1. The Dark Age and Cosmology Xuelei Chen ( 陈学雷 ) National Astronomical Observarories of China The 2nd Sino-French Workshop on the Dark Universe, Aug 31st 2006, Beijing

2. The Cosmic History z ~ 1000z ~ 30z ~ 6z ~ 0

3. First Stars and Reionization small perturbations collapse to form dark halos gravity gas accreate and cool form stars and galaxy Barkana & Loeb 2001

4. Observational Probes metal poor stars high redshift galaxies and quasars (IR, submm, radio) photometric drop-out technic high redshift GRB spectral lines: 21cm, Lyman alpha, H alpha, OI, OH... CMB Hubble UDF

5. Lyman alpha Absorption Fan et al 2006 Gunn-Peterson neutral fraction

6. High Redshift Sources Observation indicates that quasar density drops by a factor of 40 from z=2.5 to 6, they will not be sufficient to reionize Universe at z=6 if the shape of LF is similar to lower redshift. galaxies should be sufficient. quasargalaxy

7. Reionization and CMB polarization last scattering shell reionization To produce polarization, needs anisotropic radiation field bulk velocity of electrons Thompson scattering

8. WMAP Results WMAP 1 year WMAP 3 year

9. WMAP results on Reionization

10. Simple Model of Reionization Chen et al (2003) Expansion of HII (ionized) region: f star predicted with structure formation theory

11. Decaying Dark Matter Chen & Kamionkowski, 2004 If Dark Matter can decay, part of the energy is deposited in IGM and could ionize the gas

12. Annihilating Dark Matter L. Zhang et al., astro-ph/0603425 If dark matter mass is 1-100 MeV instead of 100 GeV (neutralino), then the number density is much higher. Annihilation rate ~ n 2 Boehm, Hooper & Silk 2003 Inconsistencies among e + e -, gamma-ray, CMB and Supernovae

13. The 21cm tomographic probe Furlanetto, Sokasian, Hernquist 2003 Probe the reionization process with 21cm tomography ( Madau, Meiksen & Rees 1997 )

14. Foreground X. Wang et al astro-ph/0501081

15. Ongoing 21cm projects MWA 21CMA/PAST First generation dedicated projects: 21CMA, LOFAR, MWA interferometers clustered dipoles typical baseline: a few km collecting area: 10 4-5 m 2 Using existing telescopes: VLA, GMRT More to come: FAST, MWA5000, SKA 21CMA/PAST FAST

16. The physics of 21cm line spontanous transition F=1 F=0 Lyman series scattering (Wouthousian-Field mechanism) Ly  collision induced transition CMB induced transition CMB n=0 n=1 21cm Ly  n=2

17. Spin Temperature Ly  collision Thermal systems: spin atomic motion CMB Ly  photons

18. Lyman alpha photons injected photons: photons emitted/scattered at Ly alpha frequency, produced by recombination Continuum photons: UV photon between Ly alpha and Ly beta, redshift to Ly alpha frequency Once enter Ly alpha frequency (Doppler core), resonant scattering & confined locally. At Ly alpha frequency, color temperature equals to kinetic temperature leaking by 2 photon process higher Lyman series

19. Evolution of global spin temperature CMB gas spin star formation z>150: T k =T cmb =T s 50<z<150: T s =T k <T cmb collisional coupling 25<z<50: T k <T s = T cmb no coupling 15<z<25: T k <T s <T cmb Ly alpha coupling 10 T s >T cmb Ly alpha coupling

20. The temperature of gas spin temperature evolution 21cm brightness temperature Chen & Miralda-Escude 2004 Heating of IGM: Shock ionizing radiation Lyman alpha? No (Madau, Meiksen, Rees 1997, Chen & Miralda-Escude 2004, Hirata 2006, chuzhoy & Shapiro 2006, Rybicki 2006, Meiksen 2006, Pritchard & Furlanetto 2006) X-ray

21. Modulation of 21cm signal  density (cosmic web, minihalo)  ionization fraction (galaxy, cosmic HII region)  spin temperature: temperature, density, Ly alpha flux dark age: density & peculiar velocity first light: density & spin temperature reionization: density & ionization When Ts >> Tcmb: emission saturates perturbation

22. Lyman alpha sphere around first stars first stars: 100 solar mass metal free star radiating at Eddington limit (Bromm et al 2001) NOT TO SCALE life time of the star ~ 3 Myr, Hubble time ~ 10 8 yr light propagation time ~ size of Lya sphere (10 kpc) halo virial radius ~ 0.1 kpc Chen & Miralda-Escude 2006

23. Formation Rate of first stars Minimal mass requirement: T vir > 2000 K One star formed per halo Star died after 3 Myr, so exist only in halos just formed This breaks down at low redshift: (1) halo destruction (2) feed back

24. The effect of heating no heatingwith heating

25. Cross Section Map Ly alpha background reduce contrast of Ly alpha sphere If gas heated above CMB, no absorption signal absorption signal much stronger than emission

26. The bubble model of reionization For an isolated region, condition for ionization: but so Zahn et al 2006

27. Bubble model bubble size distribution

28. high redshift fluctuation Barkana & Loeb 2005 density fluctuation during dark age large scale spin-temperature variation induced by first galaxies Barkana & Loeb 2004

29. Cosmology with 21 cm fluctuation AP testpeculiar velocity AP test better measurement of power spectrum but: ionization-induced fluctuation is astrophysical higher redshift: difficult due to stronger foreground

30. Summary Current information come from: Ly alpha, high redshift galaxy, CMB Future: 21cm Dark matter decay and annihilation during dark age Model of Reionization Cosmology with 21cm

31. Merci!