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Evidence for Primordial Black Hole Final Evaporation: Swift, BATSE and
KONUS and Comparisons of VSGRBs and Observations of VSB That Have PBH Time
Signatures: More than a decade ago we identified a class of VSGRB (T90 < 100 ms) as
having unusual properties: (1) galactic position asymmetry, (2) very hard gamma
spectrum, (3) possible evidence for galactic origin of these events. We now
study the recent Swift data and show that a VSGRB enhancement consistent BATSE
and KONUS exists. We estimate that this is now a total 4.5sigma observation. We
then study the VSB for evidence of the time structure expected for PBH
evaporation. Several of the events show the general time structure expected for
PBH evaporation. If correct, then PBH must exist in this galaxy. Since even
large detectors like BATSE record only a few VSB per year the density of PBH
can still be very small and it is hard to predict a rate for the Fermi
spacecraft LAT. | The [O III] Nebula of the Merger Remnant NGC 7252: A Likely Faint
Ionization Echo: We present images and spectra of a ~10 kpc-sized emission-line nebulosity
discovered in the prototypical merger remnant NGC 7252 and dubbed the `[O III]
nebula' because of its dominant [O III]_5007 line. This nebula seems to yield
the first sign of episodic AGN activity still occurring in the remnant, ~220
Myr after the coalescence of two gas-rich galaxies. Its location and kinematics
suggest it belongs to a stream of tidal-tail gas falling back into the remnant.
Its integrated [O III]_5007 luminosity is 1.4x10^40 erg/s, and its spectrum
features some high-excitation lines, including He II_4686. In diagnostic line-
ratio diagrams, the nebula lies in the domain of Seyfert galaxies, suggesting
that it is photoionized by a source with a power-law spectrum. Yet, a search
for AGN activity in NGC 7252 from X-rays to radio wavelengths yields no
detection, with the most stringent upper limit set by X-ray observations. The
upper luminosity limit of L_{2-10 keV,0} < 5x10^39 erg/s estimated for the
nucleus is ~10^3 times lower than the minimum ionizing luminosity of >5x10^42
erg/s necessary to excite the nebula. This large discrepancy suggests that the
nebula is a faint ionization echo excited by a mildly active nucleus that has
declined by ~3 orders of magnitude over the past 20,000-200,000 years. In many
ways this nebula resembles the prototypical `Hanny's Voorwerp' near IC 2497,
but its size is 3x smaller and its [O III] luminosity ~100x lower. We propose
that it be classified as an extended emission-line region (EELR). The [O III]
nebula is then the lowest-luminosity ionization echo and EELR discovered so
far, indicative of recent, probably sputtering AGN activity of Seyfert-like
intensity in NGC 7252. |
Quasi-periodical features in the distribution of Luminous Red Galaxies: A statistical analysis of radial distributions of Luminous Red Galaxies
(LRGs) from the Sloan Digital Sky Survey (SDSS DR7) catalogue within an
interval $0.16 \leq z \leq 0.47$ is carried out. We found that the radial
distribution of $\sim$ 106,000 LRGs incorporates a few quasi-periodical
components relatively to a variable $\eta$, dimensionless line-of-sight
comoving distance calculated for the $\Lambda$CDM cosmological model. The most
significant peaks of the power spectra are obtained for two close periodicities
corresponding to the spatial comoving scales $(135 \pm 12) h^{-1}$ Mpc and
$(101 \pm 6)h^{-1}$ Mpc. The latter one is dominant and consistent with the
characteristic scale of the baryon acoustic oscillations. We analyse also the
radial distributions of two other selected LRG samples: $\sim$ 33,400 bright
LRGs ($-23.2 < M \leq -21.8$) and $\sim$ 60,300 all LRGs within a rectangle
region on the sky, and show differences of the quasi-periodical features
characteristic for different samples. Being confirmed the results would allow
to give preference of the spatial against temporal models which could explain
the quasi-periodicities discussed here. As a caveat we show that estimations of
the significance levels of the peaks strongly depend on a smoothed radial
function (trend) as well as characteristics of random fluctuations. | Limits on the fluctuating part of $y$-type distortion monopole from
Planck and SPT results: We use the published Planck and SPT cluster catalogs and recently published
$y$-distortion maps to put strong observational limits on the contribution of
the fluctuating part of the $y$-type distortions to the $y$-distortion
monopole. Our bounds are $5.4\times 10^{-8} < \langle y\rangle < 2.2\times
10^{-6}$. Our upper bound is a factor of 6.8 stronger than the currently best
upper $95\%$ confidence limit from COBE-FIRAS of $\langle y\rangle <15\times
10^{-6}$. In the standard cosmology, large scale structure is the only source
of such distortions and our limits therefore constrain the baryonic physics
involved in the formation of the large scale structure. Our lower limit, from
the detected clusters in the Planck and SPT catalogs, also implies that a
Pixie-like experiment should detect the $y$-distortion monopole at
$>27$-$\sigma$. The biggest sources of uncertainty in our upper limit are the
monopole offsets between different HFI channel maps that we estimate to be
$<10^{-6}$. |
Planck Constraint on Relic Primordial Black Holes: We investigate constraints on the abundance of primordial black holes (PBHs)
in the mass range 10^{15}-10^{17} g using data from the Cosmic Microwave
Background (CMB) and MeV extragalactic gamma-ray background (EGB). Hawking
radiation from PBHs with lifetime greater than the age of the universe leaves
an imprint on the CMB through modification of the ionization history and the
damping of CMB anisotropies. Using a model for redshift dependent energy
injection efficiencies, we show that a combination of temperature and
polarization data from Planck provides the strongest constraint on the
abundance of PBHs for masses \sim 10^{15}-10^{16} g, while the EGB dominates
for masses \gtrsim 10^{16} g. Both the CMB and EGB now rule out PBHs as the
dominant component of dark matter for masses \sim 10^{16}-10^{17} g. Planned
MeV gamma-ray observatories are ideal for further improving constraints on PBHs
in this mass range. | An Effective Field Theory Analysis of the First LUX Dark Matter Search: The Large Underground Xenon (LUX) dark matter search was a 250-kg active mass
dual-phase time projection chamber that operated by detecting light and
ionization signals from particles incident on a xenon target. In December 2015,
LUX reported a minimum 90% upper C.L. of 6e-46 cm^2 on the spin-independent
WIMP-nucleon elastic scattering cross section based on a 1.4e4 kg*day exposure
in its first science run. Tension between experiments and the absence of a
definitive positive detection suggest it would be prudent to search for WIMPs
outside the standard spin-independent/spin-dependent paradigm. Recent
theoretical work has identified a complete basis of 14 independent effective
field theory (EFT) operators to describe WIMP-nucleon interactions. In addition
to spin-independent and spin-dependent nuclear responses, these operators can
produce novel responses such as angular-momentum-dependent and spin-orbit
couplings. Here we report on a search for all 14 of these EFT couplings with
data from LUX's first science run. Limits are placed on each coupling as a
function of WIMP mass. |
Deep Spectroscopy of Ultra-Strong Emission Line Galaxies: Ultra strong emission-line galaxies (USELs) with extremely high equivalent
widths (EW(H beta) > 30A) can be used to pick out galaxies of extremely low
metallicity in the z=0-1 redshift range. Large numbers of these objects are
easily detected in deep narrow band searches and, since most have detectable
[OIII] 4363, their metallicities determined using the direct method. These
large samples hold the possibility for determining if there is a metallicity
floor for the galaxy population. Here we describe results of an extensive
spectroscopic follow-up of the Kakazu et al. (2007) catalog of 542 USELs using
the DEIMOS spectrograph on Keck, with high S/N spectra of 348 galaxies. The two
lowest metallicity galaxies in our sample have 12+log(O/H)=6.97+/-0.17 and
7.25+/-0.03 -- values comparable to the lowest metallicity galaxies found to
date. We determine an empirical metallicity-R23 parameter relation for our
sample, and compare this to the relationship for low redshift galaxies. The
determined metallicity-luminosity relation is compared with those of magnitude
selected samples in the same redshift range. The emission line selected
galaxies show a metal-luminosity relation where the metallicity decreases with
luminosity and they appear to define the lower bound of the galaxy metallicity
distribution at a given continuum luminosity. We also compute the H alpha
luminosity function of the USELs as a function of redshift and use this to
compute an upper bound on the Ly alpha emitter luminosity function over the
z=0-1 redshift range. | Cosmic mysteries and the hydrogen 21-cm line: bridging the gap with
lunar observations: The hydrogen 21-cm signal is predicted to be the richest probe of the young
Universe including eras known as the cosmic Dark Ages, the Cosmic Dawn when the
first star and black hole formed, and the Epoch of Reionization. This signal
holds the key to deciphering processes that take place at the early stages of
cosmic history. In this opinion piece, we discuss the potential scientific
merit of lunar observations of the 21-cm signal and their advantages over more
affordable terrestrial efforts. The moon is a prime location for radio
cosmology which will enable precision observations of the low-frequency radio
sky. The uniqueness of such observations is that they will provide an
unparalleled opportunity to test cosmology and the nature of dark matter using
the Dark Ages 21-cm signal. No less enticing is the opportunity to obtain a
much clearer picture of Cosmic Dawn than what is achievable from the ground,
which will allow us to probe properties of the first stars and black holes. |
Dynamically Driven Evolution of the Interstellar Medium in M51: We report the highest-fidelity observations of the spiral galaxy M51 in CO
emission, revealing the evolution of giant molecular clouds (GMCs) vis-a-vis
the large-scale galactic structure and dynamics. The most massive GMCs
(so-called GMAs) are first assembled and then broken up as the gas flow through
the spiral arms. The GMAs and their H2 molecules are not fully dissociated into
atomic gas as predicted in stellar feedback scenarios, but are fragmented into
smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as
the chains of GMCs that emerge from the spiral arms into interarm regions. The
kinematic shear within the spiral arms is sufficient to unbind the GMAs against
self-gravity. We conclude that the evolution of GMCs is driven by large-scale
galactic dynamics --their coagulation into GMAs is due to spiral arm streaming
motions upon entering the arms, followed by fragmentation due to shear as they
leave the arms on the downstream side. In M51, the majority of the gas remains
molecular from arm entry through the inter-arm region and into the next spiral
arm passage. | Non-Gaussianities from isocurvature modes: This contribution discusses isocurvature modes, in particular the
non-Gaussianities of local type generated by these modes. Since the
isocurvature transfer functions differ from the adiabatic one, the coexistence
of a primordial isocurvature mode with the usual adiabatic mode leads to a rich
structure of the angular bispectrum, which can be decomposed into six
elementary bispectra. Future analysis of the CMB data will enable to measure
their relative weights, or at least constrain them. Non-Gaussianity thus
provides a new window on isocurvature modes. This is particularly relevant for
some scenarios, such as those presented here, which generate isocurvature modes
whose contribution in the power spectrum is suppressed, as required by present
data, but whose contribution in the non-Gaussianities could be dominant and
measurable. |
An Optical Catalog of Galaxy Clusters Obtained from an Adaptive Matched
Filter Finder Applied to SDSS DR9 Data: We present a new galaxy cluster catalog constructed from SDSS DR9 using an
Adaptive Matched Filter technique. Our main catalog has 46,479 galaxy clusters
with richness $\Lambda_{200} > 20$ in the redshift range 0.045 $\le z <$ 0.641
in $\sim$11,500 $deg^{2}$ of the sky. Angular position, richness, core and
virial radii and redshift estimates for these clusters, as well as their error
analysis are provided. We also provide an extended version with a lower
richness cut, containing 79,368 clusters. This version, in addition to the
clusters in the main catalog, also contains those clusters (with richness
$<20$) which have a one-to-one match in the DR8 catalog developed by Wen et al
(WHL). We obtain probabilities for cluster membership for each galaxy and
implement several procedures for the identification and removal of false
cluster detections.
We compare our catalog with other SDSS-based ones such as the redMaPPer
(26,350 clusters) and the WHL (132,684 clusters) in the same area of the sky
and in the overlapping redshift range. We match 97$\%$ of the richest Abell
clusters, the same as WHL, while redMaPPer matches $\sim 90\%$ of these
clusters. Considering AMF DR9 richness bins, redMaPPer consistently does not
possess one-to-one matches for $\sim$20$\%$ AMF DR9 clusters with
$\Lambda_{200}>40$, while WHL matches $\geq$70$\%$ of these missed clusters on
average. We also match the AMF catalog with the X-ray cluster catalogs BAX,
MCXC and a combined catalog from NORAS and REFLEX. We consistently obtain a
greater number of one-to-one matches for X-ray clusters across higher
luminosity bins ($L_x>6 \times 10^{44}$ ergs/sec) than redMaPPer while WHL
matches the most clusters overall. For the most luminous clusters ($L_x>8$),
our catalog performs equivalently to WHL. This new catalog provides a wider
sample than redMaPPer while retaining many fewer objects than WHL. | Galaxy Clusters around radio-loud AGN at 1.3 < z < 3.2 as seen by
Spitzer: We report the first results from the Clusters Around Radio-Loud AGN (CARLA)
program, a Cycle 7 and 8 Spitzer Space Telescope snapshot program to
investigate the environments of a large sample of obscured and unobscured
luminous radio-loud AGN at 1.2 < z < 3.2. These data, obtained for 387 fields,
reach 3.6 and 4.5 um depths of [3.6] (AB) = 22.6 and [4.5] (AB) = 22.9 at the
95% completeness level, which is two to three times fainter than L* in this
redshift range. By using the color cut [3.6]-[4.5] > -0.1 (AB), which
efficiently selects high-redshift (z > 1.3) galaxies of all types, we identify
galaxy cluster member candidates in the fields of the radio-loud AGN. The local
density of these IRAC-selected sources is compared to the density of similarly
selected sources in blank fields. We find that 92% of the radio-loud AGN reside
in environments richer than average. The majority (55%) of the radio-loud AGN
fields are found to be overdense at a > 2 {\sigma} level; 10% are overdense at
a > 5 {\sigma} level. A clear rise in surface density of IRAC-selected sources
towards the position of the radio-loud AGN strongly supports an association of
the majority of the IRAC-selected sources with the radio-loud AGN. Our results
provide solid statistical evidence that radio-loud AGN are likely beacons for
finding high-redshift galaxy (proto-)clusters. We investigate how environment
depends on AGN type (unobscured radio-loud quasars vs. obscured radio
galaxies), radio luminosity and redshift, finding no correlation with either
AGN type or radio luminosity. We find a decrease in density with redshift,
consistent with galaxy evolution for this uniform, flux-limited survey. These
results are consistent with expectations from the orientation-driven AGN
unification model, at least for the high radio luminosity regimes considered in
this sample. |
The impact of dark energy perturbations on the growth index: We show that in clustering dark energy models the growth index of linear
matter perturbations, $\gamma$, can be much lower than in $\Lambda$CDM or
smooth quintessence models and present a strong variation with redshift. We
find that the impact of dark energy perturbations on $\gamma$ is enhanced if
the dark energy equation of state has a large and rapid decay at low redshift.
We study four different models with these features and show that we may have
$0.33<\gamma\left(z\right)<0.48$ at $0<z<3$. We also show that the constant
$\gamma$ parametrization for the growth rate, $f=d\ln\delta_{m}/d\ln
a=\Omega_{m}^{\gamma}$, is a few percent inaccurate for such models and that a
redshift dependent parametrization for $\gamma$ can provide about four times
more accurate fits for $f$. We discuss the robustness of the growth index to
distinguish between General Relativity with clustering dark energy and modified
gravity models, finding that some $f\left(R\right)$ and clustering dark energy
models can present similar values for $\gamma$. | Suppression of Star Formation in the central 200 kpc of a z = 1.4 Galaxy
Cluster [Erratum added]: We present the results of an extended narrow-band H{\alpha} study of the
massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. This paper represents a
follow up study to our previous investigation of star-formation in the cluster
centre, extending our analysis out to a projected cluster radius of 1.5 Mpc.
Using the Near InfraRed Imager and Spectrograph (NIRI) on Gemini North we
obtained deep H narrow-band imaging corresponding to the rest-frame wavelength
of H{\alpha} at the cluster's redshift. We identify a total of 163 potential
cluster members in both pointings, excluding stars based on their near-IR
colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are
spectroscopically confirmed cluster members, and 20% are excess line-emitters.
We find no evidence of star formation activity within a radius of 200 kpc of
the brightest cluster galaxy in the cluster core. Dust-corrected star formation
rates (SFR) of excess emitters outside this cluster quenching radius, RQ \sim
200 kpc, are on average <SFR> = 2.7 \pm 1.0 M\odot yr-1, but do not show
evidence of increasing star-formation rates toward the extreme 1.5 Mpc radius
of the cluster. No individual cluster galaxy exceeds an SFR of 6 M\odot yr-1 .
Massive galaxies (log M\ast /M\odot > 10.75) all have low specific SFRs (SSFRs,
i.e. SFR per unit stellar mass). At fixed stellar mass, galaxies in the cluster
centre have lower SSFRs than the rest of the cluster galaxies, which in turn
have lower SSFRs than field galaxies at the same redshift by a factor of a few
to 10. For the first time we can demonstrate through measurements of individual
SFRs that already at very early epochs (at an age of the Universe of \sim4.5
Gyr) the suppression of star-formation is an effect of the cluster environment
which persists at fixed galaxy stellar mass. [Erratum added after the original
paper] |
The BAHAMAS project: Effects of a running scalar spectral index on
large-scale structure: Recent analyses of the cosmic microwave background (CMB) and the Lyman-alpha
forest indicate a mild preference for a deviation from a power law primordial
matter power spectrum (a so-called negative `running'). We use an extension to
the BAHAMAS suite of cosmological hydrodynamic simulations to explore the
effects that a running scalar spectral index has on large-scale structure
(LSS), using Planck CMB constraints to initialize the simulations. We focus on
5 key statistics: i) the non-linear matter power spectrum ii) the halo mass
function; iii) the halo two-point auto correlation function; iv) total mass
halo density profiles; and v) the halo concentration-mass relation. In terms of
the matter power spectrum, we find that a running scalar spectral index affects
all k-scales examined in this study, with a negative (positive) running leading
to an amplification (suppression) of power. These effects should be easily
detectable with upcoming surveys such as LSST and Euclid. In the mass range
sampled, a positive running leads to an increase in the mass of galaxy groups
and clusters, with the favoured negative running leading to a decrease in mass
of lower-mass (M <~ 10^13 M_solar) halos, but an increase for the most massive
(M >~ 10^13 M_solar) halos. Changes in the mass are generally confined to 5-10%
which, while not insignificant, cannot by itself reconcile the claimed tension
between the primary CMB and cluster number counts. We find that running does
not significantly affect the shapes of density profiles of matched halos,
changing only their amplitude. Finally, we demonstrate that the observed
effects on LSS due to a running scalar spectral index are separable from those
of baryonic effects to typically a few percent precision. | Interacting viscous dark fluids: We revise the conditions for the physical viability of a cosmological model
in which dark matter has bulk viscosity and also interacts with dark energy. We
have also included radiation and baryonic matter components; all matter
components are represented by perfect fluids, except the dark matter, that is
treated as an imperfect fluid. We impose upon the model the condition of a
complete cosmological dynamics that results in an either null or negative bulk
viscosity, but the latter also disagrees with the Local Second Law of
Thermodynamics. The model is also compared with cosmological observations at
different redshifts: type Ia supernova, the shift parameter of CMB, the
acoustic peak of BAO, and the Hubble parameter H(z). In general, observations
consistently point out to a negative value of the bulk viscous coefficient, and
in overall the fitting procedure shows no preference for the model over the
standard LCDM model. |
Broad spectral line and continuum variabilities in QSO spectra induced
by microlensing of diffusive massive substructure: We investigate the variability of the continuum and broad lines in QSO
spectra (particularly in the H$\beta$ line and continuum at $\lambda$ 5100 \AA
) caused by microlensing of a diffuse massive structure (like an open star
cluster). We modeled the continuum and line emitting region and simulate a
lensing event by a star cluster located in an intervening galaxy. Such a type
of microlensing event can have a significant influence on magnification and
centroid shift of the broad lines and continuum source. We explore
relationships between the continuum and broad line flux variability during the
microlensing event. | Cosmic distance determination from photometric redshift samples using
BAO peaks only: The galaxy distributions along the line-of-sight are significantly
contaminated by the uncertainty on redshift measurements obtained through
multiband photometry, which makes it difficult to get cosmic distance
information measured from baryon acoustic oscillations, or growth functions
probed by redshift distortions. We investigate the propagation of the
uncertainties into large scale clustering by exploiting all known estimators,
and propose the wedge approach as a promising analysis tool to extract cosmic
distance information still remaining in the photometric galaxy samples. We test
our method using simulated galaxy maps with photometric uncertainties of
$\sigma_{0} =\left(0.01, 0.02, 0.03\right)$. The measured anisotropy
correlation function $\xi$ is binned into the radial direction of $s$ and the
angular direction of $\mu$, and the variations of $\xi(s,\mu)$ with
perpendicular and radial cosmic distance measures of $D_A$ and $H^{-1}$ are
theoretically estimated by an improved RSD model. Although the radial cosmic
distance $H^{-1}$ is unable to be probed from any of the three photometric
galaxy samples, the perpendicular component of $D_A$ is verified to be
accurately measured even after the full marginalisation of $H^{-1}$. We measure
$D_A$ with approximately 6% precision which is nearly equivalent to what we can
expect from spectroscopic DR12 CMASS galaxy samples. |
The effects of a hot gaseous halo on disc thickening in galaxy minor
mergers: We employ hydrodynamical simulations to study the effects of dissipational
gas physics on the vertical heating and thickening of disc galaxies during
minor mergers. For the first time we present a suite of simulations that
includes a diffuse, rotating, cooling, hot gaseous halo, as predicted by
cosmological hydrodynamical simulations as well as models of galaxy formation.
We study the effect of this new gaseous component on the vertical structure of
a Milky Way-like stellar disc during 1:10 and 1:5 mergers. For 1:10 mergers we
find no increased final thin disc scale height compared to the isolated
simulation, leading to the conclusion that thin discs can be present even after
a 1:10 merger if a reasonable amount of hot gas is present. The reason for this
is the accretion of new cold gas, leading to the formation of a massive new
thin stellar disc that dominates the surface brightness profile. In a previous
study, in which we included only cold gas in the disk, we showed that the
presence of cold gas decreased the thickening by a minor merger relative to the
no-gas case. Here, we show that the evolution of the scale height in the
presences of a cooling hot halo is dominated by the formation of the new
stellar disc. In this scenario, the thick disc is the old stellar disc that has
been thickened in a minor merger at z>1, while the thin disc is the new stellar
disc that reforms after this merger. In addition, we study the evolution of the
scale height during a 1:5 merger and find that a thin disc can be present even
after this merger, provided enough hot gas is available. The final scale height
in our simulations depends on the mass of the hot gaseous halo, the efficiency
of the winds and the merger mass ratio. We find post-merger values in the range
0.5<z0<1.0 kpc in good agreement with observational constraints by local
galaxies. | Pseudo-conformal Universe: late-time contraction and generation of
tensor modes: We consider a bouncing Universe model which explains the flatness of the
primordial scalar spectrum via complex scalar field that rolls down its
negative quartic potential and dominates in the Universe. We show that in this
model, there exists a rapid contraction regime of classical evolution. We
calculate the power spectrum of tensor modes in this scenario. We find that it
is blue and its amplitude is typically small, leading to mild constraints on
the parameters of the model. |
Local-Group tests of dark-matter Concordance Cosmology: Towards a new
paradigm for structure formation: (abridged) Predictions of the Concordance Cosmological Model (CCM) of the
structures in the environment of large spiral galaxies are compared with
observed properties of Local Group galaxies. Five new most probably
irreconcilable problems are uncovered. However, the Local Group properties
provide hints that may lead to a solution of the above problems The DoS and
bulge--satellite correlation suggest that dissipational events forming bulges
are related to the processes forming phase-space correlated satellite
populations. Such events are well known to occur since in galaxy encounters
energy and angular momentum are expelled in the form of tidal tails, which can
fragment to form populations of tidal-dwarf galaxies (TDGs) and associated star
clusters. If Local Group satellite galaxies are to be interpreted as TDGs then
the sub-structure predictions of CCM are internally in conflict. All findings
thus suggest that the CCM does not account for the Local Group observations and
that therefore existing as well as new viable alternatives have to be further
explored. These are discussed and natural solutions for the above problems
emerge. | Physical evolution of dark matter halo around the depletion boundary: We investigate the build-up of the halo profile out to large scale in a
cosmological simulation, focusing on the roles played by the recently proposed
depletion radii. We explicitly show that halo growth is accompanied by the
depletion of the environment, with the inner depletion radius demarcating the
two. This evolution process is also observed via the formation of a trough in
the bias profile, with the two depletion radii identifying key scales in the
evolution. The ratio between the inner depletion radius and the virial radius
is approximately a constant factor of 2 across redshifts and halo masses. The
ratio between their enclosed densities is also close to a constant of 0.18.
These simple scaling relations reflect the largely universal scaled mass
profile on these scales, which only evolves weakly with redshift. The overall
picture of the boundary evolution can be broadly divided into three stages
according to the maturity of the depletion process, with cluster halos lagging
behind low mass ones in the evolution. We also show that the traditional slow
and fast accretion dichotomy of halo growth can be identified as accelerated
and decelerated depletion phases respectively. |
Novel aspects of C-theories in Cosmology: The field equations in FRW background for the so called C-theories are
presented and investigated. In these theories the usual Ricci scalar is
substituted with $f(\mathcal{R})$ where $\mathcal{R}$ is a Ricci scalar related
to a conformally scaled metric $\hat{g}_{\mu\nu} =
\mathcal{C}(\mathcal{R})g_{\mu\nu}$, where the conformal factor itself depends
on $\mathcal{R}$. It is shown that homogeneous perturbations of this Ricci
scalar around general relativity FRW background of a large class of these
theories are either inconsistent or unstable. | Magnification and evolution biases in large-scale structure surveys: Measurements of galaxy clustering in upcoming surveys such as those planned
for the Euclid and Roman satellites, and the SKA Observatory, will be sensitive
to distortions from lensing magnification and Doppler effects, beyond the
standard redshift-space distortions. The amplitude of these contributions
depends sensitively on magnification bias and evolution bias in the galaxy
number density. Magnification bias quantifies the change in the observed number
of galaxies gained or lost by lensing magnification, while evolution bias
quantifies the physical change in the galaxy number density relative to the
conserved case. These biases are given by derivatives of the number density,
and consequently are very sensitive to the form of the luminosity function. We
give a careful derivation of the magnification and evolution biases, clarifying
a number of results in the literature. We then examine the biases for a variety
of surveys, encompassing galaxy surveys and line intensity mapping at radio and
optical/near-infrared wavelengths. |
Constraints on $Λ(t)$CDM models as holographic and agegraphic dark
energy with the observational Hubble parameter data: The newly released observational $H(z)$ data (OHD) is used to constrain
$\Lambda(t)$CDM models as holographic and agegraphic dark energy. By the use of
the length scale and time scale as the IR cut-off including Hubble horizon
(HH), future event horizon (FEH), age of the universe (AU), and conformal time
(CT), we achieve four different $\Lambda(t)$CDM models which can describe the
present cosmological acceleration respectively. In order to get a comparison
between such $\Lambda(t)$CDM models and standard $\Lambda$CDM model, we use the
information criteria (IC), $Om(z)$ diagnostic, and statefinder diagnostic to
measure the deviations. Furthermore, by simulating a larger Hubble parameter
data sample in the redshift range of $0.1<z<2.0$, we get the improved
constraints and more sufficient comparison. We show that OHD is not only able
to play almost the same role in constraining cosmological parameters as SNe Ia
does but also provides the effective measurement of the deviation of the DE
models from standard $\Lambda$CDM model. In the holographic and agegraphic
scenarios, the results indicate that the FEH is more preferable than HH
scenario. However, both two time scenarios show better approximations to
$\Lambda$CDM model than the length scenarios. | WarmAndFuzzy: the halo model beyond CDM: Cold dark matter (CDM) is a well established paradigm to describe
cosmological structure formation, and works extraordinarily well on large,
linear, scales. Progressing further in dark matter physics requires being able
to understand structure formation in the non-linear regime, both for CDM and
its alternatives. This short note describes a calculation, and accompanying
code, WarmAndFuzzy, incorporating the popular models of warm and fuzzy dark
matter (WDM and FDM) into the standard halo model to compute the non-linear
matter power spectrum. The FDM halo model power spectrum has not been computed
before. The FDM implementation models ultralight axions and other scalar fields
with $m_a\approx 10^{-22}\text{ eV}$. The WDM implementation models thermal WDM
with mass $m_X\approx 1\text{ keV}$. The halo model shows that differences
between WDM, FDM, and CDM survive at low redshifts in the quasi-linear and
fully non-linear regimes. The code uses analytic transfer functions for the
linear power spectrum, modified collapse barriers in the halo mass function,
and a modified concentration-mass relationship for the halo density profiles.
