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Dynamic Dark Energy Equation of State (EoS) and Hubble Constant analysis
using type Ia supernovae from Union 2.1 dataset: This paper constraints dynamic dark energy equation of state (EoS) parameters
using the type Ia supernovae from Union 2.1 dataset. The paper also discusses
the dependency of dynamic dark energy EoS parameters on the chosen or assumed
value of the Hubble Constant. To understand the correlation between the Hubble
Constant values and measured dynamic dark energy EoS parameters, we used recent
surveys being done through various techniques such as cosmic microwave
background studies, gravitational waves, baryonic acoustic oscillations and
standard candles to set values for different Hubble Constant values as fixed
parameters with CPL and WCDM models. Then we applied trust region reflective
(TRF) and dog leg (dogbox) algorithms to fit dark energy density parameter and
dynamic dark energy EoS parameters. We found a significant negative correlation
between the fixed Hubble Constant parameter and measured EoS parameter, w0.
Then we used two best fit Hubble Constant values (70 and 69.18474) km $s^{-1}$
$Mpc^{-1}$ based on Chi-square test to test more dark energy EoS parameters
like: JBP, BA, PADE-I, PADE-II, and LH4 models and compared the results with
$\Lambda$-CDM with constant $w_{de}$=-1, WCDM and CPL models. We conclude that
flat $\Lambda$-CDM and WCDM models clearly provide best results while using the
BIC criteria as it severely penalizes the use of extra parameters. However, the
dependency of EoS parameters on Hubble Constant value and the increasing
tension in the measurement of Hubble Constant values using different techniques
warrants further investigation into looking for optimal dynamic dark energy EoS
models to optimally model the relation between the expansion rate and evolution
of dark energy in our universe. | Primordial feature constraints from BOSS+eBOSS: Understanding the universe in its pristine epoch is crucial in order to
obtain a concise comprehension of the late-time universe. Although current data
in cosmology are compatible with Gaussian primordial perturbations whose power
spectrum follows a nearly scale-invariant power law, this need not be the case
when a fundamental theoretical construction is assumed. These extended models
lead to sharp features in the primordial power spectrum, breaking its scale
invariance. In this work, we obtain combined constraints on four primordial
feature models by using the final data release of the BOSS galaxies and eBOSS
quasars. By pushing towards the fundamental mode of these surveys and using the
larger eBOSS volume, we were able to extend the feature parameter space (i.e.
the feature frequency $\omega$) by a factor of four compared to previous
analyses using BOSS. While we did not detect any significant features, previous
work showed that next-generation galaxy surveys such as DESI will improve the
sensitivity to features by a factor of 7, and will also extend the parameter
space by a factor of 2.5. |
Intensity mapping of molecular gas during cosmic reionization: I present a simple calculation of the expected mean CO brightness temperature
from the large scale distribution of galaxies during cosmic reionization. The
calculation is based on the cosmic star formation rate density required to
reionize, and keep ionized, the intergalactic medium, and uses standard
relationships between star formation rate, IR luminosity, and CO luminosity
derived for star forming galaxies over a wide range in redshift. I find that
the mean CO brightness temperature resulting from the galaxies that could
reionize the Universe at $z = 8$ is $T_B \sim 1.1 (C/5) (f_{esc}/0.1)^{-1}
\mu$K, where $f_{esc}$ is the escape fraction of ionizing photons from the
first galaxies, and $C$ is the IGM clumping factor. Intensity mapping of the CO
emission from the large scale structure of the star forming galaxies during
cosmic reionization on scales of order $10^2$ to 10$^3$ deg$^2$, in combination
with HI 21cm imaging of the neutral IGM, will provide a comprehensive study of
the earliest epoch of galaxy formation. | Using Lagrangian perturbation theory for precision cosmology: We explore the Lagrangian perturbation theory (LPT) at 1-loop order with
Gaussian initial conditions. We present an expansion method to approximately
compute the power spectrum in LPT. Our approximate solution has good
convergence in the series expansion and enables us to compute the power
spectrum in LPT accurately and quickly. Non-linear corrections in the
Lagrangian perturbation theory naturally satisfy the law of conservation of
mass because the relation between matter density and the displacement vector of
dark matter corresponds to the conservation of mass. By matching the 1-loop
solution in LPT to the 2-loop solution in standard perturbation theory, we
present an approximate solution of the power spectrum which has higher order
corrections than the 2-loop order in standard perturbation theory with the
conservation of mass satisfied. With this approximation, we can use LPT to
compute a non-linear power spectrum without any free parameters, and this
solution agrees with numerical simulations at $k=0.2$ $h{\rm Mpc}^{-1}$ and
$z=0.35$ to better than 2%. |
Relieving the $H_0$ tension with a new interacting dark energy model: We investigate an extended cosmological model motivated by the asymptotic
safety of gravitational field theory, in which the matter and radiation
densities and the cosmological constant receive a correction parametrized by
the parameters $\delta_G$ and $\delta_\Lambda$, leading to that both the
evolutions of the matter and radiation densities and the cosmological constant
slightly deviate from the standard forms. Here we explain this model as a
scenario of vacuum energy interacting with matter and radiation. We consider
two cases of the model: {(i) ${\tilde\Lambda}$CDM with one additional free
parameter $\delta_G$, with $\delta_{\rm G}$ and $\delta_\Lambda$ related by a
low-redshift limit relation and (ii) e${\tilde\Lambda}$CDM with two additional
free parameters $\delta_G$ and $\delta_\Lambda$ that are independent of each
other.} We use two data combinations, CMB+BAO+SN (CBS) and CMB+BAO+SN+$H_0$
(CBSH), to constrain the models. We find that, in the case of using the CBS
data, neither ${\tilde\Lambda}$CDM nor e${\tilde\Lambda}$CDM can effectively
alleviate the $H_0$ tension. However, it is found that using the CBSH data the
$H_0$ tension can be greatly relieved by the models. In particular, in the case
of e${\tilde\Lambda}$CDM, the $H_0$ tension can be resolved to 0.71$\sigma$. We
conclude that as an interacting dark energy model, ${\tilde\Lambda}$CDM is much
better than $\Lambda(t)$CDM in the sense of both relieving the $H_0$ tension
and fitting to the current observational data. | C2-GaMe: Classification of Cluster Galaxy Membership with Machine
Learning: We present Classification of Cluster GAlaxy MEmbers (C$^2$-GaMe), a
classification algorithm based on a suite of machine learning models that
differentiates galaxies into orbiting, infalling, and background (interloper)
populations, using phase space information as input. We train and test
C$^2$-GaMe with the galaxies from UniverseMachine mock catalog based on
Multi-Dark Planck 2 N-body simulations. We show that probabilistic
classification is superior to deterministic classification in estimating the
physical properties of clusters, including density profiles and velocity
dispersion. We propose a set of estimators to get an unbiased estimation of
cluster properties. We demonstrate that C$^2$-GaMe can recover the distribution
of orbiting and infalling galaxies' position and velocity distribution with
$<1\%$ statistical error when using probabilistic predictions in the presence
of interlopers in the projected phase space. Additionally, we demonstrate the
robustness of trained models by applying them to a different simulation.
Finally, adding a specific star formation rate and the ratio of the galaxy's
halo mass to the cluster's halo mass as additional features improves the
classification performance. We discuss potential applications of this technique
to enhance cluster cosmology and galaxy quenching. |
Star Formation Rates and Stellar Masses of H-alpha Selected Star-Forming
Galaxies at z=0.84: A Quantification of the Downsizing: In this work we analyze the physical properties of a sample of 153 star
forming galaxies at z~0.84, selected by their H-alpha flux with a NB filter.
B-band luminosities of the objects are higher than those of local star forming
galaxies. Most of the galaxies are located in the blue cloud, though some
objects are detected in the green valley and in the red sequence. After the
extinction correction is applied virtually all these red galaxies move to the
blue sequence, unveiling their dusty nature. A check on the extinction law
reveals that the typical extinction law for local starbursts is well suited for
our sample but with E(B-V)_stars=0.55 E(B-V)_gas. We compare star formation
rates (SFR) measured with different tracers (H-alpha, UV and IR) finding that
they agree within a factor of three after extinction correction. We find a
correlation between the ratios SFR_FUV/SFR_H-alpha, SFR_IR/SFR_H-alpha and the
EW(H-alpha) (i.e. weighted age) which accounts for part of the scatter. We
obtain stellar mass estimations fitting templates to multi-wavelength
photometry. The typical stellar mass of a galaxy within our sample is ~10^10
Msun. The SFR is correlated with stellar mass and the specific star formation
rate (sSFR) decreases with it, indicating that massive galaxies are less
affected by star formation processes than less massive ones. This result is
consistent with the downsizing scenario. To quantify this downsizing we
estimated the quenching mass M_Q for our sample at z~0.84, finding that it
declines from M_Q ~10^12 Msun to M_Q ~8x10^10 Msun at the local Universe. | A Ten Billion Solar Mass Outflow of Molecular Gas Launched by Radio
Bubbles in the Abell 1835 Brightest Cluster Galaxy: We report ALMA Early Science observations of the Abell 1835 brightest cluster
galaxy (BCG) in the CO (3-2) and CO (1-0) emission lines. We detect 5E10 solar
masses of molecular gas within 10 kpc of the BCG. Its velocity width of ~130
km/s FWHM is too narrow to be supported by dynamical pressure. The gas may
instead be supported in a rotating, turbulent disk oriented nearly face-on. The
disk is forming stars at a rate of 100-180 solar masses per year. Roughly 1E10
solar masses of molecular gas is projected 3-10 kpc to the north-west and to
the east of the nucleus with line of sight velocities lying between -250 km/s
to +480 km/s with respect to the systemic velocity. Although inflow cannot be
ruled out, the rising velocity gradient with radius is consistent with a broad,
bipolar outflow driven by radio jets or buoyantly rising X-ray cavities. The
molecular outflow may be associated with an outflow of hot gas in Abell 1835
seen on larger scales. Molecular gas is flowing out of the BCG at a rate of
approximately 200 solar masses per year, which is comparable to its star
formation rate. How radio bubbles lift dense molecular gas in their updrafts,
how much gas will be lost to the BCG, and how much will return to fuel future
star formation and AGN activity are poorly understood. Our results imply that
radio-mechanical (radio mode) feedback not only heats hot atmospheres
surrounding elliptical galaxies and BCGs, it is able to sweep higher density
molecular gas away from their centers. |
Large-scale clustering of galaxies in general relativity: Several recent studies have shown how to properly calculate the observed
clustering of galaxies in a relativistic context, and uncovered corrections to
the Newtonian calculation that become significant on scales near the horizon.
Here, we retrace these calculations and show that, on scales approaching the
horizon, the observed galaxy power spectrum depends strongly on which gauge is
assumed to relate the intrinsic fluctuations in galaxy density to matter
perturbations through a linear bias relation. Starting from simple physical
assumptions, we derive a gauge-invariant expression relating galaxy density
perturbations to matter density perturbations on large scales, and show that it
reduces to a linear bias relation in synchronous-comoving gauge, corroborating
an assumption made in several recent papers. We evaluate the resulting observed
galaxy power spectrum, and show that it leads to corrections similar to an
effective non-Gaussian bias corresponding to a local (effective) fNL < 0.5.
This number can serve as a guideline as to which surveys need to take into
account relativistic effects. We also discuss the scale-dependent bias induced
by primordial non-Gaussianity in the relativistic context, which again is
simplest in synchronous-comoving gauge. | The First Observations of Low Redshift Damped Lyman-alpha Systems with
the Cosmic Origins Spectrograph: We report on the first Cosmic Origins Spectrograph (COS) observations of
damped and sub-damped Lyman-alpha (DLA) systems discovered in a new survey of
the gaseous halos of low-redshift galaxies. From observations of 37 sightlines,
we have discovered three DLAs and four sub-DLAs. We measure the neutral gas
density Omega(HI), and redshift density dN/dz, of DLA and sub-DLA systems at
z<0.35. We find dN/dz=0.25 and Omega(HI)=1.4x10^-3 for DLAs, and dN/dz=0.08
with Omega(HI)=4.2x10^-5 for sub-DLAs over a redshift path delta z=11.9. To
demonstrate the scientific potential of such systems, we present a detailed
analysis of the DLA at z=0.1140 in the spectrum of SDSS J1009+0713. Profile
fits to the absorption lines determine log N(H I)=20.68pm0.10 with a
metallicity determined from the undepleted element Sulfur of [S/H]=-0.62pm0.18.
The abundance pattern of this DLA is similar to that of higher z DLAs, showing
mild depletion of the refractory elements Fe and Ti with [S/Fe]=+0.24pm0.22 and
[S/Ti]=+0.28pm0.15. Nitrogen is underabundant in this system with
[N/H]=-1.40pm0.14, placing this DLA below the plateau of the [N/alpha]
measurements in the local Universe at similar metallicities. This DLA has a
simple kinematic structure with only two components required to fit the
profiles and a kinematic width of 52 km/s. Imaging of the QSO field with WFC3
reveals a spiral galaxy at very small impact parameter to the QSO and several
galaxies within 10". Followup spectra with LRIS reveal that none of the nearby
galaxies are at the redshift of the DLA. The spiral galaxy is identified as the
host galaxy of the QSO based on the near perfect alignment of the nucleus and
disk of the galaxy as well as spectra of an H II region showing emission lines
at the QSO redshift. A small feature appears 0.70" from the nucleus of the QSO
after PSF subtraction, providing another candidate for the host galaxy of the
DLA. (abb) |
Diagnostics of the Molecular Component of PDRs with Mechanical Heating: Context. Multitransition CO observations of galaxy centers have revealed that
significant fractions of the dense circumnuclear gas have high kinetic
temperatures, which are hard to explain by pure photon excitation, but may be
caused by dissipation of turbulent energy.
Aims. We aim to determine to what extent mechanical heating should be taken
into account while modelling PDRs. To this end, the effect of dissipated
turbulence on the thermal and chemical properties of PDRs is explored. Methods.
Clouds are modelled as 1D semi-infinite slabs whose thermal and chemical
equilibrium is solved for using the Leiden PDR-XDR code.
Results. In a steady-state treatment, mechanical heating seems to play an
important role in determining the kinetic temperature of the gas in molecular
clouds. Particularly in high-energy environments such as starburst galaxies and
galaxy centers, model gas temperatures are underestimated by at least a factor
of two if mechanical heating is ignored. The models also show that CO, HCN and
H2 O column densities increase as a function of mechanical heating. The HNC/HCN
integrated column density ratio shows a decrease by a factor of at least two in
high density regions with n \sim 105 cm-3, whereas that of HCN/HCO+ shows a
strong dependence on mechanical heating for this same density range, with
boosts of up to three orders of magnitude.
Conclusions. The effects of mechanical heating cannot be ignored in studies
of the molecular gas excitation whenever the ratio of the star formation rate
to the gas density is close to, or exceeds, 7 \times 10-6 M yr-1 cm4.5 . If
mechanical heating is not included, predicted column densities are
underestimated, sometimes even by a few orders of magnitude. As a lower bound
to its importance, we determined that it has non-negligible effects already
when mechanical heating is as little as 1% of the UV heating in a PDR. | Large scale outflows from z ~ 0.7 starburst galaxies identified via
ultra-strong MgII quasar absorption lines: (Abridged) Star formation-driven outflows are a critical phenomenon in
theoretical treatments of galaxy evolution, despite the limited ability of
observations to trace them across cosmological timescales. If the strongest
MgII absorption-line systems detected in the spectra of background quasars
arise in such outflows, "ultra-strong" MgII (USMgII) absorbers would identify
significant numbers of galactic winds over a huge baseline in cosmic time, in a
manner independent of the luminous properties of the galaxy. To this end, we
present the first detailed imaging and spectroscopic study of the fields of two
USMgII absorber systems culled from a statistical absorber catalog, with the
goal of understanding the physical processes leading to the large velocity
spreads that define such systems. Each field contains two bright emission-line
galaxies at similar redshift (dv < 300 km/s) to that of the absorption.
Lower-limits on their instantaneous star formation rates (SFR) from the
observed OII and Hb line fluxes, and stellar masses from spectral template
fitting indicate specific SFRs among the highest for their masses at z~0.7.
Additionally, their 4000A break and Balmer absorption strengths imply they have
undergone recent (~0.01 - 1 Gyr) starbursts. The concomitant presence of two
rare phenomena - starbursts and USMgII absorbers - strongly implies a causal
connection. We consider these data and USMgII absorbers in general in the
context of various popular models, and conclude that galactic outflows are
generally necessary to account for the velocity extent of the absorption. We
favour starburst driven outflows over tidally-stripped gas from a major
interaction which triggered the starburst as the energy source for the majority
of systems. Finally, we discuss the implications of these results and speculate
on the overall contribution of such systems to the global SFR density at z~0.7. |
Pulsar timing array results sheds light on Hubble tension during the end
of inflation: Recently, pulsar timing array (PTA) collaborations, including NANOGrav, have
reported evidence of a stochastic gravitational wave background within the nHz
frequency range.\ It can be interpreted by gravitational waves from preheating
era. In this context, we demonstrate that the emission of this stochastic
gravitational wave background can be attributed to fluctuations occurring at
the end of inflation, thus giving rise to the Hubble tension issue. At the
onset of inflation, the value of the frequency of the gravitational wave signal
stood at $f=0.08nHz$, but it rapidly transitioned to $f=1nHz$ precisely at the
end of inflation. However, just before the end of inflation, a phase
characterized by curvature perturbation is known to occur, causing a swift
increase in the frequency. | Super-Resolution Emulation of Large Cosmological Fields with a 3D
Conditional Diffusion Model: High-resolution (HR) simulations in cosmology, in particular when including
baryons, can take millions of CPU hours. On the other hand, low-resolution (LR)
dark matter simulations of the same cosmological volume use minimal computing
resources. We develop a denoising diffusion super-resolution emulator for large
cosmological simulation volumes. Our approach is based on the image-to-image
Palette diffusion model, which we modify to 3 dimensions. Our super-resolution
emulator is trained to perform outpainting, and can thus upgrade very large
cosmological volumes from LR to HR using an iterative outpainting procedure. As
an application, we generate a simulation box with 8 times the volume of the
Illustris TNG300 training data, constructed with over 9000 outpainting
iterations, and quantify its accuracy using various summary statistics. |
Spurious correlations between galaxies and multi-epoch image stacks in
the DESI Legacy Surveys: A non-negligible source of systematic bias in cosmological analyses of galaxy
surveys is the on-sky modulation caused by foregrounds and variable image
characteristics such as observing conditions. Standard mitigation techniques
perform a regression between the observed galaxy density field and sky maps of
the potential contaminants. Such maps are ad-hoc, lossy summaries of the
heterogeneous sets of co-added exposures that contribute to the survey. We
present a methodology to address this limitation, and extract the spurious
correlations between the observed distribution of galaxies and arbitrary stacks
of single-epoch exposures. We study four types of galaxies (LRGs, ELGs, QSOs,
LBGs) in the three regions of the DESI Legacy Surveys (North, South, DES),
which results in twelve samples with varying levels and type of contamination.
We find that the new technique outperforms the traditional ones in all cases,
and is able to remove higher levels of contamination. This paves the way for
new methods that extract more information from multi-epoch galaxy survey data
and mitigate large-scale biases more effectively. | A slow bar in the dwarf irregular galaxy NGC 3741: Using the Tremaine-Weinberg method, we measure the speed of the HI bar seen
in the disk of NGC 3741. NGC 3741 is an extremely gas rich galaxy with an
{H\,{\sc i}} disk which extends to about 8.3 times its Holmberg radius. It is
also highly dark matter-dominated. Our calculated value of the pattern speed
$\Omega_p$ is 17.1 $\pm$ 3.4 km $\textrm{s}^{-1}\textrm{kpc}^{-1}$. We also
find the ratio of the co-rotation radius to the bar semi-major axis to be (1.6
$\pm$ 0.3), indicating a slow bar. This is consistent with bar models in which
dynamical friction results in a slow bar in dark matter dominated galaxies. |
Spatially Resolved Spectroscopy of Starburst and Post-Starburst Galaxies
in The Rich z~0.55 Cluster CL0016+16: We have used the Low Resolution Imaging Spectrograph (LRIS) on the W.M. Keck
I telescope to obtain spatially resolved spectroscopy of a small sample of six
post-starburst and three dusty-starburst galaxies in the rich cluster CL0016+16
at z=0.55. We use this to measure radial profiles of the Hdelta and OII3727
lines which are diagnostic probes of the mechanisms that give rise to the
abrupt changes in star-formation rates in these galaxies. In the post-starburst
sample we are unable to detect any radial gradients in the Hdelta line
equivalent width - although one galaxy exhibits a gradient from one side of the
galaxy to the other. The absence of Hdelta gradients in these galaxies is
consistent with their production via interaction with the intra-cluster medium,
however, our limited spatial sampling prevents us from drawing robust
conclusions. All members of the sample have early type morphologies, typical of
post-starburst galaxies in general, but lack the high incidence of tidal tails
and disturbances seen in local field samples. This argues against a merger
origin and adds weight to a scenario where truncation by the intra-cluster
medium is at work. The post-starburst spectral signature is consistent over the
radial extent probed with no evidence of OII3727 emission and strong Hdelta
absorption at all radii i.e. the post-starburst classification is not an
aperture effect. In contrast the dusty-starburst sample shows a tendency for a
central concentration of OII3727 emission. This is most straightforwardly
interpreted as the consequence of a central starburst. However, other
possibilities exist such as a non-uniform dust distribution (which is expected
in such galaxies) and/or a non-uniform starburst age distribution. The sample
exhibit late type and irregular morphologies. | CMB lensing with shear-only reconstruction on the full sky: Reconstruction of gravitational lensing effects in the CMB from current and
upcoming surveys is still dominated by temperature anisotropies. Extragalactic
foregrounds in temperature maps can induce significant biases in the lensing
power spectrum obtained with the standard quadratic estimators. Techniques such
as masking cannot remove these foregrounds fully, and the residuals can still
lead to large biases if unaccounted for. In this paper, we study the
"shear-only" estimator, an example of a class of geometric methods that
suppress extragalactic foreground contamination while making only minimal
assumptions about foreground properties. The shear-only estimator has only been
formulated in the flat-sky limit and so is not easily applied to wide surveys.
Here, we derive the full-sky version of the shear-only estimator and its
generalisation to an $m=2$ multipole estimator that has improved performance
for lensing reconstruction on smaller scales. The multipole estimator is
generally not separable, and so is expensive to compute. We explore separable
approximations based on a singular-value decomposition, which allow efficient
evaluation of the estimator with real-space methods. Finally, we apply these
estimators to simulations that include extragalactic foregrounds and verify
their efficacy in suppressing foreground biases. |
Probing the Outskirts of the Early Stage Galaxy Cluster Merger A1750: We present results from recent Suzaku and Chandra X-ray, and MMT optical
observations of the strongly merging "double cluster" A1750 out to its virial
radius, both along and perpendicular to a putative large-scale structure
filament. Some previous studies of individual clusters have found evidence for
ICM entropy profiles that flatten at large cluster radii, as compared with the
self-similar prediction based on purely gravitational models of hierarchical
cluster formation, and gas fractions that rise above the mean cosmic value.
Weakening accretion shocks and the presence of unresolved cool gas clumps, both
of which are expected to correlate with large scale structure filaments, have
been invoked to explain these results. In the outskirts of A1750, we find
entropy profiles that are consistent with self-similar expectations, and gas
fractions that are consistent with the mean cosmic value, both along and
perpendicular to the putative large scale filament. Thus, we find no evidence
for gas clumping in the outskirts of A1750, in either direction. This may
indicate that gas clumping is less common in lower temperature (kT~4keV), less
massive systems, consistent with some (but not all) previous studies of low
mass clusters and groups. Cluster mass may therefore play a more important role
in gas clumping than dynamical state. Finally, we find evidence for diffuse,
cool (<1 keV) gas at large cluster radii (R200) along the filament, which is
consistent with the expected properties of the denser, hotter phase of the
WHIM. | Is there evidence for CIDER in the Universe?: In this work we analyze the full linear behaviour of the constrained
interacting dark energy (CIDER) model, which is a conformally coupled
quintessence model tailored to mimic a $\Lambda$CDM expansion. We compute the
matter and temperature anisotropies power spectra and test the model against
recent observational data. We shed light on some particular subtleties of the
background behaviour that were not fully captured in previous works, and study
the physics of the linear cosmological observables. One novelty found was that
matter perturbations are enhanced at large scales when compared with the ones
of the standard $\Lambda$CDM. The reason and impact of this trend on the
cosmological observables and on the physics of the early Universe are
considered. We find that the introduction of the coupling parameter alleviates
the $\sigma_8$ tension between early and late time probes although Planck data
favours the $\Lambda$CDM limit of the model. |
New Constraints on Anisotropic Rotation of CMB Polarization: The coupling of a scalar field to electromagnetic field via the Chern-Simons
term will rotate the polarization directions of the cosmic microwave background
radiation. The rotation angle which relies on the distribution of the scalar
field on the CMB sky is direction dependent. Such anisotropies will give rise
to new distortions to the power spectra of CMB polarization and it can be used
to probe the detailed physics of the scalar field. In this paper we use the
updated observational data to constrain the anisotropic rotation angle in a
model independent way. We find that the dominant effect of the anisotropic
rotation on CMB comes from its variance and it is constrained tightly by the
current data. | Searching for Oscillations in the Primordial Power Spectrum: Constraints
from Planck (Paper II): We apply our recently developed code to search for resonance features in the
Planck CMB temperature data. We search both for log spaced oscillations or
linear spaced oscillations and compare our findings with results of our WMAP9
analysis and the Planck team analysis. While there are hints of log spaced
resonant features present in the WMAP9 data, the significance of these features
weaken with more data. With more accurate small scale measurements, we also
find that the best fit frequency has shifted and the amplitude has been
reduced. We confirm the presence of a several low frequency peaks, earlier
identified by the Planck team, but with a better improvement of fit (delta
chi^2 ~ 12). We further investigate this improvement by allowing the lensing
potential to vary as well, showing mild correlation between the amplitude of
the oscillations and the lensing amplitude. We find that the improvement of the
fit increases even more (delta chi^2 ~ 14) for the low frequencies that modify
the spectrum in a way that mimics the lensing effect. Since these features were
not present in the WMAP data, they are primarily due to better measurements of
Planck at small angular scales. For linear spaced oscillations we find a
maximum delta chi^2 ~ 13 scanning two orders of magnitude in frequency space,
and the biggest improvements are at extremely high frequencies. We recover a
best fit frequency very close to the one found in WMAP9, which confirms that
the fit improvement is driven by low l. Further comparisons with WMAP9 show
Planck contains many more features, both for linear and log space oscillations,
but with a smaller improvement of fit. We discuss the improvement as a function
of the number of modes and study the effect of the 217 GHz map, which appears
to drive most of the improvement for log spaced oscillations. We conclude that
none of the detected features are statistically significant. |
Angular momentum in cluster Spherical Collapse Model: Our new formulation of the Spherical Collapse Model (SCM-L) takes into
account the presence of angular momentum associated with the motion of galaxy
groups infalling towards the centre of galaxy clusters. The angular momentum is
responsible for an additional term in the dynamical equation which is useful to
describe the evolution of the clusters in the non-equilibrium region which is
investigated in the present paper. Our SCM-L can be used to predict the
profiles of several strategic dynamical quantities as the radial and tangential
velocities of member galaxies, and the total cluster mass.
A good understanding of the non-equilibrium region is important since it is
the natural scenario where to study the infall in galaxy clusters and the
accretion phenomena present in these objects. Our results corroborate previous
estimates and are in very good agreement with the analysis of recent
observations and of simulated clusters. | Quasar emission lines, radio structures and radio unification: Unified schemes of radio sources, which account for different types of radio
AGN in terms of anisotropic radio and optical emission, together with different
orientations of the ejection axis to the line of sight, have been invoked for
many years. Recently, large samples of optical quasars, mainly from the Sloan
Digital Sky Survey, together with large radio samples, such as FIRST, have
become available. These hold the promise of providing more stringent tests of
unified schemes but, compared to previous samples, lack high resolution radio
maps. Nevertheless they have been used to investigate unified schemes, in some
cases yielding results which appear inconsistent with such theories. Here we
investigate using simulations how the selection effects to which such
investigations are subject can influence the conclusions drawn. In particular,
we find that the effects of limited resolution do not allow core-dominated
radio sources to be fully represented in the samples, that the effects of
limited sensitivity systematically exclude some classes of sources and the lack
of deep radio data make it difficult to decide to what extent closely separated
radio sources are associated. Nevertheless, we conclude that relativistic
unified schemes are entirely compatible with the current observational data.
