WALLABY Pilot Survey and ASymba: Comparing H i Detection Asymmetries to the SIMBA Simulation

Abstract

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.

Keywords

• Galaxy structure
• H I line emission
• Hydrodynamical simulations