HIPASS in Fornax

At the nominal cluster distance of ~20Mpc, this corresponds to an elongated structure more than 10Mpc in extent. A velocity gradient across the structure is detected, with radial velocities increasing by ~500km/s from south-east to north-west. The clustering of galaxies evident in optical surveys is only weakly suggested in the spatial distribution of our HI detections.

Of 62 HI detections within a 10{deg} projected radius of the cluster centre, only two are within the core region (projected radius <1{deg}) and less than 30 per cent are within 3.5{deg}, suggesting a considerable deficit of HI-rich galaxies in the centre of the cluster. However, relative to the field, there is a 3(+/-1)-fold excess of HI-rich galaxies in the outer parts of the cluster where galaxies may be infalling towards the cluster for the first time.