Another Piece to the Puzzle: Radio Detection of a JWST-detected Active Galactic Nucleus Candidate

Abstract

Radio observations can provide crucial insight into the nature of a new abundant and mysterious population of dust-reddened active galactic nuclei (AGN) candidates discovered by the James Webb Space Telescope (JWST), including “Little Red Dots.” In this study, we search for radio bright sources in a large sample of ∼700 JWST-discovered AGN candidates ( z ∼ 2–11) in the 0.144–3 GHz frequency range, utilizing deep radio imaging in the Cosmic Evolution Survey and Great Observatories Origins Deep Survey North and South. Only one source, PRIMER-COS 3866 at z = 4.66, is significantly detected in our radio surveys, which has been previously identified as an X-ray AGN. Its radio properties are consistent with both an AGN and star formation origin with a spectral index of $\alpha =-0.7{6}_{-0.09}^{+0.11}$ , radio-loudness of R ≈ 0.5, and brightness temperature limit of T _b ≳ 10 ^3 K. Our stacking results of both spectroscopically and photometrically selected AGN candidates yield nondetections in all fields, with 3 σ limits of L _1.4 GHz < 8.6 × 10 ^39 erg s ^−1 (spectroscopic sample) and L _1.3 GHz < 1.3 × 10 ^39 erg s ^−1 (photometric sample). We demonstrate that these results are still consistent with expectations from the empirical L _X – L _H _α and L _X – L _R correlations established for local AGN. We argue that current radio observations in these studied fields have insufficient depth to claim JWST-discovered AGN candidates are radio weak. We project that future surveys carried out by the Square Kilometer Array and Next Generation Very Large Array should be able to obtain significant detections within a few hours, providing crucial measurements of their brightness temperature, which would allow for distinguishing between AGN and starburst-driven origins of this new abundant population.

Keywords

• High-redshift galaxies
• Radio continuum emission
• Active galactic nuclei
• James Webb Space Telescope