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Gravitational lensing effects of supermassive black holes in cluster
environments: This study explores the gravitational lensing effects of supermassive black
holes (SMBHs) in galaxy clusters. While the presence of central SMBHs in
galaxies is firmly established, recent work from high-resolution simulations
predict the existence of an additional population of wandering SMBHs. Though
the masses of these SMBHs are a minor perturbation on the larger scale and
individual galaxy scale dark matter components in the cluster, they can impact
statistical lensing properties and individual lensed image configurations.
Probing for these potentially observable signatures, we find that SMBHs imprint
detectable signatures in rare, higher-order strong lensing image configurations
although they do not manifest any statistically significant detectable evidence
in either the magnification distribution or the integrated shear profile.
Investigating specific lensed image geometries, we report that a massive, near
point-like, potential of an SMBH causes the following detectable effects: (i)
image splitting leading to the generation of extra images; (ii) positional and
magnification asymmetries in multiply imaged systems; and (iii) the apparent
disappearance of a lensed counter-image. Of these, image splitting inside the
cluster tangential critical curve, is the most prevalent notable observational
signature. We demonstrate these possibilities in two cases of observed giant
arcs in $SGAS\,J003341.5+024217$ and $RX\,J1347.5-1145$, wherein specific image
configurations seen can be reproduced with SMBHs. Future observations with
high-resolution instrumentation (e.g. MAVIS-Very Large Telescope,
MICADO-Extremely Large Telescope, and the upgraded ngVLA, along with data from
the \textit{Euclid} \& \textit{Nancy Grace Roman} Space Telescopes and the
Rubin LSST Observatory are likely to allow us to probe these unique yet rare
SMBHs lensing signatures. | Anisotropic Distance Ladder in Pantheon+ Supernovae: We decompose Pantheon+ Type Ia supernovae (SN) in hemispheres on the sky
finding angular variations up to $4$ km/s/Mpc in the Hubble constant $H_0$ both
in the SH0ES redshift range $0.0233 < z < 0.15$ and in extended redshift
ranges. The variations are driven largely by variations in absolute magnitude
from SN in Cepheid hosts, but are reinforced by SN in the Hubble flow. $H_0$ is
larger in a hemisphere encompassing the CMB dipole direction. The variations we
see exceed the errors on the recent SH0ES determination, $H_0 = 73.04 \pm 1.04$
km/s/Mpc, but are not large enough to explain early versus late Universe
discrepancies in the Hubble constant. Nevertheless, the Cepheid-SN distance
ladder is anisotropic at current precision. The anisotropy may be due to a
breakdown in the Cosmological Principle, or mundanely due to a statistical
fluctuation in a small sample of SN in Cepheid host galaxies. |
The dusty heart of nearby active galaxies -- II. From clumpy torus
models to physical properties of dust around AGN: The dusty environments (= "dust tori'') of AGN are now in reach of
observations. Following our paper I on ground-based mid-IR spectro-photometry
(H\"onig et al. 2010), we present an upgrade to our radiative transfer model of
3-dimensional clumpy dust tori. The upgrade with respect to H\"onig et al.
(2006) concerns an improved handling of the diffuse radiation field in the
torus which is approximated by a statistical approach. The models are presented
as tools to translate classical and interferometric observations into
characteristic properties of the dust distribution. We compare model SEDs for
different chemical and grain-size compositions of the dust and find that clouds
with standard ISM dust and optical depth tau_V~50 appear in overall agreement
with observed IR SEDs. By studying parameter dependencies, it is shown that
type 1 AGN SEDs, in particular the mid-IR spectral index, can be used to
constrain the radial dust cloud distribution power-law index 'a', while other
parameters are more difficult to assess using SEDs only. Interferometry adds
important additional information for modeling when interpreted simultaneously
with the SED. Although type 2 AGN can, in principle, be used to constrain model
parameters as well, obscuration effects make the analysis more ambiguous. We
propose a simple, interferometry-based method to distinguish between "compact''
and "extended'' radial dust distributions without detailed modeling of the data
and introduce a way to easily determine individual or sample average model
parameters using the observed optical depth in the silicate feature and the
mid-IR spectral index. | Baryon Acoustic Oscillations in the Sloan Digital Sky Survey Data
Release 7 Galaxy Sample: The spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) galaxy
sample represents the final set of galaxies observed using the original SDSS
target selection criteria. We analyse the clustering of galaxies within this
sample, including both the Luminous Red Galaxy (LRG) and Main samples, and also
include the 2-degree Field Galaxy Redshift Survey (2dFGRS) data. Baryon
Acoustic Oscillations are observed in power spectra measured for different
slices in redshift; this allows us to constrain the distance--redshift relation
at multiple epochs. We achieve a distance measure at redshift z=0.275, of
r_s(z_d)/D_V(0.275)=0.1390+/-0.0037 (2.7% accuracy), where r_s(z_d) is the
comoving sound horizon at the baryon drag epoch,
D_V(z)=[(1+z)^2D_A^2cz/H(z)]^(1/3), D_A(z) is the angular diameter distance and
H(z) is the Hubble parameter. We find an almost independent constraint on the
ratio of distances D_V(0.35)/D_V(0.2)=1.736+/-0.065, which is consistent at the
1.1sigma level with the best fit Lambda-CDM model obtained when combining our
z=0.275 distance constraint with the WMAP 5-year data. The offset is similar to
that found in previous analyses of the SDSS DR5 sample, but the discrepancy is
now of lower significance, a change caused by a revised error analysis and a
change in the methodology adopted, as well as the addition of more data. Using
WMAP5 constraints on Omega_bh^2 and Omega_ch^2, and combining our BAO distance
measurements with those from the Union Supernova sample, places a tight
constraint on Omega_m=0.286+/-0.018 and H_0 = 68.2+/-2.2km/s/Mpc that is robust
to allowing curvature and non-Lambda dark energy. This result is independent of
the behaviour of dark energy at redshifts greater than those probed by the BAO
and supernova measurements. (abridged) |
GOODS-Herschel: radio-excess signature of hidden AGN activity in distant
star-forming galaxies: We present here a new spectral energy distribution (SED) fitting approach
that we adopt to select radio-excess sources amongst distant star-forming
galaxies in the GOODS-Herschel (North) field and to reveal the presence of
hidden, highly obscured AGN. Through extensive SED analysis of 458 galaxies
with radio 1.4 GHz and mid-IR 24 um detections using some of the deepest
Chandra X-ray, Spitzer and Herschel infrared, and VLA radio data available to
date, we have robustly identified a sample of 51 radio-excess AGN (~1300
deg^-2) out to redshift z~3. These radio-excess AGN have a significantly lower
far-IR/radio ratio (q<1.68) than the typical relation observed for star-forming
galaxies (q~2.2). We find that ~45% of these radio-excess sources have a
dominant AGN component in the mid-IR band, while for the remainders the excess
radio emission is the only indicator of AGN activity. The fraction of
radio-excess AGN increases with X-ray luminosity reaching ~60% at
Lx~10^44-10^45 erg/s, making these sources an important part of the total AGN
population. However, almost half (24/51) of these radio-excess AGN are not
detected in the deep Chandra X-ray data, suggesting that some of these sources
might be heavily obscured. We also find that the specific star formation rates
(sSFRs) of the radio-excess AGN are on average lower that those observed for
X-ray selected AGN hosts, indicating that our sources are forming stars more
slowly than typical AGN hosts, and possibly their star formation is
progressively quenching. | Integral Field Spectroscopy surveys of nearby spiral and U-LIRG galaxies: We describe the observations and preliminary results of the gas-phase
analysis based on two ongoing, wide-field Integral Field Spectroscopy (IFS)
surveys: the PPAK IFS Nearby Galaxies Survey (PINGS), targeting disc galaxies;
and the VIMOS-IFU observations of low-z (Ultra)Luminous Infrared Galaxies
(U-LIRGs), the local counterpart of massive, dusty high-z star-forming
galaxies. We describe how these observations are allowing to discover and
characterise abundance differentials between galactic substructures and
differences depending on the morphologically/dynamically distinct types of
objects, which in turn will allow us to interpret the gas-phase abundances of
analogue high-z systems. |
Single parameter galaxy classification: The Principal Curve through the
multi-dimensional space of galaxy properties: We propose to describe the variety of galaxies from SDSS by using only one
affine parameter. To this aim, we build the Principal Curve (P-curve) passing
through the spine of the data point cloud, considering the eigenspace derived
from Principal Component Analysis of morphological, physical and photometric
galaxy properties. Thus, galaxies can be labeled, ranked and classified by a
single arc length value of the curve, measured at the unique closest projection
of the data points on the P-curve. We find that the P-curve has a "W" letter
shape with 3 turning points, defining 4 branches that represent distinct galaxy
populations. This behavior is controlled mainly by 2 properties, namely u-r and
SFR. We further present the variations of several galaxy properties as a
function of arc length. Luminosity functions variate from steep Schechter fits
at low arc length, to double power law and ending in Log-normal fits at high
arc length. Galaxy clustering shows increasing autocorrelation power at large
scales as arc length increases. PCA analysis allowed to find peculiar galaxy
populations located apart from the main cloud of data points, such as small red
galaxies dominated by a disk, of relatively high stellar mass-to-light ratio
and surface mass density. The P-curve allows not only dimensionality reduction,
but also provides supporting evidence for relevant physical models and
scenarios in extragalactic astronomy: 1) Evidence for the hierarchical merging
scenario in the formation of a selected group of red massive galaxies. These
galaxies present a log-normal r-band luminosity function, which might arise
from multiplicative processes involved in this scenario. 2) Connection between
the onset of AGN activity and star formation quenching, which appears in green
galaxies when transitioning from blue to red populations. (Full abstract in
downloadable version) | Toward Cosmological Standard Timers in Primordial Black Hole Binaries: We propose that primordial black hole (PBH) binary systems can lead to
standard timers in tracking the evolution of the Universe. Through
gravitational waves from monochromatic PBH binaries, the probability
distribution on major axis and eccentricity from the same redshift is obtained.
By studying the dynamical evolution of PBH binaries from the initial
probability distribution to observed redshifted ones, the redshift-time
calibration can be extracted, which can constrain cosmological models. A
general formalism of the standard timer is further concluded based on the
evolution of statistical distribution in dynamical systems. |
The reach of next-to-leading-order perturbation theory for the matter
bispectrum: We provide a comparison between the matter bispectrum derived with different
flavours of perturbation theory at next-to-leading order and measurements from
an unprecedentedly large suite of $N$-body simulations. We use the $\chi^2$
goodness-of-fit test to determine the range of accuracy of the models as a
function of the volume covered by subsets of the simulations. We find that
models based on the effective-field-theory (EFT) approach have the largest
reach, standard perturbation theory has the shortest, and `classical' resummed
schemes lie in between. The gain from EFT, however, is less than in previous
studies. We show that the estimated range of accuracy of the EFT predictions is
heavily influenced by the procedure adopted to fit the amplitude of the
counterterms. For the volumes probed by galaxy redshift surveys, our results
indicate that it is advantageous to set three counterterms of the EFT
bispectrum to zero and measure the fourth from the power spectrum. We also find
that large fluctuations in the estimated reach occur between different
realisations. We conclude that it is difficult to unequivocally define a range
of accuracy for the models containing free parameters. Finally, we
approximately account for systematic effects introduced by the $N$-body
technique either in terms of a scale- and shape-dependent bias or by boosting
the statistical error bars of the measurements (as routinely done in the
literature). We find that the latter approach artificially inflates the reach
of EFT models due to the presence of tunable parameters. | Modified Gravity: the CMB, Weak Lensing and General Parameterisations: We examine general physical parameterisations for viable gravitational models
in the $f(R)$ framework. This is related to the mass of an additional scalar
field, called the scalaron, that is introduced by the theories. Using a simple
parameterisation for the scalaron mass $M(a)$ we show there is an exact
correspondence between the model and popular parameterisations of the modified
Poisson equation $\mu(a,k)$ and the ratio of the Newtonian potentials
$\eta(a,k)$. However, by comparing the aforementioned model against other
viable scalaron theories we highlight that the common form of $\mu(a,k)$ and
$\eta(a,k)$ in the literature does not accurately represent $f(R)$ behaviour.
We subsequently construct an improved description for the scalaron mass (and
therefore $\mu(a,k)$ and $\eta(a,k)$) which captures their essential features
and has benefits derived from a more physical origin. We study the scalaron's
observational signatures and show the modification to the background Friedmann
equation and CMB power spectrum to be small. We also investigate its effects in
the linear and non linear matter power spectrum--where the signatures are
evident--thus giving particular importance to weak lensing as a probe of these
models. Using this new form, we demonstrate how the next generation Euclid
survey will constrain these theories and its complementarity to current solar
system tests. In the most optimistic case Euclid, together with a Planck prior,
can constrain a fiducial scalaron mass $M_{0} = 9.4 \times 10^{-30}{\rm eV}$ at
the $\sim 20 %$ level. However, the decay rate of the scalaron mass, with
fiducial value $\nu = 1.5$, can be constrained to $\sim 3%$ uncertainty. |
Flow Patterns around Dark Matter Halos: the Link between Halo Dynamical
Properties and Large Scale Tidal Field: We study how halo intrinsic dynamical properties are linked to their
formation processes for halos in two mass ranges, $10^{12}-10^{12.5}h^{-1}{\rm
M_\odot}$ and $\ge 10^{13}h^{-1}{\rm M_\odot}$, and how both are correlated
with the large scale tidal field within which the halos reside at present. Halo
merger trees obtained from cosmological $N$-body simulations are used to
identify infall halos that are about to merge with their hosts. We find that
the tangential component of the infall velocity increases significantly with
the strength of the local tidal field, but no strong correlation is found for
the radial component. These results can be used to explain how the internal
velocity anisotropy and spin of halos depend on environment. The position
vectors and velocities of infall halos are aligned with the principal axes of
the local tidal field, and the alignment depends on the strength of the tidal
field. Opposite accretion patterns are found in weak and strong tidal fields,
in the sense that in a weak field the accretion flow is dominated by radial
motion within the local structure, while a large tangential component is
present in a strong field. These findings can be used to understand the strong
alignments we find between the principal axes of the internal velocity
ellipsoids of halos and the local tidal field, and their dependence on the
strength of tidal field. They also explain why halo spin increases with the
strength of local tidal field, but only in weak tidal fields does the
spin-tidal field alignment follow the prediction of the tidal torque theory. We
discuss how our results may be used to understand the spins of disk galaxies
and velocity structures of elliptical galaxies and their correlations with
large-scale structure. | The LABOCA survey of the Extended Chandra Deep Field South: Two modes of
star formation in AGN hosts?: We study the co-existence of star formation and AGN activity in X-ray
selected AGN by analyzing stacked 870um submm emission from a deep and wide map
of the Extended Chandra Deep Field South, obtained with LABOCA at the APEX
telescope. The total X-ray sample of 895 sources with median redshift z~1 is
detected at a mean submm flux of 0.49+-0.04mJy, corresponding to a typical star
formation rate around 30Msun/yr for a T=35K, beta=1.5 greybody far-infrared
SED. The good S/N permits stacking analyses for subgroups. We observe a trend
of star formation rate increasing with redshift. An increase of star formation
rate with AGN luminosity is indicated at the highest L_2-10>~1E44erg/s
luminosities only. Increasing trends with X-ray obscuration as expected in some
AGN evolutionary scenarios are not observed for the bulk of the X-ray AGN
sample but may be present for the highest intrinsic luminosity objects. This
suggests a transition between two modes in the coexistence of AGN activity and
star formation. For the bulk of the sample, the X-ray luminosity and
obscuration of the AGN are not intimately linked to the global star formation
rate of their hosts. The hosts are likely massive and forming stars secularly,
at rates similar to the pervasive star formation seen in massive galaxies
without an AGN at similar redshifts. The change indicated towards more intense
star formation, and a more pronounced increase in star formation rates between
unobscured and obscured AGN at highest luminosities suggests that luminous AGN
follow an evolutionary path on which obscured AGN activity and intense star
formation are linked, possibly via merging. Comparison to local hard X-ray
selected AGN supports this interpretation. [Abridged] |
Analysis of the impact of broad absorption lines on quasar redshift
measurements with synthetic observations: Accurate quasar classifications and redshift measurements are increasingly
important to precision cosmology experiments. Broad absorption line (BAL)
features are present in 15-20\% of all quasars, and these features can
introduce systematic redshift errors, and in extreme cases produce
misclassifications. We quantitatively investigate the impact of BAL features on
quasar classifications and redshift measurements with synthetic spectra that
were designed to match observations by the Dark Energy Spectroscopic Instrument
(DESI) survey. Over the course of five years, DESI aims to measure spectra for
40 million galaxies and quasars, including nearly three million quasars. Our
synthetic quasar spectra match the signal-to-noise ratio and redshift
distributions of the first year of DESI observations, and include the same
synthetic quasar spectra both with and without BAL features. We demonstrate
that masking the locations of the BAL features decreases the redshift errors by
about 1\% and reduces the number of catastrophic redshift errors by about 80\%.
We conclude that identifying and masking BAL troughs should be a standard part
of the redshift determination step for DESI and other large-scale spectroscopic
surveys of quasars. | A self-consistent phase-space distribution function for the anisotropic
Dark Matter halo of the Milky Way: Dark Matter (DM) direct detection experiments usually assume the simplest
possible 'Standard Halo Model' for the Milky Way (MW) halo in which the
velocity distribution is Maxwellian. This model assumes that the MW halo is an
isotropic, isothermal sphere, hypotheses that are unlikely to be valid in
reality. An alternative approach is to derive a self-consistent solution for a
particular mass model of the MW (i.e. obtained from its gravitational
potential) using the Eddington formalism, which assumes isotropy. In this paper
we extend this approach to incorporate an anisotropic phase-space distribution
function. We perform Bayesian scans over the parameters defining the mass model
of the MW and parameterising the phase-space density, implementing constraints
from a wide range of astronomical observations. The scans allow us to estimate
the precision reached in the reconstruction of the velocity distribution (for
different DM halo profiles). As expected, allowing for an anisotropic velocity
tensor increases the uncertainty in the reconstruction of f(v) but the
distribution can still be determined with a precision of a factor of 4-5. The
mean velocity distribution resembles the isotropic case, however the amplitude
of the high-velocity tail is up to a factor of 2 larger. Our results agree with
the phenomenological parametrization proposed in Mao et al. (2013) as a good
fit to N-body simulations (with or without baryons), since their velocity
distribution is contained in our 68% credible interval. |
Prediction of the Cosmic Evolution of the CO-Luminosity Functions: We predict the emission line luminosity functions (LFs) of the first 10
rotational transitions of CO in galaxies at redshift z=0 to z=10. This
prediction relies on a recently presented simulation of the molecular cold gas
content in ~3e7 evolving galaxies based on the Millennium Simulation. We
combine this simulation with a model for the conversion between molecular mass
and CO-line intensities, which incorporates the following mechanisms: (i)
molecular gas is heated by the CMB, starbursts (SBs), and active galactic
nuclei (AGNs); (ii) molecular clouds in dense or inclined galaxies can overlap;
(iii) compact gas can attain a smooth distribution in the densest part of
disks; (iv) CO-luminosities scale with metallicity changes between galaxies;
(v) CO-luminosities are always detected against the CMB. We analyze the
relative importance of these effects and predict the cosmic evolution of the
CO-LFs. The most notable conclusion is that the detection of regular galaxies
(i.e. no AGN, no massive SB) at high z>7 in CO-emission will be dramatically
hindered by the weak contrast against the CMB, in contradiction to earlier
claims that CMB-heating will ease the detection of high-redshift CO. The full
simulation of extragalactic CO-lines and the predicted CO-LFs at any redshift
can be accessed online, prior registration required} and they should be useful
for the modeling of CO-line surveys with future telescopes, such as ALMA, the
LMT, or the SKA. | Dark Matter annihilations in halos and high-redshift sources of
reionization of the universe: It is well known that annihilations in the homogeneous fluid of dark matter
(DM) can leave imprints in the cosmic microwave background (CMB) anisotropy
power spectrum. However, the relevance of DM annihilations in halos for
cosmological observables is still subject to debate, with previous works
reaching different conclusions on this point. Also, all previous studies used a
single type of parameterization for the astrophysical reionization, and
included no astrophysical source for the heating of the intergalactic medium.
In this work, we revisit these problems. When standard approaches are adopted,
we find that the ionization fraction does exhibit a very particular (and
potentially constraining) pattern, but the currently measurable optical depth
to reionization is left almost unchanged: In agreement with the most of the
previous literature, for plausible halo models we find that the modification of
the signal with respect to the one coming from annihilations in the smooth
background is tiny, below cosmic variance within currently allowed parameter
space. However, if different and probably more realistic treatments of the
astrophysical sources of reionization and heating are adopted, a more
pronounced effect of the DM annihilation in halos is possible. We thus conclude
that within currently adopted baseline models the impact of the virialised DM
structures cannot be uncovered by CMB power spectra measurements, but a larger
impact is possible if peculiar models are invoked for the redshift evolution of
the DM annihilation signal or different assumptions are made for the
astrophysical contributions. A better understanding (both theoretical and
observational) of the reionization and temperature history of the universe,
notably via the 21 cm signal, seems the most promising way for using halo
formation as a tool in DM searches, improving over the sensitivity of current
cosmological probes. |
The Swift short gamma-ray burst rate density: implications for binary
neutron star merger rates: Short gamma-ray bursts (SGRBs) observed by {\it Swift} are potentially
revealing the first insight into cataclysmic compact object mergers. To
ultimately acquire a fundamental understanding of these events requires
pan-spectral observations and knowledge of their spatial distribution to
differentiate between proposed progenitor populations. Up to April 2012 there
are only some 30% of SGRBs with reasonably firm redshifts, and this sample is
highly biased by the limited sensitivity of {\it Swift} to detect SGRBs. We
account for the dominant biases to calculate a realistic SGRB rate density out
to $z\approx0.5$ using the {\it Swift} sample of peak fluxes, redshifts, and
those SGRBs with a beaming angle constraint from X-ray/optical observations. We
find an SGRB lower rate density of $8^{+5}_{-3}$
$\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$ (assuming isotropic emission), and a
beaming corrected upper limit of $1100^{+700}_{-470} $
$\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$. Assuming a significant fraction of binary
neutron star mergers produce SGRBs, we calculate lower and upper detection rate
limits of $(1-180)$ yr$^{-1}$ by an aLIGO and Virgo coincidence search. Our
detection rate is similar to the lower and realistic rates inferred from
extrapolations using Galactic pulsar observations and population synthesis. | The Subaru Ly-alpha blob survey: A sample of 100 kpc Ly-alpha blobs at
z=3: We present results of a survey for giant Ly-alpha nebulae (LABs) at z=3 with
Subaru/Suprime-Cam. We obtained Ly-alpha imaging at z=3.09+-0.03 around the
SSA22 protocluster and in several blank fields. The total survey area is 2.1
square degrees, corresponding to a comoving volume of 1.6 x 10^6 Mpc^3. Using a
uniform detection threshold of 1.4 x 10^{-18} erg s^{-1} cm^{-2} arcsec^{-2}
for the Ly-alpha images, we construct a sample of 14 LAB candidates with
major-axis diameters larger than 100 kpc, including five previously known blobs
and two known quasars. This survey triples the number of known LABs over 100
kpc. The giant LAB sample shows a possible "morphology-density relation":
filamentary LABs reside in average density environments as derived from compact
Ly-alpha emitters, while circular LABs reside in both average density and
overdense environments. Although it is hard to examine the formation mechanisms
of LABs only from the Ly-alpha morphologies, more filamentary LABs may relate
to cold gas accretion from the surrounding inter-galactic medium (IGM) and more
circular LABs may relate to large-scale gas outflows, which are driven by
intense starbursts and/or by AGN activities. Our survey highlights the
potential usefulness of giant LABs to investigate the interactions between
galaxies and the surrounding IGM from the field to overdense environments at
high-redshift. |
From the cosmological model to generation of the Hubble flow: We review different approaches to the problem of generating the observed
Hubble flow, whose discussion was pioneered by A.D. Sakharov. Extrapolating the
Cosmological Standard Model to the past makes it possible to determine physical
properties of and conditions in the early universe. We discuss a new
cosmogenesis paradigm based on studying geodesically complete geometries of
black/white holes with integrable singularities. | On the EFT of Large Scale Structures in Redshift Space: We further develop the description of redshift space distortions within the
Effective Field Theory of Large Scale Structures. First, we generalize the
counterterms to include the effect of baryonic physics and primordial
non-Gaussianity. Second, we evaluate the IR-resummation of the dark matter
power spectrum in redshift space. This requires us to identify a controlled
approximation that makes the numerical evaluation straightforward and
efficient. Third, we compare the predictions of the theory at one loop with the
power spectrum from numerical simulations up to $\ell=6$. We find that the
IR-resummation allows us to correctly reproduce the BAO peak. The $k$-reach, or
equivalently the precision for a given $k$, depends on additional counterterms
that need to be matched to simulations. Since the non-linear scale for the
velocity is expected to be longer than the one for the overdensity, we consider
a minimal and a non-minimal set of counterterms. The quality of our numerical
data makes it hard to firmly establish the performance of the theory at high
wavenumbers. Within this limitation, we find that the theory at redshift
$z=0.56$ and up to $\ell=2$ matches the data to percent level approximately up
to $k \sim 0.13 \, h { \rm Mpc^{-1}}$ or $k \sim 0.18 \, h { \rm Mpc^{-1}}$,
depending on the number of counterterms used, with potentially large
improvement over former analytical techniques. |
Evidence for departure from ΛCDM with LSS: We investigate the growth index parameter \gamma and the time variation of
the gravitational constant G_{eff} by using the currently available growth
function f(z) data at different redshifts, with and without scaling to the
fiducial \Lambda CDM model. We inquire the four different models of \gamma
including a constant \gamma. From a \chi^2 minimization, we constrain the
parameter spaces of models and show that \Lambda CDM model is excluded by
1-\sigma level from current f(z) data. G_{eff} is different from the Newton's
gravitational constant G_{N} in modified gravity theories and interestingly,
the current data shows that G_{eff} \neq G_{N} at z \gtrsim 0.2 \sim 0.3 at
3-\sigma level. From these, we conclude that Einstein's General Relativity with
\Lambda CDM is ruled out by 99% confidence level from large scale structure
observations. | Inflation and Early Dark Energy with a Stage II Hydrogen Intensity
Mapping Experiment: This white paper envisions a revolutionary post-DESI, post-LSST dark energy
program based on intensity mapping of the redshifted 21cm emission line from
neutral hydrogen at radio frequencies. The proposed intensity mapping survey
has the unique capability to quadruple the volume of the Universe surveyed by
optical programs, provide a percent-level measurement of the expansion history
to $z \sim 6$, open a window to explore physics beyond the concordance
$\Lambda$CDM model, and to significantly improve the precision on standard
cosmological parameters. In addition, characterization of dark energy and new
physics will be powerfully enhanced by cross-correlations with optical surveys
and cosmic microwave background measurements. The rich dataset obtained by the
proposed intensity mapping instrument will be simultaneously useful in
exploring the time-domain physics of fast radio transients and pulsars,
potentially in live "multi-messenger" coincidence with other observatories. The
core dark energy/inflation science advances enabled by this program are the
following: (i) Measure the expansion history of the universe over $z=0.3-6$
with a single instrument, extending the range deep into the pre-acceleration
era, providing an unexplored window for new physics; (ii) Measure the growth
rate of structure in the universe over the same redshift range; (iii) Observe,
or constrain, the presence of inflationary relics in the primordial power
spectrum, improving existing constraints by an order of magnitude; (iv)
Observe, or constrain, primordial non-Gaussianity with unprecedented precision,
improving constraints on several key numbers by an order of magnitude. Detailed
mapping of the enormous, and still largely unexplored, volume of cosmic space
will thus provide unprecedented information on fundamental questions of the
vacuum energy and early-universe physics. |
BBN And The CMB Constrain Neutrino Coupled Light WIMPs: (abridged) In the presence of a light WIMP (mass m_chi < 30 MeV), there are
degeneracies among the WIMP's nature, its couplings to standard model
particles, its mass, and the number of equivalent (additional) neutrinos, Delta
N_nu. These degeneracies cannot be broken by the CMB constraint on the
effective number of neutrinos, N_eff. However, since big bang nucleosynthesis
(BBN) is also affected by a light WIMP and equivalent neutrinos, complementary
BBN and CMB constraints can break some of the degeneracy. In a previous paper
BBN and CMB were combined to explore allowed ranges for m_chi, Delta N_nu, and
N_eff for light WIMPs that annihilate electromagnetically (EM) to photons
and/or electrons/positrons. In this paper BBN predictions with a light WIMP
that only couples to neutrinos are calculated. Recent observed abundances of
^2H and ^4He are used to limit m_chi, Delta N_nu, N_eff, and the present-day
baryon density. Allowing for a neutrino coupled light WIMP and nonzero Delta
N_nu, combined BBN and CMB data give lower limits to m_chi, with a best fit
m_chi > 35 MeV, equivalent to no light WIMP at all. All masses below 4--9 MeV
(depending on spin) are excluded. Without any light WIMP, BBN alone prefers
Delta N_nu = 0.50 +- 0.23, favoring neither Delta N_nu = 0, nor a fully
thermalized sterile neutrino (Delta N_nu = 1). This result is consistent with
the CMB constraint, N_eff = 3.30 +- 0.27, limiting "new physics" between BBN
and recombination. Combining BBN and CMB data gives Delta N_nu = 0.35 +- 0.16
and N_eff = 3.40 +- 0.16; while BBN and the CMB combined require Delta N_nu > 0
at ~98% confidence, they disfavor Delta N_nu > 1 at > 99% confidence. Allowing
a neutrino-coupled light WIMP extends the allowed range slightly downward for
Delta N_nu and slightly upward for N_eff simultaneously, leaving best-fit
values unchanged. | Constraints on the Nature of CID-42: Recoil Kick or Supermassive Black
Hole Pair?: The galaxy CXOC J100043.1+020637, also known as CID-42, is a highly unusual
object. An apparent galaxy merger remnant, it displays signatures of both an
inspiraling, kiloparsec-scale active galactic nucleus (AGN) pair and of a
recoiling AGN with a kick velocity > 1300 km s^-1. Among recoiling AGN
candidates, CID-42 alone has both spatial offsets (in optical and X-ray bands)
and spectroscopic offsets. In order to constrain the relative likelihood of
both scenarios, we develop models using hydrodynamic galaxy merger simulations
coupled with radiative transfer calculations. Our gas-rich, major merger models
are generally well matched to the galactic morphology and to the inferred
stellar mass and star formation rate. We show that a recoiling supermassive
black hole (SMBH) in CID-42 should be observable as an AGN at the time of
observation. However, in order for the recoiling AGN to produce narrow-line
emission, it must be observed shortly after the kick while it still inhabits a
dense gaseous region, implying a large total kick velocity (v_k > 2000 km
s^-1). For the dual AGN scenario, an unusually large broad-line offset is
required, and the best match to the observed morphology requires a galaxy that
is less luminous than CID-42. Further, the lack of X-ray emission from one of
the two optical nuclei is not easily attributed to an intrinsically quiescent
SMBH or to a Compton-thick galactic environment. While the current data do not
allow either the recoiling or the dual AGN scenario for CID-42 to be excluded,
our models highlight the most relevant parameters for distinguishing these
possibilities with future observations. In particular, high-quality,
spatially-resolved spectra that can pinpoint the origin of the broad and narrow
line features will be critical for determining the nature of this unique
source. |
The dust emission of high-redshift quasars: The detection of powerful near-infrared emission in high redshift (z>5)
quasars demonstrates that very hot dust is present close to the active nucleus
also in the very early universe. A number of high-redshift objects even show
significant excess emission in the rest frame NIR over more local AGN spectral
energy distribution (SED) templates. In order to test if this is a result of
the very high luminosities and redshifts, we construct mean SEDs from the
latest SDSS quasar catalogue in combination with MIR data from the WISE
preliminary data release for several redshift and luminosity bins. Comparing
these mean SEDs with a large sample of z>5 quasars we could not identify any
significant trends of the NIR spectral slope with luminosity or redshift in the
regime 2.5 < z < 6 and 10^45 < nuL_nu(1350AA) < 10^47 erg/s. In addition to the
NIR regime, our combined Herschel and Spitzer photometry provides full infrared
SED coverage of the same sample of z>5 quasars. These observations reveal
strong FIR emission (L_FIR > 10^13 L_sun) in seven objects, possibly indicating
star-formation rates of several thousand solar masses per year. The FIR excess
emission has unusally high temperatures (T ~ 65 K) which is in contrast to the
temperature typically expected from studies at lower redshift (T ~ 45 K). These
objects are currently being investigated in more detail. | CMB anisotropies generated by cosmic string loops: We investigate the contribution of cosmic string loops to the Cosmic
Microwave Background (CMB) anisotropies. This is done by extending the
Unconnected Segment Model (USM) to include the contribution of the cosmic
string loops created throughout the cosmological evolution of a cosmic string
network to the stress-energy tensor. We then implement this extended USM in the
publicly available CMBACT code and obtain the linear CDM power spectrum and the
CMB angular power spectra generated by cosmic string loops. We find that the
shape of the angular power spectra generated by loops is, in general, similar
to that of long strings. However, there is generally an enhancement of the
anisotropies on small angular scales. Vector modes produced by loops dominate
over those produced by long strings for large multipole moments $\ell$. The
contribution of loops to the CMB anisotropies generated by cosmic string
networks may reach a level of $10\%$ for large loops but decreases as the size
of loops decreases. This contribution may then be significant and, thus, this
extension provides a more accurate prediction of the CMB anisotropies generated
by cosmic string networks. |
Circular Polarization of the CMB: A probe of the First stars: While it is revealed that the Cosmic Microwave Background (CMB) is linearly
polarized at 10 % level, it is predicted that there exists no significant
intrinsic source for circular polarization (CP) in the standard cosmology.
