Constraint on Cosmic Reionization from High-z QSO Spectra Hiroi Kumiko Umemura Masayuki Nakamoto Taishi (University of Tsukuba) Mini Workshop at Niigata University

Mini Workshop When was the universe reionized? Observation of High-z QSO Observation by WMAP Is this really true ? (R. H. Becker et al. 2001, Fan et al. 2001) Strong absorption= Hydrogen exists in the neutral state Reionization redshift ： (Spergel et al. 2003, Kougut et al. 2003) Reionization redshift ： evaluated by using the simple reionization history Two independent observation about cosmic reionization epoch.

Mini Workshop The Purpose of Research  The epoch of cosmic reionization  The evolution of UV radiation intensity 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

Mini Workshop Model and Calculations 1.Random Gaussian density fields are generated by the Zel’dovich approximation at each redshift. 2.Ionization structures are calculated by solving radiative transfer equation at each redshift. 3.QSO absorption line systems are generated with the results of ionization structures.  A standard  CDM cosmology is assumed. i.e. m =0.3, Ω Λ =0.7,Ω b h 2 =0.02, H 0 =70km s -1 Mpc -1  Isotropic UV background spectrum is assumed to be I 0 =I (ν/ν L ) -1 erg s -1 cm -2 Hz -1 str -1

Mini Workshop Ionization by UV Background Radiation UV background radiation Density distributionIonization structure logX HI I 0 =I (ν/ν L ) -1 erg s -1 cm -2 Hz -1 str -1 ： Lyman-limit frequency ≤ I 21 ≤1

Mini Workshop Effects of Radiation Transfer log n H [cm -3 ] log X HI z=6 z=5 z=4 local neutral fraction vs. local hydrogen number density result of I 21 =10 -3 optically thin approximation optical depth increases Self-Shielding (radiation transfer effect) Permeation of ionization photon is obstructed. number density increases

Mini Workshop logX HI Generation of Absorption Line System Result of z=6 and I 21 =0.1  Line profile ＝ Voigt profile(T g =10 4 K) QSO z QSO observer

Mini Workshop Continuum Depression and Ionization Degree wavelength [ Å ] flux z QSO =5 z QSO =6 Large value of D A does not indicate a high fraction of neutral hydrogen. Continuum level

Mini Workshop Evolution of UVB Intensity Continuum depression D A Redshift z I 21  at 5<z<6 I 21  0.1 at z=4 I 21 =1 I 21 =0.1 I 21 =10 -2 I 21 =10 -3 Observed trend of D A between z  4 and z  6 Evolution of UV background radiation intensity

Mini Workshop Evolution of Ionization Structure fraction Mass fraction Volume fraction Results of I 21 =10 -2 z=6z=10 log X HI z=14 z=17 0.7

Mini Workshop fraction Mass fraction Volume fraction Results of I 21 =10 -3 z=6z=10 log X HI z=14 z=17 Evolution of Ionization Structure Hydrogen is mostly neutral

Mini Workshop The Electron Optical Depth ： I 21 =10 -3 ： I 21 =10 -2 ： Mean density and X e = Redshift z Optical depth τ e (z) (result of WMAP) This result suggests that, the UVB intensity needs to keep almost constant or to be stronger at z>6. I 21 ≥10 -2 at z>6

Mini Workshop Reionization Epoch log X HI z=20 z= Reionization redshift ： Volume fraction Evolution of ionization structure in the case of I 21 =10 -2 z= z r 〜 20 If the UV background intensity keeps almost constant at z>6

Mini Workshop Conclusions  The strong Ly-  absorption of high-z QSO does not indicate a high fraction of neutral hydrogen.  According as the redshift changes from z=5 to z=4, the UV background intensity must increase from I 21 =10 -2 to I 21 =0.1.  The optical depth of free electron suggests that the UVB intensity needs to keep I 21 ≥10 -2 at z>6.  If the UV background intensity keeps almost constant at z>6, the cosmic reionization epoch is assessed to be z r ~20.

Mini Workshop Observation of High-z QSO Decrease of the average flux by absorption of neutral hydrogen Wavelength ( Å ) Fan et al Lyα Lyß Continuum Depression J z=6.28 Continuum Depression (Oke & Korycansky 1982) QSO at z=6.28 D A =0.93 Strong absorption= hydrogen exists in the neutral state Strong absorption f ν con Flux (μJy)

Mini Workshop Observation by WMAP (D.N.Spergel et al. 2003) Power excess on large angular scale ： caused by free electron Reionization redshift ： ionization fraction X e =1 at z<z r, and X e =0 at z>z r