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J. R. Moore, K. M. Leighly, D. Casebeer (The University of Oklahoma)
The study of the UV \ion{Fe}{2} multiplets in quasar spectra has broad potential applications. In principle, the ratio of \ion{Fe}{2} to \ion{Mg}{2} in high redshift quasars permits a probe of the chemical evolution in the Universe. The complicated multiplets of \ion{Fe}{2} potentially hold information about the excitation and optical depths for low-ionization line emission in the broad-line region. Narrow-line quasars are the best objects to use to study low-ionization line emission, because these lines are frequently strong, and because the narrow lines reduce ambiguity arising from blending.
We present an analysis of the near-UV spectra of ~900 narrow-line quasars from the Sloan Digital Sky Survey. The sample was choosen from quasars with redshifts between 1.2 and 1.8, and with \ion{Mg}{2} FWHM less than 3000 \rm \, km\, s-1. Further screening rejected objects with lines having FWHM greater than 2600 \rm \,km\, s-1, poor signal-to-noise ratios, and intrinsic \ion{Mg}{2} absorption lines. After refining the redshifts using the narrow \ion{Mg}{2} line, and removing Galactic absorption lines, a composite spectrum was constructed. Fitting the \ion{Fe}{2} using a template created from HST spectrum of I~Zw~1 revealed an \ion{Fe}{2}-to-\ion{Mg}{2} ratio of 3.9 in the composite. This is comparable to values measured in high redshift quasars, somewhat lower than in nearby Narrow-line Seyfert 1 galaxies, and somewhat larger than in the SDSS early-release quasar composite spectrum.
Further analysis, including a study of the distribution of \ion{Fe}{2} to \ion{Mg}{2} ratios, correlations with continuum shape, line width, and luminosity, and a systematic search for objects with \ion{Fe}{2} emission differing from that of I~Zw~1 (and therefore potentially revealing different conditions in the low-ionization line emitting gas) will be presented.
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Bulletin of the American Astronomical Society, 35 #5
© 2003. The American Astronomical Soceity.