However, during the propagation through a magnetised plasma, the CP of the CMB
could be produced via the Faraday conversion (FC). The FC converts a
pre-existing linear polarization into CP in presence of a magnetic field with
relativistic electrons. In this paper, we focus on the FC due to supernova
remnants of the first stars, also called Pop III stars. We derive an analytic
form for the angular power spectrum of the CP of the CMB generated by the
general FC. We apply this result to the case of the FC triggered by explosions
of the first stars and evaluate the angular power spectrum, CV V . We show that
the amplitude of l(l + 1)C_l^V V /(2pi) > 10^-2 micro Kelvin squared for l >
100, with only one Pop III star per halo, the age of Pop III SN remnants as 104
years and frequency of CMB observation as 1 GHz. We expect the CP of the CMB to
be a very promising probe of the yet unobserved first stars, primarily due to
the expected high signal along with an unique frequency dependence. | Interacting dark energy from the joint analysis of the power spectrum
and bispectrum multipoles with the EFTofLSS: Interacting dark energy models have been suggested as alternatives to the
standard cosmological model, $\Lambda$CDM. We focus on a phenomenologically
interesting class of dark scattering models that is characterised by pure
momentum exchange between dark energy and dark matter. This model extends the
parameter space with respect to $\Lambda$CDM by two parameters, $w$ and $A$,
which define the dark energy equation of state and the strength of the coupling
between dark energy and dark matter, respectively. In order to test
non-standard cosmologies with Stage-IV galaxy clustering surveys, it is crucial
to model mildly nonlinear scales and perform precision vs accuracy tests. We
use the Effective Field Theory of Large-Scale Structure, and we perform
validation tests by means of an MCMC analysis using a large set of N-body
simulations. We find that adding the bispectrum monopole to the power spectrum
multipoles improves the constraints on the dark energy parameters by $\sim 30
\%$ for $k_{\mathrm{max}, B}^{l=0} = 0.11$ $h$ Mpc$^{-1}$ without introducing
biases in the parameter estimation. We also find that the same improvement can
be achieved with more moderate scale cuts and the use of bias relations, or
with the addition of the bispectrum quadrupole. Finally, we study degeneracies
between the dark energy parameters and the scalar amplitude $A_\mathrm{s}$ and
discuss the corresponding projection effects, as well as degeneracies with
other cosmological parameters. |
Beyond dark energy Fisher forecasts: how DESI will constrain LCDM and
quintessence models: We baseline with current cosmological observations to forecast the power of
the Dark Energy Spectroscopic Instrument (DESI) in two ways: 1. the gain in
constraining power of parameter combinations in the standard $\Lambda$CDM
model, and 2. the reconstruction of quintessence models of dark energy. For the
former task we use a recently developed formalism to extract the leading
parameter combinations constrained by different combinations of cosmological
survey data. For the latter, we perform a non-parametric reconstruction of
quintessence using the Effective Field Theory of Dark Energy. Using mock DESI
observations of the Hubble parameter, angular diameter distance, and growth
rate, we find that DESI will provide significant improvements over current
datasets on $\Lambda$CDM and quintessence constraints. Including DESI mocks in
our $\Lambda$CDM analysis improves constraints on $\Omega_m$, $H_0$, and
$\sigma_8$ by a factor of two, where the improvement results almost entirely
from the angular diameter distance and growth of structure measurements. Our
quintessence reconstruction suggests that DESI will considerably improve
constraints on a range of quintessence properties, such as the reconstructed
potential, scalar field excursion, and the dark energy equation of state. The
angular diameter distance measurements are particularly constraining in the
presence of a non-$\Lambda$CDM signal in which the potential cannot be
accounted for by shifts in $H_0$ and $\Omega_m$. | Adaptively refined large eddy simulations of clusters: We present a numerical scheme for modelling unresolved turbulence in
cosmological adaptive mesh refinement codes. As a first application, we study
the evolution of turbulence in the intra-cluster medium and in the core of a
galaxy cluster. Simulations with and without subgrid scale model are compared
in detail. Since the flow in the ICM is subsonic, the global turbulent energy
contribution at the unresolved length scales is smaller than 1% of the internal
energy. We find that the production of turbulence is closely correlated with
merger events occurring in the cluster environment, and its dissipation locally
affects the cluster energy budget. Because of this additional source of
dissipation, the core temperature is larger and the density is smaller in the
presence of subgrid scale turbulence than in the standard adiabatic run,
resulting in a higher entropy core value. |
Constraints on primordial black holes as dark matter candidates from
capture by neutron stars: We investigate constraints on primordial black holes (PBHs) as dark matter
candidates that arise from their capture by neutron stars (NSs). If a PBH is
captured by a NS, the star is accreted onto the PBH and gets destroyed in a
very short time. Thus, mere observations of NSs put limits on the abundance of
PBHs. High DM densities and low velocities are required to constrain the
fraction of PBHs in DM. Such conditions may be realized in the cores of
globular clusters if the latter are of a primordial origin. Assuming that cores
of globular clusters possess the DM densities exceeding several hundred
GeV/cm$^3$ would imply that PBHs are excluded as comprising all of the dark
matter in the mass range $3\times 10^{18} \text{g} \lesssim m_\text{BH}\lesssim
10^{24} \text{g}$. At the DM density of $2\times 10^3$ GeV/cm$^3$ that has been
found in simulations in the corresponding models, less than 5% of the DM may
consist of PBH for these PBH masses. | The Yukawa-Coupled Dark Sector Model and Cosmological Tensions: In this paper, we investigate the interaction between early dark energy (EDE)
and cold dark matter, proposing a Yukawa-coupled dark sector model to mitigate
cosmological tensions. We utilize the EDE component in the coupled model to
relieve the Hubble tension, while leveraging the interaction between dark
matter and dark energy to alleviate the large-scale structure tension. The
interaction takes the form of Yukawa coupling, which describes the coupling
between scalar field and fermion field. We employed various cosmological
datasets, including cosmic microwave background radiation, baryon acoustic
oscillations, Type Ia supernovae, the local distance-ladder data (SH0ES), and
the Dark Energy Survey Year-3 data, to analyze our novel model. Using the
Markov Chain Monte Carlo method, our findings reveal that the constrained value
of $H_0$ obtained from our new model at a 68\% confidence level is
$72.21^{+0.82}_{-0.69}$ km/s/Mpc, effectively resolving the Hubble tension.
Similar to the EDE model, the coupled model yields the $S_8$ value that still
surpasses the result of the $\Lambda$CDM model. Nevertheless, the best-fit
value of $S_8$ obtained from our new model is 0.817, which is lower than the
EDE model's result of 0.8316. Consequently, although our model fails to fully
resolve the large-scale structure tension, it mitigates the adverse effect of
the original EDE model. |
A Detection of $z$~2.3 Cosmic Voids from 3D Lyman-$α$ Forest
Tomography in the COSMOS Field: We present the most distant detection of cosmic voids ($z \sim 2.3$) and the
first detection of three-dimensional voids in the Lyman-$\alpha$ forest. We
used a 3D tomographic map of the absorption with effective comoving spatial
resolution of $2.5\,h^{-1}\mathrm{Mpc}$ and volume of $3.15\times
10^5\,h^{-3}\mathrm{Mpc}^3$, which was reconstructed from moderate-resolution
Keck-I/LRIS spectra of 240 background Lyman-break galaxies and quasars in a
$0.16\,\mathrm{deg}^2$ footprint in the COSMOS field. Voids were detected using
a spherical overdensity finder calibrated from hydrodynamical simulations of
the intergalactic medium. This allows us to identify voids in the IGM
corresponding to voids in the underlying matter density field, yielding a
consistent volume fraction of voids in both data (19.5%) and simulations
(18.2%). We fit excursion set models to the void radius function and compare
the radially-averaged stacked profiles of large voids ($r > 5$ $h^{-1}$ Mpc) to
stacked voids in mock observations and the simulated density field. Comparing
with 432 coeval galaxies with spectroscopic redshifts in the same volume as the
tomographic map, we find that the tomography-identified voids are underdense in
galaxies by 5.95$\sigma$ compared to random cells. | Loops abound in the cosmic microwave background: A $4σ$ anomaly on
super-horizon scales: We present a topological analysis of the temperature fluctuation maps from
the \emph{Planck 2020} Data release 4 (DR4) based on the \texttt{NPIPE} data
processing pipeline. For comparison, we also present the topological
characteristics of the maps from \emph{Planck 2018} Data release 3 (DR3). We
perform our analysis in terms of the homology characteristics of the maps,
invoking relative homology to account for analysis in the presence of masks. We
perform our analysis for a range of smoothing scales spanning sub- and
super-horizon scales corresponding to $FWHM = 5', 10', 20', 40', 80', 160',
320', 640'$. Our main result indicates a significantly anomalous behavior of
the loops in the observed maps compared to simulations that are modeled as
isotopic and homogeneous Gaussian random fields. Specifically, we observe a
$4\sigma$ deviation between the observation and simulations in the number of
loops at $FWHM = 320'$ and $FWHM = 640'$, corresponding to super-horizon scales
of $5$ degrees and larger. In addition, we also notice a mildly significant
deviation at $2\sigma$ for all the topological descriptors for almost all the
scales analyzed. Our results show a consistency across different data releases,
and therefore, the anomalous behavior deserves a careful consideration
regarding its origin and ramifications. Disregarding the unlikely source of the
anomaly being instrumental systematics, the origin of the anomaly may be
genuinely astrophysical -- perhaps due to a yet unresolved foreground, or truly
primordial in nature. Given the nature of the topological descriptors, that
potentially encodes information of all orders, non-Gaussianities, of either
primordial or late-type nature, may be potential candidates. Alternate
possibilities include the Universe admitting a non-trivial global topology,
including effects induced by large-scale topological defects. |
Understanding caustic crossings in giant arcs: characteristic scales,
event rates, and constraints on compact dark matter: The recent discovery of fast transient events near critical curves of massive
galaxy clusters, which are interpreted as highly magnified individual stars in
giant arcs due to caustic crossing, opens up the possibility of using such
microlensing events to constrain a range of dark matter models such as
primordial black holes and scalar field dark matter. Based on a simple analytic
model, we study lensing properties of a point mass lens embedded in a high
magnification region, and derive the dependence of the peak brightness,
microlensing time scales, and event rates on the mass of the point mass lens as
well as the radius of a source star that is magnified. We find that the lens
mass and source radius of the first event MACS J1149 Lensed Star 1 (LS1) are
constrained, with the lens mass range of $0.1~M_\odot \lesssim M \lesssim
4\times 10^3M_\odot$ and the source radius range of $40~R_\odot \lesssim R
\lesssim 260~R_\odot$. In the most plausible case with $M\approx 0.3~M_\odot$
and $R\approx 180~R_\odot$, the source star should have been magnified by a
factor of $\approx 4300$ at the peak. The derived lens properties are fully
consistent with the interpretation that MACS J1149 LS1 is a microlensing event
produced by a star that contributes to the intra-cluster light. We argue that
compact dark matter models with high fractional mass densities for the mass
range $10^{-5}M_\odot \lesssim M\lesssim 10^2M_\odot$ are inconsistent with the
observation of MACS J1149 LS1 because such models predict too low
magnifications. Our work demonstrates a potential use of caustic crossing
events in giant arcs to constrain compact dark matter. | New Light on Dark Extended Lenses with the Roman Space Telescope: The Roman Space Telescope's Galactic Bulge Time Domain Survey will constitute
the most sensitive microlensing survey of the Galactic Bulge to date, opening
up new opportunities to search for dark matter (DM). Many extensions of the
Standard Model predict the formation of extended DM substructures, such as DM
subhalos, boson/axion stars, and halo-dressed primordial black holes. We
demonstrate that for such targets, Roman will be sensitive to a broad parameter
space up to four orders of magnitude below existing constraints. Our analysis
can be readily applied to other extended DM configurations as well. |
When Is Secular Evolution Important?: This abstract has been withdrawn. The proper replacement is arXiv:0909.3306 | Statistical hierarchy of varying speed of light cosmologies: Variation of the speed of light is quite a debated issue in cosmology with
some benefits, but also with some controversial concerns. Many approaches to
develop a consistent varying speed of light (VSL) theory have been developed
recently. Although a lot of theoretical debate has sprout out about their
feasibility and reliability, the most obvious and straightforward way to
discriminate and check if such theories are really workable has been missed out
or not fully employed. What is meant here is the comparison of these theories
with observational data in a fully comprehensive way. In this paper we try to
address this point i.e., by using the most updated cosmological probes, we test
three different candidates for a VSL theory (Barrow \& Magueijo, Avelino \&
Martins, and Moffat) signal. We consider many different ans\"{a}tze for both
the functional form of $c(z)$ (which cannot be fixed by theoretical
motivations) and for the dark energy dynamics, in order to have a clear global
picture from which we extract the results. We compare these results using a
reliable statistical tool such as the Bayesian Evidence. We find that the
present cosmological data is perfectly compatible with any of these VSL
scenarios, but in one case (Moffat model) we have a higher Bayesian Evidence
ratio in favour of VSL than in the standard $c=$ constant $\Lambda$CDM
scenario. Moreover, in such a scenario, the VSL signal can help to strengthen
constraints on the spatial curvature (with indication toward an open universe),
to clarify some properties of dark energy (exclusion of a cosmological constant
at $2\sigma$ level) and is also falsifiable in the nearest future due to some
peculiar issues which differentiate this model from the standard model.
Finally, we have applied some priors which come from cosmology and, in
particular, from information theory and gravitational thermodynamics. |
Subhaloes in Self-Interacting Galactic Dark Matter Haloes: We present N-body simulations of a new class of self-interacting dark matter
models, which do not violate any astrophysical constraints due to a
non-power-law velocity dependence of the transfer cross section which is
motivated by a Yukawa-like new gauge boson interaction. Specifically, we focus
on the formation of a Milky Way-like dark matter halo taken from the Aquarius
project and re-simulate it for a couple of representative cases in the allowed
parameter space of this new model. We find that for these cases, the main halo
only develops a small core (~1 kpc) followed by a density profile identical to
that of the standard cold dark matter scenario outside of that radius. Neither
the subhalo mass function nor the radial number density of subhaloes are
altered in these models but there is a significant change in the inner density
structure of subhaloes resulting in the formation of a large density core. As a
consequence, the inner circular velocity profiles of the most massive subhaloes
differ significantly from the cold dark matter predictions and we demonstrate
that they are compatible with the observational data of the brightest Milky Way
dSphs in such a velocity-dependent self-interacting dark matter scenario.
Specifically, and contrary to the cold dark matter case, there are no subhaloes
that are more concentrated than what is inferred from the kinematics of the
Milky Way dSphs. We conclude that these models offer an interesting alternative
to the cold dark matter model that can reduce the recently reported tension
between the brightest Milky Way satellites and the dense subhaloes found in
cold dark matter simulations. | Precise limits on cosmological variability of the fine-structure
constant with zinc and chromium quasar absorption lines: The strongest transitions of Zn and CrII are the most sensitive to relative
variations in the fine-structure constant ($\Delta\alpha/\alpha$) among the
transitions commonly observed in quasar absorption spectra. They also lie
within just 40\AA\ of each other (rest frame), so they are resistant to the
main systematic error affecting most previous measurements of
$\Delta\alpha/\alpha$: long-range distortions of the wavelength calibration.
While Zn and CrII absorption is normally very weak in quasar spectra, we
obtained high signal-to-noise, high-resolution echelle spectra from the Keck
and Very Large Telescopes of 9 rare systems where it is strong enough to
constrain $\Delta\alpha/\alpha$ from these species alone. These provide 12
independent measurements (3 quasars were observed with both telescopes) at
redshifts 1.0--2.4, 11 of which pass stringent reliability criteria. These 11
are all consistent with $\Delta\alpha/\alpha=0$ within their individual
uncertainties of 3.5--13 parts per million (ppm), with a weighted mean
$\Delta\alpha/\alpha = 1.2\pm1.7_{\rm stat}\pm0.9_{\rm sys}$ ppm (1$\sigma$
statistical and systematic uncertainties), indicating no significant
cosmological variations in $\alpha$. This is the first statistical sample of
absorbers that is resistant to long-range calibration distortions (at the $<$1
ppm level), with a precision comparable to previous large samples of $\sim$150
(distortion-affected) absorbers. Our systematic error budget is instead
dominated by much shorter-range distortions repeated across echelle orders of
individual spectra. |
Probing the Dawn of Galaxies at z~9-12: New Constraints from HUDF12/XDF
and CANDELS Data: We present a comprehensive analysis of z>8 galaxies based on ultra-deep
WFC3/IR data. We constrain the evolution of the UV luminosity function (LF) and
luminosity densities from z~11 to z~8 by exploiting all the WFC3/IR data over
the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in
addition to the HUDF09 parallel field data, as well as wider area WFC3/IR
imaging over GOODS-South. Galaxies are selected based on the Lyman Break
Technique in three samples centered around z~9, z~10 and z~11, with seven z~9
galaxy candidates, and one each at z~10 and z~11. We confirm a new z~10
candidate (with z=9.8+-0.6) that was not convincingly identified in our first
z~10 sample. The deeper data over the HUDF confirms all our previous z>~7.5
candidates as genuine high-redshift candidates, and extends our samples to
higher redshift and fainter limits (H_160~29.8 mag). We perform one of the
first estimates of the z~9 UV LF and improve our previous constraints at z~10.
Extrapolating the lower redshift UV LF evolution should have revealed 17 z~9
and 9 z~10 sources, i.e., a factor ~3x and 9x larger than observed. The
inferred star-formation rate density (SFRD) in galaxies above 0.7 M_sun/yr
decreases by 0.6+-0.2 dex from z~8 to z~9, in good agreement with previous
estimates. The low number of sources found at z>8 is consistent with a very
rapid build-up of galaxies across z~10 to z~8. From a combination of all
current measurements, we find a best estimate of a factor 10x decrease in the
SFRD from z~8 to z~10, following (1+z)^(-11.4+-3.1). Our measurements thus
confirm our previous finding of an accelerated evolution beyond z~8, and
signify a rapid build-up of galaxies with M_UV<-17.7 within only ~200 Myr from
z~10 to z~8, in the heart of cosmic reionization. | The Mid-IR Contribution Of Dust Enshrouded Stars In Six Nearby Galaxies: We measure the integrated contributions of dusty AGB stars and other luminous
red mid-IR sources to the mid-IR luminosities of 6 galaxies (M81, NGC 2403, NGC
300, M33 and the Magellanic Clouds). We find the dusty AGB stars whose mid-IR
fluxes are dominated by dust rather than photospheric emission contribute from
0.6% (M81) to 5.6% (SMC) of the 3.6 micron flux and 1.0% (M81) to 10.1% (SMC)
of the 4.5 micron flux. We find a trend of decreasing AGB contribution with
increasing galaxy metallicity, luminosity and mass and decreasing SSFR.
However, these galaxy properties are strongly correlated in our sample and the
simplest explanation of the trend is galaxy metallicity. Bright, red sources
other than dusty AGB stars represent a smaller fraction of the luminosity,
~1.2% at 3.6 microns, however their dust is likely cooler and their
contributions are likely larger at longer wavelengths. Excluding the SMC, the
contribution from these red sources correlates with the specific star formation
rate as we would expect for massive stars. In total, after correcting for dust
emission at other wavelengths, the dust around AGB stars radiates 0.1-0.8% of
the bolometric luminosities of the galaxies. Thus, hot dust emission from AGB
and other luminous dusty stars represent a small fraction of the total
luminosities of the galaxies but a significant fraction of their mid-IR
emissions. |
Observational Constraints on Monomial Warm Inflation: Warm inflation is, as of today, one of the best motivated mechanisms for
explaining an early inflationary period. In this paper, we derive and analyze
the current bounds on warm inflation with a monomial potential $U\propto
\phi^p$, using the constraints from the PLANCK mission. In particular, we
discuss the parameter space of the tensor-to-scalar ratio $r$ and the potential
coupling $\lambda$ of the monomial warm inflation in terms of the number of
e-folds. We obtain that the theoretical tensor-to-scalar ratio $r\sim 10^{-8}$
is much smaller than the current observational constrain $r \lesssim 0.12$,
despite a relatively large value of the field excursion $\Delta \phi \sim
0.1\MP$. Warm inflation thus eludes the Lyth bound set on the tensor-to-scalar
ratio by the field excursion. | Solar Mass Primordial Black Holes in Moduli Dominated Universe: We explore the prospect of producing primordial black holes around the solar
mass region during an early matter domination epoch. The early matter-dominated
epoch can arise when a moduli field comes to dominate the energy density of the
Universe prior to big bang nucleosynthesis. The absence of radiation pressure
during a matter-dominated epoch enhances primordial black hole formation from
the gravitational collapse of primordial density fluctuations. In particular,
we find that primordial black holes are produced in the $0.1-10~M_{\odot}$ mass
range with a favorable choice of parameters in the theory. However, they cannot
explain all of the merger events detected by the LIGO/Virgo gravitational wave
search. In such a case, primordial black holes form about $4\%$ of the total
dark matter abundance, of which $95\%$ belongs to the LIGO/Virgo consistent
mass range. The rest of the dark matter could be in the form of particles that
are produced from the decay of the moduli field during reheating. |
Warm dark matter signatures on the 21cm power spectrum: Intensity
mapping forecasts for SKA: We investigate the impact that warm dark matter (WDM) has in terms of 21cm
intensity mapping in the post-reionization Universe at z = 3 - 5. We perform
hydrodynamic simulations for 5 different models: cold dark matter and WDM with
1,2,3,4 keV (thermal relic) mass and assign the neutral hydrogen a-posteriori
using two different methods that both reproduce observations in terms of column
density distribution function of neutral hydrogen systems. Contrary to naive
expectations, the suppression of power present in the linear and non-linear
matter power spectra, results in an increase of power in terms of neutral
hydrogen and 21cm power spectra. This is due to the fact that there is a lack
of small mass halos in WDM models with respect to cold dark matter: in order to
distribute a total amount of neutral hydrogen within the two cosmological
models, a larger quantity has to be placed in the most massive halos, that are
more biased compared to the cold dark matter cosmology. We quantify this effect
and address significance for the telescope SKA1-LOW, including a realistic
noise modeling. The results indicate that we will be able to rule out a 4 keV
WDM model with 5000 hours of observations at z > 3, with a statistical
significance of > 3 sigma, while a smaller mass of 3 keV, comparable to present
day constraints, can be ruled out at more than 2 sigma confidence level with
1000 hours of observations at z > 5. | By Dawn's Early Light: CMB Polarization Impact on Cosmological
Constraints: Cosmic microwave background polarization encodes information not only on the
early universe but also dark energy, neutrino mass, and gravity in the late
universe through CMB lensing. Ground based surveys such as ACTpol, PolarBear,
SPTpol significantly complement cosmological constraints from the Planck
satellite, strengthening the CMB dark energy figure of merit and neutrino mass
constraints by factors of 3-4. This changes the dark energy probe landscape. We
evaluate the state of knowledge in 2017 from ongoing experiments including dark
energy surveys (supernovae, weak lensing, galaxy clustering), fitting for
dynamical dark energy, neutrino mass, and a modified gravitational growth
index. Adding a modest strong lensing time delay survey improves those dark
energy constraints by a further 32%, and an enhanced low redshift supernova
program improves them by 26%. |
Large-scale magnetic fields, non-Gaussianity, and gravitational waves
from inflation: We explore the generation of large-scale magnetic fields in the so-called
moduli inflation. The hypercharge electromagnetic fields couple to not only a
scalar field but also a pseudoscalar one, so that the conformal invariance of
the hypercharge electromagnetic fields can be broken. We explicitly analyze the
strength of the magnetic fields on the Hubble horizon scale at the present
time, the local non-Gaussianity of the curvature perturbations originating from
the massive gauge fields, and the tensor-to-scalar ratio of the density
perturbations. As a consequence, we find that the local non-Gaussianity and the
tensor-to-scalar ratio are compatible with the recent Planck results. | Dark energy by natural evolution: Constraining dark energy using
Approximate Bayesian Computation: We look at dark energy from a biology inspired viewpoint by means of the
Approximate Bayesian Computation (ABC) and late time cosmological observations.
We find that dynamical dark energy comes out on top, or in the ABC language
naturally selected, over the standard $\Lambda$CDM cosmological scenario. We
confirm this conclusion is robust to whether baryon acoustic oscillations and
Hubble constant priors are considered. Our results show that the algorithm
prefers low values of the Hubble constant, consistent or at least a few
standard deviation away from the cosmic microwave background estimate,
regardless of the priors taken initially in each model. This supports the
result of the traditional MCMC analysis and could be viewed as strengthening
evidence for dynamical dark energy being a more favorable model of late time
cosmology. |
The star cluster frequency throughout the Large Magellanic Cloud: We address the issue about the variation of the star cluster frequency (CF)
in the Large Magellanic Cloud (LMC) in terms of the cluster spatial
distribution. We adopted the LMC regions traced by Harris & Zaritsky (2009) and
used an updated version of the cluster database compiled by Baumgardt et al.
