The Metallicity of the Redshift 4.16 Quasar BR2248-1242


Craig Warner, Fred Hamann, Joseph C. Shields, Anca Constantin, Craig B. Foltz, & Frederic H. Chaffee

Abstract

We estimate the metallicity in the broad emission-line region of the redshift z=4.16 quasar, BR2248-1242, by comparing line ratios involving nitrogen to theoretical predictions. BR2248-1242 has unusually narrow emission lines with large equivalent widths, thus providing a rare opportunity to measure several line-ratio abundance diagnostics. The combined diagnostics indicate a metallicity of ~2 times solar. This result suggests that an episode of vigorous star formation occurred near BR2248-1242 prior to the observed z=4.16 epoch. The time available for this enrichment episode is only ~1.5 Gyr at z=4.16 (for H0=65 km/s/Mpc, Omegam =0.3 and any OmegaLambda < 1). This evidence for high metallicities and rapid star formation is consistent with the expected early-epoch evolution of dense galactic nuclei.


This paper has been accepted by Part 1 of the Astrophysical Journal. It will tenatively appear on p.1 of the March 1, 2002 issue. This webpage will also include links to all references in the paper, the paper will appear in HTML format with tables and figures inline, and an interactive java plotting applet will allow you to dynamically zoom in on any part of the spectrum and overplot our fits to the continuum and the emission lines!

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  • Figure 1: Postscript | JPEG
    Spectrum of BR2248-1242 with our fit to the continuum overplotted (dashed line). The spectrum has been corrected for extinction.
  • Figure 2: Postscript | JPEG
    Gaussian fits of emission lines of BR2248-1242. The continuum is normalized by the power law fit shown in Figure 1. The continuum (at unity) and composite line fits are plotted as solid curves. The individual components of the fits are shown as dotted and dashed lines.
  • Figure 3: Postscript | JPEG
    Comparison of flux ratios measured in BR2248-1242 to theoretical results from Figure 5 of Hamann et al. (2001). Comparisons of our measured line ratios to the theoretical model represented by the solid line yield our preferred estimates for metallicity. The solid line is obtained from the model in Hamann et al. that uses a segmented powerlaw for the photoionizing continuum shape, which is a good approximation to the average observed continuum in quasars. The dotted line corresponds to the model that uses an incident spectrum defined by Matthews \& Ferland (1987), while the dashed line corresponds to a powerlaw with index $\alpha = -1.0$ across the infrared through X-rays .