Modified halo density profiles (for example, cores) are not included, but are
under development. Cores are expected to have very minor effects on the power
spectrum on observable scales. Applications of this code to the Lyman-$\alpha$
forest flux power spectrum and the cosmic microwave background lensing power
spectrum will be discussed in companion papers. \textsc{WarmAndFuzzy} is
available online at \url{https://github.com/DoddyPhysics/HMcode}, where
collaboration in development is welcomed. |
Photometric and spectroscopic studies of star-forming regions within
Wolf-Rayet galaxies: We present a study of the properties of star-forming regions within a sample
of 7 Wolf-Rayet (WR) galaxies. We analyze their morphologies, colours,
star-formation rate (SFR), metallicities, and stellar populations combining
broad-band and narrow-band photometry with low-resolution optical spectroscopy.
The $UBVRI$ observations were made through the 2m HCT (Himalayan Chandra
Telescope) and 1m ARIES telescope. The spectroscopic data were obtained using
the Hanle Faint Object Spectrograph Camera (HFOSC) mounted on the 2m HCT. The
observed galaxies are NGC 1140, IRAS 07164+5301, NGC 3738, UM 311, NGC 6764,
NGC 4861 and NGC 3003. The optical spectra have been used to search for the
faint WR features, to confirm that the ionization of the gas is consequence of
the massive stars, and to quantify the oxygen abundance of each galaxy using
several and independent empirical calibrations. We detected the broad features
originated by WR stars in NGC 1140 and NGC 4861 and used them to derive their
population of massive stars. Using our H$\alpha$ images we have identified tens
of regions within these galaxies, for which we derived the SFR. For all regions
we found that the most recent star-formation event is 3 - 6 Myr old. We used
the optical broad-band colours in combination with Starburst99 models to
estimate the internal reddening and the age of the dominant underlying stellar
population within all these regions. Knots in NGC 3738, NGC 6764 and NGC 3003
generally show the presence of an important old (400 - 1000 Myr) stellar
population. However, the optical colours are not able to detect stars older
than 20 - 50 Myr in the knots of the other four galaxies. This fact suggests
both the intensity of the starbursts and that the star-formation activity has
been ongoing for at least some few tens of million years in these objects. | Far-Infrared and submillimeter properties of SDSS galaxies in the
Herschel ATLAS science demonstration phase field: Using the Herschel ATLAS science demonstration phase data crossidentified
with SDSS DR7 spectra, we select 297 galaxies with F250{\mu}m > 5{\sigma}. The
sample galaxies are classified into five morphological types, and more than 40%
of the galaxies are peculiar/compact galaxies. The peculiar galaxies show
higher far-infrared/submillimeter luminosity-to-mass ratios than the other
types. We perform and analyze the correlations of far-infrared/submillimeter
and H{\alpha} luminosities for different morphological types and different
spectral types. The Spearman rank coefficient decreases and the scatter
increases with the wavelength increasing from 100 {\mu}m to 500 {\mu}m. We
conclude that a single Herschel SPIRE band is not good for tracing star
formation activities in galaxies. AGNs contribute less to the
far-infrared/submillimeter luminosities and do not show a difference from
star-forming galaxies. However, the earlier type galaxies present significant
deviations from the best fit of star-forming galaxies. |
Star formation in galaxy interactions and mergers: This lecture reviews the fundamental physical processes involved in star
formation in galaxy interactions and mergers. Interactions and mergers often
drive intense starbursts, but the link between interstellar gas physics, large
scale interactions, and active star formation is complex and not fully
understood yet. Two processes can drive starbursts: radial inflows of gas can
fuel nuclear starbursts, triggered gas turbulence and fragmentation can drive
more extended starbursts in massive star clusters with high fractions of dense
gas. Both modes are certainly required to account for the observed properties
of starbursting mergers. A particular consequence is that star formation
scaling laws are not universal, but vary from quiescent disks to starbursting
mergers. High-resolution hydrodynamic simulations are used to illustrate the
lectures. | The luminosity function of galaxies in elliptical-dominated galaxy
groups: clues on the nature of fossil groups: We have started a study of luminosity functions of Fossil Group candidates in
order to characterize the faint-end of their galaxy distribution. Here we
report on results of nine of them from SDSS photometry. |
The use of gravitational lenses in the study of distant galaxy mergers: Gravlenses are efficiently explored for detecting the most distant galaxies
(up to z=10 redshifts). As an example of the role played by gravlenses we refer
to the observation of the galaxy merger at z=3 (Borys, et al; Berciano Alba, et
al). We derived solutions for the Smoluchowski kinetic equation for the mass
function of galaxies, which describes mergers in differential approximation
(minor mergers).
It is shown that the evolution of the slope of luminosity function observed
in the Ultra Deep Hubble Field (Bouwence et al) can be described as a result of
explosive evolution driven by galaxy mergers. | Features in the primordial spectrum: new constraints from WMAP7+ACT data
and prospects for Planck: We update the constraints on possible features in the primordial inflationary
density perturbation spectrum by using the latest data from the WMAP7 and ACT
Cosmic Microwave Background experiments. The inclusion of new data
significantly improves the constraints with respect to older work, especially
to smaller angular scales. While we found no clear statistical evidence in the
data for extensions to the simplest, featureless, inflationary model, models
with a step provide a significantly better fit than standard featureless
power-law spectra. We show that the possibility of a step in the inflationary
potential like the one preferred by current data will soon be tested by the
forthcoming temperature and polarization data from the Planck satellite
mission. |
Graph Database Solution for Higher Order Spatial Statistics in the Era
of Big Data: We present an algorithm for the fast computation of the general $N$-point
spatial correlation functions of any discrete point set embedded within an
Euclidean space of $\mathbb{R}^n$. Utilizing the concepts of kd-trees and graph
databases, we describe how to count all possible $N$-tuples in binned
configurations within a given length scale, e.g. all pairs of points or all
triplets of points with side lengths $<r_{max}$. Through bench-marking we show
the computational advantage of our new graph based algorithm over more
traditional methods. We show that all 3-point configurations up to and beyond
the Baryon Acoustic Oscillation scale ($\sim$200 Mpc in physical units) can be
performed on current SDSS data in reasonable time. Finally we present the first
measurements of the 4-point correlation function of $\sim$0.5 million SDSS
galaxies over the redshift range $0.43<z<0.7$. | N-body methods for relativistic cosmology: We present a framework for general relativistic N-body simulations in the
regime of weak gravitational fields. In this approach, Einstein's equations are
expanded in terms of metric perturbations about a Friedmann-Lema\^itre
background, which are assumed to remain small. The metric perturbations
themselves are only kept to linear order, but we keep their first spatial
derivatives to second order and treat their second spatial derivatives as well
as sources of stress-energy fully non-perturbatively. The evolution of matter
is modelled by an N-body ensemble which can consist of free-streaming
nonrelativistic (e.g. cold dark matter) or relativistic particle species (e.g.
cosmic neutrinos), but the framework is fully general and also allows for other
sources of stress-energy, in particular additional relativistic sources like
modified-gravity models or topological defects. We compare our method with the
traditional Newtonian approach and argue that relativistic methods are
conceptually more robust and flexible, at the cost of a moderate increase of
numerical difficulty. However, for a LambdaCDM cosmology, where nonrelativistic
matter is the only source of perturbations, the relativistic corrections are
expected to be small. We quantify this statement by extracting post-Newtonian
estimates from Newtonian N-body simulations. |
Clustering of Primordial Black Holes from QCD Axion Bubbles: We study the clustering of primordial black holes (PBHs) and axion
miniclusters produced in the model proposed to explain the LIGO/Virgo events or
the seeds of the supermassive black holes (SMBHs) in arXiv:2006.13137. It is
found that this model predicts large isocurvature perturbations due to the
clustering of PBHs and axion miniclusters, from which we obtain stringent
constraints on the model parameters. Specifically, for the axion decay constant
$f_a=10^{16}~\mathrm{GeV}$, which potentially accounts for the seeds of the
SMBHs, the PBH fraction in dark matter should be $f_\mathrm{PBH}\lesssim7\times
10^{-10}$. Assuming that the mass of PBHs increases by more than a factor of
$\mathcal{O}(10)$ due to accretion, this is consistent with the observed
abundance of SMBHs. On the other hand, for $f_a=10^{17}~\mathrm{GeV}$ required
to produce PBHs of masses detected in the LIGO/Virgo, the PBH fraction should
be $f_\mathrm{PBH}\lesssim6\times 10^{-8}$, which may be too small to explain
the LIGO/Virgo events, although there is a significant uncertainty in
calculating the merger rate in the presence of clustering. | How Does Radio AGN Feedback Feed Back?: Radio AGN feedback is often assumed to work, but detailed physical models of
this process are not well developed. This paper examines a possible path for
radio AGN feedback to heat the gas in and around galaxies and perhaps suppress
star formation. Nearby radio AGN are almost all FR-I radio galaxies, and it is
argued that such outflows become decelerated and fully turbulent in their early
stages. A 3D non-linear MHD turbulence calculation is made to determine the
time required for this outflowing turbulent energy to be converted into heat.
Using radio and x-ray observations of nearby FR-I AGN for normalization results
in a time for the onset of heating of about 100 million years. This is
comparable to the gas cooling times in and around galaxies, and the resulting
location of heat deposition is consistent with FR-I outflows. |
Weak lensing measurements of the APEX-SZ galaxy cluster sample: We present a weak lensing analysis for galaxy clusters from the APEX-SZ
survey. For $39$ massive galaxy clusters that were observed via the
Sunyaev-Zel\textquotesingle dovich effect (SZE) with the APEX telescope, we
analyse deep optical imaging data from WFI(@2.2mMPG/ESO) and
Suprime-Cam(@SUBARU) in three bands. The masses obtained in this study,
including an X-ray selected subsample of 27 clusters, are optimised for and
used in studies constraining the mass to observable scaling relations at fixed
cosmology. A novel focus of our weak lensing analysis is the multi-colour
background selection to suppress effects of cosmic variance on the redshift
distribution of source galaxies. We investigate the effects of cluster member
contamination through galaxy density, shear profile, and recovered
concentrations. We quantify the impact of variance in source redshift
distribution on the mass estimate by studying nine sub-fields of the COSMOS
survey for different cluster redshift and manitude limits. We measure a
standard deviation of $\sim 6$\% on the mean angular diameter distance ratio
for a cluster at $z\!=\!0.45$ and shallow imaging data of $R\!\approx\!23$ mag.
It falls to $\sim 1$\% for deep, $R=26$ mag, observations. This corresponds to
8.4\% and 1.4\% scatter in $M_{200}$. Our background selection reduces this
scatter by $20-40$\%, depending on cluster redshift and imaging depth. We
derived cluster masses with and without using a mass concentration relation and
find consistent results, and concentrations consistent with the used
mass-concentration relation. | Cross-correlation of the astrophysical gravitational-wave background
with galaxy clustering: We investigate the correlation between the distribution of galaxies and the
predicted gravitational-wave background of astrophysical origin. We show that
the large angular scale anisotropies of this background are dominated by nearby
non-linear structure, which depends on the notoriously hard to model galaxy
power spectrum at small scales. In contrast, we report that the
cross-correlation of this signal with galaxy catalogues depends only on linear
scales and can be used to constrain the average contribution to the
gravitational-wave background as a function of time. Using mock data based on a
simplified model, we explore the effects of galaxy bias, angular resolution and
the matter abundance on these constraints. Our results suggest that, when
combined with galaxy surveys, the gravitational-wave background can be a
powerful probe for both gravitational-wave merger physics and cosmology. |
RingFinder: automated detection of galaxy-scale gravitational lenses in
ground-based multi-filter imaging data: We present RingFinder, a tool for finding galaxy-scale strong gravitational
lenses in multiband imaging data. By construction, the method is sensitive to
configurations involving a massive foreground early-type galaxy and a faint,
background, blue source. RingFinder detects the presence of blue residuals
embedded in an otherwise smooth red light distribution by difference imaging in
two bands. The method is automated for efficient application to current and
future surveys, having originally been designed for the 150-deg2 Canada France
Hawaii Telescope Legacy Survey (CFHTLS). We describe each of the steps of
RingFinder. We then carry out extensive simulations to assess completeness and
purity. For sources with magnification mu>4, RingFinder reaches 42% (resp. 25%)
completeness and 29% (resp. 86%) purity before (resp. after) visual inspection.
The completeness of RingFinder is substantially improved in the particular
range of Einstein radii 0.8 < REin < 2. and lensed images brighter than g =
22.5, where it can be as high as 70%. RingFinder does not introduce any
significant bias in the source or deflector population. We conclude by
presenting the final catalog of RingFinder CFHTLS galaxy-scale strong lens
candidates. Additional information obtained with Hubble Space Telescope and
Keck Adaptive Optics high resolution imaging, and with Keck and Very Large
Telescope spectroscopy, is used to assess the validity of our classification,
and measure the redshift of the foreground and the background objects. From an
initial sample of 640,000 early type galaxies, RingFinder returns 2500
candidates, which we further reduce by visual inspection to 330 candidates. We
confirm 33 new gravitational lenses from the main sample of candidates, plus an
additional 16 systems taken from earlier versions of RingFinder. First
applications are presented in the SL2S galaxy-scale Lens Sample paper series. | The effect of variations in the input physics on the cosmic distribution
of metals predicted by simulations: [Abridged] We investigate how a range of physical processes affect the cosmic
metal distribution using a suite of cosmological, hydrodynamical simulations.
Focusing on z = 0 and 2, we study the metallicities and metal mass fractions
for stars as well as for the ISM, and several more diffuse gas phases. We vary
the cooling rates, star formation law, structure of the ISM, galactic winds,
feedback from AGN, reionization history, stellar IMF, and cosmology. In all
models stars and the warm-hot IGM (WHIM) constitute the dominant repository of
metals, while for z > 2 the ISM is also important. In models with galactic
winds, predictions for the metallicities of the various phases vary at the
factor of two level and are broadly consistent with observations. The exception
is the cold-warm IGM, whose metallicity varies at the order of magnitude level
if the prescription for galactic winds is varied, even for a fixed wind energy
per unit stellar mass formed, and falls far below the observed values if winds
are not included. At the other extreme, the metallicity of the intracluster
medium (ICM) is largely insensitive to the presence of galactic winds,
indicating that its enrichment is regulated by other processes. The mean
metallicities of stars (~ Z_sun), the ICM (~ 0.1 Z_sun), and the WHIM (~ 0.1
Z_sun) evolve only slowly, while those of the cold halo gas and the IGM
increase by more than an order of magnitude from z = 5 to 0. Higher velocity
outflows are more efficient at transporting metals to low densities, but
actually predict lower metallicities for the cold-warm IGM since the winds
shock-heat the gas to high temperatures, thereby increasing the fraction of the
metals residing in, but not the metallicity of, the WHIM. Besides galactic
winds driven by feedback from star formation, the metal distribution is most
sensitive to the inclusion of metal-line cooling and feedback from AGN. |
Cross-correlating Planck with VST ATLAS LRGs: a new test for the ISW
effect in the Southern Hemisphere: The Integrated Sachs-Wolfe (ISW) effect probes the late-time expansion
history of the universe, offering direct constraints on dark energy. Here we
present our measurements of the ISW signal at redshifts of $\bar{z}=0.35$,
$0.55$ and $0.68$, using the cross-correlation of the Planck CMB temperature
map with $\sim0.5$ million Luminous Red Galaxies (LRGs) selected from the VST
ATLAS survey. We then combine these with previous measurements based on WMAP
and similar SDSS LRG samples, providing a total sample of $\sim2.1$ million
LRGs covering $\sim12000$ deg$^2$ of sky. At $\bar{z}=0.35$ and $\bar{z}=0.55$
we detect the ISW signal at $1.2\sigma$ and $2.3\sigma$ (or $2.6\sigma$
combined), in agreement with the predictions of $\Lambda$CDM. We verify these
results by repeating the measurements using the BOSS LOWZ and CMASS,
spectroscopically confirmed LRG samples. We also detect the ISW effect in three
magnitude limited ATLAS+SDSS galaxy samples extending to $z\approx0.4$ at
$\sim2\sigma$ per sample. However, we do not detect the ISW signal at
$\bar{z}=0.68$ when combining the ATLAS and SDSS results. Further tests using
spectroscopically confirmed eBOSS LRGs at this redshift remain inconclusive due
to the current low sky coverage of the survey. If the ISW signal is shown to be
redshift dependent in a manner inconsistent with the predictions of
$\Lambda$CDM, it could open the door to alternative theories such as modified
gravity. It is therefore important to repeat the high redshift ISW measurement
using the completed eBOSS sample, as well as deeper upcoming surveys such as
DESI and LSST. | Transient cosmic acceleration from interacting fluids: Recent investigations seem to favor a cosmological dynamics according to
which the accelerated expansion of the Universe may have already peaked and is
now slowing down again \cite{sastaro}. As a consequence, the cosmic
acceleration may be a transient phenomenon. We investigate a toy model that
reproduces such a background behavior as the result of a time-dependent
coupling in the dark sector which implies a cancelation of the "bare"
cosmological constant. With the help of a statistical analysis of Supernova
Type Ia (SNIa) data we demonstrate that for a certain parameter combination a
transient accelerating phase emerges as a pure interaction effect. |
Molecular Hydrogen in the Damped Lyman-alpha System towards GRB 120815A
at z=2.36: We present the discovery of molecular hydrogen (H_2), including the presence
of vibrationally-excited H_2^* in the optical spectrum of the afterglow of GRB
120815A at z=2.36 obtained with X-shooter at the VLT. Simultaneous photometric
broad-band data from GROND and X-ray observations by Swift/XRT place further
constraints on the amount and nature of dust along the sightline. The galactic
environment of GRB 120815A is characterized by a strong DLA with
log(N(H)/cm^-2) = 21.95 +/- 0.10, prominent H_2 absorption in the Lyman-Werner
bands (log(N(H_2)/cm^-2) = 20.53 +/- 0.13) and thus a molecular gas fraction
log f(H_2)=-1.14 +/- 0.15. The distance d between the absorbing neutral gas and
GRB 120815A is constrained via photo-excitation modeling of fine-structure and
meta-stable transitions of FeII and NiII to d = 0.5 +/- 0.1 kpc. The DLA
metallicity ([Zn/H] = -1.15 +/- 0.12), visual extinction (A_V < 0.15 mag) and
dust depletion ([Zn/Fe] = 1.01 +/- 0.10) are intermediate between the values of
well-studied, H_2-deficient GRB-DLAs observed at high spectral resolution, and
the approximately solar metallicity, highly-obscured and H_2-rich GRB 080607
sightline. With respect to N(H), metallicity, as well as dust-extinction and
depletion, GRB 120815A is fairly representative of the average properties of
GRB-DLAs. This demonstrates that molecular hydrogen is present in at least a
fraction of the more typical GRB-DLAs, and H_2 and H_2^* are probably more
wide-spread among GRB-selected systems than the few examples of previous
detections would suggest. | Probing the mass relation between supermassive black holes and dark
matter halos at high redshifts by gravitational wave experiments: Numerous observations have shown that almost all galaxies in our Universe
host supermassive black holes (SMBHs), but there is still much debate about
their formation and evolutionary processes. Recently, gravitational waves (GWs)
have been expected to be a new and important informative observation, in
particular, in the low-frequency region by making use of the Laser
Interferometer Space Antenna (LISA) and Pulsar Timing Arrays (PTAs). As an
evolutionary process of the SMBHs, we revisit a dark matter (DM) halo-SMBH
coevolution model based on the halo merger tree employing an ansatz for the
mass relation between the DM halos and the SMBHs at $z=6$. In this model, the
mass of SMBHs grows through their mergers associated with the halo mergers, and
hence the evolutionary information must be stored in the GWs emitted at the
mergers. We investigate the stochastic gravitational background from the
coalescing SMBH binaries, which the PTAs can detect, and also the GW bursts
emitted at the mergers, which can be detected by the mHz band observations such
as LISA. We also discuss the possibility of probing the mass relation between
the DM halos and the SMBHs at high redshift by future GW observations. |
How the Nonbaryonic Dark Matter Theory Grew: The evidence is that the mass of the universe is dominated by an exotic
nonbaryonic form of matter largely draped around the galaxies. It approximates
an initially low pressure gas of particles that interact only with gravity, but
we know little more than that. Searches for detection thus must follow many
difficult paths to a great discovery, what the universe is made of. The
nonbaryonic picture grew out of a convergence of evidence and ideas in the
early 1980s. Developments two decades later considerably improved the evidence,
and advances since then have made the case for nonbaryonic dark matter
compelling. | High-precision spectra for dynamical Dark Energy cosmologies from
constant-w models: Spanning the whole functional space of cosmologies with any admissible DE
state equations w(a) seems a need, in view of forthcoming observations, namely
those aiming to provide a tomography of cosmic shear. In this paper I show that
this duty can be eased and that a suitable use of results for constant-w
cosmologies can be sufficient. More in detail, I ``assign'' here six
cosmologies, aiming to span the space of state equations w(a) = w_o + w_a(1-a),
for w_o and w_a values consistent with WMAP5 and WMAP7 releases and run N-body
simulations to work out their non-linear fluctuation spectra at various
redshifts z. Such spectra are then compared with those of suitable auxiliary
models, characterized by constant w. For each z a different auxiliary model is
needed. Spectral discrepancies between the assigned and the auxiliary models,
up to k ~ 2-3 h Mpc^{-1}, are shown to keep within 1%. Quite in general,
discrepancies are smaller at greater z and exhibit a specific trend across the
w_o and w_a plane. Besides of aiming at simplifying the evaluation of spectra
for a wide range of models, this paper also outlines a specific danger for
future studies of the DE state equation, as models fairly distant on the w_0 -
w_a plane can be easily confused. |
Consistency test of the fine-structure constant from the whole
ionization history: In cosmology, the fine-structure constant can affect the whole ionization
history. However, the previous works confine themselves to the recombination
epoch and give various strong constraints on the fine-structure constant. In
this paper, we also take the reionization epoch into consideration and do a
consistency test of the fine-structure constant from the whole ionization
history. From the data combination of Planck 2018, BAO data, SNIa samples, SFR
density from UV and IR measurements, and the $Q_\text{HII}$ constraints, we
find the constraint on the fine-structure constant during the recombination
epoch is
$\alpha_{\text{rec}}/\alpha_{\text{EM}}=1.001494^{+0.002041}_{-0.002063}$ and
its counterpart during the reionization epoch is
$\alpha_{\text{rei}}/\alpha_{\text{EM}}=0.854034^{+0.031678}_{-0.027209}$ at
68$\%$ C.L.. They are not consistent with each other by $4.64\sigma$. A
conservative explanation for such a discrepancy is that there are some issues
in the data we used. We prefer a calibration of some important parameters
involved in reconstructing the reionization history. | High zenith angle observations of PKS 2155-304 with the MAGIC telescope: The high frequency peaked BL Lac PKS 2155-304 with a redshift z=0.116 was
discovered 1997 in the VHE range by the University of Durham Mark 6 gamma-ray
telescope in Australia with a flux corresponding to approx. 0.2 times the Crab
Nebula flux. It was later observed and detected with high significance by the
Southern observatories CANGAROO and H.E.S.S. establishing this source as the
best studied Southern TeV blazar. Detection from the Northern hemisphere was
very difficult due to challenging observation conditions under large zenith
angles. In July 2006, the H.E.S.S. collaboration reported an extraordinary
outburst of VHE gamma-emission. During the outburst, the VHE gamma-ray emission
was found to be variable on the time scales of minutes and at a mean flux of
approx. 7 times the flux observed from the Crab Nebula. The MAGIC collaboration
operates a 17m imaging air Cherenkov Telescope at La Palma (Northern
Hemisphere). Follow up observations of the extraordinary outburst have been
triggered in a Target of Opportunity program by an alert from the H.E.S.S.
collaboration. The measured spectrum and light curve are presented. |
Distance-redshift relation in plane symmetric universes: Distance measurements are usually thought to probe the background metric of
the universe, but in reality the presence of perturbations will lead to
deviations from the result expected in an exactly homogeneous and isotropic
universe. At least in principle the presence of perturbations could even
explain the observed distance-redshift relation without the need for dark
energy. In this paper we re-investigate a toy model where perturbations are
plane symmetric, and for which exact solutions are known in the fluid limit.
However, if perturbations are large, shell-crossing occurs and the fluid
approximation breaks down. This prevents the study of the most interesting
cases. Here we use a general-relativistic N-body simulation that does not
suffer from this problem and which allows us to go beyond previous works. We
show that even for very large plane-symmetric perturbations we are not able to
mimic the observed distance-redshift relation. We also discuss how the
synchronous comoving gauge breaks down when shell-crossing occurs, while metric
perturbations in the longitudinal gauge remain small. For this reason the
longitudinal (Newtonian) gauge appears superior for relativistic N-body
simulations of large-scale structure formation. | Secondary non-Gaussianity and Cross-Correlation Analysis: We develop optimised estimators of two sorts of power spectra for fields
defined on the sky, in the presence of partial sky coverage. The first is the
cross-power spectrum of two fields on the sky; the second is the skew spectrum
of three fields. These can probe the Integrated Sachs Wolfe Effect (ISW) at
large angular scales and the Sunyaev Z\'eldovich (SZ) effect from hot gas in
clusters at small angular scales. The skew spectrum, recently introduced by
Munshi & Heavens (2009), is an optimised statistic which can be tuned to study
a particular form of non-Gaussianity, such as may arise in the early Universe,
but which retains information on the nature of non-Gaussianity. In this paper
we develop the mathematical formalism for the skew spectrum of 3 different
fields. When applied to the CMB, this allows us to explore the contamination of
the skew spectrum by secondary sources of CMB fluctuations. Considering the
three-point function, the study of the bispectrum provides valuable information
regarding cross-correlation of secondaries with lensing of CMB with much higher
significance compared to just the study involving CMB sky alone. We use our
analytical models to study specific cases of cosmological interest which
include cross-correlating CMB with various large scale tracers to probe ISW and
SZ effects for cross spectral analysis and use the formalism to study the
signal-to-noise ratio for detection of the weak lensing of the CMB by
cross-correlating it with different tracers as well as point sources for CMB
experiments such as Planck (abridged). |
Is the cold spot responsible for the CMB North-South asymmetry?: Several intriguing phenomena, unlikely within the standard inflationary
cosmology, were reported in the cosmic microwave background (CMB) data from
WMAP and appear to be uncorrelated. Two of these phenomena, termed CMB
anomalies, are representative of their disparate nature: the North-South
asymmetry in the CMB angular-correlation strength, inconsistent with an
isotropic universe, and the cold spot, producing a significant deviation from
Gaussianity. We find a cause-effect relationship between them, at medium
angular scales (l = 11 - 20): we show that a successive diminution of the cold
spot (absolute-value) temperature implies a monotonic decrease of the
North-South asymmetry power, and moreover we find that the cold spot supplies
60% of such power. | Probing statistical isotropy of cosmological radio sources using SKA: There currently exist many observations which are not consistent with the
cosmological principle. We review these observations with a particular emphasis
on those relevant for Square Kilometre Array (SKA). In particular, several
different data sets indicate a preferred direction pointing approximately
towards the Virgo cluster. We also observe a hemispherical anisotropy in the
Cosmic Microwave Background Radiation (CMBR) temperature fluctuations. Although
these inconsistencies may be attributed to systematic effects, there remains
the possibility that they indicate new physics and various theories have been
proposed to explain them. One possibility, which we discuss in this review, is
the generation of perturbation modes during the early pre-inflationary epoch,
when the Universe may not obey the cosmological principle. Better measurements
will provide better constraints on these theories. In particular, we propose
measurement of the dipole in number counts, sky brightness, polarized flux and
polarization orientations of radio sources. We also suggest test of alignment
of linear polarizations of sources as a function of their relative separation.
