A New Infrared Criterion for Selecting Active Galactic Nuclei to Lower Luminosities

Abstract

We present a spectroscopic and photometric analysis of a sample of 416,288 galaxies from the Sloan Digital Sky Survey (SDSS) matched to mid-infrared (mid-IR) data from the Wide-field Infrared Survey Explorer (WISE). By using a new spectroscopic fitting package, GELATO (Galaxy/AGN Emission Line Analysis TOol), we are able to retrieve emission line fluxes and uncertainties for SDSS spectra and robustly determine the presence of broad lines and outflowing components, enabling us to investigate WISE color space as a function of optical spectroscopic properties. In addition, we pursue spectral energy distribution template fitting to assess the relative active galactic nucleus (AGN) contribution and nuclear obscuration to compare to existing mid-IR selection criteria with WISE. We present a selection criterion in mid-IR color space to select AGNs with an ∼80% accuracy and a completeness of ∼16%. This is the first mid-IR color selection defined by solely using the distribution of Type I and Type II optical spectroscopic AGNs in WISE mid-IR color space. Our selection is an improvement of ∼50% in the completeness of targeting spectroscopic AGNs with WISE down to an SDSS r < 17.77 mag. In addition, our new criterion targets a less-luminous population of AGNs, with on average lower [O iii] luminosities by ∼30% ( > 0.1 dex) compared to typical WISE color–color selections. With upcoming large photometric surveys without corresponding spectroscopy, our method presents a way to select larger populations of AGNs at lower AGN luminosities and higher nuclear obscuration levels than traditional mid-IR color selections.

The environment of AGN dwarf galaxies at z ∼ 0.7 from the VIPERS survey

“…Methods based on the emis-sion in different wavelengths (emission lines, infrared colours, X-ray and radio emissions) do not lead to the same samples and suffer from the contamination (e.g. Hviding et al 2022). Tracing the redshift evolution is even harder as the most standard AGN selection method based on the optical BPT diagram is restricted to low-redshift (z < 0.45) samples (see Sec.…”

“…There is a number of ways of selecting AGN using mid-infrared colours. In this work, we use a recently proposed selection criterion aimed at capturing a higher total number of spectroscopic AGN with the completeness of over 13.8% (Hviding et al 2022). With this method, we recover ∼ 10% of AGN from our final AGN sample (see Fig.…”

The XXL Survey L. AGN contamination in galaxy clusters: detection and cosmological impact

“…We search for all mid-infrared counterparts within an angular radius of 60 from the AC position, resulting in 33 mid-IR matches (the full AC catalogue) all within <11 of the object centre. We compute the mid-IR colour properties of each source in order to assess how many fall within the bounds of type I and II optical spectroscopic AGN, based on a new selection criteria described in Hviding et al (2022). The results are shown in Figure 6.…”

The Kiloparsec-scale Influence of the AGN in NGC 1068 with SALT RSS Fabry–Pérot Spectroscopy*

“…Following the adaptive binning, we combine the spectra in each bin by summing their flux and adding their errors in quadrature. We then fit the combined spec-trum in each bin using the Galaxy/AGN Emission Line Analysis Tool (GELATO, Hviding 2022) following the procedure outlined in Hviding et al (2022). GELATO models the continuum as a linear combination of Simple Stellar Populations (SSPs) from the Extended MILES stellar library (E-MILES; Vazdekis et al 2016) and models emission lines as Gaussians.…”