Galaxy evolution in the cosmic web: the relative impact of nodes and filaments in the EAGLE simulation

Abstract

Galaxies evolve within the intricate geometry of the cosmic web, yet the distinct roles of its primary components - nodes and filaments remain incompletely understood. Using the EAGLE cosmological hydrodynamical simulation, we investigate how distances to filament spines and cluster-scale nodes jointly and independently influence galaxy evolution. Galaxies are classified into red, green, and blue populations through a fully data-driven entropic thresholding technique, and the nodes and filaments are identified using DisPerSE. We find that red galaxies preferentially reside near filament cores and nodes, whereas blue galaxies dominate the outskirts. This spatial segregation reveals two characteristic transition scales: a node-related crossover at $\sim 2.5~\mathrm{Mpc}$ and a filament-related crossover at $\sim 0.75~\mathrm{Mpc}$. To further quantify environmental influence, we adopt an information-theoretic approach and measure the normalised mutual information between dominant mass component and galaxy colour across the $d_{\mathrm{f}}$-$d_{\mathrm{n}}$ plane. The mass-colour coupling increases with distance from nodes at fixed filament proximity, indicating a weakening of this relation in cluster-scale environments and a stronger coupling within filamentary regions. This behaviour is strongly mass dependent, with low-mass galaxies exhibiting a more pronounced environmental modulation than high-mass systems. These results support a scale-dependent view of galaxy evolution across the cosmic web, highlighting the distinct and complementary influence of nodes and filaments.

Figures (9)

• Figure 1: The left panel shows the red, green and blue galaxies identified using entropic thresholding on the $(u-r)$ colour-stellar mass plane. The PDFs of the three types of galaxy are shown in the right panel.
• Figure 2: The two panels of this figure show filament spines and nodes identified with DisPerSE, overlaid with the spatial distribution of low-mass ($\log(M_{\mathrm{tot}}/M_{\odot}) < 10.6$, left) and high-mass ($\log(M_{\mathrm{tot}}/M_{\odot}) \geq 10.6$, right) galaxies. The colours indicate distance from the nearest filament spine.
• Figure 3: Top panels of this figure show joint probability distribution functions (PDF) of red (left), green (middle), and blue (right) galaxies in the $d_{\mathrm{f}}$-$d_{\mathrm{n}}$ plane, where $d_{\mathrm{f}}$ and $d_{\mathrm{n}}$ denote distances from the filament spine and closest node, respectively. Contours enclose $50\%$, $75\%$, $90\%$, and $99\%$ of each population. The bottom two panels show corresponding relative fractions as functions of $d_{\mathrm{f}}$ (left) and $d_{\mathrm{n}}$ (right). Red galaxies dominate near filament spines and nodes, while blue galaxies preferentially occupy larger distances. The crossover between red and blue fractions occurs at $d_{\mathrm{f}} \sim 0.75~\mathrm{Mpc}$ and $d_{\mathrm{n}} \sim 2.5~\mathrm{Mpc}$ for filament and node respectively. The 1$\sigma$ error bars in each case are estimated using $100$ jackknife samples drawn from the original distributions.
• Figure 4: Joint PDF of red, green, and blue galaxies in the $d_{\mathrm{f}}$-$d_{\mathrm{n}}$ plane, shown separately for $\log(M_{\mathrm{tot}}/M_{\odot}) < 10.6$ (top) and $\log(M_{\mathrm{tot}}/M_{\odot}) \geq 10.6$ (bottom). Low-mass galaxies exhibit stronger colour segregation with respect to filament and node proximity, whereas high-mass galaxies display a broader and less contrasted distribution.
• Figure 5: Relative fractions of red, green, and blue galaxies as functions of distance from the filament spine (left) and closest node (right), shown separately for $\log(M_{\mathrm{tot}}/M_{\odot}) < 10.6$ (top) and $\log(M_{\mathrm{tot}}/M_{\odot}) \geq 10.6$ (bottom). The 1$\sigma$ errorbars are computed based on 100 jackknife resamplings of the underlying distributions.