Grain populations in the M 17 south-west star forming complex

Abstract

The different spectral components of the 3-12 mu m dust emission are imaged in the M 17 south-west molecular cloud / Hriptsize{II} region interface. The various images result from a combination of space borne (ISO) and ground based (CFHT) observations. A spatial correlation analysis shows that there are two main components, which correspond to the continuum (including broad features) and to the emission bands (3.3, 6.2, 7.7 and 11.3 mu m) respectively. The former peaks towards the Hriptsize{II} region whereas the later dominates at the molecular cloud interface. This is consistent with a model which attributes the bands to PAH molecules and the continuum to very small grains. In the frame of the coal dust model, these observations put constraints on the properties of the grains, implying a band-to-continuum ratio which varies strongly with the excitation conditions. This analysis, which points out the signature of very small particles, does not favor one model relative to the other. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA. And based on observations with the C10 μ camera at the CHFT.