On the dark matter formation scenario of NGC 4147

Abstract

We report results on the radial velocity dispersion profile built out to the outskirts of NGC 4147, aMilky Way globular cluster with detected strong tidal tails. The cluster was chosen to probe, from an observationalpoint of view, recent simulations that suggest that rising velocity dispersion profiles at large distance from theclusters’ centers would be seen in globular clusters without tidal tails. From GEMINI@GMOS spectra, centeredin the infrared CaII triplet region, of selected stars located along the onset of NGC 4147’s tidal tails, we measuredtheir radial velocities and overall metallicities. The derived metallicities were used to ultimately assessing on thehighly-ranked cluster candidates of 9 stars, located between ∼ 7 and 33 pc from the cluster’s center, suitable fortesting the aforementioned simulations. We complemented the present radial velocities with others available inthe literature for cluster’s members, and built a cluster velocity dispersion profile which suggests a mostly flat orslightly rising profile at large distances from the cluster’s center. This outcome confirms that kinematically hotoutermost cluster’s stars are seen in NGC 4147, which disproves the recent model predictions. Nevertheless, themean velocity dispersion of the outermost cluster’s stars agrees with NGC 4147 being formed in a 10 8 -10 9 Mdwarf galaxy with a cored dark matter profile that later was accreted on to the Milky Way.