Cross-correlations between X-ray clusters and the general galaxy population

This study presents highly precise measurements of the cross-correlation between volume-limited galaxy samples from the DESI Legacy Survey catalog and X-ray-selected galaxy clusters from eROSITA, which allows for a detailed analysis across redshift and color. Two key findings emerge. First, the cluster-galaxy cross-correlation, when split into quiescent and star-forming galaxies, contains significant information about the infall, feedback, and quenching processes of blue-cloud galaxies in massive environments. These results align well with existing galaxy evolution models for higher stellar masses (log10(M*[M⊙]) > 10.75), although the red fraction may be slightly underestimated in the intermediate mass range (10.25 < log10(M*[M⊙]) < 10.75). Second, the integral of the cross-correlation within 500 kpc enables a model-independent measurement of the red sequence and its scatter in clusters, providing a robust alternative to existing red-sequence calibration methods, without requiring spectroscopic redshifts or classifications of galaxies. Similar analyses on upcoming photometric surveys like Euclid and Rubin/LSST and spectroscopic samples such as 4MOST and DESI should lead to a significant increase in the signal-to-noise ratio, particularly at small separations.