The Effects of Magnetic Diffusion and Cosmic-rays on Thermal Instability

In this study, we consider the effects of the cosmic rays and the magnetic diffusion on the thermal instability in the interstellar mediums. The dynamical effect as well as the heating effect of the cosmic rays are investigated on the thermal condensation in a medium where the cosmic rays diffuse along the magnetic field lines and the magnetic diffusion is present. Two separate profiles, i.e. constant field and force-free field, are considered for the magnetic field of the medium background. The linear perturbation analysis is used for the study of the thermal instability in a medium with a point of view on the previous works. The results show that the cosmic rays reduce the growth rate of the magnetothermal condensation mode, and increase the domains of stability. However, the magnetic diffusion shows two different behaviors which depend on a number of conditions affecting the magnetic diffusivity. In other words, the magnetic diffusion increases the domains of stability for cases less than a certain value of magnetic diffusivity, and decrease the domains of stability for cases larger than this certain value. Furthermore, we found that the dynamical effect of the magnetic diffusion dominates the dynamical effect of the cosmic rays. Finally, the results address some regions in which the fragmentation of the clouds into clumps and cores can be seen with the magnetothermal condensation effects.