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The Dark Age and Cosmology

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. z ~ 1000. z ~ 30. z ~ 6. z ~ 0. The Cosmic History. small perturbations. gravity. collapse to form dark halos.

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The Dark Age and Cosmology

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

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

  4. Observational Probes Hubble UDF • 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

  5. Lyman alpha Absorption Gunn-Peterson Fan et al 2006 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. quasar galaxy

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

  8. WMAP Results WMAP 1 year WMAP 3 year

  9. WMAP results on Reionization

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

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

  12. Annihilating Dark Matter Boehm, Hooper & Silk 2003 Inconsistencies among e+e-, gamma-ray, CMB and Supernovae If dark matter mass is 1-100 MeV instead of 100 GeV (neutralino), then the number density is much higher. Annihilation rate ~ n2 L. Zhang et al., astro-ph/0603425

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

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

  15. Ongoing 21cm projects • First generation dedicated projects: 21CMA, LOFAR, MWA • interferometers • clustered dipoles • typical baseline: a few km • collecting area: 104-5 m2 Using existing telescopes: VLA, GMRT More to come: FAST, MWA5000, SKA 21CMA/PAST FAST 21CMA/PAST MWA

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

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

  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. star formation Evolution of global spin temperature z>150: Tk=Tcmb=Ts 50<z<150: Ts=Tk<Tcmb collisional coupling 25<z<50: Tk<Ts= Tcmb no coupling 15<z<25: Tk<Ts <Tcmb Ly alpha coupling 10<z<15: Tk>Ts >Tcmb Ly alpha coupling CMB spin gas

  20. 21cm brightness temperature spin temperature evolution Chen & Miralda-Escude 2004 The temperature of gas 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 perturbation • density (cosmic web, minihalo) • ionization fraction (galaxy, cosmic HII region) • spin temperature: temperature, density, Ly alpha flux When Ts >> Tcmb: emission saturates • dark age: density & peculiar velocity • first light: density & spin temperature • reionization: density & ionization

  22. Lyman alpha sphere around first stars first stars: 100 solar mass metal free star radiating at Eddington limit (Bromm et al 2001) Chen & Miralda-Escude 2006 • life time of the star ~ 3 Myr, Hubble time ~ 108 yr • light propagation time ~ size of Lya sphere (10 kpc) • halo virial radius ~ 0.1 kpc NOT TO SCALE

  23. Formation Rate of first stars • Minimal mass requirement: • Tvir > 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 heating with 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 Zahn et al 2006 For an isolated region, condition for ionization: but so

  27. Bubble model bubble size distribution

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

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

  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!

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