Finally we propose measurement of hemispherical anisotropy or equivalently
dipole modulation in radio sources. |
The jet of the BL Lacertae object PKS 2201+044: MAD near-IR adaptive
optics observations and comparison with optical, radio and X-ray data: Relativistic jets are a common feature of radio loud active galactic nuclei.
Multifrequency observations are a unique tool to constrain their physics.
We report on a detailed study of the properties of the jet of the nearby BL
Lac object PKS 2201+044, one of the rare cases where the jet is detected from
radio to X-rays. We use new adaptive optics near-IR observations of the source,
obtained with the ESO multi-conjugated adaptive optics demonstrator (MAD) at
the Very Large Telescope. These observations acquired in Ground-Layer Adaptive
Optics mode are combined with images previously achieved by HST, VLA and
Chandra to perform a morphological and photometric study of the jet. We find a
noticeable similarity in the morphology of the jet at radio, near-IR and
optical wavelengths. We construct the spectral shape of the main knot of jet
that appears dominated by synchrotron radiation. On the basis of the jet
morphology and the weak lines spectrum we suggest that PKS 2201+044 belongs to
the class of radio sources intermediate between FRIs and FRIIs. | Cosmological viability of a double field unified model from warm
inflation: In this paper, we investigate the cosmological viability of a double scalar
field model motivated by warm inflation. To this end, we first set up the
theoretical framework in which dark energy, dark matter and inflation are
accounted for in a triple unification scheme. We then compute the overall
dynamics of the model, analyzing the physical role of coupling parameters.
Focussing on the late-time evolution, we test the model against current data.
Specifically, using the low-redshift Pantheon Supernovae Ia and Hubble cosmic
chronometers measurements, we perform a Bayesian analysis through the Monte
Carlo Markov Chains method of integration on the free parameters of the model.
We find that the mean values of the free parameters constrained by observations
lie within suitable theoretical ranges, and the evolution of the scalar fields
provides a good resemblance to the features of the dark sector of the universe.
Such behaviour is confirmed by the outcomes of widely adopted selection
criteria, suggesting a statistical evidence comparable to that of the standard
$\Lambda$CDM cosmology. We finally discuss the presence of large uncertainties
over the free parameters of the model and we debate about fine-tuning issues
related to the coupling constants. |
A Census of Baryons and Dark Matter in an Isolated, Milky Way-sized
Elliptical Galaxy: We present a study of the dark and luminous matter in the isolated elliptical
galaxy NGC720, based on deep X-ray observations made with Chandra and Suzaku.
The gas is reliably measured to ~R2500, allowing us to place good constraints
on the enclosed mass and baryon fraction (fb) within this radius
(M2500=1.6e12+/-0.2e12 Msun, fb(2500)=0.10+/-0.01; systematic errors are
<~20%). The data indicate that the hot gas is close to hydrostatic, which is
supported by good agreement with a kinematical analysis of the dwarf satellite
galaxies. We confirm a dark matter (DM) halo at ~20-sigma. Assuming an NFW DM
profile, our physical model for the gas distribution enables us to obtain
meaningful constraints at scales larger than R2500, revealing that most of the
baryons are in the hot gas. We find that fb within Rvir is consistent with the
Cosmological value, confirming theoretical predictions that a ~Milky Way-mass
(Mvir=3.1e12+/-0.4e12 Msun) galaxy can sustain a massive, quasi-hydrostatic gas
halo. While fb is higher than the cold baryon fraction typically measured in
similar-mass spiral galaxies, both the gas fraction (fg) and fb in NGC720 are
consistent with an extrapolation of the trends with mass seen in massive galaxy
groups and clusters. After correcting for fg, the entropy profile is close to
the self-similar prediction of gravitational structure formation simulations,
as observed in galaxy clusters. Finally, we find a strong heavy metal abundance
gradient in the ISM similar to those observed in massive galaxy groups. | On the Recovery of the Star Formation History of the LMC from the VISTA
Survey of the Magellanic System: The VISTA near infrared survey of the Magellanic System (VMC) will provide
deep YJKs photometry reaching stars in the oldest turn-off point all over the
Magellanic Clouds (MCs). As part of the preparation for the survey, we aim to
access the accuracy in the Star Formation History (SFH) that can be expected
from VMC data, in particular for the LMC. To this aim, we first simulate VMC
images containing not only the LMC stellar populations but also the foreground
MW stars and background galaxies. We perform aperture photometry over these
simulated images, access the expected levels of photometric errors and
incompleteness, and apply the classical technique of SFH-recovery based on the
reconstruction of colour-magnitude diagrams (CMD) via the minimization of a
chi-squared-like statistics. We then evaluate the expected errors in the
recovered star formation rate as a function of stellar age, SFR(t), starting
from models with a known Age--Metallicity Relation (AMR). It turns out that,
for a given sky area, the random errors for ages older than ~0.4 Gyr seem to be
independent of the crowding. For a spatial resolution of ~0.1 sqdeg, the random
errors in SFR(t) will be below 20% for this wide range of ages. On the other
hand, due to the smaller stellar statistics for stars younger than ~0.4 Gyr,
the outer LMC regions will require larger areas to achieve the same level of
accuracy in the SFR(t). If we consider the AMR as unknown, the SFH-recovery
algorithm is able to accurately recover the input AMR, at the price of an
increase of random errors in the SFR(t) by a factor of about 2.5. Experiments
of SFH-recovery performed for varying distance modulus and reddening indicate
that the propagation of the errors in these parameters in the SFR(t) implies
systematic errors below 30%. |
The NGC 1023 Galaxy Group: An Anti-Hubble Flow?: We discuss recently published data indicating that the nearby galaxy group
NGC 1023 includes an inner virialized quasi-stationary component and an outer
component comprising a flow of dwarf galaxies falling toward the center of the
system. The inner component is similar to the Local Group of galaxies, but the
Local Group is surrounded by a receding set of dwarf galaxies forming the very
local Hubble flow, rather than a system of approaching dwarfs. This clear
difference in the structures of these two systems, which are very similar in
other respects, may be associated with the dark energy in which they are both
imbedded. Self-gravity dominates in the Local Group, while the anti-gravity
produced by the cosmic dark-energy background dominates in the surrounding
Hubble flow. In contrast, self-gravity likewise dominates throughout the NGC
1023 Group, both in its central component and in the surrounding Santi-Hubble
flow. The NGC 1023 group as a whole is apparently in an ongoing state of
formation and virialization. We may expect that there exists a receding flow
similar to the local Hubble flow at distances of 1.4-3 Mpc from the center of
the group, where anti-gravity should become stronger than the gravity of the
system. | The Cosmological Lithium Problem Revisited: After a brief review of the cosmological lithium problem, we report a few
recent attempts to find theoretical solutions by our group at Texas A&M
University (Commerce & College Station). We will discuss our studies on the
theoretical description of electron screening, the possible existence of
parallel universes of dark matter, and the use of non-extensive statistics
during the Big Bang nucleosynthesis epoch. Last but not least, we discuss
possible solutions within nuclear physics realm. The impact of recent
measurements of relevant nuclear reaction cross sections for the Big Bang
nucleosynthesis based on indirect methods is also assessed. Although our
attempts may not able to explain the observed discrepancies between theory and
observations, they suggest theoretical developments that can be useful also for
stellar nucleosynthesis. |
Dark Energy Survey Year 3 results: likelihood-free, simulation-based
$w$CDM inference with neural compression of weak-lensing map statistics: We present simulation-based cosmological $w$CDM inference using Dark Energy
Survey Year 3 weak-lensing maps, via neural data compression of weak-lensing
map summary statistics: power spectra, peak counts, and direct map-level
compression/inference with convolutional neural networks (CNN). Using
simulation-based inference, also known as likelihood-free or implicit
inference, we use forward-modelled mock data to estimate posterior probability
distributions of unknown parameters. This approach allows all statistical
assumptions and uncertainties to be propagated through the forward-modelled
mock data; these include sky masks, non-Gaussian shape noise, shape measurement
bias, source galaxy clustering, photometric redshift uncertainty, intrinsic
galaxy alignments, non-Gaussian density fields, neutrinos, and non-linear
summary statistics. We include a series of tests to validate our inference
results. This paper also describes the Gower Street simulation suite: 791
full-sky PKDGRAV dark matter simulations, with cosmological model parameters
sampled with a mixed active-learning strategy, from which we construct over
3000 mock DES lensing data sets. For $w$CDM inference, for which we allow
$-1<w<-\frac{1}{3}$, our most constraining result uses power spectra combined
with map-level (CNN) inference. Using gravitational lensing data only, this
map-level combination gives $\Omega_{\rm m} = 0.283^{+0.020}_{-0.027}$, ${S_8 =
0.804^{+0.025}_{-0.017}}$, and $w < -0.80$ (with a 68 per cent credible
interval); compared to the power spectrum inference, this is more than a factor
of two improvement in dark energy parameter ($\Omega_{\rm DE}, w$) precision. | Polarisation of Radio Relics in Galaxy Clusters: Radio emission in the form of giant radio relics is observed at the periphery
of galaxy clusters. This non-thermal emission is an important tracer for
cosmic-ray electrons and intracluster magnetic fields. One striking
observational feature of these objects is their high degree of polarisation
which provides information on the magnetic fields at the relics' positions. In
this contribution, we test if state-of-the-art high resolution cosmological
simulations are able to reproduce the polarisation features of radio relics.
Therefore, we present a new analysis of high-resolution cosmological
simulations to study the polarisation properties of radio relics in detail. In
order to compare our results with current and future radio observations, we
create mock radio observations of the diffuse polarised emission from a massive
galaxy clusters using six different projections, for different observing
frequencies and for different telescopes. Our simulations suggest that, due to
the effect of Faraday rotation, it is extremely difficult to relate the
morphology of the polarised emission for observing frequencies below $1.4 \
\mathrm{GHz}$ to the real magnetic field structure in relics. We can reproduce
the observed degree of polarisation and also several small-scale structures
observed in real radio relics, but further work would be needed to reproduce
some large-scale spectacular features as observed in real radio relics, such as
the "Sausage" and the "Toothbrush" relics. |
Dynamics and constraints of the dissipative Liouville cosmology: In this article we investigate the properties of the FLRW flat cosmological
models in which the cosmic expansion of the Universe is affected by a dilaton
dark energy (Liouville scenario). In particular, we perform a detailed study of
these models in the light of the latest cosmological data, which serves to
illustrate the phenomenological viability of the new dark energy paradigm as a
serious alternative to the traditional scalar field approaches. By performing a
joint likelihood analysis of the recent supernovae type Ia data (SNIa), the
differential ages of passively evolving galaxies, and the Baryonic Acoustic
Oscillations (BAOs) traced by the Sloan Digital Sky Survey (SDSS), we put tight
constraints on the main cosmological parameters. Furthermore, we study the
linear matter fluctuation field of the above Liouville cosmological models. In
this framework, we compare the observed growth rate of clustering measured with
those predicted by the current Liouville models. Performing a chi^2 statistical
test we show that the Liouville cosmological model provides growth rates that
match sufficiently well with the observed growth rate. To further test the
viability of the models under study, we use the Press-Schechter formalism to
derive their expected redshift distribution of cluster-size halos that will be
provided by future X-ray and Sunyaev-Zeldovich cluster surveys. We find that
the Hubble flow differences between the Liouville and the LambdaCDM models
provide a significantly different halo redshift distribution, suggesting that
the models can be observationally distinguished. | Modelling the dynamical friction timescale of sinking satellite: When a satellite galaxy falls into a massive dark matter halo, it suffers the
dynamical friction force which drag it into the halo center and finally it
merger with the central galaxy. The time interval between entry and merger is
called as the dynamical friction timescale (T_df). Many studies have been
dedicated to derive T_df using analytical models or N-body simulations. These
studies have obtained qualitative agreements on how T_df depends on the orbit
parameters, and mass ratio between satellite and host halo. However, there are
still disagreements on the accurate form of T_df . In this paper, we present a
semi-analytical model to predict T_df and we focus on interpreting the
discrepancies among different studies. We find that the treatment of mass loss
from satellite by tidal stripping dominates the behavior of T_df . We also
identify other model parameters which affect the predicted T_df. |
The Dark Energy Survey: more than dark energy - an overview: This overview article describes the legacy prospect and discovery potential
of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it
with examples from the DES early data. DES is using a wide-field camera (DECam)
on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five
filters (grizY). By its completion the survey is expected to have generated a
catalogue of 300 million galaxies with photometric redshifts and 100 million
stars. In addition, a time-domain survey search over 27 sq deg is expected to
yield a sample of thousands of Type Ia supernovae and other transients. The
main goals of DES are to characterise dark energy and dark matter, and to test
alternative models of gravity; these goals will be pursued by studying large
scale structure, cluster counts, weak gravitational lensing and Type Ia
supernovae. However, DES also provides a rich data set which allows us to study
many other aspects of astrophysics. In this paper we focus on additional
science with DES, emphasizing areas where the survey makes a difference with
respect to other current surveys. The paper illustrates, using early data (from
`Science Verification', and from the first, second and third seasons of
observations), what DES can tell us about the solar system, the Milky Way,
galaxy evolution, quasars, and other topics. In addition, we show that if the
cosmological model is assumed to be Lambda+ Cold Dark Matter (LCDM) then
important astrophysics can be deduced from the primary DES probes. Highlights
from DES early data include the discovery of 34 Trans Neptunian Objects, 17
dwarf satellites of the Milky Way, one published z > 6 quasar (and more
confirmed) and two published superluminous supernovae (and more confirmed). | The Quantum Corrected Mode Function and Power Spectrum for a Scalar
Field during Inflation: We compute the one- and two-loop corrected mode function of a massless
minimally coupled scalar endowed with a quartic self-interaction in the locally
de Sitter background of an inflating universe for a state which is released in
Bunch-Davies vacuum at time $t=0$. We then employ it to correct the scalar's
tree-order scale invariant power spectrum $\Delta^2_\varphi$. The corrections
are secular, and have scale dependent part that can be expanded in even powers
of $k/(Ha)$, where $k$ is the comoving wave number, $H$ is the expansion rate
and $a$ is the cosmic scale factor. At one-loop, the scale invariant shift in
the power spectrum grows as $(Ht)^2$ in leading order. The $k$-dependent
shifts, however, are constants for each mode, in the late time limit. At
two-loop order, on the other hand, the scale invariant shift grows as $(Ht)^4$
whereas the $k$-dependent shifts grow as $(Ht)^2$, in leading order. We finally
calculate the scalar's spectral index $n_\varphi$ and the running of the
spectral index $\alpha_\varphi$. They imply that the spectrum is slightly
red-tilted; hence, the amplitudes of fluctuations grow slightly towards the
larger scales. |
From Cavendish to PLANCK: Constraining Newton's Gravitational Constant
with CMB Temperature and Polarization Anisotropy: We present new constraints on cosmic variations of Newton's gravitational
constant by making use of the latest CMB data from WMAP, BOOMERANG, CBI and
ACBAR experiments and independent constraints coming from Big Bang
Nucleosynthesis. We found that current CMB data provide constraints at the 10%
level, that can be improved to 3% by including BBN data. We show that future
data expected from the Planck satellite could constrain G at the 1.5% level
while an ultimate, cosmic variance limited, CMB experiment could reach a
precision of about 0.4%, competitive with current laboratory measurements. | Fossil Groups Origins III. Characterization of the sample and
observational properties of fossil systems: (Abridged) Fossil systems are group- or cluster-sized objects whose
luminosity is dominated by a very massive central galaxy. In the current cold
dark matter scenario, these objects formed hierarchically at an early epoch of
the Universe and then slowly evolved until present day. That is the reason why
they are called {\it fossils}. We started an extensive observational program to
characterize a sample of 34 fossil group candidates spanning a broad range of
physical properties. Deep $r-$band images were taken for each candidate and
optical spectroscopic observations were obtained for $\sim$ 1200 galaxies. This
new dataset was completed with SDSS DR7 archival data to obtain robust cluster
membership and global properties of each fossil group candidate. For each
system, we recomputed the magnitude gaps between the two brightest galaxies
($\Delta m_{12}$) and the first and fourth ranked galaxies ($\Delta m_{14}$)
within 0.5 $R_{{\rm 200}}$. We consider fossil systems those with $\Delta
m_{12} \ge 2$ mag or $\Delta m_{14} \ge 2.5$ mag within the errors. We find
that 15 candidates turned out to be fossil systems. Their observational
properties agree with those of non-fossil systems. Both follow the same
correlations, but fossils are always extreme cases. In particular, they host
the brightest central galaxies and the fraction of total galaxy light enclosed
in the central galaxy is larger in fossil than in non-fossil systems. Finally,
we confirm the existence of genuine fossil clusters. Combining our results with
others in the literature, we favor the merging scenario in which fossil systems
formed due to mergers of $L^\ast$ galaxies. The large magnitude gap is a
consequence of the extreme merger ratio within fossil systems and therefore it
is an evolutionary effect. Moreover, we suggest that at least one candidate in
our sample could represent a transitional fossil stage. |
SuperFaB: a fabulous code for Spherical Fourier-Bessel decomposition: The spherical Fourier-Bessel (SFB) decomposition is a natural choice for the
radial/angular separation that allows extraction of cosmological information
from large volume galaxy surveys, taking into account all wide-angle effects.
In this paper we develop a SFB power spectrum estimator that allows the
measurement of the largest angular and radial modes with the next generation of
galaxy surveys. The code measures the pseudo-SFB power spectrum, and takes into
account mask, selection function, pixel window, and shot noise. We show that
the local average effect (or integral constraint) is significant only in the
largest-scale mode, and we provide an analytical covariance matrix. By imposing
boundary conditions at the minimum and maximum radius encompassing the survey
volume, the estimator does not suffer from the numerical instabilities that
have proven challenging for SFB analyses in the past. The estimator is
demonstrated on simplified but realistic Roman-like, SPHEREx-like, and
Euclid-like mask and selection functions. For intuition and validation, we also
explore the SFB power spectrum in the Limber approximation. We release the
associated public code written in Julia. | GMASS ultradeep spectroscopy of galaxies at z ~ 2 - VII. Star formation,
extinction, and gas outflows from UV spectra: We use rest-frame UV spectroscopy to investigate the properties related to
large-scale gas outflows, and to the dust extinction and star-formation rates
of a sample of z ~ 2 star-forming galaxies from the Galaxy Mass Assembly
ultradeep Spectroscopic Survey (GMASS). Dust extinction is estimated from the
rest-frame UV continuum slope and used to obtain dust-corrected star-formation
rates for the galaxies of the sample. For the entire sample, a mean value of
the continuum slope <\beta> = -1.11 \pm 0.44 (r.m.s.) was derived, while the
average SFR was found to be <SFR> = 52 \pm 48 M_sun/yr (r.m.s.). A positive
correlation between SFR and stellar mass was observed, in agreement with other
works, the logarithmic slope of the relation being 1.10 \pm 0.10.
Low-ionization absorption lines, associated with the interstellar medium, were
found to be blueshifted, with respect to the rest frame of the system, which
indicates that there is outflowing gas with typical velocities of the order of
~ 100 km/s. Finally, investigating correlations between galaxy UV spectral
characteristics and galaxy general properties, we report a possible correlation
between the equivalent width of the interstellar absorption lines and SFR,
stellar mass, and colour excess similar to that seen to hold at different
redshifts. |
Physical modelling of galaxy clusters using Einasto dark matter profiles: We derive a model for Sunyaev--Zel'dovich data from a galaxy cluster which
uses an Einasto profile to model the cluster's dark matter component. This
model is similar to the physical models for clusters previously used by the
Arcminute Microkelvin Imager (AMI) consortium, which model the dark matter
using a Navarro-Frenk-White (NFW) profile, but the Einasto profile provides an
extra degree of freedom. We thus present a comparison between two physical
models which differ only in the way they model dark matter: one which uses an
NFW profile (PM I) and one that uses an Einasto profile (PM II). We illustrate
the differences between the models by plotting physical properties of clusters
as a function of cluster radius. We generate AMI simulations of clusters which
are \textit{created} and \textit{analysed} with both models. From this we find
that for 14 of the 16 simulations, the Bayesian evidence gives no preference to
either of the models according to the Jeffreys scale, and for the other two
simulations, weak preference in favour of the correct model. However, for the
mass estimates obtained from the analyses, the values were within $1\sigma$ of
the input values for 14 out of 16 of the clusters when using the correct model,
but only in 6 out of 16 cases when the incorrect model was used to analyse the
data. Finally we apply the models to real data from cluster A611 obtained with
AMI, and find the mass estimates to be consistent with one another except in
the case of when PM II is applied using an extreme value for the Einasto shape
parameter. | Epoch of Reionisation 21cm Forecasting From MCMC-Constrained
Semi-Numerical Models: The recent low value of Planck (2016) integrated optical depth to Thomson
scattering suggests that the reionization occurred fairly suddenly, disfavoring
extended reionization scenarios. This will have a significant impact on the
21cm power spectrum. Using a semi-numerical framework, we improve our model
from Hassan et al. (2016) to include time-integrated ionisation and
recombination effects, and find that this leads to more sudden reionisation. It
also yields larger HII bubbles which leads to an order of magnitude more 21cm
power on large scales, while suppressing the small scale ionization power.
Local fluctuations in the neutral hydrogen density play the dominant role in
boosting the 21cm power spectrum on large scales, while recombinations are
subdominant. We use a Monte Carlo Markov Chain approach to constrain our model
to observations of the star formation rate functions at z = 6,7,8 from Bouwens
et al. (2015), the Planck (2016) optical depth measurements, and the Becker &
Bolton (2013) ionising emissivity data at z~5. We then use this constrained
model to perform 21cm forecasting for LOFAR, HERA, and SKA in order to
determine how well such data can characterise the sources driving reionisation.
We find that the 21cm power spectrum alone can somewhat constrain the halo mass
dependence of ionising sources, the photon escape fraction and ionising
amplitude, but combining the 21cm data with other current observations enables
us to separately constrain all these parameters. Our framework illustrates how
21cm data can play a key role in understanding the sources and topology of
reionisation as observations improve. |
Cross-correlation Techniques to Mitigate the Interloper Contamination
for Line Intensity Mapping Experiments: Line intensity mapping (LIM) serves as a potent probe in astrophysics,
relying on the statistical analysis of integrated spectral line emissions
originating from distant star-forming galaxies. While LIM observations hold the
promise of achieving a broad spectrum of scientific objectives, a significant
hurdle for future experiments lies in distinguishing the targeted spectral line
emitted at a specific redshift from undesired line emissions originating at
different redshifts. The presence of these interloping lines poses a challenge
to the accuracy of cosmological analyses. In this study, we introduce a novel
approach to quantify line-line cross-correlations (LIM-LLX), enabling us to
investigate the true signal amidst instrumental noise and interloping
emissions. For example, at a redshift of approximately $z\sim3.7$, we observed
that the measured auto-power spectrum of [CII] exhibited substantial bias, from
interloping line emission. However, cross-correlating [CII] with CO(6-5) lines
using a FYST-like experiment yielded a promising result, with a Signal-to-noise
ratio (SNR) of $\sim 10$. This measurement is notably unbiased. Additionally,
we explore the extensive capabilities of cross-correlation by leveraging
various CO transitions to probe the tomographic Universe at lower redshifts
through LIM-LLX. We further demonstrate that incorporating low-frequency
channels, such as 90 GHz and 150 GHz, into FYST's EoR-Spec-like experiment can
maximize the potential for cross-correlation studies, effectively reducing the
bias introduced by instrumental noise and interlopers. | The effect of dark matter-dark radiation interactions on halo abundance
-- a Press-Schechter approach: We study halo mass functions with the Press-Schechter formalism for
interacting dark matter models, where matter power spectra are damped due to
dark acoustic oscillations in the early universe. After adopting a smooth
window function, we calibrate the analytical model with numerical simulations
from the "effective theory of structure formation" (ETHOS) project and fix the
model parameters in the high mass regime, $M_{\rm h}\gtrsim3\times10^{10}\;{\rm
M}_{\odot}$. We also perform high-resolution cosmological simulations with halo
masses down to $M_{\rm h}\sim10^8\;{\rm M}_{\odot}$ to cover a wide mass range
for comparison. Although the model is calibrated with ETHOS1 and CDM
simulations for high halo masses at redshift $z=0$, it successfully reproduces
simulations for two other ETHOS models in the low mass regime at low and high
redshifts. As an application, we compare the cumulative number density of
haloes to that of observed galaxies at $z=6$, and find the interacting dark
matter models with a kinetic decoupling temperature below $0.5\ \rm{keV}$ is
disfavored. We also perform the abundance-matching analysis and derive the
stellar-halo mass relation for these models at $z=4$. Suppression in halo
abundance leads to less massive haloes that host observed galaxies in the
stellar mass range $M_*\simeq 10^5-10^7\ {\rm M}_{\odot}$. |
Asymmetric Sky from the Long Mode Modulations: The observed dipole asymmetry in Cosmic Microwave Background radiation may
have originated from the modulations of super-horizon long wavelength modes. In
this work we unveil different aspects of asymmetries generated from the long
wavelength mode modulations. We show that the same mechanism which leads to the
observed CMB power spectrum dipole asymmetry from the long mode modulations
also yields dipole asymmetry in (a): tensor perturbations power spectrum and
(b): the halo bias parameter. These are different phenomena relevant to
different cosmological histories but both share the same underlying mechanism
in generating asymmetries in the sky. We obtain the set of consistency
conditions relating the amplitude of dipole asymmetries generated on tensor
perturbations and halo bias parameter to the amplitude of dipole asymmetry
generated on CMB power spectrum. In addition, we show that this mechanism does
not produce dipole asymmetry in acceleration expansion in $\Lambda CDM$
universe because the super-horizon curvature perturbation is conserved in this
background. | Prospects of determination of reheating temperature after inflation by
DECIGO: If the tensor-to-scalar ratio $r$ of cosmological perturbations takes a large
value $r\sim 0.1$, which may be inferred by recent BICEP2 result, we can hope
to determine thermal history, in particular, the reheating temperature, $T_R$,
after inflation by space-based laser interferometers. It is shown that upgraded
and upshifted versions of DECIGO may be able to determine $T_R$ if it lies in
the range $6\times 10^6< T_R < 5\times 10^7$GeV and $3\times 10^7<T_R<2\times
10^8$GeV, respectively. Although these ranges include predictions of some
currently plausible inflation models, since each specification can probe $T_R$
of at most a decade range, we should determine the specifications of DECIGO
with full account of constraints on inflation models to be obtained by
near-future observations of temperature anisotropy and B-model polarization of
the cosmic microwave background radiation. |
X-ray observations of the galaxy cluster Abell 2029 to the virial radius: We present Suzaku observations of the galaxy cluster Abell 2029, which
exploit Suzaku's low particle background to probe the ICM to radii beyond those
possible with previous observations (reaching out to the virial radius), and
with better azimuthal coverage. We find significant anisotropies in the
temperature and entropy profiles, with a region of lower temperature and
entropy occurring to the south east, possibly the result of accretion activity
in this direction. Away from this cold feature, the thermodynamic properties
are consistent with an entropy profile which rises, but less steeply than the
predictions of purely gravitational hierarchical structure formation. Excess
emission in the northern direction can be explained due to the overlap of the
emission from the outskirts of Abell 2029 and nearby Abell 2033 (which is at
slightly higher redshift). These observations suggest that the assumptions of
spherical symmetry and hydrostatic equilibrium break down in the outskirts of
galaxy clusters, which poses challenges for modelling cluster masses at large
radii and presents opportunities for studying the formation and accretion
history of clusters. | Planck/SDSS Cluster Mass and Gas Scaling Relations for a Volume-Complete
redMaPPer Sample: Using Planck satellite data, we construct SZ gas pressure profiles for a
large, volume-complete sample of optically selected clusters. We have defined a
sample of over 8,000 redMaPPer clusters from the Sloan Digital Sky Survey
(SDSS), within the volume-complete redshift region 0.100 < z < 0.325, for which
we construct Sunyaev-Zel'dovich (SZ) effect maps by stacking Planck data over
the full range of richness. Dividing the sample into richness bins we
simultaneously solve for the mean cluster mass in each bin together with the
corresponding radial pressure profile parameters, employing an MCMC analysis.
