HI imaging of galaxy clusters at z approximate to 0.2, a pilot survey of Abell 963 and Abell 2192

A pilot study with the new powerful backend of the Westerbork Synthesis Radio Telescope (WSRT) of two galaxy clusters at z = 0.2 has revealed neutral hydrogen emission from 39 galaxies. At these redshifts, the WSRT provides an instantaneous velocity coverage of 18,054 km/s. The volume probed for each cluster is 1.7 x 10(4) Mpc(3), with spatial and velocity resolutions of 54 x 86 kpc(2) and 19.7 km/s, covering both clusters and the large scale structure in which they are embedded.

The spatial distribution of the HI detected galaxies is very different for the two clusters. In Abell 963, most of the gas-rich galaxies are located to the northeast, at 1-3 Mpc from the cluster center in projection. Their velocities are slightly redshifted with respect to the cluster mean. This could be a gas-rich group falling in from the front. Abell 2192 is less massive and more diffuse, with the gas-rich galaxies more uniformly spread over a large region around the cluster. The HI masses of the detected galaxies range from 5 x 10(9) to 4 x 10(10) M-circle dot. Some HI rich galaxies are spatially resolved and rudimentary rotation curves are derived, showing the prospect for Tully-Fisher studies of different galaxy populations in these environments.

Only one galaxy is detected within a I Mpc radius from the center of the Butcher-Oemler cluster Abell 963, and none of the blue B-O galaxies which are all located within the central Mpc. The HI detected galaxies outside the central Mpc are of similar colour and magnitude as the non-detected B-O galaxies, indicating that the blue B-O galaxies are gas poor compared to their counterparts in the field. (c) 2006 Elsevier B.V. All rights reserved.