XMAGNET: Velocity structure functions of active galactic nucleus-driven turbulence in the multiphase intracluster medium

¹ Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
² Department of Computational Mathematics, Science, and Engineering, Michigan State University, East Lansing, MI 48824, USA
³ Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
⁴ Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI 48824, USA
⁵ Institute for Cyber-Enabled Research, 567 Wilson Road, Michigan State University, East Lansing, MI 48824, USA
⁶ School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3AA, UK
⁷ Theoretical Division, TA-3 Bldg. 123, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
⁸ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

^⋆ Corresponding author: martin.fournier@uni-hamburg.de

Received: 26 February 2025
Accepted: 27 March 2025

Abstract

Context. Significant theoretical and observational efforts are underway to investigate the properties of the turbulence in the hot plasma that pervades galaxy clusters. Spectroscopy has been used to study the projected line-of-sight velocities in both the hot intracluster medium and the cold gas phase in combination with optical and X-ray telescopes.

Aims. In this work, we characterize the velocity structure functions (VSFs) of the multiphase intracluster medium in a simulated galaxy cluster core and study the effects of projections on the hot and cold phase of the gas.

Methods. We used the fiducial run of the XMAGNET suite, a collection of exascale magneto-hydrodynamical simulations of a cool-core cluster, to compute VSFs. The simulation includes radiative cooling as well as a model for active galactic nuclei feedback.

Results. Examining three-dimensional and line-of-sight VSFs, we find no clear correlation between the behavior of the hot (10⁶ K  ≤ T ≤ 10⁸ K) and cold (T ≤ 10⁵ K) phase VSFs. Assuming a power-law model for the VSF, we find that the power-law index m of the cold phase varies significantly throughout the 4 Gyr simulation time. We compared our VSFs with observations using mock optical and X-ray images, and we conclude that projection effects significantly impact the amplitude and power-law index of both the hot and cold phases. In the cold phase, applying a Gaussian smoothing filter to model effects of atmospheric seeing significantly increases the index of the projected VSF at scales below the filter’s kernel size. Moreover, the VSF amplitude and power-law index vary significantly depending on the viewing orientation.

Conclusions. Observational biases such as projection effects, atmospheric seeing, and the viewing angle cannot be ignored when interpreting the line-of-sight velocity structure of the intracluster medium.