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Black Hole Outflows

I show that Eddington accretion episodes in AGN are likely to produce winds with velocities $v \sim 0.1c$ and ionization parameters up to $ξ\sim 10^4$ (cgs), implying the presence of resonance lines of helium-- and hydrogenlike iron. These properties are direct consequences of momentum and mass conservation respectively, and agree with recent X-ray observations of fast outflows from AGN. Because the wind is significantly subluminal, it can persist long after the AGN is observed to have become sub--Eddington. The wind creates a strong cooling shock as it interacts with the interstellar medium of the host galaxy, and this cooling region may be observable in an inverse Compton continuum and lower--excitation emission lines associated with lower velocities. The shell of matter swept up by the (`momentum--driven') shocked wind must propagate beyond the black hole's sphere of influence on a timescale $\la 3\times 10^5$ yr. Outside this radius the shell stalls unless the black hole mass has reached the value $M_σ$ implied by the $M - σ$ relation. If the wind shock did not cool, as suggested here, the resulting (`energy--driven') outflow would imply a far smaller SMBH mass than