The birth of a galaxy – III. Propelling reionization with the faintest galaxies
The birth of a galaxy – III. Propelling reionization with the faintest galaxies
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DOI：
10.1093/mnras/stu979
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发表时间：
2014-03
影响因子：
4.8
通讯作者：
J. Wise;V. Demchenko;M. Halicek;M. Norman;M. Turk;Tom Abel;Britton D. Smith
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作者：
J. Wise;V. Demchenko;M. Halicek;M. Norman;M. Turk;Tom Abel;Britton D. Smith
一个星系的诞生- III. MNRAS 442, 2560-2579 (2014) doi:10.1093/ MNRAS /stu979用最微弱的星系推进再电离John H. Wise, 1 [Vasiliy G. Demchenko, 1 Martin T. Halicek, 1 Michael L. Norman, 2 Matthew J. Turk， 3 Tom Abel和Britton D. Smith] 1相对论天体物理中心，乔治亚理工学院，837 State Street, Atlanta, GA 30332，美国加州圣地亚哥大学天体物理和空间科学中心，La Jolla, CA 92093，美国3哥伦比亚大学天文学系，538 West 120 Street, New York, NY 10027，美国4斯坦福大学Kavli粒子天体物理与宇宙学研究所，Menlo Park, CA 94025，美国5爱丁堡大学天文学研究所，Blackford Hill, Edinburgh EH9 3HJ， UK 2中心接受2014年5月14日。收到2014年5月12日；来自星系的星光在整个宇宙再电离过程中起着关键作用。我们利用宇宙辐射流体动力学模拟，从它们的星族III祖星开始，对z bbb70处质量高达10 9m的晕中的矮星系特性进行了统计。我们发现富金属恒星的形成并不局限于原子冷却（温度≥10 4 K）的晕，而是可以发生在质量低至10 6 M的晕中，特别是在中性区域。尽管这些最小的星系只拥有104 M的恒星，但它们提供了近30%的电离光子预算。我们发现星系的光度函数在M UV ~ - 12以上趋于平缓，而在z 10处密度不变。逸入星系际介质的电离辐射的比例与晕的质量成反比，在质量范围log M/M = 7.0−8.5从50%下降到5%。利用我们在半解析再电离模型中的星系统计数据，我们发现汤姆逊散射光学深度与最新的普朗克结果一致，同时仍然与z = 4-6处Lyα森林观测提供的紫外线发射率约束一致。关键词：辐射转移方法；数值星系；矮星系；形成星系；1我N T RO D U C T I O N宇宙再电离是一个扩展的过程作为单独的H II区域生长在电离源逐渐融合,最终完全电离的宇宙,z∼6(例如Gnedin & Ostriker 1997; Razoumov et al . 2002; Ciardi,费拉拉&白色2003;Sokasian et al . 2003; Furlanetto, Zaldarriaga & Hernquist 2004; Iliev et al . 2006;罗伯逊et al . 2010; Trac & Gnedin 2011;锥盘et al . 2011;所以et al . 2014年)。然而，在再电离的时间和持续时间的观测约束之间仍然存在一些紧张。首先，z ~ 6类星体通过星系间介质（IGM）向Lyα偏蓝的透射率表明，宇宙在这一时期大部分被电离（例如Gunn & Peterson 1965； Fan et al. 2002, 2006; Willott et al. 2007; Mortlock et al. 2011）。其次，威尔金森微波各向异性探测器（WMAP）和普朗克对宇宙微波背景（CMB）的观测测量了汤姆逊散射的光学深度τ e = 0.089 +0.012−0.014，这对应于宇宙在z = 11.1±1.1时被e -mail: jwise@physics.gatech.edu ~ 50%电离（普朗克协作2013）。但是，通过Lyα森林观测在z = 4-6处测量到的电离发射率不能解释测量到的τ e，这表明再电离的结束一定是光子匮乏的（Bolton & Haehnelt 2007），并且在再电离期间的发射率一定更高。第三，通过使用南极望远镜测量动力学Sunyaev-Zel 'dovich效应，再电离持续时间1被限制在z < 7.9以内（Zahn et al. 2012）。这些观测结果表明，再电离是一个扩展过程，主要发生在6z15。什么样的电离源驱动着这种全球性的、延展性的转变？很明显，类星体和非常明亮的星系，这两者都太罕见了，对再电离的总体电离光子预算没有显著贡献（例如Shapiro 1986； Dijkstra等人2004；Willott等人2010；Grissom, Ballantyne & Wise 2014）。Zahn等人（2012）将z定义为在20%到99%电离之间经过的红移，认为来自星系的星光提供了绝大多数电离光子预算。C 2014作者由牛津大学出版社代表皇家天文学会出版，2016年9月12日由嘉宾从http://mnras.oxfordjournals.org/下载
MNRAS 442, 2560–2579 (2014) doi:10.1093/mnras/stu979 The birth of a galaxy – III. Propelling reionization with the faintest galaxies John H. Wise, 1‹ Vasiliy G. Demchenko, 1 Martin T. Halicek, 1 Michael L. Norman, 2 Matthew J. Turk, 3 Tom Abel 4 and Britton D. Smith 5 1 Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street, Atlanta, GA 30332, USA for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA 3 Department of Astronomy, Columbia University, 538 West 120th Street, New York, NY 10027, USA 4 Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Menlo Park, CA 94025, USA 5 Institute of Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK 2 Center Accepted 2014 May 14. Received 2014 May 12; in original form 2014 March 24 Starlight from galaxies plays a pivotal role throughout the process of cosmic reionization. We present the statistics of dwarf galaxy properties at z > 7 in haloes with masses up to 10 9 M , using a cosmological radiation hydrodynamics simulation that follows their buildup