Using EAGLE simulations to study the effect of observational constraints on the determination of HI asymmetries in galaxies

Abstract

We investigate the effect of observational constraints such as signal-to-noise, resolution and column density level on the HI morphological asymmetry ($\mathrm{A}_\mathrm{mod}$) and the effect of noise on the HI global profile ($\mathrm{A}_\mathrm{flux}$) asymmetry indices. Using mock galaxies from the EAGLE simulations we find an optimal combination of the observational constraints that are required for robust measurement of the $\mathrm{A}_\mathrm{mod}$ value of a galaxy: a column density threshold of $5\times10^{19}cm^{-2}$ or lower at a minimal signal-to-noise of 3 and a galaxy resolved with at least 11 beams. We also use mock galaxies to investigate the effect of noise on the $\mathrm{A}_\mathrm{flux}$ values and conclude that a global profile with signal-to-noise ratio greater than 5.5 is required to achieve a robust measurement of asymmetry. We investigate the relation between $\mathrm{A}_\mathrm{mod}$ and $\mathrm{A}_\mathrm{flux}$ indices and find them to be uncorrelated which implies that $\mathrm{A}_\mathrm{flux}$ values cannot be used to predict morphological asymmetries in galaxies.