JWST NIRCam simulations and observations of AGN ionization cones in cosmic noon galaxies

Sophie Lebowitz, Kevin Hainline, Stéphanie Juneau, Jianwei Lyu, Christina Williams, Stacey Alberts, Xiaohui Fan, Marcia Rieke

First listed 2025-01-09 | Last updated 2025-03-18

Abstract

The extended narrow line region (NLR) of Active Galactic Nuclei (AGN) provides a valuable laboratory for exploring the relationship between AGN 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 (JWST) NIRCam imaging to study the morphologies and sizes of NLRs traced by [O III] at cosmic noon ($z\sim2-3$). To determine NIRCam's ability to probe the properties of the NLR in cosmic noon galaxies, we present simulated images of AGN at $z=2-3$ created with archival data cubes from the Multi Unit Spectroscopic Explorer (MUSE) 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]$+\mathrm{H}β$ emission in twenty-seven previously identified AGN at $z=2.4-3.4$ in the Great Observatories Origins Deep Survey South (GOODS-S) field. We detect six galaxies in our observed sample with [O III]$+\mathrm{H}β$ 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 $\sim 2$.

Short digest

Simulating JWST/NIRCam narrow- and medium-band [O III] maps at z≈2–3 using MUSE datacubes of nine nearby AGN, the authors show NIRCam can recover classic ionization-cone morphologies. They then apply this to 27 known AGN in GOODS-S (z=2.4–3.4), identifying six systems with [O III]+Hβ morphologies consistent with cones and characteristic NLR sizes of 1–2.5 kpc. The simulations quantify how cosmological dimming and instrument noise bias high‑z NLR size measurements low, depressing the local NLR size–AGN luminosity relation by about a factor of two. This establishes a practical medium-band imaging path to select cone candidates and calibrate NLR size trends at cosmic noon.

Key figures to inspect

• Figure 1 (SED scaling for F182M/F210M): Check how the continuum color terms are derived per redshift bin and how the scaling factors control residuals in the [O III]+Hβ map after subtraction.
• Figure 2 (NGC 2992 at z=2.3, PSF/oversampling tests): Compare no-PSF vs WebbPSF and oversampling cases to see how cone edges, opening angle, and asymmetries survive beam smearing in the narrow-band [O III] and the continuum-subtracted map.
• Figure 3 (Narrow vs medium band [O III]): Directly compare F164N- and F162M-based [O III] maps to assess morphology fidelity versus throughput—key for deciding when medium bands can robustly reveal cones.
• Figure 4 (Noise and continuum subtraction): Contrast noiseless and noisy simulations using F182M ([O III]+cont) minus F210M (cont) to gauge detection limits and how noise drives underestimates of NLR size at z≈2–3.