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Astron. Astrophys. 321, 64-70 (1997)

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1. Introduction

The intracluster media of clusters of galaxies can be probed directly by their X-ray emission and at the same time indirectly through the morphologies of the radio sources associated with cluster members. The physical nature of radio galaxies is reflected in the structure of their emission. Studies of radio galaxies have led to a better understanding of both radio emission processes and galaxy environments. One class of interesting radio sources is the Wide-Angle-Tailed (WAT) sources. Originally defined by Owen & Rudnick (1976), WATs are characterised by a radio structure composed of twin jets separated by a wide opening angle and are associated with the dominant member of a cluster of galaxies. They are radio sources with intermediate radio luminosities in the range [FORMULA] to [FORMULA] erg s-1 (O'Donoghue 1990), comparable to the Fanaroff-Riley (1974) break between the FR class I and II. WATs are ideally suited for the study of galaxy/environment interactions. They are known to favour X-ray poor environments and almost never found in regions with cooling flows (Norman et al. 1988; Burns 1990; Zhao et al. 1990) despite being associated with galaxies most likely to be found in cooling flow regions. This implies that the radio emission and cluster gas are associated in some way.

The southern galaxy cluster A 2717 has a central D galaxy which is associated with a WAT source. A 2717 has been studied extensively in the optical (eg. Colless et al. 1987, 1989). The known properties of the cluster and its central D galaxy are summarised in Table 1 and  2.


Table 1. Optical data for the cluster A 2717


Table 2. Optical data for the D galaxy of A 2717

We present here radio and X-ray observations of the cluster. In the radio, it was originally imaged with the Molonglo Observatory Synthesis Telescope (MOST) at 843 MHz in September 1988 and the host galaxy of the WAT was found to be the dominant galaxy of the cluster. In June and October of 1989 two more images were made with the VLA in scaled arrays at 20 cm in C/D and 6 cm B/C in order to resolve the radio structure. Then, in 1992, a higher resolution image was obtained with the Australia Telescope (AT) at 6cm. Subsequently, a Rosat PSPC pointed X-ray observation was obtained for the cluster in 1993.

In Sect. 2, we present the Rosat PSPC data and the results of the analysis of both the flux densities of the discrete sources and the cluster X-ray suface brightness and temperature. In Sect.  3, we calculate the total mass, gas mass and compare the X-ray and optical results. In Sect. 4we present the radio images at 1.4 and 4.9 GHz. In Sect. 5, both limits on the radiation pressures due to the synchroton emission and the X-ray thermal pressure are calculated. A value of [FORMULA] km s-1 Mpc-1 and [FORMULA] are used throughout the paper.

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998