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De-noising non-Gaussian fields in cosmology with normalizing flows: Fields in cosmology, such as the matter distribution, are observed by
experiments up to experimental noise. The first step in cosmological data
analysis is usually to de-noise the observed field using an analytic or
simulation driven prior. On large enough scales, such fields are Gaussian, and
the de-noising step is known as Wiener filtering. However, on smaller scales
probed by upcoming experiments, a Gaussian prior is substantially sub-optimal
because the true field distribution is very non-Gaussian. Using normalizing
flows, it is possible to learn the non-Gaussian prior from simulations (or from
more high-resolution observations), and use this knowledge to de-noise the data
more effectively. We show that we can train a flow to represent the matter
distribution of the universe, and evaluate how much signal-to-noise can be
gained as a function of the experimental noise under idealized conditions. We
also introduce a patching method to reconstruct fields on arbitrarily large
images by dividing them up into small maps (where we reconstruct non-Gaussian
features), and patching the small posterior maps together on large scales
(where the field is Gaussian). | Large-scale redshift space distortions in modified gravity theories: Measurements of redshift space distortions (RSD) provide a means to test
models of gravity on large-scales. We use mock galaxy catalogues constructed
from large N-body simulations of standard and modified gravity models to
measure galaxy clustering in redshift space. We focus our attention on two of
the most representative and popular families of modified gravity models: the Hu
\& Sawicki $f(R)$ gravity and the normal branch of the DGP model. The galaxy
catalogues are built using a halo occupation distribution (HOD) prescription
with the HOD parameters in the modified gravity models tuned to match with the
number density and the real-space clustering of {\sc boss-cmass} galaxies. We
employ two approaches to model RSD: the first is based on linear perturbation
theory and the second models non-linear effects on small-scales by assuming
standard gravity and including biasing and RSD effects. We measure the monopole
to real-space correlation function ratio, the quadrupole to monopole ratio,
clustering wedges and multipoles of the correlation function and use these
statistics to find the constraints on the distortion parameter, $\beta$. We
find that the linear model fails to reproduce the N-body simulation results and
the true value of $\beta$ on scales $s < 40\Mpch$, while the non-linear
modelling of RSD recovers the value of $\beta$ on the scales of interest for
all models. RSD on large scales ($s\gtrsim20$-$40\Mpch$) have been found to
show significant deviations from the prediction of standard gravity in the DGP
models. However, the potential to use RSD to constrain $f(R)$ models is less
promising, due to the different screening mechanism in this model. |
CMB-S4: Iterative internal delensing and r constraints: The tightest constraints on the tensor-to-scalar ratio $r$ can only be
obtained after removing a substantial fraction of the lensing $B$-mode sample
variance. The planned CMB-S4 experiment will remove the lensing $B$-mode signal
internally by reconstructing the gravitational lenses from high-resolution
observations. We document here a first lensing reconstruction pipeline able to
achieve this optimally for arbitrary sky coverage. We make it part of a
map-based framework to test CMB-S4 delensing performance and its constraining
power on $r$, including inhomogeneous noise and two non-Gaussian Galactic
polarized foreground models. The framework performs component-separation of the
high-resolution maps, followed by the construction of lensing $B$-mode
templates, which are then included in a parametric small-aperture maps
cross-spectra-based likelihood for $r$. We find that the lensing reconstruction
and framework achieve the expected performance, compatible with the target
$\sigma(r) \simeq 5\cdot 10^{-4}$ in the absence of a tensor signal, after an
effective removal of $92\%$ to $93\%$ of the lensing $B$-mode variance,
depending on the simulation set. The code for the lensing reconstruction can
also be used for cross-correlation studies with large-scale structures, lensing
spectrum reconstruction, cluster lensing, or other CMB lensing-related
purposes. As part of our tests we also demonstrate joint optimal reconstruction
of the lensing potential with the lensing curl potential mode, second-order in
the density fluctuations. | The clustering of massive galaxies at z~0.5 from the first semester of
BOSS data: We calculate the real- and redshift-space clustering of massive galaxies at
z~0.5 using the first semester of data by the Baryon Oscillation Spectroscopic
Survey (BOSS). We study the correlation functions of a sample of 44,000 massive
galaxies in the redshift range 0.4<z<0.7. We present a halo-occupation
distribution modeling of the clustering results and discuss the implications
for the manner in which massive galaxies at z~0.5 occupy dark matter halos. The
majority of our galaxies are central galaxies living in halos of mass
10^{13}Msun/h, but 10% are satellites living in halos 10 times more massive.
These results are broadly in agreement with earlier investigations of massive
galaxies at z~0.5. The inferred large-scale bias (b~2) and relatively high
number density (nbar=3e-4 h^3 Mpc^{-3}) imply that BOSS galaxies are excellent
tracers of large-scale structure, suggesting BOSS will enable a wide range of
investigations on the distance scale, the growth of large-scale structure,
massive galaxy evolution and other topics. |
The Warm DM halo mass function below the cut-off scale: Warm Dark Matter (WDM) cosmologies are a viable alternative to the Cold Dark
Matter (CDM) scenario. Unfortunately, an accurate scrutiny of the WDM
predictions with N-body simulations has proven difficult due to numerical
artefacts. Here, we report on cosmological simulations that, for the first
time, are devoid of those problems, and thus, are able to accurately resolve
the WDM halo mass function well below the cut-off. We discover a complex
picture, with perturbations at different evolutionary stages populating
different ranges in the halo mass function. On the smallest mass scales we can
resolve, identified objects are typically centres of filaments that are
starting to collapse. On intermediate mass scales, objects typically correspond
to fluctuations that have collapsed and are in the process of relaxation,
whereas the high mass end is dominated by objects similar to haloes identified
in CDM simulations. We then explicitly show how the formation of low-mass
haloes is suppressed, which translates into a strong cut-off in the halo mass
function. This disfavours some analytic formulations that predict a halo mass
function that would extend well below the free streaming mass. We argue for a
more detailed exploration of the formation of the smallest structures expected
to form in a given cosmology, which, we foresee, will advance our overall
understanding of structure formation. | Slow Roll Inflation: A Somehow Different Perspective: In this note we point out that, contrary to the standard point of view, slow
roll inflation is due to high gravitational friction. We show that the
requirement of slow roll coincides with the requirement of a flat scalar field
potential in the case of minimally coupled scalar field. In this sense, the
search for a successful inflationary theory may be more fruitful by shifting
the focus on models with high gravitational friction. We review then a
gravitational mechanism, the so called "Gravitationally Enhanced Friction"
mechanism, such that high gravitational friction is dynamically generated
during inflation allowing even steep (i.e. non-flat) scalar potential to
inflate. |
An empirical approach to model selection: weak lensing and intrinsic
alignments: In cosmology, we routinely choose between models to describe our data, and
can incur biases due to insufficient models or lose constraining power with
overly complex models. In this paper we propose an empirical approach to model
selection that explicitly balances parameter bias against model complexity. Our
method uses synthetic data to calibrate the relation between bias and the
$\chi^2$ difference between models. This allows us to interpret $\chi^2$ values
obtained from real data (even if catalogues are blinded) and choose a model
accordingly. We apply our method to the problem of intrinsic alignments -- one
of the most significant weak lensing systematics, and a major contributor to
the error budget in modern lensing surveys. Specifically, we consider the
example of the Dark Energy Survey Year 3 (DES Y3), and compare the commonly
used nonlinear alignment (NLA) and tidal alignment & tidal torque (TATT)
models. The models are calibrated against bias in the $\Omega_m - S_8$ plane.
Once noise is accounted for, we find that it is possible to set a threshold
$\Delta \chi^2$ that guarantees an analysis using NLA is unbiased at some
specified level $N\sigma$ and confidence level. By contrast, we find that
theoretically defined thresholds (based on, e.g., $p-$values for $\chi^2$) tend
to be overly optimistic, and do not reliably rule out cosmological biases up to
$\sim 1-2\sigma$. Considering the real DES Y3 cosmic shear results, based on
the reported difference in $\chi^2$ from NLA and TATT analyses, we find a
roughly $30\%$ chance that were NLA to be the fiducial model, the results would
be biased (in the $\Omega_m - S_8$ plane) by more than $0.3\sigma$. More
broadly, the method we propose here is simple and general, and requires a
relatively low level of resources. We foresee applications to future analyses
as a model selection tool in many contexts. | A collisional origin for the Leo ring: Extended HI structures around galaxies are of prime importance to probe
galaxy formation scenarios. The giant HI ring in the Leo group is one of the
largest and most intriguing HI structures in the nearby Universe. Whether it
consists of primordial gas, as suggested by the apparent absence of any optical
counterpart and the absence of an obvious physical connection to nearby
galaxies, or of gas expelled from a galaxy in a collision is actively debated.
We present deep wide field-of-view optical images of the ring region obtained
with MegaCam on the CFHT. They reveal optical counterparts to several HI and UV
condensations along the ring, in the g', r', and i' bands, which likely
correspond to stellar associations formed within the gaseous ring. Analyzing
the spectral energy distribution of one of these star-forming regions, we found
it to be typical for a star-forming region in pre-enriched tidal debris. We
then use simulations to test the hypothesis that the Leo ring results from a
head-on collision between Leo group members NGC 3384 and M96. According to our
model which is able to explain, at least qualitatively, the main observational
properties of the system, the Leo ring is consistent with being a collisional
ring. It is thus likely another example of extended intergalactic gas made-up
of pre-enriched collisional debris. |
A Model-independent Method to Determine $H_0$ Using Time-Delay Lensing,
Quasars and Type Ia Supernovae: Absolute distances from strong lensing can anchor Type Ia Supernovae (SNe Ia)
at cosmological distances giving a model-independent inference of the Hubble
constant ($H_0$). Future observations could provide strong lensing time-delay
distances with source redshifts up to $z\,\simeq\,4$, which are much higher
than the maximum redshift of SNe Ia observed so far. In order to make full use
of time-delay distances measured at higher redshifts, we use quasars as a
complementary cosmic probe to measure cosmological distances at redshifts
beyond those of SNe Ia and provide a model-independent method to determine
$H_0$. In this work, we demonstrate a model-independent, joint constraint of
SNe Ia, quasars, and time-delay distances from strong lensed quasars. We first
generate mock data sets of SNe Ia, quasar, and time-delay distances based on a
fiducial cosmological model. Then, we calibrate the quasar parameters model
independently using Gaussian process (GP) regression with mock SNe Ia data.
Finally, we determine the value of $H_0$ model-independently using GP
regression from mock quasars and time-delay distances from strong lensing
systems. As a comparison, we also show the $H_0$ results obtained from mock SNe
Ia in combination with time-delay lensing systems whose redshifts overlap with
SNe Ia. Our results show that quasars at higher redshifts show great potential
to extend the redshift coverage of SNe Ia and thus enable the full use of
strong lens time-delay distance measurements from ongoing cosmic surveys and
improve the accuracy of the estimation of $H_0$ from $2.1\%$ to $1.3\%$ when
the uncertainties of the time-delay distances are $5\%$ of the distance values. | Type Ia Supernova Rate Measurements to Redshift 2.5 from CANDELS :
Searching for Prompt Explosions in the Early Universe: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)
was a multi-cycle treasury program on the Hubble Space Telescope (HST) that
surveyed a total area of ~0.25 deg^2 with ~900 HST orbits spread across 5
fields over 3 years. Within these survey images we discovered 65 supernovae
(SN) of all types, out to z~2.5. We classify ~24 of these as Type Ia SN (SN Ia)
based on host-galaxy redshifts and SN photometry (supplemented by grism
spectroscopy of 6 SN). Here we present a measurement of the volumetric SN Ia
rate as a function of redshift, reaching for the first time beyond z=2 and
putting new constraints on SN Ia progenitor models. Our highest redshift bin
includes detections of SN that exploded when the universe was only ~3 Gyr old
and near the peak of the cosmic star-formation history. This gives the CANDELS
high-redshift sample unique leverage for evaluating the fraction of SN Ia that
explode promptly after formation (<500 Myr). Combining the CANDELS rates with
all available SN Ia rate measurements in the literature we find that this
prompt SN Ia fraction is fP=0.53 +0.09 -0.10 (stat) +0.10 -0.26 (sys),
consistent with a delay time distribution that follows a simple t^{-1} power
law for all times t>40 Myr. However, a mild tension is apparent between
ground-based low-z surveys and space-based high-z surveys. In both CANDELS and
the sister HST program CLASH, we find a low rate of SN Ia at z>1. This could be
a hint that prompt progenitors are in fact relatively rare, accounting for only
~20% of all SN Ia explosions -- though further analysis and larger samples will
be needed to examine that suggestion. |
Magnification and evolution bias of transient sources: GWs and SNIa: Third-generation gravitational wave (GW) observatories such as the Einstein
Telescope and Cosmic Explorer, together with the LSST survey at the Vera Rubin
Observatory, will yield an abundance of extra-galactic transient objects. This
opens the exciting possibility of using GW sources and Supernovae Type Ia
(SNIa) as luminosity distance tracers of large-scale structure for the first
time. The large volumes accessible to these surveys imply that we may need to
include relativistic corrections, such as lensing and Doppler magnification.
However, the amplitude of these effects depends on the magnification and
evolution biases of the transient sources, which are not yet understood. In
this paper we develop comprehensive frameworks to address and model these
biases for both populations of transient objects; in particular, we define how
to compute these biases for GW sources. We then analyse the impact of
magnification and evolution biases on the relativistic corrections and on the
angular power spectrum of these sources. We show that correct modelling and
implementation of these biases is crucial for measuring the cross-correlations
of transient sources at higher redshifts. | Cosmography: Supernovae Union2, Baryon Acoustic Oscillation,
Observational Hubble Data and Gamma Ray Bursts: In this paper, a parametrization describing the kinematical state of the
universe via cosmographic approach is considered, where the minimum input is
the assumption of the cosmological principle, i.e. the
Friedmann-Robertson-Walker metric. A distinguished feature is that the result
does not depend on any gravity theory and dark energy models. As a result, a
series of cosmographic parameters (deceleration parameter $q_0$, jerk parameter
$j_0$ and snap parameter $s_0$) are constrained from the cosmic observations
which include type Ia supernovae (SN) Union2, the Baryon Acoustic Oscillation
(BAO), the observational Hubble data (OHD), the high redshift Gamma ray bursts
(GRBs). By using Markov Chain Monte Carlo (MCMC) method, we find the best fit
values of cosmographic parameters in $1\sigma$ regions:
$H_0=74.299^{+4.932}_{-4.287}$, $q_0=-0.386^{+0.655}_{-0.618}$,
$j_0=-4.925^{+6.658}_{-7.297}$ and $s_0=-26.404^{+20.964}_{-9.097}$ which are
improved remarkably. The values of $q_0$ and $j_0$ are consistent with flat
$\Lambda$CDM model in $1\sigma$ region. But the value of $s_0$ of flat
$\Lambda$CDM model will go beyond the $1\sigma$ region. |
Over-cooled haloes at z > 10: a route to form low-mass first stars: It has been shown by Shchekinov & Vasiliev2006 (SV06) that HD molecules can
be an important cooling agent in high redshift z >10 haloes if they undergo
mergers under specific conditions so suitable shocks are created. Here we build
upon Prieto et al. (2012) who studied in detail the merger-generated shocks,
and show that the conditions for HD cooling can be studied by combining these
results with a suite of dark-matter only simulations. We have performed a
number of dark matter only simulations from cosmological initial conditions
inside boxes with sizes from 1 to 4 Mpc. We look for haloes with at least two
progenitors of which at least one has mass M > M_cr (z), where M_cr (z) is the
SV06 critical mass for HD over-cooling. We find that the fraction of
over-cooled haloes with mass between M_cr (z) and 10^{0.2} M_cr (z), roughly
below the atomic cooling limit, can be as high as ~ 0.6 at z ~ 10 depending on
the merger mass ratio. This fraction decreases at higher redshift reaching a
value ~0.2 at z ~ 15. For higher masses, i.e. above 10^{0.2} M_cr (z) up to
10^{0.6} M_cr (z), above the atomic cooling limit, this fraction rises to
values ~ 0.8 until z ~ 12.5. As a consequence, a non negligible fraction of
high redshift z > 10 mini-haloes can drop their gas temperature to the Cosmic
Microwave Background temperature limit allowing the formation of low mass stars
in primordial environments. | BSG alignment of SDSS galaxy groups: We study the alignment signal between the distribution of brightest satellite
galaxies (BSGs) and the major axis of their host groups using SDSS group
catalog constructed by Yang et al. (2007). After correcting for the effect of
group ellipticity, a statistically significant (~ 5\sigma) major-axis alignment
is detected and the alignment angle is found to be 43.0 \pm 0.4 degrees. More
massive and richer groups show stronger BSG alignment. The BSG alignment around
blue BCGs is slightly stronger than that around red BCGs. And red BSGs have
much stronger major-axis alignment than blue BSGs. Unlike BSGs, other
satellites do not show very significant alignment with group major axis. We
further explore the BSG alignment in semi-analytic model (SAM) constructed by
Guo et al. (2011). We found general good agreement with observations: BSGs in
SAM show strong major-axis alignment which depends on group mass and richness
in the same way as observations; and none of other satellites exhibit prominent
alignment. However, discrepancy also exists in that the SAM shows opposite BSG
color dependence, which is most probably induced by the missing of large scale
environment ingredient in SAM. The combination of two popular scenarios can
explain the detected BSG alignment. The first one: satellites merged into the
group preferentially along the surrounding filaments, which is strongly aligned
with the major axis of the group. The second one: BSGs enter their host group
more recently than other satellites, then will preserve more information about
the assembling history and so the major-axis alignment. In SAM, we found
positive evidence for the second scenario by the fact that BSGs merged into
groups statistically more recently than other satellites. On the other hand,
although is opposite in SAM, the BSG color dependence in observation might
indicate the first scenario as well. |
Particle decay and 21 cm absorption from first minihaloes: We consider the influence of decaying dark matter (DM) particles on the
characteristics of 21 cm absorption in spectra of distant radio-loud sources -
"21 cm forest" - from minihaloes with masses $M=10^5-10^7\msun$ virialized at
$z_{vir} = 10$. We use 1D self-consistent hydrodynamic description to study
evolution of minihaloes, and follow up their absorption characteristics from
turnaround to virialization. We find that in the presence of decaying dark
matter both thermal and dynamical evolution of minihaloes demonstrate
significant deviation from those in the model without dark matter decay
(standard recombination). We show that optical depth in 21 cm line is strongly
suppressed in the presence of decaying particles: for $M=10^5-10^6\msun$
decaying dark matter with the energy rate deposited in baryonic gas $\xi_{L} =
0.59\times 10^{-25}$ s$^{-1}$ - the current upper limit of the energy deposit -
decreases the optical depth and the equivalent width by an order of magnitude
compared to the standard recombination. Thus additional ionization and heating
from decaying DM particles almost "erases" absorption features from minihaloes
with $M=10^5-10^6\msun$ for $\xi \simgt 0.3\xi_L$, which consequently
considerably decreases the number of strong absorptions: for example, the
number of absorptions with the equivalent width $W_\nu^{obs} \simgt 0.3$ kHz at
$z\simeq10$ decreases more than 2.5 times for $\xi/\xi_{L} = 0.3$ and
$\simgt$4.5 times for $\xi/\xi_{L} = 1$. We argue that "21 cm forest"
absorptions might be a powerful probe of the presence of decaying dark matter
in the early Universe. | Rapid-response mode VLT/UVES spectroscopy of super iron-rich gas exposed
to GRB 080310. Evidence of ionization in action and episodic star formation
in the host: We analyse high-resolution near-UV and optical spectra of the afterglow of
GRB 080310, obtained with the Very Large Telescope Ultraviolet and Visual
Echelle Spectrograph (VLT/UVES), to investigate the circumburst environment and
the interstellar medium of the gamma-ray burst (GRB) host galaxy. The VLT
rapid-response mode (RRM) enabled the observations to start only 13 minutes
after the Swift trigger and a series of four exposures to be collected before
dawn. A low neutral-hydrogen column-density (log N (HI) = 18.7) is measured at
the host-galaxy redshift of z = 2.42743. At this redshift, we also detect a
large number of resonance ground-state absorption lines (e.g., CII, MgII, AlII,
SiII, CrII, CIV, SiIV), as well as time-varying absorption from the
fine-structure levels of FeII. Time-varying absorption from a highly excited
FeIII energy level (7S3), giving rise to the so-called UV34 line triplet, is
also detected, for the first time in a GRB afterglow. The CrII ground-state and
all observed FeII energy levels are found to depopulate with time, whilst the
FeIII 7S3 level is increasingly populated. This absorption-line variability is
clear evidence of ionization by the GRB, which is for the first time
conclusively observed in a GRB afterglow spectrum. We derive ionic column
densities at each epoch of observations by fitting absorption lines with a
four-component Voigt-profile model. We perform CLOUDY photo-ionization
modelling of the expected pre-burst ionic column densities, to estimate that,
before the onset of the burst, [C/H] = -1.3 \pm 0.2, [O/H] < -0.8, [Si/H] =
-1.2 \pm 0.2, [Cr/H] = +0.7 \pm 0.2, and [Fe/H] = +0.2 \pm 0.2 for the
integrated line profile, indicating strong overabundances of iron and chromium.
For one of the components, we observe even more extreme ratios of [Si/Fe] \leq
-1.47 and [C/Fe] \leq -1.74. [abridged] |
Quantified HI Morphology II : Lopsidedness and Interaction in WHISP
Column Density Maps: Lopsidedness of the gaseous disk of spiral galaxies is a common phenomenon in
disk morphology, profile and kinematics. Simultaneously, the asymmetry of a
galaxy's stellar disk, in combination with other morphological parameters, has
seen extensive use as an indication of recent merger or interaction in galaxy
samples. Quantified morphology of stellar spiral disks is one avenue to
determine the merger rate over much of the age of the Universe. In this paper,
we measure the quantitative morphology parameters for the HI column density
maps from the Westerbork observations of neutral Hydrogen in Irregular and
SPiral galaxies (WHISP). These are Concentration, Asymmetry, Smoothness, Gini,
M20, and one addition of our own, the Gini parameter of the second order moment
(GM). Our aim is to determine if lopsided or interacting disks can be
identified with these parameters. Our sample of 141 HI maps have all previous
classifications on their lopsidedness and interaction. We find that the
Asymmetry, M20, and our new GM parameter correlate only weakly with the
previous morphological lopsidedness quantification. These three parameters may
be used to compute a probability that an HI disk is morphologically lopsided
but not unequivocally to determine it. However, we do find that that the
question whether or not an HI disk is interacting can be settled well using
morphological parameters. Parameter cuts from the literature do not translate
from ultraviolet to HI directly but new selection criteria using combinations
of Asymmetry and M20 or Concentration and M20, work very well. We suggest that
future all-sky HI surveys may use these parameters of the column density maps
to determine the merger fraction and hence rate in the local Universe with a
high degree of accuracy. | The long term X-ray spectral variability of AGN: We present the results from the spectral analysis of more than 7,500 RXTE
spectra of 10 AGN, which have been observed by RXTE regularly over a long
period of time ~ 7-11 years. These observations most probably sample most of
the flux and spectral variations that these objects exhibit, thus, they are
ideal for the study of their long term X-ray spectral variability. We modelled
the 3-10 spectrum of each observation in a uniform way using a simple power-law
model (with the addition of Gaussian line and/or edge to model the iron Kalpha
emission/absorption features, if necessary) to consistently parametrize the
shape of the observed X-ray continuum. We found that the average spectral slope
does not correlate with source luminosity or black hole mass, while it
correlates positively with the average accretion rate. We have also determined
the (positive) "spectral slope-flux" relation for each object, over a larger
flux range than before. We found that this correlation is similar in almost all
objects. We discuss this global "spectral slope-flux" trend in the light of
current models for spectral variability. We consider (i) intrinsic variability,
expected e.g. from Comptonization processes, (ii) variability caused by
absorption of X-rays by a single absorber whose ionization parameter varies
proportionally to the continuum flux variations, (iii) variability resulting
from the superposition of a constant reflection component and an intrinsic
power-law which is variable in flux but constant in shape, and, (iv)
variability resulting from the superposition of a constant reflection component
and an intrinsic power-law which is variable both in flux and shape. Our final
conclusion is that scenario (iv) describes better our results. |
A Proposal for a Renewed Research Emphasis in Astrophysical and
Celestial Dynamics: Given the impressive investment by the nation in observational Astronomy and
Astrophysics facilities coming on line now and in the near future, we advocate
for an increased investment in applied and fundamental research on
Astrophysical and Celestial Dynamics (ACD). Specifically we call for a)
continued and expanded support for applied research in ACD, b) creation of
support for fundamental research in ACD and its subfields, and c) the creation
of a unified program to help scientists coordinate and collaborate in their
research in these fields. The benefits of this proposal are threefold. First,
it will enable researchers to interpret and understand the implications of
newly observed phenomena that will invariably arise from new facilities and
surveys. Second, research on fundamentals will foster connections between
specialists, leveraging advances found in one sub-field and making them
available to others. Third, a coordinated approach for applied and fundamental
research in ACD will help academic institutions in the United States to produce
future researchers trained and knowledgeable in essential subfields such as
Mathematical Celestial Mechanics and able to continue its advancement in
conjunction with the increase in observations. | Cosmology with relativistically varying physical constants: We have shown that the varying physical constant model is consistent with the
recently published variational approach wherein Einstein equations are modified
to include the variation of the speed of light c, gravitational constant G and
cosmological constant {\Lambda} using the Einstein-Hilbert action. The general
constraint resulting from satisfying the local conservation laws and contracted
Bianchi identities provides the freedom to choose the form of the variation of
the constants as well as how their variations are related. When we choose
dG/Gdt=3dc/cdt, c=c_0.exp[(a^{\alpha}-1)], G=G_0.exp[3(a^{\alpha}-1)] and
{\Lambda}={\Lambda}_0.exp[(a^(-{\alpha})-1)], where a is the scale factor and
{\alpha}=1.8, we are able to show that the resulting model: (a) fits the
supernovae 1a observational data marginally better than the {\Lambda}CDM model;
(b) determines the first peak in the power spectrum of the cosmic microwave
background temperature anisotropies at multipole value of l=217.3; (c)
calculates the age of the universe as 14.1 Gyr; and (d) finds the BAO acoustic
scale to be 145.2 Mpc. These numbers are within less than 3% of the values
derived using the {\Lambda}CDM model. Surprisingly we find that the dark-energy
density is negative in a universe that has significant negative curvature and
whose expansion is accelerating at a faster rate than predicted by the
{\Lambda}CDM model. |
No clear submillimetre signature of suppressed star formation amongst
X-ray luminous AGNs: Many theoretical models require powerful active galactic nuclei (AGNs) to
suppress star formation in distant galaxies and reproduce the observed
properties of today's massive galaxies. A recent study based on Herschel-SPIRE
submillimetre observations claimed to provide direct support for this picture,
reporting a significant decrease in the mean star-formation rates (SFRs) of the
most luminous AGNs (Lx>10^44 erg/s) at z=1-3 in the Chandra Deep Field-North
(CDF-N). In this letter we extend these results using Herschel-SPIRE 250um data
in the COSMOS and CDF-S fields to achieve an order of magnitude improvement in
the number of sources at Lx>10^44 erg/s. On the basis of our analysis, we find
no strong evidence for suppressed star formation in Lx>10^44 erg/s AGNs at
z=1-3. The mean SFRs of the AGNs are constant over the broad X-ray luminosity
range of Lx~10^43-10^45 erg/s (with mean SFRs consistent with typical
star-forming galaxies at z~2; <SFRs>~100-200 Msol/yr). We suggest that the
previous CDF-N results were likely due to low number statistics. We discuss our
results in the context of current theoretical models. | Renormalization Group approach to Gravity: the running of G and L inside
galaxies and additional details on the elliptical NGC 4494: We explore the phenomenology of nontrivial quantum effects on low-energy
gravity. These effects come from the running of the gravitational coupling
parameter G and the cosmological constant L in the Einstein-Hilbert action, as
induced by the Renormalization Group (RG). The Renormalization Group corrected
General Relativity (RGGR model) is used to parametrize these quantum effects,
and it is assumed that the dominant dark matter-like effects inside galaxies is
due to these nontrivial RG effects. Here we present additional details on the
RGGR model application, in particular on the Poisson equation extension that
defines the effective potential, also we re-analyse the ordinary elliptical
galaxy NGC 4494 using a slightly different model for its baryonic contribution,
and explicit solutions are presented for the running of G and L. The values of
the NGC 4494 parameters as shown here have a better agreement with the general
RGGR picture for galaxies, and suggest a larger radial anisotropy than the
previously published result. |
Faraday Rotation as a diagnostic of Galactic foreground contamination of
CMB maps: The contribution from the residuals of the foreground can have a significant
impact on the temperature maps of the Cosmic Microwave Background (CMB).
Mostly, the focus has been on the galactic plane, when foreground cleaning has
taken place. However, in this paper, we will investigate the possible
foreground contamination, from sources outside the galactic plane in the CMB
maps. We will analyze the correlation between the Faraday rotation map and the
CMB temperature map. The Faraday rotation map is dependent on the galactic
magnetic field, as well as the thermal electron density, and both may
contribute to the CMB temperature. We find that the standard deviation for the
mean cross correlation deviate from that of simulations at the 99.9% level.
