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All-spherical telescope with extremely wide field of view: An all-spherical catadioptic telescope with the angular field of view of
several tens of degrees in diameter and spherical focal surface is proposed for
the monitoring of large sky areas. We provide a few examples of such a system
with the apertures up to 800 mm and the field of view $30^\circ$ and $40^\circ$
in diameter. The curvature of the focal surface is repaid by high performance
of the telescope. In particular, the diameter of a circle, that includes 80% of
energy in the polychromatic image of a star, is in the range $1.4'' - 1.9''$
across the field of $30^\circ$ size and $2.2'' - 2.9''$ for the field of
$40^\circ$ size. Some ways of working with curved focal surfaces are discussed. | astro-ph |
Roche tomography of cataclysmic variables - IV. Starspots and slingshot
prominences on BV Cen: We present Roche tomograms of the G5-G8 IV/V secondary star in the
long-period cataclysmic variable BV Cen reconstructed from MIKE echelle data
taken on the Magellan Clay 6.5-m telescope. The tomograms show the presence of
a number of large, cool starspots on BV Cen for the first time. In particular,
we find a large high-latitude spot which is deflected from the rotational axis
in the same direction as seen on the K3-K5 IV/V secondary star in the
cataclysmic variable AE Aqr. BV Cen also shows a similar relative paucity of
spots at latitudes between 40-50 degrees when compared with AE Aqr.
Furthermore, we find evidence for an increased spot coverage around longitudes
facing the white dwarf which supports models invoking starspots at the L1 point
to explain the low-states observed in some cataclysmic variables. In total, we
estimate that some 25 per cent of the northern hemisphere of BV Cen is spotted.
We also find evidence for a faint, narrow, transient emission line with
characteristics reminiscent of the peculiar low-velocity emission features
observed in some outbursting dwarf novae. We interpret this feature as a
slingshot prominence from the secondary star and derive a maximum source size
of 75,000 km and a minimum altitude of 160,000 km above the orbital plane for
the prominence.
The entropy landscape technique was applied to determine the system
parameters of BV Cen. We find M_1 = 1.18 (+0.28 -0.16) Msolar, M_2 = 1.05
(+0.23 -0.14) Msolar and an orbital inclination of i = 53 degrees +- 4 degrees
at an optimal systemic velocity of \gamma = -22.3 km s-1. Finally, we also
report on the previously unknown binarity of the G5IV star HD 220492. | astro-ph |
First Solar energetic particles measured on the Lunar far-side: On 2019 May 6, the Lunar Lander Neutron & Dosimetry (LND) Experiment on board
the Chang'E-4 on the far-side of the Moon detected its first small solar
energetic particle (SEP) event with proton energies up to 21MeV. Combined
proton energy spectra are studied based on the LND, SOHO/EPHIN and ACE/EPAM
measurements which show that LND could provide a complementary dataset from a
special location on the Moon, contributing to our existing observations and
understanding of space environment. Velocity dispersion analysis (VDA) has been
applied to the impulsive electron event and weak proton enhancement and the
results demonstrate that electrons are released only 22 minutes after the flare
onset and $\sim$15 minutes after type II radio burst, while protons are
released more than one hour after the electron release. The impulsive
enhancement of the in-situ electrons and the derived early release time
indicate a good magnetic connection between the source and Earth. However,
stereoscopic remote-sensing observations from Earth and STA suggest that the
SEPs are associated with an active region nearly 100$^\circ$ away from the
magnetic footpoint of Earth. This suggests that the propagation of these SEPs
could not follow a nominal Parker spiral under the ballistic mapping model and
the release and propagation mechanism of electrons and protons are likely to
differ significantly during this event. | astro-ph |
The Carnegie Supernova Project-I. Optical spectroscopy of
stripped-envelope supernovae: We present 170 optical spectra of 35 low-redshift stripped-envelope
core-collapse supernovae observed by the Carnegie Supernova Project-I between
2004 and 2009. The data extend from as early as -19 days (d) prior to the epoch
of B-band maximum to +322 d, with the vast majority obtained during the
so-called photospheric phase covering the weeks around peak luminosity. In
addition to histogram plots characterizing the red-shift distribution, number
of spectra per object, and the phase distribution of the sample, spectroscopic
classification is also provided following standard criteria. The CSP-I spectra
are electronically available and a detailed analysis of the data set is
presented in a companion paper being the fifth and final paper of the series | astro-ph |
Testing Hybrid Natural Inflation with BICEP2: We analyse Hybrid Natural Inflation in view of the recent results for the
tensor index reported by BICEP2. We find that it predicts a large running of
the scalar spectrum which is potentially detectable by large scale structure
and $21\, \mathrm{cm} $ observations. The running of the running is also
relatively large becoming close to $10^{-2}$. Along the way, we find general
consistency relations at which observables are subject if the slow-roll
approximation is imposed. Failure to satisfy these equations by the values
obtained for the observables in surveys would be a failure of the slow-roll
approximation itself. | astro-ph |
On the Application of Wesenheit Function in Deriving Distance to
Galactic Cepheids: In this work, we explore the possibility of using the Wesenheit function to
derive individual distances to Galactic Cepheids, as the dispersion of the
reddening free Wesenheit function is smaller than the optical period-luminosity
(P-L) relation. When compared to the distances from various methods, the
averaged differences between our results and published distances range from
-0.061 to 0.009, suggesting that the Wesenheit function can be used to derive
individual Cepheid distances. We have also constructed Galactic P-L relations
and selected Wesenheit functions based on the derived distances. A by-product
from this work is the derivation of Large Magellanic Cloud distance modulus
when calibrating the Wesenheit function. It is found to be 18.531 \pm 0.043
mag. | astro-ph |
A redshifted excess in the broad emission lines after the flare of the
$γ$-ray narrow-line Seyfert 1 PKS 2004-447: PKS 2004-447 is a narrow-line Seyfert 1 (NLS1) harbouring a relativistic jet
with gamma-ray emission. On 2019-10-25, the Fermi-Large Area Telescope captured
a $\gamma$-ray flare from this source, offering a chance to study the
broad-line region (BLR) and jet during such violent events. This can provide
insights to the BLR structure and jet interactions, which are important for
active galactic nuclei and host galaxy coevolution. We report X-Shooter
observations of enhancements in the broad line components of Balmer, Paschen
and He I lines seen only during the post-flare and vanishing 1.5 years after.
These features are biased redward up to $\sim$250 km s$^{-1}$ and are narrower
than the pre-existing broad line profiles. This indicates a connection between
the relativistic jet and the BLR of a young AGN, and how $\gamma$-ray
production can lead to localised addition of broad emission lines. | astro-ph |
Directionality preservation of nuclear recoils in an emulsion detector
for directional dark matter search: Nuclear emulsion is a well-known detector type proposed also for the
directional detection of dark matter. In this paper, we study one of the most
important properties of direction-sensitive detectors: the preservation by
nuclear recoils of the direction of impinging dark matter particles. For
nuclear emulsion detectors, it is the first detailed study where a realistic
nuclear recoil energy distribution with all possible recoil atom types is
exploited. Moreover, for the first time we study the granularity effect on the
emulsion detector directional performance. As well as we compare nuclear
emulsion with other directional detectors: in terms of direction preservation
nuclear emulsion outperforms the other detectors for WIMP masses above 100
GeV/c$^2$. | astro-ph |
Experimental study of an advanced concept of moderate-resolution
holographic spectrographs: We present the results of an experimental study of an advanced
moderate-resolution spectrograph based on a cascade of narrow-band holographic
gratings. The main goal of the project is to achieve a moderately high spectral
resolutionwith R up to 5000 simultaneously in the 4300-6800 A visible spectral
range on a single standard CCD, together with an increased throughput. The
experimental study consisted of (1) resolution and image quality tests
performed using the solar spectrum; and (2) a total throughput test performed
for a number of wavelengths using a calibrated lab monochromator. The measured
spectral resolving power reaches values over R>4000 while the experimental
throughput is as high as 55%, which is in good agreement with the modeling
results. Comparing the obtained characteristics of the spectrograph under
consideration with the best existing spectrographs, we conclude that the used
concept can be considered a very competitive and cheap alternative to the
existing spectrographs of the given class. We propose several astrophysical
applications for the instrument and discuss the prospect of creating its
full-scale version. | astro-ph |
Clumped stellar winds in supergiant high-mass X-ray binaries: X-ray
variability and photoionization: The clumping of massive star winds is an established paradigm confirmed by
multiple lines of evidence and supported by stellar wind theory. The purpose of
this paper is to bridge the gap between detailed models of inhomogeneous
stellar winds in single stars and the phenomenological description of donor
winds in supergiant high-mass X-ray binaries (HMXBs). We use results from
time-dependent hydrodynamical models of the instability in the line-driven wind
of a massive supergiant star to derive the time-dependent accretion rate onto a
compact object in the Bondi-Hoyle-Lyttleton approximation. The strong density
and velocity fluctuations in the wind result in strong variability of the
synthetic X-ray light curves. The model predicts a large scale X-ray
variability, up to eight orders of magnitude, on relatively short timescales.
The apparent lack of evidence for such strong variability in the observed HMXBs
indicates that the details of accretion process act to reduce the variability
due to the stellar wind velocity and density jumps. We, also, study the
absorption of X-rays in the clumped stellar wind by means of a 2-D stochastic
wind model and find that absorption of X-rays changes strongly at different
orbital phases. Furthermore, we address the photoionization in the clumped
wind, and show that the degree of ionization is affected by the wind clumping.
A correction factor for the photoionization parameter is derived. It is shown
that the photoionization parameter is reduced by a factor Xi compared to the
smooth wind models with the same mass-loss rate, where Xi is the wind
inhomogeneity parameter. We conclude that wind clumping must also be taken into
account when comparing the observed and model spectra of the photoionized
stellar wind. | astro-ph |
Hunting for wandering massive black holes: We investigate low-density accretion flows onto massive black holes (BHs)
with masses of $\gtrsim 10^5~M_\odot$ orbiting around in the outskirts of their
host galaxies, performing three-dimensional hydrodynamical simulations. Those
wandering BHs are populated via ejection from the galactic nuclei through
multi-body BH interactions and gravitational wave recoils associated with
galaxy and BH coalescences. We find that when a wandering BH is fed with hot
and diffuse plasma with density fluctuations, the mass accretion rate is
limited at $\sim 10-20\%$ of the canonical Bondi-Hoyle-Littleton rate owing to
a wide distribution of inflowing angular momentum. We further calculate
radiation spectra from radiatively inefficient accretion flows onto the
wandering BH using a semi-analytical two-temperature disk model and find that
the predicted spectra have a peak at the millimeter band, where the Atacama
Large Millimeter/submillimeter Array (ALMA) has the highest sensitivity and
spatial resolution. Millimeter observations with ALMA and future facilities
such as the next generation Very Large Array (ngVLA) will enable us to hunt for
a population of wandering BHs and push the detectable mass limit down to
$M_\bullet \simeq 2\times10^7~M_\odot$ for massive nearby ellipticals, e.g.,
M87, and $M_\bullet \simeq 10^5~M_\odot$ for the Milky Way. This radiation
spectral model, combined with numerical simulations, will be applied to give
physical interpretations of off-nuclear BHs detected in dwarf galaxies, which
may constrain BH seed formation scenarios. | astro-ph |
Carbon-enhanced stars with short orbital and spin periods: Many characteristics of dwarf carbon stars are broadly consistent with a
binary origin, including mass transfer from an evolved companion. While the
population overall appears to have old-disc or halo kinematics, roughly
2$\,$per cent of these stars exhibit H$\alpha$ emission, which in low-mass
main-sequence stars is generally associated with rotation and relative youth.
Its presence in an older population therefore suggests either irradiation or
spin-up. This study presents time-series analyses of photometric and
radial-velocity data for seven dwarf carbon stars with H$\alpha$ emission. All
are shown to have photometric periods in the range 0.2--5.2$\,$d, and orbital
periods of similar length, consistent with tidal synchronisation. It is
hypothesised that dwarf carbon stars with emission lines are the result of
close-binary evolution, indicating that low-mass, metal-weak or metal-poor
stars can accrete substantial material prior to entering a common-envelope
phase. | astro-ph |
Constraints on dark matter particles from theory, galaxy observations
and N-body simulations: Mass bounds on dark matter (DM) candidates are obtained for particles
decoupling in or out of equilibrium with {\bf arbitrary} isotropic and
homogeneous distribution functions. A coarse grained Liouville invariant
primordial phase space density $ \mathcal D $ is introduced. Combining its
value with recent photometric and kinematic data on dwarf spheroidal satellite
galaxies in the Milky Way (dShps), the DM density today and $N$-body
simulations, yields upper and lower bounds on the mass, primordial phase space
densities and velocity dispersion of the DM candidates. The mass of the DM
particles is bound in the few keV range. If chemical freeze out occurs before
thermal decoupling, light bosonic particles can Bose-condense. Such
Bose-Einstein {\it condensate} is studied as a dark matter candidate. Depending
on the relation between the critical($T_c$)and decoupling($T_d$)temperatures, a
BEC light relic could act as CDM but the decoupling scale must be {\it higher}
than the electroweak scale. The condensate tightens the upper bound on the
particle's mass. Non-equilibrium scenarios that describe particle production
and partial thermalization, sterile neutrinos produced out of equilibrium and
other DM models are analyzed in detail obtaining bounds on their mass,
primordial phase space density and velocity dispersion. Light thermal relics
with $ m \sim \mathrm{few} \mathrm{keV}$ and sterile neutrinos lead to a
primordial phase space density compatible with {\bf cored} dShps and disfavor
cusped satellites. Light Bose condensed DM candidates yield phase space
densities consistent with {\bf cores} and if $ T_c\gg T_d $ also with cusps.
