The Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum Emission
JWST has enabled the detection of the ultraviolet (UV) continuum of galaxies at z > 10, revealing extremely blue, potentially dust-free galaxies. However, interpreting UV spectra is complicated by the well-known degeneracy between stellar ages, dust reddening, and nebular continuum. The main goal...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/adb41c |
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| author | Desika Narayanan Daniel P. Stark Steven L. Finkelstein Paul Torrey Qi Li Fergus Cullen Micheal W. Topping Federico Marinacci Laura V. Sales Xuejian Shen Mark Vogelsberger |
| author_facet | Desika Narayanan Daniel P. Stark Steven L. Finkelstein Paul Torrey Qi Li Fergus Cullen Micheal W. Topping Federico Marinacci Laura V. Sales Xuejian Shen Mark Vogelsberger |
| author_sort | Desika Narayanan |
| collection | DOAJ |
| description | JWST has enabled the detection of the ultraviolet (UV) continuum of galaxies at z > 10, revealing extremely blue, potentially dust-free galaxies. However, interpreting UV spectra is complicated by the well-known degeneracy between stellar ages, dust reddening, and nebular continuum. The main goal of this paper is to develop a theoretical model for the relationship between galaxy UV slopes ( β ), bursty star formation histories, dust evolution, and nebular contributions using cosmological zoom-in simulations. We build a layered model where we simulate increasingly complex physics, including the impact of (i) unattenuated intrinsic stellar populations, (ii) reddened populations using a new on-the-fly evolving dust model, and (iii) populations including dust and nebular continuum. Unattenuated stellar populations with no nebular emission exhibit a diverse range of intrinsic UV slopes ( β _0 ≈ −3 → −2.2), with an inverse correlation between UV slope and specific star formation rate. When including dust, our model galaxies demonstrate a rapid rise in dust obscuration between z ≈ 8 and 10. This increase in dust mass is due to high grain–grain shattering rates, and enhanced growth per unit dust mass in very small grains, resulting in UV-detected galaxies at z ∼ 12 descending into Atacama Large Millimeter/submillimeter Array–detectable galaxies by z ∼ 6. The rapid rise in dust content at z ≈ 8–10 leads to a systematic reddening of the UV slopes during this redshift range. Nebular continuum further reddens UV slopes by a median Δ β _neb ≈ 0.2–0.4, though notably the highest-redshift galaxies ( z ≈ 12) are insufficiently blue compared to observations; this may imply an evolving escape fraction from H ii regions with redshift. |
| format | Article |
| id | doaj-art-59f4a8af3a9b4079a1ba6aed8f86c7a2 |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-59f4a8af3a9b4079a1ba6aed8f86c7a22025-08-20T02:47:45ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-019821710.3847/1538-4357/adb41cThe Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum EmissionDesika Narayanan0https://orcid.org/0000-0002-7064-4309Daniel P. Stark1Steven L. Finkelstein2https://orcid.org/0000-0001-8519-1130Paul Torrey3https://orcid.org/0000-0002-5653-0786Qi Li4https://orcid.org/0000-0001-8015-2298Fergus Cullen5https://orcid.org/0000-0002-3736-476XMicheal W. Topping6https://orcid.org/0000-0001-8426-1141Federico Marinacci7https://orcid.org/0000-0003-3816-7028Laura V. Sales8https://orcid.org/0000-0002-3790-720XXuejian Shen9https://orcid.org/0000-0002-6196-823XMark Vogelsberger10https://orcid.org/0000-0001-8593-7692Department of Astronomy, University of Florida , 211 Bryant Space Sciences Center, Gainesville, FL 32611, USA ; desika.narayanan@ufl.edu; Cosmic Dawn Center at the Niels Bohr Institute, University of Copenhagen and DTU-Space, Technical University of Denmark , Denmark Steward Observatory, University of Arizona , 933 N Cherry Ave, Tucson, AZ 85721, USADepartment of Astronomy, The University of Texas at Austin , Austin, TX 78712, USADepartment of Astronomy, University of Virginia , 530 McCormick Road, Charlottesville, VA 22903, USAMax Planck Institute for Astrophysics , Garching bei Munchen, GermanyInstitute for Astronomy, University of Edinburgh , Royal Observatory, Edinburgh, EH9 3HJ, UKSteward Observatory, University of Arizona , 933 N Cherry Ave, Tucson, AZ 85721, USADepartment of Physics and Astronomy “Augusto Righi,” University of Bologna , via Gobetti 93/2, 40129, Bologna, Italy; INAF , Astrophysics and Space Science Observatory Bologna, Via P. Gobetti 93/3, 40129 Bologna, ItalyDepartment of Physics and Astronomy, University of California, Riverside , Riverside, CA 92521, USADepartment of Physics, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , Cambridge, MA 02139, USADepartment of Physics, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , Cambridge, MA 02139, USAJWST has enabled the detection of the ultraviolet (UV) continuum of galaxies at z > 10, revealing extremely blue, potentially dust-free galaxies. However, interpreting UV spectra is complicated by the well-known degeneracy between stellar ages, dust reddening, and nebular continuum. The main goal of this paper is to develop a theoretical model for the relationship between galaxy UV slopes ( β ), bursty star formation histories, dust evolution, and nebular contributions using cosmological zoom-in simulations. We build a layered model where we simulate increasingly complex physics, including the impact of (i) unattenuated intrinsic stellar populations, (ii) reddened populations using a new on-the-fly evolving dust model, and (iii) populations including dust and nebular continuum. Unattenuated stellar populations with no nebular emission exhibit a diverse range of intrinsic UV slopes ( β _0 ≈ −3 → −2.2), with an inverse correlation between UV slope and specific star formation rate. When including dust, our model galaxies demonstrate a rapid rise in dust obscuration between z ≈ 8 and 10. This increase in dust mass is due to high grain–grain shattering rates, and enhanced growth per unit dust mass in very small grains, resulting in UV-detected galaxies at z ∼ 12 descending into Atacama Large Millimeter/submillimeter Array–detectable galaxies by z ∼ 6. The rapid rise in dust content at z ≈ 8–10 leads to a systematic reddening of the UV slopes during this redshift range. Nebular continuum further reddens UV slopes by a median Δ β _neb ≈ 0.2–0.4, though notably the highest-redshift galaxies ( z ≈ 12) are insufficiently blue compared to observations; this may imply an evolving escape fraction from H ii regions with redshift.https://doi.org/10.3847/1538-4357/adb41cGalaxiesHigh-redshift galaxiesStarburst galaxiesGalaxy formationAstrophysical dust processesInterstellar dust processes |
| spellingShingle | Desika Narayanan Daniel P. Stark Steven L. Finkelstein Paul Torrey Qi Li Fergus Cullen Micheal W. Topping Federico Marinacci Laura V. Sales Xuejian Shen Mark Vogelsberger The Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum Emission The Astrophysical Journal Galaxies High-redshift galaxies Starburst galaxies Galaxy formation Astrophysical dust processes Interstellar dust processes |
| title | The Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum Emission |
| title_full | The Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum Emission |
| title_fullStr | The Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum Emission |
| title_full_unstemmed | The Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum Emission |
| title_short | The Ultraviolet Slopes of Early Universe Galaxies: The Impact of Bursty Star Formation, Dust, and Nebular Continuum Emission |
| title_sort | ultraviolet slopes of early universe galaxies the impact of bursty star formation dust and nebular continuum emission |
| topic | Galaxies High-redshift galaxies Starburst galaxies Galaxy formation Astrophysical dust processes Interstellar dust processes |
| url | https://doi.org/10.3847/1538-4357/adb41c |
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