Shocked, heated, and now resolved: H₂ excitation in the low-luminosity AGN at M58 core with JWST

¹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
² INAF – Osservatorio Astrofisco di Arcetri, largo E. Fermi 5, 50127 Firenze, Italy
³ Instituto de Astrofísica de la Plata (CONICET–UNLP), Paseo del Bosque, 1900 La Plata, Argentina
⁴ Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque, 1900 La Plata, Argentina
⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁶ INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
⁷ Dipartimento di Fisica e Astronomia “Augusto Righi”, Università di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
⁸ Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII 3, 28014 Madrid, Spain
⁹ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan 1, 44001 Teruel, Spain
¹⁰ Dipartimento di Fisica e Astronomia, Universitá di Firenze, Via G. Sansone 1, 50019 Firenze, Italy
¹¹ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA
¹² I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Cologne, Germany

^⋆ Corresponding author: ivan.lopez@inaf.it

Received: 23 July 2025
Accepted: 29 September 2025

Abstract

We present JWST NIRSpec and MIRI MRS observations of the central kiloparsec of M58 (NGC 4579), a nearby galaxy hosting a low-luminosity AGN (LLAGN; L_bol ∼ 10⁴² erg s⁻¹) with a low-power jet. These data provide an unprecedented view of the warm molecular gas phase and reveal clear signatures of feedback. We detect 44 H₂ lines, including bright pure rotational lines (S(1)–S(18)) and rovibrational lines up to ν = 2, probing a wide range of excitation conditions. Excitation diagrams show that rotational lines follow a power-law temperature distribution with an exponential cutoff, consistent with heating by low-velocity shocks. H₂ rovibrational lines deviate from thermal models primarily because of sub-thermal excitation at low density. Additionally, there may be a 10% contribution powered by AGN X-ray photons in the nucleus. The dust lanes associated with the spiral inflow appear dynamically undisturbed but show signs of shock heating, while the inner ∼200 pc exhibits turbulent kinematics produced by outflowing molecular gas. These results reveal the subtle yet measurable impact of LLAGN feedback on the interstellar medium, demonstrating that even weak, vertically oriented jets and low radiative accretion rates can perturb molecular gas and regulate nuclear reservoirs. This study highlights JWST’s transformative ability to uncover hidden modes of AGN feedback.