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The supernova Ia 2011fe in M101, its tip of the red-giant branch (TRGB)
distance, and the value of H_0: The light curve parameters of the normal type Ia SN2011fe are derived from
the rich archive of the AAVSO. This leads, together with the TRGB distance
modulus of (m-M) = 29.39 +/- 0.05 of the parent galaxy M101, to maximum
magnitudes of the unreddened SN of M_B = -19.45 +/- 0.08, M_V = -19.46 +/-
0.08, and M_I = -19.25 +/- 0.06 (for the standard decline rate of Delta m_15 =
1.1). When these values are inserted into the Hubble line defined by 62 SNe Ia
with 3000 < v < 20,000 km/s - and considering also four other SNe Ia with TRGB
distances - one obtains a large-scale value of the Hubble constant of H_0 =
64.3 +/- 1.9 +/- 3.2. This value can be much improved in the future by using
only TRGB distances of SNe Ia. | Extending Semi-numeric Reionisation Models to the First Stars and
Galaxies: Semi-numeric methods have made it possible to efficiently model the epoch of
reionisation (EoR). While most implementations involve a reduction to a simple
three-parameter model, we introduce a new mass-dependent ionising efficiency
parameter that folds in physical parameters that are constrained by the latest
numerical simulations. This new parameterization enables the effective modeling
of a broad range of host halo masses containing ionising sources, extending
from the smallest Population III host halos with $M \sim 10^6 M_\odot$, which
are often ignored, to the rarest cosmic peaks with $M \sim 10^{12} M_\odot$
during EoR. We compare the resulting ionising histories with a typical
three-parameter model and also compare with the latest constraints from the
Planck mission. Our model results in a optical depth due to Thomson scattering,
$\tau_{\mathrm{e}}$ = 0.057, that is consistent with Planck. The largest
difference in our model is shown in the resulting bubble size distributions
which peak at lower characteristic sizes and are broadened. We also consider
the uncertainties of the various physical parameters and comparing the
resulting ionising histories broadly disfavors a small contribution from
galaxies. As the smallest haloes cease a meaningful contribution to the
ionising photon budget after $z = 10$, implying they play a role in determining
the start of EoR and little else. |
Strong shock in the uniformly expanding medium: Propagation of the strong shock in the flat expanding Friedman universe is
investigated using methods of dimension and similarity. Exact analytic solution
of self-similar equations is obtained, determining dependences of the radius
and velocity of the shock wave on time and radius. It is obtained, that in the
expanding medium the velocity of shock decreases as $\sim t^{-1/5}$, what is
slower than the shock velocity in the static uniform medium $\sim t^{-3/5}$.
The radius of the shock wave in the expanding self-gravitating medium increases
$\sim t^{4/5}$, more rapidly than the shock wave radius in the uniform
non-gravitating medium $\sim t^{2/5}$. So, the shock propagates in the
direction of decreasing density with larger speed, that in the static medium,
due to accelerating action of the decreasing density, even in the presence of a
self-gravitation. | Comparing Foreground Removal Techniques for Recovery of the LOFAR-EoR
21cm Power Spectrum: We compare various foreground removal techniques that are being utilised to
remove bright foregrounds in various experiments aiming to detect the
redshifted 21cm signal of neutral hydrogen from the Epoch of Reionization. In
this work, we test the performance of removal techniques (FastICA, GMCA, and
GPR) on 10 nights of LOFAR data and investigate the possibility of recovering
the latest upper limit on the 21cm signal. Interestingly, we find that GMCA and
FastICA reproduce the most recent 2$\sigma$ upper limit of $\Delta^2_{21} <$
(73)$^2$ mK$^2$ at $k=0.075~ h \mathrm{cMpc}^{-1}$, which resulted from the
application of GPR. We also find that FastICA and GMCA begin to deviate from
the noise-limit at \textit{k}-scales larger than $\sim 0.1 ~h
\mathrm{cMpc}^{-1}$. We then replicate the data via simulations to see the
source of FastICA and GMCA's limitations, by testing them against various
instrumental effects. We find that no single instrumental effect, such as
primary beam effects or mode-mixing, can explain the poorer recovery by FastICA
and GMCA at larger \textit{k}-scales. We then test scale-independence of
FastICA and GMCA, and find that lower \textit{k}-scales can be modelled by a
smaller number of independent components. For larger scales ($k \gtrsim 0.1~h
\mathrm{cMpc}^{-1}$), more independent components are needed to fit the
foregrounds. We conclude that, the current usage of GPR by the LOFAR
collaboration is the appropriate removal technique. It is both robust and less
prone to overfitting, with future improvements to GPR's fitting optimisation to
yield deeper limits. |
The escape fraction of ionizing photons from high redshift galaxies from
data-constrained reionization models: The escape fraction, f_{esc}, of ionizing photons from high-redshift galaxies
is a key parameter to understand cosmic reionization and star formation
history. Yet, in spite of many efforts, it remains largely uncertain. We
propose a novel, semi-empirical approach based on a simultaneous match of the
most recently determined Luminosity Functions (LF) of galaxies in the redshift
range 6 \leq z \leq 10 with reionization models constrained by a large variety
of experimental data. From this procedure we obtain the evolution of the
best-fit values of f_{esc} along with their 2-sigma limits. We find that,
averaged over the galaxy population, (i) the escape fraction increases from
f_{esc} = 0.068_{-0.047}^{+0.054} at z=6 to f_{esc} = 0.179_{-0.132}^{+0.331}
at z=8; (ii) at z=10 we can only put a lower limit of f_{esc} > 0.146. Thus,
although errors are large, there is an indication of a 2.6 times increase of
the average escape fraction from z=6 to z=8 which might partially release the
"starving reionization" problem. | Parity violation in the observed galaxy trispectrum: Recent measurements of the 4-point correlation function in large-scale galaxy
surveys have found apparent evidence of parity violation in the distribution of
galaxies. This cannot happen via dynamical gravitational effects in general
relativity. If such a violation arose from physics in the early Universe it
could indicate important new physics beyond the standard model, and would be at
odds with most models of inflation. It is therefore now timely to consider the
galaxy trispectrum in more detail. While the intrinsic 4-point correlation
function, or equivalently the trispectrum, its Fourier counterpart, is parity
invariant, the observed trispectrum must take redshift-space distortions into
account. Although the standard Newtonian correction also respects parity
invariance, we show that sub-leading relativistic corrections do not. We
demonstrate that these can be significant at intermediate linear scales and are
dominant over the Newtonian parity-invariant part around the equality scale and
above. Therefore when observing the galaxy 4-point correlation function, we
should expect to detect parity violation on large scales. |
Linear kinetic Sunyaev-Zel'dovich effect and void models for
acceleration: There has been considerable recent interest in cosmological models in which
the current apparent acceleration is due to a very large local underdensity, or
void, instead of some form of dark energy. Here we examine a new proposal to
constrain such models using the linear kinetic Sunyaev-Zel'dovich (kSZ) effect
due to structure within the void. The simplified "Hubble bubble" models
previously studied appeared to predict far more kSZ power than is actually
observed, independently of the details of the initial conditions and evolution
of perturbations in such models. We show that the constraining power of the kSZ
effect is considerably weakened (though still impressive) under a fully
relativistic treatment of the problem, and point out several theoretical
ambiguities and observational shortcomings which further qualify the results.
Nevertheless, we conclude that a very large class of void models is ruled out
by the combination of kSZ and other methods. | Long Range Effects in Gravity Theories with Vainshtein Screening: In this paper we study long range modifications of gravity in the consistent
framework of bigravity, which introduces a second massive spin-2 field and
allows to continuously interpolate between the regime of General Relativity
(mediated by a massless spin-2 field) and massive gravity (mediated by a
massive spin-2 field). In particular we derive for the first time the equations
for light deflection in this framework and study the effect on the lensing
potential of galaxy clusters. By comparison of kinematic and lensing mass
reconstructions, stringent bounds can be set on the parameter space of the new
spin-2 fields. Furthermore, we investigate galactic rotation curves and the
effect on the observable dark matter abundance within this framework. |
Cosmology Requirements on Supernova Photometric Redshift Systematics for
Rubin LSST and Roman Space Telescope: Some million Type Ia supernovae (SN) will be discovered and monitored during
upcoming wide area time domain surveys such as the Vera C. Rubin Observatory
Legacy Survey of Space and Time (LSST). For cosmological use, accurate
redshifts are needed among other characteristics; however the vast majority of
the SN will not have spectroscopic redshifts, even for their host galaxies,
only photometric redshifts. We assess the redshift systematic control necessary
for robust cosmology. Based on the photometric vs true redshift relation
generated by machine learning applied to a simulation of 500,000 galaxies as
observed with LSST quality, we quantify requirements on systematics in the mean
relation and in the outlier fraction and deviance so as not to bias dark energy
cosmological inference. Certain redshift ranges are particularly sensitive,
motivating spectroscopic followup of SN at $z\lesssim0.2$ and around
$z\approx0.5$-0.6. Including Nancy Grace Roman Space Telescope near infrared
bands in the simulation, we reanalyze the constraints, finding improvements at
high redshift but little at the low redshifts where systematics lead to strong
cosmology bias. We identify a complete spectroscopic survey of SN host galaxies
for $z\lesssim0.2$ as a highly favored element for robust SN cosmology. | The inflating curvaton: The primordial curvature perturbation \zeta may be generated by some curvaton
field \sigma, which is negligible during inflation and has more or less
negligible interactions until it decays. In the current scenario, the curvaton
starts to oscillate while its energy density \rho_\sigma is negligible. We
explore the opposite scenario, in which \rho_\sigma drives a few e-folds of
inflation before the oscillation begins. In this scenario for generating \zeta
it is exceptionally easy to solve the \eta problem; one just has to make the
curvaton a string axion, with anomaly-mediated susy breaking which may soon be
tested at the LHC. The observed spectral index n can be obtained with a
potential V\propto \phi^p for the first inflation; p=1 or 2 is allowed by the
current uncertainty in n but the improvement in accuracy promised by Planck may
rule out p=1. The predictions include (i) running n'\simeq 0.0026 (0.0013) for
p=1 (2) that will probably be observed, (ii) non-gaussianity parameter f_NL
\sim -1 that may be observed, (iii) tensor fraction r is probably too small to
ever observed. |
Extracting the 21 cm EoR signal using MWA drift scan data: The detection of redshifted hyperfine line of neutral hydrogen (HI) is the
most promising probe of the Epoch of Reionization (EoR). We report an analysis
of 55 hours of Murchison Widefield Array (MWA) Phase II drift scan EoR data.
The data correspond to a central frequency $\nu_0 = 154.24 \, \rm MHz$
($z\simeq 8.2$ for the redshifted HI hyperfine line) and bandwidth $B = 10.24
\, \rm MHz$. As one expects greater system stability in a drift scan, we test
the system stability by comparing the extracted power spectra from data with
noise simulations and show that the power spectra for the cleanest data behave
as thermal noise. We compute the HI power spectrum as a function of time in one
and two dimensions. The best upper limit on the one-dimensional power spectrum
are: $\Delta^2(k) \simeq (1000~\rm mK)^2$ at $k \simeq 0.2$$h~{\rm Mpc}^{-1}$
and at $k \simeq 1$$h~{\rm Mpc}^{-1}$. The cleanest modes, which might be the
most suited for obtaining the optimal signal-to-noise, correspond to $k \gtrsim
1$$h~{\rm Mpc}^{-1}$. We also study the time-dependence of the
foreground-dominated modes in a drift scan and compare with the expected
behaviour. | cosmoabc: Likelihood-free inference via Population Monte Carlo
Approximate Bayesian Computation: Approximate Bayesian Computation (ABC) enables parameter inference for
complex physical systems in cases where the true likelihood function is
unknown, unavailable, or computationally too expensive. It relies on the
forward simulation of mock data and comparison between observed and synthetic
catalogues. Here we present cosmoabc, a Python ABC sampler featuring a
Population Monte Carlo (PMC) variation of the original ABC algorithm, which
uses an adaptive importance sampling scheme. The code is very flexible and can
be easily coupled to an external simulator, while allowing to incorporate
arbitrary distance and prior functions. As an example of practical application,
we coupled cosmoabc with the numcosmo library and demonstrate how it can be
used to estimate posterior probability distributions over cosmological
parameters based on measurements of galaxy clusters number counts without
computing the likelihood function. cosmoabc is published under the GPLv3
license on PyPI and GitHub and documentation is available at
http://goo.gl/SmB8EX |
An SZ-selected sample of the most massive galaxy clusters in the
2500-square-degree South Pole Telescope survey: The South Pole Telescope (SPT) is currently surveying 2500 deg^2 of the
southern sky to detect massive galaxy clusters out to the epoch of their
formation using the Sunyaev-Zel'dovich (SZ) effect. This paper presents a
catalog of the 26 most significant SZ cluster detections in the full survey
region. The catalog includes 14 clusters which have been previously identified
and 12 that are new discoveries. These clusters were identified in fields
observed to two differing noise depths: 1500 deg^2 at the final SPT survey
depth of 18 uK-arcmin at 150 GHz, and 1000 deg^2 at a depth of 54 uK-arcmin.
Clusters were selected on the basis of their SZ signal-to-noise ratio (S/N) in
SPT maps, a quantity which has been demonstrated to correlate tightly with
cluster mass. The S/N thresholds were chosen to achieve a comparable mass
selection across survey fields of both depths. Cluster redshifts were obtained
with optical and infrared imaging and spectroscopy from a variety of ground-
and space-based facilities. The redshifts range from 0.098 \leq z \leq 1.132
with a median of z_med = 0.40. The measured SZ S/N and redshifts lead to
unbiased mass estimates ranging from 9.8 \times 10^14 M_sun/h_70 \leq
M_200(rho_mean) \leq 3.1 \times 10^15 M_sun/h_70. Based on the SZ mass
estimates, we find that none of the clusters are individually in significant
tension with the LambdaCDM cosmological model. We also test for evidence of
non-Gaussianity based on the cluster sample and find the data show no
preference for non-Gaussian perturbations. | Thawing k-essence dark energy in the PAge space: A broad class of dark energy models can be written in the form of k-essence,
whose Lagrangian density is a two-variable function of a scalar field $\phi$
and its kinetic energy $X\equiv \frac{1}{2}\partial^\mu\phi \partial_\mu\phi$.
In the thawing scenario, the scalar field becomes dynamic only when the Hubble
friction drops below its mass scale in the late universe. Thawing k-essence
dark energy models can be randomly sampled by generating the Taylor expansion
coefficients of its Lagrangian density from random matrices \cite{thaws}. Ref.
\cite{thaws} points out that the non-uniform distribution of effective equation
of state parameters $(w_0, w_a)$ of thawing k-essence model can be used to
improve the statistics of model selection. The present work studies the
statistics of thawing k-essence in a more general framework that is
Parameterized by the Age of the universe (PAge) \cite{PAge}. For fixed matter
fraction $\Omega_m$, the random thawing k-essence models cluster in a narrow
band in the PAge parameter space, providing a strong theoretical prior. We
simulate cosmic shear power spectrum data for the Chinese Space Station
Telescope optical survey, and compare the fisher forecast with and without the
theoretical prior of thawing k-essence. For an optimal tomography binning
scheme, the theoretical prior improves the figure of merit in PAge space by a
factor of $3.3$. |
Gravitational Wave Production right after a Primordial Black Hole
Evaporation: We discuss the footprint of evaporation of primordial black holes (PBHs) on
stochastic gravitational waves (GWs) induced by scalar perturbations. We
consider the case where PBHs once dominated the Universe but eventually
evaporated before the big bang nucleosynthesis. The reheating through the PBH
evaporation could end with a sudden change in the equation of state of the
Universe compared to the conventional reheating caused by particle decay. We
show that this "sudden reheating" by the PBH evaporation enhances the induced
GWs, whose amount depends on the length of the PBH-dominated era and the width
of the PBH mass function. We explore the possibility to constrain the
primordial abundance of the evaporating PBHs by observing the induced GWs. We
find that the abundance parameter $\beta \gtrsim 10^{-5} \text{ - }10^{-8}$ for
$\mathcal{O}(10^3 \text{ - } 10^5) \, \text{g}$ PBHs can be constrained by
future GW observations if the width of the mass function is smaller than about
a hundredth of the mass. | Analytic Fluid Approximation for Warm Dark Matter: We present the full evolution of the velocity of a massive particle, along
with the equation of state we can compute the energy density and pressure
evolution for the background evolution. It is also natural to compute the
perturbation equations for any massive decoupled particle, i.e. warm dark
matter (WDM) or neutrinos, in the fluid approximation. Using this approach we
analytically compute the time when the WDM stop being relativistic, $a_{nr}$,
which is 2.6\% different respect to the exact Boltzmann solution. Using the
fluid approximation the matter power spectrum is computed faster and with great
accuracy, the cut-off in structure formation due to the free-streaming
($\lambda_{fs}$) of the particle, characteristic for a WDM particle, is
replicated in both matter power spectrum and halo mass function. With this
approach, we have a deeper understanding of the WDM physics that lead us to
show that the temperature the dark matter can be computed as a function of
known properties of the WDM particle. This formulation can be integrated into
comprehensive numerical modeling reasonable increasing the performance in the
calculations, therefore, we analyze the parameter $a_{nr}$ in a $\Lambda$WDM
model using CMB Planck data combined with matter power spectrum data set of
WiggleZ, obtaining a lower bound for the WDM mass $m_{\rm wdm} = 70.3$ eV at
86\% confidence, this value is consistent with WiggleZ data set but more data
at small scales or a combination with other observations are needed to stronger
constrain the mass value of the WDM particle. |
On the suspected timing error in WMAP map-making: A large fraction of the previously estimated WMAP CMB quadrupole signal would
be an artefact of incorrect Doppler dipole subtraction if the hypothesis of a
small timing interpolation error were correct. Observations of bright
foreground objects constitute part of the time-ordered-data (TOD). Scans of an
object in different directions should be shifted by the would-be timing error,
causing a blurring effect. Three half-years of the calibrated, filtered WMAP
TOD are compiled individually for the four W band differencing assemblies
(DA's), with no masking of bright objects, giving 12 maps for each timing
offset. Percentiles of the temperature-fluctuation distribution in each map at
HEALPix resolution N_side=2048 are used to determine the dependence of all-sky
image sharpness on the timing offset. In the W band, the 99.999% percentile,
i.e. the temperature fluctuation in the approx 503-rd brightest pixel, is the
least noisy percentile. Using this statistic, the hypothesis that a -25.6 ms
offset relative to the timing adopted by the WMAP collaboration gives a focus
at least as sharp as the uncorrected timing is rejected at 4.6\sigma
significance. The Q and V band maps also reject the -25.6 ms offset hypothesis
at high statistical significance. The requirement that the correct choice of
timing offset must maximise image sharpness implies that the hypothesis of a
timing error in the WMAP collaboration's compilation of the WMAP calibrated,
filtered TOD is rejected at high statistical significance in each of the Q, V
and W wavebands. However, the hypothesis that a timing error was applied during
calibration of the raw TOD, leading to a dipole-induced difference signal, is
not excluded by this method. | The VIMOS Public Extragalactic Redshift Survey (VIPERS): Reconstruction
of the redshift-space galaxy density field: Aims. Using the VIMOS Public Extragalactic Redshift Survey (VIPERS) we aim to
jointly estimate the key parameters that describe the galaxy density field and
its spatial correlations in redshift space. Methods. We use the Bayesian
formalism to jointly reconstruct the redshift-space galaxy density field, power
spectrum, galaxy bias and galaxy luminosity function given the observations and
survey selection function. The high-dimensional posterior distribution is
explored using the Wiener filter within a Gibbs sampler. We validate the
analysis using simulated catalogues and apply it to VIPERS data taking into
consideration the inhomogeneous selection function. Results. We present joint
constraints on the anisotropic power spectrum as well as the bias and number
density of red and blue galaxy classes in luminosity and redshift bins as well
as the measurement covariances of these quantities. We find that the inferred
galaxy bias and number density parameters are strongly correlated although
these are only weakly correlated with the galaxy power spectrum. The power
spectrum and redshift-space distortion parameters are in agreement with
previous VIPERS results with the value of the growth rate $f\sigma_8 = 0.38$
with 18% uncertainty at redshift 0.7. |
Weak lensing magnification in the Dark Energy Survey Science
Verification Data: In this paper the effect of weak lensing magnification on galaxy number
counts is studied by cross-correlating the positions of two galaxy samples,
separated by redshift, using data from the Dark Energy Survey Science
Verification dataset. The analysis is carried out for two
photometrically-selected galaxy samples, with mean photometric redshifts in the
$0.2 < z < 0.4$ and $0.7 < z < 1.0$ ranges, in the riz bands. A signal is
detected with a $3.5\sigma$ significance level in each of the bands tested, and
is compatible with the magnification predicted by the $\Lambda$CDM model. After
an extensive analysis, it cannot be attributed to any known systematic effect.
The detection of the magnification signal is robust to estimated uncertainties
in the outlier rate of the pho- tometric redshifts, but this will be an
important issue for use of photometric redshifts in magnification mesurements
from larger samples. In addition to the detection of the magnification signal,
a method to select the sample with the maximum signal-to-noise is proposed and
validated with data. | Fractal Bubble Cosmology: A concordant cosmological model?: The Fractal Bubble model has been proposed as a viable cosmology that does
not require dark energy to account for cosmic acceleration, but rather
attributes its observational signature to the formation of structure. In this
paper it is demonstrated that, in contrast to previous findings, this model is
not a good fit to cosmological supernovae data; there is significant tension in
the best fit parameters obtained from different samples, whereas LCDM is able
to fit all datasets consistently. Furthermore, the concordance between galaxy
clustering scales and data from the cosmic microwave background is not achieved
with the most recent supernova compilations. The validity of the FB formalism
as a sound cosmological model is further challenged as it is shown that
previous studies of this model achieve concordance by requiring a value for the
present day Hubble constant that is derived from supernovae data containing an
arbitrary distance normalisation. |
VLBI-selected sample of Compact Symmetric Object candidates and
frequency-dependent position of hotspots: The Compact Symmetric Objects (CSOs) are small (<1 kiloparsec) and powerful
extragalactic radio sources showing emission on both sides of an active
galactic nucleus and no signs of strong relativistic beaming. They may be young
radio sources, progenitors of large FRII radio galaxies. We aim to study the
statistical properties of CSOs by constructing and investigating a new large
sample of CSO candidates on the basis of dual-frequency, parsec-scale
morphology. For the candidate selection we utilized VLBI data for 4170
extragalactic objects obtained simultaneously at 2.3 and 8.6 GHz (S and X band)
within the VLBA Calibrator Survey 1-6 and the Research and Development - VLBA
projects. Properties of their broad-band radio spectra were characterized by
using RATAN-600 observations. Numerical modeling was applied in an attempt to
explain the observed effects. A sample of 64 candidate CSOs is identified. The
median two-point S-X band spectral index of parsec-scale hotspots is found to
be -0.52; with the median brightness temperature ~10^9 K at X band. Statistical
analysis reveals a systematic difference between positions of brightest CSO
components (associated with hotspots) measured in the S and X bands. The
distance between these components is found to be on average 0.32+/-0.06 mas
greater at 8.6 GHz than at 2.3 GHz. This difference in distances cannot be
explained by different resolutions at the S and X bands. It is a manifestation
of spectral index gradients across CSO components, which may potentially
provide important physical information about them. Despite our detailed
numerical modeling of a CSO hotspot, the model was not able to reproduce the
magnitude of the observed positional difference. A more detailed modeling may
shed light on the origin of the effect. | An Improved Method to Measure the Cosmic Curvature: In this paper, we propose an improved model-independent method to constrain
the cosmic curvature by combining the most recent Hubble parameter $H(z)$ and
supernovae Ia (SNe Ia) data. Based on the $H(z)$ data, we first use the
model-independent smoothing technique, Gaussian processes, to construct
distance modulus $\mu_{H}(z)$, which is susceptible to the cosmic curvature
parameter $\Omega_{k}$. In contrary to previous studies, the light-curve
fitting parameters, which account for distance estimation of SN
($\mu_{SN}(z)$), are set free to investigate whether $\Omega_{k}$ has a
dependence on them. By comparing $\mu_{H}(z)$ to $\mu_{SN}(z)$, we put limits
on $\Omega_{k}$. Our results confirm that $\Omega_{k}$ is independent of the SN
light-curve parameters. Moreover, we show that the measured $\Omega_{k}$ is in
good agreement with zero cosmic curvature, implying that there is no
significant deviation from a flat Universe at the current observational data
level. We also test the influence of different $H(z)$ samples and different
Hubble constant $H_{0}$ values, finding that different $H(z)$ samples do not
present significant impact on the constraints. However, different $H_{0}$
priors can affect the constraints of $\Omega_{k}$ in some degree. The prior of
$H_{0}=73.24\pm1.74$ km $\rm s^{-1}$ $\rm Mpc^{-1}$ gives a value of
$\Omega_{k}$ a little bit above $1\sigma$ confidence level away from 0, but
$H_{0}=69.6\pm0.7$ km $\rm s^{-1}$ $\rm Mpc^{-1}$ gives it below $1\sigma$. |
C+ Emission from the Magellanic Clouds II. [CII] maps of star-forming
regions LMC-N 11, SMC-N 66, and several others: We study the 158 micron [CII] fine-structure line emission from star-forming
regions as a function of metallicity. We have measured and mapped the [CII]
emission from the very bright HII region complexes N 11 in the LMC and N 66 in
the SMC, as well as the SMC HII regions N 25, N 27, N 83/N 84, and N 88, with
the FIFI instrument on the Kuiper Airborne Observatory. In both the LMC and
SMC, the ratio of the [CII] line to the CO line and to the far-infrared
continuum emission is much higher than seen almost anywhere else, including
Milky Way star-forming regions and whole galaxies. In the low metallicity, low
dust-abundance environment of the LMC and the SMC, UV mean free path lengths
are much greater than those in the higher-metallicity Milky Way. The increased
photoelectric heating efficiencies cause significantly greater relative [CII]
line emission strengths. At the same time, similar decreases in PAH abundances
have the opposite effect, by diminishing photoelectric heating rates.
Consequently, in low-metallicity environments the relative [CII] strengths are
high but exhibit little further dependence on actual metallicity. Relative
[CII] strengths are slightly higher in the LMC than in the SMC, which has both
lower dust and lower PAH abundances. | Testing the interaction of dark energy to dark matter through the
analysis of virial relaxation of clusters Abell Clusters A586 and A1689 using
realistic density profiles: Interaction between dark energy and dark matter is probed through deviation
from the virial equilibrium for two relaxed clusters: A586 and A1689. The
evaluation of the virial equilibrium is performed using realistic density
profiles. The virial ratios found for the more realistic density profiles are
consistent with the absence of interaction. |
A high molecular fraction in a sub-damped absorber at z=0.56: Measuring rest-frame ultraviolet rotational transitions from the Lyman and
Werner bands in absorption against a bright background continuum is one of the
few ways to directly measure molecular hydrogen (H2). Here we report the
detection of Lyman-Werner absorption from H2 at z=0.56 in a sub-damped Ly-alpha
system with neutral hydrogen column density N(HI) = 10^(19.5 +/- 0.2) cm^-2.
This is the first H2 system analysed at a redshift < 1.5 beyond the Milky Way
halo. It has a surprisingly high molecular fraction: log f(H2) > -1.93 +/- 0.36
based on modelling the line profiles, with a robust model-independent lower
limit of f(H2) > 10^-3. This is higher than f(H2) values seen along sightlines
with similar N(HI) through the Milky Way disk and the Magellanic clouds. The
metallicity of the absorber is 0.19 +0.21 -0.10 solar, with a dust-to-gas ratio
< 0.36 times the value in the solar neighbourhood. Absorption from associated
low-ionisation metal transitions such as OI and FeII is observed in addition to
OVI. Using Cloudy models we show that there are three phases present; a ~100 K
phase giving rise to H2, a ~10^4 K phase where most of the low-ionisation metal
absorption is produced; and a hotter phase associated with OVI. Based on
similarities to high velocity clouds in the Milky Way halo showing H2 and the
presence of two nearby galaxy candidates with impact parameters of ~10 kpc, we
suggest that the absorber may be produced by a tidally-stripped structure
similar to the Magellanic Stream. | On the ISW-cluster cross-correlation in future surveys: We investigate the cosmological information contained in the
cross-correlation between the Integrated Sachs-Wolfe (ISW) of the Cosmic
Microwave Background (CMB) anisotropy pattern and galaxy clusters from future
wide surveys. Future surveys will provide cluster catalogues with a number of
objects comparable with galaxy catalogues currently used for the detection of
the ISW signal by cross-correlation with the CMB anisotropy pattern. By
computing the angular power spectra of clusters and the corresponding
cross-correlation with CMB, we perform a signal-to-noise ratio (SNR) analysis
for the ISW detection as expected from the eROSITA and the Euclid space
missions. We discuss the dependence of the SNR of the ISW-cluster
cross-correlation on the specifications of the catalogues and on the reference
cosmology. We forecast that the SNRs for ISW-cluster cross-correlation are
alightly smaller compared to those which can be obtained from future galaxy
surveys but the signal is expected to be detected at high significance, i.e.
more than $> 3\,\sigma$. We also forecast the joint constraints on parameters
of model extensions of the concordance $\Lambda$CDM cosmology by combining CMB
and the ISW-cluster cross-correlation. |
Limits on Intergalactic Dust During Reionization: In this Letter, we constrain the dust-to-gas ratio in the intergalactic
medium (IGM) at high redshifts. We employ models for dust in the local Universe
to contrain the dust-to-gas ratio during the epoch of reionization at redshifts
z ~ 6-10. The observed level of reddening of high redshift galaxies implies
that the IGM was enriched to an intergalactic dust-to-gas ratio of less than 3%
of the Milky Way value by a redshift of z=10. | Chameleons in the Early Universe: Kicks, Rebounds, and Particle
Production: Chameleon gravity is a scalar-tensor theory that includes a non-minimal
coupling between the scalar field and the matter fields and yet mimics general
relativity in the Solar System. The scalar degree of freedom is hidden in
high-density environments because the effective mass of the chameleon scalar
depends on the trace of the stress-energy tensor. In the early Universe, when
the trace of the matter stress-energy tensor is nearly zero, the chameleon is
very light, and Hubble friction prevents it from reaching the minimum of its
effective potential. Whenever a particle species becomes non-relativistic,
however, the trace of the stress-energy tensor is temporarily nonzero, and the
chameleon begins to roll. We show that these "kicks" to the chameleon field
have catastrophic consequences for chameleon gravity. The velocity imparted to
the chameleon by the kick is sufficiently large that the chameleon's mass
changes rapidly as it slides past its potential minimum. This nonadiabatic
evolution shatters the chameleon field by generating extremely high-energy
perturbations through quantum particle production. If the chameleon's coupling
to matter is slightly stronger than gravitational, the excited modes have
trans-Planckian momenta. The production of modes with momenta exceeding 1e7 GeV
can only be avoided for small couplings and finely tuned initial conditions.
