Xiaohu Yang (SJTU/SHAO) With: H. Wang, H.J. Mo, Y.P. Jing, F.C van den Bosch, W.P. Lin, D. Tweed…...
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Transcript of Xiaohu Yang (SJTU/SHAO) With: H. Wang, H.J. Mo, Y.P. Jing, F.C van den Bosch, W.P. Lin, D. Tweed…...
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Xiaohu Yang (SJTU/SHAO)
With: H. Wang, H.J. Mo, Y.P. Jing, F.C van den Bosch, W.P. Lin, D. Tweed2014.11.04, KIASExploring the Local Universe with re-Constructed Initial Density fields ELUCID
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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.
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The ELUCID Project
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Finding galaxy groups in SDSS DR7Sky coverage: 7748 deg^2
Galaxies with redshifts: 639359
Groups are found and assigned with halo masses
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Reconstruct the current density fieldusing halos above a certain mass
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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 the chosen cosmological model.
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Test with mock catalogssimulation + halo occupation + SDSS selection function + redshift space + group finder
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The SDSS MTV
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First, the linear density field (k) should obey the following distribution:
Second, the density field, mod, evolved from (k), should match a given final density field f. We seek the appropriate (k) to minimize a cost parameter:
Assuming that the likelihood of mod given f is exp(-2), the posterior probability distribution for (k) given f can be written as:
We seek the solutions for (k) that maximize this posterior probability distribution function or sample the distribution.Hamiltonian Markov Chain Monte Carlo Method(prior)(likelihood)
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Phase correlationK95: the k that haveCp=0.95
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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 (He et al. 2013)Particle-Mesh dynamics
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Checking the properties of the halos2-way halo matching: halos in catalog A and B:halos are associated by tracing particles ids only, NOT halo positionswhen comparing A to B, several halos in A can be associated to a single halo in Bwhen comparing B to A, several halos in B can be associated to a single halo in AWe 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.
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Test with SDSS Mock Catalogs
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Application to SDSS
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Formation of Coma Cluster
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Velocity field
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In a void region
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Coherent motionNo tracers here
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Model:Galaxy properties: galaxy redshift survey;ISM properties: 21cm emission, millimeter/submillimeter emissions;IGM properties: quasar absorption line systems; X-ray observations; Sunyaev-Zeldovich effect.N-body+ hydrodynamics simulation of local Universe (including radiative cooling, star formation and feedback)Semi-analytical model of galaxy formation Observation: