Supermassive Black Hole and Broad-line Region in NGC~5548: Results from Five-season Reverberation Mapping

Ka-Xing Lu, Jin-Ming Bai, Jian-Min Wang, Chen Hu, Yan-Rong Li, Pu Du, Ming Xiao, Hai-Cheng Feng, Sha-Sha Li, Jian-Guo Wang, Zhi-Xiang Zhang, Ying-Ke Huang

Submitted on 22 September 2022


NGC 5548 is one of the active galactic nuclei (AGN) selected for our long-term spectroscopic monitoring with the Lijiang 2.4~m telescope, aiming at investigating the origin and evolution of the broad-line regions (BLRs), accurately measuring the mass of the supermassive black holes (SMBHs), and understanding structure and evolution of the AGN. We have performed five-season observations for NGC~5548 with the median sampling interval ranging from 1.25 to 3 days. The light curves of the 5100~\AA\ continuum and broad emission lines are measured after subtracting contamination of the host galaxy starlight. The time lags of the broad He~{\sc ii}, He~{\sc i}, Hγ, and Hβ lines with respect to the 5100~\AA\ continuum are obtained for each season and their mean time lags over the five seasons are 0.69, 4.66, 4.60, 8.43 days, respectively. The Hγ and Hβ velocity-resolved lag profiles in the seasons of 2015, 2018, 2019, and 2021 are constructed, from which an ``M-shaped'' structure is found in 2015 but disappears after 2018. Our five-season reverberation mapping (RM) yields an averaged virial SMBH mass of M/107M=14.22, with a small standard deviation of 1.89. By combining the previous 18 RM campaigns and our five-season campaign for NGC~5548, we find that there exists a time lag of 3.5~years between the changes in the BLR size and optical luminosity. In addition, we also construct the BLR radiusluminosity relation and the virial relation for NGC~5548.


Comment: 23 pages, 15 figures, accepted for publication in ApJS

Subject: Astrophysics - Astrophysics of Galaxies