(2013). The CFs were produced by taking into account an appropriate selection
of age bins. Since the uncertainty in a cluster's age can be large compared to
the size of the age bins, we account for the fact that a cluster could actually
reside in one of a few adjacent age bins. We confirm that there exist some
variations of the LMC CFs in terms of their spatial distributions, although
some caveats should be pointed out. 30 Doradus resulted to be the region with
the highest relative frequency of youngest clusters, while the log($t$) = 9-9.5
(1-3 Gyr) age range is featured by cluster formation at a higher rate in the
inner regions than in the outer ones. We compared the observed CFs to
theoretical CFs, which are based on the star formation histories of the field
stars in each region of the LMC, and found the former predicting more or fewer
clusters than observed depending on the field and age range considered. | What is the physical origin of strong Lya emission? II. Gas Kinematics
and Distribution of Lya Emitters: We present a statistical study of velocities of Lya, interstellar (IS)
absorption, and nebular lines and gas covering fraction for Lya emitters (LAEs)
at z~2. We make a sample of 22 LAEs with a large Lya equivalent width (EW) of >
50A based on our deep Keck/LRIS observations, in conjunction with spectroscopic
data from the Subaru/FMOS program and the literature. We estimate the average
velocity offset of Lya from a systemic redshift determined with nebular lines
to be dv_Lya=234+-9 km s-1. Using a Kolmogorv-Smirnov test, we confirm the
previous claim of Hashimoto et al. (2013) that the average dv_Lya of LAEs is
smaller than that of LBGs. Our LRIS data successfully identify blue-shifted
multiple IS absorption lines in the UV continua of four LAEs on an individual
basis. The average velocity offset of IS absorption lines from a systemic
redshift is dv_IS=204+-27 km s-1, indicating LAE's gas outflow with a velocity
comparable to typical LBGs. Thus, the ratio, R^Lya_ IS = dv_Lya/dv_IS of LAEs,
is around unity, suggestive of low impacts on Lya transmission by resonant
scattering of neutral hydrogen in the IS medium. We find an anti-correlation
between Lya EW and the covering fraction, f_c, estimated from the depth of
absorption lines, where f_c is an indicator of average neutral hydrogen column
density, N_HI. The results of our study support the idea that N_HI is a key
quantity determining Lya emissivity. |
Potentialities of Hubble parameter and expansion rate function data to
alleviate Hubble tension: Taking advantage of Gaussian process (GP), we obtain an improved estimate of
the Hubble constant, $H_0=70.41\pm1.58$ km s$^{-1}$ Mpc$^{-1}$, using Hubble
parameter [$H(z)$] from cosmic chronometers (CCH) and expansion rate function
[$E(z)$], extracted from type Ia supernovae, data. We also use CCH data,
including the ones with full covariance matrix, and $E(z)$ data to obtain a
determination of $H_0=72.34_{-1.92}^{+1.90}$ km s$^{-1}$ Mpc$^{-1}$, which
implies that the involvement of full covariance matrix results in higher values
and uncertainties of $H_0$. These results are higher than those obtained by
directly reconstructing CCH data with GP. In order to estimate the potential of
future CCH data, we simulate two sets of $H(z)$ data and use them to constrain
$H_0$ by either using GP reconstruction or fitting them with $E(z)$ data. We
find that simulated $H(z)$ data alleviate $H_0$ tension by pushing $H_0$ values
higher towards $\sim70$ km s$^{-1}$ Mpc$^{-1}$. We also find that joint $H(z)$
+ $E(z)$ data favor higher values of $H_0$, which is also confirmed by
constraining $H_0$ in the flat concordance model and 2-order Taylor expansion
of $H(z)$. In summary, we conclude that more and better-quality CCH data as
well as $E(z)$ data can provide a new and useful perspective on resolving $H_0$
tension. | Radial derivatives as a test of pre-Big-Bang events on the Planck data: Although the search for azimutal patterns in cosmological surveys is useful
to characterise some effects depending exclusively on an angular distance
within the standard model, they are considered as a key distinguishing feature
of some exotic scenarios, such as bubble collisions or conformal cyclic
cosmology (CCC). In particular, the CCC is a non-stardard framework which
predicts circular patterns on the CMB intensity fluctuations. Motivated by some
previous works which explore the presence of radial gradients, we apply a
methodology based on the radial derivatives to the latest release of
\textit{Planck} data. The new approach allows exhaustive studies to be
performed at all sky directions at a HEALPix resolution of $N_{\mathrm{side}} =
1024$. Specifically, two different analyses are performed focusing on weight
functions in both small (up to a $5$-degree radius) and large scales. We
present a comparison between our results and those shown by An et al. (2017),
and An et al. (2018). In addition, a possible polarization counterpart of these
circular patterns is also analysed for the most promising case. Taking into
account the limitations to characterize the significance of the results,
including the possibility of suffering a look-elsewhere effect, no strong
evidence of the kind of circular patterns expected from CCC is found in the
\textit{Planck} data for either the small or the large scales. |
Intensity mapping of the 21cm emission: lensing: In this paper, we study lensing of 21cm intensity mapping (IM). Like in the
cosmic microwave background (CMB), there is no first order lensing in intensity
mapping. The first effects in the power spectrum are therefore of second and
third order. Despite this, lensing of the CMB power spectrum is an important
effect that needs to be taken into account, which motivates the study of the
impact of lensing on the IM power spectrum. We derive a general formula up to
third order in perturbation theory including all the terms with two derivatives
of the gravitational potential, i.e. the dominant terms on sub-Hubble scales.
We then show that in intensity mapping there is a new lensing term which is not
present in the CMB. We obtain that the signal-to-noise of 21 cm lensing for
futuristic surveys like SKA2 is about 10. We find that surveys probing only
large scales, lmax < 700, can safely neglect the lensing of the intensity
mapping power spectrum, but that otherwise this effect should be included. | A Search for Optical Variability of Type 2 Quasars in SDSS Stripe 82: Hundreds of Type 2 quasars have been identified in Sloan Digital Sky Survey
(SDSS) data, and there is substantial evidence that they are generally galaxies
with highly obscured central engines, in accord with unified models for active
galactic nuclei (AGNs). A straightforward expectation of unified models is that
highly obscured Type 2 AGNs should show little or no optical variability on
timescales of days to years. As a test of this prediction, we have carried out
a search for variability in Type 2 quasars in SDSS Stripe 82 using
difference-imaging photometry. Starting with the Type 2 AGN catalogs of
Zakamska et al. (2003) and Reyes et al. (2008), we find evidence of significant
g-band variability in 17 out of 173 objects for which light curves could be
measured from the Stripe 82 data. To determine the nature of this variability,
we obtained new Keck spectropolarimetry observations for seven of these
variable AGNs. The Keck data show that these objects have low continuum
polarizations (p<~1% in most cases) and all seven have broad H-alpha and/or
MgII emission lines in their total (unpolarized) spectra, indicating that they
should actually be classified as Type 1 AGNs. We conclude that the primary
reason variability is found in the SDSS-selected Type 2 AGN samples is that
these samples contain a small fraction of Type 1 AGNs as contaminants, and it
is not necessary to invoke more exotic possible explanations such as a
population of "naked" or unobscured Type 2 quasars. Aside from misclassified
Type 1 objects, the Type 2 quasars do not generally show detectable optical
variability over the duration of the Stripe 82 survey. |
Impact of Image Persistence in the Roman Space Telescope High-Latitude
Survey: The High Latitude Survey of the Nancy Grace Roman Space Telescope is expected
to measure the positions and shapes of hundreds of millions of galaxies in an
area of 2220 deg$^2$. This survey will provide high-quality weak lensing data
with unprecedented systematics control. The Roman Space Telescope will survey
the sky in near infrared (NIR) bands using Teledyne H4RG HgCdTe photodiode
arrays. These NIR arrays exhibit an effect called persistence: charges that are
trapped in the photodiodes during earlier exposures are gradually released into
later exposures, leading to contamination of the images and potentially to
errors in measured galaxy properties such as fluxes and shapes. In this work,
we use image simulations that incorporate the persistence effect to study its
impact on galaxy shape measurements and weak lensing signals. No significant
spatial correlations are found between the galaxy shape changes induced by
persistence. On the scales of interest for weak lensing cosmology, the effect
of persistence on the weak lensing correlation function is about two orders of
magnitude lower than the Roman Space Telescope additive shear error budget,
indicating that the persistence effect is expected to be a subdominant
contributor to the systematic error budget for weak lensing with the Roman
Space Telescope given its current design. | Bayesian large-scale structure inference and cosmic web analysis: Surveys of the cosmic large-scale structure carry opportunities for building
and testing cosmological theories about the origin and evolution of the
Universe. This endeavor requires appropriate data assimilation tools, for
establishing the contact between survey catalogs and models of structure
formation. In this thesis, we present an innovative statistical approach for
the ab initio simultaneous analysis of the formation history and morphology of
the cosmic web: the BORG algorithm infers the primordial density fluctuations
and produces physical reconstructions of the dark matter distribution that
underlies observed galaxies, by assimilating the survey data into a
cosmological structure formation model. The method, based on Bayesian
probability theory, provides accurate means of uncertainty quantification. We
demonstrate the application of BORG to the Sloan Digital Sky Survey data and
describe the primordial and late-time large-scale structure in the observed
volume. We show how the approach has led to the first quantitative inference of
the cosmological initial conditions and of the formation history of the
observed structures. We then use these results for several cosmographic
projects aiming at analyzing and classifying the large-scale structure. In
particular, we build an enhanced catalog of cosmic voids probed at the level of
the dark matter distribution, deeper than with the galaxies. We present
detailed probabilistic maps of the dynamic cosmic web, and offer a general
solution to the problem of classifying structures in the presence of
uncertainty. The results described in this thesis constitute accurate
chrono-cosmography of the inhomogeneous cosmic structure. |
Parity violation of primordial magnetic fields in the CMB bispectrum: We study the parity violation in the cosmic microwave background (CMB)
bispectrum induced by primordial magnetic fields (PMFs). Deriving a general
formula for the CMB bispectrum generated from not only non-helical but also
helical PMFs, we find that helical PMFs produce characteristic signals, which
disappear in parity-conserving cases, such as the intensity-intensity-intensity
bispectra arising from $\sum_{n=1}^3 \ell_n = {\rm odd}$. For fast numerical
calculation of the CMB bispectrum, we reduce the one-loop formula to the
tree-level one by using the so-called pole approximation. Then, we show that
the magnetic anisotropic stress, which depends quadratically on non-helical and
helical PMFs and acts as a source of the CMB fluctuation, produces the
local-type non-Gaussianity. Comparing the CMB bispectra composed of the scalar
and tensor modes with the noise spectra, we find that assuming the generation
of the nearly scale-invariant non-helical and helical PMFs from the grand
unification energy scale ($10^{14} {\rm GeV}$) to the electroweak one ($10^{3}
{\rm GeV}$), the intensity-intensity-intensity bispectrum for $\sum_{n=1}^3
\ell_n = {\rm odd}$ can be observed by the WMAP experiment under the condition
that $B_{1 \rm Mpc}^{2/3} {\cal B}_{1 \rm Mpc}^{1/3} > 2.7 - 4.5 {\rm nG}$ with
$B_{1 \rm Mpc}$ and ${\cal B}_{1 \rm Mpc}$ being the non-helical and helical
PMF strengths smoothed on 1 Mpc, respectively. | Moving mesh cosmology: properties of neutral hydrogen in absorption: We examine the distribution of neutral hydrogen in cosmological simulations
carried out with the new moving-mesh code AREPO and compare it with the
corresponding GADGET simulations based on the smoothed particle hydrodynamics
(SPH) technique. The two codes use identical gravity solvers and baryonic
physics implementations, but very different methods for solving the Euler
equations, allowing us to assess how numerical effects associated with the
hydro-solver impact the results of simulations. Here we focus on an analysis of
the neutral gas, as detected in quasar absorption lines. We find that the high
column density regime probed by Damped Lyman-alpha (DLA) and Lyman Limit
Systems (LLS) exhibits significant differences between the codes. GADGET
produces spurious artefacts in large halos in the form of gaseous clumps,
boosting the LLS cross-section. Furthermore, it forms halos with denser central
baryonic cores than AREPO, which leads to a substantially greater DLA
cross-section from smaller halos. AREPO thus produces a significantly lower
cumulative abundance of DLAs, which is intriguingly in much closer agreement
with observations. The column density function, however, is not altered enough
to significantly reduce the discrepancy with the observed value. For the low
column density gas probed by the Lyman-alpha forest, the codes differ only at
the level of a few percent, suggesting that this regime is quite well described
by both methods, a fact that is reassuring for the many Lyman-alpha studies
carried out with SPH thus far. While the residual differences are smaller than
the errors on current Lyman-alpha forest data, we note that this will likely
change for future precision experiments. |
Baryon Acoustic Oscillations in the Lyman Alpha Forest: We use hydrodynamic cosmological simulations in a (600 Mpc)^3 volume to study
the observability of baryon acoustic oscillations (BAO) in the intergalactic
medium as probed by Lyman alpha forest (LAF) absorption. The large scale
separation between the wavelength of the BAO mode (~150 Mpc) and the size of
LAF absorbers (~100 kpc) makes this a numerically challenging problem. We
report on several 2048^3 simulations of the LAF using the ENZO code. We adopt
WMAP5 concordance cosmological parameters and power spectrum including BAO
perturbations. 5000 synthetic HI absorption line spectra are generated randomly
piercing the box face. We calculate the cross-correlation function between
widely separated pairs. We detect the BAO signal at z=3 where theory predicts
to moderate statistical significance. | Cosmological forecast of the 21-cm power spectrum using the halo model
of reionization: The 21-cm power spectrum of reionization is a promising probe for cosmology
and fundamental physics. Exploiting this new observable, however, requires fast
predictors capable of efficiently scanning the very large parameter space of
cosmological and astrophysical uncertainties. In this paper, we introduce the
halo model of reionization (HMreio), a new analytical tool that combines the
halo model of the cosmic dawn with the excursion-set bubble model for
reionization, assuming an empirical correction factor to deal with overlapping
ionization bubbles. First, HMreio is validated against results from the
well-known semi-numerical code 21cmFAST, showing a good overall agreement for
wave-modes of $k\lesssim 1$ h/Mpc. Based on this result, we perform a
Monte-Carlo Markov-Chain (MCMC) forecast analysis assuming mock data from
1000-hour observations with the low-frequency part of the Square Kilometre
Array (SKA) observatory. We simultaneously vary the six standard cosmological
parameters together with seven astrophysical nuisance parameters quantifying
the abundance and spectral properties of sources. Depending on the assumed
theory error, we find very competitive constraints on cosmological parameters.
In particular, it will be possible to conclusively test current cosmological
tensions related to the Hubble parameter ($H_0$-tension) and the matter
clustering amplitude ($S_8$-tension). Furthermore, the sum of the neutrino
masses can be strongly constrained, making it possible to determine the
neutrino mass hierarchy at the $\sim 90$ percent confidence level. However,
these goals can only be achieved if the current modelling uncertainties are
substantially reduced to below $\sim 3$ percent. |
The PAU Survey: narrowband photometric redshifts using Gaussian
processes: We study the performance of the hybrid template-machine-learning photometric
redshift (photo-$z$) algorithm Delight, which uses Gaussian processes, on a
subset of the early data release of the Physics of the Accelerating Universe
Survey (PAUS). We calibrate the fluxes of the $40$ PAUS narrow bands with $6$
broadband fluxes ($uBVriz$) in the COSMOS field using three different methods,
including a new method which utilises the correlation between the apparent size
and overall flux of the galaxy. We use a rich set of empirically derived galaxy
spectral templates as guides to train the Gaussian process, and we show that
our results are competitive with other standard photometric redshift
algorithms. Delight achieves a photo-$z$ $68$th percentile error of
$\sigma_{68}=0.0081(1+z)$ without any quality cut for galaxies with
$i_\mathrm{auto}<22.5$ as compared to $0.0089(1+z)$ and $0.0202(1+z)$ for the
BPz and ANNz2 codes, respectively. Delight is also shown to produce more
accurate probability distribution functions for individual redshift estimates
than BPz and ANNz2. Common photo-$z$ outliers of Delight and BCNz2 (previously
applied to PAUS) are found to be primarily caused by outliers in the narrowband
fluxes, with a small number of cases potentially indicating spectroscopic
redshift failures in the reference sample. In the process, we introduce
performance metrics derived from the results of BCNz2 and Delight, allowing us
to achieve a photo-$z$ quality of $\sigma_{68}<0.0035(1+z)$ at a magnitude of
$i_\mathrm{auto}<22.5$ while keeping $50$ per cent objects of the galaxy
sample. | Stellar Populations of Lyman Alpha Emitters at z~6-7: Constraints on the
Escape Fraction of Ionizing Photons from Galaxy Building Blocks: We investigate the stellar populations of Lyman alpha emitters (LAEs) at
z=5.7 and 6.6 in a 0.65 deg^2 sky of the Subaru/XMM-Newton Deep Survey (SXDS)
Field, using deep images taken with Subaru/Suprime-Cam, UKIRT/WFCAM, and
Spitzer/IRAC. We produce stacked multiband images at each redshift from 165
(z=5.7) and 91 (z=6.6) IRAC-undetected objects, to derive typical spectral
energy distributions (SEDs) of z~6-7 LAEs for the first time. The stacked LAEs
have as blue UV continua as the HST/WFC3 z-dropout galaxies of similar Muv,
with a spectral slope beta ~ -3, but at the same time they have red
UV-to-optical colors with detection in the 3.6um band. Using SED fitting we
find that the stacked LAEs have low stellar masses of ~(3-10)*10^7 Msun, very
young ages of ~1-3 Myr, negligible dust extinction, and strong nebular emission
from the ionized interstellar medium, although the z=6.6 object is fitted
similarly well with high-mass models without nebular emission; inclusion of
nebular emission reproduces the red UV-to-optical color while keeping the UV
color sufficiently blue. We infer that typical LAEs at z~6-7 are building
blocks of galaxies seen at lower redshifts. We find a tentative decrease in the
Lyman alpha escape fraction from z=5.7 to 6.6, which may imply an increase in
the intergalactic medium neutral fraction. From the minimum contribution of
nebular emission required to fit the observed SEDs, we place an upper limit on
the escape fraction of ionizing photons to be f_esc^ion~0.6 at z=5.7 and ~0.9
at z=6.6. We also compare the stellar populations of our LAEs with that of
stacked HST/WFC3 z-dropout galaxies. |
O-V-S-Z and friends: Non-Gaussianity from inhomogeneous reionization: We calculate the cosmic microwave background (CMB) bispectrum due to
inhomogeneous reionization. We calculate all the terms that can contribute to
the bispectrum that are products of first order terms on all scales in
conformal Newtonian gauge. We also correctly account for the de-correlation
between the matter density and initial conditions using perturbation theory up
to third order. We find that the bispectrum is of local type as expected. For a
reasonable model of reionization, in which the Universe is completely ionized
by redshift z_{ri} ~ 8 with optical depth to the last scattering surface
\tau_0=0.087 the signal to noise for detection of the CMB temperature
bispectrum is S/N ~ 0.1 and confusion in the estimation of primordial
non-Gaussianity is f_{NL} ~ -0.1. For an extreme model with z_{ri} ~ 12.5,
\tau_0=0.14 we get S/N ~ 0.5 and f_{NL} ~ -0.2. | Scalar-Tensor Gravity Cosmology: Noether symmetries and analytical
solutions: In this paper, we present a complete Noether Symmetry analysis in the
framework of scalar-tensor cosmology. Specifically, we consider a non-minimally
coupled scalar field action embedded in the FLRW spacetime and provide a full
set of Noether symmetries for related minisuperspaces. The presence of
symmetries implies that the dynamical system becomes integrable and then we can
compute cosmological analytical solutions for specific functional forms of
coupling and potential functions selected by the Noether Approach. |
The Diversity of Core Halo Structure in the Fuzzy Dark Matter Model: In the fuzzy dark matter (FDM) model, gravitationally collapsed objects
always consist of a solitonic core located within a virialised halo. Although
various numerical simulations have confirmed that the collapsed structure can
be described by a cored NFW like density profile, there is still disagreement
about the relation between the core mass and the halo mass. To fully understand
this relation, we have assembled a large sample of cored haloes based on both
idealised soliton mergers and cosmological simulations with various box sizes.
We find that there exists a sizeable dispersion in the core-halo mass relation
that increases with halo mass, indicating that the FDM model allows cores and
haloes to coexist in diverse configurations. We provide a new empirical
equation for a core halo mass relation with uncertainties that can encompass
all previously found relations in the dispersion, and emphasise that any
observational constraints on the particle mass using a tight one-to-one
core-halo mass relation should suffer from an additional uncertainty on the
order of 50 % for halo masses $ \ge 10^9 (8 \times 10^{-23} eV/ (mc^2))^{3/2}
M_\odot$. We suggest that tidal stripping may be one of the effects
contributing to the scatter in the relation. | Modified gravity in Arnowitt-Deser-Misner formalism: Motivated by Horava-Lifshitz gravity theory, we propose and investigate two
kinds of modified gravity theories, the f(R) kind and the K-essence kind, in
the Arnowitt-Deser-Misner (ADM) formalism. The f(R) kind includes one
ultraviolet (UV) term and one infrared (IR) term together with the
Einstein-Hilbert action. We find that these two terms naturally present the
ultraviolet and infrared modifications to the Friedmann equation. The UV and IR
modifications can avoid the past Big-Bang singularity and the future Big-Rip
singularity, respectively. Furthermore, the IR modification can naturally
account for the current acceleration of the Universe. The Lagrangian of
K-essence kind modified gravity is made up of the three dimensional Ricci
scalar and an arbitrary function of the extrinsic curvature term. We find the
cosmic acceleration can also be naturally interpreted without invoking any kind
of dark energy. The static, spherically symmetry and vacuum solutions of both
theories are Schwarzschild or Schwarzschild-de Sitter solution. Thus these
modified gravity theories are viable for solar system tests. |
Evolution of the Sizes of Galaxies over 7<z<12 Revealed by the 2012
Hubble Ultra Deep Field Campaign: We analyze the redshift- and luminosity-dependent sizes of dropout galaxy
candidates in the redshift range z~7-12 using deep images from the UDF12
campaign, data which offers two distinct advantages over that used in earlier
work. Firstly, we utilize the increased S/N ratio offered by the UDF12 imaging
to provide improved size measurements for known galaxies at z=6.5-8 in the
HUDF. Specifically, we stack the new deep F140W image with the existing F125W
data in order to provide improved measurements of the half-light radii of
z-dropouts. Similarly we stack this image with the new deep UDF12 F160W image
to obtain new size measurements for a sample of Y-dropouts. Secondly, because
the UDF12 data have allowed the construction of the first robust galaxy sample
in the HUDF at z>8, we have been able to extend the measurement of average
galaxy size out to significantly higher redshifts. Restricting our size
measurements to sources which are now detected at >15sigma, we confirm earlier
indications that the average half-light radii of z~7-12 galaxies are extremely
small, 0.3-0.4 kpc, comparable to the sizes of giant molecular associations in
local star-forming galaxies. We also confirm that there is a clear trend of
decreasing half-light radius with increasing redshift, and provide the first
evidence that this trend continues beyond z~8. Modeling the evolution of the
average half-light radius as a power-law (1+z)^s, we obtain a best-fit index of
s=-1.28+/-0.13 over the redshift range z~4-12, mid-way between the physically
expected evolution for baryons embedded in dark halos of constant mass (s=-1)
and constant velocity (s=-1.5). A clear size-luminosity relation, such as that
found at lower redshift, is also evident in both our z- and Y-dropout sample.
This relation can be interpreted in terms of a constant surface density of star
formation over a range in luminosity of 0.05-1.0L*_z=3.(abridged) | Insights into neutrino decoupling gleaned from considerations of the
role of electron mass: We present calculations showing how electron rest mass influences entropy
flow, neutrino decoupling, and Big Bang Nucleosynthesis (BBN) in the early
universe. To elucidate this physics and especially the sensitivity of BBN and
related epochs to electron mass, we consider a parameter space of rest mass
values larger and smaller than the accepted vacuum value. Electromagnetic
equilibrium, coupled with the high entropy of the early universe, guarantees
that significant numbers of electron-positron pairs are present, and dominate
over the number of ionization electrons to temperatures much lower than the
vacuum electron rest mass. Scattering between the electrons-positrons and the
neutrinos largely controls the flow of entropy from the plasma into the
neutrino seas. Moreover, the number density of electron-positron-pair targets
can be exponentially sensitive to the effective in-medium electron mass. This
entropy flow influences the phasing of scale factor and temperature, the
charged current weak-interaction-determined neutron-to-proton ratio, and the
spectral distortions in the relic neutrino energy spectra. Our calculations
show the sensitivity of the physics of this epoch to three separate effects:
finite electron mass, finite-temperature quantum electrodynamic (QED) effects
on the plasma equation of state, and Boltzmann neutrino energy transport. The
ratio of neutrino to plasma component energy scales manifests in Cosmic
Microwave Background (CMB) observables, namely the baryon density and the
radiation energy density, along with the primordial helium and deuterium
abundances. Our results demonstrate how the treatment of in-medium electron
mass (i.e., QED effects) could translate into an important source of
uncertainty in extracting neutrino and beyond-standard-model physics limits
from future high-precision CMB data. |
Constraining the distance to inspiralling NS-NS with Einstein Telescope: Einstein Telescope (ET) is a planned third generation gravitational waves
detector located in Europe. Its design will be different from currently build
interferometers, because ET will consist of three interferometers rotated by a
60 deg with respect to each other in one plane. One of the biggest challenges
for ET will be to determine sky position and distance to observed sources. If
an object is observed in a few interferometers simultaneously one can estimate
the position using traingulation from time delays, but so far there are no
plans for a network of third generation detectors. Another possibility to deal
with that problem is by using multimessenger approach, because redshift and sky
position could be recovered from electromagnetic observations. In this paper we
present a novel method of estimating distance and position in the sky of
merging binaries. While our procedure is not as accurate as the multimessenger
method, it can be applied to all observations, not just the ones with
electromagnetic counterparts. We have shown that it is possible to
significantly improve distance estimates using the measurements of the signal
to noise ratio from all three interferometers . | On the Use of Ly-alpha Emitters as Probes of Reionization: We use numerical simulations to study the effects of the patchiness of a
partly reionized intergalactic medium (IGM) on the observability of Ly-alpha
emitters (LAEs) at high redshifts (z ~ 6). We present a new model that divides
the Ly-alpha radiative transfer into a (circum-)galactic and an extragalactic
(IGM) part, and investigate how the choice of intrinsic line model affects the
IGM transmission results. We use our model to study the impact of neutral
hydrogen on statistical observables such as the Ly-alpha restframe equivalent
width (REW) distribution, the LAE luminosity function and the two-point
correlation function. We find that if the observed changes in LAE luminosity
functions and equivalent width distributions between z ~ 6 and z ~ 7 are to be
explained by an increased IGM neutral fraction alone, we require an extremely
late and rapid reionization scenario, where the Universe was ~ 40 % ionized at
z = 7, ~ 50 % ionized at z = 6.5 and ~ 100 % ionized at z = 6. This is in
conflict with other observations, suggesting that intrinsic LAE evolution at z
> 6 cannot be completely neglected. We show how the two-point correlation
function can provide more robust constraints once future observations obtain
larger LAE samples, and provide predictions for the sample sizes needed to tell
different reionization scenarios apart. |
Determining accurate measurements of the growth rate from the galaxy
correlation function in simulations: We use high-resolution N-body simulations to develop a new, flexible,
empirical approach for measuring the growth rate from redshift-space
distortions (RSD) in the 2-point galaxy correlation function. We quantify the
systematic error in measuring the growth rate in a $1 \, h^{-3}$ Gpc$^3$ volume
over a range of redshifts, from the dark matter particle distribution and a
range of halo-mass catalogues with a number density comparable to the latest
large-volume galaxy surveys such as the WiggleZ Dark Energy Survey and the
Baryon Oscillation Spectroscopic Survey (BOSS). Our simulations allow us to
span halo masses with bias factors ranging from unity (probed by emission-line
galaxies) to more massive haloes hosting Luminous Red Galaxies. We show that
the measured growth rate is sensitive to the model adopted for the small-scale
real-space correlation function, and in particular that the "standard"
assumption of a power-law correlation function can result in a significant
systematic error in the growth rate determination. We introduce a new,
empirical fitting function that produces results with a lower (5-10%) amplitude
of systematic error. We also introduce a new technique which permits the galaxy
pairwise velocity distribution, the quantity which drives the non-linear growth
of structure, to be measured as a non-parametric stepwise function. Our
(model-independent) results agree well with an exponential pairwise velocity
distribution, expected from theoretical considerations, and are consistent with
direct measurements of halo velocity differences from the parent catalogues. In
a companion paper we present the application of our new methodology to the
WiggleZ Survey dataset. | Viscous Self Interacting Dark Matter and Cosmic Acceleration: Self interacting dark matter (SIDM) provides us with a consistent solution to
certain astrophysical observations in conflict with collision-less cold DM
paradigm. In this work we estimate the shear viscosity $(\eta)$ and bulk
viscosity $(\zeta)$ of SIDM, within kinetic theory formalism, for galactic and
cluster size SIDM halos. To that extent we make use of the recent constraints
on SIDM crossections for the dwarf galaxies, LSB galaxies and clusters. We also
estimate the change in solution of Einstein's equation due to these viscous
effects and find that $\sigma/m$ constraints on SIDM from astrophysical data
provide us with sufficient viscosity to account for the observed cosmic
acceleration at present epoch, without the need of any additional dark energy
component. Using the estimates of dark matter density for galactic and cluster
size halo we find that the mean free path of dark matter $\sim$ few Mpc. Thus
the smallest scale at which the viscous effect start playing the role is
cluster scale. Astrophysical data for dwarf, LSB galaxies and clusters also
seems to suggest the same. The entire analysis is independent of any specific
particle physics motivated model for SIDM. |
A "Light," Centrally-Concentrated Milky Way Halo?: We discuss a novel approach to "weighing" the Milky Way dark matter halo, one
that combines the latest samples of halo stars selected from the Sloan Digital
Sky Survey (SDSS) with state-of-the-art numerical simulations of Milky Way
analogs. The fully cosmological runs employed in the present study include
"Eris", one of the highest-resolution hydrodynamical simulations of the
formation of a M_vir=8e11 M_sun late-type spiral, and the dark-matter only
M_vir=1.7e12 M_sun "Via Lactea II" simulation. Eris provides an excellent
laboratory for creating mock SDSS samples of tracer halo stars, and we
successfully compare their density, velocity anisotropy, and radial velocity
dispersion profiles with the observational data. Most mock SDSS realizations
show the same "cold veil" recently observed in the distant stellar halo of the
Milky Way, with tracers as cold as sigma_los ~ 50 km/s between 100-150 kpc.
