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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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