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Astronomia Astrofizyka

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Astrofizyka - referaty z astro-ph updates on

We have updated the Munich galaxy formation model to the Planck first-year
cosmology, while modifying the treatment of baryonic processes to reproduce
recent data on the abundance and passive fractions of galaxies from z=3 down to
z=0. Matching these more extensive and more precise observational results
requires us to delay the reincorporation of wind ejecta, to lower the threshold
for turning cold gas into stars, to eliminate ram-pressure stripping in halos
less massive than ~10^14Msun, and to modify our model for radio-mode feedback.
These changes cure the most obvious failings of our previous models, namely the
overly early formation of low-mass galaxies and the overly large fraction of
them that are passive at late times. The new model reproduces the observed
evolution both of the stellar mass function and of the distribution of
star-formation rate at each stellar mass. Massive galaxies assemble most of
their mass before z=1 and are predominantly old and passive at z=0, while lower
mass galaxies assemble later and are predominantly blue and star-forming at
z=0. This phenomenological but physically based model allows the observations
to be interpreted in terms of the efficiency of the various processes that
control the formation and evolution of galaxies as a function of their stellar
mass, gas content, environment and time. 2014/10/04 - 22:12

We have selected SDSS J222032.50+002537.5 and SDSS J142048.01+120545.9 as
best blazar candidates out of a complete sample of extremely radio-loud quasars
at z>4, with highly massive black holes. We observed them and a third
serendipitous candidate with similar features (PMN J2134-0419) in the X-rays
with the Swift/XRT telescope, to confirm their blazar nature. We observed
strong and hard X-ray fluxes in all three cases. This allowed us to classify
our candidates as real blazars, being characterized by large Lorentz factors
(~13) and very small viewing angles (~3deg). All three sources have black hole
masses exceeding 10^9Msun and their classification provides intriguing
constraints on supermassive black hole formation and evolution models. We
confirm our earlier suggestion that there are different formation epochs of
extremely massive black holes hosted in jetted (z~4) and non-jetted systems
(z~2.5). 2014/10/04 - 22:12

The Exoplanet Euclid Legacy Survey (ExELS) proposes to determine the
frequency of cold exoplanets down to Earth mass from host separations of ~1 AU
out to the free-floating regime by detecting microlensing events in Galactic
Bulge. We show that ExELS can also detect large numbers of hot, transiting
exoplanets in the same population. The combined microlensing+transit survey
would allow the first self-consistent estimate of the relative frequencies of
hot and cold sub-stellar companions, reducing biases in comparing "near-field"
radial velocity and transiting exoplanets with "far-field" microlensing
exoplanets. The age of the Bulge and its spread in metallicity further allows
ExELS to better constrain both the variation of companion frequency with
metallicity and statistically explore the strength of star-planet tides.

We conservatively estimate that ExELS will detect ~4100 sub-stellar objects,
with sensitivity typically reaching down to Neptune-mass planets. Of these,
~600 will be detectable in both Euclid's VIS (optical) channel and NISP H-band
imager, with ~90% of detections being hot Jupiters. Likely scenarios predict a
range of 2900-7000 for VIS and 400-1600 for H-band. Twice as many can be
expected in VIS if the cadence can be increased to match the 20-minute H-band
cadence. The separation of planets from brown dwarfs via Doppler boosting or
ellipsoidal variability will be possible in a handful of cases. Radial velocity
confirmation should be possible in some cases, using 30-metre-class telescopes.
We expect secondary eclipses, and reflection and emission from planets to be
detectable in up to ~100 systems in both VIS and NISP-H. Transits of ~500
planetary-radius companions will be characterised with two-colour photometry
and ~40 with four-colour photometry (VIS,YJH), and the albedo of (and emission
from) a large sample of hot Jupiters in the H-band can be explored
statistically. 2014/10/04 - 22:12

We use Kepler short cadence light curves to constrain the oblateness of
planet candidates in the Kepler sample. The transits of rapidly rotating
planets that are deformed in shape will lead to distortions in the ingress and
egress of their light curves. We report the first tentative detection of an
oblate planet outside of the solar system, measuring an oblateness of $0.22 \pm
0.11$ for the 18 $M_J$ mass brown dwarf Kepler 39b (KOI-423.01). We also
provide constraints on the oblateness of the planets (candidates) HAT-P-7b,
KOI-686.01, and KOI-197.01 to be < 0.067, < 0.251, and < 0.186, respectively.
Using the Q'-values from Jupiter and Saturn, we expect tidal synchronization
for the spins of HAT-P-7b, KOI-686.01 and KOI-197.01, and for their rotational
oblateness signatures to be undetectable in the current data. The potentially
large oblateness of KOI-423.01 (Kepler 39b) suggests that the Q'-value of the
brown dwarf needs to be two orders of magnitude larger than that of the solar
system gas giants to avoid being tidally spun-down. 2014/10/04 - 22:12

I present an organic description of the spectrum of regimes of collisionless
tidal streams and define the orderings between the relevant physical quantities
that shape their morphology. Three dichotomies are identified and the
mechanisms through which they regulate the main qualitative properties of a
stream are illustrated. These determine (i) the speed of the differential
streaming, (ii) the internal coherence of the stream, (iii) its thickness or
opening angle. The roles of the slope of the host's density profile, the
progenitor's internal kinematics (and ordered rotation), the details of the
shedding history are systematically inspected. Within this framework, I
concentrate on the mechanism that causes the characteristic `feathering'
typical of streams of star clusters, which is found to be a natural feature of
coherent streams. Feathers appear as collections of multiple `armlets', each
composed of stars shed between two successive apocentric passages of the
progenitor. Each armlet is folded along its length, pulled at its centre by the
faster differential streaming of stars released near pericenter. The same
mechanism is capable of generating `bifurcations' (i.e. bimodal density
distributions) in the faster streams of more massive progenitors. I explore on
the conditions under which streams are internally coherent and comment on the
cases of Palomar~5, Willman~1, the Anticenter and Sagittarius' streams.
Analytic analyses are accompanied by numerical experiments, which are performed
using a purposely built generative model, also presented here. 2014/10/04 - 22:12

We present the first measurement of the projected correlation function of 485
gamma-ray selected Blazars, divided in 175 BLLacertae (BL Lacs) and 310 Flat
Spectrum Radio Quasars (FSRQs) detected in the 2-year all-sky survey by
Fermi-Large Area Telescope. We find that Fermi BL Lacs and FSRQs reside in
massive dark matter halos (DMHs) with logMh=13.35+0.20/-0.14 and logMh =
13.40+0.15/-0.19 Msun/h, respectively, at low (z=0.4) and high (z =1.2)
redshift. In terms of clustering properties, these results suggest that BL Lacs
and FSRQs are similar objects residing in the same dense environment typical of
galaxy groups, despite their different spectral energy distribution, power and
accretion rate. We find no difference in the typical bias and hosting halo mass
between Fermi Blazars and radio-loud AGN, supporting the unifcation scheme
simply equating radio-loud objects with misaligned Blazar counterparts. This
similarity in terms of typical environment they preferentially live in,
suggests that Blazars preferentially occupy the centre of DMHs, as already
pointed out for radio-loud AGN. This implies, in light of several projects
looking for the gamma-ray emission from DM annihilation in galaxy clusters, a
strong contamination from Blazars to the expected signal from DM annihilation. 2014/10/04 - 22:12

We consider an influence of a non-stationary gravitational field of the
Galaxy on the visible positions of extragalactic sources. A contribution of the
baryonic component of the galactic matter as well as of the hidden matter
(including a population of brown dwarfs) were took into account. The observed
variations of the deflection angle of light rays in a gravitational field of
randomly moving point-like masses can be considered as a stochastic process.
Using such an approach we constructed an autocorrelation function of studied
stochastic process and found that its relative changes are about 15% for one
year and about 35% for ten years. 2014/10/04 - 22:12

What do we know about voids in the dark matter distribution given the Sloan
Digital Sky Survey (SDSS) and assuming the $\Lambda\mathrm{CDM}$ model? Recent
application of the Bayesian inference algorithm BORG to the SDSS Data Release 7
main galaxy sample has generated detailed Eulerian and Lagrangian
representations of the large-scale structure as well as the possibility to
accurately quantify corresponding uncertainties. Building upon these results,
we present constrained catalogs of voids in the Sloan volume, aiming at a
physical representation of dark matter underdensities and at the alleviation of
the problems due to sparsity and biasing on galaxy void catalogs. To do so, we
generate data-constrained reconstructions of the presently observed large-scale
structure using a fully non-linear gravitational model. We then find and
analyze void candidates using the VIDE toolkit. Our methodology therefore
predicts the properties of voids based on fusing prior information from
simulations and data constraints. For usual void statistics (number function,
ellipticity distribution and radial density profile), all the results obtained
are in agreement with dark matter simulations. Our dark matter void candidates
probe a deeper void hierarchy than voids directly based on the observed
galaxies alone. The use of our catalogs therefore opens the way to
high-precision void cosmology at the level of the dark matter field. We will
make the void catalogs used in this work available at
this http URL 2014/10/04 - 22:12

The transient Swift J1644+57 is believed to have been produced by an unlucky
star wandering too close to a supermassive black hole (BH) leading to a tidal
disruption event. This unusual flare displayed highly super-Eddington X-ray
emission which likely originated in a relativistic, collimated jet. This
presents challenges to modern accretion and jet theory as upper limits of prior
BH activity, which we obtain from the radio afterglow of this event, imply that
both the pre-disruption BH and stellar magnetic fluxes fall many orders of
magnitude short of what is required to power the observed X-ray luminosity. We
argue that a pre-existing, "fossil" accretion disc can contain a sufficient
reservoir of magnetic flux and that the stellar debris stream is capable of
dragging this flux into the BH. To demonstrate this, we perform local, 3D
magnetohydrodynamic simulations of the disc--stream interaction and demonstrate
that the interface between the two is unstable to mixing. This mixing entrains
a sufficient amount of fossil disc magnetic flux into the infalling stellar
debris to power the jet. We argue that the interaction with the fossil disc can
have a pronounced effect on the structure and dynamics of mass fallback and
likely the resulting transient. Finally, we describe possible ramifications of
these interactions on unresolved problems in tidal disruption dynamics, in
particular, the efficiency of debris circularization, and effects of the
disruption on the preexisting black hole system.