Controlled experiments based on the integration of the spherical Jeans equation
as well as a particle tagging technique applied to Via Lactea II show that a
"heavy" M_vir 2e12 M_sun realistic host produces a poor fit to the kinematic
SDSS data. We argue that these results offer added evidence for a "light,"
centrally-concentrated Milky Way halo. | Thermal blocking of preheating: The parametric resonance responsible for preheating after inflation will end
when self-interactions of the resonating field and interactions of this field
with secondary degrees of freedom become important. In many cases, the effect
may be quantified in terms of an effective mass and the resulting shifting out
of the spectrum of the strongest resonance band. In certain curvaton models,
such thermal blocking can even occur before preheating has begun, delaying or
even preventing the decay of the curvaton. We investigate numerically to what
extent this thermal blocking is realised in a specific scenario, and whether
the effective mass is well approximated by the perturbative leading order
thermal mass. We find that the qualitative behaviour is well reproduced in this
approximation, and that the end of preheating can be confidently estimated. |
Cosmological Constraints from the double source plane lens
SDSSJ0946+1006: We present constraints on the equation of state of dark energy, $w$, and the
total matter density, $\Omega_{\mathrm{M}}$, derived from the
double-source-plane strong lens SDSSJ0946+1006, the first cosmological
measurement with a galaxy-scale double-source-plane lens. By modelling the
primary lens with an elliptical power-law mass distribution, and including
perturbative lensing by the first source, we are able to constrain the
cosmological scaling factor in this system to be $\beta^{-1}=1.404 \pm 0.016$,
which implies $\Omega_{\mathrm{M}}= 0.33_{-0.26}^{+0.33}$ for a flat $\Lambda$
cold dark matter ($\Lambda$CDM) cosmology. Combining with a cosmic microwave
background prior from Planck, we find $w$ = $-1.17^{+0.20}_{-0.21}$ assuming a
flat $w$CDM cosmology. This inference shifts the posterior by 1${\sigma}$ and
improves the precision by 30 per cent with respect to Planck alone, and
demonstrates the utility of combining simple, galaxy-scale
multiple-source-plane lenses with other cosmological probes to improve
precision and test for residual systematic biases. | Do blue galaxy-clusters have hot intracluster gas?: We present herein a systematic X-ray analysis of blue galaxy-clusters at
$z=0.84$ discovered by the Subaru telescope. The sample consisted of 43
clusters identified by combining red-sequence and blue-cloud surveys, covering
a wide range of emitter fractions (i.e., 0.3--0.8). The spatial extent of the
over-density region of emitter galaxies was approximately 1~Mpc in radius. The
average cluster mass was estimated as $0.6 (<1.5)\times10^{14}~{\rm M_\odot}$
from the stacked weak-lensing measurement. We analyzed the XMM-Newton archival
data, and measured the X-ray luminosity of the hot intracluster medium. As a
result, diffuse X-ray emission was marginally detected in 14 clusters, yielding
an average luminosity of $5\times 10^{42}~{\rm erg\,s^{-1}}$. On the contrary,
it was not significant in 29 clusters. The blue clusters were significantly
fainter than the red-dominated clusters, and the X-ray luminosity did not show
any meaningful correlation either with emitter fraction or richness. The X-ray
surface brightness was low, but the amount of gas mass was estimated to be
comparable to that observed in the $10^{13-14}~{\rm M_{\odot}}$ cluster. Based
on the results, we suggest that the blue clusters are at the early formation
stage, and the gas is yet to be compressed and heated up to produce appreciable
X-rays. Follow-up spectroscopic measurements are essential to clarify the
dynamical status and co-evolution of galaxies and hot gas in the blue clusters. |
The puzzling radio source in the cool core cluster A 2626: We report on new VLA radio observations performed at 1.4 GHz and 4.8 GHz with
unprecedented sensitivity and angular resolution (~1 arcsec) of the cool core
cluster A 2626, which is known to possess a radio mini-halo at its center. The
most unusual features of A 2626 are two elongated radio features detected in
previous observations to the north and south, having morphologies not common to
the typical jet-lobe structures in cool cores. In our new sensitive images the
two elongated features appears clearly as bright radio arcs, and we discover
the presence of a new arc to the west. These radio arcs are not detected at 4.8
GHz, implying a steep (alpha >1) spectrum, and their origin is puzzling. After
subtracting the flux density contributed by these discrete features from the
total flux measured at low resolution, we estimate a residual 18.0 +/- 1.8 mJy
flux density of diffuse radio emission at 1.4 GHz. We therefore confirm the
detection of diffuse radio emission, which appears distinct from the discrete
radio arcs embedded in it. Although its radio power is lower (1.4x10^23 W/Hz)
than previously known, the diffuse emission may still be classified as a radio
mini-halo. | Scale dependence of the power spectrum of the curvature perturbation
determined using a numerical method in slow-roll inflation: The Taylor expansion method has been used to investigate the scale dependence
of the power spectrum of the curvature perturbation. In the present study, an
alternative numerical method is used to clarify the $k$ dependence. Although
there is thought to be no large difference between these two methods, some
differences arise among various inflation models. For example, at $k$ = 1 Mpc,
there is a 1.4 % difference in the power spectrum, and with respect to the
angular power spectrum, the difference of the value of $\chi^2$ nearly 10 occur
in new inflation. However, in hybrid inflation, these differences do not occur.
The time dependence of the inflationary and cosmological parameters is
investigated, and differences among inflation models are clarified. |
Cosmic Microwave Background Spectral Distortions from Cosmic String
Loops: Cosmic string loops contain cusps which decay by emitting bursts of
particles. A significant fraction of the released energy is in the form of
photons. These photons are injected non-thermally and can hence cause spectral
distortions of the Cosmic Microwave Background (CMB). Under the assumption that
cusps are robust against gravitational back-reaction, we compute the fractional
energy density released as photons in the redshift interval where such
non-thermal photon injection causes CMB spectral distortions. Whereas current
constraints on such spectral distortions are not strong enough to constrain the
string tension, future missions such as the PIXIE experiment will be able to
provide limits which rule out a range of string tensions between $G \mu \sim
10^{-15}$ and $G \mu \sim 10^{-12}$, thus ruling out particle physics models
yielding these kind of intermediate-scale cosmic strings. | Characterizing EoR foregrounds: A study of the Lockman Hole Region at
325 MHz: One of the key science goals for the most sensitive telescopes, both current
and upcoming, is the detection of the redshifted 21-cm signal from the Cosmic
Dawn and Epoch of Reionization. The success of detection relies on accurate
foreground modeling for their removal from data sets. This paper presents the
characterization of astrophysical sources in the Lockman Hole region. Using 325
MHz data obtained from the GMRT, a $6^\circ \times 6^\circ$ mosaiced map is
produced with an RMS reaching 50 $\mu$Jy $\mathrm{beam}^{-1}$. A source catalog
containing 6186 sources is created, and the Euclidean normalized differential
source counts have been derived from it, consistent with previous observations
as well as simulations. A detailed comparison of the source catalog is also
made with previous findings - at both lower and higher frequencies. The angular
power spectrum (APS) of the diffuse Galactic synchrotron emission is determined
for three different galactic latitudes using the Tapered Gridded Estimator. The
values of the APS lie between $\sim$1 mK$^2$ to $\sim$100 mK$^2$. Fitting a
power law of the form $A\ell^{-\beta}$ gives values of $A$ and $\beta$ varying
across the latitudes considered. This paper demonstrates, for the first time,
the variation of the power-law index for diffuse emission at very high galactic
locations. It follows the same trend that is seen at locations near the
galactic plane, thus emphasizing the need for low-frequency observations for
developing better models of the diffuse emission. |
Cross-tests of CMB features in the primordial spectra: The recent Planck data on the power spectrum of temperature anisotropies of
the cosmic microwave background marginally support deviations from the
$\Lambda$CDM model at several multipoles. With a view towards current and
forthcoming observational surveys, we trace these features to other observables
like the scalar bispectrum and the tensor power spectrum. A possible detection
of such bumps in these channels would increase their statistical significance
shedding light on the ultra violet mechanisms responsible for their appearance
in the data. | Possibility of realizing weak gravity in redshift space distortion
measurements: We study the possibility of realizing a growth rate of matter density
perturbations lower than that in General Relativity. Using the approach of the
effective field theory of modified gravity encompassing theories beyond
Horndeski, we derive the effective gravitational coupling $G_{\rm eff}$ and the
gravitational slip parameter $\eta$ for perturbations deep inside the Hubble
radius. In Horndeski theories we derive a necessary condition for achieving
weak gravity associated with tensor perturbations, but this is not a sufficient
condition due to the presence of a scalar-matter interaction that always
enhances $G_{\rm eff}$. Beyond the Horndeski domain it is possible to realize
$G_{\rm eff}$ smaller than Newton's gravitational constant $G$, while the
scalar and tensor perturbations satisfy no-ghost and stability conditions. We
present a concrete dark energy scenario with varying $c_{\rm t}$ and
numerically study the evolution of perturbations to confront the model with the
observations of redshift-space distortions and weak lensing. |
The angular power spectrum measurement of the Galactic synchrotron
emission in two fields of the TGSS survey: Characterizing the diffuse Galactic synchrotron emission at arcminute angular
scales is needed to reliably remove foregrounds in cosmological 21-cm
measurements. The study of this emission is also interesting in its own right.
Here, we quantify the fluctuations of the diffuse Galactic synchrotron emission
using visibility data for two of the fields observed by the TIFR GMRT Sky
Survey (TGSS). We have used the 2D Tapered Gridded Estimator (TGE) to estimate
the angular power spectrum $(C_{\ell})$ from the visibilities. We find that the
sky signal, after subtracting the point sources, is likely dominated by the
diffuse Galactic synchrotron radiation across the angular multipole range $240
\le \ell \lesssim 500$. We present a power law fit,
$C_{\ell}=A\times\big(\frac{1000}{l}\big)^{\beta}$, to the measured $C_{\ell}$
over this $\ell$ range. We find that $(A,\beta)$ have values $(356\pm109~{\rm
mK^2},2.8\pm0.3)$ and $(54\pm26~{\rm mK^2},2.2\pm0.4)$ in the two fields. For
the second field, however, there is indication of a significant residual point
source contribution, and for this field we interpret the measured $C_{\ell}$ as
an upper limit for the diffuse Galactic synchrotron emission. While in both
fields the slopes are consistent with earlier measurements, the second field
appears to have an amplitude which is considerably smaller compared to similar
measurements in other parts of the sky. | High-redshift JWST Observations and Primordial Non-Gaussianity: Several bright and massive galaxy candidates at high redshifts have been
recently observed by the James Webb Space Telescope. Such early massive
galaxies seem difficult to reconcile with standard $\Lambda$ Cold Dark Matter
model predictions. We discuss under which circumstances such observed massive
galaxy candidates can be explained by introducing primordial non-Gaussianity in
the initial conditions of the cosmological perturbations. |
Component separation for future CMB B-mode satellites: Next-generation CMB satellite concepts (LiteBIRD, CORE, PIXIE, PICO) are
being proposed to detect the primordial CMB B-mode polarization at large
angular scales in the sky for tensor-to-scalar ratio values of ${r \lesssim
10^{-3}}$. Yet undetected, primordial CMB B-modes will provide the unique
signature of the primordial gravitational waves of quantum origin predicted by
inflation. We present recent forecasts on the detection of the primordial CMB
B-modes in the presence of astrophysical foregrounds and gravitational lensing
effects, in the context of the proposed CMB space mission CORE. We also discuss
the problem of foregrounds and component separation for the search for
primordial B-modes, and highlight specific challenges in this context:
frequency range, spectral degeneracies, foreground modelling, spectral
averaging effects. | AGN feedback works both ways: Simulations of galaxy growth need to invoke strong negative feedback from
active galactic nuclei (AGN) to suppress the formation of stars and thus
prevent the over-production of very massive systems. While some observations
provide evidence for such negative feedback, other studies find either no
feedback, or even positive feedback, with increased star formation associated
with higher AGN luminosities. Here we report an analysis of several hundred AGN
and their host galaxies in the Chandra Deep Field South using X-ray and radio
data for sample selection. Combined with archival far infrared data as a
reliable tracer of star formation activity in the AGN host galaxies, we find
that AGN with pronounced radio jets exhibit a much higher star formation rate
than the purely X-ray selected ones, even at the same X-ray luminosities. This
difference implies that positive AGN feedback plays an important role, too, and
therefore has to be accounted for in all future simulation work. We interpret
this to indicate that the enhanced star formation rate of radio selected AGN
arises because of jet-induced star formation, as is hinted by the different jet
powers among our AGN samples, while the suppressed star formation rate of X-ray
selected AGN is caused by heating and photo-dissociation of molecular gas by
the hot AGN accretion disc. |
Using peculiar velocity surveys to constrain the growth rate of
structure with the wide-angle effect: Amongst the most popular explanations for dark energy are modified theories
of gravity. The galaxy overdensity and peculiar velocity fields help us to
constrain the growth rate of structure and distinguish different models of
gravity. We introduce an improved method for constraining the growth rate of
structure with the galaxy overdensity and peculiar velocity fields. This method
reduces the modelling systematic error by accounting for the wide-angle effect
and the zero-point calibration uncertainty during the modelling process. We
also speed up the posterior sampling by around 30 times by first calculating
the likelihood at a small number of fiducial points and then interpolating the
likelihood values during MCMC sampling. We test the new method on mocks and we
find it is able to recover the fiducial growth rate of structure. We applied
our new method to the SDSS PV catalogue, which is the largest single peculiar
velocity catalogue to date. Our constraint on the growth rate of structure is
\(f\sigma_8 = 0.405_{-0.071}^{+0.076}\) (stat) \(\pm 0.009\) (sys) at the
effective redshift of 0.073. Our constraint is consistent with a Planck 2018
cosmological model, \(f\sigma_8 = 0.448\), within one standard deviation. Our
improved methodology will enable similar analysis on future data, with even
larger sample sizes and covering larger angular areas on the sky. | Interacting modified holographic Ricci dark energy model and statefinder
diagnosis in flat universe: In this work we have considered the modified holographic Ricci dark energy
interacting with dark matter through a non-gravitational coupling. We took
three phenomenological forms for the interaction term $Q$ in the model, where
in general $Q$ is proportional to the Hubble parameter and densities of the
dark sectors, $\rho_{de}+\rho_m, \, \rho_m$ and $\rho_{de}$ respectively. We
have obtained analytical solutions for the three interacting models, and
studied the evolutions of equations of state parameter, deceleration parameter.
The results are compared with the observationally constrained values for the
best parameters of the model. We have also done the statefinder analysis of the
model to discriminate the model from other standard models. In general we have
shown that the model is showing a de Sitter type behavior in the far future of
the evolution of the universe. |
DEMNUni: Massive neutrinos and the bispectrum of large scale structures: The main effect of massive neutrinos on the large-scale structure consists in
a few percent suppression of matter perturbations on all scales below their
free-streaming scale. Such effect is of particular importance as it allows to
constraint the value of the sum of neutrino masses from measurements of the
galaxy power spectrum. In this work, we present the first measurements of the
next higher-order correlation function, the bispectrum, from N-body simulations
that include massive neutrinos as particles. This is the simplest statistics
characterising the non-Gaussian properties of the matter and dark matter halos
distributions. We investigate, in the first place, the suppression due to
massive neutrinos on the matter bispectrum, comparing our measurements with the
simplest perturbation theory predictions, finding the approximation of
neutrinos contributing at quadratic order in perturbation theory to provide a
good fit to the measurements in the simulations. On the other hand, as
expected, a linear approximation for neutrino perturbations would lead to
O($f_{\nu}$) errors on the total matter bispectrum at large scales. We then
attempt an extension of previous results on the universality of linear halo
bias in neutrino cosmologies, to non-linear and non-local corrections finding
consistent results with the power spectrum analysis. | Variability in Quasar Broad Absorption Line Outflows: Broad absorption lines (BALs) in quasar spectra identify high velocity
outflows that likely exist in all quasars and could play a major role in
feedback to galaxy evolution. Studying the variability in these BALs can help
us understand the structure, evolution, and basic physical properties of these
outflows. We are conducting a BAL monitoring program, which so far includes 163
spectra of 24 luminous quasars, covering time-scales from \sim 1 week to 8
years in the quasar rest-frame. We investigate changes in both the CIV
{\lambda}1550 and SiIV {\lambda}1400 BALs, and we report here on some of the
results from this program. |
Polarization of the Cosmic Infrared Background Fluctuations: The cosmic infrared background (CIB) is slightly polarized. Polarization
directions of individual galaxies could be aligned with tidal fields around
galaxies, resulting in nonzero CIB polarization. We use a linear intrinsic
alignment model to theoretically predict angular correlations of the CIB
polarization fluctuations and find that electriclike and curl-like ($B$-mode)
polarization modes are equally generated with power four orders of magnitude
less than its intensity. The CIB $B$-mode signal is negligible and not a
concerning foreground for the inflationary $B$-mode searches at nominal
frequencies for cosmic microwave background measurements, but could be detected
at submillimetre wavelengths by future space missions. | Probing the First Stars and Black Holes in the Early Universe with the
Dark Ages Radio Explorer (DARE): A concept for a new space-based cosmology mission called the Dark Ages Radio
Explore (DARE) is presented in this paper. DARE's science objectives include
(1) When did the first stars form? (2) When did the first accreting black holes
form? (3) When did Reionization begin? (4) What surprises does the end of the
Dark Ages hold (e.g., Dark Matter decay)? DARE will use the highly-redshifted
hyperfine 21-cm transition from neutral hydrogen to track the formation of the
first luminous objects by their impact on the intergalactic medium during the
end of the Dark Ages and during Cosmic Dawn (redshifts z=11-35). It will
measure the sky-averaged spin temperature of neutral hydrogen at the unexplored
epoch 80-420 million years after the Big Bang, providing the first evidence of
the earliest stars and galaxies to illuminate the cosmos and testing our models
of galaxy formation. DARE's approach is to measure the expected spectral
features in the sky-averaged, redshifted 21-cm signal over a radio bandpass of
40-120 MHz. DARE orbits the Moon for a mission lifetime of 3 years and takes
data above the lunar farside, the only location in the inner solar system
proven to be free of human-generated radio frequency interference and any
significant ionosphere. The science instrument is composed of a three-element
radiometer, including electrically-short, tapered, bi-conical dipole antennas,
a receiver, and a digital spectrometer. The smooth frequency response of the
antennas and the differential spectral calibration approach using a Markov
Chain Monte Carlo technique will be applied to detect the weak cosmic 21-cm
signal in the presence of the intense solar system and Galactic foreground
emissions. |
KAT-7 Science Verification: Using HI Observations of NGC 3109 to
Understand its Kinematics and Mass Distribution: HI observations of the Magellanic-type spiral NGC 3109, obtained with the
seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass
distribution. Our results are compared to what is obtained using VLA data.
KAT-7 is the precursor of the SKA pathfinder MeerKAT, which is under
construction. The short baselines and low system temperature of the telescope
make it sensitive to large scale low surface brightness emission. The new
observations with KAT-7 allow the measurement of the rotation curve of NGC 3109
out to 32', doubling the angular extent of existing measurements. A total HI
mass of 4.6 x 10^8 Msol is derived, 40% more than what was detected by the VLA
observations.
The observationally motivated pseudo-isothermal dark matter (DM) halo model
can reproduce very well the observed rotation curve but the cosmologically
motivated NFW DM model gives a much poorer fit to the data. While having a more
accurate gas distribution has reduced the discrepancy between the observed RC
and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense
of having to use unrealistic mass-to-light ratios for the stellar disk and/or
very large values for the MOND universal constant a0. Different distances or HI
contents cannot reconcile MOND with the observed kinematics, in view of the
small errors on those two quantities. As for many slowly rotating gas-rich
galaxies studied recently, the present result for NGC 3109 continues to pose a
serious challenge to the MOND theory. | Predicted properties of multiple images of the strongly lensed supernova
SN Refsdal: We construct a mass model of the cluster MACS J1149.6+2223 to study the
expected properties of multiple images of SN Refsdal, the first example of a
gravitationally lensed supernova with resolved multiple images recently
reported by Kelly et al. We find that the best-fit model predicts six supernova
images in total, i.e., two extra images in addition to the observed four
Einstein cross supernova images S1--S4. One extra image is predicted to have
appeared about 17 years ago, whereas the other extra image is predicted to
appear in about one year from the appearance of S1--S4, which is a testable
prediction with near future observations. The predicted magnification factors
of individual supernova images range from $\sim 18$ for the brightest image to
$\sim 4$ for the faint extra images. Confronting these predictions with future
observations should provide an unprecedented opportunity to improve our
understanding of cluster mass distributions. |
Hybrid SBI or How I Learned to Stop Worrying and Learn the Likelihood: We propose a new framework for the analysis of current and future
cosmological surveys, which combines perturbative methods (PT) on large scales
with conditional simulation-based implicit inference (SBI) on small scales.
This enables modeling of a wide range of statistics across all scales using
only small-volume simulations, drastically reducing computational costs, and
avoids the assumption of an explicit small-scale likelihood. As a
proof-of-principle for this hybrid simulation-based inference (HySBI) approach,
we apply it to dark matter density fields and constrain cosmological parameters
using both the power spectrum and wavelet coefficients, finding promising
results that significantly outperform classical PT methods. We additionally lay
out a roadmap for the next steps necessary to implement HySBI on actual survey
data, including consideration of bias, systematics, and customized simulations.
Our approach provides a realistic way to scale SBI to future survey volumes,
avoiding prohibitive computational costs. | Evidence of Gunn-Peterson damping wings in high-z quasar spectra:
strengthening the case for incomplete reionization: The spectra of several high-redshift (z>6) quasars have shown evidence for a
Gunn-Peterson (GP) damping wing, indicating a substantial mean neutral hydrogen
fraction (x_HI > 0.03) in the z ~ 6 intergalactic medium (IGM). However,
previous analyses assumed that the IGM was uniformly ionized outside of the
quasar's HII region. Here we relax this assumption and model patchy
reionization scenarios for a range of IGM and quasar parameters. We quantify
the impact of these differences on the inferred x_HI, by fitting the spectra of
three quasars: SDSS J1148+5251 (z=6.419), J1030+0524 (z=6.308), and J1623+3112
(z=6.247). We find that the best-fit values of x_HI in the patchy models agree
well with the uniform case. More importantly, we confirm that the observed
spectra favor the presence of a GP damping wing, with peak likelihoods
decreasing by factors of > few - 10 when the spectra are modeled without a
damping wing. We also find that the Ly alpha absorption spectra, by themselves,
cannot distinguish the damping wing in a relatively neutral IGM from a damping
wing in a highly ionized IGM, caused either by an isolated neutral patch, or by
a damped Ly alpha absorber (DLA). However, neutral patches in a highly ionized
universe (x_HI < 0.01), and DLAs with the large required column densities (N_HI
> few x 10^{20} cm^{-2}) are both rare. As a result, when we include reasonable
prior probabilities for the line of sight (LOS) to intercept either a neutral
patch or a DLA at the required distance of ~ 40-60 comoving Mpc away from the
quasar, we find strong lower limits on the neutral fraction in the IGM, x_HI >
0.1 (at 95% confidence). This strengthens earlier claims that a substantial
global fraction of hydrogen in the z~6 IGM is in neutral form. |
A comparison of the excess mass around CFHTLenS galaxy-pairs to
predictions from a semi-analytic model using galaxy-galaxy-galaxy lensing: The matter environment of galaxies is connected to the physics of galaxy
formation and evolution. Utilising galaxy-galaxy-galaxy lensing as a direct
probe, we map out the distribution of correlated surface mass-density around
galaxy pairs for different lens separations in the Canada-France-Hawaii
Telescope Lensing Survey (CFHTLenS). We compare, for the first time, these
so-called excess mass maps to predictions provided by a recent semi-analytic
model, which is implanted within the dark-matter Millennium Simulation. We
analyse galaxies with stellar masses between $10^9-10^{11}\,{\rm M}_\odot$ in
two photometric redshift bins, for lens redshifts $z\lesssim0.6$, focusing on
pairs inside groups and clusters. To allow us a better interpretation of the
maps, we discuss the impact of chance pairs, i.e., galaxy pairs that appear
close to each other in projection only. Our tests with synthetic data
demonstrate that the patterns observed in the maps are essentially produced by
correlated pairs that are close in redshift ($\Delta z\lesssim5\times10^{-3}$).
We also verify the excellent accuracy of the map estimators. In an application
to the galaxy samples in the CFHTLenS, we obtain a $3\sigma-6\sigma$
significant detection of the excess mass and an overall good agreement with the
galaxy model predictions. There are, however, a few localised spots in the maps
where the observational data disagrees with the model predictions on a
$\approx3.5\sigma$ confidence level. Although we have no strong indications for
systematic errors in the maps, this disagreement may be related to the residual
B-mode pattern observed in the average of all maps. Alternatively, misaligned
galaxy pairs inside dark matter halos or lensing by a misaligned distribution
of the intra-cluster gas might also cause the unanticipated bulge in the
distribution of the excess mass between lens pairs. | On Separate Universes: (abridged version) The separate universe conjecture states that in General
Relativity a density perturbation behaves locally (i.e. on scales much smaller
than the wavelength of the mode) as a separate universe with different
background density and curvature. We prove this conjecture for a spherical
compensated tophat density perturbation of arbitrary amplitude and radius in
$\Lambda$CDM. We then use Conformal Fermi Coordinates to generalize this result
to scalar perturbations of arbitrary configuration and scale. In this case, the
separate universe conjecture holds for the isotropic part of the perturbations.
The anisotropic part on the other hand is exactly captured by a tidal field in
the Newtonian form. We show that the separate universe picture is restricted to
scales larger than the sound horizons of all fluid components. We then derive
an expression for the locally measured matter bispectrum induced by a
long-wavelength mode of arbitrary wavelength. We show that nonlinear
gravitational dynamics does not generate observable contributions that scale
like local-type non-Gaussianity $f_{\rm NL}^{\rm loc}$, and hence does not
contribute to a scale-dependent galaxy bias $\Delta b \propto k^{-2}$ on large
scales; rather, the locally measurable long-short mode coupling assumes a form
essentially identical to subhorizon perturbation theory results, once the
long-mode density perturbation is replaced by the synchronous-comoving gauge
density perturbation. Apparent $f_{\rm NL}^{\rm loc}$-type contributions arise
through projection effects on photon propagation, which depend on the specific
large-scale structure tracer and observable considered, and are in principle
distinguishable from the local mode coupling induced by gravity. We conclude
that any observation of $f_{\rm NL}^{\rm loc}$ beyond these projection effects
signals a departure from standard single-clock inflation. |
Subaru medium-resolution spectra of a QSO at z=6.62: Three reionization
tests: Investigating the Gunn-Peterson trough of high redshift quasars (QSOs) is a
powerful way to reveal the cosmic reionization. As one of such attempts, we
perform a series of analyses to examine the absorption lines observed with one
of the highest redshift QSOs, PSO J006.1240+39.2219, which we previously
discovered at z = 6.62. Using the Subaru telescope, we obtained
medium-resolution spectrum with a total exposure time of 7.5 hours. We
calculate the Ly$\alpha$ transmission in different redshift bins to determine
the near zone radius and the optical depth at 5.6$<$z$<$6.5. We find a sudden
change in the Ly$\alpha$ transmission at 5.75$<$z$<$5.86, which is consistent
with the result from the literature. The near zone radius of the QSO is
5.79$\pm$0.09 $p$Mpc, within the scatter of the near zone radii of other QSOs
measured in previous studies. We also analyze the dark gap distribution to
probe the neutral hydrogen fractions beyond the saturation limit of the
Gunn-Peterson trough. We extend the measurement of the dark gaps to
5.7$<$z$<$6.3. We find that the gap widths increase with increasing redshifts,
suggesting more neutral Universe at higher redshifts. However, these
measurements strongly depend on the continuum modeling. As a continuum
model-free attempt, we also perform the dark-pixel counting analysis, to find
the upper limit of $\langle x_{\rm H I} \rangle \sim$0.6 (0.8) at $z<$5.8
($z>$5.8). All three analyses based on this QSO show increasingly neutral
hydrogen towards higher redshifts, adding precious measurements up to
z$\sim$6.5. | The physical scale of the far-infrared emission in the most luminous
submillimetre galaxies II: evidence for merger-driven star formation: We present high-resolution 345 GHz interferometric observations of two
extreme luminous (L_{IR}>10^{13} L_sun), submillimetre-selected galaxies (SMGs)
in the COSMOS field with the Submillimeter Array (SMA). Both targets were
previously detected as unresolved point-sources by the SMA in its compact
configuration, also at 345 GHz. These new data, which provide a factor of ~3
improvement in resolution, allow us to measure the physical scale of the
far-infrared in the submillimetre directly. The visibility functions of both
targets show significant evidence for structure on 0.5-1 arcsec scales, which
at z=1.5 translates into a physical scale of 5-8 kpc. Our results are
consistent with the angular and physical scales of two comparably luminous
objects with high-resolution SMA followup, as well as radio continuum and CO
sizes. These relatively compact sizes (<5-10 kpc) argue strongly for
merger-driven starbursts, rather than extended gas-rich disks, as the preferred
channel for forming SMGs. For the most luminous objects, the derived sizes may
also have important physical consequences; under a series of simplifying
assumptions, we find that these two objects in particular are forming stars
close to or at the Eddington limit for a starburst. |
Unlocking the secrets of stellar haloes using combined star counts and
surface photometry: The stellar haloes of galaxies can currently be studied either through
observations of resolved halo stars or through surface photometry. Curiously,
the two methods appear to give conflicting results, as a number of surface
photometry measurements have revealed integrated colours that are too red to be
reconciled with the halo properties inferred from the study of resolved stars.
