Density Power Spectrum in Turbulent Thermally Bi-stable Flows

TL;DR

This study investigates how the density power spectrum in turbulent thermally bistable flows varies with Mach number, revealing that higher turbulence levels lead to shallower density spectra and steeper velocity spectra, aligning with observations.

Contribution

It provides the first systematic numerical analysis of the density and velocity power spectra across a range of Mach numbers in thermally bistable turbulent flows.

Findings

Density spectrum becomes shallower with increasing Mach number.

Velocity spectrum steepens as Mach number increases.

Simulation results match observational spectral indexes.

Abstract

In this paper we numerically study the behavior of the density power spectrum in turbulent thermally bistable flows. We analyze a set of five three-dimensional simulations where turbulence is randomly driven in Fourier space at a fixed wave-number and with different Mach numbers M (with respect to the warm medium) ranging from 0.2 to 4.5. The density power spectrum becomes shallower as M increases and the same is true for the column density power spectrum. This trend is interpreted as a consequence of the simultaneous turbulent compressions, thermal instability generated density fluctuations, and the weakening of thermal pressure force in diffuse gas. This behavior is consistent with the fact that observationally determined spectra exhibit different slopes in different regions. The values of the spectral indexes resulting from our simulations are consistent with observational values. We do also explore the behavior of the velocity power spectrum, which becomes steeper as M increases. The spectral index goes from a value much shallower than the Kolmogorov one for M=0.2 to a value steeper than the Kolmogorov one for M=4.5.