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NGC 2359 is an HII region located in the outer Galaxy that contains theisolated Wolf-Rayet (WR) star HD 56925. We present millimeter/submillimeterobservations of $^{12}$CO($J$ = 1-0, 3-2) line emission toward the entirenebula. We identified that there are three molecular clouds at VLSR $\sim$37,$\sim$54, and $\sim$67 km s$^{-1}$, and three HI clouds: two of them are atVLSR $\sim$54 km s$^{-1}$ and the other is at $\sim$63 km s$^{-1}$. Theseclouds except for the CO cloud at 67 km s$^{-1}$ are limb-brightened in theradio continuum, suggesting part of each cloud has been ionized. We newly foundan expanding gas motion of CO/HI, whose center and expansion velocities are$\sim$51 and $\sim$4.5 km s$^{-1}$, respectively. This is consistent with largeline widths of the CO and HI clouds at 54 km s$^{-1}$. The kinematictemperature of CO clouds at 37 and 54 km s$^{-1}$ are derived to be 17 and 61K, respectively, whereas that of the CO cloud at 67 km s$^{-1}$ is only 6 K,indicating that the former two clouds have been heated by strong UV radiation.We concluded that the 37 and 54 km s$^{-1}$ CO clouds and three HI clouds areassociated with NGC 2359, even if these clouds have different velocities.Although the velocity difference including the expanding motion are typicalsignatures of the stellar feedback from the exciting star, our analysisrevealed that the observed large momentum for the 37 km s$^{-1}$ CO cloudcannot be explained only by the total wind momentum of the WR star and itsprogenitor. We therefore propose an alternative scenario that the isolatedhigh-mass progenitor of HD 56925 was formed by a collision between the COclouds at 37 and 54 km s$^{-1}$. If we apply the collision scenario, NGC 2359corresponds to the final phase of the cloud-cloud collision.

Molecular and Atomic Clouds toward the Wolf-Rayet Nebula NGC 2359:  Possible Evidence for Isolated High-Mass Star Formation Triggered by a  Cloud-Cloud Collision