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Gradient expansion formalism for magnetogenesis in the kinetic coupling
model: In order to describe magnetogenesis during inflation in the kinetic coupling
model, we utilize a gradient expansion which is based on the fact that only
long-wavelength (superhorizon) modes undergo amplification. For this purpose,
we introduce a set of functions (bilinear combinations of electromagnetic
fields with an arbitrary number of spatial curls) satisfying an infinite chain
of equations. Apart from the usual mode enhancement due to interaction with the
inflaton, these equations also take into account the fact that the number of
relevant modes constantly grows during inflation. Truncating this chain, we
show that even with a relatively small number of equations, it is possible to
describe the electric and magnetic energy densities with a few percent accuracy
during the whole inflation stage. We arrive at this conclusion for different
types of coupling functions (increasing, decreasing, and nonmonotonic) in the
regime with strong backreaction and its absence. | Constraints on the Field Star IMF from Resolved Stellar Populations
based Star Formation Histories: Using HST/ACS observations of resolved stellar populations in nearby
galaxies, I explore the constraints one can place on the field star IMF from
star formation histories (SFHs) derived from synthetic color-magnitude diagram
(CMD) fitting. In particular, I show how reasonable variations in the slope of
the IMF, relative to a Salpeter slope, lead to only minor changes in the SFHs.
This shows that CMD-SFH fitting parameter space has a broad minimum with
respect to IMF variations and implies that CMD based SFHs can only provide weak
explicit constraints on the stellar IMF. However, observations of resolved
stellar populations in dwarf galaxies can be used to tandem with other methods
to search for variations in the upper IMF. |
Measuring galaxy segregation using the mark connection function: (abridged) The clustering properties of galaxies belonging to different
luminosity ranges or having different morphological types are different. These
characteristics or `marks' permit to understand the galaxy catalogs that carry
all this information as realizations of marked point processes. Many attempts
have been presented to quantify the dependence of the clustering of galaxies on
their inner properties. The present paper summarizes methods on spatial marked
statistics used in cosmology to disentangle luminosity, colour or morphological
segregation and introduces a new one in this context, the mark connection
function. The methods used here are the partial correlation functions,
including the cross-correlation function, the normalised mark correlation
function, the mark variogram and the mark connection function. All these
methods are applied to a volume-limited sample drawn from the 2dFGRS, using the
spectral type as the mark. We show the virtues of each method to provide
information about the clustering properties of each population, the dependence
of the clustering on the marks, the similarity of the marks as a function of
the pair distances, and the way to characterise the spatial correlation between
the marks. We demonstrate by means of these statistics that passive galaxies
exhibit stronger spatial correlation than active galaxies at small scales (r
<20 Mpc/h). The mark connection function, introduced here, is particularly
useful for understanding the spatial correlation between the marks. | Measuring the speed of light with ultra-compact radio quasars: In this paper, based on a 2.29 GHz VLBI all-sky survey of 613 milliarcsecond
ultra-compact radio sources with $0.0035<z<3.787$, we describe a method of
identifying the sub-sample which can serve as individual standard rulers in
cosmology. If the linear size of the compact structure is assumed to depend on
source luminosity and redshift as $l_m=l L^\beta (1+z)^n$, only
intermediate-luminosity quasars ($10^{27}$ W/Hz$<L<$ $10^{28}$ W/Hz) show
negligible dependence ($|n|\simeq 10^{-3}$, $|\beta|\simeq 10^{-4}$), and thus
represent a population of such rulers with fixed characteristic length
$l=11.42$ pc. With a sample of 120 such sources covering the redshift range
$0.46<z<2.80$, we confirm the existence of dark energy in the Universe with
high significance under the assumption of a flat universe, and obtain stringent
constraints on both the matter density $\Omega_m=0.323^{+0.245}_{-0.145}$ and
the Hubble constant $H_0=66.30^{+7.00}_{-8.50}$ km sec$^{-1}$ Mpc$^{-1}$.
Finally, with the angular diameter distances $D_A$ measured for quasars
extending to high redshifts ($z\sim 3.0$), we reconstruct the $D_A(z)$ function
using the technique of Gaussian processes. This allows us to identify the
redshift corresponding to the maximum of the $D_A(z)$ function: $z_m=1.70$ and
the corresponding angular diameter distance $D_A(z_m)=1719.01\pm43.46$ Mpc.
Similar reconstruction of the expansion rate function $H(z)$ based on the data
from cosmic chronometers and BAO gives us $H(z_m)=176.77\pm6.11$ km sec$^{-1}$
Mpc$^{-1}$. These measurements are used to estimate the speed of light:
$c=3.039(\pm0.180)\times 10^5$ km/s. This is the first measurement of the speed
of light in a cosmological setting referring to the distant past. |
Reconstruction in Fourier space: We present a fast iterative FFT-based reconstruction algorithm that allows
for non- parallel redshift-space distortions (RSD). We test our algorithm on
both N-body dark matter simulations and mock distributions of galaxies designed
to replicate galaxy survey conditions. We compare solenoidal and irrotational
components of the redshift distortion and show that an approximation of this
distortion leads to a better estimate of the real-space potential (and
therefore faster convergence) than ignoring the RSD when estimating the
displacement field. Our iterative reconstruction scheme converges in two
iterations for the mock samples corresponding to BOSS CMASS DR11 when we start
with an approximation of the RSD. The scheme takes six iterations when the
initial estimate, measured from the redshift-space overdensity, has no RSD
correction. Slower convergence would be expected for surveys covering a larger
angle on the sky. We show that this FFT based method provides a better estimate
of the real space displacement field than a configuration space method that
uses finite difference routines to compute the potential for the same grid
resolution. Finally we show that a lognormal transform of the overdensity, used
as a proxy for the linear overdensity, is beneficial in estimating the full
displacement field from a dense sample of tracers. However the lognormal
transform of the overdensity does not perform well when estimating the
displacements from sparser simulations with a more realistic galaxy density. | Multi-Fidelity Emulation for the Matter Power Spectrum using Gaussian
Processes: We present methods for emulating the matter power spectrum by combining
information from cosmological $N$-body simulations at different resolutions. An
emulator allows estimation of simulation output by interpolating across the
parameter space of a limited number of simulations. We present the first
implementation in cosmology of multi-fidelity emulation, where many
low-resolution simulations are combined with a few high-resolution simulations
to achieve an increased emulation accuracy. The power spectrum's dependence on
cosmology is learned from the low-resolution simulations, which are in turn
calibrated using high-resolution simulations. We show that our multi-fidelity
emulator predicts high-fidelity counterparts to percent-level relative accuracy
when using only $3$ high-fidelity simulations and outperforms a single-fidelity
emulator that uses $11$ simulations, although we do not attempt to produce a
converged emulator with high absolute accuracy. With a fixed number of
high-fidelity training simulations, we show that our multi-fidelity emulator is
$\simeq 100$ times better than a single-fidelity emulator at $k \leq 2 h
\mathrm{Mpc}^{-1}$, and $\simeq 20$ times better at $3 \leq k < 6.4 h
\mathrm{Mpc}^{-1}$. Multi-fidelity emulation is fast to train, using only a
simple modification to standard Gaussian processes. Our proposed emulator shows
a new way to predict non-linear scales by fusing simulations from different
fidelities. |
A CMB Millikan Experiment with Cosmic Axiverse Strings: We study axion strings of hyperlight axions coupled to photons. Hyperlight
axions -- axions lighter than Hubble at recombination -- are a generic
prediction of the string axiverse. These axions strings produce a distinct
quantized polarization rotation of CMB photons which is
$\mathcal{O}(\alpha_{\rm em})$. As the CMB light passes many strings, this
polarization rotation converts E-modes to B-modes and adds up like a random
walk. Using numerical simulations we show that the expected size of the final
result is well within the reach of current and future CMB experiments through
the measurement of correlations of CMB B-modes with E- and T-modes. The
quantized polarization rotation angle is topological in nature and can be seen
as a geometric phase. Its value depends only on the anomaly coefficient and is
independent of other details such as the axion decay constant. Measurement of
the anomaly coefficient by measuring this rotation will provide information
about the UV theory, such as the quantization of electric charge and the value
of the fundamental unit of charge. The presence of axion strings in the
universe relies only on a phase transition in the early universe after
inflation, after which the string network rapidly approaches an attractor
scaling solution. If there are additional stable topological objects such as
domain walls, axions as heavy as $10^{-15}$ eV would be accessible. The
existence of these strings could also be probed by measuring the relative
polarization rotation angle between different images in gravitationally lensed
quasar systems. | New fitting formula for cosmic non-linear density distribution: We have measured the probability distribution function (PDF) of cosmic matter
density field from a suite of N-body simulations. We propose the generalized
normal distribution of version 2 (Nv2) as an alternative fitting formula to the
well-known log-normal distribution. We find that Nv2 provides significantly
better fit than the log-normal distribution for all smoothing radii (2, 5, 10,
25 [Mpc/h]) that we studied. The improvement is substantial in the underdense
regions. The development of non- Gaissianities in the cosmic matter density
field is captured by continuous evolution of the skewness and shifts parameters
of the Nv2 distribution. We present the redshift evolution of these parameters
for aforementioned smoothing radii and various background cosmology models. All
the PDFs measured from large and high-resolution N-body simulations that we use
in this study can be obtained from a Web site at
https://astro.kias.re.kr/jhshin. |
Parametrising non-linear dark energy perturbations: In this paper, we quantify the non-linear effects from $k$-essence dark
energy through an effective parameter $\mu$ that encodes the additional
contribution of a dark energy fluid or a modification of gravity to the Poisson
equation. This is a first step toward quantifying non-linear effects of dark
energy/modified gravity models in a more general approach. We compare our
$N$-body simulation results from $k$-evolution with predictions from the linear
Boltzmann code $\texttt{CLASS}$, and we show that for the $k$-essence model one
can safely neglect the difference between the two potentials, $ \Phi -\Psi$,
and short wave corrections appearing as higher order terms in the Poisson
equation, which allows us to use single parameter $\mu$ for characterizing this
model. We also show that for a large $k$-essence speed of sound the
$\texttt{CLASS}$ results are sufficiently accurate, while for a low speed of
sound non-linearities in matter and in the $k$-essence field are
non-negligible. We propose a $\tanh$-based parameterisation for $\mu$,
motivated by the results for two cases with low ($c_s^2=10^{-7}$) and high
($c_s^2=10^{-4}$) speed of sound, to include the non-linear effects based on
the simulation results. This parametric form of $\mu$ can be used to improve
Fisher forecasts or Newtonian $N$-body simulations for $k$-essence models. | The molecular gas in Luminous Infrared Galaxies II: extreme physical
conditions, and their effects on the X_{co} factor: In this work we conclude the analysis of our CO line survey of Luminous
Infrared Galaxies (LIRGs: L_{IR}>=10^{11}L_{sol}) in the local Universe
(Paper\,I), by focusing on the influence of their average ISM properties on the
total molecular gas mass estimates via the so-called X_{co}=M(H_2)/L_{co,1-0}
factor. One-phase radiative transfer models of the global CO Spectral Line
Energy Distributions (SLEDs) yield an X_{co} distribution with:
<X_{co}>\sim(0.6+/-0.2) M_{sol}(K km s^{-1} pc^2)^{-1} over a significant range
of average gas densities, temperatures and dynamical states. The latter emerges
as the most important parameter in determining X_{co}, with unbound states
yielding low values and self-gravitating states the highest ones. Nevertheless
in many (U)LIRGs where available higher-J CO lines (J=3--2, 4--3, and/or
J=6--5) or HCN line data from the literature allow a separate assessment of the
gas mass at high densities (>=10^{4} cm^{-3}) rather than a simple one-phase
analysis we find that {\it near-Galactic X_{co} (3-6)\,
M_sol\,(K\,km^{-1}\,pc^2)^{-1} values become possible.} We further show that in
the highly turbulent molecular gas in ULIRGs a high-density component will be
common and can be massive enough for its high X_{co} to dominate the average
value for the entire galaxy. .........
...this may have thus resulted to systematic underestimates of molecular gas
mass in ULIRGs. |
Metallicities, dust and molecular content of a QSO-Damped Lyman-α
system reaching log N (H i) = 22: An analog to GRB-DLAs: We present the elemental abundance and H2 content measurements of a Damped
Lyman-{\alpha} (DLA) system with an extremely large H i column density, log N(H
i) (cm-2) = 22.0+/-0.10, at zabs = 3.287 towards the QSO SDSS J 081634+144612.
We measure column densities of H2, C i, C i^*, Zn ii, Fe ii, Cr ii, Ni ii and
Si ii from a high signal-to-noise and high spectral resolution VLT-UVES
spectrum. The overall metallicity of the system is [Zn/H] = -1.10 +/- 0.10
relative to solar. Two molecular hydrogen absorption components are seen at z =
3.28667 and 3.28742 (a velocity separation of \approx 52 km s-1) in rotational
levels up to J = 3. We derive a total H2 column density of log N(H2) (cm-2) =
18.66 and a mean molecular fraction of f = 2N(H2)/[2N(H2) + N(H i)] =
10-3.04+/-0.37, typical of known H2-bearing DLA systems. From the observed
abundance ratios we conclude that dust is present in the Interstellar Medium
(ISM) of this galaxy, with a enhanced abundance in the H2-bearing clouds.
However, the total amount of dust along the line of sight is not large and does
not produce any significant reddening of the background QSO. The physical
conditions in the H2-bearing clouds are constrained directly from the column
densities of H2 in different rotational levels, C i and C i^* . The kinetic
temperature is found to be T = 75 K and the particle density lies in the range
nH = 50-80 cm-3 . The neutral hydrogen column density of this DLA is similar to
the mean H i column density of DLAs observed at the redshift of {\gamma}-ray
bursts (GRBs). We explore the relationship between GRB-DLAs and high column
density end of QSO-DLAs finding that the properties (metallicity and depletion)
of DLAs with log N(H i) > 21.5 in the two populations do not appear to be
significantly different. | ETHOS - an Effective Theory of Structure Formation: detecting dark
matter interactions through the Lyman-$α$ forest: We perform a series of cosmological hydrodynamic simulations to investigate
the effects of non-gravitational dark matter (DM) interactions on the
intergalactic medium (IGM). In particular, we use the ETHOS framework
(Cyr-Racine et al. 2016; Vogelsberger et al. 2016) to compare statistics of the
Lyman-$\alpha$ forest in cold dark matter (CDM) with an alternative model in
which the DM couples strongly with a relativistic species in the early
universe. These models are characterised by a cutoff in the linear power
spectrum, followed by a series of 'dark acoustic oscillations' (DAOs) on
sub-dwarf scales. While the primordial cutoff delays the formation of the first
galaxies, structure builds-up more rapidly in the interacting DM model compared
to CDM. We show that although DAOs are quickly washed away in the non-linear
clustering of DM at $z\lesssim10$, their signature can be imprinted prominently
in the Lyman-$\alpha$ flux power spectrum at $z>5$. On scales larger than the
cutoff ($k\sim0.08$ s/km for the specific model considered here), the relative
difference to CDM is reminiscent of a warm dark matter (WDM) model with a
similar initial cutoff; however, the redshift evolution on smaller scales is
distinctly different. The appearance and disappearance of DAOs in the
Lyman-$\alpha$ flux spectrum provides a powerful way to distinguish interacting
DM models from WDM and, indeed, variations in the thermal history of the IGM
that may also induce a small-scale cutoff. |
Inflationary Perturbations in No-Scale Theories: We study the inflationary perturbations in general (classically)
scale-invariant theories. Such scenario is motivated by the hierarchy problem
and provides natural inflationary potentials and dark matter candidates. We
analyse in detail all sectors (the scalar, vector and tensor perturbations)
giving general formulae for the potentially observable power spectra, as well
as for the curvature spectral index $n_s$ and the tensor-to-scalar ratio $r$.
We show that the conserved Hamiltonian for all perturbations does not feature
negative energies even in the presence of the Weyl-squared term if the
appropriate quantization is performed and argue that this term does not lead to
phenomenological problems at least in some relevant setups. The general
formulae are then applied to a concrete no-scale model, which includes the
higgs and a scalar, "the planckion", whose vacuum expectation value generates
the Planck mass. Inflation can be triggered by a combination of the planckion
and the Starobinsky scalar and we show that no tension with observations is
present even in the case of pure planckion-inflation, if the coefficient of the
Weyl-squared term is large enough. In general, even quadratic inflation is
allowed in this case. Moreover, the Weyl-squared term leads to an isocurvature
mode, which currently satisfies the observational bounds, but may be detectable
with future experiments. | Extending the Epoch of Reionization window with apt Foreground and
Instrument modeling: It is seen that foregrounds of 21cm Epoch of Reionization experiments, which
are expected to have smooth spectral dependence, are dominant in a wedge shaped
region of the Fourier space called as Foreground Wedge. A possible way forward
to isolate the 21cm Epoch of Reionization (EoR) signal from the much larger
foreground component is to focus on the remaining portion of the Fourier space
called as the EoR window. There are in-fact three distinct regions in the
Fourier space, (i) the Foreground wedge portion, (ii) the EoR window region
which lies beyond Horizon wedge and (iii) the region in between the Horizon
wedge and the Field of View wedge. This paper addresses two questions: (1)
Whether the signal in between the two wedges is also a direct representation of
the EoR brightness temperature fluctuations? and (2) How can we extract the
cosmology information from this region considering that the foregrounds are
much larger than the signal? The answer to the first question is yes, the
visibilities as function of baseline and delay are, within a few percent, same
as the EoR brightness temperature fluctuations for the cases considered.
Secondly, the in between region is not foreground free, due to non-negligible
sidelobes. But, one can possibly extract signal from this region if one models
foregrounds and instruments accurately. As all the three components, the
cosmological signal, the foregrounds and the thermal noise are calculated in
the same space, the analysis suggested could be more straightforward. |
Modelling the correlation between the thermal Sunyaev Zel'dovich effect
and the cosmic infrared background: We show how the correlation between the thermal Sunyaev Zel'dovich effect
(tSZ) from galaxy clusters and dust emission from cosmic infrared background
(CIB) sources can be calculated in a halo model framework. Using recent tSZ and
CIB models, we find that the size of the tSZ x CIB cross-correlation is
approximately 20 per cent at 150 GHz. The contribution to the total angular
power spectrum is of order -2 \mu K^2 at ell=3000, however, this value is
uncertain by a factor of two to three, primarily because of CIB source
modelling uncertainties. We expect the large uncertainty in this component to
degrade upper limits on the kinematic Sunyaev Zel'dovich effect (kSZ), due to
similarity in the frequency dependence of the tSZ x CIB and kSZ across the
frequency range probed by current Cosmic Microwave Background missions. We also
find that the degree of tSZ x CIB correlation is higher for mm x sub-mm spectra
than mm x mm, because more of the sub-mm CIB originates at lower redshifts
(z<2), where most tSZ clusters are found. | Approximate Analytic Spectra of Reionized CMB Anisotropies and
Polarization generated by Relic Gravitational Waves: We present an approximate, analytical calculation of the reionized spectra
$C_l^{XX}$ of cosmic microwave background radiation (CMB) anisotropies and
polarizations generated by relic gravitational waves (RGWs). Three simple
models of reionization are explored, whose visibility functions are fitted by
gaussian type of functions as approximations. We have derived the analytical
polarization $\beta_l$ and temperature anisotropies $\alpha_l$, both consisting
of two terms proportional to RGWs at the decoupling and at the reionization as
well. The explicit dependence of $\beta_l$ and $\alpha_l$ upon the reionization
time $\eta_r$, the duration $\Delta\eta_r$, and the optical depth $\kappa_r$
are demonstrated. Moreover, $\beta_l$ and $\alpha_l$ contain $\kappa_r$ in
different coefficients, and the polarization spectra $C_l^{EE}$ are $C_l^{BB}$
are more sensitive probes of reionization than $C_l^{TT}$. These results
facilitate examination of the reionization effects, in particular, the
degeneracies of $\kappa_r$ with the normalization amplitude and with the
initial spectral index of RGWs. It is also found that reionization also causes
a $\kappa_r$-dependent shift $\Delta l\sim 20$ of the zero multipole $l_0$ of
$C_l^{TE}$, an effect that should be included in order to detect the traces of
RGWs. Compared with numerical results, the analytical $C_l^{XX}$ as
approximation have the limitation. For the primary peaks in the range $l\simeq
(30, 600)$, the error is $\le 3%$ in three models. In the range $l < 20$ for
the reionization bumps, the error is $\le 15%$ for $C_l^{EE}$ and $C_l^{BB}$ in
the two extended reionization models, and $C_l^{TT}$ and $C_l^{TE}$ have much
larger departures for $l<10$. The bumps in the sudden reionization model are
too low. |
Dynamics of Void and its Shape in Redshift Space: We investigate the dynamics of a single spherical void embedded in a
Friedmann-Lema\^itre universe, and analyze the void shape in the redshift
space. We find that the void in the redshift space appears as an ellipse shape
elongated in the direction of the line of sight (i.e., an opposite deformation
to the Kaiser effect). Applying this result to observed void candidates at the
redshift z~1-2, it may provide us with a new method to evaluate the
cosmological parameters, in particular the value of a cosmological constant. | A Model of Universe Anisotropization: The presence of a nonconformally invariant term in the photon sector of the
Lorentz-violating extension of Standard Model of particle physics, the
"Kosteleck\'{y} term" $\mathcal{L}_K \propto (k_F)_{\alpha \beta \mu \nu}
F^{\alpha \beta} F^{\m \nu}$, enables a superadiabatic amplification of
magnetic vacuum fluctuations during de Sitter inflation. For a particular form
of the external tensor $k_F$ that parameterizing Lorentz violation, the
generated field possesses a planar symmetry at large cosmological scales and
can have today an intensity of order of nanogauss for a wide range of values of
parameters defining inflation. This peculiar magnetic field could account for
the presently-observed galactic magnetic fields and induces a small
anisotropization of the universe at cosmological scales. The resulting Bianchi
I model could explain the presumedly low-quadrupole power in the Cosmic
Microwave Background radiation. |
Extending cosmology: the metric approach: In this chapter it is shown how the introduction of a fundamental constant of
nature with dimensions of acceleration into the theory of gravity makes it
possible to extend gravity in a very consistent manner. | Ultra slow-roll G-inflation: The conventional slow-roll approximation is broken in the so-called "ultra
slow-roll" models of inflation, for which the inflaton potential is exactly (or
extremely) flat. The interesting nature of (canonical) ultra slow-roll
inflation is that the curvature perturbation grows on superhorizon scales, but
has a scale-invariant power spectrum. We study the ultra slow-roll inflationary
dynamics in the presence of non-canonical kinetic terms of the scalar field,
namely ultra slow-roll G-inflation. We compute the evolution of the curvature
perturbation and show that the primordial power spectrum follows a broken power
law with an oscillation feature. It is demonstrated that this could explain the
lack of large-scale power in the cosmic microwave background temperature
anisotropies. We also point out that the violation of the null energy condition
is prohibited in ultra slow-roll G-inflation and hence a blue tensor tilt is
impossible as long as inflation is driven by the potential. This statement is,
however, not true if the energy density is dominated by the kinetic energy of
the scalar field. |
Variability in Quasar Light Curves: using quasars as standard candles: A relation between the variational slope, $s_F$ , and the mean absolute
magnitude, $\langle M \rangle$, in the light curves of 58 spectroscopically
confirmed quasars is measured with a dispersion of 0.15dex. Assuming it holds
for quasars in general, not only does this relation add to our working
knowledge of quasar variability but it also shows great promise at accurately
measuring luminosity distance to a quasar in a model independent way. An
accurate, model independent measure of the luminosity distance would allow
quasars to be added to the cosmic distance ladder, easily extending the ladder
out far beyond the redshifts accessible to type Ia supernovae where
cosmological parameters can be better constrained. | Evolution of Dust Temperature of Galaxies through Cosmic Time as seen by
Herschel: We study the dust properties of galaxies in the redshift range 0.1<z<2.8
observed by the Herschel Space Observatory in the field of the Great
Observatories Origins Deep Survey-North as part of PEP and HerMES key
programmes. Infrared (IR) luminosity (L_IR) and dust temperature (T_dust) of
galaxies are derived from the spectral energy distribution (SED) fit of the
far-infrared (FIR) flux densities obtained with PACS and SPIRE instruments
onboard Herschel. As a reference sample, we also obtain IR luminosities and
dust temperatures of local galaxies at z<0.1 using AKARI and IRAS data in the
field of the Sloan Digital Sky Survey. We compare the L_IR-T_dust relation
between the two samples and find that: the median T_dust of Herschel-selected
galaxies at z>0.5 with L_IR>5x10^{10} L_\odot, appears to be 2-5 K colder than
that of AKARI-selected local galaxies with similar luminosities; and the
dispersion in T_dust for high-z galaxies increases with L_IR due to the
existence of cold galaxies that are not seen among local galaxies. We show that
this large dispersion of the L_IR-T_dust relation can bridge the gap between
local star-forming galaxies and high-z submillimeter galaxies (SMGs). We also
find that three SMGs with very low T_dust (<20 K) covered in this study have
close neighbouring sources with similar 24-\mum brightness, which could lead to
an overestimation of FIR/(sub)millimeter fluxes of the SMGs. |
Beyond the Standard cosmological model with CMB: Measurements of CMB anisotropy and, more recently, polarization have played a
very important role in cosmology. Besides precise determination of various
parameters of the `standard' cosmological model, observations have also
established some important basic tenets that underlie models of cosmology and
structure formation in the universe -- `acausally' correlated, adiabatic,
primordial perturbations in a flat, statistically isotropic universe. These are
consistent with the expectation of the paradigm of inflation and the generic
prediction of the simplest realization of inflationary scenario in the early
universe. Further, gravitational instability is the established mechanism for
structure formation from these initial perturbations. Primordial perturbations
observed as the CMB anisotropy and polarization is the most compelling evidence
for new, possibly fundamental, physics in the early universe. The community is
now looking beyond the parameter estimation of the `standard' model, for
subtle, characteristic signatures of early universe physics. | On the Star Formation-AGN Connection at $z \lesssim 0.3$: Using the spectra of a sample of $\sim$28,000 nearby obscured active galaxies
from Data Release 7 of the Sloan Digital Sky Survey (SDSS), we probe the
connection between AGN activity and star formation over a range of radial
scales in the host galaxy. We use the extinction-corrected luminosity of the
[OIII] 5007 \AA\ line as a proxy of intrinsic AGN power and supermassive black
hole (SMBH) accretion rate. The star formation rates (SFRs) are taken from the
MPA-JHU value-added catalog and are measured through the 3$^{\prime\prime}$
SDSS aperture. We construct matched samples of galaxies covering a range in
redshifts. With increasing redshift, the projected aperture size encompasses
increasing amounts of the host galaxy. This allows us to trace the radial
distribution of star-formation as a function of AGN luminosity. We find that
the star formation becomes more centrally concentrated with increasing AGN
luminosity and Eddington ratio. This implies that such circumnuclear star
formation is associated with AGN activity, and that it increasingly dominates
over omnipresent disk star formation at higher AGN luminosities, placing
critical constraints on theoretical models that link host galaxy star formation
and SMBH fueling. We parametrize this relationship and find that the star
formation on radial scales $<$1.7 kpc, when including a constant disk
component, has a sub-linear dependence on SMBH accretion rate: $SFR \propto
\dot{M}^{0.36}$, suggesting that angular momentum transfer through the disk
limits accretion efficiency rather than the supply from stellar mass loss. |
The Implications of a Pre-reionization 21 cm Absorption Signal for Fuzzy
Dark Matter: The EDGES experiment recently announced evidence for a broad absorption
feature in the sky-averaged radio spectrum around 78 MHz, as may result from
absorption in the 21 cm line by neutral hydrogen at z~15-20. If confirmed, one
implication is that the spin temperature of the 21 cm line is coupled to the
gas temperature by z=20. The known mechanism for accomplishing this is the
Wouthuysen-Field effect, whereby Lyman-alpha photons scatter in the
intergalactic medium (IGM) and impact the hyperfine level populations. This
suggests that early star formation had already produced a copious Lyman-alpha
background by z=20, and strongly constrains models in which the linear matter
power spectrum is suppressed on small-scales, since halo and star formation are
delayed in such scenarios. Here we consider the case that the dark matter
consists of ultra-light axions with macroscopic de Broglie wavelengths (fuzzy
dark matter, FDM). We assume that star formation tracks halo formation and
adopt two simple models from the current literature for the halo mass function
in FDM. We further suppose that the fraction of halo baryons which form stars
is less than a conservative upper limit of $f_\star \leq 0.05$, and that ~10^4
Lyman-alpha to Lyman-limit photons are produced per stellar baryon. We find
that the requirement that the 21 cm spin temperature is coupled to the gas
temperature by $z=20$ places a lower-limit on the FDM particle mass of $m_a
\geq 5 \times 10^{-21} {\rm eV}$. The constraint is insensitive to the precise
minimum mass of halos where stars form. As the global 21 cm measurements are
refined, the coupling redshift could change and we quantify how the FDM
constraint would be modified. A rough translation of the FDM mass bound to a
thermal relic warm dark matter (WDM) mass bound is also provided. | Disentangling the dark matter halo from the stellar halo: The outer haloes of the Milky Way and Andromeda galaxies contain as much
important information on their assembly and formation history as the properties
of the discs resident in their centres. In this paper we have used the
Constrained Local UniversE Simulation project to disentangle the stellar and DM
component of three galaxies that resemble the MW, M31 and M33 using both DM
only and DM + gas-dynamical simulations. Stars that are accreted in
substructures and then stripped follow a completely different radial
distribution than the stripped DM: the stellar halo is much more centrally
concentrated than DM. In order to understand how the same physical process can
lead to different z=0 radial profiles, we examined the potential at accretion
of each stripped particle. We found that star particles sit at systematically
higher potentials than DM, making them harder to strip. We then searched for a
threshold in the potential of accreted particles \phi_[th], above which DM
particles behave as star particles. We found such a threshold at >16
\phi_{subhalo}, where \phi_{subhalo} is the potential at a subhaloes edge at
the time of accretion. Thus a rule as simple as selecting particles according
to their potential at accretion is able to reproduce the effect that the
complicated physics of star formation has on the stellar distribution. This
niversal result reproduces the stellar halo to an accuracy of within ~2%.
Studies which make use of DM particles as a proxy for stars will undoubtedly
miscalculate their proper radial distribution and structure unless particles
are selected according to their potential at accretion. Furthermore, we have
examined the time it takes to strip a given star or DM particle after
accretion. We find that, owing to their higher binding energies, stars take
longer to be stripped than DM. The stripped DM halo is thus considerably older
than the stripped stellar halo. |
The Type II Supernova Rate in z~0.1 Galaxy Clusters from the Multi-Epoch
Nearby Cluster Survey: We present 7 spectroscopically confirmed Type II cluster supernovae (SNeII)
discovered in the Multi-Epoch Nearby Cluster Survey, a supernova survey
targeting 57 low redshift 0.05 < z < 0.15 galaxy clusters with the
Canada-France-Hawaii Telescope. We find the rate of Type II supernovae within
the virial radius of these galaxy clusters to be 0.026 (+0.085 -0.018 stat;
+0.003 -0.001 sys) SNe per century per 1e10 solar masses. Surprisingly, one
SNII is in a red sequence host galaxy that shows no clear evidence of recent
star formation. This is unambiguous evidence in support of ongoing, low-level
star formation in at least some cluster elliptical galaxies, and illustrates
that galaxies that appear to be quiescent cannot be assumed to host only Type
Ia SNe. Based on this single SNII we make the first measurement of the SNII
rate in red sequence galaxies, and find it to be 0.007 (+0.014 -0.007 stat;
+0.009 -0.001 sys) SNe per century per 1e10 solar masses. We also make the
first derivation of cluster specific star formation rates (sSFR) from cluster
SNII rates. We find that for all galaxy types, sSFR is 5.1 (+15.8 -3.1 stat;
+0.9 -0.9 sys) solar masses per year per 1e12 solar masses, and for red
sequence galaxies only, it is 2.0 (+4.2 -0.9 stat; +0.4 -0.4 sys) solar masses
per year per 1e12 solar masses. These values agree with SFRs measured from
infrared and ultraviolet photometry, and H-alpha emission from optical
spectroscopy. Additionally, we use the SFR derived from our SNII rate to show
that although a small fraction of cluster Type Ia SNe may originate in the
young stellar population and experience a short delay time, these results do
not preclude the use of cluster SNIa rates to derive the late-time delay time
distribution for SNeIa. | Dynamical Dark Energy Properties Hidden in the Dark Matter Halos and
Voids: In this paper, we analysed the halos and voids properties of a GR-based
N-body simulation carried out at redshifts z= 0.0 and z= 0.8 as differences
between dynamical dark energy models (namely PL and CPL) with respect to LCDM.
Analysing the halos demonstrates that both models, PL and CPL, behave like
LCDM, despite the velocity dispersion of halos was more sensitive to the
dynamical dark energy model. In addition, a void finder was developed to
extract the properties of voids from simulated data. Further statistical model
on voids confirms that the PL model produces larger voids. In summary, our
novel simulation demonstrates void properties are better than halo properties
in discriminating between dark energy models. Hence, the results suggest to
make more use of the properties of voids in future studies of discriminating
dynamical dark energy models. |
A direct probe of cosmological power spectra of the peculiar velocity
field and the gravitational lensing magnification from photometric redshift
surveys: The cosmological peculiar velocity field (deviations from the pure Hubble
flow) of matter carries significant information on dark energy, dark matter and
the underlying theory of gravity on large scales. Peculiar motions of galaxies
introduce systematic deviations between the observed galaxy redshifts z and the
corresponding cosmological redshifts z_cos. A novel method for estimating the
angular power spectrum of the peculiar velocity field based on observations of
galaxy redshifts and apparent magnitudes m (or equivalently fluxes) is
presented. This method exploits the fact that a mean relation between z_cos and
m of galaxies can be derived from all galaxies in a redshift-magnitude survey.
Given a galaxy magnitude, it is shown that the z_cos(m) relation yields its
cosmological redshift with a 1-sigma error of sigma_z~0.3 for a survey like
Euclid (~10^9 galaxies at z<~2), and can be used to constrain the angular power
spectrum of z-z_cos(m) with a high signal-to-noise ratio. At large angular
separations corresponding to l<~15, we obtain significant constraints on the
power spectrum of the peculiar velocity field. At 15<~l<~60, magnitude shifts
in the z_cos(m) relation caused by gravitational lensing magnification
dominate, allowing us to probe the line-of-sight integral of the gravitational
potential. Effects related to the environmental dependence in the luminosity
function can easily be computed and their contamination removed from the
estimated power spectra. The amplitude of the combined velocity and lensing
power spectra at z~1 can be measured with <~5% accuracy. | Performance of Non-Parametric Reconstruction Techniques in the Late-Time
Universe: In the context of a Hubble tension problem that is growing in its statistical
significance, we reconsider the effectiveness of non-parametric reconstruction
techniques which are independent of prescriptive cosmological models. By taking
cosmic chronometers, Type Ia Supernovae and baryonic acoustic oscillation data,
we compare and contrast two important reconstruction approaches, namely
Gaussian processes (GP) and the \textbf{Lo}cally w\textbf{e}ighted
\textbf{S}catterplot \textbf{S}moothing together with \textbf{Sim}ulation and
\textbf{ex}trapolation method (LOESS-Simex or LS). In the context of these
methods, besides not requiring a cosmological model, they also do not require
physical parameters in their approach to their reconstruction of data (but they
do depend on statistical hyperparameters). We firstly show how both GP and
LOESS-Simex can be used to successively reconstruct various data sets to a high
level of precision. We then directly compare both approaches in a quantitative
manner by considering several factors, such as how well the reconstructions
approximate the data sets themselves to how their respective uncertainties
evolve. In light of the puzzling Hubble tension, it is important to consider
how the uncertain regions evolve over redshift and the methods compare for
estimating cosmological parameters at current times. For cosmic chronometers
and baryonic acoustic oscillation compiled data sets, we find that GP
generically produce smaller variances for the reconstructed data with a minimum
value of $\sigma_{\rm GP-min} = 1.1$, while the situation for LS is totally
different with a minimum of $\sigma_{\rm LS-min} = 50.8$. Moreover, some of
these characteristics can be alleviate at low $z$, where LS presents less
underestimation in comparison to GP. |
Where shadows lie: reconstruction of anisotropies in the neutrino sky: The Cosmic Neutrino Background (CNB) encodes a wealth of information, but has
not yet been observed directly. To determine the prospects of detection and to
study its information content, we reconstruct the phase-space distribution of
local relic neutrinos from the three-dimensional distribution of matter within
200 Mpc/h of the Milky Way. Our analysis relies on constrained realization
simulations and forward modelling of the 2M++ galaxy catalogue. We find that
the angular distribution of neutrinos is anti-correlated with the projected
matter density, due to the capture and deflection of neutrinos by massive
structures along the line of sight. Of relevance to tritium capture
experiments, we find that the gravitational clustering effect of the
large-scale structure on the local number density of neutrinos is more
important than that of the Milky Way for neutrino masses less than 0.1 eV.
Nevertheless, we predict that the density of relic neutrinos is close to the
cosmic average, with a suppression or enhancement over the mean of (-0.3%, +7%,
+27%) for masses of (0.01, 0.05, 0.1) eV. This implies no more than a marginal
increase in the event rate for tritium capture experiments like PTOLEMY. We
also predict that the CNB and CMB rest frames coincide for 0.01 eV neutrinos,
but that neutrino velocities are significantly perturbed for masses larger than
0.05 eV. Regardless of mass, we find that the angle between the neutrino dipole
and the ecliptic plane is small, implying a near-maximal annual modulation in
the bulk velocity. Along with this paper, we publicly release our simulation
data, comprising more than 100 simulations for six different neutrino masses. | Axions from cooling compact stars: pair-breaking processes: Once formed in a supernova explosion, a neutron star cools rapidly via
neutrino emission during the first 10^4-10^5 yr of its life-time. Here we
compute the axion emission rate from baryonic components of a star at
temperatures below their respective critical temperatures T_c for
normal-superfluid phase transition. The axion production is driven by a charge
neutral weak process, associated with Cooper pair breaking and recombination.
The requirement that the axion cooling does not overshadow the neutrino cooling
puts a lower bound on the axion decay constant f_a > 6 10^9 T_{c9}^{-1} GeV,
with T_{c9} = T_c/10^9 K. This translates into a upper bound on the axion mass
m_a < 10^{-3} T_{c9} eV. |
A cosmic string solution to the radio synchrotron background: We investigate the low-frequency spectral emission from a network of
superconducting cosmic string loops in hopes of explaining the observed radio
synchrotron background. After considering constraints from a variety of
astrophysical and cosmological measurements, we identify a best-fit solution
with string tension $G\mu \simeq 6.5 \times 10^{-12}$ and current $\mathcal{I}
\simeq 2.5 \times 10^6$ GeV. This model yields a convincing fit to the data and
may be testable in the near future by spectral distortion (TMS, BISOU) and 21
cm experiments (HERA, SKA, REACH). We also find that soft photon heating
protects us against current constraints from global $21$ cm experiments. | Unsupervised Classification of Galaxies. I. ICA feature selection: Subjective classification of galaxies can mislead us in the quest of the
origin regarding formation and evolution of galaxies since this is necessarily
limited to a few features. The human mind is not able to apprehend the complex
correlations in a manyfold parameter space, and multivariate analyses are the
best tools to understand the differences among various kinds of objects. In
this series of papers, an objective classification of 362,923 galaxies from the
Value Added Galaxy Catalogue (VAGC) is carried out with the help of two methods
of multivariate analysis. First, Independent Component Analysis (ICA) is used
to determine a set of derived independent components that are linear
combinations of 47 observed features (viz. ionized lines, Lick indices,
photometric and morphological properties, star formation rates etc.) of the
galaxies. Subsequently, a K-means cluster analysis is applied on the nine
independent components to obtain ten distinct and homogeneous groups. In this
first paper, we describe the methods and the main results. It appears that the
nine Independent Components represent a complete physical description of
galaxies (velocity dispersion, ionisation, metallicity, surface brightness and
structure). We find that our ten groups can be essentially placed into
traditional and empirical classes (from colour-magnitude and emission-line
diagnostic diagrams, early- vs late-types) despite the classical corresponding
features (colour, line ratios and morphology) being not significantly
correlated with the nine Independent Components. More detailed physical
interpretation of the groups will be performed in subsequent papers. |
The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: Baryon Acoustic Oscillations in the Data Release 10 and
11 galaxy samples: We present a one per cent measurement of the cosmic distance scale from the
detections of the baryon acoustic oscillations in the clustering of galaxies
from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the
Sloan Digital Sky Survey III (SDSS-III). Our results come from the Data Release
11 (DR11) sample, containing nearly one million galaxies and covering
approximately $8\,500$ square degrees and the redshift range $0.2<z<0.7$. We
also compare these results with those from the publicly released DR9 and DR10
samples. Assuming a concordance $\Lambda$CDM cosmological model, the DR11
sample covers a volume of 13\,Gpc${}^3$ and is the largest region of the
Universe ever surveyed at this density. We measure the correlation function and
power spectrum, including density-field reconstruction of the baryon acoustic
oscillation (BAO) feature. The acoustic features are detected at a significance
of over $7\,\sigma$ in both the correlation function and power spectrum.
Fitting for the position of the acoustic features measures the distance
relative to the sound horizon at the drag epoch, $r_d$, which has a value of
$r_{d,{\rm fid}}=149.28\,$Mpc in our fiducial cosmology. We find
$D_V=(1264\pm25\,{\rm Mpc})(r_d/r_{d,{\rm fid}})$ at $z=0.32$ and
$D_V=(2056\pm20\,{\rm Mpc})(r_d/r_{d,{\rm fid}})$ at $z=0.57$. At 1.0 per cent,
this latter measure is the most precise distance constraint ever obtained from
a galaxy survey. Separating the clustering along and transverse to the
line-of-sight yields measurements at $z=0.57$ of $D_A=(1421\pm20\,{\rm
Mpc})(r_d/r_{d,{\rm fid}})$ and $H=(96.8\pm3.4\,{\rm km/s/Mpc})(r_{d,{\rm
fid}}/r_d)$. Our measurements of the distance scale are in good agreement with
previous BAO measurements and with the predictions from cosmic microwave
background data for a spatially flat cold dark matter model with a cosmological
constant. | New constraints on cosmological parameters and neutrino properties using
the expansion rate of the Universe to z~1.75: We have assembled a compilation of observational Hubble parameter
measurements estimated with the differential evolution of cosmic chronometers,
in the redshift range 0<z<1.75. This sample has been used, in combination with
CMB data and with the most recent estimate of the Hubble constant H_0, to
derive new constraints on several cosmological parameters. The new Hubble
parameter data are very useful to break some of the parameter degeneracies
present in CMB-only analysis, and to constrain possible deviations from the
standard (minimal) flat \Lambda CDM model. The H(z) data are especially
valuable in constraining \Omega_k and \Omega_DE in models that allow a
variation of those parameters, yielding constraints that are competitive with
those obtained using Supernovae and/or baryon acoustic oscillations. We also
find that our H(z) data are important to constrain parameters that do no affect
directly the expansion history, by breaking or reducing degeneracies with other
parameters. We find that Nrel=3.45\pm0.33 using WMAP 7-years data in
combination with South Pole Telescope data and our H(z) determinations
(Nrel=3.71\pm0.45 using Atacama Cosmology Telescope data instead of South Pole
Telescope). We exclude Nrel>4 at 95% CL (74% CL) using the same datasets
combinations. We also put competitive limits on the sum of neutrino masses,
\Sigma m_\nu<0.24 eV at 68% confidence level. These results have been proven to
be extremely robust to many possible systematic effects, such as the initial
choice of stellar population synthesis model adopted to estimate H(z) and the
progenitor-bias. |
Characterisation of SCUBA-2 450um and 850um-selected Galaxies in the
COSMOS Field: We present deep 450um and 850um observations of a large, uniformly covered
394arcmin^2 area in the COSMOS field obtained with the SCUBA-2 instrument on
the James Clerk Maxwell Telescope (JCMT). We achieve root-mean-square noise
values of 4.13mJy at 450um and 0.80mJy at 850um. The differential and
cumulative number counts are presented and compared to similar previous works.
Individual point sources are identified at >3.6sigma significance, a threshold
corresponding to a 3-5% sample contamination rate. We identify 78 sources at
450um and 99 at 850um, with flux densities S450=13-37mJy and S850=2-16mJy. Only
62-76% of 450um sources are 850um detected and 61-81% of 850um sources are
450um detected. The positional uncertainties at 450um are small (1-2.5") and
therefore allow a precise identification of multiwavelength counterparts
without reliance on detection at 24um or radio wavelengths; we find that only
44% of 450um-selected galaxies and 60% of 850um-sources have 24um or radio
counterparts. 450um-selected galaxies peak at <z>=1.95+-0.19 and 850um=selected
galaxies peak at <z>=2.16+-0.11. The two samples occupy similar parameter space
in redshift and luminosity, while their median SED peak wavelengths differ by
~10-50um (translating to deltaTdust =8-12K, where 450um-selected galaxies are
warmer). The similarities of the 450um and 850um populations, yet lack of
direct overlap between them, suggests that submillimeter surveys conducted at
any single far-infrared wavelength will be significantly incomplete (~>30%) at
censusing infrared-luminous star formation at high-z. | A unified model for the spatial and mass distribution of subhaloes: N-body simulations suggest that the substructures that survive inside dark
matter haloes follow universal distributions in mass and radial number density.
We demonstrate that a simple analytical model can explain these subhalo
distributions as resulting from tidal stripping which increasingly reduces the
mass of subhaloes with decreasing halo-centric distance. As a starting point,
the spatial distribution of subhaloes of any given infall mass is shown to be
largely indistinguishable from the overall mass distribution of the host halo.
Using a physically motivated statistical description of the amount of mass
stripped from individual subhaloes, the model fully describes the joint
distribution of subhaloes in final mass, infall mass and radius. As a result,
it can be used to predict several derived distributions involving combinations
of these quantities including, but not limited to, the universal subhalo mass
function, the subhalo spatial distribution, the gravitational lensing profile,
the dark matter annihilation radiation profile and boost factor. This model
clarifies a common confusion when comparing the spatial distributions of
galaxies and subhaloes, the so called "anti-bias", as a simple selection
effect. We provide a Python code SubGen for populating haloes with subhaloes at
http://icc.dur.ac.uk/data/ |
Cosmic Voids in GAN-Generated Maps of Large-Scale Structure: A Generative Adversarial Network (GAN) was used to investigate the statistics
and properties of voids in a $\Lambda$CDMuniverse. The total number of voids
and the distribution of void sizes is similar in both sets of images and,
within the formal error bars, the mean void properties are consistent with each
other. However, the generated images yield somewhat fewer small voids than do
the simulated images. In addition, the generated images yield far fewer voids
with central density contrast $\sim$ $-$1. Because the generated images yield
fewer of the emptiest voids, the distribution of the mean interior density
contrast is systematically higher for the generated voids than it is for the
simulated voids. The mean radial underdensity profiles of the largest voids are
similar in both sets of images, but systematic differences are apparent. On
small scales (r $< 0.5r_{v}$), the underdensity profiles of the voids in the
generated images exceed those of the voids in the simulated images. On large
scales (r $> 0.5r_{v}$), the underdensity profiles of the voids in the
simulated images exceed those of the voids in the generated images. The
discrepancies between the void properties in the two sets of images are
attributable to the GAN struggling to capture absolute patterns in the data. In
particular, the GAN produces too few pixels with density contrasts $\sim$ $-$1
and too many pixels with density contrasts in the range $\sim$ $-$0.88 to
$\sim$ $-$0.63. | Magnification effect on the detection of primordial non-Gaussianity from
photometric surveys: We present forecast results for constraining the primordial non-Gaussianity
from photometric surveys through a large-scale enhancement of the galaxy
clustering amplitude. In photometric surveys, the distribution of observed
galaxies at high redshifts suffers from the gravitational-lensing
magnification, which systematically alters the number density for
magnitude-limited galaxy samples. We estimate size of the systematic bias in
the best-fit cosmological parameters caused by the magnification effect,
particularly focusing on the primordial non-Gaussianity. For upcoming deep
and/or wide photometric surveys like HSC, DES and LSST, the best-fit value of
the non-Gaussian parameter, fNL, obtained from the galaxy count data is highly
biased, and the true values of fNL would typically go outside the 3-sigma error
of the biased confidence region, if we ignore the magnification effect in the
theoretical template of angular power spectrum. The additional information from
cosmic shear data helps not only to improve the constraint, but also to reduce
the systematic bias. As a result, the size of systematic bias on fNL would
become small enough compared to the expected 1-sigma error for HSC and DES, but
it would be still serious for deep surveys with z_m > 1.5, like LSST.
Tomographic technique improves the constraint on fNL by a factor of 2-3
compared to the one without tomography, but the systematic bias would increase. |
Primordial Black Holes as Dark Matter: The possibility that the dark matter comprises primordial black holes (PBHs)
is considered, with particular emphasis on the currently allowed mass windows
at $10^{16}$ - $10^{17}\,$g, $10^{20}$ - $10^{24}\,$g and $1$ -
$10^{3}\,M_{\odot}$. The Planck mass relics of smaller evaporating PBHs are
also considered. All relevant constraints (lensing, dynamical, large-scale
structure and accretion) are reviewed and various effects necessary for a
precise calculation of the PBH abundance (non-Gaussianity, non-sphericity,
critical collapse and merging) are accounted for. It is difficult to put all
the dark matter in PBHs if their mass function is monochromatic but this is
still possible if the mass function is extended, as expected in many scenarios.
A novel procedure for confronting observational constraints with an extended
PBH mass spectrum is therefore introduced. This applies for arbitrary
constraints and a wide range of PBH formation models, and allows us to identify
which model-independent conclusions can be drawn from constraints over all mass
ranges. We focus particularly on PBHs generated by inflation, pointing out
which effects in the formation process influence the mapping from the
inflationary power spectrum to the PBH mass function. We then apply our scheme
to two specific inflationary models in which PBHs provide the dark matter. The
possibility that the dark matter is in intermediate-mass PBHs of $1$ -
$10^{3}\,M_{\odot}$ is of special interest in view of the recent detection of
black-hole mergers by LIGO. The possibility of Planck relics is also intriguing
but virtually untestable. | Is the present cosmic expansion decelerating?: We probe the recent cosmic expansion by directly reconstructing the
deceleration parameter $q(z)$ at recent times with a linear expansion at $z=0$
using the low redshift SNIa and BAO data. Our results show that the
observations seem to favor a slowing down of the present cosmic acceleration.
Using only very low redshift SNIa data, for example, those within $z<0.1$ or
$0.2$, we find that our Universe may have already entered a decelerating
expansion era since a positive $q(0)$ seems to be favored. This result is
further supported by a different approach which aims to reconstruct $q(z)$ in
the whole redshift region. So, the accelerating cosmic expansion may be just a
transient phenomenon. |
The primordial abundance of 4He: evidence for non-standard big bang
nucleosynthesis: We present a new determination of the primordial helium mass fraction Yp,
based on 93 spectra of 86 low-metallicity extragalactic HII regions, and taking
into account the latest developments concerning systematic effects. These
include collisional and fluorescent enhancements of HeI recombination lines,
underlying HeI stellar absorption lines, collisional and fluorescent excitation
of hydrogen lines and temperature and ionization structure of the HII region.
Using Monte Carlo methods to solve simultaneously for the above systematic
effects, we find the best value to be
Yp=0.2565+/-0.0010(stat.)+/-0.0050(syst.). This value is higher at the 2sigma
level than the value given by Standard Big Bang Nucleosynthesis (SBBN),
implying deviations from it. The effective number of light neutrino species Nnu
is equal to 3.68^+0.80_-0.70 (2sigma) and 3.80^+0.80_-0.70 (2sigma) for a
neutron lifetime tau(n) equal to 885.4+/-0.9 s and 878.5+/-0.8 s, respectively,
i.e. it is larger than the experimental value of 2.993+/-0.011. | Population III star explosions and Planck 2018 data: We investigate the effect of the population III (Pop III) stars supernova
explosion~(SN) on the high redshifts reionization history using the latest
Planck data. It is predicted that massive Pop~III stars~($130M_\odot\leq M\leq
270M_\odot$) explode energetically at the end of their stellar life as
pair-instability supernovae (PISNe). In the explosion, supernova remnants grow
as hot ionized bubbles and enhance the ionization fraction in the early stage
of the reionization history. This enhancement affects the optical depth of the
cosmic microwave background~(CMB) and generates the additional anisotropy of
the CMB polarization on large scales. Therefore, analyzing the Planck
polarization data allows us to examine the Pop III star SNe and the abundance
of their progenitors, massive Pop III stars. In order to model the SN
contribution to reionization, we introduce a new parameter $\zeta$, which
relates to the abundance of the SNe to the collapse fraction of the Universe.
Using the Markov chain Monte Carlo method with the latest Planck polarization
data, we obtain the constraint on our model parameter, $\zeta$. Our constraint
tells us that observed CMB polarization is consistent with the abundance of
PISNe predicted from the star formation rate and initial mass function of Pop
III stars in recent cosmological simulations. We also suggest that combining
further observations on the late reionization history such as high redshift
quasi-stellar object~(QSO) observations can provide tighter constraints and
important information on the nature of Pop III stars. |
New period-luminosity and period-color relations of classical Cepheids.
