A hot topic:

the 21cm line

II

Benedetta CiardiMPA

Timeline in cosmic historyYears 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

Timeline in cosmic historyYears 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?

Evidence for IGM reionization

absorption features at ν>νLyα

HI QSO

Evidence for IGM reionization

absorption features at ν>νLyα

HI QSO

We observe Ly-alpha emission from high-z QSOs:

this indicates that the IGM is highly ionized

)/n(n10 HHI5

HI

HI at z~6:

Redshift

Wavelength Wavelength Wavelength

Lyman Forest Absorption Black Gunn-Peterson troughPatchy Absorption

z < zi

z zi

z > zi

.

Neutral IGM

Expected reionization history

Courtesy of A. Ferrara

Constraints on the epoch of reionization Fa

n

(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

(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 a

l. 20

06

)

Constraints on the epoch of reionization

(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 a

l. 20

06

)

HI fraction

(Fan

et a

l. 20

02

)

z

Spectra of high-z QSOs are sensitive to the latest stages of reionization

Constraints on the epoch of reionization

CMB power-spectrum

(Hu

web

pag

e)

tote,ndz' ) (z' e n ... (z) Thomson scattering optical depth:

Constraints on the epoch of reionization

CMB photons interact with eˉ anisotropies

WMAP Power Spectrum

Constraints on the epoch of reionization

(Pag

e e

t al 2

00

6)

Measurements of CMB anisotropies provide an estimate of the global amount of

electrons produced during reionization, but NOT the z_reion

tote,ndz' ) (z' e n ... (z) Thomson scattering optical depth:

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?

Model of galaxy formation (feedback effects)

Modelling of cosmic reionization: ingredients

...

)(ln

)(ln2 2/0

2/12

dyncool

c

ttdt

dMM

eMMd

d

dM

dnM c

Semi-analytic model Numerical simulations

+

Model of galaxy formation (feedback effects)

Modelling of cosmic reionization: ingredients

...

)(ln

)(ln2 2/0

2/12

dyncool

c

ttdt

dMM

eMMd

d

dM

dnM c

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 …

Spectral Energy Distribution

Properties of the sources of ionizing radiation

Zero or higher metallicity?

Salpeter or Larson IMF?

? Initial Mass Function (IMF) and spectrum:

1.35MdN/dlogM

1.35crit )/MM(1dN/dlogM

Salpeter IMF:

Larson IMF:

(Yosh

ida e

t al. 2

00

7)

Properties of the sources of ionizing radiation

Gaussian

Clumpy

(BC

et a

l 20

02

)

Ionization rate [1/s]

? Escape Fraction (Fesc):

Fesc <20% but there is a big variation in the number both theoretically & observationallyFesc > 70% for primordial, very-massive stars

1+z

(Rico

tti & S

hu

ll 20

00

)

Model of galaxy formation (feedback effects)

Modelling of cosmic reionization: ingredients

...

)(ln

)(ln2 2/0

2/12

dyncool

c

ttdt

dMM

eMMd

d

dM

dnM c

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 …

Model of galaxy formation (feedback effects)

Modelling of cosmic reionization: ingredients

...

)(ln

)(ln2 2/0

2/12

dyncool

c

ttdt

dMM

eMMd

d

dM

dnM c

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 …

Simulations of reionization

M~M 910

Simulation properties Source properties

- - metal-free stars - L=20/h Mpc com. - Salpeter/Larson IMF - effect of mini-halos - Fesc=5-20%

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)

Redshift Evolution of HI density

z=18 z=16 z=14

z=12

z=13

z=11.5 z=10.5

z=9.5 z=9

z=10

z=8.5 z=8

0.0

0.015

(BC

, Sto

ehr &

White

20

03

)

zion~8 zion~13.5

Early/Late Reionization

0.040.16e (Kogut et al. 2003)

Source properties:

0.030.09e (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 WMAPBUT

better constraints are needed!

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

Zem/abs ν

10 130 MHz

15 90 MHz

20 70 MHz

)/TT3exp()T/kexp(-h/gg/nnssB0101

statistical weight spin temperatureK0.068T

21 cm line against the CMB

)e)(1B(T)eB(T)B(T sCMBbττ

22kT/c 2B(T) kTh For radio frequencies (Rayleigh-Jeans),

z1

T-TTTT CMBs

CMBbb )e(1TeTT SCMBb

ττ

CMB photonsat TCMB sT,

)B(TIκη

IddI

bτ

emission

absorption

brightness temperature

H(z)(z)n

TT

32π3A

(z)HI

s

310 λ

115

10s102.85A

spontaneous emission coeff.

