Improving bayesian posterior correlation analysis on type Ia supernova luminosity evolution

Abstract

Much of the cosmological utility thus far extracted from Type Ia supernovae (SNe Ia) relies on the assumption that SN Ia peak luminosities do not evolve significantly with the age (local or global) of their stellar environments. Two recent studies have provided conflicting results in evaluating the validity of this assumption, with one finding no correlation between Hubble residuals (HR) and stellar environment age, while the other claims a significant correlation. In this Letter we perform an independent reanalysis that rectifies issues with the statistical methods employed by both of the aforementioned studies. Our analysis follows a principled approach that properly accounts for regression dilution and critically (and unlike both prior studies) utilises the Bayesian-model-produced SN environment age estimates (posterior samples) instead of point estimates. Moreover, the posterior is used as an informative prior in the regression. We find the Pearson correlation between the HR and local (global) age to be in excess of 4σ (3σ). Assuming there exists a linear relationship between HR and local (global) age, we find a corresponding slope of −0.035 ± 0.007 mag Gyr−1 (−0.036 ± 0.007 mag Gyr−1). We encourage further use of our approach to examine HR and host environment correlations, as well as experiments in correcting for luminosity evolution in SN Ia standardisation.

An imaging polarimetry survey of Type Ia supernovae: are peculiar extinction and polarization properties produced by circumstellar or interstellar matter?

“…If true, SN Ia luminosity evolution can have a high impact on cosmology, because stellar populations get younger with increasing redshift. Ho we ver, the result is highly debated and unlikely to be correct (Lee et al 2020b(Lee et al , 2021Rose et al 2020 ;Murakami et al 2021 ;Zhang et al 2021 ). Zelaya et al ( 2017 ) have shown that the polarization angles of reddened SNe Ia tend to be aligned with galactic features, notably the spiral arms of the host galaxies.…”

The Origin and Evolution of the Normal Type Ia SN 2018aoz with Infant-phase Reddening and Excess Emission

“…Despite their fundamental importance, the explosion mechanisms and progenitor systems of Type Ia SNe remain a matter of extensive debate (Maoz et al 2014). Understanding the origins of Type Ia SNe, particularly of the normal events comprising ∼70% of their population (Blondin et al 2012), will not only clarify the end states of stellar evolution but will be essential for improving cosmological distance measurements (e.g., Wang et al 2013;Zhang et al 2021).…”

Evidence for strong progenitor age dependence of type Ia supernova luminosity standardization process

“…When the regression analysis is performed with a standard MCMC posterior sampling method, a very significant (4.3σ) correlation is obtained between population age and HR for both global age and local age near the site of SN with the slope in excellent agreement with our previous spectroscopic result from ETGs (Kang et al 2020). Recently, Zhang et al (2021) confirms that this age-HR correlation is statistically significant (5σ), although they obtained a somewhat shallower slope from a posterior sampling method adopting full posterior for the age error instead of the Gaussian error. Therefore, even the dataset originally used by Rose et al (2020) to oppose our claim is instead strongly supporting our result, and the luminosity evolution stands up to scrutiny as a serious systematic bias in SN cosmology.…”

“…In order to illustrate the level of significance of the luminosity evolution predicted from our finding, it is heuristically useful to see what they would have found if, at the discovery time, they knew the ∆HR/∆age slope reported in this paper (see also Kang et al 2020, and Zhang et al 2021 for a similar slope). Table 1 lists our predictions of the magnitude corrections for the SN Ia luminosity evolution with redshift under two different assumptions for the cosmological model in Figure 2.…”