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arxiv: 2503.13783 · v1 · pith:4YTBFWZYnew · submitted 2025-03-18 · 🌌 astro-ph.GA · astro-ph.IM

UNIONS: The Ultraviolet Near-Infrared Optical Northern Survey

classification 🌌 astro-ph.GA astro-ph.IM
keywords northernsurveyunionsdataeuclidsciencecoregalactic
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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 $ugriz$ images of a core survey region of 6250 deg$^2$ of the northern sky. The $10\sigma$ point source depth of the data, as measured within a 2-arcsecond diameter aperture, are $[u,g,r,i,z] = [23.7, 24.5, 24.2, 23.8, 23.3]$\ 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.

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Cited by 3 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Revisiting the 'Lensing is Low' Problem with UNIONS

    astro-ph.CO 2026-06 unverdicted novelty 5.0

    New UNIONS galaxy-galaxy lensing data around CMASS galaxies indicates no significant lensing is low problem, with joint HOD fits to GGL and GC favoring a slightly lower matter power spectrum amplitude than Planck.

  2. Survey Footprint Explorer: A Browser-Based Interactive Tool for Visualizing and Cross-Matching Astronomical Survey Footprints

    astro-ph.IM 2026-05 unverdicted novelty 4.0

    The Survey Footprint Explorer provides an interactive browser-based platform for visualizing and cross-matching the footprints of 13 astronomical surveys using MOC maps and Aladin Lite.

  3. UNIONS-3500 Weak Lensing: II. B-mode validation for cosmic shear

    astro-ph.CO 2026-04 accept novelty 4.0

    B-mode null tests for UNIONS-3500 cosmic shear pass after galaxy size cuts and stellar masking, with an oscillatory pattern from additive shear bias suppressed by excluding CCD angular scales.