Distribution of the extensive Doppler redshift of quasars

We make an analysis of the distribution of the extensive Doppler redshift defined as (z) over tilde (Dopp) = (z(abs) - z(em)) / (1 + z(em)) with a sample of 1317 absorption redshifts available from 401 quasars. The analysis reveals a bi-peak structure in the distribution, with one component located at (z) over tilde (Dopp) similar or equal to 0.00 and the other at (z) over tilde (Dopp) similar or equal to -0.01. A study of some possible causes suggests that the structure can be well interpreted: while the absorbers inside the same cluster as the quasar concerned could contribute to the first component and the less populated space between clusters could explain the gap between the two peaks, the typical distance between clusters could account for the second component. If the bi-peak structure is real, which needs to be confirmed by complete samples, one would be able to obtain some useful cosmological information.