Using eagle simulations to study the effect of observational constraints on the determination of H i asymmetries in galaxies

Abstract

ABSTRACT We investigate the effect of observational constraints such as signal-to-noise (S/N) ratio, resolution, and column density level on the H i morphological asymmetry (Amod) and the effect of noise on the H i global profile (Aflux) asymmetry indices. Using mock galaxies from the eagle simulations, we find an optimal combination of the observational constraints that are required for a robust measurement of the Amod value of a galaxy: a column density threshold of 5 × 1019 cm−2 or lower at a minimal S/N of 3 and a galaxy resolved with atleast 11 beams. We also use mock galaxies to investigate the effect of noise on the Aflux values and conclude that a global profile with S/N greater than 6 is required to achieve a robust measurement of asymmetry. We investigate the relation between Amod and Aflux indices and find them to be uncorrelated, which implies that Aflux values cannot be used to predict morphological asymmetries in galaxies.