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C. Warner, F. Hamann (University of Florida), M. Dietrich (Georgia State University)
We examine trends between the metallicity in the broad emission-line region (BLR) of active galactic nuclei (AGNs) and both supermassive black hole (SMBH) mass and AGN luminosity. We analyze rest-frame UV spectra for a large sample of 578 Type 1 AGNs, spanning seven orders of magnitude in luminosity, five orders of magnitude in SMBH mass, and a redshift range from 0 < z < 5. We estimate SMBH masses by applying the virial theorem, M = rv2/G to the \ion{C}{4} \lambda 1549 emission line. Warner, Hamann, & Dietrich (2003) found a relationship between SMBH mass and BLR metallicity. This can be understood in terms of more massive SMBHs residing in more massive galaxies, combined with the well-known mass-metallicity relationship among galaxies. However, because SMBH mass and AGN luminosity are tightly correlated, we could not rule out luminosity as the fundamental parameter driving BLR metallicity. In order to isolate SMBH mass and luminosity, we create composite spectra that i) span a range in SMBH mass at nearly constant luminosity and ii) span a range in luminosity at nearly constant SMBH mass. The composite spectra show that most lines diminish in equivalent width with increasing SMBH mass at a steeper slope than they do with increasing luminosity (the usual ``Baldwin Effect"). We estimate metallicities by comparing several line ratios involving nitrogen to theoretical predictions. Our results are consistent with a strong trend between SMBH mass and metallicity and no trend between AGN luminosity and metallicity.
This work was supported by NSF Grant AST 99-84040.
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Bulletin of the American Astronomical Society, 36 #2
© YEAR. The American Astronomical Soceity.