Submillimeter Observations Of The Massive Star-forming Regions

In order to investigate the diference between the molecular clouds that areassociated with massive star forming regions and those are not, we perform singledish simultaneous observations of¹²CO2-1and3-2lines toward a sample of59northern Spitzer Extended Green Objects （EGOs）. Combining our data witharchive data of¹²CO1-0observations toward the same sample of objects, westatistically investigate the correlations among the CO line widths and strengthsfor both those molecular clouds associated with EGO objects （EGO clouds） andthose do not （non-EGO clouds）. We compare the diferent statistical behaviorsbetween the two groups of molecular clouds and interpret the diferences in termsof diferent density, temperature and velocity feld distributions. Particularly, itis found that both EGO and non-EGO clouds have similar mass ranges. Weconclude that the formation of massive stars are not sensitively dependent onthe total mass of the clouds, but on the volume flling factor of the cloud clumps（or to what extent the molecular clouds have been compressed and shrinked）.