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Architectures of Planetary Systems and Implications for their Formation: Doppler planet searches revealed that many giant planets orbit close to their
host star or in highly eccentric orbits. These and subsequent observations
inspired new theories of planet formation that invoke gravitation interactions
in multiple planet systems to explain the excitation of orbital eccentricities
and even short-period giant planets. Recently, NASA's Kepler mission has
identified over 300 systems with multiple transiting planet candidates,
including many potentially rocky planets. Most of these systems include
multiple planets with closely-spaced orbits and sizes between that of Earth and
Neptune. These systems represent yet another new and unexpected class of
planetary systems and provide an opportunity to test the theories developed to
explain the properties of giant exoplanets. Presently, we have limited
knowledge about such planetary systems, mostly about their sizes and orbital
periods. With the advent of long-term, nearly continuous monitoring by Kepler,
the method of transit timing variations (TTVs) has blossomed as a new technique
for characterizing the gravitational effects of mutual planetary perturbations
for hundreds of planets. TTVs can provide precise (but complex) constraints on
planetary masses, densities and orbits, even for planetary systems with faint
host stars. In the coming years, astronomers will translate TTV observations
into increasingly powerful constraints on the formation and orbital evolution
of planetary systems with low-mass planets. Between TTVs, improved Doppler
surveys, high-contrast imaging campaigns and microlensing surveys, astronomers
can look forward to a much better understanding of planet formation in the
coming decade. | astro-ph |
HR 62: A New Evolved Chemically Peculiar Late-B Star?: The spectrum of the evolved B8 III giant HR 62 exhibits weak He-lines and
strong Mn and P lines. HR 62 therefore resembles both a HgMn star (CP3) and a
He-weak PGa star (CP4).
This study is a companion project to a high resolution survey of slowly
rotationg late-B type stars aiming at finding new chemically peculiar stars. We
have analysed the spectra of HR 62 (B8 III) and the dwarf comparison star HR
677 (B8 V) to derive their chemical abundances. Both stars have similar
effective temperatures (12500 K) and projected rotational velocities ($\sim$25
km s$^{-1}$).
The medium resolution ($R$ $\sim$14000) spectra covering the wavelength range
of 4380-7350 \AA{} of HR 62 and HR 677 have been obtained with the \'{e}chelle
spectrograph attached to the 40 cm telescope in Ankara University Kreiken
Observatory (AUKR), Turkey. We have used SYNSPEC49/SYNPLOT written by I. Hubeny
and T. Lanz to compute grids of synthetic spectra and derive elemental
abundances by modeling selected unblended lines.
We find that HR 62 exhibits underabundance of Si and remarkable overabundance
of P and Mn with respect to the Sun. In contrast, HR 677 does not have
abundances departing by more than $\pm$ 0.25 dex from solar abundances. A mass
of 5.4 $M_\odot$ and an age of 90 Myr have been estimated for HR 62.
We discuss the origin of the chemical peculiarities of HR 62 and its status
as a CP star. The effective temperature of the star (12500 K) agrees well with
those of HgMn (CP3) stars. Furthermore, the main sequence end of its
evolutionary track also intersects the domain of He-weak CP4 stars. Hence these
first results suggest that HR 62 may be a transition object between the CP4 to
CP3 subgroup. However, a more detailed analysis of higher resolution spectra at
shorter wavelengths (< 4380 \AA{}) is necessary to clearly address the nature
of this interesting object. | astro-ph |
Modelling the radio to X-ray SED of galaxies: We present our model to interpret the SED of galaxies. The model for the UV
to sub-mm SED is already well established (Silva et al 1998). We remind here
its main features and show some applications. Recently we have extended the
model to the radio range (Bressan et al 2001), and we have started to include
the X-ray emission from the stellar component. | astro-ph |
Chromospheric polarimetry through multi-line observations of the 850 nm
spectral region III: Chromospheric jets driven by twisted magnetic fields: We investigate the diagnostic potential of the spectral lines at 850 nm for
understanding the magnetism of the lower atmosphere. For that purpose, we use a
newly developed 3D simulation of a chromospheric jet to check the sensitivity
of the spectral lines to this phenomenon as well as our ability to infer the
atmospheric information through spectropolarimetric inversions of noisy
synthetic data. We start comparing the benefits of inverting the entire
spectrum at 850 nm versus only the Ca II 8542 A spectral line. We found a
better match of the input atmosphere for the former case, mainly at lower
heights. However, the results at higher layers were not accurate. After several
tests, we determined that we need to weight more the chromospheric lines than
the photospheric ones in the computation of the goodness of the fit. The new
inversion configuration allows us to obtain better fits and consequently more
accurate physical parameters. Therefore, to extract the most from multi-line
inversions, a proper set of weights needs to be estimated. Besides that, we
conclude again that the lines at 850 nm, or a similar arrangement with Ca II
8542 A plus Zeeman sensitive photospheric lines, poses the best observing
configuration for examining the thermal and magnetic properties of the lower
solar atmosphere. | astro-ph |
Cosmological implications of the KATRIN experiment: The upcoming Karlsruhe Tritium Neutrino (KATRIN) experiment will put
unprecedented constraints on the absolute mass of the electron neutrino,
$\mnue$. In this paper we investigate how this information on $\mnue$ will
affect our constraints on cosmological parameters. We consider two scenarios;
one where $\mnue=0$ (i.e., no detection by KATRIN), and one where
$\mnue=0.3$eV. We find that the constraints on $\mnue$ from KATRIN will affect
estimates of some important cosmological parameters significantly. For example,
the significance of $n_s<1$ and the inferred value of $\Omega_\Lambda$ depend
on the results from the KATRIN experiment. | astro-ph |
Transiting Planets with LSST I: Potential for LSST Exoplanet Detection: The Large Synoptic Survey Telescope (LSST) has been designed in order to
satisfy several different scientific objectives that can be addressed by a
ten-year synoptic sky survey. However, LSST will also provide a large amount of
data that can then be exploited for additional science beyond its primary
goals. We demonstrate the potential of using LSST data to search for transiting
exoplanets, and in particular to find planets orbiting host stars that are
members of stellar populations that have been less thoroughly probed by current
exoplanet surveys. We find that existing algorithms can detect in simulated
LSST light curves the transits of Hot Jupiters around solar-type stars, Hot
Neptunes around K dwarfs, and planets orbiting stars in the Large Magellanic
Cloud. We also show that LSST would have the sensitivity to potentially detect
Super-Earths orbiting red dwarfs, including those in habitable zone orbits, if
they are present in some fields that LSST will observe. From these results, we
make the case that LSST has the ability to provide a valuable contribution to
exoplanet science. | astro-ph |
The High-Resolution Coronal Imager, Flight 2.1: The third flight of the High-Resolution Coronal Imager (Hi-C 2.1) occurred on
May 29, 2018, the Sounding Rocket was launched from White Sands Missile Range
in New Mexico. The instrument has been modified from its original configuration
(Hi-C 1) to observe the solar corona in a passband that peaks near 172 Angstrom
and uses a new, custom-built low-noise camera. The instrument targeted Active
Region 12712, and captured 78 images at a cadence of 4.4 sec (18:56:22 -
19:01:57 UT; 5 min and 35 sec observing time). The image spatial resolution
varies due to quasi-periodic motion blur from the rocket; sharp images contain
resolved features of at least 0.47 arcsec. There are coordinated observations
from multiple ground- and space-based telescopes providing an unprecedented
opportunity to observe the mass and energy coupling between the chromosphere
and the corona. Details of the instrument and the data set are presented in
this paper. | astro-ph |
A possible influence on standard model of quasars and active galactic
nuclei in strong magnetic field: Recent observational evidence indicates that the center of our Milky Way
harbours a super-massive object with ultra-strong radial magnetic field
(Eatough et al., 2013). Here we demonstrate that the radiations observed in the
vicinity of the Galactic Center (GC) (Falcke and Marko 2013) cannot be emitted
by the gas of the accretion disk since the accreting plasma is prevented from
approaching to the GC by the abnormally strong radial magnetic field. These
fields obstruct the infalling accretion flow from the inner region of the disk
and the central massive black hole in the standard model. It is expected that
the observed radiations near the Galactic Center cannot be generated by the
central black hole.
We also demonstrate that the observed ultra-strong radial magnetic field near
the Galactic Center ( Eatough et al., 2013) cannot be generated by the -
turbulence dynamo mechanism of Parker since preliminary qualitative estimate in
terms of this mechanism gives a magnetic field strength six orders of magnitude
smaller than the observed field strength at . However, both these difficulties
or the dilemma of the standard model can be overcome if the central black hole
in the standard model is replaced by a supper-massive stellar object containing
magnetic monopoles ( SMSOMM, Peng and Chou, 2001). The observed power peaking
of the thermal radiation is essentially the same as our theoretical prediction.
In addition, the discovery of the ultra-strong radial magnetic field near the
Galactic Center can be naturally explained and is consistent with the
prediction of our model( Peng and Chou 2001). Furthermore, the observed
ultra-strong radial magnetic field in the vicinity of the Galactic Center may
be considered as the astronomical evidence for the existence of magnetic
monopoles as predicted by the Grand Unified Theory of particle physics. | astro-ph |
Kernel Selection for Gaussian Process in Cosmology: with Approximate
Bayesian Computation Rejection and Nested Sampling: Gaussian Process (GP) has gained much attention in cosmology due to its
ability to reconstruct cosmological data in a model-independent manner. In this
study, we compare two methods for GP kernel selection: Approximate Bayesian
Computation (ABC) Rejection and nested sampling. We analyze three types of
data: cosmic Chronometer data (CC), Type Ia Supernovae (SNIa), and Gamma Ray
Burst (GRB), using five kernel functions. To evaluate the differences between
kernel functions, we assess the strength of evidence using Bayes factors. Our
results show that, for ABC Rejection, the Mat\'ern kernel with $\nu$=5/2 (M52
kernel) outperformes the commonly used Radial Basis Function (RBF) kernel in
approximating all three datasets. Bayes factors indicate that the M52 kernel
typically supports the observed data better than the RBF kernel, but with no
clear advantage over other alternatives. However, nested sampling gives
different results, with the M52 kernel losing its advantage. Nevertheless,
Bayes factors indicate no significant dependence of the data on each kernel. | astro-ph |
Recovery from Giant Eruptions in Very Massive Stars: We use a hydro-and-radiative-transfer code to explore the behavior of a very
massive star (VMS) after a giant eruption -- i.e., following a supernova
impostor event. Beginning with reasonable models for evolved VMSs with masses
of $80~M_\odot$ and $120~M_\odot$, we simulate the change of state caused by a
giant eruption via two methods that explicitly conserve total energy: 1.
Synthetically removing outer layers of mass of a few $M_\odot$ while reducing
the energy of the inner layers. 2. Synthetically transferring energy from the
core to the outer layers, an operation that automatically causes mass ejection.
Our focus is on the aftermath, not the poorly-understood eruption itself. Then,
using a radiation-hydrodynamic code in 1D with realistic opacities and
convection, the interior disequilibrium state is followed for about 200 years.
Typically the star develops a $\sim 400 ~\rm{km}~\rm{s}^{-1}$ wind with a mass
loss rate that begins around $0.1 ~M_\odot~\rm{yr^{-1}}$ and gradually
decreases. This outflow is driven by $\kappa$-mechanism radial pulsations. The
1D models have regular pulsations but 3D models will probably be more chaotic.
In some cases a plateau in the mass-loss rate may persist about 200 years,
while other cases are more like $\eta$ Car which lost $>10~M_\odot$ and then
had an abnormal mass loss rate for more than a century after its eruption. In
our model, the post-eruption outflow carried more mass than the initial
eruption. These simulations constitute a useful preliminary reconnaissance for
3D models which will be far more difficult. | astro-ph |
The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave
Event GW170817: The historic detection of gravitational waves from a binary neutron star
merger (GW170817) and its electromagnetic counterpart led to the first accurate
(sub-arcsecond) localization of a gravitational-wave event. The transient was
found to be $\sim$10" from the nucleus of the S0 galaxy NGC 4993. We report
here the luminosity distance to this galaxy using two independent methods. (1)
Based on our MUSE/VLT measurement of the heliocentric redshift ($z_{\rm
helio}=0.009783\pm0.000023$) we infer the systemic recession velocity of the
NGC 4993 group of galaxies in the cosmic microwave background (CMB) frame to be
$v_{\rm CMB}=3231 \pm 53$ km s$^{-1}$. Using constrained cosmological
simulations we estimate the line-of-sight peculiar velocity to be $v_{\rm
pec}=307 \pm 230$ km s$^{-1}$, resulting in a cosmic velocity of $v_{\rm
cosmic}=2924 \pm 236$ km s$^{-1}$ ($z_{\rm cosmic}=0.00980\pm 0.00079$) and a
distance of $D_z=40.4\pm 3.4$ Mpc assuming a local Hubble constant of
$H_0=73.24\pm 1.74$ km s$^{-1}$ Mpc$^{-1}$. (2) Using Hubble Space Telescope
measurements of the effective radius (15.5" $\pm$ 1.5") and contained intensity
and MUSE/VLT measurements of the velocity dispersion, we place NGC 4993 on the
Fundamental Plane (FP) of E and S0 galaxies. Comparing to a frame of 10
clusters containing 226 galaxies, this yields a distance estimate of $D_{\rm
FP}=44.0\pm 7.5$ Mpc. The combined redshift and FP distance is $D_{\rm NGC
4993}= 41.0\pm 3.1$ Mpc. This 'electromagnetic' distance estimate is consistent
with the independent measurement of the distance to GW170817 as obtained from
the gravitational-wave signal ($D_{\rm GW}= 43.8^{+2.9}_{-6.9}$ Mpc) and
confirms that GW170817 occurred in NGC 4993. | astro-ph |
The Fluence Duration Bias: The fluence duration bias causes fluences and durations of faint gamma-ray
bursts to be systematically underestimated relative to their peak fluxes. Using
Monte Carlo analysis, we demonstrate how this effect explains characteristics
of structure of the fluence vs. 1024 ms peak flux diagram. Evidence of this
bias exists in the BATSE fluence duration database, and provides a partial
explanation for the existence of burst class properties. | astro-ph |
Testing the dark energy with gravitational lensing statistics: We study the redshift distribution of two samples of early-type gravitational
lenses, extracted from a larger collection of 122 systems, to constrain the
cosmological constant in the LCDM model and the parameters of a set of
alternative dark energy models (XCDM, Dvali-Gabadadze-Porrati and Ricci dark
energy models), under a spatially flat universe. The likelihood is maximized
for $\Omega_\Lambda= 0.70 \pm 0.09$ when considering the sample excluding the
SLACS systems (known to be biased towards large image-separation lenses) and
no-evolution, and $\Omega_\Lambda= 0.81\pm 0.05$ when limiting to gravitational
lenses with image separation larger than 2" and no-evolution. In both cases,
results accounting for galaxy evolution are consistent within 1$\sigma$. The
present test supports the accelerated expansion, by excluding the
null-hypothesis (i.e., $\Omega_\Lambda = 0 $) at more than 4$\sigma$,
regardless of the chosen sample and assumptions on the galaxy evolution. A
comparison between competitive world models is performed by means of the
Bayesian information criterion. This shows that the simplest cosmological
constant model - that has only one free parameter - is still preferred by the
available data on the redshift distribution of gravitational lenses. We perform
an analysis of the possible systematic effects, finding that the systematic
errors due to sample incompleteness, galaxy evolution and model uncertainties
approximately equal the statistical errors, with present-day data. We find that
the largest sources of systemic errors are the dynamical normalization and the
high-velocity cut-off factor, followed by the faint-end slope of the velocity
dispersion function. | astro-ph |
Formation of solar quiescent coronal loops through magnetic reconnection
in an emerging active region: Coronal loops are building blocks of solar active regions. However, their
formation mechanism is still not well understood. Here we present direct
observational evidence for the formation of coronal loops through magnetic
reconnection as new magnetic fluxes emerge into the solar atmosphere.
