Katherine Blundell OBE

Abstract:

We use the K - z relation for radio galaxies to illustrate why it has proved difficult to obtain definitive cosmological results from studies based entirely on catalogues of the brightest radio sources, e.g. 3C. To improve on this situation we have been undertaking redshift surveys of complete samples drawn from the fainter 6C and 7C radio catalogues. We describe these surveys, and illustrate the new studies they are allowing. We also discuss our 'filtered' 6C redshift surveys: these have led to the discovery of a radio galaxy at z = 4.4, and are sensitive to similar objects at higher redshift provided the space density of these objects, rho, is not declining too rapidly with z. There is currently no direct evidence for a sharp decline in the rho of radio galaxies for z > 4, a result only barely consistent with the observed decline of flat-spectrum radio quasars.

Abstract:

From new complete samples of radio sources selected at low flux limits in low radio frequency, which give significantly improved coverage of the luminosity-redshift plane, we are able to decouple dependencies of source properties on redshift, from those depending on luminosity. We describe, with particular reference to the unification of radio galaxies and quasars, trends in linear size and also discuss core properties of these objects.

Abstract:

We describe the selection of a sample of 34 radio sources from the 6C survey (Hales, Baldwin & Warner 1993) from a region of sky covering 0.133 sr. The selection criteria for this sample, hereafter called 6C*, were chosen to optimise the chances of finding radio galaxies at redshift z > 4. Optical follow-up observations have already led to the discovery of the most distant known radio galaxy at z = 4.41 (Rawlings et al. 1996). We present VLA radio maps and derive radio spectra for all the 6C* objects.