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

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 $⟨\rho {⟩}_L\propto L^{\alpha }$ is steep ($\alpha =-1.93$) in the former case and rather shallow ($\alpha =-0.77\pm 0.11$) 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 $⟨\rho {⟩}_L{u}_L^3/L$, 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.

Accepted for publication in MNRAS; 16 pages with Appendix, 15 figures

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• The Lognormal Probability Distribution Function of the Perseus Molecular Cloud: A Comparison of HI and Dust
• The Galactic Center Molecular Cloud Survey. II. A Lack of Dense Gas & Cloud Evolution along Galactic Center Orbits
• The Multi-phase Turbulence Density Power Spectra in the Perseus Molecular Cloud
• Criteria for gravitational instability and quasi-isolated gravitational collapse in turbulent medium
• Exact relations for energy transfer in self-gravitating isothermal turbulence
• On the extraction of power-law parts of the probability density functions in star-forming clouds
• Modelling the structure of molecular clouds: I. A multi-scale energy equipartition