Clustering of galaxies in a hierarchical universe. Pt. 2 Evolution to high redshift

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

Linking cluster formation to large scale structure

We use two high resolution CDM simulations to show that (i) when clusters of galaxies from the infall pattern of matter is not random but shows clear features which are correlated in time; (ii) in addition, the infall patterns are correlated with the cluster's surrounding Large Scale Structure; (iii) Large Scale Structure shows a mix of both filaments and sheets; (iv) the amount of mass in filaments is slightly larger for a low #OMEGA# model. (orig.)Available from TIB Hannover: RR 4697(1047) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Clustering of galaxies in a hierarchical universe. Pt. 1 Methods and results at z=0

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

Clustering of galaxies in a hierarchical universe: III. mock redshift surveys

This is the third paper in a series which combines N-body simulations and semi-analytic modelling to provide a fully spatially resolved simulation of the galaxy formation and clustering processes. Here we extract mock redshift surveys from our simulations: a Cold Dark Matter model with either #OMEGA#_0=1 (#tau#CDM) or #OMEGA#_0=0.3 and #LAMBDA#=0.7 (#LAMBDA#CDM). We compare the mock catalogues with the northern region (CfA2N) of the Center for Astrophysics (CfA) Redshift Surveys. We study the properties of galaxy groups and clusters identified using standard observational techniques and we study the relation of these groups to real virialised systems. Most features of CfA2N groups are reproduced quite well by both models with no obvious dependence on #OMEGA#_0. Redshift space correlations and pairwise velocities are also similar in the two cosmologies. The luminosity functions predicted by our galaxy formation models depend sensitively on the treatment of star formation and feedback. For the particular choices of Paper I they agree poorly with the CfA survey. To isolate the effect of this discrepancy on our mock redshift surveys, we modify galaxy luminosities in our simulations to reproduce the CfA luminosity function exactly. This adjustment improves agreement with the observed abundance of groups, which depends primarily on the galaxy luminosity density, but other statistics, connected more closely with the underlying mass distribution, remain unaffected. Regardless of the luminosity function adopted, modest differences with observation remain. These can be attributed to the presence of the 'Great Wall' in the CfA2N. It is unclear whether the greater coherence of the real structure is a result of cosmic variance, given the relatively small region studied, or reflects a physical deficiency of the models. (orig.)SIGLEAvailable from TIB Hannover: RR 4697(1141) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Peculiar velocities of galaxy clusters

We investigate the peculiar velocities predicted for galaxy clusters by theories in the cold dark matter family. A widely used hypothesis identifies rich clusters with high peaks of a suitably smoothed version of the linear density fluctuation field. Their peculiar velocities are then obtained by extrapolating the similarly smoothed linear peculiar velocities at the positions of these peaks. We test these ideas using large high resolution N-body simulations carried out within the Virgo supercomputing consortium. We find that at early times the barycentre of the material which ends up in a rich cluster is generally very close to a high peak of the initial density field. Furthermore the mean peculiar velocity of this material agrees well with the linear value at the peak. The late-time growth of peculiar velocities is, however, systematically underestimated by linear theory. At the time clusters are identified we find their rms peculiar velocity to be about 40% larger than predicted. Nonlinear effects are particularly important in superclusters. These systematics must be borne in mind when using cluster peculiar velocities to estimate the parameter combination #sigma#_8#OMEGA#"0"."6. (orig.)27 refs.Available from TIB Hannover: RR 4697(1096) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Galaxy clusters in Hubble volume simulations: Cosmological constraints from sky survey populations

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

Galaxy clusters in Hubble volume simulations: Cosmological constraints from sky survey populations

We use giga-particle N-body simulations to study galaxy cluster populations in Hubble Volumes of LCDM (Omega_m=0.3, Omega_Lambda=0.7) and tCDM (Omega_m=1) world models. Mapping past light-cones of locations in the computational space, we create mock sky surveys of dark matter structure to z~1.4 over 10,000 sq deg and to z~0.5 over two full spheres. Calibrating the Jenkins mass function at z=0 with samples of ~1.5 million clusters, we show that the fit describes the sky survey counts to <~20% acccuracy over all redshifts for systems larger than poor groups (M>5e13 Msun/h). Fitting the observed local temperature function determines the ratio beta of specific thermal energies in dark matter and intracluster gas. We derive a scaling with power spectrum normalization beta \propto sigma8^{5/3}, and measure a 4% error on sigma8 arising from cosmic variance in temperature-limited cluster samples. Considering distant clusters, the LCDM model matches EMSS and RDCS X-ray-selected survey observations under economical assumptions for intracluster gas evolution. Using transformations of mass-limited cluster samples that mimic sigma8 variation, we explore SZ search expectations for a 10 sq deg survey complete above 10^{14} Msun/h. Cluster counts are shown to be extremely sensitive to sigma8 uncertainty while redshift statistics, such as the sample median, are much more stable. For LCDM, the characteristic temperature at fixed sky surface density is a weak function of redshift, implying an abundance of hot clusters at z>1. Assuming constant beta, four kT>8 keV clusters lie at z>2 and 40 kT>5 keV clusters lie at z>3 on the whole sky. Detection of Coma-sized clusters at z>1 violate LCDM at 95% confidence if their surface density exceeds 0.003 per sq deg, or 120 on the whole sky.Comment: 44 pages, 20 figures. Revised estimate of cosmic variance error in sigma8 (3% for mass-, 4% for T-limited samples). Truncated entries (most massive ten clusters) of sky survey electronic tables added in Appendix C (See also at http://astro.physics.lsa.umich.edu/HV/tables.htm). ApJ, to appear v573 (July 1, 2002

Evolution of structure in cold dark matter universes

We present an analysis of the clustering evolution of dark matter in four cold dark matter (CDM) cosmologies. We use a suite of high resolution, 17-million particle, N-body simulations which sample volumes large enough to give clustering statistics with unprecedented accuracy. We investigate a flat model with #OMEGA#_0 = 0.3, an open model also with #OMEGA#_0 = 0.3, and two models with #OMEGA# = 1, one with the standard CDM power spectrum and the other with the same power spectrum as the #OMEGA#_0 = 0.3 models. In all cases, the amplitude of primordial fluctuations is set so that the models reproduce the observed abundance of rich galaxy clusters by the present day. The mass two-point correlation function and power spectrum of all the simulations differ significantly from those of the observed galaxy distribution, in both shape and amplitude. Thus, for any of these models to provide an acceptable representation of reality, the distribution of galaxies must be biased relative to the mass in a non-trivial, scale-dependent, fashion. In the #OMEGA# = 1 models the required bias is always greater than unity, but in the #OMEGA#_0 = 0.3 models an ''antibias'' is required on scales smaller than #propor to#5h&quot;-&quot;1 Mpc. The mass correlation functions in the simulations are well fit by recently published analytic models. The velocity fields are remarkably similar in all the models, whether they be characterised as bulk flows, single-particle or pairwise velocity dispersions. This similarity is a direct consequence of our adopted normalisation and contradicts the common belief that the amplitude of the observed galaxy velocity fields can be used to constrain the value of #OMEGA#_0. The small-scale pairwise velocity dispersion of the dark matter is somewhat larger than recent determinations from galaxy redshift surveys, but (orig.)120 refs.SIGLEAvailable from TIB Hannover: RR 4697(1048) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Genus statistics of the Virgo N-body simulations and the 1.2-Jy redshift survey

We study the topology of the Virgo N-body simulations and compare it to the 1.2-Jy redshift survey of IRAS galaxies by means of the genus statistic. Four high-resolution simulations of variants of the CDM cosmology are considered: a flat standard model (SCDM), a variant of it with more large-scale power (#tau#CDM), and two low density universes, one open (OCDM, #OMEGA#_0 = 0.3) and one flat (#LAMBDA#CDM, #OMEGA#_0 = 0.3, #LAMBDA# = 0.7). In all cases, the initial fluctuation amplitudes are chosen so that the simulations approximately reproduce the observed abundance of rich clusters of galaxies at the present day. The fully sampled N-body simulations are examined down to strongly nonlinear scales, both with spatially fixed smoothing, and with an adaptive smoothing technique. While the #tau#CDM, #LAMBDA#CDM, and OCDM simulations have very similar genus statistics in the regime accessible to fixed smoothing, they can be separated with adaptive smoothing at small mass scales. In order to compare the N-body models with the 1.2-Jy survey, we extract large ensembles of mock catalogues from the simulations. These mock surveys are used to test for various systematic effects in the genus analysis and to establish the distribution of errors of the genus curve. We find that a simple multivariate analysis of the genus measurements is compromised both by non-Gaussian distributed errors and by noise that dominates the covariance matrix. We therefore introduce a principal components analysis of the genus curve38 refs.SIGLEAvailable from TIB Hannover: RR 4697(1046) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman