The sonic scale does not determine the core separation in turbulent molecular clouds

Abstract

It has recently been suggested that the typical separation between cores in molecular clouds dominated by turbulence is determined by the sonic scale, the size scale at which the turbulent velocity dispersion equals the sound speed. In this work, we test this hypothesis using a suite of turbulent simulations with Mach numbers $\mathcal{M}=4$ and 8, and three turbulent forcing wavenumbers ($k_{\rm for}=2,4$ and 8). Dense cores are identified through dendrogram analysis of column density maps, and their separations are compared to the sonic scale measured from velocity structure functions. We find no statistical correlation between the core separation and the sonic scale nor with the driving scale. Instead, for each run, the core separation spans the entire range of values between these two scales. Our results indicate that fragmentation in turbulence-dominated clouds is not governed by an intrinsic scale in the turbulent cascade. This finding calls into question the use of the sonic scale as a predictive quantity in star formation theories and cautions against interpreting observational core spacings as evidence for universal turbulent fragmentation physics.