Modelling reverberation mapping data – I. Improved geometric and dynamical models and comparison with cross-correlation results

Abstract

We present an improved and expanded simply parameterized phenomenological\nmodel of the broad line region (BLR) in active galactic nuclei (AGN) for\nmodeling reverberation mapping data. By modeling reverberation mapping data\ndirectly, we can constrain the geometry and dynamics of the BLR and measure the\nblack hole mass without relying on the normalization factor needed in the\ntraditional analysis. For realistic simulated reverberation mapping datasets of\nhigh-quality, we can recover the black hole mass to $0.05-0.25$ dex uncertainty\nand distinguish between dynamics dominated by elliptical orbits and inflowing\ngas. While direct modeling of the integrated emission line light curve allows\nfor measurement of the mean time lag, other details of the geometry of the BLR\nare better constrained by the full spectroscopic dataset of emission line\nprofiles. We use this improved model of the BLR to explore possible sources of\nuncertainty in measurements of the time lag using cross-correlation function\n(CCF) analysis and in measurements of the black hole mass using the virial\nproduct. Sampling the range of geometries and dynamics in our model of the BLR\nsuggests that the theoretical uncertainty in black hole masses measured using\nthe virial product is on the order of 0.25 dex. These results support the use\nof the CCF to measure time lags and the virial product to measure black hole\nmasses when direct modeling techniques cannot be applied, provided the\nuncertainties associated with the interpretation of the results are taken into\naccount.\n