A SUPER-DAMPED Lyα QUASI-STELLAR OBJECT ABSORBER ATz= 2.2

Abstract

We report the discovery of a super-damped Lyα absorber at z abs = 2.2068 toward quasi-stellar object (QSO) Q1135-0010 in the Sloan Digital Sky Survey (SDSS) and follow-up Very Large Telescope (VLT) UVES spectroscopy. A Voigt profile fit to the damped Lyα (DLA) line indicates log . This is the second QSO DLA discovered to date with such high . We derive element abundances [Si/H] = –1.10 ± 0.10, [Zn/H] = –1.06 ± 0.10, [Cr/H] = –1.55 ± 0.10, [Ni/H] = –1.60 ± 0.10, [Fe/H] = –1.76 ± 0.10, [Ti/H] = –1.69 ± 0.11, [P/H] = –0.93 ± 0.23, and [Cu/H] = –0.75 ± 0.14. Our data indicate detection of Lyα emission in the DLA trough, implying a star formation rate (SFR) of ~10 M ☉ yr–1 in the absence of dust attenuation. C II* λ1336 absorption is also detected, suggesting SFR surface density M ☉ yr–1 kpc–2. We estimate electron density in the range 3.5 × 10–4 to 24.7 cm–3 from C II*/C II and ~0.5-0.9 cm–3 from Si II*/Si II. Overall, this is a robustly star-forming, moderately enriched absorber, but with relatively low dust depletion. Fitting of the SDSS spectrum yields low reddening for Milky Way, Large Magellanic Cloud, or Small Magellanic Cloud (SMC) extinction curves. No CO absorption is detected, and C I absorption is weak. The low dust and molecular content, reminiscent of some SMC sight lines, may result from the lower metallicity and a stronger radiation field (due to higher SFR). Finally, we compare this absorber with other QSO and gamma-ray burst DLAs.