Letter to the Editor

The Herschel revolution: Unveiling the morphology of the high-mass star-formation sites N44 and N63 in the LMC^*

¹ Service d'Astrophysique, CEA, Saclay, 91191 Gif-Sur-Yvette Cedex, France e-mail: sacha.hony@cea.fr
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ Steward Observatory, University of Arizona, 933 North Cherry Ave., Tucson, AZ 85721, USA
⁴ Centre d'Étude Spatiale des Rayonnements, CNRS, 9 av. du Colonel Roche, BP 4346, 31028 Toulouse, France
⁵ Department of Astronomy, Lab for Millimeter-wave Astronomy, University of Maryland. College Park, MD 20742-2421, USA
⁶ Department of Astronomy, University of Virginia, PO Box 3818, Charlottesville, VA 22903, USA 

⁷ Sterrewacht Leiden, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁸ Astronomy & Space Science, Sejong University, 143-747 Seoul, South Korea
⁹ Department of Physics and Astronomy, University of Missouri, 314 Physics Building, Columbia, MO 65211, USA
¹⁰ Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹¹ Department of Astronomy, University of Michigan, 830 Dennison Building, Ann Arbor, MI 48109-1042, USA
¹² Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile

Received: 31 March 2010
Accepted: 15 April 2010

Abstract

Aims. We study the structure of the medium surrounding sites of high-mass star formation to determine the interrelation between the H ii regions and the environment from which they were formed. The density distribution of the surroundings is key in determining how the radiation of the newly formed stars interacts with the surroundings in a way that allows it to be used as a star-formation tracer.

Methods. We present new Herschel/SPIRE 250 μm, 350 μm and 500 μm data of LHA 120-N44 and LHA 120-N63 in the LMC. We construct average spectral energy distributions (SEDs) for annuli centered on the IR bright part of the star-formation sites. The annuli cover ~10–~100 pc. We use a phenomenological dust model to fit these SEDs to derive the dust column-densities, characterize the incident radiation field and the abundance of polycyclic aromatic hydrocarbon molecules. We see a decrease of a factor 5 in the radiation field energy-density as a function of radial distance around N63. The source N44 does not show a systematic trend. We construct a simple geometrical model to derive the 3D density profile of the surroundings of these two regions.

Results. Herschel/SPIRE data have proven very efficient in deriving the dust-mass distribution. We find that the radiation field in the two sources behaves very differently. N63 is more or less spherically symmetric and the average radiation field drops with distance. N44 shows no systematic decrease of the radiation intensity, which is probably due to the inhomogeneity of the surrounding molecular material and to the complex distribution of several star-forming clusters in the region.