We describe the interplay between stellar evolution and dynamical mass loss of evolving star clusters, based on the principles of stellar evolution and cluster dynamics and on a grid of N-body simulations of cluster models. The cluster models have different initial masses, different orbits, including elliptical ones, and different initial density profiles. We use two sets of cluster models: initially Roche-lobe filling and Roche-lobe underfilling. We identify four distinct mass loss effects: (1) mass loss by stellar evolution, (2) loss of stars induced by stellar evolution and (3) relaxation-driven mass loss before and (4) after core collapse. Both the evolution-induced loss of stars and the relaxation-driven mass loss need time to build up. This is described by a delay-function of a few crossing times for Roche-lobe filling clusters and a few half mass relaxation times for Roche-lobe underfilling clusters. The relaxation-driven mass loss can be described by a simple power law dependence of the mass dM/dt =-M^{1-gamma}/t0, (with M in Msun) where t0 depends on the orbit and environment of the cluster. Gamma is 0.65 for clusters with a King-parameter W0=5 and 0.80 for more concentrated clusters with W0=7. For initially Roche-lobe underfilling clusters the dissolution is described by the same gamma=0.80. The values of the constant t0 are described by simple formulae that depend on the orbit of the cluster. The mass loss rate increases by about a factor two at core collapse and the mass dependence of the relaxation-driven mass loss changes to gamma=0.70 after core collapse. We also present a simple recipe for predicting the mass evolution of individual star clusters with various metallicities and in different environments, with an accuracy of a few percent in most cases. This can be used to predict the mass evolution of cluster systems.
Using the latest cosmological hydrodynamic N-body simulations of groups and clusters, we study how location in phase-space coordinates at $z$$=$$0$ can provide information on environmental effects acting in clusters. We confirm the results of previous authors showing that galaxies tend to follow a typical path in phase-space as they settle into the cluster potential. As such, different regions of phase-space can be associated with different times since first infalling into the cluster. However, in addition, we see a clear trend between total mass loss due to cluster tides, and time since infal…
Massive globular clusters lose stars via internal and external processes. Internal processes include mainly two-body relaxation, while external processes include interactions with the Galactic tidal field. We perform a suite of N-body simulations of such massive clusters using three different direct-summation N-body codes, exploring different Galactic orbits and particle numbers. By inspecting the rate at which a star's energy changes as it becomes energetically unbound from the cluster, we can neatly identify two populations we call kicks and sweeps, that escape through two-body encounters in…
We present the first evidence of clear signatures of tidal distortions in the density distribution of the fascinating open cluster NGC~6791. We find that the 2D density map shows a clear elongation and an irregular distribution starting from $\sim 300^{\prime\prime}$ from the cluster center and two tails extending in opposite directions beyond the tidal radius. These features are aligned to both the absolute proper motion and to the Galactic centre directions. Accordingly we find that both the surface brightness and star count density profiles reveal a departure from a King model starting from…
An Investigation of the Loss of Planet-Forming Potential in Intermediate Sized Young Embedded Star Clusters
在我们银河系中形成的大部分恒星都是在嵌入巨大分子云的星团中诞生的。在这些环境中，背景紫外线辐射场撞击在拱星盘上，通常会超过每个盘的中心恒星产生的辐射场。因此，这种背景辐射可以驱动星周盘的蒸发，并导致星团内行星形成潜力的丧失。本文提出了一个详细的分析，这一过程中的恒星成员范围内的$100 \le N \le 1000$的集群。对于这些中等大小的星团，背景紫外线场通常由质量最大的恒星成员主导。由于初始质量函数的陡峭斜率，沐浴类似大小的簇的背景UV光的量显示出显著的变化。其结果是，我们执行这个问题的统计分析，通过计算FUV通量值的分布撞击在几个集群的情况下的恒星/磁盘系统。我们发现，在没有尘埃衰减，巨大的行星形成可能会被抑制在大约一半的系统中形成的中等大小的集群，无论恒星成员。相比之下，尘埃的存在可以显着降低这个值，在人口更多的集群中，这种影响更加明显。
