Seb Oliver

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Distant Universe

• Seb Oliver
• Lecture 20 Gravitational Lensing

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What did Gravitational Lensing ever do for
cosmology?
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The Lensing Equation

• Back of the envelope calculation to show that a4
  GM/r

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Lensing Phenomena

• Microlensing
• Strong-lensing
• Multiple images
• Einstein Rings
• Arcs
• Magnification
• Time delays
• Weak-lensing
• Magnification
• Distortion/shear

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Micro-lensing

• MACHO (4 candidates 3 in bulge 1 in LMC)
  http//wwwmacho.mcmaster.ca/index.html
• EROS http//eros.in2p3.fr/
• OGLE I, II, III http//bulge.princeton.edu/ogle/
• MOA http//www3.vuw.ac.nz/scps/moa/
• PLANET http//mplanet.anu.edu.au/
• Now Catalogues of hundreds of microlensing events

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MACHO EROS
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Constraints on Halo Mass
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Micro-lensing searches today
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Strong Lensing
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Multiple Lensing
The quasar 0957561 the first multiply-imaged
source discovered by Dennis Walsh, Bob Carswell
Ray Weymann in 1979.
The multiply-imaged pair discovered in the
cluster AC114 by Ian Smail and Richard Ellis with
the HST.
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What can you do with multiple lensed systems?

• Measure the positions of the images
• Measure the relative magnification of the images
• Measure the difference in time-delays
• Model the mass distribution of the lens
• Relate proper distance (from time-delays) to
  redshifts and deduce Hubble Constant and
  acceleration constant
• Count them

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Modelling the mass distribution

• Postulate a lens mass distribution
• this might be
• Related to the light distribution
• Simple isothermal model with few parameter
• Postulate a source light distribution
• Hence predict observed light distribution
• Compare with observations
• Repeat steps 1-4 until suitable agreement

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Quasar Timings
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Time-delays
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Arcs
Abell 2218 taken with the HST Jean-Paul Kneib,
Richard Ellis and Ian Smail.
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Einstein Rings
Rings provide strong constraints on models of the
lens mass distribution
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Weak Lensing
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Weak Lensing
The average elongation of background sources
provides additional constraints on models of mass
distribution
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Weak Lensing Shear
The weak shear observed by Yannick Mellier and
colleagues in the periphery of the rich cluster
002416. Such measurements offer a promising
method of tracing the dark matter profile and
constraining the total mass density contributed
by clusters of galaxies
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Weak Lensing Shear
Grey et al. from COMBO-17 data
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Weak Lensing Shear
Grey et al. from COMBO-17 data
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What can lensing tell us?

• Mass of dark matter in Halo
• Micro-lensing
• Dark mass in external galaxies
• Modelling of multiply lensed systems
• Dark mass in clusters W0.35 0.07 (Turner 1999)
• Modelling of multiply lensed systems, arcs, and
  statstical sheer
• Magnification from statistical analysis of counts
• Dark mass in field
• Inversion of sheer fields

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What else?

• Hubbles constant
• Timing of multiply lensed quasars used to favour
  H050kms-1Mpc
• Finding distant galaxies
• Surveys targeted at clusters to
• magnify background galaxies
• separate galaxies to reduce confusion
• Cosmological parameters
• Lensing probabilty
• Timing

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References

• Yannick Mellier PROBING THE UNIVERSE WITH WEAK
  LENSING Annu. Rev. Astron. Astophys. 1999, Vol.
  37 127-189
• Alexandre Refregier Weak Gravitational Lensing by
  Large-Scale Structure Annu. Rev. Astron.
  Astophys. 10.1146/annurev.astro.41.111302
  .102207.
• RD Blandford and R Narayan Cosmological
  Applications of Gravitational Lensing Annu. Rev.
  Astron. Astophys. 1992, Vol. 30 311-358
• Bohdan Paczynski GRAVITATIONAL MICROLENSING IN
  THE LOCAL GROUP
• Annu. Rev. Astron. Astophys. 1996, Vol. 34
  419-459
• Fahlman, G.G., Kaiser, N., Squires, G. Woods,
  D. 1994,"Dark matter in ms1224 from the
  distortions of the background galaxies," Ap. J.
  437, 56.
• Kaiser, N. Squires, G. 1993, "Mapping the dark
  matter with weak gravitational lenses," Ap. J.
  404, 441.
• Refsdal, S. 1964, "The gravitational lens
  effect," M.N.R.A.S. 128, 295.
• Schneider, P., Ehlers, J. Falco, E. 1992,
  Gravitational Lenses. Springer-Verlag, Berlin.
• Surdej, J. Soucail, G. 1993, "Lists of
  accepted and proposed gravitational lens
  systems," in Surdej, J. et al (eds.)
  Gravitational Lenses in the Universe, 1993,
  Proceedings of the 31st Liège International
  Astrophysical Colloquim.
• Walsh, D. and Carswell, R.F. and Weyman, R.J.
  1979, "0957561 A,B twin quasistellar
  objects or gravitational lens?" Nature, 279, 381.
  
• Gravitational Lensing Nature's Giant Telescopes
  Jean-Paul Kneib Richard Ellis
  http//webast.ast.obs-mip.fr/people/kneib/ast_now9
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