Animations online: this http URL 2014/10/04 - 22:12

The intergalactic medium (IGM) accounts for ~90% of baryons at all epochs and
yet its three dimensional distribution in the cosmic web remains mostly
unknown. This is so because the only feasible way to observe the bulk of the
IGM is through intervening absorption line systems in the spectra of bright
background sources, which limits its characterization to being one-dimensional.
Still, an averaged three dimensional picture can be obtained by combining and
cross-matching multiple one-dimensional IGM information with three-dimensional
galaxy surveys. Here, we present our recent and current efforts to map and
characterize the IGM in the cosmic web using galaxies as tracers of the
underlying mass distribution. In particular, we summarize our results on: (i)
IGM around star-forming and non-star-forming galaxies; (ii) IGM within and
around galaxy voids; and (iii) IGM in intercluster filaments. With these
datasets, we can directly test the modern paradigm of structure formation and
evolution of baryonic matter in the Universe. 2014/10/04 - 22:12

We study the impact of the extra density fluctuations induced by primordial
magnetic fields on the reionization history in the redshift range: $6 < z <
10$. We perform a comprehensive MCMC physical analysis allowing the variation
of parameters related to primordial magnetic fields (strength, $B_0$, and
power-spectrum index $n_{\scriptscriptstyle \rm B}$), reionization, and
$\Lambda$CDM cosmological model. We find that magnetic field strengths in the
range: $B_0 \simeq 0.05{-}0.3$ nG (for nearly scale-free power spectra) can
significantly alter the reionization history in the above redshift range and
can relieve the tension between the WMAP and quasar absorption spectra data.
Our analysis puts upper-limits on the magnetic field strength $B_0 < 0.362,
0.116, 0.057$ nG (95 % c.l.) for $n_{\scriptscriptstyle \rm B} = -2.95, -2.9,
-2.85$, respectively. These represent the strongest magnetic field constraints
among those available from other cosmological observables. 2014/10/04 - 22:12

We propose a scenario for launching relativistic jets from rotating black
holes, in which small-scale magnetic flux loops, sustained by disc turbulence,
are forced to inflate and open by differential rotation between the black hole
and the accretion flow. This mechanism does not require a large-scale net
magnetic flux in the accreting plasma. Estimates suggest that the process could
operate effectively in many systems, and particularly naturally and efficiently
when the accretion flow is retrograde. We present the results of
general-relativistic force-free electrodynamic simulations demonstrating the
time evolution of the black hole's magnetosphere, the cyclic formation of jets,
and the effect of magnetic reconnection. The jets are highly variable on
timescales ~ 10-10^3 r_ g/c, where r_g is the black hole's gravitational
radius. The reconnecting current sheets observed in the simulations may be
responsible for the hard X-ray emission from accreting black holes. 2014/10/04 - 22:12

We explore the conditions for the thermal instability to operate in the
mini-spiral region of the Galactic centre (Sgr A*), where both the hot and cold
media are known to coexist. The photoionisation Cloudy calculations are
performed for different physical states of plasma. We neglect the dynamics of
the material and concentrate on the study of the parameter ranges where the
thermal instability may operate, taking into account the past history of Sgr A*
bolometric luminosity. We show that the thermal instability does not operate at
the present very low level of the Sgr A* activity. However, Sgr A* was much
more luminous in the past. For the highest luminosity states the two-phase
medium can be created up to 1.4 pc from the centre. The presence of dust grains
tends to suppress the instability, but the dust is destroyed in the presence of
strong radiation field and hot plasma. The clumpiness is thus induced in the
high activity period, and the cooling/heating timescales are long enough to
preserve later the past multi-phase structure. The instability enhances the
clumpiness of the mini-spiral medium and creates a possibility of episodes of
enhanced accretion of cold clumps towards Sgr A*. The mechanism determines the
range of masses and sizes of clouds; under the conditions of Sgr A*, the likely
values come out $1$ - $10^2M_{\oplus}$ for the cloud typical mass. 2014/10/04 - 22:12