Phase space density bounds from N-body simulations suggest a potential tension
for WIMPS with $ m \sim 100 \mathrm{GeV},T_d \sim 10 \mathrm{MeV} $. | astro-ph |
Hidden high ionization lines in the low luminosity type II SN 2021gmj: We present comprehensive optical observations of SN~2021gmj, a type II
supernova (SN~II) discovered within a day of explosion by the Distance Less
Than 40~Mpc (DLT40) survey. Follow up observations show that SN~2021gmj is a
low luminosity SN~II (LL~SN~II), with a peak magnitude $M_V = -15.45$ and Fe II
velocity of $\sim 1800 \ \mathrm{km} \ \mathrm{s}^{-1}$ at 50 days past
explosion. Using the expanding photosphere method we derive a distance of
$17.8^{+0.6}_{-0.4}$~Mpc. From the tail of the light-curve we obtain a
radioactive nickel mass of $0.014 \pm 0.001$ $\mathrm{M}_{\odot}$. The presence
of circumstellar material (CSM) is suggested by the early light curve, early
spectra and the presence of high velocity H$\alpha$ in absorption. Analytical
shock-cooling models of the early light curve cannot reproduce the fast rise,
also supporting the idea that the early emission is partially powered by the
interaction of the SN ejecta and CSM. The inferred low CSM mass of 0.025
$\mathrm{M}_{\odot}$ in our hydrodynamic-modeling light curve analysis is also
consistent with our spectroscopic observations. We observe a broad feature near
4600 A, which may be high ionization lines of C, N or/and He II. This feature
is reproduced by radiation hydrodynamic simulations of red supergiants with
extended atmospheres. Several LL~SNe~II show similar spectral features implying
that high density material around the progenitor may be common among them. | astro-ph |
An X-ray Mini-survey of Nearby Edge-on Starburst Galaxies II. The
Question of Metal Abundance: (abbreviated) We have undertaken an X-ray survey of a far-infrared flux
limited sample of seven nearby edge-on starburst galaxies. Here, we examine the
two X-ray-brightest sample members NGC 253 and M 82 in a self-consistent
manner, taking account of the spatial distribution of the X-ray emission in
choosing our spectral models. There is significant X-ray absorption in the disk
of NGC 253. When this is accounted for we find that multi-temperature thermal
plasma models with significant underlying soft X-ray absorption are more
consistent with the imaging data than single-temperature models with highly
subsolar abundances or models with minimal absorption and non-equilibrium
thermal ionization conditions. Our models do not require absolute abundances
that are inconsistent with solar values or unusually supersolar ratios of the
alpha-burning elements with respect to Fe (as claimed previously). We conclude
that with current data, the technique of measuring abundances in starburst
galaxies via X-ray spectral modeling is highly uncertain.
Based on the point-like nature of much of the X-ray emission in the PSPC
hard-band image of NGC 253, we suggest that a significant fraction of the
``extended'' X-ray emission in the 3-10 keV band seen along the disk of the
galaxy with ASCA and BeppoSAX (Cappi et al.) is comprised of discrete sources
in the disk, as opposed to purely diffuse, hot gas. This could explain the low
Fe abundances of ~1/4 solar derived for pure thermal models. | astro-ph |
A Search for Lensed Lyman-Alpha Emitters within the Early HETDEX Data
Set: The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is a large-volume
spectroscopic survey without pre-selection of sources, searching ~ 540 deg^2
for Lyman-alpha emitting galaxies (LAEs) at 1.9 < z < 3.5. Taking advantage of
such a wide-volume survey, we perform a pilot study using early HETDEX data to
search for lensed Lyman-alpha emitters. After performing a proof-of-concept
using a previously known lensed LAE covered by HETDEX, we perform a search for
previously unknown lensed LAEs in the HETDEX spectroscopic sample. We present a
catalog of 26 potential LAEs lensed by foreground, red, non-star-forming
galaxies at z ~ 0.4 - 0.7. We estimate the magnification for each candidate
system, finding 12 candidates to be within the strong lensing regime
(magnification $\mu$ > 2). Follow-up observations of these potential lensed
LAEs have the potential to confirm their lensed nature and explore these
distant galaxies in more detail. | astro-ph |
Improved Acceleration of the GPU Fourier Domain Acceleration Search
Algorithm: We present an improvement of our implementation of the Correlation Technique
for the Fourier Domain Acceleration Search (FDAS) algorithm on Graphics
Processor Units (GPUs) (Dimoudi & Armour 2015; Dimoudi et al. 2017). Our new
improved convolution code which uses our custom GPU FFT code is between 2.5 and
3.9 times faster the than our cuFFT-based implementation (on an NVIDIA P100)
and allows for a wider range of filter sizes then our previous version. By
using this new version of our convolution code in FDAS we have achieved 44%
performance increase over our previous best implementation. It is also
approximately 8 times faster than the existing PRESTO GPU implementation of
FDAS (Luo 2013). This work is part of the AstroAccelerate project (Armour et
al. 2002), a many-core accelerated time-domain signal processing library for
radio astronomy. | astro-ph |
Discovery of a disrupting open cluster far into the Milky Way halo: a
recent star formation event in the leading arm of the Magellanic stream?: We report the discovery of a young (${\rm age} \sim 130~{\rm Myr}$), low-mass
($M \sim 1200~{\rm M}_\odot$), metal-poor ($[{\rm Fe}/{\rm H}] \sim -1.1$)
stellar association at a heliocentric distance $D \approx 29~{\rm kpc}$,
placing it far into the Milky Way halo. At its present Galactocentric position
$(R, z) \sim (23, 15)~{\rm kpc}$, the association is (on the sky) near the
leading arm of the gas stream emanating from the Magellanic cloud system, but
is located $\approx 60^\circ$ from the Large Magellanic Cloud (LMC) center on
the other side of the Milky Way disk. If we assume that the cluster is
co-located with HI gas in the stream, we directly measure the distance to the
leading arm of the Magellanic stream. The measured distance is inconsistent
with stream predictions from models of the LMC/SMC interaction and infall into
the Milky Way that do not account for ram pressure and gas interaction with
Milky Way disk. The estimated age of the cluster is consistent with the time of
last passage of the leading arm gas through the Galactic midplane, and we
therefore speculate that this star-formation event was triggered by its the
last disk midplane passage. Most details of this idea remain a puzzle: the
Magellanic stream has low column density, the Milky Way disk at this large
radius has low gas density, and the relative velocity of the leading arm gas
and Milky Way gas is large. However it formed, the discovery of a young stellar
cluster in the Milky Way halo presents an interesting opportunity for study.
This cluster was discovered with Gaia astrometry and photometry alone, but
folow-up DECam photometry was crucial for measuring its properties. | astro-ph |
The Unpredictability of the Most Energetic Solar Events: Observations over the past two solar cycles show a highly irregular pattern
of occurrence for major solar flares, gamma-ray events, and solar energetic
particle (SEP) fluences. Such phenomena do not appear to follow the direct
indices of solar magnetic activity, such as the sunspot number. I show that
this results from the non-Poisson occurrence for the most energetic events.
This Letter also points out a particularly striking example of this
irregularity in a comparison between the declining phases of the recent two
solar cycles (1993-1995 and 2004-2006, respectively) and traces it through the
radiated energies of the flares, the associated SEP fluences, and the sunspot
areas. These factors suggest that processes in the solar interior involved with
the supply of magnetic flux up to the surface of the Sun have strong
correlations in space and time, leading to a complex occurrence pattern that is
presently unpredictable on timescales longer than active region lifetimes
(weeks) and not correlated well with the solar cycle itself. | astro-ph |
Strategies for spectroscopy on Extremely Large Telescopes. II - Diverse
field spectroscopy: The fields of view of Extremely Large Telescopes will contain vast numbers of
spatial sampling elements (spaxels) as their Adaptive Optics systems approach
the diffraction limit over wide fields. Since this will exceed the detection
capabilities of any realistic instrument, the field must be dilutely sampled to
extract spectroscopic data from selected regions of interest. The scientific
return will be maximised if the sampling pattern provides an adaptable
combination of separated independent spaxels and larger contiguous sub-fields,
seamlessly combining integral-field and multiple-object spectroscopy. We
illustrate the utility of this Diverse Field Spectroscopy (DFS) to cosmological
studies of galaxy assembly. We show how to implement DFS with an instrument
concept: the Celestial Selector. This integrates highly-multiplexed monolithic
fibre systems (MFS) and switching networks of the type currently available in
the telecommunications industry. It avoids bulky moving parts, whose
limitations were noted in Paper I. In Paper III we will investigate the
optimisation of such systems by varying the input-output mapping. | astro-ph |
The New Model of Chemical Evolution of r-process Elements Based on The
Hierarchical Galaxy Formation I: Ba and Eu: We investigate the chemical enrichment of r-process elements in the early
evolutionary stages of the Milky Way halo within the framework of hierarchical
galaxy formation using a semi-analytic merger tree. In this paper, we focus on
heavy r-process elements, Ba and Eu, of extremely metal-poor (EMP) stars and
give constraints on their astronomical sites. Our models take into account
changes of the surface abundances of EMP stars by the accretion of interstellar
matter (ISM). We also consider metal-enrichment of intergalactic medium (IGM)
by galactic winds and the resultant pre-enrichment of proto-galaxies. The trend
and scatter of the observed r-process abundances are well reproduced by our
hierarchical model with $\sim 10\%$ of core-collapse supernovae in low-mass end
($\sim 10M_{\odot}$) as a dominant r-process source and the star formation
efficiency of $\sim 10^{-10} \hbox{yr}^{-1}$. For neutron star mergers as an
r-process source, their coalescence timescale has to be $ \sim 10^7$yrs, and
the event rates $\sim 100$ times larger than currently observed in the Galaxy.
We find that the accretion of ISM is a dominant source of r-process elements
for stars with [Ba/H] < -3.5. In this model, a majority of stars at [Fe/H] < -3
are formed without r-process elements but their surfaces are polluted by the
ISM accretion. The pre-enrichment affects $\sim 4\%$ of proto-galaxies, and
yet, is surpassed by the ISM accretion in the surface of EMP stars. | astro-ph |
NuSTAR Tests of Sterile-Neutrino Dark Matter: New Galactic Bulge
Observations and Combined Impact: We analyze two dedicated NuSTAR observations with exposure ${\sim}190$ ks
located ${\sim}10^\circ$ from the Galactic plane, one above and the other
below, to search for x-ray lines from the radiative decay of sterile-neutrino
dark matter. These fields were chosen to minimize astrophysical x-ray
backgrounds while remaining near the densest region of the dark matter halo. We
find no evidence of anomalous x-ray lines in the energy range 5--20 keV,
corresponding to sterile neutrino masses 10--40 keV. Interpreted in the context
of sterile neutrinos produced via neutrino mixing, these observations provide
the leading constraints in the mass range 10--12 keV, improving upon previous
constraints in this range by a factor ${\sim}2$. We also compare our results to
Monte Carlo simulations, showing that the fluctuations in our derived limit are
not dominated by systematic effects. An updated model of the instrumental
background, which is currently under development, will improve NuSTAR's
sensitivity to anomalous x-ray lines, particularly for energies 3--5 keV. | astro-ph |
H.E.S.S. observations of the flaring gravitationally lensed galaxy PKS
1830-211: PKS 1830-211 is a known macrolensed quasar located at a redshift of z=2.5.
Its high-energy gamma-ray emission has been detected with the Fermi-LAT
instrument and evidence for lensing was obtained by several authors from its
high-energy data.
Observations of PKS 1830-211 were taken with the H.E.S.S. array of Imaging
Atmospheric Cherenkov Telescopes in August 2014, following a flare alert by the
Fermi- LAT collaboration. The H.E.S.S observations were aimed at detecting a
gamma-ray flare delayed by 20-27 days from the alert flare, as expected from
observations at other wavelengths.
More than twelve hours of good quality data were taken with an analysis
threshold of $\sim67$ GeV. The significance of a potential signal is computed
as a function of the date as well as the average significance over the whole
period. Data are compared to simultaneous observations by Fermi-LAT.
No photon excess or significant signal is detected. An upper limit on PKS
1830-211 flux above 67 GeV is computed and compared to the extrapolation of the
Fermi-LAT flare spectrum. | astro-ph |
X-ray Fading and Expansion in the "Miniature Supernova Remnant" of GK
Persei: We report on a second epoch of Chandra X-ray imaging spectroscopy of the
spatially-resolved old nova remnant GK Persei. An ACIS-S3 observation of 97.4
ks was conducted in November 2013 after a lapse of 13.8 years from the last
visit in 2000. The X-ray emitting nebula appeared more faint and patchy
compared with the first epoch. The flux decline was particularly evident in
fainter regions and the mean decline was 30-40 % in the 0.5-1.2 keV energy
band. A typical expansion of the brightest part of the remnant was 1.9 arcsec,
which corresponds to an expansion rate of 0.14 arcsec yr^{-1}. The soft X-ray
spectra extracted from both the 2000 and 2013 data can be explained by a
non-equilibrium ionization collisional plasma model convolved with interstellar
absorption, though do not allow us to constrain the origin of the flux
evolution. The plasma temperature has not significantly evolved since the 2000
epoch and we conclude that the fading of the X-ray emission is due largely to
expansion. This implies that recent expansion has been into a lower density
medium, a scenario that is qualitatively consistent with the structure of the
circumstellar environment photographed soon after the initial explosion more
than a century ago. Fainter areas are fading more quickly than brighter areas,
indicating that they are fainter because of a lower ambient medium density and
consequently more rapid expansion. | astro-ph |
Test magnetohydrostatic extrapolation with radiative MHD simulation of a
solar flare: Context. On the sun, the magnetic field vector is measured routinely only in
the photosphere. By using these photospheric measurements as boundary
condition, we developed the magnetohydrostatic (MHS) extrapolation to model the
solar atmosphere. The model makes assumption about the relative importance of
magnetic and non-magnetic forces. While the solar corona is force-free, this is
not the case in photosphere and chromosphere.
Aim. The model has been tested with an exact equilibria in \cite{zw18}. Here
we present a more challenging and realistic test of our model with radiative
MHD simulation of a solar flare.
Methods. By using the optimization method, the MHS model computes
self-consistently the magnetic field, plasma pressure and density. The
nonlinear force-free field (NLFFF) and gravity stratified atmosphere along the
field line are assumed as the initial condition of the optimization.
Results. Compared with NLFFF, the MHS model gives an improved magnetic field
not only in magnitude and direction, but also in the magnetic connectivity.
