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Measurement of the halo bias from stacked shear profiles of galaxy
clusters: We present the observational evidence of the 2-halo term in the stacked shear
profile of a sample of about 1200 optically selected galaxy clusters based on
imaging data and the public shear catalog from the CFHTLenS. We find that the
halo bias, a measure of the correlated distribution of matter around galaxy
clusters, has amplitude and correlation with galaxy cluster mass in very good
agreement with the predictions based on the LCDM standard cosmological model.
The mass-concentration relation is flat but higher than theoretical
predictions. We also confirm the close scaling relation between the optical
richness of galaxy clusters and their mass. | Low Surface Brightness Galaxies in the SDSS: the link between
environment, star-forming properties and AGN: Using the Sloan Digital Sky Survey (SDSS) data release 4 (DR 4), we
investigate the spatial distribution of low and high surface brightness
galaxies (LSBGs and HSBGs, respectively). In particular, we focus our attention
on the influence of interactions between galaxies on the star formation
strength in the redshift range $0.01 < z < 0.1$. With cylinder counts and
projected distance to the first and fifth-nearest neighbor as environment
tracers, we find that LSBGs tend to have a lack of companions compared to HSBGs
at small scales ($<2$ Mpc). Regarding the interactions, we have evidence that
the fraction of LSBGs with strong star formation activity increases when the
distance between pairs of galaxies ($r_{p}$) is smaller than about four times
the Petrosian radius ($r_{90}$) of one of the components. Our results suggest
that, rather than being a condition for their formation, the isolation of LSBGs
is more connected with their survival and evolution. The effect of the
interaction on the star formation strength, measured by the average value of
the birthrate parameter $b$, seems to be stronger for HSBGs than for LSBGs. The
analysis of our population of LSBGs and HSBGs hosting an AGN show that,
regardless of the mass range, the fraction of LSBGs having an AGN is lower than
the corresponding fraction of HSBGs with an AGN. Also, we observe that the
fraction of HSBGs and LSBGs having an AGN increases with the bulge luminosity.
These results, and those concerning the star-forming properties of LSBGs as a
function of the environment, fit with the scenario proposed by some authors
where, below a given threshold of surface mass density, low surface brightness
disks are unable to propagate instabilities, preventing the formation and
evolution of massive black holes in the centers of LSBGs. |
Observational tests of Galileon gravity with growth rate: We compare observational data of growth rate with the prediction by Galileon
theory. For the same value of the energy density parameter $\Omega_{m,0}$, the
growth rate in Galileon models is enhanced compared with the $\Lambda$CDM case,
due to the enhancement of Newton's constant. The smaller $\Omega_{m,0}$ is, the
more suppressed growth rate is. Hence the best fit value of $\Omega_{m,0}$ in
the Galileon model is 0.16 from only the growth rate data, which is
considerably smaller than such value obtained from observations of supernovae
Ia, the cosmic microwave background and baryon acoustic oscillations. This
result seems to be qualitatively the same in most of the generalized Galileon
models. We also find the upper limit of the Brans-Dicke parameter to be $\omega
< -40$, from the growth rate data. More and better growth rate data are
required to distinguish between dark energy and modified gravity. | Photometric selection and redshifts for quasars in the Kilo-Degree
Survey Data Release 4: We present a catalog of quasars and corresponding redshifts in the
Kilo-Degree Survey (KiDS) Data Release 4. We trained machine learning (ML)
models, using optical ugri and near-infrared ZYJHK_s bands, on objects known
from Sloan Digital Sky Survey (SDSS) spectroscopy. We define inference subsets
from the 45 million objects of the KiDS photometric data limited to 9-band
detections. We show that projections of the high-dimensional feature space can
be successfully used to investigate the estimations. The model creation employs
two test subsets: randomly selected and the faintest objects, which allows to
fit the bias versus variance trade-off. We tested three ML models: random
forest (RF), XGBoost (XGB), and artificial neural network (ANN). We find that
XGB is the most robust model for classification, while ANN performs the best
for combined classification and redshift. The inference results are tested
using number counts, Gaia parallaxes, and other quasar catalogs. Based on these
tests, we derived the minimum classification probability which provides the
best purity versus completeness trade-off: p(QSO_cand) > 0.9 for r < 22 and
p(QSO_cand) > 0.98 for 22 < r < 23.5. We find 158,000 quasar candidates in the
safe inference subset (r < 22) and an additional 185,000 candidates in the
reliable extrapolation regime (22 < r < 23.5). Test-data purity equals 97% and
completeness is 94%; the latter drops by 3% in the extrapolation to data
fainter by one magnitude than the training set. The photometric redshifts were
modeled with Gaussian uncertainties. The redshift error (mean and scatter)
equals 0.01 +/- 0.1 in the safe subset and -0.0004 +/- 0.2 in the
extrapolation, in a redshift range of 0.14 < z < 3.63. Our success of the
extrapolation challenges the way that models are optimized and applied at the
faint data end. The catalog is ready for cosmology and active galactic nucleus
(AGN) studies. |
HYMALAIA: A Hybrid Lagrangian Model for Intrinsic Alignments: The intrinsic alignment of galaxies is an important ingredient for modelling
weak-lensing measurements, and a potentially valuable cosmological and
astrophysical signal. In this paper, we present HYMALAIA: a new model to
predict the intrinsic alignments of biased tracers. HYMALAIA is based on a
perturbative expansion of the statistics of the Lagrangian shapes of objects,
which is then advected to Eulerian space using the fully non-linear
displacement field obtained from $N$-body simulations. We demonstrate that
HYMALAIA is capable of consistently describing monopole and quadrupole of halo
shape-shape and matter-shape correlators, and that, without increasing the
number of free parameters, it does so more accurately than other perturbatively
inspired models such as the non-linear alignment (NLA) model and the
tidal-alignment-tidal-torquing (TATT) model. | A new way to explore cosmological tensions using gravitational waves and
strong gravitational lensing: In recent years, a crisis in the standard cosmology has been caused by
inconsistencies in the measurements of some key cosmological parameters, Hubble
constant $H_0$ and cosmic curvature parameter $\Omega_K$ for example. It is
necessary to remeasure them with the cosmological model-independent methods. In
this paper, based on the distance sum rule, we present such a way to constrain
$H_0$ and $\Omega_K$ simultaneously in the late universe from strong
gravitational lensing time delay (SGLTD) data and gravitational wave (GW)
standard siren data simulated from the future observation of the Einstein
Telescope (ET). Based on the currently 6 observed SGLTD data, we find that the
constraint precision of $H_0$ from the combined 100 GW events can be comparable
with the measurement from SH0ES collaboration. As the number of GW events
increases to 700, the constraint precision of $H_0$ will exceed that of the
\textit{Planck} 2018 results. Considering 1000 GW events as the conservative
estimation of ET in ten-year observation, we obtain $H_0=73.69\pm 0.36
\mathrm{~km~s^{-1}~Mpc^{-1}}$ with a 0.5\% uncertainty and
$\Omega_K=0.076^{+0.068}_{-0.087}$. In addition, we simulate 55 SGL systems
with 6.6\% uncertainty for the measurement of time-delay distance. By combining
with 1000 GWs, we infer that $H_0=73.65\pm0.35 \mathrm{~km~s^{-1}~Mpc^{-1}}$
and $\Omega_K=0.008\pm0.048$. Our results suggest that this approach can play
an important role in exploring cosmological tensions. |
On Star Formation Rates and Star Formation Histories of Galaxies out to
z ~ 3: We compare multi-wavelength SFR indicators out to z~3 in GOODS-South. Our
analysis uniquely combines U-to-8um photometry from FIREWORKS, MIPS 24um and
PACS 70, 100, and 160um photometry from the PEP survey, and Ha spectroscopy
from the SINS survey. We describe a set of conversions that lead to a
continuity across SFR indicators. A luminosity-independent conversion from 24um
to total infrared luminosity yields estimates of LIR that are in the median
consistent with the LIR derived from PACS photometry, albeit with significant
scatter. Dust correction methods perform well at low to intermediate levels of
star formation. They fail to recover the total amount of star formation in
systems with large SFR_IR/SFR_UV ratios, typically occuring at the highest SFRs
(SFR_UV+IR \gtrsim 100 Msun/yr) and redshifts (z \gtrsim 2.5) probed. Finally,
we confirm that Ha-based SFRs at 1.5<z<2.6 are consistent with SFR_SED and
SFR_UV+IR provided extra attenuation towards HII regions is taken into account
(Av,neb = Av,continuum / 0.44). With the cross-calibrated SFR indicators in
hand, we perform a consistency check on the star formation histories inferred
from SED modeling. We compare the observed SFR-M relations and mass functions
at a range of redshifts to equivalents that are computed by evolving lower
redshift galaxies backwards in time. We find evidence for underestimated
stellar ages when no stringent constraints on formation epoch are applied. We
demonstrate how resolved SED modeling, or alternatively deep UV data, may help
to overcome this bias. The age bias is most severe for galaxies with young
stellar populations, and reduces towards older systems. Finally, our analysis
suggests that SFHs typically vary on timescales that are long (at least several
100 Myr) compared to the galaxies' dynamical time. | Intergalactic Gas in Groups of Galaxies: Implications for Dwarf
Spheroidal Formation and The Missing Baryons Problem: Radio galaxies with bent jets are predominantly located in groups and
clusters of galaxies. We use bent-double radio sources, under the assumption
that their jets are bent by ram-pressure, to probe intragroup medium (IGM) gas
densities in galaxy groups. This method provides a direct measurement of the
intergalactic gas density and allows us to probe IGM gas at large radii and in
systems whose IGM is too cool to be detected by the current generation of X-ray
telescopes. We find gas with densities of 10^(-3)-10^(-4) per cubic centimeter
at group radii from 15-700 kpc. A rough estimate of the total baryonic mass in
intergalactic gas is consistent with the missing baryons being located in the
IGM of galaxy groups. The neutral gas will be easily stripped from dwarf
galaxies with total masses of 10^6-10^7 solar masses in the groups studied
here. Indications are that IGM gas densities in less-massive systems like the
Local Group should be high enough to strip gas from dwarfs like Leo T and, in
combination with tides, produce dwarf spheroidals. |
Embedded Lensing Time Delays, the Fermat Potential, and the Integrated
Sachs-Wolfe Effect: We derive the Fermat potential for a spherically symmetric lens embedded in
an FLRW cosmology and use it to investigate the late-time integrated
Sachs-Wolfe (ISW) effect, i.e., secondary temperature fluctuations in the
cosmic microwave background (CMB) caused by individual large scale clusters and
voids. We present a simple analytical expression for the temperature
fluctuation in the CMB across such a lens as a derivative of the lens' Fermat
potential. This formalism is applicable to both linear and nonlinear density
evolution scenarios, to arbitrarily large density contrasts, and to all open
and closed background cosmologies. It is much simpler to use and makes the same
predictions as conventional approaches. In this approach the total temperature
fluctuation can be split into a time-delay part and an evolutionary part. Both
parts must be included for cosmic structures that evolve and both can be
equally important. We present very simple ISW models for cosmic voids and
galaxy clusters to illustrate the ease of use of our formalism. We use the
Fermat potentials of simple cosmic void models to compare predicted ISW effects
with those recently extracted from WMAP and \emph{Planck} data by stacking
large cosmic voids using the aperture photometry method. If voids in the local
universe with large density contrasts are no longer evolving we find that the
time delay contribution alone predicts values consistent with the measurements.
However, we find that for voids still evolving linearly, the evolutionary
contribution cancels a significant part of the time delay contribution and
results in predicted signals that are much smaller than recently observed. | Cluster cosmology with the NIKA2 SZ Large Program: The main limiting factor of cosmological analyses based on thermal
Sunyaev-Zel'dovich (SZ) cluster statistics comes from the bias and systematic
uncertainties that affect the estimates of the mass of galaxy clusters.
High-angular resolution SZ observations at high redshift are needed to study a
potential redshift or morphology dependence of both the mean pressure profile
and of the mass-observable scaling relation used in SZ cosmological analyses.
The NIKA2 camera is a new generation continuum instrument installed at the IRAM
30-m telescope. With a large field of view, a high angular resolution and a
high-sensitivity, the NIKA2 camera has unique SZ mapping capabilities. In this
paper, we present the NIKA2 SZ large program, aiming at observing a large
sample of clusters at redshifts between 0.5 and 0.9, and the characterization
of the first cluster oberved with NIKA2. |
Metal Enrichment and Reionization Constraints on Early Star Formation: The epoch of reionization and formation of first stars are inter-linked
topics that are of considerable interest. We use a simplified approach for
studying formation of stars in collapsed haloes, and the resulting ionization
of the inter-galactic medium (IGM). We consider a set of LCDM models allowed by
observations of CMB temperature and polarization anisotropies for this study.
We constrain parameters related to star formation with the help of
observations. We constrain subsets of these parameters independently by using
the observed metallicity of the inter-galactic medium at z ~ 5 and the
requirement that the Thomson scattering optical depth due to an ionized IGM as
determined for the model from CMB observations be reproduced. We consider a
range of initial metalicities for star forming gas, and some variations of the
initial mass function of stars. We find that a "normal" initial mass function
(IMF) may satisfy these two constraints with a raised efficiency of star
formation as compared to that seen in the local universe. Observations require
a significant fraction of metals to escape from haloes to the IGM. We can also
place constraints on the ratio of escape fraction for metals and ionizing
photons, we find that this ratio is of order unity for most models. This
highlights the importance of using the constraints arising from enrichment of
the inter-galactic medium. (Abridged) | Parameters Estimation from the 21 cm signal using Variational Inference: Upcoming experiments such as Hydrogen Epoch of Reionization Array (HERA) and
Square Kilometre Array (SKA) are intended to measure the 21cm signal over a
wide range of redshifts, representing an incredible opportunity in advancing
our understanding about the nature of cosmic Reionization. At the same time
these kind of experiments will present new challenges in processing the
extensive amount of data generated, calling for the development of automated
methods capable of precisely estimating physical parameters and their
uncertainties. In this paper we employ Variational Inference, and in particular
Bayesian Neural Networks, as an alternative to MCMC in 21 cm observations to
report credible estimations for cosmological and astrophysical parameters and
assess the correlations among them. |
Coupled quintessence with a $Λ$CDM background: removing the
$σ_8$ tension: A well-known problem of the $\Lambda$CDM model is the tension between the
relatively high level of clustering, as quantified by the parameter $\sigma_8$,
found in cosmic microwave background experiments and the smaller one obtained
from large-scale observations in the late Universe. In this paper we show that
coupled quintessence, i.e. a single dark energy scalar field conformally
coupled to dark matter through a constant coupling, can solve this problem if
the background is taken to be identical to the $\Lambda$CDM one. We show that
two competing effects arise. On one hand, the additional scalar force is
attractive, and is therefore expected to increase the clustering. On the other,
in order to obtain the same background as $\Lambda$CDM, coupled quintessence
must have a smaller amount of dark matter near the present epoch. We show that
the second effect is dominating today and leads to an overall slower growth.
Comparing to redshift distortion data, we find that coupled quintessence with
$\Lambda$CDM background solves the tension between early and late clustering.
We find for the coupling $\beta$ and for $\sigma_8$ the best fit values
$|\beta| = 0.079^{+ 0.059}_{- 0.067}$ and $\sigma_8 = 0.818^{+0.115}_{-0.088}$.
These values also fit the lensing data from the KiDS-450 survey. We also
estimate that the future missions SKA and Euclid will constrain $\beta$ with an
error of $\pm\, 1.5\times10^{-3}$ and for $\sigma_8$ of $\pm
\,1.8\times10^{-3}$ at $1\sigma$ level. | Revisiting constraints on asymmetric dark matter from collapse in white
dwarf stars: The runaway collapse phase of a small dark matter cluster inside a white
dwarf star encompasses a reversible stage, where heat can be transferred back
and forth between nuclear and dark matter. Induced nuclear burning phases are
stable and early carbon depletion undermines previous claims of type Ia
supernova ignition. Instead, mini black holes are formed at the center of the
star that either evaporate or accrete stellar material until a macroscopic
sub-Chandrasekhar-mass black hole is formed. In the latter case, a 0.1 to 1
second lasting electromagnetic transient signal can be detected upon ejection
of the white dwarf's potential magnetic field. Binary systems that transmute to
black holes and subsequently merge emit gravitational waves. Advanced
LIGO/Virgo should detect one such sub-Chandrasekhar binary black hole inspiral
per year, while future Einstein telescope-like facilities will detect thousands
per year. The effective spin parameter distribution is peaked at 0.2 and
permits future studies to disentangle from primordial sub-Chandrasekhar black
holes. Such signatures are compatible with current direct detection
constraints, as well as with neutron star constraints in the case of bosonic
dark matter, even though they remain in conflict with the fermionic case for
part of the parameter space. |
The average 0.5-200 keV spectrum of local active galactic nuclei and a
new determination of the 2-10 keV luminosity function at z \approx 0: The broadband X-ray spectra of AGNs contains information about the nuclear
environment from Schwarzschild radii scales to distances of ~1 pc. In addition,
the average shape of the X-ray spectrum is an important input into X-ray
background synthesis models. Here, local (z \approx 0) AGN luminosity functions
(LFs) in five energy bands are used as a low-resolution, luminosity-dependent
X-ray spectrometer in order to constrain the average AGN X-ray spectrum between
0.5 and 200 keV. The 15-55 keV LF measured by Swift-BAT is assumed to be the
best determination of the local LF, and then a spectral model is varied to
determine the best fit to the 0.5-2 keV, 2-10 keV, 3-20 keV and 14-195 keV LFs.
The spectral model consists of a Gaussian distribution of power-laws with a
mean photon-index <\Gamma> and cutoff energy E_cut, as well as contributions
from distant and disc reflection. The reflection strength is parameterised by
varying the Fe abundance relative to solar, A_Fe, and requiring a specific Fe K
equivalent width (EW). In this way, the presence of the X-ray Baldwin effect
can be tested. The spectral model that best fits the four LFs has <\Gamma> =
1.85 \pm 0.15, E_cut=270^{+170}_{-80} keV, A_Fe=0.3^{+0.3}_{-0.15} (90% C.L.).
The sub-solar A_Fe indicates the presence of strong reflection given the
assumed Fe K EW. Indeed, parameterising the reflection strength with the R
parameter gives R=1.7^{+1.7}_{-0.85}. There is moderate evidence for no X-ray
Baldwin effect. A critical result of our procedure is that the shape of the
local 2-10 keV LF measured by HEAO-1 and MAXI is incompatible with the LFs
measured in the hard X-rays by Swift-BAT and RXTE. We therefore present a new
determination of the local 2-10 keV LF that is consistent with all other energy
bands.This new LF should be used to revise current measurements of the evolving
AGN LF in the 2-10 keV band. | Null test of the cosmic curvature using $H(z)$ and supernovae data: We introduce a model-independent approach to the null test of the cosmic
curvature which is geometrically related to the Hubble parameter $H(z)$ and
luminosity distance $d_L(z)$. Combining the independent observations of $H(z)$
and $d_L(z)$, we use the model-independent smoothing technique, Gaussian
processes, to reconstruct them and determine the cosmic curvature
$\Omega_K^{(0)}$ in the null test relation. The null test is totally
geometrical and without assuming any cosmological model. We show that the
cosmic curvature $\Omega_K^{(0)}=0$ is consistent with current observational
data sets, falling within the $1\sigma$ limit. To demonstrate the effect on the
precision of the null test, we produce a series of simulated data of the models
with different $\Omega_K^{(0)}$. Future observations in better quality can
provide a greater improvement to constrain or refute the flat universe with
$\Omega_K^{(0)}=0$. |
High resolution deep imaging of a bright radio quiet QSO at z~3: We have obtained deep J & Ks-band images centered on a bright radio quiet QSO
UM402 (z_{em}=2.856) using IRCS camera and AO systems on Subaru Telescope, as
well as retrieved WFC3/F140W archive images. A faint galaxy (m_{k}=23.32 +/-
0.05 in the Vega system) that lies ~ 2.4" north of the QSO sightline has been
clearly resolved in all three deep high resolution datasets, and appears as an
irregular galaxy with two close components in the Ks-band images (separation ~
0.3"). Given the small impact parameter (b=19.6 kpc, at z_{lls}=2.531), as well
as the red color of (J-Ks)_{vega} ~ 1.6, it might be a candidate galaxy giving
rise to the Lyman Limit system absorption at z_{abs}=2.531 seen in the QSO
spectrum. After carefully subtracting the PSF from the QSO images, the host
galaxy of this bright radio quiet QSO at z ~ 3 was marginally revealled. We
placed a low limit of the host component of m_{k} ~ 23.3 according to our
analyses. | A study of six low redshift QSO pairs: The dynamical properties of six SDSS quasar pairs at z < 0.8 are
investigated. The pairs have proper transverse separation < 500 kpc, and
velocity difference along the line of sight < 500 km/s. If they are bound
systems their dynamical mass can be evaluated and compared with that of host
galaxies. Evidence is found of an excess of the former mass with respect to the
latter. This suggests that these quasar pairs are hosted by galaxies with
massive dark halos or that they reside in a group/cluster of galaxies. |
How chameleons core dwarfs with cusps: The presence of a scalar field that couples nonminimally and universally to
matter can enhance gravitational forces on cosmological scales while restoring
general relativity in the Solar neighborhood. In the intermediate regime,
kinematically inferred masses experience an additional radial dependence with
respect to the underlying distribution of matter, which is caused by the
increment of gravitational forces with increasing distance from the Milky Way
center. The same effect can influence the internal kinematics of subhalos and
cause cuspy matter distributions to appear core-like. Specializing to the
chameleon model as a worked example, we demonstrate this effect by tracing the
scalar field from the outskirts of the Milky Way halo to its interior,
simultaneously fitting observed velocity dispersions of chemo-dynamically
discriminated red giant populations in the Fornax and Sculptor dwarf
spheroidals. Whereas in standard gravity these observations suggest that the
matter distribution of the dwarfs is cored, we find that in the presence of a
chameleon field the assumption of a cuspy Navarro-Frenk-White profile becomes
perfectly compatible with the data. Importantly, chameleon models also predict
the existence of slopes between two stellar subcomponents that in Newtonian
gravity would be interpreted as a depletion of matter in the dwarf center.
Hence, an observation of such an apparently pathological scenario may serve as
a smoking gun for the presence of a chameleon field or a similar modification
of gravity, independent of baryonic feedback effects. In general, measuring the
dynamic mass profiles of the Milky Way dwarfs provides stronger constraints
than those inferred from the screening scale of the Solar System since these
are located at greater distances from the halo center. | Testing a prediction of the merger origin of early-type galaxies: a
correlation between stellar populations and asymmetry: One of the key predictions of the merger hypothesis for the origin of
early-type (elliptical and lenticular) galaxies is that tidally-induced
asymmetric structure should correlate with signatures of a relatively young
stellar population. Such a signature was found by Schweizer and Seitzer (1992;
AJ, 104, 1039) at roughly 4sigma confidence. In this paper, we revisit this
issue with a nearly ten-fold larger sample of 0.01<z<0.03 galaxies selected
from the Two Micron All-Sky Survey and the Sloan Digital Sky Survey. We
parameterize tidal structure using a repeatable algorithmic measure of
asymmetry, and correlate this with color offset from the early-type galaxy
color-magnitude relation. We recover the color offset-asymmetry correlation;
furthermore, we demonstrate observationally for the first time that this effect
is driven by a highly-significant trend towards younger ages at higher
asymmetry values. We present a simple model for the evolution of early-type
galaxies through gas-rich major and minor mergers that reproduces their
observed build-up from z=1 to the present day and the distribution of
present-day colors and ages. We show using this model that if both stellar
populations and asymmetry were ideal `clocks' measuring the time since last
major or minor gas-rich interaction, then we would expect a rather tight
correlation between age and asymmetry. We suggest that the source of extra
scatter is natural diversity in progenitor star formation history, gas content,
and merger mass ratio, but quantitative confirmation of this conjecture will
require sophisticated modeling. We conclude that the asymmetry-age correlation
is in basic accord with the merger hypothesis, and indicates that an important
fraction of the early-type galaxy population is affected by major or minor
mergers at cosmologically-recent times. |
The dust scaling relations of the Herschel Reference Survey: We combine new Herschel/SPIRE sub-millimeter observations with existing
multiwavelength data to investigate the dust scaling relations of the Herschel
Reference Survey, a magnitude-, volume-limited sample of ~300 nearby galaxies
in different environments. We show that the dust-to-stellar mass ratio
anti-correlates with stellar mass, stellar mass surface density and NUV-r
colour across the whole range of parameters covered by our sample. Moreover,
the dust-to-stellar mass ratio decreases significantly when moving from late-
to early-type galaxies. These scaling relations are similar to those observed
for the HI gas-fraction, supporting the idea that the cold dust is tightly
coupled to the cold atomic gas component in the interstellar medium. We also
find a weak increase of the dust-to-HI mass ratio with stellar mass and colour
but no trend is seen with stellar mass surface density. By comparing galaxies
in different environments we show that, although these scaling relations are
followed by both cluster and field galaxies, HI-deficient systems have, at
fixed stellar mass, stellar mass surface density and morphological type
systematically lower dust-to-stellar mass and higher dust-to-HI mass ratios
than HI-normal/field galaxies. This provides clear evidence that dust is
removed from the star-forming disk of cluster galaxies but the effect of the
environment is less strong than what is observed in the case of the HI disk.
Such effects naturally arise if the dust disk is less extended than the HI and
follows more closely the distribution of the molecular gas phase, i.e., if the
dust-to-atomic gas ratio monotonically decreases with distance from the
galactic center. | Maximum brightness temperature for an incoherent synchrotron radio
source: We discuss here a limit on the maximum brightness temperature achievable for
an incoherent synchrotron radio source. This limit, commonly referred to in the
literature as an inverse Compton limit, prescribes that the brightness
temperature for an incoherent synchrotron radio source may not exceed ~10^{12}
K, a fact known from observations. However one gets a somewhat tighter limit on
the brightness temperatures, T_{b}~10^{11.5} K, independent of the inverse
Compton effects, if one employs the condition of equipartition of energy in
magnetic fields and relativistic particles in a synchrotron radio source. Pros
and cons of the two brightness temperature limits are discussed. |
Joint reconstructions of growth and expansion histories from stage-IV
surveys with minimal assumptions I: Dark Energy beyond $Λ$: Combining Supernovae, Baryon Acoustic Oscillations and Redshift-Space
Distortions data from the next generation of (Stage-IV) cosmological surveys,
we aim to reconstruct the expansion history up to large redshifts using
forward-modeling of $f_{\mathrm DE}(z) =
\rho_\mathrm{DE}(z)/\rho_\mathrm{DE,0}$ with Gaussian processes (GP). In order
to reconstruct cosmological quantities at high redshifts where few or no data
are available, we adopt a new approach to GP which enforces the following
minimal assumptions: a) Our cosmology corresponds to a flat
Friedman-Lema\^itre-Robertson-Walker (FLRW) universe; b) An Einstein de Sitter
(EdS) universe is obtained on large redshifts. This allows us to reconstruct
the perturbations growth history from the reconstructed background expansion
history. Assuming various DE models, we show the ability of our reconstruction
method to differentiate them from $\Lambda$CDM at $\gtrsim2\sigma$. | The relationship between the neutral hydrogen and dark mass in the
galaxies: Starting from Bosma' (1981) paper, it was demonstrated by different authors
that the observed shape of rotation curves of many spiral galaxies can be
explained if to assume that the radial density distribution of the dark matter
is correlated with the distribution of $HI$: the column densities of the dark
matter and $HI$ are proportional. We show that this correlation is obviously to
be an artifact and can be explained by assuming that the gas surface density is
approximately equal or in general proportional to the critical density for the
local gravitational stability of gaseous layer. |
Simulation techniques for modified gravity: The standard paradigm of cosmology assumes General Relativity (GR) is a valid
theory for gravity at scales in which it has not been properly tested.
Developing novel tests of GR and its alternatives is crucial if we want to give
strength to the model or find departures from GR in the data. Since
alternatives to GR are usually defined through nonlinear equations, designing
new tests for these theories implies a jump in complexity and thus, a need for
refining the simulation techniques. We summarize existing techniques for
dealing with modified gravity (MG) in the context of cosmological simulations.
$N$-body codes for MG are usually based on standard gravity codes. We describe
the required extensions, classifying the models not according to their original
motivation, but by the numerical challenges that must be faced by numericists.