Extreme-ultraviolet observations of the Atmospheric Imaging Assembly (AIA)
onboard the Solar Dynamics Observatory (SDO) clearly show the newly formed
loops following magnetic reconnection within a plasma sheet. Formation of the
loops is also seen in the h{\alpha} line-core images taken by the New Vacuum
Solar Telescope. Observations from the Helioseismic and Magnetic Imager onboard
SDO show that a positive-polarity flux concentration moves towards a
negative-polarity one with a speed of ~0.4 km/s, before the formation of
coronal loops. During the loop formation process, we found signatures of flux
cancellation and subsequent enhancement of the transverse field between the two
polarities. The three-dimensional magnetic field structure reconstructed
through a magnetohydrostatic model shows field lines consistent with the loops
in AIA images. Numerous bright blobs with an average width of 1.37 Mm appear
intermittently in the plasma sheet and move upward with a projected velocity of
~114 km/s. The temperature, emission measure and density of these blobs are
about 3 MK, 2.0x10^(28) cm^(-5) and 1.2x10^(10) cm^(-3), respectively. A power
spectral analysis of these blobs indicates that the observed reconnection is
likely not dominated by a turbulent process. We have also identified flows with
a velocity of 20 to 50 km/s towards the footpoints of the newly formed coronal
loops. | astro-ph |
Interior properties of the inner Saturnian moons from space astrometry
data: During the thirteen years in orbit around Saturn before its final plunge, the
Cassini spacecraft provided more than ten thousand astrometric measurements.
Such large amounts of accurate data enable the search for extremely faint
signals in the orbital motion of the saturnian moons. Among these, the
detection of the dynamical feedback of the rotation of the inner moons of
Saturn on their respective orbits becomes possible. Using all the currently
available astrometric data associated with Atlas, Prometheus, Pandora, Janus
and Epimetheus, we first provide a detailed analysis of the Cassini Imaging
Science Subsystem (ISS) data, with special emphasis on their statistical
behavior and sources of bias. Then, we give updated estimates of the moons'
averaged densities and try to infer more details about their interior
properties by estimating the physical librations for Prometheus, Pandora,
Epimetheus and Janus from anomalies in their apsidal precession. Our results
are compatible with a homogeneous interior for Janus and Epimetheus, within the
uncertainty of the measurements. On the other hand, we found some inconsistency
for Pandora and Prometheus, which might result from a dynamical mismodeling of
Saturn's gravity field. Last, we show how the synergistic introduction of
libration measurements directly derived from imaging should allow the moons'
moments of inertia to be better constrained. | astro-ph |
The first estimate of radio jet proper motion at z>5: The extremely high redshift (z=5.3) radio source SDSS J102623.61+254259.5
(J1026+2542) is among the most distant and most luminous radio-loud active
galactic nuclei (AGN) known to date. Its one-sided radio jet structure on
milli-arcsecond (mas) and ~10-mas scales typical for blazars was first imaged
at 5 GHz with very long baseline interferometry (VLBI) in 2006. Here we report
on our dual-frequency (1.7 and 5 GHz) imaging observations performed with the
European VLBI Network (EVN) in 2013. The prominent jet structure allows us to
identify individual components whose apparent displacement can be detected over
the time span of 7.33 yr. This is the first time when jet proper motions are
directly derived in a blazar at z>5. The small values of up to ~0.1 mas/yr are
consistent with what is expected in a relativistic cosmological model if
redshift is a measure of distance. The apparent superluminal jet speeds,
considered tentative because derived from two epochs only, exceed 10c for three
different components along the jet. Based on modeling its spectral energy
distribution, J1026+2542 is known to have its X-ray jet oriented close to the
line of sight, with significant Doppler boosting and a large bulk Lorentz
factor (Gamma~13). The new VLBI observations, indicating ~2.3 x 10^12 K lower
limit to the core brightness temperature, are consistent with this picture. The
spectral index in the core region is -0.35. | astro-ph |
Spherical collapse and halo abundance in shift-symmetric Galileon theory: We present the nonlinear growth of bound cosmological structures using the
spherical collapse approach in the shift-symmetric Galileon theories. In
particular, we focus on the class of models belonging to the Kinetic Gravity
Braiding by adopting a general parametrization of the action encoding a large
set of models by means of four free parameters: two defining the background
evolution and two affecting the perturbations. For the latter we identify their
specific signatures on the linearised critical density contrast, nonlinear
effective gravitational coupling and the virial overdensity and how they drive
their predictions away from $\Lambda$CDM. We then use the results of the
spherical collapse model to predict the evolution of the halo mass function. We
find that the shift-symmetric model predicts a larger number of objects
compared to $\Lambda$CDM for masses $M \gtrsim 10^{14} h^{-1} \mathrm{M}_\odot$
and such number increases for larger deviations from the standard model.
Therefore, the shift-symmetric model shows detectable signatures which can be
used to distinguish it from the standard scenario. | astro-ph |
Evolution of major sedimentary mounds on Mars: We present a new database of $>$300 layer-orientations from sedimentary
mounds on Mars. These layer orientations, together with draped landslides, and
draping of rocks over differentially-eroded paleo-domes, indicate that for the
stratigraphically-uppermost $\sim$1 km, the mounds formed by the accretion of
draping strata in a mound-shape. The layer-orientation data further suggest
that layers lower down in the stratigraphy also formed by the accretion of
draping strata in a mound-shape. The data are consistent with
terrain-influenced wind erosion, but inconsistent with tilting by flexure,
differential compaction over basement, or viscoelastic rebound. We use a simple
landscape evolution model to show how the erosion and deposition of mound
strata can be modulated by shifts in obliquity. The model is driven by
multi-Gyr calculations of Mars' chaotic obliquity and a parameterization of
terrain-influenced wind erosion that is derived from mesoscale modeling. Our
results suggest that mound-spanning unconformities with kilometers of relief
emerge as the result of chaotic obliquity shifts. Our results support the
interpretation that Mars' rocks record intermittent liquid-water runoff during
a $>$10$^8$-yr interval of sedimentary rock emplacement. | astro-ph |
A high molecular fraction in a sub-damped absorber at z=0.56: Measuring rest-frame ultraviolet rotational transitions from the Lyman and
Werner bands in absorption against a bright background continuum is one of the
few ways to directly measure molecular hydrogen (H2). Here we report the
detection of Lyman-Werner absorption from H2 at z=0.56 in a sub-damped Ly-alpha
system with neutral hydrogen column density N(HI) = 10^(19.5 +/- 0.2) cm^-2.
This is the first H2 system analysed at a redshift < 1.5 beyond the Milky Way
halo. It has a surprisingly high molecular fraction: log f(H2) > -1.93 +/- 0.36
based on modelling the line profiles, with a robust model-independent lower
limit of f(H2) > 10^-3. This is higher than f(H2) values seen along sightlines
with similar N(HI) through the Milky Way disk and the Magellanic clouds. The
metallicity of the absorber is 0.19 +0.21 -0.10 solar, with a dust-to-gas ratio
< 0.36 times the value in the solar neighbourhood. Absorption from associated
low-ionisation metal transitions such as OI and FeII is observed in addition to
OVI. Using Cloudy models we show that there are three phases present; a ~100 K
phase giving rise to H2, a ~10^4 K phase where most of the low-ionisation metal
absorption is produced; and a hotter phase associated with OVI. Based on
similarities to high velocity clouds in the Milky Way halo showing H2 and the
presence of two nearby galaxy candidates with impact parameters of ~10 kpc, we
suggest that the absorber may be produced by a tidally-stripped structure
similar to the Magellanic Stream. | astro-ph |
The jet of Markarian 501 from the sub-parsec to the kpc scale: We have observed the BL Lac object Markarian 501 at 1.4 GHz with the High
Sensitivity Array and at 86 GHz with the global VLBI mm array. Thanks to the
great resolution and sensitivity provided by these instruments, we probe
regions of the radio jets never accessed before. The new data at 1.4 GHz allow
us to map the one-sided jet at large distances from the core, and to constrain
jet properties thanks to the high jet to counter-jet brightness ratio. The 86
GHz data give us a high resolution image of the nuclear region. Putting
together these new results and available published data we discuss the
properties of this source from sub-parsec to kiloparsec scales. | astro-ph |
The ESO Imaging Survey: Status Report and Preliminary Results: The ESO Imaging Survey (EIS) presented in early issues of the Messenger, and
with up-to-date information on the ongoing observations available on the Web
(http://www.eso.org/eis), is a concerted effort by ESO and the Member State
community to provide targets for the first year of operation of the VLT. It
consists of two parts: a relatively wide-angle survey (EIS-WIDE) to cover four
pre-selected patches of sky, 6 square degrees each, spread in right ascension
to search for distant clusters and quasars and a deep, multicolor survey of
four optical (SUSI-2) and two infrared (SOFI) covering the HST/Hubble Deep
Field South (HDFS) and its flanking fields (EIS-DEEP). From the start, the main
challenge has been to carry out a public survey in a limited amount of time
requiring observations, software development and data reduction with the goal
of distributing the survey data products before the call for proposal for the
VLT. To cope with this one-year timetable, a novel type of collaboration
between ESO and the community has been established which has allowed EIS to
combine the scientific and technical expertise fo the community with in-house
know-how and infrastructure. In spite of the adverse weather conditions in some
of the earlier runs, EIS has already proved to be successful experiment
achieving most of its scientific and technical goals, thereby laying the ground
work for future imaging surveys. | astro-ph |
Wolter-I-like X-ray telescope structure using one conical mirror and one
quadric mirror: Nested multilayer mirrors are commonly used in X-ray telescope structures to
increase the collecting area. To balance the difficulty and cost of producing
these mirrors, the classical Wolter-I structure has previously been replaced
with a conical Wolter-I structure, but it can lead to significantly poorer
angular resolution. In this paper, we consider changing one of the mirror
shapes (paraboloid or hyperboloid) of the Wolter-I structure to a conical
mirror shape, while the other mirror shape remains a quadric surface-type
structure, which could thus ensure the imaging quality. Based on a theoretical
analysis and the results of simulations, the cone-hyperboloid and
paraboloid-cone structures are found to provide the best angular resolutions,
and the cone-hyperboloid structure is shorter than the paraboloid-cone
structure at the focal length. The cone-hyperboloid structure is then nested to
obtain the best on-axis angular resolution and off-axis images. | astro-ph |
Dust Processing in Disks around T Tauri Stars: The 8-14 micron emission spectra of 12 T Tauri stars in the Taurus/Auriga
dark clouds and in the TW Hydrae association obtained with the Infrared
Spectrograph (IRS; The IRS is a collaborative venture between Cornell
University and Ball Aerospace Corporation funded by NASA through the Jet
Propulsion Laboratory and the Ames Research Center.) on board Spitzer are
analyzed. Assuming the 10 micron features originate from silicate grains in the
optically thin surface layers of T Tauri disks, the 8-14 micron dust emissivity
for each object is derived from its Spitzer spectrum. The emissivities are fit
with the opacities of laboratory analogs of cosmic dust. The fits include small
nonspherical grains of amorphous silicates (pyroxene and olivine), crystalline
silicates (forsterite and pyroxene), and quartz, together with large fluffy
amorphous silicate grains. A wide range in the fraction of crystalline silicate
grains as well as large silicate grains among these stars are found. The dust
in the transitional-disk objects CoKu Tau/4, GM Aur, and DM Tau has the
simplest form of silicates, with almost no hint of crystalline components and
modest amounts of large grains. This indicates that the dust grains in these
objects have been modified little from their origin in the interstellar medium.
Other stars show various amounts of crystalline silicates, similar to the wide
dispersion of the degree of crystallinity reported for Herbig Ae/Be stars of
mass <2.5 solar masses. Late spectral type, low-mass stars can have significant
fractions of crystalline silicate grains. Higher quartz mass fractions often
accompany low amorphous olivine-to-amorphous pyroxene ratios. It is also found
that lower contrast of the 10 micron feature accompanies greater crystallinity. | astro-ph |
Evolution Through the Post-Starburst Phase: Using Post-Starburst
Galaxies as Laboratories for Understanding the Processes that Drive Galaxy
Evolution: Post-starburst (or "E+A") galaxies trace the fastest and most dramatic
processes in galaxy evolution. Recent work studying the evolution of galaxies
through this phase have revealed insights on how galaxies undergo structural
and stellar population changes as well as the role of various feedback
mechanisms. In this review, I summarize recent work on identifying
post-starburst galaxies; tracing the role of this phase through cosmic time;
measuring stellar populations, on-going star formation, morphologies,
kinematics, interstellar medium properties, and AGN activity; mechanisms to
cause the recent starburst and its end; and the future evolution to quiescence
(or not). The review concludes with a list of open questions and exciting
possibilities for future facilities. | astro-ph |
A Comprehensive Consistency Check between Synchrotron radiation and the
Observed Gamma-ray Burst Spectra: We performed a time-resolved spectral analysis of 53 bright gamma-ray bursts
(GRBs) observed by \textit{Fermi}/GBM. Our sample consists of 908 individual
spectra extracted from the finest time slices in each GRB. We fitted them with
the synchrotron radiation model by considering the electron distributions in
five different cases: mono-energetic, single power-law, Maxwellian, traditional
fast cooling, and broken power-law. Our results were further qualified through
Bayesian Information Criterion (BIC) by comparing with the fit by empirical
models, namely the so-called Band function and cut-off power-law models. Our
study showed that the synchrotron models, except for the fast-cooling case, can
successfully fit most observed spectra, with the single power-law case being
the most preferred. We also found that the electron distribution indices for
the single power-law synchrotron fit in more than half of our spectra exhibits
flux-tracking behavior, i.e., the index increases/decreases with the flux
increasing/decreasing, implying that the distribution of the radiating
electrons is increasingly narrower with time before the flux peaks and becomes
more spreading afterward. Our results indicate that the synchrotron radiation
is still feasible as a radiation mechanism of the GRB prompt emission phase. | astro-ph |
The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual
Atomic and Molecular Data Centre, VAMDC: The CDMS was founded 1998 to provide in its catalog section line lists of
molecular species which may be observed in various astronomical sources using
radio astronomy. The line lists contain transition frequencies with qualified
accuracies, intensities, quantum numbers, as well as further auxilary
information. They have been generated from critically evaluated experimental
line lists, mostly from laboratory experiments, employing established
Hamiltonian models. Seperate entries exist for different isotopic species and
usually also for different vibrational states. As of December 2015, the number
of entries is 792. They are available online as ascii tables with additional
files documenting information on the entries. The Virtual Atomic and Molecular
Data Centre was founded more than 5 years ago as a common platform for atomic
and molecular data. This platform facilitates exchange not only between
spectroscopic databases related to astrophysics or astrochemistry, but also
with collisional and kinetic databases. A dedicated infrastructure was
developed to provide a common data format in the various databases enabling
queries to a large variety of databases on atomic and molecular data at once.
