Molecular cloud abundances and anomalous diffusion

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.

4 pages, 8 figures

References in corpus (5)

• Interstellar Turbulence II: Implications and Effects
• Turbulent Structure of a Stratified Supernova-Driven Interstellar Medium
• Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions
• Mixing Time Scales in a Supernova-Driven Interstellar Medium
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