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The mean free path of ionizing photons at 5 < z < 6: evidence for rapid
evolution near reionization: The mean free path of ionizing photons, $\lambda_{\rm mfp}$, is a key factor
in the photoionization of the intergalactic medium (IGM). At $z \gtrsim 5$,
however, $\lambda_{\rm mfp}$ may be short enough that measurements towards QSOs
are biased by the QSO proximity effect. We present new direct measurements of
$\lambda_{\rm mfp}$ that address this bias and extend up to $z \sim 6$ for the
first time. Our measurements at $z \sim 5$ are based on data from the Giant
Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At $z
\sim 6$ we use QSO spectra from Keck ESI and VLT X-Shooter. We measure
$\lambda_{\rm mfp} = 9.09^{+1.62}_{-1.28}$ proper Mpc and
$0.75^{+0.65}_{-0.45}$ proper Mpc (68% confidence) at $z = 5.1$ and 6.0,
respectively. The results at $z = 5.1$ are consistent with existing
measurements, suggesting that bias from the proximity effect is minor at this
redshift. At $z = 6.0$, however, we find that neglecting the proximity effect
biases the result high by a factor of two or more. Our measurement at $z = 6.0$
falls well below extrapolations from lower redshifts, indicating rapid
evolution in $\lambda_{\rm mfp}$ over $5 < z < 6$. This evolution disfavors
models in which reionization ended early enough that the IGM had time to fully
relax hydrodynamically by $z = 6$, but is qualitatively consistent with models
wherein reionization completed at $z = 6$ or even significantly later. Our mean
free path results are most consistent with late reionization models wherein the
IGM is still 20% neutral at $z=6$, although our measurement at $z = 6.0$ is
even lower than these models prefer. | astro-ph |
On the origin of cosmic web: The emergence of one and two-dimensional configurations -- Zeldovich pancakes
-- progenitors of the observed filaments and clusters and groups of galaxies,
is predicted by means of a developed kinetic approach in analyzing the
evolution of initial density perturbations. The self-consistent gravitational
interaction described by Vlasov-Poisson set of equations with branching
conditions is shown to predict two-dimensional structures as of layers of
increased density and voids between them, i.e. the cellular macro-structure of
the Universe. The modified potential of weak-field General Relativity is
involved, which enables one to explain the Hubble tension, revealing the
conceptual discrepancy in the local galactic flows and the cosmological
expansion. This demonstrates the possible essential role of self-consistent
gravity in the formation of the cosmic web. | astro-ph |
Mid-infrared spectra of T Tauri disks: Modeling the effects of a small
inner cavity on CO2 and H2O emission: [Abridged] The inner few AU of disks around young stars are best probed in
the infrared. The James Webb Space Telescope (JWST) is now starting to
characterize the chemistry of these regions in unprecedented detail. One
peculiar subset of sources are the so-called ``CO2-only sources'', in which
only a strong 15 $\mu$m CO2 feature was detected in the spectrum. One scenario
that could explain the weak emission from H2O is the presence of a small, inner
cavity in the disk. If this cavity were to extend past the H2O snowline, but
not past the CO2 snowline, this could strongly suppress the H2O line flux
w.r.t. that of CO2. In this work, we aim to test the validity of this
statement. Using the thermo-chemical code Dust And LInes (DALI), we created a
grid of T Tauri disk models with an inner cavity, meaning we fully depleted the
inner region of the disk in gas and dust starting from the dust sublimation
radius and ranging until a certain cavity radius. We present the evolution of
the CO2 and H2O spectra of a disk with inner cavity size, showing that, when a
large-enough cavity is introduced, a spectrum that was initially dominated by
H2O lines can become CO2-dominated instead. However, the cavity size needed for
this is around 4-5 AU, exceeding the nominal position of the CO2 snowline in a
full disk. The cause of this is most likely the alteration of the thermal
structure by the cavity, which pushes the snowlines outward. Alternative
explanations for bright CO2 emission are also briefly discussed. Our modeling
work shows that it is possible for the presence of a small inner cavity to
explain strong CO2 emission in a spectrum. However, the cavity needed to do so
is larger than what was initially expected. As such, this scenario will be
easier to test with sufficiently high angular resolution (millimeter)
observations. | astro-ph |
PAH and nbL Features Detection in Planetary Nebulae NGC 7027 and BD
+303639 with TIRCAM2 Instrument on 3.6m DOT: High resolution infrared imaging observations of the young Planetary Nebulae
NGC 7027 and BD +303639, taken with the newly installed TIFR Infrared Camera-II
(TIRCAM2) on 3.6m Devasthal Optical Telescope (DOT), ARIES, Nainital, are being
reported. The images are acquired in J, H, K, polycyclic aromatic hydrocarbon
(PAH) and narrow-band L (nbL) filters. The observations show emission from warm
dust and PAHs in the circumstellar shells. The imaging of the two objects are
among the first observations in PAH and nbL bands using TIRCAM2 on DOT. The NGC
7027 images in all bands show similar elliptical morphology with ~6".7 and
~4".5 semi-major and semi-minor axes. Considering size up to 10% of peak value
the nebula extends upto 8" from the central star revealing a multipolar
evolution. The relatively cooler BD +303639 shows a rectangular-ring shaped
nebula. In J and H bands it shows an angular diameter of ~8", while a smaller
~6".9 size is observed in K, PAH and nbL bands. The 3.28 micron emission
indicates presence of PAHs at about 6000 and 5000 AU from the central stars in
NGC 7027 and BD +303639 respectively. Analysis suggests domination of neutral
PAHs in BD+303639, while in NGC 7027 there is higher ionization and more
processed PAH population. | astro-ph |
Synthetic Spectra of Hydrodynamic Models of Type Ia Supernovae: We present detailed NLTE synthetic spectra of hydrodynamic SNe Ia models. We
make no assumptions about the form of the spectrum at the inner boundary. We
calculate both Chandrasekhar-mass deflagration models and sub-Chandrasekhar
``helium detonators.'' Gamma-ray deposition is handled in a simple, accurate
manner. We have parameterized the storage of energy that arises from the time
dependent deposition of radioactive decay energy in a reasonable manner, that
spans the expected range. We find that the Chandrasekhar-mass deflagration
model W7 of Nomoto etal shows good agreement with the observed spectra of SN
1992A and SN 1994D, particularly in the UV, where our models are expected to be
most accurate. The sub-Chandrasekhar models do not reproduce the UV deficit
observed in normal SNe Ia. They do bear some resemblance to sub-luminous SNe
Ia, but the shape of the spectra (i.e. the colors) are opposite to that of the
observed ones and the intermediate mass element lines such as Si II, and Ca II
are extremely weak, which seems to be a generic difficulty of the models.
Although the sub-Chandrasekhar models have a significant helium abundance
(unlike Chandrasekhar-mass models), helium lines are not prominent in the
spectra near maximum light and thus do not act as a spectral signature for the
progenitor. | astro-ph |
An External Shock Origin of GRB $\textit{141028A}$: The prompt emission of the long, smooth, and single-pulsed gamma-ray burst,
GRB $\textit{141028A}$, is analyzed under the guise of an external shock model.
First, we fit the $\gamma$-ray spectrum with a two-component photon model,
namely synchrotron+blackbody, and then fit the recovered evolution of the
synchrotron $\nu F_{\nu}$ peak to an analytic model derived considering the
emission of a relativistic blast-wave expanding into an external medium. The
prediction of the model for the $\nu F_{\nu}$ peak evolution matches well with
the observations. We observe the blast-wave transitioning into the deceleration
phase. Further we assume the expansion of the blast-wave to be nearly
adiabatic, motivated by the low magnetic field deduced from the observations.
This allows us to recover within an order of magnitude the flux density at the
$\nu F_{\nu}$ peak, which is remarkable considering the simplicity of the
analytic model. Across all wavelengths, synchrotron emission from a single
forward shock provides a sufficient solution for the observations. Under this
scenario we argue that the distinction between $\textit{prompt}$ and $\textit{
afterglow}$ emission is superfluous as both early and late time emission
emanate from the same source. While the external shock model is clearly not a
universal solution, this analysis opens the possibility that at least some
fraction of GRBs can be explained with an external shock origin of their prompt
phase. | astro-ph |
Investigation of systematic effects in Kepler data: Seasonal variations
in the light curve of HAT-P-7b: With years of Kepler data currently available, it can now be attempted to
measure variations in planetary transit depths over time. To do so, it is of
primary importance to understand which systematic effects may affect the
measurement of transits. We aim to measure the stability of Kepler measurements
over years of observations. We present a study of the depth of about 500
transit events of the Hot Jupiter HAT-P-7b, using 14 quarters (Q0-Q13) of data
from the Kepler Satellite. We find a systematic variation in the depth of the
primary transit, related to quarters of data and recurring yearly. These
seasonal variations are about 1%. Within seasons, we find no evidence for
trends. We speculate that the cause of the seasonal variations could be unknown
field crowding or instrumental artifacts. Our results show that care must be
taken when combining transits throughout different quarters of Kepler data.
Measuring the relative planetary radius of HAT-P-7b without taking these
systematic effects into account leads to unrealistically low error estimates.
This effect could be present in all Kepler targets. If so, relative radius
measurements of all Hot Jupiters to a precision much better than 1% are
unrealistic. | astro-ph |
The F-CHROMA grid of 1D RADYN flare models: Context: Solar flares are the result of the sudden release of magnetic energy
in the corona. Much of this energy goes into accelerating charged particles to
high velocity. These particles travel along the magnetic field and the energy
is dissipated when the density gets high enough, primarily in the solar
chromosphere. Modelling this region is difficult because the radiation energy
balance is dominated by strong, optically thick spectral lines.
Aims: Our aim is to provide the community with realistic simulations of a
flaring loop with an emphasis on the detailed treatment of the chromospheric
energy balance. This will enable a detailed comparison of existing and upcoming
observations with synthetic observables from the simulations, thereby
elucidating the complex interactions in a flaring chromosphere.
Methods: We used the 1D radiation hydrodynamics code RADYN to perform
simulations of the effect of a beam of electrons injected at the apex of a
solar coronal loop. A grid of models was produced, varying the total energy
input, the steepness, and low-energy cutoff of the beam energy spectrum.
Results: The full simulation results for a grid of models are made available
online. Some general properties of the simulations are discussed. | astro-ph |
Demystifying an unidentified EGRET source by VHE gamma-ray observations: In a novel approach in observational high-energy gamma-ray astronomy,
observations carried out by imaging atmospheric Cherenkov telescopes provide
necessary templates to pinpoint the nature of intriguing, yet unidentified
EGRET gamma-ray sources. Using GeV-photons detected by CGRO EGRET and taking
advantage of high spatial resolution images from H.E.S.S. observations, we were
able to shed new light on the EGRET observed gamma-ray emission in the
Kookaburra complex, whose previous coverage in the literature is somewhat
contradictory. 3EGJ1420-6038 very likely accounts for two GeV gamma-ray sources
(E>1 GeV), both in positional coincidence with the recently reported pulsar
wind nebulae (PWN) by HESS in the Kookaburra/Rabbit complex. PWN associations
at VHE energies, supported by accumulating evidence from observations in the
radio and X-ray band, are indicative for the PSR/plerionic origin of spatially
coincident, but still unidentified Galactic gamma-ray sources from EGRET. This
not only supports the already suggested connection between variable, but
unidentified low-latitude gamma-ray sources with pulsar wind nebulae
(3EGJ1420-6038 has been suggested as PWN candidate previoulsy), it also
documents the ability of resolving apparently confused EGRET sources by
connecting the GeV emission as measured from a large-aperture space-based
gamma-ray instrument with narrow field-of-view but superior spatial resolution
observations by ground-based atmospheric Cherenkov telescopes, a very promising
identification technique for achieving convincing individual source
identifications in the era of GLAST-LAT. | astro-ph |
Optical Outburst of the Gamma-Ray Blazar S4 0954+658 in March-April 2011: We present optical photopolarimetric observations of the BL Lac object S4
0954+658 obtained with the 70-cm telescope in Crimea, 40-cm telescope in
St.Petersburg, and 1.8-m Perkins telescope at Lowell Observatory (Flagstaff,
Az). After a faint state with a brightness level R ~17.6 mag registered in the
first half of January 2011, the optical brightness of the source started to
rise and reached ~14.8 mag during the middle of March, showing flare-like
behavior. The most spectacular case of intranight variability was observed
during the night of 2011 March 9, when the blazar brightened by ~0.7 mag within
~7 hours. During the rise of the flux the position angle of optical
polarization rotated smoothly over more than 200 degrees. S4 0954+658 is a
gamma-ray blazar with gamma-ray flux of (5{\pm}3)x10^{-10} phot/cm^2/s
according to the Fermi 11-month Catalog Extragalactic Sources. Our analysis of
contemporaneous Fermi LAT data does not show any sign of increased gamma-ray
activity above the detection threshold except for an elevated flux on 2011
March 5, JD2455626, coincident with the local optical maximum. | astro-ph |
ExoMol line lists XXVIII: The rovibronic spectrum of AlH: A new line list for AlH is produced. The WYLLoT line list spans two
electronic states $X\,{}^1\Sigma^+$ and $A\,{}^1\Pi$. A diabatic model is used
to model the shallow potential energy curve of the $A\,{}^1\Pi$ state, which
has a strong pre-dissociative character with only two bound vibrational states.
Both potential energy curves are empirical and were obtained by fitting to
experimentally derived energies of the $X\,{}^1\Sigma^+$ and $A\,{}^1\Pi$
electronic states using the diatomic nuclear motion codes Level and Duo. High
temperature line lists plus partition functions and lifetimes for three
isotopologues $^{27}$AlH, $^{27}$AlD and $^{26}$AlH were generated using ab
initio dipole moments. The line lists cover both the $X$--$X$ and $A$--$X$
systems and are made available in electronic form at the CDS and ExoMol
databases. | astro-ph |
Bright X-ray bursts from 1E 1724-3045 in Terzan 2: During about 3 years wide field monitoring of the Galactic Center region by
the WFC telescopes on board the BeppoSAX satellite, a total of 14 type-I X-ray
bursts were detected from the burster 1E 1724-3045 located in the globular
cluster Terzan 2. All the observed events showed evidence for photospheric
radius expansion due to Eddington-limit burst luminosity, thus leading to an
estimate of the source distance (~7.2 kpc). Preliminary results of the analysis
of the bursts are presented. | astro-ph |
Statistical properties of local and intermediate z galaxies: Galaxy evolution during the last 9 Gyr is discussed. It can be traced back
from well known present-day galaxies or directly observed for galaxies at
different look back times. This requires clear and consistently matched
selection criteria for galaxy samples. There is a net decrease of rest-frame,
UV luminosity density, at least since z = 1. It is interpreted as an important
decline of the star formation since the last ~9 Gyr. A similar trend is found
for the evolution of the IR luminosity density which accounts for heavily
extincted starbursts. Interestingly the global star formation density, after
including IR selected galaxies, is twice the value of estimates based on the UV
luminosity density, and this holds from z=0 to z=1.
Large disks are not contributing much to the observed decrease, which is
mainly related to significant changes with the epoch in the distribution of
galaxy morphologies. A significant fraction of the global star formation occurs
in luminous galaxies which are apparently small or in interacting galaxies
detected in the deepest IR or radio surveys. | astro-ph |
Asteroid Evolution: Role of Geotechnical Properties: This paper presents a brief review and latest results of the work that has
been carried out by the Planetary Science community in order to understand that
role of the geotechnical properties of granular asteroids (commonly known as
"rubble-pile" asteroids) in their formation, evolution and possible disruption.
As such, we will touch in aspects of the theoretical and numerical tools that
have been used with this objective and how the obtained results compare to the
observed asteroids. | astro-ph |
Can Gaia find planets around white dwarfs?: The Gaia spacecraft presents an unprecedented opportunity to reveal the
population of long period (a>1\,au) exoplanets orbiting stars across the H-R
diagram, including white dwarfs. White dwarf planetary systems have played an
important role in the study of planetary compositions, from their unique
ability to provide bulk elemental abundances of planetary material in their
atmospheres. Yet, very little is known about the population of planets around
white dwarfs. This paper predicts the population of planets that Gaia will
detect around white dwarfs, evolved from known planets orbiting main-sequence
stars. We predict that Gaia will detect $8\pm2$ planets around white dwarfs:
$8\pm\,3\%$ will lie inside 3\,au and $40\pm10\,\%$ will be less massive than
Jupiter. As surviving planets likely become dynamically detached from their
outer systems, those white dwarfs with Gaia detected planets may not have
planetary material in their atmospheres. Comparison between the predicted
planet population and that found by Gaia will reveal the importance of
dynamical instabilities and scattering of planets after the main-sequence, as
well as whether photoevaporation removes the envelopes of gas giants during
their giant branch evolution. | astro-ph |
Evidence for ammonia-bearing species on the Uranian satellite Ariel
supports recent geologic activity: We investigated whether ammonia-rich constituents are present on the surface
of the Uranian moon Ariel by analyzing 32 near-infrared reflectance spectra
collected over a wide range of sub-observer longitudes and latitudes. We
measured the band areas and depths of a 2.2-{\micron} feature in these spectra,
which has been attributed to ammonia-bearing species on other icy bodies. Ten
spectra display prominent 2.2-{\micron} features with band areas and depths >
2{\sigma}. We determined the longitudinal distribution of the 2.2-{\micron}
band, finding no statistically meaningful differences between Ariel's leading
and trailing hemispheres, indicating that this band is distributed across
Ariel's surface. We compared the band centers and shapes of the five Ariel
spectra displaying the strongest 2.2-{\micron} bands to laboratory spectra of
various ammonia-bearing and ammonium-bearing species, finding that the spectral
signatures of the Ariel spectra are best matched by ammonia-hydrates and flash
frozen ammonia-water solutions. Our analysis also revealed that four Ariel
spectra display 2.24-{\micron} bands (> 2{\sigma} band areas and depths), with
band centers and shapes that are best matched by ammonia ice. Because ammonia
should be efficiently removed over short timescales by ultraviolet photons,
cosmic rays, and charged particles trapped in Uranus' magnetosphere, the
possible presence of this constituent supports geologic activity in the recent
past, such as emplacement of ammonia-rich cryolavas and exposure of
ammonia-rich deposits by tectonism, impact events, and mass wasting. | astro-ph |
The Properties of Fossil Groups of Galaxies: Numerical simulations as well as optical and X-ray observations over the last
few years have shown that poor groups of galaxies can evolve to what is called
a fossil group. Dynamical friction as the driving process leads to the
coalescence of individual galaxies in ordinary poor groups leaving behind
nothing more than a central, massive elliptical galaxy supposed to contain the
merger history of the whole group. Due to merging timescales for less-massive
galaxies and gas cooling timescales of the X-ray intragroup medium exceeding a
Hubble time, a surrounding faint-galaxy population having survived this
galactic cannibalism as well as an extended X-ray halo similar to that found in
ordinary groups, is expected. Recent studies suggest that fossil groups are
very abundant and could be the progenitors of brightest cluster galaxies (BCGs)
in the centers of rich galaxy clusters. However, only a few objects are known
to the literature. This article aims to summarize the results of observational
fossil group research over the last few years and presents ongoing work by the
authors. Complementary to previous research, the SDSS and RASS surveys have
been cross-correlated to identify new fossil structures yielding 34 newly
detected fossil group candidates. Observations with ISIS at the 4.2m William
Herschel Telescope on La Palma have been carried out to study the stellar
populations of the central ellipticals of 6 fossil groups. In addition
multi-object spectroscopy with VLTs VIMOS has been performed to study the shape
of the OLF of one fossil system. | astro-ph |
A missing outskirts problem? Comparisons between stellar halos in the
Dragonfly Nearby Galaxies Survey and the TNG100 simulation: Low surface brightness galactic stellar halos provide a challenging but
promising path towards unraveling the past assembly histories of individual
galaxies. Here, we present detailed comparisons between the stellar halos of
Milky Way-mass disk galaxies observed as part of the Dragonfly Nearby Galaxies
Survey (DNGS) and stellar mass-matched galaxies in the TNG100 run of the
IllustrisTNG project. We produce stellar mass maps as well as mock $g$ and
$r$-band images for randomly oriented simulated galaxies, convolving the latter
with the Dragonfly PSF and taking care to match the background noise, surface
brightness limits and spatial resolution of DNGS. We measure azimuthally
averaged stellar mass density and surface brightness profiles, and find that
the DNGS galaxies generally have less stellar mass (or light) at large radii
(>20 kpc) compared to their mass-matched TNG100 counterparts, and that
simulated galaxies with similar surface density profiles tend to have low
accreted mass fractions for their stellar mass. We explore potential solutions
to this apparent "missing outskirts problem" by implementing several ad-hoc
adjustments within TNG100 at the stellar particle level. Although we are unable
to identify any single adjustment that fully reconciles the differences between
the observed and simulated galaxy outskirts, we find that artificially delaying
the disruption of satellite galaxies and reducing the spatial extent of in-situ
stellar populations result in improved matches between the outer profile shapes
and stellar halo masses, respectively. Further insight can be achieved with
higher resolution simulations that are able to better resolve satellite
accretion, and with larger samples of observed galaxies. | astro-ph |
A Propos Crossing the Hertzsprung Gap: The evolution of intermediate-mass and massive stars speeds up considerably
after they finish their hydrogen core-burning. Due to this accelerated
evolution, the probability to observe stars during this episode is small. In
suitable stellar aggregates, in particular star clusters of appropriate ages,
the fast evolutionary phase causes a depopulated area~--~referred to as the
Hertzsprung gap~--~in color-magnitude diagrams and derivatives therefrom. The
explanation of the speed-up usually resorts to the star's Kelvin-Helmholtz
timescale and the Sch\"onberg-Chandrasekhar instability is called upon. This
exposition challenges this viewpoint with counterexamples and argues that a
suitably defined nuclear timescale is enough to explain the fast evolution. A
thermal instability, even though it develops in stars evolving through the
Hertzsprung gap, is not a necessary condition to trigger the phenomenon. | astro-ph |
First stars in Damped Lyman Alpha systems: In order to characterize Damped Lyman Alpha systems (DLAs) potentially
hosting first stars, we present a novel approach to investigate DLAs in the
context of Milky Way (MW) formation, along with their connection with the most
metal-poor stars and local dwarf spheroidal (dSph) galaxies. The merger tree
method previously developed is extended to include inhomogeneous reionization
and metal mixing, and it is validated by matching both the Metallicity
Distribution Function of Galactic halo stars and the Fe-Luminosity relation of
dSph galaxies. The model explains the observed NHI-Fe relation of DLAs along
with the chemical abundances of [Fe/H] < -2 systems. In this picture, the
recently discovered z_abs ~ 2.34 C-enhanced DLA (Cooke et al. 2011a), pertains
to a new class of absorbers hosting first stars along with second-generation
long-living low-mass stars. These "PopIII DLAs" are the descendants of
H2-cooling minihalos with Mh ~ 10^7 Msun, that virialize at z > 8 in neutral,
primordial regions of the MW environment and passively evolve after a short
initial period of star formation. The gas in these systems is warm Tg \sim
(40-1000) K, and strongly C-enriched by long-living, extremely metal-poor stars
of total mass M* \sim 10^{2-4} Msun. | astro-ph |
The DESI One-Percent Survey: Evidence for Assembly Bias from
Low-Redshift Counts-in-Cylinders Measurements: We explore the galaxy-halo connection information that is available in
low-redshift samples from the early data release of the Dark Energy
Spectroscopic Instrument (DESI). We model the halo occupation distribution
(HOD) from z=0.1-0.3 using Survey Validation 3 (SV3; a.k.a., the One-Percent
Survey) data of the DESI Bright Galaxy Survey (BGS). In addition to more
commonly used metrics, we incorporate counts-in-cylinders (CiC) measurements,
which drastically tighten HOD constraints. Our analysis is aided by the Python
package, galtab, which enables the rapid, precise prediction of CiC for any HOD
model available in halotools. This methodology allows our Markov chains to
converge with much fewer trial points, and enables even more drastic speedups
due to its GPU portability. Our HOD fits constrain characteristic halo masses
tightly and provide statistical evidence for assembly bias, especially at lower
luminosity thresholds: the HOD of central galaxies in $z\sim0.15$ samples with
limiting absolute magnitude $M_r < -20.0$ and $M_r < -20.5$ samples is
positively correlated with halo concentration with a significance of 99.9% and
99.5%, respectively. Our models also favor positive central assembly bias for
the brighter $M_r < -21.0$ sample at $z\sim0.25$ (94.8% significance), but
there is no significant evidence for assembly bias with the same luminosity
threshold at $z\sim0.15$. We provide our constraints for each threshold
sample's characteristic halo masses, assembly bias, and other HOD parameters.
These constraints are expected to be significantly tightened with future DESI
data, which will span an area 100 times larger than that of SV3. | astro-ph |
Statistics in astronomy: Perhaps more than other physical sciences, astronomy is frequently
statistical in nature. The objects under study are inaccessible to direct
manipulation in the laboratory, so the astronomer is restricted to observing a
few external characteristics and inferring underlying properties and physics.
Astronomy played a profound role in the historical development of statistics
from the ancient Greeks through the 19th century. But the fields drifted apart
in the 20th century as astronomy turned towards astrophysics and statistics
towards human affairs. Today we see a resurgence in astrostatistical activity
with the proliferation of survey mega-datasets and the need to link complicated
data to nonlinear astrophysical models. Several contemporary astrostatistical
challenges are outlined: heteroscedastic measurement errors, censoring and
truncation in multivariate databases; time series analysis of variable objects
including dynamical models of extrasolar planetary systems; treatments of faint
sources and other Poisson processes; the anisotropic spatial point process of
galaxy clustering; and model fitting and selection for the cosmic microwave
background. | astro-ph |
The Initial Mass Functions in the Super-Star-Clusters NGC 1569A and NGC
1705-1: I use recent photometric and stellar velocity dispersion measurements of the
super-star-clusters (SSCs) NGC 1569A and NGC 1705-1 to determine their
present-day luminosity/mass (L_V/M) ratios. I then use the inferred L_V/M
ratios, together with population synthesis models of evolving star-clusters, to
constrain the initial-mass-functions (IMFs) in these objects.
I find that (L_V/M)_solar=28.9 in 1569A, and (L_V/M)_solar=126 in 1705-1. It
follows that in 1569A the IMF is steep with alpha~2.5 for m**(-alpha)dm IMFs
which extend to 0.1 M_sun. This implies that most of the stellar mass in 1569A
is contained in low-mass (< 1 M_sun) stars. However, in 1705-1 the IMF is
either flat, with alpha<2$, or it is truncated at a lower mass-limit between 1
and 3 M_sun.
I compare the inferred IMFs with the mass functions (MFs) of Galactic
globular clusters. It appears that 1569A has a sufficient reservoir of low-mass
stars for it to plausibly evolve into an object similar to Galactic globular
clusters. However, the apparent deficiency of low-mass stars in 1705-1 may make
it difficult for this SSC to become a globular cluster. If low-mass stars do
dominate the cluster mass in 1705-1, the large L_V/M ratio in this SSC may be
evidence that the most massive stars have formed close to the cluster cores. | astro-ph |
The detection of diffuse emission in HCG 16 with XMM-Newton: We report results obtained from analysis of the XMM-Newton observation of the
compact group of galaxies HCG 16. It is a peculiar system composed of 7
spirals,
6 of which are active, and its nature as a bound system has been much
debated. The EPIC camera observations give new insights into the X-ray
parameters describing the physical status of the group. We detect diffuse X-ray
emission with a rather elliptical morphology which extends to at least a radius
of 135 h^{-1}_{50} kpc from the group centre. The spectrum within this region
is well modelled by a thermal plasma with a temperature of 0.49+/-0.17 keV, and
a non-zero metallicity. We measure a bolometric X-ray luminosity of 9.6 10{^40}
h^{-2}_{50} erg/s which may be only a small fraction of the total luminosity
because of the limit in spatial detection arising from the high background
level. Despite its low temperature and luminosity, HCG 16 obeys the Lx-T
relation obtained for brighter galaxy groups even if it lies in a very extreme
position. The properties of the diffuse emission confirm the bound nature of
HCG 16 even if the gas trapped in the potential well may not yet be virialized.
