On the width and profiles of cosmic filaments

Abstract

We investigated the widths and profiles of cosmic filaments using the IllustrisTNG simulations. Filaments were identified with DisPerSE, using galaxy samples in simulations as input. Since the width of an individual filament can vary significantly along its spine, we divided each filament into segments with lengths between $1.5\,h^{-1}\,\mathrm{Mpc}$ and $2.5\,h^{-1}\,\mathrm{Mpc}$ and measure their properties. The typical width of these filament segments increases gradually from approximately $0.3\,\mathrm{Mpc}$ at redshift $z = 2.0$ to about $1.0-1.5\,\mathrm{Mpc}$ at $z = 0.0$. We find that the segment width correlates nearly linearly with the linear halo mass density, consistent with previous studies. A similar linear relation is observed between the segment width and the linear stellar mass density, providing a potential estimator for filament width. Furthermore, the density profiles of filaments with different widths exhibit self-similarity and can be described by a unified formula akin to the isothermal $\beta$-model. For segments with a given width, the rescaled density profiles show only mild evolution from $z = 2.0$ to $z = 0.0$. Within the filament width, the gas temperature decreases slowly from the center to the boundary, with thicker filaments generally containing hotter gas than thinner ones. These trends in filament width, density, and thermal profiles are consistently observed across the TNG50, TNG100, and TNG300 simulations, and align well with results from earlier studies. We briefly discuss the potential implications and applications of our findings.