1,326 research outputs found
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
Probing the evolution of the substructure frequency in galaxy clusters up to z~1
Context. Galaxy clusters are the last and largest objects to form in the
standard hierarchical structure formation scenario through merging of smaller
systems. The substructure frequency in the past and present epoch provides
excellent means for studying the underlying cosmological model. Aims. Using
X-ray observations, we study the substructure frequency as a function of
redshift by quantifying and comparing the fraction of dynamically young
clusters at different redshifts up to z=1.08. We are especially interested in
possible biases due to the inconsistent data quality of the low-z and high-z
samples. Methods. Two well-studied morphology estimators, power ratio P3/P0 and
center shift w, were used to quantify the dynamical state of 129 galaxy
clusters, taking into account the different observational depth and noise
levels of the observations. Results. Owing to the sensitivity of P3/P0 to
Poisson noise, it is essential to use datasets with similar photon statistics
when studying the P3/P0-z relation. We degraded the high-quality data of the
low-redshift sample to the low data quality of the high-z observations and
found a shallow positive slope that is, however, not significant, indicating a
slightly larger fraction of dynamically young objects at higher redshift. The
w-z relation shows no significant dependence on the data quality and gives a
similar result. Conclusions. We find a similar trend for P3/P0 and w, namely a
very mild increase of the disturbed cluster fraction with increasing redshifts.
Within the significance limits, our findings are also consistent with no
evolution.Comment: A&A in pres
The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II) IV. X-ray Luminosity Function and First Constraints on Cosmological Parameters
The X-ray luminosity function is an important statistic of the census of
galaxy clusters and an important means to probe the cosmological model of our
Universe. Based on our recently completed REFLEX II cluster sample we construct
the X-ray luminosity function of galaxy clusters for several redshift slices
from to and discuss its implications. We find no significant
signature of redshift evolution of the luminosity function in the redshift
interval. We provide the results of fits of a parameterized Schechter function
and extensions of it which provide a reasonable characterization of the data.
Using a model for structure formation and galaxy cluster evolution we compare
the observed X-ray luminosity function with predictions for different
cosmological models. For the most interesting constraints for the cosmological
parameters and we obatain
and based on the statistical uncertainty alone.
Marginalizing over the most important uncertainties, the normalisation and
slope of the scaling relation, we find
and ( confidence limits). We compare our
results with those of the SZ-cluster survey provided by the PLANCK mission and
we find very good agreement with the results using PLANCK clusters as
cosmological probes, but we have some tension with PLANCK cosmological results
from the microwave background anisotropies. We also make a comparison with
other cluster surveys. We find good agreement with these previous results and
show that the REFLEX II survey provides a significant reduction in the
uncertainties compared to earlier measurements.Comment: Submitted for publication to Astronomy and Astrophysics, 15 pages, 17
figure
RASS-SDSS Galaxy Cluster Survey. VII. On the Cluster Mass to Light ratio and the Halo Occupation Distribution
We explore the mass-to-light ratio in galaxy clusters and its relation to the
cluster mass. We study the relations among the optical luminosity (),
the cluster mass () and the number of cluster galaxies within
() in a sample of 217 galaxy clusters with confirmed 3D
overdensity. We correct for projection effects, by determining the galaxy
surface number density profile in our cluster sample. This is best fitted by a
cored King profile in low and intermediate mass systems. The core radius
decreases with cluster mass, and, for the highest mass clusters, the profile is
better represented by a generalized King profile or a cuspy Navarro, Frenk &
White profile. We find a very tight proportionality between and
, which, in turn, links the cluster mass-to-light ratio to the Halo
Occupation Distribution vs. . After correcting for
projection effects, the slope of the and
relations is found to be , close, but still significantly less
than unity. We show that the non-linearity of these relations cannot be
explained by variations of the galaxy luminosity distributions and of the
galaxy M/L with the cluster mass. We suggest that the nonlinear relation
between number of galaxies and cluster mass reflects an underlying nonlinear
relation between number of subhaloes and halo mass.Comment: 15 pages, 15 figures, accepted for publication in A&
Studying the properties of galaxy cluster morphology estimators
X-ray observations of galaxy clusters reveal a large range of morphologies
with various degrees of disturbance, showing that the assumptions of
hydrostatic equilibrium and spherical shape which are used to determine the
cluster mass from X-ray data are not always satisfied. It is therefore
important for the understanding of cluster properties as well as for
cosmological applications to detect and quantify substructure in X-ray images
of galaxy clusters. Two promising methods to do so are power ratios and center
shifts. Since these estimators can be heavily affected by Poisson noise and
X-ray background, we performed an extensive analysis of their statistical
properties using a large sample of simulated X-ray observations of clusters
from hydrodynamical simulations. We quantify the measurement bias and error in
detail and give ranges where morphological analysis is feasible. A new,
computationally fast method to correct for the Poisson bias and the X-ray
background contribution in power ratio and center shift measurements is
presented and tested for typical XMM-Newton observational data sets. We studied
the morphology of 121 simulated cluster images and establish structure
boundaries to divide samples into relaxed, mildly disturbed and disturbed
clusters. In addition, we present a new morphology estimator - the peak of the
0.3-1 r500 P3/P0 profile to better identify merging clusters. The analysis
methods were applied to a sample of 80 galaxy clusters observed with
XMM-Newton. We give structure parameters (P3/P0 in r500, w and P3/P0_max) for
all 80 observed clusters. Using our definition of the P3/P0 (w) substructure
boundary, we find 41% (47%) of our observed clusters to be disturbed.Comment: Replaced to match version published in A&A, Eq. 1 correcte
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
Metal Abundances in the ICM as a Diagnostics of the Cluster History
Galaxy clusters with a dense cooling core exhibit a central increase in the
metallicity of the intracluster medium. Recent XMM-Newton studies with detailed
results on the relative abundances of several heavy elements show that the high
central abundances are mostly due to the contribution from supernovae type Ia.
