The cluster of galaxies Abell 970^*

¹ Departamento de Astronomia do IAG/USP, Av. Miguel Stefano 4200, 04301-904 São Paulo, Brazil
² Observatoire de Paris - Section de Meudon, DAEC, 92195 Meudon Cedex, France e-mail: Dominique.Proust@obspm.fr
³ Divisão de Astrofísica INPE/MCT, 12225-010 São José dos Campos, Brazil e-mail: hugo@das.inpe.br
⁴ Departamento de Astronomia do IAG/USP, Av. Miguel Stefano 4200, 04301-904 São Paulo, Brazil e-mail: gastao@iagusp.usp.br
⁵ Departamento de Física, Universidad de La Serena, Benavente 980, La Serena, Chile e-mail: hcuevas@enterprise.dfuls.cl
⁶ Departamento de Astronomia y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 104, Santiago 22, Chile e-mail: hquintan@astro.puc.cl
⁷ European Southern Observatory, Casilla 19001, Santiago 19, Chile and Observatoire de Paris -Section de Meudon, DESPA, 92195 Meudon Cedex, France e-mail: pfouque@eso.org

Corresponding author: L. Sodré Jr., laerte@iagusp.usp.br

Received: 13 September 2000
Accepted: 14 June 2001

Abstract

We present a dynamical analysis of the galaxy cluster Abell 970 based on a new set of radial velocities measured at ESO, Pic du Midi and Haute-Provence observatories. Our analysis indicates that this cluster has a substructure and is out of dynamical equilibrium. This conclusion is also supported by differences in the positions of the peaks of the surface density distribution and X-ray emission, as well as by the evidence of a large-scale velocity gradient in the cluster. We also found a discrepancy between the masses inferred with the virial theorem and those inferred with the X-ray emission, which is expected if the galaxies and the gas inside the cluster are not in hydrostatic equilibrium. Abell 970 has a modest cooling flow, as is expected if it is out of equilibrium. We propose that cooling flows may have an intermittent behaviour, with phases of massive cooling flows being followed by phases without significant cooling flows after the accretion of a galaxy group massive enough to disrupt the dynamical equilibrium in the centre of the clusters. A massive cooling flow will be established again, after a new equilibrium is achieved.