  Dark matter (DM) halos of Sc-Im and dwarf spheroidal (dSph) galaxies satisfy
scaling laws: halos in lower-luminosity galaxies have smaller core radii,
higher central densities, and smaller velocity dispersions. These results are
based on maximum-disk rotation curve decompositions for giant galaxies and
Jeans equation analysis for dwarfs. (1) We show that spiral, Im, and Sph
galaxies with absolute magnitudes M_V > -18 form a sequence of decreasing
baryon-to-DM surface density with decreasing luminosity. We suggest that this
is a sequence of decreasing baryon retention vs. supernova-driven losses or
decreasing baryon capture after cosmological reionization. (2) The structural
differences between S+Im and Sph galaxies are small. Both are affected mostly
by the physics that controls baryon depletion. (3) There is a linear
correlation between the maximum rotation velocities of baryonic disks and the
outer circular velocities V_circ of test particles in their DM halos. Baryons
become unimportant at V_circ = 42+-4 km/s. Smaller galaxies are dim or dark.
(4) We find that, before baryon "loss", dSph galaxies were brighter by ~4 mag
and dIm galaxies were brighter by ~3.5 mag. Both have DM halos that are massive
enough to help to solve the "Too Big To Fail" problem with DM galaxy formation.
(5) We suggest that there exist many galaxies that are too dark to be
discovered by current techniques, as required by cold DM theory. (6) Projected
central densities of DM halos are constant from M_B ~ -5 to -22. This implies a
Faber-Jackson law with halo mass M ~ (halo dispersion)**4.
