{"paper":{"title":"Probing the IMF in the Early Universe -- Direct measurements in the Bo\\\"otes I UFD with JWST/NIRCam","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"The initial mass function measured in the ultra-faint dwarf Boötes I matches the Milky Way form at metallicities as low as one-hundredth solar.","cross_cats":["astro-ph.SR"],"primary_cat":"astro-ph.GA","authors_text":"Alessandro Savino, Annalisa Calamida, Cheyanne Shariat, Daniel R. Weisz, Denija Crnojevi\\'c, Evan N. Kirby, Joshua D. Simon, Kareem El-Badry, Keyi Ding, Kristen. B. W. McQuinn, Mario Gennaro, Marla Geha, Martha L. Boyer, Massimo Ricotti, Matteo Correnti, Nitya Kallivayalil, Puragra Guhathakurta, Rachael L. Beaton, Roberto J. Avila, Roger E. Cohen, Santi Cassisi, Thomas M. Brown, Vedant Chandra","submitted_at":"2026-05-14T16:57:37Z","abstract_excerpt":"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\\\"otes 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 st"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"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.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"Treating Boötes I as a local relic analogous to a high-redshift galaxy with stellar mass ≲10^5 M⊙ at z≳6; differences in dynamical history, gas conditions, or unresolved binaries could alter the inferred IMF.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"The low-mass IMF in Boötes I is consistent with the Milky Way within 68% confidence for broken power-law and lognormal forms, indicating universality at low metallicity.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"The initial mass function measured in the ultra-faint dwarf Boötes I matches the Milky Way form at metallicities as low as one-hundredth solar.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"99b3d959b2b16fb8de766d0049a84a2054ae9bf094c566fa85371d289be47e8e"},"source":{"id":"2605.15069","kind":"arxiv","version":1},"verdict":{"id":"95d742c3-77f8-4974-a756-835e910f3999","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-15T03:15:21.666746Z","strongest_claim":"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.","one_line_summary":"The low-mass IMF in Boötes I is consistent with the Milky Way within 68% confidence for broken power-law and lognormal forms, indicating universality at low metallicity.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"Treating Boötes I as a local relic analogous to a high-redshift galaxy with stellar mass ≲10^5 M⊙ at z≳6; differences in dynamical history, gas conditions, or unresolved binaries could alter the inferred IMF.","pith_extraction_headline":"The initial mass function measured in the ultra-faint dwarf Boötes I matches the Milky Way form at metallicities as low as one-hundredth solar."},"references":{"count":72,"sample":[{"doi":"10.1051/0004-6361/201322068","year":2013,"title":"P., Tollerud , E","work_id":"aeafa8f2-1c15-4f27-9682-a76b6bf42e2b","ref_index":1,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.1146/annurev-astro-082708-101642","year":2010,"title":"R., & Meyer, M","work_id":"06c4a490-9d76-48ed-a1bc-50e4f9bb36f4","ref_index":2,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.1093/mnras/stu795","year":2014,"title":"Bate, M. R. 2014, MNRAS, 442, 285, doi: 10.1093/mnras/stu795","work_id":"440d3329-b2e3-4210-bfe4-6b1546ea842f","ref_index":3,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.1093/mnras/stz103","year":2019,"title":"Bate, M. R. 2019, MNRAS, 484, 2341, doi: 10.1093/mnras/stz103","work_id":"776306f4-a363-4358-8a9d-514c8cfdf5f1","ref_index":4,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.1093/mnras/stab3629","year":2022,"title":"2022, MNRAS, 510, 3531, doi: 10.1093/mnras/stab3629","work_id":"836f99db-0043-4c2b-b484-4634e8843c85","ref_index":5,"cited_arxiv_id":"","is_internal_anchor":false}],"resolved_work":72,"snapshot_sha256":"393a2b0c7d62e35166297bbf9d039482b153adbaf2f2f917cc8240bdc834dfc3","internal_anchors":4},"formal_canon":{"evidence_count":2,"snapshot_sha256":"8d294e9c327b7c350408f1f7425baa9671df7aec020751fe009661aab29341df"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}