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Modeling galaxy clustering on small scales to tighten constraints on
dark energy and modified gravity: We present a new approach to measuring cosmic expansion history and growth
rate of large scale structure using the anisotropic two dimensional galaxy
correlation function (2DCF) measured from data; it makes use of the empirical
modeling of small-scale galaxy clustering derived from numerical simulations by
Zheng et al. (2013). We validate this method using mock catalogues, before
applying it to the analysis of the CMASS sample from the Sloan Digital Sky
Survey Data Release 10 (DR10) of the Baryon Oscillation Spectroscopic Survey
(BOSS). We find that this method enables accurate and precise measurements of
cosmic expansion history and growth rate of large scale structure. Modeling the
2DCF fully including nonlinear effects and redshift space distortions (RSD) in
the scale range of 16 to 144 Mpc/h, we find H(0.57)r_s(z_d)/c=0.0459 +/-
0.0006, D_A(0.57)/r_s(z_d)=9.011 +/- 0.073, and f_g(0.57)\sigma_8(0.57)=0.476
+/- 0.050, which correspond to precisions of 1.3%, 0.8%, and 10.5%
respectively. We have defined r_s(z_d) to be the sound horizon at the drag
epoch computed using a simple integral, f_g(z) as the growth rate at redshift
z, and \sigma_8(z) as the matter power spectrum normalization on 8Mpc/h scale
at z. We find that neglecting the small-scale information significantly weakens
the constraints on H(z) and D_A(z), and leads to a biased estimate of f_g(z).
Our results indicate that we can significantly tighten constraints on dark
energy and modified gravity by reliably modeling small-scale galaxy clustering. | Evolution of the atomic and molecular gas content of galaxies: We study the evolution of atomic and molecular gas in galaxies in
semi-analytic models of galaxy formation that include new modeling of the
partitioning of cold gas in galactic discs into atomic, molecular, and ionised
phases. We adopt two scenarios for the formation of molecules: one
pressure-based and one metallicity-based. We find that both recipes
successfully reproduce the gas fractions and gas-to-stellar mass ratios of HI
and H2 in local galaxies,as well as the HI and H2 disc sizes up to z<2. We
reach good agreement with the locally observed HI and H2 mass function,
although both recipes slightly overpredict the low-mass end of the HI mass
function. Both of our models predict that the high-mass end of the HI mass
function remains nearly constant at redshifts z < 2.0. The metallicity-based
recipe yields a higher cosmic density of cold gas and much lower cosmic H2
fraction over the entire redshift range probed than the pressure based recipe.
These strong differences in HI mass function and cosmic density between the two
recipes are driven by low mass galaxies (log (M*/Msun) < 7) residing in low
mass halos (log (Mvir/Msun) < 10). Both recipes predict that galaxy gas
fractions remain high from z ~ 6-3 and drop rapidly at lower redshift. The
galaxy H2 fractions show a similar trend, but drop even more rapidly. We
provide predictions for the CO J = 1-0 luminosity of galaxies, which will be
directly comparable with observations with sub-mm and radio instruments. |
Omniscopes: Large Area Telescope Arrays with only N log N Computational
Cost: We show that the class of antenna layouts for telescope arrays allowing cheap
analysis hardware (with correlator cost scaling as N log N rather than N^2 with
the number of antennas N) is encouragingly large, including not only previously
discussed rectangular grids but also arbitrary hierarchies of such grids, with
arbitrary rotations and shears at each level. We show that all correlations for
such a 2D array with an n-level hierarchy can be efficiently computed via a
Fast Fourier Transform in not 2 but 2n dimensions. This can allow major
correlator cost reductions for science applications requiring exquisite
sensitivity at widely separated angular scales, for example 21cm tomography
(where short baselines are needed to probe the cosmological signal and long
baselines are needed for point source removal), helping enable future 21cm
experiments with thousands or millions of cheap dipole-like antennas. Such
hierarchical grids combine the angular resolution advantage of traditional
array layouts with the cost advantage of a rectangular Fast Fourier Transform
Telescope. We also describe an algorithm for how a subclass of hierarchical
arrays can efficiently use rotation synthesis to produce global sky maps with
minimal noise and a well-characterized synthesized beam. | Pair-Instability Explosions: observational evidence: It has been theoretically predicted many decades ago that extremely massive
stars that develop large oxygen cores will become dynamically unstable, due to
electron-positron pair production. The collapse of such oxygen cores leads to
powerful thermonuclear explosions that unbind the star and can produce, in some
cases, many solar masses of radioactive 56Ni. For many years, no examples of
this process were observed in nature. Here, I briefly review recent
observations of luminous supernovae that likely result from pair-instability
explosions, in the nearby and distant Universe. |
Chemical signature of gas-rich disc-disc mergers at high redshift: We performed numerical simulations of mergers between gas-rich disc galaxies,
which result in the formation of late-type galaxies. Stars formed during the
merger end up in a thick disc that is partially supported by velocity
dispersion and has high [alpha/Fe] ratios at all metallicities. Stars formed
later end up in a thin, rotationally supported disc which has lower [alpha/Fe]
ratios. While the structural and kinematical properties of the merger remnants
depend strongly upon the orbital parameters of the mergers, we find a clear
chemical signature of gas-rich mergers. | Star Stream Folding by Dark Galactic Sub-Halos: Star streams in galactic halos are long, thin, unbound structures that will
be disturbed by the thousands dark matter sub-halos that are predicted to be
orbiting within the main halo. A sub-halo generally induces a localized wave in
the stream which often evolves into a "z-fold" as an initially trailing
innermost part rotates faster than an initially leading outermost part. The
folding, which becomes increasingly complex with time, leads to an apparent
velocity dispersion increase and thickening of the stream. We measure the
equivalent velocity dispersion around the local mean in the simulations,
finding that it rises to about 10 km/s after 5 Gyr and 20 km/s after 13 Gyr.
The currently available measurements of the velocity dispersion of halo star
streams range from as small as 2 km/s to slightly over 20 km/s. The streams
with velocity dispersions of 15-20 km/s are compatible with what sub-halo
heating would produce. A dynamical understanding of the low velocity dispersion
streams depends on the time since the progenitor's tidal disruption into a thin
stream. If the streams are nearly as old as their stars then sub-halos cannot
be present with the predicted numbers and masses. However, the dynamical age of
the streams can be significantly less than the stars. If the three lowest
velocity streams are assigned ages of 3 Gyr, they are in conflict with the
sub-halo heating. The main conclusion is that star stream heating is a powerful
and simple test for sub-halo structure. |
Young radio sources: a radio-gamma perspective: The evolutionary stage of a powerful radio source originated by an AGN is
related to its linear size. In this context, compact symmetric objects (CSOs),
which are powerful and intrinsically small (< 1 kpc) radio sources with a
convex synchrotron radio spectrum that peaks around the GHz regime, should
represent a young stage in the individual radio source life. Their radio jets
expand within the dense and inhomogeneous interstellar medium of the host
galaxy, which may influence the source growth. The radio emission is expected
to evolve as a consequence of adiabatic expansion and radiative and inverse
Compton losses. The role played by the different mechanisms in the radio and
gamma regimes is discussed. | A Survey of HC3N in Extragalactic Sources - Is HC3N a Tracer of Activity
in ULIRGs?: Context. HC3N is a molecule that is mainly associated with Galactic
star-forming regions, but it has also been detected in extragalactic
environments. Aims. To present the first extragalactic survey of HC3N, when
combining earlier data from the literature with six new single-dish detections,
and to compare HC3N with other molecular tracers (HCN, HNC), as well as other
properties (silicate absorption strength, IR flux density ratios, C II flux,
and megamaser activity). Methods. We present mm IRAM 30 m, OSO 20 m, and SEST
observations of HC3N rotational lines (mainly the J = 10-9 transition) and of
the J = 1-0 transitions of HCN and HNC. Our combined HC3N data account for 13
galaxies (excluding the upper limits reported for the non-detections), while we
have HCN and HNC data for more than 20 galaxies. Results. A preliminary
definition "HC3N-luminous galaxy" is made based upon the HC3N/HCN ratio. Most
(~80 %) HC3N-luminous galaxies seem to be deeply obscured galaxies and
(U)LIRGs. A majority (~60 % or more) of the HC3N-luminous galaxies in the
sample present OH mega- or strong kilomaser activity. A possible explanation is
that both HC3N and OH megamasers need warm dust for their excitation.
Alternatively, the dust that excites the OH megamaser offers protection against
UV destruction of HC3N. A high silicate absorption strength is also found in
several of the HC3N-luminous objects, which may help the HC3N to survive.
Finally, we find that a high HC3N/HCN ratio is related to a high dust
temperature and a low C II flux. |
A mechanism to explain Galaxy alignment over a range of scales: The observed large-scale alignment of polarization angles and galaxy axis
have been challenging the fundamental assumption of homogeneity and isotropy in
standard cosmology since more than two decades. The intergalactic magnetic
field, and its correlations in real space, potentially seems as a viable
candidate for explaining this phenomenon. It has been shown earlier that the
large-scale intergalactic magnetic field correlations can explain the alignment
signal of quasars over Gpc scale, interestingly they can also explain the radio
polarization alignment observed in JVAS/CLASS data over 100 Mpc. Motivated with
recent observations of galaxy axis alignment over several tens of Mpc, and Mpc
scale, i.e., the cluster scale, we further explore the correlations of
background magnetic field to explain these relatively small scale alignment
observations. In particular, we explore two recently claimed signals of
alignment in the radio sources in the FIRST catalog and in the ACO clusters. We
find that the FIRST alignment signal is well explained in terms of the
intergalactic magnetic field with a spectral index of $-2.62\pm 0.03$.
Furthermore, the model also partially explains the very small scale alignment
(alignment within clusters). Though the elementary model proposed in this work
seems to have its limitations at very small scales, the large-scale magnetic
field correlations potentially seem to explain the polarization and galaxy axis
alignment from Gpc to Mpc scales. | The halo squeezed-limit bispectrum with primordial non-Gaussianity: a
power spectrum response approach: Modeling the nonlinearity of the halo bispectrum remains a major challenge in
modern cosmology, in particular for ongoing and upcoming large-scale structure
observations that are performed to study the inflationary physics. The "power
spectrum response" offers a solution for bispectrum in the so-called squeezed
limit, in which one wavenumber is much smaller than the other two. As a first
step, we demonstrate that the halo squeezed-limit bispectrum computed from the
second-order standard perturbation theory agrees precisely with the responses
of linear halo power spectrum to large-scale density and potential
fluctuations. Since the halo power spectrum responses to arbitrarily small
scales can straightforwardly be obtained by separate universe simulations, the
response approach provides a novel and powerful technique for modeling the
nonlinear halo squeezed-limit bispectrum. |
Probing Dark Matter Subhalos in Galaxy Clusters Using Highly Magnified
Stars: Luminous stars in background galaxies straddling the lensing caustic of a
foreground galaxy cluster can be individually detected due to extreme
magnification factors of $\sim 10^2$--$10^3$, as recently observed in deep HST
images. We propose a direct method to probe the presence of dark matter
subhalos in galaxy clusters by measuring the astrometric perturbation they
induce on the image positions of magnified stars or bright clumps: lensing by
subhalos breaks the symmetry of a smooth critical curve, traced by the
midpoints of close image pairs. For the giant arc at $z = 0.725$ behind the
lensing cluster Abell 370 at $z = 0.375$, a promising target for detecting
image pairs of stars, we find that subhalos of masses in the range
$10^6$--$10^8\,M_\odot$ with the abundance predicted in the cold dark matter
theory should typically imprint astrometric distortions at the level of
$20$--$80\,{\rm mas}$. We estimate that $\sim 10\,$hr integrations with JWST at
$\sim 1$--$3\,\mu{\rm m}$ may uncover several magnified stars whose image
doublets will reveal the subhalo-induced structures of the critical curve. This
method can probe a dynamic range in the subhalo to cluster halo mass ratio $m/M
\sim 10^{-7}$--$10^{-9}$, thereby placing new constraints on the nature of dark
matter. | Dark Energy and QCD Ghost: It has been suggested that the dark energy that explains the observed
accelerating expansion of the universe may arise due to the contribution to the
vacuum energy of the QCD ghost in a time-dependent background. The argument
uses a four-dimensional simplified model. In this paper, we put the discussion
in more realistic model keeping all components of the QCD vector ghost and show
that indeed QCD ghost produces dark energy proportional to the Hubble parameter
$H\Lambda_{QCD}^3$ ($\Lambda_{QCD}$ is the QCD mass scale) which has the right
magnitude $\sim (3\times 10^{-3}$ eV)$^4$. |
Implication of the Shape of the EDGES Signal for the 21 cm Power
Spectrum: We revisit the 21 cm power spectrum from the epoch of cosmic dawn in light of
the recent EDGES detection of the 21 cm global signal at frequencies
corresponding to $z\sim20$. The shape of the signal suggests that the spin
temperature of neutral hydrogen was coupled to the kinetic temperature of the
gas relatively rapidly ($19\lesssim z \lesssim 21$). We therefore consider
models in which the UV photons were dominantly produced in the rarest and most
massive halos ($M\gtrsim 10^9M_\odot$), since their abundance grows fast enough
at those redshifts to account for this feature of the signal. We show that
these models predict large power spectrum amplitudes during the inhomogeneous
coupling, and then inhomogeneous heating by CMB and Lyman-$\alpha$ photons due
to the large shot noise associated with the rare sources. The power spectrum is
enhanced by more than an order of magnitude compared to previous models which
did not include the shot noise contribution, making it a promising target for
upcoming radio interferometers that aim to detect high-redshift 21 cm
fluctuations. | Fast and Slow Rotators in the Densest Environments: a SWIFT IFS study of
the Coma Cluster: We present integral-field spectroscopy of 27 galaxies in the Coma cluster
observed with the Oxford SWIFT spectrograph, exploring the kinematic
morphology-density relationship in a cluster environment richer and denser than
any in the ATLAS3D survey. Our new data enables comparison of the kinematic
morphology relation in three very different clusters (Virgo, Coma and Abell
1689) as well as to the field/group environment. The Coma sample was selected
to match the parent luminosity and ellipticity distributions of the early-type
population within a radius 15' (0.43 Mpc) of the cluster centre, and is limited
to r' = 16 mag (equivalent to M_K = -21.5 mag), sampling one third of that
population. From analysis of the lambda-ellipticity diagram, we find 15+-6% of
early-type galaxies are slow rotators; this is identical to the fraction found
in the field and the average fraction in the Virgo cluster, based on the
ATLAS3D data. It is also identical to the average fraction found recently in
Abell 1689 by D'Eugenio et al.. Thus it appears that the average slow rotator
fraction of early type galaxies remains remarkably constant across many
different environments, spanning five orders of magnitude in galaxy number
density. However, within each cluster the slow rotators are generally found in
regions of higher projected density, possibly as a result of mass segregation
by dynamical friction. These results provide firm constraints on the mechanisms
that produce early-type galaxies: they must maintain a fixed ratio between the
number of fast rotators and slow rotators while also allowing the total
early-type fraction to increase in clusters relative to the field. A complete
survey of Coma, sampling hundreds rather than tens of galaxies, could probe a
more representative volume of Coma and provide significantly stronger
constraints, particularly on how the slow rotator fraction varies at larger
radii. |
The halo model in a massive neutrino cosmology: We provide a quantitative analysis of the halo model in the context of
massive neutrino cosmologies. We discuss all the ingredients necessary to model
the non-linear matter and cold dark matter power spectra and compare with the
results of N-body simulations that incorporate massive neutrinos. Our neutrino
halo model is able to capture the non-linear behavior of matter clustering with
a $\sim 20\%$ accuracy up to very non-linear scales of $k=10~h/$Mpc (which
would be affected by baryon physics). The largest discrepancies arise in the
range $k=0.5-1~h/$Mpc where the 1-halo and 2-halo terms are comparable and are
present also in a massless neutrino cosmology. However, at scales $k<0.2~h/$Mpc
our neutrino halo model agrees with the results of N-body simulations at the
level of 8\% for total neutrino masses of $<0.3$ eV. We also model the neutrino
non-linear density field as a sum of a linear and clustered component and
predict the neutrino power spectrum and the cold dark matter-neutrino
cross-power spectrum up to $k=1~h/$Mpc with $\sim$ 30\% accuracy. For masses
below 0.15 eV the neutrino halo model captures the neutrino induced
suppression, casted in terms of matter power ratios between massive and
massless scenarios, with a 2\% agreement with the results of N-body/neutrino
simulations. Finally, we provide a simple application of the halo model: the
computation of the clustering of galaxies, in massless and massive neutrinos
cosmologies, using a simple Halo Occupation Distribution scheme and our halo
model extension. | Constraining Scale-Dependent Non-Gaussianity with Future Large-Scale
Structure and the CMB: We forecast combined future constraints from the cosmic microwave background
and large-scale structure on the models of primordial non-Gaussianity. We study
the generalized local model of non-Gaussianity, where the parameter f_NL is
promoted to a function of scale, and present the principal component analysis
applicable to an arbitrary form of f_NL(k). We emphasize the complementarity
between the CMB and LSS by using Planck, DES and BigBOSS surveys as examples,
forecast constraints on the power-law f_NL(k) model, and introduce the figure
of merit for measurements of scale-dependent non-Gaussianity. |
Resolving the molecular gas around the lensed quasar RXJ0911.4+0551: We report on high angular resolution observations of the CO(7-6) line and
millimeter continuum in the host galaxy of the gravitationally lensed (z~2.8)
quasar RXJ0911.4+0551 using the Plateau de Bure Interferometer. Our CO
observations resolve the molecular disk of the source. Using a lens model based
on HST observations we fit source models to the observed visibilities. We
estimate a molecular disk radius of 1$\pm$0.2 kpc and an inclination of
69$\pm$6\deg, the continuum is more compact and is only marginally resolved by
our observations. The relatively low molecular gas mass, $Mgas=(2.3\pm
0.5)\times 10^{9}$ Msolar, and far infrared luminosity, $LFIR=(7.2\pm 1.5)
\times 10^{11}$ Lsolar, of this quasar could be explained by its relatively low
dynamical mass, $Mdyn=(3.9\pm 0.9)\times 10^9$ Msolar. It would be a
scaled-down version the QSOs usually found at high-z. The FIR and CO
luminosities lie on the correlation found for QSOs from low to high redshifts
and the gas-to-dust ratio ($45\pm 17$) is similar to the one measured in the
z=6.4 QSO, SDSS J1148+5251. Differential magnification affects the
continuum-to-line luminosity ratio, the line profile and possibly the spectral
energy distribution. | Optical Colors of Intracluster Light in the Virgo Cluster Core: We continue our deep optical imaging survey of the Virgo cluster using the
CWRU Burrell Schmidt telescope by presenting B-band surface photometry of the
core of the Virgo cluster in order to study the cluster's intracluster light
(ICL). We find ICL features down to mu_b ~ 29 mag sq. arcsec, confirming the
results of Mihos et al. (2005), who saw a vast web of low-surface brightness
streams, arcs, plumes, and diffuse light in the Virgo cluster core using V-band
imaging. By combining these two data sets, we are able to measure the optical
colors of many of the cluster's low-surface brightness features. While much of
our imaging area is contaminated by galactic cirrus, the cluster core near the
cD galaxy, M87, is unobscured. We trace the color profile of M87 out to over
2000 arcsec, and find a blueing trend with radius, continuing out to the
largest radii. Moreover, we have measured the colors of several ICL features
which extend beyond M87's outermost reaches and find that they have similar
colors to the M87's halo itself, B-V ~ 0.8. The common colors of these features
suggests that the extended outer envelopes of cD galaxies, such as M87, may be
formed from similar streams, created by tidal interactions within the cluster,
that have since dissolved into a smooth background in the cluster potential. |
ADMX SLIC: Results from a Superconducting LC Circuit Investigating Cold
Axions: Axions are a promising cold dark matter candidate. Haloscopes, which use the
conversion of axions to photons in the presence of a magnetic field to detect
axions, are the basis of microwave cavity searches such as the Axion Dark
Matter eXperiment (ADMX). To search for lighter, low frequency axions in the
sub $2\times10^{-7}$ eV (50 MHz) range, a tunable lumped-element LC circuit has
been proposed. For the first time, through ADMX SLIC (Superconducting Lc
circuit Investigating Cold axions), a resonant LC circuit was used to probe
this region of axion mass-coupling space. The detector used a superconducting
LC circuit with piezoelectric driven capacitive tuning. The axion mass and
corresponding frequency range $1.7498 -1.7519 \times10^{-7}$ eV (42.31 -- 42.36
MHz), $1.7734 - 1.7738 \times10^{-7}$ eV (42.88 -- 42.89 MHz), and $1.8007 -
1.8015 \times10^{-7}$ eV (43.54 -- 43.56 MHz) was covered at magnetic fields of
4.5 T, 5.0 T, and 7.0 T respectively. Exclusion results from the search data,
for coupling below $10^{-12} \text{GeV}^{-1}$ are presented. | CMB ISW-lensing bispectrum from cosmic strings: We study the effect of weak lensing by cosmic (super-)strings on the
higher-order statistics of the cosmic microwave background (CMB). A cosmic
string segment is expected to cause weak lensing as well as an integrated
Sachs-Wolfe (ISW) effect, the so-called Gott-Kaiser-Stebbins (GKS) effect, to
the CMB temperature fluctuation, which are thus naturally cross-correlated. We
point out that, in the presence of such a correlation, yet another kind of the
post-recombination CMB temperature bispectra, the ISW-lensing bispectra, will
arise in the form of products of the auto- and cross-power spectra. We first
present an analytic method to calculate the autocorrelation of the temperature
fluctuations induced by the strings, and the cross-correlation between the
temperature fluctuation and the lensing potential both due to the string
network. In our formulation, the evolution of the string network is assumed to
be characterized by the simple analytic model, the velocity-dependent one scale
model, and the intercommutation probability is properly incorporated in orderto
characterize the possible superstringy nature. Furthermore, the obtained power
spectra are dominated by the Poisson-distributed string segments, whose
correlations are assumed to satisfy the simple relations. We then estimate the
signal-to-noise ratios of the string-induced ISW-lensing bispectra and discuss
the detectability of such CMB signals from the cosmic string network. It is
found that in the case of the smaller string tension, $G\mu\ll 10^{-7}$\,, the
ISW-lensing bispectrum induced by a cosmic string network can constrain the
string-model parameters even more tightly than the purely GKS-induced
bispectrum in the ongoing and future CMB observations on small scales. |
Anomalies of Cosmic Anisotropy from Holographic Universality of
Great-Circle Variance: We examine all-sky cosmic microwave background (CMB) temperature maps on
large angular scales to compare their consistency with two scenarios: the
standard inflationary quantum picture, and a distribution constrained to have a
universal variance of primordial curvature perturbations on great circles. The
latter symmetry is not a property of standard quantum inflation, but may be a
symmetry of holographic models with causal quantum coherence on null surfaces.
Since the variation of great-circle variance is dominated by the largest
angular scale modes, in the latter case the amplitude and direction of the
unobserved intrinsic dipole (that is, the $\ell=1$ harmonics) can be estimated
from measured $\ell = 2, 3$ harmonics by minimizing the variance of
great-circle variances including only $\ell =1, 2, 3$ modes. It is found that
including the estimated intrinsic dipole leads to a nearly-null angular
correlation function over a wide range of angles, in agreement with a null
anti-hemispherical symmetry independently motivated by holographic causal
arguments, but highly anomalous in standard cosmology. Simulations are used
here to show that simultaneously imposing the constraints of universal
great-circle variance and the vanishing of the angular correlation function
over a wide range of angles tends to require patterns that are unusual in the
standard picture, such as anomalously high sectorality of the $\ell = 3$
components, and a close alignment of principal axes of $\ell=2$ and $\ell = 3$
components, that have been previously noted on the actual sky. The precision of
these results appears to be primarily limited by errors introduced by models of
Galactic foregrounds. | Extended Void Merging Tree Algorithm for Self-Similar Models: In hierarchical evolution, voids exhibit two different behaviors related with
their surroundings and environments, they can merge or collapse. These two
different types of void processes can be described by the two-barrier excursion
set formalism based on Brownian random walks. In this study, the analytical
approximate description of the growing void merging algorithm is extended by
taking into account the contributions of voids that are embedded into overdense
region(s) which are destined to vanish due to gravitational collapse. Following
this, to construct a realistic void merging model that consists of both
collapse and merging processes, the two-barrier excursion set formalism of the
void population is used. Assuming spherical voids in the Einstein de Sitter
Universe, the void merging algorithm which allows us to consider the two main
processes of void hierarchy in one formalism is constructed. In addition to
this, the merger rates, void survival probabilities, void size distributions in
terms of the collapse barrier and finally, the void merging tree algorithm in
the self-similar models are defined and derived. |
Probing Quiescent Massive Black Holes: Insights from Tidal Disruption
Events: Tidal disruption events provide a unique probe of quiescent black holes in
the nuclei of distant galaxies. The next generation of synoptic surveys will
yield a large sample of flares from the tidal disruption of stars by massive
black holes that will give insights to four key science questions: 1) What is
the assembly history of massive black holes in the universe? 2) Is there a
population of intermediate mass black holes that are the primordial seeds of
supermassive black holes? 3) How can we increase our understanding of the
physics of accretion onto black holes? 4) Can we localize sources of
gravitational waves from the detection of tidal disruption events around
massive black holes and recoiling binary black hole mergers? | Power Spectra of CMB Polarization by Scattering in Clusters: Mapping CMB polarization is an essential ingredient of current cosmological
research. Particularly challenging is the measurement of an extremely weak
B-mode polarization that can potentially yield unique insight on inflation.
Achieving this objective requires very precise measurements of the secondary
polarization components on both large and small angular scales. Scattering of
the CMB in galaxy clusters induces several polarization effects whose
measurements can probe cluster properties. Perhaps more important are levels of
the statistical polarization signals from the population of clusters. Power
spectra of five of these polarization components are calculated and compared
with the primary polarization spectra. These spectra peak at multipoles $\ell
\geq 3000$, and attain levels that are unlikely to appreciably contaminate the
primordial polarization signals. |
New Star Forming Galaxies at z\approx 7 from WFC3 Imaging: The addition of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope
(HST) has led to a dramatic increase in our ability to study the z>6 Universe.
The increase in the near-infrared (NIR) sensitivity of WFC3 over previous
instruments has enabled us to reach apparent magnitudes approaching 29 (AB).
This allows us to probe the rest-frame ultraviolet (UV) continuum, redshifted
into the NIR at $z>6$. Taking advantage of the large optical depths at this
redshift, resulting in the Lyman-alpha break, we use a combination of WFC3
imaging and pre-existing Advanced Camera for Surveys (ACS) imaging to search
for z approx 7 over 4 fields. Our analysis reveals 29 new z approx 7 star
forming galaxy candidates in addition to 16 pre-existing candidates already
discovered in these fields. The improved statistics from our doubling of the
robust sample of z-drop candidates confirms the previously observed evolution
of the bright end of the luminosity function. | Quadratic energy-momentum squared gravity: constraints from big bang
nucleosynthesis: In this study, we extend the standard cosmological model within the quadratic
energy-momentum squared gravity (qEMSG) framework, introducing a nonminimal
interaction between the usual material field ($T_{\mu\nu}$) and its
accompanying quadratic energy-momentum squared field (qEMSF, $T_{\mu\nu}^{\rm
qEMSF}$), defined by $f(\mathbf{T}^2) = \alpha \mathbf{T}^2$ with
$\mathbf{T^2}=T_{\mu\nu}T^{\mu\nu}$. Focusing on high energy scales relevant to
big bang nucleosynthesis (BBN), we employ $^4$He abundance to constrain the
parameter $\alpha$. Our analysis selects the radiation-dominated universe
solution compatible with the standard cosmological model limit as $\alpha
\rightarrow 0$ and reveals that qEMSF interaction model can modify the
radiation energy density's evolution, potentially altering neutron-proton
interconversion rates and consequently affecting $^4$He abundance in various
ways. We establish the most stringent cosmological bounds on $\alpha$: $(-8.81
\leq \alpha \leq 8.14) \times 10^{-27} \, \mathrm{eV}^{-4}$ (68\% CL) from Aver
\textit{et al.}'s primordial $^4$He abundance measurements, aligning with
$\alpha=0$. Additionally, $(3.48 \leq\alpha \leq 4.43)\,\times 10^{-27}
\rm{eV}^{-4}$ (68\% CL) from Fields \textit{et al.}'s estimates, utilizing the
Planck-CMB estimated baryon density within the standard cosmological model
framework, diverges from $\alpha=0$, thereby lending support to the qEMSF
interaction model. The study also highlights the bidirectional nature of
energy-momentum/entropy transfer in qEMSF interaction model, depending on the
sign of $\alpha$. The implications of qEMSF in the presence of additional
relativistic relics are also explored, showcasing the model's potential to
accommodate deviations from standard cosmology and the Standard Model of
particle physics. |
A comparison between the low-energy spectra from CoGeNT and CDMS: A side-to-side comparison is established between the nuclear recoil energy
spectrum from CDMS germanium bolometers and its low-energy equivalent for
events in the inner bulk volume of a CoGeNT germanium diode. Acknowledging the
orthogonality of the background cuts possible with each type of detector and
following an examination of the uncertainties in these searches, a suggestive
agreement between these spectra is observed. | Seeking the Progenitors of Type Ia Supernovae: The nature of the progenitor system[s] of Type Ia Supernovae is still
unclear. In this contribution I review the projects that have been undertaken
to answer this question and the results they have led to. The conclusion is
that, as of today, we have reasonable guesses but none of them has yet been
proven by direct observations. |
Measuring the reionization 21 cm fluctuations using clustering wedges: One of the main challenges in probing the reionization epoch using the
redshifted 21 cm line is that the magnitude of the signal is several orders
smaller than the astrophysical foregrounds. One of the methods to deal with the
problem is to avoid a wedge-shaped region in the Fourier $k_{\perp} -
k_{\parallel}$ space which contains the signal from the spectrally smooth
foregrounds. However, measuring the spherically averaged power spectrum using
only modes outside this wedge (i.e., in the reionization window), leads to a
bias. We provide a prescription, based on expanding the power spectrum in terms
of the shifted Legendre polynomials, which can be used to compute the angular
moments of the power spectrum in the reionization window. The prescription
requires computation of the monopole, quadrupole and hexadecapole moments of
the power spectrum using the theoretical model under consideration and also the
knowledge of the effective extent of the foreground wedge in the $k_{\perp} -
k_{\parallel}$ plane. One can then calculate the theoretical power spectrum in
the window which can be directly compared with observations. The analysis
should have implications for avoiding any bias in the parameter constraints
using 21 cm power spectrum data. | Spherical `Top-Hat' Collapse in general Chaplygin gas dominated
universes: We expand previous works on the spherical `top-hat' collapse (SC-TH)
framework in generalized Chaplygin gas (gCg) dominated universes. Here we allow
the collapse in all energetic components within the system. We analyze the
non-linear stages of collapse for various choices of parameter \alpha of the
gCg model introducing an exact formulation for the so-called effective sound
speed, $c_{eff}^2$. We show that, within the SC-TH framework, the growth of the
structure becomes faster with increasing values of \alpha. |
Discovery of Four kpc-Scale Binary AGNs: We report the discovery of four kpc-scale binary AGNs. These objects were
originally selected from the Sloan Digital Sky Survey based on double-peaked [O
III] 4959,5007 emission lines in their fiber spectra. The double peaks could
result from pairing active supermassive black holes (SMBHs) in a galaxy merger,
or could be due to bulk motions of narrow-line region gas around a single SMBH.