IV. The low-metallicity galaxies IC 1613, WLM, Pegasus, Sextans A and B, and
Leo A in comparison to SMC: The metal-poor, fundamental-mode (P0) and first-overtone (P1) Cepheids in the
dwarf galaxies IC 1613, WLM, Pegasus, Sextans A, Sextans B, and Leo A are
compared with the about equally metal-poor Cepheids of the Small Magellanic
Cloud (SMC). The period-color (P-C) and period-luminosity (P-L) relations of
the seven galaxies are indistinguishable, but differ distinctly from those in
the Large Magellanic Cloud (LMC) and the solar neighborhood. Adopting
(m-M)^{0}_{SMC}=18.93 from independent evidence, one can determine reliable
distance moduli for the other dwarf galaxies of (m-M)^{0} = 24.34+/-0.03,
24.95+/-0.03, 24.87+/-0.06, 25.60+/-0.03 (mean for Sextans A & B), and
24.59+/-0.03, respectively. | Slow Evolution of the Specific Star Formation Rate at z>2: The Impact of
Dust, Emission Lines, and A Rising Star Formation History: We measure the evolution of the specific star formation rate (sSFR = SFR /
Mstellar) between redshift 4 and 6 to investigate the previous reports of
"constant" sSFR at z>2. We obtain photometry on a large sample of galaxies at
z~4-6 located in the GOODS-S field that have high quality imaging from HST and
Spitzer. We have derived stellar masses and star formation rates (SFRs) through
stellar population modeling of their spectral energy distributions (SEDs). We
estimate the dust extinction from the observed UV colors. In the SED fitting
process we have studied the effects of assuming a star formation history (SFH)
both with constant SFR and one where the SFR rises exponentially with time. The
latter SFH is chosen to match the observed evolution of the UV luminosity
function. We find that neither the mean SFRs nor the mean stellar masses change
significantly when the rising SFR (RSF) model is assumed instead of the
constant SFR model. When focusing on galaxies with Mstar ~ 5x10^9 Msun, we find
that the sSFR evolves weakly with redshift (sSFR(z) \propto (1+z)^(0.6+/-0.1)
Gyr^-1), consistent with previous results and with recent estimates of the sSFR
at z~2-3 using similar assumptions. We have also investigated the impact of
optical emission lines on our results. We estimate that the contribution of
emission lines to the rest-frame optical fluxes is only modest at z~4 and 5 but
it could reach ~50% at z~6. When emission lines of this strength are taken into
account, the sSFR shows somewhat higher values at high redshifts, according to
the relation sSFR(z) \propto (1+z)^(1.0+/-0.1) Gyr^-1, i.e., ~2.3x higher at
z~6 than at z~2. However, the observed evolution is substantially weaker than
that found at z<2 or that expected from current models (which corresponds to
sSFR(z) \propto (1+z)^(2.5) Gyr^-1). -abridged- |
Dark Energy Survey Year 3 Results: Constraints on extensions to
$Λ$CDM with weak lensing and galaxy clustering: We constrain extensions to the $\Lambda$CDM model using measurements from the
Dark Energy Survey's first three years of observations and external data. The
DES data are the two-point correlation functions of weak gravitational lensing,
galaxy clustering, and their cross-correlation. We use simulated data and blind
analyses of real data to validate the robustness of our results. In many cases,
constraining power is limited by the absence of nonlinear predictions that are
reliable at our required precision. The models are: dark energy with a
time-dependent equation of state, non-zero spatial curvature, sterile
neutrinos, modifications of gravitational physics, and a binned $\sigma_8(z)$
model which serves as a probe of structure growth. For the time-varying dark
energy equation of state evaluated at the pivot redshift we find $(w_{\rm p},
w_a)= (-0.99^{+0.28}_{-0.17},-0.9\pm 1.2)$ at 68% confidence with $z_{\rm
p}=0.24$ from the DES measurements alone, and $(w_{\rm p}, w_a)=
(-1.03^{+0.04}_{-0.03},-0.4^{+0.4}_{-0.3})$ with $z_{\rm p}=0.21$ for the
combination of all data considered. Curvature constraints of
$\Omega_k=0.0009\pm 0.0017$ and effective relativistic species $N_{\rm
eff}=3.10^{+0.15}_{-0.16}$ are dominated by external data. For massive sterile
neutrinos, we improve the upper bound on the mass $m_{\rm eff}$ by a factor of
three compared to previous analyses, giving 95% limits of $(\Delta N_{\rm
eff},m_{\rm eff})\leq (0.28, 0.20\, {\rm eV})$. We also constrain changes to
the lensing and Poisson equations controlled by functions $\Sigma(k,z) =
\Sigma_0 \Omega_{\Lambda}(z)/\Omega_{\Lambda,0}$ and $\mu(k,z)=\mu_0
\Omega_{\Lambda}(z)/\Omega_{\Lambda,0}$ respectively to
$\Sigma_0=0.6^{+0.4}_{-0.5}$ from DES alone and $(\Sigma_0,\mu_0)=(0.04\pm
0.05,0.08^{+0.21}_{-0.19})$ for the combination of all data. Overall, we find
no significant evidence for physics beyond $\Lambda$CDM. | A Challenge to the Standard Cosmological Model: We present the first joint analysis of catalogs of radio galaxies and quasars
to determine if their sky distribution is consistent with the standard
$\Lambda$CDM model of cosmology. This model is based on the cosmological
principle, which asserts that the universe is statistically isotropic and
homogeneous on large scales, so the observed dipole anisotropy in the cosmic
microwave background (CMB) must be attributed to our local peculiar motion. We
test the null hypothesis that there is a dipole anisotropy in the sky
distribution of radio galaxies and quasars consistent with the motion inferred
from the CMB, as is expected for cosmologically distant sources. Our two
samples, constructed respectively from the NRAO VLA Sky Survey and the
Wide-field Infrared Survey Explorer, are systematically independent and have no
shared objects. Using a completely general statistic that accounts for
correlation between the found dipole amplitude and its directional offset from
the CMB dipole, the null hypothesis is independently rejected by the radio
galaxy and quasar samples with $p$-value of $8.9\times10^{-3}$ and
$1.2\times10^{-5}$, respectively, corresponding to $2.6\sigma$ and $4.4\sigma$
significance. The joint significance, using sample size-weighted $Z$-scores, is
$5.1\sigma$. We show that the radio galaxy and quasar dipoles are consistent
with each other and find no evidence for any frequency dependence of the
amplitude. The consistency of the two dipoles improves if we boost to the CMB
frame assuming its dipole to be fully kinematic, suggesting that cosmologically
distant radio galaxies and quasars may have an intrinsic anisotropy in this
frame. |
Spectator field models in light of spectral index after Planck: We revisit spectator field models including curvaton and modulated reheating
scenarios, specifically focusing on their viability in the new Planck era,
based on the derived expression for the spectral index in general spectator
field models. Importantly, the recent Planck observations give strong
preference to a red-tilted power spectrum, while the spectator field models
tend to predict a scale-invariant one. This implies that, during inflation,
either (i) the Hubble parameter varies significantly as in chaotic inflation,
or (ii) a scalar potential for the spectator field has a relatively large
negative curvature. Combined with the tight constraint on the non-Gaussianity,
the Planck data provides us with rich implications for various spectator field
models. | Is patchy reionization an obstacle in detecting the primordial
gravitational wave signal?: The large-scale CMB B-mode polarization is the direct probe to the low
frequency primordial gravitational wave signal. However, unambiguous
measurement of this signal requires a precise understanding of the possible
contamination. One such potential contamination arises from the patchiness in
the spatial distribution of free electrons during the epoch of reionization. We
estimate the B-mode power spectrum due to patchy reionization using a
combination of \emph{photon-conserving} semi-numerical simulation and
analytical calculation, and compare its amplitude with the primordial B-mode
signal. For a reionization history which is in agreement with several latest
observations, we find that a stronger secondary B-mode polarization signal is
produced when the reionization is driven by the sources in massive halos and
its amplitude can be comparable to the recombination bump for tensor to scalar
ratio $(r) \lesssim 5 \times 10^{-4}$. If contamination from patchy
reionization is neglected in the analysis of B-mode polarization data, then for
the models of reionization considered in this analysis, we find a maximum bias
of about $30\%$ in the value of $r=\,10^{-3}$ when spatial modes between $\ell
\in [50, 200]$ are used with a delensing efficiency of $50\%$. The inferred
bias from patchy reionization is not a severe issue for the upcoming
ground-based CMB experiment Simons Observatory, but can be a potential source
of confusion for proposed CMB experiments which target to detect the value of
$r< 10^{-3}$. However, this obstacle can be removed by utilizing the difference
in the shape of the power spectrum from the primordial signal. |
Fitting the integrated Spectral Energy Distributions of Galaxies: Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years. | Latest Observational Constraints on Cardassian Models: Constraints on the original Cardassian model and the modified polytropic
Cardassian model are examined from the latest derived 397 Type Ia supernova
(SNe Ia) data, the size of baryonic acoustic oscillation peak from the Sloan
Digital Sky Survey (SDSS), the position of first acoustic peak of the Cosmic
Microwave Background radiation (CMB) from the five years Wilkinson Microwave
Anisotropy Probe (WMAP), the x-ray gas mass fractions in clusters of galaxies,
and the observational H(z) data. In the original Cardassian model with these
combined data set, we find $\Omega_{m0}=0.271^{+0.014}_{-0.014},
n=0.035^{+0.049}_{-0.049}$ at $1 \sigma$ confidence level. And in the modified
polytropic Cardassian model, we find that
$\Omega_{m0}=0.271^{+0.014}_{-0.015}$, $n=-0.091^{+0.331}_{-1.908}$ and
$\beta=0.824^{+0.750}_{-0.622}$ within $1\sigma$ confidence level. According to
these observations, the acceleration of the universe begins at
$z_T=0.55^{+0.05}_{-0.05} (1\sigma)$ for the original Cardassian model, and at
$z_T=0.58^{+0.12}_{-0.12} (1\sigma)$ for the modified polytropic Cardassian
model. Evolution of the effective equation of state $w_{eff}$ for the modified
polytropic Cardassian model is also examined here and results show that an
evolutionary quintessence dark energy model is favored. |
Curvaton decay into relativistic matter: We consider an inflationary curvaton scenario, where the curvaton decays into
two non-interacting relativistic fluids and later during the cosmological
evolution one of them becomes non-relativistic, forming dark matter component
of the universe. We study the thermic properties and the generation of
non-gaussianity in this three fluid curvaton model. By solving the evolution of
the system and using several cosmological conditions we find that the allowed
parameter space is strongly constrained. The naturalness of this curvaton
scenario is also discussed. | Observational Constraints on Gauge Field Production in Axion Inflation: Models of axion inflation are particularly interesting since they provide a
natural justification for the flatness of the potential over a super-Planckian
distance, namely the approximate shift-symmetry of the inflaton. In addition,
most of the observational consequences are directly related to this symmetry
and hence are correlated. Large tensor modes can be accompanied by the
observable effects of a the shift-symmetric coupling $\phi F\tilde F$ to a
gauge field. During inflation this coupling leads to a copious production of
gauge quanta and consequently a very distinct modification of the primordial
curvature perturbations. In this work we compare these predictions with
observations. We find that the leading constraint on the model comes from the
CMB power spectrum when considering both WMAP 7-year and ACT data. The
bispectrum generated by the non-Gaussian inverse-decay of the gauge field leads
to a comparable but slightly weaker constraint. There is also a constraint from
mu-distortion using TRIS plus COBE/FIRAS data, but it is much weaker. Finally
we comment on a generalization of the model to massive gauge fields. When the
mass is generated by some light Higgs field, observably large local
non-Gaussianity can be produced. |
Analysis of the alignment of non-random patterns of spin directions in
populations of spiral galaxies: Observations of non-random distribution of galaxies with opposite spin
directions have recently attracted considerable attention. Here, a method for
identifying cosine-dependence in a dataset of galaxies annotated by their spin
directions is described in the light of different aspects that can impact the
statistical analysis of the data. These aspects include the presence of
duplicate objects in a dataset, errors in the galaxy annotation process, and
non-random distribution of the asymmetry that does not necessarily form a
dipole or quadrupole axes. The results show that duplicate objects in the
dataset can artificially increase the likelihood of cosine dependence detected
in the data, but a very high number of duplicate objects is required to lead to
a false detection of an axis. Inaccuracy in galaxy annotations has relatively
minor impact on the identification of cosine dependence when the error is
randomly distributed between clockwise and counterclockwise galaxies. However,
when the error is not random, even a small bias of 1% leads to a statistically
significant cosine dependence that peaks at the celestial pole. Experiments
with artificial datasets in which the distribution was not random showed strong
cosine dependence even when the data did not form a full dipole axis alignment.
The analysis when using the unmodified data shows asymmetry profile similar to
the profile shown in multiple previous studies using several different
telescopes. | Exploring the Optical Transient Sky with the Palomar Transient Factory: The Palomar Transient Factory (PTF) is a wide-field experiment designed to
investigate the optical transient and variable sky on time scales from minutes
to years. PTF uses the CFH12k mosaic camera, with a field of view of 7.9 deg^2
and a plate scale of 1 asec/pixel, mounted on the the Palomar Observatory
48-inch Samuel Oschin Telescope. The PTF operation strategy is devised to probe
the existing gaps in the transient phase space and to search for theoretically
predicted, but not yet detected, phenomena, such as fallback supernovae,
macronovae, .Ia supernovae and the orphan afterglows of gamma-ray bursts. PTF
will also discover many new members of known source classes, from cataclysmic
variables in their various avatars to supernovae and active galactic nuclei,
and will provide important insights into understanding galactic dynamics
(through RR Lyrae stars) and the Solar system (asteroids and near-Earth
objects). The lessons that can be learned from PTF will be essential for the
preparation of future large synoptic sky surveys like the Large Synoptic Survey
Telescope. In this paper we present the scientific motivation for PTF and
describe in detail the goals and expectations for this experiment. |
The HBI in a quasi-global model of the intracluster medium: In this paper we investigate how convective instabilities influence heat
conduction in the intracluster medium (ICM) of cool-core galaxy clusters. The
ICM is a high-beta, weakly collisional plasma in which the transport of
momentum and heat is aligned with the magnetic field. The anisotropy of heat
conduction, in particular, gives rise to instabilities that can access energy
stored in a temperature gradient of either sign. We focus on the heat-flux
buoyancy-driven instability (HBI), which feeds on the outwardly increasing
temperature profile of cluster cool cores. Our aim is to elucidate how the
global structure of a cluster impacts on the growth and morphology of the
linear HBI modes when in the presence of Braginskii viscosity, and ultimately
on the ability of the HBI to thermally insulate cores. We employ an idealised
quasi-global model, the plane-parallel atmosphere, which captures the essential
physics -- e.g. the global radial profile of the cluster -- while letting the
problem remain analytically tractable. Our main result is that the dominant HBI
modes are localised to the the innermost (~<20%) regions of cool cores. It is
then probable that, in the nonlinear regime, appreciable field-line insulation
will be similarly localised. Thus, while radio-mode feedback appears necessary
in the central few tens of kpc, heat conduction may be capable of offsetting
radiative losses throughout most of a cool core over a significant fraction of
the Hubble time. Finally, our linear solutions provide a convenient numerical
test for the nonlinear codes that tackle the saturation of such convective
instabilities in the presence of anisotropic transport. | A note on second-order perturbations of non-canonical scalar fields: We study second-order perturbations for a general non-canonical scalar field,
minimally coupled to gravity, on the unperturbed FRW background, where metric
fluctuations are neglected a priori. By employing different approaches to
cosmological perturbation theory, we show that, even in this simplified set-up,
the second-order perturbations to the stress tensor, the energy density and the
pressure display potential instabilities, which are not present at linear
order. The conditions on the Lagrangian under which these instabilities take
place are provided. We also discuss briefly the significance of our analysis in
light of the possible linearization instability of these fields about the FRW
background. |
Detailed Cluster Mass and Light profiles of A1703, A370 and RXJ1347-11
from Deep Subaru Imaging: Weak lensing work can be badly compromised by unlensed foreground and cluster
members which dilute the true lensing signal. We show how the lensing amplitude
in multi-colour space can be harnessed to securely separate cluster members
from the foreground and background populations for three massive clusters,
A1703 (z=0.258), A370 (z=0.375) and RXJ1347-11 (z=0.451) imaged with Subaru.
The luminosity functions of these clusters when corrected for dilution, show
similar faint-end slopes, \alpha ~= -1.0, with no marked faint-end upturn to
our limit of M_R ~= -15.0, and only a mild radial gradient. In each case, the
radial profile of the M/L ratio peaks at intermediate radius, ~=0.2r_{vir}, at
a level of 300-500(M/L_R)_\odot, and then falls steadily towards
~100(M/L_R)_{\odot} at the virial radius, similar to the mean field level. This
behaviour is likely due to the relative paucity of central late-type galaxies,
whereas for the E/S0-sequence only a mild radial decline in M/L is found for
each cluster. We discuss this behaviour in the context of detailed simulations
where predictions for tidal stripping may now be tested accurately with
observations. | A Blue Tilt in the Globular Cluster System of the Milky Way-like Galaxy
NGC 5170: Here we present HST/ACS imaging, in the B and I bands, of the edge-on Sb/Sc
galaxy NGC 5170. Excluding the central disk region region, we detect a 142
objects with colours and sizes typical of globular clusters (GCs). Our main
result is the discovery of a `blue tilt' (a mass-metallicity relation), at the
3sigma level, in the metal-poor GC subpopulation of this Milky Way like galaxy.
The tilt is consistent with that seen in massive elliptical galaxies and with
the self enrichment model of Bailin & Harris. For a linear mass-metallicity
relation, the tilt has the form Z ~ L^{0.42 +/- 0.13}. We derive a total GC
system population of 600 +/- 100, making it much richer than the Milky Way.
However when this number is normalised by the host galaxy luminosity or stellar
mass it is similar to that of M31. Finally, we report the presence of a
potential Ultra Compact Dwarf of size ~ 6 pc and luminosity M_I ~ -12.5,
assuming it is physically associated with NGC 5170. |
A framework for the next generation of stationary cosmological models: According to a new tired-light cosmological model, where H(z) = H 0 (1 + z),
the number density of galaxies has been nearly constant over the last 10 Gyr,
at least, meaning that, as far as galaxy counts are concerned, the Universe has
been stationary. In this context, an analysis of the luminosity distances of
quasars and supernovae Ia shows that the Universe is far from being as
transparent as assumed nowadays, the photon lifetime along the line-of-sight
being one third of the Hubble time. Such a low value could mean that there are
huge amounts of grey dust in the inter galactic medium, that have so far
escaped detection. It could also be a signature of new physics, namely, a
consequence of the decay of photons into lighter particles. The tired-light
model advocated in the present study would be falsified if, for instance, the
time-dilation of remote events were shown to have a general character, that is,
if it were definitely observed for phenomenons other than the light curves of
supernovae Ia. On the other hand, further developments are needed in order to
turn this model into an actual cosmology. In particular, the physical origin of
the current stability of the Universe on galactic scales remains to be
identified. | Bayesian inference of CMB gravitational lensing: The Planck satellite, along with several ground based telescopes, have mapped
the cosmic microwave background (CMB) at sufficient resolution and
signal-to-noise so as to allow a detection of the subtle distortions due to the
gravitational influence of the intervening matter distribution. A natural
modeling approach is to write a Bayesian hierarchical model for the lensed CMB
in terms of the unlensed CMB and the lensing potential. So far there has been
no feasible algorithm for inferring the posterior distribution of the lensing
potential from the lensed CMB map. We propose a solution that allows efficient
Markov Chain Monte Carlo sampling from the joint posterior of the lensing
potential and the unlensed CMB map using the Hamiltonian Monte Carlo technique.
The main conceptual step in the solution is a re-parameterization of CMB
lensing in terms of the lensed CMB and the "inverse lensing" potential. We
demonstrate a fast implementation on simulated data including noise and a sky
cut, that uses a further acceleration based on a very mild approximation of the
inverse lensing potential. We find that the resulting Markov Chain has short
correlation lengths and excellent convergence properties, making it promising
for application to high resolution CMB data sets of the future. |
Constraining the optical depth of galaxies and velocity bias with
cross-correlation between kinetic Sunyaev-Zeldovich effect and peculiar
velocity field: We calculate the cross-correlation function $\langle (\Delta
T/T)(\mathbf{v}\cdot \mathbf{n}/\sigma_{v}) \rangle$ between the kinetic
Sunyaev-Zeldovich (kSZ) effect and the reconstructed peculiar velocity field
using linear perturbation theory, to constrain the optical depth $\tau$ and
peculiar velocity bias of central galaxies with Planck data. We vary the
optical depth $\tau$ and the velocity bias function
$b_{v}(k)=1+b(k/k_{0})^{n}$, and fit the model to the data, with and without
varying the calibration parameter $y_{0}$ that controls the vertical shift of
the correlation function. By constructing a likelihood function and
constraining $\tau$, $b$ and $n$ parameters, we find that the quadratic
power-law model of velocity bias $b_{v}(k)=1+b(k/k_{0})^{2}$ provides the
best-fit to the data. The best-fit values are $\tau=(1.18 \pm 0.24) \times
10^{-4}$, $b=-0.84^{+0.16}_{-0.20}$ and $y_{0}=(12.39^{+3.65}_{-3.66})\times
10^{-9}$ ($68\%$ confidence level). The probability of $b>0$ is only $3.12
\times 10^{-8}$ for the parameter $b$, which clearly suggests a detection of
scale-dependent velocity bias. The fitting results indicate that the
large-scale ($k \leq 0.1\,h\,{\rm Mpc}^{-1}$) velocity bias is unity, while on
small scales the bias tends to become negative. The value of $\tau$ is
consistent with the stellar mass--halo mass and optical depth relation proposed
in the previous literatures, and the negative velocity bias on small scales is
consistent with the peak background-split theory. Our method provides a direct
tool to study the gaseous and kinematic properties of galaxies. | Near-infrared and optical observations of galactic warps: A common,
unexplained feature of most discs: Context: Warps occurring in galactic discs have been studied extensively in
HI and in the optical, but rarely in the near-infrared (NIR) bands that trace
the older stellar populations.
Aims: We provide NIR data of nearby edge-on galaxies, combined with optical
observations, for direct comparison of the properties of galactic warps as a
function of wavelength, and calculate warp curves for each galaxy and obtain
the characteristic warp parameters. We discuss these properties as possible
constraints to the different mechanisms that have been proposed for the
development and persistence of galactic warps.
Methods: We observed 20 galaxies that were selected from a statistically
complete diameter-limited subsample of edge-on disc galaxies. We used the Cerro
Tololo Infrared Imager (CIRIM) at the CTIO 1.5m Ritchey-Chretien telescope to
acquire the NIR data. We used the 1.54m Danish and 0.92m Dutch telescopes at
the European Southern Observatory's La Silla site for our optical observations.
Results: Our results show that 13 of our 20 sample galaxies are warped, with
the warp more pronounced in the optical than at NIR wavelengths. In the
remaining seven galaxies, no warp is apparent within the limitations of our
automated detection method. The transition between the unperturbed inner disc
and the outer, warped region is rather abrupt. S0 galaxies exhibit very small
or no warps. The magnetic model remains one of a number of interesting
formation scenarios. |
Accuracy of the growth index in the presence of dark energy
perturbations: We present the analytical solutions for the evolution of matter density
perturbations, for a model with a constant dark energy equation of state $w$
but when the effects of the dark energy perturbations are properly taken into
account. We consider two cases, the first when the sound speed of the
perturbations is zero $c_s^2=0$ and the general case $0<c_s^2 \leq 1$. In the
first case our solution is exact, while in the second case we found an
approximate solution which works to better than $0.3\%$ accuracy for $k>10 H_0$
or equivalently $k/h>0.0033 \textrm{Mpc}^{-1}$. We also estimate the
corrections to the growth index $\gamma(z)$, commonly used to parametrize the
growth-rate. We find that these corrections due to the DE perturbations affect
the growth index $\gamma$ at the $3\%$ level. We also compare our new
expressions for the growth index with other expressions already present in the
literature and we find that the latter are less accurate than the ones we
propose here. Therefore, our analytical calculations are necessary as the
theoretical predictions for the fundamental parameters to be constrained by the
upcoming surveys need to be as accurate as possible, especially since we are
entering in the precise cosmology era where parameters will be measured to the
percent level. | From Simulations to Reality: Dark Energy Reconstruction with Simulated
SNIa data from the Vera C. Rubin Observatory: In this paper, we present an Artificial Neural Network (ANN) based
reconstruction analysis of the Supernova Ia (SNIa) distance moduli ($\mu(z)$),
and hence dark energy, using LSST simulated three-year SNIa data. Our ANN
reconstruction architecture can model both the distance moduli and their
corresponding error estimates. For this we employ astroANN and incorporate
Monte Carlo dropout techniques to quantify uncertainties in our predictions. We
tune our hyperparameters through advanced genetic algorithms, including
elitism, utilizing the DEAP library. We compared the performance of the ANN
based reconstruction with two theoretical descriptions of dark energy models,
$\Lambda$CDM and Chevallier-Linder-Polarski (CPL). We perform a Bayesian
analysis for these two theoretical models using the LSST simulations and also
compare with observations from Pantheon and Pantheon+ SNIa real data. We show
that our model-independent reconstruction using ANN is consistent with both of
them. We assessed the performance using mean squared error (MSE) and showed
that the ANN can produce distance estimates in better agreement with the LSST
dataset than either $\Lambda$CDM or CPL, albeit very small. We included an
additional residual analysis and a null test with $F$-scores to show that the
reconstructed distances from the ANN model, are in excellent agreement with the
$\Lambda$CDM or CPL model. |
Small scale aspects of warm dark matter : power spectra and acoustic
oscillations: We provide a semi-analytic study of the small scale aspects of the power
spectra of warm dark matter (WDM) candidates that decoupled while relativistic
with arbitrary distribution functions. These are characterized by two widely
different scales $k_{eq} \sim 0.01\,(\mathrm{Mpc})^{-1}$ and $k_{fs}=
\sqrt{3}\,k_{eq}/2\,< V^2_{eq} >^{1/2} $ with $< V^2_{eq} >^{1/2} \ll 1 $ the
velocity dispersion at matter radiation equality. Density perturbations evolve
through three stages: radiation domination when the particle is relativistic
and non-relativistic and matter domination. An early ISW effect during the
first stage leads to an enhancement of density perturbations and a plateau in
the transfer function for $k \lesssim k_{fs}$. An effective fluid description
emerges at small scales which includes the effects of free streaming in initial
conditions and inhomogeneities. The transfer function features
\emph{WDM-acoustic oscillations} at scales $k \gtrsim 2 \,k_{fs}$. We study the
power spectra for two models of sterile neutrinos with $m \sim \,\mathrm{keV}$
produced non-resonantly, at the QCD and EW scales respectively. The latter case
yields acoustic oscillations on mass scales $\sim 10^{8}\,M_{\odot}$. Our
results reveal a \emph{quasi-degeneracy} between the mass, distribution
function and decoupling temperature suggesting caveats on the constraints on
the mass of a sterile neutrino from current WDM N-body simulations and
Lyman-$\alpha$ forest data. A simple analytic interpolation of the power
spectra between large and small scales and its numerical implementation is
given. | Maximum likelihood analysis of systematic errors in interferometric
observations of the cosmic microwave background: We investigate the impact of instrumental systematic errors in
interferometric measurements of the cosmic microwave background (CMB)
temperature and polarization power spectra. We simulate interferometric CMB
observations to generate mock visibilities and estimate power spectra using the
statistically optimal maximum likelihood technique. We define a quadratic error
measure to determine allowable levels of systematic error that do not induce
power spectrum errors beyond a given tolerance. As an example, in this study we
focus on differential pointing errors. The effects of other systematics can be
simulated by this pipeline in a straightforward manner. We find that, in order
to accurately recover the underlying B-modes for r=0.01 at 28<l<384,
Gaussian-distributed pointing errors must be controlled to 0.7^\circ rms for an
interferometer with an antenna configuration similar to QUBIC, in agreement
with analytical estimates. Only the statistical uncertainty for 28<l<88 would
be changed at ~10% level. With the same instrumental configuration, we find the
pointing errors would slightly bias the 2-\sigma upper limit of the
tensor-to-scalar ratio r by ~10%. We also show that the impact of pointing
errors on the TB and EB measurements is negligibly small. |
Dark Sirens to Resolve the Hubble-Lemaître Tension: The planned sensitivity upgrades to the LIGO and Virgo facilities could
uniquely identify host galaxies of dark sirens-compact binary coalescences
without any electromagnetic counterparts-within a redshift of z = 0.1. This is
aided by the higher order spherical harmonic modes present in the
gravitational-wave signal, which also improve distance estimation. In
conjunction, sensitivity upgrades and higher modes will facilitate an accurate,
independent measurement of the host galaxy's redshift in addition to the
luminosity distance from the gravitational wave observation to infer the
Hubble-Lema\^itre constant H0 to better than a few percent in five years. A
possible Voyager upgrade or third generation facilities would further solidify
the role of dark sirens for precision cosmology in the future. | GREAT3 results I: systematic errors in shear estimation and the impact
of real galaxy morphology: We present first results from the third GRavitational lEnsing Accuracy
Testing (GREAT3) challenge, the third in a sequence of challenges for testing
methods of inferring weak gravitational lensing shear distortions from
simulated galaxy images. GREAT3 was divided into experiments to test three
specific questions, and included simulated space- and ground-based data with
constant or cosmologically-varying shear fields. The simplest (control)
experiment included parametric galaxies with a realistic distribution of
signal-to-noise, size, and ellipticity, and a complex point spread function
(PSF). The other experiments tested the additional impact of realistic galaxy
morphology, multiple exposure imaging, and the uncertainty about a
spatially-varying PSF; the last two questions will be explored in Paper II. The
24 participating teams competed to estimate lensing shears to within systematic
error tolerances for upcoming Stage-IV dark energy surveys, making 1525
submissions overall. GREAT3 saw considerable variety and innovation in the
types of methods applied. Several teams now meet or exceed the targets in many
of the tests conducted (to within the statistical errors). We conclude that the
presence of realistic galaxy morphology in simulations changes shear
calibration biases by $\sim 1$ per cent for a wide range of methods. Other
effects such as truncation biases due to finite galaxy postage stamps, and the
impact of galaxy type as measured by the S\'{e}rsic index, are quantified for
the first time. Our results generalize previous studies regarding sensitivities
to galaxy size and signal-to-noise, and to PSF properties such as seeing and
defocus. Almost all methods' results support the simple model in which additive
shear biases depend linearly on PSF ellipticity. |
Bayesian Simulation-based Inference for Cosmological Initial Conditions: Reconstructing astrophysical and cosmological fields from observations is
challenging. It requires accounting for non-linear transformations, mixing of
spatial structure, and noise. In contrast, forward simulators that map fields
to observations are readily available for many applications. We present a
versatile Bayesian field reconstruction algorithm rooted in simulation-based
inference and enhanced by autoregressive modeling. The proposed technique is
applicable to generic (non-differentiable) forward simulators and allows
sampling from the posterior for the underlying field. We show first promising
results on a proof-of-concept application: the recovery of cosmological initial
conditions from late-time density fields. | The Hubble diagram for a system within dark energy: the location of the
zero-gravity radius and the global Hubble rate: Here we continue to discuss the principle of the local measurement of dark
energy using the normalized Hubble diagram describing the environment of a
system of galaxies. We calculate the present locus of test particles injected a
fixed time ago (\sim the age of the universe), in the standard \Lambda
-cosmology and for different values of the system parameters (the model
includes a central point mass M and a local dark energy density \rho_{loc}) and
discuss the position of the zero-gravity distance R_v in the Hubble diagram.
Our main conclusions are: 1) When the local DE density \rho_{loc} is equal to
the global DE density \rho_v, the outflow reaches the global Hubble rate at the
distance R_2 = (1+z_v)R_v, where z_v is the global zero-acceleration redshift
(\approx 0.7 for the standard model). This is also the radius of the ideal
Einstein-Straus vacuole. 2) For a wide range of the local-to-global dark energy
ratio \rho_{loc}/\rho_v, the local flow reaches the known global rate (the
Hubble constant) at a distance R_2 \ga 1.5 \times R_v. Hence, R_v will be
between R_2/2 and R_2, giving upper and lower limits to \rho_{loc}/M. For the
Local Group, this supports the view that the local density is near the global
one. |
A Robust and Efficient Deep Learning Method for Dynamical Mass
Measurements of Galaxy Clusters: We demonstrate the ability of convolutional neural networks (CNNs) to
mitigate systematics in the virial scaling relation and produce dynamical mass
estimates of galaxy clusters with remarkably low bias and scatter. We present
two models, CNN$_\mathrm{1D}$ and CNN$_\mathrm{2D}$, which leverage this deep
learning tool to infer cluster masses from distributions of member galaxy
dynamics. Our first model, CNN$_\text{1D}$, infers cluster mass directly from
the distribution of member galaxy line-of-sight velocities. Our second model,
CNN$_\text{2D}$, extends the input space of CNN$_\text{1D}$ to learn on the
joint distribution of galaxy line-of-sight velocities and projected radial
distances. We train each model as a regression over cluster mass using a
labeled catalog of realistic mock cluster observations generated from the
MultiDark simulation and UniverseMachine catalog. We then evaluate the
performance of each model on an independent set of mock observations selected
from the same simulated catalog. The CNN models produce cluster mass
predictions with lognormal residuals of scatter as low as $0.132$ dex, greater
than a factor of 2 improvement over the classical $M$-$\sigma$ power-law
estimator. Furthermore, the CNN model reduces prediction scatter relative to
similar machine learning approaches by up to $17\%$ while executing in
drastically shorter training and evaluation times (by a factor of 30) and
producing considerably more robust mass predictions (improving prediction
stability under variations in galaxy sampling rate by $30\%$). | The distance to NGC1316 (Fornax A): yet another curious case: The distance of NGC1316, the brightest galaxy in Fornax, is an interesting
test for the cosmological distance scale. First, because Fornax is the 2nd
largest cluster of galaxies at <~25 Mpc after Virgo and, in contrast to Virgo,
has a small line-of-sight depth; and second, because NGC1316 is the galaxy with
the largest number of detected SNeIa, giving the opportunity to test the
consistency of SNeIa distances internally and against other indicators.
We measure SBF mags in NGC1316 from ground and space-based imaging data,
providing a homogeneous set of measurements over a wide wavelength interval.
The SBF, coupled with empirical and theoretical calibrations, are used to
estimate the distance to the galaxy. We present the first B-band SBF
measurements of NGC1316 and use them together with the optical and near-IR SBF
data to analyze the properties of field stars.
Our distance modulus m-M=31.59 +-0.05(stat) +-0.14(sys), when placed in a
consistent Cepheid distance scale, agrees with the results from other
indicators. However, our result is ~17% larger than the most recent estimate
based on SNeIa. Possible explanations for this disagreement are the
uncertainties on internal extinction, or calibration issues. Concerning the
stellar population analysis, we confirm earlier results from other indicators:
the field stars in NGC1316 are dominated by a solar metallicity, intermediate
age component. A substantial mismatch exists between B-band SBF models and
data, a behavior that can be accounted for by an enhanced percentage of hot
horizontal branch stars.
