Type Ia Supernova Distances at Redshift >1.5 from the Hubble Space Telescope Multi-cycle Treasury Programs: The Early Expansion Rate

摘要

We present an analysis of 15 Type Ia supernovae (SNe Ia) at redshift (9 at ) recently discovered in the CANDELS and CLASH Multi-Cycle Treasury programs using WFC3 on the Hubble Space Telescope. We combine these SNe?Ia with a new compilation of ~1050 SNe?Ia, jointly calibrated and corrected for simulated survey biases to produce accurate distance measurements. We present unbiased constraints on the expansion rate at six redshifts in the range based only on this combined SN?Ia sample. The added leverage of our new sample at leads to a factor of ~3 improvement in the determination of the expansion rate at z?=?1.5, reducing its uncertainty to ~20%, a measurement of . We then demonstrate that these six derived expansion rate measurements alone provide a nearly identical characterization of dark energy as the full SN sample, making them an efficient compression of the SN?Ia data. The new sample of SNe?Ia at usefully distinguishes between alternative cosmological models and unmodeled evolution of the SN?Ia distance indicators, placing empirical limits on the latter. Finally, employing a realistic simulation of a potential Wide-Field Infrared Survey Telescope SN survey observing strategy, we forecast optimistic future constraints on the expansion rate from SNe?Ia.