2010A&A...518L..76H

We study the structure of the medium surrounding sites of high-mass star formation to determine the interrelation between the HII 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. We present new Herschel/SPIRE 250µm, 350µm and 500µm 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-∼100pc. 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. 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.