Ly alpha Cloud Size Evolution and Shape from QSO Groups

Abstract

We present results from Keck HIRES, KPNO 4m/RC Spec and HST FOS spectra of a low-redshift, close QSO pair and a close, higher-redshift QSO triplet in order to explore the size evolution, shape and clustering of Ly alpha absorbers. The results we highlight here indicate that there is no strong evidence for evolution of Ly $α$ cloud size with redshift, that strong (W > 0.4A) Ly alpha forest absorbers are probably not filaments, but probably more sheet- like. For C IV absorbers a large component of clustering on 200 km/s < Delta v < 600 km/s scales along single sightlines is due to internal velocities of single absorbers, not clustering between absorbers.