A Systematic Survey for z < 0.04 Changing-Look AGNs

TL;DR

This study systematically searches for changing-look AGNs at z < 0.04 using sky surveys and photometry, identifying four candidates and confirming two new changing-look AGNs through optical and archival data.

Contribution

It introduces a new optical colour-based selection method for identifying changing-look AGNs and reports the discovery of two new such objects.

Findings

Identified four candidate changing-look AGNs.

Confirmed two new changing-look AGNs: NGC 1346 and 2MASX J20075129-1108346.

Recovered known changing-look AGNs Mrk 915 and Mrk 609 that did not meet new criteria.

Abstract

We have conducted a systematic survey for z $<$ 0.04 active Galactic nuclei (AGNs) that may have changed spectral class over the past decade. We use SkyMapper, Pan-STARRS and the V\'eron-Cetty & V\'eron (2010) catalogue to search the entire sky for these ``changing-look'' AGNs using a variety of selection methods, where Pan-STARRS has a coverage of 3$\pi$ steradians (sky north of Declination $-30^\circ$) and SkyMapper has coverage of $\sim$ 21,000$~\rm{deg^2}$ (sky south of Declination $0^\circ$). We use small aperture photometry to measure how colour and flux have changed over time, where a change may indicate a change in spectral type. Optical colour and flux are used as a proxy for changing H$\alpha$ equivalent width, while WISE 3.4 $\mu$m flux is used to look for changes in the hot dust component. We have identified four AGNs with varying spectra selected using our optical colour selection method. Three AGNs were confirmed from recent observations with WiFeS on the 2.3 m telescope at Siding Spring and the other was identified from archival spectra alone. From this, we identify two new changing look AGNs; NGC 1346 and 2MASX J20075129-1108346. We also recover Mrk 915 and Mrk 609, which are known to have varying spectra in the literature, but they do not meet our specific criteria for changing look AGNs.