The Eddington Ratio Distribution of Narrow Line Active Galactic Nuclei

Abstract: We measure the Eddington ratio distribution of local optical narrow line active galactic nuclei (AGN) as a function of host galaxy properties, as a potential test of supermassive black hole growth and feedback models in galaxy formation theory. We base our sample on integral field spectroscopy from the MaNGA data in SDSS-IV's DR17. Starting with MaNGA's calibrated row-stacked spectra, we produce new spectroscopic data cubes with minimal covariance between spaxels and higher resolution point spread functions (PSF), and then extract line fluxes for the central PSF. Using the line ratio diagnostic techniques of Ji & Yan (2020), we identify AGN galaxies and determine their H$β$ and [O III] line luminosities. For all galaxies not identified as AGN, we determine the threshold line luminosity they would have needed to be identified as AGN. These luminosity thresholds are essential to determine, because many star forming galaxies likely host AGN of significant luminosity that are unidentified because they are outshone by star formation related emission. We show that ignoring these selection effects when measuring the Eddington ratio distribution would lead to biased results. From the H$β$ luminosities and luminosity detection thresholds, accounting for selection effects, we measure the luminosity and Eddington ratio distributions of Seyferts as a function of specific star formation rate (sSFR) and stellar mass. Defining $F_{\rm AGN}$ as the occurrence rate of AGN above a fixed Eddington ratio of $10^{-3}$, we find that $F_{\rm AGN}$ is constant or increasing with stellar mass for star forming galaxies and declines strongly with stellar mass for quiescent galaxies. At stellar masses $\log_{10} M_\ast > 10.25$, the occurrence rate increases monotonically with sSFR. These patterns reveal a complicated dependence of AGN activity on galaxy properties for theoretical models to explain.