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，我们对北天的59个大质量恒星形成区的Spitzer延展绿色天体(Extended Green Objects， 简称EGO)天体视线方向进行了分子云CO，J=2-1和3-2同时频谱观测， 并与文献中对同一批天体方向观测得到的CO，1-0频谱数据合并进行分析。我们对与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， 我们讨论了这两类分子云的气体温度分布， 密度分布， 速度场分布对我们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是否充分(即分子云团块的体积填充因子是否足够大)
其他摘要
In order to investigate the difference between the molecular clouds that are associated with massive star forming regions and those are not, we perform single dish simultaneous observations of CO,J = 2-1 and 3-2 lines toward a sample of 59 northern Spitzer Extended Green Objects (EGOs). Combining our data with archive data of CO,1-0 observations toward the same sample of objects, we statistically investigate the correlations among the CO line widths and strengths for both those molecular clouds associated with EGO objects (EGO clouds) and those do not (non-EGO clouds). We compare the different statistical behaviors between the two groups of molecular clouds and interpret the differences in terms of different density,emperature 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 shrinked).
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