Galaxy cluster's rotation

Abstract

We study the possible rotation of cluster galaxies, developing, testing and\napplying a novel algorithm which identifies rotation, if such does exist, as\nwell as its rotational centre, its axis orientation, rotational velocity\namplitude and, finally, the clockwise or counterclockwise direction of rotation\non the plane of the sky. To validate our algorithms we construct realistic\nMonte Carlo mock rotating clusters and confirm that our method provides robust\nindications of rotation. We then apply our methodology on a sample of Abell\nclusters with z<~0.1 with member galaxies selected from the Sloan Digital Sky\nSurvey (SDSS) DR10 spectroscopic data base. After excluding a number of\nsubstructured clusters, which could provide erroneous indications of rotation,\nand taking into account the expected fraction of misidentified coherent\nsubstructure velocities for rotation, provided by our Monte-Carlo simulation\nanalysis, we find that ~23% of our clusters are rotating under a set of strict\ncriteria. Loosening the strictness of the criteria, on the expense of\nintroducing spurious rotation indications, we find this fraction increasing to\n~28%. We correlate our rotation indicators with the cluster dynamical state,\nprovided either by their Bautz-Morgan type or by their X-ray isophotal shape\nand find for those clusters showing rotation within 1.5 h -1 70 Mpc that the\nsignificance of their rotation is related to the dynamically younger phases of\ncluster formation but after the initial anisotropic accretion and merging has\nbeen completed. Finally, finding rotational modes in galaxy clusters could lead\nto the necessity of correcting the dynamical cluster mass calculations.\n