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First LOFAR observations at very low frequencies of cluster-scale
non-thermal emission: the case of Abell 2256: Abell 2256 is one of the best known examples of a galaxy cluster hosting
large-scale diffuse radio emission that is unrelated to individual galaxies. It
contains both a giant radio halo and a relic, as well as a number of head-tail
sources and smaller diffuse steep-spectrum radio sources. The origin of radio
halos and relics is still being debated, but over the last years it has become
clear that the presence of these radio sources is closely related to galaxy
cluster merger events. Here we present the results from the first LOFAR Low
band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our
knowledge, the image presented in this paper at 63 MHz is the deepest ever
obtained at frequencies below 100 MHz in general. Both the radio halo and the
giant relic are detected in the image at 63 MHz, and the diffuse radio emission
remains visible at frequencies as low as 20 MHz. The observations confirm the
presence of a previously claimed ultra-steep spectrum source to the west of the
cluster center with a spectral index of -2.3 \pm 0.4 between 63 and 153 MHz.
The steep spectrum suggests that this source is an old part of a head-tail
radio source in the cluster. For the radio relic we find an integrated spectral
index of -0.81 \pm 0.03, after removing the flux contribution from the other
sources. This is relatively flat which could indicate that the efficiency of
particle acceleration at the shock substantially changed in the last \sim 0.1
Gyr due to an increase of the shock Mach number. In an alternative scenario,
particles are re-accelerated by some mechanism in the downstream region of the
shock, resulting in the relatively flat integrated radio spectrum. In the radio
halo region we find indications of low-frequency spectral steepening which may
suggest that relativistic particles are accelerated in a rather inhomogeneous
turbulent region. | Age and metallicity gradients in early-type galaxies: A dwarf to giant
sequence: We studied the stellar populations of 40 early-type galaxies using medium
resolution long-slit spectroscopy along their major axes (and along the minor
axis for two of them), from 10^7 Msol to 10^12 Msol (-9.2 > M_B > -22.4 mag).
All the studied galaxies lie on the mass-metallicity and age-mass relations.
The transition type dwarfs deviate from the latter relation having younger mean
age, and the low-mass dwarf spheroidals have older ages, marking a
discontinuity in the relation, possibly due to selection effects.
In all mass regimes, the mean metallicity gradients are approximately -0.2
and the mean age gradients +0.1 dex per decade of radius. The individual
gradients are widely spread: $ -0.1 < \nabla_{\rm Age} < 0.4 $ and $-0.54 <
\nabla_{[{\rm Fe/H}]} < +0.2 $. We do not find evidence for a correlation
between the metallicity gradient and luminosity, velocity dispersion, central
age or age gradient. Likewise, we do not find a correlation between the age
gradient and any other parameter in bright early-type galaxies. In faint
early-types with $M_B \gtrsim -17$ mag, on the other hand, we find a
correlation between the age gradient and luminosity: the age gradient becomes
more positive for fainter galaxies.
We conclude that various physical mechanisms can lead to similar gradients
and that these gradients are robust against the environmental effects. In
particular, the gradients observed in dwarfs galaxies certainly survived the
transformation of the progenitors through tidal harassment or/and ram-pressure
stripping. The diversity of metallicity gradients amongst dwarf elliptical
galaxies may reflect a plurality of progenitors' morphologies. The dwarfs with
steep metallicity gradients could have originated from blue compact dwarfs and
those with flat profiles from dwarf irregulars and late type spirals.
(Abridged) |
A new era of fine structure constant measurements at high redshift: New observations of the quasar HE0515$-$4414 have been made using the HARPS
spectrograph on the ESO 3.6m telescope, aided by the Laser Frequency Comb
(LFC). We present three important advances for $\alpha$ measurements in quasar
absorption spectra from these observations. Firstly, the data have been
wavelength calibrated using LFC and ThAr methods. The LFC wavelength
calibration residuals are six times smaller than when using the standard ThAr
calibration. We give a direct comparison between $\alpha$ measurements made
using the two methods. Secondly, spectral modelling was performed using
Artificial Intelligence (fully automated, all human bias eliminated), including
a temperature parameter for each absorption component. Thirdly, in contrast to
previous work, additional model parameters were assigned to measure $\alpha$
for each individual absorption component. The increase in statistical
uncertainty from the larger number of model parameters is small and the method
allows a substantial advantage; outliers that would otherwise contribute a
significant systematic, possibly corrupting the entire measurement, are
identified and removed, permitting a more robust overall result. The $z_{abs} =
1.15$ absorption system along the HE0515$-$4414 sightline yields 40 new
$\alpha$ measurements. We constrain spatial fluctuations in $\alpha$ to be
$\Delta\alpha/\alpha \leq 9 \times 10^{-5}$ on scales $\approx 20\;{\rm
km\,s}^{-1}$, corresponding to $\approx25\;$kpc if the $z_{abs} = 1.15$ system
arises in a $1\;$Mpc cluster. Collectively, the 40 measurements yield
$\Delta\alpha/\alpha=-0.27\pm2.41\times10^{-6}$, consistent with no variation. | A local measurement of the growth rate from peculiar velocities and
galaxy clustering correlations in the 6dF Galaxy Survey: Galaxy peculiar velocities provide an integral source of cosmological
information that can be harnessed to measure the growth rate of large scale
structure and constrain possible extensions to General Relativity. In this
work, we present a method for extracting the information contained within
galaxy peculiar velocities through an ensemble of direct peculiar velocity and
galaxy clustering correlation statistics, including the effects of redshift
space distortions, using data from the 6-degree Field Galaxy Survey. Our method
compares the auto- and cross-correlation function multipoles of these
observables, with respect to the local line of sight, with the predictions of
cosmological models. We find that the uncertainty in our measurement is
improved when combining these two sources of information in comparison to
fitting to either peculiar velocity or clustering information separately. When
combining velocity and density statistics in the range $27 < s < 123 \, h^{-1}$
Mpc we obtain a value for the local growth rate of $f\sigma_8 = 0.358 \pm
0.075$ and for the linear redshift distortion parameter $\beta = 0.298 \pm
0.065$, recovering both with $20.9$ per cent and $21.8$ per cent accuracy
respectively. We conclude this work by comparing our measurement with other
recent local measurements of the growth rate, spanning different datasets and
methodologies. We find that our results are in broad agreement with those in
the literature and are fully consistent with $\Lambda$CDM cosmology. Our
methods can be readily scaled to analyse upcoming large galaxy surveys and
achieve accurate tests of the cosmological model. |
Resolving Globular Cluster Formation within a Cosmological Context: We place constraints on the formation redshifts for blue globular clusters
(BGCs), independent of the details of hydrodynamics and population III star
formation. The observed radial distribution of BGCs in the Milky Way Galaxy
suggests that they formed in biased dark matter halos at high redshift. As a
result, simulations of a ~1 Mpc box up to z~10 must resolve BGC formation in
LCDM. We find that most halo stars could be produced from destroyed BGCs and
other low-mass clusters that formed at high redshift. We present a
proof-of-concept simulation that captures the formation of globular-like star
clusters. | Constraints on Dark Energy state equation with varying pivoting redshift: We assume the DE state equations w(a) = w_0+w_a(a_p-a), and study the
dependence of the constraints on w_0 and w_a coefficients on the pivoting
redshift 1+z_p=1/a_p. Coefficients are fitted to data including WMAP7, SNIa
(Union 2.1), BAO's (including WiggleZ and SDSS results) and H_0 constraints.
The fitting algorithm is CosmoMC. We find specific differences between the
cases when neutrino mass is allowed or disregarded. More in detail: i) The z_p
value yielding uncorrelated constraints on w_0 and w_a is different in the two
cases, holding ~0.25 and ~0.35, respectively. (ii) If we consider the intervals
allowed to w_0, we find that they shift when z_p increases, in opposite
directions for vanishing or allowed neutrino mass. This leads to no overlap
between 1sigma intervals already at z_p >~0.4. (iii) The known effect that a
more negative state parameter is required to allow for neutrino mass displays
its effects on w_a, rather than on w_0. (iv) The w_0-w_a constraints found by
using any pivot z_p can be translated into constraints holding at a specific
z_p value (0 or the z_p where errors are uncorrelated). When we do so, error
ellipses exhibit a satisfactory overlap. |
Gaussianisation for fast and accurate inference from cosmological data: We present a method to transform multivariate unimodal non-Gaussian posterior
probability densities into approximately Gaussian ones via non-linear mappings,
such as Box--Cox transformations and generalisations thereof. This permits an
analytical reconstruction of the posterior from a point sample, like a Markov
chain, and simplifies the subsequent joint analysis with other experiments.
This way, a multivariate posterior density can be reported efficiently, by
compressing the information contained in MCMC samples. Further, the model
evidence integral (i.e. the marginal likelihood) can be computed analytically.
This method is analogous to the search for normal parameters in the cosmic
microwave background, but is more general. The search for the optimally
Gaussianising transformation is performed computationally through a
maximum-likelihood formalism; its quality can be judged by how well the
credible regions of the posterior are reproduced. We demonstrate that our
method outperforms kernel density estimates in this objective. Further, we
select marginal posterior samples from Planck data with several distinct
strongly non-Gaussian features, and verify the reproduction of the marginal
contours. To demonstrate evidence computation, we Gaussianise the joint
distribution of data from weak lensing and baryon acoustic oscillations (BAO),
for different cosmological models, and find a preference for flat $\Lambda$CDM.
Comparing to values computed with the Savage-Dickey density ratio, and
Population Monte Carlo, we find good agreement of our method within the spread
of the other two. | Lyα Emission from High Redshift Sources in COSMOS: We investigate spectroscopically measured Ly{\alpha} equivalent widths and
escape fractions of 244 sources of which 95 are Lyman Break Galaxies (LBGs) and
106 Lyman Alpha Emitters (LAEs) at z~4.2, z~4.8, and z~5.6 selected from
intermediate and narrow band observations. The sources were selected from the
Cosmic Evolution Survey (COSMOS), and observed with the DEIMOS spectrograph. We
find that the distribution of equivalent widths shows no evolution with
redshift for both the LBG selected sources and the intermediate/narrowband
LAEs. We also find that the Ly{\alpha} escape fraction of intermediate and
narrow band LAEs is on average higher and has a larger variation than the
escape fraction of LBG selected sources. The escape fraction does not show a
dependence with redshift. Similar to what has been found for LAEs at low
redshifts, the sources with the highest extinctions show the lowest escape
fractions. The range of escape fractions increases with decreasing extinction.
This is evidence that the dust extinction is the most important factor
affecting the escape of Ly{\alpha} photons, but at low extinctions other
factors such as HI covering fraction and gas kinematics can be just as
effective at inhibiting the escape of Ly{\alpha} photons. |
Spherical collapse in quintessence models with zero speed of sound: We study the spherical collapse model in the presence of quintessence with
negligible speed of sound. This case is particularly motivated for w<-1 as it
is required by stability. As pressure gradients are negligible, quintessence
follows dark matter during the collapse. The spherical overdensity behaves as a
separate closed FLRW universe, so that its evolution can be studied exactly. We
derive the critical overdensity for collapse and we use the extended
Press-Schechter theory to study how the clustering of quintessence affects the
dark matter mass function. The effect is dominated by the modification of the
linear dark matter growth function. A larger effect occurs on the total mass
function, which includes the quintessence overdensities. Indeed, here
quintessence constitutes a third component of virialized objects, together with
baryons and dark matter, and contributes to the total halo mass by a fraction ~
(1+w) Omega_Q / Omega_m. This gives a distinctive modification of the total
mass function at low redshift. | Star-forming regions in the intragroup medium of compact groups of
galaxies: We present the results of a multiwavelength campaign searching for young
objects in the intragroup medium of seven compact groups of galaxies: HCG 2, 7,
22, 23, 92, 100 and NGC 92. We used Fabry-Perot velocity fields and rotation
curves together with GALEX NUV and FUV images, optical R-band and HI maps to
evaluate the stage of interaction of each group. We conclude that groups (i)
HCG 7 and HCG 23 are in an early stage of interaction, (ii) HCG 2 and HCG 22
are mildly interacting, and (iii) HCG 92, HCG 100 and NGC 92 are in a late
stage of evolution. Evolved groups have a population of young objects in their
intragroup medium while no such population is found within the less evolved
groups. We also report the discovery of a tidal dwarf galaxy candidate in the
tail of NGC 92. These three groups, besides containing galaxies which have
peculiar velocity fields, also show extended HI tails. Our results indicate
that the advanced stage of evolution of a group together with the presence of
intragroup HI clouds may lead to star formation in the intragroup medium. |
ALFALFA Discovery of the Nearby Gas-Rich Dwarf Galaxy Leo~P. III. An
Extremely Metal Deficient Galaxy: We present KPNO 4-m and LBT/MODS spectroscopic observations of an HII region
in the nearby dwarf irregular galaxy Leo P discovered recently in the Arecibo
ALFALFA survey. In both observations, we are able to accurately measure the
temperature sensitive [O III] 4363 Angstrom line and determine a "direct"
oxygen abundance of 12 + log(O/H) = 7.17 +/- 0.04. Thus, Leo P is an extremely
metal deficient (XMD) galaxy, and, indeed, one of the most metal deficient
star-forming galaxies ever observed. For its estimated luminosity, Leo P is
consistent with the relationship between luminosity and oxygen abundance seen
in nearby dwarf galaxies. Leo P shows normal alpha element abundance ratios
(Ne/O, S/O, and Ar/O) when compared to other XMD galaxies, but elevated N/O,
consistent with the "delayed release" hypothesis for N/O abundances. We derive
a helium mass fraction of 0.2509 +0.0184 -0.0123 which compares well with the
WMAP + BBN prediction of 0.2483 +/- 0.0002 for the primordial helium abundance.
We suggest that surveys of very low mass galaxies compete well with emission
line galaxy surveys for finding XMD galaxies. It is possible that XMD galaxies
may be divided into two classes: the relatively rare XMD emission line galaxies
which are associated with starbursts triggered by infall of low-metallicity gas
and the more common, relatively quiescent XMD galaxies like Leo P, with very
low chemical abundances due to their intrinsically small masses. | Updated constraints from the effective field theory analysis of BOSS
power spectrum on Early Dark Energy: Analyses of the full shape of BOSS DR12 power spectrum using the one-loop
prediction from the Effective Field Theory of Large-Scale Structure (EFTBOSS)
have led to new constraints on extensions to the $\Lambda$CDM model, such as
Early Dark Energy (EDE) which has been suggested as a resolution to the "Hubble
tension". In this paper, we re-assess the constraining power of the EFTBOSS on
EDE in light of a correction to the normalization of BOSS window functions.
Overall we find that constraints from EFTBOSS on EDE are weakened, and
represent a small change compared to constraints from Planck and the
conventional BAO/$f\sigma_8$ measurements. The combination of Planck data with
EFTBOSS provides a bound on the maximal fractional contribution of EDE $f_{\rm
EDE}<0.083$ at 95% C.L. (compared to $<0.054$ with the incorrect normalization,
and $<0.088$ without full-shape data) and the Hubble tension is reduced to
$2.1\sigma$. However, the more extreme model favored by an analysis with just
data from the Atacama Cosmology Telescope is disfavored by the EFTBOSS data. We
also show that the updated Pantheon+ Type Ia supernova analysis can slightly
increase the constraints on EDE. Yet, the inclusion of the SN1a magnitude
calibration by SH0ES strongly increases the preference for EDE to above
$5\sigma$, yielding $f_{\rm EDE}\sim 0.12^{+0.03}_{-0.02}$ around the redshift
$z_c=4365^{+3000}_{-1100}$. Our results demonstrate that EFTBOSS data (alone or
combined with Planck data) do not exclude the EDE resolution of the Hubble
tension. |
HI tomographic imaging of the Cosmic Dawn and Epoch of Reionization with
SKA: We provide an overview of 21cm tomography of the Cosmic Dawn and Epoch of
Reionization as possible with SKA-Low. We show why tomography is essential for
studying CD/EoR and present the scales which can be imaged at different
frequencies for the different phases of SKA- Low. Next we discuss the different
ways in which tomographic data can be analyzed. We end with an overview of
science questions which can only be answered by tomography, ranging from the
characterization of individual objects to understanding the global processes
shaping the Universe during the CD/EoR | Spacetime variation of $α$ and the CMB power spectra after the
recombination: The possible variation of the fine structure constant may be due to the
non-minimal coupling of the electromagnetic field to a light scalar field which
can be the candidate of dark energy. Its dynamical nature renders the fine
structure constant varies with time as well as space. In this paper we point
out the spatial fluctuation of the fine structure will modify the power spectra
of the temperature and the polarization of the cosmic microwave background. We
show explicitly that the fluctuations of the coupled scalar field generate new
temperature anisotropies at the linear order and induce a $B$ mode to the
polarization at higher order in general. |
Probing Helical Magnetic Fields in AGN by Rotation Measure Gradients
Studies: One of the tools that can provide evidence about the existence of helical
magnetic fields in AGN is the observation of rotation measure gradients across
the jet. Such observations have been previously made successfully, proving that
such gradients are far from being rare, but common and typically persistent
over several years, although some of them may show a reversal in the direction
along the jet. Further studies of rotation measure gradients can help us in our
understanding of the magnetic field properties and structure in the base of the
jets. We studied Very Long Baseline Array (VLBA) polarimetric observations of 8
sources consistent of some quasars and BL Lacs at 12, 15, 22, 24 and 43 GHz and
we find that all but two sources show indications of rotation measure
gradients, either parallel or perpendicular to the jet. We interpret gradients
perpendicular to the jet as indications of the change of the line of sight of
the magnetic field due to its helicity, and gradients parallel to the jet as
the decrease of magnetic field strength and/or electron density as we move
along the jet. When comparing our results with the literature, we find
tentative evidence of a rotation measure gradient flip, which can be explained
as a change of the pitch angle or jet bending. | AGN and star formation activity in local luminous and ultraluminous
infrared galaxies: The enormous amounts of infrared (IR) radiation emitted by luminous infrared
galaxies (LIRGs, L_IR=10^11-10^12Lsun) and ultraluminous infrared galaxies
(ULIRGs, L_IR>10^12Lsun) are produced by dust heated by intense star formation
(SF) activity and/or an active galactic nucleus (AGN). The elevated star
formation rates and high AGN incidence in (U)LIRGs make them ideal candidates
to study the interplay between SF and AGN activity in the local universe. In
this paper I review recent results on the physical extent of the SF activity,
the AGN detection rate (including buried AGN), the AGN bolometric contribution
to the luminosity of the systems, as well as the evolution of local LIRGs and
ULIRGs. The main emphasis of this review is on recent results from IR
observations. |
Dependence of Fanaroff--Riley break of radio galaxies on luminosity and
redshift: We investigate the dependence of the Fanaroff-Riley (FR) 1/2 dichotomy of
radio galaxies on their luminosities and redshifts. Because of a very strong
redshift-luminosity correlation (Malmquist bias) in a flux-limited sample, any
redshift-dependent effect could appear as a luminosity related effect and vice
versa. A question could then arise - do all the morphological differences seen
in the two classes (FR 1 and 2 types) of sources, usually attributed to the
differences in their luminosities, could as well be primarily a
redshift-dependent effect? A sharp break in luminosity, seen among the two
classes, could after all reflect a sharp redshift-dependence due to a rather
critical ambient density value at some cosmic epoch. A doubt on these lines
does not seem to have been raised in past and things have never been examined
with this particular aspect in mind. We want to ascertain the customary
prevalent view in the literature that the systematic differences in the two
broad morphology types of FR 1 and 2 radio galaxies are indeed due to the
differences in their luminosities, and not due to a change in redshift. Here we
investigate the dependence of FR 1/2 dichotomy of radio galaxies on luminosity
and redshift by using the 3CR sample, where the FR 1/2 dichotomy was first
seen, supplemented by data from an additional sample (MRC), that goes about a
factor of 5 or more deeper in flux-density than the original 3CR sample. This
lets us compare sources with similar luminosities but at different redshifts as
well as examine sources at similar redshifts but with different luminosities,
thereby allowing us a successful separation of the otherwise two intricately
entangled effects. We find that the morphology type is not directly related to
redshift and the break between the two types of morphologies seems to depend
only upon the radio luminosity. | Neutrino lumps and the Cosmic Microwave Background: The interaction between the cosmon and neutrinos may solve the "why now
problem" for dark energy cosmologies. Within growing neutrino quintessence it
leads to the formation of nonlinear neutrino lumps. For a test of such models
by the integrated Sachs-Wolfe effect for the cosmic microwave background (CMB)
we estimate the size and time evolution of the gravitational potential induced
by these lumps. A population of lumps with size of 100 Mpc or more could lead
to observable effects on the CMB anisotropies for low angular momenta. The
linear approximation is found to be invalid for the relevant length scales.
Quantitative estimates depend strongly on the details of the transition between
the linear and nonlinear regimes. In particular, important backreaction effects
arise from the nonlinearities of the cosmon interactions. At the present stage
the uncertainties of the estimate make it difficult to constrain the parameter
space of growing neutrino models. We explicitly discuss scenarios and models
that are compatible with the CMB observations. |
Probing the epoch of pre-reionization by cross-correlating cosmic
microwave and infrared background anisotropies: The epoch of first star formation and the state of the intergalactic medium
(IGM) at that time are not directly observable with current telescopes. The
radiation from those early sources is now part of the Cosmic Infrared
Background (CIB) and, as these sources ionize the gas around them, the IGM
plasma would produce faint temperature anisotropies in the Cosmic Microwave
Background (CMB) via the thermal Sunyaev-Zeldovich (TSZ) effect. While these
TSZ anisotropies are too faint to be detected, we show that the
cross-correlation of maps of source-subtracted CIB fluctuations from {\it
Euclid}, with suitably constructed microwave maps at different frequencies can
probe the physical state of the gas during reionization and test/constrain
models of the early CIB sources. We identify the frequency-combined
CMB-subtracted microwave maps from space and ground-based instruments to show
that they can be cross-correlated with the forthcoming all-sky {\it Euclid} CIB
maps to detect the cross-power at scales $\sim 5'-60'$ with the signal/noise of
up to $S/N\sim 4-8$ depending on the contribution to the Thomson optical depth
during those pre-reionization epochs ($\Delta \tau\simeq 0.05$) and the
temperature of IGM (up to $\sim10^4$K). Such a measurement would offer a new
window to explore emergence and physical properties of these first light
sources. | The geometrical meaning of statistical isotropy of smooth random fields
in two dimensions: We revisit the geometrical meaning of statistical isotropy that is manifest
in excursion sets of smooth random fields in two dimensions. Using the contour
Minkowski tensor, $\W_1$, as our basic tool we first examine geometrical
properties of single structures. For simple closed curves in two dimensions we
show that $\W_1$ is proportional to the identity matrix if the curve has
$m$-fold symmetry, with $m\ge 3$. Then we elaborate on how $\W_1$ maps any
arbitrary shaped simple closed curve to an ellipse that is unique up to
translations of its centroid. We also carry out a comparison of the shape
parameters, $\alpha$ and $\beta$, defined using $\W_1$, with the filamentarity
parameter defined using two scalar Minkowski functionals - area and contour
length. We show that they contain complementary shape information, with $\W_1$
containing additional information of orientation of structures. Next, we apply
our method to boundaries of excursion sets of random fields and examine what
statistical isotropy means for the geometry of the excursion sets. Focusing on
Gaussian isotropic fields, and using a semi-numerical approach we quantify the
effect of finite sampling of the field on the geometry of the excursion sets.
In doing so we obtain an analytic expression for $\alpha$ which takes into
account the effect of finite sampling. Finally we derive an analytic expression
for the ensemble expectation of $\W_1$ for Gaussian anisotropic random fields.
Our results provide insights that are useful for designing tests of statistical
isotropy using cosmological data. |
Formation and Evolution of Primordial Black Hole Binaries in the Early
Universe: The abundance of primordial black holes (PBHs) in the mass range $0.1 - 10^3
M_\odot$ can potentially be tested by gravitational wave observations due to
the large merger rate of PBH binaries formed in the early universe. To put the
estimates of the latter on a firmer footing, we first derive analytical PBH
merger rate for general PBH mass functions while imposing a minimal initial
comoving distance between the binary and the PBH nearest to it, in order to
pick only initial configurations where the binary would not get disrupted. We
then study the formation and evolution of PBH binaries before recombination by
performing N-body simulations. We find that the analytical estimate based on
the tidally perturbed 2-body system strongly overestimates the present merger
rate when PBHs comprise all dark matter, as most initial binaries are disrupted
by the surrounding PBHs. This is mostly due to the formation of compact N-body
systems at matter-radiation equality. However, if PBHs make up a small fraction
of the dark matter, $f_{\rm PBH} \lesssim 10\%$, these estimates become more
reliable. In that case, the merger rate observed by LIGO imposes the strongest
constraint on the PBH abundance in the mass range $2 - 160 M_\odot$. Finally,
we argue that, even if most initial PBH binaries are perturbed, the present
BH-BH merger rate of binaries formed in the early universe is larger than
$\mathcal{O}(10)\,{\rm Gpc}^{-3} {\rm yr}^{-1}\, f_{\rm PBH}^3$ | The Cartwheel galaxy with XMM-Newton: The extreme environment provided by the Cartwheel ring is analyzed to study
its X-ray and optical-UV properties. We compare the Cartwheel with the other
members of its group and study the system as a whole in the X-ray band. We
analyze the data of the Cartwheel galaxy obtained with XMM-Newton in two
different periods (December 2004 and May 2005). We focus on the X-ray
properties of the system and use the OM data to obtain additional information
in the optical and UV bands. We detect a total of 8 sources associated with the
Cartwheel galaxy and three in its vicinity, including G1 and G2, all at L >=
10^39 erg/s, that is the Ultra Luminous X-ray (ULX) source range. The brightest
ULX source has been already discussed elsewhere. The spectra of the next three
brightest ULX are well fitted by a power-law model with a mean photon index of
~2. We compare the XMM-Newton and Chandra datasets to study the long-term
variability of the sources. At least three sources vary in the 5 months between
the two XMM-Newton observations and at least four in the 4-year timeframe
between Chandra and XMM-Newton observations. One Chandra source disappears and
a new one is detected by XMM-Newton in the ring. Optical-UV colors of the
Cartwheel ring are consistent with a burst of star formation that is close to
reaching its maximum, yielding a mean stellar age of about 40 Myr. The inferred
variability and age suggest that high mass X-ray binaries are the counterparts
to the ULX sources. The 3 companion galaxies have luminosities in the range
10^39-40 erg/s consistent with expectations. The hot gas of the Cartwheel
galaxy is luminous and abundant (a few 10^8 Msol) and is found both in the
outer ring, and in the inner part of the galaxy, behind the shock wave front.
We also detect gas in the group with L_X ~10^40 erg/s. |
Cosmologies of extended massive gravity: We study the background cosmology of two extensions of dRGT massive gravity.
