Fundamentals of the Dwarf Fundamental Plane
  Star-forming dwarfs are studied to elucidate the physical underpinnings of
their fundamental plane. It is confirmed that residuals in the Tully-Fisher
relation are correlated with surface brightness, but that even after
accommodating the surface brightness dependence through the dwarf fundamental
plane, residuals in absolute magnitude are far larger than expected from
observational errors. Rather, a more fundamental plane is identified which
connects the potential to HI line width and surface brightness. Residuals
correlate with the axis ratio in a way which can be accommodated by recognizing
the galaxies to be oblate spheroids viewed at varying angles. Correction of
surface brightnesses to face-on leads to a correlation among the potential,
line width, and surface brightness for which residuals are entirely
attributable to observational uncertainties. The mean mass-to-light ratio of
the diffuse component of the galaxies is constrained to be 0.88 +/- 0.20 in Ks.
Blue compact dwarfs lie in the same plane as dwarf irregulars. The dependence
of the potential on line width is less strong than expected for virialized
systems, but this may be because surface brightness is acting as a proxy for
variations in the mass-to-light ratio from galaxy to galaxy. Altogether, the
observations suggest that gas motions are predominantly disordered and
isotropic, that they are a consequence of gravity, not turbulence, and that the
mass and scale of dark matter haloes scale with the amount and distribution of
luminous matter. The tight relationship between the potential and observables
offers the promise of determining distances to unresolved star-forming dwarfs
to an accuracy comparable to that provided by the Tully-Fisher relation for
spirals.
