Daniel Zucker

Crossing the Streams: The S5 Survey’s View of the Galactic Halo

Large galaxies like the Milky Way form hierarchically, with smaller systems merging and accreting to form increasingly massive structures. Evidence for this process can be found all around us: dynamically, as stellar overdensities in phase space in the nearby Galaxy; chemically, in the form of abundance patterns distinct from those of stars which formed in situ within the Milky Way; and spatially, in the form of stellar streams and tidally disrupting satellites in the Galactic halo. This last domain – a halo dramatically criss-crossed by an abundance of stellar substructures – is the focus of the Southern Stellar Stream Spectroscopic Survey (S5), an Australian-led international collaboration using the AAT + AAOmega to study the streams and disrupting satellites surrounding the Milky Way. Its science goals include characterising the Galaxy’s accretion history and constraining the distribution of matter interior to stream orbits. Among the science results I will discuss are evidence for the influence of the LMC on halo stream orbits (and the Milky Way itself), the orbital properties of the stellar streams observed, and comparisons with simulation predictions for detectable streams and satellites. I will conclude with a look at the prospects of new facilities such as LSST and 4MOST for driving major advances in our understanding of how galaxies like the Milky Way grow.