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Sh2-48 is a Galactic HII region located at 3.8 kpc with an O9.5-type staridentified at its center. As a part of the FOREST Unbiased Galactic planeImaging survey using the Nobeyama 45-m telescope (FUGIN) project, we obtainedthe CO J=1-0 dataset for a large area of Sh2-48 at a spatial resolution of21"(~0.4 pc), which we used to find a molecular cloud with a total molecularmass of ~3.8x10^4 Mo associated with Sh2-48. The molecular cloud has asystematic velocity shift within a velocity range ~42-47 km/s . On the lowervelocity side the CO emission spatially corresponds with the bright 8 {\mu}mfilament at the western rim of Sh2-48, while the CO emission at highervelocities is separated at the eastern and western sides of the 8{\mu}mfilament. This velocity change forms V-shaped, east-west-oriented feature onthe position-velocity diagram. We found that these lower and higher-velocitycomponents are, unlike the infrared and radio continuum data, physicallyassociated with Sh2-48. To interpret the observed V-shaped velocitydistribution, we assessed a cloud-cloud collision scenario and found from acomparison between the observations and simulations that the velocitydistribution is an expected outcome of a collision between a cylindrical cloudand a spherical cloud, with the cylindrical cloud corresponding to thelower-velocity component, and the two separated components in thehigher-velocity part interpretable as the collision-broken remnants of thespherical cloud. Based on the consistency of the ~1.3Myr estimated formationtimescale of the HII region with that of the collision, we concluded that thehigh-mass star formation in Sh2-48 was triggered by the collision.

CO observations of the molecular gas in the galactic HII region Sh2-48; Evidence for cloud-cloud collision as a trigger of high-mass star formation