X-ray flux in SED modelling: An application of X-CIGALE in the XMM-XXL field

¹ Instituto de Fisica de Cantabria (CSIC-Universidad de Cantabria), Avenida de los Castros, 39005 Santander, Spain
e-mail: gmountrichas@gmail.com
² Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
e-mail: veronique.buat@lam.fr
³ Institut Universitaire de France (IUF), France
⁴ Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁵ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁶ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile

Received: 11 September 2020
Accepted: 18 November 2020

Abstract

X-CIGALE is built on the spectral energy distribution (SED) code of CIGALE and implements important new features: the code accounts for obscuring material in the poles of AGNs and has the ability to fit X-ray fluxes. In this work, we used ∼2500 spectroscopic X-ray AGNs from the XMM-XXL-north field and examined the improvements the new features bring to the SED modelling analysis. Based on our results, X-CIGALE successfully connects the X-ray with the UV luminosity in the whole range spanned by our sample (log L_X(2−10 keV) = (42−46) erg s⁻¹). The addition of the new features generally improves the efficiency of X-CIGALE in the estimation and characterisation of the AGN component. Classification as type 1 or type 2 based on their inclination angle is improved, especially at redshifts lower than 1. The statistical significance of AGN fraction, frac_AGN, measurements is increased, in particular for luminous X-ray sources (L_X >  10⁴⁵ erg s⁻¹). These conclusions hold under the condition that (mid-) IR photometry is available in the SED fitting process. The addition of polar dust increases the AGN fraction and the efficiency of the SED decomposition to detect AGNs among X-ray selected sources. X-CIGALE estimates a strong AGN (frac_AGN >  0.3) in more than 90% of the IR-selected AGNs and 75% of X-ray-detected AGNs not selected by IR colour criteria. The latter drops to ∼50% when polar dust is not included. The ability of X-CIGALE to include X-ray information in the SED fitting process can be instrumental in the optimal exploitation of the wealth of data that current (eROSITA) and future (ATHENA) missions will provide us.