Coincident, 100 kpc scale damped Lyα absorption towards a binary QSO: how large are galaxies at z ∼ 3?

We report coincident damped Lyα (DLA) and sub-DLA absorption at zabs= 2.66 and zabs= 2.94 towards the z∼ 3, 13.8 arcsec separation binary quasar SDSS 1116+4118 AB. At the redshifts of the absorbers, this angular separation corresponds to a proper transverse separation of ∼110 h−170 kpc. A third abso...

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Bibliographic Details
Published in:	Monthly notices of the Royal Astronomical Society 2007-07, Vol.378 (3), p.801-818
Main Authors:	Ellison, Sara L., Hennawi, Joseph F., Martin, Crystal L., Sommer-Larsen, Jesper
Format:	Article
Language:	eng
Subjects:	Astronomy Earth, ocean, space Exact sciences and technology galaxies: abundances galaxies: high-redshift quasars: absorption lines
Online Access:	Get full text
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Summary:	We report coincident damped Lyα (DLA) and sub-DLA absorption at zabs= 2.66 and zabs= 2.94 towards the z∼ 3, 13.8 arcsec separation binary quasar SDSS 1116+4118 AB. At the redshifts of the absorbers, this angular separation corresponds to a proper transverse separation of ∼110 h−170 kpc. A third absorber, a sub-DLA at zabs= 2.47, is detected towards SDSS 1116+4118 B, but no corresponding high column density absorber is present towards SDSS 1116+4118 A. We use high-resolution galaxy simulations and a clustering analysis to interpret the coincident absorption and its implications for galaxy structure at z∼ 3. We conclude that the common absorption in the two lines of sight is unlikely to arise from a single galaxy, or a galaxy plus satellite system, and is more feasibly explained by a group of two or more galaxies with separations ∼100 kpc. The impact of these findings on single line-of-sight observations is also discussed; we show that abundances of DLAs may be affected by up to a few tenths of a dex by line-of-sight DLA blending. From a Keck Echellette Spectrograph and Imager spectrum of the two quasars, we measure metal column densities for all five absorbers and determine abundances for the three absorbers with log N(H i) > 20. For the two highest N(H i) absorbers, we determine high levels of metal enrichment, corresponding to 1/3 and 1/5 Z⊙. These metallicities are amongst the highest measured for DLAs at any redshift and are consistent with values measured in Lyman-break galaxies at 2 < z < 3. For the DLA at zabs= 2.94 we also infer an approximately solar ratio of α-to-Fe peak elements from [S/Zn]=+0.05, and measure an upper limit for the molecular fraction in this particular line of sight of log f (H 2) < −5.5.
ISSN:	0035-8711 1365-2966