Probing the origin of peculiar dust with high far-infrared emissivity

对比利用数字化巡天I数据库直接在光学波长上测量的Av的可见光消光图和由远红外尘埃发射得到的消光图，我们发现银河系中的暗云被尘埃包围，其在远红外波长(&gt；100微米)的发射率比正常尘埃颗粒高出几倍。这种不同寻常的尘埃似乎在银河系中非常丰富，在银河系平原上无处不在。本研究的目的是通过测量这种特殊的尘埃在光学和近红外波长上的变红曲线，以及探讨云中分子气体的密度和温度对云内尘埃性质的影响，来探讨这种特殊尘埃的来源。在研究期间的第一年(2005年)，我们与日本其他射电天文小组集中开发了直径60厘米的望远镜，以便对L1251、IC5146和RHO-0PH等几种暗云进行射电观测。在第二年(2006年)，我们实际进行了中性角分辨率为10‘的^&lt；12&gt；CO和^&lt；13&gt；CO(J=2-1)观测。为了探讨云中沙尘的分布和沙尘性质的可能变化，我们还利用数据库2微米全天巡天(2MASS)绘制了色余E(J-H)和E(H-K)图。比较所有这些数据集，我们得出结论，在云层内部观察到的特殊尘埃很可能是在致密核心内生长的大颗粒。另一方面，在云层扩散边界观察到的具有高远红外发射率的尘埃很可能是蓬松的集合体，尽管它们的确切来源仍然是一个悬而未决的问题。

Comparing the visual extinction map of Av measured directly in the optical wavelengths using the data base Digitized Sky Survey I and that derived from the far-infrared dust emission, we found that the dark clouds in the Galaxy are surrounded by dust whose emissivity in the far-infrared wavelengths (>100 micron) is a few times higher than normal dust grains. Such unusual dust seems to be very abundant in the Galaxy, being ubiquitous all over the galactic plain. Purpose of the present study is to probe into the origin such peculiar dust by measuring their reddening curves in the optical and near-infrared wavelengths as well as by probing into the density and temperature of molecular gas in the clouds which may influence on the dust property inside of the clouds.During the first year of the research period (2005), we concentrated on the development of the 60cm-diameter telescope with other radio astronomical groups in Japan in order to carry out radio observations toward several dark clouds including L1251, IC5146, and rho-0ph. In the second year (2006), we actually performed the ^<12>CO and ^<13>CO (J=2-1) observations with a moderate angular resolution of 10'. In order to probe into the dust distribution and the possible change in the dust properties in the clouds, we also produced maps of color excess E(J-H) and E(H-K) using the database 2 Micron All Sky Survey (2MASS). Comparing all of these dataset, we conclude that the peculiar dust observed inside of the clouds is probably big grain growing inside of the dense cores. On the other hands, dust with high far-infrared emissivity observed in the diffuse boundary of the clouds is likely to be fluffy aggregates, although their definite origin still remains as an open question.