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

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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. 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) It has been known that IGM were reionized by z~5 from Ly-alpha forest of QSOs. (Gunn- Peterson test)

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

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WMAP Reionization Reionization = 0.1 = 0.1 Corresponds to z~10 for instantaneous reionization Corresponds to z~10 for instantaneous reionization z~20 for x e ~0.2 (gradual reionization) z~20 for x e ~0.2 (gradual reionization) Early Reionization of the Universe

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Same Flux Same Flux Electron No-Preferred DirectionUnPolarized Homogeneously Distributed Photons scattering

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Strong Flux Weak Flux Electron Preferred DirectionPolarized Photon Distributions with Quadrupole Pattern Incoming Electro-Magnetic Field scattering

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Scalar Component Reionization

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

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Page et al.

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WMAP 3yr (Spergel et al.)

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QSO Absorption Line Fan et al. astro-ph/

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Becker et al. AJ122, 2850

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

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Reionization Completed by z ~ 6 Completed by z ~ 6 = 0.1 = 0.1 What we have known so far are 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?

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

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

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

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

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

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

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21cm Hyperfine Transition of Neutral Hydrogen in IGM Fulfills all three of these criteria Fulfills all three of these criteria Excitation temperature (Spin temp.) Ts Excitation temperature (Spin temp.) Ts If Ts>Tcmb, emission, Ts Tcmb, emission, Ts

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

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n=1, singlet n=1, triplet 1, MHz 21.11cm n=1, singlet Ly n=2, triplet

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21cm Transition T S : spin temperature, T CMB : CMB temp. x H : neutral fraction, : over-density Observed brightness temperature T K : kinetic temperature, T Ly : color temperature

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Thermal History of the Universe Decouple to CMB, z<140, IGM cools adiabatically Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: T K

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

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Thermal History of the Universe Decouple to CMB, z<140, IGM cools adiabatically Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: T K

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

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Thermal History of the Universe Decouple to CMB, z<140, IGM cools adiabatically Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: T K

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Thermal History of the Universe Decouple to CMB, z<140, IGM cools adiabatically Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: T K

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

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Thermal History of the Universe Decouple to CMB, z<140, IGM cools adiabatically Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: T K

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

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Thermal History of the Universe Decouple to CMB, z<140, IGM cools adiabatically Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: T K

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Thermal History of the Universe Decouple to CMB, z<140, IGM cools adiabatically Decouple to CMB, z<140, IGM cools adiabatically until first objects collapse: T K

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

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

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

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z=18,15,13,12 Power spectrum of 21cm Use Fluctuations z~ , ~0.2-2MHz

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Observationally Challenging! Foreground Contamination Foreground Contamination T B ~180( /180MHz) -2.6 at 197> >68MHz, (6.2 >68MHz, (6.2

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21cm = 1.4GHz z:

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Observations LOFAR LOFAR Douche Project, below 250MHz, antennas (phase ), Purchase IBM blue gene Douche Project, below 250MHz, antennas (phase ), Purchase IBM blue gene MWA MWA USA (MIT) & Australia, MHz & MHz USA (MIT) & Australia, MHz & MHz 21cm/PAST 21cm/PAST Chinese, Cheap, Quick? Chinese, Cheap, Quick? SKA SKA International, 1km 2 collectiong area, a few 100’s of m antennas, $1000M, 2025? International, 1km 2 collectiong area, a few 100’s of m antennas, $1000M, 2025?

