Pettini, Max and Zych, Berkeley J. and Steidel, Charles C. and Chaffee, Fred H. (2008) C, N, O abundances in the most metal-poor damped Lyman alpha systems. Monthly Notices of the Royal Astronomical Society, 385 (4). pp. 2011-2024. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20090519-090047352
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This study focuses on some of the most metal-poor damped Lyα (DLA) absorbers known in the spectra of high-redshift QSOs, using new and archival observations obtained with ultraviolet-sensitive echelle spectrographs on the Keck and VLT telescopes. The weakness and simple velocity structure of the absorption lines in these systems allow us to measure the abundances of several elements, and in particular those of C, N and O, a group that is difficult to study in DLAs of more typical metallicities. We find that when the oxygen abundance is less than ∼1/100 of solar, the C/O ratio in high-redshift DLAs and sub-DLAs matches that of halo stars of similar metallicity and shows higher values than expected from galactic chemical evolution models based on conventional stellar yields. Furthermore, there are indications that at these low metallicities the N/O ratio may also be above simple expectations and may exhibit a minimum value, as proposed by Centurión and her collaborators in 2003. Both results can be interpreted as evidence for enhanced production of C and N by massive stars in the first few episodes of star formation, in our Galaxy and in the distant protogalaxies seen as QSO absorbers. The higher stellar yields implied may have an origin in stellar rotation which promotes mixing in the stars' interiors, as considered in some recent model calculations. We briefly discuss the relevance of these results to current ideas on the origin of metals in the intergalactic medium and the universality of the stellar initial mass function.
|Additional Information:||© 2008 The Authors. Journal compilation © 2008 RAS. Accepted 2008 January 10. Received 2008 January 8; in original form 2007 November 29. We are grateful to the Keck and ESO time assignment committees for their support of this programme and to the staff astronomers at the Keck and VLT observatories for their help in conducting the observations. Tom Barlow, Bob Carswell, Thiago Gon¸calves, Michael Murphy and Sam Rix kindly helped with different aspects of the data reduction and analysis. Martin Asplund, Damian Fabbian, Dick Henry, Poul Nissen and an anonymous referee made valuable suggestions which improved the paper. We thank the Hawaiian people for the opportunity to observe from Mauna Kea; without their hospitality, this work would not have been possible. CCS’s research is partly supported by grant AST-0606912 from the US National Science Foundation. Some of this work was carried out during a visit by Fred Chaffee to the Institute of Astronomy, Cambridge, supported by the Institute’s visitor grant.|
|Subject Keywords:||galaxies: abundances; galaxies: evolution; galaxies: ISM; cosmology: observations; quasars: absorption lines|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||24 Aug 2009 17:44|
|Last Modified:||26 Dec 2012 11:01|
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