Academia Sinica Institute for Astronomy & Astrophysics | 2018 Oct 18
Almost all galaxy clusters experience mergers. While a merger takes place, a specific pattern of "spiral" often can be observed in X-ray images. Such a spiral feature is due to the motion of the gas (induced by a merger), called "sloshing gas". Observing a phenomenon similar to sloshing gas in the daily life is easy: when you swirl a wine glass containing some water in it and you will see how the water rotates along with the glass. Discovering how fast the sloshing gas moves in galaxy clusters has profound astronomical meaning and therefore is of great interest to astronomers. A group of researchers from Taiwan and Japan has now measured it by a novel technique enabled by the finest images from the space as well as the ground telescopes available to date; their answer is: "sub-sonic!" ...
Measuring the moving gas has always been important to astronomers because motion is not only a basic aspect in physics but also an important observable of astronomical objects. The motion of astronomical object can directly tell us what has happened in the "systems". Therefore, measuring the motion is an important step towards the revealing of where or what the origin is, what the dominating mechanism is, and the nature of the astronomical object itself.
In the case of galaxy clusters, many kinds of features that indicate a presence of motion of intra-cluster medium are found. They are considered to be associated with the evolution of galaxy clusters. It is however hard to measure the motion of intra-cluster medium in galaxy clusters due to the energy resolution of X-ray CCD camera. So, astronomers' knowledge of the velocity field was limited to only a few samples out of hundreds of galaxy clusters - even through a number of observations have been done in the past two decades. In addition, the measurements were restricted to the line-of-sight velocity of the intra-cluster medium, because only the Doppler effect on emission lines of highly-ionized iron can be used to measure the velocity in X-rays. Recently, a new method is proposed to measure the velocity field by focusing on the perturbation in X-ray images, but the study based on this method is limited so far. Therefore, the measurement of motion of intra-cluster medium is still one of the hottest topics and its velocity is one of the most important physical quantities to understand the nature of galaxy clusters. ...
A Cool Core Disturbed: Observational Evidence for the Coexistence of Subsonic Sloshing Gas
and Stripped Shock-heated Gas around the Core of RX J1347.5–1145 ~ Shutaro Ueda et al
- Astrophysical Journal 866(1):48 (2018 Oct 10) DOI: 10.3847/1538-4357/aadd9d]
arXiv.org > astro-ph > arXiv:1808.09232 > 28 Aug 2018
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