Collaborative Research: A Precise and Accurate Determination of the Hubble Constant Through Stellar Kinematics of Lens Galaxies

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

The “Hubble Tension” is the statistically significant difference between direct determinations of the Hubble constant H0 in the local Universe and the value extrapolated from early universe measurements under the standard flat lambda cold dark matter model (Lambda-CDM). The team has previously published a measurement of H0 based on seven gravitational time delay lenses that reached 2% precision and was in excellent agreement with the local distance ladder method based on Cepheids and in strong tension with early universe data. However, these results depend on specific assumptions about the mass density profile of lens galaxies - the key source of systematic uncertainty in this method. A research collaboration between the University of California-Los Angeles (UCLA) and the University of California-Davis (UCD) will improve this important measurement by adding precision and using new observations to resolve some of the ambiguities in the physical models. The investigators will continue their educational/public outreach efforts, focused on increasing the number of young scientists from underrepresented groups and highlighting the importance and a real understanding of the scientific method. To address these issues, the team proposes to extend this work to a sample of 12 time delay gravitational lenses and obtain spatially resolved stellar kinematics of the deflectors. In addition, they plan to combine information from time delay lenses with that obtained from two samples of non-time delay lenses (SLACS and SL2S). The two external samples, SLACS and SL2S, provide additional statistical information about the dynamics and mass distributions of the population of lensing galaxies. The use of multiple strategies, multiple instruments, multiple samples and multiple modeling codes will allow the team to check for residual systematics and selection effects. Finally, they will use samples of elliptical galaxies that are not lenses to extract information about their mass distribution on a statistical basis and further improve the sample. At UCLA, the lead investigator will teach a new course “Energy in nature and society”, aimed at illustrating to students the scientific method and improving the use of quantitative thinking into the environmental debate, and develop an astrophysics curriculum for preschool. Similarly, the lead investigator at UCD has developed a month-long “Introduction to Astrophysics” course for high-school students on the Davis campus as part of the UC COSMOS program. This course introduces high school students, drawn from California’s diverse population, and many from small schools in isolated areas, to a research environment in which they work with data from cutting-edge facilities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.