Dr. LU Kaixing from Yunnan Observatories (YNAO) with collaborators gave a fascinating insight into the evolution of the broad emission line region, and achieved precise measurements of the supermassive black hole mass in active galactic nuclei of NGC 5548.

This research, published online in the Astrophysical Journal Supplement Series deepens the understanding of the active galactic nuclei (AGN) structure and its evolution.

“Reverberation mapping (RM) is a method to directly detect the size and structures of radiation region for the distant AGN in time domain, this research demonstrates that reverberation mapping is a reliable and effective method to accurately measure the mass of supermassive black hole (SMBH) in AGN,” said Dr. LU.

In 2015, the research team carried out a long-term spectroscopic monitoring project for a selected sample of widely known AGNs using the 2.4 m telescope of Lijiang observatory, YNAO, aiming at investigating the origin and evolution of the broad-line regions (BLRs), accurately measuring the mass of the SMBHs, and understanding structure and evolution of the AGN.

NGC 5548 with double-peaked broad-line profiles underwent extreme variability in the past two decades, and as a candidate of sub-parsec SMBH binary candidate, was the highest-priority target of the long-term spectroscopic monitoring campaign. Currently, this research performed five-season observations for NGC 5548 and obtained five times measurements of SMBH mass for this AGN, with the accuracy and precision of 13%, which is much better than previous measurement of 41%.

Added the five seasons of RM measurements, thus far there have been in total 23 seasons of RM measurements for NGC 5548, making it to be the most intensively RM monitored AGN. Combined the latest five-season results with historical data, another crucial finding is that the change of the BLR radius lags the varying optical luminosity with a timescale of 3.5 years, and found that the line dispersion (i.e., rotation velocity) of the BLR from 23 RM campaigns is not globally correlated with the optical luminosity. Both findings are not consistent with the normal “breathing effect” of the BLR, that is the BLR radius (size) increasing and the line width decreasing with continuum luminosity.

It is crucial to investigate the reasons for the abnormal “breathing effect” so as to better understand the structure and evolution of the BLR. The research team will continue to monitor NGC 5548 for this purpose.

Contact:
LU Kaixing
Yunnan Observatories, CAS
Email: lukx@ynao.ac.cn