The Dark Energy Survey Supernova Program: Slow supernovae show cosmological time dilation out to z ∼ 1.

ABSTRACT We present a precise measurement of cosmological time dilation using the light curves of 1504 Type Ia supernovae from the Dark Energy Survey spanning a redshift range 0. 1 z 1. 2. We find that the width of supernova light curves is proportional to (1+z), as expected for time dilation due to the expansion of the Universe. Assuming Type Ia supernovae light curves are emitted with a consistent duration t ₄₌, and parametrizing the observed duration as t ₎₁ₒ= t ₄₌ (1+z) ᵇ, we fit for the form of time dilation using two methods. First, we find that a power of b 1 minimizes the flux scatter in stacked subsamples of light curves across different redshifts. Secondly, we fit each target supernova to a stacked light curve (stacking all supernovae with observed bandpasses matching that of the target light curve) and find b=1. 003 0. 005 (stat) \, 0. 010 (sys). Thanks to the large number of supernovae and large redshift-range of the sample, this analysis gives the most precise measurement of cosmological time dilation to date, ruling out any non-time-dilating cosmological models at very high significance.