Monitoring AGNs with Hβ Asymmetry: V. long-term variation and evolution of the broad Hβ emission-line profiles

The physical origins of the diverse emission-line asymmetries observed in the spectra of active galactic nuclei (AGNs) are not completely understood. Monitoring the temporal variations of line profiles offers a promising approach to investigating the underlying physics. In this study, we present an analysis of the broad Hβ emission line profiles of eight AGNs observed from 2016–2023 May as part of the reverberation mapping campaign titled "Monitoring AGNs with Hβ Asymmetry," utilizing data obtained from the Wyoming Infrared Observatory 2.3 m telescope. We measure the temporal variations of line asymmetry, width, and central velocity shift for the eight objects. Our findings reveal that the variation in asymmetry is positively correlated with Hβ flux in five of the eight objects, while the remaining objects exhibit negative or complex correlations. Furthermore, we observe anticorrelations between line width and Hβ flux for most objects, indicating the presence of the "breathing" phenomenon in their Hβ emission lines. In contrast, two objects demonstrate an "anti-breathing" phenomenon or complex behavior. We discuss the physical origins of the temporal variations in line profiles and propose the possibility of decomposing the variations in Hβ asymmetry and width into components: one that corresponds to short-term variations in Hβ flux and another that reflects long-term variations in continuum light curves, perhaps driven by radiation pressure.