Astrophys. J., 765, 101 (2013/March-2)
Maps of massive clumps in the early stage of cluster formation: two modes of cluster formation, coeval or non-coeval?
HIGUCHI A.E., KURONO Y., NAOI T., SAITO M., MAUERSBERGER R. and KAWABE R.
Abstract (from CDS):
We present maps of seven young massive molecular clumps within five target regions in C18O (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 C18O clumps with radii of 0.5-1.7 pc, masses of 470-4200 M☉, and velocity widths of 1.4-3.3 km/s. 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), while the other two are unassociated with H II regions (CWOHRs). The C18O 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 C18O 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.
H II regions - ISM: kinematics and dynamics - ISM: molecules - ISM: structure - stars: formation
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