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21cm Lines and Dark Ages

21cm Lines and Dark Ages. Naoshi Sugiyama Department of Physics and Astrophysics Nagoya University. Furlanetto & Briggs astro-ph/0409205, Zaldarriaga et al, ApJ 608 (2004)622, …. Reionization of the Universe.

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21cm Lines and Dark Ages

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  1. 21cm Lines and Dark Ages Naoshi Sugiyama Department of Physics and Astrophysics Nagoya University Furlanetto & Briggs astro-ph/0409205, Zaldarriaga et al, ApJ 608 (2004)622, …

  2. Reionization of the Universe • Once Inter-Galactic Medium became neutral after recombination (400,000 yrs after big bang) • UV photons from first stars and/or QSOs made IGM reionized. • It has been known that IGM were reionized by z~5 from Ly-alpha forest of QSOs. (Gunn-Peterson test)

  3. Clues to reveal Reionization of the Universe • Gunn-Peterson Test: Ly-alpha Absorption by Neutral Hydrogen Reionization completed by z~6 • CMB Polarization: Scattering by Ionized Hydrogen (electrons) Optical depth of Thomson Scattering =0.1 Reionization took place at z~10 • 21cm Tomography

  4. Early Reionization of the Universe WMAP • Reionization •  = 0.1 • Corresponds to z~10 for instantaneous reionization • z~20 for xe~0.2 (gradual reionization)

  5. Incoming Electro-Magnetic Field Same Flux No-Preferred Direction UnPolarized Same Flux Electron scattering Homogeneously Distributed Photons

  6. Incoming Electro-Magnetic Field Weak Flux Preferred Direction Polarized Strong Flux Electron scattering Photon Distributions with Quadrupole Pattern

  7. Scalar Component Reionization

  8. Reionization Liu et al. ApJ 561 (2001) First Order Effect

  9. Page et al.

  10. WMAP 3yr (Spergel et al.)

  11. QSO Absorption Line Fan et al. astro-ph/0405138

  12. Becker et al. AJ122, 2850

  13. 1% of Hydrogen’s are Neutral at z=6 We’ve just started to see the very end of the reionization epoch Fan et al. AJ 123 1247

  14. Reionization What we have known so far are • Completed by z ~ 6 •  = 0.1 • We don’t know yet • How it occurs • How long it takes • How the ionized region evolves Start at z~20, continue until z~6? / Two stages?

  15. Complete by z=6 ionization fraction Begin at z>20

  16. Two Steps Reionization motivated by WMAP + QSO Gunn-Peterson test Neutral fraction

  17. First Epoch of Structure Formation 1 Mpc z=17 Yoshida et al. (2003)

  18. First HII Region and Reionization of the Universe Sokasian, Yoshida, Abel, Hernquist (2003) UV light from massive Start reionize IGM ionize neutrial z=24 z=22 z=21 z=20

  19. A:Growing sphere C:Low density D:Random cells Poorman’s Radiative Transfer Density Field B:High density E:Boundary

  20. Optimal Reionization Experiment Be sensitive to order unity changes in ionization fraction x (or neutral fraction) Probe crucial middle stages of reionization Well-localized along the line of sight Information as a function of redshift Not require the presence of bright background sources Bright sources are rare and short lived

  21. 21cm Hyperfine Transition of Neutral Hydrogen in IGM Provide a Three Dimension Map of Reionization (Neutral Hydrogen) Fulfills all three of these criteria Excitation temperature (Spin temp.) Ts If Ts>Tcmb, emission, Ts<Tcmb, absorption Variations of neutral hydrogen distribution appear as fluctuations in sky brightness Line transition: above fluctuations are localized in redshift space

  22. 21cm Transition Need a mechanism to decouple CMB temperature TCMB and Spin temperature Ts • Two Mechanisms are possible to couple Ts and Kinetic temperature of IGM, Tk(Tk  TCMB) • collisions between hydrogen atoms (Purcell & Field 1956) • too small if / < 30[(1+z)/10]-2 (Madau et al 1997) • scattering by Ly photons (Wouthuysen 1952; Field 1958).

  23. 1,420.406MHz 21.11cm n=1, triplet n=1, singlet Ly n=1, singlet n=2, triplet

  24. 21cm Transition Observed brightness temperature TS : spin temperature, TCMB : CMB temp. xH : neutral fraction, : over-density TK : kinetic temperature, TLy : color temperature

  25. Thermal History of the Universe • Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: TK<TCMBTS=TCMB z>25 of the Fig. • Possible formation of “mini-halos”, 106MSUN makes TS=Tvirial Emission, T~0.1-1mK, arc-minutes scale • First Light: numerous luminous sources, TS=TK <TCMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. • Uniformly Heated IGM Ly & X-ray background become sufficiently strong. Since (TS-TCMB )/TS=1, 21cm depends only on  & xH z<20 of Fig.1.

  26. Two Steps Reionization motivated by WMAP + QSO Gunn-Peterson test

  27. Thermal History of the Universe • Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: TK<TCMBTS=TCMB z>25 of the Fig. • Possible formation of “mini-halos”, 106MSUN makes TS=Tvirial Emission, T~0.1-1mK, arc-minutes scale • First Light: numerous luminous sources, TS=TK <TCMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. • Uniformly Heated IGM Ly & X-ray background become sufficiently strong. Since (TS-TCMB )/TS=1, 21cm depends only on  & xH z<20 of Fig.1.

