554 research outputs found
XMM-Newton and Gemini Observations of Eight RASSCALS Galaxy Groups
We study the distribution of gas pressure and entropy in eight groups of
galaxies belonging to the ROSAT All-Sky Survey / Center for Astrophysics Loose
Systems (RASSCALS). We use archival and proprietary XMM-Newton observations,
supplementing the X-ray data with redshifts derived from the literature; we
also list 127 new redshifts measured with the Gemini North telescope. The
groups show remarkable self-similarity in their azimuthally averaged entropy
and temperature profiles. The entropy increases with radius; the behavior of
the entropy profiles is consistent with an increasing broken power law with
inner and outer slope 0.92+0.04-0.05 and 0.42+0.05-0.04 (68% confidence),
respectively. There is no evidence of a central, isentropic core, and the
entropy distribution in most of the groups is flatter at large radii than in
the inner region, challenging earlier reports as well as theoretical models
predicting large isentropic cores or asymptotic slopes of 1.1 at large radii.
The pressure profiles are consistent with a self-similar decreasing broken
power law in radius; the inner and outer slopes are -0.78+0.04-0.03 and
-1.7+0.1-0.3, respectively. The results suggest that the larger scatter in the
entropy distribution reflects the varied gasdynamical histories of the groups;
the regularity and self-similarity of the pressure profiles is a sign of a
similarity in the underlying dark matter distributions.Comment: Accepted for publication in the Astrophysical Journa
X-ray properties of the distant cluster Cl0016+16
We present X-ray data on the distant cluster Cl0016+16 (z=0.5545) from ROSAT
PSPC and HRI observations and use them to study the physics of the intracluster
medium (ICM) and the dynamical state of the cluster. The surface brightness
distribution is not only described by a spherically symmetric model but also by
a two-dimensional -model fit. Subtracting an elliptical model cluster
as defined by the best fit parameters of the two-dimensional model we find
significant residuals, indicating an additional, extended X-ray source within
the cluster. This source, likely to be a merging subcomponent of the cluster,
coincides with a peak in the weak lensing mass map of Smail et. al. (1995). In
the course of this analysis we present a new approach to quantify the
significance of substructure in cluster X-ray images dominated by Poisson noise
and smoothed with a Gauss filter. We determine the radial mass profile
integrated out to a radius of 3Mpc and find for the total mass of the cluster a
value of \msun and
\msun for the gas mass, yielding a gas-to-total mass ratio of 14-32\%. There is
no significant radial dependence of the gas-to-total mass ratio in the cluster.Comment: 11 pages, submitted to MNRA
The 3D soft X-ray cluster-AGN cross-correlation function in the ROSAT NEP survey
X-ray surveys facilitate investigations of the environment of AGNs. Deep
Chandra observations revealed that the AGNs source surface density rises near
clusters of galaxies. The natural extension of these works is the measurement
of spatial clustering of AGNs around clusters and the investigation of relative
biasing between active galactic nuclei and galaxies near clusters.The major
aims of this work are to obtain a measurement of the correlation length of AGNs
around clusters and a measure of the averaged clustering properties of a
complete sample of AGNs in dense environments. We present the first measurement
of the soft X-ray cluster-AGN cross-correlation function in redshift space
using the data of the ROSAT-NEP survey. The survey covers 9x9 deg^2 around the
North Ecliptic Pole where 442 X-ray sources were detected and almost completely
spectroscopically identified. We detected a >3sigma significant clustering
signal on scales s<50 h70^-1 Mpc. We performed a classical maximum-likelihood
power-law fit to the data and obtained a correlation length s_0=8.7+1.2-0.3
h_70-1 Mpc and a slope gamma=1.7$^+0.2_-0.7 (1sigma errors). This is a strong
evidence that AGNs are good tracers of the large scale structure of the
Universe. Our data were compared to the results obtained by cross-correlating
X-ray clusters and galaxies. We observe, with a large uncertainty, that the
bias factor of AGN is similar to that of galaxies.Comment: 4 pages, 2 figure, proceedings of the Conference "At the edge of the
Universe", Sintra Portugal, October 2006. To be published on the Astronomical
Society of the Pacific Conference Series (ASPCS
Brightest Cluster Galaxies and Core Gas Density in REXCESS Clusters
We investigate the relationship between brightest cluster galaxies (BCGs) and
their host clusters using a sample of nearby galaxy clusters from the
Representative XMM Cluster Structure Survey (REXCESS). The sample was imaged
with the Southern Observatory for Astrophysical Research (SOAR) in R band to
investigate the mass of the old stellar population. Using a metric radius of
12h^-1 kpc, we found that the BCG luminosity depends weakly on overall cluster
mass as L_BCG \propto M_cl^0.18+-0.07, consistent with previous work. We found
that 90% of the BCGs are located within 0.035 r_500 of the peak of the X-ray
emission, including all of the cool core (CC) clusters. We also found an
unexpected correlation between the BCG metric luminosity and the core gas
density for non-cool core (non-CC) clusters, following a power law of n_e
\propto L_BCG^2.7+-0.4 (where n_e is measured at 0.008 r_500). The correlation
is not easily explained by star formation (which is weak in non-CC clusters) or
overall cluster mass (which is not correlated with core gas density). The trend
persists even when the BCG is not located near the peak of the X-ray emission,
so proximity is not necessary. We suggest that, for non-CC clusters, this
correlation implies that the same process that sets the central entropy of the
cluster gas also determines the central stellar density of the BCG, and that
this underlying physical process is likely to be mergers.Comment: 16 pages, 8 figures, accepted Astrophysical Journa
The dynamical intracluster medium: a combined approach of observations and simulations
Current high resolution observations of galaxy clusters reveal a dynamical
intracluster medium (ICM). The wealth of structures includes signatures of
interactions between active galactic nuclei (AGN) and the ICM, such as cavities
and shocks, as well as signatures of bulk motions, e.g. cold fronts. Aiming at
understanding the physics of the ICM, we study individual clusters by both,
deep high resolution observations and numerical simulations which include
processes suspected to be at work, and aim at reproducing the observed
properties. By comparing observations and simulations in detail, we gain deeper
insights into cluster properties and processes. Here we present two examples of
our approach: the large-scale shock in the Hydra A cluster, and sloshing cold
fronts.Comment: 4 pages, to appear in proceedings of "The Monster's fiery breath"
held in Madison, June 2009, eds. S. Heinz and E. Wilcots, version with full
resolution pictures at
http://www.faculty.iu-bremen.de/eroediger/PAPERS/roediger_e_madison.pd
Metal mixing by buoyant bubbles in galaxy clusters
Using a series of three-dimensional, hydrodynamic simulations on an adaptive
grid, we have performed a systematic study on the effect of bubble-induced
motions on metallicity profiles in clusters of galaxies. In particular, we have
studied the dependence on the bubble size and position, the recurrence times of
the bubbles, the way these bubbles are inflated and the underlying cluster
profile. We find that in hydrostatic cluster models, the resulting metal
distribution is very elongated along the direction of the bubbles. Anisotropies
in the cluster or ambient motions are needed if the metal distribution is to be
spherical. In order to parametrise the metal transport by bubbles, we compute
effective diffusion coefficients. The diffusion coefficients inferred from our
simple experiments lie at values of around cms at a
radius of 10 kpc. The runs modelled on the Perseus cluster yield diffusion
coefficients that agree very well with those inferred from observations.Comment: 17 pages, 12 figures. Accepted by MNRA
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