James Webb Space Telescope Feed Post

Uncovering a Massive z~7.65 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web

Abstract: In this letter, we report the discovery of the highest redshift, heavily obscured, radio-loud QSO candidate selected using JWST NIRCam/MIRI, mid-IR, sub-mm, and radio imaging in the COSMOS-Web field. Using multi-frequency radio observations and mid-IR photometry, we identify a powerful, radio-loud (RL), growing supermassive black hole (SMBH) with significant spectral steepening of the radio SED (f1.32GHz~2 mJy, q24µm=-1.1, a1.32-3GHz=-1.2, ?a=-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 QSO contribution to the UV/optical/NIR data and thus infer heavy amounts of obscuration (NH>1023 cm-2). Using the wealth of deep UV to sub-mm photometric data, we report a singular solution photo-z of zphot = 7.65+0.4-0.3 and estimate an extremely massive host-galaxy (logM?=11.92±0.06M?). This source represents the furthest known obscured RL QSO candidate, and its level of obscuration aligns with the most representative but observationally scarce population of QSOs at these epochs.