367 research outputs found
The long X-ray tail in Zwicky 8338
The interaction processes in galaxy clusters between the hot ionized gas
(ICM) and the member galaxies are of crucial importance in order to understand
the dynamics in galaxy clusters, the chemical enrichment processes and the
validity of their hydrostatic mass estimates. Recently, several X-ray tails
associated to gas which was partly stripped of galaxies have been discovered.
Here we report on the X-ray tail in the 3 keV galaxy cluster Zwicky 8338, which
might be the longest ever observed. We derive the properties of the galaxy
cluster environment and give hints on the substructure present in this X-ray
tail, which is very likely associated to the galaxy CGCG254-021. The X-ray tail
is extraordinarily luminous ( erg/s), the thermal emission has
a temperature of 0.8 keV and the X-ray luminous gas might be stripped off
completely from the galaxy. From the assumptions on the 3D geometry we estimate
the gas mass fraction (< 0.1%) and conclude that the gas has been compressed
and/or heated.Comment: 4 pages, 3 figures, accepted by A&
Details of the mass--temperature relation for clusters of galaxies
We present results on the total mass and temperature determination using two
samples of clusters of galaxies. One sample is constructed with emphasis on the
completeness of the sample, while the advantage of the other is the use of the
temperature profiles, derived with ASCA. We obtain remarkably similar fits to
the M-T relation for both samples, with the normalization and the slope
significantly different from both prediction of self-similar collapse and
hydrodynamical simulations. We discuss the origin of these discrepancies and
also combine the X-ray mass with velocity dispersion measurements to provide a
comparison with high-resolution dark matter simulations. Finally, we discuss
the importance of a cluster formation epoch in the observed M-T relation.Comment: 12 pages, A&A 2001 in pres
The galaxy cluster X-ray luminosity--gravitational mass relation in the light of the WMAP 3rd year data
The 3rd year WMAP results mark a shift in best fit values of cosmological
parameters compared to the 1st year data and the concordance cosmological
model. We test the consistency of the new results with previous constraints on
cosmological parameters from the HIFLUGCS galaxy cluster sample and the impact
of this shift on the X-ray luminosity-gravitational mass relation. The measured
X-ray luminosity function combined with the observed luminosity-mass relation
are compared to mass functions predicted for given cosmological parameter
values. The luminosity function and luminosity-mass relation derived previously
from HIFLUGCS are in perfect agreement with mass functions predicted using the
best fit parameter values from the 3rd year WMAP data (OmegaM=0.238,
sigma8=0.74) and inconsistent with the concordance cosmological model
(OmegaM=0.3, sigma8=0.9), assuming a flat Universe. Trying to force consistency
with the concordance model requires artificially decreasing the normalization
of the luminosity-mass relation by a factor of 2. The shift in best fit values
for OmegaM and sigma8 has a significant impact on predictions of cluster
abundances. The new WMAP results are now in perfect agreement with previous
results on the OmegaM-sigma8 relation determined from the mass function of
HIFLUGCS clusters and other X-ray cluster samples (the ``low cluster
normalization''). We conclude that - unless the true values of OmegaM and
sigma8 differ significantly from the 3rd year WMAP results - the
luminosity-mass relation is well described by their previous determination from
X-ray observations of clusters, with a conservative upper limit on the bias
factor of 1.5. These conclusions are currently being tested in a complete
follow-up program of all HIFLUGCS clusters with Chandra and XMM-Newton.Comment: 4 pages; A&A Letters, in press; replaced to match accepted version;
also available at http://www.reiprich.ne
Investigating the cores of fossil systems with Chandra
We investigate the cores of fossil galaxy groups and clusters (`fossil
systems') using archival Chandra data for a sample of 17 fossil systems. We
determined the cool-core fraction for fossils via three observable diagnostics,
the central cooling time, cuspiness, and concentration parameter. We quantified
the dynamical state of the fossils by the X-ray peak/brightest cluster galaxy
(BCG), and the X-ray peak/emission weighted centre separations. We studied the
X-ray emission coincident with the BCG to detect the presence of potential
thermal coronae. A deprojection analysis was performed for z < 0.05 fossils to
obtain cooling time and entropy profiles, and to resolve subtle temperature
structures. We investigated the Lx-T relation for fossils from the 400d
catalogue to see if the scaling relation deviates from that of other groups.
Most fossils are identified as cool-core objects via at least two cool-core
diagnostics. All fossils have their dominant elliptical galaxy within 50 kpc of
the X-ray peak, and most also have the emission weighted centre within that
distance. We do not see clear indications of a X-ray corona associated with the
BCG unlike that has been observed for some other objects. Fossils do not have
universal temperature profiles, with some low-temperature objects lacking
features that are expected for ostensibly relaxed objects with a cool-core. The
entropy profiles of the z < 0.05 fossil systems can be well-described by a
power law model, albeit with indices smaller than 1. The 400d fossils Lx-T
relation shows indications of an elevated normalisation with respect to other
groups, which seems to persist even after factoring in selection effects.Comment: Accepted for publication in Astronomy and Astrophysic
Investigating the hard X-ray emission from the hottest Abell cluster A2163 with Suzaku
We present the results from Suzaku observations of the hottest Abell galaxy
cluster A2163 at . To study the physics of gas heating in cluster
mergers, we investigated hard X-ray emission from the merging cluster A2163,
which hosts the brightest synchrotron radio halo. We analyzed hard X-ray
spectra accumulated from two-pointed Suzaku observations. Non-thermal hard
X-ray emission should result from the inverse Compton (IC) scattering of
relativistic electrons by the CMB photons. To measure this emission, the
dominant thermal emission in the hard X-ray band must be modeled in detail. To
this end, we analyzed the combined broad-band X-ray data of A2163 collected by
Suzaku and XMM-Newton, assuming single- and multi-temperature models for
thermal emission and the power-law model for non-thermal emission. From the
Suzaku data, we detected significant hard X-ray emission from A2163 in the
12-60 keV band at the level (or at the level if a
systematic error is considered). The Suzaku HXD spectrum alone is consistent
with the single-T thermal model of gas temperature keV. From the XMM
data, we constructed a multi-T model including a very hot ( keV)
component in the NE region. Incorporating the multi-T and the power-law models
into a two-component model with a radio-band photon index, the 12-60 keV energy
flux of non-thermal emission is constrained within . The 90% upper limit of detected IC
emission is marginal ( in the
12-60 keV). The estimated magnetic field in A2163 is .
