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

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### Abstract

We search for global rotation of the intracluster medium (ICM) in the galaxy cluster Abell 2107, where previous studies have detected rotational motion in the member galaxies with a high significance level. By fitting the centroid of the iron $$K_{\alpha}$$ line complex at 6.7--6.9 keV rest frame in {\sl Chandra} ACIS-I spectra, we identify the possible rotation axis with the line that maximizes the difference between the emission-weighted spectroscopic redshift measured in the two halves defined by the line itself. Then, we measure the emission-weighted redshift in linear regions parallel to the preferred rotation axis, and find a significant gradient as a function of the projected distance from the rotation axis, compatible with a rotation pattern with maximum tangential velocity $${\tt v}_{\rm max}=1380\pm 600$$ km/s at a radius $$\lambda_0\sim 160$$ kpc. This result, if interpreted in the framework of hydrostatic equilibrium, as suggested by the regular morphology of Abell 2107, would imply a large mass correction of the order of $$\Delta M = (6 \pm 4)\times 10^{13} M_\odot$$ at $$\sim 160$$ kpc, which is incompatible with the cluster morphology itself. A more conservative interpretation may be provided by an unnoticed off-center, head-on collision between two comparable halos. Our analysis confirms the peculiar dynamical nature of the otherwise regular cluster Abell 2107, but is not able to resolve the rotation vs merger scenario, a science case that can be addressed by the next-generation X-ray facilities carrying X-ray bolometers onboard.

### Most cited references1

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### The ATHENA x-ray integral field unit (X-IFU)

(2018)
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### Author and article information

###### Journal
09 March 2019
###### Article
10.1093/mnras/stz713
1903.03858