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Comparing the scalar-field dark energy models with recent observations: We investigate the general properties of a class of scalar-field dark energy
models (i.e., $\phi$CDM models) which behave like cosmological trackers at
early times. Particularly, we choose three $\phi$CDM models with typical
potentials, i.e., $V(\phi)\propto \phi^{-\alpha}$ (inverse power-law (IPL)
model), $V(\phi)\propto \coth^{\alpha}{\phi}$ (L-model) and $V(\phi)\propto
\cosh(\alpha\phi)$ (Oscillatory tracker model), where the latter two models are
based on the $\alpha$-attractors originated from the study of inflation. These
models, which reduce to the $\Lambda$CDM model with $\alpha \to 0$, are studied
and compared with the recent observations, including the Pantheon sample of
type Ia supernovae (SNe Ia), baryon acoustic oscillations (BAO) measurements
extracted from 6dFGS, BOSS and eBOSS, as well as the temperature and
polarization anisotropy power spectra data of cosmic microwave background
radiation (CMB) from Planck 2018 results. The observational constraints from
the combining sample (SNe Ia + BAO + CMB) indicate that none of the three
$\phi$CDM models exclude the $\Lambda$CDM model at $68.3\%$ confidence level.
We find that the CMB anisotropy data have obvious advantages in constraining
the dark energy models compared with other cosmological probes, which is
particularly evident in the L-model. Furthermore, we apply the Bayesian
evidence to compare the $\phi$CDM models and the $\Lambda$CDM model with the
analysis of the combining sample. The concordance $\Lambda$CDM model is still
the most supported one. In addition, among the three $\phi$CDM models, the IPL
model is the most competitive one, while the L-model/Oscillatory tacker model
is moderately/strongly disfavored. | Possible discrimination of black hole origins from the lensing rate of
DECIGO and B-DECIGO sources: In this paper, we forecast the expected detection rates and redshift
distributions of gravitationally lensed gravitational waves (GWs) from three
different mass distributions of primordial black holes (PBHs) and two stellar
formation models of astrophysical black holes (ABHs) in the context of
DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) and it's
smaller scale version B-DECIGO. It suggests that DECIGO will be able to detect
$10^4-10^5$ GW signals from such binary black holes (BBHs) each year and the
event rate distributions for PBHs will differ from those for ABHs due to their
different merger rate with respect to redshift. The large number of event rates
make $5-100$ detections of lensed GW signals being possible. After considering
the gravitational lensing effect, the difference between the detection rates
and distributions for PBHs and ABHs will be more significant. Therefore, this
can be served as a complementary method to distinguish PBHs from ABHs. |
Dark Matter as a Possible New Energy Source for Future Rocket Technology: Current rocket technology can not send the spaceship very far, because the
amount of the chemical fuel it can take is limited. We try to use dark matter
(DM) as fuel to solve this problem. In this work, we give an example of DM
engine using dark matter annihilation products as propulsion. The acceleration
is proportional to the velocity, which makes the velocity increase
exponentially with time in non-relativistic region. The important points for
the acceleration are how dense is the DM density and how large is the
saturation region. The parameters of the spaceship may also have great
influence on the results. We show that the (sub)halos can accelerate the
spaceship to velocity $ 10^{- 5} c \sim 10^{- 3} c$. Moreover, in case there is
a central black hole in the halo, like the galactic center, the radius of the
dense spike can be large enough to accelerate the spaceship close to the speed
of light. | SPHS: Smoothed Particle Hydrodynamics with a higher order dissipation
switch: We present a novel implementation of Smoothed Particle Hydrodynamics (SPHS)
that uses the spatial derivative of the velocity divergence as a higher order
dissipation switch. Our switch -- which is second order accurate -- detects
flow convergence before it occurs. If particle trajectories are going to cross,
we switch on the usual SPH artificial viscosity, as well as conservative
dissipation in all advected fluid quantities (for example, the entropy). The
viscosity and dissipation terms (that are numerical errors) are designed to
ensure that all fluid quantities remain single-valued as particles approach one
another, to respect conservation laws, and to vanish on a given physical scale
as the resolution is increased. SPHS alleviates a number of known problems with
`classic' SPH, successfully resolving mixing, and recovering numerical
convergence with increasing resolution. An additional key advantage is that --
treating the particle mass similarly to the entropy -- we are able to use
multimass particles, giving significantly improved control over the refinement
strategy. We present a wide range of code tests including the Sod shock tube,
Sedov-Taylor blast wave, Kelvin-Helmholtz Instability, the `blob test', and
some convergence tests. Our method performs well on all tests, giving good
agreement with analytic expectations. |
A New Probe of Gaussianity and Isotropy applied to the CMB Maps: We introduce a new mathematical tool (a direction-dependent probe) to analyse
the randomness of purported isotropic Gaussian random fields on the sphere. We
apply the probe to assess the full-sky cosmic microwave background (CMB)
temperature maps produced by the {\it Planck} collaboration (PR2 2015 and PR3
2018), with special attention to the inpainted maps. To study the randomness of
the fields represented by each map we use the autocorrelation of the sequence
of probe coefficients (which are just the full-sky Fourier coefficients
$a_{\ell,0}$ if the $z$ axis is taken in the probe direction). If the field is
{isotropic and Gaussian} then the probe coefficients for a given direction
should be realisations of uncorrelated scalar Gaussian random variables. We
introduce a particular function on the sphere (called the \emph{AC
discrepancy}) that accentuates the departure from Gaussianity and isotropy. We
find that for some of the maps, there are many directions for which the
departures are significant, especially near the galactic plane. We also study
the effect of varying the highest multipole used to calculate the AC
discrepancy from the initial value of $1500$ to $2500$. In the case of
Commander 2015, the AC discrepancy now exhibits antipodal "blobs" well away
from the galactic plane. Finally, we look briefly at the non-inpainted Planck
maps, for which the computed AC discrepancy maps have a very different
character, with features that are global rather than local. For the particular
case of the non-inpainted 2018 \texttt{SEVEM} map (which has visible equatorial
pollution), we model with partial success the observed behaviour by an
isotropic Gaussian random field added to a non-random needlet-like structure
located near the galactic centre. | Optimizing spectral stacking for 21-cm observations of galaxies:
accuracy assessment and symmetrized stacking: We present an assessment of the accuracy of common operations performed in
$21$-cm spectral line stacking experiments. To this end, we generate mock
interferometric data surveying the 21-cm emission at frequency $1310<\nu<1420$
MHz ($0.005<z<0.084$) and covering an area $\sim 6$ deg$^2$ of the sky,
mimicking the observational characteristics of real MeerKAT observations. We
find that the primary beam correction accounts for just few per cent ($\sim8\%$
at 0 primary beam power, $\sim 3\%$ at 0.6 primary beam power) deviations from
the true $M_{\rm HI}$ signal, and that weighting schemes based on noise
properties provide unbiased results. On the contrary, weighting schemes based
on distance can account for significant systematic mass differences when
applied to a flux-limited sample ($\Delta M_{\rm HI}\sim 40-50\%$ in the
studied case). We find no significant difference in the final $\braket{M_{\rm
HI}}$ obtained when spectroscopic redshift uncertainties are accounted for in
the stacking procedure ($ \Delta z\sim 0.00035$, i.e. $\Delta v \sim 100\,{\rm
km\, s}^{-1}$). We also present a novel technique to increase the effective
size of the galaxy sample by exploiting the geometric symmetries of galaxy
cubelets, potentially enhancing the SNR by a factor $\sim\sqrt{2}$ when
analyzing the final stacked spectrum (a factor 4 in a cubelet). This procedure
is found to be robustly unbiased, while efficiently increasing the SNR, as
expected. We argue that an appropriate framework employing detailed and
realistic simulations is required to exploit upcoming datasets from SKA
pathfinders in an accurate and reliable manner. |
Do cosmological observations allow a negative $Λ$?: In view of the recent measurement of $H_{0}$ from HST and SH0ES team, we
explore the possibility of existence of a negative cosmological constant (AdS
vacua in the dark energy sector) in the Universe. In this regard, we consider
quintessence fields on top of a negative cosmological constant and compare such
construction with $\Lambda$CDM model using a different combination of CMB,
SnIa, BAO and $H_{0}$ data. Various model comparison estimators show that
quintessence models with a negative $\Lambda$ is either preferred over
$\Lambda$CDM or performs equally as $\Lambda$CDM model. This suggests that the
presence of a negative $\Lambda$ (AdS ground state) in our Universe, which can
naturally arise in string theory, is consistent with cosmological observations. | Running Vacuum Cosmological Models: Linear Scalar Perturbations: In cosmology, phenomenologically motivated expressions for running vacuum are
commonly parametrized as linear functions $\Lambda(H^2)$ or $\Lambda(R)$. Such
kind of models assume an equation of state for vacuum given by $\,\overline
P_\Lambda=-\,\overline\rho_\Lambda$, relating their background pressure
$\,\overline P_\Lambda$ and mean energy density
$\,\overline\rho_\Lambda\equiv\Lambda/8\pi G$. This equation of state requires
that the dynamic for vacuum is due to the energy exchange with the material
species. Most of the approaches to background level consider only the energy
exchange between vacuum and the transient dominant material component of the
universe. We extend such models assuming the running vacuum as the sum of
independent contributions $\,\overline\rho_{\Lambda}
=\sum_i\,\overline\rho_{\Lambda i}$, associated with (and interacting with)
each of the $i$ material species. We derive the linear scalar perturbations for
two running scenarios, modeling its cosmic evolution and identifying their
different imprints on the cosmic microwave background anisotropies and the
matter power spectrum. In the $\Lambda(H^2)$ scenario the running vacuum are
coupled with all the material species in the universe, whereas the $\Lambda(R)$
description only leads to coupling between vacuum and the non-relativistic
matter components; which produces different imprints of the two models on the
matter power spectrum. A comparison with the Planck 2015 data was made in order
to constrain the free parameters of the models. In the case of the
$\Lambda(H^2)$ model, it was found that $\Omega_\Lambda=0.705\pm0.027$ and
$H_0=69.6\pm2.9\, km\, Mpc^{-1}\, s^{-1}$, which diminish the tension with the
low redshift expectations. |
Direct Dark Matter Search with the CRESST-II Experiment: The quest for the particle nature of dark matter is one of the big open
questions of modern physics. The CRESST-II experiment, located at the Gran
Sasso laboratory in Italy, is optimised for the detection of the elastic
scattering of dark matter particles with ordinary matter. We present the result
obtained with an improved detector setup with increased radiopurity and
enhanced background rejection. The limit obtained in the so-called low mass
region between one and three GeV/c2 is at the present among the best limits
obtained for direct dark matter experiments. In addition we give an outlook of
the future potential for direct dark matter detection using further improved
CRESST CaWO4 cryogenic detectors. | Faraday scaling and the Bicep2 observations: As repeatedly speculated in the past, the linear polarization of the Cosmic
Microwave Background can be rotated via the Faraday effect. An economic
explanation of the recent Bicep2 observations, not relying on long-wavelength
tensor modes of the geometry, would stipulate that the detected B mode comes
exclusively from a Faraday rotated E mode polarization. We show hereunder that
this interpretation is ruled out by the existing upper limits on the B mode
polarization obtained by independent experiments at observational frequencies
much lower than the operating frequency of the Bicep2 experiment. We then
derive the fraction of the observed B mode polarization ascribable to the
Faraday effect and suggest a dedicated experimental strategy for its detection. |
An analytic implementation of the IR-resummation for the BAO peak: We develop an analytic method for implementing the IR-resummation of
arXiv:1404.5954, which allows one to correctly and consistently describe the
imprint of baryon acoustic oscillations (BAO) on statistical observables in
large-scale structure. We show that the final IR-resummed correlation function
can be computed analytically without relying on numerical integration, thus
allowing for an efficient and accurate use of these predictions on real data in
cosmological parameter fitting. In this work we focus on the one-loop
correlation function and the BAO peak. We show that, compared with the standard
numerical integration method of IR-resummation, the new method is accurate to
better than 0.2 %, and is quite easily improvable. We also give an approximate
resummation scheme which is based on using the linear displacements of a fixed
fiducial cosmology, which when combined with the method described above, is
about six times faster than the standard numerical integration. Finally, we
show that this analytic method is generalizable to higher loop computations. | Cosmological constraints from line intensity mapping with interlopers: Understanding the formation and evolution of the Universe is crucial for
cosmological studies, and the line intensity mapping provides a powerful tool
for this kind of study. We propose to make use of multipole moments of
redshift-space line intensity power spectrum to constrain the cosmological and
astrophysical parameters, such as the equation of state of dark energy, massive
neutrinos, primordial non-Gaussianity, and star formation rate density. As an
example, we generate mock data of multipole power spectra for H-alpha 6563AA,
[OIII] 5007AA and [OII] 3727AA measured by SPHEREx experiment at z=1
considering contaminations from interloper lines, and use Markov Chain Monte
Carlo (MCMC) method to constrain the parameters in the model. We find a good
fitting result of the parameters compared to their fiducial values, which means
that the multipole power spectrum can effectively distinguish signal and
interloper lines, and break the degeneracies between parameters, such as line
mean intensity and bias. We also explore the cross power spectrum with CSST
(Chinese Space Station Telescope) spectroscopic galaxy survey in the
constraints. Since more accurate fitting results can be obtained by including
measurements of the emission lines at higher redshifts out to z=3 at least and
cross-correlations between emission lines can be involved, the line intensity
mapping is expected to offer excellent results in future cosmological and
astrophysical studies. |
Inner cusps of the first dark matter haloes: Formation and survival in a
cosmological context: We use very high resolution cosmological zoom simulations to follow the early
evolution of twelve first-generation haloes formed from gaussian initial
conditions with scale-free power spectra truncated on small scales by a
gaussian in wavenumber. Initial collapse occurs with a diverse range of sheet-
or filament-like caustic morphologies, but in almost all cases it gives rise to
a numerically converged density cusp with $\rho = Ar^{-3/2}$ and total mass
comparable to that of the corresponding peak in the initial linear density
field. The constant $A$ can be estimated to within about 10 per cent from the
properties of this peak. This outcome agrees with earlier work on the first
haloes in cold and warm dark matter universes. Within central cusps, the
velocity dispersion is close to isotropic, and the equidensity surfaces tend to
align with those of the main body of the halo at larger radii. As haloes grow,
their cusps are often (but not always) overlaid with additional material at
intermediate radii to produce profiles more similar to the Einasto or NFW forms
typical of more massive haloes. Nevertheless, to the extent that we can resolve
them, cusps survive at the smallest radii. Major mergers can disturb them, but
the effect is quite weak in the cases that we study. The cusps extend down to
the resolution limits of our simulations, which are typically a factor of
several larger than the cores that would be produced by phase-space
conservation if the initial power spectrum cutoff arises from free streaming. | The Atacama Cosmology Telescope: Delensed Power Spectra and Parameters: We present LCDM cosmological parameter constraints obtained from delensed
microwave background power spectra. Lensing maps from a subset of DR4 data from
the Atacama Cosmology Telescope (ACT) are used to undo the lensing effect in
ACT spectra observed at 150 and 98 GHz. At 150 GHz, we remove the lensing
distortion with an effective efficiency of 30% (TT), 30% (EE), 26% (TE) and 20%
(BB); this results in detections of the delensing effect at 8.7 sigma (TT), 5.1
sigma (EE), 2.6 sigma (TE), and 2.4 sigma (BB) significance. The combination of
150 and 98 GHz TT, EE, and TE delensed spectra is well fit by a standard LCDM
model. We also measure the shift in best-fit parameters when fitting delensed
versus lensed spectra; while this shift does not inform our ability to measure
cosmological parameters, it does provide a three-way consistency check among
the lensing inferred from the best-fit parameters, the lensing in the CMB power
spectrum, and the reconstructed lensing map. This shift is predicted to be zero
when fitting with the correct model since both lensed and delensed spectra
originate from the same region of sky. Fitting with a LCDM model and
marginalizing over foregrounds, we find that the shift in cosmological
parameters is consistent with zero. Our results show that gravitational lensing
of the microwave background is internally consistent within the framework of
the standard cosmological model. |
Tachyonic fields in cosmology: The possibility of explanation of accelerated expansion of the Universe by
tachyonic scalar fields which homogeneously fill the world is discussed. The
dependences of potential and kinetic term on scale factor are deduced for the
case of quintessential and phantom dark energy with generalized linear
barotropic equation of state. The possibility to distinguish the tachyonic
scalar field as dark energy from other scalar field models, especially from
classical scalar field, is analyzed. | Halo mass distribution reconstruction across the cosmic web: We study the relation between halo mass and its environment from a
probabilistic perspective. We find that halo mass depends not only on local
dark matter density, but also on non-local quantities such as the cosmic web
environment and the halo-exclusion effect. Given these accurate relations, we
have developed the HADRON-code (Halo mAss Distribution ReconstructiON), a
technique which permits us to assign halo masses to a distribution of haloes in
three-dimensional space. This can be applied to the fast production of mock
galaxy catalogues, by assigning halo masses, and reproducing accurately the
bias for different mass cuts. The resulting clustering of the halo populations
agree well with that drawn from the BigMultiDark $N$-body simulation: the power
spectra are within 1-$\sigma$ up to scales of $k=0.2\,h\,{\rm Mpc}^{-1}$, when
using augmented Lagrangian perturbation theory based mock catalogues. Only the
most massive haloes show a larger deviation. For these, we find evidence of the
halo-exclusion effect. A clear improvement is achieved when assigning the
highest masses to haloes with a minimum distance separation. We also compute
the 2- and 3-point correlation functions, and find an excellent agreement with
$N$-body results. Our work represents a quantitative application of the cosmic
web classification. It can have further interesting applications in the
multi-tracer analysis of the large-scale structure for future galaxy surveys. |
Resolving the timing problem of the globular clusters orbiting the
Fornax dwarf galaxy: We re-investigate the old problem of the survival of the five globular
clusters orbiting the Fornax dwarf galaxy in both standard and modified
Newtonian dynamics. For the first time in the history of the topic, we use
accurate mass models for the Fornax dwarf, obtained through Jeans modelling of
the recently published line of sight velocity dispersion data, and we are also
not resigned to circular orbits for the globular clusters. Previously conceived
problems stem from fixing the starting distances of the globulars to be less
than half the tidal radius. We relax this constraint since there is absolutely
no evidence for it and show that the dark matter paradigm, with either cusped
or cored dark matter profiles, has no trouble sustaining the orbits of the two
least massive globular clusters for a Hubble time almost regardless of their
initial distance from Fornax. The three most massive globulars can remain in
orbit as long as their starting distances are marginally outside the tidal
radius. The outlook for modified Newtonian dynamics is also not nearly as bleak
as previously reported. Although dynamical friction inside the tidal radius is
far stronger in MOND, outside dynamical friction is negligible due to the
absence of stars. This allows highly radial orbits to survive, but more
importantly circular orbits at distances more than 85% of Fornax's tidal radius
to survive indefinitely. The probability of the globular clusters being on
circular orbits at this distance compared with their current projected
distances is discussed and shown to be plausible. Finally, if we ignore the
presence of the most massive globular (giving it a large line of sight
distance) we demonstrate that the remaining four globulars can survive within
the tidal radius for the Hubble time with perfectly sensible orbits. | X-ray and Sunyaev-Zeldovich properties of the WHIM: We use numerical simulations to predict the soft X-ray ([0.4-0.6] keV) and
Sunyaev-Zeldovich signal (at 150 GHz) from the large scale structure in the
Universe and then compute 2-point statistics to study the spatial distribution
and time evolution of the signals. The average X-ray signal predicted for the
WHIM is in good agreement with observational constraints that set it at about
10% of the total Diffuse X-ray Background. The characteristic angle computed
with the Autocorrelation Function is of the order of some arcminutes and
becomes smaller at higher redshift. The power spectrum peak of the SZ due to
the WHIM is at l~10000 and has amplitude of ~0.2 muK^2, about one order of
magnitude below the signal measured with telescopes like Planck, ACT, and SPT.
Even if the high-redshift WHIM signal is too weak to be detected using X-rays
only, the small-scale correlation between X-ray and SZ maps is dominated by the
high-redshift WHIM. This makes the analysis of the SZ signal in support of
X-rays a promising tool to study the early time WHIM. |
Effects of superstructure environment on galaxy groups: We analyse properties of galaxy groups and their dependence on the large
scale environment as defined by superstructures. We find that group galaxy
cross correlations depend only on group properties regardless the groups reside
in superstructures. This indicates that the total galaxy density profile around
groups is independent of the global environment. At a given global luminosity,
a proxy to group total mass, groups have a larger stellar mass content by a
factor 1.3, a relative excess independent of the group luminosity. Groups in
superstructures have 40 per cent higher velocity dispersions and systematically
larger minimal enclosing radii. We also find that the stellar population of
galaxies in groups in superstructures is systematically older as infered from
the galaxy spectra Dn4000 parameter. Although the galaxy number density profile
of groups is independent of environment, the star formation rate and stellar
mass profile of the groups residing in superstructures differs from groups
elsewhere. For groups residing in superstructures, the combination of a larger
stellar mass content and star formation rate produces a larger time scale for
star formation regardless the distance to the group center. Our results provide
evidence that groups in superstructures formed earlier than elsewhere, as
expected in the assembly bias scenario. | Importance of high-frequency bands for thermal dust removal in ECHO: The Indian Consortium of Cosmologists has proposed a cosmic microwave
background (CMB) space mission, Exploring Cosmic History and Origin (ECHO). A
major scientific goal of the mission is to detect the primordial B-mode signal
of CMB polarization. The detection of the targeted signal is very challenging
as it is deeply buried under the dominant astrophysical foreground emissions of
the thermal dust and the Galactic synchrotron. To facilitate the adequate
subtraction of thermal dust, the instrument design of ECHO has included nine
dust-dominated high-frequency bands over the frequency range of 220-850 GHz. In
this work, we closely reexamine the utility of the high-frequency ECHO bands in
foreground subtraction using the Needlet Internal Linear Combination component
separation method. We consider three dust models: a physical dust model, a dust
spectral energy distribution (SED) with a single modified black body (MBB)
emission law and a multilayer dust model with frequency-frequency
decorrelation. We consider eleven ECHO bands in the 28-190 GHz range as our
baseline configuration and investigate the changes in the level foreground and
noise residuals as subsequent dust-dominated high-frequency bands are added. We
find that adding the high-frequency bands leads to a consistent decrease in the
level of residual foreground and noise, and the sensitivity of r measurement
improves. Most of the reduction in both residual levels and enhancement in the
sensitivity is achieved in the 28-600 GHz frequency range. Negligible change in
residual levels is seen by extending the frequency range from 600 GHz to 850
GHz. |
The Linear Point: A cleaner cosmological standard ruler: We show how a characteristic length scale imprinted in the galaxy two-point
correlation function, dubbed the "linear point", can serve as a comoving
cosmological standard ruler. In contrast to the Baryon Acoustic Oscillation
peak location, this scale is constant in redshift and is unaffected by
non-linear effects to within $0.5$ percent precision. We measure the location
of the linear point in the galaxy correlation function of the LOWZ and CMASS
samples from the Twelfth Data Release (DR12) of the Baryon Oscillation
Spectroscopic Survey (BOSS) collaboration. We combine our linear-point
measurement with cosmic-microwave-background constraints from the Planck
satellite to estimate the isotropic-volume distance $D_{V}(z)$, without relying
on a model-template or reconstruction method. We find $D_V(0.32)=1264\pm 28$
Mpc and $D_V(0.57)=2056\pm 22$ Mpc respectively, consistent with the quoted
values from the BOSS collaboration. This remarkable result suggests that all
the distance information contained in the baryon acoustic oscillations can be
conveniently compressed into the single length associated with the linear
point. | Dynamical cluster masses from photometric surveys: The masses of galaxy clusters can be measured using data obtained exclusively
from wide photometric surveys in one of two ways: directly from the amplitude
of the weak lensing signal or, indirectly, through the use of scaling relations
calibrated using binned lensing measurements. In this paper, we build on a
recently proposed idea and implement an alternative method based on the radial
profile of the satellite distribution. This technique relies on splashback, a
feature associated with the apocenter of recently accreted galaxies that offers
a clear window into the phase-space structure of clusters without the use of
velocity information. We carry out this dynamical measurement using the stacked
satellite distribution around a sample of luminous red galaxies in the fourth
data release of the Kilo-Degree Survey and validate our results using
abundance-matching and lensing masses. To illustrate the power of this
measurement, we combine dynamical and lensing mass estimates to robustly
constrain scalar-tensor theories of gravity at cluster scales. Our results
exclude departures from General Relativity of order unity. We conclude the
paper by discussing the implications for future data sets. Because splashback
mass measurements scale only with the survey volume, stage-IV photometric
surveys are well-positioned to use splashback to provide high-redshift cluster
masses. |
Dark Radiation in extended cosmological scenarios: Recent cosmological data have provided evidence for a "dark" relativistic
background at high statistical significance. Parameterized in terms of the
number of relativistic degrees of freedom Neff, however, the current data seems
to indicate a higher value than the one expected in the standard scenario based
on three active neutrinos. This dark radiation component can be characterized
not only by its abundance but also by its clustering properties, as its
effective sound speed and its viscosity parameter. It is therefore crucial to
study the correlations among the dark radiation properties and key cosmological
parameters, as the dark energy equation of state or the running of the scalar
spectral index, with current and future CMB data. We find that dark radiation
with viscosity parameters different from their standard values may be
misinterpreted as an evolving dark energy component or as a running spectral
index in the power spectrum of primordial fluctuations. | Testing one-loop galaxy bias: Power spectrum: We test the regime of validity of one-loop galaxy bias for a wide variety of
biased tracers. Our most stringent test asks the bias model to simultaneously
match the galaxy-galaxy and galaxy-mass spectrum, using the measured nonlinear
matter spectrum from the simulations to test one-loop effects from the bias
expansion alone. In addition, we investigate the relevance of short-range
nonlocality and halo exclusion through higher-derivative and scale-dependent
noise terms, as well as the impact of using co-evolution relations to reduce
the number of free fitting parameters. From comparing validity and merit of
these assumptions we find that a four-parameter model (linear, quadratic, cubic
nonlocal bias, and constant shot noise) with fixed quadratic tidal bias
provides a robust modeling choice for the auto power spectrum of the less
massive halos in our set of samples and their galaxy populations (up to
$k_{\mathrm{max}} = 0.35\,h/\mathrm{Mpc}$ for a sample volume of
$6\,(\mathrm{Gpc}/h)^3$). For the more biased tracers it is most beneficial to
include scale-dependent noise. This is also the preferred option when
considering combinations of the auto and cross power spectrum, which might be
relevant in joint studies of galaxy clustering and weak lensing. We also test
the use of perturbation theory to account for matter loops through gRPT, EFT
and the hybrid approach RESPRESSO. While all these have similar performance, we
find the latter to be the best in terms of validity and recovered mean
posterior values, in accordance with it being based partially on simulations. |
Extremely rapid star cluster disruption in high-shear circumnuclear
starburst rings: the unusual case of NGC 7742: All known mass distributions of recently formed star cluster populations
resemble a "universal" power-law function. Here we assess the impact of the
extremely disruptive environment in NGC 7742's circumnuclear starburst ring on
the early evolution of the galaxy's high-mass (~10^5-10^7 Msun) star cluster
population. Surprisingly, and contrary to expectations, at all ages --
including the youngest, <15 Myr -- the cluster mass functions are robustly and
verifiably represented by lognormal distributions that resemble those commonly
found only for old, evolved globular cluster systems in the local Universe.
