Tully's Smoothed Density Surfaces
Tully's Smoothed Density Surfaces
| Group Name | isoDensity |
| Reference | Tully 8,000 km/s Galaxy Catalog |
| Prepared by | R. Brent Tully (U Hawaii)
Stuart Levy (NCSA/U Illinois) |
| Labels | No |
| Files | d16_100_u02_50k.obj, d16_200_u02_10k.obj |
| Dependencies | none |
Accompanying the Tully galaxies is a model of the density of the 28,000 galaxies in that catalog. These appear as 3-D surfaces surrounding the most dense regions of galaxies. Each surface represents points of constant density. After smoothing the galaxy data, that is, averaging these data to compensate for random fluctuations, a 3-D mapping of the overall density may be displayed as surfaces of constant value.
The surfaces represent two values of constant density. The blue, inner surface is a relatively high density, while the aqua, outer surface represents a lower density. The blue contours mainly show dense galaxy clusters, like the Virgo Cluster, Fornax Cluster, and most of the Abell clusters in the Tully data group. These are the regions of highest density in our local Universe.
Some of the aqua contours resemble the blue contours in shape, but more often they reveal larger structures that connect blue contours together. The largest feature appears on the edge of the data cube and is called the Great Wall. Brighten up the Tully galaxies and, while it's still the active group, type see gw. This removes all the galaxies except those in the enormous Great Wall structure, which follow the density contours closely. Type see all to return all the Tully galaxies to view.
Isolating the Isosurfaces
If you desire to see just one of the isosurfaces, then you must change the color of the surface you wish to remove. In the extragalactic.cf file, the blue and aqua colors have a color index of 1 and 2, respectively, and are assigned these default red-green-blue colors:
cment 1 0 0 1 (blue)To see the aqua contours alone, change the blue contours to black with the command cment 1 0 0 0. Then, to emphasize the aqua contours, increase their alpha value using the Alpha Slider. The higher the value, the more opaque the surfaces become. Set alpha to its maximum value (1) and the surfaces will appear solid. If you fly inside, you will notice the smaller, black density contours are now visible. To return the higher density surfaces to blue, type cment 1 0 0 1.
cment 2 0.0 0.2 0.35 (aqua)
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott