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波段Av消光图和由远红外尘埃辐射得到的消光图，我们发现银河系中的乌云被尘埃所包围，其远红外波段（>100微米）的发射率比正常尘埃颗粒高几倍。这种不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尘埃在光学和近红外波段的红化曲线，以及探讨云内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起源。我们与日本的其他射电天文小组一起集中精力开发直径为60厘米的望远镜，以便对包括L1251、IC 5146和rho-0 ph在内的几个乌云进行射电观测。在第二年（2006年），我们实际上进行了^<12>CO和^<13>CO（J=2-1）的观测，具有中等的角分辨率为10 '。为了探讨尘埃的分布和尘埃在云中的性质可能发生的变化，我们还利用2微米全天巡天数据库（2 MASS）制作了色余E（J-H）和E（H-K）图。比较所有这些数据集，我们得出结论，云内观察到的奇特尘埃可能是致密核心内生长的大颗粒。另一方面，在云的漫射边界观察到的具有高远红外发射率的尘埃可能是蓬松的聚集体，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.