A COSMIC REST FRAME AT HIGH-REDSHIFT

We discuss a method to detect or put upper limits on our motion relative to a rest frame provided by point sources at high redshift, and we apply the technique to real and artificial redshift surveys of intergalactic gas clouds (Lyman alpha absorption systems). The redshift regime that can be sampled this way extends from z approximately 0 (UV observations) right up to the redshifts of the most distant QSO (z approximately 5 at present). The detection of our motion with respect to this high-z frame is based on the direction-dependent changes in the number of objects per redshift interval, as induced by the Doppler effect. The presently available data samples (not optimal for our purpose) enable us to establish an upper limit upsilon/c < 0.05 for the motion of the Solar system relative to the Ly alpha forest at mean redshift = 2.9.