Besides, the MHS model is able to recover the main structure of the plasma in
the photosphere and chromosphere. | astro-ph |
Dust-trapping Rossby vortices in protoplanetary disks: One of the most challenging steps in planet formation theory is the one
leading to the formation of planetesimals of kilometre size. A promising
scenario involves the existence of vortices able to concentrate a large amount
of dust and grains in their centres. Up to now this scenario has been studied
mostly in 2D razor thin disks. A 3D study including, simultaneously, the
formation and resulting dust concentration of the vortices with vertical
settling, was still missing. The Rossby wave instability self-consistently
forms 3D vortices, which have the unique quality of presenting a large scale
vertical velocity in their centre. Here we aim to study how this newly
discovered effect can alter the dynamic evolution of the dust. We perform
global 3D simulations of the RWI in a radially and vertically stratified disk
using the code MPI-AMRVAC. After the growth phase of the instability, the gas
and solid phases are modelled by a bi-fluid approach, where the dust is
considered as a fluid without pressure. Both the drag force of the gas on the
dust and the back-reaction of the dust on the gas are included. Multiple grain
sizes from 1mm to 5cm are used with a constant density distribution. We obtain
in a short timescale a high concentration of the largest grains in the
vortices. Indeed, in 3 rotations the dust-to-gas density ratio grows from 10^-2
to unity leading to a concentration of mass up to that of Mars in one vortex.
The presence of the radial drift is also at the origin of a dust pile-up at the
radius of the vortices. Lastly, the vertical velocity of the gas in the vortex
causes the sedimentation process to be reversed, the mm size dust is lifted and
higher concentrations are obtained in the upper layer than in the mid-plane. | astro-ph |
Mirror dark matter discovered?: Recent astrophysical data indicates that dark matter shows a controversial
behaviour in galaxy cluster collisions. In case of the notorious Bullet
cluster, dark matter component of the cluster behaves like a collisionless
system. However, its behaviour in the Abell 520 cluster indicates a significant
self-interaction cross-section. It is hard for the WIMP based dark matter
models to reconcile such a diverse behaviour. Mirror dark matter models, on the
contrary, are more flexible and for them diverse behaviour of the dark matter
is a natural expectation. | astro-ph |
Effects of Quasi-Static Aberrations in Faint Companion Searches: We present the first results obtained at CFHT with the TRIDENT infrared
camera, dedicated to the detection of faint companions close to bright nearby
stars. The camera's main feature is the acquisition of three simultaneous
images in three wavelengths (simultaneous differential imaging) across the
methane absorption bandhead at 1.6 micron, that enables a precise subtraction
of the primary star PSF while keeping the companion signal. The main limitation
is non-common path aberrations between the three optical paths that slightly
decorrelate the PSFs. Two types of PSF calibrations are combined with the
differential simultaneous imaging technique to further attenuate the PSF:
reference star subtraction and instrument rotation to smooth aberrations. It is
shown that a faint companion with a DeltaH of 10 magnitudes would be detected
at 0.5 arcsec from the primary. | astro-ph |
Non-Parametric Analysis for the Dark Matter Density Evolution: In this paper, we investigate a potential departure in the standard dark
matter density evolution law, $\rho_{dm} = \rho_{dm,0}(1+z)^3$. The method
involves considering a deformed evolution model, denoted as $\rho_{dm} =
\rho_{dm,0}(1+z)^3f(z)$, and searching the presence of any deviation ($f(z)\neq
1$). As one may see, $f(z)$ is a general function that parametrizes a
digression from the standard law. We use data of baryon acoustic oscillations,
type I Supernovae luminosity distances, and galaxy cluster gas mass fraction
observations to reconstruct $f(z)$ by Gaussian process regression. Unlike
previous works, it enables us to investigate a possible deviation without using
a specific function to describe it. We have obtained $f(z)=1$, the standard
model scenario, within $2\sigma$ c.l. in all the considered cases. | astro-ph |
Time-evolution of Peak Energy and Luminosity Relation within Pulses for
GRB 061007: Probing Fireball Dynamics: We perform a time-resolved spectral analysis of bright, long Gamma-ray burst
GRB 061007 using Suzaku/WAM and Swift/BAT. Thanks to the large effective area
of the WAM, we can investigate the time evolution of the spectral peak energy,
Et_peak and the luminosity Lt_iso with 1-sec time resolution, and we find that
luminosity Lt_iso with 1-sec time resolution, and we find that the
time-resolved pulses also satisfy the Epeak-Liso relation, which was found for
the time-averaged spectra of other bursts, suggesting the same physical
conditions in each pulse. Furthermore, the initial rising phase of each pulse
could be an outlier of this relation with higher Et_peak value by about factor
2. This difference could suggest that the fireball radius expands by a factor
of 2-4 and/or bulk Lorentz factor of the fireball is decelerated by a factor of
4 during the initial phase, providing a new probe of the fireball dynamics in
real time. | astro-ph |
Exoplanet population inference and the abundance of Earth analogs from
noisy, incomplete catalogs: No true extrasolar Earth analog is known. Hundreds of planets have been found
around Sun-like stars that are either Earth-sized but on shorter periods, or
else on year-long orbits but somewhat larger. Under strong assumptions,
exoplanet catalogs have been used to make an extrapolated estimate of the rate
at which Sun-like stars host Earth analogs. These studies are complicated by
the fact that every catalog is censored by non-trivial selection effects and
detection efficiencies, and every property (period, radius, etc.) is measured
noisily. Here we present a general hierarchical probabilistic framework for
making justified inferences about the population of exoplanets, taking into
account survey completeness and, for the first time, observational
uncertainties. We are able to make fewer assumptions about the distribution
than previous studies; we only require that the occurrence rate density be a
smooth function of period and radius (employing a Gaussian process). By
applying our method to synthetic catalogs, we demonstrate that it produces more
accurate estimates of the whole population than standard procedures based on
weighting by inverse detection efficiency. We apply the method to an existing
catalog of small planet candidates around G dwarf stars (Petigura et al. 2013).
We confirm a previous result that the radius distribution changes slope near
Earth's radius. We find that the rate density of Earth analogs is about 0.02
(per star per natural logarithmic bin in period and radius) with large
uncertainty. This number is much smaller than previous estimates made with the
same data but stronger assumptions. | astro-ph |
Computed Rotational Collision Rate Coefficients for Recently Detected
Anionic Cyanopolyynes: We report new results from quantum calculations of energy-transfer processes
taking place in interstellar environments and involving two newly observed
molecular species: C$_5$N$^-$ and C$_7$N$^-$ in collision with He atoms and the
p-H$_2$ molecules. These species are part of the anionic molecular chains
labeled as cyanopolyynes which have been observed over the years in
molecule-rich Circumstellar Envelopes and in molecular clouds. In the present
work, we first carry out new $ab$ $initio$ calculations for the C$_7$N$^-$
interaction potential with He atom and then obtain state-to-state rotationally
inelastic cross sections and rate coefficients involving the same transitions
which have been observed experimentally by emission in the interstellar medium
(ISM) from both of these linear species. For the C$_5$N$^-$/He system we extend
the calculations already published in our earlier work (see reference below) to
compare more directly the two molecular anions. We extend further the quantum
calculations by also computing in this work collision rate coefficients for the
hydrogen molecule interacting with C5N$^-$, using our previously computed
interaction potential. Additionally, we obtain the same rate coefficients for
the C$_7$N$^-$/H$_2$ system by using a scaling procedure that makes use of the
new C$_7$N$^-$/He rate coefficients, as discussed in detail in the present
paper. Their significance in affecting internal state populations in ISM
environments where the title anions have been found is analyzed by using the
concept of critical density indicators. Finally, similarities and differences
between such species and the comparative efficiency of their collision rate
coefficients are discussed. These new calculations suggest that, at least for
the case of these longer chains, the rotational populations could reach local
thermal equilibrium conditions within their observational environments. | astro-ph |
Line-of-sight Effects on Observability of Kink and Sausage Modes in
Coronal Structures with Imaging Telescopes: Kink modes of solar coronal structures, perturbing the loop in the direction
along the line-of-sight (LOS), can be observed as emission intensity
disturbances propagating along the loop provided the angle between the LOS and
the structure is not ninety degrees. The effect is based upon the change of the
column depth of the loop (along the LOS) by the wave. The observed amplitude of
the emission intensity variations can be larger than the actual amplitude of
the wave by a factor of two and there is an optimal angle maximizing the
observed amplitude. For other angles this effect can also attenuate the
observed wave amplitude. The observed amplitude depends upon the ratio of the
wave length of kink perturbations to the width of the structure and on the
angle between the LOS and the axis of the structure. Sausage modes are always
affected negatively from the observational point of view, as the observed
amplitude is always less than the actual one. This effect should be taken into
account in the interpretation of wave phenomena observed in the corona with
space-borne and ground-based imaging telescopes. | astro-ph |
Differential Rotation in Magnetized and Non-magnetized Stars: Effects of magnetic field on stellar differential rotation are studied by
comparing magnetohydrodynamic (MHD) models and their hydrodynamic (HD)
counterparts in the broad range of rotation rate and in varying initial
rotation profile. Fully-compressible MHD simulations of rotating penetrative
convection are performed in a full-spherical shell geometry. Critical
conditions for the transition of the differential rotation between faster
equator (solar-type) and slower equator (anti-solar type) are explored with
focusing on the "Rossby number (${\rm Ro}$)" and the "convective Rossby number
(${\rm Ro}_{\rm conv}$)". It is confirmed that the transition is more gradual
and the critical value for it is higher in the MHD model than the HD model in
the view of the ${\rm Ro}_{\rm conv}$-dependence. The rotation profile shows,
as observed in earlier studies, the bistability near the transition in the HD
model, while it disappears when allowing the growth of magnetic fields except
for the model with taking anti-solar type solution as the initial condition. We
find that the transition occurs at ${\rm Ro} \simeq 1$ both in the MHD and HD
models independently of the hysteresis. Not only the critical value, the
sharpness of the transition is also similar between the two models in the view
of the ${\rm Ro}$-dependence. The influences of the dynamo-generated magnetic
field and/or the hysteresis on convective motion are reflected in the ${\rm
Ro}$. This would be the reason why the transition is unified in the view of the
${\rm Ro}$-dependence. We finally discuss the ${\rm Ro}$-dependence of magnetic
dynamo activities with emphasis on its possible relation to the kinetic
helicity profile. | astro-ph |
Hubble Space Telescope Grism Spectroscopy of Extreme Starbursts Across
Cosmic Time: The Role of Dwarf Galaxies in the Star Formation History of the
Universe: Near infrared slitless spectroscopy with the Wide Field Camera 3, onboard the
Hubble Space Telescope, offers a unique opportunity to study low-mass galaxy
populations at high-redshift ($z\sim$1-2). While most high$-z$ surveys are
biased towards massive galaxies, we are able to select sources via their
emission lines that have very-faint continua. We investigate the star formation
rate (SFR)-stellar mass ($M_{\star}$) relation for about 1000 emission-line
galaxies identified over a wide redshift range of $0.3 \lesssim z \lesssim
2.3$. We use the H$_{\alpha}$ emission as an accurate SFR indicator and correct
the broadband photometry for the strong nebular contribution to derive accurate
stellar masses down to $M_{\star} \sim 10^{7} M_{\odot}$. We focus here on a
subsample of galaxies that show extremely strong emission lines (EELGs) with
rest-frame equivalent widths ranging from 200 to 1500 \AA. This population
consists of outliers to the normal SFR-$M_{\star}$ sequence with much higher
specific SFRs ($> 10$ Gyr$^{-1}$). While on-sequence galaxies follow a
continuous star formation process, EELGs are thought to be caught during an
extreme burst of star formation that can double their stellar mass in less than
$100$ Myr. The contribution of starbursts to the total star formation density
appears to be larger than what has been reported for more massive galaxies in
previous studies. In the complete mass range $8.2 <$ log($M_{\star}/M_{\odot}$)
$< 10$ and a SFR lower completeness limit of about 2 $M_{\odot}$ yr$^{-1}$ (10
$M_{\odot}$ yr$^{-1}$) at $z\sim1$ ($z \sim 2$), we find that starbursts having
EW$_{rest}$(H$_{\alpha}$)$>$ 300, 200, and 100 A contribute up to $\sim13$, 18,
and 34 %, respectively, to the total SFR of emission-line selected sample at
$z\sim1-2$. The comparison with samples of massive galaxies shows an increase
in the contribution of starbursts towards lower masses. | astro-ph |
Simulating young star clusters with primordial binaries: We simulate a cluster of 144179 stars including 13107 primordial hard
binaries (10% of the total number of single stars and binary centers of mass),
using direct integration of the equations of motion of all stars and binaries
and incorporating the effects of stellar and binary evolution. The initial
conditions are representative of young dense star clusters in the Local Group
and other nearby galaxies like the Antennae and M82.
We find that the early phase of core collapse, driven by mass segregation, is
not appreciably delayed by the presence of a large number of hard binaries. By
the end of the simulation, at an age of 115Myr, the cluster radius has expanded
by about a factor of two. This may be explained as adiabatic expansion driven
by the loss (via stellar evolution) of about 40% of the initial total mass.
Binary dynamics apparently has little effect on the early cluster expansion.
