The evolutionary connection between QSOs and SMGs: molecular gas in far-infrared luminous QSOs at z ~ 2.5

J.M. Simpson, Ian Smail, A. M. Swinbank, D. M. Alexander, R. Auld, M. Baes, D.G. Bonfield, D. L. Clements, A. Cooray, Kristen Coppin, A. L. R. Danielson, A. Dariush, L. Dunne, G. de Zotti, C. M. Harrison, R. Hopwood, C. Hoyos, E. Ibar, R. J. Ivison, M.J. JarvisA. Lapi, S. J. Maddox, M. J. Page, D. A. Riechers, E. Valiante, P. van der Werf

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We present IRAM Plateau de Bure Interferometer observations of the 12CO(3-2) emission from two far-infrared luminous QSOs at z ~ 2.5 selected from the Herschel-ATLAS survey. These far-infrared bright QSOs were selected to have supermassive black holes (SMBHs) with masses similar to those thought to reside in sub-millimetre galaxies (SMGs) at z ~ 2.5; making them ideal candidates as systems in transition from an ultraluminous infrared galaxy phase to a sub-mm faint, unobscured, QSO. We detect 12CO(3-2) emission from both QSOs and we compare their baryonic, dynamical and SMBH masses to those of SMGs at the same epoch. We find that these far-infrared bright QSOs have similar dynamical but lower gas masses than SMGs. In particular we find that far-infrared bright QSOs have ~50+-23% less warm/dense gas than SMGs, which combined with previous results showing the QSOs lack the extended, cool reservoir of gas seen in SMGs, suggests that they are at a different evolutionary stage. This is consistent with the hypothesis that far-infrared bright QSOs represent a short (~1Myr) but ubiquitous phase in the transformation of dust obscured, gas-rich, starburst-dominated SMGs into unobscured, gas-poor, QSOs.
Original languageEnglish
Pages (from-to)3201-10
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2012


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