Self-similarity in the chemical evolution of galaxies and the delay time distribution of SNe Ia

Recent improvements in the age dating of stellar populations and single stars allow us to study the ages and abundance of stars and galaxies with unprecedented accuracy. We here compare the relation between age and \alpha-element abundances for stars in the solar neighborhood to that of local, early-type galaxies. We find both relations to be very similar. Both fall into two regimes with a flat slope for ages younger than ~9 Gyr and a steeper slope for ages older than that value. This quantitative similarity seems surprising, given the different types of galaxies and scales involved. For the sample of early-type galaxies we also show that the data are inconsistent with literature delay time distributions of either single or double Gaussian shape. The data are consistent with a power law delay time distribution. We thus confirm that the delay time distribution inferred for the Milky Way from chemical evolution arguments also must apply to massive early-type galaxies. We also offer a tentative explanation for the seeming universality of the age-[\alpha/Fe] relation as the manifestation of averaging of different stellar populations with varying chemical evolution histories.
Comment: 8 pages, 3 figures, submitted to A&A, version in reply to first referee report