Exploring the relation between turbulent velocity and density fluctuations in the stratified intracluster medium

Abstract

Context. The dynamics of the intracluster medium (ICM) is affected by turbulence driven by several processes, such as mergers, accretion and feedback from active galactic nuclei. Aims. X-ray surface brightness fluctuations have been used to constrain turbulence in galaxy clusters. Here, we use simulations to further investigate the relation between gas density and turbulent velocity fluctuations, with a focus on the effect of the stratification of the ICM. Methods. In this work, we studied the turbulence driven by hierarchical accretion by analysing a sample of galaxy clusters simulated with the cosmological code ENZO. We used a fixed scale filtering approach to disentangle laminar from turbulent flows. Results. In dynamically perturbed galaxy clusters, we found a relation between the root mean square of density and velocity fluctuations, albeit with a different slope than previously reported. The Richardson number is a parameter that represents the ratio between turbulence and buoyancy, and we found that this variable has a strong dependence on the filtering scale. However, we could not detect any strong relation between the Richardson number and the logarithmic density fluctuations, in contrast to results by recent and more idealised simulations. In particular, we find a strong effect from radial accretion, which appears to be the main driver for the gas fluctuations. The ubiquitous radial bias in the dynamics of the ICM suggests that homogeneity and isotropy are not always valid assumptions, even if the turbulent spectra follow Kolmogorov's scaling. Finally, we find that the slope of the velocity and density spectra are independent of cluster-centric radii.

Multiphase turbulence in galactic haloes: effect of the driving

“…We find that density fluctuations for the non-radiative runs agree with this scaling relation and for the radiative runs, they are slightly larger than the prediction for the corresponding M comp,hot . Simonte et al (2022) find the density fluctuations to be independent of the degree of stratification of the ICM in their sample of galaxy clusters, with 𝜎 2 𝑠 ∼ 0.05-0.5. This is consistent with the Konstandin et al (2012) scaling relation for M comp,hot in the range 0.1-0.4.…”

“…The amplitude of the density fluctuations are also slightly larger than those predicted by Mohapatra et al (2020Mohapatra et al ( , 2021, who only considered solenoidal driving. Since the fluctuations generated by compressive motions are much larger, it explains the lack of dependence of the fluctuations on the degree of stratification in Simonte et al (2022).…”

“…The density stratification of the ICM as well as the existence of sub-structures further complicate the calculations of brightness fluctuations, since the mean brightness is a function of the radial and azimuthal co-ordinates. We refer the readers toVazza et al (2011);Simonte et al (2022) who use filtering methods to remove the effect of substructures while calculating fluctuations in cosmological simulations.MNRAS 000,1-20 (2022)…”

Life cycle of cosmic-ray electrons in the intracluster medium

“…Therefore, given that our previous analysis of similar simulations (e.g. Vazza et al 2009Vazza et al , 2011Angelinelli et al 2020;Simonte et al 2022) as well as many other independent works (e.g.…”

ThePlanckclusters in the LOFAR sky

“…The coefficient η has different values from different simulations, for example, ∼ 1 fromZhuravleva et al (2014b), 1.3 from Gaspari et al (2014, and 0.6 fromSimonte et al (2022). Different adoptions lead to different absolute values of the turbulent Mach numbers, but the relative trends with radio halo power or mass are not expected to change.…”