Thermal SZ fluctuations in the ICM: probing turbulence and thermodynamics in Coma cluster with ${\it Planck}$

TL;DR

This paper detects and analyzes thermal SZ fluctuations in the Coma cluster using Planck data, revealing turbulence properties, pressure fluctuations, and non-thermal support, advancing understanding of ICM physics and cosmological implications.

Contribution

It introduces a novel method to measure ICM turbulence and pressure fluctuations from SZ data, linking observations to hydrodynamical models and improving constraints on cluster dynamics.

Findings

Pressure fluctuation amplitude peaks at 33-74% in different regions.

ICM turbulence has a Mach number around 0.8, increasing with radius.

Hydrostatic mass bias ranges from -15% to -45%.

Abstract

We report the detection of thermal Sunyaev-Zeldovich effect (SZ) fluctuations in the intracluster medium (ICM) of Coma cluster observed with ${\it Planck}$. The SZ data links the maximum observable X-ray scale to the large Mpc scale, extending our knowledge of the power spectrum of ICM fluctuations. Deprojecting the 2-d SZ perturbations into 3-d pressure fluctuations, we find an amplitude spectrum which peaks at $\delta P/P = 33\pm 12\%$ and $74\pm19\%$ in the $15'$ and $40'$ radius region, respectively. We perform tests to ensure fluctuations are intrinsic to the cluster and not due to noise contamination. By using high-resolution hydrodynamical models, we improve the ICM turbulence constraints in Coma, finding 3-d Mach number ${\rm Ma_{3d}}= 0.8\pm0.3$ (15' region), increasing to supersonic values at larger radii (40'), and an injection scale $L_{\rm inj}\approx 500$ kpc. Such properties are consistent with driving due to mergers, in particular tied to internal galaxy groups. The large pressure fluctuations show that Coma is in adiabatic mode (mediated by sound waves), rather than isobaric mode (mediated by buoyancy waves). As predicted by turbulence models, the distribution of SZ fluctuations is log-normal with mild non-Gaussianities (heavy tails). The substantial non-thermal pressure support implies hydrostatic mass bias $b_M=-15\%$ to $-45\%$ from the core to the outskirt region, respectively. While total SZ power probes the thermal energy content, the SZ fluctuations constrain the non-thermal deviations important for precision cosmology. The proposed, novel approach can be exploited by multifrequency observations using ground based interferometers and future space CMB missions.