Inference of the Extreme-Ultraviolet Continuum Shape of Quasars

Abstract

The strength of C IV emission in weak-bump QSOs is significantly larger than that in strong-bump QSOs. Equivalent widths of Lyα, Si IV, and C III show no sign of difference between objects with various UV bump strength. The finding suggests that the "big UV bump" is a source of ionization and can be scaled by emission lines. The higher average C IV EW and C IV/Lyα ratio in weak-bump QSOs represent the values intrinsic to the bare nonthermal continuum. If the bump has a turnover between 30 and 50 eV, C IV emission would not respond as effectively as other low-ionization lines, leading to the observed correlation between C IV equivalent width and bump strength. The Baldwin effect can be explained in terms of UV bumps which are stronger at higher luminosity.