The hot intra-cluster medium (ICM hereafter) in clusters of galaxies is primarily supported by thermal pressure.
Nevertheless, hydrodynamical simulations have shown that a non-negligible contribution to the total pressure may come from non-thermal ordered motions, e.g. radial infall or coherent rotation and streams. Therefore, a correct evaluation of the ICM pressure is fundamental to obtain accurate estimates of cluster masses,
which are in turn very important for the constraining of cosmological parameters. The aim of this project is to continue the investigation of the detectability of rotational motions of the ICM through observational probes at different wavelengths, namely in the microwave region through the kinetic Sunyaev--Zel'dovich (kSZ) effect, and in the X-ray and optical bands through spectroscopic measurements from the gas and the galaxy members, respectively. In a recent work, we produced maps of the temperature distortion produced by the kSZ for the six most relaxed object in a sample of massive clusters from MUSIC simulations (Sembolini et al., 2013) that also show peculiar rotational properties, and we recovered the rotational properties within two standard deviations at most, from the fit to a suitable theoretical model. We treated both a simplified case -- accounting only for rotation -- and a complete one characterized by the adding of the cluster bulk motion. Motivated by these promising results, we are currently working on a refinement of this analysis, by properly accounting for observational effects affecting measurements on real clusters, and through complementary observational approaches towards the same synthetic data set.
With this project we aim to update the study of possible ICM rotation, focusing particularly on the kSZ,
which is still poorly explored.
Indeed, so far this topic has been addressed only from a purely analytical point of view (Cooray & Chen, 2002;
Chluba & Mannheim, 2002), and through the inspection of the kSZ maps produced from a dark matter-only cluster simulation
(Sunyaev, Norman & Bryan 2003).
More recently, the work by Bianconi, Ettori & Nipoti (2013) has provided interesting insights on the detectability
of gas rotation in X-rays, also in this case only from a theoretical point of view.
In this project, we apply for the first time the study of this topic on recent high-resolution hydrodynamical simulations
of galaxy clusters by the MUSIC project, which follow the evolution of both gas and dark matter particles.
We started studying the detectability through the kSZ effect by computing a pixel-to-pixel best fit to the data
assuming a new rotational model, and we plan to fully characterize the signal by accounting for different contaminants,
to quantify the effective sensitivity needed for a possible future detection.
To explore all possible observational approaches, we also started a preliminary study of the possible rotation of the
galaxy members, and we will start working on the X-ray signal.