The Ly$\alpha$ Forest at Z=2
Session 70 -- Active Galaxies and Intergalactic Medium
Oral presentation, Tuesday, 10, 1995, 2:00pm - 3:30pm

## [70.02] The Ly$\alpha$ Forest at Z=2

Jill Bechtold (Steward Observatory, University of Arizona), Adam Dobrzycki (CFA), Jennifer Scott, Craig Foltz, Michael Lesser (Steward Observatory, University of Arizona)

We have obtained moderate resolution ($\sim$80 km/sec FWHM) spectra of the Ly$\alpha$ forest towards 40 quasars at z$\approx$2.5 with the MMT Blue Spectrograph. This sample complements extensive data at higher redshift obtained from the ground and the low redshift data on the Ly$\alpha$ forest obtained by the HST Key Project (Bahcall et al. 1993, 1994). There appears to be a change in both the number and rate of evolution of the Ly$\alpha$ clouds between z$>$2.5 and z$<$1. This change may indicate a change in the population which is being probed, from clouds on the outskirts of galaxies at low z, to truly primordial intergalactic clouds at high redshift. In addition, our new sample places limits on the ambient EUV background at z$\approx$2 where comparison with known sources such as quasars is more straightforward than at higher redshift.