Klein, M., Grandis, S., Mohr, J. J., Paulus, M., Abbott, T. M. C., Annis, J., Avila, S., Bertin, E., Brooks, D., Buckley-Geer, E., Rosell, A. Carnero, Kind, M. Carrasco, Carretero, J., Castander, F. J., Cunha, C. E., D'Andrea, C. B., da Costa, L. N., De Vicente, J., Desai, S., Diehl, H. T., Dietrich, J. P., Doel, P., Evrard, A. E., Flaugher, B., Fosalba, P., et al
We present the MARD-Y3 catalogue of between 1086 and 2171 galaxy clusters (52 per cent and 65 per cent new) produced using multicomponent matched filter (MCMF) follow-up in 5000 deg2 of DES-Y3 optical data of the ~20 000 overlapping ROSAT All-Sky Survey source catalogue (2RXS) X-ray sources. Optical counterparts are identified as peaks in galaxy richness as a function of redshift along the line of sight towards each 2RXS source within a search region informed by an X-ray prior. All peaks are assigned a probability fcont of being a random superposition. The clusters lie at 0.02 of being a random superposition. The clusters lie at 0.02 0.5. Residual contamination is 2.6 per cent and 9.6 per cent for the cuts adopted here. For each cluster we present the optical centre, redshift, rest frame X-ray luminosity, M500 mass, coincidence with NWAY infrared sources, and estimators of dynamical state. About 2 per cent of MARD-Y3 clusters have multiple possible counterparts, the photo-z's are high quality with s?z/(1 z) = 0.0046, and ~1 per cent of clusters exhibit evidence of X-ray luminosity boosting from emission by cluster active galactic nuclei. Comparison with other catalogues (MCXC, RM, SPT-SZ, Planck) is performed to test consistency of richness, luminosity, and mass estimates. We measure the MARD-Y3 X-ray luminosity function and compare it to the expectation from a fiducial cosmology and externally calibrated luminosity- and richness-mass relations. Agreement is good, providing evidence that MARD-Y3 has low contamination and can be understood as a simple two step selection - X-ray and then optical - of an underlying cluster population described by the halo mass function.