Abstract

We present a VLT UVES spectrum of a proximate sub-damped Lyα (sub-DLA) system at zabs = 2.65618 toward the quasar Q0331-4505 (zqso= 2.6785 ± 0.0030). Absorption lines of O I, Si II, Si III, Si IV, C II, C III, C IV, Fe II, Al II, and O VI are seen in the sub-DLA, which has a neutral hydrogen column density log NHI p 19.82 ± 0.051820. The absorber is at a velocity of 1820 ± 250 km s-1 from the quasar; however, its low metallicity [O/H] p -1.64 ± 0.07, lack of partial coverage, lack of temporal variations between observations taken in 2003 and 2006, and nondetection of N v imply the absorber is not a genuine intrinsic system. By measuring the O vi column density and assuming equal metallicities in the neutral and ionized gas, we determine the column density of hot ionized hydrogen in this sub-DLA, and in two other sub-DLAs with O vi drawn from the literature. Coupling this with determinations of the typical amount of warm ionized hydrogen in sub-DLAs, we confirm that sub-DLAs are a more important metal reservoir than DLAs, in total comprising at least 6%-22% of the metal budget at. z ≈ 2.5. © 2007. The American Astronomical Society.