I can see your halo: Constraining the Milky Way halo DM with FRB population studies

TL;DR

This study uses 98 high-latitude FRBs to estimate the Milky Way's halo dispersion measure, providing a more robust average value and highlighting the importance of multiple sightlines for accurate constraints.

Contribution

It introduces a large FRB sample analysis to constrain the Galactic halo DM, improving upon previous low-DM studies and accounting for sightline fluctuations.

Findings

DM_{MW,halo} = 68^{+27}_{-24} pc/cm^3

No evidence favoring a specific halo model

Individual FRBs can significantly influence the results

Abstract

Fast radio bursts (FRBs) probe the electron column density along the line of sight and hence can be used to probe foreground structures. One such structure is the Galactic halo. In this work, we use a total of 98 high Galactic latitude ($|b| > 20^\circ$) FRBs detected by ASKAP, Parkes, DSA and FAST with 32 associated redshifts to constrain the dispersion measure (DM) contribution from the Galactic halo. We simultaneously fit unknown FRB population parameters, which show correlations with the Galactic halo but are not completely degenerate. We primarily use an isotropic model for the halo, but find no evidence favouring a particular halo model. We find DM$_{\rm MW,halo}$=$68^{+27}_{-24}$pc/cm$^3$, which is in agreement with other results within the literature. Previous constraints on DM$_{\rm MW,halo}$ with FRBs have used a few, low-DM FRBs. However, this is highly subject to fluctuations between different lines of sight, and hence using a larger number of sightlines as we do is more likely to be representative of the true average contribution. Nevertheless, we show that individual FRBs can still skew the data significantly and hence will be important in the future for more precise results.