We compute the dark matter halo mass function using the excursion set formalism for a diffusive barrier with linearly drifting average which captures the main features of the ellipsoidal collapse model. We evaluate the non-Markovian corrections due to the sharp filtering of the linear density field in real space with a path-integral method. We find an unprecedented agreement with N-body simulation data with deviations within ~5% level over the range of masses probed by the simulations. This indicates that the Excursion Set in combination with a realistic modelling of the collapse threshold can provide a robust estimation of the halo mass function.
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 ($…
The mass function of dark matter halos is one of the most fundamental statistics in structure formation. Many theoretical models (such as Press-Schechter theory) are based on the notion that it could be universal, meaning independent of redshift and cosmology, when expressed in the appropriate variables. However, simulations exhibit persistent non-universalities in the mass functions of the virial mass and other commonly used spherical overdensity definitions. We systematically study the universality of mass functions over a wide range of mass definitions, for the first time including the rece…
Universal Fitting Formulae for the Peak Concentration of Dark Matter Halos
School of Physics and Astronomy, Sun Yat-sen University（中山大学物理学院）；CSST Science Center for the Guangdong-Hongkong-Macau Greater Bay Area（中国空间站科学中心粤港澳大湾区分中心）
Magnetic fields in galaxy halos are in general very difficult to observe. Most recently, the CHANG-ES collaboration (Continuum HAlos in Nearby Galaxies - an EVLA Survey) investigated in detail the radio halos of 35 nearby edge-on spiral galaxies and detected large scale magnetic fields in 16 of them. We used the CHANG-ES radio polarization data to create Rotation Measure (RM) maps for all galaxies in the sample and stack them with the aim to amplify any underlying universal toroidal magnetic field pattern in the halo above and below the disk of the galaxy. We discovered a large-scale magnetic …
In the framework of the stochastic theory for hierarchical clustering, we investigate the time-dependent solutions of the Fokker-Planck equation describing the statistics of dark matter halos, and discuss the typical timescales needed for these to converge toward stationary states, far away enough from initial conditions. Although we show that the stationary solutions can reproduce the outcomes of state-of-the-art $N-$body simulations at $z\approx 0$ to a great accuracy, one needs to go beyond to fully account for the cosmic evolution of the simulated halo mass function toward high-redshift. S…
It is well established from cosmological simulations that dark matter haloes are not precisely self-similar and an additional parameter, beyond their concentration, is required to accurately describe their spherically-averaged mass density profiles. We present, for the first time, a model to consistently predict both halo concentration, $c$, and this additional `shape' parameter, $α$, for a halo of given mass and redshift for a specified cosmology. Following recent studies, we recast the dependency on mass, redshift, and cosmology to a dependence on `peak height'. We show that, when adopting t…
Cosmological models in which dark matter consists of cold elementary particles predict that the dark halo population should extend to masses many orders of magnitude below those at which galaxies can form. Here we report a cosmological simulation of the formation of present-day haloes over the full range of observed halo masses (20 orders of magnitude) when dark matter is assumed to be in the form of weakly interacting massive particles of mass approximately 100 gigaelectronvolts. The simulation has a full dynamic range of 30 orders of magnitude in mass and resolves the internal structure of h…
Universality of Halo Shape and its Morphological Evolution across Cosmic Time
School of Physical Sciences, National Institute of Science Education and Research（国家科学教育研究所物理科学学院）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；IISER Mohali（Mohali印度科学与教育研究院）
