2025MNRAS.543.2180R

Using the Dark Energy Survey 5-yr sample, we determine the properties of type Ia supernova (SN Ia) host galaxies across a wide multiwavelength range - from the optical to far-infrared - including data from the Herschel and Spitzer space telescopes. We categorize the SNe Ia into three distinct groups according to the distribution of their host galaxies on the star formation rate (SFR) - stellar mass ($M_\star$) plane. Each region comprises host galaxies at distinct stages in their evolutionary pathways: Region 1 - low-mass hosts; Region 2 - high-mass, star-forming hosts and Region 3 - high-mass, passive hosts. We find SNe Ia in host galaxies located in Region 1 have the steepest slope (quantified by $\beta$) between their colours and luminosities, with $\beta _{\mathrm{R_1}} = 3.51 \pm 0.16$. This differs at the ${\sim }6\sigma$ significance level to SNe Ia in Region 3, which have the shallowest colour-luminosity slope with $\beta _{\mathrm{R_3}} = 2.12 \pm 0.16$. After correcting SNe Ia in each subsample by their respective $\beta$, events in Region 3 (high-mass, passive hosts) are $0.07 - 0.12$ mag ($>3\sigma$) brighter, post-standardization. We conclude that future cosmological analyses should apply standardization relations to SNe Ia based upon the region in which the SN host galaxy lies in the SFR-$M_\star$ plane. Alternatively, cosmological analyses should restrict the SN Ia sample to events whose host galaxies occupy a single region of this plane.