### The Probability Distribution of the Flux in the Lya Forest

Vincent Desjacques

Hebrew University, Jerusalem

Abstract:

I will present a measurement of the probability distribution
function (PDF) of the Lya transmitted flux at redshift 2<z<4 from a sample
of SDSS quasars. The PDF is obtained by fitting a powerlaw continuum on a
spectrum-by-spectrum basis. The SDSS data are compared to a theoretical
PDF drawn from mock lognormal spectra, whose statistical properties have
been constrained to match the observed Lya flux PDF and power spectrum of
Keck spectra. The lognormal model fits the Keck data very well at all
redshifts. However, it produces a poor fit to the SDSS data, unless large
continuum correction are applied. A decrease of 15 per cent in the mean
quasar continuum with a rms variance at the 20 per cent level greatly
improves the fit. This strongly suggests that there is a break in the
spectral slope of high-redshift quasars around the Lya emission line.