11/13/14: SO/NOAO Joint Colloquium Series: Alis Deason, UCO/Lick

Alis Deason, UCO/Lick

Rethinking Galactic Architecture: Clues from Satellites and Destroyed Dwarfs

The cannibalistic nature of the Milky Way galaxy leads to the continuous capture and destruction of lower-mass, dwarf galaxies. The remains of destroyed dwarfs are splayed out in a diffuse stellar halo, while the "survivors" comprise the satellite population that orbits the Milky Way. These halo populations provide a unique opportunity to decipher the accretion history of the Milky Way with a level of detail that cannot be achieved in any other galaxy. I will discuss current and future projects aiming to decipher the nature of the halo's building blocks. At present, we have very little understanding of what these building blocks actually are; is the halo built up from many smaller mass dwarfs, or from one massive dwarf? I will discuss recent work comparing the results from halo star counts in SDSS with numerical simulations. This work suggests that the halo may be dominated by one massive accretion event and/or experienced a very short accretion epoch. An ongoing project utilizing multi-epoch HST photometry and Keck spectroscopy will help provide a quantitative analysis of the mass spectrum of dwarfs that built up the halo, and potentially disentangle these two scenarios. I will also discuss the "satellites of satellites" population in the Milky Way. I will present recent results suggesting that the PAndAS stream, the Segue 2 satellite (the "least luminous" galaxy) and the large TriAnd overdensity are all associated, and may be a fossil record of group-infall onto the Milky Way halo. We generally ignore the possibility that the lowest luminosity dwarfs in the Milky Way may be satellites of other satellites, and thus, we may be grossly misinterpreting their properties. Finally, I will outline the future prospects to identify associations of substructures in the Milky Way halo.