The Gaseous Extent of Galaxies and the Origin of Lyα Absorption Systems. IV. Lyα Absorbers Arising in a Galaxy Group

Abstract

We present new Goddard High Resolution Spectrograph observations of Lyα absorption lines associated with a group of galaxies toward the QSO 1545+2101. We have identified eight distinct Lyα 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-1. A group of galaxies is detected in the vicinity of this QSO at a mean redshift of ⟨z⟩ = 0.2645 and velocity dispersion of 239 km s-1. 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 Lyα 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.