Several explanations for this anomaly have been proposed - including dust
photoluminescence, extinction of extragalactic background light and a
bottom-heavy stellar initial mass function. A decisive test is, however, still
lacking. Here, we explain how observations of the halo of a nearby galaxy,
involving a combination of both surface photometry and bright star counts, can
be used to distinguish between the proposed explanations. We derive the
observational requirements for this endeavour and find that star counts in
filters VI and surface photometry in filters VIJ appears to be the optimal
strategy. Since the required halo star counts are already available for many
nearby galaxies, the most challenging part of this test is likely to be the
optical surface photometry, which requires several nights of exposure time on a
4-8 m telescope, and the near-IR surface photometry, which is most readily
carried out using the upcoming James Webb Space Telescope. | Dust-obscured star-formation in the outskirts of XMMU J2235.3-2557, a
massive galaxy cluster at z=1.4: Star-formation in the galaxy populations of local massive clusters is reduced
with respect to field galaxies, and tends to be suppressed in the core region.
Indications of a reversal of the star-formation--density relation have been
observed in a few z >1.4 clusters. Using deep imaging from 100-500um from PACS
and SPIRE onboard Herschel, we investigate the infrared properties of
spectroscopic and photo-z cluster members, and of Halpha emitters in XMMU
J2235.3-2557, one of the most massive, distant, X-ray selected clusters known.
Our analysis is based mostly on fitting of the galaxies spectral energy
distribution in the rest-frame 8-1000um. We measure total IR luminosity,
deriving star formation rates (SFRs) ranging from 89-463 Msun/yr for 13
galaxies individually detected by Herschel, all located beyond the core region
(r >250 kpc). We perform a stacking analysis of nine star-forming members not
detected by PACS, yielding a detection with SFR=48 Msun/yr. Using a color
criterion based on a star-forming galaxy SED at the cluster redshift we select
41 PACS sources as candidate star-forming cluster members. We characterize a
population of highly obscured SF galaxies in the outskirts of XMMU
J2235.3-2557. We do not find evidence for a reversal of the SF-density relation
in this massive, distant cluster. |
Low-mass stars within dense dark matter halos: We studied the formation and evolution of low-mass stars within halos with
high concentration of dark matter (DM) particles, using a highly sophisticated
expression to calculate the rate at which DM particles are captured inside the
star. For very high DM densities in the host halo (\rho_{\chi}>10^10 GeV cm^-3
for a 1 M_{\odot} star), we found that young stars stop sooner their
gravitational collapse in the pre-Main Sequence phase, reaching states of
equilibrium in which DM annihilation is their only source of energy. The lower
effective temperature of these stars, which depends on the properties of the DM
particles and DM halo, may be used as an alternative method to investigate the
nature of DM. | Testing isotropy in the Two Micron All-Sky redshift survey with
information entropy: We use information entropy to test the isotropy in the nearby galaxy
distribution mapped by the Two Micron All-Sky redshift survey (2MRS). We find
that the galaxy distribution is highly anisotropic on small scales. The radial
anisotropy gradually decreases with increasing length scales and the observed
anisotropy is consistent with that expected for an isotropic Poisson
distribution beyond a length scale of $90 \, h^{-1}\, {\rm Mpc}$. Using mock
catalogues from N-body simulations, we find that the galaxy distribution in the
2MRS exhibits a degree of anisotropy compatible with that of the $\Lambda$CDM
model after accounting for the clustering bias of the 2MRS galaxies. We also
quantify the polar and azimuthal anisotropies and identify two directions
$(l,b)=(150^{\circ}, -15^{\circ})$, $(l,b)=(310^{\circ},-15^{\circ})$ which are
significantly anisotropic compared to the other directions in the sky. We
suggest that their preferential orientations on the sky may indicate a possible
alignment of the Local Group with two nearby large scale structures. Despite
the differences in the degree of anisotropy on small scales, we find that the
galaxy distributions in both the 2MRS and the $\Lambda$CDM model are isotropic
on a scale of $90 \, h^{-1}\, {\rm Mpc}$. |
Can residuals of the Solar system foreground explain low multipole
anomalies of the CMB ?: The low multipole anomalies of the Cosmic Microwave Background has received
much attention during the last few years. It is still not ascertained whether
these anomalies are indeed primordial or the result of systematics or
foregrounds. An example of a foreground, which could generate some non-Gaussian
and statistically anisotropic features at low multipole range, is the very
symmetric Kuiper Belt in the outer solar system. In this paper, expanding upon
the methods presented by Maris et al. (2011), we investigate the contributions
from the Kuiper Belt objects (KBO) to the WMAP ILC 7 map, whereby we can
minimize the contrast in power between even and odd multipoles in the CMB,
discussed discussed by Kim & Naselsky (2010). We submit our KBO de-correlated
CMB signal to several tests, to analyze its validity, and find that
incorporation of the KBO emission can decrease the quadrupole-octupole
alignment and parity asymmetry problems, provided that the KBO signals has a
non-cosmological dipole modulation, associated with the statistical anisotropy
of the ILC 7 map. Additionally, we show that the amplitude of the dipole
modulation, within a 2 sigma interval, is in agreement with the corresponding
amplitudes, discussed by Lew (2008). | Testing Dark Energy Models with Gamma-Ray Bursts Calibrated from the
Observational $H(z)$ Data through a Gaussian Process: We use a cosmology-independent method to calibrate gamma-ray burst (GRB) from
the observational Hubble data (OHD) with the cosmic chronometers method. By
using Gaussian Process to reconstruct OHD, we calibrate the Amati relation
($E_{\rm p}$--$E_{\rm iso}$) to construct a GRB Hubble diagram with the A118
data set, and constrain Dark Energy models in a flat space with the Markov
Chain Monte Carlo numerical method. With the cosmology-independent GRBs at
$1.4<z\leq8.2$ in the A118 data set and the Pantheon sample of type Ia
supernovae (SNe Ia) at $0.01<z\leq2.3$, we obtained $\Omega_{\rm m}$ =
$0.379^{+0.033}_{-0.024}$, $h$ = $0.701^{+0.0035}_{-0.0035}$, $w$ =
$-1.25^{+0.14}_{-0.12}$, $w_a$ = $-0.84^{+0.81}_{-0.38}$ for the flat
Chevallier-Polarski-Linder model at the 1$\sigma$ confidence level. We find no
significant evidence supporting deviations from the standard $\Lambda$CDM
model. |
Even Lighter Particle Dark Matter: We report on recent progress in the search for dark matter particles with
masses from 1 MeV to 1 GeV. Several dark matter candidates in this mass range
are expected to generate measurable electronic-recoil signals in
direct-detection experiments. We focus on dark matter particles scattering with
electrons in semiconductor detectors since they have fundamentally the highest
sensitivity due to their low ionization threshold. Charge-coupled device (CCD)
silicon detectors are the leading technology, with significant progress
expected in the coming years. We present the status of the CCD program and
briefly report on other efforts. | The cosmology dependence of the concentration-mass-redshift relation: The concentrations of dark matter haloes provide crucial information about
their internal structure and how it depends on mass and redshift -- the
so-called concentration-mass-redshift relation, denoted $c(M,z)$. We present
here an extensive study of the cosmology-dependence of $c(M,z)$ that is based
on a suite of 72 gravity-only, full N-body simulations in which the following
cosmological parameters were varied: $\sigma_{8}$, $\Omega_{\mathrm{M}}$,
$\Omega_{\mathrm{b}}$, $n_{\mathrm{s}}$, $h$, $M_{\nu}$, $w_{0}$ and
$w_{\mathrm{a}}$. We characterize the impact of these parameters on
concentrations for different halo masses and redshifts. In agreement with
previous works, and for all cosmologies studied, we find that there exists a
tight correlation between the characteristic densities of dark matter haloes
within their scale radii, $r_{-2}$, and the critical density of the Universe at
a suitably defined formation time. This finding, when combined with excursion
set modelling of halo formation histories, allows us to accurately predict the
concentrations of dark matter haloes as a function of mass, redshift, and
cosmology. We use our simulations to test the reliability of a number of
published models for predicting halo concentration and highlight when they
succeed or fail to reproduce the cosmological $c(M,z)$ relation. |
An Oxygen Abundance Gradient into the Outer Disk of M81: The extended HI disk and tidal tails of M81 present an interesting
environment to study the effects of galaxy interaction on star formation and
chemical evolution of the outer disk of a large spiral galaxy. We present
H{\alpha} imaging of the outer disk of M81 and luminosities for 40 HII regions
out to about 3 times the optical radius. We have also obtained MMT spectra for
21 HII regions out to more than twice the optical radius. We derive strong line
oxygen abundances for all HII regions using R_{23} based and [NII]/[OII] based
calibrations and electron temperature abundances for seven regions spanning a
galactocentric distance between 5.7 and 32 kpc. We also comment on the
abundances of HII regions near KDG 61 and the "tidal dwarf" candidate HoIX. Our
results constitute the most radially extended metallicity study for M81 to
date. With this extended data set, we find an overall oxygen abundance gradient
of -0.013 dex/kpc over the entire radial range. This is significantly flatter
than what has been found in previous studies which were limited to the optical
disk. From our temperature based abundances, we find a gradient of -0.020
dex/kpc and present the possibility of a broken gradient from these data, but
note the need to obtain more temperature based abundances at intermediate
galactocentric distances (~10-20 kpc) to verify whether or not this may be the
case. We discuss our main result of a rather flat gradient for M81 in the
context of simulations and observations of abundance gradients in other
galaxies. We find that the shallow abundance gradient of M81 is likely a result
of the interaction history of this galaxy. | Cosmic Filament Spin from Dark Matter Vortices: The recent observational evidence for cosmic filament spin on megaparsec
scales (Wang et al, Nature Astronomy 5, 839-845 (2021)) demands an explanation
in the physics of dark matter. Conventional collisionless cold particle dark
matter is conjectured to generate cosmic filament spin through tidal torquing,
but this explanation requires extrapolating from the quasi-linear regime to the
non-linear regime. Meanwhile no alternative explanation exists in the context
of ultra-light (e.g., axion) dark matter, and indeed these models would naively
predict zero spin for cosmic filaments. In this Letter we study cosmic filament
spin in theories of ultra-light dark matter, such as ultra-light axions, and
bosonic and fermionic condensates, such as superfluids and superconductors.
These models are distinguished from conventional particle dark matter models by
the possibility of dark matter vortices. We take a model agnostic approach, and
demonstrate that a collection of dark vortices can explain the data reported in
Wang et al. Modeling a collection of vortices with a simple two-parameter
analytic model, corresponding to an averaging of the velocity field, we find an
excellent fit to the data. We perform a Markov Chain Monte Carlo analysis and
find constraints on the number of vortices, the dark matter mass, and the
radius of the inner core region where the vortices are distributed, in order
for ultra-light dark matter to explain spinning cosmic filaments. |
Can Light Dark Matter Solve the Core-Cusp Problem?: Recently there has been much interest in light dark matter, especially
ultra-light axions, as they may provide a solution to the core-cusp problem at
the center of galaxies. Since very light bosons can have a de Broglie
wavelength that is of astrophysical size, they can smooth out the centers of
galaxies to produce a core, as opposed to vanilla dark matter models, and so it
has been suggested that this solves the core-cusp problem. In this work, we
critically examine this claim. While an ultra-light particle will indeed lead
to a core, we examine whether the relationship between the density of the core
and its radius matches the data over a range of galaxies. We first review data
that shows the core density of a galaxy $\rho_c$ varies as a function of the
core radius $R_c$ as $\rho_c\propto1/R_c^\beta$ with $\beta\approx1$. We then
compare this to theoretical models. We examine a large class of light scalar
dark matter models, governed by some potential $V$. For simplicity, we take the
scalar to be complex with a global $U(1)$ symmetry in order to readily organize
solutions by a conserved particle number. However, we expect our central
conclusions to persist even for a real scalar, and furthermore, a complex
scalar matches the behavior of a real scalar in the non-relativistic limit,
which is the standard regime of interest. For any potential $V$, we find the
relationship between $\rho_c$ and $R_c$ for ground state solutions is always in
one of the following regimes: (i) $\beta\gg1$, or (ii) $\beta\ll1$, or (iii)
unstable, and so it never matches the data. We also find similar conclusions
for virialized dark matter, more general scalar field theories, degenerate
fermion dark matter, superfluid dark matter, and general polytropes. We
conclude that the solution to the core-cusp problem is more likely due to
either complicated baryonic effects or some other type of dark matter
interactions. | Are Scalar and Tensor Deviations Related in Modified Gravity?: Modified gravity theories on cosmic scales have three key deviations from
general relativity. They can cause cosmic acceleration without a physical,
highly negative pressure fluid, can cause a gravitational slip between the two
metric potentials, and can cause gravitational waves to propagate differently,
e.g. with a speed different from the speed of light. We examine whether the
deviations in the metric potentials as observable through modified Poisson
equations for scalar density perturbations are related to or independent from
deviations in the tensor gravitational waves. We show analytically they are
independent instantaneously in covariant Galileon gravity -- e.g. at some time
one of them can have the general relativity value while the other deviates --
though related globally -- if one deviates over a finite period, the other at
some point shows a deviation. We present expressions for the early time and
late time de Sitter limits, and numerically illustrate their full evolution.
This in(ter)dependence of the scalar and tensor deviations highlights
complementarity between cosmic structure surveys and future gravitational wave
measurements. |
Modeling quasar accretion disc temperature profiles: Microlensing observations indicate that quasar accretion discs have
half-light radii larger than expected from standard theoretical predictions
based on quasar fluxes or black hole masses. Blackburne and colleagues have
also found a very weak wavelength dependence of these half-light radii. We
consider disc temperature profile models that might match these observations.
Nixon and colleagues have suggested that misaligned accretion discs around
spinning black holes will be disrupted at radii small enough for the
Lense-Thirring torque to overcome the disc's viscous torque. Gas in precessing
annuli torn off a disc will spread radially and intersect with the remaining
disc, heating the disc at potentially large radii. However, if the intersection
occurs at an angle of more than a degree or so, highly supersonic collisions
will shock-heat the gas to a Compton temperature of T~10^7 K, and the spectral
energy distributions (SEDs) of discs with such shock-heated regions are poor
fits to observations of quasar SEDs. Torn discs where heating occurs in
intermittent weak shocks that occur whenever the intersection angle reaches a
tenth of a degree pose less of a conflict with observations, but do not have
significantly larger half-light radii than standard discs. We also study two
phenomenological disc temperature profile models. We find that discs with a
temperature spike at relatively large radii and lowered temperatures at radii
inside the spike yield improved and acceptable fits to microlensing sizes in
most cases. Such temperature profiles could in principle occur in sub-Keplerian
discs partially supported by magnetic pressure. However, such discs overpredict
the fluxes from quasars studied with microlensing except in the limit of
negligible continuum emission from radii inside the temperature spike. | Constraining gravity with synergies between radio and optical
cosmological surveys: In this work we present updated forecasts on parameterised modifications of
gravity that can capture deviations of the behaviour of cosmological density
perturbations beyond $\Lambda$CDM. For these forecasts we adopt the SKA
Observatory (SKAO) as a benchmark for future cosmological surveys at radio
frequencies, combining a continuum survey for weak lensing and angular galaxy
clustering with an HI galaxy survey for spectroscopic galaxy clustering that
can detect baryon acoustic oscillations and redshift space distortions.
Moreover, we also add 21cm HI intensity mapping, which provides invaluable
information at higher redshifts, and can complement tomographic resolution,
thus allowing us to probe redshift-dependent deviations of modified gravity
models. For some of these cases, we combine the probes with other optical
surveys, such as the Dark Energy Spectroscopic Instrument (DESI) and the Vera
C. Rubin Observatory (VRO). We show that such synergies are powerful tools to
remove systematic effects and degeneracies in the non-linear and small-scale
modelling of the observables. Overall, we find that the combination of all SKAO
radio probes will have the ability to constrain the present value of the
functions parameterising deviations from $\Lambda$CDM ($\mu$ and $\Sigma$) with
a precision of $2.7\%$ and $1.8\%$ respectively, competitive with the
constraints expected from optical surveys and with constraints we have on
gravitational interactions in the standard model. Exploring the radio-optical
synergies, we find that the combination of VRO with SKAO can yield extremely
tight constraints on $\mu$ and $\Sigma$ ($0.9\%$ and $0.7\%$ respectively),
which are further improved when the cross-correlation between intensity mapping
and DESI galaxies is included. |
SN 2003bg: The First Type IIb Hypernova: Optical and near-infrared photometry and optical spectroscopy are reported
for SN 2003bg, starting a few days after explosion and extending for a period
of more than 300 days. Our early-time spectra reveal the presence of broad,
high-velocity Balmer lines. The nebular-phase spectra, on the other hand, show
a remarkable resemblance to those of Type Ib/c supernovae, without clear
evidence for hydrogen. Near maximum brightness SN 2003bg displayed a bolometric
luminosity comparable to that of other Type I hypernovae unrelated to gamma-ray
bursts, implying a rather normal amount of 56Ni production (0.1-0.2 Msun)
compared with other such objects. The bolometric light curve of SN 2003bg, on
the other hand, is remarkably broad, thus suggesting a relatively large
progenitor mass at the moment of explosion. These observations, together with
the large value of the kinetic energy of expansion established in the
accompanying paper (Mazzali et al. 2009), suggest that SN 2003bg can be
regarded as a Type IIb hypernova. | Inhomogeneous cosmological models and $H_0$ observations: We address some recent erroneous claim that $H_0$ observations are difficult
to accommodate with LTB cosmological models, showing how to construct solutions
in agreement with an arbitrary value of $H_0$ by re-writing the exact solution
in terms of dimensionless parameters and functions. This approach can be
applied to fully exploit LTB solutions in designing models alternative to dark
energy without making any restrictive or implicit assumption about the
inhomogeneity profile. The same solution can also be used to study structure
formation in the regime in which perturbation theory is not enough and an exact
solution of the Einstein's equation is required, or to estimate the effects of
a local inhomogeneities on the apparent equation of state of dark energy. |
Standard candles and sirens rescue $H_0$: We show that future observations of binary neutron star systems with
electromagnetic counterparts together with the traditional probes of low- and
high-redshift Type Ia supernovae (SNe Ia) can help resolve the Hubble tension.
The luminosity distance inferred from these probes and its scatter depend on
the underlying cosmology. By using the gravitational lensing of light or
gravitational waves emitted by, and peculiar motion of, these systems we derive
constraints on the sum of neutrino masses, the equation of state of dark energy
parametrized in the form $w_0 + w_a (1-a)$, along with the Hubble constant and
cold dark matter density in the universe. We show that even after marginalizing
over poorly constrained physical quantities, such as the sum of neutrino masses
and the nature of dark energy, low-redshift gravitational-wave observations, in
combination with SNe Ia, have the potential to rule out new physics as the
underlying cause of the Hubble tension at $\gtrsim 5.5\sigma$. | Weak lensing in non-statistically isotropic universes: The Bipolar Spherical Harmonics (BipoSH) form a natural basis to study the
CMB two point correlation function in a non-statistically isotropic (non-SI)
universe. The coefficients of expansion in this basis are a generalisation of
the well known CMB angular power spectrum and contain complete information of
the statistical properties of a non-SI but Gaussian random CMB sky. We use
these coefficients to describe the weak lensing of CMB photons in a non-SI
universe. Finally we show that the results reduce to the standard weak lensing
results in the isotropic limit. |
On the Stellar Populations and Evolution of Star-Forming Galaxies at 6.3
< z < 8.6: We study the physical characteristics of galaxies at 6.3 < z < 8.6, selected
from deep near-infrared imaging with the Wide Field Camera 3 (WFC3) on board
the Hubble Space Telescope. Accounting for the photometric scatter using
simulations, galaxies at z ~ 7 have bluer UV colors compared to typical local
starburst galaxies at > 4 sigma confidence. Although these colors necessitate
young ages (<100 Myr), low or zero dust attenuation, and low metallicities,
these are explicable by normal (albeit unreddened) stellar populations, with no
evidence for near-zero metallicities and/or top-heavy initial mass functions.
The age of the Universe at these redshifts limits the amount of stellar mass in
late-type populations, and the WFC3 photometry implies galaxy stellar masses ~
10^8 - 10^9 Msol for Salpeter initial mass functions to a limiting magnitude of
M_1500 ~ -18. The masses of ``characteristic'' (L*) z > 7 galaxies are smaller
than those of L* Lyman break galaxies (LBGs) at lower redshifts, and are
comparable to less evolved galaxies selected on the basis of their Lyman alpha
emission at 3 < z < 6, implying that the 6.3 < z < 8.6 galaxies are the
progenitors of more evolved galaxies at lower redshifts. We estimate that Lyman
alpha emission is able to contribute to the observed WFC3 colors of galaxies at
these redshifts, with an estimated typical line flux of ~ 10^-18 erg s^-1
cm^-2, roughly a factor of four below currently planned surveys. The integrated
UV specific luminosity for the detected galaxies at z ~ 7 and z ~ 8 is within
factors of a few of that required to reionize the IGM assuming low clumping
factors, implying that in order to reionize the Universe galaxies at these
redshifts have a high ( ~ 50%) escape fraction of Lyman continuum photons,
possibly substantiated by the very blue colors of this population. | Graviton non-Gaussianities and Parity Violation in the EFT of Inflation: We study graviton non-Gaussianities in the EFT of Inflation. At leading
(second) order in derivatives, the graviton bispectrum is fixed by Einstein
gravity. There are only two contributions at third order. One of them breaks
parity. They come from operators that directly involve the foliation: we then
expect sizable non-Gaussianities in three-point functions involving both
gravitons and scalars. However, we show that at leading order in slow roll the
parity-odd operator does not modify these mixed correlators. We then identify
the operators that can affect the graviton bispectrum at fourth order in
derivatives. There are two operators that preserve parity. We show that one
gives a scalar-tensor-tensor three-point function larger than the one computed
in Maldacena, 2003 if $M^2_{\rm P}A_{\rm s}/\Lambda^2\gg 1$ (where $\Lambda$ is
the scale suppressing this operator and $A_{\rm s}$ the amplitude of the scalar
power spectrum). There are only two parity-odd operators at this order in
derivatives. |
Galaxy clustering in the NEWFIRM Medium Band Survey: the relationship
between stellar mass and dark matter halo mass at 1 < z < 2: We present an analysis of the clustering of galaxies as a function of their
stellar mass at 1 < z < 2 using data from the NEWFIRM Medium Band Survey
(NMBS). The precise photometric redshifts and stellar masses that the NMBS
produces allows us to define a series of mass limited samples of galaxies more
massive than 0.7, 1 and 3x10^10 Msun in redshift intervals centered on z = 1.1,
1.5 and 1.9 respectively. In each redshift interval we show that there exists a
strong dependence of clustering strength on the stellar mass limit of the
sample, with more massive galaxies showing a higher clustering amplitude on all
scales. We further interpret our clustering measurements in the LCDM
cosmological context using the halo model of galaxy clustering. We show that
the typical halo mass of central and satellite galaxies increases with stellar
mass, whereas the satellite fraction decreases with stellar mass, qualitatively
the same as is seen at z < 1. We see little evidence of any redshift dependence
in the stellar mass-to-halo mass relationship over our narrow redshift range.
However, when we compare with similar measurements at z~0, we see clear
evidence for a change in this relation. If we assume a universal baryon
fraction, the ratio of stellar mass to halo mass reveals the fraction of
baryons that have been converted to stars. We see that the peak in this star
formation efficiency for central galaxies shifts to higher halo masses at
higher redshift, moving from ~7x10^11 Msun at z~0 to ~3x10^12 Msun at z~1.5,
revealing evidence of `halo downsizing'. Finally we show that for highly biased
galaxy populations at z > 1 there may be a discrepancy between the measured
space density and clustering and that predicted by the halo model. This could
imply that there is a problem with one or more ingredients of the halo model at
these redshifts, for instance the halo bias relation or the halo profile. | The massive elliptical galaxy NGC 4649 from the perspective of extended
gravity: Elliptical galaxies are systems where dark matter is usually less necessary
to explain observed dynamics than in the case of spiral galaxies, however there
are some instances where Newtonian gravity and the observable mass are
insufficient to explain their observed structure and kinematics. Such is the
case of NGC 4649, a massive elliptical galaxy in the Virgo cluster for which
recent studies report a high fraction of dark matter, 0.78 at $4R_e$. However
this galaxy has been studied within the MOND hypothesis, where a good agreement
with the observed values of velocity dispersion is found. Using a MONDian
gravity force law, here we model this galaxy as a self-consistent gravitational
equilibrium dynamical system. This force law reproduces the MOND phenomenology
in the $a<a_{0}$ regime, and reduces to the Newtonian case when $a>a_{0}$.
Within the MONDian $a<a_{0}$ scales, centrifugal equilibrium or dispersion
velocities become independent of radius, and show a direct proportionality to
the fourth root of the total baryonic mass, $V^{4}\propto(M G a_{0})$. We find
that the recent detailed observations of the surface brightness profile and the
velocity dispersion profile for this galaxy are consistent with the
phenomenology expected in MONDian theories of modified gravity, without the
need of invoking the presence of any hypothetical dark matter. |
Improving initialization and evolution accuracy of cosmological neutrino
simulations: Neutrino mass constraints are a primary focus of current and future
large-scale structure (LSS) surveys. Non-linear LSS models rely heavily on
cosmological simulations -- the impact of massive neutrinos should therefore be
included in these simulations in a realistic, computationally tractable, and
controlled manner. A recent proposal to reduce the related computational cost
employs a symmetric neutrino momentum sampling strategy in the initial
conditions. We implement a modified version of this strategy into the
Hardware/Hybrid Accelerated Cosmology Code (HACC) and perform convergence tests
on its internal parameters. We illustrate that this method can impart
$\mathcal{O}(1\%)$ numerical artifacts on the total matter field on small
scales, similar to previous findings, and present a method to remove these
artifacts using Fourier-space filtering of the neutrino density field.
Moreover, we show that the converged neutrino power spectrum does not follow
linear theory predictions on relatively large scales at early times at the
$15\%$ level, prompting a more careful study of systematics in particle-based
neutrino simulations. We also present an improved method for backscaling linear
transfer functions for initial conditions in massive neutrino cosmologies that
is based on achieving the same relative neutrino growth as computed with
Boltzmann solvers. Our self-consistent backscaling method yields sub-percent
accuracy in the total matter growth function. Comparisons for the non-linear
power spectrum with the Mira-Titan emulator at a neutrino mass of
$m_{\nu}=0.15~\mathrm{eV}$ are in very good agreement with the expected level
of errors in the emulator and in the direct N-body simulation. | Connecting stellar mass and star-formation rate to dark matter halo mass
out to z ~ 2: We have constructed an extended halo model (EHM) which relates the total
stellar mass and star-formation rate (SFR) to halo mass (M_h). An empirical
relation between the distribution functions of total stellar mass of galaxies
and host halo mass, tuned to match the spatial density of galaxies over 0<z<2
and the clustering properties at z~0, is extended to include two different
scenarios describing the variation of SFR on M_h. We also present new
measurements of the redshift evolution of the average SFR for star-forming
galaxies of different stellar mass up to z=2, using data from the Herschel
Multi-tiered Extragalactic Survey (HerMES) for infrared-bright galaxies.
