One possible explanation for the Balmer and Lyman line shifts in quasars
Internal line shifts in quasars spectra have played a more prominent role in our understanding of quasar structure and dynamics. The observed different redshift among broad hydrogen lines is still an amazing puzzle in the study of quasars. We have argued that the broad hydrogen lines, as well as the low-ionization lines in quasars, are significantly contributed by the Cerenkov quasi-line emission of the fast electrons in the dense clouds/filaments/sheets ($N_{\rm H}\geq 10^{14}~{\rm cm^{-3}}$); whereas this line-like radiation mechanism is invalid for producing the high ionization lines. In order to account for redshift difference, the Cerenkov line-like radiation mechanism could provide a plausible resolution: it is the `Cerenkov line redshift', which is different from line to line, causes the peculiar redshift-differences among Ly$α$, H$α$ and H$β$ lines. The different redshifts among different broad hydrogen lines could stand for an evidence to quantitatively support that the observed broad hydrogen lines should be blended by both the real line emission and the Cerenkov quasi-line emission. The good fitting to the observed redshifts of quasars confirms the existence of Cerenkov component in the broad hydrogen lines, which indicates that, in the blended Ly$α$ line, the line-intensity of the Cerenkov component approximately equals that of the accompanying `normal line' (an approximate equipartition of intensity between the two components in the broad Ly$α$ line). This result illustrates the importance of the Cerenkov component in the broad lines of quasars, which can be further confirmed by future observations.