X-ray point-like sources of Euclid (Q1)

X-ray surveys are key to this, but identifying their counterparts (CTPs) at other wavelengths remains challenging due to their larger positional uncertainties and limited availability of deeper, uniform ancillary data. Euclid is revolutionising this effort, offering extensive coverage of nearly the entire extragalactic sky, particularly in the near-infrared bands, where AGN are more easily detected.

With the first Euclid Quick Data Release (Q1), we validated methods for identifying and classifying Euclid CTPs to known point-like sources from major X-ray surveys, including XMM- Newton, Chandra, and eROSITA. Using Bayesian statistics, combined with machine learning (ML), as incorporated in the algorithm NWAY, we identify the CTPs to 11286 X-ray sources from the three X-ray telescopes. For the large majority of 10194 sources, the association is unique, with the remaining ~10% of multi-CTP cases equally split between XMM-Newton and eROSITA.