arXiv subjects

Y. P. Jing

Publications and source records attributed to Y. P. Jing.

At least 127 records · Page 7Linked to original sources

arXiv2003

Spatial and Dynamical Biases in Velocity Statistics of Galaxies

We present velocity statistics of galaxies and their biases inferred from the statistics of the underlying dark matter using a cosmological hydrodynamic simulation of galaxy formation in low-density and spatially flat cold dark matter cosmogony. We find that the pairwise velocity dispersion (PVD) of all galaxies is significantly lower than that of the dark matter particles, and that the PVD of the young galaxies is lower than that of the old types, and even of all galaxies together, especially at small separations. These results are in reasonable agreement with the recent measurements of PVDs in the Las Campanas redshift survey, the PSCz catalogue and the SDSS data. We also find that the low PVD of young galaxies is due to the effects of dynamical friction as well as the different spatial distribution. We also consider the mean infall velocity and the POTENT density reconstruction that are often used to measure the cosmological parameters, and investigate the effects of spatial bias and dynamical friction. In our simulation, the mean infall velocity of young galaxies is significantly lower than that of all the galaxies or of the old galaxies, and the dynamical bias becomes important on scales less than 3Mpc/h. The mass density field reconstructed from the velocity field of young galaxies using the POTENT-style method suffers in accuracy both from the spatial bias and the dynamical friction on the smoothing scale of R_s=8Mpc/h. On the other hand, in the case of R_s=12Mpc/h, which is typically adopted in the actual POTENT analysis, the density reconstruction based on various tracers of galaxies is reasonably accurate.

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arXiv2002

Triaxial Modeling of Halo Density Profiles with High-resolution N-body Simulations

We present a detailed non-spherical modeling of dark matter halos on the basis of a combined analysis of the high-resolution halo simulations (12 halos with $N\sim 10^6$ particles within their virial radius) and the large cosmological simulations (5 realizations with $N=512^3$ particles in a $100h^{-1}$Mpc boxsize). The density profiles of those simulated halos are well approximated by a sequence of the concentric triaxial distribution with their axis directions being fairly aligned. We characterize the triaxial model quantitatively by generalizing the universal density profile which has previously been discussed only in the framework of the spherical model. We obtain a series of practically useful fitting formulae in applying the triaxial model; the mass and redshift dependence of the axis ratio, the mean of the concentration parameter, and the probability distribution functions of the the axis ratio and the concentration parameter. These accurate fitting formulae form a complete description of the triaxial density profiles of halos in Cold Dark Matter models. Our current description of the dark halos will be particularly useful in predicting a variety of nonsphericity effects, to a reasonably reliable degree, including the weak and strong lens statistics, the orbital evolution of galactic satellites and triaxiality of galactic halos, and the non-linear clustering of dark matter. In addition, this provides a useful framework for the non-spherical modeling of the intra-cluster gas, which is crucial in discussing the gas and temperature profiles of X-ray clusters and the Hubble constant estimated via the Sunyaev -- Zel'dovich effect.

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arXiv2002

Pairwise velocity dispersion of galaxies at high redshift: theoretical predictions

We investigate the feasibility of determining the pairwise velocity dispersion (PVD) for Lyman Break Galaxies (LBGs), and of using this quantity as a discriminator among theoretical models. We find that when the Two Point Correlation Function over the range of observable separations is fixed, different schemes of galaxy formation will lead to significant changes in PVD, while influence of different cosmogonies is invisible. Our test with mock samples shows furthermore that one can discriminate among such models already with currently available observational samples (if the measurement error of the redshift is negligible) which have a typical error of $80\kms$. The error will be reduced by a factor of 2 if the samples are increased four times. We also show that an erroneous assumption about the geometry of the universe and different infall models only slightly change the results. Therefore the PVD will become another promising statistic to test galaxy formation models with redshift samples of LBGs.

