WSRT Ultradeep Neutral Hydrogen Imaging of Galaxy Clusters at z ≈ 0.2: A Pilot Survey of Abell 963 and Abell 2192

A pilot study with the powerful new backend of the Westerbork Synthesis Radio Telescope ( WSRT) of two galaxy clusters at z = 0.2 has revealed neutral hydrogen emission from 42 galaxies. The WSRT probes a total combined volume of 3.4 x 10(4) Mpc(3) at resolutions of 54 x 86 kpc(2) and 19.7 km s(-1), surveying both clusters and the large-scale structure in which they are embedded. In Abell 963, a dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction, most of the gas-rich galaxies are located between 1 and 3 Mpc in projection, northeast from the cluster core. Their velocities are slightly redshifted with respect to the cluster, and this is likely a background group. None of the blue galaxies in the core of Abell 963 are detected in H I, although they have colors and luminosities similar to those of the H I detected galaxies in the cluster outskirts and field. Abell 2192 is less massive and more diffuse. Here the gas-rich galaxies are more uniformly distributed. The detected H I masses range from 5 x 10(9) to 4 x 10(10) M circle dot. Some galaxies are spatially resolved, providing rudimentary rotation curves useful for detailed kinematic studies of galaxies in various environments. This is a pilot for ultradeep integrations down to H I masses of 8 x 10(8) M circle dot, providing a complete survey of the gas content of galaxies at, probing environments ranging from cluster cores to voids.