Linear thermal instability and formation of clumpy gas clouds including ambipolar diffusion

Abstract

Thermal instability is one of the most important processes in the formation of clumpy substructure in magnetic molecular clouds. On the other hand, ambipolar diffusion, or ion–neutral friction, has long been thought to be an important energy dissipation mechanism in these clouds. Thus, it would interesting to investigate the effect of ambipolar diffusion on the thermal instability and formation of clumps in the magnetic molecular clouds. For this purpose, as a first step, we turn our attention to the linear perturbation stage. In this way, we obtain a non-dimensional characteristic equation that reduces to the prior characteristic equation in the absence of the magnetic field and ambipolar diffusion. With numerical manipulation of this characteristic equation, we conclude that there are solutions where the thermal instability allows compression along the magnetic field but not perpendicular to it. We infer that this aspect might be in evidence in the formation of observed disc-like (oblate) clumps in magnetic molecular clouds.