title
stringlengths 4
245
| abstract
stringlengths 26
3.26k
|
|---|---|
All sky CMB map from cosmic strings integrated Sachs-Wolfe effect | By actively distorting the Cosmic Microwave Background (CMB) over our past
light cone, cosmic strings are unavoidable sources of non-Gaussianity.
Developing optimal estimators able to disambiguate a string signal from the
primordial type of non-Gaussianity requires calibration over synthetic full sky
CMB maps, which till now had been numerically unachievable at the resolution of
modern experiments. In this paper, we provide the first high resolution full
sky CMB map of the temperature anisotropies induced by a network of cosmic
strings since the recombination. The map has about 200 million sub-arcminute
pixels in the healpix format which is the standard in use for CMB analyses
(Nside=4096). This premiere required about 800,000 cpu hours; it has been
generated by using a massively parallel ray tracing method piercing through a
thousands of state of art Nambu-Goto cosmic string numerical simulations which
pave the comoving volume between the observer and the last scattering surface.
We explicitly show how this map corrects previous results derived in the flat
sky approximation, while remaining completely compatible at the smallest
scales.
|
Extended Spherical Collapse and the Accelerating Universe | The influence of the shear stress and angular momentum on the nonlinear
spherical collapse model is discussed in the framework of the Einstein-de
Sitter (EdS) and $\Lambda$CDM models. By assuming that the vacuum component is
not clustering within the homogeneous nonspherical overdensities, we show how
the local rotation and shear affects the linear density threshold for collapse
of the non-relativistic component ($\delta_\mathrm{c}$) and its virial
overdensity ($\Delta_\mathrm{V}$). It is also found that the net effect of
shear and rotation in galactic scale is responsible for higher values of the
linear overdensity parameter as compared with the standard spherical collapse
model (no shear and rotation).
|
Chromatic CCD effects on weak lensing measurements for LSST | Wavelength-dependent point spread functions (PSFs) violate an implicit
assumption in current galaxy shape measurement algorithms that deconvolve the
PSF measured from stars (which have stellar spectral energy distributions
(SEDs)) from images of galaxies (which have galactic SEDs). Since the
absorption length of silicon depends on wavelength, CCDs are a potential source
of PSF chromaticity. Here we develop two toy models to estimate the sensitivity
of the cosmic shear survey from the Large Synoptic Survey Telescope to
chromatic effects in CCDs. We then compare these toy models to simulated
estimates of PSF chromaticity derived from the LSST photon simulator PhoSim. We
find that even though sensor contributions to PSF chromaticity are subdominant
to atmospheric contributions, they can still significantly bias cosmic shear
results if left uncorrected, particularly in the redder filter bands and for
objects that are off-axis in the field of view.
|
KDG 218, a Nearby Ultra-Diffuse Galaxy | We present properties of the low-surface-brightness galaxy KDG 218 observed
with the HST/ACS. The galaxy has a half-light (effective) diameter of $a_e
=47^{\prime\prime}$ and a central surface brightness of $SB_V(0) =
24.4^m/sq^{\prime\prime}$. The galaxy remains unresolved with the HST/ACS,
which implies its distance of {$D > 13.1$ Mpc} and linear effective diameter of
$A_e >3.0$ kpc. We notice that KDG 218 is most likely associated with a galaxy
group around the massive lenticular NGC 4958 galaxy at approximately $22$ Mpc,
or with the Virgo Southern Extension filament at approximately $16.5$ Mpc. At
these distances, the galaxy is classified as an ultra-diffuse galaxy (UDG)
similar to those found in the Virgo, Fornax, and Coma clusters. We also present
a sample of 15 UDG candidates in the Local Volume. These sample galaxies have
the following mean parameters: $\langle D\rangle = 5.1$ Mpc, $\langle
A_e\rangle = 4.8$ kpc, and $\langle SB_B (e) \rangle =
27.4^m/sq^{\prime\prime}$. All the local UDG candidates reside near massive
galaxies located in the regions with the mean stellar mass density (within 1
Mpc) about 50 times greater than the average cosmic density. The local fraction
of UDGs does not exceed 1.5% of the Local Volume population. We notice that the
presented sample of local UDGs is a heterogeneous one containing irregular,
transition, and tidal types, as well as objects consisting of an old stellar
population.
|
Anisotropic inflation reexamined: upper bound on broken rotational
invariance during inflation | The presence of a light vector field coupled to a scalar field during
inflation makes a distinct prediction: the observed correlation functions of
the cosmic microwave background (CMB) become statistically anisotropic. We
study the implications of the current bound on statistical anisotropy derived
from the Planck 2013 CMB temperature data for such a model. The previous
calculations based on the attractor solution indicate that the magnitude of
anisotropy in the power spectrum is proportional to $N^2$, where $N$ is the
number of $e$-folds of inflation counted from the end of inflation. In this
paper, we show that the attractor solution is not compatible with the current
bound, and derive new predictions using another branch of anisotropic
inflation. In addition, we improve upon the calculation of the mode function of
perturbations by including the leading-order slow-roll corrections. We find
that the anisotropy is roughly proportional to
$[2(\varepsilon_H+4\eta_H)/3-4(c-1)]^{-2}$, where $\varepsilon_H$ and $\eta_H$
are the usual slow-roll parameters and $c$ is the parameter in the model,
regardless of the form of potential of an inflaton field. The bound from Planck
implies that breaking of rotational invariance during inflation (characterized
by the background homogeneous shear divided by the Hubble rate) is limited to
be less than ${\cal O}(10^{-9})$. This bound is many orders of magnitude
smaller than the amplitude of breaking of time translation invariance, which is
observed to be ${\cal O}(10^{-2})$.
|
Dual AGN candidates with double-peaked [O III] lines matching that of
confirmed dual AGNs | We have performed a spectral decomposition to search for dual active galactic
nuclei (DAGNs) in the Sloan Digital Sky Survey (SDSS) quasars with $z<0.25$.
Potential DAGN candidates are searched by referencing velocity offsets and
spectral shapes of double-peaked [O III] lines of known DAGNs. Out of 1271 SDSS
quasars, we have identified 77 DAGN candidates. Optical and mid-infrared
diagnostic diagrams are used to investigate the ionizing source in the DAGN
candidates. The optical diagnostic analysis suggests 93\% of them are powered
by AGNs, and mid-infrared diagnostic analysis suggests 97\% are powered by
AGNs. About 1/3 of the SDSS images of the DAGN candidates show signs of tidal
interaction, but we are unable to identify double nuclei in most of them due to
the low spatial resolution of the archival imaging data available for most of
the sample. The radio-loud fraction of the DAGN candidates ($\sim$10\%) is
similar to that of typical AGNs.
|
A Note on Calm Excited States of Inflation | We identify a two-parameter family of excited states within slow-roll
inflation for which either the corrections to the two-point function or the
characteristic signatures of excited states in the three-point function -- i.e.
the enhancement for the flattened momenta configurations-- are absent. These
excited states may nonetheless violate the adiabaticity condition maximally. We
dub these initial states of inflation calm excited states. We show that these
two sets do not intersect, i.e., those that leave the power-spectrum invariant
can be distinguished from their bispectra, and vice versa. The same set of calm
excited states that leave the two-point function invariant for slow-roll
inflation, do the same task for DBI inflation. However, at the level of
three-point function, the calm excited states whose flattened configuration
signature is absent for slow-roll inflation, will lead to an enhancement for
DBI inflation generally, although the signature is smaller than what suggested
by earlier analysis. This example also illustrates that imposing the Wronskian
condition is important for obtaining a correct estimate of the non-Gaussian
signatures.
|
Spatial curvature endgame: Reaching the limit of curvature determination | Current constraints on spatial curvature show that it is dynamically
negligible: $|\Omega_{\rm K}| \lesssim 5 \times 10^{-3}$ (95% CL). Neglecting
it as a cosmological parameter would be premature however, as more stringent
constraints on $\Omega_{\rm K}$ at around the $10^{-4}$ level would offer
valuable tests of eternal inflation models and probe novel large-scale
structure phenomena. This precision also represents the "curvature floor",
beyond which constraints cannot be meaningfully improved due to the cosmic
variance of horizon-scale perturbations. In this paper, we discuss what future
experiments will need to do in order to measure spatial curvature to this
maximum accuracy. Our conservative forecasts show that the curvature floor is
unreachable - by an order of magnitude - even with Stage IV experiments, unless
strong assumptions are made about dark energy evolution and the $\Lambda$CDM
parameter values. We also discuss some of the novel problems that arise when
attempting to constrain a global cosmological parameter like $\Omega_{\rm K}$
with such high precision. Measuring curvature down to this level would be an
important validation of systematics characterisation in high-precision
cosmological analyses.
|
Nearby Galaxies in More Distant Contexts | We use published reconstructions of the star formation history (SFH) of the
Large Magellanic Cloud (LMC), Small Magellanic Cloud, and NGC 300 from the
analysis of resolved stellar populations to investigate where such galaxies
might land on well-known extragalactic diagnostic plots over the galaxies'
lifetime (assuming that nothing other than their stellar populations change).
For example, we find that the evolution of these galaxies implies a complex
evolution in the Tully-Fisher relation with lookback time and that the observed
scatter is consistent with excursions these galaxies take as their stellar
populations evolve. We find that the growth of stellar mass is weighted to
early times, despite the strongly star-forming current nature of the three
systems. Lastly, we find that these galaxies can take circuitous paths across
the color-magnitude diagram. For example, it is possible, within the
constraints provided by the current determination of its SFH, that the LMC
reached the red sequence at intermediate age prior to ending back up on the
blue cloud at the current time. Unfortunately, this behavior happens at
sufficiently early times that our resolved SFH is crude and insufficiently
constraining to convincingly demonstrate that this was the actual evolutionary
path. The limited sample size precludes any general conclusions, but we present
these as examples how we can bridge the study of resolved populations and the
more distant universe.
|
HI observations of the nearest starburst galaxy NGC 253 with the SKA
precursor KAT-7 | We present HI observations of the Sculptor Group starburst spiral galaxy NGC
253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for
the SKA precursor MeerKAT, under construction. The short baselines and low
system temperature of the telescope make it very sensitive to large scale, low
surface brightness emission. The KAT-7 observations detected 33% more flux than
previous VLA observations, mainly in the outer parts and in the halo for a
total HI mass of $2.1 \pm 0.1$ $\times 10^{9}$ M$_{\odot}$. HI can be found at
large distances perpendicular to the plane out to projected distances of ~9-10
kpc away from the nucleus and ~13-14 kpc at the edge of the disk. A novel
technique, based on interactive profile fitting, was used to separate the main
disk gas from the anomalous (halo) gas. The rotation curve (RC) derived for the
HI disk confirms that it is declining in the outer parts, as seen in previous
optical Fabry-Perot measurements. As for the anomalous component, its RC has a
very shallow gradient in the inner parts and turns over at the same radius as
the disk, kinematically lagging by ~100 km/sec. The kinematics of the observed
extra planar gas is compatible with an outflow due to the central starburst and
galactic fountains in the outer parts. However, the gas kinematics shows no
evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the
star formation rate (SFR) is compatible with the starburst nature of NGC 253.
|
First Co-spatial Comparison of Stellar, Neutral-, and Ionized-gas
Metallicities in a metal-rich galaxy: M83 | We carry out a comparative analysis of the metallicities from the stellar,
neutral-gas, and ionized-gas components in the metal-rich spiral galaxy M83. We
analyze spectroscopic observations taken with the Hubble Space Telescope (HST),
the Large Binocular Telescope (LBT) and the Very Large Telescope (VLT). We
detect a clear depletion of the HI gas, as observed from the HI column
densities in the nuclear region of this spiral galaxy. We find column densities
of log[$N$(HI) cm$^{-2}$] $<$ 20.0 at galactocentric distances of $<$ 0.18 kpc,
in contrast to column densities of log[$N$(HI) cm$^{-2}$] $\sim$ 21.0 in the
galactic disk, a trend observed in other nearby spiral galaxies. We measure a
metallicity gradient of $-$0.03 $\pm$ 0.01 dex kpc$^{-1}$ for the ionized gas,
comparable to the metallicity gradient of a local benchmark of 49 nearby
star-forming galaxies of $-$0.026 $\pm$ 0.002 dex kpc$^{-1}$. Our co-spatial
metallicity comparison of the multi-phase gas and stellar populations shows
excellent agreement outside of the nucleus of the galaxy hinting at a scenario
where the mixing of newly synthesized metals from the most massive stars in the
star clusters takes longer than their lifetimes ($\sim$10 Myr). Finally, our
work shows that caution must be taken when studying the metallicity gradient of
the neutral-gas component in star-forming galaxies, since this can be strongly
biased, as these environments can be dominated by molecular gas. In these
regions the typical metallicity tracers can provide inaccurate abundances as
they may trace both the neutral- and molecular-gas components.
|
Morphological classification of compact and extended radio galaxies
using convolutional neural networks and data augmentation techniques | Machine learning techniques have been increasingly used in astronomical
applications and have proven to successfully classify objects in image data
with high accuracy. The current work uses archival data from the Faint Images
of the Radio Sky at Twenty Centimeters (FIRST) to classify radio galaxies into
four classes: Fanaroff-Riley Class I (FRI), Fanaroff-Riley Class II (FRII),
Bent-Tailed (BENT), and Compact (COMPT). The model presented in this work is
based on Convolutional Neural Networks (CNNs). The proposed architecture
comprises three parallel blocks of convolutional layers combined and processed
for final classification by two feed-forward layers. Our model classified
selected classes of radio galaxy sources on an independent testing subset with
an average of 96\% for precision, recall, and F1 score. The best selected
augmentation techniques were rotations, horizontal or vertical flips, and
increase of brightness. Shifts, zoom and decrease of brightness worsened the
performance of the model. The current results show that model developed in this
work is able to identify different morphological classes of radio galaxies with
a high efficiency and performance
|
Large-scale CO spiral arms and complex kinematics associated with the T
Tauri star RU Lup | While protoplanetary disks often appear to be compact and well-organized in
millimeter continuum emission, CO spectral line observations are increasingly
revealing complex behavior at large distances from the host star. We present
deep ALMA maps of the $J=2-1$ transition of $^{12}$CO, $^{13}$CO, and
C$^{18}$O, as well as the $J=3-2$ transition of DCO$^+$, toward the T Tauri
star RU Lup at a resolution of $\sim0.3''$ ($\sim50$ au). The CO isotopologue
emission traces four major components of the RU Lup system: a compact Keplerian
disk with a radius of $\sim120$ au, a non-Keplerian ``envelope-like'' structure
surrounding the disk and extending to $\sim260$ au from the star, at least five
blueshifted spiral arms stretching up to 1000 au, and clumps outside the spiral
arms located up to 1500 au in projection from RU Lup. We comment on potential
explanations for RU Lup's peculiar gas morphology, including gravitational
instability, accretion of material onto the disk, or perturbation by another
star. RU Lup's extended non-Keplerian CO emission, elevated stellar accretion
rate, and unusual photometric variability suggest that it could be a
scaled-down Class II analog of the outbursting FU Ori systems.
