Étude de l’impact de l’environnement galactique sur la standardisation des Supernovae de Type Ia

Type Ia Supernovae (SNe Ia) are standardizable candles that allow to measure the recent expansion rate of the Universe. However, their true nature remains unknown. Consequently, due to uncertainties in progenitor physics, potential astrophysical dependencies may bias cosmological measurements if not properly accounted for. Last decades studies have shown several relations between SNe Ia properties and those of their host galaxy. Yet, the correct way to account for astrophysical effects remains uncertain. Presently, the dependency of the intrinsic luminosity of SNe Ia with their host-galaxy environment is used to standardize SNe Ia luminosity and is commonly parameterized as a step function. This functional form implicitly assumes two-populations of SNe Ia. In the literature, multiple environmental indicators have been considered, finding different, sometimes incompatible, step function normalisation. Within this context, this PhD propose to compare these environmental analysis methods in light of a two-populations model, based on their ability to distinguish the two populations. We show that local Hα-based specific star formation rate (lsSFR) and global stellar mass are better tracers than, for instance, host galaxy morphology. We show that these tracer accuracy variations can explain the discrepancy between the observed SNe Ia magnitude offsets found in the literature. Using lsSFR or global mass to distinguish the two populations can explain all other observations, though lsSFR is favoured. As lsSFR is strongly connected to age, our results favour a prompt and delayed population model. In any case, there exists two populations that differ in standardized magnitude by at least 0.121 +/- 0.010 mag.