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David Hughes
Acceso Abierto
Dust, extinction
Infrared: ISM
ISM: structure
Submil-limeter: ISM
The submillimeter opacity of dust in the diffuse interstellar medium in the Galactic plane has been quantified using a pixel-by-pixel correlation of images of continuum emission with a proxy for column density. We used multi-wavelength continuum data: three BLAST bands at 250, 350, and 500 μm and one IRAS at 100 μm. 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 σe(1200) at 1200 GHz or 250 μm 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 (NH > 10²² cm⁻²) and small enough to ensure a uniform dust temperature. We find σe(1200) is typically 2 to 4×10⁻²⁵ cm² H⁻¹ and thus about 2 to 4 times larger than the average value in the local high Galactic latitude diffuse atomic interstellar medium. This is strong evidence for grain evolution. There is a range in total power per H nucleon absorbed (and re-radiated) by the dust, reflecting changes in the strength of the interstellar radiation field and/or the dust absorption opacity. These changes in emission opacity and power affect the equilibrium T, which is typically 15 K, colder than at high latitudes. Our analysis extends, to higher opacity and lower temperature, the trend of increasing σe(1200) 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.
The Astrophysical Journal
Público en general
Martin, Peter G., et al., (2012), Evidence for environmental changes in the submillimeter dust opacity, The Astrophysical Journal, Vol. 751(1):1-17
Versión aceptada
acceptedVersion - Versión aceptada
Appears in Collections:Artículos de Astrofísica

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