An inventory of galaxies in cosmic filaments feeding galaxy clusters: galaxy groups, backsplash galaxies, and pristine galaxies

Abstract

Galaxy clusters grow by accreting galaxies from the field and along filaments of the cosmic web. As galaxies are accreted they are affected by their local environment before they enter (pre-processing), and traverse the cluster potential. Observations that aim to constrain pre-processing are challenging to interpret because filaments comprise a heterogeneous range of environments including groups of galaxies embedded within them and backsplash galaxies that contain a record of their previous passage through the cluster. This motivates using modern cosmological simulations to dissect the population of galaxies found in filaments that are feeding clusters, to better understand their history, and aid the interpretation of observations. We use zoom-in simulations from T T H project to track halos through time and identify their environment. We establish a benchmark for galaxies in cluster infall regions that supports the reconstruction of the different modes of pre-processing. We find that up to 45% of all galaxies fall into clusters via filaments (closer than 1 ℎ −1 Mpc from the filament spine). 12% of these filament galaxies are long-established members of groups and between 30 and 60% of filament galaxies at 𝑅 200 are backsplash galaxies. This number depends on the cluster's dynamical state and sharply drops with distance. Backsplash galaxies return to clusters after deflecting widely from their entry trajectory, especially in relaxed clusters. They do not have a preferential location with respect to filaments and cannot collapse to form filaments. The remaining pristine galaxies (∼30 -60%) are environmentally effected by cosmic filaments alone.

Boundless baryons: how diffuse gas contributes to anisotropic tSZ signal around simulated Three Hundred clusters

“…The zoom regions are extended to 15 ℎ −1 Mpc from the centres of these clusters and cover over 5 × 𝑅 200𝑐 , which allows us to investigate the environments around the clusters. Many studies, such as Haggar et al (2020); Kuchner et al (2020); Rost et al (2021); Kuchner et al (2021), benefit from this large re-simulation region. Since MDPL2 adopted the Planck cosmology parameters (Planck Collaboration et al 2016), these resimulations follow the same cosmology.…”

\textsc{The Three Hundred} project: The \textsc{Gizmo-Simba} run

“…the galaxy clusters (Kuchner et al 2021a;Kotecha et al 2021), cluster backsplash galaxies (Haggar et al 2020;Knebe et al 2020), and the virial shock radius (Baxter et al 2021;Anbajagane et al 2021). The advanced input physics in the hydrodynamic simulations allow us to perform a detailed investigation on the cluster properties, such as cluster profiles (Mostoghiu et al 2019;Li et al 2020), substructure and its baryonic content (Arthur et al 2019;Haggar et al 2021;Mostoghiu et al 2021b,a), dynamical state and morphology (Capalbo et al 2021;De Luca et al 2021;Capalbo et al 2022;Zhang et al 2021), ICM (non-)thermalization (Sayers et al 2021;Sereno et al 2021), the fundamental plane (Díaz-García et al 2021), the effects of mergers on the BCG properties (Contreras-Santos et al 2022) and the hydrostatic equilibrium mass bias (Ansarifard et al 2020;Li et al 2021;Gianfagna et al 2022).…”