Dust emission in massive star-forming regions with PRONAOS: the Orion and M 17 molecular clouds

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The balloon-borne submillimeter instrument PRONAOS has observed one square degree areas towards the Orion and M 17 molecular clouds. The 2'-3.5' resolution maps obtained in four wide wavelength bands between 200 μm and 600 μm, exhibit the dust distribution in these regions. We analyze the temperature and spectral index of the dust, and we show the anticorrelation between these two parameters. We derive estimations of the ISM column densities and masses in these regions.

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New far-infrared and submillimeter data are used to solidify and to extend to long wavelengths the empirical calibration of the infrared spectral energy distribution (SED) of normal star-forming galaxies. As was found by Dale et al. (2001), a single parameter family, characterized by f_nu(60 microns)/f_nu(100 microns), is adequate to describe the range of normal galaxy spectral energy distributions observed by IRAS and ISO from 3 to 100 microns. However, predictions based on the first generation models at longer wavelengths (122 to 850 microns) are increasingly overluminous compared to the data for smaller f_nu(60 microns)/f_nu(100 microns), or alternatively, for weaker global interstellar radiation fields. After slightly modifying the far-infrared/submillimeter dust emissivity in those models as a function of the radiation field intensity to better match the long wavelength data, a suite of SEDs from 3 microns to 20 cm in wavelength is presented. Results from relevant applications are also discussed, including submillimeter-based photometric redshift indicators, the infrared energy budget and simple formulae for recovering the bolometric infrared luminosity, and dust mass estimates in galaxies. Regarding the latter, since galaxy infrared SEDs are not well-described by single blackbody curves, the usual methods of estimating dust masses can be grossly inadequate. The improved model presented herein is used to provide a more accurate relation between infrared luminosity and dust mass.
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