Towards an accurate cluster cosmology with photometric galaxy surveys

speaker: Tomomi Sunayama



Galaxy clusters are the most massive gravitationally self-bound objects in the Universe. These clusters form at the rare high peaks of the primordial density fluctuations, and they subsequently trace the growth of structure in the Universe as they grow in mass and abundance. As such, clusters constitute a natural cosmological probe for constraining the properties of the primordial fluctuations as well as cosmological parameters including the nature of dark energy. Clusters are, however, also known to be susceptible to many systematics such as selection biases and projection effects.We develop a new analysis pipeline which is full forward modeling of cluster observables (abundance, clustering, and lensing signals) with an empirical model for the projection effects (i.e., interloper galaxies along the line-of-sight are misidentified as genuine members of the cluster). The projection effects alter the mass-observable relation as well as boost the amplitude of clustering and lensing signals due to the anisotropic distribution of optical clusters. We validate our model on simulations and then apply it to the SDSS redMaPPer cluster catalog whose result favors low Omega-m and high sigma8. We discuss possible implications using Subaru HSC lensing measurements.