Cosmic Flows surveys and CLUES simulations

Courtois, H. M.; Tully, R. Brent

doi:10.1002/asna.201211682

Cited by 14 publications

(9 citation statements)

References 18 publications

(16 reference statements)

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“…This has been concluded in several previous works, and it has been shown, for example, by N-body simulations by Nagamine & Loeb (2003) based on a numerical constraint reconstruction of the local Universe by Mathis et al (2002). Inspecting the velocity flow patterns of the Local supercluster shown in Klypin et al (2003), Tully & Mohayaee (2004), and Courtois & Tully (2012), we find that only inside 10 Mpc infall velocities up to 500 km s −1 seem to occur, reaching the lower limit for a collapse. We can also use the estimate of the infall velocity profile from the constraint reconstruction of the Local supercluster by Klypin et al (2003) to find the outermost collapsing shell of the supercluster.…”

Section: Local Supercluster and Virgo Infallsupporting

confidence: 86%

On the definition of superclusters

Chon

Böhringer

Zaroubi

2015

A&A

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To obtain a physically well-motivated definition of superclusters, we proposed in our previous work to select superclusters with an overdensity criterion that selects only those objects that will collapse in the future, including those that are at a turn-around in the present epoch. In this paper we present numerical values for these criteria for a range of standard cosmological models. We express these criteria in terms of a density ratio or, alternatively, as an infall velocity and show that these two criteria give almost identical results. To better illustrate the implications of this definition, we applied our criteria to some prominent structures in the local Universe, the Local supercluster, Shapley supercluster, and the recently reported Laniakea supercluster to understand their future evolution. We find that for the Local and Shapley superclusters, only the central regions will collapse in the future, while Laniakea does not constitute a significant overdensity and will disperse in the future. Finally, we suggest that those superclusters that will survive the accelerating cosmic expansion and collapse in the future be called "superstes-clusters", where "superstes" means survivor in Latin, to distinguish them from traditional superclusters.

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Section: Local Supercluster and Virgo Infallsupporting

confidence: 86%

On the definition of superclusters

Chon

Böhringer

Zaroubi

2015

A&A

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“…It is currently not yet clear how to construct a similarly effective grouping method for data points in observational galaxy peculiar velocity surveys. This problem is a subject of ongoing research in the CLUES project(Courtois & Tully 2012a). …”

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confidence: 99%

Reconstructing cosmological initial conditions from galaxy peculiar velocities – I. Reverse Zeldovich Approximation

Doumler¹,

Hoffman²,

Courtois³

et al. 2013

Monthly Notices of the Royal Astronomical Society

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We propose a new method to recover the cosmological initial conditions of the presently observed galaxy distribution, which can serve to run constrained simulations of the Local Universe. Our method, the Reverse Zeldovich Approximation (RZA), can be applied to radial galaxy peculiar velocity data and extends the previously used Constrained Realizations (CR) method by adding a Lagrangian reconstruction step. The RZA method consists of applying the Zeldovich approximation in reverse to galaxy peculiar velocities to estimate the cosmic displacement field and the initial linear matter distribution from which the present-day Local Universe evolved. We test our method with a mock survey taken from a cosmological simulation. We show that the halo peculiar velocities at z = 0 are close to the linear prediction of the Zeldovich approximation, if a grouping is applied to the data to remove virial motions. We find that the addition of RZA to the CR method significantly improves the reconstruction of the initial conditions. The RZA is able to recover the correct initial positions of the velocity tracers with a median error of only 1.36 Mpc/h in our test simulation. For realistic sparse and noisy data, this median increases to 5 Mpc/h. This is a significant improvement over the previous approach of neglecting the displacement field, which introduces errors on a scale of 10 Mpc/h or even higher. Applying the RZA method to the upcoming high-quality observational peculiar velocity catalogues will generate much more precise constrained simulations of the Local Universe.

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“…As a practical application, we considered the evolution of density and velocity profiles of galaxies in the quasi-linear regime (δ ∼ 5), before effects of virialization become important, and investigated the dependence on w. We found that the deviations in cluster profiles due to a 50% change in w are about ∼ 100 km/s which are barely within the current observational errors in the local universe (Courtois & Tully 2012, Davis et al 2011. We also demonstrated that the degeneracy in the density and velocity profiles arising due to parameters such as σ8 can be broken if the same information is plotted on the δ − δv plot.…”

Section: Discussionmentioning

confidence: 99%

Non-linear density–velocity divergence relation from phase space dynamics

Nadkarni-Ghosh

2012

Monthly Notices of the Royal Astronomical Society

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We obtain the non-linear relation between cosmological density and velocity perturbations by examining their joint dynamics in a two dimensional density-velocity divergence phase space. We restrict to spatially flat cosmologies consisting of pressureless matter and non-clustering dark energy characterised by a constant equation of state w. Using the spherical top-hat model, we derive the coupled equations that govern the joint evolution of density and velocity perturbations and examine the flow generated by this system. In general, the initial density and velocity are independent, but requiring that the perturbations vanish at the big bang time sets a relation between the two. This traces out a curve in the instantaneous phase space, which we call the 'Zel'dovich curve'. We show that this curve acts like an attracting solution for the phase space dynamics and is the desired non-linear extension of the density-velocity divergence relation. We obtain a fitting formula which is a combination of the formulae by Bernardeau and Bilicki & Chodorowski, generalised to include the dependence on w. We find that as in the linear regime, the explicit dependence on the dark energy equation of state stays weak even in the non-linear regime.Although the result itself is somewhat expected, the new feature of this work is the interpretation of the relation in the phase space picture and the generality of the method. Finally, as an observational implication, we examine the evolution of galaxy cluster profiles using the spherical infall model for different values of w. We demonstrate that using only the density or the velocity information to constrain w is subject to degeneracies in other parameters such as σ 8 but plotting observations onto the joint density-velocity phase space can help lift this degeneracy.

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Cosmic Flows surveys and CLUES simulations

Cited by 14 publications

References 18 publications

On the definition of superclusters

On the definition of superclusters

Reconstructing cosmological initial conditions from galaxy peculiar velocities – I. Reverse Zeldovich Approximation

Non-linear density–velocity divergence relation from phase space dynamics

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