Spatial Orientation of Galaxies in Three Rotating Clusters: New Code GOBAD1.0 Proposed (original) (raw)

The formation and evolution of clusters of galaxies in different cosmogonies

Monthly Notices of the Royal Astronomical Society, 1999

The formation of galaxy clusters in hierarchically clustering universes is investigated by means of high resolution N-body simulations. The simulations are performed using a newly developed multi-mass scheme which combines a PM code with a high resolution N-body code. Numerical effects due to time stepping and gravitational softening are investigated as well as the influence of the simulation box size and of the assumed boundary conditions. Special emphasis is laid on the formation process and the influence of various cosmological parameters. Cosmogonies with massive neutrinos are also considered. Differences between clusters in the same cosmological model seem to dominate over differences due differing background cosmogony. The cosmological model can alter the time evolution of cluster collapse, but the merging pattern remains fairly similar, e.g. number of mergers and mass ratio of mergers. The gross properties of a halo, such as its size and total angular momentum, also evolve in a similar manner for all cosmogonies and can be described using analytical models. It is shown that the density distribution of a halo shows a characteristic radial dependence which follows a power law with a slope of α = −1 at small and α = −3 at large radii, independent of the background cosmogony or the considered redshift. The shape of the density profiles follows the generic form proposed by Navarro et al. (1996) for all hierarchically clustering scenarios and retains very little information about the formation process or the cosmological model. Only the central matter concentration of a halo is correlated to the formation time and therefore to the corresponding cosmogony. We emphasise the role of non-radial motions of the halo particles in the evolution of the density profile.

Mergers and Formation of Disk Galaxies in Hierarchically Clustering Universes

Proceedings of the International Astronomical Union, 1996

New simulations are presented which investigate the formation of smaller groups of galaxies in a CDM like universe. The simulations follow the evolution of dark matter and gas and are performed with an SPH code adapted for the special-purpose hardware GRAPE. The mass resolution in the baryonic component is 5 10^6 Msol, the spatial resolution is 1.5 kpc. A sufficiently large volume is simulated in order to accurately include the tidal field and the mass inflow. The mass resolution enables us to resolve the galaxies formed in the simulation. Individual properties of the galaxies, each consisting of several thousand particles, can also be investigated. It turns out, that in the center of the dark haloes the gas accumulates to form a rotationally supported disk. However, in comparison with observations, disks which form in numerical simulations are too concentrated: Due to the merging of substructures, angular momentum is transported from the gas to the dark halo, and far too much gas is accumulated at very small radii. It is argued that changing the cosmogony (e.g. to low Omega) or adding photoionisation due to an external UV background do not provide an easy fix to the angular momentum problem. Feedback processes caused by supernovae or stellar winds seem to be the most likely solution to this problem.

Universe: simulations of structure and galaxy formation

2006

. A high-resolution simulation of the formation of a single dark matter halo in a cold dark matter universe. The brighter colors indicate higher densities of dark matter. The sequence shows a series of snapshots of the evolution of the halo, at the redshifts indicated in the legend. The present-day halo displays a significant amount of substructure within its virial radius. (Courtesy of Ben Moore, Joachim Stadel, Tom Quinn and George Lake.) This figure is reproduced as Color Plate 69. those of the 1980s) can follow the evolution of 10 9 particles. Snapshots from simulations of representative, cosmological volumes are displayed in figure 2. This figure illustrates the evolution of structure in four versions of the cold dark matter model, differing only in the values of the cosmological parameters, and . At the present day, the dark matter is arranged in a complex network of voids, filaments and super-clusters (dubbed the 'Cosmic Web' by Bond, Kofman and Pogosyan). It is similar in all the sim-

The Evolution of Galaxies in Clusters

Symposium - International Astronomical Union, 2003

We report on recent numerical investigations of the dynamical evolution of galaxies in clusters. Simulations of spiral galaxies falling into forming clusters show the development of the morphology-density relationship and the formation of regular and giant elliptical galaxies. The regular elliptical merger remnants end up in a fundamental plane very similar to the observed relation. The giant ellipticals have much in common with their real counterparts but their central velocity dispersions are too high. We also quantify the amount and distribution of diffuse light in clusters.

