Probing the IMF in the Early Universe -- Direct measurements in the Boötes I UFD with JWST/NIRCam

[2605.15069] Probing the IMF in the Early Universe -- Direct measurements in the Boötes I UFD with JWST/NIRCam Skip to main content Search Submit Donate Log in Astrophysics > Astrophysics of Galaxies arXiv:2605.15069 (astro-ph) [Submitted on 14 May 2026 ( v1 ), last revised 27 Aug 2026 (this version, v2)] Title: Probing the IMF in the Early Universe -- Direct measurements in the Boötes I UFD with JWST/NIRCam Authors: Keyi Ding , Mario Gennaro , Roberto J. Avila , Massimo Ricotti , Rachael L. Beaton , Martha L. Boyer , Thomas M. Brown , Annalisa Calamida , Santi Cassisi , Vedant Chandra , Roger E. Cohen , Matteo Correnti , Denija Crnojević , Kareem El-Badry , Marla Geha , Puragra Guhathakurta , Nitya Kallivayalil , Evan N. Kirby , Kristen. B. W. McQuinn , Alessandro Savino , Cheyanne Shariat , Joshua D. Simon , Daniel R. Weisz View PDF HTML (experimental) Abstract: The dependence of the stellar initial mass function (IMF) on star-formation environment, particularly at low metallicities and high redshifts, remains poorly constrained. Ultra-faint dwarf galaxies (UFDs) are local fossils of high-redshift galaxies hosting old, metal-poor populations, and their resolved stellar populations provide unique pathways to constrain the sub-solar IMF. We investigate the low-mass IMF in the Bo{ö}tes I (Boo I) UFD with JWST/NIRCam, leveraging its capability to resolve over 10,000 stars reaching $\lesssim$0.15\msun, obtaining one of the largest, deepest resolved stellar samples for UFDs. We explore three different functional forms of the IMF with machine learning and statistical techniques, combining forward modeling of synthetic color-magnitude diagrams with simulation-based inference. We find that a single power-law IMF provides a poorer description of the observed luminosity function and yields a slope inconsistent with the canonical Salpeter IMF. Our best-fit broken power-law and lognormal IMF parameters are consistent with the Milky Way within 68\% confidence level, providing evidence that star formation at metallicities as low as $\mathrm{[Fe/H]}\approx-2.4$ follows a similar IMF as in the Milky Way. By treating Boo I as a local relic analogous to a high-redshift galaxy with a stellar mass of $\lesssim10^5\msun$ at $z\gtrsim6$, our results provide evidence for the universality of the IMF across both local and high-redshift environments. Comments: 28 pages, 17 figures, accepted for publication in ApJ Subjects: Astrophysics of Galaxies (astro-ph.GA) ; Solar and Stellar Astrophysics (astro-ph.SR) Cite as: arXiv:2605.15069 [astro-ph.GA] (or arXiv:2605.15069v2 [astro-ph.GA] for this version) https://doi.org/10.48550/arXiv.2605.15069 Focus to learn more arXiv-issued DOI via DataCite Journal reference: Keyi Ding et al 2026 ApJ 1009 94 Related DOI : https://doi.org/10.3847/1538-4357/ae9f3e Focus to learn more DOI(s) linking to related resources Submission history From: Keyi Ding [ view email ] [v1] Thu, 14 May 2026 16:57:37 UTC (15,430 KB) [v2] Thu, 27 Aug 2026 18:36:18 UTC (16,025 KB) Full-text links: Access Paper: View PDF HTML (experimental) TeX Source view license Current browse context: astro-ph.GA < prev | next > new | recent | 2026-05 Change to browse by: astro-ph astro-ph.SR References & Citations SciX Google Scholar Semantic Scholar 1 blog link ( what is this? ) export BibTeX citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer ( What is the Explorer? ) Connected Papers Toggle Connected Papers ( What is Connected Papers? ) Litmaps Toggle Litmaps ( What is Litmaps? ) scite.ai Toggle scite Smart Citations ( What are Smart Citations? ) Code, Data, Media Code, Data and Media Associated with this Article alphaXiv Toggle alphaXiv ( What is alphaXiv? ) Links to Code Toggle CatalyzeX Code Finder for Papers ( What is CatalyzeX? ) DagsHub Toggle DagsHub ( What is DagsHub? ) GotitPub Toggle Gotit.pub ( What is GotitPub? ) Huggingface Toggle Hugging Face ( What is Huggingface? ) ScienceCast Toggle ScienceCast ( What is ScienceCast? ) Demos Demos Replicate Toggle Replicate ( What is Replicate? ) Spaces Toggle Hugging Face Spaces ( What is Spaces? ) Spaces Toggle TXYZ.AI ( What is TXYZ.AI? ) Related Papers Recommenders and Search Tools Link to Influence Flower Influence Flower ( What are Influence Flowers? ) Core recommender toggle CORE Recommender ( What is CORE? ) IArxiv recommender toggle IArxiv Recommender ( What is IArxiv? ) Author Venue Institution Topic About arXivLabs arXivLabs: experimental projects with community collaborators arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website. 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