the threehundred: the structure and properties of cosmic filaments in the outskirts of galaxy clusters

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.

Virgo filaments

“…A typical filament radius d 0,fil = (2.29 ± 0.55) h −1 Mpc is inferred from our fit, which is within the range of values found in the literature. Our estimate is in fact lower than that of (5.1 ± 0.1) h −1 Mpc found by Bonjean et al (2020) by fitting an exponential profile to cosmological filaments at 0.1 < z < 0.3, but is higher than both ∼(0.2−0.9) h −1 Mpc, found by Lee et al (2021) by fitting the individual profiles of some major filaments around Virgo, and the values of ∼(0.7−1.0) h −1 Mpc recently found in hydrodynamic simulations (Kuchner et al 2020;Rost et al 2021). These different values for the filament radius, which is of the order of ∼1.0 h −1 Mpc, are not surprising.…”

Properties of gas phases around cosmic filaments atz= 0 in the IllustrisTNG simulation

“…It is interesting to note that this differs from the trends of DM and gas found in intracluster bridges and in those filaments, sometimes called 'spider-legs', that are found at the very outskirts of massive clusters (e.g. Colberg et al 2005;Dolag et al 2006;Rost et al 2021). These filamentary structures do not belong to the main stem of cosmic filaments, and we recall that they are excluded from our analysis.…”

“…However, since the outskirts of clusters are not included in the present analysis (regions within 3 × R 200 from cluster centres are excluded), the bump highlighted here is rather found to be an intrinsic property of radial accretion shocks of WHIM gas at the boundaries of filaments. Of course, this intrinsic radial feature can be enhanced by other processes, like the turbulent motions for the filamentary structures at the outskirts of clusters detected by Rost et al (2021).…”

The THREEHUNDRED project: The effect of baryon processes at galaxy cluster scale

“…Benefiting from the large volume of these re-simulated cluster regions, detailed relations between the central cluster and the filaments connecting to it have been studied [16][17][18]. Furthermore, the cluster backsplash galaxies [19,20] and shock radius [21] have also been well addressed.…”