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arXiv2002

Intrinsic correlation of halo ellipticity and its implications for large-scale weak lensing surveys

We use a large set of state-of-the-art cosmological N-body simulations [512^3 particles] to study the intrinsic ellipticity correlation functions of halos. With the simulations of different resolutions, we find that the ellipticity correlations converge once the halos have more than 160 members. For halos with fewer members, the correlations are underestimated, and the underestimation amounts to a factor of 2 when the halos have only 20 particles. After correcting for the resolution effects, we show that the ellipticity correlations of halos in the bigger box (L=300 mpc) agree very well with those obtained in the smaller box (L=100 mpc). Combining these results from the different simulation boxes, we present accurate fitting formulae for the ellipticity correlation function c_{11}(r) and for the projected correlation functions Sigma_{11}(r_p) and Sigma_{22}(r_p) over three orders of magnitude in halo mass. The latter two functions are useful for predicting the contribution of the intrinsic correlations to deep lensing surveys. With reasonable assumptions for the redshift distribution of galaxies and for the mass of galaxies, we find that the intrinsic ellipticity correlation can contribute significantly not only to shallow surveys but also to deep surveys. Our results indicate that previous similar studies significantly underestimated this contribution for their limited simulation resolutions.

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arXiv2002

An analytical model for the non-linear redshift-space power spectrum

We use N-body simulations to test the predictions of the redshift distortion in the power spectrum given by the halo model in which the clustering of dark matter particles is considered as a result both of the clustering of dark halos in space and of the distribution of dark matter particles in individual dark halo. The predicted redshift distortion depends sensitively on several model parameters in a way different from the real-space power spectrum. An accurate model of the redshift distortion can be constructed if the following properties of the halo population are modelled accurately: the mass function of dark halos, the velocity dispersion among dark halos, and the non-linear nature of halo bias on small scales. The model can be readily applied to interpreting the clustering properties and velocity dispersion of different populations of galaxies once a cluster-weighted bias (or equivalently an halo occupation number model) is specified for the galaxies. Some non-trivial bias features observed from redshift surveys of optical galaxies and of IRAS galaxies relative to the standard low-density cold dark matter model can be easily explained in the cluster weighted bias model. The halo model further indicates that a linear bias can be a good approximation only on for k <= 0.1 hMpc^{-1}.

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arXiv2002

The Angular Momentum Distribution within Halos in Different Dark Matter Models

We study the angular momentum profile of dark matter halos for a statistical sample drawn from a set of high-resolution cosmological simulations of $256^3$ particles. Two typical Cold Dark Matter (CDM) models have been analyzed, and the halos are selected to have at least $3\times 10^4$ particles in order to reliably measure the angular momentum profile. In contrast with the recent claims of Bullock et al., we find that the degree of misalignment of angular momentum within a halo is very high. About 50 percent of halos have more than 10 percent of halo mass in the mass of negative angular momentum $j$. After the mass of negative $j$ is excluded, the cumulative mass function $M(<j)$ follows approximately the universal function proposed by Bullock et al., though we still find a significant fraction of halos ($\sim 50%$) which exhibit systematic deviations from the universal function. Our results, however, are broadly in good agreement with a recent work of van den Bosch et al.. We also study the angular momentum profile of halos in a Warm Dark Matter (WDM) model and a Self-Interacting Dark Matter (SIDM) model. We find that the angular momentum profile of halos in the WDM is statistically indistinguishable from that in the CDM model, but the angular momentum of halos in the SIDM is reduced by the self-interaction of dark matter.

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arXiv2002

Slow relative motion of IRAS galaxies at small separations: implications for galaxy formation models

We report on the measurement of the two-point correlation function and the pairwise peculiar velocity of galaxies in the IRAS PSCz survey. The real space two-point correlation function can be fitted to a power law $ξ(r) = (r_0/r)^γ$ with $γ=1.69$ and $r_0=3.70 \mpc$. The pairwise peculiar velocity dispersion $σ_{12}(r_p)$ is close to $400 \kms$ at $r_p=3\mpc$ and decreases to about $150 \kms$ at $r_p \approx 0.2 \mpc$. These values are significantly lower than those obtained from the Las Campanas Redshift Survey, but agree very well with the results of blue galaxies reported by the SDSS team later on. We have constructed mock samples from N-body simulations with a cluster-weighted bias and from the theoretically constructed GIF catalog. We find that the two-point correlation function of the mock galaxies can be brought into agreemnt with the observed result, but the model does not reduce the velocity dispersions of galaxies to the level measured in the PSCz data. Thus we conclude that the peculiar velocity dispersions of the PSCz galaxies require a biasing model which substantially reduces the peculiar velocity dispersion on small scales relative to their spatial clustering. The results imply that either the cosmogony model needs to be revised or the velocity bias is important for the velocity dispersion of the IRAS galaxies.

