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Eric Gjerde, origamitessellations

ORIGAMI: Structure finding with phase-space folds Mark Neyrinck Johns Hopkins University. Eric Gjerde, origamitessellations.com. Some collaborators: Bridget Falck, Miguel Aragón-Calvo, Guilhem Lavaux, Alex Szalay Johns Hopkins University. Outline - The Universe as Origami

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Eric Gjerde, origamitessellations

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  1. ORIGAMI: Structure finding with phase-space folds Mark Neyrinck Johns Hopkins University Eric Gjerde, origamitessellations.com

  2. Some collaborators: Bridget Falck, Miguel Aragón-Calvo, Guilhem Lavaux, Alex Szalay Johns Hopkins University

  3. Outline - The Universe as Origami - Lagrangian coordinates: perhaps underappreciated for simulation analysis - Finding stream-crossings/caustics: a parameter-free morphology classifier - Stretching/contraction of the “origami sheet” in position space also useful for halo finding • Mark Neyrinck, JHU

  4. (e.g. Bertschinger 1985) Spherical collapse in phase space • Mark Neyrinck, JHU

  5. A simulation in phase space: a 2D simulation slice vx x y z x y • Mark Neyrinck, JHU

  6. ORIGAMI Order-ReversIng Gravity, Apprehended Mangling Indices - 1d: particle in a halo if its order wrt any another particle is swapped compared to the original Lagrangian ordering - 3d: particle in a halo if this condition holds along 3 orthogonal axes (2 axes=filament, 1 axis=wall, 0 axes=void) - Need some diagonal axes as well - Finds places where streams have crossed • Mark Neyrinck, JHU

  7. 200 Mpc/h simulation, 0.8 Mpc/h cells δinitial

  8. log(1+δfinal) (measured using Voronoi tessellation) plotted on Lagrangian grid

  9. 200 Mpc/h simulation: # axes along which particle has crossed another particle (on Lagrangian grid) blue: 0 (void) cyan: 1 (sheet) yellow: 2 (filament) red: 3 (halo)

  10. Morphology of particles, showing Eulerian position.

  11. A 200 Mpc/h simulation: final-conditions morphology of particles, showing Eulerian position.

  12. Lines between initial, final positions, colored according to morphology.

  13. walls+filaments+haloes Fraction of dark matter in various structures. walls+filaments walls a

  14. How to group halo particles once they’re identified? - Eulerian: group adjacent particles in Voronoi tessellation (Lagrangian grouping better?) - Halo mass function (Knebe et al, Halo-finder comparison): • Mark Neyrinck, JHU

  15. How much does the origami sheet stretch? - Look at spatial part, ∇L⋅ψ. Lagrangian displacement ψ = xf - xi. ∇L⋅ψ ~ -δL. - ∇L⋅ψ = -3: halo formation, where ∇L⋅xf=0. • Mark Neyrinck, JHU

  16. Duality between structures in Eulerian, Lagrangian coordinates - Blobs become “points” (haloes) - Discs between blobs become filaments - Haloes look like voids in Lagrangian space! - Duality in Kofman et al. 1991, adhesion approx. • Mark Neyrinck, JHU

  17. Filaments often stretched out. - Could allow access to smaller-scale initial fluctuations than naively you would think?

  18. Origami - An interesting method to detect structures, independent of density Eric Gjerde, origamitessellations.com • Mark Neyrinck, JHU

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