dc.contributor.author Garratt, T. K. dc.contributor.author Coppin, K. E. K. dc.contributor.author Geach, J. E. dc.contributor.author Almaini, O. dc.contributor.author Hartley, W. G. dc.contributor.author Maltby, D. T. dc.contributor.author Simpson, C. J. dc.contributor.author Wilkinson, A. dc.contributor.author Conselice, C. J. dc.contributor.author Franco, M. dc.contributor.author Ivison, R. J. dc.contributor.author Koprowski, M. P. dc.contributor.author Lovell, C. C. dc.contributor.author Pope, A. dc.contributor.author Scott, D. dc.contributor.author Werf, P. van der dc.date.accessioned 2021-06-03T15:30:01Z dc.date.available 2021-06-03T15:30:01Z dc.date.issued 2021-05-05 dc.identifier.citation Garratt , T K , Coppin , K E K , Geach , J E , Almaini , O , Hartley , W G , Maltby , D T , Simpson , C J , Wilkinson , A , Conselice , C J , Franco , M , Ivison , R J , Koprowski , M P , Lovell , C C , Pope , A , Scott , D & Werf , P V D 2021 , ' Cosmic evolution of the H2 mass density and the epoch of molecular gas ' , The Astrophysical Journal , vol. 912 , no. 1 , 62 . https://doi.org/10.3847/1538-4357/abec81 dc.identifier.issn 0004-637X dc.identifier.other PURE: 24855005 dc.identifier.other PURE UUID: 7663286a-3da5-4280-9af0-1c9c19ab1bcc dc.identifier.other ArXiv: http://arxiv.org/abs/2103.08613v1 dc.identifier.other ORCID: /0000-0002-0729-2988/work/95000538 dc.identifier.other ORCID: /0000-0002-3560-8599/work/95000621 dc.identifier.uri http://hdl.handle.net/2299/24552 dc.description © 2021. The American Astronomical Society. All rights reserved. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.3847/1538-4357/abec81 dc.description.abstract We present new empirical constraints on the evolution of $\rho_{\rm H_2}$, the cosmological mass density of molecular hydrogen, back to $z\approx2.5$. We employ a statistical approach measuring the average observed $850\mu{\rm m}$ flux density of near-infrared selected galaxies as a function of redshift. The redshift range considered corresponds to a span where the $850\mu{\rm m}$ band probes the Rayleigh-Jeans tail of thermal dust emission in the rest-frame, and can therefore be used as an estimate of the mass of the interstellar medium (ISM). Our sample comprises of ${\approx}150,000$ galaxies in the UKIDSS-UDS field with near-infrared magnitudes $K_{\rm AB}\leq25$ mag and photometric redshifts with corresponding probability distribution functions derived from deep 12-band photometry. With a sample approximately 2 orders of magnitude larger than in previous works we significantly reduce statistical uncertainties on $\rho_{\rm H_2}$ to $z\approx2.5$. Our measurements are in broad agreement with recent direct estimates from blank field molecular gas surveys, finding that the epoch of molecular gas coincides with the peak epoch of star formation with $\rho_{\rm H_2}\approx2\times10^7\,{\rm M_\odot}\,{\rm Mpc^{-3}}$ at $z\approx2$. We demonstrate that $\rho_{\rm H_2}$ can be broadly modelled by inverting the star-formation rate density with a fixed or weakly evolving star-formation efficiency. This 'constant efficiency' model shows a similar evolution to our statistically derived $\rho_{\rm H_2}$, indicating that the dominant factor driving the peak star formation history at $z\approx2$ is a larger supply of molecular gas in galaxies rather than a significant evolution of the star-formation rate efficiency within individual galaxies. en dc.format.extent 14 dc.language.iso eng dc.relation.ispartof The Astrophysical Journal dc.rights Open dc.subject astro-ph.GA dc.title Cosmic evolution of the H2 mass density and the epoch of molecular gas en dc.contributor.institution Centre for Astrophysics Research dc.contributor.institution School of Physics, Engineering & Computer Science dc.contributor.institution Centre of Data Innovation Research dc.contributor.institution Centre for Climate Change Research dc.contributor.institution Department of Physics, Astronomy and Mathematics dc.contributor.institution School of Health and Social Work dc.contributor.institution Centre for Research in Public Health and Community Care dc.contributor.institution School of Physics, Astronomy and Mathematics dc.description.status Peer reviewed dc.relation.school School of Physics, Engineering & Computer Science dc.relation.school School of Health and Social Work dc.description.versiontype Final Accepted Version dcterms.dateAccepted 2021-05-05 rioxxterms.version AM rioxxterms.versionofrecord https://doi.org/10.3847/1538-4357/abec81 rioxxterms.licenseref.uri Unspecified rioxxterms.type Journal Article/Review herts.preservation.rarelyaccessed true herts.rights.accesstype Open
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