These quantum effects also significantly alter the background evolution of the
chameleon field, and we develop new analytic and numerical techniques to treat
quantum particle production in the regime of strong dissipation. This analysis
demonstrates that chameleon gravity cannot be treated as a classical field
theory at the time of Big Bang Nucleosynthesis and casts doubt on chameleon
gravity's viability as an alternative to general relativity. |
Cosmological constraints on Brans-Dicke theory: We report strong cosmological constraints on the Brans-Dicke (BD) theory of
gravity using Cosmic Microwave Background data from Planck.We consider two
types of models. First, the initial condition of the scalar field is fixed to
give the same effective gravitational strength $G_{eff}$ today as the one
measured on the Earth, $G_N$. In this case the BD parameter $\omega$ is
constrained to $\omega > 692$ at the $99\%$ confidence level, an order of
magnitude improvement over previous constraints.In the second type the initial
condition for the scalar is a free parameter leading to a somewhat stronger
constraint of $\omega > 890$ while $G_{eff}$ is constrained to $0.981
<\frac{G_{eff}}{G_N} <1.285$ at the same confidence level. We argue that these
constraints have greater validity than for the BD theory and are valid for any
Horndeski theory, the most general second-order scalar-tensor theory, which
approximates BD on cosmological scales. In this sense, our constraints place
strong limits on possible modifications of gravity that might explain cosmic
acceleration. | HIDM: Emulating Large Scale HI Maps using Score-based Diffusion Models: Efficiently analyzing maps from upcoming large-scale surveys requires gaining
direct access to a high-dimensional likelihood and generating large-scale
fields with high fidelity, which both represent major challenges. Using CAMELS
simulations, we employ the state-of-the-art score-based diffusion models to
simultaneously achieve both tasks. We show that our model, HIDM, is able to
efficiently generate high fidelity large scale HI maps that are in a good
agreement with the CAMELS's power spectrum, probability distribution, and
likelihood up to second moments. HIDM represents a step forward towards
maximizing the scientific return of future large scale surveys. |
The Electron Injection Spectrum Determined by Anomalous Excesses in
Cosmic Ray, Gamma Ray, and Microwave Signals: Recent cosmic ray, gamma ray, and microwave signals observed by Fermi,
PAMELA, and WMAP indicate an unexpected primary source of e+e- at 10-1000 GeV.
We fit these data to "standard backgrounds" plus a new source, assumed to be a
separable function of position and energy. For the spatial part, we consider
three cases: annihilating dark matter, decaying dark matter, and pulsars. In
each case, we use GALPROP to inject energy in log-spaced energy bins and
compute the expected cosmic-ray and photon signals for each bin. We then fit a
linear combination of energy bins, plus backgrounds, to the data. We use a
non-parametric fit, with no prior constraints on the spectrum except smoothness
and non-negativity. In addition, we consider arbitrary modifications to the
energy spectrum of the "ordinary" primary source function, fixing its spatial
part, finding this alone to be inadequate to explain the PAMELA or WMAP
signals. We explore variations in the fits due to choice of magnetic field,
primary electron injection index, spatial profiles, propagation parameters, and
fit regularization method. Dark matter annihilation fits well, where our fit
finds a mass of ~1 TeV and a boost factor times energy fraction of ~70. While
it is possible for dark matter decay and pulsars to fit the data,
unconventionally high magnetic fields and radiation densities are required near
the Galactic Center to counter the relative shallowness of the assumed spatial
profiles. We also fit to linear combinations of these three scenarios, though
the fit is much less constrained. | Estimation of imprints of the bounce in loop quantum cosmology on the
bispectra of cosmic microwave background: Primordial non-Gaussianity has set strong constraints on models of the early
universe. Studies have shown that Loop Quantum Cosmology (LQC), which is an
attempt to extend inflationary scenario to planck scales, leads to a strongly
scale dependent and oscillatory non-Gaussianity. In particular, the
non-Gaussianity function $f_{_{\rm NL}} (k_1,\, k_2,\, k_3)$ generated in LQC,
though similar to that generated during slow roll inflation at small scales, is
highly scale dependent and oscillatory at long wavelengths. In this work, we
investigate the imprints of such a primordial bispectrum in the bispectrum of
Cosmic Microwave Background (CMB). Inspired by earlier works, we propose an
analytical template for the primordial bispectrum in LQC. We write the template
as a sum of strongly scale dependent and oscillatory part, which captures the
contribution due to the bounce, and a part which captures the scale invariant
behaviour similar to that of slow roll. We then compute the reduced bispectra
of temperature and electric polarisation and their three-point
cross-correlations corresponding to these two parts. We show that the
contribution from the bounce to the reduced bispectrum is negligible compared
to that from the scale-independent part. Thus, we conclude that the CMB
bispectra generated in LQC will be similar to that generated in slow roll
inflation. We conclude with a discussion of our results and its implications to
LQC. |
CoReCon: an open, community-powered collection of Reionization
constraints: The number of available constraints on the Universe during and before cosmic
reionization is rapidly growing. These are often scattered across inhomogeneous
formats, unit systems and sampling strategies. In this paper, I introduce
CoReCon, a Python package designed to provide a growing set of constraints on
key physical quantities related to the Epoch of Reionization and a platform for
the high-redshift research community to collect and store, in an open way,
current and forthcoming observational constraints. | Tracing the Magellanic Clouds Back in Time: A solution is presented for the past motions of the Magellanic Clouds, the
Milky Way galaxy, and M31, fitted to the measured velocities of the Clouds and
M31, under some simplifying assumptions. The galaxies are modeled as isolated
bodies back to redshift about 10, when their velocities relative to the general
expansion of the universe were small, consistent with the gravitational
instability picture for the growth of structure. Mass outside the Local Group
is modeled as a third massive dynamical actor that is responsible for the
angular momentum of the Clouds. A plausible solution under these assumptions
requires that the circular velocity v_c of the Milky Way is in the range 200 to
230 km/s. The solution seems to be unique up to the modest variations allowed
by the choices of v_c and the position of the exterior mass. In this solution
the proto-Magellanic Clouds at high redshift were near the South pole of the
Milky Way (in its present orientation), at physical distance about 200 kpc from
the Milky Way and moving away at about 200 km/s. |
Introducing the Illustris Project: Simulating the coevolution of dark
and visible matter in the Universe: We introduce the Illustris Project, a series of large-scale hydrodynamical
simulations of galaxy formation. The highest resolution simulation,
Illustris-1, covers a volume of $(106.5\,{\rm Mpc})^3$, has a dark mass
resolution of ${6.26 \times 10^{6}\,{\rm M}_\odot}$, and an initial baryonic
matter mass resolution of ${1.26 \times 10^{6}\,{\rm M}_\odot}$. At $z=0$
gravitational forces are softened on scales of $710\,{\rm pc}$, and the
smallest hydrodynamical gas cells have an extent of $48\,{\rm pc}$. We follow
the dynamical evolution of $2\times 1820^3$ resolution elements and in addition
passively evolve $1820^3$ Monte Carlo tracer particles reaching a total
particle count of more than $18$ billion. The galaxy formation model includes:
primordial and metal-line cooling with self-shielding corrections, stellar
evolution, stellar feedback, gas recycling, chemical enrichment, supermassive
black hole growth, and feedback from active galactic nuclei. At $z=0$ our
simulation volume contains about $40,000$ well-resolved galaxies covering a
diverse range of morphologies and colours including early-type, late-type and
irregular galaxies. The simulation reproduces reasonably well the cosmic star
formation rate density, the galaxy luminosity function, and baryon conversion
efficiency at $z=0$. It also qualitatively captures the impact of galaxy
environment on the red fractions of galaxies. The internal velocity structure
of selected well-resolved disk galaxies obeys the stellar and baryonic
Tully-Fisher relation together with flat circular velocity curves. In the
well-resolved regime the simulation reproduces the observed mix of early-type
and late-type galaxies. Our model predicts a halo mass dependent impact of
baryonic effects on the halo mass function and the masses of haloes caused by
feedback from supernova and active galactic nuclei. | A new method for the Alcock-Paczynski test: We argue that from observations alone, only the transverse power spectrum
$C_\ell(z_1,z_2)$ and the corresponding correlation function
$\xi(\theta,z_1,z_2)$ can be measured and that these contain the full three
dimensional information. We determine the two point galaxy correlation function
at linear order in perturbation theory. Redshift space distortions are taken
into account for arbitrary angular and redshift separations. We discuss the
shape of the longitudinal and the transversal correlation functions which are
very different from each other and from their real space counterpart. We then
go on and suggest how to measure both, the Hubble parameter, $H(z)$, and the
angular diameter distance, $D_A(z)$, separately from these correlation
functions and perform an Alcock-Paczynski test. |
A dark energy view of inflation: Traditionally, inflationary models are analyzed in terms of parameters such
as the scalar spectral index ns and the tensor to scalar ratio r, while dark
energy models are studied in terms of the equation of state parameter w.
Motivated by the fact that both deal with periods of accelerated expansion, we
study the evolution of w during inflation, in order to derive observational
constraints on its value during an earlier epoch likely dominated by a dynamic
form of dark energy. We find that the cosmic microwave background and
large-scale structure data is consistent with w_inflation=-1 and provides an
upper limit of 1+w <~ 0.02. Nonetheless, an exact de Sitter expansion with a
constant w=-1 is disfavored since this would result in ns=1. | Diffuse $γ$-ray emission from misaligned active galactic nuclei: We calculate the diffuse $\gamma$-ray emission due to the population of
misaligned AGN (MAGN) unresolved by the Large Area Telescope (LAT) on the {\it
Fermi} Gamma-ray Space Telescope ({\it Fermi}). A correlation between the
$\gamma$-ray luminosity and the radio-core luminosity is established and
demonstrated to be physical by statistical tests, as well as compatible with
upper limits based on {\it Fermi}-LAT data for a large sample of radio-loud
MAGN. We constrain the derived $\gamma$-ray luminosity function by means of the
source count distribution of the MAGN detected by the {\it Fermi}-LAT. We
finally estimate the diffuse $\gamma$-ray flux due to the whole MAGN population
which ranges from 10% up to nearly the entire measured Isotropic Gamma-Ray
Background (IGRB). We evaluate also the room left to galactic DM at high
latitudes ($>10^\circ$), by taking into account the results on the MAGN
together with the other significant galactic and extragalactic $\gamma$-rays
emitting sources. |
Gas Accretion onto a Supermassive Black Hole: a step to model AGN
feedback: We study the gas accretion onto a supermassive black hole (SMBH) using the 3D
SPH code GADGET-3 on scales of 0.1-200 pc. First we test our code with
spherically symmetric, adiabatic Bondi accretion problem. We find that our
simulation can reproduce the expected Bondi accretion flow very well for a
limited amount of time until the effect of outer boundary starts to be visible.
We also find artificial heating of gas near the inner accretion boundary due to
the artificial viscosity of SPH. Second, we implement radiative cooling and
heating due to X-rays, and examine the impact of thermal feedback by the
central X-ray source. The accretion flow roughly follows the Bondi solution for
low central X-ray luminosities, however, the flow starts to exhibit
non-spherical fragmentation due to thermal instability for a certain range of
central L_X, and a strong overall outflow develops for greater L_X. The cold
gas develops filamentary structures that fall into the central SMBH, whereas
the hot gas tries to escape through the channels in-between the cold filaments.
Such fragmentation of accreting gas can assist in the formation of clouds
around AGN, induce star-formation, and contribute to the observed variability
of narrow-line regions. | On the operation of the chemothermal instability in primordial
star-forming clouds: We investigate the operation of the chemothermal instability in primordial
star-forming clouds with a suite of three-dimensional, moving-mesh simulations.
In line with previous studies, we find that the gas at the centre of
high-redshift minihaloes becomes chemothermally unstable as three-body
reactions convert the atomic hydrogen into a fully molecular gas. The
competition between the increasing rate at which the gas cools and the
increasing optical depth to H2 line emission creates a characteristic dip in
the cooling time over the free-fall time on a scale of 100 au. As a result, the
free-fall time decreases to below the sound-crossing time, and the cloud may
become gravitationally unstable and fragment on a scale of a few tens of au
during the initial free-fall phase. In three of the nine haloes investigated,
secondary clumps condense out of the parent cloud, which will likely collapse
in their own right before they are accreted by the primary clump. In the other
haloes, fragmentation at such an early stage is less likely. However, given
that previous simulations have shown that the infall velocity decreases
substantially once the gas becomes rotationally supported, the amount of time
available for perturbations to develop may be much greater than is evident from
the limited period of time simulated here. |
Large-Scale Structure with Gravitational Waves I: Galaxy Clustering: Observed angular positions and redshifts of large-scale structure tracers
such as galaxies are affected by gravitational waves through volume distortion
and magnification effects. Thus, a gravitational wave background can in
principle be probed through clustering statistics of large-scale structure. We
calculate the observed angular clustering of galaxies in the presence of a
gravitational wave background at linear order including all relativistic
effects. For a scale-invariant spectrum of gravitational waves, the effects are
most significant at the smallest multipoles (2 <= l <= 5), but typically
suppressed by six or more orders of magnitude with respect to scalar
contributions for currently allowed amplitudes of the inflationary
gravitational wave background. We also discuss the most relevant second-order
terms, corresponding to the distortion of tracer correlation functions by
gravitational waves. These provide a natural application of the approach
recently developed in arXiv:1204.3625. | Testing atomic collision theory with the two-photon continuum of
astrophysical nebulae: Accurate rates for energy-degenerate l-changing collisions are needed to
determine cosmological abundances and recombination. There are now several
competing theories for the treatment of this process, and it is not possible to
test these experimentally. We show that the H I two-photon continuum produced
by astrophysical nebulae is strongly affected by l-changing collisions. We
perform an analysis of the different underlying atomic processes and simulate
the recombination and two-photon spectrum of a nebula containing H and He. We
provide an extended set of effective recombination coefficients and updated
l-changing 2s-2p transition rates using several competing theories. In
principle, accurate astronomical observations could determine which theory is
correct. |
The detectability of strong 21 centimetre forest absorbers from the
diffuse intergalactic medium in late reionisation models: A late end to reionisation at redshift $z\simeq 5.3$ is consistent with
observed spatial variations in the Ly$\alpha$ forest transmission and the
deficit of Ly$\alpha$ emitting galaxies around extended Ly$\alpha$ absorption
troughs at $z=5.5$. In this model, large islands of neutral hydrogen should
persist in the diffuse intergalactic medium (IGM) until $z\simeq 6$. We use a
novel, hybrid approach that combines high resolution cosmological
hydrodynamical simulations with radiative transfer to predict the incidence of
strong 21 cm forest absorbers with optical depths $\tau_{21}>10^{-2}$ from the
diffuse IGM in these late reionisation models. We include the effect of
redshift space distortions on the simulated 21 cm forest spectra, and treat the
highly uncertain heating of the pre-reionisation IGM by soft X-rays as a free
parameter. For a model with only modest IGM pre-heating, such that average gas
kinetic temperatures in the diffuse IGM remain below $T_{\rm K}\simeq 10^{2}
\rm\, K$, we find that strong 21 cm forest absorption lines should persist
until $z=6$. For a sample of $\sim 10$ sufficiently radio loud background
sources, a null-detection of 21 cm forest absorbers at $z\simeq 6$ with
SKA1-low or possibly LOFAR should provide an informative lower limit on the
still largely unconstrained soft X-ray background at high redshift and the
temperature of the pre-reionisation IGM. | UPCluster-SZ: The Updated Catalog of Galaxy Clusters from the List of
Planck Sunyaev-Zeldovich Sources: We present the updated galaxy cluster catalog of the second Planck catalog of
Sunyaev-Zeldovich sources (PSZ2) through the compilation of the data for
clusters and galaxies with spectroscopically measured redshifts in the
literature. The original version of PSZ2 comprises 1653 SZ sources, of which
1203 have been validated as genuine galaxy clusters, while the remaining 450
sources are yet to be validated. To increase the number of genuine clusters in
PSZ2, we first update the validations of the cluster candidates and their
redshift information using the data compiled for the confirmed clusters and the
member galaxies in the literature. We then use the galaxy redshift data in the
fields of the remaining cluster candidates, by searching for possible member
galaxies with measured spectroscopic redshifts around the Sunyaev-Zeldovich
centroids. In this search process, we classify clusters as strong candidates if
they contain more than nine galaxies within a 4500 km s$^{-1}$ velocity range
and within 15 arcmin around the Sunyaev-Zeldovich centroids. This process
results in the validation of 139 new genuine clusters, the update of redshift
information on 399 clusters, and the identification of 10 strong candidates,
which increases the number of validated clusters up to 1334 among the 1653 SZ
sources. Our updated galaxy cluster catalog will be very useful for the studies
of galaxy formation and cosmology through the combination with other all-sky
surveys including WISE and SPHEREx. |
Evidence for AGN-driven Outflows in Young Radio Quasars: We present near-infrared spectra of young radio quasars [P(1.4GHz) ~ 26-27
W/Hz] selected from the Wide-Field Infrared Survey Explorer. The detected
objects have typical redshifts of z ~ 1.6-2.5 and bolometric luminosities ~
10^47 erg/s. Based on the intensity ratios of narrow emission lines, we find
that these objects are mainly powered by active galactic nuclei (AGNs),
although star formation contribution cannot be completely ruled out. The host
galaxies experience moderate levels of extinction, A(V) ~ 0-1.3 mag. The
observed [O III] luminosities and rest-frame J-band magnitudes constrain the
black hole masses to lie in the range ~ 10^8.9-10^9.7 solar mass. From the
empirical correlation between black hole mass and host galaxy mass, we infer
stellar masses of ~ 10^11.3-10^12.2 solar mass. The [O III] line is
exceptionally broad, with full width at half maximum ~1300 to 2100 km/s,
significantly larger than that of ordinary distant quasars. We argue that these
large line widths can be explained by jet-induced outflows, as predicted by
theoretical models of AGN feedback. | The First Stars: Mass Growth Under Protostellar Feedback: We perform three-dimensional cosmological simulations to examine the growth
of metal-free, Population III (Pop III) stars under radiative feedback. We
begin our simulation at z=100 and trace the evolution of gas and dark matter
until the formation of the first minihalo. We then follow the collapse of the
gas within the minihalo up to densities of n = 10^12 cm^-3, at which point we
replace the high-density particles with a sink particle to represent the
growing protostar. We model the effect of Lyman-Werner (LW) radiation emitted
by the protostar, and employ a ray-tracing scheme to follow the growth of the
surrounding H II region over the next 5000 yr. We find that a disk assembles
around the first protostar, and that radiative feedback will not prevent
further fragmentation of the disk to form multiple Pop III stars. Ionization of
neutral hydrogen and photodissociation of H_2 by LW radiation leads to heating
of the dense gas to several thousand Kelvin, and this warm region expands
outward at the gas sound speed. Once the extent of this warm region becomes
equivalent to the size of the disk, the disk mass declines while the accretion
rate onto the protostars is reduced by an order of magnitude. This occurs when
the largest sink has grown to ~ 20 M_sol while the second sink has grown to 7
M_sol, and we estimate the main sink will approach an asymptotic value of ~ 30
M_sol by the time it reaches the main sequence. Our simulation thus indicates
that the most likely outcome is a massive Pop III binary. However, we simulate
only one minihalo, and the statistical variation between minihaloes may be
substantial. If Pop III stars were typically unable to grow to more than a few
tens of solar masses, this would have important consequences for the occurence
of pair-instability supernovae in the early Universe as well as the Pop III
chemical signature in the oldest stars observable today. |
A model-independent reconstruction of dark energy to very high redshift: We provide a model-independent reconstruction of dark energy from $z=0$ to $
\gtrsim 10^5$. We parameterise the model by a perfect fluid with a series of
physically well-motivated bins in energy-density, such that the equation of
state is always $-1 \le w \le 1$. Our method is capable of describing a range
of theoretical models with smooth modifications to the expansion history.
Combining the latest CMB, BAO, SN and local $H_0$ measurements, we obtain a
large improvement of $\Delta \chi^2=41.3$ over LCDM, at the expense of 33
additional parameters in the fit, with dark energy contributing significantly
between $z \sim 10^4 - 10^5$, and intriguingly with a sound speed $c_s^2 \sim
1/3$. A significant part of the $\Delta \chi^2$ improvement comes from \Planck\
+ Atacama Cosmology Telescope (\textsc{Act}) data, alleviating tension between
them within LCDM. We apply a correlation prior to penalise models with
unnecessary degrees of freedom and find no preference for deviations from LCDM
at late-times, but moderate Bayesian evidence of an early dark energy (EDE)
component. Although the model has a large amount of freedom, it is unable to
reduce $S_8 \equiv \sigma_8 (\Omega_\mathrm{c} / 0.3)^{0.5}$ below that of
\lcdm, to bring about full concordance with large-scale structure data. | Sterile Neutrinos: Cosmology vs Short-BaseLine Experiments: Cosmology and short baseline neutrino oscillation data both hint at the
existence of light sterile neutrinos with masses in the 1 eV range. Here we
perform a detailed analysis of the sterile neutrino scenario using both
cosmological and SBL data. We have additionally considered the possibility that
the extra neutrino degrees of freedom are not fully thermalised in the early
universe. Even when analyzing only cosmological data we find a preference for
the existence of massive sterile neutrinos in both (3+1) and (3+2) scenarios,
and with the inclusion of SBL data the evidence is formally at the 3.3sigma
level in the case of a (3+1) model. Interestingly, cosmological and SBL data
both point to the same mass scale of approximately 1 eV. In the (3+1) framework
WMAP9+SPT provide a value of the sterile mass eigenstate m_4 = (1.72 \pm 0.65)
eV: this result is strenghtened by adding the prior from SBL posterior to m_4 =
(1.27 \pm 0.12) eV (m_4 = (1.23 \pm 0.13) eV when SDSS is also considered in
the cosmological analysis). In the (3+2) scheme, two additional, non--fully
thermalized, neutrinos are compatible with the whole set of cosmological and
SBL data, leading to mass values of m_4 = (0.95 \pm 0.30) eV and m_5 = (1.59
\pm 0.49) eV. The inclusion of Planck data does not change our considerations
about the mass scale; concerning the extra neutrino degrees of freedom,
invoking a partial thermalisation the 3+1 model is still consistent with the
latest data. |
Radiatively enhanced elasticity and turbulence in clumpy tori of Active
Galactic Nuclei: The paper assumes radiation forces proportional to distance between equal
temperature clouds. However, we assume there are clouds in any direction. The
forces then cancel almost entirely, besides small velocity effects. Therefore,
the presented theory is inadequate. | Revisiting the cosmological bias due to local gravitational redshifts: A recent article by Wojtak {\it et al} (arXiv:1504.00718) pointed out that
the local gravitational redshift, despite its smallness ($\sim 10^{-5}$), can
have a noticeable ($\sim 1\%$) systematic effect on our cosmological parameter
measurements. The authors studied a few extended cosmological models (nonflat
$\Lambda$CDM, $w$CDM, and $w_0$-$w_a$CDM) with a mock supernova data set. We
repeat this calculation and find that the $\sim 1\%$ biases are due to strong
degeneracy between cosmological parameters. When cosmic microwave background
(CMB) data are added to break the degeneracy, the biases due to local
gravitational redshift are negligible ($\lesssim 0.1 \sigma$). |
Intrinsic Shape of Star-Forming BzK Galaxies II: Rest-Frame UV and
Optical Structures in GOODS-South and SXDS: (Abridge) We study statistical intrinsic shape of star-forming BzK galaxies
(sBzK galaxies) at z~2 in both rest-frame UV and rest-frame optical
wavelengths. The sBzK galaxies are selected down to K(AB)=24.0 mag in the
GOODS-South and SXDS fields, where high-resolution images from Hubble Space
Telescope are publicly available. 57% (583) of all 1028 galaxies in GOODS-S
show a single component in the ACS/F850LP image. As WFC3/F160W images cover
only some part of GOODS-S and SXDS, 724/1028 and 2500/29835 sBzK galaxies in
the GOODS-S and SXDS have the WFC3 coverage. 86% (626) and 82% (2044) of the
sBzK galaxies in WFC3/F160W images appear as a single component in the GOODS-S
and SXDS, respectively. Larger fraction of single-component objects in F850LP
images represents multiple star-forming regions in galaxies, while they are not
so obvious in the F160W image which appears smoother. Most of the
single-component sBzK galaxies show S\'ersic indices of n=0.5-2.5, in agreement
with those of local disk galaxies. Their effective radii are 1.0-3.0 kpc and
1.5-4.0 kpc in F850LP and F160W images, respectively, regardless of the
observed fields. Stellar surface mass density of the sBzK galaxies is also
comparable to that of the local disk galaxies. However, the intrinsic shape of
sBzK galaxies is not a round disk as seen in the local disk galaxies. By
comparing apparent axial ratio (b/a) distributions of the sBzK galaxies with
those by assuming tri-axial model with axes A>B>C, we found their intrinsic
face-on B/A ratios peak at B/A=0.70 and B/A=0.77-0.79 in the rest-frame UV and
optical, respectively and are statistically more bar-like than that of the
local disk galaxies. The intrinsic edge-on C/A ratios in both rest-frame UV and
optical wavelengths peak at 0.26, which is slightly larger than that of the
local disk galaxies. | Dissecting the Red Sequence - III. Mass-to-Light Variations in 3D
Fundamental Plane Space: The Fundamental Plane has finite thickness and is tilted from the virial
relation, indicating that dynamical mass-to-light ratios (Mdyn/L) vary among
early type galaxies. We use a sample of 16,000 quiescent galaxies from the
Sloan Digital Sky Survey to map out variations in Mdyn/L through the 3D
Fundamental Plane space defined by velocity dispersion (sigma), effective
radius (R_e), and effective surface brightness. We consider contributions to
Mdyn/L variation due to stellar population effects, IMF variations, and
variations in the dark matter fraction within one R_e. Along the FP, we find
that the stellar population contribution scales as M*/L ~ f(sigma), while the
dark matter and/or IMF contribution scales as Mdyn/M* ~ g(Mdyn). The two
contributions to the tilt of the FP rotate the plane around different axes in
the 3D space, with dark matter/IMF variations likely dominating. Through the
thickness of the FP, we find that Mdyn/L variations must be dominated either by
IMF variations or by real differences in dark matter fraction with R_e. Thus
the finite thickness of the FP is due to variations in the stellar mass surface
density within R_e, not the fading of passive stellar populations. These
structural variations are correlated with galaxy star formation histories such
that galaxies with higher Mdyn/M* at a given sigma have higher [Mg/Fe], lower
metallicities, and older mean stellar ages. It is difficult to explain the
observed correlations by allowing the IMF to vary, suggesting difference in
dark matter fraction dominate. These can be produced by variations in the
"conversion efficiency" of baryons into stars or by the redistribution of stars
and dark matter through dissipational merging. A model in which some galaxies
experience low conversion efficiencies due to premature truncation of star
formation provides a natural explanation for the observed trends. |
A gauge-invariant approach to interactions in the dark sector: We outline a gauge-invariant framework to calculate cosmological
perturbations in dark energy models consisting of a scalar field interacting
with dark matter via energy and momentum exchanges. Focusing on three
well-known models of quintessence and three common types of dark-sector
interactions, we calculate the matter and dark energy power spectra as well as
the Integrated Sachs-Wolfe (ISW) effect in these models. We show how the
presence of dark-sector interactions can produce a large-scale enhancement in
the matter power spectrum and a boost in the low multipoles of the cosmic
microwave background anisotropies. Nevertheless, we find these enhancements to
be much more subtle than those found by previous authors who model dark energy
using simple ansatz for the equation of state. We also address issues of
instabilities and emphasise the importance of momentum exchanges in the dark
sector. | Anomalies in Physical Cosmology: The $\Lambda$CDM cosmology passes demanding tests that establish it as a good
approximation to reality. The theory is incomplete, of course, and open issues
are being examined in active research programs. I offer a review of less widely
discussed anomalies that might also point to hints to a still better
cosmological theory if more closely examined. |
Sizing up Lyman-alpha and Lyman Break Galaxies: We show that populations of high redshift galaxies grow more luminous as they
grow in linear size. This is because the brightness per unit area has a
distinct upper limit due to the self-regulating nature of star-formation. As a
corollary, we show that the observed increase in characteristic luminosity of
Lyman Break Galaxies (L*) with time can be explained by their increase in size,
which scales as 1/H(z). In contrast, Lyman-alpha selected galaxies have a
characteristic, constant, small size between redshift z=2.25 and 6.5. Coupled
with a characteristic surface brightness, this can explain their non-evolving
ultraviolet continuum luminosity function. This compact physical size seems to
be a critical determining factor in whether a galaxy will show Lyman-alpha
emission. We base these conclusions on new size measurements for a sample of
about 170 Lyman-alpha selected galaxies with Hubble Space Telescope broad-band
imaging, over the redshift range 2.25 < z < 6. We combine these with a similar
number of Lyman-alpha selected galaxies with half-light radii from the
literature, and derive surface brightnesses for the entire combined sample. | How the diffuse Universe cools: In this work we investigate the cooling channels of diffuse gas (i.e. n_H<0.1
cm^-3) in cosmology. We aim to identify the wavelengths where most of the
energy is radiated in the form of emission lines or continuum radiation, and
the main elements and ions responsible for the emission. We use a subset of
cosmological, hydrodynamical runs from the OWLS project to calculate the
emission of diffuse gas and its evolution with time. We find that at z=0 (z=2)
about 70 (80) per cent of the energy emitted by diffuse gas is carried by
emission lines, with the continuum radiation contributing the remainder.
