Gravitational lensing Olaf Wucknitz wucknitz@jive.nl EVN 2006, - - PowerPoint PPT Presentation

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

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The idea

• Isaac Newton (1704)

α = ∆dz dl = 1 c2

Z

dl ∇

⊥Φ

• Henry Cavendish (1784)
• Johann Soldner (1801)
• Newtonian (Soldner):

α = 2 G c2 M r ↓

• relativistic (Einstein 1915):

α = 4 G c2 M r

α

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Rings and multiple images

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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 ]

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First observations of the source

[ Walsh (1989), LNP 330 ]

• survey

scans Jodrell Bank Mark IA

• 966 MHz
• unspectacular

source 0958+56

• combination
• f

two: NGC 3079 & 0957+561

• later

identified with

• ptical double

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Optical assistance

POSS

[ Porcas et al. (1980), MNRAS 191, 607 ]

spectra

[ Walsh et al. (1979) ]

HST

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Radio interferometric observations (5 GHz)

VLA [ Roberts et al. (1979) ] VLA [ Harvanek et al. (1997) ] Cambridge 5 km [ Pooley et al. (1979) ]

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Critical curves, caustics

zs z

• lens equation

zs = z −α(z)

• magnification

µ = dz dzs =

• 1− dα

dz −1 zs z

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Geometry in 0957+561

[ Avruch et al. (1997) ]

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First VLBI observations

(total 5 h at 1.666 GHz: Effelsberg 100 m, Dwingeloo 25 m, Jodrell 76 m) [ Porcas et al. (1979) ]

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Resolving the images

1.666 GHz [ Porcas et al. (1981) ] 5 GHz [ Campbell et al. (1995) ]

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Fields of study in lensing

• sources
• lenses
• propagation effects
• spacetime

⋆ cosmology ⋆ relativity ⋆ new physics?

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Lenses as natural telescopes

• utilise lensing magnification

⋆ improve resolution

• utilise lensing amplification

⋆ improve sensitivity

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Cluster A2218 with high redshift galaxy

z = 7 magnified µ ≈ 25 [ Kneib et al. (2004) ]

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First radio detection of a lensed star forming galaxy

[ Garrett et al. (2004) ]

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A complicated second case

[ Berciano Alba et al. (2006), A&A accepted, astro-ph/0603466 ]

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Imaging a critical curve: 2016+112

[ Nair & Garrett (1997) ] [ Koopmans et al. (2002) ]

C11 C12 C13 C2

6 cm

1 2 3 4 MilliARC SEC MilliARC SEC

• 400
• 450
• 500
• 550
• 600
• 1500
• 1510
• 1520
• 1530
• 1540
• 1550
• 1560
• 1570
• 1580
• 1590

C11 C12 C13 C2

18 cm [ see talk by Anupreeta More ]

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Mass distributions of lenses

• mass model needed for interpretation
• image configuration constrains mass models
• mass measurements for high redshift lenses

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Mass model constraints for 0957+561

[ Garrett et al. (1994) ]

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The ten image system B1933+503

[ Nair (1998) ]

1a 1 2 3 4 5 8 6 7 Relative Declination (mas) Relative Right Ascension (mas)

[ Sykes et al. (1998) ]

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Mass substructure: B0128+437

[ Phillips et al. (2000) ] [ Biggs et al. (2004) ]

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Central images?

ARC SEC ARC SEC 0.6 0.4 0.2 0.0

• 0.2
• 0.4
• 0.6

0.6 0.4 0.2 0.0

• 0.2
• 0.4
• 0.6

MilliARC SEC MilliARC SEC 60 40 20

• 20
• 40
• 60

60 40 20

• 20
• 40
• 60

MilliARC SEC MilliARC SEC 60 40 20

• 20
• 40
• 60

60 40 20

• 20
• 40
• 60

B A G

B1030+074

[ Zhang et al., in prep. ]

J1632–0033

A C B

[ Winn et al. (2003) ]

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Propagation effects etc.

• lens produces several identical copies of one source
• intrinsic properties not needed for differential

⋆ absorption ⋆ scatter broadening

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Cosmology and relativity

• tests of relativity and alternative theories
• distance measurements
• geometry and expansion: H0

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Tests of relativity

[ Will (2006) ]

• deflection angle

α = 2(1+γ)G c2 M r

• Newton:

γ = 0

• Einstein:

γ = 1

• optical: solar eclipse
• first test of GR [ Eddington (1919) ]
• VLBI:

1+γ 2 = 0.99992±0.00023

[ Shapiro et al. (2004) ]

• speed of gravity?

