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A density field mapped from a galaxy redshift survey can be used to predict the peculiar velocity field, up to normalisation and any external tidal field. Fitting such a model for the predicted peculiar velocities to those measured using a distance estimator such as the Tully-Fisher relation provides a test for theories of gravity via a measurement of the growth factor. In this end-of-thesis talk, I will present a Bayesian forward-modelling method that simultaneously determines the parameters of both the Tully-Fisher relation and the peculiar velocity field, while incorporating a selection function and an intrinsic Tully-Fisher scatter model. I will also show how this methodology can be applied to improve upon Tully-Fisher measurements of the Hubble constant and directly measure possible variations of H_0 on the sky. The former is currently limited by uncertainties in the absolute calibration, but the latter is only limited by sample size and sky/redshift coverage. These methods were applied to the Cosmicflows-4 Tully-Fisher dataset to obtain measurements on the growth rate, H_0, and a possible dipole in H_0. Using Tully-Fisher mocks of the ongoing WALLABY survey, I show the extent to which each of these constraints will be improved by next-generation datasets. |
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