MAXIMUM-ENTROPY MAPPING OF IRAS DATA .3. EVIDENCE FOR HOT DUST IN M17

A maximum entropy method (MEM) is used to construct an IRAS image of t he M17 nebula at 12 mum from the raw IRAS data; no prior information a bout the structure in the field is given to the maximum entropy routin es. The overall emission seen in this image agrees well with that obse rved at radio wavelengths. The 12-mum flux density of the M17SW region , as measured from the data, suggests the presence of a hot dust compo nent at T(d) = 108 +/- 5 K. The distribution of the emission suggests either that the hot dust is mixed with the ionized gas of the H II reg ion, or that it lies in the photo-dissociation region (PDR), and proba bly represents a population of PAHs. The data are compared with the du st model of Desert, Boulanger & Puget, which confirms that the 12-mum emission is not coming from the denser molecular cloud regions.