The recent measurement of high energy extragalactic neutrinos by the IceCube
Collaboration has opened a new window to probe non-standard neutrino
properties. Among other effects, sterile neutrino altered dispersion relations
(ADRs) due to shortcuts in an extra dimension can significantly affect
astrophysical flavor ratios. We discuss two limiting cases of this effect,
first active-sterile neutrino oscillations with a constant ADR potential and
second an MSW-like resonant conversion arising from geodesics oscillating
around the brane in an asymmetrically warped extra dimension. We demonstrate
that the second case has the potential to yield the present best fit flavor
ratio of 1:0:0. 2014/10/04 - 22:12

A new proper motion catalog is presented, combining the Sloan Digital Sky
Survey (SDSS) with second epoch observations in the r band within a portion of
the SDSS imaging footprint. The new observations were obtained with the 90prime
camera on the Steward Observatory Bok 90 inch telescope, and the Array Camera
on the U.S. Naval Observatory, Flagstaff Station, 1.3 meter telescope. The
catalog covers 1098 square degrees to r = 22.0, an additional 1521 square
degrees to r = 20.9, plus a further 488 square degrees of lesser quality data.
Statistical errors in the proper motions range from 5 mas/year at the bright
end to 15 mas/year at the faint end, for a typical epoch difference of 6 years.
Systematic errors are estimated to be roughly 1 mas/year for the Array Camera
data, and as much as 2 - 4 mas/year for the 90prime data (though typically
less). The catalog also includes a second epoch of r band photometry. 2014/10/04 - 22:12

We investigate the evolution of two bars formed in fully self-consistent
hydrodynamical simulations of the formation of Milky Way-mass galaxies. One
galaxy shows higher central mass concentration and has a longer and stronger
bar than the other at $z = 0$. The stronger bar evolves by transferring its
angular momentum mainly to the dark halo. Consequently the rotation speed of
the bar decreases with time, while the amplitude of the bar increases with
time. While these features qualitatively agree with the results obtained by
idealized simulations, our bars show some unusual behaviors. The pattern speed
of the stronger bar largely goes up and down within a half revolution in its
early evolutionary stage. This unsteady rotation occurs when the bar is
misaligned with the $m = 4$ mode Fourier component. The amplitude of the weaker
bar does not increase despite the fact that its rotation slows down with time.
This result contradicts what is expected from idealized simulations and is
caused by the decline of the central density associated with the mass loss and
feedback from the stellar populations. In both galaxies, the bars are
terminated around $4(\Omega - \Omega_\mathrm{bar}) = \kappa$ resonances, where
$\Omega$, $\Omega_\mathrm{bar}$, and $\kappa$ are, respectively, the angular
frequency of a circular orbit, the bar patter speed, and the radial angular
frequency. 2014/10/04 - 22:12

We release the spectra for the more than 57000 objects presented in the First
VIPERS Data Release. For each object we distribute the observed, wavelength and
flux calibrated spectrum, as well as cleaned spectra, where artifacts due to
fringing are removed. We also provide the sky and noise spectrum and the 2D
spectrum. Data can be downloaded from this http URL 2014/10/04 - 22:12

Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic
outflows (jets) from accreting black holes at cosmological distances. Bright
afterglows are produced when the outflow collides with the ambient medium.
Afterglow polarization directly probes the magnetic properties of the jet, when
measured minutes after the burst, and the geometric properties of the jet and
the ambient medium when measured hours to days after the burst. High values of
optical polarization detected minutes after burst in GRB 120308A indicate the
presence of large-scale ordered magnetic fields originating from the central
engine (the power source of the GRB). Theoretical models predict low degrees of
linear polarization and negligable circular polarization at late times, when
the energy in the original ejecta is quickly transferred to the ambient medium
and propagates farther into the medium as a blastwave. Here we report the
detection of circularly polarized optical light in the afterglow of GRB
121024A, measured 0.15 days after the burst. We show that the circular
polarization is intrinsic to the afterglow and unlikely to be produced by dust
scattering or plasma propagation effects. A possible explanation is to invoke
anisotropic (rather than the commonly assumed isotropic) electron pitch angle
distributions, and we suggest that new models are required to produce the
complex microphysics of realistic shocks in relativistic jets. 2014/10/04 - 22:12

Comet C2011 J2 (Linear), was discovered to the Catalina Sky Survey
Observatory, based on University of Arizona. Is an hyperbolic comet passed to
the perihelion at T 2013 Dec. 25.4020 TT. The distance q from the Sun is
3.443732 A.U., that mean that dont never cross the snow line. Also, the Sun
gravitational force is not such to determine a strong stress on the cometary
nucleus. A possible fragmentation at that distance from the Sun in general, is
unlikely, but on 2014 September 19th, the CBAT 3979 by D. Green of the ICQ,
report the discoveries of a fragment companion of the comet main body. In the
following days others observers confirms the presence of the secondary body.
(F. Manzini et al. September 2014, IAU CBET 3986, 2014 September 24th) In the
observation of the comet on 2014 September 28, using a 25 cm Newton and CCD
with R photometric filter, I detect the secondary body and assuming as possible
scenario the presence of a solid fragment in the cloud of material of the
fragmentation, I measured some physical parameters, the magnitude in R band and
Af(rho) value of the two nuclei. Here are presented the preliminaries data. 2014/10/04 - 22:12

