Emission Line and Ultraviolet to X‐Ray Continuum Correlations: Constraints on the Anisotropy of the Ionizing Continuum in Active Galactic Nuclei

Anisotropic emission of the ionizing continuum is a general prediction of theaccretion disk models. In this paper, we present the results of correlationanalysis of the UV emission line and UV to X-ray continuum properties for alarge sample of broad emission line AGNs observed with ROSAT, IUE and HST. Wefind strong correlations between the CIV/$Ly\alpha$ ratio, the equivalent widthof CIV, and the UV to soft X-ray spectral slope. The results are in goodagreement with the photoionization calculation, suggesting that the overallionizing continuum can well match the observed UV to soft X-ray spectrum. Theseresults are consistent with the assumption of isotropic ionizing continuumshape. Our analysis suggests a small range for the ``big blue bump'' cutoffenergy for the objects in this sample, consistent with the similar results ofLaor et al. (1997) and Walter & Fink (1993) based on the continuum properties .The mean UV-to-X-ray spectral slope is similar to the soft X-ray spectralslope. This similarity also holds for radio-loud and radio-quiet objectsseparately. This suggests that the two might be drawn from the samedistribution. The two spectral slopes are only weakly correlated. The UV toX-ray spectral index is correlated with absolute optical magnitude. This resultconfirms the earlier suggestion that the ionizing continua are softer forhigher luminosity objects.Comment: Accepted for publication in the Astrophysical Journal. 15 pages AAStex + 5 figures + three table