Detailed CO ($J$ = 1--0, 2--1 and 3--2) observations toward an H{\sc ii} region RCW~32 in the Vela Molecular Ridge

TL;DR

This study presents high-resolution CO observations of the RCW 32 HII region, revealing cloud interactions and proposing cloud-cloud collision as a trigger for star formation, with implications for multiple regions in the Vela Molecular Ridge.

Contribution

First high-resolution CO mapping of RCW 32 revealing cloud interactions and proposing cloud-cloud collision as a star formation trigger.

Findings

Three distinct velocity components identified.

Evidence of collisional interaction at ~4 km/s.

Collision likely triggered star formation ~2 Myr ago.

Abstract

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.