The observational signature of the first H II regions
  We use three-dimensional smoothed particle hydrodynamics simulations together
with a dynamical ray-tracing scheme to investigate the build-up of the first H
ii regions around massive Population III stars in minihaloes. We trace the
highly anisotropic breakout of the ionising radiation into the intergalactic
medium, allowing us to predict the resulting recombination radiation with
greatly increased realism. Our simulations, together with Press-Schechter type
arguments, allow us to predict the Population III contribution to the radio
background at 100 MHz via bremsstrahlung and 21 cm emission. We find a global
bremsstrahlung signal of around 1 mK, and a combined 21 cm signature which is
an order of magnitude larger. Both might be within reach of the planned Square
Kilometer Array experiment, although detection of the free-free emission is
only marginal. The imprint of the first stars on the cosmic radio background
might provide us with one of the few diagnostics to test the otherwise elusive
minihalo star formation site.
