2021MNRAS.504.4123N

We present a supermassive black hole (SMBH) mass measurement in the Seyfert 1 galaxy NGC 7469 using Atacama Large Millimeter/submillimeter Array (ALMA) observations of the atomic-[CI](1-0) and molecular-¹²CO(1-0) emission lines at the spatial resolution of ≃0_.^′′3 (or ≃100 pc). These emissions reveal that NGC 7469 hosts a circumnuclear gas disc (CND) with a ring-like structure and a two-arm/bi-symmetric spiral pattern within it, surrounded by a starbursting ring. The CND has a relatively low σ_gas/V ≃ 0.35 (r <= 0_.^′′5) and ≃0.19 (r > 0_.^′′5), suggesting that the gas is dynamically settled and suitable for dynamically deriving the mass of its central source. As is expected from X-ray dominated region (XDR) effects that dramatically increase an atomic carbon abundance by dissociating CO molecules, we suggest that the atomic [CI](1-0) emission is a better probe of SMBH masses than CO emission in active galactic nuclei (AGNs). Our dynamical model using the [CI](1-0) kinematics yields a M_ BH_=1.78+2.69^_–1.10×10^7 M_☉ and M/L_ F547M_=2.25+0.40^_–0.43 (M_☉/L_☉). The model using the ¹²CO(1-0) kinematics also gives a consistent M_BH with a larger uncertainty, up to an order of magnitude, i.e. M_ BH_=1.60+11.52^_–1.45×10^7 M_☉. This newly dynamical M_BH is ≃2 times higher than the mass determined from the reverberation mapped (RM) method using emissions arising in the unresolved broad-line region (BLR). Given this new M_BH, we are able to constrain the specific RM dimensionless scaling factor of f=7.2^+4.2_–3.4 for the AGN BLR in NGC 7469. The gas within the unresolved BLR thus has a Keplerian virial velocity component and the inclination of i~11.0^○-2.5_^+2.2, confirming its face-on orientation in a Seyfert 1 AGN by assuming a geometrically thin BLR model.