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, …

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)

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

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

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

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

Scalar Component Reionization

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

Page et al.

WMAP 3yr (Spergel et al.)

QSO Absorption Line Fan et al. astro-ph/

Becker et al. AJ122, 2850

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

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?

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

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

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

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

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

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

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<Tcmb, absorption Variations of neutral hydrogen distribution appear as fluctuations in sky brightness Variations of neutral hydrogen distribution appear as fluctuations in sky brightness Line transition: above fluctuations are localized in redshift space Line transition: above fluctuations are localized in redshift space Provide a Three Dimension Map of Reionization (Neutral Hydrogen)

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).

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

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

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 <T CMB  T S =T CMB z>25 of the Fig. Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale First Light: numerous luminous sources, T S =T K <T CMB First Light: numerous luminous sources, T S =T K <T CMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. Uniformly Heated IGM Uniformly Heated IGM Ly  & X-ray background become sufficiently strong. Since (T S -T CMB )/T S =1, 21cm depends only on  & x H z<20 of Fig.1.

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

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 <T CMB  T S =T CMB z>25 of the Fig. Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale First Light: numerous luminous sources, T S =T K <T CMB First Light: numerous luminous sources, T S =T K <T CMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. Uniformly Heated IGM Uniformly Heated IGM Ly  & X-ray background become sufficiently strong. Since (T S -T CMB )/T S =1, 21cm depends only on  & x H z<20 of Fig.1.

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

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 <T CMB  T S =T CMB z>25 of the Fig. Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale First Light: numerous luminous sources, T S =T K <T CMB First Light: numerous luminous sources, T S =T K <T CMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. Uniformly Heated IGM Uniformly Heated IGM Ly  & X-ray background become sufficiently strong. Since (T S -T CMB )/T S =1, 21cm depends only on  & x H z<20 of Fig.1.

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 <T CMB  T S =T CMB z>25 of the Fig. Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale First Light: numerous luminous sources, T S =T K <T CMB First Light: numerous luminous sources, T S =T K <T CMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. Uniformly Heated IGM Uniformly Heated IGM Ly  & X-ray background become sufficiently strong. Since (T S -T CMB )/T S =1, 21cm depends only on  & x H z<20 of Fig.1.

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

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 <T CMB  T S =T CMB z>25 of the Fig. Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale First Light: numerous luminous sources, T S =T K <T CMB First Light: numerous luminous sources, T S =T K <T CMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. Uniformly Heated IGM Uniformly Heated IGM Ly  & X-ray background become sufficiently strong. Since (T S -T CMB )/T S =1, 21cm depends only on  & x H z<20 of Fig.1.

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.

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 <T CMB  T S =T CMB z>25 of the Fig. Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale First Light: numerous luminous sources, T S =T K <T CMB First Light: numerous luminous sources, T S =T K <T CMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. Uniformly Heated IGM Uniformly Heated IGM Ly  & X-ray background become sufficiently strong. Since (T S -T CMB )/T S =1, 21cm depends only on  & x H z<20 of Fig.1.

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 <T CMB  T S =T CMB z>25 of the Fig. Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale Possible formation of “ mini-halos ”, 10 6 M SUN makes T S =T virial  Emission,  T~0.1-1mK, arc-minutes scale First Light: numerous luminous sources, T S =T K <T CMB First Light: numerous luminous sources, T S =T K <T CMB Fig., z~25, until z=21, 21cm absorption in background, but high density region can be emission. Uniformly Heated IGM Uniformly Heated IGM Ly  & X-ray background become sufficiently strong. Since (T S -T CMB )/T S =1, 21cm depends only on  & x H z<20 of Fig.1.

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

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

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!

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

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

21cm = 1.4GHz z:

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?

Low Frequency Antenna 30-80MHz

High Frequency Antenna MHz

Mileura Widefield Array

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

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

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

SKA LOFAR signal  =0.5MHz

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

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

Dark Energy Alcock-Paczynski test Alcock-Paczynski test   r || rr Nusser 2005

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

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

Sensitvie to 1/HD A

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

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

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

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

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 !

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

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

Matter Power Spectrum Induced by Magnetic Fields via Lorenz Force

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

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

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

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