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1. Aeos : The Impact of Population III Initial Mass Function and Star-by-star Models in Galaxy Simulations

   https://doi.org/10.3847/1538-4357/ae06a4  

   Brauer, Kaley; Mead, Jennifer; Wise, John H; Bryan, Greg L; Low, Mordecai-Mark Mac; Ji, Alexander P; Emerick, Andrew; Andersson, Eric P; Frebel, Anna; Côté, Benoit (October 2025, The Astrophysical Journal)

   Abstract We explore the effect of variations in the Population III initial mass function (IMF) and star-by-star feedback on early galaxy formation and evolution using the Aeossimulations. We compare simulations with two different Population III IMFs:M_char = 10M_⊙and $M_{\max }=100M_{\odot }$ (Aeos10) andM_char = 20M_⊙and $M_{\max }=300M_{\odot }$ (Aeos20). Aeos20 produces significantly more ionizing photons, ionizing 30% of the simulation volume byz ≈ 14, compared to 9% in Aeos10. This enhanced ionization suppresses galaxy formation on the smallest scales. Differences in Population III IMF also affect chemical enrichment. Aeos20 produces Population II stars with higher abundances, relative to iron, of light andα-elements, a stronger odd–even effect, and a higher frequency of carbon-enhanced metal-poor stars. The abundance scatter between different Population II galaxies dominates the differences due to Population III IMF, though, implying a need for a larger sample of Population II stars to interpret the impact of Population III IMF on early chemical evolution. We also compare the Aeossimulations to traditional simulations that use single stellar population particles. We find that star-by-star modeling produces a steeper mass–metallicity relation due to less bursty feedback. These results highlight the strong influence of the Population III IMF on early galaxy formation and chemical evolution, emphasizing the need to account for IMF uncertainties in simulations and the importance of metal-poor Population II stellar chemical abundances when studying the first stars. 

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2. AEOS: Star-by-star Cosmological Simulations of Early Chemical Enrichment and Galaxy Formation

   https://doi.org/10.3847/1538-4357/ada4a1  

   Brauer, Kaley; Emerick, Andrew; Mead, Jennifer; Ji, Alexander P; Wise, John H; Bryan, Greg L; Mac_Low, Mordecai-Mark; Côté, Benoit; Andersson, Eric P; Frebel, Anna (February 2025, The Astrophysical Journal)

   Abstract The Aeosproject introduces a series of high-resolution cosmological simulations that model star-by-star chemical enrichment and galaxy formation in the early Universe, achieving 1 pc resolution. These simulations capture the complexities of galaxy evolution within the first ~300 Myr by modeling individual stars and their feedback processes. By incorporating chemical yields from individual stars, Aeosgenerates galaxies with diverse stellar chemical abundances, linking them to hierarchical galaxy formation and early nucleosynthetic events. These simulations underscore the importance of chemical abundance patterns in ancient stars as vital probes of early nucleosynthesis, star formation histories, and galaxy formation. We examine the metallicity floors of various elements resulting from Population III enrichment, providing best-fit values for eight different metals (e.g., [O/H] = −4.0) to guide simulations without Population III models. Additionally, we identify galaxies that begin star formation with Population II after external enrichment and investigate the frequency of carbon-enhanced metal-poor stars at varying metallicities. The Aeossimulations offer detailed insights into the relationship between star formation, feedback, and chemical enrichment. Future work will extend these simulations to later epochs to interpret the diverse stellar populations of the Milky Way and its satellites. 

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3. MUSEQuBES: Physical Conditions, Origins, and Multielement Abundances of the Circumgalactic Medium of an Isolated, Star-forming Dwarf Galaxy at z = 0.57

   https://doi.org/10.3847/2041-8213/ae2f5f  

   Johnson, Sean D; Mishra, Nishant; Muzahid, Sowgat; Rudie, Gwen C; Zahedy, Fakhri S; Qu, Zhijie; Faucher-Giguère, Claude-André; Stern, Jonathan; Li, Jennifer I-Hsiu; Fuller, Elise; et al (January 2026, The Astrophysical Journal Letters)

   Abstract In dwarf galaxy models, outflows expel metal-enriched interstellar medium (ISM) into the circumgalactic medium (CGM) to reproduce their observed low metallicities, but measurements of dwarf CGM properties are scarce. We present a study of the CGM of an isolated dwarf atz= 0.5723 with a stellar mass of ≈5 × 10⁷M_⊙and star formation rate (≈0.05M_⊙yr⁻¹) and ISM metallicity ([O/H] ≈ −0.9) consistent with the star-forming main sequence and mass–metallicity relation. A background quasar sight line with archival UV spectra probes the dwarf’s CGM at a projected distance of 28 kpc, corresponding to approximately half of the estimated virial radius. The dwarf’s CGM is detected in Hi;intermediate metal ions of Ciii, Oiii, Oiv, and Sv; and kinematically broader, highly ionized Ovibut is undetected in Nivand Neviii. Photoionization modeling of the intermediate ions indicates a modest volume filling factor (∼6% along the sight line or ∼2% globally) and a mass of ∼2 × 10⁸M_⊙, ∼4× higher than the dwarf’s stellar mass but ∼10× less than the highly ionized CGM. The Ovikinematics are comparable to the dwarf’s estimated virial velocity, suggesting that it is likely associated with cool, photoionized, and volume-filling CGM, with bulk motion or turbulence dominating over thermal pressure. The metallicity inferred for the intermediate ions is [O/H] = −0.6, but with low relative abundances of [C/O] = −0.6 and [N/O] < −1.0. The [N/O] is below levels expected of the dwarf’s ISM but consistent with core-collapse supernova ejecta, suggesting that supernova-enriched gas escaped the dwarf without mixing significantly with ISM enriched in nitrogen from evolved, low-mass stars. 

