A Systematic Analysis of Stellar Populations in the Host Galaxies of
  Changing-look AGNs
  "Changing-look" active galactic nuclei (CL-AGNs) are a newly-discovered class
of AGNs that show the appearance (or disappearance) of broad emission lines
within a short time scale (months to years) and are often associated with the
dramatic change of their continuum emissions. They provide us an unprecedented
chance to directly investigate the host galaxy properties with minimal
contamination from the luminous central engine during the "turn-off" state,
which is difficult for normal luminous AGNs. In this work, for the first time,
we systematically characterize the stellar populations and star formation
histories (SFHs) of host galaxies for 26 turn-off CL-AGNs using the stellar
population synthesis code STARLIGHT. We find that the stellar populations of
CL-AGNs are similar to that of normal AGNs, excepts that the intermediate
stellar populations contribute more fraction. We estimate their stellar
velocity dispersions ($\rm \sigma_{\star}$) and black hole masses ($\rm
M_{BH,vir}$) and find that CL-AGNs also follow the overall $\rm
M_{BH}-\sigma_{\star}$ relationship. We also confirm the previous claim that
CL-AGNs tend to be biased towards lower Eddington ratio, and their extreme
variabilities are more likely due to the intrinsic changes of accretion rates.
In addition, CL-AGNs with recent star formations (SF) tend to have higher
Eddington ratio. Compared with previous studies, our analysis suggests that
there may be a correlation between the CL-AGN host galaxy properties and their
CL phenomena.