We examine the efficacy of the halo mass function as a probe of $f(R)$, symmetron and DGP gravity. We develop an excursion-set method to generalise a range of popular HMF fitting functions from GR to screened MG, considering the HMF dependence on the critical density parameter $δ_{c}$. In particular, we propose a variety of new methods to account for the environmental dependence of chameleon screening and compare their accuracy to existing ones via $N$-body data. Finally, using the nested sampling routine MultiNest, we examine two possible interpretations of the MG $N$-body results: whether th…
We study the halo mass function (HMF) in modified gravity (MG) models using a set of large $N$-body simulations -- the ELEPHANT suite. We consider two popular beyond-general relativity scenarios: the Hu-Sawicki chameleon $f(R)$ model and the normal branch of the Dvali-Gabadadze-Porrati braneworld (nDGP). We show that in MG, analytic formulation based on the Press-Schechter framework offers a grossly inaccurate description of the HMF. We find, however, that once the HMF is expressed in terms of the dimensionless multiplicity function, it approximately assumes a redshift-independent universal ch…
我们提出了一种新的算法，用于识别模拟暗物质晕内的子结构。该方法是Tormen等人（2004年）和Giocoli等人（2008年a）提出的方法的扩展，该方法将次晕确定为一组自结合粒子，这些粒子在被主晕的主要祖先吸积之前属于同一个祖先晕（以下称为卫星）。然而，这一定义并不占的事实，这些卫星晕本身也可能有子结构，从而产生子subhaloes等，我们的新算法确定在这个层次的所有级别的子结构，我们用它来确定所有子结构的质量函数（计数子haloes，子subhaloes等）。平均而言，最近形成的晕往往有一个较大的质量分数的子结构和集中度低于平均相同质量的晕。我们提供定量拟合这些相关性。尽管我们的算法与Gao et al.（2004）的算法有很大的不同，但我们也发现红移z = 0处单位质量的次晕质量函数是普适的。这种普遍性延伸到任何红移，只有当一个帐户的事实，即一个给定的质量的主机晕较少集中在较高的红移，和浓度和子结构丰度是反相关的。这种普遍性允许一个简单的参数化的subhalo质量函数集成在所有主机晕群众，在任何给定的时间。我们提供了分析适合这个功能，这应该是有用的晕模型分析，相当于星系晕子结构时，解释集群在大型巡天。最后，我们讨论了系统的subhalo质量函数的差异，所产生的（主机）晕质量的不同定义。
Quasinormal-mode redshifts of black holes in galactic halos with radial pressures
RIKEN iTHEMS（理化学研究所 iTHEMS）；Physics Department, California State University, Fresno（加州州立大学弗雷斯诺分校物理系）；Helsinki Institute of Physics, University of Helsinki（赫尔辛基大学赫尔辛基物理研究所）
We present a novel fitting formula for the halo concentration enhancement in chameleon $f(R)$ gravity relative to General Relativity (GR). The formula is derived by employing a large set of $N$-body simulations of the Hu-Sawicki $f(R)$ model which cover a wide range of model and cosmological parameters, resolutions and simulation box sizes. The complicated dependence of the concentration on halo mass $M$, redshift $z$, and the $f(R)$ and cosmological parameters can be combined into a simpler form that depends only on a rescaled mass $M/10^{p_2}$, with $p_2\equiv1.5\log_{10}\left[|{\bar{f}_R(z)…
Twenty three years ago, cosmological N-body simulations revealed quasi-universal NFW dark matter halos, whose physical origin is still unclear. This work tries to solve this issue by Landau-Ginzburg (LG) theory in equilibrium statistical mechanics. We replace the order parameter in LG theory by density and consider the dark matter halos as fluctuations from the equilibrium state of the background, which can be the main halos for the subhalos, or the homogeneous and isotropic Universe for the galaxy cluster halos. With the assumption that the fluctuations of Helmholtz free energy depend mainly …
We study the stacked filaments connecting group-mass halo pairs, using dark-matter-only N-body simulations. We calculate the dark matter over-density profile of these stacked filaments at different redshifts as a function of the distance perpendicular to the filament axis. A four-parameter universal functional form, including three comoving scale radii and one amplitude parameter (core density), provides a good fit out to a radius of 20 cMpc/h for stacked filaments over a range of redshifts, lengths and masses. The scale radii are approximately independent of redshift but increase as power-law…
We discover analytic equations that can infer the value of $Ω_{\rm m}$ from the positions and velocity moduli of halo and galaxy catalogues. The equations are derived by combining a tailored graph neural network (GNN) architecture with symbolic regression. We first train the GNN on dark matter halos from Gadget N-body simulations to perform field-level likelihood-free inference, and show that our model can infer $Ω_{\rm m}$ with $\sim6\%$ accuracy from halo catalogues of thousands of N-body simulations run with six different codes: Abacus, CUBEP$^3$M, Gadget, Enzo, PKDGrav3, and Ramses. By app…