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4. Massive stars exploding in a He-rich circumstellar medium: X. Flash spectral features in the Type Ibn SN 2019cj and observations of SN 2018jmt

   https://doi.org/10.1051/0004-6361/202451131  

   Wang, Z-Y; Pastorello, A; Maeda, K; Reguitti, A; Cai, Y-Z; Andrew_Howell, D; Benetti, S; Buckley, D_A H; Cappellaro, E; Carini, R; et al (November 2024, Astronomy & Astrophysics)

   We present optical and near-infrared observations of two Type Ibn supernovae (SNe), SN 2018jmt and SN 2019cj. Their light curves have rise times of about ten days, reaching an absolute peak magnitude ofM_g(SN 2018jmt) = −19.07 ± 0.37 andM_V(SN 2019cj) = −18.94 ± 0.19 mag, respectively. The early-time spectra of SN 2018jmt are dominated by a blue continuum, accompanied by narrow (600−1000 km s⁻¹) He Ilines with the P-Cygni profile. At later epochs, the spectra become more similar to those of the prototypical SN Ibn 2006jc. At early phases, the spectra of SN 2019cj show flash ionisation emission lines of C III, N III, and He IIsuperposed on a blue continuum. These features disappear after a few days, and then the spectra of SN 2019cj evolve similarly to those of SN 2018jmt. The spectra indicate that the two SNe exploded within a He-rich circumstellar medium (CSM) lost by the progenitors a short time before the explosion. We modelled the light curves of the two SNe Ibn to constrain the progenitor and the explosion parameters. The ejecta masses are consistent with either what is expected for a canonical SN Ib (∼2 M_⊙) or for a massive Wolf Rayet star (> ∼4 M_⊙), with the kinetic energy on the order of 10⁵¹erg. The lower limit on the ejecta mass (> ∼2 M_⊙) argues against a scenario involving a relatively low-mass progenitor (e.g.M_ZAMS ∼ 10 M_⊙). We set a conservative upper limit of ∼0.1 M_⊙for the⁵⁶Ni masses in both SNe. From the light curve modelling, we determined a two-zone CSM distribution, with an inner, flat CSM component and an outer CSM with a steeper density profile. The physical properties of SN 2018jmt and SN 2019cj are consistent with those expected from the core collapse of relatively massive envelope-stripped stars. 

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5. Catching the Nebular Needle in a Polluted Haystack: Line-emission Signatures from Population III-forming Pockets around Massive Galaxies at the End of Reionization

   https://doi.org/10.3847/1538-4357/ae7b2c  

   Venditti, Alessandra; Graziani, Luca; Schneider, Raffaella; Bromm, Volker; Muñoz, Julian B; Di_Cesare, Claudia; Valiante, Rosa; Calabrò, Antonello; Maiolino, Roberto; Finkelstein, Steven L; et al (July 2026, The Astrophysical Journal)

   Abstract Finding the first generation of (Population III or Pop III) stars is one of the most ambitious and exciting challenges of astrophysics. JWST opened concrete prospects for their detection during the Epoch of Reionization, where increasing evidence suggests that residual Pop III formation may persist, even within pristine pockets of high-mass halos, due to inhomogeneous enrichment. However, the identification of Pop III stars within globally enriched environments will be challenging. We investigate the detectability of a subdominant Pop III component in/around massive (M_⋆ ≳ 10⁹M_⊙) galaxies atz ≈ 6.5–9 from thedustyGadgetcosmological simulation suite, and the confusion arising from second-generation (Pop II) stars in their surroundings. We find that young (≲1 Myr), massive (M_III ∼ 6 × 10⁵M_⊙) Pop III clusters forming within these galaxy environments are responsible for strong HeII1640 line emission (L_HeII1640 ≳ 10⁴¹erg s⁻¹), which would be detectable with ≈10(50) hr of medium-resolution observations with NIRSpec/IFU atz ≈ 6(10). These bright luminosities cannot be produced by standard Pop II populations alone. On the other hand, the dominant Pop II component within massive “hybrid” Pop III hosts powers strong metal line emission (L_[OIII]5007 ≳ 10⁴²erg s⁻¹), indicating that the detection of metal lines alone cannot exclude the presence of Pop IIIs in high-zgalaxy environments. We further discuss candidate selection strategies based on Lyα, Hα,and Hβemission, and how spatially resolved observations may enable the detection of isolated, pristine pockets in the outskirts of massive halos. 

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