ReveaLLAGN 1: JWST Emission-line Spectra Reveal Low-luminosity Active Galactic Nucleus with Ultraviolet-deficient Spectral Energy Distributions and Warm Molecular Gas

Abstract We present near- and mid-infrared spectra of eight low-luminosity active galactic nuclei (LLAGN), spanning nearly 4 orders of magnitude in black hole mass and Eddington ratio, obtained with JWST/NIRSpec and MIRI as part of the ReveaLLAGN program, along with identical archival data of Cen A. The high spatial resolution of JWST cleanly separates active galactic nuclei (AGN) emission from host-galaxy contamination, enabling detections of high-ionization-potential lines more than an order of magnitude fainter than previously measured. Emission-line diagnostics reveal a transition at log( L bol / L Edd ) ∼−3.5, where the spectral energy distribution becomes increasingly deficient in ultraviolet photons. We find that rotational H 2 excitation temperatures are elevated (∼500 K higher) compared to both higher-luminosity AGN and star-forming galaxies, while the H 2 (0–0)S(3)/PAH 11.3 μ m ratios are consistent with those observed in the AGN population. We discuss the possible roles of outflows, jets, and X-ray-dominated regions in shaping the interstellar medium surrounding LLAGN. Silicate emission at ∼10 μ m, localized to the nuclear region, is detected in most ReveaLLAGN targets. This dataset offers the first comprehensive JWST-based characterization of infrared emission lines in the nuclear regions of LLAGN.