2016ApJ...828..100F

We present observations toward a high-mass (\gt 40 {M}_☉), low-luminosity (\lt 10 L_☉) 70 µm dark molecular core G28.34 S-A at 3.4 mm, using the IRAM 30 m telescope and the NOEMA interferometer. We report the detection of SiOJ=2→1 line emission, which is spatially resolved in this source at a linear resolution of ∼0.1 pc, while the 3.4 mm continuum image does not resolve any internal sub-structures. The SiO emission exhibits two W-E oriented lobes centering on the continuum peak. Corresponding to the redshifted and blueshifted gas with velocities up to 40 km {s}^{-1} relative to the quiescent cloud, these lobes clearly indicate the presence of a strong bipolar outflow from this 70 µm dark core, a source previously considered as one of the best candidates of "starless" core. Our SiO detection is consistent with ALMA archival data of SiOJ=5→4, whose high-velocity blueshifted gas reveals a more compact lobe spatially closer to the dust center. This outflow indicates that the central source may be in an early evolutionary stage of forming a high-mass protostar. We also find that the low-velocity components (in the range of Vlsr_{-5}^{{+3} km {s}}{-1}) have an extended, NW-SE oriented distribution. Discussing the possible accretion scenarios of the outflow-powering young stellar object, we argue that molecular line emission and the molecular outflows may provide a better indication of the accretion history of the forming young stellar object, than snapshot observations of the present bolometric luminosity. This is particularly significant for cases of episodic accretion, which may occur during the collapse of the parent molecular core.