科研之友
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摘要
We present maps of seven young massive molecular clumps within five target regions in (CO)-O-18 ( J = 1-0) line emission, using the Nobeyama 45 m telescope. These clumps, which are not associated with clusters, lie at distances between 0.7 and 2.1 kpc. We find (CO)-O-18 clumps with radii of 0.5-1.7 pc, masses of 470-4200M(circle dot), 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 Hii regions (CWHRs), while the other two are unassociated with H II regions (CWOHRs). The (CO)-O-18 clumps can be classified into two morphological types: CWHRs with a filamentary or shell-like structure and spherical CWOHRs. The two CWOHRs have systematic velocity gradients. Using the publicly released WISE database, Class I and Class II protostellar candidates are identified within the (CO)-O-18 clumps. The fraction of Class I candidates among all YSO candidates (Class I+Class II) is >= 50% in CWHRs and <= 50% in CWOHRs. We conclude that effects from the H II regions can be seen in (1) the spatial distributions of the clumps: filamentary or shell-like structure running along the H II regions; (2) the velocity structures of the clumps: large velocity dispersion along shells; and (3) the small age spreads of YSOs.The small spreads in age of the YSOs show that the presence of H II regions tends to trigger coeval cluster formation.
- 出版日期2013-3-10
- 单位中国科学院国家天文台
