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Revisiting the WMAP - NVSS angular cross correlation. A skeptic's view: In the context of the study of the ISW, we revisit the angular cross
correlation of WMAP CMB data with the NVSS radio survey. We compute 2-point
cross functions between the two surveys in real and in Fourier space, paying
particular attention on the dependence of results on the flux of NVSS radio
sources, the angular scales where correlations arise and the comparison with
theoretical expectations. We reproduce previous results that claim an excess of
correlation in the angular correlation function (ACF), and we also find some
(low significance) similarity between the CMB and radio galaxy data in the
multipole range $\el \in $ [10, 25]. However, the S/N in the ACFs increases
with higher flux thresholds for NVSS sources, but drops a $\sim$ 30 - 50% in
separations of the order of a pixel size, suggesting some residual point source
contribution. When restricting our analyses to multipoles $\el \gt $60, we fail
to find any evidence for cross correlation in the range $\el \in [2,10]$, where
according to the model predictions and our simulations $\sim$ 50% of the S/N is
supposed to arise. Also, the accumulated S/N for $\el \lt $60 is below 1, far
from the theoretical expectation of S/N$\sim 5$. Part of this disagreement may
be caused by an inaccurate modeling of the NVSS source population: as in
previous works, we find a level of large scale ($\el \lt $70) clustering in the
NVSS catalog that seems incompatible with a high redshift population. This is
unlikely to be caused by contaminants or systematics, since it is independent
of flux threshold, and hence present for the brightest ($\gt 30 \sigma$) NVSS
sources. Either our NVSS catalogs are not probing the high redshift, large
scale gravitational potential wells, or there is a clear mismatch between the
ISW component present in WMAP data and theoretical expectations. | Do Bound Structures Brake Cosmic Acceleration?: In this paper we investigate the impact of the coupling between a
quintessence field and clustered matter on the average equation of state of the
scalar field. We take the NFW profile to be characteristic of bound structures
on galactic and cluster scales, and the isothermal distribution to hold for
objects on supercluster scales. Solving analytically for the scalar-field
profile, we find that the greatest impact on the equation of state comes from
the superclusters. Employing numerical case studies, we verify this effect and
probe its dependence on the evolutionary state of the supercluster. An estimate
across the Hubble volume yields corrections to the homogeneous equation of
state of ~3%, increasing with coupling strength. |
Current Constraints on Anisotropic and Isotropic Dark Energy Models: We use Gaussian processes in combination with MCMC method to place
constraints on cosmological parameters of three dark energy models including
flat and curved FRW and Bianchi type I spacetimes. To do so, we use recently
compiled 36 measurements of the Hubble parameter $H(z)$ in the redshifts
intermediate $0.07\leqslant z \leqslant 2.36$. Moreover, we use these models to
estimate the redshift of the deceleration-acceleration transition. We consider
two Gaussian priors for current value of the Hubble constant i.e
$H_{0}=73\pm1.74 (68\pm 2.8)$ km/s/Mpc to investigate the effect of the assumed
$H_{0}$ on our parameters estimations. For statistical analysis we use NUTS
sampler which is an extension of Hamiltonian Monte Carlo algorithm to generate
MCMC chains for parameters of dark energy models. To compare the considered
cosmologies, we perform Akaike information criterion (AIC) and Bayes factor
($\Psi$). In general, when we compared our results with 9 years WMAP as well as
Planck 2015 Collaboration, we found that Bianchi type I model is slightly fits
better to the observational Hubble data with respect to the non-flat FRW model. | The Effect of Mass Ratio on the Morphology and Time-scales of Disc
Galaxy Mergers: The majority of galaxy mergers are expected to be minor mergers. The
observational signatures of minor mergers are not well understood, thus there
exist few constraints on the minor merger rate. This paper seeks to address
this gap in our understanding by determining if and when minor mergers exhibit
disturbed morphologies and how they differ from the morphology of major
mergers. We simulate a series of unequal-mass moderate gas-fraction disc galaxy
mergers. With the resulting g-band images, we determine how the time-scale for
identifying galaxy mergers via projected separation and quantitative morphology
(the Gini coefficient G, asymmetry A, and the second-order moment of the
brightest 20% of the light M20) depends on the merger mass ratio, relative
orientations and orbital parameters. We find that G-M20 is as sensitive to 9:1
baryonic mass ratio mergers as 1:1 mergers, with observability time-scales ~
0.2-0.4 Gyr. In contrast, asymmetry finds mergers with baryonic mass ratios
between 4:1 and 1:1 (assuming local disc galaxy gas-fractions). Asymmetry
time-scales for moderate gas-fraction major disc mergers are ~ 0.2-0.4 Gyr, and
less than 0.06 Gyr for moderate gas-fraction minor mergers. The relative
orientations and orbits have little effect on the time-scales for morphological
disturbances. Observational studies of close pairs often select major mergers
by choosing paired galaxies with similar luminosities and/or stellar masses.
Therefore, the various ways of finding galaxy mergers (G-M20, A, close pairs)
are sensitive to galaxy mergers of different mass ratios. By comparing the
frequency of mergers selected by different techniques, one may place empirical
constraints on the major and minor galaxy merger rates. |
How does the cosmic large-scale structure bias the Hubble diagram?: The Hubble diagram is one of the cornerstones of observational cosmology. It
is usually analysed assuming that, on average, the underlying relation between
magnitude and redshift matches the prediction of a
Friedmann-Lema\^itre-Robertson-Walker model. However, the inhomogeneity of the
Universe generically biases these observables, mainly due to peculiar
velocities and gravitational lensing, in a way that depends on the notion of
average used in theoretical calculations. In this article, we carefully derive
the notion of average which corresponds to the observation of the Hubble
diagram. We then calculate its bias at second-order in cosmological
perturbations, and estimate the consequences on the inference of cosmological
parameters, for various current and future surveys. We find that this bias
deeply affects direct estimations of the evolution of the dark-energy equation
of state. However, errors in the standard inference of cosmological parameters
remain smaller than observational uncertainties, even though they reach percent
level on some parameters; they reduce to sub-percent level if an optimal
distance indicator is used. | Structural properties of disk galaxies. II. Intrinsic shape of bulges: (Abridged) The structural parameters of a magnitude-limited sample of 148
unbarred S0-Sb galaxies were analyzed to derive the intrinsic shape of their
bulges. We developed a new method to derive the intrinsic shape of bulges based
on the geometrical relationships between the apparent and intrinsic shapes of
bulges and disks. The equatorial ellipticity and intrinsic flattening of bulges
were obtained from the length of the apparent major and minor semi-axes of the
bulge, twist angle between the apparent major axis of the bulge and the galaxy
line of nodes, and galaxy inclination. We found that the intrinsic shape is
well constrained for a subsample of 115 bulges with favorable viewing angles. A
large fraction of them is characterized by an elliptical section (B/A<0.9).
This fraction is 33%, 55%, and 43% if using their maximum, mean, or median
equatorial ellipticity, respectively. Most are flattened along their polar axis
(C<(A+B)/2). The distribution of triaxiality is strongly bimodal. This
bimodality is driven by bulges with Sersic index n>2, or equivalently, by the
bulges of galaxies with a bulge-to-total ratio B/T>0.3. In particular, bulges
with n\leq2 and with B/T\leq0.3 show a larger fraction of oblate axisymmetric
(or nearly axisymmetric) bulges, a smaller fraction of triaxial bulges, and
fewer prolate axisymmetric (or nearly axisymmetric) bulges with respect to
bulges with n>2 and with B/T>0.3, respectively. According to predictions of the
numerical simulations of bulge formation, bulges with n\leq2, which show a high
fraction of oblate axisymmetric (or nearly axisymmetric) shapes and have
B/T\leq0.3, could be the result of dissipational minor mergers. Both major
dissipational and dissipationless mergers seem to be required to explain the
variety of shapes found for bulges with n>2 and B/T>0.3. |
Non-Gaussianity in Cosmology: from Inflation to the CMB: The non-Gaussianity of inflationary perturbations, as encoded in the
bispectrum (or 3-point correlator), has become an important additional way of
distinguishing between inflation models, going beyond the linear Gaussian
perturbation quantities of the power spectrum. This habilitation thesis
provides a review of my work on both the theoretical and the observational
aspects of these non-Gaussianities. In the first part a formalism is described,
called the long-wavelength formalism, that provides a way to compute the
non-Gaussianities in multiple-field inflation. Applications of this formalism
to various classes of models, as well as its extensions, are also treated. In
the second part an estimator is described, called the binned bispectrum
estimator, that allows the extraction of information about non-Gaussianities
from data of the cosmic microwave background radiation (CMB). It was in
particular one of the three estimators applied to the data of the Planck
satellite to provide the currently best constraints on primordial
non-Gaussianity. Various extensions of the estimator and results obtained are
also discussed. | Weak lensing measurement of galaxy clusters in the CFHTLS-Wide survey: We present the first weak gravitational lensing analysis of the completed
Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We study the 64 square
degrees W1 field, the largest of the CFHTLS-Wide survey fields, and present the
largest contiguous weak lensing convergence "mass map" yet made. 2.66 million
galaxy shapes are measured, using a KSB pipeline verified against
high-resolution Hubble Space Telescope imaging that covers part of the CFHTLS.
Our i'-band measurements are also consistent with an analysis of independent
r'-band imaging. The reconstructed lensing convergence map contains 301 peaks
with signal-to-noise ratio {\nu}>3.5, consistent with predictions of a
{\Lambda}CDM model. Of these peaks, 126 lie within 3.0' of a BCG identified
from multicolor optical imaging in an independent, red sequence survey. We also
identify 7 counterparts for massive clusters previously seen in X-ray emission
within 6 square degrees XMM-LSS survey. With photometric redshift estimates for
the source galaxies, we use a tomographic lensing method to fit the redshift
and mass of each convergence peak. Matching these to the optical observations,
we confirm 85 groups/clusters with \chi^2 reduced < 3.0, at a mean redshift
<z_c> = 0.36 and velocity dispersion <\sigma_c> = 658.8 km/s. Future surveys,
such as DES, LSST, KDUST and EUCLID, will be able to apply these same
techniques to map clusters in much larger volumes and thus tightly constrain
cosmological models. |
The Effects Of Relativistic Hidden Sector Particles on the Matter Power
Spectrum: If dark matter resides in a hidden sector minimally coupled to the Standard
Model, another particle within the hidden sector might dominate the energy
density of the early universe temporarily, causing an early matter-dominated
era (EMDE). During an EMDE, matter perturbations grow more rapidly than they
would in a period of radiation domination, which leads to the formation of
microhalos much earlier than they would form in standard cosmological
scenarios. These microhalos boost the dark matter annihilation signal, but this
boost is highly sensitive to the small-scale cut-off in the matter power
spectrum. If the dark matter is sufficiently cold, this cut-off is set by the
relativistic pressure of the particle that dominates the hidden sector. We
determine the evolution of dark matter density perturbations in this scenario,
obtaining the power spectrum at the end of the EMDE. We analyze the suppression
of perturbations due to the relativistic pressure of the dominant hidden sector
particle and express the cut-off scale and peak scale for which the matter
power spectrum is maximized in terms of the properties of this particle. We
also supply transfer functions to relate the matter power spectrum with a
small-scale cut-off resulting from the pressure of the dominant hidden sector
particle to the matter power spectrum that results from a cold hidden sector.
These transfer functions facilitate the quick computation of accurate matter
power spectra in EMDE scenarios with initially hot hidden sectors and allow us
to identify which models significantly enhance the microhalo abundance. | Cosmological Constraints on sub-horizon scales modified gravity theories
with MGCLASS II: In this paper we introduce a new public Einstein-Boltzmann solver,
\texttt{MGCLASS II}, built as a modification to the publicly available
\texttt{CLASS} code, that allows to obtain cosmological observables for
Modified Gravity theories. It implements several commonly used
parameterizations of deviations from General Relativity, computing their impact
on the growth of structure as well as on the background evolution of the
Universe, together with a subset of available alternative theories, still not
completely ruled out by observations. \texttt{MGCLASS II} is built in such a
way to be compatible with parameter estimation codes such as
\texttt{MontePython} and \texttt{Cobaya}. We exploit this possibility to
constrain the parameterizations used by the Planck collaboration, in order to
validate the predictions of this new code, and a newly implemented
parameterization (z\_flex) which has different features. For the former we find
good agreement with the results existing in the literature, while we present
original constraints on the parameters of the latter, finding no significant
deviation from the standard cosmological model, $\Lambda$CDM. |
The Simultaneous Optical-to-X-ray Spectral Energy Distribution of Soft
X-ray Selected AGN observed by Swift: We report Swift observations of a sample of 92 bright soft X-ray selected
active galactic nuclei (AGN). This sample represents the largest number of AGN
observed to study the spectral energy distribution (SED) of AGN with
simultaneous optical/UV and X-ray data. The principal motivation of this study
is to understand the SEDs of AGN in the optical/UV to X-ray regime and to
provide bolometric corrections which are important in determining the Eddington
ratio L/Ledd. In particular, we rigorously explore the dependence of the UV-EUV
contribution to the bolometric correction on the assumed EUV spectral shape. We
find strong correlations of the spectral slopes alpha-x and alpha-UV with
L/Ledd. Although Narrow-Line Seyfert 1 galaxies (NLS1s) have steeper alpha-x
and higher L/Ledd than Broad-Line Seyfert 1 galaxies (BLS1s), their optical/UV
to X-ray spectral slopes alpha-ox and optical/UV slopes alpha-UV are very
similar. The mean SED of NLS1s shows that in general this type of AGN appears
to be fainter in the UV and at hard X-ray energies than BLS1s. We find a strong
correlation between alpha-x and alpha-UV for AGN with X-ray spectral slopes
alpha-x<1.6. For AGN with steeper X-ray spectra, both this relation and the
relation between alpha-x and L/Ledd break down. At alpha-x$\approx$1.6, L/Ledd
reaches unity. We note an offset in the alpha-UV - L/Ledd relation between
NLS1s and BLS1s. We argue that alpha-UV is a good estimator of L/Ledd and
suggest that alpha-UV can be used to estimate L/Ledd in high-redshift QSOs.
Although NLS1s appear to be highly variable in X-rays they only vary marginally
in the UV. | A Multifrequency Study of Double-Double Radio Galaxies: One of the striking examples of episodic activity in active galactic nuclei
are the double-double radio galaxies (DDRGs) with two pairs of
oppositely-directed radio lobes from two different cycles of activity. We
illustrate, using the DDRG J1453+3308 as an example, that observations over a
wide range of frequencies using both the GMRT and the VLA can be used to
determine the spectra of the inner and outer lobes, estimate their spectral
ages, estimate the time scales of episodic activity, and examine any difference
in the injection spectra in the two cycles of activity. Low-frequency GMRT
observations also suggest that DDRGs and triple-double radio galaxies are
rather rare. |
The Complementarity of Redshift-space Distortions and the Integrated
Sachs-Wolfe Effect: A 3D Spherical Analysis: Assuming General Relativity is correct on large-scales, Redshift-Space
Distortions (RSDs) and the Integrated Sachs-Wolfe effect (ISW) are both
sensitive to the time derivative of the linear growth function. We investigate
the extent to which these probes provide complementary or redundant information
when they are combined to constrain the evolution of the linear velocity power
spectrum, often quantified by the function $f(z)\sigma_8(z)$, where $f$ is the
logarithmic derivative of $\sigma_8$ with respect to $(1+z)$. Using a spherical
Fourier-Bessel (SFB) expansion for galaxy number counts and a spherical
harmonic expansion for the CMB anisotropy, we compute the covariance matrices
of the signals for a large galaxy redshift survey combined with a CMB survey
like Planck. The SFB basis allows accurate ISW estimates by avoiding the
plane-parallel approximation, and it retains RSD information that is otherwise
lost when projecting angular clustering onto redshift shells. It also allows
straightforward calculations of covariance with the CMB. We find that the
correlation between the ISW and RSD signals are low since the probes are
sensitive to different modes. For our default surveys, on large scales ($k<0.05
\Mpc/h$), the ISW can improve constraints on $f\sigma_8$ by more than 10%
compared to using RSDs alone. In the future, when precision RSD measurements
are available on smaller scales, the cosmological constraints from ISW
measurements will not be competitive; however, they will remain a useful
consistency test for possible systematic contamination and alternative models
of gravity. | Turbulence production and turbulent pressure support in the
intergalactic medium: The injection and evolution of turbulence in the intergalactic medium is
studied by means of mesh-based hydrodynamical simulations, including a subgrid
scale (SGS) model for small-scale unresolved turbulence. The simulations show
that the production of turbulence has a different redshift dependence in the
intracluster medium (ICM) and the warm-hot intergalactic medium (WHIM). We show
that turbulence in the ICM is produced chiefly by merger-induced shear flows,
whereas the production in the WHIM is dominated by shock interactions.
Secondly, the effect of dynamical pressure support on the gravitational
contraction has been studied. This turbulent support is stronger in the WHIM
gas at baryon overdensities 1 < delta < 100, and less relevant for the ICM.
Although the relative mass fraction of the gas with large vorticity is
considerable (52% in the ICM), we find that for only about 10% in mass this is
dynamically relevant, namely not associated to an equally large thermal
pressure support. According to this result, a significant non-thermal pressure
support counteracting the gravitational contraction is a localised
characteristic in the cosmic flow, rather than a widespread feature. |
The Axis-Symmetric Ring Galaxies: AM 0053-353, AM 0147-350, AM 1133-245,
AM 1413-243, AM 2302-322, ARP 318, and Head-On Penetrations: Axis-symmetric ring systems can be identified from the new catalog of
collisional ring galaxies in Madore et al. (2009). These are O-type-like
collisional ring galaxies. Head-on collisions by dwarf galaxies moving along
the symmetric axis were performed through N-body simulations to address their
origins. It was found that the simulations with smaller initial relative
velocities between two galaxies, or the cases with heavier dwarf galaxies,
could produce rings with higher density contrasts. There are more than one
generation of rings in one collision and the lifetime of any generation of
rings is about one dynamical time. It was concluded that head-on penetrations
could explain these O-type-like ring galaxies identified from the new catalog
in Madore et al. (2009), and the simulated rings resembling the observational
O-type-like collisional rings are those at the early stage of one of the
ring-generations. | LoCuSS: Weak-lensing mass calibration of galaxy clusters: We present weak-lensing mass measurements of 50 X-ray luminous galaxy
clusters at $0.15\le z\le0.3$, based on uniform high quality observations with
Suprime-Cam mounted on the 8.2-m Subaru telescope. We pay close attention to
possible systematic biases, aiming to control them at the $\le4$ per cent
level. The dominant source of systematic bias in weak-lensing measurements of
the mass of individual galaxy clusters is contamination of background galaxy
catalogues by faint cluster and foreground galaxies. We extend our conservative
method for selecting background galaxies with $(V-i')$ colours redder than the
red sequence of cluster members to use a colour-cut that depends on
cluster-centric radius. This allows us to define background galaxy samples that
suffer $\le1$ per cent contamination, and comprise $13$ galaxies per square
arcminute. Thanks to the purity of our background galaxy catalogue, the largest
systematic that we identify in our analysis is a shape measurement bias of $3$
per cent, that we measure using simulations that probe weak shears upto
$g=0.3$. Our individual cluster mass and concentration measurements are in
excellent agreement with predictions of the mass-concentration relation.
Equally, our stacked shear profile is in excellent agreement with the Navarro
Frenk and White profile. Our new LoCuSS mass measurements are consistent with
the CCCP and CLASH surveys, and in tension with the Weighing the Giants at
$\sim1-2\sigma$ significance. Overall, the consensus at $z\le0.3$ that is
emerging from these complementary surveys represents important progress for
cluster mass calibration, and augurs well for cluster cosmology. |
Covariant formulation of refracted gravity: We propose a covariant formulation of refracted gravity (RG), a classical
theory of gravity based on the introduction of gravitational permittivity (GP),
a monotonic function of the local mass density, in the standard Poisson
equation. GP mimics dark matter (DM) phenomenology. The covariant formulation
of RG (CRG) that we propose belongs to the class of scalar-tensor theories,
where the scalar field $\varphi$ has a self-interaction potential
$V(\varphi)=-\Xi\varphi$, with $\Xi$ a normalization constant. We show that
$\varphi$ is twice the GP in the weak-field limit. Far from a spherical source
of density $\rho_s(r)$, the transition between the Newtonian and the RG regime
appears below the acceleration scale $a_\Xi=(2\Xi-8\pi G\rho/\varphi)^{1/2}$,
with $\rho=\rho_s+\rho_{bg}$, $\rho_{bg}$ being an isotropic and homogeneous
background. In the limit $2\Xi\gg 8\pi G\rho/\varphi$, we obtain $a_\Xi\sim
10^{-10}$~m~s$^{-2}$. This is comparable to the acceleration $a_0$ originally
introduced in MOND. From CRG, we also derived the modified Friedmann equations
for an expanding, homogeneous, and isotropic universe. We find that the same
scalar field that mimics DM also drives the accelerated expansion of the
Universe. From the stress-energy tensor of $\varphi$, we derived the equation
of state of a redshift-dependent effective dark energy (DE)
$w_{DE}=p_{DE}/\rho_{DE}$. Current observational constraints on $w_{DE}$ and
distance modulus data of SNIa suggest that $\Xi$ has a comparable value to the
cosmological constant $\Lambda$ in the standard model. CRG, therefore, suggests
a natural explanation of the known relation $a_0\sim \Lambda^{1/2}$ and appears
to describe both the dynamics of cosmic structure and the expanding Universe
with a single scalar field, highlighting a possible deep connection between
phenomena currently attributed to DM and DE separately. | Evolution of the $fσ_8$ tension with the Planck15/$Λ$CDM
determination and implications for modified gravity theories: We construct an updated extended compilation of distinct (but possibly
correlated) $f\sigma_8(z)$ Redshift Space Distortion (RSD) data published
between 2006 and 2018. It consists of 63 datapoints and is significantly larger
than previously used similar datasets. After fiducial model correction we
obtain the best fit $\Omega_{0m}-\sigma_8$ $\Lambda$CDM parameters and show
that they are at a $5\sigma$ tension with the corresponding
Planck15/$\Lambda$CDM values. Introducing a nontrivial covariance matrix
correlating randomly $20\%$ of the RSD datapoints has no significant effect on
the above tension level. We show that the tension disappears (becomes less than
$1\sigma$) when a subsample of the 20 most recently published data is used. A
partial cause for this reduced tension is the fact that more recent data tend
to probe higher redshifts (with higher errorbars) where there is degeneracy
among different models due to matter domination. Allowing for a nontrivial
evolution of the effective Newton's constant as
$G_{\textrm{eff}}(z)/G_{\textrm{N}} = 1 + g_a \left(\frac{z}{1+z}\right)^2 -
g_a \left(\frac{z}{1+z}\right)^4$ ($g_a$ is a parameter) and fixing a \plcdm
background we find $g_a=-0.91\pm 0.17$ from the full $f\sigma_8$ dataset while
the 20 earliest and 20 latest datapoints imply $g_a=-1.28^{+0.28}_{-0.26}$ and
$g_a=-0.43^{+0.46}_{-0.41}$ respectively. Thus, the more recent $f\sigma_8$
data appear to favor GR in contrast to earlier data. Finally, we show that the
parametrization $f\sigma_8(z)=\lambda \sigma_8 \Omega(z)^\gamma /(1+z)^\beta$
provides an excellent fit to the solution of the growth equation for both GR
($g_a=0$) and modified gravity ($g_a\neq 0$). |
Running of the Running and Entropy Perturbations During Inflation: In single field slow-roll inflation, one expects that the spectral index $n_s
-1$ is first order in slow-roll parameters. Similarly, its running $\alpha_s =
dn_s/d \log k$ and the running of the running $\beta_s = d\alpha_s/d \log k$
are second and third order and therefore expected to be progressively smaller,
and usually negative. Hence, such models of inflation are in considerable
tension with a recent analysis hinting that $\beta_s$ may actually be positive,
and larger than $\alpha_s$. Motivated by this, in this work we ask the question
of what kinds of inflationary models may be useful in achieving such a
hierarchy of runnings, particularly focusing on two--field models of inflation
in which the late-time transfer of power from isocurvature to curvature modes
allows for a much more diverse range of phenomenology. We calculate the
runnings due to this effect and briefly apply our results to assessing the
feasibility of finding $|\beta_s| \gtrsim |\alpha_s|$ in some specific models. | Exploring Vainshtein mechanism on adaptively refined meshes: There has been a lot of research interest in modified gravity theories which
utilise the Vainshtein mechanism to recover standard general relativity in
regions with high matter density, such as the Dvali-Gabadadze-Porrati and
Galileon models. The strong nonlinearity in the field equations of these
theories implies that accurate theoretical predictions could only be made using
high-resolution cosmological simulations. Previously, such simulations were
usually done on regular meshes, which limits both their performance and the
accuracy. In this paper, we report the development of a new algorithm and code,
based on ECOSMOG, that uses adaptive mesh refinements to improve the efficiency
and precision in simulating the models with Vainshtein mechanism. We have made
various code tests against the numerical reliability, and found consistency
with previous simulations. We also studied the velocity field in the
self-accelerating branch of the DGP model. The code, parallelised using MPI, is
suitable for large cosmological simulations of Galileon-type modified gravity
theories. |
Non-minimal quintessence and phantom with nearly flat potentials: We investigate quintessence and phantom dark energy scenarios, in which the
scalar fields evolve in nearly flat potentials and are non-minimally coupled to
gravity. We show that all such models converge to a common behavior and we
provide the corresponding approximate analytical expressions for
$w(\Omega_\phi)$ and $w(a)$. We find that non-minimal coupling leads to richer
cosmological behavior comparing to its minimal counterpart. In addition,
comparison with Baryon Acoustic Oscillation and latest Supernovae data reveals
that agreement can be established more easily and with less strict constraints
on the model parameters. | Inflationary perturbations in bimetric gravity: In this paper we study the generation of primordial perturbations in a
cosmological setting of bigravity during inflation. We consider a model of
bigravity which can reproduce the $\Lambda$CDM background and large scale
structure and a simple model of inflation with a single scalar field and a
quadratic potential. Reheating is implemented with a toy-model in which the
energy density of the inflaton is entirely dissipated into radiation. We
present analytic and numerical results for the evolution of primordial
perturbations in this cosmological setting. We find that the amplitude of
tensor perturbations generated during inflation is sufficiently suppressed to
avoid the effects of the tensor instability discovered in Refs.[1,2] which
develops during the cosmological evolution in the physical sector. We argue
that from a pure analysis of the tensor perturbations this bigravity model is
compatible with present observations. However, we derive rather stringent
limits on inflation from the vector and scalar sectors. |
Non-Gaussianity with Lagrange Multiplier Field in the Curvaton Scenario: In this paper, we will use $\delta \mathcal{N}$-formalism to calculate the
primordial curvature perturbation for the curvaton model with a Lagrange
multiplier field. We calculate the non-linearity parameters $f_{NL}$ and
$g_{NL}$ in the sudden-decay approximation in this kind of model, and we find
that one could get a large non-Gaussinity even if the curvaton dominates the
total energy density before it decays, and this property will make the curvaton
model much richer. We also calculate the probability density function of the
primordial curvature perturbation in the sudden-decay approximation, as well as
some moments of it. | H0LiCOW I. $H_0$ Lenses in COSMOGRAIL's Wellspring: Program Overview: Strong gravitational lens systems with time delays between the multiple
images allow measurements of time-delay distances, which are primarily
sensitive to the Hubble constant that is key to probing dark energy, neutrino
physics, and the spatial curvature of the Universe, as well as discovering new
physics. We present H0LiCOW ($H_0$ Lenses in COSMOGRAIL's Wellspring), a
program that aims to measure $H_0$ with $<3.5\%$ uncertainty from five lens
systems (B1608+656, RXJ1131-1231, HE0435-1223, WFI2033-4723 and HE1104-1805).
We have been acquiring (1) time delays through COSMOGRAIL and Very Large Array
monitoring, (2) high-resolution Hubble Space Telescope imaging for the lens
mass modeling, (3) wide-field imaging and spectroscopy to characterize the lens
environment, and (4) moderate-resolution spectroscopy to obtain the stellar
velocity dispersion of the lenses for mass modeling. In cosmological models
with one-parameter extension to flat $\Lambda$CDM, we expect to measure $H_0$
to $<3.5\%$ in most models, spatial curvature $\Omega_{\rm k}$ to 0.004, $w$ to
0.14, and the effective number of neutrino species to 0.2 (1$\sigma$
uncertainties) when combined with current CMB experiments. These are,
respectively, a factor of $\sim15$, $\sim2$, and $\sim1.5$ tighter than CMB
alone. Our data set will further enable us to study the stellar initial mass
function of the lens galaxies, and the co-evolution of supermassive black holes
and their host galaxies. This program will provide a foundation for extracting
cosmological distances from the hundreds of time-delay lenses that are expected
to be discovered in current and future surveys. |
K2: A new method for the detection of galaxy clusters based on CFHTLS
multicolor images: We have developed a new method, K2, optimized for the detection of galaxy
clusters in multicolor images. Based on the Red Sequence approach, K2 detects
clusters using simultaneous enhancements in both colors and position. The
detection significance is robustly determined through extensive Monte-Carlo
simulations and through comparison with available cluster catalogs based on two
different optical methods, and also on X-ray data. K2 also provides
quantitative estimates of the candidate clusters' richness and photometric
redshifts. Initially K2 was applied to 161 sq deg of two color gri images of
the CFHTLS-Wide data. Our simulations show that the false detection rate, at
our selected threshold, is only ~1%, and that the cluster catalogs are ~80%
complete up to a redshift of 0.6 for Fornax-like and richer clusters and to z
~0.3 for poorer clusters. Based on Terapix T05 release gri photometric
catalogs, 35 clusters/sq deg are detected, with 1-2 Fornax-like or richer
clusters every two square degrees. Catalogs containing data for 6144 galaxy
clusters have been prepared, of which 239 are rich clusters. These clusters,
especially the latter, are being searched for gravitational lenses -- one of
our chief motivations for cluster detection in CFHTLS. The K2 method can be
easily extended to use additional color information and thus improve overall
cluster detection to higher redshifts. The complete set of K2 cluster catalogs,
along with the supplementary catalogs for the member galaxies, are available on
request from the authors. | The SAURON project - XVIII. The integrated UV-linestrength relations of
early-type galaxies: Using far (FUV) and near (NUV) ultraviolet photometry from guest investigator
programmes on the Galaxy Evolution Explorer (GALEX) satellite, optical
photometry from the MDM Observatory and optical integral-field spectroscopy
from SAURON, we explore the UV-linestrength relations of the 48 nearby
early-type galaxies in the SAURON sample. Identical apertures are used for all
quantities, avoiding aperture mismatch. We show that galaxies with purely old
stellar populations show well-defined correlations of the integrated FUV-V and
FUV-NUV colours with the integrated Mgb and Hbeta absorption linestrength
indices, strongest for FUV-NUV. Correlations with the NUV-V colour, Fe5015
index and stellar velocity dispersion are much weaker. These correlations put
stringent constraints on the origin of the UV-upturn phenomenon in early-type
galaxies, and highlight its dependence on age and metallicity. In particular,
despite recent debate, we recover the negative correlation between FUV-V colour
and Mg linestrength originally publicised by Burstein et al. (1988), which we
refer to as the "Burstein relation", suggesting a positive dependence of the
UV-upturn on metallicity. We argue that the scatter in the correlations is
real, and present mild evidence that a strong UV excess is preferentially
present in slow-rotating galaxies. We also demonstrate that most outliers in
the correlations are galaxies with current or recent star formation, some at
very low levels. We believe that this sensitivity to weak star formation,
afforded by the deep and varied data available for the SAURON sample, explains
why our results are occasionally at odds with other recent but shallower
surveys. This is supported by the analysis of a large, carefully-crafted sample
of more distant early-type galaxies from the Sloan Digital Sky Survey (SDSS),
more easily comparable with current and future large surveys. |
Constraining the photon coupling of ultra-light dark-matter axion-like
particles by polarization variations of parsec-scale jets in active galaxies: Ultra-light dark matter may consist of axion-like particles with masses below
10^(-19) eV. Two-photon interactions of these particles affect the polarization
of radiation propagating through the dark matter. Coherent oscillations of the
Bose condensate of the particles induce periodic changes in the plane of
polarisation of emission passing through the condensate. We estimate this
effect and analyze MOJAVE VLBA polarization observations of bright downstream
features in the parsec-scale jets of active galaxies. Through the
non-observation of periodic polarization changes, we are able to constrain the
photon coupling of the ultra-light dark-matter axion-like particles at the
level of <~ 10^(-12)/GeV for masses between ~5*10^(-23) eV and ~1.2*10^(-21)
eV. | Modeling dark matter subhalos in a constrained galaxy: Global mass and
boosted annihilation profiles: The interaction properties of cold dark matter (CDM) particle candidates,
such as those of weakly interacting massive particles (WIMPs), generically lead
to the structuring of dark matter on scales much smaller than typical galaxies,
potentially down to $\sim 10^{-10}M_\odot$. This clustering translates into a
very large population of subhalos in galaxies and affects the predictions for
direct and indirect dark matter searches (gamma rays and antimatter cosmic
rays). In this paper, we elaborate on previous analytic works to model the
Galactic subhalo population, while consistently with current observational
dynamical constraints on the Milky Way. In particular, we propose a
self-consistent method to account for tidal effects induced by both dark matter
and baryons. Our model does not strongly rely on cosmological simulations as
they can hardly be fully matched to the real Milky Way, but for setting the
initial subhalo mass fraction. Still, it allows to recover the main qualitative
features of simulated systems. It can further be easily adapted to any change
in the dynamical constraints, and be used to make predictions or derive
constraints on dark matter candidates from indirect or direct searches. We
compute the annihilation boost factor, including the subhalo-halo
cross-product. We confirm that tidal effects induced by the baryonic components
of the Galaxy play a very important role, resulting in a local average subhalo
mass density $\lesssim 1\%$ of the total local dark matter mass density, while
selecting in the most concentrated objects and leading to interesting features
in the overall annihilation profile in the case of a sharp subhalo mass
function. Values of global annihilation boost factors range from $\sim 2$ to
$\sim 20$, while the local annihilation rate is about half as much boosted. |
A Comparison Between the Half-Light Radii, Luminosities, and UBV Colors
of Globular Clusters in M31 and the Galaxy: The Milky Way System and the Andromeda galaxy experienced radically different
evolutionary histories. Nevertheless, it is found that these two galaxies ended
up with globular cluster systems in which individual clusters have
indistinguishable distributions of half-light radii. Furthermore globulars in
both M31 and the Galaxy are found to have radii that are independent of their
luminosities. In this respect globular clusters differ drastically from
early-type galaxies in which half-light radius and luminosity are tightly
correlated. Metal-rich globular clusters in M31 occupy a slightly larger volume
than do those in the Galaxy. The specific globular cluster frequency in the
Andromeda galaxy is found to he significantly higher than it is in the Milky
Way System. The present discussion is based on the 107 Galactic globular
clusters, and 200 putative globulars in M31, for which UBV photometry was
available. | Deriving the Hubble constant using Planck and XMM-Newton observations of
galaxy clusters: The possibility of determining the value of the Hubble constant using
observations of galaxy clusters in X-ray and microwave wavelengths through the
Sunyaev Zel\'dovich (SZ) effect has long been known. Previous measurements have
been plagued by relatively large errors in the observational data and severe
biases induced, for example, by cluster triaxiality and clumpiness. The advent
of \textit{Planck} allows us to map the Compton parameter y, that is, the
amplitude of the SZ effect, with unprecedented accuracy at intermediate
cluster-centric radii, which in turn allows performing a detailed spatially
resolved comparison with X-ray measurements. Given such higher quality
observational data, we developed a Bayesian approach that combines informed
priors on the physics of the intracluster medium obtained from hydrodynamical
simulations of massive clusters with measurement uncertainties.
We apply our method to a sample of 61 galaxy clusters with redshifts up to z
< 0.5 observed with Planck and XMM-Newton observations and find H_0=67 \pm 3 km
s^{-1} Mpc^{-1}. |
The Quest for B Modes from Inflationary Gravitational Waves: The search for the curl component (B mode) in the cosmic microwave background
(CMB) polarization induced by inflationary gravitational waves is described.
The canonical single-field slow-roll model of inflation is presented, and we
explain the quantum production of primordial density perturbations and
gravitational waves. It is shown how these gravitational waves then give rise
to polarization in the CMB. We then describe the geometric decomposition of the
CMB polarization pattern into a curl-free component (E mode) and curl component
(B mode) and show explicitly that gravitational waves induce B modes. We
discuss the B modes induced by gravitational lensing and by Galactic
foregrounds and show how both are distinguished from those induced by
inflationary gravitational waves. Issues involved in the experimental pursuit
of these B modes are described, and we summarize some of the strategies being
pursued. We close with a brief discussion of some other avenues toward
detecting/characterizing the inflationary gravitational-wave background. | Using LISA-like Gravitational Wave Detectors to Search for Primordial
Black Holes: Primordial black hole (PBH), which can be naturally produced in the early
universe, remains a promising dark matter candidate . It can merge with a
supermassive black hole (SMBH) in the center of a galaxy and generate
gravitational wave (GW) signals in the favored frequency region of LISA-like
experiments. In this work, we initiate the study on the event rate calculation
for such extreme mass ratio inspirals (EMRI). Including the sensitivities of
various proposed GW detectors, we find that such experiments offer a novel and
outstanding tool to test the scenario where PBH constitutes (fraction of) dark
matter. The PBH energy density fraction of DM ($f_\text{PBH}$) could
potentially be explored as small as $10^{-3} \sim 10^{-4}$. Further, LISA has
the capability to search for PBH mass upto $10^{-2} \sim 10^{-1} M_\odot$.
Other proposed GW experiments can probe lower PBH mass regime. |
Constraining extended cosmologies with GW$\times$LSS cross-correlations: The rapid development of gravitational wave astronomy provides the unique
opportunity of exploring the dynamics of the Universe using clustering
properties of coalescing binary black hole mergers. Gravitational wave data,
along with information coming from future galaxy surveys, have the potential of
shedding light about many open questions in Cosmology, including those
regarding the nature of dark matter and dark energy. In this work we explore
which combination of gravitational wave and galaxy survey datasets are able to
provide the best constraints both on modified gravity theories and on the
nature of the very same binary black hole events. In particular, by using the
public Boltzmann code \texttt{Multi\_CLASS}, we compare cosmological
constraints on popular $\Lambda$CDM extensions coming from gravitational waves
alone and in conjunction with either deep and localized or wide and shallow
galaxy surveys. We show that constraints on extensions of General Relativity
will be at the same level of existing limits from gravitational waves alone or
one order of magnitude better when galaxy surveys are included. Furthermore,
cross-correlating both kind of galaxy survey with gravitational waves datasets
will allow to confidently rule in or out primordial black holes as dark matter
candidate in the majority of the allowed parameter space. | Initial clustering and the primordial black hole merger rate: If the primordial curvature perturbation followed a Gaussian distribution,
primordial black holes (PBHs) will be Poisson distributed with no additional
clustering. We consider local non-Gaussianity and its impact on the initial PBH
clustering and mass function due to mode coupling between long and short
wavelength modes. We show that even a small amount of non-Gaussianity results
in a significant enhancement on the PBH initial clustering and subsequent
merger rate and that the PBH mass function shifts to higher mass PBHs. However,
as the clustering becomes strong, the local number density of PBHs becomes
large, leading to a large theoretical uncertainty in the merger rate. |
Possible hints of decreasing dark energy from supernova data: The potential energy from a time-dependent scalar field provides a possible
explanation for the observed cosmic acceleration. In this paper, we investigate
how the redshift vs brightness data from the recent Pantheon+ survey of type Ia
supernovae constrain the possible evolution of a single scalar field for the
period of time (roughly half the age of the universe) over which supernova data
are available. Taking a linear approximation to the potential, we find that
models providing a good fit to the data typically have a decreasing potential
energy at present (accounting for over 99% of the allowed parameter space) with
a significant variation in scalar potential ($\langle {\rm Range}(V)/V_0
\rangle \approx 0.97$) over the period of time corresponding to the available
data ($z < 2.3$). Including quadratic terms in the potential, the data can be
fit well for a wide range of possible potentials including those with positive
or negative $V_2$ of large magnitude, and models where the universe has already
stopped accelerating. We describe a few degeneracies and approximate
degeneracies in the model that help explain the somewhat surprising range of
allowed potentials. | Wavelet Based Statistics for Enhanced 21cm EoR Parameter Constraints: We propose a new approach to improve the precision of astrophysical parameter
constraints for the 21cm signal from Epoch of Reionization (EoR). Our method
introduces new sets of summary statistics, hereafter evolution compressed
statistics, that quantify the spectral evolution of the 2D spatial statistics
computed a fixed redshift. We defined such compressed statistics for Power
Spectrum (PS), as well as Reduced Wavelet Scattering Transform (RWST) and
Wavelet Moments (WM), which also characterise non-Gaussian features. To compare
these different statistics with fiducial 3D power spectrum, we estimate their
Fisher information on three cosmological parameters from an ensemble of
simulations of 21cm EoR data, both in noiseless and noisy scenarios using
Square Kilometre Array (SKA) noise levels equivalent to 100 and 1000 hours of
observations. For the noiseless case, the compressed wavelet statistics give
constraints up to five times higher precision than the 3D isotropic power
spectrum, while for 100h SKA noise, for which non-Gaussian features are hard to
extract, they still give constraints which are 30% better. From this study, we
demonstrate that evolution-compressed statistics extract more information than
usual 3D isotropic approaches and that our wavelet-based statistics can
consistently outmatch power spectrum-based statistics. When constructing such
wavelet-based statistics, we also emphasise the need to choose a set of
wavelets with an appropriate spectral resolution concerning the astrophysical
process studied. |
The Cool-Core Bias in X-ray Galaxy Cluster Samples I: Method And
Application To HIFLUGCS: When selecting flux-limited cluster samples, the detection efficiency of
X-ray instruments is not the same for centrally-peaked and flat objects, which
introduces a bias in flux-limited cluster samples. We quantify this effect in
the case of a well-known cluster sample, HIFLUGCS. We simulate a population of
X-ray clusters with various surface-brightness profiles, and use the
instrumental characteristics of the ROSAT All-Sky Survey (RASS) to select
flux-limited samples similar to the HIFLUGCS sample and predict the expected
bias. For comparison, we also estimate observationally the bias in the HIFLUGCS
sample using XMM-Newton and ROSAT data. We find that the selection of X-ray
cluster samples is significantly biased ($\sim29%$) in favor of the peaked,
Cool-Core (CC) objects, with respect to Non-Cool-Core (NCC) systems.
Interestingly, we find that the bias affects the low-mass, nearby objects
(groups, poor clusters) much more than the more luminous objects (i.e massive
clusters). We also note a moderate increase of the bias for the more distant
systems. Observationally, we propose to select the objects according to their
flux in a well-defined physical range excluding the cores,
$0.2r_{500}-r_{500}$, to get rid of the bias. From the fluxes in this range, we
reject 13 clusters out of the 64 in the HIFLUGCS sample, none of which appears
to be NCC. As a result, we estimate that less than half (35-37%) of the galaxy
clusters in the local Universe are strong CC. In the paradigm where the CC
objects trace relaxed clusters as opposed to unrelaxed, merging objects, this
implies that to the present day the majority of the objects are not in a
relaxed state. From this result, we estimate a rate of heating events of
$\sim1/3$ Gyr$^{-1}$ per dark-matter halo. | Probing Primordial Stochastic Gravitational Wave Background with
Multi-band Astrophysical Foreground Cleaning: The primordial stochastic gravitational wave background (SGWB) carries
first-hand messages of early-universe physics, possibly including effects from
inflation, preheating, cosmic strings, electroweak symmetry breaking, and etc.
However, the astrophysical foreground from compact binaries may mask the SGWB,
introducing difficulties in detecting the signal and measuring it accurately.
In this paper, we propose a foreground cleaning method taking advantage of
gravitational wave observations in other frequency bands. We apply this method
to probing the SGWB with space-borne gravitational wave detectors, such as the
laser interferometer space antenna (LISA). We find that the spectral density of
the LISA-band astrophysical foreground from compact binaries (black holes and
neutron stars) can be predicted with percent-level accuracy assuming 10-years'
observations of third-generation GW detectors, e.g., cosmic explorer. While
this multi-band method does not apply to binary white dwarfs (BWDs) which
usually merger before entering the frequency band of ground-based detectors, we
limit our foreground cleaning to frequency higher than $\sim5$ mHz, where all
galactic BWDs can be individually resolved by LISA and the shape of the
spectral density of the foreground from extragalactic BWDs can be reconstructed
and/or modeled with certain uncertainties. After the foreground cleaning,
LISA's sensitivity to the primordial SGWB will be substantially improved for
either two LISA constellations where SGWB can be measured by cross correlating
their outputs or only one constellation with three spacecrafts where SGWB can
be measured by contrasting the responses of a signal channel and a null
channel. |
Local non-Gaussianity from inflation: The non-Gaussian distribution of primordial perturbations has the potential
to reveal the physical processes at work in the very early Universe. Local
models provide a well-defined class of non-Gaussian distributions that arise
naturally from the non-linear evolution of density perturbations on
super-Hubble scales starting from Gaussian field fluctuations during inflation.
I describe the delta-N formalism used to calculate the primordial density
perturbation on large scales and then review several models for the origin of
local primordial non-Gaussianity, including the cuvaton, modulated reheating
and ekpyrotic scenarios. I include an appendix with a table of sign conventions
used in specific papers. | Measurement of the Cosmic Microwave Background Polarization Lensing
Power Spectrum with the POLARBEAR experiment: Gravitational lensing due to the large-scale distribution of matter in the
cosmos distorts the primordial Cosmic Microwave Background (CMB) and thereby
induces new, small-scale $B$-mode polarization. This signal carries detailed
information about the distribution of all the gravitating matter between the
observer and CMB last scattering surface. We report the first direct evidence
for polarization lensing based on purely CMB information, from using the
four-point correlations of even- and odd-parity $E$- and $B$-mode polarization
mapped over $\sim30$ square degrees of the sky measured by the POLARBEAR
experiment. These data were analyzed using a blind analysis framework and
checked for spurious systematic contamination using null tests and simulations.
Evidence for the signal of polarization lensing and lensing $B$-modes is found
at 4.2$\sigma$ (stat.+sys.) significance. The amplitude of matter fluctuations
is measured with a precision of $27\%$, and is found to be consistent with the
Lambda Cold Dark Matter ($\Lambda$CDM) cosmological model. This measurement
demonstrates a new technique, capable of mapping all gravitating matter in the
Universe, sensitive to the sum of neutrino masses, and essential for cleaning
the lensing $B$-mode signal in searches for primordial gravitational waves. |
Galaxies and Cladistics: The Hubble tuning fork diagram, based on morphology and established in the
1930s, has always been the preferred scheme for classification of galaxies.
However, the current large amount of multiwavelength data, most often spectra,
for objects up to very high distances, asks for more sophisticated statistical
approaches. Interpreting formation and evolution of galaxies as a ?transmission
with modification' process, we have shown that the concepts and tools of
phylogenetic systematics can be heuristically transposed to the case of
galaxies. This approach, which we call ?astrocladistics', has successfully been
applied on several samples. Many difficulties still remain, some of them being
specific to the nature of both galaxies and their diversification processes,
some others being classical in cladistics, like the pertinence of the
descriptors in conveying any useful evolutionary information. | Relationship between Hubble type and spectroscopic class in local
galaxies: We compare the Hubble type and the spectroscopic class of the galaxies with
spectra in SDSS/DR7. As it is long known, elliptical galaxies tend to be red
whereas spiral galaxies tend to be blue, however, this relationship presents a
large scatter, which we measure and quantify in detail. We compare the
Automatic Spectroscopic K-means based classification (ASK) with most of the
commonly used morphological classifications. All of them provide consistent
results. Given a spectral class, the morphological type wavers with a standard
deviation between 2 and 3 T types, and the same large dispersion characterizes
the variability of spectral classes fixed the morphological type. The
distributions of Hubble types given an ASK class are very skewed -- they
present long tails that go to the late morphological types for the red
galaxies, and to the early morphological types for the blue spectroscopic
classes. The scatter is not produced by problems in the classification, and it
remains when particular subsets are considered. A considerable fraction of the
red galaxies are spirals (40--60 %), but they never present very late Hubble
types (Sd or later). Even though red spectra are not associated with
ellipticals, most ellipticals do have red spectra: 97 % of the ellipticals in
the morphological catalog by Nair & Abraham, used here for reference, belong to
ASK 0, 2 or 3. It contains only a 3 % of blue ellipticals. The galaxies in the
green valley class (ASK~5) are mostly spirals, and the AGN class (ASK 6)
presents a large scatter of Hubble types from E to Sd. From redshift 0.25 to
now the galaxies redden from ASK 2 to ASK 0, as expected from the passive
evolution of their stellar populations. Two of the ASK classes (1 and 4) gather
edge-on spirals, a property of interest in studies requiring knowing the
intrinsic shape of a galaxy (e.g., weak lensing calibration). |
Structure and Dynamics of the Globular Cluster Palomar 13: We present Keck/DEIMOS spectroscopy and CFHT/MegaCam photometry for the Milky
Way globular cluster Palomar 13. We triple the number of spectroscopically
confirmed members, including many repeat velocity measurements. Palomar 13 is
the only known globular cluster with possible evidence for dark matter, based
on a Keck/HIRES 21 star velocity dispersion of sigma=2.2+/-0.4 km/s. We
reproduce this measurement, but demonstrate that it is inflated by unresolved
binary stars. For our sample of 61 stars, the velocity dispersion is
sigma=0.7(+0.6/-0.5) km/s. Combining our DEIMOS data with literature values,
our final velocity dispersion is sigma=0.4(+0.4/-0.3) km/s. We determine a
spectroscopic metallicity of [Fe/H]=-1.6+/-0.1 dex, placing a 1-sigma upper
limit of sigma_[Fe/H]~0.2 dex on any internal metallicity spread. We determine
Palomar 13's total luminosity to be M_V=-2.8+/-0.4, making it among the least
luminous known globular clusters. The photometric isophotes are regular out to
the half-light radius and mildly irregular outside this radius. The outer
surface brightness profile slope is shallower than typical globular clusters
(eta=-2.8+/-0.3). Thus at large radius, tidal debris is likely affecting the
appearance of Palomar 13. Combining our luminosity with the intrinsic velocity
dispersion, we find a dynamical mass of of M_1/2=1.3(+2.7/-1.3)x10^3 M_sun and
a mass-to-light ratio of M/L_V=2.4(+5.0/-2.4) M_sun/L_sun. Within our
measurement errors, the mass-to-light ratio agrees with the theoretical
predictions for a single stellar population. We conclude that, while there is
some evidence for tidal stripping at large radius, the dynamical mass of
Palomar 13 is consistent with its stellar mass and neither significant dark
matter, nor extreme tidal heating, is required to explain the cluster dynamics. | The Hantzsche-Wendt Manifold in Cosmic Topology: The Hantzsche-Wendt space is one of the 17 multiply connected spaces of the
three-dimensional Euclidean space E^3. It is a compact and orientable manifold
which can serve as a model for a spatial finite universe. Since it possesses
much fewer matched back-to-back circle pairs on the cosmic microwave background
(CMB) sky than the other compact flat spaces, it can escape the detection by a
search for matched circle pairs. The suppression of temperature correlations
C(theta) on large angular scales on the CMB sky is studied. It is shown that
the large-scale correlations are of the same order as for the 3-torus topology
but express a much larger variability. The Hantzsche-Wendt manifold provides a
topological possibility with reduced large-angle correlations that can hide
from searches for matched back-to-back circle pairs. |
The stellar-to-halo mass relation for Local Group galaxies: We contend that a single power law halo mass distribution is appropriate for
direct matching to the stellar masses of observed Local Group dwarf galaxies,
allowing the determination of the slope of the stellar mass-halo mass relation
for low mass galaxies. Errors in halo masses are well defined as the Poisson
noise of simulated local group realisations, which we determine using
constrained local universe simulations (CLUES). For the stellar mass range
10$^7$<M*<10$^8$M$_\odot$, for which we likely have a complete census of
observed galaxies, we find that the stellar mass-halo mass relation follows a
power law with slope of 3.1, significantly steeper than most values in the
literature. The steep relation between stellar and halo masses indicates that
Local Group dwarf galaxies are hosted by dark matter halos with a small range
of mass. Our methodology is robust down to the stellar mass to which the census
of observed Local Group galaxies is complete, but the significant uncertainty
in the currently measured slope of the stellar-to halo mass relation will
decrease dramatically if the Local Group completeness limit was
$10^{6.5}$M$\odot$ or below, highlighting the importance of pushing such limit
to lower masses and larger volumes. | The Bias to Cosmic Microwave Background Lensing Reconstruction from the
Kinematic Sunyaev-Zel'dovich Effect at Reionization: The power spectrum of reconstructed cosmic microwave background (CMB) lensing
maps is a powerful tool for constraints on cosmological parameters like the sum
of the neutrino masses and the dark energy equation of state. One possible
complication is the kinematic Sunyaev-Zel'dovich (kSZ) effect, due to the
scattering of CMB photons by moving electrons, which can bias the
reconstruction of the CMB lensing power spectrum through both kSZ-lensing
correlations and the non-Gaussianity of the kSZ temperature anisotropies. We
investigate for the first time the bias to CMB lensing reconstruction from
temperature anisotropies due to the reionization-induced kSZ signal and show
that it is negligible for both ongoing and upcoming experiments based on
current numerical simulations of reionization. We also revisit the bias induced
by the late-time kSZ field, using more recent kSZ simulations. We find that it
is potentially twice as large as found in earlier studies, reaching values as
large as several percent of the CMB lensing power spectrum signal, indicating
that this bias will have to be mitigated in upcoming data analyses. |
Constraining the Merger History of Primordial-Black-Hole Binaries from
GWTC-3: Primordial black holes (PBHs) can be not only cold dark matter candidates but
also progenitors of binary black holes observed by LIGO-Virgo-KAGRA (LVK)
Collaboration. The PBH mass can be shifted to the heavy distribution if
multi-merger processes occur. In this work, we constrain the merger history of
PBH binaries using the gravitational wave events from the third
Gravitational-Wave Transient Catalog (GWTC-3). Considering four commonly used
PBH mass functions, namely the log-normal, power-law, broken power-law, and
critical collapse forms, we find that the multi-merger processes make a
subdominant contribution to the total merger rate. Therefore, the effect of
merger history can be safely ignored when estimating the merger rate of PBH
binaries. We also find that GWTC-3 is best fitted by the log-normal form among
the four PBH mass functions and confirm that the stellar-mass PBHs cannot
dominate cold dark matter. | 21 cm signal from cosmic dawn: Imprints of spin temperature fluctuations
and peculiar velocities: The 21 cm brightness temperature $\delta T_{\rm b}$ fluctuations from
reionization promise to provide information on the physical processes during
that epoch. We present a formalism for generating the $\delta T_{\rm b}$
distribution using dark matter simulations and an one-dimensional radiative
transfer code. Our analysis is able to account for the spin temperature $T_{\rm
S}$ fluctuations arising from inhomogeneous X-ray heating and Ly$\alpha$
coupling during cosmic dawn. The $\delta T_{\rm b}$ power spectrum amplitude at
large scales ($k \sim 0.1$ Mpc$^{-1}$) is maximum when $\sim 10\%$ of the gas
(by volume) is heated above the CMB temperature. The power spectrum shows a
"bump"-like feature during cosmic dawn and its location measures the typical
sizes of heated regions. We find that the effect of peculiar velocities on the
power spectrum is negligible at large scales for most part of the reionization
history. During early stages (when the volume averaged ionization fraction
$\lesssim 0.2$) this is because the signal is dominated by fluctuations in
$T_{\rm S}$. For reionization models that are solely driven by stars within
high mass ($\gtrsim 10^9\, \rm M_{\odot}$) haloes, the peculiar velocity
effects are prominent only at smaller scales ($k \gtrsim 0.4$ Mpc$^{-1}$) where
patchiness in the neutral hydrogen density dominates the signal. The
conclusions are unaffected by changes in the amplitude or steepness in the
X-ray spectra of the sources. |
Second Data Release of the COSMOS Lyman-alpha Mapping and Tomographic
Observation: The First 3D Maps of the Detailed Cosmic Web at 2.05<z<2.55: We present the second data release of the COSMOS Lyman-Alpha Mapping And
Tomography Observations (CLAMATO) Survey conducted with the LRIS spectrograph
on the Keck-I telescope. This project used Lyman-alpha forest absorption in the
spectra of faint star forming galaxies and quasars at z ~ 2-3 to trace neutral
hydrogen in the intergalactic medium. In particular, we use 320 objects over a
footprint of ~0.2 deg^2 to reconstruct the absorption field at 2.05 < z < 2.55
at ~2 h^{-1}Mpc resolution. We apply a Wiener filtering technique to the
observed data to reconstruct three dimensional maps of the field over a volume
of 4.1 x 10^5 comoving cubic Mpc. In addition to the filtered flux maps, for
the first time we infer the underlying dark matter field through a forward
modeling framework from a joint likelihood of galaxy and Lyman-alpha forest
data, finding clear examples of the detailed cosmic web consisting of cosmic
voids, sheets, filaments, and nodes. In addition to traditional figures, we
present a number of interactive three dimensional models to allow exploration
of the data and qualitative comparisons to known galaxy surveys. We find that
our inferred over-densities are consistent with those found from galaxy fields.
