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Published January 10, 2012 | Published
Journal Article Open

Iron and α-element Production in the First One Billion Years After the Big Bang

Abstract

We present measurements of carbon, oxygen, silicon, and iron in quasar absorption systems existing when the universe was roughly one billion years old. We measure column densities in nine low-ionization systems at 4.7 < z < 6.3 using Keck, Magellan, and Very Large Telescope optical and near-infrared spectra with moderate to high resolution. The column density ratios among C II, O I, Si II, and Fe II are nearly identical to sub-damped Lyα systems (sub-DLAs) and metal-poor ([M/H] ≤ –1) DLAs at lower redshifts, with no significant evolution over 2 ≾ z ≾ 6. The estimated intrinsic scatter in the ratio of any two elements is also small, with a typical rms deviation of ≾ 0.1 dex. These facts suggest that dust depletion and ionization effects are minimal in our z > 4.7 systems, as in the lower-redshift DLAs, and that the column density ratios are close to the intrinsic relative element abundances. The abundances in our z > 4.7 systems are therefore likely to represent the typical integrated yields from stellar populations within the first gigayear of cosmic history. Due to the time limit imposed by the age of the universe at these redshifts, our measurements thus place direct constraints on the metal production of massive stars, including iron yields of prompt supernovae. The lack of redshift evolution further suggests that the metal inventories of most metal-poor absorption systems at z ≳ 2 are also dominated by massive stars, with minimal contributions from delayed Type Ia supernovae or winds from asymptotic giant branch stars. The relative abundances in our systems broadly agree with those in very metal-poor, non-carbon-enhanced Galactic halo stars. This is consistent with the picture in which present-day metal-poor stars were potentially formed as early as one billion years after the big bang.

Additional Information

© 2012 The American Astronomical Society. Received 2011 August 23; accepted 2011 November 19; published 2011 December 19. The observations were made in part at the W. M. Keck Observatory, which is operated as a scientific partnership between the California Institute of Technology and the University of California; it was made possible by the generous support of the W. M. Keck Foundation. This paper includes data gathered with the 6.5m Magellan Telescopes located at Las Campanas Observatory, Chile. Based in part on observations made with the Very Large Telescope, operated by the European Southern Observatory at Paranal Observatory, Chile, under proposal ID 084.A-0574. We thank Ryan Cooke, John Eldridge, John Norris, Max Pettini, and Andrew McWilliam for many helpful discussions throughout the course of this work. We also thank the referee for their helpful comments. We recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. G.B. has been supported by the Kavli Foundation. W.S. received support from the National Science Foundation through grant AST 06-06868. M.R. received support from the National Science Foundation through grant AST 05-06845.

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August 22, 2023
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