3. 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
4. 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
6. 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
11. Three problems with lensing:
for either tomography and cluster mass
measurements:
• Measuring shapes
• Photometric redshifts
• Intrinsic alignments
14. 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
15. 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
16. from DES Test Data in November
High Redshift Cluster Discovered by
DES
18. Intrinsic-shear correlation (GI)
Hirata&Seljak
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