|
VLTI/PIONIER survey of disks around post-AGB binaries. Dust sublimation
physics rules! | Post-AGB binaries are surrounded by circumbinary disks of gas and dust that
are similar to protoplanetary disks found around young stars. We aim to
understand the structure of these disks and identify the physical phenomena at
play in their very inner regions. We want to understand the disk-binary
interaction and to further investigate the comparison with protoplanetary
disks. We have conducted an interferometric snapshot survey of 23 post-AGB
binaries in the near-infrared (H-band) using VLTI/PIONIER. We have fitted the
multiwavelength visibilities and closure phases with purely geometrical models
with an increasing complexity in order to retrieve the sizes, temperatures and
flux ratios of the different components All sources are resolved and the
different components contributing to the H-band flux are dissected. The
environment of these targets is very complex: 13/23 targets need models with
thirteen or more parameters to fit the data. We find that the inner disk rims
follow and extend the size-luminosity relation established for disks around
young stars with an offset toward larger sizes. The measured temperature of the
near-infrared circumstellar emission of post-AGB binaries is lower (Tsub~1200K)
than for young stars, probably due to a different dust mineralogy and/or gas
density in the dust sublimation region. The dusty inner rims of the
circumbinary disks around post-AGB binaries are ruled by dust sublimation
physics. Additionally, a significant amount of the circumstellar H-band flux is
over-resolved (14 targets have more than 10% of their non-stellar flux
over-resolved) hinting for more structure from a yet unknown origin (disk
structure or outflow). The amount of over-resolved flux is larger than around
young stars. Due to the complexity of these targets, interferometric imaging is
a necessary tool to reveal the interacting inner regions in a model-independent
way.
|
CANDELS Multiwavelength catalogs: Source Identification and Photometry
in the CANDELS UKIDSS Ultra-Deep Survey Field | We present the multiwavelength - ultraviolet to mid-infrared - catalog of the
UKIDSS Ultra-Deep Survey (UDS) field observed as part of the Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS). Based on publicly
available data, the catalog includes: the CANDELS data from the Hubble Space
Telescope (near-infrared WFC3 F125W and F160W data and visible ACS F606W and
F814W data), u-band data from CFHT/Megacam, B, V, Rc, i' and z' band data from
Subaru/Suprime-Cam, Y and Ks band data from VLT/HAWK-I, J, H and K bands data
from UKIDSS (Data Release 8), and Spitzer/IRAC data (3.6, 4.5 from SEDS, 5.8
and 8.0um from SpUDS). The present catalog is F160W-selected and contains 35932
sources over an area of 201.7 square arcmin and includes radio and X-ray
detected sources and spectroscopic redshifts available for 210 sources.
|
Solar System planetary tests of \dot c/c | Analytical and numerical calculations show that a putative temporal variation
of the speed of light c, with the meaning of space-time structure constant
c_ST, assumed to be linear over timescales of about one century, would induce a
secular precession of the longitude of the pericenter \varpi of a test particle
orbiting a spherically symmetric body. By comparing such a predicted effect to
the corrections \Delta\dot\varpi to the usual Newtonian/Einsteinian perihelion
precessions of the inner planets of the Solar System, recently estimated by
E.V. Pitjeva by fitting about one century of modern astronomical observations
with the standard dynamical force models of the EPM epehemerides, we obtained
\dot c/c =(0.5 +/- 2)\times 10^-7 yr^-1. Moreover, the possibility that \dot
c/c\neq 0 over the last century is ruled out at 3-12\sigma level by taking the
ratios of the perihelia for different pairs of planets. Our results are
independent of any measurement of the variations of other fundamental constants
which may be explained by a variation of $c$ itself (with the meaning of
electromagnetic constant c_EM). It will be important to repeat such tests if
and when other teams of astronomers will estimate their own corrections to the
standard Newtonian/Einsteinian planetary perihelion precessions.
|
Gravitational-Wave Recoil from the Ringdown Phase of Coalescing Black
Hole Binaries | The gravitational recoil or "kick" of a black hole formed from the merger of
two orbiting black holes, and caused by the anisotropic emission of
gravitational radiation, is an astrophysically important phenomenon. We combine
(i) an earlier calculation, using post-Newtonian theory, of the kick velocity
accumulated up to the merger of two non-spinning black holes, (ii) a
"close-limit approximation" calculation of the radiation emitted during the
ringdown phase, and based on a solution of the Regge-Wheeler and Zerilli
equations using initial data accurate to second post-Newtonian order. We prove
that ringdown radiation produces a significant "anti-kick". Adding the
contributions due to inspiral, merger and ringdown phases, our results for the
net kick velocity agree with those from numerical relativity to 10-15 percent
over a wide range of mass ratios, with a maximum velocity of 180 km/s at a mass
ratio of 0.38.
|
Connecting Galaxies with Halos Across Cosmic Time: Stellar mass assembly
distribution modeling of galaxy statistics | In this work, I explore an empirically motivated model for investigating the
relationship between galaxy stellar masses, star formation rates and their halo
masses and mass accretion histories. The core statistical quantity in this
model is the stellar mass assembly distribution, $P(dM_{*}/dt|\mathbf{X},a)$,
which specifies the probability density distribution of stellar mass assembly
rates given a set of halo properties $\mathbf{X}$ and epoch $a$. Predictions
from this model are obtained by integrating the stellar mass assembly
distribution (SMAD) over halo merger trees, easily obtained from modern,
high-resolution $N$-body simulations. Further properties of the galaxies hosted
by the halos can be obtained by post-processing the stellar mass assembly
histories with stellar population synthesis models. In my particular example
implementation of this model, I use the \citet{behroozi13a} constraint on the
median stellar mass assembly rates of halos as a function of their mass and
redshift to construct an example parameterization of
$P(dM_{*}/dt|\mathbf{X},a)$. This SMAD is then integrated over individual halo
mass accretion histories from $N$-body merger trees starting at z = 4, using
simple rules to account for merging halos. I find that this a simple model can
reproduce qualitatively the bimodal features of the low-redshift galaxy
population, including the qualitative split in the two-point clustering as a
function of specific star formation rate. These results indicate that models
which directly couple halo and galaxy growth through simple efficiency
functions can naturally predict the star formation rate bimodality in
higher-order statistics of the galaxy field, such as its two-point correlations
or galactic conformity signals.
|
CPT-Symmetric Universe | We propose that the state of the universe does {\it not} spontaneously
violate CPT. Instead, the universe after the big bang is the CPT image of the
universe before it, both classically and quantum mechanically. The pre- and
post-bang epochs comprise a universe/anti-universe pair, emerging from nothing
directly into a hot, radiation-dominated era. CPT symmetry selects a unique QFT
vacuum state on such a spacetime, providing a new interpretation of the
cosmological baryon asymmetry, as well as a remarkably economical explanation
for the cosmological dark matter. Requiring only the standard three-generation
model of particle physics (with right-handed neutrinos), a $\mathbb{Z}_2$
symmetry suffices to render one of the right-handed neutrinos stable. We
calculate its abundance from first principles: matching the observed dark
matter density requires its mass to be $4.8\times10^{8}~{\rm GeV}$. Several
other testable predictions follow: (i) the three light neutrinos are Majorana
and allow neutrinoless double $\beta$ decay; (ii) the lightest neutrino is
massless; and (iii) there are no primordial long-wavelength gravitational
waves. We mention connections to the strong CP problem and the arrow of time.
|
CHIME FRB: An application of FFT beamforming for a radio telescope | We have developed FFT beamforming techniques for the CHIME radio telescope,
to search for and localize the astrophysical signals from Fast Radio Bursts
(FRBs) over a large instantaneous field-of-view (FOV) while maintaining the
full angular resolution of CHIME. We implement a hybrid beamforming pipeline in
a GPU correlator, synthesizing 256 FFT-formed beams in the North-South
direction by four formed beams along East-West via exact phasing, tiling a sky
area of ~250 square degrees. A zero-padding approximation is employed to
improve chromatic beam alignment across the wide bandwidth of 400 to 800 MHz.
We up-channelize the data in order to achieve fine spectral resolution of
$\Delta\nu$=24 kHz and time cadence of 0.983 ms, desirable for detecting
transient and dispersed signals such as those from FRBs.
|
C, N and O abundances in red clump stars of the Milky Way | The Hipparcos orbiting observatory has revealed a large number of
helium-core-burning "clump" stars in the Galactic field. These low-mass stars
exhibit signatures of extra-mixing processes that require modeling beyond the
first dredge-up of standard models. The 12C/13C ratio is the most robust
diagnostic of deep mixing, because it is insensitive to the adopted stellar
parameters. In this work we present 12C/13C determinations in a sample of 34
Galactic clump stars as well as abundances of nitrogen, carbon and oxygen.
Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5
A. The wavelength interval 7980-8130 A with strong CN features was analysed in
order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen
abundances were determined from the [O I] line at 6300 A. Compared with the Sun
and dwarf stars of the Galactic disk, mean abundances in the investigated clump
stars suggest that carbon is depleted by about 0.2 dex, nitrogen is enhanced by
0.2 dex and oxygen is close to abundances in dwarfs. Comparisons to
evolutionary models show that the stars fall into two groups: the one is of
first ascent giants with carbon isotope ratios altered according to the first
dredge-up prediction, and the other one is of helium-core-burning stars with
carbon isotope ratios altered by extra mixing. The stars investigated fall to
these groups in approximately equal numbers.
|
Tidal Interaction between the UX Tauri Disk A/C System Revealed by ALMA | We present sensitive and high angular resolution ($\sim$0.2-0.3$''$)
(sub)millimeter (230 and 345 GHz) continuum and CO(2$-$1)/CO(3$-$2) line
archive observations of the disk star system in UX Tauri carried out with ALMA
(The Atacama Large Millimeter/Submillimeter Array). These observations reveal
the gas and dusty disk surrounding the young star UX Tauri A with a large
signal-to-noise ratio ($>$400 in the continuum and $>$50 in the line), and for
the first time is detected the molecular gas emission associated with the disk
of UX Tauri C (with a size for the disk of $<$56 au). No (sub)millimeter
continuum emission is detected at 5$\sigma$-level (0.2 mJy at 0.85 mm)
associated with UX Tauri C. For the component UX Tauri C, we estimate a dust
disk mass of $\leq$ 0.05 M$_\oplus$. Additionally, we report a strong tidal
disk interaction between both disks UX Tauri A/C, separated 360 au in projected
distance. The CO line observations reveal marked spiral arms in the disk of UX
Tauri A and an extended redshifted stream of gas associated with the UX Tauri C
disk. No spiral arms are observed in the dust continuum emission of UX Tauri A.
Assuming a Keplerian rotation we estimate the enclosed masses (disk$+$star)
from their radial velocities in 1.4 $\pm$ 0.6 M$_\odot$ for UX Tauri A, and 70
$\pm$ 30 / $\sin i$ Jupiter masses for UX Tauri C (the latter coincides with
the mass upper limit value for a brown dwarf). The observational evidence
presented here lead us to propose that UX Tauri C is having a close approach of
a possible wide, evolving and eccentric orbit around the disk of UX Tauri A
causing the formation of spiral arms and the stream of molecular gas falling
towards UX Tauri C.
|
Dark Matter Halo Merger Histories Beyond Cold Dark Matter: I - Methods
and Application to Warm Dark Matter | We describe a methodology to accurately compute halo mass functions,
progenitor mass functions, merger rates and merger trees in non-cold dark
matter universes using a self-consistent treatment of the generalized extended
Press-Schechter formalism. Our approach permits rapid exploration of the
subhalo population of galactic halos in dark matter models with a variety of
different particle properties or universes with rolling, truncated, or more
complicated power spectra. We make detailed comparisons of analytically derived
mass functions and merger histories with recent warm dark matter cosmological
N-body simulations, and find excellent agreement. We show that, once the
accretion of smoothly distributed matter is accounted for, coarse-grained
statistics such as the mass accretion history of halos can be almost
indistinguishable between cold and warm dark matter cases. However, the halo
mass function and progenitor mass functions differ significantly, with the warm
dark matter cases being strongly suppressed below the free-streaming scale of
the dark matter. We demonstrate the importance of using the correct solution
for the excursion set barrier first-crossing distribution in warm dark matter -
if the solution for a flat barrier is used instead the truncation of the halo
mass function is much slower, leading to an overestimate of the number of low
mass halos.
|
X-Ray bright optically faint active galactic nuclei in the Subaru Hyper
Suprime-Cam wide survey | We construct a sample of X-ray bright optically faint active galactic nuclei
by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source
catalogs. 53 X-ray sources satisfying i band magnitude fainter than 23.5 mag
and X-ray counts with EPIC-PN detector larger than 70 are selected from 9.1
deg^2, and their spectral energy distributions (SEDs) and X-ray spectra are
analyzed. 44 objects with an X-ray to i-band flux ratio F_X/F_i>10 are
classified as extreme X-ray-to-optical flux sources. SEDs of 48 among 53 are
represented by templates of type 2 AGNs or starforming galaxies and show
signature of stellar emission from host galaxies in the optical in the source
rest frame. Infrared/optical SEDs indicate significant contribution of emission
from dust to infrared fluxes and that the central AGN is dust obscured.
Photometric redshifts determined from the SEDs are in the range of 0.6-2.5.