During the evolution, the total binary fraction drops at a roughly constant
rate of about 0.01% per Myr. The fraction of very hard binaries, however
increases at about 0.025% per Myr. By the end of the simulation the cluster
contains 37 binaries containing at least one black hole; roughly half (17) of
these contain two black holes. | astro-ph |
A Gradual Decline of Star Formation since Cluster In-fall: New Kinematic
Insights into Environmental Quenching at 0.3 $< z <$ 1.1: The environments where galaxies reside crucially shape their star formation
histories. We investigate a large sample of 1626 cluster galaxies located
within 105 galaxy clusters spanning a large range in redshift ($0.26 < z <
1.13)$. The galaxy clusters are massive (M$_{500} \gtrsim
2\times10^{14}$M$_{\odot}$), and are uniformly selected from the SPT and ACT
Sunyaev-Zel'dovich (SZ) surveys. With spectra in-hand for thousands of cluster
members, we use galaxies' position in projected phase space as a proxy for
their in-fall times, which provides a more robust measurement of environment
than quantities such as projected cluster-centric radius. We find clear
evidence for a gradual age increase of the galaxy's mean stellar populations
($\sim$ 0.71 $\pm$ 0.4 Gyr based on a 4000 $\r{A}$ break, $\rm D_{\rm n}4000$)
with the time spent in the cluster environment. This environmental quenching
effect is found regardless of galaxy luminosity (faint or bright) and redshift
(low-$z$ or high-$z$), although the exact stellar age of galaxies depends on
both parameters at fixed environmental effects. Such a systematic increase of
$\rm D_{\rm n}4000$ with in-fall proxy would suggest that galaxies that were
accreted into hosts earlier were quenched earlier, due to longer exposure to
environmental effects such as ram pressure stripping and starvation. Compared
to the typical dynamical time scales of $1-3$ Gyr of cluster galaxies, the
relatively small age increase ($\sim$ 0.71 $\pm$ 0.4 Gyr) found in our sample
galaxies seems to suggest that a slow environmental process such as starvation
is the dominant quenching pathway. Our results provide new insights into
environmental quenching effects spanning a large range in cosmic time ($\sim
5.2$ Gyr, $z=0.26$--1.13) and demonstrate the power of using a
kinematically-derived in-fall time proxy. | astro-ph |
Kreutz Sungrazers: Summary of Recent Modeling and Orbits of the SOHO
Objects: I summarize and streamline the results of recent modeling of the orbital
evolution and cascading fragmentation of the Kreutz sungrazers. The model
starts with Aristotle's comet -- the progenitor whose nucleus is assumed to be
a contact binary -- splitting near aphelion into the two lobes and concludes
with the SOHO dwarf objects as the end products of the fragmentation process.
The Great March Comet of 1843, a member of Population I, and the Great
September Comet of 1882, a member of Population II, are deemed the largest
surviving masses of the lobes. I establish that the Kreutz system consists
currently of nine populations, one of which -- associated with comet Pereyra --
is a side branch of Population I. The additions to the Kreutz system proposed
as part of the new model are the daylight comets of AD 363, recorded by the
Roman historian Ammianus Marcellinus, and the Chinese comets of September 1041
and September 1138, both listed in Ho's catalogue. The comets of 363 are the
first-generation fragments, the latter -- together with the Great Comet of 1106
-- the second-generation fragments. Attention is directed toward the
populations' histograms of perihelion distance of the SOHO sungrazers and the
plots of this distance as a function of the longitude of the ascending node.
Arrival of bright, naked-eye Kreutz sungrazers in the coming decades is
predicted. | astro-ph |
The Host Galaxy and Rapidly Evolving Broad-line Region in the
Changing-look Active Galactic Nucleus 1ES 1927+654: Changing-look active galactic nuclei (AGNs) present an important laboratory
to understand the origin and physical properties of the broad-line region
(BLR). We investigate follow-up optical spectroscopy spanning $\sim 500$ days
after the outburst of the changing-look AGN 1ES\,1927+654. The emission lines
displayed dramatic, systematic variations in intensity, velocity width,
velocity shift, and symmetry. Analysis of optical spectra and multi-band images
indicate that the host galaxy contains a pseudobulge and a total stellar mass
of $3.56_{-0.35}^{+0.38} \times 10^{9}\, M_\odot$. Enhanced continuum radiation
from the outburst produced an accretion disk wind, which condensed into BLR
clouds in the region above and below the temporary eccentric disk. Broad Balmer
lines emerged $\sim 100$ days after the outburst, together with an unexpected,
additional component of narrow-line emission. The newly formed BLR clouds then
traveled along a similar eccentric orbit ($e \approx 0.6$). The Balmer
decrement of the BLR increased by a factor of $\sim 4-5$ as a result of secular
changes in cloud density. The drop in density at late times allowed the
production of \hei\ and \heii\ emission. The mass of the black hole cannot be
derived from the broad emission lines because the BLR is not virialized.
Instead, we use the stellar properties of the host galaxy to estimate
$M_\mathrm{BH} = 1.38_{-0.66}^{+1.25} \times 10^{6}\, M_\odot$. The nucleus
reached near or above its Eddington limit during the peak of the outburst. We
discuss the nature of the changing-look AGN 1ES\,1927+654 in the context of
other tidal disruption events. | astro-ph |
Unidentified 3EG gamma-ray sources at low galactic latitude: We present a study on the possible association of unidentified $\gamma$-ray
sources in the Third EGRET (3EG) catalog with different types of galactic
objects such as Wolf-Rayet and Of stars, supernova remnants (SNRs), and OB
associations (considered as pulsar tracers). We have made use of numerical
simulations of galactic populations of $\gamma$-ray point sources in order to
determine the statistical significance of the positional coincidences. New
constraints on pure chance association are presented for SNRs and OB
associations, and it is shown that massive stars present marginally significant
correlation with 3EG sources at a $3\sigma$ level. | astro-ph |
Modeling the MgI from the NUV to MIR: I. The Solar Case: Semi-empirical models of the solar atmosphere are used to study the radiative
environment of any planet in our solar system. There is a need for reliable
atomic data for neutral atoms and ions in the atmosphere to obtain improved
calculated spectra. Atomic parameters are crucial to computing the correct
population of elements through the whole stellar atmosphere. Although there is
a very good agreement between the observed and calculated spectra for the Sun,
there is still a mismatch in several spectral ranges due to the lack of atomic
data and its inaccuracies, particularly for neutrals like Mg I.
To correctly represent many spectral lines of Mg I from the near-UV to the
mid-IR is necessary to add and update the atomic data involved in the atomic
processes that drive their formation. The improvements to the Mg I atomic model
are as follows: i) 127 strong lines, including their broadening data, were
added. ii) To obtain these lines, we increased from 26 to 85 the number of
energy levels. iii) Photoionization cross-section parameters were added and
updated. iv) Effective Collision Strengths (ECS) parameters were updated for
the first 25 levels using the existing data from the convergent close-coupling
(CCC) calculations. One of the most significant changes in our model is given
by the new ECS parameters for transitions involving levels between 26 and 54,
which were computed with a multi-configuration Breit-Pauli distorted-wave (DW)
method.
More than one hundred transitions were added to our calculations, increasing
our capability of reproducing important features observed in the solar spectra.
We found a remarkable improvement in matching the solar spectra for wavelengths
higher than 3 um when our new DW ECS data was used in the model. | astro-ph |
Magnitude Offset between Lensed Stars and Observed Stars - a New Probe
of the Structure of the Galactic Bar: We propose a new method that can be used to constrain the properties of the
Galactic bar (bulge). If the majority of the lensing objects are in the
Galactic bar, then we predict a systematic offset in the apparent magnitude
between lensed stars and all observed stars. Using OGLE color-magnitude diagram
data we model this effect in the region of the diagram dominated by bulge red
clump stars and find that for some models of the Galactic bar the expected
offset in the apparent magnitude may be as large as $0.2 mag$. About 100 lensed
stars in the red clump region of the color-magnitude diagram is needed to
unambiguously detect this effect, a number within the reach of current
microlensing projects. We find a good correlation between the extent of the bar
along the line of sight and the expected magnitude offset. We also obtain a
constraint for the extent of the bar along the line of sight using the observed
luminosity function for the red clump stars. | astro-ph |
Ultrahigh energy neutrinos scattering off relic light neutrinos to
explain UHECR above GZK cut off and thin blazars: UHE neutrinos may transfer highest cosmic-rays energies overcoming
$2.75K^\circ$ BBR and radio-waves opacities (the GZK cut off) from most distant
AGN sources at the age of the Universe. These UHE $\nu$ might scatter onto
those (light and cosmological) relic neutrinos clustered around our galactic
halo or nearby neutrino hot dark halo clustered around the AGN blazar and its
jets. The branched chain reactions from a primordial nucleon (via photo
production of pions and decay to UHE neutrinos) toward the consequent beam dump
scattering on galactic relic neutrinos is at least three order of magnitude
more efficient than any known neutrino interactions with Earth atmosphere or
direct nucleon propagation. Therefore the rarest cosmic rays (as the 320 EeV
event) might be originated at far $(\tilde{>} 100 Mpc)$ distances (as Seyfert
galaxy MCG 8-11-11); its corresponding UHE radiation power is in agreement with
the observed one in MeV gamma energies. The final chain products observed on
Earth by the Fly's Eye and AGASA detectors might be mainly neutron and
anti-neutrons and delayed, protons and anti-protons at symmetric off-axis
angles. These hadronic products are most probably secondaries of $W^+ W^-$ or
$ZZ$ pair productions and might be consistent with the last AGASA discoveries
of doublets and one triplet event. | astro-ph |
Impact of stochastic gas motions on galaxy cluster abundance profiles: The impact of stochastic gas motions on the metal distribution in cluster
core is evaluated. Peaked abundance profiles are a characteristic feature of
clusters with cool cores and abundance peaks are likely associated with the
brightest cluster galaxies (BCGs) which dwell in cluster cores. The width of
the abundance peaks is however significantly broader than the BCG light
distribution, suggesting that some gas motions are transporting metals
originating from within the BCG. Assuming that this process can be treated as
diffusive and using the brightest X-ray cluster A426 (Perseus) as an example,
we estimate that a diffusion coefficient of the order of $2 10^{29} {\rm cm^2
s^{-1}}$ is needed to explain the width of the observed abundance profiles.
Much lower (higher) diffusion coefficients would result in too peaked (too
shallow) profiles. Such diffusion could be produced by stochastic gas motions
and our analysis provides constraints on the product of their characteristic
velocity and their spatial coherence scale. We speculate that the activity of
the supermassive black hole of the BCG is driving the stochastic gas motions in
cluster cores. When combined with the assumption that the dissipation of the
same motions is a key gas heating mechanism, one can estimate both the velocity
and the spatial scale of such a diffusive processes. | astro-ph |
Molecular gas streamers feeding and obscuring the active nucleus of
NGC1068: We report the first direct observations of neutral, molecular gas streaming
in the nucleus of NGC1068 on scales of <30 pc using SINFONI near-infrared
integral field spectroscopy. At a resolution of 0.075", the flux map of 2.12
$\mu$m 1-0 S(1) molecular hydrogen emission around the nucleus in the central
arcsec reveals two prominent linear structures leading to the AGN from the
north and south. The kinematics of the gas in these features are dominated by
non-circular motions and indicate that material is streaming towards the
nucleus on highly elliptical or parabolic trajectories whose orientations are
compatible with that of the disk plane of the galaxy. We interpret the data as
evidence for fueling of gas to the central region. The radial transport rate
from ~30 pc to a few parsec from the nucleus is ~15 M$_\sun$ yr$^{-1}$. One of
the infalling clouds lies directly in front of the central engine. We interpret
it as a tidally disrupted streamer that forms the optically thick outerpart of
an amorphous clumpy molecular/dusty structure which contributes to the nuclear
obscuration. | astro-ph |
The Hemispheric Asymmetry of Solar Activity During the Twentieth Century
and the Solar Dynamo: We believe the Babcock--Leighton process of poloidal field generation to be
the main source of irregularity in the solar cycle. The random nature of this
process may make the poloidal field in one hemisphere stronger than that in the
other hemisphere at the end of a cycle. We expect this to induce an asymmetry
in the next sunspot cycle. We look for evidence of this in the observational
data and then model it theoretically with our dynamo code. Since actual polar
field measurements exist only from 1970s, we use the polar faculae number data
recorded by Sheeley (1991) as a proxy of the polar field and estimate the
hemispheric asymmetry of the polar field in different solar minima during the
major part of the twentieth century. This asymmetry is found to have a
reasonable correlation with the asymmetry of the next cycle. We then run our
dynamo code by feeding information about this asymmetry at the successive
minima and compare with observational data. We find that the theoretically
computed asymmetries of different cycles compare favourably with the
observational data, the correlation coefficient being 0.73. Due to the coupling
between the two hemispheres, any hemispheric asymmetry tends to get attenuated
with time. The hemispheric asymmetry of a cycle either from observational data
or from theoretical calculation statistically tends to be less than the
asymmetry in the polar field (as inferred from the faculae data) in the
preceding minimum. This reduction factor turns out to be 0.38 and 0.60
respectively in observational data and theoretical simulation. | astro-ph |
Super-horizon second-order perturbations for cosmological random
fluctuations and the Hubble-constant problem: The super-horizon second-order density perturbations corresponding to
cosmological random fluctuations are considered, their non-vanishing spatial
average is shown to be useful in solving the serious problem on the
cosmological tension between measured Hubble constants at present and those at
the early stage, and the difference from previous works on the backreaction is
discussed. | astro-ph |
Why Low-Mass Black-Hole Binaries Are Transient: We consider transient behavior in low-mass X-ray binaries. In short-period
neutron-star systems (orbital period less than ~ 1d) irradiation of the
accretion disk by the central source suppresses this except at very low mass
transfer rates. Formation constraints however imply that a significant fraction
of these neutron star systems have nuclear-evolved main-sequence secondaries
and thus mass transfer rates low enough to be transient. But most short-period
low-mass black-hole systems will form with unevolved main-sequence companions
and have much higher mass transfer rates. The fact that essentially all of them
are nevertheless transient shows that irradiation is weaker, as a direct
consequence of the fundamental black-hole property - the lack of a hard stellar
surface. | astro-ph |
Revisiting dynamical friction: the role of global modes and local wakes: The orbital decay of a perturber within a larger system plays a key role in
the dynamics of many astrophysical systems -- from nuclear star clusters or
globular clusters in galaxies, to massive black holes in galactic nuclei, to
dwarf galaxy satellites within the dark matter halos of more massive galaxies.
