependent antenna beam and geographical
position can also influence the results, so that should be carefully handled. |
Geometric Algorithms for Identifying and Reconstructing Galaxy Systems: The theme of this book chapter is to discuss algorithms for identifying and
reconstructing groups and clusters of galaxies out of the general galaxy
distribution. I review the progress of detection techniques through time, from
the very first visual-like algorithms to the most performant geometrical
methods available today. This will allow readers to understand the development
of the field as well as the various issues and pitfalls we are confronted with.
This essay is drawn from a talk given by the author at the conference "The
World a Jigsaw: Tessellations in the Sciences" held at the Lorentz Center in
Leiden. It is intended for a broad audience of scientists (and so does not
include full academic referencing), but it may be of interest to specialists. | Primordial polymer perturbations: We study the generation of primordial fluctuations in pure de Sitter
inflation where the quantum scalar field dynamics are governed by polymer (not
Schrodinger) quantization. This quantization scheme is related to, but distinct
from, the structures employed in Loop Quantum Gravity; and it modifies standard
results above a polymer energy scale $M_{\star}$. We recover the scale
invariant Harrison Zel'dovich spectrum for modes that have wavelengths bigger
than $M_{\star}^{-1}$ at the start of inflation. The primordial spectrum for
modes with initial wavelengths smaller than $M_{\star}^{-1}$ exhibits
oscillations superimposed on the standard result. The amplitude of these
oscillations is proportional to the ratio of the inflationary Hubble parameter
$H$ to the polymer energy scale. For reasonable choices of $M_{\star}$, we find
that polymer effects are likely unobservable in CMB angular power spectra due
to cosmic variance uncertainty, but future probes of baryon acoustic
oscillations may be able to directly constrain the ratio $H/M_{\star}$. |
An Improved Treatment of Optics in the Lindquist-Wheeler Models: We consider the optical properties of Lindquist-Wheeler (LW) models of the
Universe. These models consist of lattices constructed from regularly arranged
discrete masses. They are akin to the Wigner-Seitz construction of solid state
physics, and result in a dynamical description of the large-scale Universe in
which the global expansion is given by a Friedmann-like equation. We show that
if these models are constructed in a particular way then the redshifts of
distant objects, as well as the dynamics of the global space-time, can be made
to be in good agreement with the homogeneous and isotropic
Friedmann-Lemaitre-Robertson-Walker (FLRW) solutions of Einstein's equations,
at the level of <3% out to z~2. Angular diameter and luminosity distances, on
the other hand, differ from those found in the corresponding FLRW models, while
being consistent with the 'empty beam' approximation, together with the
shearing effects due to the nearest masses. This can be compared with the large
deviations found from the corresponding FLRW values obtained in a previous
study that considered LW models constructed in a different way. We therefore
advocate the improved LW models we consider here as useful constructions that
appear to faithfully reproduce both the dynamical and observational properties
of space-times containing discrete masses. | Assessing the discovery potential of directional detection of Dark
Matter: There is a worldwide effort toward the development of a large TPC (Time
Projection Chamber) devoted to directional Dark Matter detection. All current
projects are being designed to fulfill a unique goal : identifying weakly
interacting massive particle (WIMP) as such by taking advantage of the expected
direction dependence of WIMP-induced events toward the constellation Cygnus.
However such proof of discovery requires a careful statistical data treatment.
In this paper, the discovery potential of forthcoming directional detectors is
adressed by using a frequentist approach based on the profile likelihood ratio
test statistic. This allows us to estimate the expected significance of a Dark
Matter detection. Moreover, using this powerful test statistic, it is possible
to propagate astrophysical and experimental uncertainties in the determination
of the discovery potential of a given directional detection experiment. This
way, we found that a 30 kg.year CF$_4$ directional experiment could reach a
3$\sigma$ sensitivity at 90% C.L. down to $10^{-5}$ pb and $3.10^{-4}$ pb for
the WIMP-proton axial cross section in the most optimistic and pessimistic
scenario respectively. |
Structure formation with scalar field dark matter: the field approach: We study the formation of structure in the Universe assuming that dark matter
can be described by a scalar field $\tilde{\Phi}$ with a potential
$V(\Phi)=-\mathfrak{m}^{2}\tilde{\Phi}^{2}/2+\lambda\tilde{\Phi}^4/4$. We
derive the evolution equations of the scalar field in the linear regime of
perturbations. We investigate the symmetry breaking and possibly a phase
transition of this scalar field in the early Universe. At low temperatures, the
scalar perturbations have an oscillating growing mode and therefore, this kind
of dark matter could lead to the formation of gravitational structures. In
order to study the nonlinear regime, we use the spherical collapse model and
show that, in the quadratic potential limit, this kind of dark matter can form
virialized structures. The main difference with the traditional Cold Dark
Matter paradigm is that the formation of structure in the scalar field model
can occur at earlier times. Thus, if the dark matter is of scalar field nature
we expect to have large galaxies at high redshifts. | Dark Energy Survey Year 3 Results: Covariance Modelling and its Impact
on Parameter Estimation and Quality of Fit: We describe and test the fiducial covariance matrix model for the combined
2-point function analysis of the Dark Energy Survey Year 3 (DES-Y3) dataset.
Using a variety of new ansatzes for covariance modelling and testing we
validate the assumptions and approximations of this model. These include the
assumption of a Gaussian likelihood, the trispectrum contribution to the
covariance, the impact of evaluating the model at a wrong set of parameters,
the impact of masking and survey geometry, deviations from Poissonian
shot-noise, galaxy weighting schemes and other, sub-dominant effects. We find
that our covariance model is robust and that its approximations have little
impact on goodness-of-fit and parameter estimation. The largest impact on
best-fit figure-of-merit arises from the so-called $f_{\mathrm{sky}}$
approximation for dealing with finite survey area, which on average increases
the $\chi^2$ between maximum posterior model and measurement by $3.7\%$
($\Delta \chi^2 \approx 18.9$). Standard methods to go beyond this
approximation fail for DES-Y3, but we derive an approximate scheme to deal with
these features. For parameter estimation, our ignorance of the exact parameters
at which to evaluate our covariance model causes the dominant effect. We find
that it increases the scatter of maximum posterior values for $\Omega_m$ and
$\sigma_8$ by about $3\%$ and for the dark energy equation of state parameter
by about $5\%$. |
Non-Gaussianity effects on the primordial black hole abundance for
sharply-peaked primordial spectrum: We perturbatively study the effect of non-Gaussianities on the mass fraction
of primordial black holes (PBHs) at the time of formation by systematically
taking its effect into account in the one-point probability distribution
function of the primordial curvature perturbation. We focus on the bispectrum
and trispectrum and derive formulas that describe their effects on the skewness
and kurtosis of the distribution function. Then considering the case of
narrowly peaked spectra, we obtain simple formulas that concisely express the
effect of the bi- and trispectra. In particular, together with the $g_{\rm NL}$
and $\tau_{\rm NL}$ parameters of the trispectrum, we find that non-Gaussianity
parameters for various types of the bispectrum are linearly combined to give an
effective parameter, $f_{\rm NL}^{\rm eff}$, that determines the PBH mass
fraction in the narrow spectral shape limit. | Sound velocity effects on the phase transition gravitational wave
spectrum in the sound shell model: A cosmological first-order phase transition gravitational wave could provide
a novel approach to studying the early Universe. In most cases, the acoustic
gravitational wave from the sound wave mechanism is dominant. Considering
different sound velocities in symmetric and broken phases, we study sound
velocity effects on the acoustic phase transition gravitational wave spectra in
the sound shell model. We demonstrate that different sound velocities could
obviously modify the peak frequency and peak amplitude of the gravitational
wave power spectra. Therefore, taking more realistic sound velocities might
provide more accurate predictions for various gravitational wave experiments. |
Improved Primordial Non-Gaussianity Constraints from Measurements of
Galaxy Clustering and the Integrated Sachs-Wolfe Effect: We present the strongest robust constraints on primordial non-Gaussianity
(PNG) from currently available galaxy surveys, combining large-scale clustering
measurements and their cross-correlations with the cosmic microwave background.
We update the data sets used by Giannantonio et al. (2012), and broaden that
analysis to include the full set of two-point correlation functions between all
surveys. In order to obtain the most reliable constraints on PNG, we advocate
the use of the cross-correlations between the catalogs as a robust estimator
and we perform an extended analysis of the possible systematics to reduce their
impact on the results. To minimize the impact of stellar contamination in our
luminous red galaxy (LRG) sample, we use the recent Baryon Oscillations
Spectroscopic Survey catalog of Ross et al. (2011). We also find evidence for a
new systematic in the NVSS radio galaxy survey similar to, but smaller than,
the known declination-dependent issue; this is difficult to remove without
affecting the inferred PNG signal, and thus we do not include the NVSS
auto-correlation function in our analyses. We find no evidence of primordial
non-Gaussianity; for the local-type configuration we obtain for the skewness
parameter $ -36 < f_{\mathrm{NL}} < 45 $ at 95 % c.l. ($5 \pm 21$ at $1\sigma$)
when using the most conservative part of our data set, improving previous
results; we also find no evidence for significant kurtosis, parameterized by
$g_{\mathrm{NL}}$. In addition to PNG, we simultaneously constrain dark energy
and find that it is required with a form consistent with a cosmological
constant. | Angular Correlations of Cosmic Microwave Background Spectrum Distortions
from Photon Diffusion: During cosmic recombination, charged particles bind into neutral atoms and
the mean free path of photons rapidly increases, resulting in the familiar
diffusion damping of primordial radiation temperature variations. An additional
effect is a small photon spectrum distortion, because photons arriving from a
particular sky direction were originally in thermal equilibrium at various
spatial locations with different temperatures; the combination of these
different blackbody temperature distributions results in a spectrum with a
Compton $y$-distortion. Using the approximation that photons had zero mean free
path prior to their second-to-last scattering, we derive an expression for the
resulting $y$-distortion, and compute the angular correlation function of the
diffusion $y$-distortion and its cross-correlation with the square of the
photon temperature fluctuation. Detection of the cross-correlation is within
reach of existing arcminute-resolution microwave background experiments such as
the Atacama Cosmology Telescope and the South Pole Telescope. |
Induced gravitational waves from flipped SU(5) superstring theory at
$\mathrm{nHz}$: The no-scale flipped SU(5) superstring framework constitutes a very promising
paradigm for physics below the Planck scale providing us with a very rich
cosmological phenomenology in accordance with observations. In particular, it
can accommodate Starobinsky-like inflation, followed by a reheating phase,
which is driven by a light "flaton" field, and during which the GUT phase
transition occurs. In this Letter, we extract for the first time a
gravitational-wave (GW) signal which naturally arises in the context of the
flipped SU(5) cosmological phenomenology and is related to the existence of an
early matter era (eMD) driven by the flaton field. Specifically, we study GWs
non-linearly induced by inflationary perturbations and which are abundantly
produced during a sudden transition from the flaton-driven eMD era to the
late-time radiation-dominated era. Remarkably, we find a GW signal with a
characteristic peak frequency $f_\mathrm{GW,peak}$ depending only on the string
slope $\alpha'$ and reading as $f_\mathrm{GW,peak} \propto 10^{-9}
\left(\frac{\alpha'}{\alpha'_*}\right)^4 \mathrm{Hz}$, where $\alpha'_*$ is the
fiducial string slope being related directly to the reduced Planck scale
$M_\mathrm{Pl}$ as $\alpha'_* = 8/M^2_\mathrm{Pl}$. Interestingly enough,
$f_\mathrm{GW,peak}$ lies within the $\mathrm{nHz}$ frequency range; hence
rendering this primordial GW signal potentially detectable by SKA, NANOGrav and
PTA probes at their very low frequency region of their detection bands. | Lagrangian Volume Deformations around Simulated Galaxies: We present a detailed analysis of the local evolution of 206 Lagrangian
Volumes (LVs) selected at high redshift around galaxy seeds, identified in a
large-volume $\Lambda$ cold dark matter ($\Lambda$CDM) hydrodynamical
simulation. The LVs have a mass range of $1 - 1500 \times 10^{10} M_\odot$. We
follow the dynamical evolution of the density field inside these initially
spherical LVs from $z=10$ up to $z_{\rm low} = 0.05$, witnessing highly
non-linear, anisotropic mass rearrangements within them, leading to the
emergence of the local cosmic web (CW). These mass arrangements have been
analysed in terms of the reduced inertia tensor $I_{ij}^r$, focusing on the
evolution of the principal axes of inertia and their corresponding
eigendirections, and paying particular attention to the times when the
evolution of these two structural elements declines. In addition, mass and
component effects along this process have also been investigated. We have found
that deformations are led by dark matter dynamics and they transform most of
the initially spherical LVs into prolate shapes, i.e. filamentary structures.
An analysis of the individual freezing-out time distributions for shapes and
eigendirections shows that first most of the LVs fix their three axes of
symmetry (like a skeleton) early on, while accretion flows towards them still
continue. Very remarkably, we have found that more massive LVs fix their
skeleton earlier on than less massive ones. We briefly discuss the
astrophysical implications our findings could have, including the galaxy
mass-morphology relation and the effects on the galaxy-galaxy merger parameter
space, among others. |
Analytical Potentials for Flat Galaxies with Spheroidal Halos: A family of analytical potential-density pairs for flat galaxies with
spheroidal halos is presented. The potential are obtained by means of the sum
of two independent terms: a potential associated with a thin disc and a
potential associated with a spheroidal halo, which are expressed as
appropriated superpositions of products of Legendre functions, in such a way
that the model implies a linear relationship between the masses of the thin
disc and the spheroidal halo. By taking a particular case for the halo
potential, we found that the circular velocity obtained can be adjusted very
accurately to the observed rotation curves of some specific galaxies, so that
the models are stable against radial and vertical perturbations. Two particular
models for the galaxies NGC4389 and UGC6969 are obtained by adjusting the
circular velocity with data of the observed rotation curve of some galaxies of
the Ursa Mayor Cluster, as reported in Verheijen and Sancisi 2001. The values
of the halo mass and the disc mass for these two galaxies are computed
obtaining a very narrow interval of values for these quantities. Furthermore,
the values of obtained masses are in perfect agreement with the expected order
of magnitude and with the relative order of magnitude between the halo mass and
the disc mass. | Cosmological model discrimination with Deep Learning: We demonstrate the potential of Deep Learning methods for measurements of
cosmological parameters from density fields, focusing on the extraction of
non-Gaussian information. We consider weak lensing mass maps as our dataset. We
aim for our method to be able to distinguish between five models, which were
chosen to lie along the $\sigma_8$ - $\Omega_m$ degeneracy, and have nearly the
same two-point statistics. We design and implement a Deep Convolutional Neural
Network (DCNN) which learns the relation between five cosmological models and
the mass maps they generate. We develop a new training strategy which ensures
the good performance of the network for high levels of noise. We compare the
performance of this approach to commonly used non-Gaussian statistics, namely
the skewness and kurtosis of the convergence maps. We find that our
implementation of DCNN outperforms the skewness and kurtosis statistics,
especially for high noise levels. The network maintains the mean discrimination
efficiency greater than $85\%$ even for noise levels corresponding to ground
based lensing observations, while the other statistics perform worse in this
setting, achieving efficiency less than $70\%$. This demonstrates the ability
of CNN-based methods to efficiently break the $\sigma_8$ - $\Omega_m$
degeneracy with weak lensing mass maps alone. We discuss the potential of this
method to be applied to the analysis of real weak lensing data and other
datasets. |
Relativistic beaming and gamma-ray brightness of blazars: We investigate the dependence of gamma-ray brightness of blazars on intrinsic
properties of their parsec-scale radio jets and the implication for
relativistic beaming. By combining apparent jet speeds derived from
high-resolution VLBA images from the MOJAVE program with millimetre-wavelength
flux density monitoring data from Metsahovi Radio Observatory, we estimate the
jet Doppler factors, Lorentz factors, and viewing angles for a sample of 62
blazars. We study the trends in these quantities between the sources which were
detected in gamma-rays by the Fermi Large Area Telescope (LAT) during its first
three months of science operations and those which were not detected. The
LAT-detected blazars have on average higher Doppler factors than
non-LAT-detected blazars, as has been implied indirectly in several earlier
studies. We find statistically significant differences in the viewing angle
distributions between gamma-ray bright and weak sources. Most interestingly,
gamma-ray bright blazars have a distribution of comoving frame viewing angles
that is significantly narrower than that of gamma-ray weak blazars and centred
roughly perpendicular to the jet axis. The lack of gamma-ray bright blazars at
large comoving frame viewing angles can be explained by relativistic beaming of
gamma-rays, while the apparent lack of gamma-ray bright blazars at small
comoving frame viewing angles, if confirmed with larger samples, may suggest an
intrinsic anisotropy or Lorentz factor dependence of the gamma-ray emission. | CLASH-X: A Comparison of Lensing and X-ray Techniques for Measuring the
Mass Profiles of Galaxy Clusters: We present profiles of temperature (Tx), gas mass, and hydrostatic mass
estimated from new and archival X-ray observations of CLASH clusters. We
compare measurements derived from XMM and Chandra observations with one another
and compare both to gravitational lensing mass profiles derived with CLASH HST
and ground-based lensing data. Radial profiles of Chandra and XMM electron
density and enclosed gas mass are nearly identical, indicating that differences
in hydrostatic masses inferred from X-ray observations arise from differences
in Tx measurements. Encouragingly, cluster Txs are consistent with one another
at ~100-200 kpc radii but XMM Tx systematically decline relative to Chandra Tx
at larger radii. The angular dependence of the discrepancy suggests additional
investigation on systematics such as the XMM point spread function correction,
vignetting and off-axis responses. We present the CLASH-X mass-profile
comparisons in the form of cosmology-independent and redshift-independent
circular-velocity profiles. Ratios of Chandra HSE mass profiles to CLASH
lensing profiles show no obvious radial dependence in the 0.3-0.8 Mpc range.
However, the mean mass biases inferred from the WL and SaWLens data are
different. e.g., the weighted-mean value at 0.5 Mpc is <b> = 0.12 for the WL
comparison and <b> = -0.11 for the SaWLens comparison. The ratios of XMM HSE
mass profiles to CLASH lensing profiles show a pronounced radial dependence in
the 0.3-1.0 Mpc range, with a weighted mean mass bias of value rising to
<b>~0.3 at ~1 Mpc for the WL comparison and <b> of 0.25 for SaWLens comparison.
The enclosed gas mass profiles from both Chandra and XMM rise to a value 1/8
times the total-mass profiles inferred from lensing at 0.5 Mpc and remain
constant outside of that radius, suggesting that [8xMgas] profiles may be an
excellent proxy for total-mass profiles at >0.5 Mpc in massive galaxy clusters. |
Searching for ring-like structures in the Cosmic Microwave Background: In this research, we present an alternative methodology to search for
ring-like structures in the sky with unusually large temperature gradients,
namely Hawking points (HP), in the Cosmic Microwave Background (CMB), which are
possible observational effects associated with Conformal Cyclic Cosmology
(CCC). To assess the performance of our method, we constructed an artificial
data set of HP, according to CCC, and we were able to retrieve $95 \%$ of
ring-like anomalies from it. Furthermore, we scanned the \textit{Planck} CMB
sky map and compared it to simulations according to $\Lambda CDM$, where we
applied robust statistical tests to assess the existence of HP. Even though no
significant ring-like structures were observed, we report the largest excess of
HP candidates found at $\alpha = $1\% significance level for the analyzed sky
maps (CMB at 70GHz, SEVEM, SMICA, and Commander-Ruler), and we stress the need
to continue the theoretical and experimental research in this direction. | The Formation Probability of Primordial Black Holes: We calculate the exact formation probability of primordial black holes
generated during the collapse at horizon re-entry of large fluctuations
produced during inflation, such as those ascribed to a period of
ultra-slow-roll. We show that it interpolates between a Gaussian at small
values of the average density contrast and a Cauchy probability distribution at
large values. The corresponding abundance of primordial black holes may be
larger than the Gaussian one by several orders of magnitude. The mass function
is also shifted towards larger masses. |
CNN photometric redshifts in the SDSS at $r\leq 20$: We release photometric redshifts, reaching $\sim$0.7, for $\sim$14M galaxies
at $r\leq 20$ in the 11,500 deg$^2$ of the SDSS north and south galactic caps.
These estimates were inferred from a convolution neural network (CNN) trained
on $ugriz$ stamp images of galaxies labelled with a spectroscopic redshift from
the SDSS, GAMA and BOSS surveys. Representative training sets of $\sim$370k
galaxies were constructed from the much larger combined spectroscopic data to
limit biases, particularly those arising from the over-representation of
Luminous Red Galaxies. The CNN outputs a redshift classification that offers
all the benefits of a well-behaved PDF, with a width efficiently signaling
unreliable estimates due to poor photometry or stellar sources. The dispersion,
mean bias and rate of catastrophic failures of the median point estimate are of
order $\sigma_{\rm MAD}=0.014$, <$\Delta z_{\rm norm}$>$=0.0015$, $\eta(|\Delta
z_{\rm norm}|>0.05)=4\%$ on a representative test sample at $r<19.8$,
out-performing currently published estimates. The distributions in narrow
intervals of magnitudes of the redshifts inferred for the photometric sample
are in good agreement with the results of tomographic analyses. The inferred
redshifts also match the photometric redshifts of the redMaPPer galaxy clusters
for the probable cluster members. The CNN input and output are available at:
https://deepdip.iap.fr/treyer+2023. | Matter Power Spectrum Covariance Matrix from the DEUS-PUR ΛCDM
simulations: Mass Resolution and non-Gaussian Errors: The upcoming generation of galaxy surveys will probe the distribution of
matter in the universe with unprecedented accuracy. Measurements of the matter
power spectrum at different scales and redshifts will provide stringent
constraints on the cosmological parameters. However, on non-linear scales this
will require an accurate evaluation of the covariance matrix. Here, we compute
the covariance matrix of the 3D matter density power spectrum for the
concordance $\Lambda$CDM cosmology from an ensemble of N-body simulations of
the Dark Energy Universe Simulation - Parallel Universe Runs (DEUS-PUR). This
consists of 12288 realisations of a $(656\,h^{-1}\,\textrm{Mpc})^3$ simulation
box with $256^3$ particles. We combine this set with an auxiliary sample of 96
simulations of the same volume with $1024^3$ particles. We find N-body mass
resolution effect to be an important source of systematic errors on the
covariance at high redshift and small intermediate scales. We correct for this
effect by introducing an empirical statistical method which provide an accurate
determination of the covariance matrix over a wide range of scales including
the Baryon Oscillations interval. Contrary to previous studies that used
smaller N-body ensembles, we find the power spectrum distribution to
significantly deviate from expectations of a Gaussian random density field at
$k\gtrsim 0.25\,h\,\textrm{Mpc}^{-1}$ and $z<0.5$. This suggests that in the
case of finite volume surveys an unbiased estimate of the ensemble averaged
band power at these scales and redshifts may require a careful assessment of
non-Gaussian errors more than previously considered. |
LOFAR detection of extended emission around a mini-halo in the galaxy
cluster Abell 1413: The relation between giant radio halos and mini-halos in galaxy clusters is
not understood. The former are usually associated with merging clusters, the
latter are found in relaxed systems. In the last years, the advent of
low-frequency radio observations has challenged this dichotomy, finding
intermediate objects with a hybrid radio morphology. We aim to investigate the
presence of diffuse radio emission in the cluster Abell 1413 and determine its
dynamical status. We used LOFAR HBA observations centred at 144 MHz to study
the diffuse emission hosted by this cluster.To investigate the dynamical state
of the system, we complete our study with newly analysed XMM-Newton archival
data. A1413 shows features that are typically present in both relaxed (e.g.,
peaked x-ray surface brightness distribution and little large-scale
inhomogeneities) and disturbed (e.g., flatter temperature and metallicity
profiles) clusters.This evidence supports the scenario that A1413 is neither a
disturbed nor fully relaxed object. We argue that it is an intermediate-phase
cluster.Using radio observations at 144 MHz, we discover the presence of a
wider diffuse component surrounding the previously reported mini-halo at the
cluster centre. By fitting the radio surface brightness profile with a
double-exponential model, we can disentangle the two components. We find an
inner mini-halo with an e-folding radius r_e1=28 kpc and the extended component
with r_e2 = 290 kpc. We also performed point-to-point correlations between
radio and X-ray surface brightness, finding a sub-linear relation for the outer
emission and a super-linear relation for the mini-halo.The mini-halo and the
diffuse emission extend over different scales and show different features,
confirming the double nature of the radio emission and suggesting that the
mechanisms responsible for the re-acceleration of the radio-emitting particle
might be different. | A slow bar in a dark matter dominated galaxy: We report on an estimate of the bar pattern speed Omega_p for the low surface
brightness spiral galaxy UGC 628. We applied the Tremaine-Weinberg method to
high resolution Halpha velocity and integrated emission maps of this dark
matter dominated galaxy. Observations were made at the CFHT using the optical
Fabry-Perot interferometer, FaNTOmM. The Tremaine-Weinberg method estimates a
bar pattern speed of (11.3 +/- 2.0) km/s/kpc for UGC 628, which is among the
lowest values found for a spiral galaxy. The corotation radius Rc of the bar
and the gaseous disc is Rc = 9.8 (+2.9/-2.0) kpc, implying a ratio R = Rc/Ab of
2.0 (+0.5/-0.3), where Ab is the bar radius. The ratio is well beyond the usual
range of values, 1.0< R <1.4, found for fast bars of high surface brightness
barred galaxies. It implies that the bar in UGC 628 is slow. As shown through
the use of numerical simulations, fast bars survive when the inner mass
distribution of galaxies is dominated by the baryons over the dark matter. Our
result suggests that the presence of slow bars in galaxies is likely related to
the dominance of dark matter over the mass distribution. |
Testing Gravity Theories Using Stars: Modified theories of gravity have received a renewed interest due to their
ability to account for the cosmic acceleration. In order to satisfy the solar
system tests of gravity, these theories need to include a screening mechanism
that hides the modifications on small scales. One popular and well-studied
theory is chameleon gravity. Our own galaxy is necessarily screened, but less
dense dwarf galaxies may be unscreened and their constituent stars can exhibit
novel features. In particular, unscreened stars are brighter, hotter and more
ephemeral than screened stars in our own galaxy. They also pulsate with a
shorter period. In this essay, we exploit these new features to constrain
chameleon gravity to levels three orders of magnitude lower the previous
measurements. These constraints are currently the strongest in the literature. | Evidence for the Fifth Element Astrophysical status of Dark Energy: Evidence for an accelerated expansion of the universe as it has been revealed
ten years ago by the Hubble diagram of distant type Ia supernovae represents
one of the major modern revolutions for fundamental physics and cosmology. It
is yet unclear whether the explanation of the fact that gravity becomes
repulsive on large scales should be found within general relativity or within a
new theory of gravitation. However, existing evidences for this acceleration
all come from astrophysical observations. Before accepting a drastic revision
of fundamental physics, it is interesting to critically examine the present
situation of the astrophysical observations and the possible limitation in
their interpretation. In this review, the main various observational probes are
presented as well as the framework to interpret them with special attention to
the complex astrophysics and theoretical hypotheses that may limit actual
evidences for the acceleration of the expansion. Even when scrutinized with
sceptical eyes, the evidence for an accelerating universe is robust.
