Stellar Mass–Dispersion Measure Correlations Constrain Baryonic Feedback in Fast Radio Burst Host Galaxies

Abstract

Low-redshift fast radio bursts (FRBs) enable robust measurements of the host galaxy contribution to the dispersion measure (DM), offering valuable constraints on the circumgalactic medium (CGM) of FRB hosts. We curate a sample of 20 nearby FRBs with low scattering timescales and face-on host galaxies with stellar masses in the range 109 < M*/M⊙ < 1011. We fit the distribution of the host galaxy DM to a quadratic model as a function of stellar mass with a mass-independent scatter and find that the more massive the host, the lower its host DM. We report that this relation has a negative slope of m = −97 ± 44 pc cm−3 dex−1 in stellar mass. We compare this measurement against similar fits to three subgrid models implemented in the CAMELS suite of simulations from Astrid, IllustrisTNG, and SIMBA, which predict the CGM contribution to this relation, finding disagreement with the fiducial CAMELS-Astrid model, particularly for the most massive hosts (M* > 1010.5M⊙). More generally, models that attribute a positive correlation between stellar mass and host DM (m > 0) to the CGM are in tension with our measurement unless compensated by fine-tuning of the host interstellar medium contribution as a function of stellar mass, e.g., at the low-mass end. We show that this conclusion is robust to a wide range of assumptions, such as the offset distribution of FRBs from their hosts and the statistics of the cosmic contribution to the DM budget along each sight line. Our results indirectly imply a lower limit on the strength of baryonic feedback in the local Universe (z < 0.2) in isolated ∼L* halos, complementing results from weak-lensing surveys and kSZ observations that target higher halo mass and redshift ranges.