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J.K. Kuraszkiewicz, P.J. Green (Harvard-Smithsonian CfA)
Narrow absorption lines (NALs) seen in the rest-frame ultraviolet near the systemic redshift of active galactic nuclei (AGN) 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. The strong, broad emission lines (BELs) on the other hand originate in the nuclear region, where gas clouds are photoionized by the central continuum source. We have measured the N\,V/C\,IV ratio (thought to be an emission line adundance indicator - see Hamann & Ferland 1992) for both the emission and the absorption lines in an HST FOS sample of objects with 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 BELs and NALs. A control sample of AGN with NALs separated by larger velocities shows no such correlation. Our finding thus identifies a useful indicator of intrinsic absorption, and adds new insight to the nature and composition of clouds near the nucleus. It indicates that the metallicities in the NAL and BEL clouds are intimately related, and suggests that the NAL clouds are either cospatial with the BEL region or have undergone similar chemical enrichment as the clouds responsible for the emission lines.
The authors gratefully acknowledge support provided for this project by NASA through grants NAG5-6410 (LTSA), and NAS8-39073 (CXC).
The author(s) of this abstract have provided an email address for comments about the abstract: jkuraszkiewicz@head-cfa.harvard.edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.