The quiescent intracluster medium in the core of the Perseus cluster

Abstract

Clusters of galaxies are the most massive gravitationally bound objects in the Universe and are still forming. They are thus important probes of cosmological parameters and many astrophysical processes. However, knowledge of the dynamics of the pervasive hot gas, the mass of which is much larger than the combined mass of all the stars in the cluster, is lacking. Such knowledge would enable insights into the injection of mechanical energy by the central supermassive black hole and the use of hydrostatic equilibrium for determining cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50-million-kelvin diffuse hot plasma filling its gravitational potential well. The active galactic nucleus of the central galaxy NGC 1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These bubbles probably induce motions in the intracluster medium and heat the inner gas, preventing runaway radiative cooling--a process known as active galactic nucleus feedback. Here we report X-ray observations of the core of the Perseus cluster, which reveal a remarkably quiescent atmosphere in which the gas has a line-of-sight velocity dispersion of 164 ± 10 kilometres per second in the region 30-60 kiloparsecs from the central nucleus. A gradient in the line-of-sight velocity of 150 ± 70 kilometres per second is found across the 60-kiloparsec image of the cluster core. Turbulent pressure support in the gas is four per cent of the thermodynamic pressure, with large-scale shear at most doubling this estimate. We infer that a total cluster mass determined from hydrostatic equilibrium in a central region would require little correction for turbulent pressure.

Viscosity, pressure and support of the gas in simulations of merging cool-core clusters

“…In agreement with previous studies (e.g. Vazza et al 2012;Skory et al 2013;Li et al 2015;Hahn et al 2017), however, we find that the merger by itself is insufficient to lift the cool cores of the predecessors into the regime of a non-cool core in the post-merger cluster.…”

“…McNamara & Nulsen 2007;Dubois et al 2010;Borgani & Kravtsov 2011;Martizzi et al 2012;Yang et al 2012;Vazza et al 2012;Gaspari et al 2014b;Li et al 2015;Planelles et al 2017;Hahn et al 2017). It was also suggested, however, that major mergers E-mail:wolfram.schmidt@uni-hamburg.de may significantly impact the energy budget of clusters and at least partially contribute to the heating of cool cores (see Skory et al 2013;Hahn et al 2017). Observationally, this is indicated by disturbed clusters, in which cool cores tend to be underrepresented and weaker (Sanderson et al 2009;Pratt et al 2010).…”

Turbulence in the intracluster medium: simulations, observables, and thermodynamics

“…Two recent observational studies - Aharonian et al (2016) (the Hitomi collaboration) and Zhuravleva et al (2014a) -obtain a similar estimate for the turbulent velocities in the core of Perseus cluster. While Zhuravleva et al (2014a) reconstruct the velocity amplitudes by analysing the power spectrum of X-ray surface brightness fluctuations, Hitomi directly measured the line of sight velocity dispersion (σ LOS ) by analysing the broadening of Fe XXV and Fe XXVI lines.…”

“…In cool cluster cores the gas temperature distribution is bimodal (in reality the cooler phase will be emitting in Hα and CO and not in X-rays), and observations show that the hot ICM is subsonic (Aharonian et al 2016). From our simulations, we conclude that it is unlikely that pure turbulent driving on cluster core length scales (10s of kpc) can balance radiative losses in the core for ∼ 1 keV clusters, since this scenario gives a large amount of gas at intermediate temperatures and supersonic turbulence in the hot phase (subject to our assumptions as listed in subsection 5.1).…”

Testing the rotation versus merger scenario in the galaxy cluster Abell 2107

“…In any case, global rotation, if any, is expected to be characterized by velocities significantly lower than the typical velocity dispersion in clusters, which makes it very hard to blindly search for global rotation of the ICM using the available spectral resolution of CCD X-ray imagers that can at best identify velocity differences of ∼ 1000 km/s or larger, as previously mentioned. As a matter of fact, the study of ICM bulk motions will be always limited to a few cases until the advent of X-ray bolometers, which will be on board of XRISM and Athena (Guainazzi & Tashiro 2018). In the case of XRISM, the low angular resolution of the order of ∼ 1 will enable study of bulk motions only in nearby clusters, since the signal from the ICM in distant clusters will be smeared out.…”