The Evolution of the Intergalactic Medium Transmission to Redshift 6

We have measured the transmission of the Lyman alpha forest produced byneutral hydrogen scattering in the intergalactic medium between redshifts 2 and6.3 using high signal to noise, high resolution (R > 5000) observations of 50quasars spread over the redshift range. We use a uniform set of 15 Angstromintervals covering Lyman alpha, Lyman beta, and Lyman gamma absorption regionsto tabulate the forest transmission as a function of redshift. The transmittedfractions show a relatively smooth evolution over the entire range ofredshifts, which can be modelled with a smoothly decreasing ionization rate.Previous claims of an abrupt change at a redshift of approximately 6 appear inpart to be a consequence of an incorrect conversion of Lyman beta to Lymanalpha optical depths. The tabulated transmissions can be used to calculate thecolors of objects with a specified input spectrum as a function of redshift. Wecalculate the colors of a flat f_nu galaxy with a large intrinsic continuumbreak, as an important example.Comment: 32 pages, 6 figures, 6 table