1997PASP..109.1395O

In recent years evidence has been mounting that a substantial amount of baryonic matter appears to be "missing" from our current inventory of galaxies, groups and clusters. This implies that significant repositories of baryonic matter are awaiting discovery. The most likely form of this repository is a very diffuse galaxy whose existence is effectively masked by the brightness and noise of the night sky background. In order to better determine the space density of these galaxies, three observational surveys, employing different observing techniques, were undertaken to search for previously undiscovered and uncatalogued galaxies. In sum, all three survey methods proved successful, in that significant numbers of very diffuse galaxies were detected. Construction of the luminosity and/or space density functions of LSB galaxies shows that indeed much of the baryonic matter in the universe could lie in galaxies whose low surface brightness has resulted in their remaining undetected until recently. Since surface brightness selection effects are still present in all our surveys, it is clear we have yet to probe the very faint end of disk diffuseness.(c) Astronomical Society of the Pacific