This suggests that the high-shear conditions in the NGC 7742 starburst ring may
significantly speed up dynamical star cluster destruction. This enhanced
mass-dependent disruption rate at very young ages might be caused by a
combination of the starburst ring's high density and the shear caused by the
counterrotating gas disk in the galaxy's inner region. | X-ray Properties of SPT Selected Galaxy Clusters at 0.2<z<1.5 Observed
with XMM-Newton: We present measurements of the X-ray observables of the intra-cluster medium
(ICM), including luminosity $L_X$, ICM mass $M_{ICM}$, emission-weighted mean
temperature $T_X$, and integrated pressure $Y_X$, that are derived from
XMM-Newton X-ray observations of a Sunyaev-Zel'dovich Effect (SZE) selected
sample of 59 galaxy clusters from the South Pole Telescope SPT-SZ survey that
span the redshift range of $0.20 < z < 1.5$. We constrain the best-fit power
law scaling relations between X-ray observables, redshift, and halo mass. The
halo masses are estimated based on previously published SZE observable to mass
scaling relations, calibrated using information that includes the halo mass
function. Employing SZE-based masses in this sample enables us to constrain
these scaling relations for massive galaxy clusters ($M_{500}\geq 3
\times10^{14}$ $M_\odot$) to the highest redshifts where these clusters exist
without concern for X-ray selection biases. We find that the mass trends are
steeper than self-similarity in all cases, and with $\geq 2.5{\sigma}$
significance in the case of $L_X$ and $M_{ICM}$. The redshift trends are
consistent with the self-similar expectation, but the uncertainties remain
large. Core-included scaling relations tend to have steeper mass trends for
$L_X$. There is no convincing evidence for a redshift-dependent mass trend in
any observable. The constraints on the amplitudes of the fitted scaling
relations are currently limited by the systematic uncertainties on the
SZE-based halo masses, however the redshift and mass trends are limited by the
X-ray sample size and the measurement uncertainties of the X-ray observables. |
The nature of non-Gaussianity and statistical isotropy of the 408 MHz
Haslam synchrotron map: Accurate component separation of full-sky maps in the radio and microwave
frequencies, such as the cosmic microwave background (CMB), relies on a
thorough understanding of the statistical properties of the Galactic foreground
emissions. Using scalar Minkowski functionals and their tensorial
generalization known as Minkowski tensors, we analyze the statistical
properties of one of the major foreground components, namely the Galactic
synchrotron given by the full sky 408 MHz Haslam map. We focus on understanding
the nature of non-Gaussianity and statistical isotropy of the cooler regions of
the map as a function of angular scale. We find that the overall level of the
non-Gaussian deviations does decrease as more high emission regions are masked
and as we go down to smaller scales, in agreement with the results obtained in
earlier works. However, they remain significantly high, of order 3.3$\sigma$,
at the smallest angular scales relevant for the Haslam map. We carry out a
detailed examination of the non-Gaussian nature using the generalized skewness
and kurtosis cumulants that arise in the perturbative expansion of Minkowski
functionals for weakly non-Gaussian fields. We find that the leading sources of
non-Gaussianity are the kurtosis terms which are considerably larger than the
skewness terms at all angular scales. Further, for the cooler regions of the
Haslam map, we find that the non-Gaussian deviations of the Minkowski
functionals can be well explained by the perturbative expansion up to
second-order (up to kurtosis terms), with first-order terms being sub-dominant.
Lastly, we test the statistical isotropy of the Haslam map and find that it
becomes increasingly more isotropic at smaller scales. | Escape from the swamp with spectator: In the context of string theory, several conjectural conditions have been
proposed for low energy effective field theories not to be in swampland, the
UV-incomplete class. The recent ones represented by the de Sitter and
trans-Planckian censorship conjectures in particular seem to conflict with the
inflation paradigm of the early universe. We first point out that scenarios
where inflation is repeated several times (multi-phase inflation) can be easily
compatible with these conjectures. In other words, we relax the constraint on
the single inflation for the large scale perturbations to only continue at
least around 10 e-folds. In this context, we then investigate if a spectator
field can be a source of the almost scale-invariant primordial perturbations on
the large scale. As a consequence of such an isocurvature contribution, the
resultant perturbations exhibit the non-vanishing non-Gaussianity in general.
Also the perturbation amplitude on smaller scales can be completely different
from that on the large scale due to the multiplicity of inflationary phases.
These signatures will be a smoking gun of this scenario by the future
observations. |
The mass of first stars: We perform a three dimensional radiation hydrodynamics simulation to
investigate the formation of first stars from initial collapse of a primordial
gas cloud to formation and growth of protostars. The simulation is integrated
until 0.1 Myrs after the formation of the primary protostar by which the
protostars have already settled onto main sequence stars. This is the first
attempt of simulating first star formation to take into account the ultraviolet
radiative feedback effect by the multiple protostars as well as the three
dimensional effects such as fragmentation of the accretion disk. We find that
the mass accretions onto the population III protostars are significantly
suppressed by the radiative feedback from themselves. As a result, we find five
stars formed in this particular simulation, and that the final mass of the
stars are < 60Msun, including a star of 4.4Msun. Formation of such a star hints
at the existence of even lower-mass stars that would live today. | Faraday Rotation Measure due to the Intergalactic Magnetic Field: Studying the nature and origin of the intergalactic magnetic field (IGMF) is
an outstanding problem of cosmology. Measuring Faraday rotation would be a
promising method to explore the IGMF in the large-scale structure (LSS) of the
universe. We investigated the Faraday rotation measure (RM) due to the IGMF in
filaments of galaxies using simulations for cosmological structure formation.
We employed a model IGMF based on turbulence dynamo in the LSS of the universe;
it has an average strength of $< B > \sim 10$ nG and a coherence length of
several $\times\ 100\ h^{-1}$ kpc in filaments. With the coherence length
smaller than path length, the inducement of RM would be a random walk process,
and we found that the resultant RM is dominantly contributed by the density
peak along line of sight. The rms of RM through filaments at the present
universe was predicted to be $\sim 1\ {\rm rad\ m^{-2}}$. In addition, we
predicted that the probability distribution function of $|{\rm RM}|$ through
filaments follows the log-normal distribution, and the power spectrum of RM in
the local universe peaks at a scale of $\sim 1\ h^{-1}$ Mpc. Our prediction of
RM could be tested with future instruments. |
The Snapshot Hubble U-Band Cluster Survey (SHUCS). I. Survey Description
and First Application to the Mixed Star Cluster Population of NGC 4041: We present the Snapshot Hubble U-band Cluster Survey (SHUCS), a project aimed
at characterizing the star cluster populations of ten nearby galaxies (d<23
Mpc, half within 12 Mpc) through new F336W (U band equivalent) imaging from
WFC3, and archival BVI-equivalent data with HST. Completing the UBVI baseline
reduces the age-extinction degeneracy of optical colours, thus enabling the
measurement of reliable ages and masses for the thousands of clusters covered
by our survey. The sample consists chiefly of face-on spiral galaxies at low
inclination, in various degrees of isolation (isolated, in group, merging), and
includes two AGN hosts. This first paper outlines the survey itself, the
observational datasets, the analysis methods, and presents a proof-of-concept
study of the large-scale properties and star cluster population of NGC 4041, a
massive SAbc galaxy at a distance of 23 Mpc, and part of a small grouping of
six giant members. We resolve two structural components with distinct stellar
populations, a morphology more akin to merging and interacting systems. We also
find strong evidence of a truncated, Schechter-type mass function, and a
similarly segmented luminosity function. These results indicate that binning
must erase much of the substructure present in the mass and luminosity
functions, and might account for the conflicting reports on the intrinsic shape
of these functions in the literature. We also note a tidal feature in the
outskirts of the galaxy in GALEX UV imaging, and follow it up with a
comprehensive multi-wavelength study of NGC 4041 and its parent group. We
deduce a minor merger as a likely cause of its segmented structure and the
observed pattern of a radially decreasing star formation rate. We propose that
combining the study of star cluster populations with broad-band metrics is not
only advantageous, but often easily achievable through archival datasets. | Post-$Planck$ constraints on interacting vacuum energy: We present improved constraints on an interacting vacuum model using updated
astronomical observations including the first data release from Planck. We
consider a model with one dimensionless parameter, $\alpha$, describing the
interaction between dark matter and vacuum energy (with fixed equation of state
$w=-1$). The background dynamics correspond to a generalised Chaplygin gas
cosmology, but the perturbations have a zero sound speed. The tension between
the value of the Hubble constant, $H_0$, determined by Planck data plus WMAP
polarisation (Planck+WP) and that determined by the Hubble Space Telescope
(HST) can be alleviated by energy transfer from dark matter to vacuum
($\alpha>0$). A positive $\alpha$ increases the allowed values of $H_0$ due to
parameter degeneracy within the model using only CMB data. Combining with
additional datasets of including supernova type Ia (SN Ia) and baryon acoustic
oscillation (BAO), we can significantly tighten the bounds on $\alpha$.
Redshift-space distortions (RSD), which constrain the linear growth of
structure, provide the tightest constraints on vacuum interaction when combined
with Planck+WP, and prefer energy transfer from vacuum to dark matter
($\alpha<0$) which suppresses the growth of structure. Using the combined
datasets of Planck+WP+Union2.1+BAO+RSD, we obtain the constraint on $\alpha$ to
be $-0.083<\alpha<-0.006$ (95% C.L.), allowing low $H_0$ consistent with the
measurement from 6dF Galaxy survey. This interacting vacuum model can alleviate
the tension between RSD and Planck+WP in the $\Lambda$CDM model for $\alpha<0$,
or between HST measurements of $H_0$ and Planck+WP for $\alpha>0$, but not both
at the same time. |
Resolving primordial physics through correlated signatures: We discuss correlations among spectral observables as a new tool for
differentiating between models for the primordial perturbation. We show that if
generated in the isocurvature sector, a running of the scalar spectral index is
correlated with the statistical properties of non-Gaussianities. In particular,
we find a large running will inevitably be accompanied by a large running of
$f_{\rm NL}$ and enhanced $g_{\rm NL}$, with $g_{\rm NL}\gg f_{\rm NL}^2$. If
the tensor to scalar ratio is large, a large negative running must turn
positive on smaller scales. Interestingly, the characteristic scale of the
transition could potentially distinguish between the inflaton and isocurvature
fields. | Tomographic analyses of the CMB lensing and galaxy clustering to probe
the linear structure growth: In a tomographic approach, we measure the cross-correlation between the CMB
lensing reconstructed from the Planck satellite and the galaxies of the
photometric redshift catalogue based on the combination of the South Galactic
Cap u-band Sky Survey (SCUSS), Sloan Digital Sky Survey (SDSS), and Wide-field
Infrared Survey Explorer (WISE) data. We perform the analyses considering six
redshift bins spanning the range of $0.1 <z<0.7$. From the estimates of the
galaxy-galaxy and galaxy-CMB lensing power spectrum, we derive the galaxy bias
and the amplitude of the cross-correlation for each redshift bin. We have
finally applied these tomographic measurements to estimate the linear structure
growth using the bias-independent $\hat{D}_{G}$ estimator introduced by
Giannantonio et al. 2016. We find that the amplitude of the structure growth
with respect to the fiducial cosmology is $A_{D}=1.16\pm 0.13$, closely
consistent with the predictions of the $\Lambda$CDM model ($A_{D}^{\Lambda
CDM}=1$). We perform several tests for consistency of our results, finding no
significant evidence for systematic effects. |
On the absence of radio halos in clusters with double relics: Pairs of radio relics are believed to form during cluster mergers, and are
best observed when the merger occurs in the plane of the sky. Mergers can also
produce radio halos, through complex processes likely linked to turbulent
re-acceleration of cosmic-ray electrons. However, only some clusters with
double relics also show a radio halo. Here, we present a novel method to derive
upper limits on the radio halo emission, and analyse archival X-ray Chandra
data, as well as galaxy velocity dispersions and lensing data, in order to
understand the key parameter that switches on radio halo emission. We place
upper limits on the halo power below the $P_{\rm 1.4 \, GHz}\, M_{500}$
correlation for some clusters, confirming that clusters with double relics have
different radio properties. Computing X-ray morphological indicators, we find
that clusters with double relics are associated with the most disturbed
clusters. We also investigate the role of different mass-ratios and
time-since-merger. Data do not indicate that the merger mass ratio has an
impact on the presence or absence of radio halos (the null hypothesis that the
clusters belong to the same group cannot be rejected). However, the data
suggests that the absence of radio halos could be associated with early and
late mergers, but the sample is too small to perform a statistical test. Our
study is limited by the small number of clusters with double relics. Future
surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to
better address this issue. | Lenticular galaxy IC 719: current building of the counterrotating
large-scale stellar disk: We have obtained and analyzed long-slit spectral data for the lenticular
galaxy IC 719. In this gas-rich S0 galaxy, its large-scale gaseous disk
counterrotates the global stellar disk. Moreover in the IC 719 disk we have
detected a secondary stellar component corotating the ionized gas. By using
emission-line intensity ratios, we have proved the gas excitation by young
stars and so are claiming current star formation, most intense in a ring-like
zone at the radius of 10" (1.4 kpc). The oxygen abundance of the gas in the
starforming ring is about half of the solar abundance. Since the stellar disk
remains dynamically cool, we conclude that smooth prolonged accretion of the
external gas from a neighboring galaxy provides urrent building of the thin
large-scale stellar disk. |
Linear cosmological constraints on 2-body decaying dark matter scenarios
and the $S_8$ tension: The '$S_8$ tension' is a longstanding discrepancy between the cosmic
microwave background (CMB) and weak gravitational lensing determination of the
amplitude of matter fluctuations, parametrized as
$S_8\equiv\sigma_8(\Omega_m/0.3)^{0.5}$, where $\sigma_8$ is the root mean
square of matter fluctuations on a 8 $h^{-1}$Mpc scale, and $\Omega_m$ is the
total matter abundance. It was recently shown that dark matter (DM) decaying
into a massless (dark radiation) and a massive (warm DM) species, with a
lifetime $\Gamma^{-1} \simeq 55~(\varepsilon/0.007)^{1.4}$ Gyrs -- where
$\varepsilon$ represent the mass-energy fraction transferred to the massless
component -- can ease the tension. Thanks to a fast and accurate fluid
approximation scheme for the warm species, we perform a comprehensive study of
this 2-body decaying DM scenario, discussing in detail its dynamics and its
impact on the CMB and linear matter power spectra. We then investigate the
implications for the '$S_8$ tension' against a number of changes in the
analysis: different $S_8$ priors, marginalization over the lensing information
in Planck data, trading Planck high$-\ell$ polarization data for those from the
SPTpol and ACTPol surveys, and the inclusion of the recent results from the
Xenon1T collaboration. We conclude that the preference for decaying DM,
apparent only when the $S_8$ value determined from weak lensing data is added
to the analysis, does not sensibly degrade the fit to any of the cosmological
data-sets considered, and that the model could potentially explain the
anomalous electron recoil excess reported by the Xenon1T collaboration.
Furthermore, we explictly show that while current CMB data alone are not
sensitive enough to distinguish between standard CDM and decaying DM,
next-generation CMB observations (CMB-S4) can unambiguously detect its
signature. | The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation
schemes: Boltzmann codes are used extensively by several groups for constraining
cosmological parameters with Cosmic Microwave Background and Large Scale
Structure data. This activity is computationally expensive, since a typical
project requires from 10'000 to 100'000 Boltzmann code executions. The newly
released code CLASS (Cosmic Linear Anisotropy Solving System) incorporates
improved approximation schemes leading to a simultaneous gain in speed and
precision. We describe here the three approximations used by CLASS for basic
LambdaCDM models, namely: a baryon-photon tight-coupling approximation which
can be set to first order, second order or to a compromise between the two; an
ultra-relativistic fluid approximation which had not been implemented in public
distributions before; and finally a radiation streaming approximation taking
reionisation into account. |
First direct metallicity measurement of a lensed star-forming galaxy at
z=1.7: We present the rest-frame optical spectrum of a strongly lensed galaxy at
redshift z =1.7 behind the cluster Abell 1689. We detect the temperature
sensitive auroral line [O III] 4363, which allows the first direct metallicity
measurement for galaxies at z > 1. Our high signal-to-noise spectrum indicates
that the target is an extremely low metallicity star-forming galaxy.We estimate
an intrinsic absolute B band magnitude of M_{B}=-18.3 \pm 0.1$, with a stellar
mass of 4.4$\pm1.2\times10^{8}$ M$_{\odot}$. This galaxy extends the
luminosity-metallicity relation of star-forming galaxies at z > 2 by more than
an order of magnitude. Given the double-nuclei like morphology and velocity
profile of \ha, we tentatively suggest that it could be a merger or a
proto-rotating disk galaxy. | KiDS-1000 Methodology: Modelling and inference for joint weak
gravitational lensing and spectroscopic galaxy clustering analysis: We present the methodology for a joint cosmological analysis of weak
gravitational lensing from the fourth data release of the ESO Kilo-Degree
Survey (KiDS-1000) and galaxy clustering from the partially overlapping BOSS
and 2dFLenS surveys. Cross-correlations between galaxy positions and
ellipticities have been incorporated into the analysis, necessitating a hybrid
model of non-linear scales that blends perturbative and non-perturbative
approaches, and an assessment of contributions by astrophysical effects. All
weak lensing signals are measured consistently via Fourier-space statistics
that are insensitive to the survey mask and display low levels of mode mixing.
The calibration of photometric redshift distributions and multiplicative
gravitational shear bias has been updated, and a more complete tally of
residual calibration uncertainties is propagated into the likelihood. A
dedicated suite of more than 20000 mocks is used to assess the performance of
covariance models and to quantify the impact of survey geometry and spatial
variations of survey depth on signals and their errors. The sampling
distributions for the likelihood and the $\chi^2$ goodness-of-fit statistic
have been validated, with proposed changes to the number of degrees of freedom.
Standard weak lensing point estimates on $S_8=\sigma_8\,(\Omega_{\rm
m}/0.3)^{1/2}$ derived from its marginal posterior are easily misinterpreted to
be biased low, and an alternative estimator and associated credible interval
have been proposed. Known systematic effects pertaining to weak lensing
modelling and inference are shown to bias $S_8$ by no more than 0.1 standard
deviations, with the caveat that no conclusive validation data exist for models
of intrinsic galaxy alignments. Compared to the previous KiDS analyses, $S_8$
constraints are expected to improve by 20% for weak lensing alone and by 29%
for the joint analysis. [abridged] |
Cosmic evolution of radio selected active galactic nuclei in the COSMOS
field: We explore the cosmic evolution of radio AGN with low radio powers (L_1.4GHz
< 5\times10^25 W/Hz) out to z=1.3 using to-date the largest sample of ~600 low
luminosity radio AGN at intermediate redshift drawn from the VLA-COSMOS survey.
We derive the radio luminosity function for these AGN, and its evolution with
cosmic time assuming two extreme cases: i) pure luminosity and ii) pure density
evolution. The former and latter yield L_*\propto(1+z)^(0.8+/-0.1), and
Phi*\propto (1+z)^(1.1+/-0.1), respectively, both implying a fairly modest
change in properties of low radio-power AGN since z=1.3. We show that this is
in stark contrast with the evolution of powerful (L_1.4GHz > 5\times10^25 W/Hz)
radio AGN over the same cosmic time interval, constrained using the 3CRR, 6CE,
and 7CRS radio surveys by Willott et al. (2001). We demonstrate that this can
be explained through differences in black hole fueling and triggering
mechanisms, and a dichotomy in host galaxy properties of weak and powerful AGN.
Our findings suggest that high and low radio-power AGN activity is triggered in
different stages during the formation of massive red galaxies. We show that
weak radio AGN occur in the most massive galaxies already at z~1, and they may
significantly contribute to the heating of their surrounding medium and thus
inhibit gas accretion onto their host galaxies, as recently suggested for the
`radio mode' in cosmological models. | The Araucaria Project. The Distance to the Small Magellanic Cloud from
Near-Infrared Photometry of RR Lyrae Variables: We have obtained deep infrared J and K band observations of nine 4.9x4.9
arcmin fields in the Small Magellanic Cloud (SMC) with the ESO New Technology
Telescope equipped with the SOFI infrared camera. In these fields, 34 RR Lyrae
stars catalogued by the OGLE collaboration were identified. Using different
theoretical and empirical calibrations of the infrared
period-luminosity-metallicity relation, we find consistent SMC distance moduli,
and find a best true distance modulus to the SMC of 18.97 +/- 0.03
(statistical) +/- 0.12 (systematic) mag which agrees well with most independent
distance determinations to this galaxy, and puts the SMC 0.39 mag more distant
than the LMC for which our group has recently derived, from the same technique,
a distance of 18.58 mag. |
Quasar Ionization Front Lyα Emission in an Inhomogeneous
Intergalactic Medium: The conditions within the ionization front of a quasar during reionization (T
~ 30,000 K, neutral hydrogen fraction ~ 0.5) are ideal for producing
Lyman-alpha emission via collisional excitation of hydrogen atoms. Observations
of this emission, which could subtend >10 arcmin$^2$ on the sky, would
definitively demonstrate the presence of a neutral intergalactic medium at the
observed epoch, placing valuable constraints on the progress of reionization.
We find that the expected Lyman-alpha surface brightness is significantly
weaker than previously determined and may be impossible to observe with current
and near-future instruments. Past work calculated the Lyman-alpha emission from
a quasar ionization front in a homogeneous medium with a clumping factor
approximation to account for inhomogeneities. We find using 1D radiative
transfer calculations that this approximation overestimates the emission by a
factor of >3. Our calculations model the propagation of ionizing photons and
compute the Lyman-alpha emission from quasar ionization fronts on sightlines
from a hydrodynamic cosmological simulation at z = 7.1. To better understand
the physical properties of the emission, we also develop an analytic model that
accurately describes the results of the full radiative transfer calculation. | The Integrated Sachs-Wolfe Effect in Time Varying Vacuum Model: The integrated Sachs-Wolfe (ISW) effect is an important implication for dark
energy. In this paper, we have calculated the power spectrum of the ISW effect
in the time varying vacuum cosmological model, where the model parameter
$\beta=4.407$ is obtained by the observational constraint of the growth rate.
It's found that the source of the ISW effect is not only affected by the
different evolutions of the Hubble function $H(a)$ and the dimensionless matter
density $\Omega_m(a)$, but also by the different growth function $D_+(a)$, all
of which are changed due to the presence of matter production term in the time
varying vacuum model. However, the difference of the ISW effect in
$\Lambda(t)\textmd{CDM}$ model and $\Lambda \textmd{CDM}$ model is lessened to
a certain extent due to the integration from the time of last scattering to the
present. It's implied that the observations of the galaxies with high redshift
are required to distinguish the two models. |
Global e-VLBI observations of the gamma-ray narrow line Seyfert 1 PMN
J0948+0022: There is growing evidence of relativistic jets in radio-loud narrow-line
Seyfert 1 (RL-NLS1) galaxies. We constrain the observational properties of the
radio emission in the first RL-NLS1 galaxy ever detected in gamma-rays, PMN
J0948+0022, i.e., its flux density and structure in total intensity and in
polarization, its compactness, and variability. We performed three real-time
e-VLBI observations of PMN J0948+0022 at 22 GHz, using a global array including
telescopes in Europe, East Asia, and Australia. These are the first e-VLBI
science observations ever carried out with a global array, reaching a maximum
baseline length of 12458 km. The observations were part of a large
multiwavelength campaign in 2009. The source is detected at all three epochs.
The structure is dominated by a bright component, more compact than 55
microarcsec, with a fainter component at a position angle theta~ 35deg.
Relativistic beaming is required by the observed brightness temperature of
3.4x10^11 K. Polarization is detected at a level of about 1%. The parameters
derived by the VLBI observations, in addition to the broad-band properties,
confirm that PMN J0948+0022 is similar to flat spectrum radio quasars. Global
e-VLBI is a reliable and promising technique for future studies. | Observations of a nearby filament of galaxy clusters with the Sardinia
Radio Telescope: We report the detection of diffuse radio emission which might be connected to
a large-scale filament of the cosmic web covering a 8deg x 8deg area in the
sky, likely associated with a z~0.1 over-density traced by nine massive galaxy
clusters. In this work, we present radio observations of this region taken with
the Sardinia Radio Telescope. Two of the clusters in the field host a powerful
radio halo sustained by violent ongoing mergers and provide direct proof of
intra-cluster magnetic fields. In order to investigate the presence of
large-scale diffuse radio synchrotron emission in and beyond the galaxy
clusters in this complex system, we combined the data taken at 1.4 GHz obtained
with the Sardinia Radio Telescope with higher resolution data taken with the
NRAO VLA Sky Survey. We found 28 candidate new sources with a size larger and
X-ray emission fainter than known diffuse large-scale synchrotron cluster
sources for a given radio power. This new population is potentially the tip of
the iceberg of a class of diffuse large-scale synchrotron sources associated
with the filaments of the cosmic web. In addition, we found in the field a
candidate new giant radio galaxy. |
Baryon number transfer could delay Quark-Hadron transition in cosmology: In the early Universe, strongly interacting matter was a quark-gluon plasma.
Both lattice computations and heavy ion collision experiments however tell us
that, in the absence of chemical potentials, no plasma survives at $T <\sim
150$ MeV. The cosmological Quark-Hadron transition, however, seems to have been
a crossover; cosmological consequences envisaged when it was believed to be a
phase transition no longer hold. In this paper we discuss whether even a
crossover transition can leave an imprint that cosmological observations can
seek or, viceversa, there are questions cosmology should address to QCD
specialists. In particular, we argue that it is still unclear how baryons (not
hadrons) could form at the cosmological transition. A critical role should be
played by diquark states, whose abundance in the early plasma needs to be
accurately evaluated. We estimate that, if the number of quarks belonging to a
diquark state, at the beginning of the cosmological transition, is $<\sim
1:10^6$, its dynamics could be modified by the process of B-transfer from
plasma to hadrons. In turn, by assuming B-transfer to cause just mild
perturbations and, in particular, no entropy input, we study the deviations
from the tracking regime, in the frame of SCDEW models. We find that, in some
cases, residual deviations could propagate down to primeval nuclesynthesis. | Inflation Wars: A New Hope: We explore a class of primordial power spectra that can fit the observed
anisotropies in the cosmic microwave background well and that predicts a value
for the Hubble parameter consistent with the local measurement of $H_0 = 74$
km/s/Mpc. This class of primordial power spectrum consists of a continuous
deformation between the best-fit power law primordial power spectrum and the
primordial power spectrum derived from the modified Richardson-Lucy
deconvolution algorithm applied to the $C_\ell$s of best-fit power law
primordial power spectrum. We find that linear interpolation half-way between
the power law and modified Richardson-Lucy power spectra fits the Planck data
better than the best-fit $\Lambda$CDM by $\Delta\log\mathcal{L} = 2.5$. In
effect, this class of deformations of the primordial power spectra offer a new
dimension which is correlated with the Hubble parameter. This correlation
causes the best-fit value for $H_0$ to shift and the uncertainty to expand to
$H_0 = 70.2 \pm 1.2$ km/s/Mpc. When considering the Planck dataset combined
with the Cepheid $H_0$ measurement, the best-fit $H_0$ becomes $H_0 = 71.8 \pm
0.9$ km/s/Mpc. We also compute a Bayes factor of $\log K = 5.7$ in favor of the
deformation model. |
Fine structure constant measurements in quasar absorption systems: Detecting any evolution of dimensionless in the ratios of physical
quantities, such as the fine structure constant, would prove that the Weak
Equivalence Principle is violated and lead to a paradigm shift in physics. High
resolution spectroscopy of quasar absorption systems can be used to test
cosmological variations in time and/or in space. A sample of 300 measurements
using data from 8m class optical telescopes provides hints that such variations
are indeed present in a form of a spatial dipole across the sky, although
systematic effects could dominate. Two recent developments, one in
instrumentation and the other in analysis methods, promise to produce a new
sample of measurements free from all known systematic effects to test the
tentative dipole. | A Strange Mènage Á Trois: The Magellanic Clouds may have joined our Milky Way system quite recently.
The Large Magellanic Cloud turns out to be a remarkably luminous object that is
close to the upper luminosity limit of the class of magellanic irregular
galaxies. |
Short Review of the main achievements of the Scalar Field, Fuzzy,
Ultralight, Wave, BEC Dark Matter model: The Scalar Field Dark Matter model has been known in various ways throughout
its history; Fuzzy, BEC, Wave, Ultralight, Axion-like Dark Matter, etc. All of
them consist in proposing that the dark matter of the universe is a spinless
field $\Phi$ that follows the Klein-Gordon (KG) equation of motion
$\Box\Phi-dV/d\Phi=0$, for a given scalar field potential $V$. The difference
between different models is sometimes the choice of the scalar field potential
$V$. In the literature we find that people usually work in the nonrelativistic,
weak-field limit of the KG equation where it transforms into the Schr\"odinger
equation and the Einstein equations into the Poisson equation, reducing the
KG-Einstein system, to the Schr\"odinger-Poisson system. In this paper, we
review some of the most interesting achievements of this model from the
historical point of view and its comparison with observations, showing that
this model could be the last answer to the question about the nature of dark
matter in the universe. | The impact of extragalactic foregrounds on internal delensing of CMB
B-mode polarization: The search for primordial $B$-mode polarization of the CMB is limited by the
sample variance of $B$-modes produced at later times by gravitational lensing.
Constraints can be improved by `delensing': using some proxy of the matter
distribution to partially remove the lensing-induced $B$-modes. Current and
soon-upcoming experiments will infer a matter map -- at least in part -- from
the temperature anisotropies of the CMB. These reconstructions are contaminated
by extragalactic foregrounds: radio-emitting galaxies, the cosmic infrared
background, or the Sunyaev--Zel'dovich effects. Using the Websky simulations,
we show that the foregrounds add spurious power to the angular auto-spectrum of
delensed $B$-modes via non-Gaussian higher-point functions, biasing constraints
on the tensor-to-scalar ratio, $r$. We consider an idealized experiment similar
to the Simons Observatory, with no Galactic or atmospheric foregrounds. After
removing point sources detectable at 143 GHz and reconstructing lensing from
CMB temperature modes $l<3500$ using a Hu-Okamoto quadratic estimator (QE), we
infer a value of $r$ that is $1.5\,\sigma$ higher than the true $r=0$.
