Probing the large-scale galaxy density and peculiar velocity fields

This thesis focuses on constraining the linear redshift distortion parameter β, which is a critical variable in reconstructing the peculiar velocity field of the Local Universe and probing information of the distribution on dark matter. We used mock data samples of peculiar velocity fields that aim to mimic the next generation of galaxy peculiar velocity surveys such may become feasible for SKA and its precursors. The smoothed IRAS PSCz peculiar velocity field [Branchini et al., 1999] was used to generate the mock data samples, where the true value of β was considered to be 0.5 throughout this work (i.e. β(true) = 0.5). The study was carried out considering two methods. First, we applied the χ2 hypothesis test by comparing the observed and predicted peculiar velocity fields to constrain β from the mock peculiar velocity fields. In this case, the traditional distance indicators such as SNIa, TF and recently introduced gravitational wave standard sirens were considered. The distance scatter of each indicator was taken from literature and scatter in the predicted peculiar velocity (σv) was considered to be a variable. The best-fit value of β for the peculiar velocity models show a good agreement with β(true) when σv < 150 km s(−1) . Our calculations implied that, in order to fully exploit the potential of future improvement in the precision of β estimates, it is important also to improve the accuracy of the reconstructed peculiar velocity field predicted from all-sky redshift surveys. The second method is the ROBUST method originally introduced by Rauzy & Hendry for fitting peculiar velocity fields. The ROBUST method use the luminosity functions of the mock galaxies as the distance indicators, where the LF assumed to be independent of the spatial position of the galaxies. Our results are in a good agreement with β(true)= 0.5, where the best fit values of the peculiar velocity models always centred around 0.5. Our results demonstrate the potential of the method, even in cases where the luminosity function is rather broad, provided it can be applied to sufficiently large peculiar velocity surveys - such as those which may be anticipated from e.g. the 6dF and WALLABY surveys in the relatively near future