Ray-tracing Fast Radio Bursts Through IllustrisTNG: Cosmological Dispersion Measures from Redshift 0 to 5.5

Abstract

Abstract The dispersion measures (DMs) of fast radio bursts (FRBs) arise predominantly from free electrons in the large-scale structure of the Universe. The increasing number of FRB observations has started to empirically constrain the distribution of cosmic baryons, making it crucial to accurately forward model their propagation within cosmological simulations. In this work, we present a method for measuring FRB DMs in IllustrisTNG that continuously traces rays through the simulation while reconstructing all traversed line segments within the underlying Voronoi mesh. Leveraging this technique, we create over 20 publicly available DM catalogs, including full-sky DM maps observed from Milky Way–like environments. Our method addresses a problem in previous TNG-based studies, in which a sparse snapshot sampling in the path integral leads to a misestimation of the standard deviation and higher moments of the DM distribution p (DM∣ z ) by over 50%. We show that our results are consistent with the most recent observational data from the DSA-110, ASKAP, and CHIME. We offer a functional form for p (DM∣ z ) that provides very good fits across all redshifts from 0 to 5.5, showing that the previously proposed log-normal distribution is not well matched to the data. We find that using simulation box sizes of or below 35 h −1 Mpc, or low resolutions with baryonic masses exceeding 5 × 10 8 h −1 M ⊙ , can distort the derived DM signal by more than 8%. Our findings provide new insights into how the cosmic web shapes FRB signals and highlight the importance of accurate methodology when comparing cosmological simulations against observations.