Large-scale structure cosmology and the thermal history of baryons

The standard model of cosmology, the LambdaCDM model, is remarkably successful at explaining a wide range of observations of our Universe. However, it is now being subjected to much more stringent tests than ever before, and recent large-scale structure (LSS) measurements appear to be in tension with its predictions. One possible explanation for this tension is that there are (unaccounted for) systematic errors in the analysis of LSS data. The largest source of systematic uncertainty at present is from the modelling of complicated astrophysical phenomena associated with galaxy formation. In particular, energetic feedback processes associated with star formation and black hole growth can heat and expel gas from collapsed structures and modify the large-scale distribution of matter. If these effects are ignored (as is typically the case) or modeled incorrectly, they could plausibly induce a signal that explains the current tension. Cosmological hydrodynamical simulations are the only method which can follow all the relevant matter components and self-consistently capture the effects of feedback. Here we propose to use the state-of-the-art FLAMINGO simulations to perform a careful comparison with new observations that track the thermal state of normal matter in the Universe (so-called baryons). In particular, we will explore how the thermal history of baryons is affected by feedback processes and we will use the observations to perform model selection in order to evaluate whether feedback processes can indeed explain the current tension.