Letter to the Editor

Herschel photometric observations of the low metallicity dwarf galaxy NGC 1705

¹ Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK e-mail: b.ohalloran@imperial.ac.uk
² Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, Irfu/Service d'Astrophysique, 91191 Gif-sur-Yvette, France
³ School of Physics and Astronomy, Cardiff University, Queens Buildings The Parade, Cardiff CF24 3AA, UK
⁴ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
⁵ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁶ Jet Propulsion Laboratory, Pasadena, CA 91109, USA; Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
⁷ Laboratoire d'Astrophysique de Marseille, UMR6110 CNRS, 38 rue F. Joliot-Curie, 13388 Marseille, France
⁸ Instituto de Astrofisica de Canarias, C/ vía Láctea, s/n, 38205 – La Laguna (Tenerife), Spain; 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 Department of Physics & Astronomy, University of California, Irvine, CA 92697, USA
¹¹ Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center Greenbelt, MD 20771, USA
¹² Department of Astrophysical and Planetary Sciences, CASA CB-389, University of Colorado, Boulder, CO 80309, USA
¹³ Infrared Processing and Analysis Center, California Institute of Technology, Mail Code 100-22, 770 South Wilson Av, Pasadena, CA 91125, USA
¹⁴ Astronomy Centre, Department of Physics and Astronomy, University of Sussex, UK
¹⁵ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
¹⁶ Dept. of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada
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 Centre for Astrophysics Research, Science and Technology Research Centre, University of Hertfordshire, College Lane, Herts AL10 9AB, UK
²⁰ University of Padova, Department of Astronomy, Vicolo Osservatorio 3, 35122 Padova, Italy
²¹ Observatoire Astronomique de Strasbourg, UMR 7550 Université de Strasbourg – CNRS, 11 rue de l'Université, 67000 Strasbourg, France
²² UK Astronomy Technology Center, Royal Observatory Edinburgh, Edinburgh EH9 3HJ, UK
²³ Institut für Astronomie, Universität Wien, Tärkenschanzstr. 17, 1180 Wien, Austria

Received: 30 March 2010
Accepted: 11 May 2010

Abstract

We present Herschel SPIRE and PACS photometeric observations of the low metallicity (Z ~ 0.35 ) nearby dwarf galaxy, NGC 1705, in six wavelength bands as part of the Dwarf Galaxy Survey guaranteed time Herschel key program. We confirm the presence of two dominant circumnuclear IR-bright regions surrounding the central super star cluster that had been previously noted at mid-IR wavelengths and in the sub-mm by LABOCA. On constructing a global spectral energy distribution using the SPIRE and PACS photometry, in conjunction with archival IR measurements, we note the presence of an excess at sub-mm wavelengths. This excess suggests the presence of a signiPcant cold dust component within NGC 1705 and was modeled as an additional cold component in the SED. Although alternative explanations for the sub-mm excess beyond 350 μm, such as changes to the dust emissivity cannot be ruled out, the most likely explanation for the observed submillimetre excess is that of an additional cold dust component.