Strong correlation between FeII/MgII ratio and Eddington ratio of type 1
  Active galactic nuclei
  The FeII/MgII line flux ratio has been used as an indicator of the Fe/Mg
abundance ratio in the broad line region (BLR) of active galactic nuclei
(AGNs). On the basis of archival rest-frame UV spectra obtained via the Hubble
Space Telescope and the Sloan Digital Sky Survey, we investigate the FeII/MgII
ratios of type 1 AGNs at z < 2. Over wide dynamic ranges of AGN properties
(i.e., black hole mass, AGN luminosity, and Eddington ratio), we confirm that
the FeII/MgII ratio strongly correlates with Eddington ratio but not with black
hole mass, AGN luminosity, or redshift. Our results suggest that the
metallicity in the BLR are physically related to the accretion activity of
AGNs, but not to the global properties of galaxies (i.e., galaxy mass and
luminosity). With regard to the relation between the BLR metallicity and the
accretion rate of AGNs, we discuss that metal cooling may play an important
role in enhancing the gas inflow into the central region of host galaxies,
resulting in the high accretion rate of AGNs.
