Massive star formation in W51 A triggered by cloud-cloud collisions
Massive star formation in W51 A triggered by cloud-cloud collisions
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W51 A 云与云碰撞引发的大规模恒星形成
DOI：
10.1093/pasj/psz028
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发表时间：
2019
影响因子：
2.3
通讯作者：
Oasa Yumiko et al.
中科院分区：
文献类型：
--
作者：
Fujita Shinji、Torii Kazufumi、Kuno Nario,...;Ohama Akio,...;Oasa Yumiko et al.
WA是银河系中最活跃的恒星形成区域之一，包含大量的分子气体，总质量为。分子气体具有超过120 km s−1的多个速度分量，这些分量之间的相互作用被讨论为触发WA中大质量星星形成的机制。利用Nobeyama 45 m望远镜20′分辨率获得的WA 14 × 10 ~（-1）区域的~（12）CO、~（13）CO和~（18）C（J = 1-0）数据，对WA分子气体进行了观测研究。我们的CO数据分辨出了四个离散的速度云，大小和质量为1.30 pc，径向速度为50、56、60和68 km s−1。在西澳的Hii区域复合体G49.5−0.4的中心部分，也就是明亮的星团IRS 1和IRS 2所在的地方，我们发现了四个C18 O团簇，它们的大小为1.01 pc，柱密度高于1023 cm −2，它们都嵌入在四个速度云中。这四个团块集中在一个5 pc的小区域内，但在天空中显示出互补的分布。在位置-速度图中，这些团块通过具有弱强度的桥特征彼此连接。13 CO（J = 3-2）（J = 1-0）的高强度比也表明这四个云与Hii区有关，包括IRS 1和IRS 2。我们还发现，在另一个明亮的Hii区域复合体G49.4−0.3中，50、60和68 km s− 1云显示出互补的分布，在50和60 km s− 1云与60和68 km s− 1云之间有两个桥梁特征连接。位于G49.5−0.4以北约15秒差距处的一个孤立的致密Hii区G49.57−0.27也显示出互补分布和桥接特征。位置-速度图上的互补分布和宽桥特征表明，西澳地区四个速度云之间存在碰撞相互作用。碰撞的时间尺度可以估计为几个0.1百万年的碰撞的交叉时间，这是一致的，从Hii区的大小与21厘米连续统数据测量的年龄的Hii区。我们通过将这些与最近的云-云碰撞的观测和理论研究进行比较，讨论了西澳云-云碰撞和大质量星星形成的情景。
WA is one of the most active star-forming regions in the Milky Way, and includes copious amounts of molecular gas with a total mass of. The molecular gas has multiple velocity components over ∼20 km s−1, and interactions between these components have been discussed as the mechanism that triggered the massive star formation in WA. In this paper, we report on an observational study of the molecular gas in WA using the new12CO,13CO, and C18O (J = 1–0) data covering a 14 × 10 area of WA obtained with the Nobeyama 45 m telescope at 20′ resolution. Our CO data resolved four discrete velocity clouds with sizes and masses of ∼30 pc and 1.0–around radial velocities of 50, 56, 60, and 68 km s−1. Toward the central part of the Hii region complex G49.5−0.4 in WA, in which the bright stellar clusters IRS 1 and IRS 2 are located, we identified four C18O clumps having sizes of ∼1 pc and column densities of higher than 1023cm−2, which are each embedded within the four velocity clouds. These four clumps are concentrated within a small area of 5 pc, but show a complementary distribution on the sky. In the position–velocity diagram, these clumps are connected with each other by bridge features having weak intensities. The high intensity ratios of13CO (J = 3–2)(J = 1–0) also indicate that these four clouds are associated with the Hii regions, including IRS 1 and IRS 2. We also reveal that, in the other bright Hii region complex G49.4−0.3, the 50, 60, and 68 km s−1clouds show a complementary distribution, with two bridge features connecting between the 50 and 60 km s−1clouds and the 60 and 68 km s−1clouds. An isolated compact Hii region G49.57−0.27 located ∼15 pc north of G49.5−0.4 also shows a complementary distribution and a bridge feature. The complementary distribution on the sky and the broad bridge feature in the position–velocity diagram suggest collisional interactions among the four velocity clouds in WA. The timescales of the collisions can be estimated to be several 0.1 Myr as crossing times of the collisions, which are consistent with the ages of the Hii regions measured from the sizes of the Hii regions with the 21 cm continuum data. We discuss a scenario of cloud–cloud collisions and massive star formation in WA by comparing these with recent observational and theoretical studies of cloud–cloud collision.