arXiv subjects

A. Klypin

Publications and source records attributed to A. Klypin.

40 records · Page 3Linked to original sources

arXiv1994

Sizes of Voids as a test for Dark Matter Models

We use the void probability statistics to study the redshift-space galaxy distribution as described by a volume-limited subsample of the Perseus-Pisces survey. We compare the results with the same analysis realized on artificial samples, extracted from high-resolution N-body simulations by reproducing the observational biases of the real data set. Simulations are run for the Cold+HotDM model (CHDM) and for unbiased and biased (b=1.5) CDM models in a 50 Mpc/h box. We identify galaxies as residing in peaks of the evolved density field. We fragment overmerged structures into individual galaxies so as to reproduce both the correct luminosity function (after assuming M/ L values for the resulting galaxy groups) and the two-point correlation function. Our main result is that a void-probability function (VPF) from the standard CHDM model with fractions 60% cold, 30% hot, 10% barions, exceeds the observational VPF with a high confidence level. CDM models produce smaller VPF independent of the biasing parameter. We verify the robustness of this result against changing the observer position in the simulations and the galaxy identification in the evolved density field.

astro-ph↗

arXiv1994

The Angular Correlation Function of Galaxies in CDM and CHDM Models

We estimate the angular correlation function for the standard CDM, tilted $n=0.7$ CDM and hybrid (CHDM) models, and compare with observations. When compared with the APM observational results scaled to the Lick depth, there appears to be fair agreement with the estimate from the CHDM model. But a more detailed comparison using the unscaled APM data for the five magnitude slices with $Δb_j=0.5$ shows that, in fact, none of the models can actually fit w(theta) for all the slices simultaneously. As $n=0.7$ tilted CDM and SCDM bracket all possible tilted models, we conclude that none of the tilted models is consistent with the APM results. With CHDM, a \wtheta amplitude that is 30\%--40\% too high on scales $θ< 0.°5$ is predicted for the deepest slices ($b_j\approx 20$). We find that no reasonable simple variation of the parameters for the luminosity function or for the evolution of the correlation function with redshift could change the situation. Thus, the discrepancy between the APM data and the CHDM model, though small, seems to be real.

astro-ph↗

arXiv1994

Deviations from Hierarchical Clustering in Real and Redshift Space

We discuss the effects of redshift--space distortions on the estimate of high order galaxy correlation functions. We use both the Perseus--Pisces redshift survey and the results of high--resolution N--body simulations to explore the consequences of working in redshift space on the detection of deviations from hierarchical clustering. Both for real and simulated data, significant deviations from hierarchical clustering seem to be present in real space. Their behaviour is coherent with that expected from an initially biased galaxy field, once the displacement from the sites where galaxies formed, due to the nonlinear gravitational evolution, is taken into account. The passage to redshift space has the net effect of filtering out the higher powers required to fit the distribution in real space. This magnifies the distortions operated by nonlinear evolution on the initial distribution, erasing the residual narrow scale range (2--5~$h^{-1}$Mpc) where deviations from hierarchical clustering are still detectable in real space. We conclude that such deviations can hardly be estimated using data in redshift space.

astro-ph↗

arXiv1993

Non-Linear Clustering in the Cold+Hot Dark Matter Model

We use high resolution PM N-body simulations to follow the development of non-linear clustering in a flat Universe, dominated by Cold + Hot Dark Matter (CHDM) with 60% of CDM, 30% of HDM and 10% of baryons; a simulation box of 100 Mpc a side ($h=0.5$) is used. We analyze two CHDM simulations with $b =1.5$ (COBE normalization). We also compare them with CDM simulations with $b=1.5$ and $b=1$. We evaluate high-order correlation functions and the void-probability-function (VPF). Correlation functions are obtained both from counts in cells and counts of neighbors. The analysis is made for DM particles and for galaxies, identified as massive halos in the evolved density field. We also check the effects of dynamical evolution and redshift space distortions. We find that clustering of DM particles exhibits deviations from the hierarchical scaling, which decrease somewhat in redshift space. Galaxies follow hierarchical scaling far more closely, with coefficients S_3=2.5 and S_4=7.5, in general agreement with observational results, just marginally affected by redshift distortions and on the choices for the initial spectra. The hierarchical scaling of galaxy clustering is confirmed by the VPF analysis and in all the cases considered a good agreement with observational results is obtained.

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