Title: Angular momentum properties of haloes and their baryon content in the Illustris simulation Show Chinese title

Title: 晕系角动量特性及其在Illustris模拟中的重子物质含量

Abstract: The angular momentum properties of virialised dark matter haloes have been measured with good statistics in collisionless N-body simulations, but an equally accurate analysis of the baryonic spin is still missing. We employ the Illustris simulation suite, one of the first simulations of galaxy formation with full hydrodynamics that produces a realistic galaxy population in a sizeable volume, to quantify the baryonic spin properties for more than $\sim$ 320,000 haloes. We first compare the systematic differences between different spin parameter and halo definitions, and the impact of sample selection criteria on the derived properties. We confirm that dark matter only haloes exhibit a close to self-similar spin distribution in mass and redshift of lognormal form. However, the physics of galaxy formation radically changes the baryonic spin distribution. While the dark matter component remains largely unaffected, strong trends with mass and redshift appear for the spin of diffuse gas and the formed stellar component. With time the baryons staying bound to the halo develop a misalignment of their spin vector with respect to dark matter, and increase their specific angular momentum by a factor of $\sim$ 1.3 in the non-radiative case and $\sim$ 1.8 in the full physics setup at z = 0. We show that this enhancement in baryonic spin can be explained by the combined effect of specific angular momentum transfer from dark matter onto gas during mergers and from feedback expelling low specific angular momentum gas from the halo. Our results challenge certain models for spin evolution and underline the significant changes induced by baryonic physics in the structure of haloes. Show Chinese abstract

Abstract: 自引力暗物质晕的角动量特性在无碰撞N体模拟中已得到良好的统计测量，但对重子自旋的同样精确分析仍然缺失。我们使用Illustris模拟套件，这是首批包含完整流体动力学的星系形成模拟之一，能够在较大体积内产生现实的星系群体，以量化超过$\sim$320,000个晕的重子自旋特性。我们首先比较了不同自旋参数和晕定义之间的系统性差异，以及样本选择标准对所得特性的影响。我们确认仅含暗物质的晕在质量与红移上表现出接近自相似的对数正态形式的自旋分布。然而，星系形成的物理过程极大地改变了重子自旋分布。虽然暗物质成分基本不受影响，但弥散气体和形成恒星成分的自旋却显示出明显的质量和红移趋势。随着时间的推移，束缚在晕中的重子物质其自旋矢量相对于暗物质出现偏差，并在非辐射情况下和完整物理设置下在z = 0时其比角动量分别增加了$\sim$1.3倍和$\sim$1.8倍。我们表明，这种重子自旋的增强可以由合并过程中暗物质向气体传递特定角动量以及反馈将低特定角动量气体排出晕的共同作用来解释。我们的结果挑战了某些自旋演化的模型，并强调了重子物理对晕结构产生的显著变化。