Molecular Cores and Young Clusters of Star Forming Regions

Abstract

By using the 13.7 m millimeter wave telescope of the Qinghai Station of Purple Mountain Observatory at Delingha, we have performed the mapping observations simultaneously at the (J = 1–0) lines of ¹²CO, ¹³CO and C¹⁸O towards respectively the 17 star forming regions associated with clusters. All of them show rather strong C¹⁸O emission, except IRAS 04547+4753. Because of the different sizes of molecular clouds, there are 13 regions being observed to the half maximum of ¹³CO integrated intensity, and the large-area mapping observation has not been made for the other 4 regions with rather large extents. Based on the observed data, the physical properties of molecular cores are calculated, such as the line width, brightness temperature, size, density and mass. The averaged ratios of the virial mass M_vir and local thermodynamic equilibrium mass M_LTE of the ¹³CO and C¹⁸O cores are 0.66 and 0.74, respectively, suggesting that these cores are nearly at the virial equilibrium state. In order to compare the cores and clusters in morphologies, the contour maps of the integrated intensities of ¹³CO and C¹⁸O are overlaid on the K-band images of 2MASS. At the same time, the sizes and masses of the clusters associated with cores are calculated by adopting the photometric results of the near-infrared point sources in 2MASS database. Based on the derived masses of the molecular cores and clusters, the star formation efficiency (SFE) is calculated for the molecular clouds, and we find that it varies in the range from 10% to 30%.