Analysis of a New Gravitational Lens FLS Yoon Chan Taak Feb Survey Science Group Workshop

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 1919 Causes distortion of images 2

Images of GL 3 Abell 1689 cluster

Images of GL 4 Einstein Ring – SDSS J Einstein Cross – QSO

Images of GL 5

Types of GL Strong 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 source Microlensing ◦ Brightness variations ◦ Lens has stellar masses (e.g. planets) 6

Why GL? Requires only mass  Allows detection of dark matter Acts as “cosmic telescope”  Lets us see more distant objects Determines cosmological parameters ◦ Deflection depends on redshift-distance formula ◦ Time delay related to Hubble constant  Constrains geometry of universe 7

Gravitational Lensing Theory Point-mass lens Finite lens 8

Point Mass (Schwarzschild) Lens Lens (Ray-trace) equation ◦ 11 ◦ 1 9 θ S : lens-source angular distance α : deflection angle of light ray θ 1,2 : lens-img angular distances b : lens-deflection pt angular dist. α 0 : Einstein rad. [(4GM/c 2 ) (D LS /D L D S )] 1/2 α D LS θSDSθSDS (D S /D L )b

Finite Lens Ray-trace eqn is for 2-D plane ◦ Change scalars to vectors for 3-D Integrate deflection angle for all infinitesimal masses ◦ I Calculate numerical solution 10

gravlens: Software for G-Lensing Developed 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 11

FLS G-lensing image in Spitzer First Look Survey Field z lens = 0.08 z source = ◦ Closest source so far(?) RA = 17 h 18 m 17.6 s Dec = 59 d 31 m 46 s

FLS

Procedures Simulated 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

Results

Discussion Many sets of variables may yield similar images A more careful approach is necessary for constraining errors  requires analysis with more sets of variables  M gal ~ M ʘ, σ ~ 150km/s  Possibly an edge-on spiral