SDSS-IV MaNGA: local and global chemical abundance patterns in
  early-type galaxies
  Chemical enrichment signatures strongly constrain galaxy formation and
evolution, and a detailed understanding of abundance patterns provides clues
regarding the nucleosynthetic production pathways of elements. Using the
SDSS-IV MaNGA IFU survey, we study radial gradients of chemical element
abundances in detail. We use stacked spectra out to 1 Re of 366 early-type
galaxies with masses 9.9 - 10.8 log $M/M_{\odot}$ to probe the abundances of
the elements C, N, Na, Mg, Ca, and Ti, relative to the abundance of Fe, by
fitting stellar population models to a combination of Lick absorption indices.
We find that C, Mg, and Ti trace each other both as a function of galaxy radius
and galaxy mass. These similar C and Mg abundances within and across galaxies
set a lower limit for star-formation timescales. Conversely, N and Ca are
generally offset to lower abundances. The under-abundance of Ca compared to Mg
implies delayed enrichment of Ca through Type Ia supernovae, whereas the
correlated behaviour of Ti and the lighter $\alpha$ elements, C and Mg, suggest
contributions to Ti from Type II supernovae. We obtain shallow radial gradients
in [Mg/Fe], [C/Fe], and [Ti/Fe], meaning that these inferences are independent
of radius. However, we measure strong negative radial gradients for [N/Fe] and
[Na/Fe], of up to $-0.25\pm0.05$ and $-0.29\pm0.02$ dex/Re respectively. These
gradients become shallower with decreasing galaxy mass. We find that N and Na
abundances increase more steeply with velocity dispersion within galaxies than
globally, while the other elements show the same relation locally and globally.
This implies that the high Na and N abundances found in massive early type
galaxies are generated by internal processes within galaxies. These are
strongly correlated with the total metallicity, suggesting
metallicity-dependent Na enrichment, and secondary N production in massive
early-type galaxies.
