第一个Galerkin：组装、冷却和Turbulence的开始
The First Galaxies: Assembly, Cooling and the Onset of Turbulence
摘要：
我们研究的第一个星系在z > 10的高分辨率数值模拟的属性，从宇宙学的初始条件，并考虑到所有相关的原始化学和冷却。第一个星系的特征是，一旦维里温度超过10^4 K，氢原子就会开始冷却，并且能够保留光热气体。通过详细的并合树跟踪了一个5*10^7 M太阳系统的复杂吸积和恒星形成历史，并导出了在其组装之前形成的第三星族（PopIII）恒星的数量上限.我们研究了下落气体的热演化和化学演化，发现温度> 10^4 K时的部分电离催化了H2和氘化氢的形成，使气体冷却到宇宙微波背景的温度。根据辐射和化学反馈的强度，原始恒星的形成可能是由第一个星系组装过程中形成的中等质量的Pop III恒星主导的。新生星系的吸积开始于热吸积，其中气体直接从星系际介质吸积并被冲击加热到维里温度，但很快伴随着冷吸积阶段，其中气体在高速流入母晕之前冷却成细丝状。后者在星系中心驱动超音速湍流，并可能导致非常有效的化学混合。因此，第一个星系中湍流的开始可能标志着向Pop II恒星形成的过渡。
英文摘要：
We investigate the properties of the first galaxies at z > 10 with highly resolved numerical simulations, starting from cosmological initial conditions and taking into account all relevant primordial chemistry and cooling. A first galaxy is characterized by the onset of atomic hydrogen cooling, once the virial temperature exceeds 10^4 K, and its ability to retain photoheated gas. We follow the complex accretion and star formation history of a 5*10^7 M_sun system by means of a detailed merger tree and derive an upper limit on the number of Population III (Pop III) stars formed prior to its assembly. We investigate the thermal and chemical evolution of infalling gas and find that partial ionization at temperatures > 10^4 K catalyses the formation of H2 and hydrogen deuteride, allowing the gas to cool to the temperature of the cosmic microwave background. Depending on the strength of radiative and chemical feedback, primordial star formation might be dominated by intermediate-mass Pop III stars formed during the assembly of the first galaxies. Accretion on to the nascent galaxy begins with hot accretion, where gas is accreted directly from the intergalactic medium and shock-heated to the virial temperature, but is quickly accompanied by a phase of cold accretion, where the gas cools in filaments before flowing into the parent halo with high velocities. The latter drives supersonic turbulence at the centre of the galaxy and could lead to very efficient chemical mixing. The onset of turbulence in the first galaxies thus likely marks the transition to Pop II star formation.
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