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-$[\mathrm{C}\mathrm{I}]$(1-0) and molecular-${}^{12}$CO(1-0) emission lines at the spatial resolution of $\approx 0.3$" (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 $\sigma \mathrm{/}V\approx 0.35$ ($r\sim 0.5$") and $\sim 0.19$ ($r>0.5\mathrm{"}$), 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 emission is a better probe of SMBH masses than CO emission in AGNs. Our dynamical model using the ${\rm [CI]}$(1-0)kinematicsyieldsa$M_{\rm BH}=1.78^{+2.69}{-1.10}\times10^7$M$\odot$and$M/L_{\rm F547M}=2.25^{+0.40}{-0.43}$(M$\odot$\mathrm{/}L$\odot$). The model using the CO(1-0) kinematics also gives a consistent $M_{\mathrm{B}\mathrm{H}}$ with a larger uncertainty, up to an order of magnitude, i.e.\ $M{\rm BH}=1.60^{+11.52}{-1.45}\times10^7$M$\odot$\mathrm{.}Thisnewlydynamical$M_{\rm BH}$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 $M_{\mathrm{B}\mathrm{H}}$, we are able to constrain the specific RM dimensionless scaling factor of $f=7.2_{-3.4}^{+4.2}$ for the AGN BLR in NGC7469. The gas within the unresolved BLR thus has a Keplerian virial velocity component and the inclination of $i\approx {11.0}^{\circ }$${}_{-2.5}^{+2.2}$, confirming its face-on orientation in a Seyfert 1 AGN by assuming a geometrically thin BLR model.