Reconstructing instead from a minimum-variance ILC map only exacerbates the
problem, bringing the bias above $3\,\sigma$. When the $TT$ estimator is
co-added with other QEs or with external matter tracers, new couplings ensue
which partially cancel the diluted bias from $TT$. We provide a simple and
effective prescription to model these effects. In addition, we demonstrate that
the point-source-hardened or shear-only QEs can not only mitigate the biases to
acceptable levels, but also lead to lower power than the Hu-Okamoto QE after
delensing. Thus, temperature-based reconstructions remain powerful tools in the
quest to measure $r$. |
Evolution of the Red Sequence Giant to Dwarf Ratio in Galaxy Clusters
out to z ~ 0.5: We analyze deep g' and r' band data of 97 galaxy clusters imaged with MegaCam
on the Canada-France-Hawaii telescope. We compute the number of luminous
(giant) and faint (dwarf) galaxies using criteria based on the definitions of
de Lucia et al. (2007). Due to excellent image quality and uniformity of the
data and analysis, we probe the giant-to-dwarf ratio (GDR) out to z ~ 0.55.
With X-ray temperature (Tx) information for the majority of our clusters, we
constrain, for the first time, the Tx-corrected giant and dwarf evolution
separately. Our measurements support an evolving GDR over the redshift range
0.05 < z < 0.55. We show that modifying the (g'-r'), m_r' and K-correction used
to define dwarf and giant selection do not alter the conclusion regarding the
presence of evolution. We parameterize the GDR evolution using a linear
function of redshift (GDR = alpha * z + beta) with a best fit slope of alpha =
0.88 +/- 0.15 and normalization beta = 0.44 +/- 0.03. Contrary to claims of a
large intrinsic scatter, we find that the GDR data can be fully accounted for
using observational errors alone. Consistently, we find no evidence for a
correlation between GDR and cluster mass (via Tx or weak lensing). Lastly, the
data suggest that the evolution of the GDR at z < 0.2 is driven primarily by
dry merging of the massive giant galaxies, which when considered with previous
results at higher redshift, suggests a change in the dominant mechanism that
mediates the GDR. | The R_h = ct Universe: The backbone of standard cosmology is the Friedmann-Robertson-Walker solution
to Einstein's equations of general relativity (GR). In recent years,
observations have largely confirmed many of the properties of this model, which
is based on a partitioning of the universe's energy density into three primary
constituents: matter, radiation, and a hypothesized dark energy which, in
LambdaCDM, is assumed to be a cosmological constant Lambda. Yet with this
progress, several unpalatable coincidences (perhaps even inconsistencies) have
emerged along with the successful confirmation of expected features. One of
these is the observed equality of our gravitational horizon R_h(t_0) with the
distance ct_0 light has traveled since the big bang, in terms of the current
age t_0 of the universe. This equality is very peculiar because it need not
have occurred at all and, if it did, should only have happened once (right now)
in the context of LambdaCDM. In this paper, we propose an explanation for why
this equality may actually be required by GR, through the application of
Birkhoff's theorem and the Weyl postulate, at least in the case of a flat
spacetime. If this proposal is correct, R_h(t) should be equal to ct for all
cosmic time t, not just its present value t_0. Therefore models such as
LambdaCDM would be incomplete because they ascribe the cosmic expansion to
variable conditions not consistent with this relativistic constraint. We show
that this may be the reason why the observed galaxy correlation function is not
consistent with the predictions of the standard model. We suggest that an
R_h=ct universe is easily distinguishable from all other models at large
redshift (i.e., in the early universe), where the latter all predict a rapid
deceleration. |
Novel null tests for the spatial curvature and homogeneity of the
Universe and their machine learning reconstructions: A plethora of observational data obtained over the last couple of decades has
allowed cosmology to enter into a precision era and has led to the foundation
of the standard cosmological constant and cold dark matter paradigm, known as
the $\Lambda$CDM model. Given the many possible extensions of this concordance
model, we present here several novel consistency tests which could be used to
probe for deviations from $\Lambda$CDM. First, we derive a joint consistency
test for the spatial curvature $\Omega_{k,0}$ and the matter density
$\Omega_\textrm{m,0}$ parameters, constructed using only the Hubble rate
$H(z)$, which can be determined directly from observations. Second, we present
a new test of possible deviations from homogeneity using the combination of two
datasets, either the baryon acoustic oscillation (BAO) and $H(z)$ data or the
transversal and radial BAO data, while we also introduce two consistency tests
for $\Lambda$CDM which could be reconstructed via the transversal and radial
BAO data. We then reconstruct the aforementioned tests using the currently
available data in a model independent manner using a particular machine
learning approach, namely the Genetic Algorithms. Finally, we also report on a
$\sim 4\sigma$ tension on the transition redshift as determined by the $H(z)$
and radial BAO data. | Efficiently evaluating loop integrals in the EFTofLSS using QFT
integrals with massive propagators: We develop a new way to analytically calculate loop integrals in the
Effective Field Theory of Large Scale-Structure. Previous available methods
show severe limitations beyond the one-loop power spectrum due to analytical
challenges and computational and memory costs. Our new method is based on
fitting the linear power spectrum with cosmology-independent functions that
resemble integer powers of quantum field theory massive propagators with
complex masses. A remarkable small number of them is sufficient to reach enough
accuracy. Similarly to former approaches, the cosmology dependence is encoded
in the coordinate vector of the expansion of the linear power spectrum in our
basis. We first produce cosmology-independent tensors where each entry is the
loop integral evaluated on a given combination of basis vectors. For each
cosmology, the evaluation of a loop integral amounts to contracting this tensor
with the coordinate vector of the linear power spectrum. The 3-dimensional loop
integrals for our basis functions can be evaluated using techniques familiar to
particle physics, such as recursion relations and Feynman parametrization. We
apply our formalism to evaluate the one-loop bispectrum of galaxies in redshift
space. The final analytical expressions are quite simple and can be evaluated
with little computational and memory cost. We show that the same expressions
resolve the integration of all one-loop $N$-point function in the EFTofLSS.
This method, which is originally presented here, has already been applied in
the first one-loop bispectrum analysis of the BOSS data to constraint
$\Lambda$CDM parameters and primordial non-Gaussianities, see arXiv:2206.08327
and arXiv:2201.11518. |
NH and Mg Index Trends in Elliptical Galaxies: We examine the spectrum in the vicinity of the NH3360 index of Davidge &
Clark (1994), which was defined to measure the NH absorption around 3360 \AA
and which shows almost no trend with velocity dispersion (Toloba et al. 2009),
unlike other N- sensitive indices, which show a strong trend (Graves et al.
2007). Computing the effect of individual elements on the integrated spectrum
with synthetic stellar population integrated spectra, we find that, while being
well correlated with nitrogen abundance, NH3360 is almost equally well
anti-correlated with Mg abundance. This prompts the definition of two new
indices, Mg3334, which is mostly sensitive to magnesium, and NH3375, which is
mostly sensitive to nitrogen. Rather surprisingly, we find that the new NH3375
index shows a trend versus optical absorption feature indices that is as
shallow as the NH3360 index. We hypothesize that the lack of a strong index
trend in these near-UV indices is due to the presence of an old metal-poor
component of the galactic population. Comparison of observed index trends and
those predicted by models shows that a modest fraction of an old, metal-poor
stellar population could easily account for the observed flat trend in these
near-UV indices, while still allowing substantial N abundance increase in the
larger galaxies. | Gravitational waves at interferometer scales and primordial black holes
in axion inflation: We study the prospects of detection at terrestrial and space interferometers,
as well as at pulsar timing array experiments, of a stochastic gravitational
wave background which can be produced in models of axion inflation. This
potential signal, and the development of these experiments, open a new window
on inflation on scales much smaller than those currently probed with Cosmic
Microwave Background and Large Scale Structure measurements. The sourced signal
generated in axion inflation is an ideal candidate for such searches, since it
naturally grows at small scales, and it has specific properties (chirality and
non-gaussianity) that can distinguish it from an astrophysical background. We
study under which conditions such a signal can be produced at an observable
level, without the simultaneous overproduction of scalar perturbations in
excess of what is allowed by the primordial black hole limits. We also explore
the possibility that scalar perturbations generated in a modified version of
this model may provide a distribution of primordial black holes compatible with
the current bounds, that can act as a seeds of the present black holes in the
universe. |
Halo abundances within the cosmic web: We investigate the dependence of the mass function of dark-matter haloes on
their environment within the cosmic web of large-scale structure. A dependence
of the halo mass function on large-scale mean density is a standard element of
cosmological theory, allowing mass-dependent biasing to be understood via the
peak-background split. On the assumption of a Gaussian density field, this
analysis can be extended to ask how the mass function depends on the
geometrical environment: clusters, filaments, sheets and voids, as classified
via the tidal tensor (the Hessian matrix of the gravitational potential). In
linear theory, the problem can be solved exactly, and the result is
attractively simple: the conditional mass function has no explicit dependence
on the local tidal field, and is a function only of the local density on the
filtering scale used to define the tidal tensor. There is nevertheless a strong
implicit predicted dependence on geometrical environment, because the local
density couples statistically to the derivatives of the potential. We compute
the predictions of this model and study the limits of their validity by
comparing them to results deduced empirically from $N$-body simulations. We
have verified that, to a good approximation, the abundance of haloes in
different environments depends only on their densities, and not on their tidal
structure. In this sense we find relative differences between halo abundances
in different environments with the same density which are smaller than 13%.
Furthermore, for sufficiently large filtering scales, the agreement with the
theoretical prediction is good, although there are important deviations from
the Gaussian prediction at small, non-linear scales. We discuss how to obtain
improved predictions in this regime, using the 'effective-universe' approach. | The evolution of the star formation activity per halo mass up to
redshift ~ 1.6 as seen by Herschel: Star formation in massive galaxies is quenched at some point during
hierarchical mass assembly. To understand where and when the quenching
processes takes place, we study the evolution of the total star formation rate
per unit total halo mass (\Sigma(SFR/M)) in three different mass scales: low
mass halos (field galaxies), groups, and clusters, up to a redshift ~1.6. We
use deep far-infrared PACS data at 100 and 160 um to accurately estimate the
total star formation rate of the Luminous Infrared Galaxy population of 9
clusters with mass ~10^{15} M_{\odot}, and 9 groups/poor clusters with mass ~ 5
x 10^{13} M_{\odot}. Estimates of the field \Sigma(SFR/M) are derived from the
literature, by dividing the star formation rate density by the mean comoving
matter density of the universe. The field \Sigma(SFR/M) increases with redshift
up to z~1 and it is constant thereafter. The evolution of the \Sigma(SFR/M)-z
relation in galaxy systems is much faster than in the field. Up to redshift
z~0.2, the field has a higher \Sigma(SFR/M) than galaxy groups and galaxy
clusters. At higher redshifts, galaxy groups and the field have similar
\Sigma(SFR/M), while massive clusters have significantly lower \Sigma(SFR/M)
than both groups and the field. There is a hint of a reversal of the SFR
activity vs. environment at z~1.6, where the group \Sigma(SFR/M) lies above the
field \Sigma(SFR/M)-z relation. We discuss possible interpretations of our
results in terms of the processes of downsizing, and star-formation quenching. |
Averaging the AGN X-ray spectra from deep Chandra fields: The X-ray spectra of Active Galactic Nuclei (AGN) carry the signatures of the
emission from the central region, close to the Super Massive Black Hole (SMBH).
For this reason, the study of deep X-ray spectra is a powerful instrument to
investigate the origin of their emission.
The emission line most often observed in the X-ray spectra of AGN is Fe K. It
is known that it can be broadened and deformed by relativistic effects if
emitted close enough to the central SMBH. In recent statistical studies of the
X-ray spectra of AGN samples, it is found that a narrow Fe line is ubiquitous,
while whether the broad features are as common is still uncertain. We present
here the results of an investigation on the characteristics of the Fe line in
the average X-ray spectra of AGN in deep Chandra fields.
The average spectrum of the AGN is computed using Chandra spectra with more
than 200 net counts from the AEGIS, Chandra Deep Field North and Chandra Deep
Field South surveys. The sample spans a broader range of X-ray luminosities
than other samples studied with stacking methods up to z=3.5. We analyze the
average spectra of this sample using our own averaging method, checking the
results against extensive simulations. Subsamples defined in terms of column
density of the local absorber, luminosity and z are also investigated.
We found a very significant Fe line with a narrow profile in all our samples
and in almost all the subsamples that we constructed. The equivalent width (EW)
of the narrow line estimated in the average spectrum of the full sample is 74
eV. The broad line component is significantly detected in the subsample of AGN
with L<1.43 1E44 cgs and z<0.76, with EW=108 eV.
We concluded that the narrow Fe line is an ubiquitous feature of the X-ray
spectra of the AGN up to z=3.5.The broad line component is significant in the
X-ray spectra of the AGN with low luminosity and low z. | SPT 0538-50: Physical conditions in the ISM of a strongly lensed dusty
star-forming galaxy at z=2.8: We present observations of SPT-S J053816-5030.8, a gravitationally-lensed
dusty star forming galaxy (DSFG) at z = 2.7817, first discovered at millimeter
wavelengths by the South Pole Telescope. SPT 0538-50 is typical of the
brightest sources found by wide-field millimeter-wavelength surveys, being
lensed by an intervening galaxy at moderate redshift (in this instance, at z =
0.441). We present a wide array of multi-wavelength spectroscopic and
photometric data on SPT 0538-50, including data from ALMA, Herschel PACS and
SPIRE, Hubble, Spitzer, VLT, ATCA, APEX, and the SMA. We use high resolution
imaging from HST to de-blend SPT 0538-50, separating DSFG emission from that of
the foreground lens. Combined with a source model derived from ALMA imaging
(which suggests a magnification factor of 21 +/- 4), we derive the intrinsic
properties of SPT 0538-50, including the stellar mass, far-IR luminosity, star
formation rate, molecular gas mass, and - using molecular line fluxes - the
excitation conditions within the ISM. The derived physical properties argue
that we are witnessing compact, merger-driven star formation in SPT 0538-50,
similar to local starburst galaxies, and unlike that seen in some other DSFGs
at this epoch. |
Growth rate of cosmological perturbations at z ~ 0.1 from a new
observational test: Spatial variations in the distribution of galaxy luminosities, estimated from
redshifts as distance proxies, are correlated with the peculiar velocity field.
Comparing these variations with the peculiar velocities inferred from galaxy
redshift surveys is a powerful test of gravity and dark energy theories on
cosmological scales. Using ~ 2 $\times$ 10$^{5}$ galaxies from the SDSS Data
Release 7, we perform this test in the framework of gravitational instability
to estimate the normalized growth rate of density perturbations f$\sigma_{8}$ =
0.37 +/- 0.13 at z ~ 0.1, which is in agreement with the $\Lambda$CDM scenario.
This unique measurement is complementary to those obtained with more
traditional methods, including clustering analysis. The estimated accuracy at z
~ 0.1 is competitive with other methods when applied to similar datasets. | Magnified or multiply imaged? - Search strategies for gravitationally
lensed supernovae in wide-field surveys: Strongly lensed supernovae can be detected as multiply imaged or highly
magnified transients. In order to compare the performances of these two
observational strategies, we calculate expected discovery rates as a function
of survey depth in five grizy filters and for different classes of supernovae
(Ia, IIP, IIL, Ibc and IIn). We find that detections via magnification is the
only effective strategy for relatively shallow pre-LSST surveys. For survey
depths about the LSST capacity, both strategies yield comparable numbers of
lensed supernovae. Supernova samples from the two methods are to a large extent
independent and combining them increases detection rates by about 50 per cent.
While the number of lensed supernovae detectable via magnification saturates at
the limiting magnitudes of LSST, detection rates of multiply imaged supernova
still go up drastically at increasing survey depth. Comparing potential
discovery spaces, we find that lensed supernovae found via image multiplicity
exhibit longer time delays and larger image separations making them more
suitable for cosmological constraints than their counterparts found via
magnification.
We find that the ZTF will find about 2 type Ia and 4 core-collapse lensed
supernovae per year at a limiting magnitude of 20.6 in the r band. Applying a
hybrid method which combines searching for highly magnified or multiply imaged
transients, we find that LSST will detect 89 type Ia and 254 core-collapse
lensed supernovae per year. In all cases, lensed core-collapsed supernovae will
be dominated by type IIn supernovae contributing to 80 per cent of the total
counts, although this prediction relies quite strongly on the adopted spectral
templates for this class of supernovae. Revisiting the case of the lensed
supernova iPTF16geu, we find that it is consistent within the 2\sigma contours
of predicted redshifts and magnifications for the iPTF survey. |
Extending and Calibrating the Velocity dependent One-Scale model for
Cosmic Strings with One Thousand Field Theory Simulations: Understanding the evolution and cosmological consequences of topological
defect networks requires a combination of analytic modeling and numerical
simulations. The canonical analytic model for defect network evolution is the
Velocity-dependent One-Scale (VOS) model. For the case of cosmic strings, this
has so far been calibrated using small numbers of Goto-Nambu and field theory
simulations, in the radiation and matter eras, as well as in Minkowski
spacetime. But the model is only as good as the available simulations, and it
should be extended as further simulations become available. In previous work we
presented a General Purpose Graphics Processing Unit implementation of the
evolution of cosmological domain wall networks, and used it to obtain an
improved VOS model for domain walls. Here we continue this effort, exploiting a
more recent analogous code for local Abelian-Higgs string networks. The
significant gains in speed afforded by this code enabled us to carry out 1032
field theory simulations of $512^3$ size, with 43 different expansion rates.
This detailed exploration of the effects of the expansion rate on the network
properties in turn enables a statistical separation of various dynamical
processes affecting the evolution of the network. We thus extend and accurately
calibrate the VOS model for cosmic strings, including separate terms for energy
losses due to loop production and scalar/gauge radiation. By comparing this
newly calibrated VOS model with the analogous one for domain walls we
quantitatively show that energy loss mechanisms are different for the two types
of defects. | Black Holes in our Galactic Halo: Compatibility with FGST and PAMELA
Data and Constraints on the First Stars: 10 to 10^5 solar mass black holes with dark matter spikes that formed in
early minihalos and still exist in our Milky Way Galaxy today are examined in
light of recent data from the Fermi Gamma-Ray Space Telescope (FGST). The dark
matter spikes surrounding black holes in our Galaxy are sites of significant
dark matter annihilation. We examine the signatures of annihilations into
gamma-rays, electrons and positrons, and neutrinos. We find that some
significant fraction of the point sources detected by FGST might be due to dark
matter annihilation near black holes in our Galaxy. We obtain limits on the
properties of dark matter annihilations in the spikes using the information in
the FGST First Source Catalog as well as the diffuse gamma-ray flux measured by
FGST. We determine the maximum fraction of high redshift minihalos that could
have hosted the formation of the first generation of stars and, subsequently,
their black hole remnants. The strength of the limits depends on the choice of
annihilation channel and black hole mass; limits are strongest for the heaviest
black holes and annhilation to $b \bar{b}$ and $W^+W^-$ final states. The
larger black holes considered in this paper may arise as the remnants of Dark
Stars after the dark matter fuel is exhausted and thermonuclear burning runs
its course; thus FGST observations may be used to constrain the properties of
Dark Stars. Additionally, we comment on the excess positron flux found by
PAMELA and its possible interpretation in terms of dark matter annihilation
around these black hole spikes. |
A Revised Broad-Line Region Radius and Black Hole Mass for the
Narrow-Line Seyfert 1 NGC 4051: We present the first results from a high sampling rate, multi-month
reverberation mapping campaign undertaken primarily at MDM Observatory with
supporting observations from telescopes around the world. The primary goal of
this campaign was to obtain either new or improved Hbeta reverberation lag
measurements for several relatively low luminosity AGNs. We feature results for
NGC 4051 here because, until now, this object has been a significant outlier
from AGN scaling relationships, e.g., it was previously a ~2-3sigma outlier on
the relationship between the broad-line region (BLR) radius and the optical
continuum luminosity - the R_BLR-L relationship. Our new measurements of the
lag time between variations in the continuum and Hbeta emission line made from
spectroscopic monitoring of NGC 4051 lead to a measured BLR radius of R_BLR =
1.87 (+0.54 -0.50) light days and black hole mass of M_BH = 1.73 (+0.55 -0.52)
x 10^6 M_sun. This radius is consistent with that expected from the R_BLR-L
relationship, based on the present luminosity of NGC 4051 and the most current
calibration of the relation by Bentz et al. (2009a). We also present a
preliminary look at velocity-resolved Hbeta light curves and time delay
measurements, although we are unable to reconstruct an unambiguous
velocity-resolved reverberation signal. | Pioneer Anomaly in Perturbed FRW Metric: In this manuscript, it is shown that the Pioneer anomaly is the local
evidence for an expanding universe. In other words, its value is a direct
measure of the Hubble constant while its sign shows the expanding behavior of
the dynamics of the universe. This analysis is obtained by studying the radial
geodesic deviation of the light rays in the perturbed
Friedmann-Robertson-Walker metric in the Newtonian gauge. |
HI Lyman-alpha equivalent widths of stellar populations: We have compiled a library of stellar Lyman-alpha equivalent widths in O and
B stars using the model atmosphere codes CMFGEN and TLUSTY, respectively. The
equivalent widths range from about 0 to 30 \AA in absorption for early-O to
mid-B stars. The purpose of this library is the prediction of the underlying
stellar Lyman-alpha absorption in stellar populations of star-forming galaxies
with nebular Lyman-alpha emission. We implemented the grid of individual
equivalent widths into the Starburst99 population synthesis code to generate
synthetic Lyman-alpha equivalent widths for representative star-formation
histories. A starburst observed after 10 Myr will produce a stellar Lyman-alpha
line with an equivalent width of $\sim$ -10$\pm$4 \AA in absorption for a
Salpeter initial mass function. The lower value (deeper absorption) results for
an instantaneous burst, and the higher value (shallower line) for continuous
star formation. Depending on the escape fraction of nebular Lyman-alpha
photons, the effect of stellar Lyman-alpha on the total profile ranges from
negligible to dominant. If the nebular escape fraction is 10%, the stellar
absorption and nebular emission equivalent widths become comparable for
continuous star formation at ages of 10 to 20 Myr. | Enhanced Nitrogen in Morphologically Disturbed Blue Compact Galaxies at
0.20 < z < 0.35: Probing Galaxy Merging Features: We present a study of correlations between the elemental abundances and
galaxy morphologies of 91 blue compact galaxies (BCGs) at z=0.20-0.35 with
Sloan Digital Sky Survey (SDSS) DR7 data. We classify the morphologies of the
galaxies as either 'disturbed' or 'undisturbed', by visual inspection of the
SDSS images, and using the Gini coefficient and M_20. We derive oxygen and
nitrogen abundances using the T_e method. We find that a substantial fraction
of BCGs with disturbed morphologies, indicative of merger remnants, show
relatively high N/O and low O/H abundance ratios. The majority of the disturbed
BCGs exhibit higher N/O values at a given O/H value compared to the
morphologically undisturbed galaxies, implying more efficient nitrogen
enrichment in disturbed BCGs. We detect Wolf-Rayet (WR) features in only a
handful of the disturbed BCGs, which appears to contradict the idea that WR
stars are responsible for high nitrogen abundance. Combining these results with
Galaxy Evolution Explorer (GALEX) GR6 ultraviolet (UV) data, we find that the
majority of the disturbed BCGs show systematically lower values of the H alpha
to near-UV star formation rate ratio. The equivalent width of the H beta
emission line is also systematically lower in the disturbed BCGs. Based on
these results, we infer that disturbed BCGs have undergone star formation over
relatively longer time scales, resulting in a more continuous enrichment of
nitrogen. We suggest that this correlation between morphology and chemical
abundances in BCGs is due to a difference in their recent star formation
histories. |
Two-Field quintessential Higgs Inflation: We study a two-field quintessential Higgs inflation model in which a
quintessence field with an exponential potential $e^{-\beta\phi/M_P}$ is
coupled to the Higgs field from the beginning of inflation. The Higgs field
itself is also non-minimally coupled to gravity. The inflationary predictions
of this model for $n_s$ and $r$ are in good agreement with Planck 2018 data. We
calculate the observables $n_s$ and $r$ against the free parameter $\beta$.
Comparing these parameters with the observed $n_s$ and $r$ in Planck 2018
paper, we find $\beta \lesssim 8\times 10^{-3}$ that strongly disfavors the
Swampland conjecture. | Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars And
Contribution To The Extragalactic Gamma-ray Background: We present a determination of the distributions of photon spectral index and
gamma-ray flux - the so called LogN-LogS relation - for the 352 blazars
detected with a greater than approximately seven sigma detection threshold and
located above +/- 20 degrees Galactic latitude by the Large Area Telescope of
the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux
detection threshold depends on the photon index, the observed raw distributions
do not provide the true LogN-LogS counts or the true distribution of the photon
index. We use the non-parametric methods developed by Efron and Petrosian to
reconstruct the intrinsic distributions from the observed ones which account
for the data truncations introduced by observational bias and includes the
effects of the possible correlation between the two variables. We demonstrate
the robustness of our procedures using a simulated data set of blazars and then
apply these to the real data and find that for the population as a whole the
intrinsic flux distribution can be represented by a broken power law with high
and low indexes of -2.37 +/- 0.13 and -1.70 +/- 0.26, respectively, and the
intrinsic photon index distribution can be represented by a Gaussian with mean
of 2.41 +/- 0.13 and width of 0.25 +/- 0.03. We also find the intrinsic
distributions for the sub-populations of BL Lac and FSRQs type blazars
separately. We then calculate the contribution of Fermi blazars to the diffuse
extragalactic gamma-ray background radiation. Under the assumption that the
flux distribution of blazars continues to arbitrarily low fluxes, we calculate
the best fit contribution of all blazars to the total extragalactic gamma-ray
output to be 60%, with a large uncertainty. |
Multiwavelength investigations of co-evolution of bright custer galaxies: We report a systematic multi-wavelength investigation of environments of the
brightest cluster galaxies (BCGs), using the X-ray data from the Chandra
archive, and optical images taken with 34'x 27' field-of-view Subaru
Suprime-Cam. Our goal is to help understand the relationship between the BCGs
and their host clusters, and between the BCGs and other galaxies, to eventually
address a question of the formation and co-evolution of BCGs and the clusters.
Our results include: 1) Morphological variety of BCGs, or the second or the
third brightest galaxy (BCG2, BCG3), is comparable to that of other bright red
sequence galaxies, suggesting that we have a continuous variation of morphology
between BCGs, BCG2, and BCG3, rather than a sharp separation between the BCG
and the rest of the bright galaxies. 2) The offset of the BCG position relative
to the cluster centre is correlated to the degree of concentration of cluster
X-ray morphology (Spearman rho = -0.79), consistent with an interpretation that
BCGs tend to be off-centered inside dynamically unsettled clusters. 3)
Morphologically disturbed clusters tend to harbour the brighter BCGs, implying
that the "early collapse" may not be the only major mechanism to control the
BCG formation and evolution. | A mid-IR study of Hickson Compact Groups II. Multi-wavelength analysis
of the complete GALEX-Spitzer Sample: We present a comprehensive study on the impact of the environment of compact
galaxy groups on the evolution of their members using a multi-wavelength
analysis, from the UV to the infrared, for a sample of 32 Hickson compact
groups (HCGs) containing 135 galaxies. Fitting the SEDs of all galaxies with
the state-of-the-art model of da Cunha (2008) we can accurately calculate their
mass, SFR, and extinction, as well as estimate their infrared luminosity and
dust content. We compare our findings with samples of field galaxies,
early-stage interacting pairs, and cluster galaxies with similar data. We find
that classifying the groups as dynamically "old" or "young", depending on
whether or not at least one quarter of their members are early-type systems, is
physical and consistent with past classifications of HCGs based on their atomic
gas content. [...ABRIDGED...] We also examine their SF properties, UV-optical
and mid-IR colors, and we conclude that all the evidence point to an
evolutionary scenario in which the effects of the group environment and the
properties of the galaxy members are not instantaneous. Early on, the influence
of close companions to group galaxies is similar to the one of galaxy pairs in
the field. However, as the time progresses, the effects of tidal torques and
minor merging, shape the morphology and star formation history of the group
galaxies, leading to an increase of the fraction of early-type members and a
rapid built up of the stellar mass in the remaining late-type galaxies. |
Constraining the Variation of the Fine Structure Constant with
Observations of Narrow Quasar Absorption Lines: Attempts to measure the variability of the fine structure constant alpha over
cosmological time, using spectra of high redshift quasars have produced
conflicting results. We use the Many Multiplet (MM) method with Mg II and Fe II
lines on very high signal-to-noise, high resolution (R = 72,000) Keck HIRES
spectra of eight narrow quasar absorption systems and consider both systematic
uncertainties in spectrograph wavelength calibration and also velocity offsets
introduced by internal velocity structure. We find no significant change in
alpha, Delta(alpha)/alpha =(0.43 +/- 0.34)x 10^(-5), in the redshift range z =
0.7 - 1.5 (statistical and systematic). Scatter in measurements of
Delta(alpha)/alpha arising from absorption line structure can be considerably
larger than assigned statistical errors even for apparently simple and narrow
absorption systems. We find a null result of Delta(alpha)/alpha = (-0.59 +/-
0.55) x 10^(-5) in a system at z = 1.7382 using Cr II, Zn II and Mn II, whereas
using Cr II and Zn II in a system at z = 1.6614 we find a systematic velocity
trend which, interpreted as a shift in alpha, would imply Delta(alpha)/alpha =
(1.88 +/- 0.47) x 10^(-5) (statistical plus systematic). This latter result is
almost certainly caused by varying ionic abundances in subcomponents of the
line. We conclude that spectroscopic measurements of quasar absorption lines
are not yet capable of unambiguously detecting variation in alpha using the MM
method. | Unknowns and unknown unknowns: from dark sky to dark matter and dark
energy: Answering well-known fundamental questions is usually regarded as the major
goal of science. Discovery of other unknown and fundamental questions is,
however, even more important. Recognition that "we didn't know anything" is the
basic scientific driver for the next generation. Cosmology indeed enjoys such
an exciting epoch. What is the composition of our universe? This is one of the
well-known fundamental questions that philosophers, astronomers and physicists
have tried to answer for centuries. Around the end of the last century,
cosmologists finally recognized that "We didn't know anything". Except for
atoms that comprise slightly less than 5% of the universe, our universe is
apparently dominated by unknown components; 23% is the known unknown (dark
matter), and 72% is the unknown unknown (dark energy). In the course of
answering a known fundamental question, we have discovered an unknown, even
more fundamental, question: "What is dark matter? What is dark energy?" There
are a variety of realistic particle physics models for dark matter, and its
experimental detection may be within reach. On the other hand, it is fair to
say that there is no widely accepted theoretical framework to describe the
nature of dark energy. This is exactly why astronomical observations will play
a key role in unveiling its nature. I will review our current understanding of
the "dark sky", and then present on-going Japanese project, SuMIRe, to discover
even more unexpected questions. |
The core fundamental plane of B2 radio galaxies: The photometric, structural and kinematical properties of the centers of
elliptical galaxies, harbor important information of the formation history of
the galaxies. In the case of non active elliptical galaxies these properties
are linked in a way that surface brightness, break radius and velocity
dispersion of the core lie on a fundamental plane similar to that found for
their global properties. We construct the Core Fundamental Plane (CFP) for a
sizeable sample of low redshift radio galaxies and compare it with that of non
radio ellipticals. To pursue this aim we combine data obtained from high
resolution HST images with medium resolution optical spectroscopy to derive the
photometric and kinematic properties of ~40 low redshift radio galaxies. We
find that the CFPs of radio galaxies is indistinguishable from that defined by
non radio elliptical galaxies of similar luminosity. The characteristics of the
CFP of radio galaxies are also consistent (same slope) with those of the
Fundamental Plane (FP) derived from the global properties of radio (and non
radio) elliptical galaxies. The similarity of CFP and FP for radio and non
radio ellipticals suggests that the active phase of these galaxies has minimal
effects for the structure of the galaxies. | Nonlinear Structure Formation with the Environmentally Dependent Dilaton: We have studied the nonlinear structure formation of the environmentally
dependent dilaton model using $N$-body simulations. We find that the mechanism
of suppressing the scalar fifth force in high-density regions works very well.
Within the parameter space allowed by the solar system tests, the dilaton model
predicts small deviations of the matter power spectrum and the mass function
from their $\Lambda$CDM counterparts. The importance of taking full account of
the nonlinearity of the model is also emphasized. |
Infrared 3-4 Micron Spectroscopy of Nearby PG QSOs and AGN-Nuclear
Starburst Connections in High-luminosity AGN Populations: We present the results of infrared L-band (3-4 micron) slit spectroscopy of
30 PG QSOs at z < 0.17, the representative sample of local high-luminosity,
optically selected AGNs. The 3.3 micron polycyclic aromatic hydrocarbon (PAH)
emission feature is used to probe nuclear (< a few kpc) starburst activity and
to investigate the connections between AGNs and nuclear starbursts in PG QSOs.
The 3.3 micron PAH emission is detected in the individual spectra of 5/30 of
the observed PG QSOs. We construct a composite spectrum of PAH-undetected PG
QSOs and discern the presence of the 3.3 micron PAH emission therein. We
estimate the nuclear-starburst and AGN luminosities from the observed 3.3
micron PAH emission and 3.35 micron continuum luminosities, respectively, and
find that the nuclear-starburst-to-AGN luminosity ratios in PG QSOs are similar
to those of previously studied AGN populations with lower luminosities,
suggesting that AGN-nuclear starburst connections are valid over the wide
luminosity range of AGNs in the local universe. The observed
nuclear-starburst-to-AGN luminosity ratios in PG QSOs with available
supermassive black hole masses are comparable to a theoretical prediction based
on the assumption that the growth of a supermassive black hole is controlled by
starburst-induced turbulence. | The influence of galaxy mergers on the mass dispersion of brightest
cluster galaxies: The absolute magnitude of the brightest galaxy of clusters varies remarkably
little and is nearly independent of all other physical properties of the
cluster as, e.g., its spatial extension or its richness. The question arises
whether the observed small scatter is compatible with the assumption of
dynamical evolution of the cluster. This is investigated with the help of
statistical analysis of the results of cluster simulation. The underlying
interaction process is merging (and also destruction) of smaller galaxies
forming the giant galaxy. The cluster itself is supposed to be in virial
equilibrium.
We find that the evolutionary importance of merger processes grows with
decreasing scale. Rich clusters as well as their brightest members evolve
merely slowly whereas compact groups as well as their brightest members evolve
more rapidly and more violently. We also find that the number of merger
processes leading to the growth of the brightest cluster galaxy (BCG) is small
enough to keep the BCG mass dispersion below the measured value. Our
simulations substantiate that just the combination of the initial distribution
function and the following merging to form the BCG can explain the remarkably
small variance of mean BCG masses between clusters of different size and
different number of galaxies. |
Flows For The Masses: A multi-fluid non-linear perturbation theory for
massive neutrinos: Velocity dispersion of the massive neutrinos presents a daunting challenge
for non-linear cosmological perturbation theory. We consider the neutrino
population as a collection of non-linear fluids, each with uniform initial
momentum, through an extension of the Time Renormalization Group perturbation
theory. Employing recently-developed Fast Fourier Transform techniques, we
accelerate our non-linear perturbation theory by more than two orders of
magnitude, making it quick enough for practical use. After verifying that the
neutrino mode-coupling integrals and power spectra converge, we show that our
perturbation theory agrees with N-body neutrino simulations to within 10% for
neutrino fractions $\Omega_{\nu,0} h^2 \leq 0.005$ up to wave numbers of k = 1
h/Mpc, an accuracy consistent with 2.5% errors in the neutrino mass
determination. Non-linear growth represents a >10% correction to the neutrino
power spectrum even for density fractions as low as $\Omega_{\nu,0} h^2 =
0.001$, demonstrating the limits of linear theory for accurate neutrino power
spectrum predictions. Our code FlowsForTheMasses is avaliable online at
github.com/upadhye/FlowsForTheMasses . | Probing cosmic acceleration by strong gravitational lensing systems: Recently, some divergent conclusions about cosmic acceleration were obtained
using type Ia supernovae (SNe Ia), with opposite assumptions on the intrinsic
luminosity evolution. In this paper, we use strong gravitational lensing
systems to probe the cosmic acceleration. Since the theory of strong
gravitational lensing is established certainly, and the Einstein radius is
determined by stable cosmic geometry. We study two cosmological models,
$\Lambda$CDM and power-law models, through 152 strong gravitational lensing
systems, incorporating with 30 Hubble parameters $H(z)$ and 11 baryon acoustic
oscillation (BAO) measurements. Bayesian evidence are introduced to make a
one-on-one comparison between cosmological models. Basing on Bayes factors $\ln
B$ of flat $\Lambda$CDM versus power-law and $R_{h}=ct$ models are $\ln B>5$,
we find that the flat $\Lambda$CDM is strongly supported by the combination of
the datasets. Namely, an accelerating cosmology with non power-law expansion is
preferred by our numeration. |
Absolute calibration of the polarisation angle for future CMB B-mode
experiments from current and future measurements of the Crab nebula: A tremendous international effort is currently dedicated to observing the
so-called primordial B modes of the Cosmic Microwave Background (CMB)
polarisation. If measured, this faint signal imprinted by the primordial
gravitational wave background, would be an evidence of the inflation epoch and
quantify its energy scale, providing a rigorous test of fundamental physics far
beyond the reach of accelerators. At the unprecedented sensitivity level that
the new generation of CMB experiments aims to reach, every uncontrolled
instrumental systematic effect will potentially result in an analysis bias that
is larger than the much sought-after CMB B-mode signal. The absolute
calibration of the polarisation angle is particularly important in this sense,
as any associated error will end up in a leakage from the much larger E modes
into B modes. The Crab nebula (Tau A), with its bright microwave synchrotron
emission, is one of the few objects in the sky that can be used as absolute
polarisation calibrators. In this communication, we review the best current
constraints on its polarisation angle from 23 to 353 GHz, at typical angular
scales for CMB observations, from WMAP, IRAM XPOL, Planck and NIKA data. We
will show that these polarisation angle measurements are compatible with a
constant angle and we will present a study of the uncertainty on this mean
angle, making different considerations on how to combine the individual
measurement errors. For each of the cases, the potential impact on the CMB
B-mode spectrum will be explored. | Emulation of the Cosmic Dawn 21-cm Power Spectrum and Classification of
Excess Radio Models Using an Artificial Neural Network: The cosmic 21-cm line of hydrogen is expected to be measured in detail by the
next generation of radio telescopes. The enormous dataset from future 21-cm
surveys will revolutionize our understanding of early cosmic times. We present
a machine learning approach based on an Artificial Neural Network that uses
emulation in order to uncover the astrophysics in the epoch of reionization and
cosmic dawn. Using a seven-parameter astrophysical model that covers a very
wide range of possible 21-cm signals, over the redshift range 6 to 30 and
wavenumber range $0.05$ to $1 \ \rm{Mpc}^{-1}$ we emulate the 21-cm power
spectrum with a typical accuracy of $10 - 20\%$. As a realistic example, we
train an emulator using the power spectrum with an optimistic noise model of
the Square Kilometre Array (SKA). Fitting to mock SKA data results in a typical
measurement accuracy of $2.8\%$ in the optical depth to the cosmic microwave
background, $34\%$ in the star-formation efficiency of galactic halos, and a
factor of 9.6 in the X-ray efficiency of galactic halos. Also, with our
modeling we reconstruct the true 21-cm power spectrum from the mock SKA data
with a typical accuracy of $15 - 30\%$. In addition to standard astrophysical
models, we consider two exotic possibilities of strong excess radio backgrounds
at high redshifts. We use a neural network to identify the type of radio
background present in the 21-cm power spectrum, with an accuracy of $87\%$ for
mock SKA data. |
Spectral distortions from the dissipation of tensor perturbations: Spectral distortions of the cosmic microwave background (CMB) may become a
powerful probe of primordial perturbations at small scales. Existing studies of
spectral distortions focus almost exclusively on primordial scalar metric
perturbations. Similarly, vector and tensor perturbations should source CMB
spectral distortions. In this paper, we give general expressions for the
effective heating rate caused by these types of perturbations, including
previously neglected contributions from polarization states and higher
multipoles. We then focus our discussion on the dissipation of tensors, showing
that for nearly scale invariant tensor power spectra, the overall distortion is
some six orders of magnitudes smaller than from the damping of adiabatic scalar
modes. We find simple analytic expressions describing the effective heating
rate from tensors using a quasi-tight coupling approximation. In contrast to
adiabatic modes, tensors cause heating without additional photon diffusion and
thus over a wider range of scales, as recently pointed out by Ota et. al 2014.
Our results are in broad agreement with their conclusions, but we find that
small-scale modes beyond k< 2x10^4 Mpc^{-1} cannot be neglected, leading to a
larger distortion, especially for very blue tensor power spectra. At small
scales, also the effect of neutrino damping on the tensor amplitude needs to be
included. | Cosmic microwave background limits on accreting primordial black holes: Interest in the idea that primordial black holes (PBHs) might comprise some
or all of the dark matter has recently been rekindled following LIGO's first
direct detection of a binary-black-hole merger. Here we revisit the effect of
accreting PBHs on the cosmic microwave background (CMB) frequency spectrum and
angular temperature/polarization power spectra. We compute the accretion rate
and luminosity of PBHs, accounting for their suppression by Compton drag and
Compton cooling by CMB photons. We estimate the gas temperature near the
Schwarzschild radius, and hence the free-free luminosity, accounting for the
cooling resulting from collisional ionization when the background gas is mostly
neutral. We account approximately for the velocities of PBHs with respect to
the background gas. We provide a simple analytic estimate of the efficiency of
energy deposition in the plasma. We find that the spectral distortions
generated by accreting PBHs are too small to be detected by FIRAS, as well as
by future experiments now being considered. We analyze Planck CMB temperature
and polarization data and find, under our most conservative hypotheses, and at
the order-of-magnitude level, that they rule out PBHs with masses >~ 10^2 M_sun
as the dominant component of dark matter. |
Anisotropies in the stochastic gravitational-wave background: Formalism
and the cosmic string case: We develop a powerful analytical formalism for calculating the energy density
of the stochastic gravitational wave background, including a full description
of its anisotropies. This is completely general, and can be applied to any
astrophysical or cosmological source. As an example, we apply these tools to
the case of a network of Nambu-Goto cosmic strings. We find that the angular
spectrum of the anisotropies is relatively insensitive to the choice of model
for the string network, but very sensitive to the value of the string tension
$G\mu$. | Quantifying cosmic variance: We determine an expression for the cosmic variance of any "normal" galaxy
survey based on examination of M* +/- 1 mag galaxies in the SDSS DR7 data cube.
We find that cosmic variance will depend on a number of factors principally:
total survey volume, survey aspect ratio, and whether the area surveyed is
contiguous or comprised of independent sight-lines. As a rule of thumb cosmic
variance falls below 10% once a volume of 10^7h_0.7^-3Mpc^3 is surveyed for a
single contiguous region with a 1:1 aspect ratio. Cosmic variance will be lower
for higher aspect ratios and/or non-contiguous surveys. Extrapolating outside
our test region we infer that cosmic variance in the entire SDSS DR7 main
survey region is ~7% to z < 0.1. The equation obtained from the SDSS DR7 region
can be generalised to estimate the cosmic variance for any density measurement
determined from normal galaxies (e.g., luminosity densities, stellar mass
densities and cosmic star-formation rates) within the volume range 10^3 to 10^7
h^-3_0.7Mpc^3. We apply our equation to show that 2 sightlines are required to
ensure cosmic variance is <10% in any ASKAP galaxy survey (divided into dz ~0.1
intervals, i.e., ~1 Gyr intervals for z <0.5). Likewise 10 MeerKAT sightlines
will be required to meet the same conditions. GAMA, VVDS, and zCOSMOS all
suffer less than 10% cosmic variance (~3%-8%) in dz intervals of 0.1, 0.25, and
0.5 respectively. Finally we show that cosmic variance is potentially at the
50-70% level, or greater, in the HST Ultra Deep Field depending on assumptions
as to the evolution of clustering. 100 or 10 independent sightlines will be
required to reduce cosmic variance to a manageable level (<10%) for HST ACS or
HST WFC3 surveys respectively (in dz ~ 1 intervals). Cosmic variance is
therefore a significant factor in the z>6 HST studies currently underway. |
Partially Cooled Shocks: Detectable Precursors in the Warm/Hot
Intergalactic Medium: I present computations of the integrated column densities produced in the
post-shock cooling layers and in the radiative precursors of partially-cooled
fast shocks as a function of the shock age. The results are applicable to the
shock-heated warm/hot intergalactic medium (WHIM) which is expected to be a
major baryonic reservoir, and contain a large fraction of the so-called
"missing baryons". My computations indicate that readily observable amounts of
intermediate and high ions, such as CIV, NV, and OVI are created in the
precursors of young shocks, for which the shocked gas remains hot and difficult
to observe. I suggest that such precursors may provide a way to identify and
estimate the "missing" baryonic mass associated with the shocks. The
absorption-line signatures predicted here may be used to construct ion-ratio
diagrams, which will serve as diagnostics for the photoionized gas in the
precursors. In my numerical models, the time-evolution of the shock structure,
self-radiation, and associated metal-ion column densities are computed by a
series of quasi-static models, each appropriate for a different shock age. The
shock code used in this work calculates the nonequilibrium ionization and
cooling, follows the radiative transfer of the shock self-radiation through the
post-shock cooling layers, takes into account the resulting photoionization and
heating rates, follows the dynamics of the cooling gas, and self-consistently
computes the photoionization states in the precursor gas. I present a complete
set of the age-dependent post-shock and precursor columns for all ionization
states of the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe, as functions of
the shock velocity, gas metallicity, and magnetic field. I present my numerical
results in convenient online tables. | Testing and selecting cosmological models with ultra-compact radio
quasars: In this paper, we place constraints on four alternative cosmological models
under the assumption of the spatial flatness of the Universe: CPL, EDE, GCG and
MPC. A new compilation of 120 compact radio quasars observed by
very-long-baseline interferometry, which represents a type of new cosmological
standard rulers, are used to test these cosmological models. Our results show
that the fits on CPL obtained from the quasar sample are well consistent with
those obtained from BAO. For other cosmological models considered, quasars
provide constraints in agreement with those derived with other standard probes
at $1\sigma$ confidence level. Moreover, the results obtained from other
statistical methods including Figure of Merit, $Om(z)$ and statefinder
diagnostics indicate that: (1) Radio quasar standard ruler could provide better
statistical constraints than BAO for all cosmological models considered, which
suggests its potential to act as a powerful complementary probe to BAO and
galaxy clusters. (2) Turning to $Om(z)$ diagnostics, CPL, GCG and EDE models
can not be distinguished from each other at the present epoch. (3) In the
framework of statefinder diagnostics, MPC and EDE will deviate from
$\rm{\Lambda}$CDM model in the near future, while GCG model cannot be
distinguished from $\rm{\Lambda}$CDM model unless much higher precision
observations are available. |
IGM Constraints from the SDSS-III/BOSS DR9 Ly-alpha Forest Flux
Probability Distribution Function: The Ly$\alpha$ forest transmission probability distribution function (PDF) is
an established probe of the intergalactic medium (IGM) astrophysics, especially
the temperature-density relationship of the IGM. We measure the transmission
PDF from 3393 Baryon Oscillations Spectroscopic Survey (BOSS) quasars from SDSS
Data Release 9, and compare with mock spectra that include careful modeling of
the noise, continuum, and astrophysical uncertainties. The BOSS transmission
PDFs, measured at $\langle z \rangle = [2.3,2.6,3.0]$, are compared with PDFs
created from mock spectra drawn from a suite of hydrodynamical simulations that
sample the IGM temperature-density relationship, $\gamma$, and temperature at
mean-density, $T_0$, where $T(\Delta) = T_0 \Delta^{\gamma-1}$. We find that a
significant population of partial Lyman-limit systems with a column-density
distribution slope of $\beta_\mathrm{pLLS} \sim -2$ are required to explain the
data at the low-transmission end of transmission PDF, while uncertainties in
the mean Ly$\alpha$ forest transmission affect the high-transmission end. After
modelling the LLSs and marginalizing over mean-transmission uncertainties, we
find that $\gamma=1.6$ best describes the data over our entire redshift range,
although constraints on $T_0$ are affected by systematic uncertainties. Within
our model framework, isothermal or inverted temperature-density relationships
($\gamma \leq 1$) are disfavored at a significance of over 4$\sigma$, although
this could be somewhat weakened by cosmological and astrophysical uncertainties
that we did not model. | Shaken, Not Stirred: The Disrupted Disk of the Starburst Galaxy NGC 253: Near-infrared images obtained with the CFHT WIRCam are used to investigate
the recent history of the nearby Sculptor Group spiral NGC 253. The
distribution of stars in the disk is lop-sided, in the sense that the projected
density of AGB stars in the north east portion of the disk between 10 and 20
kpc from the galaxy center is ~ 0.5 dex higher than on the opposite side of the
galaxy. With the exception of the central 2 kpc, the north east portion of the
disk appears to have been the site of the highest levels of star-forming
activity in the galaxy during the past ~ 0.1 Gyr. Diffuse stellar structures
are found in the periphery of the disk, and the most prominent of these is to
the south and east of the galaxy. Bright AGB stars are detected out to 15 kpc
above the disk plane, and these are part of a diffusely distributed, flattened
extraplanar component. Comparisons between observed and model luminosity
functions suggest that the extraplanar regions contain stars that formed
throughout much of the age of the Universe. It is suggested that the disk of
NGC 253 was disrupted by a tidal encounter with a now defunct companion. The
ages of the youngest extraplanar stars suggests that the event that produced
the extraplanar population, and presumably induced the starburst, occured
within the past ~ 0.2 Gyr. |
Multiple Dark Matter as a self-regulating mechanism for dark sector
interactions: (Abridged) Present cosmological constraints and the absence of a direct
detection and identification of any dark matter particle candidate leave room
to the possibility that the dark sector of the Universe be actually more
complex than it is normally assumed. In particular, more than one new
fundamental particle could be responsible for the observed dark matter density
in the Universe, and possible new interactions between dark energy and dark
matter might characterize the dark sector. In the present work, we investigate
the possibility that two dark matter particles exist in nature, with identical
physical properties except for the sign of their coupling constant to dark
energy. Extending previous works on similar scenarios, we study the evolution
of the background cosmology as well as the growth of linear density
perturbations for a wide range of parameters of such model. Interestingly, our
results show how the simple assumption that dark matter particles carry a
"charge" with respect to their interaction with the dark energy field allows
for new long-range scalar forces of gravitational strength in the dark sector
without conflicting with present observations both at the background and linear
levels. Our scenario does not introduce new parameters with respect to the case
of a single dark matter species for which such strong dark interactions have
been already ruled out. | The effect of pressure-anisotropy-driven kinetic instabilities on
magnetic field amplification in galaxy clusters: The intracluster medium (ICM) is the low-density diffuse magnetized plasma in
galaxy clusters, which reaches virial temperatures of up to 10^8 K. Under these
conditions, the plasma is weakly collisional and therefore has an anisotropic
pressure tensor with respect to the local direction of the magnetic field. This
triggers very fast, Larmor-scale, pressure-anisotropy-driven kinetic
instabilities that alter magnetic field amplification. We study magnetic field
amplification through a turbulent small-scale dynamo, including the effects of
the kinetic instabilities, during the evolution of a typical massive galaxy
cluster. A specific aim of this work is to establish a redshift limit from
which a dynamo has to start to amplify the magnetic field up to equipartition
with the turbulent velocity field at redshift z=0. We implemented 1D radial
profiles for various plasma quantities for merger trees generated with the
Modified GALFORM algorithm. We assume that turbulence is driven by successive
mergers of dark matter halos and construct effective models for the Reynolds
number Re_eff dependence on the magnetic field in three different magnetization
regimes, including the effects of kinetic instabilities. The magnetic field
growth rate is calculated for the different Re_eff models. The model results in
a higher magnetic field growth rate at higher redshift. For all scenarios
considered, to reach equipartition at z=0, the amplification of the magnetic
field has to start at redshift z_start=1.5 and above. The time to reach
equipartition can be significantly shorter, in cases with systematically
smaller turbulent forcing scales, and for the highest Re_eff models. Merger
trees are useful tools for studying the evolution of magnetic fields in weakly
collisional plasmas. They could also be used to constrain the different stages
of the dynamo that could be observed by future radio telescopes. |
The transition from population III to population II-I star formation: We present results from the first cosmological simulations which study the
onset of primordial, metal-free (population III), cosmic star formation and the
transition to the present-day, metal-rich star formation (population II-I),
including molecular (H$_2$, HD, etc.) evolution, tracing the injection of
metals by supernov{\ae} into the surrounding intergalactic medium and following
the change in the initial stellar mass function (IMF) according to the
metallicity of the corresponding stellar population. Our investigation
addresses the role of a wide variety of parameters (critical metallicity for
the transition, IMF slope and range, SN/pair-instability SN metal yields, star
formation threshold, resolution, etc.) on the metal-enrichment history and the
associated transition in the star formation mode. All simulations present
common trends. Metal enrichment is very patchy, with rare, unpolluted regions
surviving at all redshifts, inducing the simultaneous presence of metal-free
and metal-rich star formation regimes. As a result of the rapid pollution
within high-density regions due to the first SN/pair-instability SN, local
metallicity is quickly boosted above the critical metallicity for the
transition. The population III regime lasts for a very short period during the
first stages of star formation ($\sim 10^7\,\rm yr$), and its average
contribution to the total star formation rate density drops rapidly below $\sim
10^{-3}-10^{-2}$. | Building models of the Universe with hydrodynamic simulations: Hydrodynamic simulations have become irreplaceable in modern cosmology for
exploring complex systems and making predictions to steer future observations.
In Chapter 1, we begin with a philosophical discussion on the role of
simulations in science. We argue that simulations can bridge the gap between
empirical and fundamental knowledge. The validation of simulations stresses the
importance of achieving a balance between trustworthiness and scepticism. Next,
Chapter 2 introduces the formation of structures and comparisons between
synthetic and observational data. Chapter 3 describes the production pipeline
of zoom-in simulations used to model individual objects and novel methods to
mitigate known shortcomings. Then, we assessed the weak scaling of the SWIFT
code and found it to be one of the hydrodynamic codes with the highest parallel
efficiency. In Chapter 4, we study the rotational kinetic Sunyaev-Zeldovich
(rkSZ) effect for high-mass galaxy clusters from the MACSIS simulations. We
find a maximum signal greater than 100 $\mu$K, 30 times stronger than early
predictions from self-similar models, opening prospects for future detection.
In Chapter 5, we address a tension between the distribution of entropy measured
from observations and predicted by simulations of groups and clusters of
galaxies. We find that most recent hydrodynamic simulations systematically
over-predict the entropy profiles by up to one order of magnitude, leading to
profiles that are shallower and higher than the power-law-like entropy profiles
that have been observed. We discuss the dependence on different hydrodynamic
and sub-grid parameters using variations of the EAGLE model. Chapter 6 explores
the evolution of the profiles as a function of cosmic time. We report
power-law-like entropy profiles at high redshift for both objects. However, at
late times, an entropy plateau develops and alters the shape of the profile. |
Euclid preparation. TBD. The effect of linear redshift-space distortions
in photometric galaxy clustering and its cross-correlation with cosmic shear: Cosmological surveys planned for the current decade will provide us with
unparalleled observations of the distribution of galaxies on cosmic scales, by
means of which we can probe the underlying large-scale structure (LSS) of the
Universe. This will allow us to test the concordance cosmological model and its
extensions. However, precision pushes us to high levels of accuracy in the
theoretical modelling of the LSS observables, in order not to introduce biases
in the estimation of cosmological parameters. In particular, effects such as
redshift-space distortions (RSD) can become relevant in the computation of
harmonic-space power spectra even for the clustering of the photometrically
selected galaxies, as it has been previously shown in literature studies. In
this work, we investigate the contribution of linear RSD, as formulated in the
Limber approximation by arXiv:1902.07226, in forecast cosmological analyses
with the photometric galaxy sample of the Euclid survey, in order to assess
their impact and quantify the bias on the measurement of cosmological
parameters that neglecting such an effect would cause. We perform this task by
producing mock power spectra for photometric galaxy clustering and weak
lensing, as expected to be obtained from the Euclid survey. We then use a
Markov chain Monte Carlo approach to obtain the posterior distributions of
cosmological parameters from such simulated observations. We find that
neglecting the linear RSD leads to significant biases both when using galaxy
correlations alone and when these are combined with cosmic shear, in the
so-called 3$\times$2pt approach. Such biases can be as large as
$5\,\sigma$-equivalent when assuming an underlying $\Lambda$CDM cosmology. When
extending the cosmological model to include the equation-of-state parameters of
dark energy, we find that the extension parameters can be shifted by more than
$1\,\sigma$. | Radio and Mid-Infrared Properties of Compact Starbursts: Distancing
Themselves from the Main Sequence: We investigate the relationship between 8.44\,GHz brightness temperatures and
1.4 to 8.44\,GHz radio spectral indices with 6.2\,$\mu$m polycyclic aromatic
hydrocarbon (PAH) emission and 9.7\,$\mu$m silicate absorption features for a
sample of 36 local luminous and ultra-luminous infrared galaxies. We find that
galaxies having small 6.2\,$\mu$m PAH equivalent widths (EQWs), which signal
the presence of weak PAH emission and/or an excess of very hot dust, also have
flat spectral indices. The three active galactic nuclei (AGN) identified
through their excessively large 8.44\,GHz brightness temperatures are also
identified as AGN via their small 6.2\,$\mu$m PAH EQWs. We also find that the
flattening of the radio spectrum increases with increasing silicate optical
depth, 8.44\,GHz brightness temperature, and decreasing size of the radio
source even after removing potential AGN, supporting the idea that compact
starbursts show spectral flattening as the result of increased free-free
absorption. These correlations additionally suggest that the dust obscuration
in these galaxies must largely be coming from the vicinity of the compact
starburst itself, and is not distributed throughout the (foreground) disk of
the galaxy. Finally, we investigate the location of these infrared-bright
systems relative to the main sequence (star formation rate vs. stellar mass) of
star-forming galaxies in the local universe. We find that the radio spectral
indices of galaxies flattens with increasing distance above the main sequence,
or in other words, with increasing specific star formation rate. This indicates
that galaxies located above the main sequence, having high specific star
formation rates, are typically compact starbursts hosting deeply embedded star
formation that becomes more optically thick in the radio and infrared with
increased distance above the main sequence. |
Evolution of the equation of state parameters of cosmological tachyonic
field components through mutual interaction: We study the perturbed equation of state (EOS) parameters of the cosmological
tachyonic scalar field components and their mutual time-dependent interaction.
It is shown that the discrete temperature-dependent pattern of the EOS
emerges from an initial continuum along the evolution of the universe. This
leads to two major components in form of dark energy and dark matter, and also
suggests a solution to the cosmological constant problem and the coincidence
problem. | Constraining cosmic reionization with quasar, gamma ray burst, and Lya
emitter observations: We investigate the cosmic reionization history by comparing semi-analytical
models of the Lya forest with observations of high-z quasars and gamma ray
bursts absorption spectra. In order to constrain the reionization epoch z_rei,
we consider two physically motivated scenarios in which reionization ends
either early (ERM, z_rei>= 7) or late (LRM, z_rei~6). We analyze the
transmitted flux in a sample of 17 quasars spectra at 5.7<z<6.4 and in the
spectrum of the gamma ray burst 050904 at z=6.3, studying the wide dark
portions (gaps) in the observed absorption spectra. By comparing the statistics
of these spectral features with our models, we conclude that current
observational data do not require any sudden change in the ionization state of
the IGM at z~6, favouring indeed a highly ionized Universe at these epochs, as
predicted by the ERM. Moreover, we test the predictions of this model through
Lya emitters observations, finding that the ERM provide a good fit to the
evolution of the luminosity function of Lya emitting galaxies in the redshift
range z=5.7-6.5. The overall result points towards an extended reionization
process which starts at z>=11 and completes at z_rei>=7, in agreement with the
recent WMAP5 data. |
Early star-forming galaxies and the reionization of the Universe: Star forming galaxies represent a valuable tracer of cosmic history. Recent
observational progress with Hubble Space Telescope has led to the discovery and
study of the earliest-known galaxies corresponding to a period when the
Universe was only ~800 million years old. Intense ultraviolet radiation from
these early galaxies probably induced a major event in cosmic history: the
reionization of intergalactic hydrogen. New techniques are being developed to
understand the properties of these most distant galaxies and determine their
influence on the evolution of the universe. | Reconstruction of inflationary scenarios in non-conservative unimodular
gravity: Unimodular gravity is an alternative theory of gravity to general relativity.
The gravitational field equations are given by the trace-free version of
Einstein's field equations. Due to the structure of the theory, unimodular
gravity admits a diffusion term that characterizes a possible non-conservation
of the canonical energy-momentum tensor locally. Employing this feature of
unimodular gravity, in the present work, we explicitly show how to construct an
inflationary phase that can be contrasted with current observations. In
particular, we focus on three different inflationary scenarios of physical
interest. An important element in these scenarios is that the accelerated
expansion is driven by the diffusion term exclusively, i.e. there is no
inflaton. Furthermore, the primordial spectrum during inflation is generated by
considering inhomogeneous perturbations associated to standard hydrodynamical
matter (modeled as a single ultra-relativistic fluid). For each of the
scenarios, we obtain the prediction for the primordial spectrum and contrast it
with recent observational bounds. |
The KBC Void: Consistency with Supernovae Type Ia and the Kinematic SZ
Effect in a $Λ$LTB Model: There is substantial and growing observational evidence from the normalized
luminosity density in the near-infrared that the local universe is under-dense
on scales of several hundred Megaparsecs. We test whether our parameterization
of the observational data of such a "void" is compatible with the latest
supernovae type Ia data and with constraints from line-of-sight peculiar
velocity motions of galaxy clusters with respect to the cosmic microwave
background rest frame, known as the linear kinematic Sunyaev-Zel'dovich (kSZ)
effect. Our study is based on the large local void (LLV) radial profile
observed by Keenan, Barger, and Cowie (KBC) and a theoretical void description
based on the Lema\^itre-Tolman-Bondi model with a nonzero cosmological constant
($\Lambda$LTB). We find consistency with the measured luminosity
distance-redshift relation on radial scales relevant to the KBC LLV through a
comparison with 217 low-redshift supernovae type Ia over the redshift range
$0.0233 < z < 0.15$. We assess the implications of the KBC LLV in light of the
tension between "local" and "cosmic" measurements of the Hubble constant,
$H_{0}$. We find that when the existence of the KBC LLV is fully accounted for,
this tension is reduced from $3.4\sigma$ to $2.75\sigma$. We find that previous
linear kSZ constraints, as well as new ones from the South Pole Telescope (SPT)
and the Atacama Cosmology Telescope (ACT), are fully compatible with the
existence of the KBC LLV. | Probing cosmic homogeneity in the Local Universe: We investigate the transition scale to homogeneity, $R_H$, using as cosmic
tracer the spectroscopic sample of blue galaxies from the Sloan Digital Sky
Survey (SDSS). Considering the spatial distribution of the galaxy sample we
compute the two point correlation function $\xi(r)$, the scaled counts in
spheres $\mathcal{N}(<r)$, and the fractal dimension $\mathcal{D}_2(r)$ to
quantify the homogeneity scale in the Local Universe ($0.04 < z < 0.20$). The
sample in analysis is compared with {\it random} and {\it mock} catalogues with
the same geometry, and the same number of synthetic cosmic objects as the
dataset, to calculate the covariance matrix for the errors determination. The
criteria adopted for the transition-to-homogeneity follows the literature, it
is attained when $\mathcal{D}_2(r)$ reaches the $1$ per cent level of the limit
value $3$ (i.e., where it reaches $2.97$) as the scale increases. We obtain
$R_H = 70.33 \pm 10.74$ Mpc$/h$, at the effective redshift
$z_{\text{eff}}=0.128$, for a sample containing $150\,302$ SDSS blue galaxies
with $0.04 < z < 0.20$. Additionally, we perform robustness tests by analysing
the homogeneity scale in sub-volumes of the original one, obtaining coherent
results; we also check for a possible artefact in our procedure examining a
homogeneous synthetic dataset as a pseudo-data, verifying that such systematic
is absent. Because our analyses concentrate in data at low redshifts, $z <
0.20$, we find interesting to use cosmography to calculate the radial comoving
distances; therefore in this subject our analyses do not use fiducial
cosmological model. For completeness, we evaluate the difference of the
comoving distances estimation using cosmography and fiducial cosmology. |
Precious Metals in SDSS Quasar Spectra II: Tracking the Evolution of
Strong, 0.4 < z < 2.3 MgII Absorbers with Thousands of Systems: We have performed an analysis of over 34,000 MgII doublets at 0.36 < z < 2.29
in Sloan Digital Sky Survey (SDSS) Data-Release 7 quasar spectra; the catalog,
advanced data products, and tools for analysis are publicly available. The
catalog was divided into 14 small redshift bins with roughly 2500 doublets in
each, and from Monte-Carlo simulations, we estimate 50% completeness at rest
equivalent width W_r ~ 0.8 Angstrom. The equivalent-width frequency
distribution is described well by an exponential model at all redshifts, and
the distribution becomes flatter with increasing redshift, i.e., there are more
strong systems relative to weak ones. Direct comparison with previous SDSS MgII
surveys reveal that we recover at least 70% of the doublets in these other
catalogs, in addition to detecting thousands of new systems. We discuss how
these surveys come by their different results, which qualitatively agree but,
due to the very small uncertainties, differ by a statistically significant
amount. The estimated physical cross-section of MgII-absorbing galaxy halos
increased three-fold, approximately, from z = 0.4 --> 2.3, while the W_r >= 1
Angstrom absorber line density grew, dN_MgII/dX, by roughly 45%. Finally, we
explore the different evolution of various absorber populations - damped
Lyman-alpha absorbers, Lyman-limit systems, strong CIV absorbers, and strong
and weaker MgII systems - across cosmic time (0 < z < 6). | Cosmology with Planck T-E correlation coefficient: Tensions in cosmological parameters measurement motivate a revisit of the
effects of instrumental systematics. In this article, we focus on the Pearson's
correlation coefficient of the cosmic microwave background temperature and
polarization E modes $\mathcal{R}_\ell^{\rm TE}$ which has the property of not
being biased by multiplicative instrumental systematics. We build a
$\mathcal{R}_\ell^{\rm TE}$-based likelihood for the Planck data, and present
the first constraints on $\Lambda$CDM parameters from the correlation
coefficient. Our results are compatible with parameters derived from a power
spectra based likelihood. In particular the value of the Hubble parameter $H_0$
characterizing the expansion of the Universe today, 67.5 $\pm$ 1.3 km/s/Mpc, is
consistent with the ones inferred from standard CMB analysis. We also discuss
the consistency of the Planck correlation coefficient with the one computed
from the most recent ACTPol power spectra. |
A novel approach to quantifying the sensitivity of current and future
cosmological datasets to the neutrino mass ordering through Bayesian
hierarchical modeling: We present a novel approach to derive constraints on neutrino masses from
cosmological data, while taking into account our ignorance of the neutrino mass
ordering. We derive constraints from a combination of current and future
cosmological datasets on the total neutrino mass $M_\nu$ and on the mass
fractions carried by each of the mass eigenstates, after marginalizing over the
(unknown) neutrino mass ordering, either normal (NH) or inverted (IH). The
bounds take therefore into account the uncertainty related to our ignorance of
the mass hierarchy. This novel approach is carried out in the framework of
Bayesian analysis of a typical hierarchical problem. In this context, the
choice of the neutrino mass ordering is modeled via the discrete hyperparameter
$h_{type}$. The preference for either the NH or the IH scenarios is then
encoded in the posterior distribution of $h_{type}$ itself. Current CMB
measurements assign equal odds to the two hierarchies, and are thus unable to
distinguish between them. However, after the addition of BAO measurements, a
weak preference for NH appears, with odds of 4:3 from Planck temperature and
large-scale polarization in combination with BAO (3:2 if small-scale
polarization is also included). Forecasts suggest that the combination of
upcoming CMB (COrE) and BAO surveys (DESI) may determine the neutrino mass
hierarchy at a high statistical significance if the mass is very close to the
minimal value allowed by oscillations, as for NH and $M_\nu=0.06$ eV there is a
9:1 preference of NH vs IH. On the contrary, if $M_\nu$ is of the order of 0.1
eV or larger, even future cosmological observations will be inconclusive. The
unbiased limit on $M_\nu$ we obtain with this innovative statistical strategy
is crucial for ongoing and planned neutrinoless double beta decay searches. | The SDSS Coadd: 275 deg^2 of Deep SDSS Imaging on Stripe 82: We present details of the construction and characterization of the coaddition
of the Sloan Digital Sky Survey Stripe 82 \ugriz\ imaging data. This survey
consists of 275 deg$^2$ of repeated scanning by the SDSS camera of $2.5\arcdeg$
of $\delta$ over $-50\arcdeg \le \alpha \le 60\arcdeg$ centered on the
Celestial Equator. Each piece of sky has $\sim 20$ runs contributing and thus
reaches $\sim2$ magnitudes fainter than the SDSS single pass data, i.e. to
$r\sim 23.5$ for galaxies. We discuss the image processing of the coaddition,
the modeling of the PSF, the calibration, and the production of standard SDSS
catalogs. The data have $r$-band median seeing of 1.1\arcsec, and are
calibrated to $\le 1%$. Star color-color, number counts, and psf size vs
modelled size plots show the modelling of the PSF is good enough for precision
5-band photometry. Structure in the psf-model vs magnitude plot show minor psf
mis-modelling that leads to a region where stars are being mis-classified as
galaxies, and this is verified using VVDS spectroscopy. As this is a wide area
deep survey there are a variety of uses for the data, including galactic
structure, photometric redshift computation, cluster finding and cross
wavelength measurements, weak lensing cluster mass calibrations, and cosmic
shear measurements. |
Towards Cosmography of the Local Universe: Anisotropies in the distance-redshift relation of cosmological sources are
expected due to large-scale inhomogeneities in the local Universe. When the
observed sources are tracing a large-scale matter flow in a general spacetime
geometry, the distance-redshift relation with its anisotropies can be described
with a geometrical prediction that generalises the well-known
Friedmann-Lema\^itre-Robertson-Walker result. Furthermore, it turns out that a
finite set of multipole coefficients contain the full information about a
finite-order truncation of the distance-redshift relation of a given observer.
The multipoles of the distance-redshift relation are interesting new
cosmological observables that have a direct physical interpretation in terms of
kinematical quantities of the underlying matter flow. Using light cones
extracted from $N$-body simulations we quantify the anisotropies expected in a
$\Lambda$ cold dark matter cosmology by running a Markov chain Monte Carlo
analysis on the observed data. In this observational approach the survey
selection implements an implicit smoothing scale over which the effective rest
frame of matter is fitted. The perceived anisotropy therefore depends
significantly on the redshift range and distribution of sources. We find that
the multipoles of the expansion rate, as well as the observer's velocity with
respect to the large-scale matter flow, can be determined robustly with our
approach. | Probing Dark Matter Clumps, Strings and Domain Walls with Gravitational
Wave Detectors: Gravitational wave astronomy has recently emerged as a new way to study our
Universe. In this work, we survey the potential of gravitational wave
interferometers to detect macroscopic astrophysical objects comprising the dark
matter. Starting from the well-known case of clumps we expand to cosmic strings
and domain walls. We also consider the sensitivity to measure the dark matter
power spectrum on small scales. Our analysis is based on the fact that these
objects, when traversing the vicinity of the detector, will exert a
gravitational pull on each node of the interferometer, in turn leading to a
differential acceleration and corresponding Doppler signal, that can be
measured. As a prototypical example of a gravitational wave interferometer, we
consider signals induced at LISA. We further extrapolate our results to
gravitational wave experiments sensitive in other frequency bands, including
ground-based interferometers, such as LIGO, and pulsar timing arrays, e.g. ones
based on the Square Kilometer Array. Assuming moderate sensitivity improvements
beyond the current designs, clumps, strings and domain walls may be within
reach of these experiments. |
Bayes-X: a Bayesian inference tool for the analysis of X-ray
observations of galaxy clusters: We present the first public release of our Bayesian inference tool, Bayes-X,
for the analysis of X-ray observations of galaxy clusters. We illustrate the
use of Bayes-X by analysing a set of four simulated clusters at z=0.2-0.9 as
they would be observed by a Chandra-like X-ray observatory. In both the
simulations and the analysis pipeline we assume that the dark matter density
follows a spherically-symmetric Navarro, Frenk and White (NFW) profile and that
the gas pressure is described by a generalised NFW (GNFW) profile. We then
perform four sets of analyses. By numerically exploring the joint probability
distribution of the cluster parameters given simulated Chandra-like data, we
show that the model and analysis technique can robustly return the simulated
cluster input quantities, constrain the cluster physical parameters and reveal
the degeneracies among the model parameters and cluster physical parameters. We
then analyse Chandra data on the nearby cluster, A262, and derive the cluster
physical profiles. To illustrate the performance of the Bayesian model
selection, we also carried out analyses assuming an Einasto profile for the
matter density and calculated the Bayes factor. The results of the model
selection analyses for the simulated data favour the NFW model as expected.
However, we find that the Einasto profile is preferred in the analysis of A262.
The Bayes-X software, which is implemented in Fortran 90, is available at
http://www.mrao.cam.ac.uk/facilities/software/bayesx/. | On the filamentary environment of galaxies: The correlation between the large-scale distribution of galaxies and their
spectroscopic properties at z=1.5 is investigated using the Horizon MareNostrum
cosmological run.
We have extracted a large sample of 10^5 galaxies from this large
hydrodynamical simulation featuring standard galaxy formation physics. Spectral
synthesis is applied to these single stellar populations to generate spectra
and colours for all galaxies. We use the skeleton as a tracer of the cosmic web
and study how our galaxy catalogue depends on the distance to the skeleton. We
show that galaxies closer to the skeleton tend to be redder, but that the
effect is mostly due to the proximity of large haloes at the nodes of the
skeleton, rather than the filaments themselves.
This effects translate into a bimodality in the colour distribution of our
sample. The origin of this bimodality is investigated and seems to follow from
the ram pressure stripping of satellite galaxies within the more massive
clusters of the simulation.
The virtual catalogues (spectroscopical properties of the MareNostrum
galaxies at various redshifts) are available online at
http://www.iap.fr/users/pichon/MareNostrum/catalogues |
Revisiting progenitor-age dependence of type Ia supernova luminosity
standardization process: Much of the research in supernova cosmology is based on an assumption that
the peak luminosity of type Ia supernovae (SNe Ia), after a standardization
process, is independent of the galactic environment. A series of recent studies
suggested that there is a significant correlation between the standardized
luminosity and the progenitor age of SNe Ia. The correlation found in the most
recent work by Lee et al. is strong enough to explain the extra dimming of
distant SNe Ia and therefore casts doubts on the direct evidence of cosmic
acceleration. The present work incorporates the uncertainties of progenitor
ages, which were ignored in Lee et al., into a fully Bayesian inference
framework. We find a weaker dependence of supernova standardized luminosity on
the progenitor age, but the detection of correlation remains significant
(3.5$\sigma$). Assuming that such correlation can be extended to high redshift
and applying it to the Pantheon SN Ia data set, we confirm that when the Hubble
residual does not include intrinsic scatter, the age-bias could be the primary
cause of the observed extra dimming of distant SNe Ia. Furthermore, we use the
PAge formalism, which is a good approximation to many dark energy and modified
gravity models, to do a model comparison. We find that if intrinsic scatter is
included in the Hubble residual, the Lambda cold dark matter model remains a
good fit. However, in a scenario without intrinsic scatter, the Lambda cold
dark matter model faces a challenge. | Optimal Weighting in Galaxy Surveys: Application to Redshift-Space
Distortions: Using multiple tracers of large-scale structure allows to evade the
limitations imposed by sampling variance for some parameters of interest in
cosmology. We demonstrate the optimal way of carrying out a multitracer
analysis in a galaxy redshift survey by considering the principal components of
the shot noise matrix from two-point clustering statistics. We show how to
construct two tracers that maximize the benefits of sampling variance and shot
noise cancellation using optimal weights. On the basis of high-resolution
N-body simulations of dark matter halos we apply this technique to the analysis
of redshift-space distortions and demonstrate how constraints on the growth
rate of structure formation can be substantially improved. The primary
limitation are nonlinear effects, which cause significant biases in the method
already at scales of k<0.1h/Mpc, suggesting the need to develop nonlinear
models of redshift-space distortions in order to extract the maximum
information from future redshift surveys. Nonetheless we find gains of a factor
of a few in constraints on the growth rate achievable when merely the linear
regime of a galaxy survey like EUCLID is considered. |
Cosmography of the Local Universe by Multipole Analysis of the Expansion
Rate Fluctuation Field: We explore the possibility of characterizing the expansion rate on local
cosmic scales $(z \lesssim 0.1)$, where the cosmological principle is violated,
in a model-independent manner, i.e. in a more meaningful and comprehensive way
than is possible using the $H_0$ parameter of the Standard Model alone. We do
this by means of the expansion rate fluctuation field $\eta$, an unbiased
Gaussian observable that measures deviations from isotropy in the
redshift-distance relation. We show that an expansion of $\eta$ in terms of
covariant cosmographic parameters, both kinematic (expansion rate
$\mathbb{H}_o$, deceleration $\mathbb{Q}_o$ and jerk $\mathbb{J}_o$) and
geometric (curvature $\mathbb{R}_o$), allows for a consistent description of
metric fluctuations even in a very local and strongly anisotropic universe. The
covariant cosmographic parameters critically depend on the observer's state of
motion. We thus show how the lower order multipoles of ${\eta}_{\ell}$ ($\ell
\leq 4$), measured by a generic observer in an arbitrary state of motion can be
used to disentangle expansion effects that are induced by observer's motion
from those sourced by pure metric fluctuations. We test the formalism using
analytical, axis-symmetric toy models which simulate large-scale linear
fluctuations in the redshift-distance relation in the local Universe and which
are physically motivated by available observational evidences. We show how to
exploit specific features of $\eta$ to detect the limit of validity of a
covariant cosmographic expansion in the local Universe, and to define the
region where data can be meaningfully analyzed in a model-independent way, for
cosmological inference. We also forecast the precision with which future data
sets, such as ZTF, will constrain the structure of the expansion rate
anisotropies in the local spacetime | Annihilation Signatures of Hidden Sector Dark Matter Within
Early-Forming Microhalos: If the dark matter is part of a hidden sector with only very feeble couplings
to the Standard Model, the lightest particle in the hidden sector will
generically be long-lived and could come to dominate the energy density of the
universe prior to the onset of nucleosynthesis. During this early
matter-dominated era, density perturbations will grow more quickly than
otherwise predicted, leading to a large abundance of sub-earth-mass dark matter
microhalos. Since the dark matter does not couple directly to the Standard
Model, the minimum halo mass is much smaller than expected for weakly
interacting dark matter, and the smallest halos could form during the
radiation-dominated era. In this paper, we calculate the evolution of density
perturbations within the context of such hidden sector models and use a series
of $N$-body simulations to determine the outcome of nonlinear collapse during
radiation domination. The resulting microhalos are extremely dense, which leads
to very high rates of dark matter annihilation and to large indirect detection
signals that resemble those ordinarily predicted for decaying dark matter. We
find that the Fermi Collaboration's measurement of the high-latitude gamma-ray
background rules out a wide range of parameter space within this class of
models. The scenarios that are most difficult to constrain are those that
feature a very long early matter-dominated era; if microhalos form prior to the
decay of the unstable hidden sector matter, the destruction of these microhalos
effectively heats the dark matter, suppressing the later formation of
microhalos. |
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. | From Hubble to Snap Parameters: A Gaussian Process Reconstruction: By using recent $H(z)$ and SNe Ia data, we reconstruct the evolution of
kinematic parameters $H(z)$, $q(z)$, jerk and snap, using a model-independent,
non-parametric method, namely, the Gaussian Processes. Throughout the present
analysis, we have allowed for a spatial curvature prior, based on Planck 18 [1]
constraints. In the case of SNe Ia, we modify a python package (GaPP) [2] in
order to obtain the reconstruction of the fourth derivative of a function,
thereby allowing us to obtain the snap from comoving distances. Furthermore,
using a method of importance sampling, we combine $H(z)$ and SNe Ia
reconstructions in order to find joint constraints for the kinematic
parameters. We find for the current values of the parameters: $H_0 =67.2 \pm
6.2$ km/s/Mpc, $q_0 = -0.60^{+0.21}_{-0.18}$, $j_0=0.90^{+0.75}_{-0.65}$,
$s_0=-0.57^{+0.52}_{-0.31}$ at 1$\sigma$ c.l. We find that these
reconstructions are compatible with the predictions from flat $\Lambda$CDM
model, at least for 2$\sigma$ confidence intervals. |
Discovery of large-scale diffuse radio emission and of a new galaxy
cluster in the surroundings of MACSJ0520.7-1328: We report the discovery of large-scale diffuse radio emission South-East of
the galaxy cluster MACS J0520.7-1328, detected through high sensitivity Giant
Metrewave Radio Telescope 323 MHz observations. This emission is dominated by
an elongated diffuse radio source and surrounded by other features of lower
surface brightness. Patches of these faint sources are marginally detected in a
1.4 GHz image obtained through a re-analysis of archival NVSS data.
Interestingly, the elongated radio source coincides with a previously
unclassified extended X-ray source. We perform a multi-wavelength analysis
based on archival infrared, optical and X-ray Chandra data. We find that this
source is a low-temperature (~3.6 keV) cluster of galaxies, with indications of
a disturbed dynamical state, located at a redshift that is consistent with the
one of the main galaxy cluster MACS J0520.7-132 (z=0.336). We suggest that the
diffuse radio emission is associated with the non-thermal components in the
intracluster and intergalactic medium in and around the newly detected cluster.
We are planning deeper multi-wavelength and multi-frequency radio observations
to accurately investigate the dynamical scenario of the two clusters and to
address more precisely the nature of the complex radio emission. | Samples and statistics of CSS and GPS sources: Several samples have been proposed in the last years in order to study the
properties of intrinsically small sources. In this paper, we review the
properties of the main samples that are currently available, both selected on
the basis of spectral index and of morphology. As a result of the work in this
area, large numbers of intrinsically small sources have been found. We
summarize the present status of hot spot advance measurements, listing 18
sources with available VLBI data. The mean hot spot separation velocity is
v_{sep} = (0.19 +/- 0.11)h^{-1}c and the kinematic ages span the range from 20
to 3000 years. Finally, we present a brief outlook on the use of future
instrumentation in order to improve our understanding of radio source
evolution. Prospects for VSOP2, e-VLA, e-MERLIN, LOFAR, ALMA, and Fermi are
suggested. |
Fuzzy Dark Matter and the 21cm Power Spectrum: We model the 21cm power spectrum across the Cosmic Dawn and the Epoch of
Reionization (EoR) in fuzzy dark matter (FDM) cosmologies. The suppression of
small mass halos in FDM models leads to a delay in the onset redshift of these
epochs relative to cold dark matter (CDM) scenarios. This strongly impacts the
21cm power spectrum and its redshift evolution. The 21cm power spectrum at a
given stage of the EoR/Cosmic Dawn process is also modified: in general, the
amplitude of 21cm fluctuations is boosted by the enhanced bias factor of galaxy
hosting halos in FDM. We forecast the prospects for discriminating between CDM
and FDM with upcoming power spectrum measurements from HERA, accounting for
degeneracies between astrophysical parameters and dark matter properties. If
FDM constitutes the entirety of the dark matter and the FDM particle mass is
10-21eV, HERA can determine the mass to within 20 percent at 2-sigma
confidence. | The Effect of the Peculiar Motions of the Lens, Source and the Observer
on the Gravitational Lensing Time Delay: An intervening galaxy acts as a gravitational lens and produces multiple
images of a single source such as a remote galaxy. Galaxies have peculiar
speeds in addition to the bulk motion arising due to the expansion of the
universe. There is a difference in light arrival times between lensed images.
We calculate more realistic time delays between lensed images when galaxy
peculiar motions, that is the motion of the Lens, the Source and the Observer
are taken into consideration neglecting the gravitomagnetic effects. |
Renormalization-Group Running Induced Cosmic Inflation: As a contribution to a viable candidate for a standard model of cosmology, we
here show that pre-inflationary quantum fluctuations can provide a scenario for
the long-sought initial conditions for the inflaton field. Our proposal is
based on the assumption that at very high energies (higher than the energy
scale of inflation) the vacuum-expectation value (VeV) of the field is trapped
in a false vacuum and then, due to renormalization-group (RG) running, the
potential starts to flatten out toward low energy, eventually tending to a
convex one which allows the field to roll down to the true vacuum. We argue
that the proposed mechanism should apply to large classes of inflationary
potentials with multiple concave regions. Our findings favor a particle physics
origin of chaotic, large-field inflationary models as we eliminate the need for
large field fluctuations at the GUT scale. In our analysis, we provide a
specific example of such an inflationary potential, whose parameters can be
tuned to reproduce the existing cosmological data with good accuracy. | Mergers, AGN, and 'Normal' Galaxies: Contributions to the Distribution
of Star Formation Rates and Infrared Luminosity Functions: We use a novel method to predict the contribution of normal star-forming
galaxies, merger-induced bursts, and obscured AGN, to IR luminosity functions
(LFs) and global SFR densities. We use empirical halo occupation constraints to
populate halos with galaxies and determine the distribution of normal and
merging galaxies. Each system can then be associated with high-resolution
hydrodynamic simulations. We predict the distribution of observed luminosities
and SFRs, from different galaxy classes, as a function of redshift from z=0-6.
