Joint Astrophysics Colloquium

Joint Astrophysics Seminar

Gravitational Lenses, the Hubble Constant, and Moderate-Redshift Galaxy Groups

Chris Fassnacht

UC Davis

The Hubble Constant is a cosmological parameter that sets the distance scale of the Universe. In spite of the recent beautiful results from observations of the cosmic microwave background and nearby galaxies, the value of the Hubble Constant is not as well constrained as we would hope. I will describe an elegant method for measuring the Hubble Constant that is completely independent of traditional distance measures. This method, using strong gravitational lenses, depends only on general relativity and simple geometry. I will present results from a program to measure the Hubble Constant and then discuss one of the major systematic effects in lens-based distance measurements, namely the effect of the local environment of the lens. Finally, I will describe how the investigations of lens environments can provide insights into the distributions of dark and luminous matter in moderate-redshift galaxy groups.