Black Hole Winds

Class providing models of the mechanical power in winds driven by active galactic nuclei (AGN) that couples to the surrounding galaxy. AGN-driven winds can heat or expel gas from the host galaxy, suppressing star formation. The wind power typically scales with the black hole accretion rate and radiative efficiency.

Default implementation: blackHoleWindCiotti2009

Methods

power → double precision

Computes the power in the wind that couples to the surrounding galaxy.

  • class(nodeComponentBlackHole), intent(inout) :: blackHole

blackHoleWindCiotti2009

A black hole winds class based (loosely) on the model of Ciotti et al. (2009). The wind power is given by:

\[L_\mathrm{w} = \epsilon_\mathrm{w} \epsilon_\mathrm{r} f_\mathrm{w} \dot{M}_\bullet \mathrm{c}^2,\]

where \(\dot{M}_\bullet\) is the black hole accretion rate, \(\epsilon_\mathrm{w}=\)[efficiencyWind] is an overall efficiency parameter, \(\epsilon_\mathrm{r}\) is the radiative efficiency of the accretion flow if [efficiencyWindScalesWithEfficiencyRadiative]=true, and \(1\) otherwise, and \(f_\mathrm{w}\) represents the fraction of the wind power that is coupled to the surrounding galaxy.

The model for \(f_\mathrm{w}\) is inspired by Ciotti et al. (2009) who state: If the pressure corresponding to the momentum flow within the jet or wind is much greater than the pressure in the ambient gas, very little mass, momentum and kinetic energy is taken from it and deposited in that ambient gas. But when the [ratio of ISM to wind pressure] approaches unity, the “working surface” has been reached and the jet or wind discharges its content.

The energy density (pressure) in the wind at some radius \(r\) in the galaxy is simply \(\epsilon_\mathrm{w} \epsilon_\mathrm{r} \dot{M} \mathrm{c}^2 / 4 \pi r^2 v_\mathrm{w}\) (i.e. the energy input into a shell over time \(\delta t\), \(\epsilon_\mathrm{w} \epsilon_\mathrm{r} \dot{M} \mathrm{c}^2 \delta t\), divided by the volume of the shell occupied by the wind in time \(\delta t\), \(4 \pi r^2 v_\mathrm{w} \delta t\)) where \(v_\mathrm{w}\) is the wind velocity (assumed fixed at \(10^4\) km/s). The corresponding ISM pressure is just \((3/2) \mathrm{k}T \rho(r)/m_\mathrm{H}\) where \(T\) is the ISM temperature (assumed fixed at \(10^4\) K) and \(\rho\) is the ISM density. We approximate that the spheroid ISM density as \(3 M/4/\pi/r^3\), where \(M\) is the total gas mass in the spheroid, such that we find a ratio of ISM to wind pressures of:

\[\frac{P_\mathrm{ISM}}{P_\mathrm{w}} = (3/2) \mathrm{k}T \rho(r)/m_\mathrm{H} \left/ \frac{\epsilon_\mathrm{w} \epsilon_\mathrm{r} \dot{M} \mathrm{c}^2}{4 \pi r^2 v_\mathrm{w}} \right. .\]

We then smoothly interpolate \(f_\mathrm{w}\) across the transition as:

\[\begin{split}f_\mathrm{w} = \left\{ \begin{array}{ll} 0 & \hbox{if } x \le 0 \\ 3 x^2 - 2 x^3 & \hbox{if } 0 < x < 1 \\ 1 & \hbox{if } x \ge 1, \end{array} \right.\end{split}\]

where \(x=P_\mathrm{ISM}/P_\mathrm{w}-1/2\).

(Default implementation)

Parameters

  • [efficiencyWind] (real; default 2.4d-3) — The efficiency of the black hole accretion-driven wind: \(L_\mathrm{wind} = \epsilon_\mathrm{wind} \dot{M}_\bullet \clight^2\).

  • [efficiencyWindScalesWithEfficiencyRadiative] (boolean; default .false.) — Specifies whether the black hole wind efficiency should scale with the radiative efficiency of the accretion disk.

blackHoleWindSimple

Models AGN accretion-driven winds in which a fixed fraction of the accreted rest-mass energy is injected as a mechanical wind into the host galaxy. The wind power is proportional to the black hole accretion rate, with the coupling efficiency set by the [efficiencyWind] parameter.

Methods

  • calculationReset — Reset memoized calculations.

Parameters

  • [efficiencyWind] (real; default 2.2157d-3) — The coupling efficiency of the black hole accretion-driven wind, defined as the fraction of the accreted rest-mass energy that is deposited as kinetic or thermal energy into the surrounding gas via AGN-driven outflows.