2025AJ....169..114P

An avenue for understanding cosmological galaxy formation is to compare morphometric parameters in observations and simulations of galaxy assembly. In this second paper of the ASymba: Asymmetries of H I in SIMBA Galaxies series, we measure atomic gas (H I) asymmetries in spatially resolved detections from the untargeted Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) survey, and compare them to realizations of WALLABY-like mock samples from the SIMBA cosmological simulations. We develop a Scanline Tracing method to create mock galaxy H I data cubes that minimizes shot noise along the spectral dimension, compared to particle-based methods, and thus minimizes spurious asymmetry contributions. We compute 1D and 3D asymmetries for spatially resolved WALLABY Pilot Survey detections, and we find that the highest 3D asymmetries (A_3D ≳ 0.5) stem from interacting systems or detections with strong bridges or tails. We then construct a series of WALLABY-like mock realizations drawn from the SIMBA 50 Mpc simulation volume and compare their asymmetry distributions. We find that the incidence of high A_3D detections is higher in WALLABY than in the SIMBA mocks, but that difference is not statistically significant (p-value = 0.05). The statistical power of quantitative comparisons of asymmetries such as the one presented here will improve as the WALLABY survey progresses and as simulation volumes and resolutions increase.