I show that Eddington accretion episodes in AGN are likely to produce winds with velocities v \sim 0.1 c and ionization parameters up to \xi \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 _ { \sigma } 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 . In galaxies with large bulges the black hole may grow somewhat beyond this value , suggesting that the observed M - \sigma relation may curve upwards at large M . Minor accretion events with small gas fractions can produce galaxy–wide outflows with velocities significantly exceeding \sigma , including fossil outflows in galaxies where there is little current AGN activity . Some rare cases may reveal the energy–driven outflows which sweep gas out of the galaxy and establish the black hole–bulge mass relation . However these require the quasar to be at the Eddington luminosity .