One possible explanation for the Balmer and Lyman line shifts in quasars

TL;DR

This paper proposes that Cerenkov quasi-line emission significantly contributes to broad hydrogen lines in quasars, explaining observed redshift differences and suggesting a blended emission mechanism involving both real and Cerenkov lines.

Contribution

It introduces the Cerenkov line-like radiation as a key factor in quasar broad line redshifts, providing a new explanation for line shifts and blending effects.

Findings

Cerenkov component can account for redshift differences among hydrogen lines.

The broad Lyα line likely contains roughly equal intensities of real and Cerenkov emission.

Model fitting supports the presence of Cerenkov emission in quasar spectra.

Abstract

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$\alpha$, H$\alpha$ and H$\beta$ 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$\alpha$ 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$\alpha$ line). This result illustrates the importance of the Cerenkov component in the broad lines of quasars, which can be further confirmed by future observations.