We present maps of 7 young massive molecular clumps within 5 target regions in the \mathrm { C } ^ { 18 } \mathrm { O } ( J =1–0 ) line emission , using the Nobeyama 45m telescope .
These clumps , which are not associated with clusters , lie at distances between 0.7 to 2.1 kpc .
We find \mathrm { C } ^ { 18 } \mathrm { O } clumps with radii of 0.5–1.7 pc , masses of 470–4200 M _ { \odot } , and velocity widths of 1.4–3.3 { km\ > s ^ { -1 } } .
All of the clumps are massive and approximately in virial equilibrium , suggesting they will potentially form clusters .
Three of our target regions are associated with H ii regions ( “ CWHRs ” from Clump with H ii Regions ) , and the other two are without H ii regions ( CWOHRs ) .
The \mathrm { C } ^ { 18 } \mathrm { O } clumps can be classified into two morphological types : CWHRs shape a filamentary or shell-like structure , CWOHRs are spherical .
The two CWOHRs have systematic velocity gradients .
Using the publicly released \it { WISE } database , Class I and Class II protostellar candidates were identified within the \mathrm { C } ^ { 18 } \mathrm { O } clumps .
The fraction of the Class I candidates among all YSO candidates ( Class I+Class II ) is \geq 50 \% in CWHRs , and \leq 50 \% in CWOHRs .
We conclude that effects from the H ii regions can be seen in ( 1 ) spatial distributions of the clumps : filamentary or shell-like structure running along the H ii regions , ( 2 ) velocity structures of the clumps : large velocity dispersion along shells , and ( 3 ) small age spreads of YSOs .
The small spread in age of the YSOs show that the presence of H ii regions tend to trigger coeval cluster formation .