Investigation of its very origin appears as the most fascinating challenge of
modern physics. |
The two and three-loop matter bispectrum in perturbation theories: We evaluate for the first time the dark matter bispectrum of large-scale
structure at two loops in the Standard Perturbation Theory and at three loops
in the Renormalised Perturbation Theory (MPTbreeze formalism), removing in each
case the leading divergences in the integrals in order to make them
infrared-safe. We show that the Standard Perturbation Theory at two loops can
be employed to model the matter bispectrum further into the quasi-nonlinear
regime compared to one loop, up to $k_{\text{max}} \sim 0.1 \, h/{\text{Mpc}}$
at $z = 0$, but without reaching a high level of accuracy. In the case of the
MPTbreeze method, we show that its bispectra decay at smaller and smaller
scales with increasing loop order, but with smaller improvements. At three
loops, this model predicts the bispectrum accurately up to scales
$k_{\text{max}} \sim 0.17 \, h/{\text{Mpc}}$ at $z = 0$ and $k_{\text{max}}
\sim 0.24 \, h/{\text{Mpc}}$ at $z = 1$. | Galaxy Pairs in COSMOS -- Merger Rate Evolution Since z=1: We present results of a statistical study of the cosmic evolution of the mass
dependent major-merger rate since z=1. A stellar mass limited sample of close
major-merger pairs (the CPAIR sample) was selected from the archive of the
COSMOS survey. Pair fractions at different redshifts derived using the CPAIR
sample and a local K-band selected pair sample show no significant variations
with stellar mass. The pair fraction exhibits moderately strong cosmic
evolution, with the best-fitting evolutionary index m=2.2+-0.2. The
best-fitting function for the merger rate implies that galaxies with stellar
mass between 1E+10 -- 3E+11 M_sun have undergone 0.5 -- 1.5 major-mergers since
z=1. Our results show that, for massive galaxies at z<1, major mergers
involving star forming galaxies (i.e. wet and mixed mergers) can account for
the formation of both ellipticals and red quiescent galaxies (RQGs). On the
other hand, major mergers cannot be responsible for the formation of most low
mass ellipticals and RQGs. Our quantitative estimates indicate that major
mergers have significant impact on the stellar mass assembly of the most
massive galaxies, but for less massive galaxies the stellar mass assembly is
dominated by the star formation. Comparison with the mass dependent (U)LIRG
rates suggests that the frequency of major-merger events is comparable to or
higher than that of (U)LIRGs. |
Weyl invariance and the conductivity of the protoinflationary plasma: We consider a globally neutral Lorentzian plasma as a possible remnant of a
preinflationary stage of expansion and pose the problem of the suitable initial
conditions for the evolution of the large-scale electromagnetic
inhomogeneities. During the protoinflationary regime the Weyl invariance of the
Ohmic current guarantees that the comoving conductivity is approximately
constant. The subsequent breaking of Weyl invariance by the masses of the
charge carriers drives the conductivity to zero. The newly derived conducting
initial conditions for the amplification of large-scale magnetic fields are
contrasted with the conventional vacuum initial conditions. It is shown, in a
specific class of examples, that when the number of inflationary efolds is
close to minimal the effects of the conducting initial conditions cannot be
neglected. | Measuring the expansion of the universe: We draw a figure from where it is possible to measure the number of e-folds
of expansion of the universe with a ruler. We find model independent bounds for
the number of e-folds during inflation, reheating and radiation. We also give a
lower bound to the size of the universe at the beginning of observable
inflation. Finally, we show that consistency with a relevant diagram requires
the existence of a new form of energy to drive the present expansion of the
universe. |
H_2 emission arises outside photodissociation regions in ultra-luminous
infrared galaxies: Ultra-luminous infrared galaxies are among the most luminous objects in the
local universe and are thought to be powered by intense star formation. It has
been shown that in these objects the rotational spectral lines of molecular
hydrogen observed at mid-infrared wavelengths are not affected by dust
obscuration, leaving unresolved the source of excitation of this emission. Here
I report an analysis of archival Spitzer Space Telescope data on ultra-luminous
infrared galaxies and demonstrate that star formation regions are buried inside
optically thick clouds of gas and dust, so that dust obscuration affects
star-formation indicators but not molecular hydrogen. I thereby establish that
the emission of H_2 is not co-spatial with the buried starburst activity and
originates outside the obscured regions. This is rather surprising in light of
the standard view that H_2 emission is directly associated with star-formation
activity. Instead, I propose that H_2 emission in these objects traces shocks
in the surrounding material, which are in turn excited by interactions with
nearby galaxies, and that powerful large-scale shocks cooling by means of H_2
emission may be much more common than previously thought. In the early
universe, a boost in H_2 emission by this process may speed up the cooling of
matter as it collapsed to form the first stars and galaxies and would make
these first structures more readily observable. | Testing cosmology with a catalogue of voids in the BOSS galaxy surveys: We present a public catalogue of voids in the Baryon Oscillation
Spectroscopic Survey (BOSS) Data Release 11 LOWZ and CMASS galaxy surveys. This
catalogue contains information on the location, sizes, densities, shapes and
bounding surfaces of 8956 independent, disjoint voids, making it the largest
public void catalogue to date. Voids are identified using a version of the
ZOBOV algorithm, the operation of which has been calibrated through tests on
mock galaxy populations in N-body simulations, as well as on a suite of 4096
mock catalogues which fully reproduce the galaxy clustering, survey masks and
selection functions. Based on this, we estimate a false positive detection rate
of 3%. Comparison with mock catalogues limits deviations of the void size
distribution from that predicted in the $\Lambda$CDM model to be less than 6%
for voids with effective radius $8<R_v<60\,h^{-1}$Mpc and in the redshift range
$0.15<z<0.7$. This could tightly constrain modified gravity scenarios and
models with a varying equation of state, but we identify systematic biases
which must be accounted for to reduce the theoretical uncertainty in the
predictions for these models to the current level of precision attained from
the data. We also examine the distribution of void densities and identify a
deficit of the deepest voids relative to $\Lambda$CDM expectations, which is
significant at more than the $3\sigma$ equivalent level. We discuss possible
explanations for this discrepancy but at present its cause remains unknown. |
Turning Around along the Cosmic Web: A bound-violation designates a case that the turn-around radius of a bound
object exceeds the upper limit put by the spherical collapse model based on the
standard $\Lambda$CDM paradigm. Given that the turn-around radius of a bound
object is a stochastic quantity and that the spherical model overly simplifies
the true gravitational collapse which actually proceeds anisotropically along
the cosmic web, the rarity of the occurrence of a bound violation may depend on
the web environment. Assuming a Planck cosmology, we numerically construct the
bound-zone peculiar velocity profiles along the cosmic web (filaments and
sheets) around the isolated groups with virial mass $M_{\rm v}\ge 3\times
10^{13}\,h^{-1}M_{\odot}$ identified in the Small MultiDark Planck simulations
and determine the radial distances at which their peculiar velocities equal the
Hubble expansion speed as the turn-around radii of the groups. It is found that
although the average turn-around radii of the isolated groups are well below
the spherical bound-limit on all mass scales, the bound violations are not
forbidden for individual groups and that the cosmic web has an effect of
reducing the rarity of the occurrence of a bound violation. Explaining that the
spherical bound limit on the turn-around radius in fact represents the
threshold distance up to which the intervention of the external gravitational
field in the bound-zone peculiar velocity profiles around the non-isolated
groups stays negligible, we discuss the possibility of using the threshold
distance scale to constrain locally the equation of state of dark energy . | The AKARI Deep Field South: A New Home for Multiwavelength Extagalactic
Astronomy: The importance of multiwavelength astronomical surveys is discussed in the
context of galaxy evolution. The AKARI Deep Field South (ADF-S) is a new, well
placed survey field that is already the subject of studies at a wide range of
wavelengths. A number of ADF-S observational programmes are discussed and the
prospects for the ADF-S as a future resource for extragalactic astronomy is
explored. |
Dynamical friction in dark matter superfluids: The evolution of black
hole binaries: The theory of superfluid dark matter is characterized by self-interacting
sub-eV particles that thermalize and condense to form a superfluid core in
galaxies. Massive black holes at the center of galaxies, however, modify the
dark matter distribution and result in a density enhancement in their vicinity
known as dark matter spikes. The presence of these spikes affects the evolution
of binary systems by modifying their gravitational wave emission and inducing
dynamical friction effects on the orbiting bodies. In this work, we assess the
role of dynamical friction for bodies moving through a superfluid core enhanced
by a central massive black hole. As a first step, we compute the dynamical
friction force experienced by bodies moving in a circular orbit. Then, we
estimate the gravitational wave dephasing of the binary, showing that the
effect of the superfluid drag force is beyond the reach of space-based
experiments like LISA, contrarily to collisionless dark matter, therefore
providing an opportunity to distinguish these dark matter models. | Dependence of the outer density profiles of halos on their mass
accretion rate: We present a systematic study of the density profiles of LCDM halos, focusing
on the outer regions, 0.1 < r/Rvir < 9. We show that the median and mean
profiles of halo samples of a given peak height exhibit significant deviations
from the universal analytic profiles discussed previously in the literature,
such as the Navarro-Frenk-White and Einasto profiles, at radii r > 0.5 R200m.