Additionally, a comparison between the CMB temperature extrema and the extremum
points of the Faraday rotation is also performed, showing a general overlap
between the two. Also we find that the CMB Cold Spot is located at an area of
strong negative cross correlation, meaning that it may be explained by a
galactic origin. Further, we investigate nearby supernova remnants in the
galaxy, traced by the galactic radio loops. These super nova remnants are
located at high and low galactic latitude, and thus well outside the galactic
plane. We find some correlation between the Faraday Rotation and the CMB
temperature, at select radio loops. This indicate, that the galactic
foregrounds may affect the CMB, at high galactic latitudes | The mechanism of Supernova Ia explosion in elliptical galaxies: Recent observational data on the type Ia supernova rates are in excellent
agreement with the old prediction of the population synthesis of binary stars
and confirm that the overwhelming majority of type Ia supernovas (~99%) in
elliptical galaxies form via mergers of binary white dwarfs with the total mass
exceeding the Chandrasekhar limit. |
Astrophysics Conducted by the Lunar University Network for Astrophysics
Research (LUNAR) and the Center for Lunar Origins (CLOE): [Abridged] The Moon is a unique platform from and on which to conduct
astrophysical measurements. The Lunar University Network for Astrophysics
Research (LUNAR) and the Center for Lunar Origins and Evolution (CLOE) teams
within the NASA Lunar Science Institute (NLSI) are illustrating how the Moon
can be used as a platform to advance important goals in astrophysics. Of
relevance to Astrophysics and aligned with NASA strategic goals, all three of
the primary research themes articulated by New Worlds, New Horizons in
Astronomy & Astrophysics are being addressed by LUNAR and CLOE, namely Probing
Cosmic Dawn, Understanding New Worlds, and Physics of the Universe | A Foreground-Immune CMB-Cluster Lensing Estimator: Galaxy clusters induce a distinct dipole pattern in the cosmic microwave
background (CMB) through the effect of gravitational lensing. Extracting this
lensing signal will enable us to constrain cluster masses, even for high
redshift clusters ($z \gtrsim 1$) that are expected to be detected by future
CMB surveys. However, cluster-correlated foreground signals, like the kinematic
and thermal Sunyaev-Zel'dovich (kSZ and tSZ) signals, present a challenge when
extracting the lensing signal from CMB temperature data. While CMB
polarization-based lensing reconstruction is one way to mitigate these
foreground biases, the sensitivity from CMB temperature-based reconstruction is
expected to be similar to or higher than polarization for future surveys. In
this work, we extend the cluster lensing estimator developed in Raghunathan et
al. (2019) to CMB temperature and test its robustness against systematic biases
from foreground signals. We find that the kSZ signal only acts as an additional
source of variance and provide a simple stacking-based approach to mitigate the
bias from the tSZ signal. Additionally, we study the bias induced due to
uncertainties in the cluster positions and show that they can be easily
mitigated. The estimated signal-to-noise ratio (SNR) of this estimator is
comparable to other standard lensing estimators such as the maximum likelihood
(MLE) and quadratic (QE) estimators. We predict the cluster mass uncertainties
from CMB temperature data for current and future cluster samples to be: 6.6%
for SPT-3G with 7,000 clusters, 4.1% for SO and 3.9% for SO + FYST with 25,000
clusters, and 1.8% for CMB-S4 with 100,000 clusters. |
The PSZ-MCMF catalogue of Planck clusters over the DES region: We present the first systematic follow-up of Planck Sunyaev-Zeldovich effect
(SZE) selected candidates down to signal-to-noise (S/N) of 3 over the 5000
deg$^2$ covered by the Dark Energy Survey. Using the MCMF cluster confirmation
algorithm, we identify optical counterparts, determine photometric redshifts
and richnesses and assign a parameter, $f_{\rm cont}$, that reflects the
probability that each SZE-optical pairing represents a random superposition of
physically unassociated systems rather than a real cluster. The new PSZ-MCMF
cluster catalogue consists of 853 MCMF confirmed clusters and has a purity of
90%. We present the properties of subsamples of the PSZ-MCMF catalogue that
have purities ranging from 90% to 97.5%, depending on the adopted $f_{\rm
cont}$ threshold. Halo mass estimates $M_{500}$, redshifts, richnesses, and
optical centers are presented for all PSZ-MCMF clusters. The PSZ-MCMF catalogue
adds 589 previously unknown Planck identified clusters over the DES footprint
and provides redshifts for an additional 50 previously published Planck
selected clusters with S/N>4.5. Using the subsample with spectroscopic
redshifts, we demonstrate excellent cluster photo-$z$ performance with an RMS
scatter in $\Delta z/(1+z)$ of 0.47%. Our MCMF based analysis allows us to
infer the contamination fraction of the initial S/N>3 Planck selected candidate
list, which is ~50%. We present a method of estimating the completeness of the
PSZ-MCMF cluster sample. In comparison to the previously published Planck
cluster catalogues. this new S/N>3 MCMF confirmed cluster catalogue populates
the lower mass regime at all redshifts and includes clusters up to z$\sim$1.3. | The Art of Lattice and Gravity Waves from Preheating: The nonlinear dynamics of preheating after early-Universe inflation is often
studied with lattice simulations. In this work I present a new lattice code
HLATTICE. It differs from previous public available codes in the following
three aspects: (i) A much higher accuracy is achieved with a modified
sixth-order symplectic integrator; (ii) scalar, vector, and tensor metric
perturbations in synchronous gauge and their feedback to the dynamics of scalar
fields are all included; (iii) the code uses a projector that completely
removes the scalar and vector components defined by the discrete spatial
derivatives. Such a generic code can have wide range of applications. As an
example, gravity waves from preheating after inflation are calculated with a
better accuracy. |
GBT Zpectrometer CO(1-0) Observations of the Strongly-Lensed
Submillimeter Galaxies from the Herschel ATLAS: The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) has
uncovered a population of strongly-lensed submillimeter galaxies (SMGs). The
Zpectrometer instrument on the Green Bank Telescope (GBT) was used to measure
the redshifts and constrain the masses of the cold molecular gas reservoirs for
two candidate high-redshift lensed sources. We derive CO(1-0) redshifts of
z=3.042+/-0.001 and z=2.625+/-0.001, and measure molecular gas masses of
(1--3)x10^{10}Msun, corrected for lens amplification and assuming a conversion
factor of alhpa=0.8 Msun(K km/s pc^2)^{-1}. We find typical L(IR)/L'(CO) ratios
of 120+/-40 and 140+/-50 Lsun (K km/s pc^2)^{-1}, which are consistent with
those found for local ULIRGs and other high-redshift SMGs. From analysis of
published data, we find no evidence for enhanced L(IR)/L'(CO(1-0)) ratios for
the SMG population in comparison to local ULIRGs. The GBT results highlight the
power of using the CO lines to derive blind redshifts, which is challenging for
the SMG population at optical wavelengths given their high obscuration. | Effect of Dust on Lyman-alpha Photon Transfer in Optically Thick Halo: We investigate the effects of dust on Ly{\alpha} photons emergent from an
optically thick medium by solving the integro-differential equation of the
radiative transfer of resonant photons. To solve the differential equations
numerically we use the Weighted Essentially Non-oscillatory method (WENO).
Although the effects of dust on radia-tive transfer is well known, the resonant
scattering of Ly{\alpha} photons makes the problem non-trivial. For instance,
if the medium has the optical depth of dust absorption and scattering to be
{\tau}a>>1, {\tau}>>1, and {\tau}>>{\tau}a, the effective absorption optical
depth in a random walk scenario would be equal to \surd
{\tau}a({\tau}a+{\tau}). We show, however, that for a resonant scattering at
frequency {\nu}0, the effective absorption optical depth would be even larger
than {\tau}({\nu}0). If the cross section of dust scattering and absorption is
frequency-independent, the double-peaked structure of the frequency profile
given by the resonant scattering is basically dust-independent. That is, dust
causes neither narrowing nor widening of the width of the double peaked
profile. One more result is that the time scales of the Ly{\alpha} photon
transfer in the optically thick halo are also basically independent of the dust
scattering, even when the scattering is anisotropic. This is because those time
scales are mainly determined by the transfer in the frequency space, while dust
scattering, either isotropic or anisotropic, does not affect the behavior of
the transfer in the frequency space when the cross section of scattering is
wavelength-independent. This result does not support the speculation that dust
will lead to the smoothing of the brightness distribution of Ly{\alpha} photon
source with optical thick halo. |
Multi-wavelength Analysis of the Merging Galaxy Cluster A115: A115 is a merging galaxy cluster at $z\sim0.2$ with a number of remarkable
features including a giant ($\sim2.5$ Mpc) radio relic, two asymmetric X-ray
peaks with trailing tails, and a peculiar line-of-sight velocity structure. We
present a multi-wavelength study of A115 using optical imaging data from
Subaru, X-ray data from $Chandra$, and spectroscopic data from the Keck/DEIMOS
and MMT/Hectospec instruments. Our weak-lensing analysis shows that the cluster
is comprised of two subclusters whose mass centroids are in excellent agreement
with the two BCG positions ($\lesssim10$"). By modeling A115 with a
superposition of two Navarro-Frenk-White halos, we determine the masses of the
northern and southern subclusters to be $M_{200}=1.58_{-0.49}^{+0.56}\times
10^{14} \text{M}_{\odot}$ and $3.15_{-0.71}^{+0.79}\times 10^{14}
\text{M}_{\odot}$, respectively. Combining the two halos, we estimate the total
cluster mass to be $M_{200}=6.41_{-1.04}^{+1.08}\times10^{14} \text{M}_{\odot}$
at $R_{200}=1.67_{-0.09}^{+0.10}$ Mpc. These weak-lensing masses are
significantly (a factor of 3-10) lower than what is implied by the X-ray and
optical spectroscopic data. We attribute the difference to the gravitational
and hydrodynamic disruption caused by the collision between the two
subclusters. | Comment on "CCC-predicted low-variance circles in CMB sky and LCDM": In a recent preprint ("CCC-predicted low-variance circles in the CMB sky and
LCDM"), Gurzadyan and Penrose (2011) claim for the second time to find evidence
for pre-Big Bang activity in the form of concentric circles of low variance in
the WMAP data. The same claim was made in November 2010, but quickly shown to
be false by three independent groups. The culprit was simply that Gurzadyan and
Penrose's simulations were based on an inappropriate power spectrum. In the
most recent paper, they now claim that the significance is indeed low if the
simulations are based on the realization-specific WMAP spectrum (ie., the one
directly measured from the sky maps and affected by cosmic variance), but not
if the simulations are based on a theoretical LCDM spectrum. In this respect,
we note that the three independent reanalyses all based their simulations on
the LCDM spectrum, not the observed WMAP spectrum, and this alone should
suffice to show that the updated claims are also incorrect. In fact, it is
evident from the plots shown in their new paper that the spectrum is still
incorrect, although in a different way than in their first paper. Thus,
Gurzadyan and Penrose's new claims are just as wrong as those made in the first
paper, and for the same reason: The simulations are not based on an appropriate
power spectrum. Still, while this story is of little physical interest, it may
have some important implications in terms of scienctific sociology: Looking
back at the background papers leading up to the present series by Gurzadyan and
Penrose, in particular one introducing the Kolmogorov statistic, we believe one
can find evidence that a community based and open access referee process may be
more efficient at rejecting incorrect results and claims than a traditional
journal based approach. |
On the magnetic fields in voids: We study the possible magnetization of cosmic voids by void galaxies.
Recently, observations revealed isolated starforming galaxies within the voids.
Furthermore, a major fraction of a voids volume is expected to be filled with
magnetic fields of a minimum strength of about $10^{-15}$ G on Mpc scales. We
estimate the transport of magnetic energy by cosmic rays (CR) from the void
galaxies into the voids. We assume that CRs and winds are able to leave small
isolated void galaxies shortly after they assembled, and then propagate within
the voids. For a typical void, we estimate the magnetic field strength and
volume filling factor depending on its void galaxy population and possible
contributions of strong active galactic nuclei (AGN) which border the voids. We
argue that the lower limit on the void magnetic field can be recovered, if a
small fraction of the magnetic energy contained in the void galaxies or void
bordering AGNs is distributed within the voids. | The [OIII] emission line luminosity function of optically selected
type-2 AGN from zCOSMOS: We present a catalog of 213 type-2 AGN selected from the zCOSMOS survey. The
selected sample covers a wide redshift range (0.15<z<0.92) and is deeper than
any other previous study, encompassing the luminosity range 10^{5.5} < Lsun<
L[OIII] < 10^{9.1} Lsun. We explore the intrinsic properties of these AGN and
the relation to their X-ray emission (derived from the XMM-COSMOS
observations). We study their evolution by computing the [OIII]5007A line
luminosity function (LF) and we constrain the fraction of obscured AGN as a
function of luminosity and redshift. The sample was selected on the basis of
the optical emission line ratios, after applying a cut to the signal-to-noise
ratio (S/N) of the relevant lines. We used the standard diagnostic diagrams
[OIII]/Hbeta versus [NII]/Halpha and ([OIII]/Hbeta versus [SII]/Halpha) to
isolate AGN in the redshift range 0.15<z<0.45 and the diagnostic diagram
[OIII]/Hbeta versus [OII]/Hbeta to extend the selection to higher redshift
(0.5<z<0.92). Combining our sample with one drawn from SDSS, we found that the
best description of the evolution of type-2 AGN is a luminosity-dependent
density evolution model. Moreover, using the type-1 AGN LF we were able to
constrain the fraction of type-2 AGN to the total (type-1 + type-2) AGN
population. We found that the type-2 fraction decreases with luminosity, in
agreement with the most recent results, and shows signs of a slight increase
with redshift. However, the trend with luminosity is visible only after
combining the SDSS+zCOSMOS samples. From the COSMOS data points alone, the
type-2 fraction seems to be quite constant with luminosity. |
The Radio Continuum, Far-Infrared Emission, And Dense Molecular Gas In
Galaxies: A tight linear correlation is established between the HCN line luminosity and
the radio continuum (RC) luminosity for a sample of 65 galaxies (from Gao &
Solomon's HCN survey), including normal spiral galaxies and luminous and
ultraluminous infrared galaxies (LIRGs/ULIRGs). After analyzing the various
correlations among the global far-infrared (FIR), RC, CO, and HCN luminosities
and their various ratios, we conclude that the FIR-RC and FIR-HCN correlations
appear to be linear and are the tightest among all correlations. The
combination of these two correlations could result in the tight RC-HCN
correlation we observed. Meanwhile, the non-linear RC-CO correlation shows
slightly larger scatter as compared with the RC-HCN correlation, and there is
no correlation between ratios of either RC/HCN-CO/HCN or RC/FIR-CO/FIR. In
comparison, a meaningful correlation is still observed between ratios of
RC/CO-HCN/CO. Nevertheless, the correlation between RC/FIR and HCN/FIR also
disappears, reflecting again the two tightest FIR-RC and FIR-HCN correlations
as well as suggesting that FIR seems to be the bridge that connects HCN with
RC. Interestingly, despite obvious HCN-RC and RC-CO correlations,
multi-parameter fits hint that while both RC and HCN contribute significantly
(with no contribution from CO) to FIR, yet RC is primarily determined from FIR
with a very small contribution from CO and essentially no contribution from
HCN. These analyses confirm independently the former conclusions that it is
practical to use RC luminosity instead of FIR luminosity, at least globally, as
an indicator of star formation rate in galaxies including LIRGs/ULIRGs, and HCN
is a much better tracer of star-forming molecular gas and correlates with FIR
much better than that of CO. | The DiskMass Survey. I. Overview: We present a survey of the mass surface-density of spiral disks, motivated by
outstanding uncertainties in rotation-curve decompositions. Our method exploits
integral-field spectroscopy to measure stellar and gas kinematics in nearly
face-on galaxies sampled at 515, 660, and 860 nm, using the custom-built
SparsePak and PPak instruments. A two-tiered sample, selected from the UGC,
includes 146 nearly face-on galaxies, with B<14.7 and disk scale-lengths
between 10 and 20 arcsec, for which we have obtained H-alpha velocity-fields;
and a representative 46-galaxy subset for which we have obtained stellar
velocities and velocity dispersions. Based on re-calibration of extant
photometric and spectroscopic data, we show these galaxies span factors of 100
in L(K) (0.03 < L/L(K)* < 3), 8 in L(B)/L(K), 10 in R-band disk central
surface-brightness, with distances between 15 and 200 Mpc. The survey is
augmented by 4-70 micron Spitzer IRAC and MIPS photometry, ground-based
UBVRIJHK photometry, and HI aperture-synthesis imaging. We outline the
spectroscopic analysis protocol for deriving precise and accurate line-of-sight
stellar velocity dispersions. Our key measurement is the dynamical disk-mass
surface-density. Star-formation rates and kinematic and photometric regularity
of galaxy disks are also central products of the study. The survey is designed
to yield random and systematic errors small enough (i) to confirm or disprove
the maximum-disk hypothesis for intermediate-type disk galaxies, (ii) to
provide an absolute calibration of the stellar mass-to-light ratio well below
uncertainties in present-day stellar-population synthesis models, and (iii) to
make significant progress in defining the shape of dark halos in the inner
regions of disk galaxies. |
Simulating high-z Gamma-ray Burst host galaxies: We investigate the nature of high-z host galaxies of long Gamma-Ray Bursts
(LGRBs) by means of state-of-the-art numerical simulations of cosmic structure
formation and evolution of galaxies. We combine results from different runs
with various box sizes and resolutions. By assigning to each simulated galaxy
the probability to host a LGRB, assumed to be proportional to the mass of young
stars, we provide a full description of the physical properties of high-z LGRB
host galaxy population. We find that LGRBs at z>6 are hosted in galaxies with
typical star formation rates SFR \sim 0.03-0.3 Msun yr^{-1}, stellar masses M
\sim 10^{6-8} Msun, and metallicities Z \sim 0.01-0.1 Zsun. Furthermore, the
ratio between their doubling time and the corresponding cosmic time seems to be
universally equal to ~0.1-0.3, independently from the redshift. The
distribution of their UV luminosity places LGRB hosts in the faint-end of the
galaxy luminosity function, well below the current capabilities of space- or
ground-based optical facilities. This is in line with recent reports of
non-detection of LGRB hosts using extremely deep HST and VLT observations. In
conclusion, high-z LGRBs are found to trace the position of those faint
galaxies that are thought to be the major actors in the re-ionization of the
Universe. | Equilibrium configurations of 11eV sterile neutrinos in MONDian galaxy
clusters: (Abridged) Modified Newtonian Dynamics (MOND) can fit a broad range of galaxy
kinematic data, but struggles with clusters of galaxies. MONDian clusters need
dark matter, and here we test the 11 eV sterile neutrino - used to fit the
first three acoustic peaks of the cosmic microwave background - by
investigating their equilibrium distributions in 30 groups and clusters over a
wide range of temperatures. Knowing both the sterile neutrino density and
velocity dispersion tells us the Tremaine-Gunn phase-space limit at all radii.
We find that all 30 systems serendipitously reach the Tremaine-Gunn limit by
the centre, which means a portion of the dynamical mass must always be covered
by the brightest cluster galaxy. Interestingly, the typical fitted K-band
mass-to-light ratio is unity and at most 1.2, which is very consistent -
although leaving no margin for error - with stellar population synthesis
models. Amidst the sample there are several special cases including the Coma
cluster (for which dark matter was first proposed), NGC 720 (where geometrical
evidence for dark matter was found) and the bullet cluster (where dark matter -
of some kind - in clusters was directly proven to exist). We demonstrate that
11 eV sterile neutrinos are unlikely to influence spiral galaxy rotation
curves, as they don't influence even some very massive early-types (NGC 4125
and NGC 6482). Finally, we conclude that it is intriguing that the minimum mass
of sterile neutrino particle that can match the cosmic microwave background is
identical to the minimum mass found here to be consistent with equilibrium
configurations of MONDian clusters of galaxies. |
Halo expansion in cosmological hydro simulations: towards a baryonic
solution of the cusp/core problem in massive spirals: A clear prediction of the Cold Dark Matter model is the existence of cuspy
dark matter halo density profiles on all mass scales. This is not in agreement
with the observed rotation curves of spiral galaxies, challenging on small
scales the otherwise successful CDM paradigm. In this work we employ high
resolution cosmological hydro-dynamical simulations to study the effects of
dissipative processes on the inner distribution of dark matter in Milky-Way
like objects (M~1e12 Msun). Our simulations include supernova feedback, and the
effects of the radiation pressure of massive stars before they explode as
supernovae. The increased stellar feedback results in the expansion of the dark
matter halo instead of contraction with respect to N-body simulations. Baryons
are able to erase the dark matter cuspy distribution creating a flat, cored,
dark matter density profile in the central several kpc of a massive Milky-Way
like halo. The profile is well fit by a Burkert profile, with fitting
parameters consistent with the observations. In addition, we obtain flat
rotation curves as well as extended, exponential stellar disk profiles. While
the stellar disk we obtain is still partially too thick to resemble the MW thin
disk, this pilot study shows that there is enough energy available in the
baryonic component to alter the dark matter distribution even in massive disc
galaxies, providing a possible solution to the long standing problem of cusps
vs. cores. | Gravitational waves from inflation: The production of a stochastic background of gravitational waves is a
fundamental prediction of any cosmological inflationary model. The features of
such a signal encode unique information about the physics of the Early Universe
and beyond, thus representing an exciting, powerful window on the origin and
evolution of the Universe. We review the main mechanisms of gravitational-wave
production, ranging from quantum fluctuations of the gravitational field to
other mechanisms that can take place during or after inflation. These include
e.g. gravitational waves generated as a consequence of extra particle
production during inflation, or during the (p)reheating phase. Gravitational
waves produced in inflation scenarios based on modified gravity theories and
second-order gravitational waves are also considered. For each analyzed case,
the expected power-spectrum is given. We discuss the discriminating power among
different models, associated with the validity/violation of the standard
consistency relation between tensor-to-scalar ratio $r$ and tensor spectral
index $n_{\rm T}$. In light of the prospects for (directly/indirectly)
detecting primordial gravitational waves, we give the expected present-day
gravitational radiation spectral energy-density, highlighting the main
characteristics imprinted by the cosmic thermal history, and we outline the
signatures left by gravitational waves on the Cosmic Microwave Background and
some imprints in the Large-Scale Structure of the Universe. Finally, current
bounds and prospects of detection for inflationary gravitational waves are
summarized. |
Parameter estimation of a nonlinear magnetic universe from observations: The cosmological model consisting of a nonlinear magnetic field obeying the
Lagrangian L= \gamma F^{\alpha}, F being the electromagnetic invariant, coupled
to a Robertson-Walker geometry is tested with observational data of Type Ia
Supernovae, Long Gamma-Ray Bursts and Hubble parameter measurements. The
statistical analysis show that the inclusion of nonlinear electromagnetic
matter is enough to produce the observed accelerated expansion, with not need
of including a dark energy component. The electromagnetic matter with abundance
$\Omega_B$, gives as best fit from the combination of all observational data
sets \Omega_B=0.562^{+0.037}_{-0.038} for the scenario in which \alpha=-1,
\Omega_B=0.654^{+0.040}_{-0.040} for the scenario with \alpha=-1/4 and
\Omega_B=0.683^{+0.039}_{-0.043} for the one with \alpha=-1/8. These results
indicate that nonlinear electromagnetic matter could play the role of dark
energy, with the theoretical advantage of being a mensurable field. | Perturbations of Cosmological Redshift Drift: In this paper we calculate the linear perturbations of the cosmological
redshift drift. We show explicitly that our expressions are gauge-invariant and
compute the power spectrum of the redshift drift perturbations and its
correlations with galaxy number counts within linear perturbation theory. Our
findings show that the perturbations are small, and that the peculiar velocity
and acceleration terms are dominating and cannot be neglected when modeling the
full perturbative expression for the redshift drift. We also find that the
cross-correlations with galaxy number count fluctuations might increase the
detectability of the effect and can help to separate the perturbative effects
from the background cosmological redshift drift signal. |
The dark side of curvature: Geometrical tests such as the combination of the Hubble parameter H(z) and
the angular diameter distance d_A(z) can, in principle, break the degeneracy
between the dark energy equation of state parameter w(z), and the spatial
curvature Omega_k in a direct, model-independent way. In practice, constraints
on these quantities achievable from realistic experiments, such as those to be
provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination
with CMB data, can resolve the cosmic confusion between the dark energy
equation of state parameter and curvature only statistically and within a
parameterized model for w(z). Combining measurements of both H(z) and d_A(z) up
to sufficiently high redshifts around z = 2 and employing a parameterization of
the redshift evolution of the dark energy equation of state are the keys to
resolve the w(z)-Omega_k degeneracy. | Studying the spatially resolved Schmidt-Kennicutt law in interacting
galaxies: the case of Arp 158: Recent studies have shown that star formation in mergers does not seem to
follow the same Schmidt-Kennicutt (KS) relation as in spiral disks, presenting
a higher star formation rate (SFR) for a given gas column density. In this
paper we study why and how different models of star formation arise. To do so
we examine the process of star formation in the interacting system Arp 158 and
its tidal debris. We perform an analysis of the properties of specific regions
of interest in Arp 158 using observations tracing the atomic and the molecular
gas, star formation, the stellar populations as well as optical spectroscopy to
determine their exact nature. We also fit their spectral energy distribution
with an evolutionary synthesis code. Finally, we compare star formation in
these objects to star formation in the disks of spiral galaxies and mergers.
Abundant molecular gas is found throughout the system and the tidal tails
appear to have many young stars compared to their old stellar content. One of
the nuclei is dominated by a starburst whereas the other is an active nucleus.
We estimate the SFR throughout the system and find that most regions follow
closely the KS relation seen in spiral galaxies with the exception of the
nuclear starburst and the tip of one of the tails. We examine whether this
diversity is due to uncertainties in the manner the SFR is determined or
whether the conditions in the nuclear starburst region are such that it does
not follow the same KS law as other regions. Observations of the interacting
system Arp 158 provide the first evidence in a resolved fashion that different
star-forming regions in a merger may be following different KS laws. This
suggests that the physics of the interstellar medium at a scale no larger than
1 kpc, the size of the largest gravitational instabilities and the injection
scale of turbulence, determines the origin of these laws. |
Multiwavelength campaign on Mrk 509. II. Analysis of high-quality
Reflection Grating Spectrometer spectra: We study the bright Seyfert 1 galaxy Mrk~509 with the Reflection Grating
Spectrometers (RGS) of XMM-Newton using the RGS multi-pointing mode of
XMM-Newton for the first time in order to constrain the properties of the
outflow in this object. We want to obtain the most accurate spectral properties
from the 600 ks spectrum of Mrk 509 which has excellent statistical quality. We
derive an accurate relative calibration for the effective area of the RGS,
derive an accurate absolute wavelength calibration, improve the method for
adding time-dependent spectra and enhance the efficiency of the spectral
fitting by two orders of magnitude. We show the major improvement of the
spectral data quality due to the use of the new RGS multi-pointing mode of
XMM-Newton. We illustrate the gain in accuracy by showing that with the
improved wavelength calibration the two velocity troughs observed in UV spectra
are resolved. | Primordial black holes formation in the inflationary model with
field-dependent kinetic term for quartic and natural potentials: Within the framework of inflationary model with field-dependent kinetic term
for quartic and natural potentials, we investigate generation of the primordial
black holes (PBHs) and induced gravitational waves (GWs). In this setup, we
consider a kinetic function as $G(\phi)=g_I(\phi)\big(1+g_{II}(\phi)\big)$ and
show that in the presence of first term $g_I(\phi)$ both quartic and natural
potentials, in contrast to the standard model of inflation, can be consistent,
with the 68\% CL of Planck observations. Besides, the second term
$g_{II}(\phi)$ can cause a significant enhancement in the primordial curvature
perturbations at the small scales which results the PBHs formation. For the
both potentials, we obtain an enhancement in the scalar power spectrum at the
scales $k\sim10^{12}~\rm Mpc^{-1}$, $10^{8}~\rm Mpc^{-1}$, and $10^{5}~\rm
Mpc^{-1}$, which causes PBHs production in mass scales around
$10^{-13}M_{\odot}$, $10^{-5}M_{\odot}$, and $10 M_{\odot}$, respectively.
Observational constraints confirm that PBHs with a mass scale of
$10^{-13}M_{\odot}$ can constitute the total of dark matter in the universe.
