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Aims.JWST/NIRCam provides rest-frame near-IR photometry of galaxies up toz = 2.5 with exquisite depth and accuracy. This affords us an unprecedented view of the evolution of the UV/optical/near-IR color distribution and its interpretation in terms of the evolving dust attenuation,AV. Methods.We used the value-added data products (photometric redshift, stellar mass, rest-frameU − VandV − Jcolors, andAV) provided by the public DAWN JWST Archive. These data products derive from fitting the spectral energy distributions obtained from multiple NIRCam imaging surveys, augmented with preexisting HST imaging data. Our sample consists of a stellar-mass-complete sample of ≈28 000M⋆ > 109 M⊙galaxies in the redshift range 0.5 < z < 2.5. Results.TheV − Jcolor distribution of star-forming galaxies evolves strongly, in particular for high-mass galaxies (M⋆ > 3 × 1010 M⊙), which have a pronounced tail of very red galaxies reachingV − J > 2.5 atz > 1.5 that does not exist atz < 1. Such redV − Jcan only be explained by dust attenuation, with typical values forM⋆ ≈ 1011 M⊙galaxies in the rangeAV ≈ 1.5 − 3.5 atz ≈ 2. This redshift evolution went largely unnoticed before. Today, however, photometric redshift estimates for the reddest (V − J > 2.5), most attenuated galaxies have markedly improved thanks to the new, precise photometry, which is in much better agreement with the 25 available spectroscopic redshifts for such galaxies. The reddest population readily stands out as the independently identified population of galaxies detected at submillimeter wavelengths. Despite the increased attenuation,U − Vcolors across the entire mass range are slightly bluer at higherz. A well-defined and tight color sequence exists at redshifts 0.5 < z < 2.5 forM⋆ > 3 × 1010 M⊙quiescent galaxies, in bothU − VandV − J, but inV − Jit is bluer rather than redder compared to star-forming galaxies. In conclusion, whereas the rest-frame UV-optical color distribution evolves remarkably little fromz = 0.5 toz = 2.5, the rest-frame optical/near-IR color distribution evolves strongly, primarily due to a very substantial increase with redshift in dust attenuation for massive galaxies.
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This content will become publicly available on March 10, 2026
Identification of a Turnover in the Initial Mass Function of a Young Stellar Cluster Down to 0.5 M J
Abstract A successful theory of star formation should predict the number of objects as a function of their mass produced through star-forming events. Previous studies in star-forming regions and the solar neighborhood have identified a mass function increasing from the hydrogen-burning limit down to about 10MJ. Theory predicts a limit to the fragmentation process, providing a natural turnover in the mass function down to the opacity limit of turbulent fragmentation, thought to be near 1–10MJ. Programs to date have not been sensitive enough to probe the hypothesized opacity limit of fragmentation. We present the first identification of a turnover in the initial mass function below 12MJwithin NGC 2024, a young star-forming region. With JWST/NIRCam deep exposures across 0.7–5μm, we identified several free-floating objects down to roughly 3MJwith sensitivity to 0.5MJ. We present evidence for a double power-law model increasing from about 60MJto roughly 12MJ, consistent with previous studies, followed by a decrease down to 0.5MJ. Our results support the predictions of star and brown dwarf formation theory, identifying the theoretical turnover in the mass function and suggesting the fundamental limit of turbulent fragmentation to be near 3MJ.
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- Award ID(s):
- 2303911
- PAR ID:
- 10590456
- Publisher / Repository:
- Astrophysical Journal Letters
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 981
- Issue:
- 2
- ISSN:
- 2041-8205
- Page Range / eLocation ID:
- L34
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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