Velocity fields and turbulence from cosmic filaments to galaxy clusters

¹ Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
² Astrophysics Research Center of the Open University (ARCO), The Open University of Israel, Ra’anana, Israel
³ Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands
⁴ Université de Lille, CNRS, Centrale Lille, UMR 9189 CRIStAL, F-59000 Lille, France

^⋆ Corresponding author: theo.lebeau@universite-paris-saclay.fr

Received: 16 January 2025
Accepted: 6 October 2025

Abstract

Galaxy clusters are currently the endpoint of the hierarchical structure formation; they form via the accretion of dark matter and cosmic gas from their local environment. In particular, filaments contribute greatly by accreting gas from cosmic matter sheets and underdense regions and by feeding it to the galaxy clusters. Along the way, the gas in the filaments is shocked and heated. Together with the velocity structure within the filament, this induces swirling, and thus, turbulence. We studied a constrained hydrodynamical simulation replica of the Virgo cluster at redshift z = 0 to characterise the velocity field in the two cosmic filaments that are connected to the cluster with unprecedented high resolution. First, we qualitatively examined slices extracted from the simulation. We studied the temperature and the velocity field. We then derived quantities in longitudinal cuts to study the general structure of the filaments and in transverse cuts to study their inner organisation and connection to cosmic matter sheets and underdense regions. Then, we quantitatively studied velocities in the Virgo filaments by computing the 2D power spectrum from 1 and 5 Mpc square maps extracted from the slices and centred on the core of the filaments. We show that the total power spectrum in the filaments gains in amplitude and steepens towards Virgo. Moreover, the velocity field evolves from mostly compressive far in the filaments to mostly solenoidal in the Virgo core.