Large-scale clustering of galaxies in the Universe

One of the greatest mysteries of today is the nature of the accelerating expansion of the Universe. In order to understand this, we need to probe the expansion rate as it evolves. Here I measure expansion rates H( z), angular diameter distances DA( z) and the effects of gravity on cosmic scales. These involve measuring the distribution of matter, because its clustering is sensitive to gravity and the expansion. As most of the gravitational matter is in the form of invisible dark matter, I instead use galaxies to trace the matter distribution. Here I use a sample of ∼ 100,000 luminous galaxies in the largest volume survey to date, the Sloan Digital Sky Survey. In my large-scale structure anlaysis I focus on the so-called "baryonic acoustic feature". This feature is a residual from early Universe plasma-radiation waves that left fossil signatures in the matter distribution, similar to the waves in a pond generated by a pebble. Through correlation-function analysis, I detect the feature and find that it is consistent with the standard ΛCDM model, meaning a Universe that contains an accelerating substance dubbed dark energy (Λ), and cold dark matter. Because the signature has a characteristic scale, I use it to measure the effective distance (∝ D2A /H) to redshift z ∼ 0.28 to an accuracy of ∼ 4%. To compare results to the ΛCDM model, I use large sets of realistic mock galaxy catalogs, based on N-body simulations. I find that the current volume does not appear to be large enough to convincingly measure H directly using the acoustic-feature, but that next generation surveys will be. I present new clustering analysis techniques that improve constraints on H by a factor of ∼ 20--30% compared to standard methods.