909 research outputs found
XMM-Newton and Deep Optical Observations of the OTELO fields: the Groth-Westphal Strip
OTELO (OSIRIS Tunable Emission Line Object Survey) will be carried out with
the OSIRIS instrument at the 10 m GTC telescope at La Palma, and is aimed to be
the deepest and richest survey of emission line objects to date. The deep
narrow-band optical data from OSIRIS will be complemented by means of
additional observations that include: (i) an exploratory broad-band survey that
is already being carried out in the optical domain, (ii) FIR and sub-mm
observations to be carried with the Herschel space telescope and the GTM, and
(iii) deep X-Ray observations from XMM-Newton and Chandra.Here we present a
preliminary analysis of public EPIC data of one of the OTELO targets,the
Groth-Westphal strip, gathered from the XMM-Newton Science Archive (XSA). EPIC
images are combined with optical BVRI data from our broadband survey carried
out with the 4.2m WHT at La Palma. Distance-independent diagnostics (involving
X/O ratio, hardness ratios, B/T ratio) are tested.Comment: 2 pages, 2 figures, uses graphicx package. To appear in proceedings
of "The X-Ray Universe 2005", San Lorenzo del Escorial, Spain, September
26-30, 200
X-ray Spectra of the RIXOS source sample
We present results of an extensive study of the X-ray spectral properties of
sources detected in the RIXOS survey, that is nearly complete down to a flux
limit of 3e-14 cgs (0.5-2 keV). We show that for X-ray surveys containing
sources with low count rate spectral slopes estimated using simple hardness
ratios in the ROSAT band can be biased. Instead we analyse three-colour X-ray
data using statistical techniques appropriate to the Poisson regime which
removes the effects of this bias. We have then applied this technique to the
RIXOS survey to study the spectral properties of the sample. For the AGN we
find an average energy index of 1.05+-0.05 with no evidence for spectral
evolution with redshift. Individual AGN are shown to have a range of properties
including soft X-ray excesses and intrinsic absorption. Narrow Emission Line
Galaxies also seem to fit to a power-law spectrum, which may indicate a
non-thermal origin for their X-ray emission. We infer that most of the clusters
in the sample have a bremsstrahlung temperature >3 keV, although some show
evidence for a cooling flow. The stars deviate strongly from a power-law model
but fit to a thermal model. Finally, we have analysed the whole RIXOS sample
containing 1762 sources. We find that the mean spectral slope of the sources
hardens at lower fluxes in agreement with results from other samples. However,
a study of the individual sources demonstrates that the hardening of the mean
is caused by the appearance of a population of very hard sources at the lowest
fluxes. This has implications for the nature of the soft X-ray background.Comment: 31,LaTeX file, 2 PS files with Table 2 and 22 PS figures. MNRAS in
pres
OSIRIS Software: The Mask Designer Tool
OSIRIS is a Day One instrument that will be available at the 10m GTC
telescope which is being built at La Palma observatory in the Canary Islands.
This optical instrument is designed to obtain wide-field narrow-band images
using tunable filters and to do low-resolution spectroscopy in both long-slit
and multislit modes. For the multislit spectroscopy mode, we have developed a
software to assist the observers to design focal plane masks. In this paper we
describe the characteristics of this Mask Designer tool. We discuss the main
design concepts, the functionality and particular features of the software.Comment: 6 figures; accepted for publication in Experimental Astronom
A FIRST-APM-SDSS survey for high-redshift radio QSOs
We selected from VLA-FIRST a sample of 94 objects starlike in SDSSS, and with
APM colour O-E>2, i.e. consistent with their being high-z QSOs. 78 candidates
were classified spectroscopically from published data (mainly SDSS) or
observations reported here. The fractions of QSOs (51/78) and z > 3 QSOs
(23/78) are comparable to those found in other photometric searches for high-z
QSOs. We confirm that O-E>2 ensures inclusion of all QSOs with 3.7 < z < 4.4.
