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We have carried out a survey of the dense clumps associated with 11 embedded clusters in the H13CO+ (1-0) line emission with the Nobeyama 45m telescope to reveal the physical relation between clusters and their natal clumps. In this survey we made typically 5"X 5" maps in H13CO+ around the center of the 11 regions. The target sources were selected from the Lada catalog and the results of the NH3(1,1) and H2O maser survey with the 45m telescope.
We have succeeded in obtaining the maps of all the H13CO+ clumps with the radii of 0.3 - 1 pc, LTE masses of 60 - 850 Msun , and velocity widths in FWHM of 1.6-4.5 km/s. Previously, we also carried C18O(1-0) line observation toward the same objects and obtained the clumps which cover the whole clusters. On the other hand, the H13CO+ ones are located shifted from the central position of the clusters. Our analysis showed that all the clumps are most likely to be in virial equilibrium, suggesting that the dense clumps have the potential for cluster formation. We have discovered an interesting correlation between the cluster mass and the degree of the central concentration of the clumps. We defined the central concentration as the ratio of the mass above the 6 sigma levels to the mass above the 3 sigma of the clumps. We considered that the relation shows the progress of the clusters : The larger the cluster masses, the smaller the central concentration of the H13CO+ clumps. In conclusion, we understood that the H13CO+ clumps are really sensitive to the on-going star formation.
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