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Towards a unified description of the intergalactic medium at redshift z ≈ 2.5.

Prochaska, J.X. and Madau, P. and O'Meara, J.M. and Fumagalli, M. (2014) 'Towards a unified description of the intergalactic medium at redshift z ≈ 2.5.', Monthly notices of the Royal Astronomical Society., 438 (1). pp. 476-486.


We examine recent measurements of the z ≈ 2.5 intergalactic medium (IGM) which constrain the H I frequency distribution f(NHI) and the mean free path λ912mfp to ionizing radiation. We argue that line-blending and the clustering of strong absorption-line systems have led previous authors to systematically overestimate the effective Lyman limit opacity, yielding too small of a λ912mfp for the IGM. We further show that recently published measurements of f(NHI) at NHI≈1016cm−2 lie in strong disagreement, implying underestimated uncertainty from sample variance and/or systematics like line-saturation. Allowing for a larger uncertainty in the f(NHI) measurements, we provide a new cubic Hermite spline model for f(NHI) which reasonably satisfies all of the observational constraints under the assumption of randomly distributed absorption systems. We caution, however, that this formalism is invalid in the light of absorber clustering and use a toy model to estimate the effects. Future work must properly account for the non-Poissonian nature of the IGM.

Item Type:Article
Keywords:Intergalactic medium.
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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society © 2013 The Authors Published by Oxford University Press on behalf of Royal Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:20 June 2014
Date of first online publication:February 2014
Date first made open access:No date available

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