C. -A. Faucher-Giguere, E. Quataert, N. Murray
Photoionization modeling of the low-ionization broad absorption lines of
certain quasars, known as FeLoBALs, has recently revealed the number density of
the wind absorbers and their distance from the central supermassive black hole.
From these, the feedback efficiency of the quasars can in principle be derived.
The implied properties of the FeLoBALs are, however, surprising, with the
thickness of the absorbers relative to their distance from the black hole,
Delta R/R, as small as ~10^-5. Such absorbers are unlikely to survive the
journey from the supermassive black hole to their inferred location. We show
that the observed FeLoBAL properties are readily explained if they are formed
in situ in radiative shocks produced when a quasar blast wave impacts a
moderately dense interstellar clump along the line of sight. This physical
picture differs significantly from the thin shell approximation often assumed,
and implies outflow rates, kinetic luminosities and momentum fluxes that differ
correspondingly, in some cases at the order of magnitude level. Using the
radiative shock model, we estimate the ratio of the outflow kinetic luminosity
to bolometric luminosity for three bright FeLoBAL quasars in the literature. We
find Edot/Lbol~2-5% (and corresponding momentum fluxes Pdot~2-15 Lbol/c),
similar to what is adopted in models reproducing the M-sigma relation. These
outflow properties are also comparable to those recently inferred for molecular
outflows in local ultra-luminous infrared galaxies, suggesting that active
galactic nuclei are capable of driving such outflows.
View original:
http://arxiv.org/abs/1108.0413
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