A Super-Damped Lyman-alpha QSO Absorber at z=2.2

Varsha P. Kulkarni (1), Joseph Meiring (2), Debopam Som (3), Celine Peroux (4), Donald G. York (5), Pushpa Khare (6), James T. Lauroesch (7) ((1) University of South Carolina, Columbia, USA; (2) University of Massachusetts, Amherst, USA; (3) University of South Carolina, Columbia,  USA; (4)  Universite Aix-Marseille, Marseille, France; (5)  University of Chicago, Chicago, USA; (6)Inter-University Center for Astronomy & Astrophysics, Pune, India; (7) University of Louisville, Louisville, USA)

We report the discovery of a “super-damped” Lyman-alpha absorber at z_{abs}=2.2068 toward QSO Q1135-0010 in the Sloan Digital Sky Survey, and follow-up VLT UVES spectroscopy. Voigt profile fit to the DLA line indicates log N_{H I} = 22.05 ± 0.1. This is the second QSO DLA discovered to date with such high N_{H I}. 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 of ~10 M(sun) yr^{-1} in the absence of dust attenuation. C II* λ1336 absorption is also detected, suggesting SFR surface density –2 < log (dψ_{*}/dt) < 0 M(sun) 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, LMC, or 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 GRB DLAs.

Complete preprint ==> http://arxiv.org/abs/1202.0882

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