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

TL;DR

This study uses local universe FRBs to investigate the baryon content in galaxy halos, revealing evidence of strong AGN feedback in a massive elliptical galaxy and demonstrating FRBs' potential to measure halo gas fractions across a wide mass range.

Contribution

It provides the first constraints on the CGM gas mass in local universe galaxies using FRBs, highlighting the impact of AGN feedback and showcasing FRBs as a novel probe of halo gas.

Findings

Massive elliptical galaxy shows baryon evacuation, indicating past AGN activity.

FRBs can measure halo gas fraction across a broad halo mass range.

Upcoming FRB surveys will enable precise halo gas measurements.

Abstract

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. We select a sample of five local universe FRBs whose host interstellar medium (ISM) DM is negligible and use these to constrain the mass of the CGM in each halo. We find that one of our sources, the only massive elliptical host galaxy, has been evacuated of its baryons ($M_\mathrm{gas}=0.02^{+0.02}_{-0.02}M_\mathrm{h}$, corresponding to $\sim$10$\%$ of the cosmological average $\frac{\Omega_b}{\Omega_m}$). 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 other sources are consistent with existing multiwavelength data and tentatively support more baryon retention in $L_*$ galaxies compared to group-scale halos. We show that FRBs can measure the halo gas fraction $f_\mathrm{gas}$ in halos of mass $M_\mathrm{h}\sim10^{11-13}M_\odot$, and up to $\sim10^{14}M_\odot$ if galaxy cluster hosts are included, which is a larger range than other gas probes can access. Finally, we demonstrate that a large sample of local universe FRBs, such as those expected from upcoming all-sky radio telescopes, will enable precision measurements of halo gas, which is crucial for understanding the effects of feedback.