UNCOVER/MegaScience Finds Uniform and Highly Bursty Star Formation at 3 < z < 9, consistent with the High-Redshift UV Luminosity Function
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| Format: | Preprint |
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2026
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| author | Mitsuhashi, Ikki Suess, Katherine A. Leja, Joel Bezanson, Rachel Greene, Jenny E. Burnham, Emilie Khullar, Gourav Mintz, Abby Nanayakkara, Themiya Glazebrook, Karl Price, Sedona H. Setton, David J. Wang, Bingjie Weaver, John R. Atek, Hakim Dayal, Pratika Feldmann, Robert Fujimoto, Seiji Furtak, Lukas J. Lorenz, Brian Barrera, Natalia Porraz Labbe, Ivo Brammer, Gabriel Cutler, Sam E. Pan, Richard Whitaker, Katherine E. team, the UNCOVER/MegaScience |
| author_facet | Mitsuhashi, Ikki Suess, Katherine A. Leja, Joel Bezanson, Rachel Greene, Jenny E. Burnham, Emilie Khullar, Gourav Mintz, Abby Nanayakkara, Themiya Glazebrook, Karl Price, Sedona H. Setton, David J. Wang, Bingjie Weaver, John R. Atek, Hakim Dayal, Pratika Feldmann, Robert Fujimoto, Seiji Furtak, Lukas J. Lorenz, Brian Barrera, Natalia Porraz Labbe, Ivo Brammer, Gabriel Cutler, Sam E. Pan, Richard Whitaker, Katherine E. team, the UNCOVER/MegaScience |
| contents | Star formation timescales are key to understanding fundamental physics like feedback mechanisms, as well as the abundance of bright galaxies at $z>10$. We investigate galaxy star formation histories (SFHs) and their evolution across $z\sim3$--9 by measuring the line-to-UV ratio (\rline) and line equivalent width (EW) of \hanii\ and \oiiihb\ directly from UNCOVER/MegaScience spectro-photometry without relying on a specific SFH or nebular line modeling. Our photometric measurements recover \rline\ and EW to $<10\%$ systematic accuracy compared to spectroscopy. This allows us to construct a large mass- (and flux-) complete sample and quantitatively examine how \rline\ evolves with redshift and stellar mass. We find that the intrinsic scatter in \rline\ does not significantly evolve with redshift across $3<z<7$, though it may increase at $z\gtrsim8$. We build population-level toy models using \texttt{fsps} to help interpret our observations, and find that scatter in \rline\ primarily reflects the amplitude of SFH fluctuations; this implies that our observed lack of evolution in the scatter of \rline\ is due to similar star formation burstiness from $z\sim3$ to $z\sim7$. Our observations are best reproduced by a set of SFHs with rising, long-duration, and large-amplitude bursts. Finally, we demonstrate that the toy model that best describes our $z\sim6$ data can boost UV brightness by up to $ΔM_{\rm UV}\sim-2.0\,{\rm mag}$ compared with a 200\,Myr constant SFH, and naturally produces a large number of galaxies at $z>10$. This suggests that no significant evolution in star formation burstiness is required to explain the abundance of UV-bright galaxies at high redshift. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2601_16284 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | UNCOVER/MegaScience Finds Uniform and Highly Bursty Star Formation at 3 < z < 9, consistent with the High-Redshift UV Luminosity Function Mitsuhashi, Ikki Suess, Katherine A. Leja, Joel Bezanson, Rachel Greene, Jenny E. Burnham, Emilie Khullar, Gourav Mintz, Abby Nanayakkara, Themiya Glazebrook, Karl Price, Sedona H. Setton, David J. Wang, Bingjie Weaver, John R. Atek, Hakim Dayal, Pratika Feldmann, Robert Fujimoto, Seiji Furtak, Lukas J. Lorenz, Brian Barrera, Natalia Porraz Labbe, Ivo Brammer, Gabriel Cutler, Sam E. Pan, Richard Whitaker, Katherine E. team, the UNCOVER/MegaScience Astrophysics of Galaxies Star formation timescales are key to understanding fundamental physics like feedback mechanisms, as well as the abundance of bright galaxies at $z>10$. We investigate galaxy star formation histories (SFHs) and their evolution across $z\sim3$--9 by measuring the line-to-UV ratio (\rline) and line equivalent width (EW) of \hanii\ and \oiiihb\ directly from UNCOVER/MegaScience spectro-photometry without relying on a specific SFH or nebular line modeling. Our photometric measurements recover \rline\ and EW to $<10\%$ systematic accuracy compared to spectroscopy. This allows us to construct a large mass- (and flux-) complete sample and quantitatively examine how \rline\ evolves with redshift and stellar mass. We find that the intrinsic scatter in \rline\ does not significantly evolve with redshift across $3<z<7$, though it may increase at $z\gtrsim8$. We build population-level toy models using \texttt{fsps} to help interpret our observations, and find that scatter in \rline\ primarily reflects the amplitude of SFH fluctuations; this implies that our observed lack of evolution in the scatter of \rline\ is due to similar star formation burstiness from $z\sim3$ to $z\sim7$. Our observations are best reproduced by a set of SFHs with rising, long-duration, and large-amplitude bursts. Finally, we demonstrate that the toy model that best describes our $z\sim6$ data can boost UV brightness by up to $ΔM_{\rm UV}\sim-2.0\,{\rm mag}$ compared with a 200\,Myr constant SFH, and naturally produces a large number of galaxies at $z>10$. This suggests that no significant evolution in star formation burstiness is required to explain the abundance of UV-bright galaxies at high redshift. |
| title | UNCOVER/MegaScience Finds Uniform and Highly Bursty Star Formation at 3 < z < 9, consistent with the High-Redshift UV Luminosity Function |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2601.16284 |