Black hole mass measurement using ALMA observations of [CI] and CO emissions in the Seyfert 1 galaxy NGC7469

We present a supermassive black hole (SMBH) mass measurement in the Seyfert 1 galaxy NGC7469 using Atacama Large Millimeter/submillimeter Array (ALMA) observations of the atomic-${rm [CI]}$(1-0) and molecular-$^{12}$CO(1-0) emission lines at the spatial resolution of $approx0.3$ (or $approx$ 100 pc). These emissions reveal that NGC7469 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 $sigma/Vapprox0.35$ ($rsim0.5$) and $sim0.19$ ($r>0.5$), 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 AGNs. Our dynamical model using the ${rm [CI]}$(1-0) kinematics yields a $M_{rm BH}=1.78^{+2.69}_{-1.10}times10^7$M$_odot$ and $M/L_{rm F547M}=2.25^{+0.40}_{-0.43}$ (M$_odot$/L$_odot$). The model using the CO(1-0) kinematics also gives a consistent $M_{rm BH}$ with a larger uncertainty, up to an order of magnitude, i.e. $M_{rm BH}=1.60^{+11.52}_{-1.45}times10^7$M$_odot$. This newly dynamical $M_{rm BH}$ is $approx$ 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 $M_{rm BH}$, we are able to constrain the specific RM dimensionless scaling factor of $f=7.2^{+4.2}_{-3.4}$ for the AGN BLR in NGC7469. The gas within the unresolved BLR thus has a Keplerian virial velocity component and the inclination of $iapprox11.0^circ$$_{-2.5}^{+2.2}$, confirming its face-on orientation in a Seyfert 1 AGN by assuming a geometrically thin BLR model.