Mass-density relationship in molecular cloud clumps

TL;DR

This paper investigates how mass and density relate in molecular cloud clumps, revealing a scale-dependent power-law relationship influenced by energy balances and turbulence, consistent with observations.

Contribution

It introduces a statistical model linking mass-density exponents to energy equipartitions and turbulence, highlighting scale dependence and the impact of magnetic energy.

Findings

Mass-density exponent varies between -2.5 and -0.2 across scales.

Exponent depends on energy relations and turbulence laws.

Results align with observational data.

Abstract

We study the mass-density relationship n ~ m^x in molecular cloud condensations (clumps), considering various equipartition relations between their gravitational, kinetic, internal and magnetic energies. Clumps are described statistically, with a density distribution that reflects a lognormal probability density function (pdf) in turbulent cold interstellar medium. The clump mass-density exponent $x$ derived at different scales $L$ varies in most of the cases within the range $-2.5\lesssim x \lesssim-0.2$, with a pronounced scale dependence and in consistency with observations. When derived from the global size-mass relationship m ~ l^{\gamma_{glob}} for set of clumps, generated at all scales, the clump mass-density exponent has typical values $-3.0\lesssim x(\gamma_{glob}) \lesssim -0.3$ that depend on the forms of energy, included in the equipartition relations and on the velocity scaling law whereas the description of clump geometry is important when magnetic energy is taken into account.