For CDMS, the incorporation in VAMDC was combined with several modifications on
the generation of CDMS catalog entries. Here we introduce related changes to
the data structure and the data content in the CDMS. The new data scheme allows
us to incorporate all previous data entries but in addition allows us also to
include entries based on new theoretical descriptions. Moreover, the CDMS
entries have been transferred into a mySQL database format. These developments
within the VAMDC framework have been driven by the needs of the astronomical
community to be able to deal efficiently with large data sets obtained with the
Herschel Space Telescope or, more recently, with the Atacama Large Millimeter
Array. | astro-ph |
NH$_3$(3,3) and CH$_3$OH near Supernova Remnants: GBT and VLA
Observations: We report on Green Bank Telescope 23.87 GHz NH$_3$(3,3), emission
observations in five supernova remnants interacting with molecular clouds
(G1.4$-$0.1, IC443, W44, W51C, and G5.7$-$0.0). The observations show a clumpy
gas density distribution, and in most cases the narrow line widths of
$\sim3-4$\,km\,s$^{-1}$ are suggestive of maser emission. Very Large Array
observations reveal 36~GHz and/or 44~GHz CH$_3$OH, maser emission in a majority
(72\%) of the NH$_3$, peak positions towards three of these SNRs. This good
positional correlation is in agreement with the high densities required for the
excitation of each line. Through these observations we have shown that
CH$_3$OH, and NH$_3$, maser emission can be used as indicators of high density
clumps of gas shocked by supernova remnants, and provide density estimates
thereof. Modeling of the optical depth of the NH$_3$(3,3) emission is compared
to that of CH$_3$OH, constraining the densities of the clumps to a typical
density of the order of $10^5$~cm$^{-3}$ for cospatial masers. Regions of gas
with this density are found to exist in the post-shocked gas quite close to the
SNR shock front, and may be associated with sites where cosmic rays produce
gamma-ray emission via neutral pion decay. | astro-ph |
Green's function of the cosmological thermalization problem II: effect
of photon injection and constraints: The energy spectrum of the cosmic microwave background (CMB) provides a
powerful tool for constraining standard and non-standard physics in the
primordial Universe. Previous studies mainly highlight spectral distortions
(mu-, y- and r-type) created by episodes of early energy release; however,
several processes also lead to copious photon production, which requires a
different treatment. Here, we carry out a first detailed study for the
evolution of distortions caused by photon injection at different energies in
the CMB bands. We provide detailed analytical and numerical calculations
illustrating the rich phenomenology of the associated distortion signals. We
show that photon injection at very high and very low frequencies creates
distortions that are similar to those from pure energy release. In the mu-era
(z>3x10^5), a positive or negative chemical potential can be formed, depending
on the balance between added photon energy and number. At lower redshifts
(z<3x10^5), partial information about the photon injection process (i.e.,
injection time and energy) can still be recovered, with the distortion being
found in a partially comptonized state. We briefly discuss current and future
constraints on scenarios with photon production. We also argue that more
detailed calculations for different scenarios with photon injection may be
required to assess in which regimes these can be distinguished from pure energy
release processes. | astro-ph |
The evolution of late-type galaxies from CASSOWARY lensing systems: We explore the properties of lensing galaxies and lensed faint sources at
redshifts between 1.5 and 3.0. Our sample consists of 9 carefully selected
strongly-lensed galaxies discovered by the CASSOWARY survey in the Sloan
Digital Sky Survey (SDSS) data. We find that, despite some limitations of the
original SDSS data, the homogeneous sample of lensing systems can provide a
useful insight into lens and source properties. We also explore the limitations
of using low-resolution data to model and analyse galaxy-galaxy lensing. We
derive the relative alignment of mass and light in fitted lens profiles. The
range of magnification extends above 5, hence we are able to analyse
potentially small and low-mass galaxies at high redshifts. We confirm the
likely evolution of the size-luminosity relation for blue star-forming galaxies
as a function of redshift | astro-ph |
Chandra and Hubble Space Telescope Study of the Globular Cluster NGC 288: We report on the Chandra X-ray Observatory observations of the globular
cluster NGC 288. We detect four X-ray sources within the core radius and seven
additional sources within the half-mass radius down to a limiting luminosity of
Lx=7e30 erg/s (assuming cluster membership) in the 0.3-7 keV band. We also
observed the cluster with the Hubble Space Telescope Advanced Camera for
Surveys and identify optical counterparts to seven X-ray sources out of the
nine sources within the HST field-of-view. Based on the X-ray and optical
properties, we find 2-5 candidates of cataclysmic variables (CVs) or
chromospherically active binaries, and 2-5 background galaxies inside the
half-mass radius. Since the core density of NGC 288 is very low, the faint
X-ray sources of NGC 288 found in the Chandra and HST observations is higher
than the prediction on the basis of the collision frequency. We suggest that
the CVs and chromospherically active binaries are primordial in origin, in
agreement with theoretical expectation. | astro-ph |
Astrometric Plate Reduction with Orthogonal Functions and
Milli-Arcseconds Accuracy in Deep Proper Motion Surveys: We have been doing a sample survey in UBV photometry and proper motions as
part of an investigation of galactic structure and evolution. The programme is
based on Schmidt plates (from OCA, Tautenburg, Palomar and ESO Schmidt
telescopes) digitized with the MAMA machine (CAI, Paris). The high astrometric
quality of the MAMA gives access to micronic accuracy (leading to $<$ 2 mas per
year) on proper motions with a 35 years time base. The high proper motion
accuracy for faint star probes in wide-areas give access to the properties of
star samples out of the solar neighborhood. We have analyzed components of the
UVW galactic space motions resulting from the accurate proper motion surveys.
The kinematical distribution of F and G--type stars have been probed to
distances up to 2.5 kpc above the galactic plane. We have derived the constrain
on the structural parameters of the thin and thick disk components of the
Galaxy. | astro-ph |
Comparison of modified black-body fits for the estimation of dust
optical depths in interstellar clouds: When dust far-infrared spectral energy distributions (SEDs) are fitted with a
single modified black body (MBB), the optical depths tend to be underestimated.
This is caused by temperature variations, and fits with several temperature
components could lead to smaller errors. We want to quantify the performance of
the standard model of a single MBB in comparison with some multi-component
models. We are interested in both the accuracy and computational cost. We
examine some cloud models relevant for interstellar medium studies. Synthetic
spectra are fitted with a single MBB, a sum of several MBBs, and a sum of fixed
spectral templates, but keeping the dust opacity spectral index fixed. When
observations are used at their native resolution, the beam convolution becomes
part of the fitting procedure. This increases the computational cost, but the
analysis of large maps is still feasible with direct optimisation or even with
Markov chain Monte Carlo methods. Compared to the single MBB fits,
multi-component models can show significantly smaller systematic errors, at the
cost of more statistical noise. The $\chi^2$ values of the fits are not a good
indicator of the accuracy of the $\tau$ estimates, due to the potentially
dominant role of the model errors. The single-MBB model also remains a valid
alternative if combined with empirical corrections to reduce its bias. It is
technically feasible to fit multi-component models to maps of millions of
pixels. However, the SED model and the priors need to be selected carefully,
and the model errors can only be estimated by comparing alternative models. | astro-ph |
Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). IV.
Discovery of 41 Quasars and Luminous Galaxies at 5.7 < z < 6.9: We report discovery of 41 new high-z quasars and luminous galaxies, which
were spectroscopically identified at 5.7 < z < 6.9. This is the fourth in a
series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars
(SHELLQs) project, based on the deep multi-band imaging data collected by the
Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We selected the
photometric candidates by a Bayesian probabilistic algorithm, and then carried
out follow-up spectroscopy with the Gran Telescopio Canarias and the Subaru
Telescope. Combined with the sample presented in the previous papers, we have
now spectroscopically identified 137 extremely-red HSC sources over about 650
deg2, which include 64 high-z quasars, 24 high-z luminous galaxies, 6 [O III]
emitters at z ~ 0.8, and 43 Galactic cool dwarfs (low-mass stars and brown
dwarfs). The new quasars span the luminosity range from M1450 ~ -26 to -22 mag,
and continue to populate a few magnitude lower luminosities than have been
probed by previous wide-field surveys. In a companion paper, we derive the
quasar luminosity function at z ~ 6 over an unprecedentedly wide range of M1450
~ -28 to -21 mag, exploiting the SHELLQs and other survey outcomes. | astro-ph |
Photometric Variability of the Disk Integrated Infrared Emission of the
Earth: We present an analysis of the global-integrated mid-infrared emission flux of
the Earth based on data derived from satellite measurements. We have studied
the photometric annual, seasonal, and rotational variability of the thermal
emission of the Earth to determine which properties can be inferred from the
point-like signal. We find that the analysis of the time series allows us to
determine the 24 hr rotational period of the planet for most observing
geometries, due to large warm and cold areas, identified with geographic
features, which appear consecutively in the observer's planetary view. However,
the effects of global-scale meteorology can effectively mask the rotation for
several days at a time. We also find that orbital time series exhibit a
seasonal modulation, whose amplitude depends strongly on the latitude of the
observer but weakly on its ecliptic longitude. As no systematic difference of
brightness temperature is found between the dayside and nightside, the phase
variations of the Earth in the infrared range are negligible. Finally, we also
conclude that the phase variation of a spatially unresolved Earth-Moon system
is dominated by the lunar signal. | astro-ph |
The COS-Halos Survey: Physical Conditions and Baryonic Mass in the
Low-Redshift Circumgalactic Medium: We analyze the physical conditions of the cool, photoionized (T $\sim 10^4$
K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density
measurements for 44 gaseous halos within 160 kpc of $L \sim L^*$ galaxies at $z
\sim 0.2$. These data are well described by simple photoionization models, with
the gas highly ionized (n$_{\rm HII}$/n$_{\rm H} \gtrsim 99\%$) by the
extragalactic ultraviolet background (EUVB). Scaling by estimates for the
virial radius, R$_{\rm vir}$, we show that the ionization state (tracked by the
dimensionless ionization parameter, U) increases with distance from the host
galaxy. The ionization parameters imply a decreasing volume density profile
n$_{\rm H}$ = (10$^{-4.2 \pm 0.25}$)(R/R$_{\rm vir})^{-0.8\pm0.3}$. Our derived
gas volume densities are several orders of magnitude lower than predictions
from standard two-phase models with a cool medium in pressure equilibrium with
a hot, coronal medium expected in virialized halos at this mass scale. Applying
the ionization corrections to the HI column densities, we estimate a lower
limit to the cool gas mass M$_{\rm CGM}^{\rm cool} > 6.5 \times 10^{10}$
M$_{\odot}$ for the volume within R $<$ R$_{\rm vir}$. Allowing for an
additional warm-hot, OVI-traced phase, the CGM accounts for at least half of
the baryons purported to be missing from dark matter halos at the 10$^{12}$
M$_{\odot}$ scale. | astro-ph |
On the new short orbital period cataclysmic variable Halpha0242-2802: We present results from our phase-resolved spectroscopy of the newly
identified cataclysmic variable Halpha0242-2802. Halpha0242-2802 was identified
from a deep UK Schmidt Halpha-R band survey as a candidate cataclysmic
variable. Although initial spectroscopy revealed an optical spectrum very
similar to that of the famous short orbital period system WZ Sge, the analysis
of our data shows that this is not the case. Halpha0242-28 differs from WZ Sge
in both the accretion disk structure and the orbital period. In particular,
Halpha0242-28 appears to be a system which has not reached the orbital period
minimum, yet. | astro-ph |
Modelling the WMAP large-angle anomalies as an effect of a local density
inhomogeneity: We investigate large-angle scale temperature anisotropy in the Cosmic
Microwave Background (CMB) with the Wilkinson Microwave Anisotropy Probe (WMAP)
data and model the large-angle anomalies as the effect of the CMB quadrupole
anisotropies caused by the local density inhomogeneities. The quadrupole caused
by the local density inhomogeneities is different from the special relativity
kinematic quadrupole. If the observer inhabits a strong inhomogeneous region,
the local quadrupole should not be neglected. We calculate such local
quadrupole under the assumption that there is a huge density fluctuation field
in direction $(284^{\circ},74^{\circ})$, where the density fluctuation is
$10^{-3}$, and its center is $\sim 112h^{-1} \rm {Mpc}$ away from us. After
removing such mock signals from WMAP data, the power in quadrupole, $C_2$,
increases from the range $(200\sim260\mu \rm{K^2})$ to $\sim1000\mu \rm{K^2}$.
