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A minority of the optically selected quasar population are red at opticalwavelengths due to the presence of dust along the line-of-sight. A key focus ofmany red quasar studies is to understand their relationship with the overallquasar population: are they blue quasars observed at a (slight) inclinationangle or do they represent a transitional phase in the evolution of quasars?Identifying fundamental differences between red and blue quasars is key todiscriminate between these two paradigms. To robustly explore this, we haveuniformly selected quasars from the Sloan Digital Sky Survey with mid-infraredcounterparts, carefully controlling for luminosity and redshift effects. Wetake a novel approach to distinguish between colour-selected quasars in theredshift range of $0.2 < z < 2.4$ by constructing redshift-sensitive $g^* -i^*$ colour cuts. From cross-matching this sample to the Faint Images of theRadio Sky at Twenty-centimeters (FIRST) survey, we have found a factor$\approx$ 3 larger fraction of radio-detected red quasars with respect to thatof blue quasars. Through a visual inspection of the FIRST images and anassessment of the radio luminosities (rest-frame ${L_{\rm 1.4~GHz}}$ and${L_{\rm 1.4~GHz}}/{L_{\rm 6\mu m}}$) we find that the radio-detection excessfor red quasars is primarily due to compact and radio-faint systems (around theradio quiet--radio loud threshold). We show that our results rule outorientation as the origin for the differences between red and blue quasars andargue that they provide broad agreement with an evolutionary model.

Fundamental differences in the radio properties of red and blue quasars: evolution strongly favoured over orientation