Negative gas-phase metallicity gradients in the narrow line region and galactic disc of local AGN-host galaxies (2509.12156v1)

Abstract: The gas-phase metallicity distribution in galaxies provides significant information on their evolution. We report the discovery of negative radial gradients in the gas-phase metallicity of the narrow-line region of the nine galaxies in the Measuring Active Galactic Nuclei Under MUSE Microscope (MAGNUM) galaxies: Centaurus A, Circinus, IC 5063, NGC 1068, NGC 1365, NGC 1386, NGC 2992, NGC 4945, NGC 5643. From strong-line abundance relations for active galactic nuclei (AGN) and star-forming regions, along with emission-line ratio diagnostics, we determine spatially resolved gas-phase metallicities for the kinematic components, galaxy disc and outflow. These relations involve sensitive strong emission lines, specifically [O III]5007, [N II]6584, H{\alpha}, H\b{eta}, [S II]6716, and [S II]6731. The existence of predominantly negative radial metallicity gradients in these AGN host galaxies indicates that metals are not necessarily moved from the central regions to the outskirts by AGN activity and that the gas-phase metallicity in galaxies may follow the general inside-out star formation scenario.