Approaching the Reionization: Cosmic Variance in the Transmission of the IGM at z~ 5--6

摘要: We present results of the analysis of high-S/N, medium-resolution spectra of 4 SDSS QSOs at z~ 5.73-6.28, obtained with the ESI instrument at the WMKO Keck-II telescope. The spectra show a considerable variation in the optical depth as a function of redshift at z> 5. A clumpy and gradual transition to a fully reionized IGM is generically expected in models of early structure formation, as a consequence of the biasing and a gradual appearance and early evolution of the first luminous sources. Within a small sample statistics, the data are qualitatively consistent with such expectations, suggesting that the mean ionizing flux approximation is not an adequate descriptor even at the final stages of the reionization era. We will also describe briefly a new survey for QSOs at z~ 5-6.5.