Implications of Two Type Ia Supernova Populations for Cosmological Measurements

TL;DR

This paper investigates how two distinct populations of Type Ia supernovae can bias cosmological measurements, emphasizing the importance of controlling luminosity differences to improve dark energy parameter estimates.

Contribution

It quantifies the impact of prompt and delayed supernova populations on cosmological parameters and proposes constraints to mitigate biases in dark energy measurements.

Findings

Luminosity difference between populations is constrained to (4.5 ± 8.9)%

Ignoring a 0.025 mag difference biases dark energy EOS by ~1σ

Controlling luminosity difference to <0.025 mag prevents bias and reduces uncertainty

Abstract

Recent work suggests that Type Ia supernovae (SNe) are composed of two distinct populations: prompt and delayed. By explicitly incorporating properties of host galaxies, it may be possible to target and eliminate systematic differences between these two putative populations. However, any resulting {\em post}-calibration shift in luminosity between the components will cause a redshift-dependent systematic shift in the Hubble diagram. Utilizing an existing sample of 192 SNe Ia, we find that the average luminosity difference between prompt and delayed SNe is constrained to be $(4.5 \pm 8.9)%$. If the absolute difference between the two populations is 0.025 mag, and this is ignored when fitting for cosmological parameters, then the dark energy equation of state (EOS) determined from a sample of 2300 SNe Ia is biased at $\sim1\sigma$. By incorporating the possibility of a two-population systematic, this bias can be eliminated. However, assuming no prior on the strength of the two-population effect, the uncertainty in the best-fit EOS is increased by a factor of 2.5, when compared to the equivalent sample with no underlying two-population systematic. To avoid introducing a bias in the EOS parameters, or significantly degrading the measurement accuracy, it is necessary to control the post-calibration luminosity difference between prompt and delayed SN populations to better than 0.025 mag.