The quantity S, which is used to estimate the alignment between the quadrupole
and the octopole, decreases from $(0.7\sim0.74)$ to $(0.31\sim0.37)$, while the
model predict that $C_2=1071.5\mu \rm{K^2}$, $S=0.412$. So our local density
inhomogeneity model can, in part, explain the WMAP low-$\ell$ anomalies. | astro-ph |
The Nature of LINER-like Emission in Red Galaxies: Passive red galaxies frequently contain warm ionized gas and have spectra
similar to low-ionization nuclear emission-line regions (LINERs). Here we
investigate the nature of the ionizing sources powering this emission, by
comparing nuclear spectroscopy from the Palomar survey with larger aperture
data from the Sloan Digital Sky Survey. We find the line emission in the
majority of passive red galaxies is spatially extended; the Halpha surface
brightness profile depends on radius (r) as r^(-1.28). We detect strong line
ratio gradients with radius in [N II]/Ha, [S II]/Ha, and [O III]/[S II],
requiring the ionization parameter to increase outwards. Combined with a
realistic gas density profile, this outward increasing ionization parameter
convincingly rules out AGN as the dominant ionizing source, and strongly favors
distributed ionizing sources. Sources that follow the stellar density profile
can additionally reproduce the observed luminosity-dependence of the line ratio
gradient. Post-AGB stars provide a natural ionization source candidate, though
they have an ionization parameter deficit. Velocity width differences among
different emission lines disfavor shocks as the dominant ionization mechanism,
and suggest that the interstellar medium in these galaxies contains multiple
components. We conclude that the line emission in most LINER-like galaxies
found in large aperture (>100pc) spectroscopy is not primarily powered by AGN
activity and thus does not trace the AGN bolometric luminosity. However, they
can be used to trace warm gas in these red galaxies. | astro-ph |
TEMPLATES: Direct Abundance Constraints for Two Lensed Lyman-Break
Galaxies: Using integrated spectra for two gravitationally lensed galaxies from the
JWST TEMPLATES Early Release Science program, we analyze faint auroral lines,
which provide direct measurements of the gas-phase chemical abundance. For the
brighter galaxy, SGAS1723$+$34 ($z = 1.3293$), we detect the
[OIII]$\lambda4363$, [SIII]$\lambda6312$, and [OII]$\lambda\lambda$7320,7330
auroral emission lines, and set an upper limit for the [NII]$\lambda5755$ line.
For the second galaxy, SGAS1226$+$21 ($z = 2.925$), we do not detect any
auroral lines, and report upper limits. With these measurements and upper
limits, we constrain the electron temperatures in different ionization zones
within both of these galaxies. For SGAS1723$+$34, where auroral lines are
detected, we calculate direct oxygen and nitrogen abundances, finding an N/O
ratio consistent with observations of nearby ($z\sim 0$) galaxies. These
observations highlight the potent combination of JWST and gravitational lensing
to measure faint emission lines in individual distant galaxies and to directly
study the chemical abundance patterns in those galaxies. | astro-ph |
Microquasars: Progress made and open questions: In the last talk of the conference I summarized the main progress and
contributions to high energy astrophysics made by studies of microquasars in
our Galaxy. To stimulate the general discussion I have underlined some of the
questions that will guide in the near future the research in this area of
astrophysics. Here I present the viewgraphs and questions formulated during the
general discussion. | astro-ph |
Nested and Single Bars in Seyfert and Non-Seyfert Galaxies: We analyze the observed properties of nested and single stellar bar systems
in disk galaxies. The 112 galaxies in our sample comprise the largest matched
Seyfert vs. non-Seyfert sample of nearby galaxies with complete near-infrared
or optical imaging sensitive to lengthscales ranging from tens of pc to tens of
kpc. We find that a significant fraction of the sample galaxies, 17% +/- 4%,
has more than one bar, and that 28% +/- 5% of barred galaxies have nested bars.
The bar fractions appear to be stable according to reasonable changes in our
adopted bar criteria. For these nested bars, we detect a clear division in
length between the large-scale (primary) bars and small-scale (secondary) bars,
both in absolute and normalized (to the size of the galaxy) length. We argue
that this bimodal distribution can be understood within the framework of the
inner Lindblad resonances (ILRs), which are located where the gravitational
potential of the innermost galaxy switches effectively from 3D to 2D. While
primary bars are found to correlate with the host galaxy sizes, no such
correlation is observed for the secondary bars. Moreover, we find that
secondary bars differ morphologically from single bars. Overall, our matched
Seyfert and non-Seyfert samples show a statistically significant excess of bars
among the Seyfert galaxies at practically all lengthscales. We confirm our
previous result that Seyfert galaxies always show a preponderance of "thick"
bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is
observed between the presence of a bar and that of companion galaxies, even
relatively bright ones. | astro-ph |
The linear response of stellar systems does not diverge at marginal
stability: The linear response of a stellar system's gravitational potential to a
perturbing mass comprises two distinct contributions. Most famously, the system
will respond by forming a polarization 'wake' around the perturber. At the same
time, the perturber may also excite one or more 'Landau modes', i.e. coherent
oscillations of the entire stellar system which are either stable or unstable
depending on the system parameters. The amplitude of the first (wake)
contribution is known to diverge as a system approaches marginal stability. In
this paper we consider the linear response of a homogeneous stellar system to a
point mass moving on a straight line orbit. We prove analytically that the
divergence of the wake response is in fact cancelled by a corresponding
divergence in the Landau mode response, rendering the total response finite. We
demonstrate this cancellation explicitly for a box of stars with Maxwellian
velocity distribution. Our results imply that polarization wakes may be much
less efficient drivers of secular evolution than previously thought. More
generally, any prior calculation that accounted for wakes but ignored modes -
such as those based on the Balescu-Lenard equation - may need to be revised. | astro-ph |
Cosmological constraints from 21cm surveys after reionization: 21cm emission from residual neutral hydrogen after the epoch of reionization
can be used to trace the cosmological power spectrum of density fluctuations.
Using a Fisher matrix formulation, we provide a detailed forecast of the
constraints on cosmological parameters that are achievable with this probe. We
consider two designs: a scaled-up version of the MWA observatory as well as a
Fast Fourier Transform Telescope. We find that 21cm observations dedicated to
post-reionization redshifts may yield significantly better constraints than
next generation Cosmic Microwave Background (CMB) experiments. We find the
constraints on $\Omega_\Lambda$, $\Omega_{\rm m}h^2$, and $\Omega_\nu h^2$ to
be the strongest, each improved by at least an order of magnitude over the
Planck CMB satellite alone for both designs. Our results do not depend as
strongly on uncertainties in the astrophysics associated with the ionization of
hydrogen as similar 21cm surveys during the epoch of reionization. However, we
find that modulation of the 21cm power spectrum from the ionizing background
could potentially degrade constraints on the spectral index of the primordial
power spectrum and its running by more than an order of magnitude. Our results
also depend strongly on the maximum wavenumber of the power spectrum which can
be used due to non-linearities. | astro-ph |
The relation between 13CO(2-1) line width in molecular clouds and
bolometric luminosity of associated IRAS sources: We search for evidence of a relation between properties of young stellar
objects (YSOs) and their parent molecular clouds to understand the initial
conditions of high-mass star formation. A sample of 135 sources was selected
from the Infrared Astronomical Satellite (IRAS) Point Source Catalog, on the
basis of their red color to enhance the possibility of discovering young
sources. Using the Kolner Observatorium fur SubMillimeter Astronomie (KOSMA)
3-m telescope, a single-point survey in 13CO(2-1) was carried out for the
entire sample, and 14 sources were mapped further. Archival mid-infrared (MIR)
data were compared with the 13CO emissions to identify evolutionary stages of
the sources. A 13CO observed sample was assembled to investigate the
correlation between 13CO line width of the clouds and the luminosity of the
associated YSOs. We identified 98 sources suitable for star formation analyses
for which relevant parameters were calculated. We detected 18 cores from 14
mapped sources, which were identified with eight pre-UC HII regions and one UC
HII region, two high-mass cores earlier than pre-UC HII phase, four possible
star forming clusters, and three sourceless cores. By compiling a large (360
sources) 13CO observed sample, a good correlation was found between the 13CO
line width of the clouds and the bolometric luminosity of the associated YSOs,
which can be fitted as a power law: lg(dV13/km/s)=-0.023+0.135lg(Lbol/Lsolar).
Results show that luminous (>10^3Lsolar) YSOs tend to be associated with both
more massive and more turbulent (dV13>2km/s) molecular cloud structures. | astro-ph |
A Comparative Analysis of Machine-learning Models for Solar Flare
Forecasting: Identifying High-performing Active Region Flare Indicators: Solar flares create adverse space weather impacting space and Earth-based
technologies. However, the difficulty of forecasting flares, and by extension
severe space weather, is accentuated by the lack of any unique flare trigger or
a single physical pathway. Studies indicate that multiple physical properties
contribute to active region flare potential, compounding the challenge. Recent
developments in machine learning (ML) have enabled analysis of
higher-dimensional data leading to increasingly better flare forecasting
techniques. However, consensus on high-performing flare predictors remains
elusive. In the most comprehensive study to date, we conduct a comparative
analysis of four popular ML techniques (k-nearest neighbor, logistic
regression, random forest classifier, and support vector machine) by training
these on magnetic parameters obtained from the Helioseismic and Magnetic Imager
(HMI) on board the Solar Dynamics Observatory (SDO) for the entirety of solar
cycle 24. We demonstrate that the logistic regression and support vector
machine algorithms perform extremely well in forecasting active region flaring
potential. The logistic regression algorithm returns the highest true skill
score of $0.967 \pm 0.018$, possibly the highest classification performance
achieved with any strictly parametric study. From a comparative assessment, we
establish that the magnetic properties like total current helicity, total
vertical current density, total unsigned flux, R_VALUE, and total absolute
twist are the top-performing flare indicators. We also introduce and analyze
two new performance metrics, namely, severe and clear space weather indicators.
Our analysis constrains the most successful ML algorithms and identifies
physical parameters that contribute most to active region flare productivity. | astro-ph |
Testing the accuracy of radiative cooling approximations in SPH
simulations: Hydrodynamical simulations of star formation have stimulated a need to
develop fast and robust algorithms for evaluating radiative cooling. Here we
undertake a critical evaluation of what is currently a popular method for
prescribing cooling in SPH simulations, i.e. the polytropic cooling due
originally to Stamatellos et al. This method uses the local density and
potential to estimate the column density and optical depth to each particle and
then uses these quantities to evaluate an approximate expression for the net
radiative cooling. We evaluate the algorithm by considering both spherical and
disc-like systems with analytic density and temperature structures. In
spherical systems, the total cooling rate computed by the method is within
around 20 for the astrophysically relevant case of opacity dominated by ice
grains and is correct to within a factor of order unity for a range of opacity
laws. In disc geometry, however, the method systematically under-estimates the
cooling by a large factor at all heights in the disc. For the self-gravitating
disc studied, we find that the method under-estimates the total cooling rate by
a factor of 200. This discrepancy may be readily traced to the method's
systematic over-estimate of the disc column density and optical depth, since
(being based only on the local density and potential) it does not take into
account the low column density route for photon escape normal to the disc
plane. These results raise an obvious caution about the method's use in disc
geometry whenever an accurate cooling rate is required, although we note that
there are situations where the discrepancies highlighted above may not
significantly affect the global outcome of simulations. Finally, we draw
attention to our introduction of an analytic self-gravitating disc structure
that may be of use in the calibration of future cooling algorithms. | astro-ph |
Computation of atomic astrophysical opacities: The revision of the standard Los Alamos opacities in the 1980-1990s by a
group from the Lawrence Livermore National Laboratory (OPAL) and the Opacity
Project (OP) consortium was an early example of collaborative big-data science,
leading to reliable data deliverables (atomic databases, monochromatic
opacities, mean opacities, and radiative accelerations) widely used since then
to solve a variety of important astrophysical problems. Nowadays the precision
of the OPAL and OP opacities, and even of new tables (OPLIB) by Los Alamos, is
a recurrent topic in a hot debate involving stringent comparisons between
theory, laboratory experiments, and solar and stellar observations in
sophisticated research fields: the standard solar model (SSM), helio and
asteroseismology, non-LTE 3D hydrodynamic photospheric modeling, nuclear
reaction rates, solar neutrino observations, computational atomic physics, and
plasma experiments. In this context, an unexpected downward revision of the
solar photospheric metal abundances in 2005 spoiled a very precise agreement
between the helioseismic indicators (the radius of the convection zone
boundary, the sound-speed profile, and helium surface abundance) and SSM
benchmarks, which could be somehow reestablished with a substantial opacity
increase. Recent laboratory measurements of the iron opacity in physical
conditions similar to the boundary of the solar convection zone have indeed
predicted significant increases (30-400%), although new systematic improvements
and comparisons of the computed tables have not yet been able to reproduce
them. We give an overview of this controversy, and within the OP approach,
discuss some of the theoretical shortcomings that could be impairing a more
complete and accurate opacity accounting | astro-ph |
A rival for Babcock's star: the extreme 30-kG variable magnetic field in
the Ap star HD 75049: The extraordinary magnetic Ap star HD75049 has been studied with data
obtained with the ESO VLT and 2.2-m telescopes. Direct measurements reveal that
the magnetic field modulus at maximum reaches 30kG. The star shows photometric,
spectral and magnetic variability with a rotation period of 4.049d. Variations
of the mean longitudinal magnetic field can be described to first order by a
centred dipole model with an inclination i = 25 degrees, an obliquity beta = 60
degrees, and a polar field B_p = 42kG.
The combination of the longitudinal and surface magnetic field measurements
imply a radius of R = 1.7 R sun, suggesting the star is close to the zero-age
main sequence. HD75049 displays moderate overabundances of Si, Ti, Cr, Fe and
large overabundances of rare earth elements. This star has the second strongest
magnetic field of any main sequence star after Babcock's star, HD215441, which
it rivals. | astro-ph |
Theoretical aspects of asteroseismology: small steps towards a golden
future: The current status of asteroseismic studies is here reviewed and the adequate
techniques of analysis available today for the study of the oscillation
frequencies are presented. Comments on prospects for future investigations
through the possibility of getting ever more precise asteroseismic observations
from ground and space are given. | astro-ph |
The Dilaton and Modified Gravity: We consider the dilaton in the strong string coupling limit and elaborate on
the original idea of Damour and Polyakov whereby the dilaton coupling to matter
has a minimum with a vanishing value at finite field-value. Combining this type
of coupling with an exponential potential, the effective potential of the
dilaton becomes matter density dependent. We study the background cosmology,
showing that the dilaton can play the role of dark energy. We also analyse the
constraints imposed by the absence of violation of the equivalence principle.
