The Project: The Euclid Legacy Science and the ARRAKIHS missions are two key initiatives within ESA to explore the nearby extragalactic universe to an unprecedented low level of surface brightness (SB). This new window into the local universe will provide the crucial observations to test the nature of Dark Matter from a different, but complementary, approach to Euclid’s primary scientific focus on the distant universe. The Euclid Legacy Science project will initiate the systematic exploration of the extremely low SB universe over a very large area using the Euclid Wide Survey. ARRAKIHS will push forward this initiative by obtaining deeper observations for a representative sample of nearby galaxies. Although the orbital conditions, instruments, and observational strategies of the two space missions are very different, both face similar technical challenges to achieve the exceptionally low SB values required.

The project together experts in the extreme low SB research field from the two mission Consortia in order to: (i) develop the best techniques of image processing to reach the lowest possible SB in both missions; (ii) simulate accurate mock images from Euclid and ARRAKIHS to test these techniques and assess systematics; and (iii) use the mock images to evaluate the discriminating power between dark matter model predictions as a function of the limiting SB in both missions. The resulting data reduction pipeline and mock image simulator will be used by both missions and shared by the two scientific communities. 

The questions: Through a series of 3 meetings, we plan to address the following specific questions: 

1. What are the synergies and complementarities between the ARRAKIHS and Euclid, two unique ESA cosmology missions, with extremely deep low surface brightness capability?

2. What is the optimum way in which to reduce/correct/calibrate images taken by the Euclid and ARRAKIHS missions for low surface brightness science cases?

3. How strong is the discriminating power between dark matter model predictions as a function of the limiting SB in both missions?