New Galaxies Discovered in the First Blind H I Survey of the Centaurus A Group
Abstract
We have commenced a 21 cm survey of the entire southern sky (δ<0deg, -1200 km s-1<vsolar<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 Msolar<MHI<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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1999
- DOI:
- 10.1086/307854
- arXiv:
- arXiv:astro-ph/9906146
- Bibcode:
- 1999ApJ...524..612B
- Keywords:
-
- GALAXIES: CLUSTERS: INDIVIDUAL (CENTAURUS A);
- GALAXIES: DISTANCES AND REDSHIFTS;
- GALAXIES: ISM;
- RADIO LINES: GALAXIES;
- SURVEYS;
- galaxies: clusters: individual (Centaurus A);
- Galaxies: Distances and Redshifts;
- Galaxies: ISM;
- Radio Lines: Galaxies;
- Surveys;
- Astrophysics
- E-Print:
- 19 pages Latex, 6 figures (Fig. 2 in four parts, Fig.5 in two parts). To appear in The Astrophysical Journal (Vol. 524, October 1999)