天体生物学领域在模拟银河系尺度的宜居带方面取得了巨大的进展，这些宜居带为生命的形成和复杂的进化提供了稳定的环境。最近，这个想法已经扩展到宇宙学尺度，通过对局部宇宙的可居住性进行整体建模的研究（例如Dayal et al. 2015; Li & Zhang 2015）。然而，所有这些研究都只集中在估计II型超新星（SNII）或伽马射线暴（GRB）的潜在有害影响，忽略了Ia型超新星（SNIa）和活动星系核（AGN）的贡献。在这项研究中，我们遵循两种不同的方法，基于（i）有害辐射的幅度和（ii）有害辐射照射的总行星托管体积。我们同时跟踪整个宇宙的关键天体物理源（SNII，SNIa，AGN和GRB）的贡献，以确定其在138亿年宇宙时间内的可居住性。我们发现SNII在任何宇宙时期的总辐射收支和有害辐射照射量中占主导地位，紧随其后的是SNIa（贡献为SNII的一半），GRB和AGN占微不足道的部分（<1%）。其次，由于恒星的总质量（或行星的总数）随着时间的推移而缓慢增加，而总的有害辐射密度和受影响的体积在最初的30亿年后下降，我们发现宇宙的可居住性在宇宙时间内稳步增加。我们发现，根据确切的模型假设，与40亿年前生命首次出现在地球上时相比，今天的宇宙可居住性是2.5到20倍。我们发现，这种可居住性的增加将持续到最后的恒星在接下来的数千亿年内消亡。
英文摘要：
The field of astrobiology has made tremendous progress in modelling galactic-scale habitable zones which offer a stable environment for life to form and evolve in complexity. Recently, this idea has been extended to cosmological scales by studies modelling the habitability of the local Universe in its entirety (e.g. Dayal et al. 2015; Li & Zhang 2015). However, all of these studies have solely focused on estimating the potentially detrimental effects of either Type II supernovae (SNII) or Gamma Ray Bursts (GRBs), ignoring the contributions from Type Ia supernovae (SNIa) and active galactic nuclei (AGN). In this study we follow two different approaches, based on (i) the amplitude of deleterious radiation and (ii) the total planet-hosting volume irradiated by deleterious radiation. We simultaneously track the contributions from the key astrophysical sources (SNII, SNIa, AGN and GRBs) for the entire Universe, for both scenarios, to determine its habitability through 13.8 billion years of cosmic time. We find that SNII dominate the total radiation budget and the volume irradiated by deleterious radiation at any cosmic epoch closely followed by SNIa (that contribute half as much as SNII), with GRBs and AGN making up a negligible portion (<1%). Secondly, as a result of the total mass in stars (or the total number of planets) slowly building-up with time and the total deleterious radiation density, and volume affected, falling-off after the first 3 billion years, we find that the Universe has steadily increased in habitability through cosmic time. We find that, depending on the exact model assumptions, the Universe is 2.5 to 20 times more habitable today compared to when life first appeared on the Earth 4 billion years ago. We find that this increase in habitability will persist until the final stars die out over the next hundreds of billions of years.
Iron and alpha-element Production in the First One Billion Years after the Big Bang
我们目前的测量碳，氧，硅，铁在类星体吸收系统存在时，宇宙大约是10亿岁。我们使用Keck，Magellan和VLT光学和近红外光谱测量了9个低电离系统中4.7 < z < 6.3的柱密度，具有中等到高分辨率。C II、O I、Si II和Fe II之间的柱密度比在较低的红移处与亚DLA和贫金属（[M/H] < -1）DLA几乎相同，在2 < z < 6上没有显著的演变。任何两个元素的比率的估计固有散射也很小，具有典型的r.m.s. 4.7系统的偏差<0.1 dex. These facts suggest that dust depletion and ionization effects are minimal in our z >，在较低的红移的DLAs，和柱密度比接近固有的相对元素丰度。因此，我们的z > 4.7系统中的丰度可能代表宇宙历史第一个千兆年内恒星星族的典型综合产额。由于在这些红移的宇宙年龄所施加的时间限制，我们的测量因此直接限制了大质量恒星的金属生产，包括瞬发超新星的铁产量。红移演化的缺乏进一步表明，在z > 2时，大多数贫金属吸收系统的金属库存也由大质量恒星主导，延迟的Ia型超新星或AGB风的贡献很小。我们系统中的相对丰度与金属含量非常低、非碳增强的星系晕恒星中的相对丰度大致一致。这与现今贫金属恒星可能早在大爆炸后10亿年就形成的观点一致。
Too many protoclusters? Reconciling the overabundance of cluster progenitors within the first billion years of the Universe
University of Geneva（日内瓦大学）；University of Nottingham（诺丁汉大学）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）；The Pennsylvania State University（宾夕法尼亚州立大学）；DTU Space, Technical University of Denmark（丹麦技术大学空间研究所）