The first is variable mass massive gravity, where the fixed graviton mass of
dRGT is replaced by the expectation value of a scalar field. We ask whether
self-inflation can be driven by the self-accelerated branch of this theory, and
we find that, while such solutions can exist for a short period, they cannot be
sustained for a cosmologically useful time. Furthermore, we demonstrate that
there generally exist future curvature singularities of the "big brake" form in
cosmological solutions to these theories. The second extension is the covariant
coupling of galileons to massive gravity. We find that, as in pure dRGT
gravity, flat FRW solutions do not exist. Open FRW solutions do exist -- they
consist of a branch of self-accelerating solutions that are identical to those
of dRGT, and a new second branch of solutions which do not appear in dRGT. | Constraining the relative velocity effect using the Baryon Oscillation
Spectroscopic Survey: We analyse the power spectrum of the Baryon Oscillation Spectroscopic Survey
(BOSS), Data Release 12 (DR12) to constrain the relative velocity effect, which
represents a potential systematic for measurements of the Baryon Acoustic
Oscillation (BAO) scale. The relative velocity effect is sourced by the
different evolution of baryon and cold dark matter perturbations before
decoupling. Our power spectrum model includes all $1$-loop redshift-space terms
corresponding to $v_{\rm bc}$ parameterised by the bias parameter $b_{v^2}$. We
also include the linear terms proportional to the relative density,
$\delta_{\rm bc}$, and relative velocity dispersion, $\theta_{\rm bc}$, which
we parameterise with the bias parameters $b^{\rm bc}_{\delta}$ and $b^{\rm
bc}_{\theta}$. Our data does not support a detection of the relative velocity
effect in any of these parameters. Combining the low and high redshift bins of
BOSS, we find limits of $b_{v^2} = 0.012 \pm 0.015\;(\pm 0.031)$, $b^{\rm
bc}_{\delta} = -1.0 \pm 2.5\;(\pm 6.2)$ and $b^{\rm bc}_{\theta} = -114 \pm
55\;(\pm 175)$ with $68\%$ ($95\%$) confidence levels. These constraints
restrict the potential systematic shift in $D_A(z)$, $H(z)$ and $f\sigma_8$,
due to the relative velocity, to $1\%$, $0.8\%$ and $2\%$, respectively. Given
the current uncertainties on the BAO measurements of BOSS these shifts
correspond to $0.53\sigma$, $0.5\sigma$ and $0.22\sigma$ for $D_A(z)$, $H(z)$
and $f\sigma_8$, respectively. |
Maximum Brightness Temperature of an Incoherent Synchrotron Source :
Inverse Compton Limit - a Misnomer: We show that an upper limit of ~ 10^{12} K on the peak brightness temperature
for an incoherent synchrotron radio source, commonly referred to in the
literature as an inverse Compton limit, may not really be due to inverse
Compton effects. We show that a somewhat tighter limit T_{eq} ~ 10^{11} is
actually obtained for the condition of equipartition of energy between
radiating particles and magnetic fields which happens to be a configuration of
minimum energy for a self-absorbed synchrotron radio source. An order of
magnitude change in brightness temperature from T_{eq} in either direction
would require departures from equipartition of about eight orders of magnitude,
implying a change in total energy of the system up to ~ 10^{4} times the
equipartition value. Constraints of such extreme energy variations imply that
brightness temperatures may not depart much from T_{eq}. This is supported by
the fact that at the spectral turnover, brightness temperatures much lower than
~ 10^{11} K are also not seen in VLBI observations. Higher brightness
temperatures in particular, would require in the source not only many orders of
magnitude higher additional energy for the relativistic particles but also many
order of magnitude weaker magnetic fields. Diamagnetic effects do not allow
such extreme conditions, keeping the brightness temperatures close to the
equipartition value, which is well below the limit where inverse Compton
effects become important. | Redshift drift in an inhomogeneous universe: averaging and the
backreaction conjecture: An expression for the average redshift drift in a statistically homogeneous
and isotropic dust universe is given. The expression takes the same form as the
expression for the redshift drift in FLRW models. It is used for a
proof-of-principle study of the effects of backreaction on redshift drift
measurements by combining the expression with two-region models. The study
shows that backreaction can lead to positive redshift drift at low redshifts,
exemplifying that a positive redshift drift at low redshifts does not require
dark energy. Moreover, the study illustrates that models without a dark energy
component can have an average redshift drift observationally indistinguishable
from that of the standard model according to the currently expected precision
of ELT measurements. In an appendix, spherically symmetric solutions to
Einstein's equations with inhomogeneous dark energy and matter are used to
study deviations from the average redshift drift and effects of local voids. |
Statistical methods in cosmology: The advent of large data-set in cosmology has meant that in the past 10 or 20
years our knowledge and understanding of the Universe has changed not only
quantitatively but also, and most importantly, qualitatively. Cosmologists rely
on data where a host of useful information is enclosed, but is encoded in a
non-trivial way. The challenges in extracting this information must be overcome
to make the most of a large experimental effort. Even after having converged to
a standard cosmological model (the LCDM model) we should keep in mind that this
model is described by 10 or more physical parameters and if we want to study
deviations from it, the number of parameters is even larger. Dealing with such
a high dimensional parameter space and finding parameters constraints is a
challenge on itself. Cosmologists want to be able to compare and combine
different data sets both for testing for possible disagreements (which could
indicate new physics) and for improving parameter determinations. Finally,
cosmologists in many cases want to find out, before actually doing the
experiment, how much one would be able to learn from it. For all these reasons,
sophisiticated statistical techniques are being employed in cosmology, and it
has become crucial to know some statistical background to understand recent
literature in the field. I will introduce some statistical tools that any
cosmologist should know about in order to be able to understand recently
published results from the analysis of cosmological data sets. I will not
present a complete and rigorous introduction to statistics as there are several
good books which are reported in the references. The reader should refer to
those. | Non-parametric analysis of the Hubble Diagram with Neural Networks: The recent extension of the Hubble diagram of Supernovae and quasars to
redshifts much higher than 1 prompted a revived interest in non-parametric
approaches to test cosmological models and to measure the expansion rate of the
Universe. In particular, it is of great interest to infer model-independent
constraints on the possible evolution of the dark energy component. Here we
present a new method, based on a Neural Network Regression, to analyze the
Hubble Diagram in a completely non-parametric, model-independent fashion. We
first validate the method through simulated samples with the same redshift
distribution as the real ones, and discuss the limitations related to the
"inversion problem" for the distance-redshift relation. We then apply this new
technique to the analysis of the Hubble diagram of Supernovae and quasars. We
confirm that the data up to $z \sim 1-1.5$ are in agreement with a flat
${\Lambda}CDM$ model with ${\Omega}_M \sim 0.3$, while $\sim 5$-sigma
deviations emerge at higher redshifts. A flat ${\Lambda}CDM$ model would still
be compatible with the data with ${\Omega}_M > 0.4$. Allowing for a generic
evolution of the dark energy component, we find solutions suggesting an
increasing value of ${\Omega}_M$ with the redshift, as predicted by interacting
dark sector models. |
Interactions in the dark sector of the Universe: Interactions inside the cosmological dark sector influence the cosmological
dynamics. As a consequence, the future evolution of the Universe may be
different from that predicted by the $\Lambda$CDM model. We review main
features of several recently studied models with nongravitational couplings
between dark matter and dark energy. | A Dynamically Driven, Universal Thermal Profile of Galaxy Groups and
Clusters: Large scale structures such as groups and clusters of galaxies show a
universal, nearly linear entropy radial profile $K(r)$. Using deprojected 16
clusters and 12 groups from the literature, we find that $K\propto
r^{0.96\pm0.01}$, consistent with the mean power-law index $(0.9\mbox{--}1.1)$
of previous studies. A similarly good fit is given by a $\tau\propto
r^{0.72\pm0.01}$ ratio between cooling and free-fall times. Both profiles
slightly flatten at small radii, as $\tau$ becomes of order unity. The entropy
profile is usually attributed to self-similar shock accretion (shown to be
inconsistent with the data), to non-standard heat conduction, or to turbulent
heating. We argue that a dynamical mechanism is needed to sustain such a
universal profile, oblivious to the temperature peak at the edge of the core
and to the virial shock at the outskirts, and robust to the presence of ongoing
cooling, merger, and active galactic nucleus (AGN) activity. In particular, we
show that such a profile can be naturally obtained in a spiral flow, which is
likely to underlie most galaxy aggregates according to the ubiquitous spiral
patterns and cold fronts observed. Generalizing a two-phase spiral flow model
out to the virial radius surprisingly reproduces the thermal profile. A
generalized Schwarzschild criterion indicates that observed spiral patterns
must involve a convective layer, which may regulate the thermal profile. |
Probing pre-Recombination Physics by the Cross-Correlation of Stochastic
Gravitational Waves and CMB Anisotropies: We study the effects of pre-recombination physics on the Stochastic
Gravitational Wave Background (SGWB) anisotropies induced by the propagation of
gravitons through the large-scale density perturbations and their
cross-correlation with Cosmic Microwave Background (CMB) temperature and E-mode
polarization ones. As examples of Early Universe extensions to the $\Lambda$CDM
model, we consider popular models featuring extra relativistic degrees of
freedom, a massless non-minimally coupled scalar field, and an Early Dark
Energy component. Assuming the detection of a SGWB, we perform a Fisher
analysis to assess in a quantitative way the capability of future gravitational
wave interferometers (GWIs) in conjunction with a future large-scale CMB
polarization experiment to constrain such variations. Our results show that the
cross-correlation of CMB and SGWB anisotropies will help tighten the
constraints obtained with CMB alone, with an improvement that significantly
depends on the specific model as well as the maximum angular resolution
$\ell_{\rm max}^{\rm GW}$ of the GWIs, their designed sensitivity, and the
amplitude $A_*$ of the monopole of the SGWB. | Constraints on the Local Cosmic Void from the Pantheon Supernovae Data: In principle, the local cosmic void can be simply modeled by the spherically
symmetric Lemaitre-Tolman-Bondi (LTB) metric. In practice, the real local
cosmic void is probably not spherically symmetric. In this paper, to
reconstruct a more realistic profile of the local cosmic void, we divide it
into several segments. Each segment with certain solid angle is modeled by its
own LTB metric. Meanwhile, we divide the 1048 type Ia supernovae (SNIa) of the
Pantheon Survey into corresponding subsets according to their distribution in
the galactic coordinate system. Obviously, each SNIa subset can only be used to
reconstruct the profile of one segment. Finally, we can patch together an
irregular profile for the local cosmic void with the whole Pantheon sample.
Note that, the paucity of each data subset lead us to focus on the inner part
of each void segment and assume that the half radii of the void segments are
sufficient to constrain the whole segment. We find that, despite $2\sigma$
signals of anisotropy limited to the depth of the void segments, the
constraints on every void segment are consistent with $\Lambda$CDM model at
$95\%$ CL. Moreover, our constraints are too weak to challenge the cosmic
homogeneity and isotropy. |
Direct Evidence for Termination of Obscured Star Formation by
Radiatively Driven Outflows in Reddened QSOs: We present optical to far-infrared photometry of 31 reddened QSOs that show
evidence for radiatively driven outflows originating from AGN in their
rest-frame UV spectra. We use these data to study the relationships between the
AGN-driven outflows, and the AGN and starburst infrared luminosities. We find
that FeLoBAL QSOs are invariably IR-luminous, with IR luminosities exceeding
10^{12} Solar luminosities in all cases. The AGN supplies 76% of the total IR
emission, on average, but with a range from 20% to 100%. We find no evidence
that the absolute luminosity of obscured star formation is affected by the
AGN-driven outflows. Conversely, we find an anticorrelation between the
strength of AGN-driven outflows, as measured from the range of outflow
velocities over which absorption exceeds a minimal threshold, and the
contribution from star formation to the total IR luminosity, with a much higher
chance of seeing a starburst contribution in excess of 25% in systems with weak
outflows than in systems with strong outflows. Moreover, we find no convincing
evidence that this effect is driven by the IR luminosity of the AGN. We
conclude that radiatively driven outflows from AGN can have a dramatic,
negative impact on luminous star formation in their host galaxies. We find that
such outflows act to curtail star formation such that star formation
contributes less than ~25% of the total IR luminosity. We also propose that the
degree to which termination of star formation takes place is not deducible from
the IR luminosity of the AGN. | Extrinsic Sources of Scatter in the Richness-Mass Relation of Galaxy
Clusters: Maximizing the utility of upcoming photometric cluster surveys requires a
thorough understanding of the richness-mass relation of galaxy clusters. We use
Monte Carlo simulations to study the impact of various sources of observational
scatter on this relation. Cluster ellipticity, photometric errors, photometric
redshift errors, and cluster-to-cluster variations in the properties of
red-sequence galaxies contribute negligible noise. Miscentering, however, can
be important, and likely contributes to the scatter in the richness-mass
relation of galaxy maxBCG clusters at the low mass end, where centering is more
difficult. We also investigate the impact of projection effects under several
empirically motivated assumptions about cluster environments. Using SDSS data
and the maxBCG cluster catalog, we demonstrate that variations in cluster
environments can rarely (\approx 1% - 5% of the time) result in significant
richness boosts. Due to the steepness of the mass/richness function, the
corresponding fraction of optically selected clusters that suffer from these
projection effects is \approx 5% - 15%. We expect these numbers to be generic
in magnitude, but a precise determination requires detailed, survey-specific
modeling. |
The Matter Bounce Alternative to Inflationary Cosmology: A bouncing cosmology with an initial matter-dominated phase of contraction
during which scales which are currently probed with cosmological observations
exit the Hubble radius provides a mechanism alternative to inflation for
producing a nearly scale-invariant spectrum of cosmological perturbations. In
this review article I first discuss the evolution of cosmological fluctuations
in the matter bounce scenario, and then discuss various attempts at realizing
such a scenario. Observational signatures which will allow the matter bounce to
be distinguished from the inflationary paradigm are also discussed. | Star formation histories and evolution of 35 brightest E+A galaxies from
SDSS DR5: We pick out the 35 brightest galaxies from Goto's E+A galaxies catalogue
which are selected from the Sloan Digital Sky Survey Data Release 5. The
spectra of E+As are prominently characterized by the strong Balmer absorption
lines but little [Oii] or H_alpha emission lines. In this work we study the
stellar populations of the sample galaxies by fitting their spectra using
ULySS, which is a robust full spectrum fitting method. We fit each of the
sample with 1-population (a single stellar population-a SSP) and 3-population
(3 SSPs) models, separately. By 1-population fits, we obtain SSP-equivalent
ages and metallicities which correspond to the `luminosity-weighted' averages.
By 3-population fits, we divide components into three groups in age (old
stellar population-OSP, intermediate-age stellar population-ISP, and young
stellar population-YSP), and then get the optimal age, metallicity and
population fractions in both mass and light for OSP, ISP and YSP. During the
fits, both Pegase.HR/Elodie3.1 and Vazdekis/Miles are used as two independent
population models. The two models result in generally consistent conclusions as
follows: for all the sample galaxies, YSPs (< 1Gyr) make important
contributions to the light. However, the dominant contributors to mass are
OSPs. We also reconstruct the smoothing star formation histories (SFHs) by
giving star formation rate (SFR) versus evolutionary age. In addition, we fit
the E+A sample and 34 randomly selected elliptical galaxies with 2-population
(2 SSPs) model. We obtain the equivalent age of old components for each of the
E+A sample and elliptical galaxies. By comparison, the old components of E+As
are statistically much younger than those of ellipticals. From the standpoint
of the stellar population age, this probably provides an evidence for the
proposed evolutionary link from E+As to early-types (E/S0s). |
Do the CMB Temperature Fluctuations Conserve Parity?: Observations of the Cosmic Microwave Background (CMB) have cemented the
notion that the large-scale Universe is both statistically homogeneous and
isotropic. But is it invariant also under reflections? To probe this we require
parity-sensitive statistics: for scalar observables, the simplest is the
trispectrum. We make the first measurements of the parity-odd scalar CMB,
focusing on the large-scale ($2<\ell<510$) temperature anisotropies measured by
Planck. This is facilitated by new quasi-maximum-likelihood estimators for
binned correlators, which account for mask convolution and leakage between
even- and odd-parity components, and achieve ideal variances within $\approx
20\%$. We perform a blind test for parity violation by comparing a $\chi^2$
statistic from Planck to theoretical expectations, using two suites of
simulations to account for the possible likelihood non-Gaussianity and residual
foregrounds. We find consistency at the $\approx 0.4\sigma$ level, yielding no
evidence for novel early-Universe phenomena. The measured trispectra allow for
a wealth of new physics to be constrained; here, we use them to constrain eight
primordial models, including Ghost Inflation, Cosmological Collider scenarios,
and Chern-Simons gauge fields. We find no signatures of new physics, with a
maximal detection significance of $2.0\sigma$. Our results also indicate that
the recent parity excesses seen in the BOSS galaxy survey are not primordial in
origin, given that the CMB dataset contains roughly $250\times$ more primordial
modes, and is far easier to interpret, given the linear physics, Gaussian
statistics, and accurate mocks. Tighter CMB constraints can be wrought by
including smaller scales and adding polarization data. | Halo-model Analysis of the Clustering of Photometrically Selected
Galaxies from SDSS: We measure the angular 2-point correlation functions of galaxies in a volume
limited, photometrically selected galaxy sample from the fifth data release of
the Sloan Digital Sky Survey. We split the sample both by luminosity and galaxy
type and use a halo-model analysis to find halo-occupation distributions that
can simultaneously model the clustering of all, early-, and late-type galaxies
in a given sample. Our results for the full galaxy sample are generally
consistent with previous results using the SDSS spectroscopic sample, taking
the differences between the median redshifts of the photometric and
spectroscopic samples into account. We find that our early- and late- type
measurements cannot be fit by a model that allows early- and late-type galaxies
to be well-mixed within halos. Instead, we introduce a new model that
segregates early- and late-type galaxies into separate halos to the maximum
allowed extent. We determine that, in all cases, it provides a good fit to our
data and thus provides a new statistical description of the manner in which
early- and late-type galaxies occupy halos. |
One Small Step for an Inflaton, One Giant Leap for Inflation: a novel
non-Gaussian tail and primordial black holes: We report a novel prediction from single-field inflation that even a tiny
step in the inflaton potential can change our perception of primordial
non-Gaussianities of the curvature perturbation. Our analysis focuses on the
tail of probability distribution generated by an upward step transition between
two stages of slow-roll evolution. The nontrivial background dynamics with
off-attractor behavior is identified. By using a non-perturbative $\delta N$
analysis, we explicitly show that a highly non-Gaussian tail can be generated
by a tiny upward step, even when the conventional nonlinearity parameters
$f_{NL}$, $g_{NL}$, etc. remain small. With this example, we demonstrate for
the first time the sensitive dependence of non-perturbative effects on the tail
of probability distribution. Our scenario has an inconceivable application to
primordial black holes by either significantly boosting their abundance or
completely forbidding their appearance. | Stability of BEC galactic dark matter halos: In this paper we show that spherically symmetric BEC dark matter halos, with
the $\sin r/r$ density profile, that accurately fit galactic rotation curves
and represent a potential solution to the cusp-core problem are unstable. We do
this by introducing back the density profiles into the fully time-dependent
Gross-Pitaevskii-Poisson system of equations. Using numerical methods to track
the evolution of the system, we found that these galactic halos lose mass at an
approximate rate of half of its mass in a time scale of dozens of Myr. We
consider this time scale is enough as to consider these halos are unstable and
unlikely to be formed. We provide some arguments to show that this behavior is
general and discuss some other drawbacks of the model that restrict its
viability. |
Tests of Gravity Theories Using Supermassive Black Holes: Scalar-tensor theories of gravity generally violate the strong equivalence
principle, namely compact objects have a suppressed coupling to the scalar
force, causing them to fall slower. A black hole is the extreme example where
such a coupling vanishes, i.e. black hole has no scalar hair. Following earlier
work, we explore observational scenarios for detecting strong equivalence
principle violation, focusing on galileon gravity as an example. For galaxies
in-falling towards galaxy clusters, the supermassive black hole can be offset
from the galaxy center away from the direction of the cluster. Hence, well
resolved images of galaxies around nearby clusters can be used to identify the
displaced black hole via the star cluster bound to it. We show that this signal
is accessible with imaging surveys, both ongoing ones such as the Dark Energy
Survey, and future ground and space based surveys. Already, the observation of
the central black hole in M~87 places new constraints on the galileon
parameters, which we present here. $\mathcal{O}(1)$ matter couplings are
disfavored for a large region of the parameter space. We also find a novel
phenomenon whereby the black hole can escape the galaxy completely in less than
one billion years. | Compensated isocurvature perturbations in the curvaton model: Primordial fluctuations in the relative number densities of particles, or
isocurvature perturbations, are generally well constrained by cosmic microwave
background (CMB) data. A less probed mode is the compensated isocurvature
perturbation (CIP), a fluctuation in the relative number densities of cold dark
matter and baryons. In the curvaton model, a subdominant field during inflation
later sets the primordial curvature fluctuation $\zeta$. In some curvaton-decay
scenarios, the baryon and cold dark matter isocurvature fluctuations nearly
cancel, leaving a large CIP correlated with $\zeta$. This correlation can be
used to probe these CIPs more sensitively than the uncorrelated CIPs considered
in past work, essentially by measuring the squeezed bispectrum of the CMB for
triangles whose shortest side is limited by the sound horizon. Here, the
sensitivity of existing and future CMB experiments to correlated CIPs is
assessed, with an eye towards testing specific curvaton-decay scenarios. The
planned CMB Stage 4 experiment could detect the largest CIPs attainable in
curvaton scenarios with more than 3$\sigma$ significance. The significance
could improve if small-scale CMB polarization foregrounds can be effectively
subtracted. As a result, future CMB observations could discriminate between
some curvaton-decay scenarios in which baryon number and dark matter are
produced during different epochs relative to curvaton decay. Independent of the
specific motivation for the origin of a correlated CIP perturbation,
cross-correlation of CIP reconstructions with the primary CMB can improve the
signal-to-noise ratio of a CIP detection. For fully correlated CIPs the
improvement is a factor of $\sim$2$-$3. |
Calibrating an updated SPH scheme within GCD+: We adapt a modern scheme of smoothed particle hydrodynamics (SPH) to our tree
N-body/SPH galactic chemodynamics code GCD+. The applied scheme includes imple-
mentations of the artificial viscosity switch and artificial thermal
conductivity pro- posed by Morris & Monaghan (1997), Rosswog & Price (2007) and
Price (2008), to model discontinuities and Kelvin-Helmholtz instabilities more
accurately. We first present hydrodynamics test simulations and contrast the
results to runs undertaken without artificial viscosity switch or thermal
conduction. In addition, we also explore the different levels of smoothing by
adopting larger or smaller smoothing lengths, i.e. a larger or smaller number
of neighbour particles, Nnb. We demonstrate that the new version of GCD+ is
capable of modelling Kelvin-Helmholtz instabilities to a simi- lar level as the
mesh code, Athena. From the Gresho vortex, point-like explosion and
self-similar collapse tests, we conclude that setting the smoothing length to
keep the number of neighbour particles as high as Nnb~58 is preferable to
adopting smaller smoothing lengths. We present our optimised parameter sets
from the hydrodynamics tests. | The WIRCAM Deep Infrared Cluster Survey I: Groups and Clusters at z >
1.1: We use CFHTLS deep optical data, WIRCam Deep Survey (WIRDS) NIR data and XMM
data to identify z>1.1 clusters in the CFHTLS D1 and D4 fields. Counterparts to
such clusters can not be identified without deep NIR data and as such the total
of =1deg2 of J , H & Ks band imaging provided by WIRDS is an indispensable tool
in such work. Using public XMM X-ray data, we identify extended X-ray sources
in the two fields. The resulting catalogue of extended X-ray sources was
analyzed for optical/NIR counterparts, using a red-sequence algorithm.
Redshifts of candidate groups and clusters were estimated using the median
photometric redshifts of detected counterparts and where available
spectroscopic data. Additionally, we surveyed X-ray point sources for potential
group systems at the limit of our detection range in the X-ray data. A
catalogue of z > 1.1 cluster candidates in the two fields has been compiled and
cluster masses, radii and temperatures have been estimated using the scaling
relations. The catalogue consists of 15 z > 1.1 candidates. Three of the
detections are previously published extended X-ray sources. Of note is JKSC 041
for which we identify possible structures at z = 0.8, z = 0.96, z = 1.13 and z
= 1.49. We also make an independent detection of the massive cluster, XMMXCS
J2215.9-1738. We use the z > 1.1 catalogue to compare the cluster number counts
in these fields with models based on WMAP 7-year cosmology and find that the
models slightly over-predict the observations, whilst at z>1.5 we do not detect
any clusters. We note that cluster number counts at z > 1.1 are highly
sensitive to the cosmological model, however a significant reduction in present
statistical (due to available survey area) and systematic (due to cluster
scaling relations) uncertainties is required in order to confidently constrain
cosmological parameters using cluster number counts at high redshift. |
The Lyman-alpha forest in a blazar-heated Universe: It has been realised only recently that TeV emission from blazars can
significantly heat the intergalactic medium (IGM) by pair-producing high-energy
electrons and positrons, which in turn excite vigorous plasma instabilities,
leading to a local dissipation of the pairs' kinetic energy. In this work, we
use cosmological hydrodynamical simulations to model the impact of this blazar
heating on the Lyman-alpha forest at redshifts z~2-3. We find that blazar
heating produces an inverted temperature-density relation in the IGM and
naturally resolves many of the problems present in previous simulations of the
forest that included photoheating alone. In particular, our simulations with
blazar heating simultaneously reproduce the observed effective optical depth
and temperature as a function of redshift, the observed probability
distribution functions of the transmitted flux, and the observed flux power
spectra, over the full redshift range 2<z<3 analysed here. Additionally, by
deblending the Lyman-alpha forest into a sum of thermally broadened individual
lines, we find superb agreement with the observed lower cutoff of the
line-width distribution and abundances of neutral hydrogen column densities.
Using the most recent constraints on the cosmic ultraviolet (UV) background,
this excellent agreement with observations does not require rescaling the
amplitude of the UV background; a procedure that was routinely used in the past
to match the observed level of transmitted flux. We also show that our
blazar-heated model matches the data better than standard simulations even when
such a rescaling is allowed. This concordance between Lyman-alpha data and
simulations, which are based on the most recent cosmological parameters,
suggests that the inclusion of blazar heating alleviates previous tensions on
constraints for sigma_8 derived from Lyman-alpha measurements and other
cosmological data. [abridged] | Results from a Low-Energy Analysis of the CDMS II Germanium Data: We report results from a reanalysis of data from the Cryogenic Dark Matter
Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken
between October 2006 and September 2008 using eight germanium detectors are
reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased
sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs)
with masses below ~10 GeV/c^2. This analysis provides stronger constraints than
previous CDMS II results for WIMP masses below 9 GeV/c^2 and excludes parameter
space associated with possible low-mass WIMP signals from the DAMA/LIBRA and
CoGeNT experiments. |
How to Build a Catalogue of Linearly-Evolving Cosmic Voids: Cosmic voids provide a powerful probe of the origin and evolution of
structures in the Universe because their dynamics can remain near-linear to the
present day. As a result they have the potential to connect large scale
structure at late times to early-Universe physics. Existing "watershed"-based
algorithms, however, define voids in terms of their morphological properties at
low redshift. The degree to which the resulting regions exhibit linear dynamics
is consequently uncertain, and there is no direct connection to their evolution
from the initial density field. A recent void definition addresses these issues
by considering "anti-halos". This approach consists of inverting the initial
conditions of an $N$-body simulation to swap overdensities and underdensities.
After evolving the pair of initial conditions, anti-halos are defined by the
particles within the inverted simulation that are inside halos in the original
(uninverted) simulation. In this work, we quantify the degree of non-linearity
of both anti-halos and watershed voids using the Zel'dovich approximation. We
find that non-linearities are introduced by voids with radii less than
$5\,\mathrm{Mpc}\,h^{-1}$, and that both anti-halos and watershed voids can be
made into highly linear sets by removing these voids. | Baryon Physics and Tight Coupling Approximation in Boltzmann Codes: We provide two derivations of the baryonic equations that can be
straightforwardly implemented in existing Einstein--Boltzmann solvers. One of
the derivations begins with an action principle, while the other exploits the
conservation of the stress-energy tensor. While our result is manifestly
covariant and satisfies the Bianchi identities, we point out that this is not
the case for the implementation of the seminal work by Ma and Bertschinger and
in the existing Boltzmann codes. We also study the tight coupling approximation
up to the second order without choosing any gauge using the covariant full
baryon equations. We implement the improved baryon equations in a Boltzmann
code and investigate the change in the estimate of cosmological parameters by
performing an MCMC analysis. With the covariantly correct baryon equations of
motion, we find 1% deviation for the best fit values of the cosmological
parameters that should be taken into account. While in this paper, we study the
Lambda-CDM model only, our baryon equations can be easily implemented in other
models and various modified gravity theories. |
The Linear Regime of Tachyonic Preheating: Tachyonic preheating is realized when the inflaton repeatedly returns to a
convex region of the potential during the post-inflationary oscillating phase.
This will induce a strong tachyonic instability and lead to a rapid
fragmentation of the coherent field that can complete within a fraction of an
$e$-fold. In this paper, we study the linear regime of this process in a
model-independent way. To this purpose, we construct simplified models that
provide an analytic Floquet theoretic description of mode growth. This approach
captures the essential features of well-motivated tachyonic preheating
scenarios, including scenarios in which the inflaton is part of a larger scalar
multiplet. We show that tachyonic preheating is efficient if the field
excursions are sub-Planckian, can produce gravitational waves in the frequency
range of current and future gravitational wave interferometers, and can be
consistent with any experimentally allowed tensor-to-scalar ratio. | Dynamical Delays Between Starburst and AGN Activity in Galaxy Nuclei: Observations of AGN have suggested a possible delay between the peak of star
formation (on some scale) and AGN activity. Inefficient fueling (and/or
feedback) from fast stellar winds has been invoked to explain this, but we
argue this is unlikely in bright systems accreting primarily cold dense gas. We
show that such a delay can arise even in bright quasars for purely dynamical
reasons. If some large-scale process produces rapid inflow, smaller scales will
quickly become gas-dominated. As the gas density peaks, so does the SFR.
However, gravitational torques which govern further inflow are relatively
inefficient in gas-dominated systems; as more gas is turned into stars, the
stars provide an efficient angular momentum sink allowing more rapid inflow.