Deep near-infrared (NIR) images and optical slit spectra obtained from the
Magellan 6.5 m and the APO 3.5 m telescopes strongly support the binary SMBH
scenario for the four objects. In each system, the NIR images reveal tidal
features and double stellar components with a projected separation of several
kpc, while optical slit spectra show two Seyfert 2 nuclei spatially coincident
with the stellar components, with line-of-sight velocity offsets of a few
hundred km/s. These objects were drawn from a sample of only 43 objects,
demonstrating the efficiency of this technique to find kpc-scale binary AGNs. | Effects of long-wavelength fluctuations in large galaxy surveys: In order to capture as much information as possible large galaxy surveys have
been increasing their volume and redshift depth. To face this challenge theory
has responded by making cosmological simulations of huge computational volumes
with equally increasing the number of dark matter particles and supercomputing
resources. Thus, it is taken for granted that the ideal situation is when a
single computational box encompasses the whole effective volume of the
observational survey, e.g., ~50 Gpch^3 for the DESI and Euclid surveys. Here we
study the effects of missing long-waves in a finite volume using several
relevant statistics: the abundance of dark matter halos, the PDF, the
correlation function and power spectrum, and covariance matrices. Finite volume
effects can substantially modify the results if the computational volumes are
less than ~(500Mpch)^3. However, the effects become extremely small and
practically can be ignored when the box-size exceeds ~1Gpch^3. We find that the
average power spectra of dark matter fluctuations show remarkable lack of
dependence on the computational box-size with less than 0.1% differences
between 1Gpch and 4Gpch boxes. No measurable differences are expected for the
halo mass functions for these volumes. The covariance matrices are scaled
trivially with volume, and small corrections due to super-sample modes can be
added. We conclude that there is no need to make those extremely large
simulations when a box-size of 1-1.5Gpch is sufficient to fulfil most of the
survey science requirements. |
Polarization alignments of radio quasars in JVAS/CLASS surveys: We test the hypothesis that the polarization vectors of flat-spectrum radio
sources (FSRS) in the JVAS/CLASS 8.4-GHz surveys are randomly oriented on the
sky. The sample with robust polarization measurements is made of $4155$ objects
and redshift information is known for $1531$ of them. We performed two
statistical analyses: one in two dimensions and the other in three dimensions
when distance is available. We find significant large-scale alignments of
polarization vectors for samples containing only quasars (QSO) among the
varieties of FSRS's. While these correlations prove difficult to explain either
by a physical effect or by biases in the dataset, the fact that the QSO's which
have significantly aligned polarization vectors are found in regions of the sky
where optical polarization alignments were previously found is striking. | A comparison of the R_h=ct and LCDM cosmologies using the Cosmic
Distance Duality Relation: The cosmic distance duality (CDD) relation (based on the Etherington
reciprocity theorem) plays a crucial role in a wide assortment of cosmological
measurements. Attempts at confirming it observationally have met with mixed
results, though the general consensus appears to be that the data do support
its existence in nature. A common limitation with past approaches has been
their reliance on a specific cosmological model, or on measurements of the
luminosity distance to Type Ia SNe, which introduces a dependence on the
presumed cosmology in spite of beliefs to the contrary. Confirming that the CDD
is actually realized in nature is crucial because its violation would require
exotic new physics. In this paper, we study the CDD using the observed angular
size of compact quasar cores and a Gaussian Process reconstruction of the HII
galaxy Hubble diagram---without pre-assuming any particular background
cosmology. In so doing, we confirm at a very high level of confidence that the
angular-diameter and luminosity distances do indeed satisfy the CDD. We then
demonstrate the potential power of this result by utilizing it in a comparative
test of two competing cosmological models---the R_h=ct universe and LCDM---and
show that R_h=ct is favoured by the CDD data with a likelihood ~82.3% compared
with ~17.7% for the standard model. |
The Discovery of a Large Lyman-alpha+HeII Nebula at z~1.67: A Candidate
Low Metallicity Region?: We have discovered a ~45 kpc Lya nebula (or Lya ``blob'') at z~1.67 which
exhibits strong, spatially-extended HeII emission and very weak CIV and CIII]
emission. This is the first spatially-extended Lya+HeII emitter observed and
the lowest redshift Lya blob yet found. Strong Lya and HeII-1640 emission in
the absence of metal lines has been proposed as a unique observational
signature of primordial galaxy formation (e.g., from gravitational cooling
radiation or Population III star formation), but no convincing examples of
spatially-extended Lya+HeII emitters have surfaced either in Lya-emitting
galaxy surveys at high redshifts (z > 4) or in studies of Lya nebulae at lower
redshifts. From comparisons with photoionization models, we find that the
observed line ratios in this nebula are consistent with low metallicity gas (Z
< 10^-2 - 10^-3 Z_sun), but that this conclusion depends on the unknown
ionization parameter of the system. The large HeII equivalent width (~37+/-10A)
and the large HeII/Lya ratio (0.12+/-0.04) suggest that the cloud is being
illuminated by a hard ionizing continuum, either an AGN or very low metallicity
stars, or perhaps powered by gravitational cooling radiation. Thus far there is
no obvious sign of a powerful AGN in or near the system, so in order to power
the nebula while remaining hidden from view even in the mid-infrared, the AGN
would need to be heavily obscured. Despite the strong Lya+HeII emission, it is
not yet clear what is the dominant power source for this nebula. The system
therefore serves as an instructive example of how the complexities of true
astrophysical sources will complicate matters when attempting to use a strong
Lya+HeII signature as a unique tracer of primordial galaxy formation. | Magnification relations of quad lenses and applications on Einstein
crosses: In this work, we mainly study the magnification relations of quad lens models
for cusp, fold and cross configurations. By dividing and ray-tracing in
different image regions, we numerically derive the positions and magnifications
of the four images for a point source lying inside of the astroid caustic.
Then, based on the magnifications, we calculate the signed cusp and fold
relations for the singular isothermal elliptical lenses. The signed fold
relation map has positive and negative regions, and the positive region is
usually larger than the negative region as has been confirmed before. It can
also explain that for many observed fold image pairs, the fluxes of the Fermat
minimum images are apt to be larger than those of the saddle images. We define
a new quantity cross relation which describes the magnification discrepancy
between two minimum images and two saddle images. Distance ratio is also
defined as the ratio of the distance of two saddle images to that of two
minimum images. We calculate the cross relations and distance ratios for nine
observed Einstein crosses. In theory, for most of the quad lens models, the
cross relations decrease as the distance ratios increase. In observation, the
cross relations of the nine samples do not agree with the quad lens models very
well, nevertheless, the cross relations of the nine samples do not give obvious
evidence for anomalous flux ratio as the cusp and fold types do. Then, we
discuss several reasons for the disagreement, and expect good consistencies for
more precise observations and better lens models in the future. |
Extragalactic chemical abundances: do HII regions and young stars tell
the same story? The case of the spiral galaxy NGC 300: (Abridged) We have obtained new spectrophotometric data for 28 HII regions in
the spiral galaxy NGC 300, a member of the nearby Sculptor Group. The detection
of auroral lines, including [OIII]4363, [SIII]6312 and [NII]5755, has allowed
us to measure electron temperatures and direct chemical abundances for the
whole sample. We determine for the first time in this galaxy a radial gas-phase
oxygen abundance gradient based solely on auroral lines, and obtain the
following least-square solution: 12+log(O/H)=8.57-0.41 R/R25, where the
galactocentric distance is expressed in terms of the isophotal radius R25. The
gradient corresponds to -0.077 dex/kpc, and agrees very well with the
galactocentric trend in metallicity obtained for 29 B and A supergiants in the
same galaxy. The intercept of the regression for the nebular data virtually
coincides with the intercept obtained from the stellar data. This allows little
room for depletion of nebular oxygen onto dust grains, although in this kind of
comparison we are somewhat limited by systematic uncertainties, such as those
related to the atomic parameters used to derive the chemical compositions.
We discuss the implications of our result with regard to strong-line
abundance indicators commonly used to estimate the chemical compositions of
star-forming galaxies, such as R23. By applying a few popular calibrations of
these indices based on grids of photoionization models on the NGC 300 HII
region fluxes we find metallicities that are higher by 0.3 dex (a factor of
two) or more relative to our nebular (Te-based) and stellar ones.
We confirm a metallicity dependence of the `softness' parameter
eta=(O+/O++)/(S+/S++), in the sense that softer stellar continua are found at
high metallicity. | Spatially Resolved [FeII] 1.64 μm Emission in NGC 5135. Clues for
Understanding the Origin of the Hard X-rays in Luminous Infrared Galaxies: Spatially resolved near-IR and X-ray imaging of the central region of the
Luminous Infrared Galaxy NGC 5135 is presented. The kinematical signatures of
strong outflows are detected in the [FeII]1.64 \mu m emission line in a compact
region at 0.9 kpc from the nucleus. The derived mechanical energy release is
consistent with a supernova rate of 0.05-0.1 yr$^{-1}$. The apex of the
outflowing gas spatially coincides with the strongest [FeII] emission peak and
with the dominant component of the extranuclear hard X-ray emission. All these
features provide evidence for a plausible direct physical link between
supernova-driven outflows and the hard X-ray emitting gas in a LIRG. This
result is consistent with model predictions of starbursts concentrated in small
volumes and with high thermalization efficiencies. A single high-mass X-ray
binary (HMXB) as the major source of the hard X-ray emission although not
favoured, cannot be ruled out. Outside the AGN, the hard X-ray emission in NGC
5135 appears to be dominated by the hot ISM produced by supernova explosions in
a compact star-forming region, and not by the emission due to HMXB. If this
scenario is common to U/LIRGs, the hard X-rays would only trace the most
compact (< 100 pc) regions with high supernova and star formation densities,
therefore a lower limit to their integrated star formation. The SFR derived in
NGC 5135 based on its hard X-ray luminosity is a factor of two and four lower
than the values obtained from the 24 \mu m and soft X-ray luminosities,
respectively. |
Measuring the 3D Clustering of Undetected Galaxies Through Cross
Correlation of their Cumulative Flux Fluctuations from Multiple Spectral
Lines: We discuss a method for detecting the emission from high redshift galaxies by
cross correlating flux fluctuations from multiple spectral lines. If one can
fit and subtract away the continuum emission with a smooth function of
frequency, the remaining signal contains fluctuations of flux with frequency
and angle from line emitting galaxies. Over a particular small range of
observed frequencies, these fluctuations will originate from sources
corresponding to a series of different redshifts, one for each emission line.
It is possible to statistically isolate the fluctuations at a particular
redshift by cross correlating emission originating from the same redshift, but
in different emission lines. This technique will allow detection of clustering
fluctuations from the faintest galaxies which individually cannot be detected,
but which contribute substantially to the total signal due to their large
numbers. We describe these fluctuations quantitatively through the line cross
power spectrum. As an example of a particular application of this technique, we
calculate the signal-to-noise ratio for a measurement of the cross power
spectrum of the OI(63 micron) and OIII(52 micron) fine structure lines with the
proposed Space Infrared Telescope for Cosmology and Astrophysics. We find that
the cross power spectrum can be measured beyond a redshift of z=8. Such
observations could constrain the evolution of the metallicity, bias, and duty
cycle of faint galaxies at high redshifts and may also be sensitive to the
reionization history through its effect on the minimum mass of galaxies. As
another example, we consider the cross power spectrum of CO line emission
measured with a large ground based telescope like CCAT and 21-cm radiation
originating from hydrogen in galaxies after reionization with an interferometer
similar in scale to MWA, but optimized for post-reionization redshifts. | Exploring the constraints on cosmological models with CosmoEJS: We introduce new CosmoEJS modules to improve the investigation of the
consequences of constraints on the parameter values of cosmological models. We
use CosmoMC to fit dark energy models and modified gravity models to recent
data from the cosmic microwave background measurements of the Planck satellite,
baryon acoustic oscillations, supernovae type Ia, Hubble Parameter H(z)
measurements, and redshift space distortions. While the results are in
agreement with previous constraints for these models, here, we add an
investigation into the statistical fits with CosmoEJS, an interactive Java
package of simulations that allow the user to explore the ramifications of
choosing various values for the cosmological parameters of a particular model.
We visually inspect the plots of the simulated theoretical values for
comparisons to the observational values, calculate derived cosmological values,
and finally plot the expansion history of cosmological models. These new
simulations now include modified gravity cosmological models as well as
observations of the growth of structures of galaxies for a more accurate
description of the universe's dynamics. The latest version of CosmoEJS is
available from http://www.compadre.org/osp/items/detail.cfm?ID=12406. |
Inflation driven by particle creation: The creation of ultra-light dark particles in the late-time FLRW spacetime
provides a cosmological model in accordance with precise observational tests.
The matter creation backreaction implies in this context a vacuum energy
density scaling linearly with the Hubble parameter H, which is consistent with
the vacuum expectation value of the QCD condensate in a low-energy expanding
spacetime. Both the cosmological constant and coincidence problems are
alleviated in this scenario. We also explore the opposite, high energy limit of
the particle creation process. We show that it leads to a non-singular
primordial universe where an early inflationary era takes place, with natural
reheating and exit. The generated primordial spectrum is scale invariant and,
by supposing that inflation lasts for 60 e-folds, we obtain a scalar expectral
index n = 0.97. | Does Planck really rule out monomial inflation?: We consider the modifications of monomial chaotic inflation models due to
radiative corrections induced by inflaton couplings to bosons and/or fermions
necessary for reheating. To the lowest order, ignoring gravitational
corrections and treating the inflaton as a classical background field, they are
of the Coleman-Weinberg type and parametrized by the renormalization scale
$\mu$. In cosmology, there are not enough measurements to fix $\mu$ so that we
end up with a family of models, each having a slightly different slope of the
potential. We demonstrate by explicit calculation that within the family of
chaotic $\phi^2$ models, some may be ruled out by Planck whereas some remain
perfectly viable. In contrast, radiative corrections do not seem to help
chaotic $\phi^{4}$ models to meet the Planck constraints. |
The clustering of galaxies in the SDSS-III Baryon Oscillation
Spectroscopic Survey: single-probe measurements from CMASS anisotropic galaxy
clustering: With the largest spectroscopic galaxy survey volume drawn from the SDSS-III
Baryon Oscillation Spectroscopic Survey (BOSS), we can extract cosmological
constraints from the measurements of redshift and geometric distortions at
quasi-linear scales (e.g. above 50 $h^{-1}$Mpc). We analyze the broad-range
shape of the monopole and quadrupole correlation functions of the BOSS Data
Release 12 (DR12) CMASS galaxy sample, at the effective redshift $z=0.59$, to
obtain constraints on the Hubble expansion rate $H(z)$, the angular-diameter
distance $D_A(z)$, the normalized growth rate $f(z)\sigma_8(z)$, and the
physical matter density $\Omega_mh^2$. We obtain robust measurements by
including a polynomial as the model for the systematic errors, and find it
works very well against the systematic effects, e.g., ones induced by stars and
seeing. We provide accurate measurements $\{D_A(0.59)r_{s,fid}/r_s$ $\rm Mpc$,
$H(0.59)r_s/r_{s,fid}$ $km s^{-1} Mpc^{-1}$, $f(0.59)\sigma_8(0.59)$, $\Omega_m
h^2\}$ = $\{1427\pm26$, $97.3\pm3.3$, $0.488 \pm 0.060$, $0.135\pm0.016\}$,
where $r_s$ is the comoving sound horizon at the drag epoch and
$r_{s,fid}=147.66$ Mpc is the sound scale of the fiducial cosmology used in
this study. The parameters which are not well constrained by our galaxy
clustering analysis are marginalized over with wide flat priors. Since no
priors from other data sets, e.g., cosmic microwave background (CMB), are
adopted and no dark energy models are assumed, our results from BOSS CMASS
galaxy clustering alone may be combined with other data sets, i.e., CMB, SNe,
lensing or other galaxy clustering data to constrain the parameters of a given
cosmological model. The uncertainty on the dark energy equation of state
parameter, $w$, from CMB+CMASS is about 8 per cent. The uncertainty on the
curvature fraction, $\Omega_k$, is 0.3 per cent. We do not find deviation from
flat $\Lambda$CDM. | The Gas Consumption History to z ~ 4: Using the observations of the star formation rate and HI densities to z ~ 4,
with measurements of the Molecular Gas Depletion Rate (MGDR) and local density
of H_2 at z = 0, we derive the history of the gas consumption by star formation
to z ~ 4. We find that closed-box models in which H_2 is not replenished by HI
require improbably large increases in rho(H_2) and a decrease in the MGDR with
lookback time that is inconsistent with observations. Allowing the H_2 used in
star formation to be replenished by HI does not alleviate the problem because
observations show that there is very little evolution of rho(HI) from z = 0 to
z = 4. We show that to be consistent with observational constraints, star
formation on cosmic timescales must be fueled by intergalactic ionized gas,
which may come from either accretion of gas through cold (but ionized) flows or
from ionized gas associated with accretion of dark matter halos. We constrain
the rate at which the extraglactic ionized gas must be converted into HI and
ultimately into H_2. The ionized gas inflow rate roughly traces the SFRD: about
1 - 2 x 10^8 M_sun Gyr^-1 Mpc^-3 from z ~ 1 - 4, decreasing by about an order
of magnitude from z=1 to z=0 with details depending largely on MGDR(t). All
models considered require the volume averaged density of rho(H_2) to increase
by a factor of 1.5 - 10 to z ~ 1.5 over the currently measured value. Because
the molecular gas must reside in galaxies, it implies that galaxies at high z
must, on average, be more molecule rich than they are at the present epoch,
which is consistent with observations. These quantitative results, derived
solely from observations, agree well with cosmological simulations. |
Galaxy And Mass Assembly (GAMA): The Life and Times of L* Galaxies: In this work we investigate in detail the effects local environment (groups
and pairs) has on galaxies with stellar mass similar to the Milky-Way (L*
galaxies). A volume limited sample of 6,150 galaxies is classified to determine
emission features, morphological type and presence of a disk. This sample
allows for characteristics of galaxies to be isolated (e.g. stellar mass and
group halo mass), and their codependencies determined.
We observe that galaxy-galaxy interactions play the most important role in
shaping the evolution within a group halo, the main role of halo mass is in
gathering the galaxies together to encourage such interactions. Dominant pair
galaxies find their overall star formation enhanced when the pair's mass ratio
is close to 1, otherwise we observe the same galaxies as we would in an
unpaired system. The minor galaxy in a pair is greatly affected by its
companion galaxy, and whilst the star forming fraction is always suppressed
relative to equivalent stellar mass unpaired galaxies, it becomes lower still
when the mass ratio of a pair system increases.
We find that, in general, the close galaxy-galaxy interaction rate drops as a
function of halo mass for a given amount of stellar mass. We find evidence of a
local peak of interactions for Milky-Way stellar mass galaxies in Milky-Way
halo mass groups. Low mass halos, and in particular Local Group mass halos, are
an important environment for understanding the typical evolutionary path of a
unit of stellar mass.
We find compelling evidence for galaxy conformity in both groups and pairs,
where morphological type conformity is dominant in groups, and emission class
conformity is dominant in pairs. This suggests that group scale conformity is
the result of many galaxy encounters over an extended period of time, whilst
pair conformity is a fairly instantaneous response to a transitory interaction. | The Origin of the Hubble Sequence in Lambda-CDM Cosmology: The Galform semi-analytic model of galaxy formation is used to explore the
mechanisms primarily responsible for the three types of galaxies seen in the
local universe: bulge, bulge+disk and disk, identified with the visual
morphological types E, S0/a-Sbc, and Sc-Scd, respectively. With a suitable
choice of parameters the Galform model can accurately reproduce the observed
local K_s-band luminosity function (LF) for galaxies split by visual
morphological type. The successful set of model parameters is used to populate
the Millennium Simulation with 9.4 million galaxies and their dark matter
halos. The resulting catalogue is then used to explore the evolution of
galaxies through cosmic history. The model predictions concur with recent
observational results including the galaxy merger rate, the star formation rate
and the seemingly anti-hierarchical evolution of ellipticals. However, the
model also predicts significant evolution of the elliptical galaxy LF that is
not observed. The discrepancy raises the possibility that samples of z~1
galaxies which have been selected using colour and morphological criteria may
be contaminated with galaxies that are not actually ellipticals. |
Bogoliubov Excited States and the Lyth Bound: We show that Bogoliubov excited scalar and tensor modes do not alleviate
Planckian evolution during inflation if one assumes that $r$ and the Bogoliubov
coefficients are approximately scale invariant. We constrain the excitation
parameter for the scalar fluctuations, $\beta$, and tensor perturbations,
$\tilde{\beta}$, by requiring that there be at least three decades of scale
invariance in the scalar and tensor power spectrum. For the scalar fluctuations
this is motivated by the observed nearly scale invariant scalar power spectrum.
For the tensor fluctuations this assumption may be shown to be valid or invalid
by future experiments. | CMB temperature anisotropy at large scales induced by a causal
primordial magnetic field: We present an analytical derivation of the Sachs Wolfe effect sourced by a
primordial magnetic field. In order to consistently specify the initial
conditions, we assume that the magnetic field is generated by a causal process,
namely a first order phase transition in the early universe. As for the
topological defects case, we apply the general relativistic junction conditions
to match the perturbation variables before and after the phase transition which
generates the magnetic field, in such a way that the total energy momentum
tensor is conserved across the transition and Einstein's equations are
satisfied. We further solve the evolution equations for the metric and fluid
perturbations at large scales analytically including neutrinos, and derive the
magnetic Sachs Wolfe effect. We find that the relevant contribution to the
magnetic Sachs Wolfe effect comes from the metric perturbations at
next-to-leading order in the large scale limit. The leading order term is in
fact strongly suppressed due to the presence of free-streaming neutrinos. We
derive the neutrino compensation effect dynamically and confirm that the
magnetic Sachs Wolfe spectrum from a causal magnetic field behaves as
l(l+1)C_l^B \propto l^2 as found in the latest numerical analyses. |
Planck intermediate results. XLIII. The spectral energy distribution of
dust in clusters of galaxies: Although infrared (IR) overall dust emission from clusters of galaxies has
been statistically detected using data from the Infrared Astronomical Satellite
(IRAS), it has not been possible to sample the spectral energy distribution
(SED) of this emission over its peak, and thus to break the degeneracy between
dust temperature and mass. By complementing the IRAS spectral coverage with
Planck satellite data from 100 to 857 GHz, we provide new constraints on the IR
spectrum of thermal dust emission in clusters of galaxies. We achieve this by
using a stacking approach for a sample of several hundred objects from the
Planck cluster sample; this procedure averages out fluctuations from the IR
sky, allowing us to reach a significant detection of the faint cluster
contribution. We also use the large frequency range probed by Planck, together
with component-separation techniques, to remove the contamination from both
cosmic microwave background anisotropies and the thermal Sunyaev-Zeldovich
effect (tSZ) signal, which dominate below 353 GHz. By excluding dominant
spurious signals or systematic effects, averaged detections are reported at
frequencies between 353 and 5000 GHz. We confirm the presence of dust in
clusters of galaxies at low and intermediate redshifts, yielding an SED with a
shape similar to that of the Milky Way. Planck's beam does not allow us to
investigate the detailed spatial distribution of this emission (e.g., whether
it comes from intergalactic dust or simply the dust content of the cluster
galaxies), but the radial distribution of the emission appears to follow that
of the stacked SZ signal, and thus the extent of the clusters. The recovered
SED allows us to constrain the dust mass responsible for the signal, as well as
its temperature. We additionally explore the evolution of the IR emission as a
function of cluster mass and redshift. | Aperture corrections for disk galaxy properties derived from the CALIFA
survey. Balmer emission lines in spiral galaxies: This work investigates the effect of the aperture size on derived galaxy
properties for which we have spatially-resolved optical spectra. We focus on
some indicators of star formation activity and dust attenuation for spiral
galaxies that have been widely used in previous work on galaxy evolution. We
have used 104 spiral galaxies from the CALIFA survey for which 2D spectroscopy
with complete spatial coverage is available. From the 3D cubes we have derived
growth curves of the most conspicuous Balmer emission lines (Halpha, Hbeta) for
circular apertures of different radii centered at the galaxy's nucleus after
removing the underlying stellar continuum. We find that the Halpha flux
(f(Halpha)) growth curve follows a well defined sequence with aperture radius
showing low dispersion around the median value. From this analysis, we derive
aperture corrections for galaxies in different magnitude and redshift
intervals. Once stellar absorption is properly accounted for, the
f(Halpha)/f(Hbeta) ratio growth curve shows a smooth decline, pointing towards
the absence of differential dust attenuation as a function of radius. Aperture
corrections as a function of the radius are provided in the interval
[0.3,2.5]R_50. Finally, the Halpha equivalent width (EW(Halpha)) growth curve
increases with the size of the aperture and shows a very large dispersion for
small apertures. This large dispersion prevents the use of reliable aperture
corrections for this quantity. In addition, this result suggests that
separating star-forming and quiescent galaxies based on observed EW(Halpha)
through small apertures is likely to result in low EW(Halpha) star-forming
galaxies begin classified as quiescent. |
On the Lambda-evolution of galaxy clusters: The evolution of galaxy clusters can be affected by the repulsion described
by the cosmological constant. This conclusion is reached within the modified
weak-field General Relativity approach where the cosmological constant \Lambda
enables to describe the common nature of the dark matter and the dark energy.
Geometrical methods of theory of dynamical systems and the Ricci curvature
criterion are used to reveal the difference in the instability properties of
galaxy clusters which determine their evolutionary paths. Namely, it is shown
that the clusters determined by the gravity with \Lambda-repulsion tend to
become even more unstable than those powered only by Newtonian gravity, the
effect to be felt at cosmological time scales. | Bimodal Formation Time Distribution for Infall Dark Matter Halos: We use a 200 $h^{-1}Mpc$ a side N-body simulation to study the mass accretion
history (MAH) of dark matter halos to be accreted by larger halos, which we
call infall halos. We define a quantity $a_{\rm nf}\equiv (1+z_{\rm
f})/(1+z_{\rm peak})$ to characterize the MAH of infall halos, where $z_{\rm
peak}$ and $z_{\rm f}$ are the accretion and formation redshifts, respectively.
We find that, at given $z_{\rm peak}$, their MAH is bimodal. Infall halos are
dominated by a young population at high redshift and by an old population at
low redshift. For the young population, the $a_{\rm nf}$ distribution is narrow
and peaks at about $1.2$, independent of $z_{\rm peak}$, while for the old
population, the peak position and width of the $a_{\rm nf}$ distribution both
increases with decreasing $z_{\rm peak}$ and are both larger than those of the
young population. This bimodal distribution is found to be closely connected to
the two phases in the MAHs of halos. While members of the young population are
still in the fast accretion phase at $z_{\rm peak}$, those of the old
population have already entered the slow accretion phase at $z_{\rm peak}$.
