Absorption Line Signatures of Proto-Dwarf Galaxies

SiIV Introduction A substantial fraction of the Ly clouds may be due to gas in small halos corresponding to dwarf galaxies or their progenitors. At low redshifts, for example, van Gorkom et al (1996) have identified a dwarf galaxy fainter than the SMC associated with a Ly cloud detected in the spectrum of Mrk 335. Many of the recent studies of the relationship between Ly clouds and galaxies have found Ly clouds with no corresponding galaxies within several Mpc (e.g., Morris et al 1993; Stocke et al 1995; Tripp et al 1998); these may be clouds affiliated with small halos too faint to be detected in the galaxy redshift surveys employed in the above studies. At high redshifts, it has long been suggested that Ly clouds may arise in “mini-halos” that are the progenitors of dwarf galaxies (e.g., Rees 1988), and recently the theoretical work of Bond & collaborators (c.f., Bond & Wadsley 1997) has predicted that a large number of small halos with velocity dispersions of roughly 30 km s-1 are present at high z. By calculating the absorption line signatures of gas sitting in small halos it may be possible to specifically identify these objects and test if a substantial fraction of the Ly absorbers are due to proto-dwarf galaxies.