MG models usually give rise to elliptic equations, for which multigrid
techniques are well suited. Thus, we devote a large fraction of this review to
describing this particular technique. Contrary to other reviews on multigrid
methods, we focus on the specific techniques that are required to solve MG
equations and describe useful tricks. Finally, we describe extensions for going
beyond the static approximation and dealing with baryons. | The Distortion of the Cosmic Microwave Background by the Milky Way: The Milky Way can act as a large-scale weak gravitational lens of the cosmic
microwave background (CMB). We study this effect using a photon ray-tracing
code and a Galactic mass distribution with disk, bulge and halo components. For
an observer at the Sun's coordinates in the Galaxy, the bending of CMB photon
paths is limited to less than one arcsecond, and only for rays that pass within
a few degrees of the Galactic Center. However, the entire sky is affected,
resulting in global distortions of the CMB on large angular scales. These
distortions can cause the low-order multipoles of a spherical harmonic
expansion of the CMB sky temperature to leak into higher-order modes. Thus the
component of the CMB dipole that results from the Local Group's motion relative
to the local cosmic frame of rest contributes to higher-order moments for an
observer in the solar system. With our ray-tracing code we show that the
phenomenon is not sensitive to the specific choice of Galactic potential. We
also quantitatively rule it out as a contributor to CMB anomalies such as power
asymmetry or correlated alignment of low-order multipole moments. |
$\texttt{Hi-COLA}$: Fast, approximate simulations of structure formation
in Horndeski gravity: We introduce $\texttt{Hi-COLA}$, a code designed to run fast, approximate
$\textit{N}$-body simulations of non-linear structure formation in reduced
Horndeski gravity. Given an input Lagrangian, $\texttt{Hi-COLA}$ dynamically
constructs the appropriate field equations and consistently solves for the
cosmological background, linear growth, and screened fifth force of that
theory. Hence $\texttt{Hi-COLA}$ is a general, adaptable, and useful tool that
allows the mildly non-linear regime of many Horndeski theories to be
investigated for the first time, at low computational cost. In this work, we
first describe the screening approximations and simulation setup of
$\texttt{Hi-COLA}$ for theories with Vainshtein screening. We validate the code
against traditional $\textit{N}$-body simulations for cubic Galileon gravity,
finding $2.5\%$ agreement up to $k_{\rm max}=1.2~h/{\rm Mpc}$. To demonstrate
the flexibility of $\texttt{Hi-COLA}$, we additionally run the first
simulations of an extended shift-symmetric gravity theory. We use the
consistency and modularity of $\texttt{Hi-COLA}$ to dissect how the modified
background, linear growth, and screened fifth force all contribute to
departures from $\Lambda$CDM in the non-linear matter power spectrum.
$\texttt{Hi-COLA}$ can be found at https://github.com/Hi-COLACode/Hi-COLA . | Bounding the mass of graviton in a dynamic regime with binary pulsars: In Einstein's general relativity, gravity is mediated by a massless spin-2
metric field, and its extension to include a mass for the graviton has profound
implication for gravitation and cosmology. In 2002, Finn and Sutton used the
gravitational-wave (GW) back-reaction in binary pulsars, and provided the first
bound on the mass of graviton. Here we provide an improved analysis using 9
well-timed binary pulsars with a phenomenological treatment. First, individual
mass bounds from each pulsar are obtained in the frequentist approach with the
help of an ordering principle. The best upper limit on the graviton mass,
$m_{g}<3.5\times10^{-20} \, {\rm eV}/c^{2}$ (90% C.L.), comes from the
Hulse-Taylor pulsar PSR B1913+16. Then, we combine individual pulsars using the
Bayesian theorem, and get $m_{g}<5.2\times10^{-21} \, {\rm eV}/c^{2}$ (90%
C.L.) with a uniform prior for $\ln m_g$. This limit improves the Finn-Sutton
limit by a factor of more than 10. Though it is not as tight as those from GWs
and the Solar System, it provides an independent and complementary bound from a
dynamic regime. |
Ultra-high precision cosmology from gravitational waves: We show that the Big Bang Observer (BBO), a proposed space-based
gravitational-wave (GW) detector, would provide ultra-precise measurements of
cosmological parameters. By detecting ~300,000 compact-star binaries, and
utilizing them as standard sirens, BBO would determine the Hubble constant to
0.1%, and the dark energy parameters w_0 and w_a to ~0.01 and 0.1,resp. BBO's
dark-energy figure-of-merit would be approximately an order of magnitude better
than all other proposed dark energy missions. To date, BBO has been designed
with the primary goal of searching for gravitational waves from inflation. To
observe this inflationary background, BBO would first have to detect and
subtract out ~300,000 merging compact-star binaries, out to z~5. It is
precisely this foreground which would enable high-precision cosmology. BBO
would determine the luminosity distance to each binary to ~percent accuracy.
BBO's angular resolution would be sufficient to uniquely identify the host
galaxy for most binaries; a coordinated optical/infrared observing campaign
could obtain the redshifts. Combining the GW-derived distances and EM-derived
redshifts for such a large sample of objects leads to extraordinarily tight
constraints on cosmological parameters. Such ``standard siren'' measurements of
cosmology avoid many of the systematic errors associated with other techniques.
We also show that BBO would be an exceptionally powerful gravitational lensing
mission, and we briefly discuss other astronomical uses of BBO. | The Stellar and Gas Kinematics of the LITTLE THINGS Dwarf Irregular
Galaxy NGC 1569: In order to understand the formation and evolution of dIm galaxies, one needs
to understand their three-dimensional structure. We present measurements of the
stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy.
The stellar vertical velocity dispersion, $\sigma_{\rm z}$, coupled with the
maximum rotational velocity derived from \ion{H}{1} observations, $V_{\rm
max}$, gives a measure of how kinematically hot the galaxy is, and, therefore,
indicates its structure. We conclude that the stars in NGC 1569 are in a thick
disk with a $V_{\rm max} / \sigma_{\rm z}$ = 2.4 $\pm$ 0.7. In addition to the
structure, we analyze the ionized gas kinematics from \ion{O}{3} observations
along the morphological major axis. These data show evidence for outflow from
the inner starburst region and a potential expanding shell near supermassive
star cluster (SSC) A. When compared to the stellar kinematics, the velocity
dispersion of the stars increase in the region of SSC A supporting the
hypothesis of an expanding shell. The stellar kinematics closely follow the
motion of the gas. Analysis of high resolution \ion{H}{1} data clearly reveals
the presence of an \ion{H}{1} cloud that appears to be impacting the eastern
edge of NGC 1569. Also, an ultra-dense \ion{H}{1} cloud can be seen extending
to the west of the impacting \ion{H}{1} cloud. This dense cloud is likely the
remains of a dense \ion{H}{1} bridge that extended through what is now the
central starburst area. The impacting \ion{H}{1} cloud was the catalyst for the
starburst, thus turning the dense gas into stars over a short timescale, $\sim$
1 Gyr. We performed a careful study of the spectral energy distribution using
infrared, optical, and ultraviolet photometry producing a state-of-the-art mass
model for the stellar disk. This mass modeling shows that stars dominate the
gravitational potential in the inner 1 kpc. |
Model-independent analyses of non-Gaussianity in Planck CMB maps using
Minkowski Functionals: Despite the wealth of $Planck$ results, there are difficulties in
disentangling the primordial non-Gaussianity of the Cosmic Microwave Background
(CMB) from the secondary and the foreground non-Gaussianity (NG). For each of
these forms of NG the lack of complete data introduces model-dependencies.
Aiming at detecting the NGs of the CMB temperature anisotropy $\delta T$, while
paying particular attention to a model-independent quantification of NGs, our
analysis is based upon statistical and morphological univariate descriptors,
respectively: the probability density function $P(\delta T)$, related to
${\mathrm v}_{0}$, the first Minkowski Functional (MF), and the two other MFs,
${\mathrm v}_{1}$ and ${\mathrm v}_{2}$. From their analytical Gaussian
predictions we build the discrepancy functions $\Delta_{k}$ ($k=P,0,1,2$) which
are applied to an ensemble of $10^{5}$ CMB realization maps of the $\Lambda$CDM
model and to the $Planck$ CMB maps. In our analysis we use general Hermite
expansions of the $\Delta_{k}$ up to the $12^{th}$ order, where the
coefficients are explicitly given in terms of cumulants. Assuming hierarchical
ordering of the cumulants, we obtain the perturbative expansions generalizing
the $2^{nd}$ order expansions of Matsubara to arbitrary order in the standard
deviation $\sigma_0$ for $P(\delta T)$ and ${\mathrm v}_0$, where the
perturbative expansion coefficients are explicitly given in terms of complete
Bell polynomials. The comparison of the Hermite expansions and the perturbative
expansions is performed for the $\Lambda$CDM map sample and the $Planck$ data.
We confirm the weak level of non-Gaussianity ($1$-$2$)$\sigma$ of the
foreground corrected masked $Planck$ $2015$ maps. | An Optical Observational Cluster Mass Function at $z\sim1$ with the
ORELSE Survey: We present a new mass function of galaxy clusters and groups using
optical/near-infrared wavelength spectroscopic and photometric data from the
Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey.
At $z\sim1$, cluster mass function studies are rare regardless of wavelength
and have never been attempted from an optical/near-infrared perspective. This
work serves as a proof of concept that $z\sim1$ cluster mass functions are
achievable without supplemental X-ray or Sunyaev-Zel'dovich (SZ) data.
Measurements of the cluster mass function provide important contraints on
cosmological parameters and are complementary to other probes. With ORELSE, a
new cluster finding technique based on Voronoi tessellation Monte-Carlo (VMC)
mapping, and rigorous purity and completeness testing, we have obtained
$\sim$240 galaxy overdensity candidates in the redshift range $0.55<z<1.37$ at
a mass range of $13.6<\log(M/M_{\odot})<14.8$. This mass range is comparable to
existing optical cluster mass function studies for the local universe. Our
candidate numbers vary based on the choice of multiple input parameters related
to detection and characterization in our cluster finding algorithm, which we
incorporated into the mass function analysis through a Monte-Carlo scheme. We
find cosmological constraints on the matter density of $\Omega_{m} =
0.250^{+0.104}_{-0.099}$ and on the amplitude of fluctuations of $\sigma_{8} =
1.150^{+0.260}_{-0.163}$. While our $\Omega_{m}$ value is close to concordance,
our $\sigma_{8}$ value is $\sim2\sigma$ higher because of the inflated observed
number densities compared to theoretical mass function models owing to how our
survey targeted overdense regions. With Euclid and several other large,
unbiased optical surveys on the horizon, VMC mapping will enable optical/NIR
cluster cosmology at redshifts much higher than what has been possible before. |
Radio Emission and AGN Feedback in Post-starburst Galaxies: We investigate radio-mode AGN activity among post-starburst galaxies from the
Sloan Digital Sky Survey to determine whether AGN feedback may be responsible
for the cessation of star formation. Based on radio morphology and
radio-loudness from the FIRST and NVSS data, we separate objects with radio
activity due to an AGN from ongoing residual star formation. Of 513 SDSS
galaxies with strong A-star spectra, 12 objects have 21-cm flux density above 1
mJy. These galaxies do not show optical AGN emission lines. Considering that
the lifetime of radio emission is much shorter than the typical time-scale of
the spectroscopic features of post-starburst galaxies, we conclude that the
radio-emitting AGN activity in these objects was triggered after the end of the
recent starburst, and thus cannot be an important feedback process to explain
the post-starburst phase. The radio luminosities show a positive correlation
with total galaxy stellar mass, but not with the mass of recently formed stars.
Thus the mechanical power of AGN feedback derived from the radio luminosity is
related to old stellar populations dominating the stellar mass, which in turn
are related to the masses of central supermassive black holes. | A multifrequency method based on the Matched Multifilter for the
detection of point sources in CMB maps: In this work we deal with the problem of simultaneous multifrequency
detection of extragalactic point sources in maps of the Cosmic Microwave
Background. We apply a linear filtering technique that uses spatial information
and the cross-power spectrum. To make this, we simulate realistic and
non-realistic flat patches of the sky at two frequencies of Planck: 44 and 100
GHz. We filter to detect and estimate the point sources and compare this
technique with the monofrequency matched filter in terms of completeness,
reliability, flux and spectral index accuracy. The multifrequency method
outperforms the matched filter at the two frequencies and in all the studied
cases in the work. |
General Relativistic Corrections to the Weak Lensing Convergence Power
Spectrum: We compute the weak lensing convergence power spectrum,
$C^{\kappa\kappa}(\theta)$, in a dust-filled universe using fully non-linear
general relativistic simulations. The spectrum is then compared to more
standard, approximate calculations by computing the Bardeen (Newtonian)
potentials in linearized gravity and utilizing the Born approximation. We find
corrections to the angular power spectrum amplitude of order ten percent at
very large angular scales, $\ell ~ 2-3$, and percent-level corrections at
intermediate angular scales of $\ell ~ 20-30$. | Full-shape BOSS constraints on dark matter interacting with dark
radiation and lifting the $S_8$ tension: In this work we derive constraints on interacting dark matter-dark radiation
models from a full-shape analysis of BOSS-DR12 galaxy clustering data, combined
with Planck legacy cosmic microwave background (CMB) and baryon acoustic
oscillation (BAO) measurements. We consider a set of models parameterized
within the effective theory of structure formation (ETHOS), quantifying the
lifting of the $S_8$ tension in view of KiDS weak-lensing results. The most
favorable scenarios point to a fraction $f\sim 10-100\%$ of interacting dark
matter as well as a dark radiation temperature that is smaller by a factor
$\xi\sim 0.1-0.15$ compared to the CMB, leading to a reduction of the tension
to the $\sim 1\sigma$ level. The temperature dependence of the interaction rate
favored by relaxing the $S_8$ tension is realized for a weakly coupled unbroken
non-Abelian $SU(N)$ gauge interaction in the dark sector. To map our results
onto this $SU(N)$ model, we compute higher-order corrections due to Debye
screening. We find a lower bound $\alpha_d\equiv g_d^2/(4\pi)\gtrsim 10^{-8}
(10^{-9})$ for dark matter mass $1000 (1)$ GeV for relaxing the $S_8$ tension,
consistent with upper bounds from galaxy ellipticities and compatible with
self-interactions relevant for small-scale structure formation. |
Probing the anisotropy and non-Gaussianity in redshift space through the
derivative of excursion set moments: Focusing on the redshift space observations with plane-parallel approximation
and relying on the rotational dependency of the general definition of excursion
sets, we introduce the so-called conditional moments of the first derivative
($cmd$) measures for the smoothed matter density field in $3$-Dimension. We
derive the perturbative expansion of $cmd$ for real space and redshift space
where peculiar velocity disturbs the galaxies' observed locations. Our criteria
can successfully recognize the contribution of linear Kaiser and Finger of God
effects. Our results demonstrate that the $cmd$ measure has significant
sensitivity for pristine constraining the redshift space distortion parameter
$\beta=f/b$ and interestingly, the associated normalized quantity in the
Gaussian linear Kaiser limit has only $\beta$-dependency. Implementation of the
synthetic anisotropic Gaussian field approves the consistency between the
theoretical and numerical results. Including the first-order contribution of
non-Gaussianity perturbatively in the $cmd$ criterion implies that the N-body
simulations for the Quijote suite in redshift space has been mildly skewed with
a higher value for the threshold greater than zero. The non-Gaussianity for the
perpendicular direction to the line of sight in the redshift space for
smoothing scales $R\gtrsim 20$ Mpc/h is almost the same as the real space,
while the non-Gaussianity for along to the line of sight direction in redshift
space is magnified. | Dark Radiation and Inflationary Freedom: A relaxed primordial power spectrum (PPS) of scalar perturbations arising
from inflation can impact the dark radiation constraints obtained from Cosmic
Microwave Background and other cosmological measurements. If inflation produces
a non-standard PPS for the initial fluctuations, a fully thermalized light
sterile neutrino can be favoured by CMB observations, instead of being strongly
disfavoured. In the case of a thermal axion, the constraints on the axion mass
are relaxed when the PPS is different from the standard power law. |
Probing the evolution of the substructure frequency in galaxy clusters
up to z~1: Context. Galaxy clusters are the last and largest objects to form in the
standard hierarchical structure formation scenario through merging of smaller
systems. The substructure frequency in the past and present epoch provides
excellent means for studying the underlying cosmological model. Aims. Using
X-ray observations, we study the substructure frequency as a function of
redshift by quantifying and comparing the fraction of dynamically young
clusters at different redshifts up to z=1.08. We are especially interested in
possible biases due to the inconsistent data quality of the low-z and high-z
samples. Methods. Two well-studied morphology estimators, power ratio P3/P0 and
center shift w, were used to quantify the dynamical state of 129 galaxy
clusters, taking into account the different observational depth and noise
levels of the observations. Results. Owing to the sensitivity of P3/P0 to
Poisson noise, it is essential to use datasets with similar photon statistics
when studying the P3/P0-z relation. We degraded the high-quality data of the
low-redshift sample to the low data quality of the high-z observations and
found a shallow positive slope that is, however, not significant, indicating a
slightly larger fraction of dynamically young objects at higher redshift. The
w-z relation shows no significant dependence on the data quality and gives a
similar result. Conclusions. We find a similar trend for P3/P0 and w, namely a
very mild increase of the disturbed cluster fraction with increasing redshifts.
Within the significance limits, our findings are also consistent with no
evolution. | Tracing the Sources of Reionization in Cosmological Radiation
Hydrodynamics Simulations: We use the photon flux and absorption tracer algorithm presented in Katz et
al.~2018, to characterise the contribution of haloes of different mass and
stars of different age and metallicity to the reionization of the Universe. We
employ a suite of cosmological multifrequency radiation hydrodynamics AMR
simulations that are carefully calibrated to reproduce a realistic reionization
history and galaxy properties at $z \geq 6$. In our simulations, haloes with
mass $10^9{\rm M_{\odot}}h^{-1}<M<10^{10}{\rm M_{\odot}}h^{-1}$, stars with
metallicity $10^{-3}Z_{\odot}<Z<10^{-1.5}Z_{\odot}$, and stars with age
$3\,{\rm Myr} < t < 10 \, {\rm Myr}$ dominate reionization by both mass and
volume. We show that the sources that reionize most of the volume of the
Universe by $z=6$ are not necessarily the same sources that dominate the
meta-galactic UV background at the same redshift. We further show that in our
simulations, the contribution of each type of source to reionization is not
uniform across different gas phases. The IGM, CGM, filaments, ISM, and rarefied
supernova heated gas have all been photoionized by different classes of
sources. Collisional ionisation contributes at both the lowest and highest
densities. In the early stages of the formation of individual HII bubbles,
reionization proceeds with the formation of concentric shells of gas ionised by
different classes of sources, leading to large temperature variations as a
function of galacto-centric radius. The temperature structure of individual HII
bubbles may thus give insight into the star formation history of the galaxies
acting as the first ionising sources. Our explorative simulations highlight how
the complex nature of reionization can be better understood by using our photon
tracer algorithm. |
Improving the Estimation of Star formation Rates and Stellar Population
Ages of High-redshift Galaxies from Broadband Photometry: We explore methods to improve the estimates of star formation rates and mean
stellar population ages from broadband photometry of high redshift star-forming
galaxies. We use synthetic spectral templates with a variety of simple
parametric star formation histories to fit broadband spectral energy
distributions. These parametric models are used to infer ages, star formation
rates and stellar masses for a mock data set drawn from a hierarchical
semi-analytic model of galaxy evolution. Traditional parametric models
generally assume an exponentially declining rate of star-formation after an
initial instantaneous rise. Our results show that star formation histories with
a much more gradual rise in the star formation rate are likely to be better
templates, and are likely to give better overall estimates of the age
distribution and star formation rate distribution of Lyman break galaxies. For
B- and V-dropouts, we find the best simple parametric model to be one where the
star formation rate increases linearly with time. The exponentially-declining
model overpredicts the age by 100 % and 120 % for B- and V-dropouts, on
average, while for a linearly-increasing model, the age is overpredicted by 9 %
and 16 %, respectively. Similarly, the exponential model underpredicts
star-formation rates by 56 % and 60 %, while the linearly-increasing model
underpredicts by 15 % 22 %, respectively. For U-dropouts, the models where the
star-formation rate has a peak (near z ~ 3) provide the best match for age --
overprediction is reduced from 110 % to 26 % -- and star-formation rate --
underprediction is reduced from 58 % to 22 %. We classify different types of
star-formation histories in the semi-analytic models and show how the biases
behave for the different classes. We also provide two-band calibration formulae
for stellar mass and star formation rate estimations. | Efficient sampling of fast and slow cosmological parameters: Physical parameters are often constrained from the data likelihoods using
sampling methods. Changing some parameters can be much more computationally
expensive (`slow') than changing other parameters (`fast parameters'). I
describe a method for decorrelating fast and slow parameters so that parameter
sampling in the full space becomes almost as efficient as sampling in the slow
subspace when the covariance is well known and the distributions are simple.
This gives a large reduction in computational cost when there are many fast
parameters. The method can also be combined with a fast 'dragging' method
proposed by Neal (2005) that can be more robust and efficient when parameters
cannot be fully decorrelated a priori or have more complicated dependencies. I
illustrate these methods for the case of cosmological parameter estimation
using data likelihoods from the Planck satellite observations with dozens of
fast nuisance parameters, and demonstrate a speed up by a factor of five or
more. In more complicated cases, especially where the fast subspace is very
fast but complex or highly correlated, the fast-slow sampling methods can in
principle give arbitrarily large performance gains. The new samplers are
implemented in the latest version of the publicly available CosmoMC code. |
Variable Chaplygin Gas: Constraints from Supernovae, BAO, Look Back
Time, and GRBs: We examine the variable Chaplygin gas (VCG) model with the aim of
establishing tight constraints by using type-Ia supernovae, lookback time
measurements, Baryon Acoustic Oscillations (BAO) and the Gamma Ray Bursts. We
report the parameter constraints obtained via statistical analysis of cosmic
observables namely, luminosity distance, BAO distance and lookback time
measurement | Star-Forming Galaxies at z~2: An Emerging Picture of Galaxy Dynamics and
Assembly: In these proceedings, we summarize recent results from our "SINS" VLT/SINFONI
integral-field survey, focusing on the 52 detected UV/optically-selected
star-forming galaxies at z~2. Our H-alpha emission-line imaging and kinematic
data of these systems illustrates that a substantial fraction (> 1/3) of these
galaxies are large, rotating disks and that these disks are clumpy, thick, and
forming stars rapidly. We compare these systems to local disk scaling relations
and find that the backbones of these relations are already in place at z~2.
Detailed analysis of the large disks in our sample provides strong evidence
that this population cannot result from a merger-dominated formation history
and instead must be assembled by the smooth but rapid inflow of gas along
filaments. These systems will then secularly evolve from clump-dominated disks
to bulge-dominated disks on short timescales, a phenomenon that is observed in
our SINS observations and is consistent with predictions from numerical
simulations. These results provide new and exciting insights into the formation
of bulge-dominated galaxies in the local Universe. |
Extragalactic background light inferred from AEGIS galaxy SED-type
fractions: The extragalactic background light (EBL) is of fundamental importance both
for understanding the entire process of galaxy evolution and for gamma-ray
astronomy. However, the overall spectrum of the EBL between 0.1 and 1000
microns has never been determined directly neither from observed luminosity
functions (LFs), over a wide redshift range, nor from any multiwavelength
observation of galaxy spectral energy distributions (SEDs). The evolving,
overall spectrum of the EBL is derived here utilizing a novel method based on
observations only. The changing fractions of quiescent galaxies, star-forming
galaxies, starburst galaxies and active galactic nucleus (AGN) galaxies from
redshift 0.2 to 1 are estimated, and two alternative extrapolations of SED
types to higher redshifts are considered. This allows calculation of the
evolving EBL. The EBL uncertainties in our modelling based directly on the data
are quantified, and their consequences for attenuation of very-high-energy
gamma-rays due to pair production on the EBL are discussed. It is concluded
that the EBL seems well constrained from the UV to the mid-IR at an intensity
level roughly matching galaxy count data. Independent efforts from IR and
gamma-ray astronomy are needed in order to reduce the uncertainties in the
far-IR. | Low-mass star formation triggered by early supernova explosions: We study the formation of low-mass and extremely metal-poor stars in the
early universe. Our study is motivated by the recent discovery of a low-mass (M
< 0.8 Msun) and extremely metal-poor (Z <= 4.5 x 10^{-5} Zsun) star in the
Galactic halo by Caffau et al. We propose a model that early supernova (SN)
explosions trigger the formation of low-mass stars via shell fragmentation. We
first perform one-dimensional hydrodynamic simulations of the evolution of an
early SN remnant. We show that the shocked shell undergoes efficient radiative
cooling and then becomes gravitationally unstable to fragment and collapse in
about ten million years. We then follow the thermal evolution of the collapsing
fragments using a one-zone code. Our one-zone calculation treats chemistry and
radiative cooling self-consistently in low-metallicity gas. The collapsing gas
cloud evolves roughly isothermally, until it cools rapidly by dust continuum
emission at the density 10^{13}-10^{14} /cc. The cloud core then becomes
thermally and gravitationally unstable and fragments. We argue that early SNe
can trigger the formation of low-mass stars in the extremely metal-poor
environment as Caffau et al. discovered recently. |
How well can we Measure the Intrinsic Velocity Dispersion of Distant
Disk Galaxies?: The kinematics of distant galaxies, from z=0.1 to z>2, play a key role in our
understanding of galaxy evolution from early times to the present. One of the
important parameters is the intrinsic, or local, velocity dispersion of a
galaxy, which allows one to quantify the degree of non-circular motions such as
pressure support. However, this is difficult to measure because the observed
dispersion includes the effects of (often severe) beam smearing on the velocity
gradient. Here we investigate four methods of measuring the dispersion that
have been used in the literature, to assess their effectiveness at recovering
the intrinsic dispersion. We discuss the biasses inherent in each method, and
apply them to model disk galaxies in order to determine which methods yield
meaningful quantities, and under what conditions. All the mean weighted
dispersion estimators are affected by (residual) beam smearing. In contrast,
the dispersion recovered by fitting a spatially and spectrally convolved disk
model to the data is unbiassed by the beam smearing it is trying to compensate.
Because of this, and because the bias it does exhibit depends only on the
signal-to-noise, it can be considered reliable. However, at very low
signal-to-noise, all methods should be used with caution. | The neutral hydrogen distribution in large-scale haloes from 21-cm
intensity maps: We detect the neutral hydrogen (HI) radial brightness temperature profile in
large-scale haloes by stacking 48,430 galaxies selected from the 2dFGRS
catalogue onto a set of 21-cm intensity maps obtained with the Parkes radio
telescope, spanning a total area of $\sim$1,300 $\text{deg}^2$ on the sky and
covering the redshift range $0.06\lesssim z\lesssim 0.10$. Maps are obtained by
removing both 10 and 20 foreground modes in the principal component analysis.