X-ray spectra are fitted by an absorbed power law model, and the intrinsic
absorption column densities are modest (best-fit log N_H = 20.5-23.5 cm^-2 in
most cases). The absorption corrected X-ray luminosities are in the range of
6x10^42 - 2x10^45 erg s^-1. 20 objects are classified as type 2 quasars based
on X-ray luminsosity and N_H. The optical faintness is explained by a
combination of redshifts (mostly z>1.0), strong dust extinction, and in part a
large ratio of dust/gas.
|
From radio-quiet to radio-silent: low luminosity Seyfert radio cores | A strong effort has been devoted to understand the physical origin of radio
emission from low-luminosity AGN (LLAGN), but a comprehensive picture is still
missing. We used high-resolution ($\le$1 arcsec), multi-frequency (1.5, 5.5, 9
and 14 GHz) NSF's Karl G. Jansky Very Large Array (VLA) observations to
characterise the state of the nuclear region of ten Seyfert nuclei, which are
the faintest members of a complete, distance-limited sample of 28 sources. With
the sensitivity and resolution guaranteed by the VLA-A configuration, we
measured radio emission for six sources (NGC3185, NGC3941, NGC4477, NGC4639,
NGC4698 and NGC4725), while for the remaining four (NGC0676, NGC1058, NGC2685
and NGC3486) we put upper limits at tens uJy/beam level, below the previous
0.12 mJy/beam level of Ho&Ulvestad (2001), corresponding to luminosities down
to L$\le10^{19}$ W/Hz at 1.5 GHz for the highest RMS observation. Two sources,
NGC4639 and NGC4698, exhibit spectral slopes compatible with inverted spectra
($\alpha\le$0, $S_{\nu}\,\propto\,{\nu}^{-\alpha}$), hint for radio emission
from an optically-thick core, while NGC4477 exhibits a steep (+0.52$\pm$0.09)
slope. The detected sources are mainly compact on scales $\le$ arcseconds,
predominantly unresolved, except NGC3185 and NGC3941, in which the resolved
radio emission could be associated to star-formation processes. A significant
X-ray - radio luminosities correlation is extended down to very low
luminosities, with slope consistent with inefficient accretion, expected at
such low Eddington ratios. Such sources will be one of the dominant Square
Kilometre Array (SKA) population, allowing a deeper understanding of the
physics underlying such faint AGN.
|
The EDIBLES survey IV. Cosmic ray ionization rates in diffuse clouds
from near-ultraviolet observations of interstellar OH$^+$ | We report cosmic ray ionization rates towards ten reddened stars studied
within the framework of the EDIBLES (ESO Diffuse Interstellar Bands Large
Exploration Survey) program, using the VLT-UVES. For each sightline, between 2
and 10 individual rotational lines of OH$^+$ have been detected in its (0,0)
and (1,0) $A^3\Pi-X^3\Sigma^-$ electronic band system. This allows constraining
of OH$^+$ column densities towards different objects. Results are also
presented for 28 additional sightlines for which only one or rather weak
signals are found. An analysis of these data makes it possible to derive the
primary cosmic ray ionization rate $\zeta_p$ in the targeted diffuse
interstellar clouds. For the ten selected targets, we obtain a range of values
for $\zeta_p$ equal to $(3.9-16.4) \times 10^{-16}~\mathrm{s}^{-1}$. These
values are higher than the numbers derived in previous detections of
interstellar OH$^+$ in the far-infrared / sub-millimeter-wave regions and in
other near-ultraviolet studies. This difference is a result of using new OH$^+$
oscillator strength values and a more complete picture of all relevant OH$^+$
formation and destruction routes (including the effect of proton recombinations
on PAHs), and the relatively high $N$(OH$^+$) seen toward those ten targets.
|
Rapid modelling of the redshift-space power spectrum multipoles for a
masked density field | In this work we reformulate the forward modelling of the redshift-space power
spectrum multipole moments for a masked density field, as encountered in galaxy
redshift surveys. Exploiting the symmetries of the redshift-space correlation
function, we provide a masked-field generalisation of the Hankel transform
relation between the multipole moments in real and Fourier space. Using this
result, we detail how a likelihood analysis requiring computation for a broad
range of desired $P(k)$ models may be executed $10^3-10^4$ times faster than
with other common approaches, together with significant gains in spectral
resolution. We present a concrete application to the complex angular geometry
of the VIPERS PDR-1 release and discuss the validity of this technique for
finite-angle surveys.
|
Fast Lightcones for Combined Cosmological Probes | The combination of different cosmological probes offers stringent tests of
the $\Lambda$CDM model and enhanced control of systematics. For this purpose,
we present an extension of the lightcone generator UFalcon first introduced in
Sgier et al. 2019 (arXiv:1801.05745), enabling the simulation of a
self-consistent set of maps for different cosmological probes. Each realization
is generated from the same underlying simulated density field, and contains
full-sky maps of different probes, namely weak lensing shear, galaxy
overdensity including RSD, CMB lensing, and CMB temperature anisotropies from
the ISW effect. The lightcone generation performed by UFalcon is parallelized
and based on the replication of a large periodic volume simulated with the
GPU-accelerated $N$-Body code PkdGrav3. The post-processing to construct the
lightcones requires only a runtime of about 1 walltime-hour corresponding to
about 100 CPU-hours. We use a randomization procedure to increase the number of
quasi-independent full-sky UFalcon map-realizations, which enables us to
compute an accurate multi-probe covariance matrix. Using this framework, we
forecast cosmological parameter constraints by performing a multi-probe
likelihood analysis for a combination of simulated future stage-IV-like
surveys. We find that the inclusion of the cross-correlations between the
probes significantly increases the information gain in the parameter
constraints. We also find that the use of a non-Gaussian covariance matrix is
increasingly important, as more probes and cross-correlation power spectra are
included. A version of the UFalcon package currently including weak
gravitational lensing is publicly available.
|
Photon-photon interactions as a source of CMB circular polarization | Photon-photon interactions mediated by the neutral hydrogen background can
transform plane polarization into circular polarization, through completely
forward processes, [gamma+gamma+atom-> gamma+ gamma+atom], in which only the
photon polarizations are changed. The ratio of circular to plane polarization
intensities is predicted to be at the level of several times 10^{-5} for some
regions of angular size less than 1/300 and with large plane polarizations.
|
Geoastronomy: Rocky planets as the Lavosier-Lomonosov Bridge from the
non-living to the living world | Life on Earth emerged at the interface of the geosphere, hydrosphere and
atmosphere. This setting serves as our basis for how biological systems
originate on rocky planets. Often overlooked, however, is the fact that the
chemical nature of a rocky planet is ultimately a product of galactic chemical
evolution. Elemental abundances of the major rock-forming elements can be
different for different stars and planets formed at different times in galactic
history. These differences mean that we cannot expect small rocky exoplanets to
be just like Earth. Furthermore, age of the system dictates starting nuclide
inventory from galactic chemical evolution, and past, present and future mantle
and crust thermal regimes. The bulk silicate mantle composition of a rocky
planet modulates the kind of atmosphere and hydrosphere it possesses. Hence,
the ingredients of a rocky planet are as important for its potential to host
life as proximity to the so-called habitable zone around a star where liquid
water is stable at the surface. To make sense of these variables, a new
trans-disciplinary approach is warranted that fuses the disciplines of Geology
and Astronomy into what is here termed, Geoastronomy.
|
Cosmological Inflation in a Generalized Unimodular Gravity | We study some aspects of cosmological inflation in the framework of
unimodular $f(R)$ gravity. To be more clarified, we consider a generic $f(R)$
of the type $f(R)=R+\alpha R^{n}$. By considering Einstein frame counterpart of
the unimodular $f(R)$ gravity, we set the scalaron to be responsible for
cosmological inflation in this setup. We confront our model parameters space
with observational data and impose some constraints on the value of $n$ in this
manner. We show that for the number of e-folds $N=60$, the model is consistent
with observation if $1.89<n<1.918$.
|
Forecasting isocurvature models with CMB lensing information: axion and
curvaton scenarios | Some inflationary models predict the existence of isocurvature primordial
fluctuations, in addition to the well known adiabatic perturbation. Such mixed
models are not yet ruled out by available data sets. In this paper we explore
the possibility of obtaining better constraints on the isocurva- ture
contribution from future astronomical data. We consider the axion and curvaton
inflationary scenarios, and use Planck satellite experimental specifications
together with SDSS galaxy survey to forecast for the best parameter error
estimation by means of the Fisher information matrix formal- ism. In
particular, we consider how CMB lensing information can improve this forecast.
We found substantial improvements for all the considered cosmological
parameters. In the case of isocurvature amplitude this improvement is strongly
model dependent, varying between less than 1% and above 20% around its fiducial
value. Furthermore, CMB lensing enables the degeneracy break between the
isocurvature amplitude and correlation phase in one of the models. In this
sense, CMB lensing information will be crucial in the analysis of future data.
|
First Observation of the Submillimeter Polarization Spectrum in a
Translucent Molecular Cloud | Polarized emission from aligned dust is a crucial tool for studies of
magnetism in the ISM and a troublesome contaminant for studies of CMB
polarization. In each case, an understanding of the significance of the
polarization signal requires well-calibrated physical models of dust grains.
Despite decades of progress in theory and observation, polarized dust models
remain largely underconstrained. During its 2012 flight, the balloon-borne
telescope BLASTPol obtained simultaneous broad-band polarimetric maps of a
translucent molecular cloud at 250, 350, and 500 microns. Combining these data
with polarimetry from the Planck 850 micron band, we have produced a
submillimeter polarization spectrum for a cloud of this type for the first
time. We find the polarization degree to be largely constant across the four
bands. This result introduces a new observable with the potential to place
strong empirical constraints on ISM dust polarization models in a previously
inaccessible density regime. Comparing with models by Draine and Fraisse
(2009), our result disfavors two of their models for which all polarization
arises due only to aligned silicate grains. By creating simple models for
polarized emission in a translucent cloud, we verify that extinction within the
cloud should have only a small effect on the polarization spectrum shape
compared to the diffuse ISM. Thus we expect the measured polarization spectrum
to be a valid check on diffuse ISM dust models. The general flatness of the
observed polarization spectrum suggests a challenge to models where temperature
and alignment degree are strongly correlated across major dust components.
|
The Mass and Absorption Columns of Galactic Gaseous Halos II -- The High
Ionization State Ions | The high ionization-state ions trace the hot gases in the universe, of which
gaseous halos around galaxies are a major contributor. Following Qu & Bregman
(2018), we calculate the gaseous halo contribution to the observed column
density distributions for these ions by convolving the gaseous halo model with
the observed stellar mass function. The predicted column density distribution
reproduces the general shape of the observed column density distribution -- a
broken power law with the break point at $\log N=14.0$ for {\OVI}. Our modeling
suggests that the high column density systems originate from galaxies for which
the virial temperature matches the temperature of the ionization fraction peak.
Specifically, this mass range is $\log M_\star=8.5-10$ for {\OVI}, $\log
M_\star=9.5-10.5$ for {\NeVIII}, and higher for higher ionization state ions
(assuming $T_{\rm max}=2T_{\rm vir}$). A comparison with the observed {\OVI}
column density distribution prefers a large radius model, where the maximum
radius is twice the virial radius. This model may be in conflict with the more
poorly defined {\NeVIII} column density distribution, suggesting further
observations are warranted. The redshift evolution of the high column density
systems is dominated by the change of the cosmic star formation rate, which
decreases from $z=1.0$ to the local universe. Some differences at lower columns
between our models and observations indicate that absorption by the intra-group
(cluster) medium and intergalactic medium are also contributors to the total
column density distributions.
|
The NuSTAR Extragalactic Survey of the James Webb Space Telescope North
Ecliptic Pole Time-Domain Field | We present the $NuSTAR$ extragalactic survey of the $James$ $Webb$ $Space$
$Telescope$ ($JWST$) North Ecliptic Pole (NEP) Time-Domain Field. The survey
covers a $\sim$0.16 deg$^2$ area with a total exposure of 681 ks acquired in a
total of nine observations from three epochs. The survey sensitivities at 20%
of the area are 2.39, 1.14, 2.76, 1.52, and 5.20 $\times$ 10$^{-14}$ erg
cm$^{-2}$ s$^{-1}$ in the 3-24, 3-8, 8-24, 8-16, and 16-24 keV bands,
respectively. The NEP survey is one of the most sensitive extragalactic surveys
with $NuSTAR$ so far. A total of 33 sources were detected above 95% reliability
in at least one of the five bands. We present the number counts, log$N$-log$S$,
measured in the hard X-ray 8-24 and 8-16 keV bands, uniquely accessible by
$NuSTAR$ down to such faint fluxes. We performed source detection on the
XMM-$Newton$ and $Chandra$ observations of the same field to search for soft
X-ray counterparts of each $NuSTAR$ detection. The soft band positions were
used to identify optical and infrared associations. We present the X-ray
properties (hardness ratio and luminosity) and optical-to-X-ray properties of
the detected sources. The measured fraction of candidate Compton-thick (N$\rm
_H\ge10^{24} cm^{-2}$) active galactic nuclei, derived from the hardness ratio,
is between 3% to 27%. As this survey was designed to have variability as its
primary focus, we present preliminary results on multi-epoch flux variability
in the 3-24 keV band.
|
Non--local radiative transfer in strongly inverted masers | Maser transitions are commonly observed in media exhibiting a large range of
densities and temperatures. They can be used to obtain information on the
dynamics and physical conditions of the observed regions. In order to obtain
reliable constraints on the physical conditions prevailing in the masing
regions, it is necessary to model the excitation mechanisms of the energy
levels of the observed molecules. We present a numerical method that enables us
to obtain self-consistent solutions for both the statistical equilibrium and
radiative transfer equations. Using the standard maser theory, the method of
Short Characteristics is extended to obtain the solution of the
integro-differential radiative transfer equation, appropriate to the case of
intense masing lines. We have applied our method to the maser lines of the H2O
molecule and we compare with the results obtained with a less accurate
approach. In the regime of large maser opacities we find large differences in
the intensity of the maser lines that could be as high as several orders of
magnitude. The comparison between the two methods shows, however, that the
effect on the thermal lines is modest. Finally, the effect introduced by rate
coefficients on the prediction of H2O masing lines and opacities is discussed,
making use of various sets of rate coefficients involving He, o-H2 and p-H2. We
find that the masing nature of a line is not affected by the selected
collisional rates. However, from one set to the other the modelled line
opacities and intensities can vary by up to a factor ~2 and ~10 respectively.
