Secular Evolution in Disk Galaxies
  Self-gravitating systems evolve toward the most tightly bound configuration
that is reachable via available evolution processes. The inner parts shrink and
the outer parts expand, provided that some physical process transports energy
or angular momentum outward. The evolution of stars, star clusters,
protostellar and protoplanetary disks, black hole accretion disks, and galaxy
disks are all fundamentally similar. These processes for galaxy disks are the
subjects of my lectures and of this Canary Islands Winter School. Part 1
discusses formation, growth, and death of bars. Part 2 details the slow
("secular") rearrangement of angular momentum that results from interactions
between stars or gas and nonaxisymmetries such as bars. We have a heuristic
understanding of how this forms outer rings, inner rings, and stuff dumped into
the center. Observations show that barred galaxies have central concentrations
of gas and star formation. Timescales imply that they grow central
"pseudobulges" that get mistaken for elliptical-galaxy-like classical bulges
but that formed gently out of disks. Part 3 shows how we distinguish between
classical and pseudo bulges. Part 4 reviews how environmental secular evolution
transforms gas-rich, star-forming spirals and irregulars into gas-poor, red and
dead S0 and spheroidal ("Sph") galaxies. Sphs are not ellipticals; they have
structural parameters like those of low-luminosity S+Im galaxies. So Sphs are
bulgeless S0s. Part 5 combines hierarchical clustering and secular evolution
into a comprehensive picture.