We perform the stack at the map level and extract the profile from a circularly
symmetrised version of the halo emission. We detect the HI halo emission with
the significance $12.5\sigma$ for the 10-mode and $13.5\sigma$ for the 20-mode
removed maps at the profile peak. We jointly fit for the observed halo mass
$M_{\rm v}$ and the normalisation $c_{0,\rm HI}$ for the HI concentration
parameter against the reconstructed profiles, using functional forms for the HI
halo abundance proposed in the literature. We find $\log_{10}{(M_{\rm
v}/\text{M}_{\odot})} = 16.1^{+0.1}_{-0.2}$, $c_{0,\rm HI}=3.5^{+0.7}_{-1.0}$
for the 10-mode and $\log_{10}{(M_{\rm v}/\text{M}_{\odot})} =
16.5^{+0.1}_{-0.2}$, $c_{0,\rm HI}=5.3^{+1.1}_{-1.7}$ for the 20-mode removed
maps. These estimates show the detection of the integrated contribution from
multiple galaxies located inside very massive haloes. We also consider
sub-samples of 13,979 central and 34,361 satellite 2dF galaxies separately, and
obtain marginal differences suggesting satellite galaxies are HI-richer. This
work shows for the first time the feasibility of testing theoretical models for
the HI halo content directly on profiles extracted from 21-cm maps and opens
future possibilities for exploiting upcoming HI intensity-mapping data. |
$R^2$ Dark Energy in the Laboratory: We analyse the role, on large cosmological scales and laboratory experiments,
of the leading curvature squared contributions to the low energy effective
action of gravity. We argue for a natural relationship $c_0\lambda^2\simeq 1$
at low-energy between the ${\cal R}^2$ coefficients $c_0$ of the Ricci scalar
squared term in this expansion and the dark energy scale $\Lambda=(\lambda
M_{\rm Pl})^4$ in four dimensional Planck mass units. We show how the
compatibility between the acceleration of the expansion rate of the Universe,
local tests of gravity and the quantum stability of the model all converge to
select such a relationship up to a coefficient which should be determined
experimentally. When embedding this low energy theory of gravity into
candidates for its ultraviolet completion, we find that the proposed
relationship is guaranteed in string-inspired supergravity models with modulus
stabilisation and supersymmetry breaking leading to de Sitter
compactifications. In this case, the scalar degree of freedom of ${\cal R}^2$
gravity is associated to a volume modulus. Once written in terms of a
scalar-tensor theory, the effective theory corresponds to a massive scalar
field coupled with the universal strength $\beta=1/\sqrt{6}$ to the matter
stress-energy tensor. When the relationship $c_0\lambda^2\simeq 1$ is realised
we find that on astrophysical scales and in cosmology the scalar field is
ultralocal and therefore no effect arises on such large scales. On the other
hand, the scalar field mass is tightly constrained by the non-observation of
fifth forces in torsion pendulum experiments such as E\"ot-Wash. It turns out
that the observation of the dark energy scale in cosmology implies that the
scalar field could be detectable by fifth force experiments in the near future. | Hubble constant by natural selection: Evolution chips in the Hubble
tension: The Approximate Bayesian Computation (ABC) algorithm considers natural
selection in biology as a guiding principle for statistical model selection and
parameter estimation. We take this ABC approach to cosmology and use it to
infer which model anchored on a choice of a Hubble constant prior would be
preferred by the data. We find in all of our runs that the Planck Hubble
constant ($H_0 = 67.4 \pm 0.5$ km s$^{-1}$Mpc$^{-1}$) always emerge naturally
selected by the ABC over the SH$0$ES estimate ($H_0 = 73.30 \pm 1.04$ km
s$^{-1}$Mpc$^{-1}$). The result holds regardless of how we mix our data sets,
including supernovae, cosmic chronometers, baryon acoustic oscillations, and
growth data. Compared with the traditional MCMC, we find that the ABC always
results with narrower cosmological constraints, but remain consistent inside
the corresponding MCMC posteriors. |
The cosmological constant as an eigenvalue of a Sturm-Liouville problem: It is observed that one of Einstein-Friedmann's equations has formally the
aspect of a Sturm-Liouville problem, and that the cosmological constant,
$\Lambda$, plays thereby the role of spectral parameter (what hints to its
connection with the Casimir effect). The subsequent formulation of appropriate
boundary conditions leads to a set of admissible values for $\Lambda$,
considered as eigenvalues of the corresponding linear operator. Simplest
boundary conditions are assumed, namely that the eigenfunctions belong to $L^2$
space, with the result that, when all energy conditions are satisfied, they
yield a discrete spectrum for $\Lambda>0$ and a continuous one for $\Lambda<0$.
A very interesting situation is seen to occur when the discrete spectrum
contains only one point: then, there is the possibility to obtain appropriate
cosmological conditions without invoking the anthropic principle. This
possibility is shown to be realized in cyclic cosmological models, provided the
potential of the matter field is similar to the potential of the scalar field.
The dynamics of the universe in this case contains a sudden future singularity. | Cosmological scalar fields and Big-Bang nucleosynthesis: Scalar fields are widely used in cosmology, in particular to emulate dark
energy, for example in quintessence models, or to explain dark matter, in
particular within the fuzzy dark matter model. In addition many scenarios
involving primordial scalar fields which could have driven inflation or
baryogenesis are currently under scrutiny. In this article, we study the impact
of such scalar fields on Big-Bang nucleosynthesis and derive constraints on
their parameters using the observed abundance of the elements. |
The Stochastic Gravitational-Wave Background from Primordial Black Holes
in R-Symmetric $SU(5)$ Inflation: This study explores the realization of nonminimally coupled Higgs inflation
in the context of no-scale supergravity, investigates the formation of
primordial black holes, and examines the potential for observable proton decay
within the framework of the R-symmetric $SU(5)$ model. For inflation, both
single and multifield scenarios are investigated. The prediction of the
single-field model for the tensor-to-scalar ratio, $r$, is approximately
$10^{-3}$, and the scalar spectral index falls within Plank's 1$\sigma$ range.
The running of the scalar spectral index, $-{dn_{s}}/{d\ln{k}}$, is
approximately $10^{-4}$. A realistic scenario of reheating and non-thermal
leptogenesis is employed with reheat temperature $T_r\sim10^9$ GeV. In the
multifield case, we mainly focus on Primordial Black Holes (PBHs) and
Gravitational Waves (GWs). In this inflationary framework, we demonstrate how a
suitable choice of parameters can result in an enhanced scalar power spectrum,
leading to the production of primordial black holes (PBHs) capable of fully
accounting for dark matter. We also show that this scenario leads to Scalar
Induced Gravitational Waves (SIGW) which can be detected in current and future
GW detectors. We explore different proton decay channels to look for observable
predictions for the next-generation proton decay experiments Hyper-K and DUNE
consistent with gauge coupling unification and cosmological bounds. | Measurements of the Cross Spectra of the Cosmic Infrared and Microwave
Backgrounds from 95 to 1200 GHz: We present measurements of the power spectra of cosmic infrared background
(CIB) and cosmic microwave background (CMB) fluctuations in six frequency
bands. Maps at the lower three frequency bands, 95, 150, and 220 GHz (3330,
2000, 1360 $\mu$m) are from the South Pole Telescope, while the upper three
frequency bands, 600, 857, and 1200 GHz (500, 350, 250 $\mu$m) are observed
with Herschel/SPIRE. From these data, we produce 21 angular power spectra (six
auto- and fifteen cross-frequency) spanning the multipole range $600 \le \ell
\le 11,000$. Our measurements are the first to cross-correlate measurements
near the peak of the CIB spectrum with maps at 95 GHz, complementing and
extending the measurements from Planck Collaboration et al. (2014) at 218, 550,
and 857 GHz. The observed fluctuations originate largely from clustered,
infrared-emitting, dusty star-forming galaxies, the CMB, and to a lesser extent
radio galaxies, active galactic nuclei, and the Sunyaev-Zel'dovich effect. |
Foreground-immune CMB lensing reconstruction with polarization: Extragalactic foregrounds are known to generate significant biases in
temperature-based CMB lensing reconstruction. Several techniques, which include
``source hardening'' and ``shear-only estimators'' have been proposed to
mitigate contamination and have been shown to be very effective at reducing
foreground-induced biases. Here we extend both techniques to polarization,
which will be an essential component of CMB lensing reconstruction for future
experiments, and investigate the ``large-lens'' limit analytically to gain
insight on the origin and scaling of foreground biases, as well as the
sensitivity to their profiles.Using simulations of polarized point sources, we
estimate the expected bias to both Simons Observatory and CMB-S4 like
(polarization-based) lensing reconstruction, finding that biases to the former
are minuscule while those to the latter are potentially non-negligible at small
scales ($L\sim1000-2000$). In particular, we show that for a CMB-S4 like
experiment, an optimal linear combination of point-source hardened estimators
can reduce the (point-source induced) bias to the CMB lensing power spectrum by
up to two orders of magnitude, at a $\sim4\%$ noise cost relative to the global
minimum variance estimator. | Observational tests for oscillating expansion rate of the Universe: We investigate the observational constraints on the oscillating scalar field
model using data from type Ia supernovae, cosmic microwave background
anisotropies, and baryon acoustic oscillations. According to a Fourier
analysis, the galaxy number count $N$ from redshift $z$ data indicates that
galaxies have preferred periodic redshift spacings. We fix the mass of the
scalar field as $m_\phi=3.2\times 10^{-31}h$ ${\rm eV}$ such that the scalar
field model can account for the redshift spacings, and we constrain the other
basic parameters by comparing the model with accurate observational data. We
obtain the following constraints: $\Omega_{m,0}=0.28\pm 0.03$ (95% C.L.),
$\Omega_{\phi,0} < 0.035$ (95% C.L.), $\xi > -158$ (95% C.L.) (in the range
$\xi \le 0$). The best fit values of the energy density parameter of the scalar
field and the coupling constant are $\Omega_{\phi,0}= 0.01$ and $\xi= -25$,
respectively. The value of $\Omega_{\phi,0}$ is close to but not equal to $0$.
Hence, in the scalar field model, the amplitude of the galaxy number count
cannot be large. However, because the best fit values of $\Omega_{\phi,0}$ and
$\xi$ are not $0$, the scalar field model has the possibility of accounting for
the periodic structure in the $N$--$z$ relation of galaxies. The variation of
the effective gravitational constant in the scalar field model is not
inconsistent with the bound from observation. |
Orientation Bias of Optically Selected Galaxy Clusters and Its Impact on
Stacked Weak Lensing Analyses: Weak-lensing measurements of the averaged shear profiles of galaxy clusters
binned by some proxy for cluster mass are commonly converted to cluster mass
estimates under the assumption that these cluster stacks have spherical
symmetry. In this paper we test whether this assumption holds for optically
selected clusters binned by estimated optical richness. Using mock catalogues
created from N-body simulations populated realistically with galaxies, we ran a
suite of optical cluster finders and estimated their optical richness. We
binned galaxy clusters by true cluster mass and estimated optical richness and
measure the ellipticity of these stacks. We find that the processes of optical
cluster selection and richness estimation are biased, leading to stacked
structures that are elongated along the line-of-sight. We show that
weak-lensing alone cannot measure the size of this orientation bias. Weak
lensing masses of stacked optically selected clusters are overestimated by up
to 3-6 per cent when clusters can be uniquely associated with haloes. This
effect is large enough to lead to significant biases in the cosmological
parameters derived from large surveys like the Dark Energy Survey, if not
calibrated via simulations or fitted simultaneously. This bias probably also
contributes to the observed discrepancy between the observed and predicted
Sunyaev-Zel'dovich signal of optically-selected clusters. | Baryonic effects on CMB lensing and neutrino mass constraints: Measurements of gravitational lensing of the cosmic microwave background
(CMB) hold the promise of yielding unique insights into cosmology at high
redshift. Uncertainties due to baryonic effects associated with galaxy
formation and evolution, including gas cooling, star formation, and feedback
from active galactic nuclei (AGN) and supernovae, have typically been neglected
when forecasting the sensitivity of future CMB surveys. In this paper, we
determine the impact of these effects using four suites of hydrodynamical
simulations which incorporate various prescriptions for baryonic processes,
namely OWLS, BAHAMAS, Horizon, and IllustrisTNG. Our analysis shows
characteristic power suppressions of several percent in CMB lensing due to
baryonic effects, compared to dark-matter only simulations, at experimentally
observable angular scales. We investigate the associated bias in the inferred
neutrino mass for experiments like the upcoming Simons Observatory and CMB-S4.
Depending on the experimental precision and the strength of the baryonic
feedback within the simulations, biases in the neutrino mass sum show
significant dispersion, ranging from very small to an over-estimation by
1.1$\sigma$. We conclude that baryonic effects will likely be non-negligible
for a detection of neutrino mass using CMB lensing. |
The $H_0$ Olympics: A fair ranking of proposed models: Despite the remarkable success of the $\Lambda$Cold Dark Matter
($\Lambda$CDM) cosmological model, a growing discrepancy has emerged (currently
measured at the level of $\sim 4-6 \sigma$) between the value of the Hubble
constant $H_0$ measured using the local distance ladder and the value inferred
using the cosmic microwave background and galaxy surveys. While a vast array of
$\Lambda$CDM extensions have been proposed to explain these discordant
observations, understanding the (relative) success of these models in resolving
the tension has proven difficult -- this is a direct consequence of the fact
that each model has been subjected to differing, and typically incomplete,
compilations of cosmological data. In this review, we attempt to make a
systematic comparison of sixteen different models which have been proposed to
resolve the $H_0$ tension (spanning both early- and late-Universe solutions),
and quantify the relative success of each using a series of metrics and a vast
array of data combinations. Owing to the timely appearance of this article, we
refer to this contest as the ''$H_0$ Olympics''; the goal being to identify
which of the proposed solutions, and more broadly which underlying mechanisms,
are most likely to be responsible for explaining the observed discrepancy
(should unaccounted for systematics not be the culprit). This work also
establishes a foundation of tests which will allow the success of novel
proposals to be meaningful ''benchmarked''. | Galaxy activity influenced by the environment in the cluster of galaxies
Abell 85: We analyse the relation between the dynamical state of a cluster of galaxies
and the activity (star formation and AGN) of its members. For the case of Abell
85 we find some evidence for an enhanced activity of both types in
substructures which are in the early stage of merging with the cluster. |
The soft X-ray and narrow-line emission of Mrk573 on kiloparcec scales: We present a study of the circumnuclear region of the nearby Seyfert galaxy
Mrk573 using Chandra, XMM-Newton and HST data. The X-ray morphology shows a
biconical region extending up to 12 arcsecs (4 kpc) in projection from the
nucleus. A strong correlation between the X-rays and the highly ionized gas
seen in the [O III] image is reported. Moreover, we have studied the line
intensities detected with the RGS/XMM-Newton and used them to fit the low
resolution EPIC/XMM-Newton and ACIS/Chandra spectra. The RGS spectrum is
dominated by emission lines of C VI, O VII, O VIII, Fe XVII, and Ne IX, among
others. A good fit is obtained using these emission lines found in the RGS
spectrum as a template for Chandra spectra of the nucleus and extended
emission. The photoionization model Cloudy provides a reasonable fit for both
the nuclear region and the cone-like structures. For the nucleus the emission
is modelled using two phases: a high ionization [log(U)=1.23] and a low
ionization [log(U)=0.13]. For the high ionization phase the transmitted and
reflected component are in a ratio 1:2, whereas for the low ionization the
reflected component dominates. For the extended emission, we successfully
reproduced the emission with two phases. The first phase shows a higher
ionization parameter for the NW (log(U)=0.9) than for the SE cone (log(U)=0.3).
The second phase shows a low ionization parameter (log(U)=-3) and is rather
uniform for NW and SE cones. In addition, the nuclear optical/infrared SED has
been modeled by a clumpy torus model. The torus bolometric luminosity agrees
with the AGN luminosity inferred from the observed hard X-ray spectrum. The
optical depth along the line of sight derived from the SED fit indicates a high
neutral column density in agreement with the classification of the nucleus as a
Compton-thick AGN. | Gravitational Wave Astronomy Using Pulsars: Massive Black Hole Mergers &
the Early Universe: Gravitational waves (GWs) are fluctuations in the fabric of spacetime
predicted by Einstein's theory of general relativity. Using a collection of
millisecond pulsars as high-precision clocks, the nanohertz band of this
radiation is likely to be directly detected within the next decade.
Nanohertz-frequency GWs are expected to be emitted by mergers of massive black
hole binary systems, and potentially also by cosmic strings or superstrings
formed in the early Universe. Direct detection of GWs will open a new window to
the Universe, and provide astrophysical information inaccessible via
electromagnetic observations. In this paper, we describe the potential sources
of low-frequency GWs and the current status and key advances needed for the
detection and exploitation of GWs through pulsar timing. |
Fast scalar quadratic maximum likelihood estimators for the CMB B-mode
power spectrum: Constructing a fast and efficient estimator for the B-mode power spectrum of
cosmic microwave background (CMB) is of critical importance for CMB science.
For a general CMB survey, the Quadratic Maximum Likelihood (QML) estimator for
CMB polarization has been proved to be the optimal estimator with minimal
uncertainties, but it is computationally very expensive. In this article, we
propose two new QML methods for B-mode power spectrum estimation. We use the
Smith-Zaldarriaga approach to prepare pure-B mode map, and E-mode recycling
method to obtain a leakage free B-mode map. We then use the scalar QML
estimator to analyze the scalar pure-B map (QML-SZ) or B-mode map (QML-TC). The
QML-SZ and QML-TC estimators have similar error bars as the standard QML
estimators but their computational cost is nearly one order of magnitude
smaller. The basic idea is that one can construct the pure B-mode CMB map by
using the E-B separation method proposed by Smith-Zaldarriaga (SZ) or the one
considering the template cleaning (TC) technique, then apply QML estimator to
these scalar fields. By simulating potential observations of space-based and
ground-based detectors, we test the reliability of these estimators by
comparing them with the corresponding results of the traditional QML estimator
and the pure B-mode pseudo-Cl estimator. | Supermassive black hole spin-flip during the inspiral: During post-Newtonian evolution of a compact binary, a mass ratio different
from 1 provides a second small parameter, which can lead to unexpected results.
We present a statistics of supermassive black hole candidates, which enables us
first to derive their mass distribution, then to establish a logarithmically
even probability of the mass ratios at their encounter. In the mass ratio range
(1/30,1/3) of supermassive black hole mergers representing 40% of all possible
cases, the combined effect of spin-orbit precession and gravitational radiation
leads to a spin-flip of the dominant spin during the inspiral phase of the
merger. This provides a mechanism for explaining a large set of observations on
X-shaped radio galaxies. In another 40%, with mass ratios (1/30,1/1000) a
spin-flip never occurs, while in the remaining 20% of mergers with mass ratios
(1/3,1) it may occur during the plunge. We analyze the magnitude of the
spin-flip angle occurring during the inspiral as function of the mass ratio and
original relative orientation of the spin and orbital angular momentum. We also
derive a formula for the final spin at the end of the inspiral in this mass
ratio range. |
CMB lensing from Planck PR4 maps: We reconstruct the Cosmic Microwave Background (CMB) lensing potential on the
latest Planck CMB PR4 (NPIPE) maps, which include slightly more data than the
2018 PR3 release, and implement quadratic estimators using more optimal
filtering. We increase the reconstruction signal to noise by almost $20\%$,
constraining the amplitude of the CMB-marginalized lensing power spectrum in
units of the Planck 2018 best-fit to $1.004 \pm 0.024$ ($68\%$ limits), which
is the tightest constraint on the CMB lensing power spectrum to date. For a
base $\Lambda$CDM cosmology we find $\sigma_8 \Omega_m^{0.25} = 0.599\pm 0.016$
from CMB lensing alone in combination with weak priors and element abundance
observations. Combination with baryon acoustic oscillation data gives tight
$68\%$ constraints on individual $\Lambda$CDM parameters $\sigma_8 = 0.814\pm
0.016$, $H_0 = 68.1^{+1.0}_{-1.1}$km s$^{-1}$ Mpc$^{-1}$, $\Omega_m =
0.313^{+0.014}_{-0.016}$. Planck polarized maps alone now constrain the lensing
power to $7\%$. | The Effects of Accretion Luminosity upon Fragmentation in the Early
Universe: We introduce a prescription for the luminosity from accreting protostars into
smoothed particle hydrodynamics simulation, and apply the method to simulations
of five primordial minihalos generated from cosmological initial conditions. We
find that accretion luminosity delays fragmentation within the halos, but does
not prevent it. In halos that slowly form a low number of protostars, the
accretion luminosity can reduce the number of fragments that are formed before
the protostars start ionising their surroundings. However, halos that rapidly
form many protostars become dominated by dynamical processes, and the effect of
accretion luminosity becomes negligible. Generally the fragmentation found in
the halos is highly dependent on the initial conditions. Accretion luminosity
does not substantially affect the accretion rates experienced by the
protostars, and is far less important than dynamical interactions, which can
lead to ejections that effectively terminate the accretion. We find that the
accretion rates onto the inner regions of the disks (20 AU) around the
protostars are highly variable, in contrast to the constant or smoothly
decreasing accretion rates currently used in models of the pre-main sequence
evolution of Population III stars. |
Can we explain cosmic birefringence without a new light field beyond
Standard Model?: The recent analysis of the Planck 2018 polarization data shows a nonzero
isotropic cosmic birefringence (ICB) that is not explained within the
$\Lambda$CDM paradigm. We then explore the question of whether the nonzero ICB
is interpreted by the framework of the Standard Model Effective Field Theory
(SMEFT), or at the energy scales of the cosmic microwave background, the
low-energy EFT (LEFT) whose dynamical degrees of freedom are five SM quarks and
all neutral and charged leptons. Our systematic study reveals that any operator
in the EFT on a cosmological background would not give the reported ICB angle,
which is observationally consistent with frequency independence. In particular,
we estimate the size of the ICB angle generated by the effect that the cosmic
microwave background photons travel through the medium of the cosmic neutrino
background with parity-violating neutrino-photon interactions and find that it
would be too small to explain the data. If the reported ICB angle should be
confirmed, then our result would indicate the existence of a new particle that
is lighter than the electroweak scale and feebly interacting with the SM
particles. | Enhance Primordial Black Hole Abundance through the Non-linear Processes
around Bounce Point: The non-singular bouncing cosmology is an alternative paradigm to inflation,
wherein the background energy density vanishes at the bounce point, in the
context of Einstein gravity. Therefore, the non-linear effects in the evolution
of density fluctuations ($\delta \rho$) may be strong in the bounce phase,
which potentially provides a mechanism to enhance the abundance of primordial
black holes (PBHs). This article presents a comprehensive illustration for PBH
enhancement due to the bounce phase. To calculate the non-linear evolution of
$\delta \rho$, the Raychaudhuri equation is numerically solved here. Since the
non-linear processes may lead to a non-Gaussian probability distribution
function for $\delta \rho$ after the bounce point, the PBH abundance is
calculated in a modified Press-Schechter formalism. In this case, the criterion
of PBH formation is complicated, due to complicated non-linear evolutionary
behavior of $\delta \rho$ during the bounce phase. Our results indicate that
the bounce phase indeed has potential to enhance the PBH abundance
sufficiently. Furthermore, the PBH abundance is applied to constrain the
parameters of bounce phase, providing a complementary to the surveys of cosmic
microwave background and large scale structure. |
The Light Element Abundance Distribution in NGC 5128 from Planetary
Nebulae: The light element abundance pattern from many planetary nebulae (PNe)
covering the upper 4 mag. of the [O III] luminosity function was observed with
ESO VLT FORS1 multi-slit. Spectra of 51 PNe over the wavelength range 3500-7500
Angstrom were obtained in three fields at 4, 8 and 17 kpc, for a distance of
3.8 Mpc. Emission line ratios are entirely typical of PN such as in the Milky
Way. The temperature sensitive [O III]4363A line was weakly detected in 10 PNe,
both [O II] and [O III] lines were detected in 30 PNe, and only the bright [O
III]5007A line in 7 PN. Cloudy photoionization models were run to match the
spectra by a spherical, constant density nebula ionized by a black body central
star. He, N, O and Ne abundances with respect to H were determined and, for
brighter PNe, S and Ar; central star luminosities and temperatures are also
derived. For 40 PNe with Cloudy models, from the upper 2 mag. of the luminosity
function, the most reliably estimated element, oxygen, has a mean 12+log(O/H)
of 8.52. No obvious radial gradient is apparent in O/H over a range 2-20 kpc.
Comparison of the PN abundances with the stellar population, from the spectra
of the integrated starlight on the multi-slits and photometric studies,
suggests [Fe/H]=-0.4 and [O/Fe]=0.25. The masses of the PN central stars in NGC
5128 from model tracks imply an epoch of formation more recent than for the
minority young population from colour-magnitude studies. The PNe progenitors
may belong to the young tail of a recent, minor, star formation episode or
derive from other evolutionary channels.[Abridged] | FLAMINGO: Calibrating large cosmological hydrodynamical simulations with
machine learning: To fully take advantage of the data provided by large-scale structure
surveys, we need to quantify the potential impact of baryonic effects, such as
feedback from active galactic nuclei (AGN) and star formation, on cosmological
observables. In simulations, feedback processes originate on scales that remain
unresolved. Therefore, they need to be sourced via subgrid models that contain
free parameters. We use machine learning to calibrate the AGN and stellar
feedback models for the FLAMINGO cosmological hydrodynamical simulations. Using
Gaussian process emulators trained on Latin hypercubes of 32 smaller-volume
simulations, we model how the galaxy stellar mass function and cluster gas
fractions change as a function of the subgrid parameters. The emulators are
then fit to observational data, allowing for the inclusion of potential
observational biases. We apply our method to the three different FLAMINGO
resolutions, spanning a factor of 64 in particle mass, recovering the observed
relations within the respective resolved mass ranges. We also use the
emulators, which link changes in subgrid parameters to changes in observables,
to find models that skirt or exceed the observationally allowed range for
cluster gas fractions and the stellar mass function. Our method enables us to
define model variations in terms of the data that they are calibrated to rather
than the values of specific subgrid parameters. This approach is useful,
because subgrid parameters are typically not directly linked to particular
observables, and predictions for a specific observable are influenced by
multiple subgrid parameters. |
Fast Generation of Covariance Matrices for Weak Lensing: Upcoming weak lensing surveys will probe large fractions of the sky with
unprecedented accuracy. To infer cosmological constraints, a large ensemble of
survey simulations are required to accurately model cosmological observables
and their covariances. We develop a parallelized multi-lens-plane pipeline
called UFalcon, designed to generate full-sky weak lensing maps from lightcones
within a minimal runtime. It makes use of L-PICOLA, an approximate numerical
code, which provides a fast and accurate alternative to cosmological $N$-Body
simulations. The UFalcon maps are constructed by nesting 2 simulations covering
a redshift-range from $z=0.1$ to $1.5$ without replicating the simulation
volume. We compute the convergence and projected overdensity maps for L-PICOLA
in the lightcone or snapshot mode. The generation of such a map, including the
L-PICOLA simulation, takes about 3 hours walltime on 220 cores. We use the maps
to calculate the spherical harmonic power spectra, which we compare to
theoretical predictions and to UFalcon results generated using the full
$N$-Body code GADGET-2. We then compute the covariance matrix of the full-sky
spherical harmonic power spectra using 150 UFalcon maps based on L-PICOLA in
lightcone mode. We consider the PDF, the higher-order moments and the variance
of the smoothed field variance to quantify the accuracy of the covariance
matrix, which we find to be a few percent for scales $\ell \sim 10^2$ to
$10^3$. We test the impact of this level of accuracy on cosmological
constraints using an optimistic survey configuration, and find that the final
results are robust to this level of uncertainty. The speed and accuracy of our
developed pipeline provides a basis to also include further important features
such as masking, varying noise and will allow us to compute covariance matrices
for models beyond $\Lambda$CDM. [abridged] | Axion Dark Matter Detection with CMB Polarization: We point out two ways to search for low-mass axion dark matter using cosmic
microwave background (CMB) polarization measurements. These appear, in
particular, to be some of the most promising ways to directly detect fuzzy dark
matter. Axion dark matter causes rotation of the polarization of light passing
through it. This gives rise to two novel phenomena in the CMB. First, the
late-time oscillations of the axion field today cause the CMB polarization to
oscillate in phase across the entire sky. Second, the early-time oscillations
of the axion field wash out the polarization produced at last-scattering,
reducing the polarized fraction (TE and EE power spectra) compared to the
standard prediction. Since the axion field is oscillating, the common (static)
`cosmic birefringence' search is not appropriate for axion dark matter. These
two phenomena can be used to search for axion dark matter at the lighter end of
the mass range, with a reach several orders of magnitude beyond current
constraints. We set a limit from the washout effect using existing Planck
results, and find significant future discovery potential for CMB detectors
searching in particular for the oscillating effect. |
Measuring dark energy with expansion and growth: We combine cosmic chronometer and growth of structure data to derive the
redshift evolution of the dark energy equation of state $w$, using a novel
agnostic approach. The background and perturbation equations lead to two
expressions for $w$, one purely background-based and the other relying also on
the growth rate of large-scale structure. We compare the features and
performance of the growth-based $w$ to the background $w$, using Gaussian
Processes for the reconstructions. We find that current data is not precise
enough for robust reconstruction of the two forms of $w$. By using mock data
expected from next-generation surveys, we show that the reconstructions will be
robust enough and that the growth-based $w$ will out-perform the background
$w$. Furthermore, any disagreement between the two forms of $w$ will provide a
new test for deviations from the standard model of cosmology. | On the origin of the scatter around the Fundamental Plane: correlations
with stellar population parameters: We present a fundamental plane (FP) analysis of 141 early-type galaxies in
the Shapley supercluster at z=0.049 based on spectroscopy from the AAOmega
spectrograph at the AAT and photometry from the WFI on the ESO/MPI 2.2m
telescope. The key feature of the survey is its coverage of low-mass galaxies
down to sigma_0~50km/s. We obtain a best-fitting FP relation log r_e=1.06 log
sigma_0 - 0.82 log < I >_e + cst in the R band. The shallow exponent of sigma_0
is a result of the extension of our sample to low velocity dispersions. We
investigate the origin of the intrinsic FP scatter, using estimates of age,
metallicity and alpha/Fe. We find that the FP residuals anti-correlate
(>3sigma) with the mean stellar age in agreement with previous work. However, a
stronger (>4sigma) correlation with alpha/Fe is also found. These correlations
indicate that galaxies with effective radii smaller than those predicted by the
FP have stellar populations systematically older and with alpha over-abundances
larger than average, for their sigma_0. Including alpha/Fe as a fourth
parameter in the FP, the total scatter decreases from 0.088 dex to 0.075 dex
and the estimated intrinsic scatter decreases from 0.068 dex to 0.049 dex.
