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Type Ia Supernovae (SNe Ia) are standardizable candles that allow us tomeasure the recent expansion rate of the Universe. Due to uncertainties inprogenitor physics, potential astrophysical dependencies may bias cosmologicalmeasurements if not properly accounted for. The dependency of the intrinsicluminosity of SNe Ia with their host-galaxy environment is often used tostandardize SNe Ia luminosity and is commonly parameterized as a step function.This functional form implicitly assumes two-populations of SNe Ia. In theliterature, multiple environmental indicators have been considered, findingdifferent, sometimes incompatible, step function amplitudes. We compare theseindicators in the context of a two-populations model, based on their ability todistinguish the two populations. We show that local H$\alpha$-based specificstar formation rate (lsSFR) and global stellar mass are better tracers than,for instance, host galaxy morphology. We show that tracer accuracy can explainthe discrepancy between the observed SNe Ia step amplitudes found in theliterature. Using lsSFR or global mass to distinguish the two populations canexplain all other observations, though lsSFR is favoured. As lsSFR is stronglyconnected to age, our results favour a prompt and delayed population model. Inany case, there exists two populations that differ in standardized magnitude byat least $0.121\pm0.010\,\mathrm{mag}$.

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