Aim: This work package will answer the question: what is the optimal setting of the Euclid cluster finder and mass-proxy definition to maximize the cosmological return and avoid biases? 

Within the Euclid consortium two cluster finders are currently being developed, namely AMICO [Be18, Ma19] and PZWav [Ad19]. The former is an optimal matched filter algorithm that looks for galaxy distributions whose properties closely resemble those of a cluster model provided as input, while the latter looks for overdensities of galaxies on fixed physical scales (see figure 4 for a comparison of the performance of these codes). Because of the expertise of the team, we will mainly focus on the AMICO cluster finder.

We aim at exploring different model choices and input data combinations to maximize the completeness and purity of the sample. Along with the clusters’ angular position and redshift, AMICO provides for each detected object two mass proxies, namely the amplitude A and the richness 𝜆 [Ma19]. The amplitude is a measure of the abundance of member galaxies in units of the cluster model, while the richness is the sum of the membership probabilities of the galaxies associated with a given cluster.