由不演化、弱质量依赖的恒星形成效率解释的宇宙黎明时期升高的紫外光度密度
Elevated UV luminosity density at Cosmic Dawn explained by non-evolving, weakly mass-dependent star formation efficiency
AI总结：
本文利用高分辨率宇宙学模拟 FIREbox-HR 表明，FIRE-2 物理下不随红移演化且弱依赖晕质量的 SFE 可自然解释 z~6–14 的高 UV 光度密度。
摘要：
James Webb空间望远镜（JWST）的最新观测揭示，早期宇宙在大爆炸后仅数亿年时存在出乎意料高的宇宙恒星形成活动。这些观测通常被理解为反映了恒星形成效率（SFE）的演化转变，而这种转变由这些早期时期不断变化的星系条件所导致。我们提出 FIREbox-HR，这是来自 Feedback in Realistic Environments 项目的高分辨率宇宙学流体动力学模拟，为理解宇宙时间最初十亿年内星系的 SFE 提供了洞见。FIREbox-HR 以八倍更高的质量分辨率（m_b ~ 7800 M_sun）重新模拟了原始 FIREbox 运行的宇宙体积（L = 22.1 cMpc），但在直至 z ~ 6 的范围内采用相同的物理过程。FIREbox-HR 预测的紫外（UV）光度函数与现有观测数据高度一致。该模拟还成功再现了 z ~ 6–14 处观测到的宇宙 UV 光度密度，表明早期宇宙中相对较高的恒星形成活动是 FIRE-2 模型所编码的重子过程的自然结果。根据 FIREbox-HR，中等质量晕（M_halo ~ 10^9–10^11 M_sun）的 SFE–晕质量关系不随红移显著演化，并且仅微弱地依赖于质量。SFE–晕质量关系的这些性质导致在更高 z 处低质量晕贡献更大，从而推动观测到的宇宙 UV 光度密度的逐渐演化。基于从 FIREbox-HR 推断出的 SFE–晕质量关系的理论模型，使我们能够探索其对星系演化的影响。未来对 z > 12 的 UV 暗弱星系的观测将提供进一步检验这些预测并加深我们对宇宙黎明期间恒星形成理解的机会。
英文摘要：
Recent observations with the James Webb Space Telescope (JWST) have uncovered unexpectedly high cosmic star formation activity in the early Universe, mere hundreds of millions of years after the Big Bang. These observations are often understood to reflect an evolutionary shift in star formation efficiency (SFE) caused by changing galactic conditions during these early epochs. We present FIREbox-HR, a high-resolution, cosmological hydrodynamical simulation from the Feedback in Realistic Environments project, which offers insights into the SFE of galaxies during the first billion years of cosmic time. FIREbox-HR re-simulates the cosmic volume (L = 22.1 cMpc) of the original FIREbox run with eight times higher mass resolution (m_b ~ 7800 M_sun), but with identical physics, down to z ~ 6. FIREbox-HR predicts ultraviolet (UV) luminosity functions in good agreement with available observational data. The simulation also successfully reproduces the observed cosmic UV luminosity density at z ~ 6 - 14, demonstrating that relatively high star formation activity in the early Universe is a natural outcome of the baryonic processes encoded in the FIRE-2 model. According to FIREbox-HR, the SFE - halo mass relation for intermediate mass halos (M_halo ~ 10^9 - 10^11 M_sun) does not significantly evolve with redshift and is only weakly mass-dependent. These properties of the SFE - halo mass relation lead to a larger contribution from lower mass halos at higher z, driving the gradual evolution of the observed cosmic UV luminosity density. A theoretical model based on the SFE - halo mass relation inferred from FIREbox-HR allows us to explore implications for galaxy evolution. Future observations of UV faint galaxies at z > 12 will provide an opportunity to further test these predictions and deepen our understanding of star formation during Cosmic Dawn.
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