FORGE'd In The Early Universe II: Constraining The Pop III Initial Mass Function
Abstract
We present a cosmological radiation-magnetohydrodynamics (RMHD) zoom-in simulation of $56$ Population III stars using FORGE'd in FIRE. Our simulation combines a cosmological initial condition centered on an isolated ultra-faint galaxy (Mhalo ∼ 109 M⊙ at z=0) with individual-star formation and feedback physics, reaching a maximum mass resolution of ∼ 10−2 M⊙ and spatial resolution of ∼ 10−3 pc. We follow continued star formation for just over $500$ Myr, from z ∼ 16 to z ∼ 7, substantially longer than what has been achieved before, and track star formation across five distinct minihalos. From our stellar population, we self-consistently resolve an emergent stellar initial mass function (IMF) and find α= 1.9 for dN/dM ∝ M−α at M⋆ ≳ 2.2 M⊙. Additionally, we form both single and multiple stellar systems, including binaries and higher-order multiples, as well as stars with masses below 1 M⊙. At early times, the stellar mass distribution is more top-heavy, with a high-mass slope of α∼1.4−1.5, similar to previous Pop. III simulations, and steepens as star formation continues. This suggests that differences between our final IMF and previous studies may partly reflect the much longer evolution followed here, approximately five orders of magnitude longer than in several previous Pop. III sink-particle simulations. The first star-forming minihalo, which hosts the most massive stars in our simulation, has a shallower IMF slope of α≈ 1, while later-forming minihalos produce lower maximum stellar masses in lower-density parent clouds.
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BibTeX
@misc{meziani2026forged,
title = {{FORGE'd In The Early Universe II: Constraining The Pop III Initial Mass Function}},
author = {Yasmine J. Meziani and Philip F. Hopkins and Pratik J. Gandhi and Claude-André Faucher-Giguère and Michael Y. Grudić and Shivan Khullar and Vasilii Pustovoit},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.08598},
eprint = {2611.08598},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.08598},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - FORGE'd In The Early Universe II: Constraining The Pop III Initial Mass Function
AU - Yasmine J. Meziani
AU - Philip F. Hopkins
AU - Pratik J. Gandhi
AU - Claude-André Faucher-Giguère
AU - Michael Y. Grudić
AU - Shivan Khullar
AU - Vasilii Pustovoit
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2611.08598
UR - https://arxiv.org/abs/2611.08598
AB - We present a cosmological radiation-magnetohydrodynamics (RMHD) zoom-in simulation of $56$ Population III stars using FORGE'd in FIRE. Our simulation combines a cosmological initial condition centered on an isolated ultra-faint galaxy (M_halo ∼ 10^9 M_⊙ at z=0) with individual-star formation and feedback physics, reaching a maximum mass resolution of ∼ 10^−2 M_⊙ and spatial resolution of ∼ 10^−3 pc. We follow continued star formation for just over $500$ Myr, from z ∼ 16 to z ∼ 7, substantially longer than what has been achieved before, and track star formation across five distinct minihalos. From our stellar population, we self-consistently resolve an emergent stellar initial mass function (IMF) and find α= 1.9 for dN/dM ∝ M^−α at M_⋆ ≳ 2.2 M_⊙. Additionally, we form both single and multiple stellar systems, including binaries and higher-order multiples, as well as stars with masses below 1 M_⊙. At early times, the stellar mass distribution is more top-heavy, with a high-mass slope of α∼1.4−1.5, similar to previous Pop. III simulations, and steepens as star formation continues. This suggests that differences between our final IMF and previous studies may partly reflect the much longer evolution followed here, approximately five orders of magnitude longer than in several previous Pop. III sink-particle simulations. The first star-forming minihalo, which hosts the most massive stars in our simulation, has a shallower IMF slope of α≈ 1, while later-forming minihalos produce lower maximum stellar masses in lower-density parent clouds.
ER -