For a sample selected from SDSS and FIRST which includes weak-cored triples we
find that the equivalent width of the [OIII] emission line decreases as
core-dominance increases, as expected, and also that core-dominated quasars are
optically brighter than weak-cored quasars. |
The evolution of the number density of compact galaxies: We compare the number density of compact (small size) massive galaxies at low
and high redshift using our Padova Millennium Galaxy and Group Catalogue
(PM2GC) at z=0.03-0.11 and the CANDELS results from Barro et al. (2013) at
z=1-2. The number density of local compact galaxies with luminosity weighted
(LW) ages compatible with being already passive at high redshift is compared
with the density of compact passive galaxies observed at high-z. Our results
place an upper limit of a factor ~2 to the evolution of the number density and
are inconsistent with a significant size evolution for most of the compact
galaxies observed at high-z. The evolution may be instead significant (up to a
factor 5) for the most extreme, ultracompact galaxies. Considering all compact
galaxies, regardless of LW age and star formation activity, a minority of local
compact galaxies (<=1/3) might have formed at z<1. Finally, we show that the
secular decrease of the galaxy stellar mass due to simple stellar evolution may
in some cases be a non-negligible factor in the context of the evolution of the
mass-size relation, and we caution that passive evolution in mass should be
taken into account when comparing samples at different redshifts. | The Hubble tension as a window on the gravitation of the dark matter
sector: A simple and minimal extension of the standard cosmological $\Lambda$CDM
model in which dark matter experiences an additional long-range scalar
interaction is demonstrated to alleviate the long lasting Hubble-tension while
letting primordial nucleosynthesis predictions unaffected and passing by
construction all current local tests of general relativity. The theoretical
formulation of this $\Lambda\beta$CDM model and its comparison to astrophysical
observations are presented to prove its ability to fit existing data and
potentially resolve the tension. |
A Displaced Supermassive Black Hole in M87: Isophotal analysis of M87, using data from the Advanced Camera for Surveys,
reveals a projected displacement of 6.8 +/- 0.8 pc (~ 0.1 arcsec) between the
nuclear point source (presumed to be the location of the supermassive black
hole, SMBH) and the photo-center of the galaxy. The displacement is along a
position angle of 307 +/- 17 degrees and is consistent with the jet axis. This
suggests the active SMBH in M87 does not currently reside at the galaxy center
of mass, but is displaced in the counter-jet direction. Possible explanations
for the displacement include orbital motion of an SMBH binary, gravitational
perturbations due to massive objects (e.g., globular clusters), acceleration by
an asymmetric or intrinsically one-sided jet, and gravitational recoil
resulting from the coalescence of an SMBH binary. The displacement direction
favors the latter two mechanisms. However, jet asymmetry is only viable, at the
observed accretion rate, for a jet age of >0.1 Gyr and if the galaxy restoring
force is negligible. This could be the case in the low density core of M87. A
moderate recoil ~1 Myr ago might explain the disturbed nature of the nuclear
gas disk, could be aligned with the jet axis, and can produce the observed
offset. Alternatively, the displacement could be due to residual oscillations
resulting from a large recoil that occurred in the aftermath of a major merger
any time in the last 1 Gyr. | Probing Diffuse Gas with Fast Radio Bursts: The dispersion measure -- redshift relation of Fast Radio Bursts,
$\mathrm{DM}(z)$, has been proposed as a potential new probe of the cosmos,
complementary to existing techniques. In practice, however, the effectiveness
of this approach depends on a number of factors, including (but not limited to)
the intrinsic scatter in the data caused by intervening matter inhomogeneities.
Here, we simulate a number of catalogues of mock FRB observations, and use MCMC
techniques to forecast constraints, and assess which parameters will likely be
best constrained. In all cases we find that any potential improvement in
cosmological constraints are limited by the current uncertainty on the the
diffuse gas fraction, $f_{\rm d}(z)$. Instead, we find that the precision of
current cosmological constraints allows one to constrain $f_{\rm d}(z)$, and
possibly its redshift evolution. Combining CMB + BAO + SNe + $H_0$ constraints
with just 100 FRBs (with redshifts), we find a typical constraint on the mean
diffuse gas fraction of a few percent. A detection of this nature would
alleviate the "missing baryon problem", and therefore highlights the value of
localisation and spectroscopic followup of future FRB detections. |
Spatial fluctuations of the intergalactic temperature-density relation
after hydrogen reionization: The thermal state of the post-reionization IGM is sensitive to the timing of
reionization and the nature of the ionizing sources. We have modelled here the
thermal state of the IGM in cosmological radiative transfer simulations of a
realistic, extended, spatially inhomogeneous hydrogen reionization process,
carefully calibrated with Ly-alpha forest data. We compare these with
cosmological simulations run using a spatially homogeneous ionizing background.
The simulations with a realistic growth of ionized regions and a realistic
spread in reionization redshifts show, as expected, significant spatial
fluctuations in the temperature-density relation (TDR) of the post-reionization
IGM. The most recently ionized regions are hottest and exhibit a flatter TDR.
In simulations consistent with the average TDR inferred from Ly-alpha forest
data, these spatial fluctuations have a moderate but noticeable effect on the
statistical properties of the Ly-alpha opacity of the IGM at z ~ 4-6. This
should be taken into account in accurate measurements of the thermal properties
of the IGM and the free-streaming of dark matter from Ly-alpha forest data in
this redshift range. The spatial variations of the TDR predicted by our
simulations are, however, smaller by about a factor two than would be necessary
to explain the observed large spatial opacity fluctuations on large (> 50
comoving Mpc/h) scales at z > 5.5. | SNIa-Cosmology Analysis Results from Simulated LSST Images: from
Difference Imaging to Constraints on Dark Energy: The Vera Rubin Observatory Legacy Survey of Space and Time (LSST) is expected
to process ${\sim}10^6$ transient detections per night. For precision
measurements of cosmological parameters and rates, it is critical to understand
the detection efficiency, magnitude limits, artifact contamination levels, and
biases in the selection and photometry. Here we rigorously test the LSST
Difference Image Analysis (DIA) pipeline using simulated images from the Rubin
Observatory LSST Dark Energy Science Collaboration (DESC) Data Challenge (DC2)
simulation for the Wide-Fast-Deep (WFD) survey area. DC2 is the first
large-scale (300 deg$^2$) image simulation of a transient survey that includes
realistic cadence, variable observing conditions, and CCD image artifacts. We
analyze ${\sim}$15 deg$^2$ of DC2 over a 5-year time-span in which artificial
point-sources from Type Ia Supernovae (SNIa) light curves have been overlaid
onto the images. We measure the detection efficiency as a function of
Signal-to-Noise Ratio (SNR) and find a $50\%$ efficiency at $\rm{SNR}=5.8$. The
magnitude limits for each filter are: $u=23.66$, $g=24.69$, $r=24.06$,
$i=23.45$, $z=22.54$, $y=21.62$ $\rm{mag}$. The artifact contamination is
$\sim90\%$ of detections, corresponding to $\sim1000$ artifacts/deg$^2$ in $g$
band, and falling to 300 per deg$^2$ in $y$ band. The photometry has biases
$<1\%$ for magnitudes $19.5 < m <23$. Our DIA performance on simulated images
is similar to that of the Dark Energy Survey pipeline applied to real images.
We also characterize DC2 image properties to produce catalog-level simulations
needed for distance bias corrections. We find good agreement between DC2 data
and simulations for distributions of SNR, redshift, and fitted light-curve
properties. Applying a realistic SNIa-cosmology analysis for redshifts $z<1$,
we recover the input cosmology parameters to within statistical uncertainties. |
Trajectories with suppressed tensor-to-scalar ratio in Aligned Natural
Inflation: In Aligned Natural Inflation, an alignment between different potential terms
produces an inflaton excursion greater than the axion scales in the potential.
We show that, starting from a general potential of two axions with two aligned
potential terms, the effective theory for the resulting light direction is
characterized by four parameters: an effective potential scale, an effective
axion constant, and two extra parameters (related to ratios of the axion scales
and the potential scales in the $2-$field theory). For all choices of these
extra parameters, the model can support inflation along valleys (in the
$2-$field space) that end in minima of the potential. This leads to a
phenomenology similar to that of single field Natural Inflation. For a
significant range of the extra two parameters, the model possesses also higher
altitude inflationary trajectories passing through saddle points of the
$2-$field potential, and disconnected from any minimum. These plateaus end when
the heavier direction becomes unstable, and therefore all of inflation takes
place close to the saddle point, where - due to the higher altitude - the
potential is flatter (smaller $\epsilon$ parameter). As a consequence, a
tensor-to-scalar ratio $r = {\rm O } \left( 10^{-4} - 10^{-2} \right)$ can be
easily achieved in the allowed $n_s$ region, well within the latest $1 \sigma$
CMB contours. | Clustering properties of galaxies selected in stellar mass: Breaking
down the link between luminous and dark matter in massive galaxies from z=0
to z=2: We present a study on the clustering of a stellar mass selected sample of
18,482 galaxies with stellar masses M*>10^10M(sun) at redshifts 0.4<z<2.0,
taken from the Palomar Observatory Wide-field Infrared Survey. We examine the
clustering properties of these stellar mass selected samples as a function of
redshift and stellar mass, and discuss the implications of measured clustering
strengths in terms of their likely halo masses. We find that galaxies with high
stellar masses have a progressively higher clustering strength, and amplitude,
than galaxies with lower stellar masses. We also find that galaxies within a
fixed stellar mass range have a higher clustering strength at higher redshifts.
We furthermore use our measured clustering strengths, combined with models from
Mo & White (2002), to determine the average total masses of the dark matter
haloes hosting these galaxies. We conclude that for all galaxies in our sample
the stellar-mass-to-total-mass ratio is always lower than the universal
baryonic mass fraction. Using our results, and a compilation from the
literature, we furthermore show that there is a strong correlation between
stellar-mass-to-total-mass ratio and derived halo masses for central galaxies,
such that more massive haloes contain a lower fraction of their mass in the
form of stars over our entire redshift range. For central galaxies in haloes
with masses M(halo)>10^13M(sun) we find that this ratio is <0.02, much lower
than the universal baryonic mass fraction. We show that the remaining baryonic
mass is included partially in stars within satellite galaxies in these haloes,
and as diffuse hot and warm gas. We also find that, at a fixed stellar mass,
the stellar-to-total-mass ratio increases at lower redshifts. This suggests
that galaxies at a fixed stellar mass form later in lower mass dark matter
haloes, and earlier in massive haloes. We interpret this as a "halo downsizing"
effect, however some of this evolution could be attributed to halo assembly
bias. |
The Co-evolution of Cosmic Entropy and Structures in the Universe: According to the second law of thermodynamics, the arrow of time points to an
ever increasing entropy of the Universe. However, exactly how the entropy
evolves with time and what drives the growth remain largely unknown. Here, for
the first time, we quantify the evolving entropy of cosmic structures using a
large-scale cosmological hydrodynamical simulation. Our simulation starts from
initial conditions predicted by the leading LambdaCDM cosmology,
self-consistently evolves the dynamics of both dark and baryonic matter, star
formation, black hole growth and feedback processes, from the cosmic dawn to
the present day. Tracing the entropy contributions of these distinct components
in the simulation, we find a strong link between entropy growth and structure
formation. The entropy is dominated by that of the black holes in all epochs,
and its evolution follows the same path as that of galaxies: it increases
rapidly from a low-entropy state at high redshift until z~2, then transits to a
slower growth. Our results suggest that cosmic entropy may co-evolve with
cosmic structure, and that its growth may be driven mainly by the formation of
black holes in galaxies. We predict that the entropy will continue to increase
in the near future, but likely at a constant rate. | SUNBIRD: A simulation-based model for full-shape density-split
clustering: Combining galaxy clustering information from regions of different
environmental densities can help break cosmological parameter degeneracies and
access non-Gaussian information from the density field that is not readily
captured by the standard two-point correlation function (2PCF) analyses.
However, modelling these density-dependent statistics down to the non-linear
regime has so far remained challenging. We present a simulation-based model
that is able to capture the cosmological dependence of the full shape of the
density-split clustering (DSC) statistics down to intra-halo scales. Our models
are based on neural-network emulators that are trained on high-fidelity mock
galaxy catalogues within an extended-$\Lambda$CDM framework, incorporating the
effects of redshift-space, Alcock-Paczynski distortions and models of the
halo-galaxy connection. Our models reach sub-percent level accuracy down to
$1\,h^{-1}{\rm Mpc}$ and are robust against different choices of galaxy-halo
connection modelling. When combined with the galaxy 2PCF, DSC can tighten the
constraints on $\omega_{\rm cdm}$, $\sigma_8$, and $n_s$ by factors of 2.9,
1.9, and 2.1, respectively, compared to a 2PCF-only analysis. DSC additionally
puts strong constraints on environment-based assembly bias parameters. Our code
is made publicly available on Github. |
Breaking degeneracies in modified gravity with higher (than 2nd) order
weak-lensing statistics: General relativity (GR) has been well tested up to solar system scales, but
it is much less certain that standard gravity remains an accurate description
on the largest, that is, cosmological, scales. Many extensions to GR have been
studied that are not yet ruled out by the data, including by that of the recent
direct gravitational wave detections. Degeneracies among the standard model
($\Lambda$CDM) and modified gravity (MG) models, as well as among different MG
parameters, must be addressed in order to best exploit information from current
and future surveys and to unveil the nature of dark energy. We propose various
higher-order statistics in the weak-lensing signal as a new set of observables
able to break degeneracies between massive neutrinos and MG parameters. We have
tested our methodology on so-called $f(R)$ models, which constitute a class of
viable models that can explain the accelerated universal expansion by a
modification of the fundamental gravitational interaction. We have explored a
range of these models that still fit current observations at the background and
linear level, and we show using numerical simulations that certain models which
include massive neutrinos are able to mimic $\Lambda$CDM in terms of the 3D
power spectrum of matter density fluctuations. We find that depending on the
redshift and angular scale of observation, non-Gaussian information accessed by
higher-order weak-lensing statistics can be used to break the degeneracy
between $f(R)$ models and $\Lambda$CDM. In particular, peak counts computed in
aperture mass maps outperform third- and fourth-order moments. | Evolution of density and velocity profiles of matter in large voids: We analyse the evolution of cosmological perturbations which leads to the
formation of large voids in the distribution of galaxies. We assume that
perturbations are spherical and all components of the Universe - radiation,
matter and dark energy - are continuous media with ideal fluid energy-momentum
tensors, which interact only gravitationally. Equations of the evolution of
perturbations in the comoving to cosmological background reference frame for
every component are obtained from equations of conservation and Einstein's ones
and are integrated by modified Euler method. Initial conditions are set at the
early stage of evolution in the radiation-dominated epoch, when the scale of
perturbation is mush larger than the particle horizon. Results show how the
profiles of density and velocity of matter in spherical voids with different
overdensity shells are formed. |
Abell 1201: a Minor merger at second core passage: We present an analysis of the structures and dynamics of the merging cluster
Abell~1201, which has two sloshing cold fronts around a cooling core, and an
offset gas core approximately 500kpc northwest of the center. New Chandra and
XMM-Newton data reveal a region of enhanced brightness east of the offset core,
with breaks in surface brightness along its boundary to the north and east.
This is interpreted as a tail of gas stripped from the offset core. Gas in the
offset core and the tail is distinguished from other gas at the same distance
from the cluster center chiefly by having higher density, hence lower entropy.
In addition, the offset core shows marginally lower temperature and metallicity
than the surrounding area. The metallicity in the cool core is high and there
is an abrupt drop in metallicity across the southern cold front. We interpret
the observed properties of the system, including the placement of the cold
fronts, the offset core and its tail in terms of a simple merger scenario. The
offset core is the remnant of a merging subcluster, which first passed
pericenter southeast of the center of the primary cluster and is now close to
its second pericenter passage, moving at ~1000 km/s. Sloshing excited by the
merger gave rise to the two cold fronts and the disposition of the cold fronts
reveals that we view the merger from close to the plane of the orbit of the
offset core. | A Study of Optical Observing Techniques for Extra-Galactic Supernova
Remnants: Case of NGC 300: We present the results of a study of observational and identification
techniques used for surveys and spectroscopy of candidate supernova remnants
(SNRs) in the Sculptor Group galaxy NGC 300. The goal of this study was to
investigate the reliability of using [Sii]/Halpha > 0.4 in optical SNR surveys
and spectra as an identifying feature of extra-galactic SNRs (egSNRs) and also
to investigate the effectiveness of the observing techniques (which are
hampered by seeing conditions and telescope pointing errors) using this
criterion in egSNR surveys and spectrographs. This study is based on original
observations of these objects and archival data obtained from the Hubble Space
Telescope which contained images of some of the candidate SNRs in NGC 300. We
found that the reliability of spectral techniques may be questionable and very
high-resolution images may be needed to confirm a valid identification of some
egSNRs. |
Predicting large scale cosmological structure evolution with GAN-based
autoencoders: Cosmological simulations play a key role in the prediction and understanding
of large scale structure formation from initial conditions. We make use of
GAN-based Autoencoders (AEs) in an attempt to predict structure evolution
within simulations. The AEs are trained on images and cubes issued from
respectively 2D and 3D N-body simulations describing the evolution of the dark
matter (DM) field. We find that while the AEs can predict structure evolution
for 2D simulations of DM fields well, using only the density fields as input,
they perform significantly more poorly in similar conditions for 3D
simulations. However, additionally providing velocity fields as inputs greatly
improves results, with similar predictions regardless of time-difference
between input and target. | Probing early-universe phase transitions with CMB spectral distortions: Global, symmetry-breaking phase transitions in the early universe can
generate scaling seed networks which lead to metric perturbations. The acoustic
waves in the photon-baryon plasma sourced by these metric perturbations, when
Silk damped, generate spectral distortions of the cosmic microwave background
(CMB). In this work, the chemical potential distortion ($\mu$) due to scaling
seed networks is computed and the accompanying Compton $y$-type distortion is
estimated. The specific model of choice is the $O(N)$ nonlinear $\sigma$-model
for $N\gg 1$, but the results remain the same order of magnitude for other
scaling seeds. If CMB anisotropy constraints to the $O(N)$ model are saturated,
the resulting chemical potential distortion $\mu \lesssim 2\times 10^{-9}$. |
Production of PBHs from inflaton structure: At times prior to Big Bang Nucleosynthesis, the universe could show a
primordial structure formation period if dominated by a fast oscillating
inflaton field during reheating. In this context, we have postulated a new
mechanism of primordial black hole formation [L. E. Padilla, J. C. Hidalgo, and
K. A. Malik, Phys. Rev. D, vol. 106, p. 023519, Jul 2022], that draws the
analogy between an extended reheating era and the scalar field dark matter
model, stipulating the gravitational collapse of inflaton halos and inflaton
stars. In this paper we look at the requirements for the realization of this
new mechanism. We show that a generic primordial power spectrum with a peak at
small scales is most suitable for the production of a considerable number of
PBHs. When such requirement is met, and if reheating lasts long enough, large
populations of PBHs with $M_{\rm PBH}\sim 1~\mathrm{gram}$ may be produced. We
find in particular, that the mass fraction of PBHs is orders of magnitude
larger than that obtained when PBHs form via direct collapse in a universe
dominated by radiation or pressure-less dust. Looking at observable
implications of our findings, we explore the possibility that the PBHs
component may dominate the energy density of the universe at some point after
the end of reheating. | Curvature Perturbations and non-Gaussianities from Waterfall Phase
Transition during Inflation: We consider a variant of hybrid inflation where the waterfall phase
transition happens during inflation. By adjusting the parameters associated
with the mass of the waterfall field we arrange that the phase transition is
not sharp so inflation can proceed for about 50-60 e-folds after the waterfall
phase transition. We show that one can work in the limit where the quantum
back-reactions are subdominant compared to the classical back-reactions. It is
shown that significant amount of large scale curvature perturbations are
induced from the entropy perturbations. The curvature perturbations spectral
index is either blue or red depending on whether the mode of interest leaves
the horizon before the phase transition or after the phase transition. This can
have interesting observational consequences on CMB. The non-Gaussianity
parameter $f_{NL}$ is calculated to be $\lesssim 1$ but much bigger than the
slow-roll parameters. |
X-ray selected galaxy clusters in the Pan-STARRS Medium-Deep Survey: [abridged]
We present the results of a pilot study for the extended MACS survey (eMACS),
a comprehensive search for distant, X-ray luminous galaxy clusters at z>0.5.
Our pilot study applies the eMACS concept to the 71 deg^2 area extended by the
ten fields of the Pan-STARRS1 (PS1) Medium Deep Survey (MDS). Candidate
clusters are identified by visual inspection of PS1 images in the g,r, i, and z
bands in a 5x5 arcmin^2 region around X-ray sources detected in the ROSAT
All-Sky Survey (RASS). To test and optimize the eMACS X-ray selection criteria,
our pilot study uses the largest possible RASS database, i.e., all RASS sources
listed in the Bright and Faint Source Catalogs (BSC and FSC) that fall within
the MDS footprint. Scrutiny of PS1/MDS images for 41 BSC and 200 FSC sources
combined with dedicated spectroscopic follow-up observations results in a
sample of 11 clusters with estimated or spectroscopic redshifts of z>0.3. X-ray
follow-up observations will be crucial in order to establish robust cluster
luminosities for eMACS clusters.
Although the small number of distant X-ray luminous clusters in the MDS does
not allow us to make firm predictions for the over 20,000 deg^2 of
extragalactic sky covered by eMACS, the identification of two extremely
promising eMACS cluster candidates at z>0.6 (both yet to be observed with
Chandra) in such a small solid angle is encouraging. Representing a tremendous
gain over the presently known two dozen such systems from X-ray, optical, and
SZ cluster surveys combined, the sample of over 100 extremely massive clusters
at z>0.5 expected from eMACS would be invaluable for the identification of the
most powerful gravitational lenses in the Universe, as well as for in-depth and
statistical studies of the physical properties of the most massive galaxy
clusters out to z~1. | BeyondPlanck X. Bandpass and beam leakage corrections: We discuss the treatment of bandpass and beam leakage corrections in the
Bayesian BeyondPlanck CMB analysis pipeline as applied to the Planck LFI
measurements. As a preparatory step, we first apply three corrections to the
nominal LFI bandpass profiles including removal of a known systematic effect in
the ground measuring equipment at 61 GHz; smoothing of standing wave ripples;
and edge regularization. The main net impact of these modifications is an
overall shift in the 70 GHz bandpass of +0.6 GHz; we argue that any analysis of
LFI data products, either from Planck or BeyondPlanck, should use these new
bandpasses. In addition, we fit a single free bandpass parameter for each
radiometer of the form $\Delta_i = \Delta_0 + \delta_i$, where $\Delta_0$
represents an absolute frequency shift per frequency band and $\delta_i$ is a
relative shift per detector. The absolute correction is only fitted at 30 GHz
with a full $\chi^2$-based likelihood, resulting in a correction of
$\Delta_{30}=0.24\pm0.03\,$GHz. The relative corrections are fitted using a
spurious map approach, fundamentally similar to the method pioneered by the
WMAP team, but without introducing many additional degrees of freedom. All
bandpass parameters are sampled using a standard Metropolis sampler within the
main BeyondPlanck Gibbs chain, and bandpass uncertainties are thus propagated
to all other data products in the analysis. In total, we find that our bandpass
model significantly reduces leakage effects. For beam leakage corrections, we
adopt the official Planck LFI beam estimates without additional degrees of
freedom, and only marginalize over the underlying sky model. We note that this
is the first time leakage from beam mismatch has been included for Planck LFI
maps. |
The Cosmic Microwave Background And Pseudo-Nambu-Goldstone Bosons:
Searching For Lorentz Violations In The Cosmos: One of the most powerful probes of new physics is the polarized Cosmic
Microwave Background (CMB). The detection of a nonzero polarization angle
rotation between the CMB surface of last scattering and today could provide
evidence of Lorentz-violating physics. The purpose of this paper is twofold.
First we review one popular mechanism for polarization rotation of CMB photons:
the pseudo-Nambu-Goldstone boson. Second, we propose a method to use the
Polarbear experiment to constrain Lorentz-violating physics in the context of
the Standard-Model Extension, a framework to standardize a large class of
potential Lorentz-violating terms in particle physics. | European Pulsar Timing Array Limits On An Isotropic Stochastic
Gravitational-Wave Background: We present new limits on an isotropic stochastic gravitational-wave
background (GWB) using a six pulsar dataset spanning 18 yr of observations from
the 2015 European Pulsar Timing Array data release. Performing a Bayesian
analysis, we fit simultaneously for the intrinsic noise parameters for each
pulsar, along with common correlated signals including clock, and Solar System
ephemeris errors, obtaining a robust 95$\%$ upper limit on the dimensionless
strain amplitude $A$ of the background of $A<3.0\times 10^{-15}$ at a reference
frequency of $1\mathrm{yr^{-1}}$ and a spectral index of $13/3$, corresponding
to a background from inspiralling super-massive black hole binaries,
constraining the GW energy density to $\Omega_\mathrm{gw}(f)h^2 <
1.1\times10^{-9}$ at 2.8 nHz. We also present limits on the correlated power
spectrum at a series of discrete frequencies, and show that our sensitivity to
a fiducial isotropic GWB is highest at a frequency of $\sim 5\times10^{-9}$~Hz.
Finally we discuss the implications of our analysis for the astrophysics of
supermassive black hole binaries, and present 95$\%$ upper limits on the string
tension, $G\mu/c^2$, characterising a background produced by a cosmic string
network for a set of possible scenarios, and for a stochastic relic GWB. For a
Nambu-Goto field theory cosmic string network, we set a limit
$G\mu/c^2<1.3\times10^{-7}$, identical to that set by the {\it Planck}
Collaboration, when combining {\it Planck} and high-$\ell$ Cosmic Microwave
Background data from other experiments. For a stochastic relic background we
set a limit of $\Omega^\mathrm{relic}_\mathrm{gw}(f)h^2<1.2 \times10^{-9}$, a
factor of 9 improvement over the most stringent limits previously set by a
pulsar timing array. |
Signals of Inflationary Models with Cosmic Strings: A class of well-motivated models of inflation end by producing cosmic
strings. The current status of efforts to calculate and observe the signals
from such models are outlined, with a particular emphasis on cosmic strings,
and on the Cosmic Microwave Background signal. | Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H2^{18}O, OH,
^{18}OH, O I, HCN and NH3: Herschel/PACS spectroscopy of the luminous infrared galaxies NGC4418 and
Arp220 reveals high excitation in H2O, OH, HCN, and NH3. In NGC4418, absorption
lines were detected with E_low>800 K (H2O), 600 K (OH), 1075 K (HCN), and 600 K
(NH3), while in Arp220 the excitation is somewhat lower. While outflow
signatures in moderate excitation lines are seen in Arp220 as reported in
previous studies, in NGC4418 the lines tracing its outer regions are redshifted
relative to the nucleus, suggesting an inflow with Mdot<~12 Msun yr^{-1}. Both
galaxies have warm (Tdust>~100 K) nuclear continuum components, together with a
more extended component that is much more prominent and massive in Arp220. A
chemical dichotomy is found in both sources: on the one hand, the nuclear
regions have high H2O abundances, ~10^{-5}, and high HCN/H2O and HCN/NH3 column
density ratios of 0.1-0.4 and 2-5, respectively, indicating a chemistry typical
of evolved hot cores where grain mantle evaporation has occurred. On the other
hand, the high OH abundance, with OH/H2O ratios of ~0.5, indicates the effects
of X-rays and/or cosmic rays. The nuclear media have surface brightnesses
>~10^{13} Lsun/kpc^2 and are estimated to be thick (N_H>~10^{25} cm^{-2}).
