I present the results of an investigation into the distribution of Dark Matter via observations and
analysis of both the intrinsic alignment of galaxy shapes and the weak gravitational lensing signal due
to the large-scale structure of the Universe.
The distribution of Dark Matter in the non-local Universe (z ~ 0.5) is investigated with a statistical weak lensing or ‘cosmic shear’ analysis of the COMBO-17 survey — a unique dataset with
deep R-band imaging and accurate photometric redshift information for galaxies to mᵣ ≤ 24.0.
A full maximum likelihood reconstruction of the weak lensing convergence power spectrum, Gᴷᴷ
is applied to the data and a strong measurement of the convergence power is found over the five
fields of the survey. This analysis represents the most direct measurement of the clustering properties of the Dark Matter ever obtained. The measurements are compared to the currently popular
ACDM cosmological model and show good agreement. The results have also been used to measure cosmological parameters. The normalisation of the matter power spectrum is constrained to be
δ₈ = (0.72 ± 0.09)(Ωm /0 .3 )-⁰.⁵⁰ where the errors quoted are 1-δ due to the intrinsic dispersion in
galaxy ellipticities, cosmic and sampling variance. Finally, the weak lensing measurements have been
combined with results from the 2dF Galaxy Redshift Survey and with those from recent Cosmic M icrowave Background experiments. With these additional constraints, the normalisation of the matter
power spectrum is found to be δ₈ = 0.73 ±⁺⁰.⁰⁶₋₀.₀₃ and the matter density to be Ωm= 0.27 ± 0.02.
The alignment of galaxy shapes in the local Universe (z ~ 0.1) is detected and measured with
the digitized SuperCOSMOS Sky Survey. In this analysis, the shapes of 2 x 10⁶ galaxies from approximately 10 000 deg² of sky are analysed and are found to be correlated with one another at a
small but significant level. A new minimum variance estimator is applied to this sample of galaxies
yielding ellipticity variance measurements in the range 2 x 10⁻⁴ ≥ δ²ₑ (θ) ≥ 1 x 10⁻5 over a range
of scales between 1 and 100 arcmin. This correlation is detected in two colours, bj and R and, most
significantly, in the cross-correlation between the two bands, which is less likely to be contaminated
by systematics. These measurements are compared with recent analytical and numerical predictions
made for the intrinsic shape alignment and rough agreement is found, although the predictions for
the alignment are inconclusive at present. The implications of these measurements for weak lensing
studies are examined. The measurements imply that the intrinsic shape alignment effect will dominate over the weak lensing signal for shallow surveys (e.g. the Sloan Digital Sky Survey) while it will
contribute ≤ 10% of the signal seen in deeper weak lensing studies with z ~ 1.