A Survey of Seyfert AGN: Nuclear Gas Disks and Direct Black Hole Mass Estimates

In a survey of 18 nearby Seyfert nuclei, we find evidence for geometrically thick gas disks on scales of tens of parsecs. Mapping the interstellar medium traced by H₂ ν = 1-0 S(1) emission using the infrared integral field spectrometers OSIRIS and SINFONI reveals general disk rotation with an additional significant component of random bulk motion implied by the high local velocity dispersion. The size scale of the typical nuclear gas disk is ~30 pc in radius with a comparable vertical height, and the distribution and kinematics suggest the gas is spatially mixed with the nuclear stellar population. Based on the estimated characteristic gas mass fraction of 10%, the average gas mass within this region is ~10⁷ M_⊙. This suggests column densities of N_H ~ 5 × 10²³ cm^-2, but the significantly lower densities implied by the stellar continuum extinction indicate that the gas distribution on these scales is dominated by dense clumps. We discuss the feasibility of constraining the masses of the central black holes via modeling of the gas disk kinematics, highlighting the importance of properly accounting for the gas velocity dispersion, and the use of these direct mass estimates to calibrate masses derived from the method of reverberation mapping.