Filamentary Environment and Mass Measurements of Galaxy Clusters

Yookyung Noh

November 29, 2012

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Abstract: Galaxy clusters reside at the nodes of cosmic web and are fed matter along the filaments. This filamentary environment is important to understand the formation and the evolution of galaxy clusters, and is also inevitably included when we observe them. This latter effect generates projection effects on cluster observables. Reducing errors in measuring cluster masses is of interest since a cluster’s mass is a crucial property for many areas of astrophysics and cosmology. We study the filamentary environment surrounding galaxy clusters and its effect on the cluster mass measurements by constructing a filament catalogue in a high-resolution N-body simulation. We consider the statistical properties of filaments around galaxy clusters. Not only filaments but also the majority of mass in halos and number of galaxies in the local environment of clusters tends to lie on planes which are mostly aligned with each other and with the cluster’s major axis. We show that this local planar environment can be one source of projection effects that bias cluster mass measurements. Sources of mass measurement scatters are shared between different mass measurement methods, generating correlations in their respective scatters. This correlated scatter mitigates the complementary information of cluster mass measurements in multi-wavelength observations. We study the scatter by calculating correlations/covariances between them and performing Principal Component Analysis (PCA). As expected, the scatter from different techniques tends to be correlated. We find that the combination of scatters which dominates the variance of all the measurements is common for the majority of clusters. Its dominance tends to be enhanced when observing along the cluster’s major axis. We also find shared trends among cluster mass scatter, intrinsic and environmental properties of clusters using PCA.