Caught in the cosmic web: environmental effects on subhalo abundance and internal density profiles

Using the high-resolution $N$-body cosmological simulation COLOR, we explore the cosmic web (CW) environmental effects on subhalo populations and their internal properties. We use CaCTus, which incorporates an implementation of the state-of-the-art segmentation method NEXUS+, to delineate the simulation volume into nodes, filaments, walls, and voids. We group host haloes by virial mass and segment each mass bin into consecutive CW elements. This reveals that subhalo populations in hosts within specific environments differ on average from the cosmic mean. The subhalo mass function is affected strongly, where hosts in filaments typically contain more subhaloes ($5$ to $20\%$), while hosts in voids are subhalo-poor, with $25\%$ fewer subhaloes. We find that the abundance of the most massive subhaloes, with reduced masses of $\mu\equiv M_\mathrm{sub}/M_{200}$ is most sensitive to the CW environment. A corresponding picture emerges when looking at subhalo mass fractions, $f_\mathrm{sub}$, where the filament hosts are significantly more `granular' (having higher $f_\mathrm{sub}$) than the cosmic mean, while the void hosts have much smoother density distributions (with $f_\mathrm{sub}$ lower by $2$ - $20\%$ than the mean). Finally, when we look at the subhalo internal kinematic $V_{\rm max}$-$R_{\rm max}$ relations, we find that subhaloes located in the void and wall hosts exhibit density profiles with lower concentrations than the mean, while the filament hosts demonstrate much more concentrated mass profiles. Across all our samples, the effect of the CW environment generally strengthens with decreasing host halo virial mass. Our results show that host location in the large-scale CW introduces significant systematic effects on internal subhalo properties and population statistics.