Our reduced spectra, extracted Lyman-alpha forest pixel data, and reconstructed
tomographic maps are available publicly at
https://doi.org/10.5281/zenodo.7524313 | Astrophysical constraints on massive black hole binary evolution from
Pulsar Timing Arrays: We consider the information that can be derived about massive black-hole
binary populations and their formation history solely from current and possible
future pulsar timing array (PTA) results. We use models of the stochastic
gravitational-wave background from circular massive black hole binaries with
chirp mass in the range $10^6 - 10^{11} M_\odot$ evolving solely due to
radiation reaction. Our parameterised models for the black hole merger history
make only weak assumptions about the properties of the black holes merging over
cosmic time. We show that current PTA results place an upper limit on the black
hole merger density which does not depend on the choice of a particular merger
history model, however they provide no information about the redshift or mass
distribution. We show that even in the case of a detection resulting from a
factor of 10 increase in amplitude sensitivity, PTAs will only put weak
constraints on the source merger density as a function of mass, and will not
provide any additional information on the redshift distribution. Without
additional assumptions or information from other observations, a detection
cannot meaningfully bound the massive black hole merger rate above zero or any
particular mass. |
Wide angle effects for peculiar velocities: The line-of-sight peculiar velocities of galaxies contribute to their
observed redshifts, breaking the translational invariance of galaxy clustering
down to a rotational invariance around the observer. This becomes important
when the line-of-sight direction varies significantly across a survey, leading
to what are known as `wide angle' effects in redshift space distortions.
Wide-angle effects will also be present in measurements of the momentum field,
i.e. the galaxy density-weighted velocity field, in upcoming peculiar velocity
surveys. In this work we study how wide-angle effects modify the predicted
correlation function and power spectrum for momentum statistics, both in
auto-correlation and in cross-correlation with the density field. Using both
linear theory and the Zeldovich approximation, we find that deviations from the
plane-parallel limit are large and could become important in data analysis for
low redshift surveys. We point out that even multipoles in the
cross-correlation between density and momentum are non-zero regardless of the
choice of line of sight, and therefore contain new cosmological information
that could be exploited. We discuss configuration-space, Fourier-space and
spherical analyses, providing exact expressions in each case rather than
relying on an expansion in small angles. We hope these expressions will be of
use in the analysis of upcoming surveys for redshift-space distortions and
peculiar velocities. | The Velocity Distribution Function of Galaxy Clusters as a Cosmological
Probe: We present a new approach for quantifying the abundance of galaxy clusters
and constraining cosmological parameters using dynamical measurements. In the
standard method, galaxy line-of-sight (LOS) velocities, $v$, or velocity
dispersions are used to infer cluster masses, $M$, in order to quantify the
halo mass function (HMF), $dn(M)/d\log(M)$, which is strongly affected by mass
measurement errors. In our new method, the probability distribution of
velocities for each cluster in the sample are summed to create a new statistic
called the velocity distribution function (VDF), $dn(v)/dv$. The VDF can be
measured more directly and precisely than the HMF and it can also be robustly
predicted with cosmological simulations which capture the dynamics of subhalos
or galaxies. We apply these two methods to mock cluster catalogs and forecast
the bias and constraints on the matter density parameter $\Omega_m$ and the
amplitude of matter fluctuations $\sigma_8$ in flat $\Lambda$CDM cosmologies.
For an example observation of 200 massive clusters, the VDF with (without)
velocity errors constrains the parameter combination $\sigma_8\Omega_m^{0.29\
(0.29)} = 0.587 \pm 0.011\ (0.583 \pm 0.011)$ and shows only minor bias.
However, the HMF with dynamical mass errors is biased to low $\Omega_m$ and
high $\sigma_8$ and the fiducial model lies well outside of the forecast
constraints, prior to accounting for Eddington bias. When the VDF is combined
with constraints from the cosmic microwave background (CMB), the degeneracy
between cosmological parameters can be significantly reduced. Upcoming
spectroscopic surveys that probe larger volumes and fainter magnitudes will
provide a larger number of clusters for applying the VDF as a cosmological
probe. |
WIMP Dark Matter and the First Stars: a critical overview: If Dark Matter (DM) is composed by Weakly Interacting Massive Particles, its
annihilation in the halos harboring the earliest star formation episode may
strongly influence the first generation of stars (Population III). Whereas DM
annihilation at early stages of gas collapse does not dramatically affect the
properties of the cloud, the formation of a hydrostatic object (protostar) and
its evolution toward the main sequence may be delayed. This process involves DM
concentrated in the center of the halo by gravitational drag, and no consensus
is yet reached over whether this can push the initial mass of Population III to
higher masses. DM can also be captured through scattering over the baryons in a
dense object, onto or very close to the Main Sequence. This mechanism can
affect formed stars and in principle prolonge their lifetimes. The strength of
both mechanisms depends upon several environmental conditions and on DM
parameters; such spread in the parameter space leads to very different
scenarios for the observables in the Population. Here I summarize the state of
the art in modelling and observational expectations, eventually highlighting
the most critical assumptions and sources of uncertainty. | Forecasting constraints on the high-z IGM thermal state from the
Lyman-$α$ forest flux auto-correlation function: The auto-correlation function of the Lyman-$\alpha$ (Ly$\alpha$) forest flux
from high-z quasars can statistically probe all scales of the intergalactic
medium (IGM) just after the epoch of reionization. The thermal state of the
IGM, which is determined by the physics of reionization, sets the amount of
small-scale power seen in the \lya forest. To study the sensitivity of the
auto-correlation function to the thermal state of the IGM, we compute the
auto-correlation function from cosmological hydrodynamical simulations with
semi-numerical models of the thermal state of the IGM. We create mock data sets
of 20 quasars to forecast constraints on $T_0$ and $\gamma$, which characterize
a tight temperature-density relation in the IGM, at $5.4 \leq z \leq 6$. At $z
= 5.4$ we find that an ideal data set constrains $T_0$ to 29\% and $\gamma$ to
9\%. In addition, we investigate four realistic reionization scenarios that
combine temperature and ultra-violet background (UVB) fluctuations at $z =
5.8$. We find that, when using mock data generated from a model that includes
temperature and UVB fluctuations, we can rule out a model with no temperature
or UVB fluctuations at $>1\sigma$ level 50.5\% of the time. |
An Analytical Study of the Primordial Gravitational-Wave-Induced
Contribution to the Large-Scale Structure of the Universe: The imprint of gravitational waves (GWs) on large-scale structures (LSS) is a
useful and promising way to detect or to constrain them. Tensor fossils have
been largely studied in the literature as an indirect way to detect primordial
GWs. In this paper we analyze a new effect induced by primordial GWs: a
correction to the density contrast of the underlying matter distribution of
LSS, as well as its radiation counterpart, induced by the energy density
fluctuation of the gravitational radiation. We perform our derivation of the
full analytical solution of the density contrast for waves entering the horizon
during radiation dominance. We account for two phases in the radiation era,
depending on the main contributor to the perturbed energy density of the
Universe. By comparing the density contrast of cold dark matter and radiation
-- sourced by linear gravitational waves only -- we conclude that the former
overcomes the latter at some time in the radiation era, a behaviour analogous
to their linear counterpart. Then we conclude by discussing the case of density
perturbations produced by GWs entering the Hubble radius during the matter era
as well as their evolution in the late dark-energy dominated phase. | Gravitational waves from the merger of two primordial black hole
clusters: The orbital evolution of a binary system consisting of two primordial black
hole clusters is investigated. Such clusters are predicted in some theoretical
models with broken symmetry in the inflation Lagrangian. A cluster consists of
the most massive central black hole surrounded by many smaller black holes.
Similar to single primordial black holes, clusters can form gravitationally
bounded pairs and merge during their orbital evolution. The replacement of
single black holes by such clusters significantly changes the entire merger
process and the final rate of gravitational wave bursts in some parameter
ranges (with sufficiently large cluster radii). A new important factor is the
tidal gravitational interaction of the clusters. It leads to an additional
dissipation of the orbital energy, which is transferred into the internal
energy of the clusters or carried away by black holes flying out of the
clusters. Comparison with the data of gravitational-wave telescopes allows one
to constrain the fractions of primordial black holes in clusters, depending on
their mass and compactness. Even the primordial black hole fraction in the
composition of dark matter $\simeq1$ turns out to be compatible with LIGO/Virgo
observational data, if the black holes are in clusters. |
Fast Estimators for Redshift-Space Clustering: Redshift-space distortions in galaxy surveys happen along the radial
direction, breaking statistical translation invariance. We construct estimators
for radial distortions that, using only Fast Fourier Transforms (FFTs) of the
overdensity field multipoles for a given survey geometry, compute the power
spectrum monopole, quadrupole and hexadecapole, and generalize such estimators
to the bispectrum. Using realistic mock catalogs we compare the signal to noise
of two estimators for the power spectrum hexadecapole that require different
number of FFTs and measure the bispectrum monopole, quadrupole and
hexadecapole. The resulting algorithm is very efficient, e.g. for the BOSS
survey requires about three minutes for $\ell=0,2,4$ power spectra for scales
up to $k=0.3~h/$Mpc and about fifteen additional minutes for $\ell=0,2,4$
bispectra for all scales and triangle shapes up to $k=0.2~h/$Mpc on a single
core. The speed of these estimators is essential as it makes possible to
compute covariance matrices from large number of realizations of mock catalogs
with realistic survey characteristics, and paves the way for improved
constrains of gravity on cosmological scales, inflation and galaxy bias. | Optimal analysis of azimuthal features in the CMB: We present algorithms for searching for azimuthally symmetric features in CMB
data. Our algorithms are fully optimal for masked all-sky data with
inhomogeneous noise, computationally fast, simple to implement, and make no
approximations. We show how to implement the optimal analysis in both Bayesian
and frequentist cases. In the Bayesian case, our algorithm for evaluating the
posterior likelihood is so fast that we can do a brute-force search over
parameter space, rather than using a Monte Carlo Markov chain. Our motivating
example is searching for bubble collisions, a pre-inflationary signal which can
be generated if multiple tunneling events occur in an eternally inflating
spacetime, but our algorithms are general and should be useful in other
contexts. |
Clustering properties of TGSS radio sources: We investigate the clustering properties of radio sources in the Alternative
Data Release 1 of the TIFR GMRT Sky Survey (TGSS), focusing on large angular
scales, where previous analyses have detected a large clustering signal. After
appropriate data selection, the TGSS sample we use contains ~110,000 sources
selected at 150 MHz over ~70% of the sky. The survey footprint is largely
superimposed on that of the NRAO VLA Sky Survey (NVSS) with the majority of
TGSS sources having a counterpart in the NVSS sample. These characteristics
make TGSS suitable for large-scale clustering analyses and facilitate the
comparison with the results of previous studies. In this analysis we focus on
the angular power spectrum, although the angular correlation function is also
computed to quantify the contribution of multiple-component radio sources. We
find that on large angular scales, corresponding to multipoles $2 \leq \ell
\leq 30$, the amplitude of the TGSS angular power spectrum is significantly
larger than that of the NVSS. We do not identify any observational systematic
effects that may explain this mismatch. We have produced a number of physically
motivated models for the TGSS angular power spectrum and found that all of them
fail to match observations, even when taking into account observational and
theoretical uncertainties. The same models provide a good fit to the angular
spectrum of the NVSS sources. These results confirm the anomalous nature of the
TGSS large-scale power, which has no obvious physical origin and seems to
indicate that unknown systematic errors are present in the TGSS dataset. | Large-scale anomalies from primordial dissipation: We analyze an inflationary model in which part of the power in density
perturbations arises due to particle production. The amount of particle
production is modulated by an auxiliary field. Given an initial gradient for
the auxiliary field, this model produces a hemispherical power asymmetry and a
suppression of power at low multipoles similar to those observed by WMAP and
Planck in the CMB temperature. It also predicts an additive contribution to
$\delta T$ with support only at very small $l$ that is aligned with the
direction of the power asymmetry and has a definite sign, as well as small
oscillations in the power spectrum at all $l$. |
Primordial Black Holes as a dark matter candidate: The detection of gravitational waves from mergers of tens of Solar mass black
hole binaries has led to a surge in interest in Primordial Black Holes (PBHs)
as a dark matter candidate. We aim to provide a (relatively) concise overview
of the status of PBHs as a dark matter candidate, circa Summer 2020. First we
review the formation of PBHs in the early Universe, focusing mainly on PBHs
formed via the collapse of large density perturbations generated by inflation.
Then we review the various current and future constraints on the present day
abundance of PBHs. We conclude with a discussion of the key open questions in
this field. | Effects of modified gravity on B-mode polarization: We explore the impact of modified gravity on B-modes, identifying two main
separate effects: lensing and propagation of tensor modes. The location of the
inflationary peak of the BB spectrum depends on the speed of gravitational
waves; the amplitude of the lensing contribution depends on the anisotropic
stress. We single out these effects using the quasi-static regime and
considering models for which the background and the growth of matter
perturbations are standard. Using available data we obtain that the
gravitational wave speed is compatible with the speed of light and constrained
to within about 10%. |
Probing Particle Physics from Top Down with Cosmic Strings: Making use of the wealth of new observational data coming from the sky it is
possible to constrain particle physics theories beyond the Standard Model. One
way to do this is illustrated in this article: a subset of theories admits
cosmic string solutions, topologically stable matter field configurations. In
these models, a network of cosmic strings inevitably forms in the early
universe and persists to the present time. The gravitational effects of these
strings leads to cosmological signatures which could be visible in current and
future data. The magnitude of these signatures increases as the energy scale of
the new physics involved in cosmic string formation increases. Thus, searching
for cosmological signatures of strings is a way to probe particle physics model
"from top down", as opposed to "from bottom up" as is done using data from
accelerators such as the Large Hadron Collider. Different ways of searching for
cosmic strings are illustrated in this article. They include Cosmic Microwave
Background temperature and polarization anisotropy maps, Large Scale Structure
optical and infrared surveys, and 21cm intensity maps. | The THESAN project: Lyman-alpha emission and transmission during the
Epoch of Reionization: The visibility of high-redshift Lyman-alpha emitting galaxies (LAEs) provides
important constraints on galaxy formation processes and the Epoch of
Reionization (EoR). However, predicting realistic and representative statistics
for comparison with observations represents a significant challenge in the
context of large-volume cosmological simulations. The THESAN project offers a
unique framework for addressing such limitations by combining state-of-the-art
galaxy formation (IllustrisTNG) and dust models with the Arepo-RT
radiation-magneto-hydrodynamics solver. In this initial study we present
Lyman-alpha centric analysis for the flagship simulation that resolves atomic
cooling haloes throughout a (95.5 cMpc)^3 region of the Universe. To avoid
numerical artifacts we devise a novel method for accurate frequency-dependent
line radiative transfer in the presence of continuous Hubble flow, transferable
to broader astrophysical applications as well. Our scalable approach highlights
the utility of LAEs and red damping-wing transmission as probes of
reionization, which reveal nontrivial trends across different galaxies,
sightlines, and frequency bands that can be modelled in the framework of
covering fractions. In fact, after accounting for environmental factors
influencing large-scale ionized bubble formation such as redshift and UV
magnitude, the variation across galaxies and sightlines mainly depends on
random processes including peculiar velocities and self-shielded systems that
strongly impact unfortunate rays more than others. Throughout the EoR local and
cosmological optical depths are often greater than or less than unity such that
the exp(-tau) behavior leads to anisotropic and bimodal transmissivity. Future
surveys will benefit by targeting both rare bright objects and Goldilocks zone
LAEs to infer the presence of these (un)predictable (dis)advantages. |
Effects of large-scale structure on the accuracy of weak lensing mass
measurements: Weak gravitational lensing has become an important method to determine the
masses of galaxy clusters. The intrinsic shapes of the galaxies are a dominant
source of uncertainty, but there are other limitations to the precision that
can be achieved. In this paper we revisit a typically ignored source of
uncertainty: structure along the line-of sight. Using results from the
Millennium Simulation we confirm the validity of analytical calculations that
have shown that such random projections are particularly important for studies
of the cluster density profile. In general the contribution of large-scale
structure to the total error budget is comparable to the statistical errors. We
find that the precision of the mass measurement can be improved only slightly
by modelling the large-scale structure using readily available data. | Measuring the tilt of primordial gravitational-wave power spectrum from
observations: Primordial gravitational waves generated during inflation lead to the B-mode
polarization in the cosmic microwave background and a stochastic gravitational
wave background in the Universe. We will explore the current constraint on the
tilt of primordial gravitational-wave spectrum, and forecast how the future
observations can improve the current constraint. |
Effects on Galaxy Evolution: Pair Interactions versus Environment: In a hierarchical universe, mergers may be an important mechanism not only in
increasing the mass of galaxies but also in driving the color and morphological
evolution of galaxies. We use a large sample of ~1000 simulated galaxies of
stellar mass greater than 10^9.6 solar masses (for ~4800 observations at
multiple redshifts) from a high-res (0.46 h^{-1} kpc) cosmological simulation
to determine under what circumstances being a member of a pair influences
galaxy properties at z <= 0.2. We identify gravitationally bound pairs, and
find a relative fraction of blue-blue, red-red, and blue-red pairs that agrees
with observations (Lin et al. 2010). Pairs tend to avoid the extreme
environments of clusters and void centres. While pairs in groups can include
galaxies that are both blue, both red, or one of each color, in the field it is
rare for pair galaxies to both be red. We find that physically bound pairs
closer than 250 h^{-1} kpc tend to have higher sSFRs than the galaxy population
as a whole. However, the sSFR of a bound galaxy relative to galaxies in a
comparable local density environment (determined by the distance to the fifth
nearest neighbor, rho_5), differs depending on the local density. In regions of
high rho_5 the bound population has a higher fraction of star-forming (bluer)
galaxies, whereas there is very little difference between bound and unbound
galaxies in low rho_5 regions. This effect on the star-forming fraction may be
driven by the higher fraction of bound HI-rich galaxies compared to unbound
galaxies, particularly at high local densities. It appears that being in a pair
has an incremental, but not overwhelming, effect on the star formation rate of
the paired galaxies, compared to the more pronounced trend where galaxies
overall have low sSFR (are red) in clusters and higher sSFR (blue) at the
centre of voids. This trend depends most strongly on rho_5.(abridged) | Dark Matter from the Inflaton Field: We present a model where inflation and Dark Matter takes place via a single
scalar field phi. Without introducing any new parameters we are able unify
inflation and Dark Matter using a scalar field phi that accounts for inflation
at an early epoch while it gives a Dark Matter WIMP particle at low energies.
After inflation our universe must be reheated and we must have a long period of
radiation dominated before the epoch of Dark Matter. Typically the inflaton
decays while it oscillates around the minimum of its potential. If the inflaton
decay is not complete or sufficient then the remaining energy density of the
inflaton after reheating must be fine tuned to give the correct amount of Dark
Matter. An essential feature here, is that Dark Matter-Inflaton particle is
produced at low energies without fine tuning or new parameters. This process
uses the same coupling g as for the inflaton decay. Once the field phi becomes
non-relativistic it will decouple as any WIMP particle, since n_phi is
exponentially suppressed. The correct amount of Dark Matter determines the
cross section and we have a constraint between the coupling $g$ and the mass
$m_o$ of phi. The unification scheme we present here has four free parameters,
two for the scalar potential V(phi) given by the inflation parameter lambda of
the quartic term and the mass m_o. The other two parameters are the coupling
$g$ between the inflaton phi and a scalar filed varphi and the coupling h
between varphi with standard model particles psi or chi. These four parameters
are already present in models of inflation and reheating process, without
considering Dark Matter. Therefore, our unification scheme does not increase
the number of parameters and it accomplishes the desired unification between
the inflaton and Dark Matter for free. |
Rates of Superluminous Supernovae at z~0.2: We calculate the volumetric rate of superluminous supernovae (SLSNe) based on
5 events discovered with the ROTSE-IIIb telescope. We gather light curves of 19
events from the literature and our own unpublished data and employ crude
k-corrections to constrain the pseudo-absolute magnitude distributions in the
rest frame ROTSE-IIIb (unfiltered) band pass for both the hydrogen poor
(SLSN-I) and hydrogen rich (SLSN-II) populations. We find that the peak
magnitudes of the available SLSN-I are narrowly distributed ($M = -21.7 \pm
0.4$) in our unfiltered band pass and may suggest an even tighter intrinsic
distribution when the effects of dust are considered, although the sample may
be skewed by selection and publication biases. The presence of OII features
near maximum light may uniquely signal a high luminosity event, and we suggest
further observational and theoretical work is warranted to assess the possible
utility of such SN 2005ap-like SLSN-I as distance indicators. Using the
pseudo-absolute magnitude distributions derived from the light curve sample, we
measure the SLSN-I rate to be about (32^{+77}_{-26}) events Gpc^{-3} yr^{-1}
h_{71}^{3} at a weighted redshift of z = 0.17, and the SLSN-II rate to be about
(151^{+151}_{-82}) events Gpc^{-3} yr^{-1} h_{71}^{3} at z = 0.15. Given that
the exact nature and limits of these populations are still unknown, we discuss
how it may be difficult to distinguish these rare SLSNe from other transient
phenomena such as AGN activity and tidal disruption events even when multi-band
photometry, spectroscopy, or even high resolution imaging are available.
Including one spectroscopically peculiar event, we determine a total rate for
SLSN-like events of (199^{+137}_{-86}) events Gpc^{-3} yr^{-1} h_{71}^{3} at z
= 0.16. | Leveraging cross-correlations and linear covariance-based filtering for
line-intensity map reconstructions at linear scales: We explore the possible application of linear covariance-based (LCB)
filtering to line-intensity mapping (LIM) signal reconstructions. Originally
introduced for reconstruction of the integrated Sachs-Wolfe effect in the
cosmic microwave background, the LCB filter is an optimal map estimator that
extends the simple Wiener filter by leveraging external correlated data. Given
a detectable strong LIM-galaxy or LIM-LIM cross power spectrum, we show
recovery of high-redshift, large-scale line-intensity fluctuations -- even in
the presence of bright interloper emission -- in simulations of a futuristic [C
II] LIM survey as well as simulated future iterations of the CO Mapping Array
Project (COMAP). With sufficient galaxy abundances or low LIM survey noise,
normalised cross-correlation between the LCB reconstruction and the true signal
reaches 70-90% on large, linear comoving scales corresponding to $k\sim0.1$
Mpc$^{-1}$. This suggests the possible use of such signal reconstructions in
astrophysical or cosmological contexts that require identifying the locations
of line emissivity peaks and voids, although clear shortcomings exist on
smaller scales. The successful application of the LCB filter in simulated LIM
contexts highlights the importance of cross-correlations to studies of the
reionising and reionised high-redshift universe with LIM and other large-scale
structure surveys. |
Infall Times for Milky Way Satellites From Their Present-Day Kinematics: We analyze subhalos in the Via Lactea II (VL2) cosmological simulation to
look for correlations among their infall times and z = 0 dynamical properties.
We find that the present day orbital energy is tightly correlated with the time
at which subhalos last crossed into the virial radius. This energy-infall
correlation provides a means to infer infall times for Milky Way satellite
galaxies. Assuming that the Milky Way's assembly can be modeled by VL2, we show
that the infall times of some satellites are well constrained given only their
Galactocentric positions and line-of-sight velocities. The constraints sharpen
for satellites with proper motion measurements. We find that Carina, Ursa
Minor, and Sculptor were all accreted early, more than 8 Gyr ago. Five other
dwarfs, including Sextans and Segue 1, are also probable early accreters,
though with larger uncertainties. On the other extreme, Leo T is just falling
into the Milky Way for the first time while Leo I fell in \sim 2 Gyr ago and is
now climbing out of the Milky Way's potential after its first perigalacticon.
The energies of several other dwarfs, including Fornax and Hercules, point to
intermediate infall times, 2 - 8 Gyr ago. We compare our infall time estimates
to published star formation histories and find hints of a dichotomy between
ultrafaint and classical dwarfs. The classical dwarfs appear to have quenched
star formation after infall but the ultrafaint dwarfs tend to be quenched long
before infall, at least for the cases in which our uncertainties allow us to
discern differences. Our analysis suggests that the Large Magellanic Cloud
crossed inside the Milky Way virial radius recently, within the last \sim 4
billion years. | Constraints on the End of Reionization from the Density Fields
Surrounding Two Highly Opaque Quasar Sightlines: The observed large-scale scatter in Lyman $\alpha$ opacity of the
intergalactic medium at $z<6$ implies large fluctuations in the neutral
hydrogen fraction that are unexpected long after reionization has ended. A
number of models have emerged to explain these fluctuations that make testable
predictions for the relationship between Ly$\alpha$ opacity and density. We
present selections of $z=5.7$ Ly$\alpha$-emitting galaxies (LAEs) in the fields
surrounding two highly opaque quasar sightlines with long Ly$\alpha$ troughs.
The fields lie towards the $z=6.0$ quasar ULAS J0148+0600, for which we
re-analyze previously published results using improved photometric selection,
and towards the $z=6.15$ quasar SDSS J1250+3130, for which results are
presented here for the first time. In both fields, we report a deficit of LAEs
within 20 $h^{-1}$ Mpc of the quasar. The association of highly opaque
sightlines with galaxy underdensities in these two fields is consistent with
models in which the scatter in Ly$\alpha$ opacity is driven by large-scale
fluctuations in the ionizing UV background, or by an ultra-late reionization
that has not yet concluded at $z=5.7$. |
The Molecular Gas Density in Galaxy Centers and How It Connects to
Bulges: In this paper we present gas density, star formation rate, stellar masses,
and bulge disk decompositions for a sample of 60 galaxies. Our sample is the
combined sample of BIMA SONG, CARMA STING, and PdBI NUGA surveys. We study the
effect of using CO-to-H_2 conversion factors that depend on the CO surface
brightness, and also that of correcting star formation rates for diffuse
emission from old stellar populations. We estimate that star formation rates in
bulges are typically lower by 20% when correcting for diffuse emission. We find
that over half of the galaxies in our sample have molecular gas surface density
>100 M_sun pc^-2. We find a trend between gas density of bulges and bulge
Sersic index; bulges with lower Sersic index have higher gas density. Those
bulges with low Sersic index (pseudobulges) have gas fractions that are similar
to that of disks. We also find that there is a strong correlation between
bulges with the highest gas surface density and the galaxy being barred.
However, we also find that classical bulges with low gas surface density can be
barred as well. Our results suggest that understanding the connection between
the central surface density of gas in disk galaxies and the presence of bars
should also take into account the total gas content of the galaxy and/or bulge
Sersic index. Indeed, we find that high bulge Sersic index is the best
predictor of low gas density inside the bulge (not barredness of the disk).
