Cosmology with the 6-degree Field Galaxy Survey

TL;DR

This thesis analyzes galaxy clustering in the 6dF Galaxy Survey to measure cosmic distances, test gravity theories, and explore galaxy-halo relationships, providing new constraints on cosmological parameters and galaxy evolution.

Contribution

It provides the first BAO-based distance measurement at low redshift using 6dFGS and constrains the growth index of cosmic structures, testing General Relativity.

Findings

BAO detection yields H_0 = 67.0 ± 3.2 km/s/Mpc.

Measured fσ_8(z_eff) = 0.423 ± 0.055 at z=0.106.

Growth index γ = 0.547 ± 0.088 consistent with GR.

Abstract

This thesis presents the analysis of the clustering of galaxies in the 6dF Galaxy Survey (6dFGS). At large separation scales the baryon acoustic oscillation (BAO) signal is detected which allows to make an absolute distance measurement at $z_{\rm eff} = 0.106$. Such a measurement can be used to constrain the Hubble constant, $H_0 = 67.0\pm3.2\;$km s$^{-1}\;$Mpc$^{-1}$ (4.8% precision). Modelling the 2D galaxy correlation function of 6dFGS, $\xi(r_p,\pi)$, allows a measure of the parameter combination $f(z_{\rm eff})\sigma_8(z_{\rm eff}) = 0.423 \pm 0.055$, where $f \simeq \Omega_m^{\gamma}(z)$ is the growth rate of cosmic structure and $\sigma_8$ is the r.m.s. of matter fluctuations in $8h^{-1}\,$Mpc spheres. Such a measurement allows to test the relationship between matter and gravity on cosmic scales by constraining the growth index of density fluctuations, $\gamma$. The 6dFGS measurement of $f\sigma_8$ combined with WMAP-7, results in $\gamma = 0.547 \pm 0.088$, consistent with the prediction of General Relativity ($\gamma_{\rm GR} \approx 0.55$). The last chapter of this thesis studies the stellar-mass dependence of galaxy clustering in the 6dF Galaxy Survey. Using the Halo Occupation Distribution (HOD) model, this analysis investigates the trend of dark matter halo mass and satellite fraction with stellar mass by measuring the projected correlation function, $w_p(r_p)$. The findings of this analysis are, that the typical halo mass ($M_1$) as well as the satellite power law index ($\alpha$) increase with stellar mass. The 6dFGS results are compared to two different semi-analytic models derived from the Millennium Simulation, as well as weak lensing measurements.