Oral Presentation
Constraining the Hubble Constant with Scattering in Host Galaxies of Fast Radio Bursts
Presenter: Tsung-Ching Yang (National Chung Hsing University/NCHU)
Measuring the Hubble constant (H_0) is one of the most important missions in astronomy. Nevertheless, recent studies exhibit the tension of H_0 among different measurements with ~10% systematics. Therefore, an independent method to measure H_0 is essential to address this issue. Fast radio bursts (FRBs) are coherent radio transients with large dispersion measures (DMs). DM in the intergalactic medium (IGM), DM_IGM, could open a new avenue to probe H_0. However, separating DM contributions from different components has been challenging, including DM_IGM and DM in the host galaxy (DM_h). DM_h has been unknown, which could cause significant systematic errors of DM_IGM and H_0 in the previous studies. We propose a new methodology to overcome this problem by utilizing the scattering of FRB pulses. Scattering is the temporal broadening of a radio pulse due to the propagation effect through the host galaxy plasma. Therefore, scattering carries the information on DM_h. Scattering-inferred improves the estimates of DM_h and DM_IGM, which in turn leads to a better constraint on H_0. Based on a recent model for the relation between the scattering time and DM_h, we demonstrate how our methodology works for 30 localized FRB sources with scattering and spectroscopic redshift measurements. Our result is H0 = 74-7.2+7.5 km s-1 Mpc-1, supporting local measurements than that measured by the cosmic microwave background (CMB). Our results also indicate that the median value of DMh is 103 ± 26 pc cm-3. To verify this method, we performed simulations to generate 100 mock FRBs with scattering measurements and compared our method and a previous method which assumes DM_h = 50 (pc cm-3). We demonstrate that our method reduces the systematic error of H_0 by 9.1% compared to the previous method, and the statistical error is reduced by 1%. The key point is that the reduction in systematic error is comparable to the ~10% systematics, indicating that our method is a powerful tool to address the Hubble tension using future FRB samples.
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