Finally, we show that when using the corrected star formation rates and gas
densities, the correlation between star formation rate surface density and gas
surface density of bulges is similar to that of disks. | One Hundred First Stars : Protostellar Evolution and the Final Masses: We perform a large set of radiation hydrodynamics simulations of primordial
star formation in a fully cosmological context. Our statistical sample of 100
First Stars show that the first generation of stars have a wide mass
distribution M_popIII = 10 ~ 1000 M_sun. We first run cosmological simulations
to generate a set of primordial star-forming gas clouds. We then follow
protostar formation in each gas cloud and the subsequent protostellar evolution
until the gas mass accretion onto the protostar is halted by stellar radiative
feedback. The accretion rates differ significantly among the primordial gas
clouds which largely determine the final stellar masses. For low accretion
rates the growth of a protostar is self-regulated by radiative feedback effects
and the final mass is limited to several tens of solar masses. At high
accretion rates the protostar's outer envelope continues to expand and the
effective surface temperature remains low; such protostars do not exert strong
radiative feedback and can grow in excess to one hundred solar masses. The
obtained wide mass range suggests that the first stars play a variety of roles
in the early universe, by triggering both core-collapse supernovae and
pair-instability supernovae as well as by leaving stellar mass black holes. We
find certain correlations between the final stellar mass and the physical
properties of the star-forming cloud. These correlations can be used to
estimate the mass of the first star from the properties of the parent cloud or
of the host halo, without following the detailed protostellar evolution. |
Cosmic string loop shapes: We analyze the shapes of cosmic string loops found in large-scale simulations
of an expanding-universe string network. The simulation does not include
gravitational back reaction, but we model that process by smoothing the loop
using Lorentzian convolution. We find that loops at formation consist of
generally straight segments separated by kinks. We do not see cusps or any
cusp-like structure at the scale of the entire loop, although we do see very
small regions of string that move with large Lorentz boosts. However, smoothing
of the string almost always introduces two cusps on each loop. The smoothing
process does not lead to any significant fragmentation of loops that were in
non-self-intersecting trajectories before smoothing. | Cold New Early Dark Energy pulls the trigger on the $H_0$ and $S_8$
tensions: a simultaneous solution to both tensions without new ingredients: In this work, we show that the Cold New Early Dark Energy (Cold NEDE) model
in its original form can solve both the Hubble tension and the $S_8$ tension
without adding any new ingredients at the fundamental level. So far, it was
assumed that the trigger field in the Cold NEDE model is completely
subdominant. However, relaxing this assumption and letting the trigger field
contribute a mere $0.5\%$ of the total energy density leads to a resolution of
the $S_8$ tension while simultaneously improving it as a solution to the $H_0$
tension. Fitting this model to baryonic acoustic oscillations,
large-scale-structure, supernovae (including a SH0ES prior), and cosmic
microwave background data, we report a preferred NEDE fraction of
$f_\mathrm{NEDE}= 0.134^{+0.032}_{-0.025}$ ($68\%$ C.L.), lifting its Gaussian
evidence for the first time above $5\sigma$ (up from $4 \sigma$ when the
trigger contribution to dark matter is negligible). At the same time, we find
the new concordance values $H_0 = 71.71 \pm 0.88 \,\mathrm{km}\,
\mathrm{sec}^{-1}\, \mathrm{Mpc}^{-1}$ and $S_8 = 0.793 \pm 0.018$. Excluding
large-scale structure data and the SH$_0$ES prior, both Gaussian tensions are
reduced below the $2 \sigma$ level. |
Stellar Feedback in Galaxies and the Origin of Galaxy-scale Winds: Feedback from massive stars is believed to play a critical role in driving
galactic super-winds that enrich the IGM and shape the galaxy mass function and
mass-metallicity relation. In previous papers, we introduced new numerical
methods for implementing stellar feedback on sub-GMC through galactic scales in
galaxy simulations. This includes radiation pressure (UV through IR), SNe
(Type-I & II), stellar winds ('fast' O-star through 'slow' AGB winds), and HII
photoionization. Here, we show that these feedback mechanisms drive galactic
winds with outflow rates as high as ~10-20 times the galaxy SFR. The
mass-loading efficiency (wind mass loss rate divided by SFR) scales inversely
with circular velocity, consistent with momentum-conservation expectations. We
study the contributions of each feedback mechanism to galactic winds in a range
of galaxy models, from SMC-like dwarfs & MW-analogues to z~2 clumpy disks. In
massive, gas-rich systems (local starbursts and high-z galaxies), radiation
pressure dominates the wind generation. For MW-like spirals and dwarf galaxies
the gas densities are much lower, and shock-heated gas from SNe and stellar
winds dominates production of large-scale outflows. In all models, however,
winds have a multi-phase structure that depends on interactions between
multiple feedback mechanisms operating on different spatial & time scales: any
single mechanism fails to reproduce the winds observed. We provide fitting
functions for wind mass-loading and velocities as a function of galaxy
properties, for use in cosmological simulations and semi-analytic models. These
differ from typically-adopted formulae with explicit dependence on gas surface
density that can be very important in both low-density dwarf galaxies and
high-density gas-rich galaxies. | Are small-scale sub-structures a universal property of galaxy halos? The
case of the giant elliptical NGC~5128: We present an analysis of the spatial and chemical sub-structures in a remote
halo field in the nearby giant elliptical galaxy Centaurus A (NGC~5128),
situated at about 38 kpc from the centre of the galaxy. The observations were
taken with the Advanced Camera for Surveys instrument on board the Hubble Space
Telescope, and reach down to the horizontal branch. In this relatively small
3.8 kpc by 3.8 kpc field, after correcting for Poisson noise, we do not find
any statistically strong evidence for the presence of small-scale
sub-structures in the stellar spatial distribution on scales greater than 100
pc. However, we do detect the presence of significant small spatial-scale
inhomogeneities in the stellar median metallicity over the surveyed field. We
argue that these localized chemical substructures could be associated with
not-fully mixed debris from the disruption of low mass systems. NGC 5128 joins
the ranks of the late-type spiral galaxies the Milky Way, for which the stellar
halo appears to be dominated by small-scale spatial sub-structures, and
NGC~891, where localized metallicity variations have been detected in the inner
extra-planar regions. This suggests that the presence of small-scale
sub-structures may be a generic property of stellar halos of large galaxies. |
The eROSITA Final Equatorial-Depth Survey (eFEDS): Catalog of galaxy
clusters and groups: The eROSITA Final Equatorial-Depth Survey has been carried out during the PV
phase of the SRG/eROSITA telescope and completed in November 2019. This survey
is designed to provide the first eROSITA-selected sample of galaxy clusters and
groups and to test the predictions for the all-sky survey in the context of
cosmological studies with clusters. In the 140 deg$^2$ area covered by eFEDS,
542 candidate clusters and groups are detected as extended X-ray sources, down
to a flux of $\sim10^{-14} $erg/s/cm$^2$ in the soft band (0.5-2 keV) within
1'. In this work, we provide the catalog of candidate galaxy clusters and
groups in eFEDS. We perform imaging and spectral analysis on the eFEDS clusters
with eROSITA X-ray data, and study the properties of the sample. The clusters
are distributed in the redshift range [0.01, 1.3], with the median redshift at
0.35. We obtain the ICM temperature measurement with $>2\sigma$ c.l. for
$\sim$1/5 (102/542) of the sample. The average temperature of these clusters is
$\sim$2 keV. Radial profiles of flux, luminosity, electron density, and gas
mass are measured from the precise modeling of the imaging data. The selection
function, the purity and completeness of the catalog are examined and discussed
in detail. The contamination fraction is $\sim1/5$ in this sample, dominated by
misidentified point sources. The X-ray Luminosity Function of the clusters
agrees well with the results obtained from other recent X-ray surveys. We also
find 19 supercluster candidates in eFEDS, most of which are located at
redshifts between 0.1 and 0.5. The eFEDS cluster and group catalog provides a
benchmark proof-of-concept for the eROSITA All-Sky Survey extended source
detection and characterization. We confirm the excellent performance of eROSITA
for cluster science and expect no significant deviations from our pre-launch
expectations for the final All-Sky Survey. | Bouncing cosmologies with dark matter and dark energy: We review matter bounce scenarios where the matter content is dark matter and
dark energy. These cosmologies predict a nearly scale-invariant power spectrum
with a slightly red tilt for scalar perturbations and a small tensor-to-scalar
ratio. Importantly, these models predict a positive running of the scalar
index, contrary to the predictions of the simplest inflationary and ekpyrotic
models, and hence could potentially be falsified by future observations. We
also review how bouncing cosmological space-times can arise in theories where
either the Einstein equations are modified or where matter fields that violate
the null energy condition are included. |
Distinguishing cosmologies using the turn-around radius near galaxy
clusters: Outside galaxy clusters the competition between the inwards gravitational
attraction and the outwards expansion of the Universe leads to a special radius
of velocity cancellation, which is called the turn-around radius. Measurements
of the turn-around radius hold promises of constraining cosmological
parameters, and possibly even properties of gravity. Such a measurement is,
however, complicated by the fact that the surroundings of galaxy clusters are
not spherical, but instead are a complicated collection of filaments, sheets
and voids. In this paper we use the results of numerically simulated universes
to quantify realistic error-bars of the measurement of the turn-around radius.
We find that for a $\Lambda$CDM cosmology these error-bars are typically of the
order of $20\%$. We numerically simulate three different implementations of
dark energy models and of a scalar dark sector interaction to address whether
the turn-around radius can be used to constrain non-trivial cosmologies, and we
find that only rather extreme models can be distinguished from a $\Lambda$CDM
universe due to the large error-bars arising from the non-trivial cluster
environments. | The traces of anisotropic dark energy in light of Planck: We study a dark energy model with non-zero anisotropic stress, either linked
to the dark energy density or to the dark matter density. We compute
approximate solutions that allow to characterise the behaviour of the dark
energy model and to assess the stability of the perturbations. We also
determine the current limits on such an anisotropic stress from the cosmic
microwave background data by the Planck satellite, and derive the corresponding
constraints on the modified growth parameters like the growth index, the
effective Newton's constant and the gravitational slip. |
3D Integral Field Observations of Ten Galactic Winds - I. Extended phase
(>10 Myr) of mass/energy injection before the wind blows: We present 3D spectroscopic observations of a sample of 10 nearby galaxies
with the AAOmega-SPIRAL integral field spectrograph on the 3.9m AAT, the
largest survey of its kind to date. The double-beam spectrograph provides
spatial maps in a range of spectral diagnostics: [OIII] 5007, H-beta, Mg-b,
NaD, [OI] 6300, H-alpha, [NII] 6583, [SII] 6717, 6731. All of the objects in
our survey show extensive wind-driven filamentation along the minor axis, in
addition to large-scale disk rotation. Our sample can be divided into either
starburst galaxies or active galactic nuclei (AGN), although some objects
appear to be a combination of these. The total ionizing photon budget available
to both classes of galaxies is sufficient to ionise all of the wind-blown
filamentation out to large radius. We find however that while AGN
photoionisation always dominates in the wind filaments, this is not the case in
starburst galaxies where shock ionisation dominates. This clearly indicates
that after the onset of star formation, there is a substantial delay (> 10 Myr)
before a starburst wind develops. We show why this behavior is expected by
deriving ``ionisation'' and dynamical timescales for both AGNs and starbursts.
We establish a sequence of events that lead to the onset of a galactic wind.
The clear signature provided by the ionisation timescale is arguably the
strongest evidence yet that the starburst phenomenon is an impulsive event. A
well-defined ionisation timescale is not expected in galaxies with a protracted
history of circumnuclear star formation. Our 3D data provide important
templates for comparisons with high redshift galaxies.[Abridged] | The large-scale environment from cosmological simulations II: The
redshift evolution and distributions of baryons: Following Cui et al. 2018 (hereafter Paper I) on the classification of
large-scale environments (LSE) at z = 0, we push our analysis to higher
redshifts and study the evolution of LSE and the baryon distributions in them.
Our aim is to investigate how baryons affect the LSE as a function of redshift.
In agreement with Paper I, the baryon models have negligible effect on the LSE
over all investigated redshifts. We further validate the conclusion obtained in
Paper I that the gas web is an unbiased tracer of total matter -- even better
at high redshifts. By separating the gas mainly by temperature, we find that
about 40 per cent of gas is in the so-called warm-hot intergalactic medium
(WHIM). This fraction of gas mass in the WHIM decreases with redshift,
especially from z = 1 (29 per cent) to z = 2.1 (10 per cent). By separating the
whole WHIM gas mass into the four large-scale environments (i.e. voids, sheets,
filaments, and knots), we find that about half of the WHIM gas is located in
filaments. Although the total gas mass in WHIM decreases with redshift, the
WHIM mass fractions in the different LSE seem unchanged. |
Kinematic Constraints on Spatial Curvature from Supernovae Ia and Cosmic
Chronometers: An approach to estimate the spatial curvature $\Omega_k$ from data
independently of dynamical models is suggested, through kinematic
parameterizations of the comoving distance ($D_{C}(z)$) with third degree
polynomial, of the Hubble parameter ($H(z)$) with a second degree polynomial
and of the deceleration parameter ($q(z)$) with first order polynomial. All
these parameterizations were done as function of redshift $z$. We used SNe Ia
dataset from Pantheon compilation with 1048 distance moduli estimated in the
range $0.01<z<2.3$ with systematic and statistical errors and a compilation of
31 $H(z)$ data estimated from cosmic chronometers. The spatial curvature found
for $D_C(z)$ parametrization was $\Omega_{k}=-0.03^{+0.24+0.56}_{-0.30-0.53}$.
The parametrization for deceleration parameter $q(z)$ resulted in
$\Omega_{k}=-0.08^{+0.21+0.54}_{-0.27-0.45}$. The $H(z)$ parametrization has
shown incompatibilities between $H(z)$ and SNe Ia data constraints, so these
analyses were not combined. The $D_C(z)$ and $q(z)$ parametrizations are
compatible with the spatially flat Universe as predicted by many inflation
models and data from CMB. This type of analysis is very appealing as it avoids
any bias because it does not depend on assumptions about the matter content of
the Universe for estimating $\Omega_k$. | Constraining Neutrinos and Dark Energy with Galaxy Clustering in the
Dark Energy Survey: We determine the forecast errors on the absolute neutrino mass scale and the
equation of state of dark energy by combining synthetic data from the Dark
Energy Survey (DES) and the Cosmic Microwave Background (CMB) Planck surveyor.
We use angular clustering of galaxies for DES in 7 redshift shells up to $z\sim
1.7$ including cross-correlations between different redshift shells. We study
models with massless and massive neutrinos and three different dark energy
models: $\Lambda$CDM ($w=-1$), wCDM (constant $w$), and waCDM (evolving
equation of state parameter $w(a)=w_0 + w_{a}(1-a)$). We include the impact of
uncertainties in modeling galaxy bias using a constant and a redshift-evolving
bias model. For the $\Lambda$CDM model we obtain an upper limit for the sum of
neutrino masses from DES+Planck of $\Sigma m_\nu < 0.08$ eV (95\% C.L.) for a
fiducial mass of $\Sigma m_\nu = 0.047$ eV, with a 1$\sigma$ error of 0.02 eV,
assuming perfect knowledge of galaxy bias. For the wCDM model the limit is
$\Sigma m_\nu < 0.10 $ eV. For a wCDM model where galaxy bias evolves with
redshift, the upper limit on the sum of neutrino masses increases to 0.19 eV.
DES will be able to place competitive upper limits on the sum of neutrino
masses of 0.1-0.2 eV and could therefore strongly constrain the inverted mass
hierarchy of neutrinos. In a wCDM model the 1$\sigma$ error on constant $w$ is
$\Delta w= 0.03$ from DES galaxy clustering and Planck. Allowing $\Sigma m_\nu$
as a free parameter increases the error on $w$ by a factor of 2, with $\Delta
w=0.06$. In a waCDM model, in which the dark energy equation of state varies
with time, the errors are $\Delta w_0 = 0.2$ and $\Delta w_a = 0.42$. Including
neutrinos and redshift dependent galaxy bias increases the errors to $\Delta
w_0 = 0.35$ and $\Delta w_a = 0.89$. |
Non-Gaussian Signatures in the five-year WMAP data as identified with
isotropic scaling indices: We continue the analysis of non-Gaussianities in the CMB by means of the
scaling index method (SIM, Raeth, Schuecker & Banday 2007) by applying this
method on the 5-year WMAP data. We compare each of the results with 1000 Monte
Carlo simulations mimicing the Gaussian properties of the best fit $\Lambda
CDM$-model. Based on the scaling indices, scale-dependent empirical probability
distributions, moments of these distributions and $\chi^2$-combinations of them
are calculated, obtaining similar results as in the former analysis of the
3-year data: We derive evidence for non-Gaussianity with a probability of up to
97.3% for the mean when regarding the KQ75-masked full sky and summing up over
all considered length scales by means of a diagonal $\chi^2$-statistics.
Looking at only the northern or southern hemisphere, we obtain up to 98.5% or
96.6%, respectively. For the standard deviation, these results appear as 95.6%
for the full sky (99.7% north, 89.4% south) and for a $\chi^2$-combination of
both measurements as 97.4% (99.1% north, 95.5% south). By performing an
analysis of rotated hemispheres, we detect an obvious asymmetry in the data. In
addition to these investigations, we present a method of filling the mask with
Gaussian noise to eliminate boundary effects caused by the mask. With the help
of this technique, we identify several local features on the map, of which the
most significant one turns out to be the well-known cold spot. When excluding
all these spots from the analysis, the deviation from Gaussianity increases,
which shows that the discovered local anomalies are not the reason of the
global detection of non-Gaussianity, but actually were damping the deviations
on average. Our analyses per band and per year suggest, however, that it is
very unlikely that the detected anomalies are due to foreground effects. | Big Bang Nucleosynthesis constraints on varying electron mass solution
to the Hubble tension: A cosmological model with a time-varying mass of electrons seems a promising
solution for the so-called Hubble tension. We examine the big bang
nucleosynthesis (BBN) constraints on the time-varying electron mass model,
because a larger electron mass gives rise to the smaller neutron decay rate
which could affect the light element abundance. Additionally, different
inferred cosmological parameters, primarily baryon asymmetry, to keep the
cosmic background power spectrum unchanged could affect the abundance of light
element. We find that the predicted helium fraction becomes larger and the
deuterium abundance becomes smaller as the electron mass at the BBN time
becomes larger. Thus, we conclude that an acceptable electron mass at the BBN
time would be only approximately 1% greater than the current electron mass. |
High-resolution images of five radio quasars at early cosmological
epochs: Context: Until now, there have only been seven quasars at z>4.5 whose the
high-resolution radio structure had been studied in detail with Very Long
Baseline Interferometry (VLBI) imaging. Aims: We almost double the number of
VLBI-imaged quasars at these high redshifts with the aim of studying their
redshift-dependent structural and physical properties in a larger sample.
Methods: We observed five radio quasars (J0813+3508, J1146+4037, J1242+5422,
J1611+0844, and J1659+2101) at 4.5<z<5 with the European VLBI Network (EVN) at
1.6 GHz on 29 October 2008 and at 5 GHz on 22 October 2008. The angular
resolution achieved ranges from 1.5 to 25 milli-arcseconds (mas), depending on
the observing frequency, the position angle in the sky, and the source's
celestial position. Results: The sources are all somewhat extended on mas
scales, but compact enough to be detected at both frequencies. With one
exception of a flat-spectrum source (J1611+0844), their compact emission is
characterised by a steep radio spectrum. We found no evidence of
Doppler-boosted radio emission in the quasars in our sample. The radio
structure of one of them (J0813+3508) is extended to ~7", which corresponds to
43 kpc projected linear size. Many of the highest redshift compact radio
sources are likely to be young, evolving objects, far-away cousins of the
powerful gigahertz peaked-spectrum (GPS) and compact steep-spectrum (CSS)
sources that populate the Universe at lower redshifts. | "SNe Ia twins for life" towards a precise determination of H$_{0}$: Here we present an approach to the measurement of extragalactic distances
using twin SNe Ia, taken from the early down to the nebular phase. The approach
is purely empirical, although we can give a theoretical background on why the
method is reliable. Studying those twins in galaxies where peculiar velocities
are relatively unimportant, we can tackle the H$_{0}$ tension problem. Here we
apply the method to the determination of the distances to NGC 7250 and NGC
2525, who hosted respectively SN 2013dy and SN 2018gv, twins of two different
SNe Ia prototypes: SN 2013aa/SN 2017cbv and SN2011fe. From the study of the SN
2013aa and SN 2017cbv twin pair, by comparing it with 2011fe and applying the
difference between the SN 2013aa/2017cbv and the SN 2011fe class, we find as
well a good estimate of the distance to NGC 5643. Our study points to distances
consistent with the Cepheids distance estimates by {\it SH0ES} in NGC 7250 and
NGC 2525 (within 1$\sigma$ errors). (Note that no TRGB distances are available
for NGC 7250 and NGC 2525). We get, on the other hand, a good agreement with
the distance estimates for M101 and NGC 5643 with the TRGB method. We just have
started to measure distances with this method for the samples in Freedman et al
(2019) and Riess et al (2022). Though there are differences in measured
distances to the same galaxy using Cepheids or he TRGB, the Hubble tension can
arise as well from the corrections of peculiar velocities of nearby galaxies
which are not in the Hubble flow. Thus, we expect to apply the method in
galaxies with z $>$0.02--0.03 well into the Hubble flow to obtain a reliable
value for H$_{0}$ with the use of the {\it ELT} or the {\it JWST}. |
The XMM Cluster Survey: new evidence for the 3.5 keV feature in clusters
is inconsistent with a dark matter origin: There have been several reports of a detection of an unexplained excess of
X-ray emission at $\simeq$ 3.5 keV in astrophysical systems. One interpretation
of this excess is the decay of sterile neutrino dark matter. The most
influential study to date analysed 73 clusters observed by the XMM-Newton
satellite. We explore evidence for a $\simeq$ 3.5 keV excess in the XMM-PN
spectra of 117 redMaPPer galaxy clusters ($0.1 < z < 0.6$). In our analysis of
individual spectra, we identify three systems with an excess of flux at
$\simeq$ 3.5 keV. In one case (XCS J0003.3+0204) this excess may result from a
discrete emission line. None of these systems are the most dark matter
dominated in our sample. We group the remaining 114 clusters into four
temperature ($T_{\rm X}$) bins to search for an increase in $\simeq$ 3.5 keV
flux excess with $T_{\rm X}$ - a reliable tracer of halo mass. However, we do
not find evidence of a significant excess in flux at $\simeq$ 3.5 keV in any
$T_{\rm X}$ bins. To maximise sensitivity to a potentially weak dark matter
decay feature at $\simeq$ 3.5 keV, we jointly fit 114 clusters. Again, no
significant excess is found at $\simeq$ 3.5 keV. We estimate the upper limit of
an undetected emission line at $\simeq$ 3.5 keV to be $2.41 \times 10^{-6}$
photons cm$^{-2}$ s$^{-1}$, corresponding to a mixing angle of
$\sin^2(2\theta)=4.4 \times 10^{-11}$, lower than previous estimates from
cluster studies. We conclude that a flux excess at $\simeq$ 3.5 keV is not a
ubiquitous feature in clusters and therefore unlikely to originate from sterile
neutrino dark matter decay. | Dust-free quasars in the early Universe: The most distant quasars known, at redshifts z=6, generally have properties
indistinguishable from those of lower-redshift quasars in the rest-frame
ultraviolet/optical and X-ray bands. This puzzling result suggests that these
distant quasars are evolved objects even though the Universe was only seven per
cent of its current age at these redshifts. Recently one z=6 quasar was shown
not to have any detectable emission from hot dust, but it was unclear whether
that indicated different hot-dust properties at high redshift or if it is
simply an outlier. Here we report the discovery of a second quasar without
hot-dust emission in a sample of 21 z=6 quasars. Such apparently hot-dust-free
quasars have no counterparts at low redshift. Moreover, we demonstrate that the
hot-dust abundance in the 21 quasars builds up in tandem with the growth of the
central black hole, whereas at low redshift it is almost independent of the
black hole mass. Thus z=6 quasars are indeed at an early evolutionary stage,
with rapid mass accretion and dust formation. The two hot-dust-free quasars are
likely to be first-generation quasars born in dust-free environments and are
too young to have formed a detectable amount of hot dust around them. |
Modelling the next-to-leading order matter three-point correlation
function using FFTLog: The study of higher-order statistics, particularly three-point statistics, of
the Large Scale Structure (LSS) of the Universe provides us with unique
information on the biasing relation between luminous and dark matter and on
deviations from primordial Gaussianity. As a result, much effort has been put
into improving measurement techniques as well as theoretical modelling,
especially in Fourier space. Comparatively, little progress has been made,
instead, in configuration space analyses. This work represents a first step
towards filling this gap by proposing a new strategy for modelling 3-point
statistics at higher perturbative orders in configuration space. Starting from
the next-to-leading order model for the matter bispectrum, we use 2D- FFTLog to
generate its counterpart in configuration space. We calibrate the procedure
using the leading order predictions for which an analytic model for the
three-point correlation function (3PCF) already exists. Then we assess the
goodness of the 3PCF model by comparing its predictions with measurements
performed on the matter distribution in collisionless cosmological N-body
simulations (DEMNUni). We focus on two redshifts (z = 0.49 and z = 1.05) in the
range spanned by current and future galaxy redshift surveys. The chi-square
analysis reveals that the next-to-leading order 3PCF models significantly
improve over the leading order one for all triangle configurations in both
redshifts, increasing the number of matched configurations at redshift z = 1.05
and z = 0.49, respectively. In particular, a significant improvement is also
seen on the Baryonic Acoustic Oscillations (BAO) scale for triangle
configurations whose smallest side length is well into the nonlinear regime.
The computational cost of the model proposed here is high but not prohibitively
large and represents the first step towards a complete 3PC model for the
galaxies. | Extragalactic Background Light and Gamma-Ray Attenuation: Data from (non-) attenuation of gamma rays from active galactic nuclei (AGN)
and gamma ray bursts (GRBs) give upper limits on the extragalactic background
light (EBL) from the UV to the mid-IR that are only a little above the lower
limits from observed galaxies. These upper limits now rule out some EBL models
and purported observations, with improved data likely to provide even stronger
constraints. We present EBL calculations both based on multiwavelength
observations of thousands of galaxies and also based on semi-analytic models,
and show that they are consistent with these lower limits from observed
galaxies and with the gamma-ray upper limit constraints. Such comparisons
"close the loop" on cosmological galaxy formation models, since they account
for all the light, including that from galaxies too faint to see. We compare
our results with those of other recent works, and discuss the implications of
these new EBL calculations for gamma ray attenuation. Catching a few GRBs with
groundbased atmospheric Cherenkov Telescope (ACT) arrays or water Cherenkov
detectors could provide important new constraints on the high-redshift star
formation history of the universe. |
Feedback under the microscope: thermodynamic structure and AGN driven
shocks in M87: (abridged) Using a deep Chandra exposure (574 ks), we present high-resolution
thermodynamic maps created from the spectra of $\sim$16,000 independent
regions, each with $\sim$1,000 net counts. The excellent spatial resolution of
the thermodynamic maps reveals the dramatic and complex temperature, pressure,
entropy and metallicity structure of the system. Excluding the 'X-ray arms',
the diffuse cluster gas at a given radius is strikingly isothermal. This
suggests either that the ambient cluster gas, beyond the arms, remains
relatively undisturbed by AGN uplift, or that conduction in the intracluster
medium (ICM) is efficient along azimuthal directions. We confirm the presence
of a thick ($\sim$40 arcsec or $\sim$3 kpc) ring of high pressure gas at a
radius of $\sim$180 arcsec ($\sim$14 kpc) from the central AGN. We verify that
this feature is associated with a classical shock front, with an average Mach
number M = 1.25. Another, younger shock-like feature is observed at a radius of
$\sim$40 arcsec ($\sim$3 kpc) surrounding the central AGN, with an estimated
Mach number M > 1.2. As shown previously, if repeated shocks occur every
$\sim$10 Myrs, as suggested by these observations, then AGN driven weak shocks
could produce enough energy to offset radiative cooling of the ICM. A high
significance enhancement of Fe abundance is observed at radii 350 - 400 arcsec
(27 - 31 kpc). This ridge is likely formed in the wake of the rising bubbles
filled with radio-emitting plasma that drag cool, metal-rich gas out of the
central galaxy. We estimate that at least $\sim1.0\times10^6$ solar masses of
Fe has been lifted and deposited at a radius of 350-400 arcsec; approximately
the same mass of Fe is measured in the X-ray bright arms, suggesting that a
single generation of buoyant radio bubbles may be responsible for the observed
Fe excess at 350 - 400 arcsec. | GraL spectroscopic identification of multiply imaged quasars: Gravitational lensing is proven to be one of the most efficient tools for
studying the Universe. The spectral confirmation of such sources requires
extensive calibration. This paper discusses the spectral extraction technique
for the case of multiple source spectra being very near each other. Using the
masking technique, we first detect high Signal-to-Noise (S/N) peaks in the CCD
spectral image corresponding to the location of the source spectra. This
technique computes the cumulative signal using a weighted sum, yielding a
reliable approximation for the total counts contributed by each source
spectrum. We then proceed with the subtraction of the contaminating spectra.
Applying this method, we confirm the nature of 11 lensed quasar candidates. |
Mitigating the optical depth degeneracy in the cosmological measurement
of neutrino masses using 21-cm observations: Massive neutrinos modify the expansion history of the universe and suppress
the structure formation below their free streaming scale. Cosmic microwave
background (CMB) observations at small angular scales can be used to constrain
the total mass $\Sigma m_\nu$ of the three neutrino flavors. However, at these
scales, the CMB-measured $\Sigma m_\nu$ is degenerate with $\tau$, the optical
depth to reionization, which quantifies the damping of CMB anisotropies due to
the scattering of CMB photons with free electrons along the line of sight. Here
we revisit the idea to use 21-cm power spectrum observations to provide direct
estimates for $\tau$. A joint analysis of CMB and 21-cm data can alleviate the
$\tau-\Sigma m_\nu$ degeneracy, making it possible to measure $\Sigma m_\nu$
with unprecedented precision. Forecasting for the upcoming Hydrogen Epoch of
Reionization Array (HERA), we find that a $\lesssim\mathcal{O}(10\%)$
measurement of $\tau$ is achievable, which would enable a $\gtrsim 5\sigma$
measurement of $\Sigma m_\nu=60\,[{\rm meV}]$, for any astrophysics model that
we considered. Precise estimates of $\tau$ also help reduce uncertainties in
other cosmological parameters, such as $A_s$, the amplitude of the primordial
scalar fluctuations power spectrum. | Emulating radiation transport on cosmological scale using a denoising
Unet: Semi-numerical simulations are the leading candidates for evolving
reionization on cosmological scales. These semi-numerical models are efficient
in generating large-scale maps of the 21cm signal, but they are too slow to
enable inference at the field level. We present different strategies to train a
U-Net to accelerate these simulations. We derive the ionization field directly
from the initial density field without using the ionizing sources' location,
and hence emulating the radiative transfer process. We find that the U-Net
achieves higher accuracy in reconstructing the ionization field if the input
includes either white noise or a noisy version of the ionization map beside the
density field during training. Our model reconstructs the power spectrum over
all scales perfectly well. This work represents a step towards generating
large-scale ionization maps with a minimal cost and hence enabling rapid
parameter inference at the field level. |
Probing Dark Energy Anisotropy: Wide area cosmological surveys enable investigation of whether dark energy
properties are the same in different directions on the sky. Cosmic microwave
background observations strongly restrict any dynamical effects from
anisotropy, in an integrated sense. For more local constraints we compute
limits from simulated distance measurements for various distributions of survey
fields in a Bianchi I anisotropic universe. We then consider the effects of
fitting for line of sight properties where isotropic dynamics is assumed
(testing the accuracy through simulations) and compare sensitivities of
observational probes for anisotropies, from astrophysical systematics as well
as dark energy. We also point out some interesting features of anisotropic
expansion in Bianchi I cosmology. | Machine learning constraints on deviations from general relativity from
the large scale structure of the Universe: We use a particular machine learning approach, called the genetic algorithms
(GA), in order to place constraints on deviations from general relativity (GR)
via a possible evolution of Newton's constant $\mu\equiv
G_\mathrm{eff}/G_\mathrm{N}$ and of the dark energy anisotropic stress $\eta$,
both defined to be equal to one in GR. Specifically, we use a plethora of
background and linear-order perturbations data, such as type Ia supernovae,
baryon acoustic oscillations, cosmic chronometers, redshift space distortions
and $E_g$ data. We find that although the GA is affected by the lower quality
of the currently available data, especially from the $E_g$ data, the
reconstruction of Newton's constant is consistent with a constant value within
the errors. On the other hand, the anisotropic stress deviates strongly from
unity due to the sparsity and the systematics of the $E_g$ data. Finally, we
also create synthetic data based on a next-generation survey and forecast the
limits of any possible detection of deviations from GR. In particular, we use
two fiducial models: one based on the cosmological constant $\Lambda$CDM model
and another on a model with an evolving Newton's constant, dubbed $\mu$CDM. We
find that the GA reconstructions of $\mu(z)$ and $\eta(z)$ can be constrained
to within a few percent of the fiducial models and in the case of the $\mu$CDM
mocks, they can also provide a strong detection of several $\sigma$s, thus
demonstrating the utility of the GA reconstruction approach. |
The Molecular Interstellar Medium of the Local Group Dwarf NGC6822: Do molecular clouds collapse to form stars at the same rate in all
environments? In large spiral galaxies, the rate of transformation of H2 into
stars (hereafter SFE) varies little. However, the SFE in distant objects (z~1)
is much higher than in the large spiral disks that dominate the local universe.
