Molecular cloud abundances and anomalous diffusion

TL;DR

This paper investigates how anomalous superdiffusion, unlike simple Fickian diffusion, significantly impacts molecular abundances in interstellar clouds, revealing complex and nontrivial effects on chemical distributions.

Contribution

It introduces the consideration of superdiffusion in molecular cloud chemistry modeling, highlighting its substantial influence on molecular abundances and challenging traditional diffusion assumptions.

Findings

Superdiffusion alters molecular abundances by factors of order unity.

The influence of superdiffusion on chemical distributions is highly nontrivial.

Results suggest the need to incorporate anomalous diffusion in astrophysical models.

Abstract

The chemistry of molecular clouds has been studied for decades, with an increasingly general and sophisticated treatment of the reactions involved. Yet the treatment of turbulent diffusion has remained extremely sketchy, assuming simple Fickian diffusion with a scalar diffusivity D. However, turbulent flows similar to those in the interstellar medium are known to give rise to anomalous diffusion phenomena, more specifically superdiffusion (increase of the diffusivity with the spatial scales involved). This paper considers to what extent and in what sense superdiffusion modifies molecular abundances in interstellar clouds. For this first exploration of the subject we employ a very rough treatment of the chemistry and the effect of non-unifom cloud density on the diffusion equation is also treated in a simplified way. The results nevertheless clearly demonstrate that the effect of superdiffusion is quite significant, abundance values at a given radius being modified by order of unity factors. The sense and character of this influence is highly nontrivial.