Speaker
Description
A new synergy is emerging between gravitational waves (GWs) and the study of the Universe’s large-scale structure. Along this line of research, we combine simulated observations of stellar-origin black hole mergers with neutral hydrogen 21 cm intensity mapping to probe cosmic expansion via the distance–redshift relation. GW signals from binary black holes provide direct distance measurements, while neutral hydrogen maps offer a tomographic view of the large-scale structure of the Universe. By using the 3-dimensional hydrogen density fields as a redshift prior for GW events, we introduce a novel dark-sirens-like method, which we dub radio sirens, to measure the late-time expansion history of the Universe.
We study the performance of the next-generation GW detectors, specifically the Einstein Telescope, to ensure enough statistics and access to high-redshift data. At the same time, future intensity mapping surveys with the SKA-Mid observatory are expected to trace the underlying dark matter distribution at large scales up to redshift 3. This combined methodology allows us to constrain the Hubble constant to 8% precision, using around 3,000 GW events with signal-to-noise ratios greater than 150. This corresponds to an improvement of nearly 40% compared to not considering the information from the neutral hydrogen maps.