Mysteries of Capotauro: investigating the puzzling nature of an extreme F356W-dropout
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| Formato: | Preprint |
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2025
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| author | Gandolfi, Giovanni Rodighiero, Giulia Castellano, Marco Fontana, Adriano Santini, Paola Dickinson, Mark Finkelstein, Steven Catone, Michele Calabrò, Antonello Merlin, Emiliano Pentericci, Laura Bisigello, Laura Grazian, Andrea Napolitano, Lorenzo Vulcani, Benedetta Taylor, Anthony J. Haro, Pablo Arrabal Kirkpatrick, Allison Backhaus, Bren E. Holwerda, Benne W. Giulietti, Marika Bianchetti, Alessandro Cassata, Paolo Cleri, Nikko J. Daddi, Emanuele Ferguson, Henry C. Girardi, Giorgia Hirschmann, Michaela Koekemoer, Anton M. Lapi, Andrea Pacucci, Fabio Pérez-González, Pablo G. de la Vega, Alexander Vietri, Amelia Wilkins, Stephen Yung, L. Y. Aaron Bagley, Micaela Bhatawdekar, Rachana Kartaltepe, Jeyhan Papovich, Casey Pirzkal, Nor |
| author_facet | Gandolfi, Giovanni Rodighiero, Giulia Castellano, Marco Fontana, Adriano Santini, Paola Dickinson, Mark Finkelstein, Steven Catone, Michele Calabrò, Antonello Merlin, Emiliano Pentericci, Laura Bisigello, Laura Grazian, Andrea Napolitano, Lorenzo Vulcani, Benedetta Taylor, Anthony J. Haro, Pablo Arrabal Kirkpatrick, Allison Backhaus, Bren E. Holwerda, Benne W. Giulietti, Marika Bianchetti, Alessandro Cassata, Paolo Cleri, Nikko J. Daddi, Emanuele Ferguson, Henry C. Girardi, Giorgia Hirschmann, Michaela Koekemoer, Anton M. Lapi, Andrea Pacucci, Fabio Pérez-González, Pablo G. de la Vega, Alexander Vietri, Amelia Wilkins, Stephen Yung, L. Y. Aaron Bagley, Micaela Bhatawdekar, Rachana Kartaltepe, Jeyhan Papovich, Casey Pirzkal, Nor |
| contents | JWST has uncovered a diverse population of extreme near-infrared dropouts, including ultra high-redshift ($z>15$) galaxy candidates, dust-obscured galaxies challenging dust production theories, sources with strong Balmer breaks - possibly compact AGN in dense environments - and cold, sub-stellar Galactic objects. This work presents Capotauro, a F356W-dropout in the CEERS survey with F444W AB magnitude of $\sim27.68$ and a sharp $>3$ mag flux drop between $3.5{-}4.5\,μ$m, undetected below $3.5\,μ$m. We combine JWST/NIRCam, MIRI, and NIRSpec/MSA data with HST/ACS and WFC3 observations to perform a spectro-photometric analysis of Capotauro using multiple SED-fitting codes. Our setup tests $z\geq15$ as well as $z<10$ dusty, Balmer-break or strong-line galaxy solutions, and the possibility of Capotauro being a Milky Way sub-stellar object. Among extragalactic options, our analysis favors interpreting the sharp drop as a Lyman break at $z\sim32$, consistent with the epoch of formation of the first stars and black holes, with only $\sim0.5\%$ of the posterior volume at $z<25$. Lower-redshift solutions struggle to reproduce the extreme break, suggesting that if Capotauro lies at $z<10$, it must show a non-standard combination of strong dust attenuation and/or Balmer breaks, making it a peculiar interloper. Alternatively, its properties match a very cold (Y2-Y3 type) brown dwarf or a free-floating exoplanet with a record-breaking combination of low temperature and large distance ($T_{\mathrm{eff}}<300\,\mathrm{K}$, $d\gtrsim130\,\mathrm{pc}$, up to $\sim2\,\mathrm{kpc}$). While current data cannot determine its nature, Capotauro emerges as a remarkably unique object in all plausible scenarios, and a compelling target for follow-up. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_01664 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Mysteries of Capotauro: investigating the puzzling nature of an extreme F356W-dropout Gandolfi, Giovanni Rodighiero, Giulia Castellano, Marco Fontana, Adriano Santini, Paola Dickinson, Mark Finkelstein, Steven Catone, Michele Calabrò, Antonello Merlin, Emiliano Pentericci, Laura Bisigello, Laura Grazian, Andrea Napolitano, Lorenzo Vulcani, Benedetta Taylor, Anthony J. Haro, Pablo Arrabal Kirkpatrick, Allison Backhaus, Bren E. Holwerda, Benne W. Giulietti, Marika Bianchetti, Alessandro Cassata, Paolo Cleri, Nikko J. Daddi, Emanuele Ferguson, Henry C. Girardi, Giorgia Hirschmann, Michaela Koekemoer, Anton M. Lapi, Andrea Pacucci, Fabio Pérez-González, Pablo G. de la Vega, Alexander Vietri, Amelia Wilkins, Stephen Yung, L. Y. Aaron Bagley, Micaela Bhatawdekar, Rachana Kartaltepe, Jeyhan Papovich, Casey Pirzkal, Nor Astrophysics of Galaxies Solar and Stellar Astrophysics JWST has uncovered a diverse population of extreme near-infrared dropouts, including ultra high-redshift ($z>15$) galaxy candidates, dust-obscured galaxies challenging dust production theories, sources with strong Balmer breaks - possibly compact AGN in dense environments - and cold, sub-stellar Galactic objects. This work presents Capotauro, a F356W-dropout in the CEERS survey with F444W AB magnitude of $\sim27.68$ and a sharp $>3$ mag flux drop between $3.5{-}4.5\,μ$m, undetected below $3.5\,μ$m. We combine JWST/NIRCam, MIRI, and NIRSpec/MSA data with HST/ACS and WFC3 observations to perform a spectro-photometric analysis of Capotauro using multiple SED-fitting codes. Our setup tests $z\geq15$ as well as $z<10$ dusty, Balmer-break or strong-line galaxy solutions, and the possibility of Capotauro being a Milky Way sub-stellar object. Among extragalactic options, our analysis favors interpreting the sharp drop as a Lyman break at $z\sim32$, consistent with the epoch of formation of the first stars and black holes, with only $\sim0.5\%$ of the posterior volume at $z<25$. Lower-redshift solutions struggle to reproduce the extreme break, suggesting that if Capotauro lies at $z<10$, it must show a non-standard combination of strong dust attenuation and/or Balmer breaks, making it a peculiar interloper. Alternatively, its properties match a very cold (Y2-Y3 type) brown dwarf or a free-floating exoplanet with a record-breaking combination of low temperature and large distance ($T_{\mathrm{eff}}<300\,\mathrm{K}$, $d\gtrsim130\,\mathrm{pc}$, up to $\sim2\,\mathrm{kpc}$). While current data cannot determine its nature, Capotauro emerges as a remarkably unique object in all plausible scenarios, and a compelling target for follow-up. |
| title | Mysteries of Capotauro: investigating the puzzling nature of an extreme F356W-dropout |
| topic | Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2509.01664 |