Our study of the SBF distance to NGC1316, and the comparison with distances
from other indicators, raises some concern about the homogeneity between the
calibrations of different indicators. If not properly placed in the same
reference scale, significant differences can occur, with dramatic impact on the
cosmological distance ladder. |
Physical properties of Lyman-alpha emitters at $z\sim 0.3$ from
UV-to-FIR measurements: The analysis of the physical properties of low-redshift Ly$\alpha$ emitters
(LAEs) can provide clues in the study of their high-redshift analogues. At $z
\sim 0.3$, LAEs are bright enough to be detected over almost the entire
electromagnetic spectrum and it is possible to carry out a more precise and
complete study than at higher redshifts. In this study, we examine the UV and
IR emission, dust attenuation, SFR and morphology of a sample of 23
GALEX-discovered star-forming (SF) LAEs at $z \sim 0.3$ with direct UV (GALEX),
optical (ACS) and FIR (PACS and MIPS) data. Using the same UV and IR limiting
luminosities, we find that LAEs at $z\sim 0.3$ tend to be less dusty, have
slightly higher total SFRs, have bluer UV continuum slopes, and are much
smaller than other galaxies that do not exhibit Ly$\alpha$ emission in their
spectrum (non-LAEs). These results suggest that at $z \sim 0.3$ Ly$\alpha$
photons tend to escape from small galaxies with low dust attenuation. Regarding
their morphology, LAEs belong to Irr/merger classes, unlike non-LAEs. Size and
morphology represent the most noticeable difference between LAEs and non-LAEs
at $z \sim 0.3$. Furthermore, the comparison of our results with those obtained
at higher redshifts indicates that either the Ly$\alpha$ technique picks up
different kind of galaxies at different redshifts or that the physical
properties of LAEs are evolving with redshift. | Checking the dark matter origin of 3.53 keV line with the Milky Way
center: We detect a line at 3.539 +/- 0.011 keV in the deep exposure dataset of the
Galactic Center region, observed with the XMM-Newton. The dark matter
interpretation of the signal observed in the Perseus galaxy cluster, the
Andromeda galaxy [1402.4119] and in the stacked spectra of galaxy clusters
[1402.2301], together with non-observation of the line in blank sky data, put
both lower and upper limits on the possible intensity of the line in the
Galactic Center data. Our result is consistent with these constraints for a
class of Milky Way mass models, presented previously by observers, and would
correspond to radiative decay dark matter lifetime tau_dm ~ (6-8) x 10^{27}
sec. Although it is hard to exclude an astrophysical origin of this line based
the Galactic Center data alone, this is an important consistency check of the
hypothesis that encourages to check it with more observational data that are
expected by the end of 2015. |
Discovery of Compton-thick quasars in the Sloan Digital Sky Survey: We present new and archival Chandra snapshot (10 ks each) observations of 15
optically identified (from the Sloan Digital Sky Survey, SDSS) Type 2 quasars
at z=0.40-0.73. When combined with existing X-ray data, this work provides
complete X-ray coverage for all 25 radio-quiet Type 2 quasars with
logL_[OIII]>9.28 L_sun from Zakamska et al. (2003). Two targets out of 15 were
not detected by Chandra and most of the remaining sources are X-ray weak, with
nine having less than 10 counts in the 0.5-8keV band. Low-to-moderate quality
spectral analysis was limited to three sources, whose properties are consistent
with the presence of column densities in the range NH~10^22-10^23 cm^-2 in the
source rest frame. If the [OIII] luminosity is a reliable proxy for the
intrinsic X-ray luminosity, the current X-ray data indicate that Compton-thick
quasars may hide among ~65 per cent of the SDSS Type 2 quasar population (L_{X,
meas}/L_{X, [OIII]}<0.01); however, since the Type 2 quasar sample is selected
on [OIII] luminosity, the estimated Compton-thick quasar fraction may be
overestimated. Using archival Spitzer observations, we find that ~50 per cent
of SDSS Type 2 quasars appear to be obscured by Compton-thick material based on
both the L_{X, meas}/L_{X, mid-IR} (where mid-IR corresponds to rest-frame 12.3
micron) and L_{X, meas}/L_{X, [OIII]} ratios. We use this information to
provide an estimate of the Compton-thick quasar number density at z=0.3-0.8,
which we find is in broad agreement with the expectations from X-ray background
models. | The HI gas content of galaxies around Abell 370, a galaxy cluster at z =
0.37: We used observations from the Giant Metrewave Radio Telescope to measure the
atomic hydrogen gas content of 324 galaxies around the galaxy cluster Abell 370
at a redshift of z = 0.37 (a look-back time of ~4 billion years). The HI 21-cm
emission from these galaxies was measured by coadding their signals using
precise optical redshifts obtained with the Anglo-Australian Telescope. The
average HI mass measured for all 324 galaxies is (6.6 +- 3.5)x10^9 solar
masses, while the average HI mass measured for the 105 optically blue galaxies
is (19.0 +- 6.5)x10^9 solar masses. The significant quantities of gas found
around Abell 370, suggest that there has been substantial evolution in the gas
content of galaxy clusters since redshift z = 0.37. The total amount of HI gas
found around Abell 370 is up to ~8 times more than that seen around the Coma
cluster, a nearby galaxy cluster of similar size. Despite this higher gas
content, Abell 370 shows the same trend as nearby clusters, that galaxies close
to the cluster core have lower HI gas content than galaxies further away. The
Abell 370 galaxies have HI mass to optical light ratios similar to local galaxy
samples and have the same correlation between their star formation rate and HI
mass as found in nearby galaxies. The average star formation rate derived from
[OII] emission and from de-redshifted 1.4 GHz radio continuum for the Abell 370
galaxies also follows the correlation found in the local universe. The large
amounts of HI gas found around the cluster can easily be consumed by the
observed star formation rate in the galaxies over the ~4 billion years (from z
= 0.37) to the present day. |
A Song of Shocks and Dynamo: Numerical Studies of a Galaxy Cluster
Merger in the HIMAG Project: With ENZO simulations run on the J\"ulich supercomputers, we have
investigated the evolution of magnetic fields in the largest cosmic structures
(namely galaxy clusters and filaments connecting them) with unprecedented
dynamical range. These simulations revealed the full development of the
small-scale dynamo in Eulerian cosmological magneto-hydrodynamical simulations.
The turbulent motions developed during the formation of clusters are energetic
enough to foster the growth of magnetic fields by several orders of magnitude,
starting from weak magnetic fields up strengths of $\sim \rm \mu G$ as
observed. Furthermore, shock waves are launched during cluster formation and
they are able to accelerate cosmic-ray electrons, that emit in the radio
wavelengths. Radio observations of this emission provide information on the
local magnetic field strength. We have incorporated, for the first time, the
cooling of cosmic-ray electrons when modelling this emission. In this
contribution, we present our advances in modelling these physical processes.
Here, we mostly focus on the most interesting object in our sample of galaxy
clusters, which shows the complexity of magnetic fields and the potential of
existing and future multi-wavelengths observations in the study of the weakly
collisional plasma on $\sim$ Megaparsecs scales. | Nuclear Radio Continuum Emission of Low-Luminosity Active Galactic
Nucleus NGC 4258: The nearby low-luminosity active galactic nucleus (LLAGN) NGC 4258 has a weak
radio continuum emission at the galactic center. Quasi-simultaneous
multi-frequency observations using the Very Large Array (VLA) from 5 GHz (6 cm)
to 22 GHz (1.3 cm) showed inverted spectra in all epochs, which were
intra-month variable, as well as complicated spectral features that cannot be
represented by a simple power law, indicating multiple blobs in nuclear jets.
Using the Nobeyama Millimeter Array (NMA), we discovered a large amplitude
variable emission at 100 GHz (3 mm), which had higher flux densities at most
epochs than those of the VLA observations. A James Clerk Maxwell Telescope
(JCMT) observation at 347 GHz (850 micron) served an upper limit of dust
contamination. The inverted radio spectrum of the nucleus NGC 4258 is
suggestive of an analogy to our Galactic center Sgr A*, but with three orders
of magnitude higher radio luminosity. In addition to the LLAGN M 81, we discuss
the nucleus of NGC 4258 as another up-scaled version of Sgr A*. |
Measuring Dark Matter Substructure with Galaxy-Galaxy Flexion Statistics: It is of great interest to measure the properties of substructures in dark
matter halos at galactic and cluster scales. Here we suggest a method to
constrain substructure properties using the variance of weak gravitational
flexion in a galaxy-galaxy lensing context. We show the effectiveness of
flexion variance in measuring substructures in N-body simulations of dark
matter halos, and present the expected galaxy-galaxy lensing signals. We show
the insensitivity of the method to the overall galaxy halo mass, and predict
the method's signal-to-noise for a space-based all-sky survey, showing that the
presence of substructure down to 10^9 M_\odot halos can be reliably detected. | Closing the Window on Strongly Interacting Dark Matter: Constraints are placed on the spin-independent interaction cross section of
dark matter with regular matter by refining two methods. First, dark
matter--cosmic ray interactions are considered, wherein cosmic ray protons
collide with dark matter to contribute to the gamma ray sky. This constraint is
developed using the NFW and Moore dark matter density profiles and new data
from the Fermi gamma ray space telescope. Second, the Earth capture scenario is
considered, wherein particles that are captured self-annihilate at Earth's
center, thus adding to its internal heat flow. The constraint presented here is
developed based on analysis of the drift time of dark matter particles through
Earth, modeled as a core composed of iron and a mantle composed of oxygen with
linear density gradients between layers. An analysis of the cosmic ray
constraint (which rules out dark matter--regular matter interaction cross
sections greater than its value) shows that it overlaps significantly with the
Earth drift time constraint (which rules out cross sections smaller than its
value), closing the window on strongly interacting dark matter particles up to
a mass of about 10^{17} GeV when combined with other exclusions. |
Cosmological application of the lens-redshift probability distribution
with improved galaxy-scale gravitational lensing sample: We conduct the cosmological analysis by using the lens-redshift distribution
test with updated galaxy-scale strong lensing sample, where the considered
scenarios involve three typical cosmological models (i.e., $\Lambda$CDM,
$\omega$CDM and $\omega_0\omega_a$CDM models) and three typical choices (i.e.,
non-evolving, power-law and exponential forms) for the velocity-dispersion
distribution function (VDF) of lens galaxies. It shows that degeneracies
between cosmological and VDF parameters lead to the shifts of estimates on the
parameters. The limits on $\Omega_{m0}$ from the lens-redshift distribution are
consistent with those from the Pantheon+ Type Ia supernova (SN Ia) sample at
68.3% confidence level, though the uncertainties on $\Omega_{m0}$ from the
former are about 3 to 8 times larger than those from the latter. The mean
values of $\Omega_{m0}$ shift to the larger values in the power-law VDF case
and to the lower values in the exponential VDF case, compared with those
obtained in the non-evolving VDF case. In the $\omega$CDM model, the limits on
$\omega_0$, i.e. the dark energy equation of state (EoS), are consistent with
those from the Pantheon+ sample at 68.3% confidence level, but the mean values
of $\omega_0$ from the former are significantly smaller than those from the
latter. In the $\omega_0\omega_a$CDM model, the uncertainties on $\omega_0$ are
dramatically enlarged compared with those obtained in the $\omega$CDM model;
moreover, the Markov chains of $\omega_a$, i.e. the time-varying slope of EoS,
do not achieve convergence in the three VDF cases. Overall, the lens-redshift
distribution test is more effective on constraining $\Omega_{m0}$ than on the
dark energy EoS. | AGN Feedback in the Compact Group of Galaxies HCG 62 - as revealed by
Chandra, XMM and GMRT data: As a part of an ongoing study of a sample of galaxy groups showing evidence
for AGN/hot gas interaction, we report on the preliminary results of an
analysis of new XMM and GMRT data of the X-ray bright compact group HCG 62.
This is one of the few groups known to possess very clear, small X-ray cavities
in the inner region as shown by the existing Chandra image. At higher
frequencies (>1.4 GHz) the cavities show minimal if any radio emission, but the
radio appears clearly at lower frequencies (<610 MHz). We compare and discuss
the morphology and spectral properties of the gas and of the radio source. We
find that the cavities are close to pressure balance, and that the jets have a
"light" hadronic content. By extracting X-ray surface brightness and
temperature profiles, we also identify a shock front located around 35 kpc to
the south-west of the group center. |
Luminosity Bias (II): The Cosmic Web of the First Stars: Understanding the formation and evolution of the first stars and galaxies
represents one of the most exciting frontiers in astronomy. Since the universe
was filled with neutral hydrogen at early times, the most promising method for
observing the epoch of the first stars is using the prominent 21-cm spectral
line of the hydrogen atom. Current observational efforts are focused on the
reionization era (cosmic age t ~ 500 Myr), with earlier times considered much
more challenging. However, the next frontier of even earlier galaxy formation
(t ~ 200 Myr) is emerging as a promising observational target. This is made
possible by a recently noticed effect of a significant relative velocity
between the baryons and dark matter at early times. The velocity difference
suppresses star formation, causing a unique form of early luminosity bias. The
spatial variation of this suppression enhances large-scale clustering and
produces a prominent cosmic web on 100 comoving Mpc scales in the 21-cm
intensity distribution. This structure makes it much more feasible for radio
astronomers to detect these early stars, and should drive a new focus on this
era, which is rich with little-explored astrophysics. | 3DEX: a code for fast spherical Fourier-Bessel decomposition of 3D
surveys: High-precision cosmology requires the analysis of large-scale surveys in 3D
spherical coordinates, i.e. spherical Fourier-Bessel decomposition. Current
methods are insufficient for future data-sets from wide-field cosmology
surveys. The aim of this paper is to present a public code for fast spherical
Fourier-Bessel decomposition that can be applied to cosmological data or 3D
data in spherical coordinates in other scientific fields. We present an
equivalent formulation of the spherical Fourier-Bessel decomposition that
separates radial and tangential calculations. We propose the use of the
existing pixelisation scheme HEALPix for a rapid calculation of the tangential
modes. 3DEX (3D EXpansions) is a public code for fast spherical Fourier-Bessel
decomposition of 3D all-sky surveys that takes advantage of HEALPix for the
calculation of tangential modes. We perform tests on very large simulations and
we compare the precision and computation time of our method with an optimised
implementation of the spherical Fourier-Bessel original formulation. For
surveys with millions of galaxies, computation time is reduced by a factor 4-12
depending on the desired scales and accuracy. The formulation is also suitable
for pre-calculations and external storage of the spherical harmonics, which
allows for additional speed improvements. The 3DEX code can accommodate data
with masked regions of missing data. 3DEX can also be used in other
disciplines, where 3D data are to be analysed in spherical coordinates. The
code and documentation can be downloaded at http://ixkael.com/blog/3dex. |
The Relevance of the Cosmological Constant for Lensing: This review surveys some recent developments concerning the effect of the
cosmological constant on the bending of light by a spherical mass in Kottler
(Schwarzchild-de Sitter) spacetime. Some proposals of how such an effect may be
put into a setting of gravitational lensing in cosmology are also discussed.
The picture that emerges from this review is that it seems fair to assert that
the contribution of $\Lambda$ to the bending of light has by now been well
established, while putting the $\Lambda$ light-bending terms into a
cosmological context is still subject to some interpretation and requires
further work and clarification. | Perturbation theory, effective field theory, and oscillations in the
power spectrum: We explore the relationship between the nonlinear matter power spectrum and
the various Lagrangian and Standard Perturbation Theories (LPT and SPT). We
first look at it in the context of one dimensional (1-d) dynamics, where 1LPT
is exact at the perturbative level and one can exactly resum the SPT series
into the 1LPT power spectrum. Shell crossings lead to non-perturbative effects,
and the PT ignorance can be quantified in terms of their ratio, which is also
the transfer function squared in the absence of stochasticity. At the order of
PT we work, this parametrization is equivalent to the results of effective
field theory (EFT), and can thus be expanded in terms of the same parameters.
We find that its radius of convergence is larger than the SPT loop expansion.
The same EFT parametrization applies to all SPT loop terms and, if
stochasticity can be ignored, to all N-point correlators. In 3-d, the LPT
structure is considerably more complicated, and we find that LPT models with
parametrization motivated by the EFT exhibit running with $k$ and that SPT is
generally a better choice. Since these transfer function expansions contain
free parameters that change with cosmological model their usefulness for
broadband power is unclear. For this reason we test the predictions of these
models on baryonic acoustic oscillations (BAO) and other primordial
oscillations, including string monodromy models, for which we ran a series of
simulations with and without oscillations. Most models are successful in
predicting oscillations beyond their corresponding PT versions, confirming the
basic validity of the model. |
Scale Symmetry in the Universe: Scale symmetry is a fundamental symmetry of physics that seems however not to
be fully realized in the universe. Here, we focus on the astronomical scales
ruled by gravity, where scale symmetry holds and gives rise to a truly scale
invariant distribution of matter, namely it gives rise to a fractal geometry. A
suitable explanation of the features of the fractal cosmic mass distribution is
provided by the nonlinear Poisson--Boltzmann--Emden equation. An alternative
interpretation of this equation is connected with theories of quantum gravity.
We study the fractal solutions of the equation and connect them with the
statistical theory of random multiplicative cascades, which originated in the
theory of fluid turbulence. The type of multifractal mass distributions so
obtained agrees with results from the analysis of cosmological simulations and
of observations of the galaxy distribution. | Gauge conditions in combined dark energy and dark matter systems: When analysing a system consisting of both dark matter and dark energy, an
often used practice in the literature is to neglect the perturbations in the
dark energy component. However, it has recently been argued, through the use of
numerical simulations, that one cannot do so. In this work we show that by
neglecting such perturbations one is implicitly making a choice of gauge. As
such, one no longer has the freedom to choose, for example, a gauge comoving
with the dark matter -- in fact doing so will give erroneous, gauge dependent
results. We obtain results consistent with the numerical simulations by using
the formalism of cosmological perturbation theory, and thus without resorting
to involved numerical calculations. |
Large-scale fluctuations in the cosmic ionising background: the impact
of beamed source emission: When modelling the ionisation of gas in the intergalactic medium after
reionisation, it is standard practice to assume a uniform radiation background.
This assumption is not always appropriate; models with radiative transfer show
that large-scale ionisation rate fluctuations can have an observable impact on
statistics of the Lyman-alpha forest. We extend such calculations to include
beaming of sources, which has previously been neglected but which is expected
to be important if quasars dominate the ionising photon budget. Beaming has two
effects: first, the physical number density of ionising sources is enhanced
relative to that directly observed; and second, the radiative transfer itself
is altered. We calculate both effects in a hard-edged beaming model where each
source has a random orientation, using an equilibrium Boltzmann hierarchy in
terms of spherical harmonics. By studying the statistical properties of the
resulting ionisation rate and HI density fields at redshift $z\sim 2.3$, we
find that the two effects partially cancel each other; combined, they
constitute a maximum $5\%$ correction to the power spectrum
$P_{\mathrm{HI}}(k)$ at $k=0.04 \, h/\mathrm{Mpc}$. On very large scales
($k<0.01\, h/\mathrm{Mpc}$) the source density renormalisation dominates; it
can reduce, by an order of magnitude, the contribution of ionising shot-noise
to the intergalactic HI power spectrum. The effects of beaming should be
considered when interpreting future observational datasets. | Omnipotent dark energy: A phenomenological answer to the Hubble tension: This paper introduces the class of omnipotent dark energy (DE) models
characterized by nonmonotonic energy densities that are capable of attaining
negative values with corresponding equation of state parameters featuring
phantom divide line (PDL) crossings and singularities. These nontrivial
features are phenomenologically motivated by findings of previous studies that
reconstruct cosmological functions from observations, and the success of
extensions of $\Lambda$CDM, whose actual or effective DE density is omnipotent,
in alleviating the observational discordance within $\Lambda$CDM. As an
example, we focus on one embodiment of omnipotent DE, viz., the DE
parametrization introduced in Di Valentino et al. [Dark energy with phantom
crossing and the H0 tension, Entropy 23, 404 (2021)] (DMS20). By updating and
extending the datasets used in the original paper where it was introduced, we
confirm the effectiveness of DMS20 in alleviating the observational
discrepancies. Additionally, we uncover that its negative DE density feature,
importance of which was not previously investigated, plays a crucial role in
alleviating the tensions, along with the PDL crossing feature that the
parametrization presupposes. In particular, we find that there is a positive
correlation between the $H_0$ parameter and the scale ($a_p$) at which DE
density transitions from negative to positive, in agreement with previous
studies that incorporate this transition feature. For our full dataset, the
model yields $H_0=70.05 \pm 0.64$ (68% CL) relaxing the $H_0$ tension with a
preference of crossing to negative DE densities ($a_p>0$ at 99% CL), along with
the constraint $a_m=0.922^{+0.041}_{-0.035}$ on the scale of the presupposed
PDL crossing. |
A Novel Approach to Constrain the Mass Ratio of Minor Mergers in
Elliptical Galaxies: Application to NGC 4889, the Brightest Cluster Galaxy in
Coma: Minor mergers are thought to be important for the build-up and structural
evolution of massive elliptical galaxies. In this work, we report the discovery
of a system of four shell features in NGC 4889, one of the brightest members of
the Coma cluster, using optical images taken with the Hubble Space Telescope
and the Sloan Digital Sky Survey. The shells are well aligned with the major
axis of the host and are likely to have been formed by the accretion of a small
satellite galaxy. We have performed a detailed two-dimensional photometric
decomposition of NGC 4889 and of the many overlapping nearby galaxies in its
vicinity. This comprehensive model allows us not only to firmly detect the
low-surface brightness shells, but, crucially, also to accurately measure their
luminosities and colors. The shells are bluer than the underlying stars at the
same radius in the main galaxy. We make use of the colors of the shells and the
color-magnitude relation of the Coma cluster to infer the luminosity (or mass)
of the progenitor galaxy. The shells in NGC 4889 appear to have been produced
by the minor merger of a moderate-luminosity (M_I ~ -18.7 mag) disk (S0 or
spiral) galaxy with a luminosity (mass) ratio of ~ 90:1 with respect to the
primary galaxy. The novel methodology presented in this work can be exploited
to decode the fossil record imprinted in the photometric substructure of other
nearby early-type galaxies. | Soliton Oscillations and Revised Constraints from Eridanus II of Fuzzy
Dark Matter: Fuzzy dark matter (FDM) has been a promising alternative to standard cold
dark matter. The model consists of ultralight bosons with mass $m_b \sim
10^{-22}$ eV and features a quantum-pressure-supported solitonic core that
oscillates. In this work, we show that the soliton density oscillations persist
even after significant tidal stripping of the outer halo. We report two
intrinsic yet distinct timescales associated, respectively, with the
ground-state soliton wavefunction $\tau_{00}$ and the soliton density
oscillations $\tau_\text{soliton}$, obeying $\tau_\text{soliton} /\tau_{00}
\simeq 2.3$. The central star cluster (SC) in Eridanus II has a characteristic
timescale $\tau_\text{soliton} / \tau_\text{SC} \sim 2$ to $3$ that deviates
substantially from unity. As a result, we demonstrate, both analytically and
numerically with three-dimensional self-consistent FDM simulations, that the
gravitational heating of the SC owing to soliton density oscillations is
negligible irrespective of $m_b$. We also show that the subhalo mass function
to form Eridanus II does not place a strong constraint on $m_b$. These results
are contrary to the previous findings by Marsh & Niemeyer (2019). |
The Link Between SCUBA and Spitzer: Cold Galaxies at z<1: We show that the far-IR properties of distant Luminous and Ultraluminous
InfraRed Galaxies (LIRGs and ULIRGs) are on average divergent from analogous
sources in the local Universe. Our analysis is based on Spitzer MIPS and IRAC
data of L_IR>10^10 L_solar, 70um-selected objects in the 0.1<z<2 redshift range
and supported by a comparison with the IRAS Bright Galaxy Sample. The majority
of the objects in our sample are described by Spectral Energy Distributions
(SEDs) which peak at longer wavelengths than local sources of equivalent total
infrared luminosity. This shift in SED peak wavelength implies a noticeable
change in the dust and/or star-forming properties from z~0 to the early
Universe, tending towards lower dust temperatures, indicative of strong
evolution in the cold dust, `cirrus', component. We show that these objects are
potentially the missing link between the well-studied local IR-luminous
galaxies, Spitzer IR populations and SCUBA sources -- the z<1 counterparts of
the cold z>1 SubMillimetre Galaxies (SMGs) discovered in blank-field
submillimetre surveys. The Herschel Space Observatory is well placed to fully
characterise the nature of these objects, as its coverage extends over a major
part of the far-IR/submm SED for a wide redshift range. | Classification of Extremely Red Objects in the Hubble Ultra Deep Field: In this paper we present a quantitative study of the classification of
Extremely Red Objects (EROs). The analysis is based on the multi-band spatial-
and ground-based observations (HST/ACS-$BViz$, HST/NICMOS-$JH$, VLT-$JHK$) in
the Hubble Ultra Deep Field (UDF). Over a total sky area of 5.50 arcmin$^2$ in
the UDF, we select 24 EROs with the color criterion $(i-K)_{\rm Vega}>3.9$,
corresponding to $(I-K)_{\rm Vega}\gsim4.0$, down to $\Kv=22$. We develop four
methods to classify EROs into Old passively evolving Galaxies (OGs) and Dusty
star-forming Galaxies (DGs), including $(i-K)$ vs. $(J-K)$ color diagram,
spectral energy distribution fitting method, Spitzer MIPS 24 $\mu$m image
matching, and nonparametric measure of galaxy morphology, and found that the
classification results from these methods agree well. Using these four
classification methods, we classify our EROs sample into 6 OGs and 8 DGs to
$\Kv<20.5$, and 8 OGs and 16 DGs to $\Kv<22$, respectively. The fraction of DGs
increases from 8/14 at $\Kv<20.5$ to 16/24 at $\Kv<22$. To study the morphology
of galaxies with its wavelength, we measure the central concentration and the
Gini coefficient for the 24 EROs in our sample in HST/ACS-$i,z$ and
HST/NICMOS-$J,H$ bands. We find that the morphological parameters of galaxies
in our sample depend on the wavelength of observation, which suggests that
caution is necessary when comparing single wavelength band images of galaxies
at a variety of redshifts. |
What are recent observations telling us in light of improved tests of
distance duality relation?: As an exact result required by the Etherington reciprocity theorem, the
cosmic distance duality relation (CDDR), $\eta(z)=D_L(z)(1+z)^{-2}/D_A(z)=1$
plays an essential part in modern cosmology. In this paper, we present a new
method ($\eta(z_i)/\eta(z_j)$) to use the measurements of ultra-compact
structure in radio quasars (QSO) and the latest observations of type Ia
supernova (SN Ia) to test CDDR. By taking the observations directly from SN Ia
and QSOs, one can completely eliminate the uncertainty caused by the
calibration of the absolute magnitudes of standard candles ($M_B$) and the
linear sizes of standard rulers ($l_m$). Benefit from the absence of nuisance
parameters involved in other currently available methods, our analysis
demonstrates no evidence for the deviation and redshift evolution of CDDR up to
$z=2.3$. The combination of our methodology and the machine learning Artificial
Neural Network (ANN) would produce $10^{-3}$ level constraints on the violation
parameter at high redshifts. Our results indicate perfect agreement between
observations and predictions, supporting the persisting claims that the
Etherington reciprocity theorem could still be the best description of our
universe. | Rainbow Cosmic Shear: Optimisation of Tomographic Bins: In this paper we address the problem of finding optimal cosmic shear
tomographic bins. We generalise the definition of a cosmic shear tomographic
bin to be a set of commonly labelled voxels in photometric colour space; rather
than bins defined directly in redshift. We explore this approach by using a
self-organising map to define the multi-dimensional colour space, and a we
define a 'label space' of connected regions on the self-organising map using
overlapping elliptical disks. This allows us to then find optimal labelling
schemes by searching the label space. We use a metric that is the
signal-to-noise ratio of a dark energy equation of state measurement, and in
this case we find that for up to five tomographic bins the optimal colour-space
labelling is an approximation of an equally-spaced binning in redshift; that is
in all cases the best configuration. We also show that such a redefinition is
more robust to photometric redshift outliers than a standard tomographic bin
selection. |
The Non-Gaussian Halo Mass Function with fNL, gNL and tauNL: Primordial non-Gaussianity has emerged as one of the most promising probes of
the inflationary epoch. While the cosmic microwave background and large-scale
halo bias currently provide the most stringent constraints on the non-Gaussian
parameter fNL, the abundance of dark matter halos is a complementary probe
which may allow tests of Gaussianity which are independent of the precise form
of non-Gaussian initial conditions. We study the halo mass function in N-body
simulations with a range of non-Gaussian initial conditions. In addition to the
usual fNL model, we consider gNL Phi^3-type non-Gaussianity and models where
the 4-point amplitude tauNL is an independent parameter. We introduce a new
analytic form for the halo mass function in the presence of primordial
non-Gaussianity, the "log-Edgeworth" mass function, and find good agreement
with the N-body simulations. The log-Edgeworth mass function introduces no free
parameters and can be constructed from first principles for any model of
primordial non-Gaussianity. | Cosmological imprints of string axions in plateau: We initiate a study on various cosmological imprints of string axions whose
scalar potentials have plateau regions. In such cases, we show that a delayed
onset of oscillation generically leads to a parametric resonance instability.
