A Census of the LyC Photons that Form the UV Background During Reionization

Understand

We present a new, on-the-fly photon flux and absorption tracer algorithm designed to directly measure the contribution of different source populations to the metagalactic UV background and to the ionisation fraction of gas in the Universe.

• We use a suite of multifrequency radiation hydrodynamics simulations that are carefully calibrated to reproduce a realistic reionization history and galaxy properties at $z \ge 6$, to disentangle the contribution of photons emitted by different mass haloes and by stars with different metallicities and ages to the UV background during reionization.
• While at very early cosmic times low mass, metal poor haloes provide most of the LyC photons, their contribution decreases steadily with time.
• At $z = 6$ it is the photons emitted by massive systems (${\rm M_{halo}}/{\rm M_\odot} > 10^{10} \, {\rm h ^{-1}}$) and by the metal enriched stars ($10^{-3} < Z/Z_{\rm \odot} < 10^{-1.5}$) that provide the largest contribution to the ionising UV background.