SiO collimated outflows driven by high-mass YSOs in G24.78+0.08
  We imaged the molecular outflows towards the cluster of high-mass young
stellar objects G24.78+0.08 at high-angular resolution using SiO emission,
which is considered the classical tracer of protostellar jets. We performed SiO
observations with the VLA interferometer in the J = 1-0 v=0 transition and with
the SMA array in the 5-4 transition. A complementary IRAM 30-m single-dish
survey in the (2-1), (3-2), (5-4), and (6-5) SiO lines was also carried out.
Two collimated SiO high-velocity outflows driven by the A2 and C millimeter
continuum massive cores have been imaged. On the other hand, we detected no SiO
outflow driven by the young stellar objects in more evolved evolutionary phases
that are associated with ultracompact (B) or hypercompact (A1) HII regions. The
LVG analysis reveals high-density gas (10^3-10^4 cm-3), with well constrained
SiO column densities (0.5-1 10^15 cm-2). The driving source of the A2 outflow
is associated with typical hot core tracers such as methyl formate, vinyl
cyanide, cyanoacetilene, and acetone. The driving source of the main SiO
outflow in G24 has an estimated luminosity of a few 10^4 Lsun (typical of a
late O-type star) and is embedded in the 1.3 mm continuum core A2, which in
turn is located at the centre of a hot core that rotates on a plane
perpendicular to the outflow main axis. The present SiO images support a
scenario similar to the low-mass case for massive star formation, where jets
that are clearly traced by SiO emission, create outflows of swept-up ambient
gas usually traced by CO.
