Rotation of Cosmic Voids (Lee

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Rotation of Cosmic Voids(Lee Park 2006, ApJ in
press, astro-ph/0606477)

• Jounghun Lee Deaseong Park
• (Seoul National University)

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OUTLINE

• Origin and properties of voids
• Questions about voids yet to be answered
• A new nonparametric model for voids
• key assumptions
• analytic predictions
• numerical tests
• Discussion conclusion
• Ongoing future works

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Origin of Voids and Clusters

• Local extrema of the primordial density field

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Properties of Voids

• Occupying 40 of the cosmic volume (Hoyle
  Vogeley 2004)
• Extremely underdense
• dV -0.9
• Expanding faster
• Containing bluer galaxies with higher SFR (Hoyle
  et al. 2005)

(2dFGRS, Hoyle et al. 2005)
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Unresolved Issues

• Why are voids non-spherical ?
• Not intuitive due to the very fact that they have
  low-density and undergo faster expansion
• Why are void galaxies bluer with high SFR?
• Not explained by the density-morphology relation
  (Hoyle et al. 2005)

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Clues from Previous Works

• Shandarin et al (2006, MNRAS, 367, 1629)
• Identifying voids using the excursion set
  approach in high-resolution simulations
• Quantified the nonsphericity of voids
• Suggesting that voids undergo stronger tidal
  effect

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Linear Tidal Torque Theory

• Alignments between the spin axes and the
  intermediate principal axes of the local tidal
  tensors
• Aspherical shapes of protohalos
• Misalignments between the tidal and the inertia
  tensors

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A New Theory

• Clusters form in the regions where the degree of
  alignment between T and I is strongest.
• Less vulnerable to the tidal effect
• Low spin-generation efficiency
• Voids form in the initial regions where the
  degree of misalignment between T and I is weakest
• More vulnerable to the tidal effect
• High spin-generation efficiency

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Spin Generation Efficiency
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Tidal Effect on Voids

• Generating the rotation of matter that make up
  voids around the center of mass.
• Inducing the strong alignments between the void
  spin axis and the intermediate principal axis of
  local tidal tensor

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Key Prediction I

• Correlations between the spin axes of neighbor
  spins

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Key Prediction II

• Anti-correlations between the spin axes of voids
  and the directions to the nearest voids

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Void Spin-Spin Correlations
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Void Spin-Direction Correlations
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Finding Voids from Simulations

• The Millennium-Run Galaxy Catalog
• 21603 particles
• Linear size of 500 Mpc/h
• LCDM Cosmogony
• 8964936 galaxies at z0
• The Void-Finder by Hoyle Vogeley (2002, ApJ,
  566, 641)
• 24037 voids with Ng gt 30

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Measuring Void Spin
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Void Density Distribution
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Void Spin Parameter Distribution
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Analytic vs. Numerical I
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Analytic vs. Numerical II
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Discussion

• Strong tidal effect on voids
• Deviate void shapes from spherical symmetry
• The less massive, the higher degree of
  triaxiality
• Transfer high angular momentum to void galaxies
• Block gas cooling
• Delay star formation
• Explain the high SFR and bluer colors of void
  galaxies

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Summary and Conclusion

• Constructing a new theory for cosmic voids
• Quantifying the tidal effect on the voids
• Void spin-spin correlation
• Void spin-direction anti-correlation
• Providing a quantitative physical explanations to
  the observed properties of voids
• Providing a new insight to the large-scale matter
  distribution in a cosmic web