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Title: THE RAPID DECLINE IN METALLICITY OF DAMPED Lyα SYSTEMS AT z ∼ 5

We present evidence that the cosmological mean metallicity of neutral atomic hydrogen gas shows a sudden decrease at z > 4.7 down to 〈Z〉=−2.03{sub −0.11}{sup +0.09}, which is 6σ deviant from that predicted by a linear fit to the data at lower redshifts. This measurement is made possible by the chemical abundance measurements of eight new damped Lyα (DLA) systems at z > 4.7 observed with the Echellette Spectrograph and Imager on the Keck II Telescope, doubling the number of measurements at z > 4.7 to 16. Possible explanations for this sudden decrease in metallicity include a change in the physical processes that enrich the neutral gas within disks, or an increase of the covering factor of neutral gas outside disks due to a lower ultraviolet radiation field and higher density at high redshift. The later possibility would result in a new population of presumably lower metallicity DLAs, with an increased contribution to the DLA population at higher redshifts resulting in a reduced mean metallicity. Furthermore, we provide evidence of a possible decrease at z > 4.7 in the comoving metal mass density of DLAs, ρ{sub metals}(z){sub DLA}, which is flat out to z ∼ 4.3. Such a decrease ismore » expected, as otherwise most of the metals from star-forming galaxies would reside in DLAs by z ∼ 6. While the metallicity is decreasing at high redshift, the contribution of DLAs to the total metal budget of the universe increases with redshift, with DLAs at z ∼ 4.3 accounting for ∼20% as many metals as produced by Lyman break galaxies.« less
Authors:
 [1] ; ;  [2] ;  [3] ;  [4]
  1. Infrared Processing and Analysis Center, Caltech, Pasadena, CA 91125 (United States)
  2. Department of Physics and Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093 (United States)
  3. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
  4. Department of Astronomy and Astrophysics, UCO/Lick Observatory, 1156 High Street, University of California, Santa Cruz, CA 95064 (United States)
Publication Date:
OSTI Identifier:
22363974
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 782; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; DENSITY; GALAXIES; HYDROGEN; METALLICITY; METALS; QUASARS; RED SHIFT; STAR EVOLUTION; STARS; TELESCOPES; ULTRAVIOLET RADIATION; UNIVERSE