Detailed CO ($J$ = 1--0, 2--1 and 3--2) observations toward an H{\sc ii}
  region RCW~32 in the Vela Molecular Ridge
  We made CO ($J$ = 1--0, 2--1, and 3--2) observations toward an H{\sc ii}
region RCW~32 in the Vela Molecular Ridge. The CO gas distribution associated
with the H{\sc ii} region was revealed for the first time at a high resolution
of 22 arcsec. The results revealed three distinct velocity components which
show correspondence with the optical dark lanes and/or H$\alpha$ distribution.
Two of the components show complementary spatial distribution which suggests
collisional interaction between them at a relative velocity of $\sim$4
km~s$^{-1}$. Based on these results, we present a hypothesis that cloud-cloud
collision determined the cloud distribution and triggered formation of the
exciting star ionizing RCW~32. The collision time scale is estimated from the
cloud size and the velocity separation to be $\sim$2 Myrs and the collision
terminated $\sim$1 Myr ago, which is consistent with an age of the exciting
star and the associated cluster. By combing the previous works on the H{\sc ii}
regions in the Vela Molecular Ridge, we argue that the majority, at least four,
of the H{\sc ii} regions in the Ridge were formed by triggering of cloud-cloud
collision.