Early Formation and Evolution of Galaxies

The Evolution of Galaxies, 2003

I review success and failure of the hierarchical galaxy formation model. In this scenario, the morphology of galaxies is regulated by the mode of gas accretion and intimately linked to discrete accretion events. Some of the common misconceptions about hierarchical clustering are discussed. The need of a self-consistent approach that incorporates the chemical and dynamical evolution on small scales simultaneously with the cosmological framework of structure formation on large scales is emphasized.

The large-scale environment of groups and clusters of galaxies

Proceedings of the International Astronomical Union, 2004

It appears that the dynamical status of clusters and groups of galaxies is related to the large-scale structure of the Universe. A few interesting trends have been established: (1) The Cluster Substructure -Alignment Connection by which clusters show a strong correlation between their tendency to be aligned with their neighbors and their dynamical state (as indicated by the existence of significant substructres). (2) The Cluster Dynamics -Cluster Clustering Connection by which dynamically young clusters are more clustered than the overall cluster population. (3) The Cluster-Supercluster Alignment Connection by which clusters of galaxies show a statistical significant tendency to be aligned with the projected major axis orientation of their parent supercluster. ( ) The Galaxy Alignment -Cluster Dynamics Connection by which red-sequence cluster bright galaxies show a significant trend to be aligned with their parent cluster major axis, especially in dynamically young clusters. (5) The Group Richness -Shape Connection by which groups of galaxies are flatter the poorer they are. These are strong indications that clusters develop in a hierarchical fashion by anisotropic merging of smaller units along the large-scale filamentary structures within which they are embedded.

THE ASSEMBLY OF GALAXY CLUSTERS

Astrophysical Journal, 2009

We study the formation of fifty-three galaxy cluster-size dark matter halos formed within a pair of cosmological LCDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host 0.1L* galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no pre-processing in the group environment prior to their accretion into the cluster. On average, ~70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than ~12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past (~6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass; and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for most clusters. The accretion times for z = 0 cluster members are quite extended, with ~20% incorporated into the cluster halo more than 7 Gyr ago and ~20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate timescale for late-type to early-type transformation within the cluster environment to be ~6 Gyr.

The Universe Evolution as Possible Mechanism of Formation of Galaxies and Their Clusters

Astrophysics, 2000

The Kepler problem is studied in a space with the Friedmann-Lemaitre-Robertson-Walker metrics of the expanding universe.Cosmic evolution leads to decreasing energy of particles, causing free particles to be captured in bound states, so that the evolution of the universe can be treated as a possible mechanism of the formation of galaxies and clusters of galaxies.The cosmological model is considered where the evolution of the universe plays the role usually inscribed to cold dark matter.

Origin and Evolution of Structure for Galaxies in the Local Group

Publications of The Korean Astronomical Society, 2015

The Milky Way did not form in isolation, but is the product of a complex evolution of generations of mergers, collapses, star formation, supernovae and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark-matter haloes, spiral density waves, and emerging dark energy. This paper summarizes a review of recent attempts to reconstruct this complex evolution. We compare simulated properties with various observed properties of the Local Group. Among the generic features of simulated systems is the tendency for galactic halos to form within the dark matter filaments that define a supergalactic plane. Gravitational interaction along this structure leads to a streaming flow toward the two dominant galaxies in the cluster. We analyze this alignment and streaming flow and compare with the observed properties of Local-Group galaxies. Our comparison with Local Group properties suggests that some dwarf galaxies in the Local Group are part of a local streaming flow. These simulations also suggest that a significant fraction of the Galactic halo formed at large distances and arrived later along these streaming flows.