These profiles are well detected over a much wider range of cluster mass and
radius than previous work, showing a clear trend towards larger break radius
with increasing cluster mass. Our SZ-based masses fall ~24% below the
mass-richness relations from weak lensing, in a similar fashion as the
"hydrostatic bias" related with X-ray derived masses. We correct for this bias
to derive an optimal mass-richness relation finding a slope 1.22 +/- 0.04 and a
pivot mass log(M_500/M_0)= 14.432 +/- 0.041, evaluated at a richness lambda=60.
Finally, we derive a tight Y_500-M_500 relation over a wide range of cluster
mass, with a power law slope equal to 1.72 +/- 0.07, that agrees well with the
independent slope obtained by the Planck team with an SZ-selected cluster
sample, but extends to lower masses with higher precision. |
From BeyondPlanck to Cosmoglobe: Preliminary $\mathit{WMAP}$ $\mathit
Q$-band analysis: We present the first application of the Cosmoglobe analysis framework by
analyzing 9-year $\mathit{WMAP}$ time-ordered observations using similar
machinery as BeyondPlanck utilizes for $\mathit{Planck}$ LFI. We analyze only
the $\mathit Q$-band (41 GHz) data and report on the low-level analysis process
from uncalibrated time-ordered data to calibrated maps. Most of the existing
BeyondPlanck pipeline may be reused for $\mathit{WMAP}$ analysis with minimal
changes to the existing codebase. The main modification is the implementation
of the same preconditioned biconjugate gradient mapmaker used by the
$\mathit{WMAP}$ team. Producing a single $\mathit{WMAP}$ $\mathit Q$1-band
sample requires 22 CPU-hrs, which is slightly more than the cost of a
$\mathit{Planck}$ 44 GHz sample of 17 CPU-hrs; this demonstrates that full
end-to-end Bayesian processing of the $\mathit{WMAP}$ data is computationally
feasible. In general, our recovered maps are very similar to the maps released
by the $\mathit{WMAP}$ team, although with two notable differences. In
temperature we find a $\sim2\,\mathrm{\mu K}$ quadrupole difference that most
likely is caused by different gain modeling, while in polarization we find a
distinct $2.5\,\mathrm{\mu K}$ signal that has been previously called
poorly-measured modes by the $\mathit{WMAP}$ team. In the Cosmoglobe
processing, this pattern arises from temperature-to-polarization leakage from
the coupling between the CMB Solar dipole, transmission imbalance, and
sidelobes. No traces of this pattern are found in either the frequency map or
TOD residual map, suggesting that the current processing has succeeded in
modelling these poorly measured modes within the assumed parametric model by
using $\mathit{Planck}$ information to break the sky-synchronous degeneracies
inherent in the $\mathit{WMAP}$ scanning strategy. | Black Holes in the Early Universe: The existence of massive black holes was postulated in the sixties, when the
first quasars were discovered. In the late nineties their reality was proven
beyond doubt, in the Milky way and a handful nearby galaxies. Since then,
enormous theoretical and observational efforts have been made to understand the
astrophysics of massive black holes. We have discovered that some of the most
massive black holes known, weighing billions of solar masses, powered luminous
quasars within the first billion years of the Universe. The first massive black
holes must therefore have formed around the time the first stars and galaxies
formed. Dynamical evidence also indicates that black holes with masses of
millions to billions of solar masses ordinarily dwell in the centers of today's
galaxies. Massive black holes populate galaxy centers today, and shone as
quasars in the past; the quiescent black holes that we detect now in nearby
bulges are the dormant remnants of this fiery past. In this review we report on
basic, but critical, questions regarding the cosmological significance of
massive black holes. What physical mechanisms lead to the formation of the
first massive black holes? How massive were the initial massive black hole
seeds? When and where did they form? How is the growth of black holes linked to
that of their host galaxy? Answers to most of these questions are work in
progress, in the spirit of these Reports on Progress in Physics. |
Fundamentals of the Dwarf Fundamental Plane: Star-forming dwarfs are studied to elucidate the physical underpinnings of
their fundamental plane. It is confirmed that residuals in the Tully-Fisher
relation are correlated with surface brightness, but that even after
accommodating the surface brightness dependence through the dwarf fundamental
plane, residuals in absolute magnitude are far larger than expected from
observational errors. Rather, a more fundamental plane is identified which
connects the potential to HI line width and surface brightness. Residuals
correlate with the axis ratio in a way which can be accommodated by recognizing
the galaxies to be oblate spheroids viewed at varying angles. Correction of
surface brightnesses to face-on leads to a correlation among the potential,
line width, and surface brightness for which residuals are entirely
attributable to observational uncertainties. The mean mass-to-light ratio of
the diffuse component of the galaxies is constrained to be 0.88 +/- 0.20 in Ks.
Blue compact dwarfs lie in the same plane as dwarf irregulars. The dependence
of the potential on line width is less strong than expected for virialized
systems, but this may be because surface brightness is acting as a proxy for
variations in the mass-to-light ratio from galaxy to galaxy. Altogether, the
observations suggest that gas motions are predominantly disordered and
isotropic, that they are a consequence of gravity, not turbulence, and that the
mass and scale of dark matter haloes scale with the amount and distribution of
luminous matter. The tight relationship between the potential and observables
offers the promise of determining distances to unresolved star-forming dwarfs
to an accuracy comparable to that provided by the Tully-Fisher relation for
spirals. | Metallicity map of the galaxy cluster A3667: We use XMM-Newton data of the merging cluster Abell 3667 to analyze its
metallicity distribution. A detailed abundance map of the central 1.1x1.1 Mpc
region indicates that metals are inhomogeneously distributed in the cluster
showing a non-uniform and very complex metal pattern. The highest peak in the
map corresponds to a cold region, slightly offset South of the X-ray center.
This could be interpreted as stripped gas due to a merger between a group
moving from NW towards the SE and the main cluster. We note several clumps of
high metallicity also in the opposite direction with respect to the X-ray peak.
Furthermore we determined abundances for 5 elements (O, Si, S, Ar, Fe) in four
different regions of the cluster. Comparisons between these observed abundances
and theoretical supernovae yields allow to get constraints on the relative
number of SN Ia and II contributing to the enrichment of the intra-cluster
medium. To reproduce the observed abundances of the best determined elements
(Fe, O and Si) in a region of 7 arcmin around the X-ray center, 65-80% of SN II
are needed. The comparison between the metal map, a galaxy density map obtained
using 550 spectroscopically confirmed cluster members and our simulations
suggest a recent merger between the main cluster and the group in the SE. |
Dark energy in light of the early JWST observations: case for a negative
cosmological constant?: Early data from the James Webb Space Telescope (JWST) has uncovered the
existence of a surprisingly abundant population of very massive galaxies at
extremely high redshift, which are hard to accommodate within the standard
$\Lambda$CDM cosmology. We explore whether the JWST observations may be
pointing towards more complex dynamics in the dark energy (DE) sector.
Motivated by the ubiquity of anti-de Sitter vacua in string theory, we consider
a string-inspired scenario where the DE sector consists of a negative
cosmological constant (nCC) and a evolving component with positive energy
density on top, whose equation of state is allowed to cross the phantom divide.
We show that such a scenario can drastically alter the growth of structure
compared to $\Lambda$CDM, and accommodate the otherwise puzzling JWST
observations if the dynamical component evolves from the quintessence-like
regime in the past to the phantom regime today: in particular, we demonstrate
that the presence of a nCC (which requires a higher density for the evolving
component) plays a crucial role in enhancing the predicted cumulative comoving
stellar mass density. Our work reinforces the enormous potential held by
observations of the abundance of high-$z$ galaxies in probing cosmological
models and new fundamental physics, including string-inspired ingredients. | Could Sample Variance be Responsible for the Parity-Violating Signal
Seen in the BOSS Galaxy Survey?: Recent works have uncovered an excess signal in the parity-odd four-point
correlation function measured from the BOSS spectroscopic galaxy survey. If
physical in origin, this could indicate evidence for new parity-breaking
processes in the scalar sector, most likely from inflation. At heart, these
studies compare the observed four-point correlator to the distribution obtained
from parity-conserving mock galaxy surveys; if the simulations underestimate
the covariance of the data, noise fluctuations may be misinterpreted as a
signal. To test this, we reanalyse the BOSS CMASS + LOWZ parity-odd dataset
with the noise distribution modeled using the newly developed GLAM-Uchuu suite
of mocks. These comprise full N-body simulations that follow the evolution of
$2000^3$ dark matter particles in a $\Lambda$CDM universe, and represent a
significant upgrade compared to the formerly MultiDark-Patchy mocks, which were
based on an alternative (non N-body) gravity solver. We find no significant
evidence for parity-violation in the BOSS dataset (with a baseline detection
significance of $1.4\sigma$), suggesting that the former signal ($>3.5\sigma$
with our data cuts) could be caused by an underestimation of the covariance in
MultiDark-Patchy. The significant differences between results obtained with the
two sets of BOSS-calibrated galaxy catalogs showcases the heightened
sensitivity of beyond-two-point analyses to the treatment of non-linear effects
and indicates that previous constraints may suffer from large systematic
uncertainties. |
Euclid: Cosmology forecasts from the void-galaxy cross-correlation
function with reconstruction: We investigate the cosmological constraints that can be expected from
measurement of the cross-correlation of galaxies with cosmic voids identified
in the Euclid spectroscopic survey, which will include spectroscopic
information for tens of millions of galaxies over $15\,000$ deg$^2$ of the sky
in the redshift range $0.9\leq z<1.8$. We do this using simulated measurements
obtained from the Flagship mock catalogue, the official Euclid mock that
closely matches the expected properties of the spectroscopic data set. To
mitigate anisotropic selection-bias effects, we use a velocity field
reconstruction method to remove large-scale redshift-space distortions from the
galaxy field before void-finding. This allows us to accurately model
contributions to the observed anisotropy of the cross-correlation function
arising from galaxy velocities around voids as well as from the
Alcock-Paczynski effect, and we study the dependence of constraints on the
efficiency of reconstruction. We find that Euclid voids will be able to
constrain the ratio of the transverse comoving distance $D_{\rm M}$ and Hubble
distance $D_{\rm H}$ to a relative precision of about $0.3\%$, and the growth
rate $f\sigma_8$ to a precision of between $5\%$ and $8\%$ in each of four
redshift bins covering the full redshift range. In the standard cosmological
model, this translates to a statistical uncertainty
$\Delta\Omega_\mathrm{m}=\pm0.0028$ on the matter density parameter from voids,
better than can be achieved from either Euclid galaxy clustering and weak
lensing individually. We also find that voids alone can measure the dark energy
equation of state to $6\%$ precision. | Zeldovich pancakes at redshift zero: the equilibration state and phase
space properties: One of the components of the cosmic web are sheets, which are commonly
referred to as Zeldovich pancakes. These are structures which have only
collapsed along one dimension, as opposed to filaments or galaxies and cluster,
which have collapsed along two or three dimensions. These pancakes have
recently received renewed interest, since they have been shown to be useful
tools for an independent method to determine galaxy cluster masses. We consider
sheet-like structures resulting from cosmological simulations, which were
previously used to establish the cluster mass determination method, and we show
through their level of equilibration, that these structures have indeed only
collapsed along the one dimension. We also extract the density profiles of
these pancake, which agrees acceptably well with theoretical expectations. We
derive the observable velocity distribution function (VDF) analytically by
generalizing the Eddington method to one dimension, and we compare with the
distribution function from the numerical simulation. |
Abell 1758N from an optical point of view: new insights on a merging
cluster with diffuse radio emission: We seek to explore the internal dynamics of the cluster Abell 1758N, which
has been shown to host a radio halo and two relics, and is known to be a
merging bimodal cluster. Our analysis is mainly based on new redshift data for
137 galaxies acquired at the Telescopio Nazionale Galileo, only four of which
have redshifts previously listed in the literature. We also used photometric
data from the Sloan Digital Sky Survey and from the Canada-France-Hawaii
Telescope archive. We combined galaxy velocities and positions to select 92
cluster galaxies and analyzed the internal cluster dynamics. We estimate a
cluster redshift of <z>=0.2782 and quite a high line-of-sight (LOS) velocity
dispersion of ~ 1300 km/s. Our 2D analysis confirms the presence of a bimodal
structure along the NW-SE direction. We add several pieces of information to
the previous merging scenario: the two subclusters (here A1758N(NW) and
A1758N(SE)) cannot be separated in the velocity analyses and we deduce a small
LOS velocity difference of ~300 km/s in the cluster rest-frame. The velocity
information successfully shows that A1758N is surrounded by two small groups
and active galaxies infalling onto, or escaping from, the cluster. Removing the
two groups, we estimate ~1000 km/s and ~800 km/s for the velocity dispertions
of A1758N(NW) and A1758N(SE), respectively. We find that Abell 1758N is a very
massive cluster with a range of M=2-3 10^15 solar masses, depending on the
adopted model. As expected for clusters that host powerful, extended, diffuse
radio emissions, Abell 1758N is a major cluster merger just forming a massive
system. | Projection effects on the observed angular spectrum of the astrophysical
stochastic gravitational wave background: The detection and characterization of the Stochastic Gravitational Wave
Background (SGWB) is one of the main goals of Gravitational Wave (GW)
experiments. The observed SGWB will be the combination of GWs from cosmological
(as predicted by many models describing the physics of the early Universe) and
astrophysical origins, which will arise from the superposition of GWs from
unresolved sources whose signal is too faint to be detected. Therefore, it is
important to have a proper modeling of the astrophysical SGWB (ASGWB) in order
to disentangle the two signals; moreover, this will provide additional
information on astrophysical properties of compact objects. Applying the Cosmic
Rulers formalism, we compute the observed ASGWB angular power spectrum, hence
using gauge invariant quantities, accounting for all effects intervening
between the source and the observer. These are the so-called projection
effects, which include Kaiser, Doppler and gravitational potentials effect. Our
results show that these projection effects are the most important at the
largest scales, and they contribute to up to tens of percent of the angular
power spectrum amplitude, with the Kaiser term being the largest at all scales.
While the exact impact of these results will depend on instrumental and
astrophysical details, a precise theoretical modeling of the ASGWB will
necessarily need to include all these projection effects. |
The XXL Survey: XLVIII; X-ray follow-up of distant XXL clusters: Masses,
scaling relations and AGN contamination: We use deep follow-up XMM-Newton observations of 6 clusters discovered in the
XXL Survey at $z>1$ to gain robust measurements of their X-ray properties and
to investigate the extent to which scaling relations at low redshift are valid
at $z>1$. This sample is unique as it has been investigated for AGN
contamination, which ensures measurements are not undermined by systematic
uncertainties, and pushes to lower mass at higher redshift than is usually
possible, for example with Sunyaev-Zel'dovich (SZ) selected clusters. We
determine the flux contribution of point sources to the XXL cluster flux in
order to test for the presence of AGN in other high-redshift cluster
candidates, and find 3XLSS J231626.8-533822 to be a point source misclassified
as a cluster and 3XLSS J232737.3-541618 to be a genuine cluster. We present the
first attempt to measure the hydrostatic masses in a bright subsample of $z>1$
X-ray selected galaxy clusters with a known selection function. Periods of high
particle background significantly reduced the effective exposure times of
observations (losing >50% in some cases) limiting the power of this study. When
combined with complementary SZ selected cluster samples at higher masses, the
data appear broadly consistent with the self-similar evolution of the low
redshift scaling relations between ICM properties and cluster mass, suggesting
that properties such as the X-ray temperature, gas mass and SZ signal remain
reliable mass proxies even at high redshift. | A Novel Framework for Modeling Weakly Lensing Shear Using Kinematics and
Imaging at Moderate Redshift: Kinematic weak lensing describes the distortion of a galaxy's projected
velocity field due to lensing shear, an effect recently reported for the first
time by Gurri et al. based on a sample of 18 galaxies at $z \sim 0.1$. In this
paper, we develop a new formalism that combines the shape information from
imaging surveys with the kinematic information from resolved spectroscopy to
better constrain the lensing distortion of source galaxies and to potentially
address systematic errors that affect conventional weak-lensing analyses. Using
a Bayesian forward model applied to mock galaxy observations, we model
distortions in the source galaxy's velocity field simultaneously with the
apparent shear-induced offset between the kinematic and photometric major axes.
We show that this combination dramatically reduces the statistical uncertainty
on the inferred shear, yielding statistical error gains of a factor of 2--6
compared to kinematics alone. While we have not accounted for errors from
intrinsic kinematic irregularities, our approach opens kinematic lensing
studies to higher redshifts where resolved spectroscopy is more challenging.
For example, we show that ground-based integral-field spectroscopy of
background galaxies at $z \sim 0.7$ can deliver gravitational shear
measurements with S/N $\sim 1$ per source galaxy at 1 arcminute separations
from a galaxy cluster at $z \sim 0.3$. This suggests that even modest samples
observed with existing instruments could deliver improved galaxy cluster mass
measurements and well-sampled probes of their halo mass profiles to large
radii. |
Relation between standard perturbation theory and regularized
multi-point propagator method: We investigate the relation between the regularized multi-propagator method,
called "Reg PT", and the standard perturbation theory. Reg PT is one of the
most successful models to describe nonlinear evolution of dark matter
fluctuations. However, Reg PT is a mathematically unproven interpolation
formula between the large-scale solution calculated by the standard
perturbation theory and the limiting solution in the small scale calculated by
the multi-point propagator method. In this paper, we give an alternative
explanation for Reg PT in the context of the standard perturbation theory,
showing that Reg PT does not ever have more effective information on nonlinear
matter evolution than the standard perturbation theory. In other words, the
solutions of the standard perturbation theory reproduce the results of $N$-body
simulations better than those of Reg PT, especially at the high-$k$ region.
This fact means that the standard perturbation theory at the two-loop level is
still one of the best predictions of the nonlinear power spectrum to date.
Nevertheless, the standard perturbation theory has not been preferred because
of the divergent behavior of the solution at small scales. To solve this
problem, we also propose a modified standard perturbation theory which avoids
the divergence. | Detection likelihood of cluster-induced CMB polarization: Nearby galaxy clusters can potentially induce sub-microkelvin polarization
signals in the cosmic microwave background (CMB) at characteristic scales of a
few arcminutes. We explore four such polarization signals induced in a rich
nearby fiducial cluster and calculate the likelihood of their detection by a
telescope project with capabilities such as those of the Simons Observatory
(SO). In our feasibility analysis, we include instrumental noise, primordial
CMB anisotropy, statistical thermal Sunyaev-Zeldovich (SZ) cluster signal, and
point source confusion, assuming a few percent of the nominal telescope
observation time of an SO-like project. Our analysis indicates that the thermal
SZ intensity can be sensitively mapped in rich nearby clusters and that the
kinematic SZ intensity can be measured with high statistical significance
toward a fast moving nearby cluster. The detection of polarized SZ signals will
be quite challenging but could still be feasible toward several very rich
nearby clusters with very high SZ intensity. The polarized SZ signal from a
sample of ~20 clusters can be statistically detected at S/N~3, if observed for
several months. |
A survey of Low Luminosity Compact sources: Based on the FIRST and SDSS catalogues a flux density limited sample of weak
Compact Steep Spectrum (CSS) sources with radio luminosity below 10^26 [W/Hz]
at 1.4 GHz has been constructed. Our previous multifrequency observations of
CSS sources have shown that low luminosity small-scale objects can be strong
candidates for compact faders. This finding supports the idea that some
small-size radio sources are short-lived phenomena because of a lack of
significant fuelling. They never 'grow up' to become FRI or FRII objects. This
new sample marks the start of a systematical study of the radio properties and
morphologies of the population of low luminosity compact (LLC) objects. An
investigation of this new sample should also lead to a better understanding of
compact faders. In this paper, the results of the first stage of the new
project - the L-band MERLIN observations of 44 low luminosity CSS sources are
presented. | Chiral effects in astrophysics and cosmology: The microscopic quantum nature of elementary particles, chirality, leads to
macroscopic phenomena like the chiral anomaly, chiral magnetic effect, and
chiral plasma instability. We review recent progress of the studies of these
chiral effects in high-energy astrophysics, such as pulsar kicks, magnetars,
and core-collapse supernovae, and early Universe cosmology, such as the
primordial magnetic field, baryogenesis, and chiral gravitational waves. We
also provide a pedagogical introduction to the chiral effects and low-energy
effective theories to describe them in and out of equilibrium -- the chiral
(magneto)hydrodynamics, chiral kinetic theory, and chiral radiation transport
theory for neutrinos. |
The dust content of high-z submillimeter galaxies revealed by Herschel: We use deep observations taken with the Photodetector Array Camera and
Spectrometer (PACS), on board the Herschel satellite as part of the PACS
evolutionary probe (PEP) guaranteed project along with submm ground-based
observations to measure the dust mass of a sample of high-z submillimeter
galaxies (SMGs). We investigate their dust content relative to their stellar
and gas masses, and compare them with local star-forming galaxies. High-z SMGs
are dust rich, i.e. they have higher dust-to-stellar mass ratios compared to
local spiral galaxies (by a factor of 30) and also compared to local
ultraluminous infrared galaxies (ULIRGs, by a factor of 6). This indicates that
the large masses of gas typically hosted in SMGs have already been highly
enriched with metals and dust. Indeed, for those SMGs whose gas mass is
measured, we infer dust-to-gas ratios similar or higher than local spirals and
ULIRGs. However, similarly to other strongly star-forming galaxies in the local
Universe and at high-z, SMGs are characterized by gas metalicities lower (by a
factor of a few) than local spirals, as inferred from their optical nebular
lines, which are generally ascribed to infall of metal-poor gas. This is in
contrast with the large dust content inferred from the far-IR and submm data.
In short, the metalicity inferred from the dust mass is much higher (by more
than an order of magnitude) than that inferred from the optical nebular lines.
We discuss the possible explanations of this discrepancy and the possible
implications for the investigation of the metalicity evolution at high-z. | Constraining the Anisotropic Expansion of Universe: We study the possibly existing anisotropy in the accelerating expansion
universe with the Union2 Type Ia supernovae data and Gamma-ray burst data. We
construct a direction-dependent dark energy model and constrain the anisotropy
direction and strength of modulation. We find that the maximum anisotropic
deviation direction is $(l,\,b)=(126^{\circ},\,13^{\circ})$ (or equivalently
$(l,\,b)=(306^{\circ},\,-13^{\circ})$), and the current anisotropy level is
$g_0=0.030_{+0.010}^{-0.030}$ ($1\sigma$ confidence level with Union2 data).
Our results do not show strong evidence for the anisotropic dark energy model.
