Large Scale Simulations of Reionization

1. 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

2. 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

3. 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.

4. Simulations: Pro and Cons • Limited ranges • mass resolution • spatial resolution • number of sources • Expensive • Possible saves: • No temperature • No helium • Simple source prescription • Reionization process is complex: • Source clustering • HII region overlap • Recombinations (n2) • Temperature effects • Analytical models cannot capture all of these effects, numerical models can.

5. Simulations: How? • Our motivation: large scalesimulations. • Observationally needed (~degree fields of view). • Theoretically needed (cosmic variance, size of HII regions, >>10 Mpc). • Approach: • PMFAST(Merz, Pen, Trac2005) simulations (4.3 billion particles): • Evolving density field • 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 ΛCDM (WMAP)

6. 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 xNphoton. • Choices used: f=2000 and 250. • Other source models to be explored in the future.

7. 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

8. 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

9. Statistics Full density HII density HI density • 3D powerspectra: • Poisson noise at largest 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 resemble analytical inside-out, nor outside-in results (Furlanetto et al. 2004a,b) Furlanetto et al. 2004a

10. z=11.9 z=10.8 20/h Mpc 10/h Mpc 5/h Mpc Statistics • 3D powerspectra: • Poisson noise at largest 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 resemble analytical inside-out, nor outside-in results (Furlanetto et al. 2004a,b) Furlanetto et al. 2004b

11. 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)

12. 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.

13. WMAP1 WMAP3 WMAP1 versus WMAP3 • Identical simulations (100/h Mpc, f=250), differing only in cosmological parameters: FM Band FM Band

14. 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:

15. 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 , i.e. DT max/min are in the tens of mK at ~arcmin scales. ~1° ~1°

16. 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.

17. 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.