Alis Deason (IoA, Cambridge University)

Title: "Smooth, squashed and rotating. Not the stellar halo we used to know"

Abstract:

The phase-space structure of the stellar halo is intimately linked to the formation history of the Galaxy. In this talk I will discuss the rotation properties and spatial structure of the stellar halo as traced by Blue Horizontal Branch (BHB) stars. Using SDSS spectroscopic data I find an apparent dichotomy between relatively metal-rich and metal-poor stars. I argue that a retrograde signal in the metal-poor stars is due to an underestimate of the Local Standard or Rest while the kinematic signature of the metal-rich stars is linked to a (massive) accretion event. In addition, I introduce a new method to discern BHB stars from Blue Straggler stars using a colour dependent membership probability, thus circumventing the need for spectroscopic data. This new method is applied to a sample of A-type stars selected from the latest SDSS DR8 photometric catalog. I find that the (inner) stellar halo is 'squashed, broken but smooth' and discuss the implications of this result. Finally, I compare these observational results to state-of-the-art cosmological simulations.

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Ryan Cooke (IoA, Cambridge University)

Title: "Finding the First Metals"

Abstract:

The first metals in our Universe were created and distributed by stars we still know very little about. Before these metals were incorporated in the second generation of stars, they were (presumably) stored within a large reservoir of gas. In this talk, I will present the results from my ongoing survey to search for this `missing-link' by targeting near-pristine damped Lyman-alpha systems (DLAs) at z~3. I report the discovery of a few systems that exhibit an abundance pattern inline with model calculations of metal-free nucleosynthesis, including notable enhancements in their C/Fe ratio; such an abundance pattern is akin to the carbon-enhanced metal-poor stars seen in the halo of our Galaxy. For the full sample of DLAs in this survey, I reinvestigate the trends of [C/O] and [O/Fe] with metallicity, and compare my findings to the recent measures of the abundances of C, O, and Fe from Galactic halo stars. I comment on the new insight this has afforded on the nature of the much-debated trends of these ratios when [Fe/H] < -2.0.