An H I survey for protogalaxies in the Centaurus and Fornax galaxy clusters

The results of 21-cm neutral hydrogen survey observations, made using the 64-m Parkes telescope, are presented for two 8° by 8° fields, centred on the Centaurus and Fornax galaxy clusters, and a smaller 1°.5 field in Eridanus. The purpose of the observations was to search for extended H I clouds with no clear optical counterparts. 31 previously catalogued galaxies were detected, with H I parameters for 16 being listed for the first time. One previously uncatalogued dwarf galaxy ('Wombat I', J0341-3851) was found near the Fornax cluster. Australia Telescope Compact Array observations give an Hi mass of 8 × 10⁷ M⊙ and a diameter of 4kpc for this object, which is also visible on UKST survey plates. However, no clouds with optically invisible counterparts were detected. We deduce a 99 per cent confidence limit on the total Hi density of such objects in the cluster and near-cluster environment of Ω_HI < 10^-2 h^-1 (σV/100kms^-1).