The Formation of the Magellanic Stream

Gurtina Besla

June 07, 2010

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Abstract: One of the most surprising results to come out of HST in recent years is that the Large and Small Magellanic Clouds are moving faster than previously believed (Kallivayalil et al 2006a,b) and may be on their first passage about the Milky Way (MW) (Besla et al 2007). Such a drastically different orbital history overturns a paradigm that has existed for decades and consequently demands a revision of our understanding of the interaction history of the Clouds and the accretion history of the MW and Local Group. In particular, the Magellanic Stream (MS), a coherent stream of HI filaments that trails the Clouds 100 degrees across the sky, can no longer be considered a product of MW tides or ram pressure acting on the Clouds. We propose an alternative mechanism for the formation of the MS in which material is removed by LMC tides acting on the SMC before the system is accreted by the MW. Here the orbit of the Clouds is not assumed to be a free parameter and is instead determined by the new HST proper motions. Furthermore, both Clouds are modeled as live systems instead of assuming that one is a fixed potential (or absent) as all previous models have done. The proposed scenario clearly demonstrates that it is possible to explain the properties and origin of the MS under the assumption that the Clouds have not been long term satellites of the MW. In addition, this study provides new insight into the hierarchical build up of galaxies, late accretion events, gas stripping mechanisms from satellites and dwarf-dwarf galaxy interactions.