The dominant source is the stellar population of the central cluster galaxy.
With this identification of the origin of heavy elements and the observed rates
of SN Ia in elliptical galaxies, the central abundance peak can be used as a
diagnostic for the history of the cluster core region. We find for four nearby
cooling core clusters that the enrichment times for the central peaks are
larger than 6 - 10 Gyrs even for a higher SN Ia rate in the past. This points
to an old age and a relatively quiet history of these cluster core regions. A
detailed analysis of the element abundance ratios provides evidence that the SN
Ia yields in the central cluster galaxies are more rich in intermediate mass
elements, like Si and S, compared to the SN Ia models used to explain the heavy
element enrichment in our Galaxy.Comment: Advances in Space Research in press (proceedings of the COSPAR 2004
Assembly, Paris), 9 pages, 5 figure
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
Central galaxy growth and feedback in the most massive nearby cool core cluster
We present multi-wavelength observations of the centre of RXCJ1504.1-0248 -
the galaxy cluster with the most luminous and relatively nearby cool core at
z~0.2. Although there are several galaxies within 100 kpc of the cluster core,
only the brightest cluster galaxy (BCG), which lies at the peak of the X-ray
emission, has blue colours and strong line-emission. Approximately 80 Msun/yr
of intracluster gas is cooling below X-ray emitting temperatures, similar to
the observed UV star formation rate of ~140 Msun/yr. Most star formation occurs
in the core of the BCG and in a 42 kpc long filament of blue continuum, line
emission, and X-ray emission, that extends southwest of the galaxy. The
surrounding filamentary nebula is the most luminous around any observed BCG.
The number of ionizing stars in the BCG is barely sufficient to ionize and heat
the nebula, and the line ratios indicate an additional heat source is needed.
This heat source can contribute to the H\alpha-deduced star formation rates
(SFRs) in BCGs and therefore the derived SFRs should only be considered upper
limits. AGN feedback can slow down the cooling flow to the observed mass
deposition rate if the black hole accretion rate is of the order of 0.5 Msun/yr
at 10% energy output efficiency. The average turbulent velocity of the nebula
is vturb ~325 km/s which, if shared by the hot gas, limits the ratio of
turbulent to thermal energy of the intracluster medium to less than 6%.Comment: 15 pages, 11 figures, MNRAS in press. Corrected typo in abstract
Metal-rich multi-phase gas in M87: AGN-driven metal transport, magnetic-field supported multi-temperature gas, and constraints on non-thermal emission observed with XMM-Newton
We use deep (~120 ks) XMM-Newton data of the M87 halo to analyze its
spatially resolved temperature structure and chemical composition. We focus
particularly on the regions of enhanced X-ray brightness associated with the
inner radio lobes, which are known not to be described very well by
single-temperature spectral models. Compared to a simple two-temperature fit,
we obtain a better and more physical description of the spectra using a model
that involves a continuous range of temperatures in each spatial bin. The range
of temperatures of the multiphase gas spans ~0.6-3.2 keV. Such a multiphase
structure is only possible if thermal conduction is suppressed by magnetic
fields. In the multi-temperature regions, we find a correlation between the
amount of gas cooler than the surrounding X-ray plasma and the metallicity, and
conclude that the cool gas is more metal-rich than the ambient halo. We
estimate the average Fe abundance of the cool gas to ~2.2 solar. Our results
thus point toward the key role of the active galactic nucleus (AGN) in
transporting heavy elements into the intracluster medium. The abundance ratios
of O/Si/S/Fe in and outside the X-ray arms are similar, indicating that the
dominant fraction of metals in the gas halo was uplifted by AGN outbursts
relatively recently compared to the age of M87. Our estimate for the mass of
the cool gas is 5e8 M_sun, which probably stems from a mixture of ICM, stellar
mass loss, and Type Ia supernova products. ~30-110 Myr are required to produce
the observed metals in the cool gas. Finally, we put upper limits on possible
non-thermal X-ray emission from M87 and, combining it with the 90 cm radio
maps, we put lower limits of around ~0.5-1.0 muG on the magnetic field
strength.Comment: 18 pages, accepted for publication in A&A. Some significant changes
following the referee repor
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