This reopens the debate about the real nature of spiral-dominated galaxy
groups, and on their role in a more general cosmological context. | astro-ph |
Long-term spectropolarimetric monitoring of the cool supergiant
Betelgeuse: We report on a long-term monitoring of the cool supergiant Betelgeuse, using
the NARVAL and ESPaDOnS high-resolution spectropolarimeters, respectively
installed at Telescope Bernard Lyot (Pic du Midi Observatory, France) and at
the Canada-France-Hawaii Telescope (Mauna Kea Observatory, Hawaii). The data
set, constituted of circularly polarized (Stokes V) and intensity (Stokes I)
spectra, was collected between 2010 and 2012. We investigate here the temporal
evolution of magnetic field, convection and temperature at photospheric level,
using simultaneous measurements of the longitudinal magnetic field component,
the core emission of the Ca II infrared triplet, the line-depth ratio of
selected photospheric lines and the radial velocity of the star. | astro-ph |
The Stellar Kinematics of Extragalactic Bulges: Galactic bulges are complex systems. Once thought to be small-scale versions
of elliptical galaxies, advances in astronomical instrumentation (spectroscopy
in particular) has revealed a wealth of photometric and kinematic substructure
in otherwise simple-looking components. This review provides an overview of how
our perspective on galactic bulges has changed over the years. While it is
mainly focused on aspects related to the dynamical state of their stars, there
will be natural connections to other properties (e.g. morphology, stellar
populations) discussed in other reviews in this volume. | astro-ph |
Jet quenching in the neutron star low-mass X-ray binary 1RXS
J180408.9$-$342058: We present quasi-simultaneous radio (VLA) and X-ray ($Swift$) observations of
the neutron star low-mass X-ray binary (NS-LMXB) 1RXS J180408.9$-$342058
(J1804) during its 2015 outburst. We found that the radio jet of J1804 was
bright ($232 \pm 4 \mu$Jy at $10$ GHz) during the initial hard X-ray state,
before being quenched by more than an order of magnitude during the soft X-ray
state ($19 \pm 4 \mu$Jy). The source then was undetected in radio (< $13
\mu$Jy) as it faded to quiescence. In NS-LMXBs, possible jet quenching has been
observed in only three sources and the J1804 jet quenching we show here is the
deepest and clearest example to date. Radio observations when the source was
fading towards quiescence ($L_X = 10^{34-35}$ erg s$^{-1}$) show that J1804
must follow a steep track in the radio/X-ray luminosity plane with $\beta >
0.7$ (where $L_R \propto L_X^{\beta}$). Few other sources have been studied in
this faint regime, but a steep track is inconsistent with the suggested
behaviour for the recently identified class of transitional millisecond
pulsars. J1804 also shows fainter radio emission at $L_X < 10^{35}$ erg
s$^{-1}$ than what is typically observed for accreting millisecond pulsars.
This suggests that J1804 is likely not an accreting X-ray or transitional
millisecond pulsar. | astro-ph |
[O I] 6300 A Emission from Disks Around Herbig Ae/Be Stars: We present high spectral-resolution optical spectra of 49 Herbig Ae/Be stars
in a search for the [O I] 6300.2 A line. The vast majority of the stars in our
sample show narrow (FWHM < 100 km/s) emission lines, centered on the stellar
radial velocity. Some stars in our sample show double-peaked lines profiles,
with peak-to-peak separations of about 10 km/s. The presence and strength of
the [O I] line emission appears to be well correlated with the far-infrared
energy distribution of each source: stars with a strong excess at 60 micron
have in general stronger [O I] emission than stars with weaker 60 micron
excesses. We interpret the observed [O I] 6300.2 A line profiles as arising in
the surface layers of the protoplanetary disks surrounding Herbig Ae/Be stars. | astro-ph |
Cosmic Web & Caustic Skeleton: non-linear Constrained Realizations -- 2D
case studies: The cosmic web consists of a complex configuration of voids, walls,
filaments, and clusters, which formed under the gravitational collapse of
Gaussian fluctuations. Understanding under what conditions these different
structures emerge from simple initial conditions, and how different
cosmological models influence their evolution, is central to the study of the
large-scale structure. Here, we present a general formalism for setting up
initial random density and velocity fields satisfying non-linear constraints
for specialized N-body simulations. These allow us to link the non-linear
conditions on the eigenvalue and eigenvector fields of the deformation tensor,
as specified by caustic skeleton theory, to the current-day cosmic web. By
extending constrained Gaussian random field theory, and the corresponding
Hoffman-Ribak algorithm, to non-linear constraints, we probe the statistical
properties of the progenitors of the walls, filaments, and clusters of the
cosmic web. Applied to cosmological N-body simulations, the proposed techniques
pave the way towards a systematic investigation of the evolution of the
progenitors of the present-day walls, filaments, and clusters, and the embedded
galaxies, putting flesh on the bones of the caustic skeleton. The developed
nonlinear constrained random field theory is valid for generic cosmological
conditions. For ease of visualization, the case study presented here probes the
two-dimensional caustic skeleton. | astro-ph |
Mitigating Modal Noise in Multimode Circular Fibres by Optical Agitation
using a Galvanometer: Modal noise appears due to the non-uniform and unstable distribution of light
intensity among the finite number of modes in multimode fibres. It is an
important limiting factor in measuring radial velocity precisely by fibre-fed
high-resolution spectrographs. The problem can become particularly severe as
the fibre's core become smaller and the number of modes that can propagate
reduces. Thus, mitigating modal noise in relatively small core fibres still
remains a challenge. We present here a novel technique to suppress modal noise.
Two movable mirrors in the form of a galvanometer reimage the mode-pattern of
an input fibre to an output fibre. The mixing of modes coupled to the output
fibre can be controlled by the movement of mirrors applying two sinusoidal
signals through a voltage generator. We test the technique for four multimode
circular fibres: 10 and 50 micron step-index, 50 micron graded-index, and a
combination of 50 micron graded-index and 5:1 tapered fibres (GI50t). We
present the results of mode suppression both in terms of the direct image of
the output fibre and spectrum of white light obtained with the high-resolution
spectrograph. We found that the galvanometer mitigated modal noise in all the
tested fibres, but was most useful for smaller core fibres. However, there is a
trade-off between the modal noise reduction and light-loss. The GI50t provides
the best result with about 60% mitigation of modal noise at a cost of about 5%
output light-loss. Our solution is easy to use and can be implemented in
fibre-fed spectrographs. | astro-ph |
Foraging with MUSHROOMS: A Mixed-Integer Linear Programming Scheduler
for Multimessenger Target of Opportunity Searches with the Zwicky Transient
Facility: Electromagnetic follow-up of gravitational wave detections is very resource
intensive, taking up hours of limited observation time on dozens of telescopes.
Creating more efficient schedules for follow-up will lead to a commensurate
increase in counterpart location efficiency without using more telescope time.
Widely used in operations research and telescope scheduling, mixed integer
linear programming (MILP) is a strong candidate to produce these
higher-efficiency schedules, as it can make use of powerful commercial solvers
that find globally optimal solutions to provided problems . We detail a new
target of opportunity scheduling algorithm designed with Zwicky Transient
Facility in mind that uses mixed integer linear programming. We compare its
performance to \texttt{gwemopt}, the tuned heuristic scheduler used by the
Zwicky Transient Facility and other facilities during the third LIGO-Virgo
gravitational wave observing run. This new algorithm uses variable-length
observing blocks to enforce cadence requirements and ensure field
observability, along with having a secondary optimization step to minimize slew
time. \blue{We show that by employing a hybrid method utilizing both this
scheduler and \texttt{gwemopt}, the previous scheduler used, in concert, we can
achieve an average improvement in detection efficiency of 3\%-11\% over
\texttt{gwemopt} alone} for a simulated binary neutron star merger data set
consistent with LIGO-Virgo's third observing run, highlighting the potential of
mixed integer target of opportunity schedulers for future multimessenger
follow-up surveys. | astro-ph |
Universal lateral distribution of energy deposit in air showers and its
application to shower reconstruction: The light intensity distribution in a shower image and its implications to
the primary energy reconstructed by the fluorescence technique are studied.
Based on detailed CORSIKA energy deposit simulations, a universal analytical
formula is derived for the lateral distribution of light in the shower image
and a correction factor is obtained to account for the fraction of shower light
falling into outlying pixels in the detector. The expected light profiles and
the corresponding correction of the primary shower energy are illustrated for
several typical event geometries. This correction of the shower energy can
exceed 10%, depending on shower geometry. | astro-ph |
The X-ray Luminosity Function of Nearby Rich and Poor Clusters of
Galaxies: A Cosmological Probe: In this letter, we present a new determination of the local (z<0.09) X-ray
luminosity function (XLF) using a large, statistical sample of 294 Abell
clusters and the ROSAT All-Sky-Survey. Given our large sample size, we have
reduced errors by a factor of two for L(X)(0.5-2keV)>10^43 ergs/sec. We combine
our data with previous work in order to explore possible constraints imposed by
the shape of the XLF on cosmological models. A set of currently viable
cosmologies is used to construct theoretical XLFs assuming Lx is proportional
to M^p and a sigma_8-Omega_0 constraint (from Viana & Liddle 1996) based on the
local X-ray temperature function. We fit these models to our observed XLF and
verify that the simplest adiabatic, analytic scaling relation (e.g. Kaiser
1986) disagrees strongly with observations. If we assume that clusters can be
described by the pre-heated, constant core-entropy models of Evrard & Henry
(1991) then the observed XLF is consistent only with 0.1 < Omega_0 < 0.4 if the
energy per unit mass in galaxies is roughly equal to the gas energy (ie if
beta=1). (abridged) | astro-ph |
Evidence for a Galactic Origin of Very Short Gamma Ray Bursts and
Primordial Black Hole Sources: We systematically study the shortest time duration gamma ray bursts and find
unique features that are best interpreted as sources of a galactic origin.
There is a significant angular asymmetry and the V/Vmax distribution provides
evidence for a homogenous or Euclidean source distribution. We eview the
arguments that primordial black hole evaporation can give such GRBs. The rate
of events is consistent with a PBH origin if we assume on enhanced local
density, as are the other distributions. We suggest further tests of this
hypothesis. | astro-ph |
Synchrotron X-ray diagnostics of cutoff shape of nonthermal electron
spectrum at young supernova remnants: Synchrotron X-rays can be a useful tool to investigate electron acceleration
at young supernova remnants (SNRs). At present, since the magnetic field
configuration around the shocks of SNRs is uncertain, it is not clear whether
electron acceleration is limited by SNR age, synchrotron cooling, or even
escape from the acceleration region. We study whether the acceleration
mechanism can be constrained by the cutoff shape of the electron spectrum
around the maximum energy. We derive analytical formulae of the cutoff shape in
each case where the maximum electron energy is determined by SNR age,
synchrotron cooling and escape from the shock. They are related to the energy
dependence of the electron diffusion coefficient. Next, we discuss whether
information on the cutoff shape can be provided by observations in the near
future which will simply give the photon indices and the flux ratios in the
soft and hard X-ray bands. We find that if the power-law index of the electron
spectrum is independently determined by other observations, then we can
constrain the cutoff shape by comparing theoretical predictions of the photon
indices and/or the flux ratios with observed data which will be measured by
NuSTAR and/or ASTRO-H. Such study is helpful in understanding the acceleration
mechanism. In particular, it will supply another independent constraint on the
magnetic field strength around the shocks of SNRs. | astro-ph |
Spectral Analysis Code: PARAS SPEC: The light emitted from the stellar photosphere serves as a unique signature
for the nature of stars. The behaviour of these stellar lines depend upon the
surface temperature, mass, evolutionary status and chemical composition of the
star. With the advent of high-resolution spectrographs coupled with medium to
large aperture telescopes around the globe, there is plenty of high-resolution
and high signal-to-noise ratio data available to the astronomy community. Apart
from radial velocity (RV) studies, such data offer us the unique opportunity to
study chemical composition and atmospheric properties of the star. The
procedure used to derive these parameters must be automated and well adaptable
to data available from any high-resolution spectrograph. We hereby present an
IDL code, PARAS SPEC, which was primary designed to handle high-resolution
spectroscopy data from PARAS spectrograph coupled with the 1.2~m telescope at
Mt. Abu, India. This code is designed to adapt with data from other
spectrographs as well. The code PARAS SPEC estimates the stellar atmospheric
parameters from the analysis of stellar spectra based on two primary methods,
synthetic spectral fitting and equivalent width method. Synthetic spectral
fitting method involves fitting of the observed spectrum with different
synthetic spectra for a set of stellar parameters. The second method is based
on equivalent widths (EWs) that are used to derive abundances for a set of Fe~I
and Fe~II lines from the observed spectra. The detailed methodology used to
design this code and comparison of the results from literature values are
presented in this paper. | astro-ph |
The physics of Lyman-alpha escape from disc-like galaxies: Hydrogen emission lines can provide extensive information about star-forming
galaxies in both the local and high-redshift Universe. We present a detailed
Lyman continuum (LyC), Lyman-alpha (Ly{\alpha}), and Balmer line (H{\alpha} and
H\b{eta}) radiative transfer study of a high-resolution isolated Milky-Way
simulation using the Arepo-RT radiation hydrodynamics code with the SMUGGLE
galaxy formation model. The realistic framework includes stellar feedback,
non-equilibrium thermochemistry, and dust grain evolution in the interstellar
medium (ISM). We extend our Cosmic Ly{\alpha} Transfer (COLT) code with
photoionization equilibrium Monte Carlo radiative transfer for self-consistent
end-to-end (non-)resonant line predictions. Accurate LyC reprocessing to
recombination emission requires modelling pre-absorption by dust (27.5%),
helium ionization (8.7%), and anisotropic escape fractions (7.9%), as these
reduce the available budget for hydrogen line emission (55.9%). We investigate
the role of the multiphase dusty ISM, disc geometry, gas kinematics, and star
formation activity in governing the physics of emission and escape, focusing on
the time variability, gas phase structure, and spatial, spectral, and viewing
angle dependence of the emergent photons. Isolated disc simulations are
well-suited for comprehensive observational comparisons with local H{\alpha}
surveys, but would require a proper cosmological circumgalactic medium (CGM)
environment as well as less dust absorption and rotational broadening to serve
as analogs for high-redshift Ly{\alpha} emitting galaxies. Future applications
of our framework to next-generation cosmological simulations of galaxy
formation including radiation-hydrodynamics that resolve <10 pc multiphase ISM
and <1 kpc CGM structures will provide crucial insights and predictions for
current and upcoming Ly{\alpha} observations. | astro-ph |
