Survey description

Telescopes and cameras: The three wide-field telescopes delivering the UNIONS dataset are located near the summit of two extinct shield volcanoes on neighbouring Hawaiian islands:

  • CFHT (Maunakea, Big Island), a 3.6m telescope equipped with MegaCam (380 Mpx)
  • Pan-STARRS (Haleakalā, Maui), two 1.8m telescopes equipped with a Gigapixel Camera (2 x 1400 Mpx)
  • Subaru Telescope (Maunakea, Big Island), a 8.2 m telescope equipped with Hyper Suprime-Cam (870 Mpx)

Area: The main 4,861 square degrees of UNIONS common between all three telescopes (coverage in the u&r bands by CFHT, i band by Pan-STARRS, and g&z bands by Subaru) is driven by the northernmost coverage of the Euclid mission: all the sky above a declination of +30◦ and a galactic latitude |b|>25◦. In addition, UNIONS is capitalizing on the blue sensitivity of CFHT in recognition of the fact that, once CFHT/MegaCam no longer exists, there will be no effective survey facility for the u-band in the north. The Rubin LSST will cover the northern sky up to a declination of +12◦ in ugrizy but will not survey in u beyond due to the high airmass. As such, UNIONS is aiming to cover the entire northern hemisphere away from the Galactic Plane in the u-band (total coverage goal from 8,988 up to 9,794 square degrees depending on reaching down to a declination of +18◦ or +12◦).

Depth: The three UNIONS telescopes are focused on delivering the depth required by Euclid: our full ugriz collection will reach (point source 5-sigma in a 2” diameter aperture): 24.3, 25.2, 24.9, 24.3, 24.1. The r-band component additionally delivers a low surface brightness detection performance down to 28.4 magnitude per square arcsecond for extended sources up to the degree scale (e.g. nearby galaxies, galactic cirrus), and 31.5 magnitude per square arcsecond for radially integrated galactic profiles.