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Large Scale Simulations of Reionization Garrelt Mellema Stockholm Observatory Collaborators: Ilian Iliev, Paul Shapiro, Marcelo Alvarez, Ue-Li Pen, Hugh Merz, LOFAR EoR Key Project team Contents Reionization Simulations Some results WMAP1 versus WMAP3 Secondary CMB Anisotropies Iliev et al. 2006, astro-ph/0512187 GM et al. 2006, astro-ph/0603518 Reionization A view of the epoch when the first galaxies formed. Current observational data: WMAP Thomson optical depth, SDSS QSOs, TIGM from Lyα forest Future observational data: redshifted 21cm radiation (21CMA, LOFAR, MWA, SKA); direct view of HII regions (nature of sources) and IGM density field. Simulations: Pro and Cons Reionization process is Limited ranges complex: – mass resolution – Source clustering – spatial resolution – HII region overlap – number of sources – Recombinations (n2) Expensive – Temperature effects – Possible saves: Analytical models No temperature No helium cannot capture all of Simple source these effects, numerical prescription models can. Simulations: How? Our motivation: large scale simulations. – Observationally needed (~degree fields of view). – Theoretically needed (cosmic variance, size of HII regions, >>10 Mpc). Approach: – PMFAST (Merz, Pen, Trac 2005) simulations (4.3 billion particles): Evolving density field ΛCDM (WMAP) Collapsed halo list 100/h and 35/h Mpc volumes (minimum halo masses 2.5x109 and 108 M, respectively). – C2-Ray (GM et al. 2006) postprocessing (2033, 4063): Ionized hydrogen fraction Simulations: Sources We have been working with stars as our sources of ionizing radiation. Assumptions: – M/L=const. – only atomically cooling halos contribute (M>108 M). – halos with M<109 M can be suppressed. – fixed photons/atom escaping (Iliev, Scannapieco & Shapiro 2005): f = fSF x fesc x Nphoton. Choices used: f=2000 and 250. Other source models to be explored in the future. Results: evolution Movie of density field and HII regions Green: neutral Red: Ionized Note: clustering & overlap. From z=20 to 10 (WMAP3 parameters). Overlap expected at z~7. 35/h Mpc Importance of Large Scales From our (100/h Mpc)3 volume we can analyze the reionization history of subvolumes. Large variations found, need at least volume of (30/h Mpc)3. Reionization is mostly inside-out. Reionization histories for subvolumes Statistics Full density 3D powerspectra: HII density – Poisson noise at largest HI density scales – Clear peak at some (time- dependent) characteristic scale. – Resemble analytical work (Furlanetto et al. 2004a,b) The signal is strongly non-gaussian: – Numerical results do not Furlanetto et al. 2004a resemble analytical inside- out, nor outside-in results (Furlanetto et al. 2004a,b) Statistics 3D powerspectra: z=11.9 z=10.8 – Poisson noise at largest 20/h Mpc scales 10/h Mpc – Clear peak at some (time- 5/h Mpc dependent) characteristic scale. – Resemble analytical work (Furlanetto et al. 2004a,b) The signal is strongly non-gaussian: Furlanetto et al. 2004b – Numerical results do not resemble analytical inside- out, nor outside-in results (Furlanetto et al. 2004a,b) LOS Reionization Histories From the simulations we can construct reionization histories along the line of sight. Will be used to prepare for the analysis of the LOFAR observations (2009) What Cosmology? 1st year WMAP versus 3 year WMAP: – τ: 0.17: to 0.09 (if instantanious, zreion: 16 to 11) – ns: 1.0 to 0.95, σ8: 0.9 to 0.74. Reionization happened later (good!), but structure formation also took longer. Alvarez et al. (2006): approximate scaling for simulations with similar types of sources: (1+z1)/(1+z3)≈1.4. Confirmed by new simulations. WMAP1 versus WMAP3 Identical simulations (100/h Mpc, f=250), differing only in cosmological parameters: FM Band WMAP1 FM Band WMAP3 Secondary CMB Anisotropies Patchy reionization is expected to imprint small scale anisotropies on the CMB signal through the kinetic Sunyaev-Zel’dovich effect. Several analytical estimates exist (Hu & Gruzinov 98, McQuinn et al. 2005, Santos et al. 2006, Zahn et al. 2006), with large variation in strength and scales. Now the first numerical ones. Temperature variations given by LOS integral: Sample kSZ map from patchy reionization Sample kSZ map (100/h Mpc, f=250). Range of pixel values is DT/T=-10-5 to 10-5 , ~1° i.e. DT max/min are in the tens of mK at ~arcmin scales. ~1° kSZ Power Spectra Power spectra peak at l~3000-5000, with a peak value ~1 μK. Instant reionization has order of magnitude less power for l~2000-8000, but same large-l behaviour. Uniform reionization has much less power on all scales. Conclusions Large scale simulations needed for useful results. Reionization produces a clear signature in the nHI power spectra. WMAP3 results do not require different types of sources, but move reionization by a factor ~1.4 in (1+z). kSZ due to patchy reionization produces a signal of ~μK at l~3000-5000.
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