The fraction of broad absorption line (BAL) QSOs for 2 < z < 4.4 is 27+-10 per
cent (7/26), and the estimated BAL fraction for radio loud (RL) QSOs is at
least as high as for optically selected QSOs (about 13 per cent). The high BAL
fraction and the high fraction of LoBALs in our sample are likely due to the
red colour selection. The space density of RL QSOs for 3.7 < z < 4.4, MAB (1450
A) 10^25.7 W Hz^(-1) is 1.7+-0.6 Gpc^(-3). Adopting a
RL fraction 13.4+-3 per cent, this corresponds to rho = 12.5+-5.6 Gpc^(-3), in
good agreement with the SDSS QSO luminosity function in Fan et al. (2001). We
note the unusual QSO FIRST 1413+4505 (z=3.11), which shows strong associated
Lyalpha absorption and an extreme observed luminosity, L about 2 x 10^(15)
solar luminosities.Comment: Accepted for publication in MNRAS; 9 figures and 6 tables; Table 2 is
in landscape forma
Are radio galaxies and quiescent galaxies different? Results from the analysis of HST brightness profiles
We present a study of the optical brightness profiles of early type galaxies,
using a number of samples of radio galaxies and optically selected elliptical
galaxies. For the radio galaxy samples--B2 of Fanaroff-Riley type I and 3C of
Fanaroff-Riley type II-- we determined a number of parameters that describe a
"Nuker-law" profile, which were compared with those already known for the
optically selected objects. We find that radio active galaxies are always of
the "core" type (i.e. an inner Nuker law slope gamma < 0.3). However, there are
core-type galaxies which harbor no significant radio source and which are
indistinguishable from the radio active galaxies. We do not find any radio
detected galaxy with a power law profile (gamma > 0.5). This difference is not
due to any effect with absolute magnitude, since in a region of overlap in
magnitude the dichotomy between radio active and radio quiescent galaxies
remains. We speculate that core-type objects represent the galaxies that have
been, are, or may become, radio active at some stage in their lives; active and
non-active core-type galaxies are therefore identical in all respects except
their eventual radio-activity: on HST scales we do not find any relationship
between boxiness and radio-activity. There is a fundamental plane, defined by
the parameters of the core (break radius r_b and break brightness mu_b), which
is seen in the strong correlation between r_b and mu_b. The break radius is
also linearly proportional to the optical Luminosity in the band. Moreover,
for the few galaxies with an independently measured black hole mass, the break
radius turns out to be tightly correlated with M_{BH}. The black hole mass
correlates even better with the combination of fundamental plane parameters r_b
and mu_b, which represents the central velocity dispersion.Comment: Accepted for publication in A&A, 20 Pages, 9 figure
Quasi two-dimensional antiferromagnet on a triangular lattice RbFe(MoO4)2
RbFe(MoO4)2 is a rare example of a nearly two-dimensional Heisenberg
antiferromagnet on a triangular lattice. Magnetic resonance spectra and
magnetization curves reveal that the system has a layered spin structure with
six magnetic sublattices. The sublattices within a layer are arranged in a
triangular manner with the magnetization vectors 120 degree apart. The H-T
phase diagram, containing at least five different magnetic phases is
constructed. In zero field, RbFe(MoO4)2 undergoes a phase transition at T_N=3.8
K into a non-collinear triangular spin structure with all the spins confined in
the basal plane. The application of an in-plane magnetic field induces a
collinear spin state between the fields H_c1=47 kOe and H_c2=71 kOe and
produces a magnetization plateau at one-third of the saturation moment. Both
the ESR and the magnetization measurements also clearly indicate an additional
first-order phase transition in a field of 35 kOe. The exact nature of this
phase transition is uncertain.Comment: 9 pages incl 11 figure
HST images of B2 radio galaxies: a link between circum-nuclear dust and radio properties?
Almost 60% of the B2 low luminosity radio galaxies have been observed with
the Hubble Space Telescope. We present an analysis of the dust features, which
are often present in the form of circum-nuclear disks or lanes, and show that
there are correlations between radio source and dust properties. It is found
that nearby radio sources in which a jet has been detected tend to have dust
more often than sources without jets; the dust is often in the form of disks or
lanes. Moreover the radio jets are close to perpendicular to the disk or lane
in the weaker radio sources (with P < 10^{24} W/Hz). In stronger sources the
orientation effect appears to be weak or even absent. Also the dust masses
found in the weaker radio sources are smaller than in the stronger ones (log
M/M_sun ~ 3 against 5 respectively). More generally it appears that there is a
correlation between dust mass and total radio power (for those sources in which
dust has been detected); we show that this correlation is not induced by
redshift.Comment: Accepted for publication in A&A, 10 pages, 12 figure
Spin-dynamics simulations of the triangular antiferromagnetic XY model
Using Monte Carlo and spin-dynamics methods, we have investigated the dynamic
behavior of the classical, antiferromagnetic XY model on a triangular lattice
with linear sizes . The temporal evolutions of spin configurations
were obtained by solving numerically the coupled equations of motion for each
spin using fourth-order Suzuki-Trotter decompositions of exponential operators.
From space- and time-displaced spin-spin correlation functions and their
space-time Fourier transforms we obtained the dynamic structure factor for momentum and frequency . Below
(Kosterlitz-Thouless transition), both the in-plane () and the
out-of-plane () components of exhibit very strong
and sharp spin-wave peaks. Well above , and
apparently display a central peak, and spin-wave signatures are still seen in
. In addition, we also observed an almost dispersionless domain-wall
peak at high below (Ising transition), where long-range order
appears in the staggered chirality. Above , the domain-wall peak
disappears for all . The lineshape of these peaks is captured reasonably
well by a Lorentzian form. Using a dynamic finite-size scaling theory, we
determined the dynamic critical exponent = 1.002(3). We found that our
results demonstrate the consistency of the dynamic finite-size scaling theory
for the characteristic frequeny and the dynamic structure factor
itself.Comment: 8 pages, RevTex, 10 figures, submitted to PR
Whole Exome Sequencing to Estimate Alloreactivity Potential Between Donors and Recipients in Stem Cell Transplantation
Whole exome sequencing was performed on HLA-matched stem cell donors and
transplant recipients to measure sequence variation contributing to minor
histocompatibility antigen differences between the two. A large number of
nonsynonymous single nucleotide polymorphisms were identified in each of the
nine unique donor-recipient pairs tested. This variation was greater in
magnitude in unrelated donors as compared with matched related donors.
Knowledge of the magnitude of exome variation between stem cell transplant
recipients and donors may allow more accurate titration of immunosuppressive
therapy following stem cell transplantation.Comment: 12 pages- main article, 29 pages total, 5 figures, 1 supplementary
figur
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