Telescopes and cameras: The four 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 Gigapixel Cameras (2 x 1400 Mpx)
- Subaru Telescope (Maunakea, Big Island), a 8.2 m telescope equipped with Hyper Suprime-Cam (870 Mpx)
Area: The main 5,900 square degrees of UNIONS common between all four 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 of the sky above a declination of +15◦ 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 +15◦ in ugrizy for the Northern Galactic Cap (NGC) region, and +2◦ for the Southern Galactic Cap (SGC) region. UNIONS is aiming to cover the extragalactic sky in the u-band down to +15◦ in the NGC region and to the equator in the SGC region, for a total coverage goal of 8,600 square degrees.
The UNIONS coverage region above is described by the following HEALPIX table. Note: the compressed file has a size of 213KB, but will expand to 193MB. HEALPIX File: unions.footprint.celestial.healpix.nside2048.fits.gz
Depth: The 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.
Reference: If using UNIONS data, please cite the following survey description paper: