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Measuring Galaxy Cluster Masses Using Gravitational Lensing
Blake NicholsonAstronomy 320
Overview
I. IntroductionII. Galaxy ClustersIII. Methods to Measure MassIV. History: Soldner, Einstein, ZwickyV. How Gravitational Lensing WorksVI. References
Galaxy Clusters
• Biggest gravitationally-collapsed objects• Contain between 50 and 1000 galaxies• Typical diameter of 2-10 Mpc• Typical masses of 1014 to 1015
• Velocity distributions between 800-1000 km/s
Methods to Measure Mass
Stellar Light
Velocity Dispersion
X-Ray emission from Bresstrahlung mechanism
Sunyaev-Zel’dovich effect
Weak gravitational Lensing
History1804 – Johann Soldner suggests light interacting gravitationally with massive object.1911 – Albert Einstein does work on light beam deflection due to gravitational interactions.1914 – Einstein’s predictions are wrong but are never measured due to the start of WWI.1919 – Arthur Eddington confirms Einstein’s findings on General Relativity1924 – Chwolson observes a ‘double star’1936 – Einstein publishes paper on gravitational lensings and ‘Einstein-Rings’1937 – Fritz Zwicky suggests using lensing to study galaxies.1960’s – Quasar discovery strengthens gravitational lensing as a legitimate discovery method.
How Gravitational Lensing Works
Bending of light rays by a very large mass/energy distribution
• Source: Where the light beams comes from
• Lens: Dense region that deflects the light beams
• Observer: Who sees lensing• Image: The object that the
observer sees
Types of Gravitational Lensing
Strong Lensing: Einstein-Ring, Einstein Crosses, Multiple Images
Weak Lensing: Galaxy Clusters, Useful for measuring mass, Large-Scale Universe
Microlensing: Source appears brighter, extrasolar planets
Mass Measurement Using Gravitational Lensing
Weak gravitational lensing gives us statistical information about galaxy clusters that we can use to determine mass-related properties.
Referenceshttp://www.spacetelescope.org/images/heic0814f/http://www.spacetelescope.org/static/archives/images/screen/heic0113d.jpghttp://apod.nasa.gov/apod/image/0203/simcluster_hubbleACS_big.jpghttp://astro.berkeley.edu/~jcohn/lens.htmlhttp://epsc.wustl.edu/courses/epsc210a/transparencies/bernard/gravitational_lens001.jpghttp://www.astro.gla.ac.uk/users/martin/outreach/lens_a2218.jpg
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