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Cosmic evolution of the atomic and molecular gas contents of galaxies.

Lagos, C.D.P. and Baugh, C.M. and Lacey, C.G. and Benson, A.J. and Kim, H.-S. and Power, C. (2011) 'Cosmic evolution of the atomic and molecular gas contents of galaxies.', Monthly notices of the Royal Astronomical Society., 418 (3). pp. 1649-1667.


We study the evolution of the cold gas content of galaxies by splitting the interstellar medium into its atomic and molecular hydrogen components, using the galaxy formation model GALFORM in the Λ cold dark matter framework. We calculate the molecular-to-atomic hydrogen mass ratio, H2/H I, in each galaxy using two different approaches, the pressure-based empirical relation of Blitz & Rosolowsky and the theoretical model of Krumholz, McKeee & Tumlinson, and apply them to consistently calculate the star formation rates of galaxies. We find that the model based on the Blitz & Rosolowsky law predicts an H I mass function, 12CO (1–0) luminosity function, correlations between H2/H I and stellar and cold gas mass, and infrared–12CO molecule luminosity relation in good agreement with local and high-redshift observations. The H I mass function evolves weakly with redshift, with the number density of high-mass galaxies decreasing with increasing redshift. In the case of the H2 mass function, the number density of massive galaxies increases strongly from z= 0 to 2, followed by weak evolution up to z= 4. We also find that H2/H I of galaxies is strongly dependent on stellar and cold gas mass, and also on redshift. The slopes of the correlations between H2/H I and stellar and cold gas mass hardly evolve, but the normalization increases by up to two orders of magnitude from z= 0 to 8. The strong evolution in the H2 mass function and H2/H I is primarily due to the evolution in the sizes of galaxies and, secondarily, in the gas fractions. The predicted cosmic density evolution of H I agrees with the observed evolution inferred from damped Lyα systems, and is always dominated by the H I content of low- and intermediate-mass haloes. We find that previous theoretical studies have largely overestimated the redshift evolution of the global H2/H I due to limited resolution. We predict a maximum of Graphic at z≈ 3.5.

Item Type:Article
Keywords:Stars: formation, Galaxies: evolution, Galaxies: formation, Galaxies: ISM.
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:01 December 2014
Date of first online publication:December 2011
Date first made open access:No date available

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