Evidence for Environmental Changes in the Submillimeter Dust Opacity

Peter G. Martin Arabindo Roy S. Bontemps 1 Marc-Antoine Miville-Deschênes Peter A. R. Ade James J. Bock Edward L. Chapin Mark J. Devlin Simon R. Dicker Matthew Griffin Joshua O. Gundersen Mark Halpern Peter C. Hargrave David H. Hughes Jeff Klein Gaelen Marsden Philip Mauskopf Calvin B. Netterfield Luca Olmi G. Patanchon 2 Marie Rex Douglas Scott Christopher Semisch Matthew D. P. Truch Carole Tucker Gregory S. Tucker Marco P. Viero Donald V. Wiebe
L3AB - Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux, OASU - Observatoire aquitain des sciences de l'univers, LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac], Université Sciences et Technologies - Bordeaux 1
2 APC - Cosmologie
PCC - Physique Corpusculaire et Cosmologie - Collège de France, APC - UMR 7164 - AstroParticule et Cosmologie
Abstract : The submillimeter opacity of dust in the diffuse Galactic interstellar medium (ISM) has been quantified using a pixel-by-pixel correlation of images of continuum emission with a proxy for column density. We used three BLAST bands at 250, 350, and 500 \mu m and one IRAS at 100 \mu m. The proxy is the near-infrared color excess, E(J-Ks), obtained from 2MASS. Based on observations of stars, we show how well this color excess is correlated with the total hydrogen column density for regions of moderate extinction. The ratio of emission to column density, the emissivity, is then known from the correlations, as a function of frequency. The spectral distribution of this emissivity can be fit by a modified blackbody, whence the characteristic dust temperature T and the desired opacity \sigma_e(1200) at 1200 GHz can be obtained. We have analyzed 14 regions near the Galactic plane toward the Vela molecular cloud, mostly selected to avoid regions of high column density (N_H > 10^{22} cm^-2) and small enough to ensure a uniform T. We find \sigma_e(1200) is typically 2 to 4 x 10^{-25} cm^2/H and thus about 2 to 4 times larger than the average value in the local high Galactic latitude diffuse atomic ISM. This is strong evidence for grain evolution. There is a range in total power per H nucleon absorbed (re-radiated) by the dust, reflecting changes in the interstellar radiation field and/or the dust absorption opacity. These changes affect the equilibrium T, which is typically 15 K, colder than at high latitudes. Our analysis extends, to higher opacity and lower T, the trend of increasing opacity with decreasing T that was found at high latitudes. The recognition of changes in the emission opacity raises a cautionary flag because all column densities deduced from dust emission maps, and the masses of compact structures within them, depend inversely on the value adopted.
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Soumis le : mardi 31 janvier 2012 - 12:34:44
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Peter G. Martin, Arabindo Roy, S. Bontemps, Marc-Antoine Miville-Deschênes, Peter A. R. Ade, et al.. Evidence for Environmental Changes in the Submillimeter Dust Opacity. Astrophysical Journal, American Astronomical Society, 2012, 751, pp.28. 〈10.1088/0004-637X/751/1/28〉. 〈hal-00664696〉



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