We present a combined radio, X-ray and optical study of the galaxy cluster RXCJ2003.5-2323. The cluster hosts one of the largest, most powerful and distant giant radio halos known to date, suggesting that it may be undergoing a strong merger process. The aim of our multiwavelength study is to investigate the radio-halo cluster merger scenario. We studied the radio properties of the giant radio halo in RXCJ2003.5-2323 by means of new radio data obtained at 1.4 GHz with the Very Large Array, and at 240 MHz with the Giant Metrewave Radio Telescope, in combination with previously published GMRT data at 610 MHz. The dynamical state of the cluster was investigated by means of X-ray Chandra observations and optical ESO--NTT observations. Our study confirms that RXCJ2003.5-2323 is an unrelaxed cluster. The unusual filamentary and clumpy morphology of the radio halo could be due to a combination of the filamentary structure of the magnetic field and turbulence in the inital stage of a cluster merger.
We employ a set of high resolution N-body simulations to study the merger rate of dark matter halos. We define a specific merger rate by normalizing the average number of mergers per halo with the logarithmic mass growth change of the hosts at the time of accretion. Based on the simulation results, we find that this specific merger rate, $\mathrm{d}N_{\mathrm{merge}}(ξ|M,z)/\mathrm{d}ξ/\mathrm{d}\log M(z)$, has a universal form, which is only a function of the mass ratio of merging halo pairs, $ξ$, and does not depend on the host halo mass, $M$, or redshift, $z$, over a wide range of masses ($…
Tracking the formation and evolution of dark matter haloes is a critical aspect of any analysis of cosmological $N$-body simulations. In particular, the mass assembly of a halo and its progenitors, encapsulated in the form of its merger tree, serves as a fundamental input for constructing semi-analytic models of galaxy formation and, more generally, for building mock catalogues that emulate galaxy surveys. We present an algorithm for constructing halo merger trees from AbacusSummit, the largest suite of cosmological $N$-body simulations performed to date consisting of nearly 60 trillion partic…
Virtually any investigation involving dark matter halos relies on a definition of their radius, mass, and of whether they are a subhalo. The halo boundary is most commonly defined to include a spherical overdensity contrast (such as R200c, Rvir, and R200m), but different thresholds lead to significant differences in radius and mass. The splashback radius has recently been suggested as a more physically motivated (and generally larger) halo boundary, adding to the range of definitions. It is often difficult to assess the impact of a particular choice because most halo catalogs contain only one …
We study the merger rate of primordial black holes (PBHs) in self-interacting dark matter (SIDM) halo models. To explore a numerical description for the density profile of SIDM halo models, we use the result of a previously performed simulation for SIDM halo models with $σ/m=10~{\rm cm^{2}g^{-1}}$. We also propose a concentration-mass-time relation that can explain the evolution of the halo density profile related to SIDM models. Furthermore, we investigate the encounter condition of PBHs that may have been randomly distributed in the medium of dark matter halos. Under these assumptions, we ca…
The concentration parameter is a key characteristic of a dark matter halo that conveniently connects the halo's present-day structure with its assembly history. Using 'Dark Sky', a suite of cosmological $N$-body simulations, we investigate how halo concentration evolves with time and emerges from the mass assembly history. We also explore the origin of the scatter in the relation between concentration and assembly history. We show that the evolution of halo concentration has two primary modes: (1) smooth increase due to pseudo-evolution; and (2) intense responses to physical merger events. Mer…
We have studied the merger rate of primordial black holes (PBHs) in the ellipsoidal-collapse model of halo to explain the dark matter abundance by the PBH merger estimated from the gravitational waves detections via the Advanced LIGO (aLIGO) detectors. We have indicated that the PBH merger rate within each halo for the ellipsoidal models is more significant than for the spherical models. We have specified that the PBH merger rate per unit time and per unit volume for the ellipsoidal-collapse halo models is about one order of magnitude higher than the corresponding spherical models. Moreover, w…
Cosmological N-body simulations rank among the most computationally intensive efforts today. A key challenge is the analysis of structure, substructure, and the merger history for many billions of compact particle clusters, called halos. Effectively representing the merging history of halos is essential for many galaxy formation models used to generate synthetic sky catalogs, an important application of modern cosmological simulations. Generating realistic mock catalogs requires computing the halo formation history from simulations with large volumes and billions of halos over many time steps,…
The structural properties of individual dark matter haloes, including shape, spin, concentration, and substructure, are linked to the halo's growth history, but the exact connection between the two is unclear. One open question, in particular, is the effect of major mergers on halo structure. We have performed a large set of simulations of binary equal-mass mergers between isolated haloes with various density profiles, to map out the relationship between the initial conditions and merger parameters and the structure of the final remnant. In this paper we describe our initial set-up and analysi…
