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The distribution of galaxy morphological types and the morphology–mass relation in different environments at low redshift




We use ∼2000 galaxies from PM2GC (Calvi, Poggianti & Vulcani 2011a) belonging to different environments to show how the fractions of different galaxy morphological types vary with global environment and as function of galaxy stellar mass at low redshift. Considering mass-limited galaxy samples with log10M/M≥ 10.25, we find a smooth increase/decline in the fraction of Es–S0s/late-type galaxies going from single galaxies, to binaries, to groups. Considering all environments, the fractional variation is more conspicuous for S0s and late types than for ellipticals solely due to a sharp enhancement/dearth of S0s/late types in clusters compared to other environments. The morphological distribution of galaxies in the mass range 10.25 < log10M/M < 11 is rather independent of both galaxy stellar mass and global environment, except in clusters. The morphologies of galaxies more massive than log10M/M= 11 are instead a function of both galaxy mass and global environment. The morphology–mass relation therefore changes with global environment, showing that galaxy stellar mass cannot be the only parameter driving the morphological distribution of galaxies. The morphology–mass relations for S0 and late-type galaxies in clusters are peculiar compared to other environments, and this strongly suggests that cluster-specific effects act on these two types of galaxies, and that a significant number of S0s in clusters has a different origin with respect to S0s in other environments.