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Paper: Winds and Outflows from Supermassive Black Holes
Volume: 427, Accretion and Ejection in AGN: a Global View
Page: 315
Authors: King, A. R.
Abstract: Eddington accretion episodes in AGN must be common in order for the supermassive black holes to grow. I show that they produce winds with velocities v∼0.1c and ionization parameters up to ξ ∼ 104 (cgs), implying the presence of resonance lines of helium- and hydrogen-like iron. These properties 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 shocked wind escapes the black hole’s sphere of influence on a timescale la 3×105 yr. Outside this radius the shell stalls unless the black hole mass has reached the value Mσ implied by the M–&sigma relation. If the wind shock did not cool, as suggested here, the resulting (‘energy-driven’) outflow would imply a far smaller SMBH mass than actually observed. Minor accretion events with small gas fractions can produce galaxy-wide outflows with velocities significantly exceeding σ, including fossil outflows in galaxies where there is little current AGN activity.
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