Revealing a spiral-shaped molecular cloud in our galaxy - Cloud fragmentation under rotation and gravity

TL;DR

This study investigates the role of rotation in molecular cloud evolution by analyzing a spiral-shaped Galactic cloud, revealing that rotation and gravity interplay to drive cloud fragmentation and star formation.

Contribution

It provides observational evidence that rotation influences cloud stability and fragmentation, a novel insight into star formation processes in spiral-shaped molecular clouds.

Findings

The cloud exhibits a regular velocity pattern consistent with rotational support.

The cloud is gravitationally unstable and prone to fragmentation.

Star formation occurs in gravitationally bound clumps.

Abstract

The dynamical processes that control star formation in molecular clouds are not well understood, and in particular, it is unclear if rotation plays a major role in cloud evolution. We investigate the importance of rotation in cloud evolution by studying the kinematic structure of a spiral-shaped Galactic molecular cloud G052.24+00.74. The cloud belongs to a large filament, and is stretching over ~ 100 pc above the Galactic disk midplane. The spiral-shaped morphology of the cloud suggests that the cloud is rotating. We have analysed the kinematic structure of the cloud, and study the fragmentation and star formation. We find that the cloud exhibits a regular velocity pattern along west-east direction - a velocity shift of ~ 10 km/s at a scale of ~ 30 pc. The kinematic structure of the cloud can be reasonably explained by a model that assumes rotational support. Similarly to our Galaxy, the cloud rotates with a prograde motion. We use the formalism of Toomre (1964) to study the cloud's stability, and find that it is unstable and should fragment. The separation of clumps can be consistently reproduced assuming gravitational instability, suggesting that fragmentation is determined by the interplay between rotation and gravity. Star formation occurs in massive, gravitational bound clumps.