While NGC4418 shows weak absorption in H2^{18}O and ^{18}OH, with a
^{16}O-to-^{18}O ratio of >~250-500, the strong absorption of the rare
isotopologues in Arp220 indicates ^{16}O-to-^{18}O of 70-130. Further away from
the nuclear regions, the H2O abundance decreases to <~10^{-7} and the OH/H2O
ratio is 2.5-10. Despite the different scales of NGC4418, Arp220, and Mrk231,
preliminary evidence is found for an evolutionary sequence from infall,
hot-core like chemistry, and solar oxygen isotope ratio to high velocity
outflow, disruption of the hot core chemistry and cumulative high mass stellar
processing of 18O. |
Neutrino Physics from the Cosmic Microwave Background and Large Scale
Structure: This is a report on the status and prospects of the quantification of
neutrino properties through the cosmological neutrino background for the Cosmic
Frontier of the Division of Particles and Fields Community Summer Study
long-term planning exercise. Experiments planned and underway are prepared to
study the cosmological neutrino background in detail via its influence on
distance-redshift relations and the growth of structure. The program for the
next decade described in this document, including upcoming spectroscopic galaxy
surveys eBOSS and DESI and a new Stage-IV CMB polarization experiment CMB-S4,
will achieve sigma(sum m_nu) = 16 meV and sigma(N_eff) = 0.020. Such a mass
measurement will produce a high significance detection of non-zero sum m_nu,
whose lower bound derived from atmospheric and solar neutrino oscillation data
is about 58 meV. If neutrinos have a minimal normal mass hierarchy, this
measurement will definitively rule out the inverted neutrino mass hierarchy,
shedding light on one of the most puzzling aspects of the Standard Model of
particle physics --- the origin of mass. This precise a measurement of N_eff
will allow for high sensitivity to any light and dark degrees of freedom
produced in the big bang and a precision test of the standard cosmological
model prediction that N_eff = 3.046. | Gamma ray burst constraints on cosmological models from the improved
Amati correlation: An improved Amati correlation was constructed in (ApJ 931 (2022) 50) by us
recently. In this paper, we further study constraints on the $\Lambda$CDM and
$w$CDM models from the gamma ray bursts (GRBs) standardized with the standard
and improved Amati correlations, respectively. By using the Pantheon type Ia
supernova sample to calibrate the latest A220 GRB data set, the GRB Hubble
diagram is obtained model-independently. We find that at the high redshift
region ($z>1.4$) the GRB distance modulus from the improved Amati correlation
is larger apparently than that from the standard Amati one. The GRB data from
the standard Amati correlation only give a lower bound limit on the present
matter density parameter $\Omega_{\mathrm{m0}}$, while the GRBs from the
improved Amati correlation constrain the $\Omega_{\mathrm{m0}}$ with the $68\%$
confidence level to be $0.308^{+0.066}_{-0.230}$ and $0.307^{+0.057}_{-0.290}$
in the $\Lambda$CDM and $w$CDM models, respectively, which are consistent very
well with those given by other current popular observational data including
BAO, CMB and so on. Once the $H(z)$ data are added in our analysis, the
constraint on the Hubble constant $H_0$ can be achieved. We find that two
different correlations provide slightly different $H_0$ results but the
marginalized mean values seem to be close to that from the Planck 2018 CMB
observations. |
The connection between optical and VHE gamma-ray high states in the
blazar jets: MAGIC has been performing optically triggered Target of Opportunity
observations of flaring blazars since the beginning of its scientific
operations. The alerts of flaring blazars originate from Tuorla blazar
monitoring program, which started the optical monitoring of the candidate TeV
blazars in 2002 and has now collected up to six years of data on 30 blazars.
These Target of Opportunity observations have resulted in the discovery of
three new VHE gamma-ray emitting blazars (Mrk180, 1ES1011+496 and S50716+714)
and in addition the discoveries of BLLac and 3C279 were made during a high
optical state. In this talk we present a detailed analysis of the optical light
curves which are then compared to MAGIC observations of the same sources. We
aim to answer the question "Is there a connection between optical and VHE
gamma-ray high states in blazars or have we just been lucky?" | Cosmological constraints on the new holographic dark energy model with
action principle: Recently, a New HDE model with action principle was proposed (Li and Miao,
arXiv:1210.0966). This model completely solves the causality and circular
problems in the original HDE model, and is similar to the original model except
a new term that can be interpreted as dark radiation. In this paper, we make
further investigations on this model from the aspect of cosmological
observations. Numerically, we confirm that the equations of motion force the
$L(z=-1)=0$, making the cut-off $aL$ exactly the future event horizon. We also
perform detailed analysis on the dynamical properties of the model, divided
into the $c<6$ and $c\geq6$ cases ($c$ is a dimensionless parameter which
should be decided by the data). From a combination of the present
Union2.1+BAO+CMB+$H_0$ data, we find the model yields $\chi^2_{\rm
min}=548.798$ (in a non-flat Universe), comparable to the results of the
original HDE model (549.461) and the concordant $\Lambda$CDM model (550.354).
At 95.4% CL, we get $1.41<c<3.09$ and correspondingly $-2.25<w(z=-1)<-1.39$,
implying the Big Rip fate of the Universe at a high confidence level. Besides,
for the constraints on dark radiation, we also get a rough estimation $N_{\rm
\rm eff}=3.54^{+0.32+0.67}_{\rm -0.45-0.76}$, with the central value slightly
larger than the standard value 3.046. |
The ugrizYJHK luminosity distributions and densities from the combined
MGC, SDSS and UKIDSS LAS datasets: We combine data from the MGC, SDSS and UKIDSS LAS surveys to produce
ugrizYJHK luminosity functions and densities from within a common, low redshift
volume (z<0.1, ~71,000 h_1^-3 Mpc^3 for L* systems) with 100 per cent
spectroscopic completeness. In the optical the fitted Schechter functions are
comparable in shape to those previously reported values but with higher
normalisations (typically 0, 30, 20, 15, 5 per cent higher phi*-values in u, g,
r, i, z respectively over those reported by the SDSS team). We attribute these
to differences in the redshift ranges probed, incompleteness, and adopted
normalisation methods. In the NIR we find significantly different Schechter
function parameters (mainly in the M* values) to those previously reported and
attribute this to the improvement in the quality of the imaging data over
previous studies. This is the first homogeneous measurement of the
extragalactic luminosity density which fully samples both the optical and
near-IR regimes. Unlike previous compilations that have noted a discontinuity
between the optical and near-IR regimes our homogeneous dataset shows a smooth
cosmic spectral energy distribution (CSED). After correcting for dust
attenuation we compare our CSED to the expected values based on recent
constraints on the cosmic star-formation history and the initial mass function. | Improved limits on the tensor-to-scalar ratio using BICEP and Planck: We present constraints on the tensor-to-scalar ratio r using a combination of
BICEP/Keck 2018 and Planck PR4 data allowing us to fit for r consistently with
the six parameters of the $\Lambda$CDM model without fixing any of them. In
particular, we are able to derive a constraint on the reionization optical
depth $\tau$ and thus propagate its uncertainty onto the posterior distribution
for r. While Planck sensitivity to r is no longer comparable with ground-based
measurements, combining Planck with BK18 and BAO gives results consistent with
r = 0 and tightens the constraint to r < 0.032. |
Exploring Cosmic Origins with CORE: Inflation: We forecast the scientific capabilities to improve our understanding of
cosmic inflation of CORE, a proposed CMB space satellite submitted in response
to the ESA fifth call for a medium-size mission opportunity. The CORE satellite
will map the CMB anisotropies in temperature and polarization in 19 frequency
channels spanning the range 60-600 GHz. CORE will have an aggregate noise
sensitivity of $1.7 \mu$K$\cdot \,$arcmin and an angular resolution of 5' at
200 GHz. We explore the impact of telescope size and noise sensitivity on the
inflation science return by making forecasts for several instrumental
configurations. This study assumes that the lower and higher frequency channels
suffice to remove foreground contaminations and complements other related
studies of component separation and systematic effects, which will be reported
in other papers of the series "Exploring Cosmic Origins with CORE." We forecast
the capability to determine key inflationary parameters, to lower the detection
limit for the tensor-to-scalar ratio down to the $10^{-3}$ level, to chart the
landscape of single field slow-roll inflationary models, to constrain the epoch
of reheating, thus connecting inflation to the standard radiation-matter
dominated Big Bang era, to reconstruct the primordial power spectrum, to
constrain the contribution from isocurvature perturbations to the $10^{-3}$
level, to improve constraints on the cosmic string tension to a level below the
presumptive GUT scale, and to improve the current measurements of primordial
non-Gaussianities down to the $f_{NL}^{\rm local} < 1$ level. For all the
models explored, CORE alone will improve significantly on the present
constraints on the physics of inflation. Its capabilities will be further
enhanced by combining with complementary future cosmological observations. | Magnetic power spectra from Faraday rotation maps - REALMAF and its use
on Hydra A: We develop a novel maximum-a-posteriori method to measure magnetic power
spectra from Faraday rotation data and implement it in the REALMAF code. A
sophisticated model for the magnetic autocorrelation in real space permits us
to alleviate previously required simplifying assumptions in the processing. We
also introduce a way to treat the divergence relation of the magnetic field
with a multiplicative factor in Fourier space, with which we can model the
magnetic autocorrelation as a spherically symmetric function. Applied to the
dataset of Hydra A north, we find a power law power spectrum on spatial scales
between 0.3 kpc and 8 kpc, with no visible turnover at large scales within this
range and a spectral index consistent with a Kolmogorov-like power law regime.
The magnetic field strength profile seems to follow the electron density
profile with an index alpha=1. A variation of alpha from 0.5 to 1.5 would lead
to a spectral index between 1.55 and 2.05. The extrapolated magnetic field
strength in the cluster centre highly depends on the assumed projection angle
of the jet. For an angle of 45 degree we derive extrapolated 36 muG in the
centre and directly probed 16 muG at 50 kpc radius. |
Astrometric Effects of a Stochastic Gravitational Wave Background: A stochastic gravitational wave background causes the apparent positions of
distant sources to fluctuate, with angular deflections of order the
characteristic strain amplitude of the gravitational waves. These fluctuations
may be detectable with high precision astrometry, as first suggested by
Braginsky et al. in 1990. Several researchers have made order of magnitude
estimates of the upper limits obtainable on the gravitational wave spectrum
\Omega_gw(f), at frequencies of order f ~ 1 yr^-1, both for the future
space-based optical interferometry missions GAIA and SIM, and for VLBI
interferometry in radio wavelengths with the SKA. For GAIA, tracking N ~ 10^6
quasars over a time of T ~ 1 yr with an angular accuracy of \Delta \theta ~ 10
\mu as would yield a sensitivity level of \Omega_gw ~ (\Delta \theta)^2/(N T^2
H_0^2) ~ 10^-6, which would be comparable with pulsar timing. In this paper we
take a first step toward firming up these estimates by computing in detail the
statistical properties of the angular deflections caused by a stochastic
background. We compute analytically the two point correlation function of the
deflections on the sphere, and the spectrum as a function of frequency and
angular scale. The fluctuations are concentrated at low frequencies (for a
scale invariant stochastic background), and at large angular scales, starting
with the quadrupole. The magnetic-type and electric-type pieces of the
fluctuations have equal amounts of power. | Learning Reionization History from Quasars with Simulation-Based
Inference: Understanding the entire history of the ionization state of the intergalactic
medium (IGM) is at the frontier of astrophysics and cosmology. A promising
method to achieve this is by extracting the damping wing signal from the
neutral IGM. As hundreds of redshift $z>6$ quasars are observed, we anticipate
determining the detailed time evolution of the ionization fraction with
unprecedented fidelity. However, traditional approaches to parameter inference
are not sufficiently accurate. We assess the performance of a simulation-based
inference (SBI) method to infer the neutral fraction of the universe from
quasar spectra. The SBI method adeptly exploits the shape information of the
damping wing, enabling precise estimations of the neutral fraction
$\left<x_{\rm HI}\right>_{\rm v}$ and the wing position $w_p$. Importantly, the
SBI framework successfully breaks the degeneracy between these two parameters,
offering unbiased estimates of both. This makes the SBI superior to the
traditional method using a pseudo-likelihood function. We anticipate that SBI
will be essential to determine robustly the ionization history of the Universe
through joint inference from the hundreds of high-$z$ spectra we will observe. |
Curvature perturbation spectra from waterfall transition, black hole
constraints and non-Gaussianity: We carried out numerical calculations of a contribution of the waterfall
field to the primordial curvature perturbation (on uniform density
hypersurfaces) $\zeta$, which is produced during waterfall transition in hybrid
inflation scenario. The calculation is performed for a broad interval of values
of the model parameters. We show that there is a strong growth of amplitudes of
the curvature perturbation spectrum in the limit when the bare mass-squared of
the waterfall field becomes comparable with the square of Hubble parameter. We
show that in this limit the primordial black hole constraints on the curvature
perturbations must be taken into account. It is shown that, in the same limit,
peak values of the curvature perturbation spectra are far beyond horizon, and
the spectra are strongly non-Gaussian. | The deconvolved distribution estimator: enhancing reionisation-era CO
line-intensity mapping analyses with a cross-correlation analogue for
one-point statistics: We present the deconvolved distribution estimator (DDE), an extension of the
voxel intensity distribution (VID), in the context of future observations
proposed as part of the CO Mapping Array Project (COMAP). The DDE exploits the
fact that the observed VID is a convolution of correlated signal intensity
distributions and uncorrelated noise or interloper intensity distributions. By
deconvolving the individual VID of two observables away from their joint VID in
a Fourier-space operation, the DDE suppresses sensitivity to interloper
emission while maintaining sensitivity to correlated components. The DDE thus
improves upon the VID by reducing the relative influence of uncorrelated noise
and interloper biases, which is useful in the context of COMAP observations
that observe different rotational transitions of CO from the same comoving
volume in different observing frequency bands. Fisher forecasts suggest that
the theoretical sensitivity in the DDE allows significant improvements in
constraining power compared to either the cross power spectrum or the
individual VID data, and matches the constraining power of the combination of
all other one- and two-point summary statistics. Future work should further
investigate the covariance and model-dependent behaviour of this novel
one-point cross-correlation statistic. |
A Novel Approach in Constraining Electron Spectra in Blazar Jets: The
Case of Markarian 421: We report results from the observations of the well studied TeV blazar Mrk
421 with the Swift and the Suzaku satellites in December 2008. During the
observation, Mrk 421 was found in a relatively low activity state, with the
corresponding 2-10 keV flux of $3 \times 10^{-10}$ erg/s/cm^2. For the purpose
of robust constraining the UV-to-X-ray emission continuum we selected only the
data corresponding to truly simultaneous time intervals between Swift and
Suzaku, allowing us to obtain a good-quality, broad-band spectrum despite a
modest length (0.6 ksec) exposure. We analyzed the spectrum with the parametric
forward-fitting SYNCHROTRON model implemented in XSPEC assuming two different
representations of the underlying electron energy distribution, both well
motivated by the current particle acceleration models: a power-law distribution
above the minimum energy $\gamma_{\rm min}$ with an exponential cutoff at the
maximum energy $\gamma_{\rm max}$, and a modified ultra-relativistic Maxwellian
with an equilibrium energy $\gamma_{\rm eq}$. We found that the latter implies
unlikely physical conditions within the blazar zone of Mrk 421. On the other
hand, the exponentially moderated power-law electron distribution gives two
possible sets of the model parameters: (i) flat spectrum $dN'_e/d\gamma \propto
\gamma^{-1.91}$ with low minimum electron energy $\gamma_{\rm min}<10^3$, and
(ii) steep spectrum $\propto \gamma^{-2.77}$ with high minimum electron energy
$\gamma_{\rm min}\simeq 2\times10^4$. We discuss different interpretations of
both possibilities in the context of a diffusive acceleration of electrons at
relativistic, sub- or superluminal shocks. We also comment on how exactly the
gamma-ray data can be used to discriminate between the proposed different
scenarios. | Single Field Double Inflation and Primordial Black Holes: Within the framework of scalar-tensor theories, we study the conditions that
allow single field inflation dynamics on small cosmological scales to
significantly differ from that of the large scales probed by the observations
of cosmic microwave background. The resulting single field double inflation
scenario is characterised by two consequent inflation eras, usually separated
by a period where the slow-roll approximation fails. At large field values the
dynamics of the inflaton is dominated by the interplay between its non-minimal
coupling to gravity and the radiative corrections to the inflaton
self-coupling. For small field values the potential is, instead, dominated by a
polynomial that results in a hilltop inflation. Without relying on the
slow-roll approximation, which is invalidated by the appearance of the
intermediate stage, we propose a concrete model that matches the current
measurements of inflationary observables and employs the freedom granted by the
framework on small cosmological scales to give rise to a sizeable population of
primordial black holes generated by large curvature fluctuations. We find that
these features generally require a potential with a local minimum. We show that
the associated primordial black hole mass function is only approximately
lognormal. |
Extending cosmological tests of General Relativity with the Square
Kilometre Array: Tests of general relativity (GR) are still in their infancy on cosmological
scales, but forthcoming experiments promise to greatly improve their precision
over a wide range of distance scales and redshifts. One such experiment, the
Square Kilometre Array (SKA), will carry out several wide and deep surveys of
resolved and unresolved neutral hydrogen (HI) 21cm line-emitting galaxies,
mapping a significant fraction of the sky from $0 \le z \lesssim 6$. I present
forecasts for the ability of a suite of possible SKA HI surveys to detect
deviations from GR by reconstructing the cosmic expansion and growth history.
SKA Phase 1 intensity mapping surveys can achieve sub-1\% measurements of
$f\sigma_8$ out to $z\approx 1$, with an SKA1-MID Band 2 survey out to $z
\lesssim 0.6$ able to surpass contemporary spectroscopic galaxy surveys such as
DESI and Euclid in terms of constraints on modified gravity parameters if
challenges such as foreground contamination can be tackled effectively. A more
futuristic Phase 2 HI survey of $\sim10^9$ spectroscopic galaxy redshifts would
be capable of detecting a $\sim 2\%$ modification of the Poisson equation out
to $z\approx 2$. | Modeling the nonlinear clustering in modified gravity models I: A
fitting formula for matter power spectrum of f(R) gravity: Based on a suite of N-body simulations of the Hu-Sawicki model of f(R)
gravity with different sets of model and cosmological parameters, we develop a
new fitting formula with a numeric code, MGHalofit, to calculate the nonlinear
matter power spectrum P(k) for the Hu-Sawicki model. We compare the MGHalofit
predictions at various redshifts (z<=1) to the f(R) simulations and find that
the accuracy on P(k) is 6% at k<1 h/Mpc and 12% at 1<k<10 h/Mpc respectively.
Based on a sensitivity study of an ongoing and a future spectroscopic survey,
we estimate the detectability of a signal of modified gravity described by the
Hu-Sawicki model using the power spectrum up to quasi-nonlinear scales.
MGHalofit is publicly available at
http://icosmology.info/website/MGHalofit.html. |
On the dust geometry in radio-loud active galactic nuclei: We use photometric and spectroscopic infrared observations obtained with the
Spitzer Space Telescope of 12 radio-loud active galactic nuclei (AGN) to
investigate the dust geometry. Our approach is to look at the change of the
infrared spectral energy distribution (SED) and the strength of the 10 micron
silicate feature with jet viewing angle. We find that (i) a combination of
three or four blackbodies fits well the infrared SED; (ii) the sources viewed
closer to the jet axis appear to have stronger warm (~300 - 800 K) and cold
(~150 - 250 K) dust emissions relative to the hot component; and (iii) the
silicate features are always in emission and strongly redshifted. We test
clumpy torus models and find that (i) they approximate well the mid-infrared
part of the SED, but significantly underpredict the fluxes at both near- and
far-infrared wavelengths; (ii) they can constrain the dust composition (in our
case to that of the standard interstellar medium); (iii) they require
relatively large (~10%-20% the speed of light) redward displacements; and (iv)
they give robust total mass estimates, but are insensitive to the assumed
geometry. | On the detectability of primordial black holes in the Galaxy: In the mass range of 1e15 g up to 1e26 g, primordial black holes (PBHs) as a
possible contribution to the dark matter are still unexplored. In this
contribution, we investigate the possibility of an electromagnetic signal from
PBH interactions with astrophysical objects in the Galaxy. We find that a
signal from passages cannot be observed, since, depending on the mass, either
the interaction probability or the energy loss is too small. Further, we
discuss possible effects from high-mass PBHs at masses >1e26 g, where PBHs can
still contribute to the dark matter at the order of ~10%. Here, we find that a
significant fraction of PBHs can be captured in the Hubble time. These captures
could therefore lead to detectable effects. |
A structure in the early universe at z ~ 1.3 that exceeds the
homogeneity scale of the R-W concordance cosmology: A Large Quasar Group (LQG) of particularly large size and high membership has
been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has
characteristic size (volume^1/3) ~ 500 Mpc (proper size, present epoch),
longest dimension ~ 1240 Mpc, membership of 73 quasars, and mean redshift <z> =
1.27. In terms of both size and membership it is the most extreme LQG found in
the DR7QSO catalogue for the redshift range 1.0 <= z <= 1.8 of our current
investigation. Its location on the sky is ~ 8.8 deg north (~ 615 Mpc projected)
of the Clowes & Campusano LQG at the same redshift, <z> = 1.28, which is itself
one of the more extreme examples. Their boundaries approach to within ~ 2 deg
(~ 140 Mpc projected). This new, huge LQG appears to be the largest structure
currently known in the early universe. Its size suggests incompatibility with
the Yadav et al. scale of homogeneity for the concordance cosmology, and thus
challenges the assumption of the cosmological principle. | Radio and Gamma Properties of the 2 cm Survey and MOJAVE Samples: The 2 cm VLBA Survey observed since 1994 a set of ~170 Quasars, BL Lac
objects, and radio galaxies, selected to be representative of the compact AGN
radio population. This effort was continued as the MOJAVE project, where a
statistically complete set of radio sources being monitored was defined. A
comparison of the gamma-detection rates between the members of both samples
shows that the MOJAVE-I sources, hosting generally faster jets, have a much
higher detection rate than the sources not belonging to this sample. BL Lac
objects are more favourably detected than QSOs in gamma-rays, in the same rate
for both samples. |
A Comprehensive Bayesian re-analysis of the SARAS2 data from the Epoch
of Reionization: We present a Bayesian re-analysis of the sky-averaged 21-cm experimental data
from SARAS2 using nested sampling implemented with polychord, spectrally smooth
foreground modelling implemented with maxsmooth, detailed systematic modelling
and rapid signal emulation with globalemu. Our analysis differs from previous
analysis of the SARAS2 data through the use of a full Bayesian framework and
separate modelling of the foreground and non-smooth systematics. We use the
most up-to-date signal models including Lyman-$\alpha$ and CMB heating
parameterised by astrophysical parameters such as star formation efficiency,
X-ray heating efficiency, minimal virial circular velocity of star forming
galaxies, CMB optical depth and the low energy cutoff of the X-ray spectral
energy distribution. We consider models with an excess radio background above
the CMB produced via radio emission from early galaxies and parameterised by a
radio production efficiency. A non-smooth systematic is identified and modelled
as both a frequency damped sinusoid introduced by the electronics and
separately from the sky. The latter is modulated by the total efficiency of the
antenna and marginally favoured by the data. We consider three different models
for the noise in the data. The SARAS2 constraints on individual astrophysical
parameters are extremely weak however we identify classes of disfavoured
signals. We weakly disfavour standard astrophysical models with high
Lyman-$\alpha$ fluxes and weak heating and more confidently disfavour exotic
models with high Lyman-$\alpha$ fluxes, low X-ray efficiencies and high radio
production efficiencies in early galaxies. | WMAP9 and the single field models of inflation: Using the latest release from WMAP, I find that for a reasonable number of
e-folds the tree-level potential with self coupling power p=3 is now excluded
from the 2-sigma region, the axion monodromy model with the power alpha=2/3 is
now excluded from the 1-sigma confidence region for N=47 e-folds and for N=61.
alpha=2/5 is also excluded from the 2-sigma region for N=61. I also find that
since the upper bound on the running has been reduced, a significant abundance
of PBHs requires fractional powers of self-coupling in the Hilltop-type model. |
How robust are predictions of galaxy clustering?: We use the Millennium Simulation database to compare how different versions
of the Durham and Munich semi-analytical galaxy formation models populate dark
matter haloes with galaxies. The models follow the same physical processes but
differ in how these are implemented. All of the models we consider use the
Millennium N-body Simulation; however, the Durham and Munich groups use
independent algorithms to construct halo merger histories. We compare the
predicted halo occupation distributions (HODs) and correlation functions for
galaxy samples defined by stellar mass, cold gas mass and star formation rate.
The predictions for the HOD are remarkably similar for samples ranked by
stellar mass. The predicted bias averaged over 5-25 Mpc/h is consistent between
models to within 10%. At small pair separations there is a difference in the
predicted clustering. This arises because the Durham models allow some
satellite galaxies to merge with the central galaxy in a halo when they are
still associated with resolved subhaloes. The agreement between the models is
less good for samples defined by cold gas mass or star formation rate, with the
small scale clustering differing by an order of magnitude, reflecting the
uncertainty in the modelling of star formation. The model predictions in these
cases are qualitatively similar, with a markedly shallower slope for the
correlation function than is found for stellar mass selected samples and with
the HOD displaying an asymmetric peak for central galaxies. We provide
illustrative parametric fits to the HODs predicted by the models. Our results
reveal the current limitations on how well we can predict galaxy bias in a
fixed cosmology, which has implications for the interpretation of constraints
on the physics of galaxy formation from galaxy clustering measurements and the
ability of future galaxy surveys to measure dark energy. | A blinding solution for inference from astronomical data: This paper presents a joint blinding and deblinding strategy for inference of
physical laws from astronomical data. The strategy allows for up to three
blinding stages, where the data may be blinded, the computations of theoretical
physics may be blinded, and --assuming Gaussianly distributed data-- the
covariance matrix may be blinded. We found covariance blinding to be
particularly effective, as it enables the blinder to determine close to exactly
where the blinded posterior will peak. Accordingly, we present an algorithm
which induces posterior shifts in predetermined directions by hiding
untraceable biases in a covariance matrix. The associated deblinding takes the
form of a numerically lightweight post-processing step, where the blinded
posterior is multiplied with deblinding weights. We illustrate the blinding
strategy for cosmic shear from KiDS-450, and show that even though there is no
direct evidence of the KiDS-450 covariance matrix being biased, the famous
cosmic shear tension with Planck could easily be induced by a
mischaracterization of correlations between $\xi_-$ at the highest redshift and
all lower redshifts. The blinding algorithm illustrates the increasing
importance of accurate uncertainty assessment in astronomical inferences, as
otherwise involuntary blinding through biases occurs. |
Primordial Kerr Black Holes: Primordial Black Holes (PBHs) are appealing candidates for dark matter in the
universe but are severely constrained by theoretical and observational
constraints. We will focus on the Hawking evaporation limits extended to Kerr
black holes. In particular, we will discuss the possibility to distinguish
between black holes of primordial and of stellar origins based on the Thorne
limit on their spin. We will also review the isotropic extragalactic gamma ray
background constraints and show that the ``window'' in which PBHs can
constitute all of the dark matter depends strongly on the PBH spin. Finally, we
will consider the possibility that the so-called Planet 9 is a primordial black
hole. | Hunting for extremely metal-poor emission-line galaxies in the Sloan
Digital Sky Survey: MMT and 3.5m APO observations: We present 6.5-meter MMT and 3.5m APO spectrophotometry of 69 H II regions in
42 low-metallicity emission-line galaxies, selected from the Data Release 7 of
the Sloan Digital Sky Survey to have mostly [O III]4959/Hbeta < 1 and [N
II]6583/Hbeta < 0.1. The electron temperature-sensitive emission line [O III]
4363 is detected in 53 H II regions allowing a direct abundance determination.
