2025A&A...701A..29P

Context. It has been reported that the gas-phase oxygen abundance of the circumnuclear regions around supermassive black holes (SMBHs) could be affected by the presence of an active galactic nucleus (AGN). However, there is currently no agreement on the processes behind this effect. Some studies have measured higher metallicities in the nuclear regions of AGN hosts compared to those of star-forming (SF) galaxies, while others have observed the opposite result.
Aims. In this work, we explore whether the interplay between AGN activity and the ram-pressure strippingprocesses of ram-pressure stripping (RPS) acting in the cluster environment could alter the metallicity distributions of nearby (z < 0.07) galaxies.
Methods. We measured the spatially resolved gas-phase oxygen abundances of 10 AGN hosts experiencing RPS from the GASP survey and 52 AGN hosts located in the field (and, thus, undisturbed by RP) drawn from MaNGA DR15. To measure the oxygen abundances in SF and AGN-ionized regions, we present a set of strong emission line (SEL) calibrators obtained through an indirect method. Here, the [O III]/[S II] and [N II]/[S II] line ratios, observed and predicted from CLOUDY photoionization models, were matched using the NEBULABAYES code.
Results. We find that the metallicity gradients of RPS and field AGN generally do not present significant differences within the errors. However, we also find that two two out of the ten ten RP-stripped AGNs display lower oxygen abundances at any given radius than the rest of the AGN sample. Overall, this result highlights the fact that the interplay between AGN and RPS does not seem to play a major role in shaping the metallicity distributions of stripped galaxies within 1.5 times the galaxy's effective radius (r < 1.5R_e); however,but that larger samples are needed to draw more robust conclusions. By adding a control sample of SF galaxies, both experiencing RPS and in the field, we find that the AGN hosts are more metal-enriched than SF galaxies at any given radius, but that the steepness of the gradients in the nuclear regions (r < 0.5R_e) is higher in AGN hosts than in SF galaxies. In, particular, AGN hosts show a metal enrichment in the nuclear regions that is about 1.8-2.3 times higher than the enhancement in the disk at r ∼ 1.25R_e, regardless of the host galaxy's stellar mass.
Conclusions. These results favor the hypothesis that AGN activity is the cause behind metal pollution in athe galaxy's nuclear regions.