Discovery of Gas Bulk Motion in the Galaxy Cluster Abell 2256 with Suzaku

TL;DR

Suzaku observations of galaxy cluster Abell 2256 reveal gas bulk motion associated with merging substructures, with measured velocity shifts consistent with optical galaxy velocities, demonstrating gas dynamics during cluster mergers.

Contribution

First detection of gas bulk motion in Abell 2256 using Suzaku X-ray spectroscopy, confirming gas movement with galaxy substructures in a merging galaxy cluster.

Findings

Detected a 1500 km/s velocity shift in gas substructure

X-ray redshifts match optical galaxy velocities

Gas moves coherently with galaxy substructures

Abstract

The results from Suzaku observations of the galaxy cluster Abell2256 are presented. This cluster is a prototypical and well-studied merging system, exhibiting substructures both in the X-ray surface brightness and in the radial velocity distribution of member galaxies. There are main and sub components separating by 3'.5 in the sky and by about 2000 km s$^{-1}$ in radial velocity peaks of member galaxies. In order to measure Doppler shifts of iron K-shell lines from the two gas components by the Suzaku XIS, the energy scale of the instrument was evaluated carefully and found to be calibrated well. A significant shift of the radial velocity of the sub component gas with respect to that of the main cluster was detected. All three XIS sensors show the shift independently and consistently among the three. The difference is found to be 1500 $\pm 300$ (statistical) $\pm 300$ (systematic) km s$^{-1}$. The X-ray determined absolute redshifts of and hence the difference between the main and sub components are consistent with those of member galaxies in optical. The observation indicates robustly that the X-ray emitting gas is moving together with galaxies as a substructure within the cluster. These results along with other X-ray observations of gas bulk motions in merging clusters are discussed.