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

@misc{ding2026probing,
  title = {{Probing the IMF in the Early Universe -- Direct measurements in the Boötes I UFD with JWST/NIRCam}},
  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},
  howpublished = {arXiv},
  year = {2026},
  month = aug,
  doi = {10.48550/arxiv.2605.15069},
  eprint = {2605.15069},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2605.15069},
}

TY  - UNPB
TI  - Probing the IMF in the Early Universe -- Direct measurements in the Boötes I UFD with JWST/NIRCam
AU  - Keyi Ding
AU  - Mario Gennaro
AU  - Roberto J. Avila
AU  - Massimo Ricotti
AU  - Rachael L. Beaton
AU  - Martha L. Boyer
AU  - Thomas M. Brown
AU  - Annalisa Calamida
AU  - Santi Cassisi
AU  - Vedant Chandra
AU  - Roger E. Cohen
AU  - Matteo Correnti
AU  - Denija Crnojević
AU  - Kareem El-Badry
AU  - Marla Geha
AU  - Puragra Guhathakurta
AU  - Nitya Kallivayalil
AU  - Evan N. Kirby
AU  - Kristen. B. W. McQuinn
AU  - Alessandro Savino
AU  - Cheyanne Shariat
AU  - Joshua D. Simon
AU  - Daniel R. Weisz
PY  - 2026
DA  - 2026/08/27
PB  - arXiv
DO  - 10.48550/arxiv.2605.15069
UR  - https://arxiv.org/abs/2605.15069
AB  - 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 ≲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 [Fe/H]≈−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 ≲10^5msun at z≳6, our results provide evidence for the universality of the IMF across both local and high-redshift environments.
ER  -