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

K Ding, M Gennaro, RJ Avila, M Ricotti… - arXiv preprint arXiv …, 2026 - arxiv.org
Astrophysics paper astro-ph.GA Suggest

… synthetic color-magnitude diagrams with simulation-based inference. We find that a single … We use the simulation-based inference technique to infer the single power-law, …

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BibTeX

@article{2605.15069v1,
Author        = {Keyi Ding and Mario Gennaro and Roberto J. Avila and Massimo Ricotti and Rachael L. Beaton and Martha L. Boyer and Thomas M. Brown and Annalisa Calamida and Santi Cassisi and Vedant Chandra and Roger E. Cohen and Matteo Correnti and Denija Crnojević and Kareem El-Badry and Marla Geha and Puragra Guhathakurta and Nitya Kallivayalil and Evan N. Kirby and Kristen. B. W. McQuinn and Alessandro Savino and Cheyanne Shariat and Joshua D. Simon and Daniel R. Weisz},
Title         = {Probing the IMF in the Early Universe -- Direct measurements in the Boötes I UFD with JWST/NIRCam},
Eprint        = {2605.15069v1},
ArchivePrefix = {arXiv},
PrimaryClass  = {astro-ph.GA},
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 Boötes I (Boo I) UFD with JWST/NIRCam, leveraging its capability to resolve over 10,000 stars reaching $\lesssim0.15 M_{\odot}$, 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 fails to reproduce the observed luminosity function and also deviates from 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 [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 $\lesssim10^5 M_{\odot}$ at $z\gtrsim6$, our results provide evidence for the universality of the IMF across both local and high-redshift environments.},
Year          = {2026},
Month         = {May},
Url           = {http://arxiv.org/abs/2605.15069v1},
File          = {2605.15069v1.pdf}
}

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