We have carried out a survey of the dense clumps associated with 14 embedded clusters in the \mathrm { C } ^ { 18 } \mathrm { O } ( J =1–0 ) line emission with the Nobeyama 45m telescope in order to understand the formation and evolution of stellar clusters in dense clumps of molecular clouds .
We have selected these clusters at distances from 0.3 to 2.1 kpc and have mapped about 6 ^ { \prime } \times 6 ^ { \prime } to 10 ^ { \prime } \times 10 ^ { \prime } regions ( corresponding to 3.8 pc \times 3.8 pc at 2.1 kpc ) for all the clumps with 22 ^ { \prime \prime } resolution ( corresponding to Jeans length at 2.1 kpc ) .
We have obtained dense clumps with radii of 0.40–1.6 pc , masses of 150–4600 M _ { \odot } , and velocity widths in FWHM of 1.4–3.3 { km\ > s ^ { -1 } } .
Most of the clumps are found to be approximately in virial equilibrium , which implies that \mathrm { C } ^ { 18 } \mathrm { O } gas represents parental dense clumps for cluster formation .
From the spatial relation between the distributions of clumps and clusters , we classified \mathrm { C } ^ { 18 } \mathrm { O } clumps into three types ( \it { Type A, B,and } \it { C } ) .
The \mathrm { C } ^ { 18 } \mathrm { O } clumps as classified into \it { Type A } have emission distributions with a single peak at the stellar clusters and higher brightness contrast than that of other target sources . \it { Type B } clumps have double or triple peaks which are associated with the cluster and moderately high brightness contrast structure . \it { Type C } clumps have also multiple peaks although they are not associated with the cluster and low brightness contrast structure .
We suggest that our classification represents an evolutionary trend of cluster-forming dense clumps because dense gas in molecular clouds is expected to be converted into stellar constituents , or to be dispersed by stellar activities .
Moreover , although there is a scatter , we found a tendency that the SFEs of the dense clumps increase from \it { Type A } to \it { Type C } , which also supports our scenario .