Title: A Statistical Study of Massive Cluster-Forming Clumps Show Chinese title

Title: 大规模星团形成云块的统计研究

Abstract: We report results of the observations of 15 regions in several molecular lines for a statistical study of massive cluster-forming clumps. We identified 24 clumps based on the C18O (J=1-0) data obtained by the NRO 45 m telescope, and found that 16 of them are associated with young clusters. The clumps associated with clusters have a typical mass, radius, and molecular density of ~1 X 10^3 Mo, ~0.5 pc, ~1 X 10^5 cm^-3, respectively. We categorized the clumps and clusters into four types according to the spatial coincidence of gas and star density, and discussed their evolutions: Clumps without clusters (Type 1), clumps showing good correlations with clusters (Type 2), clumps showing poor correlations with clusters (Type 3), and clusters with no associated clumps (Type 4). Analyses of the velocity structures and the chemical compositions imply that the clump + cluster systems should evolve from Type 1 to Type 4. We found that some of the Type 2 clumps are infalling on the clump-scale to form clusters at the clump center, which should commonly occur in the beginning of cluster formation. Interestingly, all of the identified Type 1 clumps are likely to be older than the Type 2 clumps in terms of chemical compositions, suggesting that they have been gravitationally stable for a long time possibly being supported by the strong magnetic field of > 1 mG.Type 1 clumps younger than the observed Type 2 clumps should be very rare to find because of their short lifetime. Show Chinese abstract

Abstract: 我们报告了对多个分子线中15个区域的观测结果，以进行大质量团块形成团的统计研究。 我们根据NRO 45米望远镜获得的C18O (J=1-0)数据识别出24个团块，并发现其中16个与年轻星团有关。 与星团相关的团块具有典型的质量、半径和分子密度分别为~1 X 10^3 Mo，~0.5 pc，~1 X 10^5 cm^-3。 我们根据气体和恒星密度的空间重合性将团块和星团分为四类，并讨论了它们的演化：无星团的团块（类型1），与星团有良好相关性的团块（类型2），与星团相关性较差的团块（类型3），以及没有相关团块的星团（类型4）。 速度结构和化学成分的分析表明，团块+星团系统应从类型1演变为类型4。 我们发现一些类型2的团块正在以团块尺度向团块中心坍缩以形成星团，这可能在星团形成的初期经常发生。 有趣的是，从化学成分来看，所有识别出的类型1的团块都可能比类型2的团块更古老，表明它们可能由于强磁场（> 1 mG）的支持而长时间处于引力稳定状态。由于寿命较短，比观测到的类型2团块更年轻的类型1团块应该非常罕见。