"6D Stellar Streams in the Southern Sky"
Nora Shipp (Chicago)
Stellar streams, the tidal remnants of accreted globular clusters and dwarf galaxies, are uniquely powerful tools for studying the Milky Way. In particular, they allow for strong constraints on the local distribution of dark matter, and they provide insight into how our Galaxy has evolved over time. However, addressing these essential questions requires a large, well-observed sample of stellar streams with full 6D phase-space measurements. I will present the first population of systematically-observed 6D stellar streams, including their discovery in the Dark Energy Survey, and the measurement of their proper motions and radial velocities with Gaia DR2 and the Southern Stellar Stream Spectroscopic Survey (S5). In addition, I will present constraints on the mass of the Milky Way’s largest satellite, the Large Magellanic Cloud, and discuss future plans for using these 6D streams to learn about our Galaxy.
"H_0 Measurement From Time-Delay Cosmography"
Geoff Chih-Fan Chen (UCLA)
The Hubble constant is one of the most important parameters in cosmology. Its value directly sets the age, the size, and the critical density of the Universe. Despite the success of the flat LCDM model, the Hubble constant derived from Planck data under the assumption of a flat LCDM model has 4.4-sigma tension with direct local measurements using distance ladder techniques. If this tension is not due to systematics, it may indicate the 3 need for new physics beyond the standard cosmological model. H_0 from time-delay lensing is a powerful independent tool for addressing the H_0 tension since it is independent of both Planck and the distance ladder.In order to improve the robustness of this technique, we need to increase the number of high-quality lens systems, since this allows us to look for correlations and other effects due to systematics, and to do hierarchical analyses to assess known systematic effects. Keck Adaptive Optices data are not only a key component in increasing the precision of the lens-based H_0 measurement but also provides systematic checks with the H_0 results based on HST imaging. In this talk, I will present the current lens-based H_0 measurement, the systematic checks that we are conducting, and the future prospects for this technique.