A Super-damped Lyα Quasi-stellar Object Absorber at z = 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 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 (SFR) of ~10 M ⊙ yr-1 in the absence of dust attenuation. C II* λ1336 absorption is also detected, suggesting SFR surface density -2 < log \dot{ψ_{*}} < 0 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.
Based on observations collected during program ESO 385.A-0778 at the European Southern Observatory with Ultraviolet and Visual Echelle Spectrograph (UVES) on the 8.2 m KUEYEN telescope operated at the Paranal Observatory, Chile.- Publication:
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The Astrophysical Journal
- Pub Date:
- April 2012
- DOI:
- 10.1088/0004-637X/749/2/176
- Bibcode:
- 2012ApJ...749..176K
- Keywords:
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- dust;
- extinction;
- quasars: absorption lines