Abstract
ABSTRACT Galaxy cluster outskirts are described by complex velocity fields induced by diffuse material collapsing towards filaments, gas, and galaxies falling into clusters, and gas shock processes triggered by substructures. A simple scenario that describes the large-scale tidal fields of the cosmic web is not able to fully account for this variety, nor for the differences between gas and collisionless dark matter. We have studied the filamentary structure in zoom-in resimulations centred on 324 clusters from the threehundred project, focusing on differences between dark and baryonic matter. This paper describes the properties of filaments around clusters out to five R200, based on the diffuse filament medium where haloes had been removed. For this, we stack the remaining particles of all simulated volumes to calculate the average profiles of dark matter and gas filaments. We find that filaments increase their thickness closer to nodes and detect signatures of gas turbulence at a distance of ${\sim}2 \rm {{{~h^{-1}\,{\rm Mpc}}}}$ from the cluster. These are absent in dark matter. Both gas and dark matter collapse towards filament spines at a rate of ${\sim}200 \,\rm {km ~ s^{-1}\, h^{-1}}$. We see that gas preferentially enters the cluster as part of filaments, and leaves the cluster centre outside filaments. We further see evidence for an accretion shock just outside the cluster. For dark matter, this preference is less obvious. We argue that this difference is related to the turbulent environment. This indicates that filaments act as highways to fuel the inner regions of clusters with gas and galaxies.
Highlights
Matter in the Universe is structured as a complex network called the cosmic web (Bond, Kofman & Pogosyan 1996)
Approximately 40 per cent of the baryons in the Universe are expected to consist of gas at temperatures of 105–107 K, the warm hot intergalactic medium (WHIM), which is investigated as a possible solution of the so-called missing baryon problem (Cen & Ostriker 1999; Daveet al. 2001; Reimers 2002; Bykov, Paerels & Petrosian 2008)
The filaments are surrounded by complex velocity fields that, to a first order, can be explained by the Zel’dovich approximation (Zel’dovich 1970). This assumption leads to the expectation of a laminar flux towards the filamentary axis, a manifestation of diffuse material collapsing into filaments along two axes. This simple approach does not account for differences between gas and collisionless dark matter or for the dynamics induced by local cosmic web components, like galaxies falling into clusters
Summary
Matter in the Universe is structured as a complex network called the cosmic web (Bond, Kofman & Pogosyan 1996). This leads to wide-ranging discrepancies in relation to the nature of identified objects found by the different filament finders (Libeskind et al 2018; Rost et al 2020), including DISPERSE (Sousbie 2011), Semita (Pereyra et al 2019), Nexus (Aragon-Calvo et al 2007; Cautun, van de Weygaert & Jones 2013), or Bisous (Tempel et al 2014) Despite these drawbacks, understanding the large-scale structures of the Universe, and how the galaxies they host evolve, remain key science challenges. This assumption leads to the expectation of a laminar flux towards the filamentary axis, a manifestation of diffuse material collapsing into filaments along two axes This simple approach does not account for differences between gas and collisionless dark matter or for the dynamics induced by local cosmic web components, like galaxies falling into clusters.
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