Infrared photometry of z ∼ 1 3 C quasars

We present JHKL photometry of a complete sample of steep-spectrum radio-loud quasars from the revised 3CR catalogue in the redshift range 0.65 ≤ z < 1.20. After correcting for contributions from emission lines and the host galaxies, we investigate their spectral energy distributions (SEDs) around 1μm. About 75% of the quasars are tightly grouped in the plane of optical spectral index, αopt, versus near-infrared spectral index, αIR, with the median value of αopt close to the canonical value, and the median αIR slightly flatter. We conclude that the fraction of moderately-obscured, red quasars decreases with increasing radio power, in accordance with the ‘receding torus’ model which can also explain the relatively flat median near-infrared spectra of the 3CR quasars. Two of the red quasars have inverted infrared spectral indices, and we suggest that their unusual SEDs might result from a combination of dust-scattered and transmitted quasar light.