Rotation of Cosmic Voids (Lee & Park 2006, ApJ in press, astro-ph/ ) Jounghun Lee & Deaseong Park (Seoul National University)

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

Origin of Voids and Clusters Local extrema of the primordial density field Local extrema of the primordial density field  x  x Clusters Voids

Properties of Voids Occupying 40% of the cosmic volume (Hoyle & Vogeley 2004) Occupying 40% of the cosmic volume (Hoyle & Vogeley 2004) Extremely underdense: Extremely underdense:  V ~ -0.9 Expanding faster Expanding faster Containing bluer galaxies with higher SFR (Hoyle et al. 2005) Containing bluer galaxies with higher SFR (Hoyle et al. 2005) ( 2dFGRS, Hoyle et al )

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

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

Linear Tidal Torque Theory Alignments between the spin axes and the intermediate principal axes of the local tidal tensors Alignments between the spin axes and the intermediate principal axes of the local tidal tensors Aspherical shapes of protohalos Aspherical shapes of protohalos Misalignments between the tidal and the inertia tensors Misalignments between the tidal and the inertia tensors

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

Spin Generation Efficiency

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

Key Prediction I Correlations between the spin axes of neighbor spins Correlations between the spin axes of neighbor spins

Key Prediction II Anti-correlations between the spin axes of voids and the directions to the nearest voids Anti-correlations between the spin axes of voids and the directions to the nearest voids

Void Spin-Spin Correlations

Void Spin-Direction Correlations

Finding Voids from Simulations The Millennium-Run Galaxy Catalog The Millennium-Run Galaxy Catalog particles particles Linear size of 500 Mpc/h Linear size of 500 Mpc/h  CDM Cosmogony  CDM Cosmogony galaxies at z= galaxies at z=0 The Void-Finder by Hoyle & Vogeley (2002, ApJ, 566, 641) The Void-Finder by Hoyle & Vogeley (2002, ApJ, 566, 641) voids with N g > voids with N g > 30

Measuring Void Spin

Void Density Distribution

Void Spin Parameter Distribution

Analytic vs. Numerical I

Analytic vs. Numerical II

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

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