Combining the EHM with the halo accretion histories from numerical
simulations, we trace the stellar mass growth and star-formation history in
halos spanning a range of masses. We find that: (1) The intensity of the
star-forming activity in halos in the probed mass range has steadily decreased
from z~2 to 0; (2) At a given epoch, halos in the mass range between a few
times 10^{11} M_Sun and a few times 10^{12} M_Sun are the most efficient at
hosting star formation; (3) The peak of SFR density shifts to lower mass halos
over time; (4) Galaxies that are forming stars most actively at z~2 evolve into
quiescent galaxies in today's group environments, strongly supporting previous
claims that the most powerful starbursts at z~2 are progenitors of today's
elliptical galaxies. |
The Survey of Extragalactic Nuclear Spectral Energies: We present the first results from the new Survey of Extragalactic Nuclear
Spectral Energies (SENSE) sample of "blazars". The sample has been chosen with
minimal selection effects and is therefore ideal to probe the intrinsic
properties of the blazar population. We report evidence for negative
cosmological evolution in this radio selected sample and give an outline of
future work related to the SENSE sample. | Holographic Ricci dark energy: Current observational constraints,
quintom feature, and the reconstruction of scalar-field dark energy: In this work, we consider the cosmological constraints on the holographic
Ricci dark energy proposed by Gao et al. [Phys. Rev. D 79, 043511 (2009)], by
using the observational data currently available. The main characteristic of
holographic Ricci dark energy is governed by a positive numerical parameter
$\alpha$ in the model. When $\alpha<1/2$, the holographic Ricci dark energy
will exhibit a quintomlike behavior; i.e., its equation of state will evolve
across the cosmological-constant boundary $w=-1$. The parameter $\alpha$ can be
determined only by observations. Thus, in order to characterize the evolving
feature of dark energy and to predict the fate of the universe, it is of
extraordinary importance to constrain the parameter $\alpha$ by using the
observational data. In this paper, we derive constraints on the holographic
Ricci dark energy model from the latest observational data including the Union
sample of 307 type Ia supernovae, the shift parameter of the cosmic microwave
background given by the five-year Wilkinson Microwave Anisotropy Probe
observations, and the baryon acoustic oscillation measurement from the Sloan
Digital Sky Survey. The joint analysis gives the best-fit results (with
1$\sigma$ uncertainty): $\alpha=0.359^{+0.024}_{-0.025}$ and $\Omega_{\rm
m0}=0.318^{+0.026}_{-0.024}$. That is to say, according to the observations,
the holographic Ricci dark energy takes on the quintom feature. Finally, in
light of the results of the cosmological constraints, we discuss the issue of
the scalar-field dark energy reconstruction, based on the scenario of the
holographic Ricci vacuum energy. |
A measurement of galaxy halo mass from the surrounding HI Lyα
absorption: We measure the dark matter halo masses of z~2.36 UV color-selected
star-forming galaxies by matching the observed median HI Ly{\alpha} absorption
around them, as observed in the spectra of background QSOs, to the absorption
around haloes above a given mass in cosmological simulations. Focusing on
transverse separations 0-2 pMpc and line of sight separations 154-616 km/s, we
find a minimum halo mass of log10(Mmin/Msun)=11.6(+0.2)(-0.2), which is in good
agreement with published halo mass estimates from clustering analyses. We
verified that the measured halo mass is insensitive to a change in the
cosmological parameters (WMAP1 vs. WMAP3) and to the inclusion of strong AGN
feedback. One unique strength of this method is that it can be used in narrow
field galaxy-QSO surveys, i.e. ~30 x 30 arcseconds. In addition, we find that
the observed anisotropy in the 2-D HI Ly{\alpha} absorption distribution on
scales of 1.5-2 pMpc is consistent with being a consequence of large-scale gas
infall into the potential wells occupied by galaxies. | Constraining high-redshift stellar-mass primordial black holes with
next-generation ground-based gravitational-wave detectors: The possible existence of primordial black holes in the stellar mass window
has received considerable attention because their mergers may contribute to
current and future gravitational-wave detections. Primordial black hole
mergers, together with mergers of black holes originating from Population~III
stars, are expected to dominate at high redshifts ($z\gtrsim 10$). However the
primordial black hole merger rate density is expected to rise monotonically
with redshift, while Population~III mergers can only occur after the birth of
the first stars. Next-generation gravitational-wave detectors such as Cosmic
Explorer~(CE) and Einstein Telescope~(ET) can access this distinctive feature
in the merger rates as functions of redshift, allowing for a direct measurement
of the abundance of the two populations, and hence for robust constraints on
the abundance of primordial black holes. We simulate four-months worth of data
observed by a CE-ET detector network and perform hierarchical Bayesian analysis
to recover the merger rate densities. We find that if the Universe has no
primordial black holes with masses of $\mathcal{O}(10M_{\odot})$, the projected
upper limit on their abundance $f_{\rm PBH}$ as a fraction of dark matter
energy density may be as low as $f_{\rm PBH}\sim \mathcal{O}({10^{-5}})$, about
two orders of magnitude lower than current upper limits in this mass range. If
instead $f_{\rm PBH}\gtrsim 10^{-4}$, future gravitational wave observations
would exclude $f_{\rm PBH}=0$ at the 95\% credible interval. |
The angular momentum of baryons and dark matter halos revisited: Recent theoretical studies have shown that galaxies at high redshift are fed
by cold, dense gas filaments, suggesting angular momentum transport by gas
differs from that by dark matter. Revisiting this issue using high-resolution
cosmological hydrodynamics simulations with adaptive mesh refinement, we find
that at the time of accretion, gas and dark matter do carry a similar amount of
specific angular momentum, but that it is systematically higher than that of
the dark matter halo as a whole. At high redshift, freshly accreted gas rapidly
streams into the central region of the halo, directly depositing this large
amount of angular momentum within a sphere of radius r=0.1rvir. In contrast,
dark matter particles pass through the central region unscathed, and a fraction
of them ends up populating the outer regions of the halo (r/rvir>0.1),
redistributing angular momentum in the process. As a result, large-scale
motions of the cosmic web have to be considered as the origin of gas angular
momentum rather than its virialised dark matter halo host. This generic result
holds for halos of all masses at all redshifts, as radiative cooling ensures
that a significant fraction of baryons remain trapped at the centre of the
halos. Despite this injection of angular momentum enriched gas, we predict an
amount for stellar discs which is in fair agreement with observations at z=0.
This arises because the total specific angular momentum of the baryons remains
close to that of dark matter halos. We propose a new scenario where gas
efficiently carries the angular momentum generated by large-scale structure
motions deep inside dark matter halos, redistributing it only in the vicinity
of the disc. | Evolution of the Fundamental Plane of 0.2<z<1.2 Early-type galaxies in
the EGS: The Fundamental Plane relates the structural properties of early-type
galaxies such as its surface brightness and effective radius with its dynamics.
The study of its evolution has therefore important implications for models of
galaxy formation and evolution. This work aims to identify signs of evolution
of early-type galaxies through the study of parameter correlations using a
sample of 135 field galaxies extracted from the Extended Groth Strip in the
redshift range 0.2<z<1.2. Using DEEP2 data, we calculate the internal velocity
dispersions by extracting the stellar kinematics from absorption line spectra,
using a maximum penalized likelihood approach. Morphology was determined
through visual classification using the V+I images of ACS. The structural
parameters of these galaxies were obtained by fitting de Vaucouleurs stellar
profiles to the ACS I-band images, using the GALFIT code. S\'ersic and
bulge-to-disc decomposition models were also fitted to our sample of galaxies,
and we found a good agreement in the Fundamental Plane derived from the three
models. Assuming that effective radii and velocity dispersions do not evolve
with redshift, we have found a brightening of 0.68 mag in the B-band and 0.52
mag in the g-band at <z>=0.7. However, the scatter in the FP is reduced by half
when we allow the FP slope to evolve, suggesting a different evolution of
early-type galaxies according to their intrinsic properties. The study of the
Kormendy relation shows the existence of a population of very compact (Re<2
Kpc) and bright galaxies (-21.5>Mg>-22.5), of which there are only a small
fraction (0.4%) at z=0. The evolution of these compact objects is mainly caused
by an increase in size that could be explained by the action of dry minor
mergers, and this population is responsible for the evolution detected in the
Fundamental Plane. |
The Linear Growth of Structure in the R_h=ct Universe: We use recently published redshift space distortion measurements of the
cosmological growth rate, f sigma_8(z), to examine whether the linear evolution
of perturbations in the R_h=ct cosmology is consistent with the observed
development of large scale structure. We find that these observations favour
R_h=ct over the version of LCDM optimized with the joint analysis of Planck and
linear growth rate data, particularly in the redshift range 0 < z < 1, where a
significant curvature in the functional form of f sigma_8(z) predicted by the
standard model---but not by R_h=ct---is absent in the data. When LCDM is
optimized using solely the growth rate measurements, however, the two models
fit the observations equally well though, in this case, the low-redshift
measurements find a lower value for the fluctuation amplitude than is expected
in Planck LCDM. Our results strongly affirm the need for more precise
measurements of f sigma_8(z) at all redshifts, but especially at z < 1. | Oscillon formation from preheating in asymmetric inflationary potentials: We investigate the possibility of oscillon formation during the preheating
phase of asymmetric inflationary potentials. We analytically establish the
existence of oscillon-like solutions for the Klein-Gordon equation for a
polynomial potential of the form $V(\phi)=\frac{1}{2}\phi^2+A\phi^3+B\phi^4$
using the small amplitude analysis, which naturally arises as a Taylor
expansion of the $\alpha$-attractor E-model for $\phi\ll M_\text{pl}$ and
$\alpha\sim\mathcal{O}(1)$. We perform a detailed numerical analysis to study
the formation of nonlinear structures in the $\alpha$-attractor E-model using
the publicly available lattice simulation code
$\mathcal{C}\text{osmo}\mathcal{L}\text{attice}$ for parameters in the range
$10^{-5}\lesssim\alpha\lesssim 5\times 10^{-4}$. We find the backreaction of
the field fluctuations onto the evolution of the homogeneous inflaton
condensate to be significant for $\alpha\lesssim 2\times 10^{-4}$ for which we
observe the formation of highly nonlinear structures with average equation of
state $w\simeq 0$. These nonlinear structures maybe interpreted as oscillons,
providing evidence that they can form during the inflaton oscillations around
an asymmetric potential and are found to be present for the entirety of the
runtime of our simulations, comprising $\gtrsim 40\%$ of the total energy
density. |
The source counts of submillimetre galaxies detected at 1.1 mm: The source counts of galaxies discovered at sub-millimetre and millimetre
wavelengths provide important information on the evolution of infrared-bright
galaxies. We combine the data from six blank-field surveys carried out at 1.1
mm with AzTEC, totalling 1.6 square degrees in area with root-mean-square
depths ranging from 0.4 to 1.7 mJy, and derive the strongest constraints to
date on the 1.1 mm source counts at flux densities S(1100) = 1-12 mJy. Using
additional data from the AzTEC Cluster Environment Survey to extend the counts
to S(1100) ~ 20 mJy, we see tentative evidence for an enhancement relative to
the exponential drop in the counts at S(1100) ~ 13 mJy and a smooth connection
to the bright source counts at >20 mJy measured by the South Pole Telescope;
this excess may be due to strong lensing effects. We compare these counts to
predictions from several semi-analytical and phenomenological models and find
that for most the agreement is quite good at flux densities > 4 mJy; however,
we find significant discrepancies (>3sigma) between the models and the observed
1.1 mm counts at lower flux densities, and none of them are consistent with the
observed turnover in the Euclidean-normalised counts at S(1100) < 2 mJy. Our
new results therefore may require modifications to existing evolutionary models
for low luminosity galaxies. Alternatively, the discrepancy between the
measured counts at the faint end and predictions from phenomenological models
could arise from limited knowledge of the spectral energy distributions of
faint galaxies in the local Universe. | A hydrodynamical halo model for weak-lensing cross correlations: On the scale of galactic haloes, the distribution of matter in the cosmos is
affected by energetic, non-gravitational processes; so-called baryonic
feedback. A lack of knowledge about the details of how feedback processes
redistribute matter is a source of uncertainty for weak-lensing surveys, which
accurately probe the clustering of matter in the Universe over a wide range of
scales. We develop a cosmology-dependent model for the matter distribution that
simultaneously accounts for the clustering of dark matter, gas and stars. We
inform our model by comparing it to power spectra measured from the BAHAMAS
suite of hydrodynamical simulations. As well as considering matter power
spectra, we also consider spectra involving the electron-pressure field, which
directly relates to the thermal Sunyaev-Zel'dovich (tSZ) effect. We fit
parameters in our model so that it can simultaneously model both matter and
pressure data and such that the distribution of gas as inferred from tSZ has
influence on the matter spectrum predicted by our model. We present two
variants; one that matches the feedback-induced suppression seen in the
matter-matter power spectrum at the per-cent level and a second that matches
the matter-matter data slightly less well (~2 per cent), but that is able to
simultaneously model the matter-electron pressure spectrum at the ~15 per-cent
level. We envisage our models being used to simultaneously learn about
cosmological parameters and the strength of baryonic feedback using a
combination of tSZ and lensing auto- and cross-correlation data. |
Observational constraints on dark matter scattering with electrons: We present new observational constraints on the elastic scattering of dark
matter with electrons for dark matter masses between 10 keV and 1 TeV. We
consider scenarios in which the momentum-transfer cross section has a power-law
dependence on the relative particle velocity, with a power-law index $n \in
\{-4,-2,0,2,4,6\}$. We search for evidence of dark matter scattering through
its suppression of structure formation. Measurements of the cosmic microwave
background temperature, polarization, and lensing anisotropy from
\textit{Planck} 2018 data and of the Milky Way satellite abundance measurements
from the Dark Energy Survey and Pan-STARRS1 show no evidence of interactions.
We use these data sets to obtain upper limits on the scattering cross section,
comparing them with exclusion bounds from electronic recoil data in direct
detection experiments. Our results provide the strongest bounds available for
dark matter--electron scattering derived from the distribution of matter in the
Universe, extending down to sub-MeV dark matter masses, where current direct
detection experiments lose sensitivity. | A practical guide to the massive black hole cosmic history: I review our current understanding of massive black hole (MBH) formation and
evolution along the cosmic history. After a brief introductory overview of the
relevance of MBHs in the hierarchical structure formation paradigm, I discuss
the main viable channels for seed BH formation at high redshift and for their
subsequent mass growth and spin evolution. The emerging hierarchical picture,
where MBHs grow through merger triggered accretion episodes, acquiring their
mass while shining as quasars, is overall robust, but too simplistic to explain
the diversity observed in MBH phenomenology. I briefly discuss which future
observations will help to shed light on the MBH cosmic history in the near
future, paying particular attention to the upcoming gravitational wave window. |
Continuous matter creation and the acceleration of the universe: a
replay: In a recent note (arXiv:1012.5069), the investigation performed by the
present authors on the evolution of density fluctuations in an accelerated
universe including matter creation was criticized. The criticism is based on
the fact that the Newtonian background is not "accelerating", invalidating the
conclusions of the linear analysis. We show that our linear equations describe
adequately an accelerating universe in which the pressure associated to the
creation process is constant, a model equivalent to the $\Lambda$CDM cosmology.
Thus, our previous conclusions remain unchanged. | Double inflation via non-minimally coupled spectator: We argue that double inflation may occur when a spectator field is
non-minimally coupled to gravity. As a concrete example, we study a two-field
inflationary model where the initial spectator field is non-minimally coupled
to gravity while the initial inflaton field is minimally coupled. The
non-minimal coupling results in the growth of the spectator field which, in
turn, drives the second stage of inflation in a significant region of parameter
space. The isocurvature fluctuations originating from the spectator field
source adiabatic ones, and hence the spectator non-minimal coupling can modify
the inflationary predictions for the spectral index and the tensor-to-scalar
ratio even though the initial inflaton field is minimally coupled to gravity.
We explicitly show that quadratic chaotic inflation can become viable by the
introduction of the spectator non-minimal coupling. |
Gravitational Stability of Vortices in Bose-Einstein Condensate Dark
Matter: We investigate a simple model for a galactic halo under the assumption that
it is dominated by a dark matter component in the form of a Bose-Einstein
condensate involving an ultra-light scalar particle. In particular we discuss
the possibility if the dark matter is in superfluid state then a rotating
galactic halo might contain quantised vortices which would be low-energy
analogues of cosmic strings. Using known solutions for the density profiles of
such vortices we compute the self-gravitational interactions in such halos and
place bounds on the parameters describing such models, such as the mass of the
particles involved. | Galaxy power spectrum and biasing results from the LOFAR Two-metre Sky
Survey (first data release): The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing survey aiming to observe
the entire Northern sky, providing an excellent opportunity to study the
distribution and evolution of the large-scale structure of the Universe. The
source catalogue from the public LoTSS first data release (DR1) covers 1% of
the sky, and shows correlated noise or fluctuations of the flux density
calibration on few degree scales. We explore the LoTSS DR1 to understand the
survey systematics and data quality of this first data release. We produce
catalog mocks to estimate uncertainties, and measure the angular clustering
statistics of LoTSS galaxies, which fit the $\Lambda$CDM cosmology reasonably
well. We employ a Markov chain Monte Carlo (MCMC) based Bayesian analysis to
recover the best galaxy biasing scheme and multi-component source fraction for
LoTSS DR1 above $1$ mJy assuming different possible redshift templates. After
masking some noisy and uneven patches and with suitable flux density cuts, the
LOFAR survey appears qualified for large-scale cosmological studies. The
upcoming data releases from LOFAR are expected to be deeper and wider, and will
therefore provide improved cosmological measurements. |
Helical magnetic fields in the M87 jet at arc-second scales: We investigate the magnetic field configuration of the M87 jet at arc-second
scales by using archival polarimetric VLA data at 8, 15, 22 and 43 GHz. By
stacking images over three years in order to enhance the sensitivity, we
reveal, for the first time, systematic transverse gradients of the Faraday
rotation measure in several knots along the jet. Combining this result with
polarization properties and the dynamics of the jet, we suggest the magnetic
structure in several knots at kiloparsec scales consists of a systematically
wrapped, tightly wound helical configuration. Our analysis brings us a new
paradigm where the M87 jet is a fundamentally current carrying system produced
in the vicinity of the supermassive black hole, transferring a huge amount of
the electromagnetic energy over the host galaxy scale. | WEAVE-QSO: A Massive Intergalactic Medium Survey for the William
Herschel Telescope: In these proceedings we describe the WEAVE-QSO survey, which will observe
around 400,000 high redshift quasars starting in 2018. This survey is part of a
broader WEAVE survey to be conducted at the 4.2m William Herschel Telescope. We
will focus on chiefly on the science goals, but will also briefly summarise the
target selection methods anticipated and the expected survey plan.
Understanding the apparent acceleration in the expansion of the Universe is
one of the key scientific challenges of our time. Many experiments have been
proposed to study this expansion, using a variety of techniques. Here we
describe a survey that can measure this acceleration and therefore help
elucidate the nature of dark energy: a survey of the Lyman-alpha forest (and
quasar absorption in general) in spectra towards z>2 quasars (QSOs). Further
constraints on neutrino masses and warm dark matter are also anticipated. The
same data will also shed light on galaxy formation via study of the properties
of inflowing/outflowing gas associated with nearby galaxies and in a cosmic web
context. Gas properties are sensitive to density, temperature, UV radiation,
metallicity and abundance pattern, and so constraint galaxy formation in a
variety of ways. WEAVE-QSO will study absorbers with a dynamic range spanning
more than 8 orders of magnitude in column density, their thermal broadening,
and a host of elements and ionization species. A core principal of the
WEAVE-QSO survey is the targeting of QSOs with near 100% efficiency principally
through use of the J-PAS (r < 23.2) and Gaia (r < 20) data. |
The Dark Energy Survey 5-year photometrically identified Type Ia
Supernovae: As part of the cosmology analysis using Type Ia Supernovae (SN Ia) in the
Dark Energy Survey (DES), we present photometrically identified SN Ia samples
using multi-band light-curves and host galaxy redshifts. For this analysis, we
use the photometric classification framework SuperNNova (SNN; M\"oller et al.
2019) trained on realistic DES-like simulations. For reliable classification,
we process the DES SN programme (DES-SN) data and introduce improvements to the
classifier architecture, obtaining classification accuracies of more than 98
per cent on simulations. This is the first SN classification to make use of
ensemble methods, resulting in more robust samples. Using photometry, host
galaxy redshifts, and a classification probability requirement, we identify
1,863 SNe Ia from which we select 1,484 cosmology-grade SNe Ia spanning the
redshift range of 0.07 < z < 1.14. We find good agreement between the
light-curve properties of the photometrically-selected sample and simulations.
Additionally, we create similar SN Ia samples using two types of Bayesian
Neural Network classifiers that provide uncertainties on the classification
probabilities. We test the feasibility of using these uncertainties as
indicators for out-of-distribution candidates and model confidence. Finally, we
discuss the implications of photometric samples and classification methods for
future surveys such as Vera C. Rubin Observatory Legacy Survey of Space and
Time (LSST). | Cosmological parameter estimation with future gravitational wave
standard siren observation from the Einstein Telescope: In this work, we use the simulated gravitational wave (GW) standard siren
data from the future observation of the Einstein Telescope (ET) to constrain
various dark energy cosmological models, including the $\Lambda$CDM, $w$CDM,
CPL, $\alpha$DE, GCG, and NGCG models. We also use the current mainstream
cosmological electromagnetic observations, i.e., the cosmic microwave
background anisotropies data, the baryon acoustic oscillations data, and the
type Ia supernovae data, to constrain these models. We find that the GW
standard siren data could tremendously improve the constraints on the
cosmological parameters for all these dark energy models. For all the cases,
the GW standard siren data can be used to break the parameter degeneracies
generated by the current cosmological electromagnetic observational data.
Therefore, it is expected that the future GW standard siren observation from
the ET would play a crucial role in the cosmological parameter estimation in
the future. The conclusion of this work is quite solid because it is based on
the analysis for various dark energy models. |
Prospects for measuring the relative velocities of galaxy clusters in
photometric surveys using the kinetic Sunyaev-Zel'dovich Effect: We consider the prospects for measuring the pairwise kinetic
Sunyaev-Zel'dovich (kSZ) signal from galaxy clusters discovered in large
photometric surveys such as the Dark Energy Survey (DES). We project that the
DES cluster sample will, in conjunction with existing mm-wave data from the
South Pole Telescope (SPT), yield a detection of the pairwise kSZ signal at the
8-13 sigma level, with sensitivity peaking for clusters separated by ~100 Mpc
distances. A next-generation version of SPT would allow for a 18-30 sigma
detection and would be limited by variance from the kSZ signal itself and
residual thermal Sunyaev-Zel'dovich (tSZ) signal. Throughout our analysis we
assume photometric redshift errors, which wash out the signal for clusters
separated by <~50 Mpc; a spectroscopic survey of the DES sample would recover
this signal and allow for a 26-43 sigma detection, and would again be limited
by kSZ/tSZ variance. Assuming a standard model of structure formation, these
high-precision measurements of the pairwise kSZ signal will yield detailed
information on the gas content of the galaxy clusters. Alternatively, if the
gas can be sufficiently characterized by other means (e.g. using tSZ, X-ray, or
weak lensing), then the relative velocities of the galaxy clusters can be
isolated, thereby providing a precision measurement of gravity on 100 Mpc
scales. We briefly consider the utility of these measurements for constraining
theories of modified gravity. | COSMOS: Stochastic bias from measurements of weak lensing and galaxy
clustering: In the theory of structure formation, galaxies are biased tracers of the
underlying matter density field. The statistical relation between galaxy and
matter density field is commonly referred as galaxy bias. In this paper, we
test the linear bias model with weak-lensing and galaxy clustering measurements
in the 2 square degrees COSMOS field (Scoville et al. 2007). We estimate the
bias of galaxies between redshifts z=0.2 and z=1, and over correlation scales
between R=0.2 h^-1 Mpc and R=15 h^-1 Mpc. We focus on three galaxy samples,
selected in flux (simultaneous cuts I_814W < 26.5 and K_s < 24), and in
stellar-mass (10^9 < M_* < 10^10 h^-2 Msun and 10^10 < M^*< 10^11 h^-2 Msun).
At scales R > 2 h^-1 Mpc, our measurements support a model of bias increasing
with redshift. The Tinker et al. (2010) fitting function provides a good fit to
the data. We find the best fit mass of the galaxy halos to be log(M_200 h^-1
Msun) = 11.7^+0.6_-1.3 and log(M_200 h^-1 Msun) = 12.4^+0.2_-2.9 respectively
for the low and high stellar-mass samples. In the halo model framework, bias is
scale-dependent with a change of slope at the transition scale between the one
and the two halo terms. We detect a scale-dependence of bias with a turn-down
at scale R=2.3\pm1.5 h^-1 Mpc, in agreement with previous galaxy clustering
studies. We find no significant amount of stochasticity, suggesting that a
linear bias model is sufficient to describe our data. We use N-body simulations
to quantify both the amount of cosmic variance and systematic errors in the
measurement. |
Localised HI 21-cm absorption towards a double-lobed z=0.24 radio galaxy: We present the results of a mini-survey for associated HI 21-cm absorption at
z < 0.42 with the Giant Metrewave Radio Telescope. Our targets are radio
galaxies, selected on the basis that the 1216 Angstrom luminosities are below
10^23 W/Hz, above which there has never been a detection of 21-cm absorption.
Of the three sources for which we obtained good data, two are unclassified
active galactic nuclei (AGN) and one is type-2. Being a non-detection, the
type-2 object is consistent with our previous result that 21-cm absorption in
radio sources is not dictated by unified schemes of AGN. In the case of the
detection, the absorption only occurs towards one of the two resolved radio
lobes in PKS 1649-062. If the absorption is due to an another intervening
galaxy, or cool HI gas in the intergalactic medium, covering only the
south-west lobe, then, being at the same redshift, this is likely to be
gravitationally bound to the optical object identified as PKS 1649-062. If the
absorption is due to an inclined disk centred between the lobes, intervening
the SW lobe while being located behind the NE lobe, by assuming that it covers
the emission peak at 150 kpc from the nucleus, we estimate a dynamical mass of
~3 x 10^12 solar masses for the disk. | Gas Sloshing and Radio Galaxy Dynamics in the Core of the 3C449 Group: We present results from a 140 ks Chandra/ACIS-S observation of the hot gas
around the canonical FR I radio galaxy 3C 449. An earlier, shorter 30 ks
Chandra observation of the group gas showed an unusual entropy distribution and
a surface brightness edge in the gas that could be a strong shock around the
inner radio lobes. In our deeper data we find no evidence for a temperature
increase inside of the brightness edge, but a temperature decrease across part
of the edge. This suggests that the edge is a "sloshing" cold front due to a
merger within the last ~1.3-1.6 Gyrs. Both the northern and the southern inner
jets are bent slightly to the west in projection as they enter their respective
lobes, suggesting that the sloshing core is moving to the east. The straight
inner jet flares at approximately the position where it crosses the contact
edge, suggesting that the jet is entraining and thermalizing some of the hot
gas as it crosses the edge. We also detect filaments of X-ray emission around
the southern inner radio jet and lobe which we attribute to low entropy
entrained gas. The lobe flaring and gas entrainment were originally predicted
in simulations of Loken et al. (1995) and are confirmed in our deep
observation. |
Generic inference of inflation models by non-Gaussianity and primordial
power spectrum reconstruction: We present a generic inference method for inflation models from observational
data by the usage of higher-order statistics of the curvature perturbation on
uniform density hypersurfaces. This method is based on the calculation of the
posterior for the primordial non-Gaussianity parameters $f_\text{NL}$ and
$g_\text{NL}$, which in general depend on specific parameters of inflation and
reheating models, and enables to discriminate among the still viable inflation
models. To keep analyticity as far as possible to dispense with numerically
expensive sampling techniques a saddle-point approximation is introduced, whose
precision is validated for a numerical toy example. The mathematical
formulation is done in a generic way so that the approach remains applicable to
cosmic microwave background data as well as to large scale structure data.
Additionally, we review a few currently interesting inflation models and
present numerical toy examples thereof in two and three dimensions to
demonstrate the efficiency of the higher-order statistics method. A second
quantity of interest is the primordial power spectrum. Here, we present two
Bayesian methods to infer it from observational data, the so called critical
filter and an extension thereof with smoothness prior, both allowing for a
non-parametric spectrum reconstruction. These methods are able to reconstruct
the spectra of the observed perturbations and the primordial ones of curvature
perturbation even in case of non-Gaussianity and partial sky coverage. We argue
that observables like $T-$ and $B-$modes permit to measure both spectra. This
also allows to infer the level of non-Gaussianity generated since inflation. | Integrated Cosmological Probes: Extended Analysis: Recent progress in cosmology has relied on combining different cosmological
probes. In earlier work, we implemented an integrated approach to cosmology
where the probes are combined into a common framework at the map level. This
has the advantage of taking full account of the correlations between the
different probes, to provide a stringent test of systematics and of the
validity of the cosmological model. We extend this analysis to include not only
CMB temperature, galaxy clustering, weak lensing from SDSS but also CMB
lensing, weak lensing from the DES SV survey, Type Ia SNe and $H_{0}$
measurements. This yields 12 auto- and cross-power spectra as well as
background probes. Furthermore, we extend the treatment of systematic
uncertainties. For $\Lambda$CDM, we find results that are consistent with our
earlier work. Given our enlarged data set and systematics treatment, this
confirms the robustness of our analysis and results. Furthermore, we find that
our best-fit cosmological model gives a good fit to the data we consider with
no signs of tensions within our analysis. We also find our constraints to be
consistent with those found by WMAP9, SPT and ACT and the KiDS weak lensing
survey. Comparing with the Planck Collaboration results, we see a broad
agreement, but there are indications of a tension from the marginalized
constraints in most pairs of cosmological parameters. Since our analysis
includes CMB temperature Planck data at $10 < \ell < 610$, the tension appears
to arise between the Planck high$-\ell$ and the other measurements.
Furthermore, we find the constraints on the probe calibration parameters to be
in agreement with expectations, showing that the data sets are mutually
consistent. In particular, this yields a confirmation of the amplitude
calibration of the weak lensing measurements from SDSS, DES SV and Planck CMB
lensing from our integrated analysis. [abridged] |
Flat-Sky Pseudo-Cls Analysis for Weak Gravitational Lensing: We investigate the use of estimators of weak lensing power spectra based on a
flat-sky implementation of the Pseudo-Cl (PCl) technique, where the masked
shear field is transformed without regard for masked regions of sky. This
masking mixes power, and E-convergence and B-modes. To study the accuracy of
forward-modelling and full-sky power spectrum recovery we consider both
large-area survey geometries, and small-scale masking due to stars and a
checkerboard model for field-of-view gaps. The power spectrum for the
large-area survey geometry is sparsely-sampled and highly oscillatory, which
makes modelling problematic. Instead, we derive an overall calibration for
large-area mask bias using simulated fields. The effects of small-area star
masks can be accurately corrected for, while the checkerboard mask has
oscillatory and spiky behaviour which leads to percent biases. Apodisation of
the masked fields leads to increased biases and a loss of information. We find
that we can construct an unbiased forward-model of the raw PCls, and recover
the full-sky convergence power to within a few percent accuracy for both
Gaussian and lognormal-distributed shear fields. Propagating this through to
cosmological parameters using a Fisher-Matrix formalism, we find we can make
unbiased estimates of parameters for surveys up to 1,200 deg$^2$ with 30
galaxies per arcmin$^2$, beyond which the percent biases become larger than the
statistical accuracy. This implies a flat-sky PCl analysis is accurate for
current surveys but a Euclid-like survey will require higher accuracy. | DBI Galileon and Late time acceleration of the universe: We consider 1+3 dimensional maximally symmetric Minkowski brane embedded in a
1+4 dimensional maximally symmetric Minkowski background. The resulting 1+3
dimensional effective field theory is of DBI (Dirac-Born-Infeld) Galileon type.
We use this model to study the late time acceleration of the universe. We study
the deviation of the model from the concordance \Lambda CDM behaviour. Finally
we put constraints on the model parameters using various observational data. |
Galaxy Infall Kinematics as a Test of Modified Gravity: Infrared modifications of General Relativity (GR) can be revealed by
comparing the mass of galaxy clusters estimated from weak lensing to that from
infall kinematics. We measure the 2D galaxy velocity distribution in the
cluster infall region by applying the galaxy infall kinematics (GIK) model
developed by Zu and Weinberg (2013) to two suites of f(R) and Galileon modified
gravity simulations. Despite having distinct screening mechanisms, namely, the
Chameleon and the Vainshtein effects, the f(R) and Galileon clusters exhibit
very similar deviations in their GIK profiles from GR, with ~ 100-200 k/s
enhancement in the characteristic infall velocity at r=5 Mpc/h and 50-100 km/s
broadening in the radial and tangential velocity dispersions across the entire
infall region, for clusters with mass ~ 10^{14} Msol/h at z=0.25. These
deviations are detectable via the GIK reconstruction of the redshift--space
cluster-galaxy cross-correlation function, xi_cg^s(r_p,r_\pi), which shows ~
1-2 Mpc/h increase in the characteristic line-of-sight distance r_\pi^c at
r_p<6 Mpc/h from GR predictions. With overlapping deep imaging and large
redshift surveys in the future, we expect that the GIK modelling of xi_cg^s, in
combination with the stacked weak lensing measurements, will provide powerful
diagnostics of modified gravity theories and the origin of cosmic acceleration. | Flow-Based Likelihoods for Non-Gaussian Inference: We investigate the use of data-driven likelihoods to bypass a key assumption
made in many scientific analyses, which is that the true likelihood of the data
is Gaussian. In particular, we suggest using the optimization targets of
flow-based generative models, a class of models that can capture complex
distributions by transforming a simple base distribution through layers of
nonlinearities. We call these flow-based likelihoods (FBL). We analyze the
accuracy and precision of the reconstructed likelihoods on mock Gaussian data,
and show that simply gauging the quality of samples drawn from the trained
model is not a sufficient indicator that the true likelihood has been learned.
We nevertheless demonstrate that the likelihood can be reconstructed to a
precision equal to that of sampling error due to a finite sample size. We then
apply FBLs to mock weak lensing convergence power spectra, a cosmological
observable that is significantly non-Gaussian (NG). We find that the FBL
captures the NG signatures in the data extremely well, while other commonly
used data-driven likelihoods, such as Gaussian mixture models and independent
component analysis, fail to do so. This suggests that works that have found
small posterior shifts in NG data with data-driven likelihoods such as these
could be underestimating the impact of non-Gaussianity in parameter
constraints. By introducing a suite of tests that can capture different levels
of NG in the data, we show that the success or failure of traditional
data-driven likelihoods can be tied back to the structure of the NG in the
data. Unlike other methods, the flexibility of the FBL makes it successful at
tackling different types of NG simultaneously. Because of this, and
consequently their likely applicability across datasets and domains, we
encourage their use for inference when sufficient mock data are available for
training. |
A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX,
And XI, And XII, and And XIII: We present the first spectroscopic analysis of the faint M31 satellite
galaxies, AndXI and AndXIII, and a reanalysis of existing spectroscopic data
for two further faint companions, And IX and AndXII. By combining data obtained
using the DEIMOS spectrograph mounted on the Keck II telescope with deep
photometry from the Suprime-Cam instrument on Subaru, we have calculated global
properties for the dwarfs, such as systemic velocities, metallicites and
half-light radii.We find each dwarf to be very metal poor ([Fe/H] -2 both
photometrically and spectroscopically, from their stacked spectrum), and as
such, they continue to follow the luminosity-metallicity relationship
established with brighter dwarfs. We are unable to resolve a dispersion for And
XI due to small sample size and low S/N, but we set a one sigma upper limit of
sigma-v <5 km/s. For And IX, And XII and And XIII we resolve velocity
dispersions of v=4.5 (+3.4,-3.2), 2.6(+5.1,-2.6) and 9.7(+8.9,-4.5) km/s, and
derive masses within the half light radii of 6.2(+5.3,-5.1)x10^6 Msun, 2.4
(+6.5,-2.4)x10^6 Msun and 1.1(+1.4,-0.7)x10^7 Msun respectively. We discuss
each satellite in the context of the Mateo relations for dwarf spheroidal
galaxies, and the Universal halo profiles established for Milky Way dwarfs
(Walker et al. 2009). For both galaxies, this sees them fall below the
Universal halo profiles of Walker et al. (2009). When combined with the
findings of McConnachie & Irwin (2006a), which reveal that the M31 satellites
are twice as extended (in terms of both half-light and tidal radii) as their
Milky Way counterparts, these results suggest that the satellite population of
the Andromeda system could inhabit halos that are significantly different from
those of the Milky Way in terms of their central densities (abridged). | Density perturbations for running vacuum: a successful approach to
structure formation and to the $σ_8$-tension: Recent studies suggest that dynamical dark energy (DDE) provides a better fit
to the rising affluence of modern cosmological observations than the
concordance model ($\Lambda$CDM) with a rigid cosmological constant, $\Lambda$.
Such is the case with the running vacuum models (RVMs) and to some extent also
with a simple XCDM parametrization. Apart from the cosmic microwave background
(CMB) anisotropies, the most crucial datasets potentially carrying the DDE
signature are: i) baryonic acoustic oscillations (BAO), and ii) direct large
scale structure (LSS) formation data (i.e. the observations on
$f(z)\sigma_8(z)$ at different redshifts). As it turns out, analyses mainly
focusing on CMB and with insufficient BAO+LSS input, or those just making use
of gravitational weak-lensing data for the description of structure formation,
generally fail to capture the DDE signature, whereas the few existing studies
using a rich set of CMB+BAO+LSS data (see in particular Sol\`a, G\'omez-Valent
& de Cruz P\'erez 2015,2017; and Zhao et al. 2017) do converge to the
remarkable conclusion that DDE might well be encoded in the current
cosmological observations. Being the issue so pressing, here we explain both
analytically and numerically the origin of the possible hints of DDE in the
context of RVMs, which arise at a significance level of $3-4\sigma$. By
performing a detailed study on the matter and vacuum perturbations within the
RVMs, and comparing with the XCDM, we show why the running vacuum fully relaxes
the existing $\sigma_8$-tension and accounts for the LSS formation data much
better than the concordance model. |
Accurate modelling of the Lyman-$α$ coupling for the 21-cm signal,
observability with NenuFAR and SKA: The measurement of the $21$ cm signal from the Cosmic Dawn is a major goal
for several existing and upcoming radio interferometers such as NenuFAR and the
SKA. During this era before the beginning of the Epoch of Reionization, the
signal is more difficult to observe due to brighter foregrounds but reveals
additional information on the underlying astrophysical processes encoded in the
spatial fluctuations of the spin temperature of hydrogen. To interpret future
measurements, controlling the level of accuracy of the Lyman-$\alpha$ flux
modelling is mandatory. In this work, we evaluate the impact of various
approximations that exist in the main fast modelling approach compared to the
results of a costly full radiative transfer simulation. The fast SPINTER code,
presented in this work, computes the Lyman-$\alpha$ flux including the effect
of wing scatterings for an inhomogeneous emissivity field, but assuming an
otherwise homogeneous expanding universe. The LICORICE code computes the full
radiative transfer in the Lyman-$\alpha$ line without any substantial
approximation. We find that the difference between homogeneous and
inhomogeneous gas density and temperature is very small for the computed flux.
On the contrary, neglecting the effect of gas velocities produces a significant
change in the computed flux. We identify the causes (mainly Doppler shifts due
to velocity gradients) and quantify the magnitude of the effect in both an
idealised setup and a realistic cosmological situation. We find that the
amplitude of the effect, up to a factor of $\sim 2$ on the $21$ cm signal power
spectrum on some scales (depending on both other model parameters and the
redshift), can be easily discriminated with an SKA-like survey and already be
approached, particularly for exotic signals, by the ongoing NenuFAR Cosmic Dawn
Key Science Program. | Long Gamma-Ray Burst Host Galaxies and their Environments: In this book-chapter we first briefly discuss some basic observational issues
related to what a GRB host galaxy is (whether they are operationally well
defined as a class) and sample completeness. We then describe some of the early
studies of GRB hosts starting with statistical studies of upper limits done
prior to the first detections, the first host detection after the BeppoSAX
breakthrough and leading up to the current Swift era. Finally, we discuss the
status of efforts to construct a more complete sample of GRBs based on Swift
and end with an outlook. We only consider the host galaxies of long-duration
GRBs. |
Determining dust temperatures and masses in the Herschel era: the
importance of observations longward of 200 micron: The properties of the dust grains (e.g., temperature and mass) can be derived
from fitting far-IR SEDs (>100 micron). Only with SPIRE on Herschel has it been
possible to get high spatial resolution at 200 to 500 micron that is beyond the
peak (~160 micron) of dust emission in most galaxies. We investigate the
differences in the fitted dust temperatures and masses determined using only
<200 micron data and then also including >200 micron data (new SPIRE
observations) to determine how important having >200 micron data is for
deriving these dust properties. We fit the 100 to 350 micron observations of
the Large Magellanic Cloud (LMC) point-by-point with a model that consists of a
single temperature and fixed emissivity law. The data used are existing
observations at 100 and 160 micron (from IRAS and Spitzer) and new SPIRE
observations of 1/4 of the LMC observed for the HERITAGE Key Project as part of
the Herschel Science Demonstration phase. The dust temperatures and masses
computed using only 100 and 160 micron data can differ by up to 10% and 36%,
respectively, from those that also include the SPIRE 250 & 350 micron data. We
find that an emissivity law proportional to lambda^-1.5 minimizes the 100-350
micron fractional residuals. We find that the emission at 500 micron is ~10%
higher than expected from extrapolating the fits made at shorter wavelengths.
We find the fractional 500 micron excess is weakly anti-correlated with MIPS 24
micron flux and the total gas surface density. This argues against a flux
calibration error as the origin of the 500 micron excess. Our results do not
allow us to distinguish between a systematic variation in the wavelength
dependent emissivity law or a population of very cold dust only detectable at
lambda > 500 micron for the origin of the 500 micron excess. | Subhalo effective density slope measurements from HST strong lensing
data with neural likelihood-ratio estimation: Examining the properties of subhalos with strong gravitational lensing images
can shed light on the nature of dark matter. From upcoming large-scale surveys,
we expect to discover orders of magnitude more strong lens systems that can be
used for subhalo studies. To optimally extract information from a large number
of strong lensing images, machine learning provides promising avenues for
efficient analysis that is unachievable with traditional analysis methods, but
application of machine learning techniques to real observations is still
limited. We build upon previous work, which uses a neural likelihood-ratio
estimator, to constrain the effective density slopes of subhalos and
demonstrate the feasibility of this method on real strong lensing observations.
To do this, we implement significant improvements to the forward simulation
pipeline and undertake careful model evaluation using simulated images.
Ultimately, we use our trained model to predict the effective subhalo density
slope from combining a set of strong lensing images taken by the \textit{Hubble
Space Telescope}. We found the subhalo slope measurement of this set of
observations to be steeper than the slope predictions of cold dark matter
subhalos. Our result adds to several previous works that also measured high
subhalo slopes in observations. Although a possible explanation for this is
that subhalos with steeper slopes are easier to detect due to selection effects
and thus contribute to statistical bias, our result nevertheless points to the
need for careful analysis of more strong lensing observations from future
surveys. |
Multicolour-metallicity Relations from Globular Clusters in NGC 4486
(M87): We present Gemini griz photometry for 521 globular cluster (GC) candidates in
a 5.5 x 5.5 arcmin field centered 3.8 arcmin to the south and 0.9 arcmin to the
west of the center of the giant elliptical galaxy NGC 4486. All these objects
have previously published (C-T1) photometry. We also present new (C-T1)
photometry for 338 globulars, within 1.7 arcmin in galactocentric radius, which
have (g-z) colors in the photometric system adopted by the Virgo Cluster Survey
of the Advanced Camera for Surveys of the Hubble Space Telescope. These
photometric data are used to define a self-consistent multicolor grid (avoiding
polynomial fits) and preliminary calibrated in terms of two chemical abundance
scales. The resulting multicolor color-chemical abundance relations are used to
test GC chemical abundance distributions. This is accomplished by modelling the
ten GC color histograms that can be defined in terms of the Cgriz bands. Our
results suggest that the best fit to the GC observed color histograms is
consistent with a genuinely bimodal chemical abundance distribution NGC(Z). On
the other side, each (blue and red) GC subpopulation follows a distinct
color-color relation. | Does the Hubble constant tension call for new physics?: The $\Lambda$ Cold Dark Matter model ($\Lambda$CDM) represents the current
standard model in cosmology. Within this, there is a tension between the value
of the Hubble constant, $H_0$, inferred from local distance indicators and the
angular scale of fluctuations in the Cosmic Microwave Background (CMB). We
investigate whether the tension is significant enough to warrant new physics in
the form of modifying or adding energy components to the standard cosmological
model. We find that late time dark energy explanations are slightly disfavoured
whereas a pre-CMB decoupling extra dark energy component has a marginally
positive Bayesian evidence. A constant equation of state of the additional
early energy density is constrained to 0.086$^{+0.04}_{-0.03}$. Although this
value deviates significantly from 1/3, valid for dark radiation, the latter is
not disfavoured based on the Bayesian evidence. If the tension persists, future
estimates of $H_0$ at the 1$\%$ level will be able to decisively determine
which of the proposed explanations is favoured. |
Small-scale systems of galaxies. IV. Searching for the faint galaxy
population associated with X-ray detected isolated E+S pairs: In hierarchical evolutionary scenarios, isolated, physical pairs may
represent an intermediate phase, or "way station", between collapsing groups
and isolated elliptical (E) galaxies (or fossil groups). We started a
comprehensive study of a sample of galaxy pairs composed of a giant E and a
spiral (S) with the aim of investigating their formation/evolutionary history
from observed optical and X-ray properties. Here we present VLT-VIMOS
observations designed to identify faint galaxies associated with the E+S
systems from candidate lists generated using photometric criteria on WFI images
covering an area of ~ 0.2 h^{-1} Mpc radius around the pairs.
The results are discussed in the context of the evolution of poor galaxy
group associations. A comparison between the Optical Luminosity Functions
(OLFs) of our E+S systems and a sample of X-ray bright poor groups suggest that
the OLF of X-ray detected poor galaxy systems is not universal. The OLF of our
X-ray bright systems suggests that they are more dynamically evolved than our
X-ray faint sample and some X-ray bright groups in the literature. However, we
suggest that the X-ray faint E+S pairs represent a phase in the dynamical
evolution of some X-ray bright poor galaxy groups. The recent or ongoing
interaction in which the E member of the X-ray faint pairs is involved could
have decreased the luminosity of any surrounding X-ray emitting gas. | A novel variability-based method for quasar selection: evidence for a
rest frame ~54 day characteristic timescale: We compare quasar selection techniques based on their optical variability
using data from the Catalina Real-time Transient Survey (CRTS). We introduce a
new technique based on Slepian wavelet variance (SWV) that shows comparable or
better performance to structure functions and damped random walk models but
with fewer assumptions. Combining these methods with WISE mid-IR colors
produces a highly efficient quasar selection technique which we have validated
spectroscopically. The SWV technique also identifies characteristic timescales
in a time series and we find a characteristic rest frame timescale of ~54 days,
confirmed in the light curves of ~18000 quasars from CRTS, SDSS and MACHO data,
and anticorrelated with absolute magnitude. This indicates a transition between
a damped random walk and $P(f) \propto f^{-1/3}$ behaviours and is the first
strong indication that a damped random walk model may be too simplistic to
describe optical quasar variability. |
Superdense Massive Galaxies in Wings Local Clusters: Massive quiescent galaxies at z>1 have been found to have small physical
sizes, hence to be superdense. Several mechanisms, including minor mergers,
have been proposed for increasing galaxy sizes from high- to low-z. We search
for superdense massive galaxies in the WIde-field Nearby Galaxy-cluster Survey
(WINGS) of X-ray selected galaxy clusters at 0.04<z<0.07. We discover a
significant population of superdense massive galaxies with masses and sizes
comparable to those observed at high redshift. They approximately represent 22%
of all cluster galaxies more massive than 3x10^10Msol, are mostly S0 galaxies,
have a median effective radius <Re> =1.61+/-0.29kpc, a median Sersic index <n>
= 3.0+/-0.6, and very old stellar populations with a median mass-weighted age
of 12.1+/-1.3Gyr. We calculate a number density of 2.9x10^-2Mpc^-3 for
superdense galaxies in local clusters, and a hard lower limit of
1.3x10^-5Mpc^-3 in the whole comoving volume between z = 0.04 and z = 0.07. We
find a relation between mass, effective radius and luminosity-weighted age in
our cluster galaxies, which can mimic the claimed evolution of the radius with
redshift, if not properly taken into account. We compare our data with
spectroscopic high-z surveys and find that -when stellar masses are considered-
there is consistency with the local WINGS galaxy sizes out to z~2, while a
discrepancy of a factor of 3 exists with the only spectroscopic z>2 study. In
contrast, there is strong evidence for a large evolution in radius for the most
massive galaxies with M*>4x10^11Msol compared to similarly massive galaxies in
WINGS, i.e. the BCGs. | Einstein's legacy in galaxy surveys: Non-Gaussianity in the primordial fluctuations that seeded structure
formation produces a signal in the galaxy power spectrum on very large scales.
This signal contains vital information about the primordial Universe, but it is
very challenging to extract, because of cosmic variance and large-scale
systematics - especially after the Planck experiment has already ruled out a
large amplitude for the signal. Cosmic variance and experimental systematics
can be alleviated by the multi-tracer method. Here we address another
systematic - introduced by not using the correct relativistic analysis of the
power spectrum on very large scales. In order to reduce the errors on fNL, we
need to include measurements on the largest possible scales. Failure to include
the relativistic effects on these scales can introduce significant bias in the
best-fit value of fNL from future galaxy surveys. |
Damped Lyman-alpha absorbers as a probe of stellar feedback: We examine the abundance, clustering and metallicity of Damped Lyman-alpha
Absorbers (DLAs) in a suite of hydrodynamic cosmological simulations using the
moving mesh code AREPO. We incorporate models of supernova and AGN feedback, as
well as molecular hydrogen formation. We compare our simulations to the column
density distribution function at $z=3$, the total DLA abundance at $z=2-4$, the
measured DLA bias at $z=2.3$ and the DLA metallicity distribution at $z=2-4$.
Our preferred models produce populations of DLAs in good agreement with most of
these observations. The exception is the DLA abundance at $z < 3$, which we
show requires stronger feedback in $10^{11-12} \, h^{-1} M_\odot$ mass halos.
While the DLA population probes a wide range of halo masses, we find the
cross-section is dominated by halos of mass $10^{10} - 10^{11} \, h^{-1}
M_\odot$ and virial velocities $50 - 100 \;\mathrm{km/s}$. The simulated DLA
population has a linear theory bias of $1.7$, whereas the observations require
$2.17 \pm 0.2$. We show that non-linear growth increases the bias in our
simulations to $2.3$ at $k=1\; \mathrm{Mpc/}h$, the smallest scale observed.
The scale-dependence of the bias is, however, very different in the simulations
compared against the observations. We show that, of the observations we
consider, the DLA abundance and column density function provide the strongest
constraints on the feedback model. | One-Dimensional Fuzzy Dark Matter Models: Structure Growth and
Asymptotic Dynamics: This paper investigates the feasibility of simulating Fuzzy Dark Matter (FDM)
with a reduced number of spatial dimensions. Our aim is to set up a realistic,
yet numerically inexpensive, toy model in $(1+1)$-dimensional space time, that
- under well controlled system conditions - is capable of realizing important
aspects of the full-fledged $(3+1)$-FDM phenomenology by means of
one-dimensional analogues. Based on the coupled, nonlinear and nonlocal
$(3+1)$-Schr\"odinger-Poisson equation under periodic boundary conditions, we
derive two distinct one-dimensional models that differ in their transversal
matter distribution and consequently in their nonlocal interaction along the
single dimension of interest. We show that these discrepancies change the
relaxation process of initial states as well as the asymptotic, i.e.,
thermalized and virialized, equilibrium state. Our investigation includes the
dynamical evolution of artificial initial conditions for non-expanding space,
as well as cosmological initial conditions in expanding space. The findings of
this work are relevant for the interpretation of numerical simulation data
modelling nonrelativistic fuzzy cold dark matter in reduced dimensions, in the
quest for testing such models and for possible laboratory implementations of
them. |
Statistical Properties of Multi-epoch Spectral Variability of SDSS
Stripe82 Quasars: We investigate the UV-optical (longward of Ly$\alpha$ 1216\AA) spectral
variability of nearly 9000 quasars ($0<z<4$) using multi-epoch photometric data
within the SDSS Stripe 82 region. The regression slope in the flux-flux space
of a quasar light curve directly measures the color of the flux difference
spectrum, then the spectral shape of the flux difference spectra can be derived
by taking a careful look at the redshift dependence of the regression slopes.
First, we confirm that the observed quasar spectrum becomes bluer when the
quasar becomes brighter. We infer the spectral index of the composite
difference spectrum as $\alpha_{\nu}^{\text{dif}}\sim +1/3$ (in the form of
$f_{\nu}\propto \nu^{\alpha_{\nu}}$), which is significantly bluer than that of
the composite spectrum $\alpha_{\nu}^{\text{com}}\sim -0.5$. We also show that
the continuum variability cannot be explained by the accretion disk models with
varying mass accretion rate. Second, we examine the effects of broad emission
line variability on the color-redshift space. The variability of the "Small
Blue Bump" is extensively discussed. We show that the low-ionization lines of
MgII and FeII are less variable compared to Balmer emission lines and
high-ionization lines, and the Balmer continuum is the dominant variable source
around $\sim 3000$\AA. These results are compared with previous studies, and
the physical mechanisms of the variability of the continuum and emission lines
are discussed. | Gravitational waves from bubble collisions: analytic derivation: We consider gravitational wave production by bubble collisions during a
cosmological first-order phase transition. In the literature, such spectra have
been estimated by simulating the bubble dynamics, under so-called thin-wall and
envelope approximations in a flat background metric. However, we show that,
within these assumptions, the gravitational wave spectrum can be estimated in
an analytic way. Our estimation is based on the observation that the two-point
correlator of the energy-momentum tensor $\langle T(x)T(y)\rangle$ can be
expressed analytically under these assumptions. Though the final expressions
for the spectrum contain a few integrations that cannot be calculated
explicitly, we can easily estimate it numerically. As a result, it is found
that the most of the contributions to the spectrum come from single-bubble
contribution to the correlator, and in addition the fall-off of the spectrum at
high frequencies is found to be proportional to $f^{-1}$. We also provide
fitting formulae for the spectrum. |
LBQS 0103-2753: A Binary Quasar in a Major Merger: We present HST and UKIRT spectra and images of the 2 kpc binary quasar LBQS
0103-2753 (z=0.858). The HST images (V- and I-band) show tidal features
demonstrating that this system is a major galaxy merger in progress. A
two-color composite image brings out knots of star formation along the tidal
arc and elsewhere. The infrared spectrum shows that both objects are at the
same redshift, and that the discrepant redshift of C IV in component A is a
consequence of the BAL absorption in the spectrum of this component. LBQS
0103-2753 is one of the most closely spaced binary QSOs known, and is one of
relatively few dual AGN showing confirmed broad emission lines from both
components. While statistical studies of binary QSOs suggest that simultaneous
fueling of both black holes during a merger may be relatively rare, LBQS
0103-2753 demonstrates that such fueling can occur at high luminosity at a late
stage in the merger at nuclear spacing of only a few kpc, without severe
obscuration of the nuclei. | $α$ attractors in Quintessential Inflation motivated by
Supergravity: An exponential kind of quintessential inflation potential motivated by
supergravity is studied. This type belongs to the class of {\alpha}-attractor
models. The model was studied for the first time by Dimopoulos and Owen in [J.
Cosmol. Astropart. Phys. 06 (2017) 027], in which the authors introduced a
negative cosmological constant in order to ensure a zero-vacuum energy density
at late times. However, in this paper, we disregard this cosmological constant,
showing that the obtained results are very close to the ones obtained recently
in the context of Lorentzian quintessential inflation and thus depicting with
great accuracy the early- and late-time acceleration of our Universe. The model
is compatible with the recent observations. Finally, we review the treatment of
the {\alpha}-attractor and we show that our potential depicts the late time
cosmic acceleration with an effective equation of state equal to -1. |
Dynamics of Scalar Field Dark Matter With a Cosh-like Potential: The dynamics of a cosmological model fueled by scalar field dark matter with
a cosh-like potential plus a cosmological constant is investigated in detail.
It is revealed that the late-time attractor is always the de Sitter solution,
and that, depending on the values of the free parameters, the oscillating
solution of the scalar field -- modeling cold dark matter -- mediates between
some early stage (say, the radiation-dominated solution) and the accelerating
de Sitter attractor. | Observational Evidence Against Long-Lived Spiral Arms in Galaxies: We test whether the spiral patterns apparent in many large disk galaxies
should be thought of as dynamical features that are stationary in a co-rotating
frame for > t_{dyn}, as implied by the density wave approach for explaining
spiral arms. If such spiral arms have enhanced star formation (SF),
observational tracers for different stages of the SF sequence should show a
spatial ordering, from up-stream to downstream in the corotating frame: dense
HI, CO, tracing molecular hydrogen gas, 24 micron emission tracing enshrouded
SF and UV emission tracing unobscured young stars. We argue that such a spatial
ordering should be reflected in the angular cross-correlation (CC, in polar
coordinates) using all azimuthal positions among pairs of these tracers; the
peak of the CC should be offset from zero, in different directions inside and
outside the corotation radius. Recent spiral SF simulations by Dobbs & Pringle,
show explicitly that for the case of a stationary spiral arm potential such
angular offsets between gas and young stars of differing ages should be
observable as cross-correlation offsets. We calculate the angular
cross-correlations for different observational SF sequence tracers in 12 nearby
spiral galaxies, drawing on a data set with high quality maps of the neutral
gas HI, THINGS), molecular gas (CO, HERACLES) along with 24 micron emission
(Spitzer, SINGS); we include FUV images (GALEX) and 3.6 $\mu$m emission
(Spitzer, IRAC) for some galaxies, tracing aging stars and longer timescales.
