Euclid Quick Data Release (Q1). XLII. Searching for radio-selected Euclid-dark galaxies in the EDF-N

We present and investigate the properties of a sample of radio-selected, Euclid-dark galaxies, identified from LOFAR HBA observations at 144,MHz within the Euclid Deep Field-North (EDF-N), covering approximately 10 deg2$. Starting from 1051 radio sources lacking optical counterparts down to a 5σ depth of 23.9 in the y band in previous surveys (but detected with /IRAC), we identified 166 galaxies with no emission at a depth of more than 3σ from Euclid Quick Release 1 (Q1) images, reaching a 5σ depth of 23.9 in the$̋E band, and no matches in the Euclid Q1 catalogue. To minimise contamination from nearby sources, we selected a sub-sample of 88 isolated galaxies. By exploiting multi-band images and catalogues available for the EDF-N, we inferred the physical properties of our sample via SED fitting. The resulting redshift distribution spans 0.4 łeq z_ łeq 5.0. We made use of recent sub-arcsecond imaging from the International LOFAR Telescope over an area of 2.5,̊m deg 〉_ Spitzer ph to constrain the nature of the compact radio emission in our targets through brightness-temperature estimates. By combining this information with the radio excess relative to the infrared/radio-correlation (IRRC), we searched for possible active galactic nucleus (AGN) activity in our sample. Approximately 30% of our sources show a radio excess relative to star formation. This fraction increases to 40% when including AGNs identified via their brightness temperature. The Euclid-dark sources detected in the far-infrared (FIR) are consistent with a population of heavily obscured (łangle A_V^ ̊m ISM = 5.0) massive (łangle łogten(M_⋆/M_⊙) 〉_ = 11.6) star forming galaxies (SFGs) with high star formation rates (łangle łogten( SFR /M_⊙,̊m -1 ) 〉_ = 3.3). Their location above the star-forming main sequence is consistent with the high-mass and high-SFR end of similar near-infrared (NIR)-dark galaxy populations selected at higher radio frequencies reported in the literature. We performed a UV-to-radio median stacking analysis, dividing the sources with LOFAR ILT imaging according to the presence of radio excess. Both sub-samples are detected in the ̋E band at 3σ and 9σ for the radio-excess and non–radio-excess sources, respectively. The two stacked populations exhibit similar global physical properties and differ primarily in their radio emission, with values consistent with those observed for individual sources, albeit with less extreme SFRs. These preliminary results indicate that, compared to similar selections carried out over smaller fields, the wide area covered by Euclid enables the identification of a higher fraction of systems in which intense star formation and AGN activity coexist, likely capturing a key phase of galaxy–black hole co-evolution.