This review summarises the main properties of Young Massive Clusters (YMCs), including their population properties, particularly focusing on extragalactic cluster samples. We discuss potential biases and caveats that can affect the construction of cluster samples and how incompleteness effects can result in erroneous conclusions regarding the long term survival of clusters. In addition to the luminosity, mass and age distributions of the clusters, we discuss the size distribution and profile evolution of the clusters. We also briefly discuss the stellar populations within YMCs. The final part …
The growth of galaxies through adiabatic accretion of dark matter is one of the main drivers of galaxy evolution. By isolating it from other processes like mergers, we analyse how it affects the evolution of star clusters. Our study comprises a fast and approximate exploration of the orbital and intrinsic cluster parameter space, and more detailed monitoring of their evolution, through N-body simulations for a handful of cases. We find that the properties of present-day star clusters and their tidal tails differ very little, whether the clusters are embedded in a growing galactic halo for 12 G…
Many scenarios for the origin of the chemical anomalies observed in globular clusters (GCs; i.e., multiple populations) require that GCs were much more massive at birth, up to $10-100\times$, than they are presently. This is invoked in order to have enough material processed through first generation stars in order to form the observed numbers of enriched stars (inferred to be second generation stars in these models). If such mass loss was due to tidal stripping, gas expulsion, or tidal interaction with the birth environment, there should be clear correlations between the fraction of enriched s…
Context: Star clusters form within giant molecular clouds that are strongly altered by the feedback action of the massive stars, but the cluster still remains embedded in a dense, highly turbulent medium and interactions with ambient structures may modify its dynamical evolution from that expected if it were isolated. Aims: We aim to study coupling mechanisms between the dynamical evolution of the cluster, accelerated by the mass segregation process, with harassment effects caused by the gaseous environment. Methods: We simulated the cluster dynamical evolution combining $N$-body and hydrodyna…
Satellite Metallicity Enhancement I: Suppressed Star Formation, Stellar Mass Loss, and Enriched Inflow of DESI and EAGLE Galaxies around Massive Clusters
State Key Laboratory of Dark Matter Physics & Tsung-Dao Lee Institute, Shanghai Jiao Tong University（暗物质物理国家重点实验室暨李政道研究所，上海交通大学）；Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University（上海交大物理与天文学院天文学系）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Department of Physics, Boston University（波士顿大学物理系）；Department of Physics & Astronomy, University College London（伦敦大学学院物理与天文系）；Instituto de Física, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）
Through a suite of direct N-body simulations, we explore how the structural and kinematic evolution of a star cluster located at the center of a dwarf galaxy is affected by the shape of its host's dark matter density profile. The stronger central tidal fields of cuspier halos minimize the cluster's ability to expand in response to mass loss due to stellar evolution during its early evolutionary stages and during its subsequent long-term evolution driven by two-body relaxation. Hence clusters evolving in cuspier dark matter halos are characterized by more compact sizes, higher velocity dispersi…
The amount of mass lost by stars during the red-giant branch (RGB) phase is one of the main parameters to understand and correctly model the late stages of stellar evolution. Nevertheless, a fully-comprehensive knowledge of the RGB mass loss is still missing. Galactic Globular Clusters (GCs) are ideal targets to derive empirical formulations of mass loss, but the presence of multiple populations with different chemical compositions has been a major challenge to constrain stellar masses and RGB mass losses. Recent work has disentangled the distinct stellar populations along the RGB and the hori…