We have recently proposed a simplified scenario for blazars in which these
sources are classified as flat-spectrum radio quasars or BL Lacs according to
the prescriptions of unified schemes, and to a varying combination of Doppler
boosted radiation from the jet, emission from the accretion disk, the broad
line region, and light from the host galaxy. This scenario has been thoroughly
tested through detailed Monte Carlo simulations and reproduces all the main
features of existing radio, X-ray, and gamma-ray surveys. In this paper we
consider the case of very high energy emission (E > 100 GeV) extrapolating from
the expectations for the GeV band, which are in full accordance with the
Fermi-LAT survey results, and make detailed predictions for current and future
Cherenkov facilities, including the Cherenkov Telescope Array. Our results
imply that >~ 100 new blazars can be detected now at very high energy and up to
z ~1, consistently with the very recent MAGIC detection of S4 0218+35 at
z=0.944. 2014/10/04 - 22:12

Energy-dependent patterns in the arrival directions of cosmic rays are
searched for using data of the Pierre Auger Observatory. We investigate local
regions around the highest-energy cosmic rays with $E \geq 6 \cdot 10^{19}$ eV
by analyzing cosmic rays with energies above $E = 5 \cdot 10^{18}$ eV arriving
within an angular separation of approximately $15{\deg}$. We characterize the
energy distributions inside these regions by two independent methods, one
searching for angular dependence of energy-energy correlations and one
searching for collimation of energy along the local system of principal axes of
the energy distribution. No significant patterns are found with this analysis.
The comparison of these measurements with astrophysical scenarios can therefore
be used to obtain constraints on related model parameters such as strength of
cosmic-ray deflection and density of point sources. 2014/10/04 - 22:12

Peculiar motion introduces systematic variations in the observed luminosity
distribution of galaxies. This allows one to constrain the cosmic peculiar
velocity field from large galaxy redshift surveys. Using around half a million
galaxies from the SDSS Data Release 7 at z ~ 0.1, we demonstrate the
applicability of this approach to large datasets and obtain bounds on peculiar
velocity moments and $\sigma_{8}$, the amplitude of the linear matter power
spectrum. Our results are in good agreement with the $\Lambda$CDM model and
consistent with the previously reported ~ 1% zero-point tilt in the SDSS
photometry. Finally, we discuss the prospects of constraining the growth rate
of density perturbations by reconstructing the full linear velocity field from
the observed galaxy clustering in redshift space. 2014/10/04 - 22:12

47 Tucanae is one of the most interesting and well observed and theoretically
studied globular clusters. This allows us to study the reliability of our
understanding of white dwarf cooling sequences, to confront different methods
to determine its age, and to assess other important characteristics, like its
star formation history. Here we present a population synthesis study of the
cooling sequence of the globular cluster 47 Tucanae. In particular, we study
the distribution of effective temperatures, the shape of the color-magnitude
diagram, and the corresponding magnitude and color distributions. We do so
using an up-to-date population synthesis code based on Monte Carlo techniques,
that incorporates the most recent and reliable cooling sequences and an
accurate modeling of the observational biases. We find a good agreement between
our theoretical models and the observed data. Thus, our study, rules out
previous claims that there are still missing physics in the white dwarf cooling
models at moderately high effective temperatures. We also derive the age of the
cluster using the termination of the cooling sequence, obtaining a good
agreement with the age determinations using the main-sequence turn-off.
Finally, we find that the star formation history of the cluster is compatible
with that btained using main sequence stars, which predict the existence of two
distinct populations. We conclude that a correct modeling of the white dwarf
population of globular clusters, used in combination with the number counts of
main sequence stars provides an unique tool to model the properties of globular
clusters. 2014/10/04 - 22:12

Embedded in the gaseous protoplanetary disk, Jupiter and Saturn naturally
become trapped in 3:2 resonance and migrate outward. This serves as the basis
of the Grand Tack model. However, previous hydrodynamical simulations were
restricted to isothermal disks, with moderate aspect ratio and viscosity. Here
we simulate the orbital evolution of the gas giants in disks with viscous
heating and radiative cooling. We find that Jupiter and Saturn migrate outward
in 3:2 resonance in modest-mass ($M_{disk} \approx M_{MMSN}$, where MMSN is the
"minimum-mass solar nebula") disks with viscous stress parameter $\alpha$
between $10^{-3}$ and $10^{-2} $. In disks with relatively low-mass ($M_{disk}
\lesssim M_{MMSN}$) , Jupiter and Saturn get captured in 2:1 resonance and can
even migrate outward in low-viscosity disks ($\alpha \le 10^{-4}$). Such disks
have a very small aspect ratio ($h\sim 0.02-0.03$) that favors outward
migration after capture in 2:1 resonance, as confirmed by isothermal runs which
resulted in a similar outcome for $h \sim 0.02$ and $\alpha \le 10^{-4}$. We
also performed N-body runs of the outer Solar System starting from the results
of our hydrodynamical simulations and including 2-3 ice giants. After dispersal
of the gaseous disk, a Nice model instability starting with Jupiter and Saturn
in 2:1 resonance results in good Solar Systems analogs. We conclude that in a
cold Solar Nebula, the 2:1 resonance between Jupiter and Saturn can lead to
outward migration of the system, and this may represent an alternative scenario
for the evolution of the Solar System. 2014/10/04 - 22:12

