Annu. Rev. Astron. Astrophys. 2000. 38: 667-715 Copyright © 2000 by Annual Reviews. All rights reserved

4.11. Intergalactic Medium

The HDF-S STIS field was selected to contain the bright, moderate redshift quasar J2233-606. Deep HST imaging of the field around the quasar during the HDF-S campaign has provided detection and morphologies of numerous galaxies near the line of sight. Moderate- to high-resolution spectra have been obtained of the quasar both from the ground and with HST covering the wavelength regime 1140-8200 Å [Savaglio 1998, Sealey et al. 1998, Outram et al. 1999, Ferguson et al. 2000], whereas follow-up observations from the ground have established the redshifts of some of the brighter galaxies in the field [Tresse et al. 1999]. Too few redshifts have yet been measured to allow detailed study of the correspondence between galaxies and QSO absorbers. A tentative detection of Ly emission surrounding the QSO was reported by [Bergeron et al. 1999].

Using the STIS UV and groundbased optical spectra, [Savaglio et al. 1999] found the number density of Ly clouds with log N_HI > 14 in the redshift interval 1.5 < z < 1.9, to be higher than that found in most previous studies, and saw no evidence for a change in the Doppler parameters of the Ly lines with redshift. The two-point correlation function of Ly clouds shows clear clustering on scales less than 300 km s^-1, especially the higher column density systems, in agreement with results from other quasars. Metal abundances in several absorption line systems have been studied by [Prochaska & Burles 1999]. [Petitjean & Srianand 1999] studied the metal lines in the absorption-line systems near the QSO redshift and found that relative line strengths of different species are best modeled with a multi-zone partial-covering model wherein different species (e.g Ne VIII, O VI) arise from gas at different distances from the AGN, and the clouds cover the central continuum emission region completely but only a fraction of the broad emission-line region.