In particular, for ultralight axions, the parametric resonance can enhance the
power spectrum slightly below the Jeans scale, alleviating the tension with the
Lyman $\alpha$ forest observations. We also argue that a long-lasting resonance
can lead to an emission of gravitational waves at the frequency bands which are
detectable by gravitational wave interferometers and pulsar timing arrays. |
Constraints on cosmological coupling from the accretion history of
supermassive black holes: Coupling of black hole mass to the cosmic expansion has been suggested as a
possible path to understanding the dark energy content of the Universe. We test
this hypothesis by comparing the supermassive black hole (SMBH) mass density at
$z=0$ to the total mass accreted in AGN since $z=6$, to constrain how much of
the SMBH mass density can arise from cosmologically-coupled growth, as opposed
to growth by accretion. Using an estimate of the local SMBH mass density of
$\approx 1.0\times10^{6}\,$M$_{\odot}\,$Mpc$^{-1}$, a radiative accretion
efficiency, $\eta$: $0.05<\eta<0.3$, and the observed AGN luminosity density at
$z\approx 4$, we constrain the value of the coupling constant between the scale
size of the Universe and the black hole mass, $k$, to lie in the range
$0<k\stackrel{<}{_{\sim}}2$, below the value of $k=3$ needed for black holes to
be the source term for dark energy. Initial estimates of the gravitational wave
background using pulsar timing arrays, however, favor a higher SMBH mass
density at $z=0$. We show that if we adopt such a mass density at $z=0$ of
$\approx 7.4\times 10^{6}\,$M$_{\odot}\,$Mpc$^{-1}$, this makes $k=3$ viable
even for low radiative efficiencies, and may exclude non-zero cosmological
coupling. We conclude that, although current estimates of the SMBH mass density
based on the black hole mass -- bulge mass relation probably exclude $k=3$, the
possibility remains open that, if the GWB is due to SMBH mergers, $k>2$ is
preferred. | Line profile and continuum variability in the very broad-line Seyfert
galaxy Mrk 926: We present results of an intensive spectroscopic variability campaign of the
very broad-line Seyfert 1 galaxy Mrk 926. Our aim is to investigate the
broad-line region (BLR) by studying the intensity and line profile variations
of this galaxy on short timescales. High signal-to-noise ratio(S/N) spectra
were taken with the 9.2m Hobby-Eberly Telescope (HET) in identical conditions
during two observing campaigns in 2004 and 2005. After the spectral reduction
and internal calibration we achieved a relative flux accuracy of better than
1%. The rms profiles of the very broad Balmer lines have shapes that differ
from their mean line profiles, consisting of two inner (v $\lesssim \pm{}$ 6000
km s$^{-1}$) and two outer (v $\gtrsim \pm{}$ 6000 km s$^{-1}$) line components
in addition to a central component (v $\lesssim \pm{}$ 600 km s$^{-1}$). These
outer and inner line segments varied with different amplitudes during our
campaign. The radius of the BLR is very small with an upper limit of 2
light-days for the H$\beta$ BLR size. We derived an upper limit to the central
black hole mass of $ M= 11.2 \times 10^{7} M_{\odot} $. The 2-D
cross-correlation functions CCF($\tau$,$v$) of H$\beta$ and H$\alpha$ are flat
within the error limits. The response of the Balmer line segments with respect
to continuum variations is different in the outer and inner wings of H$\alpha$
and H$\beta$. This double structure in the response curves - of two separate
inner and outer components - has also been seen in the rms line profiles. We
conclude that the outer and inner line segments originate in different regions
and/or under different physical conditions. |
The phase space density of fermionic dark matter haloes: We have performed a series of numerical experiments to investigate how the
primordial thermal velocities of fermionic dark matter particles affect the
physical and phase space density profiles of the dark matter haloes into which
they collect. The initial particle velocities induce central cores in both
profiles, which can be understood in the framework of phase space density
theory. We find that the maximum coarse-grained phase space density of the
simulated haloes (computed in 6 dimensional phase space using the EnBid code)
is very close to the theoretical fine-grained upper bound, while the pseudo
phase space density, Q ~ {\rho}/{\sigma}^3, overestimates the maximum phase
space density by up to an order of magnitude. The density in the inner regions
of the simulated haloes is well described by a 'pseudo-isothermal' profile with
a core. We have developed a simple model based on this profile which, given the
observed surface brightness profile of a galaxy and its central velocity
dispersion, accurately predicts its central phase space density. Applying this
model to the dwarf spheroidal satellites of the Milky Way yields values close
to 0.5 keV for the mass of a hypothetical thermal warm dark matter particle,
assuming the satellite haloes have cores produced by warm dark matter free
streaming. Such a small value is in conflict with the lower limit of 1.2 keV
set by observations of the Lyman-{\alpha} forest. Thus, if the Milky Way dwarf
spheroidal satellites have cores, these are likely due to baryonic processes
associated with the forming galaxy, perhaps of the kind proposed by Navarro,
Eke and Frenk and seen in recent simulations of galaxy formation in the cold
dark matter model. | Large Scale Structure Observations: Galaxy Surveys are enjoying a renaissance thanks to the advent of
multi-object spectrographs on ground-based telescopes. The last 15 years have
seen the fruits of this experimental advance, including the 2-degree Field
Galaxy Redshift Survey (2dFGRS; Colless et al. 2003) and the Sloan Digital Sky
Survey (SDSS; York et al. 2000). Most recently, the Baryon Oscillation
Spectroscopic Survey (BOSS; Dawson et al. 2013), part of the SDSS-III project
(Eisenstein et al. 2011), has provided the largest volume of the low-redshift
Universe ever surveyed with a galaxy density useful for high-precision
cosmology. This set of lecture notes looks at some of the physical processes
that underpin these measurements, the evolution of measurements themselves, and
looks ahead to the next 15 years and the advent of surveys such as the enhanced
Baryon Oscillation Spectroscopic Survey (eBOSS), the Dark Energy Spectroscopic
Instrument (DESI) and the ESA Euclid satellite mission. |
Fractal properties of SDSS quasars: The distribution of SDSS quasars is described. The dependence of
observational number of quasars within distances to an observer less than r on
distance r is found to be the power law with correlation dimension value equal
2,71 in redshift range 0,35 < z < 2,30 for the flat Universe filled with cold
dust. The quasar distribution on the celestial sphere is characterized by power
laws as well with correlation dimension value equal from 1,49 to 1,58 for
different redshift layers in the same range. These properties are evidences of
fractality. | The Massive and Distant Clusters of WISE Survey II: Initial
Spectroscopic Confirmation of z ~ 1 Galaxy Clusters Selected from 10,000
Square Degrees: We present optical and infrared imaging and optical spectroscopy of galaxy
clusters which were identified as part of an all-sky search for high-redshift
galaxy clusters, the Massive and Distant Clusters of WISE Survey (MaDCoWS). The
initial phase of MaDCoWS combined infrared data from the all-sky data release
of the Wide-field Infrared Survey Explorer (WISE) with optical data from the
Sloan Digital Sky Survey (SDSS) to select probable z ~ 1 clusters of galaxies
over an area of 10,000 deg^2. Our spectroscopy confirms 19 new clusters at 0.7
< z < 1.3, half of which are at z > 1, demonstrating the viability of using
WISE to identify high-redshift galaxy clusters. The next phase of MaDCoWS will
use the greater depth of the AllWISE data release to identify even higher
redshift cluster candidates. |
Spurious Shear in Weak Lensing with LSST: The complete 10-year survey from the Large Synoptic Survey Telescope (LSST)
will image $\sim$ 20,000 square degrees of sky in six filter bands every few
nights, bringing the final survey depth to $r\sim27.5$, with over 4 billion
well measured galaxies. To take full advantage of this unprecedented
statistical power, the systematic errors associated with weak lensing
measurements need to be controlled to a level similar to the statistical
errors.
This work is the first attempt to quantitatively estimate the absolute level
and statistical properties of the systematic errors on weak lensing shear
measurements due to the most important physical effects in the LSST system via
high fidelity ray-tracing simulations. We identify and isolate the different
sources of algorithm-independent, \textit{additive} systematic errors on shear
measurements for LSST and predict their impact on the final cosmic shear
measurements using conventional weak lensing analysis techniques. We find that
the main source of the errors comes from an inability to adequately
characterise the atmospheric point spread function (PSF) due to its high
frequency spatial variation on angular scales smaller than $\sim10'$ in the
single short exposures, which propagates into a spurious shear correlation
function at the $10^{-4}$--$10^{-3}$ level on these scales. With the large
multi-epoch dataset that will be acquired by LSST, the stochastic errors
average out, bringing the final spurious shear correlation function to a level
very close to the statistical errors. Our results imply that the cosmological
constraints from LSST will not be severely limited by these
algorithm-independent, additive systematic effects. | Testing Standard Cosmology with Large Scale Structure: The galaxy power spectrum contains information on the growth of structure,
the growth rate through redshift space distortions, and the cosmic expansion
through baryon acoustic oscillation features. We study the ability of two
proposed experiments, BigBOSS and JDEM-PS, to test the cosmological model and
general relativity. We quantify the latter result in terms of the gravitational
growth index \gamma, whose value in general relativity is \gamma\approx 0.55.
Significant deviations from this value could indicate new physics beyond the
standard model of cosmology. The results show that BigBOSS (JDEM-PS) would be
capable of measuring \gamma with an uncertainty \sigma(\gamma) = 0.043 (0.054),
which tightens to \sigma(\gamma) = 0.031 (0.038) if we include Stage III data
priors, marginalizing over neutrino mass, time varying dark energy equation of
state, and other parameters. For all dark energy parameters and related figures
of merit the two experiments give comparable results. We also carry out some
studies of the influence of redshift range, resolution, treatment of
nonlinearities, and bias evolution to enable further improvement. |
Do galaxies form a spectroscopic sequence?: We identify a spectroscopic sequence of galaxies, analogous to the Hubble
sequence of morphological types, based on the Automatic Spectroscopic K-means
(ASK) classification. Considering galaxy spectra as multidimensional vectors,
the majority of the spectral classes are distributed along a well defined curve
going from the earliest to the latest types, suggesting that the optical
spectra of normal galaxies can be described in terms of a single affine
parameter. Optically-bright active galaxies, however, appear as an independent,
roughly orthogonal branch that intersects the main sequence exactly at the
transition between early and late types. | Intermediate age stars as origin of the low velocity dispersion nuclear
ring in Mrk1066: We report the first two-dimensional stellar population synthesis in the
near-infrared of the nuclear region of an active galaxy, namely Mrk1066.
We have used integral field spectroscopy with adaptive optics at the Gemini
North Telescope to map the to map the age distribution of the stellar
population in the inner 300 pc at a spatial resolution of 35 pc. An old stellar
population component (age >5Gyr) is dominant within the inner ~160pc, which we
attribute to the galaxy bulge. Beyond this region, up to the borders of the
observation field (~300 pc), intermediate age components (0.3-0.7Gyr) dominate.
We find a spatial correlation between this intermediate age component and a
partial ring of low stellar velocity dispersions (sigma). Low-sigma nuclear
rings have been observed in other active galaxies and our result for Mrk1066
suggests that they are formed by intermediate age stars. This age is consistent
with an origin for the low-sigma rings in a past event which triggered an
inflow of gas and formed stars which still keep the colder kinematics (as
compared to that of the bulge) of the gas from which they have formed. At the
nucleus proper we detect, in addition, two unresolved components: a compact
infrared source, consistent with an origin in hot dust with mass ~1.9x10^{-2}
M_Sun, and a blue featureless power-law continuum, which contributes with only
~15% of the flux at 2.12 microns. |
The Dark Side of Galaxy Color: evidence from new SDSS measurements of
galaxy clustering and lensing: The age matching model has recently been shown to predict correctly the
luminosity L and g-r color of galaxies residing within dark matter halos. The
central tenet of the model is intuitive: older halos tend to host galaxies with
older stellar populations. In this paper, we demonstrate that age matching also
correctly predicts the g-r color trends exhibited in a wide variety of
statistics of the galaxy distribution for stellar mass M* threshold samples. In
particular, we present new measurements of the galaxy two-point correlation
function and the galaxy-galaxy lensing signal as a function of M* and g-r color
from the Sloan Digital Sky Survey, and show that age matching exhibits
remarkable agreement with these and other statistics of low-redshift galaxies.
In so doing, we also demonstrate good agreement between the galaxy-galaxy
lensing observed by SDSS and the signal predicted by abundance matching, a new
success of this model. We describe how age matching is a specific example of a
larger class of Conditional Abundance Matching models (CAM), a theoretical
framework we introduce here for the first time. CAM provides a general
formalism to study correlations at fixed mass between any galaxy property and
any halo property. The striking success of our simple implementation of CAM
provides compelling evidence that this technique has the potential to describe
the same set of data as alternative models, but with a dramatic reduction in
the required number of parameters. CAM achieves this reduction by exploiting
the capability of contemporary N-body simulations to determine dark matter halo
properties other than mass alone, which distinguishes our model from
conventional approaches to the galaxy-halo connection. | NSC++: Non-Standard Cosmologies in C++: We introduce NSC++, a header-only C++ library that simulates the evolution of
the plasma and a decaying fluid in the early Universe. NSC++ can be used in C++
programs or called directly from python scripts without significant overhead.
There is no special installation process or external dependencies. Furthermore,
there are example programs that can be modified to handle several cases. |
Broad HI Absorbers as Metallicity-Independent Tracers of the Warm-Hot
Intergalactic Medium: Thermally broadened Ly alpha absorbers (BLAs) offer an alternative method to
highly-ionized metal lines for tracing the WHIM. We compile a catalog of
reliable BLA candidates along seven AGN sight lines from a larger set of Lya
absorbers observed by HST/STIS. We compare our measurements based on
independent reduction and analysis of the data to those published by other
research groups. Purported BLAs are grouped into probable (15), possible (48)
and non-BLA (56) categories. We infer a line frequency (dN/dz)_BLA=18+-11,
comparable to observed OVI absorbers. There is significant overlap between BLA
and OVI absorbers (20-40%) and we find that OVI detections in BLAs are found
closer to galaxies than OVI non-detections. Based on 164 measured COG HI line
measurements, we statistically correct the observed line widths via a Monte-
Carlo simulation. Gas temperature and neutral fraction f(HI) are inferred from
these statistically-corrected line widths and lead to a distribution of total
hydrogen columns. We find Omega_BLA=(6.3+1.1-0.8)x10^-3. There are a number of
critical systematic assumptions implicit in this calculation, and we discuss
how each affects our results and those of previously published work. Taking our
value, current OVI and BLA surveys can account for ~20% of the baryons in the
local universe. Finally, we present new, high-S/N observations of several of
the BLA candidate lines from Early Release Observations made by the Cosmic
Origins Spectrograph on HST. | Driving the Gaseous Evolution of Massive Galaxies in the Early Universe: Studies of the molecular interstellar medium that fuels star formation and
supermassive black hole growth in galaxies at cosmological distances have
undergone tremendous progress over the past few years. Based on the detection
of molecular gas in >120 galaxies at z=1 to 6.4, we have obtained detailed
insight on how the amount and physical properties of this material in a galaxy
are connected to its current star formation rate over a range of galaxy
populations. Studies of the gas dynamics and morphology at high spatial
resolution allow us to distinguish between gas-rich mergers in different stages
along the "merger sequence" and disk galaxies. Observations of the most massive
gas-rich starburst galaxies out to z>5 provide insight into the role of cosmic
environment for the early growth of present-day massive spheroidal galaxies.
Large-area submillimeter surveys have revealed a rare population of extremely
far-infrared-luminous gas-rich high-redshift objects, which is dominated by
strongly lensed, massive starburst galaxies. These discoveries have greatly
improved our understanding of the role of molecular gas in the evolution of
massive galaxies through cosmic time. |
A Dark Energy Camera Search for an Optical Counterpart to the First
Advanced LIGO Gravitational Wave Event GW150914: We report initial results of a deep search for an optical counterpart to the
gravitational wave event GW150914, the first trigger from the Advanced LIGO
gravitational wave detectors. We used the Dark Energy Camera (DECam) to image a
102 deg$^2$ area, corresponding to 38% of the initial trigger high-probability
sky region and to 11% of the revised high-probability region. We observed in i
and z bands at 4-5, 7, and 24 days after the trigger. The median $5\sigma$
point-source limiting magnitudes of our search images are i=22.5 and z=21.8
mag. We processed the images through a difference-imaging pipeline using
templates from pre-existing Dark Energy Survey data and publicly available
DECam data. Due to missing template observations and other losses, our
effective search area subtends 40 deg$^{2}$, corresponding to 12% total
probability in the initial map and 3% of the final map. In this area, we search
for objects that decline significantly between days 4-5 and day 7, and are
undetectable by day 24, finding none to typical magnitude limits of i=
21.5,21.1,20.1 for object colors (i-z)=1,0,-1, respectively. Our search
demonstrates the feasibility of a dedicated search program with DECam and bodes
well for future research in this emerging field. | Search for the correlations between host properties and ${\rm
DM_{host}}$ of fast radio bursts: constraints on the baryon mass fraction in
IGM: The application of fast radio bursts (FRBs) as probes to investigate
astrophysics and cosmology requires the proper modelling of the dispersion
measures of Milky Way (${\rm DM_{MW}}$) and host galaxy (${\rm DM_{host}}$).
${\rm DM_{MW}}$ can be estimated using the Milky Way electron models, such as
NE2001 model and YMW16 model. However, ${\rm DM_{host}}$ is hard to model due
to limited information on the local environment of FRBs. In this paper, using
17 well-localized FRBs, we search for the possible correlations between ${\rm
DM_{host}}$ and the properties of host galaxies, such as the redshift, the
stellar mass, the star-formation rate, the age of galaxy, the offset of FRB
site from galactic center, and the half-light radius. We find no strong
correlation between ${\rm DM_{host}}$ and any of the host property. Assuming
that ${\rm DM_{host}}$ is a constant for all host galaxies, we constrain the
fraction of baryon mass in the intergalactic medium today to be $f_{\rm
IGM,0}=0.78_{-0.19}^{+0.15}$. If we model ${\rm DM_{host}}$ as a log-normal
distribution, however, we obtain a larger value, $f_{\rm
IGM,0}=0.83_{-0.17}^{+0.12}$. Based on the limited number of FRBs, no strong
evidence for the redshift evolution of $f_{\rm IGM}$ is found. |
Can the Near-IR Fluctuations Arise from Known Galaxy Populations?: Spatial Fluctuations in the Cosmic Infrared Background have now been measured
out to sub-degree scales showing a strong clustering signal from unresolved
sources. We attempt to explain these measurement by considering faint galaxy
populations at z<6 as the underlying sources for this signal using 233 measured
UV, optical and NIR luminosity functions (LF) from a variety of surveys
covering a wide range of redshifts. We populate the lightcone and calculate the
total emission redshifted into the near-IR bands in the observer frame and
recover the observed optical and near-IR galaxy counts to a good accuracy.
Using a halo model for the clustering of galaxies with an underlying LCDM
density field, we find that fluctuations from known galaxy populations are
unable to account for the large scale CIB clustering signal seen by HST/NICMOS,
Spitzer/IRAC and AKARI/IRC and continue to diverge out to larger angular
scales. Our purely empirical reconstruction shows that known galaxy populations
are not responsible for the bulk of the fluctuation signal seen in the
measurements and suggests an unknown population of very faint and highly
clustered sources dominating the signal. | SDSS galaxies with double-peaked emission lines: double starbursts or
AGNs?: With the aim of investigating galaxies with two strong simultaneous
starbursts, we have extracted a sample of galaxies with double-peaked emission
lines in their global spectra from the SDSS spectral database. We then fitted
the emission lines Halpha, Hbeta, [OIII]5007, [NII]6584, [SII]6717 and
[SII]6731 of 129 spectra by two Gaussians to separate the radiation of the two
(blue and red) components. A more or less reliable decomposition of the all
those emission lines have been found for 55 spectra. Using a standard BPT
classification diagram, we have been able to divide the galaxies from our
sample into two subsamples: Sample A consisting of 18 galaxies where both
components belong to the photoionised class of objects, and Sample B containing
37 galaxies which show non-thermal ionisation (AGNs). We have examined the
properties of the blue and red components, and found that the differences
between radial velocities of components lie within 200 - 400 km/s for galaxies
of both subsamples. The equivalent number of ionising stars is in the range
10^4 - 10^5 O7V stars for each component in the galaxies of Sample A. We have
estimated the oxygen and nitrogen abundances as well as the electron
temperatures for each component using the recent NS-calibration and from global
spectra for galaxies from Sample A using both the NS and ON-calibration. We
have found that the global oxygen abundance is typically in between the
measured abundances of individual components for our sample of galaxies, and
that both calibrations provide consistent global abundances. Finally, we
suggest the classical O/H -- N/O diagram is used to test the reliability of the
dividing lines between starburst-like objects and AGNs in the so-called BPT
diagram. |
Unusually Luminous Giant Molecular Clouds in the Outer Disk of M33: We use high spatial resolution (~7pc) CARMA observations to derive detailed
properties for 8 giant molecular clouds (GMCs) at a galactocentric radius
corresponding to approximately two CO scale lengths, or ~0.5 optical radii
(r25), in the Local Group spiral galaxy M33. At this radius, molecular gas
fraction, dust-to-gas ratio and metallicity are much lower than in the inner
part of M33 or in a typical spiral galaxy. This allows us to probe the impact
of environment on GMC properties by comparing our measurements to previous data
from the inner disk of M33, the Milky Way and other nearby galaxies. The outer
disk clouds roughly fall on the size-linewidth relation defined by
extragalactic GMCs, but are slightly displaced from the luminosity-virial mass
relation in the sense of having high CO luminosity compared to the inferred
virial mass. This implies a different CO-to-H2 conversion factor, which is on
average a factor of two lower than the inner disk and the extragalactic
average. We attribute this to significantly higher measured brightness
temperatures of the outer disk clouds compared to the ancillary sample of GMCs,
which is likely an effect of enhanced radiation levels due to massive star
formation in the vicinity of our target field. Apart from brightness
temperature, the properties we determine for the outer disk GMCs in M33 do not
differ significantly from those of our comparison sample. In particular, the
combined sample of inner and outer disk M33 clouds covers roughly the same
range in size, linewidth, virial mass and CO luminosity than the sample of
Milky Way GMCs. When compared to the inner disk clouds in M33, however, we find
even the brightest outer disk clouds to be smaller than most of their inner
disk counterparts. This may be due to incomplete sampling or a potentially
steeper cloud mass function at larger radii. | Decaying turbulence and magnetic fields in galaxy clusters: We explore the decay of turbulence and magnetic fields generated by
fluctuation dynamo action in the context of galaxy clusters where such a
decaying phase can occur in the aftermath of a major merger event. Using
idealized numerical simulations that start from a kinetically dominated regime
we focus on the decay of the steady state rms velocity and the magnetic field
for a wide range of conditions that include varying the compressibility of the
flow, the forcing wave number, and the magnetic Prandtl number. Irrespective of
the compressibility of the flow, both the rms velocity and the rms magnetic
field decay as a power-law in time. In the subsonic case we find that the
exponent of the power-law is consistent with the $-3/5$ scaling reported in
previous studies. However, in the transonic regime both the rms velocity and
the magnetic field initially undergo rapid decay with an $\approx t^{-1.1}$
scaling with time. This is followed by a phase of slow decay where the decay of
the rms velocity exhibits an $\approx -3/5$ scaling in time, while the rms
magnetic field scales as $\approx -5/7$. Furthermore, analysis of the Faraday
rotation measure reveals that the Faraday RM decays also decays as a power law
in time $\approx t^{-5/7}$; steeper than the $\sim t^{-2/5}$ scaling obtained
in previous simulations of magnetic field decay in subsonic turbulence. Apart
from galaxy clusters, our work can have potential implications in the study of
magnetic fields in elliptical galaxies. |
Foreground model recognition through Neural Networks for CMB B-mode
observations: In this work we present a Neural Network (NN) algorithm for the
identification of the appropriate parametrization of diffuse polarized Galactic
emissions in the context of Cosmic Microwave Background (CMB) $B$-mode
multi-frequency observations. In particular, we have focused our analysis on
low frequency foregrounds relevant for polarization observation: namely
Galactic Synchrotron and Anomalous Microwave Emission (AME). We have
implemented and tested our approach on a set of simulated maps corresponding to
the frequency coverage and sensitivity represented by future satellite and low
frequency ground based probes. The NN efficiency in recognizing the right
parametrization of foreground emission in different sky regions reaches an
accuracy of about $90\%$. We have compared this performance with the $\chi^{2}$
information following parametric foreground estimation using multi-frequency
fitting, and quantify the gain provided by a NN approach. Our results show the
relevance of model recognition in CMB $B$-mode observations, and highlight the
exploitation of dedicated procedures to this purpose. | Are Galaxy Clusters Suggesting an Accelerating Universe Independent of
SNe Ia and Gravity Metric Theory?: A kinematic method to access cosmic acceleration based exclusively on the
Sunyaev-Zel'dovich effect (SZE) and X-ray surface brightness data from galaxy
clusters is proposed. By using the SZE/X-ray data from 38 galaxy clusters
[Bonament et al., Astrop. J. 647, 25 (2006)], we find that the present Universe
is accelerating and that the transition from an earlier decelerating to a late
time accelerating regime occurred relatively recent. Such results are fully
independent on the validity of any metric gravity theory, the possible
matter-energy contents filling the Universe, as well as on the SNe type Ia
Hubble diagram from which the present acceleration was inferred. The ability of
the ongoing Planck satellite mission to obtain tighter constraints on the
expansion history through SZE/X-ray angular diameters is also discussed. Two
simple simulations of future Planck data suggest that such technique will be
competitive with supernova data besides being complementary to it. |
Observational constraints on the interacting Ricci dark energy model: We consider an extension of the holographic Ricci dark energy model by
introducing an interaction between dark energy and matter. In this model, the
dark energy density is given by $rho_{Lambda}=-frac{1}{2}alpha M_{p}^{2}{R}$,
where ${R}$ is the Ricci scalar curvature, $M_{p}$ is the reduced Planck mass,
and $alpha$ is a dimensionless parameter. The interaction rate is given by
$Q=gamma H rho_{Lambda}$, where $H$ is the Hubble expansion rate, and $gamma$
is a dimensionless parameter. We investigate current observational constraints
on this model by applying the type Ia supernovae, the baryon acoustic
oscillation and the CMB anisotropy data. It is shown that a nonvanishing
interaction rate is favored by the observations. The best fit values are
$alpha=0.45 pm 0.03$ and $gamma=0.15 pm 0.03$ for the present dark energy
density parameter $Omega_{Lambda 0}=0.73 pm0.03$. | BEC dark matter, Zeldovich approximation and generalized Burgers
equation: If the dark matter in the universe is a self-gravitating Bose-Einstein
condensate (BEC) with quartic self-interaction described by the
Gross-Pitaevskii-Poisson system, the adhesion model, the Burgers equation and
the cosmological Kardar-Parisi-Zhang (KPZ) equation that have been introduced
heuristically to solve the problems inherent to cold dark matter (CDM) models
find a natural justification and an interesting generalization. |
Fast magnetic field amplification in distant galaxyclusters: In the present-day Universe, magnetic fields pervade galaxy clusters, with
strengths of a few microGauss obtained from Faraday Rotation. Evidence for
cluster magnetic fields is also provided by Megaparsec-scale radio emission,
namely radio halos and relics. These are commonly found in merging systems and
are characterized by a steep radio spectrum. It is widely believed that
magneto-hydrodynamical turbulence and shock-waves (re-)accelerate cosmic rays,
producing halos and relics. The origin and the amplification of magnetic fields
in clusters is not well understood. It has been proposed that turbulence drives
a small-scaledynamo that amplifies seed magnetic fields (primordial and/or
injected by galactic outflows, as active galactic nuclei, starbursts, or
winds). At high redshift, radio halos are expected to be faint, due to the
Inverse Compton losses and dimming effect with distance. Moreover, Faraday
Rotation measurements are difficult to obtain. If detected, distant radio
halosprovide an alternative tool to investigate magnetic field amplification.
Here, we report LOFAR observations which reveal diffuse radio emission in
massive clusters when the Universe was only half of its present age, with a
sample occurrence fraction of about 50%. The high radio luminosities indicate
that these clusters have similar magnetic field strengths to those in nearby
clusters, and suggest that magnetic field amplification is fast during the
first phases ofcluster formation. | The Dynamic Evolution of Young Extragalactic Radio Sources: The evolution of symmetric extragalactic radio sources can be characterized
by four distinct growth stages of the radio luminosity versus size of the
source. The interaction of the jet with the ambient medium results in the
formation and evolution of sources with non-standard (flaring) morphology. In
addition, cessation or restarting of the jet power and obstruction of the jet
will also result in distinct morphological structures. The radio source
population may thus be classified in morphological types that indicate the
prevailing physical processes. Compact symmetric objects (CSOs) occupy the
earliest evolutionary phase of symmetric radio sources and their dynamical
behavior is fundamental for any further evolution. Analysis of CSO dynamics is
presented for a sample of 24 CSOs with known redshift and hotspot separation
velocity and with a large range of radio power. Observables such as radio
power, separation between two hotspots, hotspot separation velocity, and
kinematic age of the source are found to be generally consistent with the
self-similar predictions for individual sources that reflect the varying
density structure of the ambient interstellar medium. Individual sources behave
different from the group as a whole. The age and size statistics confirm that a
large fraction of CSOs does not evolve into extended doubles. |
Evolution of the Cosmological Horizons in a Concordance Universe: The particle and event horizons are widely known and studied concepts, but
the study of their properties, in particular their evolution, have only been
done so far considering a single state equation in a decelerating universe.
