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Large Separation Gravitational LensesPowerPoint Presentation

Large Separation Gravitational Lenses

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Presentation Transcript

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

Large Separation ?

- Separation = maximum separation of all pairs of images
- Large = >3 arcseconds
- Strong lensing

Do any exist ?

Castles Database – Nov 2004

Why are they interesting ?

- Cluster scales rather than galaxy
- Mass distributions on cluster scales
- Further input re dark matter

- Contribution to statistics / derived results

What’s been done before ?

None Found

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

CLASS based Search

- Objectives
- Motivation
- Possible outcomes
- Approach
- Current Status

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

Possible Outcomes

- Found
- Something new to investigate in depth !
- Lower bound on lensing probability

- Not Found
- Upper bound on lensing probability

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

Current Status

- Object separation Complete
- Compact, flat spectrum ? Ongoing
- Lens system ? Outstanding
- Statistics Outstanding

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

Compact, Flat Spectrum Check

- 15GHz VLA observations (A configuration) taken in 2003
- Eliminate
- Extended objects
- Non-flat spectrum objects

- 3 point spectral index

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

Lens System / Statistics

- MERLIN / VLBA observations
- Redshifts etc
- Chance co-incidences
- Upper / lower bounds
- Comparison with previous surveys

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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