Effects of the South Atlantic Anomaly on the muon flux at sea level: The goal of this study is to examine the response and changes of the muon
intensity at ground, due to magnetic anomaly over south Atlantic. Based on the
data of two directional muon telescopes and located at 22S and 43W. These
coordinates are inside of the South Atlantic Anomaly (SAA) region, a dip in the
magnetosphere. This characteristic offers to the muon telescopes the lowest
rigidity of response to cosmic protons and ions ($\geq 0.4$ GV). The
magnetosphere's dip is responsible for several processes, such as the high
conductivity of the atmospheric layers due to the precipitation of energetic
particles in this region and an zonal electric field known as the pre-reversal
electric field (PRE) with an enhancement at evening hours. In addition the open
magnetosphere, propitiate the magnetic reconnections of the IMF lines that will
take place in this site in the day side. These factors are responsible for an
unusually large particle flux present in the SAA region, including particles
with energies above the pion production threshold. The main effect is an
increase of the muon intensity ($E_{\mu}>0.2GeV$) at ground, in the day side,
in up to ten times. We show that it is correlated with the pre-reversal
electric field, and propitiate the observation of muon enhancements due to
small solar transient events, such as corotating interaction region (CIR) and
micro-flares. Details of these results are reported in this paper. | astro-ph |
The Star Formation Rates of Elliptical Galaxies from Core-Collapse
Supernovae: The level of star formation in elliptical galaxies is poorly constrained, due
to difficulties in quantifying the contamination of flux-based estimates of
star formation from unrelated phenomena, such as AGN and old stellar
populations. We here utilise core-collapse supernovae (CCSNe) as unambiguous
tracers of recent star formation in ellipticals within a cosmic volume. We
firstly isolate a sample of 421 z < 0.2, r < 21.8 mag CCSNe from the SDSS-II
Supernova Survey. We then introduce a Bayesian method of identifying
ellipticals via their colours and morphologies in a manner unbiased by redshift
and yet consistent with manual classification from Galaxy Zoo 1. We find ~ 25 %
of z < 0.2 r < 20 mag galaxies in the Stripe 82 region are ellipticals (~ 28000
galaxies). In total, 36 CCSNe are found to reside in ellipticals. We
demonstrate that such early-types contribute a non-negligible fraction of star
formation to the present-day cosmic budget, at 11.2 $\pm$ 3.1 (stat)
$^{+3.0}_{-4.2}$ (sys) %. Coupling this result with the galaxy stellar mass
function of ellipticals, the mean specific star formation rate (SSFR;
$\overline{S}$) of these systems is derived. The best-fit slope is given by log
($\overline{S}(M)$/yr) = - (0.80 $\pm$ 0.59) log ($M/10^{10.5}\rm{M}_{\odot}$)
- 10.83 $\pm$ 0.18. The mean SSFR for all log ($M/\rm{M}_{\odot}$) > 10.0
ellipticals is found to be $\overline{S} = 9.2 \pm 2.4$ (stat) $^{+2.7}_{-2.3}$
(sys) $\times 10^{-12}$ yr$^{-1}$, which is consistent with recent estimates
via SED-fitting, and is 11.8 $\pm$ 3.7 (stat) $^{+3.5}_{-2.9}$ (sys) % of the
mean SSFR level on the main sequence as also derived from CCSNe. We find the
median optical spectrum of elliptical CCSN hosts is statistically consistent
with that of a control sample of ellipticals that do not host CCSNe, implying
that these SN-derived results are well-representative of the total low-z
elliptical population. | astro-ph |
Chlorine Abundances in Cool Stars: Chlorine abundances are reported in 15 evolved giants and one M dwarf in the
solar neighborhood. The Cl abundance was measured using the vibration-rotation
1-0 P8 line of H$^{35}$Cl at 3.69851 $\mu$m. The high resolution L-band spectra
were observed using the Phoenix infrared spectrometer on the Kitt Peak Mayall
4m telescope. The average [$^{35}$Cl/Fe] abundance in stars with
--0.72$<$[Fe/H]$<$0.20 is [$^{35}$Cl/Fe]=(--0.10$\pm$0.15) dex. The mean
difference between the [$^{35}$Cl/Fe] ratios measured in our stars and chemical
evolution model values is (0.16$\pm$0.15) dex. The [$^{35}$Cl/Ca] ratio has an
offset of $\sim$0.35 dex above model predictions suggesting chemical evolution
models are under producing Cl at the high metallicity range. Abundances of C,
N, O, Si, and Ca were also measured in our spectral region and are consistent
with F and G dwarfs. The Cl versus O abundances from our sample match Cl
abundances measured in planetary nebula and \ion{H}{2} regions. In one star
where both H$^{35}$Cl and H$^{37}$Cl could be measured, a $^{35}$Cl/$^{37}$Cl
isotope ratio of 2.2$\pm$0.4 was found, consistent with values found in the
Galactic ISM and predicted chemical evolution models. | astro-ph |
A dynamical study on the habitability of terrestrial exoplanets I:
Tidally evolved planet-satellite pairs: We investigate the obliquity and spin period of Earth-Moon like systems after
4.5 Gyr of tidal evolution with various satellite masses and initial planetary
obliquity and discuss their relations to the habitability of the planet. We
find three possible outcomes: either i) the system is still evolving, ii) the
system is double synchronous or iii) the satellite has collided with the
planet. The transition between case i) and ii) is abrupt and occurs at slightly
larger satellite mass ($m_s \sim 0.02m_p$) than the lunar mass. We suggest that
cases ii) and iii) are less habitable than case i). Using results from models
of giant impacts and satellite accretion, we found that the systems that mimic
our own with rotation period $12 < P_p < 48$ h and current planetary obliquity
$\varepsilon_p < 40^\circ$ or $\varepsilon_p > 140^\circ$ only represent 14% of
the possible outcomes. Elser et al. (2011) conclude that the probability of a
terrestrial planet having a heavy satellite is 13%. Combining these results
suggests that the probability of ending up with a system such as our own is of
the order of 2%. | astro-ph |
The Cosmological Evolution of Self-interacting Dark Matter: We study the evolution of cosmological perturbations in dark-matter models
with elastic and velocity-independent self interactions. Such interactions are
imprinted in the matter-power spectrum as dark acoustic oscillations, which can
be experimentally explored to determine the strength of the self scatterings.
Models with self interactions have similarities to warm dark matter, as they
lead to suppression of power on small scales when the dark-matter velocity
dispersion is sizable. Nonetheless, both the physical origin and the extent of
the suppression differ for self-interacting dark matter from conventional warm
dark matter, with a dark sound horizon controlling the reduction of power in
the former case, and a free-streaming length in the latter. We thoroughly
analyze these differences by performing computations of the linear power
spectrum using a newly developed Boltzmann code. We find that while current
Lyman-$\alpha$ data disfavor conventional warm dark matter with a mass less
than 5.3 keV, when self interactions are included at their maximal value
consistent with bounds from the Bullet Cluster, the limits are relaxed to 4.4
keV. Finally, we make use of our analysis to set novel bounds on light scalar
singlet dark matter. | astro-ph |
Multiwavelength study of Cygnus A III. Evidence for relic lobe plasma: We study the particle energy distribution in the cocoon surrounding Cygnus A,
using radio images between 151 MHz and 15 GHz and a 200 ks Chandra ACIS-I
image. We show that the excess low frequency emission in the the lobe further
from Earth cannot be explained by absorption or excess adiabatic expansion of
the lobe or a combination of both. We show that this excess emission is
consistent with emission from a relic counterlobe and a relic counterjet that
are being re-energized by compression from the current lobe. We detect hints of
a relic hotspot at the end of the relic X-ray jet in the more distant lobe. We
do not detect relic emission in the lobe nearer to Earth as expected from light
travel-time effects assuming intrinsic symmetry. We determine that the duration
of the previous jet activity phase was slightly less than that of the current
jet-active phase. Further, we explain some features observed at 5 and 15 GHz as
due to the presence of a relic jet. | astro-ph |
The temperature structure in the core of Sersic 159-03: We present results from a new 120 ks XMM-Newton observation of the cluster of
galaxies Sersic 159-03. In this paper we focus on the high-resolution X-ray
spectra obtained with the Reflection Grating Spectrometer (RGS). The spectra
allow us to constrain the temperature structure in the core of the cluster and
determine the emission measure distribution as a function of temperature. We
also fit the line widths of mainly oxygen and iron lines. | astro-ph |
Squeezing $f_{\rm NL}$ out of the matter bispectrum with consistency
relations: We show how consistency relations can be used to robustly extract the
amplitude of local primordial non-Gaussianity ($f_{\rm NL}$) from the squeezed
limit of the matter bispectrum, well into the non-linear regime. First, we
derive a non-perturbative relation between primordial non-Gaussianity and the
leading term in the squeezed bispectrum, revising some results present in the
literature. This relation is then used to successfully measure $f_{\rm NL}$
from $N$-body simulations. We discuss the dependence of our results on
different scale cuts and redshifts. Specifically, the analysis is strongly
dependent on the choice of the smallest soft momentum, $q_{\rm min}$, which is
the most sensitive to primordial bispectrum contributions, but is largely
independent of the choice of the largest hard momentum, $k_{\rm max}$, due to
the non-Gaussian nature of the covariance. We also show how the constraints on
$f_{\rm NL}$ improve at higher redshift, due to a reduced off-diagonal
covariance. In particular, for a simulation with $f_{\rm NL} = 100$ and a
volume of $(2.4 \text{ Gpc}/h)^3$, we measure $f_{\rm NL} = 98 \pm 12$ at
redshift $z=0$ and $f_{\rm NL} = 97 \pm 8$ at $z=0.97$. Finally, we compare our
results with a Fisher forecast, showing that the current version of the
analysis is satisfactorily close to the Fisher error. We regard this as a first
step towards the realistic application of consistency relations to constrain
primordial non-Gaussianity using observations. | astro-ph |
Hubble Ultraviolet Spectroscopy of Jupiter Trojans: We present the first ultraviolet spectra of Jupiter Trojans. These
observations were carried out using the Space Telescope Imaging Spectrograph on
the Hubble Space Telescope and cover the wavelength range 200-550 nm at low
resolution. The targets include objects from both of the Trojan color
subpopulations (less-red and red). We do not observe any discernible absorption
features in these spectra. Comparisons of the averaged UV spectra of less-red
and red targets show that the subpopulations are spectrally distinct in the UV.
Less-red objects display a steep UV slope and a rollover at around 450 nm to a
shallower visible slope, whereas red objects show the opposite trend.
Laboratory spectra of irradiated ices with and without H$_{2}$S exhibit
distinct UV absorption features; consequently, the featureless spectra observed
here suggest H$_{2}$S alone is not responsible for the observed color
bimodality of Trojans, as has been previously hypothesized. We propose some
possible explanations for the observed UV-visible spectra, including complex
organics, space weathering of iron-bearing silicates, and masked features due
to previous cometary activity. | astro-ph |
Supernova Remnants as a Probe of Dust Grains in the Interstellar Medium: Interstellar dust grains play a crucial role in the evolution of the galactic
interstellar medium (ISM). Despite its importance, however, dust remains poorly
understood in terms of its origin, composition, and abundance throughout the
universe. Supernova remnants (SNRs) provide a laboratory for studying the
evolution of dust grains, as they are one of the only environments in the
universe where it is possible to observe grains being both created and
destroyed. SNRs exhibit collisionally heated dust, allowing dust to serve as a
diagnostic both for grain physics and for the plasma conditions in the SNR. I
present theoretical models of collisionally heated dust which calculate grain
emission as well as destruction rates. In these models, I incorporate physics
such as nonthermal sputtering caused by grain motions through the gas, a more
realistic approach to sputtering for small grains, and arbitrary grain
compositions porous and composite grains. I apply these models to infrared and
X-ray observations of Kepler's supernova and the Cygnus Loop in the galaxy, and
SNRs 0509-67.5, 0519-69.0, and 0540-69.3 in the LMC. X-ray observations
characterize the hot plasma while IR observations constrain grain properties
and destruction rates. Such a multi-wavelength approach is crucial for a
complete understanding of gas and dust interaction and evolution. Modeling of
both X-ray and IR spectra allows disentangling of parameters such as pre and
postshock gas density, as well as swept-up masses of gas and dust, and can
provide constraints on the shock compression ratio. Observations also show that
the dust-to-gas mass ratio in the ISM is lower by a factor of several than what
is inferred by extinction studies of starlight. Future observatories, such as
the James Webb Space Telescope and the International X-ray Observatory, will
allow testing of models far beyond what is possible now. | astro-ph |
Bringing 2D Eclipse Mapping out of the Shadows with Leave-one-out
Cross-validation: Eclipse mapping is a technique for inferring 2D brightness maps of transiting
exoplanets from the shape of an eclipse light curve. With JWST's unmatched
precision, eclipse mapping is now possible for a large number of exoplanets.
However, eclipse mapping has only been applied to two planets and the nuances
of fitting eclipse maps are not yet fully understood. Here, we use
Leave-one-out Cross- Validation (LOO-CV) to investigate eclipse mapping, with
application to a JWST NIRISS/SOSS observation of the ultra-hot Jupiter
WASP-18b. LOO-CV is a technique that provides insight into the out-of-sample
predictive power of models on a data-point-by-data-point basis. We show that
constraints on planetary brightness patterns behave as expected, with
large-scale variations driven by the phase-curve variation in the light curve
and smaller-scale structures constrained by the eclipse ingress and egress. For
WASP-18b we show that the need for higher model complexity (smaller-scale
features) is driven exclusively by the shape of the eclipse ingress and egress.
We use LOO-CV to investigate the relationship between planetary brightness map
components when mapping under a positive-flux constraint to better understand
the need for complex models. Finally, we use LOO-CV to understand the
degeneracy between the competing ``hotspot'' and ``plateau'' brightness map
models of WASP-18b, showing that the plateau model is driven by the ingress
shape and the hotspot model is driven by the egress shape, but preference for
neither model is due to outliers or unmodeled signals. Based on this analysis,
we make recommendations for the use of LOO-CV in future eclipse-mapping
studies. | astro-ph |
Multi-D Simulations of Ultra-Stripped Supernovae to Shock Breakout: The recent discoveries of many double neutron star systems and their
detection as LIGO-Virgo merger events call for a detailed understanding of
their origin. Explosions of ultra-stripped stars in binary systems have been
shown to play a key role in this context and have also generated interest as a
potential explanation for rapidly evolving hydrogen-free transients. Here we
present the first attempt to model such explosions based on binary evolution
calculations that follow the mass transfer to the companion to obtain a
consistent core-envelope structure as needed for reliable predictions of the
supernova transient. We simulate the explosion in 2D and 3D, and confirm the
modest explosion energies ~10^50erg and small kick velocities reported earlier
in 2D models based on bare carbon-oxygen cores. The spin-up of the neutron star
by asymmetric accretion is small in 3D with no indication of spin-kick
alignment. Simulations up to shock breakout show the mixing of sizeable amounts
of iron group material into the helium envelope. In view of recent ideas for a
mixing-length treatment (MLT) of Rayleigh-Taylor instabilities in supernovae,
we perform a detailed analysis of the mixing, which reveals evidence for
buoyancy-drag balance, but otherwise does not support the MLT approximation.
