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Galaxy Distributions

Galaxy Distributions. Analysis of Large-scale Structure Using Visualization and Percolation Technique on the SDSS Early Data Release Database. Yuk-Yan Lam August 9, 2001. General Background. Sloan Digital Sky Survey Astrophysics principles Large-scale structure.

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Galaxy Distributions

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  1. Galaxy Distributions Analysis of Large-scale Structure Using Visualization and Percolation Technique on the SDSS Early Data Release Database Yuk-Yan Lam August 9, 2001

  2. General Background • Sloan Digital Sky Survey • Astrophysics principles • Large-scale structure

  3. Mapping out the Sky:Sloan Digital Sky Survey • ¼ of the sky • >100 million celestial objects • EDR database ~42,000 galaxies • Projected galaxy spectra 1 million Apache Point Observatory, New Mexico

  4. “Pi in the sky” Total Solid Angle: 10,000 square degrees

  5. Astrophysical Principles • Redshift • Spectral classification • Galaxy types

  6. Cosmological Redshift • Stretching of light wavelength due to Universe expansion • (received wavelength of light) = (emitted wavelength) x (1 + z) • At time of light emission, Universe was a factor of (1 + z) smaller in its linear dimension

  7. Galaxies with varying redshifts: Low  High

  8. Fingerprints: Spectra QUASAR SPECTRA • Spectrogram – photograph of a spectrum • SDSS spectrograph splits light from each source into hundreds of spectra, which are photographed by digital cameras. GALAXY SPECTRA

  9. Galaxy Types • Two Important Characteristics • How much light? • How is the light divided between the bulge and the disk? • Bulge – spherical center • Disk – flat portion

  10. The Elliptical Galaxy • Massive • Spectra similar to a cool star • No discernible disk

  11. The Spiral Galaxy • Massive • Almost flat spectra • Disks with spiral patterns • Three classes: Sa Sb Sc with increasing prominence of disk and arms

  12. Other Galaxy Types Blue Compact Galaxy Irregular Galaxy Lenticular Galaxy – No arms but a disk Dwarf Galaxies

  13. Large-Scale Structure • Different Types of Topology Possible • Percolation Statistics

  14. Filamentary “Network” Topology Filamentary: Galaxies concentrated to one-dimensional threads forming a kind of three-dimensional network. More “connected” as implied by a filamentary geometry

  15. Cellular “Bubble” Topology Cellular: Galaxies concentrated in narrow walls separating large, isolated voids.

  16. “Swiss Cheese” Topology AKA Sponge: Both kinds of regions are connected, so it is possible to swim to any point through the holes or burrow to any point inside.

  17. “Meatball” Topology “Clumpier”

  18. Phase 1: Visualization • Two dimensions • Three dimensions

  19. Sample In redshift space • Galaxy query on EDR • 41,946 galaxies with their spectra found (projected into two dimensions)

  20. Position In Relation to Spectrum • Goal: See how a galaxy’s location in the sky may be related to its recorded spectrum • Plot using the following color code: RED spectrum < -0.4 YELLOW -0.4 < spectrum < -0.2 GREEN -0.2 < spectrum < 0.0 BLUE 0.0 < spectrum < 0.3 LIGHT BLUE 0.3 < spectrum < 0.6 WHITE spectrum > 0.6

  21. CAVE Components: Stereo Glasses Stereographic Projectors Interactive Wand

  22. Phase 2: Percolation • Preview: Percolation principles • Step 1: Initial Conditions • Step 2: Percolation Occurs • Step 3: Evolution Statistics

  23. Percolation Principles • The Simple Cubic Lattice • The On/Off State -> Filling Factor • Method of Expansion • Method of Grouping

  24. Two-Dimensional Analogy: Square lattice & on/off state Initial Lattice On/Off State

  25. How to expand?

  26. Grouping Neighbors • Neighbors • Groups • Largest Cluster Statistic (LCS) • Mergers Merging Groups

  27. Percolation Statistics Related to Large-Scale Topology Standards: • Faster growth of LCS -> More connected distribution • Slower growth of voids than Gaussian -> Bubble topology • Faster growth of clusters than Gaussian -> Network topology • Slower growth of clusters than Gaussian -> Meatball topology

  28. Sample Simulations Network Poisson LCS Meatball Radius Size

  29. Step 1: Initial Conditions Size used: 350 FF: .000468665 In red-shift space

  30. Step 2: E-x - p - a - n - d • Percolation Visualized • Filling Factor versus Radius Size

  31. Step 3: Evolution Statistics • Number of Groups vs. Radius • LCS vs. Radius

  32. Where now? • Compare with simulations • Improve grid accuracy • Boundary effects • Incorporate additional surveys • Visualization of technique • Comparison with other techniques • Application to other areas

  33. Acknowledgements • Mark Subbarao, Astronomy and Astrophysics Department, University of Chicago • Joshua Frieman, Astronomy and Astrophysics Department, University of Chicago • Mark Hereld, MCS Division, Argonne National Laboratory • Sloan Digital Sky Survey http://www.sdss.org

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