Thus, variations in alpha/Fe account for >> 30% of the total variance around
the FP, and >> 50% of the estimated intrinsic variance. This result indicates
that the distribution of galaxies around the FP are tightly related to the
enrichment, and hence to the timescale of star-formation. Our results appear to
be consistent with the merger hypothesis for the formation of ellipticals which
predicts that a significant fraction of the scatter is due to variations in the
importance of dissipation in forming merger remnants of a given mass. |
A Tale of Two Paradigms: the Mutual Incommensurability of LCDM and MOND: The concordance model of cosmology, LCDM, provides a satisfactory description
of the evolution of the universe and the growth of large scale structure.
Despite considerable effort, this model does not at present provide a
satisfactory description of small scale structure and the dynamics of bound
objects like individual galaxies. In contrast, MOND provides a unique and
predictively successful description of galaxy dynamics, but is mute on the
subject of cosmology. Here I briefly review these contradictory world views,
emphasizing the wealth of distinct, interlocking lines of evidence that went
into the development of LCDM while highlighting the practical impossibility
that it can provide a satisfactory explanation of the observed MOND
phenomenology in galaxy dynamics. I also briefly review the baryon budget in
groups and clusters of galaxies where neither paradigm provides an entirely
satisfactory description of the data. Relatively little effort has been devoted
to the formation of structure in MOND; I review some of what has been done. The
amplitude ratio of the first to second peak in the CMB power spectrum was
correctly predicted a priori, but the third peak is more natural to LCDM. MOND
anticipates that structure forms more quickly than in LCDM. This motivated the
prediction that reionization would happen earlier in MOND than originally
expected in LCDM, as subsequently observed. This also provides a natural
explanation for massive, early clusters of galaxies and large, empty voids.
However, it is far from obvious that the mass spectrum of galaxy clusters or
the power spectrum of galaxies can be explained in MOND, two things that LCDM
does well. Critical outstanding issues are the development of an acceptable
relativistic parent theory for MOND, and the reality of the non-baryonic dark
matter of LCDM. Do suitable dark matter particles exist, or are they a modern
aether? | Discovery of Four Doubly Imaged Quasar Lenses from the Sloan Digital Sky
Survey: We report the discovery of four doubly imaged quasar lenses. All the four
systems are selected as lensed quasar candidates from the Sloan Digital Sky
Survey data. We confirm their lensing hypothesis with additional imaging and
spectroscopic follow-up observations. The discovered lenses are SDSS J0743+2457
with the source redshift z_s=2.165, the lens redshift z_l=0.381, and the image
separation theta=1.034", SDSS J1128+2402 with z_s=1.608 and theta=0.844", SDSS
J1405+0959 with z_s=1.810, z_l~0.66, and theta=1.978", and SDSS J1515+1511 with
z_s=2.054, z_l=0.742, and theta=1.989". It is difficult to estimate the lens
redshift of SDSS J1128+2402 from the current data. Two of the four systems
(SDSS J1405+0959 and SDSS J1515+1511) are included in our final statistical
lens sample to derive constraints on dark energy and the evolution of massive
galaxies. |
A Star in the M31 Giant Stream: the Highest Negative Stellar Velocity
Known: We report on a single star, B030D, observed as part of a large survey of
objects in M31, which has the unusual radial velocity of -780 km/s. Based on
details of its spectrum, we find that the star is an F supergiant, with a
circumstellar shell. The evolutionary status of the star could be one of a
post-mainsequence close binary, a symbiotic nova, or less likely, a post-AGB
star, which additional observations could help sort out. Membership of the star
in the Andromeda Giant Stream can explain its highly negative velocity. | Interferometric HI intensity mapping: perturbation theory predictions
and foreground removal effects: We provide perturbation theory predictions for the HI intensity mapping power
spectrum multipoles using the Effective Field Theory of Large Scale Structure
(EFTofLSS), which should allow us to constrain cosmological parameters
exploiting mildly nonlinear scales. Assuming survey specifications typical of
proposed interferometric HI intensity mapping experiments like CHORD and PUMA,
and realistic ranges of validity for the perturbation theory modelling, we run
mock full shape MCMC analyses at a redshift bin centred at $z=0.5$, and compare
with Stage-IV optical galaxy surveys. We include the impact of 21cm foreground
removal using simulations-based prescriptions, and quantify the effects on the
precision and accuracy of the parameter estimation. We vary 11 parameters in
total: 3 cosmological parameters, 7 bias and counterterms parameters, and the
HI brightness temperature. Amongst them, the 4 parameters of interest are: the
cold dark matter density, $\omega_{\rm c}$, the Hubble parameter, $h$, the
primordial amplitude of the power spectrum, $A_{\rm s}$, and the linear HI
bias, $b_1$. For the best case scenario, we obtain unbiased constraints on all
parameters with $<3\%$ errors at $68\%$ confidence level. When we include the
foreground removal effects, the parameter estimation becomes strongly biased
for $\omega_{\rm c}, h$, and $b_1$, while $A_{\rm s}$ is less biased ($<
2\sigma$). We find that scale cuts $k_{\rm min} \geq 0.03 \, h/{\mathrm{Mpc}}$
are required to return accurate estimates for $\omega_{\rm c}$ and $h$, at the
price of a decrease in the precision, while $b_1$ remains strongly biased. We
comment on the implications of these results for real data analyses. |
Measurement of halo properties with weak lensing shear and flexion: We constrain properties of cluster haloes by performing likelihood analysis
using lensing shear and flexion data. We test our analysis using two mock
cluster haloes: an isothermal ellipsoid (SIE) model and a more realistic
elliptical Navarro-Frenk-White (eNFW) model. For both haloes, we find that
flexion is more sensitive to the halo ellipticity than shear. The introduction
of flexion information significantly improves the constraints on halo
ellipticity, orientation and mass. We also point out that there is a degeneracy
between the mass and the ellipticity of SIE models in the lensing signal. | Using dark energy to suppress power at small scales: The latest Planck results reconfirm the existence of a slight but chronic
tension between the best-fit Cosmic Microwave Background (CMB) and low-redshift
observables: power seems to be consistently lacking in the late universe across
a range of observables (e.g.~weak lensing, cluster counts). We propose a
two-parameter model for dark energy where the dark energy is sufficiently like
dark matter at large scales to keep the CMB unchanged but where it does not
cluster at small scales, preventing concordance collapse and erasing power. We
thus exploit the generic scale-dependence of dark energy instead of the more
usual time-dependence to address the tension in the data. The combination of
CMB, distance and weak lensing data somewhat prefer our model to $\Lambda$CDM,
at $\Delta\chi^2=2.4$. Moreover, this improved solution has $\sigma_8=0.79 \pm
0.02$, consistent with the value implied by cluster counts. |
Doppler boosted dust emission and CIB-galaxy cross-correlations: a new
probe of cosmology and astrophysics: We identify a new cosmological signal, the Doppler-boosted Cosmic Infrared
Background (DB-CIB), arising from the peculiar motion of the galaxies whose
thermal dust emission source the cosmic infrared background (CIB). This new
observable is an independent probe of the cosmic velocity field, highly
analogous to the well-known kinematic Sunyaev-Zel'dovich (kSZ) effect.
Interestingly, DB-CIB does not suffer from the 'kSZ optical depth degeneracy',
making it immune from the complex astrophysics of galaxy formation. We forecast
that the DB-CIB effect is detectable in the cross-correlation of CCAT-Prime and
DESI-like experiments. We show that it also acts as a new CMB foreground which
can bias future kSZ cross-correlations, if not properly accounted for. | HST/COS Observations of the Quasar Q0302-003: Probing the He II
Reionization Epoch and QSO Proximity Effects: Q0302-003 ($z=3.2860 \pm 0.0005$) was the first quasar discovered that showed
a He II Gunn-Peterson trough, a sign of incomplete helium reionization at $z >
2.9$. We present its HST/Cosmic Origins Spectrograph far-UV medium-resolution
spectrum, which resolves many spectral features for the first time, allowing
study of the quasar itself, the intergalactic medium, and quasar proximity
effects. Q0302-003 has a harder intrinsic extreme-UV spectral index than
previously claimed, as determined from both a direct fit to the spectrum
(yielding $\alpha_{\nu} = -0.8$) and the helium-to-hydrogen ion ratio in the
quasar's line-of-sight proximity zone. Intergalactic absorption along this
sightline shows that the helium Gunn-Peterson trough is largely black in the
range $2.87 < z < 3.20$, apart from ionization due to local sources, indicating
that helium reionization has not completed at these redshifts. However, we
tentatively report a detection of nonzero flux in the high-redshift trough when
looking at low-density regions, but zero flux in higher-density regions. This
constrains the He II fraction to be a few percent, suggesting helium
reionization has progressed substantially by $z \sim 3.1$. The Gunn-Peterson
trough recovers to a He II Ly$\alpha$ forest at $z < 2.87$. We confirm a
transmission feature due to the ionization zone around a $z = 3.05$ quasar just
off the sightline, and resolve the feature for the first time. We discover a
similar such feature possibly caused by a luminous $z = 3.23$ quasar further
from the sightline, which suggests that this quasar has been luminous for >34
Myr. |
Focusing on Warm Dark Matter with Lensed High-redshift Galaxies: We propose a novel use of high-redshift galaxies, discovered in deep Hubble
Space Telescope (HST) fields around strong lensing clusters. These fields probe
small comoving volumes (about 1000 cubic Mpc) at high magnification ({\mu} >
10), and can detect otherwise inaccessible ultra-faint galaxies. Even a few
galaxies found in such small volumes require a very high number density of
collapsed dark matter (DM) halos. This implies significant primordial power on
small scales, allowing these observations to rule out popular alternatives to
standard cold dark matter (CDM) models, such as warm dark matter (WDM). In this
work, we analytically compute WDM halo mass functions at z = 10, including the
effects of both particle free-streaming and residual velocity dispersion. The
preliminary number density corresponding to the two galaxies at z about 10
already detected by the Cluster Lensing And Supernova survey with Hubble
(CLASH) constrains the WDM particle mass to m_x > 1 (0.9) keV at 84% (99.9%)
confidence limit (for a thermal relic relativistic at decoupling). This limit
depends only on the WDM halo mass function and, unlike previous constraints on
m_x, is independent of any astrophysical modeling. The forthcoming HST Frontier
Fields can significantly tighten these constraints. | The homogeneity scale and the growth rate of cosmic structures: We propose a novel approach to obtain the growth rate of cosmic structures,
$f(z)$, from the evolution of the cosmic homogeneity scale, $R_{\text{H}}(z)$.
Our methodology needs two ingredients in a specific functional form:
$R_{\text{H}}(z)$ data and the matter two-point correlation function today,
i.e., $\xi(r, z=0)$. We use a Gaussian Process approach to reconstruct the
function $R_{\text{H}}$. In the absence of suitable observational information
of the matter correlation function in the local Universe, $z \simeq 0$, we
assume a fiducial cosmology to obtain $\xi(r, z=0)$. For this reason, our final
result turns out to be a consistency test of the cosmological model assumed.
Our results show a good agreement between: (i) the growth rate
$f^{R_{\text{H}}}(z)$ obtained through our approach, (ii) the
$f^{\Lambda\text{CDM}}(z)$ expected in the fiducial model, and (iii) the
best-fit $f(z)$ from data compiled in the literature. Moreover, using this data
compilation, we perform a Gaussian Process to reconstruct the growth rate
function $f^{\text{data}}(z)$ and compare it with the function
$f^{R_{\text{H}}}(z)$ finding a concordance of $< \!2 \,\sigma$, a good result
considering the few data available for both reconstruction processes. With more
accurate $R_{\text{H}}(z)$ data, from forthcoming surveys, the homogeneity
scale function might be better determined and would have the potential to
discriminate between $\Lambda$CDM and alternative scenarios as a new
cosmological observable. |
Were you born in an aborted primordial black hole?: We propose a novel mechanism of electroweak baryogenesis based on the
standard model only and explaining the coincidence between the baryon and dark
matter densities in the Universe, as well as the observed value of the
baryon-to-photon ratio. In our scenario, large curvature fluctuations slightly
below the threshold for Primordial Black Hole (PBH) formation locally reheat
the plasma above the sphaleron barrier when they collapse gravitationally but
without forming a black hole. This rapid process can lead to a maximal
baryogenesis in those regions at the Quantum Chromodynamics (QCD) epoch at
thermal temperatures between 20 MeV and 50 MeV. Compared to another mechanism
relying on shock waves associated to the formation of PBHs, our mechanism
instead applies to aborted PBHs. Using simulations in numerical relativity, we
calculate the overdensity threshold for baryogenesis and show that the
baryon-to-photon ratio is generically between two and three times larger than
the relative abundance of PBHs formed at those temperatures. Finally, we show
that PBH formation models at the QCD epoch leading to an abundance comparable
to the dark matter could have generated a baryon density and an averaged
baryon-to-photon ratio consistent with observations. | Ultracompact minihalos as probes of inflationary cosmology: Cosmological inflation generates primordial density perturbations on all
scales, including those far too small to contribute to the cosmic microwave
background. At these scales, isolated ultracompact minihalos of dark matter can
form well before standard structure formation, if the perturbations have
sufficient amplitude. Minihalos affect pulsar timing data and are potentially
bright sources of gamma rays. The resulting constraints significantly extend
the observable window of inflation in the presence of cold dark matter,
coupling two of the key problems in modern cosmology. |
The Structure of the Interstellar Medium of Star Forming Galaxies: We present numerical methods for including stellar feedback in galaxy-scale
simulations. We include heating by SNe (I & II), gas recycling and
shock-heating from O-star & AGB winds, HII photoionization, and radiation
pressure from stellar photons. The energetics and time-dependence are taken
directly from stellar evolution models. We implement these in simulations with
pc-scale resolution, modeling galaxies from SMC-like dwarfs and MW analogues to
massive z~2 starburst disks. Absent feedback, gas cools and collapses without
limit. With feedback, the ISM reaches a multi-phase steady state in which GMCs
continuously form, disperse, and re-form. Our primary results include: (1) Star
forming galaxies generically self-regulate at Toomre Q~1. Most of the volume is
in diffuse hot gas with most of the mass in dense GMC complexes. The phase
structure and gas mass at high densities are much more sensitive probes of
stellar feedback physics than integrated quantities (Toomre Q or gas velocity
dispersion). (2) Different feedback mechanisms act on different scales:
radiation & HII pressure are critical to prevent runaway collapse of dense gas
in GMCs. SNe and stellar winds dominate the dynamics of volume-filling hot gas;
however this primarily vents out of the disk. (3) The galaxy-averaged SFR is
determined by feedback. For given feedback efficiency, restricting star
formation to molecular gas or modifying the cooling function has little effect;
but changing feedback mechanisms directly translates to shifts off the
Kennicutt-Schmidt relation. (4) Self-gravity leads to marginally-bound GMCs
with an ~M^-2 mass function with a cutoff at the Jeans mass; they live a few
dynamical times before being disrupted by stellar feedback and turn ~1-10% of
their mass into stars (increasing from dwarfs through starburst galaxies).
Low-mass GMCs are preferentially unbound. | Galaxy-Galaxy Lensing in the DES Science Verification Data: We present galaxy-galaxy lensing results from 139 square degrees of Dark
Energy Survey (DES) Science Verification (SV) data. Our lens sample consists of
red galaxies, known as redMaGiC, which are specifically selected to have a low
photometric redshift error and outlier rate. The lensing measurement has a
total signal-to-noise of 29 over scales $0.09 < R < 15$ Mpc/$h$, including all
lenses over a wide redshift range $0.2 < z < 0.8$. Dividing the lenses into
three redshift bins for this constant moving number density sample, we find no
evidence for evolution in the halo mass with redshift. We obtain consistent
results for the lensing measurement with two independent shear pipelines, ngmix
and im3shape. We perform a number of null tests on the shear and photometric
redshift catalogs and quantify resulting systematic uncertainties. Covariances
from jackknife subsamples of the data are validated with a suite of 50 mock
surveys. The results and systematics checks in this work provide a critical
input for future cosmological and galaxy evolution studies with the DES data
and redMaGiC galaxy samples. We fit a Halo Occupation Distribution (HOD) model,
and demonstrate that our data constrains the mean halo mass of the lens
galaxies, despite strong degeneracies between individual HOD parameters. |
Metallicity and Far-Infrared Luminosity of High Redshift Quasars: We present the results of an exploratory study of broad line region (BLR)
metallicity in 34 2.2 < z < 4.6 quasars with far-infrared (FIR) luminosities
(L_FIR) from 10^13.4 to 10^12.1 L_\odot . Quasar samples sorted by L_FIR might
represent an evolutionary sequence if the star formation rates (SFRs) in quasar
hosts generally diminish across quasar lifetimes. We use rest-frame ultraviolet
spectra from the Sloan Digital Sky Survey to construct three composite spectra
sorted by L_FIR, corresponding to average SFRs of 4980, 2130 and 340 M_\odot
yr^-1 after correcting for a nominal quasar FIR contribution. The measured N V
{\lambda} 1240/C IV {\lambda} 1550 and Si IV {\lambda} 1397+O IV] {\lambda}
1402/C IV {\lambda} 1550 emission line ratios indicate super-solar BLR
metallicities in all three composites, with no evidence for a trend with the
star formation rate. The formal derived metallicities, Z ~ 5-9 Z_\odot , are
similar to those derived for the BLRs of other quasars at similar redshifts and
luminosities. These results suggest that the ongoing star formation in the host
is not responsible for the metal enrichment of the BLR gas. Instead, the BLR
gas must have been enriched before the visible quasar phase. These results for
high quasar metallicities, regardless of L_FIR, are consistent with evolution
scenarios wherein visibly bright quasars appear after the main episode(s) of
star formation and metal enrichment in the host galaxies. Finally, young
quasars, those more closely associated with a recent merger or a blowout of gas
and dust, may exhibit tracers of these events, such as redder continuum slopes
and higher incidence of narrow absorption lines. With the caveat of small
sample sizes, we find no relation between L_FIR and the reddening or the
incidence of absorption lines. | Constraining the topology of the Universe using the polarised CMB maps: We study the possibility for constraining the topology of the Universe by
means of the matched circles statistic applied to polarised cosmic microwave
background (CMB) anisotropy maps. The advantages of using the CMB polarisation
maps in studies of the topology over simply analysing the temperature data as
has been done to-date are clearly demonstrated. We test our algorithm to search
for pairs of matched circles on simulated CMB maps for a universe with the
topology of 3-torus. It is found that the noise levels of both Planck and next
generation CMB experiments data are no longer prohibitive and should be low
enough to enable the use of the polarisation maps for such studies. For such
experiments the minimum radius of the back-to-back matched circles which can be
detected are determined. We also showed that the polarisation generated after
reionisation does not have an impact on detectability of the matched circles. |
Measuring line-of-sight shear with Einstein rings: a proof of concept: Line-of-sight effects in strong gravitational lensing have long been treated
as a nuisance. However, it was recently proposed that the line-of-sight shear
could be a cosmological observable in its own right, if it is not degenerate
with lens model parameters. We firstly demonstrate that the line-of-sight shear
can be accurately measured from a simple simulated strong lensing image with
percent precision. We then extend our analysis to more complex simulated images
and stress test the recovery of the line-of-sight shear when using deficient
fitting models, finding that it escapes from degeneracies with lens model
parameters, albeit at the expense of the precision. Lastly, we check the
validity of the tidal approximation by simulating and fitting an image
generated in the presence of many line-of-sight dark matter haloes, finding
that an explicit violation of the tidal approximation does not necessarily
prevent one from measuring the line-of-sight shear. | Effect of Redshift Distributions of Fast Radio Bursts on Cosmological
Constraints: Nowadays, fast radio bursts (FRBs) have been a promising probe for astronomy
and cosmology. However, it is not easy to identify the redshifts of FRBs to
date. Thus, no sufficient actual FRBs with identified redshifts can be used to
study cosmology currently. In the past years, one has to use the simulated FRBs
with "known" redshifts instead. To simulate an FRB, one should randomly assign
a redshift to it from a given redshift distribution. But the actual redshift
distribution of FRBs is still unknown so far. Therefore, many redshift
distributions have been assumed in the literature. In the present work, we
study the effect of various redshift distributions on cosmological constraints,
while they are treated equally. We find that different redshift distributions
lead to different cosmological constraining abilities from the simulated FRBs.
This result emphasizes the importance to find the actual redshift distribution
of FRBs, and reminds us of the possible bias in the FRB simulations due to the
redshift distributions. |
HI intensity mapping : a single dish approach: We discuss the detection of large scale HI intensity fluctuations using a
single dish approach with the ultimate objective of measuring the Baryonic
Acoustic Oscillations and constraining the properties of dark energy. We
present 3D power spectra, 2D angular power spectra for individual redshift
slices, and also individual line-of-sight spectra, computed using the S^3
simulated HI catalogue which is based on the Millennium Simulation. We consider
optimal instrument design and survey strategies for a single dish observation
at low and high redshift for a fixed sensitivity. For a survey corresponding to
an instrument with T_sys=50 K, 50 feed horns and 1 year of observations, we
find that at low redshift (z \approx 0.3), a resolution of 40 arc min and a
survey of 5000 deg^2 is close to optimal, whereas at higher redshift (z \approx
0.9) a resolution of 10 arcmin and 500 deg^2 would be necessary. Continuum
foreground emission from the Galaxy and extragalactic radio sources are
potentially a problem. We suggest that it could be that the dominant
extragalactic foreground comes from the clustering of very weak sources. We
assess its amplitude and discuss ways by which it might be mitigated. We then
introduce our concept for a single dish telescope designed to detect BAO at low
redshifts. It involves an under-illumintated static 40 m dish and a 60 element
receiver array held 90 m above the under-illuminated dish. Correlation
receivers will be used with each main science beam referenced against an
antenna pointing at one of the Celestial Poles for stability and control of
systematics. We make sensitivity estimates for our proposed system and
projections for the uncertainties on the power spectrum after 1 year of
observations. We find that it is possible to measure the acoustic scale at
z\approx 0.3 with an accuracy 2.4% and that w can be measured to an accuracy of
16%. | Probing the Curious Case of a Galaxy Cluster Merger in Abell 115 with
High Fidelity Chandra X-ray Temperature and Radio Maps: We present results from an X-ray and radio study of the merging galaxy
cluster Abell 115. We use the full set of 5 Chandra observations taken of A115
to date (360 ks total integration) to construct high-fidelity temperature and
surface brightness maps. We also examine radio data from the Very Large Array
at 1.5 GHz and the Giant Metrewave Radio Telescope at 0.6 GHz. We propose that
the high X-ray spectral temperature between the subclusters results from the
interaction of the bow shocks driven into the intracluster medium by the motion
of the subclusters relative to one another. We have identified morphologically
similar scenarios in Enzo numerical N-body/hydrodynamic simulations of galaxy
clusters in a cosmological context. In addition, the giant radio relic feature
in A115, with an arc-like structure and a relatively flat spectral index, is
likely consistent with other shock-associated giant radio relics seen in other
massive galaxy clusters. We suggest a dynamical scenario that is consistent
with the structure of the X-ray gas, the hot region between the clusters, and
the radio relic feature. |
Fitting the Constitution SNIa Data with Redshift Binned Parameterization
Method: In this work, we explore the cosmological consequences of the recently
released Constitution sample of 397 Type Ia supernovae (SNIa). By revisiting
the Chevallier-Polarski-Linder (CPL) parameterization, we find that, for
fitting the Constitution set alone, the behavior of dark energy (DE)
significantly deviate from the cosmological constant $\Lambda$, where the
equation of state (EOS) $w$ and the energy density $\rho_{\Lambda}$ of DE will
rapidly decrease along with the increase of redshift $z$. Inspired by this
clue, we separate the redshifts into different bins, and discuss the models of
a constant $w$ or a constant $\rho_{\Lambda}$ in each bin, respectively. It is
found that for fitting the Constitution set alone, $w$ and $\rho_{\Lambda}$
will also rapidly decrease along with the increase of $z$, which is consistent
with the result of CPL model. Moreover, a step function model in which
$\rho_{\Lambda}$ rapidly decreases at redshift $z\sim0.331$ presents a
significant improvement ($\Delta \chi^{2}=-4.361$) over the CPL
parameterization, and performs better than other DE models. We also plot the
error bars of DE density of this model, and find that this model deviates from
the cosmological constant $\Lambda$ at 68.3% confidence level (CL); this may
arise from some biasing systematic errors in the handling of SNIa data, or more
interestingly from the nature of DE itself. In addition, for models with same
number of redshift bins, a piecewise constant $\rho_{\Lambda}$ model always
performs better than a piecewise constant $w$ model; this shows the advantage
of using $\rho_{\Lambda}$, instead of $w$, to probe the variation of DE. | Resilience of the standard predictions for primordial tensor modes: We show that the prediction for the primordial tensor power spectrum cannot
be modified at leading order in derivatives. Indeed, one can always set to
unity the speed of propagation of gravitational waves during inflation by a
suitable disformal transformation of the metric, while a conformal one can make
the Planck mass time-independent. Therefore, the tensor amplitude unambiguously
fixes the energy scale of inflation. Using the Effective Field Theory of
Inflation, we check that predictions are independent of the choice of frame, as
expected. The first corrections to the standard prediction come from two parity
violating operators with three derivatives. Also the correlator
$<\gamma\gamma\gamma>$ is standard and only receives higher derivative
corrections. These results hold also in multifield models of inflation and in
alternatives to inflation and make the connection between a (quasi)
scale-invariant tensor spectrum and inflation completely robust. |
Effects of the Non-Equipartition of Electrons and Ions in the Outskirts
of Relaxed Galaxy Clusters: (abridged) We have studied the effects of electron-ion non-equipartition in
the outer regions of relaxed clusters for a wide range of masses in the
\LambdaCDM cosmology using one-dimensional hydrodynamic simulations. The
effects of the non-adiabatic electron heating efficiency, \beta, on the degree
of non-equipartition are also studied. Using the gas fraction f_gas = 0.17
(which is the upper limit for a cluster), we give a conservative lower limit of
the non-equipartition effect on clusters. Beyond the virial radius, the
non-equipartition effect depends rather strongly on \beta, and such a strong
dependence at the shock radius can be used to distinguish shock heating models
or constrain the shock heating efficiency of electrons. We have also studied
systematically the signatures of non-equipartition on X-ray and SZ observables.
We have calculated the effect of non-equipartition on the projected temperature
and X-ray surface brightness profiles using the MEKAL emission model. The
non-equipartition effect can introduce a ~10% bias in the projected temperature
at R_vir for a wide range of \beta. We also found that the effect of
non-equipartition on the projected temperature profiles can be enhanced by
increasing metallicity. We found that for our model in the \LambdaCDM Universe,
the integrated SZ bias, Y_{non-eq}/Y_{eq}, evolves slightly (at a percentage
level) with redshift, which is in contrast to the self-similar model in the
Einstein-de Sitter Universe. This may introduce biases in cosmological studies
using the f_gas technique. We discussed briefly whether the equipartition and
non-equipartition models near the shock region can be distinguished by future
radio observations with, for example, ALMA. | Calibration of star formation rate tracers for short- and long-lived
star formation episodes: To derive the history of star formation in the Universe a set of calibrated
star formation rate tracers at different wavelengths is required. The
calibration has to consistently take into account the effects of extinction,
star formation regime (short or long-lived) and evolutionary state to avoid
biases at different redshift ranges. We use evolutionary synthesis models
optimized for intense episodes of star formation in order to compute a
consistent calibration of the most usual star formation rate tracers at
different energy ranges, from X-ray to radio luminosities. Nearly-instantaneous
and continuous star formation regimes, and the effect of interstellar
extinction are considered, as well as the effect of metallicity on the
calibration of the different estimators. A consistent calibration of a complete
set of star formation rate tracers is presented, computed for the most usual
star-forming regions conditions: evolutionary state, star formation regime,
interstellar extinction and initial mass function. We discuss the validity of
the different tracers in different star formation scenarios and compare our
predictions with previous calibrations of general use. Nearly-instantaneous and
continuous star formation regimes must be distinguished. While the Star
Formation Strength (\msun) should be used for the former, the more common Star
Formation Rate (\msun yr$^{-1}$) is only valid for episodes forming stars at a
constant rate during extended periods for time. Moreover, even for the latter,
the evolutionary state should be taken into account, since most SFR tracers
stabilize only after 100 Myr of evolution. |
A doubled double hotspot in J0816+5003 and the logarithmic slope of the
lensing potential: We present an analysis of observations of the doubly-lensed double hotspot in
the giant radio galaxy J0816+5003 from MERLIN, MDM, WIYN, WHT, UKIRT and the
VLA. The images of the two hotspot components span a factor of two in radius on
one side of the lensing galaxy at impact parameters of less than 500pc. Hence
we measure the slope of the lensing potential over a large range in radius,
made possible by significant improvement in the accuracy of registration of the
radio and optical frame and higher resolution imaging data than previously
available. We also infer the lens and source redshifts to be 0.332 and > 1
respectively. Purely on the basis of lens modelling, and independently of
stellar velocity dispersion measurements, we find the potential to be very
close to isothermal. | The contribution of high redshift galaxies to the Near-Infrared
Background: Several independent measurements have confirmed the existence of fluctuations
($\delta F_{\rm obs}\approx 0.1 \rm nW/m^{2}/sr$ at $3.6 \rm \mu m$) up to
degree angular scales in the source-subtracted Near InfraRed Background (NIRB)
whose origin is unknown. By combining high resolution cosmological
N-body/hydrodynamical simulations with an analytical model, and by matching
galaxy Luminosity Functions (LFs) and the constraints on reionization
simultaneously, we predict the NIRB absolute flux and fluctuation amplitude
produced by high-$z$ ($z > 5$) galaxies (some of which harboring Pop III stars,
shown to provide a negligible contribution). This strategy also allows us to
make an empirical determination of the evolution of ionizing photon escape
fraction: we find $f_{\rm esc} = 1$ at $z \ge 11$, decreasing to $\approx 0.05$
at $z = 5$. In the wavelength range $1.0-4.5 \rm \mu m$, the predicted
cumulative flux is $F =0.2-0.04 \rm nW/m^2/sr$. However, we find that the
radiation from high-$z$ galaxies (including those undetected by current
surveys) is insufficient to explain the amplitude of the observed fluctuations:
at $l=2000$, the fluctuation level due to $z > 5$ galaxies is $\delta F =
0.01-0.002 \rm nW/m^2/sr$, with a relative wavelength-independent amplitude
$\delta F/F = 4$%. The source of the missing power remains unknown. This might
indicate that an unknown component/foreground, with a clustering signal very
similar to that of high-$z$ galaxies, dominates the source-subtracted NIRB
fluctuation signal. |
PTF11mnb: the first analog of supernova 2005bf: We study PTF11mnb, a He-poor supernova (SN) whose pre-peak light curves (LCs)
resemble those of SN 2005bf, a peculiar double-peaked stripped-envelope (SE)
SN. LCs, colors and spectral properties are compared to those of SN 2005bf and
normal SE SNe. A bolometric LC is built and modeled with the SNEC
hydrodynamical code explosion of a MESA progenitor star, as well as with
semi-analytic models. The LC of PTF11mnb turns out to be similar to that of SN
2005bf until $\sim$50 d, when the main (secondary) peaks occur at $-18.5$ mag.
The early peak occurs at $\sim$20 d, and is about 1.0 mag fainter. After the
main peak, the decline rate of PTF11mnb is remarkably slower than that of SN
2005bf, and it traces the $^{56}$Co decay rate. The spectra of PTF11mnb reveal
no traces of He unlike in the case of SN Ib 2005bf. The bolometric LC is well
reproduced by the explosion of a massive ($M_{ej} =$ 7.8 $M_{\odot}$), He-poor
star with a double-peaked $^{56}$Ni distribution, a total $^{56}$Ni mass of
0.59 $M_{\odot}$ and an explosion energy of 2.2$\times$10$^{51}$ erg.
Alternatively, a normal SN Ib/c explosion [M($^{56}$Ni)$=$0.11 $M_{\odot}$,
$E_{K}$ = 0.2$\times$10$^{51}$ erg, $M_{ej} =$ 1 $M_{\odot}$] can power the
first peak while a magnetar ($B$=5.0$\times$10$^{14}$ G, $P=18.1$ ms) provides
energy for the main peak. The early $g$-band LC implies a radius of at least 30
$R_{\odot}$. If PTF11mnb arose from a massive He-poor star characterized by a
double-peaked $^{56}$Ni distribution, the ejecta mass and the absence of He
imply a large ZAMS mass ($\sim85 M_{\odot}$) for the progenitor, which most
likely was a Wolf-Rayet star, surrounded by an extended envelope formed either
by a pre-SN eruption or due to a binary configuration. Alternatively, PTF11mnb
could be powered by a normal SE SN during the first peak and by a magnetar
afterwards. | Inflationary gravitational waves and exotic pre Big Bang Nucleosynthesis
cosmology: According to the most popular scenario, the early Universe should have
experienced an accelerated expansion phase, called Cosmological Inflation,
after which the standard Big Bang Cosmology would have taken place giving rise
to the radiation-dominated epoch. However, the details of the inflationary
scenario are far to be completely understood. Thus, in this paper we study if
possible additional (exotic) cosmological phases could delay the beginning of
the standard Big Bang history and alter some theoretical predictions related to
the inflationary cosmological perturbations, like, for instance, the order of
magnitude of the tensor-to-scalar ratio $r$. |
Reevaluating LSST's Capability for Time Delay Measurements in Quasar
Accretion Discs: The Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory
is poised to observe thousands of quasars using the Deep Drilling Fields (DDF)
across six broadband filters over a decade. Understanding quasar accretion disc
(AD) time delays is pivotal for probing the physics of these distant objects.
Pozo Nu\~nez et al. (2023) has recently demonstrated the feasibility of
recovering AD time delays with accuracies ranging from 5\% to 20\%, depending
on the quasar's redshift and time sampling intervals. Here we reassess the
potential for measuring AD time delays under the current DDF observing cadence,
which is placeholder until a final cadence is decided. We find that contrary to
prior expectations, achieving reliable AD time delay measurements for quasars
is significantly more challenging, if not unfeasible, due to the limitations
imposed by the current observational strategies. | Spatial Curvature at the Sound Horizon: The effect of spatial curvature on primordial perturbations is controlled by
$ \Omega_{K,0}/c_{s}^{2} $, where $ \Omega_{K,0} $ is today's fractional
density of spatial curvature and $ c_{s} $ is the speed of sound during
inflation. Here we study these effects in the limit $ c_{s}\ll 1 $. First, we
show that the standard cosmological soft theorems in flat universes are
violated in curved universes and the soft limits of correlators can have
non-universal contributions even in single-clock inflation. This is a
consequence of the fact that, in the presence of spatial curvature, there is a
gap between the spectrum of residual diffeomorphisms and that of physical
modes. Second, there are curvature corrections to primordial correlators, which
are not scale invariant. We provide explicit formulae for these corrections to
the power spectrum and the bispectrum to linear order in curvature in
single-clock inflation. We show that the large-scale CMB anisotropies could
provide interesting new constraints on these curvature effects, and therefore
on $ \Omega_{K,0}/c_{s}^{2} $, but it is necessary to go beyond our
linear-order treatment. |
Galaxy-galaxy weak-lensing measurement from SDSS: II. host halo
properties of galaxy groups: As the second paper of a series on studying galaxy-galaxy lensing signals
using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we present our
measurement and modelling of the lensing signals around groups of galaxies. We
divide the groups into four halo mass bins, and measure the signals around four
different halo-center tracers: brightest central galaxy (BCG),
luminosity-weighted center, number-weighted center and X-ray peak position. For
X-ray and SDSS DR7 cross identified groups, we further split the groups into
low and high X-ray emission subsamples, both of which are assigned with two
halo-center tracers, BCGs and X-ray peak positions. The galaxy-galaxy lensing
signals show that BCGs, among the four candidates, are the best halo-center
tracers. We model the lensing signals using a combination of four
contributions: off-centered NFW host halo profile, sub-halo contribution,
stellar contribution, and projected 2-halo term. We sample the posterior of 5
parameters i.e., halo mass, concentration, off-centering distance, sub halo
mass, and fraction of subhalos via a MCMC package using the galaxy-galaxy
lensing signals. After taking into account the sampling effects (e.g. Eddington
bias), we found the best fit halo masses obtained from lensing signals are
quite consistent with those obtained in the group catalog based on an abundance
matching method, except in the lowest mass bin. Subject headings: (cosmology:)
gravitational lensing, galaxies: clusters: general | The Redshift-Space Momentum Power Spectrum I: Optimal Estimation From
Peculiar Velocity Surveys: Low redshift surveys of galaxy peculiar velocities provide a wealth of
cosmological information. We revisit the idea of extracting this information by
directly measuring the redshift-space momentum power spectrum from such
surveys. We provide a comprehensive theoretical and practical framework for
estimating and fitting this from data, analogous to well understood techniques
used to measure the galaxy density power spectrum from redshift surveys. We
formally derive a new estimator, which includes the effects of shot noise and
survey geometry; we evaluate the variance of the estimator in the Gaussian
regime; we compute the optimal weights for the estimator; we demonstrate that
the measurements are Gaussian distributed, allowing for easy extraction of
cosmological parameters; and we explore the effects of peculiar velocity
measurement errors. We finish with a proof-of-concept using realistic mock
galaxy catalogues, which demonstrates that we can measure and fit both the
redshift-space galaxy density and momentum power spectra from peculiar velocity
surveys and that including the latter substantially improves our constraints on
the growth rate of structure. We also provide theoretical descriptions for
modelling the non-linear redshift-space density and momentum power spectrum
multipoles, and forecasting the constraints on cosmological parameters using
the Fisher information contained in these measurements for arbitrary weights.
These may be useful for measurements of the galaxy density power spectrum even
in the absence of peculiar velocities. |
Anisotropic Trispectrum of Curvature Perturbations Induced by Primordial
Non-Abelian Vector Fields: Motivated by the interest in models of the early universe where statistical
isotropy is broken and can be revealed in cosmological observations, we
consider an SU(2) theory of gauge interactions in a single scalar field
inflationary scenario. We calculate the trispectrum of curvature perturbations,
as a natural follow up to a previous paper of ours, where we studied the
bispectrum in the same kind of models. The choice of a non-Abelian set-up turns
out to be very convenient: on one hand, gauge boson self-interactions can be
very interesting being responsible for extra non-trivial terms (naturally
absent in the Abelian case) appearing in the cosmological correlation
functions; on the other hand, its results can be easily reduced to the U(1)
case. As expected from the presence of the vector bosons, preferred spatial
directions arise and the trispectrum reveals anisotropic signatures. We
evaluate its amplitude tau_{NL}, which receives contributions both from scalar
and vector fields, and verify that, in a large subset of its parameter space,
the latter contributions can be larger than the former. We carry out a shape
analysis of the trispectrum; in particular we discuss, with some examples, how
the anisotropy parameters appearing in the analytic expression of the
trispectrum can modulate its profile and we show that the amplitude of the
anisotropic part of the trispectrum can be of the same order of magnitude as
the isotropic part. | The Cosmic Chemical Evolution as seen by the Brightest Events in the
Universe: Gamma-ray bursts (GRBs) are the brightest events in the universe. They have
been used in the last five years to study the cosmic chemical evolution, from
the local universe to the first stars. The sample size is still relatively
small when compared to field galaxy surveys. However, GRBs show a universe that
is surprising. At z > 2, the cold interstellar medium in galaxies is chemically
evolved, with a mean metallicity of about 1/10 solar. At lower redshift (z <
1), metallicities of the ionized gas are relatively low, on average 1/6 solar.
Not only is there no evidence of redshift evolution in the interval 0 < z <
6.3, but also the dispersion in the ~ 30 objects is large. This suggests that
the metallicity of host galaxies is not the physical quantity triggering GRB
events. From the investigation of other galaxy parameters, it emerges that
active star-formation might be a stronger requirement to produce a GRB. Several
recent striking results strongly support the idea that GRB studies open a new
view on our understanding of galaxy formation and evolution, back to the very
primordial universe at z ~ 8. |
Cosmology with the pairwise kinematic SZ effect: Calibration and
validation using hydrodynamical simulations: We study the potential of the kinematic SZ effect as a probe for cosmology,
focusing on the pairwise method. The main challenge is disentangling the
cosmologically interesting mean pairwise velocity from the cluster optical
depth and the associated uncertainties on the baryonic physics in clusters.
Furthermore, the pairwise kSZ signal might be affected by internal cluster
motions or correlations between velocity and optical depth. We investigate
these effects using the Magneticum cosmological hydrodynamical simulations, one
of the largest simulations of this kind performed to date. We produce tSZ and
kSZ maps with an area of $\simeq 1600~\mathrm{deg}^2$, and the corresponding
cluster catalogues with $M_{500c} \gtrsim 3 \times 10^{13}~h^{-1}M_\odot$ and
$z \lesssim 2$. From these data sets we calibrate a scaling relation between
the average Compton-$y$ parameter and optical depth. We show that this relation
can be used to recover an accurate estimate of the mean pairwise velocity from
the kSZ effect, and that this effect can be used as an important probe of
cosmology. We discuss the impact of theoretical and observational systematic
effects, and find that further work on feedback models is required to interpret
future high-precision measurements of the kSZ effect. | Gravitational wave emission from binary supermassive black holes: Massive black hole binaries (MBHBs) are unavoidable outcomes of the
hierarchical structure formation process, and according to the theory of
general relativity are expected to be the loudest gravitational wave (GW)
sources in the Universe. In this article I provide a broad overview of MBHBs as
GW sources. After reviewing the basics of GW emission from binary systems and
of MBHB formation, evolution and dynamics, I describe in some details the
connection between binary properties and the emitted gravitational waveform.
Direct GW observations will provide an unprecedented wealth of information
about the physical nature and the astrophysical properties of these extreme
objects, allowing to reconstruct their cosmic history, dynamics and coupling
with their dense stellar and gas environment. In this context I describe
ongoing and future efforts to make a direct detection with space based
interferometry and pulsar timing arrays, highlighting the invaluable scientific
payouts of such enterprises. |
Gas infall into atomic cooling haloes: on the formation of protogalactic
disks and supermassive black holes at z > 10: We have performed cosmo-hydro simulations using the RAMSES code to study
atomic cooling (ACHs) haloes at z=10 with masses 5E7Msun<~M<~2E9Msun. We assume
primordial gas and H2-cooling and prior star-formation have been suppressed. We
analysed 19 haloes (gas and DM) at a resolution of ~10 (proper) pc, selected
from a total volume of ~2E3 (comoving) Mpc3. This is the largest statistical
hydro-sim. study of ACHs at z>10 to date. We examine the morphology, angular
momentum (AM), thermodynamic, and turbulence of these haloes, in order to
assess the prevalence of disks and supermassive black holes (SMBHs). We find no
correlation between either the magnitude or the direction of the AM of the gas
and its parent DM halo. Only 3 haloes form rotationally supported cores. Two of
the most massive haloes form massive, compact overdense blobs. These blobs have
an accretion rate ~0.5 Msun/yr (at a distance of 100 pc), and are possible
sites of SMBH formation. Our results suggest that the degree of rotational
support and the fate of the gas in a halo is determined by its large-scale
environment and merger history. In particular, the two haloes forming blobs are
located at knots of the cosmic web, cooled early on, and experienced many
mergers. The gas in these haloes is lumpy and highly turbulent, with Mach N. >~
5. In contrast, the haloes forming rotationally supported cores are relatively
more isolated, located midway along filaments, cooled more recently, and
underwent fewer mergers. Thus, the gas in these haloes is less lumpy and less
turbulent (Mach <~ 4), and could retain most of its AM. The remaining 14 haloes
have intermediate properties. If verified in a larger sample of haloes and with
additional physics, our results will have implications for observations of the
highest-redshift galaxies and quasars with JWST. | Exotic Image Formation in Strong Gravitational Lensing by Clusters of
Galaxies -- II: Uncertainties: Due to the finite amount of observational data, the best-fit parameters
corresponding to the reconstructed cluster mass have uncertainties. In turn,
these uncertainties affect the inferences made from these mass models.
Following our earlier work, we have studied the effect of such uncertainties on
the singularity maps in simulated and actual galaxy clusters. The mass models
for both simulated and real clusters have been constructed using grale. The
final best-fit mass models created using grale give the simplest singularity
maps and a lower limit on the number of point singularities that a lens has to
offer. The simple nature of these singularity maps also puts a lower limit on
the number of three image (tangential and radial) arcs that a cluster lens has.
Hence, we estimate the number of galaxy sources giving rise to the three image
arcs, which can be observed with the James Webb Space Telescope (JWST). We find
that we expect to observe at least 20-30 tangential and 5-10 radial three-image
arcs in the Hubble Frontier Fields cluster lenses with the JWST. |
Is the Observable Universe Consistent with the Cosmological Principle?: The Cosmological Principle (CP) -- the notion that the Universe is spatially
isotropic and homogeneous on large scales -- underlies a century of progress in
cosmology. It is conventionally formulated through the
Friedmann-Lema\^itre-Robertson-Walker (FLRW) cosmologies as the spacetime
metric, and culminates in the successful and highly predictive
$\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged
within the $\Lambda$CDM model, most notably a statistically significant
discrepancy in the value of the Hubble constant, $H_0$. Since the notion of
cosmic expansion determined by a single parameter is intimately tied to the CP,
implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP
itself. This review surveys current observational hints for deviations from the
expectations of the CP, highlighting synergies and disagreements that warrant
further study. Setting aside the debate about individual large structures,
potential deviations from the CP include variations of cosmological parameters
on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in
quasar polarizations and galaxy spins. While it is possible that a host of
observational systematics are impacting results, it is equally plausible that
precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic
but non-fundamental symmetry assumption. | Lyman-alpha emitters as tracers of the transitioning Universe: Of the many ways of detecting high redshift galaxies, the selection of
objects due to their redshifted Ly-alpha emission has become one of the most
successful. But what types of galaxies are selected in this way? Until
recently, Ly-alpha emitters were understood to be small star-forming galaxies,
possible building-blocks of larger galaxies. But with increased number of
observations of Ly-alpha emitters at lower redshifts, a new picture emerges.
Ly-alpha emitters display strong evolution in their properties from higher to
lower redshift. It has previously been shown that the fraction of
ultra-luminous infrared galaxies (ULIRGs) among the Ly-alpha emitters increases
dramatically between redshift three and two. Here, the fraction of AGN among
the LAEs is shown to follow a similar evolutionary path. We argue that Ly-alpha
emitters are not a homogeneous class of objects, and that the objects selected
with this method reflect the general star forming and active galaxy populations
at that redshift. Ly-alpha emitters should hence be excellent tracers of galaxy
evolution in future simulations and modeling. |
Pressure Support vs. Thermal Broadening in the Lyman-alpha Forest II:
Effects of the Equation of State on Transverse Structure: We examine the impact of gas pressure on the transverse coherence of
high-redshift (2 <= z <= 4) Lyman-alpha forest absorption along neighboring
lines of sight that probe the gas Jeans scale (projected separation Delta r <=
500 kpc/h comoving; angular separation Delta theta <= 30"). We compare
predictions from two smoothed particle hydrodynamics (SPH) simulations that
have different photoionization heating rates and thus different
temperature-density relations in the intergalactic medium (IGM). We also
compare spectra computed from the gas distributions to those computed from the
pressureless dark matter. The coherence along neighboring sightlines is
markedly higher for the hotter, higher pressure simulation, and lower for the
dark matter spectra. We quantify this coherence using the flux
cross-correlation function and the conditional distribution of flux decrements
as a function of transverse and line-of-sight (velocity) separation. Sightlines
separated by Delta theta <= 15" are ideal for probing this transverse
coherence. Higher pressure decreases the redshift-space anisotropy of the flux
correlation function, while higher thermal broadening increases the anisotropy.
In contrast to the longitudinal (line-of-sight) structure of the Lya forest,
the transverse structure on these scales is dominated by pressure effects
rather than thermal broadening. With the rapid recent growth in the number of
known close quasar pairs, paired line-of-sight observations offer a promising
new route to probe the IGM temperature-density relation and test the
unexpectedly high temperatures that have been inferred from single sightline
analyses. | Spherical Cows in Dark Matter Indirect Detection: Dark matter (DM) halos have long been known to be triaxial, but in studies of
possible annihilation and decay signals they are often treated as approximately
spherical. In this work, we examine the asymmetry of potential indirect
detection signals of DM annihilation and decay, exploiting the large statistics
of the hydrodynamic simulation Illustris. We carefully investigate the effects
of the baryons on the sphericity of annihilation and decay signals for both the
case where the observer is at 8.5 kpc from the center of the halo (exemplified
in the case of Milky Way-like halos), and for an observer situated well outside
the halo. In the case of Galactic signals, we find that both annihilation and
decay signals are expected to be quite symmetric, with axis ratios very
different from 1 occurring rarely. In the case of extragalactic signals, while
decay signals are still preferentially spherical, the axis ratio for
annihilation signals has a much flatter distribution, with elongated profiles
appearing frequently. Many of these elongated profiles are due to large
subhalos and/or recent mergers. Comparing to gamma-ray emission from the Milky
Way and X-ray maps of clusters, we find that the gamma-ray background appears
less spherical/more elongated than the expected DM signal from the large
majority of halos, and the Galactic gamma ray excess appears very spherical,
while the X- ray data would be difficult to distinguish from a DM signal by
elongation/sphericity measurements alone. |
Unveiling the nature of M94's (NGC4736) outer region: a panchromatic
perspective: We have conducted a deep multi-wavelength analysis (0.15-160 mum) to study
the outer region of the nearby galaxy M94. We show that the non-optical data
support the idea that the outskirts of this galaxy is not formed by a closed
stellar ring (as traditionally claimed in the literature) but by a spiral arm
structure. In this sense, M94 is a good example of a Type III (anti-truncated)
disk galaxy having a very bright outer disk. The outer disk of this galaxy
contains ~23% of the total stellar mass budget of the galaxy and contributes
~10% of the new stars created showing that this region of the galaxy is active.
In fact, the specific star formation rate of the outer disk (~0.012 Gyr^{-1})
is a factor of ~2 larger (i.e. the star formation is more efficient per unit
stellar mass) than in the inner disk. We have explored different scenarios to
explain the enhanced star formation in the outer disk. We find that the inner
disk (if considered as an oval distortion) can dynamically create a spiral arm
structure in the outer disk which triggers the observed relatively high star
formation rate as well as an inner ring similar to what is found in this
galaxy. | Cosmic homogeneity: a spectroscopic and model-independent measurement: Cosmology relies on the Cosmological Principle, i.e., the hypothesis that the
Universe is homogeneous and isotropic on large scales. This implies in
particular that the counts of galaxies should approach a homogeneous scaling
with volume at sufficiently large scales. Testing homogeneity is crucial to
obtain a correct interpretation of the physical assumptions underlying the
current cosmic acceleration and structure formation of the Universe. In this
Letter, we use the Baryon Oscillation Spectroscopic Survey to make the first
spectroscopic and model-independent measurements of the angular homogeneity
scale $\theta_{\rm h}$. Applying four statistical estimators, we show that the
angular distribution of galaxies in the range 0.46 < z < 0.62 is consistent
with homogeneity at large scales, and that $\theta_{\rm h}$ varies with
redshift, indicating a smoother Universe in the past. These results are in
agreement with the foundations of the standard cosmological paradigm. |
Direct Numerical Simulation of Reionization II: Recombinations, Clumping
Factors, and the Photon Budget for Reionization: In this first of several application papers, we investigate the mechanics of
reionization from stellar sources in high-z galaxies, the utility of various
clumping factors on estimating the recombination time in the IGM, and the
photon budget required to achieve reionization. We test the accuracy of the
static and time-dependent models of Madau et al. as predictors of reionization
completion/maintenance. We simulate a WMAP7 LCDM cosmological model in a 20 Mpc
comoving cube with 800^3 uniform fluid cells and dark matter particles. By
tuning our star formation to approximately match the observed star formation
rate density and luminosity function, we created a fully coupled
radiation-hydro realization of H reionization which begins to ionize at z~10
and completes at z~5.8. We find that roughly 2 ionizing photons per H atom are
required to convert the neutral IGM to a highly ionized state, which supports
the "photon starved" scenario discussed by Bolton & Haehnelt. The events during
reionization that lead to this number can generally be described as inside-out,
but in reality the narrative depends on the level of ionization of the gas one
attributes to as ionized. We find that the formula for the UV photon production
rate dN/dt_ion(z) needed to maintain the IGM in an ionized state derived by
Madau et al. should not be used to predict the epoch of reionization completion
because it ignores history-dependent terms in the global ionization balance
which are not ignorable. We find that the time-dependent model for the ionized
volume fraction Q_HII is more predictive, but overestimates the redshift of
reionization completion by delta_z~1. We propose a revised formulation of the
time-dependent model which agrees with our simulation to O(1%). Finally, we use
our simulation to estimate a global UV escape fraction due to circumgalactic
gas resolved on our mesh to be <f_esc>~0.7. | Modified initial power spectrum and too big to fail problem: The galactic scale challenges of dark matter such as "missing satellite"
problem and "too big to fail" problem are the main caveats of standard model of
cosmology. These challenges could be solved either by implementing the
complicated baryonic physics or it could be considered as an indication to a
new physics beyond the standard model of cosmology. The modification of
collisionless dark matter models or the standard initial conditions are two
promising venues for study. In this work, we investigate the effects of the
deviations from scale invariant initial curvature power spectrum on number
density of dark matter halos. We develop the non-Markov extension of the
excursion set theory to calculate the number density of dark matter
substructures and dark matter halo progenitor mass distribution. We show that
the plausible solution to "too big to fail" problem could be obtained by a
Gaussian excess in initial power in the scales of $k_* \sim 3 \text{h/Mpc}$
that is related to the mass scale of $M_* \sim 10^{11} M_{\odot}$. We show that
this deviation leads to the decrement of dark matter sub-halos in galactic
scale, which is consistent with the current status of the non-linear power
spectrum. Our proposal also has a prediction that the number density of Milky
way type galaxies must be higher than the standard case. |
Expectations for Horizon-Scale Supermassive Black Hole Population
Studies with the ngEHT: We present estimates for the number of supermassive black holes (SMBHs) for
which the next-generation Event Horizon Telescope (ngEHT) can identify the
black hole ``shadow,'' along with estimates for how many black hole masses and
spins the ngEHT can expect to constrain using measurements of horizon-resolved
emission structure. Building on prior theoretical studies of SMBH accretion
flows and analyses carried out by the Event Horizon Telescope (EHT)
collaboration, we construct a simple geometric model for the polarized emission
structure around a black hole, and we associate parameters of this model with
the three physical quantities of interest. We generate a large number of
realistic synthetic ngEHT datasets across different assumed source sizes and
flux densities, and we estimate the precision with which our defined proxies
for physical parameters could be measured from these datasets. Under April
weather conditions and using an observing frequency of 230~GHz, we predict that
a ``Phase 1'' ngEHT can potentially measure $\sim$50 black hole masses,
$\sim$30 black hole spins, and $\sim$7 black hole shadows across the entire
sky. | PAndAS' cubs: discovery of two new dwarf galaxies in the surroundings of
the Andromeda and Triangulum galaxies: We present the discovery of two new dwarf galaxies, Andromeda XXI and
Andromeda XXII, located in the surroundings of the Andromeda and Triangulum
galaxies (M31 and M33). These discoveries stem from the first year data of the
Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the
M31/M33 group conducted with the Megaprime/MegaCam wide-field camera mounted on
the Canada-France-Hawaii Telescope. Both satellites appear as spatial
overdensities of stars which, when plotted in a color-magnitude diagram, follow
metal-poor, [Fe/H]=-1.8, red giant branches at the distance of M31/M33.
