The Euclid Deep Fields
The location of the three Euclid Deep Fields on an all-sky map based on data from ESA's Gaia mission. The sky is shown in the Galactic coordinate system, with the bright horizontal band corresponding to the plane of our Milky Way galaxy, where most of its stars reside.
Euclid is an ESA mission that will image billions of galaxies across the Universe to investigate the past ten billion years of our cosmic history. The largest fraction of the mission's observations will be devoted to a wide survey, covering more than one third of the sky; this is complemented by a deep survey, taking about 10% of the total observing time and repeatedly observing just three patches of the sky: the Euclid Deep Fields.
The Euclid Deep Field North – highlighted in yellow, towards the top left in this view – has an area of 20 square degrees and is located very close to the Northern Ecliptic Pole, in the constellation Draco, the dragon. The proximity to the ecliptic pole ensures maximum coverage throughout the year; the exact position was chosen to obtain maximum overlap with one of the deep fields surveyed by NASA's infrared workhorse, the Spitzer Space Telescope.
The other two fields are located in the southern sky. The challenge entailed selecting a region as close as possible to the Southern Ecliptic Pole, which would provide the best time coverage, while at the same time avoiding bright sources in that area, which is home to the Large Magellanic Cloud, one of the galactic neighbours of our Milky Way – visible to the lower right of the Galactic Centre.
The Euclid Deep Field Fornax – highlighted in yellow, in the lower right of the image – also spans 10 square degrees and is located in the southern constellation Fornax, the furnace. It encompasses the much smaller Chandra Deep Field South, a 0.11 square degree region of the sky that has been extensively surveyed in the past couple of decades with NASA's Chandra and ESA's XMM-Newton X-ray observatories, as well as the NASA/ESA Hubble Space Telescope and major ground-based telescopes.
The third and largest of the fields is the Euclid Deep Field South – highlighted in yellow, between the Large Magellanic Cloud and the Euclid Deep Field Fornax. It covers 20 square degrees in the southern constellation of Horologium, the pendulum clock. The most complex of the three to select because of various technical reasons, this field has not been covered to date by any deep sky survey and so has a huge potential for new, exciting discoveries.
Note: based on the need for a larger area of calibration observations for the Euclid spectroscopic sample characterisation, the Euclid Science Team has endorsed in April 2022 the request to extend the Euclid Deep Field North from 10 deg2 to 20 square degrees.