On the shape and completeness of the column density probability distribution function of molecular clouds. Issue 4 (10th November 2018)

• Record Type: Journal Article
• Authors: Körtgen, Bastian; Federrath, Christoph; Banerjee, Robi
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 482:Issue 4(2019)
• Page Start: 5233
• Page End: 5240
• Publication Date: 2018-11-10
• Subjects: MHD -- turbulence -- methods: numerical -- stars: formation -- ISM: clouds -- ISM: kinematics and dynamics; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty3071
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Both observational and theoretical research over the past decade has demonstrated that the probability distribution function (PDF) of the gas density in turbulent molecular clouds is a key ingredient for understanding star formation. It has recently been argued that the PDF of molecular clouds is a pure power-law distribution. It has been claimed that the log-normal part is ruled out when using only the part of the PDF up/down to which it is complete, that is where the column density contours are still closed. By using the results from high-resolution magnetohydrodynamical simulations of molecular cloud formation and evolution, we find that the column density PDF is indeed composed of a log-normal and, if including self-gravity, a power-law part. We show that insufficient sampling of a molecular cloud results in closed contours that cut-off the log-normal part. In contrast, systematically increasing the field of view and sampling the entire cloud yields a completeness limit at the lower column densities, which also recovers the log-normal part. This demonstrates that the field of view must be sufficiently large for the PDF to be complete down to its log-normal part, which has important implications for predictions of star formation activity based on the PDF.