|
Primordial mass segregation of star clusters with primordial binaries | Observations of young star-forming regions suggest that star clusters are
born completely mass segregated. These initial conditions are, however,
gradually lost as the star cluster evolves dynamically. For star clusters with
single stars only and a canonical initial mass function, it has been suggested
that traces of these initial conditions vanish at a time $\tau_\mathrm{v}$
between 3 and $3.5\,t_\mathrm{rh}$ (initial half-mass relaxation times). Since
a significant fraction of stars are observed in binary systems and it is widely
accepted that most stars are born in binary systems, we aim to investigate what
role a primordial binary population (even up to $100\,\%$ binaries) plays in
the loss of primordial mass segregation of young star clusters. We used
numerical $N$-body models similar in size to the Orion Nebula Cluster (ONC) --
a representative of young open clusters -- integrated over several relaxation
times to draw conclusions on the evolution of its mass segregation. We also
compared our models to the observed ONC. We found that $\tau_\mathrm{v}$
depends on the binary star fraction and the distribution of initial binary
parameters that include a semi-major axis, eccentricity, and mass ratio. For
instance, in the models with $50\,\%$ binaries, we find $\tau_\mathrm{v} = (2.7
\pm 0.8)\,t_\mathrm{rh}$, while for $100\,\%$ binary fraction, we find a lower
value $\tau_\mathrm{v} = (2.1 \pm 0.6)\,t_\mathrm{rh}$. We also conclude that
the initially completely mass segregated clusters, even with binaries, are more
compatible with the present-day ONC than the non-segregated ones.
|
Scalar and Fermion Two-component SIMP Dark Matter with an Accidental
$\mathbb{Z}^{}_4$ Symmetry | In this paper, we construct for the first time a two-component strongly
interacting massive particles (SIMP) dark matter (DM) model, where a complex
scalar and a vector-like fermion play the role of the SIMP DM candidates. These
two particles are stable due to an accidental $\mathbb{Z}^{}_4$ symmetry after
the breaking of a $\text{U}(1)^{}_\textsf{D}$ gauge symmetry. By introducing
one extra complex scalar as a mediator between the SIMP particles, this model
can have $3 \to 2$ processes that determine the DM relic density. On the other
hand, the SIMP DM particles can maintain kinetic equilibrium with the thermal
bath until the DM freeze-out temperature via the $\text{U}(1)^{}_\textsf{D}$
gauge couplings. Most importantly, we find an unavoidable two-loop induced $2
\to 2$ process tightly connecting to the $3 \to 2$ process that would
redistribute the SIMP DM number densities after the chemical freeze-out of DM.
Moreover, this redistribution would significantly modify the predictions of the
self-interacting cross section of DM compared with other SIMP models. It is
crucial to include the two-loop induced $2 \to 2$ annihilations to obtain the
correct DM phenomenology.
|
As a matter of tension -- kinetic energy spectra in MHD turbulence | Magnetized turbulence is ubiquitous in many astrophysical and terrestrial
systems but no complete, uncontested theory even in the simplest form,
magnetohydrodynamics (MHD), exists. Many theories and phenomenologies focus on
the joint (kinetic and magnetic) energy fluxes and spectra. We highlight the
importance of treating kinetic and magnetic energies separately to shed light
on MHD turbulence dynamics. We conduct an implicit large eddy simulation of
subsonic, super-Alfv\'enic MHD turbulence and analyze the scale-wise energy
transfer over time. Our key finding is that the kinetic energy spectrum
develops a scaling of approximately $k^{-4/3}$ in the stationary regime as the
kinetic energy cascade is suppressed by magnetic tension. This motivates a
reevaluation of existing MHD turbulence theories with respect to a more
differentiated modeling of the energy fluxes.
|
Recent developments in astrophysical and cosmological exploitation of
microwave surveys | In this article we focus on the astrophysical results and the related
cosmological implications derived from recent microwave surveys, with emphasis
to those coming from the Planck mission. We critically discuss the impact of
systematics effects and the role of methods to separate the cosmic microwave
background signal from the astrophysical emissions and each different
astrophysical component from the others. We then review of the state of the art
in diffuse emissions, extragalactic sources, cosmic infrared back- ground, and
galaxy clusters, addressing the information they provide to our global view of
the cosmic structure evolution and for some crucial physical parameters, as the
neutrino mass. Finally, we present three different kinds of scientific
perspectives for fundamental physics and cosmology offered by the analysis of
on-going and future cosmic microwave background projects at different angular
scales dedicated to anisotropies in total intensity and polarization and to
absolute temperature.
|
Quintessence and (Anti-)Chaplygin Gas in Loop Quantum Cosmology | The concordance model of cosmology contains several unknown components such
as dark matter and dark energy. Many proposals have been made to describe them
by choosing an appropriate potential for a scalar field. We study four models
in the realm of loop quantum cosmology (LQC): the Chaplygin gas, an
inflationary and radiation-like potential, quintessence and an anti-Chaplygin
gas. For the latter we show that all trajectories start and end with a type II
singularity and, depending on the inital value, may go through a bounce. On the
other hand the evolution under the influence of the first three scalar fields
behaves classically at times far away from the big bang singularity and bounces
as the energy density approaches the critical density.
|
Mapping the Diffuse Ultraviolet Sky with GALEX | We present a map of the diffuse ultraviolet cosmic background in two
wavelength bands (FUV: 1530 {\AA}; NUV: 2310 {\AA}) over almost 75% of the sky
using archival data from the GALEX mission. Most of the diffuse flux is due to
dust-scattered starlight and follows a cosecant law with slopes of 545 photons
cm-2 s-1 sr-1 {\AA}-1 and 433 photons cm-2 s-1 sr-1 {\AA}-1 in the FUV and NUV
bands, respectively. There is a strong correlation with the 100 {\mu}m IRAS
flux with an average UV/IR ratio of 300 photons cm-2 s-1 sr-1 {\AA}-1 (MJy
sr-1)-1 in the FUV band and 220 photons cm-2 s-1 sr-1 {\AA}-1 (MJy sr-1)-1 in
the NUV but with significant variations over the sky. In addition to the large
scale distribution of the diffuse light, we note a number of individual
features including bright spots around the hot stars Spica and Achernar.
|
Simulating the formation of massive seed black holes in the early
Universe. III: The influence of X-rays | The direct collapse black hole (DCBH) model attempts to explain the observed
number density of supermassive black holes in the early Universe by positing
that they grew from seed black holes with masses of $10^{4}$-$10^{5} \: {\rm
M_{\odot}}$ that formed by the quasi-isothermal collapse of gas in metal-free
protogalaxies cooled by atomic hydrogen emission. For this model to work,
H$_{2}$ formation must be suppressed in at least some of these systems by a
strong extragalactic radiation field. The predicted number density of DCBH
seeds is highly sensitive to the minimum value of the ultraviolet (UV) flux
required to suppress H$_{2}$ formation, $J_{\rm crit}$. In this paper, we
examine how the value of $J_{\rm crit}$ varies as we vary the strength of a
hypothetical high-redshift X-ray background. We confirm earlier findings that
when the X-ray flux $J_{\rm X}$ is large, the critical UV flux scales as
$J_{\rm crit} \propto J_{\rm X}^{1/2}$. We also carefully explore possible
sources of uncertainty arising from how the X-rays are modelled. We use a
reaction-based reduction technique to analyze the chemistry of H$_{2}$ in the
X-ray illuminated gas and identify a critical subset of 35 chemical reactions
that must be included in our chemical model in order to predict $J_{\rm crit}$
accurately. We further show that $J_{\rm crit}$ is insensitive to the details
of how secondary ionization or He$^{+}$ recombination are modelled, but does
depend strongly on the assumptions made regarding the column density of the
collapsing gas.
|
The $\Lambda_2$ limit of massive gravity | Lorentz-invariant massive gravity is usually associated with a strong
coupling scale $\Lambda_3$. By including non-trivial effects from the
Stueckelberg modes, we show that about these vacua, one can push the strong
coupling scale to higher values and evade the linear vDVZ-discontinuity. For
generic parameters of the theory and generic vacua for the Stueckelberg fields,
the $\Lambda_2$-decoupling limit of the theory is well-behaved and free of any
ghost or gradient-like instabilities. We also discuss the implications for
nonlinear sigma models with Lorentzian target spaces.
|
GRB Afterglow Polarimetry: Past, Present and Future | Gamma-ray bursts and their afterglows are thought to be produced by an
ultrarelativistic jet. One of the most important open questions is the outflow
composition: the energy may be carried out from the central source either as
kinetic energy (of baryons and/or pairs), or in electromagnetic form (Poynting
flux). While the total observable flux may be indistinguishable in both cases,
its polarization properties are expected to differ markedly. The later time
evolution of afterglow polarization is also a powerful diagnostic of the jet
geometry. Again, with subtle and hardly detectable differences in the output
flux, we have distinct polarization predictions.
|
The Race for Supersymmetric Dark Matter at XENON100 and the LHC: Stringy
Correlations from No-Scale F-SU(5) | The discovery of supersymmetry (SUSY) via action of the cold dark matter
candidate is being led on the indirect collider production front by the LHC,
and correspondingly by the XENON100 collaboration on the direct detection
front. We undertake a dual case study of the specific SUSY signatures which the
No-Scale flipped SU(5) x U(1)_X grand unified theory with TeV-scale vector-like
particles (No-Scale F-SU(5)) would exhibit at each of these experiments. We
demonstrate a correlation between the near-term prospects of these two distinct
approaches. We feature a dark matter candidate which is over 99% bino due to a
comparatively large Higgs bilinear mass \mu-term around the electroweak scale,
and thus automatically satisfy the current constraints from the XENON100 and
CDMS/EDELWEISS experiments. We do however expect that the ongoing extension of
the XENON100 run may effectively probe our model. Likewise, our model is also
currently being probed by the LHC via a search for events with ultra-high
multiplicity hadronic jets, which are a characteristic feature of the
distinctive No-Scale F-SU(5) mass hierarchy.
|
Significant foreground unrelated non-acoustic anisotropy on the one
degree scale in WMAP 5-year observations | The spectral variation of the cosmic microwave background (CMB) as observed
by WMAP was tested using foreground reduced WMAP5 data, by producing
subtraction maps at the 1$^\circ$ angular resolution between the two
cosmological bands of V and W, for masked sky areas that avoid the Galactic
disk. The resulting $V-W$ map revealed a non-acoustic signal over and above the
WMAP5 pixel noise, with two main properties. Firstly, it possesses quadrupole
power at the $\approx$ 1 $\mu K$ level which may be attributed to foreground
residuals. Second, it fluctuates also at all values of $\ell >$ 2, especially
on the $1^\circ$ scale ($200 \lesssim \ell \lesssim 300$). The behavior is {\it
random and symmetrical} about zero temperature with a r.m.s. amplitude of
$\approx$ 7 $\mu K$, or 10 % of the maximum CMB anisotropy, which would require
a `cosmic conspiracy' among the foreground components if it is a consequence of
their existences. Both anomalies must be properly diagnosed and corrected if
`precision cosmology' is the claim. The second anomaly is, however, more
interesting because it opens the question on whether the CMB anisotropy
genuinely represents primordial density seeds.
|
Discovery and Follow-up of a Nearby Galaxy from the Arecibo Zone of
Avoidance Survey | The Arecibo L-Band Feed Array Zone of Avoidance (ALFA ZOA) Survey has
discovered a nearby galaxy, ALFA ZOA J1952+1428, at a heliocentric velocity of
+279 km s-1. The galaxy was discovered at low Galactic latitude by 21-cm
emission from neutral hydrogen (Hi). We have obtained follow-up observations
with the EVLA and the 0.9-m SARA optical telescope. The Hi distribution
overlaps an uncataloged, potential optical counterpart. The Hi linear size is
1.4 kpc at our adopted distance of D = 7 Mpc, but the distance estimate is
uncertain as Hubble's law is unreliable at low recessional velocities. The
optical counterpart has mB = 16.9 mag and B - R = 0.1 mag. These
characteristics, including MHI = 107.0 M\odot and LB = 107.5 L\odot, if at 7
Mpc, indicate that this galaxy is a blue compact dwarf, but this remains
uncertain until further follow-up observations are complete. Optical follow-up
observations are ongoing and near infrared follow-up observations have been
scheduled.
|
Delayed Shock-induced Dust Formation in the Dense Circumstellar Shell
Surrounding the Type IIn Supernova SN 2010jl | The light curves of Type IIn supernovae are dominated by the radiative energy
released through the interaction of the supernova shockwaves with their dense
circumstellar medium (CSM). The ultraluminous Type IIn supernova SN 2010jl
exhibits an infrared emission component that is in excess of the extrapolated
UV-optical spectrum as early as a few weeks post-explosion. This emission has
been attributed by some as evidence for rapid formation of dust in the cooling
postshock CSM. We investigate the physical processes that may inhibit or
facilitate the formation of dust in the CSM. When only radiative cooling is
considered, the temperature of the dense shocked gas rapidly drops below the
dust condensation temperature. However, by accounting for the heating of the
postshock gas by the downstream radiation from the shock, we show that dust
formation is inhibited until the radiation from the shock weakens, as the shock
propagates into the less dense outer regions of the CSM. In SN 2010jl dust
formation can therefore only commence after day 380. Only the IR emission since
that epoch can be attributed to the newly formed CSM dust. Observations on day
460 and later show that the IR luminosity exceeds the UV-optical luminosity.
