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9th of May 2023
Hydra cluster galaxies in the radio and ultra-violet
by Holwerda et al.
The 21cm line emission of neutral hydrogen (HI) is a rich source of information about gas-rich galaxies. This gas usually spans a larger disk than stars and it is believed to be more sensitive to early interactions. The outskirts of spiral galaxy disks are the sites of the most recent acquisition of gas by the galaxy, and also low-level star-formation. This low-level star-formation was studied by the GALEX ultraviolet mission, which operated from 2003--2013. Further studies have revealed that galaxy morphology in atomic hydrogen (HI) and in the ultraviolet (UV) are closely linked.

Holwerda et al. have used archival GALEX ultra-violet imaging toegther with ASKAP WALLABY Pilot Survey data to study this correlation further. They find that extended HI and UV discs can be readily identified from their respective concentrations. Combined with WALLABY HI data, even the shallowest GALEX data are sufficient to identify extended UV discs. The image above shows GALEX observations of the Hydra cluster. WALLABY HI detections are marked in blue. There is an overlap of 30 HI detections in the GALEX fields with associated GALEX data. The bright UV source with no associated HI is a foreground galactic star "photobombing" the image of the cluster!

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