Volume 565, May 2014
|Number of page(s)||6|
|Published online||16 May 2014|
Gas reservoir of a hyper-luminous quasar at z = 2.6⋆
IRAM – Institut de RadioAstronomie Millimétrique,
300 rue de la Piscine,
Saint Martin d’Hères
2 INAF – Osservatorio astronomico di Roma, via Frascati 33 00040 Monteporzio Catone, Italy
3 University of Bologna, Department of Physics and Astronomy, viale Berti Pichat 6/2, 40127 Bologna, Italy
4 Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching bei München, Germany
5 INAF – Osservatorio Astronomico di Bologna, via Ranzani 1 40127 Bologna, Italy
6 Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, Orme des Merisiers France, 91191 Gif-sur-Yvette Cedex, France
7 Departamento de Ciencias Fisicas, Universidad Andres Bello, Av. Republica 252, Santiago, Chile
8 Cavendish Laboratory, University of Cambridge 19 J. J. Thomson Avenue, Cambridge CB3 0HE, UK
9 Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
10 Astronomy Centre, Dept. of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9QH, UK
Received: 27 February 2014
Accepted: 18 March 2014
Context. Understanding the relationship between the formation and evolution of galaxies and their central super-massive black holes (SMBH) is one of the main topics in extragalactic astrophysics. Links and feedback may reciprocally affect both black hole and galaxy growth.
Aims. Observations of the CO line at the main epoch of galaxy and SMBH assembly (z = 2−4) are crucial to investigating the gas mass, star formation, and accretion onto SMBHs, and the effect of AGN feedback. Potential correlations between AGN and host galaxy properties can be highlighted by observing extreme objects.
Methods. We targeted CO(3–2) in ULAS J1539+0557, a hyper-luminous quasar (Lbol > 1048 erg/s) at z = 2.658, selected through its unusual red colour in the UKIDSS Large Area Survey (ULAS).
Results. We find a molecular gas mass of 4.1 ± 0.8 × 1010 M⊙, by adopting a conversion factor α = 0.8 M⊙ K-1 km s-1 pc2, and a gas fraction of ~0.4−0.1, depending mostly on the assumed source inclination. We also find a robust lower limit to the star-formation rate (SFR = 250−1600 M⊙/yr) and star-formation efficiency (SFE = 25−350 L⊙/(K km s-1 pc2) by comparing the observed optical-near-infrared spectral energy distribution with AGN and galaxy templates. The black hole gas consumption timescale, M(H2) /Ṁacc, is ~160 Myr, similar to or higher than the gas consumption timescale.
Conclusions. The gas content and the star formation efficiency are similar to those of other high-luminosity, highly obscured quasars, and at the lower end of the star-formation efficiency of unobscured quasars, in line with predictions from AGN-galaxy co-evolutionary scenarios. Further measurements of the (sub)mm continuum in this and similar sources are mandatory to obtain a robust observational picture of the AGN evolutionary sequence.
Key words: galaxies: evolution / galaxies: active / quasars: general / quasars: emission lines
© ESO, 2014
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