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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. 

Abstract Most galaxies, including the Milky Way, host a supermassive black hole (SMBH) at the center. These SMBHs can be observed out to high redshifts (z≥ 6) if the accretion rate is sufficiently large. However, we do not fully understand the mechanism through which these black holes form at early times. The heavy (or direct collapse) seeding mechanism has emerged as a probable contender in which the core of an atomic cooling halo directly collapses into a dense stellar cluster that could host supermassive stars that proceed to form a black hole seed of mass ∼ 10⁵M_⊙. We use the Renaissance Simulations to investigate the properties of 35 direct collapse black hole (DCBH) candidate host halos atz = 15–24 and compare them to noncandidate halos. We aim to understand what features differentiate halos capable of hosting a DCBH from the general halo population with the use of statistical analysis and machine learning methods. We examine 18 halo, central, and environmental properties. We find that DCBH candidacy is more dependent on a halo’s core internal properties than on exterior factors such as Lyman–Werner (LW) flux and distance to the closest galaxy; our analysis selects density and radial mass influx as the most important features (outside candidacy establishing features). Our results concur with the recent suggestion that DCBH host halos neither need to lie within a “Goldilocks zone” nor have a significant amount of LW flux to suppress cooling. This paper presents insight to the dynamics possibly occurring in potential DCBH host halos and seeks to provide guidance to DCBH subgrid formation models. 

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. 

Abstract We investigate how stellar feedback from the first stars (Population III) distributes metals through the interstellar and intergalactic medium using the star-by-star cosmological hydrodynamics simulation, Aeos. We find that energy injected from the supernovae (SNe) of the first stars is enough to expel a majority of gas and injected metals beyond the virial radius of halos with massM_dm ≲ 10⁷M_⊙, regardless of the number of SNe. This prevents self-enrichment and results in a nonmonotonic increase in metallicity at early times. Most minihalos (M_dm ≳ 10⁵M_⊙) do not retain significant fractions of the yields produced within their virial radii until they have grown to halo masses ofM_dm ≳ 10⁷M_⊙. The loss of metals to regions well beyond the virial radius delays the onset of enriched star formation and extends the period that Population III star formation can persist. We also explore the contributions of different nucleosynthetic channels to 10 individual elements. On the timescale of the simulation (lowest redshiftz= 14.3), enrichment is dominated by core-collapse supernovae for all elements, but with a significant contribution from asymptotic giant branch winds to thes-process elements, which are normally thought to only be important at late times. In this work, we establish important mechanisms for early chemical enrichment, which allows us to apply Aeosin later epochs to trace the evolution of enrichment during the complete transition from Population III to Population II stars. 

Abstract We present a method that calibrates a semianalytic model to the Renaissance Simulations, a suite of cosmological hydrodynamical simulations with high-redshift galaxy formation. This approach combines the strengths of semianalytic techniques and hydrodynamical simulations, enabling the extension to larger volumes and lower redshifts that are inaccessible to simulations due to computational expense. Using a sample of Renaissance star formation histories from an average density region of the Universe, we construct a four-parameter prescription for metal-enriched star formation characterized by an initial bursty stage followed by a steady stage where stars are formed at constant efficiencies. Our model also includes a treatment of Pop III star formation where a minimum halo mass and log-normal distribution of stellar mass are adopted to match the numerical simulations. Star formation is generally well reproduced for halos with masses ≲10⁹M_⊙. Between 11 <z< 25 our model produces metal-enriched star formation rate densities (SFRDs) that typically agree with Renaissance within a factor of ∼2 for the average density region. Additionally, the total metal-enriched stellar mass only differs from Renaissance by about 10% atz∼ 11. For regions that are either more overdense or rarefied and not included in the calibration, we produce metal-enriched SFRDs that agree with Renaissance within a factor of ∼2 at high-zbut eventually differ by higher factors for later times. This is likely due to environmental dependencies not included in the model. Our star formation prescriptions can easily be adopted in other analytic or semianalytic works to match our calibration to Renaissance. 

Abstract Theoretical models of galaxy formation and evolution are primarily investigated through cosmological simulations and semi-analytical models. The former method consumes $\mathcal{O}\left({10}^6\right)$core-hours explicitly modeling the dynamics of the galaxies, whereas the latter method only requires $\mathcal{O}\left({10}^3\right)$core-hours foregoing directly simulating internal structure for computational efficiency. In this work, we present a proof-of-concept machine learning regression model, using a graph neural network architecture, to predict the stellar mass of high-redshift galaxies solely from their dark matter merger trees, trained from a radiation hydrodynamics cosmological simulation of the first galaxies. 