The post-shock dust cannot extinct the radiation emitted by the expanding SN
shock. Therefore, its IR emission must be powered by an interior source, which
we identify with the reverse shock propagating through the SN ejecta. IR
emission before day 380 must therefore be an IR echo from preexisting CSM dust.
|
Extended Red Emission in IC59 and IC63 | We analysed new wide-field, wide- and narrow-band optical images of IC 59 and
IC 63, two nebulae which are externally illuminated by the early B-star
{\gamma} Cas, with the objective of mapping the extended red emission (ERE), a
dust-related photoluminescence process that is still poorly understood, in
these two clouds. The spatial distribution of the ERE relative to the direction
of the incident radiation and relative to other emission processes, whose
carriers and excitation requirements are known, provides important constraints
on the excitation of the ERE. In both nebulae, we find the ERE intensity to
peak spatially well before the more extended distribution of mid-infrared
emission in the unidentified infrared bands, supporting earlier findings that
point toward far-ultraviolet (11 eV < E$_\mathrm{{photon}}$ < 13.6 eV) photons
as the source of ERE excitation. The band-integrated absolute intensities of
the ERE in IC 59 and IC 63 measured relative to the number density of photons
available for ERE excitation are lower by about two orders of magnitude
compared to ERE intensities observed in the high-latitude diffuse interstellar
medium (ISM). This suggests that the lifetime of the ERE carriers is
significantly reduced in the more intense radiation field prevailing in IC 59
and IC 63, pointing toward potential carriers that are only marginally stable
against photo-processing under interstellar conditions. A model involving
isolated molecules or molecular ions, capable of inverse internal conversion
and recurrent fluorescence, appears to provide the most likely explanation for
our observational results.
|
From birth associations to field stars: mapping the small-scale orbit
distribution in the Galactic disc | Stars born at the same time in the same place should have formed from gas of
the same element composition. But most stars subsequently disperse from their
birth siblings, in orbit and orbital phase, becoming 'field stars'. Here we
explore and provide direct observational evidence for this process in the Milky
Way disc, by quantifying the probability that orbit-similarity among stars
implies indistinguishable metallicity. We define the orbit similarity among
stars through their distance in action-angle space, $\Delta (J,\theta)$, and
their abundance similarity simply by $\Delta$[Fe/H]. Analyzing a sample of main
sequence stars from Gaia DR2 and LAMOST, we find an excess of pairs with the
same metallicity ($\Delta\mathrm{[Fe/H]}<0.1$) that extends to remarkably large
separations in $\Delta (J,\theta)$ that correspond to nearly 1 kpc distances.
We assess the significance of this effect through a mock sample, drawn from a
smooth and phase-mixed orbit distribution. Through grouping such star pairs
into associations with a friend-of-friends algorithm linked by $\Delta
(J,\theta)$, we find 100s of mono-abundance groups with $\ge 3$ (to $\gtrsim
20$) members; these groups -- some clusters, some spread across the sky -- are
over an order-of-magnitude more abundant than expected for a smooth phase-space
distribution, suggesting that we are witnessing the 'dissolution' of stellar
birth associations into the field.
|
About the nature of Mercer14 | We used UKIRT near infrared (NIR) broad band JHK photometry, narrow band
imaging of the 1-0S(1) molecular hydrogen emission line and mid infrared
Spitzer IRAC data to investigate the nature of the young cluster Mercer14.
Foreground star counts in decontaminated NIR photometry and a comparison with
the Besancon Galaxy Model are performed to estimate the cluster distance. This
method yields a distance of 2.5kpc with an uncertainty of about 10% and can be
applied to other young and embedded clusters. Mercer14 shows clear signs of
ongoing star formation with several detected molecular hydrogen outflows, a
high fraction of infrared excess sources and an association to a small gas and
dust cloud. Hence, the cluster is less than 4Myrs old and has a line of sight
extinction of A_K=0.8mag. Based on the most massive cluster members we find
that Mercer14 is an intermediate mass cluster with about 500Mo.
|
On the mode structure of imperfect fluids | This paper tries to obtain a simple picture of several aspects of the mode
structure in relativistic non-equilibrium thermodynamics. Its pedagogical focus
is on the relation between long-wavelength perturbation modes of the causal
M\"{u}ller-Israel-Stewart (MIS) theory and those of the traditional Eckart
theory. Principally, this issue was clarified in a series of papers by Hiscock
and Lindblom (see [8-10]). Here, I put together some essential features which
do not require the entire formalism of the complete theory.
|
One-fluid relativistic magnetohydrodynamics equations for a two-fluid
plasma with the Landau-Lifshitz radiation reaction force | By taking into account the radiation reaction force, we derive a set of
one-fluid relativistic magnetohydrody-namics (RMHD) equations with the
Landau-Lifshitz radiation reaction force based on a relativistic two-fluid
plasma. These equations could be used to situations where spatiotemporal scales
of plasma's motion are suffi-ciently large.
|
Small Field Coleman-Weinberg Inflation driven by Fermion Condensate | We revisit the small field Coleman-Weinberg (CW) inflation, which has the
following two problems. First, the smallness of the slow roll parameter
$\epsilon$ requires the inflation scale to be very low. Second, the spectral
index $n_s \approx1+2 \eta$ tends to become smaller compared to the observed
value. In this letter, we consider two possible effects on the dynamics of
inflation: radiatively generated non-minimal coupling to gravity $\xi \phi^2
{\cal R}$ and condensation of fermions coupled to the inflaton as $\phi
\bar\psi \psi$. We show that the fermion condenate can solve the above
problems.
|
The primordial matter power spectrum on sub-galactic scales | The primordial matter power spectrum quantifies fluctuations in the
distribution of dark matter immediately following inflation. Over cosmic time,
over-dense regions of the primordial density field grow and collapse into dark
matter halos, whose abundance and density profiles retain memory of the initial
conditions. By analyzing the image magnifications in eleven strongly-lensed and
quadruply-imaged quasars, we infer the abundance and concentrations of low-mass
halos, and cast the measurement in terms of the amplitude of the primordial
matter power spectrum. We anchor the power spectrum on large scales, isolating
the effect of small-scale deviations from the $\Lambda$CDM prediction. Assuming
an analytic model for the power spectrum and accounting for several sources of
potential systematic uncertainty, including three different models for the halo
mass function, we obtain correlated inferences of $\log_{10}\left(P /
P_{\Lambda \rm{CDM}}\right)$, the power spectrum amplitude relative to the
predictions of the concordance cosmological model, of $0.0_{-0.4}^{+0.5}$,
$0.1_{-0.6}^{+0.7}$, and $0.2_{-0.9}^{+1.0}$ at k = 10, 25 and 50
$\rm{Mpc^{-1}}$ at $68 \%$ confidence, consistent with cold dark matter and
single-field slow-roll inflation.
|
Accurate estimate of the relic density and the kinetic decoupling in
non-thermal dark matter models | Non-thermal dark matter generation is an appealing alternative to the
standard paradigm of thermal WIMP dark matter. We reconsider non-thermal
production mechanisms in a systematic way, and develop a numerical code for
accurate computations of the dark matter relic density. We discuss in
particular scenarios with long-lived massive states decaying into dark matter
particles, appearing naturally in several beyond the standard model theories,
such as supergravity and superstring frameworks. Since non-thermal production
favors dark matter candidates with large pair annihilation rates, we analyze
the possible connection with the anomalies detected in the lepton cosmic-ray
flux by Pamela and Fermi. Concentrating on supersymmetric models, we consider
the effect of these non-standard cosmologies in selecting a preferred mass
scale for the lightest supersymmetric particle as dark matter candidate, and
the consequent impact on the interpretation of new physics discovered or
excluded at the LHC. Finally, we examine a rather predictive model, the
G2-MSSM, investigating some of the standard assumptions usually implemented in
the solution of the Boltzmann equation for the dark matter component, including
coannihilations. We question the hypothesis that kinetic equilibrium holds
along the whole phase of dark matter generation, and the validity of the
factorization usually implemented to rewrite the system of coupled Boltzmann
equation for each coannihilating species as a single equation for the sum of
all the number densities. As a byproduct we develop here a formalism to compute
the kinetic decoupling temperature in case of coannihilating particles, which
can be applied also to other particle physics frameworks, and also to standard
thermal relics within a standard cosmology.
|
The Hector Survey: integral field spectroscopy of 100,000 galaxies | In March 2013, the Sydney--AAO Multi-object Integral field spectrograph
(SAMI) began a major survey of 3400 galaxies at the AAT, the largest of its
kind to date. At the time of writing, over a third of the targets have been
observed and the scientific impact has been immediate. The Manga galaxy survey
has now started at the SDSS telescope and will target an even larger sample of
nearby galaxies. In Australia, the community is now gearing up to deliver a
major new facility called Hector that will allow integral field spectroscopy of
100 galaxies observed simultaneously. By the close of the decade, it will be
possible to obtain integral field spectroscopy of 100,000 galaxies over 3000
square degrees of sky down to r=17 (median). Many of these objects will have HI
imaging from the new ASKAP radio surveys. We discuss the motivation for such a
survey and the use of new cosmological simulations that are properly matched to
the integral field observations. The Hector survey will open up a new and
unique parameter space for galaxy evolution studies.
|
Relieving tensions related to the lensing of CMB temperature power
spectra | The angular power spectra of the cosmic microwave background (CMB)
temperature anisotropies reconstructed from Planck data seem to present too
much gravitational lensing distortion. This is quantified by the control
parameter $A_L$ that should be compatible with unity for a standard cosmology.
With the Class Boltzmann solver and the profile-likelihood method, for this
parameter we measure a 2.6$\sigma$ shift from 1 using the Planck public
likelihoods. We show that, owing to strong correlations with the reionization
optical depth $\tau$ and the primordial perturbation amplitude $A_s$, a
$\sim2\sigma$ tension on $\tau$ also appears between the results obtained with
the low ($\ell\leq 30$) and high ($30<\ell\lesssim 2500$) multipoles
likelihoods. With Hillipop, another high-$\ell$ likelihood built from Planck
data, this difference is lowered to $1.3\sigma$. In this case, the $A_L$ value
is still in disagreement with unity by $2.2\sigma$, suggesting a non-trivial
effect of the correlations between cosmological and nuisance parameters. To
better constrain the nuisance foregrounds parameters, we include the very high
$\ell$ measurements of the Atacama Cosmology Telescope (ACT) and South Pole
Telescope (SPT) experiments and obtain $A_L = 1.03 \pm 0.08$. The
Hillipop+ACT+SPT likelihood estimate of the optical depth is
$\tau=0.052\pm{0.035,}$ which is now fully compatible with the low $\ell$
likelihood determination. After showing the robustness of our results with
various combinations, we investigate the reasons for this improvement that
results from a better determination of the whole set of foregrounds parameters.
We finally provide estimates of the $\Lambda$CDM parameters with our combined
CMB data likelihood.
|
Chemical evolution of galaxies: emerging dust and the different gas
phases in a new multiphase code | Dust plays an important role in the evolution of a galaxy, since it is one of
the main ingredients for efficient star formation. Dust grains are also a
sink/source of metals when they are created/destroyed, and, therefore, a
self-consistent treatment is key in order to correctly model chemical
evolution. In this work, we discuss the implementation of dust physics into our
current multiphase model, which also follows the evolution of atomic, ionised
and molecular gas. Our goal is to model the conversion rates among the
different phases of the interstellar medium, including the creation, growth and
destruction of dust, based on physical principles rather than phenomenological
recipes inasmuch as possible. We first present the updated set of differential
equations and then discuss the results. We calibrate our model against
observations of the Milky Way Galaxy and compare its predictions with extant
data. Our results are broadly consistent with the observed data for
intermediate and high metallicities, but the models tend to produce more dust
than observed in the low metallicity regime.
|
Star formation in Perseus - V. Outflows detected by HARP | Molecular outflows provide an alternative method of identifying protostellar
cores, complementary to recent mid-infrared studies. Continuing our studies of
Perseus, we investigate whether all Spitzer-identified protostars, and
particularly those with low luminosities, drive outflows, and if any new
protostellar cores (perhaps harbouring low-mass sources) can be identified via
their outflows alone. We have used the heterodyne array receiver HARP on JCMT
to make deep 12CO 3-2 maps of submm cores in Perseus, extending and deepening
our earlier study with RxB and bringing the total number of SCUBA cores studied
up to 83. Our survey includes 23/25 of the Dunham et al. (2008) Spitzer
low-luminosity objects believed to be embedded protostars, including three
VeLLOs. All but one of the cores identified as harbouring embedded YSOs have
outflows, confirming outflow detections as a good method for identifying
protostars. We detect outflows from 20 Spitzer low-luminosity objects. We do
not conclusively detect any outflows from IR-quiet cores, though confusion in
clustered regions such as NGC1333 makes it impossible to identify all the
individual driving sources. This similarity in detection rates despite the
difference in search methods and detection limits suggests either that the
sample of protostars in Perseus is now complete, or that the existence of an
outflow contributes to the Spitzer detectability, perhaps through the
contribution of shocked H2 emission in the IRAC bands. For five of the
low-luminosity sources, there is no protostellar envelope detected at 350
microns and the Spitzer emission is entirely due to shocks. Additionally, we
detect the outflow from IRAS 03282+3035 at 850 microns with SCUBA due to CO
line contamination in the continuum passband.
|
Multiversality | Valid ideas that physical reality is vastly larger than human perception of
it, and that the perceived part may not be representative of the whole, exist
on many levels and have a long history. After a brief general inventory of
those ideas and their implications, I consider the cosmological "multiverse"
much discussed in recent scientific literature. I review its theoretical and
(broadly) empirical motivations, and its disruptive implications for the
traditional program of fundamental physics. I discuss the inflationary axion
cosmology, which provides an example where firmly rooted, plausible ideas from
microphysics lead to a well-characterized "mini-multiverse" scenario, with
testable phenomenological consequences.
|
Stable solutions of inflation driven by vector fields | Many models of inflation driven by vector fields alone have been known to be
plagued by pathological behaviors, namely ghost and/or gradient instabilities.
In this work, we seek a new class of vector-driven inflationary models that
evade all of the mentioned instabilities. We build our analysis on the
Generalized Proca Theory with an extension to three vector fields to realize
isotropic expansion. We obtain the conditions required for quasi de-Sitter
solutions to be an attractor analogous to the standard slow-roll one and those
for their stability at the level of linearized perturbations. Identifying the
remedy to the existing unstable models, we provide a simple example and
explicitly show its stability. This significantly broadens our knowledge on
vector inflationary scenarios, reviving potential phenomenological interests
for this class of models.
|
Neutrino mass eigenstates and their ordering: a Bayesian approach | One of the not-yet determined properties of neutrinos is the ordering of
their mass eigenstates. We combine the available data from neutrino
oscillations, neutrinoless double beta decay and Cosmic Microwave Background
observations to derive robust constraints on the mass ordering in a Bayesian
context. Based on arxiv:1801.04946.
|
Examples of backreaction of small scale inhomogeneities in cosmology | In previous work, we introduced a new framework to treat large scale
backreaction effects due to small scale inhomogeneities in general relativity.
