Accretion around Supermassive Black Holes: The Detection of the Balmer Edge Signature from Quasars

The ultraviolet/optical continuum of quasars is thought to be from anaccretion flow around a supermassive black hole, and it dominates the radiativeoutput of quasars. However, the nature of this emission, often called the BigBlue Bump, has not been well understood. Robust evidence for its thermal naturewould be a continuum opacity edge feature intrinsic to this component, but thishas not been clearly confirmed despite the predictions by many models. We arenow developing and exploiting a new method to detect the Balmer edge ofhydrogen opacity. The method overcomes for certain objects the major obstacleof the heavy contamination from emissions outside the nucleus by taking thepolarized flux spectrum. If our interpretation of the polarized flux iscorrect, our data show that the Big Blue Bump emission has a Balmer edge inabsorption, indicating that the emission is indeed thermal, and the emitter isoptically thick.Comment: 4 pages, a talk contribution to the conference "Stellar-mass, Intermediate-mass, and Supermassive Black Holes", held in Kyoto, Japan, Octorber 28-31, 2003, to be published in Progress of Theoretical Physics Supplemen