A common origin for quasar extended emission-line regions and their broad-line regions

We present a correlation between the presence of luminous extended emission-line regions (EELRs) and the metallicity of the broad-line regions (BLRs) of low-redshift quasars. The result is based on ground-based [O III] lambda 5007 narrowband imaging and Hubble Space Telescope UV spectra of 12 quasars at 0.20 <= z <= 0.45. Quasars showing luminous EELRs have low-metallicity BLRs (Z less than or similar to 0.6 Z(circle dot)), while the remaining quasars show typical metal-rich gas (Z > Z(circle dot)). Previous studies have shown that EELRs themselves also have low metallicities (Z less than or similar to 0.5 Z(circle dot)). The correlation between the occurrence of EELRs and the metallicity of the BLRs, strengthened by the subsolar metallicity in both regions, indicates a common external origin for the gas, almost certainly from the merger of a gas-rich galaxy. Our results provide the first direct observational evidence that the gas from a merger can indeed be driven down to the immediate vicinity (< 1 pc) of the central black hole.