Kavli Affiliate: Lile Wang
| First 5 Authors: Shuting Lin, Shuting Lin, , ,
| Summary:
Outflows are key indicators of ongoing star formation. We report the
discovery of an unanchored forked stream within the propagating path of an
extremely young protostellar outflow in the 70 $mu$m-dark clump G34.74-0.12,
based on ALMA 1.3 mm observations with an angular resolution of 1”.6 (~ 5000
au). This outflow originate from a 9.7 $M_odot$ core, exhibits a fork-shaped
stream structure in its red-shifted lobe, which is traced by CO (2-1), SiO
(5-4), and H$_2$CO (3$_0,3$-2$_0,2$). It has a momentum of 13 $M_odot$
km s$^-1$, an energy of 107 $M_odot$ km$^2$ s$^-2$, and a dynamical
timescale of ~10$^4$ yr. Significantly, the enhanced relative abundances of
SiO, H$_2$CO, and CH$_3$OH with respect to CO, along with the increased
temperature at the forked point, indicate a collisional origin. The forked
point does not coincide with any dust continuum core > 0.1 $M_odot$.
Moreover, CO (2-1) emission also traces three other outflows in this region,
characterized by their masses (0.40, 0.02 and 0.15 $M_odot$) and momenta
(5.2, 0.2, 1.8 $M_odot$ km s$^-1$), as part of the ALMA Survey of 70
$mu$m dark High-mass clumps in Early Stages (ASHES) project. All the newly
discovered morphological and kinematic features associated with these extremely
young protostellar outflows (with timescales of 10$^3$ – 10$^4$ years) suggest
that the initial stages of star formation are more complicated than previously
understood.
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