Accuracy of environmental tracers and consequence for determining the Type Ia Supernovae magnitude step

Type Ia Supernovae (SNeIa) are standard candles that enable us to measure the recent expansion rate of the Universe. However, their true nature remains unknown, and potential astrophysical dependences of SNeIa that may vary between redshift and/or survey may bias cosmological measurements if not properly accounted for. Last decades studies have shown several relations between SNeIa properties and those of their host galaxy. Yet, the correct way to account for the astrophysical effects remains uncertain as various teams find various results — sometime even discrepant — when using various tracers.

We propose to compare these previous various environmental analyses methods in light of their ability to accurately trace fundamental SN astrophysical parameters, and notably the progenitor age. We show, as expected, that host colors and H⍺-based specific star formation rate are better age indicator than, say, morphology. More importantly we show that these known accuracy variations actually explain the discrepancy between the SN magnitude step observed when using different environmental tracers.