Riess

Dark Energy and The Hubble Constant from HST, Version 2.0
Adam Riess (STScI)

The expansion rate and its evolution must be empirically determined for our Universe to reveal its composition, scale, age, and fate. The Hubble Space Telescope is unique in its ability to measure the keystones of cosmic expansion, distant type Ia supernovae and Cepheid variables in their hosts. In 1998, high-redshift SNe Ia provided the first direct evidence for an accelerating Universe and the existence of dark energy. More recently, ACS and NICMOS on HST have become tools to calibrate the Hubble diagram of SNe Ia with modern data and to extend its reach to z>1 when cosmic expansion was still decelerating.

I will present the status of a "next generation" effort called SHOES to improve the precision of the Hubble constant measured with HST by the use of a streamlined distance ladder. By observing Cepheids in the near-IR and by minimizing the dominant sources of past systematic uncertainty we expect to reach a precision of ~4%.

A measurement of the Hubble constant to a precision of a few percent would be a powerful aid to the investigation of the nature of dark energy and a potent "end-to- end" test of the present cosmological model.

Future improvements in measuring the Hubble constant should make it one of the leading constraints on dark energy.