Candidates (proto-)clusters in the near-infrared wide field SHARKS survey: preparing the path to Euclid

I have constructed a catalog of galaxy clusters and proto-clusters using data from the Southern H-ATLAS Regions Ks-band Survey (SHARKS). This is an ESO public survey in Ks photometric band, covering almost the entire GAlaxy Mass Assembly (GAMA) fields for a total of ∼300 square degrees in the sky. I used data from the first public release (dr1), that includes an area of ∼20 square degrees including parts of GAMA-12, GAMA-15 and South Galactic Pole (SGP) regions. I removed spurious sources from the public catalog, calculated the completeness level and removed Galactic sources to have a complete catalog of galaxies. The sensitivity level at 5σ in AB magnitudes as described in the public release is 22.7 mag. I calculated an average completeness level of 22.1 mag, varying along the different areas of the survey. I performed the search for clusters in the catalog using a Friends-of-Friends (FoF) algorithm from part of the Python library nbodykit. The algorithm was originally developed to perform analysis on N-body cosmological simulations, however I applied it to a two-dimensional sky-projection of the distribution of galaxies. This required a new definition of the parameters governing the algorithm, that was tested and discussed for the entire dr1 catalog. To construct the catalog, instead, I have combined SHARKS data to data from the photometric Y band of the Dark Energy Survey (DES). I used observations in Y and Ks band to develop a color-redshift relation calibrated for the galaxy red sequence. I have then assigned redshift values for each galaxy and divided the catalog in bins in the redshift space of width ∆z=0.3 from z=0 to z=4. The FoF algorithm was applied to each bin. This analysis was performed in the overlapping area between SHARKS and DES: ∼8 squared degrees in the SGP region. The resulting catalog contains 186 galaxy clusters and proto-clusters between redshift z∼0.6 and z∼3 in such an area, for an average of 23 clusters per squared degree. This seems consistent by order of magnitude with analysis from Kilo Degree Survey (KiDS), having 11 clusters per squared degree, and DES, having 28 clusters per squared degree at the same photometric limit of SHARKS.