Revisiting the Claim for a Direct-Collapse Black Hole in UHZ1 at $z=10.05$
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| Format: | Preprint |
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2026
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| _version_ | 1866908914265620480 |
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| author | Zou, Fan Gallo, Elena Zuo, Zihao Hodges-Kluck, Edmund Nguyen, Dieu D. Roberts-Borsani, Guido Madau, Piero Pacucci, Fabio Seth, Anil C. Treu, Tommaso |
| author_facet | Zou, Fan Gallo, Elena Zuo, Zihao Hodges-Kluck, Edmund Nguyen, Dieu D. Roberts-Borsani, Guido Madau, Piero Pacucci, Fabio Seth, Anil C. Treu, Tommaso |
| contents | We reassess the direct collapse black hole (DCBH) interpretation of UHZ1 (UNCOVER-26185), a gravitationally lensed galaxy at $z_\mathrm{spec}=10.054$. That interpretation rests on a hard ($2-7$ keV) X-ray excess detected with Chandra, attributed to a Compton-thick AGN with an inferred $2-10$ keV luminosity of $L_\mathrm{X,int}\sim10^{46}~\mathrm{erg~s^{-1}}$ (Bogdan et al. 2024). The resulting extreme X-ray to rest-frame optical-IR ratio was taken as the hallmark signature of an "outsize black hole galaxy" at cosmic dawn. We analyse the full 2.2 Ms Chandra imaging dataset -- including 0.95 Ms of unpublished observations -- and present new JWST/MIRI photometry at $λ_\mathrm{obs}>5~μ\mathrm{m}$. Across the full range of plausible Chandra data reductions, the $2-7$ keV excess at the position of UHZ1 reaches a significance of only $2.3-2.9σ$; the originally reported $4.2-4.4σ$ detection is sensitive to the specific astrometric alignment adopted and is not robustly reproducible. Moreover, the hard X-ray signal does not grow with the additional exposure, contrary to expectations for a steady source, indicating that any excess is not persistent. UHZ1 is also undetected in all nine MIRI imaging bands. Fitting red/obscured AGN SED templates to the tightest MIRI upper limit, we constrain the bolometric luminosity of any buried AGN to $L_\mathrm{bol}<1.3\times10^{45}~\mathrm{erg~s^{-1}}$. These conclusions are further supported by independent JWST spectroscopy (Alvarez-Marquez et al. 2026), which reveals no AGN signatures in the rest-frame UV or optical. Taken together, the multiwavelength data paint a consistent picture of UHZ1 as a low-mass, metal-poor, star-forming galaxy in the early Universe, with no compelling evidence for a luminous obscured AGN, regardless of its proposed formation channel. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_24893 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Revisiting the Claim for a Direct-Collapse Black Hole in UHZ1 at $z=10.05$ Zou, Fan Gallo, Elena Zuo, Zihao Hodges-Kluck, Edmund Nguyen, Dieu D. Roberts-Borsani, Guido Madau, Piero Pacucci, Fabio Seth, Anil C. Treu, Tommaso Astrophysics of Galaxies High Energy Astrophysical Phenomena We reassess the direct collapse black hole (DCBH) interpretation of UHZ1 (UNCOVER-26185), a gravitationally lensed galaxy at $z_\mathrm{spec}=10.054$. That interpretation rests on a hard ($2-7$ keV) X-ray excess detected with Chandra, attributed to a Compton-thick AGN with an inferred $2-10$ keV luminosity of $L_\mathrm{X,int}\sim10^{46}~\mathrm{erg~s^{-1}}$ (Bogdan et al. 2024). The resulting extreme X-ray to rest-frame optical-IR ratio was taken as the hallmark signature of an "outsize black hole galaxy" at cosmic dawn. We analyse the full 2.2 Ms Chandra imaging dataset -- including 0.95 Ms of unpublished observations -- and present new JWST/MIRI photometry at $λ_\mathrm{obs}>5~μ\mathrm{m}$. Across the full range of plausible Chandra data reductions, the $2-7$ keV excess at the position of UHZ1 reaches a significance of only $2.3-2.9σ$; the originally reported $4.2-4.4σ$ detection is sensitive to the specific astrometric alignment adopted and is not robustly reproducible. Moreover, the hard X-ray signal does not grow with the additional exposure, contrary to expectations for a steady source, indicating that any excess is not persistent. UHZ1 is also undetected in all nine MIRI imaging bands. Fitting red/obscured AGN SED templates to the tightest MIRI upper limit, we constrain the bolometric luminosity of any buried AGN to $L_\mathrm{bol}<1.3\times10^{45}~\mathrm{erg~s^{-1}}$. These conclusions are further supported by independent JWST spectroscopy (Alvarez-Marquez et al. 2026), which reveals no AGN signatures in the rest-frame UV or optical. Taken together, the multiwavelength data paint a consistent picture of UHZ1 as a low-mass, metal-poor, star-forming galaxy in the early Universe, with no compelling evidence for a luminous obscured AGN, regardless of its proposed formation channel. |
| title | Revisiting the Claim for a Direct-Collapse Black Hole in UHZ1 at $z=10.05$ |
| topic | Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2603.24893 |