On the star-forming ability of Molecular Clouds

TL;DR

This study investigates how the impact parameter in colliding flows influences the star-forming ability of molecular clouds, revealing that off-centre collisions lead to less efficient dense gas formation and potentially explain observed star-formation rate variations.

Contribution

The paper introduces self-gravitating hydrodynamic simulations of colliding flows with varying impact parameters, linking collision geometry to star-formation efficiency in molecular clouds.

Findings

Strong shear from off-centre collisions reduces dense gas formation.

Large impact parameter collisions can explain sluggish star-formation in some clouds.

Compressional modes alone are insufficient for high star-formation efficiency.

Abstract

The star-forming ability of a molecular cloud depends on the fraction of gas it can cycle into the dense-phase. Consequently, one of the crucial questions in reconciling star-formation in clouds is to understand the factors that control this process. While it is widely accepted that the variation in ambient conditions can alter significantly the ability of a cloud to spawn stars, the observed variation in the star-formation rate in nearby clouds that experience similar ambient conditions, presents an interesting question. In this work we attempted to reconcile this variation within the paradigm of colliding flows. To this end we develop self-gravitating, hydrodynamic realisations of identical flows, but allowed to collide off-centre. Typical observational diagnostics such as the gas-velocity dispersion, the fraction of dense-gas, the column density distribution ({\small N-PDF}), the distribution of gas mass as a function of $K$-band extinction and the strength of compressional/solenoidal modes in the post-collision cloud were deduced for different choices of the impact parameter of collision. We find that a strongly sheared cloud is terribly inefficient in cycling gas into the dense phase and that such a cloud can possibly reconcile the sluggish nature of star-formation reported for some clouds. Within the paradigm of cloud-formation via colliding flows this is possible in case of flows colliding with a relatively large impact parameter. We conclude that compressional modes - though probably essential - are insufficient to ensure a relatively higher star-formation efficiency in a cloud.