The origin of the intrinsic scatter in the relation between black hole mass and bulge luminosity for nearby active galaxies

We investigate the origin of the intrinsic scatter in the correlation between black hole mass (M_BH) and bulge luminosity (L_bul) in a sample of 45 massive, local (z ≲ 0.35) type 1 active galactic nuclei (AGNs). We derive M_BH from published optical spectra assuming a spherical broad-line region, and L_bul from detailed two-dimensional decomposition of archival optical Hubble Space Telescope images. AGNs follow the M_BH-L_bul relation of inactive galaxies, but the zero point is shifted by an average of Δ log M_BH ≈ -0.3 dex. We show that the magnitude of the zero point oflfset, which is responsible for the intrinsic scatter in the M_BH-L_bul relation, is correlated with several AGN and host galaxy properties, all of which are ultimately related to, or directly impact, the BH mass accretion rate. At a given bulge luminosity, sources with higher Eddington ratios have lower M_BH. The zero point offset can be explained by a change in the normalization of the virial product used to estimate M_BH , in conjunction with modest BH growth (∼10%-40%) during the AGN phase. Galaxy mergers and tidal interactions appear to play an important role in regulating AGN fueling in low-redshift AGNs.