1. Andrea Ferrara SISSA/International School for Advanced Studies, Trieste Cosmic Dawn and IGM Reionization

2. Sequence of Events At z=1000 the Universe has cooled down to 3000 K. Hydrogen becomes neutral (“Recombination”). At z < 20 the first “PopIII” star (clusters)/small galaxies form. At z ~ 6-15 these gradually photo- ionize the hydrogen in the IGM (“Reionization”). At z<6 galaxies form most of their stars and grow by merging. At z<1 massive galaxy clusters are assembled. Time

3. Infall Rate: 0.01 M o /yr Envelope: 10 3 M o Core:10 -2 M o density temperature

4. Salvaterra & AF 2002; Best fit model to NIR data z end = 8.8 f   30% IR Background Data Points Pop III stars can explain observed NIRB excess if VMS dominate IMF ~ (1+z end ) λ Lyα PopIII Stars+Galaxies First Light at Cosmic Dawn: Very Massive Stars Magliocchetti, Salvaterra & AF 2003 Galaxies

5. Reionization by Very Massive Stars ? z = 17 NIRB - fitting evolution

6. WMAP results: reionization at z > 10 ? Reionization Tests Temperature-Polarization Cross Power Spectrum τ e = 0.17± 0.04

7. Inhomogeneous Reionization Choudhury & AF 2005 Choudhury & AF 2005 Self-consistent treatment of the evolution of ionized regions and thermal history Follow evolution of neutral, HII and HeIII regions; treat IGM as multiphase gas Inhomogeneous density distribution: log-normal model Three sources of ionizing radiation:  PopIII stars: early redshifts, high mass, zero metallicity  PopII stars: Salpeter IMF, transition from PopIII @ z < 9  Quasars: significant @ z < 6, using  -M BH relation Radiative feedback suppressing SF in low-mass halos, set by:  Molecular cooling in neutral regions  Photoionization temperature in ionized regions

8. Experimental constraints Ionized regions filling factor Photo-rates HI HeII LLS statistics GP optical depth e.s. optical depth Mean density temperature log

9. Inhomogeneous Reionization Additional hints from CMB+21cm line (  T/T 0 ) CMB (  T b /T 0 ) 21CM late reionization early reionization 115 MHz90 MHz CROSS CORRELATE Salvaterra, Ciardi, AF & Baccigalupi 2005

10. Inhomogeneous Reionization Salvaterra, Ciardi, AF & Baccigalupi 2005 early late Size of HII region (Mpc) from zero of correlation fct. HII regions: size evolution Bandwidth

11. Miniati, AF, White & Bianchi 2004 The UVB in the Post-Reionization Epoch Ionizing photons from structure formation  Mass range: log M = 11 – 13  Virial temperatures: log T  6  Bremsstrahlung + line emission  Escape fraction  1 Galaxies QSOs Thermal

12. Miniati et al 2004 The UVB in the Post-Reionization Epoch Ionizing photons from structure formation Photoionization rates Total QSOs GalaxiesThermal Thermal, no feedback Thermal Thermal, no feedback QSOs Galaxies Fan 2002 HIHeII

13. Maselli & AF, in prep Radiative Transfer Effects on the Ly  Forest UVB fluctuations See Maselli’s poster Photoionization rates fluctuations through a box at z=3.27  HI  HeII  Power spectrum  Temperature  Elemental abundances  Eta parameter

14. Radiative Transfer Effects on the Ly  Forest UVB fluctuations Maselli & AF, in prep Optically thin HeII HI

15. Brief Summary Photoionization rate fluctuations (10%, 60%) for (HI, HeII) induced by RT effects Massive first stars likely responsible for NIRB excess can reionize the IGM at z  15 Early reionization not in contrast with any constraint from QSO absorption line data Detailed reionization history from coupled CMB/21cm experiments HeII reionization more complex; affected by thermal radiation from structure formation

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17. THE END