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16th of December 2021
WALLABY observations of the Hydra I Cluster
by Reynolds et al.
Reynolds et al. present results from their analysis of the Hydra I cluster observed in neutral atomic hydrogen (HI) as part of the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). These WALLABY observations cover a 60-square-degree field of view with uniform sensitivity and a spatial resolution of 30 arcseconds. These wide-field observations are used to investigate the effect of galaxy environment on HI gas removal and star formation quenching by comparing the properties of cluster galaxies, infalling galaxies, and field galaxies surrounding the cluster. They find a sharp decrease in the HI-detected fraction of infalling galaxies toward the outskirts of the cluster, and evidence for the cluster environment removing gas from the outskirts of HI-detected cluster and infall galaxies. As a galaxy's HI gas normally extends to the outskirts of a galaxy it is generally the first easily detectable component of a galaxy to be influenced by the environment.

The figure above shows the position of nearby galaxies in the 60-square-degree WALLABY footprint. As a blind HI survey, WALLABY is most sensitive to gas-rich galaxies and will detect few gas-poor galaxies, which are the dominant type of galaxy found in clusters. HI detections and non-detections are indicated by the filled circles and unfilled squares, respectively. The cluster, infall and field galaxy populations are coloured blue, purple and orange, respectively. The grey dashed circle indicates the virial radius of the Hydra I cluster (which roughly separates bound galaxies from galaxies which may either be infalling or unbound) and the grey star indicates the positions of NGC 3311 and NGC 3309 (i.e., the approximate centre of the cluster). The paper will be published in Monthly Notices of the Royal Astronomical Society.

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