This bimodal distribution is not found for the whole halo population, nor is it
seen in halo merger trees generated with the extended Press-Schechter
formalism. The infall halo population at $z_{\rm peak}$ are, on average,
younger than the whole halo population of similar masses identified at the same
redshift. We discuss the implications of our findings in connection to the
bimodal color distribution of observed galaxies and to the link between central
and satellite galaxies. |
The effects of halo alignment and shape on the clustering of galaxies: We investigate the effects of halo shape and its alignment with larger scale
structure on the galaxy correlation function. We base our analysis on the
galaxy formation models of Guo et al., run on the Millennium Simulations. We
quantify the importance of these effects by randomizing the angular positions
of satellite galaxies within haloes, either coherently or individually, while
keeping the distance to their respective central galaxies fixed. We find that
the effect of disrupting the alignment with larger scale structure is a ~2 per
cent decrease in the galaxy correlation function around r=1.8 Mpc/h. We find
that sphericalizing the ellipsoidal distributions of galaxies within haloes
decreases the correlation function by up to 20 per cent for r<1 Mpc/h and
increases it slightly at somewhat larger radii. Similar results apply to power
spectra and redshift-space correlation functions. Models based on the Halo
Occupation Distribution, which place galaxies spherically within haloes
according to a mean radial profile, will therefore significantly underestimate
the clustering on sub-Mpc scales. In addition, we find that halo assembly bias,
in particular the dependence of clustering on halo shape, propagates to the
clustering of galaxies. We predict that this aspect of assembly bias should be
observable through the use of extensive group catalogues. | Constraining blazar distances with combined Fermi and TeV data: an
empirical approach: We discuss a method to constrain the distance of blazars with unknown
redshift using combined observations in the GeV and TeV regimes. We assume that
the VHE spectrum corrected for the absorption through the interaction with the
Extragalactic Background Light can not be harder than the spectrum in the
Fermi/LAT band. Starting from the observed VHE spectral data we derive the
EBL-corrected spectra as a function of the redshift z and fit them with power
laws to be compared with power law fits to the LAT data. We apply the method to
all TeV blazars detected by LAT with known distance and derive an empirical law
describing the relation between the upper limits and the true redshifts that
can be used to estimate the distance of unknown redshift blazars. Using
different EBL models leads to systematic changes in the derived upper limits.
Finally, we use this relation to infer the distance of the unknown redshift
blazar PKS 1424+240. |
Contribution of Lensed SCUBA Galaxies to the Cosmic Infrared Background: The surface density of submillimeter (sub-mm) galaxies as a function of flux,
usually termed the source number counts, constrains models of the evolution of
the density and luminosity of starburst galaxies. At the faint end of the
distribution, direct detection and counting of galaxies are not possible.
However, gravitational lensing by clusters of galaxies allows detection of
sources which would otherwise be too dim to study. We have used the largest
catalog of sub-mm-selected sources along the line of sight to galaxy clusters
to estimate the faint end of the 850 micron number counts; integrating to S =
0.10 mJy the equivalent flux density at 850 microns is v I_{v} = 0.24 +/- 0.03
nW/m^2/sr. This provides a lower limit to the extragalactic far-infrared
background and is consistent with direct estimates of the full intensity from
the FIRAS. The results presented here can help to guide strategies for upcoming
surveys carried out with single dish sub-mm instruments. | GOODS-Herschel: Separating High Redshift active galactic Nuclei and star
forming galaxies Using Infrared Color Diagnostics: We have compiled a large sample of 151 high redshift (z=0.5-4) galaxies
selected at 24 microns (S24>100 uJy) in the GOODS-N and ECDFS fields for which
we have deep Spitzer IRS spectroscopy, allowing us to decompose the
mid-infrared spectrum into contributions from star formation and activity in
the galactic nuclei. In addition, we have a wealth of photometric data from
Spitzer IRAC/MIPS and Herschel PACS/SPIRE. We explore how effective different
infrared color combinations are at separating our mid-IR spectroscopically
determined active galactic nuclei from our star forming galaxies. We look in
depth at existing IRAC color diagnostics, and we explore new color-color
diagnostics combining mid-IR, far-IR, and near-IR photometry, since these
combinations provide the most detail about the shape of a source's IR spectrum.
An added benefit of using a color that combines far-IR and mid-IR photometry is
that it is indicative of the power source driving the IR luminosity. For our
data set, the optimal color selections are S250/S24 vs. S8.0/S3.6 and S100/S24
vs. S8.0/S3.6; both diagnostics have ~10% contamination rate in the regions
occupied primarily by star forming galaxies and active galactic nuclei,
respectively. Based on the low contamination rate, these two new IR color-color
diagnostics are ideal for estimating both the mid-IR power source of a galaxy
when spectroscopy is unavailable and the dominant power source contributing to
the IR luminosity. In the absence of far-IR data, we present color diagnostics
using the WISE mid-IR bands which can efficiently select out high z (z~2) star
forming galaxies. |
Dense Molecular Gas Excitation in Nuclear Starbursts at High Redshift:
HCN, HNC, and HCO+(J=6-5) Emission in the z=3.91 Quasar Host of APM08279+5255: We report the detection of surprisingly strong HCN, HNC, and HCO+(J=6-5)
emission in the host galaxy of the z=3.91 quasar APM08279+5255 through
observations with CARMA. HCN, HNC, and HCO+ are typically used as star
formation indicators, tracing dense molecular hydrogen gas [n(H2) > 10^5,cm^-3]
within star-forming molecular clouds. However, the strength of their respective
line emission in the J=6-5 transitions in APM08279+5255 is extremely high,
suggesting that they are excited by another mechanism besides collisions in the
dense molecular gas phase alone. We derive J=6-5 line luminosities of
L'(HCN)=(4.9+/-0.6), L'(HNC)=(2.4+/-0.7), and L'(HCO+)=(3.0+/-0.6)x10^10
(mu_L)^-1 K km/s pc^2 (where mu_L is the lensing magnification factor),
corresponding to L' ratios of ~0.23-0.46 relative to CO(J=1-0). Such high line
ratios would be unusual even in the respective ground-state (J=1-0)
transitions, and indicate exceptional, collisionally and radiatively driven
excitation conditions in the dense, star-forming molecular gas in
APM08279+5255. Through an expansion of our previous modeling of the HCN line
excitation in this source, we show that the high rotational line fluxes are
caused by substantial infrared pumping at moderate opacities in a ~220K warm
gas and dust component. This implies that standard M_dense/L' conversion
factors would substantially overpredict the dense molecular gas mass M_dense.
We also find a HCN J=6-5/5-4 L' ratio greater than 1 (1.36+/-0.31) - however,
our models show that the excitation is likely not `super-thermal', but that the
high line ratio is due to a rising optical depth between both transitions.
These findings are consistent with the picture that the bulk of the gas and
dust in this source is situated in a compact, nuclear starburst, where both the
highly active galactic nucleus and star formation contribute to the heating. | A divergence-free parametrization for dynamical dark energy: We introduce a new parametrization for the dark energy, led by the same idea
to the linear expansion of the equation of state in scale factor $a$ and in
redshift $z$, which diverges neither in the past nor future and contains the
same number of degrees of freedom with the former two. We present constraints
of the cosmological parameters using the most updated baryon acoustic
oscillation (BAO) measurements along with cosmic microwave background (CMB)
data and a recent reanalysis of Type Ia supernova (SN) data. This new
parametrization allowed us to carry out successive observational analyses by
decreasing its degrees of freedom systematically until ending up with a
dynamical dark energy model that has the same number of parameters with
$\Lambda$CDM. We found that the dark energy source with a dynamical equation of
state parameter equal $-2/3$ at the early universe and $-1$ today fits the data
slightly better than $\Lambda$. |
Galaxy Velocity Bias in Cosmological Simulations: Towards Percent-level
Calibration: Galaxy cluster masses, rich with cosmological information, can be estimated
from internal dark matter (DM) velocity dispersions, which in turn can be
observationally inferred from satellite galaxy velocities. However, galaxies
are biased tracers of the DM, and the bias can vary over host halo and galaxy
properties as well as time. We precisely calibrate the velocity bias, b_v --
defined as the ratio of galaxy and DM velocity dispersions -- as a function of
redshift, host halo mass, and galaxy stellar mass threshold (Mstarsat), for
massive halos (M200c > 1e13.5 msun) from five cosmological simulations:
IllustrisTNG, Magneticum, Bahamas + Macsis, The Three Hundred Project, and
MultiDark Planck-2. We first compare scaling relations for galaxy and DM
velocity dispersion across simulations; the former is estimated using a new
ensemble velocity likelihood method that is unbiased for low galaxy counts per
halo, while the latter uses a local linear regression. The simulations show
consistent trends of b_v increasing with M200c and decreasing with redshift and
Mstarsat. The ensemble-estimated theoretical uncertainty in b_v is 2-3% but
becomes percent-level when considering only the three highest resolution
simulations. We update the mass-richness normalization previously estimated by
Farahi et al. (2016) for an SDSS redMaPPer cluster sample. The improved
accuracy of our b_v estimates reduces the mass normalization uncertainty from
22% to 8%, demonstrating that dynamical estimation techniques can be
competitive with weak lensing in calibrating population mean masses. We discuss
necessary steps for further improving this precision. Our estimates for
b_v(M200c, Mstarsat, z) are made publicly available. | Dark matter-rich early-type galaxies in the CASSOWARY 5 strong lensing
system: We study the strong gravitational lensing system number 5 identified by the
CASSOWARY survey. In this system, a source at redshift 1.069 is lensed into
four detected images by two early-type galaxies at redshift 0.388. The observed
positions of the multiple images are well reproduced by a model in which the
total mass distribution of the deflector is described in terms of two singular
isothermal sphere profiles. By modelling the lens galaxy spectral energy
distributions, we measure the lens luminous masses and stellar mass-to-light
ratios. These values are used to disentangle the luminous and dark matter
components in the vicinity of the multiple images. We estimate that the dark
over total mass ratio projected within a cylinder centred on the primary lens
and with a radius of 12.6 kpc is 0.8 +/- 0.1. We contrast these measurements
with the typical values found at similar distances (in units of the effective
radius) in isolated lens galaxies and show that the amount of dark matter
present in these lens galaxies is almost a factor four larger than in field
lens galaxies with comparable luminous masses. Data and models are therefore
consistent with interpreting the lens of this system as a galaxy group. We
infer that the overdense environment and dark matter concentration in these
galaxies must have affected the assembly of the lens luminous mass components.
We conclude that further multi-diagnostics analyses on the internal properties
of galaxy groups have the potential of providing us a unique insight into the
complex baryonic and dark-matter physics interplay that rules the formation of
cosmological structures. |
Star Formation Rate Indicators: What else can be said about star formation rate indicators that has not been
said already many times over? The `coming of age' of large ground-based surveys
and the unprecedented sensitivity, angular resolution and/or field-of-view of
infrared and ultraviolet space missions have provided extensive, homogeneous
data on both nearby and distant galaxies, which have been used to further our
understanding of the strengths and pitfalls of many common star formation rate
indicators. The synergy between these surveys has also enabled the calibration
of indicators for use on scales that are comparable to those of star-forming
regions, thus much smaller than an entire galaxy. These are being used to
investigate star formation processes at the sub-galactic scale. I review
progress in the field over the past decade or so. | Tomographic weak lensing shear spectra from large N-body and
hydrodynamical simulations: Forthcoming experiments will enable us to determine tomographic shear spectra
at a high precision level. Most predictions about them have until now been
biased on algorithms yielding the expected linear and non-linear spectrum of
density fluctuations. Even when simulations have been used, so-called Halofit
(Smith et al 2003) predictions on fairly large scales have been needed. We wish
to go beyond this limitation. We perform N-body and hydrodynamical simulations
within a sufficiently large cosmological volume to allow a direct connection
between simulations and linear spectra. While covering large length-scales, the
simulation resolution is good enough to allow us to explore the high-l
harmonics of the cosmic shear (up to l ~ 50000), well into the domain where
baryon physics becomes important. We then compare shear spectra in the absence
and in presence of various kinds of baryon physics, such as radiative cooling,
star formation, and supernova feedback in the form of galactic winds. We
distinguish several typical properties of matter fluctuation spectra in the
different simulations and test their impact on shear spectra. We compare our
outputs with those obtainable using approximate expressions for non--linear
spectra, and identify substantial discrepancies even between our results and
those of purely N-body results. Our simulations and the treatment of their
outputs however enable us, for the first time, to obtain shear results taht are
fully independent of any approximate expression, also in the high-l range,
where we need to incorporate a non-linear power spectrum of density
perturbations, and the effects of baryon physics. This will allow us to fully
exploit the cosmological information contained in future high--sensitivity
cosmic shear surveys, exploring the physics of cosmic shears via weak lensing
measurements. |
Comment on "Multiscatter stellar capture of dark matter": Bramante, Delgado, and Martin [Phys. Rev. D96, 063002(2017)., hereafter
BDM17] extended the analytical formalism of dark matter (DM) capture in a very
important way, which allows, in principle, the use of compact astrophysical
objects, such as neutron stars (NS), as dark matter detectors. In this comment,
we point out the existence of a region in the dark matter neutron scattering
cross section $(\sigma_{nX})$ vs. dark matter mass $(m_{X})$ where the
constraining power of this method is lost. This corresponds to a maximal
temperature ($T_{crit}$) the NS has to have, in order to serve as a dark matter
detector. In addition, we point out several typos and errors in BDM17 that do
not affect drastically their conclusions. Moreover, we provide semi-analytical
approximations for the total capture rates of dark matter particle of arbitrary
mass for various limiting regimes. Those analytical approximations are used to
validate our numerical results. | Probing Axion-like Particles via CMB Polarization: Axion-like particles (ALPs) rotate the linear polarization of photons through
the ALP-photon coupling and convert the cosmic microwave background (CMB)
$E$-mode to the $B$-mode. We derive the relation between the ALP dynamics and
the rotation angle by assuming that the ALP $\phi$ has a quadratic potential,
$V=m^2\phi^2/2$. We compute the current and future sensitivities of CMB
observations to the ALP-photon coupling $g$, which can reach $g=4\times
10^{-21}\,\mathrm{GeV}^{-1}$ for $10^{-32}\,\mathrm{eV}\lesssim m\lesssim
10^{-28}\,\mathrm{eV}$ and extensively exceed the other searches for any mass
$m\lesssim 10^{-25}\,\mathrm{eV}$. We find that the fluctuation of the ALP
field at the observer, which has been neglected in previous studies, can induce
significant isotropic rotation of the CMB polarization. The measurements of
isotropic and anisotropic rotation allow us to put bounds on relevant
quantities such as the ALP mass $m$ and the ALP density parameter
$\Omega_\phi$. In particular, if LiteBIRD detects anisotropic rotation, we
obtain the lower bound on the tensor-to-scalar ratio as $r > 5 \times 10^{-9}$. |
Inflationary Super-Hubble Waves and the Size of the Universe: The effect of the scalar spectral index on inflationary super-Hubble waves is
to amplify/damp large wavelengths according to whether the spectrum is red
($n_{s}<1$) or blue ($n_{s}>1$). As a consequence, the large-scale temperature
correlation function will unavoidably change sign at some angle if our spectrum
is red, while it will always be positive if it is blue. We show that this
inflationary filtering property also affects our estimates of the size of the
homogeneous patch of the universe through the Grishchuk-Zel'dovich effect.
Using the recent quadrupole measurement of ESA's Planck mission, we find that
the homogeneous patch of universe is at least 87 times bigger than our visible
universe if we accept Planck's best fit value $n_{s}=0.9624$. An independent
estimation of the size of the universe could be used to independently constrain
$n_{s}$, thus narrowing the space of inflationary models. | Dust, Gas, and Metallicities of Cosmologically Distant Lens Galaxies: We homogeneously analyzed the \chandra\ X-ray observations of 10
gravitational lenses, HE 0047-1756, QJ 0158-4325, SDSS 0246-0805, HE 0435-1223,
SDSS 0924+0219, SDSS 1004+4112, HE 1104-1805, PG 1115+080, Q 1355-2257, and Q
2237+0305, to measure the differential X-ray absorption between images, the
metallicity, and the dust-to-gas ratio of the lens galaxies. We detected
differential absorption in all lenses except SDSS 0924+0219 and HE 1104-1805.
This doubles the sample of dust-to-gas ratio measurements in cosmologically
distant lens galaxies. We successfully measured the gas phase metallicity of
three lenses, Q 2237+0305, SDSS 1004+4112, and B 1152+199 from the X-ray
spectra. Our results suggest a linear correlation between metallicity and
dust-to-gas ratio (i.e., a constant metal-to-dust ratio), consistent with what
is found for nearby galaxies. We obtain an average dust-to-gas ratio
$E(B-V)/N_H=1.17^{+0.41}_{-0.31} \times 10^{-22}\rm mag\,cm^2\,atom^{-1}$ in
the lens galaxies, with an intrinsic scatter of $\rm0.3\,dex$. Combining these
results with data from GRB afterglows and quasar foreground absorbers, we found
a mean dust-to-gas ratio $\mdtg,$ now significantly lower than the average
Galactic value, $1.7\,\times 10^{-22}\,\rm mag\, cm^{2}\, atoms^{-1}.$ This
suggests evolution of dust-to-gas ratios with redshift and lower average
metallicities for the higher redshift galaxies, consistent with current metal
and dust evolution models of interstellar medium. The slow evolution in the
metal-to-dust ratio with redshift implies very rapid dust formation in high
redshift ($z>2$) galaxies. |
The Herschel Virgo Cluster Survey: II. Truncated dust disks in
HI-deficient spirals: By combining Herschel-SPIRE observations obtained as part of the Herschel
Virgo Cluster Survey with 21 cm HI data from the literature, we investigate the
role of the cluster environment on the dust content of Virgo spiral galaxies.We
show for the first time that the extent of the dust disk is significantly
reduced in HI-deficient galaxies, following remarkably well the observed
'truncation' of the HI disk. The ratio of the submillimetre-to- optical
diameter correlates with the HI-deficiency, suggesting that the cluster
environment is able to strip dust as well as gas. These results provide
important insights not only into the evolution of cluster galaxies but also
into the metal enrichment of the intra-cluster medium. | Lensing power spectrum of the Cosmic Microwave Background with deep
polarization experiments: Precise reconstruction of the cosmic microwave background lensing potential
can be achieved with deep polarization surveys by iteratively removing
lensing-induced $B$ modes. We introduce a lensing spectrum estimator and its
likelihood for such optimal iterative reconstruction. Our modelling share
similarities to the state-of-the-art likelihoods for quadratic estimator-based
(QE) lensing reconstruction. In particular, we generalize the $N_L^{(0)}$ and
$N_L^{(1)}$ lensing biases, and design a realization-dependent spectrum
debiaser, making this estimator robust to uncertainties in the data modelling.
We demonstrate unbiased recovery of the cosmology using map-based
reconstructions, focussing on lensing-only cosmological constraints and
neutrino mass measurement in combination with CMB spectra and acoustic
oscillation data. We find this spectrum estimator is essentially optimal and
with a diagonal covariance matrix. For a CMB-S4 survey, this likelihood can
double the constraints on the lensing amplitude compared to the QE on a wide
range of scales, while at the same time keeping numerical cost under control
and being robust to errors. |
Cosmological viability of massive gravity with generalized matter
coupling: There is a no-go theorem forbidding flat and closed FLRW solutions in massive
gravity on a flat reference metric, while open solutions are unstable. Recently
it was shown that this no-go theorem can be overcome if at least some matter
couples to a hybrid metric composed of both the dynamical and the fixed
reference metric. We show that this is not compatible with the standard
description of cosmological sources in terms of effective perfect fluids, and
the predictions of the theory become sensitive either to the detailed
field-theoretical modelling of the matter content or to the presence of
additional dark degrees of freedom. This is a serious practical complication.
Furthermore, we demonstrate that viable cosmological background evolution with
a perfect fluid appears to require the presence of fields with highly contrived
properties. This could be improved if the equivalence principle is broken by
coupling only some of the fields to the composite metric, but viable
self-accelerating solutions due only to the massive graviton are difficult to
obtain. | Cosmological Tests of Gravity: Modifications of general relativity provide an alternative explanation to
dark energy for the observed acceleration of the universe. We review recent
developments in modified gravity theories, focusing on higher dimensional
approaches and chameleon/f(R) theories. We classify these models in terms of
the screening mechanisms that enable such theories to approach general
relativity on small scales (and thus satisfy solar system constraints). We
describe general features of the modified Friedman equation in such theories.
The second half of this review describes experimental tests of gravity in
light of the new theoretical approaches. We summarize the high precision tests
of gravity on laboratory and solar system scales. We describe in some detail
tests on astrophysical scales ranging from ~kpc (galaxy scales) to ~Gpc
(large-scale structure). These tests rely on the growth and inter-relationship
of perturbations in the metric potentials, density and velocity fields which
can be measured using gravitational lensing, galaxy cluster abundances, galaxy
clustering and the Integrated Sachs-Wolfe effect. A robust way to interpret
observations is by constraining effective parameters, such as the ratio of the
two metric potentials. Currently tests of gravity on astrophysical scales are
in the early stages --- we summarize these tests and discuss the interesting
prospects for new tests in the coming decade. |
Radio observations of Planck clusters: Recently, a number of new galaxy clusters have been detected by the
ESA-Planck satellite, the South Pole Telescope and the Atacama Cosmology
Telescope using the Sunyaev-Zeldovich effect. Several of the newly detected
clusters are massive, merging systems with disturbed morphology in the X-ray
surface brightness. Diffuse radio sources in clusters, called giant radio halos
and relics, are direct probes of cosmic rays and magnetic fields in the
intra-cluster medium. These radio sources are found to occur mainly in massive
merging clusters. Thus, the new SZ-discovered clusters are good candidates to
search for new radio halos and relics. We have initiated radio observations of
the clusters detected by Planck with the Giant Metrewave Radio Telescope. These
observations have already led to the detection of a radio halo in
PLCKG171.9-40.7, the first giant halo discovered in one of the new Planck
clusters. | Gravity heats the Universe: Structure in the Universe grew through gravitational instability from very
smooth initial conditions. Energy conservation requires that the growing
negative potential energy of these structures is balanced by an increase in
kinetic energy. A fraction of this is converted into heat in the collisional
gas of the intergalactic medium. Using a toy model of gravitational heating we
attempt to link the growth of structure in the Universe and the average
temperature of this gas. We find that the gas is rapidly heated from collapsing
structures at around $z {\sim} 10$, reaching a temperature ${>} 10^6$K today,
depending on some assumptions of our simplified model. Before that there was a
cold era from $z\sim100$ to $\sim10$ in which the matter temperature is below
that of the Cosmic Microwave Background. |
The Knotted Sky I: Planck constraints on the primordial power spectrum: Using the temperature data from Planck we search for departures from a
power-law primordial power spectrum, employing Bayesian model-selection and
posterior probabilities. We parametrize the spectrum with $n$ knots located at
arbitrary values of $\log{k}$, with both linear and cubic splines. This
formulation recovers both slow modulations and sharp transitions in the
primordial spectrum. The power spectrum is well-fit by a featureless, power-law
at wavenumbers $k>10^{-3} \, \mathrm{Mpc}^{-1}$. A modulated primordial
spectrum yields a better fit relative to $\Lambda$CDM at large scales, but
there is no strong evidence for a departure from a power-law spectrum.
Moreover, using simulated maps we show that a local feature at $k \sim 10^{-3}
\, \mathrm{Mpc}^{-1}$ can mimic the suppression of large-scale power. With
multi-knot spectra we see only small changes in the posterior distributions for
the other free parameters in the standard $\Lambda$CDM universe. Lastly, we
investigate whether the hemispherical power asymmetry is explained by
independent features in the primordial power spectrum in each ecliptic
hemisphere, but find no significant differences between them. | MUSTANG High Angular Resolution Sunyaev-Zel'dovich Effect Imaging of
Sub-Structure in Four Galaxy Clusters: We present 10" to 18" images of four massive clusters of galaxies through the
Sunyaev-Zel'dovich Effect (SZE). These measurements, made at 90~GHz with the
MUSTANG receiver on the Green Bank Telescope (GBT), reveal pressure
sub-structure to the intra-cluster medium (ICM) in three of the four systems.
We identify the likely presence of a previously unknown weak shock-front in
MACS0744+3927. By fitting the Rankine-Hugoniot density jump conditions in a
complementary SZE/X-ray analysis, we infer a Mach number of M =
1.2^{+0.2}_{-0.2} and a shock-velocity of 1827^{+267}_{-195}~km/s. In
RXJ1347-1145, we present a new reduction of previously reported data and
confirm the presence of a south-east SZE enhancement with a significance of
13.9 sigma when smoothed to 18" resolution. This too is likely caused by
shock-heated gas produced in a recent merger. In our highest redshift system,
CL1226+3332, we detect sub-structure at a peak significance of 4.6 sigma in the
form of a ridge oriented orthogonally to the vector connecting the main mass
peak and a sub-clump revealed by weak lensing. We also conclude that the gas
distribution is elongated in a south-west direction, consistent with a
previously proposed merger scenario. The SZE image of the cool core cluster
Abell 1835 is, in contrast, consistent with azimuthally symmetric signal only.
This pilot study demonstrates the potential of high-resolution SZE images to
complement X-ray data and probe the dynamics of galaxy clusters |
Precision cosmology and the stiff-amplified gravitational-wave
background from inflation: NANOGrav, Advanced LIGO-Virgo and the Hubble
tension: The recent NANOGrav finding of a common-spectrum process has invited
interpretations as possible evidence of a primordial stochastic
gravitational-wave background (SGWB) stronger than predicted by standard
inflation+LCDM. Such an SGWB would contribute an extra radiation component to
the background Universe which may affect its expansion history. As such, it may
help alleviate the current Hubble tension, a novel connection between
gravitational waves and cosmology. We demonstrate this by considering a
cosmological model, the "standard inflation + stiff amplification" scenario,
with two components added to the LCDM model: a stiff component (w=1) and the
primordial SGWB. Previously, we showed that even for standard inflation, the
SGWB may be detectable at the high frequencies probed by laser interferometers,
if it is amplified by a possible early stiff era after reheating. Models that
boost the SGWB enough to cause significant backreaction, however, must still
preserve the well-measured radiation-matter equality, as precision cosmology
demands. For that, we calculate the fully-coupled evolution of the SGWB and
expansion history, sampling parameter space (tensor-to-scalar ratio, reheating
temperature and temperature at stiff-to-radiation equality). We then perform a
joint analysis of the NANOGrav results and latest upper bounds from Planck, big
bang nucleosynthesis and Advanced LIGO-Virgo, to constrain the model. The
resulting blue-tilted, stiff-amplified SGWB is still too small to explain the
NANOGrav results. However, if someday, Advanced LIGO-Virgo detects the SGWB,
our model can explain it within standard inflation (without requiring an
initial blue tilt). Meanwhile, this model may bring current high-z measurements
of the Hubble constant within 3.4 sigma of the low-z measurements by SH0ES
(from 4.4 sigma) and within 2.6 sigma of those by H0LiCOW (from 3.1 sigma),
reducing the tension. | The inner structure of very massive elliptical galaxies: implications
for the inside-out formation mechanism of z~2 galaxies: We analyze a sample of 23 supermassive elliptical galaxies (central velocity
dispersion larger than 330 km s-1), drawn from the SDSS. For each object, we
estimate the dynamical mass from the light profile and central velocity
dispersion, and compare it with the stellar mass derived from stellar
population models. We show that these galaxies are dominated by luminous matter
within the radius for which the velocity dispersion is measured. We find that
the sizes and stellar masses are tightly correlated, with Re ~ M*^{1.1}$,
making the mean density within the de Vaucouleurs radius a steeply declining
function of M*: rho_e ~ M*^{-2.2}. These scalings are easily derived from the
virial theorem if one recalls that this sample has essentially fixed (but
large) sigma_0. In contrast, the mean density within 1 kpc is almost
independent of M*, at a value that is in good agreement with recent studies of
z ~ 2 galaxies. The fact that the mass within 1 kpc has remained approximately
unchanged suggests assembly histories that were dominated by minor mergers --
but we discuss why this is not the unique way to achieve this. Moreover, the
total stellar mass of the objects in our sample is typically a factor of ~ 5
larger than that in the high redshift (z ~ 2) sample, an amount which seems
difficult to achieve. If our galaxies are the evolved objects of the recent
high redshift studies, then we suggest that major mergers were required at z >
1.5, and that minor mergers become the dominant growth mechanism for massive
galaxies at z < 1.5. |
Searching for the earliest galaxies in the 21 cm forest: We use a model developed by Xu et al. (2010) to compute the 21 cm line
absorption signatures imprinted by star-forming dwarf galaxies (DGs) and
starless minihalos (MHs). The method, based on a statistical comparison of the
equivalent width (W_\nu) distribution and flux correlation function, allows us
to derive a simple selection criteria for candidate DGs at very high (z >= 8)
redshift. We find that ~ 18% of the total number of DGs along a line of sight
to a target radio source (GRB or quasar) can be identified by the condition
W_\nu < 0; these objects correspond to the high-mass tail of the DG
distribution at high redshift, and are embedded in large HII regions. The
criterion W_\nu > 0.37 kHz instead selects ~ 11% of MHs. Selected candidate DGs
could later be re-observed in the near-IR by the JWST with high efficiency,
thus providing a direct probe of the most likely reionization sources. | Metallicity Diagnostics with Infrared Fine-Structure Lines: Although measuring the gas metallicity in galaxies at various redshifts is
crucial to constrain galaxy evolutionary scenarios, only rest-frame optical
emission lines have been generally used to measure the metallicity. This has
prevented us to accurately measure the metallicity of dust-obscured galaxies,
and accordingly to understand the chemical evolution of dusty populations, such
as ultraluminous infrared galaxies. Here we propose diagnostics of the gas
metallicity based on infrared fine structure emission lines, which are nearly
unaffected by dust extinction even the most obscured systems. Specifically, we
focus on fine-structure lines arising mostly from HII regions, not in
photo-dissociation regions, to minimize the dependence and uncertainties of the
metallicity diagnostics from various physical parameters. Based on
photoionization models, we show that the emission-line flux ratio of
([OIII]51.80+[OIII]88.33)/[NIII]57.21 is an excellent tracer of the gas
metallicity. The individual line ratios [OIII]51.80/[NIII]57.21 or
[OIII]88.33/[NIII]57.21 can also be used as diagnostics of the metallicity, but
they suffer a stronger dependence on the gas density. The line ratios
[OIII]88.33/[OIII]51.80 and [NII]121.7/[NIII]57.21 can be used to measure and,
therefore, account for the dependences on the of the gas density and ionization
parameter, respectively. We show that these diagnostic fine-structure lines are
detectable with Herschel in luminous infrared galaxies out z=0.4. Metallicity
measurements with these fine-structure lines will be feasible at relatively
high redshift (z=1 or more) with SPICA, the future infrared space observatory. |
The Optical and Ultraviolet Emission-Line Properties of Bright Quasars
with Detailed Spectral Energy Distributions: We present measurements and statistical properties of the optical and
ultraviolet emission lines present in the spectra of 85 bright quasars which
have detailed spectral energy distributions. This heterogeneous sample has
redshifts up to z=1.5 and is comprised of three subsamples that may be of
particular utility: ultraviolet excess Palomar-Green quasars, quasars with
far-ultraviolet coverage from FUSE, and radio-loud quasars selected to have
similar extended radio luminosity originally selected for orientation studies.