Furthermore, we estimate the energy density parameter of induced GWs which can
be examined by the observation. Also we conclude that it can be parametrized as
a power-law function $\Omega_{\rm GW}\sim (f/f_c)^n$, where the power index
equals $n=3-2/\ln(f_c/f)$ in the infrared limit $f\ll f_{c}$. |
Exploring the expansion dynamics of the universe from galaxy cluster
surveys: To understand the expansion dynamics of the universe from galaxy cluster
scales, using the angular diameter distance (ADD) data from two different
galaxy cluster surveys, we constrain four cosmological models to explore the
underlying value of $H_0$ and employ the model-independent Gaussian Processes
to investigate the evolution of the equation of state of dark energy. The ADD
data in the X-ray bands consists of two samples covering the redshift ranges
[0.023, 0.784] and [0.14, 0.89], respectively. We find that: (i) For these two
samples, the obtained values of $H_0$ are more consistent with the recent local
observation by Riess et al. than the global measurement by the Plank
Collaboration, and the $\Lambda$CDM model is still preferred utilizing the
information criterions; (ii) For the first sample, there is no evidence of
dynamical dark energy (DDE) at the $2\sigma$ confidence level (CL); (iii) For
the second one, the reconstructed equation of state of dark energy exhibits a
phantom-crossing behavior in the relatively low redshift range over the
$2\sigma$ CL, which gives a hint that the late-time universe may be actually
dominated by the DDE from galaxy cluster scales; (iv) By adding a combination
of Type Ia Supernovae, cosmic chronometers and Planck-2015 shift parameter and
HII galaxy measurements into both ADD samples, the DDE exists evidently over
the $2\sigma$ CL. | Polarized CMB recovery with sparse component separation: The polarization modes of the cosmological microwave background are an
invaluable source of information for cosmology, and a unique window to probe
the energy scale of inflation. Extracting such information from microwave
surveys requires disentangling between foreground emissions and the
cosmological signal, which boils down to solving a component separation
problem. Component separation techniques have been widely studied for the
recovery of CMB temperature anisotropies but quite rarely for the polarization
modes. In this case, most component separation techniques make use of
second-order statistics to discriminate between the various components. More
recent methods, which rather emphasize on the sparsity of the components in the
wavelet domain, have been shown to provide low-foreground, full-sky estimate of
the CMB temperature anisotropies. Building on sparsity, the present paper
introduces a new component separation technique dubbed PolGMCA (Polarized
Generalized Morphological Component Analysis), which refines previous work to
specifically tackle the estimation of the polarized CMB maps: i) it benefits
from a recently introduced sparsity-based mechanism to cope with partially
correlated components, ii) it builds upon estimator aggregation techniques to
further yield a better noise contamination/non-Gaussian foreground residual
trade-off. The PolGMCA algorithm is evaluated on simulations of full-sky
polarized microwave sky simulations using the Planck Sky Model (PSM), which
show that the proposed method achieve a precise recovery of the CMB map in
polarization with low noise/foreground contamination residuals. It provides
improvements with respect to standard methods, especially on the galactic
center where estimating the CMB is challenging. |
Unveiling the Galaxy Cluster - Cosmic Web Connection with X-ray
observations in the Next Decade: In recent years, the outskirts of galaxy clusters have emerged as one of the
new frontiers and unique laboratories for studying the growth of large scale
structure in the universe. Modern cosmological hydrodynamical simulations make
firm and testable predictions of the thermodynamic and chemical evolution of
the X-ray emitting intracluster medium. However, recent X-ray and
Sunyaev-Zeldovich effect observations have revealed enigmatic disagreements
with theoretical predictions, which have motivated deeper investigations of a
plethora of astrophysical processes operating in the virialization region in
the cluster outskirts. Much of the physics of cluster outskirts is
fundamentally different from that of cluster cores, which has been the main
focus of X-ray cluster science over the past several decades. A next-generation
X-ray telescope, equipped with sub-arcsecond spatial resolution over a large
field of view along with a low and stable instrumental background, is required
in order to reveal the full story of the growth of galaxy clusters and the
cosmic web and their applications for cosmology. | Foreground Biases on Primordial Non-Gaussianity Measurements from the
CMB Temperature Bispectrum: Implications for Planck and Beyond: The cosmic microwave background (CMB) temperature bispectrum is currently the
most precise tool for constraining primordial non-Gaussianity (NG). The Planck
temperature data tightly constrain the amplitude of local-type NG: $f_{\rm
NL}^{\rm loc} = 2.5 \pm 5.7$. Here, we compute previously-neglected foreground
biases in temperature-based $f_{\rm NL}^{\rm loc}$ measurements, due to the
integrated Sachs-Wolfe (ISW) effect, gravitational lensing, the thermal and
kinematic Sunyaev-Zel'dovich effects, and the cosmic infrared background. While
standard analyses already subtract a significant bias on $f_{\rm NL}^{\rm loc}$
due to the ISW-lensing bispectrum, many other secondary anisotropy terms are
present in the temperature bispectrum. We compute the dominant biases on
$f_{\rm NL}^{\rm loc}$ arising from these signals. Most of the biases are
non-blackbody, and are thus reduced by multifrequency component separation
methods; however, recent analyses have found that extragalactic foregrounds are
present at non-negligible levels in the Planck component-separated maps.
Moreover, the Planck FFP8 simulations do not include the foreground
correlations that generate these biases. We compute the biases for individual
frequencies; some are comparable to the statistical error bar on $f_{\rm
NL}^{\rm loc}$, even for the main CMB channels (100, 143, and 217 GHz). For
future experiments, they greatly exceed the statistical error (considering
temperature only). Alternatively, the foreground contributions can be
marginalized over, but this leads to a non-negligible increase in the error bar
on $f_{\rm NL}^{\rm loc}$. A full assessment will require calculations in
tandem with component separation, ideally using simulations. We also compute
these biases for equilateral and orthogonal NG, finding large effects for the
latter. We conclude that the search for primordial NG using Planck data may not
yet be over. |
Morphology of CMB fields -- effect of weak gravitational lensing: We study the morphology of the cosmic microwave background temperature and
polarization fields using the shape and alignment parameters, $\beta$ and
$\alpha$, that are constructed from the contour Minkowski tensor. The primary
goal of our paper is to understand the effect of weak gravitational lensing on
the morphology of the CMB fields. In order to isolate different physical
effects that can be potentially confused with the effect of lensing, we first
study the effect of varying the cosmology on $\alpha$ and $\beta$, and show
that they are relatively insensitive to variation of cosmological parameters.
Next we analyze the signatures of hemispherical anisotropy, and show that
information of such anisotropy in $\alpha$ gets washed out at small angular
scales and become pronounced only at large angular scales. For $\beta$ we find
characteristic distortions which vary with the field threshold. We then study
the effect of weak gravitational lensing using simulations of lensed
temperature and $E$ and $B$ modes. We quantify the distortion induced in the
fields across different angular scales. We find that lensing makes structures
of all fields increasingly more anisotropic as we probe down to smaller scales.
We find distinct behaviour of morphological distortions as a function of
threshold for the different fields. The effect is small for temperature and $E$
mode, while it is significantly large for $B$ mode. Further, we find that
lensing does not induce statistical anisotropy, as expected from the isotropic
distribution of large scale structure of matter. We expect that the results
obtained in this work will provide insights on the reconstruction of the
lensing potential. | Deep slitless infrared spectroscopic surveys with HST/WFC3: HST is commonly thought of as an optical-IR imaging or UV-spectroscopy
observatory. However, the advent of WFC3-IR made it possible to do slitless
infrared spectroscopic surveys over an area significant for galaxy evolution
studies (~0.15 deg^2). Slitless infrared spectroscopy is uniquely possible from
space due to the reduced background. Redshift surveys with WFC3-IR offer probes
of the astrophysics of the galaxy population at z=1-3 from line features, and
the true redshift and spatial distribution of galaxies, that cannot be done
with photometric surveys alone. While HST slitless spectroscopy is low spectral
resolution, its high multiplex advantage makes it competitive with future
ground based IR spectrographs, its flux calibration is stable, and its high
spatial resolution allows measuring the spatial extent of emission lines, which
only HST can do currently for large numbers of objects. A deeper slitless IR
spectroscopic survey over hundreds of arcmin^2 (eg one or more GOODS fields) is
one of the remaining niches for large galaxy evolution studies with HST, and
would produce a sample of thousands of spectroscopically confirmed galaxies at
1<z<3 to H=25 and beyond, of great interest to a large community of
investigators. Finally, although JWST multislit spectroscopy will outstrip HST
in resolution and sensitivity, I believe it is critical to have a spectroscopic
sample in hand before JWST flies. This applies scientifically, to be prepared
for the questions we want to answer with JWST, and observationally, because
JWST's lifetime is limited and a classic problem in targeted spectroscopy has
been the turn-around time for designing surveys and for deciding which classes
of objects to target. This white paper is released publicly to stimulate open
discussion of future large HST programs. |
Do WMAP5 data favor neutrino mass and a coupling between Cold Dark
Matter and Dark Energy?: We fit WMAP5 and related data by allowing for a CDM--DE coupling and
non--zero neutrino masses, simultaneously. We find a significant correlation
between these parameters, so that simultaneous higher coupling and \nu--masses
are allowed. Furthermore, models with a significant coupling and \nu--mass are
statistically favoured in respect to a cosmology with no coupling and
negligible neutrino mass (our best fits are: C ~ 1/2m_p, m_\nu ~ 0.12eV per
flavor). We use a standard Monte Carlo Markov Chain approach, by assuming DE to
be a scalar field self--interacting through Ratra--Peebles or SUGRA potentials. | Particle acceleration in a nearby galaxy cluster pair: the role of
cluster dynamics: Diffuse radio emission associated with the intra-cluster medium (ICM) is
observed in a number of merging galaxy clusters. It is currently believed that
in mergers a fraction of the kinetic energy is channeled into non-thermal
components, such as turbulence, cosmic rays and magnetic fields, that may lead
to the formation of giant synchrotron sources in the ICM. Studying merging
galaxy clusters in different evolutionary phases is fundamental to
understanding the origin of radio emission in the ICM. We observed the nearby
galaxy cluster pair RXC J1825.3+3026 ($z\sim0.065$) and CIZA J1824.1+3029
($z\sim0.071$) at 120-168 MHz with the LOw Frequency ARray (LOFAR) and made use
of a deep (240 ks) XMM-Newton dataset to study the non-thermal and thermal
properties of the system. RXC J1825.3+3026 is in a complex dynamical state,
with a primary on-going merger in the E-W direction and a secondary later stage
merger with a group of galaxies in the SW, while CIZA J1824.1+3029 is
dynamically relaxed. These two clusters are in a pre-merger phase. We report
the discovery of a Mpc-scale radio halo with a low surface brightness extension
in RXC J1825.3+3026 that follows the X-ray emission from the cluster center to
the remnant of a galaxy group in the SW. This is among the least massive
systems and the faintest giant radio halo known to date. Contrary to this, no
diffuse radio emission is observed in CIZA J1824.1+3029 nor in the region
between the pre-merger cluster pair. The power spectra of the X-ray surface
brightness fluctuations of RXC J1825.3+3026 and CIZA J1824.1+3029 are in
agreement with the findings for clusters exhibiting a radio halo and the ones
where no radio emission has been detected, respectively. We provide
quantitative support to the idea that cluster mergers play a crucial role in
the generation of non-thermal components in the ICM. |
Uncertain Times: The Redshift-Time Relation from Cosmology and Stars: Planck data provide precise constraints on cosmological parameters when
assuming the base $\Lambda$CDM model, including a $0.17\%$ measurement of the
age of the Universe, $t_0=13.797 \pm 0.023\,{\rm Gyr}$. However, the
persistence of the "Hubble tension" calls the base $\Lambda$CDM model's
completeness into question and has spurred interest in models such as Early
Dark Energy (EDE) that modify the assumed expansion history of the Universe. We
investigate the effect of EDE on the redshift-time relation $z \leftrightarrow
t$ and find that it differs from the base $\Lambda$CDM model by at least
${\approx} 4\%$ at all $t$ and $z$. As long as EDE remains observationally
viable, any inferred $t \leftarrow z$ or $z \leftarrow t$ quoted to a higher
level of precision do not reflect the current status of our understanding of
cosmology. This uncertainty has important astrophysical implications: the
reionization epoch - $10>z>6$ - corresponds to disjoint lookback time periods
in the base $\Lambda$CDM and EDE models, and the EDE value of $t_0=13.25 \pm
0.17~{\rm Gyr}$ is in tension with published ages of some stars, star clusters,
and ultra-faint dwarf galaxies. However, most published stellar ages do not
include an uncertainty in accuracy (due to, e.g., uncertain distances and
stellar physics) that is estimated to be $\sim7-10\%$, potentially reconciling
stellar ages with $t_{0,\rm EDE}$. We discuss how the big data era for stars is
providing extremely precise ages ($<1\%$) and how improved distances and
treatment of stellar physics such as convection could result in ages accurate
to $4-5\%$, comparable to the current accuracy of $t \leftrightarrow z$. Such
precise and accurate stellar ages can provide detailed insight into the
high-redshift Universe independent of a cosmological model. | Direct signatures of the formation time of galaxies: We show that it is possible to directly measure the formation time of
galaxies using large-scale structure. In particular, we show that the
large-scale distribution of galaxies is sensitive to whether galaxies form over
a narrow period of time before their observed times, or are formed over a time
scale on the order of the age of the Universe. Along the way, we derive simple
recursion relations for the perturbative terms of the most general bias
expansion for the galaxy density, thus fully extending the famous dark-matter
recursion relations to generic tracers. |
Cool Core Clusters from Cosmological Simulations: We present results obtained from a set of cosmological hydrodynamic
simulations of galaxy clusters, aimed at comparing predictions with
observational data on the diversity between cool-core (CC) and non-cool-core
(NCC) clusters. Our simulations include the effects of stellar and AGN feedback
and are based on an improved version of the smoothed particle hydrodynamics
code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical
instabilities by including a suitable artificial thermal diffusion. In this
Letter, we focus our analysis on the entropy profiles, the primary diagnostic
we used to classify the degree of cool-coreness of clusters, and on the iron
profiles. In keeping with observations, our simulated clusters display a
variety of behaviors in entropy profiles: they range from steadily decreasing
profiles at small radii, characteristic of cool-core systems, to nearly flat
core isentropic profiles, characteristic of non-cool-core systems. Using
observational criteria to distinguish between the two classes of objects, we
find that they occur in similar proportions in both simulations and in
observations. Furthermore, we also find that simulated cool-core clusters have
profiles of iron abundance that are steeper than those of NCC clusters, which
is also in agreement with observational results. We show that the capability of
our simulations to generate a realistic cool-core structure in the cluster
population is due to AGN feedback and artificial thermal diffusion: their
combined action allows us to naturally distribute the energy extracted from
super-massive black holes and to compensate for the radiative losses of
low-entropy gas with short cooling time residing in the cluster core. | The LSST Dark Energy Science Collaboration (DESC) Science Requirements
Document: The Large Synoptic Survey Telescope (LSST) Dark Energy Science Collaboration
(DESC) will use five cosmological probes: galaxy clusters, large scale
structure, supernovae, strong lensing, and weak lensing. This Science
Requirements Document (SRD) quantifies the expected dark energy constraining
power of these probes individually and together, with conservative assumptions
about analysis methodology and follow-up observational resources based on our
current understanding and the expected evolution within the field in the coming
years. We then define requirements on analysis pipelines that will enable us to
achieve our goal of carrying out a dark energy analysis consistent with the
Dark Energy Task Force definition of a Stage IV dark energy experiment. This is
achieved through a forecasting process that incorporates the flowdown to
detailed requirements on multiple sources of systematic uncertainty. Future
versions of this document will include evolution in our software capabilities
and analysis plans along with updates to the LSST survey strategy. |
Detecting gravitational waves from cosmological phase transitions with
LISA: an update: We investigate the potential for observing gravitational waves from
cosmological phase transitions with LISA in light of recent theoretical and
experimental developments. Our analysis is based on current state-of-the-art
simulations of sound waves in the cosmic fluid after the phase transition
completes. We discuss the various sources of gravitational radiation, the
underlying parameters describing the phase transition and a variety of viable
particle physics models in this context, clarifying common misconceptions that
appear in the literature and identifying open questions requiring future study.
We also present a web-based tool, PTPlot, that allows users to obtain
up-to-date detection prospects for a given set of phase transition parameters
at LISA. | A cosmological dust model with extended f(chi) gravity: Introducing a fundamental constant of nature with dimensions of acceleration
into the theory of gravity makes it possible to extend gravity in a very
consistent manner. At the non-relativistic level a MOND-like theory with a
modification in the force sector is obtained, which is the limit of a very
general metric relativistic theory of gravity. Since the mass and length scales
involved in the dynamics of the whole universe require small accelerations of
the order of Milgrom's acceleration constant a_0, it turns out that the
relativistic theory of gravity can be used to explain the expansion of the
universe. In this work it is explained how to use that relativistic theory of
gravity in such a way that the overall large-scale dynamics of the universe can
be treated in a pure metric approach without the need to introduce dark matter
and/or dark energy components. |
Gemini Spectroscopic Survey of Young Star Clusters in
Merging/Interacting Galaxies. IV. Stephan's Quintet: We present a spectroscopic survey of 21 young massive clusters and complexes
and one tidal dwarf galaxy candidate (TDG) in Stephan's Quintet, an interacting
compact group of galaxies. All of the selected targets lie outside the main
galaxies of the system and are associated with tidal debris. We find clusters
with ages between a few and 125 Myr and confirm the ages estimated through HST
photometry by Fedotov et al. (2011), as well as their modelled interaction
history of the Quintet. Many of the clusters are found to be relatively
long-lived, given their spectrosopically derived ages, while their high masses
suggest that they will likely evolve to eventually become intergalactic
clusters. One cluster, T118, is particularly interesting, given its age (\sim
125 Myr), high mass (\sim 2\times10^6 M\odot) and position in the extreme outer
end of the young tidal tail. This cluster appears to be quite extended (Reff
\sim 12 - 15 pc) compared to clusters observed in galaxy disks (Reff \sim 3 - 4
pc), which confirms an effect we previously found in the tidal tails of NGC
3256, where clusters are similarly extended. We find that star and cluster
formation can proceed at a continuous pace for at least \sim 150 Myr within the
tidal debris of interacting galaxies. The spectrum of the TDG candidate is
dominated by a young population (\sim 7 Myr), and assuming a single age for the
entire region, has a mass of at least 10^6 M\odot. | Optimal analysis of the CMB trispectrum: We develop a general framework for data analysis and phenomenology of the CMB
four-point function or trispectrum. To lowest order in the derivative
expansion, the inflationary action admits three quartic operators consistent
with symmetry: $\dot\sigma^4$, $\dot\sigma^2 (\partial\sigma^2)$, and
$(\partial\sigma)^4$. In single field inflation, only the first of these
operators can be the leading non-Gaussian signal. A Fisher matrix analysis
shows that there is one near-degeneracy among the three CMB trispectra, so we
parameterize the trispectrum with two coefficients $g_{NL}^{\dot\sigma^4}$ and
$g_{NL}^{(\partial\sigma)^4}$, in addition to the coefficient $g_{NL}^{\rm
loc}$ of $\zeta^3$-type local non-Gaussianity. This three-parameter space is
analogous to the parameter space $(f_{NL}^{\rm loc}, f_{NL}^{\rm equil},
f_{NL}^{\rm orth})$ commonly used to parameterize the CMB three-point function.
We next turn to data analysis and show how to represent these trispectra in a
factorizable form which leads to computationally fast operations such as
evaluating a CMB estimator or simulating a non-Gaussian CMB. We discuss
practical issues in CMB analysis pipelines, and perform an optimal analysis of
WMAP data. Our minimum-variance estimates are $g_{NL}^{\rm loc} = (-3.80 \pm
2.19) \times 10^5$, $g_{NL}^{\dot\sigma^4} = (-3.20 \pm 3.09) \times 10^6$, and
$g_{NL}^{(\partial\sigma)^4} = (-10.8 \pm 6.33) \times 10^5$ after correcting
for the effects of CMB lensing. No evidence of a nonzero inflationary
four-point function is seen. |
Are primordial black holes produced by entropy perturbations in single
field inflationary models?: We show that in single field inflationary models the super-horizon evolution
of curvature perturbations on comoving slices $\mathcal{R}$, which can cause
the production of primordial black holes (PBH), is not due to entropy
perturbations, but to the background evolution effect on the conversion between
entropy and curvature perturbations. We derive a general relation between the
time derivative of comoving curvature perturbations and entropy perturbations,
in terms of a conversion factor depending on the background evolution. Contrary
to previous results derived in the uniform density gauge assuming the gradient
term can be neglected on super-horizon scales, the relation is valid on any
scale for any minimally coupled single scalar field model, also on sub-horizon
scales where gradient terms are large.
We apply it to the case of quasi-inflection inflation, showing that while
entropy perturbations are decreasing, $\mathcal{R}$ can grow on super-horizon
scales, due to a large increase of the conversion factor. This happens in the
time interval during which a sufficiently fast decrease of the equation of
state $w$ transforms into a growing mode that in slow-roll models would be a
decaying mode. The same mechanism also explains the super-horizon evolution of
$\mathcal{R}$ in globally adiabatic systems, for which entropy perturbations
vanish on any scale, such as ultra slow-roll inflation and its generalizations. | High-resolution SZ imaging of clusters of galaxies with the NIKA2 camera
at the IRAM 30-m telescope: The development of precision cosmology with clusters of galaxies requires
high-angular resolution Sunyaev-Zel'dovich (SZ) observations. As for now,
arcmin resolution SZ observations (e.g. SPT, ACT and Planck) only allowed
detailed studies of the intra cluster medium for low redshift clusters (z<0.2).
With both a wide field of view (6.5 arcmin) and a high angular resolution (17.7
and 11.2 arcsec at 150 and 260 GHz), the NIKA2 camera installed at the IRAM
30-m telescope (Pico Veleta, Spain), will bring valuable information in the
field of SZ imaging of clusters of galaxies. The NIKA2 SZ observation program
will allow us to observe a large sample of clusters (50) at redshifts between
0.4 and 0.9. As a pilot study for NIKA2, several clusters of galaxies have been
observed with the pathfinder, NIKA, at the IRAM 30-m telescope to cover the
various configurations and observation conditions expected for NIKA2. |
Can galaxy clusters, type Ia supernovae and cosmic microwave background
rule out a class of modified gravity theories?: In this paper we study cosmological signatures of modified gravity theories
that can be written as a coupling between a extra scalar field and the
electromagnetic part of the usual Lagrangian for the matter fields. In these
frameworks all the electromagnetic sector of the theory is affected and
variations of fundamental constants, of the cosmic distance duality relation
and of the evolution law of the cosmic microwave background radiation (CMB) are
expected and are related each other. In order to search these variations we
perform jointly analyses with angular diameter distances of galaxy clusters,
luminosity distances of type Ia supernovae and $T_{CMB}(z)$ measurements. We
obtain tight constraints with no indication of violation of the standard
framework. | Observational constraints on tensor perturbations in cosmological models
with dynamical dark energy: We constrain the contribution of tensor-mode perturbations with free $n_t$ in
the models with dynamical dark energy with the barotropic equation of state
using Planck-2015 data on CMB anisotropy, polarization and lensing, BICEP2/Keck
Array data on B-mode polarization, power spectrum of galaxies from WiggleZ and
SN Ia data from the JLA compilation. We also investigate the uncertainties of
reconstructed potential of the scalar field dark energy. |
The Primordial Black Hole Dark Matter - LISA Serendipity: There has recently been renewed interest in the possibility that the dark
matter in the universe consists of primordial black holes (PBHs). Current
observational constraints leave only a few PBH mass ranges for this
possibility. One of them is around $10^{-12} M_\odot$. If PBHs with this mass
are formed due to an enhanced scalar-perturbation amplitude, their formation is
inevitably accompanied by the generation of gravitational waves (GWs) with
frequency peaked in the mHz range, precisely around the maximum sensitivity of
the LISA mission. We show that, if these primordial black holes are the dark
matter, LISA will be able to detect the associated GW power spectrum. Although
the GW source signal is intrinsically non-Gaussian, the signal measured by LISA
is a sum of the signal from a large number of independent sources suppressing
the non-Gaussianity at detection to an unobservable level. We also discuss the
effect of the GW propagation in the perturbed universe. PBH dark matter
generically leads to a detectable, purely isotropic, Gaussian and unpolarised
GW signal, a prediction that is testable with LISA. | The polar ring galaxy AM 2040-620 and its possible companion: Polar ring galaxies (PRGs) are peculiar systems where a gas-rich, nearly
polar ring surrounds a host galaxy. They are the result of galaxy interactions
that form mainly by tidal accretion of material from a gas rich donor galaxy.
There is a number of formation mechanisms for PRGs: minor or major mergers,
tidal accretion events, or direct cold gas accretion from filaments of the
cosmic web. These objects can be used to probe the three-dimensional shape of
dark matter haloes, provided that the ring is in equilibrium with the
gravitational potential of the host galaxy. The polar ring galaxy, AM 2040-620,
which has not yet been well studied, is the subject of this work. This galaxy
contains an almost perpendicular warped ring and one possible companion galaxy
to the NW. The radial velocity of this object is 3301\pm65 km/s and is part of
a group of fifteen possible polar ring galaxies, according to the literature.
In order to better understand this system, images and long slit spectra were
observed with the 1.60 m OPD/LNA telescope. In the I band image, the outer
parts of the ring are not symmetrical. A disturbance in the Eastern side and a
faint plume were detected. Two small satellites are located to the north. The
bulge is elliptical but not perfectly symmetrical in this image. The B-band
image shows material that extends beyond the ring in the western and eastern
directions. After processing, the B-image shows that the possible companion
galaxy 2MASX J20441668-6158092 has a tidally disturbed disk. Its radial
velocity is unknown, but the spectroscopy, which is still under analysis, will
furnish this information. |
A deep search for decaying dark matter with XMM-Newton blank-sky
observations: Sterile neutrinos with masses in the keV range are well-motivated extensions
to the Standard Model that could explain the observed neutrino masses while
also making up the dark matter (DM) of the Universe. If sterile neutrinos are
DM then they may slowly decay into active neutrinos and photons, giving rise to
the possibility of their detection through narrow spectral features in
astrophysical X-ray data sets. In this work, we perform the most sensitive
search to date for this and other decaying DM scenarios across the mass range
from 5 to 16 keV using archival XMM-Newton data. We reduce 547 Ms of data from
both the MOS and PN instruments using observations taken across the full sky
and then use this data to search for evidence of DM decay in the ambient halo
of the Milky Way. We determine the instrumental and astrophysical baselines
with data taken far away from the Galactic Center, and use Gaussian Process
modeling to capture additional continuum background contributions. No evidence
is found for unassociated X-ray lines, leading us to produce the strongest
constraints to date on decaying DM in this mass range. | A Comparison of Maps and Power Spectra Determined from South Pole
Telescope and Planck Data: We study the consistency of 150 GHz data from the South Pole Telescope (SPT)
and 143 GHz data from the Planck satellite over the patch of sky covered by the
SPT-SZ survey. We first visually compare the maps and find that the residuals
appear consistent with noise after accounting for differences in angular
resolution and filtering. We then calculate (1) the cross-spectrum between two
independent halves of SPT data, (2) the cross-spectrum between two independent
halves of Planck data, and (3) the cross-spectrum between SPT and Planck data.
We find the three cross-spectra are well-fit (PTE = 0.30) by the null
hypothesis in which both experiments have measured the same sky map up to a
single free calibration parameter---i.e., we find no evidence for systematic
errors in either data set. As a by-product, we improve the precision of the SPT
calibration by nearly an order of magnitude, from 2.6% to 0.3% in power.
Finally, we compare all three cross-spectra to the full-sky Planck power
spectrum and find marginal evidence for differences between the power spectra
from the SPT-SZ footprint and the full sky. We model these differences as a
power law in spherical harmonic multipole number. The best-fit value of this
tilt is consistent among the three cross-spectra in the SPT-SZ footprint,
implying that the source of this tilt is a sample variance fluctuation in the
SPT-SZ region relative to the full sky. The consistency of cosmological
parameters derived from these datasets is discussed in a companion paper. |
Systematic variation of the stellar Initial Mass Function with velocity
dispersion in early-type galaxies: An essential component of galaxy formation theory is the stellar initial mass
function (IMF), that describes the parent distribution of stellar mass in star
forming regions. We present observational evidence in a sample of early-type
galaxies (ETGs) of a tight correlation between central velocity dispersion and
the strength of several absorption features sensitive to the presence of
low-mass stars. Our sample comprises ~40,000 ETGs from the SPIDER survey
(z<0.1). The data, extracted from the Sloan Digital Sky Survey, are combined,
rejecting both noisy data, and spectra with contamination from telluric lines,
resulting in a set of 18 stacked spectra at high signal-to-noise ratio (S/N>
400 per A). A combined analysis of IMF-sensitive line strengths and spectral
fitting is performed with the latest state-of the art population synthesis
models (an extended version of the MILES models). A significant trend is found
between IMF slope and velocity dispersion, towards an excess of low-mass stars
in the most massive galaxies. Although we emphasize that accurate values of the
IMF slope will require a detailed analysis of chemical composition (such as
[a/Fe] or even individual element abundance ratios), the observed trends
suggest that low-mass ETGs are better fit by a Kroupa-like IMF, whereas massive
galaxies require bottom-heavy IMFs, exceeding the Salpeter slope at velocity
dispersions above 200km/s. | Dust attenuation in the restframe ultraviolet: constraints from
star-forming galaxies at z~1: A novel technique is employed for estimating attenuation curves in galaxies
where only photometry and spectroscopic redshifts are available. This technique
provides a powerful measure of particular extinction features such as the UV
bump at 2175\A, which has been observed in environments ranging from the Milky
Way to high-redshift star-forming galaxies. Knowledge of the typical strength
of the UV bump as a function of environment and redshift is crucial for
converting restframe UV flux into star formation rates. The UV bump will impart
a unique signature as it moves through various filters due to redshifting; its
presence can therefore be disentangled from other stellar population effects.