In particular, at these radii the logarithmic slope of the median density
profiles of massive or rapidly accreting halos steepens more sharply than
predicted. The steepest slope of the profiles occurs at r ~ R200m, and its
absolute value increases with increasing peak height or mass accretion rate,
reaching slopes of -4 and steeper. Importantly, we find that the outermost
density profiles at r > R200m are remarkably self-similar when radii are
rescaled by R200m. This self-similarity indicates that radii defined with
respect to the mean density are preferred for describing the structure and
evolution of the outer profiles. However, the inner density profiles are most
self-similar when radii are rescaled by R200c. We propose a new fitting formula
that describes the median and mean profiles of halo samples selected by their
peak height or mass accretion rate with accuracy < 10% at all radii, redshifts
and masses we studied, r < 9 Rvir, 0 < z < 6 and Mvir > 1.7E10 Msun/h. We
discuss observational signatures of the profile features described above, and
show that the steepening of the outer profile should be detectable in future
weak-lensing analyses of massive clusters. Such observations could be used to
estimate the mass accretion rate of cluster halos. |
Tomographic local 2D analyses of the WISExSuperCOSMOS all-sky galaxy
catalogue: The recent progress in obtaining larger and deeper galaxy catalogues is of
fundamental importance for cosmological studies, especially to robustly measure
the large scale density fluctuations in the Universe. The present work uses the
Minkowski Functionals (MF) to probe the galaxy density field from the
WISExSuperCOSMOS (WSC) all-sky catalogue by performing tomographic local
analyses in five redshift shells (of thickness $\delta z = 0.05$) in the total
range of $0.10 < z < 0.35$. Here, for the first time, the MF are applied to 2D
projections of the galaxy number count (GNC) fields with the purpose of looking
for regions in the WSC catalogue with unexpected features compared to
$\Lambda$CDM mock realisations. Our methodology reveals 1 - 3 regions of the
GNC maps in each redshift shell with an uncommon behaviour (extreme regions),
i.e., $p$-value $<$ 1.4\%. Indeed, the resulting MF curves show signatures that
suggest the uncommon behaviour to be associated with the presence of over- or
under-densities there, but contamination due to residual foregrounds is not
discarded. Additionally, even though our analyses indicate a good agreement
among data and simulations, we identify 1 highly extreme region, seemingly
associated to a large clustered distribution of galaxies. Our results confirm
the usefulness of the MF to analyse GNC maps from photometric galaxy datasets. | A wide search for obscured Active Galactic Nuclei using XMM-Newton and
WISE: We use a combination of the XMM-Newton serendipitous X-ray survey with the
optical SDSS, and the infrared WISE all-sky survey in order to check the
efficiency of the low X-ray to infrared luminosity selection method in finding
heavily obscured AGN. We select sources in the 2-8 keV X-ray band which have a
redshift determination in the SDSS catalogue. We match this sample with the
WISE catalogue, and fit the SEDs of the 2844 sources which have three, or more,
photometric data-points in the infrared. We then select the heavily obscured
AGN candidates by comparing their 12 micron AGN luminosity to the observed 2-10
keV X-ray luminosity and their expected intrinsic relation. With this approach
we find 20 candidates, and we examine their X-ray and optical spectra. Of the
20 initial candidates, we find nine (64%; out of the 14, for which X-ray
spectra could be fit) based on the X-ray spectra, and seven (78%; out of the
nine detected spectroscopically in the SDSS) based on the [OIII] line fluxes.
Combining all criteria, we determine the final number of heavily obscured AGN
to be 12-19, and the number of Compton-thick AGN to be 2-5, showing that the
method is reliable in finding obscured AGN, but not Compton-thick. However
those numbers are smaller than what would be expected from X-ray background
population synthesis models, which demonstrates how the optical-infrared
selection and the scatter of the L_x-L_MIR relation introduced by observational
constraints limit the efficiency of the method. Finally, we test popular
obscured AGN selection methods based on mid-infrared colours, and find that the
probability of an AGN to be selected by its mid-infrared colours increases with
the X-ray luminosity. However, a selection scheme based on a relatively low
X-ray luminosity and mid-infrared colours characteristic of QSOs would not
select ~25% of the heavily obscured AGN of our sample. (abridged) |
The broadening of Lyman-alpha forest absorption lines: We provide an analytical description of the line broadening of HI absorbers
in the Lyman-alpha forest resulting from Doppler broadening and Jeans
smoothing. We demonstrate that our relation captures the dependence of the
line-width on column density for narrow lines in z~3 mock spectra remarkably
well. Broad lines at a given column density arise when the underlying density
structure is more complex, and such clustering is not captured by our model.
Our understanding of the line broadening opens the way to a new method to
characterise the thermal state of the intergalactic medium and to determine the
sizes of the absorbing structures. | On the variable color of the images of a single source in a
gravitational mirage: consequences for the photometric redshift: In gravitational lensing the average colors of the images are not identical
to the average color of the source. The highly non-linear mapping of
gravitational lensing does not preserve the color balance of the source, and
this mapping is different for each image. The color distortion of the images is
illustrated using HST images of the lens SL2SJ02140. It is shown that in this
lens the color of the images is variable, reflecting the variable color of the
source. The average color of the images in SL2SJ02140 are interpreted as a
variable amplification of different sources regions with different colors. The
variation of the average image colors affects the measurements of the
photometric redshift of the images. This is especially true for SL2SJ02140
where the color variations due to the non-linear mapping of the lens simulates
pseudo redshifts variations. |
The extensive age gradient of the Carina dwarf galaxy: The evolution of small systems such as dwarf spheroidal galaxies (dSph) is
likely to have been a balance between external environmental effects and
internal processes within their own relatively shallow potential wells.
Assessing how strong such environmental interactions may have been is therefore
an important element in understanding the baryonic evolution of dSphs and their
derived dark matter distribution.
Here we present results from a wide-area CTIO/MOSAIC II photometric survey of
the Carina dSph, reaching down to about two magnitudes below the oldest main
sequence turn-off (MSTO). This data-set enables us to trace the structure of
Carina in detail out to very large distances from its center, and as a function
of stellar age.
We observe the presence of an extended structure made up primarily of ancient
MSTO stars, at distances between 25arcmin-60arcmin from Carina's center,
confirming results in the literature that Carina extends well beyond its
nominal tidal radius.
The large number statistics of our survey reveals features such as isophote
twists and tails that had gone undetected in other previous shallower surveys.
