SOFIA observations of S106: Dynamics of the warm gas
  Context. The HII region/PDR/molecular cloud complex S106 is excited by a
single O-star. The full extent of the warm and dense gas close to the star has
not been mapped in spectrally resolved high-J CO or [CII] lines, so the
kinematics of the warm, partially ionized gas, are unknown. Whether the
prominent dark lane bisecting the hourglass-shaped nebula is due solely to the
shadow cast by a small disk around the exciting star or also to extinction in
high column foreground gas was an open question until now. Aims. To disentangle
the morphology and kinematics of warm neutral and ionized gas close to the
star, study their relation to the bulk of the molecular gas, and to investigate
the nature of the dark lane. Methods. We use the heterodyne receiver GREAT on
board SOFIA to observe velocity resolved spectral lines of [C II] and CO 11-10
in comparison with so far unpublished submm continuum data at 350 micron
(SHARC-II) and complementary molecular line data. Results. The high angular and
spectral resolution observations show a very complex morphology and kinematics
of the inner S106 region, with many different components at different
excitation conditions contributing to the observed emission. The [C II] lines
are found to be bright and very broad, tracing high velocity gas close to the
interface of molecular cloud and HII region. CO 11-10 emission is more
confined, both spatially and in velocity, to the immediate surroundings of S106
IR showing the presence of warm, high density (clumpy) gas. Our high angular
resolution submm continuum observations rule out the scenario where the dark
lane separating the two lobes is due solely to the shadow cast by a small disk
close to the star. The lane is clearly seen also as warm, high column density
gas at the boundary of the molecular cloud and HII region.
