Large scale structures around high redshift radio galaxies

Narrowband Ly <F>α</F> imaging has been carried out around eight radio galaxies at <F>2<z<5.2</F> to search for (proto-)cluster galaxies at the same redshift. Subsequent spectroscopy has led to the discovery of six protoclusters at redshifts <F>z=</F>2.2, 2.9, 2.9, 3.1, 3.2 and <F>4.1</F>, with velocity dispersions between 300 km s<F>−1</F> and 1000 km s<F>−1</F>. The estimated masses are in the range <F>1014</F>–<F>1016</F> M<F>⊙</F>, comparable to the mass of present day rich clusters of galaxies. [Copyright &y& Elsevier]