QSO Emission Line Redshift Differences

Redshift differences between QSO emission lines reflect the kinematical differences between the regions where the lines are produced. Gaskell (1982) discovered a systematic redshift difference between the broad lines of high ionization and the narrow forbidden lines that amounted to a blueshifting of C IV λ1549 by 600 km s−1. Gaskell obtained this result basically by comparing C IV emission and Mg II λ2798 emission in one sample of QSOs and by comparing Mg II emission and the narrow forbidden lines in a different sample. So the distribution of C IV emission redshifts relative to the narrow forbidden lines was not sampled directly by Gaskell. By observing QSOs with redshifts near 1.3, it is possible to directly sample the redshift difference between C IV and the narrow forbidden lines. This redshift difference and its distribution should provide kinematical information on the clouds of gas that give rise to the broad lines of high ionization. The narrow forbidden lines are the preferred velocity reference because they may reflect the systemic velocity of the QSO.

Cosmological implication of the emission line redshift distribution of quasars

The peaks and dips in the quasar redshift distribution seem to be incompatible with the cosmological principle. This lays the cosmological redshift hypothesis under suspicion and censure, and has been considered by some investigators as a manifestation of the intrinsic nature of quasar's redshift. So it is worthwhile studying whether the redshift distribution of quasars could be explained in the framework of cosmological redshift. As we know, this distribution is affected not only by the possible physical origin of redshift but also by the selection effects in the observations (Zhou, Deng, Zhou 1983). From this we have the redshift distribution function f(z) = P(z)R(z), where P(z) is the real distribution function which depends on the evolutionary properties of quasars and the space-time structure of the Universe, and R(z) is the factor caused by the selection effect in the line identification.