Discovery of a Primitive Damped Lyα Absorber near an X‐Ray–bright Galaxy Group in the Virgo Cluster

Abstract

We present a new ultraviolet echelle spectrum of PG 1216+069, obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, that reveals damped Ly absorption, as well as O i,Cii,Siii, and Fe ii absorption lines, at zabs 0:00632 near the NGC 4261 galaxy group in the periphery of the Virgo Cluster. The absorber shows no evidence of highly ionized gas, which places constraints on ‘‘warm-hot’ ’ missing baryons in the X-ray–bright NGC 4261 group. The well-developed damping wings of the Ly line tightly constrain the H i column density; we find log N(Hi) 19:32 0:03. The metallicity of this subdamped Ly absorber (sub-DLA) is remarkably low, O=HŠ 1:60þ0:09 0:11, comparable to many analogous high-redshift systems, and the iron abundance indicates that this absorber contains little or no dust. Nitrogen is underabundant: we detect neither N i nor N ii, and we show that the absence of nitrogen is not due to ionization effects but rather indicates that N=OŠ 0:28 (3). Despite the proximity of the sight line to the NGC 4261 group, there are no bright galaxies with small impact parameters at the absorption redshift: the nearest known galaxy is a sub-L * galaxy with a projected distance of 86 h 1 1 75 kpc, while the closest L * galaxyisNGC4260,at 246 h75 kpc. The low metallicity and nitrogen