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Suzaku discovers gas motion in a galaxy cluster

X-ray spectrum from the galaxy cluster A2256 observed with SUZAKU

What is a difference between the above two plots ?

A galaxy cluster, the largest structure in the universe, is filled with X-ray emitting plasma. This figure shows X-ray spectrum from the cluster A2256. A bump around 6.5 keV is an X-ray line from iron ions. By measuring the line energy, you can find a redshift, or a recession velocity of the emitting material.

This data is extracted from a sub part of the cluster (mini cluster). Two plots show the same data in cross with error bars but with different models (solid-lines). The left model has -1500 km/s velocity for the mini cluster, while the right has zero velocity. You can see that the left model reproduces the data better than the right. Using this kind of analysis, a gas motion with a velocity (toward us) of about 1500 km/s of the mini cluster has been discovered. This is the first detection of such motion in X-ray emitting plasma. In the universe, small structures collide with others and merge into larger one. This observation confirmed this formation model in a merging cluster.

This result (Tamura et al. 2011) will be published on the PASJ (special issue of SUZAKU/MAXI) in this autumn. You can check the data by yourself using UDON (QL analysis) or JUDO (on the sky). Please find more using the Suzaku data.

Takayuki TAMURA(ISAS/JAXA)

June, 2011