Exploring the contamination of the DES-Y1 cluster sample with SPT-SZ selected clusters

Grandis, S.; Mohr, J. J.; Costanzi, M.; Saro, A.; Bocquet, S.; Klein, M.; Aguena, M.; Allam, S.; Annis, J.; Ansarinejad, B.; Bacon, D.; Bertin, E.; Bleem, L.; Brooks, D.; Burke, D. L.; Carnero Rosel, A.; Carrasco Kind, M.; Carretero, J.; Castander, F. J.; Choi, A.; da Costa, L. N.; De Vincente, J.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Eifler, T. F.; Everett, S.; Ferrero, I.; Floyd, B.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gupta, N.; Gutierrez, G.; Hinton, S. R.; Hollowood, D. L.; Honscheid, K.; James, D. J.; Jeltema, T.; Kuehn, K.; Lahav, O.; Lidman, C.; Lima, M.; Maia, M. A. G.; March, M.; Marshall, J. L.; Melchior, P.; Menanteau, F.; Miquel, R.; Morgan, R.; Myles, J.; Ogando, R.; Palmese, A.; Paz-Chinchón, F.; Plazas, A. A.; Reichardt, C. L.; Romer, A. K.; Sanchez, E.; Scarpine, V.; Serrano, S.; Sevilla-Noarbe, I.; Singh, P.; Smith, M.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; To, C.; Weller, J.; Wilkinson, R. D.; Wu, H.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society

Advertised on:
6
2021
Number of authors
76
IAC number of authors
1
Citations
30
Refereed citations
27
Description
We perform a cross validation of the cluster catalogue selected by the red-sequence Matched-filter Probabilistic Percolation algorithm (redMaPPer) in Dark Energy Survey year 1 (DES-Y1) data by matching it with the Sunyaev-Zel'dovich effect (SZE) selected cluster catalogue from the South Pole Telescope SPT-SZ survey. Of the 1005 redMaPPer selected clusters with measured richness \hatλ > 40 in the joint footprint, 207 are confirmed by SPT-SZ. Using the mass information from the SZE signal, we calibrate the richness-mass relation using a Bayesian cluster population model. We find a mass trend λ ∝ MB consistent with a linear relation (B ∼ 1), no significant redshift evolution and an intrinsic scatter in richness of σλ = 0.22 ± 0.06. By considering two error models, we explore the impact of projection effects on the richness-mass modelling, confirming that such effects are not detectable at the current level of systematic uncertainties. At low richness SPT-SZ confirms fewer redMaPPer clusters than expected. We interpret this richness dependent deficit in confirmed systems as due to the increased presence at low richness of low-mass objects not correctly accounted for by our richness-mass scatter model, which we call contaminants. At a richness \hatλ = 40, this population makes up > 12 per cent (97.5 percentile) of the total population. Extrapolating this to a measured richness \hatλ = 20 yields > 22 per cent (97.5 percentile). With these contamination fractions, the predicted redMaPPer number counts in different plausible cosmologies are compatible with the measured abundance. The presence of such a population is also a plausible explanation for the different mass trends (B ∼ 0.75) obtained from mass calibration using purely optically selected clusters. The mean mass from stacked weak lensing (WL) measurements suggests that these low-mass contaminants are galaxy groups with masses ∼3-5 × 1013 M⊙ which are beyond the sensitivity of current SZE and X-ray surveys but a natural target for SPT-3G and eROSITA.
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