This is the first time that such unambiguous signs of tidal disruption have
been found in a Milky Way "classical" dwarf other than Sagittarius.
We also demonstrate the presence of a negative age gradient in Carina
directly from its MSTOs, and trace it out to very large distances from the
galaxy center. The signs of interaction with the Milky Way make it unclear
whether the age gradient was already in place before Carina underwent tidal
disruption. | Validating Planck SZ2 Clusters with Optical Counterparts: We perform an extensive analysis of optical counterparts of Planck PSZ2
clusters, considering matches with three recent catalogs built from SDSS data:
AMF DR9, redMaPPer (v6.3) and Wen et al (WHL). We significantly extend the
number of optical counterparts of detected Planck clusters, and characterize
the optical properties when multiple identifications in different catalogs
exist. For Planck clusters which already possess an external validation, we
analyze the redshift assignment for both optical and X--ray determinations. We
then analyze the Planck Cosmology sample and comment on redshift determination
and potential mass mis-determinations due to alignment issues. Finally, we
inspect the reconstructed $y$ map from Planck and reason on the detectability
of optical clusters. Overall, AMF DR9 main (extended) finds 485 (511) optical
matches, with 45 (55) previously unmatched PSZ2 clusters, to be compared with
the 374 optical matches already present in PSZ2. 29 of the 55 previously
unmatched clusters do not yet have a followup in the literature. 18 of these
are found in more than one SDSS catalog with consistent redshifts. We provide
redshift and mass estimates for the newly matched clusters, and discuss the
comparison with the follow-ups, when present. We find good agreement between
the redMaPPer and AMF DR9 redshift determinations. From the Planck Cosmology
sample, we find 14 clusters which merit further investigation, and discuss
possible alignment issues for 9 of these clusters. After inspecting the $y$
map, we provide a list of 229 optical clusters not included in the Planck PSZ2
catalog but showing a prominent $y$ signal. We have further investigated the 86
clusters with Planck S/N $>4.5$ using the MMF technique (applied to the Planck
HFI maps), and were able to detect 20 new cluster candidates that are not
included in the PSZ2 catalog. |
Exploring reionisation and high-z galaxy observables with recent
multi-redshift MWA upper limits on the 21-cm signal: We use the latest multi-redshift ($z=6.5-8.7$) upper limits on the 21-cm
signal from the Murchison Widefield Array (MWA) to explore astrophysical models
which are inconsistent with the data. These upper limits are achieved using 298
h of carefully excised data over four observing seasons. To explore these upper
limits in the context of reionisation astrophysics, we use 21CMMC. We then
connect the disfavoured regions of parameter space to existing observational
constraints on reionisation such as high-$z$ galaxy ultra-violet (UV)
luminosity functions, background UV photoionisation rate, intergalactic medium
(IGM) neutral fraction, the electron scattering optical depth and the soft-band
X-ray emissivity. We find the vast majority of models disfavoured by the MWA
limits are already inconsistent with existing observational constraints. These
inconsistent models arise from two classes of models: (i) `cold' reionisation
and (ii) pure matter density fluctuations (i.e. no reionisation). However, a
small subsample of models are consistent implying the existing MWA limits
provide unique information in disfavouring models of reionisation, albeit
extremely weakly. We also provide the first limits on the soft-band X-ray
emissivity from galaxies at high redshifts, finding $1\sigma$ lower limits of
$\epsilon_{{\rm X},0.5-2~{\rm keV}}\gtrsim10^{34.5}$ erg s$^{-1}$ Mpc$^{-3}$.
Finally, we recover 95 per cent disfavoured limits on the IGM spin temperature
of $\bar{T}_{\rm S}\lesssim$ 1.3, 1.4, 1.5, 1.8, 2.1, 2.4 K at $z=6.5, 6.8,
7.1, 7.8, 8.2, 8.7$. With this we infer the IGM must have undergone, at the
very least, a small amount of X-ray heating. Note, the limits on
$\epsilon_{{\rm X},0.5-2~{\rm keV}}$ and $\bar{T}_{\rm S}$ are conditional on
the IGM neutral fraction. | Accurate Analytic Mass-Scale Relations for Dark Matter Haloes of all
Masses and Redshifts: CUSP is a powerful formalism that recovers, from first principles and with no
free parameter, all the macroscopic properties of dark matter haloes found in
cosmological N-body simulations and unveils the origin of their characteristic
features. Since it is not restricted by the limitations of simulations, it
covers the whole mass and redshift ranges. In the present Paper we use CUSP to
calculate the mass-scale relations holding for halo density profiles fitted to
the usual NFW and Einasto functions in the most relevant cosmologies and for
the most usual mass definitions. We clarify the origin of these relations and
provide accurate analytic expressions holding for all masses and redshifts. The
performance of those expressions is compared to that of previous models and to
the mass-concentration relation spanning more than 20 orders of magnitude in
mass at $z=0$ obtained in recent simulations of a 100 GeV WIMP universe. |
Statistical recovery of 21cm visibilities and their power spectra with
Gaussian constrained realisations and Gibbs sampling: Radio interferometers designed to probe the 21cm signal from Cosmic Dawn and
the Epoch of Reionisation must contend with systematic effects that make it
difficult to achieve sufficient dynamic range to separate the 21cm signal from
foreground emission and other effects. For instance, the instrument's chromatic
response modulates the otherwise spectrally smooth foregrounds, making them
difficult to model, while a significant fraction of the data must be excised
due to the presence of radio frequency interference (RFI), leaving gaps in the
data. Errors in modelling the (modulated and gappy) foregrounds can easily
generate spurious contamination of what should otherwise be 21cm
signal-dominated modes. Various approaches have been developed to mitigate
these issues by (e.g.) using non-parametric reconstruction of the foregrounds,
in-painting the gaps, and weighting the data to reduce the level of
contamination. We present a Bayesian statistical method that combines these
approaches, using the coupled techniques of Gaussian constrained realisations
(GCR) and Gibbs sampling. This provides a way of drawing samples from the joint
posterior distribution of the 21cm signal modes and their power spectrum in the
presence of gappy data and an uncertain foreground model in a computationally
scalable manner. The data are weighted by an inverse covariance matrix that is
estimated as part of the inference, along with a foreground model that can then
be marginalised over. We demonstrate the application of this technique on a
simulated HERA-like delay spectrum analysis, comparing three different
approaches for accounting for the foreground components. | Origins, Structure, and Inflows of m=1 Modes in Quasi-Keplerian Disks: Simulations show eccentric disks (m=1 modes) forming around quasi-Keplerian
potentials, a topic of interest for fueling quasars, forming super-massive BHs,
planet formation and migration, explaining the origin and properties of nuclear
eccentric stellar disks like that in M31, and driving the formation of the
obscuring AGN torus. We consider the global, linear normal m=1 modes in
collisionless disks, without the restriction that the disk mass be negligible
relative to the central (Keplerian) mass. We derive their structure and key
resonance features, and show how they arise, propagate inwards, and drive both
inflow/outflow and eccentricities in the disk. We compare with hydrodynamic
simulations of such disks around a super-massive BH, with star formation, gas
cooling, and feedback. We derive the dependence of the normal mode structure on
disk structure, mass profiles, and thickness, and mode pattern speeds and
growth rates. We show that, if the disk at some radii has mass of >~10% the
central point mass, the modes are linearly unstable and are self-generating.
They arise as 'fast modes' with pattern speed of order the local angular
velocity at these radii. The characteristic global normal modes have pattern
speeds comparable to the linear growth rate, of order (G*M_0*R_0^{-3})^{1/2},
where M_0 is the central mass and R_{0} is the radius where the enclosed disk
mass ~M_{0}. They propagate inwards by exciting eccentricities towards smaller
and smaller radii, until at small radii these are 'slow modes.' With moderate
amplitude, the global normal modes can lead to shocks and significant gas
inflows at near-Eddington rates at all radii inside several ~R_0. |
Cosmological constraints on $Λ(α)$CDM models with
time-varying fine structure constant: We study the $\Lambda(\alpha)$CDM models with $\Lambda(\alpha)$ being a
function of the time-varying fine structure constant $\alpha$. We give a close
look at the constraints on two specific $\Lambda(\alpha)$CDM models with one
and two model parameters, respectively, based on the cosmological observational
measurements along with 313 data points for the time-varying $\alpha$. We find
that the model parameters are constrained to be around $10^{-4}$, which are
similar to the results discussed previously but more accurately. | The spectral energy distributions of K+A galaxies from the UV to the
mid-IR: stellar populations, star formation and hot dust: We present spectrum synthesis fits to 808 K+A galaxies selected from the
Sloan Digital Sky Survey (SDSS) and population synthesis of their spectral
energy distributions, extending from the far UV (0.15 micron) to the mid IR (22
micron), based on the results of STARLIGHT code fitting to the SDSS spectra.