We also discuss potential methods that may distinguish the peculiar velocity
field from the anisotropic dark energy model. |
Statistical anisotropies in temperature and polarization fluctuations
from a scale-dependent trispectrum: We study statistical anisotropies generated in the observed two-point
function of the cosmic microwave background (CMB) fluctuations if the
primordial statistics are non-Gaussian. Focusing on the dipole modulations of
the anisotropies, we find that the hemispherical power asymmetry observed in
the CMB temperature fluctuations can be modeled by a local-type trispectrum
with amplitude $\tau_{\rm NL}(k_p=0.05~{\rm Mpc}^{-1}) \approx 2 \times 10^4$
and a large red tilt $n\approx -0.68$. We numerically evaluate the non-Gaussian
covariance of the modulation estimators for both temperature and E-mode
polarization fluctuations and discuss the prospects of constraining the model
using Planck satellite data. We then discuss other effects of the
scale-dependent trispectrum that could be used to distinguish this scenario
from other explanations of the power asymmetry: higher-order modulations of the
two-point function and the non-Gaussian angular power spectrum covariance. As
an important consequence of the non-Gaussian power spectrum covariance, we
discuss how the CMB-inferred spectral index of primordial scalar fluctuations
can be significantly biased in the presence of a scale-dependent local-type
trispectrum. | Accurate Model of the Projected Velocity Distribution of Galaxies in
Dark Matter Halos: We present a percent-level accurate model of the line-of-sight velocity
distribution of galaxies around dark matter halos as a function of projected
radius and halo mass. The model is developed and tested using synthetic galaxy
catalogs generated with the UniverseMachine run on the Multi-Dark Planck 2
N-body simulations. The model decomposes the galaxies around a cluster into
three kinematically distinct classes: orbiting, infalling, and interloping
galaxies. We demonstrate that: 1) we can statistically distinguish between
these three types of galaxies using only projected line-of-sight velocity
information; 2) the halo edge radius inferred from the line-of-sight velocity
dispersion is an excellent proxy for the three-dimensional halo edge radius; 3)
we can accurately recover the full velocity dispersion profile for each of the
three populations of galaxies. Importantly, the velocity dispersion profiles of
the orbiting and infalling galaxies contain five independent parameters --
three distinct radial scales and two velocity dispersion amplitudes -- each of
which is correlated with mass. Thus, the velocity dispersion profile of galaxy
clusters has inherent redundancies that allow us to perform nontrivial
systematics check from a single data set. We discuss several potential
applications of our new model for detecting the edge radius and constraining
cosmology and astrophysics using upcoming spectroscopic surveys. |
CLUMP-3D: Three-dimensional Shape and Structure of 20 CLASH Galaxy
Clusters from Combined Weak and Strong Lensing: We perform a three-dimensional triaxial analysis of 16 X-ray regular and 4
high-magnification galaxy clusters selected from the CLASH survey by combining
two-dimensional weak-lensing and central strong-lensing constraints. In a
Bayesian framework, we constrain the intrinsic structure and geometry of each
individual cluster assuming a triaxial Navarro-Frenk-White halo with arbitrary
orientations, characterized by the mass $M_{200\mathrm{c}}$, halo concentration
$C_{200\mathrm{c}}$, and triaxial axis ratios ($q_{\mathrm{a}} \le
q_{\mathrm{b}}$), and investigate scaling relations between these halo
structural parameters. From triaxial modeling of the X-ray-selected subsample,
we find that the halo concentration decreases with increasing cluster mass,
with a mean concentration of $C_{200\mathrm{c}} = 4.82\pm0.30$ at the pivot
mass $M_{200\mathrm{c}}=10^{15}M_{\odot}h^{-1}$. This is consistent with the
result from spherical modeling, $C_{200\mathrm{c}}=4.51\pm 0.14$. Independently
of the priors, the minor-to-major axis ratio $q_{\mathrm{a}}$ of our full
sample exhibits a clear deviation from the spherical configuration
($q_{\mathrm{a}}=0.52 \pm 0.04$ at $10^{15}M_{\odot}h^{-1}$ with uniform
priors), with a weak dependence on the cluster mass. Combining all 20 clusters,
we obtain a joint ensemble constraint on the minor-to-major axis ratio of
$q_{\mathrm{a}}=0.652^{+0.162}_{-0.078}$ and a lower bound on the
intermediate-to-major axis ratio of $q_{\mathrm{b}}>0.63$ at the $2\sigma$
level from an analysis with uniform priors. Assuming priors on the axis ratios
derived from numerical simulations, we constrain the degree of triaxiality for
the full sample to be $\mathcal{T}=0.79 \pm 0.03$ at $10^{15}M_{\odot}h^{-1}$,
indicating a preference for a prolate geometry of cluster halos. We find no
statistical evidence for an orientation bias ($f_{\mathrm{geo}}=0.93 \pm 0.07$)
(abridged) | Magnetic field strength in cosmic web filaments: We used the Rotation Measure (RM) catalogue derived from the LOFAR Two-metre
Sky Survey Data Release 2 (LoTSS DR2) at 144-MHz to measure the evolution with
redshift of the extragalactic RM (RRM: Residual RM) and the polarization
fraction ($p$) of sources in low density environments. We also measured the
same at 1.4-GHz by cross-matching with the NRAO VLA Sky Survey RM catalogue. We
find that RRM versus redshift is flat at 144-MHz, but, once redshift-corrected,
it shows evolution at high significance. Also $p$ evolves with redshift with a
decrement by a factor of $\sim$8 at $z\sim2$. Comparing the 144-MHz and 1.4-GHz
data, we find that the observed RRM and $p$ are most likely to have an origin
local to the source at 1.4-GHz, while a cosmic web filament origin is favoured
at 144-MHz. If we attribute the entire signal to filaments, we infer a mean
rest frame RRM per filament of RRM_{0,f} = 0.71 \pm 0.07 rad m^{-2} and a
magnetic field per filament of B_f = 32 \pm 3 nG. This is in agreement with
estimates obtained with a complementary method based on synchrotron emission
stacking, and with cosmological simulations if primordial magnetic fields are
amplified by astrophysical source field seeding. The measurement of an
RRM_{0,f} supports the presence of diffuse baryonic gas in filaments. We also
estimated a conservative upper limit of the filament magnetic turbulence of
\sigma_{ RRM_{0,f}} =0.039 \pm 0.001 rad m^{-2}, concluding that the ordered
magnetic field component dominates in filaments. |
Making use of sub-resolution halos in N-body simulations: Conservative mass limits are often imposed on the dark matter halo catalogues
extracted from N-body simulations. By comparing simulations with different mass
resolutions, at $z=0$ we find that even for halos resolved by 100 particles,
the lower resolution simulation predicts a cumulative halo abundance that is 5
per cent lower than in the higher resolution simulation. We propose a simple
weighting scheme to utilise the halos that are usually regarded as being
`sub-resolution'. With the scheme, we are able to use halos which contain only
11 particles to reproduce the clustering measured in the higher resolution
simulation to within 5 per cent on scales down to $2 h^{-1}$ Mpc, thereby
extending the useful halo resolution by a factor of ten below the mass at which
the mass functions in the two simulations first start to deviate. The
performance of the method is slightly worse at higher redshift. Our method
allows a simulation to be used to probe a wider parameter space in clustering
studies, for example, in a halo occupation distribution analysis. This reduces
the cost of generating many simulations to estimate the covariance matrix on
measurements or using a larger volume simulation to make large-scale clustering
predictions. | Models of dark matter halos based on statistical mechanics: II. The
fermionic King model: We discuss the nature of phase transitions in the fermionic King model which
describes tidally truncated quantum self-gravitating systems. This distribution
function takes into account the escape of high energy particles and has a
finite mass. On the other hand, the Pauli exclusion principle puts an upper
bound on the phase space density of the system and stabilizes it against
gravitational collapse. As a result, there exists a statistical equilibrium
state for any accessible values of energy and temperature. We plot the caloric
curves and investigate the nature of phase transitions as a function of the
degeneracy parameter in both microcanonical and canonical ensembles. We
consider stable and metastable states and emphasize the importance of the
latter for systems with long-range interactions. Phase transitions can take
place between a "gaseous" phase unaffected by quantum mechanics and a
"condensed" phase dominated by quantum mechanics. The phase diagram exhibits
two critical points, one in each ensemble, beyond which the phase transitions
disappear. There also exist a region of negative specific heats and a situation
of ensemble inequivalence for sufficiently large systems. We apply the
fermionic King model to the case of dark matter halos made of massive
neutrinos. The gaseous phase describes large halos and the condensed phase
describes dwarf halos. Partially degenerate configurations describe
intermediate size halos. We argue that large dark matter halos cannot harbor a
fermion ball because these nucleus-halo configurations are thermodynamically
unstable (saddle points of entropy). Large dark matter halos may rather contain
a central black hole resulting from a dynamical instability of relativistic
origin occurring during the gravothermal catastrophe. |
Curvature perturbations from preheating with scale dependence: We extend the formalism to calculate non-Gaussianity of primordial curvature
perturbations produced by preheating in the presence of a light scalar field.
The calculation is carried out in the separate universe approximation using the
non-perturbative delta N formalism and lattice field theory simulations.
Initial conditions for simulations are drawn from a statistical ensemble
determined by modes that left the horizon during inflation, with the
time-dependence of Hubble rate during inflation taken into account. Our results
show that cosmic variance, i.e., the contribution from modes with wavelength
longer than the size of the observable universe today, plays a key role in
determining the dominant contribution. We illustrate our formalism by applying
it to an observationally-viable preheating model motivated by non-minimal
coupling to gravity, and study its full parameter dependence. | Sterile neutrino fits to dark matter mass profiles in the Milky Way and
in galaxy clusters: In several recent papers it was claimed that SN 1987A data supports the
existence of 4.0 eV and 21.4 eV active neutrino mass eigenstates, and it was
shown that such large masses could be made consistent with existing constraints
including neutrino oscillation data and upper limits on the neutrino flavor
state masses, provided that there also exist a pair of sterile neutrino mass
states whose masses are nearly degenerate with the active ones, plus a third
active-sterile doublet that is tachyonic ($m^2 <0$). Here, independent evidence
is presented for the existence of sterile neutrinos with the previously claimed
masses based on fits to the dark matter distributions in the Milky Way galaxy
and four clusters of galaxies. The fits are in excellent agreement with
observations. In addition, sterile neutrinos having the suggested masses
address the "cusp" problem and the missing satellites problem, as well as that
of the "top down" scenario of structure formation -- previously a chief
drawback of HDM particles. Nevertheless, the highly controversial nature of the
claim, and the need for two free parameters in the dark matter fits, additional
confirming evidence will be required before it can be considered proven. |
Moment transport equations for non-Gaussianity: We present a novel method for calculating the primordial non-Gaussianity
produced by super-horizon evolution during inflation. Our method evolves the
distribution of coarse-grained inflationary field values using a transport
equation. We present simple evolution equations for the moments of this
distribution, such as the variance and skewness. This method possesses some
advantages over existing techniques. Among them, it cleanly separates multiple
sources of primordial non-Gaussianity, and is computationally efficient when
compared with popular alternatives, such as the "delta N" framework. We adduce
numerical calculations demonstrating that our new method offers good agreement
with those already in the literature. We focus on two fields and the fNL
parameter, but we expect our method will generalize to multiple scalar fields
and to moments of arbitrarily high order. We present our expressions in a
field-space covariant form which we postulate to be valid for any number of
fields. | Strengthening the bound on the mass of the lightest neutrino with
terrestrial and cosmological experiments: We determine the upper limit on the mass of the lightest neutrino from the
most robust recent cosmological and terrestrial data. Marginalizing over
possible effective relativistic degrees of freedom at early times
($N_\mathrm{eff}$) and assuming normal mass ordering, the mass of the lightest
neutrino is less than 0.037 eV at 95% confidence; with inverted ordering, the
bound is 0.042 eV. These results improve upon the strength and robustness of
other recent limits and constrain the mass of the lightest neutrino to be
barely larger than the largest mass splitting. We show the impacts of realistic
mass models, and different sources of $N_\mathrm{eff}$. |
Cosmological Evolution of Semilocal String Networks: Semilocal strings -- a particular limit of electroweak strings -- are an
interesting example of a stable non-topological defect whose properties
resemble those of their topological cousins, the Abrikosov-Nielsen-Olesen
vortices. There is, however, one important difference: a network of semilocal
strings will contain segments. These are 'dumbbells' whose ends behave almost
like global monopoles that are strongly attracted to one another. While closed
loops of string will eventually shrink and disappear, the segments can either
shrink or grow, and a cosmological network of semilocal strings will reach a
scaling regime. We discuss attempts to find a "thermodynamic" description of
the cosmological evolution and scaling of a network of semilocal strings, by
analogy with well-known descriptions for cosmic strings and for monopoles. We
propose a model for the time evolution of an overall lengthscale and typical
velocity for the network as well as for its segments, and some supporting
(preliminary) numerical evidence. | BAL Outflow Contribution to AGN Feedback: Frequency of S iv Outflows in
the SDSS: We present a study of Broad Absorption Line (BAL) quasar outflows that show S
IV ?1063 and S IV* ?1073 troughs. The fractional abundance of S IV and C IV
peak at similar value of the ionization parameter, implying that they arise
from the same physical component of the outflow. Detection of the S IV* troughs
will allow us to determine the distance to this gas with higher resolution and
higher signal-to-noise spectra, therefore providing the distance and energetics
of the ubiquitous C IV BAL outflows. In our bright sample of 156 SDSS quasars
14% show C IV and 1.9% S IV troughs, which is consistent with a fainter
magnitude sample with twice as many objects. One object in the fainter sample
shows evidence of a broad S IV trough without any significant trough present
from the excited state line, which implies that this outflow could be at a
distance of several kpc. Given the fractions of C IV and S IV, we establish
firm limits on the global covering factor on S IV that ranges from 2.8% to 21%
(allowing for the k-correction). Comparison of the expected optical depth for
these ions with their detected percentage suggests that these species arise
from common outflows with a covering factor closer to the latter. |
Harmonic analysis of isotropic fields on the sphere with arbitrary masks: Obtaining constraints from the largest scales of a galaxy survey is
challenging due to the survey mask allowing only partial measurement of large
angular modes. This scatters information from the harmonic-space 2-point
function away from the diagonal and introduces coupling between modes. In this
paper, we derive a custom eigenbasis adapted to any particular survey geometry
so that all information is retained on the diagonal. At the expense of a
somewhat complex pixel- and selection-function-window, the result is a diagonal
2-point function with a simple shot noise, and a diagonal covariance matrix in
the case of a Gaussian random field. We derive the basis on the surface of a
sphere, and we use it to construct a 3D spherical Fourier-Bessel power spectrum
estimator assuming a survey geometry that is separable in the angular and
radial directions. | Fast and Reliable Time Delay Estimation of Strong Lens Systems Using
Method of Smoothing and Cross-Correlation: The observable time delays between the multiple images of strong lensing
systems with time variable sources can provide us with some valuable
information to probe the expansion history of the Universe. Estimation of these
time delays can be very challenging due to complexities of the observed data
where there are seasonal gaps, various noises and systematics such as unknown
microlensing effects. In this paper we introduce a novel approach to estimate
the time delays for strong lensing systems implementing various statistical
methods of data analysis including the method of smoothing and
cross-correlation. The method we introduce in this paper has been recently used
in TDC0 and TDC1 Strong Lens Time Delay Challenges and has shown its power in
reliable and precise estimation of time delays dealing with data with different
complexities. |
Non-universality of halo profiles and implications for dark matter
experiments: We explore the cosmological halo-to-halo scatter of the distribution of mass
within dark matter halos utilizing a well-resolved statistical sample of
clusters from the cosmological Millennium simulation. We find that at any
radius, the spherically-averaged dark matter density of a halo (corresponding
to the "smooth-component") and its logarithmic slope are well-described by a
Gaussian probability distribution. At small radii (within the scale radius),
the density distribution is fully determined by the measured Gaussian
distribution in halo concentrations. The variance in the radial distribution of
mass in dark matter halos is important for the interpretation of direct and
indirect dark matter detection efforts. The scatter in mass profiles imparts
approximately a 25 percent cosmological uncertainty in the dark matter density
at the Solar neighborhood and a factor of ~3 uncertainty in the expected
Galactic dark matter annihilation flux. The aggregate effect of halo-to-halo
profile scatter leads to a small (few percent) enhancement in dark matter
annihilation background if the Gaussian concentration distribution holds for
all halo masses versus a 10 percent enhancement under the assumption of a
log-normal concentration distribution. The Gaussian nature of the cluster
profile scatter implies that the technique of "stacking" halos to improve
signal to noise should not suffer from bias. | Spherical spaces for cosmic topology and multipole selection rules: Spherical manifolds yield cosmic spaces with positive curvature. They result
by closing pieces from the sphere used by Einstein for his initial cosmology.
Harmonic analysis on the manifolds aims at explaining the observed low
amplitudes at small multipole orders of the cosmic microwave background. We
analyze assumptions of point symmetry and randomness for spherical spaces.
There emerge four spaces named orbifolds, with low volume fraction from the
sphere and sharp multipole selection rules in their eigenmodes. |
Measurements of 4He in Metal-Poor Extragalactic HII Regions: the
Primordial Helium Abundance and the Delta Y / Delta O Ratio: We present a review on the determination of the primordial helium abundance
Yp, based on the study of hydrogen and helium recombination lines in
extragalactic HII regions. We also discuss the observational determinations of
the increase of helium to the increase of oxygen by mass Delta Y / Delta O, and
compare them with predictions based on models of galactic chemical evolution. | The Well-Tempered Cosmological Constant: Fugue in B$^\flat$: Zero point fluctuations of quantum fields should generate a large
cosmological constant energy density in any spacetime. How then can we have
anything other than de Sitter space without fine tuning? Well tempering --
dynamical cancellation of the cosmological constant using degeneracy within the
field equations -- can replace a large cosmological constant with a much lower
energy state. Here we give an explicit mechanism to obtain a Minkowski
solution, replacing the cosmological constant with zero, and testing its
attractor nature and persistence through a vacuum phase transition. We derive
the general conditions that Horndeski scalar-tensor gravity must possess, and
evolve in a fugue of functions, to deliver nothing and make the universe be
flat. |
Radiation from Global Topological Strings using Adaptive Mesh
Refinement: Massive Modes: We implement adaptive mesh refinement (AMR) simulations of global topological
strings using the public code, GRChombo. We perform a quantitative
investigation of massive radiation from single sinusoidally displaced string
configurations, studying a range of string widths defined by the coupling
parameter $\lambda$ over two orders of magnitude, effectively varying the mass
of radiated particles $m_H \sim \sqrt{\lambda}$. We perform an in-depth
investigation into the effects of AMR on massive radiation emission, including
radiation trapping and the refinement required to resolve high frequency modes.
We use quantitative diagnostic tools to determine the eigenmode decomposition,
showing a complex superposition of high frequency propagating modes with
different phase and group velocities. We conclude that massive radiation is
generally strongly suppressed relative to the preferred massless channel, with
suppression increasing at lower amplitudes and higher $\lambda$. Only in
extreme nonlinear regimes (e.g.\ with relative amplitude $\varepsilon \sim 1.5$
and $\lambda < 1$) do we observe massive and massless radiation to be emitted
at comparable magnitude. We find that massive radiation is emitted in distinct
high harmonics of the fundamental frequency of the string, and we demonstrate
that, for the sinusoidal configurations studied, massive radiation is
exponentially suppressed with $\sqrt{\lambda}$ (i.e. the particle mass).
Finally, we place these results in the context of axions and gravitational
waves produced by cosmological cosmic string networks, and note that AMR
provides a significant opportunity to explore higher $\lambda$ (thin string)
regimes whilst using fewer computational resources. | General quadrupolar statistical anisotropy: Planck limits: Several early Universe scenarios predict a direction-dependent spectrum of
primordial curvature perturbations. This translates into the violation of the
statistical isotropy of cosmic microwave background radiation. Previous
searches for statistical anisotropy mainly focussed on a quadrupolar
direction-dependence characterised by a single multipole vector and an overall
amplitude $g_*$. Generically, however, the quadrupole has a more complicated
geometry described by two multipole vectors and $g_*$. This is the subject of
the present work. In particular, we limit the amplitude $g_*$ for different
shapes of the quadrupole by making use of Planck 2015 maps. We also constrain
certain inflationary scenarios which predict this kind of more general
quadrupolar statistical anisotropy. |
Stellar feedback by radiation pressure and photoionization: The relative impact of radiation pressure and photoionization feedback from
young stars on surrounding gas is studied with hydrodynamic radiative transfer
(RT) simulations. The calculations focus on the single-scattering (direct
radiation pressure) and optically thick regime, and adopt a moment-based
RT-method implemented in the moving-mesh code AREPO. The source luminosity, gas
density profile and initial temperature are varied. At typical temperatures and
densities of molecular clouds, radiation pressure drives velocities of order
~20 km/s over 1-5 Myr; enough to unbind the smaller clouds. However, these
estimates ignore the effects of photoionization that naturally occur
concurrently. When radiation pressure and photoionization act together, the
latter is substantially more efficient, inducing velocities comparable to the
sound speed of the hot ionized medium (10-15 km/s) on timescales far shorter
than required for accumulating similar momentum with radiation pressure. This
mismatch allows photoionization to dominate the feedback as the heating and
expansion of gas lowers the central densities, further diminishing the impact
of radiation pressure. Our results indicate that a proper treatment of the
impact of young stars on the interstellar medium needs to primarily account for
their ionization power whereas direct radiation pressure appears to be a
secondary effect. This conclusion may change if extreme boosts of the radiation
pressure by photon trapping are assumed. | Condensation and Evaporation of Boson Stars: Axion-like particles, including the QCD axion, are well-motivated dark matter
candidates. Numerical simulations have revealed coherent soliton
configurations, also known as boson stars, in the centers of axion halos. We
study evolution of axion solitons immersed into a gas of axion waves with
Maxwellian velocity distribution. Combining analytical approach with controlled
numerical simulations we find that heavy solitons grow by condensation of
axions from the gas, while light solitons evaporate. We deduce the parametric
dependence of the soliton growth/evaporation rate and show that it is
proportional to the rate of the kinetic relaxation in the gas. The
proportionality coefficient is controlled by the product of the soliton radius
and the typical gas momentum or, equivalently, the ratio of the gas and soliton
virial temperatures. We discuss the asymptotics of the rate when this parameter
is large or small. |
Distinguishing between inhomogeneous model and $Λ\textrm{CDM}$
model with the cosmic age method: Cosmological observables could be used to construct cosmological models,
however, a fixed number of observables limited on the light cone is not enough
to uniquely determine a certain model. A reconstructed spherically symmetric,
inhomogeneous model that share the same angular-diameter-distance-redshift
relationship $d_A(z)$ and Hubble parameter $H(z)$ besides $\Lambda\textrm{CDM}$
model (which we call LTB-$\Lambda\textrm{CDM}$ model in this paper), may
provide another solution. Cosmic age, which is off the light cone, could be
employed to distinguish these two models. We derive the formulae for age
calculation with origin conditions. From the data given by 9-year WMAP
measurement, we compute the likelihood of the parameters in these two models
respectively by using the Distance Prior method and do likelihood analysis by
generating Monte Carlo Markov Chain for the purpose of breaking the degeneracy
of $\Omega_m$ and $H_0$ (the parameters that we use for calculation). The
results yield to be: $t_{\Lambda\textrm{CDM}} =13.76 \pm 0.09 ~\rm Gyr$,
$t_{\rm {LTB}-\Lambda\textrm{CDM}} =11.38 \pm 0.15 ~\rm Gyr$, both in $1\sigma$
agreement with the constraint of cosmic age given by metal-deficient stars. The
cosmic age method that is set in this paper enables us to distinguish between
the inhomogeneous model and $\Lambda\textrm{CDM}$ model. | Accelerating expansion in the swisscheese model: A version of the Swiss-cheese model is investigated. The flat
Friedmann-Robertson-Walker (FRW) universe is modified by the addition of
several spherical regions with Lemaitre-Tolman-Bondi metric.
We discuss light propagation in this model in detail to pave the way for a
detailed numerical study of the Hubble diagram. |
Cosmology with weak-lensing peak counts: Weak gravitational lensing (WL) causes distortions of galaxy images and
probes massive structures on large scales, allowing us to understand the
late-time evolution of the Universe. One way to extract the cosmological
information from WL is to use peak statistics. Peaks are tracers of massive
halos and therefore probe the mass function. They retain non-Gaussian
information and have already been shown as a promising tool to constrain
cosmology. In this work, we develop a new model to predict WL peak counts. The
model generates fast simulations based on halo sampling and selects peaks from
the derived lensing maps. This approach has three main advantages. First, the
model is very fast: only several seconds are required to perform a realization.
Second, including realistic conditions is straightforward. Third, the model
provides the full distribution information because of its stochasticity. We
show that our model agrees well with N-body simulations. Then, we study the
impacts of the cosmology-dependent covariance on constraints and explore
different parameter inference methods. A special focus is put on approximate
Bayesian computation (ABC), an accept-reject sampler without the need to
estimate the likelihood. We show that ABC is able to yield robust constraints
with much reduced time costs. Several filtering techniques are studied to
improve the extraction of multiscale information. Finally, the new model is
applied to the CFHTLenS, KiDS DR1/2, and DES SV data sets. Our preliminary
results agree with the Planck constraints assuming the Lambda-CDM model.
Overall, this thesis forges an innovative tool for future WL surveys. The
manuscript provides a brief review on WL peak counts. | Planck 2018 results. VI. Cosmological parameters: We present cosmological parameter results from the final full-mission Planck
measurements of the CMB anisotropies. We find good consistency with the
standard spatially-flat 6-parameter $\Lambda$CDM cosmology having a power-law
spectrum of adiabatic scalar perturbations (denoted "base $\Lambda$CDM" in this
paper), from polarization, temperature, and lensing, separately and in
combination. A combined analysis gives dark matter density $\Omega_c h^2 =
0.120\pm 0.001$, baryon density $\Omega_b h^2 = 0.0224\pm 0.0001$, scalar
spectral index $n_s = 0.965\pm 0.004$, and optical depth $\tau = 0.054\pm
0.007$ (in this abstract we quote $68\,\%$ confidence regions on measured
parameters and $95\,\%$ on upper limits). The angular acoustic scale is
measured to $0.03\,\%$ precision, with $100\theta_*=1.0411\pm 0.0003$. These
results are only weakly dependent on the cosmological model and remain stable,
with somewhat increased errors, in many commonly considered extensions.
Assuming the base-$\Lambda$CDM cosmology, the inferred late-Universe parameters
are: Hubble constant $H_0 = (67.4\pm 0.5)$km/s/Mpc; matter density parameter
$\Omega_m = 0.315\pm 0.007$; and matter fluctuation amplitude $\sigma_8 =
0.811\pm 0.006$. We find no compelling evidence for extensions to the
base-$\Lambda$CDM model. Combining with BAO we constrain the effective extra
relativistic degrees of freedom to be $N_{\rm eff} = 2.99\pm 0.17$, and the
neutrino mass is tightly constrained to $\sum m_\nu< 0.12$eV. The CMB spectra
continue to prefer higher lensing amplitudes than predicted in base
-$\Lambda$CDM at over $2\,\sigma$, which pulls some parameters that affect the
lensing amplitude away from the base-$\Lambda$CDM model; however, this is not
supported by the lensing reconstruction or (in models that also change the
background geometry) BAO data. (Abridged) |
Toward Unbiased Galaxy Cluster Masses from Line of Sight Velocity
Dispersions: We study the use of red sequence selected galaxy spectroscopy for unbiased
estimation of galaxy cluster masses. We use the publicly available galaxy
catalog produced using the semi-analytic model of De Lucia & Blaizot (2007) on
the Millenium Simulation (Springel et al. 2005). We explore the impacts on
selection using galaxy color, projected separation from the cluster center, and
galaxy luminosity. We study the relationship between cluster mass and velocity
dispersion and identify and characterize the following sources of bias and
scatter: halo triaxiality, dynamical friction of red luminous galaxies and
interlopers. We show that due to halo triaxiality the intrinsic scatter of
estimated line of sight dynamical mass is about three times larger (30-40%)
than the one estimated using the 3D velocity dispersion (~12%) and a small bias
(~1%) is induced. We find evidence of increasing scatter as a function of
redshift and provide a fitting formula to account for it. We characterize the
amount of bias and scatter introduced by dynamical friction when using
subsamples of red-luminous galaxies to estimate the velocity dispersion. We
study the presence of interlopers in spectroscopic samples and their effect on
the estimated cluster dynamical mass. Our results show that while cluster
velocity dispersions extracted from a few dozen red sequence selected galaxies
do not provide precise masses on a single cluster basis, an ensemble of cluster
velocity dispersions can be combined to produce a precise calibration of a
cluster survey mass observable relation. Currently, disagreements in the
literature on simulated subhalo velocity dispersion mass relations place a
systematic floor on velocity dispersion mass calibration at the 15% level in
mass. We show that the selection related uncertainties are small by comparison,
providing hope that with further improvements this systematic floor can be
reduced. | Cosmology with X-RAY galaxy cluster surveys ?: This talk reviews the scientific motivations, the potential difficulty and
recent advances in cosmology using cluster number-counts in the X-ray band. Our
forward modelling approach shows that many of the practical and conceptual
shortcomings can now be overcome. We present recent results from the XMM-XXL
survey. The next step is to apply artificial intelligence techniques on
simulations. This allows us to bypass the unnecessarily complicated scaling
relation formalism. The net gain is to significantly reduce the number of free
parameters and to provide direct access both to the cosmological parameters and
to truly physical ingredients, such as AGN feedback. In this way, we achieve
cluster cosmology without explicit cluster mass calculation. |
James Webb Space Telescope: data, problems, and resolution: It is argued that the data presented by Hubble Space Telescope and James Webb
Space Telescope, that seem to be at odds with the canonical big bang cosmology,
find simple explanation if galaxy formation is seeded by massive primordial
black holes (PBH), as anticipated in 1993 (A. Dolgov and J. Silk, later DS).
The statement that the galaxy formation might be seeded by PBH is now
rediscovered in several works. The predicted by DS log-normal mass spectrum of
PBHs very well agrees with astronomical data. Abundant BH population of the
Galaxy with masses of the order of tens solar masses is predicted. Extended
mass spectrum of PBH together with their possible clustering allows them to
make 100\% contribution into the cosmological dark matter. Another prediction
of DS mechanism on noticeable amount of antimatter in the Milky Way also seems
to be confirmed by the data. | Observational detection of correlation between galaxy spins and initial
conditions: Galaxy spins can be predicted from the initial conditions in the early
Universe through the tidal tensor twist. In simulations, their directions are
well preserved through cosmic time, consistent with expectations of angular
momentum conservation. We report a $\sim 3 \sigma$ detection of correlation
between observed oriented directions of galaxy angular momenta and their
predictions based on the initial density field reconstructed from the positions
of SDSS galaxies. The detection is driven by a group of spiral galaxies
classified by the Galaxy Zoo as (anti-)clockwise, with a modest improvement
from adding galaxies from MaNGA and SAMI surveys. This is the first such
detection of the oriented galaxy spin direction, which opens a way to use
measurements of galaxy spins to probe fundamental physics in the early
Universe. |
Interacting dark energy models in fractal cosmology: We investigate interacting dark energy models in the framework of fractal
cosmology. We discuss a fractal FRW universe filled with the dark energy and
dark matter which interact with each other. We obtain the equation for the
relative density of dark matter and dark energy and the deceleration parameter.