Andromeda XXI is a moderately bright dwarf galaxy (M_V=-9.9+/-0.6), albeit with
low surface brightness, emphasizing again that many relatively luminous M31
satellites still remain to be discovered. It is also a large satellite, with a
half-light radius close to 1 kpc, making it the fourth largest Local Group
dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda
II and Sagittarius around the Milky Way, and supports the trend that M31
satellites are larger than their Milky Way counterparts. Andromeda XXII is much
fainter (M_V=-6.5+/-0.8) and lies a lot closer in projection to M33 than it
does to M31 (42 vs. 224 kpc), suggesting that it could be the first Triangulum
satellite to be discovered. Although this is a very exciting possibility in the
context of a past interaction of M33 with M31 and the fate of its satellite
system, a confirmation will have to await a good distance estimate to confirm
its physical proximity to M33. Along with the dwarf galaxies found in previous
surveys of the M31 surroundings, these two new satellites bring the number of
dwarf spheroidal galaxies in this region to 20. |
Impact of scale-dependent bias and nonlinear evolution on the ISW: I summarize recent results from Smith, Hernandez-Monteagudo & Seljak (2009),
a study of the impact of nonlinear evolution of gravitational potentials in the
LCDM model on the Integrated Sachs-Wolfe (ISW) contribution to the cross-power
spectrum of the CMB and a set of biased tracers of the mass. We use a large
ensemble of N-body simulations to directly follow the potentials and compare
the results to analytic perturbation theory (PT) methods. The PT predictions
match our results to high precision for k<0.2 Mpc/h. We analyze the CMB-density
tracer cross-spectrum using simulations and renormalized bias PT, and find good
agreement. The usual assumption is that nonlinear evolution enhances the growth
of structure and counteracts the linear ISW on small scales, leading to a
change in sign of the CMB-LSS cross-spectrum at small scales. However, PT
analysis suggests that this trend reverses at late times when the logarithmic
growth rate f=d ln D/d ln a<1/2 or Omega_m (z)<0.3. Numerical results confirm
these expectations and we find nonlinear enhancement of the ISW signal on small
scales at late-times. On computing the total contribution to the angular
spectrum, we find that nonlinearity and scale dependence of the bias are unable
to influence the signal-to-noise of the current and future measurements. | Radio multifrequency observations of galaxy clusters. The Abell
399$-$401 pair: Galaxy clusters are assembled via merging of smaller structures, in a process
that generates shocks and turbulence in the intra cluster medium and produces
radio diffuse emission in the form of halos and relics. The cluster pair
A399-A401 represents a special case: both clusters host a radio halo. Recent
Low Frequency Array (LOFAR) observations at 140 MHz revealed the presence of a
radio bridge connecting the two clusters along with two relic candidates. These
relics include one South of A399 and the other in between the two clusters, in
proximity of a shock front detected in X-ray observations. In this paper we
present observations of the A399-A401 cluster pair at 1.7, 1.4, 1.2 GHz and 346
MHz from the Westerbork Synthesis Radio Telescope (WSRT). We detect the radio
halo in the A399 cluster at 346 MHz, extending up to $\sim 650$ kpc and with a
$125 \pm 6$ mJy flux density. Its spectral index between 140 MHz and 346 MHz is
$\alpha = 1.75 \pm 0.14$. The two candidate relics are also seen at 346 MHz and
we determine their spectral indices to be $\alpha = 1.10 \pm 0.14$ and $\alpha
= 1.46 \pm 0.14$. The low surface brightness bridge connecting the two clusters
is below the noise level at 346 MHz, therefore we constrain the bridge average
spectral index to be steep, i.e. $\alpha > 1.5$ at 95% confidence level. This
result favours the scenario where dynamically-induced turbulence is a viable
mechanism to reaccelerate a population of mildly relativistic particles and
amplify magnetic fields on scales of a few Mpcs.
Key words: galaxies: clusters: general - galaxies: clusters: individual:
Abell 399 - radio continuum: general |
The large-scale environment of thermonuclear and core-collapse
supernovae: The new generation of wide-field time-domain surveys has made it feasible to
study the clustering of supernova (SN) host galaxies in the large-scale
structure (LSS) for the first time. We investigate the LSS environment of SN
populations, using 106 dark matter density realisations with a resolution of
$\sim$ 3.8 Mpc, constrained by the 2M++ galaxy survey. We limit our analysis to
redshift $z<0.036$, using samples of 498 thermonuclear and 782 core-collapse
SNe from the Zwicky Transient Facility's Bright Transient Survey and Census of
the Local Universe catalogues. We detect clustering of SNe with high
significance; the observed clustering of the two SNe populations is consistent
with each other. Further, the clustering of SN hosts is consistent with that of
the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey
(BOSS) DR12 spectroscopic galaxy sample in the same redshift range. Using a
tidal shear classifier, we classify the LSS into voids, sheets, filaments and
knots. We find that both SNe and SDSS galaxies are predominantly found in
sheets and filaments. SNe are significantly under-represented in voids and
over-represented in knots compared to the volume fraction in these structures.
This work opens the potential for using forthcoming wide-field deep SN surveys
as a complementary LSS probe. | The Photon Spectrum of Asymmetric Dark Stars: Asymmetric Dark Stars, i.e., compact objects formed from the collapse of
asymmetric dark matter could potentially produce a detectable photon flux if
dark matter particles self-interact via dark photons that kinetically mix with
ordinary photons. The morphology of the emitted spectrum is significantly
different and therefore distinguishable from a typical black-body one. Given
the above and the fact that asymmetric dark stars can have masses outside the
range of neutron stars, the detection of such a spectrum can be considered as a
smoking gun signature for the existence of these exotic stars. |
The WISE view of the disc-torus connection in z~0.6 Active Galactic
Nuclei: We selected all radio-quiet AGN in the latest release of Sloan digital sky
survey quasar catalog, with redshift in the range 0.56-0.73. About 4000 (~80%)
of these have been detected in all four IR-bands of WISE (Wide-field Infrared
Survey Explorer). This is the largest sample suitable to study the disc-torus
connection. We find that the torus reprocesses on average ~1/3-1/2 of the
accretion disc luminosity. | Halo Models of Large Scale Structure and Reliability of Cosmological
N-Body Simulations: Halo models of the large scale structure of the Universe are critically
examined, focusing on the definition of halos as smooth distributions of cold
dark matter. This definition is essentially based on the results of
cosmological N-body simulations. By a careful analysis of the standard
assumptions of halo models and N-body simulations and by taking into account
previous studies of self-similarity of the cosmic web structure, we conclude
that N-body cosmological simulations are not fully reliable in the range of
scales where halos appear. Therefore, to have a consistent definition of halos,
it is necessary either to define them as entities of arbitrary size with a
grainy rather than smooth structure or to define their size in terms of
small-scale baryonic physics. |
Radio Detection of Green Peas: Implications for Magnetic Fields in Young
Galaxies: Green Peas are a new class of young, emission line galaxies that were
discovered by citizen volunteers in the Galaxy Zoo project. Their low stellar
mass, low metallicity and very high star formation rates make Green Peas the
nearby (z~0.2) analogs of the Lyman-break Galaxies (LBGs) which account for the
bulk of the star formation in the early universe (z~2-5). They thus provide
accessible laboratories in the nearby Universe for understanding star
formation, supernova feedback, particle acceleration and magnetic field
amplification in early galaxies. We report the first direct radio detection of
Green Peas with low frequency GMRT observations and our stacking detection with
archival VLA FIRST data. We show that the radio emission implies that these
extremely young galaxies already have magnetic fields (>30 muG) even larger
than that of the Milky Way. This is at odds with the present understanding of
magnetic field growth based on amplification of seed fields by dynamo action
over a galaxy's lifetime. Our observations strongly favor models with
pregalactic magnetic fields at muG levels. | Dark matter halo mass functions and density profiles from mass and
energy cascade: Without relying on a spherical or ellipsoidal collapse model, we analytically
derive the halo mass function and cuspy halo density (inner slope of -4/3)
based on the mass and energy cascade theory in dark matter flow. The
hierarchical halo structure formation leads to halo or particle random walk
with a position-dependent waiting time $\tau_g$. The inverse mass cascade from
small to large scales leads to the halo random walk in mass space with
$\tau_g\propto m_h^{-\lambda}$, where $m_h$ is the halo mass and $\lambda$ is a
halo geometry parameter with predicted value of 2/3. The corresponding
Fokker-Planck solution for halo random walk in mass space gives rise to the
halo mass function with a power-law behavior on small scale and exponential
decay on large scale. This can be further improved by considering two different
$\lambda$ for haloes below and above a critical mass scale $m_h^*$, i.e. a
double-$\lambda$ halo mass function. A double-$\gamma$ density profile can be
derived based on the particle random walk in 3D space with a position-dependent
waiting time $\tau_g \propto \Phi(r)^{-1} \propto r^{-\gamma}$, where $\Phi$ is
the gravitational potential and $r$ is the particle distance to halo center.
Theory predicts $\gamma=2/3$ that leads to a cuspy density profile with an
inner slope of -4/3, consistent with the predicted scaling laws from energy
cascade. The Press-Schechter mass function and Einasto density profile are
special cases of proposed models. The small scale permanence can be identified
due to the scale-independent rates of mass and energy cascade, where density
profiles of different halo masses and redshifts converge to the $-4/3$ scaling
law ($\rho_h \propto r^{-4/3}$) on small scales. Theory predicts halo number
density scales with mass as $\propto m_h^{-1.9}$, while halo mass density
scales as $\propto m_h^{4/9}$. Results were compared against the Illustris
simulations. |
Flat Patterns in Cosmic Structure: It is natural to wonder how far the flat pattern in the distribution of
galaxies and clusters of galaxies around the de Vaucoueurs Local Supercluster
extends, and whether there are other similarly extended flat patterns in cosmic
structure. I present evidence of two extended flat sheet-like patterns in the
distributions of galaxies and clusters detected at redshifts less than 0.021.
Sheet A contains our position and is tilted 11 degrees from the supergalactic
pole, meaning the Local Supercluster is a moderately bent part of the more
extended Sheet A. The continuation of this sheet is detected in the disjoint
sample of galaxies at redshifts 0.021 to 0.041 and of galaxies and clusters of
galaxies at redshifts 0.042 to 0.085. Sheet B is 15 Mpc from us at its closest
point. It is detected at redshift less than 0.021 and at redshift 0.021 to
0.041. These results make a serious case for the reality of signatures of close
to flat extended sheet-like patterns. | Cosmic Shear Systematics: Software-Hardware Balance: Cosmic shear measurements rely on our ability to measure and correct the
Point Spread Function (PSF) of the observations. This PSF is measured using
stars in the field, which give a noisy measure at random points in the field.
Using Wiener filtering, we show how errors in this PSF correction process
propagate into shear power spectrum errors. This allows us to test future
space-based missions, such as Euclid or JDEM, thereby allowing us to set clear
engineering specifications on PSF variability. For ground-based surveys, where
the variability of the PSF is dominated by the environment, we briefly discuss
how our approach can also be used to study the potential of mitigation
techniques such as correlating galaxy shapes in different exposures. To
illustrate our approach we show that for a Euclid-like survey to be statistics
limited, an initial pre-correction PSF ellipticity power spectrum, with a
power-law slope of -3 must have an amplitude at l =1000 of less than 2 x
10^{-13}. This is 1500 times smaller than the typical lensing signal at this
scale. We also find that the power spectrum of PSF size \dR^2) at this scale
must be below 2 x 10^{-12}. Public code available as part of iCosmo at
http://www.icosmo.org |
Semi-Numerical Simulation of Reionization with Semi-Analytical Modeling
of Galaxy Formation: In a semi-numerical model of reionization, the evolution of ionization
fraction is simulated approximately by the ionizing photon to baryon ratio
criterion. In this paper we incorporate a semi-analytical model of galaxy
formation based on the Millennium II N-body simulation into the semi-numerical
modeling of reionization. The semi-analytical model is used to predict the
production of ionizing photons, then we use the semi-numerical method to model
the reionization process. Such an approach allows more detailed modeling of the
reionization, and also connects observations of galaxies at low and high
redshifts to the reionization history. The galaxy formation model we use was
designed to match the low-$z$ observations, and it also fits the high redshift
luminosity function reasonably well, but its prediction on the star formation
falls below the observed value, and we find that it also underpredicts the
stellar ionizing photon production rate, hence the reionization can not be
completed at $z \sim 6$ without taking into account some other potential
sources of ionization photons. We also considered simple modifications of the
model with more top heavy initial mass functions (IMF), with which the
reionization can occur at earlier epochs. The incorporation of the
semi-analytical model may also affect the topology of the HI regions during the
EoR, and the neutral regions produced by our simulations with the
semi-analytical model appeared less poriferous than the simple halo-based
models. | Our Peculiar Motion Inferred from Number Counts of Mid Infra Red AGNs
and the Discordance Seen with the Cosmological Principle: The dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR) has
given a peculiar velocity vector 370 km s$^{-1}$ along
$l=264^\circ,b=48^\circ$. However, some other dipoles, for instance, from the
number counts, sky brightness or redshift distributions in large samples of
distant Active Galactic Nuclei (AGNs), have yielded values of the peculiar
velocity many times larger than that from the CMBR, though surprisingly, in all
cases the directions agreed with the CMBR dipole. Here we determine our
peculiar motion from a sample of ~0.28 million AGNs, selected from the Mid
Infra Red Active Galactic Nuclei (MIRAGN) sample comprising more than a million
sources. From this, we find a peculiar velocity, which is more than four times
the CMBR value, although the direction seems to be within $\sim 2\sigma$ of the
CMBR dipole. A genuine value of the solar peculiar velocity should be the same
irrespective of the data or the technique employed to estimate it. Therefore,
such discordant dipole amplitudes, might mean that the explanation for these
dipoles, including that of the CMBR, might in fact be something else. But, the
observed fact that the direction in all cases, is the same, though obtained
from completely independent surveys using different instruments and techniques,
by different sets of people employing different computing routines, might
nonetheless indicate that these dipoles are not merely due to some systematics,
otherwise why would they all be pointing along the same direction. It might
instead suggest a preferred direction in the Universe, implying a genuine
anisotropy, which would violate the Cosmological Principle, the core of the
modern cosmology. |
Laboratory constraints on chameleon dark energy and power-law fields: We report results from the GammeV Chameleon Afterglow Search---a search for
chameleon particles created via photon/chameleon oscillations within a magnetic
field. This experiment is sensitive to a wide class of chameleon power-law
models and dark energy models not previously explored. These results exclude
five orders of magnitude in the coupling of chameleons to photons covering a
range of four orders of magnitude in chameleon effective mass and, for
individual chameleon models, exclude between 4 and 12 orders of magnitude in
chameleon couplings to matter. | Effect of a High-Precision Semi-Analytical Mass Function on the Merger
Rate of Primordial Black Holes in Dark Matter Halos: In this work, we study the effect of a high-precision semianalytical mass
function on the merger rate of primordial black holes (PBHs) in dark matter
halos. For this purpose, we first explain a theoretical framework for dark
matter halo models and introduce relevant quantities such as halo density
profile, concentration parameter, and a high-precision semianalytical function
namely Del Popolo (DP) mass function. In the following, we calculate the merger
rate of PBHs in the framework of ellipsoidal-collapse dark matter halo models
while considering the DP mass function, and compare it with our previous study
for the Sheth-Tormen (ST) mass function. The results show that by taking the
mass of PBHs as $M_{\rm PBH} = 30M_{\odot}$, the DP mass function can
potentially amplify the merger rate of PBHs. Moreover, we calculate the merger
rate of PBHs for the DP mass function as a function of their mass and fraction
and compare it with the black hole mergers recorded by the LIGO-Virgo detectors
during the latest observing run. Our findings show that the merger rate of PBHs
will fall within the LIGO-Virgo band if $f_{\rm PBH} \gtrsim
\mathcal{O}(10^{-1})$. This implies that the DP mass function can be used to
strengthen constraints on the fraction of PBHs. |
Spectroscopy of z~5 Lyman Break Galaxies in the ESO Remote Galaxy Survey: (ABRIDGED) We present the global results of a large spectroscopic survey
carried out in order to identify z~ 5 Lyman break galaxies (LBGs) across ten
widely-separated fields to I_{AB}=26.3. The redshifts of seventy 4.6<z<5.6 LBGs
were identified. We find no significant difference in the frequency of high
equivalent-width line emitters between z~3 and our z~5 samples. The rest-frame
UV continuum slope of a typical z~5 line-emitting galaxy is bluer than that of
a typical break-only galaxy, a difference that is difficult to explain purely
by differences in the ages of their stellar populations. Variation in
metallicity and/or dust extinction can more straightforwardly account for this
difference. Given their UV-continuum slopes, the typical z~5 LBGs have
metallicities a factor of three lower than those of LBGs at z~3. HST imaging
indicates that a large majority of the spectroscopically-confirmed LBGs in our
sample are members of multiple systems and/or show disturbed morphology. Using
local LBG analogues as a model, this multiplicity could be explained either by
super-starburst regions within a larger unseen structure, or by a high
incidence of merging events at this epoch. The current data cannot distinguish
between these two possibilities. The surface density of z~5 LBGs in two fields
is considerably higher than in the rest. Both show clear spikes in their
redshift distributions indicating strong three-dimensional clustering. Neither
structure can be bound given their depth in redshift and probably extend beyond
the observed fields. The three-dimensional distances between LBGs in the
structures are too large for them to have triggered their starbursts through
mutual gravitational interaction, and so it is likely that the short-lived LBGs
represent only a small fraction of the baryons in the structures. | Dark Energy Survey Year 1: An independent E/B-mode cosmic shear analysis: We present an independent cosmic shear analysis of the non-cosmological
B-mode distortions within the public first year data from the Dark Energy
Survey (DES). We find no significant detection of B-modes in a full tomographic
analysis of the primary METACALIBRATION shear catalogue. This is in contrast to
the secondary IM3SHAPE shear catalogue, where we detect B- modes at a
significance of $\sim 3\sigma$ with a pattern that is consistent with the
B-mode signature of a repeating additive shear bias across the survey. We use
the COSEBIs statistic to cleanly separate the B-modes from the gravitational
lensing signal (E-modes). We find good agreement between the measured E-modes
and their theoretical expectation given the DES cosmological parameter
constraints. |
New physics, the cosmic ray spectrum knee, and $pp$ cross section
measurements: We explore the possibility that a new physics interaction can provide an
explanation for the knee just above $10^6$ GeV in the cosmic ray spectrum. We
model the new physics modifications to the total proton-proton cross section
with an incoherent term that allows for missing energy above the scale of new
physics. We add the constraint that the new physics must also be consistent
with published $pp$ cross section measurements, using cosmic ray observations,
an order of magnitude and more above the knee. We find that the rise in cross
section required at energies above the knee is radical. The increase in cross
section suggests that it may be more appropriate to treat the scattering
process in the black disc limit at such high energies. In this case there may
be no clean separation between the standard model and new physics contributions
to the total cross section. We model the missing energy in this limit and find
a good fit to the Tibet III cosmic ray flux data. We comment on testing the new
physics proposal for the cosmic ray knee at the Large Hadron Collider. | Gravitational and mass distribution effects on stationary superwinds II.
Extended dark matter haloes: In this second part, we generalize the results of the previous paper. We
present an analytic superwind solution considering extended
gravitationally-interacting dark-matter and baryonic haloes. The incorporation
of the latter is critical, since they can have a substantial effect on the
hydrodynamics of superwinds generated by massive galaxies. Although the
presence of extended and massive haloes does not change the limit for the
closed-box enrichment of galaxies established in the first paper, they can
trigger an earlier activation of the open-box enrichment scenario, since their
gravitational potentials can contribute to the inhibition of the free
superwind. Moreover, the incorporation of the extended haloes will also enhance
the physical setting behind the superwind model, as we consider mass
distributions with properties that emulate the results of recent simulations of
$\Lambda$CDM haloes. |
Dust May Be More Rare Than Expected in Metal Poor Galaxies: 'Normal' galaxies observed at z>6, when the Universe was <1 billion years
old, thus far show no evidence of the cold dust that accompanies star formation
in the local Universe, where the dust-to-gas mass ratio is 1%. A prototypical
example is 'Himiko' (z=6.6), which a mere 840 Myr after the Big Bang is forming
stars at a rate of 30-100 Msun/yr, yielding a mass assembly time M^{star}/SFR
150x10^6 yr. Himiko is estimated to have a low fraction (2-3% of the Solar
value) of elements heavier than helium (metallicity), and although its gas mass
cannot be asserted at this time its dust-to-stellar mass ratio is constrained
to be <0.05%. The local galaxy I Zw 18, with a metallicity 4% solar and forming
stars less rapidly than Himiko but still vigorously for its mass (M^{star}/SFR
1.6x10^9 yr), is also very dust deficient and perhaps one of the best analogues
of primitive galaxies accessible to detailed study. Here we report observations
of dust emission from I Zw 18 from which we determine its dust mass to be
450-1800 Msun, yielding a dust-to-stellar mass ratio \approx 10^{-6}-10^{-5}
and a dust-to-gas mass ratio 3.2-13x10^{-6}. If I Zw 18 is a reasonable analog
of Himiko, then Himiko's dust mass is \approx 50,000 Msun, a factor of 100
below the current upper limit. These numbers are considerably uncertain, but if
most high-z galaxies are more like Himiko than like the quasar host SDSS
J114816.64+525150.3, then the prospects for detecting the gas and dust in them
are much poorer than hitherto anticipated. | Searching for the highest redshift sources in 250-500 micron
submillimeter surveys: We explore a technique for identifying the highest redshift (z>4) sources in
Herschel/SPIRE and BLAST submillimeter surveys by localizing the position of
the far-infrared dust peak. Just as Spitzer/IRAC was used to identify stellar
`bump' sources, the far-IR peak is also a redshift indicator; although, the
latter also depends on the average dust temperature. We demonstrate the wide
range of allowable redshifts for a reasonable range of dust temperatures and
show that it is impossible to constraint the redshift of individual objects
using solely the position of the far-IR peak. By fitting spectral energy
distribution models to simulated Herschel/SPIRE photometry we show the utility
of radio and/or far-infrared data in breaking this degeneracy. With prior
knowledge of the dust temperature distribution it is possible to obtain
statistical samples of high redshift submillimeter galaxy candidates. We apply
this technique to the BLAST survey of ECDFS to constrain the number of dusty
galaxies at z>4. We find 8 +/- 2 galaxies with flux density ratios of
S500>S350; this sets an upper limit of 17 +/- 4 deg-2 if we assume all are at
z>4. This is <35% of all 500 micron-selected galaxies down to S500>45 mJy
(LIR>2e13Lsun for z>4). Modeling with conventional temperature and redshift
distributions estimates the percentage of these 500 micron peak galaxies at z>4
to be between 10-85%. Our results are consistent with other estimates of the
number density of very high redshift submillimeter galaxies and follows the
decline in the star formation rate density at z>4. |
Lya escape from z~0.03 star-forming galaxies: the dominant role of
outflows: The usefulness of H I Lyman-alpha photons for characterizing star formation
in the distant universe is limited by our understanding of the astrophysical
processes that regulate their escape from galaxies. These processes can only be
observed in detail out to a few x100 Mpc. Past nearby (z<0.3) spectroscopic
studies are based on small samples and/or kinematically unresolved data. Taking
advantage of the high sensitivity of HST's COS, we observed the Lyman-alpha
lines of 20 H-alpha-selected galaxies located at <z>=0.03. The galaxies cover a
broad range of luminosity, oxygen abundance, and reddening. In this paper, we
characterize the observed Lyman-alpha lines and establish correlations with
fundamental galaxy properties. We find seven emitters. These host young (\le 10
Myr) stellar populations, have rest-frame equivalent widths in the range 1-12
\AA, and have Lyman-alpha escape fractions within the COS aperture in the range
1-12 %. One emitter has a double-peaked Lyman-alpha with peaks 370 km/s apart
and a stronger blue peak. Excluding this object, the emitters have Lyman-alpha
and O I \lambda 1302 offsets from H-alpha in agreement with expanding shell
models and LBG observations. The absorbers have offsets that are almost
consistent with a static medium. We find no one-to-one correspondence between
Lyman-alpha emission and age, metallicity, or reddening. Thus, we confirm that
Lyman-alpha is enhanced by outflows and is regulated by the dust and H I column
density surrounding the hot stars. | Co-planar streams, pancakes, and angular-momentum exchange in high-z
disc galaxies: We study the feeding of massive galaxies at high redshift through streams
from the cosmic web using the Mare Nostrum hydro-cosmological simulation. Our
statistical sample consists of 350 dark-matter haloes of ~10^12 Msun at z =
2.5. We find that ~70% of the influx into the virial radius Rv is in narrow
streams covering 10% of the virial shell. On average 64% of the stream influx
is in one stream, and 95% is in three dominant streams. The streams that feed a
massive halo tend to lie in a plane that extends from half to a few Rv,
hereafter "the stream plane" (SP). The streams are typically embedded in a thin
sheet of low-entropy gas, a Zel'dovich pancake, which carries ~20% of the
influx into Rv. The filaments-in-a-plane configuration about the massive haloes
at the nodes of the cosmic web differs from the large- scale structure of the
web where the filaments mark the intersections of slanted sheets. The stream
plane is only weakly aligned with the angular momentum (AM) near Rv, consistent
with the fact that typically 80% of the AM is carried by one dominant stream.
The galactic disc plane shows a weak tendency to be perpendicular to the
large-scale SP, consistent with tidal-torque theory. Most interesting, the
direction of the disc AM is only weakly correlated with the AM direction at Rv.
This indicates a significant AM exchange at the interphase between streams and
disc in the greater environment of the disc inside an "AM sphere" of radius
~0.3Rv . The required large torques are expected based on the perturbed
morphology and kinematics within this interaction sphere. This AM exchange may
or may not require a major modification of the standard disc modeling based on
AM conservation, depending on the extent to which the amplitude of the disc AM
is affected, which is yet to be studied. |
Thermal state of the intergalactic medium at $z\sim2-4$: We present a new method to infer parameters of the temperature-density
relation in the intergalactic medium in the post-reionization epoch at $z\sim
2-4$. This method is based on the analysis of the Ly$\alpha$ absorbers
distribution over column densities and Doppler parameters by the model joint
probability density function. This approach allows us to measure the power-law
index $\gamma$ of the temperature-density relation and a certain combination of
the temperature at the mean density $T_0$ and hydrogen photoionization rate
$\Gamma$. To estimate $T_0$ and $\Gamma$ separately, we employ measurements of
the Ly$\alpha$ forest effective opacity and the model gas probability density
function. We show that $\gamma$ tends to be lower than 1.6 and reaches 1.3 at
redshift $\sim3$. The inferred temperatures at the mean density are
$\sim(2\pm0.5)\times10^4$ K in the studied redshift range. Both these estimates
favour HeII reionization at $z\gtrsim3$. We find that the hydrogen
photoionization rate is $\sim0.6\times10^{-12}$ s$^{-1}$, which is consistent
with previous measurements. | CARMA follow-up of the northern unconfirmed PLANCK galaxy cluster
candidates: We present CARMA observations of the three northern unconfirmed galaxy
clusters discovered by the PLANCK satellite. We confirm the existence of two
massive clusters (PLCKESZ G115.71+17.52 and PLCKESZ G121.11+57.01) at high
significance. For these clusters, we present refined centroid locations from
the 31 GHz CARMA data, as well as mass estimates obtained from a joint analysis
of CARMA and PLANCK data. We do not detect the third candidate, PLCKESZ
G189.84-37.24, and place an upper limit on its mass of M500 < 3.2 X 10^(14)
M_SUN at 68% confidence. Considering our data and the characteristics of the
PLANCK Early Release SZ Catalog, we conclude that this object is likely to be a
cold-core object in the plane of our Galaxy. As a result, we estimate the
purity of the ESZ Catalog to be greater than 99.5%. |
Correlations of Quasar Optical Spectra with Radio Morphology: (Abridged) With the largest homogeneous quasar sample with optical spectra
and robust radio morphology classifications assembled to date, we investigate
quasar radio and optical properties with unprecedented statistical power. The
data consist of 4714 radio quasars from FIRST with S_{20}>2mJy and SDSS
spectra. Radio morphology classes include core-only (core), core-lobe (lobe),
core-jet (jet), lobe-core-lobe (triple), and double-lobe. We examine the
optical colors of radio-morphology subsamples and find that radio quasars with
core emission unresolved by FIRST (on 5" scale) have a redder color
distribution than radio-quiet quasars (S_{20}<1mJy); other classes of radio
quasars have optical color distributions similar to the radio-quiet quasars.
