Uncovering a Massive z~7.7 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web

Kavli Affiliate: John D. Silverman

| First 5 Authors: Erini Lambrides, Marco Chiaberge, Arianna Long, Daizhong Liu, Hollis B. Akins

| Summary:

In this letter, we report the discovery of the highest redshift, heavily
obscured, radio-loud AGN 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 ($f_{1.28 mathrm{GHz}} sim 2$ mJy, $q_{24mu m} = -1.1$,
$alpha_{1.28-3mathrm{GHz}}=-1.2$, $Delta alpha = -0.4$). 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/NIR data and thus infer heavy amounts of
obscuration (N$_{mathrm{H}} > 10^{23}$ cm$^{-2}$). Using the wealth of deep UV
to sub-mm photometric data, we report a singular solution photo-z of
$z_mathrm{phot}$ = 7.7$^{+0.4}_{-0.3}$ and estimate an extremely massive
host-galaxy ($log M_{star} = 11.4 -12,mathrm{M}_{odot}$) hosting a
powerful, growing SMBH (L$_{mathrm{Bol}} = 4-12 times 10^{46}$ erg s$^{-1}$).
This source represents the furthest 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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