ZTF SN Ia DR2: Improved SN Ia colors through expanded dimensionality with SALT3+

Understand

Type Ia supernovae (SNe Ia) are a key probe in modern cosmology, as they can be used to measure luminosity distances at gigaparsec scales.

• Models of their light-curves are used to project heterogeneous observed data onto a common basis for analysis.
• The SALT model currently used for SN Ia cosmology describes SNe as having two sources of variability, accounted for by a color parameter c, and a "stretch parameter" x1.
• We extend the model to include an additional parameter we label x2, to investigate the cosmological impact of currently unaddressed light-curve variability.