A Phase Change scenario for Galaxy Formation
  The 5 independent correlations between the properties of galaxies observed
outside big clusters must set such strong constraints on any theory of galaxy
formation that it is hard to imagine any but the right one passing muster;
certainly the standard model of Hierarchical Formation does not. Furthermore
those global correlations imply that such galaxies must be remarkably simple,
i.e. have virtually all of their variance attributable to a single Principal
Component. That being so the correlations ought to give strong hints as to the
process of formation. Two in particular: all galaxies have the same
Luminosity-Density, while Luminosity and Dynamical Mass are everywhere tightly
correlated, hint that formation took place at the epoch of Recombination.
Halving of particle numbers then will set up strong pressure-forces which could
fragment the medium and halt the expansion of neutral fragments, if they are
not too large. We find that fragments between $10^{11} $ and $10^{6} $ solar
masses (baryonic) will collapse gravitationally upon themselves, mostly
flattening in one dimension, to form galaxies between 10 kpc. and 0.3 kpc. in
size, and in two distinct classes. Those below $10^{8}$ solar masses will
remain transparent and cool, eventually sub-fragmenting into stars with a warm,
spheroidal distribution, while those above will become opaque and thus too hot
to form stars until after they have radiated away most of their axial binding
energy. They will then settle into thin discs with a low axial velocity
dispersion. This simple scenario generates most of the properties of the
galaxies but not flat rotation-curves. Finally we attempt to weigh up its pros
and cons as a viable theory of galaxy formation and conclude that it is much
superior to the Hierarchical model when it comes to fitting most observations.
At the very least it deserves further critical evaluation.
