A radio view of high-redshift quasars
The sparsely-populated radio sky is dominated by extragalactic objects, and radio surveys have long proven effective at identifying distant quasars. In this work, I describe the discovery of the only known z > 6 radio-loud quasar. This unique object, J1427+3312, was found through examination of the optical and infrared counterparts to radio sources in a four square degree region of the sky. I summarize the results of high-resolution radio imaging which constrains models of gravitational lensing for this object, and which indicate that the radio emission may have only recently turned on.
The discovery of J1427+3312 motivated further attempts to locate high-redshift quasars in radio surveys. I present a method for identifying quasar candidates from faint, red optical counterparts to radio sources using wide-field survey data from FIRST and SDSS. This method can be used to target the rare population of highly-luminous, radio-loud quasars at z > 6.
Radio data can also be used to examine the effectiveness of optical selection, by efficiently identifying quasar candidates with weaker constraints on their optical colors. I describe a spectroscopic survey of red, star-like counterparts to radio sources designed to probe the z > 3.5 quasar population. By deriving a radio-loud quasar luminosity function and comparing to optical results at the same redshift, I find that optical surveys are effective at identifying quasars in this redshift range. On the other hand, the radio-selected sample contains a large number of lowredshift, reddened quasars which are missed by optical surveys. I show that the red colors of these objects are consistent with having been caused by dust extinction.
Lastly, I examine the environments of z > 1 radio-loud quasars. While an accumulating body of evidence suggests that powerful AGN strongly affect their environments, it is also possible that the local environment affects the nature of the radio source. In particular, the morphology of radio sources may be influenced by the local density, which determines whether the radio jets can propagate unimpeded to large distances. I present deep infrared imaging of the fields surrounding ten radio-loud quasars, and compare the counts of faint nearby galaxies likely to be within the local environments of the quasars.