Studying Type II supernovae as cosmological standard candles using the Dark Energy Survey
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Despite vast improvements in the measurement of the cosmological parameters, the nature of dark energy and an accurate value of the Hubble constant (H0) in the HubbleLematre law remain unknown. To break the current impasse, it is necessary to develop as many independent techniques as possible, such as the use of Type II supernovae (SNeII). The goal of this paper is to demonstrate the utility of SNeII for deriving accurate extragalactic distances, which will be an asset for the next generation of telescopes where more-distant SNeII will be discovered. More specifically, we present a sample from the Dark Energy Survey Supernova Program (DES-SN) consisting of 15 SNeII with photometric and spectroscopic information spanning a redshift range up to 0.35. Combining our DES SNe with publicly available samples, and using the standard candle method (SCM), we construct the largest available Hubble diagram with SNeII in the Hubble flow (70 SNeII) and find an observed dispersion of 0.27mag. We demonstrate that adding a colour term to the SNII standardization does not reduce the scatter in the Hubble diagram. Although SNeII are viable as distance indicators, this work points out important issues for improving their utility as independent extragalactic beacons: find new correlations, define a more standard subclass of SNeII, construct new SNII templates, and dedicate more observing time to high-redshift SNeII. Finally, for the first time, we perform simulations to estimate the redshift-dependent distance-modulus bias due to selection effects.