Formation of the Young Massive Cluster R136 triggered by Tidally-driven
  Colliding HI Flows
  Understanding of massive cluster formation is one of the important issues of
astronomy. By analyzing the HI data, we have identified that the two HI
velocity components (L- and D-components) are colliding toward the HI Ridge, in
the southeastern end of the LMC, which hosts the young massive cluster R136 and
$\sim$400 O/WR stars (Doran et al. 2013) including the progenitor of SN1987A.
The collision is possibly evidenced by bridge features connecting the two HI
components and complementary distributions between them. We frame a hypothesis
that the collision triggered the formation of R136 and the surrounding
high-mass stars as well as the HI & Molecular Ridge. Fujimoto & Noguchi (1990)
advocated that the last tidal interaction between the LMC and the SMC about 0.2
Gyr ago induced collision of the L- and D-components. This model is consistent
with numerical simulations (Bekki & Chiba 2007b). We suggest that a dense HI
partly CO cloud of 10$^{6}$ $M_{\odot}$, a precursor of R136, was formed at the
shock-compressed interface between the colliding L- and D-components. We
suggest that part of the low-metalicity gas from the SMC was mixed in the tidal
interaction based on the $Planck/IRAS$ data of dust optical depth (Planck
Collaboration et al. 2014).
