Internal, slow (secular) evolution of galaxy disks occurs when nonaxisymmetries such as bars and spiral structure redistribute energy and angular momentum and rearrange disk structure. Environmentally driven evolution can also be secular (e. g., galaxy harassment), although better known processes are rapid (mergers). We concentrate on one consequence of environmental secular evolution. It is one of several processes that can transform late-type dwarfs into "spheroidals", i. e., galaxies that are morphologically similar to ellipticals but that have different structural parameter correlations indicative of different formation physics. Figure 1 puts these galaxy formation processes into a more general context.
Figure 1. Summary of galactic evolution processes (Kormendy & Kennicutt 2004: KK04). Processes are divided vertically into fast (top) and slow (bottom). Fast evolution happens on a free-fall timescale, tff ~ (G )-1/2, where is volume density and G is the gravitational constant. Slow means many galaxy rotation periods. Ram-pressure stripping is likely to be fast for dwarf galaxies and slow for giant galaxies. Processes are divided horizontally into ones that happen internally in one galaxy (left) and ones that are driven by environmental effects such as galaxy interactions (right). The processes at center affect all types of galaxy evolution. This paper reviews internal secular evolution in galaxy disks (lower-left) and the nature of spheroidal galaxies as defunct late-type galaxies transformed (right) by galaxy harassment, ram-pressure stripping, and other processes.