A newly discovered DLA and associated Lyα emission in the spectra of the gravitationally lensed quasar UM 673A,B
Abstract
The sightline to the brighter member of the gravitationally lensed quasar pair UM 673A,B intersects a damped Lyα system (DLA) at z = 1.62650 which, because of its low redshift, has not been recognized before. Our high-quality echelle spectra of the pair, obtained with HIRES on the Keck I telescope, show a drop in neutral hydrogen column density N(H i) by a factor of at least 400 between UM 673A and UM 673B, indicating that the DLA's extent in this direction is much less than the 2.7 h^(−1)_(70) kpc separation between the two sightlines at z = 1.62650. By re-assessing this new case together with published data on other quasar pairs, we conclude that the typical size (radius) of DLAs at these redshifts is R ≃ (5 ± 3) h^(−1)_(70) kpc, smaller than previously realized. Highly ionized gas associated with the DLA is more extended, as we find only small differences in the C iv absorption profiles between the two sightlines. Coincident with UM 673B, we detect a weak and narrow Lyα emission line which we attribute to star formation activity at a rate SFR ≳ 0.2 M_⊙ yr^(−1). The DLA in UM 673A is metal poor, with an overall metallicity Z_(DLA) ≃ 1/30 Z_⊙, and has a very low internal velocity dispersion. It exhibits some apparent peculiarities in its detailed chemical composition, with the elements Ti, Ni and Zn being deficient relative to Fe by factors of 2–3. The [Zn/Fe] ratio is lower than those measured in any other DLA or Galactic halo star, presumably reflecting somewhat unusual previous enrichment by stellar nucleosynthesis. We discuss the implications of these results for the nature of the galaxy hosting the DLA.
Additional Information
© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 July 7; Received 2010 July 6; in original form 2010 February 10. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. We are grateful to the staff astronomers at the Keck Observatory for their assistance with the observations. It is a pleasure to acknowledge advice and help with various aspects of the work described in this paper by George Becker, Sebastiano Cantalupo, Bob Carswell, Martin Haehnelt, Paul Hewett, Geraint Lewis, Eric Monier and Sam Rix. We thank the Hawaiian people for the opportunity to observe from Mauna Kea; without their hospitality, this work would not have been possible. RC is jointly funded by the Cambridge Overseas Trust and the Cambridge Commonwealth/Australia Trust with an Allen Cambridge Australia Trust Scholarship. CCS's research is partly supported by grants AST-0606912 and AST-0908805 from the US National Science Foundation. MP would like the express his gratitude to the members of the International Centre for Radio Astronomy Research at the University of Western Australia for their generous hospitality during the progress of this work.Attached Files
Published - Cooke2010p12126Mon_Not_R_Astron_Soc.pdf
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Additional details
- Eprint ID
- 21542
- Resolver ID
- CaltechAUTHORS:20110103-110312343
- Cambridge Overseas Trust
- Cambridge Commonwealth/Australia Trust
- AST-0606912
- NSF
- AST-0908805
- NSF
- W. M. Keck Foundation
- Created
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2011-01-04Created from EPrint's datestamp field
- Updated
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2021-11-09Created from EPrint's last_modified field