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Large Separation Gravitational Lenses

Large Separation Gravitational Lenses. Dick Long Jodrell Bank Observatory April, 2005. Structure for Today. Large Separation Overview CLASS based search currently in progress. Large Separation. What is meant by large separation Why they are interesting What has happened so far etc.

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Large Separation Gravitational Lenses

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  1. Large SeparationGravitational Lenses Dick Long Jodrell Bank ObservatoryApril, 2005

  2. Structure for Today • Large Separation Overview • CLASS based search • currently in progress

  3. Large Separation • What is meant by large separation • Why they are interesting • What has happened so far • etc

  4. Large Separation ? • Separation = maximum separation of all pairs of images • Large = >3 arcseconds • Strong lensing

  5. 1013 Msun Cluster Lens Environment >10” 1011 Msun Image Separation Galaxy <3”

  6. Do any exist ? Castles Database – Nov 2004

  7. > 3 arcseconds separation

  8. Why are they interesting ? • Cluster scales rather than galaxy • Mass distributions on cluster scales • Further input re dark matter • Contribution to statistics / derived results

  9. What’s been done before ? None Found

  10. How many are there ? • Phillips et al 2001 >6” <3 x 10-4 • Ofek et al 2001/2 >5” <3.7 x 10-4 • Li & Ostriker 2003 >5” 7x10-7 to 10-3 • 104 to 105 sample size required to find one

  11. CLASS based Search • Objectives • Motivation • Possible outcomes • Approach • Current Status

  12. Objectives & Motivation • Search for large separation lenses in the CLASS survey with separation 15 – 60” • Motivation • Lensing probability • SDSS => 14.62” image separation • CLASS survey size

  13. Possible Outcomes • Found • Something new to investigate in depth ! • Lower bound on lensing probability • Not Found • Upper bound on lensing probability

  14. Approach • Using CLASS 8.4GHz catalogue + FIRST & NVSS 1.4GHz catalogues • Object separation • Candidate list of potential (paired) images • Compactness, flat spectrum check • Lens system determination • Statistics

  15. Current Status • Object separation Complete • Compact, flat spectrum ? Ongoing • Lens system ? Outstanding • Statistics Outstanding

  16. Object Separation • Computer based search of CLASS + FIRST / NVSS • Primary object at same position in both catalogues • Look for secondary objects (at same position) within 120” • Completed in 2003 • Initial candidate list of 420 sources • 210 pairs

  17. Compact, Flat Spectrum Check • 15GHz VLA observations (A configuration) taken in 2003 • Eliminate • Extended objects • Non-flat spectrum objects • 3 point spectral index

  18. 15GHz Observations • VLA (A config) taken in 2003 • 3 datasets • AIPS used for analysis • Issues = IF, correlator, antenna, phase • 5 image pairs => to further investigation

  19. Lens System / Statistics • MERLIN / VLBA observations • Redshifts etc • Chance co-incidences • Upper / lower bounds • Comparison with previous surveys

  20. In Conclusion • Large separation in general • Specific search based on CLASS • Likely outcome ? Watch this space But don’t hold your breath !!

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