We provide fitting functions for the predicted LFs, quantify the uncertainties,
and compare with observations. At all redshifts, 'normal' galaxies dominate the
LF at moderate luminosities ~L* (the 'knee'). Merger-induced bursts
increasingly dominate at L>>L*; at the most extreme luminosities, AGN are
important. However, all populations increase in luminosity at higher redshifts,
owing to increasing gas fractions. Thus the 'transition' between normal and
merger-dominated sources increases from the LIRG-ULIRG threshold at z~0 to
bright Hyper-LIRG thresholds at z~2. The transition to dominance by obscured
AGN evolves similarly, at factor of several higher L_IR. At all redshifts,
non-merging systems dominate the total luminosity/SFR density, with
merger-induced bursts constituting ~5-10% and AGN ~1-5%. Bursts contribute
little to scatter in the SFR-stellar mass relation. In fact, many systems
identified as 'ongoing' mergers will be forming stars in their 'normal'
(non-burst) mode. Counting this as 'merger-induced' star formation leads to a
stronger apparent redshift evolution in the contribution of mergers to the SFR
density. |
Dark energy and matter interacting scenario can relieve $H_0$ and $S_8$
tensions: We consider a new cosmological model (named $\tilde\Lambda$CDM) in which the
vacuum energy interacts with matter and radiation, and test this model using
the current cosmological observations. Using the CMB+BAO+SN (CBS) data set to
constrain the model, we find that the $H_0$ and $S_8$ tensions are relieved to
$2.87\sigma$ and $2.77\sigma$, respectively. However, in this case, the
$\tilde\Lambda$CDM model is not favored by the data, compared with
$\Lambda$CDM. We find that when the $H_0$ and $S_8$ data are added into the
data combination, the situation is significantly improved. In the CBS+$H_0$
case, we find that the model relieves the $H_0$ tension to $0.47\sigma$, and in
this case, the model is favored over $\Lambda$CDM. In the CBS+$H_0$+$S_8$ case,
we get a synthetically best situation in which the $H_0$ and $S_8$ tensions are
relieved to $0.72\sigma$ and $2.11\sigma$, respectively. In this case, the
model is most favored by the data. Therefore, such a cosmological model can
greatly relieve the $H_0$ tension, and at the same time, it can also
effectively alleviate the $S_8$ tension. | The virialization density of peaks with general density profiles under
spherical collapse: We calculate the non-linear virialization density, $\Delta_c$, of halos under
spherical collapse from peaks with an arbitrary initial and final density
profile. This is in contrast to the standard calculation of $\Delta_c$ which
assumes top-hat profiles. Given our formalism, the non-linear halo density can
be calculated once the shape of the initial peak's density profile and the
shape of the virialized halo's profile are provided. We solve for $\Delta_c$
for halos in an Einstein de-Sitter and $\Lambda$CDM universe. As examples, we
consider power-law initial profiles as well as spherically averaged peak
profiles calculated from the statistics of a Gaussian random field.
We find that, depending on the profiles used, $\Delta_c$ is smaller by a
factor of a few to as much as a factor of 10 as compared to the density given
by the standard calculation ($\approx 200$). Using our results, we show that,
for halo finding algorithms that identify halos through an over-density
threshold, the halo mass function measured from cosmological simulations can be
enhanced at all halo masses by a factor of a few. This difference could be
important when using numerical simulations to assess the validity of analytic
models of the halo mass function. |
The H alpha Galaxy Survey. VIII. Close companions and interactions, and
the definition of starbursts: (Shortened) We consider the massive star formation properties, radial
profiles, and atomic gas masses of those galaxies in our H alpha Galaxy Survey,
a representative sample of the local Universe of 327 disk galaxies, that have
close companion galaxies, in comparison with a matched control sample of
galaxies without companions. We find that the presence of a close companion
raises the star formation rate by a factor of just under two, while increasing
hardly at all the equivalent width of the H alpha emission. This means that
although statistically galaxies with close companions form stars at a higher
rate, they do this over extended periods of time, and not as bursts. We find no
significant increase in the central concentration of the star formation as a
result of the presence of a close companion. The fraction of truly interacting
or merging galaxies is very small in the local Universe, at around 2%, and
possibly 4% of bright galaxies. Most of these interacting galaxies currently
have unremarkable star formation properties. We also study the properties of
the Survey galaxies with the most extreme values for star formation indicators
such as rate, equivalent width, star formation rate per area, and gas depletion
timescale. We find that each of these indicators favors a different subset of
galaxies, and use this information to discuss critically the possible
definitions of the term starburst to describe galaxies with enhanced star
formation activity. We conclude that no one starburst definition can be devised
which is objective and generally discriminant. Unless one restricts the use of
the term "starburst" to a very small number of galaxies, the term will continue
to be used for a heterogeneous and wide-ranging collection of objects with no
physical basis for their classification as starburst. | Three-dimensional Keplerian orbit-superposition models of the nucleus of
M31: We present three-dimensional eccentric disc models of the nucleus of M31,
modelling the disc as a linear combination of thick rings of massless stars
orbiting in the potential of a central black hole. Our models are nonparametric
generalisations of the parametric models of Peiris & Tremaine. The models
reproduce well the observed WFPC2 photometry, the detailed line-of-sight
velocity distributions from STIS observations along P1 and P2, together with
the qualitative features of the OASIS kinematic maps. We confirm Peiris &
Tremaine's finding that nuclear discs aligned with the larger disc of M31 are
strongly ruled out. Our optimal model is inclined at 57 degrees with respect to
the line of sight of M31 and has a position angle of 55 degrees. It has a
central black hole of mass 10^8 solar masses, and, when viewed in three
dimensions, shows a clear enhancement in the density of stars around the black
hole. The distribution of orbit eccentricities in our models is similar to
Peiris & Tremaine's model, but we find significantly different inclination
distributions, which might provide valuable clues to the origin of the disc. |
Polarimetric imaging with the GMRT: We present the first set of polarimetric images made with the GMRT. These
were obtained as part of the program to commission the polarization mode at the
telescope. We find that the instrumental polarization leakage at the GMRT
varies with frequency. It is hence necessary to solve for the leakage as a
function of spectral channel. Once this is done however, it is possible to
calibrate these terms to better than 1% accuracy, making it feasible to study
sources that are polarized at the few percent level. We present 610 MHz
polarization images of two extended FR-II radio galaxies, viz. 3C 79 and 3C
265. These were selected from the sample of sources for which the total
polarization fraction at 610 MHz is known from the survey of Conway & Strom
(1984). We present high resolution polarization images of these two sources and
also find that the polarization fractions of the two sources as seen at the
GMRT are consistent with those reported by Conway & Strom (1984). | The Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS): The Role
of Environment and Self-Regulation in Galaxy Evolution at z ~ 1: We evaluate the effects of environment and stellar mass on galaxy properties
at 0.85 < z < 1.20 using a 3.6um-selected spectroscopic sample of 797 cluster
and field galaxies drawn from the GCLASS survey. We confirm that for galaxies
with LogM* > 9.3 the well-known correlations between environment and properties
such as star-forming fraction (f_SF), SFR, SSFR, D(4000), and color are already
in place at z ~ 1. We separate the effects of environment and stellar mass on
galaxies by comparing the properties of star-forming and quiescent galaxies at
fixed environment, and fixed stellar mass. The SSFR of star-forming galaxies at
fixed environment is correlated with stellar mass; however, at fixed stellar
mass it is independent of environment. The same trend exists for the D(4000)
measures of both the star-forming and quiescent galaxies and shows that their
properties are determined primarily by their stellar mass, not by their
environment. Instead, it appears that environment's primary role is to control
the fraction of star-forming galaxies. Using the spectra we identify candidate
poststarburst galaxies and find that those with 9.3 < LogM* < 10.7 are 3.1 +/-
1.1 times more common in high-density regions compared to low-density regions.
The clear association of poststarbursts with high-density regions as well as
the lack of a correlation between the SSFRs and D(4000)s of star-forming
galaxies with their environment suggests that at z ~ 1 the
environmental-quenching timescale must be rapid. Lastly, we construct a simple
quenching model which demonstrates that the lack of a correlation between the
D(4000) of quiescent galaxies and their environment results naturally if self
quenching dominates over environmental quenching at z > 1, or if the evolution
of the self-quenching rate mirrors the evolution of the environmental-quenching
rate at z > 1, regardless of which dominates. |
Studying Inflation with Future Space-Based Gravitational Wave Detectors: Motivated by recent progress in our understanding of the $B$-mode
polarization of cosmic microwave background (CMB), which provides important
information about the inflationary gravitational waves (IGWs), we study the
possibility to acquire information about the early universe using future
space-based gravitational wave (GW) detectors. We perform a detailed
statistical analysis to estimate how well we can determine the reheating
temperature after inflation as well as the amplitude, the tensor spectral
index, and the running of the inflationary gravitational waves. We discuss how
the accuracies depend on noise parameters of the detector and the minimum
frequency available in the analysis. Implication of such a study on the test of
inflation models is also discussed. | Radio Planetary Nebulae in the Magellanic Clouds: We report the extragalactic radio-continuum detection of 15 planetary nebulae
(PNe) in the Magellanic Clouds (MCs) from recent Australia Telescope Compact
Array+Parkes mosaic surveys. These detections were supplemented by new and high
resolution radio, optical and IR observations which helped to resolve the true
nature of the objects. Four of the PNe are located in the Small Magellanic
Cloud (SMC) and 11 are located in the Large Magellanic Cloud (LMC). Based on
Galactic PNe the expected radio flux densities at the distance of the LMC/SMC
are up to ~2.5 mJy and ~2.0 mJy at 1.4 GHz, respectively. We find that one of
our new radio PNe in the SMC has a flux density of 5.1 mJy at 1.4 GHz, several
times higher than expected. We suggest that the most luminous radio PN in the
SMC (N S68) may represent the upper limit to radio peak luminosity because it
is ~3 times more luminous than NGC 7027, the most luminous known Galactic PN.
We note that the optical diameters of these 15 MCs PNe vary from very small
(~0.08 pc or 0.32"; SMP L47) to very large (~1 pc or 4"; SMP L83). Their flux
densities peak at different frequencies, suggesting that they may be in
different stages of evolution. We briefly discuss mechanisms that may explain
their unusually high radio-continuum flux densities. We argue that these
detections may help solve the "missing mass problem" in PNe whose central stars
were originally 1-8 Msun. We explore the possible link between ionised halos
ejected by the central stars in their late evolution and extended radio
emission. Because of their higher than expected flux densities we tentatively
call this PNe (sub)sample - "Super PNe". |
Death and Serious Injury by Dark Matter: Macroscopic dark matter refers to a variety of dark matter candidates that
would be expected to (elastically) scatter off of ordinary matter with a large
geometric cross-section. A wide range of macro masses $M_X$ and cross-sections
$\sigma_X$ remain unprobed. We show that over a wide region within the
unexplored parameter space, collisions of a macro with a human body would
result in serious injury or death. We use the absence of such unexplained
impacts with a well-monitored subset of the human population to exclude a
region bounded by $\sigma_X \geq 10^{-8} - 10^{-7}$ cm$^2$ and $M_X < 50$ kg.
Our results open a new window on dark matter: the human body as a dark matter
detector. | The Contribution from Scattered Light to Quasar Galaxy Hosts: We present models representing the scattering of quasar radiation off free
electrons and dust grains in geometries that approximate the structure of
quasar host galaxies. We show that, for reasonable assumptions, scattering
alone can easily produce ratios of nuclear (point source) to extended fluxes
comparable to those determined in studies of quasar hosts. This result suggests
that scattered quasar light, as well as stellar emission from the host galaxy,
contributes significantly to the detected extended flux, leading to uncertainty
in the inferred properties of quasar host. A significant contribution from
scattered quasar light will lead to overestimates of the luminosity and hence
mass of the host galaxy, and may also distort its morphology. Scattering of
quasar light within the host galaxy may provide alternative explanations for
the apparent peak in host luminosity at z = 2-3; possibly the overall average
higher luminosity of radio-loud host galaxies relative to those of radio-quiet
quasars (RQQs), and the apparent preference of high-luminosity RQQs for
spheroidal rather than disk galaxies. |
Extragalactic millimeter-wave sources in South Pole Telescope survey
data: source counts, catalog, and statistics for an 87 square-degree field: We report the results of an 87 square-degree point-source survey centered at
R.A. 5h30m, decl. -55 deg. taken with the South Pole Telescope (SPT) at 1.4 and
2.0 mm wavelengths with arc-minute resolution and milli-Jansky depth. Based on
the ratio of flux in the two bands, we separate the detected sources into two
populations, one consistent with synchrotron emission from active galactic
nuclei (AGN) and one consistent with thermal emission from dust. We present
source counts for each population from 11 to 640 mJy at 1.4 mm and from 4.4 to
800 mJy at 2.0 mm. The 2.0 mm counts are dominated by synchrotron-dominated
sources across our reported flux range; the 1.4 mm counts are dominated by
synchroton-dominated sources above ~15 mJy and by dust-dominated sources below
that flux level. We detect 141 synchrotron-dominated sources and 47
dust-dominated sources at S/N > 4.5 in at least one band. All of the most
significantly detected members of the synchrotron-dominated population are
associated with sources in previously published radio catalogs. Some of the
dust-dominated sources are associated with nearby (z << 1) galaxies whose dust
emission is also detected by the Infrared Astronomy Satellite (IRAS). However,
most of the bright, dust-dominated sources have no counterparts in any existing
catalogs. We argue that these sources represent the rarest and brightest
members of the population commonly referred to as sub-millimeter galaxies
(SMGs). Because these sources are selected at longer wavelengths than in
typical SMG surveys, they are expected to have a higher mean redshift
distribution and may provide a new window on galaxy formation in the early
universe. | Revealing the galaxy-halo connection in IllustrisTNG: We use the IllustrisTNG (TNG) simulations to explore the galaxy-halo
connection as inferred from state-of-the-art cosmological,
magnetohydrodynamical simulations. With the high mass resolution and large
volume achieved by combining the 100 Mpc (TNG100) and 300 Mpc (TNG300) volumes,
we establish the mean occupancy of central and satellite galaxies and their
dependence on the properties of the dark matter haloes hosting them. We derive
best-fitting HOD parameters from TNG100 and TNG300 for target galaxy number
densities of $\bar{n}_g = 0.032\,h^3$Mpc$^{-3}$ and $\bar{n}_g =
0.016\,h^3$Mpc$^{-3}$, respectively, corresponding to a minimum galaxy stellar
mass of $M_\star\sim1.9\times10^9\,{\rm M}_\odot$ and
$M_\star\sim3.5\times10^9\,{\rm M}_\odot$, respectively, in hosts more massive
than $10^{11}\,{\rm M}_\odot$. Consistent with previous work, we find that
haloes located in dense environments, with low concentrations, later formation
times, and high angular momenta are richest in their satellite population. At
low mass, highly-concentrated haloes and those located in overdense regions are
more likely to contain a central galaxy. The degree of environmental dependence
is sensitive to the definition adopted for the physical boundary of the host
halo. We examine the extent to which correlations between galaxy occupancy and
halo properties are independent and demonstrate that HODs predicted by halo
mass and present-day concentration capture the qualitative dependence on the
remaining halo properties. At fixed halo mass, concentration is a strong
predictor of the stellar mass of the central galaxy, which may play a defining
role in the fate of the satellite population. The radial distribution of
satellite galaxies, which exhibits a universal form across a wide range of host
halo mass, is described accurately by the best-fit NFW density profile of their
host haloes. |
Self-Similar Dynamical Relaxation of Dark Matter Halos in an Expanding
Universe: We investigate the structure of cold dark matter halos using advanced models
of spherical collapse and accretion in an expanding Universe. These base on
solving time-dependent equations for the moments of the phase-space
distribution function in the fluid approximation; our approach includes
non-radial random motions, and most importantly, an advanced treatment of both
dynamical relaxation effects that takes place in the infalling matter:
phase-mixing associated to shell crossing, and collective collisions related to
physical clumpiness. We find self-similar solutions for the
spherically-averaged profiles of mass density rho(r), pseudo phase-space
density Q(r) and anisotropy parameter beta(r). These profiles agree with the
outcomes of state-of-the-art N-body simulations in the radial range currently
probed by the latter; at smaller radii, we provide specific predictions. In the
perspective provided by our self-similar solutions we link the halo structure
to its two-stage growth history, and propose the following picture. During the
early fast collapse of the inner region dominated by a few merging clumps,
efficient dynamical relaxation plays a key role in producing a closely
universal mass density and pseudo phase-space density profiles; in particular,
these are found to depend only weakly on the detailed shape of the initial
perturbation and the related collapse times. The subsequent inside-out growth
of the outer regions feeds on the slow accretion of many small clumps and
diffuse matter; thus the outskirts are only mildly affected by dynamical
relaxation but are more sensitive to asymmetries and cosmological variance. | KiDS-1000 catalogue: Weak gravitational lensing shear measurements: We present weak lensing shear catalogues from the fourth data release of the
Kilo-Degree Survey, KiDS-1000, spanning 1006 square degrees of deep and
high-resolution imaging. Our `gold-sample' of galaxies, with well-calibrated
photometric redshift distributions, consists of 21 million galaxies with an
effective number density of $6.17$ galaxies per square arcminute. We quantify
the accuracy of the spatial, temporal, and flux-dependent point-spread function
(PSF) model, verifying that the model meets our requirements to induce less
than a $0.1\sigma$ change in the inferred cosmic shear constraints on the
clustering cosmological parameter $S_8 = \sigma_8\sqrt{\Omega_{\rm m}/0.3}$.
Through a series of two-point null-tests, we validate the shear estimates,
finding no evidence for significant non-lensing B-mode distortions in the data.
The PSF residuals are detected in the highest-redshift bins, originating from
object selection and/or weight bias. The amplitude is, however, shown to be
sufficiently low and within our stringent requirements. With a shear-ratio
null-test, we verify the expected redshift scaling of the galaxy-galaxy lensing
signal around luminous red galaxies. We conclude that the joint KiDS-1000 shear
and photometric redshift calibration is sufficiently robust for combined-probe
gravitational lensing and spectroscopic clustering analyses. |
Consistent and simultaneous modelling of galaxy clustering and
galaxy-galaxy lensing with Subhalo Abundance Matching: The spatial distribution of galaxies and their gravitational lensing signal
offer complementary tests of galaxy formation physics and cosmology. However,
their synergy can only be fully exploited if both probes are modelled
accurately and consistently. In this paper, we demonstrate that this can be
achieved using an extension of Subhalo Abundance Matching, dubbed SHAMe.
Specifically, we use mock catalogues built from the TNG300 hydrodynamical
simulation to show that SHAMe can simultaneously model the multipoles of the
redshift-space galaxy correlation function and galaxy-galaxy lensing, without
noticeable bias within the statistical sampling uncertainties of a SDSS volume
and on scales r = [0.6-30] Mpc/h. Modelling the baryonic processes in
galaxy-galaxy lensing with a baryonification scheme allows SHAMe's range of
validity to be extended to r = [0.1-30] Mpc/h. Remarkably, our model achieves
this level of precision with just five free parameters beyond those describing
the baryonification model. At fixed cosmology, we find that galaxy-galaxy
lensing provides a general consistency test but little additional information
on galaxy modelling parameters beyond that encoded in the redshift-space
multipoles. It does, however, improve constraints if only the projected
correlation function is available, as in surveys with only photometric
redshifts. We expect SHAMe to have a higher fidelity across a wider range of
scales than more traditional methods such as Halo Occupation Distribution
modelling. Thus it should provide a significantly more powerful and more robust
tool for analysing next-generation large-scale surveys. | CosmicNet I: Physics-driven implementation of neural networks within
Boltzmann-Einstein solvers: Einstein-Boltzmann Solvers (EBSs) are run on a massive scale by the cosmology
community when fitting cosmological models to data. We present a new concept
for speeding up such codes with neural networks. The originality of our
approach stems from not substituting the whole EBS by a machine learning
algorithm, but only its most problematic and least parallelizable step: the
integration of perturbation equations over time. This approach offers two
significant advantages: the task depends only on a subset of cosmological
parameters, and it is blind to the characteristics of the experiment for which
the output must be computed (for instance, redshift bins). These allow us to
construct a fast and highly re-usable network. In this proof-of-concept paper,
we focus on the prediction of CMB source functions, and design our networks
according to physical considerations and analytical approximations. This allows
us to reduce the depth and training time of the networks compared to a
brute-force approach. Indeed, the calculation of the source functions using the
networks is fast enough so that it is not a bottleneck in the EBS anymore.
Finally, we show that their accuracy is more than sufficient for accurate MCMC
parameter inference from Planck data. This paves the way for a new project,
CosmicNet, aimed at gradually extending the use and the range of validity of
neural networks within EBSs, and saving massive computational time in the
context of cosmological parameter extraction. |
A tale of dark matter capture, sub-dominant WIMPs, and neutrino
observatories: Weakly Interacting Massive Particles (WIMPs), which are among the best
motivated dark matter (DM) candidates, could make up all or only a fraction of
the total DM budget. We consider a scenario in which WIMPs are a sub-dominant
DM component; such a scenario would affect both current direct and indirect
bounds on the WIMP-nucleon scattering cross section. In this paper we focus on
indirect searches for the neutrino flux produced by annihilation of
sub-dominant WIMPs captured by the Sun or the Earth via either spin-dependent
or spin-independent scattering. We derive the annihilation rate and the
expected neutrino flux at neutrino observatories. In our computation, we
include an updated chemical composition of the Earth with respect to the
previous literature, leading to an increase of the Earth's capture rate for
spin-dependent scattering by a factor three. Results are compared with current
bounds from Super-Kamiokande and IceCube. We discuss the scaling of bounds from
both direct and indirect detection methods with the WIMP abundance. | Long-term variability of extragalactic radio sources in the Planck Early
Release Compact Source Catalogue: Combining measurements taken using the Wilkinson Microwave Anisotropy Probe
(WMAP) from 2001 to 2008 with measurements taken using Planck from 2009 to
2010, we investigate the long-term flux density variability of extragalactic
radio sources selected from the Planck Early Release Compact Source Catalogue.
The single-year, single-frequency WMAP maps are used to estimate
yearly-averaged flux densities of the sources in the four WMAP bands: Ka (33
GHz), Q (41 GHz), V (61 GHz), and W (94 GHz). We identify 82, 67, 32, and 15
sources respectively as variable at greater than 99% confidence level in these
four bands. The amplitudes of variation are comparable between bands, and are
not correlated with either the flux densities or the spectral indices of the
sources. The number counts of WMAP Ka-band sources are stable from year to year
despite the fluctuation caused by individual source variability. Most of our
sources show strong correlation in variability between bands. Almost all the
sources that show variability are blazars. We have attempted to fit two simple,
four-parameter models to the time-series of 32 sources showing correlated
variability at multiple frequencies - a long-term flaring model and a
rotating-jet model. We find that 19 sources (60%) can be fit with the simple
rotating-jet model, and ten of these also fit the simple long-term flaring
model. The remaining 13 sources (40%) show more complex variability behaviour
that is not consistent with either model. Extended radio galaxies in our sample
show no sign of variability, as expected, with the exception of Pictor A for
which we report evidence for a millimetre flare lasting between 2002 and 2010. |
Platonic topology and CMB fluctuations: Homotopy, anisotropy, and
multipole selection rules: The Cosmic Microwave Background CMB originates from an early stage in the
history of the universe. Observed low multipole contributions of CMB
fluctuations have motivated the search for selection rules from the underlying
topology of 3-space. Everitt (2004) has generated all homotopies for Platonic
spherical 3-manifolds by face gluings. We transform the glue generators into
isomorphic deck transformations. The deck transformations act on a spherical
Platonic 3-manifold as prototile and tile the 3-sphere by its images. A
complete set of orthonormal functions on the 3-sphere is spanned by the Wigner
harmonic polynomials. For a tetrahedral, two cubic and three octahedral
manifolds we construct algebraically linear combinations of Wigner polynomials,
invariant under deck transformations and with domain the manifold. We prove
boundary conditions on polyhedral faces from homotopy. By algebraic means we
pass to a multipole expansion. Assuming random models of the CMB radiation, we
derive multipole selection rules, depending on the point symmetry of the
manifold. | The stellar mass structure of massive galaxies from z=0 to z=2.5;
surface density profiles and half-mass radii: We present stellar mass surface density profiles of a mass-selected sample of
177 galaxies at 0.5 < z < 2.5, obtained using very deep HST optical and
near-infrared data over the GOODS-South field, including recent CANDELS data.
Accurate stellar mass surface density profiles have been measured for the first
time for a complete sample of high-redshift galaxies more massive than 10^10.7
M_sun. The key advantage of this study compared to previous work is that the
surface brightness profiles are deconvolved for PSF smoothing, allowing
accurate measurements of the structure of the galaxies. The surface brightness
profiles account for contributions from complex galaxy structures such as rings
and faint outer disks. Mass profiles are derived using radial rest-frame u-g
color profiles and a well-established empirical relation between these colors
and the stellar mass-to-light ratio. We derive stellar half-mass radii from the
mass profiles, and find that these are on average ~25% smaller than rest-frame
g band half-light radii. This average size difference of 25% is the same at all
redshifts, and does not correlate with stellar mass, specific star formation
rate, effective surface density, Sersic index, or galaxy size. Although on
average the difference between half-mass size and half-light size is modest,
for approximately 10% of massive galaxies this difference is more than a factor
two. These extreme galaxies are mostly extended, disk-like systems with large
central bulges. These results are robust, but could be impacted if the central
dust extinction becomes high. ALMA observations can be used to explore this
possibility. These results provide added support for galaxy growth scenarios
wherein massive galaxies at these epochs grow by accretion onto their outer
regions. |
ScamPy -- A sub-halo clustering & abundance matching based Python
interface for painting galaxies on the dark matter halo/sub-halo hierarchy: We present a computational framework for "painting" galaxies on top of the
Dark Matter Halo/Sub-Halo hierarchy obtained from N-body simulations. The
method we use is based on the sub-halo clustering and abundance matching (SCAM)
scheme which requires observations of the 1- and 2-point statistics of the
target (observed) population we want to reproduce. This method is particularly
tailored for high redshift studies and thereby relies on the observed
high-redshift galaxy luminosity functions and correlation properties. The core
functionalities are written in c++ and exploit Object Oriented Programming,
with a wide use of polymorphism, to achieve flexibility and high computational
efficiency. In order to have an easily accessible interface, all the libraries
are wrapped in python and provided with an extensive documentation. We validate
our results and provide a simple and quantitative application to reionization,
with an investigation of physical quantities related to the galaxy population,
ionization fraction and bubble size distribution. | Hyperluminous infrared galaxies from IIFSCz: We present a catalogue of 179 hyperluminous infrared galaxies (HLIRGs) from
the Imperial IRAS-FSS Redshift (IIFSCz) Catalogue. Of the 92 with detections in
at least two far infrared bands, 62 are dominated by an M82-like starburst, 22
by an Arp220-like starburst and 8 by an AGN dust torus. On the basis of
previous gravitational lensing studies and an examination of HST archive images
for a further 5 objects, we estimate the fraction of HLIRGs that are
significantly lensed to be 10-30%. We show simple infrared template fits to the
SEDs of 23 HLIRGs with spectroscopic redshifts and at least 5 photometric
bands. Most can be fitted with a combination of two simple templates: an AGN
dust torus and an M82-like starburst. In the optical, 17 of the objects are
fitted with QSO templates, 6 are fitted with galaxy templates. 20 of the 23
objects (87%) show evidence of an AGN either from the optical continuum or from
the signature of an AGN dust torus, but the starburst component is the dominant
contribution to bolometric luminosity in 14 out of 23 objects (61%). The
implied star-formation rates, even after correcting for lensing magnification,
are in excess of 1000 Mo /yr. We use infrared template-fitting models to
predict fluxes for all HLIRGs at submillimetre wavelengths, and show
predictions at 350 and 850 mu. Most would have 850 mu fluxes brighter than 5
mJy so should be easily detectable with current submillimetre telescopes. At
least 15% should be detectable in the Planck all-sky survey at 350 mu and all
Planck all-sky survey sources with z < 0.9 should be IIFSCz sources. From the
luminosity-volume test we find that HLIRGs show strong evolution. A simple
exponential luminosity evolution applied to all HLIRGs would be consistent with
the luminosity functions found in redshift bins 0.3-0.5, 0.5-1 and 1-2. |
Gravitational redshift in the void-galaxy cross-correlation function in
redshift space: We construct an analytic model for the void-galaxy cross-correlation function
that enables theoretical predictions of the dipole signal produced dominantly
by the gravitational redshift within voids for the first time. By extending a
theoretical formulation for the redshift-space distortion of galaxies to
include the second order terms of the galaxy peculiar velocity $\bm v$ and the
gravitational potential, we formulate the void-galaxy cross-correlation
function multipoles in the redshift space, the monopole $\xi_0^{(s)}$, dipole
$\xi_1^{(s)}$ and quadrupole $\xi_2^{(s)}$. We find that the dipole
$\xi_1^{(s)}$ is dominated by the gravitational redshift, which provide a
unique opportunity to detect the gravitational potential of voids. Thus, for
the dipole $\xi_1^{(s)}(s)$, the gravitational redshift is crucial. Although
the higher order effect is almost negligible on the monopole $\xi_0^{(s)}$, it
has an influence on the quadrupole $\xi_2^{(s)}$. The effects from the random
velocity of galaxies and the definition of the void center on the dipole signal
are also discussed. Our model offers a new theoretical probe for the detection
of gravitational redshift with voids and further tests on cosmology and
gravity. | Radiation and energy release in a background field of axion-like dark
matter: We find that a fuzzy dark matter background and the mG scale magnetic field
in the galactic center can give rise to a radiation with a very large energy
release. The frequency of the radiation field is the same as the frequency of
the oscillating axion-like background field. We show that there is an energy
transfer between the fuzzy dark matter sector and the electromagnetic sector
because of the presence of the generated radiation field and the galactic
magnetic field. The energy release rate of radiation is found to be very slow
in comparison with the energy of fuzzy dark matter but could be significant
comparing with the energy of galactic magnetic field in the source region.
