The baryonic Tully-Fisher relation and galactic outflows
  Most of the baryons in the Universe are not in the form of stars and cold gas
in galaxies. Galactic outflows driven by supernovae/stellar winds are the
leading mechanism for explaining this fact. The scaling relation between galaxy
mass and outer rotation velocity (also known as the baryonic Tully-Fisher
relation, BTF) has recently been used as evidence against this viewpoint. We
use a LCDM based semi-analytic disk galaxy formation model to investigate these
claims. In our model, galaxies with less efficient star formation and higher
gas fractions are more efficient at ejecting gas from galaxies. This is due to
the fact that galaxies with less efficient star formation and higher gas
fractions tend to live in dark matter haloes with lower circular velocities,
from which less energy is required to escape the potential well. In our model
the intrinsic scatter in the BTF is 0.15 dex, and mostly reflects scatter in
dark halo concentration. The observed scatter, equal to 0.24 dex, is dominated
by measurement errors. The best estimate for the intrinsic scatter is that it
is less than 0.15 dex, and thus our LCDM based model (which does not include
all possible sources of scatter) is only just consistent with this. In our
model, gas rich galaxies, at fixed virial velocity (V_vir), with lower stellar
masses have lower baryonic masses. This is consistent with the expectation that
galaxies with lower stellar masses have had less energy available to drive an
outflow. However, when the outer rotation velocity (V_flat) is used the
correlation has the opposite sign, with a slope in agreement with observations.
This is due to scatter in the relation between V_flat and V_vir. In summary,
contrary to some previous claims, we show that basic features of the BTF are
consistent with a LCDM based model in which the low efficiency of galaxy
formation is determined by galactic outflows.