This work presents the first results from an ESO Large Programme carried out
using the OSIRIS instrument on the 10m GTC telescope (La Palma). We have
observed a large sample of galaxies in the region of the Abell 901/902 system
(z ~ 0.165) which has been extensively studied as part of the STAGES project.
We have obtained spectrally and spatially resolved H-alpha and [NII] emission
maps for a very large sample of galaxies covering a broad range of
environments. The new data are combined with extensive multi-wavelength
observations which include HST, COMBO-17, Spitzer, Galex and XMM imaging to
study star formation and AGN activity as a function of environment and galaxy
properties such as luminosity, mass and morphology. The ultimate goal is to
understand, in detail, the effect of the environment on star formation and AGN
activity. 2014/10/04 - 22:12

We point out that the direct detection of dark matter via its
electro-magnetic polarizability is described by two new nuclear form factors,
which are controlled by the 2-nucleon nuclear density. The signature manifests
a peculiar dependence on the atomic and mass numbers of the target nuclei, as
well as on the momentum transfer, and can differ significantly from experiment
to experiment. We also discuss UV completions of our scenario. 2014/10/04 - 22:12

We report the discovery of 1SWASP J022916.91-395901.4 = GSC 07552-00389, a
possible new VY Sculptoris variable in Eridanus, which is associated with the
X-ray source 1RXS J022917.1-395851. 2014/10/04 - 22:12

Twenty years ago, construction began on the Laser Interferometer
Gravitational-wave Observatory (LIGO). Two facilities with $4~{\rm km}$ long
L-shaped vacuum envelops were built at two sites in Washington state and
Louisiana. Initial LIGO reached its design sensitivity and finished observing
in 2010. Advanced LIGO has just been installed in the same facility and will
have 10 times better sensitivity than Initial LIGO. Looking further into the
future, design studies for third generation detectors in the same facility are
in progress. However, they are severely restricted by the size of the existing
vacuum system, leading to no more than a factor of a few improvement in
sensitivity. We make a case for the advantages of longer arm cavities and show
that a ten-fold increase in sensitivity over Advanced LIGO is possible.
Furthermore, this can be achieved by reusing existing Advanced LIGO hardware
with only modest changes. This third generation observatory would be able to
see binary black hole mergers up to a horizon distance of redshift 7. 2014/10/04 - 22:12

Context. Ultraviolet radiation plays a crucial role in molecular clouds.
Radiation and matter are tightly coupled and their interplay influences the
physical and chemical properties of gas. In particular, modeling the radiation
propagation requires calculating column densities, which can be numerically
expensive in high-resolution multidimensional simulations. Aims. Developing
fast methods for estimating column densities is mandatory if we are interested
in the dynamical influence of the radiative transfer. In particular, we focus
on the effect of the UV screening on the dynamics and on the statistical
properties of molecular clouds. Methods. We have developed a tree-based method
for a fast estimate of column densities, implemented in the adaptive mesh
refinement code RAMSES. We performed numerical simulations using this method in
order to analyze the influence of the screening on the clump formation.
Results. We find that the accuracy for the extinction of the tree-based method
is better than 10%, while the relative error for the column density can be much
more. We describe the implementation of a method based on precalculating the
geometrical terms that noticeably reduces the calculation time. To study the
influence of the screening on the statistical properties of molecular clouds we
present the probability distribution function (PDF) of gas and the associated
temperature per density bin and the mass spectra for different density
thresholds. Conclusions. The tree-based method is fast and accurate enough to
be used during numerical simulations since no communication is needed between
CPUs when using a fully threaded tree. It is then suitable to parallel
computing. We show that the screening for far UV radiation mainly affects the
dense gas, thereby favoring low temperatures and affecting the fragmentation. 2014/10/04 - 22:12

Thanks to the data from Planck Collaboration, the scalar spectral index of
primordial fluctuations is known with a very high accuracy. The recent findings
of the BICEP2 collaboration, although still under scrutiny, fix also the ratio
between the tensor and the scalar power spectra to a value that implies a
non-negligible production of gravitational waves in the inflationary Universe.
In this letter we show that purely quadratic, renormalizable, and
scale-invariant gravity, implemented by loop- corrections, yields very precise
predictions when compared to these data. In addition, this model naturally
exits inflation towards a standard reheating phase. In contrast to other
scale-invariant models, our scenario does not need matter fields coupled to
gravity to explain inflation. 2014/10/04 - 22:12

