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Host Cluster (host + cluster)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

New scaling relations in cluster radio haloes and the re-acceleration model

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
R. Cassano
ABSTRACT In this paper we derive new expected scaling relations for clusters with giant radio haloes in the framework of the re-acceleration scenario in a simplified, but physically motivated, form, namely: radio power (PR) versus size of the radio emitting region (RH), and PR versus total cluster mass (MH) contained in the emitting region and cluster velocity dispersion (,H) in this region. We search for these correlations by analysing the most recent radio and X-ray data available in the literature for a well-known sample of clusters with giant radio haloes. In particular we find a good correlation between PR and RH and a very tight ,geometrical' scaling between MH and RH. From these correlations PR is also expected to scale with MH and ,H and this is confirmed by our analysis. We show that all the observed trends can be well reconciled with expectations in the case of a slight variation of the mean magnetic field strength in the radio halo volume with MH. A byproduct correlation between RH and ,H is also found, and can be further tested by optical studies. In addition, we find that observationally RH scales non-linearly with the virial radius of the host cluster, and this immediately means that the fraction of the cluster volume which is radio emitting increases with cluster mass and thus that the non-thermal component in clusters is not self-similar. [source]

The NOAO Fundamental Plane Survey , III.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
Variations in the stellar populations of red-sequence galaxies from the cluster core to the virial radius
ABSTRACT We analyse absorption line-strength indices for ,3000 red-sequence galaxies in 94 nearby clusters to investigate systematic variations of their stellar content with location in the host cluster. The data are drawn from the National Optical Astronomy Observatory (NOAO) Fundamental Plane Survey. Our adopted method is a generalization of that introduced by Nelan et al. to determine the global age,mass and metallicity,mass relations from the same survey. We find strong evidence for a change in galaxy properties, at fixed mass, over a range from the cluster centre to the virial radius, R200. For example, red-sequence galaxies further out in the clusters have weaker Mgb5177 (at ,8, significance) and stronger H, and H, absorption (,3,, ,4,) than galaxies of the same velocity dispersion in the cluster cores. The Fe5270 and Fe5335 indices show only very weak trends with radius. Using a total of 12 indices, the pattern of cluster-centric gradients is considered in light of their different dependences on stellar age and chemical composition. The measured gradients for all 12 indices can be reproduced by a model in which red-sequence galaxies at ,1 R200 have on average younger ages (by 15 ± 4 per cent) and lower ,-element abundance ratios (by 10 ± 2 per cent) than galaxies of the same velocity dispersion but located near the cluster centres. For the total metallicity, Z/H, no significant gradient is found (2 ± 3 per cent larger at R200 than in the cores). There are hints that the age trend may be stronger for galaxies of lower mass and/or for galaxies with more discy morphology. We show, however, that the trends cannot be driven primarily by changes in the morphological mix as a function of radius. The cluster-centric age and [,/Fe] gradients are in the sense expected if galaxies in the cluster core were accreted at an earlier epoch than those at larger radii, and if this earlier accretion contributed to an earlier cessation of star formation. The size of the observed age trend is comparable to predictions from semi-analytic models of hierarchical galaxy formation. [source]

Drag-gravity torques on galaxies in clusters: radial small-scale alignment effects

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010
Alejandro González-Sánchez
ABSTRACT We calculate the torque on galaxies in clusters due to gravity and to dynamical friction forces in order to study the possible origin of small-scale alignment effects as the result of interactions with their environment. The equation of motion for the position angle of a galaxy is derived by using a simple model. We find that weak radial alignment effects can be produced by this mechanism involving only the most massive galaxies. We also introduce a dependence on the cluster eccentricity to our equations in order to explore the alignment of galaxies with the cluster's major axis. We find that in the inner regions of high eccentricity clusters, alignments of massive galaxies with the cluster's major axis dominate over the radial ones. This mechanism could account for the observed alignment effects of the most massive galaxies with the major axis of their host cluster. Our results suggest that dynamical friction is a viable generator of alignment only for the most massive cluster galaxies. For the observed alignments of normal galaxies a primordial origin has to be explored. [source]

Ram pressure stripping of disk galaxies in galaxy clusters

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
E. Roediger
Abstract While galaxies move through the intracluster medium of their host cluster, they experience a ram pressure which removes at least a significant part of their interstellar medium. This ram pressure stripping appears to be especially important for spiral galaxies: this scenario is a good candidate to explain the differences observed between cluster spirals in the nearby universe and their field counterparts. Thus, ram pressure stripping of disk galaxies in clusters has been studied intensively during the last decade. I review advances made in this area, concentrating on theoretical work, but continuously comparing to observations (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]