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arXiv2002

High-resolution numerical simulations for galaxy formation

Understanding of the structure evolution in the Universe has been greatly advanced with a rapid progress in high-resolution cosmological simulations. In this contribution, we report a new set of cosmological simulations with $512^3$ ($\sim 1.4\times 10^8$) particles in a simulation box of $100\mpc$. With this unprecedented resolution, we have successfully overcomed the over-merging problem while retaining a cosmological volume size that is crucial for the statistical analysis. The simulations are being applied to studying important astrophysical problems that are sensitive to the simulation resolution.

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arXiv2002

Warm Dark Matter Model of Galaxy Formation

Cold Dark Matter (CDM) models of galaxy formation had been remarkably successful to explain a number of observations in the past decade. However, with both the theoretical modeling and the observations being improved, CDM models have been very recently shown to have excessive clustering on the sub-galactic scale. Here I discuss a solution, based on our high-resolution numerical simulations, to this outstanding problem by considering Warm Dark Matter (WDM). Our results show that the over-clustering problem on sub-galactic scales can be overcome by WDM models, and all the advantages of CDM models are preserved by WDM models. Therefore, the WDM model will become an interesting alternative to the well-studied CDM models.

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arXiv2001

Spatial correlation functions and the pairwise peculiar velocity dispersion of galaxies in the PSCz survey: implications for the galaxy biasing in cold dark matter models

We report on the measurement of the two-point correlation function, and the pairwise peculiar velocity of galaxies in the IRAS PSCz survey. We compute these statistics first in redshift space, and then obtain the projected functions which have simple relations to the real-space correlation functions on the basis of the method developed earlier in analyzing the Las Campanas Redshift Survey (LCRS) by Jing, Mo, & Börner (1998). We find that the real space two-point correlation function can be fitted to a power law $ξ(r) = (r_0/r)^γ$ with $γ=1.69$ and $r_0=3.70 \mpc$. The pairwise peculiar velocity dispersion $σ_{12}(r_p)$ is close to $400 \kms$ at $r_p=3\mpc$ and decreases to about $150 \kms$ at $r_p \approx 0.2 \mpc$. These values are significantly lower than those obtained from the LCRS. In order to understand the implications of those measurements on the galaxy biasing, we construct mock samples for a low density spatially-flat cold dark matter model ($Ω_0 = 0.3$, $λ_0=0.7$, $Γ=0.2$, $σ_8=1$) using a set of high-resolution N-body simulations. Applying a stronger cluster-underweight biasing ($\propto M^{-0.25}$) than for the LCRS ($\propto M^{-0.08}$), we are able to reproduce these observational data, except for the strong decrease of the pairwise peculiar velocity at small separations. This is qualitatively ascribed to the different morphological mixture of galaxies in the two catalogues. Disk-dominated galaxy samples drawn from the theoretically constructed GIF catalog yield results rather similar to our mock samples with the simple cluster-underweight biasing.

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arXiv2001

The Fundamental Plane of Spiral Galaxies: Search from Observational Data

The fundamental plane of spiral galaxies was searched from observational data, which can be approximately represented in observational parameters by $ L \propto V^2 R $, where $L$, $R$, and $V$ are the luminosity, the linear size of galactic disk, and the rotation velocity. This plane exists at all optical bands in our samples of more than 500 spiral galaxies in total. It is more fundamental than the relationship between any two of the parameters, and can reduce the residual of the Tully--Fisher $L$--$V$ relations by about 50\%. Noticed that the power index of $V$ is doubled from that of $R$, which implies that the total mass and the mass distribution of galaxies plays an important role in forming the fundamental plane. Involving the third parameter of galactic size has a strong physical implication on galaxy formation and the dark--mass distribution.

