Discovery of Star Formation in the Extreme Outer Galaxy Possibly Induced
  by a High-velocity Cloud Impact
  We report the discovery of star formation activity in perhaps the most
distant molecular cloud in the extreme outer galaxy. We performed deep near
infrared imaging with the Subaru 8.2 m telescope, and found two young embedded
clusters at two CO peaks of Digel Cloud 1 at the kinematic distance of D = 16
kpc (Galactocentric radius RG = 22 kpc). We identified 18 and 45 cluster
members in the two peaks, and the estimated stellar density are ~ 5 and ~ 3
pc^-2, respectively. The observed K-band luminosity function suggests that the
age of the clusters is less than 1 Myr and also the distance to the clusters is
consistent with the kinematic distance. On the sky, Cloud 1 is located very
close to the H I peak of high-velocity cloud (HVC) Complex H, and there are
some H I intermediate velocity structures between the Complex H and the
Galactic disk, which could indicate an interaction between them. We suggest
possibility that Complex H impacting on the Galactic disk has triggered star
formation in Cloud 1 as well as the formation of Cloud 1 molecular cloud.