The mixing may have implications for the spectroscopic signatures of
ultra-stripped supernovae that need to be investigated in the future. Our
stellar evolution calculation also predicts presupernova mass loss due to an
off-centre silicon deflagration flash, which suggests that supernovae from
extremely stripped cores may show signs of interactions with circumstellar
material. | astro-ph |
An Ultraviolet Spectrum of the Tidal Disruption Flare ASASSN-14li: We present a Hubble Space Telescope STIS spectrum of ASASSN-14li, the first
rest-frame UV spectrum of a tidal disruption flare (TDF). The underlying
continuum is well fit by a blackbody with $T_{\mathrm{UV}} = 3.5 \times 10^{4}$
K, an order of magnitude smaller than the temperature inferred from X-ray
spectra (and significantly more precise than previous efforts based on optical
and near-UV photometry). Super-imposed on this blue continuum, we detect three
classes of features: narrow absorption from the Milky Way (probably a
high-velocity cloud), and narrow absorption and broad (FWHM $\approx 2000$-8000
km s$^{-1}$) emission lines at/near the systemic host velocity. The absorption
lines are blueshifted with respect to the emission lines by $\Delta v =
-(250$-400) km s$^{-1}$. Due both to this velocity offset and the lack of
common low-ionization features (Mg II, Fe II), we argue these arise from the
same absorbing material responsible for the low-velocity outflow discovered at
X-ray wavelengths. The broad nuclear emission lines display a remarkable
abundance pattern: N III], N IV], He II are quite prominent, while the common
quasar emission lines of C III] and Mg II are weak or entirely absent. Detailed
modeling of this spectrum will help elucidate fundamental questions regarding
the nature of the emission process(es) at work in TDFs, while future UV
spectroscopy of ASASSN-14li would help to confirm (or refute) the previously
proposed connection between TDFs and "N-rich" quasars. | astro-ph |
Detection and Characterization of Exoplanets and Disks using Projections
on Karhunen-Loeve Eigenimages: We describe a new method to achieve point spread function (PSF) subtractions
for high- contrast imaging using Principal Component Analysis (PCA) that is
applicable to both point sources or extended objects (disks). Assuming a
library of reference PSFs, a Karhunen-Lo`eve transform of theses references is
used to create an orthogonal basis of eigenimages, on which the science target
is projected. For detection this approach provides comparable suppression to
the Locally Optimized Combination of Images (LOCI) algorithm, albeit with
increased robustness to the algorithm parameters and speed enhancement. For
characterization of detected sources the method enables forward modeling of
astrophysical sources. This alleviates the biases in the astrometry and
photometry of discovered faint sources, which are usually associated with LOCI-
based PSF subtractions schemes. We illustrate the algorithm performance using
archival Hubble Space Telescope (HST) images, but the approach may also be
considered for ground-based data acquired with Angular Differential Imaging
(ADI) or integral-field spectrographs (IFS). | astro-ph |
Rotational broadening and conservation of angular momentum in
post-extreme horizontal branch stars: We show that the recent realization that isolated post-extreme horizontal
branch (post-EHB) stars are generally characterized by rotational broadening
with values of $V_{\rm rot} \sin i$ between 25 and 30 km~s$^{-1}$ can be
explained as a natural consequence of the conservation of angular momentum from
the previous He-core burning phase on the EHB. The progenitors of these evolved
objects, the EHB stars, are known to be slow rotators with an average value of
$V_{\rm rot} \sin i$ of $\sim$7.7 km~s$^{-1}$. This implies significant spin-up
between the EHB and post-EHB phases. Using representative evolutionary models
of hot subdwarf stars, we demonstrate that angular momentum conservation in
uniformly rotating strutures (rigid-body rotation) boosts that value of the
projected equatorial rotation speed by a factor $\sim$3.6 by the time the model
has reached the region of the surface gravity-effective temperature plane where
the newly-studied post-EHB objects are found. This is exactly what is needed to
account for their observed atmospheric broadening. We note that the decrease of
the moment of inertia causing the spin-up is mostly due to the redistribution
of matter that produces more centrally-condensed structures in the post-EHB
phase of evolution, not to the decrease of the radius per se. | astro-ph |
Laboratory experiments and simulations on jets: Astrophysical jets have been studied with observations, theoretical models
and numerical simulations for decades. Recently, supersonic magnetized jets
have been formed in laboratory experiments of high-energy density plasmas. I
will review these studies and discuss the experimental setup that has been used
to form millimeter-scale jets driven by strong toroidal magnetic fields in a
MAGPIE generator. The physical conditions of these experiments are such that
they can be scaled to astrophysical scenarios. These laboratory jets provide
insights on the underlying physics of magnetic tower jets and help constrain
some models of astrophysical jets. In this context, we also discuss the
connection between the laboratory jets and recent 3D-MHD numerical simulations
of Poynting flux dominated jets. The simulations allow us to investigate the
effects of thermal energy losses and base rotation on the growth rate of kink
mode perturbations, and to compare the evolution of PFD jets with a
hydrodynamic counterpart of the same energy flux. | astro-ph |
Time-Delayed transfer functions simulations for LMXBs: Recent works (Steeghs & Casares 2002, Casares et al. 2003, Hynes et al. 2003)
have demonstrated that Bowen flourescence is a very efficient tracer of the
companion star in LMXBs. We present a numerical code to simulate time-delayed
transfer functions in LMXBs, specific to the case of reprocessing in emission
lines. The code is also able to obtain geometrical and binary parameters by
fitting observed (X-ray + optical) light curves using simulated annealing
methods. In this work we present the geometrical model for the companion star
and the analytical model for the disc and show synthetic time-delay transfer
functions for different orbital phases and system parameters. | astro-ph |
A New View of the Super Star Clusters in the Low-Metallicity Galaxy SBS
0335-052: We present a study of the individual super star clusters (SSCs) in the
low-metallicity galaxy SBS 0335-052 using new near-infrared and archival
optical Hubble Space Telescope observations. The physical properties of the
SSCs are derived from fitting model spectral energy distributions (SEDs) to the
optical photometry, as well as from the H_alpha and Pa_alpha nebular emission.
Among the clusters, we find a significant age spread that is correlated with
position in the galaxy, suggesting successive cluster formation occurred in SBS
0335-052 triggered by a large-scale disturbance traveling through the galaxy at
a speed of ~35 km/s. The SSCs exhibit I-band (~0.8 um) and near-IR (~1.6-2.1
um) excesses with respect to model SEDs fit to the optical data. We hypothesize
that the I-band excess is dominated by a photoluminescent process known as
Extended Red Emission; however, this mechanism cannot account for the excesses
observed at longer near-IR wavelengths. From the cluster SEDs and colors, we
find that the primary origin of the near-IR excess observed in the youngest
SSCs (<3 Myr) is hot dust emission, while evolved red supergiants dominate the
near-IR light in the older (>7 Myr) clusters. We also find evidence for a
porous and clumpy interstellar medium (ISM) surrounding the youngest, embedded
SSCs: the ionized gas emission underpredicts the expected ionizing luminosities
from the optical stellar continuum, suggesting ionizing photons are leaking out
of the immediate vicinity of the clusters before ionizing hydrogen. The
corrected, intrinsic ionizing luminosities of the two SSCs younger than ~3 Myr
are each ~ 5x10^52 s^-1, which is equivalent to each cluster hosting ~5000 O7.5
V stars. The inferred masses of these SSCs are ~10^6 M_sun. | astro-ph |
The role of electron heating physics in images and variability of the
Galactic Centre black hole Sagittarius A*: The accretion flow around the Galactic Center black hole Sagittarius A* (Sgr
A*) is expected to have an electron temperature that is distinct from the ion
temperature, due to weak Coulomb coupling in the low-density plasma. We present
four two-temperature general relativistic radiative magnetohydrodynamic
(GRRMHD) simulations of Sgr A* performed with the code KORAL. These simulations
use different electron heating prescriptions, motivated by different models of
the underlying plasma microphysics. We compare the Landau-damped turbulent
cascade model used in previous work with a new prescription we introduce based
on the results of particle-in-cell simulations of magnetic reconnection. With
the turbulent heating model, electrons are preferentially heated in the polar
outflow, whereas with the reconnection model electrons are heated by nearly the
same fraction everywhere in the accretion flow. The spectra of the two models
are similar around the submillimetre synchrotron peak, but the models heated by
magnetic reconnection produce variability more consistent with the level
observed from Sgr A*. All models produce 230~GHz images with distinct black
hole shadows which are consistent with the image size measured by the Event
Horizon Telescope, but only the turbulent heating produces an anisotropic
`disc-jet' structure where the image is dominated by a polar outflow or jet at
frequencies below the synchrotron peak. None of our models can reproduce the
observed radio spectral slope, the large near-infrared and X-ray flares, or the
near-infrared spectral index, all of which suggest non-thermal electrons are
needed to fully explain the emission from Sgr A*. | astro-ph |
Comparative clustering analysis of Ca II 854.2 nm spectral profiles from
simulations and observations: We aim to compare and contrast the typical shapes of synthetic Ca II 854.2 nm
spectra found in Bifrost simulations having different magnetic activity with
the spectral shapes found in a quiet Sun observation from the Swedish 1-m Solar
Telescope (SST). We use clustering techniques to extract the typical Ca II
854.2 nm profile shapes synthesized from Bifrost simulations with varying
amounts of magnetic activity. We degrade the synthetic profiles to
observational conditions and repeat the clustering, and we compare our
synthetic results with actual observations. While the mean spectra for our high
resolution simulations compare reasonably well with the observations, we find
that there are considerable differences between the clusters of observed and
synthetic intensity profiles, even after the synthetic profiles have been
degraded. The typical absorption profiles from the simulations are both
narrower and display a steeper transition from the inner wings to the line
core. Furthermore, even in our most quiescent simulation we find a far larger
fraction of profiles with local emission around the core, or other exotic
profile shapes, than in the observations. Looking into the atmospheric
structure for a selected set of synthetic clusters, we find distinct
differences in the temperature stratification for the clusters most and least
similar to the observations. The narrow and steep profiles are associated with
either weak gradients in temperature, or temperatures rising to a local maximum
in the line wing forming region before sinking to a minimum in the line core
forming region. The profiles that display less steep transitions show extended
temperature gradients that are steeper in the range $-3 \lesssim \log
\tau_{5000} \lesssim -1$. | astro-ph |
Hydrogenation of small aromatic heterocycles at low temperatures: The recent wave of detections of interstellar aromatic molecules has sparked
interest in the chemical behavior of aromatic molecules under astrophysical
conditions. In most cases, these detections have been made through chemically
related molecules, called proxies, that implicitly indicate the presence of a
parent molecule. In this study, we present the results of the theoretical
evaluation of the hydrogenation reactions of different aromatic molecules
(benzene, pyridine, pyrrole, furan, thiophene, silabenzene, and phosphorine).
The viability of these reactions allows us to evaluate the resilience of these
molecules to the most important reducing agent in the interstellar medium, the
hydrogen atom (H). All significant reactions are exothermic and most of them
present activation barriers, which are, in several cases, overcome by quantum
tunneling. Instanton reaction rate constants are provided between 50 K and 500
K. For the most efficiently formed radicals, a second hydrogenation step has
been studied. We propose that hydrogenated derivatives of furan, pyrrole, and
specially 2,3-dihydropyrrole, 2,5-dihydropyrrole, 2,3-dihydrofuran, and
2,5-dihydrofuran are promising candidates for future interstellar detections. | astro-ph |
Parallax Results From URAT Epoch Data: We present 1103 trigonometric parallaxes and proper motions from the United
States Naval Observatory (USNO) Robotic Astrometric Telescope (URAT)
observations taken at the Naval Observatory Flagstaff Station (NOFS) over a 3
year period from April 2012 to June 2015 covering the entire sky north of about
minus 10 deg declination. We selected 2 samples previously suspected nearby
stars from known photometric distances and stars showing a large, significant
parallax signature in URAT epoch data without any prior selection criteria. All
systems presented in this paper have an observed parallax greater than equal to
40 mas with no previous published trigonometric parallax. The formal errors on
these weighted parallax solutions are mostly between 4 and 10 mas. This sample
gives a significant (order 50%) increase to the number of known systems having
a trigonometric parallax to be within 25 pc of the Sun (without applying Lutz
Kelker bias corrections). A few of these are found to be within 10 pc. Many of
these new nearby stars display a total proper motion of less than 200 mas per
year. URAT parallax results have been verified against Hipparcos and Yale data
for stars in common. The publication of all significant parallax observations
from URAT data is in preparation for CDS. | astro-ph |
A Quasar Wind Model: A quasar wind model is proposed to describe the spatial and velocity
structure of the broad line region. This model requires detailed
photoionization and magnetohydrodynamic simulation, as the broad line region it
too small for direct spatial resolution. The emission lines are Doppler
broadened, since the gas is moving at high velocity. The high velocity is
attained by the gas from a combination of radiative and magnetic driving
forces. Once this model is complete, the model predictions will be tested
against recent microlensing data in conjunction with diverse existing
observations. | astro-ph |
Relativistic effects in galaxy clustering in a parametrized
post-Friedmann universe: We explore the signatures of quintessence and modified gravity theories in
the relativistic description of galaxy clustering within a parametrized
post-Friedmann framework. For this purpose, we develop a calibration method to
consistently account for horizon-scale effects in the linear parametrized
Post-Friedmann perturbations of minimally and nonminimally coupled
scalar-tensor theories and test it against the full model-specific
fluctuations. We further study the relativistic effects in galaxy clustering
for the normal and self-accelerating branches of the Dvali-Gabadadze-Porrati
braneworld model as well as for phenomenological modifications of gravity. We
quantify the impact of modified gravity and dark energy models on galaxy
clustering by computing the velocity-to-matter density ratio F, the velocity
contribution R, and the potential contribution P and give an estimate of their
detectability in future galaxy surveys. Our results show that, in general, the
relativistic correction contains additional information on gravity and dark
energy, which needs to be taken into account in consistent horizon-scale tests
of departures from LCDM using the galaxy-density field. | astro-ph |
Core-collapse explosions of Wolf-Rayet stars and the connection to type
IIb/Ib/Ic supernovae: We present non-LTE time-dependent radiative-transfer simulations of supernova
(SN) IIb/Ib/Ic spectra and light curves, based on ~1B-energy piston-driven
ejecta, with and without 56Ni, produced from single and binary Wolf-Rayet (W-R)
stars evolved at solar and sub-solar metallicities. Our bolometric light curves
show a 10-day long post-breakout plateau with a luminosity of 1-5x10^7Lsun. In
our 56Ni-rich models, with ~3Msun ejecta masses, this plateau precedes a
20-30-day long re-brightening phase initiated by the outward-diffusing heat
wave powered by radioactive decay at depth. In low ejecta-mass models with
moderate mixing, Gamma-ray leakage starts as early as ~50d after explosion and
causes the nebular luminosity to steeply decline by ~0.02mag/d. Such
signatures, which are observed in standard SNe IIb/Ib/Ic, are consistent with
low-mass progenitors derived from a binary-star population. We propose that the
majority of stars with an initial mass ~<20Msun yield SNe II-P if 'effectively"
single, SNe IIb/Ib/Ic if part of a close binary system, and SN-less black holes
if more massive. Our ejecta, with outer hydrogen mass fractions as low as
~>0.01 and a total hydrogen mass of ~>0.001Msun, yield the characteristic SN
IIb spectral morphology at early times. However, by ~15d after the explosion,
only Halpha may remain as a weak absorption feature. Our binary models,
characterised by helium surface mass fractions of ~>0.85, systematically show
HeI lines during the post-breakout plateau, irrespective of the 56Ni abundance.