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arXiv2001

Nonlinear Stochastic Biasing of Galaxies and Dark Halos in Cosmological Hydrodynamic Simulations

We perform an extensive analysis of nonlinear and stochastic biasing of galaxies and dark halos in spatially flat low-density CDM universe using cosmological hydrodynamic simulations. We compare their biasing properties with the predictions of an analytic halo biasing model. Dark halos in our simulations exhibit reasonable agreement with the predictions only on scales larger than 10h^{-1}Mpc, and on smaller scales the volume exclusion effect of halos due to their finite size becomes substantial. Interestingly the biasing properties of galaxies are better described by extrapolating the halo biasing model predictions. We also find the clear dependence of galaxy biasing on their formation epoch; the distribution of old populations of galaxies tightly correlates with the underlying mass density field, while that of young populations is slightly more stochastic and anti-biased relative to dark matter. The amplitude of two-point correlation function of old populations is about 3 times larger than that of the young populations. Furthermore, the old population of galaxies reside within massive dark halos while the young galaxies are preferentially formed in smaller dark halos. Assuming that the observed early and late-type galaxies correspond to the simulated old and young populations of galaxies, respectively, all of these segregations of galaxies are consistent with observational ones for the early and late-type of galaxies such as the morphology--density relation of galaxies.

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arXiv2001

Implication of Omega_m through the Morphological Analysis of Weak Lensing Fields

We apply the morphological descriptions of two-dimensional contour map, the so-called Minkowski functionals (the area fraction, circumference, and Euler characteristics), to the convergence field $κ(\bmθ)$ of the large-scale structure reconstructed from the shear map produced by the ray-tracing simulations. The perturbation theory of structure formation has suggested that the non-Gaussian features on the Minkowski functionals with respect to the threshold in the weakly nonlinear regime are induced by the three skewness parameters of $κ$ that are sensitive to the density parameter of matter, $Ω_{\rm m}$. We show that, in the absence of noise due to the intrinsic ellipticities of source galaxies with which the perturbation theory results can be recovered, the accuracy of $Ω_{\rm m}$ determination is improved by $\sim 20%$ using the Minkowski functionals compared to the conventional method of using the direct measure of skewness.

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arXiv2001

The Scaling of the Redshift Power Spectrum: Observations from the Las Campanas Redshift Survey

In a recent paper we have studied the redshift power spectrum $P^S(k,μ)$ in three CDM models with the help of high resolution simulations. Here we apply the method to the largest available redshift survey, the Las Campanas Redshift Survey (LCRS). The basic model is to express $P^S(k,μ)$ as a product of three factors P^S(k,μ)=P^R(k)(1+βμ^2)^2 D(k,μ). Here $μ$ is the cosine of the angle between the wave vector and the line of sight. The damping function $D$ for the range of scales accessible to an accurate analysis of the LCRS is well approximated by the Lorentz factor D=[1+{1\over 2}(kμσ_{12})^2]^{-1}. We have investigated different values for $β$ ($β=0.4$, 0.5, 0.6), and measured $P^R(k)$ and $σ_{12}(k)$ from $P^S(k,μ)$ for different values of $μ$. The velocity dispersion $σ_{12}(k)$ is nearly a constant from $k=0.5$ to 3 $\mpci$. The average value for this range is $510\pm 70 \kms$. The power spectrum $P^R(k)$ decreases with $k$ approximately with $k^{-1.7}$ for $k$ between 0.1 and 4 $\mpci$. The statistical significance of the results, and the error bars, are found with the help of mock samples constructed from a large set of high resolution simulations. A flat, low-density ($Ω_0=0.2$) CDM model can give a good fit to the data, if a scale-dependent special bias scheme is used which we have called the cluster-under-weighted bias (Jing et al.).

