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The neutral hydrogen cosmological mass density at z = 5

Research output: Contribution to journalArticle

  • Neil H. M. Crighton
  • Michael T. Murphy
  • J. Xavier Prochaska
  • Gábor Worseck
  • Marc Rafelski
  • George D. Becker
  • Sara L. Ellison
  • Michele Fumagalli
  • Sebastian Lopez
  • Avery Meiksin
  • John M. O'Meara

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Original languageEnglish
Pages (from-to)217-234
JournalMonthly Notices of the Royal Astronomical Society
Publication statusPublished - 1 Sep 2015


We present the largest homogeneous survey of z > 4.4 damped Lyαsystems (DLAs) using the spectra of 163 QSOs that comprise the GiantGemini GMOS (GGG) survey. With this survey we make the most precisehigh-redshift measurement of the cosmological mass density of neutralhydrogen, Ω_{H I}. At such high redshift, important systematicuncertainties in the identification of DLAs are produced by strongintergalactic medium absorption and QSO continuum placement. These cancause spurious DLA detections, result in real DLAs being missed or biasthe inferred DLA column density distribution. We correct for theseeffects using a combination of mock and higher resolution spectra, andshow that for the GGG DLA sample the uncertainties introduced aresmaller than the statistical errors on Ω_{H I}. We find Ω_{H I}=0.98^{+0.20}_{-0.18}× 10^{-3} at = 4.9, assuminga 20 per cent contribution from lower column density systems below theDLA threshold. By comparing to literature measurements at lowerredshifts, we show that Ω_{H I} can be described by the functionalform Ω _{H I}(z)∝ (1+z)^{0.4}. This gradual decrease from z =5 to 0 is consistent with the bulk of H I gas being a transitory phasefuelling star formation, which is continually replenished by more highlyionized gas from the intergalactic medium and from recycled galacticwinds.

    Research areas

  • quasars: absorption lines, cosmological parameters

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