starting with their Population III progenitors. We find that metal-enriched star formation is not restricted to atomic cooling (T vir ≥ 10 4 K) haloes, but can occur in haloes down to masses ∼10 6 M , especially in neutral regions. Even though these smallest galaxies only host up to 10 4 M of stars, they provide nearly 30 per cent of the ionizing photon budget. We find that the galaxy luminosity function flattens above M UV ∼ −12 with a number density that is unchanged at z 10. The fraction of ionizing radiation escaping into the intergalactic medium is inversely dependent on halo mass, decreasing from 50 to 5 per cent in the mass range log M/M = 7.0−8.5. Using our galaxy statistics in a semi-analytic reionization model, we find a Thomson scattering optical depth consistent with the latest Planck results, while still being consistent with the UV emissivity constraints provided by Lyα forest observations at z = 4–6. Key words: radiative transfer – methods: numerical – galaxies: dwarf – galaxies: formation – galaxies: high-redshift – dark ages, reionization, first stars. 1 I N T RO D U C T I O N Cosmic reionization is an extended process as individual H II regions grow around ionizing sources that gradually coalesce, culminating in a fully ionized Universe by z ∼ 6 (e.g. Gnedin & Ostriker 1997; Razoumov et al. 2002; Ciardi, Ferrara & White 2003; Sokasian et al. 2003; Furlanetto, Zaldarriaga & Hernquist 2004; Iliev et al. 2006; Robertson et al. 2010; Trac & Gnedin 2011; Zahn et al. 2011; So et al. 2014). However, there is still some tension between observational constraints on the timing and duration of reioniza- tion. First, the transmission fraction of z ∼ 6 quasar light blueward of Lyα through the intergalactic medium (IGM) indicates that the Universe was mostly ionized by this epoch (e.g. Gunn & Peterson 1965; Fan et al. 2002, 2006; Willott et al. 2007; Mortlock et al. 2011). Secondly, observations of the cosmic microwave background (CMB) from the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck have measured the optical depth to Thomson scat- tering τ e = 0.089 +0.012 −0.014 , which corresponds to the Universe being E-mail: jwise@physics.gatech.edu ∼50 per cent ionized at z = 11.1 ± 1.1 (Planck Collaboration 2013). But the ionizing emissivity measured at z = 4–6 through Lyα forest observations cannot account for this measured τ e , indi- cating that the end of reionization must be photon starved (Bolton & Haehnelt 2007) and that the emissivity must have been higher during reionization. Third, the duration 1 of reionization has been constrained to occur within z < 7.9 by measuring the kinetic Sunyaev–Zel’dovich effect with the South Pole Telescope (Zahn et al. 2012). These observations suggest that reionization was an extended process, mainly occurring at 6 z 15. What population of ionizing sources drives this global and ex- tended transition? It is clear that quasars and the very brightest galaxies, both of which are too rare, do not significantly contribute to the overall ionizing photon budget of reionization (e.g. Shapiro 1986; Dijkstra et al. 2004; Willott et al. 2010; Grissom, Ballantyne & Wise 2014). Starlight from galaxies is thought to provide the vast majority of the ionizing photon budget from extrapolating the 1 Zahn et al. (2012) define z as the redshift elapsed between 20 and 99 per cent ionized. C 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society Downloaded from http://mnras.oxfordjournals.org/ by guest on September 12, 2016 ABSTRACT