1. A hot topic: the 21cm line II Benedetta Ciardi MPA

2. Timeline in cosmic history Years since the Big Bang ~350000 (z~1300) ~100 million (z~20-40) ~1 billion (z~6) ~13 billion (z=0)  Big Bang: the Universe is filled with hot plasma  The gas cools and becomes neutral: recombination  The first structures begin to form: reionization starts  Reionization is complete  Today’s structures

3. Timeline in cosmic history Years since the Big Bang ~350000 (z~1300) ~100 million (z~20-40) ~1 billion (z~6) ~13 billion (z=0)  Cosmic Microwave Background UV/Optical/IR FIR/Radio?

4. Evidence for IGM reionization absorption features at ν>ν Lyα HIQSO

5. Evidence for IGM reionization absorption features at ν>ν Lyα HIQSO We observe Ly-alpha emission from high-z QSOs: this indicates that the IGM is highly ionized HI at z~6:

6. Redshift Wavelength Lyman Forest Absorption Black Gunn-Peterson trough Patchy Absorption z < z i z  z i z > z i. Neutral IGM Expected reionization history Courtesy of A. Ferrara

7. Constraints on the epoch of reionization Fan

8. (Fan) Spectra of high-z QSOs The IGM is highly ionized @ z<6 The HI abundance increases with increasing redshift Constraints on the epoch of reionization

9. (Fan) Spectra of high-z QSOs The IGM is highly ionized @ z<6 The HI abundance increases with increasing redshift Ly-α optical depth (Fan et al. 2006) Constraints on the epoch of reionization

10. (Fan) Spectra of high-z QSOs The IGM is highly ionized @ z<6 The HI abundance increases with increasing redshift Ly-α optical depth (Fan et al. 2006) HI fraction (Fan et al. 2002) z Spectra of high-z QSOs are sensitive to the latest stages of reionization Constraints on the epoch of reionization

11. CMB power-spectrum (Hu webpage) Thomson scattering optical depth: Constraints on the epoch of reionization CMB photons interact with eˉ  anisotropies

12. WMAP Power Spectrum Constraints on the epoch of reionization (Page et al 2006) Measurements of CMB anisotropies provide an estimate of the global amount of electrons produced during reionization, but NOT the z_reion Thomson scattering optical depth:

13. Constraints on the epoch of reionization High-z QSOs  latest stages of reionization at z~6 & galaxies CMB anisotropies  global amount of electrons Which are the first sources of ionizing radiation? How did the reionization process evolve?

14. Model of galaxy formation (feedback effects) Modelling of cosmic reionization: ingredients Semi-analytic model Numerical simulations +

15. Model of galaxy formation (feedback effects) Modelling of cosmic reionization: ingredients Semi-analytic model Numerical simulations + Properties of the sources of ionizing radiation Stellar type Quasars DM annihilation/decay light dark matter gravitinos neutralinos sterile neutrinos …

16. Spectral Energy Distribution Properties of the sources of ionizing radiation Zero or higher metallicity? Salpeter or Larson IMF? ? Initial Mass Function (IMF) and spectrum: Salpeter IMF: Larson IMF:

17. (Yoshida et al. 2007) Properties of the sources of ionizing radiation Gaussian Clumpy (BC et al 2002) Ionization rate [1/s] ? Escape Fraction (Fesc): Fesc <20% but there is a big variation in the number both theoretically & observationally Fesc > 70% for primordial, very-massive stars 1+z (Ricotti & Shull 2000)

18. Model of galaxy formation (feedback effects) Modelling of cosmic reionization: ingredients Semi-analytic model Numerical simulations + Properties of the sources of ionizing radiation Stellar type Quasars DM annihilation/decay light dark matter gravitinos neutralinos sterile neutrinos …

19. Model of galaxy formation (feedback effects) Modelling of cosmic reionization: ingredients Semi-analytic model Numerical simulations + Properties of the sources of ionizing radiation Stellar type Quasars Radiative transfer of ionizing radiation DM annihilation/decay light dark matter gravitinos neutralinos sterile neutrinos …

20. Simulations of reionization Simulation properties Source properties - - metal-free stars - L=20/h Mpc com. - Salpeter/Larson IMF - effect of mini-halos - Fesc=5-20% l Simulations of galaxy formation  gas & galaxy properties (Springel et al. 2000; Stoehr 2004) l Stellar type sources  emission properties l  propagation of ionizing photons (BC et al. 2001; Maselli, Ferrara & BC 2003; Maselli, BC & Kanekar 2008)

21. Redshift Evolution of HI density z=18z=16z=14 z=12 z=13 z=11.5 z=10.5 z=9.5 z=9 z=10 z=8.5z=8 0.0 0.015 (BC, Stoehr & White 2003)

22. z ion ~8z ion ~13.5 Early/Late Reionization (Kogut et al. 2003) Source properties: (Spergel et al. 2006) S5: Salpeter IMF+fesc=5% (late reion. case) S20: Salpeter IMF+fesc=20% L20: Larson IMF+fesc=20% (early reion. case) L20 + MHs: addition of sub-grid physics to include MHs absorption/photoevap BC, Ferrara & White 2003; BC et al. 2006 WMAP1 WMAP3 Models are consistent with WMAP BUT better constraints are needed!

