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A hot topic: the 21cm line II

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

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A hot topic: the 21cm line II

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  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 FIR/Radio? UV/Optical/IR

  4. HI QSO absorption features at ν>νLyα Evidence for IGM reionization

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

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

  7. Fan Constraints on the epoch of reionization

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

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

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

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

  12. Constraints on the epoch of reionization (Page et al 2006) WMAP Power Spectrum 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 Which are the first sources of ionizing radiation? How did the reionization process evolve? CMB anisotropies  global amount of electrons

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

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

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

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

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

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

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

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

  22. zion~8 zion~13.5 WMAP1 (Kogut et al. 2003) (Spergel et al. 2006) WMAP3 Early/Late Reionization BC, Ferrara & White 2003 ; BC et al. 2006 Source properties: 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 Models are consistent with WMAP BUT better constraints are needed!

  23. spin temperature statistical weight 21 cm line • Associated with hyperfine transition of HI • Ideal probe of the evolution of HI: • Population of the states is described by the Boltzmann equation:

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

  25. Blackbody spectrum

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

  27. no signal absorption emission Absorption or emission? Ts and TCMB needs to be decoupled to observe 21cm line

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

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

  30. Wouthuysen-Field effect

  31. Spin temperature 1 21 cm 0 HI ground state • 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

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

  33. Spin temperature 1 21 cm 0 HI ground state • 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

  34. ~(1+z) ~(1+z)² Spin temperature evolution z

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

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

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

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

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

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

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

  42. 21cm line diagnostic The 21cm line is observed in emission if:

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

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