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Issue A&A
Volume 472, Number 2, September III 2007
Page(s) L33 - L37
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20078136



A&A 472, L33-L37 (2007)
DOI: 10.1051/0004-6361:20078136

Letter

Molecular gas in QSO host galaxies at z > 5

R. Maiolino1, R. Neri2, A. Beelen3, F. Bertoldi4, C. L. Carilli5, P. Caselli6, 7, P. Cox2, K. M. Menten8, T. Nagao6, 9, A. Omont10, C. M. Walmsley6, F. Walter11, and A. Weiß8

1  INAF - Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
    e-mail: maiolino@oa-roma.inaf.it
2  IRAM, 300 rue de la Piscine, 38406 St.-Martin-d'Hères, France
3  Institut d'Astrophysique Spatiale, Université Paris-Sud, 91405 Orsay, France
4  Argelander-Institut für Astronomie, University of Bonn, Auf dem Hugel 71, 53121 Bonn, Germany
5  National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
6  INAF - Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, 50125 Firenze, Italy
7  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
8  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
9  National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
10  Institut d'Astrophysique de Paris, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
11  Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

(Received 22 June 2007 / Accepted 17 July 2007)

Abstract
We present observations with the IRAM Plateau de Bure Interferometer of three QSOs at z>5 aimed at detecting molecular gas in their host galaxies as traced by CO transitions. CO (5-4) is detected in SDSS J033829.31+002156.3 at z=5.0267, placing it amongst the most distant sources detected in CO. The CO emission is unresolved with a beam size of ~1'', implying that the molecular gas is contained within a compact region, less than ~3 kpc in radius. We infer an upper limit on the dynamical mass of the CO emitting region of ~ $3\times 10^{10}~M_{\odot}/\!\sin(i)^2$. The comparison with the Black Hole mass inferred from near-IR data suggests that the BH-to-bulge mass ratio in this galaxy is significantly higher than in local galaxies. From the CO luminosity we infer a mass reservoir of molecular gas as high as $M\rm (H_2)=2.2\times 10^{10}$ $M_{\odot}$, implying that the molecular gas accounts for a significant fraction of the dynamical mass. When compared to the star formation rate derived from the far-IR luminosity, we infer a very short gas exhaustion timescale (~107 years), comparable to the dynamical timescale. CO is not detected in the other two QSOs ( SDSS J083643.85+005453.3 and SDSS J163033.90+401209.6 ) and upper limits are given for their molecular gas content. When combined with CO observations of other type 1 AGNs, spanning a wide redshift range (0< z <6.4), we find that the host galaxy CO luminosity (hence molecular gas content) and the AGN optical luminosity (hence BH accretion rate) are correlated, but the relation is not linear: $L'_{\rm CO}\propto [\lambda L_{\lambda}(4400~\AA)]^{0.72}$. Moreover, at high redshifts (and especially at z>5) the CO luminosity appears to saturate. We discuss the implications of these findings in terms of black hole-galaxy co-evolution.


Key words: galaxies: high-redshift -- galaxies: ISM -- galaxies: quasars: general -- infrared: galaxies -- submillimeter



© ESO 2007


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