We considered one-parameter families of spacetimes for which such backreaction
effects can occur, and we proved that, provided the weak energy condition on
matter is satisfied, the leading effect of small scale inhomogeneities on large
scale dynamics is to produce a traceless effective stress-energy tensor that
itself satisfies the weak energy condition. In this work, we illustrate the
nature of our framework by providing two explicit examples of one-parameter
families with backreaction. The first, based on previous work of Berger, is a
family of polarized vacuum Gowdy spacetimes on a torus, which satisfies all of
the assumptions of our framework. As the parameter approaches its limiting
value, the metric uniformly approaches a smooth background metric, but
spacetime derivatives of the deviation of the metric from the background metric
do not converge uniformly to zero. The limiting metric has nontrivial
backreaction from the small scale inhomogeneities, with an effective
stress-energy that is traceless and satisfies the weak energy condition, in
accord with our theorems. Our second one-parameter family consists of metrics
which have a uniform Friedmann-Lemaitre-Robertson-Walker limit. This family
satisfies all of our assumptions with the exception of the weak energy
condition for matter. In this case, the limiting metric has an effective
stress-energy tensor which is not traceless. We emphasize the importance of
imposing energy conditions on matter in studies of backreaction.
|
General Relativity and Gravitation: A Centennial Perspective | To commemorate the 100th anniversary of general relativity, the International
Society on General Relativity and Gravitation (ISGRG) commissioned a Centennial
Volume, edited by the authors of this article. We jointly wrote introductions
to the four Parts of the Volume which are collected here. Our goal is to
provide a bird's eye view of the advances that have been made especially during
the last 35 years, i.e., since the publication of volumes commemorating
Einstein's 100th birthday. The article also serves as a brief preview of the 12
invited chapters that contain in-depth reviews of these advances. The volume
will be published by Cambridge University Press and released in June 2015 at a
Centennial conference sponsored by ISGRG and the Topical Group of Gravitation
of the American Physical Society.
|
Active Galactic Nuclei and their Large-scale Structure: an eROSITA mock
catalogue | In the context of the upcoming SRG/eROSITA survey, we present an N-body
simulation-based mock catalogue for X-ray selected AGN samples. The model
reproduces the observed hard X-ray AGN luminosity function (XLF) and the soft
X-ray logN-logS from redshift 0 to 6. The XLF is reproduced to within $\pm5\%$
and the logN-logS to within $\pm20\%$. We develop a joint X-ray -- optical
extinction and classification model. We adopt a set of empirical spectral
energy distributions to predict observed magnitudes in the UV, optical and NIR.
With the latest eROSITA all sky survey sensitivity model, we create a
high-fidelity full-sky mock catalogue of X-ray AGN. It predicts their
distributions in right ascension, declination, redshift and fluxes. Using
empirical medium resolution optical spectral templates and an exposure time
calculator, we find that $1.1\times10^6$ ($4\times10^5$) fiber-hours are needed
to follow-up spectroscopically from the ground the detected X-ray AGN with an
optical magnitude $21<r<22.8$ ($22.8<r<25$) with a 4-m (8-m) class multi-object
spectroscopic facility. We find that future clustering studies will measure the
AGN bias to the percent level at redshift $z<1.2$ and should discriminate
possible scenarios of galaxy-AGN co-evolution. We predict the accuracy to which
the baryon acoustic oscillation standard ruler will be measured using X-ray
AGN: better than 3\% for AGN between redshift 0.5 to 3 and better than 1\%
using the Ly$\alpha$ forest of X-ray QSOs discovered between redshift 2 and 3.
eROSITA will provide an outstanding set of targets for future galaxy evolution
and cosmological studies.
|
Predicting the Sufficient-Statistics Power Spectrum for Galaxy Surveys:
A Recipe for $P_{A*}(k)$ | Future galaxy surveys hope to realize significantly tighter constraints on
various cosmological parameters. The higher number densities achieved by these
surveys will allow them to probe the smaller scales affected by non-linear
clustering. However, in these regimes, the standard power spectrum can extract
only a portion of such surveys' cosmological information. In contrast, the
alternate statistic $A^*$ has the potential to double these surveys'
information return, provided one can predict the $A^*$-power spectrum for a
given cosmology. Thus, in this work we provide a prescription for this power
spectrum $P_{A^*}(k)$, finding that the prescription is typically accurate to
about 5 per cent for near-concordance cosmologies. This prescription will thus
allow us to multiply the information gained from surveys such as Euclid and
WFIRST.
|
A detailed study of Andromeda XIX, an extreme local analogue of ultra
diffuse galaxies | With a central surface brightness of $\mu_0=29.3$ mag. per sq. arcsec, and
half-light radius of $r_{\rm half}=3.1^{+0.9}_{-1.1}$~kpc, Andromeda XIX (And
XIX) is an extremely diffuse satellite of Andromeda. We present spectra for
$\sim100$ red giant branch stars in this galaxy, plus 16 stars in a nearby
stellar stream. With this exquisite dataset, we re-derive the properties of And
XIX, measuring a systemic velocity of $v_r=-109.0\pm1.6$ km/s and a velocity
dispersion of $\sigma_v = 7.8^{+1.7}_{-1.5}$ km/s (higher than derived in our
previous work). We marginally detect a velocity gradient along the major axis
of ${\rm d}v/{\rm d}r = -2.1\pm1.8$ km/s kpc$^{-1}$. We find its mass-to-light
ratio is higher than galaxies of comparable stellar mass ($[M/L]_{\rm half} =
278^{+146}_{-198}M_\odot/L_\odot$), but its dynamics place it in a halo with a
similar total mass to these galaxies. This could suggest that And XIX is a
"puffed up" dwarf galaxy, whose properties have been altered by tidal
processes, similar to its Milky Way counterpart, Antlia II. For the nearby
stream, we measure $v_r=-279.2\pm3.7$ km/s, and $\sigma_v=13.8^{+3.5}_{-2.6}$
km/s. We measure its metallicity, and find it to be more metal rich than And
XIX, implying that the two features are unrelated. Finally, And XIX's dynamical
and structural properties imply it is a local analogue to ultra diffuse
galaxies (UDGs). Its complex dynamics suggest that the masses of distant UDGs
measured from velocity dispersions alone should be carefully interpreted
|
On the Absorption Properties of Metallic Needles | Needle-like metallic particles have been suggested to explain a wide variety
of astrophysical phenomena, ranging from the mid-infrared interstellar
extinction to the thermalization of starlight to generate the cosmic microwave
background. These suggestions rely on the amplitude and the wavelength
dependence of the absorption cross sections of metallic needles. On the absence
of an exact solution to the absorption properties of metallic needles, their
absorption cross sections are often derived from the antenna approximation.
However, it is shown here that the antenna approximation is not an appropriate
representation since it violates the Kramers-Kronig relation. Stimulated by the
recent discovery of iron whiskers in asteroid Itokawa and graphite whiskers in
carbonaceous chondrites, we call for rigorous calculations of the absorption
cross sections of metallic needle-like particles, presumably with the discrete
dipole approximation. We also call for experimental studies of the formation
and growth mechanisms of metallic needle-like particles as well as experimental
measurements of the absorption cross sections of metallic needles of various
aspect ratios over a wide wavelength range to bound theoretical calculations.
|
Perturbative treatment of the luminosity distance | We derive a generalized luminosity distance versus redshift relation for a
linearly perturbed FLRW (Friedmann-Lemaitre-Robertson-Walker) metric with two
scalar mode excitations. We use two equivalent approaches, based on the Jacobi
map and the van Vleck determinant respectively. We apply the resultant formula
to two simple models - an exact FLRW universe and an approximate FLRW universe
perturbed by a single scalar mode sinusoidally varying with time. For both
models we derive a cosmographic expansion for d_L in terms of z. We comment on
the interpretation of our results and their possible application to more
realistic cosmological models.
|
The Stellar Mass Components of Galaxies: Comparing Semi-Analytical
Models with Observation | We compare the stellar masses of central and satellite galaxies predicted by
three independent semianalytical models with observational results obtained
from a large galaxy group catalogue constructed from the Sloan Digital Sky
Survey. In particular, we compare the stellar mass functions of centrals and
satellites, the relation between total stellar mass and halo mass, and the
conditional stellar mass functions, which specify the average number of
galaxies of stellar mass M_* that reside in a halo of mass M_h. The
semi-analytical models only predict the correct stellar masses of central
galaxies within a limited mass range and all models fail to reproduce the sharp
decline of stellar mass with decreasing halo mass observed at the low mass end.
In addition, all models over-predict the number of satellite galaxies by
roughly a factor of two. The predicted stellar mass in satellite galaxies can
be made to match the data by assuming that a significant fraction of satellite
galaxies are tidally stripped and disrupted, giving rise to a population of
intra-cluster stars in their host halos. However, the amount of intra-cluster
stars thus predicted is too large compared to observation. This suggests that
current galaxy formation models still have serious problems in modeling star
formation in low-mass halos.
|
Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies
around the Milky Way | The goal of this paper is to demonstrate the outstanding quality of the
second data release of the Gaia mission and its power for constraining many
different aspects of the dynamics of the satellites of the Milky Way. We focus
here on determining the proper motions of 75 Galactic globular clusters, nine
dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small
Magellanic Clouds. Using data extracted from the Gaia archive, we derived the
proper motions and parallaxes for these systems, as well as their
uncertainties. We demonstrate that the errors, statistical and systematic, are
relatively well understood. We integrated the orbits of these objects in three
different Galactic potentials, and characterised their properties. We present
the derived proper motions, space velocities, and characteristic orbital
parameters in various tables to facilitate their use by the astronomical
community. Our limited and straightforward analyses have allowed us for example
to (i) determine absolute and very precise proper motions for globular
clusters; (ii) detect clear rotation signatures in the proper motions of at
least five globular clusters; (iii) show that the satellites of the Milky Way
are all on high-inclination orbits, but that they do not share a single plane
of motion; (iv) derive a lower limit for the mass of the Milky Way of
9.8^{+6.7}_{-2.7} x 10^{11} Msun based on the assumption that the Leo I dwarf
spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud
based solely on proper motions that is competitive with line-of-sight velocity
curves, now using many orders of magnitude more sources; and (vi) unveil the
dynamical effect of the bar on the motions of stars in the Large Magellanic
Cloud. All these results highlight the incredible power of the Gaia astrometric
mission, and in particular of its second data release.
|
Are Active Galactic Nuclei the Solution to the Excess Cosmic Radio
Background at 1.4 GHz? | Recently the ARCADE 2 experiment measured the cosmic radio background (CRB)
and found the brightness temperature of the CRB at 1.4 GHz to be ~480 mK.
Integrating the flux density from the observed 1.4 GHz radio source count
produces a brightness temperature of ~100 mK---less than a quarter of the
observed CRB at 1.4 GHz. Radio quiet AGN are a large fraction of the 1.4 GHz
uJy sources and typically host significant star formation. Thus, it is possible
that AGN and host star formation could be responsible for some fraction of the
excess CRB at 1.4 GHz. Here, an X-ray background population synthesis model is
used in conjunction with empirical radio to X-ray luminosity ratios to
calculate the AGN contribution to the CRB at 1.4 GHz including the emission
from host star formation. It is found that AGN and host star formation
contribute <~9% of the CRB at 1.4 GHz. When all known 1.4 GHz radio source
classes are considered, <~60% of the CRB at 1.4 GHz is accounted for;
therefore, it is necessary that either known radio sources evolve significantly
at flux densities below current survey sensitivity limits or a new population
of low flux density radio sources exist.
|
Inflation in the Mixed Higgs-$R^2$ Model | We analyze a two-field inflationary model consisting of the Ricci scalar
squared ($R^2$) term and the standard Higgs field non-minimally coupled to
gravity in addition to the Einstein $R$ term. Detailed analysis of the power
spectrum of this model with mass hierarchy is presented, and we find that one
can describe this model as an effective single-field model in the slow-roll
regime with a modified sound speed. The scalar spectral index predicted by this
model coincides with those given by the $R^2$ inflation and the Higgs inflation
implying that there is a close relation between this model and the $R^2$
inflation already in the original (Jordan) frame. For a typical value of the
self-coupling of the standard Higgs field at the high energy scale of
inflation, the role of the Higgs field in parameter space involved is to modify
the scalaron mass, so that the original mass parameter in the $R^2$ inflation
can deviate from its standard value when non-minimal coupling between the Ricci
scalar and the Higgs field is large enough.
|
Measuring the mass of the central black hole in the bulgeless galaxy NGC
4395 from gas dynamical modeling | NGC 4395 is a bulgeless spiral galaxy, harboring one of the nearest known
type 1 Seyfert nuclei. Although there is no consensus on the mass of its
central engine, several estimates suggest it to be one of the lightest massive
black holes (MBHs) known. We present the first direct dynamical measurement of
the mass of this MBH from a combination of two-dimensional gas kinematic data,
obtained with the adaptive optics assisted near infrared integral field
spectrograph Gemini/NIFS, and high-resolution multiband photometric data from
Hubble Space Telescope's Wide Field Camera 3 (HST/WFC3). We use the photometric
data to model the shape and stellar mass-to-light ratio (M/L) of the nuclear
star cluster. From the Gemini/NIFS observations, we derive the kinematics of
warm molecular hydrogen gas as traced by emission through the H$_2$ 1--0 S(1)
transition. These kinematics show a clear rotational signal, with a position
angle orthogonal to NGC 4395's radio jet. Our best fitting tilted ring models
of the kinematics of the molecular hydrogen gas contain a black hole with mass
$M=4_{-3}^{+8}\times 10^5$ M$_\odot$ (3$\sigma$ uncertainties) embedded in a
nuclear star cluster of mass $M=2 \times 10^6$ M$_\odot$. Our black hole mass
measurement is in excellent agreement with the reverberation mapping mass
estimate of Peterson et al. (2005), but shows some tension with other mass
measurement methods based on accretion signals.
|
Estimating stellar birth radii and the time evolution of the Milky Way's
ISM metallicity gradient | We present a semi-empirical, largely model-independent approach for
estimating Galactic birth radii, r_birth, for Milky Way disk stars. The
technique relies on the justifiable assumption that a negative radial
metallicity gradient in the interstellar medium (ISM) existed for most of the
disk lifetime. Stars are projected back to their birth positions according to
the observationally derived age and [Fe/H] with no kinematical information
required. Applying our approach to the AMBRE:HARPS and HARPS-GTO local samples,
we show that we can constrain the ISM metallicity evolution with Galactic
radius and cosmic time, [Fe/H]_ISM(r, t), by requiring a physically meaningful
r_birth distribution. We find that the data are consistent with an ISM radial
metallicity gradient that flattens with time from ~-0.15 dex/kpc at the
beginning of disk formation, to its measured present-day value (-0.07 dex/kpc).
