Infrared Imaging of SDSS Quasars: Implications for the Quasar K correction

Abstract

We have imaged 45 quasars from the Sloan Digital Sky Survey (SDSS) with redshifts 1.85 < z < 4.26 in JHKs with the KPNO SQIID imager. By combining these data with optical magnitudes from the SDSS we have computed the restframe optical spectral indices of this sample and investigate their relation to quasar redshift. We find a mean spectral index of <alpha_o> = -0.55+/-0.42 with a large spread in values. We also find possible evolution of the form alpha_o = (0.148+/-0.068)z - (0.964+/-0.200)$ in the luminosity range -28.0 < M_i < -26.5. Such evolution suggests changes in the accretion process in quasars with time and is shown to have an effect on computed quasar luminosity functions.

20 pages, 10 figures, 3 tables, accepted to the Astronomical Journal

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• An Apparent Redshift Dependence of Quasar Continuum: Implication for Cosmic Dust Extinction?
• Early Science Result from the Japanese Virtual Observatory: AGN and Galaxy Clustering at z = 0.3 to 3.0
• Study of the observational compatibility of an inhomogeneous cosmology with linear expansion according to SNe Ia
• An estimate of the gravitational-wave background from the observed cosmological distribution of quasars
• In The Neighbourhood of Tame Monsters: A study of galaxies near low-redshift quasars
• A Treasure Hunt in the Pool of Spectra Classified as High-redshift QSOs by the Spectroscopic Pipeline of the SDSS DR16
• A new model of quasar mass evolution