Absorption-Line Systems and Galaxies in Front of the Second-brightest Quasar, PHL 1811

Abstract

The extraordinarily bright quasar PHL 1811, at a redshift zem = 0.192, provides an attractive opportunity to use ultraviolet absorption-line spectroscopy to study the properties of gas systems in the local universe. A short (11.3 ks), exploratory spectrum of this object was obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE) with a signal-to-noise ratio of 20 per λ/20,000 resolution element over the most relevant portions of the coverage from 907 to 1185 A. This spectrum reveals seven extragalactic absorption systems, one of which is a Lyman limit system at zabs = 0.08093 with 17.5 < log N(H ) < 19.5. Three of the remaining systems have zabs values that differ by less than 0.008 from that of the Lyman limit system. The abundance of O with respect to Fe in the Lyman limit system is not much different from the solar abundance ratio. The opacity of the Lyman limit system below 990 A and the numerous features arising from Galactic H2 block a moderate fraction of important extragalactic features in the FUSE wavelength band. Nevertheless, supplementary spectra at low resolution plus a moderate-resolution, near-UV spectrum over a limited wavelength range recorded by the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope helped to substantiate our identifications of systems in the FUSE spectrum. The low-resolution STIS spectrum also revealed four absorption features shortward of the quasar's Lyα emission, which we interpret as arising from additional systems showing only the Lyα feature. Spectroscopy of seven galaxies with MR -20 within approximately 2' of PHL 1811 indicated that two of them are near the redshift of the quasar and four have redshifts within 850 km s-1 of the extragalactic absorption systems. The Lyman limit system is likely associated with an L* galaxy at z = 0.0808 lying 23'' (34 h kpc) from the sight line, with absorption arising in the halo of the galaxy or in an unusually large galactic disk. It is also possible that the absorbing material may be tidal debris arising from the galaxy's interactions with a neighbor lying 88 h kpc from the sight line or more extensive intragroup or intracluster gas. Finally, in addition to prominent features at very low velocities arising from the disk of our Galaxy, the strong resonance transitions of C II and Mg II show evidence of material at v ≈ -200 km s-1; the column densities of these two species suggest that 17.7 < log N(H ) < 18.1 if the material has a solar composition.