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Cosmology and Clusters: The Coma Cluster

Cosmology and Clusters: The Coma Cluster. Ken Zhao and Arthur Su Chandra Astrophysics Institute 12/16/2006. Outline. Introduction Cosmology and Clusters Questions What is the MASS of clusters? In particular, the Coma Cluster Methods/Data How are we going to collect data Formulas used

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Cosmology and Clusters: The Coma Cluster

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  1. Cosmology and Clusters:The Coma Cluster Ken Zhao and Arthur Su Chandra Astrophysics Institute 12/16/2006

  2. Outline • Introduction • Cosmology and Clusters • Questions • What is the MASS of clusters? • In particular, the Coma Cluster • Methods/Data • How are we going to collect data • Formulas used • Pictures on ds9 • Discussion • Analysis of measurements • Do we have a better idea about clusters? • Error Analysis

  3. Introduction • Clusters are made of galaxies • Clusters are largest gravitational bound systems - Can help us get a big picture when answering cosmological questions • What is our universe made of? • How did our universe form? • What lies in its future?

  4. Questions The Coma Cluster • Home to about 1000 galaxies • What is the size of galaxy clusters? • More important, the MASS?

  5. Methods • X-Ray Imaging from Ds9 shows galaxy clusters made of hot X-Ray emitting gas. • X-Ray image of Coma • Gas spread throughout galaxy • NEED TO FIND MASS OF THIS GAS • Assuming that all the gas is Hydrogen, used luminosity X-Ray gas to find the mass of gas in cluster • Also found Visible Galaxy mass • Both account for what “looks like” the total mass • Used Virial theorem for another mass estimate of the TOTAL MASS (Counts or # of Photons detected)

  6. As the galaxies move away from us, their recessional velocity (relative to our galaxy) is proportional to their distance from our galaxy. This proportion is Hubble’s constant.

  7. Size Angular Size = Diameter Distance • Half-light circle radius – Circle that encompasses half of the total light detected from the cluster (more accurate assumption of total light due to background radiation) • Angular Size = 500 Arc Seconds • Hubble’s Law of universe expansion – Coma’s recessional velocity (determined by redshift) is proportional to distance. 500 Arc seconds (Counts or # of Photons detected)

  8. Mass Estimate Parameters used to determine Mass d=distance V=volume of emitting region n=electron number density Cluster MASS = 3.5 x 1013 solar masses Note: 1 solar mass = 2 × 1030 kilograms

  9. The Virial Theorem: Another Mass Estimate • Using the laws of gravitational motion: V2 V1 FGravity FGravity M2 M1

  10. Estimated Masses of Objects in Coma This means 96% of our estimated galaxy cluster mass is dark matter

  11. Conclusions • Found Mass estimates using different techniques • Discrepancy in results compared to values of accepted dark matter composition due to: • Accuracy of Bremstrahlung fit • Volume estimate • Pressure unaccounted • Electron density estimation

  12. Further Investigation • Morphology and shape of galaxy cluster • Properties of galaxy clusters • How relates to dark matter and composition The Bullet Cluster(chandra.harvard.edu/press/06_releases/press_082106.html) The Perseus Cluster(chandra.harvard.edu/photo/2003/perseus/more.html) • Dark Matter Issues • Gravitational Lensing & Black hole “bubbles”

  13. Credits • Much thanks to the CAI staff • Mark and Andy for helping us put this project together • Our friendly classmates • The viewers

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