MAGAZ3NE: Spatially Resolved Ages and Chemical Abundances of Ultra-Massive Quiescent Galaxies at z $\sim$ 3.5 using JWST/NIRSpec IFU

Abstract

We present spatially-resolved measurements of stellar age, [Fe/H], and [$\hat{I}\pm$/Fe] in three ultra-massive ($\log ({\mathrm{M}}_{\ast }/{\mathrm{M}}_{\odot })>11$), compact (${\mathrm{R}}_{\mathrm{e}}\lesssim 2$ kpc) quiescent galaxies at $z\sim 3.5$ using JWST/NIRSpec IFU spectroscopy. These observations provide the first spatially-resolved constraints on $\hat{I}\pm$-enhancement at this epoch, enabling a direct test of quenching mechanisms before late-time assembly processes such as mergers can erase chemical signatures. The central regions of all three galaxies show both uniformly young ages ($\approx 0.6-0.7$ Gyr) and elevated [$\hat{I}\pm$/Fe] ($\approx 0.2-0.5$), indicating rapid, enhanced star formation shortly before recent quenching. Beyond the cores, two galaxies display positive age gradients and negative [$\hat{I}\pm$/Fe] gradients, consistent with rapid merger-driven quenching, while the third shows a flat age profile indicative of uniform quenching. The [Fe/H] gradients are also consistent with these trends, though we note that the metallicities reported by codes using $\hat{I}\pm$-enhanced models differ significantly ($\approx 0.2-0.4$ dex) from those reported using solar-scaled templates. These data demonstrate that quenching pathways are diverse by $z\sim 3.5$, with rapid, merger-driven quenching already operating in a subset of massive quiescent galaxies in the first two billion years of cosmic time. Furthermore, these results establish that explicit treatment of $\hat{I}\pm$-enhancement is essential for interpreting the star-formation histories of the earliest quenched systems.

Submitted to ApJ