Kavli Affiliate: Kaisey Mandel
| Summary:
We fit the multi-band light curves of 2,205 Type Ia supernovae (SNe~Ia) from the Zwicky Transient Facility DR2 with a one-zone radioactive decay model with a phenomenological addition to include Fe recombination physics. We find a strong correlation between inferred nickel mass and SALT2 stretch, which within our simplified modelling is linked to larger ejecta masses providing longer diffusion times, providing a physical basis for the brighter-slower relation. SN~Ia in low-mass hosts ($log_10(M_*/M_odot) < 10$) produce $12%$ more $^56$Ni than those in high-mass hosts ($ΔM_rm Ni = 0.13~M_odot$), linking the host-galaxy mass step to ejecta properties and hinting at metallicity or age-dependent burning efficiencies. This suggests that standardisation based on physical parameters may remove the mass-step. SN~1991T-like events show higher ejecta masses (median $1.64~M_odot$ vs. $1.38~M_odot$ for normals) and produce $30%$ more $^56$Ni, with $84%$ having super-Chandrasekhar masses. Through Hierarchical modelling of $902$ SNe ($z leq 0.06$), we find thermonuclear supernovae can be well described by a Gaussian distribution in ejecta mass and nickel mass with $μ_rm ej = 1.26 pm 0.01~M_odot$ ($σ_rm ej = 0.33 pm 0.01~M_odot$) and $μ_rm Ni = 0.64 pm 0.06~M_odot$ ($σ_rm Ni = 0.42 pm 0.02~M_odot$), respectively. This leads to inferred fractions of $43 pm 2%$ sub-$M_rm Ch$ ($<1.2~M_odot$), $34 pm 1%$ near-$M_rm Ch$ ($1.2$–$1.5~M_odot$), and $24 pm 2%$ super-$M_rm Ch$ ($>1.5~M_odot$) events. This work provides a step towards holistic physical characterization of the local SN~Ia population, reinforcing the physical basis of SN~Ia standardization while quantifying diversity and environmental dependencies critical for understanding progenitor physics and mitigating systematics in precision cosmology.
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