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

通过比较数字化巡天I数据库直接测量的可见光消光图和远红外尘埃发射的消光图，我们发现，银河系中的乌云被尘埃包围，这些尘埃在远红外波长的发射率（bbb100微米）比普通尘埃颗粒高几倍。这种不寻常的尘埃在银河系中似乎非常丰富，在银河系平原无处不在。本研究的目的是通过测量其在光学和近红外波段的变红曲线，以及探测云中可能影响云内尘埃性质的分子气体的密度和温度，来探讨这种特殊尘埃的起源。在研究的第一年（2005年），我们与日本其他射电天文团体共同开发了直径60厘米的望远镜，以便对L1251、IC5146和rho-0ph等几个黑云进行射电观测。在第二年（2006年），我们实际进行了^<12>CO和^<13>CO （J=2-1）观测，角分辨率为10'。为了探究尘埃的分布和云中尘埃特性可能发生的变化，我们还利用2微米巡天（2MASS）数据库制作了彩色过量E（J-H）和E（H-K）图。比较所有这些数据集，我们得出结论，在云内部观察到的特殊尘埃可能是在密集的核心内部生长的大颗粒。另一方面，在云的扩散边界观测到的具有高远红外发射率的尘埃很可能是蓬松的聚集体，尽管它们的确切起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.