We present several chemo-kinematical relations in terms of mono-r_birth
populations. One remarkable result is that the kinematically hottest stars
would have been born locally or in the outer disk, consistent with thick disk
formation from the nested flares of mono-age populations and predictions from
cosmological simulations. This phenomenon can be also seen in the observed
age-velocity dispersion relation, in that its upper boundary is dominated by
stars born at larger radii. We also find that the flatness of the local
age-metallicity relation (AMR) is the result of the superposition of the AMRs
of mono-r_birth populations, each with a well-defined negative slope. The solar
birth radius is estimated to be 7.3+-0.6 kpc, for a current Galactocentric
radius of 8 kpc.
|
Metallicity Gradient of the Thick Disc Progenitor at High Redshift | We have developed a novel Markov Chain Mote Carlo (MCMC) chemical "painting"
technique to explore possible radial and vertical metallicity gradients for the
thick disc progenitor. In our analysis we match an N-body simulation to the
data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
survey. We assume that the thick disc has a constant scale-height and has
completed its formation at an early epoch, after which time radial mixing of
its stars has taken place. Under these assumptions, we find that the initial
radial metallicity gradient of the thick disc progenitor should not be
negative, but either flat or even positive, to explain the current negative
vertical metallicity gradient of the thick disc. Our study suggests that the
thick disc was built-up in an inside-out and upside-down fashion, and older,
smaller and thicker populations are more metal poor. In this case, star forming
discs at different epochs of the thick disc formation are allowed to have
different radial metallicity gradients, including a negative one, which helps
to explain a variety of slopes observed in high redshift disc galaxies. This
scenario helps to explain the positive slope of the metallicity-rotation
velocity relation observed for the Galactic thick disc. On the other hand,
radial mixing flattens the slope of an existing gradient.
|
ShapeFit: extracting the power spectrum shape information in galaxy
surveys beyond BAO and RSD | In the standard (classic) approach, galaxy clustering measurements from
spectroscopic surveys are compressed into baryon acoustic oscillations and
redshift space distortions measurements, which in turn can be compared to
cosmological models. Recent works have shown that avoiding this intermediate
step and fitting directly the full power spectrum signal (full modelling) leads
to much tighter constraints on cosmological parameters. Here we show where this
extra information is coming from and extend the classic approach with one
additional effective parameter, such that it captures, effectively, the same
amount of information as the full modelling approach, but in a
model-independent way. We validate this new method (ShapeFit) on mock catalogs,
and compare its performance to the full modelling approach finding both to
deliver equivalent results. The ShapeFit extension of the classic approach
promotes the standard analyses at the level of full modelling ones in terms of
information content, with the advantages of i) being more model independent;
ii) offering an understanding of the origin of the extra cosmological
information; iii) allowing a robust control on the impact of observational
systematics.
|
Kinetic Sunyaev-Zel'dovich tomography with line-intensity mapping | The kinetic Sunyaev-Zel'dovich (kSZ) effect is a secondary cosmic microwave
background (CMB) anisotropy induced by the scattering of CMB photons off
intervening electrons. Through cross-correlations with tracers of large-scale
structure, the kSZ effect can be used to reconstruct the 3-dimensional
radial-velocity field, a technique known as kSZ tomography. We explore the
cross-correlation between the CMB and line-intensity fluctuations to retrieve
the late-time kSZ signal across a wide redshift range. We focus on the CII
emission line, and predict the signal-to-noise ratio of the kSZ tomography
signal between redshifts $z=1-5$ for upcoming experiments. We show that while
instruments currently under construction may reach a low-significance detection
of kSZ tomography, next-generation experiments will achieve greater
sensitivity, with a detection significance of $\mathcal{O}(10^2-10^3)$. Due to
sample-variance cancellation, the cross-correlation between the reconstructed
velocity field from kSZ tomography and intensity fluctuations can improve
measurements of %the scale-dependent bias contributions from new physics to the
power spectrum at large scales. To illustrate this improvement, we consider
models of the early Universe that induce primordial local-type non-gaussianity
and correlated compensated isocurvature perturbations. We show that with CMB-S4
and an AtLAST-like survey, the uncertainty on $f_{\rm NL}$ and $A_{\rm CIP}$
can be reduced by a factor of $\sim 3$, achieving $\sigma(f_{\rm NL}) \lesssim
1$. We further show that probing both low and high redshifts is crucial to
break the degeneracy between the two parameters.
|
The SLUGGS Survey: globular clusters and the dark matter content of
early-type galaxies | A strong correlation exists between the total mass of a globular cluster (GC)
system and the virial halo mass of the host galaxy. However, the total halo
mass in this correlation is a statistical measure conducted on spatial scales
that are some ten times that of a typical GC system. Here we investigate the
connection between GC systems and galaxy's dark matter on comparable spatial
scales, using dynamical masses measured on a galaxy-by-galaxy basis. Our sample
consists of 17 well-studied massive (stellar mass $\sim$10$^{11}$ M$_{\odot}$)
early-type galaxies from the SLUGGS survey. We find the strongest correlation
to be that of the blue (metal-poor) GC subpopulation and the dark matter
content. This correlation implies that the dark matter mass of a galaxy can be
estimated to within a factor of two from careful imaging of its GC system. The
ratio of the GC system mass to that of the enclosed dark matter is nearly
constant. We also find a strong correlation between the fraction of blue GCs
and the fraction of enclosed dark matter, so that a typical galaxy with a blue
GC fraction of 60 per cent has a dark matter fraction of 86 per cent over
similar spatial scales. Both halo growth and removal (via tidal stripping) may
play some role in shaping this trend. In the context of the two-phase model for
galaxy formation, we find galaxies with the highest fractions of accreted stars
to have higher dark matter fractions for a given fraction of blue GCs.
|
The DESI $N$-body Simulation Project II: Suppressing Sample Variance
with Fast Simulations | Dark Energy Spectroscopic Instrument (DESI) will construct a large and
precise 3D map of our Universe. The survey effective volume reaches $\sim20$
Gpc$^3h^{-3}$. It is a great challenge to prepare high-resolution simulations
with a much larger volume for validating the DESI analysis pipelines.
AbacusSummit is a suite of high-resolution dark-matter-only simulations
designed for this purpose, with $200$ Gpc$^3h^{-3}$ (10 times DESI volume) for
the base cosmology. However, further efforts need to be done to provide more
precise analysis of the data and to cover also other cosmologies. Recently, the
CARPool method was proposed to use paired accurate and approximate simulations
to achieve high statistical precision with a limited number of high-resolution
simulations. Relying on this technique, we propose to use fast quasi-$N$-body
solvers combined with accurate simulations to produce accurate summary
statistics. This enables us to obtain 100 times smaller variances than the
expected DESI statistical variance at the scales we are interested in, e.g., $k
< 0.3~h$Mpc$^{-1}$. We further generalize the method for other cosmologies with
only one realization in AbacusSummit suite to extend the effective volume $\sim
20$ times. In summary, our proposed strategy of combining high fidelity
simulations with fast approximate gravity solvers and a series of variance
suppression techniques sets the path for a robust cosmological analysis of
galaxy survey data.
|
Detection of interstellar oxidaniumyl: abundant H2O+ towards the
star-forming regions DR21, Sgr B2, and NGC6334 | We identify a prominent absorption feature at 1115 GHz, detected in first
HIFI spectra towards high-mass star-forming regions, and interpret its
astrophysical origin. The characteristic hyperfine pattern of the H2O+
ground-state rotational transition, and the lack of other known low-energy
transitions in this frequency range, identifies the feature as H2O+ absorption
against the dust continuum background and allows us to derive the velocity
profile of the absorbing gas. By comparing this velocity profile with velocity
profiles of other tracers in the DR21 star-forming region, we constrain the
frequency of the transition and the conditions for its formation. In DR21, the
velocity distribution of H2O+ matches that of the [CII] line at 158\mu\m and of
OH cm-wave absorption, both stemming from the hot and dense clump surfaces
facing the HII-region and dynamically affected by the blister outflow. Diffuse
foreground gas dominates the absorption towards Sgr B2. The integrated
intensity of the absorption line allows us to derive lower limits to the H2O+
column density of 7.2e12 cm^-2 in NGC 6334, 2.3e13 cm^-2 in DR21, and 1.1e15
cm^-2 in Sgr B2.
|
Do we need soft cosmology? | We examine the possibility of "soft cosmology", namely small deviations from
the usual framework due to the effective appearance of soft-matter properties
in the Universe sectors. One effect of such a case would be the dark energy to
exhibit a different equation-of-state parameter at large scales (which
determine the universe expansion) and at intermediate scales (which determine
the sub-horizon clustering and the large scale structure formation). Concerning
soft dark matter, we show that it can effectively arise due to the dark-energy
clustering, even if dark energy is not soft. We propose a novel parametrization
introducing the "softness parameters" of the dark sectors. As we see, although
the background evolution remains unaffected, due to the extreme sensitivity and
significant effects on the global properties even a slightly non-trivial
softness parameter can improve the clustering behavior and alleviate e.g. the
$f\sigma_8$ tension. Lastly, an extension of the cosmological perturbation
theory and a detailed statistical mechanical analysis, in order to incorporate
complexity and estimate the scale-dependent behavior from first principles, is
necessary and would provide a robust argumentation in favour of soft cosmology.
|
Ohmic currents and pre-decoupling magnetism | Ohmic currents induced prior to decoupling are investigated in a standard
transport model accounting both for the expansion of the background geometry as
well as of its relativistic inhomogeneities. The relative balance of the Ohmic
electric fields in comparison with the Hall and thermoelectric contributions is
specifically addressed. The impact of the Ohmic currents on the evolution of
curvature perturbations is discussed numerically and it is shown to depend
explicitly upon the evolution of the conductivity.
|
Chemical and kinematic structure of extremely high-velocity molecular
jets in the Serpens Main star-forming region | The fastest molecular component to the protostellar outflows -- extremely
high-velocity (EHV) molecular jets -- are still puzzling since they are seen
only rarely. The first aim is to analyze the interaction between the EHV jet
and the slow outflow by comparing their outflow force content. The second aim
is to analyze the chemical composition of the different outflow velocity
components and to reveal the spatial location of molecules. ALMA 3 mm and 1.3
mm observations of five outflow sources at 130 -- 260 au resolution in the
Serpens Main cloud are presented. Observations of CO, SiO, H$_2$CO and HCN
reveal the kinematic and chemical structure of those flows. Three velocity
components are distinguished: the slow and the fast wing, and the EHV jet. Out
of five sources, three have the EHV component. Comparison of outflow forces
reveals that only the EHV jet in the youngest source Ser-emb 8 (N) has enough
momentum to power the slow outflow. The SiO abundance is generally enhanced
with velocity, while HCN is present in the slow and the fast wing, but
disappears in the EHV jet. For Ser-emb 8 (N), HCN and SiO show a bow-shock
shaped structure surrounding one of the EHV peaks suggesting sideways ejection
creating secondary shocks upon interaction with the surroundings. Also, the SiO
abundance in the EHV gas decreases with distance from this protostar, whereas
that in the fast wing increases. H$_2$CO is mostly associated with low-velocity
gas but also appears surprisingly in one of the bullets in the Ser-emb~8~(N)
EHV jet. The high detection rate suggests that the presence of the EHV jet may
be more common than previously expected. The origin and temporal evolution of
the abundances of SiO, HCN and H$_2$CO through high-temperature chemistry are
discussed. The data are consistent with a low C/O ratio in the EHV gas versus
high C/O ratio in the fast and slow wings.
|
A distortion of very--high--redshift galaxy number counts by
gravitational lensing | The observed number counts of high-redshift galaxy candidates have been used
to build up a statistical description of star-forming activity at redshift z >~
7, when galaxies reionized the Universe. Standard models predict that a high
incidence of gravitational lensing will probably distort measurements of flux
and number of these earliest galaxies. The raw probability of this happening
has been estimated to be ~ 0.5 percent, but can be larger owing to
observational biases. Here we report that gravitational lensing is likely to
dominate the observed properties of galaxies with redshifts of z >~ 12, when
the instrumental limiting magnitude is expected to be brighter than the
characteristic magnitude of the galaxy sample. The number counts could be
modified by an order of magnitude, with most galaxies being part of multiply
imaged systems, located less than 1 arcsec from brighter foreground galaxies at
z ~ 2. This lens-induced association of high-redshift and foreground galaxies
has perhaps already been observed among a sample of galaxy candidates
identified at z ~ 10.6. Future surveys will need to be designed to account for
a significant gravitational lensing bias in high-redshift galaxy samples.
|
A model for the cosmological evolution of low frequency radio sources | We present a new evolutionary model that describes the population properties
of radio sources at frequencies <5 GHz, thus complementing the De Zotti et al.
(2005) model, holding at higher frequencies. We find that simple analytic
luminosity evolution is still sufficient to fit the wealth of available data on
local luminosity functions, multi-frequency source counts, and redshift
distributions. However, the fit requires a luminosity-dependent decline of
source luminosities at high redshifts, at least for steep-spectrum sources,
thus confirming earlier indications of a "downsizing" also for radio sources.
