Black hole mass measurement using ALMA observations of [CI] and CO emissions in the Seyfert 1 galaxy NGC 7469
Résumé
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 σgas/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 MBH = 1.78-1.10+2.69 × 107 M⊙ and M/LF547M = 2.25-0.43+0.40 (M⊙/L⊙). The model using the 12CO(1-0) kinematics also gives a consistent MBH with a larger uncertainty, up to an order of magnitude, i.e. MBH = 1.60-1.45+11.52 × 107 M⊙. This newly dynamical MBH 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 MBH, we are able to constrain the specific RM dimensionless scaling factor of f = 7.2-2.5+2.2 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.
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