Displaying N-body Galaxy Simulations: More than Just Pretty Pictures

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Session 77 -- Spirals II
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[77.19] Displaying N-body Galaxy Simulations: More than Just Pretty Pictures

S. Lester (Louisiana State University), G. Byrd (University of Alabama, Tuscaloosa)

Although current n-body simulations of disk galaxies permit use of hundreds of thousands of particles, several problems commonly are seen in displays of simulation results. Plotting of individual particles results in particle overlap in the populous central regions to create an uninformative ``blob." Use of a subset of the particles removes the overlap but also throws away information about the simulation via an increase in random noise or granularity. The point overlap problem is overcome by using different degrees of shading or color to represent the increasing number of particles per unit area rather than plotting them individually. The particle numbers are computed in individual bins of a cartesian grid typically of 256x256 cells providing good resolution of features.

However, simple bin number densities do not solve all display problems. Even with the particle numbers possible today, simulations do not contain ``billions of stars." Consequently, the particles are so sparsely distributed in the intermediate and outer regions that there is considerable random noise or they are even seen individually in bins. To solve this problem, the color/density method must be made more sophisticated. We discuss methods of creating a smoothed number density over the simulation disk which approximates the particle density distribution if billions of particles had been used. The smoothing method only displays peaks or valleys in the particle distribution if they exceed a chosen level of statistical significance. Display of number density via shading or color along with a smoothing method which judges the significance of a feature permits use of the quantitative techniques observers have developed for CCD images to be used on simulations also. Finally! , when the smoothing and shading i

s done, the final image is more esthetically pleasing!

This work was supported by NSF grants REU AST 9300413, EPSCoR RII8996152 and AST 9014137.

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