采用可变恒星初始质量函数的高红移星系群体的宇宙学模拟
Cosmological simulations of the high-redshift galaxy population adopting a variable stellar initial mass function
AI总结：
研究高红移星系群体，采用COLIBRE星系形成模型结合密度依赖的可变恒星初始质量函数，通过模拟再现相关函数且紫外线连续谱斜率与观测一致，展示了重质量初始质量函数对缓解与JWST数据矛盾的潜力。
AI中文摘要：
詹姆斯·韦布空间望远镜（JWST）的观测显示，高红移紫外线亮星系的空间密度比传统星系形成模型预测的要大。我们展示了一个边长为100cMpc的宇宙学模拟结果，该模拟采用COLIBRE星系形成模型演化到红移z = 5，该模型采用密度依赖的恒星初始质量函数（IMF），即由致密气体形成的恒星群体具有重质量的初始质量函数。关键的是，重元素和尘埃产量以及超新星反馈能量学都能根据变化的初始质量函数进行自洽调整。我们模拟了星系的紫外线/光学发射（包括星云发射）及其被尘埃的衰减。通过允许很大一部分高红移恒星形成采用重质量的初始质量函数，相对于假设通用Chabrier初始质量函数的基准COLIBRE L100m6模拟，早期星系的静止远紫外线光度提高了约4倍。这使得在z = 15时能够形成观测亮度高达$M_{\rm UV} \simeq -20$的星系（对比基准模拟中的$M_{\rm UV} \simeq -18.5$），说明了重质量初始质量函数的恒星形成缓解与JWST数据矛盾的潜力。后来，远紫外线发射的增强部分被尘埃表面密度增加导致的衰减抵消，这是由于i）核心坍缩超新星额外喷出尘埃颗粒和ii）富含金属的星际气体促进了尘埃颗粒的有效生长。该模拟再现了红移z = 5时的星系恒星质量函数和静止光学光度函数，其精度与基准模拟相当，并且两个模拟显示的紫外线连续谱斜率与JWST观测一致。
英文摘要：
JWST surveys reveal a greater space density of high-redshift UV-bright galaxies than predicted by conventional galaxy formation models. We present results from a $L=100$ cMpc cosmological simulation evolved to $z=5$ with a variation of the COLIBRE galaxy formation model that adopts a density-dependent stellar initial mass function (IMF), such that stellar populations formed from dense gas are born with a top-heavy IMF. Crucially, heavy element and dust yields, and supernova feedback energetics, are self-consistently adjusted to the changing IMF. We model UV/optical emission (including nebular emission) from galaxies and its attenuation by dust. By allowing a significant fraction of high-redshift star formation to proceed with a top-heavy IMF, the rest-frame far-UV luminosities of early galaxies are elevated by up to a factor of $\simeq4$ with respect to the fiducial COLIBRE L100m6 simulation, which assumes a universal Chabrier IMF. This enables the formation of galaxies with observed brightness up to $M_{\rm UV} \simeq -20$ at $z=15$ (c.f. $M_{\rm UV} \simeq -18.5$ in the fiducial simulation), illustrating the potential of star formation with a top-heavy IMF to alleviate tensions with JWST data. Later, the boost in far-UV emission is partly offset by attenuation due to increased dust surface densities from i) additional dust grain ejection from core-collapse supernovae and ii) efficient grain growth promoted by more metal-rich interstellar gas. The simulation reproduces the $z=5$ galaxy stellar mass function and rest-frame optical luminosity function with comparable accuracy to the fiducial simulation, and both simulations exhibit UV continuum slopes that are consistent with JWST observations.
