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

We present line and continuum measurements for 9818 SDSS type-I activegalactic nuclei (AGNs) with z le 0.75. The data are used to study the fourdimensional space of black hole mass, normalized accretion rate (Ledd),metalicity and redshift. The main results are: 1. Ledd is smaller for largermass black holes at all redshifts. 2. For a given black hole mass Ledd proptoz^gamma or (1+z)^delta where the slope gamma increases with black hole mass.The mean slope is similar to the star formation rate slope over the sameredshift interval. 3. The FeII/Hb line ratio is significantly correlated withLedd. It also shows a weaker negative dependence on redshift. Combined with theknown dependence of metalicity on accretion rate, we suggest that the FeII/Hbline ratio is a metalicity indicator. 4. Given the measured accretion rates,the growth times of most AGNs exceed the age of the universe. This suggestspast episodes of faster growth for all those sources. Combined with the FeII/Hbresult, we conclude that the broad emission lines metalicity goes throughcycles and is not a monotonously decreasing function of redshift. 5. FWHM(OIII)is a poor proxy of sigma_* especially for high Ledd. 6. We define a group ofnarrow line type-I AGNs (NLAGN1s) by their luminosity (or mass) dependent Hbline width. Such objects have Ledd>0.25 and they comprise 8% of the type-Ipopulation. Other interesting results include negative Baldwin relationshipsfor EW(Hb) and EW(FeII) and a relative increase of the red part of the Hb linewith luminosity.Comment: 10 pages 8 figures, accepted for publication in Ap