42 research outputs found
The faintest star forming galaxies
I briefly report on the X-ray detection of 10 radio sub-mJy sources in the 2
Ms Chandra observation of the Hubble Deep Field North region. These sources
follow the same radio/X-ray luminosities relation which holds for nearby
galaxies. Making use of this relation, X-ray number counts from star forming
galaxies are predicted from the deep radio Log N-Log S's.Comment: 1 page, 2 figures. Proc. workshop "X-ray surveys in the light of the
new observatories" held in Santander (E) 2002. LaTeX, anabs.cls include
Astrometry and exoplanets in the Gaia era: a Bayesian approach to detection and parameter recovery
(abridged) We develop Bayesian methods and detection criteria for orbital
fitting, and revise the detectability of exoplanets in light of the in-flight
properties of Gaia. Limiting ourselves to one-planet systems as a first step of
the development, we simulate Gaia data for exoplanet systems over a grid of
S/N, orbital period, and eccentricity. The simulations are then fit using
Markov chain Monte Carlo methods. We investigate the detection rate according
to three information criteria and the delta chi^2. For the delta chi^2, the
effective number of degrees of freedom depends on the mission length. We find
that the choice of the Markov chain starting point can affect the quality of
the results; we therefore consider two limit possibilities: an ideal case, and
a very simple method that finds the starting point assuming circular orbits.
Using Jeffreys' scale of evidence, the fraction of false positives passing a
strong evidence criterion is < ~0.2% (0.6%) when considering a 5 yr (10 yr)
mission and using the Akaike information criterion or the Watanabe-Akaike
information criterion, and <0.02% (<0.06%) when using the Bayesian information
criterion. We find that there is a 50% chance of detecting a planet with a
minimum S/N=2.3 (1.7). This sets the maximum distance to which a planet is
detectable to ~70 pc and ~3.5 pc for a Jupiter-mass and Neptune-mass planet,
respectively, assuming a 10 yr mission, a 4 au semi-major axis, and a 1 M_sun
star. The period is the orbital parameter that can be determined with the best
accuracy, with a median relative difference between input and output periods of
4.2% (2.9%) assuming a 5 yr (10 yr) mission. The median accuracy of the
semi-major axis of the orbit can be recovered with a median relative error of
7% (6%). The eccentricity can also be recovered with a median absolute accuracy
of 0.07 (0.06).Comment: 18 pages, 11 figures. New version accepted by A&A for publicatio
The 31 Deg Release of the Stripe 82 X-ray Survey: The Point Source Catalog
We release the next installment of the Stripe 82 X-ray survey point-source
catalog, which currently covers 31.3 deg of the Sloan Digital Sky Survey
(SDSS) Stripe 82 Legacy field. In total, 6181 unique X-ray sources are
significantly detected with {\it XMM-Newton} () and {\it Chandra}
(). This catalog release includes data from {\it XMM-Newton} cycle
AO 13, which approximately doubled the Stripe 82X survey area. The flux limits
of the Stripe 82X survey are erg s cm,
erg s cm, and erg
s cm in the soft (0.5-2 keV), hard (2-10 keV), and full bands
(0.5-10 keV), respectively, with approximate half-area survey flux limits of
erg s cm, erg s
cm, and erg s cm. We matched the X-ray
source lists to available multi-wavelength catalogs, including updated matches
to the previous release of the Stripe 82X survey; 88\% of the sample is matched
to a multi-wavelength counterpart. Due to the wide area of Stripe 82X and rich
ancillary multi-wavelength data, including coadded SDSS photometry,
mid-infrared {\it WISE} coverage, near-infrared coverage from UKIDSS and VHS,
ultraviolet coverage from {\it GALEX}, radio coverage from FIRST, and
far-infrared coverage from {\it Herschel}, as well as existing 30\%
optical spectroscopic completeness, we are beginning to uncover rare objects,
such as obscured high-luminosity AGN at high-redshift. The Stripe 82X point
source catalog is a valuable dataset for constraining how this population grows
and evolves, as well as for studying how they interact with the galaxies in
which they live.Comment: accepted for publication in ApJ; 23 pages (emulateapj
X-ray Spectral Study of the extended emission,'the Cap', located 11.6 kpc above the disk of M82
The extended X-ray emission from 'the Cap' region located 11' (11.6 kpc)
above the disk of the starburst galaxy M82 has been observed with Suzaku and
XMM-Newton. Owing to the good energy resolution and the large collecting area
of the XIS on Suzaku, combined with similar properties of the EPIC instrument
on XMM-Newton, we have clearly detected K-shell emission lines from O VII, O
VIII, Ne X, Mg XI, Mg XII and the Fe-L complex. Two optically-thin thermal
plasma components are required to fit the observed X-ray spectra. We have
determined the metal abundances of O, Ne, Mg, Si and Fe in this region for the
first time. Their metal abundance ratios agree well with those of metal-poor
stars and the model prediction of metals synthesized by type-II supernovae, but
they are not consistent with the metallicities of type-Ia supernovae. This
result is support for the idea that the origin of the metals in the Cap is
type-II supernovae explosions occurring in the starburst regions in the M82
galaxy. We discuss the possible contribution from sputtered dust grains to the
metals in the Cap. An emission line consistent with the C VI transition of n=4
to 1 at 0.459 keV is marginally detected, although it is not statistically
significant at the 99% confidence level; the presence of this line would
suggest charge-exchange processes in the Cap.Comment: 16 pages, 10 figuer