AGN candidates in the VVV near-IR galaxy catalogue

TL;DR

This study identifies potential Active Galactic Nuclei in the Galactic disc using near-infrared and mid-infrared data, variability analysis, and color diagnostics, highlighting four candidates and one young stellar object.

Contribution

It presents a method combining infrared color analysis and variability metrics to identify AGN candidates at low Galactic latitudes.

Findings

Four galaxies are likely type-1 AGN candidates.

One source is probably a young stellar object.

Variability amplitudes and light curve slopes match known AGN characteristics.

Abstract

The goal of this work is to search for Active Galactic Nuclei (AGN) in the Galactic disc at very low latitudes with |b| $<$ 2$^\circ$. For this, we studied the five sources from the VVV near-infrared galaxy catalogue that have also WISE counterparts and present variability in the VIrac VAriable Classification Ensemble (VIVACE) catalogue. In the near-infrared colour-colour diagrams, these objects have in general redder colours compared to the rest of the sources in the field. In the mid-infrared ones, they are located in the AGN region, however there is a source that presents the highest interstellar extinction and different mid-IR colours to be a young stellar object (YSO). We also studied the source variability using two different statistical methods. The fractional variability amplitude $\sigma_{rms}$ ranges from 12.6 to 33.8, being in concordance with previous results found for type-1 AGNs. The slopes of the light curves are in the range (2.6$-$4.7) $\times 10^{-4}$ mag/day, also in agreement with results reported on quasars variability. The combination of all these results suggest that four galaxies are type-1 AGN candidates whereas the fifth source likely a YSO candidate.