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

TL;DR

The paper presents spatially resolved measurements of gas-phase metallicity in nine local AGN-host galaxies by decomposing disc and outflow components in MAGNUM/MUSE data. Using strong-line calibrations (SF: O3N2; AGN: Storchi-Bergmann 1998 with n_e corrections), the authors derive radial Z_gas profiles centered on the [O III]5007 peak and fit gradients for disc and outflow components. They find predominantly negative metallicity gradients in both redshifted and blueshifted outflows, suggesting AGN-driven winds do not substantially redistribute metals to galactic outskirts, while discs show a mix of positive and negative gradients reflecting inside-out growth and environmental effects; NGC 1365 is a notable case with positive gradients across components. Overall, the results support a limited role for low-luminosity AGN feedback in altering global chemical evolution, consistent with other IFU studies and simulations, and underscore the importance of combining kinematic decomposition with robust metallicity diagnostics. Higher-resolution observations are encouraged to better quantify outflow properties and their potential, smaller-scale chemical impacts.

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, Hα, 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.

Figures (7)

• Figure 1: BPT diagnostic diagram for Circinus and IC 5063 to distinguish between AGN and SF ionised regions. The solid black line and the solid blue line show the discrimination between the two populations according to the boundaries from Kewley_bpt and kauffmann_bpt, respectively. Blue stars and red circles mark AGN- and SF-dominated regions, respectively, while small gray dots demonstrate the entire set of spaxel data.
• Figure 2: Distribution of $Z_{\rm gas}$ for the AGN parts in disc(red), redshifted (black) and blueshifted (green) outflow. SF-regions in disk is plotted in blue color. The vertical dashed lines show the median value of $Z_{\rm gas}$ for each of the components in the same color. The $Z_{\rm gas}$
• Figure 3: Centaurs A, Circinus, and IC 5063 metallicity gradient profiles for disc (left column), redshifted (middle column) and blueshifted (right column) outflow of MAGNUM galaxies using the Storchi-Bergmann_1998 and pettini metallicity relations for AGNs (red circles) and SF regions (blue circles), respectively, with the radius (in pc) given on the bottom axis. Overplotted are binned linear fits to the radial metallicity gradient in AGNs (dotted red lines) and SF regions (dotted blue lines). The bigger dots mark the binned median values, and error bars represent the scatter in the data within each bin.
• Figure 4: Same as Fig \ref{['fig_zr_3_1']}, but for NGC 1068, NGC 1365, and NGC 1386.
• Figure 5: Same as Fig \ref{['fig_zr_3_1']}, but for NGC 2992, NGC 4945,NGC 5643.