Constraining the Hubble constant with scattering in host galaxies of fast radio bursts

¹ Department of Physics, National Chung Hsing University, 145, Xingda Road, Taichung 40227 Taiwan, ROC
² Institute of Astronomy, National Tsing Hua University, 101, Section 2. Kuang-Fu Road, Hsinchu 30013, Taiwan ROC
³ Department of Physics, National Tsing Hua University, 101, Section 2. Kuang-Fu Road, Hsinchu 30013 Taiwan, ROC
⁴ Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611 Australia
⁵ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218 Hawthorn, VIC 3122 Australia
⁶ OzGrav: The Australian Research Council Centre of Excellence for Gravitational Wave Discovery, Hawthorn, VIC 3122 Australia
⁷ ASTRO3D: The Australian Research Council Centre of Excellence for All-sky Astrophysics in 3D, ACT 2611, Australia
⁸ Sabancı University, Faculty of Engineering and Natural Sciences, 34956 Istanbul, Turkey

^⋆ Corresponding author; tetsuya@phys.nchu.edu.tw

Received: 22 May 2024
Accepted: 21 October 2024

Abstract

Aims. Measuring the Hubble constant (H₀) is one of the most important missions in astronomy. Nevertheless, recent studies exhibit differences between the employed methods.

Methods. Fast radio bursts (FRBs) are coherent radio transients with large dispersion measures (DM) with a duration of millisecondsḊM_IGM, the free electron column density along a line of sight in the intergalactic medium (IGM), could open a new avenue for probing H₀. However, it has been challenging to separate DM contributions from different components (i.e., the IGM and the host galaxy plasma), and this hampers the accurate measurements of DM_IGM and hence H₀. We adopted a method to overcome this problem by using the temporal scattering of the FRB pulses due to the propagation effect through the host galaxy plasma (scattering time). The scattering-inferred DM in a host galaxy improves the estimate of DM_IGM, which in turn leads to a better constraint on H₀. In previous studies, a certain value or distribution has conventionally been assumed of the dispersion measure in host galaxies (DM_h). We compared this method with ours by generating 100 mock FRBs, and we found that our method reduces the systematic (statistical) error of H₀ by 9.1% (1%) compared to the previous method.

Results. We applied our method to 30 localized FRB sources with both scattering and spectroscopic redshift measurements to constrain H₀. Our result is H₀ = 74_−7.2^+7.5 km s⁻¹ Mpc⁻¹, where the central value prefers the value obtained from local measurements over the cosmic microwave background. We also measured DM_h with a median value of 103₋₄₈⁺⁶⁸ pc cm⁻³.

Conclusions. The DM_h had to be assumed in previous works to derive DM_IGM. Scattering enables us to measure DM_IGM without assuming DM_h to constrain H₀. The reduction in systematic error is comparable to the Hubble tension (∼10%). Combined with the fact that more localized FRBs will become available, our result indicates that our method can be used to address the Hubble tension using future FRB samples.