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Large Scale Distribution of Galaxies and Voids

Large Scale Distribution of Galaxies and Voids. A Hip-Hop Opera in C#. starring: Sir Johnathan Bongaarts James Pogemiller, III Directed by Senior Spielbergo. log(t). P(k). k. high-k small scale perturbations grow fast, non-linearly. P(k). Now. z=1. k. baryonic oscillations

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Large Scale Distribution of Galaxies and Voids

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  1. Large Scale Distribution of Galaxies and Voids A Hip-Hop Opera in C# starring: Sir Johnathan Bongaarts James Pogemiller, III Directed by Senior Spielbergo

  2. log(t) P(k) k high-k small scale perturbations grow fast, non-linearly P(k) Now z=1 k baryonic oscillations appear – the P(k0 equivalent of CMB T power spectrum CMB P(k) Evolution of matter power spectrum MRE k sub-horizon perturb. do not grow during radiation dominated epoch P(k) k P(k) k Harrison-Zeldovich spectrum P(k)~k from inflation P(k) EoIn k log(rcomov) log(k) Williams, L.L.R., 2006

  3. Overview • Large Scale Structure • Classifications • Quantifying LSS • Simulated vs. Observed • Voids • Definition • Halos Near Voids • Local Void • What to do now

  4. Large Scale Structure (LSS) • Baryonic and Dark Matter collapsing under gravity into a “frothy” structure • Think: “cosmic sponge” or “soap bubbles” • Filaments (matter) • Bubbles (voids) Z ~ 30

  5. LSS: Structure Classification • Two-Point Correlation Function • “Fair-Sample Hypothesis” • Different regions of the universe are described by the same physical processes, but can be taken independently • Independent regions can then be taken to represent a statistical collection

  6. LSS: Two-Point Correlation Function Two-point correlation function for galaxies: ξ(r) ≡ < δ(x)δ(x+r)> (δ is the density perturbation field)

  7. LSS: Two-Point Correlation Function Power law model approximation: ξ(r) = (r0/r)γ r0 = 5.4 ± 1 h-1Mpc, γ = 1.77 ± 0.04 • Power law accuracy? • ~galactic radii (10kpc) to ~10Mpc (falls below ξ(r)) • at ~25Mpc (rises above ξ(r))

  8. LSS: Analytic Scaling Prediction • ρ vs. r scalings should describe observed clustering • For Harrison-Zel’dovich, n=1 and γ=-2, a good approximation for small k-modes • n=1 used by Millennium simulation shown later

  9. LSS: Probability Function • Differential form: dP = n2[1+ξ(r)]dV1dV2 Gives the probability that, provided one galaxy in dV1, another galaxy will be found in dV2 at a distance r

  10. LSS: Probability Function dP = n2[1+ξ(r)]dV1dV2 • Assumes: • dV is small enough that finding two galaxies within it is negligible • Redshift to distance distorts the function

  11. LSS: Voids vs Filaments • Wall Galaxies: exist at the void wall • Field Galaxies: exist elsewhere • Typically in filaments • Can exist in voids provided void definition isn’t extremely rigid • Filaments are over-dense regions of space comprised of Dark and Baryonic Matter (Field and Wall Galaxies)

  12. LSS: Helpful Picture • Filaments • Voids • Galaxies: • Wall • Field (Filament) • Field (Void) Simulation data of LSS

  13. LSS: Power Spectrum • Fourier transform of correlation function • Amplitude relates to the expected amount of structuring at a given λ • Data suggests that filaments occur around 100 to 1000 Mpc/h

  14. LSS: Current Events • Cosmological Perturbation Theory: • Clustering will occur due to gravity seeding an early homogeneous universe • Accurate on large scales only (must go to N-Body simulations…) • N-Body Simulations: • Accurate on smaller scales • Clustering occurs due to gravity

  15. LSS: Simulation/Observation • Simulations • Provide a guide for checking theoretical models • Millennium Simulation • Observations • Sloan Digital Sky Survey (SDSS) (ongoing) • 2dF Galaxy Redshift Survey (2dF) (completed, 2004) • Las Campanas Redshift Survey

  16. LSS: Millennium Simulation z = 18.3 (t = 0.21 Gyr)

  17. LSS: Millennium Simulation z = 0 (t = 13.6 Gyr)

  18. LSS: Observations Data from the 2dF Galaxy Redshit Survey

  19. LSS: Observations Las Campanas Redshift Survey data

  20. Voids Not much to talk about…

  21. LSS: Void Definition • Nutshell: any under-dense region of space with a diameter >10-25 Mpc • ∆ρ/ρ ~ -0.8 to -0.96 • Assuming spherical region: • V ~ 8x10^3 Mpc^3 • A ~ 500 Mpc^2 • Less luminous galaxies

  22. LSS: Other Void Definitions • “Regions of low density in a suitably smoothed density field” • Regions with no objects of a certain types, for example: • Rich clusters • Poor clusters • Galaxies of various morphological types • Objects over a specified luminosity limit Lindner et al, 1997

  23. Void probability function (It gets a little “emotional”) Under-density probability function Probability that an under-dense ( δρ/ρ) region of volume V will be found at a distance r. LSS: Quantifying Voids

  24. LSS: Void Hierarchy

  25. LSS: Void Hierarchy Similar to galaxies and clusters, but void hierarchy depends on surrounding structures

  26. LSS: Perspective • Voids occupy ~90% of total observed space • Boötes Void: d ~124 Mpc (assume spherical) • Volume ~ 10^6 Mpc^3 ~ 10^73 m^3 • Compare: Sloan Great Wall ~10^54 m^3 • Boötes Void is ~10^20 times larger than the Sloan Great Wall

  27. LSS: Boötes Void

  28. LSS: Getting Involved in the Community • Millennium Simulation used to study DM halos around voids (Brunino et al., 2006) • Used ΩΛ=0.75, ΩM=0.25, Ωb=0.045, h=0.73, n=1, and σ8=0.9 • Comoving box of side 500 h-1 Mpc • Spatial resolution of 5 h-1 kpc • Sample size of 2932 voids, median radius of 14 h-1 Mpc

  29. LSS: Getting Involved in the Community • DM halos have “frozen in” inertia tensors and angular momentum vectors from turn-around • According to Tidal-Torque theory, they should be preferentially aligned depending on the neighbors • Could contaminate weak lensing signals, if you’re into that kind of stuff

  30. Leaning towards parallel Parallel to void surface Perpendicular to void surface No correlation here… Brunino et al., 2006

  31. But what if we just look at DM halos with spirals at the center?

  32. Brunino et al., 2006

  33. LSS: The Northern Local Void • MW has a component of peculiar velocity away from the NLV • Faint galaxy in the center is moving quickly towards the edge • Other galaxies to the south do not show this trend • Negative gravity?! (Well…no…)

  34. LSS: Local Void Figure from Tully

  35. LSS: What to do now • LSS formation is fairly well understood on bigger scales • Smaller scales are non-linear and more difficult to deal with • Dynamical range is a limitation of simulations • Dark matter and baryonic matter • Baryons trace DM on large scales • What scales do they separate on?

  36. LSS: References • Brunino, R., Trujillo, I., Pearce, F.R., Thomas, P.A., 2006, astro-ph/0609629 • El-Ad, H., Piran, T., 1997, astro-ph/9702135 • Gaite, J., 2005, astro-ph/0510328 • Lindner, U., Fricke K.J., Einasto, J., Einasto, M., 1997, astro-ph/9711046 • Peebles, P.J.E., 2001, astro-ph/0101127 • Peebles, P.J.E., 1993, Principles of Physical Cosmology • Rood, H. J. 1988, ARA&A • Ryden, B.S., 1995, astro-ph/9510108 • Tully, R.B., 2006, astro-ph/0611357 • Williams, L.L.R., 2006, Private conversations • Williams. L.L.R., 2004, AST 5022 course notes, Sec. 4.2. • Las Campanas Redshift Survey, 1998, http://qold.astro.utoronto.ca/~lin/lcrs.html

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