Newly Discovered Changing-look Active Galactic Nuclei from SDSS and LAMOST Surveys

Abstract

Changing-look Active Galactic Nuclei (CL AGNs) exhibit drastic variations in broad emission lines (BELs), the mechanism of which remains unclear. Expanding the sample of CL AGNs is helpful to reveal the mechanism. This study aims to identify more CL AGNs by cross-matching spectroscopic data from the Sloan Digital Sky Survey (SDSS) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Our approach to identify CL AGNs is based on the automatic spectral fitting, followed by detailed visual inspections. We identify a sample of $51$ CL AGNs through this method, in which $40$ CL AGNs are newly discovered. Within this sample, $41$ CL AGNs primarily show the variability of the H$\beta$ line, nine exhibit obvious changes in both the H$\beta$ and H$\alpha$ lines, and one source mainly displays variations in the H$\alpha$ line. Our findings reveal that the sequence of appearance and disappearance of the BELs aligns with the known CL sequence. In addition, we identify 31 candidates exhibiting drastic variations in BELs without accompanying significant photometric variability. We estimate the black hole mass and Eddington ratio for all sources, which range from $2.5\times 10^6$ to $8.0\times 10^8 M_\odot$ and from $0.001$ to $0.13$, respectively. Similar to other studies, we also find that the Eddington ratios of CL AGNs and candidates are lower than those of typical AGNs. Our results support the hypothesis that the CL behavior is driven by the state transitions of the accretion disk.