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

TL;DR

This study uses EAGLE simulations to determine optimal observational constraints for accurately measuring HI asymmetries in galaxies, highlighting the effects of noise and resolution on different asymmetry indices.

Contribution

It identifies specific observational thresholds for reliable HI asymmetry measurements and clarifies that flux and morphological asymmetries are uncorrelated.

Findings

Optimal column density and S/N thresholds for morphological asymmetry measurement.

A S/N > 5.5 is needed for robust flux asymmetry.

Flux and morphological asymmetries are uncorrelated.

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.