RSAA Colloquia / Seminars / Feast-of-Facts: Thursday, 15 December 2016, 11:00-12:00; Duffield Lecture Theatre

Pete Kuzma

"Extended Structures in Globular Clusters - End of Thesis Colloquium"

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 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 from the stars outside the 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 structure 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 to the formation of the globular clusters themselves, or the shape and formation of the Milky Way’s halo. This thesis focuses on exploring extended features of Milky Way globular clusters. Firstly, 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 determined members in the tidal stream through radial velocities, line strengths and photometric information. Secondly, we performed a wide field photometric survey of southern Galactic globular clusters with the complementary photometric cameras MegaCam and the DECam. 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 brightness stellar envelopes embedding NGC 1261, NGC 1851 and M2, with a tentative detection of an envelope embedding NGC 5824. We will 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.