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Interferences in the Stochastic Gravitational Wave Background: Although the expansion of the Universe explicitly breaks the time-translation
symmetry, cosmological predictions for the stochastic gravitational wave
background (SGWB) are usually derived under the so-called stationary
hypothesis. By dropping this assumption and keeping track of the time
dependence of gravitational waves at all length scales, we derive the expected
unequal-time (and equal-time) waveform of the SGWB generated by scaling
sources, such as cosmic defects. For extinct and smooth enough sources, we show
that all observable quantities are uniquely and analytically determined by the
holomorphic Fourier transform of the anisotropic stress correlator. Both the
strain power spectrum and the energy density parameter are shown to have an
oscillatory fine structure, they significantly differ on large scales while
running in phase opposition at large wavenumbers $k$. We then discuss scaling
sources that are never extinct nor smooth and which generate a singular Fourier
transform of the anisotropic stress correlator. For these, we find the
appearance of interferences on top of the above-mentioned fine-structure as
well as atypical behaviour at small scales. For instance, we expect the
rescaled strain power spectrum $k^2 \mathcal{P}_h$ generated by long cosmic
strings in the matter era to oscillate around a scale invariant plateau. These
singular sources are also shown to produce orders of magnitude difference
between the rescaled strain spectra and the energy density parameter suggesting
that only the former should be used for making reliable observable predictions.
Finally, we discuss how measuring such a fine structure in the SGWB could
disambiguate the possible cosmological sources. | astro-ph_CO |
Diffuse Radio Emission in Abell 754: We present a low frequency study of the diffuse radio emission in the galaxy
cluster A754. We present new 150 MHz image of the galaxy cluster A754 made with
the Giant Metrewave Radio Telescope (GMRT) and discuss the detection of 4
diffuse features. We compare the 150 MHz image with the images at 74, 330 and
1363 MHz; one new diffuse feature is detected. The flux density upperlimits at
330 and 1363 MHz imply a synchrotron spectral index, $\alpha > 2$, ($S\propto
\nu^{-\alpha}$) for the new feature. The 'west relic' detected at 74 MHz
(Kassim et al 2001) is not detected at 150 MHz and is thus consistent with its
non-detection at 1363 MHz (Bacchi et al 2003) and 330 MHz(Kassim et al 2001).
Integrated spectra of all the diffuse features are presented. The fourth
diffuse feature is located along the proposed merger axis (Zabludoff et al
1995) in A754 and 0.7 Mpc away from the peak of X-ray emission. We have made
use of the framework of adiabatic compression model (Ensslin & Gopal-Krishna
2001) to obtain spectra. We show that the spectrum of the fourth diffuse
feature is consistent with that of a cocoon of a radio galaxy lurking for about
$9\times10^{7}$ yr; no shock compression is required. The other three diffuse
emission have spectra steeper than 1.5 and could be cocoons lurking for longer
time. We discuss other possibilities such as shocks and turbulent
reacceleration being responsible for the diffuse emission in A754. | astro-ph_CO |
The slope of the Baryonic Tully-Fisher relation: We present the results of a baryonic Tully-Fisher relation (BTFR) study for a
local sample of relatively isolated disk galaxies. We derive a BTFR with a
slope near 3 measured over about 4 dex in baryon mass for our combined
\textrm{H\,\scriptsize{I}} and bright spiral disk samples. This BTFR is
significantly flatter and has less scatter than the TFR (stellar mass only)
with its slope near 4 reported for other samples and studies. A BTFR slope near
3 is in better agreement with the expected slope from simple $\Lambda$CDM
cosmological simulations that include both stellar and gas baryons. The scatter
in the TFR/BTFR appears to depend on $W_{20}$: galaxies that rotate slower have
more scatter. The atomic gas--to--stars ratio shows a break near $W_{20} = 250$
\kms\, probably associated with a change in star formation efficiency. In
contrast the absence of such a break in the BTFR suggests that this relation
was probably set at the main epoch of baryon dissipation rather than as a
product of later galactic evolution. | astro-ph_CO |
The CMB Dipole: Eppur Si Muove: The largest temperature anisotropy in the cosmic microwave background (CMB)
is the dipole. The simplest interpretation of the dipole is that it is due to
our motion with respect to the rest frame of the CMB. As well as creating the
$\ell$=1 mode of the CMB sky, this motion affects all astrophysical
observations by modulating and aberrating sources across the sky. It can be
seen in galaxy clustering, and in principle its time derivative through a
dipole-shaped acceleration pattern in quasar positions. Additionally, the
dipole modulates the CMB temperature anisotropies with the same frequency
dependence as the thermal Sunyaev-Zeldovich (tSZ) effect and so these modulated
CMB anisotropies can be extracted from the tSZ maps produced by Planck.
Unfortunately, this measurement cannot determine if the dipole is due to our
motion, but it does provide an independent measure of the dipole and a
validation of the y maps. This measurement, and a description of the
first-order terms of the CMB dipole, are outlined here. | astro-ph_CO |
Large non-Gaussian Halo Bias from Single Field Inflation: We calculate Large Scale Structure observables for non-Gaussianity arising
from non-Bunch-Davies initial states in single field inflation. These scenarios
can have substantial primordial non-Gaussianity from squeezed (but observable)
momentum configurations. They generate a term in the halo bias that may be more
strongly scale-dependent than the contribution from the local ansatz. We also
discuss theoretical considerations required to generate an observable
signature. | astro-ph_CO |
Improving lensing cluster mass estimate with flexion: Gravitational lensing has long been considered as a valuable tool to
determine the total mass of galaxy clusters. The shear profile as inferred from
the statistics of ellipticity of background galaxies allows to probe the
cluster intermediate and outer regions thus determining the virial mass
estimate. However, the mass sheet degeneracy and the need for a large number of
background galaxies motivate the search for alternative tracers which can break
the degeneracy among model parameters and hence improve the accuracy of the
mass estimate. Lensing flexion, i.e. the third derivative of the lensing
potential, has been suggested as a good answer to the above quest since it
probes the details of the mass profile. We investigate here whether this is
indeed the case considering jointly using weak lensing, magnification and
flexion. We use a Fisher matrix analysis to forecast the relative improvement
in the mass accuracy for different assumptions on the shear and flexion signal
- to - noise (S/N) ratio also varying the cluster mass, redshift, and
ellipticity. It turns out that the error on the cluster mass may be reduced up
to a factor 2 for reasonable values of the flexion S/N ratio. As a general
result, we get that the improvement in mass accuracy is larger for more
flattened haloes, but extracting general trends is a difficult because of the
many parameters at play. We nevertheless find that flexion is as efficient as
magnification to increase the accuracy in both mass and concentration
determination. | astro-ph_CO |
Possible Alternate Scenario for short Duration GRBs: In this paper we look at new class of objects made up entirely of dark matter
particles. We look at these objects as possible candidate for short duration
gamma ray bursts eliminating the baryon load problem. These could also provide
a possible scenario for the formation of sub-stellar black holes, distinct from
the usual Hawking black hole. | astro-ph_CO |
Constraints on Primordial Magnetic Fields from Planck combined with the
South Pole Telescope CMB B-mode polarization measurements: A primordial magnetic field (PMF) present before recombination can leave
specific signatures on the cosmic microwave background (CMB) fluctuations. Of
particular importance is its contribution to the B-mode polarization power
spectrum. Indeed, vortical modes sourced by the PMF can dominate the B-mode
power spectrum on small scales, as they survive damping up to a small fraction
of the Silk length. Therefore, measurements of the B-mode polarization at
high-$\ell$ , such as the one recently performed by the South Pole Telescope
(SPT), have the potential to provide stringent constraints on the PMF. We use
the publicly released SPT B-mode polarization spectrum, along with the
temperature and polarization data from the Planck satellite, to derive
constraints on the magnitude, the spectral index and the energy scale at which
the PMF was generated. We find that, while Planck data constrains the magnetic
amplitude to $B_{1 \, \text{Mpc}} < 3.3$ nG at 95\% confidence level (CL), the
SPT measurement improves the constraint to $B_{1 \, \text{Mpc}} < 1.5$ nG. The
magnetic spectral index, $n_B$, and the time of the generation of the PMF are
unconstrained. For a nearly scale-invariant PMF, predicted by simplest
inflationary magnetogenesis models, the bound from Planck+SPT is $B_{1 \,
\text{Mpc}} < 1.2$ nG at 95% CL. For PMF with $n_B=2$, expected for fields
generated in post-inflationary phase transitions, the 95% CL bound is $B_{1 \,
\text{Mpc}} < 0.002$ nG, corresponding to the magnetic fraction of the
radiation density $\Omega_{B\gamma} < 10^{-3}$ or the effective field $B_{\rm
eff} < 100$ nG. The patches for the Boltzmann code CAMB and the Markov Chain
Monte Carlo engine CosmoMC, incorporating the PMF effects on CMB, are made
publicly available. | astro-ph_CO |
Testing consistency of general relativity with kinematic and dynamical
probes: In this work, we test consistency relations between a kinematic probe, the
observational Hubble data, and a dynamical probe, the growth rates for cosmic
large scale structure, which should hold if general relativity is the correct
theory of gravity on cosmological scales. Moreover, we summarize the
development history of parametrization in testings and make an improvement of
it. Taking advantage of the Hubble parameter given from both parametric and
non-parametric methods, we propose three equations and test two of them
performed by means of two-dimensional parameterizations, including one using
trigonometric functions we propose. As a result, it is found that the
consistency relations satisfies well at $1\sigma$ CL and trigonometric
functions turn out to be efficient tools in parameterizations. Furthermore, in
order to confirm the validity of our test, we introduce a model of modified
gravity, DGP model and compare the testing results in the cases of
$\Lambda$CDM, "DGP in GR" and DGP model with mock data. It can be seen that it
is the establishing of consistency relations which dominates the results of the
testing. Overall, the present observational Hubble data and growth rate data
favor convincingly that the general relativity is the correct theory of gravity
on cosmological scales. | astro-ph_CO |
Testing General Relativity using the Environmental Dependence of Dark
Matter Halos: In this Letter, we investigate the environmental dependence of dark matter
halos in theories that attempt to explain the accelerated expansion of the
Universe by modifying general relativity (GR). Using high-resolution N-body
simulations in f(R) gravity models which recover GR in dense environments by
virtue of the chameleon mechanism, we find a strong environmentally-dependent
difference between the lensing mass and dynamical mass estimates of dark matter
halos. This environmental dependence of the halo properties can be used as a
smoking gun to test GR observationally. | astro-ph_CO |
The Formation of the Local Group Planes of Galaxies: The confinement of most satellite galaxies in the Local Group to thin planes
presents a challenge to the theory of hierarchical galaxy clustering. The
PAndAS collaboration has identified a particularly thin configuration with
kinematic coherence among companions of M31 and there have been long standing
claims that the dwarf companions to the Milky Way lie in a plane roughly
orthogonal to the disk of our galaxy. This discussion investigates the possible
origins of four Local Group planes: the plane similar, but not identical to
that identified by PAndAS, an adjacent slightly tilted plane, and two planes
near the Milky Way: one with nearer galaxies and the other with more distant
ones. Plausible orbits are found by using a combination of Numerical Action
methods and a backward in time integration procedure. For M31, M33, IC10, and
LeoI, solutions are found that are consistent with measurements of their proper
motions. For galaxies in planes, there must be commonalities in their proper
motions, and this constraint greatly limits the number of physically plausible
solutions. Key to the formation of the planar structures has been the
evacuation of the Local Void and consequent build-up of the Local Sheet, a wall
of this void. Most of the M31 companion galaxies were born in early-forming
filamentary or sheet-like substrata that chased M31 out of the void. M31 is a
moving target because of its attraction toward the Milky Way, and the result
has been alignments stretched toward our galaxy. In the case of the
configuration around the Milky Way, it appears that our galaxy was in a
three-way competition for companions with M31 and Centaurus A. Only those
within a modest band fell our way. The Milky Ways' attraction toward the Virgo
Cluster resulted in alignments along the Milky Way-Virgo Cluster line. | astro-ph_CO |
Taxonomy of Dark Energy Models: The accelerated expansion of the Universe is one of the main discoveries of
the past decades, indicating the presence of an unknown component: the dark
energy. Evidence of its presence is being gathered by a succession of
observational experiments with increasing precision in its measurements.
However, the most accepted model for explaining the dynamic of our Universe,
the so-called Lambda cold dark matter, face several problems related to the
nature of such energy component. This has lead to a growing exploration of
alternative models attempting to solve those drawbacks. In this review, we
briefly summarize the characteristics of a (non-exhaustive) list of dark energy
models as well as some of the most used cosmological samples. Next, we discuss
how to constrain each model's parameters using observational data. Finally, we
summarize the status of dark energy modeling. | astro-ph_CO |
Reconstructing the Initial Density Field of the Local Universe: Method
and Test with Mock Catalogs: Our research objective in this paper is to reconstruct an initial linear
density field, which follows the multivariate Gaussian distribution with
variances given by the linear power spectrum of the current CDM model and
evolves through gravitational instability to the present-day density field in
the local Universe. For this purpose, we develop a Hamiltonian Markov Chain
Monte Carlo method to obtain the linear density field from a posterior
probability function that consists of two components: a prior of a Gaussian
density field with a given linear spectrum, and a likelihood term that is given
by the current density field. The present-day density field can be
reconstructed from galaxy groups using the method developed in Wang et al.
(2009a). Using a realistic mock SDSS DR7, obtained by populating dark matter
haloes in the Millennium simulation with galaxies, we show that our method can
effectively and accurately recover both the amplitudes and phases of the
initial, linear density field. To examine the accuracy of our method, we use
$N$-body simulations to evolve these reconstructed initial conditions to the
present day. The resimulated density field thus obtained accurately matches the
original density field of the Millennium simulation in the density range 0.3 <=
rho/rho_mean <= 20 without any significant bias. Especially, the Fourier phases
of the resimulated density fields are tightly correlated with those of the
original simulation down to a scale corresponding to a wavenumber of ~ 1 h/Mpc,
much smaller than the translinear scale, which corresponds to a wavenumber of ~
0.15 h\Mpc. | astro-ph_CO |
Anisotropic Galactic Outflows and Enrichment of the Intergalactic
Medium. II. Numerical Simulations: We combine an analytic model for anisotropic outflows and galaxy formation
with numerical simulations of large-scale structure and halo formation to study
the impact of galactic outflows on the evolution of the IGM. We have simulated
the evolution of a comoving volume (15 Mpc)^3 in the LCDM universe. We follow
the formation of 20000-60000 galaxies and simulate the galactic outflows
produced by these galaxies, for five outflow opening angles, alpha=60, 90, 120,
150, and 180 degrees (isotropic outflows). Anisotropic outflows follow the path
of least resistance and thus travel preferentially into low-density regions,
away from cosmological structures where galaxies form. These anisotropic
outflows are less likely to overlap with one another, or to hit pre-galactic
collapsing halos and strip them of their gas, preventing a galaxy from forming.
