Evidence of Feedback Effects in Low-luminosity Active Galactic Nuclei Revealed by JWST Spectroscopy

Lulu Zhang, Chris Packham, Erin K. S. Hicks, Ric I. Davies, Daniel E. Delaney, Francoise Combes, Miguel Pereira-Santaella, Almudena Alonso-Herrero, Claudio Ricci, Omaira González-Martín, Laura Hermosa Muñoz, Ismael García-Bernete, Cristina Ramos Almeida, Dimitra Rigopoulou, Fergus R. Donnan, Enrica Bellocchi, Nancy A. Levenson, Martin J. Ward, Santiago García-Burillo, Sebastian F. Hoenig

First listed 2026-01-12 | Last updated 2026-01-12

Abstract

This letter presents an analysis of the infrared ($\sim 3-28\,μm$) spectra extracted from the nuclear ($r < 150$ pc) regions of four low-luminosity active galactic nuclei (AGN), observed by JWST NIRSpec/IFU and MIRI/MRS as an extension of the Galaxy Activity, Torus, and Outflow Survey (GATOS). We find that, compared to higher-luminosity AGN, these low-luminosity AGN exhibit distinct properties in their emission of ionized gas, polycyclic aromatic hydrocarbons (PAHs), and molecular hydrogen (H$_2$). Specifically, the low-luminosity AGN exhibit relatively weak high-ionization potential lines (e.g., [Ne V] and [O IV]), and the line ratios suggest that fast radiative shocks (with $v_{\rm s}$ of $\sim \rm 100s\,km\,s^{-1}$) are the primary excitation source of ionized gas therein. Under the low-excitation conditions of their nuclear regions, these low-luminosity AGN generally exhibit a higher fraction of PAHs with large size ($N_{\rm C} \gtrsim 200$), reflecting the preferential destruction of smaller PAH molecules by AGN feedback. Furthermore, the H$_2$ transitions in these low-luminosity AGN are not fully thermalized, with slow, plausibly jet-driven molecular shocks (with $v_{\rm s} \leq \rm 10\,km\,s^{-1}$) likely being the extra excitation source. Taken together with results from the literature, these findings indicate that feedback operates in both low- and high-luminosity AGN, albeit its impact varies with AGN luminosity. In particular, systematic variations in PAH band ratios are found across AGN, demonstrating the differing influence of feedback in AGN of varying luminosities and highlighting the potential of PAH band ratios as diagnostics for distinguishing kinetic- and radiative-mode AGN feedback.

Short digest

JWST NIRSpec/IFU + MIRI/MRS nuclear (r < 150 pc) spectra of four SINGS low-luminosity AGN (GATOS extension) reveal weak high-ionization lines and ionized-gas ratios consistent with fast radiative shocks at hundreds of km s^-1. PAH band ratios point to a population skewed toward large molecules (Nc ≳ 200), implying preferential destruction of small PAHs by feedback. The H2 ladder is sub-thermal, requiring an extra component from slow, likely jet-driven molecular shocks (≤10 km s^-1). Together with literature trends, the authors argue that feedback operates across AGN luminosities and that PAH ratios can diagnose kinetic- versus radiative-mode feedback.

Key figures to inspect

• Figure 1: Inspect the PAH decomposition across 3–28 μm to see silicate/ice absorption placement, the dominance of large-PAH features (6.2/7.7/11.3/17 μm), and which emission lines remain in the residuals after continuum and PAH modeling.
• Figure 2: Compare ionized ([Fe II], [Ar II], [Ne II], [Ne III]) and adjacent H2 line profiles versus instrumental FWHM to assess whether shocks broaden the ionized gas while H2 stays narrower, supporting distinct excitation channels.
• Figure 3: Place each nucleus on [Ne V]/[Ne III] vs [O IV]/[Ne III] and [Ne V]/[Fe II] vs [O IV]/[Fe II] against AGN-photoionization and fast-shock model contours; note NGC 1266 upper limits and the systematic shift toward the shock region relative to higher-luminosity Seyferts.
• Figure 4: Read the 11.3/7.7 vs 6.2/7.7 and 11.3/7.7 vs 11.3/3.3 grids to infer PAH size and ionization; LLAGN points lie toward large, more neutral PAHs compared to SINGS star-forming contours, with NGC 4736 showing a 3.3 μm non-detection limit.
• Appendix A (A1–A3): Galaxy-by-galaxy spectral fits for NGC 1266, NGC 3190, and NGC 4736 to verify the robustness of the PAH component retrieval and the masking of ice/CO features.