The utility of this technique is demonstrated with a large sample of galaxies
drawn from the DEEP2 Galaxy Redshift Survey. The observed B-R color of
star-forming galaxies at 0.6<z<1.4 disfavors the presence of a UV bump as
strong as observed in the Milky Way, and instead favors restframe UV
(1800A<lambda<3000A) attenuation curves similar to the Milky Way without a UV
bump or a power-law with index delta=-0.7. Stronger constraints on the strength
of the UV bump in galaxies can be achieved if independent constraints on the
V-band optical depth are available. |
Instability in axion inflation with strong backreaction from gauge modes: We perform an analytical study of the stability of the background solution of
the model in which an inflaton, through an axionic coupling to a $U(1)$ gauge
field, causes an amplification of the gauge field modes that strongly backreact
on its dynamics. To this goal, we study the evolution of the gauge field modes
coupled to the inflaton zero mode, treating perturbatively the deviation of the
inflaton velocity from its mean-field value. As long as the system is in the
strong backreaction regime we find that the inflaton velocity performs
oscillations of increasing amplitude about the value it would have in the
approximation of constant velocity, confirming an instability that has been
observed in numerical studies. | Generalized LTB model with Inhomogeneous Isotropic Dark Energy:
Observational Constraints: We consider on-center and off-center observers in an inhomogeneous,
spherically symmetric, isocurvature (flat) concentration of dark energy with
typical size of a few Gpc. Such a concentration could be produced e.g. by a
recently formed global monopole with core size that approaches the Hubble
scale. In this case we would have what may be called `topological quintessence'
in analogy with the well-known topological inflation. We show that the minimum
comoving radius r_{0min} of such a dark energy inhomogeneity that is consistent
with the Union2 Type Ia supernovae (SnIa) data at the 3\sigma level is
r_{0min}\simeq 1.8 Gpc. As expected, the best-fit fractional dark energy
density at the center, \Omega_X,in, approaches the corresponding LCDM value
\Omega_X,in =0.73 for large enough values of the inhomogeneity radius r_0 (r_0
> 4Gpc). Using the Union2 data, we show that the maximum allowed shift
r_{obs-max} of the observer from the center of the inhomogeneity is about 0.7
r_0 which respects the Copernican principle. The model naturally predicts the
existence of a preferred axis and alignment of the low CMB multipoles. However,
the constraints on r_{obs-max} coming from the magnitude of the CMB dipole
remain a severe challenge to the Copernican principle and lead to r_{obs-max}<
110 Mpc even for an inhomogeneity radius as large as r_0=7 Gpc. |
More galaxies in the Local Volume imaged in H-alpha: We have carried out an H-alpha flux measurement for 52 nearby galaxies as
part of a general H-alpha imaging survey for the Local Volume sample of
galaxies within 10 Mpc. Most of the objects are probable members of the groups
around Maffei 2/IC 342, NGC 672/IC 1727, NGC 784, and the Orion galaxy. The
measured H-alpha fluxes corrected for extinction are used to derive the galaxy
star formation rate (SFR). We briefly discuss some basic scaling relations
between SFR, hydrogen mass and absolute magnitude of the Local Volume galaxies.
The total SFR density in the local (z = 0) universe is estimated to be
(0.019+/-0.003) M_sun yr/Mpc^3. | H0LiCOW - IX. Cosmographic analysis of the doubly imaged quasar SDSS
1206+4332 and a new measurement of the Hubble constant: We present a blind time-delay strong lensing (TDSL) cosmographic analysis of
the doubly imaged quasar SDSS 1206+4332. We combine the relative time delay
between the quasar images, Hubble Space Telescope imaging, the Keck stellar
velocity dispersion of the lensing galaxy, and wide-field photometric and
spectroscopic data of the field to constrain two angular diameter distance
relations. The combined analysis is performed by forward modelling the
individual data sets through a Bayesian hierarchical framework, and it is kept
blind until the very end to prevent experimenter bias. After unblinding, the
inferred distances imply a Hubble constant $H_0 = 68.8^{+5.4}_{-5.1}$
kms$^{-1}$Mpc$^{-1}$, assuming a flat Lambda cold dark matter cosmology with
uniform prior on $\Omega_{\rm m}$ in [0.05, 0.5]. The precision of our
cosmographic measurement with the doubly imaged quasar SDSS 1206+4332 is
comparable with those of quadruply imaged quasars and opens the path to perform
on selected doubles the same analysis as anticipated for quads. Our analysis is
based on a completely independent lensing code than our previous three H0LiCOW
systems and the new measurement is fully consistent with those. We provide the
analysis scripts paired with the publicly available software to facilitate
independent analysis. The consistency between blind measurements with
independent codes provides an important sanity check on lens modelling
systematics. By combining the likelihoods of the four systems under the same
prior, we obtain $H_0 = 72.5^{+2.1}_{-2.3}$kms$^{-1}$Mpc$^{-1}$. This
measurement is independent of the distance ladder and other cosmological
probes. |
Cool core remnants in galaxy clusters: X ray clusters are conventionally divided into two classes: "cool core" (CC)
and "non cool core" (NCC) objects, on the basis of the observational properties
of their central regions. Recent results have shown that the cluster population
is bimodal (Cavagnolo et al. 2009). We want to understand whether the observed
distribution of clusters is due to a primordial division into two distinct
classes rather than to differences in how these systems evolve across cosmic
time. We systematically search the ICM of NCC clusters in a subsample of the
B55 flux limited sample of clusters for regions which have some characteristics
typical of cool cores, namely low entropy gas and high metal abundance We find
that most NCC clusters in our sample host regions reminiscent of CC, i. e.
characterized by relative low entropy gas (albeit not as low as in CC systems)
and a metal abundance excess. We have dubbed these structures "cool core
remnants", since we interpret them as what remains of a cool core after a
heating event (AGN giant outbursts in a few cases and more commonly mergers).
We infer that most NCC clusters have undergone a cool core phase during their
life. The fact that most cool core remnants are found in dynamically active
objects provides strong support to scenarios where cluster core properties are
not fixed "ab initio" but evolve across cosmic time. | Optimising Boltzmann codes for the Planck era: High precision measurements of the Cosmic Microwave Background (CMB)
anisotropies, as can be expected from the Planck satellite, will require
high-accuracy theoretical predictions as well. One possible source of
theoretical uncertainty is the numerical error in the output of the Boltzmann
codes used to calculate angular power spectra. In this work, we carry out an
extensive study of the numerical accuracy of the public Boltzmann code CAMB,
and identify a set of parameters which determine the error of its output. We
show that at the current default settings, the cosmological parameters
extracted from data of future experiments like Planck can be biased by several
tenths of a standard deviation for the six parameters of the standard
Lambda-CDM model, and potentially more seriously for extended models. We
perform an optimisation procedure that leads the code to achieve sufficient
precision while at the same time keeping the computation time within reasonable
limits. Our conclusion is that the contribution of numerical errors to the
theoretical uncertainty of model predictions is well under control -- the main
challenges for more accurate calculations of CMB spectra will be of an
astrophysical nature instead. |
Phantom dark energy as a natural selection of evolutionary processes
$\hat{\rm a}$ $\textit{la}$ $\textit{genetic algorithm}$ and cosmological
tensions: We study the late-time cosmological tensions using the low-redshift
background and redshift-space distortion data by employing a machine learning
(ML) technique. By comparing the generated observables with the standard
cosmological scenario, our findings indicate support for the phantom nature of
dark energy, which ultimately leads to a reduction in the existing tensions.
The model-independent approach also enables us to examine the combined
background and perturbative history, where tensions are reduced. Moreover, from
a statistical perspective, we have shown that our results exhibit a better fit
to the data when compared to the $\Lambda$CDM model. | Probing multiple populations of compact binaries with third-generation
gravitational-wave detectors: Third-generation (3G) gravitational-wave (GW) detectors will be able to
observe binary-black-hole mergers (BBHs) up to redshift of $\sim 30$. This
gives unprecedented access to the formation and evolution of BBHs throughout
cosmic history. In this paper we consider three sub-populations of BBHs
originating from the different evolutionary channels: isolated formation in
galactic fields, dynamical formation in globular clusters and mergers of black
holes formed from Population III (Pop III) stars at very high redshift. Using
input from populations synthesis analyses, we created two months of simulated
data of a network of 3G detectors made of two Cosmic Explorers and an Einstein
Telescope, consisting of $\sim16000$ field and cluster BBHs as well as
$\sim400$ Pop III BBHs. First, we show how one can use non-parametric models to
infer the existence and characteristic of a primary and secondary peak in the
merger rate distribution. In particular, the location and the height of the
secondary peak around $z\approx 12$, arising from the merger of Pop III
remnants, can be constrained at $\mathcal{O}(10\%)$ level. Then we perform a
modeled analysis, using phenomenological templates for the merger rates of the
three sub-population, and extract the branching ratios and the characteristic
parameters of the merger rate densities of the individual formation channels.
With this modeled method, the uncertainty on the measurement of the fraction of
Pop III BBHs can be improved to $\lesssim 10\%$, while the ratio between field
and cluster BBHs can be measured with an uncertainty of $\sim 50\%$. |
Blinded challenge for precision cosmology with large-scale structure:
results from effective field theory for the redshift-space galaxy power
spectrum: An accurate theoretical template for the galaxy power spectrum is a key for
the success of ongoing and future spectroscopic surveys. We examine to what
extent the Effective Field Theory of Large Scale Structure is able to provide
such a template and correctly estimate cosmological parameters. To that end, we
initiate a blinded challenge to infer cosmological parameters from the
redshift-space power spectrum of high-resolution mock catalogs mimicking the
BOSS galaxy sample but covering a hundred times larger cumulative volume. This
gigantic simulation volume allows us to separate systematic bias due to
theoretical modeling from the statistical error due to sample variance. The
challenge task was to measure three unknown input parameters used in the
simulation: the Hubble constant, the matter density fraction, and the
clustering amplitude. We present analyses done by two independent teams, who
have fitted the mock simulation data generated by yet another independent
group. This allows us to avoid any confirmation bias by analyzers and pin down
possible tuning of the specific EFT implementations. Both independent teams
have recovered the true values of the input parameters within sub-percent
statistical errors corresponding to the total simulation volume. | Measuring the level of nuclear activity in Seyfert galaxies and the
unification scheme: Context: The unification scheme of Seyfert galaxies hypothesizes that Seyfert
type 1s and type 2s are intrinsically similar and the observed differences
between the two subtypes are solely due to the differing orientations of
toroidal-shaped obscuring material around the AGN. In the framework of the
unification scheme, both the Seyfert subtypes are expected to show similar
intrinsic nuclear properties, such as the absorption-corrected AGN X-ray
luminosity, bolometric luminosity, accretion rate and the mass of the
supermassive black hole. Aims: To test the predictions of the Seyfert
unification scheme, we make statistical comparison of the distributions of: (i)
the absorption-corrected 2.0 - 10 keV X-ray luminosities, (ii) the bolometric
luminosities, (iii) the black hole masses and, (iv) the Eddington ratios, of
Seyfert type 1s and type 2s. Methods: We use an optically selected Seyfert
sample in which type 1s and type 2s are matched in properties that are
independent to the orientation of the obscuring torus, the AGN axis and the
host galaxy. Results: The distributions of the absorption-corrected 2.0 - 10
keV X-ray luminosities, the bolometric luminosities, the black masses and, the
Eddington ratios are statistically similar for the two Seyfert subtypes,
consistent with the orientation and obscuration based Seyfert unification
scheme. The Eddington ratio distributions suggest that both the Seyfert
subtypes are accreting at sub-Eddington level with wide span of Eddington
ratios i.e., 10^-4 - 10^-1. |
Emergent Unparticles Dark Energy can restore cosmological concordance: Addressing the discrepancy between the late and early time measurements of
the Hubble parameter, $H_0$, and the so-called $S_8$ parameter has been a
challenge in precision cosmology. Several models are present to address these
tensions, but very few of them can do so simultaneously. In the past, we have
suggested Banks-Zaks/Unparticles as an emergent Dark Energy model and claimed
that it can ameliorate the Hubble tension. In this work, we test this claim and
perform a likelihood analysis of the model and its parameters are given current
data and compare it to $\Lambda$CDM. The model offers a possible resolution of
Hubble tension and softens the Large Scale Structure (LSS) tension without
employing a scalar field or modifying the gravitational sector. Our analysis
shows a higher value of $H_0 \sim 70 - 73$ km/sec/Mpc and a slightly lower
value of $S_8$ for various combinations of data sets. Consideration of Planck
CMB data combined with the Pantheon sample and SH0ES priors lowers the $H_0$
and $S_8$ tension to $0.96 \sigma$ and $0.94 \sigma$ respectively with best-fit
$\Delta \chi^2 \approx -10$ restoring cosmological concordance. Significant
improvement in the likelihood persists for other combinations of data sets as
well. Evidence for the model is given by inferring one of its parameters to be
$x_0\simeq-4.36$. | Tracing the molecular gas in distant submillimetre galaxies via CO(1-0)
imaging with the EVLA: We report the results of a pilot study with the EVLA of 12CO J=1-0 emission
from four SMGs at z=2.2-2.5, each with an existing detection of CO J=3-2. Using
the EVLA's most compact configuration we detect strong, broad J=1-0 line
emission from all of our targets. The median line width ratio,
sigma(1-0)/sigma(3-2) = 1.15 +/- 0.06, suggests that the J=1-0 is more
spatially extended than the J=3-2 emission, a situation confirmed by our maps
which reveal velocity structure in several cases and typical sizes of ~16 kpc
FWHM. The median Tb ratio is r(3-2/1-0) = 0.55 +/- 0.05, noting that our value
may be biased high because of the J=3-2-based sample selection. Naively, this
suggests gas masses ~2x higher than estimates made using higher-J transitions
of CO, with the discrepency due to the difference in assumed Tb ratio. We also
estimate masses using the 12CO J=1-0 line and the observed global Tb ratios,
assuming standard underlying Tb ratios as well as a limiting SFE, i.e. without
calling upon X(CO). Using this new method, we find a median molecular gas mass
of (2.5 +/- 0.8) x 10^10 Msun, with a plausible range stretching 3x higher.
Even larger masses cannot be ruled out, but are not favoured by dynamical
constraints: the median dynamical mass for our sample is (2.3 +/- 1.4) x 10^11
Msun. We examine the Schmidt-Kennicutt relation for all the distant galaxy
populations for which CO J=1-0 or J=2-1 data are available, finding small
systematic differences. These have previously been interpreted as evidence for
different modes of star formation, but we argue that these differences are to
be expected, given the still considerable uncertainties. Finally, we discuss
the morass of degeneracies surrounding molecular gas mass estimates, the
possibilities for breaking them, and the future prospects for imaging and
studying cold, quiescent molecular gas at high redshifts [abridged]. |
Probing the primordial universe with gravitational waves detectors: The spectrum of primordial gravitational waves (GWs), especially its tilt
$n_T$, carries significant information about the primordial universe. Combining
recent aLIGO and Planck2015+BK14 data, we find that the current limit is
$n_T=0.016^{+0.614}_{-0.989}$ at 95% C.L. We also estimate the impacts of
Einstein Telescope and LISA on constraining $n_T$. Moreover, based on the
effective field theory of cosmological perturbations, we make an attempt to
confront some models of early universe scenarios, which produce blue-tilted GWs
spectrum ($n_T>0$), with the corresponding datasets. | Age and mass constraints for a young massive cluster in M31 based on
spectral-energy-distribution fitting: VDB0-B195D is a massive, blue star cluster in M31. It was observed as part of
the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey using 15
intermediate-band filters covering a wavelength range of 3000--10,000 \AA.
Based on aperture photometry, we obtain its spectral-energy distribution (SED)
as defined by the 15 BATC filters. We apply previously established relations
between the BATC intermediate-band and the Johnson-Cousins $UBVRI$ broad-band
systems to convert our BATC photometry to the standard system. A detailed
comparison shows that our newly derived $VRI$ magnitudes are fully consistent
with previous results, while our new $B$ magnitude agrees to within $2\sigma$.
In addition, we determine the cluster's age and mass by comparing its SED (from
3000 to 20,000{\AA}, comprising photometric data in the 15 BATC intermediate
bands, optical broad-band $BVRI$, and 2MASS near-infrared $JHK_{\rm s}$ data)
with theoretical stellar population synthesis models, resulting in age and mass
determinations of $60.0\pm 8.0$~Myr and $(1.1-1.6) \times 10^5 M_\odot$,
respectively. This age and mass confirms previous suggestions that VDB0-B195D
is a young massive cluster in M31. |
Hosts and environments: a (large-scale) radio history of AGN and
star-forming galaxies: Despite their relative sparseness, during the recent years it has become more
and more clear that extragalactic radio sources (both AGN and star-forming
galaxies) constitute an extremely interesting mix of populations, not only
because of their intrinsic value, but also for their fundamental role in
shaping our Universe the way we see it today. Indeed, radio-active AGN are now
thought to be the main players involved in the evolution of massive galaxies
and clusters. At the same time, thanks to the possibility of being observed up
to very high redshifts, radio galaxies can also provide crucial information on
both the star-formation history of our Universe and on its Large-Scale
Structure properties and their evolution. In the light of present and
forthcoming facilities such as LOFAR, MeerKAT and SKA that will probe the radio
sky to unprecedented depths and widths, this review aims at providing the
current state of the art on our knowledge of extragalactic radio sources in
connection with their hosts, large-scale environments and cosmological context. | Constraints on Cardassian universe from Gamma ray bursts: Constraints on the original Cardassian model and the modified polytropic
Cardassian model are examined from the recently derived 42 gamma-ray bursts
(GRBs) data calibrated with the method avoiding the circularity problem. The
results show that GRBs can be an optional observation to constrain on the
Cardassian models. Combining the GRBs data with the newly derived size of
baryonic acoustic oscillation peak from the Sloan Digital Sky Survey (SDSS),
and the position of first acoustic peak of the Cosmic Microwave Background
radiation (CMB) from Wilkinson Microwave Anisotropy Probe (WMAP), we find
$\Omega_{m0}=0.27_{-0.02}^{+0.02}, n=0.06_{-0.08}^{+0.07}$ ($1\sigma$) for the
original Cardassian model, and $\Omega_{m0}=0.27^{+0.03}_{-0.02}$,
$n=-0.09_{-1.91}^{+0.23}, \beta=0.82_{-0.62}^{+2.10}$ ($1\sigma$) for the
modified polytropic Cardassian model. |
The integrated angular bispectrum of weak lensing: We investigate three-point statistics in weak lensing convergence, through
the integrated bispectrum. This statistic involves measuring power spectra in
patches, and is thus easy to measure, and avoids the complexity of estimating
the very large number of possible bispectrum configurations. The integrated
bispectrum principally probes the squeezed limit of the bispectrum. To be
useful as a set of summary statistics, accurate theoretical predictions of the
signal are required, and, assuming Gaussian sampling distributions, the
covariance matrix. In this paper, we investigate through simulations how
accurate are theoretical formulae for both the integrated bispectrum and its
covariance, finding that there a small inaccuracies in the theoretical signal,
and more serious deviations in the covariance matrix, which may need to be
estimated using simulations. | Implications of Dramatic Broad Absorption Line Variability in the Quasar
FBQS J1408+3054: We have observed a dramatic change in the spectrum of the formerly heavily
absorbed `overlapping-trough' iron low-ionization broad absorption line
(FeLoBAL) quasar FBQS J1408+3054. Over a time span of between 0.6 to 5
rest-frame years, the Mg II trough outflowing at 12,000 km/s decreased in
equivalent width by a factor of two and the Fe II troughs at the same velocity
disappeared. The most likely explanation for the variability is that a
structure in the BAL outflow moved out of our line of sight to the ultraviolet
continuum emitting region of the quasar's accretion disk. Given the size of
that region, this structure must have a transverse velocity of between 2600
km/s and 22,000 km/s. In the context of a simple outflow model, we show that
this BAL structure is located between approximately 5800 and 46,000
Schwarzschild radii from the black hole. That distance corresponds to 1.7 to 14
pc, 11 to 88 times farther from the black hole than the H-beta broad-line
region. The high velocities and the parsec-scale distance for at least this one
FeLoBAL outflow mean that not all FeLoBAL outflows can be associated with
galaxy-scale outflows in ultraluminous infrared galaxies transitioning to
unobscured quasars. The change of FBQS J1408+3054 from an FeLoBAL to a LoBAL
quasar also means that if (some) FeLoBAL quasars have multiwavelength
properties which distinguish them from HiBAL quasars, then some LoBAL quasars
will share those properties. Finally, we extend previous work on how
multiple-epoch spectroscopy of BAL and non-BAL quasars can be used to constrain
the average lifetime of BAL episodes (currently >60 rest-frame years at 90%
confidence). |
Fossil Systems in the 400d Cluster Catalog: We report the discovery of seven new fossil systems in the 400d cluster
survey. Our search targets nearby, $z\le0.2$, and X-ray bright, $L_X\ge
10^{43}$ erg sec$^{-1}$, clusters of galaxies. Where available, we measure the
optical luminosities from Sloan Digital Sky Survey images, thereby obtaining
uniform sets of both X-ray and optical data. Our selection criteria identify 12
fossil systems, out of which five are known from previous studies. While in
general agreement with earlier results, our larger sample size allows us to put
tighter constraints on the number density of fossil clusters. It has been
previously reported that fossil groups are more X-ray bright than other X-ray
groups of galaxies for the same optical luminosity. We find, however, that the
X-ray brightness of massive fossil systems is consistent with that of the
general population of galaxy clusters and follows the same $L_X-L_{\rm opt}$
scaling relation. | AGN feedback drives the colour evolution of local galaxies: We investigate the effects of AGN feedback on the colour evolution of
galaxies found in local (z<0.2) groups and clusters. Galaxies located within
the lobes of powerful Fanaroff-Riley type II (edge-brightened) sources show
much redder colours than neighbouring galaxies that are not spatially
coincident with the radio source. By contrast, no similar effect is seen near
Fanaroff-Riley type I (core-dominated) radio sources. We show that these
colours are consistent with FR-IIs truncating star formation as the expanding
bow shock overruns a galaxy. We examine a sample of clusters with no detectable
radio emission and show that galaxy colours in these clusters carry an imprint
of past AGN feedback. AGN activity in the low-redshift Universe is
predominantly driven by low-luminosity radio sources with short duty cycles.
Our results show that, despite their rarity, feedback from powerful radio
sources is an important driver of galaxy evolution even in the local volume. |
Calibration of colour gradient bias in shear measurement using
HST/CANDELS data: Accurate shape measurements are essential to infer cosmological parameters
from large area weak gravitational lensing studies. The compact
diffraction-limited point-spread function (PSF) in space-based observations is
greatly beneficial, but its chromaticity for a broad band observation can lead
to new subtle effects that could hitherto be ignored: the PSF of a galaxy is no
longer uniquely defined and spatial variations in the colours of galaxies
result in biases in the inferred lensing signal. Taking Euclid as a reference,
we show that this colourgradient bias (CG bias) can be quantified with high
accuracy using available multi-colour Hubble Space Telescope (HST) data. In
particular we study how noise in the HST observations might impact such
measurements and find this to be negligible. We determine the CG bias using HST
observations in the F606W and F814W filters and observe a correlation with the
colour, in line with expectations, whereas the dependence with redshift is
weak. The biases for individual galaxies are generally well below 1%, which may
be reduced further using morphological information from the Euclid data. Our
results demonstrate that CG bias should not be ignored, but it is possible to
determine its amplitude with sufficient precision, so that it will not
significantly bias the weak lensing measurements using Euclid data. | Emulating the CFHTLenS Weak Lensing data: Cosmological Constraints from
moments and Minkowski functionals: Weak gravitational lensing is a powerful cosmological probe, with
non--Gaussian features potentially containing the majority of the information.
We examine constraints on the parameter triplet $(\Omega_m,w,\sigma_8)$ from
non-Gaussian features of the weak lensing convergence field, including a set of
moments (up to $4^{\rm th}$ order) and Minkowski functionals, using publicly
available data from the 154deg$^2$ CFHTLenS survey. We utilize a suite of
ray--tracing N-body simulations spanning 91 points in $(\Omega_m,w,\sigma_8)$
parameter space, replicating the galaxy sky positions, redshifts and shape
noise in the CFHTLenS catalogs. We then build an emulator that interpolates the
simulated descriptors as a function of $(\Omega_m,w,\sigma_8)$, and use it to
compute the likelihood function and parameter constraints. We employ a
principal component analysis to reduce dimensionality and to help stabilize the
constraints with respect to the number of bins used to construct each
statistic. Using the full set of statistics, we find
$\Sigma_8\equiv\sigma_8(\Omega_m/0.27)^{0.55}=0.75\pm0.04$ (68% C.L.), in
agreement with previous values. We find that constraints on the
$(\Omega_m,\sigma_8)$ doublet from the Minkowski functionals suffer a strong
bias. However, high-order moments break the $(\Omega_m,\sigma_8)$ degeneracy
and provide a tight constraint on these parameters with no apparent bias. The
main contribution comes from quartic moments of derivatives. |
Simulations of isolated dwarf galaxies formed in dark matter halos with
different mass assembly histories: We present high-resolution N-body/hydrodynamics simulations of dwarf galaxies
formed in isolated CDM halos with the same virial mass, Mv~2.5x10^10 Msun at
z=0, in order to (1) study the mass assembly histories (MAHs) of the halo,
stars, and gas components, and (2) explore the effects of the halo MAHs on the
stellar/baryonic assembly of the simulated dwarfs and on their z~0 properties.
Overall, the simulated dwarfs are roughly consistent with observations. Our
main results are: a) The stellar-to-halo mass ratio is ~0.01 and remains
roughly constant since z~1 (the stellar MAHs follow closely the halo MAHs),
with a smaller value at higher z's for those halos that assemble their mass
later. b) The evolution of the galaxy gas fraction, fg, is episodic and higher,
most of the time, than the stellar fraction. When fg decreases (increases), the
gas fraction in the halo typically increases (decreases), showing that the SN
driven outflows play an important role in regulating the gas fractions -and
hence the SFR- of the dwarfs. However, in most cases, an important fraction of
the gas escapes the virial radius, Rv; at z=4 the total baryon fraction inside
Rv is 1.5-2 times smaller than the universal one, while at z=0 is 2-6 times
smaller, with the earlier assembled halos ejecting more gas. c) The SF
histories are episodic with changes in the SFRs of factors 2-10 on average. d)
Although the dwarfs formed in late assembled halos show more extended SF
histories, their z~0 SFRs are still below the ones measured for local isolated
dwarfs. e) The effects of baryons on Mv are such that at almost any time Mv is
10-20% smaller than the corresponding Mv obtained in pure N-body simulations.
Our results suggest that rather than increasing the strength of the SN-driven
outflows, processes that reduce the SF efficiency even more will help to solve
the potential issues faced by the CDM-based simulations of dwarfs. | An 8\% Determination of the Hubble Constant from localized Fast Radio
Bursts: The $\Lambda$CDM model successfully explains the majority of cosmological
observations. However, the $\Lambda$CDM model is challenged by Hubble tension,
a remarkable difference of Hubble constant $H_0$ between measurements from
local probe and the prediction from Planck cosmic microwave background
observations under $ \Lambda$CDM model. So one urgently needs new distance
indicators to test the Hubble tension. Fast radio bursts (FRBs) are
millisecond-duration pulses occurring at cosmological distances, which are
attractive cosmological probes. However, there is a thorny problem that the
dispersion measures (DMs) contributed by host galaxy and the inhomogeneities of
intergalactic medium cannot be exactly determined from observations. Previous
works assuming fixed values for them bring uncontrolled systematic error in
analysis. A reasonable approach is to handle them as probability distributions
extracted from cosmological simulations. Here we report a measurement of ${H_0}
= 64.67^{+5.62}_{-4.66} {\rm \ km \ s^{-1} \ Mpc^{-1}}$ using fourteen
localized FRBs, with an uncertainty of 8.7\% at 68.3 per cent confidence.
