A first measurement of baryonic feedback with Fast Radio Bursts

Baryonic feedback fundamentally alters the total matter distribution on small to intermediate cosmological scales, posing a significant challenge for contemporary cosmological analyses. Direct tracers of the baryon distribution are therefore key for unearthing cosmological information buried under astrophysical effects. Fast Radio Bursts (FRBs) have emerged as a novel and direct probe of baryons, tracing the integrated ionised electron density along the line of sight, quantified by the dispersion measure (DM). The scatter of the DM as a function of redshift provides insight into the lumpiness of the electron distribution and, consequently, baryonic feedback processes. Using a model calibrated to the BAHAMAS hydrodynamic simulation suite, we forward-model the statistical properties of the DM as a function of redshift. Applying this model to approximately 100 localised FRBs, we robustly constrain the governing feedback parameter, at 68% confidence. Our findings represent the first measurement of baryonic feedback using FRBs, relating to power spectrum suppression and demonstrating a strong rejection of no-feedback scenarios at greater than 99.7% confidence ( 3 σ ), depending on the FRB sample. We find that FRBs prefer fairly strong feedback, consistent with other measurements of the baryon distribution, as inferred from the thermal and kinetic Sunyaev-Zel’dovich effects. The results are robust against sightline correlations and modelling assumptions. We emphasise the importance of accurate calibration of the host galaxy and Milky Way contributions to the DM. Furthermore, we discuss implications for future FRB surveys and necessary improvements to current models to ensure accurate fitting of upcoming data, particularly that from low-redshift FRBs.