JWST/NIRSpec and MIRI observations of an expanding, jet-driven bubble of warm H₂ in the radio galaxy 3C 326 N

The physical link between AGN activity and the suppression of star formation in their host galaxies is one of the major open questions of the AGN feedback scenario. The Spitzer space mission revealed a subset of powerful nearby radio galaxies with unusually bright line emission from warm (T ≥ 100 K) molecular hydrogen, while typical star-formation tracers such as polycyclic aromatic hydrocarbons (PAHs) or a dust continuum have been exceptionally faint or undetected. Here, we present JWST NIRSpec and MIRI MRS IFU observations of one of the best studied galaxies of this class, 3C 326 N at z = 0.09. We identified a total of 19 lines of the S, O, and Q series of ro-vibrational H₂ emission with NIRSpec at a 0.11″ spatial resolution, probing a small quantity (1.4 × 10⁴ M_⊙) of gas at temperatures of T ~ 1000 K. We also mapped the rotational mid-infrared lines of H₂ 0- 0 S(3), S(5), and S(6) at a spatial resolution of 0.4″ with MIRI/MRS, probing most of the 2 × 10⁹ M_⊙ of warm H₂ in this galaxy. The CO band heads show a stellar component consistent with a 'slow-rotator'that is typical of a massive (3 × 10¹¹ M_⊙) galaxy, offering a reliable systemic redshift of z = 0.08979±0.0003. The extended line emission shows a bipolar bubble expanding through the molecular disk at velocities of up to 380 km s^-1, delineated by several bright clumps along the northern outer rim, potentially coming from gas fragmentation. Throughout the disk, H₂ is very broadly dispersed, with an FWHM of ~100-1300 km s^-1 and complex, dual-component Gaussian line profiles. The extended [FeII]λ1.644 and Paα follow the same morphology, however, [NeIII]λ15.56 is more symmetric about the nucleus. We show that most of the gas (with the exception of [NeIII]λ15.56) is predominantly heated by shocks driven by the radio jets into the gas, both for the ro-vibrational and rotational H₂ lines. In addition, the accompanying line broadening is sufficient to suppress star formation in the molecular gas. We also compared the morphology and kinematics of the rotational and ro-vibrational lines, finding the latter to be a good proxy to the global morphology and kinematic properties of the former in strongly turbulent environments. This demonstrates the potential of using the higher frequency ro-vibrational lines in studying turbulent molecular gas. Provided they are bright enough, they would allow us to examine turbulence in galaxies during the early phases of cosmic history, while most rotational lines are red-shifted out of the MIRI bandpass for z ≥ 1.5.