Most of the objects have quasi-simultaneous optical-ultraviolet spectra, with
significant coverage in the radio-to-X-ray wavebands. The parameters of all
strong emission lines are measured by detailed spectral fitting. Many
significant correlations previously found among quasar emission-line properties
are also present in this sample, e.g., the Baldwin effect, the optical
correlations collectively known as eigenvector 1, and others. Finally, we use
our measurements plus scaling relationships to estimate black hole masses and
Eddington fractions. We show the mass estimates from different emission lines
are usually in agreement within a factor of 2, but nearly a third show larger
differences. We suggest using multiple mass scaling relationships to estimate
black hole masses when possible, and adopting a median of the estimates as the
black hole mass for individual objects. Line measurements and derived AGN
properties will be used for future studies examining the relationships among
quasar emission lines and their spectral energy distributions. | Footprint of Two-Form Field: Statistical Anisotropy in Primordial
Gravitational Waves: We study the observational signatures of two-form field in the inflationary
cosmology. In our setup a two-form field is kinetically coupled to a spectator
scalar field and generates sizable gravitational waves and smaller curvature
perturbation. We find that the sourced gravitational waves have a distinct
signature: they are always statistically anisotropic and their spherical
moments are non-zero for hexadecapole and tetrahexacontapole, while the
quadrupole moment vanishes. Since their amplitude can reach
$\mathcal{O}(10^{-3})$ in the tensor-to-scalar ratio, we expect this novel
prediction will be tested in the next generation of the CMB experiments. |
Tensor to scalar ratio from single field magnetogenesis: The tensor to scalar ratio is affected by the evolution of the large-scale
gauge fields potentially amplified during an inflationary stage of expansion.
After deriving the exact evolution equations for the scalar and tensor modes of
the geometry in the presence of dynamical gauge fields, it is shown that the
tensor to scalar ratio is bounded from below by the dominance of the adiabatic
contribution and it cannot be smaller than one thousands whenever the
magnetogenesis is driven by a single inflaton field. | Clustering at 74 MHz: In order to construct accurate point sources simulations at the frequencies
relevant to 21 cm experiments, the angular correlation of radio sources must be
taken into account. Using the 74 MHz VLSS survey, we measured the angular
2-point correlation function, w(\theta). We obtain the first measurement of
clustering at the low frequencies relevant to 21 cm tomography. We find that a
single power law with shape w(\theta) = A \theta^{-\gamma} fits well the data.
For a galactic cut of 10 degrees, with a data cut of \delta less than -10
degrees, and a flux limit of S = 770 mJy, we obtain a slope of \gamma = (-1.2
+/- 0.35). This value of \gamma is consistent with that measured from other
radio catalogues at the millimeter wavelengths. The amplitude of clustering has
a length of 0.2 degrees - 0.6 degrees, and it is independent of the
flux-density threshold. |
On astrophysical explanations due to cosmological inhomogeneities for
the observational acceleration: We review various cosmological models with a local underdense region (local
void) and the averaged models with the backreaction of inhomogeneities, which
have been proposed to explain (without assuming a positive cosmological
constant) the observed accelerating behaviors appearing in the
magnitude-redshift relation of SNIa. To clarify their reality, we consider
their consistency with the other observational studies such as CMB temperature
anisotropy, baryon acoustic oscillation, kinematic Sunyaev-Zeldovich effect,
and so on. It is found as a result that many inhomogeneous models seem to be
ruled out and only models with the parametrs in the narrow range remain to be
examined, and that, unless we assume very high amplitudes of perturbations or
gravitational energies, the averaged models cannot have the accelerated
expansion and the fitted effective Lambda has not the value necessary for the
observed acceleration. | Testing Large-Scale Structure Measurements Against Fisher Matrix
Predictions: We compare Baryonic Acoustic Oscillation (BAO) and Redshift Space Distortion
(RSD) measurements from recent galaxy surveys with their Fisher matrix based
predictions. Measurements of the position of the BAO signal lead to constraints
on the comoving angular diameter distance $D_{M}$ and the Hubble distance
$D_{H}$ that agree well with their Fisher matrix based expectations. However,
RSD-based measurements of the growth rate $f \sigma_{8}$ do not agree with the
predictions made before the surveys were undertaken, even when repeating those
predictions using the actual survey parameters. We show that this is due to a
combination of effects including degeneracies with the geometric parameters
$D_{M}$ and $D_{H}$, and optimistic assumptions about the scale to which the
linear signal can be extracted. We show that measurements using current data
and large-scale modelling techniques extract an equivalent amount of signal to
that in the linear regime for $k < 0.08 \,h\,{\rm Mpc}^{-1}$, remarkably
independent of the sample properties and redshifts covered. |
Growth index with the cosmological constant: We obtain the exact analytic form of the growth index at present epoch
($a=1$) in a flat universe with the cosmological constant ({\it i.e.} the dark
energy with its equation of state $\omega_{de} = -1$). For the cosmological
constant, we obtain the exact value of the current growth index parameter
$\gamma = 0.5547$, which is very close to the well known value 6/11. We also
obtain the exact analytic solution of the growth factor for $\omega_{de}$ =
-1/3 or -1. We investigate the growth index and its parameter at any epoch with
this exact solution. In addition to this, we are able to find the exact
$\Omega_{m}^{0}$ dependence of those observable quantities. The growth index is
quite sensitive to $\Omega_{m}^{0}$ at $z = 0.15$, where we are able to use 2dF
observation. If we adopt 2dF value of growth index, then we obtain the
constrain $0.11 \leq \Omega_{m}^{0} \leq 0.37$ for the cosmological constant
model. Especially, the growth index is quite sensitive to $\Omega_{m}^{0}$
around $z \leq 1$. We might be able to obtain interesting observations around
this epoch. Thus, the analytic solution for this growth factor provides the
very useful tools for future observations to constrain the exact values of
observational quantities at any epoch related to growth factor for $\omega_{de}
= -1$ or -1/3. | The orientation of elliptical galaxies: We determine the orientations of the light distribution of individual
elliptical galaxies by combining the profiles of photometric data from the
literature with triaxial models. The orientation is given by a Bayesian
probability distribution. The likelihood of obtaining the data from a model is
a function of the parameters describing the intrinsic shape and the
orientation. Integrating the likelihood over the shape parameters, we obtain
the estimates of the orientation. We find that the position angle difference
between the two suitably chosen points from the profiles of the photometric
data plays a key role in constraining the orientation of the galaxy. We apply
the methodology to a sample of ten galaxies. The alignment of the intrinsic
principle axes of the NGC 3379, 4486 and NGC 5638 are studied. |
Nuclear Reaction Uncertainties, Massive Gravitino Decays and the
Cosmological Lithium Problem: We consider the effects of uncertainties in nuclear reaction rates on the
cosmological constraints on the decays of unstable particles during or after
Big-Bang nucleosynthesis (BBN). We identify the nuclear reactions due to
non-thermal hadrons that are the most important in perturbing standard BBN,
then quantify the uncertainties in these reactions and in the resulting
light-element abundances. These results also indicate the key nuclear processes
for which improved cross section data would allow different light-element
abundances to be determined more accurately, thereby making possible more
precise probes of BBN and evaluations of the cosmological constraints on
unstable particles. Applying this analysis to models with unstable gravitinos
decaying into neutralinos, we calculate the likelihood function for the
light-element abundances measured currently, taking into account the current
experimental errors in the determinations of the relevant nuclear reaction
rates. We find a region of the gravitino mass and abundance in which the
abundances of deuterium, He4 and Li7 may be fit with chi^2 = 5.5, compared with
chi^2 = 31.7 if the effects of gravitino decays are unimportant. The best-fit
solution is improved to chi^2 ~ 2.0 when the lithium abundance is taken from
globular cluster data. Some such re-evaluation of the observed light-element
abundances and/or nuclear reaction rates would be needed if this region of
gravitino parameters is to provide a complete solution to the cosmological Li7
problem. | Line-of-sight structure of troughs identified in Subaru Hyper
Suprime-Cam Year 3 weak lensing mass maps: We perform the weak lensing mass mapping analysis to identify troughs, which
are defined as local minima in the mass map. Since weak lensing probes
projected matter along the line-of-sight, these troughs can be produced by
single voids or multiple voids projected along the line-of-sight. To scrutinise
the origins of the weak lensing troughs, we systematically investigate the
line-of-sight structure of troughs selected from the latest Subaru Hyper
Suprime-Cam (HSC) Year 3 weak lensing data covering $433.48 \, \mathrm{deg}^2$.
From a curved sky mass map constructed with the HSC data, we identify 15
troughs with the signal-to-noise ratio higher than $5.7$ and address their
line-of-sight density structure utilizing redshift distributions of two galaxy
samples, photometric luminous red galaxies observed by HSC and spectroscopic
galaxies detected by Baryon Oscillation Spectroscopic Survey. While most of
weak lensing signals due to the troughs are explained by multiple voids aligned
along the line-of-sight, we find that two of the 15 troughs potentially
originate from single voids at redshift $\sim 0.3$. The single void
interpretation appears to be consistent with our three-dimensional mass mapping
analysis. We argue that single voids can indeed reproduce observed weak lensing
signals at the troughs if these voids are not spherical but are highly
elongated along the line-of-sight direction. |
Stellar Populations: This is a summary of my lectures during the 2011 IAC Winter School in Puerto
de la Cruz. I give an introduction to the field of stellar populations in
galaxies, and highlight some new results. Since the title of the Winter School
was {\it Secular Evolution of Galaxies} I mostly concentrate on nearby
galaxies, which are best suited to study this theme. Of course, the
understanding of stellar populations is intimately connected to understanding
the formation and evolution of galaxies, one of the great outstanding problems
of astronomy. We are currently in a situation where very large observational
advances have been made in recent years. Galaxies have been detected up to a
redshift of 10. A huge effort has to be made so that stellar population theory
can catch up with observations. Since most galaxies are far away, information
about them has to come from stellar population synthesis of integrated light.
Here I will discuss how stellar evolution theory, together with observations in
our Milky Way and Local Group, are used as building blocks to analyze these
integrated stellar populations. | Non-linear dynamics of the minimal theory of massive gravity: We investigate cosmological signatures of the minimal theory of massive
gravity (MTMG). To this aim, we simulate the normal branch of the MTMG by
employing the \textsc{Ramses} \mbox{$N$-body} code and extending it with an
effective gravitational constant $G_{\rm eff}$. We implement an
environment-dependent $G_{\rm eff}$ as a function of the graviton mass and the
local energy density as predicted by MTMG. We find that halo density profiles
are not a good probe for MTMG, because deviations from general relativity (GR)
are quite small. Similarly, the matter power spectra show deviations only at
the percentage level. However, we find a clear difference between MTMG and GR
in that voids are denser in MTMG than in GR. As measuring void profiles is
quite a complex task from an observational point of view, a better probe of
MTMG would be the halo abundances. In this case, MTMG creates a larger amount
of massive halos, while there is a suppression in the abundance of small halos. |
Determining all gas properties in galaxy clusters from the dark matter
distribution alone: We demonstrate that all properties of the hot X-ray emitting gas in galaxy
clusters are completely determined by the underlying dark matter (DM)
structure. Apart from the standard conditions of spherical symmetry and
hydrostatic equilibrium for the gas, our proof is based on the Jeans equation
for the DM and two simple relations which have recently emerged from numerical
simulations: the equality of the gas and DM temperatures, and the almost linear
relation between the DM velocity anisotropy profile and its density slope. For
DM distributions described by the NFW or the Sersic profiles, the resulting gas
density profile, the gas-to-total-mass ratio profile, and the entropy profile
are all in good agreement with X-ray observations. All these profiles are
derived using zero free parameters. Our result allows us to predict the X-ray
luminosity profile of a cluster in terms of its DM content alone. As a
consequence, a new strategy becomes available to constrain the DM morphology in
galaxy clusters from X-ray observations. Our results can also be used as a
practical tool for creating initial conditions for realistic cosmological
structures to be used in numerical simulations. | Neutrino mass and dark energy constraints from redshift-space
distortions: Cosmology in the near future promises a measurement of the sum of neutrino
masses, a fundamental Standard Model parameter, as well as
substantially-improved constraints on the dark energy. We use the shape of the
BOSS redshift-space galaxy power spectrum, in combination with CMB and
supernova data, to constrain the neutrino masses and the dark energy. Essential
to this calculation are several recent advances in non-linear cosmological
perturbation theory, including FFT methods, redshift space distortions, and
scale-dependent growth. Our 95% confidence upper bound of 180 meV on the sum of
masses degrades substantially to 540 meV when the dark energy equation of state
and its first derivative are also allowed to vary, representing a significant
challenge to current constraints. We also study the impact of additional galaxy
bias parameters, finding that a greater allowed range of scale-dependent bias
only slightly shifts the preferred neutrino mass value, weakens its upper bound
by about 20%, and has a negligible effect on the other cosmological parameters. |
Stars and ionized gas in S0 galaxy NGC 7743: an inclined large-scale
gaseous disk: We used deep long-slit spectra and integral-field spectral data to study the
stars and ionized gas kinematics and stellar population properties in the
lenticular barred galaxy NGC 7743. We have shown that ionized gas at the
distances larger than 1.5 kpc from the nucleus settles in the disk which is
significantly inclined to the stellar disk of the galaxy. Making different
assumptions about the geometry of the disks and involving different sets of
emission lines into the fitting, under the assumption of thin flat disk
circular rotation, we obtain the full possible range of angle between the disks
to be 34+/-9 or 77+/-9 deg. The most probable origin of the inclined disk is
the external gas accretion from a satellite, orbiting the host galaxy with a
corresponding angular momentum direction. The published data on the HI
distribution around NGC 7743 suggest that the galaxy has a gas-rich
environment. The emission-line ratio diagrams imply the domination of shock
waves in the ionization state of the gaseous disk, whereas the contribution of
photoionization by recent star formation seems to be negligible. In some parts
of the disk a difference between the velocities of the gas emitting in the
forbidden lines and in the Balmer lines is detected. It may be caused by the
fact that the inclined disk is mainly shock-excited, whereas some fraction of
the Balmer-line emission is produced by a small amount of gas excited by young
stars in the main stellar disk of NGC 7743. In the circumnuclear region (R< 200
pc) some evidences of the AGN jet interaction with an ambient interstellar
medium were found. | Aberrating the CMB sky: fast and accurate computation of the aberration
kernel: It is well known that our motion with respect to the cosmic microwave
background (CMB) rest frame introduces a large dipolar CMB anisotropy, with an
amplitude ~beta=v/c~10^{-3}. In addition it should lead to a small breaking of
statistical isotropy which becomes most notable at higher multipoles. In
principle this could be used to determine our velocity with respect to the CMB
rest frame using high angular resolution data from Planck, without directly
relying on the amplitude and direction of the CMB dipole, allowing us to
constrain cosmological models in which the cosmic dipole arises partly from
large-scale isocurvature perturbations instead of being fully motion-induced.
Here we derive simple recursion relations that allow precise computation of the
motion-induced coupling between different spherical harmonic coefficients.
Although the lowest order approximations for the coupling kernel can be
deficient by factors of 2-5 at multipoles l~1000-3000, using our results for
the aberration kernel we explicitly confirm that for a statistical detection of
the aberration effect only first order terms in beta matter. However, the
expressions given here are not restricted to beta~10^{-3}, but can be used at
much higher velocities. We demonstrate the robustness of these formulae,
illustrating the dependence of the kernel on beta, as well as the spherical
harmonic indices l and m. |
Effect of nonlinearity between density and curvature perturbations on
the primordial black hole formation: We study the effect of the nonlinear relation between density and curvature
perturbations on the formation of PBHs. By calculating the variance and
skewness of the density perturbation we derive the non-Gaussian property. As a
criterion for PBH formation, the compaction function is used and it is found
that larger curvature perturbations are required due to the nonlinear effect.
We estimate the PBH abundance based on the Press-Schechter formalism with
non-Gaussian probability density function during Radiation dominated era. It is
found that the nonlinear effect slightly suppresses the PBH formation and the
suppression is comparable to that expected if the primordial curvature
perturbation would have the local form of non-Gaussianity with nonlinear
parameter $f_\text{NL} \sim -1$. | Modelling baryonic feedback for survey cosmology: Observational cosmology in the next decade will rely on probes of the
distribution of matter in the redshift range between $0<z<3$ to elucidate the
nature of dark matter and dark energy. In this redshift range, galaxy formation
is known to have a significant impact on observables such as two-point
correlations of galaxy shapes and positions, altering their amplitude and scale
dependence beyond the expected statistical uncertainty of upcoming experiments
at separations under 10 Mpc. Successful extraction of information in such a
regime thus requires, at the very least, unbiased models for the impact of
galaxy formation on the matter distribution, and can benefit from complementary
observational priors. This work reviews the current state of the art in the
modelling of baryons for cosmology, from numerical methods to approximate
analytical prescriptions, and makes recommendations for studies in the next
decade, including a discussion of potential probe combinations that can help
constrain the role of baryons in cosmological studies. We focus, in particular,
on the modelling of the matter power spectrum, $P(k,z)$, as a function of scale
and redshift, and of the observables derived from this quantity. This work is
the result of a workshop held at the University of Oxford in November of 2018. |
Revisting the boiling of quark nuggets at nonzero chemical potential: The boiling of possible quark nuggets during the quark-hadron phase
transition of the Universe at nonzero chemical potential is revisited within
the microscopic Brueckner-Hartree-Fock approach employed for the hadron phase,
using two kinds of baryon interactions as fundamental inputs. To describe the
deconfined phase of quark matter, we use a recently developed quark mass
density-dependent model with a fully self-consistent thermodynamic treatment of
confinement. We study the baryon number limit $A_{\rm boil}$ (above which
boiling may be important) with three typical values for the confinement
parameter $D$. It is firstly found that the baryon interaction with a softer
equation of state for the hadron phase would only lead to a small increase of
$A_{\rm boil}$. However, results depend sensitively on the confinement
parameter in the quark model. Specifically, boiling might be important during
the Universe cooling for a limited parameter range around $D^{1/2} = 170$ MeV,
a value satisfying recent lattice QCD calculations of the vacuum chiral
condensate, while for other choices of this parameter, boiling might not happen
and cosmological quark nuggets of $10^2 < A < 10^{50}$ could survive. | The Power of Locality: Primordial Non-Gaussianity at the Map Level: Primordial non-Gaussianity is a sensitive probe of the inflationary era, with
a number of important theoretical targets living an order of magnitude beyond
the reach of current CMB constraints. Maps of the large-scale structure of the
universe, in principle, have the raw statistical power to reach these targets,
but the complications of nonlinear evolution are thought to present serious, if
not insurmountable, obstacles to reaching these goals. In this paper, we will
argue that the challenge presented by nonlinear structure formation has been
overstated. The information encoded in primordial non-Gaussianity resides in
nonlocal correlations of the density field at three or more points separated by
cosmological distances. In contrast, nonlinear evolution only alters the
density field locally and cannot create or destroy these long-range
correlations. This locality property of the late-time non-Gaussianity is
obscured in Fourier space and in the standard bispectrum searches for
primordial non-Gaussianity. We therefore propose to measure non-Gaussianity in
the position space maps of the large-scale structure. As a proof of concept, we
study the case of equilateral non-Gaussianity, for which the degeneracy with
late-time nonlinearities is the most severe. We show that a map-level analysis
is capable of breaking this degeneracy and thereby significantly improve the
constraining power over previous estimates. Our findings suggest that
"simulation-based inference" involving the forward modeling of large-scale
structure maps has the potential to dramatically impact the search for
primordial non-Gaussianity. |
Unravelling the formation of the first supermassive black holes with the
SKA pulsar timing array: Galaxy mergers at high redshifts trigger the activity of their central
supermassive black holes, eventually also leading to their coalescence -- and a
potential source of low-frequency gravitational waves detectable by the SKA
Pulsar Timing Array (PTA). Two key parameters related to the fuelling of black
holes are the Eddington ratio of quasar accretion $\eta_{\rm Edd}$, and the
radiative efficiency of the accretion process, $\epsilon$ (which affects the
so-called active lifetime of the quasar, $t_{\rm QSO}$). We forecast the regime
of detectability of gravitational wave events with SKA PTA, finding the
associated binaries to have orbital periods on the order of weeks to years,
observable through relativistic Doppler velocity boosting and/or optical
variability of their light curves. Combining the SKA regime of detectability
with the latest observational constraints on high-redshift black hole mass and
luminosity functions, and theoretically motivated prescriptions for the merger
rates of dark matter haloes, we forecast the number of active counterparts of
SKA PTA events expected as a function of primary black hole mass at $z \gtrsim
6$. We find that the quasar counterpart of the most massive black holes will be
${uniquely \ localizable}$ within the SKA PTA error ellipse at $z \gtrsim 6$.
We also forecast the number of expected counterparts as a function of the
quasars' Eddington ratio and active lifetime. Our results show that SKA PTA
detections can place robust constraints on the seeding and growth mechanisms of
the first supermassive black holes. | Natural Hybrid Inflation Model with Large Non-Gaussianity: We propose an inflationary model ("natural hybrid model"), which combines the
supersymmetric hybrid model and the natural inflation model to achieve the
spectral index of 0.96, and the axion decay constant smaller than the Planck
scale, f<< M_P. By introducing both U(1)_R and a shift symmetry and employing
the minimal Kahler potential, the eta-problem can be still avoided. The two
inflaton fields in this model can admit large non-Gaussianity. |
An Atlas of Predicted Exotic Gravitational Lenses: Wide-field optical imaging surveys will contain tens of thousands of new
strong gravitational lenses. Some of these will have new and unusual image
configurations, and so will enable new applications: for example, systems with
high image multiplicity will allow more detailed study of galaxy and group mass
distributions, while high magnification is needed to super-resolve the faintest
objects in the high redshift universe. Inspired by a set of six unusual lens
systems [including five selected from the Sloan Lens ACS (SLACS) and Strong
Lensing Legacy (SL2S) surveys, plus the cluster Abell 1703], we consider
several types of multi-component, physically-motivated lens potentials, and use
the ray-tracing code "glamroc" to predict exotic image configurations. We also
investigate the effects of galaxy source profile and size, and use realistic
sources to predict observable magnifications and estimate very approximate
relative cross-sections. We find that lens galaxies with misaligned disks and
bulges produce swallowtail and butterfly catastrophes, observable as "broken"
Einstein rings. Binary or merging galaxies show elliptic umbilic catastrophes,
leading to an unusual Y-shaped configuration of 4 merging images. While not the
maximum magnification configuration possible, it offers the possibility of
mapping the local small-scale mass distribution. We estimate the approximate
abundance of each of these exotic galaxy-scale lenses to be ~1 per all-sky
survey. In higher mass systems, a wide range of caustic structures are
expected, as already seen in many cluster lens systems. We interpret the
central ring and its counter-image in Abell 1703 as a "hyperbolic umbilic"
configuration, with total magnification ~100 (depending on source size). The
abundance of such configurations is also estimated to be ~1 per all-sky survey. | Powering The Intra-cluster Filaments in Cool-Core Clusters of Galaxies: The first radio surveys of the sky discovered that some large clusters of
galaxies contained powerful sources of synchrotron emission. Optical images
showed that long linear filaments with bizarre emission-line spectra permeated
the intra-cluster medium. Recent observations in the infrared and radio show
that these filaments have very strong emission lines of molecular hydrogen and
carbon monoxide. The mass of molecular material is quite large, the gas is
quite warm, and the filaments have not formed stars despite their ~Gyr age. I
will discuss the general astrophysical context of large clusters of galaxies
and how large masses of molecular gas can be heated to produce what we observe.
The unique properties of the filaments are a result of the unique
environment. Magnetically confined molecular filaments are surrounded by the
hot intra-cluster medium. Thermal particles with keV energies enter atomic and
molecular regions and produce a shower of secondary nonthermal electrons. These
secondaries collisionally heat, excite, dissociate, and ionize the cool gas.
While ionization is dominated by these secondary particles, recombination is
controlled by charge exchange, which produces the unusual optical emission line
spectrum. I will describe some of the physical processes that are unique to
this environment and outline some of the atomic physics issues. |
Early-Universe Constraints on Dark Matter-Baryon Scattering and their
Implications for a Global 21cm Signal: We present and compare several cosmological constraints on the cross section
for elastic scattering between dark matter (DM) and baryons, for cross sections
with a range of power-law dependences on the DM-baryon relative velocity $v$,
especially focusing on the case of $\sigma \propto v^{-4}$. We study
constraints spanning a wide range of epochs in cosmological history, from
pre-recombination distortions to the blackbody spectrum and anisotropies of the
cosmic microwave background (CMB), to modifications to the intergalactic medium
temperature and the resulting 21cm signal, and discuss the allowed signals in
the latter channels given the constraints from the former. We improve previous
constraints on DM-baryon scattering from the CMB anisotropies, demonstrate via
principal component analysis that the effect on the CMB can be written as a
simple function of DM mass, and map out the redshifts dominating this signal.
We show that given high-redshift constraints on DM-baryon scattering, a
$v^{-4}$ scaling of the cross section for light DM would be sufficient to
explain the deep 21cm absorption trough recently claimed by the EDGES
experiment, if 100% of the DM scatters with baryons. For millicharged DM models
proposed to explain the observation, where only a small fraction of the DM
interacts, we estimate that a PIXIE-like future experiment measuring CMB
spectral distortion could test the relevant parameter space. | Effect of gravitational lensing on the distribution of gravitational
waves from distant binary black hole mergers: The detailed observation of the distribution of redshifts and chirp masses of
binary black hole mergers is expected to provide a clue to their origin. In
this paper, we develop a hybrid model of the probability distribution function
of gravitational lensing magnification taking account of both strong and weak
gravitational lensing, and use it to study the effect of gravitational lensing
magnification on the distribution of gravitational waves from distant binary
black hole mergers detected in ongoing and future gravitational wave
observations. We find that the effect of gravitational lensing magnification is
significant at high ends of observed chirp mass and redshift distributions.
While a high mass tail in the observed chirp mass distribution is produced by
highly magnified gravitational lensing events, we find that highly demagnified
images of strong lensing events produce a high redshift ($z_{\rm obs}> 15$)
tail in the observed redshift distribution, which can easily be observed in the
third-generation gravitational wave observatories. Such a demagnified,
apparently high redshift event is expected to be accompanied by a magnified
image that is observed typically $10-100$ days before the demagnified image.
For highly magnified events that produce apparently very high chirp masses, we
expect pairs of events with similar magnifications with time delays typically
less than a day. This work suggests the critical importance of gravitational
lensing (de-)magnification on the interpretation of apparently very high mass
or redshift gravitational wave events. |
The Automatic Galaxy Collision Software: The key to understanding the physical processes that occur during galaxy
interactions is dynamical modeling, and especially the detailed matching of
numerical models to specific systems. To make modeling interacting galaxies
more efficient, we have constructed the `Automatic Galaxy Collision' (AGC)
code, which requires less human intervention in finding good matches to data.
