Near‐Infrared Spectroscopy of High‐Redshift Active Galactic Nuclei. I. A Metallicity–Accretion Rate Relationship

We present new near infrared spectroscopic measurements of the H_beta regionfor a sample of 29 luminous high redshift quasars. We have measured the widthof H_beta in those sources, and added archival H_beta width measurements, tocreate a sample of 92 active galactic nuclei (AGNs) for which H_beta width andrest-frame UV measurements of N V \lambda 1240 and C IV \lambda 1549emission-lines are available. Our sample spans six orders of magnitude inluminosity and includes 31 radio-loud AGNs. It also includes 10 narrow-lineSeyfert 1 galaxies and one broad absorption-line quasar. We find thatmetallicity, indicated by the N V/C IV line ratio, is primarily correlated withaccretion rate, which is a function of luminosity and H_beta line-width. Thismay imply an intimate relation between starburst, responsible for the metalenrichment of the nuclear gas, and AGN fueling, represented by the accretionrate. The correlation of metallicity with luminosity, or black hole (BH) mass,is weaker in contrast with recent results which were based on measurements ofthe width of C IV. We argue that using C IV as a proxy to H_beta in estimatingM_BH might be problematic and lead to spurious BH mass and accretion rateestimates in individual sources. We discuss the potential implications of ournew result in the framework of the starburst-AGN connection and theories of BHgrowth.Comment: 11 pages (emulateapj), 8 figures. Accepted by Ap