SIMBAD references

We have calculated the Doppler redshifts for a sample of quasars from their observed emission and absorption redshifts. We selected only those absorption redshifts that are larger than the corresponding emission redshifts (i.e., z_abs>z_em). The sample was extracted from a quasar catalog that contains spectra of 784 quasars, for which 11,298 absorption systems and 20,837 absorption lines were detected. We obtained 256 absorption systems with z_abs>z_em from 123 quasars. We find that there is a bimodal structure in the distribution of the Doppler redshifts, with one peak being located at z_Dopp≃0.00 and the other at z_Dopp≃0.01. Around the second peak, z_Dopp≃0.01, we identify a subset of quasars with Doppler redshifts greater than 0.0088. Our analysis shows that quasars in this subset are generally brighter than those with Doppler redshifts less than 0.0088. The Doppler velocities of the absorbers of these quasars are concentrated around ∼3000 km/s. This velocity likely arises from material falling toward the central region of the quasars that originates beyond the torus.