Hydrogen lines in the Lyman series are the primary contributors to the line
emission, with a share of 16 (20) per cent. Oxygen lines are the main metal
contributors at high redshift, while silicon, carbon and iron lines are
strongest at low redshift, when the contributions of AGB stars and supernova Ia
explosions to the metal budget become important and when there is more hot gas.
The ionic species carrying the most energy are OIII, CII, CIII, SiII, SiIII,
FeII and SIII. The great majority of energy is emitted in the UV band
(lambda=100-4000 A), both as continuum radiation and line emission. With almost
no exception, all the strongest lines fall in this band. At high energies,
continuum radiation is dominant (e.g., 80 per cent in the X-ray band), while
lines contribute progressively more at lower energies. While the results do
depend on the details of the numerical implementation of the physical processes
modelled in the simulations, the comparison of results from different
simulations demonstrates that the variations are overall small, and that the
conclusions are fairly robust. Given the overwhelming importance of UV emission
for the cooling of diffuse gas, it is desirable to build instruments dedicated
to the detection and characterisation of diffuse UV emission. |
Recovering Stellar Population Properties and Redshifts from Broad-Band
Photometry of Simulated Galaxies: Lessons for SED Modeling: We present a detailed analysis of our ability to determine stellar masses,
ages, reddening and extinction values, and star formation rates of
high-redshift galaxies by modeling broad-band SEDs with stellar population
synthesis. In order to do so, we computed synthetic optical-to-NIR SEDs for
model galaxies taken from hydrodynamical merger simulations placed at redshifts
1.5 < z < 3. Viewed under different angles and during different evolutionary
phases, the simulations represent a wide variety of galaxy types (disks,
mergers, spheroids). We show that simulated galaxies span a wide range in SEDs
and color, comparable to these of observed galaxies. In all star-forming
phases, dust attenuation has a large effect on colors, SEDs, and fluxes. The
broad-band SEDs were then fed to a standard SED modeling procedure and
resulting stellar population parameters were compared to their true values.
Disk galaxies generally show a decent median correspondence between the true
and estimated mass and age, but suffer from large uncertainties. During the
merger itself, we find larger offsets (e.g., log M_recovered - log M_true =
-0.13^{+0.10}_{-0.14}). E(B-V) values are generally recovered well, but the
estimated total visual absorption Av is consistently too low, increasingly so
for larger optical depths. Since the largest optical depths occur during the
phases of most intense star formation, it is for the highest SFRs that we find
the largest underestimates. The masses, ages, E(B-V), Av, and SFR of merger
remnants (spheroids) are very well reproduced. We discuss possible biases in
SED modeling results caused by mismatch between the true and template star
formation history, dust distribution, metallicity variations and AGN
contribution. | Planck 2013 results. IV. Low Frequency Instrument beams and window
functions: This paper presents the characterization of the in-flight beams, the beam
window functions and the associated uncertainties for the Planck Low Frequency
Instrument (LFI). Knowledge of the beam profiles is necessary for determining
the transfer function to go from the observed to the actual sky anisotropy
power spectrum. The main beam distortions affect the beam window function,
complicating the reconstruction of the anisotropy power spectrum at high
multipoles, whereas the sidelobes affect the low and intermediate multipoles.
The in-flight assessment of the LFI main beams relies on the measurements
performed during Jupiter observations. By stacking the data from multiple
Jupiter transits, the main beam profiles are measured down to -20 dB at 30 and
44 GHz, and down to -25 dB at 70 GHz. The main beam solid angles are determined
to better than 0.2% at each LFI frequency band. The Planck pre-launch optical
model is conveniently tuned to characterize the main beams independently of any
noise effects. This approach provides an optical model whose beams fully
reproduce the measurements in the main beam region, but also allows a
description of the beams at power levels lower than can be achieved by the
Jupiter measurements themselves. The agreement between the simulated beams and
the measured beams is better than 1% at each LFI frequency band. The simulated
beams are used for the computation of the window functions for the effective
beams. The error budget for the window functions is estimated from both main
beam and sidelobe contributions, and accounts for the radiometer bandshapes.
The total uncertainties in the effective beam window functions are: 2% and 1.2%
at 30 and 44 GHz, respectively (at $\ell \approx 600$), and 0.7% at 70 GHz (at
$\ell \approx 1000$). |
Probing Theories of Gravity with Phase Space-Inferred Potentials of
Galaxy Clusters: Modified theories of gravity provide us with a unique opportunity to generate
innovative tests of gravity. In Chameleon f(R) gravity, the gravitational
potential differs from the weak-field limit of general relativity (GR) in a
mass dependent way. We develop a probe of gravity which compares high mass
clusters, where Chameleon effects are weak, to low mass clusters, where the
effects can be strong. We utilize the escape velocity edges in the
radius/velocity phase space to infer the gravitational potential profiles on
scales of 0.3-1 virial radii. We show that the escape edges of low mass
clusters are enhanced compared to GR, where the magnitude of the difference
depends on the background field value |fR0|. We validate our probe using N-body
simulations and simulated light cone galaxy data. For a DESI (Dark Energy
Spectroscopic Instrument) Bright Galaxy Sample, including observational
systematics, projection effects, and cosmic variance, our test can
differentiate between GR and Chameleon f(R) gravity models, |fR0| = 4e-6 (2e-6)
at > 5{\sigma} (> 2{\sigma}), more than an order of magnitude better than
current cluster-scale constraints. | Big Bang Nucleosynthesis constraints on $f(T, \mathcal{T})$ gravity: Big Bang Nucleosynthesis provides us with an observational insight into the
very early Universe. Since this mechanism of light element synthesis comes out
of the standard model of particle cosmology which follows directly from General
Relativity, it is expected that any modifications to GR will result in
deviations in the predicted observable parameters which are mainly, the
neutron-to-proton ratio and the baryon-to-photon ratio. We use the measured
neutron-to-proton ratio and compare the theoretically obtained expressions to
constrain two models in the framework of $ f(T,\mathcal{T}) $ gravity. The
theoretically constrained models are then tested against observational data
from the Hubble dataset and the $ \Lambda $CDM model to explain the accelerated
expansion of the Universe. |
Radio studies of galaxy formation: Dense Gas History of the Universe: Line and continuum studies at centimeter through submillimeter wavelengths
address probe deep into the earliest, most active and dust obscured phases of
galaxy formation, and reveal the molecular and cool atomic gas. We summarize
the techniques of radio astronomy to perform these studies, then review the
progress on radio studies of galaxy formation. The dominant work over the last
decade has focused on massive, luminous starburst galaxies (submm galaxies and
AGN host galaxies). The far infrared luminosities are ~ 1e13 Lsun, implying
star formation rates, SFR > 1e3 Msun/year. Molecular gas reservoirs are found
with masses: M(H_2) > 1e10 (alpha/0.8}) Msun. The CO excitation in these
luminous systems is much higher than in low redshift spiral galaxies. Imaging
of the gas distribution and dynamics suggests strongly interacting and merging
galaxies, indicating gravitationally induced, short duration (~ 1e7 year)
starbursts. These systems correspond to a major star formation episode in
massive galaxies in proto-clusters at intermediate to high redshift. Recently,
radio observations have probed the more typical star forming galaxy population
(SFR ~ 100 Msun/year), during the peak epoch of Universal star formation (z ~
1.5 to 2.5). These observations reveal massive gas reservoirs without
hyper-starbursts, and show that active star formation occurs over a wide range
in galaxy stellar mass. The conditions in this gas are comparable to those
found in the Milky Way disk. A key result is that the peak epoch of star
formation in the Universe also corresponds to an epoch when the baryon content
of star forming galaxies was dominated by molecular gas, not stars. We consider
the possibility of tracing out the dense gas history of the Universe, and
perform initial, admittedly gross, calculations. ABRIDGED | Exploring the Hubble Tension: A Novel Approach through Cosmological
Observations: The simplest cosmological model ($\Lambda$CDM) is well-known to suffer from
the Hubble tension, namely an almost $5 \sigma$ discrepancy between the
(model-based) early-time determination of the Hubble constant $H_0$ and its
late-time (and model-independent) determination. To circumvent this, we
introduce an additional energy source that varies with the redshift as $(1 +
z)^n$, where $0 < n < 3$, and test it against the Pantheon Compilation of Type
Ia Supernovae as well as the CMBR observations (at $z \approx 1100$). The
deduced $H_0$ is now well-consistent with the value obtained from local
observations of Cepheid variables. Suggesting a non-zero value for the
curvature density parameter, positive (negative) for $n > 2$ ($n < 2$), the
resolution is also consistent with the BAO data. |
The scatter about the "Universal" dwarf spheroidal mass profile: A
kinematic study of the M31 satellites, And V and And VI: While the satellites of the Milky Way (MW) have been shown to be largely
consistent in terms of their mass contained within one half--light radius
(M_{half}) with a "Universal" mass profile, a number of M31 satellites are
found to be inconsistent with such relations, and seem kinematically colder in
their central regions than their MW cousins. In this work, we present new
kinematic and updated structural properties for two M31 dSphs, And V and And VI
using data from the Keck Low Resolution Imaging Spectrograph (LRIS) and the
DEep Imaging Multi-Object Spectrograph (DEIMOS) instruments and the Subaru
Suprime-Cam imager. We measure systemic velocities of v_r=-393.1+/-4.2km/s and
-344.8+/-2.5km/s, and dispersions of sigma_v=11.5{+5.3}{-4.4}km/s and
sigma_v=9.4{+3.2}{-2.4}km/s for And V and And VI respectively, meaning these
two objects are consistent with the trends in sigma_v and r_{half} set by their
MW counterparts. We also investigate the nature of this scatter about the MW
dSph mass profiles for the "Classical" (i.e. M_V<-8) MW and M31 dSphs. When
comparing both the "classical" MW and M31 dSphs to the best--fit mass profiles
in the size--velocity dispersion plane, we find general scatter in both the
positive (i.e. hotter) and negative (i.e. colder) directions from these
profiles. However, barring one exception (CVnI) only the M31 dSphs are found to
scatter towards a colder regime, and, excepting the And I dSph, only MW objects
scatter to hotter dispersions. We also note that the scatter for the combined
population is greater than expected from measurement errors alone. We assess
this divide in the context of the differing disc-to-halo mass (i.e. stars and
baryons to total virial mass) ratios of the two hosts and argue that the
underlying mass profiles for dSphs differ from galaxy to galaxy, and are
modified by the baryonic component of the host. | Scaling Relations Between Low-mass Black Holes and Their Host Galaxies: It is well established that supermassive black holes in nearby elliptical
galaxies correlate tightly with the kinematic property ($\mbhsigma$
correlation) and stellar mass ($\mbhhost$ correlation) of their host spheroids.
However, it is not clear what the relations would be at the low-mass end, and
how they evolve. Here, we investigate these relations in low-mass systems
($\MBH \sim \rm{10^{6}- 10^{8}}\, \Msun$) using the Aquila Simulation, a
high-resolution cosmological hydrodynamic simulation which follows the
formation and evolution of stars and black holes in a Milky Way-size galaxy and
its substructures. We find a number of interesting results on the origin and
evolution of the scaling relations in these systems: (1) there is a strong
redshift evolution in the $\mbhsigma$ relation, but a much weaker one in the
$\mbhhost$ relation; (2) there is a close link between the $\mbhsigma$ relation
and the dynamical state of the system -- the galaxies that fall on the observed
correlation appear to have reached virial equilibrium. (3) the star formation
and black hole growth are self-regulated in galaxies -- the ratio between black
hole accretion rate and star formation rate remains nearly constant in a wide
redshift span $z = 0-6$. These findings suggest that the observed correlations
have different origins: the $\mbhsigma$ relation may be the result of virial
equilibrium, while the $\mbhhost$ relation may the result of self-regulated
star formation and black hole growth in galaxies. |
Planck constraints on neutrino isocurvature density perturbations: The recent Cosmic Microwave Background data from the Planck satellite
experiment, when combined with HST determinations of the Hubble constant, are
compatible with a larger, non-standard, number of relativistic degrees of
freedom at recombination, parametrized by the neutrino effective number
$N_{eff}$. In the curvaton scenario, a larger value for $N_{eff}$ could arise
from a non-zero neutrino chemical potential connected to residual neutrino
isocurvature density (NID) perturbations after the decay of the curvaton field,
parametrized by the amplitude $\alpha^{NID}$. Here we present new constraints
on $N_{eff}$ and $\alpha^{NID}$ from an analysis of recent cosmological data.
We found that the Planck+WP dataset does not show any indication for a neutrino
isocurvature component, severly constraining its amplitude, and that current
indications for a non-standard $N_{eff}$ are further relaxed. | The intriguing life of star-forming galaxies in the redshift range 1 < z
< 2 using MASSIV: MASSIV (Massiv Assembly Survey with SINFONI in VVDS) is an ESO large program
which consists of 84 star-forming galaxies, spanning in a wide range of stellar
masses, observed with the IFU SINFONI on the VLT, in the redshift range 1 < z <
2. To be representative of the normal galaxy population, the sample has been
selected from a well-defined, complete and representative parent sample. The
kinematics of individual galaxies reveals that 58% of the galaxies are slow
rotators, which means that a high fraction of these galaxies should probably be
formed through major merger processes which might have produced gaseous thick
or spheroidal structures supported by velocity dispersion rather than by
rotation. Computations on the major merger rate from close pairs indicate that
a typical star-forming galaxy underwent ~0.4 major mergers since ~9.5 Gyr,
showing that merging is a major process driving mass assembly into the red
sequence galaxies. These objects are also intriguing due to the fact that more
than one galaxy over four is more metal-rich in its outskirts than in its
center. |
Dark Matter Velocity Distributions: Comparing Numerical Simulations to
Analytic Results: We test the consistency of dark matter velocity distributions obtained from
dark matter-only numerical simulations with analytic predictions, using the
publicly available Via Lactea 2 dataset as an example. We find that, well
inside the scale radius, the velocity distribution obtained from numerical
simulation is consistent with a function of a single integral of motion -- the
energy -- and moreover is consistent with the result obtained from Eddington
inversion. This indicates that the assumptions underlying the analytic result,
namely, spherical symmetry, isotropy, and a static potential, are sufficiently
accurate to govern the coarse properties of the velocity distribution in the
inner regions of the halo. We discuss implications for the behavior of the
high-velocity tail of the distribution, which can dominate dark matter
annihilation from a $p$- or $d$-wave state. | A buyer's guide to the Hubble Constant: Since the expansion of the universe was first established by Edwin Hubble and
Georges Lemaitre about a century ago, the Hubble constant H0 which measures its
rate has been of great interest to astronomers. Besides being interesting in
its own right, few properties of the universe can be deduced without it. In the
last decade a significant gap has emerged between different methods of
measuring it, some anchored in the nearby universe, others at cosmological
distances. The SH0ES team has found $H_0 = 73.2 \pm 1.3$ km sec$^{-1}$
Mpc$^{-1}$ locally, whereas the value found for the early universe by the
Planck Collaboration is $H_0 = 67.4 \pm 0.5$ km sec$^{-1}$ Mpc$^{-1}$ from
measurements of the cosmic microwave background. Is this gap a sign that the
well-established $\Lambda$CDM cosmological model is somehow incomplete? Or are
there unknown systematics? And more practically, how should humble astronomers
pick between competing claims if they need to assume a value for a certain
purpose? In this article, we review results and what changes to the
cosmological model could be needed to accommodate them all. For astronomers in
a hurry, we provide a buyer's guide to the results, and make recommendations. |
Beyond Spherical Top Hat Collapse: We study the evolution of inhomogeneous spherical perturbations in the
universe in a way that generalizes the spherical top hat collapse in a
straightforward manner. For that purpose we derive a dynamical equation for the
evolution of the density contrast in the context of a Lemaitre-Tolman-Bondi
metric and construct solutions with and without a cosmological constant for the
evolution of a spherical perturbation with a given initial radial profile. | Slowly fading super-luminous supernovae that are not pair-instability
explosions: Super-luminous supernovae that radiate more than 10^44 ergs per second at
their peak luminosity have recently been discovered in faint galaxies at
redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability'
supernovae. Such models involve stars with original masses 140-260 times that
of the Sun that now have carbon-oxygen cores of 65-30 solar masses. In these
stars, the photons that prevent gravitational collapse are converted to
electron-positron pairs, causing rapid contraction and thermonuclear
explosions. Many solar masses of 56Ni are synthesized; this isotope decays to
56Fe via 56Co, powering bright light curves. Such massive progenitors are
expected to have formed from metal-poor gas in the early Universe. Recently,
supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after
the Big Bang) with a metallicity one-third that of the Sun was observed to look
like a fading pair-instability supernova. Here we report observations of two
slow-to-fade super-luminous supernovae that show relatively fast rise times and
blue colours, which are incompatible with pair-instability models. Their
late-time light-curve and spectral similarities to supernova 2007bi call the
nature of that event into question. Our early spectra closely resemble typical
fast-declining super-luminous supernovae, which are not powered by
radioactivity. Modelling our observations with 10-16 solar masses of
magnetar-energized ejecta demonstrates the possibility of a common explosion
mechanism. The lack of unambiguous nearby pair-instability events suggests that
their local rate of occurrence is less than 6x10^-6 times that of the
core-collapse rate. |
Dark matter haloes determine the masses of supermassive black holes: The energy and momentum deposited by the radiation from accretion onto the
supermassive black holes (BHs) that reside at the centres of virtually all
galaxies can halt or even reverse gas inflow, providing a natural mechanism for
supermassive BHs to regulate their growth and to couple their properties to
those of their host galaxies. However, it remains unclear whether this
self-regulation occurs on the scale at which the BH is gravitationally
dominant, on that of the stellar bulge, the galaxy, or that of the entire dark
matter halo. To answer this question, we use self-consistent simulations of the
co-evolution of the BH and galaxy populations that reproduce the observed
correlations between the masses of the BHs and the properties of their host
galaxies. We first confirm unambiguously that the BHs regulate their growth:
the amount of energy that the BHs inject into their surroundings remains
unchanged when the fraction of the accreted rest mass energy that is injected,
is varied by four orders of magnitude. The BHs simply adjust their masses so as
to inject the same amount of energy. We then use simulations with artificially
reduced star formation rates to demonstrate explicitly that BH mass is not set
by the stellar mass. Instead, we find that it is determined by the mass of the
dark matter halo with a secondary dependence on the halo concentration, of the
form that would be expected if the halo binding energy were the fundamental
property that controls the mass of the BH. We predict that the logarithmic
slope of the relation between dark matter halo mass and black hole mass is
1.55+/-0.05 and that the scatter around the mean relation in part reflects the
scatter in the halo concentration-mass relation. | Beyond the best-fit parameter: new insight on galaxy structure
decomposition from GALPHAT: We introduce a novel image decomposition package, GALPHAT, that provides
robust estimates of galaxy surface brightness profiles using Bayesian Markov
Chain Monte Carlo. The GALPHAT-determined posterior distribution of parameters
enables us to assign rigorous statistical confidence intervals to maximum a
posteriori estimates and to test complex galaxy formation and evolution
hypotheses. We describe the GALPHAT algorithm, assess its performance using
test image data, and demonstrate that it has sufficient speed for production
analysis of a large galaxy sample. Finally we briefly introduce our ongoing
science program to study the distribution of galaxy structural properties in
the local universe using GALPHAT. |
Exploration of the polarization angle variability of the Crab Nebula
with POLARBEAR and its application to the search for axion-like particles: The Crab Nebula, also known as Tau A, is a polarized astronomical source at
millimeter wavelengths. It has been used as a stable light source for
polarization angle calibration in millimeter-wave astronomy. However, it is
known that its intensity and polarization vary as a function of time at a
variety of wavelengths. Thus, it is of interest to verify the stability of the
millimeter-wave polarization. If detected, polarization variability may be used
to better understand the dynamics of Tau A, and for understanding the validity
of Tau~A as a calibrator. One intriguing application of such observation is to
use it for the search of axion-light particles (ALPs). Ultralight ALPs couple
to photons through a Chern-Simons term, and induce a temporal oscillation in
the polarization angle of linearly polarized sources. After assessing a number
of systematic errors and testing for internal consistency, we evaluate the
variability of the polarization angle of the Crab Nebula using 2015 and 2016
observations with the 150 GHz POLARBEAR instrument. We place a median 95% upper
bound of polarization oscillation amplitude $A < 0.065^\circ$ over the
oscillation frequencies from $0.75~\mathrm{year}^{-1}$ to
$0.66~\mathrm{hour}^{-1}$. Assuming that no sources other than ALP are causing
Tau A's polarization angle variation, that the ALP constitutes all the dark
matter, and that the ALP field is a stochastic Gaussian field, this bound
translates into a median 95% upper bound of ALP-photon coupling
$g_{a\gamma\gamma} < 2.16\times10^{-12}\,\mathrm{GeV}^{-1}\times(m_a/10^{-21}
\mathrm{eV})$ in the mass range from $9.9\times10^{-23} \mathrm{eV}$ to
$7.7\times10^{-19} \mathrm{eV}$. This demonstrates that this type of analysis
using bright polarized sources is as competitive as those using the
polarization of cosmic microwave background in constraining ALPs. | Modelling Baryon Acoustic Oscillations with Perturbation Theory and
Stochastic Halo Biasing: In this work we investigate the generation of mock halo catalogues based on
perturbation theory and nonlinear stochastic biasing with the novel
PATCHY-code. In particular, we use Augmented Lagrangian Perturbation Theory
(ALPT) to generate a dark matter density field on a mesh starting from Gaussian
fluctuations and to compute the peculiar velocity field. ALPT is based on a
combination of second order LPT (2LPT) on large scales and the spherical
collapse model on smaller scales. We account for the systematic deviation of
perturbative approaches from N-body simulations together with halo biasing
adopting an exponential bias model. We then account for stochastic biasing by
defining three regimes: a low, an intermediate and a high density regime, using
a Poisson distribution in the intermediate regime and the negative binomial
distribution to model over-dispersion in the high density regime. Since we
focus in this study on massive halos, we suppress the generation of halos in
the low density regime. The various nonlinear and stochastic biasing
parameters, and density thresholds (five) are calibrated with the large
BigMultiDark N-body simulation to match the power spectrum of the corresponding
halo population. Our mock catalogues show power spectra, both in real- and
redshift-space, which are compatible with N-body simulations within about 2% up
to k ~ 1 h Mpc^-1 at z = 0.577 for a sample of halos with the typical BOSS
CMASS galaxy number density. The corresponding correlation functions are
compatible down to a few Mpc. We also find that neglecting over-dispersion in
high density regions produces power spectra with deviations of 10% at k ~ 0.4 h
Mpc^-1. These results indicate the need to account for an accurate statistical
description of the galaxy clustering for precise studies of large-scale
surveys. |
The formation of massive Pop III stars in the presence of turbulence: Population III stars forming in the infant universe at z=30 heralded the end
of the cosmic dark ages. They are presumed to be assembled in so-called
minihaloes with virial temperatures of a few thousand K where collapse is
triggered by molecular hydrogen cooling. A central question concerns their
final masses, and whether fragmentation occurs during their formation. While
studies employing Lagrangian codes suggest fragmentation via a self-gravitating
disk, recent high resolution simulations indicated that disk formation is
suppressed. Here we report the first high-resolution large-eddy simulations
performed with the Eulerian grid-based code Enzo following the evolution beyond
the formation of the first peak, to investigate the accretion of the central
massive clump and potential fragmentation. For a total of 3 halos, we see that
a disk forms around the first clump. The central clump reaches $\sim10$ solar
masses after 40 years, while subsequent accretion is expected at a rate of
$10^{-2}$ solar masses per year. In one of these halos, additional clumps form
as a result of fragmentation which proceeds at larger scales. We note that
subgrid-scale turbulence yields relevant contributions to the stability of the
protostellar disks. We conclude that the first protostar may reach masses up to
$\rm 40-100 M_{\odot}$, which are only limited by the effect of radiative
feedback. | Curvature perturbation and waterfall dynamics in hybrid inflation: We investigate the parameter spaces of hybrid inflation model with special
attention paid to the dynamics of waterfall field and curvature perturbations
induced from its quantum fluctuations. Depending on the inflaton field value at
the time of phase transition and the sharpness of the phase transition
inflation can have multiple extended stages. We find that for models with mild
phase transition the induced curvature perturbation from the waterfall field is
too large to satisfy the COBE normalization. We investigate the model parameter
space where the curvature perturbations from the waterfall quantum fluctuations
vary between the results of standard hybrid inflation and the results obtained
here. |
Global 21-cm Signal Extraction from Foreground and Instrumental Effects
II: Efficient and Self-Consistent Technique for Constraining Nonlinear Signal
Models: We present the completion of a data analysis pipeline that self-consistently
separates global 21-cm signals from large systematics using a pattern
recognition technique. In the first paper of this series, we obtain optimal
basis vectors from signal and foreground training sets to linearly fit both
components with the minimal number of terms that best extracts the signal given
its overlap with the foreground. In this second paper, we utilize the spectral
constraints derived in the first paper to calculate the full posterior
probability distribution of any signal parameter space of choice. The spectral
fit provides the starting point for a Markov Chain Monte Carlo (MCMC) engine
that samples the signal without traversing the foreground parameter space. At
each MCMC step, we marginalize over the weights of all linear foreground modes
and suppress those with unimportant variations by applying priors gleaned from
the training set. This method drastically reduces the number of MCMC
parameters, augmenting the efficiency of exploration, circumvents the need for
selecting a minimal number of foreground modes, and allows the complexity of
the foreground model to be greatly increased to simultaneously describe many
observed spectra without requiring extra MCMC parameters. Using two nonlinear
signal models, one based on EDGES observations and the other on
phenomenological frequencies and temperatures of theoretically expected
extrema, we demonstrate the success of this methodology by recovering the input
parameters from multiple randomly simulated signals at low radio frequencies
(10-200 MHz), while rigorously accounting for realistically modeled
beam-weighted foregrounds. | Beyond the fibre: Resolved properties of SDSS galaxies: We have used the VIMOS integral field spectrograph to map the emission line
properties in a sample of 24 star forming galaxies selected from the SDSS
database. In this data paper we present and describe the sample, and explore
some basic properties of SDSS galaxies with resolved emission line fields. We
fit the Halpha+[NII] emission lines in each spectrum to derive maps of
continuum, Halpha flux, velocity and velocity dispersion. The Halpha, Hbeta,
[NII] and [OIII] emission lines are also fit in summed spectra for circular
annuli of increasing radius. A simple mass model is used to estimate dynamical
mass within 10 kpc, which compared to estimates of stellar mass shows that
between 10 and 100% of total mass is in stars. We present plots showing the
radial behaviour of EW[Halpha], u-i colour and emission line ratios. Although
EW[Halpha] and u-i colour trace current or recent star formation, the radial
profiles are often quite different. Whilst line ratios do vary with annular
radius, radial gradients in galaxies with central line ratios typical of AGN or
LINERS are mild, with a hard component of ionization required out to large
radii. We use our VIMOS maps to quantify the fraction of Halpha emission
contained within the SDSS fibre, taking the ratio of total Halpha flux to that
of a simulated SDSS fibre. A comparison of the flux ratios to colour-based SDSS
extrapolations shows a 175% dispersion in the ratio of estimated to actual
corrections in normal star forming galaxies, with larger errors in galaxies
containing AGN. We find a strong correlation between indicators of nuclear
activity: galaxies with AGN-like line ratios and/or radio emission frequently
show enhanced dispersion peaks in their cores, requiring non-thermal sources of
heating. Altogether, about half of the galaxies in our sample show no evidence
for nuclear activity or non-thermal heating. |
Chandra Survey of Nearby Highly Inclined Disc Galaxies - II: Correlation
Analysis of Galactic Coronal Properties: X-ray observations provide a key tool for exploring the properties of
galactic coronae and their formation processes. In an earlier paper, we have
presented a Chandra data analysis of the coronae of 53 nearby highly-inclined
disc galaxies. Here we study the correlation of the X-ray measurements with
other galaxy properties and compare the results with those obtained for
elliptical galaxies. A good correlation is present between the coronal
luminosity Lx and the SFR. But we find a better correlation between Lx and the
total SN mechanical energy input rate (ESN), including the expected
contribution from core collapsed (CC) and Ia SNe. The X-ray radiation
efficiency (eta=Lx/ESN) has a mean value of ~0.4% with an rms of ~0.5dex. eta
further correlates with MTF/M* (MTF is the baryon mass measured from the
rotation velocity and the Tully-Fisher relation, M* is the stellar mass
measured from the K-band luminosity) and the CC SN rate surface density (FSN,
in units of SN/yr/kpc^2), which can be characterized as: eta=0.41%MTF/M* and
eta=1.4%FSN^-0.3. These correlations reflect the roles played by the
gravitational mass and energetic feedback concentrations in determining eta.
