Cosmic Evolution of Mass Accretion Rate and Metalicity in Active Galactic Nuclei

We present line and continuum measurements for 9818 SDSS type-I active galactic nuclei (AGNs) with z ≤ 0.75. The data are used to study the four dimensional space of black hole mass, normalized accretion rate (L/LEdd), metalicity and redshift. The main results are: 1. L/LEdd is smaller for larger mass black holes at all redshifts. 2. For a given black hole mass, L/LEdd∝ zγ or (1 + z)δ where the slope γ increases with black hole mass. The mean slope is similar to the star formation rate slope over the same redshift interval. 3. The FeII/Hβ line ratio is significantly correlated with L/LEdd . It also shows a weaker negative dependence on redshift. Combined with the known dependence of metalicity on accretion rate, we suggest that the FeII/Hβ line ratio is a metalicity indicator. 4. Given the measured accretion rates, the growth times of most AGNs exceed the age of the universe. This suggests past episodes of faster growth for all those sources. Combined with the FeII/Hβ result, we conclude that the broad emission lines metalicity goes through cycles and is not a monotonously decreasing function of redshift. 5. FWHM([O III] λ 5007) is a poor proxy of σ∗ especially for high L/LEdd . 6. We define a group of narrow line type-I AGNs (NLAGN1s) by their luminosity (or mass) dependent Hβ line width. Such objects have L/LEdd≥ 0.25 and they comprise 8% of the type-I population. Other interesting results include negative Baldwin relationships for EW(Hβ ) and EW(FeII) and a relative increase of the red part of the Hβ line with luminosity. Subject headings: Galaxies: Abundances – Galaxies: Active – Galaxies: Nuclei – Galaxies: Starburst – Galaxies: Quasars: Emission Lines