Environmental Dependence of the Nature of Gaseous Envelopes of Galaxies   at z < 1
  We present new statistical study on the origin of Lyman-alpha absorption systems that are detected in QSO fields. The primary objective is to investigate environmental dependence of the relationship between galaxies and Lyman-alpha absorption systems. We find that galaxies exhibit no environmental dependence in giving rise to Lyman-alpha absorbers in their halos. Conversely, Lyman-alpha absorbers do not exhibit preference as to the environment where they reside. 
Noriaki Yahata(1), Kenneth M. Lanzetta(1), John K. Webb(2), Xavier   Barcons(3) ((1) SUNY at Stony Brook, (2) UNSW, (3) Sant...