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

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 similar to 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> 10(45) 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 similar 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.

Automated summary

X-CIGALE, based on the spectral energy distribution (SED) code of CIGALE, introduces important new features such as accounting for obscuring material in the poles of AGNs and fitting X-ray fluxes. The study demonstrates that X-CIGALE successfully connects X-ray and UV luminosity, improves efficiency in estimating and characterising AGN components, and enhances the statistical significance of AGN fraction measurements.