High entropy and evidence for a merger in the low surface brightness cluster Abell 2399

Abstract

Abstract We present results of the X-ray analyses of the nearby cluster of galaxies Abell 2399 ($z$ = 0.058) using the XMM–Newton and Suzaku satellites. This cluster is classified as a low surface brightness (LSB) cluster. It has a bimodal structure in X-rays, and the X-ray-emission peaks are significantly offset from the peaks in gas temperature. By de-projecting the annular spectra, the temperature and electron density in the central r < 0.1 r200 region are measured to be 3.6 keV and 1.4 × 10−3 cm−3, respectively. This yields a very high gas entropy, ∼300 keV cm2, in the central region, comparable to the values observed in other LSB clusters. The scaled entropy of Abell 2399 is the highest among the REXCESS cluster sample. The spatial distribution of the member galaxies exhibits multiple substructures, the locations of which are significantly different from those in the X-ray image. We discovered a clear discontinuity in the X-ray brightness and temperature distributions in the western gas clump, which provides evidence of the presence of a cold front. Therefore, our results strongly suggest that A2399 has experienced a merger and that the high central entropy originates from the merger activity.