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