The Global Evolution of Giant Molecular Clouds II: The Role of Accretion

TL;DR

This paper develops virial models incorporating accretion to explain the evolution of giant molecular clouds, matching observed scaling relations and providing insights into their growth, turbulence, and star formation feedback.

Contribution

It introduces a virial model that includes accretion effects, accurately reproducing observed properties and evolution of giant molecular clouds.

Findings

Accretion and star formation contribute equally to turbulence.

Clouds maintain constant surface densities around 50-200 Msun/pc^2.

Linewidth-size relation acts as an age indicator.

Abstract

We present virial models for the global evolution of giant molecular clouds. Focusing on the presence of an accretion flow, and accounting for the amount of mass, momentum, and energy supplied by accretion and star formation feedback, we are able to follow the growth, evolution, and dispersal of individual giant molecular clouds. Our model clouds reproduce the scaling relations observed in both galactic and extragalactic clouds. We find that accretion and star formation contribute contribute roughly equal amounts of turbulent kinetic energy over the lifetime of the cloud. Clouds attain virial equilibrium and grow in such a way as to maintain roughly constant surface densities, with typical surface densities of order 50 - 200 Msun pc^-2, in good agreement with observations of giant molecular clouds in the Milky Way and nearby external galaxies. We find that as clouds grow, their velocity dispersion and radius must also increase, implying that the linewidth-size relation constitutes an age sequence. Lastly, we compare our models to observations of giant molecular clouds and associated young star clusters in the LMC and find good agreement between our model clouds and the observed relationship between H ii regions, young star clusters, and giant molecular clouds.