2025ApJ...984...13L

The extended narrow-line region (NLR) of active galactic nuclei (AGNs) provides a valuable laboratory for exploring the relationship between AGNs and their host galaxies, often appearing as an “ionization cone” that can extend out to the very edge of the galaxy. We use new James Webb Space Telescope NIRCam imaging to study the morphologies and sizes of NLRs traced by [O III] at cosmic noon (z ∼ 2-3). To determine NIRCam's ability to probe the properties of the NLR in cosmic noon galaxies, we present simulated images of AGNs at z = 2-3 created with archival data cubes from the Multi Unit Spectroscopic Explorer of nine nearby (z < 0.05) AGN host galaxies with previously confirmed extended NLRs. Our simulated images show that NIRCam is able to resolve the morphologies of NLRs at z = 2-3 with narrow- and medium-band observations. We then search for extended NLRs with NIRCam medium-band observations targeting the [O III] + Hβ emission in 27 previously identified AGNs at z = 2.4-3.4 in the Great Observatories Origins Deep Survey South field. We detect six galaxies in our observed sample with [O III] + Hβ morphologies consistent with AGN ionization cones with characteristic NLR sizes of 1-2.5 kpc. Thanks to our simulated data, we can predict the effects of cosmological surface brightness dimming and instrument noise on the NLR size measurements at high redshift, which has the biasing effect of lowering the NLR size-AGN luminosity trend that is observed at low redshift by a factor of ∼2.