Spatially Resolved AGN Ionization and Star Formation at Cosmic Noon with JWST/JEMS

TL;DR

This study uses JWST imaging to map ionized gas in galaxies at cosmic noon, revealing larger ionization regions in AGN hosts and a correlation with AGN luminosity, shedding light on galaxy evolution.

Contribution

First spatially resolved analysis of ionized gas in a large sample of high-redshift galaxies using JWST, linking gas extent to AGN activity and luminosity.

Findings

AGN hosts have larger ionized gas extents than control galaxies.

[O III]+Hβ emission is more extended than Paβ by ~0.1 dex.

Ionized gas extent correlates with AGN luminosity at z~3.

Abstract

At Cosmic Noon ($z\approx 2-3$), both star formation and Active Galactic Nuclei (AGN) activity peaked, each playing a significant role in ionizing interstellar gas on galaxy-wide scales. The spatial distribution of this ionized gas provides a direct probe of how AGN and stellar ionization shape the gaseous reservoirs of their host galaxies. Using JWST/NIRCam imaging from the JWST Extragalactic Medium-band Survey (JEMS) we spatially map two complementary tracers of ionized gas, [O III]$+\mathrm{H}\beta$ and Pa$\beta$, in $\sim200$ galaxies at $2.5 < z < 2.9$. We apply multiwavelength AGN diagnostics to divide the sample into AGN hosts (33 galaxies), Pa$\beta$-detected systems (32 galaxies), and control objects (175 galaxies). We measure the [O III]$+\mathrm{H}\beta$ and Pa$\beta$ spatial extents in each population and relate them to AGN and host properties derived from Spectral Energy Distribution (SED) modeling. Both tracers exhibit systematically larger maximum radial extents in AGN hosts than in control galaxies (by $\sim0.3$ dex), with [O III]$+\mathrm{H}\beta$ emission modestly more extended than Pa$\beta$ by $\sim0.1$ dex. With this statistically robust AGN sample, we measure the [O III]$+\mathrm{H}\beta$ radial extent-AGN luminosity relation at $z\sim3$ and derive a slope of $\sim0.2$, consistent with the shallow end of values reported at low redshift. The larger ionized gas extents among AGN hosts relative to the control sample, combined with the strong correlation between [O III]$+\mathrm{H}\beta$ extent and AGN luminosity suggest that AGN activity may dominate gas ionization in galaxies with mixed AGN and star-forming activity at Cosmic Noon, although stellar processes can still contribute significantly on kiloparsec scales.