Periodic variations of the first and second moments of broad Balmer emission lines from central accretion disks

Abstract

Broad emission line regions (BLRs) lying into central accretion disks has been widely accepted to explain the unique double-peaked broad emission lines in Active Galactic Nuclei (double-peaked BLAGNs). Here, accepted the accretion disk origin, periodic variations of central wavelength $\lambda_{0}$ (the first moment) and line width $\sigma$ (the second moment) of double-peaked broad emission lines are theoretically simulated and determined. Furthermore, through theoretically simulated periodicities of $T_{\lambda0}$ and $T_{\sigma}$ for variations of $\lambda_0$ and $\sigma$, periodicity ratio $R_{fs}$ of $T_{\lambda0}$ to $T_{\sigma}$ to be around 2 can be applied to support the spiral arms to be more preferred in BLRs lying into central accretion disks. Then, periodic variations of $\lambda_0$ and $\sigma$ are determined and shown in the known double-peaked BLAGN NGC1097, leading to the parameter $R_{fs}\sim2$, which can be applied as clues to support that the structure of spiral arms in disk-like BLRs in central accretion disk should be the most compelling interpretation to the variability of double-peaked broad H$\alpha$ in NGC1097. The results provide clean criteria to test accretion disk origins of double-peaked broad emission lines in AGN.