A Search for Late-type Brown Dwarfs in the Euclid Quick Data Release 1

Abstract We present the identification and characterization of 15 mid-to-late T dwarf candidates in the Euclid Quick Release 1 (Q1) data set, based on a combined photometric and spectroscopic analysis. Candidates were initially selected via color-based cuts in the Euclid Y E − J E and J E − H E color–color space, targeting the region occupied by ultracool dwarfs (UCDs) in synthetic photometry from the A. Sanghi et al. sample. From an initial pool of 38,845 sources, we extracted low-resolution near-infrared spectra from the Euclid Near-Infrared Spectrometer and Photometer instrument and applied a two-stage validation procedure that included spectral template fitting followed by visual inspection. Eight of the 15 validated candidates are newly identified objects with no prior literature association. We examined their morphological and photometric properties, and compared them with established spectral standards. Photometric distances were derived using band-averaged distance modulus estimates. We discuss the limitations and promise of the Euclid survey for UCD studies, and demonstrate the potential for discovering substellar populations beyond the reach of current wide-field surveys.