MSA-3D: Uncovering Weak Active Galactic Nuclei and Resolved Outflows in Disguise in z ∼ 1 Star-forming Galaxies

Abstract

We present spatially resolved rest-optical spectroscopy of 38 star-forming galaxies at 0.5 < z < 1.5 from the JWST/NIRSpec Micro-Shutter Assembly (MSA)-3D survey, which employs a slit-stepping strategy to build integral field unit–like data cubes with a spatial sampling of ∼0.1. We map emission-line morphology, excitation, and kinematics of the warm-ionized gas using [N II]/Hα, [S II]/Hα, and [O III]/Hβ. Relative to z ∼ 0 galaxies at fixed stellar mass, our sources show systematically lower [N II]/Hα and [S II]/Hα and elevated [O III]/Hβ, consistent with harder radiation fields and lower metallicities. Radially, [O III]/Hβ profiles are typically flat or mildly positive, whereas [N II]/Hα also remains flat or declines outward, mirroring metallicity trends. On kiloparsec scales, we find a strong positive correlation between [N II]/Hα and velocity dispersion (σ), linking local excitation to turbulent or shock-driven kinematics. Six galaxies (∼16% of the sample) host spatially localized regions with elevated [N II]/Hα, high EW(Hα), and Vrms V + > 250 km s 2 2 1, indicative of weak active galactic nucleus (AGN) activity, shocks, or outflows. For these candidates, we infer modest warm-ionised outflow rates of 1−4 M⊙ yr−1 and kinetic powers ∼0.1%−1% of the AGN bolometric luminosity (from central [O III] or Hα). These values place our sample at the low-energy tail of known AGN-driven outflows yet in continuity with Mout–LAGN scaling relations across 0 < z < 6. A completeness assessment shows MSA-3D is sensitive to AGN with LAGN ≳ 1043 erg s−1, underscoring both the promise and current limitations of detecting weak AGN activity in distant galaxies with resolved spectroscopy.