Quasar Environment in the Context of Large Scale Structure at z ∼ 0 . 3

We are looking 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 are using Voronoi tessellation applied in colour (BJ−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 plates. By reconstructing the largescale 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.