In this work, we study the effect of a high-precision semianalytical mass function on the merger rate of primordial black holes (PBHs) in dark matter halos. For this purpose, we first explain a theoretical framework for dark matter halo models and introduce relevant quantities such as halo density profile, concentration parameter, and a high-precision semianalytical function namely Del Popolo (DP) mass function. In the following, we calculate the merger rate of PBHs in the framework of ellipsoidal-collapse dark matter halo models while considering the DP mass function, and compare it with our …
We introduce and apply a new approach to probe the response of galactic stellar haloes to the interplay between cosmological merger histories and galaxy formation physics. We perform dark matter-only, zoomed simulations of two Milky Way-mass hosts and make targeted, controlled changes to their cosmological histories using the genetic modification technique. Populating each history's stellar halo with a semi-empirical, particle tagging approach then enables a controlled study, with all instances converging to the same large-scale structure, dynamical and stellar mass at $z=0$ as their reference…
Numerical simulations have shown that massive dark matter haloes, which today host galaxy clusters, assemble their mass over time alternating periods of quiescent accretion and phases of rapid growth associated with major merger episodes. Observations of such events in clusters can provide insights on the astrophysical processes that characterise the properties of the intra-cluster medium, as well as the gravitational processes that contribute to their assembly. It is therefore of prime interest to devise a fast and reliable way of detecting such perturbed systems. We present a novel approach …
Primordial black holes (PBHs), as a potential macroscopic candidate for dark matter, can encounter other compact objects in dark matter halos because of their random distribution. Besides, the detection of gravitational waves (GWs) related to the stellar-mass black hole-neutron star (BH-NS) mergers raises the possibility that the BHs involved in such events may have a primordial origin. In this work, we calculate the merger rate of PBH-NS binaries within the framework of ellipsoidal-collapse dark matter halo models and compare it with the corresponding results derived from spherical-collapse d…
Universidad Autónoma de Madrid（马德里自治大学）；The University of Melbourne（墨尔本大学）；Pontificia Universidad Católica de Chile（智利天主教大学）；University of Campinas（坎皮纳斯大学）；Universidad Diego Portales（迭戈·波塔莱斯大学）
Semi-analytic models are best suited to compare galaxy formation and evolution theories with observations. These models rely heavily on halo merger trees, and their realistic features (i.e., no drastic changes on halo mass or jumps on physical locations). Our aim is to provide a new framework for halo merger tree generation that takes advantage of the results of large volume simulations, with a modest computational cost. We treat halo merger tree construction as a matrix generation problem, and propose a Generative Adversarial Network that learns to generate realistic halo merger trees. We eva…
Halo Occupation Distributions of Moderate X-ray AGNs through Major and Minor Mergers in a $Λ$-CDM Cosmology
受Allevato et al.（2012）在COSMOS领域中最近推断的X射线选定活动星系核晕占据分布（HOD）形式的启发，我们使用一个基于$Λ$ -CDM宇宙学中暗物质晕（DMH）之间合并活动的简单模型，研究了中等亮度X射线活动星系核（mXAGN）的HOD性质。在上述情况下，在$z=0.5$模拟的mXAGN的HOD和数密度与Allevato等人（2012）的结果进行比较。我们发现，模拟的HOD的主要和次要合并，和观察到的mXAGN是一致的。我们的主要结果是，未成年人合并，相反，人们可能会期望，可以发挥重要作用的活动mAGN。
The First Systematic Survey of Stellar Halos in High-Inclination Galaxies Reveals Unusually Quiescent Merger Histories of Nearby Galaxies
University of Science and Technology of China（中国科学技术大学）；Shanghai Jiao Tong University（上海交通大学）；University of Oxford（牛津大学）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉各拉纳大学）
Mergers Matter: Gravothermal Collapse in Dwarf Halos with Self-Interacting Dark Matter
University of California, Irvine（加州大学尔湾分校）；DARK, Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所DARK）；Massachusetts Institute of Technology（麻省理工学院）；University of Washington（华盛顿大学）；Flatiron Institute（平顿研究所）；Princeton University（普林斯顿大学）；Northeastern University（东北大学）
Linking the properties of galaxies to the assembly history of their dark matter haloes is a central aim of galaxy evolution theory. This paper introduces a dimensionless parameter $s\in[0,1]$, the "tree entropy", to parametrise the geometry of a halo's entire mass assembly hierarchy, building on a generalisation of Shannon's information entropy. By construction, the minimum entropy ($s=0$) corresponds to smoothly assembled haloes without any mergers. In contrast, the highest entropy ($s=1$) represents haloes grown purely by equal-mass binary mergers. Using simulated merger trees extracted from…
We present a statistical analysis of flybys of dark matter halos compared to mergers using cosmological $N$-body simulations. We mainly focus on gravitationally interacting target halos with mass of $10^{10.8}-10^{13.0}h^{-1}M_{\odot}$, and their neighbors are counted only when the mass ratio is 1:3$-$3:1 and the distance is less than the sum of the virial radii of target and neighbor. The neighbors are divided into the flyby or merger samples if the pair's total energy is greater or smaller, respectively, than the capture criterion with consideration of dynamical friction. The main results ar…
Universidad Autónoma de Madrid（马德里自治大学）；King’s College London（伦敦国王学院）；The University of Melbourne（墨尔本大学）；Pontificia Universidad Católica de Chile（智利天主教大学）；University of Oslo（奥斯陆大学）；Universidad Diego Portales（迭戈·波塔莱斯大学）
A key ingredient for semi-analytic models (SAMs) of galaxy formation is the mass assembly history of haloes, encoded in a tree structure. The most commonly used method to construct halo merger histories is based on the outcomes of high-resolution, computationally intensive N-body simulations. We show that machine learning (ML) techniques, in particular Generative Adversarial Networks (GANs), are a promising new tool to tackle this problem with a modest computational cost and retaining the best features of merger trees from simulations. We train our GAN model with a limited sample of merger tre…