Imposing these constraints and assuming that the dilaton plays the role of dark
energy, we consider the consequences of the dilaton on large scale structures
and in particular the behaviour of the slip functions and the growth index at
low redshift. | astro-ph |
Search for an annual modulation of dark-matter signals with a germanium
spectrometer at the Sierra Grande Laboratory: Data collected during three years with a germanium spectrometer at the Sierra
Grande underground laboratory have been analyzed for distinctive features of
annual modulation of the signal induced by WIMP dark matter candidates. The
main motivation for this analysis was the recent suggestion by the DAMA/NaI
Collaboration that a yearly modulation signal could not be rejected at the 90%
confidence level when analyzing data obtained with a high-mass low-background
scintillator detector. We performed two different analyses of the data: First,
the statistical distribution of modulation-significance variables (expected
from an experiment running under the conditions of Sierra Grande) was compared
with the same variables obtained from the data. Second, the data were analyzed
in energy bins as an independent check of the first result and to allow for the
possibility of a crossover in the expected signal. In both cases no
statistically significant deviation from the null result was found, which could
support the hypothesis that the data contain a modulated component. A plot is
also presented to enable the comparison of these results to those of the DAMA
collaboration. | astro-ph |
The Early-time Optical Properties of Gamma-Ray Burst Afterglows: We present a multiwavelength analysis of 63 Gamma-Ray Bursts observed with
the world's three largest robotic optical telescopes, the Liverpool and Faulkes
Telescopes (North and South). Optical emission was detected for 24 GRBs with
brightnesses ranging from R = 10 to 22 mag in the first 10 minutes after the
burst. By comparing optical and X-ray light curves from t = 100 to about 10^6
seconds, we introduce four main classes, defined by the presence or absence of
temporal breaks at optical and/or X-ray wavelengths. While 15/24 GRBs can be
modelled with the forward-shock model, explanation of the remaining nine is
very challenging in the standard framework even with the introduction of energy
injection or an ambient density gradient. Early X-ray afterglows, even segments
of light curves described by a power-law, may be due to additional emission
from the central engine. 39 GRBs in our sample were not detected and have deep
upper limits (R < 22 mag) at early time. Of these, only ten were identified by
other facilities, primarily at near infrared wavelengths, resulting in a dark
burst fraction of about 50%. Additional emission in the early time X-ray
afterglow due to late-time central engine activity may also explain some dark
bursts by making the bursts brighter than expected in the X-ray band compared
to the optical band. | astro-ph |
Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes). II. Expanded
Survey Description and the Stripe 82 Catalog: We present 226 large ultra-diffuse galaxy (UDG) candidates ($r_e >
5.3$\arcsec, $\mu_{0,g} > 24$ mag arcsec$^{-2}$) in the SDSS Stripe 82 region
recovered using our improved procedure developed in anticipation of processing
the entire Legacy Surveys footprint. The advancements include less constrained
structural parameter fitting, expanded wavelet filtering criteria,
consideration of Galactic dust, estimates of parameter uncertainties and
completeness based on simulated sources, and refinements of our automated
candidate classification. We have a sensitivity $\sim$1 mag fainter in
$\mu_{0,g}$ than the largest published catalog of this region. Using our
completeness-corrected sample, we find that (1) there is no significant decline
in the number of UDG candidates as a function of $\mu_{0,g}$ to the limit of
our survey ($\sim$ 26.5 mag arcsec$^{-2}$); (2) bluer candidates have smaller
S\'ersic $n$; (3) most blue ($g-r < 0.45$ mag) candidates have $\mu_{0,g}
\lesssim 25$ mag arcsec$^{-2}$ and will fade to populate the UDG red sequence
we observe to $\sim 26.5$ mag arcsec$^{-2}$; (4) any red UDGs that exist
significantly below our $\mu_{0,g}$ sensitivity limit are not descended from
blue UDGs in our sample; and (5) candidates with lower $\mu_{0,g}$ tend to
smaller $n$. We anticipate that the final SMUDGes sample will contain $\sim$
30$\times$ as many candidates. | astro-ph |
The First Two Years of Electromagnetic Follow-Up with Advanced LIGO and
Virgo: We anticipate the first direct detections of gravitational waves (GWs) with
Advanced LIGO and Virgo later this decade. Though this groundbreaking technical
achievement will be its own reward, a still greater prize could be observations
of compact binary mergers in both gravitational and electromagnetic channels
simultaneously. During Advanced LIGO and Virgo's first two years of operation,
2015 through 2016, we expect the global GW detector array to improve in
sensitivity and livetime and expand from two to three detectors. We model the
detection rate and the sky localization accuracy for binary neutron star (BNS)
mergers across this transition. We have analyzed a large, astrophysically
motivated source population using real-time detection and sky localization
codes and higher-latency parameter estimation codes that have been expressly
built for operation in the Advanced LIGO/Virgo era. We show that for most BNS
events the rapid sky localization, available about a minute after a detection,
is as accurate as the full parameter estimation. We demonstrate that Advanced
Virgo will play an important role in sky localization, even though it is
anticipated to come online with only one-third as much sensitivity as the
Advanced LIGO detectors. We find that the median 90% confidence region shrinks
from ~500 square degrees in 2015 to ~200 square degrees in 2016. A few distinct
scenarios for the first LIGO/Virgo detections emerge from our simulations. | astro-ph |
COMPTEL observations of the quasar PKS 0528+134 during the first 3.5
years of the CGRO mission: The COMPTEL observations of the blazar-type quasar PKS 0528+134 in the energy
range 0.75 MeV to 30 MeV carried out between April 1991 and September 1994 have
been analyzed. During the first two years PKS 0528+134 was most significantly
detected at energies above 3 MeV. During the last year there is only evidence
for the quasar at energies below 3 MeV indicating a spectral change. The
time-averaged COMPTEL energy spectrum between 0.75 MeV and 30 MeV is well
represented by a power-law shape. Spectra collected from different
observational periods reveal different power-law shapes: a hard state during
flaring observations reported by EGRET, and a soft state otherwise. The
combined simultaneous EGRET and COMPTEL spectra indicate these two spectral
states as well. During low intensisty gamma-ray phases no spectral break is
obvious from the combined COMPTEL and EGRET measurements. For the gamma-ray
flaring phases however, the combined COMPTEL and EGRET data require a spectral
bending at MeV-energies. By fitting broken power-law functions the best-fit
values for the break in photon index range between 0.6 and 1.7, and for the
break energy between ~5 MeV and ~20 MeV. Because the flux values measured by
COMPTEL below 3 MeV in both states are roughly equal, the observations would be
consistent with an additional spectral component showing up during gamma-ray
flaring phases of PKS 0528+134. Such a component could be introduced by e.g. a
high-energy electron-positron population with a low-energy cutoff in their bulk
Lorentz factor distribution. The multiwavelength spectrum of PKS 0528+134 for
gamma-ray flaring phases shows that the major energy release across the entire
electro-magnetic spectrum is measured at MeV-energies. | astro-ph |
Temperature measurements with the relativistic Sunyaev-Zel'dovich effect: At temperatures above ~5 keV, the non-relativistic approximation used to
derive the classical thermal Sunyaev-Zel'dovich effect spectrum begins to fail.
When relativistic effects are included, the spectrum becomes
temperature-dependent. This leads to both a problem and an opportunity: a
problem, because when the temperature dependence is not accounted for the
Compton-y estimate is biased; and an opportunity, because it represents a new
way to measure the temperature of the intracluster medium independently of
X-ray observations. This work presents current results from investigating the
impact of relativistic effects on Planck cluster observations, and projections
for future measurements of cluster temperatures using the Atacama Large
Aperture Sub-millimetre Telescope. | astro-ph |
Parameter estimation for coalescing massive binary black holes with LISA
using the full 2-post-Newtonian gravitational waveform and spin-orbit
precession: With one exception, previous analyses of the measurement accuracy of
gravitational wave experiments for comparable-mass binary systems have
neglected either spin-precession effects or subdominant harmonics and amplitude
modulations. Here we give the first explicit description of how these effects
combine to improve parameter estimation. We consider supermassive black hole
binaries as expected to be observed with the planned space-based interferometer
LISA, and study the measurement accuracy for several astrophysically
interesting parameters obtainable taking into account the full 2PN waveform for
spinning bodies, as well as spin-precession effects. We find that for binaries
with a total mass in the range 10^5 M_Sun < M < 10^7 M_Sun at a redshift of 1,
a factor ~1.5 is in general gained in accuracy, with the notable exception of
the determination of the individual masses in equal-mass systems, for which a
factor ~5 can be gained. We also find, as could be expected, that using the
full waveform helps increasing the upper mass limit for detection, which can be
as high as M = 10^8 M_Sun at a redshift of 1, as well as the redshift limit
where some information can be extracted from a system, which is roughly z = 10
for M < 10^7 M_Sun, 1.5-5 times higher than with the restricted waveform. We
computed that the full waveform allows to use supermassive black hole binaries
as standard sirens up to a redshift of z = 1.6, about 0.4 larger than what
previous studies allowed. We found that for lower unequal-mass binary systems,
the measurement accuracy is not as drastically improved as for other systems.
This suggests that for these systems, adding parameters such as eccentricity or
alternative gravity parameters could be achieved without much loss in the
accuracy. | astro-ph |
Observable tests of self-interacting dark matter in galaxy clusters: BCG
wobbles in a constant density core: Models of Cold Dark Matter predict that the distribution of dark matter in
galaxy clusters should be cuspy, centrally concentrated. Constant density cores
would be strong evidence for beyond-CDM physics, such as Self-Interacting Dark
Matter (SIDM). An observable consequence would be oscillations of the Brightest
Cluster Galaxy (BCG) in otherwise relaxed galaxy clusters. Offset BCGs have
indeed been observed - but only interpreted via a simplified, analytic model of
oscillations. We compare these observations to the BAHAMAS-SIDM suite of
cosmological simulations, which include SIDM and a fully hydrodynamical
treatment of star formation and feedback. We predict that the median offset of
BCGs increases with the SIDM cross-section, cluster mass and the amount of
stellar mass within 10kpc, while CDM exhibits no trend in mass. Interpolating
between the simulated cross-sections, we find that the observations (of 10
clusters) is consistent with CDM at the ~1.5$\sigma$ level, and prefer
cross-section $\sigma$/m < 0.12(0.39)cm$^2$/g at 68% (95%) confidence level.
This is on the verge of ruling out velocity-independent dark matter
self-interactions as the solution to discrepancies between the predicted and
observed behaviour of dwarf galaxies, and will be improved by larger surveys by
Euclid or SuperBIT. | astro-ph |
Star formation history and environment of the dwarf galaxy UGCA 92: We present a quantitative star formation history of the nearby dwarf galaxy
UGCA 92. This irregular dwarf is situated in the vicinity of the Local Group of
galaxies in a zone of strong Galactic extinction (IC 342 group of galaxies).
The galaxy was resolved into stars with HST/ACS including old red giant branch.
We have constructed a model of the resolved stellar populations and measured
the star formation rate and metallicity as function of time. The main star
formation activity period occurred about 8 - 14 Gyr ago. These stars are mostly
metal-poor, with a mean metallicity [Fe/H] ~ -1.5 -- -2.0 dex. About 84 per
cent of the total stellar mass was formed during this event. There are also
indications of recent star formation starting about 1.5 Gyr ago and continuing
to the present. The star formation in this event shows moderate enhancement
from ~ 200 Myr to 300 Myr ago. It is very likely that the ongoing star
formation period has higher metallicity of about -0.6 -- -0.3 dex. UGCA 92 is
often considered to be the companion to the starburst galaxy NGC 1569.
Comparing our star formation history of UGCA 92 with that of NGC 1569 reveals
no causal or temporal connection between recent star formation events in these
two galaxies. We suggest that the starburst phenomenon in NGC 1569 is not
related to the galaxy's closest dwarf neighbours and does not affect their star
formation history. | astro-ph |
Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment: The ratios of fluxes of heavy nuclei from sulfur (Z=16) to chromium (Z=24) to
the flux of iron were measured by the ATIC-2 experiment. The ratios are
decreasing functions of energy from 5 GeV/n to approximately 80 GeV/n, as
expected. However, an unexpected sharp upturn in the ratios are observed for
energies above 100 GeV/n for all elements from Z=16 to Z=24. Similar upturn but
with lower amplitude was also discovered in the ATIC-2 data for the ratio of
fluxes of abundant even nuclei (C, O, Ne, Mg, Si) to the flux of iron.
Therefore the spectrum of iron is significantly different from the spectra of
other abundant even nuclei. | astro-ph |
Revisiting the Integrated Star Formation Law. Paper I: Non-Starbursting
Galaxies: We use new and updated gas and dust-corrected SFR surface densities to
revisit the integrated star formation law for local "quiescent" spiral, dwarf,
and low-surface-brightness galaxies. Using UV-based SFRs with individual
IR-based dust corrections, we find that "normal" spiral galaxies alone define a
tight $\Sigma_{(\textrm{HI}+\textrm{H}_{2})}$-$\Sigma_{\textrm{SFR}}$ relation
described by a $n=1.41^{+0.07}_{-0.07}$ power law with a dispersion of
$0.28^{+0.02}_{-0.02}$ (errors reflect fitting and statistical uncertainties).
The SFR surface densities are only weakly correlated with HI surface densities
alone, but exhibit a stronger and roughly linear correlation with H$_{2}$
surface densities, similar to what is seen in spatially-resolved measurements
of disks. However, many dwarf galaxies lie below the star formation law defined
by spirals, suggesting a low-density threshold in the integrated star formation
law. We consider alternative scaling laws that better describe both spirals and
dwarfs. Our improved measurement precision also allows us to determine that
much of the scatter in the star formation law is intrinsic, and we search for
correlations between this intrinsic scatter and secondary physical parameters.
We find that dwarf galaxies exhibit second-order correlations with total gas
fraction, stellar mass surface density, and dynamical time that may explain
much of the scatter in the star formation law. Finally, we discuss various
systematic uncertainties that should be kept in mind when interpreting any
study of the star formation law, particularly the $X(\textrm{CO})$ conversion
factor and the diameter chosen to define the star-forming disk in a galaxy. | astro-ph |
The X-ray Telescope of the CAST Experiment: The CERN Axion Solar Telescope (CAST) searches for solar axions employing a 9
Tesla superconducting dipole magnet equipped with 3 independent detection
systems for X-rays from axion-photon conversions inside the 10 m long magnetic
field. Results of the first 6 months of data taking in 2003 imply a 95 % CL
upper limit on the axion-photon coupling constant of 1.16x10(-10) GeV(-1) for
axion masses < 0.02 eV. The most sensitive detector of CAST is a X-ray
telescope consisting of a Wolter I type mirror system and a fully depleted
pn-CCD as focal plane detector. Exploiting the full potential of background
suppression by focussing X-rays emerging from the magnet bore, the axion
sensitivity obtained with telescope data taken in 2004, for the first time in a
controlled laboratory experiment, will supersede axion constraints derived from
stellar energy loss arguments. | astro-ph |
Differences between CO- and calcium triplet-derived velocity dispersions
in spiral galaxies: evidence for central star formation?: We examine the stellar velocity dispersions (sigma) of a sample of 48
galaxies, 35 of which are spirals, from the Palomar nearby galaxy survey. It is
known that for ultra-luminous infrared galaxies (ULIRGs) and merger remnants
thesigma derived from the near-infrared CO band-heads is smaller than that
measured from optical lines, while no discrepancy between these measurements is
found for early-type galaxies. No such studies are available for spiral
galaxies - the subject of this paper. We used cross-dispersed spectroscopic
data obtained with the Gemini Near-Infrared Spectrograph (GNIRS), with spectral
coverage from 0.85 to 2.5um, to obtain sigma measurements from the 2.29 $\mu$m
CO band-heads (sigma_{CO}), and the 0.85 um calcium triplet (sigma_{CaT}). For
the spiral galaxies in the sample, we found that sigma_{CO} is smaller than
sigma_{CaT}, with a mean fractional difference of 14.3%. The best fit to the
data is given by sigma_{opt} = (46.0+/-18.1) + (0.85+/-0.12)sigma_{CO}. This
"sigma discrepancy" may be related to the presence of warm dust, as suggested
by a slight correlation between the discrepancy and the infrared luminosity.
