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We thank the referee for providing useful feedback to this study. This work has been made possible by THE THREEHUNDRED collaboration, which benefits from financial support of the European Union's Horizon 2020 Research and Innovation programme under the Marie Sklodowskaw-Curie grant agreement number 734374, i.e. the LACEGAL project. THE THREEHUNDRED simulations used in this paper have been performed in the MareNostrum Supercomputer at the Barcelona Supercomputing Center, thanks to CPU time granted by the Red Espa ~nola de Supercomputaci ' on. UK acknowledges support from the Science and Technology Facilities Council through grant number RA27PN. AK is supported by the Ministerio de Ciencia, Innovaci ' on y Universidades (MICIU/FEDER) under research grant PGC2018-094975-C21 and further thanks Matt Haynes and Clare Wadd for Sarah Records. WC is supported by the European Research Council under grant number 670193 and by the STFC AGP Grant ST/V000594/1. He further acknowledges the science research grants from the China Manned Space Project with numbers CMS-CSST2021-A01 and CMS-CSST-2021-B01. The authors contributed to this paper in the following ways: UK, AAS, MEG and FRP formed the core team. UK identified filaments, analysed the data, produced the plots (with the exception of Fig. 5) and wrote the paper with ongoing input from the core team and comments from co-authors. RH calculated the relaxedness parameter R based on dynamical state parameters produced by WC and provided identification of the backsplash galaxies incl. Fig. 5; GY supplied the simulation data; AK the halo catalogues.

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

Publicated to:MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. 510 (1): 581-592 - 2022-02-01 510(1), DOI: 10.1093/mnras/stab3419

Authors: Kuchner, Ulrike; Haggar, Roan; Aragon-Salamanca, Alfonso; Pearce, Frazer R.; Gray, Meghan E.; Rost, Agustin; Cui, Weiguang; Knebe, Alexander; Yepes, Gustavo;

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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 haloes 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 percent of all galaxies fall into clusters via filaments (closer than 1 h(-1) Mpc from the filament spine). 12 percent of these filament galaxies are long-established members of groups and between 30 and 60 percent 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 (similar to 30-60 percent) are environmentally affected by cosmic filaments alone.

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