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 $5\times 10^{19}c{m}^{-2}$ 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.

arXiv comment19 pages, 12 figures and 2 appendices. Accepted for publication in the Monthly Notices of the Royal Astronomical Soceity

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