Quasar environment in the context of large-scale structure atz∼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 usingVoronoitessellation applied in colour (B J −R) slices for the detection of galaxyclustersand the minimal spanning tree (MST) to delineate the large-scale structure. This newcluster-detection method allows us to find reliably galaxy clusters at z < 0.3 fromSuperCOSMOS measurements of UK Schmidt plates. By reconstructing the large-scale structure in a relatively narrow redshift band (0.2 < z < 0.3), we show thatquasars follow the large-scale structure traced by galaxy clusters. None of the quasarsin ourradio-quiet sample is located in the central areaofa galaxycluster. Two quasars,found in a very rich environment, are actually located between two very close galaxyclusters, consistent with results on z ∼ 1 quasars suggesting that cluster mergers maybe involved in one of the quasar formation mechanisms.Key words: galaxies: clusters: general – quasars: general – cosmology: large-scalestructure of Universe.