Radial Gradients and Intrinsic Scatter in MaNGA Galaxies

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 ($σ$) 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 $\logσ< 2.0$ but steepens to nearly double slope for $\logσ> 2.0$) with $\logσ$. [Fe/H] peaks at $\logσ\sim 2.0$ 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-$σ$ galaxies, especially for Fe and N. Internally, age gradients are nearly flat in low-$σ$ galaxies and slightly negative in high-$σ$ 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 $σ$, while light elements (except Na) show $\sim$-0.03 dex per decade gradients. Scatter in gradients peaks in high-$σ$ 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 $\logσ\sim 2.0$, and flat gradients, though they overpredict absolute abundances.