[ Kopeikin (2001), Fomalont & Kopeikin (2003), etc. ]

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Measuring distances with time-delays

Ds Dds Dd

• bserver

source l e n s

• distance ratios known
• angles measurable
• geometry can be determined
• need one length for scale

use time-delay ! Refsdal (1964), MNRAS 128, 307 : ∆t ∝ DdDs Dds ∝ 1 H0

• can determine Hubble constant!

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B0218+357

unlensed

[ Wucknitz et al. (2004) ]

lensed

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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) ]

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B0218+357: lens position and H 0

H0 = 78±6 kms−1Mpc−1

[ Wucknitz et al. (2004) ] confirmed by York et al. (2005)

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Propagation effects in B0218+357

[ Mittal et al. (2006) ]

• 4
• 3
• 2
• 1

1 2 3

R.A. (mas)

• 2
• 1

1 2 3 4 5

• Dec. (mas)

1.65 GHz

Centroid A

2.25 GHz 15.35 GHz 8.4 GHz 4.96 GHz

• 4
• 3
• 2
• 1

1 2 3

R.A. (mas)

• 3
• 2
• 1

1 2 3

• Dec. (mas)

1.65 GHz

Centroid B

15.35 GHz 2.25 GHz 4.96 GHz 8.4 GHz

• flux density ratio A/B

frequency dependent

• source shift plus magni-

fication gradient?

• free-free absorption in the lensing

galaxy?

• measure fluxes of extended images
• take into account magnification

gradients

• fit ff-absorption

200 400 600 800 1000 1200 1400 1 2 4 6 10 14 Flux density (mJy) Frequency (GHz) FB

• bs

FA

mod

FA

• bs

FA

ff

[ Mittal et al. (2006), A&A submitted, astro-ph/0607623 ]

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The first real-time EVN image: B0218+357

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B0218+357 at 90 cm

90cm VLBI 2cm VLA + Pie Town

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Wide field 90 cm mapping

poster by Emil Lenc

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Future

• VLBI

⋆ higher sensitivity ⋆ better uv coverage ⋆ wider fields

• EVLA and e-MERLIN: much bet-

ter maps of extended structures (e.g. star-forming galaxies) J1131–1231

[ Claeskens et al. (2006) ]

• new lens surveys with extended LOFAR
• better analysis methods (LensClean and beyond)
• everything else with SKA . . .

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Summary

• lensing provides unique information for the study of

⋆ lensed sources ⋆ lens mass distributions ⋆ propagation effects ⋆ cosmology and relativity

• why radio?

⋆ probes widest range of scales ⋆ source structure on all scales ⋆ absorption and microlensing less severe ⋆ lensing as trigger for new analysis methods

• not mentioned: microlensing, weak lensing, milli-lenses,

lensing surveys (CLASS), transversal motion, measuring time-delays, B1608+656, . . .

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Contents

1 Gravitational lensing (+ VLBI) 2 The idea 3 Rings and multiple images 4 The first lens 0957+561 5 First observations of the source 6 Optical assistance 7 Radio interferometric observations (5 GHz) 8 Critical curves, caustics 9 Geometry in 0957+561 10 First VLBI observations 11 Resolving the images 12 Fields of study in lensing 13 Lenses as natural telescopes 14 Cluster A2218 with high redshift galaxy 15 First radio detection of a lensed star forming galaxy 16 A complicated second case 17 Imaging a critical curve: 2016+112

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18 Mass distributions of lenses 19 Mass model constraints for 0957+561 20 The ten image system B1933+503 21 Mass substructure: B0128+437 22 Central images? 23 Propagation effects etc. 24 Cosmology and relativity 25 Tests of relativity 26 Measuring distances with time-delays 27 B0218+357 28 Hubble constant from B0218+357 ? 29 B0218+357: lens position and H0 30 Propagation effects in B0218+357 31 The first real-time EVN image: B0218+357 32 B0218+357 at 90 cm 33 Wide field 90 cm mapping 34 Future 35 Summary 36 Contents

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