Letter to the Editor

FIR colours and SEDs of nearby galaxies observed with Herschel^*

¹ Laboratoire d'Astrophysique de Marseille, UMR6110 CNRS, 38 rue F. Joliot-Curie, 13388 Marseille, France e-mail: Alessandro.Boselli@oamp.fr
² School of Physics and Astronomy, Cardiff University, Queens Buildings The Parade, Cardiff CF24 3AA, UK
³ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
⁴ Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
⁵ INAF - Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁶ Jet Propulsion Laboratory, Pasadena, CA 91109, USA; Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
⁷ Astronomical Institute, Ruhr-University Bochum, Universitaetsstr. 150, 44780 Bochum, Germany
⁸ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38200 La Laguna, Spain
⁹ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
¹⁰ INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
¹¹ Department of Physics & Astronomy, University of California, Irvine, CA 92697, USA
¹² Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, Irfu/Service d'Astrophysique, 91191 Gif-sur-Yvette, France
¹³ Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center Greenbelt, MD 20771, USA
¹⁴ NASA Herschel Science Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
¹⁵ ESO, Alonso de Cordova 3107, Vitacura, Santiago, Chile
¹⁶ Universita' di Milano-Bicocca, piazza della Scienza 3, 20100 Milano, Italy
¹⁷ Department of Astrophysical and Planetary Sciences, CASA CB-389, University of Colorado, Boulder, CO 80309, USA
¹⁸ Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
¹⁹ ESA Astrophysics Missions Division, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands
²⁰ Institut d'Astrophysique Spatiale (IAS), Batiment 121, Universite Paris-Sud 11 and CNRS, 91405 Orsay, France
²¹ Astronomy Centre, Department of Physics and Astronomy, University of Sussex, UK
²² Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
²³ Dept. of Physics & Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada
²⁴ Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, Postfach 1312, 85741 Garching, Germany
²⁵ School of Physics & Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
²⁶ INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, via Fosso del Cavaliere 100, 00133 Roma, Italy
²⁷ Infrared Processing and Analysis Center, California Institute of Technology, Mail Code 100-22, 770 South Wilson Av, Pasadena, CA 91125, USA
²⁸ Centre for Astrophysics Research, Science and Technology Research Centre, University of Hertfordshire, College Lane, Herts AL10 9AB, UK
²⁹ University of Padova, Department of Astronomy, Vicolo Osservatorio 3, 35122 Padova, Italy
³⁰ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³¹ Observatoire Astronomique de Strasbourg, UMR 7550 Université de Strasbourg – CNRS, 11 rue de l'Université, 67000 Strasbourg, France
³² Institute of Astronomy and Astrophysics, National Observatory of Athens, I. Metaxa and Vas. Pavlou, P. Penteli, 15236 Athens, Greece
³³ Institut für Astronomie, Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria
³⁴ Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany

Received: 29 March 2010
Accepted: 9 April 2010

Abstract

We present infrared colours (in the 25–500 μm spectral range) and UV to radio continuum spectral energy distributions of a sample of 51 nearby galaxies observed with SPIRE on Herschel. The observed sample includes all morphological classes, from quiescent ellipticals to active starbursts. Active galaxies have warmer colour temperatures than normal spirals. In ellipticals hosting a radio galaxy, the far-infrared (FIR) emission is dominated by the synchrotron nuclear emission. The colour temperature of the cold dust is higher in quiescent E-S0a than in star-forming systems probably because of the different nature of their dust heating sources (evolved stellar populations, X-ray, fast electrons) and dust grain properties. In contrast to the colour temperature of the warm dust, the f350/f500 index sensitive to the cold dust decreases with star formation and increases with metallicity, suggesting an overabundance of cold dust or an emissivity parameter β < 2 in low metallicity, active systems.