Synthetic spectra show a strong sensitivity to metallicity, which offers the
possibility to constrain it directly from SN spectroscopic modelling. | astro-ph |
Multiple Populations in NGC 1851: Abundance Variations and UV
Photometric Synthesis in the Washington and HST/WFC3 Systems: The analysis of multiple populations (MPs) in globular clusters, both
spectroscopically and photometrically, is key in understanding their formation
and evolution. The relatively narrow Johnson U, F336W, and Stromgren and Sloan
u filters have been crucial in exhibiting these MPs photometrically, but in
Paper I we showed that the broader Washington C filter can more efficiently
detect MPs in the test case globular cluster NGC 1851. In Paper I we also
detected a double MS that has not been detected in previous observations of NGC
1851. We now match this photometry to NGC 1851's published RGB abundances and
find the two RGB branches observed in C generally exhibit different abundance
characteristics in a variety of elements (e.g., Ba, Na, and O) and in CN band
strengths, but no single element can define the two RGB branches. However,
simultaneously considering [Ba/Fe] or CN strengths with either [Na/Fe], [O/Fe],
or CN strengths can separate the two photometric RGB branches into two distinct
abundance groups. Matches of NGC 1851's published SGB and HB abundances to the
Washington photometry shows consistent characterizations of the MPs, which can
be defined as an O-rich/N-normal population and an O-poor/N-rich population.
Photometric synthesis for both the Washington C filter and the F336W filter
finds that these abundance characteristics, with appropriate variations in He,
can reproduce for both filters the photometric observations in both the RGB and
the MS. This photometric synthesis also confirms the throughput advantages that
the C filter has in detecting MPs. | astro-ph |
TOROS Optical follow-up of the Advanced LIGO-VIRGO O2 second
observational campaign: We present the results of the optical follow-up, conducted by the TOROS
collaboration, of gravitational wave events detected during the Advanced
LIGO-Virgo second observing run (Nov 2016 -- Aug 2017). Given the limited field
of view ($\sim100\arcmin$) of our observational instrumentation we targeted
galaxies within the area of high localization probability that were observable
from our sites. We analyzed the observations using difference imaging, followed
by a Random Forest algorithm to discriminate between real and bogus transients.
For all three events that we respond to, except GW170817, we did not find any
bona fide optical transient that was plausibly linked with the observed
gravitational wave event. Our observations were conducted using telescopes at
Estaci\'{o}n Astrof\'{\i}sica de Bosque Alegre, Cerro Tololo Inter-American
Observatory, and the Dr. Cristina V. Torres Memorial Astronomical Observatory.
Our results are consistent with the LIGO-Virgo detections of a binary black
hole merger (GW170104) for which no electromagnetic counterparts were expected,
as well as a binary neutron star merger (GW170817) for which an optical
transient was found as expected. | astro-ph |
Short-lived Radio Bursts from the Crab Pulsar: Our high-time-resolution observations reveal that individual main pulses from
the Crab pulsar contain one or more short-lived microbursts. Both the energy
and duration of bursts measured above 1 GHz can vary dramatically in less than
a millisecond. These fluctuations are too rapid to be caused by propagation
through turbulence in the Crab Nebula or the interstellar medium; they must be
intrinsic to the radio emission process in the pulsar. The mean duration of a
burst varies with frequency as $\nu^{-2}$, significantly different from the
broadening caused by interstellar scattering. We compare the properties of the
bursts to some simple models of microstructure in the radio emission region. | astro-ph |
The Millennium Galaxy Catalogue: The luminosity functions of bulges and
discs and their implied stellar mass densities: We derive the luminosity functions of elliptical galaxies, galaxy bulges,
galaxy pseudo-bulges and galaxy discs from our structural catalogue of 10,095
galaxies. In addition we compute their associated luminosity and stellar mass
densities. We show that spheroidal systems (elliptical galaxies and the bulges
of disc galaxies) exhibit a strong color bimodality indicating two distinct
types of spheroid which are separated by a core color of (u-r) ~ 2 mag. We
argue that the similarity of the red elliptical and the red bulge luminosity
functions supports our previous arguments that they share a common origin and
surprisingly find that the same follows for the blue ellipticals and blue
bulges, the latter of which we refer to as pseudo-bulges. In terms of the
stellar mass budget we find that $58\pm6$ per cent is currently in the form of
discs, 39+/-6 per cent in the form of red spheroids (13+/-4 per cent
ellipticals, 26+/-4 per cent bulges) and the remainder is in the form of blue
spheroidal systems (~1.5 per cent blue ellipticals and ~1.5 per cent
pseudo-bulges). In terms of galaxy formation we argue that our data on galaxy
components strongly supports the notion of a two-stage formation process
(spheroid first, disc later) but with the additional complexity of secular
evolution occurring in quiescent discs giving rise to two distinct bulge types:
genuine 'classical' bulges and pseudo-bulges. We therefore advocate that there
are three significant structures underpinning galaxy evolution: classical
spheroids (old); pseudo-bulges (young) and discs (intermediate). The luminous
nearby galaxy population is a mixture of these three structural types.
[abridged]. | astro-ph |
The effects of drift and winds on the propagation of Galactic cosmic
rays: We study the effects of drift motions and the advection by a Galactic wind on
the propagation of cosmic rays in the Galaxy. We employ a simplified magnetic
field model, based on (and similar to) the Jansson-Farrar model for the
Galactic magnetic field. Diffusion is allowed to be anisotropic. The relevant
equations are solved numerically, using a set of stochastic differential
equations. Inclusion of drift and a Galactic wind significantly shortens the
residence time of cosmic rays, even for moderate wind speeds | astro-ph |
A vestige low metallicity gas shell surrounding the radio galaxy
0943-242 at z=2.92: Observations are presented showing the doublet CIV 1550 absorption lines
superimposed on the CIV emission in the radio galaxy 0943-242. Within the
errors, the redshift of the absorption system that has a column density of
N_CIV = 10^{14.5 +- 0.1} cm-2 coincides with that of the deep Ly-alpha
absorption trough observed by Rottgering et al. (1995). The gas seen in
absorption has a resolved spatial extent of at least 13 kpc (the size of the
extended emission line region). We first model the absorption and emission gas
as co-spatial components with the same metallicity and degree of excitation.
Using the information provided by the emission and absorption line ratios of
CIV and Ly-alpha, we find that the observed quantities are incompatible with
photoionization or collisional ionization of cloudlets with uniform properties.
We therefore reject the possibility that the absorption and emission phases are
co-spatial and favour the explanation that the absorption gas has low
metallicity and is located further away from the host galaxy (than the emission
line gas). The estimated low metallicity for the absorption gas in 0943-242 (Z
\~ 1% solar) and its proposed location -outer halo outside the radio cocoon-
suggest that its existence preceeds the observed AGN phase and is a vestige of
the initial starburst at the onset of formation of the parent galaxy. | astro-ph |
Isodensity Statistics on Clustering of High-z Objects in Cosmological
Redshift-spaces: We discuss the systematic effects arising from the cosmological
redshift-space (geometric) distortion on the statistical analysis of isodensity
contour using high-redshift catalogs. Especially, we present a simple
theoretical model for isodensity statistics in cosmological redshift-space, as
a generalization of the work by Matsubara (1996). The statistical quantities
considered here are the two- and three-dimensional genus of isodensity contour,
the area of surface, the length of contour intersecting with a plane and the
number of the crossing points of isodensity contour on a line. We give useful
analytic formulae for the isodensity statistics, which take into account the
corrections from the geometric distortion, the nonlinear clustering and the
nonlinear velocity distortion phenomenologically. We then demonstrate how the
geometric distortion and the nonlinear corrections alter shapes of the
statistical quantities on the basis of plausible cosmological models. Our
results show that the nonlinear correction can be sensitive to a choice of the
redshift-space coordinate as increasing the redshift. The low-dimensional
quantities such as two-dimensional genus systematically yield anisotropy due to
the geometric and velocity distortions and their angle-dependence shows the
$10\sim20%$ difference of amplitude. Sensitivity for typical high-redshift
samples are estimated in an analytic manner, and the influence of the
light-cone effect for the isodensity statistics is also discussed. | astro-ph |
Evidence for Core Collapse in the Type Ib/c SN 1999ex: We present optical and infrared spectra of SN 1999ex that reveal a clear
example of an intermediate Type Ib/c case. This suggests a continuous
spectroscopic sequence between Type Ib and Type Ic supernovae. We report UBVRIz
photometric observations of SN 1999ex that started only one day after
explosion, which permitted us to witness an elusive transient cooling phase
that lasted 4 days. The initial cooling and subsequent radioactive heating
produced a dip in the lightcurve which is consistent with explosion models
involving core collapse of evolved massive helium stars, and inconsistent with
lightcurves resulting from the thermonuclear runaway of compact white dwarfs. | astro-ph |
Abundances of lithium, oxygen, and sodium in the turn-off stars of
Galactic globular cluster 47 Tuc: We aim to determine abundances of Li, O and Na in a sample of of 110 turn-off
(TO) stars, in order to study the evolution of light elements in this cluster
and to put our results in perspective with observations of other globular and
open clusters, as well as with field stars. We use medium resolution spectra
obtained with the GIRAFFE spectrograph at the ESO 8.2m Kueyen VLT telescope and
use state of the art 1D model atmospheres and NLTE line transfer to determine
the abundances. We also employ CO5BOLD hydrodynamical simulations to assess the
impact of stellar granulation on the line formation and inferred abundances.
Our results confirm the existence of Na-O abundance anti-correlation and hint
towards a possible Li-O anti-correlation in the TO stars of 47 Tuc. We find no
convincing evidence supporting the existence of Li-Na correlation. The obtained
3D NLTE mean lithium abundance in a sample of 94 TO stars where Li lines were
detected reliably, $\langle A({\rm Li})_{\rm 3D~NLTE}\rangle = 1.78 \pm 0.18$
dex, appears to be significantly lower than what is observed in other globular
clusters. At the same time, star-to-star spread in Li abundance is also larger
than seen in other clusters. The highest Li abundance observed in 47 Tuc is
about 0.1 dex lower than the lowest Li abundance observed among the un-depleted
stars of the metal-poor open cluster NGC 2243. The lithium abundances in 47
Tuc, when put into context with observations in other clusters and field stars,
suggest that stars that are more metal-rich than [FeH] \sim -1.0 experience
significant lithium depletion during their lifetime on the main sequence, while
the more metal-poor stars do not. Rather strikingly, our results suggest that
initial lithium abundance with which the star was created may only depend on
its age (the younger the star, the higher its Li content) and not on its
metallicity. | astro-ph |
Missing Link Found? --- The ``runaway'' path to supermassive black holes: Observations of stellar kinematics, gas dynamics and masers around galactic
nuclei have now firmly established that many galaxies host central supermassive
black holes (SMBHs) with masses in the range $10^6 \sim 10^9$M$_{\odot}$.
However, how these SMBHs formed is not well understood. One reason for this
situation is the lack of observations of intermediate-mass BHs (IMBHs), which
could bridge the gap between stellar-mass BHs and SMBHs. Recently, this missing
link (i.e., an IMBH) has been found in observations made by the ASCA and the
Chandra of the central region of the starburst galaxy M82 \citep{MT99, PG99,
MT01, Ka01}. Subsequent observations by SUBARU have revealed that this IMBH
apparently coincides with a young compact star cluster. Based on these
findings, we suggest a new formation scenario for SMBHs. In this scenario,
IMBHs first form in young compact star clusters through runaway merging of
massive stars. While these IMBHs are forming, the host star clusters sink
toward the galactic nucleus through dynamical friction, and upon evaporation
deposit their IMBHs near the galactic center. The IMBHs then form binaries and
eventually merge via gravitational radiation, forming an SMBH. | astro-ph |
The search for galactic dark matter clump candidates with Fermi and
MAGIC: We present a systematic search for potential dark matter clumps in our Galaxy
among the 630 unassociated sources included in the LAT 1-year Point Source
Catalog. Assuming a dark matter particle that generates observable gamma-ray
photons beyond the Fermi energy range through self-annihilation, we compile a
list of reasonable targets for the MAGIC Imaging Atmospheric Cherenkov
Telescopes. In order to narrow down the origin of these enigmatic sources, we
summarize ongoing multiwavelength studies including X-ray, radio, and optical
spectroscopy. We report on observations of two of these candidates using the
MAGIC Telescopes. We find that the synergy between Fermi and Cherenkov
telescopes, along with multiwavelength observations, could play a key role in
indirect searches for dark matter. | astro-ph |
Early Solar System $r$-process Abundances Limit Collapsar Origin: Heavy elements produced exclusively through rapid neutron capture (the
'$r$-process') originate from violent cosmic explosions. While neutron star
mergers are the primary candidates, another plausible production site are
'collapsars'---collapsing massive stars that form a black hole with an
accretion disk. Here we show that collapsars are too rare to be the prime
origin of $r$-process elements in the Solar System. By comparing numerical
simulations with the early Solar System abundances of actinides produced
exclusively through the $r$-process, we exclude higher than 20% contribution
from collapsars with 90% confidence. We additionally limit $r$-process ejecta
masses from collapsars to less than 10% of the ejecta mass from neutron star
mergers, about $10^{-2}$M$_\odot$. | astro-ph |
Opening the 21cm EoR Window: Measurements of Foreground Isolation with
PAPER: We present new observations with the Precision Array for Probing the Epoch of
Reionization (PAPER) with the aim of measuring the properties of foreground
emission for 21cm Epoch of Reionization experiments at 150 MHz. We focus on the
footprint of the foregrounds in cosmological Fourier space to understand which
modes of the 21cm power spectrum will most likely be compromised by foreground
emission. These observations confirm predictions that foregrounds can be
isolated to a "wedge"-like region of 2D (k-perpendicular, k-parallel)-space,
creating a window for cosmological studies at higher k-parallel values. We also
find that the emission extends past the nominal edge of this wedge due to
spectral structure in the foregrounds, with this feature most prominent on the
shortest baselines. Finally, we filter the data to retain only this "unsmooth"
emission and image specific k-parallel modes of it. The resultant images show
an excess of power at the lowest modes, but no emission can be clearly
localized to any one region of the sky. This image is highly suggestive that
the most problematic foregrounds for 21cm EoR studies will not be easily
identifiable bright sources, but rather an aggregate of fainter emission. | astro-ph |
Calibration of photometry from the Gemini Multi-Object Spectrograph on
Gemini North: All available observations of photometric standard stars obtained with the
Gemini Multi-Object Spectrograph at Gemini North in the period from August 2001
to December 2003 have been used to establish the calibrations for photometry
obtained with the instrument. The calibrations presented in this paper are
based on significantly more photometric standard star observations than usually
used by the individual users. Nightly photometric zero points as well as color
terms are determined. The color terms are expected to be valid for all
observations taken prior to UT 2004 November 21 at which time the Gemini North
primary mirror was coated with silver instead of aluminum. While the nightly
zero points are accurate to 0.02 mag or better (random errors), the accuracy of
the calibrations is limited by systematic errors from so-called "sky
concentration", an effect seen in all focal reducer instruments. We conclude
that an accuracy of 0.035 to 0.05 mag can be achieved by using calibrations
derived in this paper. The color terms are strongest for very red objects, e.g.
