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Exploring the Local Universe with Re-Constructed Initial Density Fields (ELUCID)

The ELUCID project aims to accurately reconstruct the initial conditions of the local Universe in order to directly compare data and theory. This includes a galaxy redshift survey, constrained simulations, and the use of a group finder to reconstruct the current density field. The project also involves testing with mock catalogs and applying the techniques to real observations.

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Exploring the Local Universe with Re-Constructed Initial Density Fields (ELUCID)

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  1. Exploring the Local Universe with re-Constructed Initial Density fields （ELUCID） Xiaohu Yang (SJTU/SHAO) With: H. Wang, H.J. Mo, Y.P. Jing, F.C van den Bosch, W.P. Lin, D. Tweed… 2014.11.04, KIAS

  2. Motivation Shortcomings in comparing theory (simulations) with data in a statistical way: (1) cosmic variance (environmental effects); (2) only part of information is used. If we can accurately reconstruct the initial condition of the local Universe, we can compare data and theory ‘directly’.

  3. The ELUCID Project Future works Galaxy redshift survey Reconstructed initial conditions Constrained simulation (formation history of local universe) Simulation code Group finder Yang et al. 2005;2007 HMC+PM (Wang et al. 2013;2014) Domain cross correlation Correct redshift distortion Reconstructed mass density field of local universe group catalogue (“real space”) group catalogue (redshift space) Wang et al. 2009;2013 Wang et al. 2012

  4. Finding galaxy groups in SDSS DR7 Sky coverage: 7748 deg^2 Galaxies with redshifts: 639359 Groups are found and assigned with halo masses

  5. Reconstruct the current density field using halos above a certain mass

  6. Method: (1) Each point in space is assigned to its nearest halo according to distance scaled by halo virial radius; (2) The density at the point is given by the cross-correlation between halos and mass given by thechosen cosmological model.

  7. Test with mock catalogs simulation + halo occupation + SDSS selection function + redshift space + group finder

  8. The SDSS MTV

  9. Hamiltonian Markov Chain Monte Carlo Method • First, the linear density field δ(k) should obey the following distribution: • Second, the density field, ρmod, evolved from δ(k), should match a given final density field ρf. Weseek the appropriate δ(k) to minimize a ‘cost parameter’: • Assuming that the likelihood of ρmod given ρf is exp(-χ2), the posterior probability distribution for δ(k) givenρf can be written as: • We seek the solutions for δ(k) that maximize this posterior probability distribution function or sample the distribution. (prior) (likelihood)

  10. Phase correlation K95: the k that have Cp=0.95

  11. Particle-Mesh dynamics • ZA: k95~0.3 h/Mpc (Nusser & Dekel 1992; many previous works) • MZA: k95=0.33 h/Mpc (Wang et al. 2013) • 2LPT: k95=0.37 h/Mpc (Jasche & Wandelt 2013; Kitaura 2013) • ALPT: k95=0.45 h/Mpc (Heβ et al. 2013)

  12. Checking the properties of the halos • 2-way halo matching: halos in catalog A and B: • halos are associated by tracing particles ids only, NOT halo positions • when comparing A to B, several halos in A can be associated to a single halo in B • when comparing B to A, several halos in B can be associated to a single halo in A • We consider halos in A and B to be a "match", if only the association is consistent when I compare A to B and B to A.  • We consider halos in one catalog to be a "double", if the association only goes one way. 

  13. Test with SDSS Mock Catalogs re-simulation original reconstructed

  14. Application to SDSS The Great Wall Region z=3 z=2 z=1 z=0

  15. z=3 z=2 z=1 z=0 Formation of Coma Cluster

  16. Velocity field

  17. In a void region

  18. Coherent motion No tracers here

  19. Model: • Galaxy properties: galaxy redshift survey; • ISM properties: 21cm emission, millimeter/submillimeter emissions; • IGM properties: quasar absorption line systems; X-ray observations; Sunyaev-Zel’dovich effect. • N-body+ hydrodynamics simulation of local Universe (including radiative cooling, star formation and feedback) • Semi-analytical model of galaxy formation Observation:

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