Gravitational lensing Olaf Wucknitz wucknitz@jive.nl EVN 2006, Torun, 27 September 2006
Gravitational lensing (+ VLBI) • History: idea and observations • Sources • Lenses • Intervening matter • “Intervening” spacetime • B0218+357 • Summary titlepage introduction summary contents back forward previous next fullscreen 1
The idea α = ∆ d z d l = 1 Z • Isaac Newton (1704) d l ∇ ⊥ Φ c 2 • Henry Cavendish (1784) • Johann Soldner (1801) α = 2 G M • Newtonian (Soldner): c 2 r ↓ α α = 4 G M • relativistic (Einstein 1915): c 2 r titlepage introduction summary contents back forward previous next fullscreen 2
Rings and multiple images titlepage introduction summary contents back forward previous next fullscreen 3
The first lens 0957+561 • two QSOs with 6 ′′ separation • very similar redshifts and spectra • z = 1.4 • chance alignment unlikely • two images of one object? [ Walsh, Carswell & Weymann (1979), Nature 279, 381 ] titlepage introduction summary contents back forward previous next fullscreen 4
First observations of the source • survey scans Jodrell Bank Mark IA • 966 MHz • unspectacular source 0958+56 • combination of two: NGC 3079 & 0957+561 • later identified with optical double [ Walsh (1989), LNP 330 ] titlepage introduction summary contents back forward previous next fullscreen 5
Optical assistance spectra HST POSS [ Porcas et al. (1980), MNRAS 191, 607 ] [ Walsh et al. (1979) ] titlepage introduction summary contents back forward previous next fullscreen 6
Radio interferometric observations (5 GHz) VLA [ Roberts et al. (1979) ] VLA [ Harvanek et al. (1997) ] Cambridge 5 km [ Pooley et al. (1979) ] titlepage introduction summary contents back forward previous next fullscreen 7
Critical curves, caustics z s z s z • lens equation z s = z − α ( z ) z � − 1 µ = d z � 1 − d α • magnification = d z s d z titlepage introduction summary contents back forward previous next fullscreen 8
Geometry in 0957+561 [ Avruch et al. (1997) ] titlepage introduction summary contents back forward previous next fullscreen 9
First VLBI observations (total 5 h at 1.666 GHz: Effelsberg 100 m, Dwingeloo 25 m, Jodrell 76 m) [ Porcas et al. (1979) ] titlepage introduction summary contents back forward previous next fullscreen 10
Resolving the images 5 GHz 1.666 GHz [ Porcas et al. (1981) ] [ Campbell et al. (1995) ] titlepage introduction summary contents back forward previous next fullscreen 11
Fields of study in lensing • sources • spacetime ⋆ cosmology • lenses ⋆ relativity ⋆ new physics? • propagation effects titlepage introduction summary contents back forward previous next fullscreen 12
Lenses as natural telescopes • utilise lensing magnification ⋆ improve resolution • utilise lensing amplification ⋆ improve sensitivity titlepage introduction summary contents back forward previous next fullscreen 13
Cluster A2218 with high redshift galaxy z = 7 magnified µ ≈ 25 [ Kneib et al. (2004) ] titlepage introduction summary contents back forward previous next fullscreen 14
First radio detection of a lensed star forming galaxy [ Garrett et al. (2004) ] titlepage introduction summary contents back forward previous next fullscreen 15
A complicated second case [ Berciano Alba et al. (2006), A&A accepted, astro-ph/0603466 ] titlepage introduction summary contents back forward previous next fullscreen 16
Imaging a critical curve: 2016+112 [ Nair & Garrett (1997) ] 6 cm C2 C13 C12 C11 0 1 2 3 4 [ Koopmans et al. (2002) ] -1500 18 cm -1510 -1520 C2 -1530 MilliARC SEC C13 C12 C11 -1540 -1550 -1560 -1570 -1580 -1590 -400 -450 -500 -550 -600 MilliARC SEC [ see talk by Anupreeta More ] titlepage introduction summary contents back forward previous next fullscreen 17
Mass distributions of lenses • mass model needed for interpretation • image configuration constrains mass models • mass measurements for high redshift lenses titlepage introduction summary contents back forward previous next fullscreen 18
Mass model constraints for 0957+561 [ Garrett et al. (1994) ] titlepage introduction summary contents back forward previous next fullscreen 19
The ten image system B1933+503 Relative Declination (mas) 1a 1 2 3 4 7 5 6 8 [ Nair (1998) ] [ Sykes et al. (1998) ] Relative Right Ascension (mas) titlepage introduction summary contents back forward previous next fullscreen 20
