Discovery of an Mg II Changing-look Active Galactic Nucleus and Its Implications for a Unification Sequence of Changing-look Active Galactic Nuclei

Hengxiao Guo, Mouyuan Sun, Xin Liu, Tinggui Wang, Minzhi Kong, Shu Wang, Zhenfeng Sheng, Zhicheng He

Research output: Contribution to journalArticle

Abstract

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 (≲1 yr to a few decades). While previous studies have found Balmer-line (broad Hα and/or Hβ) 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 AGNs from other normal indicators such as broad Hα and Hβ or blue power-law continua) from the Sloan Digital Sky Survey Data Release 14. We present the discovery of the first unambiguous case of a Mg ii CL AGN, SDSS J152533.60+292012.1 (at redshift z = 0.449), which is turning off within rest-frame 286 days. The dramatic diminishing of Mg ii equivalent width (from 110 ± 26 Å to being consistent with zero), together with little optical continuum variation (ΔV max-min = 0.17 ± 0.05 mag) coevally over ∼10 yr, rules out dust extinction or a tidal disruption event. Combined with previously known Hβ CL AGNs, we construct a sequence that represents different temporal stages of CL AGNs. This CL sequence is best explained by the photoionization model of Guo et al. In addition, we present two candidate turn-on Mg ii CL AGNs and a sample of 361 Mg ii-emitters for future Mg ii CL AGN searches.

Original languageEnglish (US)
Article numberL44
JournalAstrophysical Journal Letters
Volume883
Issue number2
DOIs
StatePublished - Oct 1 2019

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active galactic nuclei
power law
extinction
dust
timescale
continuums
emitters
indicator
photoionization
emerging
time measurement

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Discovery of an Mg II Changing-look Active Galactic Nucleus and Its Implications for a Unification Sequence of Changing-look Active Galactic Nuclei. / Guo, Hengxiao; Sun, Mouyuan; Liu, Xin; Wang, Tinggui; Kong, Minzhi; Wang, Shu; Sheng, Zhenfeng; He, Zhicheng.

In: Astrophysical Journal Letters, Vol. 883, No. 2, L44, 01.10.2019.

Research output: Contribution to journalArticle

Guo, Hengxiao ; Sun, Mouyuan ; Liu, Xin ; Wang, Tinggui ; Kong, Minzhi ; Wang, Shu ; Sheng, Zhenfeng ; He, Zhicheng. / Discovery of an Mg II Changing-look Active Galactic Nucleus and Its Implications for a Unification Sequence of Changing-look Active Galactic Nuclei. In: Astrophysical Journal Letters. 2019 ; Vol. 883, No. 2.
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AU - Wang, Tinggui

AU - Kong, Minzhi

AU - Wang, Shu

AU - Sheng, Zhenfeng

AU - He, Zhicheng

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