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Description
Using data from the HI Parkes All Sky Survey (HIPASS), we have searched for neutral hydrogen in galaxies in a region <25x25{deg}^2^ centred on NGC 1399, the nominal centre of the Fornax cluster. Within a velocity search range of 300-3700km/s and to a 3 lower flux limit of ~40mJy, 110 galaxies with HI emission were detected, one of which is previously uncatalogued. None of the detections has early-type morphology. Previously unknown velocities for 14 galaxies have been determined, with a further four velocity measurements being significantly dissimilar to published values. Identification of an optical counterpart is relatively unambiguous for more than ~90 per cent of our HI galaxies. The galaxies appear to be embedded in a sheet at the cluster velocity which extends for more than 30across the search area. 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.
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