Abstract
Type Ia Supernovae (SNe Ia) are standardizable candles that allow us to measure the recent expansion rate of the Universe. Due to uncertainties in progenitor physics, potential astrophysical dependencies may bias cosmological measurements if not properly accounted for. The dependency of the intrinsic luminosity of SNe Ia with their host-galaxy environment is often 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 amplitudes. We compare these indicators in the context 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 tracer accuracy can explain the discrepancy between the observed SNe Ia step amplitudes found in the literature. Using lsSFR or global mass to identify 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.
Highlights
Type Ia supernovae (SNe Ia) are powerful empirically standardized distance indicators
We used the global host mass-step from Roman et al (2018) for it is derived using the state-of-the-art Betoule et al (2014) + Supernova Legacy Survey (SNLS) five-year sample and the Malmquist bias correction were not made using the 5D implementation of the Beams with Bias Correction (BBC; Scolnic & Kessler 2016; Kessler & Scolnic 2017)
We used the global host mass step from Smith et al (2020). We plotted in this figure the local (4 kpc) U − R and stellar mass from Kelsey et al (2021) with a transparent marker, as γ is fitted after the standardization in that paper
Summary
Type Ia supernovae (SNe Ia) are powerful empirically standardized distance indicators. When calibrating the SNe Ia absolute luminosity using the Cepheid period–luminosity relation, this direct H0 measurement is 4.4σ higher than expectation based on the Lambda cold dark matter (ΛCDM) model anchored by Planck Collaboration VI (2020) data (Riess et al 2019; Reid et al 2019). This “tension” has received a great deal of attention as it could be a sign of new fundamental physics (Knox & Millea 2020). Freedman et al (2019) find a lower H0 value when using tip of the red giant branch (TRGB) distances in place of the Cepheids
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