148 research outputs found
X-ray Observations of the Chemical Abundances in the Intra-Cluster Medium
Clusters of galaxies as the largest clearly defined objects in our Universe
are ideal laboratories to study the distribution of the most abundant chemical
elements heavier than hydrogen and helium and the history of their production.
The cluster environment allows us to study the element abundances not only
inside the galaxies, but also in the intergalactic space, the intracluster
medium. Since the intracluster medium is heated to temperatures of several ten
Million degrees, we can study the chemical composition of this medium through
X-ray spectroscopy. Up to 13 heavy elements have been detected by X-ray
spectroscopy so far. The element most easily detected in the X-ray spectra is
iron. In massive galaxy clusters we find a larger mass of heavy elements in the
intracluster medium than in the galaxies. The consideration of the intracluster
medium is therefore vital for an understanding of the complete history of
nucleosynthesis of the heavy elements. The observed abundances for all elements
heavier than nitrogen can roughly be modeled by using two types of sources:
core collapse supernovae and supernovae type Ia. So called cool-core galaxy
clusters show a larger heavy element abundance in the cluster center which
seems to be enriched primarily by products of supernovae of type Ia. The
evidence for observations of an evolution of the heavy element abundance with
redshift has still a moderate significance.Comment: To be published by Mem. S.A.It., Conference Proceedings of the
Rencontre de l'Observatoire 2013 ESO Workshop on Metal Production in a
Hierachical Universe, 8 pages, 9 figure
The ROSAT-ESO Flux-Limited X-Ray (REFLEX) Galaxy Cluster Survey VI: Constraints on the cosmic matter density from the KL power spectrum
The Karhunen-Lo\'{e}ve (KL) eigenvectors and eigenvalues of the sample
correlation matrix are used to analyse the spatial fluctuations of the REFLEX
clusters of galaxies. The method avoids the disturbing effects of correlated
power spectral densities which affects all previous cluster measurements on Gpc
scales. Comprehensive tests use a large set of independent REFLEX-like mock
cluster samples extracted from the Hubble Volume Simulation. It is found that
unbiased measurements on Gpc scales are possible with the REFLEX data. The
distribution of the KL eigenvalues are consistent with a Gaussian random field
on the 93.4% confidence level. Assuming spatially flat cold dark matter models,
the marginalization of the likelihood contours over different sample volumes,
fiducial cosmologies, mass/X-ray luminosity relations and baryon densities,
yields the 95.4% confidence interval for the matter density of
. The N-body simulations show that cosmic variance,
although difficult to estimate, is expected to increase the confidence
intervals by about 50%.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Optical and X-ray profiles in the REXCESS sample of galaxy clusters
Galaxy clusters' structure, dominated by dark matter, is traced by member
galaxies in the optical and hot intra-cluster medium (ICM) in X-rays. We
compare the radial distribution of these components and determine the
mass-to-light ratio vs. system mass relation.
We use 14 clusters from the REXCESS sample which is representative of
clusters detected in X-ray surveys. Photometric observations with the Wide
Field Imager on the 2.2m MPG/ESO telescope are used to determine the number
density profiles of the galaxy distribution out to . These are
compared to electron density profiles of the ICM obtained using XMM-Newton, and
dark matter profiles inferred from scaling relations and an NFW model.
While red sequence galaxies trace the total matter profile, the blue galaxy
distribution is much shallower. We see a deficit of faint galaxies in the
central regions of massive and regular clusters, and strong suppression of
bright and faint blue galaxies in the centres of cool-core clusters,
attributable to ram pressure stripping of gas from blue galaxies in high
density regions of ICM and disruption of faint galaxies due to galaxy
interactions. We find a mass-to-light ratio vs. mass relation within
of at
with slope , consistent with most
previous results
Galaxies and Cluster of Galaxies as Peak Patches of the Density Field
The mass function of galaxies and clusters of galaxies can be derived
observationally based on different types of observations. In this study we test
if these observations can be combined to a consistent picture which is also in
accord with structure formation theory. The galaxy data comprise the optical
galaxy luminosity function and the gravitational lensing signature of the
galaxies, while the galaxy cluster mass function is derived from the X-ray
luminosity distribution of the clusters. We show the results of the comparison
in the form of the mass density fraction that is contained in collapsed objects
relative to the mean matter density in the Universe. The mass density fraction
in groups and clusters of galaxies extrapolated to low masses agrees very well
with that of the galaxies: both converge at the low mass limit to a mass
fraction of about 28\% if the outer radii of the objects are taken to be
. Most of the matter contained in collapsed objects is found in the
mass range , while a larger
amount of the cosmic matter resides outside of objects with radius .Comment: To appear in MNRA
Abell 3627: A Nearby, X-ray Bright, and Massive Galaxy Cluster
The cluster A3627 was recently recognized to be a very massive, nearby
cluster in a galaxy survey close to the galactic plane. We are reporting on
ROSAT PSPC observations of this object which confirm that the cluster is indeed
very massive. The X-ray emission detected from the cluster extends over almost
1 degree in radius. The X-ray image is not spherically symmetric and shows
indications of an ongoing cluster merger. Due to the strong interstellar
absorption the spectral analysis and the gas temperature determination are
difficult. The data are consistent with an overall gas temperature in the range
5 to 10 keV. There are signs of temperature variations in the merger region. A
mass estimate based on the X-ray data yields values of \msu \ if extrapolated to the virial radius of Mpc. In
the ROSAT energy band (0.1 - 2.4 keV) the cluster emission yields a flux of
about erg s cm which makes A3627 the 6
brightest cluster in the ROSAT All Sky Survey. The cluster was missed in
earlier X-ray surveys because it was confused with a neighbouring X-ray bright,
galactic X-ray binary (1H1556-605). The large X-ray flux makes A3627 an
important target for future studies.Comment: 14 pages, Latex file, including aaspp.sty, 9 postscript figures and 1
table, accepted for publication by the Astrophysical Journa
XMM observation of M~87 II. Abundance structure of the interstellar and intergalactic medium
Based on a detailed study of the temperature structure of the intracluster
medium in the halo of M~87, abundance profiles of 7 elements, O, Mg, Si, S, Ar,
Ca, and Fe are derived. In addition, abundance ratios are derived from the
ratios of line strengths, whose temperature dependences are small within the
temperature range of the ICM of M~87. The abundances of Si, S, Ar, Ca and Fe
show strong decreasing gradients outside 2 and become nearly constant within
the radius at solar. The Fe/Si ratio is determined to be 0.9 solar
with no radial gradient. In contrast, the O abundance is less than a half of
the Si abundance at the center and has a flatter gradient. The Mg abundance is
1 solar within 2, which is close to stellar abundance within the same
radius. The O/Si/Fe pattern of M~87 is located at the simple extension of that
of Galactic stars. The observed Mg/O ratio is about 1.25 solar, which is also
the same ratio as for Galactic stars. The O/Si/Fe ratio indicates that the SN
Ia contribution to Si and Fe becomes important towards the center and SN Ia
products have similar abundances of Si and Fe at least around M~87, which may
reflect dimmer SN Ia observed in old stellar systems. The S abundance is
similar to the Si abundance at the center, but has a steeper gradient. This
result suggests that the S/Si ratio of SN II products is much smaller than the
solar ratio.Comment: 20 pages, 20 figures, to appear in Astronomy & Astrophysic
Violent Relaxation of Indistinguishable Objects and Neutrino Hot Dark Matter in Clusters of Galaxies
The statistical mechanical investigation of violent relaxation (Lynden-Bell
1967) is extended to indistinguishable objects. It is found that,
coincidentally, the equilibrium distribution is the same as that obtained for
classical objects. For massive neutrinos, the Tremaine \& Gunn (1979) phase
space bound is revisited and reinterpretated as the limit indicating the onset
of degeneracy related to the coarse-grained phase space distribution. In the
context of one of the currently most popular cosmological models, the Cold and
Hot Dark Matter (CHDM) model (Primack et al. 1995), the onset of degeneracy may
be of importance in the core region of clusters of galaxies. Degeneracy allows
the neutrino HDM density to exceed the limit imposed by the Tremaine \& Gunn
(1979) bound while accounting for the phase space bound.Comment: AASTeX, 16 pages, 2 EPS figures, uses aas2pp4.sty. Accepted by ApJ
Letter
FPGA-based operational concept and payload data processing for the Flying Laptop satellite
Flying Laptop is the first small satellite developed by the Institute of Space Systems at the UniversitÀt Stuttgart. It is a test bed for an on-board computer with a reconfigurable, redundant and self-controlling high computational ability based on the field pro- grammable gate arrays (FPGAs). This Technical Note presents the operational concept and the on-board payload data processing of the satellite. The designed operational concept of Flying Laptop enables the achievement of mission goals such as technical demonstration, scientific Earth observation, and the payload data processing methods. All these capabilities expand its scientific usage and enable new possibilities for real-time applications. Its hierarchical architecture of the operational modes of subsys- tems and modules are developed in a state-machine diagram and tested by means of MathWorks Simulink-/Stateflow Toolbox. Furthermore, the concept of the on-board payload data processing and its implementation and possible applications are described
The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II)\\ II. Construction and Properties of the Survey
Galaxy clusters provide unique laboratories to study astrophysical processes
on large scales and are important probes for cosmology. X-ray observations are
currently the best means of detecting and characterizing galaxy clusters. In
this paper we describe the construction of the REFLEX II galaxy cluster survey
based on the southern part of the ROSAT All-Sky Survey. REFLEX II extends the
REFLEX I survey by a factor of about two down to a flux limit of erg s cm (0.1 - 2.4 keV). We describe the determination
of the X-ray parameters, the process of X-ray source identification, and the
construction of the survey selection function. The REFLEX II cluster sample
comprises currently 915 objects. A standard selection function is derived for a
lower source count limit of 20 photons in addition to the flux limit. The
median redshift of the sample is . Internal consistency checks and
the comparison to several other galaxy cluster surveys imply that REFLEX II is
better than 90\% complete with a contamination less than 10\%.Comment: Astronomy and Astrophysics Vol. 555, A30 - 15 pages, 20 figure
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