This analysis also suggests that optical colors of z<2.7 SDSS quasars are not
strongly (<0.1mag) biased blue. We show that the radio core-to-lobe flux
density ratio (R) and the radio-to-optical (i-band) ratio of the quasar core
(RI) are correlated, suggesting that both parameters are indicative of
line-of-sight orientation. We investigate spectral line equivalent widths as a
function of R and RI, including the [OIII] narrow line doublet and the CIV
{\lambda}1549 and MgII {\lambda}2799 broad lines. We find that the rest
equivalent widths (EWs) of the broad lines correlate positively with RI at the
4-8{\sigma} level. But we find no strong dependence of EW on R, in contrast to
previous results. One interpretation is that EWs increase as the line-of-sight
angle to the radio-jet axis decreases. These results are in stark contrast to
commonly accepted orientation-based theories, which suggest that continuum
emission should increase as the angle to the radio-jet axis decreases,
resulting in smaller EW of emission lines (assumed isotropic). Finally, we find
that the Baldwin effect in our sample does not depend on quasar radio
morphology. | Gravitational lens equation. Critical solutions and magnification near
folds and cusps: We study approximate solutions of the gravitational lens equation and
corresponding lens magnification factor near the critical point. This
consideration is based on the Taylor expansion of the lens potential in powers
of coordinates and an introduction of a proximity parameter characterising the
closeness of a point source to the caustic. Second-order corrections to known
approximate solutions and magnification are found in case of a general fold
point. The first-order corrections near a general cusp are found as well. Key
words: gravitational lensing, methods: analytical |
Accurate Baryon Acoustic Oscillations reconstruction via semi-discrete
optimal transport: Optimal transport theory has recently reemerged as a vastly resourceful field
of mathematics with elegant applications across physics and computer science.
Harnessing methods from geometry processing, we report on the efficient
implementation for a specific problem in cosmology -- the reconstruction of the
linear density field from low redshifts, in particular the recovery of the
Baryonic Acoustic Oscillation (BAO) scale. We demonstrate our algorithm's
accuracy by retrieving the BAO scale in noise-less cosmological simulations
that are dedicated to cancel cosmic variance; we find uncertainties to be
reduced by a factor of 4.3 compared with performing no reconstruction, and a
factor of 3.1 compared with standard reconstruction. | Understanding micro-image configurations in quasar microlensing: The micro-arcsecond scale structure of the seemingly point-like images in
lensed quasars, though unobservable, is nevertheless much studied
theoretically, because it affects the observable (or macro) brightness, and
through that provides clues to substructure in both source and lens. A curious
feature is that, while an observable macro-image is made up of a very large
number of micro-images, the macro flux is dominated by a few micro-images.
Micro minima play a key role, and the well-known broad distribution of macro
magnification can be decomposed into narrower distributions with 0,1,2,3,...
micro minima. This paper shows how the dominant micro-images exist alongside
the others, using the ideas of Fermat's principle and arrival-time surfaces,
alongside simulations. |
Characterizing the post-inflationary reheating history, Part II:
Multiple interacting daughter fields: We characterize the post-inflationary dynamics of an inflaton $\phi$ coupled
to multiple interacting daughter fields $X_n$ ($n=1,\dots N_d$) through
quadratic-quadratic interactions $g_n^ 2\phi^2 X_n^2$. We assume a monomial
inflaton potential $V(\phi) \propto |\phi|^p$ ($p \geq 2$) around the minimum.
By simulating the system in 2+1-dimensional lattices, we study the
post-inflationary evolution of the energy distribution and equation of state,
from the end of inflation until a stationary regime is achieved. We show that
in this scenario, the energy transferred to the daughter field sector can be
larger than $50\%$, surpassing this way the upper bound found previously for
single daughter field models. In particular, for $p \geq 4$ the energy at very
late times is equally distributed between all fields, and only $100/(N_d + 1)
\%$ of the energy remains in the inflaton. We also consider scenarios in which
the daughter fields have scale-free interactions $\lambda_{nm} X_n^2 X_m^2$,
including the case of quartic daughter field self-interactions (for $n=m$). We
show that these interactions trigger a resonance process during the non-linear
regime, which in the single daughter field case already allows to deplete more
than $50\%$ of the energy from the inflaton for $p\geq 4$. | Relativistic effects in Lyman-alpha forest: We present the calculation of the Lyman-alpha (Lyman-$\alpha$) transmitted
flux fluctuations with full relativistic corrections to the first order. Even
though several studies exist on relativistic effects in galaxy clustering, this
is the first study to extend the formalism to a different tracer of underlying
matter at unique redshift range ($z=2-5$). Furthermore, we show a comprehensive
application of our calculations of the Quasar-Lyman-$\alpha$ cross-correlation
function. Our results indicate that the signal of relativistic effects is
sizeable at Baryonic Acoustic Oscillation (BAO) scale mainly due to the large
difference in density bias factors of our tracers. We construct an observable,
the anti-symmetric part of the cross-correlation function, that is dominated by
the relativistic signal and offers a new way to measure the relativistic terms
at relatively small scales. The analysis shows that relativistic effects are
important when considering cross-correlations between tracers with very
different biases, and should be included in the data analysis of the current
and future surveys. Moreover, the idea presented in this paper is highly
complementary to other techniques and observable trying to isolate the effect
of the relativistic corrections and thus test the validity of the theory of
gravity beyond the Newtonian regime. |
Effect of the Early Reionization on the Cosmic Microwave Background and
Cosmological Parameter Estimates: The early reionization (ERE) is supposed to be a physical process which
happens after recombination, but before the instantaneous reionization caused
by the first generation of stars. We investigate the effect of the ERE on the
temperature and polarization power spectra of cosmic microwave background
(CMB), and adopt principal components analysis (PCA) to model-independently
reconstruct the ionization history during the ERE. In addition, we also discuss
how the ERE affects the cosmological parameter estimates, and find that the ERE
does not impose any significant influences on the tensor-to-scalar ratio $r$
and the neutrino mass at the sensitivities of current experiments. The better
CMB polarization data can be used to give a tighter constraint on the ERE and
might be important for more precisely constraining cosmological parameters in
the future. | Spatial correlation between submillimetre and Lyman-alpha galaxies in
the SSA 22 protocluster: Lyman-alpha emitters are thought to be young, low-mass galaxies with ages of
~10^8 yr. An overdensity of them in one region of the sky (the SSA 22 field)
traces out a filamentary structure in the early Universe at a redshift of z =
3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to
mark a forming protocluster. Galaxies that are bright at (sub)millimetre
wavelengths are undergoing violent episodes of star formation, and there is
evidence that they are preferentially associated with high-redshift radio
galaxies, so the question of whether they are also associated with the most
significant large-scale structure growing at high redshift (as outlined by
Lyman-alpha emitters) naturally arises. Here we report an imaging survey of
1,100-um emission in the SSA 22 region. We find an enhancement of submillimetre
galaxies near the core of the protocluster, and a large-scale correlation
between the submillimetre galaxies and the low-mass Lyman-alpha emitters,
suggesting synchronous formation of the two very different types of
star-forming galaxy within the same structure at high redshift. These results
are in general agreement with our understanding of the formation of cosmic
structure. |
Cosmic magnetization out from the vacuum: The large-scale magnetic fields we observe today in galaxies and galaxy
clusters could be the result of a pure quantum effect taking place during
inflation, to wit, the creation of particles (photons) out from the vacuum in a
curved spacetime. We show that, whenever the conformal invariance of
electromagnetism is broken during inflation, the actual magnetic field
spectrum, in the classical limit, is given by $B_k \simeq k^2
\sqrt{n_{\mathbf{k}} }$, where $n_{\mathbf{k}} \gg 1$ is the number of created
photons with wavenumber $k$. In particular, a scale-invariant magnetic field of
order of $10^{12}$G can emerge in the simplest model of cosmic magnetogenesis,
the one where the inflaton is kinetically coupled to the photon. Moreover, and
contrarily to the general belief, we show that such a model is free from the
so-called strong-coupling and backreaction problems. This conclusion follows,
indirectly, from the observation that post-inflationary electric currents,
which in the literature are incorrectly supposed to freeze superhorizon
magnetic fields after inflation, are indeed vanishing on superhorizon scales
due to causality. | Bounds on Parity Violation In the Cosmological Redshift: Parity (P) violation in gravity would be a sure sign of new physics. We
examine the possibility of P violation in the cosmological redshift. If right-
and left-circularly polarized photons experience the redshift differently, the
radiation from distant sources would tend to be depolarized, since the
polarizations states would accumulate different phases during propagation. The
resulting birefringence has an unusual signature--depending on z^2--quite
unlike what is seen in other theories, including those with violation of local
boost invariance. The observed broad-spectrum polarization of $\gamma$-ray
bursts constrains the fractional difference between the right- and left-handed
redshifts at the 6 x 10^(-37) level. |
Modeling the Infrared Emission in Cygnus A: We present new Spitzer IRS spectroscopy of Cygnus A, one of the most luminous
radio sources in the local universe. Data on the inner 20" are combined with
new reductions of MIPS and IRAC photometry as well as data from the literature
to form a radio through mid-infrared spectral energy distribution (SED). This
SED is then modeled as a combination of torus reprocessed active galactic
nucleus (AGN) radiation, dust enshrouded starburst, and a synchrotron jet. This
combination of physically motivated components successfully reproduces the
observed emission over almost 5 dex in frequency. The bolometric AGN luminosity
is found to be 10^12 L_\odot (90% of LIR), with a clumpy AGN-heated dust medium
extending to \sim130 pc from the supermassive black hole. Evidence is seen for
a break or cutoff in the core synchrotron emission. The associated population
of relativistic electrons could in principle be responsible for some of the
observed X-ray emission though the synchrotron self-Compton mechanism. The SED
requires a cool dust component, consistent with dust-reprocessed radiation from
ongoing star formation. Star formation contributes at least 6 \times 10^10
L_\odot to the bolometric output of Cygnus A, corresponding to a star formation
rate of \sim10 M_\odot yr-1. | High-redshift post-reionization cosmology with 21cm intensity mapping: We investigate the possibility of performing cosmological studies in the
redshift range $2.5<z<5$ through suitable extensions of existing and upcoming
radio-telescopes like CHIME, HIRAX and FAST. We use the Fisher matrix technique
to forecast the bounds that those instruments can place on the growth rate, the
BAO distance scale parameters, the sum of the neutrino masses and the number of
relativistic degrees of freedom at decoupling, $N_{\rm eff}$. We point out that
quantities that depend on the amplitude of the 21cm power spectrum, like
$f\sigma_8$, are completely degenerate with $\Omega_{\rm HI}$ and $b_{\rm HI}$,
and propose several strategies to independently constraint them through
cross-correlations with other probes. Assuming $5\%$ priors on $\Omega_{\rm
HI}$ and $b_{\rm HI}$, $k_{\rm max}=0.2~h{\rm Mpc}^{-1}$ and the primary beam
wedge, we find that a HIRAX extension can constrain, within bins of $\Delta
z=0.1$: 1) the value of $f\sigma_8$ at $\simeq4\%$, 2) the value of $D_A$ and
$H$ at $\simeq1\%$. In combination with data from Euclid-like galaxy surveys
and CMB S4, the sum of the neutrino masses can be constrained with an error
equal to $23$ meV ($1\sigma$), while $N_{\rm eff}$ can be constrained within
0.02 ($1\sigma$). We derive similar constraints for the extensions of the other
instruments. We study in detail the dependence of our results on the
instrument, amplitude of the HI bias, the foreground wedge coverage, the
nonlinear scale used in the analysis, uncertainties in the theoretical modeling
and the priors on $b_{\rm HI}$ and $\Omega_{\rm HI}$. We conclude that 21cm
intensity mapping surveys operating in this redshift range can provide
extremely competitive constraints on key cosmological parameters. |
Regional variations in the dense gas heating and cooling in M51 from
Herschel far-infrared spectroscopy: We present Herschel PACS and SPIRE spectroscopy of the most important
far-infrared cooling lines in M51, [CII](158 \mu m), [NII](122 & 205 \mu m),
[OI](63 and 145 \mu m) and [OIII](88 \mu m). We compare the observed flux of
these lines with the predicted flux from a photon dominated region model to
determine characteristics of the cold gas such as density, temperature and the
far-ultraviolet radiation field, G_0, resolving details on physical scales of
roughly 600 pc. We find an average [CII]/F_TIR of 4 x 10^{-3}, in agreement
with previous studies of other galaxies. A pixel-by-pixel analysis of four
distinct regions of M51 shows a radially decreasing trend in both the
far-ultraviolet (FUV) radiation field, G_0 and the hydrogen density, n, peaking
in the nucleus of the galaxy, then falling off out to the arm and interarm
regions. We see for the first time that the FUV flux and gas density are
similar in the differing environments of the arm and interarm regions,
suggesting that the inherent physical properties of the molecular clouds in
both regions are essentially the same. | Optical discovery of probable stellar tidal disruption flares: Using archival SDSS multi-epoch imaging data (Stripe 82), we have searched
for the tidal disruption of stars by super-massive black holes in non-active
galaxies. Two candidate tidal disruption events (TDEs) are identified. They
have optical black-body temperatures 2 10^4 K and observed peak luminosities
M_g=-18.3 and -20.4; their cooling rates are very low, qualitatively consistent
with expectations for tidal disruption flares. Their properties are examined
using i) SDSS imaging to compare them to other flares observed in the search,
ii) UV emission measured by GALEX and iii) spectra of the hosts and of one of
the flares. Our pipeline excludes optically identifiable AGN hosts, and our
variability monitoring over 9 years provides strong evidence that these are not
flares in hidden AGNs. The spectra and color evolution of the flares are unlike
any SN observed to date, their strong late-time UV emission is particularly
distinctive, and they are nuclear at high resolution, arguing against their
being first cases of a previously-unobserved class of SNe or more extreme
examples of known SN types. Taken together, the observed properties are
difficult to reconcile with a SN or AGN-flare explanation, although an entirely
new process specific to the inner few-hundred parsecs of non-active galaxies
cannot be excluded. Our observed rate and method show the feasibility of
obtaining a candidate TDE sample of hundreds of events and O(1) purity, using
geometric resolution and host and flare color alone. A by-product of this work
is quantification of the power-spectrum of extreme flares in AGNs. |
The effect of neutrinos on the matter distribution as probed by the
Intergalactic Medium: We present a suite of full hydrodynamical cosmological simulations that
quantitatively address the impact of neutrinos on the (mildly non-linear)
spatial distribution of matter and in particular on the neutral hydrogen
distribution in the Intergalactic Medium (IGM), which is responsible for the
intervening Lyman-alpha absorption in quasar spectra. The free-streaming of
neutrinos results in a (non-linear) scale-dependent suppression of power
spectrum of the total matter distribution at scales probed by Lyman-alpha
forest data which is larger than the linear theory prediction by about 25% and
strongly redshift dependent. By extracting a set of realistic mock quasar
spectra, we quantify the effect of neutrinos on the flux probability
distribution function and flux power spectrum. The differences in the matter
power spectra translate into a ~2.5% (5%) difference in the flux power spectrum
for neutrino masses with Sigma m_{\nu} = 0.3 eV (0.6 eV). This rather small
effect is difficult to detect from present Lyman-alpha forest data and nearly
perfectly degenerate with the overall amplitude of the matter power spectrum as
characterised by sigma_8. If the results of the numerical simulations are
normalized to have the same sigma_8 in the initial conditions, then neutrinos
produce a smaller suppression in the flux power of about 3% (5%) for Sigma
m_{\nu} = 0.6$ eV (1.2 eV) when compared to a simulation without neutrinos. We
present constraints on neutrino masses using the Sloan Digital Sky Survey flux
power spectrum alone and find an upper limit of Sigma m_{\nu} < 0.9$ eV (2
sigma C.L.), comparable to constraints obtained from the cosmic microwave
background data or other large scale structure probes. | Flexion in Abell 2744: We present the first flexion-focused gravitational lensing analysis of the
first of the strong-lensing "cosmic telescope" galaxy clusters, observed as
part of the Hubble Frontier Fields initiative. Using HST observations of Abell
2744 (z = 0.308), we apply a modified Analytic Image Model (AIM) technique to
measure source galaxy flexion and shear values at a final number density of 82
arcmin$^{-2}$. By using flexion data alone we are able to identify the primary
mass structure aligned along the heart of the cluster in addition to a major
substructure peak offset 1.43' from the cluster core. We generate two types of
nonparametric reconstructions: a flexion aperture mass map, which identifies
the central potential and substructure peak with mass signal-to-noise of
3.5$\sigma$ and 2.3$\sigma$ respectively; and a convergence map derived
directly from the smoothed flexion field. For the primary peak we find a mass
of $1.93\times10^{14}\,h^{-1}\,M_{\odot}$ within a 45" (145h$^{-1}$ kpc)
aperture, and for the western substructure we find a mass of
$7.12\times10^{13}\,h^{-1}\,M_{\odot}$ within a 25" (80h$^{-1}$ kpc) aperture.
The associated peak velocity dispersions were determined to be $\sigma_v$ =
1630 km/s and $\sigma_v$ = 766 km/s, respectively, by fitting nonsingular
isothermal sphere profiles to the flexion data. Additionally, we use
simultaneous shear measurements to independently reconstruct the broader
cluster mass structure, and find that it is unable to reproduce the small-scale
structure associated with the flexion reconstructions. Finally, we perform the
same analysis on the Abell 2744 parallel sky field, and find no strong phantom
signals in the noise reconstructions. |
Detecting Baryon Acoustic Oscillations with third generation
gravitational wave observatories: We explore the possibility of detecting Baryon Acoustic Oscillations (BAO)
solely from gravitational wave observations of binary neutron star mergers with
third generation (3G) gravitational wave (GW) detectors like Cosmic Explorer
and the Einstein Telescope. These measurements would provide a new independent
probe of cosmology. The detection of the BAO peak with current generation GW
detectors (solely from GW observations) is not possible because i) unlike
galaxies, the GW mergers are poorly localized and ii) there are not enough
merger events to probe the BAO length scale. With the 3G GW detector network,
it is possible to observe $\sim \mathcal{O}(1000)$ binary neutron star mergers
per year localized well within one square degree in the sky for redshift $z
\leq 0.3$. We show that 3G observatories will enable precision measurements of
the BAO feature in the large-scale two-point correlation function; the effect
of BAO can be independently detected at different reshifts, with a log-evidence
ratio of $\sim$ 23, 17, or 3 favouring a model with a BAO peak at redshift of
0.2, 0.25, or 0.3, respectively, using a redshift bin corresponding to a shell
of thickness $150 h^{-1}$ Mpc. | Sizing up Partially-Depleted Galaxy Cores: We have modelled the inner surface brightness profiles of 39 alleged `core'
galaxies with the core-Sersic model, and provide new physical parameters for
the largest ever sample of `core' galaxies fit with this model. When present,
additional nuclear components were simultaneously modelled and the typical rms
scatter of the fits (out to ~10 arcsec) is 0.02 mag/arcsec^2. Model-independent
estimates of each core's break radius are shown to agree with those from the
core-Sersic model, and a comparison with the Nuker model is provided. We found
an absence of cores in what amounts to 18% of the sample which are reclassified
here as Sersic galaxies with low values of n (< ~ 4) and thus shallow inner
profile slopes. In general, galaxies with n<3 and sigma < 183 km/s do not have
depleted cores. We derive updated relations between core-Sersic break radii,
their associated surface brightness, bulge luminosity, central velocity
dispersion, and predicted black hole mass for galaxies with depleted cores.
With the possible exception of NGC 584, we confirm that the inner negative
logarithmic profile slopes gamma are < ~ 0.3 for the `core' galaxies, and 0 >
gamma > -0.1 for six of these. Finally, the central stellar mass deficits are
found to have values typically within a factor of 4 of the expected central
black hole mass. |
On the progenitor and early evolution of the type II supernova 2009kr: We report the identification of a source coincident with SN 2009kr in HST
pre-explosion images. The object appears to be a single point source with an
intrinsic colour V-I = 1.1 and M_V = -7.6. If this is a single star it would be
a yellow supergiant of log L/L_{sol} \sim 5.1 and a mass of 15 (+5/-4) M_{sol}.
The spatial resolution does not allow us yet to definitively determine if the
progenitor object is a single star, a binary system, or a compact cluster. We
show that the early lightcurve is flat, similar to IIP SNe, but that the the
spectra are somewhat peculiar, displaying unusual P-Cygni profiles. The
evolution of the expanding ejecta will play an important role in understanding
the progenitor object. | Cosmology from cross correlation of CMB lensing and galaxy surveys: In recent years cross correlation of lensing of the Cosmic Microwave
Background (CMB) with other large scale structure (LSS) tracers has been used
as a method to detect CMB lensing. Current experiments are also becoming
sensitive enough to measure CMB lensing without the help of auxiliary tracers.
As data quality improves rapidly, it has been suggested that the CMB
lensing-LSS cross correlation may provide new insights into parameters
describing cosmological structure growth. In this work we perform forecasts
that combine the lensing potential auto power spectrum from various future CMB
experiments, the galaxy power spectrum from galaxy surveys, as well as the
cross power spectrum between the two, marginalizing over a number galactic and
non-galactic cosmological parameters. We find that the CMB lensing-LSS cross
correlation contains significant information on parameters such as the redshift
distribution and bias of LSS tracers. We also find that the cross correlation
information will lead to independent probes of cosmological parameters such as
neutrino mass and the reionization optical depth. |
Kinetically stabilized inflation: In this work, we propose a string-inspired two fields inflation model to
address the fine-tuning problem that the standard inflation model suffers. The
fast-rolling tachyon $\mathcal{T}$ originated from the D-brane and anti-D-brane
pair annihilation locks the inflaton $\varphi$ slowly rolling on a Higgs-like
potential $V(\varphi)=-m_\varphi^2\varphi^2+\lambda \varphi^4$ and drives a
kinetically stabilized (KS) inflation. Our numerical simulation confirms such a
solution is a dynamic attractor. In particular, for $\lambda< 0.8\times
10^{-3}$, the e-folding number contributed by the KS inflation phase can be
larger than $62$ to solve the horizon and flatness problems of Big Bang theory.
Notably, this KS inflation generates a nearly scale-invariant primordial
curvature perturbations spectrum consistent with current cosmic microwave
background (CMB) observations. It predicts a low tensor-to-scalar ratio, which
the current primordial gravitational wave background (the B-modes in CMB)
searches favor. | Field Level Neural Network Emulator for Cosmological N-body Simulations: We build a field level emulator for cosmic structure formation that is
accurate in the nonlinear regime. Our emulator consists of two convolutional
neural networks trained to output the nonlinear displacements and velocities of
N-body simulation particles based on their linear inputs. Cosmology dependence
is encoded in the form of style parameters at each layer of the neural network,
enabling the emulator to effectively interpolate the outcomes of structure
formation between different flat $\Lambda$CDM cosmologies over a wide range of
background matter densities. The neural network architecture makes the model
differentiable by construction, providing a powerful tool for fast field level
inference. We test the accuracy of our method by considering several summary
statistics, including the density power spectrum with and without redshift
space distortions, the displacement power spectrum, the momentum power
spectrum, the density bispectrum, halo abundances, and halo profiles with and
without redshift space distortions. We compare these statistics from our
emulator with the full N-body results, the COLA method, and a fiducial neural
network with no cosmological dependence. We find our emulator gives accurate
results down to scales of $k \sim 1\ \mathrm{Mpc}^{-1}\, h$, representing a
considerable improvement over both COLA and the fiducial neural network. We
also demonstrate that our emulator generalizes well to initial conditions
containing primordial non-Gaussianity, without the need for any additional
style parameters or retraining. |
Searching for Light in the Darkness: Bounds on ALP Dark Matter with the
optical MUSE-Faint survey: We use MUSE spectroscopic observations of the dwarf spheroidal galaxy Leo T
between 470 and 935 nm to search for radiative decays of axion like particles
(ALPs). Under the assumption that ALPs constitute the dark matter component of
the Leo T halo, we derive bounds on the effective ALP-two-photon coupling. We
improve existing limits by more than one order of magnitude in the ALP mass
range 2.7-5.3 eV. | Some aspects of the orientation of galaxies in clusters: The analysis of Tully's groups of galaxies belonging to the Local
Supercluster (LSC) was performed. In the 1975 Hawley and Peebles presented the
method for investigations of the galaxies orientation in the large structures.
In our previous papers statistical test proposed by Hawley and Peebles for
investigation of this problem was analyzed in details and some improvements
were suggested. On this base the new method of the analysis of galactic
alignment in clusters was proposed. Using this method, God{\l}owski (2012)
analyzed the orientation of galaxies inside Tully's group founding no
significant deviations from isotropy both in orientation of position angles and
$\delta_D$ and $\eta$ angles as well, giving the spatial orientation of galaxy
planes. In the present paper we examined carefully and methodically the
dependence of alignment in Tully's groups on morphological type of galaxies.