The oxygen abundance in the remaining 16 H II regions is derived using a
semi-empirical method. The oxygen abundance of the galaxies in our sample
ranges from 12 + log O/H ~ 7.1 to ~ 7.9, with 14 H II regions in 7 galaxies
with 12 +log O/H < 7.35. In 5 of the latter galaxies, the oxygen abundance is
derived here for the first time. Including other known extremely
metal-deficient emission-line galaxies from the literature, e.g. SBS 0335-052W,
SBS 0335-052E and I Zw 18, we have compiled a sample of the 17 most
metal-deficient (with 12 +log O/H < 7.35) emission-line galaxies known in the
local universe. There appears to be a metallicity floor at 12 +log O/H ~ 6.9,
suggesting that the matter from which dwarf emission-line galaxies formed was
pre-enriched to that level by e.g. Population III stars. |
Quijote PNG: The information content of the halo power spectrum and
bispectrum: We investigate how much can be learnt about four types of primordial
non-Gaussianity (PNG) from small-scale measurements of the halo field. Using
the QUIJOTE-PNG simulations, we quantify the information content accessible
with measurements of the halo power spectrum monopole and quadrupole, the
matter power spectrum, the halo-matter cross spectrum and the halo bispectrum
monopole. This analysis is the first to include small, non-linear scales, up to
$k_\mathrm{max}=0.5 \mathrm{h/Mpc}$, and to explore whether these scales can
break degeneracies with cosmological and nuisance parameters making use of
thousands of N-body simulations. We perform all the halo measurements in
redshift space with a single sample comprised of all halos with mass $>3.2
\times 10^{13}~h^{-1}M_\odot$. For local PNG, measurements of the scale
dependent bias effect from the power spectrum using sample variance
cancellation provide significantly tighter constraints than measurements of the
halo bispectrum. In this case measurements of the small scales add minimal
additional constraining power. In contrast, the information on equilateral and
orthogonal PNG is primarily accessible through the bispectrum. For these
shapes, small scale measurements increase the constraining power of the halo
bispectrum by up to $\times4$, though the addition of scales beyond $k\approx
0.3 \mathrm{h/Mpc}$ improves constraints largely through reducing degeneracies
between PNG and the other parameters. These degeneracies are even more
powerfully mitigated through combining power spectrum and bispectrum
measurements. However even with combined measurements and small scale
information, equilateral non-Gaussianity remains highly degenerate with
$\sigma_8$ and our bias model. | Testing the speed of light over cosmological distances: the combination
of strongly lensed and unlensed supernova Ia: Probing the speed of light is as an important test of General Relativity but
the measurements of $c$ using objects in the distant universe have been almost
completely unexplored. In this letter, we propose an idea to use the multiple
measurements of galactic-scale strong gravitational lensing systems with type
Ia supernova acting as background sources to estimate the speed of light. This
provides an original method to measure the speed of light using objects located
at different redshifts which emitted their light in a distant past. Moreover,
we predict that strongly lensed SNe Ia observed by the LSST would produce
robust constraints on $\Delta c/c$ at the level of $10^{-3}$. We also discuss
whether the future surveys such as LSST may succeed in detecting any
hypothetical variation of $c$ predicted by theories in which fundamental
constants have dynamical nature. |
Non-oscillating Early Dark Energy and Quintessence from Alpha-Attractors: Early dark energy (EDE) is one of the most promising possibilities in order
to resolve the Hubble tension: the discrepancy between early and late-Universe
measurements of the Hubble constant. In this paper we propose a model of a
scalar field which can explain both EDE and late Dark Energy (DE) in a joined
manner without additional fine-tuning. The field features kinetic poles as with
alpha-attractors. Our model provides an injection of EDE near matter-radiation
equality, and redshifts away shortly after via free-fall, later refreezing to
become late-time DE at the present day. Using reasonable estimates of the
current constraints on EDE from the literature, we find that the parameter
space is narrow but viable. As such our model is readily falsifiable. In
contrast to other work in EDE, our model is non-oscillatory, which causes its
decay to be faster than that of the usual oscillatory EDE, thereby achieving
better agreement with observations. | Temperature, Abundance, and Mass Density Profiling of the Perseus Galaxy
Cluster: Detailed temperature and abundance radial profile maps have revealed a
significant lack of homogeneity within the Perseus Galaxy cluster. Previous
surveys of Perseus with the Suzaku telescope, which has a worse angular
resolution and less light collecting area than XMM-Newton, revealed
over-densities of X-Ray emission. These results provide evidence that the
baryon fraction exceeds the universal average, which we had initially hoped to
study. We have yet to confirm or deny the existence of clumping in these
regions, which could explain such over-abundance of X-Ray emission. This
project offers a framework of efficient, automated processing techniques to
"clean" images of noise from the mechanics of the telescope, background
radiation from local sources such as the solar wind, and more distant sources
such as background AGN. The galaxy cluster studied in this project contains
high levels of contamination due to its line-of-sight position close to the
dust- and star-filled arms of the Milky Way galaxy. Rigorous spectral model
fitting of the cluster employ multiple parameters dedicated to accounting for
these contaminations. The framework created from this analysis technique will
provide the opportunity to expand this analysis to any nearby galaxy cluster,
such as the Virgo, Coma, and Ophiuchus Clusters. This research should provide
significant insight into how matter, both baryonic and dark matter, is
distributed throughout diffuse cluster systems, as well as give clues to the
origin of the ICM. |
Theoretical and numerical perspectives on cosmic distance averages: The interpretation of cosmological observations relies on a notion of an
average Universe, which is usually considered as the homogeneous and isotropic
Friedmann-Lema\^itre-Robertson-Walker (FLRW) model. However, inhomogeneities
may statistically bias the observational averages with respect to FLRW, notably
for distance measurements, due to a number of effects such as gravitational
lensing and redshift perturbations. In this article, we review the main known
theoretical results on average distance measures in cosmology, based on
second-order perturbation theory, and we fill in some of their gaps. We then
comprehensively test these theoretical predictions against ray tracing in a
high-resolution dark-matter $N$-body simulation. This method allows us to
describe the effect of small-scale inhomogeneities deep into the non-linear
regime of structure formation on light propagation up to $z=10$. We find that
numerical results are in remarkably good agreement with theoretical predictions
in the limit of super-sample variance. No unexpectedly large bias originates
from very small scales, whose effect is fully encoded in the non-linear power
spectrum. Specifically, the directional average of the inverse amplification
and the source-averaged amplification are compatible with unity; the change in
area of surfaces of constant cosmic time is compatible with zero; the biases on
other distance measures, which can reach slightly less than $1\%$ at high
redshift, are well understood. As a side product, we also confront the
predictions of the recent finite-beam formalism with numerical data and find
excellent agreement. | Dual black holes in merger remnants. I: linking accretion to dynamics: We study the orbital evolution and accretion history of massive black hole
(MBH) pairs in rotationally supported circumnuclear discs up to the point where
MBHs form binary systems. Our simulations have high resolution in mass and
space which, for the first time, makes it feasible to follow the orbital decay
of a MBH either counter- or co-rotating with respect to the circumnuclear disc.
We show that a moving MBH on an initially counter-rotating orbit experiences an
"orbital angular momentum flip" due to the gas-dynamical friction, i.e., it
starts to corotate with the disc before a MBH binary forms. We stress that this
effect can only be captured in very high resolution simulations. Given the
extremely large number of gas particles used, the dynamical range is
sufficiently large to resolve the Bondi-Hoyle-Lyttleton radii of individual
MBHs. As a consequence, we are able to link the accretion processes to the
orbital evolution of the MBH pairs. We predict that the accretion rate is
significantly suppressed and extremely variable when the MBH is moving on a
retrograde orbit. It is only after the orbital angular momentum flip has taken
place that the secondary rapidly "lights up" at which point both MBHs can
accrete near the Eddington rate for a few Myr. The separation of the double
nucleus is expected to be around ~10 pc at this stage. We show that the
accretion rate can be highly variable also when the MBH is co-rotating with the
disc (albeit to a lesser extent) provided that its orbit is eccentric. Our
results have significant consequences for the expected number of observable
double AGNs at separations of <100 pc. |
A detailed statistical analysis of the mass profiles of galaxy clusters: The distribution of mass in the halos of galaxies and galaxy clusters has
been probed observationally, theoretically, and in numerical simulations. Yet
there is still confusion about which of several suggested parameterized models
is the better representation, and whether these models are universal. We use
the temperature and density profiles of the intracluster medium as measured by
X-ray observations of 11 relaxed galaxy clusters to investigate mass models for
the halo using a thorough Bayesian statistical analysis. We make careful
comparisons between two- and three-parameter models, including the issue of a
universal third parameter. We find that, of the two-parameter models, the NFW
is the best representation, but we also find moderate statistical evidence that
a generalized three-parameter NFW model with a freely varying inner slope is
preferred, despite penalizing against the extra degree of freedom. There is a
strong indication that this inner slope needs to be determined for each cluster
individually, i.e. some clusters have central cores and others have steep
cusps. The mass-concentration relation of our sample is in reasonable agreement
with predictions based on numerical simulations. | The diffuse radio filament in the merging system ZwCl 2341.1+0000: In some clusters of galaxies, a diffuse non-thermal emission is present, not
obviously associated with any individual galaxy. These sources have been
identified as relics, mini-halos, and halos according to their properties and
position with respect to the cluster center. Moreover in a few cases have been
reported the existence of a diffuse radio emission not identified with a
cluster, but with a large scale filamentary region. The aim of this work is to
observe and discuss the diffuse radio emission present in the complex merging
structure of galaxies ZwCl 2341.1+0000. We have obtained VLA observations at
1.4 GHz to derive a deep radio image of the diffuse emission. Low resolution
VLA images show a diffuse radio emission associated to the complex merging
region with a largest size = 2.2 Mpc. In addition to the previously reported
peripheral radio emission, classified as a double relic, diffuse emission is
detected along the optical filament of galaxies. The giant radio source
discussed here shows that magnetic fields and relativistic particles are
present also in filamentary structures. Possible alternate scenarios are: a
giant radio halo in between two symmetric relics, or the merging of two
clusters both hosting a central radio halo. |
Searching for Dust Reddening in SDSS Spectra with Damped Lyman
$α${} Systems: We searched for evidence of reddening of background SDSS QSO spectra due to
dust in intervening DLA systems. We utilise the Data Releases 5 and 7 to arrive
at sample sizes of 475 (DR5) and 676 (DR7) absorbers, based on two different
published lists of SDSS DLAs. Both samples span roughly the redshift range of
2.2 < z_abs < 5.2, with a mean of z~3.0, and the majority of the DLAs (75%)
below z=3.3. We construct geometric mean spectra in the absorber restframes
ranging from 1240 to ~2800 A, and composite spectra of samples matching the
'DLA' QSOs in i band magnitude and emission redshift z_em, but without
absorption lines. By comparing the slopes of these composite spectra with their
matched counterparts, we find no sign of reddening in the ensemble of the
absorbers from these samples. Owing to both the unprecedently large sizes of
the DLA samples themselves and the non-DLA SDSS QSO sample, from which we can
draw our matching spectra, we can place very tight limits for this
non-detection (<E(B-V)> =-0.0013+-0.0025 (DR5) and <E(B-V)> =-0.0017+-0.0022
(DR7). Interestingly, when applying our technique to the samples of York et.
al. (2006), vandenBerk et al. (2008) (intervening and intrinsic MgII absorbers)
and the smaller DLA-subsample and pool of comparison QSOs of Vladilo et al.
(2008), we do recover their results, i.e. detect the same amount of reddening
as these authors do. Furthermore, we have tested whether subsamples of our
large sample in categories involving the absorbers (HI column densities,
presence or absence of accompanying metal absorption, absorber redshift) or the
background quasars (emission redshift, brightness) do reveal dust extinction,
but found no trends. These results are at odds with both detections of dust
reddening from previous studies, and also with expectations from observations
of high-redshift galaxies. (abridged) | Measuring the EoR Power Spectrum Without Measuring the EoR Power
Spectrum: The large-scale structure of the Universe should soon be measured at high
redshift during the Epoch of Reionization (EoR) through line-intensity mapping.
A number of ongoing and planned surveys are using the 21 cm line to trace
neutral hydrogen fluctuations in the intergalactic medium (IGM) during the EoR.
These may be fruitfully combined with separate efforts to measure large-scale
emission fluctuations from galactic lines such as [CII], CO, H-$\alpha$, and
Ly-$\alpha$ during the same epoch. The large scale power spectrum of each line
encodes important information about reionization, with the 21 cm power spectrum
providing a relatively direct tracer of the ionization history. Here we show
that the large scale 21 cm power spectrum can be extracted using only
cross-power spectra between the 21 cm fluctuations and each of two separate
line-intensity mapping data cubes. This technique is more robust to residual
foregrounds than the usual 21 cm auto-power spectrum measurements and so can
help in verifying auto-spectrum detections. We characterize the accuracy of
this method using numerical simulations and find that the large-scale 21 cm
power spectrum can be inferred to an accuracy of within 5% for most of the EoR,
reaching 0.6% accuracy on a scale of $k\sim0.1\,\text{Mpc}^{-1}$ at $\left< x_i
\right> = 0.36$ ($z = 8.34$ in our model). An extension from two to $N$
additional lines would provide $N(N-1)/2$ cross-checks on the large-scale 21 cm
power spectrum. This work strongly motivates redundant line-intensity mapping
surveys probing the same cosmological volumes. |
The DEEP2 Galaxy Redshift Survey: Design, Observations, Data Reduction,
and Redshifts: We describe the design and data sample from the DEEP2 Galaxy Redshift Survey,
the densest and largest precision-redshift survey of galaxies at z ~ 1
completed to date. The survey has conducted a comprehensive census of massive
galaxies, their properties, environments, and large-scale structure down to
absolute magnitude M_B = -20 at z ~ 1 via ~90 nights of observation on the
DEIMOS spectrograph at Keck Observatory. DEEP2 covers an area of 2.8 deg^2
divided into four separate fields, observed to a limiting apparent magnitude of
R_AB=24.1. Objects with z < 0.7 are rejected based on BRI photometry in three
of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5
times more efficiently than in a purely magnitude-limited sample. Approximately
sixty percent of eligible targets are chosen for spectroscopy, yielding nearly
53,000 spectra and more than 38,000 reliable redshift measurements. Most of the
targets which fail to yield secure redshifts are blue objects that lie beyond z
~ 1.45. The DEIMOS 1200-line/mm grating used for the survey delivers high
spectral resolution (R~6000), accurate and secure redshifts, and unique
internal kinematic information. Extensive ancillary data are available in the
DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into
one of the richest multiwavelength regions on the sky. DEEP2 surpasses other
deep precision-redshift surveys at z ~ 1 in terms of galaxy numbers, redshift
accuracy, sample number density, and amount of spectral information. We also
provide an overview of the scientific highlights of the DEEP2 survey thus far.
This paper is intended as a handbook for users of the DEEP2 Data Release 4,
which includes all DEEP2 spectra and redshifts, as well as for the
publicly-available DEEP2 DEIMOS data reduction pipelines. [Abridged] | Optimising Gaussian processes for reconstructing dark energy dynamics
from supernovae: Gaussian processes are a fully Bayesian smoothing technique that allows for
the reconstruction of a function and its derivatives directly from
observational data, without assuming a specific model or choosing a
parameterization. This is ideal for constraining dark energy because physical
models are generally phenomenological and poorly motivated. Model-independent
constraints on dark energy are an especially important alternative to
parameterized models, as the priors involved have an entirely different source
so can be used to check constraints formulated from models or
parameterizations. A critical prior for Gaussian process reconstruction lies in
the choice of covariance function. We show how the choice of covariance
function affects the result of the reconstruction, and present a choice which
leads to reliable results for present day supernovae data. We also introduce a
method to quantify deviations of a model from the Gaussian process
reconstructions. |
CMB constraints on primordial black hole dark matter: We revisit cosmic microwave background (CMB) constraints on primordial black
hole dark matter. Spectral distortion limits from COBE/FIRAS do not impose a
relevant constraint. Planck CMB anisotropy power spectra imply that primordial
black holes with $m_{BH}\gtrsim 5~M_{\odot}$ are disfavored. However, this is
susceptible to sizeable uncertainties due to the treatment of the black hole
accretion process. These constraints are weaker than those quoted in earlier
literature for the same observables. | Comments on "First Dark Matter Results from the XENON100 Experiment": The XENON100 collaboration has recently released new dark matter limits,
placing particular emphasis on their impact on searches known to be sensitive
to light-mass (below 10 GeV/c^2) Weakly Interacting Massive Particles (WIMPs),
such as DAMA and CoGeNT. We describe here several sources of uncertainty and
bias in their analysis that make their new claimed sensitivity presently
untenable. In particular, we point out additional work in this field and simple
kinematic arguments that indicate that liquid xenon (LXe) may be a relatively
insensitive detection medium for the recoil energies (few keV_r) expected from
such low mass WIMPs. |
Constraining the dark energy and smoothness parameter with type Ia
Supernovae and Gamma-Ray Bursts: The existence of inhomogeneities in the observed Universe modifies the
distance-redshift relations thereby affecting the results of cosmological tests
in comparison to the ones derived assuming spatially uniform models. By
modeling the inhomogeneities through a Zeldovich-Kantowski-Dyer-Roeder (ZKDR)
approach which is phenomenologically characterized by a smoothness parameter
$\alpha$, we rediscuss the constraints on the cosmic parameters based on
Supernovae type Ia and Gamma-Ray Bursts (GRBs) data. The present analysis is
restricted to a flat $\Lambda$CDM model with the reasonable assumption that
$\Lambda$ does not clump. A $\chi^{2}$-analysis using 557 SNe Ia data from the
Union2 Compilation Data (Amanullah {\it et al.} 2010) constrains the pair of
parameters ($\Omega_m, \alpha$) to $\Omega_m=0.27_{-0.03}^{+0.08}$($2\sigma$)
and $\alpha \geq 0.25$. A similar analysis based only on 59 Hymnium GRBs (Wei
2010) constrains the matter density parameter to be $\Omega_m=
0.35^{+0.62}_{-0.24}$ ($2\sigma$) while all values for the smoothness parameter
are allowed. By performing a joint analysis, it is found that $\Omega_m =
0.27^{+0.06}_{-0.03}$ and $\alpha \geq 0.52$. As a general result, although
considering that current GRB data alone cannot constrain the smoothness
$\alpha$ parameter our analysis provides an interesting cosmological probe for
dark energy even in the presence of inhomogeneities. | Testing the cosmological Poisson equation in a model-independent way: We show how one can test the cosmological Poisson equation by requiring only
the validity of three main assumptions: the energy-momentum conservation
equations of matter, the equivalence principle, and the cosmological principle.
We first point out that one can only measure the combination ${\mathcal
M}\equiv \Omega_m^{(0)}\mu$, where $\mu$ quantifies the deviation of the
Poisson equation from the standard one and $\Omega_m^{(0)}$ is the fraction of
matter density at present. Then we employ a recent model-independent forecast
for the growth rate $f(z)$ and the expansion rate $E(z)$ to obtain constraints
on ${\mathcal M}$ for a survey that approximates a combination of the Dark
Energy Spectroscopic Instrument (DESI) and Euclid. We conclude that a constant
${\mathcal M}$ can be measured with a relative error
$\sigma_{\mathcal{M}}=4.5\%$, while if ${\mathcal M}$ is arbitrarily varying in
redshift, it can be measured only to within $13.4\%$ (1 $\sigma$ c.l.) at
redshift $z=0.9$, and 15-22\% up to $z=1.5$. We also project our constraints on
some parametrizations of ${\mathcal M}$ proposed in literature, while still
maintaining model-independence for the background expansion, the power spectrum
shape, and the non-linear corrections. Generally speaking, as expected, we find
much weaker model-independent constraints than found so far for such models.
This means that the cosmological Poisson equation remains quite open to various
alternative gravity and dark energy models. |
Dwarf Galaxies in the Coma Cluster: I. Velocity Dispersion Measurements: We present the study of a large sample of early-type dwarf galaxies in the
Coma cluster observed with DEIMOS on the Keck II to determine their internal
velocity dispersion. We focus on a subsample of 41 member dwarf elliptical
galaxies for which the velocity dispersion can be reliably measured, 26 of
which were studied for the first time. The magnitude range of our sample is
$-21<M_R<-15$ mag.
This paper (paper I) focuses on the measurement of the velocity dispersion
and their error estimates. The measurements were performed using {\it pPXF
(penalised PiXel Fitting)} and using the Calcium triplet absorption lines. We
use Monte Carlo bootstrapping to study various sources of uncertainty in our
measurements, namely statistical uncertainty, template mismatch and other
systematics. We find that the main source of uncertainty is the template
mismatch effect which is reduced by using templates with a range of spectral
types.
Combining our measurements with those from the literature, we study the
Faber-Jackson relation ($L\propto\sigma^\alpha$) and find that the slope of the
relation is $\alpha=1.99\pm0.14$ for galaxies brighter than $M_R\simeq-16$ mag.
A comprehensive analysis of the results combined with the photometric
properties of these galaxies is reported in paper II. | Observable Small-scale Effects of Thermal Inflation: Thermal inflation, a brief low energy inflation after the primordial
inflation, resolves the moduli problem in the context of supersymmetric
cosmology. In the thermal inflation scenario, the primordial power spectrum is
modestly redshifted on large scales, but suppressed by a factor of 1/50 on
scales smaller than the horizon size at the beginning of thermal inflation. We
compare the thermal inflation model with the warm dark matter and $\Lambda$CDM
scenarios by studying CMB spectral distortions, halo abundances, and 21cm
hydrogen lines. |
Matter perturbations in Galileon cosmology: We study the evolution of matter density perturbations in Galileon cosmology
where the late-time cosmic acceleration can be realized by a field kinetic
energy. We obtain full perturbation equations at linear order in the presence
of five covariant Lagrangians ${cal L}_i$ ($i=1,...,5$) satisfying a Galilean
symmetry in the flat space-time. The equations for a matter perturbation as
well as an effective gravitational potential are derived under a quasi-static
approximation on sub-horizon scales. This approximation can reproduce full
numerical solutions with high accuracy for the wavelengths relevant to
large-scale structures. For the model parameters constrained by the background
expansion history of the Universe the growth rate of matter perturbations is
larger than that in the LCDM model, with the growth index $gamma$ today
typically smaller than 0.4. We also find that, even on very large scales
associated with the Integrated-Sachs-Wolfe (ISW) effect in Cosmic Microwave
Background (CMB) temperature anisotropies, the effective gravitational
potential exhibits a temporal growth during the transition from the matter era
to the epoch of cosmic acceleration. These properties are useful to distinguish
the Galileon model from the LCDM in future high-precision observations. | Constraints on the topology of the Universe derived from the 7-year WMAP
data: We impose constraints on the topology of the Universe determined from a
search for matched circles in the temperature anisotropy patterns of the 7-year
WMAP data. We pay special attention to the sensitivity of the method to
residual foreground contamination of the sky maps, and show that for a full sky
estimate of the CMB signal (the ILC map) such residuals introduce a
non-negligible effect on the statistics of matched circles. In order to reduce
this effect, we perform the analysis on maps for which the most contaminated
regions have been removed. A search for pairs of matched back-to-back circles
in the higher resolution WMAP W-band map allows tighter constraints to be
imposed on topology. Our results rule out universes with topologies that
predict pairs of such circles with radii larger than \alpha_min \approx 10
degrees. This places a lower bound on the size of the fundamental domain for a
flat universe of about 27.9 Gpc. This bound is close to the upper limit on the
size of Universe possible to detect by the method of matched circles, i.e. the
diameter of the observable Universe is 28.3 Gpc. |
Cosmological constraint on Brans-Dicke Model: We combine new Cosmic Microwave Background (CMB) data from Planck with Baryon
Acoustic Oscillation (BAO) data to constrain the Brans-Dicke (BD) theory, in
which the gravitational constant $G$ evolves with time. Observations of type Ia
supernovae (SNeIa) provide another important set of cosmological data, as they
may be regarded as standard candles after some empirical corrections. However,
in theories that include modified gravity like the BD theory, there is some
risk and complication when using the SNIa data because their luminosity may
depend on $G$. In this paper, we assume a power law relation between the SNIa
luminosity and $G$, but treat the power index as a free parameter. We then test
whether the difference in distances measured with SNIa data and BAO data can be
reduced in such a model. We also constrain the BD theory and cosmological
parameters by making a global fit with the CMB, BAO and SNIa data set. For the
CMB+BAO+SNIa data set, we find $0.08\times10^{-2} < \zeta <0.33\times10^{-2} $
at the 68\% confidence level (CL) and $-0.01\times10^{-2} <\zeta <0.43\times
10^{-2} $ at the 95\% CL, where $\zeta$ is related to the {BD} parameter
$\omega$ by $\zeta=\ln(1+1/\omega)$. | CMB lensing forecasts for constraining the primordial perturbations:
adding to the CMB temperature and polarization information: We forecast how current ({\planck}) and future ({\prism}) cosmic microwave
background (CMB) experiments constrain the adiabatic mode and its admixtures
with primordial isocurvature modes, using measurements of the reconstructed CMB
lensing potential and lensing-induced CMB B-mode polarization anisotropies in
combination with the CMB temperature and E-mode polarization anisotropies. We
first study the characteristic features of the CMB temperature, polarization
and lensing spectra for adiabatic and isocurvature modes. We then consider how
lensing-induced B-mode polarization and lensing potential information can
improve constraints on an admixture of adiabatic and three correlated
isocurvature modes. We find that the CMB lensing spectrum improves constraints
on isocurvature modes by at most 10% for the {\planck} and {\prism}
experiments, with the limited improvement a result of the low amplitude of
isocurvature lensing spectra and cancellations between these spectra rendering
them only slightly detectable. There is a larger gain from using the
lensing-induced CMB B-mode polarization spectrum, as measured by {\prism}, with
constraints on isocurvature mode amplitudes improving by as much as 40%
relative to the CMB temperature and E-mode polarization constraints. The
addition of both lensing and lensing-induced B-mode polarization information
constrains isocurvature mode amplitudes at the few percent level or better,
with percent level constraints or better possible in the case of admixtures of
the adiabatic mode with one or two correlated isocurvature modes. We
investigate the dependence of our results to various assumptions in our
analysis, such as the inclusion of dark energy parameters, the CMB
temperature-lensing correlation, and the presence of primordial tensor modes,
and find that these assumptions do not significantly change our main results. |
Looking through the same lens: shear calibration for LSST, Euclid &
WFIRST with stage 4 CMB lensing: The next generation weak lensing surveys (i.e., LSST, Euclid and WFIRST) will
require exquisite control over systematic effects. In this paper, we address
shear calibration and present the most realistic forecast to date for
LSST/Euclid/WFIRST and CMB lensing from a stage 4 CMB experiment (CMB S4). We
use the CosmoLike code to simulate a joint analysis of all the two-point
functions of galaxy density, galaxy shear and CMB lensing convergence. We
include the full Gaussian and non-Gaussian covariances and explore the
resulting joint likelihood with Monte Carlo Markov Chains. We constrain shear
calibration biases while simultaneously varying cosmological parameters, galaxy
biases and photometric redshift uncertainties. We find that CMB lensing from
CMB S4 enables the calibration of the shear biases down to 0.2% - 3% in 10
tomographic bins for LSST (below the ~0.5% requirements in most tomographic
bins), down to 0.4% - 2.4% in 10 bins for Euclid and 0.6% - 3.2% in 10 bins for
WFIRST. For a given lensing survey, the method works best at high redshift
where shear calibration is otherwise most challenging. This self-calibration is
robust to Gaussian photometric redshift uncertainties and to a reasonable level
of intrinsic alignment. It is also robust to changes in the beam and the
effectiveness of the component separation of the CMB experiment, and slowly
dependent on its depth, making it possible with third generation CMB
experiments such as AdvACT and SPT-3G, as well as the Simons Observatory. | Euclid preparation: IX. EuclidEmulator2 -- Power spectrum emulation with
massive neutrinos and self-consistent dark energy perturbations: We present a new, updated version of the EuclidEmulator (called
EuclidEmulator2), a fast and accurate predictor for the nonlinear correction of
the matter power spectrum. Percent-level accurate emulation is now supported in
the eight-dimensional parameter space of $w_0w_a$CDM$+\sum m_\nu$models between
redshift $z=0$ and $z=3$ for spatial scales within the range 0.01 $h$/Mpc $\leq
k \leq$ 10 $h$/Mpc. In order to achieve this level of accuracy, we have had to
improve the quality of the underlying N-body simulations used as training data:
(1) we use self-consistent linear evolution of non-dark matter species such as
massive neutrinos, photons, dark energy and the metric field, (2) we perform
the simulations in the so-called N-body gauge, which allows one to interpret
the results in the framework of general relativity, (3) we run over 250
high-resolution simulations with $3000^3$ particles in boxes of 1
(Gpc/$h$)${}^3$ volumes based on paired-and-fixed initial conditions and (4) we
provide a resolution correction that can be applied to emulated results as a
post-processing step in order to drastically reduce systematic biases on small
scales due to residual resolution effects in the simulations. We find that the
inclusion of the dynamical dark energy parameter $w_a$ significantly increases
the complexity and expense of creating the emulator. The high fidelity of
EuclidEmulator2 is tested in various comparisons against N-body simulations as
well as alternative fast predictors like Halofit, HMCode and CosmicEmu. A blind
test is successfully performed against the Euclid Flagship v2.0 simulation.
Nonlinear correction factors emulated with EuclidEmulator2 are accurate at the
level of 1% or better for 0.01 $h$/Mpc $\leq k \leq$ 10 $h$/Mpc and $z\leq3$
compared to high-resolution dark matter only simulations. EuclidEmulator2 is
publicly available at https://github.com/miknab/EuclidEmulator2 . |
New agegraphic dark energy as a rolling tachyon: Combining the general relativity and the uncertainty relation in quantum
mechanics, the energy density of quantum fluctuations of space-time can be
viewed as dark energy. The so-called agegraphic dark energy model is just based
on this viewpoint, in which the age of the universe is introduced as the length
measure. Recently, the new agegraphic dark energy model was proposed, where the
dynamical dark energy is measured by the conformal age of the universe. On the
other hand, scalar-field dark energy models like tachyon are often regarded as
an effective description of some underlying theory of dark energy. In this
paper, we show that the new agegraphic dark energy can be described completely
by a tachyon scalar-field. We thus reconstruct the potential and the dynamics
of the tachyon scalar-field, according to the evolution of the new agegraphic
dark energy. | Fast Theoretical Predictions for Spherical Fourier Analysis of
Large-Scale Structures: On-going or soon to come cosmological large-scale structure surveys such as
DESI, SPHEREx, Euclid, or the High-Latitude Spectroscopic Survey of the Nancy
Grace Roman Space Telescope promise unprecedented measurement of the clustering
of galaxies on large scales. When quantified with the Cartesian Fourier basis,
the measurement of these large scales requires the introduction of so-called
wide-angle corrections. By contrast, the measurement of the power spectrum in a
spherical Fourier Bessel (SFB) basis does not require such corrections and
naturally accounts for the spherical survey geometries. Here, we develop and
implement a fast code to construct the SFB power spectrum and investigate how
line of sight effects, physics such as non-Gaussianity, and differing survey
geometries affect SFB power spectrum estimates. We then leverage our program to
predict the tightness of cosmic growth constraints from realistic survey
specifications using a Fisher matrix formalism. |
Estimator for the anisotropic stress using relativistic effects in
Large-Scale Structure: The large-scale structure of the Universe is a rich source of information to
test the consistency of General Relativity on cosmological scales. We briefly
describe how the observed distributions of galaxies is affected by
redshift-space distortions, but also by gravitational lensing and other
relativistic effects. Then, we show how one of this relativistic effects, the
gravitational redshift, can be used to build a model independent test that
directly measures the anisotropic stress, i.e. the difference between the two
gravitational potentials that describe spacetime fluctuations of the geometry. | Distinguishing standard reionization from dark matter models: The Wilkinson Microwave Anisotropy Probe (WMAP) experiment has detected
reionization at the $5.5 \sigma$ level and has reported a mean optical depth of
$0.088 \pm 0.015$. A powerful probe of reionization is the large-angle $EE$
polarization power spectrum, which is now (since the first five years of data
from WMAP) cosmic variance limited for $2\le l \le6$. Here we consider partial
reionization caused by WIMP dark matter annihilation, and calculate the
expected polarization power spectrum. We compare the dark matter models with a
standard 2-step reionization theory, and examine whether the models may be
distinguished using current, and future CMB observations. We consider dark
matter annihilation at intermediate redshifts ($z<60$) due to halos, as well as
annihilation at higher redshifts due to free particles. In order to study the
effect of high redshift dark matter annihilation on CMB power spectra, it is
essential to include the contribution of residual electrons (left over from
recombination) to the ionization history. Dark matter halos at redshifts $z<60$
influence the low multipoles $l<20$ in the $EE$ power spectrum, while the
annihilation of free particle dark matter at high redshifts $z>100$ mainly
affects multipoles $l>10$. |
Covariance matrices for variance-suppressed simulations: Cosmological $N$-body simulations provide numerical predictions of the
structure of the Universe against which to compare data from ongoing and future
surveys, but the growing volume of the Universe mapped by surveys requires
correspondingly lower statistical uncertainties in simulations, usually
achieved by increasing simulation sizes at the expense of computational power.
