Outflow detection in a 70 $\mu$m dark high-mass core
  We present observations towards a high-mass ($\rm >40\,M_{\odot}$), low
luminosity ($\rm <10\,L_{\odot}$) $\rm 70\,\mu$m dark molecular core G 28.34
S-A at 3.4 mm, using the IRAM 30 m telescope and the NOEMA interferometer. We
report the detection of $\rm SiO$ $J=\rm 2\rightarrow1$ line emission, which is
spatially resolved in this source at a linear resolution of $\sim$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 centring on the continuum peak.
Corresponding to the red-shifted and blue-shifted gas with velocities up to
$\rm 40\,km\,s^{-1}$ relative to the quiescent cloud, these lobes clearly
indicate the presence of a strong bipolar outflow from this $\rm 70\,\mu$m 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
$\rm SiO$ $J=\rm 5\rightarrow4$, whose high-velocity blue-shifted 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 $\rm V_{lsr}$$\rm_{-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 the molecular line
emission and the molecular outflows may provide a better indication of the
accretion history when forming young stellar object, than that from a snapshot
observations of the present bolometric luminosity. This is particularly
significant for the cases of episodic accretion, which may occur during the
collapse of the parent molecular core.