for objects with (r'-z')=3.0 the resulting z' magnitudes will be ~0.35 mag too
bright if the color term is ignored. The calibrations are of importance to the
large Gemini user community with data obtained prior to UT 2004 November 21, as
well as future users of achive data from this period in time. | astro-ph |
Mid-infrared observations of the nucleus of comet P/2016 BA14
(PANSTARRS): We present mid-infrared observations of comet P/2016 BA14 (PANSTARRS), which
were obtained on UT 2016 March 21.3 at heliocentric and geocentric distances of
1.012 au and 0.026 au, respectively, approximately 30 hours before its closest
approach to Earth (0.024 au) on UT 2016 March 22.6. Low-resolution
($\lambda$/$\Delta \lambda$~250) spectroscopic observations in the N-band and
imaging observations with four narrow-band filters (centered at 8.8, 12.4, 17.7
and 18.8 $\mu$m) in the N- and Q-bands were obtained using the Cooled
Mid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru
telescope atop Maunakea, Hawaii. The observed spatial profiles of P/2016 BA14
at different wavelengths are consistent with a point-spread function. Owing to
the close approach of the comet to the Earth, the observed thermal emission
from the comet is dominated by the thermal emission from its nucleus rather
than its dust coma. The observed spectral energy distribution of the nucleus at
mid-infrared wavelengths is consistent with a Planck function at temperature
T~350 K, with the effective diameter of P/2016 BA14 estimated as ~0.8 km (by
assuming an emissivity of 0.97). The normalized emissivity spectrum of the
comet exhibits absorption-like features that are not reproduced by the
anhydrous minerals typically found in cometary dust coma, such as olivine and
pyroxene. Instead, the spectral features suggest the presence of large grains
of phyllosilicate minerals and organic materials. Thus, our observations
indicate that an inactive small body covered with these processed materials is
a possible end state of comets. | astro-ph |
On the cosmological mass function theory: This paper provides, from one side, a review of the theory of the
cosmological mass function from a theoretical point of view, starting from the
seminal paper of Press & Shechter (1974) to the last developments (Del Popolo &
Gambera (1998, 1999), Sheth & Tormen 1999 (ST), Sheth, Mo & Tormen 2001 (ST1),
Jenkins et al. 2001 (J01), Shet & Tormen 2002 (ST2), Del Popolo 2002a, Yagi et
al. 2004 (YNY)), and from another side some improvements on the multiplicity
function models in literature. ... | astro-ph |
Perturbations in Tachyon Dark Energy and their Effect on Matter
Clustering: A non-canonical scalar tachyon field is a viable candidate for dark energy
and has been found to be in good agreement with observational data. Background
data alone cannot completely rule out degeneracy between this model and others.
To further constrain the parameters, apart from the distance measurements, we
study perturbations in the tachyon scalar field and how they affect matter
clustering. We consider two tachyon potentials for this study, an inverse
square potential and an exponential potential. We study the evolution of the
gravitational potential, matter density contrast, and dark energy density
contrast, and compare them with the evolution in the $\Lambda CDM $ model.
Although perturbations in dark energy at sub-Hubble scales are negligible in
comparison with matter perturbations, they cannot be ignored at Hubble and
super-Hubble scales ($\lambda_p > 1000$ Mpc). We also study the evolution of
growth function and growth rate of matter, and find that the growth rate is
significantly suppressed in dark energy dominated era with respect to the
growth rate for $\Lambda CDM$ model. A comparison of these models with Redshift
Space Distortion growth rate data is presented by way of calculating
$f\sigma_8(z)$. There is a tension of $2.9\sigma$ ($2.26\sigma$ ) between
growth rate data and Planck-2015 (Planck-2018) Cosmic Microwave Background
Radiation data for $\Lambda CDM$ model. We present constraints on free
parameters of these models and show that perturbations in the tachyon scalar
field reduce this tension between different data sets. | astro-ph |
Determination of the Sun's Offset from the Galactic Plane Using Pulsars: We derive the Sun's offset from the local mean Galactic plane($z_\odot$)
using the observed $z$ distribution of young pulsars. Pulsar distances are
obtained from measurements of annual parallax, HI absorption spectra or
associations where available and otherwise from the observed pulsar dispersion
and a model for the distribution of free electrons in the Galaxy. We fit the
cumulative distribution function for a ${\rm sech}^2(z)$ distribution function,
representing an isothermal self-gravitating disk, with uncertainties being
estimated using the bootstrap method. We take pulsars having characteristic age
$\tau_c<10^{6.5}$~yr and located within 4.5~kpc of the Sun, omitting those
within the local spiral arm and those significantly affected by the Galactic
warp, and solve for $z_\odot$ and the scale height, $H$, for different cutoffs
in $\tau_c$. We compute these quantities using just the independently
determined distances, and these together with DM-based distances separately
using the YMW16 and NE2001 Galactic electron density models. We find that an
age cutoff at $10^{5.75}$~yr with YMW16 DM-distances gives the best results
with a minimum uncertainty in $z_\odot$ and an asymptotically stable value for
$H$ showing that, at this age and below, the observed pulsar $z$-distribution
is dominated by the dispersion in their birth locations. From this sample of
115 pulsars, we obtain $z_\odot=13.4\pm$4.4~pc and $H=56.9\pm$6.5~pc, similar
to estimated scale heights for OB stars and open clusters. Consistent results
are obtained using the independent-only distances and using the NE2001 model
for the DM-based distances. | astro-ph |
Extra galactic sources of high energy neutrinos: The main goal of the construction of large volume, high energy neutrino
telescopes is the detection of extra-Galactic neutrino sources. The existence
of such sources is implied by observations of ultra-high energy, >10^{19} eV,
cosmic-rays (UHECRs), the origin of which is a mystery. The observed UHECR flux
sets an upper bound to the extra-Galactic high energy neutrino intensity, which
implies that the detector size required to detect the signal in the energy
range of 1 TeV to 1 PeV is >=1 giga-ton, and much larger at higher energy.
Optical Cerenkov neutrino detectors, currently being constructed under ice and
water, are expected to achieve 1 giga-ton effective volume for 1 TeV to 1 PeV
neutrinos. Coherent radio Cerenkov detectors (and possibly large air-shower
detectors) will provide the >> 1 giga-ton effective volume required for
detection at ~10^{19} eV. Detection of high energy neutrinos associated with
electromagnetically identified sources will allow to identify the sources of
UHECRs, will provide a unique probe of the sources, which may allow to resolve
open questions related to the underlying physics of models describing these
powerful accelerators, and will provide information on fundamental neutrino
properties. | astro-ph |
Testing a Galactic Lensing Hypothesis with the Prompt Emission of GRB
221009A: Even at modest amplification, the optical depth to gravitational lensing
through the Galaxy is $<10^{-5}$. However, the large apparent
isotropic-equivalent energy of GRB 221009A coupled with a path through low
Galactic latitude suggests that the conditional probability that this
particular GRB was lensed is greater than the very low a priori expectation.
With the extreme brightness of the prompt emission, this Galactic lensing
hypothesis can be constrained by autocorrelation analysis of Fermi photons on
0.1-1000 ms timescales. In relating lensing mass, magnification, and
autocorrelation timescale, I show that a lensed-induced autocorrelation
signature by stellar lenses falls below the minimal variability timescale (MVT)
expected from a black hole central engine. However, lensing by Galactic dark
matter MACHOs ($M_l > 10-1000\,M_\odot$) could be confirmed with this approach.
Regardless, at a peak $\gamma$-ray photon rate of $>30$ ms$^{-1}$, GRB 221009A
represents a prime opportunity to measure the smallest MVTs of GRBs. | astro-ph |
Potential of radio telescopes as high-frequency gravitational wave
detectors: In the presence of magnetic fields, gravitational waves are converted into
photons and vice versa. We demonstrate that this conversion leads to a
distortion of the cosmic microwave background (CMB), which can serve as a
detector for MHz to GHz gravitational wave sources active before reionization.
The measurements of the radio telescope EDGES can be cast as a bound on the
gravitational wave amplitude, $h_c < 10^{-21} (10^{-12})$ at 78 MHz, for the
strongest (weakest) cosmic magnetic fields allowed by current astrophysical and
cosmological constraints. Similarly, the results of ARCADE 2 imply $h_c <
10^{-24} (10^{-14})$ at $3 - 30$ GHz. For the strongest magnetic fields, these
constraints exceed current laboratory constraints by about seven orders of
magnitude. Future advances in 21cm astronomy may conceivably push these bounds
below the sensitivity of cosmological constraints on the total energy density
of gravitational waves. | astro-ph |
The Evolution of [OII] Emission from Cluster Galaxies: We investigate the evolution of the star formation rate in cluster galaxies.
We complement data from the CNOC1 cluster survey (0.15<z<0.6) with measurements
from galaxy clusters in the 2dF galaxy redshift survey (0.05<z<0.1) and
measurements from recently published work on higher redshift clusters, up to
almost z=1. We focus our attention on galaxies in the cluster core, ie.
galaxies with r<0.7h^{-1}_{70}Mpc. Averaging over clusters in redshift bins, we
find that the fraction of galaxies with strong [OII] emission is < 20% in
cluster cores, and the fraction evolves little with redshift. In contrast,
field galaxies from the survey show a very strong increase over the same
redshift range. It thus appears that the environment in the cores of rich
clusters is hostile to star formation at all the redshifts studied. We compare
this result with the evolution of the colours of galaxies in cluster cores,
first reported by Butcher & Oemler (1984). Using the same galaxies for our
analysis of the [OII] emission, we confirm that the fraction of blue galaxies,
which are defined as galaxies 0.2 mag bluer in the rest frame B-V than the red
sequence of each cluster, increases strongly with redshift. Since the colours
of galaxies retain a memory of their recent star formation history, while
emission from the [OII] line does not, we suggest that these two results can
best be reconciled if the rate at which the clusters are being assembled is
higher in the past, and the galaxies from which it is being assembled are
typically bluer. | astro-ph |
A search for rapid optical variability in radio-quiet quasars: The detection of rapid variability on a time-scale of hours in radio-quiet
quasars (RQQSOs) could be a powerful discriminator between starburst, accretion
disc and relativistic jet models of these sources. This paper contains an
account of a dedicated search for rapid optical variability in RQQSOs. The
technique used differential photometry between the RQQSO and stars in the same
field of view of the CCD. The 23 RQQSOs that were observed all have high
luminosities (-27 < Mv <- 30), and 22 of these sources are at redshifts z > 1.
The total amount of observation time was about 60 hours and these observations
are part of an ongoing programme, started in September 1990, to search for
rapid variability in RQQSOs. No evidence for short-term variability greater
than about 0.1 magnitudes was detected in any of the 23 sources, however
long-term variability was recorded for the radio-quiet quasar PG 2112+059. The
finding charts are included here because they identify the RQQSO and the
reference stars used in the photometry, and hence are available for use by
other observers. | astro-ph |
H.E.S.S. observations of the supernova remnant RX J0852.0-4622:
shell-type morphology and spectrum of a widely extended VHE gamma-ray source: The shell-type supernova remnant RX J0852.0-4622 was observed with the High
Energy Stereoscopic System (H.E.S.S.) of Atmospheric Cherenkov Telescopes
between December 2004 and May 2005 for a total observation time of 33 hours,
above an average gamma-ray energy threshold of 250 GeV. The angular resolution
of ~0.06 degree (for events triggering 3 or 4 telescopes) and the large field
of view of H.E.S.S. ($5^{\circ}$ diameter) are well adapted to studying the
morphology of the object in very high energy gamma-rays, which exhibits a
remarkably thin shell very similar to the features observed in the radio range
and in X-rays. The spectral analysis of the source from 300 GeV to 20 TeV is
also presented. Finally, the possible origins of the very high energy gamma-ray
emission (Inverse Compton scattering by electrons or the decay of neutral pions
produced by proton interactions) are discussed, on the basis of morphological
and spectral features obtained at different wavelengths. | astro-ph |
Dwarf Galaxies of Tidal Origin -- Relevant for Cosmology ?: Evolutionary synthesis models for Tidal Dwarf Galaxies (TDGs) are presented
that allow to have varying proportions of young stars formed in the
merger-induced starburst and of stars from the merging spirals' disks. The
specific metallicities as well as the gaseous emission of actively star forming
TDGs are consistently accounted for. Comparison of models with observational
data (e.g. Duc, this volume) gives information on the present evolutionary
state and possible future luminosity evolution of TDGs. The redshift evolution
of merger rates and of the gas content and metallicities of spiral galaxies are
used to estimate the number of TDGs at various redshifts and to investigate
their contribution to magnitude limited surveys. | astro-ph |
Mass Assembly of Stellar Systems and their Evolution with the SMA
(MASSES) -- Full Data Release: We present and release the full dataset for the Mass Assembly of Stellar
Systems and their Evolution with the SMA (MASSES) survey. This survey used the
Submillimeter Array (SMA) to image the 74 known protostars within the Perseus
molecular cloud. The SMA was used in two array configurations to capture
outflows for scales $>$30$^{\prime\prime}$ ($>$9000 au) and to probe scales
down to $\sim$1$^{\prime\prime}$ ($\sim$300 au). The protostars were observed
with the 1.3 mm and 850 $\mu$m receivers simultaneously to detect continuum at
both wavelengths and molecular line emission from CO(2-1), $^{13}$CO(2-1),
C$^{18}$O(2-1), N$_2$D$^+$(3-2), CO(3-2), HCO$^+$(4-3), and
H$^{13}$CO$^+$(4-3). Some of the observations also used the SMA's recently
upgraded correlator, SWARM, whose broader bandwidth allowed for several more
spectral lines to be observed (e.g., SO, H$_2$CO, DCO$^+$, DCN, CS, CN). Of the
main continuum and spectral tracers observed, 84% of the images and cubes had
emission detected. The median C$^{18}$O(2-1) linewidth is $\sim$1.0 km
s$^{-1}$, which is slightly higher than those measured with single-dish
telescopes at scales of 3000-20000 au. Of the 74 targets, six are suggested to
be first hydrostatic core candidates, and we suggest that L1451-mm is the best
candidate. We question a previous continuum detection toward L1448 IRS2E. In
the SVS13 system, SVS13A certainly appears to be the most evolved source, while
SVS13C appears to be hotter and more evolved than SVS13B. The MASSES survey is
the largest publicly available interferometric continuum and spectral line
protostellar survey to date, and is largely unbiased as it only targets
protostars in Perseus. All visibility ($uv$) data and imaged data are publicly
available at https://dataverse.harvard.edu/dataverse/full_MASSES/. | astro-ph |
Galaxy And Mass Assembly (GAMA): The absence of stellar mass segregation
in galaxy groups and consistent predictions from GALFORM and EAGLE
simulations: We investigate the contentious issue of the presence, or lack thereof, of
satellites mass segregation in galaxy groups using the Galaxy And Mass Assembly
(GAMA) survey, the GALFORM semi-analytic and the EAGLE cosmological
hydrodynamical simulation catalogues of galaxy groups. We select groups with
halo mass $12 \leqslant \log(M_{\text{halo}}/h^{-1}M_\odot) <14.5$ and redshift
$z \leqslant 0.32$ and probe the radial distribution of stellar mass out to
twice the group virial radius. All the samples are carefully constructed to be
complete in stellar mass at each redshift range and efforts are made to
regularise the analysis for all the data. Our study shows negligible mass
segregation in galaxy group environments with absolute gradients of
$\lesssim0.08$ dex and also shows a lack of any redshift evolution. Moreover,
we find that our results at least for the GAMA data are robust to different
halo mass and group centre estimates. Furthermore, the EAGLE data allows us to
probe much fainter luminosities ($r$-band magnitude of 22) as well as
investigate the three-dimensional spatial distribution with intrinsic halo
properties, beyond what the current observational data can offer. In both cases
we find that the fainter EAGLE data show a very mild spatial mass segregation
at $z \leqslant 0.22$, which is again not apparent at higher redshift.