It was recently proposed to reduce simulation variance without incurring
additional computational costs by adopting fixed-amplitude initial conditions.
This method has been demonstrated not to introduce bias in various statistics,
including the two-point statistics of galaxy samples typically used for
extracting cosmological parameters from galaxy redshift survey data, but
requires us to revisit current methods for estimating covariance matrices of
clustering statistics for simulations. In this work, we find that it is not
trivial to construct covariance matrices analytically for fixed-amplitude
simulations, but we demonstrate that EZmock (Effective Zel'dovich approximation
mock catalogue), the most efficient method for constructing mock catalogues
with accurate two- and three-point statistics, provides reasonable covariance
matrix estimates for such simulations. We further examine how the variance
suppression obtained by amplitude-fixing depends on three-point clustering,
small-scale clustering, and galaxy bias, and propose intuitive explanations for
the effects we observe based on the EZmock bias model. | The SDSS-IV eBOSS: emission line galaxy catalogues at z=0.8 and study of
systematic errors in the angular clustering: We present two wide-field catalogs of photometrically-selected emission line
galaxies (ELGs) at z=0.8 covering about 2800 deg^2 over the south galactic cap.
The catalogs were obtained using a Fisher discriminant technique described in a
companion paper. The two catalogs differ by the imaging used to define the
Fisher discriminant: the first catalog includes imaging from the Sloan Digital
Sky Survey and the Wide-Field Infrared Survey Explorer, the second also
includes information from the South Galactic Cap U-band Sky Survey (SCUSS).
Containing respectively 560,045 and 615,601 objects, they represent the largest
ELG catalogs available today and were designed for the ELG programme of the
extended Baryon Oscillation Spectroscopic Survey (eBOSS). We study potential
sources of systematic variation in the angular distribution of the selected
ELGs due to fluctuations of the observational parameters. We model the
influence of the observational parameters using a multivariate regression and
implement a weighting scheme that allows effective removal of all of the
systematic errors induced by the observational parameters. We show that
fluctuations in the imaging zero-points of the photometric bands have minor
impact on the angular distribution of objects in our catalogs. We compute the
angular clustering of both catalogs and show that our weighting procedure
effectively removes spurious clustering on large scales. We fit a model to the
small scale angular clustering, showing that the selections have similar biases
of 1.35/D_a(z) and 1.28/D_a(z). Both catalogs are publicly available. |
How the Coherent Tides Obstruct the Radial Infalls of Satellite Galaxies
onto Clusters: A direct numerical evidence for the obstructing effect of the coherent tides
on the infall-zone satellites around the cluster halos is presented. Analyzing
the numerical data from a high-resolution N-body simulation, we calculate the
mean fractions of the radial and tangential velocities of the infall-zone
satellites around the cluster halos and investigate if and how they depend on
the tidal coherence defined as the alignments between the major principal axes
of the local tidal fields smoothed on the linear and nonlinear scales. It is
found that the infall-zone satellites located in the regions with higher tidal
coherence have significantly smaller and larger mean fractions of the radial
and tangential velocities, respectively, which indicates that the radial infall
of satellites onto host clusters are obstructed by the coherent tides. We also
show that those satellites separated by shorter distances from the host
clusters, having lower-masses, and embedded in the anisotropic large-scale
environments like filaments and sheets, are more vulnerable to the obstructing
effect of the coherent tides. | The Physics of the FIR-Radio Correlation: II. Synchrotron Emission as a
Star-Formation Tracer in High-Redshift Galaxies: We construct one-zone steady-state models of cosmic ray (CR) injection,
cooling, and escape over the entire dynamic range of the FIR-radio correlation
(FRC), from normal galaxies to starbursts, over the redshift interval 0 <= z <=
10. Normal galaxies with low star-formation rates become radio-faint at high z,
because Inverse Compton (IC) losses off the CMB cool CR electrons and positrons
rapidly, suppressing their nonthermal radio emission. However, we find that
this effect occurs at higher redshifts than previously expected, because
escape, bremsstrahlung, ionization, and starlight IC losses act to counter this
effect and preserve the radio luminosity of galaxies. The radio dimming of
star-forming galaxies at high z is not just a simple competition between
magnetic field energy density and the CMB energy density; the CMB must also
compete with every other loss process. We predict relations for the critical
redshift when radio emission is significantly suppressed compared to the z ~ 0
FRC as a function of star-formation rate per unit area. Additionally, we
provide a quantitative explanation for the relative radio brightness of some
high-z submillimeter galaxies. We show that at fixed star formation rate
surface density, galaxies with larger CR scale heights are radio bright with
respect to the FRC, because of weaker bremsstrahlung and ionization losses
compared to compact starbursts. We predict that these "puffy starbursts" should
have steeper radio spectra than compact galaxies with the same star-formation
rate surface density. We find that radio bright submillimeter galaxies alone
cannot explain the excess radio emission reported by ARCADE2, but they may
significantly enhance the diffuse radio background with respect to a naive
application of the z ~ 0 FRC. |
Cosmology in Minkowski space: Theoretical and observational challenges to standard cosmology such as the
cosmological constant problem and tensions between cosmological model
parameters inferred from different observations motivate the development and
search of new physics. A less radical approach to venturing beyond the standard
model is the simple mathematical reformulation of our theoretical frameworks
underlying it. While leaving physical measurements unaffected, this can offer a
reinterpretation and even solutions of these problems. In this spirit, metric
transformations are performed here that cast our Universe into different
geometries. Of particular interest thereby is the formulation of cosmology in
Minkowski space. Rather than an expansion of space, spatial curvature, and
small-scale inhomogeneities and anisotropies, this frame exhibits a variation
of mass, length and time scales across spacetime. Alternatively, this may be
interpreted as an evolution of fundamental constants. As applications of this
reframed cosmological picture, the naturalness of the cosmological constant is
reinspected and promising candidates of geometric origin are explored for dark
matter, dark energy, inflation and baryogenesis. An immediate observation
thereby is the apparent absence of the cosmological constant problem in the
Minkowski frame. The formalism is also applied to identify new observable
signatures of conformal inhomogeneities, which have been proposed as
simultaneous solution of the observational tensions in the Hubble constant, the
amplitude of matter fluctuations, and the gravitational lensing amplitude of
cosmic microwave background anisotropies. These are found to enhance redshifts
to distant galaxy clusters and introduce a mass bias with cluster masses
inferred from gravitational lensing exceeding those inferred kinematically or
dynamically. | Cosmic shear statistics in cosmologies with non-Gaussian initial
conditions: We computed the power spectrum of weak cosmic shear in models with
non-Gaussian primordial density fluctuations. Cosmological initial conditions
deviating from Gaussianity have recently attracted much attention in the
literature, especially with respect to their effect on the formation of
non-linear structures and because of the bounds that they can put on the
inflationary epoch. The fully non-linear matter power spectrum was evaluated
with the use of the physically motivated, semi-analytic halo model, where the
mass function and linear halo bias were suitably corrected for non-Gaussian
cosmologies. In agreement with previous work, we found that a level of
non-Gaussianity compatible with CMB bounds and with positive skewness produces
an increase in power of the order of a few percent at intermediate scales. We
then used the matter power spectrum, together with observationally motivated
background source redshift distributions in order to compute the cosmological
weak lensing power spectrum. We found that the degree of deviation from the
power spectrum of the reference Gaussian model is small compared to the
statistical error expected from even future weak lensing surveys. However,
summing the signal over a large range of multipoles can beat down the noise,
bringing to a significant detection of non-Gaussianity at the level of
$|f_\mathrm{NL}| \simeq $ few tens, when all other cosmological parameters are
held fixed. Finally, we have shown that the constraints on the level of
non-Gaussianity can be improved by $\sim 20%$ with the use of weak lensing
tomography. |
The darkness that shaped the void: dark energy and cosmic voids: Aims: We assess the sensitivity of void shapes to the nature of dark energy
that was pointed out in recent studies. We investigate whether or not void
shapes are useable as an observational probe in galaxy redshift surveys. We
focus on the evolution of the mean void ellipticity and its underlying physical
cause. Methods: We analyse the morphological properties of voids in five sets
of cosmological N-body simulations, each with a different nature of dark
energy. Comparing voids in the dark matter distribution to those in the halo
population, we address the question of whether galaxy redshift surveys yield
sufficiently accurate void morphologies. Voids are identified using the
parameter free Watershed Void Finder. The effect of redshift distortions is
investigated as well. Results: We confirm the statistically significant
sensitivity of voids in the dark matter distribution. We identify the level of
clustering as measured by \sigma_8(z) as the main cause of differences in mean
void shape <\epsilon>. We find that in the halo and/or galaxy distribution it
is practically unfeasible to distinguish at a statistically significant level
between the various cosmologies due to the sparsity and spatial bias of the
sample. | On non-linear CMB temperature anisotropy from gravitational
perturbations: Non-linear CMB temperature anisotropies up to the third-order on large scales
are calculated. On large scales and in the Sachs-Wolfe limit, we give the
explicit expression for the observed temperature anisotropy in terms of the
primordial curvature perturbation up to the third-order. We derived the final
bispectrum and trispectrum of anisotropies and the corresponding non-linear
parameters, in which the contributions to the observed non-Gaussianity from
primordial perturbations and from the non-linear mapping from primordial
curvature perturbation to the temperature anisotropy are transparently
separated. |
Search for a distance-dependent Baryonic Tully-Fisher Relation at low
redshifts: A recent work (arXiv:2104.14481) has found a statistically significant
transition in the Baryonic Tully-Fisher relation (BTFR) using low redshift data
($z<0.1$), with the transitions occurring at about 9 and 17 Mpc. Motivated by
this finding, we carry out a variant of this analysis by fitting the data to an
augmented BTFR, where both the exponent as well as normalization constant vary
as a function of distance. We find that both the exponent and normalization
constant show only a marginal variation with distance, and are consistent with
a constant value, to within $2\sigma$. We also checked to see if there is a
statistically significant difference between the BTFR results after bifurcating
the dataset at distances of 9 and 17 Mpc. We find that almost all the sets of
subsamples obey the BTFR with $\chi^2$/dof close to 1 and the best-fit
parameters consistent across the subsamples. Only the subsample with $D<17$ Mpc
shows a marginal discrepancy (at $1.75\sigma$) with respect to the BTFR.
Therefore, we do not find any evidence for statistically significant
differences in the BTFR at distances of 9 and 17 Mpc. | Primordial Black Holes Around Us Now, Long Before, and Far away: Recent astronomical data on Black hole observations are reviewed. The
arguments in favor that the observed black holes are predominantly primordial
(PBH) are presented. The mass spectrum of PBH is best fit to the log-normal
one. A model of PBH formation with log-normal spectrum is briefly described. |
Forecast Analysis on Interacting Dark Energy Models from Future
Generation PICO and DESI Missions: The next-generation CMB satellite missions are expected to provide robust
constraints on a wide range of cosmological parameters with unprecedented
precision. But these constraints on the parameters could weaken if we do not
attribute dark energy to a cosmological constant. The cosmological models
involving interaction between dark energy and dark matter can give rise to
comparable energy densities at the present epoch, thereby alleviating the
so-called cosmic coincidence problem. In the present paper, we perform a
forecast analysis to test the ability of the future generation high-sensitive
Cosmic Microwave Background (CMB), and Baryon Acoustic Oscillation (BAO)
experiments to constrain phenomenological interacting dark energy models. We
consider cosmic variance limited future CMB polarization experiment PICO along
with BAO information from the DESI experiment to constrain the parameters of
the interacting dark sector. Based on the stability of the cosmological
perturbations, we consider two possibilities for the interaction scenario. We
investigate the impact of both the coupling constant and the equation of state
parameter of dark energy on the CMB temperature power spectrum, matter power
spectrum, and $f\sigma_8$. We have used simulated temperature and polarization
data from PICO within the multipole ranges ($\ell = 2 - 4000$), and as
expected, we do see PICO alone produces better constraints than Planck on the
$\Lambda$CDM parameters. With the integration of the PICO and DESI missions, we
observe a significant improvement in the constraints on several cosmological
parameters, especially the equation of state parameter of dark energy. However,
we note that additional data is required to constrain a small positive coupling
constant. | Dynamical friction of star clusters against disk field stars in
galaxies: Implications on stellar nucleus formation and globular cluster
luminosity functions: We numerically investigate orbital evolution of star clusters (SCs) under the
influence of dynamical friction by field stars of their host disk galaxies
embedded in dark matter halos. We find that SCs with masses larger than 2 *
10^5 M_sun can show significant orbital decay within less than 1 Gyr due to
dynamical friction by disk field stars in galaxies with disk masses M_d less
than 10^9 M_sun. We also find that orbital decay of SCs due to dynamical
friction is more remarkable in disk galaxies with smaller M_d and higher
mass-ratios of disks to dark matter halos. The half-number radii R_h, sc and
mean masses within R_h,sc of the SC systems (SCSs) in low-mass disk galaxies
with M_d < 10^9 M_sun are found to evolve significantly with time owing to
dynamical friction of SCs. More massive SCs that can spiral-in to the central
regions of disks can form multiple SC systems with smaller velocity dispersions
so that they can merge with one another to form single stellar nuclei with
their masses comparable to ~0.4% of their host disk masses. Based on these
results, we suggest that luminosity functions (LFs) for more massive globular
clusters (GCs) with masses larger than 2 * 10^5 M_sun can steepen owing to
transformation of the more massive GCs into single stellar nuclei through GC
merging in less luminous galaxies. We also suggest that the half-number radii
of GC systems can evolve owing to dynamical friction only for galaxies with
their total masses smaller than ~ 10^{10} M_sun. |
MAGIICAT I. The MgII Absorber-Galaxy Catalog: We describe the MgII Absorber-Galaxy Catalog, MAGIICAT, a compilation of 182
spectroscopically identified intermediate redshift (0.07 < z < 1.1) galaxies
with measurements of MgII 2796, 2803 absorption from their circumgalactic
medium within projected distances of 200 kpc from background quasars. In this
work, we present "isolated" galaxies, which are defined as having no
spectroscopically identified galaxy within a projected distance of 100 kpc and
a line of sight velocity separation of 500 km/s. We standardized all galaxy
properties to the Lambda CDM cosmology and galaxy luminosities, absolute
magnitudes, and rest-frame colors to the B- and K-band on the AB system. We
present galaxy properties and rest-frame MgII equivalent width, Wr(2796),
versus galaxy redshift. The well-known anti-correlation between Wr(2796) and
quasar-galaxy impact parameter, D, is significant to the 8 sigma level. The
mean color of MAGIICAT galaxies is consistent with an Sbc galaxy for all
redshifts. We also present B- and K-band luminosity functions for different
Wr(2796) and redshift subsamples: "weak absorbing" [Wr(2796) < 0.3 Ang],
"strong absorbing" [Wr(2796) > 0.3 Ang], low redshift (z < zmed), and high
redshift (z > zmed), where zmed = 0.359 is the median galaxy redshift.
Rest-frame color B-K correlates with M_K at the 8 sigma level for the whole
sample but is driven by the strong absorbing, high redshift subsample (6
sigma). Using M_K as a proxy for stellar mass and examining the luminosity
functions, we infer that in lower stellar mass galaxies, MgII absorption is
preferentially detected in blue galaxies and the absorption is more likely to
be weak. | Improving constraints on the neutrino mass using sufficient statistics: We use the "Dark Energy and Massive Neutrino Universe" (DEMNUni) simulations
to compare the constraining power of "sufficient statistics" with the standard
matter power spectrum on the sum of neutrino masses, $M_\nu \equiv \sum m_\nu$.
In general, the power spectrum, even supplemented with higher moments of the
distribution, captures only a fraction of the available cosmological
information due to correlations between the Fourier modes. In contrast, the
non-linear transform of sufficient statistics, approximated by a logarithmic
mapping A=ln(1+\delta), was designed to capture all the available cosmological
information contained in the matter clustering; in this sense it is an optimal
observable. Our analysis takes advantage of the recent analytical model
developed by Carron et al. 2014 to estimate both the matter power spectrum and
the A-power spectrum covariance matrices. Using a Fisher information approach,
we find that using sufficient statistics increases up to 8 times the available
information on the total neutrino mass at z=0, thus tightening the constraints
by almost a factor of 3 compared to the matter power spectrum. |
Slow Diffusive Gravitational Instability Before Decoupling: Radiative diffusion damps acoustic modes at large comoving wavenumber (k)
before decoupling (``Silk damping''). In a simple WKB analysis, neglecting
moments of the temperature distribution beyond the quadrupole, damping appears
in the acoustic mode as a term of order ik^2/(taudot) where taudot is the
scattering rate per unit conformal time. Although the Jeans instability is
stabilized on scales smaller than the adiabatic Jeans length, I show that the
medium is linearly unstable to first order in (1/taudot) to a slow diffusive
mode. At large comoving wavenumber, the characteristic growth rate becomes
independent of spatial scale and constant: (t_{KH}a)^-1 ~ (128 pi G/9 kappa_T
c)(rho_m/rho_b), where "a" is the scale factor, rho_m and rho_b are the matter
and baryon energy density, respectively, and kappa_T is the Thomson opacity.
This is the characteristic timescale for a fluid parcel to radiate away its
thermal energy content at the Eddington limit, analogous to the Kelvin-Helmholz
(KH) time for a massive star or the Salpeter time for black hole growth.
Although this mode grows at all times prior to decoupling and on scales smaller
than the horizon, the growth time is long, about 100 times the age of the
universe at decoupling. Thus, it modifies the density and temperature
perturbations on small scales only at the percent level. The physics of this
mode is already accounted for in the popular codes CMBFAST and CAMB, but is
typically neglected in analytic studies of the growth of primordial
perturbations. This work clarifies the physics of this instability in the epoch
before decoupling, and emphasizes that the universe is formally unstable on
scales below the horizon, even in the limit of large taudot. Analogous
instabilities at yet earlier epochs are also mentioned. (Abridged) | Ionization State of Inter-Stellar Medium in Galaxies: Evolution,
SFR-M_star-Z Dependence, and Ionizing Photon Escape: We present a systematic study for ionization state of inter-stellar medium in
galaxies at z=0-3 with ~140,000 SDSS galaxies and 108 intermediate to high
redshift galaxies from the literature, using an ionization-parameter sensitive
line ratio of [OIII]5007/[OII]3727 and photoionization models. We confirm that
z=2-3 galaxies show an [OIII]/[OII] ratio significantly higher than a typical
star-forming galaxy of SDSS by a factor of >~10, and the photoionization models
reveal that these high-z galaxies have an ionization parameter of log(qion/cm
s^{-1})~7.6-9.0, a factor of ~4-10 higher than local galaxies. For galaxies at
any redshift, we identify a correlation between the [OIII]/[OII] ratio and
galaxy global properties of star-formation rate (SFR), stellar mass (M_star),
and metallicity (Z). We extend the fundamental metallicity relation (FMR) and
develop the fundamental ionization relation (FIR), a four-dimensional relation
of ionization parameter, SFR, M_star, and Z. The intermediate and high-z
galaxies up to z~3 follow the FIR defined with the local galaxies, in contrast
with the FMR whose possible evolution from z~2 to 3 is reported. We find that
the FMR evolution of z~2-3 appears, if one omits ionization parameter
differences, and that the FMR evolution does not exist for an average
metallicity solution of z~3 galaxies with a high-ionization parameter.
Interestingly, all of two local Lyman-continuum emitting galaxies (LyC leakers)
have a high [OIII]/[OII] ratio, indicating a positive correlation between
[OIII]/[OII] and ionizing photon escape fraction (fesc), which is successfully
explained by our photoionization models. Because [OIII]/[OII] ratios of z~2-3
galaxies, especially Ly-alpha emitters (LAEs), are comparable to, or higher
than, those of the local LyC leakers, these high-z galaxies are candidates of
Lyman-continuum emitting objects. (abridged) |
Exploring the Energetics of Intracluster Gas with a Simple and Accurate
Model: The state of the hot gas in clusters of galaxies is investigated with a set
of model clusters, created by assuming a polytropic equation of state
(Gamma=1.2) and hydrostatic equilibrium inside gravitational potential wells
drawn from a dark matter simulation. Star formation, energy input, and
nonthermal pressure support are included. To match the gas fractions seen in
non-radiative hydrodynamical simulations, roughly 5% of the binding energy of
the dark matter must be transferred to the gas during cluster formation; the
presence of nonthermal pressure support increases this value. In order to match
X-ray observations, scale-free behavior must be broken. This can be due to
either variation of the efficiency of star formation with cluster mass M_500,
or the input of additional energy proportional to the formed stellar mass M_F.
These two processes have similar effects on X-ray scalings. If 9% of the gas is
converted into stars, independent of cluster mass, then feedback energy input
of 1.2e-5*M_Fc^2 (or ~1.0 keV per particle) is required to match observed
clusters. Alternatively, if the stellar mass fraction varies as M_500^-0.26
then a lower feedback of 4e-6*M_Fc^2 is needed, and if the stellar fraction
varies as steeply as M_500^-0.49 then no additional feedback is necessary. The
model clusters reproduce the observed trends of gas temperature and gas mass
fraction with cluster mass, as well as observed entropy and pressure profiles;
thus they provide a calibrated basis with which to interpret upcoming SZ
surveys. One consequence of the increased gas energy is that the baryon
fraction inside the virial radius is less than roughly 90% of the cosmic mean,
even for the most massive clusters. | Stochastic inflation and primordial black holes: During inflation, vacuum quantum fluctuations are amplified and stretched to
astrophysical distances. They give rise to fluctuations in the cosmic microwave
background (CMB) temperature and polarisation, and to large-scale structures in
our universe. They can also trigger the formation of primordial black holes
(PBHs). Such objects could provide the progenitors of the recently detected
black-hole mergers, and constitute part or all of the dark matter. Their
observation would give invaluable access to parts of the inflationary sector
that are unconstrained by the CMB. Since PBHs require large inhomogeneities to
form, they are produced in scenarios where quantum fluctuations substantially
modify the dynamics of the universe. In this habilitation thesis, this
"backreaction" effect is investigated using the stochastic inflation formalism,
an effective theory for the long-wavelengths of quantum fields during
inflation, which can be described in a classical but stochastic way once the
small wavelengths have been integrated out. It describes an inflating
background that gets randomly corrected by the vacuum quantum fluctuations as
they get stretched to large distances. After a brief review of the stochastic
inflation formalism, we explain how it can be combined with standard techniques
of cosmological perturbation theory (the $\delta N$ formalism) to provide the
full probability density function of curvature perturbations in the presence of
non-perturbative quantum diffusion. These results are then applied to PBHs,
where we show that quantum diffusion can change the expected abundance by
several orders of magnitude. Finally, since inflationary models giving rise to
cosmologically relevant PBHs often feature violations of slow roll, the
stochastic-$\delta N$ formalism is generalised to non slow-roll dynamics. We
conclude by highlighting several research directions that remain to be
explored. |
Searching for anisotropy in the distribution of binary black hole
mergers: The standard model of cosmology is underpinned by the assumption of the
statistical isotropy of the Universe. Observations of the cosmic microwave
background, galaxy distributions, and supernovae, among other media, support
the assumption of isotropy at scales $\gtrsim 100$\,Mpc. The recent detections
of gravitational waves from merging stellar-mass binary black holes provide a
new probe of anisotropy; complementary and independent of all other probes of
the matter distribution in the Universe. We present an analysis using a
spherical harmonic model to determine the level of anisotropy in the first
LIGO/Virgo transient catalog. We find that the ten binary black hole mergers
within the first transient catalog are consistent with an isotropic
distribution. We carry out a study of simulated events to assess the prospects
for future probes of anisotropy. Within a single year of operation,
third-generation gravitational-wave observatories will probe anisotropies with
an angular scale of $\sim36^\circ$ at the level of $\lesssim0.1\%$. | The Skeleton: Connecting Large Scale Structures to Galaxy Formation: We report on two quantitative, morphological estimators of the filamentary
structure of the Cosmic Web, the so-called global and local skeletons. The
first, based on a global study of the matter density gradient flow, allows us
to study the connectivity between a density peak and its surroundings, with
direct relevance to the anisotropic accretion via cold flows on galactic halos.
