1 Introduction

The rapid development of multifiber spectroscopy in recent years has made possible the simultaneous acquisition of large numbers of galaxy spectra. The obtention of extensive and complete redshift data bases for clusters of galaxies has hastened the investigation of the physical properties of their visual component which, in turn, is allowing for a better understanding of the characteristics of the dark matter distribution on Mpc scales. Here, we report a total of 104 redshift measurements for 99 galaxies in the field of A3733 and use these data, in combination with a previously published sample of 39 redshifts, to perform a kinematic and spatial analysis of the central regions of this cluster.

A3733 is a southern galaxy cluster listed in the ACO catalog (Abell et al. 1989) as of intermediate Abell's morphological type and richness class R=1. This cluster hosts a central cD galaxy, included in the Wall & Peacock (1985) all-sky catalog of brightest extragalactic radio sources at 2.7 GHz, which has led to its classification as of Bautz-Morgan type I-II (Bautz & Morgan 1970). A3733 is also one of the 107 nearby rich ACO clusters ($R\ge 1$, $z\le 0.1$) included by Katgert et al. (1996) in the ESO Nearby Cluster Survey (ENACS), as well as one of the X-ray-brightest Abell clusters detected in the ROSAT All-Sky Survey by Ebeling et al. (1996).

The only major kinematical study of A3733 done so far is that of Stein (1997). From a sample of 27 cluster members located within from the cluster center, this author has found no evidence of significant substructure in the cluster core. This study of A3733, which is part of a more general investigation of the frequency of substructure in the cluster cores from an optical spectroscopic survey conducted on a sample of 15 nearby () galaxy clusters (Stein 1996), is based on a dataset that has many characteristics in common with the ENACS data gathered for the same field. Indeed, the two datasets have been obtained with the OPTOPUS multifiber spectrograph at the ESO 3.6-m telescope and cover essentially the same area on the sky. Besides, they have also a very similar number of galaxies: 39 and 44, respectively (28 of which are shared).

The MEFOS redshift dataset for A3733 reported in this paper contains two and a half times the number of galaxy radial velocities reported by Stein (1996), including 26 reobservations, while it covers a circular region around the center of A3733 four times larger. Furthermore, its high degree of completeness offers the possibility of extracting a complete magnitude-limited subset with a number of galaxies large enough for its use on statistical analysis. The plan of the paper is as follows. In Sect. 2 we discuss the MEFOS spectroscopic observations and data reduction, and present a final sample with 112 entries built by the combination of the MEFOS and Stein's (1996) data. Section 3 begins with a brief description of the tools which will be used for the analysis of the data. Next, we identify the galaxies in our sample that belong to A3733, and use this dataset and a nearly complete magnitude-limited subset of it to examine the kinematical properties and structure of the central regions of the cluster. Section 4 summarizes the results of our study.