The characteristic temperature of the corona shows little dependence on the
total or specific SFR, the cold gas content, or Lx. The coronae of disc
galaxies tend to be more X-ray luminous, hotter, and lower in Fe/O abundance
ratio than those of elliptical ones of similar masses. Early-type non-starburst
disc galaxies tend to be more Fe-rich, while starburst ones have a roughly
constant abundance ratio of Fe/O~0.36solar. Our results are consistent with the
coronal gas being mainly provided by stellar feedback in a mass range of
M*~10^{8.7-11}Msun. In addition, processes such as charge exchange at cool/hot
gas interfaces, as well as various environmental effects, are also needed to
explain the diversity of coronal properties. | The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies with
GEAR: We present a fully parallel chemo-dynamical Tree/SPH code, GEAR, which allows
to perform high resolution simulations with detailed chemical diagnostics.
Starting from the public version of Gadget-2, we included the complex treatment
of the baryon physics: gas cooling, star formation law, chemical evolution and
supernovae feedback. We qualified the performances of GEAR with the case of
dSph galaxies. GEAR conserves the total energy budget of the systems to better
than 5% over 14Gyr and proved excellent convergence of the results with
numerical resolution. We showed that models of dSphs in a static Euclidean
space, where the expansion of the universe is neglected are valid. In addition,
we tackled some of the existing open questions in the field, like the stellar
mass fraction of dSphs and its link with the predicted dark matter halo mass
function, the effect of the supernova feedback, the spatial distribution of the
stellar populations, and the origin of the diversity in star formation
histories and chemical abundance patterns. Strong supernovae driven winds seem
incompatible with the observed metallicities and luminosities. Despite the fact
that newly formed stars are preferentially found in the galaxy central parts,
turbulent motions in the gas can quickly erase any metallicity gradient. The
variety in dSph properties result from a range of total masses as well as from
a dispersion in central densities. The latter is also seen in the haloes
emerging from a LCDM cosmogony. |
Decision Tree Classifiers for Star/Galaxy Separation: We study the star/galaxy classification efficiency of 13 different decision
tree algorithms applied to photometric objects in the Sloan Digital Sky Survey
Data Release Seven (SDSS DR7). Each algorithm is defined by a set of parameters
which, when varied, produce different final classification trees. We
extensively explore the parameter space of each algorithm, using the set of
$884,126$ SDSS objects with spectroscopic data as the training set. The
efficiency of star-galaxy separation is measured using the completeness
function. We find that the Functional Tree algorithm (FT) yields the best
results as measured by the mean completeness in two magnitude intervals: $14\le
r\le21$ ($85.2%$) and $r\ge19$ ($82.1%$). We compare the performance of the
tree generated with the optimal FT configuration to the classifications
provided by the SDSS parametric classifier, 2DPHOT and Ball et al. (2006). We
find that our FT classifier is comparable or better in completeness over the
full magnitude range $15\le r\le21$, with much lower contamination than all but
the Ball et al. classifier. At the faintest magnitudes ($r>19$), our classifier
is the only one able to maintain high completeness ($>$80%) while still
achieving low contamination ($\sim2.5%$). Finally, we apply our FT classifier
to separate stars from galaxies in the full set of $69,545,326$ SDSS
photometric objects in the magnitude range $14\le r\le21$. | An EFT description of galaxy intrinsic alignments: We present a general perturbative effective field theory (EFT) description of
galaxy shape correlations, which are commonly known as intrinsic alignments.
This rigorous approach extends current analytical modelling strategies in that
it only relies on the equivalence principle. We present our results in terms of
three-dimensional statistics for two- and three-point functions of both galaxy
shapes and number counts. In case of the two-point function, we recover the
well-known linear alignment result at leading order, but also present the full
next-to-leading order expressions. In case of the three-point function we
present leading order results for all the auto- and cross-correlations of
galaxy shapes and densities. We use a spherical tensor basis to decompose the
tensor perturbations in different helicity modes, which allows us to make use
of isotropy and parity properties in the correlators. Combined with the results
on projection presented in a forthcoming companion paper, our framework is
directly applicable to accounting for intrinsic alignment contamination in weak
lensing surveys, and to extracting cosmological information from intrinsic
alignments. |
Photometric Redshifts and Model Spectral Energy Distributions of
Galaxies From the SDSS-III BOSS DR10 Data: We construct a set of model spectra specifically designed to match the
colours of the BOSS CMASS galaxies and to be used with photometric redshift
template fitting techniques. As a basis we use a set of spectral energy
distributions (SEDs) of single and composite stellar population models. These
models cannot describe well the whole colour range populated by the CMASS
galaxies at all redshifts, wherefore we modify them by multiplying the SEDs
with $\lambda^{-\beta}$ for $\lambda>\lambda_i$ for different values of
$\lambda_i$ and $\beta$. When fitting these SEDs to the colours of the CMASS
sample, with a burst and dust components in superposition, we can recreate the
location in colour spaces inhabited by the CMASS galaxies. From the best
fitting models we select a small subset in a two-dimensional plane, whereto the
galaxies were mapped by a self-organizing map. These models are used for the
estimation of photometric redshifts with a Bayesian template fitting code. The
photometric redshifts with the novel templates have a very small outlier rate
of $0.22\,\%$, a low bias $\langle\Delta z/(1+z)\rangle=2.0\cdot10^{-3}$, and
scatter of $\sigma_{68}=0.026$ in the restframe. Using our models, the galaxy
colours are reproduced to a better extent with the photometric redshifts of
this work than with photometric redshifts of SDSS. | Electromagnetic Radiation from Binary Stars Mediated by Ultralight
Scalar: Neutron star contains a large number of nucleons and muons, if coupled with
hidden ultralight particles, the orbit motion can produce sizable energy flux
in addition to the gravitational quadrupole radiation. Here, we explore a
scenario in which the scalar boson sourced by the binary is also coupled to the
lowest dimensional photon operator, through which indirect electromagnetic
radiation is generated for orbital frequency below the scalar's mass threshold.
Using the observational data of two pulsar binaries, we place simultaneous
constraints on the strength of such couplings. |
Constraining the local variance of $H_0$ from directional analyses: We evaluate the local variance of the Hubble Constant $H_0$ with low-z Type
Ia Supernovae (SNe). Our analyses are performed using a hemispherical
comparison method in order to test whether taking the bulk flow motion into
account can reconcile the measurement of the Hubble Constant $H_0$ from
standard candles ($H_0 = 73.8 \pm 2.4 \; \mathrm{km \; s}^{-1}\;
\mathrm{Mpc}^{-1}$) with that of the Planck's Cosmic Microwave Background data
($H_0 = 67.8 \pm 0.9 \; \mathrm{km \; s}^{-1} \mathrm{Mpc}^{-1}$). We obtaina
Hubble Constant maximal variance of $\delta H_0 = (2.30 \pm 0.86) \; \mathrm{km
\; s}^{-1} \mathrm{Mpc}^{-1}$ towards the $(l,b) = (315^{\circ},27^{\circ})$
direction. Interestingly, this result agrees with the bulk flow direction
estimates found in the literature, as well as previous evaluations of the $H_0$
variance due to the presence of nearby inhomogeneities. We assess the
statistical significance of this result with different prescriptions of Monte
Carlo simulations, obtaining moderate statistical significance, i.e., $68.7$\%
confidence level (CL) for such variance. Furthermore, we test the hypothesis of
a higher $H_0$ value in the presence of a bulk flow velocity dipole, finding
some evidence for this result which, however, cannot be claimed to be
significant due to the current large uncertainty in the SNe distance modulus.
Then, we conclude that the tension between different $H_0$ determinations can
plausibly be caused to the bulk flow motion of the local Universe, even though
the current incompleteness of the SNe data set, both in terms of celestial
coverage and distance uncertainties, does not allow a high statistical
significance for these results or a definitive conclusion about this issue. | CMB temperature lensing power reconstruction: We study reconstruction of the lensing potential power spectrum from CMB
temperature data, with an eye to the Planck experiment. We work with the
optimal quadratic estimator of Okamoto and Hu, which we characterize thoroughly
in application to reconstruction of the lensing power spectrum. We find that at
multipoles L<250 our current understanding of this estimator is biased at the
15% level by beyond-gradient terms in the Taylor expansion of lensing effects.
We present the full lensed trispectrum to fourth order in the lensing potential
to explain this effect. We show that the low-L bias, as well as a previously
known bias at high-L, is relevant to the determination of cosmology and must be
corrected for in order to avoid significant parameter errors. We also
investigate the covariance of the reconstructed power, finding broad
correlations of ~0.1%. Finally, we discuss several small improvements which may
be made to the optimal estimator to mitigate these problems. |
Effects of Multiphase Gas and Projection on X-ray Observables in
Simulated Galaxy Clusters as Seen by eROSITA: The number density of galaxy clusters as a function of mass and redshift is a
sensitive function of the cosmological parameters. To use clusters for
cosmological parameter studies, it is necessary to determine their masses as
accurately as possible, which is typically done via mass-observable scaling
relations. X-ray observables can be biased by multiphase gas and projection
effects, especially in the case where cluster temperatures and luminosities are
estimated from single-model fits to all of the emission with a given radius.
Using simulated galaxy clusters from a realistic cosmological simulation, we
seek to determine the importance of these biases in the context of
Spectrum-Roentgen-Gamma/eROSITA observations of clusters. We extract clusters
from the Magneticum suite, and simulate eROSITA observations of these clusters
using PHOX and SIXTE. We compare the fitted observables from these observations
to those derived from the simulations. We fitted an intrinsically scattered
$L_{\rm X}-T$ scaling relation to these measurements following a Bayesian
approach with which we fully took into account the selection effects and the
mass function. The largest biases on the cluster observables come from the
inadequacy of single-temperature model fits to represent emission from
multiphase gas, as well as a bias arising from cluster emission within the
projected $r_{500c}$ along the line of sight but outside of the spherical
$r_{500c}$. We find that the biases on temperature and luminosity due to the
projection of emission from other clusters within $r_{500c}$ is small. We find
that our simulated clusters follow a $L_{\rm X}-T$ scaling relation that has a
broadly consistent but slightly shallower slope compared to the literature, and
that the intrinsic scatter of $L_{\rm X}$ at given T is lower compared to the
recent observational results where the selection effects are fully considered. | Ram pressure stripping in the z~0.5 galaxy cluster MS 0451.6-0305: The pressure exerted by the ambient hot X-ray gas on cluster galaxies can
lead to the presence of ram pressure stripped (RPS) galaxies, characterized by
asymmetric shapes, and, in some cases, tails of blue stars and/or X-ray gas,
with increased star formation. We searched for such galaxies in the cluster MS
0451.6-0305 at z~0.5, based on Hubble Space Telescope (HST) imaging covering a
region of about 6x6 Mpc^2, an eight magnitude ground-based catalogue with
photometric redshifts, and a spectroscopic redshift catalogue. We defined as
cluster members a spectroscopic redshift sample of 359 galaxies within 4sigma_v
of the mean cluster velocity, and a photometric redshift sample covering the
[0.48,0.61] range. We searched for RPS galaxies and tested the error on their
classification with a Zooniverse collaboration, and computed the phase space
diagram for the spectroscopic sample. We ran the LePhare stellar population
synthesis code to analyze and compare the properties of RPS and non-RPS
galaxies. We find 56 and 273 RPS candidates in the spectroscopic and
photometric redshift samples, respectively, distributed throughout the cluster
and tending to avoid high density regions. The phase space diagram gives the
percentages of virialized, backsplash, and infall galaxies. RPS galaxy
candidates typically show rather high star formation rates, young ages, and
relatively low masses. This study confirms that RPS galaxies host, on average,
younger stellar populations and strongly form stars when compared with non-RPS
counterparts. The fact that RPS candidates with spectroscopic and with
photometric redshifts have comparable properties shows that large samples of
such objects could be gathered based on multi-band photometry only, a promising
result in view of future very large imaging surveys. |
Halo-to-Halo Similarity and Scatter in the Velocity Distribution of Dark
Matter: We examine the Velocity Distribution Function (VDF) in dark matter halos from
Milky Way to cluster mass scales. We identify an empirical model for the VDF
with a wider peak and a steeper tail than a Maxwell--Boltzmann distribution,
and discuss physical explanations. We quantify sources of scatter in the VDF of
cosmological halos and their implication for direct detection of dark matter.
Given modern simulations and observations, we find that the most significant
uncertainty in the VDF of the Milky Way arises from the unknown radial position
of the solar system relative to the dark matter halo scale radius. | Kinetic Field Theory: Effects of momentum correlations on the cosmic
density-fluctuation power spectrum: In earlier work, we have developed a Kinetic Field Theory (KFT) for
cosmological structure formation and showed that the non-linear
density-fluctuation power spectrum known from numerical simulations can be
reproduced quite well even if particle interactions are taken into account to
first order only. Besides approximating gravitational interactions, we had to
truncate the initial correlation hierarchy of particle momenta at the second
order. Here, we substantially simplify KFT. We show that its central object,
the free generating functional, can be factorized, taking the full hierarchy of
momentum correlations into account. The factors appearing in the generating
functional, which we identify as non-linearly evolved density-fluctuation power
spectra, have a universal form and can thus be tabulated for fast access in
perturbation schemes.
In this paper, we focus on a complete evaluation of the free generating
functional of KFT, not including particle interactions yet. This implies that
the non-linearly evolved power spectra contain a damping term which reflects
that structures are being wiped out at late times by free streaming. Once
particle interactions will be taken into account, they will compensate this
damping. If we suppress this damping in a way suggested by the
fluctuation-dissipation relations of KFT, our results show that the complete
hierarchy of initial momentum correlations is responsible for a large part of
the characteristic non-linear deformation and the mode transport in the
density-fluctuation power spectrum. Without any adjustable parameters, KFT
accurately reproduces the scale at which non-linear evolution sets in.
Finally, we further develop perturbation theory based on the factorization of
the generating functional and propose a diagrammatic scheme for the
perturbation terms. |
ASTE Simultaneous HCN(4-3) and HCO+(4-3) Observations of the Two
Luminous Infrared Galaxies NGC 4418 and Arp 220: We report the results of HCN(J=4-3) and HCO+(J=4-3) observations of two
luminous infrared galaxies (LIRGs), NGC 4418 and Arp 220, made using the
Atacama Submillimeter Telescope Experiment (ASTE). The ASTE wide-band
correlator provided simultaneous observations of HCN(4-3) and HCO+(4-3) lines,
and a precise determination of their flux ratios. Both galaxies showed high
HCN(4-3) to HCO+(4-3) flux ratios of >2, possibly due to AGN-related phenomena.
The J = 4-3 to J = 1-0 transition flux ratios for HCN (HCO+) are similar to
those expected for fully thermalized (sub-thermally excited) gas in both
sources, in spite of HCN's higher critical density. If we assume collisional
excitation and neglect an infrared radiative pumping process, our non-LTE
analysis suggests that HCN traces gas with significantly higher density than
HCO+. In Arp 220, we separated the double-peaked HCN(4-3) emission into the
eastern and western nuclei, based on velocity information. We confirmed that
the eastern nucleus showed a higher HCN(4-3) to HCN(1-0) flux ratio, and thus
contained a larger amount of highly excited molecular gas than the western
nucleus. | X-ray characterisation of the massive galaxy clusterClG-J104803.7+313843
at z=0.76 with XMM-Newton: We present the characterisation of the massive cluster ClG-J$104803.7+313843$
at $z=0.76$ performed using a serendipitous XMM-Newton observation. High
redshift and massive objects represent an ideal laboratory to benchmark our
understanding of how cluster form and assembly formation driven mainly by
gravity.Leveraging the high throughput of XMM-Newton we were firstly able to
determine the redshift of the object, shedding light on ambiguous photometric
redshift associations. We investigated the morphology of this cluster which
shows signs of merging activities in the outskirts and a flat core. We also
measured the radial density profile up to $R_{500}$. With these quantities in
hand, we were able to determine the mass, $M_{500}=5.64^{+0.79}_{-0.62} \times
10^{14}M_{\odot}$, using the YX proxy. This quantity improves previous
measurement of the mass of this object by a factor of $\sim 3.5$. The
characterisation of one cluster at such mass and redshift regime is fundamental
as these objects are intrinsically rare, the number of objects discovered so
far being less than $\sim 25$. Our study highlights the importance of using
X-ray observations in combination with ancillary multi-wavelength data to
improve our understanding of high-z and massive clusters |
Search for topological defect dark matter with a global network of
optical magnetometers: Ultralight bosons such as axion-like particles are viable candidates for dark
matter. They can form stable, macroscopic field configurations in the form of
topological defects that could concentrate the dark matter density into many
distinct, compact spatial regions that are small compared to the galaxy but
much larger than the Earth. Here, we report the results of a search for
transient signals from axion-like particle domain walls with the Global Network
of Optical Magnetometers for Exotic physics searches (GNOME). We search the
data, consisting of correlated measurements from optical atomic magnetometers
located in laboratories all over the world, for patterns of signals propagating
through the network consistent with domain walls. The analysis of data from a
continuous month-long operation of the GNOME finds no statistically significant
signals, thus placing experimental constraints on such dark matter scenarios. | The CMB flexes its BICEPs while walking the Planck: Recent microwave polarization measurements from the BICEP2 experiment may
reveal a long-sought signature of inflation. However, these new results appear
inconsistent with the best-fit model from the Planck satellite. We suggest a
particularly simple idea for reconciling these data-sets, and for explaining a
wide range of phenomena on the cosmic microwave sky. |
Thermal and Chemical Evolution of Collapsing Filaments: Intergalactic filaments form the foundation of the cosmic web that connect
galaxies together, and provide an important reservoir of gas for galaxy growth
and accretion. Here we present very high resolution two-dimensional simulations
of the thermal and chemical evolution of such filaments, making use of a 32
species chemistry network that tracks the evolution of key molecules formed
from hydrogen, oxygen, and carbon. We study the evolution of filaments over a
wide range of parameters including the initial density, initial temperature,
strength of the dissociating UV background, and metallicity. In low-redshift,
$Z \approx 0.1 Z_\odot $ filaments, the evolution is determined completely by
the initial cooling time. If this is sufficiently short, the center of the
filament always collapses to form dense, cold core containing a substantial
fraction of molecules. In high-redshift, $Z=10^{-3} Z_\odot$ filaments, the
collapse proceeds much more slowly. This is due mostly to the lower initial
temperatures, which leads to a much more modest increase in density before the
atomic cooling limit is reached, making subsequent molecular cooling much less
efficient.
Finally, we study how the gravitational potential from a nearby dwarf galaxy
affects the collapse of the filament and compare this to NGC 5253, a nearby
starbusting dwarf galaxy thought to be fueled by the accretion of filament gas.
In contrast to our fiducial case, a substantial density peak forms at the
center of the potential. This peak evolves faster than the rest of the filament
due to the increased rate at which chemical species form and cooling occur. We
find that we achieve similar accretion rates as NGC 5253 but our
two-dimensional simulations do not recover the formation of the giant molecular
clouds that are seen in radio observations. | Effect of Dissipation on Warm Chromo-Natural Inflation: We examined the chromo-natural inflation in the context of warm inflation
with variable dissipation coefficient. The dynamical equations of this model
are obtained. We studied the cosmological perturbation theory in this model.
The sources of density fluctuations in this model are mainly the thermal
fluctuations of the inflaton field like general warm inflationary model.
Finally, cosmological observables, namely, the spectral index and tensor to
scalar ratio are calculated. It is found that the cosmological observables are
consistent with observational data and the tensor to scalar ratio is smaller
than that in the chromo-natural inflation. |
The distribution of equivalent widths in long GRB afterglow spectra: The extreme brightness of gamma-ray burst (GRB) afterglows and their simple
spectral shape make them ideal beacons to study the interstellar medium of
their host galaxies through absorption line spectroscopy. Using 69
low-resolution GRB afterglow spectra, we conduct a study of the rest-frame
equivalent width (EW) distribution of features with an average rest-frame EW
larger than 0.5 A. To compare an individual GRB with the sample, we develop EW
diagrams as a graphical tool, and we give a catalogue with diagrams for the 69
spectra. We introduce a line strength parameter (LSP) that allows us to
quantify the strength of the absorption features as compared to the sample by a
single number. Using the distributions of EWs of single-species features, we
derive the distribution of column densities by a curve of growth (CoG) fit. We
find correlations between the LSP and the extinction of the GRB, the UV
brightness of the host galaxies and the neutral hydrogen column density.
However, we see no significant evolution of the LSP with the redshift. There is
a weak correlation between the ionisation of the absorbers and the energy of
the GRB, indicating that, either the GRB event is responsible for part of the
ionisation, or that galaxies with high-ionisation media produce more energetic
GRBs. Spectral features in GRB spectra are, on average, 2.5 times stronger than
those seen in QSO intervening damped Lyman-alpha (DLA) systems and slightly
more ionised. In particular we find larger excess in the EW of CIV1549 relative
to QSO DLAs, which could be related to an excess of Wolf-Rayet stars in the
environments of GRBs. From the CoG fitting we obtain an average number of
components in the absorption features of GRBs of 6.00(-1.25,+1.00). The most
extreme ionisation ratios in our sample are found for GRBs with low neutral
hydrogen column density, which could be related to ionisation by the GRB
emission. | Modeling of weak lensing statistics. II. Configuration-space statistics: We investigate the performance of an analytic model of the 3D matter
distribution, which combines perturbation theory with halo models, for
weak-lensing configuration-space statistics. We compared our predictions for
the weak-lensing convergence two-point and three-point correlation functions
with numerical simulations and fitting formulas proposed in previous works. We
also considered the second- and third-order moments of the smoothed convergence
and of the aperture-mass. As in our previous study of Fourier-space
weak-lensing statistics, we find that our model agrees better with simulations
than previously published fitting formulas. Moreover, we recover the dependence
on cosmology of these weak-lensing statistics and we can describe multi-scale
moments. This approach allows us to obtain the quantitative relationship
between these integrated weak-lensing statistics and the various contributions
to the underlying 3D density fluctuations, decomposed over perturbative,
two-halo, or one-halo terms. |
Fluctuations in the Ginzburg-Landau Theory of Dark Energy: internal
(in-)consistencies in PLANCK data set: In this work, predictions of the Ginzburg-Landau theory of dark energy (GLT)
for CMB lensing are studied. We find that the time and scale dependence of the
dark energy fluctuations in this semi-phenomenological model is favored by data
in several ways. Firstly, unlike $\Lambda$CDM, $\ell\leq801$ and $\ell>801$
ranges of the CMB angular power spectrum are consistent in this framework.
Secondly, the lensing amplitude $A_L$ is completely consistent with unity when
GLT is confronted with CMB data, even without including CMB lensing data.
Therefore lensing anomaly is absent in this model. Furthermore, the background
evolution of dark energy in this model is able to reconcile the $H_0$ inferred
from CMB with that of directly measured through observing nearby standard
candles. | Probing beyond-Horndeski gravity on ultra-large scales: The beyond-Horndeski gravity has recently been reformulated in the dark
energy paradigm - which has been dubbed, Unified Dark Energy (UDE). The
evolution equations for the given UDE appear to correspond to a
non-conservative dark energy scenario, in which the total energy-momentum
tensor is not conserved. We investigate both the background cosmology and, the
large-scale imprint of the UDE by probing the angular power spectrum of galaxy
number counts, on ultra-large scales; taking care to include the full
relativistic corrections in the observed overdensity. The background evolution
shows that only an effective mass smaller than the Planck mass is needed in the
early universe in order for predictions in the given theory to match current
observational constraints. We found that the effective mass-evolution-rate
parameter, which drives the evolution of the UDE, acts to enhance the observed
power spectrum and, hence, relativistic effects (on ultra-large scales) by
enlarging the UDE sound horizon. Conversely, both the (beyond) Horndeski
parameter and the kineticity act to diminish the observed power spectrum, by
decreasing the UDE sound horizon. Our results show that, in a universe with
UDE, a multi-tracer analysis will be needed to detect the relativistic effects
in the large-scale structure. In the light of a multi-tracer analysis, the
various relativistic effects hold the potential to distinguish different
gravity models. Moreover, while the Doppler effect will remain significant at
all epochs and, thus can not be ignored, the integrated Sachs-Wolfe, the
time-delay and the potential (difference) effects, respectively, will only
become significant at epochs near z=3 and beyond, and may be neglected at late
epochs. In the same vein, the Doppler effect alone can serve as an effective
cosmological probe for the large-scale structure or gravity models, in the
angular power spectrum - at all z. |
On the hunt for ultramassive black holes in brightest cluster galaxies: We investigate where brightest cluster galaxies (BCGs) sit on the fundamental
plane of black hole (BH) activity, an established relation between the X-ray
luminosity, the radio luminosity and the mass of a BH. Our sample mostly
consists of BCGs that lie at the centres of massive, strong cooling flow
clusters, therefore requiring extreme mechanical feedback from their central
active galactic nucleus (AGN) to offset cooling of the intracluster plasma
(L_mech>10^44-45 erg/s). Based on the BH masses derived from the M_BH-sigma and
M_BH-M_K correlations, we find that all of our objects are offset from the
plane such that they appear to be less massive than predicted from their X-ray
and radio luminosities (to more than a 99 per cent confidence level). For these
objects to be consistent with the fundamental plane, the M_BH-sigma and
M_BH-M_K correlations therefore seem to underestimate the BH masses of BCGs, on
average by a factor of 10. Our results suggest that the standard relationships
between BH mass and host galaxy properties no longer hold for these extreme
galaxies. Furthermore, our results imply that if these BHs follow the
fundamental plane, then many of those that lie in massive, strong cool core
clusters must be ultramassive with M_BH>10^10M_sun. This rivals the largest BH
masses known and has important ramifications for our understanding of the
formation and evolution of BHs. | Reconstructing the evolution of dark energy with variations of
fundamental parameters: Under the assumption that the variations of parameters of nature and the
current acceleration of the universe are related and governed by the evolution
of a single scalar field, we show how information can be obtained on the nature
of dark energy from observational detection of (or constraints on) cosmological
variations of the fine structure constant and the proton-to-electron mass
ratio. We also comment on the current observational status, and on the
prospects for improvements with future spectrographs such as ESPRESSO and
CODEX. |
Artificial Neural Networks for Galaxy Clustering. Learning from the
two-point correlation function of BOSS galaxies: The increasingly large amount of cosmological data coming from ground-based
and space-borne telescopes requires highly efficient and fast enough data
analysis techniques to maximise the scientific exploitation. In this work, we
explore the capabilities of supervised machine learning algorithms to learn the
properties of the large-scale structure of the Universe, aiming at constraining
the matter density parameter, Omega m. We implement a new Artificial Neural
Network for a regression data analysis, and train it on a large set of galaxy
two-point correlation functions in standard cosmologies with different values
of Omega m. The training set is constructed from log-normal mock catalogues
which reproduce the clustering of the Baryon Oscillation Spectroscopic Survey
(BOSS) galaxies. The presented statistical method requires no specific
analytical model to construct the likelihood function, and runs with negligible
computational cost, after training. We test this new Artificial Neural Network
on real BOSS data, finding Omega m=0.309p/m0.008, which is remarkably
consistent with standard analysis results. | Ultraviolet number counts of galaxies from Swift UV/Optical Telescope
deep imaging of the Chandra Deep Field South: Deep Swift UV/Optical Telescope (UVOT) imaging of the Chandra Deep Field
South is used to measure galaxy number counts in three near ultraviolet (NUV)
filters (uvw2: 1928 A, uvm2: 2246 A, uvw1: 2600 A) and the u band (3645 A).
