EVIDENCE FOR ENVIRONMENTAL CHANGES IN THE SUBMILLIMETER DUST OPACITY
EVIDENCE FOR ENVIRONMENTAL CHANGES IN THE SUBMILLIMETER DUST OPACITY
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亚毫米级尘埃不透明度的环境变化证据
DOI：
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发表时间：
2011
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通讯作者：
D. Wiebe
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作者：
P. Martin;A. Roy;S. Bontemps;M. Miville;P. Ade;J. Bock;E. Chapin;M. Devlin;S. Dicker;M. Griffin;J. Gundersen;M. Halpern;P. Hargrave;D. Hughes;J. Klein;G. Marsden;P. Mauskopf;C. Netterfield;L. Olmi;G. Patanchon;M. Rex;D. Scott;C. Semisch;M. Truch;C. Tucker;G. Tucker;M. Viero;D. Wiebe
银河系平面漫射星际介质（ISM）中尘埃的亚毫米不透明度已通过连续发射图像与柱密度代理的逐像素相关性进行了量化。我们使用了多波长连续体数据：250、350和500 μm的三个气球载大孔径亚毫米望远镜波段和100 μm的一个IRAS波段。代表的是近红外颜色过剩，E(J−Ks)，从2微米全天巡天获得。根据对恒星的观察，我们展示了这种颜色过剩与中度消光区域的氢柱总密度之间的关系。发射率与柱密度的比值，即发射率，就可以从相关性中得知，作为频率的函数。该发射率的光谱分布可以用修正黑体拟合，得到1200 GHz和250 μm下的特征尘埃温度T和期望的不透明度σe（1200）。我们分析了靠近银道面朝向船帆分子云的14个区域，这些区域大多是为了避免高柱密度（NH > - 1022 cm - 2）和小到足以确保均匀的尘埃温度的区域而选择的。我们发现σe（1200）通常是（2-4）× 10−25 cm2 H−1，因此大约是本星系高纬度漫射原子ISM平均值的2-4倍。这是谷物进化的有力证据。尘埃吸收（和再辐射）的每H核子总功率有一个范围，反映了星际辐射场强度和/或尘埃吸收不透明度的变化。这些发射不透明度和功率的变化影响平衡温度，通常为15 K，比高纬度地区冷。在高不透明度和低温度地区，σe（1200）随T的减小而增大。对发射不透明度变化的识别提出了一个警告，因为从尘埃发射图中推断出的所有柱密度，以及其中紧凑结构的质量，都与所采用的值成反比。
The submillimeter opacity of dust in the diffuse interstellar medium (ISM) 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 Balloon-borne Large Aperture Submillimeter Telescope bands at 250, 350, and 500 μm and one IRAS band at 100 μm. The proxy is the near-infrared color excess, E(J − Ks), obtained from the Two Micron All Sky Survey. 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 (2–4) × 10−25 cm2 H−1 and thus about 2–4 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 (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.