Abstract

The 21cm hyperfine transition of neutral hydrogen is a powerful probe of Cosmic Dawn and the Epoch of Reionisation. Global 21cm experiments like REACH aim to detect this faint 21cm hydrogen signal, which relies on modelling and removing the bright astrophysical foregrounds from the calibrated sky temperature. In addition to detecting the 21cm signal, this allows us to recover low-frequency radio foreground maps at continuous frequencies.

To build these radio maps, we divide the sky into regions parametrised by their spectral index, scale using an existing base map, then convolve with the antenna beam. Fitting the foreground model using nested sampling yields the Bayesian evidence, which is used to set the model complexity. We compare the effect of different foreground models on the recovered sky maps. Our goal is to produce the first continuous-frequency sky map in the 50 – 150 MHz REACH band.