During his PhD in Göttingen, T. Tepper Garcia has investigated the stochastic effects in the attenuation by intergalactic HI, mostly in the form of Lyman-alpha clouds, on the luminosities and colours of distant galaxies. Using recent observed distributions for the number densities of clouds as a function of redshift, their column densities and Doppler parameters, he performed Monte Carlo realisations  of thousands of lines of sight with hundreds to thousands of Lyman-alpha clouds each. His results for the 1-, 2-, 3-sigma scatter around the mean attenuation are included in the GALEV models and used in our interpretation of high-z galaxies. As an independent consistency check for his Monte-Carlo Lyman-alpha cloud distributions he calculated the mean cosmic flux decrement and, for the first time ever, the scatter to be expected around its mean value due to cosmic variance, which turned out to be significant at all redshifts. The cosmic flux decrement is not only valuable to correct QSO continuum fluxes and constrain the Gunn Peterson trough, but also to estimate the baryonic mass density as a function of redshift. He found different methods used to evaluate it on QSO spectra in the literature, giving discrepant results, closely investigated them and considerably improved the accuracy (Tepper Garcia & Fritze, submitted). In collaboration with him (now in Potsdam) and P. Richter (Potsdam), we plan to extend these studies and achieve a significantly improved determination of the redshift evolution of the cosmic baryon content and its scatter.

References: