Simulating non-linear structure formation in dark energy cosmologies

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1 Simulating non-linear structure formation in dark energy cosmologies Volker Springel Distribution of WIMPS in the Galaxy Early Dark Energy Models (Margherita Grossi) Coupled Dark Energy (Marco Baldi) Fifth Forces in the Bullet Cluster Meeting of TR 33, The Dark Universe Heidelberg, June 2009

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3 Zooming in on dark matter halos reveals a huge abundance of dark matter substructure DARK MATTER DISTRIBUTION IN A MILKY WAY SIZED HALO AT DIFFERENT RESOLUTION

4 The Milky Way 200 Billion stars within lightyears

5 The spherically averaged density profiles at z = 0.0 show good convergence DENSITY PROFILE AS A FUNCTION OF RADIUS Fundamental importance for: Rotation curve of galaxies Internal structure of galaxy clusters Gravitational lensing DM annihilation Galaxy mergers

6 The velocity distribution of dark matter at the Sun's position shows residual structure DISTRIBUTION OF VELOCITY COMPONENTS AND VELOCITY MODULUS

7 Wiggles in the distribution of the modulus of the velocity point to residual structure in energy space DISTRIBUTION OF THE VELOCITY MODULUS

8 The wiggles are the same in wellseparated boxes at the same radial distance, and are reproduced in simulations of different resolution DISTRIBUTION OF THE VELOCITY MODULUS IN DIFFERENT WELLSEPARATED BOXES

9 The velocity wiggles are generic and reflect the formation history of the halo VELOCITY MODULUS IN THE SIX AQUARIUS HALOS

10 The non-gaussian features in the velocity distribution imply ~10% corrections in the count rates of WIMP recoil searches IMPACT ON THE COUNT RATES FOR TYPICAL DIRECT DETECTION EXPERIMENTS (averaged over 1 yr) annual modulation

11 The presence of dark energy is a deep mystery A repulsive form of energy dominates the universe today P = w ρ c2 Cosmological constant: wλ = -1 Generalized dark energy models, e.g. quintessence: w(z) Many questions: How did the equation of state parameter evolve with time? Was there early dark energy? Does the dark energy field couple to (dark) matter? What are the observable consequences of dark energy? What is the physical nature of dark energy? Observational constraints: SN type Ia CMB BAO in galaxy surveys Weak lensing Cluster counts

12 So called early dark energy (EDE) models are characterized by a non-vanishing dark energy contribution even at very high redshift PARAMETERIZATION OF EDE MODELS Parameterizarion in terms of: Effective contribution during structure formation : Ω de,sf 0.04 Ωde, 0, w0, Ωde,e Wetterich (2004)

13 Theoretical predictions for EDE models suggest significant modifications of the expected abundance of non-linear objects EDE EXPECTATIONS Generalized spherical collapse model predicts: Change of virial overdensity Reduction of linear overdensity threshold for collapse dn/dm (M, z) Substantial increase in the expected abundance of halos at high-z Need N-body simulations to check. Bartelmann, Doran, Wetterich (2006) vir

14 We use a set of high-resolution simulations to study non-linear structure formation in different early dark energy models density contributions CONSIDERED MODELS Models: LCDM Ωm,0 = 0.25, Ωde,0 = 0.75, H0 = 0.7 σ8 = 0.8 w = -1 DECDM w = EDE1 w0 = Ωde,e = EDE2 w0 = Ωde,e = equation of state parameter 512^3 particles L= 100 Mpc/h m = 5*10^9 Msun Grossi & Springel (2008) Dark energy in early dark energy model Dark energy in ΛCDM expansion rate

15 Structures need to grow earlier in EDE models to reach the same amplitude today LINEAR GROWTH FACTOR Upper curves: Models normalized at z =0 Lower curves: Models normalized at z=

16 By construction, the models give the same power spectrum and halo abundance today HALO ABUNDANCE AT REDSHIFT Z=0 FOF, b=0.2

17 For equal present-day normalization, the early dark energy models show a much earlier growth of structure HALO ABUNDANCE AT DIFFERENT REDSHIFTS

18 Contrary to expectations from the generalized top-hat collapse model, a modified virial overdensity in EDE worsens the mass function description ERRORS IN MASS FUNCTION PREDICTIONS AT DIFFERENT REDSHIFTS Consistent also with Francis, Lewis & Linder (2008)

19 The standard mass-function model of Sheth & Tormen continues to work accurately for early dark energy models ERRORS IN MASS FUNCTION PREDICTIONS AT DIFFERENT REDSHIFTS Contrary to theoretical predictions, a reduced linear overdensity value for collapse does not improve the fit. δ c = 1.689

20 Early dark energy models produce more concentrated halos HALO CONCENTRATIONS AS A FUNCTION OF MASS Matches theoretical expectations Eke et al. (2001) works for EDE without modifications

21 The evolution of cluster/group abundance can be probed by counting them as a function of velocity dispersion of their galaxies CUMULATIVE COUNTS ABOVE A DISPERSION THRESHOLD σ SH =300km /sec robust against choice of richness threshold differences more evident than in the mass function

22 Clusters of galaxies remain observable in the Sunyaev-Zeldovich effect to relatively high redshift SZ MAPS IN DIFFERENT DARK ENERGY COSMOLOGIES Log(y) Y Log(y) 1.e-6 1.e-5 1.e-4 0 < z < 10.3

23 EDE cosmologies produce noticeably more SZ power SZ ANGULAR POWER SPECTRUM ν = 30 GHz

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36 The bullet cluster

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38 Fitting the density jump in the X-ray surface brightness profile allows a measurement of the shock's Mach number X-RAY SURFACE BRIGHTNESS PROFILE Markevitch et al. (2006) shock strength: M = 3.0 ± 0.4 shock velocity: vs = 4700 km/s

39 Models with a fifth force in the dark sector can speed up the bullet, but seem not required to match the bullet system SPEED OF THE BULLET IN FIFTH FORCE MERGERS (proposed by Farrar & Rosen 2006) = 1.0 vb = 3800 km/s = 1.0, rs = 4 Mpc = 0.3, rs = 4 Mpc = 1.0 = 0.3 vb = 3010 km/s =0 vb = 2600 km/s Springel & Farrar (2006)

40 An ordinary infall on a parabolic orbit produces a good match to the observations in ΛCDM SIMULATED X-RAY MAP COMPARED TO OBSERVATIONS Candra 500 ks image bullet cluster simulation

41 Despite a shock speed of ~4500 km/s, the bullet moves considerably slower VELOCITIES AND POSITIONS OF MAIN BULLET CLUSTER FEATURES AS A FUNCTION OF TIME Shock speed: 4500 km/s Pre-shock infall: km/s Shock speed relative to bullet: -800 km/s Speed of bullet: 2600 km/s

42 For c=3.0 for the parent cluster, the model can simultaneously fit the clusterbullet separation and the offset between the bullet's gas and mass peak SEPARATION OF FEATURS AS A FUNCTION OF TIME