Cosmology Seminar- Environmental dependence of SN Ia i-band secondary maximum

It has long been established that the properties of type Ia supernovae (SNe Ia) depend on their local environment, even after typical standardisation methods. This is typically referred to as the mass step, where SNe Ia in high-mass galaxies are on average brighter than their low-mass counterparts post-standardisation, although trends have been established with other environmental properties including colour, specific star formation rate and distance from the centre of the galaxy. There has been ongoing debate in the field about what is driving these differences, in particular the relative contribution of intrinsic variation and dust extinction. I will present recent analysis, using the probabilistic SN Ia SED model BayeSN, which found an intrinsic contribution to the mass step and particularly strong differences around the i-band secondary maximum. These results demonstrate that there are intrinsic differences between SNe Ia in different environments and raise an interesting question about what is driving these results; understanding this finding can help reveal the underlying physical cause of the environmental dependence of SNe Ia.