Research Byte
Published in the RSAA Lunations
Vol1 Issue49 1–31 March 2024
We have recently submitted a paper (Boubel et al. 2023, in review) in which a forward-modelling approach is applied to the Cosmicflows-4 (CF4) Tully-Fisher catalogue (Kourkchi et al. 2020b), to simultaneously infer the parameters of the Tully-Fisher relation and the peculiar velocity field. This yields new constraints for the growth rate of structure and thus provides a test for theories of gravity. The significance lies in the methodology's ability to bypass the need for prior Tully-Fisher calibration or detailed selection function characterization.
WALLABY is expected to measure Tully-Fisher distances for approximately 84,000 late-type galaxies across the southern sky by 2027 (Courtois et al, 2022; Westmeier et al. 2022), increasing the Tully-Fisher sample by an order of magnitude. This presents an unprecedented opportunity for peculiar velocity studies such as ours. We have demonstrated our proposed analysis on the WALLABY reference simulation(Koribalski et al. 2020), and find that WALLABY alone would provide a factor of 2-3 improvement on the constraint for the growth rate compared to CF4 (see bottom left Fig. 1). The magnitude of this improvement in large part depends on the intrinsic scatter of the Tully-Fisher relation within the WALLABY sample, which we assume to be 20% at best (see top right of Fig. 1). In addition, we find that the precision to which the peculiar velocity field can be constrained by a particular dataset is closely linked to its sky coverage; a version of the WALLABY mock in which sky positions were randomised over the whole sky resulted in almost a factor of 2 improvement on parameter constraints. This suggests that, when we combine WALLABY with peculiar velocities measurements in the northern sky, we should expect to measure the growth rate to even higher precision.
-Paula Boubel-
Figure 1 caption: Bottom left panel: Comparison of peculiar velocity field parameter constraints obtained from the previous analysis on CF4 data (purple) and forecast constraints from a WALLABY mock with 20% distance errors (green). Top right panel: Tully-Fisher relation for the WALLABY mock. Cyan lines and shading show the fits to the Tully-Fisher relation and scatter model.
