Measuring Galaxy Asymmetry in Different Dimensions

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Authors
Perron-Cormier, Mathieu
Keyword
Galaxies , Cosmological Simulations
Abstract
Galaxy Asymmetry is correlated to a wide variety of phenomena, such as galaxy interactions, merger history, galaxy color and structure. The upcoming SKA radio-telescopes will record unprecedented numbers of HI cubes. An SKA pathfinder, the upcoming WALLABY survey will record thousands of HI galaxy cubes. Galaxy Asymmetry can be used as a fast non-parametric measure to infer the physical properties of the galaxies imaged by WALLABY and future widefield HI surveys. Conventional definitions use either the 1D spectral or spatial 2D components of datacubes and are computed using absolute values. We show how asymmetry can be generalised to utilise the full 3D of the datacube. Additionally, the absolute difference method is shown to entangle noise and signal into the measure. Instead, we demonstrate how a squared difference approach can be used to allow a more rigorous background correction. We show how these new method create a more robust parameter to resolution effects, inclination effects and noise effects, allowing the method to be applied to WALLABY data. We create a sample of mock cubes using the SIMBA cosmological simulation using SKA pathfinder observational parameters of the MeerKAT radio-telescope and WALLABY survey. The asymmetries of the sample are computed and we find little correlation between 2D and 1D asymmetries. We also find a strong correlation between 2D + 1D asymmetry and 3D. We reproduce previous findings that 1D asymmetry is negatively correlated with HI mass. We find that 2D asymmetry is correlated with HI mass, but this may be caused by the increased resolution of massive galaxies. This thesis lays the groundwork for detailed statistical comparisons between HI surveys and cosmological simulations.
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