Implications and Applications of Kinematic Galaxy Scaling Relations
  Galaxy scaling relations, which describe a connection between ostensibly
unrelated physical characteristics of galaxies, testify to an underlying order
in galaxy formation that requires understanding. I review the development of a
scaling relation that 1) unites the well-known Fundamental Plane (FP) relation
of giant elliptical galaxies and Tully-Fisher (TF) relation of disk galaxies,
2) fits low mass spheroidal galaxies, including the ultra-faint satellites of
our Galaxy, 3) explains the apparent shift of lenticular (S0) galaxies relative
to both FP or TF, 3) describes all stellar dynamical systems, including systems
with no dark matter (stellar clusters), 4) associates explicitly the numerical
coefficients that account for the apparent "tilt" of the FP away from the
direct expectation drawn from the virial theorem with systematic variations in
the total mass-to-light ratio of galaxies within the half-light radius, 5)
connects with independent results that demonstrate the robustness of mass
estimators when applied at the half-light radius, and 6) results in smaller
scatter for disk galaxies than the TF relation. The relation develops naturally
from the virial theorem, but implies the existence of additional galaxy
formation physics that must now be a focus of galaxy formation studies. More
pragmatically, the relation provides a lynchpin that can be used to measure
distances and galaxy masses. I review two applications: 1) the
cross-calibration of distance measurement methods, and 2) the determination of
mass-to-light ratios of simple stellar populations as a function of age, and
implications of the latter for the stellar initial mass function.
