IGCs in the Virgo Cluster
ABSTRACT Preliminary results of the ACS Virgo Cluster Survey WFPC2 parallel observations are presented. We searched for intergalactic
globular clusters in 100 WFPC2 fields within the Virgo Cluster. We find globular clusters preferentially near the most luminous
cluster galaxies (M87, M49, and M60). For M87, the number density of globular clusters out to 70 kpc is consistent with that
determined by ground based studies of the globular cluster systems. The intergalactic nature of the population of globular
clusters we are detecting is still a matter of controversy.
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ABSTRACT: We present a new multiwavelength analysis of the Coma cluster subclustering based on recent X-ray data and on a compilation of nearly 900 redshifts. We characterize subclustering using the Serna&Gerbal (1996) hierarchical method which makes use of galaxy positions, redshifts, and magnitudes, and identify 17 groups. One of these groups corresponds to the main cluster, one is the well known group associated with the infalling galaxy NGC4839 and one is associated with NGC4911/NGC4926. About one third of the 17 groups have velocity distributions centered on the velocities of the very bright cluster galaxies they contain (magnitudes R<13). In order to search for additional substructures, we make use of the isophotes of X-ray brightness residuals left after the subtraction of the best-fit beta-model from the overall X-ray gas distribution (Neumann et al. 2003). We select galaxies within each of these isophotes and compare their velocity distributions with that of the whole cluster. We confirm in this way the two groups associated, respectively, with NGC4839, and with the southern part of the extended western substructure visible in X-rays. We discuss the group properties in the context of a scenario in which Coma is built by the accretion of groups infalling from the surrounding large scale structure. We estimate the recent mass accretion rate of Coma and compare it with hierarchical models of cluster evolution. Comment: 12 pages, 10 Postscript figures, accepted in A&AAstronomy and Astrophysics 07/2005; · 5.08 Impact Factor