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Session 59 - Milky Way, Center & Halo.
Oral session, Tuesday, January 16
Salon del Rey Central, Hilton

[59.04] Fossil Signatures of Ancient Accretion Events in the Halo

K. V. Johnston (UCSC)

The extent of the role that minor mergers have played in the formation and evolution of the Milky Way is still an open question, about which there is much current debate. We use numerical simulations to explore the behaviour of tidal debris, with the aim of developing a method that can identify and quantify distinctive signatures of accretion in a survey of the distribution of halo stars. For simulations run assuming a Milky Way having a spherical halo, we find that debris from minor mergers can remain aligned along a single great circle throughout the lifetime of the Galaxy. We exploit this characterisitic behaviour to develope the method of Great Circle Cell Counts (GC3), which we test by applying it to artificially constructed halo distributions. Our results suggest that if \ge 1% of the stars in a halo survey are accreted from the disruption of a single subsystem smaller than the Large Magellanic Cloud, GC3 can recover the great circle associated with this debris. The dispersion in GC3 can also be used to detect the presence of structure characteristic of accretion in distributions containing a much smaller percentage of material accreted from any single satellite.

Program listing for Tuesday