From the second, based on a local constraint equation involving the
derivatives of the field, we can derive predictions for powerful statistics,
such as the differential length and the relative saddle to extrema counts of
the Cosmic web as a function of density threshold (with application to
percolation of structures and connectivity), as well as a theoretical framework
to study their cosmic evolution through the onset of gravity-induced
non-linearities. |
Quasi-Molecular mechanism of cosmological recombination: a scheme of
calculation: For a quasi-molecular mechanism of cosmological recombination, a scheme of
calculation based on a rigorous quantum-mechanical approach is elaborated. The
probability of free-bound radiative transition into an excited state of a
quasi-molecule temporarily formed by a colliding electron and two nearest
neighboring protons is derived in a closed algebraic form. | Particle Models and the Small-Scale Structure of Dark Matter: The kinetic decoupling of weakly interacting massive particles (WIMPs) in the
early universe sets a scale that can directly be translated into a small-scale
cutoff in the spectrum of matter density fluctuations. The formalism presented
here allows a precise description of the decoupling process and thus the
determination of this scale to a high accuracy from the details of the
underlying WIMP microphysics. With decoupling temperatures of several MeV to a
few GeV, the smallest protohalos to be formed range between 10^{-11} and almost
10^{-3} solar masses -- a somewhat smaller range than what was found earlier
using order-of-magnitude estimates for the decoupling temperature; for a given
WIMP model, the actual cutoff mass is typically about a factor of 10 greater
than derived in that way, though in some cases the difference may be as large
as a factor of several 100. Observational consequences and prospects to probe
this small-scale cutoff, which would provide a fascinating new window into the
particle nature of dark matter, are discussed |
Atomic beings and the discovery of gravity: We aim to bring a new perspective about some aspects of the current research
in Cosmology. We start with a brief introduction about the main developments of
the field in the last century; then we introduce an analogy that shall
elucidate the main difficulties that observational sciences involve, which
might be part of the issue related to some of the contemporary cosmological
problems. The analogy investigates how microscopic beings could ever discover
and understand gravitational phenomena. | Breaking the mass-sheet degeneracy with gravitational wave interference
in lensed events: The mass-sheet degeneracy is a well-known problem in gravitational lensing
which limits our capability to infer astrophysical lens properties or
cosmological parameters from observations. As the number of gravitational wave
observations grows, detecting lensed events will become more likely, and to
assess how the mass-sheet degeneracy may affect them is crucial. Here we study
both analytically and numerically how the lensed waveforms are affected by the
mass-sheet degeneracy computing the amplification factor from the diffraction
integral. In particular, we differentiate between the geometrical optics, wave
optics and interference regimes, focusing on ground-based gravitational waves
detectors. In agreement with expectations of gravitational lensing of
electromagnetic radiation, we confirm how, in the geometrical optics scenario,
the mass-sheet degeneracy cannot be broken with only one lensed image. However,
we find that in the interference regime, and in part in the wave-optics regime,
the mass-sheet degeneracy can be broken with only one lensed waveform thanks to
the characteristic interference patterns of the signal. Finally, we quantify,
through template matching, how well the mass-sheet degeneracy can be broken. We
find that, within present GW detector sensitivities and considering signals as
strong as those which have been detected so far, the mass-sheet degeneracy can
lead to a $1\sigma$ uncertainty on the lens mass of $\sim 12\%$. With these
values the MSD might still be a problematic issue. But in case of signals with
higher signal-to-noise ratio, the uncertainty can drop to $\sim 2\%$, which is
less than the current indeterminacy achieved by dynamical mass measurements. |
Novel cosmological bounds on thermally-produced axion-like particles: We constrain the coupling of thermally-produced axion-like particles (here
axions) with photons and gluons, using data from the cosmic microwave
background (CMB) spectra and baryon acoustic oscillations. The axion possesses
an explicit soft breaking mass term and it is produced thermally in the early
Universe from either axion-photon or axion-gluon processes, accounting for the
recent progresses in the field. We derive the most stringent bounds on the
axion-gluon coupling to date on the mass range considered $10^{-4} \lesssim
m_a/{\rm eV} \lesssim 100$, superseding the current bounds from SN1987A. The
bounds on the axion-photon coupling are competitive with the results from the
CAST collaboration for the axion mass $m_a \gtrsim 3\,$eV. We comment on the
forecast reaches that will be available given the sensitivity of future CMB-S4
missions. | Neutrino Signatures on the High Transmission Regions of the Lyman-alpha
Forest: We quantify the impact of massive neutrinos on the statistics of low density
regions in the intergalactic medium (IGM) as probed by the Lyman-alpha forest
at redshifts z=2.2--4. Based on mock but realistic quasar (QSO) spectra
extracted from hydrodynamic simulations with cold dark matter, baryons and
neutrinos, we find that the probability distribution of weak Lyman-alpha
absorption features, as sampled by Lyman-alpha flux regions at high
transmissivity, is strongly affected by the presence of massive neutrinos. We
show that systematic errors affecting the Lyman-alpha forest reduce but do not
erase the neutrino signal. Using the Fisher matrix formalism, we conclude that
the sum of the neutrino masses can be measured, using the method proposed in
this paper, with a precision smaller than 0.4 eV using a catalog of 200 high
resolution (S/N~100) QSO spectra. This number reduces to 0.27 eV by making use
of reasonable priors in the other parameters that also affect the statistics of
the high transitivity regions of the Lyman-alpha forest. The constraints
obtained with this method can be combined with independent bounds from the CMB,
large scale structures and measurements of the matter power spectrum from the
Lyman-alpha forest to produce tighter upper limits on the sum of the masses of
the neutrinos. |
Self-interacting dark matter solves the final parsec problem of
supermassive black hole mergers: Evidence for a stochastic gravitational wave (GW) background, plausibly
originating from the merger of supermassive black holes (SMBHs), is
accumulating with observations from pulsar timing arrays. An outstanding
question is how inspiraling SMBHs get past the "final parsec" of separation,
where they have a tendency to stall before GW emission alone can make the
binary coalesce. We argue that dynamical friction from the dark matter (DM)
spike surrounding the black holes is sufficient to resolve this puzzle, if the
DM has a self-interaction cross section of order $0.2-5\,$cm$^2$/g. The same
effect leads to a softening of the GW spectrum at low frequencies as suggested
by the current data. For collisionless cold DM, the friction deposits so much
energy that the spike is disrupted and cannot bridge the final parsec, while
for self-interacting DM, the isothermal core of the halo can act as a reservoir
for the energy liberated from the SMBH orbits. A realistic velocity dependence,
such as generated by the exchange of a massive mediator like a dark photon, is
favored to give a good fit to the GW spectrum while providing a large enough
core. A similar velocity dependence has been advocated for solving the
small-scale structure problems of cold DM. | Weak lensing of large scale structure in the presence of screening: A number of alternatives to general relativity exhibit gravitational
screening in the non-linear regime of structure formation. We describe a set of
algorithms that can produce weak lensing maps of large scale structure in such
theories and can be used to generate mock surveys for cosmological analysis. By
analysing a few basic statistics we indicate how these alternatives can be
distinguished from general relativity with future weak lensing surveys. |
Molecular Gas and Star Formation in Local Early-Type Galaxies: The molecular gas content of local early-type galaxies is constrained and
discussed in relation to their evolution. First, as part of the Atlas3D survey,
we present the first complete, large (260 objects), volume-limited single-dish
survey of CO in normal local early-type galaxies. We find a surprisingly high
detection rate of 22%, independent of luminosity and at best weakly dependent
on environment. Second, the extent of the molecular gas is constrained with CO
synthesis imaging, and a variety of morphologies is revealed. The kinematics of
the molecular gas and stars are often misaligned, implying an external gas
origin in over a third of the systems, although this behaviour is drastically
diffferent between field and cluster environments. Third, many objects appear
to be in the process of forming regular kpc-size decoupled disks, and a star
formation sequence can be sketched by piecing together multi-wavelength
information on the molecular gas, current star formation, and young stars.
Last, early-type galaxies do not seem to systematically obey all our usual
prejudices regarding star formation, following the standard Schmidt-Kennicutt
law but not the far infrared-radio correlation. This may suggest a greater
diversity in star formation processes than observed in disk galaxies. Using
multiple molecular tracers, we are thus starting to probe the physical
conditions of the cold gas in early-types. | Indications of a sub-linear and non-universal Kennicutt-Schmidt
relationship: We estimate the parameters of the Kennicutt-Schmidt (KS) relationship,
linking the star formation rate (Sigma_SFR) to the molecular gas surface
density (Sigma_mol), in the STING sample of nearby disk galaxies using a
hierarchical Bayesian method. This method rigorously treats measurement
uncertainties, and provides accurate parameter estimates for both individual
galaxies and the entire population. Assuming standard conversion factors to
estimate Sigma_SFR and Sigma_mol from the observations, we find that the KS
parameters vary between galaxies, indicating that no universal relationship
holds for all galaxies. The KS slope of the whole population is 0.76, with the
2sigma range extending from 0.58 to 0.94. These results imply that the
molecular gas depletion time is not constant, but varies from galaxy to galaxy,
and increases with the molecular gas surface density. Therefore, other galactic
properties besides just Sigma_mol affect Sigma_SFR, such as the gas fraction or
stellar mass. The non-universality of the KS relationship indicates that a
comprehensive theory of star formation must take into account additional
physical processes that may vary from galaxy to galaxy. |
Model independent evidence for dark energy evolution from Baryon
Acoustic Oscillations: Baryon Acoustic Oscillations (BAO) allow us to determine the expansion
history of the Universe, thereby shedding light on the nature of dark energy.
Recent observations of BAO's in the SDSS DR9 and DR11 have provided us with
statistically independent measurements of $H(z)$ at redshifts of 0.57 and 2.34,
respectively. We show that these measurements can be used to test the
cosmological constant hypothesis in a model independent manner by means of an
improved version of the $Om$ diagnostic. Our results indicate that the SDSS
DR11 measurement of $H(z) = 222 \pm 7$ km/sec/Mpc at $z = 2.34$, when taken in
tandem with measurements of $H(z)$ at lower redshifts, imply considerable
tension with the standard $\Lambda$CDM model. Our estimation of the new
diagnostic $Omh^2$ from SDSS DR9 and DR11 data, namely $Omh^2 \approx 0.122 \pm
0.01$, which is equivalent to $\Omega_{0m}h^2$ for the spatially flat
$\Lambda$CDM model, is in tension with the value $\Omega_{0m}h^2 = 0.1426 \pm
0.0025$ determined for $\Lambda$CDM from Planck+WP. This tension is alleviated
in models in which the cosmological constant was dynamically screened
(compensated) in the past. Such evolving dark energy models display a pole in
the effective equation of state of dark energy at high redshifts, which emerges
as a smoking gun test for these theories. | High energy emission and polarisation limits for the INTEGRAL burst GRB
061122: (Abridged) GRB 061122 is one of the brightest GRBs detected within INTEGRAL's
field of view to date. The two gamma-ray detectors on INTEGRAL were used to
investigate the spectral characteristics of GRB 061122. A search for linear
polarisation in the prompt emission was carried out using the SPI multiple
event data in the energy range 100 keV-1 MeV.
The prompt spectrum was best fit by a combination of a blackbody and a
power--law model (the quasithermal model), with evidence for high energy
emission continuing above 8 MeV. A pseudo-redshift value of pz = 0.95 +/- 0.18
was determined using the spectral fit parameters. The isotropic energy at this
pseudo-redshift is 8.5 x 10^{52} erg. The jet opening angle was estimated to be
smaller than 2.8 deg or larger than 11.9 deg from the X-ray lightcurve. An
upper limit of 60% polarisation was determined for the prompt emission of GRB
061122, using the multiple event data.
The high energy emission observed in the spectrum may be due to the reverse
shock interacting with the GRB ejecta when it is decelerated by the circumburst
medium. This behaviour has been observed in a small fraction of GRBs to date,
but is expected to be more commonly observed by the Fermi Gamma-ray Space
Telescope. The conditions for polarisation are met if the jet opening angle is
less than 2.8 deg, but further constraints on the level of polarisation are not
possible. |
MultiCAM: A multivariable framework for connecting the mass accretion
history of haloes with their properties: Models that connect galaxy and halo properties often summarize a halo's mass
accretion history (MAH) with a single value, and use this value as the basis
for predictions. However, a single-value summary fails to capture the
complexity of MAHs and information can be lost in the process. We present
MultiCAM, a generalization of traditional abundance matching frameworks, which
can simultaneously connect the full MAH of a halo with multiple halo and/or
galaxy properties. As a first case study, we apply MultiCAM to the problem of
connecting dark matter halo properties to their MAHs in the context of a dark
matter-only simulation. While some halo properties, such as concentration, are
more strongly correlated to the early-time mass growth of a halo, others, like
the virial ratio, have stronger correlations with late-time mass growth. This
highlights the necessity of considering the impact of the entire MAH on halo
properties. For most of the halo properties we consider, we find that MultiCAM
models that use the full MAH achieve higher accuracy than conditional abundance
matching models which use a single epoch. We also demonstrate an extension of
MultiCAM that captures the covariance between predicted halo properties. This
extension provides a baseline model for applications where the covariance
between predicted properties is important. | Stellar Ages and Metallicities of Central and Satellite Galaxies:
Implications for Galaxy Formation and Evolution: Using a large SDSS galaxy group catalogue, we study how the stellar ages and
metallicities of central and satellite galaxies depend on stellar mass and halo
mass. We find that satellites are older and metal-richer than centrals of the
same stellar mass. In addition, the slopes of the age-stellar mass and
metallicity-stellar mass relations are found to become shallower in denser
environments. This is due to the fact that the average age and metallicity of
low mass satellite galaxies increase with the mass of the halo in which they
reside. A comparison with the semi-analytical model of Wang et al. (2008) shows
that it succesfully reproduces the fact that satellites are older than centrals
of the same stellar mass and that the age difference increases with the halo
mass of the satellite. This is a consequence of strangulation, which leaves the
stellar populations of satellites to evolve passively, while the prolonged star
formation activity of centrals keeps their average ages younger. The resulting
age offset is larger in more massive environments because their satellites were
accreted earlier. The model fails, however, in reproducing the halo mass
dependence of the metallicities of low mass satellites, yields
metallicity-stellar mass and age-stellar mass relations that are too shallow,
and predicts that satellite galaxies have the same metallicities as centrals of
the same stellar mass, in disagreement with the data. We argue that these
discrepancies are likely to indicate the need to (i) modify the recipes of both
supernova feedback and AGN feedback, (ii) use a more realistic description of
strangulation, and (iii) include a proper treatment of the tidal stripping,
heating and destruction of satellite galaxies. [Abridged] |
The Last Eight-Billion Years of Intergalactic SiIV Evolution: We identified 24 SiIV absorption systems with z <~ 1 from a blind survey of
49 low-redshift quasars with archival Hubble Space Telescope ultraviolet
spectra. We relied solely on the characteristic wavelength separation of the
doublet to automatically detect candidates. After visual inspection, we defined
a sample of 20 definite (group G = 1) and 4 "highly-likely" (G = 2) doublets
with rest equivalent widths W_r for both lines detected at > 3 sigma. The
absorber line density of the G = 1 doublets was dN_SiIV/dX = 1.4+0.4/-0.3 for
log N(Si+3) > 12.9. The best-fit power law to the G = 1 frequency distribution
of column densities f(N(Si+3)) had normalization k = (1.2+0.5/-0.4) x 10^-14
cm2 and slope alpha = -1.6+0.3/-0.3. Using the power-law model of f(N(Si+3)),
we measured the Si+3 mass density relative to the critical density: Omega(Si+3)
= (3.7+2.8/-1.7) x 10^-8 for 13 < log N(Si+3) < 15. From Monte Carlo sampling
of the distributions, we estimated our value to be a factor of 4.8+3.0/-1.9
higher than the 2 < z < 4.5 <Omega(Si+3)>. From a simple linear fit to
Omega(Si+3) over the age of the Universe, we estimated a slow and steady
increase from z = 5.5 --> 0 with dOmega/dt_age = (0.61+/-0.23) x 10^-8 Gyr^-1.
We compared our ionic ratios N(Si+3)/N(C+3) to a 2 < z < 4.5 sample and
concluded, from survival analysis, that the two populations are similar, with
median <N(Si+3)/N(C+3)> = 0.16. | BR1202-0725: An Extreme Multiple Merger at z = 4.7: The radio-quiet quasar BR1202-0725 (z=4.695) is a remarkable source with a
bright Northwest (NW) companion detected at submm and radio wavelengths but
invisible in the optical. In the absence of amplification by gravitational
lensing, BR1202-0725 would be the most luminous binary CO and FIR source in the
Universe. In this paper, we report observations with the IRAM Plateau de Bure
interferometer of BR1202-0725 in the redshifted emission of the CO(5-4) and
(7-6) lines, the [C I](3P2-3P1) line, a high angular resolution (0.3 x 0.8
arcsec) 1.3 mm map of the rest-frame, far-IR dust continuum, and a search for
the CO(11-10) line. We compare these results with recent ALMA data in the [C
II] line. Both the quasar host galaxy and its NW companion are spatially
resolved in the molecular line emission and the dust continuum. The CO profile
of the NW companion is very broad with a full width at half maximum of 1000 +/-
130 km/s, compared to 360 +/- 40 km/s for the quasar host galaxy to the
Southeast (SE). The difference in linewidths and center velocities, and the
absence of any lens candidate or arc-like structure in the field, at any
wavelength, show that the obscured NW galaxy and the SE quasar host galaxy
cannot be lensed images of the same object. Instead, we find morphological and
kinematic evidence for sub-structures in both the NW and SE sources. We
interpret these results as strong indications that the BR1202-0725 complex is a
group of young, interacting, and highly active starburst galaxies. |
Simulating the LOcal Web (SLOW) -- III: Synchrotron Emission from the
Local Cosmic Web: Aims: Detecting diffuse synchrotron emission from the cosmic web is still a
challenge for current radio telescopes. We aim to make predictions for the
detectability of cosmic web filaments from simulations. Methods: We present the
first cosmological MHD simulation of a 500 $h^{-1} c$Mpc volume with an
on-the-fly spectral cosmic ray (CR) model. This allows us to follow the
evolution of populations of CR electrons and protons within every resolution
element of the simulation. We model CR injection at shocks, while accounting
for adiabatic changes to the CR population and high energy loss processes of
electrons. The synchrotron emission is then calculated from the aged electron
population, using the simulated magnetic field, as well as different models for
origin and amplification of magnetic fields. We use constrained initial
conditions, which closely resemble the local Universe and compare the results
of the cosmological volume to zoom-in simulation of the Coma cluster, to study
the impact of resolution and turbulent re-acceleration of CRs on the results.
Results: We find consistent injection of CRs at accretion shocks onto cosmic
web filaments and galaxy clusters. This leads to diffuse emission from
filaments of the order $S_\nu \approx 0.1 \: \mu$Jy beam$^{-1}$ for a potential
LOFAR observation at 144 MHz, when assuming the most optimistic magnetic field
model and the inclusion of an on-the-fly treatment of re-acceleration of
electrons by turbulence. The flux can be increased by up-to two orders of
magnitude for different choices of CR injection parameters. This can bring the
flux within a factor of 10 of the current limits for direct detection. We find
a spectral index of the simulated synchrotron emission from filaments of
{\alpha} {\approx} 1.0 - 1.5. | Comparisons of the environmental dependence of galaxy properties between
galaxies above and below M: From the Main galaxy sample of the Sloan Digital Sky Survey Data Release 6
(SDSS DR6), we construct two volume-limited samples above and below the value
of M, to explore the difference of the environmental dependence of galaxy
properties between galaxies above and below the value of M . We measure the
local three-dimensional galaxy density in a comoving sphere with a radius of
the distance to the 5th nearest galaxy for each galaxy, and compare basic
properties of galaxies in the lowest density regime with those of galaxies in
the densest regime. It is found that the galaxy luminosity strongly depend on
local environments only for galaxies above M, but this dependence is very weak
for galaxies below M . It is worth noting that g-r color, concentration index
ci and galaxy morphologies strongly depend on local environments for all
galaxies with different luminosities. This shows that M is an characteristic
parameter only for the environmental dependence of galaxy luminosity. |
The effects of baryon physics, black holes and AGN feedback on the mass
distribution in clusters of galaxies: The spatial distribution of matter in clusters of galaxies is mainly
determined by the dominant dark matter component, however, physical processes
involving baryonic matter are able to modify it significantly. We analyse a set
of 500 pc resolution cosmological simulations of a cluster of galaxies with
mass comparable to Virgo, performed with the AMR code RAMSES. We compare the
mass density profiles of the dark, stellar and gaseous matter components of the
cluster that result from different assumptions for the subgrid baryonic physics
and galaxy formation processes. First, the prediction of a gravity only N-body
simulation is compared to that of a hydrodynamical simulation with standard
galaxy formation recipes, then all results are compared to a hydrodynamical
simulation which includes thermal AGN feedback from Super Massive Black Holes
(SMBH). We find the usual effects of overcooling and adiabatic contraction in
the run with standard galaxy formation physics, but very different results are
found when implementing SMBHs and AGN feedback. Star formation is strongly
quenched, producing lower stellar densities throughout the cluster, and much
less cold gas is available for star formation at low redshifts. At redshift z =
0 we find a flat density core of radius 10 kpc in both of the dark and stellar
matter density profiles. We specu- late on the possible formation mechanisms
able to produce such cores and we conclude that they can be produced through
the coupling of different processes: (I) dynamical friction from the decay of
black hole orbits during galaxy mergers; (II) AGN driven gas outflows producing
fluctuations of the gravitational potential causing the removal of
collisionless matter from the central region of the cluster; (III) adiabatic
expansion in response to the slow expulsion of gas from the central region of
the cluster during the quiescent mode of AGN activity. | The Hubble Flow of Plateau Inflation: In the absence of CMB precision measurements, a Taylor expansion has often
been invoked to parametrize the Hubble flow function during inflation. The
standard "horizon flow" procedure implicitly relies on this assumption.
However, the recent Planck results indicate a strong preference for plateau
inflation, which suggests the use of Pad\'e approximants instead. We propose a
novel method that provides analytic solutions of the flow equations for a given
parametrization of the Hubble function. This method is illustrated in the
Taylor and Pad\'e cases, for low order expansions. We then present the results
of a full numerical treatment scanning larger order expansions, and compare
these parametrizations in terms of convergence, prior dependence, predictivity
and compatibility with the data. Finally, we highlight the implications for
potential reconstruction methods. |
CASSOWARY 20: a Wide Separation Einstein Cross Identified with the
X-shooter Spectrograph: We have used spectra obtained with X-shooter, the triple arm optical-infrared
spectrograph recently commissioned on the Very Large Telescope of the European
Southern Observatory, to confirm the gravitational lens nature of the CASSOWARY
candidate CSWA 20. This system consists of a luminous red galaxy at redshift
z(abs) = 0.741, with a very high velocity dispersion sigma(lens) = 500 km/s,
which lenses a blue star-forming galaxy at z(em) = 1.433 into four images with
mean separation of about 6 arcseconds. The source shares many of its properties
with those of UV-selected galaxies z = 2-3: it is forming stars at a rate of 25
solar masses per year, has a metallicity of about 1/4 solar, and shows nebular
emission from two components separated by 0.4 arcseconds in the image plane,
possibly indicating a merger. It appears that foreground interstellar material
within the galaxy has been evacuated from the sight-line along which we observe
the starburst, giving an unextinguished view of its stars and H II regions.
CSWA 20, with its massive lensing galaxy producing a high magnification of an
intrinsically luminous background galaxy, is a promising target for future
studies at a variety of wavelengths. | An emulator-based halo model in modified gravity -- I. The halo
concentration-mass relation and density profile: In this series of papers we present an emulator-based halo model for the
non-linear clustering of galaxies in modified gravity cosmologies. In the first
paper, we present emulators for the following halo properties: the halo mass
function, concentration-mass relation and halo-matter cross-correlation
function. The emulators are trained on data extracted from the \textsc{FORGE}
and \textsc{BRIDGE} suites of $N$-body simulations, respectively for two
modified gravity (MG) theories: $f(R)$ gravity and the DGP model, varying three
standard cosmological parameters $\Omega_{\mathrm{m0}}, H_0, \sigma_8$, and one
MG parameter, either $\bar{f}_{R0}$ or $r_{\mathrm{c}}$. Our halo property
emulators achieve an accuracy of $\lesssim 1\%$ on independent test data sets.
We demonstrate that the emulators can be combined with a galaxy-halo connection
prescription to accurately predict the galaxy-galaxy and galaxy-matter
correlation functions using the halo model framework. |
Influence of electromagnetic fields on the evolution of initially
homogeneous and isotropic universe: Simple exact solutions presented here describe the universes which spatial
geometries are asymptotically homogeneous and isotropic near the initial
singularity, but which evolution goes under the influence of primordial
magnetic fields. In all these "deformed" Friedmann models (spatially flat, open
or closed), the initial magnetic fields are concentrated near some axis of
symmetry and their lines are the circles -- the lines of the azimuthal
coordinate $\varphi$. Caused by the expansion of the universe, the
time-dependence of a magnetic field induces (in accordance with the Faraday
law) the emergence of source-free electric fields. In comparison with the
Friedmann models, the cosmological expansion goes with acceleration in spatial
directions across the magnetic field, and with deceleration along the magnetic
lines, so that in flat and open models, in fluid comoving coordinates, the
lengths of $\varphi$-circles of large enough radius or for late enough times
decrease and vanish for $t\to\infty$. This means that in flat and open models,
we have a partial dynamical closure of space-time at large distances from the
axis, i.e. from the regions where the electromagnetic fields in our solutions
are concentrated. To get simple exact solutions of the Einstein-Maxwell and
perfect fluid equations, we assume for the perfect fluid (which supports the
isotropic and homogeneous "background" Friedmann geometries) rather exotic,
stiff matter equation of state $\varepsilon=p$. However, it seems reasonable to
expect that similar effects might take place in the mutual dynamics of geometry
and strong electromagnetic fields in the universes with more realistic matter
equations of state. | Large-scale dark matter simulations: We review the field of collisionless numerical simulations for the
large-scale structure of the Universe. We start by providing the main set of
equations solved by these simulations and their connection with General
Relativity. We then recap the relevant numerical approaches: discretization of
the phase-space distribution (focusing on N-body but including alternatives,
e.g., Lagrangian submanifold and Schr\"odinger-Poisson) and the respective
techniques for their time evolution and force calculation (Direct summation,
mesh techniques, and hierarchical tree methods). We pay attention to the
creation of initial conditions and the connection with Lagrangian Perturbation
Theory. We then discuss the possible alternatives in terms of the
micro-physical properties of dark matter (e.g., neutralinos, warm dark matter,
QCD axions, Bose-Einstein condensates, and primordial black holes), and
extensions to account for multiple fluids (baryons and neutrinos), primordial
non-Gaussianity and modified gravity. We continue by discussing challenges
involved in achieving highly accurate predictions. A key aspect of cosmological
simulations is the connection to cosmological observables, we discuss various
techniques in this regard: structure finding, galaxy formation and baryonic
modelling, the creation of emulators and light-cones, and the role of machine
learning. We finalise with a recount of state-of-the-art large-scale
simulations and conclude with an outlook for the next decade. |
The Galaxy Population of Abell 1367: The Stellar Mass-Metallicity
Relation: Using wide baseline broad-band photometry, we analyse the stellar population
properties of a sample of 72 galaxies, spanning a wide range of stellar masses
and morphological types, in the nearby spiral-rich and dynamically young galaxy
cluster Abell 1367. The sample galaxies are distributed from the cluster centre
out to approximately half the cluster Abell radius. The optical/near-infrared
colours are compared with simple stellar population synthesis models from which
the luminosity-weighted stellar population ages and metallicities are
determined. The locus of the colours of elliptical galaxies traces a sequence
of varying metallicity at a narrow range of luminosity-weighted stellar ages.
Lenticular galaxies in the red sequence, however, exhibit a substantial spread
of luminosity-weighted stellar metallicities and ages. For red sequence
lenticular galaxies and blue cloud galaxies, low mass galaxies tend to be on
average dominated by stellar populations of younger luminosity-weighted ages.
Sample galaxies exhibit a strong correlation between integrated stellar mass
and luminosity-weighted stellar metallicity. Galaxies with signs of
morphological disturbance and ongoing star formation activity, tend to be
underabundant with respect to passive galaxies in the red sequence of
comparable stellar masses. We argue that this could be due to tidally-driven
gas flows toward the star-forming regions, carrying less enriched gas and
diluting the pre-existing gas to produce younger stellar populations with lower
metallicities than would be obtained prior to the interaction. Finally, we find
no statistically significant evidence for changes in the luminosity-weighted
ages and metallicities for either red sequence or blue cloud galaxies, at fixed
stellar mass, with location within the cluster. | Fe K emission from active galaxies in the COSMOS field: We present a rest-frame spectral stacking analysis of ~1000 X-ray sources
detected in the XMM-COSMOS field in order to investigate the iron K line
properties of active galaxies beyond redshift z~1. In Type I AGN that have a
typical X-ray luminosity of Lx~1.5e44 erg/s and z~1.6, the cold Fe K at 6.4 keV
is weak (EW~0.05keV), in agreement with the known trend. In contrast,
high-ionization lines of Fe XXV and Fe XXVI are pronounced. These
high-ionization Fe K lines appear to have a connection with high accretion
rates. While no broad Fe emission is detected in the total spectrum, it might
be present, albeit at low significance, when the X-ray luminosity is restricted
to the range below 3e44 erg/s, or when an intermediate range of Eddington ratio
around 0.1 is selected. In Type II AGN, both cold and high-ionzation lines
become weak with increasing X-ray luminosity. However, strong high-ionization
Fe K (EW~0.3 keV) is detected in the spectrum of objects at z>2, while no 6.4
keV line is found. It is then found that the primary source of the
high-ionization Fe K emission is those objects detected with Spitzer-MIPS at 24
micron. Given their median redshift of z=2.5, their bolometric luminosity is
likely to reach 10^13 Lsun and the MIPS-detected emission most likely
originates from hot dust heated by embedded AGN, probably accreting at high
Eddington ratio. These properties match those of rapidly growing black holes in
ultra-luminous infrared galaxies at the interesting epoch (z=2-3) of galaxy
formation. |
Core Gas Sloshing in Abell 1644: We present an analysis of a 72 ks Chandra observation of the double cluster
Abell 1644 (z=0.047). The X-ray temperatures indicate the masses are
M500=2.6+/-0.4 x10^{14} h^{-1} M_sun for the northern subcluster and
M500=3.1+/-0.4 x10^{14} h^{-1} M_sun for the southern, main cluster. We
identify a sharp edge in the radial X-ray surface brightness of the main
cluster, which we find to be a cold front, with a jump in temperature of a
factor of ~3. This edge possesses a spiral morphology characteristic of core
gas sloshing around the cluster potential minimum. We present observational
evidence, supported by hydrodynamic simulations, that the northern subcluster
is the object which initiated the core gas sloshing in the main cluster at
least 700 Myr ago. We discuss reheating of the main cluster's core gas via two
mechanisms brought about by the sloshing gas: first, the release of
gravitational potential energy gained by the core's displacement from the
potential minimum, and second, a dredging inwards of the outer, higher entropy
cluster gas along finger-shaped streams. We find the available gravitational
potential energy is small compared to the energy released by the cooling gas in
the core. | On the phenomenology of extended Brans-Dicke Gravity: We introduce a designer approach for extended Brans-Dicke gravity that allows
us to obtain the evolution of the scalar field by fixing the Hubble parameter
to that of a $w$CDM model. We obtain analytical approximations for $\phi$ as a
function of the scale factor and use these to build expressions for the
effective Newton's constant at the background and at the linear level and the
slip between the perturbed Newtonian potentials. By doing so, we are able to
explore their dependence on the fundamental parameters of the theory. |
Magnetic Fields of Agns and Standard Accretion Disk Model: Testing by
Optical Polarimetry: We have developed the method that allows us to estimate the magnetic field
strength at the horizon of a supermassive black hole (SMBH) through the
observed polarization of optical emission of the accreting disk surrounding
SMBH. The known asymptotic formulae for the Stokes parameters of outgoing
radiation are azimuthal averaged, which corresponds to an observation of the
disk as a whole. We consider two models of the embedding 3D-magnetic field, the
regular field, and the regular field with an additional chaotic (turbulent)
component. It is shown that the second model is preferable for estimating the
magnetic field in NGC 4258. For estimations we used the standard accretion disk
model assuming that the same power-law dependence of the magnetic field follows
from the range of the optical emission down to the horizon. The observed
optical polarization from NGC 4258 allowed us to find the values 10^3 - 10^4
Gauss at the horizon, depending on the particular choice of the model
parameters. We also discuss the wavelength dependencies of the light
polarization, and possibly applying them for a more realistic choice of
accretion disk parameters. | The extended ionized gas around the z=2.44 radio galaxy MRC 0406-244:
the nature of the superbubbles and the optical line brightness asymmetries: In this letter, we investigate the nature of the dramatic `super-bubble'
emission structures associated with the z=2.44 radio galaxy MRC 0406-244, using
rest-frame optical spectroscopy and an archival HST NICMOS image. Based on the
optical line ratios and the HST morphology, we conclude that the gas in the
superbubbles is photoionized by the obscured active nucleus. We suggest that
this type of structure might be related to the spatially extended HI absorbers
that are detected in front of many high-z radio galaxies. We also suggest that
we may be witnessing the destruction of the extended emission line region. In
addition, we investigate the nature of the emission line brightness asymmetry
in MRC 0406-244: we conclude that this asymmetry is due to an asymmetry in the
mass of ionized gas, confirming the scenario of McCarthy, van Breugel & Kapahi,
and leading us to reject that of Gopal-Krishna & Wiita. |
Dark Matter Primordial Black Holes and Inflation Models: A broad range of single field models of inflation are analyzed in light of
all relevant recent cosmological data, checking whether they can lead to the
formation of long--lived Primordial Black Holes (PBHs) as candidate for dark
matter. To that end we calculate the spectral index of the power spectrum of
primordial perturbations as well as its first and second derivatives. PBH
formation is possible only if the spectral index $n_S(k_0)$ increases
significantly at small scales. Since current data indicate that the first
derivative $\alpha_S$ of the spectral index is negative at the pivot scale, PBH
formation is only possible in the presence of a sizable and positive second
derivative ("running of the running") $\beta_S$. Among the three small-field
and five large-field models we analyze, only the "running-mass" model allows
PBH formation, for a narrow range of parameters. | Raising the bar: new constraints on the Hubble parameter with cosmic
chronometers at z$\sim$2: One of the most compelling tasks of modern cosmology is to constrain the
expansion history of the Universe, since this measurement can give insights on
the nature of dark energy and help to estimate cosmological parameters. In this
letter are presented two new measurements of the Hubble parameter H(z) obtained
with the cosmic chronometer method up to $z\sim2$. Taking advantage of
near-infrared spectroscopy of the few very massive and passive galaxies
observed at $z>1.4$ available in literature, the differential evolution of this
population is estimated and calibrated with different stellar population
synthesis models to constrain H(z), including in the final error budget all
possible sources of systematic uncertainties (star formation history, stellar
metallicity, model dependencies). This analysis is able to extend significantly
the redshift range coverage with respect to present-day constraints, crossing
for the first time the limit at $z\sim1.75$. The new H(z) data are used to
estimate the gain in accuracy on cosmological parameters with respect to
previous measurements in two cosmological models, finding a small but
detectable improvement ($\sim$5 %) in particular on $\Omega_{M}$ and $w_{0}$.
