Mapping and characterization of cosmic filaments in galaxy cluster outskirts: strategies and forecasts for observations from simulations

Abstract

Upcoming wide-field surveys are well suited to studying the growth of galaxy clusters by tracing galaxy and gas accretion along cosmic filaments. We use hydrodynamic simulations of volumes surrounding 324 clusters from The ThreeHundred project to develop a framework for identifying and characterizing these filamentary structures and associating galaxies with them. We define three-dimensional reference filament networks reaching 5R200 based on the underlying gas distribution and quantify their recovery using mock galaxy samples mimicking observations such as those of the WEAVE Wide-Field Cluster Survey. Since massive galaxies trace filaments, they are best recovered by mass-weighting galaxies or imposing a bright limit (e.g. >L*) on their selection. We measure the transverse gas density profile of filaments, derive a characteristic filament radius of ≃ 0.7–1 h−1Mpc, and use this to assign galaxies to filaments. For different filament extraction methods, we find that at R > R200, ∼15–$20{{\ \rm per\ cent}}$ of galaxies with M* > 3 × 109M⊙ are in filaments, increasing to $\sim 60{{\ \rm per\ cent}}$ for galaxies more massive than the Milky Way. The fraction of galaxies in filaments is independent of cluster mass and dynamical state and is a function of cluster-centric distance, increasing from ∼13 per cent at 5R200 to ∼21 per cent at 1.5R200. As a bridge to the design of observational studies, we measure the purity and completeness of different filament galaxy selection strategies. Encouragingly, the overall three-dimensional filament networks and ∼67 per cent of the galaxies associated with them are recovered from two-dimensional galaxy positions.

Shape and connectivity of groups and clusters: Effect of the dynamical state and accretion history

“…To understand this anisotropic environmental effect on the shape, we probed the possible relations between the accretion of infalling matter at the present time and the halo anisotropy proxies (both ellipticity and connectivity). In addition to the overall picture that groups and clusters are preferentially aligned with their main connected filaments as supported by previous theoretical (Gouin et al 2017;Okabe et al 2020a;Kuchner et al 2020) and observational (Einasto et al 2020;Okabe et al 2020b;Gouin et al 2020) studies, Morinaga & Ishiyama (2020) have recently shown that ellipticity is correlated with the filamentary accretion.…”

“…Groups and clusters with χ DS ≥ 1 were considered as dynamically relaxed (see, e.g., Kuchner et al 2020).…”

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

“…While the example shown in Fig. 1 offers an obvious clue that the identified network indeed traces the underlying structure of the density field, we refer the reader to Kuchner et al (2020), in which detailed tests of the filament extraction method on gas and mock galaxies in the same simulations, as well as comparisons between detections in 2D and 3D are presented.…”

The Three Hundred Project: Substructure in hydrodynamical and dark matter simulations of galaxy groups around clusters

“…The hydrodynamical clusters consist of dark matter and gas particles, and star particles of variable masses, typically with mstar ∼ 4 × 10 7 h −1 M , produced by the stochastic star-formation that is implemented by gadgetX (Tornatore et al 2007;Murante et al 2010;Rasia et al 2015). TheThreeHundred dataset is described in more extensive detail in Cui et al (2018), and has been used in previous studies to examine cluster density profiles (Mostoghiu et al 2019;Li et al 2020), environments (Wang et al 2018;Kuchner et al 2020), ram pressure (Arthur et al 2019), the hydrostatic equilibrium mass bias (Ansarifard et al 2020), backsplash galaxies (Haggar et al 2020), and the shapes and alignments of galaxies (Knebe et al 2020). Table 1.…”