Uncovering a Massive z~7.65 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web
Authors: Erini Lambrides, Marco Chiaberge, Arianna Long, Daizhong Liu, Hollis B. Akins, Andrew F. Ptak, Irham Taufik Andika, Alessandro Capetti, Caitlin M. Casey, Jaclyn B. Champagne, Katherine Chworowsky, Olivia R. Cooper, Xuheng Ding, Andreas L. Faisst, Maximilien Franco, Steven Gillman, Ghassem Gozaliasl, Kirsten R. Hall, Santosh Harish, Christopher C. Hayward, Michaela Hirschmann, Taylor A. Hutchison, Knud Jahnke, Shuowen Jin, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Vasily Kokorev, Sinclaire M. Manning, Crystal L. Martin, Jed McKinney, Colin Norman, Masafusa Onoue, Brant E. Robertson, Marko Shuntov, John D. Silverman, Massimo Stiavelli, Benny Trakhtenbrot, Eleni Vardoulaki, Jorge A. Zavala, Natalie Allen, Olivier Ilbert, Henry Joy McCracken, Louise Paquereau, Jason Rhodes, Sune Toft
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 ($f_{1.32 \mathrm{GHz}} \sim 2$ mJy, $q_{24\mu m} = -1.1$, $\alpha_{1.32-3\mathrm{GHz}}=-1.2$, $\Delta \alpha = -0.4$). 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 QSO 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 $z_\mathrm{phot}$ = 7.65$^{+0.4}_{-0.3}$ and estimate an extremely massive host-galaxy ($\log M_{\star} = 11.92 \pm 0.06\,\mathrm{M}_{\odot}$). 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.
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