Systematically asymmetric: a comparison of H I profile asymmetries in real and simulated galaxies

We examine different measures of asymmetry for galaxy H I velocity profiles. We introduce the channel-by-channel asymmetry and the velocity-of-equality statistics to quantify profile asymmetries. Using a sample of simulated galaxies, we examine how these and the standard lopsidedness morphometric statistic depend on a variety of observational effects, including the viewing angle and inclination. We find that our newly introduced channel-by-channel asymmetry is less sensitive to the effects of viewing angle and inclination than other morphometrics. Applying our statistics to the WHISP (Westerbork H I survey of Irregular and SPiral galaxies) H I galaxy sample, we also find that the channel-by-channel asymmetry is a better indicator of visually classified asymmetric profiles. In addition, we find that the lopsidedness-velocity of equality space can be used to identify profiles with deep central dips without visual inspection.