As we showed in previous work, the dynamics and gravitational emission of
binary neutron star systems in scalar-tensor theories can differ significantly
from that expected from General Relativity in the coalescing stage. In this
work we examine whether the characteristics of the electromagnetic counterparts
to these binaries -- driven by magnetosphere interactions prior to the merger
event -- can provide an independent way to test gravity in the most strongly
dynamical stages of binary mergers. We find that the electromagnetic flux
emitted by binaries in scalar-tensor theories can show deviations from the GR
prediction in particular cases. These differences are quite subtle, thus
requiring delicate measurements to differentiate between GR and the type of
scalar-tensor theories considered in this work using electromagnetic
observations alone. However, if coupled with a gravitational-wave detection,
electromagnetic measurements might provide a way to increase the confidence
with which GR will be confirmed (or ruled out) by gravitational observations. 2014/10/04 - 22:12

We extend the theory of astrophysical maser propagation through a medium with
a Zeeman-split molecular response to the case of a non-uniform magnetic field,
and allow a component of the electric field of the radiation in the direction
of propagation: a characteristic of radiation with orbital angular momentum. A
classical reduction of the governing equations leads to a set of nine
differential equations for the evolution of intensity-like parameters for each
Fourier component of the radiation. Four of these parameters correspond to the
standard Stokes parameters, whilst the other five represent the $z$-component
of the electric field, and its coupling to the conventional components in the
$x-y$-plane. A restricted analytical solution of the governing equations
demonstrates a non-trivial coupling of the Stokes parameters to those
representing orbital angular momentum: the $z$-component of the electric field
can grow from a background in which only Stokes-$I$ is non-zero. A numerical
solution of the governing equations reveals radiation patterns with a radial
and angular structure for the case of an ideal quadrupole magnetic field
perpendicular to the propagation direction. In this ideal case generation of
radiation orbital angular momentum, like polarization, can approach 100 per
cent. 2014/10/04 - 22:12

We report the first results of DarkSide-50, a direct search for dark matter
operating in the underground Laboratori Nazionali del Gran Sasso (LNGS) and
searching for the rare nuclear recoils possibly induced by weakly interacting
massive particles (WIMPs). The dark matter detector is a Liquid Argon Time
Projection Chamber with a (46.4+-0.7) kg active mass, operated inside a 30 t
organic liquid scintillator neutron veto, which is in turn installed at the
center of a 1 kt water Cherenkov veto for the residual flux of cosmic rays. We
report here the null results of a dark matter search for a (1422+-67) kg d
exposure with an atmospheric argon fill. This is the most sensitive dark matter
search performed with an argon target, corresponding to a 90% CL upper limit on
the WIMP-nucleon spin-independent cross section of 6.1x10^-44 cm^2 for a WIMP
mass of 100 GeV/c^2. 2014/10/04 - 22:12

Neutron star (NS) masses and radii can be estimated from observations of
photospheric radius-expansion X-ray bursts, provided the chemical composition
of the photosphere, the spectral colour-correction factors in the observed
luminosity range, and the emission area during the bursts are known. By
analysing 246 X-ray bursts observed by the Rossi X-ray Timing Explorer from 11
low-mass X-ray binaries, we find a dependence between the persistent spectral
properties and the time evolution of the black body normalisation during the
bursts. All NS atmosphere models predict that the colour-correction factor
decreases in the early cooling phase when the luminosity first drops below the
limiting Eddington value, leading to a characteristic pattern of variability in
the measured blackbody normalisation. However, the model predictions agree with
the observations for most bursts occurring in hard, low-luminosity, 'island'
spectral states, but rarely during soft, high-luminosity, 'banana' states. The
observed behaviour may be attributed to the accretion flow, which influences
cooling of the NS preferentially during the soft state bursts. This result
implies that only the bursts occurring in the hard, low-luminosity spectral
states can be reliably used for NS mass and radius determination. 2014/10/04 - 22:12

We derive a model for the motion of a rotating flat ellispoid with a
stochastic flattening based on an invariance theorem for stochastic
differential equations. A numerical study of a toy-model is performed leading
to an intriguing coincidence with observational data. 2014/10/04 - 22:12

Galaxy clusters are predicted to produce gamma-rays through cosmic ray
interactions and/or dark matter annihilation, potentially detectable by the
Fermi Large Area Telescope (Fermi-LAT). We present a new, independent stacking
analysis of Fermi-LAT photon count maps using the 78 richest nearby clusters
(z<0.12) from the Two Micron All-Sky Survey (2MASS) cluster catalog. We obtain
the lowest limit on the photon flux to date, 2.3e-11 ph/s/cm^2 (95% confidence)
per cluster in the 0.8-100 GeV band, which corresponds to a luminosity limit of
3.5e44 ph/s. We also constrain the emission limits in a range of narrower
energy bands. Scaling to recent cosmic ray acceleration and gamma-ray emission
models, we find that cosmic rays represent a negligible contribution to the
intra-cluster energy density and gas pressure. 2014/10/04 - 22:12