UVOT observations cover the break in the slope of the NUV number counts with
greater precision than the number counts by the Hubble Space Telescope (HST)
Space Telescope Imaging Spectrograph (STIS) and the Galaxy Evolution Explorer
(GALEX), spanning a range from 21 < m_AB < 25. Number counts models confirm
earlier investigations in favoring models with an evolving galaxy luminosity
function. |
Multiwavelength classification of X-ray selected galaxy cluster
candidates using convolutional neural networks: Galaxy clusters appear as extended sources in XMM-Newton images, but not all
extended sources are clusters. So, their proper classification requires visual
inspection with optical images, which is a slow process with biases that are
almost impossible to model. We tackle this problem with a novel approach, using
convolutional neural networks (CNNs), a state-of-the-art image classification
tool, for automatic classification of galaxy cluster candidates. We train the
networks on combined XMM-Newton X-ray observations with their optical
counterparts from the all-sky Digitized Sky Survey. Our data set originates
from the X-CLASS survey sample of galaxy cluster candidates, selected by a
specially developed pipeline, the XAmin, tailored for extended source detection
and characterisation. Our data set contains 1 707 galaxy cluster candidates
classified by experts. Additionally, we create an official Zooniverse citizen
science project, The Hunt for Galaxy Clusters, to probe whether citizen
volunteers could help in a challenging task of galaxy cluster visual
confirmation. The project contained 1 600 galaxy cluster candidates in total of
which 404 overlap with the expert's sample. The networks were trained on expert
and Zooniverse data separately. The CNN test sample contains 85
spectroscopically confirmed clusters and 85 non-clusters that appear in both
data sets. Our custom network achieved the best performance in the binary
classification of clusters and non-clusters, acquiring accuracy of 90 %,
averaged after 10 runs. The results of using CNNs on combined X-ray and optical
data for galaxy cluster candidate classification are encouraging and there is a
lot of potential for future usage and improvements. | Galaxy Cluster Pressure Profiles as Determined by Sunyaev Zel'dovich
Effect Observations with MUSTANG and Bolocam II: Joint Analysis of Fourteen
Clusters: We present pressure profiles of galaxy clusters determined from high
resolution Sunyaev-Zel'dovich (SZ) effect observations of fourteen clusters,
which span the redshift range $ 0.25 < z < 0.89$. The procedure simultaneously
fits spherical cluster models to MUSTANG and Bolocam data. In this analysis, we
adopt the generalized NFW parameterization of pressure profiles to produce our
models. Our constraints on ensemble-average pressure profile parameters, in
this study $\gamma$, $C_{500}$, and $P_0$, are consistent with those in
previous studies, but for individual clusters we find discrepancies with the
X-ray derived pressure profiles from the ACCEPT2 database. We investigate
potential sources of these discrepancies, especially cluster geometry, electron
temperature of the intracluster medium, and substructure. We find that the
ensemble mean profile for all clusters in our sample is described by the
parameters: $[\gamma,C_{500},P_0] = [0.3_{-0.1}^{+0.1}, 1.3_{-0.1}^{+0.1},
8.6_{-2.4}^{+2.4}]$, for cool core clusters: $[\gamma,C_{500},P_0] =
[0.6_{-0.1}^{+0.1}, 0.9_{-0.1}^{+0.1}, 3.6_{-1.5}^{+1.5}]$, and for disturbed
clusters: $[\gamma,C_{500},P_0] = [0.0_{-0.0}^{+0.1},
1.5_{-0.2}^{+0.1},13.8_{-1.6}^{+1.6}]$. Four of the fourteen clusters have
clear substructure in our SZ observations, while an additional two clusters
exhibit potential substructure. |
On a novel approach using massive clusters at high redshifts as
cosmological probe: In this work we propose a novel method for testing the validity of the
fiducial LCDM cosmology by measuring the cumulative distribution function of
the most massive haloes in a sample of subvolumes of identical size tiled on
the sky at a fixed redshift. The fact that the most massive clusters probe the
high-mass tail of the mass function, where the difference between LCDM and
alternative cosmological models is strongest, makes our method particularly
interesting as a cosmological probe. We utilise general extreme value
statistics (GEV) to obtain a cumulative distribution function of the most
massive objects in a given volume. We sample this distribution function
according to the number of patches covered by the survey area for a range of
different "test cosmologies" and for differently accurate mass estimations of
the haloes. By fitting this sample with the GEV distribution function, we can
study which parameters are the most sensitive with respect to the test
cosmologies. We find that the peak of the probability distribution function of
the most massive halo is well suited to test the validity of the fiducial LCDM
model, once we are able to establish a sufficiently complete large-area survey
with M_lim=10^14.5 M_sun/h (M_lim=10^14 M_sun/h) at redshifts above z=1
(z=1.5). Being of cumulative nature the proposed measure is robust and an
accuracy of 20-30% in the cluster masses would be sufficient to test for
alternative models. Since one only needs the most massive system in each
angular patch, this method would be ideally suited as a first fast consistency
check before going into a more complex statistical analysis of the observed
halo sample. | XMM-Newton Observation of the Northwest Radio Relic Region in Abell 3667: Abell 3667 is the archetype of a merging cluster with radio relics. The NW
radio relic is the brightest cluster relic or halo known, and is believed to be
due to a strong merger shock. We have observed the NW relic for 40 ksec of net
XMM time. We observe a global decline of temperature across the relic from 6 to
1 keV, similar to the Suzaku results. Our new observations reveal a sharp
change of both temperature and surface brightness near the position of the
relic. The increased X-ray emission on the relic can be equivalently well
described by either a thermal or nonthermal spectral model. The parameters of
the thermal model are consistent with a Mach number M~2 shock and a shock speed
of ~1200 km s^-1. The energy content of the relativistic particles in the radio
relic can be explained if they are (re)-accelerated by the shock with an
efficiency of ~0.2%. Comparing the limit on the inverse Compton X-ray emission
with the measured radio synchrotron emission, we set a lower limit to the
magnetic field in the relic of 3 muG. If the emission from the relic is
non-thermal, this lower limit is in fact the required magnetic field. |
Primordial Stochastic Gravitational Wave Backgrounds from a Sharp
Feature in Three-field Inflation I: The Radiation Era: The detection of a primordial stochastic gravitational wave background has
the potential to reveal unprecedented insights into the early universe, and
possibly into the dynamics of inflation. Generically, UV-complete inflationary
models predict an abundance of light scalars, so any inflationary stochastic
background may well be formed in a model with several interacting degrees of
freedom. The stochastic backgrounds possible from two-field inflation have been
well-studied in the literature, but it is unclear how similar they are to the
possibilities from many-field inflation. In this work we study stochastic
backgrounds from more-than-two field inflation for the first time, focusing on
the scalar-induced background produced during the radiation era by a brief turn
in three-field space. We find an analytic expression for the enhancement in the
power spectrum as a function of the turn rate and the torsion, and show that
unique signatures of three-field dynamics are possible in the primordial power
spectrum and gravitational wave spectrum. We confirm our analytic results with
a suite of numerical simulations and find good agreement in the shape and
amplitude of the power spectra. We also comment on the detection prospects in
LISA and other future detectors. We do not expect the moderately large growth
of the inflationary perturbations necessary for detection to cause a breakdown
of perturbation theory, but this must be verified on a case-by-case basis for
specific microphysical models to make a definitive claim. | Galaxy And Mass Assembly (GAMA): The 0.013 < z < 0.1 cosmic spectral
energy distribution from 0.1 micron to 1mm: We use the GAMA I dataset combined with GALEX, SDSS and UKIDSS imaging to
construct the low-redshift (z<0.1) galaxy luminosity functions in FUV, NUV,
ugriz, and YJHK bands from within a single well constrained volume of 3.4 x
10^5 (Mpc/h)^{3}. The derived luminosity distributions are normalised to the
SDSS DR7 main survey to reduce the estimated cosmic variance to the 5 per cent
level. The data are used to construct the cosmic spectral energy distribution
(CSED) from 0.1 to 2.1 \mum free from any wavelength dependent cosmic variance
for both the elliptical and non-elliptical populations. The two populations
exhibit dramatically different CSEDs as expected for a predominantly old and
young population respectively. Using the Driver et al. (2008) prescription for
the azimuthally averaged photon escape fraction, the non-ellipticals are
corrected for the impact of dust attenuation and the combined CSED constructed.
The final results show that the Universe is currently generating (1.8 +/- 0.3)
x 10^{35} h W Mpc^{-3} of which (1.2 +/- 0.1) x 10^{35} h W Mpc^{-3} is
directly released into the inter-galactic medium and (0.6 +/- 0.1) x 10^{35} h
W Mpc^{-3} is reprocessed and reradiated by dust in the far-IR. Using the GAMA
data and our dust model we predict the mid and far-IR emission which agrees
remarkably well with available data. We therefore provide a robust description
of the pre- and post dust attenuated energy output of the nearby Universe from
0.1micron to 0.6mm. The largest uncertainty in this measurement lies in the mid
and far-IR bands stemming from the dust attenuation correction and its
currently poorly constrained dependence on environment, stellar mass, and
morphology. |
Simulations of the galaxy population constrained by observations from
z=3 to the present day: implications for galactic winds and the fate of their
ejecta: We apply Monte Carlo Markov Chain (MCMC) methods to large-scale simulations
of galaxy formation in a LambdaCDM cosmology in order to explore how star
formation and feedback are constrained by the observed luminosity and stellar
mass functions of galaxies. We build models jointly on the Millennium and
Millennium-II simulations, applying fast sampling techniques which allow
observed galaxy abundances over the ranges 7<log(M*/Msun)<12 and z=0 to z=3 to
be used simultaneously as constraints in the MCMC analysis. When z=0
constraints alone are imposed, we reproduce the results of previous modelling
by Guo et al. (2012), but no single set of parameters can reproduce observed
galaxy abundances at all redshifts simultaneously, reflecting the fact that
low-mass galaxies form too early and thus are overabundant at high redshift in
this model. The data require the efficiency with which galactic wind ejecta are
reaccreted to vary with redshift and halo mass quite differently than
previously assumed, but in a similar way as in some recent hydrodynamic
simulations of galaxy formation. We propose a specific model in which
reincorporation timescales vary inversely with halo mass and are independent of
redshift. This produces an evolving galaxy population which fits observed
abundances as a function of stellar mass, B- and K-band luminosity at all
redshifts simultaneously. It also produces a significant improvement in two
other areas where previous models were deficient. It leads to present day dwarf
galaxy populations which are younger, bluer, more strongly star-forming and
more weakly clustered on small scales than before, although the passive
fraction of faint dwarfs remains too high. | Do We Expect Most AGN to Live in Disks?: Recent observations have indicated that a large fraction of the low to
intermediate luminosity AGN population lives in disk-dominated hosts, while the
more luminous quasars live in bulge-dominated hosts, in conflict with some
previous model predictions. We therefore build and compare a semi-empirical
model for AGN fueling which accounts for both merger and non-merger
'triggering.' In particular, we show that the 'stochastic accretion' model - in
which fueling in disk galaxies is essentially a random process arising whenever
dense gas clouds reach the nucleus - provides a good match to the present
observations at low/intermediate luminosities. However it falls short of the
high-luminosity population. We combine this with models for major
merger-induced AGN fueling, which lead to rarer but more luminous events, and
predict the resulting abundance of disk-dominated and bulge-dominated AGN host
galaxies as a function of luminosity and redshift. We compile and compare
observational constraints from z~0-2. The models and observations generically
show a transition from disk to bulge dominance in hosts near the Seyfert-quasar
transition, at all redshifts. 'Stochastic' fueling dominates AGN by number
(dominant at low luminosity), and dominates BH growth below the knee in the
present-day BH mass function (<10^7 M_sun). However it accounts for just ~10%
of BH mass growth at masses >10^8 M_sun. In total, fueling in disky hosts
accounts for ~30% of the total AGN luminosity density/BH mass density. The
combined model also accurately predicts the AGN luminosity function and
clustering/bias as a function of luminosity and redshift; however, we argue
that these are not sensitive probes of BH fueling mechanisms. |
NGC 3934: a shell galaxy in a compact galaxy environment: We investigate the NGC 3933 poor galaxy association, that contains NGC 3934,
which is classified as a polar-ring galaxy. The multi-band photometric analysis
of NGC 3934 allows us to investigate the nature of this galaxy and to re-define
the NGC 3933 group members with the aim to characterize the group dynamical
properties and its evolutionary phase. We imaged the group in the far
(FUV,lambda = 1530A) and near (NUV, lambda=2316A) ultraviolet (UV) bands of the
Galaxy Evolution Explorer (GALEX). From the deep optical imaging we determined
the fine structure of NGC 3934. We measured the recession velocity of PGC
213894 which shows that it belongs to the NGC 3933 group. We derived the
spectral energy distribution (SED) from FUV (GALEX) to far-IR emission of the
two brightest members of the group. We compared a grid of smooth particle
hydrodynamical (SPH) chemo-photometric simulations with the SED and the
integrated properties of NGC 3934 and NGC 3933 to devise their possible
formation/evolutionary scenarios. The NGC 3933 group has six bright members: a
core composed of five galaxies, which have Hickson's compact group
characteristics, and a more distant member, PGC 37112. The group velocity
dispersion is relatively low (157+-44 km s-1). The projected mass, from the NUV
photometry, is ~7$\times$10^12 M\odot with a crossing time of 0.04 Hubble
times, suggesting that at least in the center the group is virialized. We do
not find evidence that NGC 3934 is a polar-ring galaxy, as suggested by the
literature, but find that it is a disk galaxy with a prominent dust-lane
structure and a wide type-II shell structure. NGC 3934 is a quite rare example
of a shell galaxy in a likely dense galaxy region. The comparison between
physically motivated SPH simulations with multi-band integrated photometry
suggests that NGC 3934 is the product of a major merger. | Unsupervised Searches for Cosmological Parity-Violation: An
Investigation with Convolutional Neural Networks: Recent measurements of the $4$-point correlation functions (4PCF) from
spectroscopic surveys provide evidence for parity-violations in the large-scale
structure of the Universe. If physical in origin, this could point to exotic
physics during the epoch of inflation. However, searching for parity-violations
in the 4PCF signal relies on a large suite of simulations to perform a rank
test, or an accurate model of the 4PCF covariance to claim a detection, and
this approach is incapable of extracting parity information from the
higher-order $N$-point functions. In this work we present an unsupervised
method which overcomes these issues, before demonstrating the approach is
capable of detecting parity-violations in a few toy models using convolutional
neural networks. This technique is complementary to the 4-point method and
could be used to discover parity-violations in several upcoming surveys
including DESI, Euclid and Roman. |
Nature of Lyman Alpha Blobs: Powered by Extreme Starbursts: We present a new model for the observed Lyman alpha blobs (LABs) within the
context of the standard cold dark matter model. In this model, LABs are the
most massive halos with the strongest clustering (proto-clusters) undergoing
extreme starbursts in the high-z universe. Aided by calculations of detailed
radiative transfer of Lya photons through ultra-high resolution (159pc)
large-scale (>30Mpc) adaptive mesh-refinement cosmological hydrodynamic
simulations with galaxy formation, this model is shown to be able to, for the
first time, reproduce simultaneously the global Lya luminosity function and
luminosity-size relation of the observed LABs. Physically, a combination of
dust attenuation of Lya photons within galaxies, clustering of galaxies, and
complex propagation of Lya photons through circumgalactic and intergalactic
medium gives rise to the large sizes and frequently irregular isophotal shapes
of LABs that are observed. A generic and unique prediction of this model is
that there should be strong far-infrared (FIR) sources within each LAB, with
the most luminous FIR source likely representing the gravitational center of
the proto-cluster, not necessarily the apparent center of the Lya emission of
the LAB or the most luminous optical source. Upcoming ALMA observations should
unambiguously test this prediction. If verified, LABs will provide very
valuable laboratories for studying formation of galaxies in the most overdense
regions of the universe at a time when global star formation is most vigorous. | Feedback and Recycled Wind Accretion: Assembling the z=0 Galaxy Mass
Function: We analyse cosmological hydrodynamic simulations that include
observationally-constrained prescriptions for galactic outflows. If these
simulated winds accurately represent winds in the real Universe, then material
previously ejected in winds provides the dominant source of gas infall for new
star formation at redshifts z<1. This recycled wind accretion, or wind mode,
provides a third physically distinct accretion channel in addition to the "hot"
and "cold" modes emphasised in recent theoretical studies. Because of the
interaction between outflows and gas in and around halos, the recycling
timescale of wind material (t_rec) is shorter in higher-mass systems, which
reside in denser gaseous environments. In these simulations, this differential
recycling plays a central role in shaping the present-day galaxy stellar mass
function (GSMF). If we remove all particles that were ever ejected in a wind,
then the predicted GSMFs are much steeper than observed; galaxy masses are
suppressed both by the direct removal of gas and by the hydrodynamic heating of
their surroundings, which reduces subsequent infall. With wind recycling
included, the simulation that incorporates our favoured momentum-driven wind
scalings reproduces the observed GSMF for stellar masses 10^9 < M < 5x10^10
Msolar. At higher masses, wind recycling leads to excessive galaxy masses and
excessive star formation rates relative to observations. In these massive
systems, some quenching mechanism must suppress the re-accretion of gas ejected
from star-forming galaxies. In short, as has long been anticipated, the form of
the GSMF is governed by outflows; the unexpected twist here for our simulated
winds is that it is not primarily the ejection of material but how the ejected
material is re-accreted that governs the GSMF. |
Distinguishing between AGN and Star-Forming Galaxies in ATLAS: The Australia Telescope Large Area Survey (ATLAS) is the widest deep radio
survey ever attempted, covering 7 square degrees of sky in two separate fields,
with extensive multi-wavelength data. The primary aim of this research is to
investigate all possible discriminants between active galactic nuclei (AGN) and
star-formation (SF) in ATLAS, with the goal of comparing discriminants,
identifying the strengths and weaknesses, and establishing an optimum technique
given the available data. Ultimately, all possible discriminants will be
utilized, including optical/infrared SEDs, spectroscopic line widths, optical
line ratios, radio spectral indices, variability, morphology, polarization and
the radio/FIR correlation. A preliminary investigation using only the available
spectroscopic data in ATLAS is ongoing. Results from this investigation are
presented, exploring the proportion of AGN/SF galaxies as a function of radio
flux density down to 150 microJy. Three faint GPS candidates are also
presented, as a preliminary result from ATLAS. | Constraints on Primordial Magnetic Fields from Planck combined with the
South Pole Telescope CMB B-mode polarization measurements: A primordial magnetic field (PMF) present before recombination can leave
specific signatures on the cosmic microwave background (CMB) fluctuations. Of
particular importance is its contribution to the B-mode polarization power
spectrum. Indeed, vortical modes sourced by the PMF can dominate the B-mode
power spectrum on small scales, as they survive damping up to a small fraction
of the Silk length. Therefore, measurements of the B-mode polarization at
high-$\ell$ , such as the one recently performed by the South Pole Telescope
(SPT), have the potential to provide stringent constraints on the PMF. We use
the publicly released SPT B-mode polarization spectrum, along with the
temperature and polarization data from the Planck satellite, to derive
constraints on the magnitude, the spectral index and the energy scale at which
the PMF was generated. We find that, while Planck data constrains the magnetic
amplitude to $B_{1 \, \text{Mpc}} < 3.3$ nG at 95\% confidence level (CL), the
SPT measurement improves the constraint to $B_{1 \, \text{Mpc}} < 1.5$ nG. The
magnetic spectral index, $n_B$, and the time of the generation of the PMF are
unconstrained. For a nearly scale-invariant PMF, predicted by simplest
inflationary magnetogenesis models, the bound from Planck+SPT is $B_{1 \,
\text{Mpc}} < 1.2$ nG at 95% CL. For PMF with $n_B=2$, expected for fields
generated in post-inflationary phase transitions, the 95% CL bound is $B_{1 \,
\text{Mpc}} < 0.002$ nG, corresponding to the magnetic fraction of the
radiation density $\Omega_{B\gamma} < 10^{-3}$ or the effective field $B_{\rm
eff} < 100$ nG. The patches for the Boltzmann code CAMB and the Markov Chain
Monte Carlo engine CosmoMC, incorporating the PMF effects on CMB, are made
publicly available. |
The Extreme Small Scales: Do Satellite Galaxies Trace Dark Matter?: We investigate the radial distribution of galaxies within their host dark
matter halos by modeling their small-scale clustering, as measured in the Sloan
Digital Sky Survey. Specifically, we model the Jiang et al. (2011) measurements
of the galaxy two-point correlation function down to very small projected
separations (10 < r < 400 kpc/h), in a wide range of luminosity threshold
samples (absolute r-band magnitudes of -18 up to -23). We use a halo occupation
distribution (HOD) framework with free parameters that specify both the number
and spatial distribution of galaxies within their host dark matter halos. We
assume that the first galaxy in each halo lives at the halo center and that
additional satellite galaxies follow a radial density profile similar to the
dark matter Navarro-Frenk-White (NFW) profile, except that the concentration
and inner slope are allowed to vary. We find that in low luminosity samples,
satellite galaxies have radial profiles that are consistent with NFW. M_r < -20
and brighter satellite galaxies have radial profiles with significantly steeper
inner slopes than NFW (we find inner logarithmic slopes ranging from -1.6 to
-2.1, as opposed to -1 for NFW). We define a useful metric of concentration,
M_(1/10), which is the fraction of satellite galaxies (or mass) that are
enclosed within one tenth of the virial radius of a halo. We find that M_(1/10)
for low luminosity satellite galaxies agrees with NFW, whereas for luminous
galaxies it is 2.5-4 times higher, demonstrating that these galaxies are
substantially more centrally concentrated within their dark matter halos than
the dark matter itself. Our results therefore suggest that the processes that
govern the spatial distribution of galaxies, once they have merged into larger
halos, must be luminosity dependent, such that luminous galaxies become poor
tracers of the underlying dark matter. | Spherical Orbifolds for Cosmic Topology: Harmonic analysis is a tool to infer cosmic topology from the measured
astrophysical cosmic microwave background CMB radiation. For overall positive
curvature, Platonic spherical manifolds are candidates for this analysis. We
combine the specific point symmetry of the Platonic manifolds with their deck
transformations. This analysis in topology leads from manifolds to orbifolds.
We discuss the deck transformations of the orbifolds and give eigenmodes for
the harmonic analysis as linear combinations of Wigner polynomials on the
3-sphere. These provide new tools for detecting cosmic topology from the CMB
radiation. |
Time delay in the Einstein-Straus solution: The time delay of strong lensing is computed in the framework of the
Einstein-Straus solution. The theory is compared to the observational bound on
the time delay of the lens SDSS J1004+4112. | Spectral Distortion Signatures of Step-like Inflationary Potential: In this work, we analyze a power-law inflationary potential enhanced with a
step that can introduce features in the primordial power spectrum. We focus on
the computation of the Spectral Distortions (SD) induced by these features
obtained from the inflationary dynamics. In this scenario, we explore the
potential of upcoming experimental missions like PIXIE to detect the SD of the
model within a power of $n = 2/3$, a power that agrees with recent
tensor-to-scalar ratio constraints. The model offers insights into models with
cosmological phases and different scalar field dynamics. Introducing a step in
the inflaton potential leads to distinct features in the primordial power
spectrum, such as oscillations and localized enhancements/suppressions at
specific scales. We analyze the impact of three primary parameters$-\beta$,
$\delta$, and $\phi_{\text{step}}-$on the amplitude and characteristics of the
SD. The $\phi_{\rm step}$ places the onset of the oscillations in the
primordial power spectrum. The $\beta$ parameter significantly influences the
magnitude of the $\mu$-SD, with its increase leading to larger SD and vice
versa. Similarly, the $\delta$ parameter affects the smoothness of the step in
the potential, with larger values resulting in smaller SD. Our findings
indicate a distinct parameter space defined by $0.02 <\delta/{\rm M_{pl}}
\lesssim 0.026$, $0.10 \lesssim \beta < 0.23$, and $ 7.53 \lesssim \phi_{\rm
step}/{\rm M_{pl}} \lesssim 7.55$, which produces SD potentially detectable by
PIXIE. This region also corresponds to the maximum observed values of $\mu$ and
$y$ SD, which in special cases are an order of magnitude larger than the
expected for $\Lambda$CDM. However, we also identify parameter ranges where
$\mu$ and $y$ SD may not be detectable due to the limitations of current
observational technology. |
The Chemistry of the Early Universe: The chemistry of the early Universe is a fascinating field of study. Even in
the absence of any elements heavier than lithium, a surprising degree of
chemical complexity proves to be possible, giving the topic considerable
interest in its own right. In addition, the fact that molecular hydrogen plays
a key role in the formation of the first stars and galaxies means that if we
want to understand the formation of these objects, we must first develop a good
understanding of the chemical evolution of the gas. In this review, I first
give a brief introduction to the chemistry occurring in the gas prior to the
formation of the first stars and galaxies, and then go on to discuss in more
detail the main chemical processes occurring during the gravitational collapse
of gas from intergalactic to protostellar densities, and how these processes
influence the final outcome of the collapse. | The strong flaring activity of M87 in early 2008 as observed by the
MAGIC telescope: M87 is the first known radio galaxy to emit very high energy (VHE)
gamma-rays. During a monitoring program of M87, a rapid flare in VHE gamma-rays
was detected by the MAGIC telescope in early 2008. The flux was found to be
variable on a timescale as short as 1 day, reaching 15% of the Crab Nebula flux
above 350 GeV. In contrast, the flux at lower energies (150 GeV to 350 GeV) is
compatible with being constant. We present light curves and energy spectra, and
argue that the observed day-scale flux variability favours the M87 core as
source of the gamma-ray emission rather than the bright know HST-1 in the jet
of M87. |
Cosmic Flows : Green Bank and Parkes HI observations: The neutral hydrogen properties of 1,822 galaxies are being studied with the
Green Bank 100m and the Parkes 64m telescopes as part of the 'Cosmic Flows'
program. Observed parameters include systemic velocities, profile line widths,
and fluxes. The line width information can be combined with optical and
infrared photometry to obtain distances. The 1,822 HI observations complement
an inventory of archives. All told, HI line width information is available for
almost all of five samples: (i) luminosity-line width correlation calibrators,
(ii) zero-point calibrators for the supernova Ia scale, (iii) a dense local
sample of spiral galaxies with M_{Ks} < -21 within 3,000 km/s, (iv) a sparser
sample of 60 $\mu$m selected galaxies within 6,000 km/s that provides all-sky
coverage of our extended supercluster complex, and (v) an even sparser sample
of flat galaxies, extreme edge-on spirals, extending in a volume out to 12,000
km/s. The HI information for 13,941 galaxies, whether from the archives or
acquired as part of the Cosmic Flows observational program, is uniformly
re-measured and made available through the Extragalactic Distance Database web
site. | First study of reionization in the Planck 2015 normalized closed
$Λ$CDM inflation model: We study reionization in two non-flat $\Lambda$CDM inflation models that best
fit the Planck 2015 cosmic microwave background anisotropy observations,
ignoring or in conjunction with baryon acoustic oscillation distance
measurements. We implement a principal component analysis (PCA) to estimate the
uncertainties in the reionization history from a joint quasar-CMB dataset. A
thorough Markov Chain Monte Carlo analysis is done over the parameter space of
PCA modes for both non-flat $\Lambda$CDM inflation models as well as the
original Planck 2016 tilted, spatially-flat $\Lambda$CDM inflation model.
Although both flat and non-flat models can closely match the low-redshift
($z\lesssim6$) observations, we notice a possible tension between high-redshift
($z\sim8$) Lyman-$\alpha$ emitter data and the non-flat models. This is solely
due to the fact that the closed models have a relatively higher reionization
optical depth compared to the flat one, which in turn demands more
high-redshift ionizing sources and favors an extended reionization starting as
early as $z\approx14$. We conclude that as opposed to flat-cosmology, for the
non-flat cosmology models (i) the escape fraction needs steep redshift
evolution and even unrealistically high values at some redshifts and (ii) most
of the physical parameters require to have non-monotonic redshift evolution,
especially apparent when Lyman-$\alpha$ emitter data is included in the
analysis. |
Dark energy explained by a bias in the measurements: Typical cosmological models are based on the postulate that space is
homogeneous. Space however contains overdense regions in which matter is
concentrating, leaving underdense regions of almost void. The evolution of the
scale factor of the universe has been established from measurements on SNIa.
