Gemini andChandraObservations of Abell 586, A Relaxed Strong‐lensing Cluster

We analyze the mass content of the massive strong-lensing cluster Abell 586($z = 0.17$). We use optical data (imaging and spectroscopy) obtained with theGemini Multi-Object Spectrograph (GMOS) mounted on the 8-m Gemini-Northtelescope, together with publicly available X-ray data taken with the\textit{Chandra} space telescope. Employing different techniques -- velocitydistribution of galaxies, weak gravitational lensing, and X-ray spatiallyresolved spectroscopy -- we derive mass and velocity dispersion estimates fromeach of them. All estimates agree well with each other, within a 68% confidencelevel, indicating a velocity dispersion of 1000 -- 1250 \kms. The projectedmass distributions obtained through weak-lensing and X-ray emission arestrikingly similar, having nearly circular geometry. We suggest that Abell 586is probably a truly relaxed cluster, whose last major merger occurred more than$\sim 4$ Gyr agoComment: ApJ accepted, 20 pages, 11 figures; Figure 1 fixe