Letter to the Editor

Mapping the interstellar medium in galaxies with Herschel/SPIRE^*

¹ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK e-mail: Steve.Eales@astro.cf.ac.uk
² Dept. of Physics & Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada
³ Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
⁴ Laboratoire d'Astrophysique de Marseille, UMR6110 CNRS, 38 rue F. Joliot-Curie, 13388 Marseille France
⁵ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
⁶ Dept. of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁷ Jet Propulsion Laboratory, Pasadena, CA 91109, California Institute of Technology, Pasadena, CA 91125, USA
⁸ Instituto de Astrofísica de Canarias (IAC) and Departmento de Astrofísica, Universidad de la Laguna (ULL), La Laguna, Tenerife, Spain
⁹ CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, 91191 Gif-sur-Yvette, France
¹⁰ Institut d'Astrophysique de Paris, UMR7095 CNRS, 98bis boulevard Arago, 75014 Paris, France
¹¹ Dept. of Physics & Astronomy, University of California, Irvine, CA 92697, USA
¹² Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center Greenbelt, MD 20771, USA
¹³ Department of Astrophysical and Planetary Sciences, CASA CB-389, University of Colorado, Boulder, CO 80309, US

¹⁴ ESA Astrophysics Missions Division, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands
¹⁵ Astronomy Centre, Department of Physics and Astronomy, University of Sussex, UK
¹⁶ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
¹⁷ School of Physics & Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
¹⁸ Istituto di Fisica dello Spazio Interplanetario, INAF, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁹ Infrared Processing and Analysis Center, California Institute of Technology, 770 South Wilson Av, Pasadena, CA 91125, USA
²⁰ Centre for Astrophysics Research, Science and Technology Research Centre, University of Hertfordshire, Herts AL10 9AB, UK
²¹ University of Padova, Department of Astronomy, Vicolo Osservatorio 3, 35122 Padova, Italy
²² Observatoire Astronomique de Strasbourg, UMR 7550 Université de Strasbourg - CNRS, 11 rue de l'Université, 67000 Strasbourg, France
²³ UK Astronomy Technology Center, Royal Observatory Edinburgh, Edinburgh EH9 3HJ, UK
²⁴ Institut für Astronomie, Universitt Wien, Trkenschanzstr. 17, 1180 Wien, Austria

Received: 29 March 2010
Accepted: 19 April 2010

Abstract

The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies M 99 and M 100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies using both methods. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies.