Quasars Disks and Cosmology

Abstract

Much of the optical and ultraviolet radiation of bright quasars may originate in a massive accretion disk around a central black hole. Most searches for the signature of such disks gave ambiguous results but lately there are new ideas that may lead to their discovery. In particular, the apparent brightness of thin disks depend on their inclination to the observer's line of sight and this may be detected by the equivalent width of some emission lines (Netzer 1985, 1986). This idea may change our view on the inner structure of quasars and other AGN. In addition, it points to a potential selection effect that has not been taken into account so far. Magnitude limited optical quasar samples may contain, preferentially, face-on disks, thus cosmological evolution based on such samples may be biased. There are other implications, especially to the observed correlation of L_op with L_x in quasars.