A Near‐Solar Metallicity, Nitrogen‐deficient Lyman Limit Absorber Associated with Two S0 Galaxies

Abstract

The UV spectrum of the bright quasar PHL 1811 at z em = 0.192 reveals a foreground gas system at z = 0.080923 with log N (H ##IMG## [http://ej.iop.org/images/0004-637X/623/2/767/img1.gif] {img1.gif} ) = 17.98 ± 0.05. We have determined the abundances of various atomic species in this system from a spectrum covering the wavelength range 1160-1730 Å recorded at 7 km s -1 resolution by the E140M grating of the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope ( HST ), supplemented by coverage at shorter wavelengths by the Far Ultraviolet Spectroscopic Explorer ( FUSE ). The abundances of C II , Si II , S II , and Fe II compared to that of O I indicate that a considerable fraction of the gas is in locations where the hydrogen is ionized. An oxygen abundance [O/H] = -0.19 ± 0.08 in the H I -bearing gas indicates that the chemical enrichment of the gas is unusually high for an extragalactic QSO absorption system. However, this same material has an unusually low abundance of nitrogen, [N/O] 10 -3 cm -3 by modeling the ionization by the intergalactic radiation field and an upper bound n ( e ) < 0.07 cm -3 from the absence of much C II in an excited fine-structure level. The thermal pressure in the range 4 cm -3 K < 140 cm -3 K could be confined by a warm-hot intergalactic medium (WHIM) structure with ρ/ ##IMG## [http://ej.iop.org/images/0004-637X/623/2/767/img3.gif] {img3.gif} ~ 20 that might accompany a wall of galaxies at the same redshift, seen in data from the Sloan Digital Sky Survey. An r -band image of the field surrounding PHL 1811 recorded by the ACS instrument on HST shows that two galaxies at the same redshift as the gas are S0 galaxies, separated by only 34 and 87 h ##IMG## [http://ej.iop.org/images/0004-637X/623/2/767/img4.gif] {img4.gif} kpc from the line of sight. One or both of these galaxies may be the source of the material in the Lyman limit system, which may have been expelled from them in a fast wind, by tidal stripping, or by ram pressure stripping. Subtraction of the ACS point-spread function from the image of the QSO reveals the presence of a face-on spiral galaxy under the glare of the quasar; while it is possible that this galaxy may be responsible for the Lyman limit absorption, the exact alignment of the QSO with the center of the galaxy suggests that the spiral is the quasar host.