The faintest galaxies have a range of colors, each one's color depending on its type and its distance from us. The most distant galaxies have their spectra shifted to longer, redder wavelengths by the Hubble expansion, and their light has taken up to ten billion years to travel to us. Using the colors of the galaxies, it is possible to gauge the distance to the background galaxies. Mirages also rely on distance. This is the clue that unlocks the universe of mass in three dimensions; the more distant the source, the more warped its image. If there is a foreground mass, the mirage effect on the background galaxies is stronger for more distant galaxies. Take a look at mass tomography images in this Power Point Presentation.
By measuring both the warp and the distances to the background galaxies, it is possible to reconstruct the mass map and also to place the mass at its correct distance. This enables the exploration of mass in the universe, independent of light, since only the light from the background galaxies is used. By exploring mass in the universe in three dimensions we are also exploring mass at various cosmic ages. This is because mass seen at great distance is mass seen at a much earlier time. So we can chart the evolution of dark matter structure with cosmic time.
Surveying the numbers of cosmic mass clusters in our universe will ultimately lead to precision tests of theories of dark energy. To fully open this novel window of the three-dimensional universe of mass history, we need a new telescope and camera very unlike what we have now. We need LSST. Advances in technology have equipped us to mine the distant galaxies for data — in industrial quantity. LSST's wide-angle gravitational lens survey will generate millions of gigabytes of data and intriguing opportunities for unique understanding of the development of cosmic structure. Our challenge is twofold. These galaxies are faint, and we need to capture images of billions of them. LSST's combination of large light-collecting capability and unprecedented field of view will for the first time open this unique window on the physics of our universe. LSST will provide a wide and deep view of the universe, allowing us to conduct full 3-D mass tomography to chart not only dark matter, but the presence and influence of dark energy.
Do we trust our current view of the universe? Combining these results with other cosmic probes will lead to multiple tests of the foundations of our model for the universe. What will our concept of the universe be when those answers are in? Perhaps the most interesting outcome will be the unexpected; a clash between different precision measurements might prove to be a hint of a grander structure, possibly in higher dimensions. LSST provides that opportunity.
- Gavazzi & Soucail, (2006) astro-ph/0605591
- Hu, ApJ 522, L2 (1999)
- Tyson, Physica Scripta T85, 259 (2000)
- Wittman et al, ApJL 557, L89, (2001)
- Wittman et al, ApJ 597, 218 (2003)
- Wittman, et al, ApJ 643, 128 (2006) [First catalog of clusters discovered this way]