The optical-infrared relation for active galactic nuclei: The role of contaminations

TL;DR

This study calibrates the optical-infrared luminosity relation for quasars, accounting for contaminations like host galaxy emissions, polar dust, and stellar contributions, to improve their use as cosmological probes.

Contribution

It introduces empirical calibrations for the OPT-IR relation considering contaminations, enhancing the accuracy of quasar luminosity estimates for cosmology.

Findings

Photometric estimates align with SED-based luminosities above 10^45 erg/s.

Polar dust marginally affects luminosity but influences SED fitting parameters.

Stellar emission dominates optical contamination; cold dust and disk emission dominate IR contamination.

Abstract

The main objective is to calibrate the OPT-IR luminosity relation for quasars, focusing on accurate estimations of dusty torus and accretion disk luminosities. We analyzed contaminations related to host galaxies, particularly from polar dust, the interstellar medium, and stellar emission that affect the optical and infrared. We used a sample of nearly 400 quasars with photometrical observations and spectroscopical redshift divided into four redshift bins (0.7-2.4). Full spectral energy distribution (SED) fitting was performed with the CIGALE code, and results were compared with simplified photometric luminosity estimates. The impact of non-active galactic nucleus components and the role of polar dust in the fitting process were assessed. We show that for sources with a disk luminosity above 10^45 [erg/s], the photometric estimates are consistent with SED-based values. While polar dust contributes marginally to luminosity, its presence significantly alters SED fitting, particularly the torus opening angle and cold dust properties. In the optical domain, stellar emission is the dominant contamination. In the infrared, disk emission and cold dust play major roles. We propose two empirical calibrations for the OPT-IR relation. We conclude that the optical band is dominated by the accretion disk component above 10^45 or 10^46 [erg/s] depending on redshift, while IR luminosity is dominated by the dusty torus emission above 1.6 $\times$ 10^45 or 2 $\times$ 10^46 [erg/s] depending on the redshift. In this high-luminosity regime, simplified photometric methods yield reliable disk and torus luminosity estimates. The aim of the analysis we present is to test the parameter space in order to build a well behaving OPT-IR nonlinear luminosity relation for quasars that could serve as a cosmological probe.