Ca, Fe, and Mg Trends Among and Within Elliptical Galaxies. (arXiv:1212.2675v1 [astro-ph.CO])

Ca, Fe, and Mg Trends Among and Within Elliptical Galaxies. (arXiv:1212.2675v1 [astro-ph.CO]):
In a sample of elliptical galaxies that span a large range of mass, a
previously unused Ca index, CaHK, shows that [Ca/Fe] and [Ca/Mg] systematically
decrease with increasing elliptical galaxy mass. Metallicity mixtures, age
effects, stellar chromospheric emission effects, and low-mass initial mass
function (IMF) boost effects are ruled out as causes. A [Ca/Fe] range of less
than 0.3 dex is sufficient to blanket all observations. Feature gradients
within galaxies imply a global Ca deficit rather than a radius-dependent
phenomenon. Some, but not all, Type II supernova nucleosynthetic yield
calculations indicate a decreasing Ca/Fe yield ratio in more massive
supernovae, lending possible support to the hypothesis that more massive
elliptical galaxies have an IMF that favors more massive stars. No Type II
supernova nucleosynthetic yield calculations show significant leverage in the
Ca/Fe ratio as a function of progenitor metallicity. Therefore, it seems
unlikely that the Ca behavior can be explained as a built-in metallicity
effect, and this argues against explanations that vary only the Type II to Type
Ia supernova enrichment ratio.