SIMBAD references

Although there is a wealth of column density tracers for both the molecular and diffuse interstellar medium, there are few observational studies investigating the relationship between the density variance (σ²) and the sonic Mach number ( M_s). This is in part due to the fact that the σ²- M_s relationship is derived, via MHD simulations, for the three-dimensional (3D) density variance only, which is not a direct observable. We investigate the utility of a 2D column density σ²_Σ/Σ0 - M_s relationship using solenoidally driven isothermal MHD simulations and find that the best fit follows closely the form of the 3D density σ²_ρ/ρ0- M_s trend but includes a scaling parameter A such that σ²_ln(Σ/Σ0₎ = A x ln(1+b²M_s²), where A = 0.11 and b = 1/3. This relation is consistent with the observational data reported for the Taurus and IC 5146 molecular clouds with b = 0.5 and A = 0.16, and b = 0.5 and A = 0.12, respectively. These results open up the possibility of using the 2D column density values of σ² for investigations of the relation between the sonic Mach number and the probability distribution function (PDF) variance in addition to existing PDF sonic Mach number relations.