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Low Frequency Antenna 30-80MHz

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High Frequency Antenna MHz

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Mileura Widefield Array

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

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Ulastai Ustir station 42º 55’N 86º 45’ E elev 2600m Urumqi 150 km Ground shield ： 5000m mountains on all sides

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SKA Requirements 6 >70MHz 6 >70MHz 1-20 arcmin scales are important 1-20 arcmin scales are important To see the structure, ~0.2-2MHz, z~ To see the structure, ~0.2-2MHz, z~ Large Collecting Area Large Collecting Area T B ~ T sys / f ( t int ) T B ~ T sys / f ( t int ) : f array filling factor : f array filling factor

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SKA LOFAR signal =0.5MHz

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What we can learn from 21cm - future prospects - Reionization History: Patchy reionization Reionization History: Patchy reionization Dark Energy Dark Energy Dark Matter Dark Matter Cosmological Parameter Cosmological Parameter Non-Gaussian Fields Non-Gaussian Fields Primordial Magnetic Fields Primordial Magnetic Fields

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What we can learn from 21cm - future prospects - Reionization History: Patchy reionization Reionization History: Patchy reionization Dark Energy Dark Energy Dark Matter Dark Matter Cosmological Parameter Cosmological Parameter Non-Gaussian Fields Non-Gaussian Fields Primordial Magnetic Fields Primordial Magnetic Fields

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Dark Energy Alcock-Paczynski test Alcock-Paczynski test r || rr Nusser 2005

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Geometric Distortion r || =c z/H(z) r || =c z/H(z) r =(1+z) D A (z) r =(1+z) D A (z)

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Density field in real space Density field in redshift space Distortion by velocity fileds Geometric distortion in r|| Geometric distortion in r

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Sensitvie to 1/HD A

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What we can learn from 21cm - future prospects - Reionization History: Patchy reionization Reionization History: Patchy reionization Dark Energy Dark Energy Dark Matter Dark Matter Cosmological Parameter Cosmological Parameter Non-Gaussian Fields Non-Gaussian Fields Primordial Magnetic Fields Primordial Magnetic Fields

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Non-Gaussianity Measure of the Non-Gaussianity Measure of the Non-Gaussianity f NL =-5/12(n s -1)+5/6+3/10f(k) ~O(0.1) CMB can restrict only f NL >3 (cosmic variance) Advantage of 21cm Advantage of 21cm To probe multiple redshirts based on frequency selection To probe multiple redshirts based on frequency selection Non damping tail at l=2000, unlike CMB (Silk damping) Non damping tail at l=2000, unlike CMB (Silk damping) A. Cooray 2006

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Non Gaussian squared 21cm anisotropy bispectrum Non-Gaussian squared anisotropty

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At z=100, f NL =1 cumulative S/N f NL

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S/N ~13 f NL at z=100, S/N~5 f NL at z=30 If use multi-frequency information between 14MHz (z~100) and 45MHz (z~30), S/N~100 f NL for full sky coverage Can probe f NL ~0.01 !

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What we can learn from 21cm - future prospects - Reionization History: Patchy reionization Reionization History: Patchy reionization Dark Energy Dark Energy Dark Matter Dark Matter Cosmological Parameter Cosmological Parameter Non-Gaussian Fields Non-Gaussian Fields Primordial Magnetic Fields Primordial Magnetic Fields

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Primordial Magnetic Due to the Lorentz force, primordial magnetic fields can induce structure formation Due to the Lorentz force, primordial magnetic fields can induce structure formation Small amount of residual protons after recombination (fraction~10 -4 ) is enough Small amount of residual protons after recombination (fraction~10 -4 ) is enough Possible Effects Possible Effects Induce Formation of First stars and Reionization of the Universe Induce Formation of First stars and Reionization of the Universe Heating due to diffusion of Magnetic fields Heating due to diffusion of Magnetic fields CMB brightness temperature fluctuations by the 21cm line Tashiro & N.S. 2005

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Matter Power Spectrum Induced by Magnetic Fields via Lorenz Force

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Cumulative number of Photons from PopIII S tructure formation by magnetic fields induce Reionization If B>1nG, magnetic Jeans scale becomes large and suppress structure formation Tashiro &NS 2005

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Heating of IGM from diffusion of Magnetic Fields Ambipolar diffusion: velocity difference between ionized and neutral fluid

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Tashiro &NS 2006 The angular power spectra of CMB brightness temperature fluctuations by the 21-cm line

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Stay Tune! We will soon hear from LOFAR! More detailed theoretical works are needed.

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