Euclid Quick Data Release (Q1). The active galaxies of Euclid

We present three catalogues of candidate active galactic nuclei (AGN) in the Euclid Quick Release (Q1) fields. For each Euclid source, we collected multi-wavelength photometric and spectroscopic information from surveys such as the Galaxy Evolution Explorer (GALEX) the Dark Energy Survey (DES), the Wide-field Infrared Survey Explorer (WISE) Spitzer the Dark Energy Spectroscopic Instrument (DESI), and the Sloan Digital Sky Survey (SDSS), including spectroscopic redshifts from public compilations when available. We investigated the AGN content of the Q1 fields using multiple selection methods. Applying Euclid colours and WISE-AllWISE cuts, we identified 292,222 and 65,131 candidates, respectively. We compiled a high-purity QSO catalogue based on DR3 information, containing 1971 candidates. Using spectroscopic information from DESI, we performed broad-line and narrow-line AGN selections, yielding 4392 AGN candidates across the Q1 fields. We investigated and refined the Euclid Q1 probabilistic random forest QSO population, selecting a refined sample of 180,666 candidates. Additionally, we performed spectral energy distribution (SED) fitting on sources with available z_ spec and utilising the derived AGN fraction, we identified 7766 AGN candidates. To improve the purity of the selection, we defined two new colour criteria (JH_I_E Y and I_E H_gz), finding 313,714 and 267,513 candidates, respectively, across the Q1 fields. We have found a total of 229,779 AGN candidates equivalent to an AGN surface density of 3641 deg^-2 for $18< 24.5$ and a subsample of 30,422 candidates corresponding to an AGN surface density of 482 deg^-2 when limiting the depth to $18< 22$. The AGN surface densities recovered are consistent with predictions based on AGN X-ray luminosity functions.