Analytical halo models of cosmic tidal fields

Abstract

ABSTRACT The non-linear cosmic web environment of dark matter haloes plays a major role in shaping their growth and evolution, and potentially also affects the galaxies that reside in them. We develop an analytical (halo model) formalism to describe the tidal field of anisotropic halocentric density distributions, as characterized by the halocentric tidal tensor $\left\langle \, T_{ij}\, \right\rangle (\lt R)$ spherically averaged on scale R ∼ 4Rvir for haloes of virial radius Rvir. We focus on axisymmetric anisotropies, which allows us to explore simple and intuitive toy models of (sub)halo configurations that exemplify some of the most interesting anisotropies in the cosmic web. We build our models around the spherical Navarro–Frenk–White profile after describing it as a Gaussian mixture, which leads to almost fully analytical expressions for the ‘tidal anisotropy’ scalar α(< 4Rvir) extracted from the tidal tensor. Our axisymmetric examples include (i) a spherical halo at the axis of a cylindrical filament, (ii) an off-centred satellite in a spherical host halo, and (iii) an axisymmetric halo. Using these, we demonstrate several interesting results. For example, the tidal tensor at the axis of a pure cylindrical filament gives α(fil)(< R) = 1/2 exactly, for any R. Also, α(< 4Rvir,sat) for a satellite of radius Rvir,sat as a function of its hostcentric distance is a sensitive probe of dynamical mass-loss of the satellite in its host environment. Finally, we discuss a number of potentially interesting extensions and applications of our formalism that can deepen our understanding of the multiscale phenomenology of the cosmic web.