Our modelling shows that K+A galaxies have undergone a large starburst,
involving a median 50% of their present stellar masses, superposed over an
older stellar population. The metal abundance of the intermediate-age stars
shows that star formation did not take place in pristine gas, but was part of a
dramatic increase in the star formation rates for originally gas-rich objects.
We find no evidence for on-going QSO activity in the UV, which is well modeled
by the emission of intermediate-age stars. We use K+A galaxies as local
counterparts of high redshift objects to test for the presence of Thermally
Pulsing AGB stars in similarly-aged populations and find no excess in the
infrared due to emission from such stars, arguing that more distant galaxies
are indeed old and massive at their redshift. All of our galaxies show
significant excesses in the mid-IR compared to the light from their stars. We
fit this ad hoc with a 300K blackbody. Possible sources include TP-AGB stars,
obscured young star clusters and hidden AGNs, heating a significant dust
component. |
An Improved [O III] Line Width to Stellar Velocity Dispersion
Calibration: Curvature, Scatter, and Lack of Evolution in the Black-Hole Mass
Versus Stellar Velocity Dispersion Relationship: An improved transformation of the full width at half maxima (FWHM) of the [O
III] 5007 line in AGNs to the stellar velocity dispersion, sigma, of the host
galaxy is given. This significantly reduces the systematic errors in using the
[O III] FWHM as a proxy for sigma. AGN black hole masses, M, estimated using
the Dibai single epoch spectrum method, are combined with the new estimates of
sigma to give a revised AGN M-sigma relationship extending up to high masses.
This shows that the masses of the most massive black holes are systematically
higher than predicted by extrapolation of M \propto sigma^4 to high masses.
This supports recent suggestions that stellar dynamical masses of the most
massive black holes have been systematically underestimated. The steepening of
the M-sigma relationship is consistent with the absence of very high sigma
galaxies in the local universe and with the curvature of the Faber-Jackson
relationship. There appears to be significantly less intrinsic scatter in the
M-sigma relationship for galaxies with black hole masses > 10^9 solar masses.
It is speculated that this is connected with the core elliptical versus
extra-light elliptical dichotomy. The low scatter in the high end of the
M-sigma relationship implies that the transformation proposed here and the
Dibai method are good indicators of stellar velocity dispersion and mass
respectively. There is no evidence for evolution of the M-sigma relationship
over time. | Exploring the relation between turbulent velocity and density
fluctuations in the stratified intracluster medium: The dynamics of the intracluster medium (ICM) is affected by turbulence
driven by several processes, such as mergers, accretion and feedback from
active galactic nuclei. X-ray surface brightness fluctuations have been used to
constrain turbulence in galaxy clusters. Here, we use simulations to further
investigate the relation between gas density and turbulent velocity
fluctuations, with a focus on the effect of the stratification of the ICM. In
this work, we studied the turbulence driven by hierarchical accretion by
analysing a sample of galaxy clusters simulated with the cosmological code
ENZO. We used a fixed scale filtering approach to disentangle laminar from
turbulent flows. In dynamically perturbed galaxy clusters, we found a relation
between the root mean square of density and velocity fluctuations, albeit with
a different slope than previously reported. The Richardson number is a
parameter that represents the ratio between turbulence and buoyancy, and we
found that this variable has a strong dependence on the filtering scale.
However, we could not detect any strong relation between the Richardson number
and the logarithmic density fluctuations, in contrast to results by recent and
more idealised simulations. In particular, we find a strong effect from radial
accretion, which appears to be the main driver for the gas fluctuations. The
ubiquitous radial bias in the dynamics of the ICM suggests that homogeneity and
isotropy are not always valid assumptions, even if the turbulent spectra follow
Kolmogorov's scaling. Finally, we find that the slope of the velocity and
density spectra are independent of cluster-centric radii. |
Galaxy mergers on a moving mesh: a comparison with smoothed-particle
hydrodynamics: Galaxy mergers have been investigated for decades using smoothed particle
hydrodynamics (SPH), but recent work highlighting inaccuracies inherent in the
traditional SPH technique calls into question the reliability of previous
studies. We explore this issue by comparing a suite of Gadget-3 SPH simulations
of idealised (i.e., non-cosmological) isolated discs and galaxy mergers with
otherwise identical calculations performed using the moving-mesh code Arepo.
When black hole (BH) accretion and active galactic nucleus (AGN) feedback are
not included, the star formation histories (SFHs) obtained from the two codes
agree well. When BHs are included, the code- and resolution-dependent
variations in the SFHs are more significant, but the agreement is still good,
and the stellar mass formed over the course of a simulation is robust to
variations in the numerical method. During a merger, the gas morphology and
phase structure are initially similar prior to the starburst phase. However,
once a hot gaseous halo has formed from shock heating and AGN feedback (when
included), the agreement is less good. In particular, during the post-starburst
phase, the SPH simulations feature more prominent hot gaseous haloes and
spurious clumps, whereas with Arepo, gas clumps and filaments are less apparent
and the hot halo gas can cool more efficiently. We discuss the origin of these
differences and explain why the SPH technique yields trustworthy results for
some applications (such as the idealised isolated disc and galaxy merger
simulations presented here) but not others (e.g., gas flows onto galaxies in
cosmological hydrodynamical simulations). | Matrix Formalism of Excursion Set Theory: A new approach to statistics
of dark matter halo counting: Excursion set theory (EST) is an analytical framework to study the
large-scale structure of the Universe. EST introduces a procedure to calculate
the number density of structures by relating the cosmological linear
perturbation theory to the nonlinear structures in late time. In this work, we
introduce a novel approach to reformulate the EST in matrix formalism. We
propose that the matrix representation of EST will facilitate the calculations
in this framework. The method is to discretize the two-dimensional plane of
variance and density contrast of EST, where the trajectories for each point in
the Universe lived there. The probability of having a density contrast in a
chosen variance is represented by a probability ket. Naturally, the concept of
the transition matrix pops up to define the trajectories. We also define the
probability transition rate which is used to obtain the first up-crossing of
trajectories and the number count of the structures. In this work we show that
the discretization let us study the non-Markov processes by forcing them to
look like a Wiener process. Also we discuss that the zero drift processes with
Gaussian and also non-Gaussian initial conditions can be studied by this
formalism. The continuous limit of the formalism is discussed, and the known
Fokker-Planck dispersion equation is recovered. Finally we show that the
probability of the most massive progenitors can be extracted in this framework. |
Investigating the compatibility of exact solutions in Weyl-type $f(Q,T)$
gravity with observational data: In this study, we investigate the dynamics of the Universe during the
observed late-time acceleration phase within the framework of the Weyl-type
$f(Q,T)$ theory. Specifically, we consider a well-motivated model with the
functional form $f(Q,T)=\alpha Q+\frac{\beta }{6\kappa ^2}T$, where $Q$
represents the scalar of non-metricity and $T$ denotes the trace of the
energy-momentum tensor. In this context, the non-metricity $Q_{\mu\alpha\beta}$
of the space-time is established by the vector field $w_\mu$. The parameters
$\alpha$ and $\beta$ govern the gravitational field and its interaction with
the matter content of the Universe. By considering the case of dust matter, we
obtain exact solutions for the field equations and observe that the Hubble
parameter $H(z)$ follows a power-law behavior with respect to redshift $z$. To
constrain the model parameters, we analyze various datasets including the
$Hubble$, $Pantheon$ datasets, and their combination. Our results indicate that
the Weyl-type $f(Q,T)$ theory offers a viable alternative to explain the
observed late-time acceleration of the Universe avoiding the use of dark
energy. | Substructure in the Most Massive GEEC Groups: Field-like Populations in
Dynamically Active Groups: The presence of substructure in galaxy groups and clusters is believed to be
a sign of recent galaxy accretion and can be used not only to probe the
assembly history of these structures, but also the evolution of their member
galaxies. Using the Dressler-Shectman (DS) Test, we study substructure in a
sample of intermediate redshift (z ~ 0.4) galaxy groups from the Group
Environment and Evolution Collaboration (GEEC) group catalog. We find that 4 of
the 15 rich GEEC groups, with an average velocity dispersion of ~525 km s-1,
are identified as having significant substructure. The identified regions of
localized substructure lie on the group outskirts and in some cases appear to
be infalling. In a comparison of galaxy properties for the members of groups
with and without substructure, we find that the groups with substructure have a
significantly higher fraction of blue and star-forming galaxies and a parent
colour distribution that resembles that of the field population rather than the
overall group population. In addition, we observe correlations between the
detection of substructure and other dynamical measures, such as velocity
distributions and velocity dispersion profiles. Based on this analysis, we
conclude that some galaxy groups contain significant substructure and that
