Constraints on galactic wind models
  Observational implications are derived for two standard models of
supernovae-driven galactic winds: a freely expanding steady-state wind and a
wind sourced by a self-similarly expanding superbubble including thermal heat
conduction. It is shown that, for the steady-state wind, matching the measured
correlation between the soft x-ray luminosity and star formation rate of
starburst galaxies is equivalent to producing a scaled wind mass-loading factor
relative to the star-formation rate of 0.5 - 3, in agreement with the amount
inferred from metal absorption line measurements. The match requires the
asymptotic wind velocity v_inf to scale with the star formation rate SFR (in
solar masses per year) approximately as v_inf ~ (700 - 1000) km/s SFR^{1/6}.
The corresponding mass injection rate is close to the amount naturally provided
by thermal evaporation from the wall of a superbubble in a galactic disc,
suggesting thermal evaporation may be a major source of mass-loading. The
predicted mass-loading factors from thermal evaporation within the galactic
disc alone, however, are somewhat smaller, 0.2 - 2, so that a further
contribution from cloud ablation or evaporation may be required. Both models
may account for the 1.4GHz luminosity of unresolved radio sources within
starburst galaxies for plausible parameters describing the distribution of
relativistic electrons. Further observational tests to distinguish the models
are suggested.
