Selection function of clusters in Dark Energy Survey year 3 data from cross-matching with South Pole Telescope detections

Grandis, S. and Costanzi, M. and Mohr, J.J. and Bleem, L.E. and Wu, H.-Y. and Aguena, M. and Allam, S. and Andrade-Oliveira, F. and Bocquet, S. and Brooks, D. and Carnero Rosell, A. and Carretero, J. and Da Costa, L.N. and Pereira, M.E.S. and Davis, T.M. and Desai, S. and Diehl, H.T. and Doel, P. and Everett, S. and Flaugher, B. and Frieman, J. and García-Bellido, J. and Gaztanaga, E. and Gruen, D. and Gruendl, R.A. and Gutierrez, G. and Hinton, S.R. and Hlacacek-Larrondo, J. and Hollowood, D.L. and Honscheid, K. and James, D.J. and Klein, M. and Marshall, J.L. and Mena-Fernández, J. and Miquel, R. and Palmese, A. and Plazas Malagón, A.A. and Reichardt, C.L. and Romer, A.K. and Samuroff, S. and Sanchez Cid, D. and Sanchez, E. and Santiago, B. and Saro, A. and Sevilla-Noarbe, I. and Smith, M. and Soares-Santos, M. and Sommer, M.W. and Suchyta, E. and Tarle, G. and To, C. and Tucker, D.L. and Weaverdyck, N. and Weller, J. and Wiseman, P. (2025) Selection function of clusters in Dark Energy Survey year 3 data from cross-matching with South Pole Telescope detections. Astronomy and Astrophysics, 700: A15. ISSN 1432-0746

Abstract

Context. Galaxy clusters selected based on overdensities of galaxies in photometric surveys provide the largest cluster samples. However, modeling the selection function of such samples is complicated by noncluster members projected along the line of sight (projection effects) and the potential detection of unvirialized objects (contamination). Aims. We empirically constrained the magnitude of these effects by cross-matching galaxy clusters selected in the Dark Energy Survey data with the redMaPPer  algorithm with significant detections in three South Pole Telescope surveys (SZ, pol-ECS, pol-500d). Methods. For matched clusters, we augmented the redMaPPer catalog with the SPT detection significance. For unmatched objects we used the SPT detection threshold as an upper limit on the SZe signature. Using a Bayesian population model applied to the collected multiwavelength data, we explored various physically motivated models to describe the relationship between observed richness and halo mass. Results. Our analysis reveals a clear preference for models with an additional skewed scatter component associated with projection effects over a purely log-normal scatter model. We rule out significant contamination by unvirialized objects at the high-richness end of the sample. While dedicated simulations offer a well-fitting calibration of projection effects, our findings suggest the presence of redshift-dependent trends that these simulations may not have captured. Our findings highlight that modeling the selection function of optically detected clusters remains a complicated challenge that requires a combination of simulation and data-driven approaches.