Analysis of a New Gravitational Lens FLS 1718+59
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Transcript of Analysis of a New Gravitational Lens FLS 1718+59
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Analysis of a New Gravita-tional Lens FLS 1718+59
Yoon Chan Taak
Feb 14 2013Survey Science Group Workshop 2013
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What is Gravitational Lensing?Deflection of light by body of mass◦Deflection angle greater for GR (factor of
2) vs (r: source-lens distance)
◦e.g. Solar eclipse of May 1919Causes distortion of images
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Images of GL
Abell 1689 cluster
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Images of GLEinstein Ring – SDSS J073728.45+321618.5
Einstein Cross –QSO 2237+030
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Images of GL
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Types of GLStrong GL◦Big distortions, e.g. rings, arcs, multiple img◦Lens is galaxy or cluster
Weak GL◦Shear distortion◦Lens is galaxy or cluster, but further away from
sourceMicrolensing◦Brightness variations◦Lens has stellar masses (e.g. planets)
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Why GL?Requires only mass
Allows detection of dark matterActs as “cosmic telescope”
Lets us see more distant objectsDetermines cosmological parameters◦Deflection depends on redshift-distance
formula◦Time delay related to Hubble constant Constrains geometry of universe
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Gravitational Lensing TheoryPoint-mass lensFinite lens
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Point Mass (Schwarzschild) LensLens (Ray-trace) equation◦11
◦1
θS : lens-source angular distanceα : deflection angle of light rayθ1,2: lens-img angular distancesb : lens-deflection pt angular dist.α0 : Einstein rad. [(4GM/c2) (DLS/DLDS)]1/2
θSD S=( D S
DL)b−𝛼DLS(𝛼=2𝐺𝑀
𝑐2𝑏 )θ1,2=
12 (θS±√4 α 02+θS2 )
αDLS
θSDS
(DS/DL)b
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Finite LensRay-trace eqn is for 2-D plane◦Change scalars to vectors for 3-D
Integrate deflection angle for all infini-tesimal masses◦I
Calculate numerical solution
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gravlens: Software for G-LensingDeveloped by C. Keeton (Rutgers)Useful for various g-lens images◦Able to find best set of lens parameters for
multiple images (lensmodel)Contains 20+ lens models◦Can be superposed, diverse potentials
possible
FLS 1718+59G-lensing image in
Spitzer First Look Survey Field
zlens = 0.08zsource = 0.245◦Closest source so far(?)
RA = 17h 18m 17.6s
Dec = 59d 31m 46s
FLS 1718+59
ProceduresSimulated lensing images with several
sets of input variables◦Mass scale of lens◦X coord. of source◦Ellipticity (angle) of source◦Ellipticity (angle) of lens*
Assumed no external shear
* Obtained from original HST image
Softened Power Law Ellipsoid
s : size of flat core◦s = 0 : singular isothermal ellipsoid◦s ≠ 0 : nonsingular isothermal ellipsoid
Results
Discussion
Many sets of variables may yield similar imagesA more careful approach is necessary for con-
straining errors requires analysis with more sets of variables
Mgal ~ 1010.75Mʘ, σ ~ 150km/s
Possibly an edge-on spiral