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arXiv · 2508.11044

JWST NIRCam Imaging of NGC 4258: I. Observation Overview

Travis C. Fischer·Nicholas F. Cothard·Omnarayani Nayak·Henrique Schmitt·Erin Smith·Jason Glenn
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Abstract

We present James Webb Space Telescope (JWST) NIRCam 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 impact 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 co-spatial [Fe II] and H$_2$ emission indicate multi-phase shocks, PAH emission is relatively weaker or absent in 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.

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Travis C. Fischer, Nicholas F. Cothard, Omnarayani Nayak, Henrique Schmitt, Erin Smith, Jason Glenn. 2025-08-14. JWST NIRCam Imaging of NGC 4258: I. Observation Overview. https://arxiv.org/abs/2508.11044

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