2021ApJ...915L...9W

We present the first ever models of a broad line region (BLR) at the peak of active galactic nucleus (AGN) activity using the multiply imaged z = 2.805 quasar SDSS J2222+2745. The modeled data consist of monthly spectra covering the broad C IV emission line over a 5.3 yr baseline. The models suggest a thick disk BLR that is inclined by ∼40° to the observer's line of sight and with an emissivity weighted median radius of r_median=33.0_–2.1^+2.4 light days. The kinematics are dominated by near-circular Keplerian motion with the remainder inflowing. The rest-frame lag one would measure from the models is τ_median=36.4_–1.8^+1.8 days, which is consistent with measurements based on cross-correlation. We show a possible geometry and transfer function based on the model fits and find that the model-produced velocity-resolved lags are consistent with those from cross-correlation. We measure a black hole mass of log₁₀(M_BH/M_☉)=8.31_–0.06^+0.07, which requires a scale factor of log₁₀(f_mean,σ)=0.20_–0.07^+0.09. This is the most precise M_BH measurement for any AGN at cosmological distances and it demonstrates that the precision required for BH-host coevolution studies is attainable.