A2111: A z=0.23 Butcher-Oemler Cluster with a Non-isothermal Atmosphere and Normal Metallicity

Abstract

We report results from an X-ray study of the Abell 2111 galaxy cluster using the Advanced Satellite for Astrophysics and Cosmology ASCA and the ROSAT Position Sensitive Proportional Counter (PSPC). By correcting for the energy-dependent point-spread function of the ASCA instruments, we have examined the temperature structure of the cluster. The cluster's core within 3' is found to have a temperature of 6.46+-0.87 keV, significantly higher than 3.10+-1.19 keV in the surrounding region of r = 3 - 6'. This radially decreasing temperature structure can be parameterized by a polytropic index of $γ$ $\simeq$ 1.45. The X-ray morphology of the cluster appears elongated and clumpy on scales $\le$1'. These results, together with earlier {\it ROSAT} and optical studies which revealed that the X-ray centroid and ellipticity of A2111 shift with spatial scale, are consistent with the hypothesis that the cluster is a dynamically young system. Most likely, the cluster has recently undergone a merger, which may also be responsible for the high fraction of blue galaxies observed in the cluster. Alternatively, the temperature structure may also be due to the gravitational potential of the cluster. We have further measured the emission weighted abundance of the X-ray-emitting intracluster medium as 0.25$\pm$0.14 solar. This value is similar to those of nearby clusters which do not show a large blue galaxy fraction, indicating that star formation in disk galaxies and subsequent loss to the medium do not drastically alter the average abundance of a cluster. This is consistent with recent results which indicate that cluster abundances have remained constant since at least z ~ 0.3.