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This Week at Physics

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Events on Thursday, March 30th, 2017

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Micro-X: A Sounding Rocket Dark Matter Search
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Antonia Hubbard, Northwestern
Abstract: The Micro-X sounding rocket uses a Transition Edge Sensor (TES) array to make X-ray observations. The improved energy resolution of TESs compared to traditional space-based X-ray detectors brings new precision to both supernova observations and the X-ray search for sterile neutrino dark matter. Current X-ray observations disagree over the potential presence of a 3.5 keV X-ray line consistent with a sterile neutrino interaction, and Micro-X is in a unique position to establish or refute the presence of this line. We present the construction status of the instrument and expectations for flight observations, with special emphasis given to the prospects of sterile neutrino studies.
Host: Kim Palladino
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Astronomy Colloquium
"Towards understanding the inefficiency of star formation in galaxies"
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and Cookies 3:30 pm, Talk begins 3:45 pm
Speaker: Andrey Kravtsov, The University of Chicago
Abstract: One of the long-standing puzzles of galaxy formation is the global inefficiency with which galaxies convert baryonic matter available to them into stars. This inefficiency is manifested in 1) the fact that ratio of baryon mass observed within galaxies to the total inferred mass of their host halos is much smaller than the universal baryon fraction and 2) the fact that galaxies convert their observed gas into stars on ~2-10 Gyr time scale (gas depletion time), which is much longer than any dynamical time scale within galaxies.

I will review recent progress in galaxy formation simulations due to improvements in treatment of stellar feedback and star formation, which sheds light into the 1st aspect of inefficiency. I will present a new model, in which local star formation efficiency is modelled "on the fly" using a turbulence-based subgrid model based on results of high-resolution simulations of molecular clouds. The model predicts a wide variation of star formation efficiency per free fall time at odds with the usual assumption of constant efficiency. At the same time, our model predicts distribution of star formation rates in broad agreement with observations of both local and resolved extragalactic GMCs. I will show that with realistic implementation of stellar feedback this modelling can reproduce the basic properties of star formation and the Kennicutt-Schmidt relation in galaxies, such as the Milky Way. Finally, using insights from such simulations I will present a simple model explaining why star formation in galaxies is inefficient and depletion times are long.
Host: Astronomy Department and Physics
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