Going from 180 deg to 60 deg, the number of galaxies that actually form
doubles, producing twice as many outflows, and these outflows overlap to a
lesser extent. As a result, the metal volume filling factor of the IGM goes
from 8% for isotropic outflows up to 28% for anisotropic ones. High density
regions are more efficiently enriched than low density ones (~80% compared to
~20% by volume), even though most enriched regions are low densities.
Increasing the anisotropy of outflows increases the extent of enrichment at all
densities, low and high. This is in part because anisotropic outflows are more
numerous. When this effect is factored-out, we find that the probability a
galaxy will enrich systems at densities up to 10 rho_mean is higher for
increasingly anisotropic outflows. This is an effect of the dynamical evolution
of the IGM. Anisotropic outflows expand preferentially into underdense gas, but
that gas can later accrete onto overdense structures. | astro-ph_CO |
Gravitational energy as dark energy: Average observational quantities: In the timescape scenario cosmic acceleration is understand as an apparent
effect, due to gravitational energy gradients that grow when spatial curvature
gradients become significant with the nonlinear growth of cosmic structure.
This affects the calibratation of local geometry to the solutions of the
volume-average evolution equations corrected by backreaction. In this paper I
discuss recent work on defining observational tests for average geometric
quantities which can distinguish the timescape model from a cosmological
constant or other models of dark energy. | astro-ph_CO |
Production of EMRIs in Supermassive Black Hole Binaries: We consider the formation of extreme mass-ratio inspirals (EMRIs) sourced
from a stellar cusp centred on a primary supermassive black hole (SMBH) and
perturbed by an inspiraling less massive secondary SMBH. The problem is
approached numerically, assuming the stars are non-interacting over these short
timescales and performing an ensemble of restricted three-body integrations.
From these simulations we see that not only can EMRIs be produced during this
process, but the dynamics are also quite rich. In particular, most of the EMRIs
are produced through a process akin to the Kozai-Lidov mechanism, but with
strong effects due to the non-Keplerian stellar potential, general relativity,
and non-secular oscillations in the angular momentum on the orbital timescale
of the binary SMBH system. | astro-ph_CO |
The SLUGGS Survey: Globular cluster system kinematics and substructure
in NGC 4365: We present a kinematic analysis of the globular cluster (GC) system of the
giant elliptical galaxy NGC 4365 and find several distinct kinematic
substructures. This analysis is carried out using radial velocities for 269
GCs, obtained with the DEIMOS instrument on the Keck II telescope as part of
the SAGES Legacy Unifying Globulars and Galaxies Survey (SLUGGS). We find that
each of the three (formerly identified) GC colour subpopulations reveal
distinct rotation properties. The rotation of the green GC subpopulation is
consistent with the bulk of NGC 4365's stellar light, which `rolls' about the
photometric major axis. The blue and red GC subpopulations show `normal'
rotation about the minor axis. We also find that the red GC subpopulation is
rotationally dominated beyond 2.5 arcmin (~17 kpc) and that the root mean
squared velocity of the green subpopulation declines sharply with radius
suggesting a possible bias towards radial orbits relative to the other GC
subpopulations. Additionally, we find a population of low velocity GCs that
form a linear structure running from the SW to the NE across NGC 4365 which
aligns with the recently reported stellar stream towards NGC 4342. These low
velocity GCs have g'-i' colours consistent with the overall NGC 4365 GC system
but have velocities consistent with the systemic velocity of NGC 4342. We
discuss the possible formation scenarios for the three GC subpopulations as
well as the possible origin of the low velocity GC population. | astro-ph_CO |
A new probe of the small-scale primordial power spectrum: astrometric
microlensing by ultracompact minihalos: The dark matter enclosed in a density perturbation with a large initial
amplitude (delta-rho/rho > 1e-3) collapses shortly after recombination and
forms an ultracompact minihalo (UCMH). Their high central densities make UCMHs
especially suitable for detection via astrometric microlensing: as the UCMH
moves, it changes the apparent position of background stars. A UCMH with a mass
larger than a few solar masses can produce a distinctive astrometric
microlensing signal that is detectable by the space astrometry mission Gaia. If
Gaia does not detect gravitational lensing by any UCMHs, then it establishes an
upper limit on their abundance and constrains the amplitude of the primordial
power spectrum for k~2700 Mpc^{-1}. These constraints complement the upper
bound on the amplitude of the primordial power spectrum derived from limits on
gamma-ray emission from UCMHs because the astrometric microlensing signal
produced by an UCMH is maximized if the dark-matter annihilation rate is too
low to affect the UCMH's density profile. If dark matter annihilation within
UCMHs is not detectable, a search for UCMHs by Gaia could constrain the
amplitude of the primordial power spectrum to be less than 1e-5; this bound is
three orders of magnitude stronger than the bound derived from the absence of
primordial black holes. | astro-ph_CO |
Discovery of a supercluster in the ZOA in Vela: We report the discovery of a potentially major supercluster that extends
across the Galactic Plane in the constellation of Vela, at a mean recessional
velocity of ~18,000 km/s. Recent multi-object spectroscopic observations of
this Vela Supercluster (VSCL), using AAOmega+2dF and the Southern African Large
Telescope, confirm an extended galaxy overdensity in the Zone of Avoidance
(ZOA) located where residual bulk flows predict a considerable mass excess. We
present a preliminary analysis of ~4,500 new spectroscopic galaxy redshifts
obtained in the ZOA centred on the Vela region (l=272.5+-20 deg, b=0+-10 deg).
The presently sparsely-sampled dataset traces an overdensity that covers 25 deg
in Galactic longitude on either side of the Plane, suggesting an extent of 25
deg x 20 deg, corresponding to ~115 x 90 $h_{70}$ Mpc at the supercluster
redshift. In redshift space, the overdensity appears to consist of two merging
wall-like structures, interspersed with clusters and groups. Both the velocity
histogram and the morphology of the multi-branching wall structure are
consistent with a supercluster classification. $K_s^o$ galaxy counts show an
enhancement of ~1.2 over the survey area for galaxies brighter than $M_K^*$ at
the VSCL distance, and a galaxy overdensity of $\delta=0.50\rm{-}0.77$ within a
photometric redshift shell around the VSCL, when compared to various Two-Micron
All-Sky Survey samples. Taking account of selection effects, the VSCL is
estimated to contribute $v_\rm{LG} \gtrsim 50$ km/s to the motion of the Local
Group. | astro-ph_CO |
Modified Starobinsky Inflation: Starobinsky has suggested an inflation model which is obtained from the
vacuum Einstein's equations modified by the one-loop corrections due to
quantized matter fields. Although the one-loop gravitational action is not
known for a general FRW background, it can be obtained in a de Sitter space to
give $\Mp^2 R + \alpha R^2 + \beta R^2 \ln (R/M^2)$. Thus, one needs to
investigate the inflationary behavior of this model compared to the Starobinsky
model (i.e. $\beta = 0$). The coefficient $\alpha$ can be changed by varying
the renormalization scale $M^2$ and $\beta$ is obtained from the quantum
anomaly which is related to the numbers of quantum fields. It has been assumed
that $\alpha \gg \beta$. We investigate the viable values of $\alpha$ and
$\beta$ based on the CMB observation. We also scrutinize the reheating process
in this model. | astro-ph_CO |
The eROSITA Final Equatorial-Depth Survey (eFEDS): LOFAR view of
brightest cluster galaxies and AGN feedback: During the performance verification phase of the SRG/eROSITA telescope, the
eROSITA Final Equatorial-Depth Survey (eFEDS) has been carried out. It covers a
140 deg$^2$ field located at 126$^\circ <$ R.A. $< 146^\circ$ and -3$^\circ <$
Dec. $< +6^\circ$ with a nominal exposure over the field of 2.2 ks. 542
candidate clusters were detected in this field, down to a flux limit $F_X \sim
10^{-14}$ erg s$^{-1}$ cm$^{-2}$ in the 0.5-2 keV band. In order to understand
radio-mode feedback in galaxy clusters, we study the radio emission of
brightest cluster galaxies of eFEDS clusters, and we relate it to the X-ray
properties of the host cluster. Using LOFAR we identify 227 radio galaxies
hosted in the BCGs of the 542 galaxy clusters and groups detected in eFEDS. We
treat non-detections as radio upper limits. We analyse the properties of radio
galaxies, such as redshift and luminosity distribution, offset from the cluster
centre, largest linear size and radio power. We study their relation to the
intracluster medium of the host cluster. We perform statistical tests to deal
with upper limits on the radio luminosities. BCGs with radio-loud AGN are more
likely to lie close to the cluster centre than radio-quiet BCGs. There is a
clear relation between the cluster's X-ray luminosity and the radio power of
the BCG. Statistical tests indicate that this correlation is not produced by
selection effects in the radio band. We see no apparent link between largest
linear size of the radio galaxy and central density of the host cluster.
Converting the radio luminosity to kinetic luminosity, we find that radiative
losses of the intracluster medium are in an overall balance with the heating
provided by the central AGN. Finally, we tentatively classify our objects into
disturbed and relaxed, and we show that the link between the AGN and the ICM
apparently holds regardless of the dynamical state of the cluster. | astro-ph_CO |
Exploring suppressed long-distance correlations as the cause of
suppressed large-angle correlations: The absence of large-angle correlations in the map of cosmic microwave
background temperature fluctuations is among the well-established anomalies
identified in full-sky and cut-sky maps over the past three decades. Suppressed
large-angle correlations are rare statistical flukes in standard inflationary
cosmological models. One natural explanation could be that the underlying
primordial density perturbations lack correlations on large distance scales. To
test this idea, we replace Fourier modes by a wavelet basis with compact
spatial support. While the angular correlation function of perturbations can
readily be suppressed, the observed monopole and dipole-subtracted correlation
function is not generally suppressed. This suggests that suppression of
large-angle temperature correlations requires a mechanism that has both
real-space and harmonic-space effects. | astro-ph_CO |
Reconstructing the interaction between dark energy and dark matter using
Gaussian Processes: We present a nonparametric approach to reconstruct the interaction between
dark energy and dark matter directly from SNIa Union 2.1 data using Gaussian
processes, which is a fully Bayesian approach for smoothing data. In this
method, once the equation of state ($w$) of dark energy is specified, the
interaction can be reconstructed as a function of redshift. For the decaying
vacuum energy case with $w=-1$, the reconstructed interaction is consistent
with the standard $\Lambda$CDM model, namely, there is no evidence for the
interaction. This also holds for the constant $w$ cases from $-0.9$ to $-1.1$
and for the Chevallier-Polarski-Linder (CPL) parametrization case. If the
equation of state deviates obviously from $-1$, the reconstructed interaction
exists at $95\%$ confidence level. This shows the degeneracy between the
interaction and the equation of state of dark energy when they get constraints
from the observational data. | astro-ph_CO |
Reconstructing the baryon acoustic oscillations using biased tracers: The reconstruction of the initial conditions of the Universe is an important
topic in cosmology, particularly in the context of sharpening the measurement
of the baryon acoustic oscillation (BAO) peak. Nonlinear reconstruction
algorithms developed in recent years, when applied to late-time matter fields,
can recover to a substantial degree the initial density distribution, however,
when applied to sparse tracers of the matter field, the performance is poorer.
In this paper we apply the Shi et al. non-linear reconstruction method to
biased tracers in order to establish what factors affect the reconstruction
performance. We find that grid resolution, tracer number density and mass
assignment scheme all have a significant impact on the performance of our
reconstruction method, with triangular-shaped-cloud (TSC) mass assignment and a
grid resolution of ${\sim}1{-}2h^{-1}$ Mpc being the optimal choice. We also
show that our method can be easily adapted to include generic tracer biases up
to quadratic order in the reconstruction formalism. Applying the reconstruction
to halo and galaxy samples with a range of tracer number densities, we find
that the linear bias is by far the most important bias term, while including
nonlocal and nonlinear biases only leads to marginal improvements on the
reconstruction performance. Overall, including bias in the reconstruction
substantially improves the recovery of BAO wiggles, down to
$k\sim0.25~h\text{Mpc}^{-1}$ for tracer number densities between
$2\times10^{-4}$ and $2\times10^{-3}~(h^{-1}\text{Mpc})^{-3}$. | astro-ph_CO |
Symmetry of the CMB sky as a new test of its statistical isotropy. Non
Cosmological Octupole?: In this article we propose a novel test for statistical anisotropy of the
CMB. The test is based on the fact, that the Galactic foregrounds have a
remarcably strong symmetry with respect to their antipodal points and with
respect to the Galactic plane, while the cosmological signal should not be
symmetric or asymmetric under these transitions. We have applied the test for
the octupole component of the WMAP ILC 7 map, by looking at a_3,1 and a_3,3,
and their ratio to a_3,2 both for real and imaginary values. We find abnormal
symmetry of the octupole component at the level of 0.58%, compared to Monte
Carlo simulations. By using the analysis of the phases of the octupole we found
remarkably strong cross-correlations between the phases of kinematic dipole and
ILC 7 octupole, in full agreement with previous results. We further test the
multipole range 2<l<100, by investigating the ratio between the l+m=even and
l+m=odd parts of power spectra. We compare the results to simulations of a
Gaussian random sky, and find significant departure from the statistically
isotropic and homogeneous case, for a very broad range of multipoles. We found
that for the most prominent peaks of our estimator, the phases of the
corresponding harmonics are coherent with phases of the octupole. We believe,
our test would be very useful for detections of various types of residuals of
the foreground and systematic effects at very a broad range of multipoles 2 < l
< 1500-3000 for the forthcoming PLANCK CMB map, before any conclusions about
primordial non-Gaussianity and statistical anisotropy of the CMB. | astro-ph_CO |
Discriminating power of milli-lensing observations for dark matter
models: The nature of dark matter (DM) is still under intense debate. Sub-galactic
scales are particularly critical, as different, currently viable DM models make
diverse predictions on the expected abundance and density profile of DM haloes
on these scales. We investigate the ability of sub-galactic DM haloes to act as
strong lenses on background compact sources, producing gravitational lensing
events on milli-arcsecond scales (milli-lenses), for different DM models. For
each DM scenario, we explore whether a sample of $\sim$ 5000 distant sources is
sufficient to detect at least one milli-lens. We develop a semi-analytical
model to estimate the milli-lensing optical depth as a function of the source's
redshift for various DM models. We employ the Press-Schechter formalism, as
well as results from recent N-body simulations to compute the halo mass
function, taking into account the appropriate spherically averaged density
profile of haloes for each DM model. We treat the lensing system as a
point-mass lens and invoke the effective surface mass density threshold to
calculate the fraction of a halo that acts as a gravitational lens. We study
three classes of dark matter models: cold DM, warm DM, and self-interacting DM.
