Kinematical and Chemical Probes of Milky Way Satellite Accretion

Carlin, Jeffrey Lee, Department of Astronomy, University of Virginia
Majewski, Steven, Department of Astronomy, University of Virginia

The currently-favored Cold Dark Matter cosmological model predicts that structure in the Universe builds up from the hierarchical agglomeration of subunits. These models, while successful on large scales, require further refinement to properly reproduce structures on the scale of our Milky Way galaxy and its system of luminous subhalos (the satellite dwarf galaxies). In this thesis we explore the hierarchical accretion paradigm at galaxy scales from the study of intact, but tidally disturbed satellite dwarf galaxies to "end-stage", remnant stellar streams produced by the complete dissolution of late-infalling, luminous subhalos. We present work that integrates observed proper motions, radial velocities, and spectroscopically-derived metal abundances to probe various systems being accreted into the Milky Way halo. Nearly all of the projects presented make use of a software pipeline (EZ SPAM) we developed to measure stellar metallicities to ∼ 0.3 dex accuracy from low-resolution spectra. The kinematical studies include the first spectroscopic observations of the Boötes III stellar overdensity, a peculiar object that we determine likely to be a dwarf galaxy in the final stages of tidal disruption. In another study, we find that the 3-D space motions for Anticenter Stream debris in our pencil-beam survey are inclined by 30 ◦ to the path of the stream on the sky as traced by stellar overdensities, and suggest that we are sampling a kinematically cold subcomponent (e.g., a shredded star cluster) of an infalling galactic progenitor. Our extensive study spanning ∼ 60 ◦ of the Sagittarius trailing tidal tail constrains the 3-D space velocity of Sgr debris to ∼ 50 km s −1 , but, more significantly, constrains the rotational velocity of the Milky Way at the solar circle to be ≈ 270 ± 30 km s −1 . The latter reassessment of this fundamental constant implies a greater Milky Way mass, and therefore greater tidal forces, than traditionally adopted in Galactic accreiii tion models. Finally, we present the initial phases of an effort to measure the proper motion of the Carina dwarf galaxy, with the hope of reconciling the discrepancy between the predicted orbit based on Carina's observed tidal extension versus that from previous measurements of its space motion.

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PHD (Doctor of Philosophy)
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