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