JWST NIRCam Imaging of NGC 4258. I. Observation Overview

We present James Webb Space Telescope (JWST) Near-Infrared Camera imaging of the nearby Seyfert 1.9 galaxy NGC 4258, which hosts strong star formation regions as well as an anomalous jet-like radio structure that extends through a significant portion of its disk. This galaxy provides a unique environment to study active galactic nucleus (AGN)–driven shocks and their impacts on the interstellar medium (ISM), as its proximity allows for narrow-band observations of various near-infrared tracers sensitive to multiple levels of shock and radiative excitation: [Fe ii ] (1.64 μ m), Pa α (1.87 μ m), H 2 (2.21 μ m), 3.3 μ m polycyclic aromatic hydrocarbon (PAH) emission, Br α (4.05 μ m), and Pf β (4.66 μ m), allowing us to trace shocks with parsec-scale resolution. Comparing these near-infrared observations with available ultraviolet, optical, radio, and X-ray imaging, we find that shocks present in the brightest regions of the anomalous radio structure are likely of low velocity (50–100 km s −1 ), suggesting that these features originate from AGN-driven winds that interact with the host medium and mechanically impart energy into the disk. Further, while the cospatial [Fe ii ] and H 2 emissions indicate multiphase shocks, PAH emission is relatively weaker in or absent from the most shock-excited regions, consistent with the destruction of small dust grains. Finally, we propose that surveys identifying enhanced [Fe ii ] in AGN host galaxies may systematically reveal a key population, where AGN feedback is significantly coupled with the surrounding ISM and actively shaping galaxy evolution.