2025A&A...694A.182A

Turbulent gas motions are expected to dominate the non-thermal energy budget of the intracluster medium (ICM). The measurement of pressure fluctuations from high angular resolution Sunyaev-Zel'dovich imaging opens a new avenue to study ICM turbulence, complementary to X-ray density fluctuation measures. We developed a methodological framework designed to optimally extract information on the ICM pressure fluctuation power spectrum statistics, and publicly released the associated software named PITSZI (Probing ICM Turbulence from Sunyaev-Zel'dovich Imaging). We applied this tool to the New IRAM KIDs Array (NIKA) data of the merging cluster MACS J0717.5+3745 to measure its pressure fluctuation power spectrum at high significance, and to investigate the implications for its non-thermal content. Depending on the choice of the radial pressure model and the details of the applied methodology, we measured an energy injection scale L_inj ∼ 800 kpc. The power spectrum normalization corresponds to a characteristic amplitude reaching $ A_{\delta P / \bar{P}}(k_{\mathrm{peak}}) \sim 0.4 $. These results were obtained assuming that the ICM of MACS J0717.5+3745 can be described as pressure fluctuations on top of a single (smooth) halo, and were dominated by systematics due to the choice of the radial pressure model. Using simulations, we determined that fitting a radial model to the data can suppress the observed fluctuations by up to ∼50%, while a poorly representative radial model can induce spurious fluctuations, which we also quantified. Assuming standard scaling relations between the pressure fluctuations and turbulence, we find that MACS J0717.5+3745 presents a turbulent velocity dispersion σ_v ∼ 1200 km/s, a kinetic to kinetic plus thermal pressure fraction P_kin/P_kin + th_ ∼ 20%, and we estimate the hydrostatic mass bias to b_HSE ∼ 0.3 - 0.4. Our results are in excellent agreement with alternative measurements obtained from X-ray surface brightness fluctuations, and in agreement with the fluctuations being adiabatic in nature.