A scenario of galaxy formation whereby massive galaxies formed earlier in the history of the → Universe (i.e. at high → redshifts) and completed their → star formation process more rapidly than low-mass galaxies. This scenario contrasts with what might be expected from simple → hierarchical structure formation scenarios, which predict that large galaxies formed in more recent times through the → merging of small galaxies.
Downsizing, first suggested by Cowie et al. (1996, AJ 112, 839), from downsize (v.), is a new sense for this term. Its current main meaning in non astrophysical contexts is "to make in a smaller size, or become smaller in size (in particular in economic vocabulary, by reductions in personnel)," from → down + → size.