Physics of Non-Universal Larson's Relation

TL;DR

This paper re-examines the Larson's Relation in interstellar clouds, deriving a new form based on turbulence and self-gravity, and shows that its amplitude varies across different galactic environments.

Contribution

It introduces a revised Larson's Relation incorporating the virial parameter and turbulence spectrum, and demonstrates its non-universality across galactic regions.

Findings

New Larson's Relation form with a 3/5 power law

Amplitude of Larson's Relation varies between Galactic disk and center

Observational data supports non-universality of turbulence strength

Abstract

From a new perspective, we re-examine self-gravity and turbulence jointly, in hopes of understanding the physical basis for one of the most important empirical relations governing clouds in the interstellar medium (ISM), the Larson's Relation relating velocity dispersion ($\sigma_R$) to cloud size ($R$). We report on two key new findings. First, the correct form of the Larson's Relation is $\sigma_R=\alpha_v^{1/5}\sigma_{pc}(R/1pc)^{3/5}$, where $\alpha_v$ is the virial parameter of clouds and $\sigma_{pc}$ is the strength of the turbulence, if the turbulence has the Kolmogorov spectrum. Second, the amplitude of the Larson's Relation, $\sigma_{pc}$, is not universal, differing by a factor of about two between clouds on the Galactic disk and those at the Galactic center, evidenced by observational data.