Red synchrotron jets in Parkes quasars

We present model fits to spectral energy distributions in the optical and n ear-infrared of >100 flat-spectrum radio quasars from the Parkes Half-Jansk y Flat-spectrum Sample. We find that similar to 40 per cent of the sources have power-law spectral energy distributions (SEDs), while a similar number show evidence for two primary components: a blue power law and optical syn chrotron emission. The blue power law is similar to the dominant component observed in the spectra of optically selected quasars. There is strong evid ence that the synchrotron component has a turnover in the ultraviolet-optic al rest frame of the spectrum. In the remaining sources, it is likely that the synchrotron peaks at longer wavelengths. This mixture of two components is supported by optical polarization measurements in a subgroup of the sou rces. The sources with power-law SEDs show evidence for an excess number of red power-law slopes compared with optically selected quasars. There are a dditional spectral components in some of the sources, such as dust and the underlying galaxy, which have not been considered here.