Infrared imaging of sloan digital sky survey 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 Kitt Peak National Observatory simultaneous quad infrared imaging device imager. By combining these data with optical magnitudes from the SDSS we have computed the rest-frame optical spectral indices of this sample and investigate their relation with quasar redshift. We find a mean spectral index of 〈α o〉 = -0.55 0.42 with a large spread in values. We also find possible evolution of the form αo = (0.148 0.068)z - (0.964 0.200) in the luminosity range -28.0 < Mi < -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. © 2008. The American Astronomical Society. All rights reserved.