Since such events occur in regions were matter is present, we may expect that
most of the SNIa are located in overdense regions. This means that the
evolution of the scale factor has been established in a biased manner, by
considering only information coming from overdense regions, excluding the one
from the underdense regions. We develop a simple model to analyze the effect of
this bias, and show that it leads to the appearance of a new tensor in the
Einstein equation of general relativity, which can account for the apparent
acceleration of the expansion of the universe. We further show that this tensor
tends to be proportional to the FLRW metric tensor, and that the constant of
proportionality quantitatively corresponds to the measured cosmological
constant with a remarkable accuracy. We finally explain why these properties
remain valid for other techniques used in determining the dynamics of the
universe, such as the baryon acoustic oscillations. | Dynamical models of the elliptical galaxy NGC 4494: We present dynamical models of NGC 4494, which we built using our iterative
method presented in a previous paper. These models are live N-body models
consisting of equal mass particles, and they are steady state as confirmed by a
fully self-consistent evolution. Our goals were twofold. The first one --
namely to test whether our iterative method could indeed be used to construct
galactic models following given observational constraints, both photometric and
kinematic -- was fully achieved. Our method allowed us to go beyond a simple
spherical model and to make full sets of rotating, axisymmetric models without
any limitations to the velocity distribution. Our second goal was to understand
better the structure of NGC 4494, and more specifically to set constraints on
its halo mass. For this we tried three families of models: without halo, with a
light halo and with a heavy halo, respectively. Our models reproduce well the
photometry and the kinematics, the latter except specific regions where some
non-equilibrium or non-axisymmetric structure could be present in the galaxy
(e.g. the kinematically decoupled core). However, the lower order moments of
the velocity distribution (up to and including the second order) do not allow
us to discriminate between the three halos. On the other hand, when we extend
the comparison to the higher order moments of the velocity distribution
obtained from the long-slit data, we find that our light halo model fits the
data better than the no halo, or the heavy halo models. They also reproduce the
shape of the angular dependence of the PNe velocity dispersion in the outermost
parts of the galaxy, but not the amplitude of its azimuthal variation. This may
imply that a yet more general class of models, such as triaxial, may be
necessary for a yet better fit. |
A hierarchy of voids: More ado about nothing: We extend earlier work on the problem of estimating the void-volume function
-- the abundance and evolution of large voids which grow gravitationally in an
expanding universe -- in two ways. The first removes an ambiguity about how the
void-in-cloud process, which erases small voids, should be incorporated into
the excursion set approach. The main technical change here is to think of voids
within a fully Eulerian, rather than purely Lagrangian, framework. The second
accounts for correlations between different spatial scales in the initial
conditions. We provide numerical and analytical arguments showing how and why
both changes modify the predicted abundances substantially. In particular, we
show that the predicted importance of the void-in-cloud process depends
strongly on whether or not one accounts for correlations between scales. With
our new formulation, the void-in-cloud process dramatically reduces the
predicted abundances of voids if such correlations are ignored, but only
matters for the smallest voids in the more realistic case in which the spatial
correlations are included. | Measurements of Secondary Cosmic Microwave Background Anisotropies with
the South Pole Telescope: We report cosmic microwave background (CMB) power spectrum measurements from
the first 100 sq. deg. field observed by the South Pole Telescope (SPT) at 150
and 220 GHz. On angular scales where the primary CMB anisotropy is dominant,
ell ~< 3000, the SPT power spectrum is consistent with the standard LambdaCDM
cosmology. On smaller scales, we see strong evidence for a point source
contribution, consistent with a population of dusty, star-forming galaxies.
After we mask bright point sources, anisotropy power on angular scales of 3000
< ell < 9500 is detected with a signal-to-noise > 50 at both frequencies. We
combine the 150 and 220 GHz data to remove the majority of the point source
power, and use the point source subtracted spectrum to detect
Sunyaev-Zel'dovich (SZ) power at 2.6 sigma. At ell=3000, the SZ power in the
subtracted bandpowers is 4.2 +/- 1.5 uK^2, which is significantly lower than
the power predicted by a fiducial model using WMAP5 cosmological parameters.
This discrepancy may suggest that contemporary galaxy cluster models
overestimate the thermal pressure of intracluster gas. Alternatively, this
result can be interpreted as evidence for lower values of sigma8. When combined
with an estimate of the kinetic SZ contribution, the measured SZ amplitude
shifts sigma8 from the primary CMB anisotropy derived constraint of 0.794 +/-
0.028 down to 0.773 +/- 0.025. The uncertainty in the constraint on sigma8 from
this analysis is dominated by uncertainties in the theoretical modeling
required to predict the amplitude of the SZ power spectrum for a given set of
cosmological parameters. |
Cosmology in front of the background: studying the growth of structure
at CMB wavelengths: Canada has thriving communities in CMB (cosmic microwave background) studies,
cosmology and submillimetre (submm) astronomy, with involvement in many
facilities that featured prominently in previous Astronomy Long Range Plans.
The standard cosmological model continues to be well fit using a small number
of parameters. No one expects this model to be complete and so we need to
continue to challenge it with data; moreover, it does not explain how galaxies
and other structures form. So, how do we improve the precision of our
understanding of structure formation within this model? Wavelengths from the
microwave to the submm will be particularly fruitful for answering this
question. That's because, in addition to the CMB anisotropies, there are other
signals that can be extracted from large maps at these wavelengths -
particularly the cosmic infrared and submm backgrounds, the thermal and kinetic
Sunyaev-Zeldovich effects, and CMB lensing. Such signals carry a wealth of
information about the cosmological model, as well as how dust, gas and
star-formation evolve within dark-matter halos. Cross-correlations between
these signals and those coming from the radio, optical and X-ray surveys, will
provide even more information. Canadians are already members of teams for
several related facilities and are working to be involved in others. In order
for Canada to be fully engaged in exploiting the detailed information coming
from these cosmological signatures, it is crucial that we find the resources to
participate competitively in a combination of projects currently being planned.
Examples include CMB-S4, CCAT-prime, AtLAST, a new camera for JCMT, balloon
projects such as BFORE and a future ambitious CMB satellite. | The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: measuring structure growth using passive galaxies: We explore the benefits of using a passively evolving population of galaxies
to measure the evolution of the rate of structure growth between z=0.25 and
z=0.65 by combining data from the SDSS-I/II and SDSS-III surveys. The
large-scale linear bias of a population of dynamically passive galaxies, which
we select from both surveys, is easily modeled. Knowing the bias evolution
breaks degeneracies inherent to other methodologies, and decreases the
uncertainty in measurements of the rate of structure growth and the
normalization of the galaxy power-spectrum by up to a factor of two. If we
translate our measurements into a constraint on sigma_8(z=0) assuming a
concordance cosmological model and General Relativity (GR), we find that using
a bias model improves our uncertainty by a factor of nearly 1.5. Our results
are consistent with a flat Lambda Cold Dark Matter model and with GR. |
Quantifying the coherent outflows of galaxies around voids in the SDSS
DR7: We report the detection, with a high level of confidence, of coherent
outflows around voids found in the seventh data release of the Sloan Digital
Sky Survey (SDSS DR7). In particular, we developed a robust <|cos theta|>
statistical test to quantify the strength of redshift-space distortions (RSD)
associated with extended coherent velocity fields. We consistently find that
the vector that joins void centers with galaxies that lie in shells around them
is more likely to be perpendicular to the line-of-sight than parallel to it.
This effect is clear evidence for the existence of outflows in the vicinity of
voids. We show that the RSD exist for a wide range of void radius and shell
thickness, but they are more evident in the largest voids in our sample. For
instance, we find that the <|cos theta|> for galaxies located in shells within
2 h^-1 Mpc from the edge of voids larger than 15 h^-1 Mpc deviates 3.81sigma
from uniformity. The measurements presented in this work provide useful
information to constrain cosmological parameters, in particular Omega_m and
Sigma_8. | The effect of bars and transient spirals on the vertical heating in disk
galaxies: The nature of vertical heating of disk stars in the inner as well as the
outer region of disk galaxies is studied. The galactic bar (which is the
strongest non-axisymmetric pattern in the disk) is shown to be a potential
source of vertical heating of the disk stars in the inner region. Using a
nearly self-consistent high-resolution N-body simulation of disk galaxies, the
growth rate of the bar potential is found to be positively correlated with the
vertical heating exponent in the inner region of galaxies. We also characterize
the vertical heating in the outer region where the disk dynamics is often
dominated by the presence of transient spiral waves and mild bending waves. Our
simulation results suggest that the non-axisymmetric structures are capable of
producing the anisotropic heating of the disk stars. |
Evolutionary Stellar Population Synthesis with MILES. Part I: The Base
Models and a New Line Index System: [Abridged]. We present SEDs for single-age, single-metallicity stellar
populations (SSPs) covering the optical range at resolution 2.3A (FWHM). These
SEDs constitute our base models, as they combine scaled-solar isochrones with
MILES empirical stellar library, which follows the chemical evolution pattern
of the solar neighbourhood. The models rely as much as possible on empirical
ingredients, not just on the stellar spectra, but also on extensive photometric
libraries. The unprecedented stellar parameter coverage of MILES allowed us to
safely extend our optical SSP SED predictions from intermediate- to very-old
age regimes, and the metallicity coverage of the SSPs from super-solar to
[M/H]=-2.3. SSPs with such low metallicities are particularly useful for
globular cluster studies. Observed spectra can be studied by means of full
spectrum fitting or line-strengths. For the latter we propose a new Line Index
System (LIS) to avoid the intrinsic uncertainties associated with the popular
Lick/IDS system and provide more appropriate, uniform, spectral resolution.
Apart from constant resolution as function of wavelength the system is also
based on flux-calibrated spectra. Data can be analyzed at three different
resolutions: 5A, 8.4A and 14A (FWHM), which are appropriate for studying
globular cluster, low and intermediate-mass galaxies, and massive galaxies,
respectively. Polynomials to transform current Lick/IDS line index measurements
to the new system are provided. A web-page with a suite of on-line tools to
facilitate the handling and transformation of the spectra is available at
http://miles.iac.es. | Lensing anomaly and oscillations in the primordial power spectrum: The latest analysis of the cosmic microwave background by the Planck team
finds more smoothing of the acoustic peaks in the temperature power spectrum
than predicted by $\Lambda$CDM. Here we investigate whether this additional
smoothing can be mimicked by an oscillatory feature, generated during
inflation, that is similar to the acoustic peaks but out of phase. We consider
oscillations generated by oscillating modulations of the background -- e.g.,
due to heavy fields or modulated potentials -- and by sharp features. We show
that it is difficult to induce oscillations that are linear (or almost linear)
in $k$ by oscillatory modulations of the background. We find, however, that a
sharp bumpy feature in the sound speed of perturbations is able to produce the
desired oscillations. The scenario can be tested by combining CMB and BAO data. |
The Galaxy Major Merger Fraction to z ~ 1: Aims: We study the major merger fraction in a SPITZER/IRAC-selected catalogue
in the GOODS-S field up to z ~ 1 for luminosity- and mass-limited samples.
Methods: We select disc-disc merger remnants on the basis of morphological
asymmetries, and address three main sources of systematic errors: (i) we
explicitly apply morphological K-corrections, (ii) we measure asymmetries in
galaxies artificially redshifted to z_d = 1.0 to deal with loss of
morphological information with redshift, and (iii) we take into account the
observational errors in z and A, which tend to overestimate the merger
fraction, though use of maximum likelihood techniques.
Results: We obtain morphological merger fractions (f_m) below 0.06 up to z ~
1. Parameterizing the merger fraction evolution with redshift as f_m(z) =
f_m(0) (1+z)^m, we find that m = 1.8 +/- 0.5 for M_B <= -20 galaxies, while m =
5.4 +/- 0.4 for M_star >= 10^10 M_Sun galaxies. When we translate our merger
fractions to merger rates (R_m), their evolution, parameterized as R_m(z) =
R_m(0) (1+z)^n, is quite similar in both cases: n = 3.3 +/- 0.8 and n = 3.5 +/-
0.4, respectively.
Conclusions: Our results imply that only ~8% of today's M_star >= 10^10 M_Sun
galaxies have undergone a disc-disc major merger since z ~ 1. In addition, ~21%
of this mass galaxies at z ~ 1 have undergone one of these mergers since z ~
1.5. This suggests that disc-disc major mergers are not the dominant process in
the evolution of M_star >= 10^10 M_Sun galaxies since z ~ 1, but may be an
important process at z > 1. | Density Variations in the NW Star Stream of M31: The Pan Andromeda Archeological Survey (PAndAS) CFHT Megaprime survey of the
M31-M33 system has found a star stream which extends about 120 kpc NW from the
center of M31. The great length of the stream, and the likelihood that it does
not significantly intersect the disk of M31, means that it is unusually well
suited for a measurement of stream gaps and clumps along its length as a test
for the predicted thousands of dark matter sub-halos. The main result of this
paper is that the density of the stream varies between zero and about three
times the mean along its length on scales of 2 to 20 kpc. The probability that
the variations are random fluctuations in the star density is less than 10^-5.
As a control sample we search for density variations at precisely the same
location in stars with metallicity higher than the stream, [Fe/H]=[0, -0.5] and
find no variations above the expected shot noise. The lumpiness of the stream
is not compatible with a low mass star stream in a smooth galactic potential,
nor is it readily compatible with the disturbance caused by the visible M31
satellite galaxies. The stream's density variations appear to be consistent
with the effects of a large population of steep mass function dark matter
sub-halos, such as found in LCDM simulations, acting on an approximately 10Gyr
old star stream. The effects of a single set of halo substructure realizations
are shown for illustration, reserving a statistical comparison for another
study. |
Fractal Structure of Isothermal Lines and Loops on the Cosmic Microwave
Background: The statistics of isothermal lines and loops of the Cosmic Microwave
Background (CMB) radiation on the sky map is studied and the fractal structure
is confirmed in the radiation temperature fluctuation. We estimate the fractal
exponents, such as the fractal dimension $D_{\mathrm{e}}$ of the entire pattern
of isothermal lines, the fractal dimension $D_{\mathrm{c}}$ of a single
isothermal line, the exponent $\zeta$ in Kor\v{c}ak's law for the size
distribution of isothermal loops, the two kind of Hurst exponents,
$H_{\mathrm{e}}$ for the profile of the CMB radiation temperature, and
$H_{\mathrm{c}}$ for a single isothermal line. We also perform fractal analysis
of two artificial sky maps simulated by a standard model in physical cosmology,
the WMAP best-fit $\Lambda$ Cold Dark Matter ($\Lambda$CDM) model, and by the
Gaussian free model of rough surfaces. The temperature fluctuations of the real
CMB radiation and in the simulation using the $\Lambda$CDM model are
non-Gaussian, in the sense that the displacement of isothermal lines and loops
has an antipersistent property indicated by $H_{\mathrm{e}} \simeq 0.23 < 1/2$. | Inflationary predictions of double-well, Coleman-Weinberg, and hilltop
potentials with non-minimal coupling: We discuss how the non-minimal coupling $\xi\phi^2R$ between the inflaton and
the Ricci scalar affects the predictions of single field inflation models where
the inflaton has a non-zero vacuum expectation value (VEV) $v$ after inflation.
We show that, for inflaton values both above the VEV and below the VEV during
inflation, under certain conditions the inflationary predictions become
approximately the same as the predictions of the Starobinsky model. We then
analyze inflation with double-well and Coleman-Weinberg potentials in detail,
displaying the regions in the $v$-$\xi$ plane for which the spectral index
$n_s$ and the tensor-to-scalar ratio $r$ values are compatible with the current
observations. $r$ is always larger than 0.002 in these regions. Finally, we
consider the effect of $\xi$ on small field inflation (hilltop) potentials. |
How the cosmic web induces intrinsic alignments of galaxies: Intrinsic alignments are believed to be a major source of systematics for
future generation of weak gravitational lensing surveys like Euclid or LSST.
Direct measurements of the alignment of the projected light distribution of
galaxies in wide field imaging data seem to agree on a contamination at a level
of a few per cent of the shear correlation functions, although the amplitude of
the effect depends on the population of galaxies considered. Given this
dependency, it is difficult to use dark matter-only simulations as the sole
resource to predict and control intrinsic alignments. We report here estimates
on the level of intrinsic alignment in the cosmological hydrodynamical
simulation Horizon-AGN that could be a major source of systematic errors in
weak gravitational lensing measurements. In particular, assuming that the spin
of galaxies is a good proxy for their ellipticity, we show how those spins are
spatially correlated and how they couple to the tidal field in which they are
embedded. We also present theoretical calculations that illustrate and
qualitatively explain the observed signals. | Primordial gravitational wave phenomenology with polarized Sunyaev
Zel'dovich tomography: The detection and characterization of primordial gravitational waves through
their impact on the polarization anisotropies of the cosmic microwave
background (CMB) is a primary science goal of current and future observations
of the CMB. An ancillary dataset that will become accessible with the great
leaps in sensitivity of CMB experiments is the polarized Sunyaev Zel'dovich
(pSZ) effect, small-scale CMB polarization anisotropies induced by scattering
from free electrons in the post-reionization Universe. The cross correlation of
the pSZ effect with galaxy surveys, a technique known as pSZ tomography, can be
used to reconstruct the remote quadrupole field: the CMB quadrupole observed
from different locations in the Universe. Primordial gravitational waves leave
a distinct imprint on the remote quadrupole field, making pSZ tomography a
potential new method to characterize their properties. Building on previous
work, we explore the utility of the full set of correlations between the
primary CMB and the reconstructed remote quadrupole field to both provide
exclusion limits on the amplitude of primordial gravitational waves, as well as
to provide constraints on several phenomenological models of the tensor sector:
axion gauge field inflation, general models with chiral tensors, and models
with modified late-time decay of tensors. We find that relatively futuristic
experimental requirements are necessary to provide competitive exclusion limits
compared with the primary CMB. However, pSZ tomography can be a powerful probe
of the late-time evolution of tensors and, through cross-correlations with the
primary CMB, can provide mild improvements on parameter constraints in various
models with chiral primordial gravitational waves. |
Environmental Effects for Gravitational-wave Astrophysics: The upcoming detection of gravitational waves by terrestrial interferometers
will usher in the era of gravitational-wave astronomy. This will be
particularly true when space-based detectors will come of age and measure the
mass and spin of massive black holes with exquisite precision and up to very
high redshifts, thus allowing for better understanding of the symbiotic
evolution of black holes with galaxies, and for high-precision tests of General
Relativity in strong-field, highly dynamical regimes. Such ambitious goals
require that astrophysical environmental pollution of gravitational-wave
signals be constrained to negligible levels, so that neither detection nor
estimation of the source parameters are significantly affected. Here, we
consider the main sources for space-based detectors -- the inspiral, merger and
ringdown of massive black-hole binaries and extreme mass-ratio inspirals -- and
account for various effects on their gravitational waveforms, including
electromagnetic fields, cosmological evolution, accretion disks, dark matter,
"firewalls" and possible deviations from General Relativity. We discover that
the black-hole quasinormal modes are sharply different in the presence of
matter, but the ringdown signal observed by interferometers is typically
unaffected. The effect of accretion disks and dark matter depends critically on
their geometry and density profile, but is negligible for most sources, except
for few special extreme mass-ratio inspirals. Electromagnetic fields and
cosmological effects are always negligible. We finally explore the implications
of our findings for proposed tests of General Relativity with gravitational
waves, and conclude that environmental effects will not prevent the development
of precision gravitational-wave astronomy. | Improving models of the cosmic infrared background using CMB lensing
mass maps: The cosmic infrared background (CIB) sourced by infrared emission from dusty
star-forming galaxies is a valuable source of information on the star formation
history of the Universe. In measurements of the millimeter sky at frequencies
higher than $\sim 300$ GHz, the CIB and thermal emission from Galactic dust
dominate. A limited understanding of the CIB contribution at lower frequencies
on the other hand can hinder efforts to measure the kinetic Sunyaev-Zeldovich
spectrum on small scales as well as new physics that affects the damping tail
of the cosmic microwave background (CMB). The Planck satellite has measured
with high fidelity the CIB at 217, 353, 545 and 857 GHz. On very large scales,
this measurement is limited by our ability to separate the CIB from Galactic
dust, but on intermediate scales, the measurements are limited by sample
variance in the underlying matter field traced by the CIB. We show how
significant improvements (20-100%) can be obtained on parameters of star
formation models by cross-correlating the CIB (as measured from existing {\it
Planck} maps or upcoming CCAT-prime maps) with upcoming mass maps inferred from
gravitational lensing of the CMB. This improvement comes from improved
knowledge of the redshift distribution of star-forming galaxies as well as
through the use of the unbiased matter density inferred from CMB lensing mass
maps to cancel the sample variance in the CIB field. We also find that further
improvements can be obtained on CIB model parameters if the cross-correlation
of the CIB with CMB lensing is measured over a wider area while restricting the
more challenging CIB auto-spectrum measurement to the cleanest 5% of the sky. |
Simultaneous modelling of matter power spectrum and bispectrum in the
presence of baryons: We demonstrate that baryonification algorithms, which displace particles in
gravity-only simulations according to physically-motivated prescriptions, can
simultaneously capture the impact of baryonic physics on the 2 and 3-point
statistics of matter. Specifically, we show that our implementation of a
baryonification algorithm jointly fits the changes induced by baryons on the
power spectrum and equilateral bispectrum on scales up to k < 5 h/Mpc and
redshifts z<2, as measured in six different cosmological hydrodynamical
simulations. The accuracy of our fits are typically 1% for the power spectrum,
and for the equilateral and squeezed bispectra, which somewhat degrades to 3%
for simulations with extreme feedback prescriptions. Our results support the
physical assumptions underlying baryonification approaches, and encourage their
use in interpreting weak gravitational lensing and other cosmological
observables. | Approximate Metric for a Rotating Deformed Mass: A new Kerr-like metric with quadrupole moment is obtained by means of
perturbing the Kerr spacetime. The form of this new metric is simple as the
Kerr metric. By comparison with the exterior Hartle-Thorne metric, it is shown
that it could be matched to an interior solution. This approximate metric may
represent the spacetime of a real astrophysical object with any Kerr rotation
parameter a and slightly deformed. |
Constraints for the running index independent of the parameters of the
model: By writing the running of the scalar spectral index completely in terms of
the scalar index $n_s$ and the tensor-to-scalar ratio $r$ we are able to impose
constraints to models of inflation which are independent of the parameters of
the model in question. We write analytical expressions for the running index of
Natural Inflation, two models of the type Mutated Hilltop Inflation and the
Starobinsky model. The resulting formulae for the running depend exclusively on
$n_s$ and/or $r$ and will keep tightening the running index further as
additional conditions and observations constrain the scalar and the
tensor-to-scalar indices. | What is the source of the PTA GW signal?: The most conservative interpretation of the nHz stochastic gravitational wave
background (SGWB) discovered by NANOGrav and other Pulsar Timing Array (PTA)
Collaborations is astrophysical, namely that it originates from supermassive
black hole (SMBH) binaries. However, alternative cosmological models have been
proposed, including cosmic strings, phase transitions, domain walls, primordial
fluctuations and "audible" axions. We perform a multi-model analysis (MMA) to
compare how well these different hypotheses fit the NANOGrav data, both in
isolation and in combination with SMBH binaries, and address the questions:
Which interpretations fit the data best, and which are disfavoured? We also
discuss experimental signatures that can help discriminate between different
sources of the PTA GW signal, including fluctuations in the signal strength
between frequency bins, individual sources and how the PTA signal extends to
higher frequencies. |
Constrained evolution of effective equation of state parameter in
non-linear $f(R, L_m)$ dark energy model: Insights from Bayesian analysis of
cosmic chronometers and Pantheon samples: We conduct a Bayesian analysis of recent observational datasets, specifically
the Cosmic Chronometers (CC) dataset and Pantheon samples, to investigate the
evolution of the EoS parameter in dark energy models. Our study focused on the
effective EoS parameter, which is described by the parametric form
$\omega_{eff}=-\frac{1}{1+m(1+z)^n}$, where $m$ and $n$ are model parameters.
This parametric form is applicable within the framework of $f(R,L_m)$ gravity,
where $R$ represents the Ricci scalar and $L_m$ is the matter Lagrangian. Here,
we examine a non-linear $f(R,L_m)$ model characterized by the functional form
$f(R,L_m)=\frac{R}{2}+L_m^\alpha$, where $\alpha$ is the free parameter of the
model. We examine the evolution of several cosmological parameters, including
the effective EoS parameter $\omega_{eff}$, the deceleration parameter $q$, the
density parameter $\rho$, the pressure $p$, and the statefinder parameters. Our
analysis revealed that the constrained current value of the effective EoS
parameter, $\omega_{eff}^{0}=-0.68\pm0.06$ for both the CC and Pantheon
datasets, points towards a quintessence phase. Moreover, at redshift $z=0$, the
deceleration parameter, $q_0 = -0.61^{+0.01}_{-0.01}$, indicates that the
present Universe is undergoing accelerated expansion. | 2MTF II. New Parkes 21-cm observations of 303 southern galaxies: We present new 21-cm neutral hydrogen (HI) observations of spiral galaxies
for the 2MASS Tully Fisher (2MTF) survey. Using the 64-m Parkes radio telescope
multibeam system we obtain 152 high signal-to-noise HI spectra from which we
extract 148 high-accuracy (< 5% error) velocity widths and derive reliable
rotation velocities. The observed sample consists of 303 southern (\delta <
-40\deg) galaxies selected from the MASS Redshift Survey (2MRS) with K_s <11.25
mag, cz < 10,000 km/s and axis ratio b/a < 0.5. The HI observations reported in
this paper will be combined with new HI spectra from the Green Bank and Arecibo
telescopes, together producing the most uniform Tully-Fisher survey ever
constructed (in terms of sky coverage). In particular, due to its near infrared
selection, 2MTF will be significantly more complete at low Galactic latitude
(|b|<15\deg) and will provide a more reliable map of peculiar velocities in the
local universe. |
Reionization and Galaxy Formation in Warm Dark Matter Cosmologies: We compare model results from a semi-analytic (merger-tree based) framework
for high-redshift (z ~ 5-20) galaxy formation against reionization indicators,
including the Planck electron scattering optical depth and the ionizing photon
emissivity, to shed light on the reionization history and sources in Cold (CDM)
and Warm Dark Matter (WDM; particle masses of $m_x = 1.5,3$ and 5 keV)
cosmologies. This model includes all the key processes of star formation,
supernova feedback, the merger/accretion/ejection driven evolution of gas and
stellar mass and the effect of the ultra-violet background (UVB) in
photo-evaporating the gas content of low-mass galaxies. We find that the delay
in the start of reionization in light (1.5 keV) WDM models can be compensated
by a steeper redshift evolution of the ionizing photon escape fraction and a
faster mass assembly, resulting in reionization ending at comparable redshifts
(z~5.5) in all the DM models considered. We find the bulk of the reionization
photons come from galaxies with a halo mass $M_h < 10^9 M_\odot$ and a UV
magnitude $ -15 < M_{UV} < -10$ in CDM. The progressive suppression of low-mass
halos with decreasing $m_x$ leads to a shift in the reionization population to
larger halo masses of $M_h > 10^9 M_\odot$ and $ -17 < M_{UV} < -13$ for 1.5
keV WDM. We find that current observations of the electron scattering optical
depth and the Ultra-violet luminosity function are equally compatible with all
the (cold and warm) DM models considered in this work. We propose that global
indicators including the redshift evolution of the stellar mass density and the
stellar mass-halo mass relation, observable with the James Webb Space
Telescope, can be used to distinguish between CDM and WDM (1.5 keV)
cosmologies. | The Atacama Cosmology Telescope: Constraints on Pre-Recombination Early
Dark Energy: The early dark energy (EDE) scenario aims to increase the value of the Hubble
constant ($H_0$) inferred from cosmic microwave background (CMB) data over that
found in $\Lambda$CDM, via the introduction of a new form of energy density in
the early universe. The EDE component briefly accelerates cosmic expansion just
prior to recombination, which reduces the physical size of the sound horizon
imprinted in the CMB. Previous work has found that non-zero EDE is not
preferred by Planck CMB power spectrum data alone, which yield a 95% confidence
level (CL) upper limit $f_{\rm EDE} < 0.087$ on the maximal fractional
contribution of the EDE field to the cosmic energy budget. In this paper, we
fit the EDE model to CMB data from the Atacama Cosmology Telescope (ACT) Data
Release 4. We find that a combination of ACT, large-scale Planck TT (similar to
WMAP), Planck CMB lensing, and BAO data prefers the existence of EDE at
$>99.7$% CL: $f_{\rm EDE} = 0.091^{+0.020}_{-0.036}$, with $H_0 =
70.9^{+1.0}_{-2.0}$ km/s/Mpc (both 68% CL). From a model-selection standpoint,
we find that EDE is favored over $\Lambda$CDM by these data at roughly
$3\sigma$ significance. In contrast, a joint analysis of the full Planck and
ACT data yields no evidence for EDE, as previously found for Planck alone. We
show that the preference for EDE in ACT alone is driven by its TE and EE power
spectrum data. The tight constraint on EDE from Planck alone is driven by its
high-$\ell$ TT power spectrum data. Understanding whether these differing
constraints are physical in nature, due to systematics, or simply a rare
statistical fluctuation is of high priority. The best-fit EDE models to ACT and
Planck exhibit coherent differences across a wide range of multipoles in TE and
EE, indicating that a powerful test of this scenario is anticipated with
near-future data from ACT and other ground-based experiments. |
Extended narrow-line emission in the bright Seyfert 1.5 galaxy HE
2211-3903: Extended narrow-line regions (ENLRs) and extended emission-line regions
(EELRs) have been the focus of integral field spectroscopy aiming at the inner
kiloparsecs of nearby Seyfert galaxies as well as the larger environment of
high redshift QSOs. Based on observations with the Wide Field Spectrograph
WiFeS at the 2.3 m telescope of the Australian National University, we present
spatially resolved emission-line diagnostics of the bright Seyfert 1.5 galaxy
HE 2211-3903 which is drawn from a sample of the brightest Seyfert galaxies at
z<0.06 with luminosities around the classical Seyfert/QSO demarcation. In
addition to the previously known spiral arms of HE 2211-3903, the emission-line
maps reveal a large scale ring with a radius of about 6 kpc which is connected
to the active galactic nucleus (AGN) through a bar-like structure. The overall
gas kinematics indicates a disk rotation pattern. The emission-line ratios show
Seyfert-type, HII region-type, and composite classifications, while there is no
strong evidence of LINER-type ratios. Shock ionization is likely to be
negligible throughout the galaxy. The composite line ratios are explained via a
mixing line between AGN and HII region photoionization. Composite line ratios
are predominantly found in between the HII regions in the circum-nuclear
region, the bar-like structure to the east of the nucleus, and the eastern half
of the ring, suggesting AGN photoionization of the low-density interstellar
medium in an ENLR on galaxy scales. The line ratios in the nucleus indicate
N-enrichment, which is discussed in terms of chemical enrichment by Wolf-Rayet
and Asymptotic Giant Branch stars during past and ongoing nuclear starburst
activity. | Luminous Thermal Flares from Quiescent Supermassive Black Holes: A dormant supermassive black hole lurking in the center of a galaxy will be
revealed when a star passes close enough to be torn apart by tidal forces, and
a flare of electromagnetic radiation is emitted when the bound fraction of the
stellar debris falls back onto the black hole and is accreted. Here we present
the third candidate tidal disruption event discovered in the GALEX Deep Imaging
Survey: a 1.6x10^{43} erg s^{-1} UV/optical flare from a star-forming galaxy at
z=0.1855. The UV/optical SED during the peak of the flare measured by GALEX and
Palomar LFC imaging can be modeled as a single temperature blackbody with
T_{bb}=1.7x10^{5} K and a bolometric luminosity of 3x10^{45} erg s^{-1},
assuming an internal extinction with E(B-V)_{gas}=0.3. The Chandra upper limit
on the X-ray luminosity during the peak of the flare, L_{X}(2-10 keV)< 10^{41}
erg s^{-1}, is 2 orders of magnitude fainter than expected from the ratios of
UV to X-ray flux density observed in active galaxies. We compare the light
curves and broadband properties of all three tidal disruption candidates
discovered by GALEX, and find that (1) the light curves are well fitted by the
power-law decline expected for the fallback of debris from a tidally disrupted
solar-type star, and (2) the UV/optical SEDs can be attributed to thermal
emission from an envelope of debris located at roughly 10 times the tidal
disruption radius of a ~10^{7} M_sun central black hole. We use the observed
peak absolute optical magnitudes of the flares (-17.5 > M_{g} > -18.9) to
predict the detection capabilities of upcoming optical synoptic surveys.
