Jan 21
PG84 morphology density relation
This is the plot of the morphology density relation data from Postman & Geller (1984, ApJ 281 95; PG84). Solid histograms are for PG84 groups, dashed histograms are for PG84 clusters and solid lines are the Dressler (1980, ApJ 236 351) relation, converted by PG84 onto their density and morphology systems.