Finally, a simulation of a Euclid-like survey has been performed to forecast
the expected improvement with future data. The provided constraints have been
obtained just with the cosmic chronometers approach, without any additional
data, and the results show the high potentiality of this method to constrain
the expansion history of the Universe at these redshifts. |
New Light in Star-Forming Dwarf Galaxies: The PMAS Integral Field View
of the Blue Compact Dwarf Galaxy Mrk 409: We present an integral field spectroscopic study of the central 2x2 kpc^2 of
the blue compact dwarf galaxy Mrk 409, observed with the Potsdam MultiAperture
Spectrophotometer. This study focuses on the morphology, two-dimensional
chemical abundance pattern, excitation properties and kinematics of the ionized
interstellar medium in the starburst component. We also investigate the nature
of the extended ring of ionized gas emission surrounding the bright nuclear
starburst region of Mrk 409. PMAS spectra of selected regions along the ring,
interpreted with evolutionary and population synthesis models, indicate that
their ionized emission is mainly due to a young stellar population with a total
mass of ~1.5x10^6 M_sun, which started forming almost coevally ~10 Myr ago.
This stellar component is likely confined to the collisional interface of a
spherically expanding, starburst-driven super-bubble with denser, swept-up
ambient gas, ~600 pc away from the central starburst nucleus. The spectroscopic
properties of the latter imply a large extinction (C_H-beta>0.9), and the
presence of an additional non-thermal ionization source, most likely a
low-luminosity Active Galactic Nucleus. Mrk 409 shows a relatively large oxygen
abundance (12+log(O/H)~8.4) and no chemical abundance gradients out to R~600
pc. The ionized gas kinematics displays an overall regular rotation on a
northwest-southwest axis, with a maximum velocity of 60 km/s; the total mass
inside the star-forming ring is about 1.4x10^9 M_sun. | Gauged Quintessence: Despite its dominance in the present universe's energy budget, dark energy is
the least understood component in the universe. Although there is a popular
model for the dynamical dark energy, the quintessence scalar, the investigation
is limited because of its highly elusive character. We present a model where
the quintessence is gauged by an Abelian gauge symmetry. The quintessence is
promoted to be a complex scalar whose real part is the dark energy field while
the imaginary part is the longitudinal component of a new gauge boson. It
brings interesting characters to dark energy physics. We study the general
features of the model, including how the quintessence behavior is affected and
how the solicited dark energy properties constrain its gauge interaction. We
also note that while the uncoupled quintessence models are suffered greatly
from the Hubble tension, it can be alleviated if the quintessence is under the
gauge symmetry. |
Estimating turbulent velocities in the elliptical galaxies NGC 5044 and
NGC 5813: The interstellar and intra-cluster medium in giant elliptical galaxies and
clusters of galaxies is often assumed to be in hydrostatic equilibrium.
Numerical simulations, however, show that about 5-30% of the pressure in a
cluster is provided by turbulence induced by, for example, the central AGN and
merger activity. We aim to put constraints on the turbulent velocities and
turbulent pressure in the ICM of the giant elliptical galaxies NGC 5044 and NGC
5813 using XMM-Newton RGS observations. The magnitude of the turbulence is
estimated using the Fe XVII lines at 15.01 A, 17.05 A, and 17.10 A in the RGS
spectra. At low turbulent velocities, the gas becomes optically thick in the
15.01 A line due to resonant scattering, while the 17 A lines remain optically
thin. By comparing the (I(17.05)+I(17.10))/I(15.01) line ratio from RGS with
simulated line ratios for different Mach numbers, the level of turbulence is
constrained. The measurement is limited by systematic uncertainties in the
atomic data, which are at the 20-30% level. We find that the line ratio in NGC
5813 is significantly higher than in NGC 5044. This difference can be explained
by a higher level of turbulence in NGC 5044. The high turbulent velocities and
the fraction of the turbulent pressure support of >40% in NGC 5044, assuming
isotropic turbulence, confirm that it is a highly disturbed system, probably
due to an off-axis merger. The turbulent pressure support in NGC 5813 is more
modest at 15-45%. The (I(17.05)+I(17.10))/I(15.01) line ratio in an optically
thin plasma, calculated using AtomDB v2.0.1, is 2 sigma above the ratio
measured in NGC 5044, which cannot be explained by resonant scattering. This
shows that the discrepancies between theoretical, laboratory, and astrophysical
data on Fe XVII lines need to be reduced to improve the accuracy of the
determination of turbulent velocities using resonant scattering. | The Observational Future of Cosmological Scalar-Tensor Theories: The next generation of surveys will greatly improve our knowledge of
cosmological gravity. In this paper we focus on how Stage IV photometric
redshift surveys, including weak lensing and multiple tracers of the matter
distribution and radio experiments combined with measurements of the cosmic
microwave background will lead to precision constraints on deviations from
General Relativity. We use a broad subclass of Horndeski scalar-tensor theories
to forecast the accuracy with which we will be able to determine these
deviations and their degeneracies with other cosmological parameters. Our
analysis includes relativistic effects, does not rely on the quasi-static
evolution and makes conservative assumptions about the effect of screening on
small scales. We define a figure of merit for cosmological tests of gravity and
show how the combination of different types of surveys, probing different
length scales and redshifts, can be used to pin down constraints on the
gravitational physics to better than a few percent, roughly an order of
magnitude better than present probes. Future cosmological experiments will be
able to constrain the Brans-Dicke parameter at a level comparable to Solar
System and astrophysical tests |
On the origins of CMB anomalies and testing a new theory of inflationary
quantum fluctuations: In this paper, we present compelling evidence suggesting a statistical
violation of parity symmetry (a discrete symmetry that is separate from
isotropy) in the Cosmic Microwave Background (CMB) map, measured through
two-point temperature correlations. This parity asymmetric CMB challenges our
understanding of the quantum physics of the early Universe rather than LCDM
($\Lambda$ Cold-Dark-Matter). We commence by conducting a comprehensive
analysis of the Planck CMB, focusing on the distribution of power in
low-multipoles and temperature anticorrelations at parity conjugate points in
position space. We find tension with the near scale-invariant power-law power
spectrum of Standard Inflation (SI), with p-values of the order
$\mathcal{O}\left( 10^{-4}-10^{-3} \right)$. Subsequently, we explore the
recently proposed direct-sum inflation (DSI), where a quantum fluctuation
arises as a direct-sum of two components evolving forward and backward in time
at parity conjugate points in physical space. We found that DSI is consistent
with data on parity asymmetry, the absence of power at $\theta>60^{\circ}$, and
power suppression at low-even-multipoles which are major data anomalies in the
SI. Furthermore, we discover that the parameters characterizing the
hemispherical power asymmetry anomaly become statistically insignificant when
the large SI quadrupole amplitude is reduced to align with the data. DSI
explains this low quadrupole with a p-value of $3.5\%$, 39 times higher than
SI. Combining statistics from parameters measuring parity and low-$\ell$
angular power spectrum, we find that DSI is 50-650 times more probable than SI.
In summary, our investigation suggests that CMB temperature fluctuations
exhibit homogeneity and isotropy but parity-violating consistent with
predictions of DSI. This observation provides tantalizing evidence for the
quantum mechanical nature of gravity. | Halo velocity profiles in screened modified gravity theories: Screened modified gravity predicts potentially large signatures in the
peculiar velocity field that makes it an interesting probe to test gravity on
cosmological scales. We investigate the signatures induced by the Symmetron and
a Chameleon $f(R)$ model in the peculiar velocity field using $N$-body
simulations. By studying fifth force and halo velocity profiles we identify
three general categories of effects found in screened modified gravity models:
a fully screened regime where we recover $\Lambda$CDM to high precision, an
unscreened regime where the fifth force is in full operation, and, a partially
screened regime where screening occurs in the inner part of a halo, but the
fifth force is active at larger radii. These three regimes can be pointed out
very clearly by analyzing the deviation in the maximum cluster velocity.
Observationally, the partially screened regime is of particular interest since
an uniform increase of the gravitational force - as present in the unscreened
regime - is degenerate with the (dynamical) halo mass estimate, and, thus, hard
to detect. |
Bifurcation and Global Dynamical Behavior of the $f(T)$ Theory: Usually, in order to investigate the evolution of a theory, one may find the
critical points of the system and then perform perturbations around these
critical points to see whether they are stable or not. This local method is
very useful when the initial values of the dynamical variables are not far away
from the critical points. Essentially, the nonlinear effects are totally
neglected in such kind of approach. Therefore, one can not tell whether the
dynamical system will evolute to the stable critical points or not when the
initial values of the variables do not close enough to these critical points.
Furthermore, when there are two or more stable critical points in the system,
local analysis can not provide the informations that which one the system will
finally evolute to. In this paper, we have further developed the nullcline
method to study the bifurcation phenomenon and global dynamical behaviour of
the $f(T)$ theory. We overcome the shortcoming of local analysis. And it is
very clear to see the evolution of the system under any initial conditions. | How Gravitational-wave Observations Can Shape the Gamma-ray Burst
Paradigm: By reaching through shrouding blastwaves, efficiently discovering off-axis
events, and probing the central engine at work, gravitational wave (GW)
observations will soon revolutionize the study of gamma-ray bursts. Already,
analyses of GW data targeting gamma-ray bursts have helped constrain the
central engines of selected events. Advanced GW detectors with significantly
improved sensitivities are under construction. After outlining the GW emission
mechanisms from gamma-ray burst progenitors (binary coalescences, stellar core
collapses, magnetars, and others) that may be detectable with advanced
detectors, we review how GWs will improve our understanding of gamma-ray burst
central engines, their astrophysical formation channels, and the prospects and
methods for different search strategies. We place special emphasis on
multimessenger searches. To achieve the most scientific benefit, GW,
electromagnetic, and neutrino observations should be combined to provide
greater discriminating power and science reach. |
On estimating cosmology-dependent covariance matrices: We describe a statistical model to estimate the covariance matrix of matter
tracer two-point correlation functions with cosmological simulations. Assuming
a fixed number of cosmological simulation runs, we describe how to build a
`statistical emulator' of the two-point function covariance over a specified
range of input cosmological parameters. Because the simulation runs with
different cosmological models help to constrain the form of the covariance, we
predict that the cosmology-dependent covariance may be estimated with a
comparable number of simulations as would be needed to estimate the covariance
for fixed cosmology. Our framework is a necessary first step in planning a
simulations campaign for analyzing the next generation of cosmological surveys. | A multi-wavelength view of cooling vs. AGN heating in the X-ray luminous
cool-core of Abell 3581: We report the results of a multi-wavelength study of the nearby galaxy group,
Abell 3581 (z=0.0218). This system hosts the most luminous cool core of any
nearby group and exhibits active radio mode feedback from the super-massive
black hole in its brightest group galaxy, IC 4374. The brightest galaxy has
suffered multiple active galactic nucleus outbursts, blowing bubbles into the
surrounding hot gas, which have resulted in the uplift of cool ionised gas into
the surrounding hot intragroup medium. High velocities, indicative of an
outflow, are observed close to the nucleus and coincident with the radio jet.
Thin dusty filaments accompany the uplifted, ionised gas. No extended star
formation is observed, however, a young cluster is detected just north of the
nucleus. The direction of rise of the bubbles has changed between outbursts.
This directional change is likely due to sloshing motions of the intragroup
medium. These sloshing motions also appear to be actively stripping the X-ray
cool core, as indicated by a spiraling cold front of high metallicity, low
temperature, low entropy gas. |
A deep view on the Virgo cluster core: In this study we investigate the optical photometric properties of early-type
galaxies in the Virgo cluster core region, by analysing their location on the
colour magnitude relation (CMR) and the structural scaling relations down to
faint magnitudes, and by constructing the luminosity function to compare it
with theoretical expectations. We visually select potential cluster members
based on morphology and angular size, excluding spiral galaxies. A photometric
analysis has been carried out for 295 galaxies, using surface brightness
profile shape and colour as further criteria to identify probable background
contaminants. 216 galaxies are considered to be certain or probable Virgo
cluster members. Our study reveals 77 galaxies not catalogued in the VCC (with
13 of them already found in previous studies) that are very likely Virgo
cluster members because they follow the Virgo CMR and exhibit low Sersic
indices. Those galaxies reach -8.7 mag in V band. The CMR shows a clear change
in slope from dEs to dSphs, while the scatter of the CMR in the dSph regime
does not increase significantly. Our sample might, however, be somewhat biased
towards redder colours. The scaling relations given by the dEs appear to be
continued by the dSphs indicating a similar origin. The observed change in the
CMR slope may mark the point at which gas loss prevented significant metal
enrichment. The almost constant scatter around the CMR possibly indicates a
short formation period, resulting in similar stellar populations. The
luminosity function shows a Schechter function's faint end slope of
-1.50\pm0.17, implying a lack of galaxies related to the expected number of
low-mass dark matter haloes from theoretical models. Our findings could be
explained by suppressed star formation in low-mass dark matter halos or by
tidal disruption of dwarfs in the dense core region of the cluster. | An accurate determination of the Hubble constant from Baryon Acoustic
Oscillation datasets: Even though the Hubble constant cannot be significantly determined by the
low-redshift Baryon Acoustic Oscillation (BAO) data alone, it can be tightly
constrained once the high-redshift BAO data are combined. Combining BAO data
from 6dFGS, BOSS DR11 clustering of galaxies, WiggleZ and $z=2.34$ from BOSS
DR11 quasar Lyman-$\alpha$ forest lines, we get $H_0=68.17^{+1.55}_{-1.56}$ km
s$^{-1}$ Mpc$^{-1}$. In addition, adopting the the simultaneous measurements of
$H(z)$ and $D_A(z)$ from the two-dimensional two-point correlation function
from BOSS DR9 CMASS sample and two-dimensional matter power spectrum from SDSS
DR7 sample, we obtain $H_0=68.11\pm1.69$ km s$^{-1}$ Mpc$^{-1}$. Finally,
combining all of the BAO datasets, we conclude $H_0=68.11\pm 0.86$ km s$^{-1}$
Mpc$^{-1}$, a 1.3% determination. |
Neutrino Mass Priors for Cosmology from Random Matrices: Cosmological measurements of structure are placing increasingly strong
constraints on the sum of the neutrino masses, $\Sigma m_\nu$, through Bayesian
inference. Because these constraints depend on the choice for the prior
probability $\pi(\Sigma m_\nu)$, we argue that this prior should be motivated
by fundamental physical principles rather than the ad hoc choices that are
common in the literature. The first step in this direction is to specify the
prior directly at the level of the neutrino mass matrix $M_\nu$, since this is
the parameter appearing in the Lagrangian of the particle physics theory. Thus
by specifying a probability distribution over $M_\nu$, and by including the
known squared mass splittings, we predict a theoretical probability
distribution over $\Sigma m_\nu$ that we interpret as a Bayesian prior
probability $\pi(\Sigma m_\nu)$. We find that $\pi(\Sigma m_\nu)$ peaks close
to the smallest $\Sigma m_\nu$ allowed by the measured mass splittings, roughly
$0.06 \, {\rm eV}$ ($0.1 \, {\rm eV}$) for normal (inverted) ordering, due to
the phenomenon of eigenvalue repulsion in random matrices. We consider three
models for neutrino mass generation: Dirac, Majorana, and Majorana via the
seesaw mechanism; differences in the predicted priors $\pi(\Sigma m_\nu)$ allow
for the possibility of having indications about the physical origin of neutrino
masses once sufficient experimental sensitivity is achieved. We present fitting
functions for $\pi(\Sigma m_\nu)$, which provide a simple means for applying
these priors to cosmological constraints on the neutrino masses or
marginalizing over their impact on other cosmological parameters. | Measurements of CO redshifts with Z-Spec for lensed submillimeter
galaxies discovered in the H-ATLAS survey: We present new observations from Z-Spec, a broadband 185-305 GHz
spectrometer, of five sub-millimeter bright lensed sources selected from the
Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) science
demonstration phase (SDP) catalog. We construct a redshift finding algorithm
using combinations of the signal-to-noise of all the lines falling in the
Z-Spec bandpass to determine redshifts with high confidence, even in cases
where the signal-to-noise in individual lines is low. We measure the dust
continuum in all sources and secure CO redshifts for four out of five
(z~1.5-3). In one source, SDP.17, we tentatively identify two independent
redshifts and a water line, confirmed at z=2.308. Our sources have properties
characteristic of dusty starburst galaxies, with magnification-corrected star
formation rates of 10^(2-3) M_sun/yr. Lower limits for the dust masses (~a few
10^8 M_sun) and spatial extents (~1 kpc equivalent radius) are derived from the
continuum spectral energy distributions, corresponding to dust temperatures
between 54 and 69K. In the LTE approximation, we derive relatively low CO
excitation temperatures (< 100 K) and optical depths (tau<1). Performing a
non-LTE excitation analysis using RADEX, we find that the CO lines measured by
Z-Spec (from J=4->3 to 10->9, depending on the galaxy) localize the best
solutions to either a high-temperature / low-density region, or a
low-temperature / high-density region near the LTE solution, with the optical
depth varying accordingly. Observations of additional CO lines, CO(1-0) in
particular, are needed to constrain the non-LTE models. |
Extracting the Signal of Cosmic String Wakes from 21-cm Observations: A cosmic string wake produces a distinct non-Gaussian signal in 21-cm
intensity maps at redshifts above that of reionization. While the string signal
is (locally) larger in amplitude than the signal of the Gaussian fluctuations
of the $\Lambda$CDM model, they are overwhelmed (even locally in position
space) by astrophysical and instrumental foregrounds. Here, we study to what
extent the signal can be extracted from noisy interferometric data. The
narrowness of the string-induced feature in redshift direction allows for a
subtraction of astrophysical and instrumental foregrounds. Based on the
specific geometry of the string signal we identify a particular three-point
statistic which is promising in order to extract the signal, and we find that,
having in mind a telescope of specifications similar to that of the MWA
instrument, the string signal can be successfully extracted for a value of the
string tension of $G\mu = 3 \times 10^{-7}$. Prospects for further improvements
of the analysis are discussed. | Probing BH mass and accretion through X-ray variability in the CDFS: Recent work on nearby AGNs has shown that X-ray variability is correlated
with the mass and accretion rate onto the central SMBH. Here we present the
application of the variability-luminosity relation to high redshift AGNs in the
CDFS, making use of XMM-Newton observations. We use Monte Carlo simulations in
order to properly account for bias and uncertainties introduced by the sparse
sampling and the very low statistics. Our preliminary results indicate that BH
masses span over the range from 10^5 to 10^9 solar mass while accretion rates
range from 10^-3 up to values greater than 1, in unit of Eddington accretion
rate. |
Metal distributions out to 0.5 r180 in the intracluster medium of four
galaxy groups observed with Suzaku: We studied the distributions of metal abundances and metal-mass-to-light
ratios in the intracluster medium (ICM) of four galaxy groups, MKW 4, HCG 62,
the NGC 1550 group, and the NGC 5044 group, out to 0.5 r180 observed with
Suzaku. The Fe abundance decreases with radius, and about 0.2-0.4 solar beyond
0.1 r180. At a given radius in units of r180, the Fe abundance in the ICM of
the four galaxy groups were consistent or smaller than those of clusters of
galaxies. The Mg/Fe and Si/Fe ratios in the ICM are nearly constant at the
solar ratio out to 0.5 r180. We also studied systematic uncertainties in the
derived metal abundances comparing the results from two versions of atomic data
for astrophysicists (ATOMDB) and single- and two temperature model fits. Since
the metals have been synthesized in galaxies, we collected K-band luminosities
of galaxies from Two Micron All Sky Survey catalogue (2MASS) and calculated the
integrated iron-mass-to-light-ratios (IMLR), or the ratios of the iron mass in
the ICM to light from stars in galaxies. The groups with smaller gas mass to
light ratios have smaller IMLR values and the IMLR inversely correlated with
the entropy excess. Based on these abundance features, we discussed the past
history of metal enrichment process in groups of galaxies. | Thermal Fluctuations of Dark Matter in Bouncing Cosmology: We investigate the statistical nature of the dark matter particles produced
in bouncing cosmology, especially, the evolution of its thermal fluctuations.
By explicitly deriving and solving the equation of motion of super-horizon
mode, we fully determine the evolution of thermal perturbation of dark matter
in a generic bouncing background. And we also show that the evolution of
super-horizon modes is stable and will not ruin the background evolution of a
generic bouncing universe till the Planck scale. Given no super-horizon thermal
perturbation of dark matter appears in standard inflation scenario such as
WIMP(-less) miracles, such super-horizon thermal perturbation of dark matter
generated during the generic bouncing universe scenario may be significant for
testing and distinguishing these two scenario in near future. |
Gamma ray burst distances and the timescape cosmology: Gamma ray bursts can potentially be used as distance indicators, providing
the possibility of extending the Hubble diagram to redshifts ~7. Here we follow
the analysis of Schaefer (2007), with the aim of distinguishing the timescape
cosmological model from the \LambdaCDM model by means of the additional
leverage provided by GRBs in the range 2 < z < 7. We find that the timescape
model fits the GRB sample slightly better than the \LambdaCDM model, but that
the systematic uncertainties are still too little understood to distinguish the
models. | Holes in the static Einstein universe and the model of the cosmological
voids: Spherically symmetric, static model of the cosmological voids is constructed
in the framework of the Tolman-Oppenheimer-Volkov equation with the
cosmological constant. Extension of the Tooper result (dimensionless form of
the TOV equation) is provided for non-zero $\Lambda$. Then, the equation is
simplified in $\alpha \to 0$, $\lambda \to 0$, $\lambda/\alpha = const$ regime,
suitable for largest structures in $\Lambda$-dominated universe. Voids are
treated as an underdensity regions in the static Einstein universe. Both
overdensity and underdensity (relative to static universe) solutions exist.
They are identified with standard astrophysical spherical objects and voids,
respectively. Model is tested against observed properties (the radius - the
central density relation) and density profiles of voids. Analytical formulae
for radial density contrast profile and radii of the voids are derived. Some
consequences for cosmological n-body simulations are suggested. Hints on the
dark matter/dark energy EOS filling the voids are provided. |
Spherical collapse model with shear and angular momentum in dark energy
cosmologies: We study, for the first time, how shear and angular momentum modify typical
parameters of the spherical collapse model, in dark energy dominated universes.
In particular, we study the linear density threshold for collapse
$\delta_\mathrm{c}$ and the virial overdensity $\Delta_\mathrm{V}$, for several
dark-energy models and its influence on the cumulative mass function. The
equations of the spherical collapse are those obtained in Pace et al. (2010),
who used the fully nonlinear differential equation for the evolution of the
density contrast derived from Newtonian hydrodynamics, and assumed that dark
energy is present only at the background level. With the introduction of the
shear and rotation terms, the parameters of the spherical collapse model are
now mass-dependant. The results of the paper show, as expected, that the new
terms considered in the spherical collapse model oppose the collapse of
perturbations on galactic scale giving rise to higher values of the linear
overdensity parameter with respect to the non-rotating case. We find a similar
effect also for the virial overdensity parameter. For what concerns the mass
function, we find that its high mass tail is suppressed, while the low mass
tail is slightly affected except in some cases, e.g. the Chaplygin gas case. | Discovery of a large number of candidate proto-clusters traced by ~15
Mpc-scale galaxy overdensities in COSMOS: To demonstrate the feasibility of studying the epoch of massive galaxy
cluster formation in a more systematic manner using current and future galaxy
surveys, we report the discovery of a large sample of proto-cluster candidates
in the 1.62 deg^2 COSMOS/UltraVISTA field traced by optical/IR selected
galaxies using photometric redshifts. By comparing properly smoothed 3D galaxy
density maps of the observations and a set of matched simulations incorporating
the dominant observational effects (galaxy selection and photometric redshift
uncertainties), we first confirm that the observed ~15 comoving Mpc scale
galaxy clustering is consistent with LCDM models. Using further the relation
between high-z overdensity and the present day cluster mass calibrated in these
matched simulations, we found 36 candidate structures at 1.6<z<3.1, showing
overdensities consistent with the progenitors of M_z=0 ~10^15 M_sun clusters.
