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Physics and Astronomy


Galaxy morphology in atomic hydrogen (H I) and in the ultraviolet (UV) are closely linked. This has motivated their combined use to quantify morphology over the full H I disc for both H I and UV imaging. We apply galaxy morphometrics: concentration, asymmetry, gini, M20 and multimode-intensity-deviation statistics to the first moment-0 maps of the WALLABY Survey of galaxies in the hydra cluster centre. Taking advantage of this new H I survey, we apply the same morphometrics over the full H I extent on archival GALEX FUV and NUV data to explore how well H I truncated, extended ultraviolet disc (XUV) and other morphological phenomena can be captured using pipeline WALLABY data products. Extended H I and UV discs can be identified relatively straightforward from their respective concentration. Combined with WALLABY H I, even the shallowest GALEX data are sufficient to identify XUV discs. Our second goal is to isolate galaxies undergoing ram-pressure stripping in the H I morphometric space. We employ four different machine learning techniques, a decision tree, a k-nearest neighbour, a support-vector machine, and a random forest. Up to 80 per cent precision and recall are possible with the random forest giving the most robust results.


© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (

Original Publication Information

Benne W Holwerda and others, WALLABY Pilot Survey: hydra cluster galaxies UV and H I morphometrics, Monthly Notices of the Royal Astronomical Society, Volume 521, Issue 1, May 2023, Pages 1502–1517,