This model demonstrates new types of evolution, which are not common to
cosmological models with this type of interaction. | The central black hole mass of the high-sigma but low-bulge-luminosity
lenticular galaxy NGC 1332: The masses of the most massive supermassive black holes (SMBHs) predicted by
the M_BH-sigma and M_BH-luminosity relations appear to be in conflict. Which of
the two relations is the more fundamental one remains an open question. NGC
1332 is an excellent example that represents the regime of conflict. It is a
massive lenticular galaxy which has a bulge with a high velocity dispersion
sigma of ~320 km/s; bulge--disc decomposition suggests that only 44% of the
total light comes from the bulge. The M_BH-sigma and the M_BH-luminosity
predictions for the central black hole mass of NGC 1332 differ by almost an
order of magnitude. We present a stellar dynamical measurement of the SMBH mass
using an axisymmetric orbit superposition method. Our SINFONI integral-field
unit (IFU) observations of NGC 1332 resolve the SMBH's sphere of influence
which has a diameter of ~0.76 arcsec. The sigma inside 0.2 arcsec reaches ~400
km/s. The IFU data allow us to increase the statistical significance of our
results by modelling each of the four quadrants separately. We measure a SMBH
mass of (1.45 \pm 0.20) x 10^9 M_sun with a bulge mass-to-light ratio of 7.08
\pm 0.39 in the R-band. With this mass, the SMBH of NGC 1332 is offset from the
M_BH-luminosity relation by a full order of magnitude but is consistent with
the M_BH-sigma relation. |
Sizes and ages of SDSS ellipticals: Comparison with hierarchical galaxy
formation models: In a sample of about 45,700 early-type galaxies extracted from SDSS, we find
that the shape, normalization, and dispersion around the mean size-stellar mass
relation is the same for young and old systems, provided the stellar mass is
greater than 3*10^10 Msun. This is difficult to reproduce in pure passive
evolution models, which generically predict older galaxies to be much more
compact than younger ones of the same stellar mass. However, this aspect of our
measurements is well reproduced by hierarchical models of galaxy formation.
Whereas the models predict more compact galaxies at high redshifts, subsequent
minor, dry mergers increase the sizes of the more massive objects, resulting in
a flat size-age relation at the present time. At lower masses, the models
predict that mergers are less frequent, so that the expected anti-correlation
between age and size is not completely erased. This is in good agreement with
our data: below 3*10^10 Msun, the effective radius R_e is a factor of ~2 lower
for older galaxies. These successes of the models are offset by the fact that
the predicted sizes have other serious problems, which we discuss. | First cosmological constraints on the Superfluid Chaplygin gas model: In this work we set observational constraints of the Superfluid Chaplygin gas
model, which gives a unified description of the dark sector of the Universe as
a Bose-Einstein condensate (BEC) that behaves as dark energy (DE) while it is
in the ground state and as dark matter (DM) when it is in the excited state. We
first show and perform the various steps leading to a form of the equations
suitable for the observational tests to be carried out. Then, by using a Markov
Chain Monte Carlo (MCMC) code, we constrain the model with a sample of
cosmology-independent long gamma-ray bursts (LGRBs) calibrated using their Type
I Fundamental Plane, as well as the Union2.1 set and observational Hubble
parameter data. In this analysis, using our cosmological constraints, we sketch
the effective equation of state parameter and deceleration parameter, and we
also obtain the redshift of the transition from deceleration to acceleration:
$z_t$. |
Light axion-like dark matter must be present during inflation: Axion-like particles (ALPs) might constitute the totality of the cold dark
matter (CDM) observed. The parameter space of ALPs depends on the mass of the
particle $m$ and on the energy scale of inflation $H_I$ , the latter being
bound by the non-detection of primordial gravitational waves. We show that the
bound on HI implies the existence of a mass scale $m_\chi = 10 {\rm \,neV}
{\div} 0.5 {\rm \,peV}$, depending on the ALP susceptibility $\chi$, such that
the energy density of ALPs of mass smaller than $m_\chi$ is too low to explain
the present CDM budget, if the ALP field has originated after the end of
inflation. This bound affects Ultra-Light Axions (ULAs), which have recently
regained popularity as CDM candidates. Light ($m < m_\chi$) ALPs can then be
CDM candidates only if the ALP field has already originated during the
inflationary period, in which case the parameter space is constrained by the
non-detection of axion isocurvature fluctuations. We comment on the effects on
these bounds from additional physics beyond the Standard Model, besides ALPs. | On the small scale turbulent dynamo in the intracluster medium: A
comparison to dynamo theory: We present non-radiative, cosmological zoom-simulations of galaxy cluster
formation with magnetic fields and (anisotropic) thermal conduction of one very
massive galaxy cluster with a mass at redshift zero that corresponds to
$M_\mathrm{vir} \sim 2 \times 10^{15} M_{\odot}$. We run the cluster on three
resolution levels (1X, 10X, 25X), starting with an effective mass resolution of
$2 \times 10^8M_{\odot}$, subsequently increasing the particle number to reach
$4 \times 10^6M_{\odot}$. The maximum spatial resolution obtained in the
simulations is limited by the gravitational softening reaching $\epsilon=1.0$
kpc at the highest resolution level, allowing to resolve the hierarchical
assembly of the structures in very fine detail. All simulations presented, have
been carried out with the SPMHD-code Gadget-3 with a heavily updated SPMHD
prescription. The primary focus is to investigate magnetic field amplification
in the Intracluster Medium (ICM). We show that the main amplification mechanism
is the small scale-turbulent-dynamo in the limit of reconnection diffusion. In
our two highest resolution models we start to resolve the magnetic field
amplification driven by this process and we explicitly quantify this with the
magnetic power-spectra and the magnetic tension that limits the bending of the
magnetic field lines consistent with dynamo theory. Furthermore, we investigate
the $\nabla \cdot \mathbf{B}=0$ constraint within our simulations and show that
we achieve comparable results to state-of-the-art AMR or moving-mesh
techniques, used in codes such as Enzo and Arepo. Our results show for the
first time in a fully cosmological simulation of a galaxy cluster that dynamo
action can be resolved in the framework of a modern Lagrangian
magnetohydrodynamic (MHD) method, a study that is currently missing in the
literature. |
The Hubble constant tension with next-generation galaxy surveys: The rate at which the universe is expanding today is a fundamental parameter
in cosmology which governs our understanding of structure formation and dark
energy. However, current measurements of the Hubble constant, $H_0$, show a
significant tension ($\sim 4-6\sigma$) between early- and late-Universe
observations. There are ongoing efforts to check the diverse observational
results and also to investigate possible theoretical ways to resolve the
tension~-- which could point to radical extensions of the standard model. Here
we demonstrate the potential of next-generation spectroscopic galaxy surveys to
shed light on the Hubble constant tension. Surveys such as those with Euclid
and the Square Kilometre Array (SKA) are expected to reach sub-percent
precision on Baryon Acoustic Oscillation (BAO) measurements of the Hubble
parameter, with a combined redshift coverage of $0.1<z<3$. This wide redshift
range, together with the high precision and low level of systematics in BAO
measurements, mean that these surveys will provide independent and tight
constraints on $H(z)$. These $H(z)$ measurements can be extrapolated to $z = 0$
to provide constraints on $H_0$ using a non-parametric regression. To this end
we deploy Gaussian processes and we find that Euclid-like surveys can reach
$\sim$3\% precision on $H_0$, with SKA-like intensity mapping surveys reaching
$\sim$2\%. When we combine the low-redshift SKA-like Band 2 survey with either
its high-redshift Band 1 counterpart, or with the non-overlapping Euclid-like
survey, the precision is predicted to be close to 1\% with 40 $H(z)$ data
points. This would be sufficient to rule out the current early- or
late-Universe measurements at a $\sim$5$\sigma$ level. | Testing General Relativity with the Doppler magnification effect: The apparent sizes and brightnesses of galaxies are correlated in a dipolar
pattern around matter overdensities in redshift space, appearing larger on
their near side and smaller on their far side. The opposite effect occurs for
galaxies around an underdense region. These patterns of apparent magnification
induce dipole and higher multipole terms in the cross-correlation of galaxy
number density fluctuations with galaxy size/brightness (which is sensitive to
the convergence field). This provides a means of directly measuring peculiar
velocity statistics at low and intermediate redshift, with several advantages
for performing cosmological tests of GR. In particular, it does not depend on
empirically-calibrated scaling relations like the Tully-Fisher and Fundamental
Plane methods. We show that the next generation of spectroscopic galaxy
redshift surveys will be able to measure the Doppler magnification effect with
sufficient signal-to-noise to test GR on large scales. We illustrate this with
forecasts for the constraints that can be achieved on parametrised deviations
from GR for forthcoming low-redshift galaxy surveys with DESI and SKA2.
Although the cross-correlation statistic considered has a lower signal to noise
than RSD, it will be a useful probe of GR since it is sensitive to different
systematics. |
Negative Running of the Spectral Index, Hemispherical Asymmetry and the
Consistency of Planck with Large $r$: Planck favours a negative running of the spectral index, with the likelihood
being dominated by low multipoles $l \lesssim 50$ and no preference for running
at higher $l$. A negative spectral index is also necessary for the 2-$\sigma$
Planck upper bound on the tensor-to-scalar ratio $r$ to be consistent with
values significantly larger than 0.1. Planck has also observed a hemispherical
asymmetry of the CMB power spectrum, again mostly at low multipoles. Here we
consider whether the physics responsible for the hemispherical asymmetry could
also account for the negative running of the spectral index and the consistency
of Planck with a large value of $r$. A negative running of the spectral index
can be generated if the hemispherical asymmetry is due to a scale- and
space-dependent modulation which suppresses the CMB power spectrum at low
multipoles. We show that the observed hemispherical asymmetry at low $l$ can be
generated while satisfying constraints on the asymmetry at higher $l$ and
generating a negative spectral index of the right magnitude to account for the
Planck observation and to allow Planck to be consistent with a large value of
$r$. | HI Distribution and Tully-Fisher Distances of Gas-Poor Spiral Galaxies
in the Virgo Cluster Region: We present aperture synthesis observations in the 21 cm line of pointings
centered on the Virgo Cluster region spirals NGC 4307, NGC 4356, NGC 4411B, and
NGC 4492 using the Very Large Array (VLA) radiotelescope in its CS
configuration. These galaxies were identified in a previous study of the
three-dimensional distribution of HI emission in the Virgo region as objects
with a substantial dearth of atomic gas and Tully-Fisher (TF) distance
estimates that located them well outside the main body of the cluster. We have
detected two other galaxies located in two of our fields and observed bands,
the spiral NGC 4411A and the dwarf spiral VCC 740. We provide detailed
information of the gas morphology and kinematics for all these galaxies. Our
new data confirm the strong HI-deficiency of all the main targets but NGC
4411B, which is found to have a fairly normal neutral gas content. The VLA
observations have also been used to discuss the applicability of TF techniques
to the five largest spirals we have observed. We conclude that none of them is
actually suitable for a TF distance evaluation, whether due to the radical
trimming of their neutral hydrogen disks (NGC 4307, NGC 4356, and NGC 4492) or
to their nearly face-on orientation (NGC 4411A and B). |
The Atacama Cosmology Telescope: Two-season ACTPol Extragalactic Point
Sources and their Polarization properties: We report on measurements of the polarization of extragalactic sources at 148
GHz made during the first two seasons of the Atacama Cosmology Telescope
Polarization (ACTPol) survey. The survey covered 680 deg$^{2}$ of the sky on
the celestial equator. Polarization measurements of 169 intensity-selected
sources brighter than 30 mJy, that are predominantly Active Galactic Nuclei,
are presented. Above a total flux of 215 mJy where the noise bias removal in
the polarization measurement is reliable, we detect 26 sources, 14 of which
have a detection of linear polarization at greater than 3$\sigma_{p}$
significance. The distribution of the fractional polarization as a function of
total source intensity is analyzed. Our result is consistent with the scenario
that the fractional polarization of our measured radio source population is
independent of total intensity down to the limits of our measurements and well
described by a Gaussian distribution with a mean fractional polarization
$p=0.028\pm$0.005 and standard deviation $\sigma_{\mathrm{p}}=0.054$, truncated
at $p=0$. Extrapolating this model for the distribution of source polarization
below the ACTPol detection threshold, we predict that one could get a clean
measure of the E-mode polarization power spectrum of the microwave background
out to $\ell=6000$ with 1 $\mu$K-arcminute maps over 10$\%$ of the sky from a
future survey. We also study the spectral energy distribution of the total and
polarized source flux densities by cross-matching with low radio frequency
catalogs. We do not find any correlation between the spectral indices for total
flux and polarized flux. | Saddle-point entropy states of equilibrated self-gravitating systems: In this Letter, we investigate the stability of the statistical equilibrium
of spherically symmetric collisionless self-gravitating systems. By calculating
the second variation of the entropy, we find that perturbations of the relevant
physical quantities should be classified as long- and short-range
perturbations, which correspond to the long- and short-range relaxation
mechanisms, respectively. We show that the statistical equilibrium states of
self-gravitating systems are neither maximum nor minimum, but complex
saddle-point entropy states, and hence differ greatly from the case of ideal
gas. Violent relaxation should be divided into two phases. The first phase is
the entropy-production phase, while the second phase is the entropy-decreasing
phase. We speculate that the second-phase violent relaxation may just be the
long-wave Landau damping, which would work together with short-range
relaxations to keep the system equilibrated around the saddle-point entropy
states. |
Large-scale inhomogeneities may improve the cosmic concordance of
supernovae: We reanalyze the supernovae data from the Union Compilation including the
weak lensing effects caused by inhomogeneities. We compute the lensing
probability distribution function for each background solution described by the
parameters Omega_M, Omega_L and w in the presence of inhomogeneities,
approximately modeled with a single-mass population of halos. We then perform a
likelihood analysis in the space of FLRW-parameters and compare our results
with the standard approach. We find that the inclusion of lensing can move the
best-fit model significantly towards the cosmic concordance of the flat LCDM
model, improving the agreement with the constraints coming from the cosmic
microwave background and baryon acoustic oscillations. | Quijote-PNG: Simulations of primordial non-Gaussianity and the
information content of the matter field power spectrum and bispectrum: Primordial non-Gaussianity (PNG) is one of the most powerful probes of the
early Universe and measurements of the large scale structure of the Universe
have the potential to transform our understanding of this area. However
relating measurements of the late time Universe to the primordial perturbations
is challenging due to the non-linear processes that govern the evolution of the
Universe. To help address this issue we release a large suite of N-body
simulations containing four types of PNG: \textsc{quijote-png}. These
simulations were designed to augment the \textsc{quijote} suite of simulations
that explored the impact of various cosmological parameters on large scale
structure observables. Using these simulations we investigate how much
information on PNG can be extracted by extending power spectrum and bispectrum
measurements beyond the perturbative regime at $z=0.0$. This is the first joint
analysis of the PNG and cosmological information content accessible with power
spectrum and bispectrum measurements of the non-linear scales. We find that the
constraining power improves significantly up to $k_\mathrm{max}\approx 0.3
h/{\rm Mpc}$, with diminishing returns beyond as the statistical probes
signal-to-noise ratios saturate. This saturation emphasizes the importance of
accurately modelling all the contributions to the covariance matrix. Further we
find that combining the two probes is a powerful method of breaking the
degeneracies with the $\Lambda$CDM parameters. |
Cold dark matter heats up: One of the principal discoveries in modern cosmology is that standard model
particles (including baryons, leptons and photons) together comprise only 5% of
the mass-energy budget of the Universe. The remaining 95% consists of dark
energy and dark matter (DM). Consequently our picture of the universe is known
as {\Lambda}CDM, with {\Lambda} denoting dark energy and CDM cold dark matter.
{\Lambda}CDM is being challenged by its apparent inability to explain the low
density of DM measured at the centre of cosmological systems, ranging from
faint dwarf galaxies to massive clusters containing tens of galaxies the size
of the Milky Way. But before making conclusions one should carefully include
the effect of gas and stars, which were historically seen as merely a passive
component during the assembly of galaxies. We now understand that these can in
fact significantly alter the DM component, through a coupling based on rapid
gravitational potential fluctuations. | Helium Reionization Simulations. II. Signatures of Quasar Activity on
the IGM: We have run a new suite of simulations that solve hydrodynamics and radiative
transfer simultaneously to study helium II reionization. Our suite of
simulations employs various models for populating quasars inside of dark matter
halos, which affect the He II reionization history. In particular, we are able
to explore the impact that differences in the timing and duration of
reionization have on observables. We examine the thermal signature that
reionization leaves on the IGM, and measure the temperature-density relation.
As previous studies have shown, we confirm that the photoheating feedback from
helium II reionization raises the temperature of the IGM by several thousand
kelvin. To compare against observations, we generate synthetic Ly$\alpha$
forest sightlines on-the-fly and match the observed effective optical depth
$\tau_{\mathrm{eff}}(z)$ of hydrogen to recent observations. We show that when
the simulations have been normalized to have the same values of
$\tau_\mathrm{eff}$, the effect that helium II reionization has on observations
of the hydrogen Ly$\alpha$ forest is minimal. Specifically, the flux PDF and
the one-dimensional power spectrum are sensitive to the thermal state of the
IGM, but do not show direct evidence for the ionization state of helium. We
show that the peak temperature of the IGM typically corresponds to the time of
90%-95% helium ionization by volume, and is a relatively robust indicator of
the timing of reionization. Future observations of helium reionization from the
hydrogen Ly$\alpha$ forest should thus focus on measuring the temperature of
the IGM, especially at mean density. Detecting the peak in the IGM temperature
would provide valuable information about the timing of the end of helium II
reionization. |
The Warm Molecular Gas Around the Cloverleaf Quasar: We present the first broadband lambda = 1 mm spectrum toward the z=2.56
Cloverleaf Quasar, obtained with Z-Spec, a 1-mm grating spectrograph on the
10.4-meter Caltech Submillimeter Observatory. The 190-305 GHz observation band
corresponds to rest-frame 272 to 444 microns, and we measure the dust continuum
as well as all four transitions of carbon monoxide (CO) lying in this range.
The power-law dust emission, F_nu = 14 mJy (nu/240GHz)^3.9 is consistent with
the published continuum measurements. The CO J=6->5, J=8->7, and J=9->8
measurements are the first, and now provide the highest-J CO information in
this source. Our measured CO intensities are very close to the
previously-published interferometric measurements of J=7->6, and we use all
available transitions and our 13CO upper limits to constrain the physical
conditions in the Cloverleaf molecular gas disk. We find a large mass
(2-50x10^9 Msun) of highly-excited gas with thermal pressure nT > 10^6 Kcm^-3.
The ratio of the total CO cooling to the far-IR dust emission exceeds that in
the local dusty galaxies, and we investigate the potential heating sources for
this bulk of warm molecular gas. We conclude that both UV photons and X-rays
likely contribute, and discuss implications for a top-heavy stellar initial
mass function arising in the X-ray-irradiated starburst. Finally we present
tentative identifications of other species in the spectrum, including a
possible detection of the H20 2_0,2->1_1,1 transition at lambda_rest = 303
microns. | $Λ$CDM as a Noether Symmetry in Cosmology: The standard $\Lambda$CDM model of cosmology is formulated as a simple
modified gravity coupled to a single scalar field ("darkon") possessing a
non-trivial hidden nonlinear Noether symmetry. The main ingredient in the
construction is the use of the formalism of non-Riemannian spacetime
volume-elements. The associated Noether conserved current produces
stress-energy tensor consisting of two additive parts -- dynamically generated
dark energy and dark matter components non-interacting among themselves.
Noether symmetry breaking via an additional scalar "darkon" potential
introduces naturally an interaction between dark energy and dark matter. The
correspondence between the $\Lambda$CDM model and the present "darkon" Noether
symmetry is exhibited up to linear order w.r.t. gravity-matter perturbations. |
Cosmological Origami: Properties of Cosmic-Web Components when a
Non-Stretchy Dark-Matter Sheet Folds: In the current cosmological paradigm, an initially flat three-dimensional
manifold that pervades space (the `dark-matter sheet') folds up to build
concentrations of mass (galaxies), and a cosmic web between them. Galaxies are
nodes, connected by a network of filaments and walls. The folding is in
six-dimensional (3D position, plus 3D velocity) phase space. The positions of
creases, or caustics, mark the edges of structures.
Here, I introduce an origami approximation to cosmological structure
formation, in which the dark-matter sheet is not allowed to stretch. But it
still produces an idealized cosmic web, with nodes, filaments, walls and voids.
In 2D, nodes form in `polygonal collapse' (a twist-fold in origami),
necessarily generating filaments simultaneously. In 3D, nodes form in
`polyhedral collapse,' simultaneously generating filaments and walls. The
masses, spatial arrangement, and angular momenta of nodes and filaments are
related in the model. I describe some `tetrahedral collapse', or tetrahedral
twist-fold, models. | Search for cosmological mu variation from high redshift H2 absorption; a
status report: Observations of H2 spectra in the line-of-sight of distant quasars may reveal
a variation of the proton-electron mass ratio mu=m_p/m_e at high redshift,
typically for z>2. Currently four high-quality systems (Q0347-383, Q0405-443,
Q0528-250 and J2123-005) have been analyzed returning a constraint Dmu/mu < 1 x
10^{-5}. We present data and a mu-variation analysis of another system,
Q2348-011 at redshift z_{abs}=2.42, delivering dmu/mu = (-1.5 \pm 1.6) x
10^{-5}. In addition to observational data the status of the laboratory
measurements is reviewed. The future possibilities of deriving a competitive
constraint on Dmu/mu from the known high-redshift H2 absorbers is investigated,
resulting in the identification of a number of potentially useful systems for
detecting mu-variation. |
Testing the radio halo-cluster merger scenario. The case of
RXCJ2003.5-2323: We present a combined radio, X-ray and optical study of the galaxy cluster
RXCJ2003.5-2323. The cluster hosts one of the largest, most powerful and
distant giant radio halos known to date, suggesting that it may be undergoing a
strong merger process. The aim of our multiwavelength study is to investigate
the radio-halo cluster merger scenario. We studied the radio properties of the
giant radio halo in RXCJ2003.5-2323 by means of new radio data obtained at 1.4
GHz with the Very Large Array, and at 240 MHz with the Giant Metrewave Radio
Telescope, in combination with previously published GMRT data at 610 MHz. The
dynamical state of the cluster was investigated by means of X-ray Chandra
observations and optical ESO--NTT observations. Our study confirms that
RXCJ2003.5-2323 is an unrelaxed cluster. The unusual filamentary and clumpy
morphology of the radio halo could be due to a combination of the filamentary
structure of the magnetic field and turbulence in the inital stage of a cluster
merger. | Hot thermal universe endowed with massive dark vector fields and the
Hubble tension: The value of Hubble constant inferred from Planck measurements of
anisotropies in the cosmic microwave background is at $4.4\sigma$ tension with
direct astronomical measurements at low redshifts. Very recently, it has been
conjectured that this discrepancy may be reconciled if a small fraction of the
dark matter is described by three mutually orthogonal vector fields of the same
mass. We study the thermal description of this model and use the
observationally-inferred primordial fractions of baryonic mass in $^4{\rm He}$
to constrain its phase space. We show that while the sterile vector fields may
help to alleviate a little bit the existing tension in the measurements of the
Hubble parameter, they cannot eliminate the discrepancy between low- and
high-redshift observations. |
Impact of CP-violation on neutrino lepton number asymmetries revisited: We revisit the effect of the (Dirac) CP-violating phase on neutrino lepton
number asymmetries in both mass- and flavor-basis. We found that, even if there
are sizable effects on muon- and tau-neutrino asymmetries, the effect on the
asymmetry of electron-neutrinos is at most similar to the upper bound set by
BBN for initial neutrino degeneracy parameters smaller than order unity. We
also found that, for the asymmetries in mass-basis, the changes caused by
CP-violation is of sub-\% level which is unlikely to be accesible neither in
the current nor in the forthcoming experiments. | Simulating the Toothbrush: Evidence for a triple merger of galaxy
clusters: The newly discovered galaxy cluster 1RXS J0603.3+4214 hosts a 1.9 Mpc long,
bright radio relic with a peculiar linear morphology. Using hydrodynamical
+N-body AMR simulations of the merger between three initially hydrostatic
clusters in an idealised setup, we are able to reconstruct the morphology of
the radio relic. Based on our simulation, we can constrain the merger geometry,
predict lensing mass measurements and X-ray observations. Comparing such models
to X-ray, redshift and lensing data will validate the geometry of this complex
merger which helps to constrain the parameters for shock acceleration of
electrons that produces the radio relic. |
The role of large-scale magnetic field in the morphology and evolution
of extragalactic radio sources: We discuss a model of formation of extragalactic radio sources when the
parent optical galaxy has a large-scale dipolar magnetic field. The study of
dynamics of ejected from the central part of optical galaxy clouds of
relativistic particles in dipolar magnetic field gives a possibility to explain
main morphological features and physical properties of formed extragalactic
radio sources. We bring some results of statistical analyses and correlations
between physical parameters for more than 500 radio sources. In appendix we
present the data of all used extragalactic radio sources with the references
for them. | Towards Realizing Warm Inflation in String Theory: We give a generic argument that string theory provides a natural setting for
warm inflationary cosmology. We then explore a specific model with an inflaton
modulus field coupled to fields that provide the continuous dissipation needed
for warm inflation and argue the results are generic for a large class of
models. |
Discovery of a >13 Mpc long X-ray filament between two galaxy clusters
beyond three times their virial radii: The new Spectrum Roentgen Gamma (SRG)/eROSITA X-ray telescope has a superior
response to extended soft X-rays in terms of effective area, energy resolution,
and field-of-view (FoV). This makes SRG/eROSITA ideal for studying low X-ray
surface brightness emission of cosmic filaments. We search for extended X-ray
emission between the two nearby galaxy clusters Abell 3667 and Abell 3651 that
are separated by a projected transverse distance of ${\sim} 13\,\mathrm{Mpc}$,
using data from the SRG/eROSITA All-Sky Survey. Detailed X-ray image analysis
of the region between the two galaxy clusters and redshift analysis of sources
between them is performed. We carried out thorough surface brightness analysis
between the clusters and in their outskirts studying enhanced emission in
different directions. The analysis is complemented with an X-ray pointed
observation from XMM-Newton, infrared 2MASS data and redshift information from
NED. We discover an emission filament beyond the known radio relic in the
northwest of A3667 and even beyond three times its virial radius, smoothly
connecting to A3651. The X-ray emission in the direction of the filament shows
a $30\pm3\,\%$ enhancement with a significance of $11\,\sigma$. The 2MASS map
and redshift analysis show an alignment of sources along the filament and make
a projection effect unlikely. Taking the redshift progression of sources within
the filament into account, its three-dimensional length is estimated to be in
the range of $25\,\mathrm{Mpc} - 32\,\mathrm{Mpc}$. Surface brightness analysis
in combination with assumptions for ranges of plausible temperatures and
metallicities leads to estimates of total flux, gas mass and central baryon
overdensity of $F_\mathrm{X}= (7.1^{+2.1}_{-1.0})\times 10^{-12}\,\mathrm{erg
s^{-1} cm^{-2}}$, $M_\mathrm{g}=(2.8^{+5.4}_{-1.0})\times
10^{14}\,\mathrm{M_\odot}$ and $\delta_0=220^{+390}_{-65}$, respectively. | Using Artificial Neural Networks to extract the 21-cm Global Signal from
the EDGES data: The redshifted 21-cm signal of neutral Hydrogen is a promising probe into the
period of evolution of our Universe when the first stars were formed (Cosmic
Dawn), to the period where the entire Universe changed its state from being
completely neutral to completely ionized (Reionization). The most striking
feature of this line of neutral Hydrogen is that it can be observed across an
entire frequency range as a sky-averaged continuous signature, or its
fluctuations can be measured using an interferometer. However, the 21-cm signal
is very faint and is dominated by a much brighter Galactic and extra-galactic
foregrounds, making it an observational challenge. We have used different
physical models to simulate various realizations of the 21-cm Global signals,
including an excess radio background to match the amplitude of the EDGES 21-cm
signal. First, we have used an artificial neural network (ANN) to extract the
astrophysical parameters from these simulated datasets. Then, mock observations
were generated by adding a physically motivated foreground model and an ANN was
used to extract the astrophysical parameters from such data. The $R^2$ score of
our predictions from the mock-observations is in the range of 0.65-0.89. We
have used this ANN to predict the signal parameters giving the EDGES data as
the input. We find that the reconstructed signal closely mimics the amplitude
of the reported detection. The recovered parameters can be used to infer the
physical state of the gas at high redshifts. |
Galaxy counterparts of metal-rich damped Lyman-alpha absorbers - II. A
solar-metallicity and dusty DLA at z_abs=2.58: [Abridged]. Here, we report on the discovery of the galaxy counterpart of the
z_abs=2.58 DLA on the line-of-sight to the z=3.07 quasar SDSS
J091826.16+163609.0. The galaxy counterpart of the DLA is detected in the OIII
5007 and OII 3726,3729 emission lines redshifted into the NIR at an impact
parameter of 16 kpc. Ly-alpha emission is not detected. The upper limit implies
that Ly-alpha emission from this galaxy is suppressed by more than an order of
magnitude. The DLA is amongst the most metal-rich DLAs studied so far at
comparable redshifts. We find evidence for substantial depletion of refractory
elements onto dust grains. Fitting the main metal line component of the DLA,
which is located at z_abs=2.5832 and accounts for at least 85% of the total
column density of low-ionisation species, we measure metal abundances from
ZnII, SII, SiII, CrII, MnII, FeII and NiII of -0.12, -0.26, -0.46, -0.88,
-0.92, -1.03 and -0.78, respectively. In addition, we detect absorption in the
Lyman and Werner bands of hydrogen, which represents the first detection of H_2
molecules with X-shooter. The background quasar Q0918+1636 is amongst the
reddest QSOs at redshifts 3.02<z<3.12 from the SDSS catalogue. Its UV to NIR
spectrum is well fitted by a composite QSO spectrum reddened by SMC/LMC-like
extinction curves at z_abs=2.58 with a significant amount of extinction given
by A_V = 0.2 mag. This supports previous claims that there may be more
metal-rich DLAs missing from current samples due to dust reddening of the
background QSOs. The fact that there is evidence for dust both in the central
emitting regions of the galaxy (as evidenced by the lack of Ly-alpha emission)
and at an impact parameter of 16 kpc (as probed by the DLA) suggests that dust
is widespread in this system. | The Dark Energy Survey: Cosmology Results With ~1500 New High-redshift
Type Ia Supernovae Using The Full 5-year Dataset: We present cosmological constraints from the sample of Type Ia supernovae (SN
Ia) discovered during the full five years of the Dark Energy Survey (DES)
Supernova Program. In contrast to most previous cosmological samples, in which
SN are classified based on their spectra, we classify the DES SNe using a
machine learning algorithm applied to their light curves in four photometric
bands. Spectroscopic redshifts are acquired from a dedicated follow-up survey
of the host galaxies. After accounting for the likelihood of each SN being a SN
Ia, we find 1635 DES SN in the redshift range $0.10<z<1.13$ that pass quality
selection criteria and can be used to constrain cosmological parameters. This
quintuples the number of high-quality $z>0.5$ SNe compared to the previous
leading compilation of Pantheon+, and results in the tightest cosmological
constraints achieved by any SN data set to date. To derive cosmological
constraints we combine the DES supernova data with a high-quality external
low-redshift sample consisting of 194 SNe Ia spanning $0.025<z<0.10$. Using SN
data alone and including systematic uncertainties we find $\Omega_{\rm
M}=0.352\pm 0.017$ in a flat $\Lambda$CDM model, and $(\Omega_{\rm
M},w)=(0.264^{+0.074}_{-0.096},-0.80^{+0.14}_{-0.16})$ in a flat $w$CDM model.