For many decades, there have been various attempts to determine the underlying
physics and time-scales of the drag mechanism, ranging from the local dynamical
friction approach to descriptions based on the back-reaction of global modes
induced in the background system. We present ultra-high-resolution $N$-body
simulations of massive satellites orbiting a Milky Way-like galaxy (with $>
10^8$ particles), that appear to capture both the local "wake" and the global
"mode" induced in the primary halo. We address directly the mechanism of
orbital decay from the combined action of local and global perturbations and
specifically analyze where the bulk of the torque originates. | astro-ph |
Resonant Signatures of Heavy Scalar Fields in the Cosmic Microwave
Background: We investigate the possibility that a heavy scalar field, whose mass exceeds
the Hubble scale during inflation, could leave non-negligible signatures in the
Cosmic Microwave Background (CMB) temperature anisotropy power spectrum through
the parametric resonance between its background oscillations and the inflaton
fluctuations. By assuming the heavy scalar field couples with the inflaton
derivatively, we show that the resonance can be efficient without spoiling the
slow-roll inflation. The primordial power spectrum modulated by the resonance
has a sharp peak at a specific scale and could be an origin of the anomalies
observed in the angular power spectrum of the CMB. In some values of
parameters, the modulated spectrum can fit the observed data better than the
simple power-law power spectrum, though the resultant improvement of the fit is
not large enough and hence other observations such as non-Gaussianity are
necessary to confirm that the CMB anomalies are originated from the resonant
effect of the heavy scalar field. The resonant signatures can provide an
opportunity to observe heavy degrees of freedom during inflation and improve
our understanding of physics behind inflation. | astro-ph |
Orbital X-ray modulation study of three Supergiant HMXBs: We present the orbital X-ray modulation study of three high mass X- ray
binary systems, IGR J18027-2016, IGR J18483-0311 and IGR J16318-4848 using data
obtained with RXTE-ASM, Swift-BAT and INTEGRAL-ISGRI. Using the long term light
curves of the eclipsing HMXB IGR J18027-2016, obtained with Swift-BAT in the
energy range 15-50 keV and INTEGRAL-ISGRI in the energy range 22-40 keV, we
have determined three new mid eclipse times. The newly determined mid eclipse
times together with the known values were used to derive an accurate value of
the orbital period of 4.5693(4) d at MJD 52168 and an upper limit of
3.9(1.2)x10^-7 d d^-1 on the period derivative. We have also accurately
determined an orbital period of 18.5482(88) d for the intermediate system IGR
J18483-0311, which displays an unusual behaviour and shares many properties
with the known SFXTs and persistent supergiant systems. This is a transient
source and the outbursts occur intermittently at intervals of 18.55 d.
Similarly, in the third supergiant system, IGR J16318-4848, we have found that
the outbursts are separated by intervals of 80 d or its multiples, suggesting a
possible orbital period. | astro-ph |
Massive Galaxy Mergers Have Distinctive Global HI Profiles: The global 21 cm HI emission-line profile of a galaxy encodes valuable
information on the spatial distribution and kinematics of the neutral atomic
gas. Galaxy interactions significantly influence the HI disk and imprint
observable features on the integrated HI line profile. In this work, we study
the neutral atomic gas properties of galaxy mergers selected from the Great
Observatories All-sky LIRG Survey. The HI spectra come from new observations
with the Five-hundred-meter Aperture Spherical Telescope and from a collection
of archival data. We quantify the HI profile of the mergers with a newly
developed method that uses the curve-of-growth of the line profile. Using a
control sample of non-merger galaxies carefully selected to match the stellar
mass of the merger sample, we show that mergers have a larger proportion of
single-peaked HI profiles, as well as a greater tendency for the HI central
velocity to deviate from the systemic optical velocity of the galaxy. By
contrast, the HI profiles of mergers are not significantly more asymmetric than
those of non-mergers. | astro-ph |
Bayes-X: a Bayesian inference tool for the analysis of X-ray
observations of galaxy clusters: We present the first public release of our Bayesian inference tool, Bayes-X,
for the analysis of X-ray observations of galaxy clusters. We illustrate the
use of Bayes-X by analysing a set of four simulated clusters at z=0.2-0.9 as
they would be observed by a Chandra-like X-ray observatory. In both the
simulations and the analysis pipeline we assume that the dark matter density
follows a spherically-symmetric Navarro, Frenk and White (NFW) profile and that
the gas pressure is described by a generalised NFW (GNFW) profile. We then
perform four sets of analyses. By numerically exploring the joint probability
distribution of the cluster parameters given simulated Chandra-like data, we
show that the model and analysis technique can robustly return the simulated
cluster input quantities, constrain the cluster physical parameters and reveal
the degeneracies among the model parameters and cluster physical parameters. We
then analyse Chandra data on the nearby cluster, A262, and derive the cluster
physical profiles. To illustrate the performance of the Bayesian model
selection, we also carried out analyses assuming an Einasto profile for the
matter density and calculated the Bayes factor. The results of the model
selection analyses for the simulated data favour the NFW model as expected.
However, we find that the Einasto profile is preferred in the analysis of A262.
The Bayes-X software, which is implemented in Fortran 90, is available at
http://www.mrao.cam.ac.uk/facilities/software/bayesx/. | astro-ph |
The Flux Auto- and Cross-Correlation of the Lyman-alpha Forest. I.
Spectroscopy of QSO Pairs with Arcminute Separations and Similar Redshifts: The Lyman-alpha forest has opened a new redshift regime for cosmological
investigation. At z > 2 it provides a unique probe of cosmic geometry and an
independent constraint on dark energy that is not subject to standard candle or
ruler assumptions. In Paper I of this series on using the Lyman-alpha forest
observed in pairs of QSOs for a new application of the Alcock-Paczynski test,
we present and discuss the results of a campaign to obtain moderate-resolution
spectroscopy (FWHM ~ 2.5 Angstroms) of the Lyman-alpha forest in pairs of QSOs
with small redshift differences (Delta z < 0.25, z > 2.2) and arcminute
separations (< 5'). This data set, composed of seven individual QSOs, 35 pairs,
and one triplet, is also well-suited for future investigations of the coherence
of Lyman-alpha absorbers on ~ 1 Mpc transverse scales and the transverse
proximity effect. We note seven revisions for previously published QSO
identifications and/or redshifts. | astro-ph |
Stellar disks of Collisional Ring Galaxies I. New multiband images,
Radial intensity and color profiles, and confrontation with N-body
simulations: We present new multi-band imaging data in the optical (BVRI and Halpha) and
near infrared bands (JHK) of 15 candidate ring galaxies from the sample of
Appleton & Marston (1997). We use these data to obtain color composite images,
global magnitudes and colors of both the ring galaxy and its companion(s), and
radial profiles of intensity and colors. We find that only nine of the observed
galaxies have multi-band morphologies expected for the classical collisional
scenario of ring formation, indicating the high degree of contamination of the
ring galaxy sample by galaxies without a clear ring morphology. The radial
intensity profiles, obtained by masking the off-centered nucleus, peak at the
position of the ring, with the profiles in the continuum bands broader than
that in the Halpha line. The images as well as the radial intensity and color
profiles clearly demonstrate the existence of the pre-collisional stellar disk
outside the star-forming ring, which is in general bluer than the disk internal
to the ring. The stellar disk seems to have retained its size, with the disk
outside the ring having a shorter exponential scale length as compared to the
values expected in normal spiral galaxies of comparable masses. The rings in
our sample of galaxies are found to be located preferentially at around
half-way through the stellar disk. The most likely reason for this preference
is bias against detecting rings when they are close to the center (they would
be confused with the resonant rings), and at the edge of the disk the gas
surface density may be below the critical density required for star formation.
Most of the observed characteristics point to relatively recent collisions (<80
Myr ago) according to the N-body simulations of Gerber et al. (1996). | astro-ph |
SELENA: Semi-analytical Integrator for Lunar Artificial Satellites: The present report summarizes the main theory and implementation steps
associated with SELENA (SEmi-anaLytical intEgrator for a luNar Artificial
satellite), i.e. the semi-analytical propagator for lunar satellite orbits
developed in the framework of the the R&T R-S20/BS-0005-062 CNES research
activity in collaboration between the University of Padova (UniPd), and the
Aristotle University of Thessaloniki (AUTH), both acting as contractors with
CNES.
A detailed account of the method, algorithms and symbolic manipulations
employed in the derivation of the final theory are described in detail in this
report: they invoke the use of canonical perturbation theory in the form of Lie
series computed in `closed form', i.e., without expansions in the satellite's
orbital eccentricity. These algorithms are provided in the form of a symbolic
package accompanying the present report. The package contains symbolic algebra
programs, as well as explicit data files containing the final Hamiltonian,
equations of motion and transformations (i.e. the coefficients and exponents of
each variable in each term) leading to the averaging of the short-periodic
terms in the satellite's equations of motion. | astro-ph |
Comparison of numerical methods for computing the repeated Compton
scattering of photons in isotropic media: Repeated Compton scattering of photons with thermal electrons is one of the
fundamental processes at work in many astrophysical plasma. Solving the exact
evolution equations is hard and one common simplification is based on
Fokker-Planck (FP) approximations of the Compton collision term. Here we carry
out a detailed numerical comparison of several FP approaches with the exact
scattering kernel solution for a range of test problems assuming isotropic
media and thermal electrons at various temperatures. The Kompaneets equation,
being one of the most widely used FP approximations, fails to account for
Klein-Nishina corrections and enhanced Doppler boosts and recoil at high
energies. These can be accounted for with an alternative FP approach based on
the exact first and second moments of the scattering kernel. As demonstrated
here, the latter approach works very well in dilute media, but inherently fails
to reproduce the correct equilibrium solution in the limit of many scattering.
Conditions for the applicability of the FP approximations are clarified,
overall showing that the Kompaneets equation provides the most robust
approximation to the full problem, even if inaccurate in many cases. We close
our numerical analysis by briefly illustrating the solutions for the spectral
distortions of the cosmic microwave background (CMB) after photon injection at
redshift $z\lesssim 10^5$, when double Compton and Bremsstrahlung emission can
be omitted. We demonstrate that the exact treatment using the scattering kernel
computed with {\tt CSpack} is often needed. This work should provide an
important step towards accurate computations of the CMB spectral distortions
from high-energy particle cascades. | astro-ph |
Burst and Outburst Characteristics of Magnetar 4U 0142+61: We have compiled the most comprehensive burst sample from magnetar 4U
0142+61, comprising 27 bursts from its three burst-active episodes in 2011,
2012 and the latest one in 2015 observed with Swift/BAT and Fermi/GBM. Bursts
from 4U 0142+61 morphologically resemble typical short bursts from other
magnetars. However, 4U 0142+61 bursts are less energetic compared to the bulk
of magnetar bursts. We uncovered an extended tail emission following a burst on
2015 February 28, with a thermal nature, cooling over a time-scale of several
minutes. During this tail emission, we also uncovered pulse peak phase aligned
X-ray bursts , which could originate from the same underlying mechanism as that
of the extended burst tail, or an associated and spatially coincident but
different mechanism. | astro-ph |
Multiple BeppoSAX Observations of IC 4329A to Probe the Origin of the
Compton Reflection Component in Seyfert 1 Galaxies: IC 4329A is the brightest known Seyfert galaxy in hard (~2-30 keV) X-rays and
is likely to be representative of Seyfert 1 galaxies as a class. A recent 100
ks BeppoSAX observation (Perola et al. 1999) clearly confirmed the presence of
a warm absorber, a reflection component (R~0.6), and a high-energy cut-off in
the power law at Ec~270 keV. Its richness in spectral features, combined with
its large flux (~1.6 x 10**-10 erg/cm2s between 2-10 keV), make this target
ideal for multiple observations (in particular with BeppoSAX) to search for
spectral variations. Results obtained from 3 follow-up observations (40 ks
each) are presented here. The first and most important goal of this study was
to probe the origin of the Compton reflection component observed in Seyfert
galaxies by monitoring the variability of the reflection continuum and FeK line
in response to primary continuum variations. The second goal was to search for
variability in the high energy cutoff. We obtain however no conclusive results
on any of these issues. In fact, all four observations unfortunately caught the
source at almost the same flux, showing only little, and marginal, spectral
changes between different observations. | astro-ph |
Toward a tomographic analysis of the cross-correlation between Planck
CMB lensing and H-ATLAS galaxies: We present an improved and extended analysis of the cross-correlation between
the map of the Cosmic Microwave Background (CMB) lensing potential derived from
the \emph{Planck} mission data and the high-redshift galaxies detected by the
\emph{Herschel} Astrophysical Terahertz Large Area Survey (H-ATLAS) in the
photometric redshift range $z_{\rm ph} \ge 1.5$. We compare the results based
on the 2013 and 2015 \textit{Planck} datasets, and investigate the impact of
different selections of the H-ATLAS galaxy samples. Significant improvements
over our previous analysis have been achieved thanks to the higher
signal-to-noise ratio of the new CMB lensing map recently released by the
\textit{Planck} collaboration. The effective galaxy bias parameter, $b$, for
the full galaxy sample, derived from a joint analysis of the cross-power
spectrum and of the galaxy auto-power spectrum is found to be $b =
3.54^{+0.15}_{-0.14}$. Furthermore, a first tomographic analysis of the
cross-correlation signal is implemented, by splitting the galaxy sample into
two redshift intervals: $1.5 \le z_{\rm ph} < 2.1$ and $z_{\rm ph}\ge 2.1$. A
statistically significant signal was found for both bins, indicating a
substantial increase with redshift of the bias parameter: $b=2.89\pm0.23$ for
the lower and $b=4.75^{+0.24}_{-0.25}$ for the higher redshift bin.
Consistently with our previous analysis we find that the amplitude of the cross
correlation signal is a factor of $1.45^{+0.14}_{-0.13}$ higher than expected
from the standard $\Lambda$CDM model for the assumed redshift distribution. The
robustness of our results against possible systematic effects has been
extensively discussed although the tension is mitigated by passing from 4 to
3$\sigma$. | astro-ph |
Application of chaos indicators in the study of dynamics of S-type
extrasolar planets in stellar binaries: The orbits of two individual planets in two known binary star systems, \gamma
Cephei and HD 196885 are numerically integrated using various numerical
techniques to assess the chaotic or quasi-periodic nature of the dynamical
system considered. The Hill stability (HS) function which measures the orbital
perturbation of a planet around the primary star due to the secondary star is
calculated for each system. The maximum Lyapunov exponent (MLE) time series are
generated to measure the divergence/convergence rate of stable manifolds, which
are used to differentiate between chaotic and non-chaotic orbits. Then, we
calculate dynamical Mean Exponential Growth factor of Nearby Orbits (MEGNO)
maps from solving the variational equations along with the equations of motion.
