Query : 2014A&A...565A..24F

2014A&A...565A..24F - Astronomy and Astrophysics, volume 565A, 24-24 (2014/5-1)

On the probability distribution function of the mass surface density of molecular clouds. I.


Abstract (from CDS):

The probability distribution function (PDF) of the mass surface density is an essential characteristic of the structure of molecular clouds or the interstellar medium in general. Observations of the PDF of molecular clouds indicate a composition of a broad distribution around the maximum and a decreasing tail at high mass surface densities. The first component is attributed to the random distribution of gas which is modeled using a log-normal function while the second component is attributed to condensed structures modeled using a simple power-law. The aim of this paper is to provide an analytical model of the PDF of condensed structures which can be used by observers to extract information about the condensations. The condensed structures are considered to be either spheres or cylinders with a truncated radial density profile at cloud radius rcl. The assumed profile is of the form ρ(r)=ρc/(1+(r/r0)2)n/2 for arbitrary power n where ρc and r0 are the central density and the inner radius, respectively. An implicit function is obtained which either truncates (sphere) or has a pole (cylinder) at maximal mass surface density. The PDF of spherical condensations and the asymptotic PDF of cylinders in the limit of infinite overdensity ρc/ρ(rcl) flattens for steeper density profiles and has a power law asymptote at low and high mass surface densities and a well defined maximum. The power index of the asymptote Σ–γ of the logarithmic PDF (ΣP(Σ)) in the limit of high mass surface densities is given by γ=(n+1)/(n-1)-1 (spheres) or by γ=n/(n-1)-1 (cylinders in the limit of infinite overdensity).

Abstract Copyright:

Journal keyword(s): ISM: clouds - ISM: structure - methods: analytical - methods: statistical

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NAME Taurus Complex SFR 04 41.0 +25 52           ~ 4253 0
2 NAME Rosette Molecular Cloud MoC 06 34.7 +04 02           ~ 259 0
3 NAME Coalsack Nebula DNe 12 31 19 -63 44.6           ~ 256 0
4 Lupus 5 MoC 16 21 -37.5           ~ 63 0

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