Populations of filaments from the distribution of galaxies in numerical
  simulations
  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 (> 5 sigma) 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 (L_f < 9 Mpc) and long (L_f > 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, beta-model, a single and a double power
law) with different and distinct sets of parameters.
