Tracing back the birth environments of Type Ia supernova progenitor stars: a pilot study based on 44 early-type host galaxies

ABSTRACT The environmental dependence of Type Ia supernova (SN Ia) luminosities is well established, and efforts are being made to find its origin. Previous studies typically use the currently observed status of the host galaxy. However, given the delay time between the birth of the progenitor star and the SN Ia explosion, the currently observed status may differ from the birth environment of the SN Ia progenitor star. In this paper, employing the chemical evolution and accurately determined stellar population properties of 44 early-type host galaxies, we, for the first time, estimate the SN Ia progenitor star birth environment, specifically Fe/HBirth and α/FeBirth. We show that α/FeBirth has a 30. 4^+10. 6-₁₀. ₁{\ per\ cent} wider range than the currently observed α/FeCurrent, while the range of Fe/HBirth is not statistically different (17. 9^+26. 0-₂₇. ₁{\ per\ cent}) to that of Fe/HCurrent. The birth and current environments of Fe/H and α/Fe are sampled from different populations (p-values of the Kolmogorov–Smirnov test 0. 01). We find that light-curve fit parameters are insensitive to Fe/HBirth (0. 9σ for the non-zero slope), while a linear trend is observed with Hubble residuals (HRs) at the 2. 4σ significance level. With α/FeBirth, no linear trends (1. 1σ) are observed. Interestingly, we find that α/FeBirth clearly splits the SN Ia sample into two groups: SN Ia exploded in α/FeBirth-rich or α/FeBirth-poor environments. SNe Ia exploded in different α/FeBirth groups have different weighted-means of light-curve shape parameters: 0. 81 ± 0. 33 (2. 5σ). They are thought to be drawn from different populations (p-value = 0. 01). Regarding SN Ia colour and HRs, there is no difference (1. 0σ) in the weighted-means and distribution (p-value 0. 27) of each α/FeBirth group.