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arXiv2001

A new test for the stable clustering hypothesis

The stable clustering hypothesis is a fundamental assumption about the nonlinear clustering of matter in cosmology. It states that the mean physical separation of particles is a constant on sufficiently small scales. While many authors have attempted to test the hypothesis with cosmological N-body simulations, no consensus has been reached on whether and where the hypothesis is valid, because of the limited dynamical range this type of simulations can achieve. In this Letter, we propose to test the hypothesis with high resolution halo simulations, since the individual halo simulations can resolve much better the fine structures of the halos and since almost all pairs of particles with small separations are presumed to be inside virialized halos. We calculated the mean pair velocity for 14 high resolution halos of $\sim 1$ million particles in a low-density flat cold dark matter model. The result agrees very well with the stable clustering prediction within the measurement uncertainty $\sim 30%$ over a large range of scales where the overdensity is $10^3$ to $10^6$. The accuracy of the test can be improved to $\sim 10%$ if some 100 halos with a similar resolution are analyzed.

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arXiv2000

Nonlinear Stochastic Biasing of Peaks and Halos: Scale-Dependence, Time-Evolution, and Redshift-Space Distortion from Cosmological N-body Simulations

We quantify the degree of nonlinearity and stochasticity of the clustering of biased objects, using cosmological N-body simulations. Adopting the peaks and the halos as representative biasing models, we focus on the two-point correlation of the biased objects, dark matter and their cross-correlation. Especially, we take account of the effect of redshift-space distortion and attempt to clarify the scale-dependence and the time-dependence by analyzing the biasing factor and the cross-correlation factor. On small scales, stochasticity and nonlinearity become appreciable and strongly object-dependent, especially in redshift space due to the pair-wise velocity dispersion of the biased objects. Nevertheless, an approximation of deterministic linear biasing $δ_{\rm obj}\simeq b_{\rm obj} δ_{\rm mass}$ works reasonably well even in the quasi-linear regime $r > 10 h^{-1}$ Mpc, and linear redshift-space distortion explains the clustering amplitudes in redshift space in this regime.

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arXiv2000

Scaling properties of the redshift power spectrum: theoretical models

We report the results of an analysis of the redshift power spectrum $P^S(k,μ)$ in three typical Cold Dark Matter (CDM) cosmological models, where $μ$ is the cosine of the angle between the wave vector and the line-of-sight. Two distinct biased tracers derived from the primordial density peaks of Bardeen et al. and the cluster-underweight model of Jing, Mo, & Börner are considered in addition to the pure dark matter models. Based on a large set of high resolution simulations, we have measured the redshift power spectrum for the three tracers from the linear to the nonlinear regime. We investigate the validity of the relation - guessed from linear theory - in the nonlinear regime $$ P^S(k,μ)=P^R(k)[1+βμ^2]^2D(k,μ,σ_{12}(k)), $$ where $P^R(k)$ is the real space power spectrum, and $β$ equals $Ω_0^{0.6}/b_l$. The damping function $D$ which should generally depend on $k$, $μ$, and $σ_{12}(k)$, is found to be a function of only one variable $kμσ_{12}(k)$. This scaling behavior extends into the nonlinear regime, while $D$ can be accurately expressed as a Lorentz function - well known from linear theory - for values $D > 0.1$. The difference between $σ_{12}(k)$ and the pairwise velocity dispersion defined by the 3-D peculiar velocity of the simulations (taking $r=1/k$) is about 15%. Therefore $σ_{12}(k)$ is a good indicator of the pairwise velocity dispersion. The exact functional form of $D$ depends on the cosmological model and on the bias scheme. We have given an accurate fitting formula for the functional form of $D$ for the models studied.

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arXiv2000

Dark Matter Halos Simulated with Million Particles

We report a series of high-resolution N-body simulations designed to examine the internal physical properties of dark matter halos. A total of fifteen halos, each represented by $\sim 1$ million particles within the virial radius, have been simulated covering the mass range of $2\times10^{12}\sim 5\times10^{14} h^{-1}{\rm M_\odot}$. As the first application of these simulations, we have examined the density profiles of the halos. We found a clear systematic correlation between the halo mass and the slope of the density profile at one percent of the virial radius, in addition to the variations of the slope among halos of the similar mass. More specifically, the slope is $\sim - 1.5$, -1.3, and -1.1 for galaxy, group, and cluster mass halos, respectively. Thus we conclude that the dark matter density profiles, especially in the inner region, are not universal.

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