Volume 518, July-August 2010
Herschel: the first science highlights
|Number of page(s)||4|
|Published online||16 July 2010|
Letter to the Editor
Cool gas and dust in M 33: Results from the HERschel M 33 Extended Survey (HERM33ES)*
Laboratoire d'Astrophysique de Bordeaux, Université Bordeaux 1,
Observatoire de Bordeaux, OASU, UMR 5804, CNRS/INSU, BP 89, 33270 Floirac, France e-mail: Braine@obs.u-bordeaux1.fr
2 Instituto Radioastronomia Milimetrica (IRAM), Av. Divina Pastora 7, Nucleo Central, 18012 Granada, Spain
3 Institute of Astronomy and Astrophysics, National Observatory of Athens, P. Penteli, 15236 Athens, Greece
4 University of British Columbia, Okanagan, 3333 University Way, Kelowna BC V1V 1V7 Canada
5 Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
6 Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany, Argelander Institut fr Astronomie. Auf dem Hügel 71, 53121 Bonn, Germany
7 Dept. Física Teórica y del Cosmos, Universidad de Granada, Spain
8 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
9 SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
10 Onsala Space Observatory, Chalmers University of Technology, 43992 Onsala, Sweden
11 Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France
12 Observatorio Astronómico Nacional (OAN) - Observatorio de Madrid, Alfonso XII 3, 28014 Madrid, Spain
13 Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 1710, Australia
14 Department of Astronomy & Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, 400005 Mumbai, India
15 KOSMA, I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
16 IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France
17 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
18 Argelander Institut fr Astronomie. Auf dem Hügel 71, 53121 Bonn, Germany
Accepted: 11 May 2010
We present an analysis of the first space-based far-IR-submm observations of M 33, which measure the emission from the cool dust and resolve the giant molecular cloud complexes. With roughly half-solar abundances, M 33 is a first step towards young low-metallicity galaxies where the submm may be able to provide an alternative to CO mapping to measure their H2 content. In this Letter, we measure the dust emission cross-section σ using SPIRE and recent CO and H i observations; a variation in σ is present from a near-solar neighborhood cross-section to about half-solar with the maximum being south of the nucleus. Calculating the total H column density from the measured dust temperature and cross-section, and then subtracting the H i column, yields a morphology similar to that observed in CO. The H2/H i mass ratio decreases from about unity to well below 10% and is about 15% averaged over the optical disk. The single most important observation to reduce the potentially large systematic errors is to complete the CO mapping of M 33.
Key words: galaxies: individual: M 33 / Local Group / galaxies: evolution / galaxies: ISM / ISM: clouds / stars: formation
© ESO, 2010
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