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Events on Thursday, May 14th, 2015

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Anomalous reactor antineutrino flux and spectrum measurements
Time: 2:30 pm
Place: 5310 Chamberlin Hall
Speaker: Bryce Littlejohn, Illinois Institute of Technology
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Astronomy Colloquium
A "New" Galaxy Formation Mechanism from Joint Galactic and High Redshift Constraints
Time: 3:45 pm
Place: 4421 Sterling Hall
Speaker: Jonathan Bird, Vanderbilt University

Very different data sets guide galaxy formation theory across cosmic history: from the global properties of >10^7 galaxies at high redshift (z>0.5) to the kinematics and chemistry of >10^6 stars here in the Milky Way. Traditional observational and computational limitations have dictated independent study of these two regimes. I will discuss how this picture is changing rapidly and how viewing the MW as important boundary condition on galaxy evolution puts unprecedented demands on galaxy formation theory. In particular, I will discuss a novel disk formation mechanism and its signature in current observations of the Milky Way and the resolved kinematics of high redshift galaxies.

Modern, high-resolution, cosmological galaxy formation simulations reveal that disks can grow ‘upside-down’ in the sense that progressively younger stellar populations are born with increasingly smaller vertical velocity dispersion, tracing the kinematics of the collapsing gas disk from which they form. We find that the upside-down model matches the most stringent observational constraints here in the MW, including the steep stellar age-velocity relationship measured in the solar neighborhood. I will argue that traditional interpretations of disk evolution from MW data contradict evidence from Integral Field Unit observations of high-redshift disk galaxies and must be revised. Our findings suggest that the ‘upside-down’ model is currently the only self-consistent formation mechanism able to match kinematic constraints from z~2 to z~0. I will conclude with preliminary, yet tantalizing, evidence connecting the star formation history of simulated galaxies with their detailed morphology.

Host: Professor Matt Bershady
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