Letter to the Editor

Herschel ATLAS: The cosmic star formation history of quasar host galaxies^*

¹ Dept. of Physics and Astronomy, The Open University, Milton Keynes, MK7 6AA, UK
² Argelander Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, Room 1.22, 53121 Bonn
³ Caltech, MS247-19, 1200 East California Blvd., Pasadena, CA 91125, USA
⁴ Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
⁵ Dept. of Physics & Astronomy, University of California, Irvine, CA 92697, USA
⁶ Scuola Internazionale Superiore di Studi Avanzati, via Beirut 2-4, 34151 Trieste, Italy
⁷ UK Astronomy Technology Center, Royal Observatory Edinburgh, Edinburgh, EH9 3HJ, UK
⁸ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
⁹ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
¹⁰ Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Herts AL10 9AB, UK
¹¹ European Southern Observatory, Karl-Schwarzschild-Str., 85748 Garching b. Muenchen, Germany
¹² Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Luis Enrique Erro No.1, Tonantzintla, Puebla, C.P. 72840, Mexico
¹³ Astronomy Program, Department of Physics and Astronomy, Seoul National University, Shillim Dong, Kwan-ak Gu 151-742, Seoul, Korea
¹⁴ Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ, UK
¹⁵ Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
¹⁶ University College London, Department of Space & Climate Physics, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
¹⁷ Space Science & Technology Dept., CCLRC Rutherford Appleton Laboratory, Oxfordshire, OX11 0QX, UK
¹⁸ Institute for Space Imaging Science, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
¹⁹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
²⁰ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
²¹ Laboratoire d'Astrophysique de Marseille, UMR6110 CNRS, 38 rue F. Joliot-Curie, 13388 Marseille, France
²² INAF - Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
²³ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38200 La Laguna, Spain
²⁴ National Radio Astronomy Observatory, PO Box 2, Green Bank, WV 24944, USA
²⁵ Instituto de Física de Cantabria (CSIC-UC), Santander 39005, Spain
²⁶ Institut d'Astrophysique Spatiale (IAS), Bâtiment 121, 91405 Orsay, France; and Université Paris-Sud 11 and CNRS (UMR 8617), France
²⁷ Astrophysics Branch, NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035, USA
²⁸ University of Padova, Department of Astronomy, Vicolo Osservatorio 3, 35122 Padova, Italy
²⁹ Herschel Science Centre, ESAC, ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
³⁰ Oxford Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford, OX1 3RH

Received: 30 March 2010
Accepted: 7 May 2010

Abstract

We present a derivation of the star formation rate per comoving volume of quasar host galaxies, derived from stacking analyses of far-infrared to mm-wave photometry of quasars with redshifts 0 < z < 6 and absolute I-band magnitudes -22 > I_AB > -32 We use the science demonstration observations of the first ~16 deg² from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) in which there are 240 quasars from the Sloan Digital Sky Survey (SDSS) and a further 171 from the 2dF-SDSS LRG and QSO (2SLAQ) survey. We supplement this data with a compilation of data from IRAS, ISO, Spitzer, SCUBA and MAMBO. H-ATLAS alone statistically detects the quasars in its survey area at >5σ at 250,350 and 500 μm. From the compilation as a whole we find striking evidence of downsizing in quasar host galaxy formation: low-luminosity quasars with absolute magnitudes in the range -22 > I_AB > -24 have a comoving star formation rate (derived from 100 μm rest-frame luminosities) peaking between redshifts of 1 and 2, while high-luminosity quasars with I_AB < -26 have a maximum contribution to the star formation density at z ~ 3. The volume-averaged star formation rate of -22 > I_AB > -24 quasars evolves as (1 + z)^2.3±0.7 at z < 2, but the evolution at higher luminosities is much faster reaching (1 + z)^10±1 at -26 > I_AB > -28. We tentatively interpret this as a combination of a declining major merger rate with time and gas consumption reducing fuel for both black hole accretion and star formation.