These maps allow us to accurately differentiate between stable and unstable
dynamical systems. The results obtained from the analysis of HS, MLE, and MEGNO
maps are analysed for their dynamical variations and resemblance. The HS test
for the planets shows stability and quasi-periodicity for at least ten million
years. The MLE and the MEGNO maps have also indicated the local
quasi-periodicity and global stability in a relatively short integration
period. The orbital stability of the systems is tested using each indicator for
various values of planet inclinations (i_{pl} \le 25^\circ) and binary
eccentricities. The reliability of HS criterion is also discussed based on its
stability results compared with the MLE and MEGNO maps. | astro-ph |
The U.S. Eclipse Megamovie in 2017: a white paper on a unique outreach
event: Totality during the solar eclipse of 2017 traverses the entire breadth of the
continental United States, from Oregon to South Carolina. It thus provides the
opportunity to assemble a very large number of images, obtained by amateur
observers all along the path, into a continuous record of coronal evolution in
time; totality lasts for an hour and a half over the continental U.S. While we
describe this event here as an opportunity for public education and outreach,
such a movie -with very high time resolution and extending to the chromosphere
- will also contain unprecedented information about the physics of the solar
corona. | astro-ph |
Simulations of coronagraphy with a dynamic hologram for the direct
detection of exo-planets: In a previous paper, we discussed an original solution to improve the
performances of coronagraphs by adding, in the optical scheme, an adaptive
hologram removing most of the residual speckle starlight.
In our simulations, the detection limit in the flux ratio between a host star
and a very near planet (5 lambda/D) improves over a factor 1000 (resp. 10000)
when equipped with a hologram for cases of wavefront bumpiness imperfections of
lambda/20 (resp. lambda/100).
We derive, in this paper, the transmission accuracy required on the hologram
pixels to achieve such goals. We show that preliminary tests could be performed
on the basis of existing technologies. | astro-ph |
Reconciling the Metallicity Distributions of Gamma-ray Burst, Damped
Lyman-alpha, and Lyman-break Galaxies at z=3: We test the hypothesis that the host galaxies of long-duration gamma-ray
bursts (GRBs) as well as quasar-selected damped Lyman-alpha (DLA) systems are
drawn from the population of UV-selected star-forming, high-z galaxies
(generally referred to as Lyman-break galaxies). Specifically, we compare the
metallicity distributions of the GRB and DLA populations to simple models where
these galaxies are drawn randomly from the distribution of star-forming
galaxies according to their star-formation rate and HI cross-section
respectively. We find that it is possible to match both observational
distributions assuming very simple and constrained relations between
luminosity, metallicity and HI sizes. The simple model can be tested by
observing the luminosity distribution of GRB host galaxies and by measuring the
luminosity and impact parameters of DLA selected galaxies as a function of
metallicity. Our results support the expectation that GRB and DLA samples, in
contrast to magnitude limited surveys, provide an almost complete census of z=3
star-forming galaxies that are not heavily dust-obscured. | astro-ph |
Supernova ejecta interacting with a circumstellar disk. I.
two-dimensional radiation-hydrodynamic simulations: We perform a series of two-dimensional radiation-hydrodynamic simulations of
the collision between supernova ejecta and circumstellar media (CSM). The
hydrodynamic interaction of a fast flow and the surrounding media efficiently
dissipates the kinetic energy of the fast flow and considered as a dominant
energy source for a specific class of core-collapse supernovae. Despite some
observational evidence for aspherical ejecta and/or CSM structure,
multi-dimensional effects in the ejecta-CSM interaction are relatively
unexplored. Our numerical simulations equipped with an adaptive mesh refinement
technique successfully reproduce hydrodynamic instabilities developing around
the ejecta-CSM interface. We also investigate effects of disk-like CSM on the
dynamical evolution of supernova ejecta and bolometric light curves. We find
that emission powered by ejecta-disk interaction exhibits significant viewing
angle dependence. For a line of sight close to the symmetry axis, the observer
directly sees the supernova ejecta, leading to a short brightening timescale.
For an observer seeing the emission through the CSM disk, thermal photons
diffuse throughout the CSM and thus the light curve is severely smeared out. | astro-ph |
Deep Fields: The Faint sub-mJy and microJy Radio Sky - A VLBI
Perspective: Until recently, VLBI targets have been drawn almost exclusively from the
brightest and most compact radio sources in the sky, with typical flux
densities well in excess of a few tens of mJy. These sources are predominantly
identified with Active Galactic Nuclei (AGN), located at cosmological
distances. In this lecture I will attempt to summarise what is currently known
about the general properties of the faint sub-mJy and microJy radio source
population, as determined from deep multi-wavelength studies of the HDF-N. In
particular, I will try to provide a VLBI perspective, describing the first
deep, wide-field, VLBI pilot observations of the HDF, together with a summary
of the main results. The role VLBI can play in future high resolution studies
of faint radio sources is also addressed. | astro-ph |
On the stellar populations of massive galaxies: In this Letter, we analyse the predicted physical properties of massive
galaxies, in the framework of recent semi-analytic models of galaxy formation.
All models considered account for winds driven by supernovae explosions and
suppression of gas condensation at the centre of relatively massive haloes by
active galactic nuclei (AGN). We show that, while these models successfully
reproduce the old stellar populations observed for massive galaxies, they fail
in reproducing their observed chemical abundances. This problem is alleviate
but still present if AGN feedback is completely switched off. Moreover, in this
case, model predictions fail in accounting for the old stellar ages of massive
galaxies. We argue that the difficulty of semi-analytical models in
simultaneously reproducing the observed ages and metallicities of massive
galaxies, signals a fundamental problem with the schemes that are currently
adopted to model star formation, feedback, and related recycling of gas and
metals. | astro-ph |
A Ubiquitous Unifying Degeneracy in Two-Body Microlensing Systems: While gravitational microlensing by planetary systems provides unique vistas
on the properties of exoplanets, observations of a given 2-body microlensing
event can often be interpreted with multiple distinct physical configurations.
Such ambiguities are typically attributed to the close-wide and inner-outer
types of degeneracies that arise from transformation invariances and symmetries
of microlensing caustics. However, there remain unexplained inconsistencies
between aforementioned theories and observations. Here, leveraging a fast
machine learning inference framework, we present the discovery of the offset
degeneracy, which concerns a magnification-matching behaviour on the lens-axis
and is formulated independent of caustics. This offset degeneracy unifies the
close-wide and inner-outer degeneracies, generalises to resonant topologies,
and upon reanalysis, not only appears ubiquitous in previously published
planetary events with 2-fold degenerate solutions, but also resolves prior
inconsistencies. Our analysis demonstrates that degenerate caustics do not
strictly result in degenerate magnifications and that the commonly invoked
close-wide degeneracy essentially never arises in actual events. Moreover, it
is shown that parameters in offset degenerate configurations are related by a
simple expression. This suggests the existence of a deeper symmetry in the
equations governing 2-body lenses than previously recognised. | astro-ph |
On the DM interpretation of the origin of non-thermal phenomena in
galaxy clusters: (Abridged) We study the predictions of various annihilating Dark Matter (DM)
models in order to interpret the origin of non-thermal phenomena in galaxy
clusters. We consider three neutralino DM models with light (9 GeV),
intermediate (60 GeV) and high (500 GeV) mass. The secondary particles created
by neutralino annihilation produce a multi-frequency Spectral Energy
Distribution (SED), as well as heating of the intracluster gas, that are tested
against the observations available for the Coma cluster. The DM produced SEDs
are normalized to the Coma radio halo spectrum. We find that it is not possible
to interpret all non-thermal phenomena observed in Coma in terms of DM
annihilation. The DM model with 9 GeV mass produces too small power at all
frequencies, while the DM model with 500 GeV produces a large excess power at
all frequencies. The DM model with 60 GeV and $\tau^{\pm}$ composition is
consistent with the HXR and gamma-ray data but fails to reproduce the EUV and
soft X-ray data. The DM model with 60 GeV and $b{\bar b}$ composition is always
below the observed fluxes. The radio halo spectrum of Coma is well fitted only
in the $b{\bar b}$ or light and intermediate mass DM models. The heating
produced by DM annihilation in the center of Coma is always larger than the
intracluster gas cooling rate for an NFW DM density profile and it is
substantially smaller than the cooling rate only for a cored DM density profile
in DM model with 9 GeV. We conclude that the possibility of interpreting the
origin of non-thermal phenomena in galaxy clusters with DM annihilation models
requires a low neutralino mass and a cored DM density profile. If we then
consider the multimessenger constraints to the neutralino annihilation
cross-section, it turns out that such scenario would also be excluded unless we
introduce a substantial boost factor due to the presence of DM substructures. | astro-ph |
Searching for Molecular Jets from High-Mass Protostars: We report Very Large Array (VLA) observations in the Q-band toward 10 ionized
jet candidates to search for SiO emission, a well-known shocked gas tracer. We
detected 7 mm continuum counterparts toward 90% of the jet candidates. In most
cases, the jet candidate is located toward the center of the 7 mm core, and the
high masses ($\approx 100\,M_\odot$) and densities ($\approx 10^7\,
\text{cm}^{-3}$) of the cores suggest that the central objects are very young
high-mass protostars. We detected SiO $J=1-0$ emission associated with 6 target
sources. In all cases, the morphology and spectrum of the emission is
consistent with what is expected for molecular jets along an outflow axis, thus
confirming the jet nature of 60% of our sample. Our data suggest a positive
correlation between the SiO luminosity $L_{SiO}$, and both the bolometric
luminosity $L_{Bol}$ and the radio luminosity $S_\nu d^2$ of the driving
sources. | astro-ph |
CO Cameron band and CO2+ UV doublet emissions in the dayglow of Venus:
Role of CO in the Cameron band production: Present study deals with the model calculations of CO Cameron band and CO2+
ultraviolet doublet emissions in the dayglow of Venus. The overhead and limb
intensities of CO Cameron band and CO2+ UV doublet emissions are calculated for
low, moderate, and high solar activity conditions. Using updated cross
sections, the impact of dierent e-CO cross section for Cameron band production
is estimated. The electron impact on CO is the major source mechanism of
Cameron band, followed by electron and photon impact dissociation of CO2. The
overhead intensities of CO Cameron band and CO2+ UV doublet emissions are about
a factor of 2 higher in solar maximum than those in solar minimum condition.
The effect of solar EUV flux models on the emission intensity is ~30-40% in
solar minimum condition and ~2-10% in solar maximum condition. At the altitude
of emission peak (135 km), the model predicted limb intensity of CO Cameron
band and CO2+ UV doublet emissions in moderate (F10.7 = 130) solar activity
condition is about 2400 and 300 kR, respectively, which is in agreement with
the very recently published SPICAV/Venus Express observation. The model limb
intensity profiles of CO Cameron band and CO2+ UV doublet are compared with
SPICAV observation. We also calculated intensities of N2 Vegard-Kaplan UV bands
and OI 2972 {\AA} emissions during moderate and high solar activity conditions. | astro-ph |
Early assembly of the most massive galaxies: The current consensus is that galaxies begin as small density fluctuations in
the early Universe and grow by in situ star formation and hierarchical merging.
Stars begin to form relatively quickly in sub-galactic sized building blocks
called haloes which are subsequently assembled into galaxies. However, exactly
when this assembly takes place is a matter of some debate. Here we report that
the stellar masses of brightest cluster galaxies, which are the most luminous
objects emitting stellar light, some 9 billion years ago are not significantly
different from their stellar masses today. Brightest cluster galaxies are
almost fully assembled 4-5 Gyrs after the Big Bang, having grown to more than
90% of their final stellar mass by this time. Our data conflict with the most
recent galaxy formation models based on the largest simulations of dark matter
halo development. These models predict protracted formation of brightest
cluster galaxies over a Hubble time, with only 22% of the stellar mass
assembled at the epoch probed by our sample. Our findings suggest a new picture
in which brightest cluster galaxies experience an early period of rapid growth
rather than prolonged hierarchical assembly. | astro-ph |
The chemical composition of Ultracompact Dwarf Galaxies in the Virgo and
Fornax Clusters: We present spectroscopic observations of ultra compact dwarf (UCD) galaxies
in the Fornax and Virgo Clusters made to measure and compare their stellar
populations. The spectra were obtained on the Gemini-North (Virgo) and
Gemini-South (Fornax) Telescopes using the respective Gemini Multi-Object
Spectrographs.
We estimated the ages, metallicities and abundances of the objects from mea-
surements of Lick line-strength indices in the spectra; we also estimated the
ages and metallicities independently using a direct spectral fitting technique.
Both methods re- vealed that the UCDs are old (mean age 10.8 \pm 0.7 Gyr) and
(generally) metal-rich (mean [Fe/H] = -0.8 \pm 0.1). The alpha-element
abundances of the objects measured from the Lick indices are super-Solar.
We used these measurements to test the hypothesis that UCDs are formed by the
tidal disruption of present-day nucleated dwarf elliptical galaxies. The data
are not consistent with this hypothesis because both the ages and abundances
are significantly higher than those of observed dwarf galaxy nuclei (this does
not exclude disruption of an earlier generation of dwarf galaxies). They are
more consistent with the properties of globular star clusters, although at
higher mean metallicity. The UCDs display a very wide range of metallicity
(-1.7 <[Fe/H]< 0.0), spanning the full range of both globular clusters and
dwarf galaxy nuclei.
We confirm previous reports that most UCDs have high metalliticities for
their luminosities, lying significantly above the canonical
metallicitiy-luminosity relation followed by early-type galaxies. In contrast
to previous work we find that there is no significant difference in either the
mean ages or the mean metallicities of the Virgo and Fornax UCD populations. | astro-ph |
Polarization in microlensing towards the Galactic bulge: Gravitational microlensing, when finite size source effects are relevant,
provides an unique tool for the study of source star stellar atmospheres
through an enhancement of a characteristic polarization signal. This is due to
the differential magnification induced during the crossing of the source star.