Thanks to the high event rate of FRBs and localization capability of radio
telescopes (i.e., Australian Square Kilometre Array Pathfinder and Very Large
Array), future observations of a reasonably sized sample ($\sim$100 localized
FRBs) will provide a new way of measuring $H_0$ with a high precision
($\sim$2.6\%) to test the Hubble tension. |
What do we learn from CMB observations: We give an account, at non-expert and quantitative level, of physics behind
the CMB temperature anisotropy and polarization and their peculiar features. We
discuss, in particular, how cosmological parameters are determined from the CMB
measurements and their combinations with other observations. We emphasize that
CMB is the major source of information on the primordial density perturbations
and, possibly, gravitational waves, and discuss the implication for our
understanding of the extremely early Universe. | The Cosmic Background Imager 2: We describe an upgrade to the Cosmic Background Imager instrument to increase
its surface brightness sensitivity at small angular scales. The upgrade
consisted of replacing the thirteen 0.9-m antennas with 1.4-m antennas
incorporating a novel combination of design features, which provided excellent
sidelobe and spillover performance for low manufacturing cost. Off-the-shelf
spun primaries were used, and the secondary mirrors were oversized and shaped
relative to a standard Cassegrain in order to provide an optimum compromise
between aperture efficiency and low spillover lobes. Low-order distortions in
the primary mirrors were compensated for by custom machining of the secondary
mirrors. The secondaries were supported on a transparent dielectric foam cone
to minimize scattering. The antennas were tested in the complete instrument,
and the beam shape and spillover noise contributions were as expected. We
demonstrate the performance of the telescope and the inter-calibration with the
previous system using observations of the Sunyaev-Zel'dovich effect in the
cluster Abell 1689. The enhanced instrument has been used to study the cosmic
microwave background, the Sunyaev-Zel'dovich effect and diffuse Galactic
emission. |
Planck 2015 results. VI. LFI mapmaking: This paper describes the mapmaking procedure applied to Planck LFI (Low
Frequency Instrument) data. The mapmaking step takes as input the calibrated
timelines and pointing information. The main products are sky maps of $I,Q$,
and $U$ Stokes components. For the first time, we present polarization maps at
LFI frequencies. The mapmaking algorithm is based on a destriping technique,
enhanced with a noise prior. The Galactic region is masked to reduce errors
arising from bandpass mismatch and high signal gradients. We apply horn-uniform
radiometer weights to reduce effects of beam shape mismatch. The algorithm is
the same as used for the 2013 release, apart from small changes in parameter
settings. We validate the procedure through simulations. Special emphasis is
put on the control of systematics, which is particularly important for accurate
polarization analysis. We also produce low-resolution versions of the maps, and
corresponding noise covariance matrices. These serve as input in later analysis
steps and parameter estimation. The noise covariance matrices are validated
through noise Monte Carlo simulations. The residual noise in the map products
is characterized through analysis of half-ring maps, noise covariance matrices,
and simulations. | Spectral Distortion of the CMB by the Cumulative CO Emission from
Galaxies throughout Cosmic History: We show that the cumulative CO emission from galaxies throughout cosmic
history distorts the spectrum of the cosmic microwave background (CMB) at a
level that is well above the detection limit of future instruments, such as the
Primordial Inflation Explorer (PIXIE). The modeled CO signal has a prominent
bump in the frequency interval 100-200 GHz, with a characteristic peak
intensity of ~ 2$\times$10$^{-23}$ W m$^{-2}$ Hz$^{-1}$ sr$^{-1}$. Most of the
CO foreground originates from modest redshifts, z ~ 2-5, and needs to be
efficiently removed for more subtle distortions from the earlier universe to be
detected. |
Interacting dark energy axions in light of the Hubble tension: A current problem within the {\Lambda}CDM framework is the tension between
late and early time measurements of the Hubble parameter today, H0. We
entertain the possibility that dark energy modeled as multiple interacting
axion-like-particle species can alleviate the current Hubble tension. We then
test these parameters against the milder tension between the CMB and large
scale structure (LSS) observations of {\sigma}8 to ensure that these models do
not exacerbate the tension. We find that there exist parameter spaces for
models of two and three axion-like-particles which can potentially alleviate
the Hubble tension as well as the {\sigma}8 tension. | Cosmic reionization of hydrogen and helium: contribution from both
mini-quasars and stars: Observations on the high-redshift galaxies at $z>6$ imply that their ionizing
emissivity is unable to fully reionize the Universe at $z\sim 6$. Either a high
escape fraction of ionizing photons from these galaxies or a large population
of faint galaxies below the detection limit are required. However, these
requirements are somewhat in tension with present observations. In this work,
we explored the combined contribution of mini-quasars and stars to the
reionization of cosmic hydrogen and helium. Our model is roughly consistent
with: (1) the low escape fractions of ionizing photons from the observed
galaxies, (2) the optical depth of Cosmic Microwave Background (CMB) measured
by the WMAP-7, and (3) the redshift of the end of hydrogen and helium
reionization at $z\approx 6$ and $z\approx 3$, respectively. Neither an
extremely high escape fraction nor a large population of fainter galaxies is
required in this scenario. In our most optimistic model, more than $\sim20\%$
of the cosmic helium is reionized by $z\sim6$, and the ionized fraction of
cosmic helium rapidly climbs to more than $50\%$ by $z\sim5$. These results may
imply that better measurements of helium reionization, especially at high
redshifts, could be helpful in constraining the growth of intermediate-mass
black holes (IMBHs) in the early Universe, which would shed some light on the
puzzles concerning the formation of supermassive black holes (SMBHs). |
Is Quasar Optical Variability a Damped Random Walk?: The damped random walk (DRW) model is increasingly used to model the
variability in quasar optical light curves, but it is still uncertain whether
the DRW model provides an adequate description of quasar optical variability
across all time scales. Using a sample of OGLE quasar light curves, we consider
four modifications to the DRW model by introducing additional parameters into
the covariance function to search for deviations from the DRW model on both
short and long time scales. We find good agreement with the DRW model on time
scales that are well sampled by the data (from a month to a few years),
possibly with some intrinsic scatter in the additional parameters, but this
conclusion depends on the statistical test employed and is sensitive to whether
the estimates of the photometric errors are correct to within ~10%. On very
short time scales (below a few months), we see some evidence of the existence
of a cutoff below which the correlation is stronger than the DRW model, echoing
the recent finding of Mushotzky et al. (2011) using quasar light curves from
Kepler. On very long time scales (> a few years), the light curves do not
constrain models well, but are consistent with the DRW model. | Parametrizing the transition to the phantom epoch with Supernovae Ia and
Standard Rulers: The reconstruction of a (non)canonical scalar field Lagrangian from the dark
energy Equation of State (EoS) parameter is studied, where it is shown that any
EoS parametrization can be well reconstructed in terms of scalar fields.
Several examples of EoS parameters are studied and the particular scalar field
Lagrangian is reconstructed. Then, we propose some new parametrizations that
may present a (fast) transition to a phantom dark energy EoS (where
$w_{DE}<-1$) and the scalar field Lagrangian is also reconstructed numerically.
Furthermore, the properties of these parametrizations of the dark energy EoS
are studied by using supernovae Ia data (HST Cluster Supernova Survey) combined
with Standard Ruler datasets [Cosmic Microwave Background (CMB) and Baryon
Acoustic Oscillations (BAO)] and its comparison with the $\Lambda$CDM model is
analyzed. Then, the best fit of the models is obtained, which provides some
information about whether a phantom transition may be supported by the
observations. In this regard, the crossing of the phantom barrier is allowed
statistically but the occurrence of a future singularity seems unlikely. |
The Probability Distribution of Astrophysical Gravitational-Wave
Background Fluctuations: The coalescence of compact binary stars is expected to produce a stochastic
background of gravitational waves (GW) observable with future GW detectors.
Such backgrounds are usually characterized by their power spectrum as a
function of frequency. Here, we present a method to calculate the full 1-point
distribution of strain fluctuations. We focus on time series data, but our
approach generalizes to the frequency domain. We illustrate how this
probability distribution can be evaluated numerically. In addition, we derive
accurate analytical asymptotic expressions for the large strain tail, which
demonstrate that it is dominated by the nearest source. As an application, we
calculate the distribution of strain fluctuations for the astrophysical GW
background produced by binary mergers of compact stars in the Universe, and the
distribution of the observed confusion background obtained upon subtracting
bright, resolved sources from the signal. We quantify the extent to which they
deviate from a Gaussian distribution. Our approach could be useful for the
spectral shape reconstruction of stochastic GW backgrounds. | Shocked Superwinds from the z~2 Clumpy Star-forming Galaxy, ZC406690: We have obtained high-resolution data of the z 2 ring-like, clumpy
star-forming galaxy (SFG) ZC406690 using the VLT/SINFONI with AO (in K-band)
and in seeing-limited mode (in H- and J-band). Our data includes all of the
main strong optical emission lines: [OII], [OIII], Ha, Hb, [NII] and [SII]. We
find broad, blueshifted Ha and [OIII] emission line wings in the spectra of the
galaxy's massive, star-forming clumps (sigma \sim 85 km s^-1) and even broader
wings (up to 70% of the total Ha flux, with sigma \sim 290 km s^-1) in regions
spatially offset from the clumps by \sim 2 kpc. The broad emission likely
originates from large-scale outflows with mass outflow rates from individual
clumps that are 1-8x the SFR of the clumps. Based on emission line ratio
diagnostics ([NII]/Ha and [SII]/Ha) and photoionization and shock models, we
find that the emission from the clumps is due to a combination of
photoionization from the star-forming regions and shocks generated in the
outflowing component, with 5-30% of the emission deriving from shocks. In terms
of the ionization parameter (6x10^7-10^8 cm/s, based on both the SFR and the
O32 ratio), density (local electron densities of 300-1800 cm^-3 in and around
the clumps, and ionized gas column densities of 1200-8000 Msol/pc^2), and SFR
(10-40 Msol/yr), these clumps more closely resemble nuclear starburst regions
of local ULIRGs and dwarf irregulars than HII regions in local galaxies.
However, the star-forming clumps are not located in the nucleus as in local
starburst galaxies but instead are situated in a ring several kpc from the
center of their high-redshift host galaxy, and have an overall disk-like
morphology. The two brightest clumps are quite different in terms of their
internal properties, energetics and relative ages, and thus we are given a
glimpse at two different stages in the formation and evolution of rapidly
star-forming giant clumps at high-z. |
Interferences in the Stochastic Gravitational Wave Background: Although the expansion of the Universe explicitly breaks the time-translation
symmetry, cosmological predictions for the stochastic gravitational wave
background (SGWB) are usually derived under the so-called stationary
hypothesis. By dropping this assumption and keeping track of the time
dependence of gravitational waves at all length scales, we derive the expected
unequal-time (and equal-time) waveform of the SGWB generated by scaling
sources, such as cosmic defects. For extinct and smooth enough sources, we show
that all observable quantities are uniquely and analytically determined by the
holomorphic Fourier transform of the anisotropic stress correlator. Both the
strain power spectrum and the energy density parameter are shown to have an
oscillatory fine structure, they significantly differ on large scales while
running in phase opposition at large wavenumbers $k$. We then discuss scaling
sources that are never extinct nor smooth and which generate a singular Fourier
transform of the anisotropic stress correlator. For these, we find the
appearance of interferences on top of the above-mentioned fine-structure as
well as atypical behaviour at small scales. For instance, we expect the
rescaled strain power spectrum $k^2 \mathcal{P}_h$ generated by long cosmic
strings in the matter era to oscillate around a scale invariant plateau. These
singular sources are also shown to produce orders of magnitude difference
between the rescaled strain spectra and the energy density parameter suggesting
that only the former should be used for making reliable observable predictions.
Finally, we discuss how measuring such a fine structure in the SGWB could
disambiguate the possible cosmological sources. | Chandra follow up of the Hectospec Cluster Survey: Comparison of Caustic
and Hydrostatic Masses and Constraints on the Hydrostatic Bias: Clusters of galaxies are powerful probes with which to study cosmology and
astrophysics. However, for many applications an accurate measurement of a
cluster's mass is essential. A systematic underestimate of hydrostatic masses
from X-ray observations (the so-called hydrostatic bias) may be responsible for
tension between the results of different cosmological measurements. We compare
X-ray hydrostatic masses with masses estimated using the caustic method (based
on galaxy velocities) in order to explore the systematic uncertainties of both
methods and place new constraints on the level of hydrostatic bias. Hydrostatic
and caustic mass profiles were determined independently for a sample of 44
clusters based on Chandra observations of clusters from the Hectospec Cluster
Survey. This is the largest systematic comparison of its kind. Masses were
compared at a standardised radius ($R_{500}$) using a model that includes
possible bias and scatter in both mass estimates. The systematics affecting
both mass determination methods were explored in detail. The hydrostatic masses
were found to be systematically higher than caustic masses on average, and we
found evidence that the caustic method increasingly underestimates the mass
when fewer galaxies are used to measure the caustics. We limit our analysis to
the 14 clusters with the best-sampled caustics where this bias is minimised
($\ge210$ galaxies), and find that the average ratio of hydrostatic to caustic
mass at $R_{500}$ is $M_X/M_C=1.12^{+0.11}_{-0.10}$. We interpret this result
as a constraint on the level of hydrostatic bias, favouring small or zero
levels of hydrostatic bias (less than $20\%$ at the $3\sigma$ level). However,
we find systematic uncertainties associated with both mass estimation methods
remain at the $10-15\%$ level, which would permit significantly larger levels
of hydrostatic bias. |
Cross-correlation of Planck CMB lensing with DESI galaxy groups: We measure the cross-correlation between galaxy groups constructed from DESI
Legacy Imaging Survey DR8 and \emph{Planck} CMB lensing, over overlapping sky
area of 16876 $\rm deg^2$. The detections are significant and consistent with
the expected signal of the large-scale structure of the universe, over group
samples of various redshift, mass, richness $N_{\rm g}$ and over various scale
cuts. The overall S/N is 40 for a conservative sample with $N_{\rm g}\geq 5$,
and increases to $50$ for the sample with $N_{\rm g}\geq 2$. Adopting the
\emph{Planck} 2018 cosmology, we constrain the density bias of groups with
$N_{\rm g}\geq 5$ as $b_{\rm g}=1.31\pm 0.10$, $2.22\pm 0.10$, $3.52\pm 0.20$
at $0.1<z\leq 0.33$, $0.33<z\leq 0.67$, $0.67<z\leq1$ respectively. The group
catalog provides the estimation of group halo mass and therefore allows us to
detect the dependence of bias on group mass with high significance. It also
allows us to compare the measured bias with the theoretically predicted one
using the estimated group mass. We find excellent agreement for the two high
redshift bins. However, it is lower than the theory by $\sim 3\sigma$ for the
lowest redshift bin. Another interesting finding is the significant impact of
the thermal Sunyaev Zel'dovich (tSZ). It contaminates the galaxy group-CMB
lensing cross-correlation at $\sim 30\%$ level, and must be deprojected first
in CMB lensing reconstruction. | Properties of Dark Matter Haloes and their Correlations: the Lesson from
Principal Component Analysis: We study the correlations between the structural parameters of dark matter
haloes using Principal Component Analysis (PCA). We consider a set of eight
parameters, six of which are commonly used to characterize dark matter halo
properties: mass, concentration, spin, shape, overdensity, and the angle
($\Phi_L$) between the major axis and the angular momentum vector. Two
additional parameters ($\x_{off}$ and $\rho_{rms}$) are used to describe the
degree of `relaxedness' of the halo. We find that we can account for much of
the variance of these properties with halo mass and concentration, on the one
hand, and halo relaxedness on the other. Nonetheless, three principle
components are usually required to account for most of the variance. We argue
that halo mass is not as dominant as expected, which is a challenge for halo
occupation models and semi-analytic models that assume that mass determines
other halo (and galaxy) properties. In addition, we find that the angle
$\Phi_L$ is not significantly correlated with other halo parameters, which may
present a difficulty for models in which galaxy disks are oriented in haloes in
a particular way. Finally, at fixed mass, we find that a halo's environment
(quantified by the large-scale overdensity) is relatively unimportant. |
Using clusters in SZE + x-ray surveys as an ensemble of rulers to
constrain cosmology: Ongoing and upcoming surveys in x-rays and SZE are expected to jointly detect
many clusters due to the large overlap in sky coverage. We show that, these
clusters can be used as an ensemble of rulers to estimate the angular diameter
distance, d_A(z). This comes at no extra observational cost, as these clusters
form a subset of a much larger sample, assembled to build cluster number counts
dn/dz. On using this d_A(z), the dark energy constraints can be improved by
factors of 1.5 - 4, over those from just dn/dn. Even in the presence of a mass
follow-up of 100 clusters (done for mass calibration), the dark energy
constraints can be further tightened by factors of 2 - 3 . Adding d_A(z) from
clusters is similar to adding d_L(z), from the SNe observations; for eg., dn/dn
(from ACT/SPT) plus d_A(z) is comparable to dn/dz plus d_L(z) in constraining
Omega_m and sigma_8. | Observational strategies for varying constants with ESPRESSO and
ELT-HIRES: The observational evidence for the acceleration of the universe demonstrates
that canonical theories of cosmology and particle physics are incomplete, if
not incorrect. Several few-sigma hints of new physics, discussed in this
workshop, are arguably smoke without a smoking gun. Forthcoming high-resolution
ultra-stable spectrographs will play a crucial role in this quest for new
physics, by enabling a new generation of precision consistency tests. Here we
focus on astrophysical tests of the stability of nature's fundamental
couplings, discussing the improvements that can be expected with ESPRESSO and
ELT-HIRES and their impact on fundamental cosmology. We find that the current
E-ELT configuration has the potential to constrain dark energy more strongly
than standard surveys with thousands of low-redshift ($z<2$) supernovas. |
Effects of type Ia supernovae absolute magnitude priors on the Hubble
constant value: We systematically explore the influence of the prior of the peak absolute
magnitude ($M$) of type Ia supernovae (SNe Ia) on the measurement of the Hubble
constant ($H_0$) from SNe Ia observations. We consider five different
data-motivated $M$ priors, representing varying levels of dispersion, and
assume the spatially-flat $\Lambda$CDM cosmological model. Different $M$ priors
lead to relative changes in the mean values of $H_0$ from 2% to 7%. Loose
priors on $M$ yield $H_0$ estimates consistent with both the Planck 2018 result
and the SH0ES result at the 68% confidence level. We also examine the potential
impact of peculiar velocity subtraction on the value of $H_0$, and show that it
is insignificant for the SNe Ia observations with redshift $z > 0.01$ used in
our analyses. We also repeat the analysis in the cosmography model and find
very similar results. This suggests that our results are robust and model
independent. | Analytic formula for the dynamics around inflation end and implications
on primordial gravitational waves: We argue that primordial gravitational waves have a spectral break and its
information is quite useful for exploring the early universe. Indeed, such a
spectral break can be a fingerprint of the end of inflation, and the amplitude
and the frequency at the break can tell us the energy scale of inflation and
the reheating temperature simultaneously. In order to investigate the spectral
break, we give an analytic formula for evolution of the Hubble parameter around
the end of inflation where the slow roll approximation breaks down. We also
evaluate the spectrum of primordial gravitational waves around the break point
semi-analytically using the analytic formula for the inflation dynamics. |
Thermal Tachyacoustic Cosmology: An intriguing possibility that can address pathologies in both early universe
cosmology (i.e. the horizon problem) and quantum gravity (i.e.
non-renormalizability), is that particles at very high energies and/or
temperatures could propagate arbitrarily fast. A concrete realization of this
possibility for the early universe is the Tachyacoustic (or Speedy Sound)
cosmology, which could also produce a scale-invariant spectrum for scalar
cosmological perturbations. Here, we study Thermal Tachyacoustic Cosmology
(TTC), i.e. this scenario with thermal initial conditions. We find that a phase
transition in the early universe, around the scale of Grand Unified Theories
(GUT scale; $T\sim 10^{15}$ GeV), during which the speed of sound drops by $25$
orders of magnitude within a Hubble time, can fit current CMB observations. We
further discuss how production of primordial black holes constrains the
cosmological acoustic history, while coupling TTC to Horava-Lifshitz gravity
leads to a lower limit on the amplitude of tensor modes ($r \gtrsim 10^{-3}$),
that are detectable by CMBPol (and might have already been seen by the
BICEP-Keck collaboration). | The linearization method and new classes of exact solutions in cosmology: We develop a method for constructing exact cosmological solutions of the
Einstein equations based on representing them as a second-order linear
differential equation. In particular, the method allows using an arbitrary
known solution to construct a more general solution parameterized by a set of
3\textit{N} constants, where \textit{N} is an arbitrary natural number. The
large number of free parameters may prove useful for constructing a theoretical
model that agrees satisfactorily with the results of astronomical observations.
Cosmological solutions on the Randall-Sundrum brane have similar properties. We
show that three-parameter solutions in the general case already exhibit
inflationary regimes. In contrast to previously studied two-parameter
solutions, these three-parameter solutions can describe an exit from inflation
without a fine tuning of the parameters and also several consecutive
inflationary regimes. |
The central surface density of "dark halos" predicted by MOND: Prompted by the recent claim, by Donato et al., of a quasi-universal central
surface density of galaxy dark matter halos, I look at what MOND has to say on
the subject. MOND, indeed, predicts a quasi-universal value of this quantity
for objects of all masses and of any internal structure, provided they are
mostly in the Newtonian regime; i.e., that their mean acceleration is at or
above a0. The predicted value is qSm, with Sm= a0/2 pi G= 138 solar masses per
square parsec for the nominal value of a0, and q a constant of order 1 that
depends only on the form of the MOND interpolating function. This gives in the
above units log(Sm)=2.14, which is consistent with that found by Doanato et al.
of 2.15+-0.2. MOND predicts, on the other hand, that this quasi-universal value
is not shared by objects with much lower mean accelerations. It permits halo
central surface densities that are arbitrarily small, if the mean acceleration
inside the object is small enough. However, for such low-surface-density
objects, MOND predicts a halo surface density that scales as the square root of
the baryonic one, and so the range of the former is much compressed relative to
the latter. This explains, in part, the finding of Donato et al. that the
universal value applies to low acceleration systems as well. Looking at
literature results for a number of the lowest surface-density disk galaxies
with rotation-curve analysis, I find that, indeed, their halo surface densities
are systematically lower then the above "universal" value. The prediction of Sm
as an upper limit, and accumulation value, of halo central surface densities,
pertains, unlike most other MOND predictions, to a pure "halo" property, not to
a relation between baryonic and "dark matter" properties. | Precious Metals in SDSS Quasar Spectra I: Tracking the Evolution of
Strong, 1.5 < z < 4.5 CIV Absorbers with Thousands of Systems: We have vastly increased the CIV statistics at intermediate redshift by
surveying the thousands of quasars in the Sloan Digital Sky Survey Data-Release
7. We visually verified over 16,000 CIV systems with 1.46 < z < 4.55---a sample
size that renders Poisson error negligible. Detailed Monte Carlo simulations
show we are approximately 50% complete down to rest equivalent widths W_r ~ 0.6
\AA. We analyzed the sample as a whole and in ten small redshift bins with
approximately 1500 doublets each. The equivalent width frequency distributions
f(W_r) were well modeled by an exponential, with little evolution in shape. In
contrast with previous studies that modeled the frequency distribution as a
single power law, the fitted exponential gives a finite mass density for the
CIV ions. The co-moving line density dN_CIV/dX evolved smoothly with redshift,
increasing by a factor of 2.37+/-0.09 from z = 4.55 to 1.96, then plateauing at
dN_CIV/dX ~ 0.34 for z = 1.96 to 1.46. Comparing our SDSS sample with z < 1
(ultraviolet) and z > 5 (infrared) surveys, we see an approximately 10-fold
increase in dN_CIV/dX over z ~ 6 --> 0, for W_r >= 0.6 \AA. This suggests a
monotonic and significant increase in the enrichment of gas outside galaxies
over the 12 Gyr lifetime of the universe. |
Quasar Accretion Disks Are Strongly Inhomogeneous: Active galactic nuclei (AGN) have been observed to vary stochastically with
10-20 rms amplitudes over a range of optical wavelengths where the emission
arises in an accretion disk. Since the accretion disk is unlikely to vary
coherently, local fluctuations may be significantly larger than the global rms
variability. We investigate toy models of quasar accretion disks consisting of
a number of regions, n, whose temperatures vary independently with an amplitude
of \sigma_T in dex. Models with large fluctuations (\sigma_T=0.35-0.50) in
100-1000 independently fluctuating zones for every factor of two in radius can
explain the observed discrepancy between thin accretion disk sizes inferred
from microlensing events and optical luminosity while matching the observed
optical variability. For the same range of \sigma_T, inhomogeneous disk spectra
provide excellent fits to the HST quasar composite without invoking global
Compton scattering atmospheres to explain the high levels of observed UV
emission. Simulated microlensing light curves for the Einstein cross from our
time-varying toy models are well fit using a time-steady power-law temperature
disk, and produce magnification light curves that are consistent with current
microlensing observations. Deviations due to the inhomogeneous, time-dependent
disk structure should occur above the 1% level in the light curves, detectable
in future microlensing observations with millimag sensitivity. | On the Disappearance of the Broad-Line Region in Low-Luminosity Agns: The disk-wind scenario for the broad-line region (BLR) and toroidal
obscuration in active galactic nuclei predicts the disappearance of the BLR at
low luminosities. In accordance with the model predictions, data from a nearly
complete sample of nearby AGNs show that the BLR disappears at luminosities
lower than $5\times\E{39} (M/10^7\Mo)^{2/3}$ erg s$^{-1)$, where $M$ is the
black hole mass. The radiative efficiency of accretion onto the black hole is
$\la \E{-3}$ for these sources, indicating that their accretion is
advection-dominated. |
The angular momentum of cold dark matter haloes with and without baryons: We investigate the magnitude and internal alignment of the angular momentum
of cold dark matter haloes in simulations with and without baryons. We analyse
the cumulative angular momentum profiles of hundreds of thousands of haloes in
the Millennium simulation and in a smaller, but higher resolution, simulation,
in total spanning 5 orders of magnitude in mass. For haloes of a given mass,
the median specific angular momentum increases as j(<r) proportional to r. The
direction of the vector varies considerably with radius: the median angle
between the inner (< 0.25 Rvir) and total (< Rvir) angular momentum vectors is
about 25degr. To investigate how baryons affect halo spin, we use another high
resolution simulation, which includes gas cooling, star formation and feedback.
This simulation produces a sample of galaxies with a realistic distribution of
disc-to-total ratios. The formation of the galaxy spins up the dark matter
within 0.1 Rvir such that the specific halo angular momentum increases by
approx 50% in the median. The dark matter angular momentum becomes better
aligned, but there remains a broad distribution of (mis-)alignments between the
halo and the central galaxy, with a median angle between their angular momenta
of ~ 30degr. Galaxies have a range of orientations relative to the shape of the
halo: half of them have their minor axes misaligned by more than 45degr.
Finally, we align a sample of haloes according to the orientation of their
galaxies and stack the projected mass distributions. Although the individual
haloes are aspherical, galaxy--halo misalignments produce a stacked mass
distribution that is indistinguishable from circular. If the misalignment found
in our simulations is realistic, it will be extremely difficult for weak
lensing studies to measure the shape of dark haloes using this technique. | Classifying Radio Emitters from the Sloan Digital Sky Survey:
Spectroscopy and Diagnostics: A cross-correlation of the SDSS DR7 with the FIRST radio survey makes it
possible to conduct a joined multiwavelength statistical study of radio-optical
galaxy properties on a very large number of sources. Our goal is to improve the
study of the combined radio-optical data by investigating if there is a
correlation between the radio luminosity at 20 cm over the luminosity of the
optical H\alpha line (L[20 cm]/L[H\alpha]) and line excitation ratios, where
the latter provide the spectroscopic classification in Seyferts, low-ionization
nuclear emission-line regions (LINERs) and star-forming galaxies. We found that
the percentage of detected AGNs (Seyferts and LINERs) or composites is much
higher in the optical-radio sample than in the optical sample alone. There is a
progressive shift of the sources towards the AGN region of the diagram with
increasing L[20 cm]/L[H\alpha], with an indication for a different behavior for
LINERs and Seyferts. The classification appears to slightly depend on the
redshift. A comparison with photoionization and shock models shows that the
large fraction of LINERs identified in our study have emission lines that may
be explained by shocks. The [NII]/H\alpha vs. equivalent width of the H\alpha
line (WHAN) diagram confirms the LINER classification for most of those that
have been identified with the traditional diagnostic diagrams. The correlation
between L[20 cm]/L[H\alpha] and optical emission line ratios suggests the
nuclear origin of the emission from the most powerful radio-galaxies. |
Analysis of $\sim10^6$ spiral galaxies from four telescopes shows
large-scale patterns of asymmetry in galaxy spin directions: The ability to collect unprecedented amounts of astronomical data has enabled
the studying scientific questions that were impractical to study in the
pre-information era. This study uses large datasets collected by four different
robotic telescopes to profile the large-scale distribution of the spin
directions of spiral galaxies. These datasets cover the Northern and Southern
hemispheres, in addition to data acquired from space by the Hubble Space
Telescope. The data were annotated automatically by a fully symmetric
algorithm, as well as manually through a long labor-intensive process, leading
to a dataset of nearly $10^6$ galaxies. The data shows possible patterns of
asymmetric distribution of the spin directions, and the patterns agree between
the different telescopes. The profiles also agree when using automatic or
manual annotation of the galaxies, showing very similar large-scale patterns.
Combining all data from all telescopes allows the most comprehensive analysis
of its kind to date in terms of both the number of galaxies and the footprint
size. The results show a statistically significant profile that is consistent
across all telescopes. The instruments used in this study are DECam, HST, SDSS,
and Pan-STARRS. The paper also discusses possible sources of bias, and analyzes
the design of previous work that showed different results. Further research
will be required to understand and validate these preliminary observations. | The Expansion of the Universe is Faster than Expected: The present rate of the expansion of our Universe, the Hubble constant, can
be predicted from the cosmological model using measurements of the early
Universe, or more directly measured from the late Universe. But as these
measurements improved, a surprising disagreement between the two appeared. In
2019, a number of independent measurements of the late Universe using different
methods and data provided consistent results making the discrepancy with the
early Universe predictions increasingly hard to ignore. We review key advances
realized by 2019:
-- The local or late Universe measurement of the Hubble constant improved
from 10% uncertainty twenty years ago to under 2% by the end of 2019.
-- In 2019, multiple independent teams presented measurements with different
methods and different calibrations to produce consistent results.
