Searches for High Redshift Radio Galaxies

Abstract

We have started a search for High Redshift Radio Galaxies (HZRGs) in an area covering 7 sr by selecting a sample of Ultra Steep Spectrum (USS) sources with a low flux density cut-off S₁₄₀₀ > 10 mJy and a steep spectral index cut-off of α < -1.3 (S ∝ v ^α) from the WENSS, NVSS and TEXAS surveys. Our first results for 27 sources show that we are almost twice as effective in finding HZRGs than than surveys of relatively bright radio sources with a spectral index cut-off of α < -1.0. The redshift distribution is consistent with an extension of the z - α relation to α < -1.3, but a large fraction of our sample (40%) consists of objects which are too faint to observe with 3–4m class telescopes. Our search is aimed at increasing the number of very high redshift radio galaxies for further detailed studies of the formation and evolution of massive galaxies and their environment.