Evidence of a Strong N V/C IV Correlation between Emission and Absorption Lines in Active Galactic Nuclei

Abstract

The narrow absorption lines (NALs) that are seen in the rest-frame ultraviolet near the systemic redshift of active galactic nuclei (AGNs) are not always intrinsic to the near-nuclear region but may originate in the host galaxy or in neighboring galaxies intervening along the line of sight. A variety of criteria have been sought-and several identified-as evidence of an intrinsic origin. We have measured both emission and absorption lines in a Hubble Space Telescope Faint Object Spectrograph sample of objects with both C IV and N V NALs within +/-5000 km s^-1 of the systemic redshift. We find a strong (>99.5% confidence) linear correlation between the N V/C IV ratio in broad emission lines and that in NALs. A control sample of AGNs with NALs separated by larger velocities shows no such correlation. Our finding thus identifies an additional test for the intrinsic nature of NALs in any given object. The correlation shows that the chemical-enrichment histories and/or ionization parameters of the NAL clouds are closely related to those of clouds that produce the broad emission lines.