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High-redshift Metals. II. Probing Reionization Galaxies with Low-ionization Absorption Lines at Redshift Six

Becker, George D. and Sargent, Wallace L. W. and Rauch, Michael and Calverley, Alexander P. (2011) High-redshift Metals. II. Probing Reionization Galaxies with Low-ionization Absorption Lines at Redshift Six. Astrophysical Journal, 735 (2). Art. No. 93. ISSN 0004-637X.

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We present a survey for low-ionization metal absorption line systems toward 17 QSOs at redshifts z_(em) = 5.8-6.4. Nine of our objects were observed at high resolution with either Keck/HIRES or Magellan/MIKE, and the remainder at moderate resolution with Keck/ESI. The survey spans 5.3 < z _(abs) < 6.4 and has a path length interval ΔX = 39.5 or Δz = 8.0. In total we detect ten systems, five of which are new discoveries. The line-of-sight number density, ℓ(X) = 0.25^(+0.21)_(– 0.13) (95% confidence), is consistent with the combined number density at z ~ 3 of damped Lyα systems (DLAs) and sub-DLAs, which comprise the main population of low-ionization systems at lower redshifts. This apparent lack of evolution may occur because low-ionization systems are hosted by lower-mass halos at higher redshifts, or because the mean cross section of low-ionization gas at a given halo mass increases with redshift due to the higher densities and lower ionizing background. The roughly constant number density notably contrasts with the sharp decline at z > 5.3 in the number density of highly ionized systems traced by C IV. The low-ionization systems at z ~ 6 span a similar range of velocity widths as lower-redshift sub-DLAs but have significantly weaker lines at a given width. This may imply that the mass-metallicity relation of the host galaxies evolves toward lower metallicities at higher redshifts. These systems lack strong Si IV and C IV, which are common among lower-redshift DLAs and sub-DLAs. This is consistent, however, with a similar decrease in the metallicity of the low- and high-ionization phases, and does not necessarily indicate a lack of nearby, highly ionized gas. The high number density of low-ionization systems at z ~ 6 suggests that we may be detecting galaxies below the current limits of i-dropout and Lyα emission galaxy surveys. These systems may therefore be the first direct probes of the "typical" galaxies responsible for hydrogen reionization.

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Additional Information:© 2011 The American Astronomical Society. Received 2011 January 24; accepted 2011 April 26; published 2011 June 21. The observations were made 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 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. We thank Bob Carswell, Andrew Fox, Max Pettini, and Andrew Pontzen for many useful discussions during the course of this work, and the anonymous referee for their helpful comments. We also 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. A.C. has been supported by the UK Science and Technology Facilities Council.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Kavli FoundationUNSPECIFIED
Science and Technology Facilities Council (UK)UNSPECIFIED
Subject Keywords:cosmology: observations; early universe; intergalactic medium; quasars: absorption lines
Issue or Number:2
Classification Code:PACS: 98.54.Aj; 98.62.Gq; 98.62.Py; 98.62Ra; 98.62.Bj
Record Number:CaltechAUTHORS:20110712-102317606
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Official Citation:High-redshift Metals. II. Probing Reionization Galaxies with Low-ionization Absorption Lines at Redshift Six George D. Becker, Wallace L. W. Sargent, Michael Rauch and Alexander P. Calverley doi: 10.1088/0004-637X/735/2/93
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24375
Deposited By: Ruth Sustaita
Deposited On:12 Jul 2011 17:54
Last Modified:03 Oct 2019 02:55

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