Alfven heating in optical filaments in cooling flows

Abstract

One of the major problems concerning cooling flows is the nature of the mechanism powering the emission lines of the optical filaments seen in the inner regions of cooling flows. In this work we investigate the plausibility of Alfvén heating (AH) as a heating/excitation mechanism of optical filaments in cooling flows. We use a time-dependent hydrodynamical code to follow the evolution of cooling condensations arising from the $10^7$ K cooling flow. The filaments contain magnetic fields and AH is at work at several degrees of efficiency (including no AH at all). We consider two damping mechanisms of Alfvén waves: nonlinear and turbulent. We calculate the optical line emission associated with the filaments and compare our results to the observations. We find that AH can be an important ionizing and heating source for class I filaments in the line-ratio scheme of Heckman et al. In addition, AH can be an important contributor to [OI]$λ6300$ emission even for the more luminous class II systems.