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 The ThreeHundred 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−1Mpc from the filament spine). 12% of these filament galaxies are long-established members of groups and between 30 and 60% of filament galaxies at R200 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.

A major galaxy cluster merger caught by eROSITA: weak lensing mass distribution and kinematic description

“…It clearly shows a bimodal distribution, corresponding to the pair eFEDS4748 and eFEDS4910, and a third clump reasonable away from the previous overdensity that is related to eFEDS5418. An interesting feature is the two prickle-like structures emanating from eFEDS4910, which could be the end of large scale filaments that we believe to be feeding galaxy clusters (Kuchner et al 2022).…”

Superclustering with the Atacama Cosmology Telescope and Dark Energy Survey. I. Evidence for Thermal Energy Anisotropy Using Oriented Stacking

“…However, the dynamics and assembly history of such objects is interesting in its own right. Studying how the cluster gas orientation relates to its surrounding filament(s) could provide insight into the process by which the cosmic web feeds cold gas and galaxies into clusters (e.g., as recently studied in The ThreeHundred project in Kotecha et al 2022;Kuchner et al 2022).…”

Tracking Halo Orbits and Their Mass Evolution around Large-scale Filaments

“…This is because those galaxies experienced so-called "pre-processing" in smaller groups prior to accretion on to massive clusters (Fujita 2004). Reminding of the large-scale structure formation process, the pre-processing does not need to be limited to mechanisms that are at play within fully collapsed (halo-like) structures, but could be used in a broader context that includes various types of large-scale structures such as large-scale filaments (e.g., Sarron et al 2019;Kuchner et al 2022).…”