Stellar and Gas Properties of High HiMass-to-Light Ratio Galaxies in the Local Universe

We present a multi-wavelength study (BVRI band photometry and HI lineinterferometry) of nine late-type galaxies selected from the HIPASS BrightGalaxy Catalog on the basis of apparently high HI mass-to-light ratios (3M_sun/L_sun < M_HI/L_B < 27 M_sun/L_sun). We found that most of the originalestimates for M_HI/L_B based on available photographic magnitudes in theliterature were too high, and conclude that genuine high HI mass-to-light ratio(>5 M_sun/L_sun) galaxies are rare in the Local Universe. Extreme high M_HI/L_Bgalaxies like ESO215-G?009 appear to have formed only the minimum number ofstars necessary to maintain the stability of their HI disks, and could possiblybe used to constrain galaxy formation models. They may to have been formingstars at a low, constant rate over their lifetimes. The best examples all havehighly extended HI disks, are spatially isolated, and have normal baryoniccontent for their total masses but are deficent in stars. This suggests thathigh M_HI/L_B galaxies are not lacking the baryons to create stars, but areunderluminous as they lack either the internal or external stimulation for moreextensive star formation.Comment: 29 Pages, 59 Figures. Accepted for publication in AJ (to be published ~April 2006