Kavli Affiliate: Lile Wang
| First 5 Authors: Shuting Lin, Shuting Lin, , ,
| Summary:
We report the discovery of a dense molecular ring-like structure in a dense
(10$^5$ cm$^-3$), cold (pc-scale CO depletion at a factor of 5), and young
(10$^4$ year) star-forming region G34.74-0.12, revealed by C$^18$O (2-1), HNC
(1-0), and N$_2$H$^+$ (1-0) observations with the Atacama Large
Millimeter/submillimeter Array (ALMA). The ring-like structure is redshifted
with respect to the clump, spanning from $V_rm sys,lsr + 0.9$ to $V_rm
sys,lsr + 2.9$ km s$^-1$, with a total mass of 109 $M_odot$. It is
spatially coincident with 1.3 mm and 3.0 mm dust continuum emission from cores,
and several protostellar outflows. However, no free-free emission or
Htextscii region is detected in association with this structure. With a slow
expansion speed indicated by the position-velocity diagram, this ring structure
differs from rings previously identified in more evolved star-forming regions.
Possible explanations for the ring-like structure include a relic wind-blown
bubble produced by a deeply embedded young stellar object, a hollow cavity
formed by cloud-cloud interactions, a gas ring resulting from a temperature
gradient, or a line-of-sight superposition of multiple outflows or dense
clouds. This discovery offers a rare observational glimpse into the earliest
dynamical processes involved in massive star formation.
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