Moreover, the gas provided to the central regions in mergers or strong disk
instabilities will typically be ~100 times larger than that needed to fuel the
BH; the system is effectively in the 'infinite gas supply' limit. BH growth can
therefore continue for some time while the gas supply exhausts, until it has
significantly depleted to the point where the BH is finally 'starved.' Both of
these effects act together with comparable magnitude, and mean that the peak of
BH growth can lag the peak in the SFR measured at a given scale by a timescale
corresponding to the gas exhaustion time on that scale (~ 10-100 local
dynamical times). This predicts that the inferred delay will vary in a specific
manner with the radius over which the star formation rate is measured. We
discuss possible implications for the role of AGN feedback in suppressing star
formation activity. |
The Halo Mass Function from Excursion Set Theory with a Non-Gaussian
Trispectrum: A sizeable level of non-Gaussianity in the primordial cosmological
perturbations may be induced by a large trispectrum, i.e. by a large connected
four-point correlation function. We compute the effect of a primordial
non-Gaussian trispectrum on the halo mass function, within excursion set
theory. We use the formalism that we have developed in a previous series of
papers and which allows us to take into account the fact that, in the presence
of non-Gaussianity, the stochastic evolution of the smoothed density field, as
a function of the smoothing scale, is non-markovian. In the large mass limit,
the leading-order term that we find agrees with the leading-order term of the
results found in the literature using a more heuristic Press-Schecther
(PS)-type approach. Our approach however also allows us to evaluate
consistently the subleading terms, which depend not only on the four-point
cumulant but also on derivatives of the four-point correlator, and which cannot
be obtained within non-Gaussian extensions of PS theory. We perform explicitly
the computation up to next-to-leading order. | The Hot and Cold Outflows of NGC 3079: Very deep neutral hydrogen (HI) observations of the edge-on spiral galaxy NGC
3079 with the Westerbork Synthesis Radio Telescope (WSRT) are presented. The
galaxy has been studied extensively in different wavelengths and known for its
several unique and complex features. However, the new data still revealed
several new features and show that the galaxy is even more complicated and
interesting than previously thought. In the new data a large stream of gas,
encircling the entire galaxy, was discovered, while the data also show, for the
first time, that not only hot gas is blown into space by the starburst/AGN, but
also large amounts of cold gas, despite the high energies involved in the
outflow. |
Escape Fraction of Ionizing Radiation from Starburst Galaxies at High
Redshifts: Recent data indicates that the cosmic UV emissivity decreased with decreasing
redshift z near the end of reionization. Lacking evidence for very massive
early stars, this could signal a decline with time in the mass-averaged escape
fraction of ionizing radiation from galaxies <fesc> at z > 6. We calculate the
evolution of ionization fronts in dark matter halos which host gas in
hydrostatic equilibrium at its cooling temperature floor (T~10^4 K for atomic
hydrogen). We find a high escape fraction only for the lowest mass halos (with
M< 10^8.7 Msun at (1+z)=10) provided their star formation efficiency f_star >
10^-3. Since the low-mass galaxy population is depleted by radiative feedback,
we find that indeed <fesc> decreases with time during reionization. | Observational constraints on scalar field models of dark energy with
barotropic equation of state: We constrain the parameters of dynamical dark energy in the form of a
classical or tachyonic scalar field with barotropic equation of state jointly
with other cosmological ones using the combined datasets which include the CMB
power spectra from WMAP7, the baryon acoustic oscillations in the space
distribution of galaxies from SDSS DR7, the power spectrum of luminous red
galaxies from SDSS DR7 and the light curves of SN Ia from 2 different
compilations: Union2 (SALT2 light curve fitting) and SDSS (SALT2 and MLCS2k2
light curve fittings). It has been found that the initial value of dark energy
equation of state parameter is constrained very weakly by most of the data
while the rest of main cosmological parameters are well constrained: their
likelihoods and posteriors are similar, have the forms close to Gaussian (or
half-Gaussian) and their confidential ranges are narrow. The most reliable
determinations of the best fitting value and $1\sigma$ confidence range for the
initial value of dark energy equation of state parameter were obtained from the
combined datasets including SN Ia data from the full SDSS compilation with
MLCS2k2 fitting of light curves. In all such cases the best fitting value of
this parameter is lower than the value of corresponding parameter for current
epoch. Such dark energy loses its repulsive properties and in future the
expansion of the Universe will change into contraction. We also perform an
error forecast for the Planck mock data and show that they narrow essentially
the confidential ranges of cosmological parameters values, moreover, their
combination with SN SDSS compilation with MLCS2k2 light curve fitting may
exclude the fields with initial equation of state parameter $>-0.1$ at
2$\sigma$ confidential level. |
Constraints on dark matter annihilation from CMB observations before
Planck: We compute the bounds on the dark matter (DM) annihilation cross section
using the most recent Cosmic Microwave Background measurements from WMAP9,
SPT'11 and ACT'10. We consider DM with mass in the MeV-TeV range annihilating
100% into either an e+e- or a mu+mu- pair. We consider a realistic energy
deposition model, which includes the dependence on the redshift, DM mass and
annihilation channel. We exclude the canonical thermal relic abundance cross
section (<sigma v> = 3 x 10^{-26} cm^3 s^{-1}) for DM masses below 30 GeV and
15 GeV for the e+e- and mu+mu- channels, respectively. A priori, DM
annihilating in halos could also modify the reionization history of the
Universe at late times. We implement a realistic halo model taken from results
of state-of-the-art N-body simulations and consider a mixed reionization
mechanism, consisting on reionization from DM as well as from first stars. We
find that the constraints on DM annihilation remain unchanged, even when large
uncertainties on the halo model parameters are considered. | Direct Gravitational Imaging of Intermediate Mass Black Holes in
Extragalactic Halos: A galaxy halo may contain a large number of intermediate mass black holes
(IMBHs) with masses in the range of 10^{2-6} solar mass. We propose to directly
detect these IMBHs by observing multiply imaged QSO-galaxy or galaxy-galaxy
strong lens systems in the submillimeter bands with high angular resolution.
The silhouette of an IMBH in the lensing galaxy halo would appear as either a
monopole-like or a dipole-like variation at the scale of the Einstein radius
against the Einstein ring of the dust-emitting region surrounding the QSO. We
use a particle tagging technique to dynamically populate a Milky Way-sized dark
matter halo with black holes, and show that the surface mass density and number
density of IMBHs have power-law dependences on the distance from the center of
the host halo if smoothed on a scale of ~ 1 kpc. Most of the black holes
orbiting close to the center are freely roaming as they have lost their dark
matter hosts during infall due to tidal stripping. Next generation
submillimeter telescopes with high angular resolution (< 0.3 mas) will be
capable of directly mapping such off-nuclear freely roaming IMBHs with a mass
of ~ 10^6 solar mass in a lensing galaxy that harbours a O(10^9) solar mass
supermassive black hole in its nucleus. |
Self-consistency of the Excursion Set Approach: The excursion set approach provides a framework for predicting how the
abundance of dark matter halos depends on the initial conditions. A key
ingredient of this formalism comes from the physics of halo formation: the
specification of a critical overdensity threshold (barrier) which protohalos
must exceed if they are to form bound virialized halos at a later time. Another
ingredient is statistical, as it requires the specification of the appropriate
statistical ensemble over which to average when making predictions. The
excursion set approach explicitly averages over all initial positions, thus
implicitly assuming that the appropriate ensemble is that associated with
randomly chosen positions in space, rather than special positions such as peaks
of the initial density field. Since halos are known to collapse around special
positions, it is not clear that the physical and statistical assumptions which
underlie the excursion set approach are self-consistent. We argue that they are
at least for low mass halos, and illustrate by comparing our excursion set
predictions with numerical data from the DEUS simulations. | Partial Ly$α$ thermalization in an analytic nonlinear diffusion
model: During recombination, the cosmic background radiation is disturbed, in
particular, by Lyman-alpha emissions from neutral hydrogen. It is proposed to
account for the subsequent time-dependent partial thermalization of the
Lyman-alpha energy content in an analytically solvable nonlinear diffusion
model. The amplitude of the partially thermalized and redshifted Ly-$\alpha$
line is found to be too low to be visible in the cosmic microwave spectrum, in
accordance with previous numerical models and Planck observations. |
A direct measurement of tomographic lensing power spectra from CFHTLenS: We measure the weak gravitational lensing shear power spectra and their
cross-power in two photometric redshift bins from the Canada-France-Hawaii
Telescope Lensing Survey (CFHTLenS). The measurements are performed directly in
multipole space in terms of adjustable band powers. For the extraction of the
band powers from the data we have implemented and extended a quadratic
estimator, a maximum likelihood method that allows us to readily take into
account irregular survey geometries, masks, and varying sampling densities. We
find the 68 per cent credible intervals in the $\sigma_8$-$\Omega_{\rm
m}$-plane to be marginally consistent with results from $Planck$ for a simple
five parameter $\Lambda$CDM model. For the projected parameter $S_8 \equiv
\sigma_8(\Omega_{\rm m}/0.3)^{0.5}$ we obtain a best-fitting value of $S_8 =
0.768_{-0.039}^{+0.045}$. This constraint is consistent with results from other
CFHTLenS studies as well as the Dark Energy Survey. Our most conservative
model, including modifications to the power spectrum due to baryon feedback and
marginalization over photometric redshift errors, yields an upper limit on the
total mass of three degenerate massive neutrinos of $\Sigma m_\nu < 4.53 \,
{\rm eV}$ at 95 per cent credibility, while a Bayesian model comparison does
not favour any model extension beyond a simple five parameter $\Lambda$CDM
model. Combining the shear likelihood with $Planck$ breaks the
$\sigma_8$-$\Omega_{\rm m}$-degeneracy and yields $\sigma_8=0.818 \pm 0.013$
and $\Omega_{\rm m} = 0.300 \pm 0.011$ which is fully consistent with results
from $Planck$ alone. | Impact of baryon physics on dark matter structures: a detailed
simulation study of halo density profiles: The back-reaction of baryons on the dark matter halo density profile is of
great interest, not least because it is an important systematic uncertainty
when attempting to detect the dark matter. Here, we draw on a large suite of
high resolution cosmological hydrodynamical simulations, to systematically
investigate this process and its dependence on the baryonic physics associated
with galaxy formation. The inclusion of baryons results in significantly more
concentrated density profiles if radiative cooling is efficient and feedback is
weak. The dark matter halo concentration can in that case increase by as much
as 30 (10) per cent on galaxy (cluster) scales. The most significant effects
occur in galaxies at high redshift, where there is a strong anti-correlation
between the baryon fraction in the halo centre and the inner slope of both the
total and the dark matter density profiles. If feedback is weak, isothermal
inner profiles form, in agreement with observations of massive, early-type
galaxies. However, we find that AGN feedback, or extremely efficient feedback
from massive stars, is necessary to match observed stellar fractions in groups
and clusters, as well as to keep the maximum circular velocity similar to the
virial velocity as observed for disk galaxies. These strong feedback models
reduce the baryon fraction in galaxies by a factor of 3 relative to the case
with no feedback. The AGN is even capable of reducing the baryon fraction by a
factor of 2 in the inner region of group and cluster haloes. This in turn
results in inner density profiles which are typically shallower than isothermal
and the halo concentrations tend to be lower than in the absence of baryons. |
Angular systematics-free cosmological analysis of galaxy clustering in
configuration space: Galaxy redshift surveys are subject to incompleteness and inhomogeneous
sampling due to the various constraints inherent to spectroscopic observations.
This can introduce systematic errors on the summary statistics of interest,
which need to be mitigated in cosmological analysis to achieve high accuracy.
Standard practices involve applying weighting schemes based on completeness
estimates across the survey footprint, possibly supplemented with additional
weighting schemes accounting for density-dependent effects. In this work, we
concentrate on pure angular systematics and describe an alternative approach
consisting in analysing the galaxy two-point correlation function where angular
modes are nulled. By construction, this procedure removes all possible known
and unknown sources of angular observational systematics, but also part of the
cosmological signal.We use a modified Landy-Szalay estimator for the two-point
correlation function that relies on an additional random catalogue where
angular positions are randomly drawn from the galaxy catalogue, and provide an
analytical model to describe this modified statistic. We test the model by
performing an analysis of the full anisotropic clustering in mock catalogues of
luminous red and emission-line galaxies at 0.43 < z < 1.1. We find that the
model fully accounts for the modified correlation function in redshift space,
without introducing new nuisance parameters. The derived cosmological
parameters from the analysis of baryon acoustic oscillations and redshift-space
distortions display slightly larger statistical uncertainties, mostly for the
growth rate of structure parameter fs8 that exhibits a 50% statistical error
increase, but free from angular systematic error. | Cosmological gravity probes: connecting recent theoretical developments
to forthcoming observations: Since the discovery of the accelerated expansion of the present Universe,
significant theoretical developments have been made in the area of modified
gravity. In the meantime, cosmological observations have been providing more
high-quality data, allowing us to explore gravity on cosmological scales. To
bridge the recent theoretical developments and observations, we present an
overview of a variety of modified theories of gravity and the cosmological
observables in the cosmic microwave background and large-scale structure,
supplemented with a summary of predictions for cosmological observables derived
from cosmological perturbations and sophisticated numerical studies. We
specifically consider scalar-tensor theories in the Horndeski and DHOST family,
massive gravity/bigravity, vector-tensor theories, metric-affine gravity, and
cuscuton/minimally-modified gravity, and discuss the current status of those
theories with emphasis on their physical motivations, validity, appealing
features, the level of maturity, and calculability. We conclude that the
Horndeski theory is one of the most well-developed theories of modified
gravity, although several remaining issues are left for future observations.
The paper aims to help to develop strategies for testing gravity with ongoing
and forthcoming cosmological observations. |
Constraints to Holographic Dark Energy Model via Type Ia Supernovae,
Baryon Acoustic Oscillation and WMAP: In this paper, the holographic dark energy (HDE) model, where the future
event horizon is taken as an IR cut-off, is confronted by using currently
available cosmic observational data sets which include type Ia supernovae,
baryon acoustic oscillation and cosmic microwave background radiation from full
information of WMAP-7yr. Via the Markov Chain Monte Carlo method, we obtain the
values of model parameter $c= 0.696_{- 0.0737- 0.132- 0.190}^{+ 0.0736+ 0.159+
0.264}$ with $1,2,3\sigma$ regions. Therefore one can conclude that at lest
$3\sigma$ level the future Universe will be dominated by phantom like dark
energy. It is not consistent with positive energy condition, however this
condition must be satisfied to derive the holographic bound. It implies that
the current cosmic observational data points disfavor the HDE model. | Big Bang Nucleosynthesis: The Strong Nuclear Force meets the Weak
Anthropic Principle: Contrary to a common argument that a small increase in the strength of the
strong force would lead to destruction of all hydrogen in the big bang due to
binding of the diproton and the dineutron with a catastrophic impact on life as
we know it, we show that provided the increase in strong force coupling
constant is less than about 50% substantial amounts of hydrogen remain. The
reason is that an increase in strong force strength leads to tighter binding of
the deuteron, permitting nucleosynthesis to occur earlier in the big bang at
higher temperature than in the standard big bang. Photodestruction of the less
tightly bound diproton and dineutron delays their production to after the bulk
of nucleosynthesis is complete. The decay of the diproton can, however, lead to
relatively large abundances of deuterium. |
Correlations between cosmic strings and extra relativistic species: The recent observation that the Cosmic Microwave Background (CMB) may prefer
a neutrino excess has triggered a number of works studying this possibility.
The effect obtained by the non-interacting massless neutrino excess could be
mimicked by some extra radiation component in the early universe, such as a
cosmological gravitational wave background. Prompted by the fact that a
possible candidate to source those gravitational waves would be cosmic strings,
we perform a parameter fitting study with models which considers both cosmic
strings and the effective number of neutrinos as free parameters, using CMB and
non-CMB data. We find that there is a correlation between cosmic strings and
the number of extra relativistic species, and that strings can account for all
the extra radiation necessary. In fact, CMB data prefer strings at a 2sigma
level, paying the price of a higher extra radiation component. CMB data also
give a moderate preference for a model with ns=1. The inclusion of non-CMB data
lowers both the preference for strings and for the extra relativistic species. | Discovering the missing 2.2<z<3 quasars by combining optical variability
and optical/near-IR colors: The identifications of quasars in the redshift range 2.2<z<3 are known to be
very inefficient as their optical colors are indistinguishable from those of
stars. Recent studies have proposed to use optical variability or near-IR
colors to improve the identifications of the missing quasars in this redshift
range. Here we present a case study by combining both factors. We select a
sample of 70 quasar candidates from variables in SDSS Stripe 82, which are
non-UV excess sources and have UKIDSS near-IR public data. They are clearly
separated into two parts on the Y-K/g-z color-color diagram, and 59 of them
meet or lie close to a newly proposed Y-K/g-z selection criterion for z<4
quasars. 44 of these 59 sources have been previously identified as quasars in
SDSS DR7, and 35 among them are quasars at 2.2<z<3. We present spectroscopic
observations of 14 of 15 remaining quasar candidates using the Bok 2.3m
telescope and the MMT 6.5m telescope, and successfully identify all of them as
new quasars at z=2.36 to 2.88. We also apply this method to a sample of 643
variable quasar candidates with SDSS-UKIDSS nine-band photometric data selected
from 1875 new quasar candidates in SDSS Stripe 82 given by Butler & Bloom based
on the time-series selections, and find that 188 of them are probably new
quasars with photometric redshifts at 2.2<z<3. Our results indicate that the
combination of optical variability and optical/near-IR colors is probably the
most efficient way in finding 2.2<z<3 quasars and very helpful for constructing
a complete quasar sample. We discuss its implications to the ongoing and
upcoming large optical and near-IR sky surveys. |
Detecting Chameleon Dark Energy via Electrostatic Analogy: The late-time accelerated expansion of the universe could be caused by a
scalar field that is screened on small scales, as in chameleon or symmetron
scenarios. We present an analogy between thin shell configurations of such
scalar fields and electrostatics, which allows calculation of the field profile
for general extended bodies. Interestingly, the field demonstrates a `lightning
rod' effect, where it becomes enhanced near the ends of a pointy or elongated
object. Drawing from this correspondence, we show that non-spherical test
bodies immersed in a background field will experience a net torque caused by
the scalar field. This effect, with no counterpart in the gravitational case,
can be potentially tested in future experiments. | Impact of tidal environment on galaxy clustering in GAMA: We constrain models of the galaxy distribution in the cosmic web using data
from the Galaxy and Mass Assembly (GAMA) survey. We model the redshift-space
behaviour of the 2-point correlation function (2pcf) and the recently proposed
Voronoi volume function (VVF) -- which includes information beyond 2-point
statistics. We extend the standard halo model using extra satellite degrees of
freedom and two assembly bias parameters, $\alpha_{\rm cen}$ and $\alpha_{\rm
sat}$, which respectively correlate the occupation numbers of central and
satellite galaxies with their host halo's tidal environment. We measure
$\alpha_{\rm sat}=1.44^{+0.25}_{-0.43}$ and $\alpha_{\rm
cen}=-0.79^{+0.29}_{-0.11}$ using a combination of 2pcf and VVF measurements,
representing a detection of assembly bias at the 3.3$\sigma$ (2.4$\sigma$)
significance level for satellite (central) galaxies. This result remains robust
to possible anisotropies in the halo-centric distribution of satellites as well
as technicalities of estimating the data covariance. We show that the growth
rate ($f\sigma_8$) deduced using models with assembly bias is about 7\% (i.e.
$1.5\sigma$) lower than if assembly bias is ignored. When projected onto the
$\Omega_m$-$\sigma_8$ plane, the model constraints without assembly bias
overlap with Planck expectations, while allowing assembly bias introduces
significant tension with Planck, preferring either a lower $\Omega_m$ or a
lower $\sigma_8$. Finally, we find that the all-galaxy weak lensing signal is
unaffected by assembly bias, but the central and satellite sub-populations
individually show significantly different signals in the presence of assembly
bias. Our results illustrate the importance of accurately modelling galaxy
formation for cosmological inference from future surveys. |
Gravitational waves induced from primordial black hole fluctuations: The
effect of an extended mass function: The gravitational potential of initially Poisson distributed primordial black
holes (PBH) can induce a stochastic gravitational-wave background (SGWB) at
second order in cosmological perturbation theory. This SGWB was previously
studied in the context of general relativity (GR) and modified gravity setups
by assuming a monochromatic PBH mass function. Here we extend the previous
analysis in the context of GR by studying the aforementioned SGWB within more
physically realistic regimes where PBHs have different masses. In particular,
starting from a power-law cosmologically motivated primordial curvature power
spectrum with a running spectral index we extract the extended PBH mass
function and the associated to it PBH gravitational potential which acts as the
source of the scalar induced SGWB. At the end, by taking into account the
dynamical evolution of the PBH gravitational potential during the transition
from the matter era driven by PBHs to the radiation era we extract the
respective GW signal today. Interestingly, in order to trigger an early
PBH-dominated era and avoid the GW constraints at BBN we find that the running
of the spectral index $\alpha_\mathrm{s}$ of our primordial curvature power
spectrum should be within the narrow range
$\alpha_\mathrm{s}\in[3.316,3.355]\times 10^{-3}$ while at the same time the GW
signal is found to be potentially detectable by LISA. | A Census of Nuclear Stellar Disks in Early-type Galaxies: Nuclear Stellar Disks (NSDs), of a few tens to hundreds of parsec across, are
a common and yet poorly studied feature of early-type galaxies. Still, such
small disks represent a powerful tool to constrain the assembling history of
galaxies, since they can be used to trace to the epoch when galaxies
experienced their last major merger event. By studying the fraction and stellar
age of NSDs it is thus possible to test the predictions for the assembly
history of early-type galaxies according the current hierarchical paradigm for
galaxy formation. In this paper we have produced the most comprehensive census
of NSDs in nearby early-type galaxies by searching for such disks in objects
within 100 Mpc and by using archival images from the Hubble Space Telescope. We
found that NSDs are present in approximately 20% of early-type galaxies, and
that the fraction of galaxies with NSDs does not depend on their Hubble type
nor on their galactic environment, whereas the incidence of NSDs appears to
decline in the most massive systems. Furthermore, we have separated the light
contribution of twelve such disks from that of their surrounding stellar bulge
in order to extract their physical properties. This doubles the number of
decomposed NSDs and although the derived values for their central surface
brightness and scale-length are consistent with previous studies they also give
a hint of possible different characteristics due to different formation
scenario between nuclear disks and other kinds of large galactic disks. |
Constructing a cosmological model-independent Hubble diagram of type Ia
supernovae with cosmic chronometers: We apply two methods, namely the Gaussian processes and the non-parametric
smoothing procedure, to reconstruct the Hubble parameter $H(z)$ as a function
of redshift from 15 measurements of the expansion rate obtained from age
estimates of passively evolving galaxies. These reconstructions enable us to
derive the luminosity distance to a certain redshift $z$, calibrate the
light-curve fitting parameters accounting for the (unknown) intrinsic magnitude
of type Ia supernova (SNe Ia) and construct cosmological model-independent
Hubble diagrams of SNe Ia. In order to test the compatibility between the
reconstructed functions of $H(z)$, we perform a statistical analysis
considering the latest SNe Ia sample, the so-called JLA compilation. We find
that, for the Gaussian processes, the reconstructed functions of Hubble
parameter versus redshift, and thus the following analysis on SNe Ia
calibrations and cosmological implications, are sensitive to prior mean
functions. However, for the non-parametric smoothing method, the reconstructed
functions are not dependent on initial guess models, and consistently require
high values of $H_0$, which are in excellent agreement with recent measurements
of this quantity from Cepheids and other local distance indicators. | Astrophysical Tests of Dark Matter Self-Interactions: Self-interacting dark matter (SIDM) arises generically in scenarios for
physics beyond the Standard Model that have dark sectors with light mediators
or strong dynamics. The self-interactions allow energy and momentum transport
through halos, altering their structure and dynamics relative to those produced
by collisionless dark matter. SIDM models provide a promising way to explain
the diversity of galactic rotation curves, and they form a predictive and
versatile framework for interpreting astrophysical phenomena related to dark
matter. This review provides a comprehensive explanation of the physical
effects of dark matter self-interactions in objects ranging from galactic
satellites (dark and luminous) to clusters of galaxies and the large-scale
structure. The second major part describes the methods used to constrain SIDM
models including current constraints, with the aim of advancing tests with
upcoming galaxy surveys. This part also provides a detailed review of the
unresolved small-scale structure formation issues and concrete ways to test
simple SIDM models. The review is rounded off by a discussion of the
theoretical motivation for self-interactions, degeneracies with baryonic and
gravitational effects, extensions to the single-component elastic-interactions
SIDM framework, and future observational and theoretical prospects. |
Observational constraints on finite scale factor singularities: We discuss the combined constraints on a Finite Scale Factor Singularity
(FSF) universe evolution scenario, which come from the shift parameter R,
baryon acoustic oscillations (BAO) A, and from the type Ia supernovae. We show
that observations allow existence of such singularities in the 2x10^9 years, in
future, at the 1{\sigma} CL, and that at the present moment of the cosmic
evolution, one cannot differentiate between cosmological scenario which allow
finite scale factor singularities and the standard dark energy models. We also
show that there is an allowed value of m = 2/3 within 1{\sigma} CL, which
corresponds to a dust-filled Einstein-de-Sitter universe limit of the early
time evolution. | Black hole growth and host galaxy morphology: We use data from large surveys of the local Universe (SDSS+Galaxy Zoo) to
show that the galaxy-black hole connection is linked to host morphology at a
fundamental level. The fraction of early-type galaxies with actively growing
black holes, and therefore the AGN duty cycle, declines significantly with
increasing black hole mass. Late-type galaxies exhibit the opposite trend: the
fraction of actively growing black holes increases with black hole mass. |
The Densest Galaxy: We report the discovery of a remarkable ultra-compact dwarf galaxy around the
massive Virgo elliptical galaxy NGC 4649 (M60), which we term M60-UCD1. With a
dynamical mass of 2.0 x 10^8 M_sun but a half-light radius of only ~ 24 pc,
M60-UCD1 is more massive than any ultra-compact dwarfs of comparable size, and
is arguably the densest galaxy known in the local universe. It has a
two-component structure well-fit by a sum of Sersic functions, with an
elliptical, compact (r_h=14 pc; n ~ 3.3) inner component and a round,
exponential, extended (r_h=49 pc) outer component. Chandra data reveal a
variable central X-ray source with L_X ~ 10^38 erg/s that could be an active
galactic nucleus associated with a massive black hole or a low-mass X-ray
binary. Analysis of optical spectroscopy shows the object to be old (~> 10 Gyr)
and of solar metallicity, with elevated [Mg/Fe] and strongly enhanced [N/Fe]
that indicates light element self-enrichment; such self-enrichment may be
generically present in dense stellar systems. The velocity dispersion (~ 70
km/s) and resulting dynamical mass-to-light ratio (M/L_V=4.9 +/- 0.7) are
consistent with---but slightly higher than---expectations for an old,
metal-rich stellar population with a Kroupa initial mass function. The presence
of a massive black hole or a mild increase in low-mass stars or stellar
remnants is therefore also consistent with this M/L_V. The stellar density of
the galaxy is so high that no dynamical signature of dark matter is expected.
However, the properties of M60-UCD1 suggest an origin in the tidal stripping of
a nucleated galaxy with M_B ~ -18 to -19. | Quantitative measure of evolution of bright cluster galaxies at moderate
redshifts: Using archival data from the Hubble Space Telescope, we study the
quantitative morphological evolution of spectroscopically confirmed bright
galaxies in the core regions of nine clusters ranging in redshift from $z =
0.31$ to $z = 0.84$. We use morphological parameters derived from two
dimensional bulge-disk decomposition to study the evolution. We find an
increase in the mean bulge-to-total luminosity ratio $B/T$ as the Universe
evolves. We also find a corresponding increase in the fraction of early type
galaxies and in the mean S\'ersic index. We discuss these results and their
implications to physical mechanisms for evolution of galaxy morphology. |
J-PLUS: On the identification of new cluster members in the double
galaxy cluster A2589 & A2593 using PDFs: We aim to use multi-band imaging from the Phase-3 Verification Data of the
J-PLUS survey to derive accurate photometric redshifts (photo-z) and look for
potential new members in the surroundings of the nearby galaxy clusters A2589
(z=0.0414) & A2593 (z=0.0440), using redshift probability distribution
functions. The ultimate goal is to demonstrate the usefulness of a 12-band
filter system in the study of large-scale structure in the local universe. We
present an optimized pipeline for the estimation of photo-z in clusters of
galaxies. We tested our photo-z with a sample of 296 spectroscopically
confirmed cluster members with a magnitude of <r>= 16.6 and redshift <z>=0.041.
The combination of seven narrow and five broadband filters with a typical
photometric-depth of r<21.5 provides dz/(1+z)=0.01 photo-z estimates. A
precision of dz/(1+z)=0.005 is obtained for the 177 galaxies brighter than
magnitude r<17. To foresee the precision beyond the spectroscopic sample, we
designed a set of simulations in which real cluster galaxies are modeled and
reinjected inside the images at different signal-to-noise. A precision of
dz/(1+z)=0.02 and dz/(1+z)=0.03 is expected at <r>= 18-22, respectively.
Complementarily, we used SDSS/DR12 data to derive photo-z estimates for the
same galaxy sample, demonstrating that the wavelength-resolution of the J-PLUS
can double the precision achieved by SDSS for galaxies with a high S/N. We find
as much as 170 new candidates across the entire field. The spatial distribution
of these galaxies may suggest an overlap between the systems with no evidence
of a clear filamentary structure connecting the clusters. These preliminary
results show the potential of J-PLUS data to revisit membership of groups and
clusters from nearby galaxies, important for the determination of luminosity
and mass functions and environmental studies at the intermediate and low-mass
regime. | Galaxy Cluster Mass Estimates in the Presence of Substructure: We develop and implement a model to analyze the internal kinematics of galaxy
clusters that may contain subpopulations of galaxies that do not independently
trace the cluster potential. The model allows for substructures within the
cluster environment, disentangles cluster members from contaminating foreground
and background galaxies, and includes an overall cluster rotation term as part
of the cluster kinematics. We estimate the cluster velocity dispersion and/or
mass while marginalizing over uncertainties in all of the above complexities.
In a first application to our published data for Abell 267 (A267), we find no
evidence for cluster rotation but we identify up to five distinct galaxy
subpopulations. We use these results to explore the sensitivity of inferred
cluster properties to the treatment of substructure. Compared to a model that
assumes no substructure, our substructure model reduces the dynamical mass of
A267 by $\sim 20\%$ and shifts the cluster mean velocity by $\sim 100$ km
s$^{-1}$, approximately doubling the offset with respect to the velocity of
A267's brightest cluster galaxy. Embedding the spherical Jeans equation within
this framework, we infer for A267 a dark matter halo of mass
$M_{200}=6.77\pm1.06\times10^{14}M_\odot/h$, concentration
$\log_{10}c_{200}=0.61\pm0.39$, consistent with the mass-concentration relation
found in cosmological simulations. |
Squeezing Cosmological Phase Transitions with International Pulsar
Timing Array: A first-order MeV-scale cosmological phase transition (PT) can generate a
peak in the power spectrum of stochastic gravitational wave background around
nanohertz frequencies. With the recent International Pulsar Timing Array data
release two covering nanohertz frequencies, we search for such a phase
transition signal. For the standard 4-parameter PT model, we obtain the PT
temperature $T_\star\in$ [66 MeV, 30 GeV], which indicates that dark or QCD
phase transitions occurring below 66 MeV have been ruled out at $2\,\sigma$
confidence level. This constraint is much tighter than $T_\star\sim$ [1 MeV,
100 GeV] from NANOGrav. We also give much tighter $2\,\sigma$ bounds on the PT
duration $H_\star/\beta>0.1$, strength $\alpha_\star>0.39$ and friction
$\eta<2.74$ than NANOGrav. For the first time, we find a positive correlation
between $\mathrm{log}_{10}T_\star$ and $\mathrm{log}_{10}H_\star/\beta$
implying that PT temperature increases with increasing bubble nucleation rate.
To avoid large theoretical uncertainties in calculating PT spectrum, we make
bubble spectral shape parameters $a$, $b$, $c$ and four PT parameters free
together, and confront this model with data. We find that pulsar timing is very
sensitive to the parameter $a$, and give the first clear constraint
$a=1.27_{-0.54}^{+0.71}$ at $1\,\sigma$ confidence level. | Simulating cosmic reionization: How large a volume is large enough?: We present the largest-volume (425 Mpc/h=607 Mpc on a side) full radiative
transfer simulation of cosmic reionization to date. We show that there is
significant additional power in density fluctuations at very large scales. We
systematically investigate the effects this additional power has on the
progress, duration and features of reionization, as well as on selected
reionization observables. We find that comoving simulation volume of ~100 Mpc/h
per side is sufficient for deriving a convergent mean reionization history, but
that the reionization patchiness is significantly underestimated. We use
jackknife splitting to quantify the convergence of reionization properties with
simulation volume for both mean-density and variable-density sub-regions. We
find that sub-volumes of ~100 Mpc/h per side or larger yield convergent
reionization histories, except for the earliest times, but smaller volumes of
~50 Mpc/h or less are not well converged at any redshift. Reionization history
milestones show significant scatter between the sub-volumes, of Delta z=0.6-1
for ~50 Mpc/h volumes, decreasing to Delta z=0.3-0.5 for ~100 Mpc/h volumes,
and $\Delta z$~0.1 for ~200 Mpc/h volumes. If we only consider mean-density
sub-regions the scatter decreases, but remains at Delta z~0.1-0.2 for the
different size sub-volumes. Consequently, many potential reionization
observables like 21-cm rms, 21-cm PDF skewness and kurtosis all show good
convergence for volumes of ~200 Mpc/h, but retain considerable scatter for
smaller volumes. In contrast, the three-dimensional 21-cm power spectra at
large scales (k<0.25 h/Mpc) do not fully converge for any sub-volume size.
These additional large-scale fluctuations significantly enhance the 21-cm
fluctuations, which should improve the prospects of detection considerably,
given the lower foregrounds and greater interferometer sensitivity at higher
frequencies. (abridged) |
CMB anisotropies from patchy reionisation and diffuse Sunyaev-Zel'dovich
effects: Anisotropies in the Cosmic Microwave Background (CMB) can be induced during
the later stages of cosmic evolution, and in particular during and after the
Epoch of Reionisation. Inhomogeneities in the ionised fraction, but also in the
baryon density, in the velocity fields and in the gravitational potentials are
expected to generate correlated CMB perturbations. We present a complete
relativistic treatment of all these effects, up to second order in perturbation
theory, that we solve using the numerical Boltzmann code SONG. The physical
origin and relevance of all second order terms are carefully discussed. In
addition to collisional and gravitational contributions, we identify the
diffuse analogue of the blurring and kinetic Sunyaev-Zel'dovich (SZ) effects.
Our approach naturally includes the correlations between the imprint from
patchy reionisation and the diffuse SZ effects thereby allowing us to derive
reliable estimates of the induced temperature and polarisation CMB angular
power spectra. In particular, we show that the B-modes generated at
intermediate length-scales (l~100) have the same amplitude as the B-modes
coming from primordial gravitational waves with a tensor-to-scalar ratio
r=10^{-4}. | Extended percolation analysis of the cosmic web: Aims. We develop an extended percolation method to allow the comparison of
geometrical properties of the real cosmic web with the simulated dark matter
web for an ensemble of over- and under-density systems. Methods. We scan
density fields of dark matter (DM) model and SDSS observational samples, and
find connected over- and underdensity regions in a large range of threshold
densities. Lengths, filling factors and numbers of largest clusters and voids
as functions of the threshold density are used as percolation functions.
Results. We find that percolation functions of DM models of different box sizes
are very similar to each other. This stability suggests that properties of the
cosmic web, as found in the present paper, can be applied to the cosmic web as
a whole. Percolation functions depend strongly on the smoothing length. At
smoothing length 1 $h^{-1}$ Mpc the percolation threshold density for clusters
is $\log P_C = 0.718 \pm 0.014$, and for voids is $\log P_V = -0.816 \pm
0.015$, very different from percolation thresholds for random samples, $\log
P_0 = 0.00 \pm 0.02$. Conclusions. The extended percolation analysis is a
versatile method to study various geometrical properties of the cosmic web in a
wide range of parameters. Percolation functions of the SDSS sample are very
different from percolation functions of DM model samples. The SDSS sample has
only one large percolating void which fills almost the whole volume. The SDSS
sample contains numerous small isolated clusters at low threshold densities,
instead of one single percolating DM cluster. These differences are due to the
tenuous dark matter web, present in model samples, but absent in real
observational samples. |
Updated constraint on a primordial magnetic field during big bang
nucleosynthesis and a formulation of field effects: A new upper limit on the amplitude of primordial magnetic field (PMF) is
derived by a comparison between a calculation of elemental abundances in big
bang nucleosynthesis (BBN) model and the latest observational constraints on
the abundances. Updated nuclear reaction rates are adopted in the calculation.
Effects of PMF on the abundances are consistently taken into account in the
numerical calculation with the precise formulation of changes in physical
variables. We find that abundances of 3He and 6Li increase while that of 7Li
decreases when the PMF amplitude increases, in the case of the baryon-to-photon
ratio determined from the measurement of cosmic microwave background radiation.
We derive a constraint on the present amplitude of PMF, i.e., B(0)<1.5 micro G
[corresponding to the amplitude less than 2.0x10^{11} G at BBN temperature of
T=10^9 K] based on the rigorous calculation. | Testing inflationary consistency relations by the potential CMB
observations: Testing the so-called consistency relations plays an important role for
distinguishing the different classes of inflation models. In this paper, we
investigate the possible testing based on the potential observations of the
cosmic microwave background (CMB) radiation, including the planned CMBPol
mission and the ideal CMB experiment where only the reduced cosmic weak lensing
contamination for the B-mode polarization is considered. We find that for the
canonical single-field inflation and the phantom inflation, the consistency
relations are quite hard to be tested: the testing is possible only if $r>0.14$
for CMBPol mission, and $r>0.06$ for the ideal experiment. However, the
situation could become much better for the general Lorentz invariant
single-field inflation with large non-gaussian signal and the two-field
inflation with strong correlation between the adiabatic and the isocurvature
perturbations. We find that for these two classes of inflation the testing is
possible if $r\gtrsim 10^{-2}$ or even smaller for both CMB experiments. |
Merger Signatures in the Galaxy Cluster Abell 98: We present results from Chandra and XMM-Newton observations of Abell 98
(A98), a galaxy cluster with three major components: a relatively bright
subcluster to the north (A98N), a disturbed subcluster to the south (A98S), and
a fainter subcluster to the far south (A98SS). We find evidence for surface
brightness and temperature asymmetries in A98N consistent with a shock-heated
region to the south, which could be created by an early stage merger between
A98N and A98S. Deeper observations are required to confirm this result. We also
find that A98S has an asymmetric core temperature structure, likely due to a
separate ongoing merger. Evidence for this is also seen in optical data. A98S
hosts a wide-angle tail (WAT) radio source powered by a central active galactic
nucleus (AGN). We find evidence for a cavity in the intracluster medium (ICM)
that has been evacuated by one of the radio lobes, suggesting that AGN feedback
is operating in this system. Examples of cavities in non-cool core clusters are
relatively rare. The three subclusters lie along a line in projection,
suggesting the presence of a large-scale filament. We observe emission along
the filament between A98N and A98S, and a surface brightness profile shows
emission consistent with the overlap of the subcluster extended gas haloes. We
find the temperature of this region is consistent with the temperature of the
gas at similar radii outside this bridge region. Lastly, we examine the cluster
dynamics using optical data. We conclude A98N and A98S are likely bound to one
another, with a 67% probability, while A98S and A98SS are not bound at a high
level of significance. | Constraints on the Holographic Dark Energy Model from Type Ia
Supernovae, WMAP7, Baryon Acoustic Oscillation and Redshift-Space Distortion: In this paper, we use the joint measurement of geometry and growth rate from
matter density perturbations to constrain the holographic dark energy model.
The geometry measurement includes type Ia supernovae (SN Ia) Union2.1, full
information of cosmic microwave background (CMB) from WMAP-7yr and baryon
acoustic oscillation (BAO). For the growth rate of matter density
perturbations, the results $f(z)\sigma_8(z)$ measured from the redshift-space
distortion (RSD) in the galaxy power spectrum are employed. Via the Markov
Chain Monte Carlo method, we try to constrain the model parameters space. The
jointed constraint shows that $c=0.750_{- 0.0999- 0.173- 0.226}^{+ 0.0976+
0.215+ 0.319}$ and $\sigma_8=0.763_{- 0.0465- 0.0826- 0.108}^{+ 0.0477+ 0.0910+
0.120}$ with $1,2,3\sigma$ regions. After marginalizing the other irrelevant
model parameters, we show the evolution of the equation of state of HDE with
respect to the redshift $z$. Though the current cosmic data points favor a
phantom like HDE Universe for the mean values of the model parameters in the
future, it can behave like quintessence in $3\sigma$ regions. |
Harmonics in the Dark-Matter Sky: Directional Detection in the
Fourier-Bessel Basis: Details about the velocity distribution of weakly interacting massive
particle (WIMP) dark matter in our galaxy may be revealed by nuclear-recoil
detectors with directional sensitivity. Previous studies have assumed that the
velocity distribution takes a simple functional form characterized by a small
number of parameters. More recent work has shown that basis-function expansions
may allow for more general parameterization; such an approach has been
considered for both the one-dimensional speed and momentum distributions, and
also for three-dimensional velocity distributions obeying certain equilibrium
conditions. In this work, I extend this basis-function approach to allow for
arbitrary velocity distributions by working in the Fourier-Bessel basis,
deriving an analytic expression for the directional recoil spectrum. Such an
approach is completely general, and may be useful if the velocity distribution
is too complex to be characterized by simple functional forms or is not
completely virialized. Results concerning the three-dimensional Radon transform
of the Fourier-Bessel basis functions may be of general interest for
tomographic applications. | Prospects for clustering and lensing measurements with forthcoming
intensity mapping and optical surveys: We explore the potential of using intensity mapping surveys (MeerKAT, SKA)
and optical galaxy surveys (DES, LSST) to detect HI clustering and weak
gravitational lensing of 21cm emission in auto- and cross-correlation. Our
forecasts show that high precision measurements of the clustering and lensing
signals can be made in the near future using the intensity mapping technique.
Such studies can be used to test the intensity mapping method, and constrain
parameters such as the HI density $\Omega_{\rm HI}$, the HI bias $b_{\rm HI}$
and the galaxy-HI correlation coefficient $r_{\rm HI-g}$. |
VLT/X-shooter observations of blue compact galaxies Haro 11 and ESO
338-IG 004: (abridged) Strongly star-forming galaxies of subsolar metallicities are
typical of the high-redshift universe. Here we therefore provide accurate data
for two low-z analogs, the well-known low-metallicity emission-line galaxies
Haro 11 and ESO 338-IG 004. On the basis of Very Large Telescope/X-shooter
spectroscopic observations in the wavelength range 3000-24000\AA, we use
standard direct methods to derive physical conditions and element abundances.
Furthermore, we use X-shooter data together with Spitzer observations in the
mid-infrared range to attempt to find hidden star formation. We derive
interstellar oxygen abundances of 12 + log O/H = 8.33+/-0.01, 8.10+/-0.04, and
7.89+/-0.01 in the two HII regions B and C of Haro 11 and in ESO 338-IG 004,
respectively. The observed fluxes of the hydrogen lines correspond to the
theoretical recombination values after correction for extinction with a single
value of the extinction coefficient C(Hbeta) across the entire wavelength range
from the near-ultraviolet to the NIR and mid-infrared for each of the studied
HII regions. Therefore there are no emission-line regions contributing to the
line emission in the NIR range, which are hidden in the optical range. The
agreement between the extinction-corrected and CLOUDY-predicted fluxes implies
that a HII region model including only stellar photoionisation is able to
account for the observed fluxes, in both the optical and NIR ranges. All
observed spectral energy distributions (SEDs) can be reproduced quite well
across the whole wavelength range by model SEDs except for Haro 11B, where
there is a continuum flux excess at wavelengths >1.6mum. It is possible that
one or more red supergiant stars are responsible for the NIR flux excess in
Haro 11B. We find evidence of a luminous blue variable (LBV) star in Haro 11C. | Detection of X-ray galaxy clusters based on the Kolmogorov method: The detection of clusters of galaxies in large surveys plays an important
part in extragalactic astronomy, and particularly in cosmology, since cluster
counts can give strong constraints on cosmological parameters. X-ray imaging is
in particular a reliable means to discover new clusters, and large X-ray
surveys are now available. Considering XMM-Newton data for a sample of 40 Abell
clusters, we show that their analysis with a Kolmogorov distribution can
provide a distinctive signature for galaxy clusters. The Kolmogorov method is
sensitive to the correlations in the cluster X-ray properties and can therefore
be used for their identification, thus allowing to search reliably for clusters
in a simple way. |
Gravitational Fermion Production in Inflationary Cosmology: We revisit the gravitational production of massive Dirac fermions in
inflationary cosmology with a focus on clarifying the analytic computation of
the particle number density in both the large and the small mass regimes. For
the case in which the masses of the gravitationally produced fermions are small
compared to the Hubble expansion rate at the end of inflation, we obtain a
universal result for the number density that is nearly independent of the
details of the inflationary model. The result is identical to the case of
conformally coupled scalars up to an overall multiplicative factor of order
unity for reasons other than just counting the fermionic degrees of freedom. | A Preferred Mass Range for Primordial Black Hole Formation and Black
Holes as Dark Matter Revisited: Bird, et. al. and Sasaki, et. al. have recently proposed the intriguing
possibility that the black holes detected by LIGO could be all or part of the
cosmological dark matter. This offers an alternative to WIMPs and axions, where
dark matter could be comprised solely of Standard Model particles. The mass
range lies within an observationally viable window and the predicted merger
rate can be tested by future LIGO observations. In this paper, we argue that
non-thermal histories favor production of black holes near this mass range --
with heavier ones unlikely to form in the early universe and lighter black
holes being diluted through late-time entropy production. We discuss how this
prediction depends on the primordial power spectrum, the likelihood of black
hole formation, and the underlying model parameters. We find the prediction for
the preferred mass range to be rather robust assuming a blue spectral index
less than two. We consider the resulting relic density in black holes, and
using recent observational constraints, establish whether they could account
for all of the dark matter today. |
Robustness to systematics for future dark energy probes: We extend the Figure of Merit formalism usually adopted to quantify the
statistical performance of future dark energy probes to assess the robustness
of a future mission to plausible systematic bias. We introduce a new robustness
Figure of Merit which can be computed in the Fisher Matrix formalism given
arbitrary systematic biases in the observable quantities. We argue that
robustness to systematics is an important new quantity that should be taken
into account when optimizing future surveys. We illustrate our formalism with
toy examples, and apply it to future type Ia supernova (SNIa) and baryonic
acoustic oscillation (BAO) surveys. For the simplified systematic biases that
we consider, we find that SNIa are a somewhat more robust probe of dark energy
parameters than the BAO. We trace this back to a geometrical alignement of
systematic bias direction with statistical degeneracy directions in the dark
energy parameter space. | Exploring the Redshift-Space Peculiar Velocity Field and its Power
Spectrum: Redshift-space distortions (RSD) generically affect any spatially-dependent
observable that is mapped using redshift information. The effect on the
observed clustering of galaxies is the primary example of this. This paper is
devoted to another example: the effect of RSD on the apparent peculiar motions
of tracers as inferred from their positions in redshift space (i.e. the
observed distance). Our theoretical study is motivated by practical
considerations, mainly, the direct estimation of the velocity power spectrum,
which is preferably carried out using the tracer's redshift-space position (so
as to avoid uncertainties in distance measurements). We formulate the
redshift-space velocity field and show that RSD enters as a higher-order
effect. Physically, this effect may be interpreted as a dissipative correction
to the usual perfect-fluid description of dark matter. We show that the effect
on the power spectrum is a damping on relatively large, quasilinear scales
($k>0.01\,h\,{\rm Mpc}^{-1}$), as was observed, though unexplained, in $N$-body
simulations elsewhere. This paper presents two power spectrum models for the
peculiar velocity field in redshift space, both of which can be considered
velocity analogues of existing clustering models. In particular, we show that
the "Finger-of-God" effect, while also present in the velocity field, cannot be
entirely blamed for the observed damping in simulations. Our work provides some
of the missing modelling ingredients required for a density--velocity
multi-tracer analysis, which has been proposed for upcoming redshift surveys. |
Selection constraints on high redshift quasar searches in the VISTA
kilo-degree infrared galaxy survey: The European Southern Observatory's (ESO) Visible and Infrared Survey
Telescope for Astronomy (VISTA) is a 4-m class survey telescope for wide-field
near-infrared imaging. VISTA is currently running a suite of six public
surveys, which will shortly deliver their first Europe wide public data
releases to ESO. The VISTA Kilo-degree Infrared Galaxy Survey (VIKING) forms a
natural intermediate between current wide shallow, and deeper more concentrated
surveys, by targeting two patches totalling 1500 sq.deg in the northern and
southern hemispheres with measured 5-sigma limiting depths of Z ~ 22.4, Y ~
21.4, J ~ 20.9, H ~ 19.9 and Ks ~19.3 (Vega). This architecture forms an ideal
working parameter space for the discovery of a significant sample of 6.5 <= z
<= 7.5 quasars. In the first data release priority has been placed on small
areas encompassing a number of fields well sampled at many wavelengths, thereby
optimising science gains and synergy whilst ensuring a timely release of the
first products. For rare object searches e.g. high-z quasars, this policy is
not ideal since photometric selection strategies generally evolve considerably
with the acquisition of data. Without a reasonably representative data set
sampling many directions on the sky it is not clear how a rare object search
can be conducted in a highly complete and efficient manner.
In this paper, we alleviate this problem by supplementing initial data with a
realistic model of the spatial, luminosity and colour distributions of sources
known to heavily contaminate photometric quasar selection spaces, namely dwarf
stars of spectral type M, L and T. We use this model along with a subset of
available data to investigate contamination of quasar selection space by cool
stars and galaxies and lay down a set of benchmark selection constraints that
limit contamination to reasonable levels whilst maintaining high
completeness... | The Parameter Space of Galaxy Formation: Semi-analytic models are a powerful tool for studying the formation of
galaxies. However, these models inevitably involve a significant number of
poorly constrained parameters that must be adjusted to provide an acceptable
match to the observed universe. In this paper, we set out to quantify the
degree to which observational data-sets can constrain the model parameters. By
revealing degeneracies in the parameter space we can hope to better understand
the key physical processes probed by the data. We use novel mathematical
techniques to explore the parameter space of the GALFORM semi-analytic model.
We base our investigation on the Bower et al. 2006 version of GALFORM, adopting
the same methodology of selecting model parameters based on an acceptable match
to the local bJ and K luminosity functions. The model contains 16 parameters
that are poorly constrained, and we investigate this parameter space using the
Model Emulator technique, constructing a Bayesian approximation to the GALFORM
model that can be rapidly evaluated at any point in parameter space. By
combining successive waves of emulation, we show that only 0.26% of the initial
volume is of interest for further exploration. However, within this region we
show that the Bower et al. 2006 model is only one choice from an extended
sub-space of model parameters that can provide equally acceptable fits. We
explore the geometry of this region and begin to explore the physical
connections between parameters that are exposed by this analysis. We also
consider the impact of adding additional observational data to further
constrain the parameter space. |
IDCS J1426.5+3508: The Most Massive Galaxy Cluster at $z > 1.5$: We present a deep (100 ks) Chandra observation of IDCS J1426.5+3508, a
spectroscopically confirmed, infrared-selected galaxy cluster at $z = 1.75$.
This cluster is the most massive galaxy cluster currently known at $z > 1.5$,
based on existing Sunyaev-Zel'dovich (SZ) and gravitational lensing detections.
We confirm this high mass via a variety of X-ray scaling relations, including
$T_X$-M, $f_g$-M, $Y_X$-M and $L_X$-M, finding a tight distribution of masses
from these different methods, spanning M$_{500}$ = 2.3-3.3 $\times 10^{14}$
M$_{\odot}$, with the low-scatter $Y_X$-based mass $M_{500,Y_X} =
2.6^{+1.5}_{-0.5} \times 10^{14}$ M$_\odot$. IDCS J1426.5+3508 is currently the
only cluster at $z > 1.5$ for which X-ray, SZ and gravitational lensing mass
estimates exist, and these are in remarkably good agreement. We find a
relatively tight distribution of the gas-to-total mass ratio, employing total
masses from all of the aforementioned indicators, with values ranging from
$f_{gas,500}$ = 0.087-0.12. We do not detect metals in the intracluster medium
(ICM) of this system, placing a 2$\sigma$ upper limit of $Z(r < R_{500}) < 0.18
Z_{\odot}$. This upper limit on the metallicity suggests that this system may
still be in the process of enriching its ICM. The cluster has a dense,
low-entropy core, offset by $\sim$30 kpc from the X-ray centroid, which makes
it one of the few "cool core" clusters discovered at $z > 1$, and the first
known cool core cluster at $z > 1.2$. The offset of this core from the
large-scale centroid suggests that this cluster has had a relatively recent
($\lesssim$500 Myr) merger/interaction with another massive system. | Revisiting the statistical isotropy of GRB sky distribution: The assumption of homogeneity and isotropy on large scales is one of the main
hypotheses of the standard cosmology. In this paper, we test the hypothesis of
isotropy from the two-point angular correlation function of 2626 gamma-ray
bursts (GRB) of the FERMI GRB catalogue. We show that the uncertainties in the
GRB positions induce spurious anisotropic signals in their sky distribution.
However, when such uncertainties are taken into account no significant evidence
against the large-scale statistical isotropy is found. This result remains
valid even for the sky distribution of short-lived GRB, contrarily to previous
reports. |
Non-Gaussian Correlations Outside the Horizon in Local Thermal
Equilibrium: Making a connection between observations of cosmological correlation
functions and those calculated from theories of the early universe requires
that these quantities are conserved through the periods of the universe which
we do not understand. In this paper, the results of [0810.2831] are extended to
show that tree-approximation correlation functions of Heisenberg picture
operators for the reduced spatial metric are constant outside the horizon
during local thermal equilibrium with no non-zero conserved quantum numbers. | Cosmic Reionization Study : Principle Component Analysis After Planck: The study of reionization history plays an important role in understanding
the evolution of our universe. It is commonly believed that the intergalactic
medium (IGM) in our universe are fully ionized today, however the reionizing
process remains to be mysterious. A simple instantaneous reionization process
is usually adopted in modern cosmology without direct observational evidence.
However, the history of ionization fraction, $x_e(z)$ will influence cosmic
microwave background (CMB) observables and constraints on optical depth $\tau$.
With the mocked future data sets based on featured reionization model, we find
the bias on $\tau$ introduced by instantaneous model can not be neglected. In
this paper, we study the cosmic reionization history in a model independent
way, the so called principle component analysis (PCA) method, and reconstruct
$x_e (z)$ at different redshift $z$ with the data sets of Planck, WMAP 9 years
temperature and polarization power spectra, combining with the baryon acoustic
oscillation (BAO) from galaxy survey and type Ia supernovae (SN) Union 2.1
sample respectively. The results show that reconstructed $x_e(z)$ is consistent
with instantaneous behavior, however, there exists slight deviation from this
behavior at some epoch. With PCA method, after abandoning the noisy modes, we
get stronger constraints, and the hints for featured $x_e(z)$ evolution could
become a little more obvious. |
Beyond $Λ$CDM with $f(z)$CDM: criticalities and solutions of
Padé Cosmography: Recently, cosmography emerged as a valuable tool to effectively describe the
vast amount of astrophysical observations without relying on a specific
cosmological model. Its model-independent nature ensures a faithful
representation of data, free from theoretical biases. Indeed, the commonly
assumed fiducial model, the $\Lambda$CDM, shows some shortcomings and tensions
between data at late and early times that need to be further investigated. In
this paper, we explore an extension of the standard cosmological model by
adopting the $f(z)$CDM approach, where $f(z)$ represents the cosmographic
series characterizing the evolution of recent universe driven by dark energy.
To construct $f(z)$, we take into account the Pad\'e series, since this
rational polynomial approximation offers a better convergence at high redshifts
than the standard Taylor series expansion. Several orders of such an
approximant have been proposed in previous works, here we want to answer the
questions: What is the impact of the cosmographic series choice on the
parameter constraints? Which series is the best for the analysis? So, we
analyse the most promising ones by identifying which order is preferred in
terms of stability and goodness of fit. Theoretical predictions of the
$f(z)$CDM model are obtained by the Boltzmann solver code and the posterior
distributions of the cosmological and cosmographic parameters are constrained
by a Monte Carlo Markov Chains analysis. We consider a joint data set of cosmic
microwave background temperature measurements from the Planck collaboration,
type Ia supernovae data from the latest Pantheon+ sample, baryonic acoustic
oscillations and cosmic chronometers data. In conclusions, we state which
series can be used when only late time data are used, while which orders has to
be considered in order to achieve the necessary stability when large redshifts
are considered. | Tracing the Reionization-Epoch Intergalactic Medium with Metal
Absorption Lines: IGM metal absorption lines observed in z>6 spectra offer the opportunity to
probe early feedback processes, the nature of enriching sources, and the
topology of reionization. We run high-resolution cosmological simulations
including galactic outflows to study the observability and physical properties
of 5 ions (C II, C IV, O I, Si II, Si IV) in absorption between z=8->5. We
apply three cases for ionization conditions: Fully neutral, fully reionized,
and a patchy model based on the flux from the nearest galaxy. We find that our
simulations broadly fit available z~5-6 IGM metal-line data, although all
observations cannot be accommodated with a single ionization condition.
Variations in O I absorbers among sight lines seen by Becker et al. (2006)
suggest significant neutral IGM patches down to z~6. Strong C IV absorbers at
z~6 may be the result of ionization by their parent galaxy. Our outflows have
typical speeds of ~200 km/s and mass loading factors of ~6. Such high mass
loading is critical for enriching the IGM to the observed levels while
curtailing star formation to match the observed z~6 rest-frame UV luminosity
function. The volume filling factor of metals increases during this epoch, but
only reaches ~1% for Z>10^(-3) Zsolar by z=5. C IV is an ideal tracer of IGM
metals at z~5-6, with dropping global ionization fractions to either higher or
lower redshifts. This results in a strongly increasing global Omega(C IV) from
z=8->5, in contrast to its relative constancy from z=5->2. Our simulations do
not support widespread early IGM enrichment from e.g. Pop III stars. High-z
absorbers arise from metals on their first outward journey from galaxies, at
distances less than 50 kpc. The galaxies responsible for early IGM enrichment
have typical M*=10^(7.0-8.5) Msolar. |
Star formation in the intragroup medium and other diagnostics of the
evolutionary stages of compact groups of galaxies: Context: Compact groups of galaxies are entities that have high densities of
galaxies and serve as laboratories to study galaxy interactions, intergalactic
star formation and galaxy evolution.
Aims: The main goal of this study is to search for young objects in the
intragroup medium of seven compact groups of galaxies: HCG 2, 7, 22, 23, 92,
100 and NGC 92 as well as to evaluate the stage of interaction of each group.
Methods: We used Fabry-Perot velocity fields and rotation curves together
with GALEX NUV and FUV images and optical R-band and HI maps.
Results: (i) HCG 7 and HCG 23 are in early stages of interaction, (ii) HCG 2
and HCG 22 are mildly interacting, and (iii) HCG 92, HCG 100 and NGC 92 are in
late stages of evolution. We find that all three evolved groups contain
populations of young blue objects in the intragroup medium, consistent with
ages < 100 Myr, of which several are younger than < 10 Myr. We also report the
discovery of a tidal dwarf galaxy candidate in the tail of NGC 92. These three
groups, besides containing galaxies that have peculiar velocity fields, also
show extended HI tails.
Conclusions: Our results indicate that the advanced stage of evolution of a
group, together with the presence of intragroup HI clouds, may lead to star
formation in the intragroup medium. A table containing all intergalactic HII
regions and tidal dwarf galaxies confirmed to date is appended. | The mass profile and dynamical status of the z~0.8 galaxy cluster LCDCS
0504: Constraints on the mass distribution in high-redshift clusters of galaxies
are not currently very strong. We aim to constrain the mass profile, M(r), and
dynamical status of the $z \sim 0.8$ LCDCS 0504 cluster of galaxies
characterized by prominent giant gravitational arcs near its center. Our
analysis is based on deep X-ray, optical, and infrared imaging, as well as
optical spectroscopy. We model the mass distribution of the cluster with three
different mass density profiles, whose parameters are constrained by the strong
lensing features of the inner cluster region, by the X-ray emission from the
intra-cluster medium, and by the kinematics of 71 cluster members. We obtain
consistent M(r) determinations from three methods (dispersion-kurtosis,
caustics and MAMPOSSt), out to the cluster virial radius and beyond. The mass
profile inferred by the strong lensing analysis in the central cluster region
is slightly above, but still consistent with, the kinematics estimate. On the
other hand, the X-ray based M(r) is significantly below both the kinematics and
strong lensing estimates. Theoretical predictions from $\Lambda$CDM cosmology
for the concentration--mass relation are in agreement with our observational
results, when taking into account the uncertainties in both the observational
and theoretical estimates. There appears to be a central deficit in the
intra-cluster gas mass fraction compared to nearby clusters. Despite the
relaxed appearance of this cluster, the determinations of its mass profile by
different probes show substantial discrepancies, the origin of which remains to
be determined. The extension of a similar dynamical analysis to other clusters
of the DAFT/FADA survey will allow to shed light on the possible systematics
that affect the determination of mass profiles of high-z clusters, possibly
related to our incomplete understanding of intracluster baryon physics. |
A Multi-frequency analysis of dark matter annihilation interpretations
of recent anti-particle and gamma-ray excesses in cosmic structures: The Fermi-LAT observation of a gamma-ray excess from the galactic-centre, as
well as the PAMELA, AMS, and AMS-2 anti-particle excesses, and the recent claim
of a Fermi-LAT excess in the Reticulum-2 dwarf galaxy have been put forward as
signatures compatible with of neutralino dark matter. These are of particular
interest as the neutralino annihilation models which fit these observations
might have observable consequences from radio to gamma-ray emission. Since dark
matter is expected to be a major matter constituent of cosmic structure, these
multi-frequency consequences should also be common to structures across the
mass spectrum. Thus, in this work we make predictions for the multi-frequency
spectra of three well-known sources dominated by dark matter, e.g. the Coma
cluster, the galaxy M81, and the Draco dwarf galaxy using models favoured by
dark matter interpretations of the aforementioned observations. We pay special
attention to the consequences for these models when their cross-sections are
renormalised to reproduce the recent gamma-ray excess observed in the
Reticulum-2 dwarf galaxy, which throw a dark matter interpretation of this
excess into doubt. We find that the multi-frequency data of Coma and Draco
disfavour the dark matter interpretation of the AMS, PAMELA and Fermi
anti-particle excess. Models derived from Fermi-LAT galactic centre
observations present somewhat lesser conflicts. We determine the detection
prospects of the Square Kilometre Array, the Cherenkov Telescope Array, as well
as the ASTROGAM and ASTRO-H satellites for the studied models. This
demonstrates that ASTRO-H is well positioned to probe the X-ray emissions from
neutralino annihilation. Thus, multi-frequency observation with the next
generation experiments will allow for unprecedented sensitivity to the
neutralino parameter space. | BICEP2 II: Experiment and Three-Year Data Set: We report on the design and performance of the BICEP2 instrument and on its
three-year data set. BICEP2 was designed to measure the polarization of the
cosmic microwave background (CMB) on angular scales of 1 to 5 degrees
($\ell$=40-200), near the expected peak of the B-mode polarization signature of
primordial gravitational waves from cosmic inflation. Measuring B-modes
requires dramatic improvements in sensitivity combined with exquisite control
of systematics. The BICEP2 telescope observed from the South Pole with a 26~cm
aperture and cold, on-axis, refractive optics. BICEP2 also adopted a new
detector design in which beam-defining slot antenna arrays couple to
transition-edge sensor (TES) bolometers, all fabricated on a common substrate.
The antenna-coupled TES detectors supported scalable fabrication and
multiplexed readout that allowed BICEP2 to achieve a high detector count of 500
bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree
angular scales. After optimization of detector and readout parameters, BICEP2
achieved an instrument noise-equivalent temperature of 15.8 $\mu$K sqrt(s). The
full data set reached Stokes Q and U map depths of 87.2 nK in square-degree
pixels (5.2 $\mu$K arcmin) over an effective area of 384 square degrees within
a 1000 square degree field. These are the deepest CMB polarization maps at
degree angular scales to date. The power spectrum analysis presented in a
companion paper has resulted in a significant detection of B-mode polarization
at degree scales. |
NGC 3627: a galaxy-dwarf collision?: Group galaxies very often show distinct signs of interaction with both
companion galaxies and the intragroup medium. X-ray observations are
particularly helpful because they provide information on the temperatures and
the densities of the hot gas in galaxies and intergalactic space. This can put
important constraints on the nature and timescales of these interactions. We
use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy
group to explain peculiar features visible in the polarized radio maps. We
analyzed soft X-ray (0.2-1 keV) emission from NGC 3627 to study the
distribution of the hot gas and its temperature in different areas of the
galaxy. Any change throughout the disk can reflect distortions visible in the
radio polarized emission. We also studied two bright point sources that are
probably tightly linked to the evolution of the galaxy. We find an increase in
the temperature of the hot gas in the area of the polarized radio ridge in the
western arm of the galaxy. In the eastern part of the disk we find two
ultra-luminous X-ray sources. We note a large hot gas temperature difference
(by a factor of 2) between the two bar ends. The polarized radio ridge in the
western arm of NGC 3627 is most likely formed by ram-pressure effects caused by
the movement of the galaxy through the intragroup medium. To explain the
distortions visible in the eastern part of the disk in polarized radio maps,
the asymmetry of the bar, and the distortion of the eastern arm, we propose a
recent collision of NGC 3627 with a dwarf companion galaxy. | The clustering of galaxies in the completed SDSS-IV extended Baryon
Oscillation Spectroscopic Survey: Primordial non-Gaussianity in Fourier Space: We present measurements of the local primordial non-Gaussianity parameter
\fNLloc from the clustering of 343,708 quasars with redshifts 0.8 < z < 2.2
distributed over 4808 square degrees from the final data release (DR16) of the
extended Baryon acoustic Oscillation Spectroscopic Survey (eBOSS), the largest
volume spectroscopic survey up to date. Our analysis is performed in Fourier
space, using the power spectrum monopole at very large scales to constrain the
scale dependent halo bias. We carefully assess the impact of systematics on our
measurement and test multiple contamination removal methods. We demonstrate the
robustness of our analysis pipeline with EZ-mock catalogues that simulate the
eBOSS DR16 target selection. We find $f_\mathrm{NL}=-12\pm 21$ (68\%
confidence) for the main clustering sample including quasars with redshifts
between 0.8 and 2.2, after exploiting a novel neural network scheme for
cleaning the DR16 sample and in particular after applying redshift weighting
techniques, designed for non-Gaussianity measurement from large scales
structure, to optimize our analysis, which improve our results by 37\%. |
Euclid: The importance of galaxy clustering and weak lensing
cross-correlations within the photometric Euclid survey: The data from the Euclid mission will enable the measurement of the
photometric redshifts, angular positions, and weak lensing shapes for over a
billion galaxies. This large dataset will allow for cosmological analyses using
the angular clustering of galaxies and cosmic shear. The cross-correlation (XC)
between these probes can tighten constraints and it is therefore important to
quantify their impact for Euclid. In this study we carefully quantify the
impact of XC not only on the final parameter constraints for different
cosmological models, but also on the nuisance parameters. In particular, we aim
at understanding the amount of additional information that XC can provide for
parameters encoding systematic effects, such as galaxy bias or intrinsic
alignments (IA). We follow the formalism presented in Euclid Collaboration:
Blanchard et al. (2019) and make use of the codes validated therein. We show
that XC improves the dark energy Figure of Merit (FoM) by a factor $\sim 5$,
whilst it also reduces the uncertainties on galaxy bias by $\sim 17\%$ and the
uncertainties on IA by a factor $\sim 4$. We observe that the role of XC on the
final parameter constraints is qualitatively the same irrespective of the
galaxy bias model used. We also show that XC can help in distinguishing between
different IA models, and that if IA terms are neglected then this can lead to
significant biases on the cosmological parameters. We find that the XC terms
are necessary to extract the full information content from the data in future
analyses. They help in better constraining the cosmological model, and lead to
a better understanding of the systematic effects that contaminate these probes.
Furthermore, we find that XC helps in constraining the mean of the
photometric-redshift distributions, but it requires a more precise knowledge of
this mean in order not to degrade the final FoM. [Abridged] | The Atlas3D Project - VI. Simulations of binary galaxy mergers and the
link with Fast Rotators, Slow Rotators, and Kinematically Distinct Cores: We study the formation of early-type galaxies through mergers with a sample
of 70 high-resolution (softening length < 60 pc and 12*10^6 particles)
numerical simulations of binary mergers of disc galaxies and 16 simulations of
ETG remergers. These simulations, designed to accompany observations and models
conducted within the Atlas3D project, encompass various mass ratios (from 1:1
to 6:1), initial conditions and orbital parameters. The progenitor disc
galaxies are spiral-like with bulge to disc ratios typical of Sb and Sc
galaxies. We find that binary mergers of disc galaxies with mass ratios of 3:1
and 6:1 are nearly always classified as Fast Rotators according to the Atlas3D
criterion (based on the lambda_R parameter): they preserve the structure of the
input fast rotating spiral progenitors. They have intrinsic ellipticities
larger than 0.5, cover intrinsic lambda_R values between 0.2 and 0.6, within
the range of observed Fast Rotators. Major disc mergers (mass ratios of 2:1 and
1:1) lead to both Fast and Slow Rotators. Most of the Fast Rotators produced in
major mergers have intermediate flattening, with ellipticities between 0.4 and
0.6. Most Slow Rotators formed in these binary disc mergers hold a stellar
Kinematically Distinct Core (KDC) in their 1-3 central kilo-parsec: these KDCs
are built from the stellar components of the progenitors. Besides a handful of
specific observed systems -- the counter-rotating discs (2-sigma galaxies) --
these therefore cannot reproduce the observed population of Slow Rotators in
the nearby Universe. The mass ratio of the progenitors is a fundamental
parameter for the formation of Slow Rotators in these binary mergers, but it
also requires a retrograde spin for the earlier-type (Sb) progenitor galaxy
with respect to the orbital angular momentum. (Abridged) |
Beam profile sensitivity of the WMAP CMB power spectrum: Using the published WMAP 5-year data, we first show how sensitive the WMAP
power spectra are to the form of the WMAP beam. It is well known that the beam
profile derived from observations of Jupiter is non-Gaussian and indeed
extends, in the W band for example, well beyond its 12.'6 FWHM core out to more
than 1 degree in radius. This means that even though the core width corresponds
to wavenumber l\approx1800, the form of the beam still significantly affects
the WMAP results even at l\approx200 which is the scale of the first acoustic
peak. The difference between the beam convolved C_l and the final C_l is
\approx70% at the scale of the first peak, rising to \approx400% at the scale
of the second.
New estimates of the Q, V and W-band beam profiles are then presented, based
on a stacking analysis of the WMAP5 radio source catalogue and temperature
maps. The radio sources show a significantly (3-4\sigma) broader beam profile
on scales of 10'-30' than that found by the WMAP team whose beam analysis is
based on measurements of Jupiter. Beyond these scales the beam profiles from
the radio sources are too noisy to give useful information. Furthermore, we
find tentative evidence for a non-linear relation between WMAP and ATCA/IRAM 95
GHz source fluxes. We discuss whether the wide beam profiles could be caused
either by radio source extension or clustering and find that neither
explanation is likely. We also argue against the possibility that Eddington
bias is affecting our results. The reasons for the difference between the radio
source and the Jupiter beam profiles are therefore still unclear. If the radio
source profiles were then used to define the WMAP beam, there could be a
significant change in the amplitude and position of even the first acoustic
peak. It is therefore important to identify the reasons for the differences
between these two beam profile estimates. | The dark matter halo concentration and stellar initial mass function of
a CASSOWARY group: We exploit the group environment of the CAmbridge Sloan Survey Of Wide ARcs
in the skY (CASSOWARY) z=0.3 lens J2158+0257 to measure the group dynamical
mass as a complement to the central dynamical and lensing mass constraints.
Follow-up spectroscopy of candidate group members is performed using VLT/FORS2.
From the resulting N=21 confirmed members we measure the group dynamical mass
by calibrating an analytic tracer mass estimator with cosmological simulations.
The luminosity weighted line-of-sight velocity dispersion and the Einstein
radius of the lens are used as mass probes in the inner regions of the galaxy.
Combining these three observational probes allows us to independently constrain
the mass and concentration of the dark matter halo, in addition to the total
stellar mass of the central galaxy. We find a dark matter halo in remarkably
good agreement with simulations (log_10 M_200/M_sun = 14.2 +/- 0.2, c_200 = 4.4
(+1.6, -1.4)) and a stellar mass-to-light ratio which favors a Salpeter initial
mass function ((M/L)* = 5.7 +/- 1.2). Our measurement of a normal halo
concentration suggests that there is no discrepancy between simulations and
observations at the group mass scale. This is in contrast to the cluster mass
scale for which a number of studies have claimed over-concentrated halos. While
the halo mass is robustly determined, and the halo concentration is not
significantly affected by systematics, the resulting stellar mass-to-light
ratio is sensitive to the choice of stellar parameters, such as density profile
and velocity anisotropy. |
Investigating the Contribution of Extended Radio Sources to the Epoch of
Reionisation Power Spectrum: We investigate the contribution of extended radio sources such as Centaurus
A, and Galactic supernova remnants (SNRs) to our ability to detect the
statistical $21\,\rm{cm}$ signal from the Epoch of Reionisation (EoR) with the
Murchison Widefield Array (MWA). These sources are typically ignored because
they are in highly attenuated parts of the MWA primary beam, however in
aggregate these sources have apparent flux densities of $10\,\rm{Jy}$ on
angular scales we expect to detect the $21\,\rm{cm}$ signal. We create bespoke
multi-component 2D Gaussian models for Galactic SNRs and for Centaurus A, and
simulate the visibilities for two MWA snapshot observations. We grid those
visibilities and then Fourier transform them with respect to frequency,
averaging them both spherically and cylindrically to produce the 1D and 2D
power spectra. We compare the simulated 1D power spectra to the expected
$21\,\rm{cm}$ power spectrum. We find that although these extended sources are
in highly attenuated parts of the MWA primary beam pattern, collectively they
have enough power ($\sim10^4-10^5\,\rm{mK^2}\,\it{h^{-3}} \,\rm{Mpc^{3}}$) on
EoR significant modes ($|\mathbf{k}| \leq 0.1 h \rm{Mpc}^{-1}$) to prohibit
detection of the $21\,\rm{cm}$ signal ($10^4\,\rm{mK^2}\,\it{h^{-3}}
\,\rm{Mpc^{3}}$). We find that $50-90\%$ of sources must be removed in order to
reduce leakage to a level of $10-20\%$ of the $21\,\rm{cm}$ power spectrum on
EoR significant modes. The effects of widefield extended sources will have
implications on the detectability of the $21\,\rm{cm}$ signal for the MWA and
with the future Square Kilometre Array (SKA). | CMB $μT$ cross-correlations as a probe of PBH scenarios: We propose a new method for probing inflationary models of primordial black
hole (PBH) production, using only CMB physics at relatively large scales. In
PBH scenarios, the primordial power spectrum profile for curvature
perturbations is characterized by a pronounced dip, followed by a rapid growth
towards small scales, leading to a peak responsible for PBH formation. We focus
on scales around the dip that are well separated from the peak to analytically
compute expressions for the curvature power spectrum and bispectrum. The size
of the squeezed bispectrum is enhanced at the position of the dip, and it
acquires a characteristic scale dependence that can be probed by
cross-correlating CMB $\mu$-distortions and temperature fluctuations. We
quantitatively study the properties of such cross-correlations and how they
depend on the underlying model, discussing how they can be tested by the next
generation of CMB $\mu$-distortion experiments. This method allows one to
experimentally probe inflationary PBH scenarios using well-understood CMB
physics, without considering non-linearities associated with PBH formation and
evolution. |
New limits on light dark matter - proton cross section from the cosmic
large-scale structure: We set the strongest limits to-date on the velocity-independent dark matter
(DM) - proton cross section $\sigma$ for DM masses $m = 10\,\mathrm{keV}$ to
$100\,\mathrm{GeV}$, using large-scale structure traced by the Lyman-alpha
forest: e.g., a 95% lower limit $\sigma < 6 \times 10^{-30}\,\mathrm{cm}^2$,
for $m = 100\,\mathrm{keV}$. Our results complement direct detection, which has
limited sensitivity to sub-GeV DM. We use an emulator of cosmological
simulations, combined with data from the smallest cosmological scales used
to-date, to model and search for the imprint of primordial DM-proton
collisions. Cosmological bounds are improved by up to a factor of 25. | Irreducible cosmic production of relic vortons: The existence of a scaling network of current-carrying cosmic strings in our
Universe is expected to continuously create loops endowed with a conserved
current during the cosmological expansion. These loops radiate gravitational
waves and may stabilise into centrifugally supported configurations. We show
that this process generates an irreducible population of vortons which has not
been considered so far. In particular, we expect vortons to be massively
present today even if no loops are created at the time of string formation. We
determine their cosmological distribution, and estimate their relic abundance
today as a function of both the string tension and the current energy scale.
This allows us to rule out new domains of this parameter space. At the same
time, given some conditions on the string current, vortons are shown to provide
a viable and original dark matter candidate, possibly for all values of the
string tension. Their mass, spin and charge spectrum being broad, vortons would
have an unusual phenomenology in dark matter searches. |
Is there another coincidence problem at the reionization epoch?: The cosmological coincidences between the matter and radiation energy
densities at recombination as well as between the densities of matter and the
cosmological constant at present time are well known. We point out that
moreover the third intersection between the energy densities of radiation and
the cosmological constant coincides with the reionization epoch. To quantify
the statistical relevance of this concurrence, we compute the Bayes factor
between the concordance cosmology with free Thomson scattering optical depth
and a model for which this parameter is inferred from imposing a match between
the time of density equality and the epoch of reionization. This is to
characterize the potential explanatory gain if one were to find a
parameter-free physical connection. We find a very strong preference for such a
concurrence on the Jeffreys scale from current cosmological observations. We
furthermore discuss the effect of choice of priors, changes in reionization
history, and free sum of neutrino masses. We also estimate the impact of adding
intermediate polarization data from the Planck High Frequency Instrument and
prospects for future 21 cm surveys. In the first case, preference for the
correlation remains substantial, whereas future data may give results more
decisive in pro or substantial in contra. Finally, we provide a discussion on
different interpretations of these findings. In particular, we show how a
connection between the star-formation history and the cosmological background
dynamics can give rise to this concurrence. | The properties of warm dark matter haloes: Well-motivated elementary particle candidates for the dark matter, such as
the sterile neutrino, behave as warm dark matter (WDM).For particle masses of
order a keV, free streaming produces a cutoff in the linear fluctuation power
spectrum at a scale corresponding to dwarf galaxies. We investigate the
abundance and structure of WDM haloes and subhaloes on these scales using high
resolution cosmological N-body simulations of galactic haloes of mass similar
to the Milky Way's. On scales larger than the free-streaming cutoff, the
initial conditions have the same power spectrum and phases as one of the cold
dark matter (CDM) haloes previously simulated by Springel et al as part of the
Virgo consortium Aquarius project. We have simulated four haloes with WDM
particle masses in the range 1.4-2.3keV and, for one case, we have carried out
further simulations at varying resolution. N-body simulations in which the
power spectrum cutoff is resolved are known to undergo artificial fragmentation
in filaments producing spurious clumps which, for small masses (<10^7Msun in
our case) outnumber genuine haloes. We have developed a robust algorithm to
identify these spurious objects and remove them from our halo catalogues. We
find that the WDM subhalo mass function is suppressed by well over an order
magnitude relative to the CDM case for masses <10^9Msun. Requiring that there
should be at least as many subhaloes as there are observed satellites in the
Milky Way leads to a conservative lower limit to the (thermal equivalent) WDM
particle mass of ~1.5\rmn{keV}. WDM haloes and subhaloes have cuspy density
distributions that are well described by NFW or Einasto profiles. Their central
densities are lower for lower WDM particle masses and none of the models we
have considered suffer from the "too big to fail" problem recently highlighted
by Boylan-Kolchin et al. |
Gravitational waves from a universe filled with primordial black holes: Ultra-light primordial black holes, with masses
$m_\mathrm{PBH}<10^9\mathrm{g}$, evaporate before big-bang nucleosynthesis and
can therefore not be directly constrained. They can however be so abundant that
they dominate the universe content for a transient period (before reheating the
universe via Hawking evaporation). If this happens, they support large
cosmological fluctuations at small scales, which in turn induce the production
of gravitational waves through second-order effects. Contrary to the primordial
black holes, those gravitational waves survive after evaporation, and can
therefore be used to constrain such scenarios. In this work, we show that for
induced gravitational waves not to lead to a backreaction problem, the relative
abundance of black holes at formation, denoted $ \Omega_\mathrm{PBH,f} $,
should be such that $ \Omega_\mathrm{PBH,f}
<10^{-4}(m_\mathrm{PBH}/10^9\mathrm{g})^{-1/4}$. In particular, scenarios where
primordial black holes dominate right upon their formation time are all
excluded (given that $m_\mathrm{PBH}>10\, \mathrm{g}$ for inflation to proceed
at $\rho^{1/4}<10^{16}\mathrm{GeV}$). This sets the first constraints on
ultra-light primordial black holes. | A Spectroscopic Model of the Type Ia Supernova--Host Galaxy Mass
Correlation from SALT3: The unknown cause of the correlation between Type Ia supernova (SN Ia) Hubble
residuals and their host-galaxy masses (the "mass step") may bias cosmological
parameter measurements. To better understand the mass step, we develop a SALT3
light-curve model for SN cosmology that uses the host-galaxy masses of 296
low-redshift SNe Ia to derive a spectral-energy distribution--host-galaxy mass
relationship. The resulting model has larger Ca II H&K, Ca II near-infrared
triplet, and Si II equivalent widths for SNe in low-mass host galaxies at
2.2-2.7$\sigma$ significance; this indicates higher explosion energies per unit
mass in low-mass-hosted SNe. The model has phase-dependent changes in SN Ia
colors as a function of host mass, indicating intrinsic differences in mean
broadband light curves. Although the model provides a better fit to the SN data
overall, it does not substantially reduce data--model residuals for a typical
light curve in our sample nor does it significantly reduce Hubble residual
dispersion. This is because we find that previous SALT models parameterized
most host-galaxy dependencies with their first principal component, although
they failed to model some significant spectral variations. Our new model is
luminosity and cosmology independent, and applying it to data reduces the mass
step by $0.021\pm0.002$ mag (uncertainty accounts for correlated data sets);
these results indicate that $\sim$35% of the mass step can be attributed to
luminosity-independent effects. This SALT model version could be trained using
alternative host-galaxy properties and at different redshifts, and therefore
will be a tool for understanding redshift-dependent correlations between SNe Ia
and their host properties as well as their impact on cosmological parameter
measurements. |
The Extreme Hosts of Extreme Supernovae: We use GALEX ultraviolet (UV) and optical integrated photometry of the hosts
of seventeen luminous supernovae (LSNe, having peak M_V < -21) and compare them
to a sample of 26,000 galaxies from a cross-match between the SDSS DR4 spectral
catalog and GALEX interim release 1.1. We place the LSNe hosts on the galaxy
NUV-r versus M_r color magnitude diagram (CMD) with the larger sample to
illustrate how extreme they are. The LSN hosts appear to favor low-density
regions of the galaxy CMD falling on the blue edge of the blue cloud toward the
low luminosity end. From the UV-optical photometry, we estimate the star
formation history of the LSN hosts. The hosts have moderately low star
formation rates (SFRs) and low stellar masses (M_*) resulting in high specific
star formation rates (sSFR). Compared with the larger sample, the LSN hosts
occupy low-density regions of a diagram plotting sSFR versus M_* in the area
having higher sSFR and lower M_*. This preference for low M_*, high sSFR hosts
implies the LSNe are produced by an effect having to do with their local
environment. The correlation of mass with metallicity suggests that perhaps
wind-driven mass loss is the factor that prevents LSNe from arising in
higher-mass, higher-metallicity hosts. The massive progenitors of the LSNe
(>100 M_sun), by appearing in low-SFR hosts, are potential tests for theories
of the initial mass function that limit the maximum mass of a star based on the
SFR. | High precision measurement of cosmic curvature: from gravitational waves
and cosmic chronometer: Although the spatial curvature has been measured with very high precision, it
still suffers from the well known cosmic curvature tension. In this paper, we
propose an improved method to determine the cosmic curvature, by using the
simulated data of binary neutron star mergers observed by the second generation
space-based DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO).
By applying the Hubble parameter observations of cosmic chronometers to the
DECIGO standard sirens, we explore different possibilities of making
measurements of the cosmic curvature referring to a distant past: one is to
reconstruct the Hubble parameters through the Gaussian process without the
influence of hypothetical models, and the other is deriving constraints on
$\Omega_K$ in the framework of non-flat $\Lambda$ cold dark matter model. It is
shown that in the improved method DECIGO could provide a reliable and stringent
constraint on the cosmic curvature ($\Omega_{K} = -0.007\pm0.016$), while we
could only expect the zero cosmic curvature to be established at the precision
of $\Delta \Omega_K=0.12$ in the second model-dependent method. Therefore, our
results indicate that in the framework of methodology proposed in this paper,
the increasing number of well-measured standard sirens in DECIGO could
significantly reduce the bias of estimations for cosmic curvature. Such
constraint is also comparable to the precision of Planck 2018 results with the
newest cosmic microwave background (CMB) observations ($\Delta \Omega_{K}
\approx 0.018$), based on the concordance $\Lambda$CDM model. |
Extent radiation in different types of radio sources: The contribution of an extent component of source radio emission is estimated
for quasars and galaxies. The consideration of source radio structures at
kiloparsec scales is used at the decameter and the higher frequency bands. The
determination of the contribution of an extent component to source radio
emission as well as main physical parameters of sample sources is carried out.
We found that especially extent sources, giant radio galaxies, have smaller
luminosity of core region, weaker magnetic field and greater characteristic age
in comparison with compact radio galaxies and quasars. As it follows from our
examination, the extent component contribution to source emission may be the
indicator of the radio source age. | Multi-wavelength Observations of the Enduring Type IIn Supernovae 2005ip
and 2006jd: We present an observational study of the Type IIn supernovae (SNe IIn) 2005ip
and 2006jd. Broad-band UV, optical and near-IR photometry, and
visual-wavelength spectroscopy of SN 2005ip complement and extend upon
published observations to 6.5 years past discovery. Our observations of SN
2006jd extend from UV to mid-infrared wavelengths, and like SN 2005ip, are
compared to reported X-ray measurements to understand the nature of the
progenitor. Both objects display a number of similarities with the 1988Z-like
subclass of SN IIn including: (i) remarkably similar early- and late-phase
optical spectra, (ii) a variety of high ionization coronal lines, (iii)
long-duration optical and near-IR emission and, (iv) evidence of cold and warm
dust components. However, diversity is apparent including an unprecedented
late-time r-band excess in SN 2006jd.The observed differences are attributed to
differences between the mass-loss history of the progenitor stars. We conclude
that the progenitor of SN 2006jd likely experienced a significant mass-loss
event during its pre-SN evolution akin to the great 19th century eruption of
\eta Carinae. Contrarily, as advocated by Smith et al. (2009), we find the
circumstellar environment of SN 2005ip to be more consistent with a clumpy wind
progenitor. |
The O3N2 and N2 abundance indicators revisited: improved calibrations
based on CALIFA and Te-based literature data: The use of IFS is since recently allowing to measure the emission line fluxes
of an increasingly large number of star-forming galaxies both locally and at
high redshift. The main goal of this study is to review the most widely used
empirical oxygen calibrations, O3N2 and N2, by using new direct abundance
measurements. We pay special attention to the expected uncertainty of these
calibrations as a function of the index value or abundance derived and the
presence of possible systematic offsets. This is possible thanks to the
analysis of the most ambitious compilation of Te-based HII regions to date.
This new dataset compiles the Te-based abundances of 603 HII regions extracted
from the literature but also includes new measurements from the CALIFA survey.
Besides providing new and improved empirical calibrations for the gas
abundance, we also present here a comparison between our revisited calibrations
with a total of 3423 additional CALIFA HII complexes with abundances derived
using the ONS calibration by Pilyugin et al. (2010). The combined analysis of
Te-based and ONS abundances allows us to derive their most accurate calibration
to date for both the O3N2 and N2 single-ratio indicators, in terms of all
statistical significance, quality and coverage of the space of parameters. In
particular, we infer that these indicators show shallower abundance
dependencies and statistically-significant offsets compared to those of Pettini
and Pagel (2004), Nagao et al. (2006) and P\'erez-Montero and Contini (2009).
The O3N2 and N2 indicators can be empirically applied to derive oxygen
abundances calibrations from either direct abundance determinations with random
errors of 0.18 and 0.16, respectively, or from indirect ones (but based on a
large amount of data) reaching an average precision of 0.08 and 0.09 dex
(random) and 0.02 and 0.08 dex (systematic; compared to the direct
estimations),respectively. | The Cross-correlation of MgII Absorption and Galaxies in BOSS: We present a measurement of the cross-correlation of MgII absorption and
massive galaxies, using the DR11 main galaxy sample of the Baryon Oscillation
Spectroscopic Survey of SDSS-III (CMASS galaxies), and the DR7 quasar spectra
of SDSS-II. The cross-correlation is measured by stacking quasar absorption
spectra shifted to the redshift of galaxies that are within a certain impact
parameter bin of the quasar, after dividing by a quasar continuum model. This
results in an average MgII equivalent width as a function of impact parameter
from a galaxy, ranging from 50 kpc to more than 10 Mpc in proper units, which
includes all MgII absorbers. We show that special care needs to be taken to use
an unbiased quasar continuum estimator, to avoid systematic errors in the
measurement of the mean stacked MgII equivalent width. The measured
cross-correlation follows the expected shape of the galaxy correlation
function, although measurement errors are large. We use the cross-correlation
amplitude to derive the bias factor of MgII absorbers, finding bMgII = 2.33
\pm? 0.19, where the error accounts only for the statistical uncertainty in
measuring the mean equivalent width. This bias factor is larger than that
obtained in previous studies and may be affected by modeling uncertainties that
we discuss, but if correct it suggests that MgII absorbers at redshift z \simeq
0:5 are spatially distributed on large scales similarly to the CMASS galaxies
in BOSS.
Keywords: galaxies: haloes, galaxies: formation, quasars: absorption lines,
large-scale structure of universe |
Constraints on the Assembly and Dynamics of Galaxies: I. Detailed
Rest-frame Optical Morphologies on Kiloparsec-scale of z ~ 2 Star-forming
Galaxies: We present deep and high-resolution HST/NIC2 F160W imaging at 1.6micron of
six z~2 star-forming galaxies with existing near-IR integral field spectroscopy
from SINFONI at the VLT. The unique combination of rest-frame optical imaging
and nebular emission-line maps provides simultaneous insight into morphologies
and dynamical properties. The overall rest-frame optical emission of the
galaxies is characterized by shallow profiles in general (Sersic index n<1),
with median effective radii of ~5kpc. The morphologies are significantly clumpy
and irregular, which we quantify through a non-parametric morphological
approach, estimating the Gini (G), Multiplicity (Psi), and M_20 coefficients.
The strength of the rest-frame optical emission lines in the F160W bandpass
indicates that the observed structure is not dominated by the morphology of
line-emitting gas, and must reflect the underlying stellar mass distribution of
the galaxies. The sizes and structural parameters in the rest-frame optical
continuum and Halpha emission reveal no significant differences, suggesting
similar global distributions of the on-going star formation and more evolved
stellar population. While no strong correlations are observed between stellar
population parameters and morphology within the NIC2/SINFONI sample itself, a
consideration of the sample in the context of a broader range of z~2 galaxy
types indicates that these galaxies probe the high specific star formation rate
and low stellar mass surface density part of the massive z~2 galaxy population,
with correspondingly large effective radii, low Sersic indices, low G, and high
Psi and M_20. The combined NIC2 and SINFONI dataset yields insights of
unprecedented detail into the nature of mass accretion at high redshift.
[Abridged] | Distance Determination To Eight Galaxies Using Expanding Photosphere
Method: Type IIP supernovae are recognized as independent extragalactic distance
indicators, however, keeping in view of the diverse nature of their observed
properties as well as the availability of good quality data, more and newer
events need to be tested for their applicability as a reliable distance
indicators. We use early photometric and spectroscopic data of eight type-IIP
SNe to derive distances to their host galaxies using the expanding photosphere
method (EPM). For five of these, EPM is applied for the first time. In this
work, we improved EPM application by using SYNOW estimated velocities and by
semi-deconvolving the broadband filter responses while deriving color
temperatures and black-body angular radii. We find that the derived EPM
distances are consistent with that derived using other redshift independent
methods. |
Dark matter decay in the Milky Way halo: Dark matter may be detected in X-ray decay, including from the decay of the
dark matter particles that make up the Milky Way (MW) halo. We use a range of
density profiles to compute X-ray line intensity profiles, with a focus on the
resonantly produced sterile neutrino dark matter candidate. Compared to the
Navarro--Frenk--White density profile, we show that using an adiabatically
contracted halo profile suppresses the line intensity in the halo outskirts and
enhances it in the Galactic Centre (GC), although this enhancement is
eliminated by the likely presence of a core within 3~kpc. Comparing our results
to MW halo observations, other X-ray observations, and structure formation
constraints implies a sterile neutrino mixing angle parameter
$s_{11}\equiv\sin^{2}(2\theta)\times10^{11}\sim[3,4]$ (particle lifetime
$\tau_{28}\equiv\tau/(10^{28}\mathrm{sec})\sim[1.0,1.3]$), which is
nevertheless is strong tension with some reported non-detections. We make
predictions for the likely decay flux that the XRISM satellite would measure in
the GC, plus the Virgo and Perseus clusters, and outline further steps to
determine whether the dark matter is indeed resonantly produced sterile
neutrinos as detected in X-ray decay. | CMB lensing power spectrum estimation without instrument noise bias: The power spectrum of cosmic microwave background (CMB) lensing will be
measured to sub-percent precision with upcoming surveys, enabling tight
constraints on the sum of neutrino masses and other cosmological parameters.
Measuring the lensing power spectrum involves the estimation of the connected
trispectrum of the four-point function of the CMB map, which requires the
subtraction of a large Gaussian disconnected noise bias. This reconstruction
noise bias receives contributions both from CMB and foreground fluctuations as
well as instrument noise (both detector and atmospheric noise for ground-based
surveys). The debiasing procedure therefore relies on the quality of
simulations of the instrument noise which may be expensive or inaccurate. We
propose a new estimator that makes use of at least four splits of the CMB maps
with independent instrument noise. This estimator makes the CMB lensing power
spectrum completely insensitive to any assumptions made in modeling or
simulating the instrument noise. We show that this estimator, in many practical
situations, leads to no substantial loss in signal-to-noise. We provide an
efficient algorithm for its computation that scales with the number of splits
$m$ as $\mathcal{O}(m^2)$ as opposed to a naive $\mathcal{O}(m^4)$ expectation. |
Quantiles as Robust Probes of Non-Gaussianity in 21-cm Images: The early epoch in which the first stars and galaxies formed is among the
most exciting unexplored eras of the Universe. A major research effort focuses
on probing this era with the 21-cm spectral line of hydrogen. While most
research focused on statistics like the 21-cm power spectrum or the
sky-averaged global signal, there are other ways to analyze tomographic 21-cm
maps, which may lead to novel insights. We suggest statistics based on
quantiles as a method to probe non-Gaussianities of the 21-cm signal. We show
that they can be used in particular to probe the variance, skewness, and
kurtosis of the temperature distribution, but are more flexible and robust than
these standard statistics. We test these statistics on a range of possible
astrophysical models, including different galactic halo masses, star-formation
efficiencies, and spectra of the X-ray heating sources, plus an exotic model
with an excess early radio background. Simulating data with angular resolution
and thermal noise as expected for the Square Kilometre Array (SKA), we conclude
that these statistics can be measured out to redshifts above 20 and offer a
promising statistical method for probing early cosmic history. | The intergalactic magnetic field constrained by Fermi/LAT observations
of the TeV blazar 1ES 0229+200: TeV photons from blazars at relatively large distances, interacting with the
optical-IR cosmic background, are efficiently converted into electron-positron
pairs. The produced pairs are extremely relativistic (Lorentz factors of the
order of 1e6 1e7 and promptly loose their energy through inverse Compton
scatterings with the photons of the microwave cosmic background, producing
emission in the GeV band. The spectrum and the flux level of this reprocessed
emission is critically dependent on the intensity of the intergalactic magnetic
field, B, that can deflect the pairs diluting the intrinsic emission over a
large solid angle. We derive a simple relation for the reprocessed spectrum
expected from a steady source. We apply this treatment to the blazar 1ES
0229+200, whose intrinsic very hard TeV spectrum is expected to be
approximately steady. Comparing the predicted reprocessed emission with the
upper limits measured by the Fermi/Large Area Telescope, we constrain the value
of the intergalactic magnetic field to be larger than $B \simeq 5\times
10^{-15}$ Gauss, depending on the model of extragalactic background light. |
The Two-Halo Term in Stacked Thermal Sunyaev-Zel'dovich Measurements:
Implications for Self-Similarity: The relation between the mass and integrated electron pressure of galaxy
group and cluster halos can be probed by stacking maps of the thermal
Sunyaev-Zel'dovich (tSZ) effect. Perhaps surprisingly, recent observational
results have indicated that the scaling relation between integrated pressure
and mass follows the prediction of simple, self-similar models down to halo
masses as low as $10^{12.5} \, M_{\odot}$. Hydrodynamical simulations that
incorporate energetic feedback processes suggest that gas should be depleted
from such low-mass halos, thus decreasing their tSZ signal relative to
self-similar predictions. Here, we build on the modeling of Vikram, Lidz, and
Jain (2017) to evaluate the bias in the interpretation of stacked tSZ
measurements due to the signal from correlated halos (the "two-halo" term),
which has generally been neglected in the literature. We fit theoretical models
to a measurement of the tSZ -- galaxy group cross-correlation function,
accounting explicitly for the one- and two- halo contributions. We find
moderate evidence of a deviation from self-similarity in the pressure -- mass
relation, even after marginalizing over conservative miscentering effects. We
explore pressure -- mass models with a break at $10^{14} \, M_{\odot}$, as well
as other variants. We discuss and test for sources of uncertainty in our
analysis, in particular a possible bias in the halo mass estimates and the
coarse resolution of the Planck beam. We compare our findings with earlier
analyses by exploring the extent to which halo isolation criteria can reduce
the two-halo contribution. Finally, we show that ongoing third-generation CMB
experiments will explicitly resolve the one-halo term in low-mass groups; our
methodology can be applied to these upcoming data sets to obtain a clear answer
to the question of self-similarity and an improved understanding of hot gas in
low-mass halos. | Scalar runnings and a test of slow roll from CMB distortions: A future measurement of cosmic microwave \mu-distortions by an experiment
with the specifications of PIXIE will provide an equivalent 3-sigma detection
of the running of running of the spectral index of scalar perturbations, \beta
= d\alpha/dln(k), if \mu > 7.75 E-8, covering much of the PIXIE sensitivity
range. This corresponds to a resolution limit of \beta > 0.015 which is
relatively large given any presumption of slow roll, a result of the current
tight constraints on \alpha < 0 on CMB scales. We show that a detection of
\beta at this level is in conflict with slow roll conditions if the primordial
signal can be distinguished from any post-inflationary contamination. |
Radiative feedback and cosmic molecular gas: numerical method: We present results from self-consistent 3D numerical simulations of cosmic
structure formation with a multi-frequency radiative transfer scheme and
non-equilibrium molecular chemistry of 13 primordial species (e-, H, H+, H-,
He, He+, He++, H2, H2+, D, D+, HD, HeH+), performed by using the simulation
code GADGET. We describe our implementation and show tests for ionized sphere
expansion in a static and dynamic density field around a central radiative
source, and for cosmological abundance evolution coupled with the cosmic
microwave background radiation. As a demonstrative application of radiative
feedback on molecular gas, we run also cosmological simulations of early
structure formation in a ~1Mpc size box. Our tests agree well with analytical
and numerical expectations. Consistently with other works, we find that
ionization fronts from central sources can boost H2 fractions in
shock-compressed gas. The tight dependence on H2 lead to a corresponding boost
of HD fractions, as well. We see a strong lowering of the the typical molecular
abundances up to several orders of magnitudes which partially hinders further
gas collapse of pristine neutral gas, and clearly suggests the need of
re-ionized gas or metal cooling for the formation of the following generation
of structures. | Primordial magnetic fields during the cosmic dawn in light of EDGES
21-cm signal: We study prospects of constraining the primordial magnetic field (PMF) and
its evolution during the dark ages and cosmic dawn in light of EDGES 21-cm
signal. Our analysis has been carried out on a `colder IGM' background which is
one of the promising avenues to interpret the EDGES signal. We consider the
dark matter-baryon interactions for the excess cooling. We find that the colder
IGM suppresses both the residual free electron fraction and the coupling
coefficient between the ionised and neutral components. The Compton heating
also gets affected in colder IGM background. Consequently, the IGM heating rate
due to the PMF enhances compared to the standard scenario. Thus, a significant
fraction of the magnetic energy, for $B_0 \lesssim 0.5 \, {\rm nG}$, gets
transferred to the IGM and the magnetic field decays at a much faster rate
compared to the simple $(1+z)^2$ scaling during the dark ages and cosmic dawn.
This low PMF is an unlikely candidate for explaining the rise of the EDGES
absorption signal at lower redshift. We also see that the PMF and DM-baryon
interaction together introduces a plateau-like feature in the redshift
evolution of the IGM temperature. We find that the upper limit on the PMF
depends on the underlying DM-baryon interaction. Higher PMF can be allowed when
the interaction cross-section is higher and/or the DM particle mass is lower.
Our study shows that the PMF with $B_0$ up to $\sim 0.4 \, {\rm nG}$, which is
ruled out in the standard model, can be allowed if DM-baryon interaction with
suitable cross-section and DM mass is considered. |
Deep learning for Sunyaev-Zel'dovich detection in Planck: The Planck collaboration has extensively used the six Planck HFI frequency
maps to detect the Sunyaev-Zel'dovich (SZ) effect with dedicated methods, e.g.,
by applying (i) component separation to construct a full sky map of the y
parameter or (ii) matched multi-filters to detect galaxy clusters via their hot
gas. Although powerful, these methods may still introduce biases in the
detection of the sources or in the reconstruction of the SZ signal due to prior
knowledge (e.g., the use of the GNFW profile model as a proxy for the shape of
galaxy clusters, which is accurate on average but not on individual clusters).
In this study, we use deep learning algorithms, more specifically a U-Net
architecture network, to detect the SZ signal from the Planck HFI frequency
maps. The U-Net shows very good performance, recovering the Planck clusters in
a test area. In the full sky, Planck clusters are also recovered, together with
more than 18,000 other potential SZ sources, for which we have statistical
hints of galaxy cluster signatures by stacking at their positions several full
sky maps at different wavelengths (i.e., the CMB lensing map from Planck, maps
of galaxy over-densities, and the ROSAT X-ray map). The diffuse SZ emission is
also recovered around known large-scale structures such as Shapley, A399-A401,
Coma, and Leo. Results shown in this proof-of-concept study are promising for
potential future detection of galaxy clusters with low SZ pressure with this
kind of approach, and more generally for potential identification and
characterisation of large-scale structures of the Universe via their hot gas. | CALIFA, the Calar Alto Legacy Integral Field Area survey: Early Report: We present the Calar Alto Legacy Integral Field Area survey (CALIFA).
CALIFA's main aim is to obtain spatially resolved spectroscopic information for
~600 galaxies of all Hubble types in the Local Universe (0.005< z <0.03). The
survey has been designed to allow three key measurements to be made: (a)
Two-dimensional maps of stellar populations (star formation histories, chemical
elements); (b) The distribution of the excitation mechanism and element
abundances of the ionized gas; and (c) Kinematic properties (velocity fields,
velocity dispersion), both from emission and from absorption lines. To cover
the full optical extension of the target galaxies (i.e. out to a 3sigma depth
of ~23 mag/arcsec2), CALIFA uses the exceptionally large field of view of the
PPAK/PMAS IFU at the 3.5m telescope of the Calar Alto observatory. We use two
grating setups, one covering the wavelength range between 3700 and 5000 AA at a
spectral resolution R~1650, and the other covering 4300 to 7000 AA at R~850.
The survey was allocated 210 dark nights, distributed in 6 semesters and
starting in July 2010 and is carried out by the CALIFA collaboration,
comprising ~70 astronomers from 8 different countries. As a legacy survey, the
fully reduced data will be made publically available, once their quality has
been verified. We showcase here early results obtained from the data taken so
far (21 galaxies). |
Multi-field formulation of gravitational particle production after
inflation: We study multi-field inflation models that contain a non-trivial field-space
metric and a non-minimal coupling between the gravity and inflaton sectors. In
such models it is known that even in the absence of explicit interaction terms
the inflaton sector can decay into matter as a result of its non-minimal
coupling to gravity, thereby reheating the Universe gravitationally. Using the
Bogoliubov approach we evaluate the gravitational decay rates of the inflaton
fields into both scalars and fermions, and analyse the reheating dynamics. We
also discuss how the interpretation of the reheating dynamics differs in the
so-called Jordan and Einstein frames, highlighting that the calculation of the
Bogoliubov coefficients is independent of the frame in which one starts. | Metal Production in Galaxy Clusters: The Non-Galactic Component: The metallicity in galaxy clusters is expected to originate from the stars in
galaxies, with a population dominated by high mass stars likely being the most
important stellar component, especially in rich clusters. We examine the
relationship between the metallicity and the prominence of galaxies as measured
by the star to baryon ratio, M$_*$/M$_{bary}$. Counter to expectations, we rule
out a metallicity that is proportional to M$_*$/M$_{bary}$, where the best fit
has the gas phase metallicity decreasing with M$_*$/M$_{bary}$, or the
metallicity of the gas plus the stars being independent of M$_*$/M$_{bary}$.
This implies that the population of stars responsible for the metals is largely
proportional to the total baryonic mass of the cluster, not to the galaxy mass
within the cluster. If generally applicable, most of the heavy elements in the
universe were not produced within galaxies. |
The galaxy environment of a QSO at z ~ 5.7: High-redshift quasars are believed to reside in massive halos in the early
universe and should therefore be located in fields with overdensities of
galaxies, which are thought to evolve into galaxy clusters seen in the local
universe. However, despite many efforts, the relationship between galaxy
overdensities and z~6 quasars is ambiguous. This can possibly be attributed to
the difficulty of finding galaxies with accurate redshifts in the vicinity of
z~6 quasars. So far, overdensity searches around z~6 quasars have been based on
studies of Lyman break galaxies (LBGs), which probe a redshift range of Delta z
~ 1. This range is large enough to select galaxies that may not be physically
related to the quasar. We use deep narrow- and broadband imaging to study the
environment of the z=5.72 quasar ULAS J0203+0012. The redshift range probed by
our narrow-band selection of Lyman alpha emitters (LAEs) is Delta z ~ 0.1,
which is significantly narrower than the LBG searches. This is the first time
that LAEs were searched for near a z~6 quasar, in an effort to provide clues
about the environments of quasars at the end of the epoch of reionization. We
find no enhancement of LAEs in the surroundings of ULAS J0203+0012 in
comparison with blank fields. We explore different explanations and
interpretations for this non-detection of a galaxy overdensity, including that
(1) the strong ionization from the quasar may prevent galaxy formation in its
immediate vicinity and (2) high-redshift quasars may not reside in the center
of the most massive dark matter halos. | Observable Signatures of the low-z Circum-Galactic and Inter-Galactic
Medium : UV Line Emission in Simulations: We present for the first time predictions for UV line emission of
intergalactic and circumgalactic gas from Adaptive Mesh Resolution (AMR) Large
Scale Structure (LSS) simulations at redshifts 0.3<z<1.2, with specific
emphasis on observability with current and near-future UV instrumentation. In
three transitions of interest (Lya, OVI and CIV) there is a clear bimodality in
the type of objects : the overwhelming majority of flux stems from discrete,
compact sources, while a much larger volume fraction is filled by more tenuous
gas. We characterise both object types with regard to number density, physical
size and shape, brightness, luminosity, velocity structure, mass, temperature,
ionisation state, and metal content. Degrading AMR grids to characteristic
resolutions of available (such as FIREBall) or foreseeable instrumentation,
allows to assess which inferences can be drawn from currently possible
observations, and set foundations to prepare observing strategies for future
missions. In general, the faint emission of the IGM and filamentary structure
remains beyond capabilities of instruments with only short duration exposure
potential (stratospheric balloons), even for optimistic assumptions for Lya,
while the yet fainter metal line transitions for these structures will remain
challenging for long duration exposures (space-based telescopes), mostly due to
low metallicity pushing them more than three orders of magnitudes in brightness
below Lya radiation. For the circum-galactic medium (CGM) the situation is more
promising, and it is foreseeable that in the near future we will not only just
dectect such sources, but the combination of all three lines in addition to
velocity information will yield valuable insight into the physical processes at
hand, illuminating important mechanisms during the formation of galaxies and
their backreaction onto the IGM from whence they formed. (abrigded) |
A class of transient acceleration models consistent with Big Bang
Cosmology: Is it possible that the current cosmic accelerating expansion will turn into
a decelerating one? Can this transition be realized by some viable theoretical
model that is consistent with the standard Big Bang cosmology? We study a class
of phenomenological models of a transient acceleration, based on a dynamical
dark energy with a very general form of equation of state
$p_{de}=\alpha\rho_{de}-\beta\rho_{de}^m$. It mimics the cosmological constant
$\rho_{de}\rightarrow$ const for small scale factor $a$, and behaves as a
barotropic gas with $\rho_{de}\rightarrow a^{-3(\alpha+1)}$ with $\alpha\ge 0$
for large $a$. The cosmic evolution of four models in the class has been
examined in details, and all yields a smooth transient acceleration. Depending
on the specific model, the future universe may be dominated either by the dark
energy or by the matter. In two models, the dynamical dark energy can be
explicitly realized by a scalar field with an analytical potential $V(\phi)$.
Moreover, the statistical analysis shows that the models can be as robust as
$\Lambda$CDM in confronting the observational data of SN Ia, CMB, and BAO. As
improvements over the previous studies, our models overcome the over-abundance
problem of dark energy during early eras, and satisfy the constraints on the
dark energy from WMAP observations of CMB. | $Om$ Diagnostic for Dilaton Dark Energy: $Om$ diagnostic can differentiate between different models of dark energy
without the accurate current value of matter density. We apply this geometric
diagnostic to dilaton dark energy(DDE) model and differentiate DDE model from
LCDM. We also investigate the influence of coupled parameter $\alpha$ on the
evolutive behavior of $Om$ with respect to redshift $z$. According to the
numerical result of $Om$, we get the current value of equation of state
$\omega_{\sigma0}$=-0.952 which fits the WMAP5+BAO+SN very well. |
Simulating high-redshift galaxies: Recent observations have gathered a considerable sample of high redshift
galaxy candidates and determined the evolution of their luminosity function
(LF). To interpret these findings, we use cosmological SPH simulations
including, in addition to standard physical processes, a detailed treatment of
the Pop III-Pop II transition in early objects. The simulated high-z galaxies
match remarkably well the amplitude and slope of the observed LF in the
redshift range 5<z<10. The LF shifts towards fainter luminosities with
increasing redshift, while its faint-end slope keeps an almost constant value,
\alpha ~-2. The stellar populations of high-z galaxies have ages of 100-300
(40-130) Myr at z=5 (z=7-8), implying an early (z>9.4) start of their star
formation activity; the specific star formation rate is almost independent of
galactic stellar mass. These objects are enriched rapidly with metals and
galaxies identified by HST/WFC3 (M_UV < -18) show metallicities ~0.1 Zsun even
at z=7-8. Most of the simulated galaxies at z~7 (noticeably the smallest ones)
are virtually dust-free, and none of them has an extinction larger than E(B-V)
= 0.01. The bulk (50%) of the ionizing photons is produced by objects
populating the faint-end of the LF (M_UV < -16), which JWST will resolve up to
z=7.3. PopIII stars continue to form essentially at all redshifts; however, at
z=6 (z=10) the contribution of Pop III stars to the total galactic luminosity
is always less than 5% for M_UV < -17 (M_UV < -16). The typical high-z galaxies
closely resemble the GRB host galaxy population observed at lower redshifts,
strongly encouraging the use of GRBs to detect the first galaxies. | On the importance of lensing for galaxy clustering in photometric and
spectroscopic surveys: We study the importance of gravitational lensing in the modelling of the
number counts of galaxies. We confirm previous results for photometric surveys,
showing that lensing cannot be neglected in a survey like LSST since it would
infer a significant shift of cosmological parameters. For a spectroscopic
survey like SKA2, we find that neglecting lensing in the monopole, quadrupole
and hexadecapole of the correlation function also induces an important shift of
parameters. For ${\Lambda}$CDM parameters, the shift is moderate, of the order
of 0.6${\sigma}$ or less. However, for a model-independent analysis, that
measures the growth rate of structure in each redshift bin, neglecting lensing
introduces a shift of up to 2.3${\sigma}$ at high redshift. Since the growth
rate is directly used to test the theory of gravity, such a strong shift would
wrongly be interpreted as the breakdown of General Relativity. This shows the
importance of including lensing in the analysis of future surveys. On the other
hand, for a survey like DESI, we find that lensing is not important, mainly due
to the value of the magnification bias parameter of DESI, $s(z)$, which
strongly reduces the lensing contribution at high redshift. We also propose a
way of improving the analysis of spectroscopic surveys, by including the
cross-correlations between different redshift bins (which is neglected in
spectroscopic surveys) from the spectroscopic survey or from a different
photometric sample. We show that including the cross-correlations in the SKA2
analysis does not improve the constraints. On the other hand replacing the
cross-correlations from SKA2 by cross-correlations measured with LSST improves
the constraints by 10 to 20 %. Interestingly, for ${\Lambda}$CDM parameters, we
find that LSST and SKA2 are highly complementary, since they are affected
differently by degeneracies between parameters. |
A statistical-mechanical explanation of dark matter halo properties: Cosmological N-body simulations have revealed many empirical relationships of
dark matter halos, yet the physical origin of these halo properties still
remains unclear. On the other hand, the attempts to establish the statistical
mechanics for self-gravitating systems have encountered many formal
difficulties, and little progress has been made for about fifty years. The aim
of this work is to strengthen the validity of the statistical-mechanical
approach we have proposed previously to explain the dark matter halo
properties. By introducing an effective pressure instead of the radial pressure
to construct the specific entropy, we use the entropy principle and proceed in
a similar way as previously to obtain an entropy stationary equation. An
equation of state for equilibrated dark halos is derived from this entropy
stationary equation, by which the dark halo density profiles with finite mass
can be obtained. We also derive the anisotropy parameter and pseudo-phase-space
density profile. All these predictions agree well with numerical simulations in
the outer regions of dark halos. Our work provides further support to the idea
that statistical mechanics for self-gravitating systems is a viable tool for
investigation. | Turbulent and fast motions of H2 gas in active galactic nuclei: Querying the Spitzer archive for optically-selected active galactic nuclei
(AGN) observed in high-resolution mode spectroscopy, we identified radio and/or
interacting galaxies with highly turbulent motions of the H2 gas at a
temperature of a few hundred Kelvin. Unlike all other AGN that have unresolved
H2 line profiles at a spectral resolution of ~600, 3C236, 3C293,
IRAS09039+0503, MCG-2-58-22, and Mrk463E have intrinsic velocity dispersions
exceeding 200 km/s for at least two of the rotational S0, S1, S2, and S3 lines.
In a sixth source, 4C12.50, a blue wing was detected in the S1 and S2 line
profiles, indicating the presence of a warm molecular gas component moving at
-640 km/s with respect to the bulk of the gas at systemic velocity. Its mass is
5.2*10^7 M_sun, accounting for more than one fourth of the H2 gas at 374K, but
less than 1% of the cold H2 gas computed from CO observations. Because no
diffuse gas component of 4C12.50 has been observed to date to be moving at more
than 250 km/s from systemic velocity, the H2 line wings are unlikely to be
tracing gas in shock regions along the tidal tails of this merging system. They
can instead be tracing gas driven by a jet or entrained by a nuclear outflow,
which is known to emerge from the west nucleus of 4C12.50. It is improbable
that such an outflow, with an estimated mass loss rate of 130 M_sun/yr,
entirely quenches the star formation around this nucleus. |
The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey:
measurement of the growth rate of structure from the small-scale clustering
of the luminous red galaxy sample: We measure the small-scale clustering of the Data Release 16 extended Baryon
Oscillation Spectroscopic Survey Luminous Red Galaxy sample, corrected for
fibre-collisions using Pairwise Inverse Probability weights, which give
unbiased clustering measurements on all scales. We fit to the monopole and
quadrupole moments and to the projected correlation function over the
separation range $7-60\,h^{-1}$Mpc with a model based on the Aemulus
cosmological emulator to measure the growth rate of cosmic structure,
parameterized by $f\sigma_8$. We obtain a measurement of
$f\sigma_8(z=0.737)=0.408\pm0.038$, which is $1.4\sigma$ lower than the value
expected from 2018 Planck data for a flat $\Lambda$CDM model, and is more
consistent with recent weak-lensing measurements. The level of precision
achieved is 1.7 times better than more standard measurements made using only
the large-scale modes of the same sample. We also fit to the data using the
full range of scales $0.1-60\,h^{-1}$Mpc modelled by the Aemulus cosmological
emulator and find a $4.5\sigma$ tension in the amplitude of the halo velocity
field with the Planck+$\Lambda$CDM model, driven by a mismatch on the
non-linear scales. This may not be cosmological in origin, and could be due to
a breakdown in the Halo Occupation Distribution model used in the emulator.
Finally, we perform a robust analysis of possible sources of systematics,
including the effects of redshift uncertainty and incompleteness due to target
selection that were not included in previous analyses fitting to clustering
measurements on small scales. | The cold gas content of post-starburst galaxies: Post-starburst galaxies, or E+A galaxies, are characterized by optical
spectra showing strong Balmer absorption lines, indicating a young stellar
population, and little or no emission lines, implying no active star formation.
These galaxies are interpreted as a transitional population between
star-forming, disk-dominated galaxies and spheroidal quiescent, non-star
forming galaxies. Here, we present single dish HI 21-cm emission line
measurements of a sample of eleven of these galaxies at redshifts z<0.05. We
detect H I emission in six of the E+A galaxies. In combination with earlier
studies, the total number of E+A galaxies with measured cold gas components is
now eleven. Roughly half of the E+As studied so far have detectable HI. The gas
fractions of these galaxies, measured with respect to their stellar mass, are
between 1 and 10 percent and are at the high end of the gas fractions measured
in gas-bearing early type galaxies and typically lower than seen in late-type
galaxies with comparable stellar masses. This finding is consistent with the
idea that E+As are currently evolving from the blue cloud to the red sequence.
However, the question of why the star formation has ceased in these galaxies
while a significant gas reservoir is still present can only be answered by
higher spatial resolution observations of the cold gas. |
A comprehensive study of Modulation effects on CMB Polarization: The Cosmic Microwave Background is characterized by temperature and linear
polarization fields. Dipole modulation in the temperature field has been
extensively studied in the context of hemispherical power asymmetry. In this
article, we show that a dipole modulation, and in general, any kind of
modulation isn't allowed in the $E$ and $B$ modes. This is the main result of
this paper. This result explains why no evidence of modulation in $E$ mode has
been found in the literature. On the contrary, the linear polarization fields
$Q$ and $U$ have no such restrictions. We show that modulation under certain
situations can be thought of as local $U(1)$ gauge transformations on the
surface of a sphere. As far as the modulation function is concerned, we show
that physical considerations enforce it to be (i) a spin $0$ field and (ii) a
scalar under parity. As masking is a specific type of modulation, our study
suggests that direct masking of $E$ mode isn't also possible. Masking in the
$E$ map can only be applied through $Q$ and $U$ fields. This means that in
principle, leaking of $E$ and $B$ mode powers into each other is unavoidable. | Evolution of dark matter microhalos through stellar encounters: In the cold dark matter scenario, the smallest dark matter halos may be earth
mass or smaller. These microhalos would be the densest dark matter objects in
the Universe, making their accurate characterization important for
astrophysical dark matter detection efforts. Moreover, their properties are
closely linked to the nature of dark matter and the physics of the early
universe, making them valuable cosmological probes. Dark matter microhalos
survive as subhalos within larger galactic halos, but due to their small size,
they are susceptible to encounters with individual stars. We use a large number
of $N$-body simulations to develop a framework that can predict the evolution
of a microhalo's density profile due to stellar encounters. We find that there
is a universal density profile for microhalos subjected to stellar encounters,
and each encounter alters a microhalo's scale parameters in a way that is
simply related to the energy the encounter injects. Our framework can rapidly
and accurately characterize the impact of stellar encounters on whole ensembles
of microhalos, making it a promising tool for understanding the populations of
microhalos within galactic halos. |
The H alpha Galaxy Survey VII. The spatial distribution of star
formation within disks and bulges: We analyse the current build-up of stellar mass within the disks and bulges
of nearby galaxies through a comparison of the spatial distributions of forming
and old stellar populations. H alpha and R-band imaging are used to determine
the distributions of young and old stellar populations in 313 S0a - Im field
galaxies out to 40 Mpc. Concentration indices and mean normalised light
profiles are calculated as a function of galaxy type and bar classification.
