Kavli Affiliate: Kiyoshi W. Masui
| First 5 Authors: Adam E. Lanman, Adam E. Lanman, , ,
| Summary:
Fast radio bursts (FRBs) provide a sensitive probe of diffuse baryons: their
dispersion measures (DMs) measure electron density independent of temperature
and scale linearly with gas density. This makes them particularly well suited
to studying the intragroup medium (IGrM), where traditional probes such as
X-ray emission and the SZ effect are weak. Evidence suggests that the baryon
content of group mass halos ($M_500sim10^13-10^14$ M$_odot$) is
strongly affected by galactic feedback, creating deviations from cluster
scaling relations. Three FRBs from the first CHIME/FRB Outrigger sample come
from host galaxies found within or behind galaxy clusters and groups. Using
integrated halo density models, we estimate the DM contribution of each
ICM/IGrM, accounting for uncertainties in halo mass and the distance to the
host galaxy relative to the cluster center. For the more massive halos,
predicted cluster DMs agree with the extragalactic DM budget. One burst, FRB
20230703A, intersects three groups yet has a low extragalactic DM. By comparing
model predictions with the measured DM, we constrain the baryon fraction
$f_g(R)$ in these halos. Comparing with published $M-f_g$ relations, we find
consistency with recent eROSITA results at $R_500$, mild tension at
$R_200$, and strong tensions with earlier X-ray-based relations. As CHIME/FRB
Outriggers build a large catalog of localized FRBs, many additional sightlines
through groups and clusters will be obtained. These will enable systematic
tests of intragroup and intracluster gas properties and sharpen constraints on
the distribution of baryons in massive halos.
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