Double-lobed radio quasars from the Sloan Digital Sky Survey

We have combined a sample of 44,984 quasars selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 with the FIRST radio survey. Using a novel technique in which the optical quasar position is matched to the complete radio environment within 45000, we are able to characterize the radio morphological makeup of what is essentially an optically selected quasar sample, regardless of whether the quasar (nucleus) itself has been detected in the radio. About 10% of the quasar population has radio cores brighter than 0.75 mJy at 1.4 GHz, and 1.7% have double-lobed FR2-like radio morphologies. About 75% of the FR2 sources have a radio core (> 0.75 mJy). A significant fraction (similar to 40%) of the FR2 quasars are bent by more than 10 degrees, indicating interactions of the radio plasma with either the intra-cluster medium or intergalactic medium. We found no evidence for correlations with redshift among our FR2 quasars; radio lobe flux densities and radio source diameters of the quasars have similar distributions at low (mean 0.77) and high (mean 2.09) redshifts. Using a smaller high-reliability FR2 sample of 422 quasars and two comparison samples of radio-quiet and non-FR2 radio-loud quasars matched in their redshift distributions, we constructed composite optical spectra from the SDSS spectroscopic data. Based on these spectra we can conclude that the FR2 quasars have stronger high-ionization emission lines compared to both the radio-quiet and non-FR2 radio-loud sources. This is consistent with the notion that the emission lines are brightened by ongoing shock ionization of ambient gas in the quasar host as the radio source expands.