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}.Comment: 10 pages, 10 figures, accepted for publication in MNRA

The growth and structure of dark matter haloes

SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Random variations of the pulse period of X-ray binaries with wind accretion

In this paper we first summarise earlier results about the randomness of pulse period variations in wind fed X-ray pulsars. Then we present two types of models for the random spin-up and spin-down of rotating neutron stars which accrete mass from a stellar wind. We show that the irregularities in accretion flows which were discovered in numerical models have too low amplitudes in order to explain the observations. Therefore we discuss an alternative model which is based upon the existence of a Kepler disc around the neutron star. We argue that such a model can give an explanation of the observations. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Pairwise velocity dispersion of galaxies at high redshift: theoretical predictions

SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Spatial correlation function and pairwise velocity dispersion of galaxies: CDM models versus the Las Campanas Survey

We show, with the help of large N-body simulations, that the real-space two-point correlation function and pairwise velocity dispersion of galaxies can both be measured reliably from the Las Campanas Redshift Survey. The real-space correlation function is well fitted by the power law #xi#(r)=(r_0/r)&quot;#gamma# with r_0=(5.06#+-#0.12) h&quot;-&quot;1 Mpc and #gamma#=1.862#+-#0.034, and the pairwise velocity dispersion at 1 h&quot;-&quot;1 Mpc is (570#+-#80) km s&quot;-&quot;1. A detailed comparison between these observational results and the predictions of current CDM cosmogonies is carried out. We construct 60 mock samples for each theoretical model from a large set of high resolution N-body simulations, which allows us to include various observational selection effects in the analyses and to use exactly the same methods for both real and theoretical samples. We demonstrate that such a procedure is essential in the comparison between models and observations. The observed two-point correlation function is significantly flatter than the mass correlation function in current CDM models on scales &lt;or#approx#1 h&quot;-&quot;1 Mpc. The observed pairwise velocity dispersion is also lower than that of dark matter particles in these models. We propose a simple antibias model to explain these discrepancies. This model assumes that the number of galaxies per unit dark matter mass, N/M, decreases with the mass of dark haloes. The predictions of CDM models with #sigma#_8#OMEGA#_0&quot;0&quot;.&quot;6#propor to#0.4-0.5 and #GAMMA##propor to#0.2 are in agreement with the observational results, if the trend of N/M with M is at the level already observed for rich clusters of galaxies. Thus CDM models with #GAMMA##propor to#0.2 and with cluster-abundance normalization are consistent with the observed correlation function and pairwise velocity dispersion of galaxies. A high level of velocity bias is not required in these models. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Proceedings of the workshop on 'From stars to galaxies to the universe'

The following topics were dealt with: Large scale structure of the Universe, dark matter, clusters of galaxies, galaxy formation and evolution, stellar evolutionAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Low redshift QSO Ly#alpha# absorption line systems associated with galaxies

SIGLEAvailable from: http://www.mpa-garching.mpg.de / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The Zel'dovich-type approximation for an inhomogeneous universe in general relativity: second-order solutions

The gravitational instability of inhomogeneities in the expanding universe is studied by the relativistic second-order approximation. Using the tetrad formalism we consider irrotational dust universes and get equations very similar to those given in the Lagrangian perturbation theory in Newtonian cosmology. Neglecting the cosmological constant and assuming a flat background model we give the solutions of the nonlinear dynamics of cosmological perturbations. We present the complete second-order solutions, which extend and improve earlier works. (orig.)Available from TIB Hannover: RR 4697(904) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Three-point correlation function of galaxy clusters in cosmological models: a strong dependence on triangle shapes

In this paper, we use large P&quot;3M N-body simulations to study the three-point correlation function #zeta# of clusters in two theoretical models. The first model (LCDM) is a low-density flat model of #OMEGA#_0 = 0.3, #LAMBDA#_0 = 0.7 and h = 0.75, and the second model (PIM) is an Einstein-de-Sitter model with its linear power spectrum obtained from observations. We found that the scaled function Q(r,u,v), which is definded as the ratio of #zeta#(r,ru,ru+rv) to the hierarchical sum #xi#(r)#xi#(ru)#xi#(ru+rv)+#xi#(ru+rv)#xi#(r) (where #xi# is the two-point correlation function of clusters), depends weakly on r and u, but very strongly on v. Q(r,u,v) is about 0.2 at v = 0.1 and 1.8 at v = 0.9. A model of Q(r,u,v) = #THETA#10&quot;1&quot;.&quot;3&quot;v&quot;&quot;2 can fit the data of #zeta# very nicely with #THETA##approx# 0.14. This model is found to be universal for the LCDM clusters and for the PIM clusters. Furthermore, Q(r,u,v) is found to be insensitive to the cluster richness. We have compared our N-body results with simple analytical theories. We found that these theories of cluster formation do not provide an adequate description for the three-point function of clusters. We have also examined the observational data of #zeta# presently available, and have not found any contradiction between the observations and our model predictions. The v-dependence of Q found in the three-dimensional case. This is probably the reason why the v-dependence of Q has not been found in an angular correlation function analysis of the Abell catalogue. The v-dependence found in this paper might be an important feature of clusters formed in the Gaussian graviatational instability theories. Therefore it would be important to search for the v-dependence of Q in redshift samples of rich clusters. (orig.)Available from TIB Hannover: RR 4697(882) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

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

SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman