A Common Origin for Quasar Extended Emission-Line Regions and Their Broad-Line Regions

Abstract

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] λ5007 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 0.6 Z☉), while the remaining quasars show typical metal-rich gas (Z > Z☉). Previous studies have shown that EELRs themselves also have low metallicities (Z 0.5 Z☉). 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.