Active Galactic Nuclei in the Sloan Digital Sky Survey. II. Emission-Line Luminosity Function

Abstract

The emission line luminosity function of active galactic nuclei (AGN) is\nmeasured from about 3000 AGN included in the main galaxy sample of the Sloan\nDigital Sky Survey within a redshift range of $0<z<0.15$. The $\\Ha$ and\n[OIII]$\\lambda 5007$ luminosity functions for Seyferts cover luminosity range\nof $10^{5-9}$$L_\\odot$ in H$\\alpha$ and the shapes are well fit by broken power\nlaws, without a turnover at fainter nuclear luminosities. Assuming a universal\nconversion from emission line strength to continuum luminosity, the inferred B\nband magnitude luminosity function is comparable both to the AGN luminosity\nfunction of previous studies and to the low redshift quasar luminosity function\nderived from the 2dF redshift survey. The inferred AGN number density is\napproximately 1/5 of all galaxies and about $6\\times 10^{-3}$ of the total\nlight of galaxies in the $r$-band comes from the nuclear activity. The numbers\nof Seyfert 1s and Seyfert 2s are comparable at low luminosity, while at high\nluminosity, Seyfert 1s outnumber Seyfert 2s by a factor of 2-4. In making the\nluminosity function measurements, we assumed that the nuclear luminosity is\nindependent of the host galaxy luminosity, an assumption we test {\\it a\nposteriori}, and show to be consistent with the data. Given the relationship\nbetween black hole mass and host galaxy bulge luminosity, the lack of\ncorrelation between nuclear and host luminosity suggests that the main variable\nthat determines the AGN luminosity is the Eddington ratio, not the black hole\nmass. This appears to be different from luminous quasars, which are most likely\nto be shining near the Eddington limit.\n