对59个北天EGO天体方向上的分子云^(12)COJ=2-1和J=3-2频谱观测研究

^(12)CO J=2-1 and J=3-2 Line Observations of Molecular Clouds toward the Direction of 59 Extended Green Objects in the Northern Sky

为了研究有大质量恒星形成的分子云与其它分子云之间的差异,对北天的59个作为大质量恒星形成区的Spitzer延展绿色天体(Extended Green Objects,简称EGOs)视线方向进行了分子云^(12)CO J=2-1和J=3-2频谱观测,并与文献中对同一批天体方向观测得到的^(12)CO J=1-0频谱数据合并进行分析.对与EGO天体成协的分子云(简称EGO分子云)和其它non-EGO分子云进行了CO多跃迁谱线强度和宽度的统计比较分析.在数据统计的基础上,讨论了这两类分子云的气体温度分布、密度分布、速度场分布对观测数据统计特征的影响.分析结果表明,直接决定是否有大质量恒星形成的关键因素可能并不是巨分子云的质量是否足够大,而是巨分子云的引力塌缩程度足否充分(即分子云团块的体积填充因子是否足够大).

In order to investigate the differences between the molecular clouds that are associated with massive star forming regions and those not, we perform single dish simulta- neous observations of 12CO J = 2-1 and J=3-2 lines toward a sample of 59 Spitzer Extended Green Objects （EGOs） in the northern sky. Combining our results with the archive data of 12CO J=l-0 observations toward the same sample of objects, we statistically investigate the correlations between the CO line widths and strengths for both those molecular clouds asso- ciated with EGO objects （EGO clouds） and those not （non-EGO clouds）. We compare the different statistical behaviors between the two groups of molecular clouds, and interpret the differences in terms of density, temperature, and velocity field distributions. Particularly, it is found that both EGO and non-EGO clouds have similar mass ranges. We conclude that the formation of massive stars are not sensitively dependent on the total mass of the clouds, but on the volume filling factor of the cloud clumps （or to what extent the molecular clouds have been compressed and shrunk）.