-- These late Universe estimations disagree at 4$\sigma$ to 6$\sigma$ with
predictions made from the Cosmic Microwave Background in conjunction with the
standard cosmological model, a disagreement that is hard to explain or ignore. |
Explaining two circumnuclear star forming rings in NGC5248: The distribution of gas in the central kiloparsec of a galaxy has a
dynamically rapid evolution. Nonaxisymmetries in the gravitational potential of
the galactic disk, such as a large scale stellar bar or spiral, can lead to
significant radial motion of gaseous material from larger radii to the central
region. The large influx of gas and the subsequent star formation keep the
central region constantly changing. However, the ability of gas to reach the
nucleus proper to fuel an AGN phase is not guaranteed. Gas inflow can be halted
at a circumnuclear star forming ring several hundred parsec away. The nearby
galaxy NGC5248 is especially interesting in this sense since it is said to host
2 circumnuclear star forming rings at 100pc and 370pc from its quiescent
nucleus. Here we present new subarcsecond PdBI+30m CO(2-1) emission line
observations of the central region. For the first time the molecular gas
distribution at the smallest stellar ring is resolved into a gas ring,
consistent with the presence of a quiescent nucleus. However, the molecular gas
shows no ring structure at the larger ring. We combine analyses of the gaseous
and stellar content in the central kiloparsec of this galaxy to understand the
gas distribution and dynamics of this star forming central region. We discuss
the probability of two scenarios leading to the current observations, given our
full understanding of this system, and discuss whether there are really two
circumnuclear star forming rings in this galaxy. | Probing the nature of dark energy through galaxy redshift surveys with
radio telescopes: Galaxy redshift surveys using optical telescopes have, in combination with
other cosmological probes, enabled precision measurements of the nature of dark
energy. We show that radio telescopes are rapidly becoming competitive with
optical facilities in spectroscopic surveys of large numbers of galaxies. Two
breakthroughs are driving this change. Firstly, individual radio telescopes are
more efficient at mapping the sky thanks to the large field-of-view of new
phased-array feeds. Secondly, ever more dishes can be correlated in a
cost-effective manner with rapid increases in computing power. The next decade
will see the coming of age of the 21cm radio wavelength as a cosmological probe
as first the Pathfinders then, ultimately, the Square Kilometre Array is
constructed. The latter will determine precise 3D positions for a billion
galaxies, mapping the distribution of matter in the Universe over the last 12
billion years. This radio telescope will be able to constrain the equation of
state of dark energy, and its potential evolution, to a precision rivalling
that of future optical facilities such as DESI and Euclid. |
Projected Cosmological Constraints from Strongly Lensed Supernovae with
the Roman Space Telescope: One of the primary mission objectives for the Roman Space Telescope is to
investigate the nature of dark energy with a variety of methods. Observations
of Type Ia supernovae (SNIa) will be one of the principal anchors of the Roman
cosmology program, through traditional luminosity distance measurements. This
SNIa cosmology program can provide another valuable cosmological probe, without
altering the mission strategy: time delay cosmography with gravitationally
lensed SN. In this work, we forecast lensed SN cosmology constraints with the
Roman Space Telescope, while providing useful tools for future work. Using
anticipated characteristics of the Roman SNIa survey, we have constructed mock
catalogs of expected resolved lensing systems, as well as strongly lensed Type
Ia and core-collapse (CC) SN light curves, including microlensing effects. We
predict Roman will find ~11 lensed SNIa and ~20 CCSN, dependent on the survey
strategy. Next, we estimate the time delay precision obtainable with Roman (Ia:
~2 days, CC: ~3 days), and use a Fisher matrix analysis to derive projected
constraints on $H_0$,$\Omega_m$, and the dark energy Equation of State (EOS),
$w$, for each SNIa survey strategy. A strategy optimized for high-redshift SNIa
discovery is preferred when considering the constraints possible from both SNIa
and lensed SN cosmology, also delivering ~1.5 times more lensed SN than other
proposed survey strategies. | GAMA/H-ATLAS: The ultraviolet spectral slope and obscuration in galaxies: We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) and
Herschel ATLAS (H-ATLAS) surveys to compare the relationship between various
dust obscuration measures in galaxies. We explore the connections between the
ultraviolet (UV) spectral slope, $\beta$, the Balmer decrement, and the far
infrared (IR) to $150\,$nm far ultraviolet (FUV) luminosity ratio. We explore
trends with galaxy mass, star formation rate (SFR) and redshift in order to
identify possible systematics in these various measures. We reiterate the
finding of other authors that there is a large scatter between the Balmer
decrement and the $\beta$ parameter, and that $\beta$ may be poorly constrained
when derived from only two broad passbands in the UV. We also emphasise that
FUV derived SFRs, corrected for dust obscuration using $\beta$, will be
overestimated unless a modified relation between $\beta$ and the attenuation
factor is used. Even in the optimum case, the resulting SFRs have a significant
scatter, well over an order of magnitude. While there is a stronger correlation
between the IR to FUV luminosity ratio and $\beta$ parameter than with the
Balmer decrement, neither of these correlations are particularly tight, and
dust corrections based on $\beta$ for high redshift galaxy SFRs must be treated
with caution. We conclude with a description of the extent to which the
different obscuration measures are consistent with each other as well as the
effects of including other galactic properties on these correlations. |
X-ray Signatures of Circumnuclear Gas in AGN: X-ray spectra of AGN are complex. X-ray absorption and emission features
trace gas covering a wide range of column densities and ionization states. High
resolution spectra show the absorbing gas to be outflowing, perhaps in the form
of an accretion disk wind. The absorbing complex shapes the form of the X-ray
spectrum while X-ray reverberation and absorption changes explain the spectral
and timing behaviour of AGN. We discuss recent progress, highlighting some new
results and reviewing the implications that can be drawn from the data. | Prospects for kSZ$^2$-Galaxy Cross-Correlations during Reionization: We explore a new approach for extracting reionization-era contributions to
the kinetic Sunyaev-Zel'dovich (kSZ) effect. Our method utilizes the
cross-power spectrum between filtered and squared maps of the cosmic microwave
background (CMB) and photometric galaxy surveys during the Epoch of
Reionization (EoR). This kSZ$^2$-galaxy cross-power spectrum statistic has been
successfully detected at lower redshifts ($z \lesssim 1.5$). Here we extend
this method to $z \gtrsim 6$ as a potential means to extract signatures of
patchy reionization. We model the expected signal across multiple photometric
redshift bins using semi-numeric simulations of the reionization process. In
principle, the cross-correlation statistic robustly extracts reionization-era
contributions to the kSZ signal, while its redshift evolution yields valuable
information regarding the timing of reionization. Specifically, the model
cross-correlation signal near $\ell \sim 1,000$ peaks during the early stages
of the EoR, when about 20% of the volume of the universe is ionized. Detectible
$\ell$ modes mainly reflect squeezed triangle configurations of the related
bispectrum, quantifying correlations between the galaxy overdensity field on
large scales and the smaller-scale kSZ power. We forecast the prospects for
detecting this signal using future wide-field samples of Lyman-break galaxies
from the Roman Space Telescope and next-generation CMB surveys including the
Simons Observatory, CMB-S4, and CMB-HD. We find that a roughly 13$\sigma$
detection is possible for CMB-HD and Roman after summing over all $\ell$ modes.
We discuss the possibilities for improving this approach and related
statistics, with the aim of moving beyond simple detections to measure the
scale and redshift dependence of the cross-correlation signals. |
The Young and Bright Type Ia Supernova ASASSN-14lp: Discovery,
Early-Time Observations, First-Light Time, Distance to NGC 4666, and
Progenitor Constraints: On 2014 Dec. 9.61, the All-Sky Automated Survey for SuperNovae (ASAS-SN or
"Assassin") discovered ASASSN-14lp just $\sim2$ days after first light using a
global array of 14-cm diameter telescopes. ASASSN-14lp went on to become a
bright supernova ($V = 11.94$ mag), second only to SN 2014J for the year. We
present prediscovery photometry (with a detection less than a day after first
light) and ultraviolet through near-infrared photometric and spectroscopic data
covering the rise and fall of ASASSN-14lp for more than 100 days. We find that
ASASSN-14lp had a broad light curve ($\Delta m_{15}(B) = 0.80 \pm 0.05$), a
$B$-band maximum at $2457015.82 \pm 0.03$, a rise time of $16.94^{+ 0.11 }_{-
0.10 }$ days, and moderate host--galaxy extinction ($E(B-V)_{\textrm{host}} =
0.33 \pm 0.06$). Using ASASSN-14lp we derive a distance modulus for NGC 4666 of
$\mu = 30.8 \pm 0.2$ corresponding to a distance of $14.7 \pm 1.5$ Mpc.
However, adding ASASSN-14lp to the calibrating sample of Type Ia supernovae
still requires an independent distance to the host galaxy. Finally, using our
early-time photometric and spectroscopic observations, we rule out red giant
secondaries and, assuming a favorable viewing angle and explosion time, any
non-degenerate companion larger than $0.34 R_{\textrm{sun}}$. | Galactic Winds in Cosmological Simulations of the Circumgalactic Medium: (Abridged) We explore new observationally-constrained sub-resolution models
of galactic outflows and investigate their impact on the circumgalactic medium
(CGM) over redshifts z = 2 - 4. We perform cosmological hydrodynamic
simulations, including star formation, chemical enrichment, and four cases of
SNe-driven outflows: no wind (NW), an energy-driven constant velocity wind
(CW), a radially varying wind (RVWa) where the outflow velocity has a positive
correlation with galactocentric distance (r), and a RVW with additional
dependence on halo mass (RVWb). Overall, we find that the outflows expel
metal-enriched gas away from galaxies, significantly quench star formation, and
enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy
centers are most sensitive to the choice of the wind model for halo masses
(10^9 - 10^11) M_sun. We infer that the RVWb model is similar to the NW case,
except that it substantially enriches the CGM: the carbon metallicity (Z_C) is
10 times higher in RVWb than in NW at r > R_200; and the warm gas of 10^4 -
10^5 K and delta < 100 is enriched to 50 times higher than in NW. We also find
that the impact of models CW and RVWa are similar, with the following
differences. RVWa causes a greater suppression of star formation rate at z < 5,
and has a higher fraction of low-density (delta < 10), warm-hot (10^4 - 10^6 K)
gas than in CW. Outflows in CW produce a higher and earlier enrichment of some
IGM phases than RVWa. By visual inspection, we note that the RVWa model shows
more pronounced bipolar outflows and galactic disks. We present fitting
formulae for [Z_C-delta] and [Z_C-r], also for the abundance of CIV as a
function of r. We predict observational diagnostics to distinguish between
different outflow scenarios: Z_C of the CGM gas at r = (30 - 300) kpc/h
comoving, and CIV fraction of the inner gas at r < (4 - 5) kpc/h comoving. |
High resolution tomography for galaxy spectroscopic surveys with angular
redshift fluctuations: In the context of next-generation spectroscopic galaxy surveys, new
statistics of the distribution of matter are currently being developed. Among
these, we investigated the angular redshift fluctuations (ARF), which probe the
information contained in the projected redshift distribution of galaxies.
Relying on the Fisher formalism, we show how ARF will provide complementary
cosmological information compared to traditional angular galaxy clustering. We
tested both the standard $\mathrm{\Lambda CDM}$ model and the $\mathrm{wCDM}$
extension. We find that the cosmological and galaxy bias parameters express
different degeneracies when inferred from ARF or from angular galaxy
clustering. As such, combining both observables breaks these degeneracies and
greatly decreases the marginalised uncertainties by a factor of at least two on
most parameters for the $\mathrm{\Lambda CDM}$ and $\mathrm{wCDM}$ models. We
find that the ARF combined with angular galaxy clustering provide a great way
to probe dark energy by increasing the figure of merit of the $w_0$-$w_{\rm a}$
parameter set by a factor of more than ten compared to angular galaxy
clustering alone. Finally, we compared ARF to the CMB lensing constraints on
the galaxy bias parameters. We show that a joint analysis of ARF and angular
galaxy clustering improves constraints by $\sim 40\%$ on galaxy bias compared
to a joint analysis of angular galaxy clustering and CMB lensing. | Evolution of dark matter velocity dispersion: Cosmological perturbation theory for the late Universe dominated by dark
matter is extended beyond the perfect fluid approximation by taking the dark
matter velocity dispersion tensor as an additional field into account. A proper
tensor decomposition of the latter leads to two additional scalar fields, as
well as a vector and a tensor field. Most importantly, the trace of the
velocity dispersion tensor can have a spatially homogeneous and isotropic
expectation value. While it decays at early times, we show that a back-reaction
effect quadratic in perturbations makes it grow strongly at late times. We
compare sterile neutrinos as a candidate for comparatively warm dark matter to
weakly interacting massive particles as a rather cold dark matter candidate and
show that the late time growth of velocity dispersion is stronger for the
latter. Another feature of a non-vanishing velocity dispersion expectation
value is that it destroys the apparent self-consistency of the single-stream
approximation and allows thereby to treat times and scales beyond
shell-crossing. |
Metal Abundance and Kinematical Properties of M81 Globular Cluster
System: In this paper, we presented metal abundance properties of 144 M81 globular
clusters. These globulars consist of the largest globular cluster sample in M81
till now. Our main results are: the distribution of metallicities are bimodal,
with metallicity peaks at [Fe/H]\sim-1.51 and -0.58, and the metal-poor
globular clusters tend to be less spatially concentrated than the metal-rich
ones; the metal-rich globular clusters in M81 do not demonstrate a centrally
concentrated spatial distribution as the metal-rich ones in M31 do; like our
Galaxy and M31, the globular clusters in M81 have a small radial metallicity
gradient. These results are consistent with those obtained based on a small
sample of M81 globular clusters. In addition, this paper showed that there is
evidence that a strong rotation of the M81 globular cluster system around the
minor axis exists, and that rotation is present in the metal-rich globular
cluster subsample, while the metal-poor globular cluster subsample shows no
evidence for rotation. The most significant difference between the rotation of
the metal-rich and metal-poor globular clusters occurs at intermediate
projected galactocentric radii. The results of this paper confirm the
conclusion of Schroder et al. that M81's metal-rich globular clusters at
intermediate projected radii were associated with a thick disk of M81. | Combining spectroscopic and photometric surveys using angular
cross-correlations I: Algorithm and modelling: Weak lensing (WL) clustering is studied using 2D (angular) coordinates, while
redshift space distortions (RSD) and baryon acoustic oscillations (BAO) use 3D
coordinates, which requires a model dependent conversion of angles and
redshifts into comoving distances. This is the first paper of a series, which
explore modelling multi-tracer galaxy clustering (of WL, BAO and RSD), using
only angular (2D) cross-correlations in thin redshift bins. This involves
evaluating many thousands cross-correlations, each a multidimensional integral,
which is computationally demanding. We present a new algorithm that performs
these calculations as matrix operations.
Nearby narrow redshift bins are intrinsically correlated, which can be used
to recover the full (radial) 3D information. We show that the Limber
approximation does not work well for this task. In the exact calculation, both
the clustering amplitude and the RSD effect increase when decreasing the
redshift bin width. For narrow bins, the cross-correlations has a larger BAO
peak than the auto-correlation because smaller scales are filtered out by the
radial redshift separation. Moreover, the BAO peak shows a second (ghost) peak,
shifted to smaller angles. We explore how WL, RSD and BAO contribute to the
cross-correlations as a function of the redshift bin width and present a first
exploration of non-linear effects and signal-to-noise ratio on these
quantities. This illustrates that the new approach to clustering analysis
provides new insights and is potentially viable in practice. |
Cosmology with decaying cosmological constant -- exact solutions and
model testing: We study dynamics of $\Lambda(t)$ cosmological models which are a natural
generalization of the standard cosmological model (the $\Lambda$CDM model). We
consider a class of models: the ones with a prescribed form of
$\Lambda(t)=\Lambda_{\text{bare}}+\frac{\alpha^2}{t^2}$. This type of a
$\Lambda(t)$ parametrization is motivated by different cosmological approaches.
We interpret the model with running Lambda ($\Lambda(t)$) as a special model of
an interacting cosmology with the interaction term $-d\Lambda(t)/dt$ in which
energy transfer is between dark matter and dark energy sectors. For the
$\Lambda(t)$ cosmology with a prescribed form of $\Lambda(t)$ we have found the
exact solution in the form of Bessel functions. Our model shows that fractional
density of dark energy $\Omega_e$ is constant and close to zero during the
early evolution of the universe.
We have also constrained the model parameters for this class of models using
the astronomical data such as SNIa data, BAO, CMB, measurements of $H(z)$ and
the Alcock-Paczy{\'n}ski test. In this context we formulate a simple criterion
of variability of $\Lambda$ with respect to $t$ in terms of variability of the
jerk or sign of estimator $(1-\Omega_{\text{m},0}-\Omega_{\Lambda,0})$. The
case study of our model enable us to find an upper limit $\alpha^2 < 0.012$
($2\sigma$ C.L.) describing the variation from the cosmological constant while
the LCDM model seems to be consistent with various data. | A survey for HI in the distant Universe: the detection of associated
21-cm absorption at z=1.28: We have undertaken a survey for HI 21-cm absorption within the host galaxies
of z ~ 1.2 - 1.5 radio sources, in the search of the cool neutral gas currently
"missing" at z > 1. This deficit is believed to be due to the optical selection
of high redshift objects biasing surveys towards sources of sufficient
ultra-violet luminosity to ionise all of the gas in the surrounding galaxy. In
order to avoid this bias, we have selected objects above blue magnitudes of
B~20, indicating ultra-violet luminosities below the critical value above which
21-cm has never been detected. As a secondary requirement to the radio flux and
faint optical magnitude, we shortlist targets with radio spectra suggestive of
compact sources, in order to maximise the coverage of background emission. From
this, we obtain one detection out of ten sources searched, which at z=1.278 is
the third highest redshift detection of associated 21-cm absorption to date.
Accounting for the spectra compromised by radio frequency interference, as well
as various other possible pitfalls (reliable optical redshifts and turnover
frequencies indicative of compact emission), we estimate a detection rate of
~30%, close to that expected for L_UV < 1e23 W/Hz sources. |
Cosmological constraints without fingers of God: Non-linear redshift-space distortions ("fingers of God") are challenging to
model analytically, a fact that limits the applicability of perturbation theory
in redshift space as compared to real space. We show how this problem can be
mitigated using a new observable, $Q_0$, which can be easily estimated from the
redshift space clustering data and is approximately equal to the real space
power spectrum. The new statistic does not suffer from fingers of God and can
be accurately described with perturbation theory down to $k_{\rm max}\simeq
0.4~h~\text{Mpc}^{-1}$. It can be straightforwardly included in the likelihood
at negligible additional computational cost, and yields noticeable improvements
on cosmological parameters compared to standard power spectrum multipole
analyses. Using both simulations and observational data from the Baryon
Oscillation Spectroscopic Survey, we show that improvements vary from $10\%$ to
$100\%$ depending on the cosmological parameter considered, the galaxy sample
and the survey volume. | The Radial Dependence of Temperature and Iron Abundance: Galaxy Clusters
from z=0.14 to z=0.89: Using archival Chandra and XMM-Newton data on 35 galaxy clusters, we measured
average temperature and metallicity profiles for clusters based separated by
temperature, cooling time, and redshift. Our results show no evidence for
significant changes in the metallicity or temperature profiles with redshift
once these selection effects are taken into account. |
Does accelerating universe indicates Brans-Dicke theory: The evolution of universe in Brans-Dicke (BD) theory is discussed in this
paper.
Considering a parameterized scenario for BD scalar field
$\phi=\phi_{0}a^{\alpha}$ which plays the role of gravitational "constant" $G$,
we apply the Markov Chain Monte Carlo method to investigate a global
constraints on BD theory with a self-interacting potential according to the
current observational data: Union2 dataset of type supernovae Ia (SNIa),
high-redshift Gamma-Ray Bursts (GRBs) data, observational Hubble data (OHD),
the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and
the cosmic microwave background (CMB) data. It is shown that an expanded
universe from deceleration to acceleration is given in this theory, and the
constraint results of dimensionless matter density $\Omega_{0m}$ and parameter
$\alpha$ are, $\Omega_{0m}=0.286^{+0.037+0.050}_{-0.039-0.047}$ and
$\alpha=0.0046^{+0.0149+0.0171}_{-0.0171-0.0206}$ which is consistent with the
result of current experiment exploration, $\mid\alpha\mid \leq 0.132124$. In
addition, we use the geometrical diagnostic method, jerk parameter $j$, to
distinguish the BD theory and cosmological constant model in Einstein's theory
of general relativity. | How Cold is Cold Dark Matter?: If cold dark matter consists of particles, these must be non-interacting and
non-relativistic by definition. In most cold dark matter models however, dark
matter particles inherit a non-vanishing velocity dispersion from interactions
in the early universe, a velocity that redshifts with cosmic expansion but
certainly remains non-zero. In this article, we place model-independent
constraints on the dark matter temperature to mass ratio, whose square root
determines the dark matter velocity dispersion. We only assume that dark matter
particles decoupled kinetically while non-relativistic, when galactic scales
had not entered the horizon yet, and that their momentum distribution has been
Maxwellian since that time. Under these assumptions, using cosmic microwave
background and matter power spectrum observations, we place upper limits on the
temperature to mass ratio of cold dark matter today (away from collapsed
structures). These limits imply that the present cold dark matter velocity
dispersion has to be smaller than 54 m/s. Cold dark matter has to be quite
cold, indeed. |
The Sphericalization of Dark Matter Halos by Galaxy Disks: Cosmological simulations indicate that cold dark matter (CDM) halos should be
triaxial. Verifying observationally this theoretical prediction is, however,
less than straightforward because the assembly of galaxies is expected to
modify the halo shapes and to render them more axisymmetric. We use a suite of
N-body simulations to investigate quantitatively the effect of the growth of a
central disk galaxy on the shape of triaxial dark matter halos. As expected,
the halo responds to the presence of the disk by becoming more spherical. The
net effect depends only weakly on the orientation of the disk relative to the
halo principal axes or the timescale of disk assembly, but strongly on the
overall gravitational importance of the disk. Our results show that exponential
disks whose contribution peaks at less than ~50% of their circular velocity are
unable to modify noticeably the shape of the gravitational potential of their
surrounding halos. Many dwarf and low surface brightness galaxies are expected
to be in this regime, and therefore their detailed kinematics could be used to
probe halo triaxiality, one of the basic predictions of the CDM paradigm. We
argue that the complex disk kinematics of the dwarf galaxy NGC 2976 might be
the reflection of a triaxial halo. Such signatures of halo triaxiality should
be common in galaxies where the luminous component is subdominant. | Transitioning from Stage-III to Stage-IV: Cosmology from
galaxy$\times$CMB lensing and shear$\times$CMB lensing: We examine the cosmological constraining power from two cross-correlation
probes between galaxy and CMB surveys: the cross-correlation of lens galaxy
density with CMB lensing convergence $\langle\delta\kappa\rangle$, and source
galaxy weak lensing shear with CMB lensing convergence
$\langle\gamma\kappa\rangle$. These two cross-correlation probes provide an
independent cross-check of other large-scale structure constraints and are
insensitive to galaxy-only or CMB-only systematic effects. In addition, when
combined with other large-scale structure probes, the cross-correlations can
break degeneracies in cosmological and nuisance parameters, improving both the
precision and robustness of the analysis. In this work, we study how the
constraining power of $\langle\delta\kappa\rangle+\langle\gamma\kappa\rangle$
changes from Stage-III (ongoing) to Stage-IV (future) surveys. Given the
flexibility in selecting the lens galaxy sample, we also explore systematically
the impact on cosmological constraints when we vary the redshift range and
magnitude limit of the lens galaxies using mock galaxy catalogs. We find that
in our setup, the contribution to cosmological constraints from
$\langle\delta\kappa\rangle$ and $\langle\gamma\kappa\rangle$ are comparable in
the Stage-III datasets; but in Stage-IV surveys, the noise in
$\langle\delta\kappa\rangle$ becomes subdominant to cosmic variance, preventing
$\langle\delta\kappa\rangle$ to further improve the constraints. This implies
that to maximize the cosmological constraints from future
$\langle\delta\kappa\rangle+\langle\gamma\kappa\rangle$ analyses, we should
focus more on the requirements on $\langle\gamma\kappa\rangle$ instead of
$\langle\delta\kappa\rangle$. Furthermore, the selection of the lens sample
should be optimized in terms of our ability to characterize its redshift or
galaxy bias instead of its number density. |
Running Hubble constant from the SNe Ia Pantheon sample?: The mismatch between different independent measurements of the expansion rate
of the Universe is known as the Hubble constant ($H_0$) tension, and it is a
serious and pressing problem in cosmology. We investigate this tension
considering the dataset from the Pantheon sample, a collection of 1048 Type Ia
Supernovae (SNe Ia) with a redshift range $0<z<2.26$. We perform a binned
analysis in redshift to study if the $H_0$ tension also occurs in SNe Ia data.
Hence, we build equally populated subsamples in three and four bins, and we
estimate $H_{0}$ in each bin considering the $\Lambda$CDM and $w_{0}w_{a}$CDM
cosmological models. We perform a statistical analysis via a Markov Chain Monte
Carlo (MCMC) method for each bin. We observe that $H_0$ evolves with the
redshift, using a fit function $H_{0}(z)=\tilde{H}_{0} (1+z)^{-\alpha}$ with
two fitting parameters $\alpha$ and $\tilde{H}_{0}$. Our results show a
decreasing behavior of $H_0$ with $\alpha\sim 10^{-2}$ and a consistency with
no evolution between 1.2 $\sigma$ and 2.0 $\sigma$. Considering the $H_0$
tension, we extrapolate $H_{0}(z)$ until the redshift of the last scattering
surface, $z=1100$, obtaining values of $H_0$ consistent in 1 $\sigma$ with the
cosmic microwave background (CMB) measurements by Planck. Finally, we discuss
possible $f(R)$ modified gravity models to explain a running Hubble constant
with the redshift, and we infer the form of the scalar field potential in the
dynamically equivalent Jordan frame. | A new bound on the low reheating temperature with dark matter: We investigate a new bound on the low reheating temperature in a scenario
where the Universe experiences early matter-domination before reheating after
which the standard big bang cosmology begins. In many models of dark matter
(DM), the small scale fluctuations of DM grow during the early
matter-domination era and seed the formation of the ultracompact minihalos
(UCMHs). Using the constraints on the number of UCMHs from gamma-ray
observations, we find a lower bound on the reheating temperature between ${\cal
O}(10)~{\rm MeV} - {\cal O}(100)~{\rm MeV}$ for WIMP dark matter depending on
the nature of DM. A similar bound could be obtained for non-WIMP dark matter by
observing UCMHs gravitationally such as pulsar timing, microlensing and so on
in some future observations. |
Intrinsic alignments of galaxies in the EAGLE and cosmo-OWLS simulations: We report results for the alignments of galaxies in the EAGLE and cosmo-OWLS
simulations as a function of galaxy separation and halo mass. The combination
of these hydro-cosmological simulations enables us to span four orders of
magnitude in halo mass ($10.7<log_{10}(M_{200}/[h^{-1}M_\odot])<15$) and a
large range of separations ($-1<log_{10}(r/[h^{-1}Mpc])< 2$). We focus on two
classes of alignments: the orientations of galaxies with respect to either the
directions to, or the orientations of, surrounding galaxies. We find that the
strength of the alignment is a strongly decreasing function of the distance
between galaxies. The orientation-direction alignment can remain significant up
to ~100 Mpc, for galaxies hosted by the most massive haloes in our simulations.
Galaxies hosted by more massive subhaloes show stronger alignment. At a fixed
halo mass, more aspherical or prolate galaxies exhibit stronger alignments. The
spatial distribution of satellites is anisotropic and significantly aligned
with the major axis of the main host halo. The major axis of satellite
galaxies, when all stars are considered, are preferentially aligned towards the
centre of the main host halo. The predicted projected direction-orientation
alignment, $\epsilon_{g+}(r_{p})$, is in broad agreement with recent
observations when only stars within the typical observable extent of a galaxy
are used to define galaxy orientations. We find that the
orientation-orientation alignment is weaker than the orientation-direction
alignment on all scales. Overall, the strength of galaxy alignments depends
strongly on the subset of stars that are used to measure the orientations of
galaxies and it is always weaker than the alignment of the dark matter haloes.
Thus, alignment models that use halo orientation as a direct proxy for galaxy
orientation will overestimate the impact of intrinsic alignments on weak
lensing analyses. | PACS and SPIRE photometer maps of M33: First results of the Herschel M33
extended survey (HERM33ES): Within the framework of the HERM33ES key project, we are studying the star
forming interstellar medium in the nearby, metal-poor spiral galaxy M33,
exploiting the high resolution and sensitivity of Herschel. We use PACS and
SPIRE maps at 100, 160, 250, 350, and 500 micron wavelength, to study the
variation of the spectral energy distributions (SEDs) with galacto-centric
distance. Detailed SED modeling is performed using azimuthally averaged fluxes
in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance.
Simple isothermal and two-component grey body models, with fixed dust
emissivity index, are fitted to the SEDs between 24 and 500 micron using also
MIPS/Spitzer data, to derive first estimates of the dust physical conditions.
The far-infrared and submillimeter maps reveal the branched, knotted spiral
structure of M33. An underlying diffuse disk is seen in all SPIRE maps (250-500
micron). Two component fits to the SEDs agree better than isothermal models
with the observed, total and radially averaged flux densities. The two
component model, with beta fixed at 1.5, best fits the global and the radial
SEDs. The cold dust component clearly dominates; the relative mass of the warm
component is less than 0.3% for all the fits. The temperature of the warm
component is not well constrained and is found to be about 60K plus/minus 10K.
