Estimation of the space density of low surface brightness galaxies

The space density of low surface brightness and tiny gas-rich dwarf galaxies are estimated for two recent catalogs: the Arecibo Survey of Northern Dwarf and Low Surface Brightness Galaxies and the Catalog of Low Surface Brightness Galaxies, List II. The goals are (1) to evaluate the additions to the completeness of the Fisher & Tully 10 Mpc sample and (2) to estimate whether the density of galaxies contained in the new catalogs adds a significant amount of neutral gas mass to the the inventory of H I already identified in the nearby, present-epoch universe. Although tiny dwarf galaxies (M-H I less than or similar to 10(7) M.) may be the most abundant type of extragalactic stellar system in the nearby universe, if the new catalogs are representative, the low surface brightness and dwarf populations they contain make only a small addition (less than or similar to 10%) to the total H I content of the local universe and probably constitute even smaller fractions of its luminous and dynamical mass.