Title: Formation of satellites from cold collapse Show Chinese title

Title: 卫星从冷坍缩形成

Abstract: We study the collapse of an isolated, initially cold, irregular (but almost spherical) and (slightly) inhomogeneous cloud of self-gravitating particles. The cloud is driven towards a virialized quasi-equilibrium state by a fast relaxation mechanism, occurring in a typical time $\tau_c$, whose signature is a large change in the particle energy distribution. Post-collapse particles are divided into two main species: bound and free, the latter being ejected from the system. Because of the initial system's anisotropy, the time varying gravitational field breaks spherical symmetry so that the ejected mass can carry away angular momentum and the bound system can gain a non-zero angular momentum. In addition, while strongly bound particles form a compact core, weakly bound ones may form, in a time scale of the order of $\tau_c$, several satellite sub-structures. These satellites have a finite lifetime that can be longer than $\tau_c$ and generally form a flattened distribution. Their origin and their abundance are related to the amplitude and nature of initial density fluctuations and to the initial cloud deviations from spherical symmetry, which are both amplified during the collapse phase. Satellites show a time dependent virial ratio that can be different from the equilibrium value $b\approx -1$: although they are bound to the main virialized object, they are not necessarily virially relaxed. Show Chinese abstract

Abstract: 我们研究了一个孤立的、初始冷的、不规则（但几乎球形）且（轻微）不均匀的自引力粒子云的坍缩。 该云通过一个快速弛豫机制向一个准平衡状态演化，其典型时间是$\tau_c$，其特征是粒子能量分布的显著变化。 坍缩后的粒子分为两种主要种类：束缚的和自由的，后者被从系统中抛出。 由于初始系统的各向异性，随时间变化的引力场破坏了球对称性，使得抛出的质量可以带走角动量，而束缚系统可以获得非零的角动量。 此外，虽然强束缚粒子形成一个致密的核心，弱束缚粒子可能在时间尺度约为$\tau_c$的时间内形成几个卫星子结构。 这些卫星具有有限的寿命，可能比$\tau_c$更长，并通常形成扁平的分布。 它们的起源和数量与初始密度扰动的幅度和性质以及初始云偏离球对称性的程度有关，这些都在坍缩阶段被放大。 卫星显示一个随时间变化的维里比，可能不同于平衡值$b\approx -1$：尽管它们束缚于主要的准平衡物体，但并不一定处于维里平衡状态。