[PWC2006b] 1238 , the SIMBAD biblio

We present an imaging and spectroscopic survey of galaxies in fields around QSOs HE 0226-4110, PKS 0405-123, and PG 1216+069. The fields are selected to have ultraviolet echelle spectra available, which uncover 195 Lyα absorbers and 13 absorbers along the three sightlines. We obtain robust redshifts for 1104 galaxies of rest-frame absolute magnitude M_R- 5log h ≲ -16 and at projected physical distances ρ ≲ 4 h.^–1 Mpc from the QSOs. Hubble Space Telescope (HST)/WFPC2 images of the fields around PKS 0405-123 and PG 1216+069 are available for studying the optical morphologies of absorbing galaxies. Combining the absorber and galaxy data, we perform a cross-correlation study to understand the physical origin of Lyα and absorbers and to constrain the properties of extended gas around galaxies. The results of our study are: (1) both strong Lyα absorbers of and absorbers exhibit a comparable clustering amplitude as emission-line-dominated galaxies and a factor of ~ 6 weaker amplitude than absorption-line-dominated galaxies on comoving projected distance scales of r_p< 3 h.^–1 Mpc; (2) weak Lyα absorbers of appear to cluster very weakly around galaxies; (3) none of the absorption-line-dominated galaxies at r_p≤ 250 h.^–1 kpc has a corresponding absorber to a sensitive upper limit of W(1031) ≲ 0.03 Å, while the covering fraction of absorbing gas around emission-line-dominated galaxies is found to be κ ~ 64%; and (4) high-resolution images of five absorbing galaxies show that these galaxies exhibit disk-like morphologies with mildly disturbed features on the edge. Together, the data indicate that absorbers arise preferentially in gas-rich galaxies. In addition, tidal debris in groups/galaxy pairs may be principally responsible for the observed absorbers, particularly those of W(1031)>70 mÅ.