We consider the reasons why a cuspy NFW-like profile persistently occurs in
N-body simulations, in contradiction to some astronomical observations. The
routine method of testing the convergence of N-body simulations (in particular,
the negligibility of two-body scattering effect) is to find the conditions
under which the shape of the formed structures is insensitive to numerical
parameters. The results obtained with this approach suggest a surprisingly
minor role of the particle collisions: the central density profile remains
untouched and close to NFW, even if the simulation time significantly exceeds
the collisional relaxation time $\tau_r$. We analyze the test body distribution
in the halo center with help of the Fokker-Planck equation. It turns out that
the Fokker-Planck diffusion transforms any reasonable initial distribution into
NFW-like profile $\rho\propto r^{-1}$ in a time shorter than $\tau_r$. On the
contrary, profile $\rho\propto r^{-1}$ should survive much longer, being a sort
of attractor: the Fokker-Planck diffusion is self-compensated in this case.
Thus the test body scattering may create a stable NFW-like pseudosolution that
can be mixed up with the real convergence. This fact might help to eliminate
the well-known 'cusp vs. core' problem. 2014/10/04 - 22:12

The theory of nonlinear massive gravity can be extended into the F(R) form as
developed in Phys.Rev.D90, 064051 (2014). Being free of the Boulware-Deser
ghost, such a construction has the additional advantage of exhibiting no linear
instabilities around a cosmological background. We investigate various
cosmological evolutions of a universe governed by this generalized massive
gravitational theory. Specifically, under the Starobinsky ansantz, this model
provides a unified description of the cosmological history, from early-time
inflation to late-time self-acceleration. Moreover, under viable F(R) forms,
the scenario leads to a very interesting dark-energy phenomenology, including
the realization of the quintom scenario without any pathology. Finally, we
provide a detailed analysis of the cosmological perturbations at linear order,
as well as the Hamiltonian constraint analysis, in order to examine the
physical degrees of freedom. 2014/10/04 - 22:12

The standard cosmological model, LCDM, provides an excellent fit to Cosmic
Microwave Background (CMB) data. However, the model has well known problems.
For example, the cosmological constant, is fine-tuned to 1 part in 10^100 and
the cold dark matter (CDM) particle is not yet detected in the laboratory.
Shanks previously investigated a model which assumed neither exotic particles
nor a cosmological constant but instead postulated a low Hubble constant (H_0)
to allow a baryon density compatible with inflation and zero spatial curvature.
However, recent Planck results make it more difficult to reconcile such a model
with CMB power spectra. Here we relax the previous assumptions to assess the
effects of assuming three active neutrinos of mass ~5eV. If we assume a low
H_0~45kms^-1Mpc^-1 then, compared to the previous purely baryonic model, we
find a significantly improved fit to the first 3 peaks of the Planck power
spectrum. Nevertheless, the goodness-of-fit is still significantly worse than
for LCDM and would require appeal to unknown systematic effects for the fit
ever to be considered acceptable. A further serious problem is that the
amplitude of fluctuations is low (sigma_8~0.2) making it difficult to form
galaxies by the present day. This might then require seeds, perhaps from a
primordial magnetic field, to be invoked for galaxy formation. These and other
problems demonstrate the difficulties faced by models other than LCDM in
fitting ever more precise cosmological data. 2014/10/04 - 22:12

We investigate the consequences of superkicks on the population of
supermassive black holes (SMBHs) in the Universe residing in brightest cluster
galaxies (BCGs). There is strong observational evidence that BCGs grew
prominently at late times (up to a factor 2-4 in mass from z=1), mainly through
mergers with satellite galaxies from the cluster, and they are known to host
the most massive SMBHs ever observed. Those SMBHs are also expected to grow
hierarchically, experiencing a series of mergers with other SMBHs brought in by
merging satellites. Because of the net linear momentum taken away from the
asymmetric gravitational wave emission, the remnant SMBH experiences a kick in
the opposite direction. Kicks may be as large as ~5000 Km/s ("superkicks"),
pushing the SMBHs out in the cluster outskirts for a time comparable to
galaxy-evolution timescales. We predict, under a number of plausible
assumptions, that superkicks can efficiently eject SMBHs from BCGs, bringing
their occupation fraction down to a likely range 0.9<f<0.99 in the local
Universe. Future thirty-meter-class telescopes like ELT and TMT will be capable
of measuring SMBHs in hundreds of BCGs up to z=0.2, testing the occurrence of
superkicks in nature and the strong-gravity regime of SMBH mergers. 2014/10/04 - 22:12