Some small local group galaxies share at least some of the characteristics of
intermediate-redshift objects, such as size or color. Recent work has suggested
that the Star Formation Efficiency (SFE, defined as the SFRate per unit H2) in
local Dwarf galaxies may be as high as in the distant objects. A fundamental
difficulty in these studies is the independent measure of the H2 mass in
metal-deficient environments. At 490 kpc, NGC6822 is an excellent choice for
this study; it has been mapped in the CO(2-1) line using the multibeam receiver
HERA on the 30 meter IRAM telescope, yielding the largest sample of giant
molecular clouds (GMCs) in this galaxy. Despite the much lower metallicity, we
find no clear difference in the properties of the GMCs in NGC 6822 and those in
the Milky Way except lower CO luminosities for a given mass. Several
independent methods indicate that the total H2 mass in NGC 6822 is about 5 x
10^6 Msun in the area we mapped and less than 10^7 Msun in the whole galaxy.
This corresponds to a NH2/ICO ~ 4 x 10^{21} cm^-2 /(Kkm/s) over large scales,
such as would be observed in distant objects, and half that in individual GMCs.
No evidence was found for H2 without CO emission. Our simulations of the
radiative transfer in clouds are entirely compatible with these NH2/ICO values.
The SFE implied is a factor 5 - 10 higher than what is observed in large local
universe spirals. | SN 2010jl in UGC 5189: Yet another luminous type IIn supernova in a
metal-poor galaxy: We present ASAS data starting 25 days before the discovery of the recent type
IIn SN 2010jl, and we compare its light curve to other luminous IIn SNe,
showing that it is a luminous (M_I ~ -20.5) event. Its host galaxy, UGC 5189,
has a low gas-phase oxygen abundance (12 + log(O/H) = 8.2), which reinforces
the emerging trend that over-luminous core-collapse supernovae are found in the
low-metallicity tail of the galaxy distribution, similar to the known trend for
the hosts of long GRBs. We compile oxygen abundances from the literature and
from our own observations of UGC 5189, and we present an unpublished spectrum
of the luminous type Ic SN 2010gx that we use to estimate its host metallicity.
We discuss these in the context of host metallicity trends for different
classes of core-collapse objects. The earliest generations of stars are known
to be enhanced in [O/Fe] relative to the Solar mixture; it is therefore likely
that the stellar progenitors of these overluminous supernovae are even more
iron-poor than they are oxygen-poor. A number of mechanisms and massive star
progenitor systems have been proposed to explain the most luminous
core-collapse supernovae; any successful theory will need to include the
emerging trend that points towards low-metallicity for the massive progenitor
stars. This trend for very luminous supernovae to strongly prefer
low-metallicity galaxies should be taken into account when considering various
aspects of the evolution of the metal-poor early universe. (abridged) |
Search For Type Ia Supernova NUV-Optical Subclasses: In response to a recently reported observation of evidence for two classes of
Type Ia Supernovae (SNe Ia) distinguished by their brightness in the rest-frame
near ultraviolet (NUV), we search for the phenomenon in publicly available
light-curve data. We use the SNANA supernova analysis package to simulate SN
Ia-light curves in the Sloan Digital Sky Survey Supernova Search (SDSS) and the
Supernova Legacy Survey (SNLS) with a model of two distinct ultraviolet classes
of SNe Ia and a conventional model with a single broad distribution of SN-Ia
ultraviolet brightnesses. We compare simulated distributions of rest-frame
colors with these two models to those observed in 158 SNe Ia in the SDSS and
SNLS data. The SNLS sample of 99 SNe Ia is in clearly better agreement with a
model with one class of SN Ia light curves and shows no evidence for distinct
NUV sub-classes. The SDSS sample of 59 SNe Ia with poorer color resolution does
not distinguish between the two models. | Subaru Studies of the Cosmic Dawn: An overview on the current status of the census of the early universe
population is given. Observational surveys of high redshift objects provide
direct opportunities to study the early epoch of the Universe. The target
population included are Lyman Alpha Emitters (LAE), Lyman Break Galaxies (LBG),
gravitationally lensed galaxies, quasars and gamma-ray bursts (GRB). The basic
properties of these objects and the methods used to study them are reviewed.
The present paper highlights the fact that the Subaru Telescope group made
significant contributions in this field of science to elucidate the epoch of
the cosmic dawn and to improve the understanding of how and when infant
galaxies evolve into mature ones. |
On the Assembly Bias of Cool Core Clusters Traced by H$α$ Nebulae: Do cool-core (CC) and noncool-core (NCC) clusters live in different
environments? We make novel use of H$\alpha$ emission lines in the central
galaxies of redMaPPer clusters as proxies to construct large (1,000's) samples
of CC and NCC clusters, and measure their relative assembly bias using both
clustering and weak lensing. We increase the statistical significance of the
bias measurements from clustering by cross-correlating the clusters with an
external galaxy redshift catalog from the Sloan Digital Sky Survey III, the
LOWZ sample. Our cross-correlations can constrain assembly bias up to a
statistical uncertainty of 6%. Given our H$\alpha$ criteria for CC and NCC, we
find no significant differences in their clustering amplitude. Interpreting
this difference as the absence of halo assembly bias, our results rule out the
possibility of having different large-scale (tens of Mpc) environments as the
source of diversity observed in cluster cores. Combined with recent
observations of the overall mild evolution of CC and NCC properties, such as
central density and CC fraction, this would suggest that either the cooling
properties of the cluster core are determined early on solely by the local
(<200 kpc) gas properties at formation or that local merging leads to
stochastic CC relaxation and disruption in a periodic way, preserving the
average population properties over time. Studying the small-scale clustering in
clusters at high redshift would help shed light on the exact scenario. | The Dynamics of Inhomogeneous Dark Energy: In this paper, by analyzing the dynamics of the inhomogeneous quintessence
dark energy, we find that the gradient energy of dark energy will oscillate and
gradually vanish, which indicates the gradient energy of the scalar field
present in the early universe does not affect the current dynamics of the
universe. Moreover, with the decaying of gradient energy, there exists a
possible mutual transformation between kinetic energy and gradient energy. In
the framework of interacting dark energy models, we argue that inhomogeneous
dark energy may have a significant effect on the evolution of the cosmic
background, the investigation of which still requires fully relativistic
$N$-body numerical simulations in the future. |
Dynamics of the Local Universe: cosmic velocity flows and voids: A valuable amount of information is available in peculiar velocities of
galaxies. Peculiar velocity surveys have recently allowed the discovery of
potential problems with LCDM. Nonetheless, their direct observation through
distance measurements remains a daunting task. Another way of considering the
problem is to use orbit reconstruction methods assuming some mass-to-light
assignment for galaxies. We give here two applications of this procedure for
the study of large-scale bulk flows and the dynamics of voids in the Local
Universe. We concentrate our study on the use of the Monge-Ampere-Kantorovitch
reconstruction technique. Using peculiar velocities reconstructed from the
2MASS Galaxy Redshift Survey, and after comparison with the NGB-3k peculiar
velocity catalog, we look in the details of these peculiar velocities. More
particularly, we estimate the constraints that the peculiar velocities put on
the cosmology. The information on dynamics that is included in reconstructed
orbits of galaxies also allows us to have a much better prescription for
defining and identifying voids in simulations and redshift catalogs. We present
this new technique and how voids may give us additional constraints on
cosmology with current and future surveys. | The discovery of high power - high synchrotron peak blazars: We study the quasi-simultaneous near-IR, optical, UV, and X-ray photometry of
eleven gamma-ray selected blazars for which redshift estimates larger than 1.2
have been recently provided. Four of these objects turn out to be high-power
blazars with the peak of their synchrotron emission between ~ 3 x 10^15 and ~
10^16 Hz, and therefore of a kind predicted to exist but never seen before.
This discovery has important implications for our understanding of physical
processes in blazars, including the so-called "blazar sequence", and might also
help constraining the extragalactic background light through gamma-ray
absorption since two sources are strongly detected even in the 10 - 100 GeV
Fermi-LAT band. Based on our previous work and their high powers, these sources
are very likely high-redshift flat-spectrum radio quasars with their emission
lines swamped by the non-thermal continuum. |
Solving the Hubble tension at intermediate redshifts with dynamical dark
energy: The current expansion rate of the Universe, the Hubble constant $H_0$, is an
important cosmological quantity. However, two different ways to measure its
value do not agree -- building a low-redshift distance ladder leads to a higher
value of $H_0$ than inferring it from high-redshift observations in a
$\Lambda$CDM cosmology. Most approaches to solve this tension either act at
very low redshift by modifying the local distance ladder, or at high redshift
by introducing new physics that changes the normalization of the inverse
distance ladder. Here we discuss a way to address the Hubble tension at
intermediate redshifts instead. By keeping the low- and high-redshift
normalizations unchanged, we find a violation of the distance duality in the
redshift range where luminosity and angular diameter distances overlap. We
'solve' this problem by introducing a redshift-dependent systematic effect that
brings the luminosity distance into agreement with the angular diameter
distance. The resulting expansion history is no longer compatible with
$\Lambda$CDM, but this can be fixed with a dynamical dark energy component. In
this way, we are able to solve the Hubble tension at intermediate redshifts. | Maximum Cosmological Information from Type-Ia Supernova Observations: Type-Ia supernova observations yield estimates of the luminosity distance,
which includes not only the background luminosity distance, but also the
fluctuation due to inhomogeneities in the Universe. In particular, the spatial
correlation of the host galaxies is a dominant source of the fluctuation in the
luminosity distance measurements. Utilizing the recent theoretical framework
that accurately quantifies the information contents accounting for the
three-dimensional correlation of the observables on the past-light cone, we
compute the maximum cosmological information obtainable from idealized
supernova surveys as a function of maximum redshift $z_m$. Here we consider two
cosmological parameters $\Omega_m$ and $w_0$ and show that these parameters can
be constrained at maximum 1% levels in an idealized survey with $z_m=1$. We
discuss how these fundamental limits set by cosmic variance can be overcome. |
A Consistent Approach to Falsifying Lambda-CDM with Rare Galaxy Clusters: We consider methods with which to answer the question "is any observed galaxy
cluster too unusual for Lambda-CDM?" After emphasising that many previous
attempts to answer this question will overestimate the confidence level at
which Lambda-CDM can be ruled out, we outline a consistent approach to these
rare clusters, which allows the question to be answered. We define three
statistical measures, each of which are sensitive to changes in cluster
populations arising from different modifications to the cosmological model. We
also use these properties to define the 'equivalent mass at redshift zero' for
a cluster --- the mass of an equally unusual cluster today. This quantity is
independent of the observational survey in which the cluster was found, which
makes it an ideal proxy for ranking the relative unusualness of clusters
detected by different surveys. These methods are then used on a comprehensive
sample of observed galaxy clusters and we confirm that all are less than
2-sigma deviations from the Lambda-CDM expectation. Whereas we have only
applied our method to galaxy clusters, it is applicable to any isolated,
collapsed, halo. As motivation for future surveys, we also calculate where in
the mass redshift plane the rarest halo is most likely to be found, giving
information as to which objects might be the most fruitful in the search for
new physics. | Decaying dark energy in light of the latest cosmological dataset: Decaying Dark Energy models modify the background evolution of the most
common observables, such as the Hubble function, the luminosity distance and
the Cosmic Microwave Background temperature-redshift scaling relation. We use
the most recent observationally-determined datasets, including Supernovae Type
Ia and Gamma Ray Bursts data, along with $H(z)$ and Cosmic Microwave Background
temperature versus $z$ data and the reduced Cosmic Microwave Background
parameters, to improve the previous constraints on these models. We perform a
Monte Carlo Markov Chain analysis to constrain the parameter space, on the
basis of two distinct methods. In view of the first method, the Hubble constant
and the matter density are left to vary freely. In this case, our results are
compatible with previous analyses associated with decaying Dark Energy models,
as well as with the most recent description of the cosmological background. In
view of the second method, we set the Hubble constant and the matter density to
their best fit values obtained by the {\it Planck} satellite, reducing the
parameter space to two dimensions, and improving the existent constraints on
the model's parameters. Our results suggest that the accelerated expansion of
the Universe is well described by the cosmological constant, and we argue that
forthcoming observations will play a determinant role to constrain/rule out
decaying Dark Energy. |
Herschel-ATLAS: Dust temperature and redshift distribution of SPIRE and
PACS detected sources using submillimetre colours: We present colour-colour diagrams of detected sources in the Herschel-ATLAS
Science Demonstration Field from 100 to 500 microns using both PACS and SPIRE.
We fit isothermal modified black bodies to the spectral energy distribution
(SED) to extract the dust temperature of sources with counterparts in Galaxy
And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a
photometric redshift. For a subsample of 330 sources detected in at least three
FIR bands with a significance greater than 3 $\sigma$, we find an average dust
temperature of $(28 \pm 8)$K. For sources with no known redshift, we populate
the colour-colour diagram with a large number of SEDs generated with a broad
range of dust temperatures and emissivity parameters, and compare to colours of
observed sources to establish the redshift distribution of this sample. For
another subsample of 1686 sources with fluxes above 35 mJy at 350 microns and
detected at 250 and 500 microns with a significance greater than 3$\sigma$, we
find an average redshift of $2.2 \pm 0.6$. | Mass scaling relations for dark halos from an analytic universal outer
density profile: The average matter density within the turnaround scale, which demarcates
where galaxies shift from clustering around a structure to joining the
expansion of the Universe, is an important cosmological probe. However, a
measurement of the mass enclosed by the turnaround radius is difficult.
Analyses of the turnaround scale in simulated galaxy clusters place the
turnaround radius at about three times the virial radius in a \(\Lambda CDM\)
universe and at a (present-day) density contrast with the background matter
density of the Universe of \(\delta \sim 11\). Assessing the mass at such
extended distances from a cluster's center is a challenge for current mass
measurement techniques. Consequently, there is a need to develop and validate
new mass-scaling relations, to connect observable masses at cluster interiors
with masses at greater distances. Our research aims to establish an analytical
framework for the most probable mass profile of galaxy clusters, leading to
novel mass scaling relations, allowing us to estimate masses at larger scales.
We derive such analytical mass profiles and compare them with those from
cosmological simulations. We use excursion set theory, which provides a
statistical framework for the density and local environment of dark matter
halos, and complement it with the spherical collapse model to follow the
non-linear growth of these halos. The profile we developed analytically shows a
good agreement (better than 30\%, and dependent on halo mass) with the mass
profiles of simulated galaxy clusters. Mass scaling relations are obtained from
the analytical profile with offset better than 15\% from the simulated ones.
This level of precision highlights the potential of our model for probing
structure formation dynamics at the outskirts of galaxy clusters. |
Combining Planck and SPT cluster catalogs: cosmological analysis and
impact on Planck scaling relation calibration: We provide the first combined cosmological analysis of South Pole Telescope
(SPT) and Planck cluster catalogs. The aim is to provide an independent
calibration for Planck scaling relations, exploiting the cosmological
constraining power of the SPT-SZ cluster catalog and its dedicated weak lensing
(WL) and X-ray follow-up observations. We build a new version of the Planck
cluster likelihood. In the $\nu \Lambda$CDM scenario, focusing on the mass
slope and mass bias of Planck scaling relations, we find $\alpha_{\text{SZ}} =
1.49_{-0.10}^{+0.07}$ and $(1-b)_{\text{SZ}} = 0.69_{-0.14}^{+0.07}$
respectively. The results for the mass slope show a $\sim 4 \, \sigma$
departure from the self-similar evolution, $\alpha_{\text{SZ}} \sim 1.8$. This
shift is mainly driven by the matter density value preferred by SPT data,
$\Omega_m = 0.30 \pm 0.03$, lower than the one obtained by Planck data alone,
$\Omega_m = 0.37_{-0.06}^{+0.02}$. The mass bias constraints are consistent
both with outcomes of hydrodynamical simulations and external WL calibrations,
$(1-b) \sim 0.8$, and with results required by the Planck cosmic microwave
background cosmology, $(1-b) \sim 0.6$. From this analysis, we obtain a new
catalog of Planck cluster masses $M_{500}$. We estimate the ratio between the
published Planck $M_{\text{SZ}}$ masses and our derived masses $M_{500}$, as a
"measured mass bias", $(1-b)_M$. We analyse the mass, redshift and detection
noise dependence of $(1-b)_M$, finding an increasing trend towards high
redshift and low mass. These results mimic the effect of departure from
self-similarity in cluster evolution, showing different dependencies for the
low-mass high-mass, low-z high-z regimes. | A Y-band look of the sky with 1-m class telescopes: Y -band is a broad passband that is centered at ~ 1 micron. It is becoming a
new, popular window for extragalactic study especially for observation of red
objects thanks to recent CCD technology developments. In order to better
understand the general characteristics of objects in Y -band, and to
investigate the promise of Y -band observations with small telescopes, we
carried out imaging observation of several extragalactic fields, brown dwarfs
and high redshift quasars with Y -band filter at the Mt. Lemmon Optical
Astronomy Observatory and the Maidanak observatory. From our observations, we
constrain the bright end of the galaxy and the stellar number counts in Y
-band. Also, we test the usefulness of high redshift quasar (z > 6) selection
via i-z-Y color-color diagram, to demonstrate that the i-z-Y color-color
diagram is effective for the selection of high redshift quasars even with a
conventional optical CCD camera installed at a 1-m class telescope. |
Using the outskirts of galaxy clusters to determine their mass accretion
rate: We explore the possibility of using the external regions of galaxy clusters
to measure their mass accretion rate (MAR). The main goal is to provide a
method to observationally investigate the growth of structures on the nonlinear
scales of galaxy clusters. We derive the MAR by using the mass profile beyond
the splashback radius, evaluating the mass of a spherical shell and the time it
takes to fall in. The infall velocity of the shell is extracted from $N$-body
simulations. The average MAR returned by our prescription in the redshift range
$z=[0, 2]$ is within $20-40 \%$ of the average MAR derived from the merger
trees of dark matter haloes in the reference $N$-body simulations. Our result
suggests that the external regions of galaxy clusters can be used to measure
the mean MAR of a sample of clusters. | The NGC7771+NGC7770 Minor Merger: Harassing the Little One?: Numerical simulations of minor mergers, typically having mass ratios greater
than 3:1, predict little enhancement in the global star formation activity.
However, these models also predict that the satellite galaxy is more
susceptible to the effects of the interaction than the primary. We use optical
integral field spectroscopy and deep optical imaging to study the
NGC7771+NGC7770 interacting system (~10:1 stellar mass ratio) to test these
predictions. We find that the satellite galaxy NGC7770 is currently
experiencing a galaxy-wide starburst with most of the optical light being from
young and post-starburst stellar populations(<1Gyr). This galaxy lies off of
the local star-forming sequence for composite galaxies with an enhanced
integrated specific star formation rate. We also detect in the outskirts of
NGC7770 Halpha emitting gas filaments. This gas appears to have been stripped
from one of the two galaxies and is being excited by shocks. All these results
are consistent with a minor-merger induced episode(s) of star formation in
NGC7770 after the first close passage. Such effects are not observed on the
primary galaxy NGC7771. |
Measuring the total and baryonic mass profiles of the very massive
CASSOWARY 31 strong lens. A fossil system at z ~ 0.7?: We investigate the total and baryonic mass distributions in deflector number
31 of the Cambridge And Sloan Survey Of Wide ARcs in the skY (CASSOWARY). We
confirm spectroscopically a four-image lensing system at redshift 1.4870 with
VLT/X-shooter observations. The lensed images are distributed around a bright
early-type galaxy at redshift 0.683, surrounded by several smaller galaxies at
similar photometric redshifts. We use available optical and X-ray data to
constrain the deflector total, stellar, and hot gas mass through, respectively,
strong lensing, stellar population analysis, and plasma modelling. We derive a
total mass projected within the Einstein radius R_Ein = 70 kpc of (40 +/- 1) x
10^12 M_Sun, and a central logarithmic slope of -1.7 +/- 0.2 for the total mass
density. Despite a very high stellar mass and velocity dispersion of the
central galaxy of (3 +/- 1) x 10^12 M_Sun and (450 +/- 80) km/s, respectively,
the cumulative stellar-to-total mass profile of the deflector implies a
remarkably low stellar mass fraction of 20% (3%-6%) in projection within the
central galaxy effective radius R_e = 25 kpc (R = 100 kpc). We also find that
the CSWA 31 deflector has properties suggesting it to be among the most distant
and massive fossil systems studied so far. The unusually strong central dark
matter dominance and the possible fossil nature of this system renders it an
interesting target for detailed tests of cosmological models and structure
formation scenarios. | Galaxy evolution in groups and clusters: star formation rates, red
sequence fractions, and the persistent bimodality: Using galaxy group/cluster catalogs created from the Sloan Digital Sky Survey
Data Release 7, we examine in detail the specific star formation rate (SSFR)
distribution of satellite galaxies and its dependence on stellar mass, host
halo mass, and halo-centric radius. All galaxies, regardless of
central-satellite designation, exhibit a similar bimodal SSFR distribution,
with a strong break at SSFR ~ 10^-11 yr^-1 and the same high SSFR peak; in no
regime is there ever an excess of galaxies in the `green valley'. Satellite
galaxies are simply more likely to lie on the quenched (`red sequence') side of
the SSFR distribution. Furthermore, the satellite quenched fraction excess
above the field galaxy value is nearly independent of galaxy stellar mass. An
enhanced quenched fraction for satellites persists in groups with halo masses
down to 3 x 10^11 Msol and increases strongly with halo mass and toward halo
center. We find no detectable quenching enhancement for galaxies beyond ~2R_vir
around massive clusters once these galaxies have been decomposed into centrals
and satellites. These trends imply that (1) galaxies experience no significant
environmental effects until they cross within ~R_vir of a more massive host
halo, (2) after this, star formation in active satellites continues to evolve
in the same manner as active central galaxies for several Gyrs, and (3) once
begun, satellite star formation quenching occurs rapidly. These results place
strong constraints on satellite-specific quenching mechanisms, as we will
discuss further in companion papers. |
The Dependence of Subhalo Abundance on Halo Concentration: Hierarchical structure formation implies that the number of subhalos within a
dark matter halo depends not only on halo mass, but also on the formation
history of the halo. This dependence on the formation history, which is highly
correlated with halo concentration, can account for the super-Poissonian
scatter in subhalo occupation at a fixed halo mass that has been previously
measured in simulations. Here we propose a model to predict the subhalo
abundance function for individual host halos, that incorporates both halo mass
and concentration. We combine results of cosmological simulations with a new
suite of zoom-in simulations of Milky Way-mass halos to calibrate our model. We
show the model can successfully reproduce the mean and the scatter of subhalo
occupation in these simulations. The implications of this correlation between
subhalo abundance and halo concentration are further investigated. We also
discuss cases in which inferences about halo properties can be affected if this
correlation between subhalo abundance and halo concentration is ignored; in
these cases our model would give a more accurate inference. We propose that
with future deep surveys, satellite occupation in the low-mass regime can be
used to verify the existence of halo assembly bias. | Halo model description of the non-linear dark matter power spectrum at
$k \gg 1$ Mpc$^{-1}$: Accurate knowledge of the non-linear dark-matter power spectrum is important
for understanding the large-scale structure of the Universe, the statistics of
dark-matter haloes and their evolution, and cosmological gravitational lensing.
We analytically model the dark-matter power spectrum and its cross-power
spectrum with dark-matter haloes. Our model extends the halo-model formalism,
including realistic substructure population within individual dark-matter
haloes and the scatter of the concentration parameter at fixed halo mass. We
consider three prescriptions for the mass-concentration relation and two for
the substructure distribution in dark-matter haloes. We show that this
extension of the halo model mainly increases the predicted power on the small
scales, and is crucial for proper modeling the cosmological weak-lensing signal
due to low-mass haloes. Our extended formalism shows how the halo model
approach can be improved in accuracy as one increases the number of ingredients
that are calibrated from n-body simulations. |
Chandra observations of the Abell S0295 cluster: We present deep ($205 \rm ks$), \Chandra observations of the \ab295 binary
merging cluster ($z=0.30$). In the X-ray image, the secondary component is
clearly visible as a surface brightness peak, while the primary cluster has a
flatter distribution. We found cool gas ($\sim 6 \rm keV$) associated with the
secondary, while the central temperature of the primary does not deviate
significantly from the mean temperature of the cluster of $\sim 9.5 \rm keV$.
In the vicinity of the primary's core we found the hottest region in the
cluster accompanied by a surface brightness discontinuity. We propose that this
region corresponds to a shock, for which we estimate a Mach number of
$1.24_{-0.22}^{+0.30}$. We found other merger signatures such as a plume of
cool gas emerging from the primary cluster and a cold front and a possible bow
shock (Mach number of $1.74_{-0.74}^{+1.02}$) leading the secondary cluster.
Based on the observed properties in comparison to binary merger simulations
from the literature we propose for \ab295 a low mass ratio, off-axis merging
scenario, with secondary close to first apocentre. Comparison of our results
with strong lensing observations of \ab295 from \cite{Cibirka2018} shows an
offset between the total mass peak and the bulk of the gas distribution in the
primary cluster. The properties of the merger and the existence of the offset
between mass peak and gas make \ab295 a promising candidate for the study of
mergers involving non-cool core clusters and the nature of dark matter. | Constraining Entropic Cosmology: It has been recently proposed that the interpretation of gravity as an
emergent, entropic force might have nontrivial implications to cosmology. Here
two approaches are investigated: in one, the Friedman equation receives
entropic contributions from the usually neglected surface terms, and in
another, the extra terms are derived from quantum corrections to the entropy
formula. UV terms may drive inflation, avoiding a recently derived no-go
theorem, though in some cases leading to a graceful exit problem. IR terms can
generate dark energy, alleviating the cosmological constant problem. The
quantum corrections are bounded by their implications to the BBN, and the
surface terms are constrained in addition by their effect upon the behavior of
matter. Likelihood analyses are performed to constrain the modifications by the
SNeIa, BAO and CMB data. It is found that a monomial correction to the
area-entropy formula results in late acceleration in very good agreement with
observations, which then turn out to be compatible with positive curvature. The
evolution of perturbations is deduced by assuming the Jebsen-Birkhoff theorem.
Distinct signatures can then be identified in the large scale structure
formation. Furthermore, it is shown that the visible universe satisfies the
Bekenstein bound. |
Constraining cosmology and ionization history with combined 21 cm power
spectrum and global signal measurements: Improvements in current instruments and the advent of next-generation
instruments will soon push observational 21 cm cosmology into a new era, with
high significance measurements of both the power spectrum and the mean
("global") signal of the 21 cm brightness temperature. In this paper we use the
recently commenced Hydrogen Epoch of Reionization Array as a worked example to
provide forecasts on astrophysical and cosmological parameter constraints. In
doing so we improve upon previous forecasts in a number of ways. First, we
provide updated forecasts using the latest best-fit cosmological parameters
from the Planck satellite, exploring the impact of different Planck datasets on
21 cm experiments. We also show that despite the exquisite constraints that
other probes have placed on cosmological parameters, the remaining
uncertainties are still large enough to have a non-negligible impact on
upcoming 21 cm data analyses. While this complicates high-precision constraints
on reionization models, it provides an avenue for 21 cm reionization
measurements to constrain cosmology. We additionally forecast HERA's ability to
measure the ionization history using a combination of power spectrum
measurements and semi-analytic simulations. Finally, we consider ways in which
21 cm global signal and power spectrum measurements can be combined, and
propose a method by which power spectrum results can be used to train a compact
parameterization of the global signal. This parameterization reduces the number
of parameters needed to describe the global signal, increasing the likelihood
of a high significance measurement. | Clustering GCG: a viable option for unified dark matter-dark energy?: We study the clustering Generalized Chaplygin Gas (GCG) as a possible
candidate for dark matter-dark energy unification. The vanishing speed of sound
($c_{s}^2 = 0$) for the GCG fluid can be obtained by incorporating higher
derivative operator in the original K-essence Lagrangian. The evolution of the
density fluctuations in the GCG+Baryon fluid is studied in the linear regime.
