# A new look at the molecular gas in M42 and M43; possible evidence for cloud-cloud collision which triggered formation of the OB stars in the Orion Nebula Cluster

## TL;DR

This study analyzes molecular data of the Orion Nebula to suggest that cloud-cloud collision likely triggered the formation of high-mass stars in M42 and M43, providing evidence for a rapid star formation process.

## Contribution

It presents new evidence of cloud-cloud collision in Orion, linking it to high-mass star formation, based on detailed molecular data analysis and comparison with other cases.

## Key findings

- Identification of complementary velocity components suggesting cloud collision
- Estimated collision timescale of ~0.1 Myr matching young star ages
- Support for cloud collision as a trigger for high-mass star formation in Orion

## Abstract

The Orion Nebula Cluster toward the HII region M42 is the most outstanding young cluster at the smallest distance 410pc among the rich high-mass stellar clusters. By newly analyzing the archival molecular data of the 12CO(J=1-0) emission at 21" resolution, we identified at least three pairs of complementary distributions between two velocity components at 8km/s and 13km/s. We present a hypothesis that the two clouds collided with each other and triggered formation of the high-mass stars, mainly toward two regions including the nearly ten O stars, theta1 Ori and theta2 Ori, in M42 and the B star, NU Ori, in M43. The timescale of the collision is estimated to be ~0.1Myr by a ratio of the cloud size and velocity corrected for projection, which is consistent with the age of the youngest cluster members less than 0.1Myr. The majority of the low-mass cluster members were formed prior to the collision in the last one Myr. We discuss implications of the present hypothesis and the scenario of high-mass star formation by comparing with the other eight cases of triggered O star formation via cloud-cloud collision.