Cosmology and Clusters: The Coma Cluster

1
Cosmology and ClustersThe Coma Cluster

• Ken Zhao and Arthur Su
• Newton North High School
• Chandra Astrophysics Institute
• May 12, 2007

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

• 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 Hubbles 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
• Hubbles Law of universe expansion Comas
  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
• ddistance
• Vvolume of emitting region
• nelectron 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_r
eleases/press_082106.html)
The Perseus Cluster (chandra.harvard.edu/photo/200
3/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