High-mass star formation triggered by collision between CO filaments in
  N159 West in the Large Magellanic Cloud
  We have carried out 13CO(J=2-1) observations of the active star-forming
region N159 West in the LMC with ALMA. We have found that the CO distribution
at a sub-pc scale is highly elongated with a small width. These elongated
clouds called "filaments" show straight or curved distributions with a typical
width of 0.5-1.0pc and a length of 5-10pc. All the known infrared YSOs are
located toward the filaments. We have found broad CO wings of two molecular
outflows toward young high-mass stars in N159W-N and N159W-S, whose dynamical
timescale is ~10^4 yrs. This is the first discovery of protostellar outflow in
external galaxies. For N159W-S which is located toward an intersection of two
filaments we set up a hypothesis that the two filaments collided with each
other ~10^5 yrs ago and triggered formation of the high-mass star having ~37
Mo. The colliding clouds show significant enhancement in linewidth in the
intersection, suggesting excitation of turbulence in the shocked interface
layer between them as is consistent with the magneto-hydro-dynamical numerical
simulations (Inoue & Fukui 2013). This turbulence increases the mass accretion
rate to ~6x10^-4 Mo yr^-1, which is required to overcome the stellar feedback
to form the high-mass star.