Mass substructure: B0128+437 [ Phillips et al. (2000) ] [ Biggs et al. (2004) ] titlepage introduction summary contents back forward previous next fullscreen 21
Central images? 60 40 20 B1030+074 MilliARC SEC 0.6 A 0 -20 0.4 -40 -60 0.2 60 40 20 0 -20 -40 -60 MilliARC SEC ARC SEC J1632–0033 0.0 -0.2 [ Winn et al. (2003) ] -0.4 G 60 A -0.6 40 B 20 MilliARC SEC 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 0 ARC SEC B C -20 -40 [ Zhang et al., in prep. ] -60 60 40 20 0 -20 -40 -60 MilliARC SEC titlepage introduction summary contents back forward previous next fullscreen 22
Propagation effects etc. • lens produces several identical copies of one source • intrinsic properties not needed for differential ⋆ absorption ⋆ scatter broadening titlepage introduction summary contents back forward previous next fullscreen 23
Cosmology and relativity • tests of relativity and alternative theories • distance measurements • geometry and expansion: H 0 titlepage introduction summary contents back forward previous next fullscreen 24
Tests of relativity α = 2(1+ γ ) G M • deflection angle c 2 r • Newton: γ = 0 • Einstein: γ = 1 • optical: solar eclipse • first test of GR [ Eddington (1919) ] 1+ γ • VLBI: = 0.99992 ± 0.00023 2 [ Shapiro et al. (2004) ] • speed of gravity? [ Kopeikin (2001), [ Will (2006) ] Fomalont & Kopeikin (2003) , etc. ] titlepage introduction summary contents back forward previous next fullscreen 25
Measuring distances with time-delays source • distance ratios known Dds • angles measurable s n e l Ds • geometry can be determined • need one length for scale Dd � use time-delay ! observer Refsdal (1964), MNRAS 128, 307 : ∆t ∝ D d D s ∝ 1 can determine Hubble constant! � D ds H 0 titlepage introduction summary contents back forward previous next fullscreen 26
B0218+357 lensed [ Wucknitz et al. (2004) ] unlensed titlepage introduction summary contents back forward previous next fullscreen 27
Hubble constant from B0218+357 ? • time-delay measured: ∆T = (10.5 ± 0.4)d [ Biggs et al. (1999) , see also Cohen et al. (2000) ] • accurate positions of images A + B • VLBI substructure good for radial mass profile: β ≈ 1.04 [ Biggs et al. (2003) ] • well constrained lens models, but . . . • lens position was not known! � indirect determination with LensClean [ Wucknitz (2004) , Wucknitz et al. (2004) ] titlepage introduction summary contents back forward previous next fullscreen 28
B0218+357: lens position and H 0 H 0 = 78 ± 6 kms − 1 Mpc − 1 [ Wucknitz et al. (2004) ] confirmed by York et al. (2005) titlepage introduction summary contents back forward previous next fullscreen 29
[ Mittal et al. (2006), A&A submitted, astro-ph/0607623 ] Propagation effects in B0218+357 [ Mittal et al. (2006) ] 5 Centroid A Centroid B 3 • flux density ratio A / B 4 1.65 GHz 2 frequency dependent 3 1 15.35 GHz 1.65 GHz 2 Dec. (mas) Dec. (mas) 2.25 GHz 0 1 8.4 GHz 2.25 GHz • source shift plus magni- 4.96 GHz -1 4.96 GHz 15.35 GHz 0 8.4 GHz -2 fication gradient? -1 -3 -2 3 2 1 0 -1 -2 -3 -4 3 2 1 0 -1 -2 -3 -4 R.A. (mas) R.A. (mas) • free-free absorption in the lensing 1400 obs F B galaxy? mod 1200 F A obs F A 1000 Flux density (mJy) ff F A • measure fluxes of extended images 800 600 • take into account magnification 400 gradients 200 0 • fit ff-absorption 1 2 4 6 10 14 Frequency (GHz) titlepage introduction summary contents back forward previous next fullscreen 30
The first real-time EVN image: B0218+357 titlepage introduction summary contents back forward previous next fullscreen 31
B0218+357 at 90 cm 90cm VLBI 2cm VLA + Pie Town titlepage introduction summary contents back forward previous next fullscreen 32
Wide field 90 cm mapping poster by Emil Lenc titlepage introduction summary contents back forward previous next fullscreen 33
Future [ Claeskens et al. (2006) ] • VLBI J1131–1231 ⋆ higher sensitivity ⋆ better uv coverage ⋆ wider fields • EVLA and e -MERLIN: much bet- ter maps of extended structures (e.g. star-forming galaxies) • new lens surveys with extended LOFAR • better analysis methods (LensClean and beyond) • everything else with SKA . . . titlepage introduction summary contents back forward previous next fullscreen 34
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