Previous
abstract 
Next
abstract
The discovery of Ly$\alpha$ absorbers at low redshift allows us to estimate for the first time what fraction of them are (i) randomly distributed, (ii) distributed like galaxies but not physically associated with luminous objects, (iii) actually part of the halos of luminous galaxies, or (iv) tidal tails within galaxy groups. It seems likely that these proportions will turn out to be a function of column density. Detailed analysis of the absorber-galaxy correlation function from the sightline to the QSO 3C273, where the brightness of the background QSO allows very low column density absorbers to be observed, suggest that the majority of such absorbers are not associated with galaxies, but that there is a significant subset that are. The absorbers associated with galaxies may be produced in enormous gaseous disks surrounding normal spiral galaxies, or may be tidal material bound up in small groups of galaxies.