The temperature of the cold component drops significantly from about 24K in the
inner 2 kpc radius to 13K beyond 6 kpc radial distance, for the best fitting
model. The gas-to-dust ratio for beta=1.5, averaged over the galaxy, is higher
than the solar value by a factor of 1.5 and is roughly in agreement with the
subsolar metallicity of M33. |
Cosmological Density Fluctuations on 100Mpc Scales and their ISW Effect: We measure the matter probability distribution function (PDF) via counts in
cells in a volume limited subsample of the Sloan Digital Sky Survey Luminous
Red Galaxy Catalog on scales from $30 h^{-1}$Mpc to $150 h^{-1}$Mpc and
estimate the linear Integrated Sachs--Wolfe effect produced by supervoids and
superclusters in the tail of the PDF. We characterize the PDF by the variance,
$S_3$, and $S_4$, and study in simulations the systematic effects due to finite
volume, survey shape and redshift distortion. We compare our measurement to the
prediction of $\Lambda$CDM with linear bias and find a good agreement. We use
the moments to approximate the tail of the PDF with analytic functions. A
simple Gaussian model for the superstructures appears to be consistent with the
claim by Granett et al. that density fluctuations on $100 h^{-1}$Mpc scales
produce hot and cold spots with $\Delta T \approx 10\mu K$ on the cosmic
microwave background. | Canonical Hubble-Tension-Resolving Early Dark Energy Cosmologies are
Inconsistent with the Lyman-$α$ Forest: Current cosmological data exhibit discordance between indirect and some
direct inferences of the present-day expansion rate, $H_0$. Early dark energy
(EDE), which briefly increases the cosmic expansion rate prior to
recombination, is a leading scenario for resolving this "Hubble tension" while
preserving a good fit to cosmic microwave background (CMB) data. However, this
comes at the cost of changes in parameters that affect structure formation in
the late-time universe, including the spectral index of scalar perturbations,
$n_s$. Here, we present the first constraints on axion-like EDE using data from
the Lyman-$\alpha$ forest, i.e., absorption lines imprinted in background
quasar spectra by neutral hydrogen gas along the line of sight. We consider two
independent measurements of the one-dimensional Ly$\alpha$ forest flux power
spectrum, from the Sloan Digital Sky Survey (SDSS eBOSS) and from the
MIKE/HIRES and X-Shooter spectrographs. We combine these with a baseline
dataset comprised of Planck CMB data and baryon acoustic oscillation (BAO)
measurements. Combining the eBOSS Ly$\alpha$ data with the CMB and BAO dataset
reduces the 95% confidence level (CL) upper bound on the maximum fractional
contribution of EDE to the cosmic energy budget, $f_{\rm EDE}$, from 0.07 to
0.03 and constrains $H_0=67.9_{-0.4}^{+0.4}$ km/s/Mpc (68% CL), with maximum a
posteriori value $H_0=67.9$ km/s/Mpc. Similar results are obtained for the
MIKE/HIRES and X-Shooter Ly$\alpha$ data. Our Ly$\alpha$-based EDE constraints
yield $H_0$ values that are in $>4\sigma$ tension with the SH0ES
distance-ladder measurement and are driven by the preference of the Ly$\alpha$
forest data for $n_s$ values lower than those required by EDE cosmologies that
fit Planck CMB data. Taken at face value, the Ly$\alpha$ forest severely
constrains canonical EDE models that could resolve the Hubble tension. |
SMILE: Search for MIlli-LEnses: Dark Matter (DM) halos with masses below $\sim10^{8}$ $M_{\odot}$, which
would help to discriminate between DM models, may be detected through their
gravitational effect on distant sources. The same applies to primordial black
holes, considered as an alternative scenario to DM particle models. However,
there is still no evidence for the existence of such objects. With the aim of
finding compact objects in the mass range $\sim$ 10$^{6}$ --
10$^{9}$$M_{\odot}$, we search for strong gravitational lenses on milli
(mas)-arcseconds scales (< 150 mas). For our search, we used the Astrogeo VLBI
FITS image database -- the largest publicly available database, containing
multi-frequency VLBI data of 13828 individual sources. We used the citizen
science approach to visually inspect all sources in all available frequencies
in search for images with multiple compact components on mas-scales. At the
final stage, sources were excluded based on the surface brightness preservation
criterion. We obtained a sample of 40 sources that passed all steps and
therefore are judged to be milli-arcsecond lens candidates. These sources are
currently followed-up with on-going European VLBI Network (EVN) observations at
5 and 22 GHz. Based on spectral index measurements, we suggest that two of our
candidates have a higher probability to be associated with gravitational
lenses. | Separable triaxial potential-density pairs in MOND: We study mass models that correspond to MOND (triaxial) potentials for which
the Hamilton-Jacobi equation separates in ellipsoidal coordinates. The problem
is first discussed in the simpler case of deep-MOND systems, and then
generalized to the full MOND regime. We prove that the Kuzmin property for
Newtonian gravity still holds, i.e., that the density distribution of separable
potentials is fully determined once the density profile along the minor axis is
assigned. At variance with the Newtonian case, the fact that a positive density
along the minor axis leads to a positive density everywhere remains unproven.
We also prove that (i) all regular separable models in MOND have a vanishing
density at the origin, so that they would correspond to centrally dark-matter
dominated systems in Newtonian gravity; (ii) triaxial separable potentials
regular at large radii and associated with finite total mass leads to density
distributions that at large radii are not spherical and decline as ln(r)/r^5;
(iii) when the triaxial potentials admit a genuine Frobenius expansion with
exponent 0<epsilon<1, the density distributions become spherical at large
radii, with the profile ln(r)/r^(3+2epsilon). After presenting a suite of
positive density distributions associated with MOND separable potentials, we
also consider the important family of (non-separable) triaxial potentials V_1
introduced by de Zeeuw and Pfenniger, and we show that, as already known for
Newtonian gravity, they obey the Kuzmin property also in MOND. The ordinary
differential equation relating their potential and density along the z-axis is
an Abel equation of the second kind that, in the oblate case, can be explicitly
reduced to canonical form. |
Constraining the mass-concentration relation through weak lensing peak
function: Halo masses and concentrations have been studied extensively, by means of
N-body simulations as well as observationally, during the last decade.
Nevertheless, the exact form of the mass-concentration relation is still widely
debated. One of the most promising method to estimate masses and concentrations
relies on gravitational lensing from massive halos. Here we investigate the
impact of the mass-concentration relation on halo peak abundance in weak
lensing shear maps relying on the aperture mass method for peak detections.
After providing a prescription to take into account the concentration
dispersion (always neglected in previous works) in peak number counts
predictions, we assess their power to constrain the mass-concentration relation
by means of Fisher matrix technique. We find that, when combined with different
cosmological probes, peak statistics information from near-future weak lensing
surveys provides an interesting and complementary alternative method to lessen
the long standing controversy about the mass-concentration relation. | Supermassive Black Holes and Kinematics of Disc Galaxies: The statistical relations between the masses of supermassive black holes
(SMBHs) in disk galaxies and the kinematic properties of their host galaxies
are analyzed. We use the radial velocity profiles for several galaxies obtained
earlier at the 6-m telescope of the Special Astrophysical Observatory of the
Russian Academy of Sciences parallel with the data for other galaxies taken
from the literature. We demonstrate that the SMBH masses correlate well with
the velocities of rotation of disks at a fixed distance R \approx 1 kpc (V1),
which characterize the mean density of the central region of the galaxy. The
SMBH masses correlate appreciably weaker with the asymptotic velocity at large
distances from the center and with the angular velocity at the optical radius
R_{25}. We suggest that the growth of the SMBH occurs inside of the forming
"classical" bulge during a monolithic collapse of gas in the central kpc-size
region of the protogalaxy. We have also found a correlation between the SMBH
mass and the total (indicative) mass of the galaxy M_{25} within the optical
radius R_{25}, which includes both baryonic and "dark" mass. The masses of the
nuclear star clusters in early-type disk galaxies (based on the catalog of Seth
et al.) are also scaled with the dynamical mass M_{25}, whereas the
correlations with the luminosity and velocity of rotation of galaxies are
practically absent for them. For a given M_{25} the masses of the nuclear
clusters are, on average, nearly order of magnitude higher in S0-Sbc galaxies
than in late-type galaxies. |
Bayesian evidence-driven likelihood selection for sky-averaged 21-cm
signal extraction: We demonstrate that the Bayesian evidence can be used to find a good
approximation of the ground truth likelihood function of a dataset, a goal of
the likelihood-free inference (LFI) paradigm. As a concrete example, we use
forward modelled sky-averaged 21-cm signal antenna temperature datasets where
we artificially inject noise structures of various physically motivated forms.
We find that the Gaussian likelihood performs poorly when the noise
distribution deviates from the Gaussian case e.g. heteroscedastic radiometric
or heavy-tailed noise. For these non-Gaussian noise structures, we show that
the generalised normal likelihood is on a similar Bayesian evidence scale with
comparable sky-averaged 21-cm signal recovery as the ground truth likelihood
function of our injected noise. We therefore propose the generalised normal
likelihood function as a good approximation of the true likelihood function if
the noise structure is a priori unknown. | Cosmology from the two-dimensional renormalization group acting as the
Ricci flow: The two-dimensional renormalization group acting as the Ricci flow
$\Lambda\frac{\partial}{\partial\Lambda} g_{\mu\nu} = R_{\mu\nu}$ produces a
specific 1+3 dimensional space-time metric which describes an expanding
universe that starts with a big bang $a \sim t^{\scriptscriptstyle 1/\sqrt3}$
then decelerates until $z=0.2$ then accelerates until ending at
$t_{\max}=1.6\,t_{H}$ with a big blowup $a \sim
(t_{\max}-t)^{\scriptscriptstyle -1/\sqrt3}$. The only free parameters are the
overall time scale and the value of the present time $t_{0}$. These are fixed
by the Hubble constant $H_{0}=t_{H}^{-1}$ and the present deceleration
parameter $q(t_{0})$. This crude calculation of cosmology omits all but the
gravitational field. The only energy-momentum is purely gravitational dark
matter and energy. This is a preliminary exploration towards a specific,
comprehensive, testable calculation of cosmology from a fundamental theory in
which physics is produced by a quantum version of the two-dimensional
renormalization group. |
Cosmic backreaction and the mean redshift drift from symbolic regression: The possibility of obtaining symbolic expressions for cosmic backreaction is
explored through a case study of so-called 2-region models. By using the
publicly available symbolic regression algorithm AI Feynman, it is shown that
the kinematical backreaction from a single 2-region model can be well described
as a function of the mean redshift (or, equivalently, the volume averaged scale
factor). A single expression depending on the redshift/scale factor as well as
a model parameter, $f$, that can accurately describe the backreaction for a
significant range of models is naturally more complicated but is also achieved
with percent-level accuracy. \newline\indent Data sets of redshift drift in the
2-region models are also considered. Again utilizing AI Feynman, expressions
for the redshift drift are found. In particular, an expression for the
difference between the mean redshift drift and the drift of the mean redshift
in terms of the kinematical backreaction is easily obtained for a single
2-region model. An accurate symbolic expression that describes this difference
for an array of 2-region models is achieved by using the redshift as a feature
instead of the kinematical backreaction. | Observational prospects for phase transitions at LISA: Fisher matrix
analysis: A first order phase transition at the electroweak scale would lead to the
production of gravitational waves that may be observable at upcoming
space-based gravitational wave (GW) detectors such as LISA (Laser
Interferometer Space Antenna). As the Standard Model has no phase transition,
LISA can be used to search for new physics by searching for a stochastic
gravitational wave background. In this work we investigate LISA's sensitivity
to the thermodynamic parameters encoded in the stochastic background produced
by a phase transition, using the sound shell model to characterise the
gravitational wave power spectrum, and the Fisher matrix to estimate
uncertainties. We explore a parameter space with transition strengths $\alpha <
0.5$ and phase boundary speeds $0.4 < v_\text{w} < 0.9$, for transitions
nucleating at $T_{\text{N}} = 100$ GeV, with mean bubble spacings $0.1$ and
$0.01$ of the Hubble length, and sound speed $c/\sqrt{3}$. We show that the
power spectrum in the sound shell model can be well approximated by a
four-parameter double broken power law, and find that the peak power and
frequency can be measured to approximately 10% accuracy for signal-to-noise
ratios (SNRs) above 20. Determinations of the underlying thermodynamic
parameters are complicated by degeneracies, but in all cases the phase boundary
speed will be the best constrained parameter. Turning to the principal
components of the Fisher matrix, a signal-to-noise ratio above 20 produces a
relative uncertainty less than 3% in the two highest-order principal
components, indicating good prospects for combinations of parameters. The
highest-order principal component is dominated by the wall speed. These
estimates of parameter sensitivity provide a preliminary accuracy target for
theoretical calculations of thermodynamic parameters. |
Cosmic Expansion in Extended Quasidilaton Massive Gravity: Quasidilaton massive gravity offers a physically well-defined gravitational
theory with non-zero graviton mass. We present the full set of dynamical
equations governing the expansion history of the universe, valid during
radiation domination, matter domination, and a late-time self-accelerating
epoch related to the graviton mass. The existence of self-consistent solutions
constrains the amplitude of the quasi-dilaton field and the graviton mass, as
well as other model parameters. We point out that the effective mass of
gravitational waves can be significantly larger than the graviton mass, opening
the possibility that a single theory can explain both the late-time
acceleration of the cosmic expansion and modifications of structure growth
leading to the suppression of large-angle correlations observed in the cosmic
microwave background. | Strong Bayesian Evidence for the Normal Neutrino Hierarchy: The configuration of the three neutrino masses can take two forms, known as
the normal and inverted hierarchies. We compute the Bayesian evidence
associated with these two hierarchies. Previous studies found a mild preference
for the normal hierarchy, and this was driven by the asymmetric manner in which
cosmological data has confined the available parameter space. Here we identify
the presence of a second asymmetry, which is imposed by data from neutrino
oscillations. By combining constraints on the squared-mass splittings with the
limit on the sum of neutrino masses of $\Sigma m_\nu < 0.13$ eV, and using a
minimally informative prior on the masses, we infer odds of 42:1 in favour of
the normal hierarchy, which is classified as "strong" in the Jeffreys' scale.
We explore how these odds may evolve in light of higher precision cosmological
data, and discuss the implications of this finding with regards to the nature
of neutrinos. Finally the individual masses are inferred to be $m_1 =
3.80^{+26.2}_{-3.73} \, \text{meV}, m_2 = 8.8^{+18}_{-1.2} \, \text{meV}, m_3 =
50.4^{+5.8}_{-1.2} \, \text{meV}$ ($95\%$ credible intervals). |
Gamma-ray burst host galaxies at low and high redshift: The galaxies hosting the most energetic explosions in the universe, the
gamma-ray bursts (GRBs), are generally found to be low-mass, metal poor, blue
and star forming galaxies. However, the majority of the targets investigated so
far (less than 100) are at relatively low redshift, z < 2. We know that at low
redshift, the cosmic star formation is predominantly in small galaxies.
Therefore, at low redshift, long-duration GRBs, which are associated with
massive stars, are expected to be in small galaxies. Preliminary investigations
of the stellar mass function of z < 1.5 GRB hosts does not indicate that these
galaxies are different from the general population of nearby star-forming
galaxies. At high-z, it is still unclear whether GRB hosts are different.
Recent results indicate that a fraction of them might be associated with dusty
regions in massive galaxies. Remarkable is the a super-solar metallicity
measured in the interstellar medium of a z = 3.57 GRB host. | Lack of Interaction between the Dust Grains and the Anomalous Radio Jet
in the Nearby Spiral Galaxy NGC 4258: We obtained Spitzer/IRAC 3.6-8 micron images of the nearby spiral galaxy NGC
4258 to study possible interactions between dust and the radio jet. In our
analysis we also included high-resolution radio continuum, H-alpha, CO, and
X-ray data. Our data reveal that the 8 micron emission, believed to originate
largely from PAH molecules and hot dust, is an excellent tracer of the normal
spiral structure in NGC 4258, and hence it originates from the galactic plane.
We investigated the possibility of dust destruction by the radio jet by
calculating correlation coefficients between the 8 micron and radio continuum
emissions along the jet in two independent ways, namely (i) from
wavelet-transformed maps of the original images at different spatial scales,
and (ii) from one-dimensional intensity cuts perpendicular to the projected
path of the radio jet on the sky. No definitive sign of a correlation (or
anticorrelation) was detected on relevant spatial scales with either approach,
implying that any dust destruction must take place at spatial scales that are
not resolved by our observations. |
Radio spectral index images of the spiral galaxies NGC 0628, NGC 3627,
and NGC 7331: In order to understand the cosmic ray propagation mechanism in galaxies, and
its correlation with the sites of star formation, we compare the spatially
resolved radio spectral index of three spiral galaxies with their IR
distribution. We present new low-frequency radio continuum observations of the
galaxies NGC 0628, NGC 3627, and NGC 7331, taken at 327 MHz with the Very Large
Array. We complemented our data set with sensitive archival observations at 1.4
GHz and we studied the variations of the radio spectral index within the disks
of these spiral galaxies. We also compared the spectral index distribution and
the IR distribution, using 70 $\mu$m Spitzer observations. We found that in
these galaxies the non-thermal spectral index is anticorrelated with the radio
brightness. Bright regions, like the bar in NGC 3627 or the circumnuclear
region in NGC 7331, are characterized by a flatter spectrum with respect to the
underlying disk. Therefore, a systematic steepening of the spectral index with
the increasing distance from the center of these galaxies is observed.
Furthermore, by comparing the radio images with the 70 $\mu$m images of the
Spitzer satellite we found that a similar anticorrelation exists between the
radio spectral index and the infrared brightness, as expected on the basis of
the local correlation between the radio continuum and the infrared emission.
Our results support the idea that in regions of intense star formation the
electron diffusion must be efficient. The observed anticorrelation between
radio brightness and spectral index, may imply that the cosmic ray density and
the magnetic field strength are significantly higher in these regions than in
their surroundings. | Painting halos from cosmic density fields of dark matter with physically
motivated neural networks: We present a novel halo painting network that learns to map approximate 3D
dark matter fields to realistic halo distributions. This map is provided via a
physically motivated network with which we can learn the non-trivial local
relation between dark matter density field and halo distributions without
relying on a physical model. Unlike other generative or regressive models, a
well motivated prior and simple physical principles allow us to train the
mapping network quickly and with relatively little data. In learning to paint
halo distributions from computationally cheap, analytical and non-linear
density fields, we bypass the need for full particle mesh simulations and halo
finding algorithms. Furthermore, by design, our halo painting network needs
only local patches of dark matter density to predict the halos, and as such, it
can predict the 3D halo distribution for any arbitrary simulation box size. Our
neural network can be trained using small simulations and used to predict large
halo distributions, as long as the resolutions are equivalent. We evaluate our
model's ability to generate 3D halo count distributions which reproduce, to a
high degree, summary statistics such as the power spectrum and bispectrum, of
the input or reference realizations. |
Unveiling the singular dynamics in the cosmic large-scale structure: It is known that the gravitational collapse of cold dark matter leads to
infinite-density caustics that seed the primordial dark-matter halos in the
large-scale structure. The development of these caustics begins, generically,
as an almost one-dimensional phenomenon with the formation of pancakes.
Focusing on the one-dimensional case, we identify a landscape of
non-differentiable, and thus, singular features in the particle acceleration
that emerge after the first crossing of particle trajectories. We complement
our fully analytical studies by high-resolution simulations and find
outstanding agreement, particularly shortly after the first crossing. We
develop the methods in one space dimension but outline briefly the necessary
steps for the 3D case. | Strong biases in infrared-selected gravitational lenses: Bright submm-selected galaxies have been found to be a rich source of strong
gravitational lenses. However, strong gravitational lensing of extended sources
leads inevitably to differential magnification. In this paper I quantify the
effect of differential magnification on simulated far-infrared and submm
surveys of strong gravitational lenses, using a foreground population of
Navarro-Frenk-White plus de Vaucouleurs' density profiles, with a model source
resembling the Cosmic Eyelash and QSO J1148+5251. Some emission line
diagnostics are surprisingly unaffected by differential magnification effects:
for example, the bolometric fractions of [C II] 158um and CO(J=1-0), often used
to infer densities and ionisation parameters, have typical differential
magnification effects that are smaller than the measurement errors. However,
the CO ladder itself is significantly affected. Far-infrared lensed galaxy
surveys (e.g. at 60um) strongly select for high-redshift galaxies with caustics
close to AGN, boosting the apparent bolometric contribution of AGN. The lens
configuration of IRAS F10214+4724 is naturally explained in this context.
Conversely, submm/mm-wave surveys (e.g. 500-1400um) strongly select for
caustics close to knots of star formation boosting the latter's bolometric
fraction. In general, estimates of bolometric fractions from spectral energy
distributions of strongly lensed infrared galaxies are so unreliable as to be
useless, unless a lens mass model is available to correct for differential
magnification. |
Large-scale assembly bias of dark matter halos: We present precise measurements of the assembly bias of dark matter halos,
i.e. the dependence of halo bias on other properties than the mass, using
curved "separate universe" N-body simulations which effectively incorporate an
infinite-wavelength matter overdensity into the background density. This method
measures the LIMD (local-in-matter-density) bias parameters $b_n$ in the
large-scale limit. We focus on the dependence of the first two Eulerian biases
$b^E_1$ and $b^E_2$ on four halo properties: the concentration, spin, mass
accretion rate, and ellipticity. We quantitatively compare our results with
previous works in which assembly bias was measured on fairly small scales.
Despite this difference, our findings are in good agreement with previous
results. We also look at the joint dependence of bias on two halo properties in
addition to the mass. Finally, using the excursion set peaks model, we attempt
to shed new insights on how assembly bias arises in this analytical model. | Studying the WHIM Content of the Galaxy Large-Scale Structures along the
Line of Sight to H 2356-309: We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309,
combined with a lower S/N spectrum of the same target, to search for the
presence of warm-hot absorbing gas associated with two Large-Scale Structures
(LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster,
PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically
significant (>=3sigma) individual absorption is detected from any of the strong
He- or H-like transitions of C, O and Ne at the redshifts of the structures.
However we are still able to constrain the physical and geometrical parameters
of the associated putative absorbing gas, by performing joint spectral fit of
marginal detections and upper limits of the strongest expected lines with our
self-consistent hybrid ionization WHIM spectral model. At the redshift of the
PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H
=19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase
with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For
the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our
constraints allow us to estimate the cumulative number density per unit
redshifts of OVII WHIM absorbers. We also estimate the cosmological mass
density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent
with the mass density of the intergalactic 'missing baryons' for high
metallicities. |
Chirality of the gravitational-wave background and pulsar-timing arrays: We describe the signatures of a circularly polarized gravitational-wave
background on the timing residuals obtained with pulsar-timing arrays. Most
generally, the circular polarization will depend on the gravitational-wave
direction, and we describe this angular dependence in terms of spherical
harmonics. While the amplitude of the monopole (the overall chirality of the
gravitational-wave background) cannot be detected, measures of the anisotropy
are theoretically conceivable. We provide expressions for the minimum-variance
estimators for the circular-polarization anisotropy. We evaluate the smallest
detectable signal as a function of the signal-to-noise ratio with which the
isotropic GW signal is detected and the number of pulsars (assumed to be
roughly uniformly spread throughout the sky) in the survey. We find that the
overall dipole of the circular polarization and a few higher overall
multipoles, are detectable in a survey with $\gtrsim100$ pulsars if their
amplitude is close to maximal and once the isotropic signal is established with
a signal-to-noise ratio $\gtrsim400$. Even if the anisotropy can be
established, though, there will be limited information on its direction.
Similar arguments apply to astrometric searches for gravitational waves. | Constraints on compact dark matter with fast radio burst observations: Fast Radio Bursts (FRBs) are bright radio transients with millisecond
duration at cosmological distances. Since compact dark matter/objects (COs)
could act as lenses and cause split of this kind of very short duration
signals, Mu$\rm{\tilde{n}}$oz et al. (2016) has proposed a novel method to
probe COs with lensing of FRBs. In this Letter, we for the first time apply
this method to real data and give constraints of the nature of COs with
currently available FRB observations. We emphasize the information from dynamic
spectra of FRBs is quite necessary for identifying any lensed signals and find
no echoes in the existing data. The null search gives a constraint comparable
to that from galactic wide binaries, though the methods of redshift inference
from dispersion measure would impact a little. Furthermore, we make an improved
forecast basing on the distributions of real data for the ongoing and upcoming
telescopes. Finally, we discuss the situation where one or more lensed signals
will be detected. In such a case, the parameter space of COs can be pinned down
very well since the lens mass can be directly determined through the observed
flux ratio and time delay between split images. |
Gravitational Lensing and the Power Spectrum of Dark Matter
Substructure: Insights from the ETHOS N-body Simulations: Strong gravitational lensing has been identified as a promising astrophysical
probe to study the particle nature of dark matter. In this paper we present a
detailed study of the power spectrum of the projected mass density
(convergence) field of substructure in a Milky Way-sized halo. This power
spectrum has been suggested as a key observable that can be extracted from
strongly lensed images and yield important clues about the matter distribution
within the lens galaxy. We use two different $N$-body simulations from the
ETHOS framework: one with cold dark matter and another with self-interacting
dark matter and a cutoff in the initial power spectrum. Despite earlier works
that identified $ k \gtrsim 100$ kpc$^{-1}$ as the most promising scales to
learn about the particle nature of dark matter we find that even at lower
wavenumbers - which are actually within reach of observations in the near
future - we can gain important information about dark matter. Comparing the
amplitude and slope of the power spectrum on scales $0.1 \lesssim k/$kpc$^{-1}
\lesssim 10$ from lenses at different redshifts can help us distinguish between
cold dark matter and other exotic dark matter scenarios that alter the
abundance and central densities of subhalos. Furthermore, by considering the
contribution of different mass bins to the power spectrum we find that subhalos
in the mass range $10^7 - 10^8$ M$_{\odot}$ are on average the largest
contributors to the power spectrum signal on scales $2 \lesssim k/$kpc$^{-1}
\lesssim 15$, despite the numerous subhalos with masses $> 10^8$ M$_{\odot}$ in
a typical lens galaxy. Finally, by comparing the power spectra obtained from
the subhalo catalogs to those from the particle data in the simulation
snapshots we find that the seemingly-too-simple halo model is in fact a fairly
good approximation to the much more complex array of substructure in the lens. | The XXL Survey XLIV. Sunyaev-Zel'dovich mapping of a low-mass cluster at
z~1: a multi-wavelength approach: In this paper, we present resolved observations of the Sunyaev-Zel'dovich
(SZ) effect, obtained with the NIKA2 camera, towards the cluster of galaxies
XLSSC102, a relatively low-mass system ($M_{500} \sim 2 \times 10^{14}$
M$_{\odot}$) at $z = 0.97$ detected from the XXL survey. We combine NIKA2 SZ
data, XMM-Newton X-ray data, and Megacam optical data to explore, respectively,
the spatial distribution of the gas electron pressure, the gas density, and the
galaxies themselves. We find significant offsets between the X-ray peak, the SZ
peak, the brightest cluster galaxy, and the peak of galaxy density.
Additionally, the galaxy distribution and the gas present elongated
morphologies. This is interpreted as the sign of a recent major merging event,
which induced a local boost of the gas pressure towards the north of XLSSC102
and stripped the gas out of the galaxy group. The NIKA2 data are also combined
with XXL data to construct the thermodynamic profiles of XLSSC102, obtaining
relatively tight constraints up to about $\sim r_{500}$, and revealing
properties that are typical of disturbed systems. We also explore the impact of
the cluster centre definition and the implication of local pressure
substructure on the recovered profiles. Finally, we derive the global
properties of XLSSC102 and compare them to those of high-mass-and-low-redshift
systems, finding no strong evidence for non-standard evolution. We also use
scaling relations to obtain alternative mass estimates from our profiles. The
variation between these different mass estimates reflects the difficulty to
accurately measure the mass of low-mass clusters at z$\sim$1, especially with
low signal-to-noise ratio (S/N) data and for a disturbed system. However, it
also highlights the strength of resolved SZ observations alone and in
combination with survey-like X-ray data. |
Primordial black holes and gravitational waves from non-canonical
inflation: Primordial black holes (PBHs) can generically form in inflationary setups
through the collapse of enhanced cosmological perturbations, providing us
access to the early Universe through their associated observational signatures.
In the current work we propose a new mechanism of PBH production within
non-canonical inflation, using a class of steep-deformed inflationary
potentials compatible with natural values for the non-canonical exponents. In
particular, by requiring significant PBH production we extract constraints on
the non-canonical exponents. Additionally, we find that our scenario can lead
to the formation of asteroid-mass PBHs, which can account for the totality of
the dark matter, as well as to production of solar-mass PBHs within the
LIGO/VIRGO detection band. Finally, we find that the enhanced cosmological
perturbations which collapse to form PBHs can produce a stochastic
gravitational-wave (GW) background induced by second-order gravitational
interactions. Very interestingly, we obtain a GW signal detectable by future GW
experiments, in particular by SKA, LISA and BBO. | The implications of dust for high-redshift protogalaxies and the
formation of binary disks: Numerical simulations suggest that the first galaxies are formed in
protogalactic halos with virial temperatures >= 10^4 K. It is likely that such
halos are polluted with trace amounts of metals produced by the first
generation of stars. The presence of dust can significantly change the
chemistry and dynamics of early galaxies. In this article, we aim to assess the
role of dust on the thermal and dynamical evolution of the first galaxies in
the presence of a background UV flux, and its implications for the
observability of Lyman alpha emitters and sub-mm sources. We have performed
high resolution cosmological simulations using the adaptive mesh refinement
code FLASH to accomplish this goal. We have developed a chemical network
appropriate for these conditions and coupled it with the FLASH code. The main
ingredients of our chemical model include the formation of molecules, a
multi-level treatment of atomic hydrogen, line trapping of Lyman alpha photons
and, photoionization and photodissociation processes in a UV background. We
found that the formation of molecules (H_{2} and HD) is significantly enhanced
in the presence of dust grains. The presence of a background UV flux strongly
influences the formation of molecules by photodissociating them. We explore the
evolution after a major merger, leading to the formation of a binary disk.
These disks have gas masses of ~10^{7} M_sun at a redshift of 5.4. Each disk
lies in a separate subhalo as a result of the merger event. The disks are
supported by turbulent pressure due to the highly supersonic turbulence present
in the halo. The presence of dust does not significantly reduce the Lyman alpha
emission. The emission of Lyman alpha is extended and originates from the
envelope of the halo due to line trapping effects. We also find that dust
masses of 10^8 M_sun are required to observe the dust continuum emission from z
5 galaxies with ALMA. |
The MICE Grand Challenge Lightcone Simulation II: Halo and Galaxy
catalogues: This is the second in a series of three papers in which we present an
end-to-end simulation from the MICE collaboration, the MICE Grand Challenge
(MICE-GC) run. The N-body contains about 70 billion dark-matter particles in a
$(3 \, h^{-1} \, {\rm Gpc})^3$ comoving volume spanning 5 orders of magnitude
in dynamical range. Here we introduce the halo and galaxy catalogues built upon
it, both in a wide ($5000 \,{\rm deg}^2$) and deep ($z<1.4$) light-cone and in
several comoving snapshots. Halos were resolved down to few $10^{11}
\,h^{-1}\,{\rm M_{\odot}}$. This allowed us to model galaxies down to absolute
magnitude M$_r<-18.9$. We used a new hybrid Halo Occupation Distribution and
Abundance Matching technique for galaxy assignment. The catalogue includes the
Spectral Energy Distributions of all galaxies. We describe a variety of halo
and galaxy clustering applications. We discuss how mass resolution effects can
bias the large scale $2$-pt clustering amplitude of poorly resolved halos at
the $\lesssim 5\%$ level, and their $3$-pt correlation function. We find a
characteristic scale dependent bias of $\lesssim 6\%$ across the BAO feature
for halos well above $M_{\star}\sim 10^{12}\,h^{-1}\,{\rm M_{\odot}}$ and for
LRG like galaxies. For halos well below $M_{\star}$ the scale dependence at
$100\,{\rm Mpc} h^{-1}$ is $\lesssim 2\%$. Lastly we discuss the validity of
the large-scale Kaiser limit across redshift and departures from it towards
nonlinear scales. We make the current version of the light-cone halo and galaxy
catalogue (MICECATv1.0) publicly available through a dedicated web portal,
http://cosmohub.pic.es, to help develop and exploit the new generation of
astronomical surveys. | Evaluating and Improving Semi-analytic modeling of Dust in Galaxies
based on Radiative Transfer Calculations II: Dust Emission in the Infrared: Interstellar dust grains are responsible for modifying the spectral energy
distribution (SED) of galaxies, both absorbing starlight at UV and optical
wavelengths and converting this energy into thermal emission in the infrared.