In this paper we consider a specific set of reported highly magnified, both
single and binary exoplanetary systems, microlensing events towards the
Galactic bulge and evaluate the expected polarization signal. To this purpose,
we consider several polarization models which apply to different types of
source stars: hot, late type main sequence and cool giants. As a result we
compute the polarization signal P,which goes up to P=0.04% for late type stars
and up to a few percent for cool giants, depending on the underlying physical
polarization processes and atmosphere model parameters. Given a I band
magnitude at maximum magnification of about 12, and a typical duration of the
polarization signal up to 1 day, we conclude that the currently available
technology, in particular the polarimeter in FORS2 on the VLT, potentially may
allow the detection of such signals. This observational programme may take
advantage of the currently available surveys plus follow up strategy already
routinely used for microlensing monitoring towards the Galactic bulge (aimed at
the detection of exoplanets). In particular, this allows one to predict in
advance for which events and at which exact time the observing resources may be
focused to make intensive polarization measurements. | astro-ph |
Probing the Curious Case of a Galaxy Cluster Merger in Abell 115 with
High Fidelity Chandra X-ray Temperature and Radio Maps: We present results from an X-ray and radio study of the merging galaxy
cluster Abell 115. We use the full set of 5 Chandra observations taken of A115
to date (360 ks total integration) to construct high-fidelity temperature and
surface brightness maps. We also examine radio data from the Very Large Array
at 1.5 GHz and the Giant Metrewave Radio Telescope at 0.6 GHz. We propose that
the high X-ray spectral temperature between the subclusters results from the
interaction of the bow shocks driven into the intracluster medium by the motion
of the subclusters relative to one another. We have identified morphologically
similar scenarios in Enzo numerical N-body/hydrodynamic simulations of galaxy
clusters in a cosmological context. In addition, the giant radio relic feature
in A115, with an arc-like structure and a relatively flat spectral index, is
likely consistent with other shock-associated giant radio relics seen in other
massive galaxy clusters. We suggest a dynamical scenario that is consistent
with the structure of the X-ray gas, the hot region between the clusters, and
the radio relic feature. | astro-ph |
A New Sample of Cool Subdwarfs from SDSS: Properties and Kinematics: We present a new sample of M subdwarfs compiled from the 7th data release of
the Sloan Digital Sky Survey. With 3517 new subdwarfs, this new sample
significantly increases the number of spectroscopically confirmed low-mass
subdwarfs. This catalog also includes 905 extreme and 534 ultra sudwarfs. We
present the entire catalog including observed and derived quantities, and
template spectra created from co-added subdwarf spectra. We show color-color
and reduced proper motion diagrams of the three metallicity classes, which are
shown to separate from the disk dwarf population. The extreme and ultra
subdwarfs are seen at larger values of reduced proper motion as expected for
more dynamically heated populations. We determine 3D kinematics for all of the
stars with proper motions. The color-magnitude diagrams show a clear separation
of the three metallicity classes with the ultra and extreme subdwarfs being
significantly closer to the main sequence than the ordinary subdwarfs. All
subdwarfs lie below (fainter) and to the left (bluer) of the main sequence.
Based on the average $(U,V,W)$ velocities and their dispersions, the extreme
and ultra subdwarfs likely belong to the Galactic halo, while the ordinary
subdwarfs are likely part of the old Galactic (or thick) disk. An extensive
activity analysis of subdwarfs is performed using H$\alpha$ emission and 208
active subdwarfs are found. We show that while the activity fraction of
subdwarfs rises with spectral class and levels off at the latest spectral
classes, consistent with the behavior of M dwarfs, the extreme and ultra
subdwarfs are basically flat. | astro-ph |
Probing the Astrophysics of Cluster Outskirts: In galaxy clusters the entropy distribution of the IntraCluster Plasma
modulates the latter's equilibrium within the Dark Matter gravitational wells,
as rendered by our Supermodel. We argue the entropy production at the boundary
shocks to be reduced or terminated as the accretion rates of DM and
intergalactic gas peter out; this behavior is enforced by the slowdown in the
outskirt development at late times, when the Dark Energy dominates the
cosmology while the outer wings of the initial perturbation drive the growth.
In such conditions, we predict the ICP temperature profiles to steepen into the
cluster outskirts. The detailed expectations from our simple formalism agree
with the X-ray data concerning five clusters whose temperature profiles have
been recently measured out to the virial radius. We predict steep temperature
declines to prevail in clusters at low redshift, tempered only by rich environs
including adjacent filamentary structures. | astro-ph |
Zel'dovich approximation and General Relativity: We show how the Zel'dovich approximation and the second order displacement
field of Lagrangian perturbation theory can be obtained from a general
relativistic gradient expansion in \Lambda{}CDM cosmology. The displacement
field arises as a result of a second order non-local coordinate transformation
which brings the synchronous/comoving metric into a Newtonian form. We find
that, with a small modification, the Zel'dovich approximation holds even on
scales comparable to the horizon. The corresponding density perturbation is not
related to the Newtonian potential via the usual Poisson equation but via a
modified Helmholtz equation. This is a consequence of causality not present in
the Newtonian theory. The second order displacement field receives relativistic
corrections that are subdominant on short scales but are comparable to the
second order Newtonian result on scales approaching the horizon. The
corrections are easy to include when setting up initial conditions in large
N-body simulations. | astro-ph |
APSYNSIM: An Interactive Tool To Learn Interferometry: The APerture SYNthesis SIMulator is a simple interactive tool to help the
students visualize and understand the basics of the Aperture Synthesis
technique, applied to astronomical interferometers. The users can load many
different interferometers and source models (and also create their own), change
the observing parameters (e.g., source coordinates, observing wavelength,
antenna location, integration time, etc.), and even deconvolve the
interferometric images and corrupt the data with gain errors (amplitude and
phase). The program is fully interactive and all the figures are updated in
real time. APSYNSIM has already been used in several interferometry schools and
has got very positive feedback from the students. | astro-ph |
Effects of Radiation Pressure on the Evaporative Wind of HD 209458b: The role of radiation pressure in shaping exoplanet photoevaporation remains
a topic of contention. Radiation pressure from the exoplanet's host star has
been proposed as a mechanism to drive the escaping atmosphere into a "cometary"
tail and explain the high velocities observed in systems where mass loss is
occurring. In this paper we present results from high-resolution 3-D
hydrodynamic simulations of a planet similar to HD 209458b. We
self-consistently launch a wind flowing outward from the planet by calculating
the ionization and heating resulting from incident high-energy radiation, and
account for radiation pressure. We first present a simplified calculation,
setting a limit on the Lyman-$\alpha$ flux required to drive the
photo-evaporated planetary material to larger radii and line-of-sight
velocities. We then present the results of our simulations, which confirm the
limits determined by our analytic calculation. We thus demonstrate that, within
the limits of our hydrodynamic simulation and for the Lyman-$\alpha$ fluxes
expected for HD 209458, radiation pressure is unlikely to significantly affect
photoevaporative winds or to explain the high velocities at which wind material
is observed, though further possibilities remain to be investigated. | astro-ph |
The GRB/SN Connection: An Improved Spectral Flux Distribution for the
Supernova Candidate Associated with GRB 970228: We better determine the spectral flux distribution of the supernova candidate
associated with GRB 970228 by modeling the spectral flux distribution of the
host galaxy of this burst, fitting this model to measurements of the host
galaxy, and using the fitted model to better subtract out the contribution of
the host galaxy to measurements of the afterglow of this burst. | astro-ph |
Distinguishing Propagation vs. Launch Physics of Astrophysical Jets and
the Role of Experiments: The absence of other viable momentum sources for collimated flows leads to
the likelihood that magnetic fields play a fundamental role in jet launch
and/or collimation in astrophysical jets. To best understand the physics of
jets, it is useful to distinguish between the launch region where the jet is
accelerated and the larger scales where the jet propagates as a collimated
structure. Observations presently resolve jet propagation, but not the launch
region. Simulations typically probe the launch and propagation regions
separately, but not both together. Here, I identify some of the physics of jet
launch vs. propagation and what laboratory jet experiments to date have probed.
Reproducing an astrophysical jet in the lab is unrealistic, so maximizing the
benefit of the experiments requires clarifying the astrophysical connection. | astro-ph |
Evidence for a Non-Expanding Universe: Surface Brightness Data From HUDF: Surface brightness data can distinguish between a Friedman-Robertson-Walker
expanding universe and a non-expanding universe. For surface brightness
measured in AB magnitudes per angular area, all FRW models, regardless of
cosmological parameters, predict that surface brightness declines with redshift
as (z+1)^-3, while any non-expanding model predicts that surface brightness is
constant with distance and thus with z. High-z UV surface brightness data for
galaxies from the Hubble Ultra Deep Field and low-z data from GALEX are used to
test the predictions of these two models up to z=6. A preliminary analysis
presented here of samples observed at the same at-galaxy wavelengths in the UV
shows that surface brightness is constant, mu=kz^0.026+-0.15, consistent with
the non-expanding model. This relationship holds if distance is linearly
proportional to z at all redshifts, but seems insensitive to the particular
choice of d-z relationship. Attempts to reconcile the data with FRW predictions
by assuming that high-z galaxies have intrinsically higher surface brightness
than low-z galaxies appear to face insurmountable problems. The intrinsic FUV
surface brightness required by the FRW models for high-z galaxies exceeds the
maximum FUV surface brightness of any low-z galaxy by as much as a factor of
40. Dust absorption appears to make such extremely high intrinsic FUV surface
brightness physically impossible. If confirmed by further analysis, the
impossibility of such high-surface-brightness galaxies would rule out all FRW
expanding universe (big bang) models. | astro-ph |
Simulations at the Dwarf Scale: From Violent Dwarfs at Cosmic Dawn and
Cosmic Noon to Quiet Discs today: Dwarf galaxies with stellar masses around 10^9 Msun can be explored at high
and low redshifts and they give a glimpse of the different conditions of galaxy
formation at different epochs. Using a large sample of about 300 zoom-in
cosmological hydrodynamical simulations of galaxy formation I will briefly
describe the formation of dwarfs at this mass scale at 3 different epochs:
cosmic dawn (Ceverino, Klessen, Glover 2018), cosmic noon (Ceverino, Primack,
Dekel 2015), and today (Ceverino et al. 2017). I will describe the FirstLight
simulations of first galaxies at redshifts 5-15. These first dwarfs have
extremely high star formation efficiencies due to high gas fractions and high
gas accretion rates. These simulations will make predictions that will be
tested for the first time with the James Webb Space Telescope (JWST). At cosmic
noon, z = 2, galaxy formation is still a very violent and dynamic process. The
VELA simulations have generated a set of dispersion-dominated dwarfs that show
an elongated morphology due to their prolate dark-matter halos. Between z = 1
and 0, the AGORA simulation shows the formation of a low-mass disc due to slow
gas accretion. The disc agrees with many local scaling relations, such as the
stellar-mass-halo-mass and the baryonic Tully-Fisher relation. | astro-ph |
SN 2005ip: A Luminous Type IIn Supernova Emerging from a Dense
Circumstellar Medium as Revealed by X-Ray Observations: We report on X-ray spectral evolution of the nearby Type IIn supernova (SN)
2005ip, based on Chandra and Swift observations covering from ~1 to 6 years
after the explosion. X-ray spectra in all epochs are well fitted by a thermal
emission model with kT > 7 keV. The somewhat high temperature suggests that the
X-ray emission mainly arises from the circumstellar medium heated by the
forward shock. We find that the spectra taken 2-3 years since the explosion are
heavily absorbed N_H ~ 5e22 cm^{-2}, but the absorption gradually decreases to
the level of the Galactic absorption N_H ~ 4e20 cm^{-2} at the final epoch.
This indicates that the SN went off in a dense circumstellar medium and that
the forward shock has overtaken it. The intrinsic X-ray luminosity stays
constant until the final epoch when it drops by a factor of ~2. The intrinsic
0.2-10 keV luminosity during the plateau phase is measured to be ~1.5e41 erg/s,
ranking SN 2005ip as one of the brightest X-ray SNe. Based on the column
density, we derive a lower-limit of a mass-loss rate to be M_dot ~ 0.015
(V_w/100 km/s) M_sun/yr, which roughly agrees with that inferred from the X-ray
luminosity, M_dot ~ 0.02 (V_w/100 km/s) M_sun/yr, where V_w is the
circumstellar wind speed. Such a high mass-loss rate suggests that the
progenitor star had eruptive mass ejections like a luminous blue variable star.
The total mass ejected in the eruptive period is estimated to be ~15 M_sun,
indicating that the progenitor mass is greater than ~25 M_sun. | astro-ph |
Kinematical evolution of multiple stellar populations in star clusters: We present the results of a suite of \Nbody simulations aimed at
understanding the fundamental aspects of the long-term evolution of the
internal kinematics of multiple stellar populations in globular clusters. Our
models enable us to study the cooperative effects of internal,
relaxation-driven processes and external, tidally-induced perturbations on the
structural and kinematic properties of multiple-population globular clusters.
To analyse the dynamical behaviour of the multiple stellar populations in a
variety of spin-orbit coupling conditions, we have considered three reference
cases in which the tidally perturbed star cluster rotates along an axis
oriented in different directions with respect to the orbital angular momentum
vector. We focus specifically on the characterisation of the evolution of the
degree of differential rotation and anisotropy in the velocity space, and we
quantify the process of spatial and kinematic mixing of the two populations. In
light of recent and forthcoming explorations of the internal kinematics of this
class of stellar systems by means of line-of sight and astrometric
measurements, we also investigate the implications of projection effects and
spatial distribution of the stars adopted as tracers. The kinematic and
structural richness emerging from our models further emphasises the need and
the importance of observational studies aimed at building a complete
kinematical picture of the multiple population phenomenon. | astro-ph |
The X-ray activity-rotation relation of T Tauri stars in Taurus-Auriga: The Taurus-Auriga star-forming complex hosts the only population of T Tauri
stars in which an anticorrelation of X-ray activity and rotation period has
been observed. We have used XMM-Newton's European Photon Imaging Cameras to
perform the most sensitive survey to date of X-ray emission (0.3-10 keV) from
young stars in Taurus-Auriga and investigate the dependences of X-ray activity
measures -- X-ray luminosity, Lx, its ratio with the stellar luminosity,
Lx/Lstar, and the surface-averaged X-ray flux, Fxs -- on rotation period. We
tested for differences in the distributions of Lx/Lstar of fast and slow
rotators, accretors and non-accretors, and compared the dependence of Lx/Lstar
on the ratio of the rotation period and the convective turnover timescale, the
Rossby number, with that of late-type main-sequence stars. We found significant
anticorrelations of Lx and Fxs with rotation period, but these could be
explained by the typically higher stellar luminosity and effective temperature
of fast-rotators in Taurus-Auriga and a near-linear dependence of Lx on Lstar.
