Tracing the general structure of Galactic molecular clouds using Planck data: I. The Perseus region as a test case

TL;DR

This study analyzes the structure of the Perseus molecular cloud using Planck data, revealing two distinct physical regimes—gravoturbulent within the cloud and turbulent in its surroundings—based on probability distribution functions of dust opacity.

Contribution

It introduces a detailed analysis of column density PDFs in Perseus, identifying a transition between gravoturbulent and turbulent regimes through density scaling laws.

Findings

PDFs fit by lognormal plus power-law tail in Perseus

Steep density scaling law in the cloud, shallow in surroundings

Identification of a transition from gravoturbulent to turbulent regime

Abstract

We present an analysis of probability distribution functions (pdfs) of column density in different zones of the star-forming region Perseus and its diffuse environment based on the map of dust opacity at 353 GHz available from the Planck archive. The pdf shape can be fitted by a combination of a lognormal function and an extended power-law tail at high densities, in zones centred at the molecular cloud Perseus. A linear combination of several lognormals fits very well the pdf in rings surrounding the cloud or in zones of its diffuse neighbourhood. The slope of the mean density scaling law $\langle\rho\rangle_L \propto L^\alpha$ is steep ($\alpha=-1.93$) in the former case and rather shallow ($\alpha=-0.77\pm0.11$) in the rings delineated around the cloud. We interpret these findings as signatures of two distinct physical regimes: i) a gravoturbulent one which is characterized by nearly linear scaling of mass and practical lack of velocity scaling; and ii) a predominantly turbulent one which is best described by steep velocity scaling and by invariant for compressible turbulence $\langle\rho\rangle_L u_L^3/L$, describing a scale-independent flux of the kinetic energy per unit volume through turbulent cascade. The gravoturbulent spatial domain can be identified with the molecular cloud Perseus while a relatively sharp transition to predominantly turbulent regime occurs in its vicinity.