Interestingly, our results are in contrast to some earlier findings using the
Sloan Digital Sky Survey. We investigate the source of the disagreement and
suggest that subtle differences between the group finding algorithms could be
the root cause. | astro-ph |
Structure and Evolution of the Envelopes of Deeply Embedded Massive
Young Stars: The physical structure of the envelopes around a sample of fourteen massive
(1000-100,000 solar L) young stars is investigated on 100- 100,000 AU scales
using maps and spectra in submillimeter continuum and lines of C17O, CS and
H2CO. The total column densities and the temperature profiles are obtained by
fitting self-consistent dust models to submillimeter photometry. Both the
molecular line and dust emission data indicate density gradients ~r^{-alpha},
with alpha=1.0-1.5, significantly flatter than the alpha=2.0 generally found
for low-mass objects. This flattening may indicate that in massive young
stellar objects, nonthermal pressure is more important for the support against
gravitational collapse, while thermal pressure dominates for low-mass sources.
We find alpha=2 for two hot core-type sources, but regard this as an upper
limit since in these objects, the CS abundance may be enhanced in the warm gas
close to the star. | astro-ph |
High-Precision Measurements of Brightness Variation of Nereid: Nereid, a satellite of Neptune, has a highly eccentric prograde orbit with a
semi-major axis larger than 200 Neptune radius and is classified as an
irregular satellite. Although the capture origin of irregular satellites has
been widely accepted, several previous studies suggest that Nereid was formed
in the circumplanetary disk of Neptune and was ejected outward to the present
location by Triton. Our time-series photometric observations confirm that the
spin is stable and non-chaotic with a period of 11.5 hr as indicated by Grav et
al. (2003). The optical colors of Nereid are indistinguishable from those of
trans-Neptunian objects and Centaurs, especially those with neutral colors. We
also find the consistency of Nereid's rotation with the size-rotation
distribution of small outer bodies. It is more likely that Nereid originates in
an immigrant body captured from a heliocentric orbit which was 4-5 AU away from
Neptune's orbit. | astro-ph |
Giant Metrewave Radio Telescope limits on cool HI in galaxy groups: We present Giant Metrewave Radio Telescope 21-cm HI observations towards a
sample of compact radio sources behind galaxy groups, to search for cool HI.
The results -- from high dynamic range spectra for 8 lines-of-sight through 7
galaxy groups -- do not show any evidence for absorption by cool HI. At a
resolution of 20 km/s, the optical depth upper limits obtained were between
0.0075 and 0.035 (3sigma); these correspond to upper limits of a few times
10**23 m**-2 for the column density of any cool HI along these lines of sight
(assuming a spin temperature of 100 K). | astro-ph |
Hα and UV luminosities and star formation rates in a large sample
of luminous compact galaxies: We present the results of a statistical study of the star formation rates
(SFR) derived from the Galaxy Evolution Explorer (GALEX) observations in the
ultraviolet continuum and in the H\alpha emission line for a sample of about
800 luminous compact galaxies (LCGs). Galaxies in this sample have a compact
structure and include one or several regions of active star formation. Global
galaxy characteristics (metallicity, luminosity, stellar mass) are intermediate
between ones of the nearby blue compact dwarf (BCD) galaxies and Lyman-break
galaxies (LBGs) at high redshifts z > 2 - 3. SFRs were corrected for
interstellar extinction which was derived from the optical Sloan Digital Sky
Survey (SDSS) spectra. We find that SFRs derived from the galaxy luminosities
in the far ultraviolet (FUV) and near ultraviolet (NUV) ranges vary in a wide
range from 0.18 M_Sun/yr to 113 M_Sun/yr with median values of 3.8 M_Sun/yr and
5.2 M_Sun/yr, respectively. Simple regression relations are found for
luminosities L(H\alpha) and L(UV) as functions of the mass of the young stellar
population, the starburst age, and the galaxy metallicity. We consider the
evolution of L(H\alpha), L(FUV) and L(NUV) with a starburst age and introduce
new characteristics of star formation, namely the initial H\alpha, FUV and NUV
luminosities at zero starburst age. | astro-ph |
Recent Developments in Weak Lensing: Measurement of the gravitational distortion of images of distant galaxies is
rapidly becoming established as a powerful probe of the dark mass distribution
in clusters of galaxies. With the advent of large mosaics of CCD's these
methods should provide a composite total mass profile for galaxy haloes and
also measure the power spectrum of mass fluctuations on supercluster scales. We
describe how HST observations have been used to place the observational
measurement of the shear on a quantitative footing. By artifically stretching
and then degrading WFPC2 images to simulate ground based observing it is now
possible to directly calibrate the effect of atmospheric seeing. Similar
experiments show that one can remove the effect of artificial image anisotropy
arising in the atmosphere or telescope. There have also been important advances
in the interpretation of the shear: reconstruction techniques have been
extended to encompass the strong distortion regime of giant arcs etc., progress
has been made in removing a bias present in earlier reconstruction techniques,
and we describe new techniques for `aperture densitometry'. We present some new
results on clusters of galaxies, and discuss the intimate connections between
weak lensing and deep spectroscopy. | astro-ph |
Dust Reddened Quasars in FIRST and UKIDSS: Beyond the Tip of the Iceberg: We present the results of a pilot survey to find dust-reddened quasars by
matching the FIRST radio catalog to the UKIDSS near-infrared survey, and using
optical data from SDSS to select objects with very red colors. The deep K-band
limit provided by UKIDSS allows for finding more heavily-reddened quasars at
higher redshifts as compared with previous work using FIRST and 2MASS. We
selected 87 candidates with K<=17.0 from the UKIDSS Large Area Survey (LAS)
First Data Release (DR1) which covers 190 deg2. These candidates reach up to
~1.5 magnitudes below the 2MASS limit and obey the color criteria developed to
identify dust-reddened quasars. We have obtained 61 spectroscopic observations
in the optical and/or near-infrared as well as classifications in the
literature and have identified 14 reddened quasars with E(B-V)>0.1, including
three at z>2. We study the infrared properties of the sample using photometry
from the WISE Observatory and find that infrared colors improve the efficiency
of red quasar selection, removing many contaminants in an infrared-to-optical
color-selected sample alone. The highest-redshift quasars (z > 2) are only
moderately reddened, with E(B-V) ~ 0.2-0.3. We find that the surface density of
red quasars rises sharply with faintness, comprising up to 17% of blue quasars
at the same apparent K-band flux limit. We estimate that to reach more heavily
reddened quasars (i.e., E(B-V) > 0.5) at z>2 and a depth of K=17 we would need
to survey at least ~2.5 times more area. | astro-ph |
Are fulleranes responsible for the 21 micron feature?: Recent detections of C$_{60}$, C$_{70}$, and C$_{60}^+$ in space induced
extensive studies of fullerene derivatives in circumstellar environments. As
the promising fullerene sources, protoplanetary nebulae (PPNe) show a number of
unidentified bands in their infrared spectra, among which a small sample
exhibits an enigmatic feature at $\sim21$\,$\mu$m. Hydrogenation of fullerenes
can produce fulleranes emitting new infrared bands. In this paper, we
investigate the possibility of fulleranes (C$_{60}$H$_m$) as the carrier of the
21\,$\mu$m feature in terms of theoretical vibrational spectra of fulleranes.
The evidences favoring and disfavoring the fullerane hypothesis are presented.
We made an initial guess for the hydrogen coverage of C$_{60}$H$_m$ that may
contribute to the 21\,$\mu$m feature. | astro-ph |
Impact of SZ cluster residuals in CMB maps and CMB-LSS
cross-correlations: Residual foreground contamination in cosmic microwave background (CMB) maps,
such as the residual contamination from thermal Sunyaev-Zeldovich (SZ) effect
in the direction of galaxy clusters, can bias the cross-correlation
measurements between CMB and large-scale structure optical surveys. It is thus
essential to quantify those residuals and, if possible, to null out SZ cluster
residuals in CMB maps. We quantify for the first time the amount of SZ cluster
contamination in the released Planck 2015 CMB maps through (i) the stacking of
CMB maps in the direction of the clusters, and (ii) the computation of
cross-correlation power spectra between CMB maps and the SDSS-IV large-scale
structure data. Our cross-power spectrum analysis yields a $30\sigma$ detection
at the cluster scale ($\ell=1500-2500$) and a $39\sigma$ detection on larger
scales ($\ell=500-1500$) due to clustering of SZ clusters, giving an overall
$54\sigma$ detection of SZ cluster residuals in the Planck CMB maps. The Planck
2015 NILC CMB map is shown to have $44\pm4\%$ of thermal SZ foreground emission
left in it. Using the 'Constrained ILC' component separation technique, we
construct an alternative Planck CMB map, the 2D-ILC map, which is shown to have
negligible SZ contamination, at the cost of being slightly more contaminated by
Galactic foregrounds and noise. We also discuss the impact of the SZ residuals
in CMB maps on the measurement of the ISW effect, which is shown to be
negligible based on our analysis. | astro-ph |
Optical Gravitational Lensing Experiment. Distance to the Magellanic
Clouds with the Red Clump Stars: Are the Magellanic Clouds 15% Closer than
Generally Accepted?: We present a new distance determination to the Large and Small Magellanic
Clouds using the newly developed red clump stars method (Paczynski and Stanek
1998). This new, single-step, Hipparcos calibrated method seems to be one of
the most precise techniques of distance determination with very small
statistical error due to large number of red clump stars usually available. The
distances were determined independently along four lines-of-sight located at
opposite sides of each Magellanic Cloud. The results for each line-of-sight are
very consistent. For the SMC we obtain the distance modulus:
m-M=18.56+/-0.03+/-0.06 mag (statistical and systematic errors, respectively)
and for the LMC: m-M=18.08+/-0.03+/-0.12} mag where systematic errors are
mostly due to uncertainty in reddening estimates. Both distances will be
refined and systematic errors reduced when accurate reddening maps for our
fields are available. Distance moduli to both Magellanic Clouds are ~0.4 mag
smaller than generally accepted values. The modulus to the LMC is in good
agreement with the recent determinations from RR Lyrae type stars and upper
limit resulting from the SN1987A echo. We suspect that the distance to the LMC
and SMC is shorter by about 15% than previously assumed: 42 kpc and 52 kpc,
respectively.
We also present our color-magnitude diagrams around the red clump for the LMC
and SMC. We identify vertical red clump, first noted by Zaritsky and Lin
(1997), in the color-magnitude diagram of both Magellanic Clouds and we
interpret it as an evolutionary feature rather than unknown stellar population
between the LMC and our Galaxy. | astro-ph |
Newly Identified Star Clusters in M33. I. Integrated Photometry and
Color-Magnitude Diagrams: We present integrated photometry and color-magnitude diagrams (CMDs) for 24
star clusters in M33, of which 12 were previously uncataloged. These results
are based on Advanced Camera for Surveys observations from the Hubble Space
Telescope of two fields in M33. Our integrated V magnitudes and V-I colors for
the previously identified objects are in good agreement with published
photometry. We are able to estimate ages for 21 of these clusters using
features in the CMDs, including isochrone fitting to the main sequence turnoffs
for 17 of the clusters. Comparisons of these ages with the clusters' integrated
colors and magnitudes suggest that simple stellar population models perform
reasonably well in predicting these properties. | astro-ph |
SuperAGILE: the hard X-ray Imager for the AGILE space mission: SuperAGILE is a coded mask experiment based on silicon microstrip detectors.
It operates in the 15-45 keV nominal energy range, providing crossed
one-dimensional images of the X-ray sky with an on-axis angular resolution of 6
arcmin, over a field of view in excess of 1 steradian. It was designed as the
hard X-ray monitor of the AGILE space mission, a small satellite of the Italian
Space Agency devoted to image the gamma-ray sky in the 30 MeV - 50 GeV energy
band. The AGILE mission was launched in a low-earth orbit on 23^{rd} April
2007. In this paper we describe the SuperAGILE experiment, its construction and
test processes, and its performance before flight, based on the on-ground test
and calibrations. | astro-ph |