Abstract

Having settled the decades-long bitter debate over the value of the Hubble constant, research on the Extragalactic Distance Scale has seen a remarkable transformation over the past decade. The focus is now on a proper accounting of all sources of uncertainty (specially systematics) and the development of new techniques to further increase the accuracy and precision in the measurement of H₀.

What is the motivation for further work on the Hubble constant? Measuring H₀ at the percent level will significantly improve the constraints on the equation of state of dark energy and other cosmological parameters, and may reveal physics beyond the standard LCDM model. The current uncertainty on H₀ is 2.4% [1] and a 1% measurement should be achievable by the end of the decade based on Gaia parallaxes and observations with JWST. 

I will review recent progress in the field, including near-infrared observations of Galactic and extragalactic Cepheids, the absolute calibration of the luminosity of type Ia SNe, and a comparison of our local determination of H₀ with predictions based on observations of baryon acoustic oscillations and the cosmic microwave background. I will present results from recent searches for extragalactic Miras using novel astro-statistical techniques. Lastly, I will discuss ongoing and future activities using HST, Gaiaand JWST.

[1] Riess, Macri, Hoffmann, et al. ApJ 828, 56 (2017) http://arxiv.org/abs/1604.01424