Combining Direct Black Hole Mass Measurements and Spatially Resolved Stellar Kinematics to Calibrate the $M_{\rm BH}$-$σ_\star$ Relation of Active Galaxies

Abstract: The origin of the tight scaling relation between the mass of supermassive black holes (SMBHs; $M_{\rm BH}$) and their host-galaxy properties remains unclear. Active galactic nuclei (AGNs) probe phases of ongoing SMBH growth and offer the only opportunity to measure $M_{\rm BH}$ beyond the local Universe. However, determining AGN host galaxy stellar velocity dispersion $\sigma_\star$, and their galaxy dynamical masses $M_{\rm dyn}$, is complicated by AGN contamination, aperture effects and different host galaxy morphologies. We select a sample of AGNs for which $M_{\rm BH}$ has been independently determined to high accuracy by state-of-the-art techniques: dynamical modeling of the reverberation signal and spatially resolving the broad-line region with VLTI/GRAVITY. Using IFU observations, we spatially map the host galaxy stellar kinematics across the galaxy and bulge effective radii. We find that that the dynamically hot component of galaxy disks correlates with $M_{\rm BH}$; however, the correlations are tightest for aperture-integrated $\sigma_\star$ measured across the bulge. Accounting for the different $M_{\rm BH}$ distributions, we demonstrate - for the first time - that AGNs follow the same $M_{\rm BH}$-$\sigma_\star$ and $M_{\rm BH}$-$M_{\rm bulge, dyn}$ relations as quiescent galaxies. We confirm that the classical approach of determining the virial factor as sample-average, yielding ${\rm log }f= 0.65 \pm 0.18$, is consistent with the average $f$ from individual measurements. The similarity between the underlying scaling relations of AGNs and quiescent galaxies implies that the current AGN phase is too short to have altered BH masses on a population level. These results strengthen the local calibration of $f$ for measuring single-epoch $M_{\rm BH}$ in the distant Universe.