The near-IR properties and continuum shapes of high redshift quasars from the Sloan Digital Sky Survey

¹ Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117, Heidelberg, Germany
² Instituto de Astrofisica de Canarias, 38205 La Laguna, Tenerife, Spain
³ Steward Observatory, The University of Arizona 933 N. Cherry Ave, Tucson, AZ 85721-0065 Arizona, USA
⁴ Princeton University Observatory, Princeton 08544, USA
⁵ Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
⁶ Apache Point Observatory PO Box 59, Sunspot, NM 88349-0059, USA

Corresponding author: L. Pentericci, laura@mpia.de

Received: 22 January 2003
Accepted: 4 July 2003

Abstract

We present photometry for a sample of 45 high redshift quasars found by the Sloan Digital Sky Survey. The sample was originally selected on the basis of optical colors and spans a redshift range from 3.6 to 5.03. Our photometry reflects the rest-frame SED longward of Lyα for all redshifts. The results show that the near-IR colors of high redshift quasars are quite uniform. We have modelled the continuum shape of the quasars (from just beyond  to ~4000 Å) with a power law of the form , and find with a scatter of 0.33. This value is similar to what is found for lower redshift quasars over the same restframe wavelength range, and we conclude that there is hardly any evolution in the continuum properties of optically selected quasars up to redshift 5. The spectral indices found by combining near-IR with optical photometry are in general consistent but slightly flatter than what is found for the same quasars using the optical spectra and photometry alone, showing that the continuum region used to determine the spectral indices can somewhat influence the results.