FOREST unbiased Galactic plane imaging survey with the Nobeyama 45 m telescope (FUGIN). VI. Dense gas and mini-starbursts in the W 43 giant molecular cloud complex

We performed new large-scale ¹²CO, ¹³CO, and C¹⁸O J = 1-0 observations of the W 43 giant molecular cloud complex in the tangential direction of the Scutum arm (l ∼30°) as a part of the FUGIN project. The low-density gas traced by ¹²CO is distributed over 150 pc × 100 pc (l × b), and has a large velocity dispersion (20-30 km s^-1). However, the dense gas traced by C¹⁸O is localized in the W 43 Main, G30.5, and W 43 South (G29.96-0.02) high-mass star-forming regions in the W 43 giant molecular cloud (GMC) complex, which have clumpy structures. We found at least two clouds with a velocity difference of ∼10-20 km s^-1, both of which are likely to be physically associated with these high-mass star-forming regions based on the results of high ¹³CO J = 3-2 to J = 1-0 intensity ratio and morphological correspondence with the infrared dust emission. The velocity separation of these clouds in W 43 Main, G30.5, and W 43 South is too large for each cloud to be gravitationally bound. We also revealed that the dense gas in the W 43 GMC has a high local column density, while "the current SFE" (star formation efficiency) of the entire GMC is low ( $\sim\!\! 4\%$ ) compared with the W 51 and M 17 GMC. We argue that the supersonic cloud-cloud collision hypothesis can explain the origin of the local mini-starbursts and dense gas formation in the W 43 GMC complex.