JWST/NIRSpec and MIRI observations of an expanding, jet-driven bubble of warm H$_2$ in the radio galaxy 3C 326 N

TL;DR

This study uses JWST observations to analyze a jet-driven bubble of warm H$_2$ in galaxy 3C 326 N, revealing shock heating, gas dynamics, and suppression of star formation, advancing understanding of AGN feedback mechanisms.

Contribution

First detailed JWST NIRSpec and MIRI observations of warm H$_2$ in a radio galaxy, linking shock heating and jet activity to star formation suppression.

Findings

Bipolar bubble expanding at up to 380 km/s.

Warm H$_2$ predominantly heated by shocks from the radio jet.

Line broadening suppresses star formation in the galaxy.

Abstract

The physical link between AGN activity and the suppression of star formation in their host galaxies is one of the major open questions of AGN feedback. The Spitzer space mission revealed a subset of nearby radio galaxies with unusually bright line emission from warm ($T\ge 100$ K) H$_2$, while typical star-formation tracers were exceptionally faint or undetected. We present JWST NIRSpec and MIRI IFU observations of 3C 326 N at z=0.09 and identify 19 ro-vibrational H$_2$ emission lines that probe hot ($T\sim 1000$ K) gas as well as the rotational lines of H$_2$ 0--0 S(3), S(5), and S(6) which probe most of the $2\times 10^9$ M$_\odot$ of warm H$_2$ in this galaxy. CO band heads show a stellar component consistent with a "slow-rotator", typical of a massive $3\times10^{11}$ M$_\odot$ galaxy, and provide us with a reliable redshift of $z=0.08979\pm 0.0003$. 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 from gas fragmentation. Throughout the disk, the H$_2$ is very broad, FWHM ~100-1300 km s$^{-1}$, and shows dual-component Gaussian line profiles. [FeII]$\lambda$1.644 and Pa$\alpha$ follow the same morphology, however [NeIII]$\lambda$15.56 is more symmetric about the nucleus. We show that the gas, with the exception of [NeIII]$\lambda$15.56, is predominantly heated by shocks driven by the radio jet and that the accompanying line broadening is sufficient to suppress star formation. We also compare the rotational and ro-vibrational lines, finding that the latter can be a good proxy to the global morphology and kinematic properties of the former in strongly turbulent environments. This enables studies of turbulence in galaxies at intermediate and high redshifts while most rotational lines are redshifted out of the MIRI bandpass for $z$>1.5.