  28. Two Steps Reionization motivated by WMAP + QSO Gunn-Peterson test

  29. Thermal History of the Universe • Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: TK<TCMBTS=TCMB z>25 of the Fig. • Possible formation of “mini-halos”, 106MSUN makes TS=Tvirial Emission, T~0.1-1mK, arc-minutes scale • First Light: numerous luminous sources, TS=TK <TCMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. • Uniformly Heated IGM Ly & X-ray background become sufficiently strong. Since (TS-TCMB )/TS=1, 21cm depends only on  & xH z<20 of Fig.1.

  30. Thermal History of the Universe • Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: TK<TCMBTS=TCMB z>25 of the Fig. • Possible formation of “mini-halos”, 106MSUN makes TS=Tvirial Emission, T~0.1-1mK, arc-minutes scale • First Light: numerous luminous sources, TS=TK <TCMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. • Uniformly Heated IGM Ly & X-ray background become sufficiently strong. Since (TS-TCMB )/TS=1, 21cm depends only on  & xH z<20 of Fig.1.

  31. Two Steps Reionization motivated by WMAP + QSO Gunn-Peterson test

  32. Thermal History of the Universe • Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: TK<TCMBTS=TCMB z>25 of the Fig. • Possible formation of “mini-halos”, 106MSUN makes TS=Tvirial Emission, T~0.1-1mK, arc-minutes scale • First Light: numerous luminous sources, TS=TK <TCMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. • Uniformly Heated IGM Ly & X-ray background become sufficiently strong. Since (TS-TCMB )/TS=1, 21cm depends only on  & xH z<20 of Fig.1.

  33. Perhaps, a bit more complicated? Tokutani et al. • Collapse of Dense Gas Cloud to form a first object • Higher Kinetic Temperature: Tk>Tcmb • Emission • Formation of a First Object • Ionized hydrogen gas: Less 21cm emission • Die immediate (~1million yr.) • Radiative Transfer is needed

  34. Thermal History of the Universe • Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: TK<TCMBTS=TCMB z>25 of the Fig. • Possible formation of “mini-halos”, 106MSUN makes TS=Tvirial Emission, T~0.1-1mK, arc-minutes scale • First Light: numerous luminous sources, TS=TK <TCMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. • Uniformly Heated IGM Ly & X-ray background become sufficiently strong. Since (TS-TCMB )/TS=1, 21cm depends only on  & xH z<20 of Fig.1.

  35. Thermal History of the Universe • Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: TK<TCMBTS=TCMB z>25 of the Fig. • Possible formation of “mini-halos”, 106MSUN makes TS=Tvirial Emission, T~0.1-1mK, arc-minutes scale • First Light: numerous luminous sources, TS=TK <TCMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. • Uniformly Heated IGM Ly & X-ray background become sufficiently strong. Since (TS-TCMB )/TS=1, 21cm depends only on  & xH z<20 of Fig.1.

  36. Two Steps Reionization motivated by WMAP + QSO Gunn-Peterson test

  37. We can make a three dimensional Map of reionization! Life is not so easy!

  38. 21cm brightness temperature z=12.1 z=9.2 z=7.6 T=1-10mK, which is 10-5 of the brightness of the radio sky, dominated by synchrotron from the Galaxy Sounds impossible, but statistically may possible!

  39. Use Fluctuations Power spectrum of 21cm z=18,15,13,12 z~0.02-0.2, ~0.2-2MHz

  40. Observationally Challenging! • Foreground Contamination • TB~180(/180MHz)-2.6 at 197>>68MHz, (6.2<z<20) • Galactic Synchrotron is smooth at min. scales • How Can We Remove? • Resolve away DC term, by interferometric antenna array • subtraction of Strong radio sources • Pixel by pixel, continuum subtraction, assuming spectral smoothness

  41. 21cm = 1.4GHz z:100 10 0

  42. Observations • LOFAR • Douche Project, below 250MHz, 25000 antennas (phase 1 15000), Purchase IBM blue gene • MWA • USA (MIT) & Australia, 80-300MHz & 800-1600MHz • 21cm/PAST • Chinese, Cheap, Quick? • SKA • International, 1km2collectiong area, a few 100’s of 100-200m antennas, $1000M, 2025?

  43. Low Frequency Antenna 30-80MHz

  44. High Frequency Antenna 120-240MHz

  45. Mileura Widefield Array

  46. 21CMA/PASTdata analysis Ue-Li Pen 彭威礼 Chris Hirata Xiang-Ping Wu 武向平, Jeff Peterson

  47. Ulastai Urumqi150 km 42º 55’N86º 45’ E elev 2600m Ustir station Ground shield：5000mmountains on all sides

  48. SKA Requirements • 6<z<20: 200>>70MHz • 1-20 arcmin scales are important • To see the structure, ~0.2-2MHz, z~0.02-0.2 • Large Collecting Area • TB~ Tsys/f (  tint) : f array filling factor

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