This is consistent with studies that have found no sigma-discrepancy in
dust-poor early-type galaxies, and a much larger discrepancy in dusty merger
remnants and ULIRGs. That sigma_{CO}$ is lower than sigma_{opt} may also
indicate the presence of a dynamically cold stellar population component. This
would agree with the spatial correspondence between low sigma_{CO} and
young/intermediate-age stellar populations that has been observed in
spatially-resolved spectroscopy of a handful of galaxies. | astro-ph |
Minimal tau approximation and simulations of the alpha effect: The validity of a closure called the minimal tau approximation (MTA), is
tested in the context of dynamo theory, wherein triple correlations are assumed
to provide relaxation of the turbulent electromotive force. Under MTA, the
alpha effect in mean field dynamo theory becomes proportional to a relaxation
time scale multiplied by the difference between kinetic and current helicities.
It is shown that the value of the relaxation time is positive and, in units of
the turnover time at the forcing wavenumber, it is of the order of unity. It is
quenched by the magnetic field -- roughly independently of the magnetic
Reynolds number. However, this independence becomes uncertain at large magnetic
Reynolds number. Kinetic and current helicities are shown to be dominated by
large scale properties of the flow. | astro-ph |
Accretion Flow Along a Dipolar Field: Application to Intermediate Polars: A hydrodynamic formulation for accretion flow channeled by a dipolar magnetic
field is constructed using a curvi-linear coordinate system natural to the
field structure. We solve the hydrodynamic equations and determine the
velocity, density and temperature profiles of the post-shock accretion flow.
The results are applied to accretion flows in intermediate polars. We have
found that for systems with massive white dwarfs (~1Msolar) the temperature
profiles in the flow can differ significantly to those obtained from models in
which the accretion column is assumed to be cylindrical. | astro-ph |
All NIRspec needs is HST/WFC3 pre-imaging? The use of Milky Way Stars in
WFC3 Imaging to Register NIRspec MSA Observations: The James Webb Space Telescope (JWST) will be an exquisite new near-infrared
observatory with imaging and multi-object spectroscopy through ESA's NIRspec
instrument with its unique Micro-Shutter Array (MSA), allowing for slits to be
positioned on astronomical targets by opening specific 0.002"-wide micro
shutter doors.
To ensure proper target acquisition, the on-sky position of the MSA needs to
be verified before spectroscopic observations start. An onboard centroiding
program registers the position of pre-identified guide stars in a Target
Acquisition (TA) image, a short pre-spectroscopy exposure without dispersion
(image mode) through the MSA with all shutters open.
The outstanding issue is the availability of Galactic stars in the right
luminosity range for TA relative to typical high redshift targets. We explore
this here using the stars and $z\sim8$ candidate galaxies identified in the
source extractor catalogs of Brightest of Reionizing Galaxies survey
(BoRG[z8]), a pure-parallel program with Hubble Space Telescope Wide-Field
Camera 3.
We find that (a) a single WFC3 field contains enough Galactic stars to
satisfy the NIRspec astrometry requirement (20 milli-arcseconds), provided its
and the NIRspec TA's are $m_{lim}>24.5$ AB in WFC3 F125W, (b) a single WFC3
image can therefore serve as the pre-image if need be, (c) a WFC3 mosaic and
accompanying TA image satisfy the astrometry requirement at $\sim23$ AB mag in
WFC3 F125W, (d) no specific Galactic latitude requires deeper TA imaging due to
a lack of Galactic stars, and (e) a depth of $\sim24$ AB mag in WFC3 F125W is
needed if a guide star in the same MSA quadrant as a target is required.
We take the example of a BoRG identified $z\sim8$ candidate galaxy and
require a Galactic star within 20" of it. In this case, a depth of 25.5 AB in
F125W is required (with $\sim$97% confidence). | astro-ph |
A Comparison of Semi-Analytic and Smoothed Particle Hydrodynamics Galaxy
Formation: We compare the statistical properties of galaxies found in two different
models of hierarchical galaxy formation: the semi-analytic model of Cole et al.
and the smoothed particle hydrodynamics (SPH) simulations of Pearce et al.
Using a `stripped-down' version of the semi-analytic model which mimics the
resolution of the SPH simulations and excludes physical processes not included
in them, we find that the two models produce an ensemble of galaxies with
remarkably similar properties, although there are some differences in the gas
cooling rates and in the number of galaxies that populate halos of different
mass. The full semi-analytic model, which has effectively no resolution limit
and includes a treatment of star formation and supernovae feedback, produces
somewhat different (but readily understandable) results. Agreement is
particularly good for the present-day global fractions of hot gas, cold dense
(i.e. galactic) gas and uncollapsed gas, for which the SPH and stripped-down
semi-analytic calculations differ by at most 25%. In the most massive halos,
the stripped-down semi-analytic model predicts, on the whole, up to 50% less
gas in galaxies than is seen in the SPH simulations. The two techniques
apportion this cold gas somewhat differently amongst galaxies in a given halo.
This difference can be tracked down to the greater cooling rate in massive
halos in the SPH simulation compared to the semi-analytic model. (abridged) | astro-ph |
Modes of Accretion in X-ray Sources: Three classical modes of accretion are briefly discussed: wind-fed,
spherical, and disk. The three modes are illustrated with the mass transfer
onto black holes in high-mass X-ray binaries. Then a new regime of mini-disk
accretion is described and it is argued that observed wind-fed X-ray sources
are likely to accrete in this regime. Switching from one accretion mode to
another can cause the observed spectral state transitio ns. | astro-ph |
Is there a correlation between radio and gamma ray luminosities of AGN ?: The possibility of a correlation between the radio (cm)- and $\gamma$-ray
luminosity of variable AGN seen by EGRET is investigated. We performed
Monte-Carlo simulations of typical data sets and applied different correlation
techniques (partial correlation analysis, $\chi^2$-test applied on flux-flux
relations) in view of a truncation bias caused by sensitivity limits of the
surveys. For K-corrected flux densities, we find that with the least squares
method only a linear correlation can be recovered. Partial correlation analysis
on the other side provides a robust tool to detect correlations even in
flux-limited samples if intrinsic scatter does not exceed $\sim 40$ \% of the
original $\gamma$-ray luminosity. The analysis presented in this paper takes
into account redshift bias and truncation effects simultaneously which was
never considered in earlier papers.
Applying this analysis to simultaneously observed radio- and $\gamma$-ray
data, no correlation is found. However, an artificial correlation appears when
using the mean flux. This is probably due to the reduction of the dynamical
range in the flux-flux relation. Furthermore, we show that comparing the
emission in both spectral bands at a high activity state leads to no convincing
correlation.
In conclusion, we can not confirm a correlation between radio and
$\gamma$-ray luminosities of AGN which is claimed in previous works. | astro-ph |
Glancing through the debris disk: Photometric analysis of DE Boo with
CHEOPS: DE Boo is a unique system, with an edge-on view through the debris disk
around the star. The disk, which is analogous to the Kuiper belt in the Solar
System, was reported to extend from 74 to 84 AU from the central star. The high
photometric precision of the Characterising Exoplanet Satellite (CHEOPS)
provided an exceptional opportunity to observe small variations in the light
curve due to transiting material in the disk. This is a unique chance to
investigate processes in the debris disk. Photometric observations of DE Boo of
a total of four days were carried out with CHEOPS. Photometric variations due
to spots on the stellar surface were subtracted from the light curves by
applying a two-spot model and a fourth-order polynomial. The photometric
observations were accompanied by spectroscopic measurements with the 1m RCC
telescope at Piszk\'estet\H{o} and with the SOPHIE spectrograph in order to
refine the astrophysical parameters of DE Boo. We present a detailed analysis
of the photometric observation of DE Boo. We report the presence of nonperiodic
transient features in the residual light curves with a transit duration of
0.3-0.8 days. We calculated the maximum distance of the material responsible
for these variations to be 2.47 AU from the central star, much closer than most
of the mass of the debris disk. Furthermore, we report the first observation of
flaring events in this system. We interpreted the transient features as the
result of scattering in an inner debris disk around DE Boo. The processes
responsible for these variations were investigated in the context of
interactions between planetesimals in the system. | astro-ph |
New approach to primary mass composition analysis with simultaneous use
of ground and fluorescence detectors data: We study the possibility to reconstruct primary mass composition with the use
of combinations of basic shower characteristics, measured in hybrid
experiments, such as depth of shower maximum from fluorescence side and signal
in water Cherenkov tanks or in plastic scintillators from the ground side. To
optimize discrimination performance of shower observables combinations we apply
Fisher's discriminant analysis and give statistical estimates of separation of
the obtained distributions on Fisher variables for proton and iron primaries.
At the final stage we apply Multiparametric Topological Analysis to these
distributions to extract composition from prepared mixtures with known
fractions of showers from different primary particles. It is shown, that due to
high sensitivity of water tanks to muons, combination of signal in them with
$\xmax$ looks especially promising for mass composition analysis, provided the
energy is determined from longitudinal shower profile. | astro-ph |
The metallicity dependence of WR wind models: With the advance of stellar atmosphere modelling during the last few years,
large progress in the understanding of Wolf-Rayet (WR) mass loss has been
achieved. In the present paper we review the most recent developments,
including our own results from hydrodynamic non-LTE model atmospheres. In
particular, we address the important question of the Z-dependence of WR mass
loss. We demonstrate that models for radiatively driven winds imply a rather
strong dependence on Z. Moreover, we point out the key role of the L/M-ratio
for WR-type mass loss. | astro-ph |
A numerical approach to stochastic inflation and primordial black holes: Certain models of cosmic inflation produce strong cosmological perturbations
at short length scales, which may later collapse into primordial black holes.
To find the statistics of these strong perturbations and the ensuing black
holes, it is necessary to go beyond linear perturbation theory. Stochastic
inflation provides a way to take the leading non-linear effects into account.
In this contribution, I discuss recent progress in numerical computations of
stochastic inflation. A numerical approach can include more of the
non-linearities than an analytical calculation, and can be applied to
single-field inflationary models with any potential. | astro-ph |
CosTuuM: polarized thermal dust emission by magnetically oriented
spheroidal grains: We present the new open source C++-based Python library CosTuuM that can be
used to generate infrared absorption and emission coefficients for arbitrary
mixtures of spheroidal dust grains that are (partially) aligned with a magnetic
field. We outline the algorithms underlying the software, demonstrate the
accuracy of our results using benchmarks from literature, and use our tool to
investigate some commonly used approximative recipes. We find that the linear
polarization fraction for a partially aligned dust grain mixture can be
accurately represented by an appropriate linear combination of perfectly
aligned grains and grains that are randomly oriented, but that the commonly
used picket fence alignment breaks down for short wavelengths. We also find
that for a fixed dust grain size, the absorption coefficients and linear
polarization fraction for a realistic mixture of grains with various shapes
cannot both be accurately represented by a single representative grain with a
fixed shape, but that instead an average over an appropriate shape distribution
should be used. Insufficient knowledge of an appropriate shape distribution is
the main obstacle in obtaining accurate optical properties. CosTuuM is
available as a standalone Python library and can be used to generate optical
properties to be used in radiative transfer applications. | astro-ph |
The smooth cyclotron line in Her X-1 as seen with NuSTAR: Her X-1, one of the brightest and best studied X-ray binaries, shows a
cyclotron resonant scattering feature (CRSF) near 37 keV. This makes it an
ideal target for detailed study with the Nuclear Spectroscopic Telescope Array
(NuSTAR), taking advantage of its excellent hard X-ray spectral resolution. We
observed Her X-1 three times, coordinated with Suzaku, during one of the high
flux intervals of its 35d super-orbital period. This paper focuses on the shape
and evolution of the hard X-ray spectrum. The broad-band spectra can be fitted
with a powerlaw with a high-energy cutoff, an iron line, and a CRSF. We find
that the CRSF has a very smooth and symmetric shape, in all observations and at
all pulse-phases. We compare the residuals of a line with a Gaussian optical
depth profile to a Lorentzian optical depth profile and find no significant
differences, strongly constraining the very smooth shape of the line. Even
though the line energy changes dramatically with pulse phase, we find that its
smooth shape does not. Additionally, our data show that the continuum is only
changing marginally between the three observations. These changes can be
explained with varying amounts of Thomson scattering in the hot corona of the
accretion disk. The average, luminosity-corrected CRSF energy is lower than in
past observations and follows a secular decline. The excellent data quality of
NuSTAR provides the best constraint on the CRSF energy to date. | astro-ph |
Flashes in a Star Stream: Automated Classification of Astronomical
Transient Events: An automated, rapid classification of transient events detected in the modern
synoptic sky surveys is essential for their scientific utility and effective
follow-up using scarce resources. This presents some unusual challenges: the
data are sparse, heterogeneous and incomplete; evolving in time; and most of
the relevant information comes not from the data stream itself, but from a
variety of archival data and contextual information (spatial, temporal, and
multi-wavelength). We are exploring a variety of novel techniques, mostly
Bayesian, to respond to these challenges, using the ongoing CRTS sky survey as
a testbed. The current surveys are already overwhelming our ability to
effectively follow all of the potentially interesting events, and these
challenges will grow by orders of magnitude over the next decade as the more
ambitious sky surveys get under way. While we focus on an application in a
specific domain (astrophysics), these challenges are more broadly relevant for
event or anomaly detection and knowledge discovery in massive data streams. | astro-ph |
A New 100-GHz Band Front-End System with a Waveguide-Type
Dual-Polarization Sideband-Separating SIS Receiver for the NRO 45-m Radio
Telescope: We developed a waveguide-type dual-polarization sideband-separating SIS
receiver system of the 100-GHz band for the 45-m radio telescope at the
Nobeyama Radio Observatory, Japan. This receiver is composed of an ortho-mode
transducer and two sideband-separating SIS mixers, which are both based on the
waveguide technique. The receiver has four intermediate frequency bands of
4.0--8.0 GHz. Over the radio frequency range of 80--120 GHz, the
single-sideband receiver noise temperatures are 50--100 K and the image
rejection ratios are greater than 10 dB. We developed new matching optics for
the telescope beam as well as new IF chains for the four IF signals. The new
receiver system was installed in the telescope, and we successfully observed
the 12CO, 13CO and C18O emission lines simultaneously toward the Sagittarius B2
region to confirm the performance of the receiver system. The SSB noise
temperature of the system, including the atmosphere, became approximately half
of that of the previous receiver system. The Image Rejection Ratios (IRRs) of
the two 2SB mixers were calculated from the 12CO and HCO+ spectra from the W51
giant molecular cloud, resulting in > 20 dB for one polarization and > 12 dB
for the other polarization. | astro-ph |
A Complete Census of Circumgalactic MgII at Redshift z<~ 0.5: We present a survey of MgII absorbing gas in the vicinity of 380 random
galaxies, using 156 background quasi-stellar objects(QSOs) as absorption-line
probes. The sample comprises 211 isolated (73 quiescent and 138 star-forming
galaxies) and 43 non-isolated galaxies with sensitive constraints for both MgII
absorption and Ha emission. The projected distances span a range from d=9 to
497 kpc, redshifts of the galaxies range from z=0.10 to 0.48, and rest-frame
absolute B-band magnitudes range from $M_{\rm B}=-16.7$ to $-22.8$. Our
analysis shows that the rest-frame equivalent width of MgII, $W_r$(2796),
depends on halo radius($R_h$), $B$-band luminosity($L_{\rm B}$) and stellar
mass ($M_{\rm star}$) of the host galaxies, and declines steeply with
increasing $d$ for isolated, star-forming galaxies. $W_r$(2796) exhibits no
clear trend for either isolated, quiescent galaxies or non-isolated galaxies.
