Abstract
Cosmic rays generated by supernovae carry away a significant portion of the lifetime energy emission of their parent star, making them a plausible mechanism for heating the early universe intergalactic medium (IGM). Following a review of the existing literature on cosmic ray heating, we develop a flexible model of this heating mechanism for use in 3D semi-numerical 21-cm signal simulations and conduct the first investigations of the signatures it imprints on the 21-cm power spectrum and tomographic maps. We find that cosmic ray heating of the IGM is short-ranged, leading to heating clustered around star-forming sites, and a sharp contrast between heated regions of 21-cm emission and unheated regions of absorption. This contrast results in greater small-scale power for cosmic ray heated scenarios compared to what is found for X-ray heating, thus suggesting a way to test the nature of IGM heating with future 21-cm observations. Finally, we find an unexpectedly rich thermal history in models where cosmic rays can only escape efficiently from low-mass halos, such as in scenarios where these energetic particles originate from population III star supernovae remnants. The interplay of heating and the Lyman-Werner feedback in these models can produce a local peak in the IGM kinetic temperature and, for a limited parameter range, a flattened absorption trough in the global 21-cm signal.TGJ would like to thank the Science and Technology Facilities Council (UK) for their continued support through grant number ST/V506606/1.
AF is supported by a Royal Society University Research Fellowship \#180523.
EdLA acknowledges the support of the Science and Technology Facilities Council (UK) through a Rutherford Fellowship.
WJH thanks the Royal Society for their support through a Royal Society University Research Fellowship.
RB acknowledges the support of the Israel Science Foundation (grant No.\ 2359/20), the Ambrose Monell Foundation, the Institute for Advanced Study, the Vera Rubin Presidential Chair in Astronomy, and the Packard Foundation
