Stellar Populations with MaNGA: Iron Kink and Nitrogen Fuzz

Abstract

Recent analysis of 2968 MaNGA early type galaxies has yielded two notable trends with velocity dispersion ($\sigma$) not previously discussed in the literature. First, Fe abundance rises with $\sigma$, but only until $\sigma \approx 100$ km s${}^{-1}$, after which it falls. This kink is reproduced by TNG100 simulations, implying that hierarchical merger processes might explain it. Second, astrophysical scatter in N is high for galaxies with $\sigma <100$ km s${}^{-1}$. Due to the restricted list of nucleosynthetic sources for N, it is likely that asymptotic giant branch stars provide most of this N. A varied star formation history (compared to that of massive galaxies) along with variable retention and recycling of N-enriched gas might explain the fuzz of N abundance in low-$\sigma$ galaxies. Because a timescale argument seems necessary to explain the nitrogen fuzz, and an initial mass function argument is ruled out, similar timescale arguments for the [Mg/Fe] trend as a function of velocity dispersion are supported.

5 pages, 5 figures, accepted, Astrophysical Journal