SkyMapper colours of Seyfert galaxies and Changing-look AGN-II. Newly discovered Changing-look AGN

TL;DR

This study identifies and confirms changing-look AGN using SkyMapper colours, revealing a significant rate of type transitions over 15 years and presenting atypical cases that challenge existing models.

Contribution

It introduces a new method for detecting Turn-On CLAGN using SkyMapper photometry and spectroscopic data, expanding the understanding of CLAGN frequency and phenomenology.

Findings

12% Turn-On CLAGN rate over 15 years

Total CLAGN rate estimated at ~25% over this period

Discovery of atypical CLAGN cases challenging existing models

Abstract

Changing-look Active Galactic Nuclei (CLAGN) are AGN that change type as their broad emission lines appear or disappear, which is usually accompanied by strong flux changes inn their blue featureless continuum. We search for Turn-On CLAGN by selecting type-2 AGN from the spectroscopic 6dF Galaxy Survey, whose photometry, as observed over a decade later by the SkyMapper Southern Survey, is consistent with type-1 AGN. Starting from a random sample of 235 known type-2 AGN we select 18 candidates and confirm 13 AGN to have changed into type-1 spectra; observations of an incomplete sample reveal nine further Turn-On CLAGN. While our search was not intended to reliably discover Turn-Off CLAGN, we discover four such cases as well. This result suggests a Turn-On CLAGN rate of 12% over ~15 years and imply a total CLAGN rate of ~25% over this period. Finally, we present observations of AGN that are atypical for the CLAGN phenomenology, including J1109146 - a CLAGN that did not appear as an AGN in 6dFGS; J1406507 - the second reported Changinglook NLS1; and J1340153 - a CLAGN with a change timescale of three months.