Letter to the Editor

Herschel and SCUBA-2 imaging and spectroscopy of a bright, lensed submillimetre galaxy at z = 2.3^*

¹ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK e-mail: rji@roe.ac.uk
² Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
³ Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK
⁴ Space Science & Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK
⁵ Institute for Space Imaging Science, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
⁶ Astrophysics, Oxford University, Keble Road, Oxford, OX1 3RH, UK
⁷ Observatoire Astronomique de Marseille-Provence, 2 Pl Le Verrier, 13248, Marseille, Cedex 04, France
⁸ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁹ California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA
¹⁰ Jet Propulsion Laboratory, Pasadena, California 91109-8099, USA
¹¹ Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
¹² Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA

¹³ Observational Cosmology Laboratory, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁴ Dipartimento di Astronomia, Universita' di Padova, vic. Osservatorio, 3, 35122 Padova, Italy
¹⁵ Blue Sky Spectroscopy, Lethbridge, Alberta, Canada
¹⁶ Department of Astrophysical and Planetary Sciences, CASA 389-UCB, University of Colorado, Boulder, CO 80309, USA
¹⁷ Cardiff School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
¹⁸ Astronomy Centre, Department of Physics & Astronomy, University of Sussex, Falmer, East Sussex BN1 9QH, UK
¹⁹ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
²⁰ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
²¹ Departamento de Astrofísica, Universidad de La Laguna (ULL), La Laguna, Tenerife, Spain
²² Department of Engineering, University of Cambridge, Cambridge CB3 0FA, UK
²³ Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
²⁴ European Space Astronomy Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
²⁵ Institut d'Astrophysique de Paris, 98bis, bd Arago – 75014 Paris, France

Received: 30 March 2010
Accepted: 20 April 2010

Abstract

We present a detailed analysis of the far-infrared (-IR) properties of the bright, lensed, z = 2.3, submillimetre-selected galaxy (SMG), SMM J2135-0102 (hereafter SMM J2135), using new observations with Herschel, SCUBA-2 and the Very Large Array (VLA). These data allow us to constrain the galaxy's spectral energy distribution (SED) and show that it has an intrinsic rest-frame 8-1000-μm luminosity, L_bol, of (2.3±0.2) × 10¹²  and a likely star-formation rate (SFR) of ~400  yr^-1. The galaxy sits on the far-IR/radio correlation for far-IR-selected galaxies. At 70 μm, the SED can be described adequately by dust components with dust temperatures, T_d ~ 30 and 60 k. Using SPIRE's Fourier- transform spectrometer (FTS) we report a detection of the [C ii] 158 μm cooling line. If the [C ii], CO and far-IR continuum arise in photo-dissociation regions (PDRs), we derive a characteristic gas density, n ~ 10³ cm^-3, and a far-ultraviolet (-UV) radiation field, G₀, 10³× stronger than the Milky Way. L_[CII]/L_bol is significantly higher than in local ultra-luminous IR galaxies (ULIRGs) but similar to the values found in local star-forming galaxies and starburst nuclei. This is consistent with SMM J2135 being powered by starburst clumps distributed across ~2 kpc, evidence that SMGs are not simply scaled-up ULIRGs. Our results show that SPIRE's FTS has the ability to measure the redshifts of distant, obscured galaxies via the blind detection of atomic cooling lines, but it will not be competitive with ground-based CO-line searches. It will, however, allow detailed study of the integrated properties of high-redshift galaxies, as well as the chemistry of their interstellar medium (ISM), once more suitably bright candidates have been found.