We find that haloes consisting of warm DM turn out to be optically thin for
strong gravitational milli-lensing (zero expected lensing events). CDM haloes
may produce lensing events depending on the steepness of the concentration-mass
relation. Self-interacting DM haloes can efficiently act as gravitational
milli-lenses only if haloes experience gravothermal collapse, resulting in
highly dense central cores. | astro-ph_CO |
Steep Faint-end Slopes of Galaxy Mass and Luminosity Functions at z>=6
and the Implications for Reionisation: We present the results of a numerical study comparing photometric and
physical properties of simulated z=6-9 galaxies to the observations taken by
the WFC3 instrument aboard the Hubble Space Telescope. Using cosmological
hydrodynamical simulations we find good agreement with observations in
color-color space at all studied redshifts. We also find good agreement between
observations and our Schechter luminosity function fit in the observable range,
Muv<= -18, provided that a moderate dust extinction effect exists for massive
galaxies. However beyond what currently can be observed, simulations predict a
very large number of low-mass galaxies and evolving steep faint-end slopes from
alpha_L = -2.15 at z=6 to alpha_L = -2.64 at z=9, with a dependence of
|alpha_L| \propto (1+z)^0.59. During the same epoch, the normalization phi*
increases and the characteristic magnitude Muv* becomes moderately brighter
with decreasing redshift. We find similar trends for galaxy stellar mass
function with evolving low-mass end slope from alpha_M = - 2.26 at z=6 to
alpha_M = -2.87 at z=9, with a dependence of |alpha_M| \propto (1+z)^0.65.
Together with our recent result on the high escape fraction of ionizing photons
for low-mass galaxies, our results suggest that the low-mass galaxies are
important contributor of ionizing photons for the reionisation of the Universe
at z>=6. | astro-ph_CO |
Herschel-ATLAS: far-infrared properties of radio-selected galaxies: We use the Herschel-ATLAS science demonstration data to investigate the
star-formation properties of radio-selected galaxies in the GAMA-9h field as a
function of radio luminosity and redshift. Radio selection at the lowest radio
luminosities, as expected, selects mostly starburst galaxies. At higher radio
luminosities, where the population is dominated by AGN, we find that some
individual objects are associated with high far-infrared luminosities. However,
the far-infrared properties of the radio-loud population are statistically
indistinguishable from those of a comparison population of radio-quiet galaxies
matched in redshift and K-band absolute magnitude. There is thus no evidence
that the host galaxies of these largely low-luminosity (Fanaroff-Riley class
I), and presumably low-excitation, AGN, as a population, have particularly
unusual star-formation histories. Models in which the AGN activity in
higher-luminosity, high-excitation radio galaxies is triggered by major mergers
would predict a luminosity-dependent effect that is not seen in our data (which
only span a limited range in radio luminosity) but which may well be detectable
with the full Herschel-ATLAS dataset. | astro-ph_CO |
Beyond the Boost: Measuring the intrinsic dipole of the CMB using the
spectral distortions of the monopole and quadrupole: We present a general framework for accurate spectral modeling of the low
multipoles of the cosmic microwave background (CMB) as observed in a boosted
frame. In particular, we demonstrate how spectral measurements of the low
multipoles can be used to separate the motion-induced dipole of the CMB from a
possible intrinsic dipole component. In a moving frame, the leakage of an
intrinsic dipole moment into the CMB monopole and quadrupole induces spectral
distortions with distinct frequency functions that respectively peak at 337 GHz
and 276 GHz. The leakage into the quadrupole moment also induces a geometrical
distortion to the spatial morphology of this mode. The combination of these
effects can be used to lift the degeneracy between the motion-induced dipole
and any intrinsic dipole that the CMB might possess. Assuming the current
peculiar velocity measurements, the leakage of an intrinsic dipole with an
amplitude of $\Delta T = 30\mu$K into the monopole and quadrupole moments will
be detectable by a PIXIE--like experiment at $\sim 40~$nK ($2.5\sigma$) and
$\sim 130~$nK ($11\sigma$) level at their respective peak frequencies. | astro-ph_CO |
Using Cumulative Number Densities to Compare Galaxies across Cosmic Time: Comparing galaxies across redshifts at fixed cumulative number density is a
popular way to estimate the evolution of specific galaxy populations. This
method ignores scatter in mass accretion histories and galaxy-galaxy mergers,
which can lead to errors when comparing galaxies over large redshift ranges
(Delta z > 1). We use abundance matching in the LCDM paradigm to estimate the
median change in number density with redshift and provide a simple fit (+0.16
dex per unit Delta z) for progenitors of z = 0 galaxies. We find that galaxy
descendants do not evolve in the same way as galaxy progenitors, largely due to
scatter in mass accretion histories. We also provide estimates for the 1-sigma
range of number densities corresponding to galaxy progenitors and descendants.
Finally, we discuss some limits on number density comparisons, which arise due
to difficulties measuring physical quantities (e.g., stellar mass) consistently
across redshifts. A public tool to calculate number density evolution for
galaxies, as well as approximate halo masses, is available online. | astro-ph_CO |
Constraints on primordial magnetic fields from the optical depth of the
cosmic microwave background: Damping of magnetic fields via ambipolar diffusion and decay of
magnetohydrodynamical (MHD) turbulence in the post decoupling era heats the
intergalactic medium (IGM). Delayed recombination of hydrogen atoms in the IGM
yields an optical depth to scattering of the cosmic microwave background (CMB).
The optical depth generated at $z\gg 10$ does not affect the "reionization
bump" of the CMB polarization power spectrum at low multipoles, but affects the
temperature and polarization power spectra at high multipoles. Writing the
present-day energy density of fields smoothed over the damping scale at the
decoupling epoch as $\rho_{B,0}=B_{0}^2/2$, we constrain $B_0$ as a function of
the spectral index, $n_B$. Using the Planck 2013 likelihood code that uses the
Planck temperature and lensing data together with the WMAP 9-year polarization
data, we find the 95% upper bounds of $B_0<0.63$, 0.39, and 0.18~nG for
$n_B=-2.9$, $-2.5$, and $-1.5$, respectively. For these spectral indices, the
optical depth is dominated by dissipation of the decaying MHD turbulence that
occurs shortly after the decoupling epoch. Our limits are stronger than the
previous limits ignoring the effects of the fields on ionization history.
Inverse Compton scattering of CMB photons off electrons in the heated IGM
distorts the thermal spectrum of CMB. Our limits on $B_0$ imply that the
$y$-type distortion from dissipation of fields in the post decoupling era
should be smaller than $10^{-9}$, $4\times10^{-9}$, and $10^{-9}$,
respectively. | astro-ph_CO |
The cosmic shallows I: interaction of CMB photons in extended galaxy
halos: We report and analyse the presence of foregrounds in the cosmic microwave
background (CMB) radiation associated to extended galactic halos. Using the
cross correlation of Planck and WMAP maps and the 2MRS galaxy catalogue, we
find that the mean temperature radial profiles around nearby galaxies at $cz\le
4500~\rm{km~s^{-1}}$ show a statistically significant systematic decrease of
$\sim 15~\mu \rm{K}$ extending up to several galaxy radii. This effect strongly
depends on the galaxy morphological type at scales within several tens of times
the galaxy size, becoming nearly independent of galaxy morphology at larger
scales. The effect is significantly stronger for the more extended galaxies,
with galaxy clustering having a large impact on the results. Our findings
indicate the presence of statistically relevant foregrounds in the CMB maps
that should be considered in detailed cosmological studies. Besides, we argue
that these can be used to explore the intergalactic medium surrounding bright
late-type galaxies and allow for diverse astrophysical analyses. | astro-ph_CO |
The observed galaxy bispectrum from single-field inflation in the
squeezed limit: Using the consistency relation in Fourier space, we derive the observed
galaxy bispectrum from single-field inflation in the squeezed limit, in which
one of the three modes has a wavelength much longer than the other two. This
provides a non-trivial check of the full computation of the bispectrum based on
second-order cosmological perturbation theory in this limit. We show that gauge
modes need to be carefully removed in the second-order cosmological
perturbations in order to calculate the observed galaxy bispectrum in the
squeezed limit. We then give an estimate of the effective non-Gaussianity due
to general relativistic lightcone effects that could mimic a primordial
non-Gaussian signal. | astro-ph_CO |
The environment and redshift dependence of accretion onto dark matter
halos and subhalos: A dark-matter-only Horizon Project simulation is used to investigate the
environment- and redshift- dependence of accretion onto both halos and
subhalos. These objects grow in the simulation via mergers and via accretion of
diffuse non-halo material, and we measure the combined signal from these two
modes of accretion. It is found that the halo accretion rate varies less
strongly with redshift than predicted by the Extended Press-Schechter (EPS)
formalism and is dominated by minor-merger and diffuse accretion events at z=0,
for all halos. These latter growth mechanisms may be able to drive the
radio-mode feedback hypothesised for recent galaxy-formation models, and have
both the correct accretion rate and form of cosmological evolution. The low
redshift subhalo accretors in the simulation form a mass-selected subsample
safely above the mass resolution limit that reside in the outer regions of
their host, with ~70% beyond their host's virial radius, where they are
probably not being significantly stripped of mass. These subhalos accrete, on
average, at higher rates than halos at low redshift and we argue that this is
due to their enhanced clustering at small scales. At cluster scales, the mass
accretion rate onto halos and subhalos at low redshift is found to be only
weakly dependent on environment and we confirm that at z~2 halos accrete
independently of their environment at all scales, as reported by other authors.
