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Dissecting the properties of optically thick hydrogen at the peak of cosmic star formation history.

Fumagalli, M. and O'Meara, J.M. and Prochaska, J.X. and Worseck, G. (2013) 'Dissecting the properties of optically thick hydrogen at the peak of cosmic star formation history.', Astrophysical journal., 775 (1). p. 78.

Abstract

We present the results of a blind survey of Lyman limit systems (LLSs) detected in absorption against 105 quasars at z ~ 3 using the blue sensitive MagE spectrograph at the Magellan Clay telescope. By searching for Lyman limit absorption in the wavelength range λ ~ 3000-4000 Å, we measure the number of LLSs per unit redshift ℓ(z) = 1.21 ± 0.28 at z ~ 2.8. Using a stacking analysis, we further estimate the mean free path of ionizing photons in the z ~ 3 universe $\lambda ^{912}_{\rm mfp} = 100 \pm 29 \ h_{70.4}^{-1}\ {\rm Mpc}$. Combined with our LLS survey, we conclude that systems with log N H I ≥ 17.5 cm–2 contribute only ~40% to the observed mean free path at these redshifts. Furthermore, with the aid of photoionization modeling, we infer that a population of ionized and metal poor systems is likely required to reproduce the metal line strengths observed in a composite spectrum of 20 LLSs with log N H I ~ 17.5-19 cm–2 at z ~ 2.6-3.0. Finally, with a simple toy model, we deduce that gas in the halos of galaxies can alone account for the totality of LLSs at z lsim 3, but a progressively higher contribution from the intergalactic medium is required beyond z ~ 3.5. We also show how the weakly evolving number of LLSs per unit redshift at z lsim 3 can be modeled either by requiring that the spatial extent of the circumgalactic medium is redshift invariant in the last ~10 Gyr of cosmic evolution or by postulating that LLSs arise in halos that are rare fluctuations in the density field at each redshift.

Item Type:Article
Keywords:Cosmology: observations, Galaxies: halos, Galaxies: high-redshift, Intergalactic medium, Quasars: absorption lines.
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1088/0004-637X/775/1/78
Publisher statement:© 2013. The American Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:30 June 2014
Date of first online publication:September 2013
Date first made open access:No date available

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