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

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 similar to 0.3 quasars. We use Voronoi tessellation applied in colour (B-J - 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 similar to 1 quasars, suggesting that cluster mergers may be involved in one of the quasar formation mechanisms.