Molecular Clouds: Internal Properties, Turbulence, Star Formation and Feedback

TL;DR

This paper reviews the properties, dynamics, and star formation processes in molecular clouds, emphasizing turbulence, feedback, and the formation of star clusters within giant molecular clouds.

Contribution

It provides a comprehensive synthesis of observational and theoretical insights into GMCs, highlighting the role of turbulence, collisions, and feedback in star formation.

Findings

Most GMCs are gravitationally bound.

Star formation within GMCs is highly clustered but inefficient.

Feedback mechanisms regulate star formation efficiency.

Abstract

All stars are born in molecular clouds, and most in giant molecular clouds (GMCs), which thus set the star formation activity of galaxies. We first review their observed properties, including measures of mass surface density, Sigma, and thus mass, M. We discuss cloud dynamics, concluding most GMCs are gravitationally bound. Star formation is highly clustered within GMCs, but overall is very inefficient. We compare properties of star-forming clumps with those of young stellar clusters (YSCs). The high central densities of YSCs may result via dynamical evolution of already-formed stars during and after star cluster formation. We discuss theoretical models of GMC evolution, especially addressing how turbulence is maintained, and emphasizing the importance of GMC collisions. We describe how feedback limits total star formation efficiency, epsilon, in clumps. A turbulent and clumpy medium allows higher epsilon, permitting formation of bound clusters even when escape speeds are less than the ionized gas sound speed.