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

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 $(\mathrm{log}{M}_{\star }=11.92\pm 0.5{M}_{\odot})$ 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.