The upturn of source counts at sub-mJy levels is accounted for by a
straightforward extrapolation, using the empirical far-IR/radio correlation, of
evolutionary models matching the far-IR counts and redshift distributions of
star-forming galaxies. We also discuss the implications of the new model for
the interpretation of data on large-scale clustering of radio sources and on
the Integrated Sachs-Wolfe (ISW) effect, and for the investigation of the
contribution of discrete sources to the extragalactic background. As for the
ISW effect, a new analysis exploiting a very clean CMB map, yields at a
substantially higher significance than reported before.
|
Primordial Spikes from Wrapped Brane Inflation | Cosmic inflation driven by branes wrapping the extra dimensions involves
Kaluza-Klein (KK) degrees of freedom in addition to the zero-mode position of
the brane which plays the role of the inflaton. As the wrapped brane passes by
localized sources or features along its inflationary trajectory in the extra
dimensional space, the KK modes along the wrapped direction are excited and
start to oscillate during inflation. We show that the oscillating KK modes
induce parametric resonance for the curvature perturbations, generating sharp
signals in the perturbation spectrum. The effective four dimensional picture is
a theory where the inflaton couples to the heavy KK modes. The Nambu-Goto
action of the brane sources couplings between the inflaton kinetic terms and
the KK modes, which trigger significant resonant amplification of the curvature
perturbations. We find that the strong resonant effects are localized to narrow
wave number ranges, producing spikes in the perturbation spectrum.
Investigation of such resonant signals opens up the possibility of probing the
extra dimensional space through cosmological observations.
|
Constraining the neutral fraction of hydrogen in the IGM at redshift 7.5 | We present a large spectroscopic campaign with Keck/MOSFIRE targeting
Lyman-alpha emission (Ly$\alpha$) from intrinsically faint Lyman-break Galaxies
(LBGs) behind 12 efficient galaxy cluster lenses. Gravitational lensing allows
us to probe the more abundant faint galaxy population to sensitive Ly$\alpha$
equivalent width limits. During the campaign we targeted 70 LBG candidates with
MOSFIRE Y-band, selected photometrically to cover Ly$\alpha$ over the range
$7<z<8.2$. We detect $S/N>5$ emission lines in 2 of these galaxies and find
that they are likely Ly$\alpha$ at $z=7.148\pm0.001$ and $z=7.161\pm0.001$. We
present new lens models for 4 of the galaxy clusters, using our previously
published lens models for the remaining clusters to determine the magnification
factors for the source galaxies. Using a Bayesian framework that employs large
scale reionization simulations of the intergalactic medium (IGM) as well as
realistic properties of the interstellar medium and circumgalactic medium, we
infer the volume-averaged neutral hydrogen fraction,
$\overline{x}_{\mathrm{HI}}$, in the IGM during reionization to be
$\overline{x}_{\mathrm{HI}}=0.88^{+0.05}_{-0.10}$ at $z=7.6\pm0.6$. Our result
is consistent with a late and rapid reionization scenario inferred by Planck.
|
Diagnostic of $f(R)$ under the $Om(z)$ function | We perform the two$-$point diagnostic for the $Om(z)$ function proposed by
Sahni ${\it et al}$ in 2014 for the Starobinsky and Hu & Sawicki models in
$f(R)$ gravity. We show that the observed values of the $Omh^2$ function can be
explained in $f(R)$ models while in LCDM the $Omh^2$ funticon is expected to be
a redshift independent number. We perform the analysis for some particular
values of $\Omega_m^0$ founding a cumulative probability ($P(\chi^2 \leq
\chi^2_{{\it model}})$) $P \sim 0.16$ or $\sim0.09$ for the better cases versus
a cumulative probability of $P \sim 0.98$ in the $\Lambda$CDM scenario. We also
show that these models present a characteristic signature around the interval
between $z\sim 2$ and $z\sim 4$, that could be confronted with future
observations using the same test.
|
Structure Formation Constraints on Sommerfeld-Enhanced Dark Matter
Annihilation | We study the growth of cosmic structure under the assumption that dark matter
self-annihilates with an averaged cross section times relative velocity that
grows with the scale factor, an increase known as Sommerfeld-enhancement. Such
an evolution is expected in models in which a light force carrier in the dark
sector enhances the annihilation cross section of dark matter particles, and
has been invoked, for instance, to explain anomalies in cosmic ray spectra
reported in the past. In order to make our results as general as possible, we
assume that dark matter annihilates into a relativistic species that only
interacts gravitationally with the standard model. This assumption also allows
us to test whether the additional relativistic species mildly favored by
cosmic-microwave background data could originate from dark matter annihilation.
We do not find evidence for Sommerfeld-enhanced dark matter annihilation and
derive the corresponding upper limits on the annihilation cross-section.
|
B2 0003+38A: a classical flat-spectrum radio quasar hosted by a
rotation-dominated galaxy with a peculiar massive outflow | We present a detailed analysis of the single-slit optical spectrum of the
Flat-Spectrum Radio Quasar (FSRQ) B2 0003+38A, taken by the Echellette
Spectrograph and Imager (ESI) on the Keck II telescope. This classical
low-redshift FSRQ ($z=0.22911$, as measured from the stellar absorption lines)
remains underexplored in its emission lines, though its broad-band continuum
properties from radio to X-ray is well-studied. After removing the unresolved
quasar nucleus and the starlight from the host galaxy, we obtain a
spatially-resolved 2-D spectrum, which clearly shows three components,
indicating a rotating disk, an extended emission line region (EELR) and an
outflow. The bulk of the EELR, with a characteristic mass $M_{\rm EELR}\sim
10^{7}~\rm M_{\odot}$, and redshifted by $v_{\rm EELR}\approx 120$ km s$^{-1}$
with respect to the quasar systemic velocity, shows a one-sided structure
stretching to a projected distance of $r_{\rm EELR}\sim 20$ kpc from the
nucleus. The rotation curve of the rotating disk is well consistent with that
of a typical galactic disk, suggesting that the FSRQ is hosted by a disk
galaxy. This conclusion is in accordance with the facts that strong absorption
in the HI 21-cm line was previously observed, and that Na
I$\lambda\lambda5891,5897$ and Ca II$\lambda\lambda3934,3969$ doublets are
detected in the optical ESI spectrum. B2 0003+38A will become the first FSRQ
discovered to be hosted by a gas-rich disk galaxy, if this is confirmed by
follow-up deep imaging and/or IFU mapping with high spatial resolution. These
observations will also help unravel the origin of the EELR.
|
An efficient approach to extract parameters from star cluster CMDs:
fitCMD | This work presents an approach (fitCMD) designed to obtain a comprehensive
set of astrophysical parameters from colour-magnitude diagrams (CMDs) of star
clusters. Based on initial mass function (IMF) properties taken from
isochrones, fitCMD searches for the values of total (or cluster) stellar mass,
age, global metallicity, foreground reddening, distance modulus, and
magnitude-dependent photometric completeness that produce the artificial CMD
that best reproduces the observed one; photometric scatter is also taken into
account in the artificial CMDs. Inclusion of photometric completeness proves to
be an important feature of fitCMD, something that becomes apparent especially
when luminosity functions are considered. These parameters are used to build a
synthetic CMD that also includes photometric scatter. Residual minimization
between the observed and synthetic CMDs leads to the best-fit parameters. When
tested against artificial star clusters, fitCMD shows to be efficient both in
terms of computational time and ability to recover the input values.
|
Cosmic recombination history in light of EDGES measurements of the
cosmic dawn 21-cm signal | The recent EDGES measurements of the global 21-cm signal from the cosmic dawn
suggest that the kinetic temperature of the inter-galactic medium (IGM) might
be significantly lower compared to its expected value. The colder IGM directly
affects the hydrogen recombination of the universe during the cosmic dawn and
dark ages by enhancing the rate of recombinations. Here, we study and quantify,
the impact of the colder IGM scenario on the recombination history of the
universe in the context of DM-baryonic interaction model which is widely used
to explain the depth of the EDGES 21-cm signal. We find that, in general, the
hydrogen ionisation fraction gets suppressed during the dark ages and cosmic
dawn and the suppression gradually increases at lower redshifts until X-ray
heating turns on. However, accurate estimation of the ionisation fraction
requires knowledge of the entire thermal history of the IGM, from the epoch of
thermal decoupling of hydrogen gas and the CMBR to the cosmic dawn. It is
possible that two separate scenarios which predict very similar HI differential
temperature during the cosmic dawn and are consistent with the EDGES 21-cm
signal might have very different IGM temperature during the dark ages. The
evolutions of the ionisation fraction in these two scenarios are quite
different. This prohibits us to accurately calculate the ionisation fraction
during the cosmic dawn using the EDGES 21-cm signal alone. We find that the
changes in the ionisation fraction w.r.t the standard scenario at redshift $z
\sim 17 $ could be anything between $\sim 0 \%$ to $\sim 36 \%$. This
uncertainty may be reduced if measurements of HI 21-cm differential temperature
at multiple redshifts are simultaneously used.
|
Black hole formation in the context of dissipative dark matter | Black holes with masses of $\rm 10^6-10^9~M_{\odot}$ dwell in the centers of
most galaxies, but their formation mechanisms are not well known. A subdominant
dissipative component of dark matter with similar properties to the ordinary
baryons, known as mirror dark matter, may collapse to form massive black holes
during the epoch of first galaxies formation. In this study, we explore the
possibility of massive black hole formation via this alternative scenario. We
perform three-dimensional cosmological simulations for four distinct halos and
compare their thermal, chemical and dynamical evolution in both the ordinary
and the mirror sectors. We find that the collapse of halos is significantly
delayed in the mirror sector due to the lack of $\rm H_2$ cooling and only
halos with masses above $ \rm \geq 10^7~ M_{\odot}$ are formed. Overall, the
mass inflow rates are $\rm \geq 10^{-2}~M_{\odot}/yr$ and there is less
fragmentation. This suggests that the conditions for the formation of massive
objects, including black holes, are more favorable in the mirror sector.
|
Vortex Structures in a Rotating BEC Dark Matter Component | We study the effects of a dark matter component that consists of bosonic
particles with ultralight masses in the condensed state. We compare previous
studies for both non-interacting condensates and with repulsive two-body terms
and show consistency between the proposals. Furthermore, we explore the effects
of rotation on a superfluid dark matter condensate, assuming that a vortex
lattice forms as seen in ultracold atomic gas experiments. The influence of
such a lattice in virialization of gravitationally bound structures and on
galactic rotation velocity curves is explored. With fine-tuning of the bosonic
particle mass and the two-body repulsive interaction strength, we find that one
can have sub-structure on rotation curves that resembles some observations in
spiral galaxies. This occurs when the dark matter halo has an array of hollow
cylinders. This can cause oscillatory behavior in the galactic rotation curves
in similar fashion to the well-known effect of the spiral arms. We also
consider how future experiments and numerical simulations with ultracold atomic
gases could tell us more about such exotic dark matter proposals.
|
Relations between three-point configuration space shear and convergence
statistics | With the growing interest in and ability of using weak lensing studies to
probe the non-Gaussian properties of the matter density field, there is an
increasing need for the study of suitable statistical measures, e.g. shear
three-point statistics. In this paper we establish the relations between the
three-point configuration space shear and convergence statistics, which are an
important missing link between different weak lensing three-point statistics
and provide an alternative way of relating observation and theory. The method
we use also allows us to derive the relations between other two- and
three-point correlation functions. We show the consistency of the relations
obtained with already established results and demonstrate how they can be
evaluated numerically. As a direct application, we use these relations to
formulate the condition for E/B-mode decomposition of lensing three-point
statistics, which is the basis for constructing new three-point statistics
which allow for exact E/B-mode separation. Our work applies also to other
two-dimensional polarization fields such as that of the Cosmic Microwave
Background.
|
A low-luminosity type-1 QSO sample. V. Overluminous host spheroids and
their excitation mechanisms | We present near-infrared (NIR) $H+K$-band longslit spectra of eleven galaxies
which are obtained with SOFI at the NTT (ESO). The galaxies are chosen from the
low-luminosity type-1 quasi-stellar object (LLQSO) sample which comprises the
99 closest ($z\leq 0.06$) QSOs from the Hamburg/ESO survey for bright UV-excess
QSOs. These objects are ideal targets to study the gap between local Seyfert
galaxies and high-redshift quasars, since they show much stronger AGN activity
compared to local objects but are still close enough for a detailed structural
analysis.
We fit hydrogen recombination, molecular hydrogen, and [FeII] lines after
carefully subtracting the continuum emission. From the broad Pa$\alpha$
components, we estimate black hole masses and enlarge the sample of LLQSOs that
show a deviation from the $M_\mathrm{BH}-L_\mathrm{bulge}$ relations of
inactive galaxies from 12 to 16 objects.
All objects show emission from hot dust ($T\sim 1200\,\mathrm{K}$) as well as
stellar contribution. However, the particular fractions vary a lot between the
objects. More than half of the objects show H$_2$ emission lines that are
indicating a large reservoir of molecular gas which is needed to feed the AGN
and star formation.
In the NIR diagnostic diagram all objects lie in the location of AGN
dominated objects. However, most of the objects show indications of star
formation activity, suggesting that their offset location with respect to
$M_\mathrm{BH}-L_\mathrm{bulge}$ relations of inactive galaxies may be a
consequence of overluminous bulges.
|
Boxy H$\alpha$ Emission Profiles in Star-Forming Galaxies | We assemble a sample of disk star-forming galaxies from the Sloan Digital Sky
Survey Data Release 7, studying the structure of H$\alpha$ emission lines,
finding a large fraction of this sample contains boxy H$\alpha$ line profiles.
This fraction depends on galaxy physical and geometric parameters in the
following way: (1) it increases monotonically with star formation rate per unit
area ($\Sigma_{\rm SFR}$), and stellar mass ($M_*$), with the trend being much
stronger with $M_*$, from $\sim$0% at $M_*=10^{10}M_{\odot}$ to about 50% at
$M_*=10^{11}M_\odot$; (2) the fraction is much smaller in face-on systems than
in edge-on systems. It increases with galaxy inclination ($i$) while $i <
60\,^{\circ}$ and is roughly a constant of 25% beyond this range; (3) for the
sources which can be modeled well with two velocity components, blueshifted and
redshifted from the systemic velocity, these is a positive correlation between
the velocity difference of these two components and the stellar mass, with a
slope similar to the Tully-Fisher relation; (4) the two components are very
symmetric in the mean, both in velocity and in amplitude. The four findings
listed above can be understood as a natural result of a rotating galaxy disk
with a kpc-scale ring-like H$\alpha$ emission region.
|