Tracing extratidal stars of Galactic globular clusters
thesisposted on 28.03.2022, 13:21 authored by Colin Anthony Navin
The Milky Way Galaxy is surrounded by many satellite dwarf galaxies and globular clusters, as well as individual ﬁeld stars, in a vast stellar halo extending further than 100 kpc. There is no doubt that many of the ﬁeld stars in the Galactic bulge and halo formed in these satellites,which are all in the process of being disrupted and losing stars. The processes that produce this loss are thought to be well-understood and are used in simulations that predict the present-day destruction rates. Generally, however, these models are poorly constrained by observations. This thesis looks at the identiﬁcation of individual extratidal stars that have escaped from a number of globular clusters,uses these stars to estimate the actual destruction rates of the clusters,and compares them with the predicted destruction rates from the models. Paper I identiﬁed four extratidal stars of the globular cluster NGC 1851 in an analysis of AAO mega spectra. The destruction rate that corresponds to these stars was calculated in Paper III and was found to be several orders of magnitude greater than predicted by one of the models. Paper II identiﬁed eight extratidal stars around the globular cluster M3 and twelve around M13 in the LAMOST stellar spectroscopic survey catalog. The destruction rates corresponding to these stars were calculated and found to be several orders of magnitude greater than predicted by the models for both clusters. The AEGIS stellar spectroscopic survey catalog was searched for globular cluster extratidal stars in Paper VII. This identiﬁed 20, 6, 1, and 6 extratidal stars around the four globular clusters ω Cen, NGC 6541, M70 and M55, respectively. The destruction rates for these clusters was calculated and, inline with previous results, found to be several orders of magnitude greater than predicted by the models. This work has identiﬁed intriguing discrepancies between predictions of globular cluster destruction rates based on existing models of cluster destruction and observations. If future studies conﬁrm that the discrepancies apply to a signiﬁcant fraction of the globular cluster population of the Milky Way, it points to higher initial masses of globular clusters and a signiﬁcant contribution to the stellar halo ﬁeld star population from globular clusters.