Abstract We  present the demography of the dynamics and gas mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of 0.015–0.195Z_⊙and low stellar masses of 10⁴–10⁸M_⊙in the local universe. We conduct deep optical integral field spectroscopy (IFS) for the low-mass EMPGs with the medium-high resolution (R= 7500) grism of the 8 m Subaru FOCAS IFU instrument by the EMPRESS 3D survey, and investigate the Hαemission of the EMPGs. Exploiting the resolution high enough for the low-mass galaxies, we derive gas dynamics with the Hαlines by the fitting of three-dimensional disk models. We obtain an average maximum rotation velocity (v_rot) of 15 ± 3 km s⁻¹and an average intrinsic velocity dispersion (σ₀) of 27 ± 10 km s⁻¹for 15 spatially resolved EMPGs out of 33 EMPGs, and find that all 15 EMPGs havev_rot/σ₀< 1 suggesting dispersion-dominated systems. There is a clear decreasing trend ofv_rot/σ₀with the decreasing stellar mass and metallicity. We derive the gas mass fraction (f_gas) for all 33 EMPGs, and find no clear dependence on stellar mass and metallicity. Thesev_rot/σ₀andf_gastrends should be compared with young high-zgalaxies observed by the forthcoming JWST IFS programs to understand the physical origins of the EMPGs in the local universe. 

Abstract We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098Z_⊙) and low stellar masses (10^4.7–10^7.6M_⊙). Taking deep medium/high-resolution (R∼ 7500) integral-field spectra with 8.2 m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hαemission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed Hαflux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities (v_rot) of 5–23 km s⁻¹smaller than the velocity dispersions (σ₀) of 17–31 km s⁻¹, indicating dispersion-dominated (v_rot/σ₀= 0.29–0.80 < 1) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions off_gas≃ 0.9–1.0. Comparing our results with other Hαkinematics studies, we find thatv_rot/σ₀decreases andf_gasincreases with decreasing metallicity, decreasing stellar mass, and increasing specific star formation rate. We also find that simulated high-z(z∼ 7) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope observations atz∼ 7. 

Abstract We introduce the Phoenix Simulations, a suite of highly resolved cosmological simulations featuring hydrodynamics, primordial gas chemistry, primordial and enriched star formation and feedback, UV radiative transfer, and saved outputs with Δt= 200 kyr. We observe 73,523 individual primordial stars within 3313 distinct regions forming 2110 second-generation enriched star clusters byz≥ 12 within a combined 177.25 Mpc³volume across three simulations. The regions that lead to enriched star formation can contain ≳150 primordial stars, with 80% of regions having experienced combinations of primordial Type II, hypernovae, and/or pair-instability supernovae. Primordial supernovae enriched 0.8% of the volume, with 2% of enriched gas enriched by later-generation stars. We determine the extent of a primordial stellar region by its metal-rich or ionized hydrogen surrounding cloud; the metal-rich and ionized regions have time-dependent average radiir≲ 3kpc. 7 and 17% of regions haver> 7 kpc for metal-rich and ionized radii, respectively. We find that the metallicity distribution function of second-generation stars overlaps that of subsequent Population II star formation, spanning metal-deficient (∼7.94 × 10⁻⁸Z_⊙) to supersolar (∼3.71Z_⊙), and that 30.5% of second-generation stars haveZ> 10⁻²Z_⊙. We find that the metallicity of second-generation stars depends on progenitor configuration, with metals from pair-instability supernovae contributing to the most metal-rich clusters; these clusters form promptly after the supernova event. Finally, we create an interpretable regression model to predict the radius of the metal-rich influence of Population III star systems within the first 7–18 Myr after the first Population III stars form in the region. 

Context.One of the surprising early findings with JWST has been the discovery of a strong “roll-over” or a softening of the absorption edge of Lyαin a large number of galaxies atz≳ 6, in addition to systematic offsets from photometric redshift estimates and fundamental galaxy scaling relations. This has been interpreted as strong cumulative damped Lyαabsorption (DLA) wings from high column densities of neutral atomic hydrogen (H I), signifying major gas accretion events in the formation of these galaxies. Aims.To explore this new phenomenon systematically, we assembled the JWST/NIRSpec PRImordial gas Mass AssembLy (PRIMAL) legacy survey of 584 galaxies atz = 5.0 − 13.4, designed to study the physical properties and gas in and around galaxies during the reionization epoch. Methods.We characterized this benchmark sample in full and spectroscopically derived the galaxy redshifts, metallicities, star formation rates, and ultraviolet (UV) slopes. We defined a new diagnostic, the Lyαdamping parameterD_Lyα, to measure and quantify the net effect of Lyαemission strength, the H Ifraction in the intergalactic medium, or the local H Icolumn density for each source. The JWST-PRIMAL survey is based on the spectroscopic DAWN JWST Archive (DJA-Spec). We describe DJA-Spec in this paper, detailing the reduction methods, the post-processing steps, and basic analysis tools. All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. Results.We find that the fraction of galaxies showing strong integrated DLAs withN_HI > 10²¹ cm⁻²only increases slightly from ≈60% atz ≈ 6 up to ≈65 − 90% atz > 8. Similarly, the prevalence and prominence of Lyαemission is found to increase with decreasing redshift, in qualitative agreement with previous observational results. Strong Lyαemitters (LAEs) are predominantly found to be associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties, but predominantly at high redshifts and low metallicities. Conclusions.Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine H Igas accretion. Atz = 8 − 10, this gas gradually cools and forms into stars that ionize their local surroundings, forming large ionized bubbles and producing strong observed Lyαemission atz < 8.