1. High Redshift QUASAR Spectra as Probe of Reionization of IGM

2. Fan et al., 2002, AJ, 123, 1247 White et al., 2003, AJ, 126,1 Fan et al., 2006, AJ, 132, 117 Maselli et al., 2009, MNRAS, 395, 1925 Mortlock et al., 2011, Nature, 474, 616 Bolton et al., 2011, MNRAS Letters, 291B

3. Fan et al., 2002, AJ, 123, 1247 White et al., 2003, AJ, 126,1 Fan et al., 2006, AJ, 132, 117 Maselli et al., 2009, MNRAS, 395, 1925 Mortlock et al., 2011, Nature, 474, 616 Bolton et al., 2011, MNRAS Letters, 291B

9. Max. Lya absorption redshift that is not affected by the proximity effect of the quasar itself.

10. Intrinsic Spectra +

14. for Lyb Need correction in t GP for foreground Lya absorption

15. using

17. Combining t GP from all sources Lya -Lyb conversion factor Calculate avg. transmitted flux ratios in Lya -Lyb over same redshift range and define conversion factor as --

19. ● At z<6 Lya & Lyb mesurements are consistent. At very high z when no Lya flux is detected, Lyb gives a secure optical depth or more stringent lower limit in t GP. ● Accelerated evolution above z>5.5 ● Also there is an increase in dispersion of optical depth at high z. This is due to the fact that some LOS have complete GP trough while some others have t GP mildly higher than low z power law extrapolation.

20. Evolution of Neutral Fraction If we consider IGM is isothermal and photoionized by a uniform UV background, where

21. is volume weighted density distribution function Evolution of Neutral Fraction

25. Distribution of Dark Gaps

27. ● The transition from isolated, short gaps to deep, long troughs cannot be explained by gradual thickening of Lya forest, it implies a phase transition in IGM geometry. ● At high z avg. drak gap length increases dramatically but remains finite, which implies presence of already ionized regions formed by galaxies. ● Modelling galaxy luminosity, age and escape fraction of UV photons from galaxies, one can put a upper limit on IGM neutral fraction from the dark length distribution.

28. HII Regions around Quasars Stromgren Radius when recombination is not important

29. Uncertainties HII Regions around Quasars ● Uncertainty in quasar lifetime. Observations suggest in range 10 5 – 10 8 yr. Most of the time assumed as ~ 10 7 yr = Eddington timescale for BH growth. ● Value of ● Clumpiness & radiative transfer effect within HII region which changes LOS size of HII region. ● Ionizing photon contribution from galaxies in overdense environment of quasar ● Large-scale clustering of IGM around quasar, which will affect the estimation of neutral fraction.

30. Uncertainties HII Regions around Quasars Boundary of HII region is difficult to measure from observation, it cannot be defined by the point where flux is zero, ---- ● If IGM is highly ionized the flux never reaches zero, also it has large fluctuations. ● Using zero flux as boundry is restricted by the resolution and the smoothing length. ● Even if IGM is neutral, reaching zero flux does not mean boundary of HII region, the IGM could still be ionized by quasar to a level much higher than surrounding IGM but with a optical depth higher than detection limit

31. Proximity zones around Quasars The region (R p ) inside which the transmitted flux ratio is above 0.1 when smoothed to a resolution of 20 Angstrom Uncertainty – max. uncertainlty from quasar redshift

32. Rp scaled to a common absolute magnitude

33. Absorption Profile in Proximity zones

34. Estimation of Neutral Fraction For an IGM with f HI << 1, after scaling out the dependence on quasar luminosity, proximity zone evolves as Thus a decrease of HII region size by a factor of 2.8 in between z =5.7 to 6.4 suggests an increase of neutral fraction by a factor of 14. GP optical depth estimates volume and mass avg neutral fractions are 9.3x10 -5 and 2.8x10 -3 at z~5.7, while proximity zone estimates them as 1.3x10 -3 and 0.04 at z~6.4.

35. Conclusions ● Strong evolution of IGM ionization state at high z (~5.7) is observed via GP optical depth evolution. Neutral fraction increases by a factor 7 in between z=5.5 to 6.2. ● Dispersion of IGM properties increases with z, fluctuations increases by a factor ~4. ● From proximity zone evolution it is found that neutral fraction has increased by a factor ~14 in between z=5.5 to 6.4 ● There is no evidence that IGM is largely neutral at z~6.4, on the contrary finite length of dark gaps in the spectra implies an upper limit on the neutral fraction less than 50%, likely even more lower.