| Authors | Banks, G. D.; Disney, M. J.; Knezek, P. M.; Jerjen, H.; Barnes, D. G.; Bhatal, R.; de Blok, W. J. G.; Boyce, P. J.; Ekers, R. D.; Freeman, K. C.; Gibson, B. K.; Henning, P. A.; Kilborn, V.; Koribalski, B.; Kraan-Korteweg, R. C.; Malin, D. F.; Minchin, R. F.; Mould, J. R.; Oosterloo, T.; Price, R. M.; Putman, M. E.; Ryder, S. D.; Sadler, E. M.; Staveley-Smith, L.; Stewart, I.; Stootman, F.; Vaile, R. A.; Webster, R. L.; Wright, A. E. |
| Abstract | We have commenced a 21 cm survey of the entire southern sky (δ<0deg, -1200 km s-1solar<12,700 km s-1) that is ``blind,'' i.e., unbiased by previous optical information. In the present paper we report on the results of a pilot project that is based on data from this all-sky survey. The project was carried out on an area of 600 deg2 centered on the nearby Centaurus A (Cen A) group of galaxies at a mean velocity of vsolar~500 km s-1. This was recently the subject of a separate and thorough optical survey. We found 10 new group members to add to 21 galaxies already known in the Cen A group: five of these are previously uncataloged galaxies, while five were previously catalogued but not known to be associated with the group. Most of the new members have H I masses close to our survey limit of 107 Msolar at the assumed group distance of 3.5 Mpc. The new detection with the largest H I mass is ESO 174-G?001 with MHI=2.1×108 Msolar. Prior to our survey this galaxy was an uncertain optical identification because of high Galactic extinction. We found optical counterparts for all the H I detections, most of them intrinsically very faint (MB>-13.0), low surface brightness dwarf galaxies with H I profile line-widths suggestive of dynamics dominated by dark matter. The new group members add approximately 6% to the H I mass of the group and 4% to its light. The H I mass function, derived from all the known group galaxies in the interval 107 MsolarHI<109 Msolar, has a faint-end slope of 1.30+/-0.15, allowing us to rule out a slope of 1.7 at 95% confidence. Even if the number in the lowest mass bin is increased by 50%, the slope only increases to 1.45+/-0.15. |
