【作者】 王蕾；

【导师】 向守平； 袁业飞；

【作者基本信息】 中国科学技术大学 ， 天体物理， 2008， 博士

【摘要】 在过去的几十年里,ACDM宇宙学模型及大尺度结构形成的自下而上的等级成团理论已经获得了很多来自不同巡天项目（例如:HST,WMAP,SDSS）的观测的支持,并且在高分辨率的数值模拟（例如:N-body,hydrodynamics等等。）中也有很好的验证。然而由于重子在辐射背景和引力场中演化的高度复杂性,使得许多问题并未被充分澄清,包括星系在暗物质晕中的演化细节（如气体凝聚冷却,星系中的恒星形成历史及来自发光天体的反馈作用）和再电离历史等。这些不确定性与我们尚不能直接观测第一代天体是有直接关联的。尽管如此,基于一些现有的观测,我们仍然可以在此领域做一些理论模型,甚至给出一些预言来指导观测。正在进行中的WMAP卫星对宇宙微波背景（CMB）的观测以及对最高红移类星体（QSOs）的研究给宇宙再电离历史以很强的限制。最近对z（?）6的QSOs的光谱上的Gunn-Peterson吸收槽[Gunn & Peterson 1965]的探测,表明在红移z～6.5左右中性氢的分数是少于50%的[Wyithe et al.2005,Fan et al.2006]。另一方面,来自CMB的观测表明Thomson电子散射光深τ_e=0.084（?）[WMAP5年的数据+Ia型超新星+重子声峰震荡（Baryon Acoustic Oscillations）,详见Komatsu et al.（2008）],意味着宇宙在红移9.4≤z_re≤12.2期间被电离完。我们知道比锂元素重的金属是恒星核反应的特产（而不是来自早期宇宙大爆炸的核合成）。一些第一代恒星（也就是所谓的星族Ⅲ的恒星,PopⅢ）会以超新星爆发的形式结束自己的一生,这就会把大量重元素抛到星系际介质（IGM）中。当IGM中的金属丰度到达某一临界值Z_crit的时候,气体就不会再形成PopⅢ的恒星了,而是星族Ⅱ（PopⅡ/Ⅰ）的恒星。PopⅡ会逐渐取代第一代恒星继续照亮宇宙。作为最早期的重元素的散布者,PopⅢ的SNe主导了从第一代恒星到第二代恒星的转变过程。尽管PopⅢ的存在有利于解释诸如从原初的Z（?）10^-12-10^-10到PopⅡ的Z（?）10^-4-10^-3的金属增丰问题,超大质量黑洞的形成问题,宇宙再电离和G矮星等问题[Ciardi & Ferrara 2005],但是要观测PopⅢ似乎是毫无希望的,除非哈勃太空望远镜（HST）的接班人James Webb Space Telescope（JWST）升空[Barkana & Loeb 2001]。以上罗列的一些事实要求人们去关注高红移宇宙发生的事情。在没有很高红移（z≥10）观测数据的支持的情况下,人们经常求助于数值模拟。有的作者关注第一代超新星的爆发效应[Yoshida et al.2003,Kitayama & Yoshida 2005,Greif et al.2007],也有人关注来自PopⅢ的星风影响[Meynet et al.2006,Ricotti et al.2008]。我们的理论工作就是基于类似的数值模拟的结果。在本文中,我们研究了恒星形成过程中的负反馈效应。我们发现辐射反馈对于第一代天体很重要,能显著抑制第一代天体（恒星）的形成。然而来自超新星的力学反馈却不能明显地抑制早期的恒星形成。辐射和力学反馈共同主导了第二代或者第三代恒星的形成率。来自第一代恒星的反馈很强,不能被忽视。但其对再电离以及Thomson电子散射光深的贡献不占主导。此外,在早期小暗物质晕里的恒星形成很有可能是自我调节的。本文第一章介绍了ACDM宇宙学模型的框架。我们的工作就是在此框架下展开的。第二章中我们介绍了重子的演化情况。包括第一代天体的形成,演化,终结;宇宙再电离和概括地提及各类反馈效应。第三章中我们着重研究了来自SNe的负的力学反馈效应,其中我们假设了一个PopⅢ的质量比率,这对分开研究不同星族的影响有较大用处。辐射反馈效应在第四章中讨论,我们建立一个解析模型来计算PopⅢ的小暗物质晕中的光致蒸发反馈,另一个解析模型讨论了大暗物质晕受的再电离辐射背景的反馈。最后在第五章中给出了我们的一些讨论和结论。更多还原

【Abstract】 In the past decades,the Lambda Cold Dark Matter（ACDM） cosmological model and the so-called "bottom-up" hierarchical theory for large scale structure formation have got decisive supports from different probing projects（e.g. HST,WMAP,SDSS） and high-resolution numerical simulations（such as N-body, hydrodynamics etc.） However,many questions including the details of the galaxy evolution in halos（e.g.the gas cooling and condensation,the starformation history（SFH） in galaxies and the feedback from luminous objects） and the reionization history of the IGM are not fully understood yet owing to the complexity of the baryonic evolution in the radiative background and gravitational field.These uncertainties are linked to the early formed objects which are not observable at present.Nevertheless we can still do something in this field based on the current observation data.Recent detections of Gunn-Peterson trough[Gunn & Peterson 1965]in the spectra of QSOs with z（?）6 indicate less 50%neutral hydrogen at z（?）6.5[Wyithe et al.2005,Fan et al.2006].The ongoing observations of the WMAP satellite on Cosmic Microwave Background （CMB） and the highest redshift QSOs study put very tight constraints on the reionization history of the Universe.The CMB observation（WMAP 5 years data） manifests the optical depth to Thomson electron scattering,τ_e=0.084（?） [Komatsu et al.2008],which suggests that our Universe might be reionized during the period of redshift 9.4≤z_re≤12.2. It is well-known that the chemical elements heavier than lithium are produced exclusively through stellar nucleosynthesis.Some of the first generation stars（the so-called populationⅢstars,hereafter,PopⅢ） die as SNe explosions, which can expel the heavy elements into the intergalactic medium（IGM）.When the metal elements in IGM are enriched to a certain threshold Z_crit,the populationⅡ/Ⅰ（hereafter PopⅡ/Ⅰ） stars will form and take the place of the first stars to light the universe.As the earliest distributors of heavy elements,the SNe from PopⅢstars determine the transition from PopⅢto PopⅡ/Ⅰ.The existence of PopⅢstars can help explaining the metal enrichment(from Z（?）10^-12-10^-10 to the lowest metallicity of PopⅡstars Z（?）10^-4-10^-3),the formation of massive black holes,the reionization of the universe and the starting engine for the formation of the first galaxies and the G-dwarf,and so on[Ciardi & Ferrara 2005].But it is hopeless to observe the first generation stars until the launch of the successor of the Hubble Space Telescope（HST）,called James Webb Space Telescope （JWST）[Barkana & Loeb 2001].JWST will show us Pair Instability SNe（PISNe） from massive PopⅢstars if the current theory is reasonable[Wise & Abel 2005].These facts demand people to pay attention to the high redshift objects and study their evolution processes.In the absence of the observational data of very high redshift（z≥10） objects,people often seek help from numerical simulations. Some authors concentrated on the effects of the first generation SNe explosions[Yoshida et al.2003,Kitayama & Yoshida 2005,Greif et al.2007],some studied the strong stellar and galactic winds from PopⅢstars[Meynet et al.2006, Ricotti et al.2008].Based on their works,we can obtain a model to describe the global effects from the PopⅢstars at early time（like the SFR density,the IGM reionization and so on.）In this PhD thesis,we studied the negative feedback effect from both supernovae （SNe） explosions and the stellar radiation.And we find the radiative feedback is important for the early generation stars.It can suppress the star formation significantly.But the mechanical feedback from the SNe explosions is not able to affect the early star formation considerably.The radiative and mechanical feedback dominates the star formation rate of the second or third generation stars.The feedback from first generation stars is very strong and should not be neglected.However,the effect on reionization from early stars is not significant,which results in a little contribution on the Thomson electron scattering optical depth.The early star formation in small-halo objects is likely to be self-regulated.We introduce the ACDM cosmological model in the first chapter.In chapter 2,we discuss the evolution of baryons,including the formation, evolution and extinction of the first stars,cosmological reionization and all kinds of feedback effects.In chapter 3,we emphasize the negative feedback from SNe.The radiative feedback effect will be calculated in chapter 4.Finally,we present our discussion and conclusion in the last chapter.更多还原