The observational signature of the first H II regions

TL;DR

This paper uses advanced simulations to predict the radio signatures of the first H II regions around Population III stars, providing potential observational targets for upcoming radio telescopes.

Contribution

It introduces a detailed 3D simulation approach with ray-tracing to model ionising radiation breakout and predicts the radio background contributions from the first stars.

Findings

Global bremsstrahlung signal of about 1 mK

21 cm emission signature ten times larger

Potential detectability with the Square Kilometer Array

Abstract

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.