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Metal Abundances and Ionization in QSO Broad Emission-Line Regions

Published online by Cambridge University Press:  12 April 2016

F. Hamann ,
J.C. Shields ,
R. D. Cohen ,
V.T. Junkkarinen  and
E.M. Burbidge
F. Hamann
Affiliation:
Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA
J.C. Shields
Affiliation:
Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
R. D. Cohen
Affiliation:
Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA
V.T. Junkkarinen
Affiliation:
Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA
E.M. Burbidge
Affiliation:
Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA

Abstract

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We describe two ongoing studies of QSO broad emissionline regions (BELRs). The first employs the N V λ1240/He II λ1640 and N V/C IV λ1549 line ratios as diagnostics of QSO metallicities. Hamann & Ferland and Ferland et al. showed that many observed N V ratios require enhanced N abundances and Z > Z⊙. Here we present new measurements of large line ratios at redshifts z > 4, which indicate super-solar abundances within ~1 Gyr of the Big Bang (for q0 ≈ 0.5). We also note that the N V line is relatively stronger in more luminous QSOs, in contrast to the well-known Baldwin effect in Lyα, C IV, and O VI λ1034. This unusual behavior in N V could be due to a luminosity-metallicity correlation among QSOs that is coupled to a mass-metallicity relation in their host galaxies.

Our second study involves Ne VIII λ774 as a probe of highly ionized gas. We show that a broad emission feature near 774 Å is common in QSOs. Photoionization models indicate that Ne VIII is the most likely identification for this feature. The models also indicate that the Ne VIII emitting gas covers > 40% of the continuum source, has a total hydrogen column density of NH > 1022 cm−2 (for solar abundances) and an ionization parameter of U > 5 (for a nominal QSO continuum shape). This gas would be an X-ray “warm73x201D; absorber — with O VII–O VIII bound-free edges — if it lies along our line-of-sight to the X-ray continuum source.

Type
II. Broad Emission Lines
Information
International Astronomical Union Colloquium , Volume 159: Emission Lines in Active Galaxies: New Methods and Techniques , 1997 , pp. 96 - 103
Copyright
Copyright © Astronomical Society of the Pacific 1997

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