CHANGES OF DUST OPACITY WITH DENSITY IN THE ORION A MOLECULAR CLOUD
CHANGES OF DUST OPACITY WITH DENSITY IN THE ORION A MOLECULAR CLOUD
复制标题
猎户座分子云中尘埃不透明度随密度的变化
DOI：
--
复制
发表时间：
2012
期刊：
影响因子：
--
通讯作者：
G. White
中科院分区：
文献类型：
--
作者：
A. Roy;P. Martin;D. Polychroni;S. Bontemps;A. Abergel;P. Andre';D. Arzoumanian;J. di Francesco;T. Hill;V. Konyves;Q. Nguyen;S. Pezzuto;N. Schneider;L. Testi;G. White
我们已经研究了亚毫米波长尘埃颗粒的不透明度，方法是估算赫歇尔·古尔德带探测器在160、250、350和500 μm处成像的光学厚度，并将其与从两微米全天探测器获得的柱密度进行比较，得出颜色过剩E(J−Ks)。我们的主要目标是研究不同环境条件下“大”颗粒引起的不透明度的空间变化，从而量化粉尘的排放特性随柱(和体积)密度的变化。本文研究的猎户座A分子云的中部和南部区域，NH值在1.5×1021 cm−2到50×1021 cm−2之间，非常适合于这种方法。我们用改进的黑体对每个像素的多频率赫歇尔谱能量分布(SED)进行了拟合，得到了基准频率为1200 GHz(250τm)下的温度、温度和光学厚度， μ1200。利用对星际介质的NH/E(J−Ks)的定标，我们得到了每个像素的不透明度(每H核子的尘埃发射截面)σe(1200)。从高纬度扩散ISM典型的最低柱密度下的值∼1×10−25cm2 H−1开始，σe(1200)在所研究的范围内随着N0.28H的增加而增加。这暗示了颗粒的进化。在频率上积分SED，还计算了大颗粒的比功率P(每H发射功率)。在尘埃云光学厚度小于星际辐射场的低柱密度区，P通常为3.7×10−31W H−1，再次接近高纬度漫射辐射场。然而，我们发现了在高柱密度区域P减少的证据，这将是加热颗粒的ISRF衰减的自然结果，以及附近恒星或嵌入的原恒星照射的尘埃局部增加的结果。
We have studied the opacity of dust grains at submillimeter wavelengths by estimating the optical depth from imaging at 160, 250, 350, and 500 μm from the Herschel Gould Belt Survey and comparing this to a column density obtained from the Two Micron All Sky Survey derived color excess E(J − Ks). Our main goal was to investigate the spatial variations of the opacity due to “big” grains over a variety of environmental conditions and thereby quantify how emission properties of the dust change with column (and volume) density. The central and southern areas of the Orion A molecular cloud examined here, with NH ranging from 1.5 × 1021 cm−2 to 50 × 1021 cm−2, are well suited to this approach. We fit the multi-frequency Herschel spectral energy distributions (SEDs) of each pixel with a modified blackbody to obtain the temperature, T, and optical depth, τ1200, at a fiducial frequency of 1200 GHz (250 μm). Using a calibration of NH/E(J − Ks) for the interstellar medium (ISM) we obtained the opacity (dust emission cross-section per H nucleon), σe(1200), for every pixel. From a value ∼1 × 10−25 cm2 H−1 at the lowest column densities that is typical of the high-latitude diffuse ISM, σe(1200) increases as N0.28H over the range studied. This is suggestive of grain evolution. Integrating the SEDs over frequency, we also calculated the specific power P (emission power per H) for the big grains. In low column density regions where dust clouds are optically thin to the interstellar radiation field (ISRF), P is typically 3.7 × 10−31 W H−1, again close to that in the high-latitude diffuse ISM. However, we find evidence for a decrease of P in high column density regions, which would be a natural outcome of attenuation of the ISRF that heats the grains, and for localized increases for dust illuminated by nearby stars or embedded protostars.