Normalized distribution of the overdensity significance around z < 1.5 quasar pairs (red), z ∼ 1 single quasars (green), and random galaxy fields (grey). The overdensity significance |$\sigma _\mathrm{peak, 2^{\prime }}$| is defined as the peak significance within a two-arcminute radius from quasars or galaxies. The pair center is used for the case of quasar pairs. The negative significance means that all the area inside the two-arcminute radius have smaller galaxy densities than the average. The median value for each distribution (pair: 1.97; single: 1.47; random: 1.75σ) is indicated with a vertical line. (Color online)