This paper is the first of two where we study this problem from a general point
of view. Specifically, this paper is devoted to the study of the evolution of
these cosmological horizons in an accelerated universe with two state
equations, cosmological constant and dust. We have obtained closed-form
expressions for the horizons, which have allowed us to compute their velocities
in terms of their respective recession velocities that generalize the previous
results for one state equation only. With the equations of state considered, it
is proved that both velocities remain always positive. | Comparative Study of Asymmetry Origin of Galaxies in Different
Environments. II. Near-Infrared observations: In this second paper of two analyses, we present near-infrared (NIR)
morphological and asymmetry studies performed in sample of 92 galaxies found in
different density environments: galaxies in Compact Groups (HCGs), Isolated
Pairs of Galaxies (KPGs), and Isolated Galaxies (KIGs). Both studies have
proved useful for identifying the effect of interactions on galaxies. In the
NIR, the properties of the galaxies in HCGs, KPGs, and KIGs are more similar
than they are in the optical. This is because the NIR band traces the older
stellar populations, which formed earlier and are more relaxed than the younger
populations. However, we found asymmetries related to interactions in both KPG
and HCG samples. In HCGs, the fraction of asymmetric galaxies is even higher
than what we found in the optical. In the KPGs the interactions look like very
recent events, while in the HCGs galaxies are more morphologically evolved and
show properties suggesting they suffered more frequent interactions. The key
difference seems to be the absence of star formation in the HCGs; while
interactions produce intense star formation in the KPGs, we do not see this
effect in the HCGs. This is consistent with the dry merger hypothesis (Coziol &
Plauchu-Frayn 2007); the interaction between galaxies in compact groups, (CGs),
is happening without the presence of gas. If the gas was spent in stellar
formation (to build the bulge of the numerous early-type galaxies), then the
HCGs possibly started interacting sometime before the KPGs. On the other hand,
the dry interaction condition in CGs suggests that the galaxies are on merging
orbits, and consequently such system cannot be that much older either.
[abridge] |
A Giant Metrewave Radio Telescope/Chandra view of IRAS 09104+4109: A
type 2 QSO in a cooling flow: IRAS 09104+4109 is a rare example of a dust enshrouded type 2 QSO in the
centre of a cool-core galaxy cluster. Previous observations of this z=0.44
system showed that as well as powering the hyper-luminous infrared emission of
the cluster-central galaxy, the QSO is associated with a double-lobed radio
source. However, the steep radio spectral index and misalignment between the
jets and ionised optical emission suggested that the orientation of the QSO had
recently changed. We use a combination of new, multi-band Giant Metrewave Radio
Telescope observations and archival radio data to confirm that the jets are no
longer powered by the QSO, and estimate their age to be 120-160 Myr. This is in
agreement with the ~70-200 Myr age previously estimated for star-formation in
the galaxy. Previously unpublished Very Long Baseline Array data reveal a 200
pc scale double radio source in the galaxy core which is more closely aligned
with the current QSO axis and may represent a more recent period of jet
activity. These results suggest that the realignment of the QSO, the cessation
of jet activity, and the onset of rapid star-formation may have been caused by
a gas-rich galaxy merger. A Chandra X-ray observation confirms the presence of
cavities associated with the radio jets, and we estimate the energy required to
inflate them to be ~7.7x10^60 erg. The mechanical power of the jets is
sufficient to balance radiative cooling in the cluster, provided they are
efficiently coupled to the intra-cluster medium (ICM). We find no evidence of
direct radiative heating and conclude that the QSO either lacks the radiative
luminosity to heat the ICM, or that it requires longer than 100-200 Myr to
significantly impact its environment. [Abridged] | Enhanced global signal of neutral hydrogen due to excess radiation at
cosmic dawn: We revisit the global 21cm signal calculation incorporating a possible radio
background at early times, and find that the global 21cm signal shows a much
stronger absorption feature, which could enhance detection prospects for future
21 cm experiments. In light of recent reports of a possible low-frequency
excess radio background, we propose that detailed 21 cm calculations should
include a possible early radio background. |
A Compact Early-type Galaxy at z = 0.6 Under a Magnifying Lens: Evidence
For Inside-out Growth: We use Keck laser guide star adaptive optics imaging and exploit the
magnifying effects of strong gravitational lensing (the effective resolution is
FWHM ~ 200 pc) to investigate the sub-kpc scale of an intermediate-redshift (z
= 0.63) massive early-type galaxy being lensed by a foreground early-type
galaxy; we dub this class of strong gravitational lens systems EELs, e.g.,
early-type/early-type lenses. We find that the background source is massive (M*
= 10^{10.9} M_sun) and compact (r_e = 1.1 kpc), and a two-component fit is
required to model accurately the surface brightness distribution, including an
extended low-surface-brightness component. This extended component may arise
from the evolution of higher-redshift `red nuggets' or may already be in place
at z ~ 2 but is unobservable due to cosmological surface brightness dimming. | An updated Type II supernova Hubble diagram: We present photometry and spectroscopy of nine Type II-P/L supernovae (SNe)
with redshifts in the 0.045 < z < 0.335 range, with a view to re-examining
their utility as distance indicators. Specifically, we apply the expanding
photosphere method (EPM) and the standardized candle method (SCM) to each
target, and find that both methods yield distances that are in reasonable
agreement with each other. The current record-holder for the highest-redshift
spectroscopically confirmed SN II-P is PS1-13bni (z = 0.335 +0.009 -0.012), and
illustrates the promise of Type II SNe as cosmological tools. We updated
existing EPM and SCM Hubble diagrams by adding our sample to those previously
published. Within the context of Type II SN distance measuring techniques, we
investigated two related questions. First, we explored the possibility of
utilising spectral lines other than the traditionally used Fe II 5169 to infer
the photospheric velocity of SN ejecta. Using local well-observed objects, we
derive an epoch-dependent relation between the strong Balmer line and Fe II
5169 velocities that is applicable 30 to 40 days post-explosion. Motivated in
part by the continuum of key observables such as rise time and decline rates
exhibited from II-P to II-L SNe, we assessed the possibility of using
Hubble-flow Type II-L SNe as distance indicators. These yield similar distances
as the Type II-P SNe. Although these initial results are encouraging, a
significantly larger sample of SNe II-L would be required to draw definitive
conclusions. |
Analysis of NILC performance on B-modes data of sub-orbital experiments: The observation of primordial B-modes in the Cosmic Microwave Background
(CMB) represents the main scientific goal of most of the future CMB
experiments. This signal is predicted to be much lower than polarised Galactic
emission (foregrounds) in any region of the sky pointing to the need for
effective components separation methods, such as the Needlet-ILC (NILC). In
this work, we explore the possibility of employing NILC for B-mode maps
reconstructed from partial-sky data of sub-orbital experiments, addressing the
complications that such an application yields: E-B leakage, needlet filtering
and beam convolution. We consider two complementary simulated datasets from
future experiments: the balloon-borne SWIPE telescope of the Large Scale
Polarization Explorer, which targets the observation of both reionisation and
recombination peaks of the primordial B-mode angular power spectrum, and the
ground-based Small Aperture Telescope of Simons Observatory, which is designed
to observe only the recombination bump. We assess the performance of two
alternative techniques to correct for the CMB E-B leakage: the recycling
technique (Liu et al. 2019) and the ZB method (Zhao & Baskaran 2010). We find
that they both reduce the E-B leakage residuals at a negligible level given the
sensitivity of the considered experiments, except for the recycling method in
the SWIPE patch at $\ell < 20$. Thus, we implement two extensions of the
pipeline, the iterative B-decomposition and the diffusive inpainting, which
enable us to recover the input CMB B-mode power for $\ell \geq 5$. We
demonstrate that needlet filtering and beam convolution do not affect the
B-mode reconstruction. Finally, with an appropriate masking strategy, we find
that NILC foregrounds subtraction allows to achieve sensitivities for the
tensor-to-scalar ratio compatible to the targets of the considered CMB
experiments. | Properties of gas in and around galaxy haloes: We study the properties of gas inside and around galaxy haloes as a function
of radius and halo mass, focussing mostly on z=2, but also showing some results
for z=0. For this purpose, we use a suite of large cosmological, hydrodynamical
simulations from the OverWhelmingly Large Simulations project. The properties
of cold- and hot-mode gas, which we separate depending on whether the
temperature has been higher than 10^5.5 K while it was extragalactic, are
clearly distinguishable in the outer parts of massive haloes (virial
temperatures >> 10^5 K. The differences between cold- and hot-mode gas resemble
those between inflowing and outflowing gas. The cold-mode gas is mostly
confined to clumpy filaments that are approximately in pressure equilibrium
with the diffuse, hot-mode gas. Besides being colder and denser, cold-mode gas
typically has a much lower metallicity and is much more likely to be infalling.
However, the spread in the properties of the gas is large, even for a given
mode and a fixed radius and halo mass, which makes it impossible to make strong
statements about individual gas clouds. Metal-line cooling causes a strong
cooling flow near the central galaxy, which makes it hard to distinguish gas
accreted through the cold and hot modes in the inner halo. Stronger feedback
results in larger outflow velocities and pushes hot-mode gas to larger radii.
The gas properties evolve as expected from virial arguments, which can also
account for the dependence of many gas properties on halo mass. We argue that
cold streams penetrating hot haloes are observable as high-column density HI
Lyman-alpha absorption systems in sightlines near massive foreground galaxies. |
Signatures of the Primordial Universe from Its Emptiness: Measurement of
Baryon Acoustic Oscillations from Minima of the Density Field: Sound waves from the primordial fluctuations of the Universe imprinted in the
large-scale structure, called baryon acoustic oscillations (BAOs), can be used
as standard rulers to measure the scale of the Universe. These oscillations
have already been detected in the distribution of galaxies. Here we propose to
measure BAOs from the troughs (minima) of the density field. Based on two sets
of accurate mock halo catalogues with and without BAOs in the seed initial
conditions, we demonstrate that the BAO signal cannot be obtained from the
clustering of classical disjoint voids, but is clearly detected from
overlapping voids. The latter represent an estimate of all troughs of the
density field. We compute them from the empty circumsphere centers constrained
by tetrahedra of galaxies using Delaunay triangulation. Our theoretical models
based on an unprecedented large set of detailed simulated void catalogues are
remarkably well confirmed by observational data. We use the largest recently
publicly available sample of luminous red galaxies from SDSS-III BOSS DR11 to
unveil for the first time a >3$\sigma$ BAO detection from voids in
observations. Since voids are nearly isotropically expanding regions, their
centers represent the most quiet places in the Universe, keeping in mind the
cosmos origin and providing a new promising window in the analysis of the
cosmological large-scale structure from galaxy surveys. | The integrated Sachs-Wolfe effect in the AvERA cosmology: The recent AvERA cosmological simulation of R\'acz et al. (2017) has a
$\Lambda \mathrm{CDM}$-like expansion history and removes the tension between
local and Planck (cosmic microwave background) Hubble constants. We contrast
the AvERA prediction of the integrated Sachs--Wolfe (ISW) effect with that of
$\Lambda \mathrm{CDM}$. The linear ISW effect is proportional to the derivative
of the growth function, thus it is sensitive to small differences in the
expansion histories of the respective models. We create simulated ISW maps
tracing the path of light-rays through the Millennium XXL cosmological
simulation, and perform theoretical calculations of the ISW power spectrum.
AvERA predicts a significantly higher ISW effect than $\Lambda \mathrm{CDM}$,
$A=1.93-5.29$ times larger depending on the $l$ index of the spherical power
spectrum, which could be utilized to definitively differentiate the models. We
also show that AvERA predicts an opposite-sign ISW effect in the redshift range
$z \approx 1.5 - 4.4$, in clear contrast with $\Lambda \mathrm{CDM}$. Finally,
we compare our ISW predictions with previous observations. While at present
these cannot distinguish between the two models due to large error bars, and
lack of internal consistency suggesting systematics, ISW probes from future
surveys will tightly constrain the models. |
Tracing Cold HI Gas in Nearby, Low-Mass Galaxies: We analyze line-of-sight atomic hydrogen (HI) line profiles of 31 nearby,
low-mass galaxies selected from the Very Large Array - ACS Nearby Galaxy Survey
Treasury (VLA-ANGST) and The HI Nearby Galaxy Survey (THINGS) to trace regions
containing cold (T $\lesssim$ 1400 K) HI from observations with a uniform
linear scale of 200 pc/beam. Our galaxy sample spans four orders of magnitude
in total HI mass and nine magnitudes in M_B. We fit single and multiple
component functions to each spectrum to isolate the cold, neutral medium given
by a low dispersion (<6 km/s) component of the spectrum. Most HI spectra are
adequately fit by a single Gaussian with a dispersion of 8-12 km/s. Cold HI is
found in 23 of 27 (~85%) galaxies after a reduction of the sample size due to
quality control cuts. The cold HI contributes ~20% of the total line-of-sight
flux when found with warm HI. Spectra best fit by a single Gaussian, but
dominated by cold HI emission (i.e., have velocity dispersions <6 km/s) are
found primarily beyond the optical radius of the host galaxy. The cold HI is
typically found in localized regions and is generally not coincident with the
very highest surface density peaks of the global HI distribution (which are
usually areas of recent star formation). We find a lower limit for the mass
fraction of cold-to-total HI gas of only a few percent in each galaxy. | Dark Radiation after Planck: We present new constraints on the relativistic neutrino effective number
N_eff and on the Cosmic Microwave Background power spectrum lensing amplitude
A_L from the recent Planck 2013 data release. Including observations of the CMB
large angular scale polarization from the WMAP satellite, we obtain the bounds
N_eff = 3.71 +/- 0.40 and A_L = 1.25 +/- 0.13 at 68% c.l.. The Planck dataset
alone is therefore suggesting the presence of a dark radiation component at
91.1% c.l. and hinting for a higher power spectrum lensing amplitude at 94.3%
c.l.. We discuss the agreement of these results with the previous constraints
obtained from the Atacama Cosmology Telescope (ACT) and the South Pole
Telescope (SPT). Considering the constraints on the cosmological parameters, we
found a very good agreement with the previous WMAP+SPT analysis but a tension
with the WMAP+ACT results, with the only exception of the lensing amplitude. |
Cosmological N-body simulations with generic hot dark matter: We have calculated the non-linear effects of generic fermionic and bosonic
hot dark matter components in cosmological N-body simulations. For sub-eV
masses, the non-linear power spectrum suppression caused by thermal
free-streaming resembles the one seen for massive neutrinos, whereas for masses
larger than 1eV, the non-linear relative suppression of power is smaller than
in linear theory. We furthermore find that in the non-linear regime, one can
map fermionic to bosonic models by performing a simple transformation. | Anomalous parity asymmetry of the Wilkinson Microwave Anisotropy Probe
power spectrum data at low multipoles: We have investigated non-Gaussianity of our early Universe by comparing the
parity asymmetry of the WMAP power spectrum with simulations. We find that
odd-parity preference of the WMAP data (2<= l <=18) is anomalous at 4-in-1000
level. We find it likely that low quadrupole power is part of this parity
asymmetry rather than an isolated anomaly. Futher investigation is required to
find out whether the origin of this anomaly is cosmological or systematic
effect. The data from Planck surveyor, which has systematics distinct from the
WMAP, will help us to resolve the origin of the anomalous odd-parity
preference. |
An extended XMM-Newton observation of the Seyfert galaxy NGC 4051. I.
Evidence for a shocked outflow: An extended XMM-Newton observation of the Seyfert 1 galaxy NGC 4051 has
revealed a rich absorption line spectrum indicating the presence of a
photoionized outflow with a wide range of velocities and ionization parameter.
At low continuum fluxes an emission line spectrum is well defined with both
narrow and broad components of several abundant metal ions. The absorption line
velocity structure and a broad correlation of velocity and ionization parameter
are consistent with an outflow scenario where a highly ionized, high velocity
wind, perhaps launched during intermittent super-Eddington accretion, runs into
the interstellar medium or previous ejecta, losing much of its kinetic energy
in the resultant strong shock. We explore the possibility that a quasi-constant
soft X-ray emission component may be evidence of this post-shock cooling. This
revised view of AGN outflows is consistent with multiple minor Eddington
accretion episodes creating a momentum-driven feedback linking black hole and
host galaxy growth. | Cosmic microwave background with Brans-Dicke gravity II: constraints
with the WMAP and SDSS data: Using the covariant formalism developed in a companion paper (paper I), we
derive observational constraint on the Brans-Dicke model in a flat FLRW
universe with cosmological constant and cold dark matter. The CMB observations
we use include the WMAP five year data, the ACBAR 2007 data, the CBI
polarization data, and the BOOMERanG 2003 flight data. For the large scale
structure we use the matter power spectrum data measured with the LRG survey of
the SDSS DR4. We parameterize the Brans-Dicke parameter $\omega$ with a new
parameter $\zeta=\ln(1/\omega+1)$, and use the Markov-Chain Monte Carlo method
to explore the parameter space. We find that using CMB data alone, one could
place some constraint on positive $\zeta$ or $\omega$, but negative $\zeta$ or
$\omega$ could not be constrained effectively. However, with additional large
scale structure data, one could break the degeneracy at $\zeta<0$. The
$2\sigma$ (95.5%) bound on $\zeta$ is $-0.00837<\zeta<0.01018$ (corresponding
to $\omega < -120.0$ or $\omega > 97.8$). We also obtained constraint on
$\dot{G}/G$, the rate of change of $G$ at present, as $-1.75 \times 10^{-12}
\yr^{-1}<\dot{G}/G < 1.05 \times 10^{-12}\yr^{-1}$, and $\delta G/G$, the total
variation of $G$ since the epoch of recombination, as $ -0.083 < \delta{G}/G <
0.095$ at $2\sigma$ confidence level. |
Model-independent measurement of cosmic curvature with the latest $H(z)$
and SNe Ia data: A comprehensive investigation: In the context of the discrepancies between the early and late universe, we
emphasize the importance of independent measurements of the cosmic curvature in
the late universe. We present an investigation of the model-independent
measurement of the cosmic curvature parameter $\Omega_k$ in the late universe
with the latest Hubble parameter $H(z)$ measurements and type Ia supernovae
(SNe Ia) data. For that, we use two reconstruction methods, the Gaussian
process (GP) and artificial neural network (ANN) methods, to achieve the
distance construction from $H(z)$ data. Our analysis reveals that the GP method
provides the most precise constraint on $\Omega_k$, with a constraint precision
of $\xi(\Omega_k)=0.13$, surpassing recent estimations using similar methods.
The GP method consistently indicates a preference for a flat universe at the
2$\sigma$ confidence level. Moreover, we find that the choice of reconstruction
method influences the estimation of $\Omega_k$. The ANN reconstruction method
exhibits higher sensitivity to the addition of BAO $H(z)$ data, resulting in
comparable constraint precision to the GP method. A discrepancy exists between
the best-fit values obtained by these two reconstruction methods, indicating
their dependence on the reconstruction approach. However, we anticipate that
with the improvement of sample size and precision of observational $H(z)$ data,
the estimation of $\Omega_k$ using this approach will become more robust and
reliable. | Probing cosmology via the clustering of critical points: Exclusion zones in the cross-correlations between critical points (peak-void,
peak-wall, filament-wall, filament-void) of the density field define
quasi-standard rulers that can be used to constrain dark matter and dark energy
cosmological parameters. The average size of the exclusion zone is found to
scale linearly with the typical distance between extrema. The latter changes as
a function of the matter content of the universe in a predictable manner, but
its comoving size remains essentially constant in the linear regime of
structure growth on large scales, unless the incorrect cosmology is assumed in
the redshift-distance relation. This can be used to constrain the dark energy
parameters when considering a survey that scans a range of redshifts. The
precision of the parameter estimation is assessed using a set of cosmological
simulations, and is found to be a 4$\sigma$ detection of a change in matter
content of 5%, or about 3.8$\sigma$ detection of 50% shift in the dark energy
parameter using a full sky survey up to redshift 0.5. |
Learning to Concentrate: Multi-tracer Forecasts on Local Primordial
Non-Gaussianity with Machine-Learned Bias: Local primordial non-Gaussianity (LPNG) is predicted by many non-minimal
models of inflation, and creates a scale-dependent contribution to the power
spectrum of large-scale structure (LSS) tracers, whose amplitude is
characterized by $b_{\phi}$. Knowledge of $b_{\phi}$ for the observed tracer
population is therefore crucial for learning about inflation from LSS.
Recently, it has been shown that the relationship between linear bias $b_1$ and
$b_{\phi}$ for simulated halos exhibits significant secondary dependence on
halo concentration. We leverage this fact to forecast multi-tracer constraints
on $f_{NL}^{\mathrm{loc}}$. We train a machine learning model on observable
properties of simulated Illustris-TNG galaxies to predict $b_{\phi}$ for
samples constructed to approximate DESI emission line galaxies (ELGs) and
luminous red galaxies (LRGs). We find $\sigma(f_{NL}^{\mathrm{loc}}) = 2.3$,
and $\sigma(f_{NL}^{\mathrm{loc}}) = 3.7$, respectively. These forecasted
errors are roughly factors of 3, and 35\% improvements over the single-tracer
case for each sample, respectively. When considering both ELGs and LRGs in
their overlap region, we forecast $\sigma(f_{NL}^{\mathrm{loc}}) = 1.5$ is
attainable with our learned model, more than a factor of 3 improvement over the
single-tracer case, while the ideal split by $b_{\phi}$ could reach
$\sigma(f_{NL}^{\mathrm{loc}}) <1$. We also perform multi-tracer forecasts for
upcoming spectroscopic surveys targeting LPNG (MegaMapper, SPHEREx) and show
that splitting tracer samples by $b_{\phi}$ can lead to an order-of-magnitude
reduction in projected $\sigma(f_{NL}^{\mathrm{loc}})$ for these surveys. | The HST/ACS+WFC3 Survey for Lyman Limit Systems II: Science: We present the first science results from our Hubble Space Telescope Survey
for Lyman limit absorption systems (LLS) using the low dispersion spectroscopic
modes of the Advanced Camera for Surveys and the Wide Field Camera 3. Through
an analysis of 71 quasars, we determine the incidence frequency of LLS per unit
redshift and per unit path length, l(z) and l(x) respectively, over the
redshift range 1 < z< 2.6, and find a weighted mean of l(x)=0.29 +/-0.05 for
2.0 < z < 2.5 through a joint analysis of our sample and that of Ribaudo et al.
(2011). Through stacked spectrum analysis, we determine a median (mean) value
of the mean free path to ionizing radiation at z=2.4 of lambda_mfp =
243(252)h^(-1) Mpc, with an error on the mean value of +/- 43h^(-1) Mpc. We
also re-evaluate the estimates of lambda_mfp from Prochaska et al. (2009) and
place constraints on the evolution of lambda_mfp with redshift, including an
estimate of the "breakthrough" redshift of z = 1.6. Consistent with results at
higher z, we find that a significant fraction of the opacity for absorption of
ionizing photons comes from systems with N_HI <= 10^{17.5} cm^(-2) with a value
for the total Lyman opacity of tau_lyman = 0.40 +/- 0.15. Finally, we determine
that at minimum, a 5-parameter (4 power-law) model is needed to describe the
column density distribution function f(N_HI, X) at z \sim 2.4, find that
f(N_HI,X) undergoes no significant change in shape between z \sim 2.4 and z
\sim 3.7, and provide our best fit model for f(N_HI,X). |
Setting the Stage for Cosmic Chronometers. I. Assessing the Impact of
Young Stellar Populations on Hubble Parameter Measurements: The expansion history of the Universe can be constrained in a
cosmology-independent way by measuring the differential age evolution of cosmic
chronometers. This yields a measurement of the Hubble parameter $H(z)$ as a
function of redshift. The most reliable cosmic chronometers known so far are
extremely massive and passively evolving galaxies. Age-dating these galaxies
is, however, a difficult task, and even a small contribution of an underlying
young stellar population could, in principle, affect the age estimate and its
cosmological interpretation. We present several spectral indicators to detect,
quantify and constrain such contamination in old galaxies, and study how their
combination can be used to maximize the purity of cosmic chronometers
selection. In particular, we analyze the CaII H/K ratio, the presence (or
absence) of H$\alpha$ and [OII] emission lines, higher order Balmer absorption
lines, and UV flux; each indicator is especially sensitive to a particular age
range, allowing us to detect young components ranging between 10 Myr and 1 Gyr.
The combination of these indicators minimizes the contamination to a level
below 1% in the case of ideal data. More importantly, it offers a way to
control the systematic error on $H(z)$ as a function of the contamination by
young stellar populations. We show that for our previous measurements of the
Hubble parameter, the possible bias induced by the presence of a younger
component is well below the current errors. We envision that these indicators
will be instrumental in paving the road for a robust and reliable dating of the
old population and its cosmological interpretation. | Cosmicflows-3: Two Distance$-$Velocity Calculators: Tools are provided at the Extragalactic Distance Database website that
provide relationships between the distances and velocities of galaxies based on
smoothed versions of the velocity fields derived by the Cosmicflows program. |
Comments on Unified dark energy and dark matter from a scalar field
different from quintessence: In a recent paper by C. Gao, M. Kunz, A. Liddle and D. Parkinson
[arXiv:0912.0949], the unification of dark matter and dark energy was explored
within a theory containing a scalar field of non-Lagrangian type. This scalar
field, different from the classic quintessence, can be obtained from the scalar
field representation of an interacting two-fluid mixture described in the paper
by L.P. Chimento and M. Forte [arXiv:0706.4142] | On the nature of the first galaxies selected at 350 microns: [abridged] We present constraints on the nature of the first galaxies
selected at 350 microns. The sample includes galaxies discovered in the deepest
blank-field survey at 350 microns (in the Bootes Deep Field) and also later
serendipitous detections in the Lockman Hole. Spectral energy distribution
templates are fit to identified counterparts, and the sample is found to
comprise IR-luminous galaxies at 1<z<3 predominantly powered by star formation.
The first spectrum of a 350-micron-selected galaxy provides an additional
confirmation, showing prominent dust grain features typically associated with
star-forming galaxies.
Compared to submillimeter galaxies selected at 850 and 1100 microns, galaxies
selected at 350 microns have a similar range of far-infrared color
temperatures. However, no 350-micron-selected sources are reliably detected at
850 or 1100 microns. Galaxies in our sample with redshifts 1<z<2 show a tight
correlation between the far- and mid-infrared flux densities, but galaxies at
higher redshifts show a large dispersion in their mid- to far-infrared colors.
The 350-micron flux densities (15<S(350)<40 mJy) place these objects near the
Herschel/SPIRE 350-micron confusion threshold, with the lower limit on the star
formation rate density suggesting the bulk of the 350-micron contribution will
come from less luminous infrared sources and normal galaxies. |
Galaxy Properties in Clusters: Dependence on the Environment and the
Cluster Identification Techniques: We investigate the dependence of several galaxy properties on the environment
and cluster identification techniques. We select clusters of galaxies from two
catalogues based on the SDSS: the ROSAT-SDSS Galaxy Cluster Survey, and the
MaxBCG Catalogue. Based on a volume limited sample of galaxies drawn from the
spectroscopic DR5 SDSS, we constructed sub-samples of clusters of galaxies with
more than ten members. Scaling relations as well as segregation of galaxy
properties as a function of the normalized clustocentric radii are analyzed.
