We present new GHRS observations of Lyman alpha absorption lines associated
with a group of galaxies towards the QSO 1545+2101. We have identified eight
distinct Lyman alpha absorption features in the spectrum of QSO 1545+2101 at a
mean redshift of z=0.2648 with a velocity dispersion of 163 km/s. A group of
galaxies is detected in the vicinity of this QSO at a mean redshift of z=0.2645
and velocity dispersion 239 km/s.
The identification of discrete absorption systems indicates that they arise
in clouds of neutral hydrogen rather than in a diffuse intragroup medium. Our
analysis suggests that the Lyman alpha absorption lines are associated with
individual galaxies in the group, although a one-to-one relationship between
absorbers and galaxies is difficult to establish in such a dense environment.Comment: 16 pages, 3 figures. Accepted for publication in Ap