Rotation of Two Micron All Sky Survey Clumps in Molecular Clouds

We have analyzed the rotational properties of 12 clumps using 13CO (1–0) and C18O (1–0) maps of the Five College Radio Astronomy Observatory 13.7 m radio telescope. The clumps, located within molecular clouds, have radii (R) in the range of 0.06 – 0.27 pc. The direction of clump elongation is not correlated with the direction of the velocity gradient. We measured the specific angular momentum (J/M) to be between 0.0031 and 0.036 pc kms−1 based on 13CO images, and between 0.0036 and 0.030 pc kms−1 based on C18O images. The consistency of J/M based on different tracers indicates the 13CO and C18O in dense clumps trace essentially the same material despite significantly different opacities. We also found that J/M increases monotonically as a function of R in power–law form, J/M / R1.75 ± 0.45. The ratio between rotation energy and gravitational energy, !, ranges from 0.0018 to 0.053. The small values of ! imply that rotation alone is not sufficient to support the clump against gravitational collapse.

我们利用五校射电天文观测站（Five College Radio Astronomy Observatory）13.7米射电望远镜的13CO（1–0）和C18O（1–0）图谱，分析了12个云团（clumps）的旋转特性。这些位于分子云内部的云团，其半径（R）范围为0.06–0.27秒差距（pc）。云团的伸长方向与速度梯度（velocity gradient）方向无相关性。基于13CO图像测得的比角动量（specific angular momentum，J/M）介于0.0031至0.036 pc kms−1之间，基于C18O图像测得的值则介于0.0036至0.030 pc kms−1之间。不同示踪剂（tracers）测得的J/M具有一致性，这表明尽管不透明度（opacities）存在显著差异，致密云团中的13CO和C18O本质上示踪的是相同物质。我们还发现，J/M随半径R呈幂律（power-law）形式单调递增，即J/M ∝ R^(1.75±0.45)。旋转能与引力能的比值!范围为0.0018至0.053。!的小值意味着仅靠旋转不足以支撑云团抵御引力坍缩。