By comparing our results with an observational study of black hole growth, we
support previous suggestions that at z>1, dark matter halos and their
associated central black holes grew coevally, but show that by the present day,
dark matter halos could be accreting at fractional rates that are up to a
factor 3-4 higher than their associated black holes. | astro-ph_CO |
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. | astro-ph_CO |
Extracting the Global 21-cm signal from Cosmic Dawn and Epoch of
Reionization in the presence of Foreground and Ionosphere: Detection of redshifted \ion{H}{i} 21-cm emission is a potential probe for
investigating the Universe's first billion years. However, given the
significantly brighter foreground, detecting 21-cm is observationally
difficult. The Earth's ionosphere considerably distorts the signal at low
frequencies by introducing directional-dependent effects. Here, for the first
time, we report the use of Artificial Neural Networks (ANNs) to extract the
global 21cm signal characteristics from the composite all-sky averaged signal,
including foreground and ionospheric effects such as refraction, absorption,
and thermal emission from the ionosphere's F and D-layers. We assume a
'perfect' instrument and neglect instrumental calibration and beam effects. To
model the ionospheric effect, we considered the static and time-varying
ionospheric conditions for the mid-latitude region where LOFAR is situated. In
this work, we trained the ANN model for various situations using a synthetic
set of the global 21cm signals created by altering its parameter space based on
the "$\rm \tanh$" parameterized model and the Accelerated Reionization Era
Simulations (ARES) algorithm. The obtained result shows that the ANN model can
extract the global signal parameters with an accuracy of $\ge 96 \% $ in the
final study when we include foreground and ionospheric effects. On the other
hand, a similar ANN model can extract the signal parameters from the final
prediction dataset with an accuracy ranging from $97 \%$ to $98 \%$ when
considering more realistic sets of the global 21cm signals based on physical
models. | astro-ph_CO |
ALMA Observations of SPT-Discovered, Strongly Lensed, Dusty,
Star-Forming Galaxies: We present Atacama Large Millimeter/submillimeter Array (ALMA) 860 micrometer
imaging of four high-redshift (z=2.8-5.7) dusty sources that were detected
using the South Pole Telescope (SPT) at 1.4 mm and are not seen in existing
radio to far-infrared catalogs. At 1.5 arcsec resolution, the ALMA data reveal
multiple images of each submillimeter source, separated by 1-3 arcsec,
consistent with strong lensing by intervening galaxies visible in near-IR
imaging of these sources. We describe a gravitational lens modeling procedure
that operates on the measured visibilities and incorporates
self-calibration-like antenna phase corrections as part of the model
optimization, which we use to interpret the source structure. Lens models
indicate that SPT0346-52, located at z=5.7, is one of the most luminous and
intensely star-forming sources in the universe with a lensing corrected FIR
luminosity of 3.7 X 10^13 L_sun and star formation surface density of 4200
M_sun yr^-1 kpc^-2. We find magnification factors of 5 to 22, with lens
Einstein radii of 1.1-2.0 arcsec and Einstein enclosed masses of 1.6-7.2x10^11
M_sun. These observations confirm the lensing origin of these objects, allow us
to measure the their intrinsic sizes and luminosities, and demonstrate the
important role that ALMA will play in the interpretation of lensed
submillimeter sources. | astro-ph_CO |
Primordial Non-Gaussianity in the Cosmic Microwave Background: In the last few decades, advances in observational cosmology have given us a
standard model of cosmology. We know the content of the universe to within a
few percent. With more ambitious experiments on the way, we hope to move beyond
the knowledge of what the universe is made of, to why the universe is the way
it is. In this review paper we focus on primordial non-Gaussianity as a probe
of the physics of the dynamics of the universe at the very earliest moments. We
discuss 1) theoretical predictions from inflationary models and their
observational consequences in the cosmic microwave background (CMB)
anisotropies; 2) CMB--based estimators for constraining primordial
non-Gaussianity with an emphasis on bispectrum templates; 3) current
constraints on non-Gaussianity and what we can hope to achieve in the near
future; and 4) non-primordial sources of non-Gaussianities in the CMB such as
bispectrum due to second order effects, three way cross-correlation between
primary-lensing-secondary CMB, and possible instrumental effects. | astro-ph_CO |
Loop contributions to the scalar power spectrum due to quartic order
action in ultra slow roll inflation: [Abridged] In contemporary literature, the calculation of modifications to
the inflationary scalar power spectrum due to the loops from the higher order
interaction terms in the Hamiltonian have led to a discussion regarding the
validity of perturbation theory. Recently, there have been efforts to examine
the contributions to the scalar power spectrum due to the loops arising from
the cubic order terms in the action describing the perturbations, specifically
in inflationary scenarios that permit an epoch of ultra slow roll (USR). A
phase of USR inflation leads to significant observational consequences, such as
the copious production of primordial black holes. In this work, we study the
loop contributions to the scalar power spectrum in a scenario of USR inflation
arising due to the quartic order terms in the action describing the scalar
perturbations. We compute the loop contributions to the scalar power spectrum
due to the dominant term in the action at the quartic order. We consider a
scenario wherein a phase of USR is sandwiched between two stages of slow roll
inflation and analyze the behavior of the loop contributions in terms of the
parameters involved. We examine the late, intermediate and early epochs of USR
during inflation. In the inflationary scenario involving a late phase of USR,
for reasonable choices of the parameters, we show that the loop corrections are
negligible for the entire range of wave numbers. In the intermediate case, the
contributions from the loops prove to be scale invariant over large scales, and
we find that these contributions can amount to 30% of the leading order power
spectrum. In the case wherein USR sets in early, we find that the loop
contributions could be negative and can dominate the power spectrum at the
leading order, which indicates a breakdown of the perturbative expansion. We
conclude with a brief summary and outlook. | astro-ph_CO |
Explaining Excess Dipole in NVSS Data Using Superhorizon Perturbation: Many observations in recent times have shown evidence against the standard
assumption of isotropy in the Big Bang model. Introducing a superhorizon scalar
metric perturbation has been able to explain some of these anomalies. In this
work, we probe the net velocity arising due to the perturbation. We find that
this extra component does not contribute to the CMB dipole amplitude while it
does contribute to the dipole in large scale structures. Thus, within this
model's framework, our velocity with respect to the large scale structure is
not the same as that extracted from the CMB dipole, assuming it to be of purely
kinematic origin. Taking this extra velocity component into account, we study
the superhorizon mode's implications for the excess dipole observed in the NRAO
VLA Sky Survey (NVSS). We find that the mode can consistently explain both the
CMB and NVSS observations. We also find that the model leads to small
contributions to the local bulk flow and the dipole in Hubble parameter, which
are consistent with observations. The model leads to several predictions which
can be tested in future surveys. In particular, it implies that the observed
dipole in large scale structure should be redshift dependent and should show an
increase in amplitude with redshift. We also find that the Hubble parameter
should show a dipole anisotropy whose amplitude must increase with redshift in
the CMB frame. Similar anisotropic behaviour is expected for the observed
redshift as a function of the luminosity distance. | astro-ph_CO |
Cosmological backreaction: This work summarises some of the attempts to explain the phenomenon of dark
energy as an effective description of complex gravitational physics and the
proper interpretation of observations. Cosmological backreaction has been shown
to be relevant for observational (precision) cosmology, nevertheless no
convincing explanation of dark energy by means of backreaction has been given
so far. | astro-ph_CO |
Unleashing Positive Feedback: Linking the Rates of Star Formation,
Supermassive Black Hole Accretion and Outflows in Distant Galaxies: Pressure-regulated star formation is a simple variant on the usual
supernova-regulated star formation efficiency that controls the global star
formation rate as a function of cold gas content in star-forming galaxies, and
accounts for the Schmidt-Kennicutt law in both nearby and distant galaxies.
Inclusion of AGN-induced pressure, by jets and/or winds that flow back onto a
gas-rich disk, can lead under some circumstances to significantly enhanced star
formation rates, especially at high redshift and most likely followed by the
more widely accepted phase of star formation quenching. Simple expressions are
derived that relate supermassive black hole growth, star formation and outflow
rates. The ratios of black hole to spheroid mass and of both black hole
accretion and outflow rates to star formation rate are predicted as a function
of time. I suggest various tests of the AGN-triggered star formation
hypothesis. | astro-ph_CO |
Flaring Patterns in Blazars: Blazars radiate from relativistic jets launched by a supermassive black hole
along our line of sight; the subclass of FSRQs exhibits broad emission lines, a
telltale sign of a gas-rich environment and high accretion rate, contrary to
the other subclass of the BL Lacertae objects. We show that this dichotomy of
the sources in physical properties is enhanced in their flaring activity. The
BL Lac flares yielded spectral evidence of being driven by further acceleration
of highly relativistic electrons in the jet. Here we discuss spectral fits of
multi-lambda data concerning strong flares of the two flat spectrum radio
quasars 3C 454.3 and 3C 279 recently detected in gamma rays by the AGILE and
Fermi satellites. We find that optimal spectral fits are provided by external
Compton radiation enhanced by increasing production of thermal seed photons by
growing accretion. We find such flares to trace patterns on the jet power -
electron energy plane that diverge from those followed by flaring BL Lacs, and
discuss why these occur. | astro-ph_CO |
The origin of the WMAP quadrupole: The cosmic microwave background (CMB) temperature maps from the Wilkinson
Microwave Anisotropy Probe (WMAP) are of great importance for cosmology. In
previous work we had developed a pipeline for map-making independently of the
WMAP team. The new maps produced from the WMAP raw data by our pipeline are
notably different to the official ones, and the power spectrum as well as the
best-fit cosmological parameters are significantly different too. What's more,
by revealing the inconsistency between the WMAP raw data and their official
map, we had pointed out that there must exist an unexpected problem in the WMAP
team's pipeline. In this work, we find that the trouble comes from the
inaccuracy of antenna pointing direction caused by a systematical time drift
between the attitude data and the science data in the WMAP raw time-order data
(TOD). The CMB quadrupole in the WMAP release can be exactly generated from a
differential dipole field which is completely determined by the spacecraft
velocity and the antenna directions without using any CMB signal. After
correcting the WMAP team's error, the CMB quadrupole component disappears.
Therefore, the released WMAP CMB quadrupole is almost completely artificial and
the real quadrupole of the CMB anisotropy should be near zero. Our finding is
important for understanding the early universe. | astro-ph_CO |
Density Perturbation Growth in Teleparallel Cosmology: We study the cosmological perturbations in teleparallel dark energy models in
which there is a dynamical scalar field with a non-minimal coupling to gravity.
We find that the propagating degrees of freedom are the same as in quintessence
cosmology despite that variables of the perturbed vierbein field are greater
than those in metric theories. We numerically show some evident discrepancy
from general relativity in the evolutions of the perturbations on all scales of
the universe. We also demonstrate that the gravitational interactions are
enhanced during the unique tracker evolutions in these models. | astro-ph_CO |
Testing the Alignment Tendency of Some Polarized Radio Sources: Measuring the alignment of polarized radio sources requires comparing vectors
at different locations on the sky, i.e. on a sphere. A test of alignment is
derived herein. While both large scale and coordinate independent, the test
avoids the mathematical subtleties involved when comparing vectors at different
locations on a curved surface. Applied to 5442 sources drawn from a published
catalog, the analysis finds a level of alignment that would be matched by only
7% to 14% of data sets with the same sources but with random polarization
directions. The locations of the sources involved and the directions that the
vectors favor and the regions avoided are described as well. | astro-ph_CO |
Non-Gaussianity of diffuse Galactic synchrotron emission at 408 MHz: Diffuse Galactic emission at low frequencies is a major contaminant for
studies of redshifted $21$ cm line studies. Removal of these foregrounds is
essential for exploiting the signal from neutral hydrogen at high redshifts.
Analysis of foregrounds and its characteristics is thus of utmost importance.
It is customary to test efficacy of foreground removal techniques using
simulated foregrounds. Most simulations assume that the distribution of the
foreground signal is a Gaussian random field. In this work we test this
assumption by computing the binned bispectrum for the all-sky $408$ MHz map.
This is done by applying different brightness temperature ($T$) thresholds in
order to assess whether the cooler parts of the sky have different
characteristics. We find that regions with a low brightness temperature $T <
25$ K indeed have smaller departures from a Gaussian distribution. Therefore,
these regions of the sky are ideal for future H{\sc i} intensity mapping
surveys. | astro-ph_CO |
Spherical collapse model with non-clustering dark energy: We investigate a spherical overdensity model for the non-clustering dark
energy (DE) with the constant equation of state, w in a flat universe. In this
case, the exact solution for the evolution of the scale factor is obtained for
general w. We also obtain the exact (when w = - 1/3) and the approximate (when
w neq -1/3) solutions for the ratio of the overdensity radius to its value at
the turnaround epoch (y) for general cosmological parameters. Also the exact
and approximate solutions of the overdensity at the turnaround epoch (zeta) are
obtained for general w. Thus, we are able to obtain the non-linear overdensity
Delta = 1 + delta at any epoch for the given DE model. The non-linear
overdensity at the virial epoch (Delta_{vir}) is obtained by using the virial
theorem and the energy conservation. The non-linear overdensity of every DE
model converges to that of the Einstein de Sitter universe ~ 147 when
z_{vir}increases. We find that the observed quantities at high redshifts are
insensitive to the different w models. The low-redshift cluster (z_{vir} ~
0.04, i.e., z_{ta} ~ 0.7) shows the most model dependent feature and it should
be a suitable object for testing DE models. Also as Omo increases, the model
dependence of the observed quantities decreases. The error in the approximate
solutions is at most 2% for a wide range of the parameter space. Even though
the analytic forms of y and \zeta are obtained for the constant w, they can be
generalized to the slowly varying w. Thus, these analytic forms of the scale
factor, y, and zeta provide a very accurate and useful tool for measuring the
properties of DE. | astro-ph_CO |
The Size, Shape and Orientation of Cosmological Voids in the Sloan
Digital Sky Survey: We present a detailed description of our void finding algorithm which is an
extension of the prescription by Hoyle and Vogeley (2002). We include a
discussion of the reproducibility and robustness of the algorithm as well as
the statistical significance of the detected voids. We apply our void finder to
the Data Release 5 (DR5) of the Sloan Digital Sky Survey (SDSS) and identify
232 cosmological voids. A void catalog which contains the most salient
properties of the detected voids is created. We present a statistical analysis
of the distribution of the size, shape and orientation of our identified
cosmological voids. We also investigate possible trends with redshift for 0.04
< z < 0.16. We compare our results to those from an identical analysis of a
mock catalog based on the LambdaCDM model and find reasonable agreement.
However, some statistically significant differences in the overall orientation
of cosmological voids are present and will have to be reconciled by further
refinement of the simulations. | astro-ph_CO |
The Origin of Dust in Early-Type Galaxies and Implications for Accretion
onto Supermassive Black Holes: We have conducted an archival Spitzer study of 38 early-type galaxies (ETGs)
in order to determine the origin of the dust in approximately half of this
population. Our sample galaxies generally have good wavelength coverage from
3.6um to 160um, as well as visible-wavelength HST images. We use the Spitzer
data to estimate dust masses, or establish upper limits, and find that all of
the ETGs with dust lanes in the HST data are detected in all of the Spitzer
bands and have dust masses of ~10^{5-6.5} Msun, while galaxies without dust
lanes are not detected at 70um and 160um and typically have <10^5 Msun of dust.