The covering fraction of MgII absorbing gas $\langle \kappa \rangle$ is high
with $\langle \kappa \rangle\gtrsim 60$% at $<40$ kpc for isolated galaxies and
declines rapidly to $\langle \kappa \rangle\approx 0$ at $d\gtrsim100$ kpc.
Within the gaseous radius, $\langle \kappa \rangle$ depends sensitively on both
$M_{\rm star}$ and the specific star formation rate inferred from Ha. Different
from massive quiescent halos, the observed velocity dispersion of MgII gas
around star-forming galaxies is consistent with expectations from virial
motion, which constrains individual clump mass to $m_{\rm cl} \gtrsim 10^5
\,\rm M_\odot$ and cool gas accretion rate of $\sim 0.7-2 \,M_\odot\,\rm
yr^{-1}$. We find no strong azimuthal dependence of MgII absorption for either
star-forming or quiescent galaxies. Our results highlight the need of a
homogeneous, absorption-blind sample for establishing a holistic description of
chemically-enriched gas in the circumgalactic space. | astro-ph |
Quiescent Ultra-diffuse galaxies in the field originating from
backsplash orbits: Ultra-diffuse galaxies (UDGs) are the lowest-surface brightness galaxies
known, with typical stellar masses of dwarf galaxies but sizes similar to
larger galaxies like the Milky Way. The reason for their extended sizes is
debated, with suggested internal processes like angular momentum, feedback or
mergers versus external mechanisms or a combination of both. Observationally,
we know that UDGs are red and quiescent in groups and clusters while their
counterparts in the field are blue and star-forming. This dichotomy suggests
environmental effects as main culprit. However, this scenario is challenged by
recent observations of isolated quiescent UDGs in the field. Here we use
$\Lambda$CDM cosmological hydrodynamical simulation to show that isolated
quenched UDGs are formed as backsplash galaxies that were once satellites of
another galactic, group or cluster halo but are today a few Mpc away from them.
These interactions, albeit brief, remove the gas and tidally strip the
outskirts of the dark matter haloes of the now quenched seemingly-isolated
UDGs, which are born as star-forming field UDGs occupying dwarf-mass dark
matter haloes. Quiescent UDGs may therefore be found in non-negligible numbers
in filaments and voids, bearing the mark of past interactions as stripped outer
haloes devoid of dark matter and gas compared to dwarfs with similar stellar
content. | astro-ph |
Suzaku Metal Abundance Patterns in the Outflow Region of M82 and the
Importance of Charge Exchange: We performed spectral analysis of Suzaku data of the galactic disk and
outflow regions of the starburst galaxy M82. Thermal modeling of the central
disk regions requires at least three temperature components. The Ly$\beta$ line
fluxes of O VIII and Ne X exceed those expected from a plasma in collisional
ionization equilibrium. The ratios of Ly$\beta$/Ly$\alpha$ lines for O VIII and
Ne X are higher than those of collisional ionization equilibrium, which may be
caused by the process of charge exchange. In the outflow wind region, the
spectra are well reproduced with two-temperature thermal models, and we have
derived the metal abundances of O, Ne, Mg, and Fe in the outflow. The ratios of
O/Fe, Ne/Fe, and Mg/Fe are about 2, 3, and 2, respectively, relative to the
solar value determined by Lodders (2003). Since there is no evidence of charge
exchange in outflow region, the metal abundances should be more reliable than
those in the central region. This abundance pattern indicates that starburst
activity enriches the outflow through SN II metal ejection into intergalactic
space. | astro-ph |
The structure of steady, relativistic, magnetised jets with rotation: We present equilibrium models of relativistic magnetised, infinite,
axisymmetric jets with rotation propagating through an homogeneous,
unmagnetised ambient medium at rest. The jet models are characterised by six
functions defining the radial profiles of density, pressure, and the toroidal
and axial components of velocity and magnetic field. Fixing the ambient
pressure and the jet rest-mass density and axial components of the flow
velocity and magnetic field, we analyze the influence of the toroidal magnetic
field and several rotation laws on the structure of the equilibrium models. Our
approach excludes by construction the analysis of the self-consistently
magnetically launched jet models or the force-free equilibrium solutions.
Several forbidden regions in the magnetic pitch angle/magnetization plane are
found where models of the class considered in our study could not be settled.
These forbidden regions are associated with the existence of maximum axial and
toroidal magnetic field components compatible with the prescribed equilibrium
condition at the jet surface, and/or an excess of centrifugal force producing
gaps with negative pressures in the jet. The present study can be easily
extended to jet models with different transversal profiles and magnetic field
configurations.
In the last part of the paper, we test the ability of our RMHD code to
maintain steady equilibrium models of axisymmetric RMHD jets in one and two
spatial dimensions. The one dimensional numerical simulations serve also as a
consistency proof of the fidelity of the analytical steady solutions discussed
in the first part of the paper. The present study allows us to build initial
equilibrium jet models with selected properties for dynamical (and emission)
simulations of magnetised relativistic jets with rotation. | astro-ph |
Core collapse supernovae as Cosmic Ray sources: Core collapse supernovae (CCSNe) produce fast shocks which pervade the dense
circum-stellar medium (CSM) of the stellar progenitor. Cosmic rays (CRs) if
accelerated at these shocks can induce the growth of electromagnetic
fluctuations in the foreshock medium. In this study, using a self-similar
description of the shock evolution, we calculate the growth timescales of
CR-driven instabilities. We select a sample of nearby core collapse radio
supernova of type II and Ib/Ic. From radio data we infer the parameters which
enter in the calculation of the instability growth times. We find that extended
IIb SNe shocks can trigger fast intra day instabilities, strong magnetic field
amplification and CR acceleration. In particular, the non-resonant streaming
instability can contribute to about 50\% of the magnetic field intensity
deduced from radio data. This results in the acceleration of CRs in the range
1-10 PeV within a few days after the shock breakout. In order to produce strong
magnetic field amplification and CR acceleration a fast shocks pervading a
dense CSM is necessary. In that aspect IIn supernov\ae~are also good
candidates. But a detailed modeling of the blast wave dynamics coupled with
particle acceleration is mandatory for this class of object before providing
any firm conclusions. Finally, we find that the trans-relativistic object SN
2009bb even if it produces more modest magnetic field amplification can
accelerate CRs up to 2-3 PeV within 20 days after the outburst. | astro-ph |
Polarized QED Cascades over Pulsar Polar Caps: The formation of $e^\pm$ plasmas within pulsar magnetospheres through quantum
electrodynamics (QED) cascades in vacuum gaps is widely acknowledged. This
paper aims to investigate the effect of photon polarization during the QED
cascade occurring over the polar cap of a pulsar. We employ a Monte Carlo-based
QED algorithm that accurately accounts for both spin and polarization effects
during photon emission and pair production in both single-particle and
particle-in-cell (PIC) simulations. Our findings reveal distinctive properties
in the photon polarization of curvature radiation (CR) and synchrotron
radiation (SR). CR photons exhibit high linear polarization parallel to the
plane of the curved magnetic field lines, whereas SR photons, on average,
demonstrate weak polarization. As the QED cascade progresses, SR photons
gradually dominate over CR photons, thus reducing the average degree of photon
polarization. Additionally, our study highlights an intriguing observation: the
polarization of CR photons enhances $e^\pm$ pair production by approximately
5%, in contrast to the inhibition observed in laser-plasma interactions. Our
self-consistent QED PIC simulations in the corotating frame reproduce the
essential results obtained from single-particle simulations. | astro-ph |
Analyzing spatial coherence using a single mobile field sensor: According to the Van Citter-Zernike theorem the intensity distribution of a
spatially incoherent source and the mutual coherence function of the light
impinging on two wave sensors are related. It is the comparable relationship
using a single mobile sensor moving at a certain velocity relative to the
source which is calculated in this article. The autocorelation function of the
electric field at the sensor contains information about the intensity
distribution. This expression could be employed in aperture synthesis. | astro-ph |
Radiation-Dominated Disks Are Thermally Stable: When the accretion rate is more than a small fraction of Eddington, the inner
regions of accretion disks around black holes are expected to be
radiation-dominated. However, in the alpha-model, these regions are also
expected to be thermally unstable. In this paper, we report two 3-d radiation
MHD simulations of a vertically-stratified shearing box in which the ratio of
radiation to gas pressure is ~ 10, and yet no thermal runaway occurs over a
timespan ~ 40 cooling times. Where the time-averaged dissipation rate is
greater than the critical dissipation rate that creates hydrostatic equilibrium
by diffusive radiation flux, the time-averaged radiation flux is held to the
critical value, with the excess dissipated energy transported by radiative
advection. Although the stress and total pressure are well-correlated as
predicted by the alpha-model, we show that stress fluctuations precede pressure
fluctuations, contrary to the usual supposition that the pressure controls the
saturation level of the magnetic energy. This fact explains the thermal
stability. Using a simple toy-model, we show that independently-generated
magnetic fluctuations can drive radiation pressure fluctuations, creating a
correlation between the two while maintaining thermal stability. | astro-ph |
Velocity-dependent J-factors for annihilation radiation from
cosmological simulations: We determine the dark matter pair-wise relative velocity distribution in a
set of Milky Way-like halos in the Auriga and APOSTLE simulations. Focusing on
the smooth halo component, the relative velocity distribution is well-described
by a Maxwell-Boltzmann distribution over nearly all radii in the halo. We
explore the implications for velocity-dependent dark matter annihilation,
focusing on four models which scale as different powers of the relative
velocity: Sommerfeld, s-wave, p-wave, and d-wave models. We show that the
J-factors scale as the moments of the relative velocity distribution, and that
the halo-to-halo scatter is largest for d-wave, and smallest for Sommerfeld
models. The J-factor is strongly correlated with the dark matter density in the
halo, and is very weakly correlated with the velocity dispersion. This implies
that if the dark matter density in the Milky Way can be robustly determined,
one can accurately predict the dark matter annihilation signal, without the
need to identify the dark matter velocity distribution in the Galaxy. | astro-ph |
Radiation Magnetohydrodynamics Simulation of Proto-Stellar Collapse:
Two-Component Molecular Outflow: We perform a three-dimensional nested-grid radiation magneto-hydrodynamics
(RMHD) simulation with self-gravity to study the early phase of the low-mass
star formation process from a rotating molecular cloud core to a first
adiabatic core just before the second collapse begins. Radiation transfer is
handled with the flux-limited diffusion approximation, operator-splitting and
implicit time-integrator. In the RMHD simulation, the outer region of the first
core attains a higher entropy and the size of first core is larger than that in
the magnetohydrodynamics simulations with the barotropic approximation. Bipolar
molecular outflow consisting of two components is driven by magnetic Lorentz
force via different mechanisms, and shock heating by the outflow is observed.
Using the RMHD simulation we can predict and interpret the observed properties
of star-forming clouds, first cores and outflows with millimeter/submillimeter
radio interferometers, especially the Atacama Large Millimeter/submillimeter
Array (ALMA). | astro-ph |
Balmer line shifts in quasars: We offer a broad review of Balmer line phenomenology in type 1 active
galactic nuclei, briefly sum- marising luminosity and radio loudness effects,
and discussing interpretation in terms of nebular physics along the 4D
eigenvector 1 sequence of quasars. We stress that relatively rare, peculiar
Balmer line profiles (i.e., with large shifts with respect to the rest frame or
double and multiple peaked) that start attracted attentions since the 1970s are
still passable of multiple dynamical interpretation. More mainstream objects
are still not fully understood as well, since competing dynamical models and
geometries are possible. Further progress may come from inter-line comparison
across the 4D Eigenvector 1 sequence. | astro-ph |
The velocity dispersion and mass-to-light ratio of the remote halo
globular cluster NGC 2419: Precise radial velocity measurements from HIRES on the Keck I telescope are
presented for 40 stars in the outer halo globular cluster NGC 2419. These data
are used to probe the cluster's stellar mass function and search for the
presence of dark matter in this cluster. NGC 2419 is one of the best Galactic
globular clusters for such a study due to its long relaxation time (T_{r0} ~
10^{10} yr) and large Galactocentric distance (R_{GC} ~ 90 kpc) -- properties
that make significant evolutionary changes in the low-mass end of the cluster
mass function unlikely. We find a mean cluster velocity of <v_r>=-20.3 +- 0.7
km/sec and an internal velocity dispersion of \sigma = 4.14 +- 0.48 km/sec,
leading to a total mass of (9.0 +- 2.2) * 10^5 Msun and a global mass-to-light
ratio of M/L_V = 2.05 +- 0.50 in solar units. This mass-to-light ratio is in
good agreement with what one would expect for a pure stellar system following a
standard mass function at the metallicity of NGC 2419. In addition, the
mass-to-light ratio does not appear to rise towards the outer parts of the
cluster. Our measurements therefore rule out the presence of a dark matter halo
with mass larger than ~10^7 Msun inside the central 500 pc, which is lower than
what is found for the central dark matter densities of dSph galaxies. We also
discuss the relevance of our measurements for alternative gravitational
theories such as MOND, and for possible formation scenarios of ultra-compact
dwarf galaxies. | astro-ph |
The JCMT Gould Belt Survey: Evidence for Dust Grain Evolution in Perseus
Star-forming Clumps: The dust emissivity spectral index, $\beta$, is a critical parameter for
deriving the mass and temperature of star-forming structures, and consequently
their gravitational stability. The $\beta$ value is dependent on various dust
grain properties, such as size, porosity, and surface composition, and is
expected to vary as dust grains evolve. Here we present $\beta$, dust
temperature, and optical depth maps of the star-forming clumps in the Perseus
Molecular Cloud determined from fitting SEDs to combined Herschel and JCMT
observations in the 160 $\mu$m, 250 $\mu$m, 350 $\mu$m, 500 $\mu$m, and 850
$\mu$m bands. Most of the derived $\beta$, and dust temperature values fall
within the ranges of 1.0 - 2.7 and 8 - 20 K, respectively. In Perseus, we find
the $\beta$ distribution differs significantly from clump to clump, indicative
of grain growth. Furthermore, we also see significant, localized $\beta$
variations within individual clumps and find low $\beta$ regions correlate with
local temperature peaks, hinting at the possible origins of low $\beta$ grains.
