Multiphase plasma in sub-damped Lyα systems: A hidden metal reservoir

Fox, Andrew J. ; Petitjean, Patrick ; Ledoux, Cédric ; Srianand, Raghunathan (2007) Multiphase plasma in sub-damped Lyα systems: A hidden metal reservoir The Astrophysical Journal Letters, 668 (1). L15-L18. ISSN 0571-7248

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We present a VLT/UVES spectrum of a proximate sub-damped Lyman-α (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 N H 1= 19.82 ± 0.05. The absorber is at a velocity of 1820 ± 250 km s-1 from the quasar; however, its low metallicity [O/H] = -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.

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Source:Copyright of this article belongs to IOP Publishing.
ID Code:55025
Deposited On:18 Aug 2011 08:06
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