Moreover, we discussed the consequences of different approximation of "true
shape" of the galaxies for different morphological types, possible influence of
this problem for investigation of spatial orientation of galaxies. In addition,
we discussed the implications of the obtained results for the theory of galaxy
formation as well. |
The Activity of the Neighbours of AGN and Starburst Galaxies: Towards an
evolutionary sequence of AGN activity: We present a follow-up study of a series of papers concerning the role of
close interactions as a possible triggering mechanism of the activity of AGN
and starburst (SB) galaxies. We have already studied the close (<100 kpc) and
the large scale (<1 Mpc) environment of Sy1, Sy2 and Bright IRAS galaxies and
their respective control samples (Koulouridis et al.). The results led us to
the conclusion that a close encounter appears capable of activating a sequence
where a normal galaxy becomes first a starburst, then a Sy2 and finally a Sy1
galaxy. However since both galaxies of an interacting pair should be affected,
we present here optical spectroscopy and X-ray imaging of the neighbouring
galaxies around our Seyfert and BIRG galaxy samples. We find that more than 70%
of all neighbouring galaxies exhibit thermal or/and nuclear activity (namely
enhanced star formation, starbursting and/or AGN) and furthermore we discovered
various trends regarding the type and strength of the neighbour's activity with
respect to the activity of the central galaxy, the most important of which is
that the neighbours of Sy2 are systematically more ionized, and their straburst
is younger, than the neighbours of Sy1s. Our results not only strengthen the
link between close galaxy interactions and activity but also provide more clues
regarding the evolutionary sequence inferred by previous results. | Dust Reddened Quasars in FIRST and UKIDSS: Beyond the Tip of the Iceberg: We present the results of a pilot survey to find dust-reddened quasars by
matching the FIRST radio catalog to the UKIDSS near-infrared survey, and using
optical data from SDSS to select objects with very red colors. The deep K-band
limit provided by UKIDSS allows for finding more heavily-reddened quasars at
higher redshifts as compared with previous work using FIRST and 2MASS. We
selected 87 candidates with K<=17.0 from the UKIDSS Large Area Survey (LAS)
First Data Release (DR1) which covers 190 deg2. These candidates reach up to
~1.5 magnitudes below the 2MASS limit and obey the color criteria developed to
identify dust-reddened quasars. We have obtained 61 spectroscopic observations
in the optical and/or near-infrared as well as classifications in the
literature and have identified 14 reddened quasars with E(B-V)>0.1, including
three at z>2. We study the infrared properties of the sample using photometry
from the WISE Observatory and find that infrared colors improve the efficiency
of red quasar selection, removing many contaminants in an infrared-to-optical
color-selected sample alone. The highest-redshift quasars (z > 2) are only
moderately reddened, with E(B-V) ~ 0.2-0.3. We find that the surface density of
red quasars rises sharply with faintness, comprising up to 17% of blue quasars
at the same apparent K-band flux limit. We estimate that to reach more heavily
reddened quasars (i.e., E(B-V) > 0.5) at z>2 and a depth of K=17 we would need
to survey at least ~2.5 times more area. |
Redshift space distortions in the presence of non-minimally coupled dark
matter: In this paper, we fully investigate cosmological scenarios in which dark
matter is non-minimally coupled to an extra scalar degree of freedom. The
interaction is realized by means of conformal and disformal terms in the
transformed gravitational metric. Considering linear perturbation theory, we
show that the growth rate of dark matter differs from the uncoupled case and
that the well-known Kaiser formula undergoes modification. As a result,
redshift space distortion measurements cease to be a direct probe of the linear
growth rate of total matter, since the distortion factor has an extra,
coupling-dependent term. We study the effect of the coupling in three
cosmological models, two conformally and one disformally coupled, and forecast
the constraints on the coupling, and other cosmological parameters, from future
galaxy surveys. | Type Ia supernovae data with scalar-tensor gravity: We study the use of type Ia supernovae (SNe Ia) in the context of
scalar-tensor theories of gravity, taking as a working example induced gravity,
equivalent to Jordan-Brans-Dicke theory. Winking at accurate and precision
cosmology, we test the correction introduced by a time variation of the
Newton's constant, predicted by scalar-tensor theories, on the SNe distance
modulus relation. We find that for induced gravity the coupling parameter is
constrained from $\xi < 0.0095$ (95\% CL) using Pantheon SNe data alone down to
$\xi < 0.00063$ (95\% CL) in combination with {\em Planck} data release DR3 and
a compilation of baryon acoustic oscillations (BAO) measurements from BOSS
DR12. In this minimal case the improvements in terms of constraints on the
cosmological parameters coming from the addition of SNe data to cosmic
microwave background (CMB) and BAO measurements is limited, $\sim7\%$ on the
95\% CL upper bound on $\xi$. Allowing for the value of the gravitational
constant today to depart from the Newton constant, we find that the addition of
SNe further tightens the constraints obtained by CMB and BAO data on the
standard cosmological parameters and by 22\% on the coupling parameter, i.e.,
$\xi < 0.00064$ at 95\% CL. We finally show that in this class of modified
gravity models the use a prior on the absolute magnitude $M_B$ in combination
with the Pantheon SNe sample leads to results which are very consistent with
those obtained by imposing a prior on $H_0$, as happens for other {\em
early-type} models which accommodate a larger value of $H_0$ compared to the
$\Lambda$CDM results. |
Perceiving the equation of state of Dark Energy while living in a Cold
Spot: The Cold Spot could be an adiabatic perturbation on the surface of last
scattering, in which case it is an over-density with comoving radius of the
order of 1 Gpc. We assess the effect that living in a similar structure,
without knowing it, has on our perception of the equation of state of Dark
Energy. We find that structures of dimensions such that they could cause the
Cold Spot on the CMB, affect the perceived equation of state of Dark Energy
possibly up to ten percent. | Interacting Dark Energy: Possible Explanation for 21-cm Absorption at
Cosmic Dawn: A recent observation points to an excess in the expected 21-cm brightness
temperature from cosmic dawn. In this paper, we present an alternative
explanation of this phenomenon, an interaction in the dark sector. Interacting
dark energy models have been extensively studied recently and there is a whole
variety of such in the literature. Here we particularize to a specific model in
order to make explicit the effect of an interaction. |
Current constraints on the epoch of cosmic acceleration: The cosmographic expansion history of the universe is investigated by using
the 557 type Ia supernovae from the Union2 Compilation set along with the
current estimates involving the product of the CMB acoustic scale $\ell_{A}$
and the BAO peak at two different redshifts. Using a well-behaved
parameterization for the deceleration parameter, $q(z) = q_0 + q_1z/(1 + z)$,
we estimate the accelerating redshift $z_{acc}=-q_0/(q_0 + q_1)$ (at which the
universe switches from deceleration to acceleration) and investigate the
influence of a non-vanishing spatial curvature on these estimates. We also use
the asymptotic value of $q(z)$ at high-$z$ to place more restrictive bounds on
the model parameters $q_0$ and $q_1$, which results in a more precise
determination of the epoch of cosmic acceleration. | White Dwarf Critical Tests for Modified Gravity: Scalar-tensor theories of gravity can lead to modifications of the
gravitational force inside astrophysical objects. We exhibit that compact stars
such as white dwarfs provide a unique set-up to test beyond Horndeski theories
of ${\rm G}^3$ type. We obtain stringent and independent constraints on the
parameter $\Upsilon$ characterizing the deviations from Newtonian gravity using
the mass-radius relation, the Chandrasekhar mass limit and the maximal
rotational frequency of white dwarfs. We find that white dwarfs impose stronger
constraints on $\Upsilon$ than red and brown dwarfs. |
An AzTEC 1.1-mm Survey for ULIRGs in the field of the Galaxy Cluster MS
0451.6-0305: We have undertaken a deep (sigma~1.1 mJy) 1.1-mm survey of the z=0.54 cluster
MS 0451.6-0305 using the AzTEC camera on the James Clerk Maxwell Telescope. We
detect 36 sources with S/N>3.5 in the central 0.10 deg^2 and present the AzTEC
map, catalogue and number counts. We identify counterparts to 18 sources (50%)
using radio, mid-infrared, Spitzer IRAC and Submillimeter Array data. Optical,
near- and mid-infrared spectral energy distributions are compiled for the 14 of
these galaxies with detectable counterparts, which are expected to contain all
likely cluster members. We then use photometric redshifts and colour selection
to separate background galaxies from potential cluster members and test the
reliability of this technique using archival observations of submillimetre
galaxies. We find two potential MS 0451-03 members, which, if they are both
cluster galaxies have a total star-formation rate (SFR) of ~100 solar masses
per year -- a significant fraction of the combined SFR of all the other
galaxies in MS 0451-03. We also examine the stacked rest-frame mid-infrared,
millimetre and radio emission of cluster members below our AzTEC detection
limit and find that the SFRs of mid-IR selected galaxies in the cluster and
redshift-matched field populations are comparable. In contrast, the average SFR
of the morphologically classified late-type cluster population is ~3 times less
than the corresponding redshift-matched field galaxies. This suggests that
these galaxies may be in the process of being transformed on the red-sequence
by the cluster environment. Our survey demonstrates that although the
environment of MS 0451-03 appears to suppress star-formation in late-type
galaxies, it can support active, dust-obscured mid-IR galaxies and potentially
millimetre-detected LIRGs. | Cosmological evolution of warm dark matter fluctuations I: Efficient
computational framework with Volterra integral equations: We study the complete cosmological evolution of dark matter (DM) density
fluctuations for DM particles that decoupled being ultrarelativistic during the
radiation dominated era which is the case of keV scale warm DM (WDM). The new
framework presented here can be applied to other types of DM and in particular
we extend it to cold DM (CDM). The collisionless and linearized
Boltzmann-Vlasov equations (B-V) for WDM and neutrinos in the presence of
photons and coupled to the linearized Einstein equations are studied in detail
in the presence of anisotropic stress with the Newtonian potential generically
different from the spatial curvature perturbations. We recast this full system
of B-V equations for DM and neutrinos into a system of coupled Volterra
integral equations. These Volterra-type equations are valid both in the
radiation dominated (RD) and matter dominated (MD) eras during which the WDM
particles are ultrarelativistic and then nonrelativistic. This generalizes the
so-called Gilbert integral equation only valid for nonrelativistic particles in
the MD era. We succeed to reduce the system of four Volterra integral equations
for the density and anisotropic stress fluctuations of DM and neutrinos into a
system of only two coupled Volterra equations. The kernels and inhomogeneities
in these equations are explicitly given functions. Combining the
Boltzmann-Vlasov equations and the linearized Einstein equations constrain the
initial conditions on the distribution functions and gravitational potentials.
In the absence of neutrinos the anisotropic stress vanishes and the
Volterra-type equations reduce to a single integral equation. These Volterra
integral equations provide a useful and precise framework to compute the
primordial WDM fluctuations over a wide range of scales including small scales
up to k ~ 1/5 kpc. |
Semi-numeric simulations of helium reionization and the fluctuating
radiation background: Recent He II Lyman-alpha forest observations from 2.0 < z < 3.2 show large
fluctuations in the optical depth at z > 2.7. These results point to a
fluctuating He-ionizing background, which may be due to the end of helium
reionization of this era. We present a fast, semi-numeric procedure to
approximate detailed cosmological simulations. We compute the distribution of
dark matter halos, ionization state of helium, and density field at z = 3 in
broad agreement with recent simulations. Given our speed and flexibility, we
investigate a range of ionizing source and active quasar prescriptions.
Spanning a large area of parameter space, we find order-of-magnitude
fluctuations in the He II ionization rate in the post-reionization regime.
During reionization, the fluctuations are even stronger and develop a bimodal
distribution, in contrast to semi-analytic models and the hydrogen equivalent.
These distributions indicate a low-level ionizing background even at
significant He II fractions. | Astrometric Image Centroid Displacements due to Gravitational
Microlensing by the Ellis Wormhole: Continuing work initiated in an earlier publication (Abe, ApJ, 725 (2010)
787), we study the gravitational microlensing effects of the Ellis wormhole in
the weak-field limit. First, we find a suitable coordinate transformation, such
that the lens equation and analytic expressions of the lensed image positions
can become much simpler than the previous ones. Second, we prove that two
images always appear for the weak-field lens by the Ellis wormhole. By using
these analytic results, we discuss astrometric image centroid displacements due
to gravitational microlensing by the Ellis wormhole. The astrometric image
centroid trajectory by the Ellis wormhole is different from the standard one by
a spherical lensing object that is expressed by the Schwarzschild metric. The
anomalous shift of the image centroid by the Ellis wormhole lens is smaller
than that by the Schwarzschild lens, provided that the impact parameter and the
Einstein ring radius are the same. Therefore, the lensed image centroid by the
Ellis wormhole moves slower. Such a difference, though it is very small, will
be in principle applicable for detecting or constraining the Ellis wormhole by
using future high-precision astrometry observations. In particular, the image
centroid position gives us an additional information, so that the parameter
degeneracy existing in photometric microlensing can be partially broken. The
anomalous shift reaches the order of a few micro arcsec. if our galaxy hosts a
wormhole with throat radius larger than $10^5$ km. When the source moves
tangentially to the Einstein ring for instance, the maximum position shift of
the image centroid by the Ellis wormhole is 0.18 normalized by the Einstein
ring radius. For the same source trajectory, the maximum difference between the
centroid displacement by the Ellis wormhole lens and that by the Schwarzschild
one is -0.16 in the units of the Einstein radius. |
Dynamical analysis of galaxy cluster merger Abell 2146: We present a dynamical analysis of the merging galaxy cluster system Abell
2146 using spectroscopy obtained with the Gemini Multi-Object Spectrograph on
the Gemini North telescope. As revealed by the Chandra X-ray Observatory, the
system is undergoing a major merger and has a gas structure indicative of a
recent first core passage. The system presents two large shock fronts, making
it unique amongst these rare systems. The hot gas structure indicates that the
merger axis must be close to the plane of the sky and that the two merging
clusters are relatively close in mass, from the observation of two shock
fronts. Using 63 spectroscopically determined cluster members, we apply various
statistical tests to establish the presence of two distinct massive structures.
With the caveat that the system has recently undergone a major merger, the
virial mass estimate is M_vir = 8.5 +4.3 -4.7 x 10 ^14 M_sol for the whole
system, consistent with the mass determination in a previous study using the
Sunyaev-Zeldovich signal. The newly calculated redshift for the system is z =
0.2323. A two-body dynamical model gives an angle of 13-19 degrees between the
merger axis and the plane of the sky, and a timescale after first core passage
of 0.24-0.28 Gyr. | A Test for Cosmological Parity Violation Using the 3D Distribution of
Galaxies: We show that the galaxy 4-Point Correlation Function (4PCF) can test for
cosmological parity violation. The detection of cosmological parity violation
would reflect previously unknown forces present at the earliest moments of the
Universe. Recent developments both in rapidly evaluating galaxy $N$-Point
Correlation Functions (NPCFs) and in determining the corresponding covariance
matrices make the search for parity violation in the 4PCF possible in current
and upcoming surveys such as those undertaken by Dark Energy Spectroscopic
Instrument (DESI), the $Euclid$ satellite, and the Vera C. Rubin Observatory
(VRO). |
The Wouthuysen Field Absorption Trough in Cosmic Strings Wakes: The baryon density enhancement in cosmic string wakes leads to a stronger
coupling of the spin temperature to the gas kinetic temperate inside these
string wakes than in the intergalactic medium (IGM). The Wouthuysen Field (WF)
effect has the potential to enhance this coupling to such an extent that it may
result in the strongest and cleanest cosmic string signature in the currently
planned radio telescope projects. Here we consider this enhancement under the
assumption that X-ray heating is not significant. We show that the size of this
effect in a cosmic string wake leads to a brightness temperature at least two
times more negative than in the surrounding IGM. If the SCI-HI [1, 2] or EDGES
[3, 4] experiment confirm a WF absorption trough in the cosmic gas, then cosmic
string wakes should appear clearly in 21 cm redshift surveys of z = 10 to 30. | Multi-wavelength landscape of the young galaxy cluster RXJ1257.2+4738 at
z=0.866: I. The infrared view: We performed a thorough analysis of the star formation activity in the young
massive galaxy cluster RXJ1257+4738 at z=0.866, with emphasis on the
relationship between the local environment of the cluster galaxies and their
star formation activity. We present an optical and IR study that benefited from
the large amount of data available for this cluster, including new OSIRIS/GTC
and Herschel imaging observations. Using a optical-to-NIR multi-wavelength
catalogue, we measured photometric redshifts through a chi2 SED-fitting
procedure. We implemented a reliable and carefully chosen cluster membership
selection criterion including Monte Carlo simulations and derived a sample of
292 reliable cluster member galaxies for which we measured the following
properties: optical colours, stellar masses, ages, ultraviolet luminosities and
local densities. Using the MIPS 24um and Herschel data, we measured total IR
luminosities and SFR. Of the sample of 292 cluster galaxies, 38 show FIR
emission with an SFR between 0.5 and 45 Msun/yr. The spatial distribution of
the FIR emitters within the cluster density map and the filament-like
overdensities observed suggest that RXJ1257 is not virialised, but is in the
process of assembly. The average star formation as a function of the cluster
environment parametrised by the local density of galaxies does not show any
clear trend. However, the fraction of SF galaxies unveils that the cluster
intermediate-density regions is preferred for the SF activity to enhance, since
we observe a significant increase of the FIR-emitter fraction in this
environment. Focusing on the optically red SF galaxies, we can support the
interpretation of this population as dusty red galaxies, since we observe an
appreciable difference in their extinction compared with the blue population. |
SZ contribution to characterize the shape of galaxy cluster haloes: We present the on-going activity to characterize the geometrical properties
of the gas and dark matter haloes using multi-wavelength observations of galaxy
clusters. The role of the SZ signal in describing the gas distribution is
discussed for the pilot case of the CLASH object MACS J1206.2-0847. Preliminary
images of the NIKA2 and ALMA exposures are presented. | Testing the warmness of dark matter: Dark matter (DM) as a pressureless perfect fluid provides a good fit of the
standard $\Lambda$CDM model to the astrophysical and cosmological data. In this
paper, we investigate two extended properties of DM: a possible time dependence
of the equation of state of DM via Chevallier-Polarski-Linder parametrization,
$w_{\rm dm} = w_{\rm dm 0} + w_{\rm dm 1}(1-a)$, and the constant non-null
sound speed $\hat{c}^2_{\rm s,dm}$. We analyze these DM properties on top of
the base $\Lambda$CDM model by using the data from Planck cosmic microwave
background (CMB) temperature and polarization anisotropy, baryonic acoustic
oscillations (BAO) and the local value of the Hubble constant from the Hubble
Space Telescope (HST). We find new and robust constraints on the extended free
parameters of DM. The most tight constraints are imposed by CMB + BAO data
where the three parameters $w_{\rm dm0}$, $w_{\rm dm1}$ and $\hat{c}^2_{\rm
s,dm}$ are respectively constrained to be less than $1.43\times 10^{-3}$,
$1.44\times 10^{-3}$ and $1.79\times 10^{-6}$ at 95\% CL. All the extended
parameters of DM show consistency with zero at 95\% CL, indicating no evidence
beyond the CDM paradigm. We notice that the extended properties of DM
significantly affect several parameters of the base $\Lambda$CDM model. In
particular, in all the analyses performed here, we find significantly larger
mean values of $H_0$ and lower mean values of $\sigma_8$ in comparison to the
base $\Lambda$CDM model. Thus, the well-known $H_0$ and $\sigma_8$ tensions
might be reconciled in the presence of extended DM parameters within the
$\Lambda$CDM framework. Also, we estimate the warmness of DM particles as well
as its mass scale and find a lower bound: $\sim$ 500 eV from our analyses. |
On the discreteness effects in $N$-body simulations of warm dark matter: In cosmological $N$-body simulations of warm dark matter, thermal velocities
of dark-matter particles are sometimes taken into account by adding random
initial velocities to the particles of simulation. However, a particle in the
$N$-body system represents a huge collection of dark-matter particles, whose
average thermal velocity is very close to zero. We consider the issue of
justification of the procedure of adding thermal velocities in $N$-body
simulations and build a simple model of their influence on the power spectrum.
Our model captures the physical effect of suppression of the power spectrum at
small wavenumbers and also explains its artificial enhancement at large
wavenumbers, observed in numerical simulations with added thermal velocities.
The cause of this enhancement is the disturbance of the growth rate of the
density profile introduced when adding random initial thermal velocities.
Specifically, the model predicts a turnover in the behavior of the simulated
power spectrum at a certain wavenumber $k_*$, beyond which it grows as $P (k)
\propto k^2$. Our treatment is generalized to a system consisting of several
matter components with different thermal velocity dispersion. We also estimate
the effects of discreteness related to the bulk velocity field and establish
the conditions under which these effects dominate over those of thermal
velocities. | Generalized massive optimal data compression: Data compression has become one of the cornerstones of modern astronomical
data analysis, with the vast majority of analyses compressing large raw
datasets down to a manageable number of informative summaries. In this paper we
provide a general procedure for optimally compressing $N$ data down to $n$
summary statistics, where $n$ is equal to the number of parameters of interest.
We show that compression to the score function -- the gradient of the
log-likelihood with respect to the parameters -- yields $n$ compressed
statistics that are optimal in the sense that they preserve the Fisher
information content of the data. Our method generalizes earlier work on linear
Karhunen-Lo\'{e}ve compression for Gaussian data whilst recovering both
lossless linear compression and quadratic estimation as special cases when they
are optimal. We give a unified treatment that also includes the general
non-Gaussian case as long as mild regularity conditions are satisfied,
producing optimal non-linear summary statistics when appropriate. As a worked
example, we derive explicitly the $n$ optimal compressed statistics for
Gaussian data in the general case where both the mean and covariance depend on
the parameters. |
A blind HI survey in the Canes Venatici region: We have carried out a blind HI survey using the Westerbork Synthesis Radio
Telescope to make an inventory of objects with small HI masses (between 10^6
and 10^8 Msol) and to constrain the low-mass end of the HI mass function. The
survey has been conducted in a part of the volume containing the nearby Canes
Venatici groups of galaxies. The surveyed region covers an area on the sky of
about 86 square degrees and a range in velocity from about -450 to about 1330
km/s. We find 70 sources in the survey by applying an automated searching
algorithm. Two of the detections have not been catalogued previously, but they
can be assigned an optical counterpart, based on visual inspection of the
second generation Digital Sky Survey images. Only one of the HI detections is
without an optical counterpart. This object is detected in the vicinity of
NGC4822 and it has been already detected in previous HI studies. Nineteen of
the objects have been detected for the first time in the 21-cm emission line in
this survey. The distribution of the HI properties of our detections confirms
our ability to find low mass objects. 86% of the detections have profile widths
less than 130 km/s and can be considered dwarf galaxy candidates. The HI fluxes
measured imply that this survey goes about 10 times deeper than any previous
blind HI survey. The HI mass function and the optical properties of the
detected sources will be discussed in future papers. | Stochastic Gravitational Waves from Post-inflationary Structure
Formation: Following inflation, the Universe may pass through an early matter-dominated
phase supported by the oscillating inflaton condensate. Initially small
fluctuations in the condensate grow gravitationally on subhorizon scales and
can collapse to form nonlinear ``inflaton halos''. Their formation and
subsequent tidal interactions will source gravitational waves, resulting in a
stochastic background in the present Universe. We extend N-body simulations
that model the growth and interaction of collapsed structures to compute the
resulting gravitational wave emission. The spectrum of this radiation is
well-matched by semi-analytical estimates based on the collapse of inflaton
halos and their tidal evolution. We use this semi-analytic formalism to infer
the spectrum for scenarios where the early matter-dominated phase gives way to
a thermalized universe at temperatures as low as $100\,\mathrm{MeV}$ and we
discuss the possible experimental opportunities created by this signal in
inflationary models in which thermalization takes place long after inflation
has completed. |
The many faces of the gas in Centaurus A (NGC5128): Centaurus A (NGC5128) is a fantastic object, ideal for investigating the
characteristics and the role of the gas in an early-type galaxy in the presence
of a radio-loud active nucleus. The different phases of the gas - hot (X-ray),
warm (ionised) and cold (HI and molecular) - are all detected in this object
and can be studied, due to its proximity, at very high spatial resolution. This
richness makes Centaurus A truly unique. Spatially, these gas structures span
from the pc to the tens of kpc scale. Thus, they allow us to trace very
different phenomena, from the formation and evolution of the host galaxy, to
the interplay between nuclear activity and ISM and the feeding mechanism of the
central black hole. A lot of work has been done to study and understand the
characteristics of the gas in this complex object and here I summarise what has
been achieved so far. | Reconstructing teleparallel gravity with cosmic structure growth and
expansion rate data: In this work, we use a combined approach of Hubble parameter data together
with redshift-space-distortion $(f\sigma_8)$ data, which together are used to
reconstruct the teleparallel gravity (TG) Lagrangian via Gaussian processes
(GP). The adopted Hubble data mainly comes from cosmic chronometers, while for
the Type Ia supernovae data we use the latest jointly calibrated Pantheon
compilation. Moreover, we consider two main GP covariance functions, namely the
squared-exponential and Cauchy kernels in order to show consistency (to within
1$\sigma$ uncertainties). The core results of this work are the numerical
reconstructions of the TG Lagrangian from GP reconstructed Hubble and growth
data. We take different possible combinations of the datasets and kernels to
illustrate any potential differences in this regard. We show that nontrivial
cosmology beyond $\Lambda$CDM falls within the uncertainties of the
reconstructions from growth data, which therefore indicates no significant
departure from the concordance cosmological model. |
NMAGIC made-to-measure particle models of galaxies: The parallel code NMAGIC is an implementation of a particle-based method to
create made-to-measure models in agreement with observations of galaxies. It
works by slowly correcting the particle weights of an evolving N-body system,
until a satisfactory compromise is achieved between the goodness of the fit to
a given set of observational data, and some degree of smoothness
(regularization) of the underlying particle model. We briefly describe the
method together with a new regularization scheme in phase-space, which improves
recovering the correct orbit structure in the models. We also mention some
practical applications showing the power of the technique in investigating the
dynamics of galaxies. | Quantized Vortices in Superfluid Dark Matter: In 2015 Berezhiani & Khoury proposed a Superfluid Dark Matter (SFDM) model
where dark matter condenses and forms a superfluid on galactic scales. In the
superfluid state phonons interact with baryons, resulting in a behavior similar
to that of Modified Newtonian Dynamics (MOND). If one assumes that the DM
condensate rotates along with the galaxy, a grid of vortices should form
throughout the superfluid component if the rotation is fast enough. We aim to
investigate the size and impact of the vortices on surrounding baryons, and to
further investigate the parameter space of the model. We also look for a
possible vortex solution of the Lagrangian presented for the SFDM theory. We
first take a simple approach and investigate vortex properties in a constant
density DM halo, applying knowledge from condensed matter physics. We then use
the zero-temperature condensate density profile as a template to vary the DM
particle mass and the energy scale, $\Lambda$, of the SFDM model. Further, we
attempt to find a vortex solution of the theory by extracting the
Euler-Lagrange equation with respect to the modulus of the condensate
wavefunction from the full relativistic SFDM Lagrangian. For the constant
density approach we find that the vortices are on millimeter scale, and
separated by distances $\sim0.002\,\rm{AU}$. The parameter space of the model
is found to be substantial and a reduction in the DM particle mass leads to
larger vortices with a higher energy. However, none of the parameter
combinations explored here give both realistic values of $\Lambda$ and vortices
energetic enough to have an observational impact on the galaxy as a whole. The
vortex equation extracted from the Lagrangian of the model is unstable, and no
solution exhibiting the standard properties of a vortex solution is found. |
The CIV Baldwin effect in QSOs from Seventh Data Release of the Sloan
Digital Sky Survey: Using the properties of SDSS DR7 QSOs catalog from Shen et al., the Baldwin
effect, its slope evolution, the underlying drive for a large sample of 35019
QSOs with reliable spectral analysis are investigated. We find that the Baldwin
effect exists in this large QSOs sample, which is almost the same in 11
different redshift bins, up to $z\sim 5$. The slope is -0.238 by the BCES
(\civ\ EW depends on the continuum), -0.787 by the BCES bisector. For 11
redshift-bins, there is an increasing of the Baldwin effect slope from
$z\sim1.5$ to $z\sim2.0$. From $z\sim2.0$ to $z\sim5.0$, the slope change is
not clear considering their uncertainties or larger redshift bins. There is a
strong correlation between the rest-frame \civ\ EW and \civ-based \mbh while
the relation between the \civ\ EW and \mgii-based \mbh is very weak. With the
correction of \civ-based \mbh from the \civ\ blueshift relative to \mgii, we
suggest that this strong correlation is due to the bias of the \civ-based \mbh,
with respect to that from the \mgii\ line. Considering the \mgii-based \mbh, a
medium strong correlation is found between the \civ\ EW and the Eddington
ratio, which implies that the Eddington ratio seems to be a better underlying
physical parameter than the central black hole mass. | Low-Density Structures in the Local Universe. II. Nearby Cosmic Voids: We present the results of the search for spherical volumes containing no
galaxies with luminosities brighter than the Magellanic Clouds in the Local
Supercluster and its vicinity. Within a distance of 40 Mpc from us, 89 cosmic
voids were discovered with the diameters of 24 to 12 Mpc, containing no
galaxies with absolute magnitudes brighter than M_K < -18.4. A list of these
voids and the sky distribution maps are given. It was found that 93% of
spherical voids overlap, forming three more extended percolated voids
(hypervoids). The largest of them, HV1, has 56 initial spherical cells and
extends in a horseshoe shape, enveloping the Local Volume and the Virgo
cluster. The Local Void (Tully, 1988) in the Hercules-Aquila region is the
closest part of the HV1. Another hypervoid, HV2, contains 22 spherical voids in
the Eridanus constellation, and the third compact hypervoid (HV3) comprises 6
spherical cells in the Bootes. The total volume of these voids incorporates
about 30% of the Local Universe. Among 2906 dwarf galaxies excluded from the
original sample (n = 10502) in the search for spherical volumes, only 68 are
located in the voids we have discovered. They are characterized by late
morphological types (85% are Ir, Im, BCD, Sm), absolute magnitudes M_B ranging
from -13.0 to -16.7, moderate star formation rates (log SSFR ~ -10
M_sun/(yr*L_sun) and gas reserves per luminosity unit twice to three times
larger than in the other dwarf galaxies located in normal environments. The
dwarf population of the voids shows a certain tendency to sit shallow near the
surfaces of cosmic voids. |
Cosmography beyond standard candles and rulers: We perform a cosmographic analysis using several cosmological observables
such as the luminosity distance moduli, the volume distance, the angular
diameter distance and the Hubble parameter. These quantities are determined
using different data sets: Supernovae type Ia and Gamma Ray Bursts, the
Baryonic Acoustic Oscillations, the cosmic microwave background power spectrum
and the Hubble parameter as measured from surveys of galaxies. This data set
allows to put constraints on the cosmographic expansion with unprecedented
precision. We also present forecasts for the coefficients of the kinematic
expansion using future but realistic data sets: constraints on the coefficients
of the expansions are likely to improve by a factor ten with the upcoming large
scale structure probes. Finally, we derive the set of the cosmographic
parameters for several cosmological models (including $\Lambda$CDM) and compare
them with our best fit set. While distance measurements are unable to
discriminate among these models, we show that the inclusion of the Hubble data
set leads to strong constraints on the lowest order coefficients and in
particular it is incompatible with $\Lambda$CDM at 3-$\sigma$ confidence level.
We discuss the reliability of this determination and suggest further
observations which might be of crucial importance for the viability of
cosmographic tests in the next future. | Implications of Graviton-Graviton Interaction to Dark Matter: Our present understanding of the universe requires the existence of dark
matter and dark energy. We describe here a natural mechanism that could make
exotic dark matter and possibly dark energy unnecessary. Graviton-graviton
interactions increase the gravitational binding of matter. This increase, for
large massive systems such as galaxies, may be large enough to make exotic dark
matter superfluous. Within a weak field approximation we compute the effect on
the rotation curves of galaxies and find the correct magnitude and distribution
without need for arbitrary parameters or additional exotic particles. The
Tully-Fisher relation also emerges naturally from this framework. The
computations are further applied to galaxy clusters. |
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