We present some preliminary results from this code for the well-studied system
Arp 284 (NGC 7714/5), and address questions of uniqueness of solutions. | A Lyα blob and zabs {\approx} zem damped Lyα absorber in
the dark matter halo of the binary quasar Q 0151+048: Q0151+048 is a physical QSO pair at z ~ 1.929 with a separation of 3.3 arcsec
on the sky. In the spectrum of Q0151+048A (qA), a DLA is observed at a higher
redshift. We have previously detected the host galaxies of both QSOs, as well
as a Lya blob. We performed low-resolution spectroscopy with the slit aligned
with the extended emission. We also observed the system using the
medium-resolution VLT/X-shooter spectrograph and the slit aligned with the two
QSOs. We measure systemic redshifts of zem(A)=1.92924{\pm}0.00036 and
zem(B)=1.92863{\pm}0.00042 from the H{\beta} and H{\alpha} emission lines,
respectively. We estimate the masses of the black holes of the two QSOs to be
10^9.33 M{\odot} and 10^8.38 M{\odot} for qA and qB, respectively. From this we
infered the mass of the dark matter halos hosting the two QSOs: 10^13.74
M{\odot} and 10^13.13 M{\odot} for qA and qB, respectively. We observe a
velocity gradient along the major axis of the Lya blob consistent with the
rotation curve of a large disk galaxy, but it may also be caused by gas inflow
or outflow. We detect residual continuum in the DLA trough which we interpret
as emission from the host galaxy of qA. The derived H0 column density of the
DLA is log NH0 = 20.34 {\pm} 0.02. Metal column densities results in an overall
metallicity of 0.01 Z{\odot}. We detect CII* which allows us to make a physical
model of the DLA cloud. From the systemic redshifts of the QSOs, we conclude
that the Lya blob is associated with qA rather than with the DLA. The DLA must
be located in front of both the Lya blob and qA at a distance larger than 30
kpc. The two QSOs accrete at normal eddington ratios. The DM halo of this
double quasar will grow to the mass of our local super-cluster at z=0. We point
out that those objects therefore form an ideal laboratory to study the physical
interactions in a z=2 pre-cursor of our local super-cluster. |
Galaxy cluster aperture masses are more robust to baryonic effects than
3D halo masses: Systematic uncertainties in the mass measurement of galaxy clusters limit the
cosmological constraining power of future surveys that will detect more than
$10^5$ clusters. Previously, we argued that aperture masses can be inferred
more accurately and precisely than 3D masses without loss of cosmological
constraining power. Here, we use the Baryons and Haloes of Massive Systems
(BAHAMAS) cosmological, hydrodynamical simulations to show that aperture masses
are also less sensitive to changes in mass caused by galaxy formation
processes. For haloes with $m_\mathrm{200m,dmo} > 10^{14} \, h^{-1} \,
\mathrm{M}_\odot$, binned by their 3D halo mass, baryonic physics affects
aperture masses and 3D halo masses similarly when measured within apertures
similar to the halo virial radius, reaching a maximum reduction of $\approx 3
\, \%$. For lower-mass haloes, $10^{13.5} < m_\mathrm{200m,dmo} / (h^{-1} \,
\mathrm{M}_\odot) < 10^{14}$, and aperture sizes $\sim 1 \, h^{-1} \,
\mathrm{cMpc}$, representative of weak lensing observations, the aperture mass
is consistently reduced less ($\lesssim 5 \, \%$) than the 3D halo mass
($\lesssim 10 \, \%$ for $m_\mathrm{200m}$). The halo mass reduction evolves
only slightly, by up to $2$ percentage points, between redshift 0.25 and 1 for
both the aperture mass and $m_\mathrm{200m}$. Varying the strength of the
simulated feedback so the mean simulated hot gas fraction covers the observed
scatter inferred from X-ray observations, we find that the aperture mass is
consistently less biased than the 3D halo mass, by up to $2 \, $ percentage
points at $m_\mathrm{200m,dmo} = 10^{14} \, h^{-1} \, \mathrm{M}_\odot$.
Therefore, cluster aperture mass calibrations provide a fruitful path forward
for future cluster surveys to reduce their sensitivity to systematic
uncertainties. | The Stellar Populations of Bright Coma Cluster Galaxies: In this paper we study the stellar populations of 356 bright, $M_{r}$ $\leq$
-19, Coma cluster members located in a 2 degree field centred on the cluster
core using SDSS DR7 spectroscopy. For the quiescent galaxies we find strong
correlations between absorption line index strength and velocity dispersion
($\sigma$) for CN2, C4668, Mgb and H$\beta$. We find significant
cluster-centric radial gradients in H$\beta$, Mgb and C4668 for the passive
galaxies. We use state-of-the-art stellar population models \citep{schiavon07}
and the measured absorption line indices to infer the
single-stellar-population-equivalent (SSP-equivalent) age and [Fe/H] for each
galaxy, as well as their abundance patterns in terms of [Mg/Fe], [C/Fe], [N/Fe]
and [Ca/Fe]. For the passive galaxy subsample we find strong evidence for
"archaeological downsizing", with age $\propto \sigma^{0.90 \pm 0.06}$. We
recover significant cluster-centric radial stellar population gradients for the
passive sample in SSP-equivalent age, [Mg/Fe], [C/Fe] and [N/Fe]. These trends
are in the sense that, at fixed velocity dispersion, passive galaxies on the
outskirts of the cluster are 24% $\pm$ 9% younger with lower [Mg/Fe] and [N/Fe]
but higher [C/Fe] than those in the cluster core. We find no significant
increase in cluster-centric radial stellar population gradients when fitting to
a passive galaxy subset selected to cover the cluster core and South-West
region, which contains the NGC 4839 subgroup. Thus we conclude that the NGC
4839 in-fall region is not unique, at least in terms of the stellar populations
of bright galaxies. We speculate that the more pronounced cluster-centric
radial gradients seen by other recent studies may be attributed to the
luminosity range spanned by their samples, rather than to limited azimuthal
coverage of the cluster.(abridged) |
Comment on "Hubble flow variations as a test for inhomogeneous
cosmology": Saulder et al [2019, A&A, 622, A83; arXiv:1811.11976] have performed a novel
observational test of the local expansion of the Universe for the standard
cosmology as compared to an alternative model with differential cosmic
expansion. Their analysis employs mock galaxy samples from the Millennium
Simulation, a Newtonian $N$-body simulation on a $\Lambda$CDM background. For
the differential expansion case the simulation has been deformed in an attempt
to incorporate features of a particular inhomogeneous cosmology: the timescape
model. It is shown that key geometrical features of the timescape cosmology
have been omitted in this rescaling. Consequently, the differential expansion
model tested by Saulder et al (2019) cannot be considered to approximate the
timescape cosmology. | Estimating Black Hole Masses in Active Galactic Nuclei Using the MgII
2800 Emission Line: We investigate the relationship between the linewidths of broad Mg II
\lambda2800 and Hbeta in active galactic nuclei (AGNs) to refine them as tools
to estimate black hole (BH) masses. We perform a detailed spectral analysis of
a large sample of AGNs at intermediate redshifts selected from the Sloan
Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra
for nearby sources monitored with reverberation mapping. Careful attention is
devoted to accurate spectral decomposition, especially in the treatment of
narrow-line blending and Fe II contamination. We show that, contrary to popular
belief, the velocity width of Mg II tends to be smaller than that of Hbeta,
suggesting that the two species are not cospatial in the broad-line region.
Using these findings and recently updated BH mass measurements from
reverberation mapping, we present a new calibration of the empirical
prescriptions for estimating virial BH masses for AGNs using the broad Mg II
and Hbeta lines. We show that the BH masses derived from our new formalisms
show subtle but important differences compared to some of the mass estimators
currently used in the literature. |
Degeneracy pressure of mass dimension one fermionic fields and the dark
matter halo of galaxies: In this paper, the recently proposed mass dimension one fermionic field is
supposed to be responsible for the dark matter halo around galactic nuclei,
through the quantum degeneracy pressure effect of the field. It will be showed
that the mass-ratio relation for dwarf galaxies can be well explained for a
particle dark matter mass of about $100 - 200$eV. For a large galaxy, as Milky
Way, the observational data for rotation curve can be well reproduced for a
particle mass of about 23eV, with the addition of other substructures. | The SuperCOSMOS all-sky galaxy catalogue: We describe the construction of an all-sky galaxy catalogue, using
SuperCOSMOS scans of Schmidt photographic plates from the UKST and POSS2
surveys. The photographic photometry is calibrated using SDSS data, with
results that are linear to 2% or better. All-sky photometric uniformity is
achieved by matching plate overlaps and also by requiring homogeneity in
optical-to-2MASS colours, yielding zero points that are uniform to 0.03 mag. or
better. The typical AB depths achieved are B_J<21, R_F<19.5 and I_N<18.5, with
little difference between hemispheres. In practice, the I_N plates are
shallower than the B_J & R_F plates, so for most purposes we advocate the use
of a catalogue selected in these two latter bands. At high Galactic latitudes,
this catalogue is approximately 90% complete with 5% stellar contamination; we
quantify how the quality degrades towards the Galactic plane. At low latitudes,
there are many spurious galaxy candidates resulting from stellar blends: these
approximately match the surface density of true galaxies at |b|=30 deg. Above
this latitude, the catalogue limited in B_J & R_F contains in total about 20
million galaxy candidates, of which 75% are real. This contamination can be
removed, and the sky coverage extended, by matching with additional datasets.
This SuperCOSMOS catalogue has been matched with 2MASS and with WISE, yielding
quasi-allsky samples of respectively 1.5 million and 18.5 million galaxies, to
median redshifts of 0.08 and 0.20. This legacy dataset thus continues to offer
a valuable resource for large-angle cosmological investigations. |
Violent and mild relaxation of an isolated self-gravitating uniform and
spherical cloud of particles: The collapse of an isolated, uniform and spherical cloud of self-gravitating
particles represents a paradigmatic example of a relaxation process leading to
the formation of a quasi-stationary state in virial equilibrium. We consider
several N-body simulations of such a system, with the initial velocity
dispersion as a free parameter. We show that there is a clear difference
between structures formed when the initial virial ratio is b_0 =2K_0/W_0 <
b_0^c ~ -1/2 and b_0> b_0^c. These two sets of initial conditions give rise
respectively to a mild and violent relaxation occurring in about the same time
scale: however in the latter case the system contracts by a large factor, while
in the former it approximately maintains its original size. Correspondingly the
resulting quasi equilibrium state is characterized by a density profile
decaying at large enough distances as ~1/r^4 or with a sharp cut-off. The case
b_0<b_0^c can be well described by the Lynden-Bell theory of collisionless
relaxation considering the system confined in a box. On the other hand the
relevant feature for b_0>b_0^c is the ejection of particles and energy, which
is not captured by such a theoretical approach: for this case we introduce a
simple physical model to explain the formation of the power-law density
profile. This model shows that the behavior n(r) ~1/r^4 is the typical density
profile that is obtained when the initial conditions are cold enough that mass
and energy ejection occurs. In addition, we clarify the origin of the critical
value of the initial virial ratio b_0^c. | Planck intermediate results. XL. The Sunyaev-Zeldovich signal from the
Virgo cluster: The Virgo cluster is the largest Sunyaev-Zeldovich (SZ) source in the sky,
both in terms of angular size and total integrated flux. Planck's wide angular
scale and frequency coverage, together with its high sensitivity, allow a
detailed study of this large object through the SZ effect. Virgo is well
resolved by Planck, showing an elongated structure, which correlates well with
the morphology observed from X-rays, but extends beyond the observed X-ray
signal. We find a good agreement between the SZ signal (or Compton paranmeter,
y_c) observed by Planck and the expected signal inferred from X-ray
observations and simple analytical models. Due to its proximity to us, the gas
beyond the virial radius can be studied with unprecedented sensitivity by
integrating the SZ signal over tens of square degrees. We study the signal in
the outskirts of Virgo and compare it with analytical models and a constrained
simulation of the environment of Virgo. Planck data suggest that significant
amounts of low-density plasma surround Virgo out to twice the virial radius. We
find the SZ signal in the outskirts of Virgo to be consistent with a simple
model that extrapolates the inferred pressure at lower radii while assuming
that the temperature stays in the keV range beyond the virial radius. The
observed signal is also consistent with simulations and points to a shallow
pressure profile in the outskirts of the cluster. This reservoir of gas at
large radii can be linked with the hottest phase of the elusive warm/hot
intergalactic medium. Taking the lack of symmetry of Virgo into account, we
find that a prolate model is favoured by the combination of SZ and X-ray data,
in agreement with predictions. |
Erratic Jet Wobbling in the BL Lacertae Object OJ287 Revealed by Sixteen
Years of 7mm VLBA Observations: We present the results from an ultra-high-resolution 7mm Very Long Baseline
Array (VLBA) study of the relativistic jet in the BL Lacertae object OJ287 from
1995 to 2011 containing 136 total intensity images. Analysis of the image
sequence reveals a sharp jet-position-angle swing by >100 deg. during
[2004,2006], as viewed in the plane of the sky, that we interpret as the
crossing of the jet from one side of the line of sight to the other during a
softer and longer term swing of the inner jet. Modulating such long term swing,
our images also show for the first time a prominent erratic wobbling behavior
of the innermost ~0.4mas of the jet with fluctuations in position angle of up
to ~40 deg. over time scales ~2yr. This is accompanied by highly superluminal
motions along non-radial trajectories, which reflect the remarkable
non-ballistic nature of the jet plasma on these scales. The erratic nature and
short time scales of the observed behavior rules out scenarios such as binary
black hole systems, accretion disk precession, and interaction with the ambient
medium as possible origins of the phenomenon on the scales probed by our
observations, although such processes may cause longer-term modulation of the
jet direction. We propose that variable asymmetric injection of the jet flow;
perhaps related to turbulence in the accretion disk; coupled with hydrodynamic
instabilities, leads to the non-ballistic dynamics that cause the observed
non-periodic changes in the direction of the inner jet. | Reconstruction of energy conditions from observations and implications
for extended theories of gravity: The attempt to describe the recent accelerated expansion of the Universe
includes different propositions for dark energy models and modified gravity
theories. Establish their features in order to discriminate and even rule out
part of these models using observational data is a fundamental issue of
cosmology. In the present work we consider a class of extended theories of
gravity (ETG) that are minimally coupled to the ordinary matter fields. In this
context, and assuming a homogeneous and isotropic spacetime, we derive the
energy conditions for this ETG class. We then put constraints on these
conditions using a model-independent approach to reconstruct the deceleration
function along with the Joint Light-curve Analysis (JLA) supernova sample, 11
baryon acoustic oscillation and 22 cosmic-chronometer measurements. We also
consider an additional condition imposing the strong energy condition only on
the ordinary matter. This is to guarantee the presence of only attractive
matter in the energy-momentum tensor, at least in the redshift range of the
observations, i.e., the recent accelerated expansion of the Universe is due
solely to the modifications in the gravity theory. The main result of this work
is a general reconstruction of the energy conditions valid for every considered
ETG. |
Galaxy Pairs in the Sloan Digital Sky Survey - III: Evidence of Induced
Star Formation from Optical Colours: We have assembled a large, high quality catalogue of galaxy colours from the
Sloan Digital Sky Survey Data Release 7, and have identified 21,347 galaxies in
pairs spanning a range of projected separations (r_p < 80 h_{70}^{-1} kpc),
relative velocities (\Delta v < 10,000 km/s, which includes projected pairs
that are essential for quality control), and stellar mass ratios (from 1:10 to
10:1). We find that the red fraction of galaxies in pairs is higher than that
of a control sample matched in stellar mass and redshift, and demonstrate that
this difference is likely due to the fact that galaxy pairs reside in higher
density environments than non-paired galaxies. We detect clear signs of
interaction-induced star formation within the blue galaxies in pairs, as
evidenced by a higher fraction of extremely blue galaxies, along with blueward
offsets between the colours of paired versus control galaxies. These signs are
strongest in close pairs (r_p < 30 h_{70}^{-1} kpc and \Delta v < 200 km/s),
diminish for more widely separated pairs (r_p > 60 h_{70}^{-1} kpc and \Delta v
< 200 km/s) and disappear for close projected pairs (r_p < 30 h_{70}^{-1} kpc
and \Delta v > 3000 km/s). These effects are also stronger in central (fibre)
colours than in global colours, and are found primarily in low- to
medium-density environments. Conversely, no such trends are seen in red
galaxies, apart from a small reddening at small separations which may result
from residual errors with photometry in crowded fields. When interpreted in
conjunction with a simple model of induced starbursts, these results are
consistent with a scenario in which close peri-centre passages trigger induced
star formation in the centres of galaxies which are sufficiently gas rich,
after which time the galaxies gradually redden as they separate and their
starbursts age. | The Third Data Release of the KODIAQ Survey: We present and make publicly available the third data release (DR3) of the
Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey.
KODIAQ DR3 consists of a fully-reduced sample of 727 quasars at 0.1 < z < 6.4
observed with ESI at moderate resolution (4000 < R < 10000). DR3 contains 872
spectra available in flux calibrated form, representing a sum total exposure
time of approximately 2.8 megaseconds. These co-added spectra arise from a
total of 2753 individual exposures of quasars taken from the Keck Observatory
Archive (KOA) in raw form and uniformly processed using a data reduction
package made available through the XIDL distribution. DR3 is publicly available
to the community, housed as a higher level science product at the KOA and in
the igmspec database. |
A data-driven Reconstruction of Horndeski gravity via the Gaussian
processes: We reconstruct the Hubble function from cosmic chronometers, supernovae, and
baryon acoustic oscillations compiled data sets via the Gaussian process (GP)
method and use it to draw out Horndeski theories that are fully anchored on
expansion history data. In particular, we consider three well-established
formalisms of Horndeski gravity which single out a potential through the
expansion data, namely: quintessence potential, designer Horndeski, and
tailoring Horndeski. We discuss each method in detail and complement it with
the GP reconstructed Hubble function to obtain predictive constraints on the
potentials and the dark energy equation of state. | Examining the Effects of Dark Matter Spikes on Eccentric Intermediate
Mass Ratio Inspirals Using $N$-body Simulations: Recent studies have postulated that the presence of dark matter (DM) spikes
around IMBHs could lead to observable dephasing effects in gravitational wave
(GW) signals emitted by Intermediate Mass Ratio Inspirals (IMRIs). While prior
investigations primarily relied on non-self-consistent analytic methods to
estimate the influence of DM spikes on eccentric IMRIs, our work introduces the
first self-consistent treatment of this phenomenon through $N$-body
simulations. Contrary to previous studies, which suggested that dynamical
friction (DF), a cumulative effect of two-body encounters, is the primary
mechanism responsible for energy dissipation, we reveal that the slingshot
mechanism, a three-body effect, plays a more significant role in driving the
binary system's energy loss and consequent orbital shrinkage, similar to
stellar loss cone scattering in Massive Black Hole (MBH) binaries. Furthermore,
our work extends its analysis to include rotation in DM spikes, a factor often
overlooked in previous studies. We find that binaries that counter-rotate with
respect to the spike particles merge faster, while binaries that co-rotate
merge slower, in opposition to the expectation from DF theory. While our models
are idealistic, they offer findings that pave the way for a more comprehensive
understanding of the complex interactions between DM spikes, IMRIs, GW
emission, and the ability to constrain DM microphysics. Our work systematically
includes Post-Newtonian (PN) effects until 2.5 order and our results are
accurate and robust. |
Reconstructing Probability Distributions with Gaussian Processes: Modern cosmological analyses constrain physical parameters using Markov Chain
Monte Carlo (MCMC) or similar sampling techniques. Oftentimes, these techniques
are computationally expensive to run and require up to thousands of CPU hours
to complete. Here we present a method for reconstructing the log-probability
distributions of completed experiments from an existing MCMC chain (or any set
of posterior samples). The reconstruction is performed using Gaussian process
regression for interpolating the log-probability. This allows for easy
resampling, importance sampling, marginalization, testing different samplers,
investigating chain convergence, and other operations. As an example use-case,
we reconstruct the posterior distribution of the most recent Planck 2018
analysis. We then resample the posterior, and generate a new MCMC chain with
forty times as many points in only thirty minutes. Our likelihood
reconstruction tool can be found online at
https://github.com/tmcclintock/AReconstructionTool. | Vorticity generation in the Universe: A perturbative approach: We compute the generation of vorticity from velocity dispersion in the dark
matter fluid. For dark matter at zero temperature Helmholtz's theorem dictates
that no vorticity is generated and we therefore allow the dark matter fluid to
have a non-vanishing velocity dispersion. This implies a modification to the
usual hydrodynamical system (continuity and Euler equations): we have to
consider the Boltzmann hierarchy up to the second moment. This means that the
Euler equation is modified with a source term that describes the effect of
non-zero velocity dispersion. We write an equation for the Eulerian vorticity
in Lagrangian coordinates and show that it has a growing mode already at second
order in perturbation theory. We compute the power spectrum of the vorticity
and the rotational velocity at second order in perturbation theory. |
The TT, TB, EB and BB correlations in anisotropic inflation: The ongoing and future experiments will measure the B-mode from different sky
coverage and frequency bands, with the potential to reveal non-trivial features
in polarization map. In this work we study the TT, TB, EB and BB correlations
associated with the B-mode polarization of CMB map in models of charged
anisotropic inflation. The model contains a chaotic-type large field complex
inflaton which is charged under the $U(1)$ gauge field. We calculate the
statistical anisotropies generated in the power spectra of the curvature
perturbation, the tensor perturbation and their cross-correlation. It is shown
that the asymmetry in tensor power spectrum is a very sensitive probe of the
gauge coupling. While the level of statistical anisotropy in temperature power
spectrum can be small and satisfy the observational bounds, the interactions
from the gauge coupling can induce large directional dependence in tensor
modes. This will leave interesting anisotropic fingerprints in various
correlations involving the B-mode polarization such as the TB cross-correlation
which may be detected in upcoming Planck polarization data. In addition, the TT
correlation receives an anisotropic contribution from the tensor sector which
naturally decays after $l \gtrsim 100$. We expect that the mechanism of using
tensor sector to induce asymmetry at low $l$ to be generic which can also be
applied to address other low $l$ CMB anomalies. | Multifield Cosmology with Artificial Intelligence: Astrophysical processes such as feedback from supernovae and active galactic
nuclei modify the properties and spatial distribution of dark matter, gas, and
galaxies in a poorly understood way. This uncertainty is one of the main
theoretical obstacles to extract information from cosmological surveys. We use
2,000 state-of-the-art hydrodynamic simulations from the CAMELS project
spanning a wide variety of cosmological and astrophysical models and generate
hundreds of thousands of 2-dimensional maps for 13 different fields: from dark
matter to gas and stellar properties. We use these maps to train convolutional
neural networks to extract the maximum amount of cosmological information while
marginalizing over astrophysical effects at the field level. Although our maps
only cover a small area of $(25~h^{-1}{\rm Mpc})^2$, and the different fields
are contaminated by astrophysical effects in very different ways, our networks
can infer the values of $\Omega_{\rm m}$ and $\sigma_8$ with a few percent
level precision for most of the fields. We find that the marginalization
performed by the network retains a wealth of cosmological information compared
to a model trained on maps from gravity-only N-body simulations that are not
contaminated by astrophysical effects. Finally, we train our networks on
multifields -- 2D maps that contain several fields as different colors or
channels -- and find that not only they can infer the value of all parameters
with higher accuracy than networks trained on individual fields, but they can
constrain the value of $\Omega_{\rm m}$ with higher accuracy than the maps from
the N-body simulations. |
Comprehensive Assessment of the Too-Big-to-Fail Problem: We use a semi-analytical model for the substructure of dark matter haloes to
assess the too-big-to-fail (TBTF) problem. The model accurately reproduces the
average subhalo mass and velocity functions, as well as their halo-to-halo
variance, in N-body simulations. We construct thousands of realizations of
Milky Way (MW) size host haloes, allowing us to investigate the TBTF problem
with unprecedented statistical power. We examine the dependence on host halo
mass and cosmology, and explicitly demonstrate that a reliable assessment of
TBTF requires large samples of hundreds of host haloes. We argue that previous
statistics used to address TBTF suffer from the look-elsewhere effect and/or
disregard certain aspects of the data on the MW satellite population. We devise
a new statistic that is not hampered by these shortcomings, and, using only
data on the 9 known MW satellite galaxies with $V_{\rm max}>15{\rm kms}^{-1}$,
demonstrate that $1.4^{+3.3}_{-1.1}\%$ of MW-size host haloes have a subhalo
population in statistical agreement with that of the MW. However, when using
data on the MW satellite galaxies down to $V_{\rm max}=8{\rm kms}^{-1}$, this
MW consistent fraction plummets to $<5\times10^{-4}$ (at 68% CL). Hence, if it
turns out that the inventory of MW satellite galaxies is complete down to
8km/s, then the maximum circular velocities of MW satellites are utterly
inconsistent with $\Lambda$CDM predictions, unless baryonic effects can
drastically increase the spread in $V_{\rm max}$ values of satellite galaxies
compared to that of their subhaloes. | On the connection between the metal-enriched intergalactic medium and
galaxies: an OVI-galaxy cross-correlation study at $z < 1$: We present new results on the auto- and cross-correlation functions of
galaxies and OVI absorbers in a $\sim 18~\textrm{Gpc}^3$ comoving volume at $z
< 1$. We use a sample of 51,296 galaxies and 140 OVI absorbers in the column
density range $13 \lesssim \log N \lesssim 15$ to measure two-point correlation
functions in the two dimensions transverse and orthogonal to the line-of-sight
$\xi(r_{\perp}, r_{\parallel})$. We furthermore infer the corresponding
'real-space' correlation functions, $\xi(r)$, by projecting $\xi(r_{\perp},
r_{\parallel})$ along $r_{\parallel}$, and assuming a power-law form, $\xi(r) =
(r / r_0)^{-\gamma}$. Comparing the results from the absorber-galaxy
cross-correlation function, $\xi_{\textrm{ag}}$, the galaxy auto-correlation
function, $\xi_{\textrm{gg}}$, and the absorber auto-correlation function,
$\xi_{\textrm{aa}}$, we constrain the statistical connection between galaxies
and the metal-enriched intergalactic medium as a function of star-formation
activity. We also compare these results to predictions from the EAGLE
cosmological hydrodynamical simulation and find a reasonable agreement. We find
that: (i) OVI absorbers show very little velocity dispersion with respect to
galaxies on $\sim$ Mpc scales, likely $\lesssim$ 100 \kms; (ii) OVI absorbers
and galaxies may not linearly trace the same underlying distribution of matter
in general. In particular, our results demonstrate that OVI absorbers are less
clustered, and potentially more extended around galaxies than galaxies are
around themselves; (iii) On $\gtrsim 100$ kpc scales, the likelihood of finding
OVI absorbers around star-forming galaxies is similar to the likelihood of
finding OVI absorbers around non star-forming galaxies (abridged) |
On the Bispectra of Very Massive Tracers in the Effective Field Theory
of Large-Scale Structure: The Effective Field Theory of Large-Scale Structure (EFTofLSS) provides a
consistent perturbative framework for describing the statistical distribution
of cosmological large-scale structure. In a previous EFTofLSS calculation that
involved the one-loop power spectra and tree-level bispectra, it was shown that
the $k$-reach of the prediction for biased tracers is comparable for all
investigated masses if suitable higher-derivative biases, which are less
suppressed for more massive tracers, are added. However, it is possible that
the non-linear biases grow faster with tracer mass than the linear bias,
implying that loop contributions could be the leading correction to the
bispectra. To check this, we include the one-loop contributions in a fit to
numerical data in the limit of strongly enhanced higher-order biases. We show
that the resulting one-loop power spectra and higher-derivative plus leading
one-loop bispectra fit the two- and three-point functions respectively up to
$k\simeq 0.19\ h\ \rm{Mpc}^{-1}$ and $k\simeq 0.14\ h\ \rm{Mpc}^{-1}$ at the
percent level. We find that the higher-order bias coefficients are not strongly
enhanced, and we argue that the gain in perturbative reach due to the leading
one-loop contributions to the bispectra is relatively small. Thus, we conclude
that higher-derivative biases provide the leading correction to the bispectra
for tracers of a very wide range of masses. | One-dimensional model of cosmological perturbations: direct integration
in the Fourier space: We propose a method of calculation of the power spectrum of cosmological
perturbations by means of a direct numerical integration of hydrodynamic
equations in the Fourier space for a random ensemble of initial conditions with
subsequent averaging procedure. This method can be an alternative to the
cosmological N-body simulations. We test realizability of this method in case
of one-dimensional motion of gravitating matter pressureless shells. In order
to test the numerical simulations, we found an analytical solution which
describes one-dimensional collapse of plane shells. The results are used to
study a nonlinear interaction of different Fourier modes. |
Revealing the late-time transition of $H_{0}$: relieve the Hubble crisis: The discrepancy between the value of the Hubble constant $H_0$ measured from
the local distance ladder and from the cosmic microwave background is the most
serious challenge to the standard $\Lambda$CDM model. Various models have been
proposed to solve or relieve it, but no satisfactory solution has been given
until now. Here, we report a late-time transition of $H_{0}$, i.e., $H_0$
changes from a low value to a high one from early to late cosmic time, by
investigating the Hubble parameter $H(z)$ data based on the Gaussian process
(GP) method. This finding effectively reduces the Hubble crisis by 70\%. Our
results are also consistent with the descending trend of $H_0$ measured using
time-delay cosmography of lensed quasars at 1$\sigma$ confidence level, and
support the idea that the Hubble crisis arises from new physics beyond the
standard $\Lambda$CDM model. In addition, in the $\Lambda$CDM model and $w$CDM
model, there is no transition behavior of $H_{0}$. | An Integral Field Study of Abundance Gradients in Nearby LIRGs: We present for the first time metallicity maps generated using data from the
Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies
(LIRGs) and discuss the abundance gradients and distribution of metals in these
systems. We have carried out optical integral field spectroscopy (IFS) of
several several LIRGs in various merger phases to investigate the merger
process. In a major merger of two spiral galaxies with preexisting disk
abundance gradients, the changing distribution of metals can be used as a
tracer of gas flows in the merging system as low metallicity gas is transported
from the outskirts of each galaxy to their nuclei. We employ this fact to probe
merger properties by using the emission lines in our IFS data to calculate the
gas-phase metallicity in each system. We create abundance maps and subsequently
derive a metallicity gradient from each map. We compare our measured gradients
to merger stage as well as several possible tracers of merger progress and
observed nuclear abundances. We discuss our work in the context of previous
abundance gradient observations and compare our results to new galaxy merger
models which trace metallicity gradient. Our results agree with the observed
flattening of metallicity gradients as a merger progresses. We compare our
results with new theoretical predictions that include chemical enrichment. Our
data show remarkable agreement with these simulations. |
Detecting circular polarisation in the stochastic gravitational-wave
background from a first-order cosmological phase transition: We discuss the observability of circular polarisation of the stochastic
gravitational-wave background (SGWB) generated by helical turbulence following
a first-order cosmological phase transition, using a model that incorporates
the effects of both direct and inverse energy cascades. We explore the strength
of the gravitational-wave signal and the dependence of its polarisation on the
helicity fraction, $\zeta_*$, the strength of the transition, $\alpha$, the
bubble size, $R_*$, and the temperature, $T_*$, at which the transition
finishes. We calculate the prospective signal-to-noise ratios of the SGWB
strength and polarisation signals in the LISA experiment, exploring the
parameter space in a way that is minimally sensitive to the underlying particle
physics model. We find that discovery of SGWB polarisation is generally more
challenging than measuring the total SGWB signal, but would be possible for
appropriately strong transitions with large bubble sizes and a substantial
polarisation fraction. | Mass of the Southern Black Hole in NGC 6240 from Laser Guide Star
Adaptive Optics: NGC 6240 is a pair of colliding disk galaxies, each with a black hole in its
core. We have used laser guide star adaptive optics on the Keck II telescope to
obtain high-resolution ($\sim 0.06$") near-infrared integral-field spectra of
the region surrounding the supermassive black hole in the south nucleus of this
galaxy merger. We use the K-band CO absorption bandheads to trace stellar
kinematics. We obtain a spatial resolution of about 20 pc and thus directly
resolve the sphere of gravitational influence of the massive black hole. We
explore two different methods to measure the black hole mass. Using a Jeans
Axisymmetric Multi-Gaussian mass model, we investigate the limit that a relaxed
mass distribution produces all of the measured velocity dispersion, and find an
upper limit on the black hole mass at $2.0 \pm 0.2 \times 10^9 M_{\sun}$. When
assuming the young stars whose spectra we observe remain in a thin disk, we
compare Keplerian velocity fields to the measured two-dimensional velocity
field measured and fit for a mass profile containing a black hole point mass
plus a radially-varying spherical component, which suggests a lower limit for
the black hole mass of $8.7 \pm 0.3 \times 10^8 M_{\sun}$. Our measurements of
the stellar velocity dispersion place this AGN within the scatter of the
$M_{BH}$-$\sigma_{*}$ relation. As NGC 6240 is a merging system, this may
indicate that the relation is preserved during a merger at least until the
final coalescence of the two nuclei. |
The Structure of Dissipative Dark Matter Halos: Dissipative dark matter self-interactions can affect halo evolution and
change its structure. We perform a series of controlled N-body simulations to
study impacts of the dissipative interactions on halo properties. The interplay
between gravitational contraction and collisional dissipation can significantly
speed up the onset of gravothermal collapse, resulting in a steep inner density
profile. For reasonable choices of model parameters controlling the
dissipation, the collapse timescale can be a factor of 10-100 shorter than that
predicted in purely elastic self-interacting dark matter. The effect is
maximized when energy loss per collision is comparable to characteristic
kinetic energy of dark matter particles in the halo. Our simulations provide
guidance for testing the dissipative nature of dark matter with astrophysical
observations. | The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey:
Cosmological Implications from two Decades of Spectroscopic Surveys at the
Apache Point observatory: We present the cosmological implications from final measurements of
clustering using galaxies, quasars, and Ly$\alpha$ forests from the completed
Sloan Digital Sky Survey (SDSS) lineage of experiments in large-scale
structure. These experiments, composed of data from SDSS, SDSS-II, BOSS, and
eBOSS, offer independent measurements of baryon acoustic oscillation (BAO)
measurements of angular-diameter distances and Hubble distances relative to the
sound horizon, $r_d$, from eight different samples and six measurements of the
growth rate parameter, $f\sigma_8$, from redshift-space distortions (RSD). This
composite sample is the most constraining of its kind and allows us to perform
a comprehensive assessment of the cosmological model after two decades of
dedicated spectroscopic observation. We show that the BAO data alone are able
to rule out dark-energy-free models at more than eight standard deviations in
an extension to the flat, $\Lambda$CDM model that allows for curvature. When
combined with Planck Cosmic Microwave Background (CMB) measurements of
temperature and polarization the BAO data provide nearly an order of magnitude
improvement on curvature constraints. The RSD measurements indicate a growth
rate that is consistent with predictions from Planck primary data and with
General Relativity. When combining the results of SDSS BAO and RSD with
external data, all multiple-parameter extensions remain consistent with a
$\Lambda$CDM model. Regardless of cosmological model, the precision on
$\Omega_\Lambda$, $H_0$, and $\sigma_8$, remains at roughly 1\%, showing
changes of less than 0.6\% in the central values between models. The inverse
distance ladder measurement under a o$w_0w_a$CDM yields $H_0= 68.20 \pm 0.81 \,
\rm km\, s^{-1} Mpc^{-1}$, remaining in tension with several direct
determination methods. (abridged) |
Empowering line intensity mapping to study early galaxies: Line intensity mapping is a superb tool to study the collective radiation
from early galaxies. However, the method is hampered by the presence of strong
foregrounds, mostly produced by low-redshift interloping lines. We present here
a general method to overcome this problem which is robust against foreground
residual noise and based on the cross-correlation function $\psi_{\alpha L}(r)$
between diffuse line emission and Ly$\alpha$ emitters (LAE). We compute the
diffuse line (Ly$\alpha$ is used as an example) emission from galaxies in a
$(800{\rm Mpc})^3$ box at $z = 5.7$ and $6.6$. We divide the box in slices and
populate them with $14000(5500)$ LAEs at $z = 5.7(6.6)$, considering duty
cycles from $10^{-3}$ to $1$. Both the LAE number density and slice volume are
consistent with the expected outcome of the Subaru HSC survey. We add gaussian
random noise with variance $\sigma_{\rm N}$ up to 100 times the variance of the
Ly$\alpha$ emission, $\sigma_\alpha$, to simulate foregrounds and compute
$\psi_{\alpha L}(r)$. We find that the signal-to-noise of the observed
$\psi_{\alpha L}(r)$ does not change significantly if $\sigma_{\rm N} \le 10
\sigma_\alpha$ and show that in these conditions the mean line intensity,
$I_{Ly\alpha}$, can be precisely recovered independently of the LAE duty cycle.