Taking into account the significant upward scattering of lower mass structures,
the probabilities for the candidates to have at least M_z=0 ~10^14 M_sun are
~70%. For each structure, about 15%-40% of photometric galaxy candidates are
expected to be true proto-cluster members that will merge into a cluster-scale
halo by z=0. With solely photometric redshifts, we successfully rediscover two
spectroscopically confirmed structures in this field, suggesting that our
algorithm is robust. This work generates a large sample of uniformly-selected
proto-cluster candidates, providing rich targets for spectroscopic follow-up
and subsequent studies of cluster formation. Meanwhile, it demonstrates the
potential for probing early cluster formation with upcoming redshift surveys
such as the Hobby-Eberly Telescope Dark Energy Experiment and the Subaru Prime
Focus Spectrograph survey. |
The Greater Impact of Mergers on the Growth of Massive Galaxies:
Implications for Mass Assembly and Evolution Since z~1: Using deep infrared observations conducted with the MOIRCS on the Subaru
Telescope in GOODS-N combined with public surveys in GOODS-S, we investigate
the dependence on stellar mass, M_*, and galaxy type of the close pair fraction
(5 kpc < r < 20 kpc) and implied merger rate. In common with some recent
studies we find that the fraction of paired systems that could result in major
mergers is low (~4%) and does not increase significantly with redshift to
z~1.2, with (1+z)^{1.6 \pm 1.6}. Our key finding is that massive galaxies with
M_* > 1E11 Msun are more likely to host merging companions than less massive
systems (M_* ~ 1E10 Msun). We find evidence for a higher pair fraction for red,
spheroidal hosts compared to blue, late-type systems, in line with expectations
based on clustering at small scales. So-called "dry" mergers between early-type
galaxies represent nearly 50% of close pairs with M_* > 3E10 Msun at z~0.5, but
less than 30% at z~1. This result can be explained by the increasing abundance
of red, early-type galaxies at these masses. We compare the volumetric merger
rate of galaxies with different masses to mass-dependent trends in galaxy
evolution, finding that major mergers cannot fully account for the formation of
spheroidal galaxies since z~1. In terms of mass assembly, major mergers
contribute little to galaxy growth below M_* ~ 3E10 Msun but are more
significant among galaxies with M_* > 1E11 Msun, 30% of which have undergone
mostly dry mergers over the observed redshift range. Overall, the relatively
more rapid coalescence of high mass galaxies mirrors the expected hierarchical
growth of halos and is consistent with recent model predictions, even if the
downsizing of star formation and morphological evolution involves additional
physical processes. | Parameter inference with estimated covariance matrices: When inferring parameters from a Gaussian-distributed data set by computing a
likelihood, a covariance matrix is needed that describes the data errors and
their correlations. If the covariance matrix is not known a priori, it may be
estimated and thereby becomes a random object with some intrinsic uncertainty
itself. We show how to infer parameters in the presence of such an estimated
covariance matrix, by marginalising over the true covariance matrix,
conditioned on its estimated value. This leads to a likelihood function that is
no longer Gaussian, but rather an adapted version of a multivariate
t-distribution, which has the same numerical complexity as the multivariate
Gaussian. As expected, marginalisation over the true covariance matrix improves
inference when compared with Hartlap et al.'s method, which uses an unbiased
estimate of the inverse covariance matrix but still assumes that the likelihood
is Gaussian. |
Probing cosmic opacity at high redshifts with gamma-ray bursts: Probing the evolution of the universe at high redshifts with standard candles
is a powerful way to discriminate dark energy models, where an open question
nowadays is whether this component is constant or evolves with time. One
possible source of ambiguity in this kind of analyses comes from cosmic
opacity, which can mimick a dark enery behaviour. However, most tests of cosmic
opacity have been restricted to the redshift range $z<2$. In this work, by
using luminosity distances of gamma-ray bursts (GRBs), {given the validity of
the Amati relation}, and the latest $H(z)$ data we determine constraints on the
cosmic opacity at high redshifts ($z>2$) for a flat $\Lambda$CDM model. A
possible degenerescence of the results with the adopted cosmological model is
also investigated by considering a flat XCDM model. The limits on cosmic
opacity in the redshift range $0<z<2$ are updated with type Ia supernovae (SNe
Ia) from the Union2.1 sample, where we added the most distant ($z=1.713$)
spectroscopically confirmed SNe Ia. From the analyses performed, we find that
both SNe Ia and GRBs samples are compatible with a transparent universe at
$1\sigma$ level and the results are independent of the dark energy equation of
state parameter $w$. | Priors on the effective Dark Energy equation of state in scalar-tensor
theories: Constraining the Dark Energy (DE) equation of state, w, is one of the primary
science goals of ongoing and future cosmological surveys. In practice, with
imperfect data and incomplete redshift coverage, this requires making
assumptions about the evolution of w with redshift z. These assumptions can be
manifested in a choice of a specific parametric form, which can potentially
bias the outcome, or else one can reconstruct w(z) non-parametrically, by
specifying a prior covariance matrix that correlates values of w at different
redshifts. In this work, we derive the theoretical prior covariance for the
effective DE equation of state predicted by general scalar-tensor theories with
second order equations of motion (Horndeski theories). This is achieved by
generating a large ensemble of possible scalar-tensor theories using a Monte
Carlo methodology, including the application of physical viability conditions.
We also separately consider the special sub-case of the minimally coupled
scalar field, or quintessence. The prior shows a preference for tracking
behaviors in the most general case. Given the covariance matrix, theoretical
priors on parameters of any specific parametrization of w(z) can also be
readily derived by projection. |
Detection and analysis of cluster-cluster filaments: In this work, we identify and analyse the properties of cluster-cluster
filaments within a cosmological simulation assuming that they are structures
connecting maxima of the density field defined by dark matter halos with masses
$M \, \ge 10^{14}\, h^{-1} \mathrm{M_{\odot}}$. To extract these filaments we
develop an identification algorithm based on two standard tools: the Minimal
Spanning Tree (MST) and the Friends of Friends (FoF) algorithm. Focusing our
analysis on the densest dark matter filaments, we found that the radial density
profile, at scales around $1\, h^{-1} \mathrm{Mpc}$, approximately follow a
power-law function with index -2. Without making any assumption about the
velocity field, our algorithm finds that the saddle point arises as a natural
characteristic of the filamentary structure. In addition, its location along
the filament depends on the masses of the halos at the filament ends. We also
found that the infall velocities follow a cross-pattern near the saddle point,
being perpendicular to the filament spine when approaching from low-density
regions, and parallel away from the saddle point towards the ends of the
filament. Following theoretical prescriptions, we estimate the linear density
from the transverse velocity dispersion, finding a good correspondence with the
measured mass per unit length of our filaments. Our results can be applied to
observational samples of filaments in order to link the saddle point location
and the mass per unit length with measurements obtained from observations such
as cluster masses and the velocity dispersion of galaxies. | Inflation Story: slow-roll and beyond: We present constraints on inflationary dynamics and features in the
primordial power spectrum of scalar perturbations using the Cosmic Microwave
Background temperature, polarization data from Planck 2018 data release and
updated likelihoods. We constrain the slow-roll dynamics using Hilltop Quartic
Potential and Starobinsky $R+R^2$ model in the Einstein frame using the Planck
2018 binned Plik likelihood. Using the Hilltop as base potential we construct
Whipped Inflation potential to introduce suppression in the scalar power
spectrum at large angular scales. We notice marginal (68% C.L.) preference of
suppression from the large scale temperature angular power spectrum. However,
large-scale E-mode likelihood, based on high frequency instrument cross
spectrum, does not support this suppression and in the combined data the
preference towards the suppression becomes negligible. Based on the Hilltop and
Starobinsky model we construct the Wiggly Whipped Inflation potentials to
introduce oscillatory features along with the suppression. We use unbinned data
from the recently released CamSpec v12.5 likelihood which updates Planck 2018
results. We compare the Bayesian evidences of the feature models with their
baseline slow-roll potentials. We find that the complete slow-roll baseline
potential is moderately preferred against potentials which generate features.
Compared to Planck 2015 PlikHM bin1 likelihood, we find that the significance
of sharp features has decreased owing to the updates in the data analysis
pipeline. We also compute the bispectra for the best fit candidates obtained
from our analysis. |
Future Observations of Cosmic Magnetic Fields with the SKA and its
Precursors: The origin of magnetic fields in the Universe is an open problem in
astrophysics and fundamental physics. Polarization observations with the
forthcoming large radio telescopes, especially the Square Kilometre Array
(SKA), will open a new era in the observation of magnetic fields and should
help to understand their origin. Low-frequency radio synchrotron emission, to
be observed with LOFAR, MWA and the SKA, traces low-energy cosmic ray electrons
and allows us to map the structure of weak magnetic fields in the outer regions
and halos of galaxies, in halos and relics of galaxy clusters and in the Milky
Way. Polarization at higher frequencies (1-10 GHz), to be observed with the SKA
and its precursors ASKAP and MeerKAT, will trace magnetic fields in the disks
and central regions of galaxies and in cluster relics in unprecedented detail.
All-sky surveys of Faraday rotation measures towards a dense grid of polarized
background sources with ASKAP (project POSSUM) and the SKA are dedicated to
measure magnetic fields in intervening galaxies, clusters and intergalactic
filaments, and will be used to model the overall structure and strength of
magnetic fields in the Milky Way. "Cosmic Magnetism" is key science for LOFAR,
ASKAP and the SKA. | Generation of Primordial Magnetic Fields on Linear Over-density Scales: Magnetic fields appear to be present in all galaxies and galaxy clusters.
Recent measurements indicate that a weak magnetic field may be present even in
the smooth low density intergalactic medium. One explanation for these
observations is that a seed magnetic field was generated by some unknown
mechanism early in the life of the Universe, and was later amplified by various
dynamos in nonlinear objects like galaxies and clusters. We show that a
primordial magnetic field is expected to be generated in the early Universe on
purely linear scales through vorticity induced by scale-dependent temperature
fluctuations or equivalently, a spatially varying speed of sound of the gas.
Residual free electrons left over after recombination tap into this vorticity
to generate magnetic field via the Biermann battery process. Although the
battery operates even in the absence of any relative velocity between dark
matter and gas at the time of recombination, the presence of such a relative
velocity modifies the predicted spatial power spectrum of the magnetic field.
At redshifts of order a few tens, we estimate a root mean square field strength
of order 1e-25 -1e-24 G on comoving scales~10 kpc. This field, which is
generated purely from linear perturbations, is expected to be amplified
significantly after reionization, and to be further boosted by dynamo processes
during nonlinear structure formation. |
CMB lensing reconstruction from the WMAP 7-year data: We attempt to make a direct measurement of the weak lensing signal from the
WMAP 7-year data. We apply the real-space implementation of the optimal
quadratic estimator on the maps produced by the W-band Differencing Assemblies.
We obtain a weak lensing amplitude parameter of $A_{L}=0.99\pm1.67$ after
correcting for several sources of bias. The error budget includes a
contribution from the bias removal procedure. Despite the demonstrated
insensitivity of the real-space estimator to uncorrelated noise, we conclude
that this detection is not statistically significant. We expect that a
full-sky, higher-sensitivity experiment such as Planck will allow us to make a
more significant measurement. | Squeezed primordial bispectrum from general vacuum state: We study the general relation between the power spectrum and the squeezed
limit of the bispectrum of the comoving curvature perturbation produced during
single-field slow-roll inflation when the initial state is a general vacuum.
Assuming the scale invariance of the power spectrum, we derive a formula for
the squeezed limit of the bispectrum, represented by the parameter fNL, which
is not slow-roll suppressed and is found to contain a single free parameter for
a given amplitude of the power spectrum. Then we derive the conditions for
achieving a scale-invariant fNL, and discuss a few examples. |
The Emission by Dust and Stars of Nearby Galaxies in the Herschel
KINGFISH Survey: Using new far-infrared imaging from the Herschel Space Observatory with
ancillary data from ultraviolet to submillimeter wavelengths, we estimate the
total emission from dust and stars of 62 nearby galaxies in the KINGFISH survey
in a way that is as empirical and model-independent as possible. We collect and
exploit these data in order to measure from the spectral energy distributions
(SEDs) precisely how much stellar radiation is intercepted and re-radiated by
dust, and how this quantity varies with galaxy properties. By including SPIRE
data, we are more sensitive to emission from cold dust grains than previous
analyses at shorter wavelengths, allowing for more accurate estimates of dust
temperatures and masses.
The dust/stellar flux ratio, which we measure by integrating the SEDs, has a
range of nearly three decades. The inclusion of SPIRE data shows that estimates
based on data not reaching these far-IR wavelengths are biased low. We find
that the dust/stellar flux ratio varies with morphology and total IR
luminosity. We also find that dust/stellar flux ratios are related to gas-phase
metallicity, while the dust/stellar mass ratios are less so. The substantial
scatter between dust/stellar flux and dust/stellar mass indicates that the
former is a poor proxy of the latter. Comparing the dust/stellar flux ratios
and dust temperatures, we show that early-types tend to have slightly warmer
temperatures than spiral galaxies, which may be due to more intense
interstellar radiation fields, or to different dust grain compositions.
Finally, we show that early-types and early-type spirals have a strong
correlation between the dust/stellar flux ratio and specific star formation
rate, which suggests that the relatively bright far-IR emission of some of
these galaxies is due to ongoing star formation and the radiation field from
older stars. | The Type Ia Supernova Rate in Radio and Infrared Galaxies from the CFHT
Supernova Legacy Survey: We have combined the large SN Ia database of the Canada-France-Hawaii
Telescope Supernova Legacy Survey and catalogs of galaxies with photometric
redshifts, VLA 1.4 GHz radio sources, and Spitzer infrared sources. We present
eight SNe Ia in early-type host galaxies which have counterparts in the radio
and infrared source catalogs. We find the SN Ia rate in subsets of radio and
infrared early-type galaxies is ~1-5 times the rate in all early-type galaxies,
and that any enhancement is always <~ 2 sigma. Rates in these subsets are
consistent with predictions of the two component "A+B" SN Ia rate model. Since
infrared properties of radio SN Ia hosts indicate dust obscured star formation,
we incorporate infrared star formation rates into the "A+B" model. We also show
the properties of SNe Ia in radio and infrared galaxies suggest the hosts
contain dust and support a continuum of delay time distributions for SNe Ia,
although other delay time distributions cannot be ruled out based on our data. |
Collapse threshold for a cosmological Klein Gordon field: Oscillating scalar fields are useful to model a variety of matter components
in the universe. One or more scalar fields participate in the reheating process
after inflation, while at much lower energies scalar fields are robust dark
matter candidates. Pertaining structure formation in these models, it is well
known that inhomogeneities of the Klein-Gordon field are unstable above the
characteristic De Broglie wavelength. In this paper we show that such
instability implies the existence of a threshold amplitude for the collapse of
primordial fluctuations. We use this threshold to correctly predict the
cut--off scale of the matter power spectrum in the scalar field dark matter
model. Furthermore, for a Klein-Gordon field during reheating we show that this
same threshold allows for abundant production of structure (oscillons but not
necessarily black holes). Looking at the production of Primordial Black Holes
(PBHs) in this scenario we note that the sphericity condition yields a much
lower probability of PBH formation at the end of inflation. Remarkably, even
after meeting such stringent condition, we find that PBHs may be overproduced
during reheating. We finally constrain the epochs at which an oscillating
Klein-Gordon field could dominate the early universe. | Galaxy Cluster Mass Reconstruction Project: I. Methods and first results
on galaxy-based techniques: This paper is the first in a series in which we perform an extensive
comparison of various galaxy-based cluster mass estimation techniques that
utilise the positions, velocities and colours of galaxies. Our primary aim is
to test the performance of these cluster mass estimation techniques on a
diverse set of models that will increase in complexity. We begin by providing
participating methods with data from a simple model that delivers idealised
clusters, enabling us to quantify the underlying scatter intrinsic to these
mass estimation techniques. The mock catalogue is based on a Halo Occupation
Distribution (HOD) model that assumes spherical Navarro, Frenk and White (NFW)
haloes truncated at R_200, with no substructure nor colour segregation, and
with isotropic, isothermal Maxwellian velocities. We find that, above 10^14
M_solar, recovered cluster masses are correlated with the true underlying
cluster mass with an intrinsic scatter of typically a factor of two. Below
10^14 M_solar, the scatter rises as the number of member galaxies drops and
rapidly approaches an order of magnitude. We find that richness-based methods
deliver the lowest scatter, but it is not clear whether such accuracy may
simply be the result of using an over-simplistic model to populate the galaxies
in their haloes. Even when given the true cluster membership, large scatter is
observed for the majority non-richness-based approaches, suggesting that mass
reconstruction with a low number of dynamical tracers is inherently
problematic. |
SED-inferred properties and morphology of Lyman-break galaxies at $z\sim
1$ in the CDF-S: After carefully cross-identifying a previously discovered GALEX-selected
Lyman Break Galaxy (LBG) candidates one-to-one with their optical counterparts
in the field of the CDF-S, we re-estimate their photometric redshifts using
multi-wavelength data from UV, optical to NIR. We refine a new updated sample
of 383 LBGs at $0.7\la z \la 1.4$.
Most LBGs are classified as starburst and irregular types. Ages spread from
several Myr to 1.5Gyr. Their dust-corrected star formation rates (SFRs) and
stellar masses ($M_*$) are from $4\my$ to $220\my$ and from $2.3\times 10^8
\msun$ to $4 \times 10^{11} \msun$. The rest-frame FUV luminosity function of
LBGs are presented. LBGs of irregular types mainly distribute along the "main
sequence" of star forming galaxies while most LBGs of starburst types locate in
the starburst region. A "downsizing" effect is clearly found and LBGs
distribute in the "blue" cloud.
HST images in F606W ($V$ band) and F850LP ($z$ band) are taken from the GEMS
and GOODS-S surveys. SExtractor and GALFIT are applied to get their
morphological parameters. A morphological sample of 142 LBGs with reliable
results of $\sersic$ and sizes in both bands is defined. We find that LBGs at
$z\sim 1 $ are dominated by disk-like galaxies. Correlations between
photometric and morphological properties of LBGs are investigated. Strong
correlations between their half-light radii and $M_*$, i.e., size-stellar mass
relations, are found in both bands. Physical connections between correlations
and the "downsizing" effect are discussed. | Survival of molecular gas in Virgo's hot intracluster medium: CO near
M86: We carried out CO(1-0) and CO(2-1) observations of 21 different regions in
the vicinity of M86, NGC4438, and along the 120 kpc-long, Ha-emitting
filamentary trail that connects them, aiming to test whether molecular gas can
survive to be transferred from a spiral to an elliptical galaxy in Virgo's
10^7K intracluster medium (ICM). We targeted Ha-emitting regions that could be
associated with the interface between cold molecular clouds and the hot ionized
ICM. The data, obtained with the 30m telescope of the Institut de
Radioastronomie Millimetrique, led to the detection of molecular gas close to
M86. CO gas with a recession velocity that is similar to that of the stars,
-265 km/s, and with a corresponding H2 mass of 2*10^7 M_sun, was detected ~10
kpc southeast of the nucleus of M86, near the peak of its HI emission. We argue
that it is possible for this molecular gas either to have formed in situ from
HI, or to have been stripped from NGC4438 directly in molecular form. In situ
formation is nonetheless negligible for the 7*10^6 M_sun of gas detected at
12:26:15.9+12:58:49, at ~10 kpc northeast of M86, where no (strong) HI emission
is present. This detection provides evidence for the survival of molecular gas
in filaments for timescales of ~100 Myr. An amount equivalent to 5*10^7 M_sun
of H2 gas that could be lost to the ICM or to neighboring galaxies was also
discovered in the tidal tail northwest of NGC4438. A scenario of gas being
alternatively brought to M86 from NGC4388 on its south was also examined but it
was considered unlikely due to the non detection of CO below or at the HI
stream velocities, 2000-2700 km/s. |
Disentangling correlated scatter in cluster mass measurements: The challenge of obtaining galaxy cluster masses is increasingly being
addressed by multiwavelength measurements. As scatters in measured cluster
masses are often sourced by properties of or around the clusters themselves,
correlations between mass scatters are frequent and can be significant, with
consequences for errors on mass estimates obtained both directly and via
stacking. Using a high resolution 250 Mpc/h side N-body simulation, combined
with proxies for observational cluster mass measurements, we obtain mass
scatter correlations and covariances for 243 individual clusters along ~96
lines of sight each, both separately and together. Many of these scatters are
quite large and highly correlated. We use principal component analysis (PCA) to
characterize scatter trends and variations between clusters. PCA identifies
combinations of scatters, or variations more generally, which are uncorrelated
or non-covariant. The PCA combination of mass measurement techniques which
dominates the mass scatter is similar for many clusters, and this combination
is often present in a large amount when viewing the cluster along its long
axis. We also correlate cluster mass scatter, environmental and intrinsic
properties, and use PCA to find shared trends between these. For example, if
the average measured richness, velocity dispersion and Compton decrement mass
for a cluster along many lines of sight are high relative to its true mass, in
our simulation the cluster's mass measurement scatters around this average are
also high, its sphericity is high, and its triaxiality is low.
Our analysis is based upon estimated mass distributions for fixed true mass.
Extensions to observational data would require further calibration from
numerical simulations, tuned to specific observational survey selection
functions and systematics. | Gravitational Lens Modeling with Genetic Algorithms and Particle Swarm
Optimizers: Strong gravitational lensing of an extended object is described by a mapping
from source to image coordinates that is nonlinear and cannot generally be
inverted analytically. Determining the structure of the source intensity
distribution also requires a description of the blurring effect due to a point
spread function. This initial study uses an iterative gravitational lens
modeling scheme based on the semilinear method to determine the linear
parameters (source intensity profile) of a strongly lensed system. Our
'matrix-free' approach avoids construction of the lens and blurring operators
while retaining the least squares formulation of the problem. The parameters of
an analytical lens model are found through nonlinear optimization by an
advanced genetic algorithm (GA) and particle swarm optimizer (PSO). These
global optimization routines are designed to explore the parameter space
thoroughly, mapping model degeneracies in detail. We develop a novel method
that determines the L-curve for each solution automatically, which represents
the trade-off between the image chi-square and regularization effects, and
allows an estimate of the optimally regularized solution for each lens
parameter set. In the final step of the optimization procedure, the lens model
with the lowest chi-square is used while the global optimizer solves for the
source intensity distribution directly. This allows us to accurately determine
the number of degrees of freedom in the problem to facilitate comparison
between lens models and enforce positivity on the source profile. In practice
we find that the GA conducts a more thorough search of the parameter space than
the PSO. |
AMiBA: Broadband Heterodyne CMB Interferometry: The Y. T. Lee Array for Microwave Background (AMiBA) has reported the first
science results on the detection of galaxy clusters via the Sunyaev Zel'dovich
effect. The science objectives required small reflectors in order to sample
large scale structures (20') while interferometry provided modest resolutions
(2'). With these constraints, we designed for the best sensitivity by utilizing
the maximum possible continuum bandwidth matched to the atmospheric window at
86-102GHz, with dual polarizations. A novel wide-band analog correlator was
designed that is easily expandable for more interferometer elements. MMIC
technology was used throughout as much as possible in order to miniaturize the
components and to enhance mass production. These designs will find application
in other upcoming astronomy projects. AMiBA is now in operations since 2006,
and we are in the process to expand the array from 7 to 13 elements. | CO in GN20: The Nature of a z=4 Submillimeter Galaxy: We present a study of the formation of clustered, massive galaxies at large
look--back times, via high resolution spectroscopic imaging of CO in the unique
GN20 proto-cluster. The data reveal evidence for rich structure and gas
dynamics in unprecedented detail, allowing us to image the molecular gas with a
resolution of only 1 kpc just 1.5 Gyr after the Big Bang. These
state-of-the-art data give new insight into the detailed physical processes
involved in early massive galaxy formation, and they provide a first glimpse of
the morphological studies that will become feasible on a regular basis with
ALMA. |
Using Large Scale Structure to test Multifield Inflation: Primordial non-Gaussianity of local type is known to produce a
scale-dependent contribution to the galaxy bias. Several classes of multi-field
inflationary models predict non-Gaussian bias which is stochastic, in the sense
that dark matter and halos don't trace each other perfectly on large scales. In
this work, we forecast the ability of next-generation Large Scale Structure
surveys to constrain common types of primordial non-Gaussianity like $f_{NL}$,
$g_{NL}$ and $\tau_{NL}$ using halo bias, including stochastic contributions.
We provide fitting functions for statistical errors on these parameters which
can be used for rapid forecasting or survey optimization. A next-generation
survey with volume $V = 25 h^{-3}$Gpc$^3$, median redshift $z = 0.7$ and mean
bias $b_g = 2.5$, can achieve $\sigma(f_{NL}) = 6$, $\sigma(g_{NL}) = 10^5$ and
$\sigma(\tau_{NL}) = 10^3$ if no mass information is available. If halo masses
are available, we show that optimally weighting the halo field in order to
reduce sample variance can achieve $\sigma(f_{NL}) = 1.5$, $\sigma(g_{NL}) =
10^4$ and $\sigma(\tau_{NL}) = 100$ if halos with mass down to $M_{min} =
10^{11}$ $h^{-1} M_\odot $ are resolved, outperforming Planck by a factor of 4
on $f_{NL}$ and nearly an order of magnitude on $g_{NL}$ and $\tau_{NL}$.
Finally, we study the effect of photometric redshift errors and discuss
degeneracies between different non-Gaussian parameters, as well as the impact
of marginalizing Gaussian bias and shot noise. | Testing $Λ$CDM with eBOSS data using a model independent
diagnostic: The $Om3$ diagnostic (Shafieloo et al. 2012) tests the consistency of the
cosmological constant as a candidate for dark energy using Baryon Acoustic
Oscillation (BAO) data. An important feature of $Om3$ is that it is independent
of any parametric assumption for dark energy, neither does it depend upon the
dynamics of the Universe during the pre-recombination nor post-recombination
eras. In other words, $Om3$ can be estimated using BAO observables and used
either to confirm or falsify the cosmological constant independently of the
value of the Hubble constant $H_0$ (expansion rate at $z=0$), and the comoving
sound horizon at the baryon drag epoch, $r_d$ (which is a function of the
physics of the Universe prior to recombination). Consequently, $Om3$ can play a
key role in identifying the nature of dark energy (DE) regardless of the
existing tensions in the standard model of cosmology and the possible presence
of systematics in some of the data sets. We revisit $Om3$ using the most recent
BAO observables from the eBOSS survey in order to test the consistency of the
cosmological constant with this data. Our results show the consistency of dark
energy being the cosmological constant. Moreover, with eBOSS data, we have
achieved a precision of $1.5\%$ for this three-point diagnostic. This
demonstrates that $Om3$ can be a potent diagnostic of dark energy when used in
conjunction with the high precision data expected from forthcoming large scale
structure surveys such as the Dark Energy Spectroscopic Instrument (DESI) and
Euclid. |
An optical spectroscopic survey of the 3CR sample of radio galaxies with
z<0.3. V. Implications for the unified model for FRIIs: We explore the implications of our optical spectroscopic survey of 3CR radio
sources with z<0.3 for the unified model (UM) for radio-loud AGN, focusing on
objects with a FRII radio morphology. The sample contains 33 high ionization
galaxies (HIGs) and 18 broad line objects (BLOs). According to the UM, HIGs,
the narrow line sources, are the nuclearly obscured counterparts of BLOs. The
fraction of HIGs indicates a covering factor of the circumnuclear matter of 65%
that corresponds, adopting a torus geometry, to an opening angle of 50+/-5
degree. No dependence on redshift and luminosity on the torus opening angle
emerges. We also consider the implications for a 'clumpy' torus. The
distributions of radio luminosity of HIGs and BLOs are not statistically
distinguishable, as expected from the UM. Conversely, BLOs have a radio core
dominance, R, more than ten times larger than HIGs, as expected in case of jet
Doppler boosting. Modeling the R distributions leads to an estimate of the jet
bulk Lorentz factor of Gamma ~3-5. The test of the UM based on the radio source
size is not conclusive due to the limited number of objects. Studying the
emission line ([OIII], [OII]and [OI]) properties of HEGs and BLOs, we find
evidences of a narrow line region (NLR) density stratification and its partial
obscuration from the torus. In conclusion, the radio and NLR properties of HIGs
and BLOs are consistent with the UM predictions. We also explored the radio
properties of 21 3CR FRII low-ionization galaxies (LIGs) at z<0.3. We find that
they cannot be part of the model that unifies HIGs and BLOs, but they are
instead intrinsically different source, still reproduced by a randomly oriented
population. | Chemical behavior of the Dwarf Irregular Galaxy NGC 6822. Its PN and HII
region abundances: We aim to derive the chemical behavior of a significant sample of PNe and HII
regions in the irregular galaxy NGC 6822 The selected objects are distributed
in different zones of the galaxy. Due to the faintness of PNe and HII regions
in NGC 6822, to gather spectroscopic data with large telescopes is necessary.
We obtained a well suited sample of spectra by employing VLT-FORS 2 and
Gemini-GMOS spectrographs. Ionic and total abundances are calculated for the
objects where electron temperatures can be determined through the detection of
[OIII] \lambda 4363 or/and [NII] \lambda 5755 lines. A "simple" chemical
evolution model has been developed and the observed data are used to compute a
model for NGC 6822 in order to infer a preliminary chemical history in this
galaxy. Confident determinations of He, O, N, Ne, S and Ar abundances were
derived for a sample of 11 PNe and one HII region. We confirm that the present
ISM is chemically homogeneous, at least in the central 2 kpc of the galaxy,
showing a value 12+log O/H = 8.06$\pm$0.04. From the abundance pattern of PNe,
we identified two populations: a group of young PNe with abundances similar to
HII regions and a group of older objects with abundances a factor of two lower.
A couple of extreme Type I PNe were found. No third dredge-up O enrichement was
detected in PNe of this galaxy. The abundance determinations allow us to
discuss the chemical behavior of the present and past ISM in NGC 6822. Our
preliminary chemical evolution model predicts that an important gas-mass lost
occurred during the first 5.3 Gyr, that no star higher than 40 M$_\odot$ was
formed, and that 1% of all 3-15 M$_\odot$ stars became binary systems
progenitors to SNIa. |
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