A Model For Intergalactic Filaments and Galaxy Formation During the
  First Gigayear
  We propose a physically based, analytic model for intergalactic filaments
during the first gigayear of the universe. The structure of a filament is based
upon a gravitationally bound, isothermal cylinder of gas. The model
successfully predicts for a cosmological simulation the total mass per unit
length of a filament (dark matter plus gas) based solely upon the sound speed
of the gas component, contrary to the expectation for collisionless dark matter
aggregation. It argues that the gas, through its hydrodynamic properties, plays
a key role in filament structure rather than being a passive passenger in a
preformed dark matter potential. The dark matter of a galaxy follows the
classic equation of collapse of a spherically symmetric overdensity in an
expanding universe. In contrast, the gas usually collapses more slowly. The
relative rates of collapse of these two components for individual galaxies can
explain the varying baryon deficits of the galaxies under the assumption that
matter moves along a single filament passing through the galaxy centre, rather
than by spherical accretion. The difference in behaviour of the dark matter and
gas can be simply and plausibly related to the model. The range of galaxies
studied includes that of the so-called "too big to fail" galaxies, which are
thought to be problematic for the standard Lambda-CDM model of the universe.
The isothermal-cylinder model suggests a simple explanation for why these
galaxies are, unaccountably, missing from the night sky.
