Modelling the structure of molecular clouds: I. A multi-scale energy equipartition

TL;DR

This paper introduces a multi-scale energy equipartition model to describe the structure of molecular clouds at early stages, linking size, energy balance, and density distribution, applicable to both star-forming and non-star-forming regions.

Contribution

It presents a novel model connecting energy equipartition, size, and density in molecular clouds, incorporating scale-dependent relations and lognormal density distributions.

Findings

Best fits for low star formation regions like Pipe and Polaris.

Model applies to star-forming regions with lognormal column density.

Numerical tests support applicability to early cloud evolution before star formation.

Abstract

We present a model for describing the general structure of molecular clouds (MCs) at early evolutionary stages in terms of their mass-size relationship. Sizes are defined through threshold levels at which equipartitions between gravitational, turbulent and thermal energy $|W| \sim f(E_{\rm kin} + E_{\rm th})$ take place, adopting interdependent scaling relations of velocity dispersion and density and assuming a lognormal density distribution at each scale. Variations of the equipartition coefficient $1\le f\le 4$ allow for modelling of star-forming regions at scales within the size range of typical MCs ($\gtrsim$4 pc). Best fits are obtained for regions with low or no star formation (Pipe, Polaris) as well for such with star-forming activity but with nearly lognormal distribution of column density (Rosette). An additional numerical test of the model suggests its applicability to cloud evolutionary times prior to the formation of first stars.