The properties of galaxies in clusters are compared with those of field
galaxies. Galaxies in X-ray and MaxBCG selected clusters show similar
size-luminosity relations. At equal luminosity, late type galaxies in the field
have sizes smaller than cluster galaxies of the same morphological type. The
Faber-Jackson relation for early-type galaxies in clusters is also the same for
X-ray selected and MaxBCG clusters. We found clear differences between the
dynamical properties of galaxies in clusters, the brightest cluster galaxies
($BCG_s$) and field galaxies. Using several criteria to classify galaxies into
morphological types, we reproduce the well know morphological segregation. The
correlation is up to $r/r_{200} \sim 1$. For the whole range of clustocentric
distances, X-ray selected clusters present a higher fraction of early type
galaxies than MaxBCG clusters. We also found that bright galaxies
preferentially inhabit the cluster centers. Median sizes of galaxies, such as
the radius that enclose 50% of petrosian flux $r_{50}$, present a behaviour
that also depends on the cluster selection criteria. The resultsare discussed
in terms of the different processes that affect the evolution of galaxies in
different environments. | A General Theory of Turbulent Fragmentation: We develop an analytic framework to understand fragmentation in turbulent,
self-gravitating media. Previously, we showed some properties of turbulence can
be predicted with the excursion-set formalism. Here, we generalize to fully
time-dependent gravo-turbulent fragmentation & collapse. We show that turbulent
systems are always gravitationally unstable (in a probabilistic sense). The
fragmentation mass spectra, size/mass relations, correlation functions, range
of scales over which fragmentation occurs, & time-dependent rates of
fragmentation are predictable. We show how this depends on bulk turbulent
properties (Mach numbers & power spectra). We also generalize to include
rotation, complicated equations of state, collapsing/expanding backgrounds,
magnetic fields, intermittency, & non-normal statistics. We derive how
fragmentation is suppressed with 'stiffer' equations of state or different
driving mechanisms. Suppression appears at an 'effective sonic scale' where
Mach(R,rho)~1. Gas becomes stable below this scale for polytropic gamma>4/3,
but fragmentation still occurs on larger scales. The scale-free nature of
turbulence and gravity generically drives mass spectra and correlation
functions towards universal shapes, with weak dependence on many properties of
the media. Correlated fluctuation structures, non-Gaussian density
distributions, & intermittency have surprisingly small effects on the
fragmentation process. This is because fragmentation cascades on small scales
are 'frozen in' when large-scale modes push the 'parent' region above the
collapse threshold; though they collapse, their statistics are only weakly
modified by the collapse process. With thermal support, structure develops
'top-down' in time via fragmentation cascades; but strong rotational support
reverses this to 'bottom-up' growth via mergers & introduces a maximal
instability scale distinct from the Toomre scale. |
Hot-Dust (690K) Luminosity Density and its Evolution in the last 7.5Gyr: [Abridged] We study the contribution of hot-dust to the luminosity density of
galaxies and its evolution with cosmic time. Using the Spitzer-IRAC data in the
COSMOS field, we estimate the contribution from hot-dust at rest-frame 4.2um
(from ~0 < z < ~0.2 up to ~0.5 < z < ~0.9). This wavelength corresponds to
black-body temperature of ~690K. The contribution due to stellar emission is
estimated from the rest-frame 1.6um luminosity (assumed to result from stellar
emission alone) and subtracted from the mid-infrared luminosity of galaxies to
measure hot-dust emission. In order to attempt the study of the 3.3um-PAH
feature, we use the rest-frame 4.2um to infer the hot-dust flux at 3.3um. This
study is performed for different spectral types of galaxies: early-type,
late-type, starburst, and IR-selected AGN. We find that: (a) the decrease of
the hot-dust luminosity density since ~0.5 < z < ~1 is steeper (by at least
~0.5dex) compared to that of the cold-dust, giving support to the scenario
where galaxy obscuration increases with redshift, as already proposed in the
literature; (b) hot-dust and PAH emission evolution seems to be correlated with
stellar mass, where rest-frame 1.6um luminous non-AGN galaxies (i.e., massive
systems) show a stronger decrement (with decreasing redshift) in hot-dust and
PAH emission than the less luminous (less massive) non-AGN galaxies; (c)
despite comprising < ~3% of the total sample, AGN contribute as much as a third
to the hot-dust luminosity density at z < 1 and clearly dominate the bright-end
of the total hot-dust Luminosity Density Function at ~0.5 < z < ~0.9; (d) the
average dust-to-total luminosity ratio increases with redshift, while
PAH-to-total luminosity ratio remains fairly constant; (e) at M_1.6 > -25, the
dust-to-total and PAH-to-total luminosity ratios increase with decreasing
luminosity, but deeper data is required to confirm this result. | Lopsidedness of cluster galaxies in modified gravity: We point out an interesting theoretical prediction for elliptical galaxies
residing inside galaxy clusters in the framework of modified Newtonian dynamics
(MOND), that could be used to test this paradigm. Apart from the central
brightest cluster galaxy, other galaxies close enough to the centre experience
a strong gravitational influence from the other galaxies of the cluster. This
influence manifests itself only as tides in standard Newtonian gravity, meaning
that the systematic acceleration of the centre of mass of the galaxy has no
consequence. However, in the context of MOND, a consequence of the breaking of
the strong equivalence principle is that the systematic acceleration changes
the own self-gravity of the galaxy. We show here that, in this framework,
initially axisymmetric elliptical galaxies become lopsided along the external
field's direction, and that the centroid of the galaxy, defined by the outer
density contours, is shifted by a few hundreds parsecs with respect to the
densest point. |
Primordial power spectrum in light of JWST observations of high redshift
galaxies: Early data releases of JWST have revealed several high redshift massive
galaxy candidates by photometry, and some of them have been confirmed
spectroscopically. We study their implications on the primordial power
spectrum. In the first part, we use the CEERS photometric survey data, along
with respective spectroscopic updates, to compute the cumulative comoving
stellar mass density. We find that a very high star formation efficiency
(unlikely in various theoretical scenarios) is required to explain these
observations within Lambda cold dark matter ($\Lambda$CDM) cosmology. We show
that the tension can be eased if the primordial power spectrum has a blue tilt.
In the second part, we study spectroscopically confirmed galaxies reported in
the JADES survey to investigate their implications on a red-tilted primordial
power spectrum. We estimate the star formation efficiency from an earlier
observation at similar redshift by {\it Spitzer}, and find that the star
formation efficiency is an order of magnitude smaller than required to explain
the CEERS photometric observations mentioned earlier. Using the estimated star
formation efficiency, we find the strongest constraints on the red tilt of the
power spectrum over some scales. Our study shows that JWST will be an excellent
probe of the power spectrum and can lead to novel discoveries. | Galaxy groups and clusters and their brightest galaxies within the
cosmic web: Our aim is to combine data on single galaxies, galaxy groups, their BGGs, and
their location in the cosmic web, to determine classes of groups, and to obtain
a better understanding of their properties and evolution. Data on groups and
their BGGs are based on the Sloan Digital Sky Survey DR10 MAIN spectroscopic
galaxy sample. We characterize the group environments by the luminosity-density
field and their filament membership. We divide BGGs according to their star
formation properties as quenched, and red and blue star-forming galaxies. We
apply multidimensional Gaussian mixture modelling to divide groups based on
their properties and environments. We analyse the offset of BGGs with respect
to the group centre, and the relation between the stellar velocity dispersion
of BGGs and the group velocity dispersions. We show that the groups in our
sample can be divided into two main classes: high-luminosity rich groups and
clusters, and low-luminosity poor groups with threshold luminosity $L = 15
\times 10^{10} h^{-2} L_{sun}$ and mass $M = 23 \times 10^{12} h^{-1} M_{sun}$.
In rich clusters approximately 90% of the BGGs are red and quenched galaxies,
while in poor groups only 40- 60$% of BGGs are red and quenched, and the rest
of the BGGs are star-forming, either blue (20 - 40% of BGGs) or red (17% of
BCGs). Rich groups and clusters are located in global high-density regions in
filaments or filament outskirts, while poor groups reside everywhere in the
cosmic web. Our results suggest that group and cluster properties are modulated
by their location in the cosmic web, but the properties of their BGGs are
mostly determined by processes within group or cluster dark matter halo. We
emphasize the role of superclusters as a special environment for group growth. |
WMAP anomaly : Weak lensing in disguise: Statistical isotropy (SI) has been one of the simplifying assumptions in
cosmological model building. Experiments like WMAP and PLANCK are attempting to
test this assumption by searching for specific signals in the Cosmic Microwave
Background (CMB) two point correlation function. Modifications to this
correlation function due to gravitational lensing by the large scale structure
(LSS) surrounding us have been ignored in this context. Gravitational lensing
will induce signals which mimic isotropy violation even in an isotropic
universe. The signal detected in the Bipolar Spherical Harmonic (BipoSH)
coefficients $A^{20}_{ll}$ by the WMAP team may be explained by accounting for
the lensing modifications to these coefficients. Further the difference in the
amplitude of the signal detected in the V-band and W-band maps can be explained
by accounting for the differences in the designed angular sensitivity of the
instrumental beams. The arguments presented in this article have crucial
implications for SI violation studies. Constraining SI violation will only be
possible by complementing CMB data sets with all sky measurements of the large
scale dark matter distribution. Till that time, the signal detected in the
BipoSH coefficients from WMAP-7 could also be yet another suggested evidence of
strong deviations from the standard $\Lambda$CDM cosmology based on homogeneous
and isotropic FRW models. | Testing the Cosmological Principle in the radio sky: The Cosmological Principle states that the Universe is statistically
isotropic and homogeneous on large scales. In particular, this implies
statistical isotropy in the galaxy distribution, after removal of a dipole
anisotropy due to the observer's motion. We test this hypothesis with number
count maps from the NVSS radio catalogue. We use a local variance estimator
based on patches of different angular radii across the sky and compare the
source count variance between and within these patches. In order to assess the
statistical significance of our results, we simulate radio maps with the NVSS
specifications and mask. We conclude that the NVSS data is consistent with
statistical isotropy. |
The Formation of Galaxies Hosting z~6 Quasars: We investigate the formation and properties of galaxies hosting z~6 quasars,
in the gigaparsec scale cosmological hydrodynamical simulation: MassiveBlack,
which includes a self-consistent model for star formation, black hole accretion
and associated feedback. We show that the MassiveBlack reproduces current
estimates of the galaxy stellar mass function z=5, 6. We find that quasar hosts
in the simulation are compact gas rich systems with high star formations rates
of SFR ~ 100-1000 Msun/yr consistent with observed properties of Sloan quasar
hosts in the redshift range 5.5 < z < 6.5. We show that the star-forming gas in
these galaxies predominantly originates from high density cold streams which
are able to penetrate the halo and grow the galaxy at the center. MassiveBlack
predicts a deviation from the local Mbh-sigma and Mbh-Mstar relation implying
that black holes are relatively more massive for a given stellar host at these
redshifts. | Faraday Rotation Structure on Kiloparsec Scales in the Giant Radio Lobes
of Centaurus A: We present the results of an Australia Telescope Compact Array 1.4 GHz
spectropolarimetric aperture synthesis survey of 34 square degrees centred on
Centaurus A - NGC 5128. A catalogue of 1005 extragalactic compact radio sources
in the field to a continuum flux density of 3 mJy/beam is provided along with a
table of Faraday rotation measures (RMs) and linear polarised intensities for
the 28 percent of sources with high signal-to-noise in linear polarisation. We
use the ensemble of 281 background polarised sources as line-of-sight probes of
the structure of the giant radio lobes of Centaurus A. This is the first time
such a method has been applied to radio galaxy lobes and we explain how it
differs from the conventional methods that are often complicated by depth and
beam depolarisation effects. We use an RM structure function analysis and
report the detection of a turbulent RM signal, with rms of 17 rad/m^2 and scale
size 0.3 degrees, associated with the southern giant lobe. We cannot verify
whether this signal arises from turbulent structure throughout the lobe or only
in a thin skin (or sheath) around the edge, although we favour the latter. The
RM signal is modelled as possibly arising from a thin skin with a thermal
plasma density equivalent to the Centaurus intragroup medium density and a
coherent magnetic field that reverses its sign on a spatial scale of 20 kpc. |
Dark Energy Survey Year 1 Results: Galaxy clustering for combined probes: We measure the clustering of DES Year 1 galaxies that are intended to be
combined with weak lensing samples in order to produce precise cosmological
constraints from the joint analysis of large-scale structure and lensing
correlations. Two-point correlation functions are measured for a sample of $6.6
\times 10^{5}$ luminous red galaxies selected using the \textsc{redMaGiC}
algorithm over an area of $1321$ square degrees, in the redshift range $0.15 <
z < 0.9$, split into five tomographic redshift bins. The sample has a mean
redshift uncertainty of $\sigma_{z}/(1+z) = 0.017$. We quantify and correct
spurious correlations induced by spatially variable survey properties, testing
their impact on the clustering measurements and covariance. We demonstrate the
sample's robustness by testing for stellar contamination, for potential biases
that could arise from the systematic correction, and for the consistency
between the two-point auto- and cross-correlation functions. We show that the
corrections we apply have a significant impact on the resultant measurement of
cosmological parameters, but that the results are robust against arbitrary
choices in the correction method. We find the linear galaxy bias in each
redshift bin in a fiducial cosmology to be $b(z$=$0.24)=1.40 \pm 0.08$,
$b(z$=$0.38)=1.61 \pm 0.05$, $b(z$=$0.53)=1.60 \pm 0.04$ for galaxies with
luminosities $L/L_*>$$0.5$, $b(z$=$0.68)=1.93 \pm 0.05$ for $L/L_*>$$1$ and
$b(z$=$0.83)=1.99 \pm 0.07$ for $L/L_*$$>1.5$, broadly consistent with
expectations for the redshift and luminosity dependence of the bias of red
galaxies. We show these measurements to be consistent with the linear bias
obtained from tangential shear measurements. | Deviations from the Schmidt-Kennicutt relations during early galaxy
evolution: We utilize detailed time-varying models of the coupled evolution of stars and
the HI, H_2, and CO-bright H_2 gas phases in galaxy-sized numerical simulations
to explore the evolution of gas-rich and/or metal-poor systems, expected to be
numerous in the Early Universe. The inclusion of the CO-bright H_2 gas phase,
and the realistic rendering of star formation as an H_2-regulated process (and
the new feedback processes that this entails) allows the most realistic
tracking of strongly evolving galaxies, and much better comparison with
observations. We find that while galaxies eventually settle into states
conforming to Schmidt-Kennicutt (S-K) relations, significant and systematic
deviations of their star formation rates (SFRs) from the latter occur,
especially pronounced and prolonged for ...
...This indicates potentially serious limitations of (S-K)-type relations as
reliable sub-grid elements of star formation physics in simulations of
structure formation in the Early Universe. We anticipate that galaxies with
marked deviations from the S-K relations will be found at high redshifts as
unbiased inventories of total gas mass become possible with ALMA and the EVLA. |
Buoyancy Instabilities in a Weakly Collisional Intracluster Medium: The intracluster medium of galaxy clusters is a weakly collisional, high-beta
plasma in which the transport of heat and momentum occurs primarily along
magnetic-field lines. Anisotropic heat conduction allows convective
instabilities to be driven by temperature gradients of either sign, the
magnetothermal instability (MTI) in the outskirts of non-isothermal clusters
and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We
employ the Athena MHD code to investigate the nonlinear evolution of these
instabilities, self-consistently including the effects of anisotropic viscosity
(i.e. Braginskii pressure anisotropy), anisotropic conduction, and radiative
cooling. We highlight the importance of the microscale instabilities that
inevitably accompany and regulate the pressure anisotropies generated by the
HBI and MTI. We find that, in all but the innermost regions of cool-core
clusters, anisotropic viscosity significantly impairs the ability of the HBI to
reorient magnetic-field lines orthogonal to the temperature gradient. Thus,
while radio-mode feedback appears necessary in the central few tens of kpc,
conduction may be capable of offsetting radiative losses throughout most of a
cool core over a significant fraction of the Hubble time. Magnetically-aligned
cold filaments are then able to form by local thermal instability. Viscous
dissipation during the formation of a cold filament produces accompanying hot
filaments, which can be searched for in deep Chandra observations of nearby
cool-core clusters. In the case of the MTI, anisotropic viscosity maintains the
coherence of magnetic-field lines over larger distances than in the inviscid
case, providing a natural lower limit for the scale on which the field can
fluctuate freely. In the nonlinear state, the magnetic field exhibits a folded
structure in which the field-line curvature and field strength are
anti-correlated. | Implications of Gravitational-wave Production from Dark Photon Resonance
to Pulsar-timing Observations and Effective Number of Relativistic Species: The coherent oscillation of axionic fields naturally drives copious
production of dark photon particles in the early universe, due to resonance and
tachyonic enhancement. During the process, energy is abruptly transferred from
the former to the latter, sourcing gravitational wave generation. The resulting
gravitational waves are eventually to be observed as stochastic background
today. We report analytical results of this production and connect them to the
recent pulsar-timing results by the NANOGrav collaboration. We show an
available parameter space, around the mass $m_\phi \sim 10^{-13} \, {\rm eV}$
and the decay constant $f_\phi \sim 10^{16} \, {\rm GeV}$ with a dimensionless
coupling of ${\cal O}(1)$, for our mechanism to account for the signal. A
mechanism to avoid the axion over-dominating the universe is a necessary
ingredient of this model, and we discuss a possibility to recover a symmetry
and render the axion massless after the production. We also comment on
potential implications of the required effective number of relativistic species
to the determination of the present Hubble constant. |
An Improved Statistical Point-Source Foreground Model for the Epoch of
Reionization: We present a sophisticated statistical point-source foreground model for
low-frequency radio Epoch of Reionization (EoR) experiments using the 21 cm
neutral hydrogen emission line. Motivated by our understanding of the
low-frequency radio sky, we enhance the realism of two model components
compared with existing models: the source count distributions as a function of
flux density and spatial position (source clustering), extending current
formalisms for the foreground covariance of 2D power spectral modes in 21 cm
EoR experiments. The former we generalise to an arbitrarily broken power-law,
and the latter to an arbitrary isotropically-correlated field. This paper
presents expressions for the modified covariance under these extensions, and
shows that for a more realistic source spatial distribution, extra covariance
arises in the EoR window which was previously unaccounted for. Failure to
include this contribution can yield bias in the final power spectrum and
under-estimate uncertainties, potentially leading to a false detection of
signal. The extent of this effect is uncertain, owing to ignorance of physical
model parameters, but we show that it is dependent on the relative abundance of
faint sources, to the effect that our extension will become more important for
future deep surveys. Finally, we show that under some parameter choices,
ignoring source clustering can lead to false detections on large scales, due to
both the induced bias and an artificial reduction in the estimated measurement
uncertainty. | The Dusty Nuclear Torus in NGC 4151: Constraints from Gemini
Near-Infrared Integral Field Spectrograph Observations: We have used a near-infrared nuclear spectrum (covering the Z, J, H and K
bands) of the nucleus of NGC 4151 obtained with the Gemini Near-infrared
Integral Field Spectrograph (NIFS) and adaptive optics, to isolate and
constrain the properties of a near-IR unresolved nuclear source whose spectral
signature is clearly present in our data. The near-IR spectrum was combined
with an optical spectrum obtained with the Space Telescope Imaging Spectrograph
which was used to constrain the contribution of a power-law component. After
subtraction of the power-law component, the near-IR continuum is well fitted by
a blackbody function, with $T=1285\pm50 $K, which dominates the nuclear
spectrum -- within an aperture of radius 0$\farcs$3 -- in the near-IR. We
attribute the blackbody component to emission by a dusty structure, with hot
dust mass $M_{\rm HD}=(6.9\pm 1.5) \times10^{-4} {\rm M_\odot}$, not resolved
by our observations, which provide only an upper limit for its distance from
the nucleus of 4 pc. If the reddening derived for the narrow-line region also
applies to the near-IR source, we obtain a temperature $T=1360\pm50 $K and a
mass $M_{\rm HD}=(3.1\pm 0.7) \times10^{-4} {\rm M_\odot}$ for the hot dust.
This structure may be the inner wall of the dusty torus postulated by the
Unified Model or the inner part of a dusty wind originating in the accretion
disk. |
How general is the global density slope-anisotropy inequality?: Following the seminal result of An & Evans, known as the central density
slope-anisotropy theorem, successive investigations unexpectedly revealed that
the density slope-anisotropy inequality holds not only at the center, but at
all radii in a very large class of spherical systems whenever the phase-space
distribution function is positive. In this paper we derive a criterion that
holds for all spherical systems in which the augmented density is a separable
function of radius and potential: this new finding allows to unify all the
previous results in a very elegant way, and opens the way for more general
investigations. As a first application, we prove that the global density
slope-anisotropy inequality is also satisfied by all the explored additional
families of multi-component stellar systems. The present results, and the
absence of known counter-examples, lead us to conjecture that the global
density slope-anisotropy inequality could actually be a universal property of
spherical systems with positive distribution function. | NoSOCS in SDSS III - The interplay between galaxy evolution and the
dynamical state of galaxy clusters: We investigate relations between the color and luminosity distributions of
cluster galaxies and the evolutionary state of their host clusters. Our aim is
to explore some aspects of cluster galaxy evolution and the dynamical state of
clusters as two sides of the same process. We used 10,721 member galaxies of
183 clusters extracted from the Sloan Digital Sky Survey using a list of NoSOCS
and CIRS targets. First, we classified the clusters into two categories,
Gaussian and non-Gaussian, according to their velocity distribution
measurements, which we used as an indicator of their dynamical state. We then
used objective criteria to split up galaxies according to their luminosities,
colors, and photometric mean stellar age. This information was then used to
evaluate how galaxies evolve in their host clusters. Meaningful color
gradients, i.e., the fraction of red galaxies as a function of radius from the
center, are observed for both the Gaussian velocity distribution and the
non-Gaussian velocity distribution cluster subsamples, which suggests that
member galaxy colors change on a shorter timescale than the time needed for the
cluster to reach dynamical equilibrium. We also found that larger portions of
fainter red galaxies are found, on average, in smaller radii. The luminosity
function in Gaussian clusters has a brighter characteristic absolute magnitude
and a steeper faint-end slope than it does in the non-Gaussian velocity
distribution clusters. Our findings suggest that cluster galaxies experience
intense color evolution before virialization, while the formation of faint
galaxies through dynamical interactions probably takes place on a longer
timescale, possibly longer than the virialization time. |
Exploring Primordial Black Holes and Gravitational Waves with
R-Symmetric GUT Higgs Inflation: This study investigates the realization of R-symmetric Higgs inflation within
the framework of no-scale-like supergravity, aiming to elucidate the formation
of primordial black holes and observable gravitational waves within a class of
GUT models. We explore the possibility of an ultra-slow-roll phase in a hybrid
inflation framework, where the GUT Higgs field primarily takes on the role of
the inflaton. The amplification of the scalar power spectrum gives rise to
scalar-induced gravitational waves and the generation of primordial black
holes. The predicted stochastic gravitational wave background falls within the
sensitivity range of existing and upcoming gravitational wave detectors, while
primordial black holes hold the potential to explain the abundance of dark
matter. Furthermore, we highlight the significance of the leading-order
nonrenormalizable term in the superpotential of achieving inflationary
observables consistent with the latest experimental data. Additionally, the
predicted range of the tensor-to-scalar ratio, a key measure of primordial
gravitational waves, lies within the observational window of future experiments
searching for B-mode polarization patterns in cosmic microwave background data. | The galaxy-halo connection of DESI luminous red galaxies with subhalo
abundance matching: We use subhalo abundance and age distribution matching to create
magnitude-limited mock galaxy catalogs at $z\sim0.43$, $0.52$, and $0.63$ with
$z$-band and $3.4$ micron $W1$-band absolute magnitudes and ${r-z}$ and
${r-W1}$ colors. From these magnitude-limited mocks we select mock luminous red
galaxy (LRG) samples according to the $(r-z)$-based (optical) and
$(r-W1)$-based (infrared) selection criteria for the LRG sample of the Dark
Energy Spectroscopic Instrument (DESI) Survey. Our models reproduce the number
densities, luminosity functions, color distributions, and projected clustering
of the DESI Legacy Surveys that are the basis for DESI LRG target selection. We
predict the halo occupation statistics of both optical and IR DESI LRGs at
fixed cosmology, and assess the differences between the two LRG samples. We
find that IR-based SHAM modeling represents the differences between the optical
and IR LRG populations better than using the $z$-band, and that age
distribution matching overpredicts the clustering of LRGs, implying that galaxy
color is uncorrelated with halo age in the LRG regime. Both the optical and IR
DESI LRG target selections exclude some of the most luminous galaxies that
would appear to be LRGs based on their position on the red sequence in optical
color-magnitude space. Both selections also yield populations with a
non-trivial LRG-halo connection that does not reach unity for the most massive
halos. We find the IR selection achieves greater completeness ($\gtrsim 90\%$)
than the optical selection across all redshift bins studied. |
Figures of merit and constraints from testing General Relativity using
the latest cosmological data sets including refined COSMOS 3D weak lensing: We use cosmological constraints from current data sets and a figure of merit
(FoM) approach to probe any deviations from general relativity (GR) at
cosmological scales. The FoM approach is used to study the constraining power
of various combinations of data sets on modified gravity (MG) parameters. We
use recently refined HST-COSMOS weak-lensing tomography data, ISW-galaxy cross
correlations from 2MASS and SDSS LRG surveys, matter power spectrum from
SDSS-DR7 (MPK), WMAP7 temperature and polarization spectra, BAO from 2DF and
SDSS-DR7, and Union2 compilation of supernovae, in addition to other bounds
from H_0 measurements and BBN. We use 3 parametrizations of MG parameters that
enter the perturbed field equations. In order to allow for variations with
redshift and scale, the first 2 parametrizations use recently suggested
functional forms while the third is based on binning methods. Using the first
parametrization, we find that CMB + ISW + WL provides the strongest constraints
on MG parameters followed by CMB+WL or CMB+MPK+ISW. Using the second
parametrization or binning methods, CMB+MPK+ISW consistently provides some of
the strongest constraints. This shows that the constraints are parametrization
dependent. We find that adding up current data sets does not improve
consistently uncertainties on MG parameters due to tensions between best-fit MG
parameters preferred by different data sets. Furthermore, some functional forms
imposed by the parametrizations can lead to an exacerbation of these tensions.
Next, unlike some studies that used the CFHTLS lensing data, we do not find any
deviation from GR using the refined HST-COSMOS data, confirming previous claims
in those studies that their result may have been due to some systematic effect.
Finally, we find in all cases that the values corresponding to GR are within
the 95% confidence level contours for all data set combinations. (abridged) | XENON100 Dark Matter Results from a Combination of 477 Live Days: We report on WIMP search results of the XENON100 experiment, combining three
runs summing up to 477 live days from January 2010 to January 2014. Data from
the first two runs were already published. A blind analysis was applied to the
last run recorded between April 2013 and January 2014 prior to combining the
results. The ultra-low electromagnetic background of the experiment, ~$5 \times
10^{-3}$ events/(keV$_{\mathrm{ee}}\times$kg$\times$day) before electronic
recoil rejection, together with the increased exposure of 48 kg $\times$ yr
improves the sensitivity. A profile likelihood analysis using an energy range
of (6.6 - 43.3) keV$_{\mathrm{nr}}$ sets a limit on the elastic,
spin-independent WIMP-nucleon scattering cross section for WIMP masses above 8
GeV/$c^2$, with a minimum of 1.1 $\times 10^{-45}$ cm$^2$ at 50 GeV/$c^2$ and
90% confidence level. We also report updated constraints on the elastic,
spin-dependent WIMP-nucleon cross sections obtained with the same data. We set
upper limits on the WIMP-neutron (proton) cross section with a minimum of 2.0
$\times 10^{-40}$ cm$^2$ (52$\times 10^{-40}$ cm$^2$) at a WIMP mass of 50
GeV/$c^2$, at 90% confidence level. |
CMB spectral distortions from continuous large energy release: Accurate computations of spectral distortions of the cosmic microwave
background (CMB) are required for constraining energy release scenarios at
redshifts $z\gtrsim 10^3$. The existing literature focuses on distortions that
are small perturbations to the background blackbody spectrum. At high redshifts
($z\gtrsim 10^6$), this assumption can be violated, and the CMB spectrum can be
significantly distorted at least during part of its cosmic evolution. In this
paper, we carry out accurate thermalization computations, evolving the
distorted CMB spectrum in a general, fully non-linear way, consistently
accounting for the time-dependence of the injection process, modifications to
the Hubble expansion rate and relativistic Compton scattering. Specifically, we
study single energy injection and decaying particle scenarios, discussing
constraints on these cases. We solve the thermalization problem using two
independent numerical approaches that are now available in {\tt CosmoTherm} as
dedicated setups for computing CMB spectral distortions in the large distortion
regime. New non-linear effects at low frequencies are furthermore highlighted,
showing that these warrant a more rigorous study. This work eliminates one of
the long-standing simplifications in CMB spectral distortion computations,
which also opens the way to more rigorous treatments of distortions induced by
high-energy particle cascade, soft photon injection and in the vicinity of
primordial black holes. | A response to Rubin & Heitlauf: "Is the expansion of the universe
accelerating? All signs still point to yes": We have shown (Colin et al., 2019) that the acceleration of the Hubble
expansion rate inferred from Type Ia supernovae (SNe Ia) is, at $3.9\sigma$
significance, a dipole approximately aligned with the CMB dipole, while its
monopole component, which can be interpreted as due to a Cosmological Constant
or dark energy, is consistent with zero at $1.4\sigma$. This has been
challenged by Rubin & Heitlauf (2019) who assert that the dipole arises because
we made an incorrect assumption about the SNe Ia light-curve parameters (viz.
took them to be sample- and redshift independent), and did not allow for the
motion of the Solar system (w.r.t. the 'CMB frame' in which the CMB dipole
supposedly vanishes). In fact what has an even larger impact on our finding is
that we reversed the inconsistent "corrections" made for the peculiar
velocities of the SNe Ia host galaxies w.r.t the CMB frame, which in fact serve
to bias the lever arm of the Hubble diagram towards higher inferred values of
the monopole. We demonstrate that even if all such corrections are made
consistently and both sample- and redshift-dependence is allowed for in the
standardisation of supernova light curves, the evidence for isotropic
acceleration rises to just $2.8\,\sigma$. Thus the criticism of Rubin &
Heitlauf serves only to highlight that "corrections" must be made to the SNe Ia
data assuming the standard $\Lambda$CDM model, in order to recover it from the
data. |
Spatial and temporal variations of fundamental constants: Spatial and temporal variations in the electron-to-proton mass ratio, mu, and
in the fine-structure constant, alpha, are predicted in non-Standard models
aimed to explain the nature of dark energy. Among them the so-called
chameleon-like scalar field models predict strong dependence of masses and
coupling constants on the local matter density. To explore such models we
estimated the parameters Delta mu/mu = (mu_obs - mu_lab)/mu_lab and Delta
alpha/alpha = (alpha_obs - alpha_lab)/alpha_lab in two essentially different
environments, - terrestrial (high density) and interstellar (low density), -
from radio astronomical observations of cold prestellar molecular cores in the
disk of the Milky Way. We found that Delta mu/mu = (22 +/- 4_stat +/-
3_sys)x10^{-9}, and |Delta alpha/alpha| < 1.1x10^{-7}. If only a conservative
upper limit is considered, then |Delta mu/mu| <= 3x10^{-8}. We also reviewed
and re-analyzed the available data on the cosmological variation of alpha
obtained from FeI and FeII systems in optical spectra of quasars. We show that
statistically significant evidence for the changing alpha at the level of
10^{-6} has not been provided so far. The most stringent constraint on |Delta
alpha/alpha| < 2x10^{-6} was found from the FeII system at z = 1.15 towards the
bright quasar HE0515-4414. The limit of 2x10^{-6} corresponds to the utmost
accuracy which can be reached with available to date optical facilities. | An optimal survey geometry of weak lensing survey: minimizing
super-sample covariance: Upcoming wide-area weak lensing surveys are expensive both in time and cost
and require an optimal survey design in order to attain maximum scientific
returns from a fixed amount of available telescope time. The super-sample
covariance (SSC), which arises from unobservable modes that are larger than the
survey size, significantly degrades the statistical precision of weak lensing
power spectrum measurement even for a wide-area survey. Using the 1000 mock
realizations of the log-normal model, which approximates the weak lensing field
for a $\Lambda$-dominated cold dark matter model, we study an optimal survey
geometry to minimize the impact of SSC contamination. For a continuous survey
geometry with a fixed survey area, a more elongated geometry such as a
rectangular shape of 1:400 side-length ratio reduces the SSC effect and allows
for a factor 2 improvement in the cumulative signal-to-noise ratio ($S/N$) of
power spectrum measurement up to $\ell_{\rm max}\simeq $ a few $10^3$, compared
to compact geometries such as squares or circles. When we allow the survey
geometry to be disconnected but with a fixed total area, assuming $1\times 1$
sq. degrees patches as the fundamental building blocks of survey footprints,
the best strategy is to locate the patches with $\sim 15$ degrees separation.
