The CGM with local universe FRBs: evidence of strong AGN feedback in a massive elliptical galaxy

Modern cosmology and galaxy formation rely on an understanding of how cosmic baryons are distributed, a significant portion of which exist in the diffuse gas confined to halos. Fast Radio Bursts (FRBs) are a promising probe of the Universe's ionized gas. At low redshift, the contribution to the dispersion measure (DM) from the intergalactic medium (IGM) and intervening halos is subdominant, allowing us to study the circumgalactic media (CGM) of the host galaxies, if the host interstellar medium (ISM) can be sufficiently suppressed. We select a sample of five local universe FRBs with host halos spanning a wide range in mass ($\sim10^{11-13}\,M_\odot$), and with indicators that host ISM DM is negligible. We use these FRBs to constrain the CGM in each halo by comparing to simulations and measuring the CGM mass assuming a range of spherical gas profiles. We find one of our sources, the only massive elliptical host galaxy, strongly disfavors low feedback scenarios in simulations, and has been evacuated of its baryons ($\sim\,10\%$ of the cosmological average $\frac{\Omega_b}{\Omega_m}$ within $R_\mathrm{vir}$). This galaxy shows evidence of a past episode of AGN activity, consistent with the picture of strong AGN feedback in galaxy group-scale halos. The gas mass measurements for the other sources tentatively support more baryon retention in $L_*$ galaxies compared to group-scale halos. Finally, we demonstrate that a large sample of local universe FRBs will enable precision measurements of halo gas.