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Arxiv: Another piece to the puzzle: radio detection of a JWST discovered AGN candidate Published: 1/9/2025 4:05:15 AM Updated: 1/9/2025 4:05:15 AM

Paper abstract: Radio observations can provide crucial insight into the nature of a newabundant and mysterious population of dust-reddened active galactic nuclei(AGN) candidates discovered by the James Webb Space Telescope (JWST), including``Little Red Dots" (LRDs). In this study, we search for radio bright sources ina large sample of ~700 JWST discovered AGN candidates (z~2-11) in the0.144-3 GHz frequency range, utilizing deep radio imaging in COSMOS, GOODS-N,and GOODS-S. Only one source is significantly detected in our radio surveys,which is PRIMER-COS 3866 at z=4.66. Its radio properties are consistent withboth an AGN and star formation origin with a spectral index of\alpha=-0.76^{+0.11}_{-0.09} and a radio-loudness of R~0.5. Thederived brightness temperature limit of PRIMER-COS 3866 of T_b \gtrsim 10^{3}K is too low to confirm its AGN nature. Our stacking results yieldnon-detections in all fields with the most constraining 3\sigma limitL_{1.3\text{GHz}} < 1.3\times10^{39} erg s^{-1} (rms of ~0.15 \muJybeam^{-1} at z_{\text{median}}=6.1) obtained for photometrically selectedAGN candidates in the COSMOS field. This result is still consistent withexpectations from the empirical L_X - L_{\text{H}\alpha} and L_X - L_Rcorrelations established for local AGN. We conclude that current radioobservations have insufficient depth to claim JWST discovered AGN candidatesare radio-weak. We project that future surveys carried out by the SKA and ngVLAshould be able to obtain significant detections within a few hours, providingcrucial measurements of their brightness temperature, which would allow fordistinguishing between AGN and starburst-driven origins of this new abundantpopulation.