MAGNETOHYDRODYNAMIC NUMERICAL SIMULATION OF WIND PRODUCTION FROM HOT ACCRETION FLOWS AROUND BLACK HOLES AT VERY LARGE RADII

Numerical simulations of hot accretion flows around black holes have shown the existence of strong wind. Those works focused only on the region close to the black hole and thus it is unknown whether or where the wind production stops at large radii. To address this question, we have recently performed hydrodynamic (HD) simulations by taking into account the gravitational potential of both the black hole and the nuclear star cluster. The latter is assumed to be proportional to sigma(2) ln (r), with sigma being the velocity dispersion of stars and r the distance from the center of the galaxy. It was found that when the gravity is dominated by nuclear stars, i.e., outside a radius R-A GM(BH) / sigma(2), winds can no longer be produced. That work, however, neglects the magnetic field, which is believed to play a crucial dynamical role in the accretion and thus must be taken into account. In this paper, we revisit this problem by performing magnetohydrodynamic (MHD) simulations. We confirm the result of our previous paper, namely that wind cannot be produced in the region R > R-A. Our result, combined with recent results of Yuan et al., indicates that the formula describing the mass flux of wind, M-wind = M-BH(r/20r(s)), can only be applied to the region where the black hole potential is dominant. Here M-BH is the mass accretion rate at the black hole horizon and the value of R-A is similar to the Bondi radius.