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Astron. Astrophys. 320, 717-730 (1997)

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Evolution and dynamics of poor clusters of galaxies

Gastão B. Lima Neto and Frank W. Baier

Universität Potsdam, c/o Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14882 Potsdam, Germany

Received 1 April 1996 / Accepted 7 October 1996


We have performed N -body simulations of poor clusters with enough particles to resolve the individual galaxies. The main cases of initial conditions are: (i) 50 equal mass galaxies; (ii) 60 galaxies with masses drawn from a Schechter distribution function, and (iii) the collision of two subclusters each one containing 25 galaxies. The evolution and kinematics of the first ranked galaxy, the substructures, and the possible rotation of clusters are investigated.

A massive object with cD characteristics is always formed and is never found farther than 100 kpc from the centre of the cluster. This massive galaxy oscillates around the cluster centre with an average peculiar velocity of 70 km s-1. We show that increasing the initial intra-cluster medium (ICM) mass while keeping the galaxies mass and structure without change, raises the merging rate due to the dynamical friction with the ICM. Substructures are almost always present on the galaxy count contour plots. The ICM projected density, which should be similar to the X-ray emission map, presents strong substructures when we have colliding subclusters. Otherwise, in isolated clusters, the substructure is less pronounced indicating that substructures should reflect important but transient dynamical phenomena. We propose that clusters formed by an off-centre collision and subsequent merging of two approximate equal mass subclusters should show a general rotational pattern that could be detected even after the relaxation of the cluster. These clusters would have a spin parameter, [FORMULA], of about 0.3-0.5.

Key words: galaxies: clusters of; formation; elliptical and lenticular, cD – galaxies: dynamics – methods: numerical – X-rays: galaxies

Present address: Observatoire de Lyon, France

Send offprint requests to: G.B. Lima Neto

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998