Galaxy and Cluster Formation in Hierarchical Models

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Session 71 -- Galaxy and CBR Distribution
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[71.14] Galaxy and Cluster Formation in Hierarchical Models

F J Summers (Princeton U.)

The simple theoretical picture envisions that galaxies form via the collapse of a roughly spherical and homogeneous cloud of gas. Galactic disks form naturally because the collapse proceeds faster along the direction of the angular momentum vector than in the plane of rotation. Clusters of galaxies are built up by the collapse of a roughly random distribution of galaxies. In hierarchical structure formation, these ideas are simply DEAD WRONG!

We investigate galaxy and cluster formation in hierarchical models via N body simulations including dark matter, gas, gravity, and hydrodynamics. With high resolution and wide dynamic range we can resolve the larger galaxy scales (few kpc) and the smaller cosmological scales (few Mpc). Detailed pictures of the formation processes emerge. This poster is guaranteed to contain some of the most aesthetic N body figures ever produced.

Galaxies are created through the formation of long filamentary structures and the segmentation of filaments into galaxy size objects. Collapse along the filament axis produces very little angular momentum. Galactic disks form via the discrete accretion of gas clouds which carry angular momentum into the inner regions. Only then does the process of slow accretion of mass from many directions begin.

Clusters of galaxies form in several stages. First is the agglomeration of several galaxies to form a core. In the second stage, galaxies flow in along filaments aligned toward the cluster, introducing specific directions to the collapse. Radial orbits will significantly alter the relaxation process. Further stages are possible for larger clusters as they swallow complete groups and smaller clusters of galaxies.

In general, the realization must be made that infalling material is {\bf not} static, but will undergo its own collapse and clustering during the time of infall.

Friday program listing