An FRB Sent Me a DM: Constraining the Electron Column of the Milky Way Halo with Fast Radio Burst Dispersion Measures from CHIME/FRB

Abstract

The CHIME/FRB project has detected hundreds of fast radio bursts (FRBs), providing an unparalleled population to statistically probe the foreground media that they illuminate. One such foreground medium is the ionized halo of the Milky Way (MW). We estimate the total Galactic electron column density from FRB dispersion measures (DMs) as a function of Galactic latitude using four different estimators, including ones that assume spherical symmetry of the ionized MW halo and ones that imply more latitudinal variation in density. Our observation-based constraints of the total Galactic DM contribution for ∣b∣ ≥ 30°, depending on the Galactic latitude and selected model, span 87.8–141 pc cm−3. This constraint implies upper limits on the MW halo DM contribution that range over 52–111 pc cm−3. We discuss the viability of various gas density profiles for the MW halo that have been used to estimate the halo’s contribution to DMs of extragalactic sources. Several models overestimate the DM contribution, especially when assuming higher halo gas masses (∼3.5 × 1012 M ⊙). Some halo models predict a higher MW halo DM contribution than can be supported by our observations unless the effect of feedback is increased within them, highlighting the impact of feedback processes in galaxy formation.

Deep Synoptic Array Science: Two Fast Radio Burst Sources in Massive Galaxy Clusters

“…This value includes the Galactic halo. These values are based on NE2001 (Cordes & Lazio 2002) and YMW16 (Yao et al 2017) and recent evidence that the Milky Way halo contribution to DM is smaller than previously thought (Bhardwaj et al 2021;Cook et al 2023;Ravi et al 2023b). The two FRB sources are nearby on the sky, allowing us to use similar estimates for ( )  DM MW .…”

The Demographics, Stellar Populations, and Star Formation Histories of Fast Radio Burst Host Galaxies: Implications for the Progenitors

“…The FRB signal properties, namely their dispersion measure (DM), rotation measure (RM), duration, spectrotemporal morphology, and polarization, provide key information on their central engines, and serve as important probes of the intervening ionized matter (e.g., Michilli et al 2018;Hessels et al 2019;Hilmarsson et al 2021;Mannings et al 2022;Ryder et al 2022;Wu & McQuinn 2023;Cook et al 2023;Ocker et al 2023). However, these signals alone provide only a highly model-dependent, low-precision estimate of the distance to the FRB, making it difficult or impossible to infer the parent stellar populations and FRB energetics directly.…”

Pathfinding Fast Radio Bursts Localizations using Very Long Baseline Interferometry

“…We can treat this estimate as conservative, and it can be as low as 6 pc cm −3 [62]. This is also consistent with CHIME/FRB constraints on the halo DM [63]. The IGM contribution is estimated to be DM cosmic = (172 ± 90) pc cm −3 [1], where the range is due to cosmic variance in the Macquart relation out to z ≈ 0.18 [34].…”