Journal Article

Cosmic evolution of the atomic and molecular gas contents of galaxies

Claudia del P. Lagos, Carlton M. Baugh, Cedric G. Lacey, Andrew J. Benson, Han-Seek Kim and Chris Power

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 418, issue 3, pages 1649-1667
Published in print December 2011 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19583.x
Cosmic evolution of the atomic and molecular gas contents of galaxies

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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 at z≈ 3.5.

Keywords: stars: formation; galaxies: evolution; galaxies: formation; galaxies: ISM

Journal Article.  15816 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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