Radial Gradients and Intrinsic Scatter in MaNGA Galaxies

TL;DR

This study analyzes stellar population parameters and radial gradients in nearly 3000 MaNGA early-type galaxies, revealing how age and chemical abundances vary with galaxy mass and radius, supporting hierarchical galaxy formation models.

Contribution

It provides detailed measurements of stellar population gradients and their dependence on galaxy velocity dispersion, incorporating element-specific abundance responses and comparing results with simulations.

Findings

Age increases with galaxy mass, while [Fe/H] peaks at intermediate masses.

Radial gradients of [Fe/H] and light elements steepen with increasing velocity dispersion.

Scatter in gradients suggests a mix of inside-out and outside-in galaxy formation processes.

Abstract

We derive stellar population parameters and radial gradients within 0.65 $R_e$ for spatially resolved spectra of 2968 early-type galaxies from MaNGA, spanning stellar velocity dispersions ($\sigma$) of 50--340 km s$^{-1}$. Light-weighted mean age and C, N, Na, Mg, and Fe abundances are obtained by inverting metallicity-composite stellar population models with isochrones that respond in $T_{\mathrm{eff}}$ to individual element abundance changes. Globally, $\log$(age) increases ($\sim$0.53 dex per decade), [Fe/H] declines slightly ($\sim$-0.06 dex per decade), and [X/Fe] for light elements rises (0.19--0.37 dex per decade for $\log\sigma < 2.0$ but steepens to nearly double slope for $\log\sigma > 2.0$) with $\log\sigma$. [Fe/H] peaks at $\log\sigma \sim 2.0$ and falls on either side. Light-element [X/Fe] anticorrelates with [Fe/H] ($\sim$-0.1 dex per decade). Astrophysical scatter is largest in low-$\sigma$ galaxies, especially for Fe and N. Internally, age gradients are nearly flat in low-$\sigma$ galaxies and slightly negative in high-$\sigma$ systems ($\sim$-0.04 dex per decade). [Fe/H] radial gradients steepen from -0.06 dex per decade to -0.15 dex per decade across $\sigma$, while light elements (except Na) show $\sim$-0.03 dex per decade gradients. Scatter in gradients peaks in high-$\sigma$ galaxies, most strongly for Fe ($\sim$0.23 dex), suggesting comparable numbers of inside-out and outside-in formation. A near-zero ($\sim$-0.03) age and light-element gradient plus mild [Fe/H] gradients supports hierarchical merging for ETG evolution. Simulations match the observed age structure, slope change at $\log\sigma \sim 2.0$, and flat gradients, though they overpredict absolute abundances.