For a flat $w_0w_a$CDM model, we find $(\Omega_{\rm
M},w_0,w_a)=(0.495^{+0.033}_{-0.043},-0.36^{+0.36}_{-0.30},-8.8^{+3.7}_{-4.5})$,
consistent with a constant equation of state to within $\sim2 \sigma$.
Including Planck CMB data, SDSS BAO data, and DES $3\times2$-point data gives
$(\Omega_{\rm M},w)=(0.321\pm0.007,-0.941\pm0.026)$. In all cases dark energy
is consistent with a cosmological constant to within $\sim2\sigma$. In our
analysis, systematic errors on cosmological parameters are subdominant compared
to statistical errors; these results thus pave the way for future
photometrically classified supernova analyses. |
Finding new signature effects on galactic dynamics to constrain
Bose-Einstein-condensed cold dark matter: If cosmological cold dark matter (CDM) consists of light enough bosonic
particles that their phase-space density exceeds unity, they will comprise a
Bose-Einstein condensate (BEC). The nature of this BEC-CDM as a quantum fluid
may then distinguish it dynamically from the standard form of CDM involving a
collisionless gas of non-relativistic particles that interact purely
gravitationally. We summarize some of the dynamical properties of BEC-CDM that
may lead to observable signatures in galactic halos and present some of the
bounds on particle mass and self-interaction coupling strength that result from
a comparison with observed galaxies. | The Frontier Fields Lens Modeling Comparison Project: Gravitational lensing by clusters of galaxies offers a powerful probe of
their structure and mass distribution. Deriving a lens magnification map for a
galaxy cluster is a classic inversion problem and many methods have been
developed over the past two decades to solve it. Several research groups have
developed techniques independently to map the predominantly dark matter
distribution in cluster lenses. While these methods have all provided
remarkably high precision mass maps, particularly with exquisite imaging data
from the Hubble Space Telescope (HST), the reconstructions themselves have
never been directly compared. In this paper, we report the results of comparing
various independent lens modeling techniques employed by individual research
groups in the community. Here we present for the first time a detailed and
robust comparison of methodologies for fidelity, accuracy and precision. For
this collaborative exercise, the lens modeling community was provided simulated
cluster images -- of two clusters Ares and Hera -- that mimic the depth and
resolution of the ongoing HST Frontier Fields. The results of the submitted
reconstructions with the un-blinded true mass profile of these two clusters are
presented here. Parametric, free-form and hybrid techniques have been deployed
by the participating groups and we detail the strengths and trade-offs in
accuracy and systematics that arise for each methodology. We note in conclusion
that lensing reconstruction methods produce reliable mass distributions that
enable the use of clusters as extremely valuable astrophysical laboratories and
cosmological probes. |
Multi-wavelength spectroscopic probes: biases from neglecting light-cone
effects: Next-generation cosmological surveys will observe larger cosmic volumes than
ever before, enabling us to access information on the primordial Universe, as
well as on relativistic effects. In a companion paper, we applied a Fisher
analysis to forecast the expected precision on $f_{\rm NL}$ and the
detectability of the lensing magnification and Doppler contributions to the
power spectrum. Here we assess the bias on the best-fit values of $f_{\rm NL}$
and other parameters, from neglecting these light-cone effects. We consider
forthcoming 21cm intensity mapping surveys (SKAO) and optical galaxy surveys
(DESI and Euclid), both individually and combined together. We conclude that
lensing magnification at higher redshifts must be included in the modelling of
spectroscopic surveys. If lensing is neglected in the analysis, this produces a
bias of more than 1$\sigma$ - not only on $f_{\rm NL}$, but also on the
standard cosmological parameters. | LoCuSS: A Dynamical Analysis of X-ray AGN in Local Clusters: We present a study of the distribution of X-ray AGN in a representative
sample of 26 massive clusters at 0.15<z<0.30, combining Chandra observations
with highly complete spectroscopy of cluster members down to M_K*+2. In total
we identify 48 X-ray AGN among the cluster members, with luminosities
2x10^41-1x10^44erg/s. In the stacked caustic diagram, the X-ray AGN appear to
preferentially lie along the caustics, suggestive of an infalling population.
They also appear to avoid the region with lowest cluster-centric radii and
relative velocities (r_proj<0.4 r_500; |v-<v>|/sigma_v<0.8), which is dominated
by the virialized population of galaxies accreted earliest into the clusters.
Moreover the velocity dispersion of the 48 X-ray AGN is 1.51x that of the
overall cluster population, which is consistent with the sqrt(2) ratio expected
by simple energetic arguments when comparing infalling versus virialized
populations. This kinematic segregation is significant at the 4.66-sigma level.
When splitting the X-ray AGN sample into two according to X-ray or infrared
(IR) luminosity, both X-ray bright and IR-bright sub-samples show higher
velocity dispersions than their X-ray dim and IR-dim counterparts at >2sigma
significance. This is consistent with the nuclear activity responsible for the
X-ray and IR emission being slowly shut down as the host galaxies are accreted
into the cluster. Overall our results provide the strongest observational
evidence to date that X-ray AGN found in massive clusters are an infalling
population, and that the cluster environment very effectively suppresses
radiatively-efficient nuclear activity in its member galaxies. These results
are consistent with the view that for galaxies to host an X-ray AGN they should
be the central galaxy within their dark matter halo and have a ready supply of
cold gas. |
X-Ray Searches for Emission from the WHIM in the Galactic Halo and the
Intergalactic Medium: At least 50% of the baryons in the local universe are undetected and
predicted to be in a hot dilute phase (1E5-1E7 K) in low and moderate
overdensity environments. We searched for the predicted diffuse faint emission
through shadowing observations whereby cool foreground gas absorbs more distant
diffuse emission. Observations were obtained with Chandra and XMM-Newton. Using
the cold gas in two galaxies, NGC 891 and NGC 5907, shadows were not detected
and a newer observation of NGC 891 fails to confirm a previously reported X-ray
shadow. Our upper limits lie above model predictions. For Local Group studies,
we used a cloud in the Magellanic Stream and a compact high velocity cloud to
search for a shadow. Instead of a shadow, the X-ray emission was brighter
towards the Magellanic Stream cloud and there is a less significant brightness
enhancement toward the other cloud also. The brightness enhancement toward the
Magellanic Stream cloud is probably due to an interaction with a hot ambient
medium that surrounds the Milky Way. We suggest that this interaction drives a
shock into the cloud, heating the gas to X-ray emitting temperatures. | The Orientation of Galaxies in Galaxy Clusters: We present an analysis of the spatial orientations of galaxies in the 247
optically selected rich Abell clusters, having in the considered area at least
100 members. We investigated the relation between angles giving information
about galaxy angular momenta and the number of members in each structure. The
position angles of the galaxy major axes, as well as two angles describing the
spatial orientation of galaxy plane were tested for isotropy, by applying three
different statistical tests. It is found that the values of statistics increase
with the amount of galaxies' members, which is equivalent to the existence of
the relation between anisotropy and number of galaxies in cluster. The search
for connection between the galaxies alignments and Bautz - Morgan morphological
types of examined clusters gave weak dependence. The statistically marginal
relation between velocity dispersion and cluster richness was observed. In
addition, it was found that the velocity dispersion decreases with Bautz -
Morgan type at almost 3$\sigma$ level. These results shows the dependence of
alignments with respect to clusters' richness, which can be regarded as
environmental effect. |
Spatial variations of the fine-structure constant in symmetron models: We investigate the variation of the fine-structure constant, {\alpha}, in
symmetron models using N-body simulations in which the full spatial
distribution of {\alpha} at different redshifts has been calculated. In
particular, we obtain simulated sky maps for this variation, and determine its
power spectrum. We find that in high-density regions of space (such as deep
inside dark matter halos) the value of {\alpha} approaches the value measured
on Earth. In the low-density outskirts of halos the scalar field value can
approach the symmetry breaking value and leads to significantly different
values of {\alpha}. If the scalar-photon coupling strength {\beta}{\gamma} is
of order unity we find that the variation of {\alpha} inside dark matter halos
can be of the same magnitude as the recent claims by Webb et al. of a dipole
variation. Importantly, our results also show that with low-redshift symmetry
breaking these models exhibit some dependence of {\alpha} on lookback time (as
opposed to a pure spatial dipole) which could in principle be detected by
sufficiently accurate spectroscopic measurements, such as those of ALMA and the
ELT-HIRES. | Fisher matrix for multiple tracers: all you can learn from large-scale
structure without assuming a model: The galaxy power spectrum is one of the central quantities in cosmology. It
contains information about the primordial inflationary process, the matter
clustering, the baryon-photon interaction, the effects of gravity, the
galaxy-matter bias, the cosmic expansion, the peculiar velocity field, etc..
Most of this information is however difficult to extract without assuming a
specific cosmological model, for instance $\Lambda$CDM and standard gravity. In
this paper we explore instead how much information can be obtained that is
independent of the cosmological model, both at background and linear
perturbation level. We determine the full set of model-independent statistics
that can be constructed by combining two redshift bins and two distinct
tracers. We focus in particular on the statistics $r(k,z_1,z_2)$, defined as
the ratio of $f\sigma_8(z)$ at two redshift shells, and we show how to estimate
it with a Fisher matrix approach. Finally, we forecast the constraints on $r$
that can be achieved by future galaxy surveys, and compare it with the standard
single-tracer result. We find that $r$ can be measured with a precision from 3
to 11%, depending on the survey. Using two tracers, we find improvements in the
constraints up to a factor of two. |
Early type galaxies with tidal debris and their scaling relations in the
Spitzer Survey of Stellar Structure in Galaxies (S4G): Tidal debris around galaxies can yield important clues on their evolution. We
have identified tidal debris in 11 early type galaxies (T \leq 0) from a sample
of 65 early types drawn from the Spitzer Survey of Stellar Structure in
Galaxies (S4G). The tidal debris includes features such as shells, ripples and
tidal tails. A variety of techniques, including two-dimensional decomposition
of galactic structures, was used to quantify the residual tidal features. The
tidal debris contributes ~3 - 10% to the total 3.6 {\mu}m luminosity of the
host galaxy. Structural parameters of the galaxies were estimated using
two-dimensional profile fitting. We investigate the locations of galaxies with
tidal debris in the Fundamental Plane and Kormendy relation. We find that
galaxies with tidal debris lie within the scatter of early type galaxies
without tidal features. Assuming that the tidal debris is indicative of recent
gravitational interaction or merger, this suggests that these galaxies have
either undergone minor merging events so that the overall structural properties
of the galaxies are not significantly altered, or they have undergone a major
merging events but already have experienced sufficient relaxation and
phase-mixing so that their structural properties become similar to those of the
non-interacting early type galaxies. | A Comparative Study of Local Galaxy Clusters: II: X-ray and SZ Scaling
Relations: We compare cluster scaling relations published for three different samples
selected via X-ray and Sunyaev-Zel'dovich (SZ) signatures. We find tensions
driven mainly by two factors: i) systematic differences in the X-ray cluster
observables used to derive the scaling relations, and ii) uncertainty in the
modeling of how the gas mass of galaxy clusters scales with total mass. All
scaling relations are in agreement after accounting for these two effects. We
describe a multivariate scaling model that enables a fully self-consistent
treatment of multiple observational catalogs in the presence of property
covariance, and apply this formalism when interpreting published results. The
corrections due to scatter and observable covariance can be significant. For
instance, our predicted Ysz-Lx scaling relation differs from that derived using
the naive "plug in" method by \approx 25%. Finally, we test the mass
normalization for each of the X-ray data sets we consider by applying a space
density consistency test: we compare the observed REFLEX luminosity function to
expectations from published Lx-M relations convolved with the mass function for
a WMAP7 flat \Lambda CDM model. |
Data Analysis and Phenomenological Cosmology: In the era of precision cosmology, even percentage level effects are
significant on cosmological observables. The recent tension between the local
and global values of $H_0$ is much more significant than this, and any possible
solution might rely on us going beyond the standard $\Lambda$CDM cosmological
model. For much smaller, yet potentially significant effects, spatial curvature
from averaging and cosmological backreaction on observational predictions could
play a role. This is especially true with the higher precision of new
observational data and improved statistical techniques. In this paper, we
discuss the observational viability of a class of physically motivated
cosmologies which can be parametrized by a phenomenological two-scale
backreaction model with decoupled spatial curvature parameters and two Hubble
scales. Using the latest JLA Supernovae data together with some of the latest
BAO data, we perform a Bayesian model selection analysis and find that the
phenomenological models are not favoured over the standard $\Lambda$CDM
cosmological model. Although there is still a preference for non-zero and
unequal dynamic and geometric spatial curvatures, there is little evidence for
differing Hubble scales within these phenomenological template models. | Modeling Extragalactic Foregrounds and Secondaries for Unbiased
Estimation of Cosmological Parameters From Primary CMB Anisotropy: Using the latest physical modeling and constrained by the most recent data,
we develop a phenomenological parameterized model of the contributions to
intensity and polarization maps at millimeter wavelengths from external
galaxies and Sunyaev-Zeldovich effects. We find such modeling to be necessary
for estimation of cosmological parameters from Planck data. For example,
ignoring the clustering of the infrared background would result in a bias in
n_s of 7 sigma. We show that the simultaneous marginalization over a full
foreground model can eliminate such biases, while increasing the statistical
uncertainty in cosmological parameters by less than 20%. The small increases in
uncertainty can be significantly reduced with the inclusion of
higher-resolution ground-based data.
The multi-frequency analysis we employ involves modeling 46 total power
spectra and marginalization over 17 foreground parameters. We show that we can
also reduce the data to a best estimate of the CMB power spectra, and just two
principal components (with constrained amplitudes) describing residual
foreground contamination. |
Probing Compensated Isocurvature with the 21-cm Signal during Cosmic
Dawn: Upcoming measurements of the 21-cm line of neutral hydrogen will open a new
observational window into the early stages of structure growth, providing a
unique opportunity for probing large-scale cosmological signatures using the
small-scale signals from the first stars. In this paper we evaluate the
detection significance of compensated isocurvature perturbations (CIPs) from
observations of the 21-cm hydrogen-line during the cosmic-dawn era. CIPs are
modulations of the relative baryon and dark-matter density that leave the total
matter density unchanged. We find that, under different assumptions for
feedback and foregrounds, the ongoing HERA and upcoming SKA1-low experiments
will provide constraints on uncorrelated CIPs at the level of $\sigma(A_{\rm
CIP})= 10^{-3}-10^{-4}$, comparable to the sensitivity of upcoming CMB
experiments, and potentially exceeding the constraints from cosmic-variance
limited BAO surveys. | Strong shock in a uniform expanding universe. Approximate and exact
solutions of self-similar equations: Self-similar solution is obtained for propagation of a strong shock, in a
flat expanding dusty Friedman universe. Approximate analytic solution was
obtained earlier, using relation between self-similar variables, equivalent to
the exact energy conservation integral, which was obtained by L.I. Sedov for
the strong explosion in the static uniform medium. Numerical integration of
self-similar equation is made here, giving an exact solution of the problem,
which is rather close to the approximate analytic one. The differences between
these solutions are most apparent in the vicinity of the shock. For polytropic
equation of state, self-similar solutions exist in more narrow interval of the
adiabatic power than in the static case. |
Relativistic viscous effects on the primordial gravitational waves
spectrum: We study the impact of the viscous effects of the primordial plasma on the
evolution of the primordial gravitational waves (pGW) spectrum from Inflation
until today, considering a self-consistent interaction that incorporates the
back-reaction of the GW into the plasma. We use a relativistic causal
hydrodynamic framework with a positive entropy production based on a
Second-Order Theory (SOT) in which the viscous properties of the fluid are
effectively described by a new set of independent variables. We study how the
spin-2 modes typical of SOTs capture the simplest GW-fluid viscous interaction
to first order. We consider that all non-ideal properties of the primordial
plasma are due to an extra effectively massless self-interacting scalar field
whose state becomes a many-particles one after Reheating and for which an
effective fluid description is suitable. We numerically solve the evolution
equations and explicitly compute the current GW spectrum obtaining two
contributions. On the one hand we have the viscous evolution of the pGW: For
the collision-dominated regime the GW source becomes negligible while in the
collisionless limit there exists an absorption of the pGW energy due to the
damping effect produced by the free-streaming spin-2 modes of the fluid and
driven by the expansion of the Universe. The latter effect is characterized by
a relative amplitude decrease of about 1 to 10 \% with respect to the GW free
evolution spectrum. On the other hand we get the GW production due to the decay
of the initial spin-2 fluctuations of the fluid that is negligible compared
with the above-mentioned contribution.
This SOT framework captures the same qualitative effects on the evolution of
GW coupled to matter reported in previous works in which a kinetic theory
approach has been used. | Non-adiabatic dark fluid cosmology: We model the dark sector of the cosmic substratum by a viscous fluid with an
equation of state $p=-\zeta \Theta$, where $\Theta$ is the fluid-expansion
scalar and $\zeta$ is the coefficient of bulk viscosity for which we assume a
dependence $\zeta \propto \rho^{\nu}$ on the energy density $\rho$. The
homogeneous and isotropic background dynamics coincides with that of a
generalized Chaplygin gas with equation of state $p = - A/\rho^{\alpha}$. The
perturbation dynamics of the viscous model, however, is intrinsically
non-adiabatic and qualitatively different from the Chaplygin-gas case. In
particular, it avoids short-scale instabilities and/or oscillations which
apparently have ruled out unified models of the Chaplygin-gas type. We
calculate the matter power spectrum and demonstrate that the non-adiabatic
model is compatible with the data from the 2dFGRS and the SDSS surveys. A
$\chi^{2}$-analysis shows, that for certain parameter combinations the
viscous-dark-fluid (VDF) model is well competitive with the $\Lambda$CDM model.
These results indicate that \textit{non-adiabatic} unified models can be seen
as potential contenders for a General-Relativity-based description of the
cosmic substratum. |
Next-to-leading resummations in cosmological perturbation theory: One of the nicest results in cosmological perturbation theory is the
analytical resummaton of the leading corrections at large momentum, which was
obtained by Crocce and Scoccimarro for the propagator. Using an exact evolution
equation, we generalize this result, by showing that a class of next-to-leading
corrections can also be resummed at all orders in perturbation theory. The new
corrections modify the propagator by a few percent in the Baryonic Acoustic
Oscillation range of scales, and therefore cannot be neglected in resummation
schemes aiming at an accuracy compatible with future generation galaxy surveys.
Similar tools can be employed to derive improved approximations for the Power
Spectrum. | Gas sloshing, cold front formation, and metal redistribution: the Virgo
cluster as a quantitative test case: (abridged) We perform hydrodynamical simulations of minor-merger induced gas
sloshing and the subsequent formation of cold fronts in the Virgo cluster. We
show for the first time that sloshing reproduces all characteristics of the
observed cold fronts quantitatively, and we suggest a third cold front at 20
kpc NW of the Virgo core. We identify several new features typical for sloshing
cold fronts, most importantly a large-scale brightness asymmetry. We can trace
these new features not only in Virgo, but also in other sloshing cold front
clusters. By comparing synthetic and real observations, we estimate that the
original minor merger event took place about 1.5 Gyr ago when a subcluster of
2-4 \times 10^13 M\odot passed the Virgo core at 100 to 400 kpc distance, where
a smaller mass corresponds to a smaller pericentre distance, and vice versa.
From the merger geometry, we derive the current location of the disturbing
subcluster to be about 1-2 Mpc E of the Virgo core. A possible candidate is
M60. Additionally, we quantify the metal redistribution by sloshing and discuss
its importance. We verify that the subcluster required to produce the observed
cold fronts could be completely ram pressure stripped before reaching the Virgo
centre, and discuss the conditions required for this to be achieved. Finally,
we demonstrate that the bow shock of a fast galaxy passing the Virgo cluster at
~ 400 kpc distance also causes sloshing and leads to very similar cold front
structures. The responsible galaxy would be located about 2 Mpc north of the
Virgo centre. A possible candidate is M85. |
The Evolution of M_*/M_BH Between z=2 and z=0: We propose a novel method to estimate M_*/M_BH, the ratio of stellar mass
(M_*) to black hole mass (M_BH), at various redshifts using two recent
observational results: the correlation between the bolometric luminosity of
active galactic nuclei (AGN) and the star formation rate (SFR) in their host
galaxies, and the correlation between SFR and M_* in star-forming (SF)
galaxies. Our analysis is based on M_BH and L_bol measurements in two large
samples of type-I AGN at z~1 and z~2, and the measurements of M_*/M_BH in
0.05<z<0.2 red galaxies. We find that M_*/M_BH depends on M_BH at all
redshifts. At z~2, M_*/M_BH 280 and ~40 for M_BH=10^8 and M_BH=10^9 M_sol,
respectively. M_*/M_BH grows by a factor of ~4-8 from z~2 to z~0 with extreme
cases that are as large as 10-20. The evolution is steeper than reported in
other studies, probably because we treat only AGN in SF hosts. We caution that
estimates of M_*/M_BH evolution which ignore the dependence of this ratio on
M_BH can lead to erroneous conclusions. | Fast Radio Burst dispersion measures and rotation measures and the
origin of intergalactic magnetic fields: We investigate the possibility of measuring intergalactic magnetic fields
using the dispersion measures and rotation measures of fast radio bursts. With
Bayesian methods, we produce probability density functions for values of these
measures. We distinguish between contributions from the intergalactic medium,
the host galaxy and the local environment of the progenitor. To this end, we
use constrained, magnetohydrodynamic simulations of the local Universe to
compute lines-of-sight integrals from the position of the Milky Way. In
particular, we differentiate between predominantly astrophysical and primordial
origins of magnetic fields in the intergalactic medium. We test different
possible types of host galaxies and probe different distribution functions of
fast radio burst progenitor locations inside the host galaxy. Under the
assumption that fast radio bursts are produced by magnetars, we use analytic
predictions to account for the contribution of the local environment. We find
that less than 100 fast radio bursts from magnetars in stellar-wind
environments hosted by starburst dwarf galaxies at redshift $z \gtrsim 0.5$
suffice to discriminate between predominantly primordial and astrophysical
origins of intergalactic magnetic fields. However, this requires the
contribution of the Milky Way to be removed with a precision of $\approx 1
\rm~rad~m^{-2}$. We show the potential existence of a subset of fast radio
bursts whose rotation measure carry information on the strength of the
intergalactic magnetic field and its origins. |
Implicit Likelihood Inference of Reionization Parameters from the 21 cm
Power Spectrum: The first measurements of the 21 cm brightness temperature power spectrum
from the epoch of reionization will very likely be achieved in the near future
by radio interferometric array experiments such as the Hydrogen Epoch of
Reionization Array (HERA) and the Square Kilometre Array (SKA). Standard MCMC
analyses use an explicit likelihood approximation to infer the reionization
parameters from the 21 cm power spectrum. In this paper, we present a new
Bayesian inference of the reionization parameters where the likelihood is
implicitly defined through forward simulations using density estimation
likelihood-free inference (DELFI). Realistic effects including thermal noise
and foreground avoidance are also applied to the mock observations from the
HERA and SKA. We demonstrate that this method recovers accurate posterior
distributions for the reionization parameters, and outperforms the standard
MCMC analysis in terms of the location and size of credible parameter regions.
