Modelling projection effects in optically selected cluster catalogues
Abstract
The cosmological utility of galaxy cluster catalogues is primarily limited by our ability to calibrate the relation between halo mass and observable mass proxies such as cluster richness, Xray luminosity, or the SunyaevZeldovich signal. Projection effects are a particularly pernicious systematic effect that can impact observable mass proxies; structure along the line of sight can both bias and increase the scatter of the observable mass proxies used in cluster abundance studies. In this work, we develop an empirical method to characterize the impact of projection effects on redMaPPer cluster catalogues. We use numerical simulations to validate our method and illustrate its robustness. We demonstrate that modelling of projection effects is a necessary component for cluster abundance studies capable of reaching {≈ } 5{{ per cent}} mass calibration uncertainties (e.g. the Dark Energy Survey Year 1 sample). Specifically, ignoring the impact of projection effects in the observablemass relation  i.e. marginalizing over a lognormal model only  biases the posterior probability of the cluster normalization condition S_{8} ≡ σ_{8}(Ω_{m}/0.3)^{1/2} by ∆S_{8} = 0.05, more than twice the uncertainty in the posterior for such an analysis.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 January 2019
 DOI:
 10.1093/mnras/sty2665
 arXiv:
 arXiv:1807.07072
 Bibcode:
 2019MNRAS.482..490C
 Keywords:

 galaxies: clusters: general;
 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 16 pages, 11 figures