Click on an image to access an MPEG movie (the bottom row links to a single movie).
Objective: To perform hydrodynamic models of galaxy and large-scale structure formation to compare with data from NASA's Great Observatories and ground-based telescopes. The Cosmic Background Explorer (COBE) has determined the power spectrum of fluctuations on scales greater than a few hundred million light years. The Hubble Space Telescope (HST) is imaging the formation of the central regions of galaxies (a thousand light years) at redshifts z ~ 2 and following their evolution in clusters from z ~ 0.5 to the present epoch. With simulations, we tie together this vast range of data to create a unified model of structure formation and galaxy evolution.
Approach: We start with simulations of large volumes using the COBE power spectrum to determine the cosmological context of subsequent simulations. The cube at the upper left is 300 million light years on a side (we run volumes as large as 2.5 billion light years--"The Sloan Digital Sky Survey Volume"--to study extremely large and rare clusters of galaxies). From these large-scale simulations, we draw clusters of galaxies and simulate them at higher resolution (upper right), fully preserving the cosmological context. Finally, we simulate the evolution of galaxies in clusters. By nesting these simulations using our renormalization techniques, we consistently examine the dynamics of the Universe on scales from 1,000 light years to 2 billion light years.
Significance: HST had discovered that spiral galaxies with distortions and high rates of star formation pervaded clusters of galaxies just 5 billion years ago, but nearby clusters exclude spirals in favor of ellipticals. "Galaxy harassment" (frequent high-speed galaxy encounters) drives the morphological transformation in clusters, provides fuel for quasars in subluminous hosts (another recent HST discovery) and leaves detectable debris arcs (HST teams are now searching for this effect). An example of a debris arc is shown in the bottom right graphic (6 million light years across and color-coded by intensity). HST can detect anything colored yellow, red, and orange. Images from harassment simulations are shown in the bottom right together with HST images of galaxies in clusters at z ~ 0.4. These compelling image pairs have convinced the HST imaging team and most of the astronomical community that harassment drives morphological evolution in clusters.
Status/Plans: We are currently simulating the larger Sloan Volume with 46 million particles using three cosmological models. These will be used to plan data acquisition for the survey and study "weak gravitational lensing" on large scales. Using the renormalization approach, we are studying the evolution of galaxies, groups like the one containing the Milky Way, and clusters of galaxies. This approach achieves the high resolution necessary to study galaxy formation within the correct cosmological context.
Acknowledgments: The simulation in the upper left used the University of Washington's (UW) KSR2; that in the upper right used the Cornell Theory Center. Harassment runs were carried out at UW and the Arctic Region Supercomputing Center.
Point of Contact:
George Lake
University of Washington
lake@astro.washington.edu
URL: http://www-hpcc.astro.washington.edu/
