Topics in Gravitational Wave Physics: Lensing, Detection with Astrometry and Dark Siren Hubble Measurement

Citation

Wang, Yijun (2024) Topics in Gravitational Wave Physics: Lensing, Detection with Astrometry and Dark Siren Hubble Measurement. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/fjya-qm21. https://resolver.caltech.edu/CaltechTHESIS:05302024-045951995

Abstract

In this thesis, we study several subjects in gravitational wave (GW) physics, including gravitational wave lensing, detection with astrometry data and dark siren measurement of cosmological parameters.

We investigate various lensing features and their detection prospects in third-generation gravitational-wave networks. Firstly, we focus on type II lensed images which are Hilbert transforms of regular images. We compute the waveform mismatch and quantify the distinguishable fraction given Bayes factor thresholds over a range of binary mass ratio and redshifted mass. We make forecast on the detectable and distinguishable type II images in aLIGO Voyager, Cosmic Explorer and Einstein Telescope. This work shows that a significant number of type II images can be distinguished from waveforms alone, and this strategy can contribute to future pipelines for more accurate GW event inference.

We further model relativistic lensing in a large-inclination hierarchical triple system with a central Kerr supermassive black hole. We combine the elliptical integral formalism and optical scalar formalism to study image location and magnification. By analyzing the repeated lensing signature observed by the Decihertz Gravitational-wave Observatory, we examine the importance of relativistic images in detecting the presence of lensing or specifically the lens spin. We compute the detectable effective volume and estimate the upper limit for expected number of such events. This work demonstrates that lensing with relativistic images is a fruitful avenue where decihertz observation contributes to studies on intermediate-mass binary black holes and their galactic environment.

GW detection with astrometry was proposed as an alternative strategy that uses stellar astrometry data for GW measurement with flexible frequency coverage. We point out that surveys providing relative astrometry only can also be sensitive to GWs. We apply this method to the Roman Space Telescope Galactic Bulge Time Domain survey and make sensitivity forecast for both monochromatic GWs from supermassive binary black holes and stochastic GW background. We clarify the survey requirements and technical challenges for GW detection, and show that Roman will enable microhertz GW measurement for local sources. We also present on-going work to develop a data-processing pipeline to use Kepler archival data to search for GWs.

With increasing number of events in GW catalog, the GW source population offers a unique perspective into cosmology and astrophysics. In the last chapter, we use a Fisher information formalism to quantify the astrophysical model error tolerance of GW dark siren measurement on cosmological parameters. We generate galaxy catalog based on realistic survey and population parameters, and we apply expected GW uncertainties in third-generation ground-based networks. Based on simulation results, we study dominating error factors and make suggestions to dark siren selection strategy given different total error requirements.

Thesis Files