Very bright, very blue, and very red: JWST CAPERS analysis of highly luminous galaxies with extreme UV slopes at $\mathbf{z = 10}$
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| Format: | Preprint |
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2025
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| author | Donnan, Callum T. Dickinson, Mark Taylor, Anthony J. Haro, Pablo Arrabal Finkelstein, Steven L. Stanton, Thomas M. Jung, Intae Papovich, Casey Akins, Hollis B. Koekemoer, Anton M. McLeod, Derek J. Napolitano, Lorenzo Amorín, Ricardo O. Begley, Ryan Burgarella, Denis Carnall, Adam C. Casey, Caitlin M. Calabrò, Antonello Cullen, Fergus Dunlop, James S. Ellis, Richard S. Fernández, Vital Giavalisco, Mauro Hirschmann, Michaela Hu, Weida Illingworth, Garth Kartaltepe, Jeyhan S. Kocevski, Dale D. Kokorev, Vasily Leung, Ho-Hin Lucas, Ray A. Morales, Alexa M. McLure, Ross Pentericci, Laura Pérez-González, Pablo G. Somerville, Rachel S. Stevenson, Struan Trump, Jonathan R. Yung, L. Y. Aaron Zavala, Jorge A. |
| author_facet | Donnan, Callum T. Dickinson, Mark Taylor, Anthony J. Haro, Pablo Arrabal Finkelstein, Steven L. Stanton, Thomas M. Jung, Intae Papovich, Casey Akins, Hollis B. Koekemoer, Anton M. McLeod, Derek J. Napolitano, Lorenzo Amorín, Ricardo O. Begley, Ryan Burgarella, Denis Carnall, Adam C. Casey, Caitlin M. Calabrò, Antonello Cullen, Fergus Dunlop, James S. Ellis, Richard S. Fernández, Vital Giavalisco, Mauro Hirschmann, Michaela Hu, Weida Illingworth, Garth Kartaltepe, Jeyhan S. Kocevski, Dale D. Kokorev, Vasily Leung, Ho-Hin Lucas, Ray A. Morales, Alexa M. McLure, Ross Pentericci, Laura Pérez-González, Pablo G. Somerville, Rachel S. Stevenson, Struan Trump, Jonathan R. Yung, L. Y. Aaron Zavala, Jorge A. |
| contents | We present JWST/NIRSpec PRISM observations of three luminous ($M_{\rm UV}<-20$) galaxies at $z\sim10$ observed with the CAPERS Cycle 3 program. These galaxies exhibit extreme UV slopes compared to typical galaxies at $z=10$. Of the three sources, two of them are a close pair (0.22 - arcsec) of blue galaxies at $z=9.800\pm0.003$ and $z=9.808\pm0.002$ with UV slopes of $β=-2.87\pm0.15$ and $β=-2.46\pm0.10$ respectively, selected from PRIMER COSMOS NIRCam imaging. We perform spectrophotometric modeling of the galaxies which suggests extremely young stellar ages and a lack of dust attenuation. For the bluest galaxy, its UV slope also suggests significant Lyman continuum escape. In contrast, the third source (selected from CEERS NIRCam imaging) at $z=9.942\pm0.002$ exhibits a red UV slope with $β=-1.51\pm0.08$. We rule out the possibility of a strong nebular continuum due to the lack of a Balmer jump and find no evidence to support the presence of active galactic nucleus continuum due to a lack of strong UV emission lines and no broad component to H$γ$ or H$β$. Instead, it is most likely that the red UV slope is due to dust-reddening ($A_{\rm V}\simeq0.9$) implying a significant level of dust-obscured star-formation only $\simeq480\, \rm Myr$ after the Big Bang. Under standard assumptions for dust attenuation, EGS-25297 would be the most intrinsically UV-luminous galaxy ($M_{\mathrm{UV,corr}}\simeq -22.4^{+0.7}_{-1.1}$) yet spectroscopically confirmed at $z \sim 10$. This work highlights that luminous galaxies at $z\gtrsim10$ have a diversity of dust properties and that spectroscopy of these galaxies is essential to fully understand star-formation at $z\gtrsim10$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_10518 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Very bright, very blue, and very red: JWST CAPERS analysis of highly luminous galaxies with extreme UV slopes at $\mathbf{z = 10}$ Donnan, Callum T. Dickinson, Mark Taylor, Anthony J. Haro, Pablo Arrabal Finkelstein, Steven L. Stanton, Thomas M. Jung, Intae Papovich, Casey Akins, Hollis B. Koekemoer, Anton M. McLeod, Derek J. Napolitano, Lorenzo Amorín, Ricardo O. Begley, Ryan Burgarella, Denis Carnall, Adam C. Casey, Caitlin M. Calabrò, Antonello Cullen, Fergus Dunlop, James S. Ellis, Richard S. Fernández, Vital Giavalisco, Mauro Hirschmann, Michaela Hu, Weida Illingworth, Garth Kartaltepe, Jeyhan S. Kocevski, Dale D. Kokorev, Vasily Leung, Ho-Hin Lucas, Ray A. Morales, Alexa M. McLure, Ross Pentericci, Laura Pérez-González, Pablo G. Somerville, Rachel S. Stevenson, Struan Trump, Jonathan R. Yung, L. Y. Aaron Zavala, Jorge A. Astrophysics of Galaxies We present JWST/NIRSpec PRISM observations of three luminous ($M_{\rm UV}<-20$) galaxies at $z\sim10$ observed with the CAPERS Cycle 3 program. These galaxies exhibit extreme UV slopes compared to typical galaxies at $z=10$. Of the three sources, two of them are a close pair (0.22 - arcsec) of blue galaxies at $z=9.800\pm0.003$ and $z=9.808\pm0.002$ with UV slopes of $β=-2.87\pm0.15$ and $β=-2.46\pm0.10$ respectively, selected from PRIMER COSMOS NIRCam imaging. We perform spectrophotometric modeling of the galaxies which suggests extremely young stellar ages and a lack of dust attenuation. For the bluest galaxy, its UV slope also suggests significant Lyman continuum escape. In contrast, the third source (selected from CEERS NIRCam imaging) at $z=9.942\pm0.002$ exhibits a red UV slope with $β=-1.51\pm0.08$. We rule out the possibility of a strong nebular continuum due to the lack of a Balmer jump and find no evidence to support the presence of active galactic nucleus continuum due to a lack of strong UV emission lines and no broad component to H$γ$ or H$β$. Instead, it is most likely that the red UV slope is due to dust-reddening ($A_{\rm V}\simeq0.9$) implying a significant level of dust-obscured star-formation only $\simeq480\, \rm Myr$ after the Big Bang. Under standard assumptions for dust attenuation, EGS-25297 would be the most intrinsically UV-luminous galaxy ($M_{\mathrm{UV,corr}}\simeq -22.4^{+0.7}_{-1.1}$) yet spectroscopically confirmed at $z \sim 10$. This work highlights that luminous galaxies at $z\gtrsim10$ have a diversity of dust properties and that spectroscopy of these galaxies is essential to fully understand star-formation at $z\gtrsim10$. |
| title | Very bright, very blue, and very red: JWST CAPERS analysis of highly luminous galaxies with extreme UV slopes at $\mathbf{z = 10}$ |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2507.10518 |