BEGIN:VCALENDAR VERSION:2.0 CALSCALE:GREGORIAN PRODID:UW-Madison-Physics-Events BEGIN:VEVENT SEQUENCE:0 UID:UW-Physics-Event-3479 DTSTART:20141009T193000Z DTEND:20141009T203000Z DTSTAMP:20260419T161444Z LAST-MODIFIED:20140929T150338Z LOCATION:5280 Chamberlin Hall SUMMARY:Clusters of galaxies as tools for cosmology\, NPAC (Nuclear/Pa rticle/Astro/Cosmo) Forum\, Mel Ulmer\, Northwestern DESCRIPTION:Clusters of galaxies are the largest gravitationally bound systems in the Universe. Due to their large masses (~1E15 suns)\, t hey distort the background galaxies images. The distortion (lensing) d epends among other things on the angular distance to the galaxies vers us 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 e ffect is purely geometrical. As such\, it requires essentially no inp ut physics to interpret the results. The approach is so obviously int eresting that the fact it has not yet led to a definitive result indic ates it must be difficult! We discuss our own group’s efforts and g oals (http://cencosw.oamp.fr/DA FT/) and why the concept is difficult to carry out in practice. We also present one “fun” result based on using lensing and other te chniques to measure the detailed mass distribution in a cluster. The mass distribution versus radius we find is such that the ratio of bary ons to Dark Matter (DM) is not constant on large (1\,000s of light yea rs) scales. This result raises the specter that perhaps in our locatio n of the Milky Galaxy the ratio of DM/baryons also deviates from the c omic average. URL:https://www.physics.wisc.edu/events/?id=3479 END:VEVENT END:VCALENDAR