Extended Structures in Globular Clusters

Abstract

Our view and understanding of globular clusters in the Milky Way have undergone massive changes over the past few decades. No longer are globular clusters seen as the perfect example of simple stellar populations, as almost all Galactic globular clusters are now known to contain star-to-star light element abundance variations, and a small subset contain heavy element abundance ranges. However, not only can a lot be learnt from studying the stars within globular clusters, but also from the stars outside globular clusters, beyond the tidal radius. Whether the structure is in the form of tidal tails such as the iconic tails of Palomar 5, or part of a much larger scale stellar feature such as the stellar stream belonging to the disrupting dwarf galaxy Sagittarius or the wealth of streams in the halo of M31, the environs of Galactic globular clusters can be used as insights into the formation of the globular clusters themselves and to the shape and formation of the Milky Way’s halo. This thesis focuses on exploring extended features of Milky Way globular clusters. First, by increasing the spatial coverage and kinematics of the tidal tails of Palomar 5 through low to intermediate resolution spectroscopy from the 2df AAOmega spectrograph on the Anglo-Australian Telescope. We identify 39 new and recover 8 previously deter- mined members in the tidal stream through radial velocities, line strengths and photomet- ric information. Second, we performed a wide field photometric survey of southern Galactic globular clusters with the complementary imagers MegaCam on the 6.5m Clay Telescope, and the DECam, on the 4m Blanco Telescope. We present the results for the four clusters analysed during the PhD candidature: NGC 1261, NGC 1851, NGC 5824 and NGC 7089 (M2). We find diffuse large low surface density envelopes containing NGC 1261, NGC 1851 and M2, with a tentative detection of an envelope surrounding NGC 5824. We discuss the origins of the envelopes and how the features we have uncovered, along with Palomar 5’s tidal tails, may influence our understanding of the Galactic halo and globular cluster formation.