Flux-Averaged Force Multipliers

Abstract

We apply novel developments in photoionization modeling and multi-frequency radiation hydrodynamics to the study of line driven AGN disc winds. We use a flux-averaged force multiplier approach to compute the radiation force due to lines for hydrodynamics simulations using 4 frequency bands - infrared (IR), optical (O), ultraviolet (UV) and X-rays. Though line driving is dominated by the UV, contributions from the O and X-ray bands are non-negligible and can lead to enhancements in the wind both in terms of mass flux and outflow velocity. Crucially, these effects are not captured when using a ``grey'' approach to the radiation modeling in the hydrodynamics, where frequency information is averaged over during the photoionization modeling. These results further strengthen the case for frequency dependent radiation dynamics studies for line driven winds.

Figures (10)

• Figure 1: Comparisons of the energy distribution of AGN spectra (black-dashed curves) and single line force multipliers (grey scale vertical bars) for (in descending order) $\log \xi = 1, 2, 3$ and 4. The vertical bars represent the 1,000 strongest individual line force multipliers – normalized to the maximum force multiplier $M_{\rm{l,max}}$. The maximum force multiplier varies widely at different ionizations, with $\log M_{\rm{l,max}} = 2.51, 1.78, 1.81, 0.68$ for AGN1 and $\log M_{\rm{l,max}} = 2.67, 2.05, 0.25, 2.35$ for AGN2. with increasing ionization parameter. These 1,000 strongest lines have been binned into quartiles, black being the upper quartile, dark grey the second, light grey the third, and white the weakest set of lines. The black dashed line in each panel represents the assumed SED, either AGN1 (left panels) or AGN2 (right panels) that we used for both determining the ionization balance and computing $M$. The colored shading shows the frequency bands listed in Table \ref{['tab:bands']}.
• Figure 2: Force multiplier $M_{\nu}$ contributions from the IR (red), optical (orange), UV (green) and X-ray (blue) as well as the flux average (black) as a function of ionizations for a selection of optical depth parameters for an unobscured (AGN1) and obscured (AGN2) SEDs.
• Figure 3: Band fraction as a function of radius along the disc midplane in the IR (red lines), O (orange lines), UV (green lines) and X-ray (blue lines) for black hole masses $M/M_{\odot} =$$3 \times 10^6$, $10^7$, $10^8$ and $10^9$. The light shaded regions indicate radii interior to the computational domain and the dark shaded region is interior to the ISCO. For higher mass black holes, UV is dominant in the inner parts of the disc whereas for lower masses the X-ray band is dominant.
• Figure 4: Ratio of the force multiplier $M_{\rm{Flux}}/M_{\rm{AGN}}$ throughout the simulation domain (physical position x-y) for a black hole with mass $M = 10^8 M_{\odot}$. Each column represents a fixed value of the ionization parameter in the range $-2 \leq \log \xi \leq 1$ and each row represents a fixed value of the optical depth parameter in the range $-5 \leq \log t \leq -3$. The flux average force multiplier is enhanced by $\lesssim 2$ in most parts of the domain where wind launching and acceleration occur i.e. near the disc, close to the black hole and in a $45^{\circ}$ wedge above the disc. The enhancement is never more than a factor of 4, and this tends to be in the region above the corona where launching does not occur.
• Figure 5: Ionization parameter $\xi$ (top panel), the mass flux density $dm_{\theta} = \rho v_r r^2$ (middle panel) and radial velocity $v_r$ (bottom panel) at the outer boundary for the listed models. For the mass flux density, the Grey model is shown for x100 for visual clarity.