Constraint on Cosmic Reionization from High-z QSO Spectra Kumiko Hiroi (Univ. of Tsukuba) Collaborators : Masayuki Umemura, Taishi Nakamoto (Univ. of Tsukuba)

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 >4 Observation by WMAP (Spergel et al. 2003, Kougut et al. 2003) The optical depth of Thomson scattering is te=0.17±0.04 Reionization history must satisfy these observational results.

Observation of High-z QSO Continuum Depression (Oke & Korycansky 1982) decrease of the average flux by absorption of neutral hydrogen QSO at z=6.28 DA=0.93 Fan et al. 2001 J103027.10+052455.0 z=6.28 Lyα Continuum Depression Flux (μJy) fνcon Strong absorption Lyß Wavelength (Å) DA increases steeply at z >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. te=0.17±0.04

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

Models and Methods 1. A LCDM cosmology(WMAP) is assumed. i.e. Wm=0.3, WL=0.7,Ωbh2=0.02, H0=70km s-1 Mpc-1 2. Random Gaussian density fields are generated by the Truncated Zel’dovich approximation at each redshift from z=4 to z=20. 3. Isotropic UV background spectrum is assumed to be I0=I21 10-21(ν/νL)-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.

Ionization by UV Background Radiation N3＝643 in (8Mpc) 3, Nangle = 642 -2 -3 -4 -5 -6 -1 log XHI Ionization Structure (z=6, I21=0.1) -26 -27 -26.5 -27.5 -28 log rg [cm-3] Density Field at z=6 UV background radiation 10-3≤ I21 ≤1 Neutral fraction

Evolution of Ionization Structure (in the case of I21=0.1) z=12 -2 -3 -4 -5 -6 -1 log XHI Central part of over dense regions are neutral because of the self-shielding effect. z=6 The neutral fraction decreases with redshift. z=4 All regions are highly ionized.

Generation of Absorption Line System result of z=6 and I21=0.1 QSO at zQSO -2 -3 -4 -5 -6 -1 log XHI observer 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 profile：Voigt profile(Tg=104K)

Lya Absorption Line Systems zQSO=4 and I21=1 zQSO=5 and I21=0.1 normalized flux zQSO=6 and I21=0.1 wavelength [Å]

Continuum Depression and Ionization Degree Continuum Level zQSO=6 and I21=0.1 1 normalized flux 0.6 0.2 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.

Evolution of Continuum Depression The observed trend of DA between z=4 and z=6 requires the evolution of UV background intensity. I21=10-2 I21=0.1 continuum depression DA I21=1 The observational results of DA require the UV intensity to be I21 ≈ 1 at z ≈ 4 I21 ≈ 0.1 at 4<z<6 redshift z

Redshift Evolution of <XHI> The difference of the results between RT and optically thin increases with redshift. -1 0.9 -2 0.99 I21=10-2 log<XHI> <Xe> I21=0.1 -3 0.999 This mean that the self -shielding effect is prominent at higher redshift. : 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!!

The Electron Optical Depth The self-shielding is prominent at z>14 in the case of I21=0.1. 0.2 If the UV intensity keeps constant at I21=0.1, the optical depth can’t achieve the WMAP result. 0.1 optical depth τe(z) 0.04 ：I21=0.1 The UV intensity needs to be stronger at z>14. ：I21=10-2 0.02 ：optically thin 10-2 4 8 12 16 20 i.e. redshift z I21 > 0.1 at z >14

Reionization Redshift The self -shielding is prominent above a critical number density of hydrogen ncrit=1.4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 <nH(z)> = ncrit . optically thin 0.1 optical depth τe(z) 0.04 This condition gives, 1+zr≈22(R/8Mpc)-1/5I211/5 0.02 I21=0.1 I21=1 WMAP optical depth requires I21 ≥1 at z≈20. 10-2 5 10 15 20 25 redshift z Reionization epoch is assessed to be zr≈21

Evolution of UVB Intensity Redshift z<4 z≈4 4<z<6 z>14 z≈20 Method proximity effect DA te I21 0.5±0.1 Giallongo et al. 1996 I21≈1 I21≈0.1 I21 > 0.1 I21 ≥ 1 I21 free 1 0.1 0.5 4 6 14 20 Redshift

Summary The observed trend of DA at z>4 requires the evolution of the UV background intensity. The observational results of DA require the UV intensity to be I21≈1 at z≈4 and I21≈0.1 at 4<z<6 . The optical depth by free electrons requires that the UV background intensity needs to keep I21>0.1 at z>14 and I21≥1 at z≈20 . If the UV background intensity keeps I21≈1 at z>14 , the cosmic reionization epoch is assessed to be zr≈21.