New galaxies discovered in the first blind HI survey of the Centaurus A group

We have commenced a 21 cm survey of the entire southern sky (delta < 0 degr ees, -1200 km s(-1) < v. < 12,700 km s(-1)) that is "blind," i.e., unbiased by previous optical information. In the present paper we report on the res ults of a pilot project that is based on data from this all-sky survey. The project was carried out on an area of 600 deg(2) centered on the nearby Ce ntaurus A (Cen A) group of galaxies at a mean velocity of v., similar to 50 0 km s(-1). This was recently the subject of a separate and thorough optica l 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, whi le 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 10(7) M . at the assumed group distance of 3.5 Mpc. The new detection with the largest H I mass is ESO 174-G?001 with M-H I = 2.1 x 10(8) M .. Prior to our survey this galaxy was an uncertain optical identification because o f high Galactic extinction. We found optical counterparts for all the H I d etections, most of them intrinsically very faint (M (B) > - 13.0), low surf ace brightness dwarf galaxies with H I profile line-widths suggestive of dy namics 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 r mass function, d erived from all the known group galaxies in the interval 10(7) M . <M-H I < 10(9) M . 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.