Evidence for a Cloud-Cloud Collision in Sh2-233 Triggering the Formation
  of the High-mass Protostar Object IRAS 05358+3543
  We have carried out a new kinematical analysis of the molecular gas in the
Sh2-233 region by using the CO $J$ = 2-1 data taken at $\sim$0.5 pc resolution.
The molecular gas consists of a filamentary cloud of 5-pc length with 1.5-pc
width where two dense cloud cores are embedded. The filament lies between two
clouds, which have a velocity difference of 2.6 km s$^{-1}$ and are extended
over $\sim$5 pc. We frame a scenario that the two clouds are colliding with
each other and compressed the gas between them to form the filament in
$\sim$0.5 Myr which is perpendicular to the collision. It is likely that the
collision formed not only the filamentary cloud but also the two dense cores.
One of the dense cores is associated with the high-mass protostellar candidate
IRAS 05358+3543, a representative high-mass protostar. In the monolithic
collapse scheme of high mass star formation, a compact dense core of 100
$M_\odot$ within a volume of 0.1 pc radius is assumed as the initial condition,
whereas the formation of such a core remained unexplained in the previous
works. We argue that the proposed collision is a step which efficiently
collects the gas of 100 $M_\odot$ into 0.1 pc radius. This lends support for
that the cloud-cloud collision is an essential process in forming the compact
high-mass dense core, IRAS 05358+3543.
