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Title: Probing dark matter with intrinsic and extrinsic galaxy alignments
Author: Brown, M. L.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2002
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The alignment of galaxy shapes in the local Universe (z ~ 0.1) is detected and measured with the digitized SuperCOSMOS Sky Survey. 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 ³ s2e(q) ³ 1 x 10-5 over a range of scales between 1 and 100 arcmin. These measurements are compared with recent analytic 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 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. The distribution of Dark Matter in the non-local Universe (z ~ 0.5) is also investigated with a statistical weak lensing or ‘cosmic shear’ analysis of the COMBO-17 survey. A full maximum likelihood reconstruction of the weak lensing convergence power spectrum, Ckkl 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 ΛCDM 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 s8 = (0.72 ± 0.09) (Ωm /0.3)-0.50 where the errors quoted are 1-s 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 Microwave Background experiments. With these additional constraints, the normalisation of the matter power spectrum is found to be s8 = 0.73+0.06-0.03 and the matter density to be Ωm = 0.27 ± 0.01.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available