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 μm = −1.1, α_{1.28−3 GHz} = − 1.2, Δα = − 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 > 10²³ 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 × 10⁴⁶ 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.

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