In none of the resulting tracer cross-correlations for this sample do we find
systematic angular offsets, which would be expected for a stationary dynamical
spiral pattern of well-defined pattern speed. This result indicates that spiral
density waves in their simplest form are not an important aspect of explaining
spirals in large disk galaxies. |
Capse.jl: efficient and auto-differentiable CMB power spectra emulation: We present Capse.jl, a novel neural network-based emulator designed for rapid
and accurate prediction of Cosmic Microwave Background (CMB) temperature,
polarization, and lensing angular power spectra. The emulator computes
predictions in just a few microseconds with emulation errors below $0.1\sigma$
for all the scales relevant for the upcoming CMB-S4 survey. Capse.jl can also
be trained in an hour's time on a 8-cores CPU. We test Capse.jl on Planck 2018,
ACT DR4, and 2018 SPT-3G data and demonstrate its capability to derive
cosmological constraints comparable to those obtained by traditional methods,
but with a computational efficiency that is three to six orders of magnitude
higher. We take advantage of the differentiability of our emulators to use
gradient-based methods, such as Pathfinder and Hamiltonian Monte Carlo (HMC),
which speed up the convergence and increase sampling efficiency. Together,
these features make Capse.jl a powerful tool for studying the CMB and its
implications for cosmology. When using the fastest combination of our
likelihoods, emulators, and analysis algorithm, we are able to perform a
Plancky TT + TE + EE analysis in less than a second. To ensure full
reproducibility, we provide open access to the codes and data required to
reproduce all the results of this work. | An Atlas of Galaxy Spectral Energy Distributions from the Ultraviolet to
the Mid-Infrared: We present an atlas of 129 spectral energy distributions for nearby galaxies,
with wavelength coverage spanning from the UV to the mid-infrared. Our atlas
spans a broad range of galaxy types, including ellipticals, spirals, merging
galaxies, blue compact dwarfs and luminous infrared galaxies. We have combined
ground-based optical drift-scan spectrophotometry with infrared spectroscopy
from Spitzer and Akari, with gaps in spectral coverage being filled using
MAGPHYS spectral energy distribution models. The spectroscopy and models were
normalized, constrained and verified with matched-aperture photometry measured
from Swift, GALEX, SDSS, 2MASS, Spitzer and WISE images. The availability of 26
photometric bands allowed us to identify and mitigate systematic errors present
in the data. Comparison of our spectral energy distributions with other
template libraries and the observed colors of galaxies indicates that we have
smaller systematic errors than existing atlases, while spanning a broader range
of galaxy types. Relative to the prior literature, our atlas will provide
improved K-corrections, photometric redshifts and star-formation rate
calibrations. |
Exploring the Galaxy Mass-Metallicity Relation at z~3-5: Long-duration gamma-ray bursts (GRBs) provide a premier tool for studying
high-redshift star-forming galaxies thanks to their extreme brightness and
association with massive stars. Here we use GRBs to study the galaxy stellar
mass-metallicity (M*-Z) relation at z~3-5, where conventional direct
metallicity measurements are extremely challenging. We use the ISM
metallicities of LGRB hosts derived from afterglow absorption spectroscopy
(Z~0.01-1 solar), in conjunction with host galaxy stellar masses determined
from deep Spitzer 3.6 micron observations of 20 GRB hosts. We detect about 1/4
of the hosts with I-band magnitudes ~ -21.5 to -22.5 AB mag, and place a limit
of M > -19 mag on the remaining hosts from a stacking analysis. Using these
observations, we present the first rest-frame optical luminosity distribution
of long GRB hosts at z>3 and find that it is similar to the distribution of
long GRB hosts at z~1. In comparison to Lyman-break galaxies at the same
redshift, GRB hosts are generally fainter, but the sample is too small to rule
out an overall similar luminosity function. On the other hand, the GRB hosts
appear to be more luminous than the population of Lyman-alpha emitters at
z~3-4. Using a conservative range of mass-to-light ratios for simple stellar
populations (with ages of 70 Myr to ~2 Gyr), we infer the host stellar masses
and present mass-metallicity measurements at z~3-5 (<z> ~ 3.5). We find that
the detected GRB hosts, with M*~2e10 solar masses, display a wide range of
metallicities, but that the mean metallicity at this mass scale, Z~0.1 solar,
is lower than measurements at z<3. Combined with stacking of the non-detected
hosts with M*< 3e9 solar masses and Z<0.03 solar, we find evidence for the
existence of an M*-Z relation at z~3.5 and continued evolution of this relation
to systematically lower metallicities from z~2. | Interplanetary Dust as a Foreground for the LiteBIRD CMB Satellite
Mission: As ever-more sensitive experiments are made in the quest for primordial CMB B
Modes, the number of potentially significant astrophysical contaminants becomes
larger as well. Thermal emission from interplanetary dust, for example, has
been detected by the Planck satellite. While the polarization fraction of this
Zodiacal, or interplanetary dust emission (IPDE) is expected to be low, it is
bright enough to be detected in total power. Here, estimates of the magnitude
of the effect as it might be seen by the LiteBIRD satellite are made. The COBE
IPDE model from Kelsall et al. (1998) is combined with a model of the LiteBIRD
experiment's scanning strategy to estimate potential contamination of the CMB
in both total power and in polarization power spectra. LiteBIRD should detect
IPDE in temperature across all of its bands, from 40 through 402 GHz, and
should improve limits on the polarization fraction of IPDE at the higher end of
this frequency range. If the polarization fraction of IPDE is of order 1%, the
current limit from ISO/CAM measurements in the mid-infrared, it may induce
large-scale polarization B Modes comparable to cosmological models with an r of
order 0.001. In this case, the polarized IPDE would also need to be modeled and
removed. As a CMB foreground, IPDE will always be subdominant to Galactic
emissions, though because it caused by emission from grains closer to us, it
appears variable as the Earth travels around the Sun, and may thereby
complicate the data analysis somewhat. But with an understanding of some of the
symmetries of the emission and some flexibility in the data processing, it
should not be the primary impediment to the CMB polarization measurement. |
Effects of thermal inflation on small scale density perturbations: In cosmological scenarios with thermal inflation, extra eras of moduli matter
domination, thermal inflation and flaton matter domination exist between
primordial inflation and the radiation domination of Big Bang nucleosynthesis.
During these eras, cosmological perturbations on small scales can enter and
re-exit the horizon, modifying the power spectrum on those scales. The largest
modified scale, $k_\mathrm{b}$, touches the horizon size when the expansion
changes from deflation to inflation at the transition from moduli domination to
thermal inflation. We analytically calculate the evolution of perturbations
from moduli domination through thermal inflation and evaluate the curvature
perturbation on the constant radiation density hypersurface at the end of
thermal inflation to determine the late time curvature perturbation. Our
resulting transfer function suppresses the power spectrum by a factor $\sim 50$
at $k \gg k_\mathrm{b}$, with $k_\mathrm{b}$ corresponding to anywhere from
megaparsec to subparsec scales depending on the parameters of thermal
inflation. Thus, thermal inflation might be constrained or detected by small
scale observations such as CMB distortions or 21cm hydrogen line observations. | Cosmic slowing down of acceleration for several dark energy
parametrizations: We further investigate slowing down of acceleration of the universe scenario
for five parametrizations of the equation of state of dark energy using four
sets of supernovae data. In a maximal probability analysis we also use the
baryon acoustic oscillation and cosmic microwave background observations. We
found the low redshift transition of the deceleration parameter appears,
independently of the parametrization, using supernovae data alone except for
the Union 2.1 sample. This feature disappears once we combine the supernova
data with high redshift data. We conclude that the rapid variation of the
deceleration parameter is independent of the parametrization. We also found
more evidence for a tension among the supernovae samples, as well as for the
low and high redshift data. |
Fast LiH destruction in reaction with H: quantum calculations and
astrophysical consequences: We present a quantum-mechanical study of the exothermic 7LiH reaction with H.
Accurate reactive probabilities and rate coefficients are obtained by solving
the Schrodinger equation for the motion of the three nuclei on a single
Born-Oppenheimer potential energy surface (PES) and using a coupled-channel
hyperspherical coordinate method. Our new rates indeed confirm earlier,
qualitative predictions and some previous theoretical calculations, as
discussed in the main text. In the astrophysical domain we find that the
depletion process largely dominates for redshift (z) between 400 and 100, a
range significant for early Universe models. This new result from
first-principle calculations leads us to definitively surmise that LiH should
be already destroyed when the survival processes become important. Because of
this very rapid depletion reaction, the fractional abundance of LiH is found to
be drastically reduced, so that it should be very difficult to manage to
observe it as an imprinted species in the cosmic background radiation (CBR).
The present findings appear to settle the question of LiH observability in the
early Universe. We further report several state-to-state computed reaction
rates in the same range of temperatures of interest for the present problem. | Comparative Analysis of TRGBs (CATs) from Unsupervised, Multi-Halo-Field
Measurements: Contrast is Key: The Tip of the Red Giant Branch (TRGB) is an apparent discontinuity in the
color-magnitude diagram (CMD) along the giant branch due to the end of the red
giant evolutionary phase and is used to measure distances in the local
universe. In practice, the tip is often fuzzy and its localization via edge
detection response (EDR) relies on several methods applied on a case-by-case
basis. It is hard to evaluate how individual choices affect a distance
estimation using only a single host field while also avoiding confirmation
bias. To devise a standardized approach, we compare unsupervised, algorithmic
analyses of the TRGB in multiple halo fields per galaxy, up to 11 fields for a
single host and 50 fields across 10 galaxies, using high signal-to-noise
stellar photometry obtained by the GHOSTS survey with the Hubble Space
Telescope. We first optimize methods for the lowest field-to-field dispersion
including spatial filtering to remove star forming regions, smoothing and
weighting of the luminosity function, selection of the RGB by color, and tip
selection based on the number of likely RGB stars and the ratio of stars above
versus below the tip ($R$). We find $R$, which we call the tip `contrast', to
be the most important indicator of the quality of EDR measurements; we find
that field-to-field EDR repeatability varies from 0.3 mag to $\leq$ 0.05 mag
for $R=4$ to 7, respectively, though less than half the fields reach the higher
quality. Further, we find that $R$, which varies with the age/metallicity of
the stellar population based on models, correlates with the magnitude of the
tip (and after accounting for low internal extinction), i.e., a tip-contrast
relation with slope of $-0.023\pm0.0046$ mag/ratio, a $\sim 5\sigma$ result
that improves standardization of the TRGB. We discuss the value of consistent
TRGB standardization across rungs for robust distance ladder measurements. |
Dark-ages Reionization and Galaxy Formation Simulation XX. The
Ly$α$ IGM transmission properties and environment of bright galaxies
during the Epoch of Reionization: The highly neutral inter-galactic medium (IGM) during the Epoch of
Reionization (EoR) is expected to suppress Ly$\alpha$ emission with
damping-wing absorption, causing nearly no Ly$\alpha$ detection from
star-forming galaxies at $z{\sim}8$. However, spectroscopic observations of the
4 brightest galaxies (${\rm H}_{160}{\sim}25$ mag) at these redshifts do reveal
prominent Ly$\alpha$ line, suggesting locally ionised IGM. In this paper, we
explore the Ly$\alpha$ IGM transmission and environment of bright galaxies
during the EoR using the Meraxes semi-analytic model. We find brighter galaxies
to be less affected by damping-wing absorption as they are effective at
ionizing surrounding neutral hydrogen. Specifically, the brightest sources
(${\rm H}_{160}{\lesssim}25.5$ mag) lie in the largest ionized regions in our
simulation, and have low attenuation of their Ly$\alpha$ from the IGM (optical
depth ${<}1$). Fainter galaxies (25.5 mag${<}{\rm H}_{160}{<}27.5$ mag) have
transmission that depends on UV luminosity, leading to a lower incidence of
Ly$\alpha$ detection at fainter magnitudes. This luminosity-dependent
attenuation explains why Ly$\alpha$ has only been observed in the brightest
galaxies at $z{\sim}8$. Follow-up observations have revealed counterparts in
the vicinity of these confirmed $z{\sim}8$ Ly$\alpha$ emitters. The
environments of our modelled analogues agree with these observations in the
number of nearby galaxies, which is a good indicator of whether Ly$\alpha$ can
be detected among fainter galaxies. At the current observational limit,
galaxies with ${\ge}2$--5 neighbours within $2'{\times}2'$ are ${\sim}2$--3
times more likely to show Ly$\alpha$ emission. JWST will discover an order of
magnitude more neighbours, revealing ${\gtrsim}50$ galaxies in the largest
ionizing bubbles and facilitating direct study of reionization morphology. | Constraining the inflationary potential with spectral distortions: Measuring spectral distortions (SDs) of the cosmic microwave background (CMB)
will provide new constraints on previously unexplored scales of the primordial
power spectrum, allowing us to extend the probed parameter space by several
orders of magnitude in $k$-space, which could have significant implications in
the context of primordial black holes and gravitational waves, among others.
Here we discuss how various models of inflation can be tightly constrained by
the combination of current and future CMB SD and anisotropy experiments. In
particular, we investigate the constraining power of SD experiments such as
FIRAS, PIXIE, and PRISM in conjunction with CMB anisotropy probes such as
Planck or CMB-S4 plus LiteBIRD. Building on the latest version of the Boltzmann
solver CLASS (v3.0), here we also consistently marginalize over the possible
galactic and extra-galactic foregrounds for the SD missions. With this
numerical setup, we are able to realistically forecast the improvements that
the increased lever-arm provided by the addition of the various SD missions
will bring for several combinations of the aforementioned experiments. As a
result, in all considered models we observe that SDs provide a highly
significant tightening of the constraints by up to 640%, and increase the
figure of merit up to a factor of around 1600. |
Using galaxy pairs as cosmological tracers: The Alcock-Paczynski (AP) effect uses the fact that, when analyzed with the
correct geometry, we should observe structure that is statistically isotropic
in the Universe. For structure undergoing cosmological expansion with the
background, this constrains the product of the Hubble parameter and the angular
diameter distance. However, the expansion of the Universe is inhomogeneous and
local curvature depends on density. We argue that this distorts the AP effect
on small scales. After analyzing the dynamics of galaxy pairs in the Millennium
simulation, we find an interplay between peculiar velocities, galaxy properties
and local density that affects how pairs trace cosmological expansion. We find
that only low mass, isolated galaxy pairs trace the average expansion with a
minimum "correction" for peculiar velocities. Other pairs require larger, more
cosmology and redshift dependent peculiar velocity corrections and, in the
small-separation limit of being bound in a collapsed system, do not carry
cosmological information. | Efficiency of pseudo-spectrum methods for estimation of Cosmic Microwave
Background B-mode power spectrum: Estimation of the B-mode angular power spectrum of polarized anisotropies of
the cosmic microwave background (CMB) is a key step towards a full exploitation
of the scientific potential of this probe. In the context of pseudo-spectrum
methods the major challenge is related to a contamination of the B-mode
spectrum estimate with residual power of much larger E-mode. This so-called
E-to-B leakage is unavoidably present whenever an incomplete sky map is only
available, as is the case for any realistic observation. The leakage has to be
then minimized or removed and ideally in such a way that neither a bias nor
extra variance is introduced. In this paper, we compare from these two
perspectives three different methods proposed recently in this context Refs.
Smith 2006, Zhao & Baskaran 2010, Kim & Naselsky 2010, which we first introduce
within a common algebraic framework of the so-called chi-fields and then study
their performance on two different experimental configurations - one
corresponding to a small-scale experiment covering 1% of the sky motivated by
current ground-based or balloon-borne experiments and another - to a nearly
full-sky experiment, e.g., a possible CMB B-mode satellite mission. We find
that though all these methods allow to reduce significantly the level of the
E-to-B leakage, it is the method of Smith 2006, which at the same time ensures
the smallest error bars in all experimental configurations studied here, owing
to the fact that it permits straightforwardly for an optimization of the sky
apodization of the polarization maps used for the estimation. For a
satellite-like experiment, this method enables a detection of B-mode power
spectrum at large angular scales but only after appropriate binning. The method
of Zhao & Baskaran 2010 is a close runner-up in the case of a nearly full sky
coverage. |
Seeing in the dark -- II. Cosmic shear in the Sloan Digital Sky Survey: Statistical weak lensing by large-scale structure -- cosmic shear -- is a
promising cosmological tool, which has motivated the design of several large
upcoming surveys. Here, we present a measurement of cosmic shear using coadded
Sloan Digital Sky Survey (SDSS) imaging in 168 square degrees of the equatorial
region, with r<23.5 and i<22.5, a source number density of 2.2 galaxies per
square arcminute and median redshift of 0.52. These coadds were generated using
a new method described in the companion Paper I that was intended to minimise
systematic errors in the lensing measurement due to coherent PSF anisotropies
that are otherwise prevalent in the SDSS imaging data. We present measurements
of cosmic shear out to angular separations of 2 degrees, along with systematics
tests that (combined with those from Paper I on the catalogue generation)
demonstrate that our results are dominated by statistical rather than
systematic errors. Assuming a cosmological model corresponding to WMAP7 and
allowing only the amplitude of matter fluctuations to vary, we find a best-fit
value of sigma_8=0.636 +0.109 -0.154 (1-sigma); without systematic errors this
would be sigma_8=0.636 +0.099 -0.137 (1-sigma). Assuming a flat LCDM model, the
combined constraints with WMAP7 are sigma_8=0.784 +0.028 -0.026 (1-sigma),
+0.055 -0.054 (2-sigma) and Omega_m h^2=0.1303 +0.0047 -0.0048 (1-sigma)+0.009
-0.009 (2-sigma); the 2-sigma error ranges are respectively 14 and 17 per cent
smaller than WMAP7 alone. Aside from the intrinsic value of such cosmological
constraints from the growth of structure, we identify some important lessons
for upcoming surveys that may face similar issues when combining multi-epoch
data to measure cosmic shear. | Relativistic collapse and explosion of rotating supermassive stars with
thermonuclear effects: We present results of general relativistic simulations of collapsing
supermassive stars with and without rotation using the two-dimensional general
relativistic numerical code Nada, which solves the Einstein equations written
in the BSSN formalism and the general relativistic hydrodynamics equations with
high resolution shock capturing schemes. These numerical simulations use an
equation of state which includes effects of gas pressure, and in a tabulated
form those associated with radiation and the electron-positron pairs. We also
take into account the effect of thermonuclear energy released by hydrogen and
helium burning. We find that objects with a mass of 5x10^{5} solar mass and an
initial metallicity greater than Z_{CNO}~0.007 do explode if non-rotating,
while the threshold metallicity for an explosion is reduced to Z_{CNO}~0.001
for objects uniformly rotating. The critical initial metallicity for a
thermonuclear explosion increases for stars with mass ~10^{6} solar mass. For
those stars that do not explode we follow the evolution beyond the phase of
black hole formation. We compute the neutrino energy loss rates due to several
processes that may be relevant during the gravitational collapse of these
objects. The peak luminosities of neutrinos and antineutrinos of all flavors
for models collapsing to a BH are ~10^{55} erg/s. The total radiated energy in
neutrinos varies between ~10^{56} ergs for models collapsing to a BH, and
~10^{45}-10^{46} ergs for models exploding. |
Multi-Messenger Astrophysics with the Cosmic Neutrino Background: The massive neutrinos of the Cosmic Neutrino Background (C$\nu$B) are
fundamental ingredients of the radiation-dominated early universe and are
important non-relativistic probes of the large-scale structure formation in the
late universe. The dominant source of anisotropies in the neutrino flux
distribution on the sky are highly amplified integrals of metric perturbations
encountered during the non-relativistic phase of the C$\nu$B. This paper
numerically compares the line-of-sight methods for computing C$\nu$B
anisotropies with the Einstein-Boltzmann hierarchy solutions in linear theory
for a range of neutrino masses. Angular power spectra are computed that are
relevant to a future polarized tritium target run of the PTOLEMY experiment.
Correlations between the C$\nu$B sky maps and galactic survey data are derived
using line-of-sight techniques and discussed in the context of multi-messenger
astrophysics. | Multi-Frequency Optical-Depth Maps and the Case for Free-Free Absorption
in Two Compact Symmetric Radio Sources: the CSO candidate J1324+4048 and the
CSO J0029+3457: We obtained dual-polarization VLBI observations at six frequencies of the
compact symmetric object J0029+3457 and the CSO candidate J1324+4048. By
comparing the three lower-frequency maps with extrapolations of the high
frequency maps we produced maps of the optical depth as a function of
frequency. The morphology of the optical-depth maps of J1324+4048 is strikingly
smooth, suggestive of a foreground screen of absorbing gas. The spectra at the
intensity peaks fit a simple free-free absorption model, with a reduced chi
square ~ 2, better than a simple synchrotron self-absorption model, in which
the reduced chi square ~ 3.5 - 5.5. We conclude that the case for free-free
absorption in J1324+4048 is strong. The optical-depth maps of J0029+3457
exhibit structure, but the morphology does not correlate with that in the
intensity maps. The fit of the spectra at the peaks to a simple free-free
absorption model yields a reduced chi square ~ 1, but since the turnover is
gradual the fit is relatively insensitive to the input parameters. We find that
free-free absorption by a thin amount of gas in J0029+3457 is likely, but not
definitive. One compact feature in J0029+3457 has an inverted spectrum even at
the highest frequencies. We infer this to be the location of the core and
estimate an upper limit to the magnetic field of order 3 Gauss at a radius of
order 1 pc. In comparison with maps from observations at earlier epochs, no
apparent growth in either J1324+4048 or J0029+3457 is apparent, with upper
limits of 0.03 and 0.02 mas per yr, corresponding to maximum linear separation
speeds of 0.6c and 0.4c. |
Cosmological particle-in-cell simulations with ultralight axion dark
matter: We study cosmological structure formation with ultralight axion dark matter,
or "fuzzy dark matter (FDM), using a particle-mesh scheme to account for the
quantum pressure arising in the Madelung formulation of the
Schr\"odinger-Poisson equations. Subpercent-level energy conservation and
correct linear behavior are demonstrated. Whereas the code gives rise to the
same core-halo profiles as direct simulations of the Schr\"odinger equation, it
does not reproduce the detailed interference patterns. In cosmological
simulations with FDM initial conditions, we find a maximum relative difference
of O($10\%$) in the power spectrum near the quantum Jeans length compared to
using a standard N-body code with identical initial conditions. This shows that
the effect of quantum pressure during nonlinear structure formation cannot be
neglected for precision constraints on a dark matter component consisting of
ultralight axions. | Vibrationally excited HC3N in NGC 4418: We investigate the molecular gas properties of the deeply obscured luminous
infrared galaxy NGC 4418. We address the excitation of the complex molecule
HC3N to determine whether its unusually luminous emission is related to the
nature of the buried nuclear source. We use IRAM 30m and JCMT observations of
rotational and vibrational lines of HC3N to model the excitation of the
molecule by means of rotational diagrams. We report the first confirmed
extragalactic detection of vibrational lines of HC3N. We detect 6 different
rotational transitions ranging from J=10-9 to J=30-29 in the ground vibrational
state and obtain a tentative detection of the J=38-37 line. We also detect 7
rotational transitions of the vibrationally excited states v6 and v7, with
angular momenta ranging from J=10-9 to 28-27. The energies of the upper states
of the observed transitions range from 20 to 850 K. In the optically thin
regime, we find that the rotational transitions of the vibrational ground state
can be fitted for two temperatures, 30 K and 260 K, while the vibrationally
excited levels can be fitted for a rotational temperature of 90 K and a
vibrational temperature of 500 K. In the inner 300 pc of NGC 4418, we estimate
a high HC3N abundance, of the order of 10^-7. The excitation of the HC3N
molecule responds strongly to the intense radiation field and the presence of
warm, dense gas and dust at the center of NGC 4418. The intense HC3N line
emission is a result of both high abundances and excitation. The properties of
the HC3N emitting gas are similar to those found for hot cores in Sgr B2, which
implies that the nucleus (< 300 pc) of NGC 4418 is reminiscent of a hot core.
The potential presence of a compact, hot component (T=500 K) is also discussed. |
Primordial quantum nonequilibrium and large-scale cosmic anomalies: We study incomplete relaxation to quantum equilibrium at long wavelengths,
during a pre-inflationary phase, as a possible explanation for the reported
large-scale anomalies in the cosmic microwave background (CMB). Our scenario
makes use of the de Broglie-Bohm pilot-wave formulation of quantum theory, in
which the Born probability rule has a dynamical origin. The large-scale power
deficit could arise from incomplete relaxation for the amplitudes of the
primordial perturbations. We show, by numerical simulations for a spectator
scalar field, that if the pre-inflationary era is radiation dominated then the
deficit in the emerging power spectrum will have a characteristic shape (an
inverse-tangent dependence on wavenumber k, with oscillations). It is found
that our scenario is able to produce a power deficit in the observed region and
of the observed (approximate) magnitude for an appropriate choice of
cosmological parameters. We also discuss the large-scale anisotropy, which
might arise from incomplete relaxation for the phases of the primordial
perturbations. We present numerical simulations for phase relaxation, and we
show how to define characteristic scales for amplitude and phase
nonequilibrium. The extent to which the data might support our scenario is left
as a question for future work. Our results suggest that we have a potentially
viable model that might explain two apparently independent cosmic anomalies by
means of a single mechanism. | Emergence of the Temperature-Density Relation in the Low Density
Intergalactic Medium: We examine the evolution of the phase diagram of the low-density
intergalactic medium (IGM) during the Epoch of Reionization in simulation boxes
with varying reionization histories from the Cosmic Reionization on Computers
project. The PDF of gas temperature at fixed density exhibits two clear modes:
a warm and cold temperature mode, corresponding to the gas inside and outside
of ionized bubbles. We find that the transition between the two modes is
"universal" in the sense that its timing is accurately parameterized by the
value of the volume-weighted neutral fraction for any reionization history.
This "universality" is more complex than just a reflection of the fact that
ionized gas is warm and neutral gas is cold: it holds for the transition at a
fixed value of gas density, and gas at different densities transitions from the
cold to the warm mode at different values of the neutral fraction, reflecting a
non-trivial relationship between the ionization history, the evolving gas
density PDF, and the spectrum of ionizing radiation. Furthermore, the
"emergence" of the tight temperature-density relation in the warm mode is also
approximately "universally" controlled by the volume-weighted neutral fraction
for any reionization history. In particular, the "emergence" of the
temperature-density relation (as quantified by the rapid decrease in its width)
occurs when the neutral fraction is $10^{-4}\lesssim X_\mathrm{HI}
\lesssim10^{-3}$ for any reionization history. Our results indicate that the
neutral fraction is a primary quantity controlling the various properties of
the temperature-density relation, regardless of reionization history. |
Dynamical friction in cuspy galaxies: In this paper we treat the problem of the dynamical friction decay of a
massive object moving in an elliptical galaxy with a cuspidal inner
distribution of the mass density. We present results obtained by both
self-consistent, direct summation, N-body simulations, as well as by a new
semi-analytical treatment of dynamical friction valid in such cuspy central
regions of galaxies. A comparison of these results indicates that the proposed
semi-analytical approximation is the only reliable in cuspy galactic central
regions, where the standard Chandrasekhar's local approximation fails, and,
also, gives estimates of decay times that are correct at 1% respect to those
given by N-body simulations. The efficiency of dynamical friction in cuspy
galaxies is found definitively higher than in core galaxies, especially on more
radially elongated satellite orbits. As another relevant result, we find a
proportionality of the dynamical friction decay time to the -0.67 power of the
satellite mass, M, shallower than the standardly adopted 1/M dependence. | Test of the cosmic evolution using Gaussian processes: Much focus was on the possible slowing down of cosmic acceleration under the
dark energy parametrization. In the present paper, we investigate this subject
using the Gaussian processes (GP), without resorting to a particular template
of dark energy. The reconstruction is carried out by abundant data including
luminosity distance from Union2, Union2.1 compilation and gamma-ray burst, and
dynamical Hubble parameter. It suggests that slowing down of cosmic
acceleration cannot be presented within 95\% C.L., in considering the influence
of spatial curvature and Hubble constant. In order to reveal the reason of
tension between our reconstruction and previous parametrization constraint for
Union2 data, we compare them and find that slowing down of acceleration in some
parametrization is only a "mirage". Although these parameterizations fits well
with the observational data, their tension can be revealed by high order
derivative of distance $D$. Instead, GP method is able to faithfully model the
cosmic expansion history. |
Constraints on Dark Matter-Photon Coupling in the Presence of
Time-Varying Dark Energy: In a recent work [Phys. Rev. D 98, 043521 (2018)], we have investigated a
dark matter (DM)-photon coupling model in which the DM decays into photons in
the presence of dark energy (DE) with the constant equation of state (EoS)
parameter. Here, we study an extension of the DM-photon coupling model by
considering a time-varying EoS of DE via Chevalier-Polarski-Linder (CPL)
parametrization. We derive observational constraints on the model parameters by
using the data from cosmic microwave background (CMB), baryonic acoustic
oscillations (BAO), the local value of Hubble constant from Hubble Space
Telescope (HST), and large scale structure (LSS) information from the abundance
of galaxy clusters, in four different combinations. We find that in the present
DM-photon coupling scenario the mean values of $w_{\rm de0}$ are in
quintessence region ($w_{\rm de0} > -1$) whereas they were in the phantom
region ($w_{\rm de0} < -1$) in our previous study with all data combinations.
The constraints on the DM-photon coupling parameter do not reflect any
significant deviation from the previous results. Due to the decay of DM into
photons, we obtain higher values of $H_0$, consistent with the local
measurements, similar to our previous study. But, the time-varying DE leads to
lower values of $\sigma_8$ in the DM-photon coupling model with all data
combinations, in comparison to the results in our previous study. Thus,
allowing time-varying DE in the DM-photon coupling scenario is useful to
alleviate the $H_0$ and $\sigma_8$ tensions. | On the Dynamics of Non-Relativistic Flavor-Mixed Particles: Evolution of a system of interacting non-relativistic quantum flavor-mixed
particles is considered both theoretically and numerically. It was shown that
collisions of mixed particles not only scatter them elastically, but can also
change their mass eigenstates thus affecting particles' flavor composition and
kinetic energy. The mass eigenstate conversions and elastic scattering are
related but different processes, hence the conversion $S$-matrix elements can
be arbitrarily large even when the elastic scattering $S$-matrix elements
vanish. The conversions are efficient when the mass eigenstates are
well-separated in space but suppressed if their wave-packets overlap; the
suppression is most severe for mass-degenerate eigenstates in flat space-time.
The mass eigenstate conversions can lead to an interesting process, called
`quantum evaporation,' in which mixed particles, initially confined deep inside
a gravitational potential well and scattering only off each other, can escape
from it without extra energy supply leaving nothing behind inside the potential
at $t\to \infty$. Implications for the cosmic neutrino background and the
two-component dark matter model are discussed and a prediction for the direct
detection dark matter experiments is made. |
Time Variable Cosmological Constant from Renormalization Group Equations: In this paper, a time variable cosmological constant (CC) from
renormalization group equations (RGEs) is explored, where the renormalization
scale $\mu^2=R^{-2}_{CC}=Max(\dot{H}+2H^2,-\dot{H})$ is taken. The cosmological
parameters, such as dimensionless energy density, deceleration parameter and
effective equation of state of CC etc, are derived. Also, the cosmic
observational constraints are implemented to test the model's consistence. The
results show that it is compatible with cosmic data. So, it would be a viable
dark energy model. | Image simulations for strong and weak gravitational lensing: Gravitational lensing has been identified as a powerful tool to address
fundamental problems in astrophysics at different scales, ranging from
exoplanet identification to dark energy and dark matter characterization in
cosmology. Image simulations have played a fundamental role in the realization
of the full potential of gravitational lensing by providing a means to address
needs such as systematic error characterization, pipeline testing, calibration
analyses, code validation, and model development. We present a general overview
of the generation and applications of image simulations in strong and weak
gravitational lensing |
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