Gravitational Lensing in Clusters of Galaxies<br />Stefanie A. Gallegos<br />   Dr. Michael Gladders<br />
What are gravitational lenses?<br />A gravitational lens is the result of the bending of light from a distant source aroun...
Research Motivation<br />Credit: SDSS<br />Credit: Gemini<br />Lenses are very rare events<br />Can be predicted in detail...
Research Goals<br />Credit: Gemini<br />Credit: Gemini<br />Theory suggests that lensing clusters are a biased (concentrat...
Data Sources<br />Credit: Gemini Observatory<br />Credit: SDSS<br />Sloan Digital Sky Survey (SDSS) and the Gemini Observa...
Findings -- Offsets<br /><ul><li>Positional offset of central galaxy to weighted mean position of the other cluster members
Comparison sample  </li></ul> 31±1.6arcsec<br /><ul><li>Lensing sample </li></ul>24±3.5 arcsec<br /><ul><li>Large Einste...
Conclusions<br />Magnitude differences between central galaxies of lensing sample vs. comparison sample<br />   Lensing c...
Theoretical Expectations forLensing<br /><ul><li>Hypothesis 1: Lenses are seen typically in old, relaxed clusters of extre...
Future Prospects<br />Shapes, concentration and substructure<br />Cluster mass estimates<br />With this data supporting co...
Gravitational Lensing and Stuff
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Gravitational Lensing and Stuff

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My girlfriend made a presentation summarizing her REU experience. It is about gravitational lensing and the work she did trying to distinguish characteristics of lenses caused by galactic clusters. That is the best summary I can give.

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Gravitational Lensing and Stuff

  1. 1. Gravitational Lensing in Clusters of Galaxies<br />Stefanie A. Gallegos<br /> Dr. Michael Gladders<br />
  2. 2. What are gravitational lenses?<br />A gravitational lens is the result of the bending of light from a distant source around a massive object<br />Giant arcs are the result of strong lensing<br />Deviation angle is a function of the mass of the lens (more mass=larger angle) and the observer-lens-source geometry<br />Credit: SDSS<br />Credit: Gemini<br />Credit: Gemini<br />
  3. 3. Research Motivation<br />Credit: SDSS<br />Credit: Gemini<br />Lenses are very rare events<br />Can be predicted in detail from simulations<br />Great way to see background universe (objects that are too faint)<br />Help further define cosmological parameters and understand the nature of dark matter<br />
  4. 4. Research Goals<br />Credit: Gemini<br />Credit: Gemini<br />Theory suggests that lensing clusters are a biased (concentrated, aligned etc.) subset of all clusters. <br />QUESTION: Do we see any evidence in the galaxy population of lensing clusters to suggest that this is true?<br />
  5. 5. Data Sources<br />Credit: Gemini Observatory<br />Credit: SDSS<br />Sloan Digital Sky Survey (SDSS) and the Gemini Observatory for follow-up images<br /><ul><li> The Sloan Digital Sky Survey (SDSS) is a multi-filter imaging and spectroscopic redshift survey using a 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico</li></li></ul><li>Research Approach<br />Do the same thing with a comparison sample, which consists of clusters of the same richness and at the same redshift<br />Measure galaxy properties from both samples<br />Credit: Gemini<br /><ul><li>Begin by looking through a catalog of follow-up images and identifying cluster centers and positions</li></li></ul><li>Findings -- Luminosities<br />Comparison sample  <br /> -1.26 magnitudes brighter than M*<br />Lensing sample <br /> -1.78 <br />Large Einstein Radii <br /> -2.05 <br />Lenses with Einstein radii &lt; 7.5 arcsec <br /> -1.60 <br /> Note: Uncertainty &lt;&lt;0.1<br />
  6. 6. Findings -- Offsets<br /><ul><li>Positional offset of central galaxy to weighted mean position of the other cluster members
  7. 7. Comparison sample  </li></ul> 31±1.6arcsec<br /><ul><li>Lensing sample </li></ul>24±3.5 arcsec<br /><ul><li>Large Einstein Radii </li></ul>21±2.2 arcsec<br /><ul><li>Lenses with Einstein radii < 7.5 arcsec </li></ul>32±2.7<br />In the absence of central galaxy, cluster median is found from moment distributions<br />
  8. 8. Conclusions<br />Magnitude differences between central galaxies of lensing sample vs. comparison sample<br />  Lensing clusters have much more luminous <br /> central galaxies!<br />Positional offsets are smaller in lensing clusters<br />  Lensing clusters are more relaxed<br />
  9. 9. Theoretical Expectations forLensing<br /><ul><li>Hypothesis 1: Lenses are seen typically in old, relaxed clusters of extreme density</li></ul>Hypothesis 2: Lenses are the result of temporarily intense moments of density due to mergers<br /> What we found: Hypothesis 2 appears <br /> unlikely<br /> This is because the central galaxies are so luminous and well-centered that the clusters must be old and dynamically relaxed<br />Credit: Gemini<br />
  10. 10. Future Prospects<br />Shapes, concentration and substructure<br />Cluster mass estimates<br />With this data supporting common characteristics of lensing clusters, it will be easier to identify them in future surveys.<br />Mass to light ratios dark matter halos<br />Credit: KICP Giant Arcs Collaboration Effort<br />

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