演講資訊

摘要：

This talk will include two topics about fast radio bursts (FRBs) as cosmic probes:
(i) missing baryon problem and (ii) the Hubble tension.
The enigma of the missing baryons poses a prominent and unresolved problem in astronomy. Dispersion measures (DM), serving as a distinctive observable of fast radio bursts (FRBs), quantify the electron column density along each line of sight, revealing the missing baryons described in the Macquart (DM-z) relation. The scatter of this relation is anticipated to be caused by the variation of cosmic structure. However, this is not yet statistically confirmed. Here, we present the statistical evidence of the cosmological baryonic fluctuation by measuring the foreground galaxy number densities around localized FRBs with galaxy catalogues.We found a positive correlation between the excess of DM contributed by the medium outside galaxies and the foreground galaxy number density. Our findings indicate that baryonic matters outside galaxies exceed its cosmic average along the line of sight to high galaxy-density regions, whereas there is less amount of baryons along the line of sight to low-density regions, presenting the statistical evidence of the cosmological fluctuation of the missing baryons.
Measuring the Hubble constant (H0) is one of the most important missions in astronomy. Nevertheless, recent studies exhibit the tension of H0 among different measurements. DM measured by FRBs could open a new avenue to probe H0 because the cosmic average of the intergalactic component, DM_IGM, is proportional to H0. I will present a new methodology to constrain H0 by utilizing the temporal scattering of the FRB pulses. This method could reduce the systematic error of H0 measurements with FRBs by ~9%. This systematics is comparable to the Hubble tension, indicating the feasibility of our method to address the Hubble tension using future FRB samples.