Radiation driven outflow in active galactic nuclei: the feedback effects of scattered and locally produced photons. (arXiv:1304.4689v1 [astro-ph.HE])

Radiation driven outflow in active galactic nuclei: the feedback effects of scattered and locally produced photons. (arXiv:1304.4689v1 [astro-ph.HE]):
We perform time-dependent, two-dimensional, hydrodynamical, numerical
simulations to study the dynamics of a slowly rotating accretion flow from
sub-pc to pc scales under the irradiation from the central AGN. Compared to
previous work, we improve the calculation of the radiative force due to X-rays.
More importantly, in addition to radiative pressure and radiative
heating/cooling directly from the central AGN, in the momentum equation we also
include the force due to the scattered and locally produced photons. We find
that the accretion flow properties change significantly due to this
"re-radiation" effect. The inflow rate at the inner boundary is reduced, while
the outflow rate at the outer boundary is enhanced by about one order of
magnitude. This effect is more significant when the density at the outer
boundary is higher. The properties of outflows such as velocity, momentum and
energy fluxes, and the ratio of outflow rate and the accretion rate, are
calculated. We find that the efficiency of transferring the radiation power
into the kinetic power of outflow is typically $10^{-3}$, far below the value
of $\sim 0.05$ which is assumed in some cosmological simulations. The effect of
the temperature of the gas at the outer boundary ($T_0$) is investigated. When
$T_0$ is high, the emitted luminosity of the accretion flow oscillates because
of the strong radiative heating. Another question we hope to address by this
work is the so-called "sub-Eddington" puzzle. That is, observations show that
the luminosity of almost all AGNs are sub-Eddington, while theoretically the
luminosity of an accretion flow can easily be super-Eddington. We find that
even when the re-radiation effect is included and outflow does become much
stronger, the luminosity, while reduced, can still be super-Eddington. Other
observational implications and some caveats of our calculations are discusse