these groups have properties and galaxy populations that differ from groups
with no detected substructure. These results indicate that the substructure
galaxies, which lie preferentially on the group outskirts and could be
infalling, do not exhibit signs of environmental effects, since little or no
star-formation quenching is observed in these systems. |
Water Masers Associated with Star Formation in the Antennae Galaxies: We present Very Large Array observations with 80 milliarcsecond resolution
(~9 pc) of the recently discovered Galactic-analog water masers in the Antennae
interacting galaxies (NGC 4038/NGC 4039; Arp244). Three regions of water maser
emission are detected: two in the ``interaction region'' (IAR) and the third
~5.6'' (> 600 pc) west of the NGC 4039 nucleus. The isotropic water maser
luminosities range from 1.3 to 7.7 L_sun. All three maser regions are mostly
obscured in the optical/near-infrared continuum, and are coincident with
massive CO-identified molecular clouds. The water maser velocities are in
excellent agreement with those of the molecular gas. We also present archival
VLA 3.6 cm data with ~0.28" (~30 pc) and ~0.8" (~90 pc) resolution toward the
maser locations. All three maser regions are coincident with compact 3.6 cm
radio continuum emission, and two are dominated by thermal ionized gas,
suggesting the presence of natal super star clusters containing the equivalent
of a few thousand O stars. We also present detailed comparisons between the
radio data and existing HST ACS (optical) and NICMOS (near-IR) data and find
that both maser regions in the IAR are also associated with Pa\alpha emission
and neither source is detected shortward of 2 microns. These results highlight
the potential of using Galactic-analog water masers to pinpoint sites of young
super star cluster formation with exquisite angular resolution. | Non-Gaussianity and the CMB Bispectrum: confusion between Primordial and
Lensing-Rees Sciama contribution?: We revisit the predictions for the expected Cosmic Microwave Background
bispectrum signal from the primary-lensing-Rees-Sciama correlation; we point
out that it can be a significant contaminant to the bispectrum signal from
primordial non-Gaussianity of the local type. This non-Gaussianity, usually
parameterized by the non-Gaussian parameter f_NL, arises, for example, in
multi-field inflation. In particular both signals are frequency independent,
and are maximized for nearly squeezed configurations. While their detailed
scale-dependence and harmonic imprints are different for generic bispectrum
shapes, we show that, if not included in the modeling, the
primary-lensing-Rees-Sciama contribution yields an effective f_{NL} of 10 when
using a bispectrum estimator optimized for local non-Gaussianity. Considering
that expected 1-sigma errors on f_{NL} are < 10 from forthcoming experiments,
we conclude that the contribution from this signal must be included in future
constraints on f_{NL} from the Cosmic Microwave Background bispectrum. |
Loop-Induced Stochastic Bias at Small Wavevectors: Primordial non-Gaussianities enhanced at small wavevectors can induce a power
spectrum of the galaxy overdensity that differs greatly from that of the matter
overdensity at large length scales. In previous work, it was shown that
"squeezed" three-point and "collapsed" four-point functions of the curvature
perturbation $\zeta$ can generate these non-Gaussianities and give rise to
so-called scale-dependent and stochastic bias in the galaxy overdensity power
spectrum. We explore a third way to generate non-Gaussianities enhanced at
small wavevectors: the infrared behavior of quantum loop contributions to the
four-point correlations of $\zeta$. We show that these loop effects lead to
stochastic bias, which can be observable in the context of quasi-single field
inflation. | Closed String Thermodynamics and a Blue Tensor Spectrum: The BICEP-2 team has reported the detection of primordial cosmic microwave
background B-mode polarization, with hints of a suppression of power at large
angular scales relative to smaller scales. Provided that the B-mode
polarization is due to primordial gravitational waves, this might imply a blue
tilt of the primordial gravitational wave spectrum. Such a tilt would be
incompatible with standard inflationary models, although it was predicted some
years ago in the context of a mechanism that thermally generates the primordial
perturbations through a Hagedorn phase of string cosmology. The purpose of this
note is to encourage greater scrutiny of the data with priors informed by a
model that is immediately falsifiable, but which \textit{predicts} features
that might be favoured by the data-- namely a blue tensor tilt with an induced
and complimentary red tilt to the scalar spectrum, with a naturally large
tensor to scalar ratio that relates to both. |
Recovering dark-matter clustering from galaxies with Gaussianization: The Gaussianization transform has been proposed as a method to remove the
issues of scale-dependent galaxy bias and nonlinearity from galaxy clustering
statistics, but these benefits have yet to be thoroughly tested for realistic
galaxy samples. In this paper, we test the effectiveness of the Gaussianization
transform for different galaxy types by applying it to realistic simulated blue
and red galaxy samples. We show that in real space, the shapes of the
Gaussianized power spectra of both red and blue galaxies agree with that of the
underlying dark matter, with the initial power spectrum, and with each other to
smaller scales than do the statistics of the usual (untransformed) density
field. However, we find that the agreement in the Gaussianized statistics
breaks down in redshift space. We attribute this to the fact that red and blue
galaxies exhibit very different fingers of god in redshift space. After
applying a finger-of-god compression, the agreement on small scales between the
Gaussianized power spectra is restored. We also compare the Gaussianization
transform to the clipped galaxy density field and find that while both methods
are effective in real space, they have more complicated behaviour in redshift
space. Overall, we find that Gaussianization can be useful in recovering the
shape of the underlying dark matter power spectrum to k ~ 0.5 h/Mpc and of the
initial power spectrum to k ~ 0.4 h/Mpc in certain cases at z = 0. | Tensor Modes in Bigravity: Primordial to Present: Massive bigravity, a theoretically consistent modification of general
relativity with an additional dynamical rank two tensor, successfully describes
the observed accelerated expansion of the Universe without a cosmological
constant. Recent analyses of perturbations around a cosmological background
have revealed power law instabilities in both scalar and tensor perturbations,
motivating an analysis of the initial conditions, evolution, and cosmological
observables to determine the viability of these theories. In this paper we
focus on the tensor sector, and study a primordial stochastic gravitational
wave background in massive bigravity. The phenomenology can differ from
standard General Relativity due to non-trivial mixing between the two
linearized tensor fluctuations in the theory, only one of which couples to
matter. We study perturbations about two classes of cosmological solutions in
bigravity, computing the tensor contribution to the temperature anisotropies in
the Cosmic Microwave Background radiation and the present stochastic
gravitational wave background. The result is strongly dependent on the choice
of cosmological background and initial conditions. One class of background
solution generically displaying tremendous growth in the amplitude of
large-wavelength gravitational waves, while the other remains observationally
indistinguishable from standard General Relativity for a wide variety of
initial conditions. We analyze the initial conditions for tensor modes expected
in an inflationary cosmology, finding again that there is a strong dependence
on the assumed background. For one choice of background, the semi-classical
theory is beyond the perturbative regime. For the other choice, inflation
generically yields initial conditions that, when evolved, give rise to a
stochastic background observationally indistinguishable from standard General
Relativity. |
Cosmic bubble and domain wall instabilities III: The role of oscillons
in three-dimensional bubble collisions: We study collisions between pairs of bubbles nucleated in an ambient false
vacuum. For the first time, we include the effects of small initial (quantum)
fluctuations around the instanton profiles describing the most likely initial
bubble profile. Past studies of this problem neglect these fluctuations and
work under the assumption that the collisions posess an exact SO(2,1) symmetry.
We use three-dimensional lattice simulations to demonstrate that for
double-well potentials, small initial perturbations to this symmetry can be
amplified as the system evolves. Initially the amplification is well-described
by linear perturbation theory around the SO(2,1) background, but the onset of
strong nonlinearities amongst the fluctuations quickly leads to a drastic
breaking of the original SO(2,1) symmetry and the production of oscillons in
the collision region. We explore several single-field models, and we find it is
hard to both realize inflation inside of a bubble and produce oscillons in a
collision. Finally, we extend our results to a simple two-field model. The
additional freedom allowed by the second field allows us to construct viable
inflationary models that allow oscillon production in collisions. The breaking
of the SO(2,1) symmetry allows for a new class of observational signatures from
bubble collisions that do not posess azimuthal symmetry, including the
production of gravitational waves which cannot be supported by an SO(2,1)
spacetime. | Dressed Power-law Inflation with Cuscuton: We study dressed inflation with a cuscuton and find a novel exact power-law
solution. It is well known that the conventional power-law inflation is
inconsistent with the Planck data. In contrast to this standard lore, we find
that power-law inflation with a cuscuton can be reconciled with the Planck
data. Moreover, we argue that the cuscuton generally ameliorates inflation
models so that predictions are consistent with observations. |
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