The apparently dust-free galaxies do have 24um emission that scales with the
shorter wavelength flux, yet substantially exceeds the expectations of
photospheric emission by approximately a factor of three. We conclude this
emission is dominated by hot, circumstellar dust around evolved stars that does
not survive to form a substantial interstellar component. The order of
magnitude variations in dust masses between galaxies with similar stellar
populations rules out a subtantial contribution from continual, internal
production in spite of the clear evidence for circumstellar dust. We
demonstrate that the interstellar dust is not due to purely external accretion,
unless the product of the merger rate of dusty satellites and the dust lifetime
is at least an order of magnitude higher than expected. We propose that dust in
ETGs is seeded by external accretion, yet the accreted dust is maintained by
continued growth in externally-accreted cold gas beyond the nominal lifetime of
individual grains. The several Gyr depletion time of the cold gas is long
enough to reconcile the fraction of dusty ETGs with the merger rate of gas-rich
satellites. As the majority of dusty ETGs are also low-luminosity AGN and
likely fueled by this cold gas, their lifetime should similarly be several Gyr. | astro-ph_CO |
Accounting for selection effects in the BH-bulge relations: No evidence
for cosmological evolution: The redshift evolution of the black hole - bulge relations is an essential
observational constraint for models of black hole - galaxy coevolution. In
addition to the observational challenges for these studies, conclusions are
complicated by the influence of selection effects. We demonstrate that there is
presently no statistical significant evidence for cosmological evolution in the
black hole-bulge relations, once these selection effects are taken into account
and corrected for. We present a fitting method, based on the bivariate
distribution of black hole mass and galaxy property, that accounts for the
selection function in the fitting and is therefore able to recover the
intrinsic black hole - bulge relation unbiased. While prior knowledge is
restricted to a minimum, we at least require knowledge of either the sample
selection function and the mass dependence of the active fraction, or the
spheroid distribution function and the intrinsic scatter in the black hole -
bulge relation. We employed our fitting routine to existing studies of the
black hole-bulge relation at z~1.5 and z~6, using our current best knowledge of
the distribution functions. There is no statistical significant evidence for
positive evolution in the MBH-M* ratio out to z~2. At z~6 the current
constraints are less strong, but we demonstrate that the large observed
apparent offset from the local black hole-bulge relation at z~6 is fully
consistent with no intrinsic offset. The method outlined here provides a tool
to obtain more reliable constraints on black hole - galaxy co-evolution in the
future. | astro-ph_CO |
Enhancing Bispectrum Estimators for Galaxy Redshift Surveys with
Velocities: We forecast the ability of bispectrum estimators to constrain primordial
non-Gaussianity using future photometric galaxy redshift surveys. A full-sky
survey with photometric redshift resolution of $\sigma_z/(1+z)=0.05$ in the
redshift range $0.2<z<2$ can provide constraints
$\sigma(f^\mathrm{local}_\mathrm{NL})=3.4$,
$\sigma(f^\mathrm{equil}_\mathrm{NL})=15$, and
$\sigma(f^\mathrm{orth}_\mathrm{NL})=17$ for the local, equilateral, and
orthogonal shapes respectively, delivering constraints on primordial
non-Gaussianities competitive to those from the cosmic microwave background. We
generalize these results by deriving a scaling relation for the constraints on
the amplitude of primordial non-Gaussianity as a function of redshift error,
depth, sky coverage, and nonlinear scale cutoff. Finally, we investigate the
impact that photometric calibration errors on the largest scales will have on
the constraining power of future experiments. We show that peculiar velocities
reconstructed via kinetic Sunyaev Zeldovich tomography can be used to mitigate
the impact of calibration errors on primordial non-Gaussianity constraints. | astro-ph_CO |
Dark matter decay in the Milky Way halo: Dark matter may be detected in X-ray decay, including from the decay of the
dark matter particles that make up the Milky Way (MW) halo. We use a range of
density profiles to compute X-ray line intensity profiles, with a focus on the
resonantly produced sterile neutrino dark matter candidate. Compared to the
Navarro--Frenk--White density profile, we show that using an adiabatically
contracted halo profile suppresses the line intensity in the halo outskirts and
enhances it in the Galactic Centre (GC), although this enhancement is
eliminated by the likely presence of a core within 3~kpc. Comparing our results
to MW halo observations, other X-ray observations, and structure formation
constraints implies a sterile neutrino mixing angle parameter
$s_{11}\equiv\sin^{2}(2\theta)\times10^{11}\sim[3,4]$ (particle lifetime
$\tau_{28}\equiv\tau/(10^{28}\mathrm{sec})\sim[1.0,1.3]$), which is
nevertheless is strong tension with some reported non-detections. We make
predictions for the likely decay flux that the XRISM satellite would measure in
the GC, plus the Virgo and Perseus clusters, and outline further steps to
determine whether the dark matter is indeed resonantly produced sterile
neutrinos as detected in X-ray decay. | astro-ph_CO |
Constraints on primordial black holes with CMB spectral distortions: In the mixed dark matter scenarios consisting of primordial black holes
(PBHs) and weakly interacting massive particles (WIMPs), WIMPs can be accreted
onto PBHs to form ultracompact minihalos (UCMHs) with a density spike in the
early universe. Compared with the classical dark matter halo, UCMHs are formed
earlier and have a higher density of center. Since the annihilation rate is
proportional to the squared number density of WIMPs, it is expected that WIMPs
annihilation within UCMHs is enhanced and has influences on the early universe.
Between the time of recombination and matter-radiation equality, the energy
released from WIMPs annihilation within UCMHs is injected into the Universe
resulting in CMB $y$-type distortion. We investigate these effects and derive
the upper limits on the abundance of PBHs taking advantage of the observational
results of Far Infrared Absolute Spectrophotometer (FIRAS). We find that for
the WIMPs mass range $1\le m_{\chi}\le 1000~\rm GeV$, the upper limits on the
abundance of PBHs are $5\times 10^{-3}\le \Omega_{\rm PBH}\le 5\times 10^{-2}$. | astro-ph_CO |
New polarimetric constraints on axion-like particles: We show that the parameter space of axion-like particles can be severly
constrained using high-precision measurements of quasar polarisations. Robust
limits are derived from the measured bounds on optical circular polarisation
and from the distribution of linear polarisations of quasars. As an outlook,
this technique can be improved by the observation of objects located behind
clusters of galaxies, using upcoming space-borne X-ray polarimeters. | astro-ph_CO |
Are "Changing-Look'' Active Galactic Nuclei Special in the Coevolution
of Supermassive Black Holes and their Hosts? I: The nature of the so-called ``changing-look'' (CL) active galactic nucleus
(AGN), which is characterized by spectral-type transitions within $\sim10$~yr,
remains an open question. As the first in our series of studies, we here
attempt to understand the CL phenomenon from a view of the coevolution of AGNs
and their host galaxies (i.e., if CL-AGNs are at a specific evolutionary stage)
by focusing on the SDSS local ``partially obscured'' AGNs in which the stellar
population of the host galaxy can be easily measured in the integrated spectra.
A spectroscopic follow-up program using the Xinglong 2.16~m, Lick/Shane 3~m,
and Keck 10~m telescopes enables us to identify in total 9 CL-AGNs from a
sample of 59 candidates selected by their mid-infrared variability. Detailed
analysis of these spectra shows that the host galaxies of the CL-AGNs are
biased against young stellar populations and tend to be dominated by
intermediate-age stellar populations. This motivates us to propose that CL-AGNs
are probably particular AGNs at a specific evolutionary stage, such as a
transition stage from ``feast'' to ``famine'' fueling of the supermassive black
hole. In addition, we reinforce the previous claim that CL-AGNs tend to be
biased against both a high Eddington ratio and a high bolometric luminosity,
suggesting that the disk-wind broad-line-region model is a plausible
explanation of the CL phenomenon. | astro-ph_CO |
Spectrum of the Anomalous Microwave Emission in the North Celestial Pole
with WMAP 7-Year data: We estimate the frequency spectrum of the diffuse anomalous microwave
emission (AME) on the North Celestial Pole (NCP) region of the sky with the
Correlated Component Analysis (CCA) component separation method applied to WMAP
7-yr data. The NCP is a suitable region for this analysis because the AME is
weakly contaminated by synchrotron and free-free emission. By modeling the AME
component as a peaked spectrum we estimate the peak frequency to be
$21.7\pm0.8$\,GHz, in agreement with previous analyses which favored $\nu_{\rm
p}<23$\,GHz. The ability of our method to correctly recover the position of the
peak is verified through simulations. We compare the estimated AME spectrum
with theoretical spinning dust models to constrain the hydrogen density $n_{\rm
H}$. The best results are obtained with densities around 0.2--0.3\,cm$^{-3}$,
typical of warm ionised medium (WIM) to warm neutral medium (WNM) conditions.
The degeneracy with the gas temperature prevents an accurate determination of
$n_{\rm H}$, especially for low hydrogen ionization fractions, where densities
of a few cm$^{-3}$ are also allowed. | astro-ph_CO |
The modified gravity lightcone simulation project I: Statistics of
matter and halo distributions: We introduce a set of four very high resolution cosmological simulations for
exploring $f(R)$-gravity, with $2048^3$ particles in $768\,h^{-1}\textrm{Mpc}$
and $1536\,h^{-1}\textrm{Mpc}$ simulation boxes, both for a
$|\overline{f_{R0}}| = 10^{-5}$ model and a $\Lambda$CDM comparison universe,
making the set the largest simulations of $f(R)$-gravity to date. In order to
mimic real observations, the simulations include a continuous 2D and 3D
lightcone output which is dedicated to study lensing and clustering statistics
in modified gravity. In this work, we present a detailed analysis and
resolution study for the matter power spectrum in $f(R)$-gravity over a wide
range of scales. We also analyse the angular matter power spectrum and lensing
convergence on the lightcone. In addition, we investigate the impact of
modified gravity on the halo mass function, matter and halo auto-correlation
functions, linear halo bias and the concentration-mass relation. We find that
the impact of $f(R)$-gravity is generally larger on smaller scales and
increases with decreasing redshift. Comparing our simulations to
state-of-the-art hydrodynamical simulations we confirm a degeneracy between
$f(R)$-gravity and baryonic feedback in the matter power spectrum on small
scales, but also find that scales around $k = 1\, h\, {\rm Mpc}^{-1}$ are
promising to distinguish both effects. The lensing convergence power spectrum
is increased in $f(R)$-gravity. Interestingly available numerical fits are in
good agreement overall with our simulations for both standard and modified
gravity, but tend to overestimate their relative difference on non-linear
scales by few percent. We also find that the halo bias is lower in
$f(R)$-gravity compared to general relativity, whereas halo concentrations are
increased for unscreened halos. | astro-ph_CO |
Simultaneous modelling of matter power spectrum and bispectrum in the
presence of baryons: We demonstrate that baryonification algorithms, which displace particles in
gravity-only simulations according to physically-motivated prescriptions, can
simultaneously capture the impact of baryonic physics on the 2 and 3-point
statistics of matter. Specifically, we show that our implementation of a
baryonification algorithm jointly fits the changes induced by baryons on the
power spectrum and equilateral bispectrum on scales up to k < 5 h/Mpc and
redshifts z<2, as measured in six different cosmological hydrodynamical
simulations. The accuracy of our fits are typically 1% for the power spectrum,
and for the equilateral and squeezed bispectra, which somewhat degrades to 3%
for simulations with extreme feedback prescriptions. Our results support the
physical assumptions underlying baryonification approaches, and encourage their
use in interpreting weak gravitational lensing and other cosmological
observables. | astro-ph_CO |
The role of quasars in galaxy formation: We discuss evidence that quasars, and more generally radio jets, may have
played an active role in the formation stage of galaxies by inducing star
formation, i.e. through positive feedback. This mechanism first proposed in the
70's has been considered as anecdotic until now, contrary to the opposite
effect that is generally put forward, the quenching of star formation in
massive galaxies to explain the galaxy bimodality, downsizing and the universal
black hole mass over bulge stellar mass ratio. This suggestion is based on the
recent discovery of an ultra-luminous infrared galaxies, i.e. an extreme
starburst, which appears to be triggered by a radio jet from the QSO
HE0450-2958 at z=0.2863, together with the finding in several systems of an
offset between molecular gas and quasars, which may be explained by the
positive feedback effect of radio jets on their local environment. | astro-ph_CO |
A Hydrodynamical Approach to CMB mu-distortions: Spectral distortion of the cosmic microwave background provides a unique
opportunity to probe primordial perturbations on very small scales by
performing large-scale measurements. We discuss in a systematic and pedagogic
way all the relevant physical phenomena involved in the production and
evolution of the mu-type spectral distortion. Our main results agree with
previous estimates (in particular we show that a recently found factor of 3/4
arises from relativistic corrections to the wave energy). We also discuss
several subleading corrections such as adiabatic cooling and the effects of
bulk viscosity, baryon loading and photon heat conduction. Finally we calculate
the transfer function for mu-distortions between the end of the mu-era and now. | astro-ph_CO |
Extending the Coyote emulator to dark energy models with standard
$w_0$-$w_a$ parametrization of the equation of state: We discuss an extension of the Coyote emulator to predict non-linear matter
power spectra of dark energy (DE) models with a scale factor dependent equation
of state of the form w = w_0 + ( 1 - a )w_a . The extension is based on the
mapping rule between non-linear spectra of DE models with constant equation of
state and those with time varying one originally introduced in ref. [40]. Using
a series of N-body simulations we show that the spectral equivalence is
accurate to sub-percent level across the same range of modes and redshift
covered by the Coyote suite. Thus, the extended emulator provides a very
efficient and accurate tool to predict non-linear power spectra for DE models
with w_0 - w_a parametrization. According to the same criteria we have
developed a numerical code, and we have implemented in a dedicated module for
the CAMB code, that can be used in combination with the Coyote Emulator in
likelihood analyses of non-linear matter power spectrum measurements. All codes
can be found at https://github.com/luciano-casarini/PKequal | astro-ph_CO |
Corrective effect of many-body interactions in dynamical friction: Dynamical friction is a fundamental and important phenomenon in astrophysics.
The Chandrasekhar formula is a well-known analytical estimation of the effect.
However, current astrophysicists have realized that the formula is not correct
in some cases because of several approximations dared in the formulation and/or
complex non-linearities in the real universe. For example, it has been
indicated that the dynamical friction doesn't work in cored density profiles
(constant density in the central region) despite that the Chandrasekhar formula
predicts drag force even in the constant densities. In the former half of this
paper, I discuss by N-body simulations that many-body interactions are also
important in actual dynamical friction though derivation of the Chandrasekhar
formula is based on the assumption of two-body interaction. In the simulation,
the many-body interactions are caused by a very small number of field particles
co-rotating with a perturber. However, the contribution from the many-body
interactions accounts for a non-negligible fraction of the actual dynamical
friction. In the latter half, I discuss why the cored profiles suppress the
dynamical friction. One possible explanation is that corrective effect of the
many-body interactions drive orbital motion of the perturber. The cessation of
dynamical friction by this corrective effect would be feasible even in shallow
cusp density profiles although the shallow cusp may evolve into a constant
density. | astro-ph_CO |
Non-linear Matter Spectra in Coupled Quintessence: We consider cosmologies in which a dark-energy scalar field interacts with
cold dark matter. The growth of perturbations is followed beyond the linear
level by means of the time-renormalization-group method, which is extended to
describe a multi-component matter sector. Even in the absence of the extra
interaction, a scale-dependent bias is generated as a consequence of the
different initial conditions for baryons and dark matter after decoupling. The
effect is enhanced significantly by the extra coupling and can be at the 2-3
percent level in the range of scales of baryonic acoustic oscillations. We
compare our results with N-body simulations, finding very good agreement. | astro-ph_CO |
The H0 trouble: Confronting Non-thermal Dark Matter and Phantom
Cosmology with the CMB, BAO, and Type Ia Supernovae data: We have witnessed different values of the Hubble constant being found in the
literature in the past years. Albeit, early measurements often result in an
$H_0$ much smaller than those from late-time ones, producing a statistically
significant discrepancy, and giving rise to the so-called Hubble tension. The
trouble with the Hubble constant is often treated as a cosmological problem.
