Quasar environment in the context of large-scale structure at z similar to 0.3

Abstract

We look at quasar environment in the context of large-scale structure (LSS) – a new approach, giving a more informed interpretation of quasar–galaxy correlations. This paper presents our first results for a sample of z , 0:3 quasars. We use Voronoi tessellation applied in colour BJ 2 R slices for the detection of galaxy clusters and the minimal spanning tree (MST) to delineate the large-scale structure. This new cluster detection method allows us to find reliably galaxy clusters at z , 0:3 from SuperCOSMOS measurements of UK Schmidt Telescope plates. By reconstructing the large-scale structure in a relatively narrow redshift band 0:2 , z , 0:3 , we show that quasars follow the large-scale structure traced by galaxy clusters. None of the quasars in our radio-quiet sample is located in the central area of a galaxy cluster. Two quasars, found in a very rich environment, are actually located between two very close galaxy clusters, consistent with results on z , 1 quasars, suggesting that cluster mergers may be involved in one of the quasar formation mechanisms.