Populations of filaments from the distribution of galaxies in numerical simulations

Abstract

We present a statistical study of the filamentary structures of the cosmic web in the large hydro-dynamical simulations Illustris-TNG, Illustris, and Magneticum at redshift z = 0. We focus on the radial distribution of the galaxy density around filaments detected using the Discrete Persistent Structure Extractor (DisPerSE). We show that the average profile of filaments presents an excess of galaxy density (> 5σ) up to radial distances of 27 Mpc from the core. The relation between galaxy density and the length of filaments is further investigated showing that short (Lf < 9 Mpc) and long (Lf ≥ 20 Mpc) filaments are two statistically different populations. Short filaments are puffier, denser, and more connected to massive objects, whereas long filaments are thinner, less dense, and more connected to less massive structures. These two populations trace different environments and may correspond to bridges of matter between over-dense structures (short filaments), and to cosmic filaments shaping the skeleton of the cosmic web (long filaments). Through Markov chain Monte Carlo (MCMC) explorations, we find that the density profiles of both short and long filaments can be described by the same empirical models (generalised Navarro, Frenk and White, β-model, a single and a double power law) with different and distinct sets of parameters.

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

“…Filaments run from a node to a saddle point and at least two are needed to bridge between haloes. studies mentioned above, the trend of having a lower population for longer filaments seen here is widely observed in the literature (Bond, Strauss & Cen 2010;Galárraga-Espinosa et al 2020;Malavasi et al 2020;Rost et al 2020). Note also that the recovered length and number of filaments depend on the persistence level chosen during filament extraction, with a lower level leading to more nodes and a finer network.…”

“…A similar shape is also seen in other works with different emphases and starting points, e.g. Colberg et al (2005) who used CDM numerical simulations to study the filaments between pairs of clusters, and Dolag et al (2006) who studied gas density profiles in hydrodynamical resimulations (see also Aragón-Calvo, van de Weygaert & Jones 2010; also Bonjean et al 2019;Galárraga-Espinosa et al 2020). Note, however, that the shape of the gas density profile is resolution and cooling model dependent.…”

“…Others define the distance at which the density drops below a certain threshold (Dolag et al 2006), which leads to higher values of 5 h −1 Mpc radius. Yet others use the scale parameters that fit the data using a certain model, finding thickness parameter values of r 2 = 2−3 h −1 Mpc, with long filaments being thinner than short filaments (Galárraga-Espinosa et al 2020), or r m ≈ 7.5 Mpc for a exponential decay fit for long filaments >20 Mpc (Bonjean et al 2019).…”

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

“…The catalogue of filaments used in this work was constructed in Galárraga-Espinosa et al (2020), which provides details and technicalities. Here, we simply summarise the main important points.…”

“…In the present paper, we study gas around cosmic filaments detected with the DisPerSE algorithm (Sousbie 2011;Sousbie et al 2011) in the galaxy distribution of the Illustris The Next Generation simulation (IllustrisTNG, Nelson et al 2019) at redshift zero. We separate the gas into different density and temperature states, called phases, and we study the gas properties around the different populations of filaments identified in Galárraga-Espinosa et al (2020). We map the distribution of the different baryonic phases around filaments by building phase fraction profiles, and we characterise their thermodynamical properties by means of temperature and pressure profiles.…”