ESO215-G?009: An Extreme HI-Rich Dwarf Irregular Galaxy
  We present deep BVRI band images and HI line observations of the nearby, low surface brightness galaxy ESO215-G?009 which were obtained with the ANU 2.3-m Telescope and the Australia Telescope Compact Array, respectively. ESO215-G?009 was selected from the HIPASS Bright Galaxy Catalog because it has the second highest HI mass-to-light ratio of the galaxies with measured B band apparent magnitudes. We find that it is an isolated dwarf irregular galaxy with an old stellar population. We place an upper limit on the current star formation rate of ~2.5 x 10^-3 M_sun/yr. The extended HI disk shows regular rotation (v_rot = 51 +/- 8 km/s), and at a column density of ~5.0 x 10^19 atoms/cm^2 can be traced out to over six times the Holmberg radius of the stellar component (radius at mu_B = 26.6 mag/arcsec^2). After foreground star subtraction, we measure a B band apparent magnitude of 16.13 +/- 0.07 mag within a radius of 80". The HI flux density is 122 +/- 4 Jy km/s within a radius of 370". Given a Galactic extinction of A_B = 0.95 +/- 0.15 mag, we derive an HI mass-to-light ratio of 22 +/- 4 M_sun/L_sun for ESO215-G?009. To our knowledge this is the highest ratio for a galaxy to be confirmed by accurate measurement to date. 
Bradley E. Warren (RSAA), Helmut Jerjen (RSAA), Baerbel S. Koribalski   (ATNF)