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M. Bogosavljevic, S.G. Djorgovski, A. Mahabal, D. Thompson, S. Castro (Caltech)
We have performed high S/N, near-IR (J and Ks bands) photometry of a sample of 35 PSS quasars at redshifts z ~4.0 - 4.5. Using these measurements we have derived precise power-law slopes for their restframe UV/optical continuum emission. The observed spectral index distribution has a mean value \alpha = -0.49, and a fairly wide dispersion, with a Gaussian \sigma = 0.38. This is in an excellent agreement with previous work for lower redshift QSOs, and with measurements of a SDSS color-selected QSO sample by Pentericci et al. (2003) at similar redshifts.
Using this confident continuum slope determination for each source, we measured the total observed flux of LyA + N V lines using echelle spectra obtained at the Keck telescope, and supplemented the sample with high-quality measurements taken from the literature. We find a weak correlation in the sense that QSOs with the bluest continua also have the lowest emission-line equivalent widths. We investigate the possibility that both the spread of the observed spectral indices and their correlation with equivalent widths can be explained as orientation effects, which would be in accordance with some theoretical models of AGN. If proved correct, this correlation would represent the first orientation indicator for radio-quiet QSOs. Further studies along these lines could lead to new insights into AGN unification models. This work was supported in part by the NSF grant AST-0407448.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.