Molecular clouds have power-law probability distribution functions

Abstract

In this Letter we investigate the shape of the probability distribution of column densities (PDF) in molecular clouds. Through the use of low-noise, extinction-calibrated \textit{Herschel}/\textit{Planck} emission data for eight molecular clouds, we demonstrate that, contrary to common belief, the PDFs of molecular clouds are not described well by log-normal functions, but are instead power laws with exponents close to two and with breaks between $A_K\simeq 0.1$ and $0.2\mathrm{mag}$, so close to the CO self-shielding limit and not far from the transition between molecular and atomic gas. Additionally, we argue that the intrinsic functional form of the PDF cannot be securely determined below $A_K\simeq 0.1\mathrm{mag}$, limiting our ability to investigate more complex models for the shape of the cloud PDF.

Letter to the Editor, to appear in A&A

References in corpus (10)

• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• 2MASS wide field extinction maps - I. The Pipe nebula
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• Unfolding the Laws of Star Formation: The Density Distribution of Molecular Clouds
• NICEST, a near-infrared color excess method tailored for small-scale structures
• Understanding star formation in molecular clouds I. Effects of line-of-sight contamination on the column density structure
• 2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
• Herschel's view of the large-scale structure in the Chamaeleon dark clouds
• Evolving Molecular Cloud Structure and the Column Density Probability Distribution Function

Cited by in corpus (18)

• Multi-temperature mapping of dust structures throughout the Galactic Plane using the PPMAP tool with Herschel Hi-GAL data
• Evolution of column density distributions within Orion~A
• Numerical Simulations of Turbulent, Molecular Clouds Regulated by Radiation Feedback Forces I: Star Formation Rate and Efficiency
• Millimeter-Wave Line Ratios and Sub-beam Volume Density Distributions
• CO line emission from galaxies in the Epoch of Reionization
• The shapes of column density PDFs - The importance of the last closed contour
• The Razor's Edge of Collapse: The Transition Point from Lognormal to Powerlaw in Molecular Cloud PDFs
• Cloud Structure of Galactic OB Cluster Forming Regions from Combining Ground and Space Based Bolometric Observations
• HP2 survey: III The California Molecular Cloud--A Sleeping Giant Revisited
• Energy budget of forming clumps in numerical simulations of collapsing clouds
• The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds
• Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces II: Radiation-Gas Interactions and Outflows
• The Relationship between CO Emission and Visual Extinction Traced by Dust Emission in the Magellanic Clouds
• Identifying Tools for Comparing Simulations and Observations of Spectral-line Data Cubes
• Statistical link between the structure of molecular clouds and their density distribution
• The Effect of Magnetic Fields and Ambipolar Diffusion on the Column Density Probability Distribution Function in Molecular Clouds
• Quantifying the interplay between gravity and magnetic field in molecular clouds - a possible multi-scale energy equipartition in NGC6334
• On the star-forming ability of Molecular Clouds