On the Possibility that Mg II Absorbers Can Track the Merger Evolution of Galaxy Groups from High Redshift

The properties of Mg II absorption-selected systems show a large variety of kinematics and higher ionization conditions. A multivariate taxonomic study of Mg II absorbers has yielded an “extreme” class of “Double” systems. These Double systems are characterized by kinematic velocity spreads up to 400 km/s, and by twice the Ly alpha, Mg II, Fe II, and C IV absorption strengths of the more typical, “Classic”, Mg II system. Evolution in the number per unit redshift of these systems is compared to the redshift evolution in the number of close pairs of galaxies. It is found to be a plausible scenario that Double systems arise in small groups of galaxies, implying that they might trace close pair evolution to high redshifts.