Thermal wind from hot accretion flows at large radii

Abstract

We study slowly rotating accretion flow at parsec and sub-parsec scale irradiated by a low luminosity active galactic nuclei. We take into account the Compton heating, photoionization heating by the central X-rays. The bremsstrahlung cooling, recombination and line cooling are also included. We find that due to the Compton heating, wind can be thermally driven. The power of wind is in the range $(10^{-6}-10^{-3}) L_{\rm Edd}$, with $L_{\rm Edd}$ being the Eddington luminosity. The mass flux of wind is in the range $(0.01-1) \dot M_{\rm Edd}$ ($\dot M_{\rm Edd}= L_{\rm Edd}/0.1c^2$ is the Eddington accretion rate, $c$ is speed of light). We define the wind generation efficiency as $\epsilon = P_W/\dot {M}_{\rm BH}c^2$, with $P_W$ being wind power, $\dot M_{\rm BH}$ being the mass accretion rate onto the black hole. $\epsilon$ lies in the rage $10^{-4}-1.18$. Wind production efficiency decreases with increasing mass accretion rate. The possible role of the thermally driven wind in the active galactic feedback is briefly discussed.