发表机构
University of Chicago; Kavli Institute for Cosmological Physics, University of Chicago; Sub-department of Astrophysics, University of Oxford; Institut d’Astrophysique de Paris, Sorbonne Universites, CNRS, UMR 7095; University of Bath; Universite Claude Bernard Lyon 1, CRAL UMR5574, ENS de Lyon, CNRS; Cosmic Dawn Center (DAWN); Niels Bohr Institute, University of Copenhagen; Institute for Astronomy, University of Edinburgh; Department of Astronomy, Yonsei University; Sterrenkundig Observatorium Department of Physics and Astronomy Universiteit Gent（芝加哥大学; 芝加哥大学卡弗里宇宙物理学研究所; 牛津大学天体物理子部门; 巴黎天体物理研究所，索邦大学，法国国家科学研究中心，UMR 7095; 巴斯大学; 里昂第一大学，CRAL UMR5574，里昂高等师范学校，法国国家科学研究中心; 宇宙黎明中心（DAWN）; 哥本哈根大学尼尔斯·玻尔研究所; 爱丁堡大学天文研究所; 延世大学天文学系; 根特大学物理与天文学系天文观测站）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过辐射流体动力学模拟揭示，高红移极蓝紫外谱斜率并非唯一对应高电离光子逃逸分数，部分极蓝星系逃逸分数极低，其蓝斜率源于星云发射滞后，强调非平衡发射的重要性。
AI 中文摘要
紫外（UV）谱斜率β是探究星系中恒星族性质与星际介质条件的基本探针。在高红移处，一小部分星系已被确认具有极蓝的谱斜率（β<-2.8），这是通过光谱直接测量得到的。对此类星系的一种解释是，它们泄漏出大量电离光子，使得这些光子从未被处理成星云连续谱，我们观测到的是恒星族更蓝的内禀斜率。在此，我们利用一套具有秒差距级分辨率和非平衡化学的详细辐射流体动力学模拟，来阐明高红移处极蓝紫外谱斜率的物理起源。我们表明，虽然一些极蓝星系（EBGs）确实具有高逃逸分数，但第二类EBG的f_esc<1%。在这第二类中，ISM气体密度往往低得多，电离前沿到达其斯特龙根半径的时间尺度可能比大质量恒星的主序寿命更长，从而导致星云发射的滞后。我们的结果表明，极蓝紫外谱斜率并不唯一地意味着高逃逸分数，这凸显了时间依赖（非平衡）星云发射对于解释早期宇宙星系光谱的重要性。
英文摘要
The ultraviolet (UV) spectral slope, $β$, serves as a fundamental probe of stellar population properties and interstellar medium conditions in galaxies. At high redshift, a small sample of galaxies have been confirmed to have extremely blue spectral slopes of $β<-2.8$, as measured directly from spectroscopy. One explanation for such galaxies is that they are leaking copious amounts of ionizing photons such that these photons are never processed into the nebular continuum and we are observing the bluer intrinsic slopes of the stellar populations. Here, we use a detailed set of radiation hydrodynamics simulations with parsec-scale resolution and non-equilibrium chemistry to elucidate the physical origin of extremely blue UV slopes at high redshift. We show that, while some extremely blue galaxies (EBGs) do indeed have high escape fractions, a second population of EBGs has $f_{\rm esc}<1\%$. In this second population, the ISM gas densities tend to be much lower, and the timescale for ionization fronts to reach their Strömgren radii can be longer than the main-sequence lifetime of massive stars, leading to a lag in nebular emission. Our results demonstrate that extremely blue UV slopes do not uniquely imply high escape fractions, which highlights the importance of time-dependent (non-equilibrium) nebular emission for interpreting the spectra of galaxies in the early Universe.
Comments11 Pages, & Figures, Accepted to OJA
