510 research outputs found
The dynamics and high-energy emission of conductive gas clouds in supernova-driven galactic superwinds
In this paper we present high-resolution hydrodynamical models of warm
ionized clouds embedded in a superwind, and compare the OVI and soft X-ray
properties to the existing observational data. These models include thermal
conduction, which we show plays an important role in shaping both the dynamics
and radiative properties of the resulting wind/cloud interaction. Heat
conduction stabilizes the cloud by inhibiting the growth of K-H and R-T
instabilities, and also generates a shock wave at the cloud's surface that
compresses the cloud. This dynamical behaviour influences the observable
properties. We find that while OVI emission and absorption always arises in
cloud material at the periphery of the cloud, most of the soft X-ray arises in
the region between the wind bow shock and the cloud surface, and probes either
wind or cloud material depending on the strength of conduction and the relative
abundances of the wind with respect to the cloud. In general only a small
fraction (<1%) of the wind mechanical energy intersecting a cloud is radiated
away at UV and X-ray wavelengths, with more wind energy going into accelerating
the cloud. Models with heat conduction at Spitzer-levels are found to produce
observational properties closer to those observed in superwinds than models
with no thermal conduction, in particular in terms of the OVI-to-X-ray
luminosity ratio, but cloud life times are uncomfortably short (<1Myr) compared
to the dynamical ages of real winds. We experimented with reducing the thermal
conductivity and found that even when we reduced conduction by a factor of 25
that the simulations retained the beneficial hydrodynamical stability and low
O{\sc vi}-to-X-ray luminosity ratio found in the Spitzer-level conductive
models, while also having reduced evaporation rates.Comment: 27 pages, 12 figures (4 in color), MNRAS accepte
Black Hole Mass, Host galaxy classification and AGN activity
We investigate the role of host galaxy classification and black hole mass in
a heterogeneous sample of 276 mostly nearby (z<0.1) X-ray and IR selected AGN.
Around 90% of Seyfert 1 AGN in bulge-dominated host galaxies (without disk
contamination) span a very narrow range in the observed 12um to 2-10keV
luminosity ratio (1<R_{IR/X}<7). This narrow dispersion incorporates all
possible variations among AGN central engines, including accretion mechanism
and efficiency, disk opening angle, orientation to sightline, covering fraction
of absorbing material, patchiness of X-ray corona and measured variability. As
a result, all models of X-ray and IR production in AGN are very strongly
constrained. Among Seyfert 1 AGN, median X-ray and IR luminosities increase
with black hole mass at >99% confidence. Using ring morphology of the host
galaxy as a proxy for lack of tidal interaction, we find that AGN luminosity in
host galaxies within 70Mpc is independent of host galaxy interaction for
Gyrs, suggesting that the timescale of AGN activity due to secular evolution is
much shorter than that due to tidal interactions. We find that LINER hosts have
lower 12um luminosity than the median 12um luminosity of normal disk- and
bulge-dominated galaxies which may represent observational evidence for past
epochs of feedback that supressed star formation in LINER host galaxies. We
propose that nuclear ULXs may account for the X-ray emission from LINER 2s
without flat-spectrum, compact radio cores. We confirmed the robustness of our
results in X-rays by comparing them with the 14-195keV 22-month BAT survey of
AGN, which is all-sky and unbiased by photoelectric absorption.Comment: MNRAS accepted. 14 pages, 11 figures, complete Table 1 in online
journa
Unusual magneto-optical behavior induced by local dielectric variations under localized surface plasmon excitations
We study the effect of global and local dielectric variations on the polarization conversion rps response of ordered nickel nanowires embedded in an alumina matrix. When considering local changes, we observe a non-monotonous behavior of the rps, its intensity unusually modified far beyond to what it is expected for a monotonous change of the whole refractive index of the embedding medium. This is related to the local redistribution of the electromagnetic field when a localized surface plasmon is excited. This finding may be employed to develop and improve new biosensing magnetoplasmonic devices
First upper limits from LIGO on gravitational wave bursts
We report on a search for gravitational wave bursts using data from the first
science run of the LIGO detectors. Our search focuses on bursts with durations
ranging from 4 ms to 100 ms, and with significant power in the LIGO sensitivity
band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than
1.6 events per day at 90% confidence level. This result is interpreted in terms
of the detection efficiency for ad hoc waveforms (Gaussians and sine-Gaussians)
as a function of their root-sum-square strain h_{rss}; typical sensitivities
lie in the range h_{rss} ~ 10^{-19} - 10^{-17} strain/rtHz, depending on
waveform. We discuss improvements in the search method that will be applied to
future science data from LIGO and other gravitational wave detectors.Comment: 21 pages, 15 figures, accepted by Phys Rev D. Fixed a few small typos
and updated a few reference
Analysis of LIGO data for gravitational waves from binary neutron stars
We report on a search for gravitational waves from coalescing compact binary
systems in the Milky Way and the Magellanic Clouds. The analysis uses data
taken by two of the three LIGO interferometers during the first LIGO science
run and illustrates a method of setting upper limits on inspiral event rates
using interferometer data. The analysis pipeline is described with particular
attention to data selection and coincidence between the two interferometers. We
establish an observational upper limit of 1.7 \times 10^{2}M_\odot$.Comment: 17 pages, 9 figure
Detector Description and Performance for the First Coincidence Observations between LIGO and GEO
For 17 days in August and September 2002, the LIGO and GEO interferometer
gravitational wave detectors were operated in coincidence to produce their
first data for scientific analysis. Although the detectors were still far from
their design sensitivity levels, the data can be used to place better upper
limits on the flux of gravitational waves incident on the earth than previous
direct measurements. This paper describes the instruments and the data in some
detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial
change
From Geometry to Numerics: interdisciplinary aspects in mathematical and numerical relativity
This article reviews some aspects in the current relationship between
mathematical and numerical General Relativity. Focus is placed on the
description of isolated systems, with a particular emphasis on recent
developments in the study of black holes. Ideas concerning asymptotic flatness,
the initial value problem, the constraint equations, evolution formalisms,
geometric inequalities and quasi-local black hole horizons are discussed on the
light of the interaction between numerical and mathematical relativists.Comment: Topical review commissioned by Classical and Quantum Gravity.
Discussion inspired by the workshop "From Geometry to Numerics" (Paris, 20-24
November, 2006), part of the "General Relativity Trimester" at the Institut
Henri Poincare (Fall 2006). Comments and references added. Typos corrected.
Submitted to Classical and Quantum Gravit
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III
The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from
submitted version
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