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Cosmology and the Shape of Large-Scale Structure

Cosmology and the Shape of Large-Scale Structure. Neta A. Bahcall Princeton University. What is the Shape of Large-Scale Structure?. [Clusters, Superclusters] Why important?  What is the Universe like?  Formation & Evolution of Structure

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Cosmology and the Shape of Large-Scale Structure

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  1. Cosmology and the Shape of Large-Scale Structure Neta A. Bahcall Princeton University

  2. What is the Shape of Large-Scale Structure? [Clusters, Superclusters] Why important?  What is the Universe like?  Formation & Evolution of Structure  Proper Use of Clusters  Cosmology

  3. Topics  The Shape of Clusters  Alignment of Cluster Pairs  Evolution of Shape & Alignment New Tool in Cosmology:  Cluster Ellipticity  Superclusters: Filaments or Pancakes?

  4. Hot Gas in Clusters(X-rays;SZ)

  5. Clusters and Cosmology  Mass-to-Light Function  M/L x Lo  m = 0.2+-0.05  Cluster Abundance and Evolution  ncl(z)  m = 0.2 +- 0.05 8 = 0.9 +- 0.1  Baryon Fraction: b/m = 0.18  m = 0.23 +- 0.05  Mass ~ Light

  6. Shape Impact Clusters typically assumed spherical Impact of Non-Sphericity: • Selection Bias (in lensing; optical; X-ray; SZ) ‘pointed’ clusters affect Rcl, Vcl, Mcl, ncl(>threshold) • Impacts Ho from Clusters(X-Rays + SZ) (Ho too low if ‘pointed’ clusters prefered)  Other • New Tool for Cosmology, Structure Formation

  7. Cluster Shape • Large-Scale Simulations of LCDM [15003 Mpc3; m= 0.27; Dark-Matter; 1.2E11 Mo/p] • 106 Clusters[M180 > 2E13 h-1 Mo] z = 0 to 3 Determine Cluster Best-Fit Ellipse (2nd-moment of particles) (Iij = XiXj ) a1 > a2 > a3   = 1 - a2/a1  E2D = 1 - a22D/a12D (projected)  <E> ~ 0.3 - 0.5

  8. Cluster Ellipticity Distribution(Hopkins, Bahcall, Bode 2005) Ncl Z=0.03 Z=0.34 Z=0.71 Z=1.08 Z=1.70 Z=2.52 Ellipticity 0 0.5 1 0.5 1

  9. Evolution of Cluster Ellipticity<E> versus Redshift and Mass 0.6 <E> 0.5 0.4 0.3 2 3 1 0 Redshift

  10. Mean Cluster EllipticityEcl versus z, R, M FOF 1.5 1.0 0.5 (Evans &Bridle ’09) (Hoekstra etal ’04)

  11. Clusters Shape  Large Ellipticities: <E> ~ 0.3 - 0.5 a2/a1 ~ 0.5 - 0.7  <E> increases with Mcl, Rcl, z  <E> = 0.33 + 0.05z  <E> ~ 0.3 at z ~ 0 ~0.5 at z ~ 3

  12. Cosmology • Ωm: Mass-Density of Universe (Ωm = m/critical)  8: Amplitude of Mass Fluctuations (on 8 Mpc scale)  8Ωm0.6~ 0.35 +- 0.05 (From observed cluster abundance) 8 ~ 0.9 Ωm ~ 0.2 0.7 0.3 0.6 0.4 Amplitude 8 Not well determined

  13. Cluster Abundance and Evolution  Powerful method to determine mand 8 8 = Amplitude of mass fluctuations (initial ‘seeds’) • ncl (z~0) 8m0.6~ 0.35 • ncl (hi z)Breaks degeneracy  m= 0.2 +- 0.05 and 8 = 0.9 +- 0.1  • 8(galaxies)(obs) ~ 0.9 • If Mass ~ Light (on large scale)  8(m) ~ 0.9

  14. Cluster Mass-Function(SDSS)(Bahcall, Dong, et al ‘03)Best-fit MF: m=0.2 and 8=0.9 Fit: m=0.2 8=0.9

  15. Ωm -  (Clusters MF)

  16. m - 8 constraints from SDSS cluster MF[Bahcall etal ‘03 Rozo etal ’09] m=0.2, 8=0.9

  17. Cluster Abundance Evolution  8(Bahcall & Bode ‘03) 8

  18. Cosmological Constraints (Bahcall & Bode)(from Low and Hi redshift cluster abundance)  - m Low z Hi z WMAP5

  19. Cluster Ellipticity  (Ho, Bahcall, Bode ‘06)

  20. Alignment of Clusters(Hopkins, Bahcall, Bode 05) Alignment Z=0-0.5 Z=0.5-1 Z=1.5-2 Z=1-1.5 Z=2-2.5 Z=2.5-3 1 10 100 Cluster pair separation (Mpc)

  21. Alignments in Filaments(Hopkins, Bahcall, Bode ‘05) Overdensity In Filament Cluster Alignment

  22. Cluster Alignment Function(Hopkins, Bahcall, Bode ‘05)  Alignment of Clusters to ~100 Mpc • Alignment increases with cluster Mass • Alignment increases with Redshift • Alignment happens alongFilaments  Clusters start highly elliptical and aligned; both decrease with time!  Predictions can be tested against observations

  23. Superclusters (SDSS)

  24. Large-Scale Structure; Superclusters

  25. Superclusters • Filaments? ‘Pancakes’?Properties? • Defined: Clusters of Clusters • Select using F.O.F. of Clusters (= Percolation) • Function of Percolation Length L b = L/rcc ~ 0.15 - 0.5; L ~ 3 - 10 Mpc, z ~ 0, Mcl > 1.75E13 Mo • Use LCDM Simulations

  26. Superclusters Map(Wray, Bahcall, Bode, etal ‘06)

  27. Superclusters Size Distribution ncl Size (Radius in Mpc) 100 1 10

  28. Superclusters Axis-Ratio:a2/a1(Wray, Bahcall, Bode etal) Nsc 0 1 Axis-Ratio: a2/a1

  29. Superclusters Axis-Ratio:a3/a1 Axis Ratio a3/a1

  30. Filaments or Pancakes?(Wray, Bahcall, Bode, etal ‘06) 1 1D - Filaments 3D - Spherical a3/a2 Triaxial 2D - Pancakes 0 a2/a1 0 1 0.6

  31. Conclusions Superclusters • Supeclusters are Triaxial > More so at ealier times • Size: reaching ~200h-1 Mpc • Shape: <a2/a1> ~ 0.6, <a3/a1> ~ 0.1-0.2 e.g., ~ 100 x 60 x 10-20 Mpc(z ~ 0)  Nearing ‘Pancakes’ at z ~ 0

  32. Conclusions Clusters • Clusters are Triaxial > More so at earlier times • <Ecl> ~ 0.3 to 0.5(z ~ 0 to 3) • Strong Cluster Alignment to ~100 Mpc • Alignment and Ellipticity increase with z  New ToolinCosmology: <Ecl>  8, m

  33. Cluster Ellipticity (z)(Ho, Bahcall, Bode 07)

  34. Supercluster Axis-Ratio:a3/a2 Axis-Ratio: a3/a2

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