The CaFe Project: Optical FeII and Near-Infrared Ca II triplet emission
  in active galaxies. II. The driver(s) of the Ca II and Fe II and its
  potential use as a chemical clock
  In this second paper in the series, we carefully analyze the observational
properties of the optical FeII and NIR CaII triplet in Active Galactic Nuclei,
as well as the luminosity, black hole mass, and Eddington ratio in order to
define the driving mechanism behind the properties of our sample. The CaII
shows an inverse Baldwin effect, bringing out the particular behavior of this
ion with respect to the other low-ionization lines such as H$\beta$. We
performed a Principal Component Analysis, where 81.2% of the variance can be
explained by the first three principal components drawn from the FWHMs,
luminosity, and equivalent widths. The first principal component (PC1) is
primarily driven by the combination of black hole mass and luminosity with a
significance over 99.9%, which in turn is reflected in the strong correlation
of the PC1 with the Eddington ratio. The observational correlations are better
represented by the Eddington ratio, thus it could be the primary mechanism
behind the strong correlations observed in the CaII-FeII sample. Since calcium
belongs to the $\alpha$-elements, the FeII/CaII flux ratio can be used as a
chemical clock for determining the metal content in AGN and trace the evolution
of the host galaxies. We confirm the de-enhancement of the ratio FeII/CaII by
the Eddington ratio, suggesting a metal enrichment of the BLR in
intermediate-$z$ with respect to low-$z$ objects. A larger sample, particularly
at $z$>2, is needed to confirm the present results.
