Constraint on Cosmic Reionization from Highz QSO Spectra

1
Constraint on Cosmic Reionization from High-z QSO
Spectra

• Kumiko Hiroi
• (Univ. of Tsukuba)

Collaborators Masayuki Umemura, Taishi
Nakamoto (Univ. of Tsukuba)
2
Requirements for Reionization History
There are two independent observations related to
cosmic reionization.
Observation of High-z QSO
(R. H. Becker et al. 2001, Fan et al. 2001)
DA increases steeply at z gt4
Observation by WMAP
(Spergel et al. 2003, Kougut et al. 2003)
The optical depth of Thomson scattering is
te0.170.04
Reionization history must satisfy these
observational results.
3
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)
DA increases steeply at z gt4
4
Observation by WMAP
(D.N.Spergel et al. 2003)
Polarization cross-power spectra
The solid line is the predicted signal based on
temperature power spectra.
The excess power at large angular scale was
caused by Thomson scattering.
te0.170.04
5
The Purpose of Research
We simulate the cosmic reionization by solving 3D
radiative transfer of ionizing photons in an
inhomogeneous universe.
By comparing the calculation results with
observational data, we attempt to estimate

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

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Models and Methods
1. A LCDM cosmology(WMAP) is assumed.
i.e. Wm0.3, WL0.7,Obh20.02, H070km s-1 Mpc-1
2. Random Gaussian density fields are generated
by the Truncated Zeldovich approximation at each
redshift from z4 to z20.

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

4. The Ionization structures are calculated by
solving 3D radiative transfer at each redshift.
The ionization degrees are calculated assuming
ionization equilibrium.
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Ionization by UV Background Radiation
N3643 in (8Mpc) 3, Nangle 642
UV background radiation
10-3 I21 1
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Evolution of Ionization Structure
(in the case of I210.1)
z12
Central part of over dense regions are neutral
because of the self-shielding effect.
z6
The neutral fraction decreases with redshift.
z4
All regions are highly ionized.
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Generation of Absorption Line System
result of z6 and I210.1
1. We place a QSO at zQSO.
2. A line of sight is randomly selected.
3. We calculate the amount of neutral hydrogen at
each point on a line of sight. Then absorption
lines are generated.

• line profileVoigt profile(Tg104K)

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Lya Absorption Line Systems
normalized flux
wavelength Å
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Continuum Depression andIonization Degree
Continuum Level
zQSO6 and I210.1
1
normalized flux
0.6
0.2
0
8500
8100
8200
8300
8400
wavelength Å
continuum depression of this spectrum
spatial mean of the neutral hydrogen fraction
Large value of DA does not indicate a high
fraction of neutral hydrogen.
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Evolution of Continuum Depression
I2110-3
The observed trend of DA between z4 and z6
requires the evolution of UV background
intensity.
I2110-2
I210.1
continuum depression DA
I211
The observational results of DA require the UV
intensity to be
I21 1 at z 4
I21 0.1 at 4ltzlt6
redshift z
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Redshift Evolution of ltXHIgt
I2110-3
0
The difference of the results between RT and
optically thin increases with redshift.
0
-1
0.9
-2
0.99
I2110-2
ltXegt
logltXHIgt
I210.1
-3
This mean that the self -shielding effect is
prominent at higher redshift.
0.999
RT
-4
0.9999
optically thin
-5
4
6
8
10
12
14
16
18
redshift z
The self-shielding effect can reduce the electron
optical depth significantly!!
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The Electron Optical Depth
The self-shielding is prominent at zgt14 in the
case of I210.1.
0.2
If the UV intensity keeps constant at I210.1,
the optical depth cant achieve the WMAP result.
0.1
optical depth te(z)
0.04
I210.1
The UV intensity needs to be stronger at zgt14.
I2110-2
0.02
optically thin
10-2
4
8
12
16
20
i.e.
redshift z
I21 gt 0.1 at z gt14
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Reionization Redshift
The self -shielding is prominent above a
critical number density of hydrogen
ncrit1.4?10-2cm-3(M/108 Msun)-1/5I213/5
for 104 K gas
(Tajiri and Umemura 1998)
0.2
Reionization redshift can be predicted by
ltnH(z)gt ncrit .
optically thin
0.1
optical depth te(z)
0.04
0.02
I211
I210.1
WMAP optical depth requires I21 1 at z20.
10-2
15
5
10
20
25
redshift z
Reionization epoch is assessed to be zr21
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Evolution of UVB Intensity
I21
Redshift
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Summary

• The observed trend of DA at zgt4 requires the
  evolution of the UV background intensity.
• The observational results of DA require the UV
  intensity to be I211 at z4 and I210.1 at 4ltzlt6
  .
• The optical depth by free electrons requires
  that the UV background intensity needs to keep
  I21gt0.1 at zgt14 and I211 at z20 .
• If the UV background intensity keeps I211 at
  zgt14 , the cosmic reionization epoch is assessed
  to be zr21.