Characterizing circumgalactic gas around massive ellipticals at z ∼ 0.4 – I. Initial results★

We present a new Hubble Space Telescope Cosmic Origins Spectrograph (COS) absorption-line survey to study halo gas around 16 luminous red galaxies (LRGs) at $z$ = 0.21–0.55. The LRGs are selected uniformly with stellar mass ${\rm{M_{\rm star}}}>10^{11}\,{\rm{M_{\odot }}}$ and no prior knowledge of the presence/absence of any absorption features. Based on observations of the full Lyman series, we o...