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 \mathrm { 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 \mathrm { h ^ { -1 } } Mpc from the cluster center ) , that leads to a virial mass of \mathrm { M = 1.6 } – 2.2 \times 10 ^ { 15 } \mathrm { 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 .