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

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.

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.

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.