Uncovering a Massive z ∼ 7.7 Galaxy Hosting a Heavily Obscured Radio-loud Active Galactic Nucleus Candidate in COSMOS-Web

Abstract

In this Letter, we report the discovery of the highest redshift, heavily obscured, radio-loud (RL) active galactic nucleus (AGN) candidate selected using JWST NIRCam/MIRI, mid-IR, submillimeter, and radio imaging in the COSMOS-Web field. Using multifrequency radio observations and mid-IR photometry, we identify a powerful, RL, growing supermassive black hole with significant spectral steepening of the radio spectral energy distribution ( f 1.28 GHz ∼ 2 mJy, q 24 μ m = −1.1, α 1.28−3 GHz = − 1.2, Δ α = − 0.4). In conjunction with ALMA, deep ground-based observations, ancillary space-based data, and the unprecedented resolution and sensitivity of JWST, we find no evidence of AGN contribution to the UV/optical/near-infrared (NIR) data and thus infer heavy amounts of obscuration ( N H > 10 23 cm −2 ). Using the wealth of deep UV to submillimeter photometric data, we report a singular solution photo- z of z phot = 7.7 − 0.3 + 0.4 and estimate an extremely massive host galaxy ( log M ⋆ = 11.92 ± 0.5 M ⊙ ) hosting a powerful, growing supermassive black hole​​​​​ ( L Bol = 4−12x × 10 46 erg s −1 ). This source represents the farthest known obscured RL AGN candidate, and its level of obscuration aligns with the most representative but observationally scarce population of AGN at these epochs.