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The neutral hydrogen cosmological mass density at z = 5.

Crighton, N.H.M. and Murphy, M.T. and Prochaska, J.X. and Worseck, G. and Rafelski, M. and Becker, G.D. and Ellison, S.L. and Fumagalli, M. and Lopez, S. and Meiksin, A. and O'Meara, J.M. (2015) 'The neutral hydrogen cosmological mass density at z = 5.', Monthly notices of the Royal Astronomical Society., 452 (1). pp. 217-234.


We present the largest homogeneous survey of z > 4.4 damped Lyα systems (DLAs) using the spectra of 163 QSOs that comprise the Giant Gemini GMOS (GGG) survey. With this survey we make the most precise high-redshift measurement of the cosmological mass density of neutral hydrogen, ΩHi. At such high redshift, important systematic uncertainties in the identification of DLAs are produced by strong intergalactic medium absorption and QSO continuum placement. These can cause spurious DLA detections, result in real DLAs being missed or bias the inferred DLA column density distribution. We correct for these effects using a combination of mock and higher resolution spectra, and show that for the GGG DLA sample the uncertainties introduced are smaller than the statistical errors on ΩHi. We find ΩHI=0.98+0.20−0.18×10−3 at 〈z〉 = 4.9, assuming a 20 per cent contribution from lower column density systems below the DLA threshold. By comparing to literature measurements at lower redshifts, we show that ΩHi can be described by the functional form ΩHI(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 phase fuelling star formation, which is continually replenished by more highly ionized gas from the intergalactic medium and from recycled galactic winds.

Item Type:Article
Keywords:Quasars: absorption lines, Cosmological parameters.
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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:21 May 2015
Date deposited:20 August 2015
Date of first online publication:September 2015
Date first made open access:No date available

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