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A search for signatures of quasar evolution: Comparison of the shapes of the rest-frame optical/UV continua of quasars at z> 3 and z ∼ 0.1 1

By Olga Kuhn, Martin Elvis, Jill Bechtold and Richard Elston

Abstract

For 15 bright (V< 17.5), high redshift (z> 3) quasars, we have obtained infrared spectra and photometry, and optical spectrophotometry and photometry, which we use to construct their spectral energy distributions (SEDs) from λrest ∼ 1285 − 5100˚A. High resolution spectroscopy for 7 enable measurements of their continua shortwards of Lyα, and L ′ detections of 4 of these extend their SEDs redwards to λrest ∼ 7500˚A. We examine the optical/UV continuum shapes, and compare these to those of a set of 27 well-studied low redshift (z ∼ 0.1) quasars (Elvis et al. 1994a) which are matched to the high redshift ones in evolved luminosity. Single power law fits to the average fluxes within a set of narrow, line-free, windows between 1285˚A and 5100˚A, but excluding the 2000 − 4000˚A region of the FeII+BaC ‘small bump’, are adequate for most of the objects. For both the high and low redshift samples, the distributions of spectral indices, αouv (Fν ∼ ν αouv) span a wide range, with ∆αouv ∼ 1. The cause of such diversity is investigated, and our analysis is consistent with the conclusion of Rowan-Robinso

Year: 2001
OAI identifier: oai:CiteSeerX.psu:10.1.1.315.264
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