Constraint on Cosmic Reionization from Highz QSO Spectra

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Constraint on Cosmic Reionization from High-z QSO
Spectra

• Hiroi Kumiko
• Umemura Masayuki
• Nakamoto Taishi
• (University of Tsukuba)

2003.9.3-4 Mini Workshop at Niigata University
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When was the universe reionized?
Two independent observation about cosmic
reionization epoch.
Observation of High-z QSO
(R. H. Becker et al. 2001, Fan et al. 2001)
Is this really true ?
Observation by WMAP
(Spergel et al. 2003, Kougut et al. 2003)
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The Purpose of Research
Simulations of cosmic reionization are performed
and the QSO absorption line systems are
generated.
By confronting the generated spectra with
observation data,
we attempt to estimate

• The epoch of cosmic reionization
• The evolution of UV radiation intensity

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Model and Calculations

• A standard LCDM cosmology is assumed.

i.e. Om0.3, O?0.7,Obh20.02, H070km s-1 Mpc-1

• Random Gaussian density fields are generated by
  the Zeldovich approximation at each redshift.

• Isotropic UV background spectrum is assumed to
  be
• I0I21 10-21(?/?L)-1 erg s-1 cm-2 Hz-1
  str-1

• Ionization structures are calculated by solving
  radiative transfer equation at each redshift.

• QSO absorption line systems are generated with
  the results of ionization structures.

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Ionization by UV Background Radiation
UV background radiation
I0I21 10-21(?/?L)-1 erg s-1 cm-2 Hz-1 str-1
10-3 I21 1
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Effects of Radiation Transfer
local neutral fraction vs. local hydrogen number
density
result of I2110-3
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Generation of Absorption Line System
Result of z6 and I210.1

• Line profileVoigt profile(Tg104K)

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Continuum Depression and Ionization Degree
zQSO5
flux
zQSO6
zQSO6
Continuum level
wavelength Å
Large value of DA does not indicate a high
fraction of neutral hydrogen.
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Evolution of UVB Intensity
Observed trend of DA between z ?4 and z?6
I2110-3
I2110-2
Evolution of UV background radiation intensity
I210.1
Continuum depression DA
I21 ? 0.1 at z4
I211
I21 ? 10-2 at 5ltzlt6
Redshift z
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Evolution of Ionization Structure
Results of I21 10-2
Mass fraction
Volume fraction
z6
z10
fraction
0.7
z14
z17
log XHI
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Evolution of Ionization Structure
Mass fraction
Volume fraction
Results of I21 10-3
z6
z10
fraction
z14
z17
log XHI
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The Electron Optical Depth
0.2
(result of WMAP)
0.1
This result suggests that,
Optical depth te(z)
the UVB intensity needs to keep almost constant
or to be stronger at zgt6.
0.04
Mean density and Xe1
I2110-2
0.02
I2110-3
10-2
5
10
15
20
25
Redshift z
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Reionization Epoch
Evolution of ionization structure in the case of
I2110-2
z24
z17
0.98
z20
0.87
Volume fraction
0.70
log XHI
If the UV background intensity keeps almost
constant at zgt6
Reionization redshift
zr?20
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Conclusions

• The strong Ly-a absorption of high-z QSO does
  not indicate a high fraction of neutral hydrogen.
• According as the redshift changes from z5 to
  z4, the UV background intensity must increase
  from I2110-2 to I210.1.
• The optical depth of free electron suggests
  that the UVB intensity needs to keep I2110-2 at
  zgt6.
• If the UV background intensity keeps almost
  constant at zgt6, the cosmic reionization epoch is
  assessed to be zr20.

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Observation of High-z QSO
Continuum Depression (Oke Korycansky 1982)
Decrease of the average flux by absorption of
neutral hydrogen
Fan et al. 2001
J103027.10052455.0 z6.28
Lya
Flux (µJy)
f?con
Strong absorption
Lyß
Wavelength (Å)
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Observation by WMAP
(D.N.Spergel et al. 2003)
Power excess on large angular scale
caused by free electron
ionization fraction Xe1 at zltzr , and Xe0 at
zgtzr.
Reionization redshift