arXiv subjects

Yipeng Jing

Publications and source records attributed to Yipeng Jing.

94 records · Page 6Linked to original sources

arXiv2005

An Analytic Model for the Axis-Ratio Distribution of Dark Matter Halos from the Primordial Gaussian Density Field

We present an analytic expression for the axis ratio distribution of triaxial dark matter halos driven from physical principles. Adopting the picture of triaxial collapse based on the Zel'dovich approximation, we derive analytically both the minor-to-major and the conditional intermediate-to-major axis ratio distributions, and examine how they depend on the halo mass, redshift, and cosmology. Our analytic model is tested against the simulation data given by Jing & Suto in 2002, and found to reproduce the conditional intermediate-to-major axis ratio distribution successfully and the minor-to-major axis ratio distribution approximately. However, the trends of our analytic axis-ratio distributions with mass and redshift are opposite to what is found in N-body simulations. This failure of our analytic model puts a limitation on analytic approaches based on the Lagrangian theory to the halo ellipticity. Given the overall agreement with the simulation results, our model provides a new theoretical step toward using the axis-ratio distribution of dark halos as a cosmological probe. We also discuss several possibilities to improve the model.

astro-ph↗

arXiv2004

An Analysis of the Large Scale N-body Simulation using the Minkowski Functionals

We analyze the Minkowski functionals with a large $N$-body simulation of a standard $Λ$CDM model, focusing on transition scales between linear and non-linear gravitational evolution. We numerically calculate the Minkowski functionals with sufficient accuracies to investigate the transition scales, 10--$50\himpc$. The results are compared with analytic formulae of linear and second-order perturbation theories. We first show that the skewness parameters of the density fluctuations, which are important in second-order analytic formulae of the Minkowski functionals, are in good agreement with the perturbation theory. Considering relative differences between the Minkowski functionals of the analytic formulae and that of the simulation data, we evaluate accuracy levels of the predictions of the perturbation theory. When the straightforward threshold $ν$ by density value is used in Minkowski functionals, the accuracy of the second-order perturbation theory is within 10% for smoothing length $R > 15\himpc$, and within a several % for $R > 20\himpc$. The accuracies of the linear theory are 2--5 times worse than that. When the rescaled threshold by volume fraction, $ν_{\rm f}$ is used, accuracies of both linear and second-order theories are within a few % on all scales of $10\himpc < R < 50\himpc$.

astro-ph↗

arXiv2003

Hydrogen Clouds before Reionization: a Lognormal Model Approach

We study the baryonic gas clouds (the IGM) in the universe before the reionization with the lognormal model which is shown to be dynamcially legitimate in describing the fluctuation evolution in quasilinear as well as nonlinear regimes in recent years. The probability distribution function of the mass field in the LN model is long tailed and so plays an important role in rare events, such as the formation of the first generation of baryonic objects. We calculate density and velocity distributions of the IGM at very high spatial resolutions, and simulate the distributions at resolution of 0.15 kpc from z=7 to 15 in the LCDM cosmological model. We performed a statistics of the hydrogen clouds including column densities, clumping factors, sizes, masses, and spatial number density etc. One of our goals is to identify which hydrogen clouds are going to collapse. By inspecting the mass density profile and the velocity profile of clouds, we found that the velocity outflow significantly postpones the collapsing process in less massive clouds, in spite of their masses are larger than the Jeans mass. Consequently, only massive (> 10^5 M_sun) clouds can form objects at higher redshift, and less massive (10^4-10^5) collapsed objects are formed later. For example, although the mass fraction in clouds with sizes larger than the Jeans length is already larger than 1 at z=15, there is only a tiny fraction of mass (10^{-8}) in the clouds which are collapsed at that time. If all the ionizing photons, and the 10^{-2} metallicity observed at low redshift are produced by the first 1% mass of collapsed baryonic clouds, the majority of those first generation objects would not happen until z=10.

astro-ph↗

arXiv2002

The Growth and Structure of Dark Matter Haloes

In this paper, we analyse in detail the mass-accretion histories and structural properties of dark haloes in high-resolution N-body simulations. Modeling the density distribution in individual haloes with the NFW profile, we find, for all main progenitors of a given halo, there is a tight correlation between its inner scale radius $r_s$ and the mass within it, $M_s$, which is the basic reason why halo structural properties are closely related to their mass-accretion histories. This correlation can be used to predict accurately the structural properties of a dark halo at any time from its mass-accretion history. We also test our model with a large sample of GIF haloes. The build-up of dark haloes in CDM models generally consists of an early phase of fast accretion and a late phase of slow accretion [where $M_h$ increases with time approximately as the expansion rate]. These two phases are separated at a time when the halo concentration parameter $c\sim 4$. Haloes in the two accretion phases show systematically different properties, for example, the circular velocity $v_h$ increases rapidly with time in the fast accretion phase but remain almost constant in the slow accretion phase,the inner properties of a halo, such as $r_s$ and $M_s$ increase rapidly with time in the fast accretion phase but change only slowly in the slow accretion phase. The potential well associated with a halo is built up mainly in the fast accretion phase, even though a large amount of mass (over 10 times) can be accreted in the slow accretion phase. We discuss our results in connection to the formation of dark haloes and galaxies in hierarchical models.

astro-ph↗