On the Relationship between Type Ia Supernova Peak Luminosity and Host-Galaxy Properties

A string of recent studies have debated the exact form and physical origin of an evolutionary trend between the peak luminosity attained by Type Ia supernovae (SNe Ia) and the properties of the galaxies that host them. We shed new light on the discussion by presenting (i) an improved statistical method to analyze the slope and correlation specific to the model assumptions of these two variables, (ii) a statistical analysis of about 200 low-redshift SNe Ia in which we measure the separation of Hubble residuals (HR; as a probe of luminosity) between two host-galaxy morphological types (as a probe of galaxy properties), and (iii) an overview of the degree and significance of the bias introduced by different evolutionary population synthesis (EPS) models that are utilized to estimate the galaxy properties. Our results identify the existence of SN Ia luminosity differences that are measurable in relation to a number of host-galaxy properties, including morphology, mass, age, star-formation rate, and dust, though the degree of correlation varies and the physical origin remains unclear. We find that some such parameters are strongly dependent on EPS-model choice, suggesting that there are significant systematic effects to understand before claiming robust and actionable (e.g., in a cosmological sense) evolutionary trends in SN Ia luminosity.