The detailed description of these phenomena is of fundamental importance in
order to compare the predictions of theoretical models of galaxy formation and
evolution with the most recent observations in the infrared region. In this
paper we compare the results of GRASIL, a code explicitly solving for the
equation of radiative transfer in a dusty medium, with the predictions of a
variety of IR template libraries. We employ star formation history samples
extracted from the semi-analytical galaxy formation model MORGANA to create
libraries of synthetic SEDs from the near- to the far-infrared. We consider
model predictions at different redshift ranges to explore any possible
influence in the shape and normalization of the SEDs due to the expected
evolution of the galaxy properties. We compute the total absorbed starlight
predicted by GRASIL at optical wavelengths to statistically compare the
synthetic SEDs with the selected IR templates. We show that synthetic SEDs at a
given total infrared luminosity are predicted to be systematically different at
different redshift and for different properties of the underlying model galaxy.
However, we determine spectral regions where the agreement between the results
of radiative transfer and IR templates is good in a statistical sense (i.e. in
terms of the luminosity functions). Moreover, we highlight some potentially
relevant discrepancies between the different approaches, both in the region
dominated by PAH emission and at sub-mm wavelengths. These results determine
potentially critical issues in the infrared luminosity functions as predicted
by semi-analytical models coupled with different IR flux estimators. |
Resolving galaxies in time and space: I: Applying STARLIGHT to CALIFA
data cubes: Fossil record methods based on spectral synthesis techniques have matured
over the past decade, and their application to integrated galaxy spectra
fostered substantial advances on the understanding of galaxies and their
evolution. Yet, because of the lack of spatial resolution, these studies are
limited to a global view, providing no information about the internal physics
of galaxies. Motivated by the CALIFA survey, which is gathering Integral Field
Spectroscopy over the full optical extent of 600 galaxies, we have developed an
end-to-end pipeline which: (i) partitions the observed data cube into Voronoi
zones in order to, when necessary and taking due account of correlated errors,
increase the S/N, (ii) extracts spectra, including propagated errors and
bad-pixel flags, (iii) feeds the spectra into the STARLIGHT spectral synthesis
code, (iv) packs the results for all galaxy zones into a single file, (v)
performs a series of post-processing operations, including zone-to-pixel image
reconstruction and unpacking the spectral and stellar population properties
into multi-dimensional time, metallicity, and spatial coordinates. This paper
provides an illustrated description of this whole pipeline and its products.
Using data for the nearby spiral NGC 2916 as a show case, we go through each of
the steps involved, presenting ways of visualizing and analyzing this manifold.
These include 2D maps of properties such as the v-field, stellar extinction,
mean ages and metallicities, mass surface densities, star formation rates on
different time scales and normalized in different ways, 1D averages in the
temporal and spatial dimensions, projections of the stellar light and mass
growth (x,y,t) cubes onto radius-age diagrams, etc. The results illustrate the
richness of the combination of IFS data with spectral synthesis, providing a
glimpse of what is to come from CALIFA and future surveys. (Abridged) | Anomalous variance in the WMAP data and Galactic Foreground residuals: A previous work (Monteser\'in et al. 2008) estimated the CMB variance from
the three-year WMAP data, finding a lower value than expected from Gaussian
simulations using the WMAP best-fit cosmological model. We repeat the analysis
on the five-year WMAP data using a new estimator with lower bias and variance.
Our results confirm this anomaly at higher significance, namely with a p-value
of 0.31%. We perform the analysis using different exclusion masks, showing that
a particular region of the sky near the Galactic plane shows a higher variance
than 95.58% of the simulations whereas the rest of the sky has a lower variance
than 99.96% of the simulations. The relative difference in variance between
both regions is bigger than in 99.64% of the simulations. This anisotropic
distribution of power seems to be causing the anomaly since the model assumes
isotropy. Furthermore, this region has a clear frequency dependence between
41GHz and 61GHz or 94GHz suggesting that Galactic foreground residuals could be
responsible for the anomaly. Moreover, removing the quadrupole and the octopole
from data and simulations the anomaly disappears. The variance anomaly and the
previously reported quadrupole and octopole alignment seem therefore to be
related and could have a common origin. We discuss different possible causes
and Galactic foreground residuals seem to be the most likely one. These
residuals would affect the estimation of the angular power spectrum from the
WMAP data, which is used to generate Gaussian simulations, giving rise to an
inconsistency between the estimated and expected CMB variance. If the presence
of residuals is confirmed, the estimation of the cosmological parameters could
be affected. |
Dedicated Indirect Searches for Dark Matter Using Antideuterons: This white paper describes the basic idea for indirect dark matter searches
using antideuterons. Low energy antideuterons produced by dark matter
annihilations/decays provide an attractive dark matter signature, due to the
low astrophysical background. The current and future experiments have a strong
potential to detect antideuterons from dark matter. They are complementary not
only with each other, but also with other dark matter searches. | Accuracy of environmental tracers and consequence for determining the
Type Ia Supernovae magnitude step: Type Ia Supernovae (SNe Ia) are standardizable candles that allow us to
measure the recent expansion rate of the Universe. Due to uncertainties in
progenitor physics, potential astrophysical dependencies may bias cosmological
measurements if not properly accounted for. The dependency of the intrinsic
luminosity of SNe Ia with their host-galaxy environment is often used to
standardize SNe Ia luminosity and is commonly parameterized as a step function.
This functional form implicitly assumes two-populations of SNe Ia. In the
literature, multiple environmental indicators have been considered, finding
different, sometimes incompatible, step function amplitudes. We compare these
indicators in the context of a two-populations model, based on their ability to
distinguish the two populations. We show that local H$\alpha$-based specific
star formation rate (lsSFR) and global stellar mass are better tracers than,
for instance, host galaxy morphology. We show that tracer accuracy can explain
the discrepancy between the observed SNe Ia step amplitudes found in the
literature. Using lsSFR or global mass to distinguish the two populations can
explain all other observations, though lsSFR is favoured. As lsSFR is strongly
connected to age, our results favour a prompt and delayed population model. In
any case, there exists two populations that differ in standardized magnitude by
at least $0.121\pm0.010\,\mathrm{mag}$. |
FIR colours of nearby late-type galaxies in the Herschel Reference
Survey: We study the far infrared (60-500 $\mu$m) colours of late-type galaxies in
the $Herschel$ Reference Survey, a K-band selected, volume limited sample of
nearby galaxies. The far infrared colours are correlated with each other, with
tighter correlations for the indices that are closer in wavelength. We also
compare the different colour indices to various tracers of the physical
properties of the target galaxies, such as the surface brightness of the
ionising and non-ionising stellar radiation, the dust attenuation and the
metallicity. The emission properties of the cold dust dominating the far
infrared spectral domain are regulated by the properties of the interstellar
radiation field. Consistent with that observed in nearby, resolved galaxies,
our analysis shows that the ionising and the non-ionising stellar radiation,
including that emitted by the most evolved, cold stars, both contribute to the
heating of the cold dust component. This work also shows that metallicity is
another key parameter characterising the cold dust emission of normal,
late-type galaxies. A single modified black body with a grain emissivity index
$\beta$=1.5 better fits the observed SPIRE flux density ratios $S250/S350$ vs.
$S350/S500$ than $\beta$=2, although values of $\beta$ $\simeq$ 2 are possible
in metal rich, high surface brightness galaxies. Values of $\beta$ $\lesssim$
1.5 better represent metal poor, low surface brightness objects. This
observational evidence provides strong constraints for dust emission models of
normal, late type galaxies. | The role of Dark Matter sub-halos in the non-thermal emission of galaxy
clusters: Annihilation of Dark Matter (DM) particles has been recognized as one of the
possible mechanisms for the production of non-thermal particles and radiation
in galaxy clusters. Previous studies have shown that, while DM models can
reproduce the spectral properties of the radio halo in the Coma cluster, they
fail in reproducing the shape of the radio halo surface brightness because they
produce a shape that is too concentrated towards the center of the cluster with
respect to the observed one. However, in previous studies the DM distribution
was modeled as a single spherically symmetric halo, while the DM distribution
in Coma is found to have a complex and elongated shape. In this work we
calculate a range of non-thermal emissions in the Coma cluster by using the
observed distribution of DM sub-halos. We find that, by including the observed
sub-halos in the DM model, we obtain a radio surface brightness with a shape
similar to the observed one, and that the sub-halos boost the radio emission by
a factor between 5 and 20%, thus allowing to reduce the gap between the
annihilation cross section required to reproduce the radio halo flux and the
upper limits derived from other observations, and that this gap can be
explained by realistic values of the boosting factor due to smaller
substructures. Models with neutralino mass of 9 GeV and composition $\tau^+
\tau^-$, and mass of 43 GeV and composition $b \bar b$ can fit the radio halo
spectrum using the observed properties of the magnetic field in Coma, and do
not predict a gamma-ray emission in excess compared to the recent Fermi-LAT
upper limits. These findings make these DM models viable candidate to explain
the origin of radio halos in galaxy clusters. [abridged] |
Impact of the latest measurement of Hubble constant on constraining
inflation models: We investigate how the constraint results of inflation models are affected by
considering the latest local measurement of $H_0$ in the global fit. We use the
observational data, including the Planck CMB full data, the BICEP2 and Keck
Array CMB B-mode data, the BAO data, and the latest measurement of Hubble
constant, to constrain the $\Lambda$CDM+$r$+$N_{\rm eff}$ model, and the
obtained 1$\sigma$ and 2$\sigma$ contours of $(n_s, r)$ are compared to the
theoretical predictions of selected inflationary models. We find that, in this
fit, the scale invariance is only excluded at the 3.3$\sigma$ level, and
$\Delta N_{\rm eff}>0$ is favored at the 1.6$\sigma$ level. The natural
inflation model is now excluded at more than 2$\sigma$ level; the Starobinsky
$R^2$ model becomes only favored at around 2$\sigma$ level; the most favored
model becomes the spontaneously broken SUSY inflation model; and, the brane
inflation model is also well consistent with the current data, in this case. | The Catalina Real-time Transient Survey: The Catalina Real-time Transient Survey (CRTS) currently covers 33,000 deg^2
of the sky in search of transient astrophysical events, with time baselines
ranging from 10 minutes to ~7 years. Data provided by the Catalina Sky Survey
provides an unequaled baseline against which >4,000 unique optical transient
events have been discovered and openly published in real-time. Here we
highlight some of the discoveries of CRTS. |
Properties of the stochastic astrophysical gravitational wave
background: astrophysical sources dependencies: This article explores the properties (amplitude and shape) of the angular
power spectrum of the anisotropies of the astrophysical gravitational wave
background (AGWB) focusing on the signatures of the astrophysical models
describing sub-galactic physics. It demonstrates that while some parameters
have negligible impact others, and in particular the stellar evolution models,
the metallicity and the merger time delay distribution can result in relative
differences of order 40% in the angular power spectrum of anisotropies in both
the LIGO/Virgo and LISA frequency bands. It is also shown that the monopole and
the anisotropic components of the AGWB are complementary and sensitive to
different astrophysical parameters. It follows that AGWB anisotropies are a new
observable with the potential to provide new astrophysical information that can
not be accessed otherwise. | Quenching Massive Galaxies with On-the-fly Feedback in Cosmological
Hydrodynamic Simulations: Massive galaxies today typically are not forming stars despite being
surrounded by hot gaseous halos with short central cooling times. This likely
owes to some form of "quenching feedback" such as merger-driven quasar activity
or radio jets emerging from central black holes. Here we implement heuristic
prescriptions for these phenomena on-the-fly within cosmological hydrodynamic
simulations. We constrain them by comparing to observed luminosity functions
and color-magnitude diagrams from SDSS. We find that quenching from mergers
alone does not produce a realistic red sequence, because 1 - 2 Gyr after a
merger the remnant accretes new fuel and star formation reignites. In contrast,
quenching by continuously adding thermal energy to hot gaseous halos
quantitatively matches the red galaxy luminosity function and produces a
reasonable red sequence. Small discrepancies remain - a shallow red sequence
slope suggests that our models underestimate metal production or retention in
massive red galaxies, while a deficit of massive blue galaxies may reflect the
fact that observed heating is intermittent rather than continuous. Overall,
injection of energy into hot halo gas appears to be a necessary and sufficient
condition to broadly produce red and dead massive galaxies as observed. |
Particle mesh simulations of the Lyman-alpha forest and the signature of
Baryon Acoustic Oscillations in the intergalactic medium: We present a set of ultra-large particle-mesh simulations of the LyA forest
targeted at understanding the imprint of baryon acoustic oscillations (BAO) in
the inter-galactic medium. We use 9 dark matter only simulations which can, for
the first time, simultaneously resolve the Jeans scale of the intergalactic gas
while covering the large volumes required to adequately sample the acoustic
feature. Mock absorption spectra are generated using the fluctuating
Gunn-Peterson approximation which have approximately correct flux probability
density functions (PDFs) and small-scale power spectra. On larger scales there
is clear evidence in the redshift space correlation function for an acoustic
feature, which matches a linear theory template with constant bias. These
spectra, which we make publicly available, can be used to test pipelines, plan
future experiments and model various physical effects. As an illustration we
discuss the basic properties of the acoustic signal in the forest, the scaling
of errors with noise and source number density, modified statistics to treat
mean flux evolution and misestimation, and non-gravitational sources such as
fluctuations in the photo-ionizing background and temperature fluctuations due
to HeII reionization. | Power law pseudo phase-space density profiles of dark matter halos:
fluke of physics?: It has been known for nearly 20 years that the pseudo phase-space density
profile of equilibrium simulated dark matter halos, $\rho(r)/\sigma^3(r)$, is
well described by a power law over 3 decades in radius, even though both the
density $\rho(r)$, and the velocity dispersion $\sigma(r)$ deviate
significantly from power laws. The origin of this scale-free behavior is not
understood. It could be an inherent property of self-gravitating collisionless
systems, or it could be a mere coincidence. To address the question we work
with equilibrium halos, and more specifically, the second derivative of the
Jeans equation, which, under the assumptions of (i) Einasto density profile,
(ii) linear velocity anisotropy - density slope relation, and (iii)
$\rho/\sigma^3\propto r^{-\alpha}$, can be transformed from a differential
equation to a cubic algebraic equation. Relations (i)-(iii) are all observed in
numerical simulations, and are well parametrized by a total of 4 or 6 model
parameters. We do not consider dynamical evolution of halos; instead, taking
advantage of the fact that the algebraic Jeans equation for equilibrium halos
puts relations (i)-(iii) on the same footing, we study the (approximate)
solutions of this equation in the 4 and 6 dimensional spaces. We argue that the
distribution of best solutions in these parameter spaces is inconsistent with
$\rho/\sigma^3\propto r^{-\alpha}$ being an fundamental property of
gravitational evolution, and conclude that the scale-free nature of this
quantity is likely to be a fluke. |
Planck Limits on Non-canonical Generalizations of Large-field Inflation
Models: In this paper, we consider two case examples of Dirac-Born-Infeld (DBI)
generalizations of canonical large-field inflation models, characterized by a
reduced sound speed, $c_{S} < 1$. The reduced speed of sound lowers the
tensor-scalar ratio, improving the fit of the models to the data, but increases
the equilateral-mode non-Gaussianity, $f^\mathrm{equil.}_\mathrm{NL}$, which
the latest results from the Planck satellite constrain by a new upper bound. We
examine constraints on these models in light of the most recent Planck and
BICEP/Keck results, and find that they have a greatly decreased window of
viability. The upper bound on $f^\mathrm{equil.}_\mathrm{NL}$ corresponds to a
lower bound on the sound speed and a corresponding lower bound on the
tensor-scalar ratio of $r \sim 0.01$, so that near-future Cosmic Microwave
Background observations may be capable of ruling out entire classes of DBI
inflation models. The result is, however, not universal: infrared-type DBI
inflation models, where the speed of sound increases with time, are not subject
to the bound. | Perturbations in Matter Bounce with Non-minimal Coupling: In this paper, we investigate the perturbations in matter bounce induced from
Lee-Wick lagrangian with the involvement of non-minimal coupling to the
Einstein Gravity. We find that this extra non-minimal coupling term can cause a
red-tilt on the primordial metric perturbation at extremely large scales. It
can also lead to large enhancement of reheating of the normal field particles
compared to the usual minimal coupling models. |
The baryonic self similarity of dark matter: The cosmological simulations indicates that the dark matter haloes have
specific self similar properties. However the halo similarity is affected by
the baryonic feedback, the momentum injected by the supernovae re-shape the
dark matter core and transform it to a flat density core, with a scale length
imposed by the baryonic feedback. Additionally the baryon feedback impose also
an equilibrium condition, which when coupled with the imposed baryonic scale
length induce a new type of similarity. The new self similar solution implies
that the acceleration generated by dark matter is scale free, which in turns
implies that the baryonic acceleration at a reference radius is also scale
free. Constant dark matter and baryonic accelerations at a reference radius
have effectively been observed for a large class of different galaxies, which
is in support of this approach. The new self similar properties implies that
the total acceleration at larger distances is scale free, the transition
between the dark matter and baryons dominated regime occurs at a constant
acceleration, and the maximum of the velocity curve which defines the amplitude
of the velocity curve at larger distances is proportional to $M^{\frac{1}{4}}$.
These results demonstrates that in this self similar model, cold dark matter is
consistent with the basics of MOND phenomenology for the galaxies. In agreement
with the observation the coincidence between the self similar model and MOND is
expected to break at the scale of clusters of galaxies. Some numerical
experiments shows that the behavior of the density near the origin is closely
approximated by a Einasto profile. | Compact radio emission from z~0.2 X-ray bright AGN: Radio and X-ray emission of AGN appears to be correlated. The details of the
underlying physical processes, however, are still not fully understood, i.e.,
to what extent is the X-ray and radio emission originating from the same
relativistic particles or from the accretion-disk or corona or both. We study
the cm radio emission of an SDSS/ROSAT/FIRST matched sample of 13 X-raying AGN
in the redshift range 0.11< z < 0.37 at high angular resolution with the goal
of searching for jet structures or diffuse, extended emission on sub-kpc
scales. We use MERLIN at 18 cm for all objects and Western EVN at 18 cm for
four objects to study the radio emission on scales of ~500 pc and ~40 pc for
the MERLIN and EVN observations, respectively. The detected emission is
dominated by compact nuclear radio structures. We find no kpc collimated jet
structures. The EVN data indicate for compact nuclei on 40 pc scales, with
brightness temperatures typical for accretion-disk scenarios. Comparison with
FIRST shows that the 18 cm emission is resolved out up to 50% by MERLIN.
Star-formation rates based on large aperture SDSS spectra are generally too
small to produce considerable contamination of the nuclear radio emission. We
can, therefore, assume the 18 cm flux densities to be produced in the nuclei of
the AGN. Together with the ROSAT soft X-ray luminosities and black hole mass
estimates from the literature, our sample objects follow closely the Merloni et
al. (2003) fundamental plane relation, which appears to trace the accretion
processes. Detailed X-ray spectral modeling from deeper hard X-ray observations
and higher angular resolution at radio wavelengths are required to further
proceed in the disentangling of jet and accretion related processes. |
Testing Graviton Parity and Gaussianity with Planck T-, E- and B-mode
Bispectra: Many inflationary theories predict a non-Gaussian spectrum of primordial
tensor perturbations, sourced from non-standard vacuum fluctuations, modified
general relativity or new particles such as gauge fields. Several such models
also predict a chiral spectrum in which one polarization state dominates. In
this work, we place constraints on the non-Gaussianity and parity properties of
primordial gravitational waves utilizing the Planck PR4 temperature and
polarization dataset. Using recently developed quasi-optimal bispectrum
estimators, we compute binned parity-even and parity-odd bispectra for all
combinations of CMB T-, E- and B-modes with $2\leq \ell<500$, and perform both
blind tests, sensitive to arbitrary three-point functions, and targeted
analyses of a well-motivated equilateral gravitational wave template (sourced
by gauge fields), with amplitude $f_{\rm NL}^{ttt}$. This is the first time
B-modes have been included in primordial non-Gaussianity analyses; they are
found to strengthen constraints on the parity-even sector by $\simeq 30\%$ and
dominate the parity-odd bounds, without inducing bias. We report no detection
of non-Gaussianity (of either parity), with the template amplitude constrained
to $f_{\rm NL}^{ttt}=900\pm 700$ (stable with respect to a number of analysis
variations), compared to $1300\pm1200$ in Planck 2018. The methods applied
herein can be reapplied to upcoming CMB datasets such as LiteBIRD, with the
inclusion of B-modes poised to dramatically improve future bounds on tensor
non-Gaussianity. | Optical microvariability properties of BALQSOs: We present optical light curves of 19 radio quiet (RQ) broad absorption line
(BAL) QSOs and study their rapid variability characteristics. Systematic CCD
observations, aided by a careful data analysis procedure, have allowed us to
clearly detect any such microvariability exceeding 0.01--0.02 mag. Our
observations cover a total of 13 nights (~72 hours) with each quasar monitored
for about 4 hours on a given night. Our sample size is a factor of three larger
than the number of radio-quiet BALQSOs previously searched for
microvariability. We introduce a scaled F-test statistic for evaluating the
presence of optical microvariability and demonstrate why it is generally
preferable to the statistics usually employed for this purpose. Considering
only unambiguous detections of microvariability we find that ~11 per cent of
radio-quiet BALQSOs (two out of 19 sources) show microvariability for an
individual observation length of about 4 hr. This new duty cycle of 11 per cent
is similar to the usual low microvariability fraction of normal RQQSOs with
observation lengths similar to those of ours. This result provides support for
models where radio-quiet BALQSO do not appear to be a special case of the
RQQSOs in terms of their microvariability properties. |
Cluster formation and the Sunyaev-Zel'dovich power spectrum in modified
gravity: the case of a phenomenologically extended DGP model: We investigate the effect of modified gravity on cluster abundance and the
Sunyaev-Zel'dovich angular power spectrum. Our modified gravity is based on a
phenomenological extension of the Dvali-Gabadadze-Porrati model which includes
two free parameters characterizing deviation from Lambda-CDM cosmology.
Assuming that Birkhoff's theorem gives a reasonable approximation, we study the
spherical collapse model of structure formation and show that while the growth
function changes to some extent, modified gravity gives rise to no significant
change in the linear density contrast at collapse time. The growth function is
enhanced in the so called normal branch, while in the "self-accelerating"
branch it is suppressed. The Sunyaev-Zel'dovich angular power spectrum is
computed in the normal branch, which turns out to be amplified compared to the
Lambda-CDM case. This allows us to put observational constraints on the
parameters of the modified gravity model using small scale CMB observation
data. | Lyman break and UV-selected galaxies at $z \sim 1$ I. Stellar
populations from ALHAMBRA survey: We take advantage of the exceptional photometric coverage provided by the
combination of GALEX data in the UV and the ALHAMBRA survey in the optical and
near-IR to analyze the physical properties of a sample of 1225 GALEX-selected
Lyman break galaxies (LBGs) at $0.8 \lesssim z \lesssim 1.2$ located in the
COSMOS field. This is the largest sample of LBGs studied at that redshift range
so far. According to a spectral energy distribution (SED) fitting with
synthetic stellar population templates, we find that LBGs at $z \sim 1$ are
mostly young galaxies with a median age of 341 Myr and have intermediate dust
attenuation, $\ < E_s (B-V) \ > \sim 0.20$. Due to their selection criterion,
LBGs at $z \sim 1$ are UV-bright galaxies and have high dust-corrected total
SFR, with a median value of 16.9 $M_\odot {\rm yr}^{-1}$. Their median stellar
mass is $\log{\left(M_*/M_\odot \right)} = 9.74$. We obtain that the
dust-corrected total SFR of LBGs increases with stellar mass and the specific
SFR is lower for more massive galaxies. Only 2% of the galaxies selected
through the Lyman break criterion have an AGN nature. LBGs at $z \sim 1$ are
mostly located over the blue cloud of the color-magnitude diagram of galaxies
at their redshift, with only the oldest and/or the dustiest deviating towards
the green valley and red sequence. Morphologically, 69% of LBGs are disk-like
galaxies, with the fraction of interacting, compact, or irregular systems being
much lower, below 12%. LBGs have a median effective radius of 2.5 kpc and
bigger galaxies have higher total SFR and stellar mass. Comparing to their
high-redshift analogues, we find evidence that LBGs at lower redshifts are
bigger, redder in the UV continuum, and have a major presence of older stellar
populations in their SEDs. However, we do not find significant difference in
the distributions of stellar mass or dust attenuation. |
Dynamical analysis of generalized Galileon cosmology: We perform a detailed dynamical analysis of generalized Galileon cosmology,
incorporating also the requirements of ghost and instabilities absence. We find
that there are not any new stable late-time solutions apart from those of
standard quintessence. Furthermore, depending on the model parameters the
Galileons may survive at late times or they may completely disappear by the
dynamics, however the corresponding observables are always independent of the
Galileon terms, determined only by the usual action terms. Thus, although the
Galileons can play an important role at inflationary or at recent times, in the
future, when the universe will asymptotically reach its stable state, they will
not have any effect on its evolution. | On rates of supernovae strongly lensed by galactic haloes in Millennium
Simulation: We make use of publicly available results from N-body Millennium Simulation
to create mock samples of lensed supernovae type Ia and core-collapse.
Simulating galaxy-galaxy lensing we derive the rates of lensed supernovae and
find than at redshifts higher that 0.5 about 0.06 per cent of supernovae will
be lensed by a factor two or more. Future wide field surveys like Gaia or LSST
should be able to detect lensed supernovae in their unbiased sky monitoring.
Gaia (from 2013) will detect at least 2 cases whereas LSST (from 2018) will see
more than 500 a year. Large number of future lensed supernovae will allow to
verify results of cosmological simulations. The strong galaxy- galaxy lensing
gives an opportunity to reach high-redshift supernovae type Ia and extend the
Hubble diagram sample. |
Gravitational Lensing of Gravitational Waves: Effect of Microlens
Population in Lensing Galaxies: With increasing sensitivities of the current ground-based gravitational-wave
(GW) detectors, the prospects of detecting a strongly lensed GW signal are
going to be high in the coming years. When such a signal passes through an
intervening lensing galaxy or galaxy cluster, the embedded stellar-mass
microlenses lead to interference patterns in the signal that may leave
observable signatures. In this work, we present an extensive study of these
wave effects in the LIGO/Virgo frequency band ($10$-$10^4$ Hz) due to the
presence of the microlens population in galaxy-scale lenses for the first time.
We consider a wide range of strong lensing (macro) magnifications and the
corresponding surface microlens densities found in lensing galaxies and use
them to generate realisations of the amplification factor. The methodologies
for simulating amplification curves for both types of images (minima and saddle
points) are also discussed. We then study how microlensing is broadly affected
by the parameters like macro-magnifications, stellar densities, the initial
mass function (IMF), types of images, and microlens distribution around the
source. In general, with increasing macro-magnification values, the effects of
microlensing become increasingly significant regardless of other parameters.
Mismatch analysis between the lensed and the unlensed GW waveforms from
chirping binaries suggests that, while inferring the source parameters,
microlensing can not be neglected for macro-magnification $\gtrsim 15$.
Furthermore, for extremely high macro-magnifications $\gtrsim 100$, the
mismatch can even exceed $5\%$, which can result in both a missed detection
and, consequently, a missed lensed signal. | The HI column density distribution function in faint dwarf galaxies: We present the HI column density distribution function,\fnh, as measured from
dwarf galaxies observed as part of the Faint Irregular Galaxy GMRT (FIGGS)
survey. We find that the shape of the dwarf galaxy \fnh\ is significantly
different from the \fnh\ for high redshift Damped \lya\ absorbers (DLAs) or the
\fnh\ for a representative sample of $z = 0$ gas rich galaxies. The dwarf \fnh\
falls much more steeply at high HI column densities as compared to the other
determinations. While $\sim 10%$ of the cross section above $\nh = 10^{20.3}
\acc$ at $z = 0$ is provided by dwarf galaxies, the fraction falls to $\lesssim
1%$ by $\nh \sim 10^{21.5} \acc.$ In the local universe, the contribution to
the high \nh\ end of the \fnh\ distribution comes predominantly from the
inclined disks of large galaxies. Dwarf galaxies, both because of their smaller
scale lengths, and their larger intrinsic axial ratios do not produce large HI
column densities even when viewed edge-on. If high column density DLAs/GRB
hosts correspond to galaxies like the local dwarfs, this would require either
that (i) the absorption arises from merging and not isolated systems or (ii)
the observed lines of sight are strongly biased towards high column density
regions. |
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