Using this example, we show that the fuzzy dark matter together with a large
scale magnetic field is possible to give rise to fruitful physics. |
Density profiles and voids in modified gravity models: We study the formation of voids in a modified gravity model in which gravity
is generically stronger or weaker on large scales. We show that void abundances
provide complementary information to halo abundances: if normalized to the CMB,
models with weaker large-scale gravity have smaller large scale power, fewer
massive halos and fewer large voids, although the scalings are not completely
degenerate with $\sigma_8$. Our results suggest that, in addition to their
abundances, halo and void density profiles may also provide interesting
constraints on such models: stronger large scale gravity produces more
concentrated halos, and thinner void walls. This potentially affects the
scaling relations commonly assumed to translate cluster observables to halo
masses, potentially making these too, useful probes of gravity. | A 22-year Southern Sky Survey for Transient and Variable Radio Sources
using the Molonglo Observatory Synthesis Telescope: We describe a 22-year survey for variable and transient radio sources,
performed with archival images taken with the Molonglo Observatory Synthesis
Telescope (MOST). This survey covers $2775 \unit{deg^2}$ of the sky south of
$\delta < -30\degree$ at an observing frequency of 843 MHz, an angular
resolution of $45 \times 45 \csc | \delta| \unit{arcsec^2}$ and a sensitivity
of $5 \sigma \geq 14 \unit{mJy beam^{-1}}$. We describe a technique to
compensate for image gain error, along with statistical techniques to check and
classify variability in a population of light curves, with applicability to any
image-based radio variability survey. Among radio light curves for almost 30000
sources, we present 53 highly variable sources and 15 transient sources. Only 3
of the transient sources, and none of the variable sources have been previously
identified as transient or variable. Many of our variable sources are suspected
scintillating Active Galactic Nuclei. We have identified three variable sources
and one transient source that are likely to be associated with star forming
galaxies at $z \simeq 0.05$, but whose implied luminosity is higher than the
most luminous known radio supernova (SN1979C) by an order of magnitude. We also
find a class of variable and transient source with no optical counterparts. |
Secular evolution of galaxies and galaxy clusters in decaying dark
matter cosmology: If the dark matter sector in the universe is composed by metastable
particles, galaxies and galaxy clusters are expected to undergo significant
secular evolution from high to low redshift. We show that the decay of dark
matter, with a lifetime compatible with cosmological constraints, can be at the
origin of the observed evolution of the Tully-Fisher relation of disk galaxies
and alleviate the problem of the size-evolution of elliptical galaxies, while
being consistent with the current observational constraints on the gas fraction
of clusters of galaxies. | A simulation-based inference pipeline for cosmic shear with the
Kilo-Degree Survey: The standard approach to inference from cosmic large-scale structure data
employs summary statistics that are compared to analytic models in a Gaussian
likelihood with pre-computed covariance. To overcome the idealising assumptions
about the form of the likelihood and the complexity of the data inherent to the
standard approach, we investigate simulation-based inference (SBI), which
learns the likelihood as a probability density parameterised by a neural
network. We construct suites of simulated, exactly Gaussian-distributed data
vectors for the most recent Kilo-Degree Survey (KiDS) weak gravitational
lensing analysis and demonstrate that SBI recovers the full 12-dimensional KiDS
posterior distribution with just under $10^4$ simulations. We optimise the
simulation strategy by initially covering the parameter space by a hypercube,
followed by batches of actively learnt additional points. The data compression
in our SBI implementation is robust to suboptimal choices of fiducial parameter
values and of data covariance. Together with a fast simulator, SBI is therefore
a competitive and more versatile alternative to standard inference. |
Statistics of cosmic density profiles from perturbation theory: The joint probability distribution function (PDF) of the density within
multiple concentric spherical cells is considered. It is shown how its cumulant
generating function can be obtained at tree order in perturbation theory as the
Legendre transform of a function directly built in terms of the initial
moments. In the context of the upcoming generation of large-scale structure
surveys, it is conjectured that this result correctly models such a function
for finite values of the variance. Detailed consequences of this assumption are
explored. In particular the corresponding one-cell density probability
distribution at finite variance is computed for realistic power spectra, taking
into account its scale variation. It is found to be in agreement with
$\Lambda$-CDM simulations at the few percent level for a wide range of density
values and parameters. Related explicit analytic expansions at the low and high
density tails are given. The conditional (at fixed density) and marginal
probability of the slope -- the density difference between adjacent cells --
and its fluctuations is also computed from the two-cells joint PDF; it also
compares very well to simulations, in particular in under-dense regions, with a
significant reduced cosmic scatter compared to over-dense regions. It is
emphasized that this could prove useful when studying the statistical
properties of voids as it can serve as a statistical indicator to test gravity
models and/or probe key cosmological parameters. | Correlation and time delays of the X-ray and optical emission of the
Seyfert Galaxy NGC3783: We present simultaneous X-ray and optical B and V band light curves of the
Seyfert Galaxy NGC3783 spanning 2 years. The flux in all bands is highly
variable and the fluctuations are significantly correlated. As shown before by
Stirpe et al. the optical bands vary simultaneously, with a delay of less than
1.5 days but both B and V bands lag the X-ray fluctuations by 3-9 days. This
delay points at optical variability produced by X-ray reprocessing and the
value of the lag places the reprocessor close to the broad line region. A power
spectrum analysis of the light curve, however, shows that the X-ray variability
has a power law shape bending to a steeper slope at a time-scale ~2.9 days
while the variability amplitude in the optical bands continues to grow towards
the longest time-scale covered, ~ 300 days. We show that the power spectra
together with the small value of the time delay is inconsistent with a picture
where all the optical variability is produced by X-ray reprocessing, though the
small amplitude, rapid optical fluctuations might be produced in this way. We
detect larger variability amplitudes on long time-scales in the optical bands
than in the X-rays. This behaviour adds to similar results recently obtained
for at least three other AGN and indicates a separate source of long term
optical variability, possibly accretion rate or thermal fluctuations in the
optically emitting accretion disc. |
The Rethermalizing Bose-Einstein Condensate of Dark Matter Axions: The axions produced during the QCD phase transition by vacuum realignment,
string decay and domain wall decay thermalize as a result of their
gravitational self-interactions when the photon temperature is approximately
500 eV. They then form a Bose-Einstein condensate (BEC). Because the axion BEC
rethermalizes on time scales shorter than the age of the universe, it has
properties that distinguish it from other forms of cold dark matter. The
observational evidence for caustic rings of dark matter in galactic halos is
explained if the dark matter is axions, at least in part, but not if the dark
matter is entirely WIMPs or sterile neutrinos. | How much a galaxy knows about its large-scale environment?: An
information theoretic perspective: The small-scale environment characterized by the local density is known to
play a crucial role in deciding the galaxy properties but the role of
large-scale environment on galaxy formation and evolution still remain a less
clear issue. We propose an information theoretic framework to investigate the
influence of large-scale environment on galaxy properties and apply it to the
data from the Galaxy Zoo project which provides the visual morphological
classifications of $\sim 1$ million galaxies from the Sloan Digital Sky Survey.
We find a non-zero mutual information between morphology and environment which
decreases with increasing length scales but persists throughout the entire
length scales probed. We estimate the conditional mutual information and the
interaction information between morphology and environment by conditioning the
environment on different length scales and find a synergic interaction between
them which operates upto at least a length scales of $ \sim 30 \, h^{-1}\, {\rm
Mpc}$. Our analysis indicates that these interactions largely arise due to the
mutual information shared between the environments on different length scales. |
Constraints on neutrino masses from Lyman-alpha forest power spectrum
with BOSS and XQ-100: We present constraints on masses of active and sterile neutrinos. We use the
one-dimensional Ly$\alpha$-forest power spectrum from the Baryon Oscillation
Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) and from
the VLT/XSHOOTER legacy survey (XQ-100). In this paper, we present our own
measurement of the power spectrum with the publicly released XQ-100 quasar
spectra.
Fitting Ly$\alpha$ data alone leads to cosmological parameters in excellent
agreement with the values derived independently from Planck 2015 Cosmic
Microwave Background (CMB) data. Combining BOSS and XQ-100 Ly$\alpha$ power
spectra, we constrain the sum of neutrino masses to $\sum m_\nu < 0.8$ eV (95\%
C.L). With the addition of CMB data, this bound is tightened to $\sum m_\nu <
0.14$ eV (95\% C.L.).
With their sensitivity to small scales, Ly$\alpha$ data are ideal to
constrain $\Lambda$WDM models. Using XQ-100 alone, we issue lower bounds on
pure dark matter particles: $m_X \gtrsim 2.08 \: \rm{keV}$ (95\% C.L.) for
early decoupled thermal relics, and $m_s \gtrsim 10.2 \: \rm{keV}$ (95\% C.L.)
for non-resonantly produced right-handed neutrinos. Combining the 1D Ly$\alpha$
forest power spectrum measured by BOSS and XQ-100, we improve the two bounds to
$m_X \gtrsim 4.17 \: \rm{keV}$ and $m_s \gtrsim 25.0 \: \rm{keV}$ (95\% C.L.).
The $3~\sigma$ bound shows a more significant improvement, increasing from $m_X
\gtrsim 2.74 \: \rm{keV}$ for BOSS alone to $m_X \gtrsim 3.10 \: \rm{keV}$ for
the combined BOSS+XQ-100 data set.
Finally, we include in our analysis the first two redshift bins ($z=4.2$ and
$z=4.6$) of the power spectrum measured with the high-resolution HIRES/MIKE
spectrographs. The addition of HIRES/MIKE power spectrum allows us to further
improve the two limits to $m_X \gtrsim 4.65 \: \rm{keV}$ and $m_s \gtrsim 28.8
\: \rm{keV}$ (95\% C.L.). | Searching for axion-like particles through CMB birefringence from
string-wall networks: Axion-like particles (ALPs) can form a network of cosmic strings and domain
walls that survives after recombination and leads to anisotropic birefringence
of the cosmic microwave background (CMB). In addition to studying cosmic
strings, we clarify and emphasize how the formation of ALP-field domain walls
impacts the cosmic birefringence signal; these observations provide a unique
way of probing ALPs with masses in the range $3H_0 \lesssim m_a \lesssim
3H_{\rm cmb}$. Using measurements of CMB birefringence from several telescopes,
we find no evidence for axion-defect-induced anisotropic birefringence of the
CMB. We extract constraints on the model parameters that include the ALP mass
$m_a$, ALP-photon coupling $\mathcal{A} \propto g_{a\gamma\gamma} f_a$, the
domain wall number $N_{\rm dw}$, and parameters characterizing the abundance
and size of defects in the string-wall network. Considering also recent
evidence for isotropic CMB birefringence, we find it difficult to accommodate
this with the non-detection of anisotropic birefringence under the assumption
that the signal is generated by an ALP defect network. |
Towards distinguishing variants of non-minimal inflation: We study models of inflation where the scalar field $\phi$ that drives
inflation is coupled non-minimally to gravity via $\xi \phi^2 R$, or where the
gravity sector is enlarged by an $R^2$ term. We consider the original Higgs
inflation, Starobinsky inflation, and two different versions of a scenario
where the inflaton is a scalar field other than the Higgs, and discuss if they
can be distinguished from each other by measuring the tensor-to-scalar ratio
and runnings of the spectral index of primordial curvature perturbations, on
top of the amplitude and spectral index of the perturbations. We consider both
metric and Palatini theories of gravity, showing how detailed studies of
non-minimally coupled models can help to identify the inflaton field and how
they may provide for a way to also distinguish between different theories of
gravity in the present context. | The Faint End of the Luminosity Function and Low Surface Brightness
Galaxies: SHELS (Smithsonian Hectospec Lensing Survey) is a dense redshift survey
covering a 4 square degree region to a limiting R = 20.6. In the construction
of the galaxy catalog and in the acquisition of spectroscopic targets, we paid
careful attention to the survey completeness for lower surface brightness dwarf
galaxies. Thus, although the survey covers a small area, it is a robust basis
for computation of the slope of the faint end of the galaxy luminosity function
to a limiting M_R = -13.3 + 5logh. We calculate the faint end slope in the
R-band for the subset of SHELS galaxies with redshif ts in the range 0.02 <= z
< 0.1, SHELS_{0.1}. This sample contains 532 galaxies with R< 20.6 and with a
median surface brightness within the half light radius of SB_{50,R} = 21.82 mag
arcsec^{-2}. We used this sample to make one of the few direct measurements of
the dependence of the faint end of the galaxy luminosity function on surface
brightness. For the sample as a whole the faint end slope, alpha = -1.31 +/-
0.04, is consistent with both the Blanton et al. (2005b) analysis of the SDSS
and the Liu et al. (2008) analysis of the COSMOS field. This consistency is
impressive given the very different approaches of th ese three surveys. A
magnitude limited sample of 135 galaxies with optical spectroscopic reds hifts
with mean half-light surface brightness, SB_{50,R} >= 22.5 mag arcsec^{-2} is
unique to SHELS_{0.1}. The faint end slope is alpha_{22.5} = -1.52+/- 0.16.
SHELS_{0.1} shows that lower surface brightness objects dominate the faint end
slope of the l uminosity function in the field, underscoring the importance of
surface brightness limits in evaluating measurements of the faint end slope and
its evolution. |
Testing the coincidence problem with strong gravitational lens, Type Ia
supernovae and Hubble parameter observational data: In this paper, we use three different kinds of observational data, including
130 strong gravitational lensing (SGL) systems, type Ia supernovae (SNeIa:
Pantheon and Union2.1) and 31 Hubble parameter data points ($H(z)$) from cosmic
chronometers to constrain the phenomenological model ($\rho_x\varpropto\rho_m
a^{\xi}$). By combining these three kinds of data (Union2.1+SGL+$H(z)$), we get
the parameter value at the confidence interval of $2\sigma$, $\Omega_{X,0} =
0.69\pm0.34$, $\omega_x = -1.24\pm0.61$, $\xi = 3.8\pm3.9$ and $H_0 =
70.22\pm0.86$ kms$^{-1}$Mpc$^{-1}$. According to our results, we find that the
$\Lambda$CDM model is still the model which is in best agreement with the
observational data at present, and the coincidence problem is not alleviated.
In addition, the $\Omega_X$ and $\Omega_m$ have the same order of magnitude in
$0<z<1.26$. At last, we obtain the transition redshift $z_T=0.645$. If the
transition occurs in $z>0.645$, it is necessary to introduce the dark energy
interacting with dark matter. | Cosmological constraints from HSC survey first-year data using deep
learning: We present cosmological constraints from the Subaru Hyper Suprime-Cam (HSC)
first-year weak lensing shear catalogue using convolutional neural networks
(CNNs) and conventional summary statistics. We crop 19
$3\times3\,\mathrm{{deg}^2}$ sub-fields from the first-year area, divide the
galaxies with redshift $0.3\le z\le1.5$ into four equally-spaced redshift bins,
and perform tomographic analyses. We develop a pipeline to generate simulated
convergence maps from cosmological $N$-body simulations, where we account for
effects such as intrinsic alignments (IAs), baryons, photometric redshift
errors, and point spread function errors, to match characteristics of the real
catalogue. We train CNNs that can predict the underlying parameters from the
simulated maps, and we use them to construct likelihood functions for Bayesian
analyses. In the $\Lambda$ cold dark matter model with two free cosmological
parameters $\Omega_\mathrm{m}$ and $\sigma_8$, we find
$\Omega_\mathrm{m}=0.278_{-0.035}^{+0.037}$,
$S_8\equiv(\Omega_\mathrm{m}/0.3)^{0.5}\sigma_8=0.793_{-0.018}^{+0.017}$, and
the IA amplitude $A_\mathrm{IA}=0.20_{-0.58}^{+0.55}$. In a model with four
additional free baryonic parameters, we find
$\Omega_\mathrm{m}=0.268_{-0.036}^{+0.040}$, $S_8=0.819_{-0.024}^{+0.034}$, and
$A_\mathrm{IA}=-0.16_{-0.58}^{+0.59}$, with the baryonic parameters not being
well-constrained. We also find that statistical uncertainties of the parameters
by the CNNs are smaller than those from the power spectrum (5--24 percent
smaller for $S_8$ and a factor of 2.5--3.0 smaller for $\Omega_\mathrm{m}$),
showing the effectiveness of CNNs for uncovering additional cosmological
information from the HSC data. With baryons, the $S_8$ discrepancy between HSC
first-year data and Planck 2018 is reduced from $\sim2.2\,\sigma$ to
$0.3\text{--}0.5\,\sigma$. |
Deep learning reconstruction of the large scale structure of the
Universe from luminosity distance observations: Supernovae Ia (SNe) can provide a unique window on the large scale structure
(LSS) of the Universe at redshifts where few other observations are available,
by solving the inversion problem (IP) consisting in reconstructing the LSS from
its effects on the observed luminosity distance. So far the IP was solved
assuming some restrictions about space-time, such as spherical symmetry for
example, while we obtain for the first time solutions of the IP problem for
arbitrary space-time geometries using deep learning. The method is based on the
use of convolutional neural networks (CNN) trained on simulated data. The
training data set is obtained by first generating random density and velocity
fields, and then computing their effects on the luminosity distance. The CNN,
based on an appriately modified version of U-Net to account for the
tridimensionality of the data, is then trained to reconstruct the density and
velocity fields from the luminosity distance.
We find that the velocity field inversion is more accurate than the density
field, because the effects of the velocity on the luminosity distance only
depend on the source velocity, while in the case of the density it is an
integrated effect along the line of sight, giving rise to more degeneracy in
the solution of the IP. Improved versions of these neural networks, modified to
accommodate the non uniform distribution of the SNe, can be applied to
observational data to reconstruct the large scale structure of the Universe at
redshifts at which few other observations are available. | Premature Black Hole Death of Population III Stars by Dark Matter: Population III stars were the first generation of stars, formed in minihalos
of roughly primordial element abundances, and therefore metal-free. They are
thought to have formed at the cores of dense dark matter clouds. Interactions
between baryons and dark matter can therefore have had an important impact on
their evolution. In this paper we consider the capture of non- or
weakly-annihilating dark matter by these early massive stars. In a wide region
of parameter space, interactions of dark matter with baryons lead to premature
death of the star as a black hole. We sketch how this modification of the
standard evolutionary history of Population III stars might impact the epoch of
reionisation, by modifying the amount of UV emission, the transition to
Population II star formation, and the X-ray and radio emission from accretion
onto the black hole remnants. Signals of massive black holes originating from
Population III stars could be observed through gravitational waves from their
mergers. Finally, the observation of pair-instability supernovae could
effectively preclude premature black hole death across a wide range of
parameter space, ranging in mass from $m_{DM} \sim 0.1\text{ GeV}$ to $m_{DM}
\sim m_{\rm Pl}$. |
Machine Learning Classification to Identify Catastrophic Outlier
Photometric Redshift Estimates: We present results of using a basic binary classification neural network
model to identify likely catastrophic outlier photometric redshift estimates of
individual galaxies, based only on the galaxies' measured photometric band
magnitude values. We find that a simple implementation of this classification
can identify a significant fraction of galaxies with catastrophic outlier
photometric redshift estimates while falsely categorizing only a much smaller
fraction of non-outliers. These methods have the potential to reduce the errors
introduced into science analyses by catastrophic outlier photometric redshift
estimates. | The 21-cm bispectrum from neutral hydrogen islands at z < 6: Spatial variations in the Lyman-$\alpha$ forest opacity at $z<6$ seem to
require a late end to cosmic reionization. In this picture, the universe
contains neutral hydrogen 'islands' of up to 100 cMpc$/h$ in extent down to
redshifts as low as $z\sim 5.3$. This delayed end to reionization also seems to
be corroborated by various other observables. An implication of this scenario
is that the power spectrum of the cosmological 21-cm signal at $z<6$ is
enhanced relative to conventional reionization models by orders of magnitude.
However, these neutral hydrogen islands are also predicted to be at the
locations of the deepest voids in the cosmological large-scale structure. As a
result, the distribution of the 21-cm signal from them is highly non-Gaussian.
We derive the 21-cm bispectrum signal from these regions using
high-dynamic-range radiative transfer simulations of reionization. We find that
relative to conventional models in which reionization is complete at $z>6$, our
model has a significantly larger value of the 21-cm bispectrum. The neutral
islands also imprint a feature in the isosceles bispectrum at a characteristic
scale of $\sim 1$ cMpc$^{-1}$. We also study the 21-cm bispectrum for general
triangle configuration by defining a triangle index. It should be possible to
detect the 21-cm bispectrum signal at $\nu\gtrsim 200$ MHz using SKA1-LOW for
1080 hours of observation, assuming optimistic foreground removal. |
Structure formation simulations with momentum exchange: alleviating
tensions between high-redshift and low-redshift cosmological probes: Persisting tensions between the cosmological constraints derived from
low-redshift probes and the ones obtained from temperature and polarisation
anisotropies of the Cosmic Microwave Background -- although not yet providing
compelling evidence against the $\Lambda $CDM model -- seem to consistently
indicate a slower growth of density perturbations as compared to the
predictions of the standard cosmological scenario. Such behavior is not easily
accommodated by the simplest extensions of General Relativity, such as f(R)
models, which generically predict an enhanced growth rate. In the present work
we present the outcomes of a suite of large N-body simulations carried out in
the context of a cosmological model featuring a non-vanishing scattering cross
section between the dark matter and the dark energy fields, for two different
parameterisations of the dark energy equation of state. Our results indicate
that these Dark Scattering models have very mild effects on many observables
related to large-scale structures formation and evolution, while providing a
significant suppression of the amplitude of linear density perturbations and
the abundance of massive clusters. Our simulations therefore confirm that these
models offer a promising route to alleviate existing tensions between
low-redshift measurements and those of the CMB. | Science with the space-based interferometer eLISA. III: Probing the
expansion of the Universe using gravitational wave standard sirens: We investigate the capability of various configurations of the space
interferometer eLISA to probe the late-time background expansion of the
universe using gravitational wave standard sirens. We simulate catalogues of
standard sirens composed by massive black hole binaries whose gravitational
radiation is detectable by eLISA, and which are likely to produce an
electromagnetic counterpart observable by future surveys. The main issue for
the identification of a counterpart resides in the capability of obtaining an
accurate enough sky localisation with eLISA. This seriously challenges the
capability of four-link (2 arm) configurations to successfully constrain the
cosmological parameters. Conversely, six-link (3 arm) configurations have the
potential to provide a test of the expansion of the universe up to $z\sim 8$
which is complementary to other cosmological probes based on electromagnetic
observations only. In particular, in the most favourable scenarios, they can
provide a significant constraint on $H_0$ at the level of 0.5%. Furthermore,
$(\Omega_M, \Omega_\Lambda)$ can be constrained to a level competitive with
present SNIa results. On the other hand, the lack of massive black hole binary
standard sirens at low redshift allows to constrain dark energy only at the
level of few percent. |
Gravitational Wave signatures of inflationary models from Primordial
Black Hole Dark Matter: Primordial Black Holes (PBH) could be the cold dark matter of the universe.
They could have arisen from large (order one) curvature fluctuations produced
during inflation that reentered the horizon in the radiation era. At reentry,
these fluctuations source gravitational waves (GW) via second order anisotropic
stresses. These GW, together with those (possibly) sourced during inflation by
the same mechanism responsible for the large curvature fluctuations, constitute
a primordial stochastic GW background (SGWB) that unavoidably accompanies the
PBH formation. We study how the amplitude and the range of frequencies of this
signal depend on the statistics (Gaussian versus $\chi^2$) of the primordial
curvature fluctuations, and on the evolution of the PBH mass function due to
accretion and merging. We then compare this signal with the sensitivity of
present and future detectors, at PTA and LISA scales. We find that this SGWB
will help to probe, or strongly constrain, the early universe mechanism of PBH
production. The comparison between the peak mass of the PBH distribution and
the peak frequency of this SGWB will provide important information on the
merging and accretion evolution of the PBH mass distribution from their
formation to the present era. Different assumptions on the statistics and on
the PBH evolution also result in different amounts of CMB $\mu$-distortions.
Therefore the above results can be complemented by the detection (or the
absence) of $\mu$-distortions with an experiment such as PIXIE. | Gravitational Lensing Signatures of Axion Dark Matter Minihalos in
Highly Magnified Stars: Axions are a viable candidate for Cold Dark Matter (CDM) which should
generically form minihalos of sub-planetary masses from white-noise
isocurvature density fluctuations if the Peccei-Quinn phase transition occurs
after inflation. Despite being denser than the larger halos formed out of
adiabatic fluctuations from inflation, axion minihalos have surface densities
much smaller than the critical value required for gravitational lensing to
produce multiple images or high magnification, and hence are practically
undetectable as lenses in isolation. However, their lensing effect can be
enhanced when superposed near critical curves of other lenses. We propose a
method to detect them through photometric monitoring of recently discovered
caustic transiting stars behind cluster lenses, under extreme magnification
factors $\mu \gtrsim 10^3$--$10^4$ as the lensed stars cross microlensing
caustics induced by intracluster stars. For masses of the first gravitationally
collapsed minihalos in the range $\sim 10^{-15}$--$10^{-8}\,h^{-1}\,M_\odot$,
we show that axion minihalos in galaxy clusters should collectively produce
subtle surface density fluctuations of amplitude $\sim 10^{-4}$--$10^{-3}$ on
projected length scales of $\sim 10$--$10^4\,$AU, which imprint irregularities
in the microlensing light curves of caustic transiting stars. We estimate that,
inside a cluster halo and over the age of the Universe, most of these minihalos
are likely to avoid dynamic disruption by encounters with stars or other
minihalos. |
Constraints of the equation of state of dark energy from current and
future observational data by piecewise parametrizations: The model-independent piecewise parametrizations (0-spline, linear-spline and
cubic-spline) are used to estimate constraints of equation of state of dark
energy ($w_{de}$) from current observational data (including SNIa, BAO and
Hubble parameter) and the simulated future data. A combination of fitting
results of $w_{de}$ from these three spline methods reveal essential properties
of real equation of state $w_{de}$. It is shown that $w_{de}$ beyond redshift
$z\sim0.5$ is poorly constrained from current data, and the mock future
$\sim2300$ supernovae data give poor constraints of $w_{de}$ beyond $z\sim1$.
The fitting results also indicate that there might exist a rapid transition of
$w_{de}$ around $z\sim0.5$. The difference between three spline methods in
reconstructing and constraining $w_{de}$ has also been discussed. | A major galaxy cluster merger caught by eROSITA: weak lensing mass
distribution and kinematic description: We present the weak lensing mass distribution of a triple merging cluster
candidate at $z_{\rm photo}\sim 0.36$ belonging to a supercluster recently
discovered during the eROSITA Performance Verification phase. Our analysis
solved a previous tension in the merger classification by confirming that the
cluster pair eFEDS J093513.3+004746 and eFEDS J093510.7+004910 is undergoing a
major merger with a mass ratio $1.7_{-0.7}^{+0.5}$. According to our two-body
kinematic description, the encounter happened $0.58_{-0.20}^{+0.15}$ Gyr ago,
in a scenario that supports the observed radio relic position at the cluster
outskirts. However, the same analysis showed that the companion cluster, eFEDS
J093501.1+005418, is not gravitationally bound to the interacting system and
therefore it is not part of the supercluster. We also checked the impact of
adopting a scaling relation to determine the halo concentration $c_{200}$. At
the observed merger stage, where the clusters have travelled $\sim$55 per cent
of the path to reach the apoapsis, the choice of the $c_{200}$ (whether from a
scaling relation or a free parameter in the mass model) does not change
significantly either the cluster masses or the kinematic description. |
The Absolute Magnitudes of Type Ia Supernovae in the Ultraviolet: We examine the absolute magnitudes and light-curve shapes of 14
nearby(redshift z = 0.004--0.027) Type Ia supernovae (SNe~Ia) observed in the
ultraviolet (UV) with the Swift Ultraviolet/Optical Telescope. Colors and
absolute magnitudes are calculated using both a standard Milky Way (MW)
extinction law and one for the Large Magellanic Cloud that has been modified by
circumstellar scattering. We find very different behavior in the near-UV
filters (uvw1_rc covering ~2600-3300 A after removing optical light, and u
~3000--4000 A) compared to a mid-UV filter (uvm2 ~2000-2400 A). The uvw1_rc-b
colors show a scatter of ~0.3 mag while uvm2-b scatters by nearly 0.9 mag.
Similarly, while the scatter in colors between neighboring filters is small in
the optical and somewhat larger in the near-UV, the large scatter in the
uvm2-uvw1 colors implies significantly larger spectral variability below 2600
A. We find that in the near-UV the absolute magnitudes at peak brightness of
normal SNe Ia in our sample are correlated with the optical decay rate with a
scatter of 0.4 mag, comparable to that found for the optical in our sample.
