An Overview of Gravitational Lensing
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Review talk by Dr Filipe Abdalla at the SuperJEDI Conference, July 2013
Transcript of An Overview of Gravitational Lensing
Gravitational Lensing
Filipe B. Abdalla
Apparent deflection angle α
• = 4 G M / (c2 b)• NB. Independent of light
wavelength
b
Observer
Dark matter halos
Background sources
Statistical measure of shear pattern, ~1% distortion Radial distances depend on geometry of Universe Foreground mass distribution depends on growth of structure
Dark matter halos
Background sources
Dark matter halos
Background sources
Dark matter halos
Observer
Background sources
Dark matter halos
Observer
Dark matter halos
Background sources
Statistical measure of shear pattern, ~1% distortion Radial distances depend on geometry of Universe Foreground mass distribution depends on growth of structure
Dark matter halos
Background sources
Dark matter halos
Background sources
Dark matter halos
Observer
Background sources
Dark matter halos
Mass Mapping CFHTLS
Cluster Weak Lensing
• Weak Lensing measures cluster masses, which are needed to use them as Dark Energy probes
• Preliminary cluster mass map (contours) from DES Weak Lensing
Cosmic shear two point tomography
q
Data from CFHTLS
Three problems with lensing: for either tomography and cluster mass measurements:
• Measuring shapes• Photometric redshifts• Intrinsic alignments
Measuring the shear!
Measuring shapes is hard
Galaxy spectrum at 2 different redshifts, overlaid on griz and IR bandpasses
• Photometric redshifts (photo-z’s) are determined from the fluxes of galaxies through a set of filters• May be thought of as
low-resolution spectroscopy
• Photo-z signal comes primarily from strong galaxy spectral features, like the 4000 Å break, as they redshift through the filter bandpasses
Photometric Redshifts
Hyper-Z: the first photo-z code
• Simple chi squared fit of fluxes to the data
• Very simple and very successful
• Has limitations:- Degeneracy, flat chi squared- Mis-identification of features- contamination from AGN- are errors reliable?
Credit: M. Bolzonella
from DES Test Data in November
High Redshift Cluster Discovered by DES
Cosmic shear
Additional contributions
What we measure
Intrinsic alignements.
Intrinsic-shear correlation (GI)
Hir
ata
& S
elja
k
High z galaxy gravitationally sheared tangentially
Dark matter at z1 Net anti-correlation between galaxy ellipticities with no prefered scale
Galaxy at z1 is tidally sheared
END
