Abstract

We present a multiwavelength study of the poor cluster RX J1117.4+0743 ([ VMF 98] 097) at z = 0.485, based on GMOS/Gemini South g′ and r′ photometry and spectroscopy, and XMM-Newton observations. We examine its nature and surroundings by analyzing the projected galaxy distribution, the galaxy velocity distribution, the weak-lensing mass reconstruction, and the X-ray spectroscopy and imaging. The cluster is composed by at least two structures along the line of sight, with σV = 592 ± 82 and 391 ± 85 km s-1 respectively. Other structures are also detected in X-ray, in the galaxy projected number density map, and by weak lensing. The derived temperature and bolometric X-ray luminosity reveal that [VMF 98] 097 behaves like a normal cluster, in agreement with LX-TX correlation found for z = 0 and at z ∼ 0.4 clusters. The mass determination inferred from weak lensing is on average 3-4.8 times higher than the X-ray mass. We have two possible explanations for this discrepancy: (1) the cluster is in nonequilibrium, then the deviation of the X-ray estimated mass from the true value can be as high as a factor of 2; (2) the intervening mass along the line of sight of the cluster is producing an overestimation of the weak-lensing mass. Based on the analysis, we conclude that [VMF 98] 097 is a perturbed cluster with at least two substructures in velocity space and with other nearby structures at projected distances of about 1 h70 -1 Mpc. This is an example of a poor cluster caught in the process of accreting substructures to become a rich cluster. © 2007. The American Astronomical Society. All rights reserved.