The spatial distribution of Ly \alpha forest absorption systems toward a group of 8 , closely spaced QSOs has been analysed and evidence for large scale structure has been found at \langle z \rangle = 2.8 .
Our technique is based on the first and second moments of the transmission probability density function which is capable of identifying and assessing the significance of regions of over- or underdense Ly \alpha absorption .
The data has revealed at least two interesting features .
1 .
An overdense structure at z = 2.27 which extends at least over \sim 8 h ^ { -1 } comoving Mpc ( q _ { 0 } = 0.5 ) in the plane of the sky .
Metal absorption lines have been found at the same redshift and thus a cluster or proto-cluster of galaxies seems to have been discovered .
2 .
A void at z = 2.97 , extending over \sim 20 h ^ { -1 } comoving Mpc in the plane of the sky , possibly caused by a locally increased UV ionising flux due to a foreground QSO .