IR photometry of flat spectrum radio sources

IR measurements of optically faint, flat spectrum radio sources have implied the possible existence of a new class of quasar, with IR excess more extreme than that of any extragalactic object. In the present preliminary study, 18 Parkes flat spectrum sources have been observed in the IR without regard to optical morphology, and the red sources are found to be just the tail of the normal distribution of quasar colours. The results imply that a considerable fraction of flat spectrum sources from complete samples may have properties similar to the BL Lac objects.