arXiv subjects

Andrey Kravtsov

Publications and source records attributed to Andrey Kravtsov.

58 records · Page 4Linked to original sources

arXiv1998

Galaxies in N-body simulations: overcoming the overmerging problem

We present analysis of the evolution of dark matter halos in dense environments of groups and clusters in dissipationless cosmological simulations. The premature destruction of halos in such environments, known as the overmerging, reduces the predictive power of N-body simulations and makes difficult any comparison between models and observations. We analyze the possible processes that cause the overmerging and assess the extent to which this problem can be cured with current computer resources and codes. Using both analytic estimates and high resolution numerical simulations, we argue that the overmerging is mainly due to the lack of numerical resolution. We find that the force and mass resolution required for a simulated halo to survive in galaxy groups and clusters is extremely high and was almost never reached before: ~1-3 kpc and 10^8-10^9 Msun, respectively. We use the high-resolution Adaptive Refinement Tree (ART) N-body code to run cosmological simulations with the particle mass of \approx 2x10^8/h Msun} and the spatial resolution of \approx 1-2/h kpc, and show that in these simulations the halos do survive in regions that would appear overmerged with lower force resolution. Nevertheless, the halo identification in very dense environments remains a challenge even with the resolution this high. We present two new halo finding algorithms developed to identify both isolated and satellite halos that are stable (existed at previous moments) and gravitationally bound. To illustrate the use of the satellite halos that survive the overmerging, we present a series of halo statistics, that can be compared with those of observed galaxies. (Abridged)

astro-ph↗

arXiv1998

Evolution of isolated halos and halos inside of groups and clusters in a LCDM model

A significant fraction of mass in the universe is believed to be in the form of dark matter (DM). Due to gravitational instability, the DM collapses hierarchically into DM halos. In this contribution we present a study of the formation and evolution of such DM halos in a COBE-normalized spatially flat LCDM model (Omega_0=1-Omega_L=0.3; h=0.7) using high-resolution N-body simulations. The novelty of this study is use of the newly developed halo-finding algorithms to study the evolution of both isolated and satellite (located inside virial radii of larger group- and cluster-size systems) halos. The force and mass resolution required for a simulated halo to survive in the high-density environments typical of groups and clusters is high: ~1-3 kpc and \~10^9 M_sun, respectively. We use the high-resolution Adaptive Refinement Tree (ART) N-body code to follow the evolution of 256^3 dark matter particles with dynamic range in spatial resolution of 32,000 in a box of 60/h Mpc. We show that the correlation function of these halos is anti-biased with respect to the dark matter correlation function and is high and steeper than the correlation function of the isolated virialized objects. The correlation function evolves only mildly between z=3 and z=1. The mass evolution of isolated virialized objects determined from the simulation is in good agreement with prediction of semi-analytical models. The differences exist, however, if we include satellite halos in the halo catalogs.

astro-ph↗

arXiv1998

Evolution of halo-halo clustering and bias in a LCDM model

We study the evolution of the halo-halo correlation function and bias in a LCDM model using very high-resolution N-body simulations. The high force and mass resolution allows dark matter (DM) halos to survive in the tidal fields in high-density regions and thus prevents the ambiguities related with the ``overmerging problem.'' Numbers of galaxy-size halos in cluster-like objects in our simulation are similar to the numbers of galaxies observed in real clusters. This allows us to estimate for the first time the evolution of the correlation function and bias at small (down to ~100/h kpc) scales. We compare particle distribution, dark matter correlation function, density profiles, and halo mass function produced with our N-body code and corresponding results of the AP3M simulations. We find that at all epochs the 2-point correlation function of galaxy-size halos xihh is well approximated by a power-law with slope ~1.6-1.8. The difference between the shape of xihh and the shape of the correlation function of matter results in the scale-dependent bias at scales <7/h Mpc, which we find to be a generic prediction of the hierarchical models, independent of the epoch and of the model details. We find that our results agree well with existing clustering data at different redshifts, indicating the general success of the picture of structure formation in which galaxies form inside the host DM halos. Particularly, we find an excellent agreement in both slope and the amplitude between xihh(z=0) in our simulation and the galaxy correlation function measured using the APM galaxy survey. At high redshifts, the observed clustering of the Lyman-break galaxies is also reasonably well reproduced by the models.

astro-ph↗

arXiv1998

Evolution of bias in different cosmological models

We study the evolution of the halo-halo correlation function and bias in four cosmological models (LCDM, OCDM, tauCDM, and SCDM) using very high-resolution N-body simulations. The high force and mass resolution allows dark matter (DM) halos to survive in the tidal fields of high-density regions and thus prevents the ambiguities related with the ``overmerging problem.'' This allows us to estimate for the first time the evolution of the correlation function and bias at small (down to ~100/h kpc) scales. We find that at all epochs the 2-point correlation function of galaxy-size halos xi_hh is well approximated by a power-law with slope ~1.6-1.8. The difference between the shape of xi_hh and the shape of the correlation function of matter results in the scale-dependent bias at scales <7/h Mpc, which we find to be a generic prediction of the hierarchical models. The bias evolves rapidly from a high value of ~2-5 at z~3-7 to the anti-bias of b~0.5-1 at small <5/h Mpc scales at z=0. We find that our results agree well with existing clustering data at different redshifts. Particularly, we find an excellent agreement in both slope and the amplitude between xi_hh(z=0) in our LCDM simulation and the galaxy correlation function measured using the APM galaxy survey. At high redshifts, the observed clustering of the Lyman-break galaxies is also well reproduced by the models. The agreement with the data at high and low z indicates the general success of the hierarchical models of structure formation in which galaxies form inside the host DM halos. (Abridged)

astro-ph↗