Even if $\sigma_{\rm N} = 100 \sigma_\alpha$, $I_\alpha$ can be constrained
within a factor $2$. The method works equally well for any other line (e.g. HI
21 cm, [CII], HeII) used for the intensity mapping experiment. | A fundamental plane for field star-forming galaxies: Star formation rate (SFR), metallicity and stellar mass are within the
important parameters of star--forming galaxies that characterize their
formation and evolution. They are known to be related to each other at low and
high redshift in the mass--metallicity, mass--SFR, and metallicity--SFR
relations. In this work we demonstrate the existence of a plane in the 3D space
defined by the axes SFR [log(SFR)(M_sun yr^-1)], gas metallicity [12+log(O/H)],
and stellar mass [log(M_star/M_sun)] of star-forming galaxies. We used
star--forming galaxies from the "main galaxy sample" of the Sloan Digital Sky
Survey--Data Release 7 (SDSS-DR7) in the redshift range 0.04 < z < 0.1 and
r-magnitudes between 14.5 and 17.77. Metallicities, SFRs, and stellar masses
were taken from the Max-Planck-Institute for Astrophysics-John Hopkins
University (MPA-JHU) emission line analysis database. From a final sample of
44214 galaxies, we find for the first time a fundamental plane for field
galaxies relating the SFR, gas metallicity, and stellar mass for star--forming
galaxies in the local universe. One of the applications of this plane would be
estimating stellar masses from SFR and metallicity. High redshift data from the
literature at redshift ~2.2 and 3.5, do not show evidence for evolution in this
fundamental plane. |
Measuring Dark Energy Properties with Photometrically Classified
Pan-STARRS Supernovae. II. Cosmological Parameters: We use 1169 Pan-STARRS supernovae (SNe) and 195 low-$z$ ($z < 0.1$) SNe Ia to
measure cosmological parameters. Though most Pan-STARRS SNe lack spectroscopic
classifications, in a previous paper (I) we demonstrated that photometrically
classified SNe can be used to infer unbiased cosmological parameters by using a
Bayesian methodology that marginalizes over core-collapse (CC) SN
contamination. Our sample contains nearly twice as many SNe as the largest
previous SN Ia compilation. Combining SNe with Cosmic Microwave Background
(CMB) constraints from Planck, we measure the dark energy equation of state
parameter $w$ to be -0.989$\pm$0.057 (stat$+$sys). If $w$ evolves with redshift
as $w(a) = w_0 + w_a(1-a)$, we find $w_0 = -0.912 \pm 0.149$ and $w_a =$
-0.513$\pm$0.826. These results are consistent with cosmological parameters
from the Joint Lightcurve Analysis and the Pantheon sample. We try four
different photometric classification priors for Pan-STARRS SNe and two
alternate ways of modeling CC SN contamination, finding that no variant gives a
$w$ differing by more than 2% from the baseline measurement. The systematic
uncertainty on $w$ due to marginalizing over CC SN contamination,
$\sigma_w^{\textrm{CC}} = 0.012$, is the third-smallest source of systematic
uncertainty in this work. We find limited (1.6$\sigma$) evidence for evolution
of the SN color-luminosity relation with redshift, a possible systematic that
could constitute a significant uncertainty in future high-$z$ analyses. Our
data provide one of the best current constraints on $w$, demonstrating that
samples with $\sim$5% CC SN contamination can give competitive cosmological
constraints when the contaminating distribution is marginalized over in a
Bayesian framework. | Sturm und Drang: Supernova-Driven Turbulence, Magnetic Fields, and
Cosmic Rays in the Chaotic Starburst Interstellar Medium: Frequent supernova explosions in compact starburst regions are a main shaper
of these regions' interstellar media (ISM). In most starbursts, the supernova
remnants blast open a hot phase that fills the regions and launches a
superwind. Denser starbursts are too overpressured for hot wind formation, but
supernovae still stir up the ISM. I argue that supernovae power ubiquitous
turbulence through each of the starburst ISM phases, including the hot wind,
and that a fluctuation dynamo amplifies magnetic fields until they are in
equipartition with the turbulence. Supernovae can drive turbulence with speeds
of ~1000 km/s in the hot wind and ~20 km/s in the cold molecular gas, depending
on the outer scale. I predict magnetic field strengths of 70 muG in the
Galactic Center starburst, 300 muG in M82 and NGC 253, and 2 mG in Arp 220's
nuclei. The mean magnetic field strengths are a few times stronger in molecular
gas than in hot winds, but do not vary strongly with density within a
starburst. I explain how the dominance of supernova-driven turbulence leads to
near equipartition between the components of starburst ISM. I also consider
implications for cosmic ray (CR) diffusion in starbursts. The high amounts of
power cascading to small scales could confine CRs very effectively in
starbursts, so much that CR transport is dominated by the flow of gas rather
than diffusion through the gas. In addition, I discuss the effects of
turbulence on X-ray line width, the far-infrared--radio correlation, observed
radio polarization, and Faraday rotation measures. Finally, I discuss the many
questions raised regarding the physics of turbulence in starbursts. |
The clustering of X-ray selected AGN at z=0.1: The clustering properties of moderate luminosity ($L_X = \rm 10^{41} -
10^{44} \, erg \,s^{-1}$) X-ray selected AGN at $z\approx0.1$ are explored.
X-ray sources in the redshift interval $0.03<z<0.2$ are selected from a
serendipitous XMM survey of the SDSS footprint (XMM/SDSS) and are
cross-correlated with the SDSS Main galaxy sample. The inferred X-ray AGN
auto-correlation function is described by a power law with amplitude
$r_0\approx5\,$h$^{-1}$Mpc and slope $\gamma\approx2.0$. The corresponding mass
of the dark matter haloes that host X-ray AGN at $z\approx0.1$ is $\approx
10^{13} \,h ^{-1} \, M_{\sun}$. Comparison with studies at higher redshift
shows that this mass scale is characteristic of moderate luminosity X-ray AGN
out to $z\approx 1$. Splitting the AGN sample by rest-frame color shows that
X-ray sources in red hosts are more clustered than those associated with blue
galaxies, in agreement with results at $z\approx1$. We also find that the host
galaxies of X-ray AGN have lower stellar masses compared to the typical central
galaxy of a $\approx 10^{13} \,h ^{-1} \, M_{\sun}$ dark matter halo. AGN hosts
either have experienced less stellar mass growth compared to the average
central galaxy of a $\approx 10^{13} \,h ^{-1} \, M_{\sun}$ halo or a fraction
of them are associated with satellite galaxies. | Measuring the scale dependence of intrinsic alignments using multiple
shear estimates: We present a new method for measuring the scale dependence of the intrinsic
alignment (IA) contamination to the galaxy-galaxy lensing signal, which takes
advantage of multiple shear estimation methods applied to the same source
galaxy sample. By exploiting the resulting correlation of both shape noise and
cosmic variance, our method can provide an increase in the signal-to-noise of
the measured IA signal as compared to methods which rely on the difference of
the lensing signal from multiple photometric redshift bins. For a galaxy-galaxy
lensing measurement which uses LSST sources and DESI lenses, the
signal-to-noise on the IA signal from our method is predicted to improve by a
factor of $\sim 2$ relative to the method of Blazek et al. 2012, for pairs of
shear estimates which yield substantially different measured IA amplitudes and
highly correlated shape noise terms. We show that statistical error necessarily
dominates the measurement of intrinsic alignments using our method. We also
consider a physically motivated extension of the Blazek et al. 2012 method
which assumes that all nearby galaxy pairs, rather than only excess pairs, are
subject to IA. In this case, the signal-to-noise of the method of Blazek et al.
2012 is improved. |
Blazar properties: an update from recent results: After a brief critical overview of the main properties of blazars and their
classification, some significant results from recent multiwavelength
observations are summarized, in the context of the jet physics. | The SAURON project-XXI. The spatially-resolved UV-line strength
relations of early-type galaxies: The unexpected rising flux of early-type galaxies at decreasing ultraviolet
(UV) wavelengths is a long-standing mystery. One important observational
constraint is the correlation between UV-optical colours and Mg2 line strengths
found by Burstein et al. (1988). The simplest interpretation of this phenomenon
is that the UV strength is related to the Mg line strength. Under this
assumption, we expect galaxies with larger Mg gradients to have larger UV
colour gradients. By combining UV imaging from GALEX, optical imaging from MDM
and SAURON integral-field spectroscopy, we investigate the spatially-resolved
relationships between UV colours and stellar population properties of 34
early-type galaxies from the SAURON survey sample. We find that galaxies with
old stellar populations show tight correlations between the FUV colours (FUV-V
and FUV-NUV) and the Mgb index, H{\beta} index and metallicity [Z/H]. The
equivalent correlations for the Fe5015 index, {\alpha}-enhancement
[{\alpha}/Fe] and age are present but weaker. We have also derived logarithmic
internal radial colour, measured line strength and derived stellar population
gradients for each galaxy and again found a strong dependence of the FUV-V and
FUV-NUV colour gradients on both the Mg b line strength and the metallicity
gradients for galaxies with old stellar populations. In particular, global
gradients of Mg b and [Z/H] with respect to the UV colour across galaxies are
consistent with their local gradients within galaxies, suggesting that the
global correlations also hold locally. From a simple model based on multi-band
colour fits of UV upturn and UV-weak galaxies, we have identified a plausible
range of parameters that reproduces the observed radial colour profiles. In
these models, the centers of elliptical galaxies, where the UV flux is strong,
are enhanced in metals by roughly 60% compared to UV-weak regions. |
Mock Quasar-Lyman-α Forest Data-sets for the SDSS-III Baryon
Oscillation Spectroscopic Survey: We describe mock data-sets generated to simulate the high-redshift quasar
sample in Data Release 11 (DR11) of the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS). The mock spectra contain Ly{\alpha} forest
correlations useful for studying the 3D correlation function including Baryon
Acoustic Oscillations (BAO). They also include astrophysical effects such as
quasar continuum diversity and high-density absorbers, instrumental effects
such as noise and spectral resolution, as well as imperfections introduced by
the SDSS pipeline treatment of the raw data. The Ly{\alpha} forest BAO analysis
of the BOSS collaboration, described in Delubac et al. 2014, has used these
mock data-sets to develop and cross-check analysis procedures prior to
performing the BAO analysis on real data, and for continued systematic cross
checks. Tests presented here show that the simulations reproduce sufficiently
well important characteristics of real spectra. These mock data-sets will be
made available together with the data at the time of the Data Release 11. | Estimating the Sunyaev - Zel'dovich signal from quasar hosts using a
Halo Occupation Distribution based approach: The Sunyaev-Zeldovich (SZ) effect is a spectral distortion in the Cosmic
Microwave Background (CMB), caused due to up-scattering of CMB photons by high
energy electron distributions. The largest SZ distortion in the CMB is caused
by the hot electrons present in the intra-cluster medium (ICM). However,
several other small scale astrophysical processes can also contribute to the SZ
distortion in the CMB.
Analytic studies have shown that the interstellar (ISM) electron gas of the
host galaxy heated by quasar feedback can also cause substantial SZ effect. For
successful detection of the quasar feedback signal, the SZ signal from the
virialized gas in the host halos of quasars needs to be properly quantified. In
this dissertation work, I have estimated the SZ signal from quasar hosts using
analytic models of the virialized gas in the ICM/ISM. As a new extension to
existing work I have used the measured Halo Occupation Distribution properties
of quasar hosts. The results show that the average SZ signal from quasar hosts
decreases with redshift. This result is consist what what has been observed by
the Planck team.
I have compared by calculations with the experimental results of Ruan et al.
(2015). While Ruan et al. (2015) claim their detection to be from quasar
feedback, I find that within the errors of my model, their detection can be
explained with halo signal alone, without introducing feedback. |
Improving Constraints on Fundamental Physics Parameters with the
Clustering of Sunyaev-Zeldovich Selected Galaxy Clusters: Upcoming millimeter experiments that probe the cosmic microwave background
(CMB) will observe tens of thousands of galaxy clusters through the thermal
Sunyaev-Zeldovich (tSZ) effect. tSZ selected clusters are powerful probes of
cosmological models, as they trace the late-time growth of structure. Late-time
structure growth is highly sensitive to extensions to the standard cosmological
model ($\Lambda$CDM), such as the sum of the neutrino masses, the dark energy
equation of state, and modifications to general relativity. The nominal
statistic used for cluster observations is their abundances as a function of
redshift. We investigate what additional cosmological information is gained
after including the clustering signal of clusters, the cluster power spectrum.
We forecast the cluster power spectra for the upcoming Simons Observatory and a
CMB Stage-4-like experiment and find that the cluster power spectrum reduces
marginalized constraints on the dark energy equation of state by $3$--$12\%$
and the growth index by $5$--$8\%$, for example. We present the constraints
using a generalized figure of merit and find improvements ranging from
$12$--$18\%$ for extensions, $12$--$19\%$ for the astrophysical nuisance
parameters, and $14$--$25\%$ for $\Lambda$CDM parameters. We also find that if
the bias of clusters as a tracer of the matter density can be measured to
within $3\%$ or better, these improvements can be increased by up to a factor
of $6$. We discuss the possibility of utilizing the clustering signal to
address specific systematic uncertainties present in cluster abundance
measurements. | A complex stellar line-of-sight velocity distribution in the lenticular
galaxy NGC 524: We present the detailed study of the stellar and gaseous kinematics of the
luminous early-type galaxy NGC 524 derived from the long-slit spectroscopic
observations obtained with the Russian 6-m telescope and the IFU data from the
SAURON survey. The stellar line-of-sight velocity distribution (LOSVD) of NGC
524 exhibits strong asymmetry. We performed the comprehensive analysis of the
LOSVD using two complementary approaches implemented on top of the nbursts full
spectral fitting technique, (a) a nonparametric LOSVD recovery and (b) a
parametric recovery of two Gaussian kinematical components having different
stellar populations. We discuss the origin of the complex stellar LOSVD of NGC
524. |
Dusty Winds: Extraplanar PAH Features of Nearby Galaxies: Recent observations have shown the presence of dust and molecular material in
galactic winds, but relatively little is known about the distribution of these
outflow components. To shed some light on this issue, we have used IRAC images
from the Spitzer Space Telescope archive to investigate polycyclic aromatic
hydrocarbon (PAH) emission from a sample of 16 local galaxies with known winds.
Our focus on nearby sources (median distance 8.6 Mpc) has revealed detailed PAH
structure in the winds and allowed us to measure extraplanar PAH emission. We
have identified extraplanar PAH features on scales of ~ 0.8 - 6.0 kpc. We find
a nearly linear correlation between the amount of extraplanar PAH emission and
the total infrared flux, a proxy for star formation activity in the disk. Our
results also indicate a correlation between the height of extraplanar PAH
emission and star formation rate surface density, which supports the idea of a
surface density threshold on the energy or momentum injection rate for
producing detectable extraplanar wind material. | Galaxy power spectrum in redshift space: combining perturbation theory
with the halo model: Theoretical modeling of the redshift-space power spectrum of galaxies is
crucially important to correctly extract cosmological information from redshift
surveys. The task is complicated by the nonlinear biasing and redshift space
distortion effects, which change with halo mass, and by the wide distribution
of halo masses and their occupations by galaxies. One of the main modeling
challenges is the existence of satellite galaxies that have both radial
distribution and large virial velocities inside halos, a phenomenon known as
the Finger-of-God effect. We present a model for the galaxy power spectrum of
in which we decompose a given galaxy sample into central and satellite galaxies
and relate different contributions to 1- and 2-halo terms in a halo model. Our
primary goal is to ensure that any parameters that we introduce have physically
meaningful values, and are not just fitting parameters. For the 2-halo terms we
use the previously developed RSD modeling of halos in the context of
distribution function and perturbation theory approach. This term needs to be
multiplied by the effect of radial distances and velocities of satellites
inside the halo. To this one needs to add the 1-halo terms, which are
non-perturbative. We show that the real space 1-halo terms can be modeled as
almost constant, with the finite extent of the satellites inside the halo
inducing a small k^2R^2 term, where R is related to the size of the halo. We
adopt a similar model for FoG in redshift space, ensuring that FoG velocity
dispersion is related to the halo mass. For FoG k^2 type expansions do not work
and FoG resummation must be used instead. We test several damping functions to
model the velocity dispersion FoG effect. Applying the formalism to mock
galaxies modeled after the "CMASS" sample of the BOSS survey, we find that our
predictions for the redshift-space power spectra are accurate up to k~0.4Mpc/h. |
Cosmological constraints on neutrino masses in light of JWST red and
massive candidate galaxies: The overabundance of the red and massive candidate galaxies observed by the
James Webb Space Telescope (JWST) implies efficient structure formation or
large star formation efficiency at high redshift $z\sim 10$. In the scenario of
a low or moderate star formation efficiency, because massive neutrinos tend to
suppress the growth of structure of the universe, the JWST observation tightens
the upper bound of the neutrino masses. Assuming $\Lambda$ cold dark matter
cosmology and a star formation efficiency $ \in [0.05, 0.3]$ (flat prior), we
perform joint analyses of Planck+JWST and Planck+BAO+JWST, and obtain improved
constraints $\sum m_\nu < 0.196\,\mathrm{eV}$ and $\sum m_\nu <
0.111\,\mathrm{eV}$ at 95% confidence level, respectively. Based on the above
assumptions, the inverted mass ordering, which implies $\sum m_\nu\geq
0.1\mathrm{eV}$, is excluded by Planck+BAO+JWST at 92.7% confidence level. | Suzaku Monitoring of the Seyfert 1 Galaxy NGC5548: Warm Absorber
Location and its Implication for Cosmic Feedback: (Abridged) We present a two month Suzaku X-ray monitoring of the Seyfert 1
galaxy NGC 5548. The campaign consists of 7 observations. We analyze the
response in the opacity of the gas that forms the ionized absorber to ionizing
flux variations. Despite variations by a factor of 4 in the impinging
continuum, the soft X-ray spectra of the source show little spectral
variations, suggesting no response from the ionized absorber. A detailed time
modeling confirms the lack of opacity variations for an absorbing component
with high ionization. Instead, the models tentatively suggest that the
ionization parameter of a low ionization absorbing component might be changing
with the ionizing flux, as expected for gas in photoionization equilibrium.
Using the lack of variations, we set an upper limit of n_e <2.0E7 cm-3 for the
electron density of the gas forming the high ionization, high velocity
component. This implies a large distance from the continuum source (R > 0.033
pc). If the variations in the low ionization component are real, they imply n_e
>9.8E4 cm-3 and R < 3 pc. We discuss our results in terms of two different
scenarios: a large scale outflow originating in the inner parts of the
accretion disk, or a thermally driven wind originating much farther out. Given
the large distance of the wind, the implied mass outflow rate is also large (Mw
> 0.08 Maccr). The associated total kinetic energy deployed by the wind in the
host galaxy (>1.2E56 erg) can be enough to disrupt the interstellar medium,
possibly regulating large scale star formation. The total mass and energy
ejected by the wind is still lower than the one required for cosmic feedback,
even when extrapolated to quasar luminosities. Such feedback would require that
we are observing the wind before it is fully accelerated. |
Determination of the Galaxy Cluster Orientation Using X-ray Images by
FOCAS Method: In our work we considered orientations of bright X-ray halos of the galaxy
clusters (mainly Abell clusters). 78 appropriate clusters were selected using
data from Xgal sample of extragalactic objects in XMM-Newton observation
archive. Position angles and eccentricities of these halos were calculated
applying FOCAS method. No privileged orientations were found. | Primordial Bispectrum and Trispectrum Contributions to the Non-Gaussian
Excursion Set Halo Mass Function with Diffusive Drifting Barrier: The high-mass end of the halo mass function is a sensitive probe of
primordial non-Gaussianity (NG). In a recent study [9] we have computed the NG
halo mass function in the context of the Excursion Set theory and shown that
the primordial NG imprint is coupled to that induced by the non-linear collapse
of dark matter halos. We also found an excellent agreement with N-body
simulation results. Here, we perform a more accurate computation which accounts
for the interval validity of the bispectrum expansion to next-to-leading order
and extend the calculation to the case of a non-vanishing primordial
trispectrum. |
The VIMOS Public Extragalactic Redshift Survey (VIPERS). Luminosity and
stellar mass dependence of galaxy clustering at 0.5<z<1.1: We investigate the dependence of galaxy clustering on luminosity and stellar
mass in the redshift range 0.5<z<1.1, using the first ~55000 redshifts from the
VIMOS Public Extragalactic Redshift Survey (VIPERS). We measured the
redshift-space two-point correlation functions (2PCF), and the projected
correlation function, in samples covering different ranges of B-band absolute
magnitudes and stellar masses. We considered both threshold and binned galaxy
samples, with median B-band absolute magnitudes -21.6<MB-5log(h)<-19.5 and
median stellar masses 9.8<log(M*[Msun/h^2])<10.7. We assessed the real-space
clustering in the data from the projected correlation function, which we model
as a power law in the range 0.2<r_p[Mpc/h]<20. Finally, we estimated the galaxy
bias as a function of luminosity, stellar mass, and redshift, assuming a flat
LCDM model to derive the dark matter 2PCF. We provide the best-fit parameters
of the power-law model assumed for the real-space 2PCF -- the correlation
length and the slope -- as well as the linear bias parameter, as a function of
the B-band absolute magnitude, stellar mass, and redshift. We confirm and
provide the tightest constraints on the dependence of clustering on luminosity
at 0.5<z<1.1. We prove the complexity of comparing the clustering dependence on
stellar mass from samples that are originally flux-limited and discuss the
possible origin of the observed discrepancies. Overall, our measurements
provide stronger constraints on galaxy formation models, which are now required
to match, in addition to local observations, the clustering evolution measured
by VIPERS galaxies between z=0.5 and z=1.1 for a broad range of luminosities
and stellar masses. | The Simons Observatory: a new open-source power spectrum pipeline
applied to the Planck legacy data: We present a reproduction of the Planck 2018 angular power spectra at $\ell >
30$, and associated covariance matrices, for intensity and polarization maps at
100, 143 and 217 GHz. This uses a new, publicly available, pipeline that is
part of the PSpipe package. As a test case we use the same input maps,
ancillary products, and analysis choices as in the Planck 2018 analysis, and
find that we can reproduce the spectra to 0.1$\sigma$ precision, and the
covariance matrices to 10%. We show that cosmological parameters estimated from
our re-derived products agree with the public Planck products to 0.1$\sigma$,
providing an independent cross-check of the Planck team's analysis. Going
forward, the publicly-available code can be easily adapted to use alternative
input maps, data selections and analysis choices, for future optimal analysis
of Planck data with new ground-based Cosmic Microwave Background data. |
Primordial black holes and gravitational waves induced by
exponential-tailed perturbations: Primordial black holes (PBHs) whose masses are in
$\sim[10^{-15}M_\odot,10^{-11}M_{\odot}]$ have been extensively studied as a
candidate of whole dark matter (DM). One of the probes to test such a PBH-DM
scenario is scalar-induced stochastic gravitational waves (GWs) accompanied
with the enhanced primordial fluctuations to form the PBHs with frequency
peaked in the mHz band being targeted by the LISA mission. In order to utilize
the stochastic GWs for checking the PBH-DM scenario, it needs to exactly relate
the PBH abundance and the amplitude of the GWs spectrum. Recently in Kitajima
et al., the impact of the non-Gaussianity of the enhanced primordial curvature
perturbations on the PBH abundance has been investigated based on the peak
theory, and they found that a specific non-Gaussian feature called the
exponential tail significantly increases the PBH abundance compared with the
Gaussian case. In this work, we investigate the spectrum of the induced
stochastic GWs associated with PBH DM in the exponential-tail case. In order to
take into account the non-Gaussianity properly, we employ the diagrammatic
approach for the calculation of the spectrum. We find that the amplitude of the
stochastic GW spectrum is slightly lower than the one for the Gaussian case,
but it can still be detectable with the LISA sensitivity. We also find that the
non-Gaussian contribution can appear on the high-frequency side through their
complicated momentum configurations. Although this feature emerges under the
LISA sensitivity, it might be possible to obtain information about the
non-Gaussianity from GW observation with a deeper sensitivity such as the
DECIGO mission. | High Velocity Dispersion in A Rare Grand Design Spiral Galaxy at
Redshift z=2.18: Although relatively common in the local Universe, only one grand-design
spiral galaxy has been spectroscopically confirmed to lie at z>2 (HDFX 28;
z=2.011), and may prove to be a major merger that simply resembles a spiral in
projection. The rarity of spirals has been explained as a result of disks being
dynamically 'hot' at z>2 which may instead favor the formation of
commonly-observed clumpy structures. Alternatively, current instrumentation may
simply not be sensitive enough to detect spiral structures comparable to those
in the modern Universe. At redshifts <2, the velocity dispersion of disks
decreases, and spiral galaxies are more numerous by z~1. Here we report
observations of the grand design spiral galaxy Q2343-BX442 at z=2.18.
