Thermal conduction in clumpy discs and BLR clouds

Abstract

ABSTRACT We investigate the dynamics of clumps that coexisted with/in advection-dominated accretion flows (ADAFs) by considering thermal conductivity. Thermal conduction can be one of the effective factors in the energy transportation of ADAFs; hence it may indirectly affect the dynamics of clumps by means of a contact force between them and their host medium. We first study the ensemble of clumps by assuming them as collisionless particles, and secondly we find the orbital motion of these clouds as individuals. For both parts, clumps are subject to the gravity of the central object and a drag force. The strong coupling between clumps and ADAF leads to equality between the average treatment of the clumps and the dynamics of their background. By employing the collisionless Boltzmann equation, we calculate the velocity dispersion of the clumps, which turns out to be approximately one order of magnitude higher than the ADAF. In fact, involving drag force in such a system causes the angular momentum of the clumps to be transported outwards by the ADAF, and hence the clouds eventually will be captured at the tidal radius. The results show that the presence of thermal conduction increases the root of the averaged radial velocity square, and this, in turn, speeds up the process of capturing the clouds through the tidal force. In the end, we focus on a typical individual cloud; the spiral orbits appear only due to the toroidal component of friction force. The parametric study again proves that the operation of thermal conduction helps in decreasing the lifetime of clumps.