116 research outputs found
Stent-grafting for a thoracic aortic aneurysm ruptured into the right pleural cavity
AbstractEur J Vasc Endovasc Surg 25, 185–187 (2003
X-ray Diagnostics of Thermal Conditions of the Hot Plasmas in the Centaurus Cluster
X-ray data of the Centaurus cluster, obtained with {\it XMM-Newton} for 45
ksec, were analyzed. Deprojected EPIC spectra from concentric thin shell
regions were reproduced equally well by a single-phase plasma emission model,
or by a two-phase model developed by {\it ASCA}, both incorporating cool
(1.7--2.0 keV) and hot ( keV) plasma temperatures. However, EPIC
spectra with higher statistics, accumulated over 3-dimentional thick shell
regions, were reproduced better by the two-phase model than by the singe-phase
one. Therefore, hot and cool plasma phases are inferred to co-exist in the
cluster core region within kpc. The iron and silicon abundances of
the plasma were reconfirmed to increase significantly towards the center, while
that of oxygen was consistent with being radially constant. The implied
non-solar abundance ratios explains away the previously reported excess X-ray
absorption from the central region. Although an additional cool (
keV) emission was detected within kpc of the center, the RGS data
gave tight upper limits on any emission with a tempeartures below
keV. These results are compiled into a magnetosphere model, which interprets
the cool phase as confined within closed magnetic loops anchored to the cD
galaxy. When combined with so-called Rosner-Tucker-Vaiana mechanism which
applies to solar coronae, this model can potentially explain basic properties
of the cool phase, including its temperature and thermal stability.Comment: 53 pages, 11 figures, accepted for publication in Astrophysical
Journa
Weak Lensing Mass Measurements of Substructures in COMA Cluster with Subaru/Suprime-Cam
We obtain the projected mass distributions for two Subaru/Suprime-Cam fields
in the southwest region (r\simlt 60') of the Coma cluster (z=0.0236) by weak
lensing analysis and detect eight subclump candidates. We quantify the
contribution of background large-scale structure (LSS) on the projected mass
distributions using SDSS multi-bands and photometric data, under the assumption
of mass-to-light ratio for field galaxies. We find that one of eight subclump
candidates, which is not associated with any member galaxies, is significantly
affected by LSS lensing. The mean projected mass for seven subclumps extracted
from the main cluster potential is = (5.06\pm1.30)10^12h^-1 M_sun
after a LSS correction. A tangential distortion profile over an ensemble of
subclumps is well described by a truncated singular-isothermal sphere model and
a truncated NFW model. A typical truncated radius of subclumps, r_t\simeq 35
h^-1 kpc, is derived without assuming any relations between mass and light for
member galaxies. The radius coincides well with the tidal radius, \sim42 h^-1
kpc, of the gravitational force of the main cluster. Taking into account the
incompleteness of data area, a projection effect and spurious lensing peaks, it
is expected that mass of cluster substructures account for 19 percent of the
virial mass, with 13 percent statistical error. The mass fraction of cluster
substructures is in rough agreement with numerical simulations.Comment: ApJ, accepted, 16 pages, 10 figures and 4 tables. High-resolution
pictures available at http://www.asiaa.sinica.edu.tw/~okabe/files/comaWL.pd
A parametric physical model for the intracluster medium and its use in joint SZ/X-ray analyses of galaxy clusters
We present a parameterized model of the intra-cluster medium that is suitable
for jointly analysing pointed observations of the Sunyaev-Zel'dovich (SZ)
effect and X-ray emission in galaxy clusters. The model is based on assumptions
of hydrostatic equilibrium, the Navarro, Frenk and White (NFW) model for the
dark matter, and a softened power law profile for the gas entropy. We test this
entropy-based model against high and low signal-to-noise mock observations of a
relaxed and recently-merged cluster from N-body/hydrodynamic simulations, using
Bayesian hyper-parameters to optimise the relative statistical weighting of the
mock SZ and X-ray data. We find that it accurately reproduces both the global
values of the cluster temperature, total mass and gas mass fraction (fgas), as
well as the radial dependencies of these quantities outside of the core (r >
kpc). For reference we also provide a comparison with results from the single
isothermal beta model. We confirm previous results that the single isothermal
beta model can result in significant biases in derived cluster properties.Comment: Published in MNRAS. 20 pages. 9 figure
The gas distribution in the outer regions of galaxy clusters
We present the analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy
clusters with the aim of measuring the density of the X-ray emitting gas in
cluster outskirts. We compare our results with numerical simulations to set
constraints on the azimuthal symmetry and gas clumping in the outer regions of
galaxy clusters. We exploit the large field-of-view and low instrumental
background of ROSAT/PSPC to trace the density of the intracluster gas out to
the virial radius. We perform a stacking of the density profiles to detect a
signal beyond r200 and measure the typical density and scatter in cluster
outskirts. We also compute the azimuthal scatter of the profiles with respect
to the mean value to look for deviations from spherical symmetry. Finally, we
compare our average density and scatter profiles with the results of numerical
simulations. As opposed to some recent Suzaku results, and confirming previous
evidence from ROSAT and Chandra, we observe a steepening of the density
profiles beyond \sim r500. Comparing our density profiles with simulations, we
find that non-radiative runs predict too steep density profiles, whereas runs
including additional physics and/or treating gas clumping are in better
agreement with the observed gas distribution. We report for the first time the
high-confidence detection of a systematic difference between cool-core and
non-cool core clusters beyond \sim 0.3r200, which we explain by a different
distribution of the gas in the two classes. Beyond \sim r500, galaxy clusters
deviate significantly from spherical symmetry, with only little differences
between relaxed and disturbed systems. We find good agreement between the
observed and predicted scatter profiles, but only when the 1% densest clumps
are filtered out in the simulations. [Abridged]Comment: The data for the average profiles and individual clusters can be
downloaded at:
http://www.isdc.unige.ch/~deckert/newsite/The_Planck_ROSAT_project.htm
Testing the Low-Mass End of X-Ray Scaling Relations with a Sample of Chandra Galaxy Groups
Well-determined scaling relations between X-ray observables and cluster mass
are essential for using large cluster samples for cosmology. Cluster relations
such as the Lx-T, M-T, Lx-M relations, have been investigated extensively,
however the question remains whether these relations hold true also for groups.
Some evidence supports a break at low masses, possibly caused by the influence
of non-gravitational physics on low-mass systems. The main goal of this work is
to test scaling relations for the low-mass range to check whether there is a
systematic difference between clusters and groups, and to extend this method of
reliable cluster mass determination for future samples down to the group
regime. We compiled a statistically complete sample of 112 X-ray galaxy groups,
26 with Chandra data. Temperature, metallicity, and surface brightness profiles
were created, and used to determine the main physical quantities and scaling
relations. We then compared the group properties to the HIFLUGCS clusters and
other samples. We present profiles and scaling relations of the whole sample. T
and Z profiles behave universally, except for the cores. The Lx-T, M-T, Lx-M,
Mg-M, M-Yx, and Lx-Yx relations are in good agreement with clusters. The Lx-T
relation steepens for T<3keV, which could point to a larger impact of heating
mechanisms on cooler systems. We found a strong drop in the gas mass fraction
below 1keV, which indicates the ICM is less dominant in groups and the galaxies
have a stronger influence on the system. In all relations the intrinsic scatter
for groups is larger, which appears not correlated with merger activity but
could be due to scatter caused by baryonic physics in the group cores. We also
demonstrate the importance of selection effects. We have found evidence for a
similarity break between groups and clusters. However this does not have a
strong effect on scaling relations.Comment: 31 pages, accepted to A&
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