The observational constraints on the model are obtained using latest data from
SNIa, $H(z)$, BAO and also for the $f\sigma_{8}$ measurements. The matter power
spectra for the allowed parameter values are well behaved without any
unphysical features. |
The Mysterious Merger of NGC6868 and NGC6861 in the Telescopium Group: We use Chandra X-ray observations of the hot gas in and around NGC6868 and
NGC6861 in the Telescopium galaxy group (AS0851) to probe the interaction
history between these galaxies. Mean surface brightness profiles for NGC6868
and NGC6861 are each well described by double beta-models, suggesting that they
are each the dominant galaxy in a galaxy subgroup about to merge. Surface
brightness and temperature maps of the brightest group galaxy NGC6868 show a
cold front edge ~23 kpc to the north, and a cool 0.62 keV spiral-shaped tail to
the south. Analysis of the temperature and density across the cold front
constrains the relative motion between NGC6868 and the ambient group gas to be
at most transonic; while the spiral morphology of the tail strongly suggests
that the cold front edge and tail are the result of gas sloshing due to the
subgroup merger. The cooler central region of NGC6861 is surrounded by a sheath
of hot gas to the east and hot, bifurcated tails of X-ray emission to the west
and northwest. We discuss supersonic infall of the NGC6861 subroup, sloshing
from the NGC6868 and NGC6861 subgroup merger, and AGN heating as possible
explanations for these features, and discuss possible scenarios that may
contribute to the order of magnitude discrepancy between the Margorrian and
black hole mass - sigma predictions for its central black hole. | X-ray, lensing and Sunyaev Zel'dovich triaxial analysis of Abell 1835
out to R_{200}: Measuring the intrinsic shape and orientation of dark matter (DM) and
intracluster (IC) gas in galaxy clusters is crucial to constraining their
formation and evolution, and for enhancing the use of clusters as more precise
cosmological probes. Extending our previous works, we present for the first
time results from a triaxial joint analysis of the galaxy cluster Abell 1835,
by means of X-ray, strong lensing (SL) and Sunyaev Zel'dovich (SZ) data. We
parametrically reconstruct the full three-dimensional structure (triaxial shape
and principal axis orientation) of both the DM and the IC gas, and the level of
non-thermal pressure of the IC gas. We find that the intermediate-major and
minor-major axis ratios of the DM are 0.71+/-0.08 and 0.59+/-0.05,
respectively, and the major axis of the DM halo is inclined with respect to the
line of sight at 18.3+/-5.2 deg. We present the first observational measurement
of the non-thermal pressure out to R_{200}, which has been evaluated to be a
few percent of the total energy budget in the internal regions, while reaching
approximately 20% in the outer volumes. We discuss the implications of our
method for the viability of the CDM scenario, focusing on the concentration
parameter C and the inner slope of the DM gamma in order to test the cold dark
matter (CDM) paradigm for structure formation: we measure gamma=1.01+/-0.06 and
C=4.32+/-0.44, values which are close to the predictions of the CDM model. The
combination of X-ray/SL data at high spatial resolution, capable of resolving
the cluster core, with the SZ data, which are more sensitive to the cluster
outer volume, allows us to characterize the level and the gradient of the gas
entropy distribution and non-thermal pressure out to R_{200}, breaking the
degeneracy among the physical models describing the thermal history of the ICM. |
Cluster abundance in chameleon $f(R)$ gravity I: toward an accurate halo
mass function prediction: We refine the mass and environment dependent spherical collapse model of
chameleon $f(R)$ gravity by calibrating a phenomenological correction inspired
by the parameterized post-Friedmann framework against high-resolution $N$-body
simulations. We employ our method to predict the corresponding modified halo
mass function, and provide fitting formulas to calculate the fractional
enhancement of the $f(R)$ halo abundance with respect to that of General
Relativity (GR) within a precision of $\lesssim 5\%$ from the results obtained
in the simulations. Similar accuracy can be achieved for the full $f(R)$ mass
function on the condition that the modeling of the reference GR abundance of
halos is accurate at the percent level. We use our fits to forecast constraints
on the additional scalar degree of freedom of the theory, finding that upper
bounds competitive with current Solar System tests are within reach of cluster
number count analyses from ongoing and upcoming surveys at much larger scales.
Importantly, the flexibility of our method allows also for this to be applied
to other scalar-tensor theories characterized by a mass and environment
dependent spherical collapse. | Simulations of cm-wavelength Sunyaev-Zel'dovich galaxy cluster and point
source blind sky surveys and predictions for the RT32/OCRA-f and the Hevelius
100-m radio telescope: We investigate the effectiveness of blind surveys for radio sources and
galaxy cluster thermal Sunyaev-Zel'dovich effects (TSZEs) using the four-pair,
beam-switched OCRA-f radiometer on the 32-m radio telescope in Poland. The
predictions are based on mock maps that include the cosmic microwave
background, TSZEs from hydrodynamical simulations, and unresolved radio
sources. We estimate the effects of source clustering towards galaxy clusters
from NVSS source counts around Planck-selected cluster candidates, and include
appropriate correlations in our mock maps. The study allows us to quantify the
effects of halo line-of-sight alignments, source confusion, and telescope
angular resolution on the detections of TSZEs.
We perform a similar analysis for the planned 100-m Hevelius radio telescope
(RTH) equipped with a 49-beam radio camera.
We find that RT32/OCRA-f will be suitable for small-field blind radio source
surveys, and will detect $33^{+17}_{-11}$ new radio sources brighter than 0.87
mJy at 30~GHz in a 1 deg$^2$ field at $>5\sigma$ CL during a one-year,
non-continuous, observing campaign, taking account of Polish weather
conditions. It is unlikely that any galaxy cluster will be detected at
$3\sigma$ CL in such a survey. A $60$-deg$^2$ survey, with field coverage of
$2^2$ beams per pixel, at 15 GHz with the RTH, would find <1.5 galaxy clusters
per year brighter than 60 $\mu$Jy (at $3\sigma$ CL), and would detect about
$3.4 \times 10^4$ point sources brighter than 1 mJy at $5\sigma$ CL, with
confusion causing flux density errors $\lesssim 2\%$ (20%) in 68% (95%) of the
detected sources.
A primary goal of the planned RTH will be a wide-area ($\pi$~sr) radio source
survey at 15 GHz. This survey will detect nearly $3 \times 10^5$ radio sources
at $5\sigma$ CL down to 1.3 mJy, and tens of galaxy clusters, in one year of
operation with typical weather conditions. ABRIDGED |
New detections of radio minihalos in cool cores of galaxy clusters: Cool cores of some galaxy clusters exhibit faint radio "minihalos." Their
origin is unclear; their study has been limited by their small number. We
undertook a systematic search for minihalos in a large sample of X-ray luminous
clusters with high-quality radio data. In this paper, we report four new
minihalos (A 478, ZwCl 3146, RXJ 1532.9+3021 and A 2204), and five candidates,
found in the reanalyzed archival Very Large Array observations. The radio
luminosities of our minihalos and candidates are in the range $10^{23-25}$ W
Hz$^{-1}$ at 1.4 GHz, consistent with this type of radio sources. Their sizes
(40-160 kpc in radius) are somewhat smaller than those of the previously known
minihalos. We combine our new detections with previously known minihalos,
obtaining a total sample of 21 objects, and briefly compare the cluster radio
properties to the average X-ray temperature and the total masses estimated from
Planck. We find that nearly all clusters hosting minihalos are hot and massive.
Beyond that, there is no clear correlation between the minihalo radio power and
cluster temperature or mass (in contrast with the giant radio halos found in
cluster mergers, whose radio luminosity correlates with the cluster mass).
Chandra X-ray images indicate gas sloshing in the cool cores of most of our
clusters, with minihalos contained within the sloshing regions in many of them.
This supports the hypothesis that radio-emitting electrons are reaccelerated by
sloshing. Advection of relativistic electrons by the sloshing gas may also play
a role in the formation of the less-extended minihalos. | Mass profiles and galaxy orbits in nearby galaxy clusters from the
analysis of the projected phase-space: We analyze kinematic data of 41 nearby (z<0.1) relaxed galaxy clusters in
terms of the projected phase-space density using a phenomenological, fully
anisotropic model of the distribution function. We apply the Markov Chain Monte
Carlo approach to place constraints on total mass distribution approximated by
the universal NFW profile and the profile of the anisotropy of galaxy orbits.
We find the normalization of the mean mass-concentration relation is
c=6.9_{-0.7}^{+0.6} at the virial mass M_v=5x10^{14}M_sun. Assuming a
one-to-one correspondence between sigma_8 and the normalization of the
mass-concentration relation in the framework of the concordance model we
estimate the normalization of the linear power spectrum to be
sigma_8=0.91_{-0.08}^{+0.07}. Our constraints on the parameters of the mass
profile are compared with estimates from other methods. We show that galaxy
orbits are isotropic at the cluster centres (with the mean ratio of the
radial-to-tangential velocity dispersions sigma_r/sigma_theta=0.97+/-0.04) and
radially anisotropic at the virial sphere (with the mean ratio
sigma_r/sigma_theta=1.75^{+0.23}_{-0.19}). Although the value of the central
anisotropy appears to be universal, the anisotropy at the virial radius differs
between clusters within the range 1<(sigma_r/sigma_theta)<2. Utilizing the
Bautz-Morgan morphological classification and information on the prominence of
a cool core we select two subsamples of galaxy clusters corresponding to less
and more advanced evolutionary states. It is demonstrated that less evolved
clusters have shallower mass profiles and their galaxy orbits are more radially
biased at the virial sphere. This property is consistent with the expected
evolution of the mass profiles as well as with the observed orbital segregation
of late and early type galaxies. |
Non-Equilibrium Ionization State and Two-Temperature Structure in the
Bullet Cluster 1E0657-56: We investigate a non-equilibrium ionization state and an electron-ion
two-temperature structure of the intracluster medium in the merging galaxy
cluster, 1E0657-56 (the Bullet cluster), using a series of N-body and
hydrodynamic simulations. We find that the electron temperature at the shock
layer associated with the X-ray sub peak (bullet) is quite different depending
on the thermal relaxation model between electrons and ions; ~25 keV for the
Coulomb thermal relaxation model and ~45 keV for the instantaneous thermal
relaxation model in the simulations which reproduce the observed X-ray
morphology. Furthermore, both of Fe xxv and Fe xxvi are overabundant compared
with the ionization equilibrium state around the shock layer, and thus, the
intensity ratio between Fe xxv and Fe xxvi K alpha lines are significantly
altered from that in the ionization equilibrium state. We also carry out the
simulations with various sets of merger parameters, and discuss a possible
range of the non-equilibrium effects in this system. Our results could be
tested with future X-ray observations such as Astro-H with better sensitivity
in high energy band. | Measuring Lensing Magnification of Quasars by Large Scale Structure
using the Variability-Luminosity Relation: We introduce a technique to measure gravitational lensing magnification using
the variability of type I quasars. Quasars' variability amplitudes and
luminosities are tightly correlated, on average. Magnification due to
gravitational lensing increases the quasars' apparent luminosity, while leaving
the variability amplitude unchanged. Therefore, the mean magnification of an
ensemble of quasars can be measured through the mean shift in the
variability-luminosity relation. As a proof of principle, we use this technique
to measure the magnification of quasars spectroscopically identified in the
Sloan Digital Sky Survey, due to gravitational lensing by galaxy clusters in
the SDSS MaxBCG catalog. The Palomar-QUEST Variability Survey, reduced using
the DeepSky pipeline, provides variability data for the sources. We measure the
average quasar magnification as a function of scaled distance (r/R200) from the
nearest cluster; our measurements are consistent with expectations assuming NFW
cluster profiles, particularly after accounting for the known uncertainty in
the clusters' centers. Variability-based lensing measurements are a valuable
complement to shape-based techniques because their systematic errors are very
different, and also because the variability measurements are amenable to
photometric errors of a few percent and to depths seen in current wide-field
surveys. Given the data volume expected from current and upcoming surveys, this
new technique has the potential to be competitive with weak lensing shear
measurements of large scale structure. |
Are SMBHs shrouded by "super-Oort" clouds of comets and asteroids?: The last decade has seen a dramatic confirmation that an in situ star
formation is possible inside the inner parsec of the Milky Way. Here we suggest
that giant planets, solid terrestrial-like planets, comets and asteroids may
also form in these environments, and that this may have observational
implications for Active Galactic Nuclei (AGN). Like in debris discs around main
sequence stars, collisions of large solid objects should initiate strong
fragmentation cascades. The smallest particles in such a cascade - the
microscopic dust - may provide a significant opacity. We put a number of
observational and physical constraints on AGN obscuring torii resulting from
such fragmentation cascades. We find that torii fed by fragmenting asteroids
disappear at both low and high AGN luminosities. At high luminosities, $L \sim
L_{\rm Edd}$, where $L_{\rm Edd}$ is the Eddington limit, the AGN radiation
pressure blows out the microscopic dust too rapidly. At low luminosities, on
the other hand, the AGN discs may avoid gravitational fragmentation into stars
and solids. We also note that these fragmentation cascades may be responsible
for astrophysically "large" dust particles of approximately micrometer sizes
that were postulated by some authors to explain unusual absorption properties
of the AGN torii. | Cosmography and large scale structure by f(R) gravity: new results: Cosmography and galaxy clusters are discussed in the framework of
f(R)-gravity giving a comprehensive review of recent results. |
Galaxy Zoo : 'Hanny's Voorwerp', a quasar light echo?: We report the discovery of an unusual object near the spiral galaxy IC 2497,
discovered by visual inspection of the Sloan Digital Sky Survey (SDSS) as part
of the Galaxy Zoo project. The object, known as Hanny's Voorwerp, is bright in
the SDSS g band due to unusually strong OIII 4959-5007 emission lines. We
present the results of the first targeted observations of the object in the
optical, UV and X-ray, which show that the object contains highly ionized gas.
Although the line ratios are similar to extended emission-line regions near
luminous AGN, the source of this ionization is not apparent. The emission-line
properties, and lack of x-ray emission from IC 2497, suggest either a highly
obscured AGN with a novel geometry arranged to allow photoionization of the
object but not the galaxy's own circumnuclear gas, or, as we argue, the first
detection of a quasar light echo. In this case, either the luminosity of the
central source has decreased dramatically or else the obscuration in the system
has increased within 10^5 years. This object may thus represent the first
direct probe of quasar history on these timescales. | High-Redshift Star-Forming Galaxies: Angular Momentum and Baryon
Fraction, Turbulent Pressure Effects and the Origin of Turbulence: The structure of a sample of high-redshift (z=2), rotating galaxies with high
star formation rates and turbulent gas velocities of sigma=40-80 km/s is
investigated. Fitting the observed disk rotational velocities and radii with a
Mo, Mao, White (1998) (MMW) model requires unusually large disk spin parameters
lambda_d>0.1 and disk-to-dark halo mass fraction m_d=0.2, close to the cosmic
baryon fraction. The galaxies segregate into dispersion-dominated systems with
1<vmax/sigma<3, maximum rotational velocities vmax<200 km/s and disk half-light
radii rd=1-3 kpc and rotation-dominated systems with vmax>200 km/s,
vmax/sigma>3 and rd=4-8 kpc. For the dispersion-dominated sample, radial
pressure gradients partly compensate the gravitational force, reducing the
rotational velocities. Including this pressure effect in the MMW model,
dispersion-dominated galaxies can be fitted well with spin parameters lf
lambda_d=0.03-0.05 for high disk mass fractions of m_d=0.2 and with
lambda_d=0.01-0.03 for m_d=0.05. These values are in good agreement with
cosmological expectations. For the rotation-dominated sample however pressure
effects are small and better agreement with theoretically expected disk spin
parameters can only be achieved if the dark halo mass contribution in the
visible disk regime (2-3*rd) is smaller than predicted by the MMW model. We
argue that these galaxies can still be embedded in standard cold dark matter
halos if the halos did not contract adiabatically in response to disk
formation. It is shown that the observed high turbulent gas motions of the
galaxies are consistent with a Toomre instability parameter Q=1 which is equal
to the critical value, expected for gravitational disk instability to be the
major driver of turbulence. The dominant energy source of turbulence is then
the potential energy of the gas in the disk. |
Observational constraints on the cosmological expansion rate and spatial
curvature: Observations conducted over the last few decades show that the expansion of
the Universe is accelerating. In the standard model of cosmology, this
accelerated expansion is attributed to a dark energy in the form of a
cosmological constant. It is conceivable, however, for the dark energy to
exhibit mild dynamics (so that its energy density changes with time rather than
having a constant value), or for the accelerated expansion of the Universe to
be caused by some mechanism other than dark energy. In this work I will
investigate both of these possibilities by using observational data to place
constraints on the parameters of simple models of dynamical dark energy as well
as cosmological models without dark energy. I find that these data favor the
standard model while leaving some room for dynamical dark energy.
The standard model also holds that the Universe is flat on large spatial
scales. The same observational data used to test dark energy dynamics can be
used to constrain the large-scale curvature of the Universe, and these data
generally favor spatial flatness, with some mild preference for spatial
curvature in some data combinations. | Redshift remapping and cosmic acceleration in dark-matter-dominated
cosmological models: The standard relation between the cosmological redshift and cosmic scale
factor underlies cosmological inference from virtually all kinds of
cosmological observations, leading to the emergence of the LambdaCDM
cosmological model. This relation is not a fundamental theory and thus
observational determination of this function (redshift remapping) should be
regarded as an insightful alternative to holding its standard form in analyses
of cosmological data. Here we present non-parametric reconstructions of
redshift remapping in dark-matter-dominated models and constraints on
cosmological parameters from a joint analysis of all primary cosmological
probes including the local measurement of the Hubble constant, Type Ia
supernovae, baryonic acoustic oscillations (BAO), Planck observations of the
cosmic microwave background (CMB) radiation (temperature power spectrum) and
cosmic chronometers. The reconstructed redshift remapping points to an
additional boost of redshift operating in late epoch of cosmic evolution, but
affecting both low-redshift observations and the CMB. The model predicts a
significant difference between the actual Hubble constant, h=0.48+/-0.02, and
its local determination, h_obs=0.73+/-0.02. The ratio of these two values
coincides closely with the maximum expansion rate inside voids formed in the
corresponding open cosmological model with Omega_m=0.87+/-0.03, whereas the
actual value of the Hubble constant implies the age of the Universe that is
compatible with the Planck LambdaCDM cosmology. The new dark-matter-dominated
model with redshift remapping provides excellent fits to all data and
eliminates recently reported tensions between the Planck LambdaCDM cosmology,
the local determination of the Hubble constant and the BAO measurements from
the Ly-alpha forest of high-redshift quasars. |
Isolating non-linearities of light propagation in inhomogeneous
cosmologies: A new formulation for light propagation in geometric optics by means of the
Bi-local Geodesic Operators is considered. We develop the BiGONLight
Mathematica package, uniquely designed to apply this framework to compute
optical observables in Numerical Relativity. Our package can be used for light
propagation on a wide range of scales and redshifts and accepts numerical as
well as analytical input for the spacetime metric. In this paper we focus on
two cosmological observables, the redshift and the angular diameter distance,
specializing our analysis to a wall universe modeled within the post-Newtonian
approximation. With this choice and the input metric in analytical form, we are
able to estimate non-linearities of light propagation by comparing and
isolating the contributions coming from Newtonian and post-Newtonian
approximations as opposed to linear perturbation theory. We also clarify the
role of the dominant post-Newtonian contribution represented by the linear
initial seed which, strictly speaking, is absent in the Newtonian treatment. We
found that post-Newtonian non-linear corrections are below $1\%$, in agreement
with previous results in the literature. | A Newly-Discovered Radio Halo in Merging Cluster MACS J2243.3-0935: We report the discovery of a radio halo in the massive merging cluster
MACSJ2243.3-0935, as well as a new radio relic candidate, using the Giant
Meterwave Radio Telescope and the KAT-7 telescope. The radio halo is coincident
with the cluster X-ray emission and has a largest linear scale of approximately
0.9 Mpc. We measure a flux density of $10.0\pm 2.0$ mJy at 610 MHz for the
radio halo. We discuss equipartition estimates of the cluster magnetic field
and constrain the value to be of the order of 1 $\mu$G. The relic candidate is
detected at the cluster virial radius where a filament meets the cluster. The
relic candidate has a flux density of $5.2\pm 0.8$ mJy at 610 MHz. We discuss
possible origins of the relic candidate emission and conclude that the
candidate is consistent with an infall relic. |
The BINGO Project VI: HI Halo Occupation Distribution and Mock Building: BINGO (Baryon Acoustic Oscillations from Integrated Neutral Gas
Observations.) is a radio telescope designed to survey from 980 MHz to 1260
MHz, observe the neutral Hydrogen (HI) 21-cm line and detect BAO (Baryon
Acoustic Oscillation) signal with Intensity Mapping technique. Here we present
our method to generate mock maps of the 21-cm Intensity Mapping signal covering
the BINGO frequency range and related test results. (Abridged) | Looking for Intermediate-Mass Black Holes: A discussion of the entropy of the universe leads to the suggestion of very
many intermediate-mass black holes between thirty and three hundred thousand
solar masses in the halo. It is consistent with observations on wide binaries
as well as microlensing and considerations of disk stability that such IMBHs
constitute all cold dark matter |
Deep multi-redshift limits on Epoch of Reionisation 21cm Power Spectra
from Four Seasons of Murchison Widefield Array Observations: We compute the spherically-averaged power spectrum from four seasons of data
obtained for the Epoch of Reionisation (EoR) project observed with the
Murchison Widefield Array (MWA). We measure the EoR power spectrum over $k=
0.07-3.0~h$Mpc$^{-1}$ at redshifts $z=6.5-8.7$. The largest aggregation of 110
hours on EoR0 high-band (3,340 observations), yields a lowest measurement of
(43~mK)$^2$ = 1.8$\times$10$^3$ mK$^2$ at $k$=0.14~$h$Mpc$^{-1}$ and $z=6.5$
(2$\sigma$ thermal noise plus sample variance). Using the Real-Time System to
calibrate and the CHIPS pipeline to estimate power spectra, we select the best
observations from the central five pointings within the 2013--2016 observing
seasons, observing three independent fields and in two frequency bands. This
yields 13,591 2-minute snapshots (453 hours), based on a quality assurance
metric that measures ionospheric activity. We perform another cut to remove
poorly-calibrated data, based on power in the foreground-dominated and
EoR-dominated regions of the two-dimensional power spectrum, reducing the set
to 12,569 observations (419 hours). These data are processed in groups of 20
observations, to retain the capacity to identify poor data, and used to analyse
the evolution and structure of the data over field, frequency, and data
quality. We subsequently choose the cleanest 8,935 observations (298 hours of
data) to form integrated power spectra over the different fields, pointings and
redshift ranges. | Precision simulation of ground-based lensing data using observations
from space: Current and upcoming wide-field, ground-based, broad-band imaging surveys
promise to address a wide range of outstanding problems in galaxy formation and
cosmology. Several such uses of ground-based data, especially weak
gravitational lensing, require highly precise measurements of galaxy image
statistics with careful correction for the effects of the point-spread function
(PSF). In this paper, we introduce the SHERA (SHEar Reconvolution Analysis)
software to simulate ground-based imaging data with realistic galaxy
morphologies and observing conditions, starting from space-based data (from
COSMOS, the Cosmological Evolution Survey) and accounting for the effects of
the space-based PSF. This code simulates ground-based data, optionally with a
weak lensing shear applied, in a model-independent way using a general Fourier
space formalism. The utility of this pipeline is that it allows for a precise,
realistic assessment of systematic errors due to the method of data processing,
for example in extracting weak lensing galaxy shape measurements or galaxy
radial profiles, given user-supplied observational conditions and real galaxy
morphologies. Moreover, the simulations allow for the empirical test of error
estimates and determination of parameter degeneracies, via generation of many
noise maps. The public release of this software, along with a large sample of
cleaned COSMOS galaxy images (corrected for charge transfer inefficiency),
should enable upcoming ground-based imaging surveys to achieve their potential
in the areas of precision weak lensing analysis, galaxy profile measurement,
and other applications involving detailed image analysis. |
Structure Formation and Microlensing with Axion Miniclusters: If the symmetry breaking responsible for axion dark matter production occurs
during the radiation-dominated epoch in the early Universe, then this produces
large amplitude perturbations that collapse into dense objects known as axion
miniclusters. The characteristic minicluster mass, $M_0$, is set by the mass
inside the horizon when axion oscillations begin. For the QCD axion $M_0\sim
10^{-10}M_\odot$, however for an axion-like particle $M_0$ can approach
$M_\odot$ or higher. Using the Press-Schechter formalism we compute the mass
function of halos formed by hierarchical structure formation from these seeds.
We compute the concentrations and collapse times of these halos and show that
they can grow to be as massive as $10^6M_0$. Within the halos, miniclusters
likely remain tightly bound, and we compute their gravitational microlensing
signal taking the fraction of axion dark matter collapsed into miniclusters,
$f_{\rm MC}$, as a free parameter. A large value of $f_{\rm MC}$ severely
weakens constraints on axion scenarios from direct detection experiments. We
take into account the non-Gaussian distribution of sizes of miniclusters and
determine how this effects the number of microlensing events. We develop the
tools to consider microlensing by an extended mass function of non-point-like
objects, and use microlensing data to place the first observational constraints
on $f_{\rm MC}$. This opens a new window for the potential discovery of the
axion. | On the detectability of HI 21-cm in MgII absorption system: We investigate the effect of two important, but oft neglected, factors which
can affect the detectability of HI 21-cm absorption in MgII absorption systems:
The effect of line-of-sight geometry of the coverage of the background radio
flux and any possible correlation between the 21-cm line strength and the rest
frame equivalent width of the MgII line. Regarding the former, while the
observed detection rate at small angular diameter distance ratios is a near
certainty, for an unbiased sample, where either a detection or a non-detection
are equally likely, at ratios > 0.8 the observed detection rate has an 8 sigma
significance, suggesting that the mix of ratios values at z < 1 is correlated
with the mix of detections and non-detections at low redshift, while the
exclusively high values of the ratio at z > 1 contribute to the low detection
rates at high redshift. In DLAs, the correlation between the 21-cm line
strength and the MgII equivalent width is dominated by the velocity spread of
the 21-cm line. This has recently been shown not to hold for MgII systems in
general. However, we do find the significance of the correlation to increase
when the MgII absorbers with MgI equivalent widths of >0.5 A are added to the
DLA sample. Large values of the angular diameter distance ratio may explain why
the absorbers which have similar equivalent widths to the detections remain
undetected. We do, however, also find the neutral hydrogen column densities of
the non-detections to be significantly lower. Applying the 21-cm line
strength/equivalent width correlation to yield column densities for the MgII
absorbers in which this is unmeasured, we find no evidence of a cosmological
evolution in the neutral hydrogen column density. |
Kriging interpolating cosmic velocity field. II. Taking anistropies and
multistreaming into account: Measuring the volume-weighted peculiar velocity statistics from
inhomogeneously and sparsely distributed galaxies/halos, by existing velocity
assignment methods, suffers from a significant sampling artifact. As an
alternative, the Kriging interpolation based on Gaussian processes was
introduced and evaluated [Y. Yu, J. Zhang, Y. Jing, and P. Zhang, Phys. Rev. D
92, 083527 (2015)]. Unfortunately, the most straightforward application of
Kriging does not perform better than the existing methods in the literature. In
this work, we investigate two physically motivated extensions. The first takes
into account of the anisotropic velocity correlations. The second introduces
the nugget effect, on account of multi-streaming of the velocity field. We find
that the performance is indeed improved. For sparsely sampled data
[$n_P\lesssim 6\times 10^{-3}(h^{-1} {\rm Mpc})^{-3}$] where the sampling
artifact is the most severe, the improvement is significant and is two-fold: 1)
The scale of reliable measurement of the velocity power spectrum is extended by
a factor $\sim 1.6$, and 2) the dependence on the velocity correlation prior is
weakened by a factor of $\sim 2$. We conclude that such extensions are
desirable for accurate velocity assignment by Kriging. | First detections of the [NII] 122 μm line at high redshift:
Demonstrating the utility of the line for studying galaxies in the early
universe: We report the first detections of the [NII] 122 {\mu}m line from a high
redshift galaxy. The line was strongly (> 6{\sigma}) detected from
SMMJ02399-0136, and H1413+117 (the Cloverleaf QSO) using the Redshift(z) and
Early Universe Spectrometer (ZEUS) on the CSO. The lines from both sources are
quite bright with line-to-FIR continuum luminosity ratios that are
~7.0\times10^{-4} (Cloverleaf) and 2.1\times10^{-3} (SMMJ02399). With ratios
2-10 times larger than the average value for nearby galaxies, neither source
exhibits the line-to-continuum deficits seen in nearby sources. The line
strengths also indicate large ionized gas fractions, ~8 to 17% of the molecular
gas mass. The [OIII]/[NII] line ratio is very sensitive to the effective
temperature of ionizing stars and the ionization parameter for emission arising
in the narrow-line region (NLR) of an AGN. Using our previous detection of the
[OIII] 88 {\mu}m line, the [OIII]/[NII] line ratio for SMMJ02399-0136 indicates
the dominant source of the line emission is either stellar HII regions ionized
by O9.5 stars, or the NLR of the AGN with ionization parameter log(U) = -3.3 to
-4.0. A composite system, where 30 to 50% of the FIR lines arise in the NLR
also matches the data. The Cloverleaf is best modeled by a superposition of
~200 M82 like starbursts accounting for all of the FIR emission and 43% of the
[NII] line. The remainder may come from the NLR. This work demonstrates the
utility of the [NII] and [OIII] lines in constraining properties of the ionized
medium. |
Lyman-alpha emitters in a cosmological volume II: the impact of the
intergalactic medium: In the near future galaxy surveys will target Lyman alpha emitting galaxies
(LAEs) to unveil the nature of the dark energy. It has been suggested that the
observability of LAEs is coupled to the large scale properties of the
intergalactic medium. Such coupling could introduce distortions into the
observed clustering of LAEs, adding a new potential difficulty to the
interpretation of upcoming surveys. We present a model of LAEs that
incorporates Lyman-alpha radiative transfer processes in the interstellar and
intergalactic medium. The model is implemented in the GALFORM semi-analytic
model of galaxy of formation and evolution. We find that the radiative transfer
inside galaxies produces selection effects over galaxy properties. In
particular, observed LAEs tend to have low metallicities and intermediate star
formation rates. At low redshift we find no evidence of a correlation between
the spatial distribution of LAEs and the intergalactic medium properties.
