Structure and Evolution of Dwarf Galaxies
  Different structural parameter correlations show how classical bulge
components and elliptical galaxies are different from spiral and S0 galaxy
disks, irregular (Im) galaxies, and spheroidal (Sph) galaxies. In contrast, the
latter, apparently diverse galaxies or galaxy components have almost identical
parameter correlations. This shows that they are related. A review of galaxy
transformation processes suggests that S0 and spheroidal galaxies are
star-formation-quenched, "red and dead" versions of spiral and Im galaxies. In
particular, Sph galaxies are bulgeless S0s. This motivates a parallel sequence
galaxy classification in which an S0a-S0b-S0c-Sph sequence of decreasing
bulge-to-total ratios is juxtaposed to an Sa-Sb-Sc-Im sequence of star-forming
galaxies. All parameter sequences show a complete continuity from giant
galaxies to the tiniest dwarfs. Dwarfs are not a new or different class of
galaxies. Rather, they are the extreme products of transformation processes
that get more important as gravitational potential wells get more shallow.
Smaller Sph and S+Im galaxies have lower stellar densities because they retain
fewer baryons. Comparison of the baryonic parameter correlations with those for
dark matter halos allows us to estimate baryon loss as a function of galaxy
mass. Extreme dwarfs are almost completely dominated by dark matter.
