Simbasimulation: the effect of feedback physics on matter distribution in the cosmic web

Abstract

The discrepancy between the early-time estimation and late-time observation of the cosmic baryon content – the ‘missing baryon problem’ – is a long-standing problem in cosmology. Although recent studies with fast radio bursts (FRBs) have largely addressed this discrepancy, the precise spatial distribution of these baryons remains uncertain due to the effects of galaxy feedback. Cosmological hydrodynamical simulations such as Simba have shown that the partitioning of baryons between the intergalactic medium (IGM) and haloes is sensitive to feedback models, motivating the connection between baryon distribution and feedback physics. With the Simba simulation suite, this study investigates how feedback affects the distribution of matter within large-scale cosmic structures, with implications for FRB foreground modelling. We apply the T-web method to classify the cosmic web into different structures: knots, filaments, sheets, and voids. We then analyse how the different feedback variants of Simba affect the distribution of matter within each structure. Our results show that in Simba, the fractions of IGM gas in different cosmic web structures vary by only a few per cent under different feedback models. However, jet feedback produces noticeable changes in the gas distribution within structures, enhancing the diffuse IGM on the outskirts of filaments and knots, potentially biassing the empirical relation between matter distribution and dispersion measure. This research provides a new perspective on the impact of feedback on the IGM and motivates a refined data model for FRB foreground mapping.