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O. Kuhn (Joint Astronomy Centre)
The positive luminosity evolution which quasars undergo implies, in the general accretion paradigm, that the central engines of high redshift quasars are more massive and accreting at higher rates than those of low redshift quasars.
About 10 years ago, much effort was directed to fitting the spectral energy distributions (SEDs) of sets of quasars and AGN with disk models (e.g. Sun and Malkan 1989, ApJ, 346, 68; Laor and Netzer 1989, MNRAS, 238, 897, Siemiginowska et al. 1995, ApJ, 454, 77). The quasars studied were primarily at low redshift, though Tripp et al. (1994, ApJ, 433, 533) considered z~-2 quasars and Bechtold et al. (1994, AJ, 108, 374) showed fits to the SEDs of a couple of z>3 quasars.
We have constructed rest-frame optical/UV SEDs for 15 of the brightest z>3 quasars. The continuum properties of these (optical/UV continuum slope, shape, luminosity) are compared with predictions of models for geometrically thin/optically thick accretion disks around Kerr black holes to determine their central engine parameters and compare with those of lower redshift quasars. Factors extrinsic to the continuum from the central engine: intrinsic reddening; blended FeII+BaC emission; and a non-thermal contribution extending to the rest-frame optical; are considered.
The distributions of models and data on slope-luminosity plots indicate, as expected, that these z>3 quasars are more massive (~09-1010 M\odot) and are accreting at higher rates (close to or above the Eddington limit) than the low redshift ones.
A few of them have optical/UV (1285-5100Å) continuum slopes too blue and luminosities too great to be fit with this simple disk model, unless the assumption of either an edge-on viewing angle or super-Eddington accretion is made.
Further z>3 quasars are out-of-range on a plot of UV minus optical slope (turnover taken at ~000Å) against luminosity | they are too flat to be well fit at least with the disk models used here.
Non-steady disks (e.g. irradiated by an X-ray source) or slim disks
may provide better fits and will be considered in future work.
The author(s) of this abstract have provided an email address for comments about the abstract: o.kuhn@jach.hawaii.edu