Environmental density vs. colour indices of the low-redshift galaxies

We applied 3D Voronoi tessellation method to determine the environmental density of the low-redshift galaxies selected from SDSS DR9 (0.02 < z <0.1 and m_r< 17.7). The sample was divided into two groups: the bright central galaxies with M_r< -20.7 (N ~ 120000) and the satellite galaxies with M_r> -20.7 (N ~ 140000). We characterized the environmental density of galaxies as the reverse volume of a Voronoi cell. We confirmed the tendency of evolutionary decrease of a relative number of early type galaxies (with quenching star formation) with increasing redshift. It was also shown that the higher the environmental density near the central galaxy, the more likely that it has an early morphological type. The fraction of the early type galaxies among the bright central galaxies is higher (78 per cent) than in the sample of satellite galaxies (26 per cent). In addition, the higher percentage of the central early-type galaxies in the sample, the greater their share in the denser environments