Evolution of the Quasar `Big Bump'

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Session 34 -- Spectroscopy of AGN II: Broad Lines and Spectral Evolution
Oral presentation, Monday, 9, 1995, 2:00pm - 3:30pm

[34.04D] Evolution of the Quasar `Big Bump'

Olga Kuhn, Martin Elvis (SAO), Jill Bechtold (Steward Observatory, Univ. of Arizona), Belinda Wilkes (SAO)

We have undertaken a extensive program of near-infrared spectroscopy and photometry and optical spectrophotometry of 10 $z\sim1$ and 16 $z\ge3$ quasars with the aim of determining how the optical/UV `big bump' evolves. The `big bump' contains a significant fraction (15-60\%; Elvis et al. 1994, ApJ, in press) of the bolometric luminosity and is widely believed to originate in the central engine. The sample quasars were chosen to follow the decay of $L_{*}(z)$ over 4.5 magnitudes, from its maximum at $z\ge3$, through its midpoint at $z\sim1$, to its minimum at $z\sim0.1$. Most of the sample quasars have luminosities within 1 to 6 $\times L_{*}(z)$ and so represent similar quasars at each epoch. Our VLA fluxes or limits for sample quasars of previously unknown radio-loudness give almost equal numbers of radio-loud and radio-quiet quasars in each sample, enabling a separate examination of the continuum evolution for each class.

We present the rest-frame optical/UV continua for these quasars and estimate physical parameters in the emitting region by fitting these with both accretion disk (e.g., Sun and Malkan 1989, ApJ, 346, 68) and free-free (Barvainis 1993, ApJ, 412, 513) models. We discuss the differences between the continua at high and low redshifts and their implications for models of quasar formation and evolution.

For the $z\ge3$ quasars, Ly$\alpha$ through H$\beta$/[OIII] are observed in the optical and IR spectra. We use the emission line ratios to place constraints on the intrinsic reddening and UV continuum shape. The equivalent widths are used to investigate the Baldwin relationship at the highest luminosities and to test claims that it is produced by a trend in UV continuum shape with luminosity (Zheng and Malkan 1993, ApJ, 415, 517).

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