Properties of IR selected Active Galactic Nuclei

TL;DR

This study investigates properties of IR-selected AGNs, confirming their identification through optical and X-ray data, and analyzing their host galaxy features, morphology, and emission properties to improve AGN selection methods.

Contribution

It compares different IR-based AGN selection techniques and evaluates their effectiveness using optical, X-ray, and morphological diagnostics, highlighting the most efficient methods.

Findings

Combination IR methods recover 61% of AGNs

Power-law emission method effectively identifies AGNs

AGN hosts tend to have bulge+disk morphologies

Abstract

Context. Active galactic nuclei (AGN) of galaxies play an important role in the life and evolution of galaxies due to the impact they exert on certain properties and the evolutionary path of galaxies. It is well known that infrared (IR) emission is useful for selecting galaxies with AGNs, although it has been observed that there is contamination by star-forming galaxies. Aims. In this work we investigate galaxy properties hosting AGNs identified at mid and near-IR wavelengths. The sample of AGNs selected at IR wavelengths was confirmed using optical spectroscopy and X-ray photometry. We study the near-UV, optical, near and mid-IR (MIR) properties, as well as [O III] {\lambda}5007 luminosity, black hole mass and morphology properties of optical and IR colour selected AGNs. Methods. We selected AGN candidates using two mid-IR colour selection techniques, a power-law emission method and a combination of mid and near-IR selection techniques. We confirm the AGN selection with two line diagnostic diagrams that use the ratio [O III]/H\b{eta} and the emission line width {\sigma} [O III] (kinematics-excitation diagram, KEx) and the host galaxy stellar mass (mass-excitation diagram, MEx), as well as X-ray photometry. Results. According to the diagnostic diagrams, the methods with the greatest success in selecting AGNs are those that use a combination of a mid and near-IR selection technique and a power-law emission. The method that use a combination of mid and near-IR observation selects a large number of AGNs, and is reasonably efficient in both the success rate (61%) and total number of AGN recovered. We also find that the KEx method presents contamination of SF galaxies within the AGN selection box. According to morphological studies based on the S\'ersic index, AGN samples have higher percentages of galaxy morphologies with bulge+disk components compared to galaxies without AGNs.