Formation of the young massive cluster R136 triggered by tidally-driven colliding H i flows

Abstract

Abstract Understanding massive cluster formation is one of the important issues of astronomy. By analyzing the H i data, we have identified that the two H i velocity components (L- and D-components) are colliding toward the H i Ridge, in the southeastern end of the Large Magellanic Cloud (LMC), which hosts the young massive cluster R136 and ∼400 O/Wolf–Rayet stars (Doran et al. 2013, A&A, 558, A134) including the progenitor of SN 1987A. The collision is possibly evidenced by bridge features connecting the two H i components and by 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 H i Ridge and the Molecular Ridge. Fujimoto and Noguchi (1990, PASJ, 42, 505) advocated that the last tidal interaction between the LMC and the Small Magellanic Cloud (SMC) induced collision of the L- and D-components about 0.2 Gyr ago. This model is consistent with numerical simulations (Bekki & Chiba 2007a, MNRAS, 381, L16). We suggest that a dense H i, cloud of 106 M⊙ partly including CO, 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-metallicity gas from the SMC was mixed in the tidal interaction based on the Planck/IRAS data of dust optical depth (Planck Collaboration 2014, A&A, 571, A11).