Very Bright, Very Blue, and Very Red: JWST CAPERS Analysis of Highly Luminous Galaxies with Extreme Ultraviolet Slopes at <i>z</i> = 10
Abstract We present JWST/NIRSpec PRISM observations of three luminous ( M UV < −20) galaxies at z ∼ 10 observed with the CANDELS-Area Prism Epoch of Reionization Survey (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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 22) of blue galaxies at z = 9.800 ± 0.003 and z = 9.808 ± 0.002 with UV slopes of β = −2.87 ± 0.15 and β = −2.46 ± 0.10, 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 ± 0.002 exhibits a red UV slope with β = −1.51 ± 0.08. 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 an 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 V ≃ 0.9) implying a significant level of dust-obscured star formation only ≃480 Myr after the Big Bang. Under standard assumptions for dust attenuation, EGS-25297 would be the most intrinsically UV-luminous galaxy ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">UV</mml:mi> <mml:mo>,</mml:mo> <mml:mi mathvariant="normal">corr</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≃</mml:mo> <mml:mo>−</mml:mo> <mml:mn>22</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) yet spectroscopically confirmed at z ∼ 10. This work highlights that luminous galaxies at z ≳ 10 have a diversity of dust properties and that spectroscopy of these galaxies is essential to fully understand star formation at z ≳ 10.
Authors
- Ray A. Lucas (ORCID: https://orcid.org/0000-0003-1581-7825)
- Mauro Giavalisco (ORCID: https://orcid.org/0000-0002-7831-8751)
- Adam C. Carnall (ORCID: https://orcid.org/0000-0002-1482-5818)
- Alexa M. Morales (ORCID: https://orcid.org/0000-0003-4965-0402)
- R Begley (ORCID: https://orcid.org/0000-0003-0629-8074)
- G. D. Illingworth (ORCID: https://orcid.org/0000-0002-8096-2837)
- Intae Jung (ORCID: https://orcid.org/0000-0003-1187-4240)
- Hollis B. Akins (ORCID: https://orcid.org/0000-0003-3596-8794)
- L. Pentericci (ORCID: https://orcid.org/0000-0001-8940-6768)
- D. Burgarella (ORCID: https://orcid.org/0000-0002-4193-2539)
- Vasily Kokorev (ORCID: https://orcid.org/0000-0002-5588-9156)
- T M Stanton (ORCID: https://orcid.org/0000-0002-0827-9769)
- Jorge A. Zavala (ORCID: https://orcid.org/0000-0002-7051-1100)
- Rachel S. Somerville (ORCID: https://orcid.org/0000-0002-6748-6821)
- J. S. Dunlop (ORCID: https://orcid.org/0000-0002-1404-5950)
- Callum T. Donnan (ORCID: https://orcid.org/0000-0002-7622-0208)
- Pablo Arrabal Haro (ORCID: https://orcid.org/0000-0002-7959-8783)
- Casey Papovich (ORCID: https://orcid.org/0000-0001-7503-8482)
- Anton M. Koekemoer (ORCID: https://orcid.org/0000-0002-6610-2048)
- Anthony J. Taylor (ORCID: https://orcid.org/0000-0003-1282-7454)
- Pablo G. Pérez‐González (ORCID: https://orcid.org/0000-0003-4528-5639)
- Caitlin M. Casey (ORCID: https://orcid.org/0000-0002-0930-6466)
- Antonello Calabrò (ORCID: https://orcid.org/0000-0003-2536-1614)
- D J McLeod (ORCID: https://orcid.org/0000-0003-4368-3326)
- L. Y. Aaron Yung (ORCID: https://orcid.org/0000-0003-3466-035X)
- Fergus Cullen (ORCID: https://orcid.org/0000-0002-3736-476X)
- Struan Stevenson (ORCID: https://orcid.org/0000-0001-5642-752X)
- Ho-Hin Leung (ORCID: https://orcid.org/0000-0003-0486-5178)
- Jonathan R. Trump (ORCID: https://orcid.org/0000-0002-1410-0470)
- Steven L. Finkelstein (ORCID: https://orcid.org/0000-0001-8519-1130)
- Mark Dickinson (ORCID: https://orcid.org/0000-0001-5414-5131)
- R. Amorín (ORCID: https://orcid.org/0000-0001-5758-1000)
- Vital Fernández (ORCID: https://orcid.org/0000-0003-0531-5450)
- Dale D. Kocevski (ORCID: https://orcid.org/0000-0002-8360-3880)
- Richard S. Ellis (ORCID: https://orcid.org/0000-0001-7782-7071)
- Weida Hu (ORCID: https://orcid.org/0000-0003-3424-3230)
- Jeyhan S. Kartaltepe (ORCID: https://orcid.org/0000-0001-9187-3605)
- Michaela Hirschmann (ORCID: https://orcid.org/0000-0002-3301-3321)
- Lorenzo Napolitano (ORCID: https://orcid.org/0000-0002-8951-4408)
- R. J. McLure
Publication Details
- Journal
- The Astrophysical Journal
- Published
- 2025-11-06
- DOI
- https://doi.org/10.3847/1538-4357/ae0a1f
- Citations
- 7
- Primary Topic
- Galaxies: Formation, Evolution, Phenomena
- Type
- article
- Field-Weighted Citation Impact
- 8.08
Funders
- National Aeronautics and Space Administration
- Space Telescope Science Institute
- UK Research and Innovation
- National Research Foundation
- Danmarks Grundforskningsfond