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This Week at Physics

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Events on Thursday, October 9th, 2014

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Clusters of galaxies as tools for cosmology
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Mel Ulmer, Northwestern
Abstract: Clusters of galaxies are the largest gravitationally bound systems in the Universe. Due to their large masses (~1E15 suns), they distort the background galaxies images. The distortion (lensing) depends among other things on the angular distance to the galaxies versus redshift. The effect can be used to set limits to the Dark Energy equation of state w and even dw/dz. The exciting aspect is that the effect is purely geometrical. As such, it requires essentially no input physics to interpret the results. The approach is so obviously interesting that the fact it has not yet led to a definitive result indicates it must be difficult! We discuss our own group’s efforts and goals (http://cencosw.oamp.fr/DAFT/) and why the concept is difficult to carry out in practice. We also present one “fun” result based on using lensing and other techniques to measure the detailed mass distribution in a cluster. The mass distribution versus radius we find is such that the ratio of baryons to Dark Matter (DM) is not constant on large (1,000s of light years) scales. This result raises the specter that perhaps in our location of the Milky Galaxy the ratio of DM/baryons also deviates from the comic average.
Host: Dan McCammon
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Astronomy Colloquium
"Puzzles in the Structure of Disk Galaxies"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Stephane Courteau, Queen's University
Abstract: Galaxies can be described in terms of their structure, dynamics<br>
and stellar populations. Some very robust correlations between<br>
various galaxy structural properties, such as total luminosity,<br>
maximum circular velocity, and size show rather small scatter,<br>
hinting at well-regulated galaxy formation processes. A major<br>
challenge to understanding these scaling relations, and ultimately<br>
galaxy formation and evolution, is the elusive interplay between<br>
visible and dark matter. I will discuss the latest derivations<br>
of galaxy scaling relations and their link with modern<br>
cosmological models.
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Graduate Introductory Seminar
Atomic, Molecular, and Optical Physics
Time: 4:30 pm
Place: 5280 Chamberlin Hall
Speaker: Lawler, Lin, Saffman, Walker, Yavuz
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