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

S. Grandis , J. J. Mohr , M. Costanzi , A. Saro , S. Bocquet , M. Klein , M. Aguena , S. Allam , J. Annis , B. Ansarinejad , D. Bacon , E. Bertin (1) , L. Bleem , D. Brooks , D. L. Burke , A. Carnero Rosel , M. Carrasco Kind , J. Carretero , F. J. Castander , A. Choi , L. N. da Costa , J. de Vincente , S. Desai , H. T. Diehl , J. P. Dietrich , P. Doel , T. F. Eifler , S. Everett , I. Ferrero , B. Floyd , P. Fosalba , J. Frieman , J. García-Bellido , E. Gaztanaga , D. Gruen , R. A. Gruendl , J. Gschwend , N. Gupta , G. Gutierrez , S. R. Hinton , D. L. Hollowood , K. Honscheid , D. J. James , T. Jeltema , K. Kuehn , O. Lahav , C. Lidman , M. Lima , M. A. G. Maia , M. March , J. L. Marshall , P. Melchior , F. Menanteau , R. Miquel , R. Morgan , J. Myles , R. Ogando , A. Palmese , F. Paz-Chinchón , A. A. Plazas , C. L. Reichardt , A. K. Romer , E. Sanchez , V. Scarpine , S. Serrano , I. Sevilla-Noarbe , P. Singh , M. Smith , E. Suchyta , M. E. C. Swanson , G. Tarle , D. Thomas , C. To , J. Weller , R. D. Wilkinson , H. Wu

1 IAP - Institut d'Astrophysique de Paris

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 $\hat{\lambda } 40$ 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 ∝ M^B consistent with a linear relation (B ~ 1), no significant redshift evolution and an intrinsic scatter in richness of σ_λ = 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 $\hat{\lambda }=40$, this population makes up ${}12{{\ \rm per\ cent}}$ (97.5 percentile) of the total population. Extrapolating this to a measured richness $\hat{\lambda }=20$ yields ${}22{{\ \rm per\ cent}}$ (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.

Keywords: methods: statistical; galaxies: clusters: general; large-scale structure of Universe; Astrophysics - Cosmology and Nongalactic Astrophysics

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

S. Grandis, J. J. Mohr, M. Costanzi, A. Saro, S. Bocquet, et al.. Exploring the contamination of the DES-Y1 cluster sample with SPT-SZ selected clusters. Monthly Notices of the Royal Astronomical Society, 2021, 504, pp.1253-1272. ⟨10.1093/mnras/stab869⟩. ⟨insu-03748203⟩