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

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

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

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

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

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

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

WMAP Results WMAP 1 year WMAP 3 year

WMAP results on Reionization

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

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

Annihilating Dark Matter L. Zhang et al., astro-ph/ If dark matter mass is 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

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

Foreground X. Wang et al astro-ph/

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

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

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

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

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

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

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

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

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

The effect of heating no heatingwith heating

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

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

Bubble model bubble size distribution

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

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

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

Merci!