EDP Sciences
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Volume 397, Number 2, January II 2003
Page(s) 431 - 443
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20021495

A&A 397, 431-443 (2003)
DOI: 10.1051/0004-6361:20021495

Structure and evolution of galaxy clusters: Internal dynamics of ABCG 209 at $z\;\sim$ 0.21

A. Mercurio1, M. Girardi1, W. Boschin1, P. Merluzzi2 and G. Busarello2

1  Dipartimento di Astronomia, Università degli Studi di Trieste, via Tiepolo 11, 34100 Trieste, Italy
    e-mail: mercurio,girardi,boschin@ts.astro.it
2  INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80100 Napoli, Italy
    e-mail: merluzzi,busarello@na.astro.it

(Received 24 July 2002 / Accepted 11 October 2002)

We study the internal dynamics of the rich galaxy cluster ABGC 209 on the basis of new spectroscopic and photometric data. The distribution in redshift shows that ABCG 209 is a well isolated peak of 112 detected member galaxies at z=0.209, characterised by a high value of the line-of-sight velocity dispersion, $\mathrm{\sigma_v=1250}$- 1400 km s -1, on the whole observed area (1  h-1 Mpc $\;$ from the cluster center), that leads to a virial mass of M=1.6- $2.2\times 10^{15}$ ${h^{-1} \ M_{\odot} \;}$within the virial radius, assuming the dynamical equilibrium. The presence of a velocity gradient in the velocity field, the elongation in the spatial distribution of the colour-selected likely cluster members, the elongation of the X-ray contour levels in the Chandra image, and the elongation of cD galaxy show that ABCG 209 is characterised by a preferential NW-SE direction. We also find a significant deviation of the velocity distribution from a Gaussian, and relevant evidence of substructure and dynamical segregation. All these facts show that ABCG 209 is a strongly evolving cluster, possibly in an advanced phase of merging.

Key words: galaxies: clusters: general -- galaxies: clusters: individual: ABCG 209 -- galaxies: distances and redshifts -- intergalactic medium -- cosmology: observations

Offprint request: A. Mercurio, mercurio@na.astro.it
or mercurio@ts.astro.it

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