However, at high redshift the LAEs are linked to the line of sight velocity and
density gradient of the intergalactic medium. The strength of the coupling
depends on the outflow properties of the galaxies and redshift. This effect
modifies the clustering of LAEs on large scales, adding non linear features. In
particular, our model predicts modifications to the shape and position of the
baryon acoustic oscillation peak. This work highlights the importance of
including radiative transfer physics in the cosmological analysis of LAEs. | Lyman-$α$ coupling and heating at Cosmic Dawn: The global 21-cm signal from the cosmic dawn is affected by a variety of
heating and cooling processes. We investigate the impact of heating due to
Lyman-$\alpha$ (Ly~$\alpha$) photons on the global 21-cm signal at cosmic dawn
using an analytical expression of the spectrum around the Ly~$\alpha$ resonance
based on the so-called `wing approximation'. We derive a new expression for the
scattering correction and for the first time give a simple close-form
expression for the cooling due to injected Ly~$\alpha$ photons. We perform a
short parameter study by varying the Ly~$\alpha$ background intensity by four
orders of magnitude and establish that a strong Ly~$\alpha$ background is
necessary, although not sufficient, in order to reproduce the recently detected
stronger-than-expected 21-cm signal by the EDGES Collaboration. We show that
the magnitude of this Ly~$\alpha$ heating is smaller than previously estimated
in the literature by two orders of magnitude or more. As a result, even a
strong Ly~$\alpha$ background is consistent with the EDGES measurement. We also
provide a detailed discussion on different expressions of the Ly~$\alpha$
heating rate used in the literature. |
Decaying Dark Matter in Halos of Primordial Black Holes: We investigate photon signatures of general decaying dark-matter particles in
halos of primordial black holes. We derive the halo-profile density and the
total decay rate for these combined dark-matter scenarios. For the case of
axion-like particles of masses below $\mathcal{O}( 1 )\,$keV, we find strong
bounds on the decay constant which are several orders of magnitude stronger
than the strongest existing bounds, for all halo masses above $\mathcal{O}(
10^{-5} )$ solar masses. Using future X-ray measurements, it will be possible
to push these bounds on such combined dark-matter scenarios even further. | Data Compression and Inference in Cosmology with Self-Supervised Machine
Learning: The influx of massive amounts of data from current and upcoming cosmological
surveys necessitates compression schemes that can efficiently summarize the
data with minimal loss of information. We introduce a method that leverages the
paradigm of self-supervised machine learning in a novel manner to construct
representative summaries of massive datasets using simulation-based
augmentations. Deploying the method on hydrodynamical cosmological simulations,
we show that it can deliver highly informative summaries, which can be used for
a variety of downstream tasks, including precise and accurate parameter
inference. We demonstrate how this paradigm can be used to construct summary
representations that are insensitive to prescribed systematic effects, such as
the influence of baryonic physics. Our results indicate that self-supervised
machine learning techniques offer a promising new approach for compression of
cosmological data as well its analysis. |
Fast computation of the non-Gaussian covariance of redshift-space galaxy
power spectrum multipoles: The non-Gaussian part of the covariance matrix of the galaxy power spectrum
involves the connected four-point correlation in Fourier space, i.e.
trispectrum. This paper introduces a fast method to compute the non-Gaussian
part of the covariance matrix of the galaxy power spectrum multipoles in
redshift space at tree-level standard perturbation theory. For the tree-level
galaxy trispectrum, the angular integral between two wavevectors can be
evaluated analytically by employing an FFTLog. The new implementation computes
the non-Gaussian covariance of the power spectrum monopole, quadrupole,
hexadecapole and their cross-covariance in $O(10)$ seconds, for an effectively
arbitrary number of instances of cosmological and galaxy bias parameters and
redshift, without any parallelization or acceleration. It is a large advantage
over conventional numerical integration. We demonstrate that the computation of
the covariance at $k = 0.005 - 0.4\,h\,\mathrm{Mpc}^{-1}$ gives results with
$0.1 - 1\%$ accuracy. The efficient computation of the analytic covariance can
be useful for future galaxy surveys, especially utilizing multi-tracer
analysis. | Numerical stochastic inflation constrained by frozen noise: Stochastic inflation can resolve strong inflationary perturbations, which
seed primordial black holes. I present a fast and accurate way to compute these
perturbations in typical black hole producing single-field models, treating the
short-wavelength Fourier modes beyond the de Sitter approximation. The
squeezing and freezing of the modes reduces the problem to one dimension, and
the resulting new form of the stochastic equations, dubbed `constrained
stochastic inflation,' can be solved efficiently with semi-analytical
techniques and numerical importance sampling. In an example case, the
perturbation distribution is resolved in seconds deep into its non-Gaussian
tail, a speed-up of factor $10^9$ compared to a previous study. Along the way,
I comment on the role of the momentum constraint in stochastic inflation. |
Reionization and dark matter decay: Cosmic reionization and dark matter decay can impact observations of the
cosmic microwave sky in a similar way. A simultaneous study of both effects is
required to constrain unstable dark matter from cosmic microwave background
observations. We compare two reionization models with and without dark matter
decay. We find that a reionization model that fits also data from quasars and
star forming galaxies results in tighter constraints on the reionization
optical depth $\tau_{\text{reio}}$, but weaker constraints on the spectral
index $n_{\text{s}}$ than the conventional parametrization. We use the Planck
2015 data to constrain the effective decay rate of dark matter to $\Gamma_{\rm
eff} < 2.9 \times 10^{-25}/$s at $95$\% C.L. This limit is robust and model
independent. It holds for any type of decaying dark matter and it depends only
weakly on the chosen parametrization of astrophysical reionization. For light
dark matter particles that decay exclusively into electromagnetic components
this implies a limit of $\Gamma < 5.3 \times 10^{-26}/$s at $95$\% C.L.
Specifying the decay channels, we apply our result to the case of keV-mass
sterile neutrinos as dark matter candidates and obtain constraints on their
mixing angle and mass, which are comparable to the ones from the diffuse X-ray
background. | Cosmology with Superluminous Supernovae: We predict cosmological constraints for forthcoming surveys using
Superluminous Supernovae (SLSNe) as standardisable candles. Due to their high
peak luminosity, these events can be observed to high redshift (z~3), opening
up new possibilities to probe the Universe in the deceleration epoch. We
describe our methodology for creating mock Hubble diagrams for the Dark Energy
Survey (DES), the "Search Using DECam for Superluminous Supernovae" (SUDSS) and
a sample of SLSNe possible from the Large Synoptic Survey Telescope (LSST),
exploring a range of standardisation values for SLSNe. We include uncertainties
due to gravitational lensing and marginalise over possible uncertainties in the
magnitude scale of the observations (e.g. uncertain absolute peak magnitude,
calibration errors). We find that the addition of only ~100 SLSNe from SUDSS to
3800 Type Ia Supernovae (SNe Ia) from DES can improve the constraints on w and
Omega_m by at least 20% (assuming a flat wCDM universe). Moreover, the
combination of DES SNe Ia and 10,000 LSST-like SLSNe can measure Omega_m and w
to 2% and 4% respectively. The real power of SLSNe becomes evident when we
consider possible temporal variations in w(a), giving possible uncertainties of
only 2%, 5% and 14% on Omega_m, w_0 and w_a respectively, from the combination
of DES SNe Ia, LSST-like SLSNe and Planck. These errors are competitive with
predicted Euclid constraints, indicating a future role for SLSNe for probing
the high redshift Universe. |
Quantifying resolution in cosmological N-body simulations using
self-similarity: We demonstrate that testing for self-similarity in scale-free simulations
provides an excellent tool to quantify the resolution at small scales of
cosmological N-body simulations. Analysing two-point correlation functions
measured in simulations using ABACUS, we show how observed deviations from
self-similarity reveal the range of time and distance scales in which
convergence is obtained. While the well-converged scales show accuracy below 1
percent, our results show that, with a small force softening length, the
spatial resolution is essentially determined by the mass resolution. At later
times the lower cut-off scale on convergence evolves in comoving units as
$a^{-1/2}$ ($a$ being the scale factor), consistent with a hypothesis that it
is set by two-body collisionality. A corollary of our results is that N-body
simulations, particularly at high red-shift, contain a significant spatial
range in which clustering appears converged with respect to the time-stepping
and force softening but has not actually converged to the physical continuum
result. The method developed can be applied to determine the resolution of any
clustering statistic and extended to infer resolution limits for non-scale-free
simulations. | Peaks theory and the excursion set approach: We describe a model of dark matter halo abundances and clustering which
combines the two most widely used approaches to this problem: that based on
peaks and the other based on excursion sets. Our approach can be thought of as
addressing the cloud-in-cloud problem for peaks and/or modifying the excursion
set approach so that it averages over a special subset, rather than all
possible walks. In this respect, it seeks to account for correlations between
steps in the walk as well as correlations between walks. We first show how the
excursion set and peaks models can be written in the same formalism, and then
use this correspondence to write our combined excursion set peaks model. We
then give simple expressions for the mass function and bias, showing that even
the linear halo bias factor is predicted to be k-dependent as a consequence of
the nonlocality associated with the peak constraint. At large masses, our model
has little or no need to rescale the variable delta_c from the value associated
with spherical collapse, and suggests a simple explanation for why the linear
halo bias factor appears to lie above that based on the peak-background split
at high masses when such a rescaling is assumed. Although we have concentrated
on peaks, our analysis is more generally applicable to other traditionally
single-scale analyses of large-scale structure. |
Probing Large Scale Ionizing Background Fluctuation with Lyman $α$
Forest and Galaxy Cross-correlation at z=2.4: The amplitude of the metagalactic ultraviolet background (UVB) at
large-scales is impacted by two factors. First, it naturally attenuates at
scales larger than mean-free-path of UVB photons due to the absorption by
neutral intergalactic medium. Second, there are discrete and rare ionizing
sources distributing in the Universe, emitting the UVB photons, and thus
enhancing the local UVB amplitude. Therefore, for cosmological probe that is
sensitive to the UVB amplitude and capable of detecting the large scale like
Lyman-$\alpha$ forest spectrum, the fluctuation due to the clustering of
ionizing sources becomes a significant factor for Lyman-$\alpha$ flux
transmission and leave imprints on Lyman-$\alpha$ flux power spectrum at these
large scales. In this work, we make use of a radiative transfer model that
parametrizes the UVB source distribution by its bias $b_{\rm j}$ and shot noise
$\overline{n}_{\rm j}$. We estimate the constraints on this model through the
cross-correlation between Lyman-$\alpha$ forest survey and galaxy survey, using
the DESI Lyman-$\alpha$ forest survey and the Roman Space Telescope emission
line galaxy survey as an example. We show the detection sensitivity improvement
for UVB parameters from disjoint to maximal overlap of DESI+Roman survey
strategy. We also show that the degeneracy of two ionizing source parameters
can be broken by increasing the overlapping survey area. Our results motivate
survey strategies more dedicated to probe the UVB large-scale fluctuations. | X-Ray observations of a subhalo associated with the NGC 4839 group
infalling toward the Coma cluster: We report $Suzaku$ X-ray observations of the dark subhalo associated with the
merging group of NGC 4839 in the Coma cluster. The X-ray image exhibits an
elongated tail toward the southwest. The X-ray peak shifts approximately $1'$
away from the weak-lensing mass center toward the opposite direction of the
Coma cluster center. We investigated the temperature, normalization, pressure,
and entropy distributions around the subhalo. Excluding the X-ray tail, the
temperature beyond the truncation radius is 8-10$~\rm keV$, which is two times
higher than that of the subhalo and the X-ray tail. The pressure is nearly
uniform excluding southern part of the subhalo at two times of the truncation
radius. We computed the gas mass within the truncation radius and the X-ray
tail. While the gas fraction within the truncation radius is about 5 times
smaller than that of regular groups, the gas mass in the subhalo and the X-ray
tail to weak-lensing mass ratio is consistent with that of regular groups.
Assuming the infall velocity, $2000~\rm km~s^{-1}$, the ram pressure is 1.4
times greater than gravitational force per unit area. Assuming the
Kelvin-Helmholtz instabilities, the total lost mass is approximately
$3\times10^{11}~M_{\odot}$. If this gas had originally been within the
truncation radius, the gas mass fraction of the subhalo would have been
comparable with those of regular groups before infalling to the Coma cluster. |
Constraints on the mass and self-coupling of Ultra-Light Scalar Field
Dark Matter using observational limits on galactic central mass: It is well known that Ultra-Light Dark Matter (ULDM), usually scalar fields
of mass $m \sim 10^{-22}~{\rm eV}$, can solve some of the outstanding problems
of the Cold Dark Matter (CDM) paradigm. Such a scalar field could have
non-negligible self-coupling $\lambda$. In this work, using the known
observational upper limit on the amount of centrally concentrated dark matter
in a galaxy, we arrive at the observational constraints in the $\lambda - m$
(self coupling $-$ mass) parameter space. It is found that the observational
limit on the mass $m$ of the ULDM depends upon the sign and strength of the
self-interactions. We demonstrate that, for $m \sim 10^{-22}~{\rm eV}$,
self-coupling values of ${\cal O}(10^{-96})$ (corresponding to a scattering
length of $a_s \sim 10^{-82}~{\rm m}$) can be probed using limits on the dark
matter mass within 10 pc of the centre of M87 galaxy. Our analysis suggests
that if Ultra Light Axions (ULAs) form all of dark matter, its mass has to be
less than $\sim 6 \times 10^{-23}$ eV. | Hiding neutrino mass in modified gravity cosmologies: Cosmological observables show a dependence with the neutrino mass, which is
partially degenerate with parameters of extended models of gravity. We study
and explore this degeneracy in Horndeski generalized scalar-tensor theories of
gravity. Using forecasted cosmic microwave background and galaxy power spectrum
datasets, we find that a single parameter in the linear regime of the effective
theory dominates the correlation with the total neutrino mass. For any given
mass, a particular value of this parameter approximately cancels the power
suppression due to the neutrino mass at a given redshift. The extent of the
cancellation of this degeneracy depends on the cosmological large-scale
structure data used at different redshifts. We constrain the parameters and
functions of the effective gravity theory and determine the influence of
gravity on the determination of the neutrino mass from present and future
surveys. |
Modified gravity a la Galileon: Late time cosmic acceleration and
observational constraints: In this paper we examine the cosmological consequences of fourth order
Galileon gravity. We carry out detailed investigations of the underlying
dynamics and demonstrate the stability of one de Sitter phase. The stable de
Sitter phase contains a Galileon field $\pi$ which is an increasing function of
time (\dot{\pi}>0). Using the required suppression of the fifth force,
supernovae, BAO and CMB data, we constrain parameters of the model. We find
that the $\pi$ matter coupling parameter $\beta$ is constrained to small
numerical values such that $\beta$<0.02. We also show that the parameters of
the third and fourth order in the action (c_3,c_4) are not independent and with
reasonable assumptions, we obtain constraints on them. We investigate the
growth history of the model and find that the sub-horizon approximation is not
allowed for this model. We demonstrate strong scale dependence of linear
perturbations in the fourth order Galileon gravity. | Cosmological nonlinear density and velocity power spectra including
nonlinear vector and tensor modes: We present the leading order non-linear density and velocity power spectra in
the complete form; previous studies have omitted the vector- and tensor-type
perturbations simultaneously excited by the scalar-type perturbation in
nonlinear order. These additional contributions are comparable to the
scalar-type purely relativistic perturbations, and thus negligible in the
current paradigm of concordance cosmology: i.e., concerning density and
velocity perturbations of the pressureless matter in perturbation regime well
inside of matter-dominated epoch, we show that pure Einstein's gravity
contributions appearing from the third order are entirely negligible (five
orders of magnitude smaller than the Newtonian contributions) in all scales. We
thus prove that Newtonian perturbation theory is quite reliable in calculating
the amplitude of matter fluctuations even in the precision era of cosmology.
Therefore, besides the ones imprinted as the initial condition generated in the
earlier phase, the other relativistic effect relevant for interpreting
observational data must be the projection effect that occurs when mapping
galaxies on to the observed coordinate. |
Galaxy filaments as pearl necklaces: Context. Galaxies in the Universe form chains (filaments) that connect groups
and clusters of galaxies. The filamentary network includes nearly half of the
galaxies and is visually the most striking feature in cosmological maps.
Aims. We study the distribution of galaxies along the filamentary network,
trying to find specific patterns and regularities.
Methods. Galaxy filaments are defined by the Bisous model, a marked point
process with interactions. We use the two-point correlation function and the
Rayleigh Z-squared statistic to study how galaxies and galaxy groups are
distributed along the filaments.
Results. We show that galaxies and groups are not uniformly distributed along
filaments, but tend to form a regular pattern. The characteristic length of the
pattern is around 7 Mpc/h. A slightly smaller characteristic length 4 Mpc/h can
also be found, using the Z-squared statistic.
Conclusions. We find that galaxy filaments in the Universe are like pearl
necklaces, where the pearls are galaxy groups distributed more or less
regularly along the filaments. We propose that this well defined characteristic
scale could be used to test various cosmological models and to probe
environmental effects on the formation and evolution of galaxies. | LimberJack.jl: auto-differentiable methods for angular power spectra
analyses: We present LimberJack.jl, a fully auto-differentiable code for cosmological
analyses of 2 point auto- and cross-correlation measurements from galaxy
clustering, CMB lensing and weak lensing data written in Julia. Using Julia's
auto-differentiation ecosystem, LimberJack.jl can obtain gradients for its
outputs up to an order of magnitude faster than traditional finite difference
methods. This makes LimberJack.jl greatly synergistic with gradient-based
sampling methods, such as Hamiltonian Monte Carlo, capable of efficiently
exploring parameter spaces with hundreds of dimensions. We first prove
LimberJack.jl's reliability by reanalysing the DES Y1 3$\times$2-point data. We
then showcase its capabilities by using a O(100) parameters Gaussian Process to
reconstruct the cosmic growth from a combination of DES Y1 galaxy clustering
and weak lensing data, eBOSS QSO's, CMB lensing and redshift-space distortions.
Our Gaussian process reconstruction of the growth factor is statistically
consistent with the $\Lambda$CDM Planck 2018 prediction at all redshifts.
Moreover, we show that the addition of RSD data is extremely beneficial to this
type of analysis, reducing the uncertainty in the reconstructed growth factor
by $20\%$ on average across redshift. LimberJack.jl is a fully open-source
project available on Julia's general repository of packages and GitHub. |
MC^2: A deeper look at ZwCl 2341.1+0000 with Bayesian galaxy clustering
and weak lensing analyses: ZwCl 2341.1+0000, a merging galaxy cluster with disturbed X-ray morphology
and widely separated ($\sim$3 Mpc) double radio relics, was thought to be an
extremely massive ($10-30 \times 10^{14} M_\odot$) and complex system with
little known about its merger history. We present JVLA 2-4 GHz observations of
the cluster, along with new spectroscopy from our Keck/DEIMOS survey, and apply
Gaussian Mixture Modeling to the three-dimensional distribution of 227
confirmed cluster galaxies. After adopting the Bayesian Information Criterion
to avoid overfitting, which we discover can bias total dynamical mass estimates
high, we find that a three-substructure model with a total dynamical mass
estimate of $9.39 \pm 0.81 \times 10^{14} M_\odot$ is favored. We also present
deep Subaru imaging and perform the first weak lensing analysis on this system,
obtaining a weak lensing mass estimate of $5.57 \pm 2.47 \times 10^{14}
M_\odot$. This is a more robust estimate because it does not depend on the
dynamical state of the system, which is disturbed due to the merger. Our
results indicate that ZwCl 2341.1+0000 is a multiple merger system comprised of
at least three substructures, with the main merger that produced the radio
relics occurring near to the plane of the sky, and a younger merger in the
North occurring closer to the line of sight. Dynamical modeling of the main
merger reproduces observed quantities (relic positions and polarizations,
subcluster separation and radial velocity difference), if the merger axis angle
of $\sim$10$^{+34}_{-6}$ degrees and the collision speed at pericenter is
$\sim$1900$^{+300}_{-200}$ km/s. | Alternative High-z Cosmic Tracers and the Dark Energy Equation of State: We propose to use alternative cosmic tracers to measure the dark energy
equation of state and the matter content of the Universe [w(z) & \Omega_m]. Our
proposed method consists of two components: (a) tracing the Hubble relation
using HII-like starburst galaxies, as an alternative to SNIa, which can be
detected up to very large redshifts, z~4, and (b) measuring the clustering
pattern of X-ray selected AGN at a median redshift of ~1. Each component of the
method can in itself provide interesting constraints on the cosmological
parameters, especially under our anticipation that we will reduce the
corresponding random and systematic errors significantly. However, by joining
their likelihood functions we will be able to put stringent cosmological
constraints and break the known degeneracies between the dark energy equation
of state (whether it is constant or variable) and the matter content of the
universe and provide a powerful and alternative rute to measure the
contribution to the global dynamics, and the equation of state, of dark energy.
A preliminary joint analysis of X-ray selected AGN (based on a small XMM
survey) and the currently largest SNIa sample (Kowalski et al 2008), provides:
Omega_m=0.28^{+0.02}_{-0.04} and w=-1.0 +-0.1. |
Evolution of hierarchical clustering in the CFHTLS-Wide since z~1: We present measurements of higher order clustering of galaxies from the
latest release of the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS)
Wide. We construct a volume-limited sample of galaxies that contains more than
one million galaxies in the redshift range 0.2<z<1 distributed over the four
independent fields of the CFHTLS. We use a counts in cells technique to measure
the variance <xi_2> and the hierarchical moments S_n = <xi_n>/<xi_2>^(n-1)
(3<n<5) as a function of redshift and angular scale.The robustness of our
measurements if thoroughly tested, and the field-to-field scatter is in very
good agreement with analytical predictions. At small scales, corresponding to
the highly non-linear regime, we find a suggestion that the hierarchical
moments increase with redshift. At large scales, corresponding to the weakly
non-linear regime, measurements are fully consistent with perturbation theory
predictions for standard LambdaCDM cosmology with a simple linear bias. | The Santiago-Harvard-Edinburgh-Durham void comparison II: unveiling the
Vainshtein screening using weak lensing: We study cosmic voids in the normal-branch Dvali-Gabadadze-Porrati (nDGP)
braneworld models, which are representative of a class of modified gravity
theories where deviations from General Relativity are usually hidden by the
Vainshtein screening in high-density environments. This screening is less
efficient away from these environments, which makes voids ideally suited for
testing this class of models. We use N-body simulations of $\Lambda$-cold dark
matter ($\Lambda$CDM) and nGDP universes, where dark matter haloes are
populated with mock galaxies that mimic the clustering and number densities of
the BOSS CMASS galaxy sample. We measure the force, density and weak lensing
profiles around voids identified with six different algorithms. Compared to
$\Lambda$CDM, voids in nDGP are more under-dense due to the action of the fifth
force that arises in these models, which leads to a faster evacuation of matter
from voids. This leaves an imprint on the weak lensing tangential shear profile
around nDGP voids, an effect that is particularly strong for 2D underdensities
that are identified in the plane-of-the-sky. We make predictions for the
feasibility of distinguishing between nDGP and $\Lambda$CDM using void lensing
in upcoming large-scale surveys such as LSST and Euclid. We compare with the
analysis of voids in chameleon gravity theories and find that the weak lensing
signal for 3D voids is similar to nDGP, whereas for 2D voids the differences
with $\Lambda$CDM are much stronger for the chameleon gravity case, a direct
consequence of the different screening mechanisms operating in these theories. |
Constraints on cosmological birefringence from Planck and Bicep2/Keck
data: The polarization of cosmic microwave background (CMB) can be used to
constrain cosmological birefringence, the rotation of the linear polarization
of CMB photons potentially induced by parity violating physics beyond the
standard model. This effect produces non-null CMB cross correlations between
temperature and B mode-polarization, and between E- and B-mode polarization.
Both cross-correlations are otherwise null in the standard cosmological model.
We use the recently released 2015 Planck likelihood in combination with the
Bicep2/Keck/Planck (BKP) likelihood to constrain the birefringence angle
$\alpha$. Our findings, that are compatible with no detection, read $\alpha =
0.0^{\circ} \pm 1.3^{\circ} \mbox{ (stat)} \pm 1^{\circ} \mbox{ (sys)} $ for
{\sc Planck} data and $\alpha = 0.30^{\circ} \pm 0.27^{\circ} \mbox{ (stat)}
\pm 1^{\circ} \mbox{(sys)} $ for BKP data. We finally forecast the expected
improvements over present constraints when the Planck BB, TB and EB spectra at
high $\ell$ will be included in the analysis. | Isotropy of low redshift type Ia Supernovae: A Bayesian analysis: The standard cosmology strongly relies upon the Cosmological Principle, which
consists on the hypotheses of large scale isotropy and homogeneity of the
Universe. Testing these assumptions is, therefore, crucial to determining if
there are deviations from the standard cosmological paradigm. In this paper, we
use the latest type Ia supernova compilations, namely JLA and Union2.1 to test
the cosmological isotropy at low redshift ranges ($z<0.1$). This is performed
through a Bayesian selection analysis, in which we compare the standard,
isotropic model, with another one including a dipole correction due to peculiar
velocities. We find that the Union2.1 sample favors the dipole-corrected model,
but the opposite happens for the JLA. Nonetheless, the velocity dipole results
are in good agreement with previous analyses carried out with both datasets. We
conclude that there are no significant indications for large anisotropic
signals from nearby supernova compilations, albeit this test should be greatly
improved with the upcoming cosmological surveys. |
Towards $21$-cm intensity mapping at $z=2.28$ with uGMRT using the
tapered gridded estimator III: Foreground removal: Neutral hydrogen (HI) $21$-cm intensity mapping (IM) is a promising probe of
the large-scale structures in the Universe. However, a few orders of magnitude
brighter foregrounds obscure the IM signal. Here we use the Tapered Gridded
Estimator (TGE) to estimate the multi-frequency angular power spectrum (MAPS)
$C_{\ell}(\Delta\nu)$ from a $24.4\,\rm{MHz}$ bandwidth uGMRT Band $3$ data at
$432.8\,\rm{MHz}$. In $C_{\ell}(\Delta\nu)$ foregrounds remain correlated
across the entire $\Delta\nu$ range, whereas the $21$-cm signal is localized
within $\Delta\nu\le[\Delta \nu]$ (typically $0.5-1\,\rm{MHz}$). Assuming the
range $\Delta\nu>[\Delta \nu]$ to have minimal $21$-cm signal, we use
$C_{\ell}(\Delta\nu)$ in this range to model the foregrounds. This foreground
model is extrapolated to $\Delta\nu\leq[\Delta \nu]$, and subtracted from the
measured $C_{\ell}(\Delta\nu)$. The residual $[C_{\ell}(\Delta\nu)]_{\rm res}$
in the range $\Delta\nu\le[\Delta\nu]$ is used to constrain the $21$-cm signal,
compensating for the signal loss from foreground subtraction.
