Colloquia Schedule

Jo Bovy (University of Toronto)

Dec. 3, 2015, 3:45 p.m. — 1033 LGRT
Title: What drives the evolution of the Milky Way's disk?

Abstract: Observations of the structure and dynamics of different stellar populations in the Milky Way's disk provide a unique perspective on Galactic growth, evolution, and dynamics over cosmic time. I will review our current knowledge of the chemo-orbital structure of the disk and the major outstanding questions. I will then discuss new measurements of the kinematics and chemistry of stars over a large part of the Galactic disk from the APOGEE survey and the new insights these measurements provide about the formation and evolution of the Milky Way's disk.

Juna Kollmeier (Carnegie Observatory)

Dec. 10, 2015, 3:45 p.m. — 1033 LGRT
Title: Cosmological Calorimetry:The nature of the intergalactic mediu

Abstract: The Lyman alpha forest remains one of the most robust predictions of cosmological hydrodynamic simulations. Lyman alpha absorption lines have been used for decades to trace cosmic structures that -- only recently, with the exquisite sensitivity achievable with modern instruments -- are beginning to be detected in emission as well. I will discuss the predicted morphology of the Lyman alpha forest and the possibility of revealing this structure with Lyman alpha imaging surveys. The emission signal is dependent on the ionizing background radiation which, at high redshift, is well-understood and constrained. However, I will show that at low redshift there is a huge mismatch between our expectations and observations. I describe a factor of 5 discrepancy between the value of the photoionization rate required to match cosmological models of the z = 0.1 intergalactic medium to observations of the Lyman alpha forest and the value predicted by state-of-the-art models that account for the emissivity of stars and quasars over time. Examining potential resolutions to this problem, I will demonstrate that solving it requires, at minimum, a substantial revision of our thinking about the low redshift universe.