Simulations of the Large-Scale Structure Formation & the Evolution of the Lyman-α Forest Comparison With Observations

Abstract

The study of the Lya absorbers seen in quasar spectra is a very sensitive way to probe the baryonic material in the whole redshift range 0 < z < 5. In particular the evolution of the spatial distribution of the Lyα clouds offers the unique chance to obtain direct information about the structure formation processes throughout a wide redshift range. During recent years considerable success has been obtained in modeling the distribution of the neutral hydrogen gas in the context of the evolution of large-scale structure (Cen et al. 1994, Petitjean et al. 1995, Mücket et al. 1996, Hernquist et al. 1996, Miralda-Escudé et al. 1996, Zhang et al. 1996, Bi & Davidsen 1996) By means of simulations many of the characteristics of the Lyα forest could be reproduced. One of the outstanding problems is the relation between the Lyman-α forest and galaxies. Although conclusions are uncertain, it seems that at least the strongest lines in the Lyman-α forest at low redshift are anyhow associated with galaxies (Lanzetta et al. 1995, Le Brun et al. 1996) since the density of the intergalactic gas is expected to be higher in the vicinity of the galactic potential wells. The case for the weak line to be associated with galaxies is less clear. Indeed observations of the line of sight to 3C273 that are the most sensitive to the presence of weak lines (Morris et al. 1991, Bahcall et al. 1991) indicate the presence of a large number of these lines and no clear association with galaxies is seen (Morris et al. 1993). Moreover, Stocke et al. (1995) have detected weak absorption lines located in regions devoided of galaxies.