Dr. LU Kaixing from Yunnan Observatories of the Chinese Academy of Sciences and his collaborators developed a spectroscopic monitoring project for two active galactic nuclei (AGN) of Mrk 817 and NGC 7469, and they found that the gravity-bounded broad-line region (BLR) in both AGNs are disturbed by other non-gravitational forces. The study was published online in The Astrophysical Journal.

In 2019, in order to enhance the understanding of the physics of BLR, the researchers used the 2.4-m telescope of Lijiang observatory, Yunnan Observatories, to study the BLR physics of Mrk 817 and NGC 7469. They obtained the spectral properties by spectral fitting and decomposition, and studied the physical properties of BLR using reverberation mapping method.

"Reverberation mapping is extensively used to detect the size and structure of radiation region in time domain. Because the star and gas dynamical method is invalid in distant AGN, reverberation mapping become the most reliable and effective method to measure the mass of supermassive black hole (SMBH) in AGN," said Dr. LU.

The researchers found that, in both AGNs, the variabilities of different broad emission lines show different time delays relative to the varying AGN continuum at 5100 (angstrom), which indicates that their BLR are stratified. They also found that mass of SMBH in Mrk 817 and NGC 7469 are 80 million and 10 million times that of the sun, respectively. For NGC 7469, the mass of SMBH measured in this study is consistent with the atom-based or molecular-based dynamical mass.

By analyzing the observation results and historical data, the researchers found that the rotation speed of the BLR in both AGNs is inversely proportional to the square of the radius, showing that the gravity-bounded BLR is virialized.

Besides, this study constructed the velocity-delay relationship of multiple broad emission lines in both AGNs from the observation data in 2019, and revealed that the blue-shifted broad-line emitters are closer to the central SMBH than the red-shifted emitters, which is consistent with the outflow gas motion.

These results showed that the BLR should suffer from other non-gravitational forces during the long-term virialized motion, and they are consistent with the finding of the researchers in 2016 that the ionizing radiation pressure could act on the BLR.

This study enables people to better understand the dynamics and kinematics of the BLR in AGN, and is helpful for developing the research on the origins and evolutions of the BLR.