Chemical enrichment in LINERs from MaNGA. II. Characterizing the shape of their radial metallicity gradients

TL;DR

This paper addresses how gas-phase metallicity gradients behave in LINER-like galaxies using MaNGA data, focusing on both $12+\log(O/H)$ and $\\log(N/O)$ across disks and nuclei. It employs HII-CHI-Mistry to derive abundances and a flexible piecewise fit to capture multiple gradient breaks, revealing a diversity of gradient shapes and a general decoupling between O/H and N/O gradients. The study finds that nuclear LINER activity and multi-scale gas dynamics can imprint breaks and varied slope patterns, with no strong correlation to global galaxy properties, and it proposes a bathtub-inspired model that integrates AGN feed/feedback to explain the observed trends. The results have implications for interpreting chemical enrichment in LLAGN hosts and motivate further comparative analyses with control samples and higher-resolution inner-disk data to quantify AGN-driven chemical evolution.

Abstract

Chemical abundance radial gradients provide key information on how the processes that affect chemical enrichment of the gas-phase interstellar medium (ISM) act at different galaxy scales. Whereas in the last decades there has been an increase in the number of galaxies studied with integral field spectroscopy, there is still not a clear picture on a subsequent characterization of the chemical abundance radial gradients in galaxies hosting Active Galactic Nuclei (AGNs). This lack of analysis is even more accentuated in the case of low-ionization nuclear emission-line regions (LINERs). For the first time, we analyze the chemical abundance radial gradients in a sample of LINER-like galaxies, whose nuclear emission has been previously (Paper I) discussed. We use a sample of 97 galaxies from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), whose nuclear regions show LINER-like emission. We use the open-source code HII-CHI-Mistry to estimate the chemical abundance ratios 12+log(O/H) and log(N/O) in the HII regions across the disks in our sample, as well as in the nuclear parts where the LINER-like activity dominates. To fit the radial profiles we use a piecewise methodology which uses a non-fixed number of breaks to find the best fit for the data. We obtain that majority of our sample of galaxies exhibits departures from the single linear gradient both in 12+log(O/H) and log(N/O) (as expected from the inside-out scenario). We investigate whether these departures are driven by galaxy properties (stellar mass, neutral gas mass, stellar velocity dispersion), finding not correlation at all. We also report that in most cases there is no correlation between the shape of the 12+log(O/H) and log(N/O) radial profiles. We propose a model in which AGN (feed)back, acting at different scales depending on the galaxy and its evolutionary stage, might be responsible for these departures.

Figures (14)

• Figure 1: Root Square Error (RSE) for the different techniques used to fit the radial metallicity gradients of 12+log(O/H) (a) and log(N/O) (b) in our sample of LINERs. The sample is segregated according to the number of breaks used by piecewise fit for each chemical abundance ratio.
• Figure 2: Comparison between the breaks found for the log(N/O) radial gradients (y-axis) and 12+log(O/H) radial gradients (x-axis) in our sample. Green dots correspond to LINERs showing one break in both gradients, whereas red dots correspond to LINERs showing two breaks. The solid black lines represent the one-to-one relation, the dotted lines represent the median offset, and the shaded gray area the deviation.
• Figure 3: Histogram of the obtained gradient slopes in the fits for both 12+log(O/H) and log(N/O) for different categories attending to the number of obtained breaks. Slopes for 12+log(O/H): a) galaxies with no breaks, b) galaxies with one single break, and c) galaxies with two breaks. Lower plots d), e) and f) are similar to the above ones but for log(N/O) radial gradient. For all plots, solid black lines represent the flatten profile ($\nabla = 0$).
• Figure 4: Comparison of the abundances obtained as intersects from the fits with the abundances estimated in the nuclear regions both for 12+log(O/H) (left column) and log(N/O) (right column). Plots a) and b) represent the extrapolation of the innermost radial fits, while plots c) and d) represent the extrapolation of the middle radial fits, and plots e) and f) the extrapolations of the outer radial fits. For all plots, Blue dots represent galaxies with no breaks in their corresponding fits, green dots galaxies with one break, and red dots galaxies with two breaks. The solid black lines represent the one-to-one relation, the dotted lines represent the median offset, and the shaded gray areas the deviation.
• Figure 5: Relation between stellar mass and the slopes for the radial fits of 12+log(O/H) (left column) and log(N/O) (right column). Panels a) and b) represent the slopes of the inner radial fits, panels c) and d) the slopes of the middle radial fits, and panels e) and f) the slopes of the outer radial fits. For all plots, Blue dots represent galaxies with no breaks, green dots with one break, and red dots with two breaks. Solid black lines represent the flatten profile ($\nabla = 0$).