The first Population II stars formed in externally enriched mini-haloes
The first Population II stars formed in externally enriched mini-haloes
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第一批 II 族恒星在外部富集的迷你晕中形成
DOI：
10.1093/mnras/stv1509
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发表时间：
2015
影响因子：
4.8
通讯作者：
S. Khochfar
中科院分区：
文献类型：
--
作者：
Britton D. Smith;J. Wise;B. O’Shea;M. Norman;S. Khochfar
周一。不是。 R.阿斯特朗。苏克。 000, 1–15 (2015) 2015 年 7 月 31 日印刷（MN L A TEX 样式文件 v2.2） 第一批 II 星在外部富集迷你光环中形成 Britton D. Smith 1？ , John H. Wise 2 , Brian W. O’Shea 3 † , Michael L. Norman 4 , and Sadegh Khochfar 1 爱丁堡大学天文学研究所，爱丁堡皇家天文台 EH9 3HJ，英国相对论天体物理学，佐治亚理工学院，837 State Street 亚特兰大，GA 30332，美国 3 密歇根州物理与天文学系州立大学，东兰辛，MI 48824，美国 4 加州大学圣地亚哥分校天体物理和空间科学中心，拉霍亚，CA 92093，美国 arXiv:1504.07639v2 [astro-ph.GA] 2015 年 7 月 30 日 2 中心 2015 年 7 月 31 日 摘要 我们提出了对最早的星族 II 恒星形成的模拟，从宇宙学的初始条件和当第一颗超新星中产生的金属被纳入坍缩的气体云时的结束。这种情况发生在超新星爆炸波与附近的迷你光环碰撞后，引发进一步的湍流，从而有效地将金属混合到光环中心的致密气体中。首先塌陷的气体已富集到金属丰度Z ∼ 2 × 10 -5 Z 。由于金属丰度极低，塌缩过程类似于无金属气体，直到灰尘冷却在高密度下变得有效，导致云破碎成大量低质量物体。这种外部富集机制为观测到的大多数贫金属恒星（例如 SMSS J031300.36-670839.3）提供了合理的起源，这些恒星似乎是由单个超新星富集的气体形成的。该机制的运行时间尺度比低质量迷你光环（M 6 5 × 10 5 M）在经历超新星后恢复气体的时间更短。因此，如果条件适合的话，富含金属的恒星很可能首先通过这个通道形成。我们发现了许多其他可能以这种方式形成恒星的外部富集光晕。这些光晕的金属丰度高达 0.01 Z ，这表明第一代富含金属的恒星的一些成员可能隐藏在当前的恒星巡天中。关键词：宇宙学、流体动力学、辐射传输、方法：数值、星系：恒星形成 引言 在宇宙历史的大部分时间里，与恒星形成相关的物理过程共同产生了主要是低质量的恒星。恒星初始质量函数（IMF）似乎对环境变化非常稳健，以至于关于其普遍性的争论主要涉及“IMF 是普遍的”这一说法是否应该包括“几乎”这个词。 Kroupa (2002) 和最近的 Bastian 等人对此主题提供了精彩的评论。 （2010）。 IMF 普遍性的一个值得注意的例外是无金属（星族 III 或星族 III）恒星的情况。 2000 年代中期是该主题质量审查的热潮（Barkana & Loeb 2001；Bromm & Larson 2004；Ciardi & Ferrara 2005；Glover 2005；Ripamonti & Abel 2006；Bromm et al. 2009）。简而言之，中性无金属气体的冷却效率非常低，因为它的冷却效率非常低。莱曼布里格斯学院；密歇根州立大学核天体物理联合研究所，东兰辛，MI 48824，美国 c 2015 RAS 故障，导致 Jeans 产生数千 M 量级的大规模碎片。早期模拟发现，这导致仅形成一个（Abel 等人，2002 年；Bromm 等人，2002 年；Yoshida 等人，2006 年；O’Shea 和 Norman 2007 年）或两个（Turk 等人，2009 年；Stacy 等人，2010 年）致密核心，这些核心可以从这个巨大的包膜中自由增生并不受争议地生长。最近的模拟发现，围绕大质量中央核心的圆盘可能不稳定而容易碎裂，这可能为低质量 Pop III 恒星提供通道（Clark 等人，2011 年；Greif 等人，2011 年；Stacy 和 Bromm，2014 年）。然而，对中心天体后期吸积进行的模拟发现，它们的最终大小将增长到 M 的 10 到 1000 倍（Hosokawa 等人，2011 年；Hirano 等人，2014 年、2015 年；Susa 等人，2014 年），这非常清楚地表明，Pop III 恒星形成模式至少是毫无疑问是不同的。即使在 Pop III IMF 的低质量端，Hartwig 等人。 (2015) 声称，银河系低金属丰度恒星调查的现有样本量已经可以以 95% 的确定性排除 0.65 M 以下无金属恒星的存在，除非通过星际介质中的金属吸积来富集（Johnson
Mon. Not. R. Astron. Soc. 000, 1–15 (2015) Printed 31 July 2015 (MN L A TEX style file v2.2) The First Population II Stars Formed in Externally Enriched Mini-halos Britton D. Smith 1? , John H. Wise 2 , Brian W. O’Shea 3 †, Michael L. Norman 4 , and Sadegh Khochfar 1 Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street Atlanta, GA 30332, USA 3 Department of Physics & Astronomy, Michigan State University, East Lansing, MI 48824, USA 4 Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA arXiv:1504.07639v2 [astro-ph.GA] 30 Jul 2015 2 Center 31 July 2015 ABSTRACT We present a simulation of the formation of the earliest Population II stars, starting from cosmological initial conditions and ending when metals created in the first supernovae are in- corporated into a collapsing gas-cloud. This occurs after a supernova blast-wave collides with a nearby mini-halo, inducing further turbulence that efficiently mixes metals into the dense gas in the center of the halo. The gas that first collapses has been enriched to a metallicity of Z ∼ 2 × 10 −5 Z . Due to the extremely low metallicity, collapse proceeds similarly to metal- free gas until dust cooling becomes efficient at high densities, causing the cloud to