However, in the mid-UV the scatter is larger, ~1 mag, possibly indicating
differences in metallicity. We find no strong correlation between either the UV
light-curve shapes or the UV colors and the UV absolute magnitudes. With larger
samples, the UV luminosity might be useful as an additional constraint to help
determine distance, extinction, and metallicity in order to improve the utility
of SNe Ia as standardized candles. | Resolving the problem of galaxy clustering on small scales: any new
physics needed?: Galaxy clustering sets strong constraints on the physics governing galaxy
formation and evolution. However, most current models fail to reproduce the
clustering of low-mass galaxies on small scales ($r<1Mpc/h$). In this paper we
study the galaxy clusterings predicted from a few semi-analytical models. We
firstly compare two Munich versions, Guo et al. (2011, Guo11) and De Lucia \&
Blazoit (2007, DLB07). The Guo11 model well reproduces the galaxy stellar mass
function, but over-predicts the clustering of low-mass galaxies on small
scales. The DLB07 model provides a better fit to the clustering on small
scales, but over-predicts the stellar mass function. These seem to be puzzling.
We find that there is slightly more fraction of satellite galaxies residing in
massive haloes in the Guo11 model, which is the dominant contribution to the
clustering discrepancy between the two models. However, both models still
over-predict the clustering at $0.1Mpc/h<r<10Mpc/h$ for low mass galaxies. This
is because both models over-predict the number of satellites by $30\%$ in
massive halos than the data. Actually, the better agreement of DLB07 model with
the data on small scales comes as a coincidence as it predicts too many
low-mass central galaxies which are less clustered and thus bring down the
total clustering. Finally, we show the predictions from the semi-analytical of
Kang et al. (2012). We find that this model can simultaneously fit the stellar
mass function and galaxy clustering if the supernova feedback in satellite
galaxies is stronger. We conclude that semi-analytical models are now able to
solve the small-scales clustering problem, without invoking of any other new
physics or changing the dark matter properties, such as the recent favored warm
dark matter. |
Science with CMB spectral distortions: The measurements of COBE/FIRAS have shown that the CMB spectrum is extremely
close to a perfect blackbody. There are, however, a number of processes in the
early Universe that should create spectral distortions at a level which is
within reach of present day technology. In this talk, I will give a brief
overview of recent theoretical and experimental developments, explaining why
future measurements of the CMB spectrum will open up an unexplored window to
early-universe and particle physics with possible non-standard surprises but
also several guaranteed signals awaiting us. | Constraints on the Hubble constant from Supernova Refsdal's reappearance: The gravitationally lensed Supernova Refsdal appeared in multiple images,
produced through gravitational lensing by a massive foreground galaxy cluster.
After the supernova appeared in 2014, lens models of the galaxy cluster
predicted an additional image of the supernova would appear in 2015, which was
subsequently observed. We use the time delays between the images to perform a
blinded measurement of the expansion rate of the Universe, quantified by the
Hubble constant (H0). Using eight cluster lens models, we infer H0 = 64.8
+4.4-4.3 km / s / Mpc, where Mpc is the megaparsec. Using the two models most
consistent with the observations, we find H0 = 66.6 +4.1-3.3 km / s / Mpc. The
observations are best reproduced by models that assign dark-matter halos to
individual galaxies and the overall cluster. |
Spin Alignment in Analogues of The Local Sheet: Tidal torque theory and simulations of large scale structure predict spin
vectors of massive galaxies should be coplanar with sheets in the cosmic web.
Recently demonstrated, the giants (K$_{s}$ $\leq$ -22.5 mag) in the Local
Volume beyond the Local Sheet have spin vectors directed close to the plane of
the Local Supercluster, supporting the predictions of Tidal Torque Theory.
However, the giants in the Local Sheet encircling the Local Group display a
distinctly different arrangement, suggesting that the mass asymmetry of the
Local Group or its progenitor torqued them from their primordial spin
directions. To investigate the origin of the spin alignment of giants locally,
analogues of the Local Sheet were identified in the SDSS DR9. Similar to the
Local Sheet, analogues have an interacting pair of disk galaxies isolated from
the remaining sheet members. Modified sheets in which there is no interacting
pair of disk galaxies were identified as a control sample.
Galaxies in face-on control sheets do not display axis ratios predominantly
weighted toward low values, contrary to the expectation of tidal torque theory.
For face-on and edge-on sheets, the distribution of axis ratios for galaxies in
analogues is distinct from that in controls with a confidence of 97.6 $\%$ $\&$
96.9$\%$, respectively. This corroborates the hypothesis that an interacting
pair can affect spin directions of neighbouring galaxies. | Stellar sources of dust in the high redshift Universe: With the aim of investigating whether stellar sources can account for the
>10^8 Msun dust masses inferred from mm/sub-mm observations of samples of
5<z<6.4 quasars,we develop a chemical evolution model which follows the
evolution of metals and dust on the stellar characteristic lifetimes, taking
into account dust destruction mechanisms.Using a grid of stellar dust yields as
a function of the initial mass and metallicity over the range 1-40 Msun and 0-1
Zsun,we show that the role of AGB stars in cosmic dust evolution at high
redshift might have been over-looked.We apply the chemical evolution model with
dust to the host galaxy of the most distant quasar at z=6.4, SDSS
J1148+5251.Given the current uncertainties on the star formation history of the
host galaxy, we have considered two models: (i) a star formation history
obtained in a numerical simulation by Li et al.(2007) which predicts that a
large stellar bulge is already formed at z=6.4,and (ii) a constant star
formation rate of 1000 Msun/yr, as suggested by the observations if most of the
FIR luminosity is due to young stars.The total mass of dust predicted at z=6.4
by the first model is 2x10^8Msun,within the range of values inferred by
observations,with a substantial contribution (80%) of AGB-dust.When a constant
star formation rate is adopted,the contribution of AGB-dust decreases to 50%
but the total mass of dust formed is a factor 2 smaller.Both models predict a
rapid enrichment of the ISM with metals and a relatively mild evolution of the
carbon abundance,in agreement with observational constraints. This supports the
idea that stellar sources can account for the dust observed but show that the
contribution of AGB stars to dust production cannot be neglected, even at the
most extreme redshifts currently accessible to observations. |
Mass bound for primordial black hole from trans-Planckian censorship
conjecture: The recently proposed trans-Planckian censorship conjecture (TCC) imposes a
strong constraint on the inflationary Hubble scale, of which the upper bound
could be largely relaxed by considering a noninstantaneous reheating history.
In this paper we will show that, if the primordial black holes (PBHs) are
formed at reentry in the radiation-dominated era from the enhanced curvature
perturbations at small scales, the TCC would impose a lower bound on the PBH
mass $M_\mathrm{PBH}>\gamma(H_\mathrm{end}/10^9\,\mathrm{GeV})^2\,M_\odot$
regardless of the details for reheating history, where $\gamma$ is the collapse
efficiency factor and $H_\mathrm{end}$ is the Hubble scale at the end of
inflation. In particular, the current open window for PBHs to make up all the
cold dark matter could be totally ruled out if the inflationary Hubble scale is
larger than 10 TeV. For the case of PBHs formed in an early matter-dominated
era, an upper mass bound is obtained. | Correcting for peculiar velocities of Type Ia Supernovae in clusters of
galaxies: Type Ia Supernovae (SNe Ia) are widely used to measure the expansion of the
Universe. To perform such measurements the luminosity and cosmological redshift
($z$) of the SNe Ia have to be determined. The uncertainty on $z$ includes an
unknown peculiar velocity, which can be very large for SNe Ia in the virialized
cores of massive clusters. We determine which SNe Ia exploded in galaxy
clusters. We then study how the correction for peculiar velocities of host
galaxies inside the clusters improves the Hubble residuals. Using 145 SNe Ia
from the Nearby Supernova Factory we found 11 candidates for membership in
clusters. To estimate the redshift of a cluster we applied the bi-weight
technique. Then, we use the galaxy cluster redshift instead of the host galaxy
redshift to construct the Hubble diagram. For SNe Ia inside galaxy clusters the
dispersion around the Hubble diagram when peculiar velocities are taken into
account is smaller in comparison with a case without peculiar velocity
correction, with a $wRMS=0.130\pm0.038$ mag instead of $wRMS=0.137\pm0.036$
mag. The significance of this improvement is 3.58 $\sigma$. If we remove the
very nearby Virgo cluster member SN2006X ($z<0.01$) from the analysis, the
significance decreases to 1.34 $\sigma$. The peculiar velocity correction is
found to be highest for the SNe Ia hosted by blue spiral galaxies, with high
local specific star formation rate and smaller stellar mass, seemingly counter
to what might be expected given the heavy concentration of old, massive
elliptical galaxies in clusters. As expected, the Hubble residuals of SNe Ia
associated with massive galaxy clusters improve when the cluster redshift is
taken as the cosmological redshift of the SN. This fact has to be taken into
account in future cosmological analyses in order to achieve higher accuracy for
cosmological redshift measurements. Here we provide an approach to do so. |
Primordial black holes from sound speed resonance in the
inflaton-curvaton mixed scenario: We study sound speed resonance (SSR) mechanism for primordial black hole
(PBH) formation in an early universe scenario with inflaton and curvaton being
mixed. In this scenario, the total primordial density perturbations can be
contributed by the fluctuations from both the inflaton and curvaton fields, in
which the inflaton fluctuations lead to the standard adiabatic perturbations,
while the sound speed of the curvaton fluctuations are assumed to be
oscillating during inflation. Due to the narrow resonance effect of SSR
mechanism, we acquire the enhanced primordial density perturbations on small
scales and it remains nearly scale-invariant on large scales, which is
essential for PBH formation. Finally, we find that the PBHs with specific mass
spectrum can be produced with a sufficient abundance for dark matter in the
mixed scenario. | Investigating the large-scale environment of wide-angle tailed radio
galaxies in the local Universe: We present a statistical analysis of the large-scale (up to 2 Mpc)
environment of an homogeneous and complete sample, both in radio and optical
selection, of wide-angle tailed radio galaxies (WATs) in the local Universe
(i.e., with redshifts $z\lesssim$ 0.15). The analysis is carried out using the
parameters obtained from cosmological neighbors within 2 Mpc of the target
source. Results on WATs large-scale environments are then compared with that of
Fanaroff-Riley type I (FR Is) and type II (FR IIs) radio galaxies, listed in
two others homogeneous and complete catalogs, and selected with the same
criterion adopted for the WATs catalog. We obtain indication that at low
redshift WATs inhabit environments with a larger number of galaxies than that
of FR Is and FR IIs. In the explored redshift range, the physical size of the
galaxy group/cluster in which WATs reside appears to be almost constant with
respect to FR Is and FR IIs, being around 1 Mpc. From the distribution of the
concentration parameter, defined as the ratio between the number of
cosmological neighbors lying within 500 kpc and within 1 Mpc, we conclude that
WATs tend to inhabit the central region of the group/cluster in which they
reside, in agreement with the general paradigm that WATs are the cluster BCG. |
Forty Years of Research on Isolated Galaxies: Isolated galaxies have not been a hot topic over the past four decades. This
is partly due to uncertainties about their existence. Are there galaxies
isolated enough to be interesting? Do they exist in sufficient numbers to be
statistically useful? Most attempts to compile isolated galaxy lists were
marginally successful--too small number and not very isolated galaxies. If
really isolated galaxies do exist then their value becomes obvious in a
Universe where effects of interactions and environment (i.e. nurture) are
important. They provide a means for better quantifying effects of nurture. The
Catalog of Isolated Galaxies (CIG) compiled by Valentina Karachentseva appeared
near the beginning of the review period. It becomes the focus of this review
because of its obvious strengths and because the AMIGA project has increased
its utility through a refinement (a vetted CIG). It contains almost 1000
galaxies with nearest neighbor crossing times of 1-3Gyr. It is large enough to
serve as a zero-point or control sample. The galaxies in the CIG (and the
distribution of galaxy types) may be significantly different than those in even
slightly richer environments. The AMIGA-CIG, and future iterations, may be able
to tell us something about galaxy formation. It may also allow us to better
define intrinsic (natural) correlations like e.g. Fisher-Tully and FIR-OPTICAL.
Correlations can be better defined when the dispersion added by external
stimuli (nurture) is minimized or removed. | Exploring the inner region of Type 1 AGNs with the Keck interferometer: The exploration of extragalactic objects with long-baseline interferometers
in the near-infrared has been very limited. Here we report successful
observations with the Keck interferometer at K-band (2.2 um) for four Type 1
AGNs, namely NGC4151, Mrk231, NGC4051, and the QSO IRAS13349+2438 at z=0.108.
For the latter three objects, these are the first long-baseline interferometric
measurements in the infrared. We detect high visibilities (V^2 ~ 0.8-0.9) for
all the four objects, including NGC4151 for which we confirm the high V^2 level
measured by Swain et al.(2003). We marginally detect a decrease of V^2 with
increasing baseline lengths for NGC4151, although over a very limited range,
where the decrease and absolute V^2 are well fitted with a ring model of radius
0.45+/-0.04 mas (0.039+/-0.003 pc). Strikingly, this matches independent radius
measurements from optical--infrared reverberations that are thought to be
probing the dust sublimation radius. We also show that the effective radius of
the other objects, obtained from the same ring model, is either roughly equal
to or slightly larger than the reverberation radius as a function of AGN
luminosity. This suggests that we are indeed partially resolving the dust
sublimation region. The ratio of the effective ring radius to the reverberation
radius might also give us an approximate probe for the radial structure of the
inner accreting material in each object. This should be scrutinized with
further observations. |
Cosmological Simulations for Combined-Probe Analyses: Covariance and
Neighbour-Exclusion Bias: We present a public suite of weak lensing mock data, extending the Scinet
Light Cone Simulations (SLICS) to simulate cross-correlation analyses with
different cosmological probes. These mocks include KiDS-450- and LSST-like
lensing data, cosmic microwave background lensing maps and simulated
spectroscopic surveys that emulate the GAMA, BOSS and 2dFLenS galaxy surveys.
With 844 independent realisations, our mocks are optimised for combined-probe
covariance estimation, which we illustrate for the case of a joint measurement
involving cosmic shear, galaxy-galaxy lensing and galaxy clustering from
KiDS-450 and BOSS data. With their high spatial resolution, the SLICS are also
optimal for predicting the signal for novel lensing estimators, for the
validation of analysis pipelines, and for testing a range of systematic effects
such as the impact of neighbour-exclusion bias on the measured tomographic
cosmic shear signal. For surveys like KiDS and DES, where the rejection of
neighbouring galaxies occurs within ~2 arcseconds, we show that the measured
cosmic shear signal will be biased low, but by less than a percent on the
angular scales that are typically used in cosmic shear analyses. The amplitude
of the neighbour-exclusion bias doubles in deeper, LSST-like data. The
simulation products described in this paper are made available at
http://slics.roe.ac.uk/. | Arc Statistics: The existence of an arc statistics problem was at the center of a strong
debate in the last fifteen years. With the aim to clarify if the optical depth
for giant gravitational arcs by galaxy clusters in the so called concordance
model is compatible with observations, several studies were carried out which
helped to significantly improve our knowledge of strong lensing clusters,
unveiling their extremely complex internal structure. In particular, the
abundance and the frequency of strong lensing events like gravitational arcs
turned out to be a potentially very powerful tool to trace the structure
formation. However, given the limited size of observational and theoretical
data-sets, the power of arc statistics as a cosmological tool has been only
minimally exploited so far. On the other hand, the last years were
characterized by significant advancements in the field, and several cluster
surveys that are ongoing or planned for the near future seem to have the
potential to make arc statistics a competitive cosmological probe.
Additionally, recent observations of anomalously large Einstein radii and
concentrations in galaxy clusters have reinvigorated the debate on the arc
statistics problem. In this paper, we review the work done so far on arc
statistics, focussing on what is the lesson we learned and what is likely to
improve in the next years. |
BAO scale inference from biased tracers using the EFT likelihood: The physical scale corresponding to baryon acoustic oscillations (BAO), the
size of the sound horizon at recombination, is precisely determined by CMB
experiments. Measuring the apparent size of the BAO scale imprinted in the
clustering of galaxies gives us a direct estimate of the angular-diameter
distance and the Hubble parameter as a function of redshift. The BAO feature is
damped by non-linear structure formation, which reduces the precision with
which we can infer the BAO scale from standard galaxy clustering analysis
methods. Many methods to undo this damping via the so-called BAO reconstruction
have so far been proposed; however, they all rely on backward modeling. In this
paper, we present the first results of BAO inference from rest-frame halo
catalogs using forward modeling combined with the EFT likelihood, in the case
where the initial phases of the density field are fixed. We show that the
remaining systematic bias is less than 2% when we consider cutoff values of
$\Lambda \leq 0.25 \,h\,{\rm Mpc}^{-1}$ for all halo samples considered, and
below 1% and consistent with zero for all but the most highly biased samples.
We also demonstrate that, when compared to the standard power spectrum
likelihood approach under the same assumption of fixed phases, the 1$\sigma$
errors associated to the field level inference of the BAO scale are 1.1 to 3.3
times smaller, depending on the value of the cutoff and the halo sample. Our
analysis therefore unveils another promising feature of using field-level
inference for high-precision cosmology. | The GALEX Arecibo SDSS Survey V: The Relation between the HI Content of
Galaxies and Metal Enrichment at their Outskirts: We have obtained long-slit spectra of 174 star-forming galaxies with stellar
masses greater than 10^10 M_\odot from the GALEX Arecibo SDSS (GASS) survey.
These galaxies have both HI and H_2 mass measurements. The average metallicity
profile is strikingly flat out to R_90, the radius enclosing 90% of the r-band
light. Metallicity profiles which decline steadily with radius are found
primarily for galaxies in our sample with low stellar mass (Log(M_*)<10.2),
concentration, and/or mean stellar mass density. Beyond ~R_90, however, around
10 percent of the galaxies in our sample exhibit a sharp downturn in
metallicity. Remarkably, we find that the magnitude of the outer metallicity
drop is well correlated with the total HI content of the galaxy (measured as
f_HI=M_HI/M_*). We examine the radial profiles of stellar population ages and
star formation rate densities, and conclude that the galaxies with largest
outer metallicity drops are actively growing their stellar disks, with mass
doubling times across the whole disk only one third as long as a typical GASS
galaxy. We also describe a correlation between local stellar mass density and
metallicity, which is valid across all galaxies in our sample. We argue that
much of the recent stellar mass growth at the edges of these galaxies can be
linked to the accretion or radial transport of relatively pristine gas from
beyond the galaxies' stellar disks. |
Exploring interacting holographic dark energy in a perturbed universe
with parameterized post-Friedmann approach: The model of holographic dark energy in which dark energy interacts with dark
matter is investigated in this paper. In particular, we consider the
interacting holographic dark energy model in the context of a perturbed
universe, which was never investigated in the literature. To avoid the
large-scale instability problem in the interacting dark energy cosmology, we
employ the generalized version of the parameterized post-Friedmann approach to
treat the dark energy perturbations in the model. We use the current
observational data to constrain the model. Since the cosmological perturbations
are considered in the model, we can then employ the redshift-space distortions
(RSD) measurements to constrain the model, in addition to the use of the
measurements of expansion history, which was either never done in the
literature. We find that, for both the cases with $Q=\beta H\rho_{\rm c}$ and
$Q=\beta H_0\rho_{\rm c}$, the interacting holographic dark energy model is
more favored by the current data, compared to the holographic dark energy model
without interaction. It is also found that, with the help of the RSD data, a
positive coupling $\beta$ can be detected at the $2.95\sigma$ statistical
significance for the case of $Q=\beta H_0\rho_{\rm c}$. | On primordial black holes from an inflection point: Recently, it has been claimed that inflationary models with an inflection
point in the scalar potential can produce a large resonance in the power
spectrum of curvature perturbation. In this paper however we show that the
previous analyses are incorrect. The reason is twofold: firstly, the inflaton
is over-shot from a stage of standard inflation and so deviates from the
slow-roll attractor before reaching the inflection. Secondly, on the (or close
to) the inflection point, the ultra-slow-roll trajectory supersede the
slow-roll one and thus, the slow-roll approximations used in the literature
cannot be used. We then reconsider the model and provide a recipe for how to
produce nevertheless a large peak in the matter power spectrum via fine-tuning
of parameters. |
Illuminating the Darkest Galaxies: Low luminosity dwarf galaxies provide stringent constraints on the nature of
dark matter. Establishing these constraints depends on precise kinematic
measurements of individual stars. In this overview for non-specialists, we
describe current and future prospects for three unique tests of dark matter
using resolved stellar kinematics in low luminosity galaxies: the overall
number of satellite galaxies around the Milky Way, dark-matter annihilation
radiation from dwarf galaxies, and their internal density profiles. We then
assess the prospects for meaningfully testing theories of dark matter based on
the improved kinematic precision expected from upcoming facilities. | The Impact of Assuming Flatness in the Determination of Neutrino
Properties from Cosmological Data: Cosmological data have provided new constraints on the number of neutrino
species and the neutrino mass. However these constraints depend on assumptions
related to the underlying cosmology. Since a correlation is expected between
the number of effective neutrinos N_{eff}, the neutrino mass \sum m_\nu, and
the curvature of the universe \Omega_k, it is useful to investigate the current
constraints in the framework of a non-flat universe. In this paper we update
the constraints on neutrino parameters by making use of the latest cosmic
microwave background (CMB) data from the ACT and SPT experiments and consider
the possibility of a universe with non-zero curvature. We first place new
constraints on N_{eff} and \Omega_k, with N_{eff} = 4.03 +/- 0.45 and 10^3
\Omega_k = -4.46 +/- 5.24. Thus, even when \Omega_k is allowed to vary, N_{eff}
= 3 is still disfavored with 95% confidence. We then investigate the
correlation between neutrino mass and curvature that shifts the 95% upper limit
of \sum m_\nu < 0.45 eV to \sum m_\nu < 0.95 eV. Thus, the impact of assuming
flatness in neutrino cosmology is significant and an essential consideration
with future experiments. |
Inflation with shallow dip and primordial black holes: Primordial black holes may arise through ultra slow-roll inflation. In this
work we study a toy model of ultra slow-roll inflation with a shallow dip. The
ultra slow-roll stage enhances the curvature perturbations and thus the
primordial scalar power spectrum. We analyze the features of the power spectrum
numerically and analytically, and then give a rough estimate of the lower and
upper bound of the enhancement. These large perturbations also produce second
order gravitational waves, which are in the scope of future observations. | Dark Matter with N-Body Numerical Simulations: The development of numerical N -body simulations have allowed to study
formation process and evolution of galaxies at different scales. This paper
presents the fundamental concepts of N-body systems applied to the cosmological
evolution of the $\Lambda$-Cold Dark Matter ($\Lambda$CDM) model. In order to
perform structure formation in the Universe, we provide an introduction to the
basic equations and their implementation on the GADGET-2 software. We also
present a simple guide to modify this code. First, we briefly describe the dark
matter in the Universe as well as the theoretical and experimental basis of the
$\Lambda$CDM model. Then, we focus on the simulation codes and provide the
equations that govern most of the N-body simulations to model the dark matter.
We describe the Smoothed Particle Hydrodynamics method used for simulating the
gas, star dynamics and structure formation in these simulations. Then,
cautiously, we guide the reader to the installation of GADGET-2 on a
Linux-based computer, as well as to carry out a couple of examples to operate
the code. Finally, by using a computational cluster, we show several results of
a large structure simulation, analyse the outputs to display the matter power
spectrum, and compare the outcome with theoretical predictions. |
Could fresh lava be (warm) dark matter?: Dark matter models can be classified according to their impact on the
properties of galaxies, including cold dark matter (CDM), warm dark matter
(WDM), self-interacting dark matter (SIDM) and fuzzy dark matter (FDM). In
celebration of April Fool's Day, and also of the 1-year anniversary of the
start of the 2022 volcanic eruption at Fagradalsfjall here in Iceland, we
explore fresh lava as a candidate for WDM specifically. We verify first hand
that lava is indeed warm (exhibits free-streaming and retains temperature for
several months after the eruption ends, is 1000K, sets fire to grass, can feel
one's eyebrows singe at a distance of 4m) and dark once sufficiently decoupled
from its source of production. | Separate Universe Simulations: The large-scale statistics of observables such as the galaxy density are
chiefly determined by their dependence on the local coarse-grained matter
density. This dependence can be measured directly and efficiently in N-body
simulations by using the fact that a uniform density perturbation with respect
to some fiducial background cosmology is equivalent to modifying the background
and including curvature, i.e., by simulating a "separate universe". We derive
this mapping to fully non-linear order, and provide a step-by-step description
of how to perform and analyse the separate universe simulations. This technique
can be applied to a wide range of observables. As an example, we calculate the
response of the non-linear matter power spectrum to long-wavelength density
perturbations, which corresponds to the angle-averaged squeezed limit of the
matter bispectrum and higher $n$-point functions. Using only a modest
simulation volume, we obtain results with percent-level precision over a wide
range of scales. |
Thermal abundance of non-relativistic relics with Sommerfeld enhancement: We propose an analytic treatment for computing the relic abundances of
non-relativistic particles whose annihilation rate at chemical decoupling is
increased by Sommerfeld enhancement. We find approximate rational functions
that closely fit the thermal average of Sommerfeld-enhanced cross sections in
the massless limit of force carriers for s- and p-wave annihilations. We
demonstrate that, with the approximate thermally-averaged cross sections
implemented, the standard analytic method for the final relic abundances
provides accuracy to within 1% even for the case of Sommerfeld enhancement. | The Zurich Environmental Study of Galaxies in Groups along the Cosmic
Web. III. Galaxy Photometric Measurements and the Spatially-Resolved Color
Properties of Early- and Late-Type Satellites in Diverse Environments: We present photometric measurements for the galaxies - and when possible
their bulges and disks - in the 0.05<z<0.0585 groups of the Zurich
Environmental Study (ZENS); these measurements include (B-I) colors, color
gradients and maps, color dispersions, as well as stellar masses and
star-formation rates. The ZENS galaxies are classified into quenched,
moderately star-forming, and strongly star-forming using a combination of
spectral features and FUV-to-optical colors; this approach optimally
distinguishes quenched systems from dust-reddened star-forming galaxies. The
latter contribute up to 50% to the (B-I) "red sequence" at ~10^10Msun. At fixed
morphological or spectral type, we find that galaxy stellar masses are largely
independent of environment, and especially of halo mass. As a first utilization
of our photometric database, we study, at fixed stellar mass and Hubble type,
how (B-I) colors, color gradients and color dispersion of disk satellites
depend on group mass (M_GROUP), group-centric distance (R/R_200) and
large-scale structure overdensity. The strongest environmental trend is found
for disk-dominated satellites with M_GROUP and R/R_200. At M<10^10 Msun,
disk-dominated satellites are redder in the inner regions of the groups than in
the outer parts. At M>10^10 Msun, these satellites have shallower color
gradients in higher mass groups and in the cores of groups compared with lower
mass groups and the outskirts of groups. Stellar population analyses and
semi-analytic models suggest that disk-dominated satellites undergo quenching
of star formation in their outer disks, on timescales ~2 Gyr, as they
progressively move inside the group potential. |
Inferring the redshift of more than 150 GRBs with a Machine Learning
Ensemble model: Gamma-Ray Bursts (GRBs), due to their high luminosities are detected up to
redshift 10, and thus have the potential to be vital cosmological probes of
early processes in the universe. Fulfilling this potential requires a large
sample of GRBs with known redshifts, but due to observational limitations, only
11\% have known redshifts ($z$). There have been numerous attempts to estimate
redshifts via correlation studies, most of which have led to inaccurate
predictions. To overcome this, we estimated GRB redshift via an ensemble
supervised machine learning model that uses X-ray afterglows of long-duration
GRBs observed by the Neil Gehrels Swift Observatory. The estimated redshifts
are strongly correlated (a Pearson coefficient of 0.93) and have a root mean
square error, namely the square root of the average squared error
$\langle\Delta z^2\rangle$, of 0.46 with the observed redshifts showing the
reliability of this method. The addition of GRB afterglow parameters improves
the predictions considerably by 63\% compared to previous results in
peer-reviewed literature. Finally, we use our machine learning model to infer
the redshifts of 154 GRBs, which increase the known redshifts of long GRBs with
plateaus by 94\%, a significant milestone for enhancing GRB population studies
that require large samples with redshift. | Unbiased clustering estimates with the DESI fibre assignment: The Emission Line Galaxy survey made by the Dark Energy Spectroscopic
Instrument (DESI) survey will be created from five passes of the instrument on
the sky. On each pass, the constrained mobility of the ends of the fibres in
the DESI focal plane means that the angular-distribution of targets that can be
observed is limited. Thus, the clustering of samples constructed using a
limited number of passes will be strongly affected by missing targets. In two
recent papers, we showed how the effect of missing galaxies can be corrected
when calculating the correlation function using a weighting scheme for pairs.
Using mock galaxy catalogues we now show that this method provides an unbiased
estimator of the true correlation function for the DESI survey after any number
of passes. We use multiple mocks to determine the expected errors given one to
four passes, compared to an idealised survey observing an equivalent number of
randomly selected targets. On BAO scales, we find that the error is a factor 2
worse after one pass, but that after three or more passes, the errors are very
similar. Thus we find that the fibre assignment strategy enforced by the design
of DESI will not affect the cosmological measurements to be made by the survey,
and can be removed as a potential risk for this experiment. |
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