$[C_{\ell}(\Delta\nu)]_{\rm{res}}$ is found to be noise-dominated without any
trace of foregrounds. Using $[C_{\ell}(\Delta\nu)]_{\rm res}$ we constrain the
$21$-cm brightness temperature fluctuations $\Delta^2(k)$, and obtain the
$2\sigma$ upper limit $\Delta_{\rm UL}^2(k)\leq(18.07)^2\,\rm{mK^2}$ at
$k=0.247\,\rm{Mpc}^{-1}$. We further obtain the $2\sigma$ upper limit $
[\Omega_{{\rm HI}}b_{{\rm HI}}]_{\rm UL}\leq0.022$ where $\Omega_{{\rm HI}}$
and $b_{{\rm HI}}$ are the comoving HI density and bias parameters
respectively. Although the upper limit is nearly $10$ times larger than the
expected $21$-cm signal, it is $3$ times tighter over previous works using
foreground avoidance on the same data. | Axion as a Cold Dark Matter candidate: Here we generally prove that the axion as a coherently oscillating scalar
field acts as a cold dark matter in nearly all cosmologically relevant scales.
The proof is made in the linear perturbation order. Compared with our previous
proof based on solutions, here we compare the equations in the axion with the
ones in the cold dark matter, thus expanding the valid range of the proof.
Deviation from purely pressureless medium appears in very small scale where
axion reveals a peculiar equation of state. Our analysis is made in the
presence of the cosmological constant, and our conclusions are valid in the
presence of other fluid and field components. |
A New Method to Quantify X-ray Substructures in Clusters of Galaxies: We present a new method to quantify substructures in clusters of galaxies,
based on the analysis of the intensity of structures. This analysis is done in
a residual image that is the result of the subtraction of a surface brightness
model, obtained by fitting a two-dimensional analytical model (beta-model or
S\'ersic profile) with elliptical symmetry, from the X-ray image. Our method is
applied to 34 clusters observed by the Chandra Space Telescope that are in the
redshift range 0.02<z<0.2 and have a signal-to-noise ratio greater than 100. We
present the calibration of the method and the relations between the
substructure level with physical quantities, such as the mass, X-ray
luminosity, temperature, and cluster redshift. We use our method to separate
the clusters in two sub-samples of high and low substructure levels. We
conclude, using Monte Carlo simulations, that the method recuperates very well
the true amount of substructure for small angular core radii clusters (with
respect to the whole image size) and good signal-to-noise observations. We find
no evidence of correlation between the substructure level and physical
properties of the clusters such as mass, gas temperature, X-ray luminosity and
redshift. The scaling relations for the two sub-samples (high and low
substructure level clusters) are different (they present an off-set, i.e.,
given a fixed mass or temperature, low substructure clusters tend to be more
X-ray luminous), which is an important result for cosmological tests using the
mass-luminosity relation to obtain the cluster mass function, since they rely
on the assumption that clusters do not present different scaling relations
according to their dynamical state. | Astrometric Reverberation Mapping: Spatially extended emission regions of Active Galactic Nuclei (AGN) respond
to continuum variations, if such emission regions are powered by energy
reprocessing of the continuum. The response from different parts of the
reverberating region arrives at different times lagging behind the continuum
variation. The lags can be used to map the geometry and kinematics of the
emission region (i.e., reverberation mapping, RM). If the extended emission
region is not spherically symmetric in configuration and velocity space,
reverberation may produce astrometric offsets in the emission region
photocenter as a function of time delay and velocity, detectable with future
micro-arcsec to tens of micro-arcsec astrometry. Such astrometric responses
provide independent constraints on the geometric and kinematic structure of the
extended emission region, complementary to traditional reverberation mapping.
In addition, astrometric RM is more sensitive to infer the inclination of a
flattened geometry and the rotation angle of the extended emission region. |
Galaxy Evolution and Star Formation Efficiency at 0.2 < z < 0.6: We present the results of a CO line survey of 30 galaxies at moderate
redshift (z \sim 0.2-0.6), with the IRAM 30m telescope, with the goal to follow
galaxy evolution and in particular the star formation efficiency (SFE) as
defined by the ratio between far-infrared luminosity and molecular gas mass
(LFIR/M(H2)). The sources are selected to be ultra-luminous infrared galaxies
(ULIRGs), with LFIR larger than 2.8 10^{12} Lsol, experiencing starbursts;
adopting a low ULIRG CO-to-H2 conversion factor, their gas consumption
time-scale is lower than 10^8 yr. To date only very few CO observations exist
in this redshift range that spans nearly 25% of the universe's age.
Considerable evolution of the star formation rate is already observed during
this period. 18 galaxies out of our sample of 30 are detected (of which 16 are
new detections), corresponding to a detection rate of 60%. The average CO
luminosity for the 18 galaxies detected is L'CO = 2 10^{10} K km/s pc^2,
corresponding to an average H2 mass of 1.6 10^{10} Msol. The FIR luminosity
correlates well with the CO luminosity, in agreement with the correlation found
for low and high redshift ULIRGs. Although the conversion factor between CO
luminosity and H2 mass is uncertain, we find that the maximum amount of gas
available for a single galaxy is quickly increasing as a function of redshift.
Using the same conversion factor, the SFEs for z\sim 0.2-0.6 ULIRGs are found
to be significantly higher, by a factor 3, than for local ULIRGs, and are
comparable to high redshift ones. We compare this evolution to the expected
cosmic H2 abundance and the cosmic star formation history. | Statistical properties of polarized radio sources at high frequency and
their impact on CMB polarization measurements: We have studied the implications of high sensitivity polarization
measurements of objects from the WMAP point source catalogue made using the VLA
at 8.4, 22 and 43 GHz. The fractional polarization of sources is almost
independent of frequency with a median of ~2 per cent and an average, for
detected sources, of ~3.5 per cent. These values are also independent of the
total intensity over the narrow range of intensity we sample. Using a
contemporaneous sample of 105 sources detected at all 3 VLA frequencies, we
have investigated the spectral behaviour as a function of frequency by means of
a 2-colour diagram. Most sources have power-law spectra in total intensity, as
expected. On the other hand they appear to be almost randomly distributed in
the polarized intensity 2-colour diagram. This is compatible with the polarized
spectra being much less smooth than those in intensity and we speculate on the
physical origins of this. We have performed an analysis of the correlations
between the fractional polarization and spectral indices including computation
of the principal components. We find that there is little correlation between
the fractional polarization and the intensity spectral indices. This is also
the case when we include polarization measurements at 1.4 GHz from the NVSS. In
addition we compute 45 rotation measures from polarization position angles
which are compatible with a \lambda^2 law. We use our results to predict the
level of point source confusion noise that contaminates CMB polarization
measurements aimed at detecting primordial gravitational waves from inflation.
We conclude that some level of source subtraction will be necessary to detect
r~0.1 below 100 GHz and at all frequencies to detect r~0.01. We present
estimates of the level of contamination expected and the number of sources
which need to be subtracted as a function of the imposed cut flux density and
frequency. |
Wavelet reconstruction of E and B modes for CMB polarisation and cosmic
shear analyses: We present new methods for mapping the curl-free (E-mode) and divergence-free
(B-mode) components of spin 2 signals using spin directional wavelets. Our
methods are equally applicable to measurements of the polarisation of the
cosmic microwave background (CMB) and the shear of galaxy shapes due to weak
gravitational lensing. We derive pseudo and pure wavelet estimators, where E-B
mixing arising due to incomplete sky coverage is suppressed in wavelet space
using scale- and orientation-dependent masking and weighting schemes. In the
case of the pure estimator, ambiguous modes (which have vanishing curl and
divergence simultaneously on the incomplete sky) are also cancelled. On
simulations, we demonstrate the improvement (i.e., reduction in leakage)
provided by our wavelet space estimators over standard harmonic space
approaches. Our new methods can be directly interfaced in a coherent and
computationally-efficient manner with component separation or feature
extraction techniques that also exploit wavelets. | Phi Zeta Delta: Growth of Perturbations in Parameterized Gravity for an
Einstein-de Sitter Universe: Parameterized frameworks for modified gravity are potentially useful tools
for model-independent tests of General Relativity on cosmological scales. The
toy model of an Einstein-de Sitter (EdS) universe provides a safe testbed in
which to improve our understanding of their behaviour. We implement a
mathematically consistent parameterization at the level of the field equations,
and use this to calculate the evolution of perturbations in an EdS scenario.
Our parameterization explicitly allows for new scalar degrees of freedom, and
we compare this to theories in which the only degrees of freedom come from the
metric and ordinary matter. The impact on the Integrated Sachs-Wolfe effect and
canonically-conserved superhorizon perturbations is considered. |
The transient acceleration from time-dependent interacting dark energy
models: The transient acceleration which the current cosmic acceleration is not
eternal is possible by introducing the interaction between dark matter and dark
energy. If the energy transfer is from dark energy to dark matter, then it is
possible to realize the transient acceleration. We study the possibility of
transient acceleration by considering two time-dependent phenomenological
interaction forms so that the energy transfer increases as the universe
evolves. Starting from a simple and extending to a more complicated ansatz, we
obtain analytical expressions for the evolutions of the deceleration and the
various energy density parameters. We find the ranges of the parameters in the
models for a transient acceleration. | Tracing the cosmic web: The cosmic web is one of the most striking features of the distribution of
galaxies and dark matter on the largest scales in the Universe. It is composed
of dense regions packed full of galaxies, long filamentary bridges, flattened
sheets and vast low density voids. The study of the cosmic web has focused
primarily on the identification of such features, and on understanding the
environmental effects on galaxy formation and halo assembly. As such, a variety
of different methods have been devised to classify the cosmic web -- depending
on the data at hand, be it numerical simulations, large sky surveys or other.
In this paper we bring twelve of these methods together and apply them to the
same data set in order to understand how they compare. In general these cosmic
web classifiers have been designed with different cosmological goals in mind,
and to study different questions. Therefore one would not {\it a priori} expect
agreement between different techniques however, many of these methods do
converge on the identification of specific features. In this paper we study the
agreements and disparities of the different methods. For example, each method
finds that knots inhabit higher density regions than filaments, etc. and that
voids have the lowest densities. For a given web environment, we find
substantial overlap in the density range assigned by each web classification
scheme. We also compare classifications on a halo-by-halo basis; for example,
we find that 9 of 12 methods classify around a third of group-mass haloes (i.e.
$M_{\rm halo}\sim10^{13.5}h^{-1}M_{\odot}$) as being in filaments. Lastly, so
that any future cosmic web classification scheme can be compared to the 12
methods used here, we have made all the data used in this paper public. |
Do primordial Lithium abundances imply there's no Dark Energy?: Explaining the well established observation that the expansion rate of the
universe is apparently accelerating is one of the defining scientific problems
of our age. Within the standard model of cosmology, the repulsive 'dark energy'
supposedly responsible has no explanation at a fundamental level, despite many
varied attempts. A further important dilemma in the standard model is the
Lithium problem, which is the substantial mismatch between the theoretical
prediction for 7-Li from Big Bang Nucleosynthesis and the value that we observe
today. This observation is one of the very few we have from along our past
worldline as opposed to our past lightcone. By releasing the untested
assumption that the universe is homogeneous on very large scales, both apparent
acceleration and the Lithium problem can be easily accounted for as different
aspects of cosmic inhomogeneity, without causing problems for other
cosmological phenomena such as the cosmic microwave background. We illustrate
this in the context of a void model. | Assessing the impact of two independent direction-dependent calibration
algorithms on the LOFAR 21-cm signal power spectrum: Detecting the 21-cm signal from the Epoch of Reionisation (EoR) is
challenging due to the strong astrophysical foregrounds, ionospheric effects,
radio frequency interference and instrumental effects. Understanding and
calibrating these effects are crucial for the detection. In this work, we
introduce a newly developed direction-dependent (DD) calibration algorithm
DDECAL and compare its performance with an existing algorithm, SAGECAL, in the
context of the LOFAR-EoR 21-cm power spectrum experiment. In our data set, the
North Celestial Pole (NCP) and its flanking fields were observed
simultaneously. We analyse the NCP and one of its flanking fields. The NCP
field is calibrated by the standard pipeline, using SAGECAL with an extensive
sky model and 122 directions, and the flanking field is calibrated by DDECAL
and SAGECAL with a simpler sky model and 22 directions. Additionally, two
strategies are used for subtracting Cassiopeia A and Cygnus A. The results show
that DDECAL performs better at subtracting sources in the primary beam region
due to the application of a beam model, while SAGECAL performs better at
subtracting Cassiopeia A and Cygnus A. This indicates that including a beam
model during DD calibration significantly improves the performance. The benefit
is obvious in the primary beam region. We also compare the 21-cm power spectra
on two different fields. The results show that the flanking field produces
better upper limits compared to the NCP in this particular observation. Despite
the minor differences between DDECAL and SAGECAL due to the beam application,
we find that the two algorithms yield comparable 21-cm power spectra on the
LOFAR-EoR data after foreground removal. Hence, the current LOFAR-EoR 21-cm
power spectrum limits are not likely to depend on the DD calibration method. |
Constraints on $τ_\mathrm{NL}$ from Planck temperature and
polarization: We update constraints on the amplitude of the primordial trispectrum, using
the final Planck mission temperature and polarization data. In the squeezed
limit, a cosmological local trispectrum would be observed as a spatial
modulation of small-scale power on the CMB sky. We reconstruct this signal as a
source of statistical anisotropy via quadratic estimator techniques. We
systematically demonstrate how the estimated power spectrum of a reconstructed
modulation field can be translated into a constraint on $\tau_\mathrm{NL}$ via
likelihood methods, demonstrating the procedures effectiveness by inferring
known $\tau_\mathrm{NL}$ signal(s) from simulations. Our baseline results
constrain $\tau_\mathrm{NL} < 1700$ at the 95\% confidence level, providing the
most stringent constraints to date. | Modeling Lyman-α Forest Cross-Correlations with LyMAS: We use the Ly-$\alpha$ Mass Association Scheme (LyMAS; Peirani et al. 2014)
to predict cross-correlations at $z=2.5$ between dark matter halos and
transmitted flux in the Ly-$\alpha$ forest, and compare to cross-correlations
measured for quasars and damped Ly-$\alpha$ systems (DLAs) from the Baryon
Oscillation Spectroscopic Survey (BOSS) by Font-Ribera et al. (2012, 2013). We
calibrate LyMAS using Horizon-AGN hydrodynamical cosmological simulations of a
$(100\ h^{-1}\ \mathrm{Mpc})^3$ comoving volume. We apply this calibration to a
$(1\ h^{-1}\ \mathrm{Gpc})^3$ simulation realized with $2048^3$ dark matter
particles. In the 100 $h^{-1}$ Mpc box, LyMAS reproduces the halo-flux
correlations computed from the full hydrodynamic gas distribution very well. In
the 1 $h^{-1}$ Gpc box, the amplitude of the large scale cross-correlation
tracks the halo bias $b_h$ as expected. We provide empirical fitting functions
that describe our numerical results. In the transverse separation bins used for
the BOSS analyses, LyMAS cross-correlation predictions follow linear theory
accurately down to small scales. Fitting the BOSS measurements requires
inclusion of random velocity errors; we find best-fit RMS velocity errors of
399 km s$^{-1}$ and 252 km s$^{-1}$ for quasars and DLAs, respectively. We
infer bias-weighted mean halo masses of $M_h/10^{12}\
h^{-1}M_\odot=2.19^{+0.16}_{-0.15}$ and $0.69^{+0.16}_{-0.14}$ for the host
halos of quasars and DLAs, with $\sim 0.2$ dex systematic uncertainty
associated with redshift evolution, IGM parameters, and selection of data
fitting range. |
A Measurement of the Rate of Type Ia Supernovae in Galaxy Clusters from
the SDSS-II Supernova Survey: ABRIDGED We present measurements of the Type Ia supernova (SN) rate in galaxy
clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova
Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4
clusters at z <0.17 and 27 SN events in 492 maxBCG clusters at 0.1 < z < 0.3$.
We find values for the cluster SN Ia rate of
$({0.37}^{+0.17+0.01}_{-0.12-0.01}) \mathrm{SNu}r h^{2}$ and
$({0.55}^{+0.13+0.02}_{-0.11-0.01}) \mathrm{SNu}r h^{2}$ ($\mathrm{SNu}x =
10^{-12} L_{x\sun}^{-1} \mathrm{yr}^{-1}$) in C4 and maxBCG clusters,
respectively, where the quoted errors are statistical and systematic,
respectively. The SN rate for early-type galaxies is found to be
$({0.31}^{+0.18+0.01}_{-0.12-0.01}) \mathrm{SNu}r h^{2}$ and
$({0.49}^{+0.15+0.02}_{-0.11-0.01})$ $\mathrm{SNu}r h^{2}$ in C4 and maxBCG
clusters, respectively. The SN rate for the brightest cluster galaxies (BCG) is
found to be $({2.04}^{+1.99+0.07}_{-1.11-0.04}) \mathrm{SNu}r h^{2}$ and
$({0.36}^{+0.84+0.01}_{-0.30-0.01}) \mathrm{SNu}r h^{2}$ in C4 and maxBCG
clusters. The ratio of the SN Ia rate in cluster early-type galaxies to that of
the SN Ia rate in field early-type galaxies is
${1.94}^{+1.31+0.043}_{-0.91-0.015}$ and ${3.02}^{+1.31+0.062}_{-1.03-0.048}$,
for C4 and maxBCG clusters. The SN rate in galaxy clusters as a function of
redshift...shows only weak dependence on redshift. Combining our current
measurements with previous measurements, we fit the cluster SN Ia rate data to
a linear function of redshift, and find $r_{L} = $ $[(0.49^{+0.15}_{-0.14}) +$
$(0.91^{+0.85}_{-0.81}) \times z]$ $\mathrm{SNu}B$ $h^{2}$. A comparison of the
radial distribution of SNe in cluster to field early-type galaxies shows
possible evidence for an enhancement of the SN rate in the cores of cluster
early-type galaxies... we estimate the fraction of cluster SNe that are
hostless to be $(9.4^+8._3-5.1)%$. | A Fast and Simple Algorithm for Detecting Large Scale Structures: Aims: we propose a gravitational potential method (GPM) as a supercluster
finder based on the analysis of the local gravitational potential distribution
measured by fast and simple algorithm applied to a spatial distribution of mass
tracers. Methodology: the GPM performs a two-step exploratory data analysis:
first, it measures the comoving local gravitational potential generated by
neighboring mass tracers at the position of a test point-like mass tracer. The
computation extended to all mass tracers of the sample provides a detailed map
of the negative potential fluctuations. The most negative gravitational
potential is provided by the highest mass density or, in other words, the
deeper is a potential fluctuations in a certain region of space and denser are
the mass tracers in that region. Therefore, from a smoothed potential
distribution, the deepest potential well detects unambiguously a high
concentration in the mass tracer distribution. Second, applying a density
contrast criterion to that mass concentration, a central bound core may be
identify and quantify in terms of memberships and total mass. Results: using a
complete volume-limited sample of galaxy clusters, a huge concentration of
galaxy clusters has been detected. In its central region, 35 clusters seem to
form a massive and bound core enclosed in a spherical volume of 51 Mpc radius.
Conclusions: the substantial agreement of our findings compared with those
obtained by different methodologies, confirms the GPM as a straightforward and
powerful as well as fast cluster finder useful for analyzing large datasets. |
Lattice Simulations of Axion-U(1) Inflation: We present the first nonlinear lattice simulation of an axion field coupled
to a U(1) gauge field during inflation. We use it to fully characterize the
statistics of the primordial curvature perturbation {\zeta}. We find high-order
statistics to be essential in describing non-Gaussianity of {\zeta} in the
linear regime of the theory. On the contrary, non-Gaussianity is suppressed
when the dynamics becomes nonlinear. This relaxes bounds from overproduction of
primordial black holes, allowing for an observable gravitational waves signal
at pulsar timing array and interferometers scales. Our work establishes lattice
simulations as a crucial tool to study the inflationary epoch and its
predictions. | Faint Extended OH Emission from the Local Interstellar Medium in the
Direction l \approx 108\circ, b \approx 5\circ: We have mapped faint 1667 OH line emission (TA \approx 20 - 40 mK in our
\approx 30' beam) along many lines of sight in the Galaxy covering an area of
\approx 4\circ \times 4\circ in the general direction of l \approx 108\circ, b
\approx 5\circ. The OH emission is widespread, similar in extent to the local
HI (r </= 2 kpc) both in space and in velocity. The OH profile amplitudes show
a good general correlation with those of HI in spectral channels of \approx 1
km/s; this relation is described by TA(OH) \approx 1.50 \times 10^{-4} TB(HI)
for values of TB(HI) </\approx 60 - 70 K. Beyond this the HI line appears to
"saturate", and few values are recorded above \approx 90 K. However, the OH
brightness continues to rise, by a further factor \approx 3. The OH velocity
profiles show multiple features with widths typically 2 - 3 km/s, but less than
10% of these features are associated with CO(1-0) emission in existing surveys
of the area smoothed to comparable resolution. |
Numerical Simulations of Galactic Outflows and Evolution of the IGM: Galactic outflows play a major role in the evolution of galaxies and the
intergalactic medium (IGM). The energy deposited into the interstellar medium
by supernovae and active galactic nuclei can accelerate the gas past the escape
velocity, and eject it into the IGM. This will affect the subsequent evolution
of the galaxy, by reducing or eliminating star formation, and quenching the
accretion of matter onto the central AGN. Galactic outflows is the main process
by which energy and processed interstellar matter is transported into the IGM.
This affects the subsequent formation of other galaxies. The energy carried by
outflows can strip protogalactic halos of their gas, preventing galaxies from
forming. Conversely, the metals carried by outflows can modify the composition
and cooling rates of the gas in protogalactic halos, favoring the formation of
galaxies. In this paper, I review the various techniques used to simulate
galactic outflows and their impact on galaxy and IGM evolution. | Sweeping Horndeski Canvas: New Growth-Rate Parameterization for
Modified-Gravity Theories: We propose and numerically validate a new fitting formula that is
sufficiently accurate to model the growth of structure in Horndeski theories of
modified gravity for upcoming Stage IV and V large-scale structure surveys.
Based on an analysis of more than 18,000 Horndeski models and adopting the
popular parameterization of the growth rate $f(z) = \Omega_{M}(z)^{\gamma}$, we
generalize the constant growth index $\gamma$ to a two-parameter
redshift-dependent quantity, $\gamma(z)$, that more accurately fits these
models. We demonstrate that the functional form $\gamma(z)=\gamma_0+\gamma_1z^2
/ (1+z)$ improves the median $\chi^2$ of the fit to viable Horndeski models by
a factor of $\sim40$ relative to that of a constant $\gamma$, and is sufficient
to obtain unbiased results even for precise measurements expected in Stage IV
and V surveys. Finally, we constrain the parameters of the new fitting formula
using current cosmological data. |
Warp Features in DBI Inflation: In Dirac-Born-Infeld inflation, changes in the sound speed that transiently
break the slow roll approximation lead to features in the power spectrum. We
develop and test the generalized slow roll approximation for calculating such
effects and show that it can be extended to treat order unity features. As in
slow-roll, model independent constraints on the potential of canonical
inflation can be directly reinterpreted in the DBI context through this
approximation. In particular, a sharp horizon scale step in the warped brane
tension can explain oscillatory features in the WMAP7 CMB power spectrum as
well as features in the potential. Differences appear only as a small
suppression of power on horizon scales and larger. | Measurement of Hubble constant with stellar-mass binary black holes: The direct detections of gravitational waves (GW) from merging binary black
holes (BBH) by aLIGO have brought us a new opportunity to utilize BBH for a
measurement of the Hubble constant. In this paper, we point out that there
exists a small number of BBH that gives significantly small sky localization
volume so that a host galaxy is uniquely identified. Then a redshift of a BBH
is obtained from a spectroscopic follow-up observation of the host galaxy.
Using these redshift-identified BBH, we show that the Hubble constant is
measured at a level of precision better than 1% with advanced detectors like
aLIGO at design sensitivity. Since a GW observation is completely independent
of other astrophysical means, this qualitatively new probe will help resolve a
well-known value discrepancy problem on the Hubble constant from cosmological
measurements and local measurements. |
The XMM Cluster Outskirts Project (X-COP): Thermodynamic properties of
the Intracluster Medium out to $R_{200}$ in Abell 2319: We present the joint analysis of the X-ray and SZ signals in A2319, the
galaxy cluster with the highest signal-to-noise ratio in Planck maps and that
has been surveyed within our XMM Cluster Outskirts Project (X-COP). We recover
the thermodynamical profiles by the geometrical deprojection of the X-ray
surface brightness, of the SZ comptonization parameter, and an accurate and
robust spectroscopic measurements of the temperature. We resolve the clumpiness
of the density to be below 20 per cent demonstrating that most of this
clumpiness originates from the ongoing merger and can be associated to
large-scale inhomogeneities. This analysis is done in azimuthally averaged
radial bins and in eight independent angular sectors, enabling us to study in
details the azimuthal variance of the recovered properties. Given the exquisite
quality of the X-ray and SZ datasets, we constrain at $R_{200}$ the total
hydrostatic mass, modelled with a NFW profile, with very high precision
($M_{200} = 9.76 \pm 0.16^{stat.} \pm 0.31^{syst.} \times 10^{14} M_\odot$). We
identify the ongoing merger and how it is affecting differently the gas
properties in the resolved azimuthal sectors. We have several indications that
the merger has injected a high level of non-thermal pressure in this system:
the clumping free density profile is above the average profile obtained by
stacking Rosat observations; the gas mass fraction exceeds the expected cosmic
gas fraction beyond $R_{500}$; the pressure profile is flatter than the fit
obtained by the Planck collaboration; the entropy profile is flatter than the
mean one predicted from non-radiative simulations; the analysis in azimuthal
sectors has revealed that these deviations occur in a preferred region of the
cluster. All these tensions are resolved by requiring a relative support of
about 40 per cent from non-thermal to the total pressure at $R_{200}$. | Mass-Richness relations for X-ray and SZE-selected clusters at $0.4 < z
<2.0$ as seen by $Spitzer$ at 4.5$μ$m: We study the mass-richness relation of 116 spectroscopically-confirmed
massive clusters at $0.4 < z < 2$ by mining the $Spitzer$ archive. We
homogeneously measure the richness at 4.5$\mu$m for our cluster sample within a
fixed aperture of $2^{\prime}$ radius and above a fixed brightness threshold,
making appropriate corrections for both background galaxies and foreground
stars. We have two subsamples, those which have a) literature X-ray
luminosities and b) literature Sunyaev-Zeldovich effect masses. For the X-ray
subsample we re-derive masses adopting the most recent calibrations. We then
calibrate an empirical mass-richness relation for the combined sample spanning
more than one decade in cluster mass and find the associated uncertainties in
mass at fixed richness to be $\pm 0.25$ dex. We study the dependance of the
scatter of this relation with galaxy concentration, defined as the ratio
between richness measured within an aperture radius of 1 and 2 arcminutes. We
find that at fixed aperture radius the scatter increases for clusters with
higher concentrations. We study the dependance of our richness estimates with
depth of the [4.5]$\mu$m imaging data and find that reaching a depth of at
least [4.5]= 21 AB mag is sufficient to derive reasonable mass estimates. We
discuss the possible extension of our method to the mid-infrared $WISE$ all-sky
survey data, and the application of our results to the $Euclid$ mission. This
technique makes richness-based cluster mass estimates available for large
samples of clusters at very low observational cost. |
{\it Gauging} the cosmic acceleration with recent type Ia supernovae
data sets: We revisit a model-independent estimator for cosmic acceleration based on
type Ia supernovae distance measurements. This approach does not rely on any
specific theory for gravity, energy content or parameterization for the scale
factor or deceleration parameter and is based on falsifying the {\it null
hypothesis} that the Universe never expanded in an accelerated way. By
generating mock catalogues of known cosmologies we test the robustness of this
estimator establishing its limits of applicability. We detail the pros and cons
of such approach. For example, we find that there are specific counterexamples
in which the estimator wrongly provides evidence against acceleration in
accelerating cosmologies. The dependence of the estimator on the $H_0$ value is
also discussed. Finally, we update the evidence for acceleration using the
recent UNION2.1 and JLA samples. Contrary to recent claims, available data
strongly favors an accelerated expansion of the Universe in complete agreement
with the standard $\Lambda$CDM model. | On the consistency of the expansion with the perturbations: Assuming a simple form for the growth index gamma(z) depending on two
parameters gamma_0 = gamma(z=0) and gamma_1 = gamma'(z=0), we show that these
parameters can be constrained using background expansion data. We explore
systematically the preferred region in this parameter space. Inside General
Relativity we obtain that models with a quasi-static growth index and gamma_1 =
-0.02 are favoured. We find further the lower bounds gamma_0 > 0.53 and gamma_1
> -0.15 for models inside GR. Models outside GR having the same background
expansion as LCDM and arbitrary gamma(z) with gamma_0 = gamma_0^{LCDM}, satisfy
G_{eff,0}>G for gamma_1 > gamma_1^{LCDM}, and G_{eff,0}<G for gamma_1 <
gamma_1^{LCDM}. The first models will cross downwards the value G_{eff}=G on
very low redshifts z<0.3, while the second models will cross upwards G_{eff}=G
in the same redshift range. This makes the realization of such modified gravity
models even more problematic. |
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