A Large-Scale CO Mapping of the Central Region of W 51

Abstract

Abstract We present a high-resolution (16$^{\prime\prime}$) ${{13\atop} \mathrm{CO}}$ ($J= 1$−$0$) map of the central region of W 51. We observed an area of about ${15\rlap {.}{}^{\mathrm {\prime }}3}\times {16\rlap {.}{}^{\mathrm {\prime }}7}$, which covers the entire region of G49.5–0.4, the brightest source in the W 51 region. Four discrete molecular clouds were identified toward G49.5–0.4, and evidence of cloud–cloud collisions was found. We speculate that a “pileup” of three molecular clouds resulted in a burst of massive star formation in G49.5–0.4.