This separation angle corresponds to the scale at which the two-point
correlation function has a negative minimum. The best configuration allows for
a factor 100 gain in the effective area coverage as well as a factor 2.5
improvement in the $S/N$ at high multipoles, yielding a much wider coverage of
multipoles than in the compact geometry. |
A spectroscopic measurement of galaxy formation timescales with ROLES: We present measurements of the specific star-formation rate (SSFR)-stellar
mass relation for star-forming galaxies. Our deep spectroscopic samples are
based on the Redshift One LDSS3 Emission line Survey, ROLES, and European
Southern Observatory, ESO, public spectroscopy at z=1, and on the Sloan Digital
Sky Survey (SDSS) at z=0.1. These datasets cover an equally deep mass range of
8.5<~log(M*/Msun)<~11 at both epochs. We find that the SSFR--mass relation
evolves in a way which is remarkably independent of stellar mass, as we
previously found for the star-formation rate density (SFRD)--mass relation. At
higher masses, such as those probed by previous surveys, the evolution in
SSFR--mass is almost independent of stellar mass. At higher masses
(log(M*/Msun)>10) the shapes of the cumulative cosmic SFRDs are very similar at
both z=0.1 and z=1.0, both showing 70% of the total SFRD above a mass of
log(M*/Msun)>10. Mass functions are constructed for star-forming galaxies and
found to evolve by only <35% between z=1 and z=0.1 over the whole mass range.
The evolution is such that the mass function decreases with increasing cosmic
time, confirming that galaxies are leaving the star-forming sequence/blue
cloud. The observational results are extended to z~2 by adding two recent Lyman
break galaxy samples, and data at these three epochs (z=0.1, 1, 2) are compared
with the GALFORM semi-analytic model of galaxy formation. GALFORM predicts an
overall SFR density (SFRD) as a function of stellar mass in reasonable
agreement with the observations. The star formation timescales inferred from
1/SSFR also give reasonable overall agreement, with the agreement becoming
worse at the lowest and highest masses. [abridged] | Attractor Behaviour in Multifield Inflation: We study multifield inflation in scenarios where the fields are coupled
non-minimally to gravity via $\xi_I(\phi^I)^n g^{\mu\nu}R_{\mu\nu}$, where
$\xi_I$ are coupling constants, $\phi^I$ the fields driving inflation,
$g_{\mu\nu}$ the space-time metric, $R_{\mu\nu}$ the Ricci tensor, and $n>0$.
We consider the so-called $\alpha$-attractor models in two formulations of
gravity: in the usual metric case where $R_{\mu\nu}=R_{\mu\nu}(g_{\mu\nu})$,
and in the Palatini formulation where $R_{\mu\nu}$ is an independent variable.
As the main result, we show that, regardless of the underlying theory of
gravity, the field-space curvature in the Einstein frame has no influence on
the inflationary dynamics at the limit of large $\xi_I$, and one effectively
retains the single-field case. However, the gravity formulation does play an
important role: in the metric case the result means that multifield models
approach the single-field $\alpha$-attractor limit, whereas in the Palatini
case the attractor behaviour is lost also in the case of multifield inflation.
We discuss what this means for distinguishing between different models of
inflation. |
Spectroscopic Confirmation of a z=2.79 Multiply Imaged Luminous Infrared
Galaxy Behind the Bullet Cluster: We report spectroscopic confirmation and high-resolution infrared imaging of
a z=2.79 triply-imaged galaxy behind the Bullet Cluster. This source, a
Spitzer-selected luminous infrared galaxy (LIRG), is confirmed via polycyclic
aromatic hydrocarbon (PAH) features using the Spitzer Infrared Spectrograph
(IRS) and resolved with HST WFC3 imaging. In this galaxy, which with a stellar
mass of M*=4e9 Msun is one of the two least massive ones studied with IRS at
z>2, we also detect H_2 S(4) and H_2 S(5) pure rotational lines (at 3.1 sigma
and 2.1 sigma) - the first detection of these molecular hydrogen lines in a
high-redshift galaxy. From the molecular hydrogen lines we infer an excitation
temperature T=377+68-84 K. The detection of these lines indicates that the warm
molecular gas mass is 6(+36-4)% of the stellar mass and implies the likely
existence of a substantial reservoir of cold molecular gas in the galaxy.
Future spectral observations at longer wavelengths with facilities like the
Herschel Space Observatory, the Large Millimeter Telescope, and the Atacama
Pathfinder EXperiment (APEX) thus hold the promise of precisely determining the
total molecular gas mass. Given the redshift, and using refined astrometric
positions from the high resolution imaging, we also update the magnification
estimate and derived fundamental physical properties of this system. The
previously published values for total infrared luminosity, star formation rate,
and dust temperature are confirmed modulo the revised magnification; however we
find that PAH emission is roughly a factor of five stronger than would be
predicted by the relations between the total infrared and PAH luminosity
reported for SMGs and starbursts in Pope et al. (2008). | A New Measurement of the Temperature Density Relation of the IGM From
Voigt Profile Fitting: We decompose the Lyman-{\alpha} (Ly{\alpha}) forest of an extensive sample of
74 high signal-to-noise ratio and high-resolution quasar spectra into a
collection of Voigt profiles. Absorbers located near caustics in the peculiar
velocity field have the smallest Doppler parameters, resulting in a low-$b$
cutoff in the $b$-$N_{\text{HI}}$ set by the thermal state of intergalactic
medium (IGM). We fit this cutoff as a function of redshift over the range
$2.0\leq z \leq 3.4$, which allows us to measure the evolution of the IGM
temperature-density ($T= T_0 (\rho/ \rho_0)^{\gamma-1}$) relation parameters
$T_0$ and $\gamma$. We calibrate our measurements against Ly$\alpha$ forest
simulations, using 21 different thermal models of the IGM at each redshift,
also allowing for different values of the IGM pressure smoothing scale. We
adopt a forward-modeling approach and self-consistently apply the same
algorithms to both data and simulations, propagating both statistical and
modeling uncertainties via Monte Carlo. The redshift evolution of $T_0$ shows a
suggestive peak at $z=2.8$, while our evolution of $\gamma$ is consistent with
$\gamma\simeq 1.4$ and disfavors inverted temperature-density relations. Our
measured evolution of $T_0$ and $\gamma$ are generally in good agreement with
previous determinations in the literature. Both the peak in the evolution of
$T_0$ at $z = 2.8$, as well as the high temperatures $T_0\simeq 15000-20000\,$K
that we observe at $2.4 < z < 3.4$, strongly suggest that a significant episode
of heating occurred after the end of HI reionization, which was most likely the
cosmic reionization of HeII. |
Blue Gravity Waves from BICEP2 ?: We present new constraints on the spectral index n_T of tensor fluctuations
from the recent data obtained by the BICEP2 experiment. We found that the
BICEP2 data alone slightly prefers a positive, "blue", spectral index with
n_T=1.36\pm0.83 at 68 % c.l.. However, when a TT prior on the tensor amplitude
coming from temperature anisotropy measurements is assumed we get
n_T=1.67\pm0.53 at 68 % c.l., ruling out a scale invariant $n_T=0$ spectrum at
more than three standard deviations. These results are at odds with current
bounds on the tensor spectral index coming from pulsar timing, Big Bang
Nucleosynthesis, and direct measurements from the LIGO experiment. Considering
only the possibility of a "red", n_T<0 spectral index we obtain the lower limit
n_T > -0.76 at 68 % c.l. (n_T>-0.09 when a TT prior is included). | Filamentary Large Scale Structure Traced by Six Ly-alpha Blobs at z=2.3: Extended nebulae of Ly-alpha emission ("Ly-alpha blobs") are known to be
associated with overdense regions at high redshift. Here we present six large
Ly-alpha blobs in a previously known protocluster with galaxy overdensity delta
~ 7 at z = 2.3; this is the richest field of giant Ly-alpha blobs detected to
date. The blobs have linear sizes >~100 kpc and Ly-alpha luminosities of ~10^43
erg/s. The positions of the blobs define two linear filaments with an extent of
at least 12 comoving Mpc; these filaments intersect at the center of one of the
blobs. Measurement of the position angles of the blobs indicates that five of
the six are aligned with these filaments to within ~10 degrees, suggesting a
connection between the physical processes powering extended Ly-alpha emission
and those driving structure on larger scales. |
A new model for the full shape of the large-scale power spectrum: We present a new model for the full shape of large-scale the power spectrum
based on renormalized perturbation theory. To test the validity of this
prescription, we compare this model against power spectra measured in a suite
of 50 large volume, moderate resolution N-body simulations. Our results
indicate that this simple model provides an accurate description of the full
shape of the power spectrum taking into account the effects of non-linear
evolution, redshift-space distortions and halo bias for scales k < 0.15 h/Mpc,
making it a valuable tool for the analysis of forthcoming galaxy surveys. Even
though its application is restricted to large scales, this prescription can
provide tighter constraints on the dark energy equation of state parameter
w_{DE} than those obtained by modelling the baryonic acoustic oscillations
signal only, where the information of the broad-band shape of the power
spectrum is discarded. Our model is able to provide constraints comparable to
those obtained by applying a similar model to the full shape of the correlation
function, which is affected by different systematics. Hence, with accurate
modelling of the power spectrum, the same cosmological information can be
extracted from both statistics. | Dark Matter Halos as Particle Colliders: A Unified Solution to
Small-Scale Structure Puzzles from Dwarfs to Clusters: Astrophysical observations spanning dwarf galaxies to galaxy clusters
indicate that dark matter (DM) halos are less dense in their central regions
compared to expectations from collisionless DM N-body simulations. Using
detailed fits to DM halos of galaxies and clusters, we show that
self-interacting DM (SIDM) may provide a consistent solution to the DM deficit
problem across all scales, even though individual systems exhibit a wide
diversity in halo properties. Since the characteristic velocity of DM particles
varies across these systems, we are able to measure the self-interaction cross
section as a function of kinetic energy and thereby deduce the SIDM particle
physics model parameters. Our results prefer a mildly velocity-dependent cross
section, from $\sigma/m \simeq 2\; {\rm cm^2/g}$ on galaxy scales to $\sigma/m
\simeq 0.1\; {\rm cm^2/g}$ on cluster scales, consistent with the upper limits
from merging clusters. Our results dramatically improve the constraints on SIDM
models and may allow the masses of both DM and dark mediator particles to be
measured even if the dark sector is completely hidden from the Standard Model,
which we illustrate for the dark photon model. |
An Improved Model of Diffuse Galactic Radio Emission from 10 MHz to 5
THz: We present an improved Global Sky Model (GSM) of diffuse galactic radio
emission from 10 MHz to 5 THz, whose uses include foreground modeling for CMB
and 21 cm cosmology. Our model improves on past work both algorithmically and
by adding new data sets such as the Planck maps and the enhanced Haslam map.
Our method generalizes the Principal Component Analysis approach to handle
non-overlapping regions, enabling the inclusion of 29 sky maps with no region
of the sky common to all. We also perform a blind separation of our GSM into
physical components with a method that makes no assumptions about physical
emission mechanisms (synchrotron, free-free, dust, etc). Remarkably, this blind
method automatically finds five components that have previously only been found
"by hand", which we identify with synchrotron, free-free, cold dust, warm dust,
and the CMB anisotropy, with maps and spectra agreeing with previous work but
in many cases with smaller error bars. The improved GSM is available online at
github.com/jeffzhen/gsm2016. | Anisotropies in the astrophysical gravitational-wave background:
Predictions for the detection of compact binaries by LIGO and Virgo: We develop a detailed anisotropic model for the astrophysical
gravitational-wave background, including binary mergers of two stellar-mass
black holes, two neutron stars, or one of each, which are expected to be the
strongest contributions in the LIGO-Virgo frequency band. The angular spectrum
of the anisotropies, quantified by the $C_\ell$ components, is calculated using
two complementary approaches: (i) a simple, closed-form analytical expression,
and (ii) a detailed numerical study using an all-sky mock light cone galaxy
catalogue from the Millennium simulation. The two approaches are in excellent
agreement at large angular scales, and differ by a factor of order unity at
smaller scales. These anisotropies are considerably larger in amplitude than
e.g. those in the temperature of the cosmic microwave background, confirming
that it is important to model these anisotropies, and indicating that this is a
promising avenue for future theoretical and observational work. |
An analytical approach to the CMB Polarization in a Spatially Closed
background: The scalar mode polarization of the cosmic microwave background is derived in
a spatially closed universe from the Boltzmann equation using the line of sight
integral method. The EE and TE multipole coefficients have been extracted
analytically by considering some tolerable approximations such as considering
the evolution of perturbation hydrodynamically and sudden transition from
opacity to transparency at the time of last scattering. As the major advantage
of analytic expressions, EE and TE multipole coefficients explicitly show the
dependencies on baryon density, matter density, curvature, primordial spectral
index, primordial power spectrum amplitude, Optical depth, recombination width
and recombination time. Using a realistic set of cosmological parameters taken
from a fit to data from Planck, the closed universe EE and TE power spectrums
in the scalar mode are compared with numerical results from the CAMB code and
also latest observational data. The analytic results agree with the numerical
ones on the big and moderate scales. The peak positions are in good agreement
with the numerical result on these scales while the peak heights agree with
that to within 20% due to the approximations have been considered for these
derivations. Also, several interesting properties of CMB polarization are
revealed by the analytic spectra. | The Atacama Cosmology Telescope: The Persistence of Neutrino
Self-Interaction in Cosmological Measurements: We use data from the Atacama Cosmology Telescope (ACT) DR4 to search for the
presence of neutrino self-interaction in the cosmic microwave background.
Consistent with prior works, the posterior distributions we find are bimodal,
with one mode consistent with $\Lambda$CDM and one where neutrinos strongly
self-interact. By combining ACT data with large-scale information from WMAP, we
find that a delayed onset of neutrino free streaming caused by significantly
strong neutrino self-interaction is compatible with these data at the
$2-3\sigma$ level. As seen in the past, the preference shifts to $\Lambda$CDM
with the inclusion of Planck data. We determine that the preference for strong
neutrino self-interaction is largely driven by angular scales corresponding to
$700 \lesssim \ell \lesssim 1000$ in the ACT E-mode polarization data. This
region is expected to be key to discriminate between neutrino self-interacting
modes and will soon be probed with more sensitive data. |
The XXL Survey IV. Mass-temperature relation of the bright cluster
sample: The XXL survey is the largest survey carried out by XMM-Newton. Covering an
area of 50deg$^2$, the survey contains $\sim450$ galaxy clusters out to a
redshift $\sim$2 and to an X-ray flux limit of
$\sim5\times10^{-15}erg\,s^{-1}cm^{-2}$. This paper is part of the first
release of XXL results focussed on the bright cluster sample. We investigate
the scaling relation between weak-lensing mass and X-ray temperature for the
brightest clusters in XXL. The scaling relation is used to estimate the mass of
all 100 clusters in XXL-100-GC. Based on a subsample of 38 objects that lie
within the intersection of the northern XXL field and the publicly available
CFHTLenS catalog, we derive the $M_{WL}$ of each system with careful
considerations of the systematics. The clusters lie at $0.1<z<0.6$ and span a
range of $ T\simeq1-5keV$. We combine our sample with 58 clusters from the
literature, increasing the range out to 10keV. To date, this is the largest
sample of clusters with $M_{WL}$ measurements that has been used to study the
mass-temperature relation. The fit ($M\propto T^b$) to the XXL clusters returns
a slope $b=1.78^{+0.37}_{-0.32}$ and intrinsic scatter $\sigma_{\ln
M|T}\simeq0.53$; the scatter is dominated by disturbed clusters. The fit to the
combined sample of 96 clusters is in tension with self-similarity,
$b=1.67\pm0.12$ and $\sigma_{\ln M|T}\simeq0.41$. Overall our results
demonstrate the feasibility of ground-based weak-lensing scaling relation
studies down to cool systems of $\sim1keV$ temperature and highlight that the
current data and samples are a limit to our statistical precision. As such we
are unable to determine whether the validity of hydrostatic equilibrium is a
function of halo mass. An enlarged sample of cool systems, deeper weak-lensing
data, and robust modelling of the selection function will help to explore these
issues further. | Dark Energy Survey Year 3 results: Marginalisation over redshift
distribution uncertainties using ranking of discrete realisations: Cosmological information from weak lensing surveys is maximised by dividing
source galaxies into tomographic sub-samples for which the redshift
distributions are estimated. Uncertainties on these redshift distributions must
be correctly propagated into the cosmological results. We present hyperrank, a
new method for marginalising over redshift distribution uncertainties in
cosmological analyses, using discrete samples from the space of all possible
redshift distributions. This is demonstrated in contrast to previous highly
simplified parametric models of the redshift distribution uncertainty. In
hyperrank the set of proposed redshift distributions is ranked according to a
small (in this work between one and four) number of summary values, which are
then sampled along with other nuisance parameters and cosmological parameters
in the Monte Carlo chain used for inference. This can be regarded as a general
method for marginalising over discrete realisations of data vector variation
with nuisance parameters, which can consequently be sampled separately to the
main parameters of interest, allowing for increased computational efficiency.
We focus on the case of weak lensing cosmic shear analyses and demonstrate our
method using simulations made for the Dark Energy Survey (DES). We show the
method can correctly and efficiently marginalise over a range of models for the
redshift distribution uncertainty. Finally, we compare hyperrank to the common
mean-shifting method of marginalising over redshift uncertainty, validating
that this simpler model is sufficient for use in the DES Year 3 cosmology
results presented in companion papers. |
Recovery of fluctuation spectrum evolution from tomographic shear
spectra: Forthcoming large angle surveys are planned to obtain high precision
tomographic shear data. In principle, they will allow us to recover the spectra
of matter density fluctuation, at various redshift, through the inversion of
the expressions yielding shear from fluctuation spectra. This was discussed in
previous work, where SVD techniques for matrix inversion were also shown to be
the optimal tool to this aim. Here we show the significant improvements
obtainable by using a 7 bin tomography, as allowed by future Euclid data, as
well as the question of error propagation from shear to fluctuation spectra. We
find that the technique is a promising tool, namely for the analysis of baryon
physics throug high-l shear spectra and to test the consistency between
expansion rate and fluctuation growth. | Constraining the masses of high-redshift clusters with weak lensing:
Revised shape calibration testing for the impact of stronger shears and
increased blending: WL measurements have well-known shear estimation biases, which can be
partially corrected for with the use of image simulations. We present an
analysis of simulated images that mimic HST/ACS observations of high-redshift
galaxy clusters, including cluster specific issues such as non-weak shear and
increased blending. Our synthetic galaxies have been generated to match the
observed properties of the background-selected samples in the real images.
First, we used simulations with galaxies on a grid to determine a revised
signal-to-noise-dependent correction for multiplicative shear measurement bias,
and to quantify the sensitivity of our bias calibration to mismatches of galaxy
or PSF properties between the real data and the simulations. We studied the
impact of increased blending and light contamination from cluster and
foreground galaxies, finding it negligible for $z>0.7$ clusters, whereas there
is an effect at the $\sim 1\%$ level for lower redshift clusters. Finally, we
studied the impact of fainter neighbours and selection bias mimicking the
positions and magnitudes of galaxies in CANDELS data. The initial SExtractor
object detection causes a selection bias of $-0.028 \pm 0.002$, reduced to
$-0.016 \pm 0.002$ by further cuts. We compared our CANDELS-based estimate to a
grid-based analysis, with added clustered galaxies reaching even fainter
magnitudes, yielding a refined estimate of $\sim -0.013$. Our pipeline is
calibrated to an accuracy of $\sim 0.015$, which is fully sufficient for
current and near-future weak lensing studies of high-redshift clusters. As an
application, we used it for a refined analysis of three highly relaxed clusters
from the SPT-SZ survey, including measurements down to $r>200$ kpc. Compared to
previously employed scales, this tightens the cluster mass constraints by a
factor 1.38 on average. |
Dark energy constraints from a space-based supernova survey: We present a forecast of dark energy constraints that could be obtained from
a large sample of distances to Type Ia supernovae detected and measured from
space. We simulate the supernova events as they would be observed by a
EUCLID-like telescope with its two imagers, assuming those would be equipped
with 4 visible and 3 near infrared swappable filters. We account for known
systematic uncertainties affecting the cosmological constraints, including
those arising through the training of the supernova model used to fit the
supernovae light curves. Using conservative assumptions and Planck priors, we
find that a 18 month survey would yield constraints on the dark energy equation
of state comparable to the cosmic shear approach in EUCLID: a variable
two-parameter equation of state can be constrained to ~0.03 at z~0.3. These
constraints are derived from distances to about 13,000 supernovae out to z=1.5,
observed in two cones of 10 and 50 deg^2. These constraints do not require
measuring a nearby supernova sample from the ground. Provided swappable filters
can be accommodated on EUCLID, distances to supernovae can be measured from
space and contribute to obtain the most precise constraints on dark energy
properties. | HII regions feeding the interstellar medium in M83: We analyse the internal dynamics of star-forming HII regions and their
efficiency in interacting with the ISM. We use GHaFaS (Fabry-Perot) data of the
nearby spiral galaxy M83 to perform multiple-Gaussian fitting to the integrated
Halpha emission line for 136 HII regions, advanced instrumental response
subtraction and to study the Luminosity-velocity dispersion relation. We find
that the best way of dealing with instrumental response effects is convolving
its actual shape with the Gaussian before fitting and that in our data almost
none of the regions need a secondary Gaussian. |
Space-time variation of the electron-to-proton mass ratio in a Weyl
model: Seeking a possible explanation for recent data indicating a space-time
variation of the electron-to-proton mass ratio within the Milky Way, we
consider a phenomenological model where the effective fermion masses depend on
the local value of the Weyl tensor. We contrast the required values of the
model's free parameters with bounds obtained from modern tests on the violation
of the Weak Equivalence Principle and we find that these quantities are
incompatible. This result indicates that the variation of nucleon and electron
masses through a coupling with the Weyl tensor is not a viable model. | A Novel Statistical Method for Measuring the Temperature-Density
Relation in the IGM Using the $b$-$N_{\text{HI}}$ Distribution of Absorbers
in the Ly$α$ Forest: We present a new method for determining the thermal state of the
intergalactic medium based on Voigt profile decomposition of the Ly$\alpha$
forest. The distribution of Doppler parameter and column density
($b$-$N_{\text{HI}}$ distribution) is sensitive to the temperature density
relation $T=T_0 (\rho/\rho_0)^{\gamma-1}$, and previous work has inferred $T_0$
and $\gamma$ by fitting its low-$b$ cutoff. This approach discards the majority
of available data, and is susceptible to systematics related to cutoff
determination. We present a method that exploits all information encoded in the
$b$-$N_{\text{HI}}$ distribution by modeling its entire shape. We apply kernel
density estimation to discrete absorption lines to generate model probability
density functions, then use principal component decomposition to create an
emulator which can be evaluated anywhere in thermal parameter space. We
introduce a Bayesian likelihood based on these models enabling parameter
inference via Markov chain Monte Carlo. The method's robustness is tested by
applying it to a large grid of thermal history simulations. By conducting 160
mock measurements we establish that our approach delivers unbiased estimates
and valid uncertainties for a 2D $(T_0, \gamma)$ measurement. Furthermore, we
conduct a pilot study applying this methodology to real observational data at
$z=2$. Using 200 absorbers, equivalent in pathlength to a single Ly$\alpha$
forest spectrum, we measure $\log T_0 =4.092^{+0.050}_{-0.055}$ and
$\gamma=1.49^{+0.073}_{-0.074}$ in excellent agreement with cutoff fitting
determinations using the same data. Our method is far more sensitive than
cutoff fitting, enabling measurements of $\log T_0$ and $\gamma$ with precision
on $\log T_0$ ($\gamma$) nearly two (three) times higher for current dataset
sizes. |
A spatial-correlation analysis of the cubic 3-torus topology based on
the Planck 2013 data: Spatial correlations of the cubic 3-torus topology are analysed using the
Planck 2013 data. The spatial-correlation method for detecting multiply
connected spaces is based on the fact that positions on the cosmic microwave
background (CMB) sky, that are separated by large angular distances, can be
spatially much nearer according to a hypothesized topology. The comparison of
the correlations computed with and without the assumed topology can reveal
whether a promising topological candidate is found. The level of the expected
correlations is estimated by CMB simulations of the cubic 3-torus topology and
compared to those obtained from the Planck data. An interesting 3-torus
configuration is discovered which possesses topological correlations of the
magnitude found in the CMB simulations based on a toroidal universe. Although
the spatial-correlation method has a high false-positive rate, it is striking
that there exists an orientation of a cubic 3-torus cell, where correlations
between points that are separated by large angular distances, mimic those of
closely separated points. | Constraining primordial non-Gaussianity with cosmological weak lensing:
shear and flexion: We examine the cosmological constraining power of future large-scale weak
lensing surveys on the model of \emph{Euclid}, with particular reference to
primordial non-Gaussianity. Our analysis considers several different estimators
of the projected matter power spectrum, based on both shear and flexion, for
which we review the covariances and Fisher matrices. The bounds provided by
cosmic shear alone for the local bispectrum shape, marginalized over
$\sigma_8$, are at the level of $\Delta f_\mathrm{NL} \sim 100$. We consider
three additional bispectrum shapes, for which the cosmic shear constraints
range from $\Delta f_\mathrm{NL}\sim 340$ (equilateral shape) up to $\Delta
f_\mathrm{NL}\sim 500$ (orthogonal shape). The competitiveness of cosmic
flexion constraints against cosmic shear ones depends on the galaxy intrinsic
flexion noise, that is still virtually unconstrained. Adopting the very high
value that has been occasionally used in the literature results in the flexion
contribution being basically negligible with respect to the shear one, and for
realistic configurations the former does not improve significantly the
constraining power of the latter. Since the flexion noise decreases with
decreasing scale, by extending the analysis up to $\ell_\mathrm{max} = 20,000$
cosmic flexion, while being still subdominant, improves the shear constraints
by $\sim 10%$ when added. However on such small scales the highly non-linear
clustering of matter and the impact of baryonic physics make any error
estimation uncertain. By considering lower, and possibly more realistic, values
of the flexion intrinsic shape noise results in flexion constraining power
being a factor of $\sim 2$ better than that of shear, and the bounds on
$\sigma_8$ and $f_\mathrm{NL}$ being improved by a factor of $\sim 3$ upon
their combination. (abridged) |
The Evolution of AGN in Groups and Clusters: The evolution of AGN in groups and clusters provides important information
about how their black holes grow, the extent to which galaxies and black holes
coevolve in dense environments, and has implications for feedback in the local
universe and at the epoch of cluster assembly. I describe new observations and
analysis that demonstrates that the AGN fraction in clusters increases by a
factor of eight from the local universe to z~1 and that this evolution is
consistent with the evolution of star-forming galaxies in clusters. The cluster
AGN fraction remains approximately an order of magnitude below the field AGN
fraction over this entire range, while a preliminary analysis of groups
indicates that they too undergo substantial evolution. | Implications of the NANOGrav result on primordial gravitational waves in
nonstandard cosmologies: Recently, the NANOGrav collaboration has reported evidence for a
common-spectrum stochastic process, which might be interpreted as the first
ever detection of stochastic gravitational wave (GW) background. We discuss the
possibility of the signal arising from the first and second-order GWs in
nonstandard cosmological history. We show that the NANOGrav observation can be
explained by the first order GWs in the nonstandard thermal history with an
early matter-dominated era, whereas the parameter space required to explain the
NANOGrav observation in the standard cosmology or in the nonstandard epoch of
kination domination is ruled out by the BBN and CMB observations. For the
second-order GWs arising from the large primordial scalar fluctuations, we
study the standard radiation domination and two specific nonstandard cases with
a few forms of the primordial power spectrum $P_{\zeta}(k)$ to achieve abundant
primordial black hole (PBH) production. We find that the NANOGrav observation
can be explained with standard radiation domination for all of these
$P_{\zeta}(k)$. Furthermore, a dustlike epoch leads to abundant PBH formation
for a lower amplitude of $P_{\zeta}(k)$ than the radiation dominated case and
complies with the NANOGrav observation only for a few of the all $P_{\zeta}(k)$
forms considered here, where the peak wavenumber is larger than the wavenumber
range probed by the NANOGrav. In this nonstandard epoch, for a broad power
spectrum, PBHs are produced in a wide mass range in the planetary mass regime.
A nonstandard epoch of kination domination cannot produce enough PBH for any of
the $P_{\zeta}(k)$ if the NANOGrav result is to be satisfied. |
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