The origin of Lyα absorption systems at z > 1:: Implications from the Hubble Deep Field

The Hubble Deep Field images have provided us with a unique chance to relate statistical properties of high-redshift galaxies to statistical properties of Ly alpha absorption systems. Combining an empirical measure of the galaxy surface density versus redshift with an empirical measure of the gaseous extent of galaxies, we predict the number density of Ly alpha absorption systems that originate in extended gaseous envelopes of galaxies versus redshift. We show that at least 50% and as much as 100% of observed Ly alpha absorption systems of W greater than or similar to 0.32 Angstrom can be explained by extended gaseous envelopes of galaxies. Therefore, we conclude that known galaxies of known gaseous extent must produce a significant fraction and perhaps all of Ly alpha absorption systems over a large redshift range.