Discovery of A Mg II Changing-look AGN and its Implications for a Unification Sequence of Changing-look AGNs

Understand

Changing-Look (CL) is a rare phenomenon of Active Galactic Nuclei (AGNs) that exhibit emerging or disappearing broad lines accompanied by continuum variations on astrophysically short timescales ($\lesssim$ 1 yr to a few decades).

• While previous studies have found Balmer-line (broad H$\alpha$ and/or H$\beta$) CL AGNs, the broad Mg II line is persistent even in dim states.
• No unambiguous Mg II CL AGN has been reported to date.
• We perform a systematic search of Mg II CL AGNs using multi-epoch spectra of a special population of Mg II-emitters (characterized by strong broad Mg II emission with little evidence for AGN from other normal indicators such as broad H$\alpha$ and H$\beta$ or blue power-law continua) from the Fourteenth Data Release of the Sloan Digital Sky Survey.