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

Adam G. Riess, Steven A. Rodney, Daniel M. Scolnic, Daniel L. Shafer, Louis Gregory Strolger, Henry C. Ferguson, Marc Postman, Or Graur, Dan Maoz, Saurabh W. Jha, Bahram Mobasher, Stefano Casertano, Brian Hayden, Alberto Molino, Jens Hjorth, Peter M. Garnavich, David O. Jones, Robert P. Kirshner, Anton M. Koekemoer, Norman A. GroginGabriel Brammer, Shoubaneh Hemmati, Mark DIckinson, Peter M. Challis, Schuyler Wolff, Kelsey I. Clubb, Alexei V. Filippenko, Hooshang Nayyeri, U. Vivian, David C. Koo, Sandra M. Faber, Dale Kocevski, Larry Bradley, Dan Coe

Research output: Contribution to journalArticlepeer-review


We present an analysis of 15 Type Ia supernovae (SNe Ia) at redshift z > 1 (9 at 1.5 < z < 2.3) 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 0.07 < z < 1.5 based only on this combined SN Ia sample. The added leverage of our new sample at z > 1.5 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 = = - H(z 1.5) H 2.69+ 0 0.52 0.86. 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 z > 1.5 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.

Original languageEnglish
Article number126
JournalAstrophysical Journal
Issue number2
StatePublished - 1 Feb 2018


FundersFunder number
National Aeronautics and Space AdministrationHST-GO-12060, HST-HF-51312, HST-GO-12099
Fundação de Amparo à Pesquisa do Estado de São Paulo2014/11806-9


    • cosmology: observations
    • methods: observational
    • supernovae: general


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