Throughout Perseus, we also see indications of heating from B stars and
embedded protostars, as well evidence of outflows shaping the local landscape. | astro-ph |
Galaxy and Mass Assembly (GAMA): Optimal Tiling of Dense Surveys with a
Multi-Object Spectrograph: A heuristic greedy algorithm is developed for efficiently tiling spatially
dense redshift surveys. In its first application to the Galaxy and Mass
Assembly (GAMA) redshift survey we find it rapidly improves the spatial
uniformity of our data, and naturally corrects for any spatial bias introduced
by the 2dF multi object spectrograph. We make conservative predictions for the
final state of the GAMA redshift survey after our final allocation of time, and
can be confident that even if worse than typical weather affects our
observations, all of our main survey requirements will be met. | astro-ph |
Exploring the Properties of the M31 Halo Globular Cluster System: Following on from our discovery of a significant population of M31 outer halo
globular clusters (GCs), and updates to the Revised Bologna Catalogue of M31
GCs, we investigate the GC system of M31 out to an unprecedented radius
(~120kpc). We derive various ensemble properties, including the magnitude,
colour and metallicity distributions, as well as the GC number density profile.
One of our most significant findings is evidence for a flattening in the radial
GC number density profile in the outer halo. Intriguingly, this occurs at a
galactocentric radius of ~2 degrees (~30 kpc) which is the radius at which the
underlying stellar halo surface density has also been shown to flatten. The GCs
which lie beyond this radius are remarkably uniform in terms of their blue
(V-I)o colours, consistent with them belonging to an ancient population with
little to no metallicity gradient. Structural parameters are also derived for a
sample of 13 newly-discovered extended clusters (ECs) and we find the lowest
luminosity ECs have magnitudes and sizes similar to Palomar-type GCs in the
Milky Way halo. We argue that our findings provide strong support for a
scenario in which a significant fraction of the outer halo GC population of M31
has been accreted. | astro-ph |
Large-amplitude rapid X-ray variability in the narrow-line Seyfert 1
galaxy PG 1404$+$226: We present the first results from a detailed analysis of a new, long
($\sim100$ ks) XMM-Newton observation of the narrow-line Seyfert 1 galaxy PG
1404$+$226 which showed a large-amplitude, rapid X-ray variability by a factor
of $\sim7$ in $\sim10$ ks with an exponential rise and a sharp fall in the
count rate. We investigate the origin of the soft X-ray excess emission and
rapid X-ray variability in the source through time-resolved spectroscopy and
fractional root-mean-squared (rms) spectral modeling. The strong soft X-ray
excess below 1 keV observed both in the time-averaged and time-resolved spectra
is described by the intrinsic disk Comptonization model as well as the
relativistic reflection model where the emission is intensive merely in the
inner regions ($r_{\rm in}<1.7 r_{\rm g}$) of an ionized accretion disk. We
detected no significant UV variability while the soft X-ray excess flux varies
together with the primary power-law emission (as $F_{{\rm primary}}\propto
F_{{\rm excess}}^{1.54}$), although with a smaller amplitude, as expected in
the reflection scenario. The observed X-ray fractional rms spectrum is
approximately constant with a drop at $\sim0.6$ keV and is described by a
non-variable emission line component with the observed energy of $\sim0.6$ keV
and two variable spectral components: a more variable primary power-law
emission and a less variable soft excess emission. Our results suggest the
`lamppost geometry' for the primary X-ray emitting hot corona which illuminates
the innermost accretion disk due to strong gravity and gives rise to the soft
X-ray excess emission. | astro-ph |
Spitzer observations of NGC2264: The nature of the disk population: NGC2264 is a young cluster with a rich circumstellar disk population which
makes it an ideal target for studying the evolution of stellar clusters. Our
goal is to study its star formation history and to analyse the primordial disk
evolution of its members. The study presented is based on data obtained with
Spitzer IRAC and MIPS, combined with deep NIR ground-based FLAMINGOS imaging
and previously published optical data. We build NIR dust extinction maps of the
molecular cloud associated with the cluster, and determine it to have a mass of
2.1x10^3Msun above an Av of 7mag. Using a differential K_s-band luminosity
function of the cluster, we estimate the size of its population to be
1436$\pm$242 members. The star formation efficiency is ~25%. We identify the
disk population: (i) optically thick inner disks, (ii) anaemic inner disks, and
(iii) disks with inner holes, or transition disks. We analyse the spatial
distribution of these sources and find that sources with thick disks segregate
into sub-clusterings, whereas sources with anaemic disks do not. Furthermore,
sources with anaemic disks are found to be unembedded (Av<3mag), whereas the
clustered sources with thick disks are still embedded within the parental
cloud. NGC2264 has undergone more than one star-forming event, where the
anaemic and extincted thick disk population appear to have formed in separate
episodes. We also find tentative evidence of triggered star-formation in the
Fox Fur Nebula. In terms of disk evolution, our findings support the emerging
disk evolution paradigm of two distinct evolutionary paths for primordial
optically thick disks: a homologous one where the disk emission decreases
uniformly at NIR and MIR wavelengths, and a radially differential one where the
emission from the inner region of the disk decreases more rapidly than from the
outer region (forming transition disks). | astro-ph |
Quantum sensor networks as exotic field telescopes for multi-messenger
astronomy: Multi-messenger astronomy, the coordinated observation of different classes
of signals originating from the same astrophysical event, provides a wealth of
information about astrophysical processes with far-reaching implications. So
far, the focus of multi-messenger astronomy has been the search for
conventional signals from known fundamental forces and standard model
particles, like gravitational waves (GW). In addition to these known effects,
quantum sensor networks could be used to search for astrophysical signals
predicted by beyond-standard-model (BSM) theories. Exotic bosonic fields are
ubiquitous features of BSM theories and appear while seeking to understand the
nature of dark matter and dark energy and solve the hierarchy and strong CP
problems. We consider the case where high-energy astrophysical events could
produce intense bursts of exotic low-mass fields (ELFs). We propose to expand
the toolbox of multi-messenger astronomy to include networks of precision
quantum sensors that by design are shielded from or insensitive to conventional
standard-model physics signals. We estimate ELF signal amplitudes, delays,
rates, and distances of GW sources to which global networks of atomic
magnetometers and atomic clocks could be sensitive. We find that, indeed, such
precision quantum sensor networks can function as ELF telescopes to detect
signals from sources generating ELF bursts of sufficient intensity. Thus ELFs,
if they exist, could act as additional messengers for astrophysical events. | astro-ph |
Perspectives for multi-messenger astronomy with the next generation of
gravitational-wave detectors and high-energy satellites: The Einstein Telescope (ET) is going to bring a revolution for the future of
multi-messenger astrophysics. In order to detect the counterparts of binary
neutron star (BNS) mergers at high redshift, the high-energy observations will
play a crucial role. Here, we explore the perspectives of ET, as single
observatory and in a network of gravitational-wave (GW) detectors, operating in
synergy with future $\gamma$-ray and X-ray satellites. We predict the
high-energy emission of BNS mergers and its detectability in a theoretical
framework which is able to reproduce the properties of the current sample of
observed short GRBs (SGRB). We estimate the joint GW and high-energy detection
rate for both the prompt and afterglow emissions, testing several combinations
of instruments and observational strategies. We find that the vast majority of
SGRBs detected in $\gamma$-rays will have a detectable GW counterpart; the
joint detection efficiency approaches $100\%$ considering a network of third
generation GW observatories. The probability of identifying the electromagnetic
counterpart of BNS mergers is significantly enhanced if the sky localisation
provided by GW instruments is observed by wide field X-ray monitors. We
emphasize that the role of the future X-ray observatories will be very crucial
for the detection of the fainter emission outside the jet core, which will
allow us to probe the yet unexplored population of low-luminosity SGRBs in the
nearby Universe, as well as to unveil the nature of the jet structure and the
connections with the progenitor properties. | astro-ph |
Accuracy of Mesh Based Cosmological Hydrocodes: Tests and Corrections: We perform a variety of tests to determine the numerical resolution of the
cosmological TVD eulerian code developed by Ryu et al (1993). Tests include
512^3 and 256^3 simulations of a Pk=k^{-1} spectrum to check for
self-similarity and comparison of results with those from higher resolution SPH
and grid-based calculations (Frenk et al 1998). We conclude that in regions
where density gradients are not produced by shocks the code degrades resolution
with a Gaussian smoothing (radius) length of 1.7 cells. At shock caused
gradients (for which the code was designed) the smoothing length is 1.1 cells.
Finally, for \beta model fit clusters, we can approximately correct numerical
resolution by the transformation R^2_{core}\to R^2_{core}-(C\Delta l)^2, where
\Delta l is the cell size and C=1.1-1.7. When we use these corrections on our
previously published computations for the SCDM and \Lambda CDM models we find
luminosity weighted, zero redshift, X-ray cluster core radii of (210\pm 86,
280\pm 67)h^{-1}kpc, respectively, which are marginally consistent with
observed (Jones & Forman 1992) values of 50-200h^{-1}kpc. Using the corrected
core radii, the COBE normalized SCDM model predicts the number of bright
L_x>10^{43}erg/s clusters too high by a factor of \sim 20 and the \Lambda CDM
model is consistent with observations. | astro-ph |
Extreme Jet Ejections from the Black Hole X-ray Binary V404 Cygni: We present simultaneous radio through sub-mm observations of the black hole
X-ray binary (BHXB) V404 Cygni during the most active phase of its June 2015
outburst. Our $4$ hour long set of overlapping observations with the Very Large
Array, the Sub-millimeter Array, and the James Clerk Maxwell Telescope
(SCUBA-2), covers 8 different frequency bands (including the first detection of
a BHXB jet at $666 \,{\rm GHz}/450\mu m$), providing an unprecedented
multi-frequency view of the extraordinary flaring activity seen during this
period of the outburst. In particular, we detect multiple rapidly evolving
flares, which reach Jy-level fluxes across all of our frequency bands. With
this rich data set we performed detailed MCMC modeling of the repeated flaring
events. Our custom model adapts the van der Laan synchrotron bubble model to
include twin bi-polar ejections, propagating away from the black hole at bulk
relativistic velocities, along a jet axis that is inclined to the line of
sight. The emission predicted by our model accounts for projection effects,
relativistic beaming, and the geometric time delay between the approaching and
receding ejecta in each ejection event. We find that a total of 8 bi-polar,
discrete jet ejection events can reproduce the emission that we observe in all
of our frequency bands remarkably well. With our best fit model, we provide
detailed probes of jet speed, structure, energetics, and geometry. Our analysis
demonstrates the paramount importance of the mm/sub-mm bands, which offer a
unique, more detailed view of the jet than can be provided by radio frequencies
alone. | astro-ph |
Broad-Band Imaging of a Large Sample of Irregular Galaxies: We present the results of UBV imaging of a large sample of irregular
galaxies: 94 Im systems, 24 Blue Compact Dwarfs (BCDs), and 18 Sm galaxies. We
also include JHK imaging of 41 of these galaxies. The sample spans a large
range in galactic parameters. Ellipse fit axial ratios, inclinations, and
position angles are derived, integrated photometry and azimuthally-averaged
surface photometry profiles are determined, and exponential fits give the
central surface brightnesses, scale lengths, and isophotal and half-power
radii. These data are used to address the shapes of Im galaxies, look for clues
to past interactions in large-scale peculiarities, examine the nature and
consequences of bars, study color gradients and large-scale color variations,
and compare the exponential disk profiles of the young and old stellar
components. For example, color gradients exhibit a great variety and not all
passbands are correlated. Bars are associated with higher star formation rates.
Many irregulars show a double exponential radial light profile that is steeper
in the outer parts, and these are reproduced by a new model of star formation
that is discussed in a companion paper. Some galaxies, primarily BCDs, have
double exponentials that are steeper (and bluer) in the inner parts, presumably
from centralized star formation. Im-types have thicker, less-prominent dust
layers than spiral galaxies because of their lower average surface densities
and midplane extinctions. | astro-ph |
Lyman-Werner UV Escape Fractions from Primordial Halos: Population III stars can regulate star formation in the primordial Universe
in several ways. They can ionize nearby halos, and even if their ionizing
photons are trapped by their own halos, their Lyman-Werner (LW) photons can
still escape and destroy H$_2$ in other halos, preventing them from cooling and
forming stars. LW escape fractions are thus a key parameter in cosmological
simulations of early reionization and star formation but have not yet been
parametrized for realistic halos by halo or stellar mass. To do so, we perform
radiation hydrodynamical simulations of LW UV escape from 9--120 M$_{\odot}$
Pop III stars in $10^5$ to $10^7$ M$_{\odot}$ halos with ZEUS-MP. We find that
photons in the LW lines (i.e. those responsible for destroying H$_{2}$ in
nearby systems) have escape fractions ranging from 0% to 85%. No LW photons
escape the most massive halo in our sample, even from the most massive star.
Escape fractions for photons elsewhere in the 11.18--13.6~eV energy range,
which can be redshifted into the LW lines at cosmological distances, are
generally much higher, being above 60% for all but the least massive stars in
the most massive halos. We find that shielding of H$_2$ by neutral hydrogen,
which has been neglected in most studies to date, produces escape fractions
that are up to a factor of three smaller than those predicted by H$_2$
self-shielding alone. | astro-ph |