While the present results represent a three-fold increase in the accuracy of
the broad band spectral model of A2163, more sensitive hard X-ray observations
are needed to decisively test for the presence of hard X-ray emission due to IC
emission.Comment: 7 pages, 7 figures, A&A accepted. Minor correctio
XMM-Newton and Chandra Cross Calibration Using HIFLUGCS Galaxy Clusters: Systematic Temperature Differences and Cosmological Impact
Cosmological constraints from clusters rely on accurate gravitational mass
estimates, which strongly depend on cluster gas temperature measurements.
Therefore, systematic calibration differences may result in biased,
instrument-dependent cosmological constraints. This is of special interest in
the light of the tension between the Planck results of the primary temperature
anisotropies of the CMB and Sunyaev-Zel'dovich plus X-ray cluster counts
analyses. We quantify in detail the systematics and uncertainties of the
cross-calibration of the effective area between five X-ray instruments,
EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the
influence on temperature measurements. Furthermore, we assess the impact of the
cross calibration uncertainties on cosmology. Using the HIFLUGCS sample,
consisting of the 64 X-ray brightest galaxy clusters, we constrain the ICM
temperatures through spectral fitting in the same, mostly isothermal, regions
and compare them. Our work is an extension to a previous one using X-ray
clusters by the IACHEC. Performing spectral fitting in the full energy band we
find that best-fit temperatures determined with XMM-Newton/EPIC are
significantly lower than Chandra/ACIS temperatures. We demonstrate that effects
like multitemperature structure and different relative sensitivities of the
instruments at certain energy bands cannot explain the observed differences. We
conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full
energy band temperature profiles for cluster mass determination results in an
8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values
in a cosmological analysis of a complete sample of galaxy clusters. Such a
shift is insufficient to significantly alleviate the tension between Planck CMB
anisotropies and SZ plus XMM-Newton cosmological constraints.Comment: Accepted by A&A; Python-Script for modification of XMM-Newton/EPIC
and Chandra/ACIS effective areas according to the stacked residual ratios:
https://wikis.mit.edu/confluence/display/iachec/Data
Scaling relations for galaxy clusters: properties and evolution
Well-calibrated scaling relations between the observable properties and the
total masses of clusters of galaxies are important for understanding the
physical processes that give rise to these relations. They are also a critical
ingredient for studies that aim to constrain cosmological parameters using
galaxy clusters. For this reason much effort has been spent during the last
decade to better understand and interpret relations of the properties of the
intra-cluster medium. Improved X-ray data have expanded the mass range down to
galaxy groups, whereas SZ surveys have openened a new observational window on
the intracluster medium. In addition,continued progress in the performance of
cosmological simulations has allowed a better understanding of the physical
processes and selection effects affecting the observed scaling relations. Here
we review the recent literature on various scaling relations, focussing on the
latest observational measurements and the progress in our understanding of the
deviations from self similarity.Comment: 38 pages. Review paper. Accepted for publication in Space Science
Reviews (eds: S. Ettori, M. Meneghetti). This is a product of the work done
by an international team at the International Space Science Institute (ISSI)
in Bern on "Astrophysics and Cosmology with Galaxy Clusters: the X-ray and
Lensing View
Projection effects in galaxy cluster samples: insights from X-ray redshifts
Up to now, the largest sample of galaxy clusters selected in X-rays comes
from the ROSAT All-Sky Survey (RASS). Although there have been many interesting
clusters discovered with the RASS data, the broad point spread function (PSF)
of the ROSAT satellite limits the amount of spatial information of the detected
objects. This leads to the discovery of new cluster features when a
re-observation is performed with higher resolution X-ray satellites. Here we
present the results from XMM-Newton observations of three clusters:
RXCJ2306.6-1319, ZwCl1665 and RXCJ0034.6-0208, for which the observations
reveal a double or triple system of extended components. These clusters belong
to the extremely expanded HIghest X-ray FLUx Galaxy Cluster Sample
(eeHIFLUGCS), which is a flux-limited cluster sample ( erg s cm in the keV energy band). For
each structure in each cluster, we determine the redshift with the X-ray
spectrum and find that the components are not part of the same cluster. This is
confirmed by an optical spectroscopic analysis of the galaxy members.
Therefore, the total number of clusters is actually 7 and not 3. We derive
global cluster properties of each extended component. We compare the measured
properties to lower-redshift group samples, and find a good agreement. Our flux
measurements reveal that only one component of the ZwCl1665 cluster has a flux
above the eeHIFLUGCS limit, while the other clusters will no longer be part of
the sample. These examples demonstrate that cluster-cluster projections can
bias X-ray cluster catalogues and that with high-resolution X-ray follow-up
this bias can be corrected
- …