The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada-France-Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain images of a core survey region of 6250 deg of the northern sky. The point source depth of the data, as measured within a 2-arcsecond diameter aperture, are \ in AB magnitudes. UNIONS is addressing some of the most fundamental questions in astronomy, including the properties of dark matter, the growth of structure in the Universe from the very smallest galaxies to large-scale structure, and the assembly of the Milky Way. It is set to become the major ground-based legacy survey for the northern hemisphere for the next decade and provides an essential northern complement to the static-sky science of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. UNIONS supports the core science mission of the {\it Euclid} space mission by providing the data necessary in the northern hemisphere for the calibration of the wavelength dependence of the {\it Euclid} point-spread function and derivation of photometric redshifts in the North Galactic Cap. This region contains the highest quality sky for {\it Euclid}, with low backgrounds from the zodiacal light, stellar density, extinction, and emission from Galactic cirrus. Here, we describe the UNIONS survey components, science goals, data products, and the current status of the overall program.
@misc{gwyn2025unionsultravioletnearinfraredoptical, title={UNIONS: The Ultraviolet Near-Infrared Optical Northern Survey}, author={Stephen Gwyn and Alan W. McConnachie and Jean-Charles Cuillandre and Ken C. Chambers and Eugene A. Magnier and Michael J. Hudson and Masamune Oguri and Hisanori Furusawa and Hendrik Hildebrandt and Raymond Carlberg and Sara L. Ellison and Junko Furusawa and Raphaël Gavazzi and Rodrigo Ibata and Yannick Mellier and Ken Osato and H. Aussel and Lucie Baumont and Manuel Bayer and Olivier Boulade and Patrick Côté and David Chemaly and Cail Daley and Pierre-Alain Duc and A. Ellien and Sébastien Fabbro and Leonardo Ferreira and Itsna K. Fitriana and Emeric Le Floc'h and Hammer and Francois and Yoshinobu Fudamoto and Hua Gao and L. W. K. Goh and Tomotsugu Goto and Sacha Guerrini and Axel Guinot and Vincent Hénault-Brunet and Yuichi Harikane and Kohei Hayashi and Nick Heesters and Kohei Ichikawa and Martin Kilbinger and P. B. Kuzma and Qinxun Li and Tobías I. Liaudat and Chien-Cheng Lin and Oliver Müller and Nicolas F. Martin and Yoshiki Matsuoka and Gustavo E. Medina and Hironao Miyatake and Satoshi Miyazaki and Charlie T. Mpetha and Tohru Nagao and Julio F. Navarro and Masafumi Niwano and Itsuki Ogami and Nobuhiro Okabe and Masafusa Onoue and Gregory S. H. Paek and Laura C. Parker and David R. Patton and Fabian Hervas Peters and Simon Prunet and Rubén Sánchez-Janssen and M. Schultheis and Federico Sestito and Simon E. T. Smith and J. -L. Starck and Else Starkenburg and Connor Stone and Christopher Storfer and Yoshihisa Suzuki and Erben and T. and Salvatore Taibi and G. F. Thomas and Zhang TianFang and Yoshiki Toba and Hisakazu Uchiyama and David Valls-Gabaud and Kim A. Venn and Ludovic Van Waerbeke and Richard J. Wainscoat and Scott Wilkinson and Anna Wittje and Taketo Yoshida and Yuxing Zhong}, year={2025}, eprint={2503.13783}, archivePrefix={arXiv}, primaryClass={astro-ph.GA}, url={https://arxiv.org/abs/2503.13783}, }