The structure and dynamics of Abell 1942 ^*,**

¹ Divisão de Astrofísica, INPE/MCT, 12227-010, São José dos Campos/S.P., Brazil
² Observatoire de Paris-Meudon, GEPI, 92195 Meudon, France e-mail: dominique.proust@obspm.fr
³ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo (IAG/USP), 05508-090 São Paulo/SP, Brazil

Received: 19 June 2008
Accepted: 13 September 2008

Abstract

Aims. We present a dynamical analysis of the galaxy cluster Abell 1942 based on a set of 128 velocities obtained at the European Southern Observatory.

Methods. Data on individual galaxies are presented and the accuracy of the determined velocities as some properties of the cluster are discussed. We have also made use of publicly available Chandra X-ray data.

Results. We obtained an improved mean redshift value z = 0.22513 ± 0.0008 and velocity dispersion km s^-1. Our analysis indicates that inside a radius of ~1.5  Mpc (~7 arcmin) the cluster is well relaxed, without any remarkable features and the X-ray emission traces the galaxy distribution fairly well. Two possible optical substructures are seen at ~5 arcmin from the centre in the northwest and the southwest directions, but are not confirmed by the velocity field. These clumps are, however, kinematically bound to the main structure of Abell 1942. X-ray spectroscopic analysis of Chandra data resulted in a temperature kT = 5.5± 0.5 keV and metal abundance Z = 0.33 ± 0.15 . The velocity dispersion corresponding to this temperature using the T_X–σ scaling relation is in good agreement with the measured galaxy velocities. Our photometric redshift analysis suggests that the weak lensing signal observed to the south of the cluster and previously attributed to a “dark clump” is produced by background sources, possibly distributed as a filamentary structure.