Kavli Affiliate: Ke Wang
| First 5 Authors: Siju Zhang, Tie Liu, Ke Wang, Annie Zavagno, Guido Garay
| Summary:
Fragmentation and evolution for the molecular shells of the compact HII
regions are less explored compared to their evolved counterparts. We map nine
compact HII regions with a typical diameter of 0.4 pc that are surrounded by
molecular shells traced by CCH. Several to a dozen dense gas fragments probed
by H13CO+ are embedded in these molecular shells. These gas fragments, strongly
affected by the HII region, have a higher surface density, mass, and turbulence
than those outside the shells but within the same pc-scale natal clump. These
features suggest that the shells swept up by the early HII regions can enhance
the formation of massive dense structures that may host the birth of
higher-mass stars. We examine the formation of fragments and find that
fragmentation of the swept-up shell is unlikely to occur in these early HII
regions, by comparing the expected time scale of shell fragmentation with the
age of HII region. We propose that the appearance of gas fragments in these
shells is probably the result of sweeping up pre-existing fragments into the
molecular shell that has not yet fragmented. Taken together, this work provides
a basis for understanding the interplay of star-forming sites with an intricate
environment containing ionization feedback such as those observed in starburst
regions.
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