Journal Article

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, K. E. K. 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. Jarvis, A. Lapi, S. J. Maddox, M. J. Page, D. A. Riechers, E. Valiante and P. P. van der Werf

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 426, issue 4, pages 3201-3210
Published in print November 2012 | ISSN: 0035-8711
Published online November 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21941.x
The evolutionary connection between QSOs and SMGs: molecular gas in far-infrared luminous QSOs at z ∼ 2.5

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Abstract

We present Institut de Radioastronomie Millimétrique 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-Astrophysical Tetrahertz Large Area Survey. These far-infrared bright QSOs were selected to have supermassive black holes (SMBHs) with masses similar to those thought to reside in submillimetre galaxies (SMGs) at z ∼ 2.5, making them ideal candidates as systems in the potential transition from an ultraluminous infrared galaxy phase to a submillimetre 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. We combine our results with literature values and find that at a fixed LFIR, far-infrared bright QSOs have ∼50 ± 30 per cent less warm/dense gas than SMGs. Taken together with previous results, which show that QSOs lack the extended, cool reservoir of gas seen in SMGs, this suggests that far-infrared bright QSOs are at a different evolutionary stage. This is consistent with the hypothesis that far-infrared bright QSOs represent a short (∼1 Myr) but ubiquitous phase in the transformation of dust-obscured, gas-rich, starburst-dominated SMGs into unobscured, gas-poor, QSOs.

Keywords: galaxies: evolution; galaxies: formation; quasars: emission lines; quasars: individual: J0908−0034; quasars: individual: J0911+0027

Journal Article.  8017 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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