The mean profiles and concentration indices show a strong and smooth dependence
on galaxy type. Apart from a central deficit due to bulge/bar light in some
galaxy types, mean H alpha and R-band profiles are very similar. Mean profiles
within a given type are remarkably constant even given wide ranges in galaxy
luminosity and size. SBc, SBbc and particularly SBb galaxies have profiles that
are markedly different from those of unbarred galaxies. H alpha emission from
SBb galaxies is studied in detail; virtually all show resolved central
components and concentrations of star formation at or just outside the bar-end
radius. In these galaxies, star formation has the same radial distribution as
R-band light, i.e. stellar mass is building at approximately constant
morphology, with no strong evidence for outer truncation or inside-out disk
formation. (Abridged.) | Spin-2 dark matter from inflation: The seed of dark matter can be generated from light spectator fields during
inflation through a similar mechanism that the seed of observed large scale
structures are produced from the inflaton field. The accumulated energy density
of the corresponding excited modes, which is subdominant during inflation,
dominates energy density of the universe later around the time of matter and
radiation equality and plays the role of dark matter. For spin-2 spectator
fields, Higuchi bound may seem to prevent excitation of such light modes since
deviation of the inflationary background from the exact de Sitter spacetime is
very small. However, sizable interactions with the inflaton field breaks (part
of) isometries of the de Sitter space in the inflationary background and
relaxes the Higuchi bound. Looking for this possibility in the context of
effective field theory of inflation, we suggest a dark matter model consisting
of spin-2 particles that produce during inflation. |
On the dust abundance gradients in late-type galaxies: I. Effects of
destruction and growth of dust in the interstellar medium: We present basic theoretical constraints on the effects of destruction by
supernovae (SNe) and growth of dust grains in the interstellar medium (ISM) on
the radial distribution of dust in late-type galaxies. The radial gradient of
the dust-to-metals ratio is shown to be essentially flat (zero) if interstellar
dust is not destroyed by SN shock waves and all dust is produced in stars. If
there is net dust destruction by SN shock waves, the dust-to-metals gradient is
flatter than or equal to the metallicity gradient (assuming the gradients have
the same sign). Similarly, if there is net dust growth in the ISM, then the
dust-to-metals gradient is steeper than or equal to the metallicity gradient.
The latter result implies that if dust gradients are steeper than metallicity
gradients, i.e., the dust-to-metals gradients are not flat, then it is unlikely
dust destruction by SN shock waves is an efficient process, while dust growth
must be a significant mechanism for dust production. Moreover, we conclude that
dust-to-metals gradients can be used as a diagnostic for interstellar dust
growth in galaxy discs, where a negative slope indicates dust growth. | Linear Systematics Mitigation in Galaxy Clustering in the Dark Energy
Survey Year 1 Data: We implement a linear model for mitigating the effect of observing conditions
and other sources of contamination in galaxy clustering analyses. Our treatment
improves upon the fiducial systematics treatment of the Dark Energy Survey
(DES) Year 1 (Y1) cosmology analysis in four crucial ways. Specifically, our
treatment: 1) does not require decisions as to which observable systematics are
significant and which are not, allowing for the possibility of multiple maps
adding coherently to give rise to significant bias even if no single map leads
to a significant bias by itself; 2) characterizes both the statistical and
systematic uncertainty in our mitigation procedure, allowing us to propagate
said uncertainties into the reported cosmological constraints; 3) explicitly
exploits the full spatial structure of the galaxy density field to
differentiate between cosmology-sourced and systematics-sourced fluctuations
within the galaxy density field; 4) is fully automated, and can therefore be
trivially applied to any data set. The updated correlation function for the DES
Y1 redMaGiC catalog minimally impacts the cosmological posteriors from that
analysis. Encouragingly, our analysis does improve the goodness of fit
statistic of the DES Y1 3$\times$2pt data set ($\Delta \chi^2 = -6.5$ with no
additional parameters). This improvement is due in nearly equal parts to both
the change in the correlation function and the added statistical and systematic
uncertainties associated with our method. We expect the difference in
mitigation techniques to become more important in future work as the size of
cosmological data sets grows. |
Swiss Cheese and a Cheesy CMB: It has been argued that the Swiss-Cheese cosmology can mimic Dark Energy,
when it comes to the observed luminosity distance-redshift relation. Besides
the fact that this effect tends to disappear on average over random directions,
we show in this work that based on the Rees-Sciama effect on the cosmic
microwave background (CMB), the Swiss-Cheese model can be ruled out if all
holes have a radius larger than about 35 Mpc. We also show that for smaller
holes, the CMB is not observably affected, and that the small holes can still
mimic Dark Energy, albeit in special directions, as opposed to previous
conclusions in the literature. However, in this limit, the probability of
looking in a special direction where the luminosity of supernovae is
sufficiently supressed becomes very small, at least in the case of a lattice of
spherical holes considered in this paper. | The imprint of $f(R)$ gravity on weak gravitational lensing I:
Connection between observables and large scale structure: We study the effect of $f(R)$ gravity on the statistical properties of
various large-scale structures which can be probed in weak gravitational
lensing measurements. A set of ray-tracing simulations of gravitational lensing
in $f(R)$ gravity enables us to explore cosmological information on (i)
stacking analyses of weak lensing observables and (ii) peak statistics in
reconstructed lensing mass maps. For the $f(R)$ model proposed by Hu \&
Sawicki, the measured lensing signals of dark matter haloes in the stacking
analysis would show a $\simlt10\%$ difference between the standard $\Lambda$CDM
and the $f(R)$ model when the additional degree of freedom in $f(R)$ model
would be $|f_{\rm R0}|\sim10^{-5}$. Among various large-scale structures to be
studied in stacking analysis, troughs, i.e, underdensity regions in projected
plane of foreground massive haloes, could be promising to constrain the model
with $|f_{\rm R0}|\sim10^{-5}$, while stacking analysis around voids is found
to be difficult to improve the constraint of $|f_{\rm R0}|$ even in future
lensing surveys with a sky coverage of $\sim1000$ square degrees. On the peak
statistics, we confirm the correspondence between local maxima and dark matter
haloes along the line of sight, regardless of the modification of gravity in
our simulation. Thus, the number count of high significance local maxima would
be useful to probe the mass function of dark matter haloes even in the $f(R)$
model with $|f_{\rm R0}|\simlt10^{-5}$. We also find that including local
minima in lensing mass maps would be helpful to improve the constant on $f(R)$
gravity down to $|f_{\rm R0}|=10^{-5}$ in ongoing weak lensing surveys. |
The Dipole Repeller: In the standard (LCDM) model of cosmology the universe has emerged out of an
early homogeneous and isotropic phase. Structure formation is associated with
the growth of density irregularities and peculiar velocities. Our Local Group
is moving with respect to the cosmic microwave background (CMB) with a velocity
631+/-20 km s-1 and participates in a bulk flow that extends out to distances
of at least 20,000 km s-1. Since the discovery of the CMB dipole, the implicit
assumption was that excesses in the abundance of galaxies induce the Local
Group motion. Yet, underdense regions push as much as overdensities attract but
they are deficient of light and consequently difficult to chart. It was
suggested a decade ago that an underdensity in the northern hemisphere roughly
15,000 km s-1 away is a significant actor in the local flow. Here we report on
kinematic evidence for such an underdensity. We map the large scale 3D velocity
field using a Wiener filter reconstruction from the Cosmicflows-2 dataset of
peculiar velocities, and identify the attractors and repellers that dominate
the local dynamics. We show here that the local flow is dominated by a single
attractor -associated with the Shapley Concentration- and a single previously
unidentified repeller. Multipole expansion of the local flow provides further
support for the existence and role played by the attractor and repeller. The
bulk flow (i.e. dipole moment) is closely (anti)aligned with the repeller at a
distance of 16,000+/-4,500 km s-1. The expansion eigenvector of the shear
tensor (quadrupole moment) is closely aligned with the Shapley Attractor out to
7,000 km s-1. The close alignment of the local bulk flow with the repeller
provides further support for its dominant role in shaping the local flow. This
Dipole Repeller is predicted to be associated with a void in the distribution
of galaxies. | Peculiar velocity measurement in a clumpy universe: In this work we address the issue of peculiar velocity measurement in a
perturbed Friedmann universe using the deviations from measured luminosity
distances of standard candles from background FRW universe. We want to show and
quantify the statement that in intermediate redshifts ($0.5< z < 2$),
deviations from the background FRW model are not uniquely governed by peculiar
velocities. Luminosity distances are modified by gravitational lensing. We also
want to indicate the importance of relativistic calculations for peculiar
velocity measurement at all redshifts.
For this task we discuss the relativistic correction on luminosity distance
and redshift measurement and show the contribution of each of the corrections
as lensing term, peculiar velocity of the source and Sachs-Wolfe effect. Then
we use the SNe Ia sample of Union 2, to investigate the relativistic effects we
consider.
We show that, using the conventional peculiar velocity method, that ignores
the lensing effect, will result in an overestimate of the measured peculiar
velocities at intermediate redshifts. Here we quantify this effect. We show
that at low redshifts the lensing effect is negligible compare to the effect of
peculiar velocity. From the observational point of view, we show that the
uncertainties on luminosity of the present SNe Ia data prevent us from precise
measuring the peculiar velocities even at low redshifts ($z<0.2$). |
The first spectral line surveys searching for signals from the Dark Ages: Our aim is to observationally investigate the cosmic Dark Ages in order to
constrain star and structure formation models, as well as the chemical
evolution in the early Universe. Spectral lines from atoms and molecules in
primordial perturbations at high redshifts can give information about the
conditions in the early universe before and during the formation of the first
stars in addition to the epoch of reionisation. The lines may arise from moving
primordial perturbations before the formation of the first stars (resonant
scattering lines), or could be thermal absorption or emission lines at lower
redshifts. The difficulties in these searches are that the source redshift and
evolutionary state, as well as molecular species and transition are unknown,
which implies that an observed line can fall within a wide range of
frequencies. The lines are also expected to be very weak. Observations from
space have the advantages of stability and the lack of atmospheric features
which is important in such observations. We have therefore, as a first step in
our searches, used the Odin satellite to perform two sets of spectral line
surveys towards several positions. The first survey covered the band 547-578
GHz towards two positions, and the second one covered the bands 542.0-547.5 GHz
and 486.5-492.0 GHz towards six positions selected to test different sizes of
the primordial clouds. Two deep searches centred at 543.250 and 543.100 GHz
with 1 GHz bandwidth were also performed towards one position. The two lowest
rotational transitions of H2 will be redshifted to these frequencies from
z~20-30, which is the predicted epoch of the first star formation. No lines are
detected at an rms level of 14-90 and 5-35 mK for the two surveys,
respectively, and 2-7 mK in the deep searches with a channel spacing of 1-16
MHz. The broad bandwidth covered allows a wide range of redshifts to be
explored for a number of atomic and molecular species and transitions. From the
theoretical side, our sensitivity analysis show that the largest possible
amplitudes of the resonant lines are about 1 mK at frequencies <200 GHz, and a
few micro K around 500-600 GHz, assuming optically thick lines and no
beam-dilution. However, if existing, thermal absorption lines have the
potential to be orders of magnitude stronger than the resonant lines. We make a
simple estimation of the sizes and masses of the primordial perturbations at
their turn-around epochs, which previously has been identified as the most
favourable epoch for a detection. This work may be considered as an important
pilot study for our forthcoming observations with the Herschel Space
Observatory. | Primordial Black Holes Confront LIGO/Virgo data: Current situation: The LIGO and Virgo Interferometers have so far provided 11 gravitational-wave
(GW) observations of black-hole binaries. Similar detections are bound to
become very frequent in the near future. With the current and upcoming wealth
of data, it is possible to confront specific formation models with
observations. We investigate here whether current data are compatible with the
hypothesis that LIGO/Virgo black holes are of primordial origin. We compute in
detail the mass and spin distributions of primordial black holes (PBHs), their
merger rates, the stochastic background of unresolved coalescences, and
confront them with current data from the first two observational runs, also
including the recently discovered GW190412. We compute the best-fit values for
the parameters of the PBH mass distribution at formation that are compatible
with current GW data. In all cases, the maximum fraction of PBHs in dark matter
is constrained by these observations to be $f_{\text{PBH}}\approx {\rm
few}\times 10^{-3}$. We discuss the predictions of the PBH scenario that can be
directly tested as new data become available. In the most likely formation
scenarios where PBHs are born with negligible spin, the fact that at least one
of the components of GW190412 is moderately spinning is incompatible with a
primordial origin for this event, unless accretion or hierarchical mergers are
significant. In the absence of accretion, current non-GW constraints already
exclude that LIGO/Virgo events are all of primordial origin, whereas in the
presence of accretion the GW bounds on the PBH abundance are the most stringent
ones in the relevant mass range. A strong phase of accretion during the cosmic
history would favour mass ratios close to unity, and a redshift-dependent
correlation between high masses, high spins and nearly-equal mass binaries,
with the secondary component spinning faster than the primary. |
Calibrating CIV-based black hole mass estimators: We present the single-epoch black hole mass estimators based on the CIV (1549
A) broad emission line, using the updated sample of the reverberation-mapped
AGNs and high-quality UV spectra. By performing multi-component spectral
fitting analysis, we measure the CIV line widths (FWHM_CIV) and line dispersion
(sigma_CIV) and the continuum luminosity at 1350 A (L_1350) to calibrate the
CIV-based mass estimators. By comparing with the Hbeta reverberation-based
masses, we provide new mass estimators with the best-fit relationships, i.e.,
M_BH \propto L_1350 ^ (0.50+-0.07) sigma_CIV ^2 and M_BH \propto L_1350 ^
(0.52+-0.09) FWHM_CIV ^ (0.56+-0.48). The new CIV-based mass estimators show
significant mass-dependent systematic difference compared to the estimators
commonly used in the literature. Using the published Sloan Digital Sky Survey
QSO catalog, we show that the black hole mass of high-redshift QSOs decreases
on average by ~0.25 dex if our recipe is adopted. | Probing the isotropy of cosmic acceleration using different supernova
samples: Recent studies have indicated that an anisotropic cosmic expansion may exist.
In this paper, we use three datasets of type Ia supernovae (SNe Ia) to probe
the isotropy of cosmic acceleration. For the Union2.1 dataset, the direction
and magnitude of the dipole are $(l=309.3^{\circ} {}^{+
15.5^{\circ}}_{-15.7^{\circ}} ,\ b = -8.9^{\circ} {}^{ +
11.2^{\circ}}_{-9.8^{\circ}} ),\ A=(1.46 \pm 0.56) \times 10^{-3}$. For the
Constitution dataset, the results are $(l=67.0^{\circ}{}^{+
66.5^{\circ}}_{-66.2^{\circ}},\ b=-0.6^{\circ}{}^{+
25.2^{\circ}}_{-26.3^{\circ}}),\ A=(4.4 \pm 5.0) \times 10^{-4}$. For the JLA
dataset, no significant dipolar deviation is found. We also explore the effects
of anisotropic distributions of coordinates and redshifts on the results using
Monte-Carlo simulations. We find that the anisotropic distribution of
coordinates can cause dipole directions and make dipole magnitude larger.
Anisotropic distribution of redshifts is found to have no significant effect on
dipole fitting results. |
Particle re-acceleration and Faraday-complex structures in the RXC
J1314.4-2515 galaxy cluster: Radio relics are sites of electron (re)acceleration in merging galaxy
clusters but the mechanism of acceleration and the topology of the magnetic
field in and near relics are yet to be understood. We are carrying out an
observational campaign on double relic galaxy clusters starting with RXC
J1314.4-2515. With $Jansky Very Large Array$ multi-configuration observations
in the frequency range 1-4 GHz, we perform both spectral and polarization
analyses, using the Rotation Measure synthesis technique. We use archival
$XMM-Newton$ observations to constrain the properties of the shocked region. We
discover a possible connection between the activity of a radio galaxy and the
emission of the eastern radio relic. In the northern elongated arc of the
western radio relic, we detect polarized emission with an average polarization
fraction of $31 \ \%$ at 3 GHz and we derive the Mach number of the underlying
X-ray shock. Our observations reveal low levels of fractional polarization and
Faraday-complex structures in the southern region of the relic, which point to
the presence of thermal gas and filamentary magnetic field morphology inside
the radio emitting volume. We measured largely different Rotation Measure
dispersion from the two relics. Finally, we use cosmological
magneto-hydrodynamical simulations to constrain the magnetic field, viewing
angle, and to derive the acceleration efficiency of the shock. We find that the
polarization properties of RXC J1314.4-2515 are consistent with a radio relic
observed at $70^{\circ}$ with respect to the line of sight and that efficient
re-acceleration of fossil electrons has taken place. | 21cmVAE: A Very Accurate Emulator of the 21-cm Global Signal: Considerable observational efforts are being dedicated to measuring the
sky-averaged (global) 21-cm signal of neutral hydrogen from Cosmic Dawn and the
Epoch of Reionization. Deriving observational constraints on the astrophysics
of this era requires modeling tools that can quickly and accurately generate
theoretical signals across the wide astrophysical parameter space. For this
purpose artificial neural networks were used to create the only two existing
global signal emulators, 21cmGEM and globalemu. In this paper we introduce
21cmVAE, a neural network-based global signal emulator, trained on the same
dataset of ~30,000 global signals as the other two emulators, but with a more
direct prediction algorithm that prioritizes accuracy and simplicity. Using
neural networks, we compute derivatives of the signals with respect to the
astrophysical parameters and establish the most important astrophysical
processes that drive the global 21-cm signal at different epochs. 21cmVAE has a
relative rms error of only 0.34 - equivalently 0.54 mK - on average, which is a
significant improvement compared to the existing emulators, and a run time of
0.04 seconds per parameter set. The emulator, the code, and the processed
datasets are publicly available at https://github.com/christianhbye/21cmVAE and
through https://zenodo.org/record/5904939. |
Refining the M_BH-V_c scaling relation with HI rotation curves of water
megamaser galaxies: Black hole - galaxy scaling relations provide information about the
coevolution of supermassive black holes and their host galaxies. We compare the
black hole mass - circular velocity (MBH - Vc) relation with the black hole
mass - bulge stellar velocity dispersion (MBH - sigma) relation, to see whether
the scaling relations can passively emerge from a large number of mergers, or
require a physical mechanism, such as feedback from an active nucleus. We
present VLA H I observations of five galaxies, including three water megamaser
galaxies, to measure the circular velocity. Using twenty-two galaxies with
dynamical MBH measurements and Vc measurements extending to large radius, our
best-fit MBH - Vc relation, log MBH = alpha + beta log(Vc /200 km s^-1), yields
alpha = 7.43+/-0.13, beta = 3.68+1.23/-1.20, and intrinsic scatter epsilon_int
= 0.51+0.11/-0.09. The intrinsic scatter may well be higher than 0.51, as we
take great care to ascribe conservatively large observational errors. We find
comparable scatter in the MBH - sigma relations, epsilon_int = 0.48+0.10/-0.08,
while pure merging scenarios would likely result in a tighter scaling with the
dark halo (as traced by Vc) than baryonic (sigma) properties. Instead, feedback
from the active nucleus may act on bulge scales to tighten the MBH - sigma
relation with respect to the MBH - Vc relation, as observed. | Can we distinguish early dark energy from a cosmological constant?: Early dark energy (EDE) models are a class of quintessence dark energy with a
dynamically evolving scalar field which display a small but non-negligible
amount of dark energy at the epoch of matter-radiation equality. Compared with
a cosmological constant, the presence of dark energy at early times changes the
cosmic expansion history and consequently the shape of the linear theory power
spectrum and potentially other observables. We constrain the cosmological
parameters in the EDE cosmology using recent measurements of the cosmic
microwave background and baryon acoustic oscillations. The best-fitting models
favour no EDE; here we consider extreme examples which are in mild tension with
current observations in order to explore the observational consequences of a
maximally allowed amount of EDE. We study the non-linear evolution of cosmic
structure in EDE cosmologies using large volume N-body simulations. Many
large-scale structure statistics are found to be very similar between the
$\Lambda$ cold dark matter ($\Lambda$CDM) and EDE models. We find that the most
promising way to distinguish EDE from $\Lambda$CDM is to measure the power
spectrum on large scales, where differences of up to 15% are expected. |
Constraints on gravity and dark energy from the pairwise kinematic
Sunyaev-Zeldovich effect: We calculate the constraints on dark energy and cosmic modifications to
gravity achievable with upcoming cosmic microwave background (CMB) surveys
sensitive to the Sunyaev-Zeldovich (SZ) effects. The analysis focuses on using
the mean pairwise velocity of clusters as observed through the kinematic SZ
effect (kSZ), an approach based on the same methods used for the first
detection of the kSZ effect, and includes a detailed derivation and discussion
of this statistic's covariance under a variety of different survey assumptions.
The potential of current, Stage II, and upcoming, Stage III and Stage IV, CMB
observations are considered, in combination with contemporaneous spectroscopic
and photometric galaxy observations. A detailed assessment is made of the
sensitivity to the assumed statistical and systematic uncertainties in the
optical depth determination, the magnitude and uncertainty in the minimum
detectable mass, and the importance of pairwise velocity correlations at small
separations, where non-linear effects can start to arise.
In combination with Stage III constraints on the expansion history, such as
those projected by the Dark Energy Task Force, we forecast 5\% and 2\% for
fractional errors on the growth factor, $\gamma$, for Stage III and Stage IV
surveys respectively, and 2\% constraints on the growth rate, $f_g$, for a
Stage IV survey for $0.2<z<0.6$. The results suggest that kSZ measurements of
cluster peculiar velocities, obtained from cross-correlation with upcoming
spectroscopic galaxy surveys, could provide robust tests of dark energy and
theories of gravity on cosmic scales. | Dynamical Modeling of Galaxy Mergers using Identikit: We present dynamical models of four interacting systems: NGC 5257/8, The
Mice, the Antennae, and NGC 2623. The parameter space of the encounters are
constrained using the Identikit model-matching and visualization tool.
Identikit utilizes hybrid N-body and test particle simulations to enable rapid
exploration of the parameter space of galaxy mergers. The Identikit-derived
matches of these systems are reproduced with self-consistent collisionless
simulations which show very similar results. The models generally reproduce the
observed morphology and \HI\ kinematics of the tidal tails in these systems
with reasonable properties inferred for the progenitor galaxies. The models
presented here are the first to appear in the literature for NGC 5257/8 and NGC
2623, and The Mice and the Antennae are compared with previously published
models. Based on the assumed mass model and our derived initial conditions, the
models indicate the four systems are currently being viewed 175-260 Myr after
first passage and cover a wide range of merger stages. In some instances there
are mismatches between the models and the data (e.g., in the length of a tail);
these are likely due to our adoption of a single mass model for all galaxies.
Despite the use of a single mass model, these results demonstrate the utility
of Identikit in constraining the parameter space for galaxy mergers when
applied to real data. |
Spectroscopically Confirmed Lyman-Alpha Emitters from Redshift 5 to 7
Behind Ten Galaxy Cluster Lenses: We present 36 spectroscopically confirmed intrinsically UV-faint Ly$\alpha$
emitting galaxies from follow-up observations with Keck/DEIMOS of
gravitationally lensed high-redshift candidates. Candidates were selected to be
between $5\lesssim z \lesssim 7$ from photometric data using \textit{HST} and
\textit{Spitzer} imaging surveys. We used photometric redshift information to
perform an integrated photometric redshift probability cut $>1\%$ between
$5<z<7$ to construct a sample of 198 high-redshift objects. Our high-redshift
sample spans intrinsic UV luminosities from a few $L^*$ down to $0.001L^*$. We
identified 19 high-confidence detections of Ly$\alpha$ and an additional 17
likely detections. We divided our sample into lower-redshift ($z\sim5.5$) and
higher-redshift ($z\sim6.5$) bins and ran Monte Carlo trials, incorporating the
strength of the Ly$\alpha$ emission and the photometric redshift of the
non-detections. Considering only objects where Ly$\alpha$ could be detected at
EW(Ly$\alpha$)$>$25{\AA} at $3\sigma$ at the fiducial depth of our survey, and
only those galaxies with EW(Ly$\alpha$)$>$25{\AA} as true LAEs, and finally,
only objects with $m_{AB}<26.8$, we found the LAE fraction to be flat, or
modestly increase from 0.26$\pm0.04$ to 0.30$\pm0.04$. These values relative to
those for lower-redshift samples are consistent with a rising LAE fraction with
redshift out to $z\sim6$, but at $z\sim6.5$ there is some tension between our
results and results from surveys at intrinsically brighter luminosities. We
conclude intrinsically fainter galaxies have Ly$\alpha$ emission, and there is
a steep drop in the LAE fraction from our high-redshift sample at $z\sim6.5$
and from similar galaxies at $z\sim7.5$. This likely indicates we are
witnessing the tail end of the epoch of reionization, as such a drop is not
expected due to changes of intrinsic galaxy properties between these redshifts. | Bridging the gap between low and high mass dwarf galaxies: While the dark matter content within the most massive giant and smallest
dwarf galaxies has been probed -- spanning a range of over one million in mass
-- an important observational gap remains for galaxies of intermediate mass.
This gap covers K band magnitudes of approximately -16 > M_K > -18 (for which
dwarf galaxies have B--K ~ 2). On the high mass side of the gap are dwarf
elliptical (dE) galaxies, that are dominated by stars in their inner regions.
While the low mass side includes dwarf spheroidal (dSph) galaxies that are dark
matter-dominated and ultra compact dwarf (UCD) objects that are star-dominated.
Evolutionary pathways across the gap have been suggested but remain largely
untested because the `gap' galaxies are faint, making dynamical measurements
very challenging. With long exposures on the Keck telescope using the ESI
instrument we have succeeded in bridging this gap by measuring the dynamical
mass for five dwarf galaxies with M_K ~ -17.5 (M_B ~ --15.5). With the
exception of our brightest dwarf galaxy, they possess relatively flat velocity
dispersion profiles of around 20 km/s. By examining their 2D scaling relations
and 3D fundamental manifold, we found that the sizes and velocity dispersions
of these gap galaxies reveal continuous trends from dE to dSph galaxies. We
conclude that low-luminosity dwarf elliptical galaxies are dominated by stars,
not by dark matter, within their half light radii. This finding can be
understood if internal feedback processes are operating most efficiently in gap
galaxies, gravitationally heating the centrally-located dark matter to larger
radii. Whereas external environmental processes, which can strip away stars,
have a greater influence on dSph galaxies resulting in their higher dark matter
fractions. Abridged. |
Distinguishing f(R) gravity with cosmic voids: We use properties of void populations identified in N-body simulations to
forecast the ability of upcoming galaxy surveys to differentiate models of f(R)
gravity from \Lambda CDM cosmology. We analyze simulations designed to mimic
the densities, volumes, and clustering statistics of upcoming surveys, using
the public VIDE toolkit. We examine void abundances as a basic probe at
redshifts 1.0 and 0.4. We find that stronger f(R) coupling strengths produce
voids up to ~20% larger in radius, leading to a significant shift in the void
number function. As an initial estimate of the constraining power of voids, we
use this change in the number function to forecast a constraint on the coupling
strength of $\Delta f_{R_{0}} = 10^{-5}$. | Cosmological Structure Formation with Augmented Lagrangian Perturbation
Theory: We present a new fast and efficient approach to model structure formation
with Augmented Lagrangian Perturbation Theory (ALPT). Our method is based on
splitting the displacement field into a long and a short-range component. The
long-range component is computed by second order LPT (2LPT). This approximation
contains a tidal nonlocal and nonlinear term. Unfortunately, 2LPT fails on
small scales due to severe shell crossing and a crude quadratic behaviour in
the low density regime. The spherical collapse (SC) approximation has been
recently reported to correct for both effects by adding an ideal collapse
truncation. However, this approach fails to reproduce the structures on large
scales where it is significantly less correlated with the N-body result than
2LPT or linear LPT (the Zeldovich approximation). We propose to combine both
approximations using for the short-range displacement field the SC solution. A
Gaussian filter with a smoothing radius r_S is used to separate between both
regimes. We use the result of 25 dark matter only N-body simulations to
benchmark at z=0 the different approximations: 1st, 2nd, 3rd order LPT, SC and
our novel combined ALPT model. This comparison demonstrates that our method
improves previous approximations at all scales showing ~25% and ~75% higher
correlation than 2LPT with the N-body solution at k = 1 and 2 h Mpc^-1,
respectively. We conduct a parameter study to determine the optimal range of
smoothing radii and find that the maximum correlation is achieved with r_S = 4
- 5 h^-1 Mpc. This structure formation approach could be used for various
purposes, such as setting-up initial conditions for N-body simulations,
generating mock galaxy catalogues, cosmic web analysis or for reconstructions
of the primordial density fluctuations. |
A metallicity study of 1987A-like supernova host galaxies: The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A
has long been debated, along with the role that its sub-solar metallicity
played. We now have a sample of 1987A-like SNe that arise from the core
collapse (CC) of BSGs. The metallicity of the explosion sites of the known BSG
SNe is investigated, as well as their association to star-forming regions. Both
indirect and direct metallicity measurements of 13 BSG SN host galaxies are
presented, and compared to those of other CC SN types. Indirect measurements
are based on the known luminosity-metallicity relation and on published
metallicity gradients of spiral galaxies. To provide direct estimates based on
strong line diagnostics, we obtained spectra of each BSG SN host both at the SN
explosion site and at the positions of other HII regions. Continuum-subtracted
Ha images allowed us to quantify the association between BSG SNe and
star-forming regions. BSG SNe explode either in low-luminosity galaxies or at
large distances from the nuclei of luminous hosts. Therefore, their indirectly
measured metallicities are typically lower than those of SNe IIP and Ibc. This
is confirmed by the direct estimates, which show slightly sub-solar values
(12+log(O/H)=8.3-8.4 dex), similar to that of the Large Magellanic Cloud (LMC),
where SN 1987A exploded. However, two SNe (1998A and 2004em) were found at near
solar metallicity. SNe IIb have a metallicity distribution similar to that of
BSG SNe. Finally, the association to star-forming regions is similar among BSG
SNe, SNe IIP and IIn. Our results suggest that LMC metal abundances play a role
in the formation of some 1987A-like SNe. This would naturally fit in a single
star scenario for the progenitors. However, the existence of two events at
nearly solar metallicity suggests that also other channels, e.g. binarity,
contribute to produce BSG SNe. | An Evolutionary Paradigm for Dusty Active Galaxies at Low Redshift: We apply methods from Bayesian inferencing and graph theory to a dataset of
102 mid-infrared spectra, and archival data from the optical to the millimeter,
to construct an evolutionary paradigm for z<0.4 infrared-luminous galaxies
(ULIRGs). We propose that the ULIRG lifecycle consists of three phases. The
first phase lasts from the initial encounter until approximately coalescence.
It is characterized by homogeneous mid-IR spectral shapes, and IR emission
mainly from star formation, with a contribution from an AGN in some cases. At
the end of this phase, a ULIRG enters one of two evolutionary paths depending
on the dynamics of the merger, the available quantities of gas, and the masses
of the black holes in the progenitors. On one branch, the contributions from
the starburst and the AGN to the total IR luminosity decline and increase
respectively. The IR spectral shapes are heterogeneous, likely due to feedback
from AGN-driven winds. Some objects go through a brief QSO phase at the end. On
the other branch, the decline of the starburst relative to the AGN is less
pronounced, and few or no objects go through a QSO phase. We show that the 11.2
micron PAH feature is a remarkably good diagnostic of evolutionary phase, and
identify six ULIRGs that may be archetypes of key stages in this lifecycle. |
Searching for Axion Dark Matter using Radio Telescopes: We investigate the use of next generation radio telescopes such as the Square
Kilometre Array (SKA) to detect axion two-photon coupling in the astrophysical
environment. The uncertainty surrounding astrophysical magnetic fields presents
new challenges, but with a frequency range corresponding to axions of mass
$1.7-57\mu$eV and a spectral profile with a number of distinguishing features,
SKA-mid offers a tantalising opportunity to constrain axion dark matter
properties. To determine the sensitivity of SKA-mid to an axion signal, we
consider observations of the Galactic centre and interstellar medium, and find
that this new telescope could allow us to probe axion couplings
$\gtrsim10^{-16}$GeV$^{-1}$. | Dark sector interactions and the curvature of the Universe in light of
Planck's 2018 data: We investigate the observational viability of a class of interacting dark
energy (iDE) models in the light of the latest Cosmic Microwave Background
(CMB), type Ia supernovae (SNe) and SH0ES Hubble parameter measurements. Our
analysis explores the assumption of a non-zero spatial curvature, the
correlation between the interaction parameter $\alpha$ and the current
expansion rate $H_0$, and updates the results reported in \cite{micol}.
Initially, assuming a spatially flat universe, the results show that the
best-fit of our joint analysis clearly favours a positive interaction, i.e., an
energy flux from dark matter to dark energy, with $\alpha \approx 0.2$, while
the non-interacting case, $\alpha = 0$, is ruled out by more than $3\sigma$
confidence level. On the other hand, considering a non-zero spatial curvature,
we find a slight preference for a negative value of the curvature parameter,
which seems to relax the correlation between the parameters $\alpha$ and $H_0$,
as well as between $H_0$ and the normalization of the matter power spectrum on
scales of 8$h^{-1}$ Mpc ($\sigma_8$). Finally, we discuss the influence of
considering the SH$0$ES prior on $H_0$ in the joint analyses, and find that
such a choice does not change considerably the standard cosmology predictions
but has a significant influence on the results of the iDE model. |
Confronting missing observations with probability weights: Fourier space
and generalised formalism: Due to instrumental limitations, the nature of which vary from case to case,
spectroscopic galaxy redshift surveys usually do not collect redshifts for all
galaxies in the population of potential targets. Especially problematic is the
entanglement between this incompleteness and the true cosmological signal,
arising from the fact that the proportion of successful observations is
typically lower in regions with higher density of galaxies. The result is a
fictitious suppression of the galaxy clustering that, if not properly
corrected, can impact severely on cosmological-parameter inference. Recent
developments in the field have shown that an unbiased estimate of the 2-point
correlation function in the presence of missing observations can be obtained by
weighting each pair by its inverse probability of being targeted. In this work
we expand on the concept of probability weights by developing a more mature
statistical formalism, which provides us with a deeper understanding of their
fundamental properties. We take advantage of this novel perspective to handle
the problem of estimating the inverse probability, specifically, we discuss how
to efficiently determine the weights from a finite set of realisations of the
targeting and how to model exactly the resulting sampling effects. This allows
us to derive an inverse-probability-based estimator for the power spectrum,
which is the main result of this work, but also to improve robustness and
computational efficiency of the already existing configuration-space estimator.
Finally, we propose a strategy to further extend the concept of inverse
probability, providing examples of how traditional missing-observation
countermeasures can be included in this more general picture. The effectiveness
of the different models and weighting schemes discussed in this work is
demonstrated using realisations of an idealised simple survey strategy. | The nature of proximate damped Lyman alpha systems: We present high resolution echelle spectra of 7 proximate damped Lyman alpha
(PDLA) systems whose relative velocity separation from the background quasar is
Delta V < 3000 km/s. Combining our sample with a further 9 PDLAs from the
literature we compare the chemical properties of the proximate systems with a
control sample of intervening DLAs. Taken at face value, the sample of 16 PDLAs
exhibits a wide range of metallicities, ranging from Z ~ 1/3 Z_sun down to Z ~
1/1000 Z_sun, including the DLA with the lowest N(SiII)/N(HI) yet reported in
the literature. We find several pieces of evidence that indicate enhanced
ionization and the presence of a hard ionizing spectrum in PDLAs which lead to
properties that contrast with the intervening DLAs, particularly when the N(HI)
is low. The abundances of Zn, Si and S in PDLAs with log N(HI) > 21, where
ionization corrections are minimized, are systematically higher than the
intervening population by a factor of around 3. We also find possible evidence
for a higher fraction of NV absorbers amongst the PDLAs, although the
statistics are still modest. 6/7 of our echelle sample show high ionization
species (SiIV, CIV, OVI or NV) offset by >100 km/s from the main low ion
absorption. We analyse fine-structure transitions of CII* and SiII* to
constrain the PDLA distance from the QSO. Lower limits range from tens of kpc
up to >160 kpc for the most stringent limit. We conclude that (at least some)
PDLAs do exhibit different characteristics relative to the intervening
population out to 3000 km/s (and possibly beyond). Nonetheless, the PDLAs
appear distinct from lower column density associated systems and the inferred
QSO-absorber separations mean they are unlikely to be associated with the QSO
host. We speculate that the PDLAs preferentially sample more massive galaxies
in more highly clustered regions of the high redshift universe. |
The zCOSMOS-SINFONI Project I: Sample Selection and Natural-Seeing
Observations: The zCOSMOS SINFONI project is aimed at studying the physical and kinematical
properties of a sample of massive z~1.4-2.5 star-forming galaxies, through
SINFONI near-IR integral field spectroscopy (IFS), combined with the
multi-wavelength information from the zCOSMOS (COSMOS) survey. The project is
based on 1 hour of natural-seeing observations per target, and Adaptive Optics
(AO) follow-up for a major part of the sample, which includes 30 galaxies
selected from the zCOSMOS/VIMOS spectroscopic survey. This first paper presents
the sample selection, and the global physical characterization of the target
galaxies from multicolor photometry, i.e., star formation rate (SFR), stellar
mass, age, etc. The Halpha integrated properties such as, flux, velocity
dispersion, and size, are derived from the natural-seeing observations, while
the follow up AO observations will be presented in the next paper of this
series. Our sample appears to be well representative of star-forming galaxies
at z~2, covering a wide range in mass and SFR. The Halpha integrated properties
of the 25 Halpha detected galaxies are similar to those of other IFS samples at
the same redshifts. Good agreement is found among the SFRs derived from Halpha
luminosity and other diagnostic methods, provided the extinction affecting the
Halpha luminosity is about twice that affecting the continuum. A preliminary
kinematic analysis, based on the maximum observed velocity difference across
the source, and on the integrated velocity dispersion, indicates that the
sample splits nearly 50-50 into rotation-dominated and velocity
dispersion-dominated galaxies, in good agreement with previous surveys. | Interpreting the unresolved intensity of cosmologically redshifted line
radiation: Intensity mapping experiments survey the spectrum of diffuse line radiation
rather than detect individual objects at high signal-to-noise. Spectral maps of
unresolved atomic and molecular line radiation contain three-dimensional
information about the density and environments of emitting gas, and efficiently
probe cosmological volumes out to high redshift. Intensity mapping survey
volumes also contain all other sources of radiation at the frequencies of
interest. Continuum foregrounds are typically ~10^2-10^3 times brighter than
the cosmological signal. The instrumental response to bright foregrounds will
produce new spectral degrees of freedom that are not known in advance, nor
necessarily spectrally smooth. The intrinsic spectra of foregrounds may also
not be well-known in advance. We describe a general class of quadratic
estimators to analyze data from single-dish intensity mapping experiments, and
determine contaminated spectral modes from the data itself. The key attribute
of foregrounds is not that they are spectrally smooth, but instead that they
have fewer bright spectral degrees of freedom than the cosmological signal.
Spurious correlations between the signal and foregrounds produce additional
bias. Compensation for signal attenuation must estimate and correct this bias.
A successful intensity mapping experiment will control instrumental systematics
that spread variance into new modes, and it must observe a large enough volume
that contaminant modes can be determined independently from the signal on
scales of interest. |
First Results from the La Silla-QUEST Supernova Survey and the Carnegie
Supernova Project: The LaSilla/QUEST Variability Survey (LSQ) and the Carnegie Supernova Project
(CSP II) are collaborating to discover and obtain photometric light curves for
a large sample of low redshift (z < 0.1) Type Ia supernovae. The supernovae are
discovered in the LSQ survey using the 1 m ESO Schmidt telescope at the La
Silla Observatory with the 10 square degree QUEST camera. The follow-up
photometric observations are carried out using the 1 m Swope telescope and the
2.5 m du Pont telescopes at the Las Campanas Observatory. This paper describes
the survey, discusses the methods of analyzing the data and presents the light
curves for the first 31 Type Ia supernovae obtained in the survey. The SALT 2.4
supernova light curve fitter was used to analyze the photometric data, and the
Hubble diagram for this first sample is presented. The measurement errors for
these supernovae averaged 4%, and their intrinsic spread was 14%. | CMB constraints on DHOST theories: We put constraints on the degenerate higher-order scalar-tensor (DHOST)
theories using the Planck 2018 likelihoods. In our previous paper, we developed
a Boltzmann solver incorporating the effective field theory parameterised by
the six time-dependent functions, $\alpha_i$ $(i={\rm B},{\rm K},{\rm T},{\rm
M},{\rm H})$ and $\beta_1$, which can describe the DHOST theories. Using the
Markov-Chain Monte-Carlo method with our Boltzmann solver, we find the viable
parameter region of the model parameters characterising the DHOST theories and
the other standard cosmological parameters. First, we consider a simple model
with $\alpha_{\rm K} = \Omega_{\rm DE}(t)/\Omega_{\rm DE}(t_0)$, $\alpha_{\rm
B}=\alpha_{\rm T}=\alpha_{\rm M}=\alpha_{\rm H}=0$ and
$\beta_1=\beta_{1,0}\Omega_{\rm DE}(t)/\Omega_{\rm DE}(t_0)$ in the
$\Lambda$CDM background where $t_0$ is the present time and obtain
$\beta_{1,0}=0.032_{-0.016}^{+0.013}$ (68\% c.l.). Next, we focus on another
theory given by $\mathcal{L}_{\rm DHOST} = X + c_3X\Box\phi/\Lambda^3+ (M_{\rm
pl}^2/2+c_4X^2/\Lambda^6)R + 48c_4^2X^2/(M_{\rm
pl}^2\Lambda^{12}+2c_4\Lambda^6X^2)\phi^\mu\phi_{\mu\rho}\phi^{\rho\nu}\phi_\nu$
with $X:=\partial_\mu\phi\partial^{\mu}\phi$ and two positive constant
parameters, $c_3$ and $c_4$. In this model, we consistently treat the
background and the perturbations, and obtain $c_3 = 1.59^{+0.26}_{-0.28}$ and
the upper bound on $c_4$, $c_4<0.0088$ (68\% c.l.). |
Normalization of the Matter Power Spectrum via the Ellipticity Function
of Giant Galaxy Voids from SDSS DR5: The ellipticity function of cosmic voids exhibits strong dependence on the
amplitude of the linear matter power spectrum. Analyzing the most recent void
catalogs constructed by Foster and Nelson from the fifth data release of the
Sloan Digital Sky Survey, we measure observationally the ellipticity function
of giant galaxy voids. Then, we incorporate the redshift distortion and galaxy
bias effect into the analytic model of the void ellipticity function and fit it
to the observational result by adjusting the value of the power-spectrum
normalization with the help of the generalized chi^{2}-minimization method. The
best-fit normalization of the linear power spectrum is found to be
sigma_{8}=0.90+/-0.04. Our result is higher than the WMAP sigma_{8}-value but
consistent with that from the recent work of Liu and Li who have constructed a
new improved CMB map independently. | The Cosmic Spiderweb and General Origami Tessellation Design: The cosmic web (the arrangement of matter in the universe), spider's webs,
and origami tessellations are linked by their geometry (specifically, of
sectional-Voronoi tessellations). This motivates origami and textile artistic
representations of the cosmic web. It also relates to the scientific insights
origami can bring to the cosmic web; we show results of some cosmological
computer simulations, with some origami-tessellation properties. We also adapt
software developed for cosmic-web research to provide an interactive tool for
general origami-tessellation design. |
The SDSS Galaxy Angular Two-Point Correlation Function: We present the galaxy two-point angular correlation function for galaxies
selected from the seventh data release of the Sloan Digital Sky Survey. The
galaxy sample was selected with $r$-band apparent magnitudes between 17 and 21;
and we measure the correlation function for the full sample as well as for the
four magnitude ranges: 17-18, 18-19, 19-20, and 20-21. We update the flag
criteria to select a clean galaxy catalog and detail specific tests that we
perform to characterize systematic effects, including the effects of seeing,
Galactic extinction, and the overall survey uniformity. Notably, we find that
optimally we can use observed regions with seeing $< 1\farcs5$, and $r$-band
extinction < 0.13 magnitudes, smaller than previously published results.
Furthermore, we confirm that the uniformity of the SDSS photometry is minimally
affected by the stripe geometry. We find that, overall, the two-point angular
correlation function can be described by a power law, $\omega(\theta) =
A_\omega \theta^{(1-\gamma)}$ with $\gamma \simeq 1.72$, over the range
$0\fdg005$--$10\degr$. We also find similar relationships for the four
magnitude subsamples, but the amplitude within the same angular interval for
the four subsamples is found to decrease with fainter magnitudes, in agreement
with previous results. We find that the systematic signals are well below the
galaxy angular correlation function for angles less than approximately
$5\degr$, which limits the modeling of galaxy angular correlations on larger
scales. Finally, we present our custom, highly parallelized two-point
correlation code that we used in this analysis. | Influence from cosmological uncertainties on galaxy number count at
faint limit: Counting galaxy number density with wide range sky surveys has been well
adopted in researches focusing on revealing evolution pattern of different
types of galaxies. As understood intuitively the astrophysics environment
physics is intimated affected by cosmology priors with theoretical estimation
or vise versa, or simply stating that the astrophysics effect couples the
corresponding cosmology observations
or the way backwards. In this article we try to quantify the influence on
galaxy number density prediction at faint luminosity limit from the
uncertainties in cosmology, and how much the uncertainties blur the detection
of galaxy evolution, with the hope that this trying may indeed help for precise
and physical cosmology study in near future or vise versa |
Supernovae in paired galaxies: We investigate the influence of close neighbor galaxies on the properties of
supernovae (SNe) and their host galaxies using 56 SNe located in pairs of
galaxies with different levels of star formation (SF) and nuclear activity. The
mean distance of type II SNe from nuclei of hosts is greater by about a factor
of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are
consistent with previous results compiled with the larger sample. For the first
time it is shown that SNe Ibc are located in pairs with significantly smaller
difference of radial velocities between components than pairs containing SNe Ia
and II. We consider this as a result of higher star formation rate (SFR) of
these closer systems of galaxies. | Imprints of anisotropic inflation on the cosmic microwave background: We study the imprints of anisotropic inflation on the CMB temperature
fluctuations and polarizations. The statistical anisotropy stems not only from
the direction dependence of curvature and tensor perturbations, but also from
the cross correlation between curvature and tensor perturbations, and the
linear polarization of tensor perturbations. We show that off-diagonal $TB$ and
$EB$ spectrum as well as on- and off-diagonal $TT, EE, BB, TE$ spectrum are
induced from anisotropic inflation. We emphasize that the off-diagonal spectrum
induced by the cross correlation could be a characteristic signature of
anisotropic inflation. |
A grounded perspective on New Early Dark Energy using ACT, SPT, and
BICEP/Keck: We examine further the ability of the New Early Dark Energy model (NEDE) to
resolve the current tension between the Cosmic Microwave Background (CMB) and
local measurements of $H_0$ and the consequences for inflation. We perform new
Bayesian analyses, including the current datasets from the ground-based CMB
telescopes Atacama Cosmology Telescope (ACT), the South Pole Telescope (SPT),
and the BICEP/Keck telescopes, employing an updated likelihood for the local
measurements coming from the S$H_0$ES collaboration. Using the S$H_0$ES prior
on $H_0$, the combined analysis with Baryonic Acoustic Oscillations (BAO),
Pantheon, Planck and ACT improves the best-fit by $\Delta\chi^2 = -15.9$ with
respect to $\Lambda$CDM, favors a non-zero fractional contribution of NEDE,
$f_{\rm NEDE} > 0$, by $4.8\sigma$, and gives a best-fit value for the Hubble
constant of $H_0 = 72.09$ km/s/Mpc (mean $71.48_{-0.81}^{+0.79}$ with $68\%$
C.L.). A similar analysis using SPT instead of ACT yields consistent results
with a $\Delta \chi^2 = - 23.1$ over $\Lambda$CDM, a preference for non-zero
$f_{\rm NEDE}$ of $4.7\sigma$ and a best-fit value of $H_0=71.77$ km/s/Mpc
(mean $71.43_{-0.84}^{+0.84}$ with $68\%$ C.L.). We also provide the
constraints on the inflation parameters $r$ and $n_s$ coming from NEDE,
including the BICEP/Keck 2018 data, and show that the allowed upper value on
the tensor-scalar ratio is consistent with the $\Lambda$CDM bound, but, as also
originally found, with a more blue scalar spectrum implying that the simplest
curvaton model is now favored over the Starobinsky inflation model. | Cluster counts. II. Tensions, massive neutrinos, and modified gravity: The $\Lambda$CDM concordance model is very successful at describing our
Universe with high accuracy and few parameters. Despite its successes, a few
tensions persist; most notably, the best-fit $\Lambda$CDM model, as derived
from the Planck CMB data, largely overpredicts the abundance of SZ clusters
when using their standard mass calibration. Whether this is a sign of an
incorrect calibration or the need for new physics remains a matter of debate.
Here we examined two simple extensions of the standard model and their ability
to release this tension: massive neutrinos and a simple modified gravity model
via a non-standard growth index $\gamma$. We used both the Planck CMB and SZ
cluster counts as datasets, with or without local X-ray clusters. In the case
of massive neutrinos, the SZ calibration $(1-b)$ is constrained to
$0.59^{+0.03}_{-0.04}$ (68\%), more than 5$\sigma$ away from its standard value
$\sim0.8$. We found little correlation between $\sum m_\nu$ and $(1-b)$,
corroborating previous conclusions derived from X-ray clusters; massive
neutrinos do not alleviate the cluster-CMB tension. With our simple $\gamma$
model, we found a large correlation between calibration and growth index but
contrary to local X-ray clusters, SZ clusters are able to break the degeneracy
between the two thanks to their extended $z$ range. The calibration $(1-b)$ was
then constrained to $0.60^{+0.05}_{-0.07}$, leading to an interesting
constraint on $\gamma=0.60\pm 0.13$. When both massive neutrinos and modified
gravity were allowed, preferred values remained centred on standard
$\Lambda$CDM values, but $(1-b)\sim0.8$ was allowed (though only at the
$2\sigma$ level) provided $\sum m_\nu\sim0.34 $ eV and $\gamma\sim0.8$. We
conclude that massive neutrinos do not relieve the cluster-CMB tension and that
a calibration close to the standard value $0.8$ would call for new physics in
the gravitational sector. |
An Empirical Connection between the UV Color of Early Type Galaxies and
the Stellar Initial Mass Function: Using new UV magnitudes for a sample of early-type galaxies, ETGs, with
published stellar mass-to-light ratios, Upsilon_*, we find a correlation
between UV color and Upsilon_* that is tighter than those previously identified
between Upsilon_* and either the central stellar velocity dispersion,
metallicity, or alpha enhancement. The sense of the correlation is that
galaxies with larger Upsilon_* are bluer in the UV. We conjecture that
differences in the lower mass end of the stellar initial mass function, IMF,
are related to the nature of the extreme horizontal branch populations that are
generally responsible for the UV flux in ETGs. If so, then UV color can be used
to identify ETGs with particular IMF properties and to estimate Upsilon_*. | Accurate Shear Measurement with Faint Sources: For cosmic shear to become an accurate cosmological probe, systematic errors
in the shear measurement method must be unambiguously identified and corrected
for. Previous work of this series has demonstrated that cosmic shears can be
measured accurately in Fourier space in the presence of background noise and
finite pixel size, without assumptions on the morphologies of galaxy and PSF.
The remaining major source of error is source Poisson noise, due to the
finiteness of source photon number. This problem is particularly important for
faint galaxies in space-based weak lensing measurements, and for ground-based
images of short exposure times. In this work, we propose a simple and rigorous
way of removing the shear bias from the source Poisson noise. Our noise
treatment can be generalized for images made of multiple exposures through
MultiDrizzle. This is demonstrated with the SDSS and COSMOS/ACS data. With a
large ensemble of mock galaxy images of unrestricted morphologies, we show that
our shear measurement method can achieve sub-percent level accuracy even for
images of signal-to-noise ratio less than 5 in general, making it the most
promising technique for cosmic shear measurement in the ongoing and upcoming
large scale galaxy surveys. |
A study of fundamental limitations to statistical detection of
redshifted HI from the epoch of reionization: In this paper we explore for the first time the relative magnitudes of three
fundamental sources of uncertainty, namely, foreground contamination, thermal
noise and sample variance in detecting the HI power spectrum from the Epoch of
Reionization (EoR). We derive limits on the sensitivity of a Fourier synthesis
telescope to detect EoR based on its array configuration and a statistical
representation of images made by the instrument. We use the Murchison Widefield
Array (MWA) configuration for our studies. Using a unified framework for
estimating signal and noise components in the HI power spectrum, we derive an
expression for and estimate the contamination from extragalactic point-like
sources in three-dimensional k-space. Sensitivity for EoR HI power spectrum
detection is estimated for different observing modes with MWA. With 1000 hours
of observing on a single field using the 128-tile MWA, EoR detection is
feasible (S/N > 1 for $k\lesssim 0.8$ Mpc$^{-1}$). Bandpass shaping and
refinements to the EoR window are found to be effective in containing
foreground contamination, which makes the instrument tolerant to imaging
errors. We find that for a given observing time, observing many independent
fields of view does not offer an advantage over a single field observation when
thermal noise dominates over other uncertainties in the derived power spectrum. | Constraining hydrostatic mass bias of galaxy clusters with
high-resolution X-ray spectroscopy: Gas motions in galaxy clusters play important roles in determining the
properties of the intracluster medium (ICM) and in the constraint of
cosmological parameters via X-ray and Sunyaev-Zel'dovich effect observations of
galaxy clusters. The Hitomi measurements of gas motions in the core of the
Perseus Cluster have provided insights into the physics in galaxy clusters. The
XARM mission, equipped with the Resolve X-ray micro-calorimeter, will continue
Hitomi's legacy by measuring ICM motions through Doppler shifting and
broadening of emission lines in a larger number of galaxy clusters, and at
larger radii. In this work, we investigate how well we can measure bulk and
turbulent gas motions in the ICM with XARM, by analyzing mock XARM simulations
of galaxy clusters extracted from cosmological hydrodynamic simulations. We
assess how photon counts, spectral fitting methods, multiphase ICM structure,
deprojections, and region selection affect the measurements of gas motions. We
first show that XARM is capable of recovering the underlying spherically
averaged turbulent and bulk velocity profiles for dynamically relaxed clusters
to within $\sim 50\%$ with a reasonable amount of photon counts in the X-ray
emission lines. We also find that there are considerable azimuthal variations
in the ICM velocities, where the velocities measured in a single azimuthal
direction can significantly deviate from the true value even in dynamically
relaxed systems. Such variation must be taken into account when interpreting
data and developing observing strategies. We will discuss the prospect of using
the upcoming XARM mission to measure non-thermal pressure and to correct for
the hydrostatic mass bias of galaxy clusters. Our results are broadly
applicable for future X-ray missions, such as Athena and Lynx. |
Molecular Hydrogen and [Fe II] in Active Galactic Nuclei III: LINERS and
Star Forming Galaxies: We study the kinematics and excitation mechanisms of H2 and [Fe II] lines in
a sample of 67 emission-line galaxies with Infrared Telescope Facility SpeX
near-infrared (NIR, 0.8-2.4 micrometers) spectroscopy together with new
photoionisation models. H2 emission lines are systematically narrower than
narrow-line region (NLR) lines, suggesting that the two are, very likely,
kinematically disconnected. The new models and emission-line ratios show that
the thermal excitation plays an important role not only in active galactic
nuclei but also in star forming galaxies. The importance of the thermal
excitation in star forming galaxies may be associated with the presence of
supernova remnants close to the region emitting H2 lines. This hypothesis is
further supported by the similarity between the vibrational and rotational
temperatures of H2. We confirm that the diagram involving the line ratios H2
2.121/Br_gamma and [Fe II] 1.257/Pa_beta is an efficient tool for separating
emission-line objects according to their dominant type of activity. We suggest
new limits to the line ratios in order to discriminate between the different
types of nuclear activity. | Non-Gaussian information from weak lensing data via deep learning: Weak lensing maps contain information beyond two-point statistics on small
scales. Much recent work has tried to extract this information through a range
of different observables or via nonlinear transformations of the lensing field.
Here we train and apply a 2D convolutional neural network to simulated
noiseless lensing maps covering 96 different cosmological models over a range
of {$\Omega_m,\sigma_8$}. Using the area of the confidence contour in the
{$\Omega_m,\sigma_8$} plane as a figure-of-merit, derived from simulated
convergence maps smoothed on a scale of 1.0 arcmin, we show that the neural
network yields $\approx 5 \times$ tighter constraints than the power spectrum,
and $\approx 4 \times$ tighter than the lensing peaks. Such gains illustrate
the extent to which weak lensing data encode cosmological information not
accessible to the power spectrum or even other, non-Gaussian statistics such as
lensing peaks. |
Cardassian Universe Constrained by Latest Observations: Several Cardassian universe models including the original, modified
polytropic and exponential Cardassian models are constrained by the latest
Constitution Type Ia supernova data, the position of the first acoustic peak of
CMB from the five years WMAP data and the size of baryonic acoustic oscillation
peak from the SDSS data. Both the spatial flat and curved universe are studied,
and we also take account of the possible bulk viscosity of the matter fluid in
the flat universe case. | CIV Emission and the Ultraviolet through X-ray Spectral Energy
Distribution of Radio-Quiet Quasars: In the restframe UV, two of the parameters that best characterize the range
of emission-line properties in quasar broad emission-line regions are the
equivalent width and the blueshift of the CIV line relative to the quasar rest
frame. We explore the connection between these emission-line properties and the
UV through X-ray spectral energy distribution (SED) for radio-quiet (RQ)
quasars. Our sample consists of a heterogeneous compilation of 406 quasars from
the Sloan Digital Sky Survey and Palomar-Green survey that have well-measured
CIV emission-line and X-ray properties (including 164 objects with measured
Gamma). We find that RQ quasars with both strong CIV emission and small CIV
blueshifts can be classified as "hard-spectrum" sources that are (relatively)
strong in the X-ray as compared to the UV. On the other hand, RQ quasars with
both weak CIV emission and large CIV blueshifts are instead "soft-spectrum"
sources that are (relatively) weak in the X-ray as compared to the UV. This
work helps to further bridge optical/soft X-ray "Eigenvector 1" relationships
to the UV and hard X-ray. Based on these findings, we argue that future work
should consider systematic errors in bolometric corrections (and thus accretion
rates) that are derived from a single mean SED. Detailed analysis of the CIV
emission line may allow for SED-dependent corrections to these quantities. |
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