Spectroscopy of ionized gas shows that the disk is dynamically hot, implying an
uncertain origin for the spiral structure. The kinematics of the galaxy are
consistent with a thick disk undergoing a minor merger, which can drive the
formation of short-lived spiral structure. A duty cycle of < 100 Myr for such
tidally-induced spiral structure in a hot massive disk is consistent with their
rarity. |
The parsec-scale structure of radio-loud broad absorption line quasars: Broad absorption line quasars (BAL QSOs) belong to a class of objects not
well-understood as yet. Their UV spectra show BALs in the blue wings of the UV
resonance lines, owing to ionized gas with outflow velocities up to 0.2 c. They
can have radio emission that is difficult to characterize and that needs to be
studied at various wavelengths and resolutions. We aim to study the pc-scale
properties of their synchrotron emission and, in particular, to determine their
core properties. We performed observations in the Very Long Baseline
Interferometry (VLBI) technique, using both the European VLBI Network (EVN) at
5 GHz, and the Very Long Baseline Array (VLBA) at 5 and 8.4 GHz to map the
pc-scale structure of the brightest radio-loud objects of our sample, allowing
a proper morphological interpretation. A variety of morphologies have been
found: 9 BAL QSOs on a total of 11 observed sources have a resolved structure.
Core-jet, double, and symmetric objects are present, suggesting different
orientations. In some cases the sources can be young GPS or CSS. The projected
linear size of the sources, also considering observations from our previous
work for the same objects, can vary from tens of pc to hundreds of kpc. In some
cases, a diffuse emission can be supposed from the missing flux-density with
respect to previous lower resolution observations. Finally, the magnetic field
strength does not significantly differ from the values found in the literature
for radio sources with similar sizes. These results are not easily interpreted
with the youth scenario for BAL QSOs, in which they are generally compact
objects still expelling a dust cocoon. The variety of orientations,
morphologies, and extensions found are presumably related to different possible
angles for the BAL producing outflows, with respect to the jet axis. Moreover,
the phenomenon could be present in various phases of the QSO evolution. | Generalised model-independent characterisation of strong gravitational
lenses V: reconstructing the lensing distance ratio by supernovae for a
general Friedmann universe: We determine the cosmic expansion rate from supernovae of type Ia to set up a
data-based distance measure that does not make assumptions about the
constituents of the universe, i.e. about a specific parametrisation of a
Friedmann cosmological model. The scale, determined by the Hubble constant
$H_0$, is the only free cosmological parameter left in the gravitational
lensing formalism. We investigate to which accuracy and precision the lensing
distance ratio $D$ is determined from the Pantheon sample. Inserting $D$ and
its uncertainty into the lensing equations for given $H_0$, esp. the time-delay
equation between a pair of multiple images, allows to determine lens
properties, esp. differences in the lensing potential ($\Delta \phi$), without
specifying a cosmological model. We expand the luminosity distances into an
analytic orthonormal basis, determine the maximum-likelihood weights for the
basis functions by a globally optimal $\chi^2$-parameter estimation, and derive
confidence bounds by Monte-Carlo simulations. For typical strong lensing
configurations between $z=0.5$ and $z=1.0$, $\Delta \phi$ can be determined
with a relative imprecision of 1.7%, assuming imprecisions of the time delay
and the redshift of the lens on the order of 1%. With only a small, tolerable
loss in precision, the model-independent lens characterisation developed in
this paper series can be generalised by dropping the specific Friedmann model
to determine $D$ in favour of a data-based distance ratio. Moreover, for any
astrophysical application, the approach presented here, provides distance
measures for $z\le2.3$ that are valid in any homogeneous, isotropic universe
with general relativity as theory of gravity. |
Partially Constrained Internal Linear Combination: a method for
low-noise CMB foreground mitigation: Internal Linear Combination (ILC) methods are some of the most widely used
multi-frequency cleaning techniques employed in CMB data analysis. These
methods reduce foregrounds by minimizing the total variance in the coadded map
(subject to a signal-preservation constraint), although often significant
foreground residuals or biases remain. A modification to the ILC method is the
constrained ILC (cILC), which explicitly nulls certain foreground components;
however, this foreground nulling often comes at a high price for ground-based
CMB datasets, with the map noise increasing significantly on small scales. In
this paper we explore a new method, the partially constrained ILC (pcILC),
which allows us to optimize the tradeoff between foreground bias and variance
in ILC methods. In particular, this method allows us to minimize the variance
subject to an inequality constraint requiring that the constrained foregrounds
are reduced by at least a fixed factor, which can be chosen based on the
foreground sensitivity of the intended application. We test our method on
simulated sky maps for a Simons Observatory-like experiment; we find that for
cleaning thermal Sunyaev-Zel'dovich (tSZ) contamination at $\ell \in
[3000,4800]$, if a small tSZ residual of 20% of the standard ILC residual can
be tolerated, the variance of the CMB temperature map is reduced by at least
50% over the cILC value. We also demonstrate an application of this method to
reduce noise in CMB lensing reconstruction. | Running of the scalar spectral index in bouncing cosmologies: We calculate the running of the scalar index in the ekpyrotic and matter
bounce cosmological scenarios, and find that it is typically negative for
ekpyrotic models, while it is typically positive for realizations of the matter
bounce where multiple fields are present. This can be compared to inflation,
where the observationally preferred models typically predict a negative
running. The magnitude of the running is expected to be between $10^{-4}$ and
up to $10^{-2},$ leading in some cases to interesting expectations for
near-future observations. |
CFHTLenS: Improving the quality of photometric redshifts with precision
photometry: Here we present the results of various approaches to measure accurate colours
and photometric redshifts (photo-z's) from wide-field imaging data. We use data
from the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS) which have been
re- processed by the CFHT Lensing Survey (CFHTLenS) team in order to carry out
a number of weak gravitational lensing studies. An emphasis is put on the
correction of systematic effects in the photo-z's arising from the different
Point Spread Functions (PSF) in the five optical bands. Different ways of
correcting these effects are discussed and the resulting photo-z accuracies are
quantified by comparing the photo-z's to large spectroscopic redshift (spec-z)
data sets. Careful homogenisation of the PSF between bands leads to increased
overall accuracy of photo-z's. The gain is particularly pronounced at fainter
magnitudes where galaxies are smaller and flux measurements are affected more
by PSF-effects. We also study possible re- calibrations of the photometric
zeropoints (ZPs) with the help of galaxies with known spec-z's. We find that if
PSF-effects are properly taken into account, a re-calibration of the ZPs
becomes much less important suggesting that previous such re-calibrations
described in the literature could in fact be mostly corrections for PSF-effects
rather than corrections for real inaccuracies in the ZPs. The implications of
this finding for future surveys like KiDS, DES, LSST, or Euclid are mixed. On
the one hand, ZP re-calibrations with spec-z's might not be as accurate as
previously thought. On the other hand, careful PSF homogenisation might provide
a way out and yield accurate, homogeneous photometry without the need for full
spectroscopic coverage. This is the first paper in a series describing the
technical aspects of CFHTLenS. (abridged) | Constraints on Star Forming Galaxies at z> 6.5 from HAWK-I Y-band
Imaging of GOODS-South: We present the results of our search for high-redshift Lyman-break galaxies
over the GOODS-South field. We use HST-ACS data in B, V, i' & z', VLT-ISAAC J
and Ks, Spitzer-IRAC 3.6, 4.5, 5.8 and 8.0 micron data in conjunction with the
new HAWK-I Y-band science verification data to search for dropout galaxies in
the redshift range 6<z<9. We survey ~119 arcmin^2 to Y_AB=25.7 (5sigma), of
which 37.5 arcmin^2 reaches Y_AB=25.9. Candidate z' and Y drop-outs were
selected on the basis of a colour cut of (Y-J)_{AB}>0.75 mag and
(z'-Y)_{AB}>1.0 mag respectively. We find no robust Y-drops (z~9) brighter than
J_{AB}<25.4. In our search for z'-band dropouts (z~6.5-7.5), we identify four
possible candidates, two with z'-drop colours and clear Spitzer-IRAC detections
and two less likely candidates. We also identify two previously-known Galactic
T-dwarf stellar contaminants with these colours, and two likely transient
objects seen in the Y-band data. The implications if all or none of our
candidates are real on the Ultra-Violet galaxy luminosity functions at z>6.5
are explored. We find our number of z'-drop candidates to be insufficient based
on the expected number of z' drops in a simple no-evolution scenario from the
z=3 Lyman-break galaxy luminosity function but we are consistent with the
observed luminosity function at z~6 (if all our candidates are real). However,
if one or both of our best z'-drop candidates are not z>6.5 galaxies, this
would demand evolution of the luminosity function at early epochs. We show that
the future surveys to be conducted with the ESO VISTA telescope over the next
five years will be able to measure the bulk of the luminosity function for both
z' and Y drop-outs. |
The intrinsic shape of bulges: The structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb
galaxies were derived using the GASP2D algorithm and then analyzed to derive
the intrinsic shape of their bulges. We developed a new method to derive the
intrinsic shape of bulges based on photometric data and on the geometrical
relationships between the apparent and intrinsic shapes of bulges and disks.
The method is conceived as completely independent of the studied class of
objects, and it can be applied whenever a triaxial ellipsoid embedded in an
axisymmetric component is considered. We found that the intrinsic shape is well
constrained for a subsample of 115 bulges with favorable viewing angles. A
large fraction of them is characterized by an elliptical section (B/A<0.9).
This fraction is 33%, 55%, and 43% if using their maximum, mean, or median
equatorial ellipticity, respectively. Most of them are flattened along their
polar axis. The distribution of triaxiality is strongly bimodal. This
bimodality is driven by bulges with Sersic index n>2, or equivalently, by the
bulges of galaxies with a bulge-to-total ratio B/T>0.3. Bulges with n<2 and
with B/T<0.3 follow a similar distribution, which is different from that of
bulges with n>2 and with B/T>0.3. In particular, bulges with n<2 and with
B/T<0.3 show a larger fraction of oblate axisymmetric (or nearly axisymmetric)
bulges, a smaller fraction of triaxial bulges, and fewer prolate axisymmetric
(or nearly axisymmetric) bulges with respect to bulges with n>2 and with
B/T>0.3, respectively. According to the numerical simulations of bulge
formation, bulges with n<2, which show a high fraction of oblate axisymmetric
(or nearly axisymmetric) shapes and have B/T<0.3, could be the result of
dissipational minor mergers. Both major dissipational and dissipationless
mergers seem to be required to explain the variety of shapes found for bulges
with n>2 and B/T>0.3. | Physical properties of the X-ray gas as a dynamical diagnosis for galaxy
clusters: We analysed XMM-{\it Newton} EPIC data for 53 galaxy clusters. Through 2D
spectral maps, we provide the most detailed and extended view of the spatial
distribution of temperature (kT), pressure (P), entropy (S) and metallicity (Z)
of galaxy clusters to date with the aim of correlating the dynamical state of
the system to six cool-core diagnoses from the literature. With the objective
of building 2D maps and resolving structures in kT, P, S and Z, we divide the
data in small regions from which spectra can be extracted. Our analysis shows
that when clusters are spherically symmetric the cool-cores (CC) are preserved,
the systems are relaxed with little signs of perturbation, and most of the CC
criteria agree. The disturbed clusters are elongated, show clear signs of
interaction in the 2D maps, and most do not have a cool-core. However, 16 well
studied clusters classified as CC by at least four criteria show spectral maps
that appear disturbed. All of these clusters but one show clear signs of recent
mergers, with a complex structure and geometry but with a cool-core that
remains preserved. Thus, although very useful for CC characterization, most
diagnoses are too simplistic to reproduce the overall structure and dynamics of
galaxy clusters, and therefore the selection of relaxed systems according to
these criteria may affect mass estimates. The complex structure of galaxy
clusters can be reliably assessed through the 2D maps presented here. |
The Spectrum of the Axion Dark Sector: Axions arise in many theoretical extensions of the Standard Model of particle
physics, in particular the "string axiverse". If the axion masses, $m_a$, and
(effective) decay constants, $f_a$, lie in specific ranges, then axions
contribute to the cosmological dark matter and dark energy densities. We
compute the background cosmological (quasi-)observables for models with a large
number of axion fields, $n_{\rm ax}\sim \mathcal{O}(10-100)$, with the masses
and decay constants drawn from statistical distributions. This reduces the
number of parameters from $2n_{\rm ax}$ to a small number of "hyperparameters".
We consider a number of distributions, from those motivated purely by
statistical considerations, to those where the structure is specified according
to a class of M-theory models. Using Bayesian methods we are able to constrain
the hyperparameters of the distributions. In some cases the hyperparameters can
be related to string theory, e.g. constraining the number ratio of axions to
moduli, or the typical decay constant scale needed to provide the correct relic
densities. Our methodology incorporates the use of both random matrix theory
and Bayesian networks. | Cosmic shear full nulling: sorting out dynamics, geometry and
systematics: An explicit full nulling scheme for cosmic shear observations is presented.
It makes possible the construction of shear maps from extended source
distributions for which the lens distance distribution is restricted to a
definite interval. Such a construction allows to build totally independent
shear maps, at all scales, that can be taken advantage of to constrain
background cosmological parameters and systematics using the full statistical
power of cosmic shear observations. Another advantage of such construction is
that, as the lens redshift distribution can be made arbitrarily narrow, scale
mixing due to projection effects can be limited allowing controlled predictions
on the large scale shear power spectrum from perturbation theory calculations. |
Polyspectra searches for sharp oscillatory features in cosmic microwave
sky data: We undertake a thorough search for signatures of sharp oscillatory features
in the WMAP9 power spectrum and bispectrum as well as in the Planck power
spectrum. For the first time, we carry out searches in both the power spectrum
and bispectrum simultaneously, employing well-defined look-elsewhere statistics
to assess significances in a rigorous manner. Developing efficient methods to
scan power spectrum likelihoods for oscillatory features, we present results
for the phenomenological bare sine and cosine modulations, allowing validation
against existing Planck Likelihood surveys, as well as templates that include
the correct sharp feature scaling. In particular, we study degeneracies between
feature and cosmological parameters. For frequencies beyond the scale set by
the acoustic peaks, the dependencies are realised through uninteresting
adjustments of the comoving distance to last scattering. Hence, it is
sufficient to keep cosmological parameters fixed and employ fast Gaussian
approximations to the likelihood as a function of the feature model amplitude.
In cases where results can be compared to the literature, our method shows
excellent agreement. We supplement results from the Planck Likelihood with an
analysis based on the Planck SMICA component separation map that, working on
the assumption that the component separation algorithm is reliable, allows for
the inclusion of a larger sky fraction. In principle, this allows us to place
the most stringent constraints to date on the amplitudes of feature models in
the temperature power spectrum. Invoking the WMAP bispectrum, we perform a
combined power spectrum and bispectrum survey. We use and slightly generalise
statistics developed in previous work to reliably judge the significance of
large feature model amplitude estimates. We conclude that our results are
entirely consistent with a featureless realisation of a Gaussian CMB. | DES Y1 Results: Validating cosmological parameter estimation using
simulated Dark Energy Surveys: We use mock galaxy survey simulations designed to resemble the Dark Energy
Survey Year 1 (DES Y1) data to validate and inform cosmological parameter
estimation. When similar analysis tools are applied to both simulations and
real survey data, they provide powerful validation tests of the DES Y1
cosmological analyses presented in companion papers. We use two suites of
galaxy simulations produced using different methods, which therefore provide
independent tests of our cosmological parameter inference. The cosmological
analysis we aim to validate is presented in DES Collaboration et al. (2017) and
uses angular two-point correlation functions of galaxy number counts and weak
lensing shear, as well as their cross-correlation, in multiple redshift bins.
While our constraints depend on the specific set of simulated realisations
available, for both suites of simulations we find that the input cosmology is
consistent with the combined constraints from multiple simulated DES Y1
realizations in the $\Omega_m-\sigma_8$ plane. For one of the suites, we are
able to show with high confidence that any biases in the inferred
$S_8=\sigma_8(\Omega_m/0.3)^{0.5}$ and $\Omega_m$ are smaller than the DES Y1
$1-\sigma$ uncertainties. For the other suite, for which we have fewer
realizations, we are unable to be this conclusive; we infer a roughly 70%
probability that systematic biases in the recovered $\Omega_m$ and $S_8$ are
sub-dominant to the DES Y1 uncertainty. As cosmological analyses of this kind
become increasingly more precise, validation of parameter inference using
survey simulations will be essential to demonstrate robustness. |
Serendipitous Discovery of Warm Absorbers in the Seyfert 2 Galaxy IRAS
18325-5926: Warm absorption is a common phenomenon in Seyfert 1s and quasars, but rare in
Seyfert 2s. In this paper, we report the detection of warm absorbers with high
energy resolution in the Seyfert 2 galaxy IRAS 18325-5926 for the first time
with Chandra HETGS spectra. An intrinsic absorbing line system with an outflow
velocity ~400 km/s was found, which is contributed by two warm absorbers with
FWHM of 570 km/s and 1360 km/s, respectively. The two absorbers were adjacent,
and doing a transverse motion across our line of sight. We constrained the
distance of the absorbers to a small value, suggesting that the absorbers may
originate from the highly ionized accretion disk wind. The perspective of this
type 2 Seyfert provides the best situation to investigate the vertical part of
the funnel-like outflows. Another weak absorbing line system with zero redshift
was also detected, which could be due to Galactic absorption with very high
temperature, or an intrinsic outflow with very high velocity ~6000 km/s. | Multi-messenger constraints on Abelian-Higgs cosmic string networks: Nielsen-Olesen vortices in the Abelian-Higgs (AH) model are the simplest
realisations of cosmic strings in a gauge field theory. Large-scale numerical
solutions show that the dominant decay channel of a network of AH strings
produced from random initial conditions is classical field radiation. However,
they also show that with special initial conditions, loops of string can be
created for which classical field radiation is suppressed, and which behave
like Nambu-Goto (NG) strings with a dominant decay channel into gravitational
radiation. This indicates that cosmic strings are generically sources of both
high-energy particles and gravitational waves. Here we adopt a simple
parametrisation of the AH string network allowing for both particle and
gravitational wave production. With a reference to a specific model for NG-like
loop distribution, this sets the basis for a ``multi-messenger'' investigation
of this model. We find that, in order to explain the NANOGrav detection of a
possible gravitational wave background, while satisfying the constraint on
NG-like loop production from simulations and bounds from the cosmic microwave
background, the tension of the AH string in Planck units $G\mu$ and the
fraction of the NG-like loops $f_{\rm NG}$ should satisfy $G\mu f_{\rm
NG}^{2.6} \gtrsim 3.2\times 10^{-13}$ at 95$\%$ confidence. On the other hand,
for such string tensions, constraints from the diffuse gamma-ray background
(DGRB) indicate that more than 97$\%$ of the total network energy should be
converted to dark matter (DM) or dark radiation. We also consider joint
constraints on the annihilation cross-section, the mass, and the relic
abundance of DM produced by decays of strings. For example, for a DM mass of
500 GeV, the observed relic abundance can be explained by decaying AH strings
that also account for the NANOGrav signal. |
Phantom behaviour and growth index anomalous evolution in viable f(R)
gravity models: We present numerical calculation of the evolution of a background space-time
metric and sub-horizon matter density perturbations in viable $f(R)$ gravity
models of present dark energy and cosmic acceleration. We found that viable
models generically exhibit recent crossing of the phantom boundary $w_{DE}=-1$.
Moreover, as a consequence of the anomalous growth of density perturbations
during the end of the matter-dominated stage, their growth index evolves
non-monotonically with time and may even become negative. | Lensing by Kerr Black Holes. I: General Lens Equation and Magnification
Formula: We develop a unified, analytic framework for gravitational lensing by Kerr
black holes. In this first paper we present a new, general lens equation and
magnification formula governing lensing by a compact object. Our lens equation
assumes that the source and observer are in the asymptotically flat region and
does not require a small angle approximation. Furthermore, it takes into
account the displacement that occurs when the light ray's tangent lines at the
source and observer do not meet on the lens plane. We then explore our lens
equation in the case when the compact object is a Kerr black hole.
Specifically, we give an explicit expression for the displacement when the
observer is in the equatorial plane of the Kerr black hole as well as for the
case of spherical symmetry. |
Star formation history of barred disc galaxies: We present the first results of a pilot study aimed at understanding the
influence of bars on the evolution of galaxy discs through the study of their
stellar content. We examine here the kinematics, star formation history,
mass-weighted, luminosity-weighted, and single stellar population (SSP)
equivalent ages and metallicities for four galaxies ranging from lenticulars to
late-type spirals. The data employed extends to 2-3 disc scalelengths, with
S/N(A)>50. Several techniques are explored to derive star formation histories
and SSP-equivalent parameters, each of which are shown to be compatible. We
demostrate that the age-metallicity degeneracy is highly reduced by using
spectral fitting techniques --instead of indices-- to derive these parameters.
We found that the majority of the stellar mass in our sample is composed of old
(~10 Gyr) stars. This is true in the bulge and the disc region, even beyond two
disc scalelengths. In the bulge region, we find that the young, dynamically
cold, structures produced by the presence of the bar (e.g., nuclear discs or
rings) are responsible for shaping the bulges' age and metallicity gradients.
In the disc region, a larger fraction of young stars is present in the external
parts of the disc compared with the inner disc. The disc growth is, therefore,
compatible with a moderate inside-out formation scenario, where the luminosity
weighted age changes from ~10 Gyrs in the centre, to ~4 Gyrs at two disc
scalelengths, depending upon the galaxy. For two galaxies, we compare the
metallicity and age gradients of the disc major axis with that of the bar,
finding very important differences. In particular, the stellar population of
the bar is more similar to the bulge than to the disc, indicating that, at
least in those two galaxies, bars formed long ago and have survived to the
present day. (abridged) | Galaxy rotation curves from General Relativity with Renormalization
Group corrections: We consider the application of quantum corrections computed using
renormalization group arguments in the astrophysical domain and show that, for
the most natural interpretation of the renormalization group scale parameter, a
gravitational coupling parameter $G$ varying $10^{-7}$ of its value across a
galaxy (which is roughly a variation of $10^{-12}$ per light-year) is
sufficient to generate galaxy rotation curves in agreement with the
observations. The quality of the resulting fit is similar to the Isothermal
profile quality once both the shape of the rotation curve and the mass-to-light
ratios are considered for evaluation. In order to perform the analysis, we use
recent high quality data from nine regular disk galaxies. For the sake of
comparison, the same set of data is modeled also for the Modified Newtonian
Dynamics (MOND) and for the recently proposed Scalar Tensor Vector Gravity
(STVG). At face value, the model based on quantum corrections clearly leads to
better fits than these two alternative theories. |
The galaxy cluster Ysz-Lx and Ysz-M relations from the WMAP 5-yr data: We use multifrequency matched filters to estimate, in the WMAP 5-year data,
the Sunyaev-Zel'dovich (SZ) fluxes of 893 ROSAT NORAS/REFLEX clusters spanning
the luminosity range Lx,[0.1-2.4]keV = 2 10^{41} - 3.5 10^{45} erg s^{-1}. The
filters are spatially optimised by using the universal pressure profile
recently obtained from combining XMM-Newton observations of the REXCESS sample
and numerical simulations. Although the clusters are individually only
marginally detected, we are able to firmly measure the SZ signal (>10 sigma)
when averaging the data in luminosity/mass bins. The comparison between the
bin-averaged SZ signal versus luminosity and X-ray model predictions shows
excellent agreement, implying that there is no deficit in SZ signal strength
relative to expectations from the X-ray properties of clusters. Using the
individual cluster SZ flux measurements, we directly constrain the Y500-Lx and
Y500-M500 relations, where Y500 is the Compton y-parameter integrated over a
sphere of radius r500. The Y500-M500 relation, derived for the first time in
such a wide mass range, has a normalisation Y*500=[1.60 pm 0.19] 10^{-3}
arcmin^2 at M500=3 10^{14} h^{1} Msun, in excellent agreement with the X-ray
prediction of 1.54 10^{-3} arcmin^2, and a mass exponent of alpha=1.79 pm 0.17,
consistent with the self-similar expectation of 5/3. Constraints on the
redshift exponent are weak due to the limited redshift range of the sample,
although they are compatible with self-similar evolution. | Bayesian Evidence for Both Astrophysical and Primordial Black Holes:
Mapping the GWTC-2 Catalog to Third-Generation Detectors: We perform a hierarchical Bayesian analysis of the GWTC-2 catalog to
investigate the mixed scenario in which the merger events are explained by
black holes of both astrophysical and primordial origin. For the astrophysical
scenario we adopt the phenomenological model used by the LIGO/Virgo
collaboration and we include the correlation between different parameters
inferred from data, the role of the spins in both the primordial and
astrophysical scenarios, and the impact of accretion in the primordial
scenario. Our best-fit mixed model has a strong statistical evidence relative
to the single-population astrophysical model, thus supporting the coexistence
of populations of black-hole mergers of two different origins. In particular,
our results indicate that the astrophysical mergers account for roughly four
times the number of primordial black hole events and predict that
third-generation detectors, such as the Einstein Telescope and Cosmic Explorer,
should detect up to hundreds of mergers from primordial black hole binaries at
redshift $z\gtrsim30$. |
Integral field spectroscopy of a sample of nearby galaxies: II.
Properties of the H ii regions: In this work we analyze the spectroscopic properties of a large number of H
ii regions, \sim2600, located in 38 galaxies. The sample of galaxies has been
assembled from the face-on spirals in the PINGS survey and a sample described
in M\'armol-Queralt\'o (2011, henceforth Paper I). All the galaxies were
observed using Integral Field Spectroscopy with a similar setup, covering their
optical extension up to \sim2.4 effective radii within a wavelength range from
\sim3700 to \sim6900{\AA}. We develop a new automatic procedure to detect H ii
regions, based on the contrast of the H{\alpha} intensity maps. Once detected,
the procedure provides us with the integrated spectra of each individual
segmented region. A well-tested automatic decoupling procedure has been applied
to remove the underlying stellar population, deriving the main proper- ties of
the strongest emission lines in the considered wavelength range (covering from
[O ii] {\lambda}3727 to [S ii] {\lambda}6731). A final catalogue of the
spectroscopic properties of these regions has been created for each galaxy. In
the current study we focused on the understanding of the average properties of
the H ii regions and their radial distributions. We find that the gas-phase
oxygen abundance and the H{\alpha} equivalent width present negative and
positive gradient, respectively. The distribution of slopes is statistically
compatible with a random Gaussian distribution around the mean value, if the
radial distances are measured in units of the respective effective radius. No
difference in the slope is found for galaxies of different morphologies:
barred/non-barred, grand-design/flocculent. Therefore, the effective radius is
a universal scale length for gradients in the evolution of galaxies. Other
properties have a larger variance across each object. | Incidence of Strong MgII Absorbers Towards Different Types of Quasars: We report the first comparative study of strong MgII absorbers seen towards
radio-loud quasars of core-dominated (CDQs) and lobe-dominated (LDQs) types and
normal QSOs. The MgII associated absorption systems having a velocity offset v
< 5000km/s from the systemic velocity of the background quasar were also
excluded. Existing spectroscopic data for redshift-matched sightlines of 3975
CDQs and 1583 LDQs, covering a emission redshift range 0.39-4.87, were analysed
and 864 strong MgII absorbers were found, covering the redshift range
0.45-2.17. The conclusions reached using this well-defined large dataset of
strong MgII absorbers are: (i) The number density, dN/dz, towards CDQs shows a
small, marginally significant excess over the estimate available for QSOs; (ii)
In the redshift space, this difference is reflected in terms of a 1.6sigma
excess of dN/dz over the QSOs, within the narrow redshift interval 1.2-1.8;
(iii) The dN/dbeta distribution (with beta=v/c) for CDQs shows a significant
excess over the distribution found for a redshift and luminosity matched sample
of QSOs, at beta in the range 0.05-0.1. This leads us to infer that a
significant fraction of strong MgII absorption systems seen in this offset
velocity range are probably associated with the CDQs and might be accelerated
into the line of sight by their powerful jets and/or due to the accretion-disk
outflows close to our direction. Support to this scenario comes from a
consistency check in which we only consider the spectral range corresponding to
beta > 0.2. The computed redshift distribution for strong MgII absorbers
towards CDQs now shows excellent agreement with that known for QSOs, as indeed
is expected for purely intervening absorption systems. Thus, it appears that
for CDQs the associated strong MgII absorbers can be seen at much larger
velocities relative to the nucleus than the commonly adopted upper limit of
5000km/s. |
MOND and the Galaxies: We review galaxy formation and dynamics under the MOND hypothesis of modified
gravity, and compare to similar galaxies in Newtonian dynamics with dark
matter. The aim is to find peculiar predictions both to discriminate between
various hypotheses, and to make the theory progress through different
constraints, touching the interpolation function, or the fundamental
acceleration scale. Galaxy instabilities, forming bars and bulges at longer
term, evolve differently in the various theories, and help to bring
constraints, together with the observations of bar frequency. Dynamical
friction and the predicted merger rate could be a sensitive test of theories.