With the minutes-level processing time once the network is trained, this
technique is a promising approach for the scientific interpretation of future
21 cm power spectrum observation data. Our code 21cmDELFI-PS is publicly
available at this link. | Reconstruction of real-space linear matter power spectrum from
multipoles of BOSS DR12 results: Recently, the power spectrum (PS) multipoles using the Baryon Oscillation
Spectroscopic Survey (BOSS) Data Release 12 (DR12) sample are analyzed
\cite{160703150}. The based model for the analysis is the so-called TNS
quasi-linear model and the analysis provides the multipoles up to the
hexadecapole \cite{TNS}. Thus, one might be able to recover the real-space
linear matter PS by using the combinations of multipoles to investigate the
cosmology \cite{0407214}. We provide the analytic form of the ratio of
quadrupole (hexadecapole) to monopole moments of the quasi-linear PS including
the Fingers-of-God (FoG) effect to recover the real-space PS in the linear
regime. One expects that observed values of the ratios of multipoles should be
consistent with those of the linear theory at large scales. Thus, we compare
the ratios of multipoles of the linear theory, including the FoG effect with
the measured values. From these, we recover the linear matter power spectra in
real-space. These recovered power spectra are consistent with the linear matter
power spectra. |
Constraints on dark matter annihilation by radio observations of M31: We used radio observations of the neighbour galaxy M31 in order to put
constraints on dark matter particle mass and annihilation cross section. Dark
matter annihilation in M31 halo produces highly energetic leptons, which emit
synchrotron radiation on radio frequencies in the galactic magnetic field. We
predicted expected radio fluxes for the two annihilation channels: \chi\chi ->
bb* and \chi\chi -> \tau^+\tau^-. We then compared them with available data on
the central radio emission of M31 as observed by four radio surveys: VLSS (74
MHz), WENSS (325 MHz), NVSS (1400 MHz) and GB6 (4850 MHz). Assuming a standard
NFW dark matter density profile and a conservative magnetic field distribution
inside the Andromeda galaxy, we find that the thermal relic annihilation cross
section <\sigma v> = 3*10^{-26} cm^3/s or higher are only allowed for WIMP
masses greater than 100 GeV and 55 GeV for annihilation into bb* and
\tau^+\tau^- respectively. Taking into account potential uncertainties in the
distributions of DM density and magnetic field, the mentioned WIMP limiting
masses can be as low as 23 GeV for both channels, and as high as 280 and 130
GeV for annihilation into bb* and \tau^+\tau^- respectively. These mass values
exceed the best up-to-day known constraints from Fermi gamma observations: 40
GeV and 19 GeV respectively [A.Geringer-Sameth and S.M.Koushiappas, Phys. Rev.
Lett. 107, 241303 (2011)]. Precise measurements of the magnetic field in the
relevant region and better reconstruction of the DM density profile of M31 will
be able to reduce the uncertainties of our exclusion limits. | Strong Lensing In The Inner Halo Of Galaxy Clusters: We present an axially symmetric formula to calculate the probability of
finding gravitational arcs in galaxy clusters, being induced by their massive
dark matter haloes, as a function of clusters redshifts and virial masses. The
formula includes the ellipticity of the clusters dark matter potential by using
a pseudo-elliptical approximation. The probabilities are calculated and
compared for two dark-matter halo profiles, the Navarro, Frenk and White (NFW)
and the Non-Singular-Isothermal-Sphere (NSIS). We demonstrate the power of our
formulation through a Kolmogorov-Smirnov (KS) test on the strong lensing
statistics of an X-ray bright sample of low redshift Abell clusters. This KS
test allows to establish limits on the values of the concentration parameter
for the NFW profile ($c_\Delta$) and the core radius for the NSIS profile
(\rc), which are related to the lowest cluster redshift ($z_{\rm cut}$) where
strong arcs can be observed. For NFW dark matter profiles, we infer cluster
haloes with concentrations that are consistent to those predicted by
$\Lambda$CDM simulations. As for NSIS dark matter profiles, we find only upper
limits for the clusters core radii and thus do not rule out a purely SIS model.
For alternative mass profiles, our formulation provides constraints through
$z_{\rm cut}$ on the parameters that control the concentration of mass in the
inner region of the clusters haloes. We find that $z_{\rm cut}$ is expected to
lie in the 0.0--0.2 redshift, highlighting the need to include very low-$z$
clusters in samples to study the clusters mass profiles. |
The role of CMB spectral distortions in the Hubble tension: a proof of
principle: Although both early and late-time modifications of the $\Lambda$CDM model
have been proposed to address the Hubble tension, compelling arguments suggest
that for a solution to be successful it needs to modify the expansion history
of the universe prior to recombination. This greatly increases the importance
of precise CMB observations, and in this letter we make the argument for CMB
spectral distortions, highlighting their potential role in constraining models
that introduce significant shifts in the standard $\Lambda$CDM parameters, such
as the scalar spectral index, in attempt to solve the Hubble tension. | Galactic winds driven by cosmic-ray streaming: Galactic winds are observed in many spiral galaxies with sizes from dwarfs up
to the Milky Way, and they sometimes carry a mass in excess of that of newly
formed stars by up to a factor of ten. Multiple driving processes of such winds
have been proposed, including thermal pressure due to supernova-heating, UV
radiation pressure on dust grains, or cosmic ray (CR) pressure. We here study
wind formation due to CR physics using a numerical model that accounts for CR
acceleration by supernovae, CR thermalization, and advective CR transport. In
addition, we introduce a novel implementation of CR streaming relative to the
rest frame of the gas. We find that CR streaming drives powerful and sustained
winds in galaxies with virial masses M_200 < 10^{11} Msun. In dwarf galaxies
(M_200 ~ 10^9 Msun) the winds reach a mass loading factor of ~5, expel ~60 per
cent of the initial baryonic mass contained inside the halo's virial radius and
suppress the star formation rate by a factor of ~5. In dwarfs, the winds are
spherically symmetric while in larger galaxies the outflows transition to
bi-conical morphologies that are aligned with the disc's angular momentum axis.
We show that damping of Alfven waves excited by streaming CRs provides a means
of heating the outflows to temperatures that scale with the square of the
escape speed. In larger haloes (M_200 > 10^{11} Msun), CR streaming is able to
drive fountain flows that excite turbulence. For halo masses M_200 > 10^{10}
Msun, we predict an observable level of H-alpha and X-ray emission from the
heated halo gas. We conclude that CR-driven winds should be crucial in
suppressing and regulating the first epoch of galaxy formation, expelling a
large fraction of baryons, and - by extension - aid in shaping the faint end of
the galaxy luminosity function. They should then also be responsible for much
of the metal enrichment of the intergalactic medium. |
Resolving the Hubble tension with Early Dark Energy: Early dark energy (EDE) offers a solution to the so-called Hubble tension.
Recently, it was shown that the constraints on EDE using Markov Chain Monte
Carlo are affected by prior volume effects. The goal of this paper is to
present constraints on the fraction of EDE, $f_\mathrm{EDE}$, and the Hubble
parameter, $H_0$, which are not subject to prior volume effects. We conduct a
frequentist profile likelihood analysis considering Planck cosmic microwave
background, BOSS full-shape galaxy clustering, DES weak lensing, and SH0ES
supernova data. Contrary to previous findings, we find that $H_0$ for the EDE
model is in statistical agreement with the SH0ES direct measurement at $\leq
1.7\,\sigma$ for all data sets. For our baseline data set (Planck + BOSS), we
obtain $f_\mathrm{EDE} = 0.087\pm 0.037$ and $H_0 = 70.57 \pm 1.36\,
\mathrm{km/s/Mpc}$ at $68\%$ confidence limit. We conclude that EDE is a viable
solution to the Hubble tension. | Semi-analytic galaxy formation in f(R)-gravity cosmologies: Modifications of the equations of general relativity at large distances offer
one possibility to explain the observed properties of our Universe without
invoking a cosmological constant. Numerous proposals for such modified gravity
cosmologies exist, but often their consequences for structure formation in the
non-linear sector are not yet accurately known. In this work, we employ
high-resolution numerical simulations of f(R)-gravity models coupled with a
semi-analytic model (SAM) for galaxy formation to obtain detailed predictions
for the evolution of galaxy properties. The f(R)-gravity models imply the
existence of a `fifth-force', which is however locally suppressed, preserving
the successes of general relativity on solar system scales. We show that dark
matter haloes in f(R)-gravity models are characterized by a modified virial
scaling with respect to the LCDM scenario, reflecting a higher dark matter
velocity dispersion at a given mass. This effect is taken into account in the
SAM by an appropriate modification of the mass--temperature relation. We find
that the statistical properties predicted for galaxies (such as the stellar
mass function and the cosmic star formation rate) in f(R)-gravity show
generally only very small differences relative to LCDM, smaller than the
dispersion between the results of different SAM models, which can be viewed as
a measure of their systematic uncertainty. We also demonstrate that galaxy bias
is not able to disentangle between f(R)-gravity and the standard cosmological
scenario. However, f(R)-gravity imprints modifications in the linear growth
rate of cosmic structures at large scale, which can be recovered from the
statistical properties of large galaxy samples. |
Snowmass2021 Cosmic Frontier CF6 White Paper: Multi-Experiment Probes
for Dark Energy -- Transients: This invited Snowmass 2021 White Paper highlights the power of joint-analysis
of astronomical transients in advancing HEP Science and presents research
activities that can realize the opportunities that come with current and
upcoming projects. Transients of interest include gravitational wave events,
neutrino events, strongly-lensed quasars and supernovae, and Type~Ia supernovae
specifically. These transients can serve as probes of cosmological distances in
the Universe and as cosmic laboratories of extreme strong-gravity, high-energy
physics. Joint analysis refers to work that requires significant coordination
from multiple experiments or facilities so encompasses Multi-Messenger
Astronomy and optical transient discovery and distributed follow-up programs. | Strong Magnetization Measured in the Cool Cores of Galaxy Clusters: Tangential discontinuities, seen as X-ray edges known as cold fronts (CFs),
are ubiquitous in cool-core galaxy clusters. We analyze all 17 deprojected CF
thermal profiles found in the literature, including three new CFs we
tentatively identify (in clusters A2204 and 2A0335). We discover small but
significant thermal pressure drops below all nonmerger CFs, and argue that they
arise from strong magnetic fields below and parallel to the discontinuity,
carrying 10%-20% of the pressure. Such magnetization can stabilize the CFs, and
explain the CF-radio minihalo connection. |
Minkowski Functionals of Convergence Maps and the Lensing Figure of
Merit: Minkowski functionals (MFs) quantify the topological properties of a given
field probing its departure from Gaussianity. We investigate their use on
lensing convergence maps in order to see whether they can provide further
insights on the underlying cosmology with respect to the standard second-order
statistics, i.e., cosmic shear tomography. To this end, we first present a
method to match theoretical predictions with measured MFs taking care of the
shape noise, imperfections in the map reconstruction, and inaccurate
description of the nonlinearities in the matter power spectrum and bispectrum.
We validate this method against simulated maps reconstructed from shear fields
generated by the MICE simulation. We then perform a Fisher matrix analysis to
forecast the accuracy on cosmological parameters from a joint MFs and shear
tomography analysis. It turns out that MFs are indeed helpful to break the
$\Omega_{\rm m}$--$\sigma_8$ degeneracy thus generating a sort of chain
reaction leading to an overall increase of the Figure of Merit. | Constrained Simulation of the Bullet Cluster: In this work, we report on a detailed simulation of the Bullet Cluster
(1E0657-56) merger, including magnetohydrodynamics, plasma cooling, and
adaptive mesh refinement. We constrain the simulation with data from
gravitational lensing reconstructions and 0.5 - 2 keV Chandra X-ray flux map,
then compare the resulting model to higher energy X-ray fluxes, the extracted
plasma temperature map, Sunyaev-Zel'dovich effect measurements, and cluster
halo radio emission. We constrain the initial conditions by minimizing the
chi-squared figure of merit between the full 2D observational data sets and the
simulation, rather than comparing only a few features such as the location of
subcluster centroids, as in previous studies. A simple initial configuration of
two triaxial clusters with NFW dark matter profiles and physically reasonable
plasma profiles gives a good fit to the current observational morphology and
X-ray emissions of the merging clusters. There is no need for unconventional
physics or extreme infall velocities. The study gives insight into the
astrophysical processes at play during a galaxy cluster merger, and constrains
the strength and coherence length of the magnetic fields. The techniques
developed here to create realistic, stable, triaxial clusters, and to utilize
the totality of the 2D image data, will be applicable to future simulation
studies of other merging clusters. This approach of constrained simulation,
when applied to well-measured systems, should be a powerful complement to
present tools for understanding X-ray clusters and their magnetic fields, and
the processes governing their formation. |
Primordial Helical Magnetic Fields from Inflation?: We revisit the mechanism of helical magnetogenesis during inflation with a
parity violating interaction using the formalism of stochastic inflation. One
of the polarization of the gauge field undergoes tachyonic growth leading to
the generation of helical magnetic fields. We obtain the Langevin equations
associated with the electromagnetic fields which are in the form of
Ornstein-Uhlenbeck stochastic differential equations. Consequently, the
tachyonic growth of the helical magnetic fields is balanced by a mean-reverting
process of stochastic dynamics such that the magnetic fields settle down to an
equilibrium state with the amplitude smaller than what is obtained in the
absence of the stochastic noises. Working in the parameter space of the model
where both the backreaction and the strong coupling problems are under control
the model does not provide large enough seed to be amplified by the galactic
dynamo as the source of the magnetic fields observed on cosmological scales. | An effective description of dark energy: from theory to phenomenology: In the last decades, a cosmological model that fits observations through a
vast range of scales emerged. It goes under the name of ${\Lambda}$CDM.
However, there are still challenging questions that remain unanswered by this
model, such as what causes the observed accelerated expansion of the universe,
and many alternatives have been proposed. This thesis concerns an approach to
test such models known as "Effective Theory of Dark Energy" . It applies to all
models where general relativity is modified by adding a single scalar degree of
freedom, called "scalar-tensor theories". In Chapter 1 I summarise the most
general class of such theories currently known, called "Degenerate higher-Order
Scalar-Tensor" (DHOST) theories. In Chapter 2, I introduce the effective theory
of dark energy. The inclusion of a general coupling between matter and the
gravitational sector is the subject of Chapter 3. Chapter 4 analyses in details
the stability of different classes of theories. Notably, I show that the most
general class of theories free from instabilities reduces to the so-called
Horndeski and beyond-Horndeski theories, up to a non minimal coupling to
matter. Another goal of the thesis is to study the observable effects of
deviations from ${\Lambda}$CDM. In Chapter 5, I consider the possibility of an
interaction between dark matter and dark energy and I analyse the constraining
power of future surveys on the free parameters of the theory. Chapter 6 focuses
on the observational effects of theories where a kinetic mixing between matter
and the scalar field exists. This gives a peculiar and potentially observable
effect, namely the weakening of gravity at large scale structure scales. |
Characterizing the bulk and turbulent gas motions in galaxy clusters: The most massive halos of matter in the Universe grow via accretion and
merger events throughout cosmic times. These violent processes generate shocks
at many scales and induce large-scale bulk and turbulent motions. These
processes inject kinetic energy at large scales, which is transported to the
viscous dissipation scales, contributing to the overall heating and
virialisation of the halo, and acting as a source of non-thermal pressure in
the intra-cluster medium. Characterizing the physical properties of these gas
motions will help us to better understand the assembly of massive halos, hence
the formation and the evolution of these large-scale structures. We base this
characterization on the study of the X-ray and Sunyaev-Zel'dovich effect
brightness fluctuations. Our work relies on three complementary samples
covering a wide range of redshifts, masses and dynamical states of clusters. We
present the results of our X-ray analysis for the low redshift sample, X-COP,
and a subsample of higher redshift clusters. We investigate the derived
properties according to the dynamical state of our clusters, and the
possibility of a self-similar behaviour based on the reconstructed gas motions
power-spectra and the correlation with various morphological indicators. | Phenomenology of Unified Dark Matter models with fast transition: A fast transition between a standard matter-like era and a late
$\Lambda$CDM-like epoch generated by a single Unified Dark Matter component can
explain the observed acceleration of the Universe. UDM models with a fast
transition should be clearly distinguishable from $\Lambda$CDM (and
alternatives) through observations. Here we focus on a particularly simple
model and analyse its viability by studying features of the background model
and properties of the adiabatic UDM perturbations. |
Constraints on Cosmological Models and Reconstructing the Acceleration
History of the Universe with Gamma-Ray Burst Distance Indicators: Gamma-ray bursts (GRBs) have been regarded as standard candles at very high
redshift for cosmology research. We have proposed a new method to calibrate GRB
distance indicators with Type Ia supernova (SNe Ia) data in a completely
cosmology-independent way to avoid the circularity problem that had limited the
direct use of GRBs to probe cosmology [N. Liang, W. K. Xiao, Y. Liu, and S. N.
Zhang, Astrophys. J. 685, 354 (2008).]. In this paper, a simple method is
provided to combine GRB data into the joint observational data analysis to
constrain cosmological models; in this method those SNe Ia data points used for
calibrating the GRB data are not used to avoid any correlation between them. We
find that the $\Lambda$CDM model is consistent with the joint data in the
1-$\sigma$ confidence region, using the GRB data at high redshift calibrated
with the interpolating method, the Constitution set of SNe Ia, the cosmic
microwave background radiation from Wilkinson Microwave Anisotropy Probe five
year observation, the baryonic acoustic oscillation from the spectroscopic
Sloan Digital Sky Survey Data Release 7 galaxy sample, the x-ray baryon mass
fraction in clusters of galaxies, and the observational Hubble parameter versus
redshift data. Comparing to the joint constraints with GRBs and without GRBs,
we find that the contribution of GRBs to the joint cosmological constraints is
a slight shift in the confidence regions of cosmological parameters to better
enclose the $\Lambda$CDM model. Finally, we reconstruct the acceleration
history of the Universe up to $z>6$ with the distance moduli of SNe Ia and GRBs
and find some features that deviate from the $\Lambda$CDM model and seem to
favor oscillatory cosmology models; however further investigations are needed
to better understand the situation. | Milliarcsecond compact structure in radio quasars and the geometry of
the universe: In this paper, by using the recently compiled set of 120
intermediate-luminosity quasars (ILQSO) observed in a single-frequency VLBI
survey, we propose an improved model-independent method to probe cosmic
curvature parameter $\Omega_k$ and make the first measurement of the cosmic
curvature referring to a distant past, with redshifts up to $z\sim 3.0$.
Compared with other methods, the proposed one involving the quasar data
achieves constraints with higher precision in this redshift range. More
importantly, our results indicate that the measured $\Omega_k$ is in good
agreement with zero cosmic curvature, implying that there is no significant
deviation from a flat Universe. Finally, we investigate the possibility of
testing $\Omega_k$ with a much higher accuracy using quasars observed in the
future VLBI surveys. It is shown that our method could provide a reliable and
tight constraint on the prior $\Omega_k$ and one can expect the zero cosmic
curvature to be established at the precision of $\Delta\Omega_k\sim 10^{-2}$
with 250 well-observed radio quasars. |
Local probes strongly favor $Λ$CDM against power-law and $R_h=ct$
universe: We constrain three cosmological models, i.e. the concordance cold dark matter
plus a cosmological constant ($\Lambda$CDM) model, Power-law (PL) model, and
$R_h=ct$ model using the available local probes, which includes the JLA
compilation of type-Ia supernovae (SNe Ia), the direct measurement of Hubble
constant (H(z)), and the baryon acoustic oscillations (BAO). For $\Lambda$CDM
model, we consider two different cases, i.e. zero and non-zero spatial
curvature. We find that by using the JLA alone, it is indistinguishable between
$\Lambda$CDM and PL models, but the $R_h=ct$ model is strongly disfavored. If
we combine JLA+H(z), the $\Lambda$CDM model is strongly favored against the
other two models. The combination of all the three datasets also supports
$\Lambda$CDM as the best model. We also use the low-redshift ($z<0.2$) data to
constrain the deceleration parameter using cosmography method, and find that
only the $\Lambda$CDM model is consistent with cosmography. However, there is
no strong evidence to distinguish between flat and non-flat $\Lambda$CDM models
by using the local data alone. | Possible Relic Lobes in Giant Radio Sources: We present low-frequency observations with the GMRT of three giant radio
sources (J0139+3957, J0200+4049 and J0807+7400) with relaxed diffuse lobes
which show no hotspots and no evidence of jets. The largest of these three,
J0200+4049, exhibits a depression in the centre of the western lobe, while
J0139+3957 and J0807+7400 have been suggested earlier by Klein et al. and Lara
et al. respectively to be relic radio sources. We estimate the spectral ages of
the lobes. All three sources have compact radio cores. Although the radio cores
suggest that the sources are currently active, we suggest that the lobes in
these sources could be due to an earlier cycle of activity. |
Upper Bound of Neutrino Masses from Combined Cosmological Observations
and Particle Physics Experiments: We investigate the impact of prior models on the upper bound of the sum of
neutrino masses, $\sum m_{\nu}$. We use data from Large Scale Structure of
galaxies, Cosmic Microwave Background, Type Ia SuperNovae, and Big Bang
Nucleosynthesis. We probe physically motivated neutrino mass models (respecting
oscillation experiment constraints) and compare them to constraints using
standard cosmological approximations. The former give a consistent upper bound
of $\sum m_{\nu} \lesssim 0.26$ eV ($95\%$ CI) and yields a strong competitive
upper bound for the lightest neutrino mass species, $m_0^{\nu} < 0.086$ eV
($95\%$ CI). By contrast one of the approximations, which is somewhat
inconsistent with oscillation experiments, yields an upper bound of $\sum
m_{\nu} \lesssim 0.15$ eV ($95\%$ CI), which differs substantially from the
former upper bound. We, therefore, argue that cosmological neutrino mass and
hierarchy determination should be pursued using physically motivated models
since approximations might lead to incorrect and nonphysical upper bounds. | Combining information from multiple cosmological surveys: inference and
modeling challenges: The tightest and most robust cosmological results of the next decade will be
achieved by bringing together multiple surveys of the Universe. This endeavor
has to happen across multiple layers of the data processing and analysis, e.g.,
enhancements are expected from combining Euclid, Rubin, and Roman (as well as
other surveys) not only at the level of joint processing and catalog
combination, but also during the post-catalog parts of the analysis such as the
cosmological inference process. While every experiment builds their own
analysis and inference framework and creates their own set of simulations,
cross-survey work that homogenizes these efforts, exchanges information from
numerical simulations, and coordinates details in the modeling of astrophysical
and observational systematics of the corresponding datasets is crucial. |
Constraining the Variation in Fine-Structure Constant Using SDSS DR8 QSO
Spectra: We report a robust constrain on the possible variation of fine-structure
constant, alpha = e^2/(hbar*c), obtained using O III 4959,5007, nebular
emission lines from QSOs. We find Delta-alpha/alpha=-(2.1 +/- 1.6) x 10^(-5)
based on a well selected sample of 2347 QSOs from Sloan Digital Sky Survey Data
Release 8 with 0.02 < z < 0.74. Our result is consistent with a non-varying
alpha at a level of 2 x 10^(-5) over approximately 7 Gyr. This is the largest
sample of extragalactic objects yet used to constrain the variation of alpha.
While this constraint is not as stringent as those determined using
many-multiplet method it is free from various systematic effects. A factor of ~
4 improvement in Delta-alpha/alpha achieved here compared to the previous study
(Bahcall et al. 2004) is just consistent with what is expected based on a
factor of 14 times bigger sample used here. This suggests that errors are
mainly dominated by the statistical uncertainty. We also find the ratio of
transition probabilities corresponding to the O III 5007 A and 4959 A lines to
be 2.933+/-0.002, in good agreement with the National Institute of Standards
and Technology measurements. | Enhanced Peculiar Velocities in Brane-Induced Gravity: The mounting evidence for anomalously large peculiar velocities in our
Universe presents a challenge for the LCDM paradigm. The recent estimates of
the large scale bulk flow by Watkins et al. are inconsistent at the nearly 3
sigma level with LCDM predictions. Meanwhile, Lee and Komatsu have recently
estimated that the occurrence of high-velocity merging systems such as the
Bullet Cluster (1E0657-57) is unlikely at a 6.5-5.8 sigma level, with an
estimated probability between 3.3x10^{-11} and 3.6x10^{-9} in LCDM cosmology.
We show that these anomalies are alleviated in a broad class of
infrared-modifed gravity theories, called brane-induced gravity, in which
gravity becomes higher-dimensional at ultra large distances. These theories
include additional scalar forces that enhance gravitational attraction and
therefore speed up structure formation at late times and on sufficiently large
scales. The peculiar velocities are enhanced by 24-34% compared to standard
gravity, with the maximal enhancement nearly consistent at the 2 sigma level
with bulk flow observations. The occurrence of the Bullet Cluster in these
theories is 10^4 times more probable than in LCDM cosmology. |
An ALMA+ACA measurement of the shock in the Bullet Cluster: The thermal Sunyaev-Zeldovich (SZ) effect presents a relatively new tool for
characterizing galaxy cluster merger shocks, traditionally studied through
X-ray observations. Widely regarded as the "textbook example" of a cluster
merger bow shock, the western shock front in the Bullet Cluster (1E0657-56)
represents the ideal test case for such an SZ study. We aim to reconstruct a
parametric model for the shock SZ signal by directly and jointly fitting deep,
high-resolution interferometric data from the Atacama Large
Millimeter/submillimeter Array (ALMA) and Atacama Compact Array (ACA) in
Fourier space. The ALMA+ACA data are primarily sensitive to the electron
pressure difference across the shock front. To estimate the shock Mach number
$M$, this difference can be combined with the value for the upstream electron
pressure derived from an independent Chandra X-ray analysis. In the case of
instantaneous electron-ion temperature equilibration, we find
$M=2.08^{+0.12}_{-0.12}$, in $\approx 2.4\sigma$ tension with the independent
constraint from Chandra, $M_X=2.74\pm0.25$. The assumption of purely adiabatic
electron temperature change across the shock leads to $M=2.53^{+0.33}_{-0.25}$,
in better agreement with the X-ray estimate $M_X=2.57\pm0.23$ derived for the
same heating scenario. We have demonstrated that interferometric observations
of the SZ effect provide constraints on the properties of the shock in the
Bullet Cluster that are highly complementary to X-ray observations. The
combination of X-ray and SZ data yields a powerful probe of the shock
properties, capable of measuring $M$ and addressing the question of
electron-ion equilibration in cluster shocks. Our analysis is however limited
by systematics related to the overall cluster geometry and the complexity of
the post-shock gas distribution. To overcome these limitations, a joint
analysis of SZ and X-ray data is needed. | The Star Formation Law at Low Surface Density: We investigate the nature of the star formation law at low gas surface
densities using a sample of 19 low surface brightness (LSB) galaxies with
existing HI maps in the literature, UV imaging from the Galaxy Evolution
Explorer satellite, and optical images from the Sloan Digital Sky Survey. All
of the LSB galaxies have (NUV-r) colors similar to those for higher surface
brightness star-forming galaxies of similar luminosity indicating that their
average star formation histories are not very different. Based upon four LSB
galaxies with both UV and FIR data, we find FIR/UV ratios significantly less
than one, implying low amounts of internal UV extinction in LSB galaxies. We
use the UV images and HI maps to measure the star formation rate and hydrogen
gas surface densities within the same region for all of the galaxies. The LSB
galaxy star formation rate surface densities lie below the extrapolation of the
power law fit to the star formation rate surface density as a function of the
total gas density for higher surface brightness galaxies. Although there is
more scatter, the LSB galaxies also lie below a second version of the star
formation law in which the star formation rate surface density is correlated
with the gas density divided by the orbital time in the disk. The downturn seen
in both star formation laws is consistent with theoretical models that predict
lower star formation efficiencies in LSB galaxies due to the declining
molecular fraction with decreasing density. |
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