Runaway collisions in dense clusters may lead to the formation of supermassive black hole (SMBH) seeds, and this process can be further enhanced by accretion, as recent models of SMBH seed formation in Population III star clusters have shown. This may explain the presence of supermassive black holes already at high redshift, $z>6$. However, in this context, mass loss during collisions was not considered and could play an important role for the formation of the SMBH seed. Here, we study the effect of mass loss, due to collisions of protostars, in the formation and evolution of a massive object …
On the dynamical evolution of globular clusters. II- The isolated cluster
本文是米歇尔·埃农的文章《全球化的动态演变》的英译本。II-L 'amas isolé”原文为法文，载于《天体物理学年鉴》，第28卷，第62页（1965年）。该系列第一篇论文的译文（“Sur l 'évolution dynamique des amas globulaires”，Hénon 1961，Annales d' Astrophysique，Vol. 24，p.369）也可提供。
The location of Galactic Globular Clusters' (GC) stars on the horizontal branch (HB) should mainly depend on GC metallicity, the "first parameter", but it is actually the result of complex interactions between the red giant branch (RGB) mass loss, the coexistence of multiple stellar populations with different helium content, and the presence of a "second parameter" which produces dramatic differences in HB morphology of GCs of similar metallicity and ages (like the pair M3--M13). In this work, we combine the entire dataset from the Hubble Space Telescope Treasury survey and stellar evolutionar…
A prescription and fast code for the long-term evolution of star clusters - II. Unbalanced and core evolution
我们介绍了快速星团演化代码Evolve Me A Cluster of StarS（EMACSS）的第二个版本。第一个版本（Alexander & Gieles）假设集群演化在生命周期的大部分时间是平衡的，这意味着集群核心的能量产生速率等于两体弛豫的能量扩散速率，这使得代码适合于在弱潮汐场中模拟集群。在这个新版本中，我们扩展了模型，包括一个不平衡的阶段的演变来描述崩溃前的演变和伴随的逃逸率，使集群在强潮汐场也可以模拟。我们还添加了处方的核心半径和密度的演变和相关的集群浓度参数。该模型同时求解了一系列关于核心半径、半质量半径和成员星数目N变化率的一阶常微分方程。大约需要2000个积分步骤来求解星团的整个演化过程，并且这个数量与N近似无关。我们比较模型的变化，这些参数从一系列的直接N体计算的单质量集群，并找到很好的协议，在所有参数的演变。相关的时间尺度，如总寿命和核心崩溃的时间，复制与各种初始半质量半径（相对于他们的雅可比半径）和不同的初始N的范围内的集群的精度约为10%，N = 65536。我们打算扩展这个框架，以包括更现实的初始条件，如恒星的质量谱和质量损失的恒星。EMACSS代码可用于星团人口的研究和模型，考虑（球状）星团和大尺度结构的共同演变。
We study the dynamical evolution of star clusters on eccentric orbits using a semi-analytical approach. In particular we adapt and extend the equations of EMACSS code, introduced by Gieles et al. (2014), to work with eccentric orbits. We follow the evolution of star clusters in terms of mass, half-mass radius, core radius, Jacobi radius and the total energy over their dissolution time. Moreover, we compare the results of our semi-analytical models against $N$-body computations of clusters with various initial half-mass radius, number of stars and orbital eccentricity to cover both tidally fill…
Evolution of a cluster of primordial black holes in the two-body relaxation approximation based on the Fokker-Planck equation is discussed. In our calculation, we consider the self-gravitating cluster with a wide range of black holes masses from $10^{-4} M_{\odot}$ up to $100 M_{\odot}$ and the total mass $10^5 M_{\odot}$. Moreover, we included a massive black hole in the cluster center which determines the evolution rate of the density profile in its vicinity.
We explore the redshift evolution of the dynamical properties of massive clusters and their brightest cluster galaxies (BCGs) at $z < 2$ based on the IllustrisTNG-300 simulation. We select 270 massive clusters with $M_{200} < 10^{14}~{\rm M}_{\odot}$ at $z = 0$ and trace their progenitors based on merger trees. From 67 redshift snapshots covering $z < 2$, we compute the 3D subhalo velocity dispersion as a cluster velocity dispersion ($σ_{\rm cl}$). We also calculate the 3D stellar velocity dispersion of the BCGs ($σ_{\rm *,~BCG}$). Both $σ_{\rm cl}$ and $σ_{\rm *,~BCG}$ increase as universe ag…
We present N-body simulations of star clusters that initially evolve within a strong compressive tidal field and then transition into extensive tidal fields of varying strengths. While subject to compressive tides, clusters can undergo significant heating due to two-body interactions and mass loss due to stellar evolution. When the cluster transitions into an extensive tidal field it is super-virialized, which leads to a rapid expansion and significant mass loss before the cluster reaches virial equilibrium. After the transition, clusters are significantly less massive, more extended and there…