(Abridged) |
The limits of cosmology: role of the Moon: The lunar surface allows a unique way forward in cosmology, to go beyond
current limits. The far side provides an unexcelled radio-quiet environment for
probing the dark ages via 21 cm interferometry to seek elusive clues on the
nature of the infinitesimal fluctuations that seeded galaxy formation.
Far-infrared telescopes in cold and dark lunar polar craters will probe back to
the first months of the Big Bang and study associated spectral distortions in
the CMB. Optical and IR megatelescopes will image the first star clusters in
the universe and seek biosignatures in the atmospheres of unprecedented numbers
of nearby habitable zone exoplanets. The goals are compelling and a stable
lunar platform will enable construction of telescopes that can access trillions
of modes in the sky, providing the key to exploration of our cosmic origins. | Weak lensing calibration of mass bias in the REFLEX+BCS X-ray galaxy
cluster catalogue: The use of large, X-ray selected galaxy cluster catalogues for cosmological
analyses requires a thorough understanding of the X-ray mass estimates. Weak
gravitational lensing is an ideal method to shed light on such issues, due to
its insensitivity to the cluster dynamical state. We perform a weak lensing
calibration of 166 galaxy clusters from the REFLEX and BCS cluster catalogue
and compare our results to the X-ray masses based on scaled luminosities from
that catalogue. To interpret the weak lensing signal in terms of cluster
masses, we compare the lensing signal to simple theoretical Navarro-Frenk-White
models and to simulated cluster lensing profiles, including complications such
as cluster substructure, projected large-scale structure, and Eddington bias.
We find evidence of underestimation in the X-ray masses, as expected, with
$\langle M_{\mathrm{X}}/M_{\mathrm{WL}}\rangle = 0.75 \pm 0.07$ stat. $\pm
0.05$ sys. for our best-fit model. The biases in cosmological parameters in a
typical cluster abundance measurement that ignores this mass bias will
typically exceed the statistical errors. |
Cosmology with matter diffusion: We construct a viable cosmological model based on velocity diffusion of
matter particles. In order to ensure the conservation of the total
energy-momentum tensor in the presence of diffusion, we include a cosmological
scalar field $\phi$ which we identify with the dark energy component of the
Universe. The model is characterized by only one new degree of freedom, the
diffusion parameter $\sigma$. The standard $\Lambda$CDM model can be recovered
by setting $\sigma=0$. If diffusion takes place ($\sigma >0$) the dynamics of
the matter and of the dark energy fields are coupled. We argue that the
existence of a diffusion mechanism in the Universe can serve as a theoretical
motivation for interacting models. We constrain the background dynamics of the
diffusion model with Supernovae, H(z) and BAO data. We also perform a
perturbative analysis of this model in order to understand structure formation
in the Universe. We calculate the impact of diffusion both on the CMB spectrum,
with particular attention to the integrated Sachs-Wolfe signal, and on the
matter power spectrum $P(k)$. The latter analysis places strong constraints on
the magnitude of the diffusion mechanism but does not rule out the model. | Internal dynamics of the galaxy cluster Abell 545: Diffuse radio emission in galaxy clusters, and their connection with cluster
mergers, are still debated. We seek to explore the internal dynamics of the
radio halo cluster Abell 545. This cluster is also peculiar for hosting in its
center a very bright, red, diffuse intracluster light due to an old, stellar
population, so bright to be named as "star pile". Our analysis is based on
redshift data for 110 galaxies. We identify 95 cluster members and analyze the
cluster internal dynamics by combining galaxy velocities and positions. We also
use both photometric and X-ray data. We estimate the cluster redshift,
z=0.1580, a velocity dispersion of 1200 km/s, and ICM temperature kT_X~8 keV.
Our optical and X-ray analyses detect substructures. Optical data reveal three
main galaxy clumps (center, NNW, and NE), and possibly a fourth clump at South.
There is not a dominant galaxy and the four brightest galaxies avoid the
cluster core (>~0.4h distant from the cluster center) and are >~1500 km/s far
from the mean cluster velocity. The analysis of the X-ray surface brightness
distribution provides us evidence of a disturbed dynamical phase. Located in
the star pile region there is the brightest galaxies of the cluster core (CBCG)
and a very compact elliptical galaxy. We show that the star pile has a similar
redshift to that of the CBCG. Both the star pile and the CBCG are at rest in
the cluster rest frame. The emerging picture of Abell 545 is that of a massive,
M(R<1.6 h_70^-1 Mpc)=1.1-1.8x10^15 h_70^-1 Msun, very complex cluster with
merging occurring along two directions. A545 gives another proof in the favor
of the connection between cluster merger and extended, diffuse radio emission.
The star pile, likely due to the process of a brightest galaxy forming in the
cluster core. A545 represents a textbook cluster where to study the
simultaneous formation of a galaxy system and its brightest galaxy. |
Impacts of dark energy on constraining neutrino mass after Planck 2018: Considering the mass splittings of three active neutrinos, we investigate how
the nature of dark energy affects the cosmological constraints on the total
neutrino mass $\sum m_\nu$ using the latest cosmological observations. In this
paper, some typical dark energy models, including $\Lambda$CDM, $w$CDM, CPL,
and HDE models, are discussed. In the analysis, we also consider the effects
from the neutrino mass hierarchies, i.e., the degenerate hierarchy (DH), the
normal hierarchy (NH), and the inverted hierarchy (IH). We employ the current
cosmological observations to do the analysis, including the Planck 2018
temperature and polarization power spectra, the baryon acoustic oscillations
(BAO), the type Ia supernovae (SNe), and the Hubble constant $H_0$ measurement.
In the $\Lambda$CDM+$\sum m_\nu$ model, we obtain the upper limits of the
neutrino mass $\sum m_\nu < 0.123$ eV (DH), $\sum m_\nu < 0.156$ eV (NH), and
$\sum m_\nu < 0.185$ eV (IH) at the $95\%$ C.L., using the Planck+BAO+SNe data
combination. For the $w$CDM+$\sum m_\nu$ model and the CPL+$\sum m_\nu$ model,
larger upper limits of $\sum m_\nu$ are obtained compared to those of the
$\Lambda$CDM+$\sum m_\nu$ model. The most stringent constraint on the neutrino
mass, $\sum m_\nu<0.080$ eV (DH), is derived in the HDE+$\sum m_\nu$ model. In
addition, we find that the inclusion of the local measurement of the Hubble
constant in the data combination leads to tighter constraints on the total
neutrino mass in all these dark energy models. | BAO angular scale at z_eff = 0.11 with the SDSS blue galaxies: We measure the transverse baryon acoustic oscillations (BAO) signal in the
local Universe using a sample of blue galaxies from the Sloan Digital Sky
Survey (SDSS) survey as a cosmological tracer. The method is weakly dependent
on a cosmological model and is suitable for 2D analyses in thin redshift bins
to investigate the SDSS data in the interval $z {\in} [0.105, 0.115]$. We
detect the transverse BAO signal ${\theta}_{BAO} = 19.8^{\deg} {\pm}
1.05^{\deg}$ at $z_{eff} = 0.11$, with a statistical significance of $2.2
{\sigma}$. Additionally, we perform tests that confirm the robustness of this
angular BAO signature. Supported by a large set of log-normal simulations, our
error analyses include statistical and systematic contributions. In addition,
considering the sound horizon scale calculated by the Planck Collaboration,
$r_{s}^{Planck}$, and the ${\theta}_{BAO}$ value obtained here, we obtain a
measurement of the angular diameter distance $D_{A}(0.11) = 258.31 {\pm} 13.71
\,Mpc/h$. Moreover, combining this ${\theta}_{BAO}$ measurement at low redshift
with other BAO angular scale data reported in the literature, we perform
statistical analyses for the cosmological parameters of some Lambda cold dark
matter (${\Lambda}$CDM) type models. |
A measurement of gravitational lensing of the microwave background using
South Pole Telescope data: We use South Pole Telescope data from 2008 and 2009 to detect the
non-Gaussian signature in the cosmic microwave background (CMB) produced by
gravitational lensing and to measure the power spectrum of the projected
gravitational potential. We constrain the ratio of the measured amplitude of
the lensing signal to that expected in a fiducial LCDM cosmological model to be
0.86 +/- 0.16, with no lensing disfavored at 6.3 sigma. Marginalizing over LCDM
cosmological models allowed by the WMAP7 results in a measurement of
A_lens=0.90+/-0.19, indicating that the amplitude of matter fluctuations over
the redshift range 0.5 <~ z <~ 5 probed by CMB lensing is in good agreement
with predictions. We present the results of several consistency checks. These
include a clear detection of the lensing signature in CMB maps filtered to have
no overlap in Fourier space, as well as a "curl" diagnostic that is consistent
with the signal expected for LCDM. We perform a detailed study of bias in the
measurement due to noise, foregrounds, and other effects and determine that
these contributions are relatively small compared to the statistical
uncertainty in the measurement. We combine this lensing measurement with
results from WMAP7 to improve constraints on cosmological parameters when
compared to those from WMAP7 alone: we find a factor of 3.9 improvement in the
measurement of the spatial curvature of the Universe, Omega_k=-0.0014+/-0.0172;
a 10% improvement in the amplitude of matter fluctuations within LCDM,
sigma_8=0.810+/ 0.026; and a 5% improvement in the dark energy equation of
state, w=-1.04+/-0.40. When compared with the measurement of w provided by the
combination of WMAP7 and external constraints on the Hubble parameter, the
addition of the lensing data improve the measurement of w by 15% to give
w=-1.087+/-0.096. | The Dark Energy Survey Supernova Program: Corrections on photometry due
to wavelength-dependent atmospheric effects: Wavelength-dependent atmospheric effects impact photometric supernova flux
measurements for ground-based observations. We present corrections on supernova
flux measurements from the Dark Energy Survey Supernova Program's 5YR sample
(DES-SN5YR) for differential chromatic refraction (DCR) and
wavelength-dependent seeing, and we show their impact on the cosmological
parameters $w$ and $\Omega_m$. We use $g-i$ colors of Type Ia supernovae (SNe
Ia) to quantify astrometric offsets caused by DCR and simulate point spread
functions (PSFs) using the GalSIM package to predict the shapes of the PSFs
with DCR and wavelength-dependent seeing. We calculate the magnitude
corrections and apply them to the magnitudes computed by the DES-SN5YR
photometric pipeline. We find that for the DES-SN5YR analysis, not accounting
for the astrometric offsets and changes in the PSF shape cause an average bias
of $+0.2$ mmag and $-0.3$ mmag respectively, with standard deviations of $0.7$
mmag and $2.7$ mmag across all DES observing bands (\textit{griz}) throughout
all redshifts. When the DCR and seeing effects are not accounted for, we find
that $w$ and $\Omega_m$ are lower by less than $0.004\pm0.02$ and
$0.001\pm0.01$ respectively, with $0.02$ and $0.01$ being the $1\sigma$
statistical uncertainties. Although we find that these biases do not limit the
constraints of the DES-SN5YR sample, future surveys with much higher
statistics, lower systematics, and especially those that observe in the $u$
band will require these corrections as wavelength-dependent atmospheric effects
are larger at shorter wavelengths. We also discuss limitations of our method
and how they can be better accounted for in future surveys. |
Cosmology with torsion: An alternative to cosmic inflation: We propose a simple scenario which explains why our Universe appears
spatially flat, homogeneous and isotropic. We use the
Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity which naturally extends
general relativity to include the spin of matter. The torsion of spacetime
generates gravitational repulsion in the early Universe filled with quarks and
leptons, preventing the cosmological singularity: the Universe expands from a
state of minimum but finite radius. We show that the dynamics of the closed
Universe immediately after this state naturally solves the flatness and horizon
problems in cosmology because of an extremely small and negative torsion
density parameter, $\Omega_S \approx -10^{-69}$. Thus the ECKS gravity provides
a compelling alternative to speculative mechanisms of standard cosmic
inflation. This scenario also suggests that the contraction of our Universe
preceding the bounce at the minimum radius may correspond to the dynamics of
matter inside a collapsing black hole existing in another universe, which could
explain the origin of the Big Bang. | Toward a Direct Measurement of the Cosmic Acceleration: We present precise HI 21 cm absorption line redshifts observed in multiple
epochs to directly constrain the secular redshift drift dz/dt_o or the cosmic
acceleration, dv/dt_o. A comparison of literature analog spectra to
contemporary digital spectra shows significant acceleration likely attributable
to systematic instrumental errors. However, we obtain robust constraints using
primarily Green Bank Telescope digital data. Ten objects spanning z=0.09-0.69
observed over 13.5 years show dz/dt_o = (-2.3 +/- 0.8) x 10^-8 yr^-1 or dv/dt_o
= -5.5 +/- 2.2 m/s/yr. The best constraint from a single object, 3C286 at <z> =
0.692153275(85), is dz/dt_o = (1.6 +/- 4.7) x 10^-8 yr^-1 or dv/dt_o =2.8 +/-
8.4 m/s/yr. These measurements are three orders of magnitude larger than the
theoretically expected acceleration at z=0.5, dz/dt_o = 2 x 10^-11 yr^-1 or
dv/dt_o = 0.3 cm/s/yr, but they demonstrate the lack of peculiar acceleration
in absorption line systems and the long-term frequency stability of modern
radio telescopes. A comparison of UV metal absorption lines to the 21 cm line
improves constraints on the cosmic variation of physical constants:
Delta(alpha^2 g_p mu)/(alpha^2 g_p mu) = (-1.2 +/- 1.4) x 10^-6 in the redshift
range z=0.24-2.04. The linear evolution over the last 10.4 Gyr is (-0.2 +/-
2.7) x 10^-16 yr^-1, consistent with no variation. The cosmic acceleration
could be directly measured in ~125 years using current telescopes or in ~5
years using a Square Kilometer Array, but systematic effects will arise at the
1 cm/s/yr level. |
Constraining a causal dissipative cosmological model: In this paper a cosmological solution of polynomial type $H \approx ( t +
const.)^{-1}$ for the causal thermodynamical approach of Isarel-Stewart, found
in \cite{MCruz:2017, Cruz2017}, is constrained using the joint of the latest
measurements of the Hubble parameter (OHD) and Type Ia Supernovae (SNIa). Since
the expansion described by this solution does not present a transition from a
decelerated phase to an accelerated one, both phases can be well modeled
connecting both phases by requiring the continuity of the Hubble parameter at
$z=z_{t}$, the accelerated-decelerated transition redshift. Our best fit
constrains the main free parameters of the model to be $A_1=
1.58^{+0.08}_{-0.07}$ ($A_2=0.84^{+0.02}_{-0.02}$) for the accelerated
(decelerated) phase. For both phases we obtain $q=-0.37^{+0.03}_{-0.03}$
($0.19^{+0.03}_{-0.03}$) and $\omega_{eff} = -0.58^{+0.02}_{-0.02}$
($-0.21^{+0.02}_{-0.02}$) for the deceleration parameter and the effective
equation of state, respectively. Comparing our model and LCDM statistically
through the Akaike information criterion and the Bayesian information criterion
we obtain that the LCDM model is preferred by the OHD+SNIa data. Finally, it is
shown that the constrained parameters values satisfy the criterion for a
consistent fluid description of a dissipative dark matter component, but with a
high value of the speed of sound within the fluid, which is a drawback for a
consistent description of the structure formation. We briefly discuss the
possibilities to overcome this problem with a non-linear generalization of the
causal linear thermodynamics of bulk viscosity and also with the inclusion of
some form of dark energy. | Current small-scale CMB constraints to axion-like early dark energy: The SPT-3G 2018 TT/TE/EE cosmic microwave background (CMB) data set
(temperature and polarization) is used to place constraints on an axion-like
model of early dark energy (EDE). These data do not favor axion-like EDE and
place an upper limit on the maximum fraction of the total energy density
$f_{\rm EDE}< 0.172$ (at the 95% confidence level, CL). This is in contrast
with ACT DR4 which gives $f_{\rm EDE}=0.150^{+0.050}_{-0.078}$. When combining
CMB measurements with measurements of the baryon acoustic oscillations and
luminosity distance to Type Ia supernovae, we show that the tension with the
S$H_0$ES measurement of the Hubble parameter goes up from 2.6$\sigma$ with
Planck to 2.9$\sigma$ with Planck+SPT-3G 2018. The additional inclusion of ACT
DR4 data leads to a reduction of the tension to $1.6\sigma$, but the
discrepancy between ACT DR4 and Planck+SPT-3G 2018 casts some doubt on the
statistical consistency of this joint analysis. The importance of improved
measurements of the CMB at both intermediate and small scales (in particular
the shape of the damping tail) as well as the interplay between temperature and
polarization measurements in constraining EDE are discussed. Upcoming
ground-based measurements of the CMB will play a crucial role in determining
whether EDE remains a viable model to address the Hubble tension. |
Radio constraints on Galactic WIMP dark matter: Synchrotron emission from electron cosmic ray populations can be used to
study both cosmic rays physics and WIMP dark matter imprints on radio skymaps.
We used available radio data - from MHz to GHz - to analyze the contribution
from galactic WIMP annihilations and impose constraints on WIMP observables:
annihilation cross section, channel and mass. Depending on the annihilation
channel we obtain as competitive bounds as those obtained in FERMI-LAT gamma
ray analysis of dwarf satellite galaxies. | The Redshift Search Receiver Observations of 12CO J=1-->0 in 29
Ultraluminous Infrared Galaxies: We present 12CO J=1-->0 observations of ultraluminous infrared galaxies
(ULIRGs) obtained using the Redshift Search Receiver (RSR) on the 14-m
telescope of the Five College Radio Astronomy Observatory. The RSR is a novel,
dual-beam, dual-polarization receiver equipped with an ultra-wideband
spectrometer backend that is being built as a facility receiver for the Large
Millimeter Telescope. Our sample consists of 29 ULIRGs in the redshift range of
0.04-0.11, including 10 objects with no prior 12CO measurements. We have
detected 27 systems (a detection rate of 93%), including 9 ULIRGs that are
detected in CO for the first time. Our study has increased the number of local
ULIRGs with CO measurements by ~15%. The CO line luminosity L'_CO, correlates
well with far-infrared luminosity L_FIR, following the general trend of other
local ULIRGs. However, compared to previous surveys we probe deeper into the
low CO luminosity end of ULIRG population as a single study by including a
number of CO faint objects in the sample. As a result, we find 1) a smoother
transition between the ULIRG population and local QSOs in L_FIR-L'_CO ("star
formation efficiency") space, and 2) a broader range of L_FIR/L'_CO flux ratio
(~60--1000 L_sun/[K km/s/pc^2]) than previously reported. In our new survey, we
also have found a small number of ULIRGs with extreme L_FIR/L'_CO which had
been known to be rare. The mid-IR color and radio-excess of 56 local ULIRGs as
a function of FIR-to-CO flux ratio is examined and compared with those of
spirals/starburst galaxies and low-z QSOs. In this paper, using a large sample
of local ULIRGs we explore the origin of their current power source and
potential evolution to QSOs. |
Investigating Dark Energy Equation of State With High Redshift Hubble
Diagram: Several independent cosmological data, collected within the last twenty
years, revealed the accelerated expansion rate of the Universe, usually assumed
to be driven by the so called dark energy, which, according to recent
estimates, provides now about 70 % of the total amount of matter-energy in the
Universe. The nature of dark energy is yet unknown. Several models of dark
energy have been proposed: a non zero cosmological constant, a potential energy
of some self interacting scalar field, effects related to the non homogeneous
distribution of matter, or effects due to alternative theories of gravity.
Recently, it turned out that the standard flat LambdaCDM is disfavored (at 4
sigma) when confronted with a high redshift Hubble diagram, consisting of
supernovae of type Ia (SNIa), quasars (QSOs) and gamma ray-bursts (GRBs)
([1-3]). Here we use the same data to investigate if this tension is confirmed,
using a different approach: actually in [1-3], the deviation between the best
fit model and the LambdaCDM model was noticed by comparing cosmological
parameters derived from cosmographic expansions of their theoretical
predictions and observed high redshift Hubble diagram. In this paper we use a
substantially different approach, based on a specific parametrization of the
redshift dependent equation of state (EOS) of dark energy component w(z). Our
statistical analysis is aimed to estimate the parameters characterizing the
dark energy EOS: our results indicate (at > 3 sigma level) an evolving dark
energy EOS, while the cosmological constant has a constant EOS, wLambda =-1.
This result not only confirms the tension previously detected, but shows that
it is not an artifact of cosmographic expansions. | Star Formation in Atomic Gas: Observations of nearby galaxies have firmly established, over a broad range
of galactic environments and metallicities, that star formation occurs
exclusively in the molecular phase of the interstellar medium (ISM).
Theoretical models show that this association results from the correlation
between chemical phase, shielding, and temperature. Interstellar gas converts
from atomic to molecular only in regions that are well shielded from
interstellar ultraviolet (UV) photons, and since UV photons are also the
dominant source of interstellar heating, only in these shielded regions does
the gas become cold enough to be subject to Jeans instability. However, while
the equilibrium temperature and chemical state of interstellar gas are
well-correlated, the time scale required to reach chemical equilibrium is much
longer than that required to reach thermal equilibrium, and both timescales are
metallicity-dependent. Here I show that the difference in time scales implies
that, at metallicities below a few percent of the Solar value, well-shielded
gas will reach low temperatures and proceed to star formation before the bulk
of it is able to convert from atomic to molecular. As a result, at extremely
low metallicities, star formation will occur in a cold atomic phase of the ISM
rather than a molecular phase. I calculate the observable consequences of this
result for star formation in low metallicity galaxies, and I discuss how some
current numerical models for H2-regulated star-formation may need to be
modified. |
Cosmological effects on the observed flux and fluence distributions of
gamma-ray bursts: Are the most distant bursts in general the faintest ones?: Several claims have been put forward that an essential fraction of
long-duration BATSE gamma-ray bursts should lie at redshifts larger than 5.
This point-of-view follows from the natural assumption that fainter objects
should, on average, lie at larger redshifts. However, redshifts larger than 5
are rare for bursts observed by Swift, seemingly contradicting the BATSE
estimates. The purpose of this article is to clarify this contradiction. We
derive the cosmological relationships between the observed and emitted
quantities, and we arrive at a prediction that can be tested on the ensembles
of bursts with determined redshifts. This analysis is independent on the
assumed cosmology, on the observational biases, as well as on any gamma-ray
burst model. Four different samples are studied: 8 BATSE bursts with redshifts,
13 bursts with derived pseudo-redshifts, 134 Swift bursts with redshifts, and 6
Fermi bursts with redshifts. The controversy can be explained by the fact that
apparently fainter bursts need not, in general, lie at large redshifts. Such a
behaviour is possible, when the luminosities (or emitted energies) in a sample
of bursts increase more than the dimming of the observed values with redshift.
In such a case dP(z)/dz > 0 can hold, where P(z) is either the peak-flux or the
fluence. All four different samples of the long bursts suggest that this is
really the case. This also means that the hundreds of faint, long-duration
BATSE bursts need not lie at high redshifts, and that the observed redshift
distribution of long Swift bursts might actually represent the actual
distribution. | Discovery, Photometry, and Kinematics of Planetary Nebulae in M 82: Using an [OIII]5007 on-band/off-band filter technique, we identify 109
planetary nebulae (PNe) candidates in M 82, using the FOCAS instrument at the
8.2m Subaru Telescope. The use of ancillary high-resolution HST ACS H-alpha
imaging aided in discriminating PNe from contaminants such as supernova
remnants and compact HII regions. Once identified, these PNe reveal a great
deal about the host galaxy; our analysis covers kinematics, stellar
distribution, and distance determination. Radial velocities were determined for
94 of these PNe using a method of slitless spectroscopy, from which we obtain a
clear picture of the galaxy's rotation. Overall, our results agree with those
derived by CO(2-1) and HI measurements that show a falling, near-Keplerian
rotation curve. However, we find a subset of our PNe that appear to lie far
above the plane (~1 kpc), yet these objects appear to be rotating as fast as
objects close to the plane. These objects will require further study to
determine if they are members of a halo population, or if they can be
interpreted as a manifestation of a thickened disk as a consequence of a past
interaction with M 81. In addition, [OIII]5007 emission line photometry of the
PNe allows the construction of a planetary nebula luminosity function (PNLF).
Our PNLF distance determination for M 82 yields a larger distance than those
derived using the TRGB, using Cepheid variable stars in nearby group member M
81, or using the PNLF of M 81. We show that this inconsistency most likely
stems from our inability to completely correct for internal extinction imparted
by this dusty, starburst galaxy. (Abridged) |
Signatures of Horndeski gravity on the Dark Matter Bispectrum: We present a detailed study of second-order matter perturbations for the
general Horn- deski class of models. Being the most general scalar-tensor
theory having second-order equations of motion, it includes many known gravity
and dark energy theories and General Relativity with a cosmological constant as
a specific case. This enables us to estimate the leading order dark matter
bispectrum generated at late-times by gravitational instability. We parametrize
the evolution of the first and second-order equations of motion as proposed by
Bellini and Sawicki (2014), where the free functions of the theory are assumed
to be proportional to the dark energy density. We show that it is unnatural to
have large 10% ( 1%) deviations of the bispectrum introducing even larger ~ 30%
(~ 5%) deviations in the linear growth rate. Considering that measurements of
the linear growth rate have much higher signal-to-noise than bispectrum
measurements, this indicates that for Horndeski models which reproduce the
expansion history and the linear growth rate as predicted by GR the dark matter
bispectrum kernel can be effectively modelled as the standard GR one. On the
other hand, an observation of a large bispectrum deviation that can not be
explained in terms of bias would imply either that the evolution of
perturbations is strongly different than the evolution predicted by GR or that
the theory of gravity is exotic (e.g., breaks the weak equivalence principle)
and/or fine-tuned. | Constraining higher-order parameters for primordial non-Gaussianities
from power spectra and bispectra of imaging survey: We investigate the statistical power of higher-order statistics and
cross-correlation statistics to constrain the primordial non-Gaussianity from
the imaging surveys. In particular, we consider the local-type primordial non-
Gaussianity and discuss how well one can tightly constrain the higher-order
non-Gaussian parameters ($g_{\rm NL}$ and $\tau_{\rm NL}$) as well as the
leading order parameter $f_{\rm NL}$ from the halo/galaxy clustering and weak
gravitational lensing measurements. Making use of a strong scale-dependent
behavior in the galaxy/halo clustering, Fisher matrix analysis reveals that the
bispectra can break the degeneracy between non-Gaussian parameters ($f_{\rm
NL}$, $g_{\rm NL}$ and $\tau_{\rm NL}$) and this will give simultaneous
constraints on those three parameters. The combination of cross-correlation
statistics further improves the constraints by factor of 2. As a result,
upcoming imaging surveys like the Large Synoptic Survey Telescope have the
potential to improve the constraints on the primordial non-Gaussianity much
tighter than those obtained from the CMB measurement by Planck, giving us an
opportunity to test the single-sourced consistency relation, $\tau_{\rm NL} \ge
(36/25) f_{\rm NL}^2$. |
Polynomial inflation models after BICEP2: Large field inflation models are favored by the recent BICEP2 that has
detected gravitational wave modes generated during inflation. We study general
large field inflation models for which the potential contains (constant)
quadratic and quartic terms of inflaton field. We show, in this framework,
those inflation models can generate the fluctuation with the tensor-to-scalar
ratio of $0.2$ as well as the scalar spectral index of $0.96$: those are very
close to the center value of the tensor-to-scalar ratio reported by BICEP2 as
well as Planck. Finally, we briefly discuss the particle physics model building
of inflation. | A new relativistic theory for Modified Newtonian Dynamics: We propose a relativistic gravitational theory leading to modified Newtonian
dynamics, a paradigm that explains the observed universal galactic acceleration
scale and related phenomenology. We discuss phenomenological requirements
leading to its construction and demonstrate its agreement with the observed
cosmic microwave background and matter power spectra on linear cosmological
scales. We show that its action expanded to second order is free of ghost
instabilities and discuss its possible embedding in a more fundamental theory. |
Testing $Λ$CDM at the lowest redshifts with SN Ia and galaxy
velocities: Peculiar velocities of objects in the nearby universe are correlated due to
the gravitational pull of large-scale structure. By measuring these velocities,
we have a unique opportunity to test the cosmological model at the lowest
redshifts. We perform this test, using current data to constrain the amplitude
of the "signal" covariance matrix describing the velocities and their
correlations. We consider a new, well-calibrated "Supercal" set of low-redshift
SNe Ia as well as a set of distances derived from the fundamental plane
relation of 6dFGS galaxies. Analyzing the SN and galaxy data separately, both
results are consistent with the peculiar velocity signal of our fiducial
$\Lambda$CDM model, ruling out the noise-only model with zero peculiar
velocities at greater than $7\sigma$ (SNe) and $8\sigma$ (galaxies). When the
two data sets are combined appropriately, the precision of the test increases
slightly, resulting in a constraint on the signal amplitude of $A =
1.05_{-0.21}^{+0.25}$, where $A = 1$ corresponds to our fiducial model.
