Stellar Populations with MaNGA: Iron Kink and Nitrogen Fuzz

TL;DR

This study analyzes MaNGA early type galaxies, revealing a non-monotonic iron abundance trend with velocity dispersion and high nitrogen scatter in low-$\sigma$ galaxies, suggesting complex chemical evolution and merger processes.

Contribution

It uncovers a previously unreported kink in iron abundance versus velocity dispersion and links nitrogen scatter to star formation history and stellar sources, supported by simulations.

Findings

Fe abundance peaks at $\sigma ext{≈} 100$ km s$^{-1}$ and then declines.

High nitrogen scatter in low-$\sigma$ galaxies indicates varied star formation histories.

Simulation results support hierarchical merger explanations for observed trends.

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 $\sigma\approx100$ 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.