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The Dark Energy Survey Supernova Program: Slow supernovae show cosmological time dilation out to z ∼1
R. M. T. White, T. M. Davis, G. F. Lewis, D. Brout, L. Galbany, K. Glazebrook, S. R. Hinton, J. Lee, C. Lidman, A. Möller, M. Sako, D. Scolnic, M. Smith, M. Sullivan, B. O. Sánchez, P. Shah, M. Vincenzi, P. Wiseman, T. M. C. Abbott, M. Aguena, S. Allam, F. Andrade-Oliveira, J. Asorey, D. Bacon, S. Bocquet, D. Brooks, E. Buckley-Geer, D. L. Burke, A. Carnero Rosell, D. Carollo, J. Carretero, L. N. da Costa, M. E. S. Pereira, J. De Vicente, S. Desai, H. T. Diehl, S. Everett, I. Ferrero, B. Flaugher, J. Frieman, J. García-Bellido, E. Gaztanaga, G. Giannini, R. A. Gruendl, D. L. Hollowood, K. Honscheid, D. J. James, R. Kessler, K. Kuehn, O. Lahav, S. Lee, M. Lima, J. L. Marshall, J. Mena-Fernández, R. Miquel, J. Myles, R. C. Nichol, R. L. C. Ogando, A. Palmese, A. Pieres, A. A. Plazas Malagón, A. K. Romer, E. Sanchez, D. Sanchez Cid, M. Schubnell, E. Suchyta, G. Tarle, B. E. Tucker, A. R. Walker, N. Weaverdyck
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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 Δtₑₘ, and parameterising the observed duration as Δt_(obs)=Δtₑₘ(1+z)ᵇ, we fit for the form of time dilation using two methods. Firstly, we find that a power of b ≈1 minimises 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.
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