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.
Categories: astro-ph.GA