ON VARIATIONS OF THE BRIGHTNESS OF TYPE Ia SUPERNOVAE WITH THE AGE OF THE HOST STELLAR POPULATION

Recent observational studies of type Ia supernovae (SNeIa) suggest correlations between the peak brightness of an event and the age of the progenitor stellar population. This trend likely follows from properties of the progenitor white dwarf (WD), such as central density, that follow from properties of the host stellar population. We present a statistically well-controlled, systematic study utilizing a suite of multi-dimensional SNeIa simulations investigating the influence of central density of the progenitor WD on the production of Fe-group material, particularly radioactive Ni-56, which powers the light curve. We find that on average, as the progenitor's central density increases, production of Fe-group material does not change but production of Ni-56 decreases. We attribute this result to a higher rate of neutronization at higher density. The central density of the progenitor is determined by the mass of the WD and the cooling time prior to the onset of mass transfer from the companion, as well as the subsequent accretion heating and neutrino losses. The dependence of this density on cooling time, combined with the result of our central density study, offers an explanation for the observed age-luminosity correlation: a longer cooling time raises the central density at ignition thereby producing less Ni-56 and thus a dimmer event. While our ensemble of results demonstrates a significant trend, we find considerable variation between realizations, indicating the necessity for averaging over an ensemble of simulations to demonstrate a statistically significant result.