Pushing the quasar redshift frontier with Euclid: a new era for z>7 quasar searches

Luminous quasars at high redshift (z ? 7) directly probe the buildup of supermassive black holes, the primeval galaxies hosting them, and the intergalactic medium during the epoch of reionisation. However, such objects remain rare and challenging to identify due to their faintness and scarcity. The launch of the Euclid satellite is dramatically changing this picture: the wide surveyed area, photometric depth, and wavelength coverage will allow us to push the redshift frontier well beyond z~7. In this talk, I will describe how we, the QSO Work Package, are actively exploiting the wealth of data made available by the Euclid collaboration and introduce our selection methods. I will focus on a novel machine learning approach that combines generative, classification, and regression models and show that it allows for an efficient and complete selection. I will then showcase how, in just 1.5 years, we more than doubled the number of known QSOs at z>7 and pushed the redshift frontier further into the epoch of reionisation. Finally, I will conclude by presenting the first results of multi-wavelength follow-up of these newly discovered objects.