a hot topic: the 21cm line ii
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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. - PowerPoint PPT PresentationTRANSCRIPT
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