NONLINEAR STUDY OF MAGNETOTHERMAL INSTABILITY IN COOLING FLOWS

We have performed two-dimensional numerical magnetohydrodynamical calculations in order to investigate the effects of magnetic field on the evolution of non-linear perturbations in cooling flows. We have shown that the vertical magnetic field can suppress vortex motion in a non-linear perturbation, and can help the growth of thermal instability. We have found that the vertical wavelength of perturbations cannot be larger than some critical value for the perturbations to be supported by the magnetic tension. This upper limit depends on the ratio of the gas pressure plasma to the magnetic pressure, plasma beta, in cooling flows, with the upper limit becoming smaller as the ratio becomes larger, and it is very small in the expected cooling flow environment of 0.017(beta/600)(-1) kpc. This small upper limit may be related to the suppression of massive-star formation in cooling flows.