A direct black hole mass measurement in a Little Red Dot at the Epoch of Reionization
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2025
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| author | Juodžbalis, Ignas Marconcini, Cosimo D'Eugenio, Francesco Maiolino, Roberto Marconi, Alessandro Übler, Hannah Scholtz, Jan Ji, Xihan Arribas, Santiago Bennett, Jake S. Bromm, Volker Bunker, Andrew J. Carniani, Stefano Charlot, Stéphane Cresci, Giovanni Dayal, Pratika Egami, Eiichi Fabian, Andrew Inayoshi, Kohei Isobe, Yuki Ivey, Lucy Jones, Gareth C. Koudmani, Sophie Laporte, Nicolas Liu, Boyuan Lyu, Jianwei Mazzolari, Giovanni Monty, Stephanie Parlanti, Eleonora Pérez-González, Pablo G. Perna, Michele Robertson, Brant Schneider, Raffaella Sijacki, Debora Tacchella, Sandro Trinca, Alessandro Valiante, Rosa Volonteri, Marta Witstok, Joris Zhang, Saiyang |
| author_facet | Juodžbalis, Ignas Marconcini, Cosimo D'Eugenio, Francesco Maiolino, Roberto Marconi, Alessandro Übler, Hannah Scholtz, Jan Ji, Xihan Arribas, Santiago Bennett, Jake S. Bromm, Volker Bunker, Andrew J. Carniani, Stefano Charlot, Stéphane Cresci, Giovanni Dayal, Pratika Egami, Eiichi Fabian, Andrew Inayoshi, Kohei Isobe, Yuki Ivey, Lucy Jones, Gareth C. Koudmani, Sophie Laporte, Nicolas Liu, Boyuan Lyu, Jianwei Mazzolari, Giovanni Monty, Stephanie Parlanti, Eleonora Pérez-González, Pablo G. Perna, Michele Robertson, Brant Schneider, Raffaella Sijacki, Debora Tacchella, Sandro Trinca, Alessandro Valiante, Rosa Volonteri, Marta Witstok, Joris Zhang, Saiyang |
| contents | Recent discoveries of faint active galactic nuclei (AGN) at the redshift frontier have revealed a plethora of broad \Halpha emitters with optically red continua, named Little Red Dots (LRDs), which comprise 15-30\% of the high redshift broad line AGN population. Due to their peculiar spectral properties and X-ray weakness, modeling LRDs with standard AGN templates has proven challenging. In particular, the validity of single-epoch virial mass estimates in determining the black hole (BH) masses of LRDs has been called into question, with some models claiming that masses might be overestimated by up to 2 orders of magnitude, and other models claiming that LRDs may be entirely stellar in nature. We report the direct, dynamical BH mass measurement in a strongly lensed LRD at $z = 7.04$. The combination of lensing with deep spectroscopic data reveals a rotation curve that is inconsistent with a nuclear star cluster, yet can be well explained by Keplerian rotation around a point mass of 50 million Solar masses, consistent with virial BH mass estimates from the Balmer lines. The Keplerian rotation leaves little room for any stellar component in a host galaxy, as we conservatively infer $M_{\rm BH}/M_{*}>2$. Such a ''naked'' black hole, together with its near-pristine environment, indicates that this LRD is a massive black hole seed caught in its earliest accretion phase. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_21748 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A direct black hole mass measurement in a Little Red Dot at the Epoch of Reionization Juodžbalis, Ignas Marconcini, Cosimo D'Eugenio, Francesco Maiolino, Roberto Marconi, Alessandro Übler, Hannah Scholtz, Jan Ji, Xihan Arribas, Santiago Bennett, Jake S. Bromm, Volker Bunker, Andrew J. Carniani, Stefano Charlot, Stéphane Cresci, Giovanni Dayal, Pratika Egami, Eiichi Fabian, Andrew Inayoshi, Kohei Isobe, Yuki Ivey, Lucy Jones, Gareth C. Koudmani, Sophie Laporte, Nicolas Liu, Boyuan Lyu, Jianwei Mazzolari, Giovanni Monty, Stephanie Parlanti, Eleonora Pérez-González, Pablo G. Perna, Michele Robertson, Brant Schneider, Raffaella Sijacki, Debora Tacchella, Sandro Trinca, Alessandro Valiante, Rosa Volonteri, Marta Witstok, Joris Zhang, Saiyang Astrophysics of Galaxies Recent discoveries of faint active galactic nuclei (AGN) at the redshift frontier have revealed a plethora of broad \Halpha emitters with optically red continua, named Little Red Dots (LRDs), which comprise 15-30\% of the high redshift broad line AGN population. Due to their peculiar spectral properties and X-ray weakness, modeling LRDs with standard AGN templates has proven challenging. In particular, the validity of single-epoch virial mass estimates in determining the black hole (BH) masses of LRDs has been called into question, with some models claiming that masses might be overestimated by up to 2 orders of magnitude, and other models claiming that LRDs may be entirely stellar in nature. We report the direct, dynamical BH mass measurement in a strongly lensed LRD at $z = 7.04$. The combination of lensing with deep spectroscopic data reveals a rotation curve that is inconsistent with a nuclear star cluster, yet can be well explained by Keplerian rotation around a point mass of 50 million Solar masses, consistent with virial BH mass estimates from the Balmer lines. The Keplerian rotation leaves little room for any stellar component in a host galaxy, as we conservatively infer $M_{\rm BH}/M_{*}>2$. Such a ''naked'' black hole, together with its near-pristine environment, indicates that this LRD is a massive black hole seed caught in its earliest accretion phase. |
| title | A direct black hole mass measurement in a Little Red Dot at the Epoch of Reionization |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2508.21748 |