Prospects for galaxy-mass relations from the 6dF Galaxy Survey

Abstract

We develop new methods to study the properties of galaxy redshift surveys and radial peculiar velocity surveys, both individually and combined. We derive the Fisher information matrix for redshift surveys, including redshift distortions and stochastic bias. We find exact results for estimating the marginalised accuracy of a two-parameter measurement of the amplitude of galaxy clustering, A_g, and the distortion parameter beta. The Fisher matrix is also derived for a radial peculiar velocity survey and we discuss optimisation of these surveys for equal timescales. The Fisher Super-Matrix, combining both surveys, is derived. We apply these results to investigate the 6 degree Field Galaxy Survey (6dFGS), currently underway on the UK Schmidt Telescope (UKST). The survey will consist of approximately 125000 K-band selected galaxies with redshifts and a subset of around 15000 galaxies with radial peculiar velocities. We find for the redshift survey that we can measure the three parameters A_g, Gamma and beta to about 3% accuracy, but will not be able to detect the baryon abundance, or the matter-galaxy correlation coefficient, r_g. The peculiar velocity survey will jointly measure the velocity amplitude A_v and Gamma to around 25% accuracy. A conditional estimate of the amplitude A_v alone, can be made to 5%. When the surveys are combined however, the major degeneracy between beta and r_g is lifted and we are able to measure A_g, Gamma, beta and r_g all to the 2% level, significantly improving on current estimates. Finally we consider scale dependence of r_g and the biassing parameter b. We find that measurements for these averaged over logarithmic passbands can be constrained to the level of a few percent.