23. o Associated with hyperfine transition of HI o Ideal probe of the evolution of HI: o Population of the states is described by the Boltzmann equation: 21 cm line Z em/abs ν 10130 MHz 1590 MHz 2070 MHz statistical weight spin temperature

24. 21 cm line against the CMB For radio frequencies (Rayleigh-Jeans), CMB photons at T CMB emission absorption brightness temperature spontaneous emission coeff. Hubble const.

25. Blackbody spectrum

26. 21 cm line against the CMB For radio frequencies (Rayleigh-Jeans), CMB photons at T CMB emission absorption brightness temperature spontaneous emission coeff. Hubble const.

27. Absorption or emission? T s and T CMB needs to be decoupled to observe 21cm line absorption emission no signal

28.  Radiative transitions (CMB)  Collisions with H, e, p  Scattering with Lyalpha photons (Wouthuysen-Field) Spin temperature 21 cm HI ground state 1 0

30. Spin temperature 21 cm HI ground state 1 0  Radiative transitions (CMB)  Collisions with H, e, p  Scattering with Lyalpha photons (Wouthuysen-Field)

31. Wouthuysen-Field effect

32. Spin temperature 21 cm HI ground state 1 0  Radiative transitions (CMB)  Collisions with H, e, p  Scattering with Lyalpha photons (Wouthuysen-Field) Field 1958, 1959 Madau, Meiksin & Rees 1997 Furlanetto, Oh & Briggs 2006

33. Spin temperature 21 cm HI ground state 1 0  Radiative transitions (CMB)  Collisions with H, e, p  Scattering with Lyalpha photons (Wouthuysen-Field) Field 1958, 1959 Madau, Meiksin & Rees 1997 Furlanetto, Oh & Briggs 2006 kinetic temperature of the gas efficiency of scattering and collisions 'color' temperature of radiation Medium optically thick, lot of scatterings 

34. Spin temperature 21 cm HI ground state 1 0  Radiative transitions (CMB)  Collisions with H, e, p  Scattering with Lyalpha photons (Wouthuysen-Field) Field 1958, 1959 Madau, Meiksin & Rees 1997 Furlanetto, Oh & Briggs 2006

35. z Spin temperature evolution ~(1+z) ~(1+z)²

36. z Spin temperature evolution - In the absence of other decoupling mechanisms 21cm line will not be visible at z<20

37. z Spin temperature evolution - In the absence of other decoupling mechanisms 21cm line will not be visible at z<20 (BC & Salvaterra 2007) Lyα background from metal-free stars with Salpeter IMF or VMS with M=300M sun s

38. z Spin temperature evolution (BC & Salvaterra 2007) - In the absence of other decoupling mechanisms 21cm line will not be visible at z<20 s

39. z Spin temperature evolution - Lyα photon scattering decouples T s from T CMB  21cm line can be observed (BC & Salvaterra 2007) - In the absence of other decoupling mechanisms 21cm line will not be visible at z<20 s

40. z Spin temperature evolution - Lyα photon scattering decouples T s from T CMB  21cm line can be observed - Lyα photon scattering heats the gas  21cm line can be observed in emission (BC & Salvaterra 2007) Metal-free stars, Salpeter IMF Very massive metal-free stars Lyα heating - In the absence of other decoupling mechanisms 21cm line will not be visible at z<20 s Lyα heating is effective for z ≤ 15

41. UV x-ray X-ray heating - X-rays from high-z SN remnants or mini-quasars 21cm (Madau, Meiksin & Rees 1997; Giroux & Shull 2001; Glover & Brand 2002; Chen & Miralda-Escude’ 2003; Gnedin & Shaver 2004; Zaroubi et al. 2006; Kuhlen & Madau 2006)

42. X-ray heating - X-rays from high-z SN remnants or mini-quasars (Pelupessy et al. 2007)

43. 21cm line diagnostic The 21cm line is observed in emission if:

44. o The IGM is highly ionized at z<6 o Information on latest stages of reionization and the global amount of e produced o Models can reproduce observations  more stringent constraints o 21cm line is the ideal probe of the reionization process o The crucial quantity for the observability of the line is Ts o We expect to observe the line in absorption against the CMB and one the IGM has been heated (but not ionized) in emission IGM reionization & 21cm line