However, the Hubble constant can be a laboratory to probe cosmology and
particle physics models. In our work, we will investigate if the possibility of
explaining the $H_0$ trouble using non-thermal dark matter production aided by
phantom-like cosmology is consistent with the Cosmic Background Radiation (CMB)
and Baryon Acoustic Oscillation (BAO) data. We performed a full Monte Carlo
simulation using CMB and BAO datasets keeping the cosmological parameters
$\Omega_b h^2$, $\Omega_c h^2$, $100\theta$, $\tau_{opt}$, and $w$ as priors
and concluded that a non-thermal dark matter production aided by phantom-like
cosmology yields at most $H_0=70.5$ km s$^{-1}$Mpc$^{-1}$ which is consistent
with some late-time measurements. However, if $H_0> 72$ km s$^{-1}$ Mpc$^{-1}$
as many late-time observations indicate, an alternative solution to the Hubble
trouble is needed. Lastly, we limited the fraction of relativistic dark matter
at the matter-radiation equality to be at most 1\%. | astro-ph_CO |
Nonstandard cosmology: Considering radial geodesics in the Robertson-Walker metric leads us to
abandon the co-moving coordinates. Instead we work in the cosmic rest frame.
Since then the matter is in motion, the solution of Einstein's equations is
more complicated. We calculate the first correction to standard cosmology which
has an off-diagonal term b dt dr in the metric. It describes the late universe.
We then solve Maxwell's equations in the new metric and discuss redshift and
luminosities. We obtain the correct age of the universe T=14 Gyr= 1/H, without
assuming a cosmological constant. | astro-ph_CO |
An ALMA survey of submillimetre galaxies in the Extended Chandra Deep
Field South: High resolution 870um source counts: We report the first counts of faint submillimetre galaxies (SMG) in the
870-um band derived from arcsecond resolution observations with the Atacama
Large Millimeter Array (ALMA). We have used ALMA to map a sample of 122
870-um-selected submillimetre sources drawn from the (0.5x0.5)deg^2 LABOCA
Extended Chandra Deep Field South Submillimetre Survey (LESS). These ALMA maps
have an average depth of sigma(870um)~0.4mJy, some ~3x deeper than the original
LABOCA survey and critically the angular resolution is more than an order of
magnitude higher, FWHM of ~1.5" compared to ~19" for the LABOCA discovery map.
This combination of sensitivity and resolution allows us to precisely pin-point
the SMGs contributing to the submillimetre sources from the LABOCA map, free
from the effects of confusion. We show that our ALMA-derived SMG counts broadly
agree with the submillimetre source counts from previous, lower-resolution
single-dish surveys, demonstrating that the bulk of the submillimetre sources
are not caused by blending of unresolved SMGs. The difficulty which
well-constrained theoretical models have in reproducing the high-surface
densities of SMGs, thus remains. However, our observations do show that all of
the very brightest sources in the LESS sample, S(870um)>12mJy, comprise
emission from multiple, fainter SMGs, each with 870-um fluxes of <9mJy. This
implies a natural limit to the star-formation rate in SMGs of <10^3 M_Sun/yr,
which in turn suggests that the space densities of z>1 galaxies with gas masses
in excess of ~5x10^10 M_Sun is <10^-5 Mpc^-3. We also discuss the influence of
this blending on the identification and characterisation of the SMG
counterparts to these bright submillimetre sources and suggest that it may be
responsible for previous claims that they lie at higher redshifts than fainter
SMGs. | astro-ph_CO |
Dynamic of the accelerated expansion of the universe in the DGP model: According to experimental data of SNe Ia (Supernovae type Ia), we will
discuss in detial dynamics of the DGP model and introduce a simple
parametrization of matter $\omega$, in order to analyze scenarios of the
expanding universe and the evolution of the scale factor. We find that the
dimensionless matter density parameter at the present epoch $\Omega^0_m=0.3$,
the age of the universe $t_0= 12.48$ Gyr,
$\frac{a}{a_0}=-2.4e^{\frac{-t}{25.56}}+2.45$. The next we study the linear
growth of matter perturbations, and we assume a definition of the growth rate,
$f \equiv \frac{dln\delta}{dlna}$. As many authors for many years, we have been
using a good approximation to the growth rate $f \approx \Omega^{\gamma(z)}_m$,
we also find that the best fit of the growth index, $\gamma(z)\approx 0.687 -
\frac{40.67}{1 + e^{1.7. (4.48 + z)}}$, or $\gamma(z)= 0.667 + 0.033z$ when
$z\ll1$. We also compare the age of the universe and the growth index with
other models and experimental data. We can see that the DGP model describes the
cosmic acceleration as well as other models that usually refers to dark energy
and Cold Dark Matter (CDM). | astro-ph_CO |
Numerical evaluation of inflationary 3-point functions on curved field
space: We extend the public CppTransport code to calculate the statistical
properties of fluctuations in multiple-field inflationary models with curved
field space. Our implementation accounts for all physical effects at tree-level
in the 'in-in' diagrammatic expansion. This includes particle production due to
time-varying masses, but excludes scenarios where the curvature perturbation is
generated by averaging over the decay of more than one particle. We test our
implementation by comparing results in Cartesian and polar field-space
coordinates, showing excellent numerical agreement and only minor degradation
in compute time. We compare our results with the PyTransport 2.0 code, which
uses the same computational approach but a different numerical implementation,
finding good agreement. Finally, we use our tools to study a class of
gelaton-like models which could produce an enhanced non-Gaussian signal on
equilateral configurations of the Fourier bispectrum. We show this is difficult
to achieve using hyperbolic field-space manifolds and simple inflationary
potentials. | astro-ph_CO |
Exploratory X-ray Monitoring of Luminous Radio-Quiet Quasars at High
Redshift: Initial Results: We present initial results from an exploratory X-ray monitoring project of
two groups of comparably luminous radio-quiet quasars (RQQs). The first
consists of four sources at 4.10 <= z <= 4.35, monitored by Chandra, and the
second is a comparison sample of three sources at 1.33 <= z <= 2.74, monitored
by Swift. Together with archival X-ray data, the total rest-frame temporal
baseline spans ~2-4 yr and ~5-13 yr for the first and second group,
respectively. Six of these sources show significant X-ray variability over
rest-frame timescales of ~10^2 - 10^3 d; three of these also show significant
X-ray variability on rest-frame timescales of ~1-10 d. The X-ray variability
properties of our variable sources are similar to those exhibited by nearby and
far less luminous active galactic nuclei (AGNs). While we do not directly
detect a trend of increasing X-ray variability with redshift, we do confirm
previous reports of luminous AGNs exhibiting X-ray variability above that
expected from their luminosities, based on simplistic extrapolation from lower
luminosity sources. This result may be attributed to luminous sources at the
highest redshifts having relatively high accretion rates. Complementary
UV-optical monitoring of our sources shows that variations in their
optical-X-ray spectral energy distribution are dominated by the X-ray
variations. We confirm previous reports of X-ray spectral variations in one of
our sources, HS 1700+6416, but do not detect such variations in any of our
other sources in spite of X-ray flux variations of up to a factor of ~4. This
project is designed to provide a basic assessment of the X-ray variability
properties of RQQs at the highest accessible redshifts that will serve as a
benchmark for more systematic monitoring of such sources with future X-ray
missions. | astro-ph_CO |
Primordial magnetic field generation via primordial black hole disks: Large scale primordial magnetic fields (PMFs) threading the intergalactic
medium are observed ubiquitously in the Universe playing a key role in the
cosmic evolution. Their origin is still debated constituting a very active
field of research. In the present article, we propose a novel natural ab initio
mechanism for the origin of such PMFs through the portal of supermassive
primordial black holes (PBHs) forming between the Big Bang Nucleosynthesis and
the recombination era. In particular, by considering PBHs furnished with a
locally isothermal disk we study the generation of a Biermann battery induced
seed magnetic field (MF) due to the vortexlike motion of the primordial plasma
around the black hole. Finally, by considering monochromatic PBH mass
distributions and deriving the relevant MF power spectrum we make a
conservative estimate for the seed PMF in intergalactic scales and at redshift
$z=30$, when typical galaxies are considered to form, which reads as $B\simeq
10^{-30}\mathrm{G}\left(\frac{\ell_\mathrm{R}}{10^6}\right)^2\left(\frac{M_\mathrm{PBH}}{10^{14}M_\odot}\right)^{5/2}$,
where $M_\mathrm{PBH}$ is the PBH mass and $\ell_\mathrm{R}\equiv
R_\mathrm{d}/R_\mathrm{ISCO}$, is the ratio of the radius of the disk,
$R_\mathrm{d}$ over the radius of the innermost stable circular orbit,
$R_\mathrm{ISCO}$. Interestingly enough, by requiring to seed a PMF of the
order of $10^{-30}\mathrm{G}$ necessary to give rise to a present day
$10^{-18}\mathrm{G}$ in intergalactic scales, we find a lower bound on the PBH
mass within the range $[10^{10}- 10^{16}]M_\odot$ depending on the radius of
the PBH disk. | astro-ph_CO |
Apparent Superluminality of Lensed Gravitational Waves: We consider gravitational wave (GW) sources with an associated
electromagnetic (EM) counterpart, and analyze the time delay between both
signals in the presence of lensing. If GWs have wavelengths comparable to the
Schwarzschild radius of astrophysical lenses, they must be treated with wave
optics, whereas EM waves are typically well within the approximation of
geometric optics. With concrete examples, we confirm that the GW signal never
arrives before its EM counterpart, if both are emitted at the same time.
However, during the inspiral of a binary, peaks of the GW waveform can arrive
before their EM counterpart. We stress this is only an apparent superluminality
since the GW waveform is both distorted and further delayed with respect to
light. In any case, measuring the multi-messenger time delay and correctly
interpreting it has important implications for unveiling the distribution of
lenses, testing the nature of gravity, and probing the cosmological expansion
history. | astro-ph_CO |
Convolution Lagrangian perturbation theory for biased tracers beyond
general relativity: We compare analytic predictions for real and Fourier space two-point
statistics for biased tracers from a variety of Lagrangian Perturbation Theory
approaches against those from state of the art N-body simulations in $f(R)$
Hu-Sawicki and the nDGP braneworld modified gravity theories.
We show that the novel physics of gravitational collapse in scalar tensor
theories with the chameleon or the Vainshtein screening mechanism can be
effectively factored in with bias parameters analytically predicted using the
Peak-Background Split formalism when updated to include the environmental
sensitivity of modified gravity theories as well as changes to the halo mass
function.
We demonstrate that Convolution Lagrangian Perturbation Theory (CLPT) and
Standard Perturbation Theory (SPT) approaches provide accurate analytic methods
to predict the correlation function and power spectra, respectively, for biased
tracers in modified gravity models and are able to characterize both the BAO,
power-law and small scale regimes needed for upcoming galaxy surveys such as
DESI, Euclid, LSST and WFIRST. | astro-ph_CO |
Test of cosmic isotropy in the Planck era: The two fundamental assumptions in cosmology are that the Universe is
statistically homogeneous and isotropic when averaged on large scales. Given
the big implication of these assumptions, there has been a lot of statistical
tests carried out to verify their validity. Since the first high-precision
Cosmic Microwave Background (CMB) data release by the WMAP satellite, many
anomalies that challenges the isotropy assumption, including dipolar power
asymmetry on large angular scales, have been reported. In this talk I will
present a brief summary of the test of cosmic isotropy we carried out in the
latest WMAP and Planck temperature data. | astro-ph_CO |
Composition of Low Redshift Halo Gas: Halo gas in low-z (z<0.5) >0.1L* galaxies in high-resolution, large-scale
cosmological hydrodynamic simulations is examined with respect to three
components: (cold, warm, hot) with temperatures equal to (<10^5, 10^{5-6},
>10^6)K, respectively. The warm component is compared, utilizing O VI
\lambda\lambda 1032, 1038 absorption lines, to observations and agreement is
found with respect to the galaxy-O VI line correlation, the ratio of O VI line
incidence rate in blue to red galaxies and the amount of O VI mass in
star-forming galaxies. A detailed account of the sources of warm halo gas
(stellar feedback heating, gravitational shock heating and accretion from the
intergalactic medium), inflowing and outflowing warm halo gas metallicity
disparities and their dependencies on galaxy types and environment is also
presented. Having the warm component securely anchored, our simulations make
the following additional predictions. First, cold gas is the primary component
in inner regions, with its mass comprising 50% of all gas within
galacto-centric radius r=(30,150)kpc in (red, blue) galaxies. Second, at
r>(30,200)kpc in (red, blue) galaxies the hot component becomes the majority.
Third, the warm component is a perpetual minority, with its contribution
peaking at ~30% at r=100-300kpc in blue galaxies and never exceeding 5% in red
galaxies. The significant amount of cold gas in low-z early-type galaxies found
in simulations, in agreement with recent observations (Thom et al.), is
intriguing, so is the dominance of hot gas at large radii in blue galaxies. | astro-ph_CO |
Describing variations of the Fisher-matrix across parameter space: Forecasts in cosmology, both with Monte-Carlo Markov-chain methods and with
the Fisher matrix formalism, depend on the choice of the fiducial model because
both the signal strength of any observable as well as the model nonlinearities
linking observables to cosmological parameters vary in the general case. In
this paper we propose a method for extrapolating Fisher-forecasts across the
space of cosmological parameters by constructing a suitable ba- sis. We
demonstrate the validity of our method with constraints on a standard dark
energy model extrapolated from a {\Lambda}CDM-model, as can be expected from
2-bin weak lensing to- mography with a Euclid-like survey, in the parameter
pairs $(\Omega_\text{m},\sigma_8)$, $(\Omega_\text{m}, w_0)$ and $(w_0,
w_\text{a})$. Our numerical results include very accurate extrapolations across
a wide range of cosmo- logical parameters in terms of shape, size and
orientation of the parameter likelihood, and a decomposition of the change of
the likelihood contours into modes, which are straightforward to interpret in a
geometrical way. We find that in particular the variation of the dark energy
figure of merit is well captured by our formalism. | astro-ph_CO |
The effects of baryon physics, black holes and AGN feedback on the mass
distribution in clusters of galaxies: The spatial distribution of matter in clusters of galaxies is mainly
determined by the dominant dark matter component, however, physical processes
involving baryonic matter are able to modify it significantly. We analyse a set
of 500 pc resolution cosmological simulations of a cluster of galaxies with
mass comparable to Virgo, performed with the AMR code RAMSES. We compare the
mass density profiles of the dark, stellar and gaseous matter components of the
cluster that result from different assumptions for the subgrid baryonic physics
and galaxy formation processes. First, the prediction of a gravity only N-body
simulation is compared to that of a hydrodynamical simulation with standard
galaxy formation recipes, then all results are compared to a hydrodynamical
simulation which includes thermal AGN feedback from Super Massive Black Holes
(SMBH). We find the usual effects of overcooling and adiabatic contraction in
the run with standard galaxy formation physics, but very different results are
found when implementing SMBHs and AGN feedback. Star formation is strongly
quenched, producing lower stellar densities throughout the cluster, and much
less cold gas is available for star formation at low redshifts. At redshift z =
0 we find a flat density core of radius 10 kpc in both of the dark and stellar
matter density profiles. We specu- late on the possible formation mechanisms
able to produce such cores and we conclude that they can be produced through
the coupling of different processes: (I) dynamical friction from the decay of
black hole orbits during galaxy mergers; (II) AGN driven gas outflows producing
fluctuations of the gravitational potential causing the removal of
collisionless matter from the central region of the cluster; (III) adiabatic
expansion in response to the slow expulsion of gas from the central region of
the cluster during the quiescent mode of AGN activity. | astro-ph_CO |
Distribution function approach to redshift space distortions. Part IV:
perturbation theory applied to dark matter: We develop a perturbative approach to redshift space distortions (RSD) using
the phase space distribution function approach and apply it to the dark matter
redshift space power spectrum and its moments. RSD can be written as a sum over
density weighted velocity moments correlators, with the lowest order being
density, momentum density and stress energy density. We use standard and
extended perturbation theory (PT) to determine their auto and cross
correlators, comparing them to N-body simulations. We show which of the terms
can be modeled well with the standard PT and which need additional terms that
include higher order corrections which cannot be modeled in PT. Most of these
additional terms are related to the small scale velocity dispersion effects,
the so called finger of god (FoG) effects, which affect some, but not all, of
the terms in this expansion, and which can be approximately modeled using a
simple physically motivated ansatz such as the halo model. We point out that
there are several velocity dispersions that enter into the detailed RSD
analysis with very different amplitudes, which can be approximately predicted
by the halo model. In contrast to previous models our approach systematically
includes all of the terms at a given order in PT and provides a physical
interpretation for the small scale dispersion values. We investigate RSD power
spectrum as a function of \mu, the cosine of the angle between the Fourier mode
and line of sight, focusing on the lowest order powers of \mu and multipole
moments which dominate the observable RSD power spectrum. Overall we find
considerable success in modeling many, but not all, of the terms in this
expansion. | astro-ph_CO |
Interplanetary Dust as a Foreground for the LiteBIRD CMB Satellite
Mission: As ever-more sensitive experiments are made in the quest for primordial CMB B
Modes, the number of potentially significant astrophysical contaminants becomes
larger as well. Thermal emission from interplanetary dust, for example, has
been detected by the Planck satellite. While the polarization fraction of this
Zodiacal, or interplanetary dust emission (IPDE) is expected to be low, it is
bright enough to be detected in total power. Here, estimates of the magnitude
of the effect as it might be seen by the LiteBIRD satellite are made. The COBE
IPDE model from Kelsall et al. (1998) is combined with a model of the LiteBIRD
experiment's scanning strategy to estimate potential contamination of the CMB
in both total power and in polarization power spectra. LiteBIRD should detect
IPDE in temperature across all of its bands, from 40 through 402 GHz, and
should improve limits on the polarization fraction of IPDE at the higher end of
this frequency range. If the polarization fraction of IPDE is of order 1%, the
current limit from ISO/CAM measurements in the mid-infrared, it may induce
large-scale polarization B Modes comparable to cosmological models with an r of
order 0.001. In this case, the polarized IPDE would also need to be modeled and
removed. As a CMB foreground, IPDE will always be subdominant to Galactic
emissions, though because it caused by emission from grains closer to us, it
appears variable as the Earth travels around the Sun, and may thereby
complicate the data analysis somewhat. But with an understanding of some of the
symmetries of the emission and some flexibility in the data processing, it
should not be the primary impediment to the CMB polarization measurement. | astro-ph_CO |
Cospatial 21 cm and metal-line absorbers in the epoch of reionization --
I : Incidence and observability: Overdense, metal-rich regions, shielded from stellar radiation might remain
neutral throughout reionization and produce metal as well as 21 cm absorption
lines. Simultaneous absorption from metals and 21 cm can complement each other
as probes of underlying gas properties. We use Aurora, a suite of high
resolution radiation-hydrodynamical simulations of galaxy formation, to
investigate the occurrence of such "aligned" absorbers. We calculate absorption
spectra for 21 cm, OI, CII, SiII and FeII. We find velocity windows with
absorption from at least one metal and 21 cm, and classify the aligned
absorbers into two categories: 'aligned and cospatial absorbers' and 'aligned
but not cospatial absorbers'. While 'aligned and cospatial absorbers' originate
from overdense structures and can be used to trace gas properties, 'aligned but
not cospatial absorbers' are due to peculiar velocity effects. The incidence of
absorbers is redshift dependent, as it is dictated by the interplay between
reionization and metal enrichment, and shows a peak at $z \approx 8$ for the
aligned and cospatial absorbers. While aligned but not cospatial absorbers
disappear towards the end of reionization because of the lack of an ambient 21
cm forest, aligned and cospatial absorbers are associated with overdense
pockets of neutral gas which can be found at lower redshift. We produce mock
observations for a set of sightlines for the next generation of telescopes like
the ELT and SKA1-LOW, finding that given a sufficiently bright background
quasar, these telescopes will be able to detect both types of absorbers
throughout reionization. | astro-ph_CO |
The Majority of Compact Massive Galaxies at z~2 are Disk Dominated: We investigate the stellar structure of massive, quiescent galaxies at z~2,
based on Hubble Space Telescope/WFC3 imaging from the Early Release Science
program. Our sample of 14 galaxies has stellar masses of M* > 10^{10.8} Msol
and photometric redshifts of 1.5 < z < 2.5. In agreement with previous work,
their half-light radii are <2 kpc, much smaller than equally massive galaxies
in the present-day universe. A significant subset of the sample appears highly
flattened in projection, which implies, considering viewing angle statistics,
that a significant fraction of the galaxies in our sample have pronounced
disks. This is corroborated by two-dimensional surface brightness profile fits.
We estimate that 65% +/- 15% of the population of massive, quiescent z~2
galaxies are disk-dominated. The median disk scale length is 1.5 kpc,
substantially smaller than the disks of equally massive galaxies in the
present-day universe. Our results provide strong observational evidence that
the much-discussed ultra-dense high-redshift galaxies should generally be
thought of as disk-like stellar systems with the majority of stars formed from
gas that had time to settle into a disk. | astro-ph_CO |
Constraining Quasar and IGM Properties Through Bubble Detection in
Redshifted 21-cm Maps: The infrared detection of a z>7 quasar has opened up a new window to directly
probe the IGM during the epoch of reionization. In this paper we theoretically
consider the possibility of detecting the ionized bubble around a z=8 quasar
using targeted redshifted 21-cm observations with the GMRT. The apparent shape
and size of the ionized bubble, as seen by a distant observer, depends on the
parameters \dot{N}_{phs}/C, x_HI/C and \tau_Q where \dot{N}_{phs}, \tau_Q, x_HI
and C are respectively the photon emission rate, age of the quasar, the neutral
fraction and clumping factor of the IGM.Here we have analytically estimated the
shape and size of a quasar's ionized bubble assuming an uniform IGM and
ignoring other ionizing sources besides the quasar, and used this as a template
for matched filter bubble search with the GMRT visibility data. We have assumed
that \dot{N}_{phs} is known from the infrared spectrum and C from theoretical
considerations, which gives us two free parameters x_HI and \tau_Q for bubble.
Considering 1,000 hr of observation, we find that there is a reasonably large
region of parameter space where a 3\sigma detection is possible. We also find
that it will be possible to place lower limits on x_HI and \tau_Q with this
observation. Deeper follow up observations can place upper limits on \tau_Q and
x_HI. Value of C affect the estimation of x_HI but the estimation of \tau_Q
remains unaffected.We have used a semi-numerical technique to simulate the
apparent shape and size of quasar ionized bubbles considering the presence of
other ionizing sources and inhomogeneities in the IGM. The presence of other
sources increase the size of the quasar bubble, leading to underestimation of
x_HI. Clustering of other ionizing sources around the quasar can produce severe
distortions in bubble's shape. However, this does not severely affect parameter
estimation in the bubbles that are large. | astro-ph_CO |
Empirical predictions for (sub-)millimeter line and continuum deep
fields: [abridged] Modern (sub-)millimeter/radio interferometers will enable us to
measure the dust and molecular gas emission from galaxies that have
luminosities lower than the Milky Way, out to high redshifts and with
unprecedented spatial resolution and sensitivity. This will provide new
constraints on the star formation properties and gas reservoir in galaxies
throughout cosmic times through dedicated deep field campaigns targeting the
CO/[CII] lines and dust continuum emission. In this paper, we present empirical
predictions for such (sub-)millimeter line and continuum deep fields. We base
these predictions on the deepest available optical/near-infrared ACS and NICMOS
data on the Hubble Ultra Deep Field. Using a physically-motivated spectral
energy distribution model, we fit the observed optical/near-infrared emission
of 13,099 galaxies with redshifts up to z=5, and obtain median likelihood
estimates of their stellar mass, star formation rate, dust attenuation and dust
luminosity. We derive statistical constraints on the dust emission in the
infrared and (sub-)millimeter which are consistent with the observed
optical/near-infrared emission in terms of energy balance. This allows us to
estimate, for each galaxy, the (sub-)millimeter continuum flux densities in
several ALMA, PdBI/NOEMA and JVLA bands. Using empirical relations between the
observed CO/[CII] line luminosities and the infrared luminosity, we infer the
flux of the CO(1-0) and [CII] lines from the estimated infrared luminosity of
each galaxy in our sample. We then predict the fluxes of higher CO transition
lines CO(2-1) to CO(7-6) bracketing two extreme gas excitation scenarios. We
use our predictions to discuss possible deep field strategies with ALMA. The
predictions presented in this study will serve as a direct benchmark for future
deep field campaigns in the (sub-)millimeter regime. | astro-ph_CO |
Photometric Calibrations for 21st Century Science: The answers to fundamental science questions in astrophysics, ranging from
the history of the expansion of the universe to the sizes of nearby stars,
hinge on our ability to make precise measurements of diverse astronomical
objects. As our knowledge of the underlying physics of objects improves along
with advances in detectors and instrumentation, the limits on our capability to
extract science from measurements is set, not by our lack of understanding of
the nature of these objects, but rather by the most mundane of all issues: the
precision with which we can calibrate observations in physical units. We stress
the need for a program to improve upon and expand the current networks of
spectrophotometrically calibrated stars to provide precise calibration with an
accuracy of equal to and better than 1% in the ultraviolet, visible and
near-infrared portions of the spectrum, with excellent sky coverage and large
dynamic range. | astro-ph_CO |
The optical spectra of X-shaped radio galaxies: X-shaped radio galaxies are defined by their peculiar large-scale radio
morphology. In addition to the classical double-lobed structure they have a
pair of low-luminosity wings that straddles the nucleus at almost right angles
to the active lobes, thus giving the impression of an 'X'. In this paper we
study for the first time the optical spectral properties of this object class
using a large sample (~50 sources). We find that the X-shaped radio population
is composed roughly equally of sources with weak and strong emission line
spectra, which makes them, in combination with the well-known fact that they
preferentially have radio powers intermediate between those of Fanaroff-Riley
type I (FR I) and type II (FR II) radio galaxies, the archetypal transition
population. We do not find evidence in support of the proposition that the
X-shape is the result of a recent merger: X-shaped radio sources do not have
unusually broad emission lines, their nuclear environments are in general not
dusty, and their host galaxies do not show signs of enhanced star formation.
Instead, we observe that the nuclear regions of X-shaped radio sources have
relatively high temperatures. This finding favours models, which propose that
the X-shape is the result of an overpressured environment. | astro-ph_CO |
Constraints on Cosmographic Functions of Cosmic Chronometers Data Using
Gaussian Processes: We study observational constraints on the cosmographic functions up to the
fourth derivative of the scale factor with respect to cosmic time, i.e., the
so-called snap function, using the non-parametric method of Gaussian Processes.
As observational data we use the Hubble parameter data. Also we use mock data
sets to estimate the future forecast and study the performance of this type of
data to constrain cosmographic functions. The combination between a
non-parametric method and the Hubble parameter data is investigated as a
strategy to reconstruct cosmographic functions. In addition, our results are
quite general because they are not restricted to a specific type of functional
dependency of the Hubble parameter. We investigate some advantages of using
cosmographic functions instead of cosmographic series, since the former are
general definitions free of approximations. In general, our results do not
deviate significantly from $\Lambda CDM$. We determine a transition redshift
$z_{tr}=0.637^{+0.165}_{-0.175}$ and $H_{0}=69.45 \pm 4.34$. Also assuming
priors for the Hubble constant we obtain $z_{tr}=0.670^{+0.210}_{-0.120}$ with
$H_{0}=67.44$ (Planck) and $z_{tr}=0.710^{+0.159}_{-0.111}$ with
$H_{0}=74.03$(SH0ES). Our main results are summarized in table 2. | astro-ph_CO |
Designing Horndeski and the effective fluid approach: We present a family of designer Horndeski models, i.e. models that have a
background exactly equal to that of the $\Lambda$CDM model but perturbations
given by the Horndeski theory. Then, we extend the effective fluid approach to
Horndeski theories, providing simple analytic formulae for the equivalent dark
energy effective fluid pressure, density and velocity. We implement the dark
energy effective fluid formulae in our code EFCLASS, a modified version of the
widely used Boltzmann solver CLASS, and compare the solution of the
perturbation equations with those of the code hi_CLASS which already includes
Horndeski models. We find that our simple modifications to the vanilla code are
accurate to the level of $\sim 0.1\%$ with respect to the more complicated
hi_CLASS code. Furthermore, we study the kinetic braiding model both on and off
the attractor and we find that even though the full case has a proper
$\Lambda$CDM model limit for large $n$, it is not appropriately smooth, thus
causing the quasistatic approximation to break down. Finally, we focus on our
designer model (HDES), which has both a smooth $\Lambda$CDM limit and
well-behaved perturbations, and we use it to perform Markov Chain Monte Carlo
analyses to constrain its parameters with the latest cosmological data. We find
that our HDES model can also alleviate the soft $2\sigma$ tension between the
growth data and Planck 18 due to a degeneracy between $\sigma_8$ and one of its
model parameters that indicates the deviation from the $\Lambda$CDM model. | astro-ph_CO |
Ghostly Galaxies as Solitons of Bose-Einstein Dark Matter: The large dark cores of common dwarf galaxies are unexplained by the standard
heavy particle interpretation of dark matter.
This puzzle is exacerbated by the discovery of a very large but barely
visible, dark matter dominated galaxy Antlia II orbiting the Milky Way,
uncovered by tracking star motions with the {\t Gaia} satellite. Although
Antlia II has a low mass, its visible radius is more than double any known
dwarf galaxy, with an unprecedentedly low density core. We show that Antlia II
favors dark matter as a Bose-Einstein condensate, for which the ground state is
a stable soliton with a core radius given by the de Broglie wavelength. The
lower the galaxy mass, the larger the de Broglie wavelength, so the least
massive galaxies should have the widest soliton cores of lowest density. An
ultra-light boson of $m_\psi \sim 1.1 \times10^{-22}$ eV, accounts well for the
large size and slowly moving stars within Antlia II, and agrees with boson mass
estimates derived from the denser cores of more massive dwarf galaxies. For
this very light boson, Antlia II is close to the lower limiting Jeans scale for
galaxy formation permitted by the Uncertainty Principle, so other examples are
expected but none significantly larger in size. This simple explanation for the
puzzling dark cores of dwarf galaxies implies dark matter as an ultra-light
boson, such as an axion generic in String Theory. | astro-ph_CO |
Neutrino signals from Neutron Star implosions to Black Holes: We calculate the neutrino luminosity in an astrophysical scenario where dark
matter is captured by a neutron star which eventually implodes to form a low
mass black hole. The Trojan horse scenario involves the collapse of a neutron
star (NS) due to the accumulation of a critical amount of dark matter (DM)
during its lifetime. As a result, a central disk forms out of the ejected
material with a finite radial extension, density, temperature, and lepton
fraction, producing fainter neutrino luminosities and colder associated spectra
than found in a regular core-collapse supernova. The emitted gravitational wave
(GW) signal from the imploding NS should be detectable at ultra-high $\gtrsim
0.1$ GHz frequencies. | astro-ph_CO |
Effect of halo bias and Lyman Limit Systems on the history of cosmic
reionization: We extend the existing analytical model of reionization by Furlanetto et al.
(2004) to include the biasing of reionization sources and additional absorption
by Lyman Limit systems. Our model is, by construction, consistent with the
observed evolution of the galaxy luminosity function at z<8 and with the
observed evolution of Ly-{\alpha} forest at z<6. We also find that, for a wide
range of values for the relative escape fraction that we consider reasonable,
and which are consistent with the observational constraints on the relative
escape fraction from lower redshifts, our reionization model is consistent with
the WMAP constraint on the Thompson optical depth and with the SPT and EDGES
constraints on the duration of reionization. We, therefore, conclude that it is
possible to develop physically realistic models of reionization that are
consistent with all existing observational constraints. | astro-ph_CO |
The WiggleZ Dark Energy Survey: measuring the cosmic expansion history
using the Alcock-Paczynski test and distant supernovae: Astronomical observations suggest that today's Universe is dominated by a
dark energy of unknown physical origin. One of the most notable consequences in
many models is that dark energy should cause the expansion of the Universe to
accelerate: but the expansion rate as a function of time has proven very
difficult to measure directly. We present a new determination of the cosmic
expansion history by combining distant supernovae observations with a
geometrical analysis of large-scale galaxy clustering within the WiggleZ Dark
Energy Survey, using the Alcock-Paczynski test to measure the distortion of
standard spheres. Our result constitutes a robust and non-parametric
measurement of the Hubble expansion rate as a function of time, which we
measure with 10-15% precision in four bins within the redshift range 0.1 < z <
0.9. We demonstrate that the cosmic expansion is accelerating, in a manner
independent of the parameterization of the cosmological model (although
assuming cosmic homogeneity in our data analysis). Furthermore, we find that
this expansion history is consistent with a cosmological-constant dark energy. | astro-ph_CO |
UV-to-FIR analysis of Spitzer/IRAC sources in the Extended Groth Strip
II: Photometric redshifts, Stellar masses and Star formation rates: Based on the ultraviolet to far-infrared photometry already compiled and
presented in a companion paper (Barro et al. 2011a, Paper I), we present a
detailed SED analysis of nearly 80,000 IRAC 3.6+4.5 micron selected galaxies in
the Extended Groth Strip. We estimate photometric redshifts, stellar masses,
and star formation rates separately for each galaxy in this large sample. The
catalog includes 76,936 sources with [3.6] < 23.75 (85% completeness level of
the IRAC survey) over 0.48 square degrees. The typical photometric redshift
accuracy is Delta z/(1+z)=0.034, with a catastrophic outlier fraction of just
2%. We quantify the systematics introduced by the use of different stellar
population synthesis libraries and IMFs in the calculation of stellar masses.
We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter
of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies,
based on several sets of dust emission templates and SFR indicators. We
evaluate the systematic differences and goodness of the different SFR
estimations using the deep FIDEL 70 micron data available in the EGS. Typical
random uncertainties of the IR-bases SFRs are a factor of two, with
non-negligible systematic effects at z$\gtrsim$1.5 observed when only MIPS 24
micron data is available. All data products (SEDs, postage stamps from imaging
data, and different estimations of the photometric redshifts, stellar masses,
and SFRs of each galaxy) described in this and the companion paper are publicly
available, and they can be accessed through our the web-interface utility
Rainbow-navigator | astro-ph_CO |
Oxford SWIFT IFS and multi-wavelength observations of the Eagle galaxy
at z=0.77: The `Eagle' galaxy at a redshift of 0.77 is studied with the Oxford Short
Wavelength Integral Field Spectrograph (SWIFT) and multi-wavelength data from
the All-wavelength Extended Groth strip International Survey (AEGIS). It was
chosen from AEGIS because of the bright and extended emission in its slit
spectrum. Three dimensional kinematic maps of the Eagle reveal a gradient in
velocity dispersion which spans 35-75 +/- 10 km/s and a rotation velocity of 25
+/- 5 km/s uncorrected for inclination. Hubble Space Telescope images suggest
it is close to face-on. In comparison with galaxies from AEGIS at similar
redshifts, the Eagle is extremely bright and blue in the rest-frame optical,
highly star-forming, dominated by unobscured star-formation, and has a low
metallicity for its size. This is consistent with its selection. The Eagle is
likely undergoing a major merger and is caught in the early stage of a
star-burst when it has not yet experienced metal enrichment or formed the mass
of dust typically found in star-forming galaxies. | astro-ph_CO |
Stellar population gradients in the cores of nearby field E+A galaxies: We have selected a sample of local E+A galaxies from the Sloan Digital Sky
Survey (SDSS) Data Release 7 for follow up integral field spectroscopy with the
Wide Field Spectrograph (WiFeS) on the ANU 2.3-m telescope. The sample was
selected using the Halpha line in place of the [OII]3727 line as the indicator
of on-going star formation (or lack thereof). This allowed us to select a lower
redshift sample of galaxies than available in the literature since the
[OII]3727 falls off the blue end of the wavelength coverage in the SDSS for the
very lowest redshift objects. This low redshift selection means that the
galaxies have a large angular to physical scale which allows us to resolve the
central ~1kpc region of the galaxies; the region where stellar population
gradients are expected. Such observations have been difficult to make using
other higher redshift samples because even at redshifts z~0.1 the angular to
physical scale is similar to the resolution provided by ground based seeing.
Our integral field spectroscopy has enabled us to make the first robust
detections of Balmer line gradients in the centres of E+A galaxies. Six out of
our sample of seven, and all the galaxies with regular morphologies, are
observed to have compact and centrally-concentrated Balmer line absorption.
This is evidence for compact young cores and stellar population gradients which
are predicted from models of mergers and tidal interactions which funnel gas
into the galaxy core. Given the generally isolated nature of our sample this
argues for the galaxies being seen in the late stage of a merger where the
progenitors have already coalesced. | astro-ph_CO |
There is No Missing Satellites Problem: A critical challenge to the cold dark matter (CDM) paradigm is that there are
fewer satellites observed around the Milky Way than found in simulations of
dark matter substructure. We show that there is a match between the observed
satellite counts corrected by the detection efficiency of the Sloan Digital Sky
Survey (for luminosities $L \gtrsim$ 340 L$_\odot$) and the number of luminous
satellites predicted by CDM, assuming an empirical relation between stellar
mass and halo mass. The "missing satellites problem", cast in terms of number
counts, is thus solved. We also show that warm dark matter models with a
thermal relic mass smaller than 4 keV are in tension with satellite counts,
putting pressure on the sterile neutrino interpretation of recent X-ray
observations. Importantly, the total number of Milky Way satellites depends
sensitively on the spatial distribution of satellites, possibly leading to a
"too many satellites" problem. Measurements of completely dark halos below
$10^8$ M$_\odot$, achievable with substructure lensing and stellar stream
perturbations, are the next frontier for tests of CDM. | astro-ph_CO |
Cosmology before noon with multiple galaxy populations: Near-future facilities observing the high-redshift universe ($2<z<5$) will
have an opportunity to take advantage of "multi-tracer" cosmology by observing
multiple tracers of the matter density field: Lyman alpha emitters (LAE), Lyman
break galaxies (LBG), and CMB lensing $\kappa$. In this work we use Fisher
forecasts to investigate the effect of multi-tracers on next-generation
facilities. In agreement with previous work, we show that multiple tracers
improve constraints primarily from degeneracy breaking, instead of the
traditional intuition of sample variance cancellation. Then, we forecast that
for both BBN and CMB primary priors, the addition of lensing and LAEs onto a
LBG-only sample will gain 25\% or more in many parameters, with the largest
gains being factor of $\sim10$ improvement for $f_{\rm EDE}$. We include a
preliminary approach towards modelling the impact of radiative transfer (RT) on
forecasts involving LAEs by introducing a simplified model at linear theory
level. Our results, albeit preliminary, show that the while RT influences
LAE-only forecasts strongly, its effect on composite multi-tracer forecasts are
limited. | astro-ph_CO |
Interpreting the Clustering of Distant Red Galaxies: We analyze the angular clustering of z~2.3 distant red galaxies (DRGs)
measured by Quadri et al 2008. We find that, with robust estimates of the
measurement errors and realistic halo occupation distribution modeling, the
measured clustering can be well fit within standard halo occupation models, in
contrast to previous results. However, in order to fit the strong break in
w(theta) at theta=10 arcsec, nearly all satellite galaxies in the DRG
luminosity range are required to be DRGs. Within this luminosity-threshold
sample, the fraction of galaxies that are DRGs is ~44%, implying that the
formation of DRGs is more efficient for satellite galaxies than for central
galaxies. Despite the evolved stellar populations contained within DRGs at
z=2.3, 90% of satellite galaxies in the DRG luminosity range have been accreted
within 500 Myr. Thus, satellite DRGs must have known they would become
satellites well before the time of their accretion. This implies that the
formation of DRGs correlates with large-scale environment at fixed halo mass,
although the large-scale bias of DRGs can be well fit without such assumptions.
Further data are required to resolve this issue. Using the observational
estimate that ~30% of DRGs have no ongoing star formation, we infer a timescale
for star formation quenching for satellite galaxies of 450 Myr, although the
uncertainty on this number is large. However, unless all non-star forming
satellite DRGs were quenched before accretion, the quenching timescale is
significantly shorter than z~0 estimates. Down to the completeness limit of the
Quadri et al sample, we find that the halo masses of central DRGs are ~50%
higher than non-DRGs in the same luminosity range, but at the highest halo
masses the central galaxies are DRGs only ~2/3 of the time. | astro-ph_CO |
Where stars form and live at high redshift: clues from the infrared: The relation between dark matter halos and the loci of star formation at high
redshift is a pressing question in contemporary cosmology. Matching the
abundance of halos to the abundance of infrared (IR) galaxies, we explicit the
link between dark matter halo mass (Mh), stellar mass (M*) and star-formation
rate (SFR) up to a redshift of 2. Our findings are five-fold. First, we find a
strong evolution of the relation between M* and SFR as a function of redshift
with an increase of sSFR = SFR/M* by a factor ~30 between z=0 and z= 2.3.
Second, we observe a decrease of sSFR with stellar mass. These results
reproduce observed trends at redshift z>0.3. Third, we find that the star
formation is most efficient in dark matter halos with Mh~5x10^11 Msun, with
hints of an increase of this mass with redshift. Fourth, we find that SFR/Mh
increases by a factor ~15 between z = 0 and z = 2.3. Finally we find that the
SFR density is dominated by halo masses close to ~7x10^11 Msun at all redshift,
with a rapid decrease at lower and higher halo masses. Despite its simplicity,
our novel use of IR observations unveils some characteristic mass-scales
governing star formation at high redshift. | astro-ph_CO |
Cyclic Cosmology from the Little Rip: We revisit a cyclic cosmology scenario proposed in 2007 to examine whether
its hypotheses can be sustained if the underlying big rip evolution, which was
assumed there, is replaced by the recently proposed little rip. We show that
the separation into causal patches at turnaround is generally valid for a
little rip, and therefore conclude that the little rip is equally as suitable a
basis for cyclicity as is the big rip. | astro-ph_CO |
Redshift drift in varying speed of light cosmology: We derive a redshift drift formula within the framework of varying speed of
light (VSL) theory using the specific ansatz for the variability of $c(t) = c_0
a^n(t)$. We show that negative values of the parameter $n$, which correspond to
diminishing value of the speed of light during the evolution of the universe,
effectively rescales dust matter to become little negative pressure matter, and
the cosmological constant to became phantom. Positive values of $n$ (growing
$c(t)$) make VSL model to become more like Cold Dark Matter (CDM) model.
Observationally, there is a distinction between the VSL model and the
$\Lambda$CDM model for the admissible values of the parameter $n \sim -
10^{-5}$, though it will be rather difficult to detect by planned extremely
large telescopes (E-ELT, TMT, GMT) within their accuracy. | astro-ph_CO |
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