fragment into a large number of low mass objects. This external enrichment mechanism provides a plau- sible origin for the most metal-poor stars observed, such as SMSS J031300.36-670839.3, that appear to have formed out of gas enriched by a single supernova. This mechanism operates on shorter timescales than the time for low-mass mini-halos (M 6 5 × 10 5 M ) to recover their gas after experiencing a supernova. As such, metal-enriched stars will likely form first via this channel if the conditions are right for it to occur. We identify a number of other externally enriched halos that may form stars in this manner. These halos have metallicities as high as 0.01 Z , suggesting that some members of the first generation of metal-enriched stars may be hiding in plain sight in current stellar surveys. Key words: cosmology, hydrodynamics, radiative transfer, methods: numerical, galaxies: star formation INTRODUCTION The physical processes relevant to star formation have conspired to produce stars of predominantly low mass for most of the history of the Universe. The stellar initial mass function (IMF) appears to be so robust to variations in environment that debate over its univer- sality primarily concerns whether the statement “the IMF is uni- versal” should include the word almost. Excellent reviews of this subject have been provided by Kroupa (2002) and more recently, Bastian et al. (2010). The one notable exception to the universal- ity of the IMF is the case of metal-free (Population III or Pop III) stars. The mid 2000s was a boom for quality reviews of this subject (Barkana & Loeb 2001; Bromm & Larson 2004; Ciardi & Ferrara 2005; Glover 2005; Ripamonti & Abel 2006; Bromm et al. 2009). In short, neutral metal-free gas cools very inefficiently as it col- e-mail:brs@roe.ac.uk † Department of Computational Mathematics, Science, and Engineering; Lyman Briggs College; and the Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824, USA c 2015 RAS lapses, resulting in Jeans mass-scale fragments that are of the order of thousands of M . Early simulations found that this resulted in the formation of only one (Abel et al. 2002; Bromm et al. 2002; Yoshida et al. 2006; O’Shea & Norman 2007) or two (Turk et al. 2009; Stacy et al. 2010) dense cores that were free to accrete from this massive envelope and grow uncontested. More recent simu- lations have found that the disks surrounding the massive, central core can be unstable to fragmentation, potentially providing a chan- nel for lower mass Pop III stars (Clark et al. 2011; Greif et al. 2011; Stacy & Bromm 2014). However, simulations that follow the late- time accretion onto the central object find that they will grow to be 10s to 1000s of M in final size (Hosokawa et al. 2011; Hirano et al. 2014, 2015; Susa et al. 2014), making it quite clear that the Pop III star formation mode is, at a bare minimum, unquestionably distinct. Even on the low mass end of the Pop III IMF, Hartwig et al. (2015) claim that the existing sample size of low-metallicity star surveys in the Milky Way can already rule out the existence of metal-free stars below 0.65 M with 95% certainty, barring enrich- ment via accretion of metals from the interstellar medium (Johnson
影响因子：
8.7
作者：
Komatsu, E.;Smith, K. M.;Wright, E. L.
通讯作者：
Wright, E. L.
自重力气体 (M)HD 模拟的新 Jean 分辨率准则：在重力驱动湍流磁场放大中的应用
DOI：
10.1088/0004-637x/731/1/62
发表时间：
2011
期刊：
The Astrophysical Journal
影响因子：
--
作者：
Christoph Federrath;Sharanya Sur;Dominik R. G Schleicher;Robi Banerjee;Ralf S. Klessen
通讯作者：
Ralf S. Klessen