Hubble const.

Kz)(1 2.73TCMB

Blackbody spectrum

21 cm line against the CMB

)e)(1B(T)eB(T)B(T sCMBbττ

22kT/c 2B(T) kTh For radio frequencies (Rayleigh-Jeans),

z1

T-TTTT CMBs

CMBbb )e(1TeTT SCMBb

ττ

CMB photonsat TCMB sT,

)B(TIκη

IddI

bτ

emission

absorption

brightness temperature

H(z)(z)n

TT

32π3A

(z)HI

s

310 λ

115

10s102.85A

spontaneous emission coeff.

Hubble const.

Kz)(1 2.73TCMB

Absorption or emission?

z1

T-TTTT CMBs

CMBb

Ts and TCMB needs to be decoupled to observe 21cm line

sT,

CMBs TT

sCMB TT absorption

emission

sCMB TT no signal

Radiative transitions (CMB) Collisions with H, e, p Scattering with Lyalpha photons (Wouthuysen-Field)

Spin temperature

21 cm

HI ground state

1

0

Spin temperature

21 cm

HI ground state

1

0

Radiative transitions (CMB) Collisions with H, e, p Scattering with Lyalpha photons (Wouthuysen-Field)

Wouthuysen-Field effect

2/322 P

2/312 P

2/112 P

2/102 P

2/111 S

2/101 S

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, 1959Madau, Meiksin & Rees 1997Furlanetto, Oh & Briggs 2006

Spin temperature

21 cm

HI ground state

1

0

Radiative transitions (CMB) Collisions with H, e, p Scattering with Lyalpha photons (Wouthuysen-Field)

c

kcCMBs yy1

TyTyTT

α

α Field 1958, 1959Madau, Meiksin & Rees 1997Furlanetto, Oh & Briggs 2006

kinetic temperature of the gas

efficiency of scattering and collisions

'color' temperature of radiation

Medium optically thick, lot of scatterings kT~T

Spin temperature

21 cm

HI ground state

1

0

Radiative transitions (CMB) Collisions with H, e, p Scattering with Lyalpha photons (Wouthuysen-Field)

c

kcCMBs yy1

)TyyTT

α

α(Field 1958, 1959Madau, Meiksin & Rees 1997Furlanetto, Oh & Briggs 2006

z

Spin temperature evolution

~(1+z)

~(1+z)²

kc

kcCMBs T

y1TyT

T

z

Spin temperature evolution

- In the absence of other decoupling mechanisms 21cm line will not be visible at z<20

z

Spin temperature evolution

- In the absence of other decoupling mechanisms 21cm line will not be visible at z<20

(BC

& S

alv

ate

rra 2

00

7)

Lyα background from metal-freestars with Salpeter IMF or VMSwith M=300Msun

s

/hJ4P

-1-1-1-2-22thth srHzscm erg z)(110JP

z

Spin temperature evolution

(BC

& S

alv

ate

rra 2

00

7)

- In the absence of other decoupling mechanisms 21cm line will not be visible at z<20

s

kkCMB

s Ty1

TyTT

z

Spin temperature evolution

- Lyα photon scattering decouples Ts from TCMB 21cm line can be observed

(BC

& S

alv

ate

rra 2

00

7)

- In the absence of other decoupling mechanisms 21cm line will not be visible at z<20

s

z

Spin temperature evolution

- 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

(BC

& S

alv

ate

rra 2

00

7)

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

UV

x-ray

1~xHII

0.3~xHII

X-ray heating

- X-rays from high-z SN remnants or mini-quasars

][cm13.6eV

106.32318

HI

υ

][ (UV)ray)-(x HI

/1

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)

X-ray heating

- X-rays from high-z SN remnants or mini-quasars

][cm13.6eV

106.32318

HI

υ

][ (UV)ray)-(x HI

/1

(Pelu

pessy

et a

l. 20

07

)

21cm line diagnostic

/k)Tlog( b

HIHI

HI

bnn

TT

1Tn )T-(TTTT

s

CMB

sCMBsCMBs

The 21cm line is observed in emission if:

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