The different scenarios of galaxy formation are compared within the various
theories and observations. | Modelling Non-Linear Effects of Dark Energy: We investigate the capabilities of perturbation theory in capturing
non-linear effects of dark energy. We test constant and evolving $\omega$
models, as well as models involving momentum exchange between dark energy and
dark matter. Specifically, we compare perturbative predictions at 1-loop level
against N-body results for four non-standard equations of state as well as
varying degrees of momentum exchange between dark energy and dark matter. The
interaction is modelled phenomenologically using a time dependent drag term in
the Euler equation. We make comparisons at the level of the matter power
spectrum and the redshift space monopole and quadrupole. The multipoles are
modelled using the Taruya, Nishimichi and Saito (TNS) redshift space spectrum.
We find perturbation theory does very well in capturing non-linear effects
coming from dark sector interaction. We isolate and quantify the 1-loop
contribution coming from the interaction and from the non-standard equation of
state. We find the interaction parameter $\xi$ amplifies scale dependent
signatures in the range of scales considered. Non-standard equations of state
also give scale dependent signatures within this same regime. In redshift space
the match with N-body is improved at smaller scales by the addition of the TNS
free parameter $\sigma_v$. To quantify the importance of modelling the
interaction, we create mock data sets for varying values of $\xi$ using
perturbation theory. This data is given errors typical of Stage IV surveys. We
then perform a likelihood analysis using the first two multipoles on these sets
and a $\xi=0$ modelling, ignoring the interaction. We find the fiducial growth
parameter $f$ is generally recovered even for very large values of $\xi$ both
at $z=0.5$ and $z=1$. The $\xi=0$ modelling is most biased in its estimation of
$f$ for the phantom $\omega=-1.1$ case. |
Tensions with the flat $\boldsymbolΛ$CDM model from
high-redshift cosmography: The longstanding search for the cosmological model that best describes the
Universe has been made more intriguing since the recent discovery of the Hubble
constant, $H_{0}$, tension observed between the value of $H_{0}$ from the
Cosmic Microwave Background and from type Ia supernovae (SNe Ia). Hence, the
commonly trusted flat $\Lambda$CDM model is under investigation. In this
scenario, cosmography is a very powerful technique to investigate the evolution
of the Universe without any cosmological assumption, thus revealing tensions
between observational data and predictions from cosmological models in a
completely model-independent way. We here employ a robust cosmographic
technique based on an orthogonal logarithmic polynomial expansion of the
luminosity distance to fit quasars (QSOs) alone and QSOs combined with
Gamma-Ray Bursts (GRBs), SNe Ia, and Baryon Acoustic Oscillations. To apply
QSOs and GRBs as probes we use, respectively, the Risaliti-Lusso relation
between ultraviolet and X-ray luminosities and the ``Dainotti GRB 3D relation"
among the rest-frame end time of the X-ray plateau emission, its corresponding
luminosity, and the peak prompt luminosity. We also correct QSOs and GRBs for
selection biases and redshift evolution and we employ both the traditional
Gaussian likelihood and the newly discovered best-fit likelihoods for each
probe investigated. This comprehensive analysis reveals a strong tension ($> 4
\, \sigma$) between our data sets and the flat $\Lambda$CDM model proving the
power of both the cosmographic approach and high-redshift sources, such as QSOs
and GRBs, which can probe the Universe at early epochs. | GOODS-Herschel: The far-infrared view of star formation in AGN host
galaxies since z~3: We present a study of the infrared properties of X-ray selected, moderate
luminosity (Lx=10^{42}-10^{44}ergs/s) active galactic nuclei (AGNs) up to z~3,
to explore the links between star formation in galaxies and accretion onto
their central black holes. We use 100um and 160um fluxes from GOODS-Herschel
-the deepest survey yet undertaken by the Herschel telescope- and show that in
>94 per cent of cases these fluxes are dominated by the host. We find no
evidence of any correlation between the X-ray and infrared luminosities of
moderate AGNs at any redshift, suggesting that star-formation is decoupled from
nuclear (AGN) activity. The star formation rates of AGN hosts increase strongly
with redshift; by a factor of 43 from z<0.1 to z=2-3 for AGNs with the same
X-ray luminosities. This increase is consistent with the factor of 25-50
increase in the specific star formation rates (SSFRs) of normal, star-forming
(main-sequence) galaxies. Indeed, the average SSFRs of AGN hosts are only
marginally (20 per cent) lower than those of main-sequence galaxies, with this
small deficit being due to a fraction of AGNs residing in quiescent (low-SSFR)
galaxies. We estimate 79+/-10 per cent of moderate AGNs are hosted in
main-sequence galaxies, 15+/-7 per cent in quiescent galaxies and <10 per cent
in strongly starbursting galaxies. The fractions of all main sequence galaxies
at z<2 experiencing a period of moderate nuclear activity is strongly dependent
on galaxy stellar mass (Mstars); rising from a few per cent at
Mstars~10^{10}Msun to >20 per cent at Mstars>10^{11}Msun. Our results indicate
that it is galaxy stellar mass that is most important in dictating whether a
galaxy hosts a moderate luminosity AGN. We argue that the majority of moderate
nuclear activity is fuelled by internal mechanisms rather than violent mergers,
suggesting that disk instabilities could be an important AGN feeding mechanism. |
Bayesian inference of galaxy formation from the K-band luminosity
function of galaxies: tensions between theory and observation: We conduct Bayesian model inferences from the observed K-band luminosity
function of galaxies in the local Universe, using the semi-analytic model (SAM)
of galaxy formation introduced in Lu et al (2011). The prior distributions for
the 14 free parameters include a large range of possible models. We find that
some of the free parameters, e.g. the characteristic scales for quenching star
formation in both high-mass and low-mass halos, are already tightly constrained
by the single data set. The posterior distribution includes the model
parameters adopted in other SAMs. By marginalising over the posterior
distribution, we make predictions that include the full inferential
uncertainties for the colour-magnitude relation, the Tully-Fisher relation, the
conditional stellar mass function of galaxies in halos of different masses, the
HI mass function, the redshift evolution of the stellar mass function of
galaxies, and the global star formation history. Using posterior predictive
checking with the available observational results, we find that the model
family (i) predicts a Tully-Fisher relation that is curved; (ii) significantly
over predicts the satellite fraction; (iii) vastly over predicts the HI mass
function; (iv) predicts high-z stellar mass functions that have too many low
mass galaxies and too few high mass ones. and (v) predicts a redshift evolution
of the stellar mass density and the star formation history that are in moderate
disagreement. These results suggest that some important processes are still
missing in the current model family and we discuss a number of possible
solutions to solve the discrepancies, such as interactions between galaxies and
dark matter halos, tidal stripping, the bimodal accretion of gas, preheating,
and a redshift-dependent initial mass function. | Properties of galaxies reproduced by a hydrodynamic simulation: Previous simulations of the growth of cosmic structures have broadly
reproduced the 'cosmic web' of galaxies that we see in the Universe, but failed
to create a mixed population of elliptical and spiral galaxies due to numerical
inaccuracies and incomplete physical models. Moreover, because of computational
constraints, they were unable to track the small scale evolution of gas and
stars to the present epoch within a representative portion of the Universe.
Here we report a simulation that starts 12 million years after the Big Bang,
and traces 13 billion years of cosmic evolution with 12 billion resolution
elements in a volume of $(106.5\,{\rm Mpc})^3$. It yields a reasonable
population of ellipticals and spirals, reproduces the distribution of galaxies
in clusters and statistics of hydrogen on large scales, and at the same time
the metal and hydrogen content of galaxies on small scales. |
[CII] and 12CO(1-0) Emission Maps in HLSJ091828.6+514223: A Strongly
Lensed Interacting System at z=5.24: We present Submillimeter Array (SMA) [CII] 158um and Jansky Very Large Array
(JVLA) $^{12}$CO(1-0) line emission maps for the bright, lensed, submillimeter
source at $z=5.2430$ behind Abell 773: HLSJ091828.6+514223 (HLS0918). We
combine these measurements with previously reported line profiles, including
multiple $^{12}$CO rotational transitions, [CI], water and [NII], providing
some of the best constraints on the properties of the interstellar medium (ISM)
in a galaxy at $z>5$. HLS0918 has a total far-infrared (FIR) luminosity
L_FIR(8-1000um) = (1.6$\pm$0.1)x10^14 L_sun/mu, where the total magnification
mu_total = 8.9$\pm$1.9, via a new lens model from the [CII] and continuum maps.
Despite a HyLIRG luminosity, the FIR continuum shape resembles that of a local
LIRG. We simultaneously fit all of the observed spectral line profiles, finding
four components which correspond cleanly to discrete spatial structures
identified in the maps. The two most redshifted spectral components occupy the
nucleus of a massive galaxy, with a source plane separation <1 kpc. The reddest
dominates the continuum map (de-magnified L_FIR = (1.1$\pm$0.2)x10^13 L_sun),
and excites strong water emission in both nuclear components via a powerful FIR
radiation field from the intense star formation. A third star-forming component
is most likely a region of a merging companion (dV ~ 500 km/s) exhibiting
generally similar gas properties. The bluest component originates from a
spatially distinct region, and photo-dissociation region (PDR) analysis
suggests that it is lower density, cooler and forming stars less vigorously
than the other components. Strikingly, it has very strong [NII] emission which
may suggest an ionized, molecular outflow. This comprehensive view of gas
properties and morphology in HLS0918 previews the science possible for a large
sample of high-redshift galaxies once ALMA attains full sensitivity. | Quantifying non-star formation associated 8um dust emission in NGC 628: Combining Ha and IRAC images of the nearby spiral galaxy NGC 628, we find
that between 30-43% of its 8um dust emission is not related to recent star
formation. Contributions from dust heated by young stars are separated by
identifying HII regions in the Ha map and using these areas as a mask to
determine the 8um dust emission that must be due to heating by older stars.
Corrections are made for sub-detection-threshold HII regions, photons escaping
from HII regions and for young stars not directly associated to HII regions
(i.e. 10-100 Myr old stars). A simple model confirms this amount of 8um
emission can be expected given dust and PAH absorption cross-sections, a
realistic star-formation history, and the observed optical extinction values. A
Fourier power spectrum analysis indicates that the 8um dust emission is more
diffuse than the Ha emission (and similar to observed HI), supporting our
analysis that much of the 8um-emitting dust is heated by older stars. The 8um
dust-to-Ha emission ratio declines with galactocentric radius both within and
outside of HII regions, probably due to a radial increase in disk transparency.
In the course of this work, we have also found that intrinsic diffuse Ha
fractions may be lower than previously thought in galaxies, if the differential
extinction between HII regions and diffuse regions is taken into account. |
The Stability of Galaxy Disks: We calculate the stellar surface mass density (Sigma_*) and two-component
(gas+stars) disk stability (Q_RW) for 25 late-type galaxies from the DiskMass
Survey. These calculations are based on fits of a dynamical model to our
ionized-gas and stellar kinematic data performed using a Markov Chain Monte
Carlo sampling of the Bayesian posterior. Marginalizing over all galaxies, we
find a median value of Q_RW=2.0+/-0.9 at 1.5 scale lengths. We also find that
Q_RW is anti-correlated with the star-formation rate surface density
(Sigma_SFR), which can be predicted using a closed set of empirical scaling
relations. Finally, we find that the star-formation efficiency
(Sigma_SFR/Sigma_g) is correlated with Sigma_* and weakly anti-correlated with
Q_RW. The former is consistent with an equilibrium prediction of
Sigma_SFR/Sigma_g propto Sigma_*^{1/2}. Despite its order-of-magnitude range,
we find no correlation of Sigma_SFR/Sigma_g/Sigma_*^{1/2} with any other
physical quantity derived by our study. | Dark Energy coupling with electromagnetism as seen from future
low-medium redshift probes: Beyond the standard cosmological model the late-time accelerated expansion of
the universe can be reproduced by the introduction of an additional dynamical
scalar field. In this case, the field is expected to be naturally coupled to
the rest of the theory's fields, unless a (still unknown) symmetry suppresses
this coupling. Therefore, this would possibly lead to some observational
consequences, such as space-time variations of nature's fundamental constants.
In this paper we investigate the coupling between a dynamical Dark Energy model
and the electromagnetic field, and the corresponding evolution of the fine
structure constant ($\alpha$) with respect to the standard local value
$\alpha_0$. In particular, we derive joint constraints on two dynamical Dark
Energy model parametrizations (the Chevallier-Polarski-Linder and Early Dark
Energy model) and on the coupling with electromagnetism $\zeta$, forecasting
future low-medium redshift observations. We combine supernovae and weak lensing
measurements from the Euclid experiment with high-resolution spectroscopy
measurements of fundamental couplings and the redshift drift from the European
Extremely Large Telescope, highlighting the contribution of each probe.
Moreover, we also consider the case where the field driving the $\alpha$
evolution is not the one responsible for cosmic acceleration and investigate
how future observations can constrain this scenario. |
ICE-COLA: fast simulations for weak lensing observables: Approximate methods to full N-body simulations provide a fast and accurate
solution to the development of mock catalogues for the modeling of galaxy
clustering observables. In this paper we extend ICE-COLA (Izard et al. 2016),
based on an optimized implementation of the approximate COLA method, to produce
weak lensing maps and halo catalogues in the light cone using an integrated and
self consistent approach. We show that despite the approximate dynamics, the
catalogues thus produced enable an accurate modeling of weak lensing
observables one decade beyond the characteristic scale where the growth becomes
non-linear. In particular, we compare ICE-COLA to the MICE-GC N-body simulation
for some fiducial cases representative of upcoming surveys and find that, for
sources at redshift $z=1$, their convergence power spectra agree to within one
percent up to high multipoles (i.e., of order $1000$). The corresponding shear
two point functions, $\xi_{+}$ and $\xi_{-}$, yield similar accuracy down to
$2$ and $20$ arcmin respectively, while tangential shear around a $z=0.5$ lens
sample is accurate down to $4$ arcmin. We show that such accuracy is stable
against an increased angular resolution of the weak lensing maps. Hence, this
opens the possibility of using approximate methods for the joint modeling of
galaxy clustering and weak lensing observables and their covariance in ongoing
and future galaxy surveys. | Spitzer Analysis of HII Region Complexes in the Magellanic Clouds:
Determining a Suitable Monochromatic Obscured Star Formation Indicator: HII regions are the birth places of stars, and as such they provide the best
measure of current star formation rates (SFRs) in galaxies. The close proximity
of the Magellanic Clouds allows us to probe the nature of these star forming
regions at small spatial scales. We aim to determine the monochromatic IR band
that most accurately traces the bolometric IR flux (TIR), which can then be
used to estimate an obscured SFR. We present the spatial analysis, via
aperture/annulus photometry, of 16 LMC and 16 SMC HII region complexes using
the Spitzer IRAC and MIPS bands. UV rocket data and SHASSA H-alpha data are
also included. We find that nearly all of the LMC and SMC HII region SEDs peak
around 70um, from ~10 to ~400 pc from the central sources. As a result, the
sizes of HII regions as probed by 70um is approximately equal to the sizes as
probed by TIR (about 70 pc in radius); the radial profile of the 70um flux,
normalized by TIR, is constant at all radii (70um ~ 0.45 TIR); the 1-sigma
standard deviation of the 70um fluxes, normalized by TIR, is a lower fraction
of the mean (0.05 to 0.12 out to ~220 pc) than the normalized 8, 24, and 160um
normalized fluxes (0.12 to 0.52); and these results are invariant between the
LMC and SMC. From these results, we argue that 70um is the most suitable IR
band to use as a monochromatic obscured star formation indicator because it
most accurately reproduces the TIR of HII regions in the LMC and SMC and over
large spatial scales. We also explore the general trends of the 8, 24, 70, and
160um bands in the LMC and SMC HII region SEDs, radial surface brightness
profiles, sizes, and normalized (by TIR) radial flux profiles. We derive an
obscured SFR equation that is modified from the literature to use 70um
luminosity, SFR(Mo/yr) = 9.7(0.7)x10^{-44} L(70)(ergs/s), which is applicable
from 10 to 300 pc distance from the center of an HII region. |
Primordial Globular Clusters, X-Ray Binaries & Cosmological Reionisation: Globular clusters are dense stellar systems that have typical ages of ~13
billion years, implying that they formed at redshifts of z>~6. Massive stars in
newly formed or primordial globular clusters could have played an important
role during the epoch of cosmological reionisation (z>~6) as sources of
energetic, neutral hydrogen ionising UV photons. We investigate whether or not
these stars could have been as important in death as sources of energetic X-ray
photons as they were during their main sequence lives. Most massive stars are
expected to form in binaries, and an appreciable fraction of these (as much as
~30%) will evolve into X-ray luminous (L_X~10^38 erg/s) high-mass X-ray
binaries (HMXBs). These sources would have made a contribution to the X-ray
background at z>~6. Using Monte Carlo models of a globular cluster, we estimate
the total X-ray luminosity of a population of HMXBs. We compare and contrast
this with the total UV luminosity of the massive stars during their main
sequence lives. For reasonable estimates, we find that the bolometric
luminosity of the cluster peaks at ~10^42 erg/s during the first few million
years, but declines to ~10^41 erg/s after ~5 million years as the most massive
stars evolve off the main sequence. From this time onwards, the total
bolometric luminosity is dominated by HMXBs and falls gradually to ~10^40 erg/s
after ~50 million years. Assuming a power-law spectral energy distribution for
the HMXBs, we calculate the effective number of neutral hydrogen ionisations
per HMXB and show that HMXBs can be as important as sources of ionising
radiation as massive stars. Finally we discuss the implications of our results
for modelling galaxy formation at high redshift and the prospects of using
globular clusters as probes of reionisation. | Evidence for IMF Variations from the Integrated Light of SDSS Galaxies: The H alpha equivalent width (EW) is the ratio of the H alpha flux to the
continuum at 6565{\AA}. In normal star forming galaxies the H alpha flux is
dominated by reprocessed photons from stars with masses greater than 10 M_o and
the 6565{\AA} continuum is predominantly due to 0.7-3.0 M_o red giant stars. In
these galaxies the H alpha EW is effectively the ratio of high mass to low mass
stars and is thus sensitive to the stellar initial mass function (IMF). In
Hoversten & Glazebrook 2008 we used ~131,000 galaxies from the Sloan Digital
Sky Survey to show evidence for systematic variations in the IMF with galaxy
luminosity. In this proceeding we use that sample, with the addition of H
delta_A measurements, to investigate other parameterizations of the IMF. We
find evidence for IMF variations with surface brightness, and also show that,
modulo uncertainties in spectral synthesis models, that 120 M_o stars are
important in accounting for the observed H alpha EW distribution. |
Hubble Frontier Fields : A High Precision Strong Lensing Analysis of
Galaxy Cluster MACSJ0416.1-2403 using ~200 Multiple Images: We present a high-precision mass model of the galaxy cluster
MACSJ0416.1-2403, based on a strong-gravitational-lensing analysis of the
recently acquired Hubble Space Telescope Frontier Fields (HFF) imaging data.
Taking advantage of the unprecedented depth provided by HST/ACS observations in
three passbands, we identify 51 new multiply imaged galaxies, quadrupling the
previous census and bringing the grand total to 68, comprising 194 individual
lensed images. Having selected a subset of the 57 most securely identified
multiply imaged galaxies, we use the Lenstool software package to constrain a
lens model comprised of two cluster-scale dark-matter halos and 98 galaxy-scale
halos. Our best-fit model predicts image positions with an $RMS$ error of
0.68'', which constitutes an improvement of almost a factor of two over
previous, pre-HFF models of this cluster. We find the total projected mass
inside a 200~kpc aperture to be $(1.60\pm0.01)\times 10^{14}\ M_\odot$, a
measurement that offers a three-fold improvement in precision, reaching the
percent level for the first time in any cluster. Finally, we quantify the
increase in precision of the derived gravitational magnification of
high-redshift galaxies and find an improvement by a factor of $\sim$2.5 in the
statistical uncertainty. Our findings impressively confirm that HFF imaging has
indeed opened the domain of high-precision mass measurements for massive
clusters of galaxies. | Cosmic transparency and acceleration: In this paper, by considering an absorption probability independent of photon
wavelength, we show that current type Ia supernovae (SNe Ia) and gamma ray
burst (GRBs) observations plus high-redshift measurements of the cosmic
microwave background (CMB) radiation temperature support cosmic acceleration
regardless of the transparent-universe assumption. Two flat scenarios are
considered in our analyses: the $\Lambda$CDM model and a kinematic model. We
consider $\tau(z)=2\ln(1+z)^{\varepsilon}$, where $\tau(z)$ denotes the opacity
between an observer at $z=0$ and a source at $z$. This choice is equivalent to
deforming the cosmic distance duality relation as $D_LD^{-1}_A = (1 +
z)^{2+\varepsilon}$ and, if the absorption probability is independent of photon
wavelength, the CMB temperature evolution law is
$T_{CMB}(z)=T_0(1+z)^{1+2\varepsilon/3 }$. By marginalizing on the
$\varepsilon$ parameter, our analyses rule out a decelerating universe at 99.99
\% c.l. for all scenarios considered. Interestingly, by considering only SNe Ia
and GRBs observations, we obtain that a decelerated universe indicated by
$\Omega_{\Lambda} \leq 0.33$ and $q_0 > 0$ is ruled out around 1.5$\sigma$ c.l.
and 2$\sigma$ c.l., respectively, regardless of the transparent-universe
assumption. |
Adiabatic versus Isocurvature Non--Gaussianity: We study the extent to which one can distinguish primordial non--Gaussianity
(NG) arising from adiabatic and isocurvature perturbations. We make a joint
analysis of different NG models based on various inflationary scenarios:
local-type and equilateral-type NG from adiabatic perturbations and local-type
and quadratic-type NG from isocurvature perturbations together with a
foreground contamination by point sources. We separate the Fisher information
of the bispectrum of CMB temperature and polarization maps by l for the skew
spectrum estimator introduced by Munshi & Heavens (2009) to study the scale
dependence of the signal-to-noise ratio of different NG components and their
correlations. We find that the adiabatic and the isocurvature modes are
strongly correlated, though the phase difference of acoustic oscillations helps
to distinguish them. The correlation between local-and equilateral-type is
weak, but the two isocurvature modes are too strongly correlated to be
discriminated. Point source contamination, to the extent to which it can be
regarded as white noise, can be almost completely separated from the primordial
components for l>100. Including correlations among the different components, we
find that the errors of the NG parameters increase by 20-30% for the WMAP
5-year observation, but 5% for Planck observations. | Black hole mergers: do gas discs lead to spin alignment?: In this Letter we revisit arguments suggesting that the Bardeen-Petterson
effect can coalign the spins of a central supermassive black hole binary
accreting from a circumbinary (or circumnuclear) gas disc. We improve on
previous estimates by adding the dependence on system parameters, and noting
that the nonlinear nature of warp propagation in a thin viscous disc affects
alignment. This reduces the disc's ability to communicate the warp, and can
severely reduce the effectiveness of disc-assisted spin alignment. We test our
predictions with a Monte Carlo realization of random misalignments and
accretion rates and we find that the outcome depends strongly on the spin
magnitude. We estimate a generous upper limit to the probability of alignment
by making assumptions which favour it throughout. Even with these assumptions,
about 40% of black holes with $a \gtrsim 0.5$ do not have time to align with
the disc. If the residual misalignment is not small and it is maintained down
to the final coalescence phase this can give a powerful recoil velocity to the
merged hole. Highly spinning black holes are thus more likely of being subject
to strong recoils, the occurrence of which is currently debated. |
Cosmic microwave background constraints on secret interactions among
sterile neutrinos: Secret contact interactions among eV sterile neutrinos, mediated by a massive
gauge boson $X$ (with $M_X \ll M_W$), and characterized by a gauge coupling
$g_X$, have been proposed as a mean to reconcile cosmological observations and
short-baseline laboratory anomalies. We constrain this scenario using the
latest Planck data on Cosmic Microwave Background anisotropies, and
measurements of baryon acoustic oscillations (BAO). We consistently include the
effect of secret interactions on cosmological perturbations, namely the
increased density and pressure fluctuations in the neutrino fluid, and still
find a severe tension between the secret interaction framework and cosmology.
In fact, taking into account neutrino scattering via secret interactions, we
derive our own mass bound on sterile neutrinos and find (at 95% CL) $m_s <
0.82$ eV or $m_s < 0.29$ eV from Planck alone or in combination with BAO,
respectively. These limits confirm the discrepancy with the laboratory
anomalies. Moreover, we constrain, in the limit of contact interaction, the
effective strength $G_X$ to be $ < 2.8 (2.0) \times 10^{10}\,G_F$ from Planck
(Planck+BAO). This result, together with the mass bound, strongly disfavours
the region with $M_X \sim 0.1$ MeV and relatively large coupling $g_X\sim
10^{-1}$, previously indicated as a possible solution to the small scale dark
matter problem. | A Spectral Atlas of HII Galaxies in the Near-Infrared: Recent models show that TP-AGB stars should dominate the NIR spectra of
populations 0.3 to 2 Gyr old, leaving unique signatures that can be used to
detect young/intermediate stellar population in galaxies. However, no
homogeneous database of star-forming galaxies is available in the NIR to fully
explore these results. With this in mind, we study the NIR spectra of a sample
of 23 HII and starburst galaxies, aimed at characterizing the most prominent
spectral features and continuum shape in the 0.8-2.4 micron region of these
objects. Spectral indices are derived for the relevant absorption lines/bands
and a comparison with optical indices of the same sample available in the
literature is made. We found no correlation between the optical and the NIR
indexes. This is probably due to the differences in aperture between these two
sets of data. That result is further supported by the absence or weakness of
emission lines in the NIR for a subsample galaxies, while in the optical the
emission lines are strong and clear, which means that the ionisation source in
many of these galaxies is not nuclear, but circumnuclear or located in hot
spots. We detected important signatures predicted for a stellar population
dominated by the TP-AGBs, like CN 1.1 micron and CO 2.3 micron. In at least one
galaxy (NGC 4102) the CN band at 1.4 micron was detected for the first time. We
also detect TiO and ZrO bands that have never been reported before in
extragalactic sources. The shape of the continuum emission is found to be
strongly correlated to the presence/lack of emission lines. An observational
template for the star-forming galaxies is derived to be used as a benchmark of
stellar population(s) in starburst galaxies against which to compare near-IR
spectroscopy of different types of galaxies, especially those with AGN activity
and/or those at high-redshift. |
Second order cross-correlation between kSZ and 21 cm fluctuations from
the EoR: The measurement of the brightness temperature fluctuations of neutral
hydrogen 21 cm lines from the Epoch of Reionisation (EoR) is expected to be a
powerful tool for revealing the reionisation process. We study the 21 cm
cross-correlation with Cosmic Microwave Background (CMB) temperature
anisotropies, focusing on the effect of the patchy reionisation. We calculate,
up to second order, the angular power spectrum of the cross-correlation between
21 cm fluctuations and the CMB kinetic Sunyaev-Zel'dovich effect (kSZ) from the
EoR, using an analytical reionisation model. We show that the kSZ and the 21 cm
fluctuations are anti-correlated on the scale corresponding to the typical size
of an ionised bubble at the observed redshift of the 21 cm fluctuations. The
amplitude of the angular power spectrum of the cross-correlation depends on the
fluctuations of the ionised fraction. Especially, in a highly inhomogeneous
reionisation model, the amplitude reaches the order of $100 \mu K^2$ at $\ell
\sim 3000$. We also show that second order terms may help in distinguishing
between reionisation histories. | Improved Treatment of Host-Galaxy Correlations in Cosmological Analyses
With Type Ia Supernovae: Improving the use of Type Ia supernovae (SNIa) as standard candles requires a
better approach to incorporate the relationship between SNIa and the properties
of their host galaxies. Using a spectroscopically-confirmed sample of
$\sim$1600 SNIa, we develop the first empirical model of underlying populations
for SNIa light-curve properties that includes their dependence on host-galaxy
stellar mass. These populations are important inputs to simulations that are
used to model selection effects and correct distance biases within the BEAMS
with Bias Correction (BBC) framework. Here we improve BBC to also account for
SNIa-host correlations, and we validate this technique on simulated data
samples. We recover the input relationship between SNIa luminosity and
host-galaxy stellar mass (the mass step, $\gamma$) to within 0.004 mags, which
is a factor of 5 improvement over the previous method that results in a
$\gamma$-bias of ${\sim}0.02$. We adapt BBC for a novel dust-based model of
intrinsic brightness variations, which results in a greatly reduced mass step
for data ($\gamma = 0.017 \pm 0.008$), and for simulations ($\gamma =0.006 \pm
0.007$). Analysing simulated SNIa, the biases on the dark energy
equation-of-state, $w$, vary from $\Delta w = 0.006(5)$ to $0.010(5)$ with our
new BBC method; these biases are significantly smaller than the $0.02(5)$
$w$-bias using previous BBC methods that ignore SNIa-host correlations. |
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