Equivalently, we report an 11% measurement of the product of the growth rate
and amplitude of mass fluctuations evaluated at $z_\text{eff} = 0.02$, $f
\sigma_8 = 0.428_{-0.045}^{+0.048}$, valid for our fiducial $\Lambda$CDM model.
We explore the robustness of the results to a number of conceivable variations
in the analysis and find that individual variations shift the preferred signal
amplitude by less than ${\sim}0.5\sigma$. We briefly discuss our Supercal SN Ia
results in comparison with our previous results using the JLA compilation. | Searching for the First Galaxies: As some of the first known objects to exist in the Universe, Lyman alpha
emitting galaxies (LAEs) naturally draw a lot of interest. First discovered
over a decade ago, they have allowed us to probe the early Universe, as their
strong emission line compensates for their faint continuum light. While
initially thought to be indicative of the first galaxies forming in the
Universe, recent studies have shown them to be increasingly complex, as some
fraction appear evolved, and many LAEs appear to be dusty, which one would not
expect from primordial galaxies. Presently, much interest resides in
discovering not only the highest redshift galaxies to constrain theories of
reionization, but also pushing closer to home, as previous ground-based studies
have only found LAEs at z > 3 due to observational limitations. In this review
talk I will cover everything from the first theoretical predictions of LAEs, to
their future prospects for study, including the HETDEX survey here in Texas. |
Results of Dark Matter Search using the Full PandaX-II Exposure: We report the dark matter search results obtained using the full 132
ton$\cdot$day exposure of the PandaX-II experiment, including all data from
March 2016 to August 2018. No significant excess of events is identified above
the expected background. Upper limits are set on the spin-independent dark
matter-nucleon interactions. The lowest 90% confidence level exclusion on the
spin-independent cross section is $2.2\times 10^{-46}$ cm$^2$ at a WIMP mass of
30 GeV/$c^2$. | Type II-P supernovae as standardised candles: improvements using near
infrared data: We present the first near infrared Hubble diagram for type II-P supernovae to
further explore their value as distance indicators. We use a modified version
of the standardised candle method which relies on the tight correlation between
the absolute magnitudes of type II-P supernovae and their expansion velocities
during the plateau phase. Although our sample contains only 12 II-P supernovae
and they are necessarily local (z < 0.02), we demonstrate using near infrared
JHK photometry that it may be possible to reduce the scatter in the Hubble
diagram to 0.1-0.15 magnitudes. While this is potentially similar to the
dispersion seen for type Ia supernovae, we caution that this needs to be
confirmed with a larger sample of II-P supernovae in the Hubble flow. |
Beware of commonly used approximations I: errors in forecasts: In the era of precision cosmology, establishing the correct magnitude of
statistical errors in cosmological parameters is of crucial importance.
However, widely used approximations in galaxy surveys analyses can lead to
parameter uncertainties that are grossly mis-estimated, even in a regime where
the theory is well understood (e.g., linear scales). These approximations can
be introduced at three different levels: in the form of the likelihood, in the
theoretical modelling of the observable and in the numerical computation of the
observable. Their consequences are important both in data analysis through
e.g., Markov Chain Monte Carlo parameter inference, and when survey instrument
and strategy are designed and their constraining power on cosmological
parameters is forecasted, for instance using Fisher matrix analyses. In this
work, considering the galaxy angular power spectrum as the target observable,
we report one example of approximation for each of such three categories:
neglecting off-diagonal terms in the covariance matrix, neglecting cosmic
magnification and using the Limber approximation on large scales. We show that
these commonly used approximations affect the robustness of the analysis and
lead, perhaps counter-intuitively, to unacceptably large mis-estimates of
parameters errors (from few~$10\%$ up to few~$100\%$) and correlations.
Furthermore, these approximations might even spoil the benefits of the nascent
multi-tracer and multi-messenger cosmology. Hence we recommend that the type of
analysis presented here should be repeated for every approximation adopted in
survey design or data analysis, to quantify how it may affect the results. To
this aim, we have developed \texttt{Multi\_CLASS}, a new extension of
\texttt{CLASS} that includes the angular power spectrum for multiple (galaxy
and other tracers such as gravitational waves) populations. | A VLT/VIMOS view of two $Planck$ multiple-cluster systems: structure and
galaxy properties: We analysed spectroscopic data obtained with VLT-VIMOS for two
multiple-cluster systems, PLCKG$214.6+36.9$ and PLCKG$334.8-38.0$, discovered
via their thermal Sunyaev-Zel'dovich signal by $Planck$. Combining the Optical
spectroscopy, for the redshift determination, and photometric data from galaxy
surveys (SDSS, WISE, DESI), we were able to study the structure of the two
multiple-cluster systems, to determine their nature and the properties of their
member galaxies. We found that the two systems are populated mainly with
passive galaxies and that PLCKG$214.6+36.9$ consists of a pair of clusters at
redshift $z = 0.445$ and a background isolated cluster at $z = 0.498$, whereas
the system PLCKG$334.8-38.0$ is a chance association of three independent
clusters at redshifts $z = 0.367$, $z =0.292$, and $z = 0.33$. We also find
evidence for remaining star formation activity in the highest-redshift cluster
of PLCKG$214.6+36.9$, at $z = 0.498$. |
Modelling Observational Constraints for Dark Matter Halos: Observations show that the underlying rotation curves at intermediate radii
in spiral and low-surface brightness galaxies are nearly universal. Further, in
these same galaxies, the product of the central density and the core radius
($\rho_{0}r_{0}$) is constant. An empirically motivated model for dark matter
halos which incorporates these observational constraints is presented and shown
to be in accord with the observations. A model fit to the observations of the
galaxy cluster Abell 611 shows that $\rho_{0}r_{0}$ for the dark matter halo in
this more massive structure is larger by a factor of $\sim 20$ over that
assumed for the galaxies. The model maintains the successful NFW form in the
outer regions although the well defined differences in the inner regions
suggest that modifications to the standard CDM picture are required. | TeV dark matter in the disk: DAMA annual modulation data and, CoGeNT, CDMS-II, EDELWEISS-II, CRESST
excesses of events over the expected background are reanalyzed in terms of a
dark matter particle signal considering the case of a rotating halo. It is
found that DAMA data favor the configurations of very high mass dark matter
particles in a corotating cold flux. A similar high-mass/low-velocity solution
would be compatible with the observed events in CoGeNT, CDMS-II, EDELWEISS-II
and CRESST experiments and could be of interest in the light of the
positron/electron excess measured by Pamela and Fermi in cosmic rays. |
VLT-VIMOS integral field spectroscopy of luminous and ultraluminous
infrared galaxies III: the atlas of the stellar and ionized gas distribution: LIRGs and ULIRGs are much more numerous at higher redshifts than locally,
dominating the star-formation rate density at redshifts ~1 - 2. Therefore, they
are important objects in order to understand how galaxies form and evolve
through cosmic time. We aim to characterize the morphologies of the stellar
continuum and the ionized gas (H_alpha) emissions from local sources, and
investigate how they relate with the dynamical status and IR-luminosity of the
sources. We use optical (5250 -- 7450 \AA) integral field spectroscopic (IFS)
data for a sample of 38 sources, taken with the VIMOS instrument, on the VLT.
We present an atlas of IFS images of continuum emission, H_alpha emission, and
H_alpha equivalent widths for the sample. The H_alpha images frequently reveal
extended structures that are not visible in the continuum, such as HII regions
in spiral arms, tidal tails, rings, of up to few kpc from the nuclear regions.
The morphologies of the continuum and H_alpha images are studied on the basis
of the C_{2kpc} parameter, which measures the concentration of the emission
within the central 2 kpc. The C_{2kpc} values found for the H_alpha images are
higher than those of the continuum for the majority (85%) of the objects in our
sample. On the other hand, most of the objects in our sample (~62%) have more
than half of their H_alpha emission outside the central 2 kpc. No clear trends
are found between the values of C_{2kpc} and the IR-luminosity of the sources.
On the other hand, our results suggest that the star formation in advance
mergers and early-stage interactions is more concentrated than in isolated
objects. We compared the H_alpha and infrared emissions as tracers of the
star-formation activity. We find that the star-formation rates derived using
the H_alpha luminosities generally underpredict those derived using the IR
luminosities, even after accounting for reddening effects. | Highly Ionised Gas as a Diagnostic of the Inner NLR: The spectra of AGN from the ultraviolet to the near infrared, exhibit
emission lines covering a wide range of ionisation states, from neutral species
such as [O I] 6300A, up to [Fe XIV] 5303A. Here we report on some recent
studies of the properties of highly ionised lines (HILs), plus two case studies
of individual objects. Future IFU observations at high spatial and good
spectral resolution, will probe the excitation and kinematics of the gas in the
zone between the extended NLR and unresolved BLR. Multi-component SED fitting
can be used to link the source of photoionisation with the strengths and ratios
of the HILs. |
Cosmic Reionization On Computers I. Design and Calibration of
Simulations: Cosmic Reionization On Computers (CROC) is a long-term program of numerical
simulations of cosmic reionization. Its goal is to model fully
self-consistently (albeit not necessarily from the first principles) all
relevant physics, from radiative transfer to gas dynamics and star formation,
in simulation volumes of up to 100 comoving Mpc, and with spatial resolution
approaching 100 pc in physical units. In this method paper we describe our
numerical method, the design of simulations, and the calibration of numerical
parameters. Using several sets (ensembles) of simulations in 20 Mpc/h and 40
Mpc/h boxes with spatial resolution reaching 125 pc at z=6, we are able to
match the observed galaxy UV luminosity functions at all redshifts between 6
and 10, as well as obtain reasonable agreement with the observational
measurements of the Gunn-Peterson optical depth at z<6. | Axion dark matter, solitons, and the cusp-core problem: Self-gravitating bosonic fields can support stable and localised field
configurations. For real fields, these solutions oscillate in time and are
known as oscillatons. The density profile is static, and is soliton. Such
solitons should be ubiquitous in models of axion dark matter, with the soliton
characteristic mass and size depending on some inverse power of the axion mass.
Stable configurations of non-relativistic axions are studied numerically using
the Schr\"{o}dinger-Poisson system. This method, and the resulting soliton
density profiles, are reviewed. Using a scaling symmetry and the uncertainty
principle, the core size of the soliton can be related to the central density
and axion mass, $m_a$, in a universal way. Solitons have a constant central
density due to pressure-support, unlike the cuspy profile of cold dark matter
(CDM). One consequence of this fact is that solitons composed of ultra-light
axions (ULAs) may resolve the `cusp-core' problem of CDM. In DM halos,
thermodynamics will lead to a CDM-like Navarro-Frenk-White profile at large
radii, with a central soliton core at small radii. Using Monte-Carlo techniques
to explore the possible density profiles of this form, a fit to
stellar-kinematical data of dwarf spheroidal galaxies is performed. In order
for ULAs to resolve the cusp-core problem (without recourse to baryon feedback
or other astrophysical effects) the axion mass must satisfy $m_a<1.1\times
10^{-22}\text{ eV}$ at 95\% C.L. On the other hand, ULAs with $m_a\lesssim
1\times 10^{-22}\text{ eV}$ are in some tension with cosmological structure
formation. An axion solution to the cusp-core problem thus makes novel
predictions for future measurements of the epoch of reionisation. On the other
hand, this can be seen as evidence that structure formation could soon impose a
\emph{Catch 22} on axion/scalar field DM, similar to the case of warm DM. |
Measuring the Small-Scale Matter Power Spectrum with High-Resolution CMB
Lensing: We present a method to measure the small-scale matter power spectrum using
high-resolution measurements of the gravitational lensing of the Cosmic
Microwave Background (CMB). To determine whether small-scale structure today is
suppressed on scales below 10 kiloparsecs (corresponding to M < 10^9 M_sun),
one needs to probe CMB-lensing modes out to L ~ 35,000, requiring a CMB
experiment with about 20 arcsecond resolution or better. We show that a CMB
survey covering 4,000 square degrees of sky, with an instrumental sensitivity
of 0.5 uK-arcmin at 18 arcsecond resolution, could distinguish between cold
dark matter and an alternative, such as 1 keV warm dark matter or 10^(-22) eV
fuzzy dark matter with about 4-sigma significance. A survey of the same
resolution with 0.1 uK-arcmin noise could distinguish between cold dark matter
and these alternatives at better than 20-sigma significance; such
high-significance measurements may also allow one to distinguish between a
suppression of power due to either baryonic effects or the particle nature of
dark matter, since each impacts the shape of the lensing power spectrum
differently. CMB temperature maps yield higher signal-to-noise than
polarization maps in this small-scale regime; thus, systematic effects, such as
from extragalactic astrophysical foregrounds, need to be carefully considered.
However, these systematic concerns can likely be mitigated with known
techniques. Next-generation CMB lensing may thus provide a robust and powerful
method of measuring the small-scale matter power spectrum. | Fossil groups origins II. Unveiling the formation of the brightest group
galaxies through their scaling relations: (Abridged) Fossil systems are galaxy associations dominated by a relatively
isolated, bright elliptical galaxy, surrounded by a group of smaller galaxies
lacking L* objects. We analyzed the near-infrared photometric and structural
properties of a sample of 20 BGGs present in FGs in order to better understand
their formation mechanisms. Their surface-brightness distribution was fitted to
a Sersic profile using the GASP2D algorithm. Then, the standard scaling
relations were derived for the first time for these galaxies and compared with
those of normal ellipticals and brightest cluster galaxies in non-fossil
systems. The BGGs presented in this study represent a subset of the most
massive galaxies in the Universe. We found that their ellipticity profiles are
continuously increasing with the galactocentric radius. Our fossil BCGs follow
closely the fundamental plane described by normal ellipticals. However, they
depart from both the log \sigma_0 vs. log L_{K_{s}} and log r_{\rm e} vs. log
L_{K_{s}} relations described by intermediate mass ellipticals. This occurs in
the sense that our BGGs have larger effective radii and smaller velocity
dispersions than those predicted by these relations. We also found that more
elliptical galaxies systematically deviate from the previous relations while
more rounder object do not. No similar correlation was found with the Sersic
index. The derived scaling relations can be interpreted in terms of the
formation scenario of the BGGs. Because our BGGs follow the fundamental plane
tilt but they have larger effective radii than expected for intermediate mass
ellipticals, we suggest that they only went through dissipational mergers in a
early stage of their evolution and then assembled the bulk of their mass
through subsequent dry mergers, contrary to previous claims that BGGs in FGs
were formed mainly by the merging of gas-rich galaxies. |
The RedGOLD Cluster Detection Algorithm and its Cluster Candidate
Catalogue for the CFHT-LS W1: RedGOLD searches for red-sequence galaxy overdensities while minimizing
contamination from dusty star-forming galaxies. It imposes an NFW profile and
calculates cluster detection significance and richness. We optimize these
latter two parameters using both simulations and X-ray detected cluster
catalogs, and obtain a catalog $\sim 80\%$ pure up to $z \sim 1$, and $\sim
100\%$ ($\sim 70\%$) complete at $z\le 0.6$ ( $z\lesssim1$) for galaxy clusters
with $M \gtrsim 10^{14}\ {\rm M_{\odot}}$ at the CFHT-LS Wide depth. In the
CFHT-LS W1, we detect 11 cluster candidates per $\rm deg^2$ out to $z\sim1.1$.
When we optimize both completeness and purity, RedGOLD obtains a cluster
catalog with higher completeness and purity than other public catalogs,
obtained using CFHT-LS W1 observations, for $M \gtrsim 10^{14}\ {\rm
M_{\odot}}$. We use X-ray detected cluster samples to extend the study of the
X-ray temperature-optical richness relation to a lower mass threshold, and find
a mass scatter at fixed richness of $\sigma_{lnM|\lambda}=0.39\pm0.07$ and
$\sigma_{lnM|\lambda}=0.30\pm0.13$ for the Gozaliasl et al. (2014) and Mehrtens
et al. (2012) samples. When considering similar mass ranges as previous work,
we recover a smaller scatter in mass at fixed richness. We recover $93\%$ of
the redMaPPer detections, and find that its richness estimates is on average
$\sim 40-50\%$ larger than ours at $z>0.3$. RedGOLD recovers X-ray cluster
spectroscopic redshifts at better than $5\%$ up to $z\sim1$, and the centers
within a few tens of arcseconds. | Catalog of narrow $C~IV$ absorption lines in BOSS (I): for quasars with
$z_{em} \leq 2.4$: We have assembled absorption systems by visually identifying
$C~IV\lambda\lambda1548,1551$ absorption doublets in the quasar spectra of the
Baryon Oscillation Spectroscopic Survey (BOSS) one by one. This paper is the
first of the series work. In this paper, we concern quasars with relatively low
redshifts and high signal-to-noise ratios for their spectra, and hence we limit
our analysis on quasars with $z_{em}\le2.4$ and on the doublets with
$W_r\lambda1548\ge0.2$ \AA. Out of the more than 87,000 quasars in the Data
Release 9, we limit our search to 10,121 quasars that have the appropriate
redshifts and spectra with high enough signal-to-noise ratios to identify
narrow C IV absorption lines. Among them, 5,442 quasars are detected to have at
least one $C~IV\lambda\lambda1548,1551$ absorption doublet. We obtain a catalog
containing 8,368 $C~IV\lambda\lambda1548,1551$ absorption systems, whose
redshifts are within $z_{abs}=1.4544$ - $2.2805$. In this catalog, about
$33.7\%$ absorbers have $0.2$ \AA$\le W_r\lambda1548<0.5$ \AA, about $45.9\%$
absorbers have $0.5$ \AA$\le W_r\lambda1548<1.0$ \AA, about $19.2\%$ absorbers
have $1.0$ \AA$\le W_r\lambda1548<2.0$ \AA, and about $1.2\%$ absorbers have
$W_r\lambda1548\ge2.0$ \AA. |
Statistical analysis of dwarf galaxies and their globular clusters in
the Local Volume: Morphological classification of dwarf galaxies into early and late type,
though can account for some of their origin and characteristics but does not
help to study their formation mechanism. So an objective classification using
Principal Component analysis together with K means Cluster Analysis of these
dwarf galaxies and their globular clusters is carried out to overcome this
problem. It is found that the classification of dwarf galaxies in the Local
Volume is irrespective of their morphological indices. The more massive (MV 0 <
-13.7) galaxies evolve through self-enrichment and harbor dynamically less
evolved younger globular clusters (GCs) whereas fainter galaxies (MV 0 > -13.7)
are influenced by their environment in the star formation process. | Measurements of the Hubble constant from combinations of supernovae and
radio quasars: In this letter, we propose an improved cosmological model independent method
of determining the value of the Hubble constant $H_0$. The method uses
unanchored luminosity distances $H_0d_L(z)$ from SN Ia Pantheon data combined
with angular diameter distances $d_A(z)$ from a sample of intermediate
luminosity radio quasars calibrated as standard rulers. The distance duality
relation between $d_L(z)$ and $d_A(z)$, which is robust and independent of any
cosmological model, allows to disentangle $H_0$ from such combination. However,
the number of redshift matched quasars and SN Ia pairs is small (37
data-points). Hence, we take an advantage from the Artificial Neural Network
(ANN) method to recover the $d_A(z)$ relation from a network trained on full
120 radio quasar sample. In this case, the result is unambiguously consistent
with values of $H_0$ obtained from local probes by SH0ES and H0LiCOW
collaborations. Three statistical summary measures: weighted mean
$\widetilde{H}_0=73.51(\pm0.67) {~km~s^{-1}~Mpc^{-1}}$, median
$Med(H_0)=74.71(\pm4.08) {~km~s^{-1}~Mpc^{-1}}$ and MCMC simulated posterior
distribution $H_0=73.52^{+0.66}_{-0.68} {~km~s^{-1}~Mpc^{-1}}$ are fully
consistent with each other and the precision reached $1\%$ level. This is
encouraging for the future applications of our method. Because individual
measurements of $H_0$ are related to different redshifts spanning the range
$z=0.5 - 2.0$, we take advantage of this fact to check if there is any
noticeable trend in $H_0$ measurements with redshift of objects used for this
purpose. However, our result is that the data we used strongly support the lack
of such systematic effects. |
Recent results and perspectives on cosmology and fundamental physics
from microwave surveys: Recent cosmic microwave background data in temperature and polarization have
reached high precision in estimating all the parameters that describe the
current so-called standard cosmological model. Recent results about the
integrated Sachs-Wolfe effect from cosmic microwave background anisotropies,
galaxy surveys, and their cross-correlations are presented. Looking at fine
signatures in the cosmic microwave background, such as the lack of power at low
multipoles, the primordial power spectrum and the bounds on non-Gaussianities,
complemented by galaxy surveys, we discuss inflationary physics and the
generation of primordial perturbations in the early Universe. Three important
topics in particle physics, the bounds on neutrinos masses and parameters, on
thermal axion mass and on the neutron lifetime derived from cosmological data
are reviewed, with attention to the comparison with laboratory experiment
results. Recent results from cosmic polarization rotation analyses aimed at
testing the Einstein equivalence principle are presented. Finally, we discuss
the perspectives of next radio facilities for the improvement of the analysis
of future cosmic microwave background spectral distortion experiments. | Consistency tests of $Λ$CDM from the early integrated Sachs-Wolfe
effect: Implications for early-time new physics and the Hubble tension: New physics increasing the expansion rate just prior to recombination is
among the least unlikely solutions to the Hubble tension, and would be expected
to leave an important signature in the early Integrated Sachs-Wolfe (eISW)
effect, a source of Cosmic Microwave Background (CMB) anisotropies arising from
the time-variation of gravitational potentials when the Universe was not
completely matter dominated. Why, then, is there no clear evidence for new
physics from the CMB alone, and why does the $\Lambda$CDM model fit CMB data so
well? These questions and the vastness of the Hubble tension theory model space
motivate general consistency tests of $\Lambda$CDM. I perform an eISW-based
consistency test of $\Lambda$CDM introducing the parameter $A_{\rm eISW}$,
which rescales the eISW contribution to the CMB power spectra. A fit to Planck
CMB data yields $A_{\rm eISW}=0.988 \pm 0.027$, in perfect agreement with the
$\Lambda$CDM expectation $A_{\rm eISW}=1$, and posing an important challenge
for early-time new physics, which I illustrate in a case study focused on early
dark energy (EDE). I explicitly show that the increase in $\omega_c$ needed for
EDE to preserve the fit to the CMB, which has been argued to worsen the fit to
weak lensing and galaxy clustering measurements, is specifically required to
lower the amplitude of the eISW effect, which would otherwise exceed
$\Lambda$CDM's prediction by $\approx 20\%$: this is a generic problem beyond
EDE and likely applying to most models enhancing the expansion rate around
recombination. Early-time new physics models invoked to address the Hubble
tension are therefore faced with the significant challenge of making a similar
prediction to $\Lambda$CDM for the eISW effect, while not degrading the fit to
other measurements in doing so. |
Probing Decoupling in Dark Sectors with the Cosmic Microwave Background: The acoustic peaks in the angular power spectrum of cosmic microwave
background (CMB) temperature and polarization anisotropies play an important
role as a probe of the nature of new relativistic particles contributing to the
radiation density in the early universe, parametrized by $\Delta N_{eff}$. The
amplitude and phase of the acoustic oscillations provide information about
whether the extra species are free-streaming particles, like neutrinos, or
tightly-coupled, like the photons, during eras probed by the CMB. On the other
hand, some extensions of the Standard Model produce new relativistic particles
that decouple from their own non-gravitational interactions after neutrinos,
but prior to photons. We study the signature of new relativistic species that
decouple during this intermediate epoch. We argue that the decoupling species
will cause a scale-dependent change in the amplitude and phase shift of the
acoustic oscillations, different from the usual constant shifts on small
scales. For intermediate decoupling times, the phase and amplitude shifts
depend not only on $\Delta N_{eff}$ but the redshift $z_{dec,X}$ at which the
new species decoupled. For $\Delta N_{eff} >0.334$, a Stage IV CMB experiment
could determine $N_{eff}$ at the percent level and $z_{dec,X}$ at the $\sim
10\%$ level. For smaller values, $\Delta N_{eff}\sim 0.1$, constraints on
$z_{dec,X}$ weaken but remain $\sim 20-50\%$ for $z_{dec,X} \sim
\mathcal{O}(10^3-10^4)$. As an application, we study the contributions to
$\Delta N_{eff}$ and determine the $z_{dec,X}$ values for simple
implementations of the so-called $N$naturalness model. | Generalized Layzer-Irvine equation: the role of dark energy
perturbations in cosmic structure formation: We derive, using the spherical collapse model, a generalized Layzer-Irvine
equation which can be used to describe the gravitational collapse of cold dark
matter in a dark energy background. We show that the usual Layzer-Irvine
equation is valid if the dark matter and the dark energy are minimally coupled
to each other and the dark energy distribution is homogeneous, independently of
its equation of state. We compute the corrections to the standard Layzer-Irvine
equation which arise in the presence of dark energy inhomogeneities. We show
that, in the case of a dark energy component with a constant equation of state
parameter consistent with the latest observational constraints, these
corrections are expected to be small, even if the dark energy has a negligible
sound speed. However, we find that, in more general models, the impact of dark
energy perturbations on the dynamics of clusters of galaxies, which will be
constrained by ESA's Euclid mission with unprecedented precision, might be
significant. |
Young ages and other intriguing properties of massive compact galaxies
in the Local Universe: We characterize the kinematics, morphology, stellar populations and star
formation histories of a sample of massive compact galaxies in the nearby
Universe, which might provide a closer look to the nature of their high
redshift (z > 1.0) massive counterparts. We find that nearby compact massive
objects show elongated morphologies and are fast rotators. New high-quality
long-slit spectra show that they have young mean luminosity-weighted ages (<
2Gyr) and solar metallicities or above ([Z/H]> 0.0). No significant stellar
population gradients are found. The analysis of their star formation histories
suggests that these objects have experienced recently enormous bursts which, in
some cases, represent unprecedented large fractions of their total stellar
mass. These galaxies seem to be truly unique, as they do not follow the
characteristic kinematical and stellar population patterns of present-day
massive ellipticals, spirals or even dwarfs. | Testing Distance Estimators with the Fundamental Manifold: We demonstrate how the Fundamental Manifold (FM) can be used to
cross-calibrate distance estimators even when those "standard candles" are not
found in the same galaxy. Such an approach greatly increases the number of
distance measurements that can be utilized to check for systematic distance
errors and the types of estimators that can be compared. Here we compare
distances obtained using SN Ia, Cepheids, surface brightness fluctuations, the
luminosity of the tip of the red giant branch, circumnuclear masers, eclipsing
binaries, RR Lyrae stars, and the planetary nebulae luminosity functions. We
find no significant discrepancies (differences are < 2 sigma) between distance
methods, although differences at the ~10% level cannot yet be ruled out. The
potential exists for significant refinement because the data used here are
heterogeneous B-band magnitudes that will soon be supplanted by homogeneous,
near-IR magnitudes. We illustrate the use of FM distances to 1) revisit the
question of the metallicity sensitivity of various estimators, confirming the
dependence of SN Ia distances on host galaxy metallicity, and 2) provide an
alternative calibration of H_0 that replaces the classical ladder approach in
the use of extragalactic distance estimators with one that utilizes data over a
wide range of distances simultaneously. |
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