# 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  
**arXiv:** [2308.12823](https://arxiv.org/abs/2308.12823)  
**Date:** 2023-08-24  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.12823v1/

## Key points

- Discovery of highest redshift, heavily obscured, radio-loud quasi-stellar object (QSO) candidate
- Combination of observations from various telescopes and instruments used
- Identification of powerful growing supermassive black hole with significant spectral steepening
- Flux density measured at approximately 2 millijanskys at 1.32 GHz
- Absence of QSO contribution to ultraviolet/optical/near-infrared data suggests heavy obscuration
- Photometric redshift determined as $z_\mathrm{phot} = 7.65^{+0.4}_{−0.3}$
- Extremely massive host galaxy with stellar mass estimated at $\log M_{\star} = 11.92 \pm 0.06\ \mathrm{M}_{\odot}$
- Furthest known obscured radio loud QSO candidate discovered

## Summary

In this letter, the authors present the discovery of a remarkable astronomical object: the highest redshift, heavily obscured, radio-loud quasi-stellar object (QSO) candidate. This discovery was made using a combination of observations from various telescopes and instruments, including the James Webb Space Telescope's Near Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI), as well as mid-infrared, sub-millimeter, and radio imaging in the COSMOS-Web field. By analyzing multi-frequency radio observations and mid-infrared photometry, the researchers were able to identify a powerful growing supermassive black hole with significant spectral steepening of the radio spectral energy distribution. The measurements revealed a flux density of approximately 2 millijanskys at 1.32 GHz ($f_{1.32 \mathrm{GHz}} \sim 2$ mJy), a value of $q_{24\mu m}$ equal to -1.1, and a spectral index $\alpha_{1.32-3\mathrm{GHz}}$ of -1.2 with a change in slope ($\Delta \alpha$) of -0.4. To further investigate this intriguing object, additional observations were conducted using ALMA (Atacama Large Millimeter/submillimeter Array), deep ground-based telescopes, and other space-based data sources alongside the unprecedented resolution and sensitivity provided by JWST. Surprisingly, no evidence of QSO contribution to the ultraviolet/optical/near-infrared data was found; this absence suggests that heavy obscuration is present in this system with an estimated column density higher than $10^{23}$ cm$^{−2}$. The wealth of deep ultraviolet to submillimeter photometric data allowed for an accurate determination of the source's photometric redshift ($z_\mathrm{phot}$). The authors report a singular solution photo-$z$ of $z_\mathrm{phot} = 7.65^{+0.4}_{−0.3}$. Additionally they estimate an extremely massive host galaxy with a stellar mass of $\log M_{\star} = 11.92 \pm 0.06\ \mathrm{M}_{\odot}$. This discovery represents the furthest known obscured radio loud QSO candidate and provides valuable insights into the population of heavily obscured QSOs during these early epochs of the universe; its level of obscuration observed aligns with most representative but observationally scarce population at this redshift range.