Dissecting the Gravitational Lens B1608+656: Implications for the Hubble Constant

Citation

Suyu, Sherry Hsuan (2008) Dissecting the Gravitational Lens B1608+656: Implications for the Hubble Constant. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/MQS2-Y860. https://resolver.caltech.edu/CaltechETD:etd-09132007-122424

Abstract

Strong gravitational lens systems provide a tool for probing galaxy mass distributions (independent of their light profiles) and for measuring cosmological parameters. In a strong lens system, the background source intensity distribution is multiply imaged. If the source intensity is time varying, then the multiple images of the variable source are delayed in time relative to each other due to the different light travel time along the multiple light paths. One can use lens systems to measure the Hubble constant by obtaining the relative time delays between the multiple images and modeling the lens potential. B1608+656 is a quadruply imaged gravitational lens system with a spatially extended source intensity distribution and two interacting galaxy lenses. This system is unique in that the three relative time delays between the four images were measured accurately with errors of only a few percent, and it thus provides an opportunity to measure the Hubble constant with high precision. The extended source intensity distribution in B1608+656 provides additional constraints on the lens potential, though simultaneous determination of the source intensity and lens potential distribution is needed. The presence of dust and interacting galaxy lenses further complicate this system. We present a comprehensive analysis in a Bayesian framework that takes into account the extended source intensity distribution, interacting galaxy lenses, and the presence of dust for reconstructing the lens potential. Using the deep HST ACS observations on B1608+656, the resulting statistical uncertainty on H_0 associated with the lens modeling is limited by the uncertainty in the best time delay measurement (~3%). The dominant systematic error on H_0 is due to the effects of the environment on B1608+656 (mass-sheet degeneracy). By using the measured velocity dispersion of the lens galaxies and considering the mass structures along the line of sight to B1608+656, we place constraints on the external convergence associated with galaxy groups and mass structure along the line of sight. The resulting Hubble constant from B1608+656 is H_0 = 72 ± 2 (stat.) ± 4 (syst.) km s^-1 Mpc^-1.

Thesis Files