The origin of an extended X-ray emission apparently associated with the globular cluster 47 Tucanae

TL;DR

This study used Suzaku to analyze extended X-ray emission near 47 Tucanae, revealing it to be a background galaxy cluster aligned by chance with the cluster's proper motion.

Contribution

First identification of the extended X-ray emission as a background galaxy cluster using spectral analysis and redshift measurement.

Findings

The X-ray emission is from a background galaxy cluster at redshift 0.34.

The cluster's temperature is approximately 2.2 keV.

The emission's luminosity and spectral properties support its background cluster nature.

Abstract

Using the Suzaku X-ray Imaging Spectrometer, we performed a 130 ks observation of an extended X-ray emission, which was shown by ROSAT and Chandra observations to apparently associate with the globular cluster 47 Tucanae. The obtained $0.5-6$ keV spectrum was successfully fitted with a redshifted thin thermal plasma emission model whose temperature and redshift are $2.2^{+0.2}_{-0.3} $keV (at the rest frame) and $0.34\pm0.02$, respectively. Derived parameters, including the temperature, redshift, and luminosity, indicate that the extended X-ray source is a background cluster of galaxies, and its projected location falls, by chance, on the direction of the proper motion of 47 Tucanae.