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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

Large SeparationGravitational Lenses

Dick Long

Jodrell Bank ObservatoryApril, 2005


Structure for today
Structure for Today

  • Large Separation Overview

  • CLASS based search

    • currently in progress


Large separation
Large Separation

  • What is meant by large separation

  • Why they are interesting

  • What has happened so far

  • etc


Large separation1
Large Separation ?

  • Separation = maximum separation of all pairs of images

  • Large = >3 arcseconds

  • Strong lensing


1013 Msun

Cluster

Lens Environment

>10”

1011 Msun

Image Separation

Galaxy

<3”


Do any exist
Do any exist ?

Castles Database – Nov 2004



Why are they interesting
Why are they interesting ?

  • Cluster scales rather than galaxy

  • Mass distributions on cluster scales

    • Further input re dark matter

  • Contribution to statistics / derived results



How many are there
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
CLASS based Search

  • Objectives

  • Motivation

  • Possible outcomes

  • Approach

  • Current Status


Objectives motivation
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
Possible Outcomes

  • Found

    • Something new to investigate in depth !

    • Lower bound on lensing probability

  • Not Found

    • Upper bound on lensing probability


Approach
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
Current Status

  • Object separation Complete

  • Compact, flat spectrum ? Ongoing

  • Lens system ? Outstanding

  • Statistics Outstanding


Object separation
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
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
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
Lens System / Statistics

  • MERLIN / VLBA observations

  • Redshifts etc

  • Chance co-incidences

  • Upper / lower bounds

  • Comparison with previous surveys


In conclusion
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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