Another piece to the puzzle: radio detection of a JWST detected AGN 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 (LRDs). In this study, we search for radio bright sources in a large sample of $\sim$700 JWST discovered AGN candidates ($z\sim 2-11$) in the 0.144-3 GHz frequency range, utilizing deep radio imaging in COSMOS, GOODS-N, and GOODS-S. 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 $\alpha =-0.76_{-0.09}^{+0.11}$, radio-loudness of $R\approx 0.5$, and brightness temperature limit of $T_b\gtrsim 10^3$ K. Our stacking results of both spectroscopically and photometrically selected AGN candidates yield non-detections in all fields, with 3$\sigma$ limits of $L_{1.4\text{GHz}}<8.6\times 10^{39}$ erg s${}^{-1}$ (spectroscopic sample) and $L_{1.3\text{GHz}}<1.3\times 10^{39}$ erg s${}^{-1}$ (photometric sample). We demonstrate that these results are still consistent with expectations from the empirical $L_X-L_{\text{H}\alpha }$ 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 SKA and ngVLA 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.

12 pages, 4 figures, Accepted by ApJ

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• Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts
• Active galactic nuclei-heated dust revealed in "little red dots"
• A weak Ly$\alpha$ halo for an extremely bright Little Red Dot: Indications of enshrouded SMBH growth
• Little Red Dots as Hidden Neutrino Sources
• Euclid: Discovery of 31 new quasars at $6.6<z<7.8$
• Mass and Spin Growth of Very Massive Stars in Star Clusters Potentially Associated with Little Red Dots
• (Re)solving the Complex Multiscale Morphology and V-shaped Spectral Energy Distribution of a Newly Discovered Strongly Lensed Little Red Dot in A383
• The Structure and Evolution of LRDs: Insights from JWST NIRSpec Medium and High Resolution Spectroscopy at $z\sim 4$