Submillimeter dust emission of the M 17 complex measured with PRONAOS

Abstract

\n We map a 50$' \\times 30'$ area in and around the M 17 molecular complex\n with the French submillimeter balloon-borne telescope PRONAOS, in order to\n better understand the thermal emission of cosmic dust and the structure of\n the interstellar medium.\nThe PRONAOS-SPM instrument has an angular resolution of\nabout 3', corresponding to a size of 2 pc at the distance of this complex,\nand a high sensitivity up to 0.8 MJy/sr.\nThe observations are made in four wide submillimeter bands corresponding to effective wavelengths\nof 200 ${\\mu}{\\rm m}$, 260 ${\\mu}{\\rm m}$, 360 ${\\mu}{\\rm m}$ and 580 ${\\mu}{\\rm m}$.\nUsing an improved map-making method for PRONAOS data, we map the M 17\ncomplex and faint condensations near the dense warm core.\nWe derive maps of both the dust temperature and the spectral index, which vary\nover a wide range, from about 10 K to 100 K for the temperature and from about 1\n to 2.5 for the spectral index.\nWe show that these parameters are anticorrelated, the\n cold areas (10–20 K) having a spectral index around 2, whereas the warm\n areas have a spectral index between 1 and 1.5.\nWe discuss possible causes of this effect, and we propose an\nexplanation involving intrinsic variations of the grain properties.\nIndeed, to match the observed spectra with two dust components having a spectral index equal to 2 leads to very large and unlikely amounts of cold dust.\nWe also give estimates of the column densities and masses of the studied\nclumps.\nThree cold clumps (14–17 K) could be gravitationally unstable.\n\n\n