The chemical properties of low-redshift QSOs
  We investigate the chemical properties of low-z QSOs, using archival UV
spectra obtained with the HST and IUE for a sample of 70 Palomar-Green QSOs at
z < 0.5. By utilizing the flux ratio of UV emission lines (i.e., NV /CIV,
(SiIV+OIV])/CIV, and NV/HeII) as metallicity indicators, we compare broad-line
region (BLR) gas metallicity with AGN properties, i.e., black hole mass,
luminosity, and Eddington ratio. We find that BLR metallicity correlates with
Eddington ratio while the dependency on black hole mass is much weaker.
Although these trends of low-z AGNs appear to be different from those of high-z
QSOs, the difference between low-z and high-z samples is partly caused by the
limited dynamical range of the samples. We find that metal enrichment at the
center of galaxies is closely connected to the accretion activity of black
holes and that the scatter of metallicity correlations with black hole mass
increases over cosmic time.