We found no evidence for a dependence of Lx/Lstar on rotation period, but for
accretors to have lower Lx/Lstar than non-accretors at all rotation periods.
The Rossby numbers of accretors and non-accretors were found to be the same as
those of late-type main-sequence stars showing saturated X-ray emission. We
conclude that non-accreting T Tauri stars show X-ray activity entirely
consistent with the saturated activity of late-type main-sequence stars.
Accreting T Tauri stars show lower X-ray activity, which cannot be attributed
to their slower rotation. | astro-ph |
Galaxy and Mass Assembly (GAMA): Probing galaxy-group correlations in
redshift space with the halo streaming model: We have studied the galaxy-group cross-correlations in redshift space for the
Galaxy And Mass Assembly (GAMA) Survey. We use a set of mock GAMA galaxy and
group catalogues to develop and test a novel 'halo streaming' model for
redshift-space distortions. This treats 2-halo correlations via the streaming
model, plus an empirical 1-halo term derived from the mocks, allowing accurate
modelling into the nonlinear regime. In order to probe the robustness of the
growth rate inferred from redshift-space distortions, we divide galaxies by
colour, and divide groups according to their total stellar mass, calibrated to
total mass via gravitational lensing. We fit our model to correlation data, to
obtain estimates of the perturbation growth rate, $f\sigma_8$, validating
parameter errors via the dispersion between different mock realizations. In
both mocks and real data, we demonstrate that the results are closely
consistent between different subsets of the group and galaxy populations,
considering the use of correlation data down to some minimum projected radius,
$r_{\rm min}$. For the mock data, we can use the halo streaming model to below
$r_{\rm min} = 5h^{-1}$ Mpc, finding that all subsets yield growth rates within
about 3% of each other, and consistent with the true value. For the actual GAMA
data, the results are limited by cosmic variance: $f\sigma_8=0.29\pm 0.10$ at
an effective redshift of 0.20; but there is every reason to expect that this
method will yield precise constraints from larger datasets of the same type,
such as the DESI bright galaxy survey. | astro-ph |
A Novel Survey for Young Substellar Objects with the W band Filter.V. IC
348 and Barnard 5 in the Perseus Cloud: We report the discovery of substellar objects in the young star cluster IC
348 and the neighboring Barnard 5 dark cloud, both at the eastern end of the
Perseus star-forming complex. The substellar candidates are selected using
narrowband imaging, i.e., on and off photometric technique with a filter
centered around the water absorption feature at 1.45 microns, a technique
proven to be efficient in detecting water-bearing substellar objects. Our
spectroscopic observations confirm three brown dwarfs in IC 348. In addition,
the source WBIS 03492858+3258064, reported in this work, is the first confirmed
brown dwarf discovered toward Barnard 5. Together with the young stellar
population selected via near- and mid-infrared colors using the Two Micron All
Sky Survey and the Wide-field Infrared Survey Explorer, we diagnose the
relation between stellar versus substellar objects with the associated
molecular clouds. Analyzed by Gaia EDR3 parallaxes and kinematics of the cloud
members across the Perseus region, we propose the star formation scenario of
the complex under influence of the nearby OB association. | astro-ph |
Rotational quenching of rotationally-excited H$_2$O in collisions with
He: Theoretical rotational quenching cross sections and rate coefficients of
ortho- and para-H$_2$O due to collisions with He atoms are presented. The
complete angular momentum close-coupling approach as well as the coupled-states
approximation for angular momentum decoupling were applied to solve the
scattering problem for a large range of rotationally-excited states of water.
Results are obtained for quenching from initial levels 1$_{1,0}$, 2$_{1,2}$,
2$_{2,1}$, 3$_{0,3}$, 3$_{1,2}$, 3$_{2,1}$, 4$_{1,4}$, 3$_{3,0}$, and 4$_{2,3}$
of ortho-H$_2$O and from initial levels 1$_{1,1}$, 2$_{0,2}$, 2$_{1,1}$,
2$_{2,0}$, 3$_{1,3}$, 3$_{2,2}$, 4$_{0,4}$, 4$_{1,3}$, and 3$_{3,1}$ of
para-H$_2$O for kinetic energies from 10$^{-5}$ to 10$^4$ cm$^{-1}$.
State-to-state and total deexcitation cross sections and rate coefficients for
temperatures between 0.1 and 3000 K are reported. The present state-to-state
rate coefficients are found to be in good agreement with previous results
obtained by Green and coworkers at high temperatures, but significant
discrepancies are obtained at lower temperatures likely due to differences in
the adopted potential energy surfaces. Astrophysical applications of the
current rate coefficients are briefly discussed. | astro-ph |
Analytical Blowup Solutions to the Isothermal Euler-Poisson Equations of
Gaseous Stars in R^N: This article is the continued version of the analytical blowup solutions for
2-dimensional Euler-Poisson equations in "M.W. Yuen, Analytical Blowup
Solutions to the 2-dimensional Isothermal Euler-Poisson Equations of Gaseous
Stars, J. Math. Anal. Appl. 341 (1)(2008), 445-456." and "M.W. Yuen, Analytical
Blowup Solutions to the 2-dimensional Isothermal Euler-Poisson Equations of
Gaseous Stars II. arXiv:0906.0176v1". With the extension of the blowup
solutions with radial symmetry for the isothermal Euler-Poisson equations in
R^2, other special blowup solutions in R^N with non-radial symmetry are
constructed by the separation method. Key words: Analytical Solutions,
Euler-Poisson Equations, Isothermal, Blowup, Special Solutions, Non-radial
Symmetry | astro-ph |
UGC 7069: The largest ring galaxy: We find that UGC 7069 is the largest ring galaxy known to date. In this
Letter, we present a multiwavelength study of this galaxy (combining radio,
2MASS, optical and ultraviolet data). The ring of UGC 7069, whose diameter
measures ~115 kpc, is also warped at its edges. The nucleus appears
double-peaked and hosts a possible LINER. The ultraviolet data indicate a
strong blue colour and suggest that UGC 7069 is a starburst galaxy. We also
present N-body simulation results, which indicate that galaxy collisions can
produce such huge rings. Large inclination angles between the target and the
intruder galaxy may account for the formation of warped rings. Multiwavelength
observations are highly essential to constrain our simulation results, which
will address the formation and evolution of such a rare galaxy. | astro-ph |
Counts and Colours of Faint Stars in 5 Fields Near the North Galactic
Pole: Faint star number counts in the photographic \jmag band and \bvcol colour
distributions are presented for a 1.08 deg$^2$ field near the North Galactic
Pole. Due to the excellent star/galaxy discrimination we count stars as faint
as \jmag = 23. We compare the number counts and colour distributions in 5
adjacent fields near SA57. The number counts and colour distributions are in
very good agreement with previous data. However, we find that the large
field-to-field scatter in the colour distributions, which we argue is real,
might prevent us setting strong limits on Galactic structure. A simple two
component standard model, Bahcall and Soneira (1984), fits the number counts
reasonably well at the bright \jmag $< 21$, but fails notably at the faint end,
even if a third component is added, as in Reid and Majewski (1993). The
standard models are in good agreement with both the number counts and colour
distribution at $20 < $\vmag$< 21$. Although the standard models bimodal shape
of the colour distribution compares well with the data at $21 < $\vmag$< 21.5$,
the number counts of stars are underestimated. | astro-ph |
A Vlbi Survey of Weak Extragalactic Radio Sources for the Alignment of
the Icrf and the Future Gaia Frame: The space astrometry mission GAIA will construct a dense optical QSO-based
celestial reference frame. For consistency between the optical and radio
positions, it will be important to align the GAIA frame and the International
Celestial Reference Frame (ICRF) with the highest accuracy. Currently, it is
found that only 10% of the ICRF sources are suitable to establish this link,
either because they are not bright enough at optical wavelengths or because
they have significant extended radio emission which precludes reaching the
highest astrometric accuracy. In order to improve the situation, we have
initiated a VLBI survey dedicated to finding additional high-quality radio
sources for aligning the two frames. The sample consists of about 450 sources,
typically 20 times weaker than the current ICRF sources, which have been
selected by cross-correlating optical and radio catalogues. The paper presents
the observing strategy and includes preliminary results of observation of 224
of these sources with the European VLBI Network in June 2007. | astro-ph |
An internally consistent distance framework in the Local Group: Accurate and precise astronomical distance determinations are crucial for
derivations of, among others, the masses and luminosities of a large variety of
distant objects. Astronomical distance determination has traditionally relied
on the concept of a `distance ladder.' Here we review our recent attempts to
establish a highly robust set of internally consistent distance determinations
to Local Group galaxies, which we recommend as the statistical basis of an
improved extragalactic distance ladder. | astro-ph |
Voids and Halos in Voids statistics as a probe of the Expansion History
of the Universe: Structures in the Universe are arranged into the cosmic web. Distributions,
statistics, and evolutions of the structures can be used as probes for
cosmological models. We investigate the number density of voids and dark matter
halos-in-voids in the Excursion Set Theory (EST). We study the Markov and
non-Markov frameworks of EST in both spherical and ellipsoidal collapse models.
Afterward, we compare the number density of voids and halos-in-voids in the
standard $\Lambda$CDM and the reconstructed model. The reconstructed model is a
model-independent reconstruction based on background observations. This work
explores the effects of the collapse model barrier in the different EST
frameworks on the statistics of voids and the statistics of halos-in-voids.
Finally, we find the hint that cosmological models can be distinguished by the
number density of halos-in-voids in the $1.0-2.5$ redshift range. The maximum
difference is observed in $z\sim1.9$. | astro-ph |
Radio light curves during the passage of cloud G2 near Sgr A*: We calculate radio light curves produced by the bow shock that is likely to
form in front of the G2 cloud when it penetrates the accretion disk of Sgr A*.
The shock acceleration of the radio-emitting electrons is captured
self-consistently by means of first-principles particle-in-cell simulations. We
show that the radio luminosity is expected to reach maximum in early 2013,
roughly a month after the bow shock crosses the orbit pericenter. We estimate
the peak radio flux at 1.4 GHz to be 1.4 - 22 Jy depending on the assumed orbit
orientation and parameters. We show that the most promising frequencies for
radio observations are in the 0.1<nu<1 GHz range, for which the bow shock
emission will be much stronger than the intrinsic radio flux for all the models
considered. | astro-ph |
Charged Cosmic Rays: a Review of Balloon and Space Borne Measurements: Current experimental data on cosmic-ray charged leptons are briefly reviewed
including measurements of the positron fraction, electron and positron spectra
and inclusive electron+positron data. Precision measurements by PAMELA and
AMS-02 of the positron spectrum and its striking difference from the electron
spectrum have prompted several theoretical speculations. In order to
discriminate among different interpretations of the 'positron anomaly', a major
step is needed to achieve an accurate direct measurement of the shape of the
inclusive electron spectrum beyond 1 TeV. Ongoing efforts along this direction
by instruments already in orbit and by the recently launched CALET and DAMPE
missions are described. A challenging experimental scenario, at variance with
the standard paradigm of a single power law spectrum, emerges for the
cosmic-ray charged hadrons after the discovery of a discrepant hardening in the
rigidity spectra of protons and He in the 200 to 300 GV region (CREAM, PAMELA,
AMS-02) and the observation by AMS-02 of a possible break in the Li spectrum.
An additional puzzle comes from the apparent violation of the universality of
spectral indices whereby He and proton spectra are progressively hardening
above ~100 GV with a similar rigidity dependence, but the He spectrum is harder
than proton's. Secondary-to-primary ratios and isotope flux ratios provide
insight into the subtleties of propagation mechanism(s) and test the internal
consistency of the models of acceleration and propagation of cosmic rays in the
galaxy. Important complementary information on the abundance of nuclei heavier
than iron comes from dedicated balloon-borne instruments as SuperTIGER or
space-based missions as ACE at L1 that provided the first measurement of a
primary "cosmic-ray clock". A brief overview of future missions is given at the
end of the paper. | astro-ph |
Propagation of Ultra High Energy Cosmic Rays and the Production of
Cosmogenic Neutrinos: We present an updated version of the {\it SimProp} Monte Carlo code to study
the propagation of ultra high energy cosmic rays in astrophysical backgrounds
computing the cosmogenic neutrino fluxes expected on earth. The study of
secondary neutrinos provides a powerful tool to constrain the source models of
these extremely energetic particles. We will show how the newly detected
IceCube neutrino events at PeV energies together with the the latest
experimental results of the Pierre Auger Observatory and Telescope Array
experiment are almost at the level of excluding several hypothesis on the
astrophysical sources of ultra high energy cosmic rays. Results presented here
can be also used to evaluate the discovery capabilities of future high energy
cosmic rays and neutrino detectors. | astro-ph |
Constraints on Pre-inflation Fluctuations in a Nearly Flat Open
ΛCDM Cosmology: We analyze constraints on parameters characterizing the pre-inflating
universe in an open inflation model with a present slightly open $\Lambda$CDM
universe. We employ an analytic model to show that for a broad class of
inflation-generating effective potentials, the simple requirement that some
fraction of the observed dipole moment represents a pre-inflation isocurvature
fluctuation allows one to set upper and lower limits on the magnitude and
wavelength scale of pre-inflation fluctuations in the inflaton field, and the
curvature of the pre-inflation universe, as a function of the fraction of the
total initial energy density in the inflaton field as inflation begins. We
estimate that if the pre-inflation contribution to the current CMB dipole is
near the upper limit set by the {\it Planck} Collaboration then the current
constraints on $\Lambda$CDM cosmological parameters allow for the possibility
of a significantly open $\Omega_{i} \le 0.4$ pre-inflating universe for a broad
range of the fraction of the total energy in the inflaton field at the onset of
inflation. This limit to $\Omega_{i}$ is even smaller if a larger dark-flow
tilt is allowed. | astro-ph |
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