MSA-3D: Uncovering Weak AGNs and Resolved Outflows in Disguise in $z\sim1$ Star-Forming Galaxies

Abstract

We present spatially resolved rest-optical spectroscopy of 38 star-forming galaxies at 0.5 < z < 1.7 from the JWST/NIRSpec MSA-3D survey, which uses slit-stepping to build IFU-like datacubes at 0.1'' resolution. We map emission-line morphology, excitation, and kinematics of the warm ionized gas using [N II]/H$\alpha$, [S II]/H$\alpha$, and [O III]/H$\beta$. Relative to z$\sim$0 galaxies at fixed stellar mass, our sources show systematically lower [N II]/H$\alpha$ and [S II]/H$\alpha$ and elevated [O III]/H$\beta$, consistent with harder radiation fields and lower metallicities. Radially, [O III]/H$\beta$ profiles are typically flat or mildly positive, whereas [N II]/H$\alpha$ also remains flat or declines outward, mirroring metallicity trends. On kpc scales, we find a strong positive correlation between [N II]/H$\alpha$ and velocity dispersion ($\sigma$), linking local excitation to turbulent or shock-driven kinematics. Six galaxies ($\sim$ 16% of the sample) host spatially localized regions with elevated [N II]/H$\alpha$, high EW(H$\alpha$), and V_RMS = $\sqrt{V^2 + \sigma^2} > 200$ km/s, indicative of weak AGN activity, shocks, or outflows. For these candidates we infer modest warm-ionized outflow rates of 1-4 Msun/yr and kinetic powers $\sim$ 0.1-1% of the AGN bolometric luminosity (from central [O III] or H$\alpha$). These values place our sample at the low-energy tail of known AGN-driven outflows yet in continuity with $\dot{M_{out}}-L_{AGN}$ scaling relations across 0 < z < 6. A completeness assessment shows MSA-3D is sensitive to AGN with $L_{AGN} \geq 10^{43}$ erg/s, underscoring both the promise and current limitations of detecting weak AGN activity in distant galaxies with resolved spectroscopy.